Carbon fiber–reinforced thermoplastic composites are gaining increasing interest in various applications thanks to their combined properties of high specific stiffness, high specific strength, and superior toughness. Their mechanical properties are highly dependent on the carbon fiber content. In this study, the carbonization-in-nitrogen method (CIN) developed in previous work is used to measure the fiber content of carbon fiber thermoplastic composites. Three types of carbon fiber thermoplastic composite samples were prepared using hot-melt impregnation. The carbon fiber thermoplastic composite sample is carbonized in a nitrogen environment alongside a neat resin sample that is used for calibrating the resin carbonization percentage. A good agreement is achieved between the nominal carbon fiber content and the carbon fiber content measured using the CIN method. It is concluded that the CIN method is an accurate and efficient way to characterize the carbon fiber content for carbon fiber thermoplastic composites. This work completes the verification of the CIN method, which enables extended application to thermoplastic composites. Moreover, it has its unique merits on evaluating the carbon fiber content for high-temperature and solvent-resistant thermoplastic composites that would encounter challenges using other methods.
The polycarbonate (PC)/polymethyl methacrylate (PMMA) (10/90) blends with microcellular foams were prepared by the two-step process using supercritical carbon dioxide as physical foaming agent. The effects of saturation temperature, saturation pressure, foaming temperature, and foaming time on the cell morphology structure were investigated by scanning electron microscopy. The results indicated that the mean diameter of cells in foamed PC/PMMA films decreased with the increment of saturation temperature and saturation pressure but increased with the increment of the foaming time. Moreover, the mean diameter of cells decreased first, but then increased with the increment of the foaming temperature. The cell density (N c) increased with the increment of saturation temperature and saturation pressure but decreased with the increment of the foaming time. However, the N c increased first but then decreased with the increment of the foaming temperature.
Novel segmented poly(urethane urea) (PUU) was prepared from polycaprolactone triol (soft segment), 4,4'-methylenebis(phenyl isocyanate) (hard segment), and hexamethylenediamine (chain extender). Graphitized carbon black (GCB) was used as filler. Conducting polythiophene (PTh) was infiltrated by chemical oxidative polymerization. The structure, morphology, mechanical properties, electrical conductivity, and voltage-triggered shape memory effect were demonstrated. The unique network morphology was observed by scanning electron microscope due to the generation of interpenetrating polymer networks (IPNs). The formation of PUU-PTh IPNs was due to the interpenetrating PTh and branched polycaprolactone triol structure. The PTh-modified PUU films reinforced with GCB showed 59% increase in tensile strength and 50% enhancement in Young’s modulus relative to the pristine matrix. The presence of PTh and increase in GCB content increased the conductivity of the composites. The conductivity of 10 wt% GCB-loaded PUU/PTh/GCB composite was raised to 0.089 Scm–1, which is higher than the neat PUU (0.91 x 10–2 Scm–1). The surface temperature of PUU/PTh/GCB 10 was also found to increase with time when a higher voltage was applied (40 V). Such a conductivity of composites was enough to show electroactive shape recovery up to 94% (40 V).
Flax fibre was treated with low concentrations of alkali and used to prepare poly(furfuryl alcohol) (PFA)-based composites through in situ polymerization of furfuryl alcohol. The properties of low concentrations of alkali-treated flax fibre and flax fibre–reinforced composites were characterized for their structure and properties by X-ray diffraction, scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis, dynamic mechanical analysis, water absorption and flexural measurements. The alkali-treated flax fibre showed increased cellulose content and crystallinity index with smooth surfaces of the microfibres. PFA composites exhibited dispersed microfibres within PFA matrix with agglomerates. There was also a clear increase in thermal stability, storage modulus and damping factor for all treated PFA composites. Poor resistance to water uptake was also observed for the PFA composites, even though the highest alkali treatment improved the resistance compared to the untreated composite. PFA–flax biocomposites were characterized by improved flexural strength and modulus, except the untreated which showed the opposite.
Ring-opening polymerization of anionic polyamide-6 (APA-6) requires both an activator and an initiator for the reaction to occur. Typical processing techniques for liquid-molded thermoplastic composite laminates involve infusion of the reinforcement with a premixed monomer solution containing both activator and initiator species. The technique described here is a step toward simplification and automation of the in situ polymerization process for composite laminates. By depositing the initiation functional group onto the reinforcement, infusion of a single stream of inert monomer solution is possible. The technique simplifies the processing equipment required and reduces the risk of contamination. Two separate methodologies derived from a silane and a diisocyanate were investigated. The soluble diisocyanate method was used to successfully demonstrate the single-stream APA-6 processing technique. Glass fiber surface-initiated polymerization was also demonstrated using the silane-derived initiator. The findings represent the first steps toward a new processing paradigm of APA-6 composites.
Automated fibre placement (AFP) is a relatively new process for the manufacturing of composite structures. Among many attractive features, it provides high-speed of material deposition, more repeatability in terms of quality of the part, less labour intensive (as compared with traditional methods of manufacturing such as Hand Lay-Up), less waste and the ability to transition more seamlessly from design to manufacturing. AFP can be used to process both thermoset composites and thermoplastic composites. Thermoplastic composites processing holds many potential benefits. This is because if the process is done right in producing parts with good quality, it is fast since it does not require a second process such as curing in an autoclave or oven. For the purpose of comparison of performance and for design, it is necessary to determine the mechanical properties of laminates made using this process. However, there are challenges in making flat coupons for the purpose of testing for mechanical properties. This article presents these challenges and the procedure developed to make flat laminates using a simple AFP machine. Mechanical properties of these laminates are also determined and compared with those obtained from laminates made using conventional autoclave moulding.
Polymeric materials can be welded by the laser transmission welding technique in order to join two or more sheets. At the interface of the polymer sheets, the released energy induces melting that is assisted by pressure, producing a fast and resistant welding. In this research, single-lap polymeric joints of biomedical ultra-high molecular weight polyethylene sheets were realized; one of the two polymer sheets was doped, at different concentrations, with carbon nanomaterials as a laser absorbent filler. A pulsed neodymium-doped yttrium aluminium garnet laser operating in the wavelength of 532 nm and of 1064 nm with an intensity of the order of 109 W/cm2 was employed to obtain a joint at the interface between the transparent polymer and the absorbent one. The mechanical shear resistance of the prepared joints was related to the optical absorption feature of the polymeric materials. Besides, surface analyses such as hardness, roughness and wettability in different inorganic and organic fluids were presented and discussed. The result of characterization analyses indicated the best filler amount in order to have a mechanically resistant joint with surface properties also suitable for the biomedical employment.
The process-induced voids during resistance welding of glass fabric-reinforced polyetherimide was investigated. The mechanisms of void formation in adherends, in particular, the residual volatile-induced voids and the fibre de-compaction-induced voids, were analysed. Due to the non-uniform temperature and stress distributions in the joints during welding, a non-uniform void distribution was observed in the joints with more voids generated in the middle of the joints than at the edges. Welding temperature and pressure were shown to have a large influence on void formation. Increasing of welding pressure was shown to effectively reduce the voids, while the residual moisture-induced voids were found more difficult to be eliminated than the fibre de-compaction-induced voids.
Polymeric nanocomposites based on poly(propylene-co-ethylene-co-1-butene) (PEBC) were elaborated by melt mixing using an organophilic montmorillonite (o-MMT) and maleated PEBC (PEBCg) as compatibilizer. The effect of clay concentration, PEBCg:o-MMT ratio, and grafting degree of the compatibilizer were studied. X-ray diffraction and scanning electron microscopy show formation of partially intercalated structures in all compatibilized composites with well-distributed small tactoids. According to the differential scanning calorimetry results, the anhydride groups of the compatibilizer have a marginal nucleating effect, while the o-MMT causes a slight decrease in the crystallization temperature of the polymer. PEBC presents the largest activation energy of crystallization (E α), while the composites show lower E α than their matrices. It is also observed that the rate of degradation of PEBC is not affected by the presence of PEBCg. The nanoclay, on the other hand, retards the decomposition process of the polymeric matrix in about 40°C and augments its rate of degradation approximately four times.
Tailoring the properties of natural polymers such as electrical conductivity is vital to widen the range of future applications. In this article, the potential of electrically conducting multi-wall carbon nanotube (MWCNT)/polylactic acid (PLA) composites produced by industrially viable melt mixing is assessed simultaneously to MWCNT influence on the composite’s mechanical strength and polymer crystallinity. Atomic force microscopy observations showed that melt mixing achieved an effective distribution and individualization of unmodified nanotubes within the polymer matrix. However, as a trade-off of the poor tube/matrix adhesion, the tensile strength was lowered. With 10 wt% MWCNT loading, the tensile strength was 26% lower than for neat PLA. Differential scanning calorimetric measurements indicated that polymer crystallization after injection moulding was nearly unaffected by the presence of nanotubes and remained at 15%. The resulting composites became conductive below 5 wt% loading and reached conductivities of 51 S m–1 at 10 wt%, which is comparable with conductivities reported for similar nanocomposites obtained at lab scale.
The effect of diisocyanate chain extender (CE) additives on the change of molecular structural characteristics, rheological, and mechanical properties of the blends comprising of poly(butylene terephthalate) (PBT) and thermoplastic polyester elastomer (TPEE) obtained by reactive compounding in the melt and having different phase structure is studied. It is shown that addition of CE in the amount of 0.2 wt% to 1.25 wt% causes an increase in viscosity of polyester melts and solutions owing to the chain extension reactions and intermolecular cross-linking of macro-chains which occur in the melt. CE has a strong effect on the character of deformation curves at straining of both polyesters in primary form and their blends irrespective of the ratio of components in them (phase structure of materials). At the increase of its concentration, values of high and low flow limits increase and the difference in values of these parameters decreases, that is, a sharp yield point is gradually degenerating. At the same time, increase in Charpy impact strength on notched specimens is observed, including the subzero temperatures range (–40°C). Besides, CE has an effect on crystallizability of both individual polyester components and their blends. The general trend (irrespective of the polyester type and phase structure of the blend) is the decrease in crystallization temperature. This fact is explained by limitation of molecular mobility due to an increase in the molecular weight of polyester and intensification of interchain interactions.
In this study, the effect of reinforcements’ shape and type on the mechanical, thermal, and morphological properties of polyvinyl chloride (PVC) foam composites is investigated. For this purpose, three different fillers, longitudinal structure glass fiber, flaky structure mica, and spherical structure fly ash, were selected to prepare PVC foam composites with 0–20 wt% loading. The tensile strength in both 10 wt% reinforced mica and glass fiber composites improved slightly, while it decreased with the addition of 10 wt% fly ash. Flexural strength reached its maximum in mica and fly ash-filled composites at 10 wt% loading. Meanwhile, flexural strength exhibited higher saturation levels of longitudinal glass fibers due to their penetration within the foam cells. Charpy impact strength measurements showed a decreasing trend with increasing the filler content; however, the rate of reduction was the lowest in PVC/glass fiber foam composites. The effect of filler type and geometry on thermal and dynamic mechanical properties of PVC foam composites was studied using thermogravimetric analyzer and dynamic mechanical analysis, respectively. First decomposition temperature of PVC composites dropped slightly with the addition of fillers, where glass fiber-reinforced foam composites exhibited the lowest rate of reduction. The second decomposition step of PVC foam composites shifted toward higher temperatures with increasing the filler content. Fly ash was found to be more effective in improving the second decomposition temperature. The dynamic modulus of mica and glass fiber-reinforced composites showed an increasing trend below and above glass transition temperature, up to 10 wt% loading, while the storage modulus in fly ash-reinforced composites increased with increasing the filler content at a constant rate. Morphological studies revealed that mica flakes with a paralleled structure within cell walls and glass fibers with a penetrated structure within the cell bubbles exhibited higher agglomeration compared to fly ash composites.
Polyphenylene sulfide (PPS)-expanded graphite (ExGr) conducting nanocomposites have been prepared by powder mixing and in situ polymerization routes after sonicating ExGr particles in acetone. Synthesized PPS has been used to make powder mixed composites. The powder mixed composites exhibit a percolation threshold of 3 wt% due to the formation of graphite nanosheets. When PPS-ExGr composites are prepared by in situ polymerization route, very low electrical percolation threshold less than 0.5 wt% ExGr is obtained. The low percolation threshold obtained is attributed to better dispersion of ExGr nanosheets in the polymer matrix when compared to powder mixed composites. The synthesized PPS has been characterized by X-ray diffraction, differential scanning calorimetry, and infrared spectroscopy. The formation of graphite nanosheets has been confirmed by transmission and scanning electron microcopy analysis.
This article establishes a reliable constitutive model to describe the behaviors of fiber-reinforced polymer composites under quasi-static and dynamic loading. This model integrates the contributions of all the three phases of a composite: the fiber, the matrix, and the fiber/matrix interphase, which make it capable of capturing the key micromechanical effect of the interphase on the macroscopic mechanical properties of composites. The interphase is taken as a transversely isotropic material together with the fiber. By analyzing glass/epoxy and carbon/epoxy composites, it was found that the model predictions agree well with the experimental data and the model is more effective particularly when the fiber volume fraction is high. The dynamic three-phase model was also established by using the coupling of the elastic and Maxwell elements for the viscoelasticity of the matrix as well as the interphase. The article concludes that the three-phase model with consideration of the interphase influence can precisely characterize the static and dynamic mechanical properties of a FRP composite.
In this article, the effect of the incorporation of three inorganic pigments on the properties of coextruded polypropylene-based composites was studied. Three different pigments were incorporated in the shell layer of the composites: iron oxide, titanium dioxide (TiO2) and zinc oxide (ZnO). The tensile properties and Charpy impact strength of the composites were tested. A water immersion test was conducted. The morphology of the fractured surfaces of composites was characterised by scanning electron microscopy. The durability of the composites was assessed by testing colour characteristics and tensile strength after 500 hours of accelerated weathering. The results revealed that the TiO2-containing composite had the highest tensile modulus and Charpy impact strength, while the ZnO-containing composite had the lowest tensile strength and Charpy impact strength. Iron oxide was found to have no effect on either the physical or mechanical properties of the composite. The porosity of composites influences their water absorption and thickness swelling. The TiO2-containing composite exhibited better colour stability.
Carbon fiber reinforced thermoplastics (CFRTPs) have high potential in high-cycle (1 min) molding as a weight-reducing material for the mass production of automobile components. However, residual voids in CFRTPs lead to diminished and unstable mechanical properties; therefore, the effective quantification of the void content in CFRTP products is necessary for developing an affordable system for mass production. In a previous study, we demonstrated that the X-ray attenuation coefficient decreases with increasing void content; thus, measurements of X-ray attenuation coefficients can be used to estimate the void contents of CFRTPs. In this study, we first investigated in detail the soft X-ray attenuation coefficients of completely impregnated composite materials with three different thicknesses; we observed that the attenuation coefficients decreased with increasing composite thickness, even though they should be independent of the thickness according to the Beer–Lambert law. We next demonstrated that although no correlation exists between the X-ray transmittance and the apparent attenuation coefficient of six composites with various void contents, the true attenuation coefficient modified to account for void content exhibits a good linear relationship with the X-ray transmittance, same as fully impregnated composites. Using the approximation line between the X-ray transmittance and the modified attenuation coefficient of CFRTP, we estimated the void content on the basis of the difference between the apparent and true X-ray attenuation coefficients. The average difference in void content determined by conventional hydrostatic weighing and that determined by the proposed X-ray transmittance method was 0.43%. We therefore concluded that the void content of CFRTPs of any thickness can be estimated nondestructively using soft X-rays.
Magnesium hydroxide (MH) was added into high-density polyethylene (HDPE)/ethylene vinyl-acetate (EVA) copolymer blends with various MH contents (30–60 wt%) to improve the flame retardancy of HDPE/EVA blends. The flammability, morphology of charred residues, thermal stability, crystallization, and mechanical properties of HDPE/EVA/MH composites were investigated by UL-94 test, limiting oxygen index (LOI), cone calorimeter test (CCT), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and tensile test. The data obtained from LOI, UL-94 test, and CCT revealed that the addition of MH provided improvements in flame retardancy by increasing the LOI values, UL-94 rating, and reducing heat release, carbon monoxide and carbon dioxide emissions along with delayed ignition with increasing the content of MH. The UL-94 V-0 rating and high LOI value were achieved with the incorporation of MH at a loading level higher than 50 wt% in HDPE/EVA blends, which suggested that the formation of intact, consolidated, and thick residue structures on the surfaces of MH-filled composites prevented the underlying polymer materials from burning. DSC results showed that the crystallinity of HDPE/EVA blends increased with increasing the content of MH, resulting in the enhancement of the strength of HDPE/EVA/MH composites. The thermal stability of HDPE/EVA blends decreased due to the addition of MH.
Flax unidirectional (UD) fabrics and polyamide 11 (PA11) are used to create a 100% bio-sourced composite. The fabrication process is hot press moulding. Different configurations are studied by varying process parameters and composite constituents. Three temperature values (190°C, 200°C and 210°C) are combined with three pressure levels (35, 65 and 100 bars). In addition, two types of flax fabric (A and B) are tested and two types of PA11 (in the form of powder or film) are used. The two forms of PA11 are characterized using differential scanning calorimetry and rheological methods. Ten different composites are then manufactured. They are compared by means of tensile tests and dynamic mechanical analysis (DMA). Results are correlated with microstructural study: measurements of porosity degree and scanning electron microscopic observations are also performed. Finally, an optimum configuration is determined: the composite flax B/PA11 film manufactured with a temperature value of 210°C and using gradual levels of pressure (25 bars during 2 min, 40 bars during 2 min and 65 bars until the end of cycle). This configuration leads to a Young’s modulus value of 36 GPa and a tensile strength of 174 MPa, with the highest storage modulus and the lowest damping factor values measured by DMA.
In the present study, polypropylene/nanoclay (PP/NC) and polypropylene/nano-calcium carbonate (PP/CC) nanocomposites with different weight percentages of filler were prepared using a twin-screw extruder. The effects of nanoparticles content on the nanocomposite were studied using the hardness measured under the applied loads in the range of 10–100 gf. It was observed that the microhardness increases with an increase in the nanofiller weight percentage. The hardness reaches its maximum for 1 wt% and 3 wt% for PP/NC and PP/CC, respectively. The results of the present study are evaluated by analytical methods proposed by Marsh and Tabor. For this purpose, mechanical properties of PP nanocomposites were obtained by uniaxial tensile and compression tests. The results were incorporated in Tabor and Marsh formula. According to the analytical methods, the results obtained from compression test were more accurate than those obtained from tensile test. In addition, variation of H/Y ratio (H and Y are microhardness and yield stress, respectively) versus the filler content under different applied loads was obtained. Finally, the Marsh model is modified in this work. The modified model proves more accurate in prediction of microhardness and H/Y ratio of PP nanocomposite at different applied loadings. The new proposed model correlates the yield stress, elastic modulus, and the applied load to microhardness.
High-performance ultra-high molecular weight polyethylene (UHMWPE) soft ballistic sub-laminates ([0/90] n , SBSL) are stacked to build a soft body armor pack (SBAP) that can defeat handgun projectiles. Transverse impact on single-layer [0/90] SBSL of different size is modeled with shell elements and is solved using LS-DYNA composite material model MAT54. The finite element (FE) model is validated using 1D and 2D theories for transverse impact. The validated FE models are then used to study the perforation behavior of a [0/90] SK76/PU SBSL under constant and variable velocity impact. Results show that the basal shape of the transverse deformation cone has a diamond shape; the cone wave speed along primary material direction agrees well with 2D membrane theory, there exists a minimum perforation velocity below which the SBSL will not perforate, the peak perforation force reduces with the size of the SBSL, and the work of perforation decreases with increasing speed. Detail perforation mechanics of [0/90] SK76/PU SBSL is presented for the first time.
Pineapple leaf fiber (PALF) was treated by silane and isocyanate treatments at 0–20% prior to being used as reinforcement in low-density polyethylene (LDPE) and polypropylene (PP) composites. The reactive groups of silane and isocyanate on PALF surface were confirmed by Fourier transform infrared spectroscopy. Scanning electron micrographs also showed the fiber surface coated with layers of treated chemicals as compared with the untreated one. These surface treatments reduced the water absorption of PALF. The physical properties of the PALF-reinforced composites were investigated. The resulting composites possessed higher tensile strength and lower crystallinity than the untreated composites. Silane treatment gave better PALF/LDPE composites in terms of composite strength as compared to isocyanate treatment. For treated PALF/PP composites, fiber pullout was reduced both silane and isocyanate treatments.
Agave Americana (agave) and Agave sisalana (sisal) fibres belong to the same family of natural fibres. Both the fibres were treated with alkali. Interestingly, alkali-treated agave fibres displayed a clean and smooth surface, whereas alkali-treated sisal fibres showed a rough surface due to the rupture of alkali-sensitive bonds. This indicated that the sisal fibres are more susceptible to alkali treatment as compared to agave fibres. The experimental studies of chemical composition, Fourier transform infrared spectroscopy and X-ray diffraction were also carried out. Both alkali-treated agave and sisal fibres were used to reinforce polyfurfuryl alcohol (PFA) matrix. The effect of these fibres on the mechanical and thermo-mechanical properties of PFA composites was examined. Mechanical, thermal and thermo-mechanical properties of the composites were studied. The results indicated the improvement in mechanical and thermal properties of the reinforced PFA.
The demand for continuous fiber-reinforced thermoplastics has steadily increased during the last years due to their specific properties. But considering the applications in large-scale production, the price for the organic sheets is still too high in order to compete with the metal counterparts. A starting point for the reduction of the total costs is the acceleration of the impregnation process by in-plane polymer flow. For this reason, this scientific report provides an insight into the production process using a continuous compression molding machine. In order to analyze the in-plane polymer flow and its driving forces, a method for the evaluation of the pressure distribution is presented in a first step. The examination revealed a significant inhomogeneous pressure distribution for the whole pressing area, which could be affected by different temperature settings. Afterward, the impregnation quality was correlated with the different settings, followed by the illustration of a huge potential for increasing the impregnation speed.
Wood–plastic composites (WPCs) present a class of materials originally developed to decrease the dependency on the mineral oil-based plastics. However, additives and coupling agents incorporated in these composites are usually derived via synthetic routes. The effect of hardwood distillate (HWD) on the properties of WPC was determined by adding various amounts (1–8 wt%) of distillate to a commercial WPC consisting of thermally treated saw dust (Scots pine) in a polypropylene matrix. The distillate was derived by converting hardwood (birch) into several liquid fractions in a two-part slow pyrolysis retort. The certain addition of particular HWD enhanced the tensile and flexural properties of the WPC studied. Furthermore, the water absorption of the samples decreased substantially, up to over 25%. Proton-transfer reactor time-of-flight mass spectrometric analyses indicated that the addition of the distillate increased the emission rates of studied volatile organic compounds (VOCs) but had no considerable effects on the emission rates of VOCs that are harmful for humans. The conversion of the emission rates into real room concentration revealed that guaiacol and monoterpenes exceed their odor thresholds and therefore can be smelled from the WPCs studied. The findings of this study show that this particulate HWD displayed good potential as an ecological additive in WPCs.
Lignin–melamine–formaldehyde (LMF) resin was prepared by three steps: (i) tosylation of lignin, (ii) synthesis of lignin-melamine (LM) copolymer, and (iii) formation of methylol LM. The synthesized resins were characterized by Fourier transform infrared (FTIR) spectroscopy and phosphorous 31 nuclear magnetic resonance analysis. The curing parameters of LMF resin were determined by differential scanning calorimetry (DSC) and thermal gravimetric analysis. The yield of tosylation is 80%. The FTIR spectrum of tosylated lignin shows the presence of two new bands at 1171 and 1370 cm–1. The formation of the LM was demonstrated by the disappearance of both bands and appearance of the absorbances at 3115, 3312, 3415, and 3470 cm–1 corresponding to the stretching vibrations of primary and secondary amine. The peaks observed at 147.0 and 148.5 ppm are attributed to the new aliphatic hydroxyl groups formed by the methylolation of LM. One exothermic peak was observed in the DSC analysis indicating a one cross-linking reaction.
Nitrile butadiene rubber (NBR) samples filled with cobalt–zinc (Co-Zn) ferrite nanoparticles (Co1–x Zn x Fe2O4, where x = 0, 0.2, 0.4, 0.6, 0.8, 0.9, 0.95 and 1) were prepared. The structure and morphology of Co-Zn ferrite nanoparticles were investigated using X-ray diffraction, transmission electron microscopy, and Fourier transform infrared (FTIR) spectroscopy, while the structure of the Co-Zn nanoferrite-filled NBR composites was studied using scanning electron microscopy and FTIR spectroscopy. The influence of ferrite composition on cure characteristics, mechanical properties and hardness showed an improvement up to x = 0.8. Dielectric parameters showed an enhancement with ferrite composition.
Composite filaments of thermoplastic polyurethane (TPU) and single-walled carbon nanotubes (SWCNTs) have been fabricated via extrusion process and their properties were studied using various characterization techniques. Twin-screw extruder has been used for making the composite filaments and the processing parameters like temperature, screw speed, and pressure were optimized. Thermal, morphological, mechanical, and electrical properties were studied by varying the weight percentage of SWCNTs. Raman shift of SWCNTs is observed for the CNTs dispersed in TPU matrix. Thermal analysis shows that there is an increase in the degradation and melting temperature of the TPU/SWCNTs blends. With the addition of SWCNTs as small filler loadings of 1 wt%, the tensile strength of the blended materials increased from 13 MPa to 21.6 MPa. The electrical conductivity of the composite filaments starts with the addition of 0.01% of SWCNTs. The highest value of electrical conductivity (3.7 x 10–7 S cm–1) obtained with 2 wt% of SWCNTs. This melt extrusion process method could open up for the preparation of new high-performance nanotube composite materials.
In the present study, solution casting method was used for the preparation of nanocomposite films. Primarily, the surface of copper (II) oxide (CuO) nanoparticles was modified with biosafe molecules such as citric acid and ascorbic acid for better dispersion in the polymer matrix. Then novel nanocomposite films were fabricated by loading various percentages of modified CuO nanoparticles in the poly(vinyl chloride) matrix. The ultraviolet (UV)-blocking effects of nanocomposites and their optical properties were studied using UV-visible spectroscopy. Also, other analyses, including Fourier transform infrared spectroscopy, mechanical tensile test, thermogravimetric analysis, and X-microscopy, were performed for investigating thermal, mechanical, and morphological properties of the hybrid materials.
An experimental study was conducted to investigate the effects of temperature and strain rate on tensile behavior of polybutylene terephthalate and polyamide-6 reinforced with short glass fibers. Tension tests were performed in several mold flow directions, at a range of temperatures between –40°C and 125°C, and a range of strain rates between 5 x 10–5 s–1 and 5 x 10–1 s–1. Mathematical relationships were developed to represent the stress–strain response, as well as tensile strength and elastic modulus in terms of strain rate and temperature. Time–temperature superposition principle was also employed to superimpose the effect of temperature and strain rate on tensile strength. A temperature-dependent shift factor of Arrhenius type is suggested, which is independent of the mold flow direction. Mechanisms of tensile failure were also identified from fractured surface of specimens.
Systematic three-dimensional finite element (FE) simulations are carried out to study the ballistic protection performance of double-layer sandwich plates having metallic pyramidal lattice truss cores filled with ceramic prism insertions and void-filling epoxy resin. Both normal and oblique projectile impacts are considered in the FE simulations that are validated against experimental measurements. The ballistic limit velocity, the energy absorbed by key constituting elements and the critical oblique angle corresponding to the transition from ballistic perforation to projectile embedment are calculated. As the oblique angle is increased, the evolution of deformation and failure in the double-layer plates as well as the underlying mechanisms are explored. It is demonstrated that the proposed double-layer sandwich plates outperform both the single-layer sandwich plates and the homogeneous (monolithic) metallic plates having equal total mass, and the top layer (the ceramic insertions in particular) of the double-layer configuration plays a more dominant role in energy absorption.
The mechanical and dynamic mechanical properties of cellulose fibers-reinforced polystyrene composites were investigated as a function of cellulose fiber content and coupling agent effect. The composites were prepared using a corotating twin-screw extruder and after injection molding. Three levels of filler loading (10, 20, and 30 wt%) and a fixed amount of coupling agent (2 wt%) were used. The results showed that a cellulose fiber loading of more than 20 wt% caused decrease in the mechanical properties. The addition of coupling agent substantially improves the mechanical and dynamic mechanical properties. The use of coupling agent improved the storage modulus and reduced the damping peak values of the composites due to the improved interfacial adhesion. The height of the damping peak was found to be dependent on the content of cellulose fiber and the interfacial adhesion between fiber and matrix. The adhesion factor values confirm that the better adhesion occurs when coupling agent is used.
In continuation to our previous work, the current investigation focuses on the effect of static applied pressure on the electrical and dielectric properties of multiwalled carbon nanotube (MWCNT)–polystyrene (PS)/2,3-hydroxy-2-naphthoic acid (β-HNA) nanocomposites. Additionally, optical properties of the nanocomposites are also investigated together with other further electrical, dielectric, and mechanical properties. Adding fixed amount of β-HNA (1.0 wt%) to MWCNTs enhances the MWCNT dispersion, reduces the percolation threshold to about 0.8 wt%, and increases the electrical conductivity up to eight orders of magnitude. The direct current (DC) and alternating current (AC) electrical properties of 1.0 wt% MWCNT–PS composites are investigated as a function of applied pressure. It is found that the current level increases while impedance values decrease with applied pressure during the cycle and the loading–unloading cycle has almost followed the same route indicating its reproducibility. Also the obtained results demonstrate that such a composite might act as pressure-sensitive conductive composite. Mechanical results show that the addition of MWCNTs (treated with β-HNA) to the neat PS increases the tensile strength and yield stress of the neat PS by about 12.39% and 12.53%, respectively, while the elastic modulus decreases by about 3.10%. However, further addition of MWCNTs decreases all mechanical parameters of prepared composites and these composites became more brittle. Besides, optical results indicate an enhancement in the neat polymer ultraviolet and visible absorption and a reduction in its optical energy gap (by about 14.1%) upon addition of 1.0 wt% MWCNTs (treated with β-HNA).
Carbon nanotube (CNT) was employed as a reinforcing material to prepare polyoxymethylene (POM)-based composite film through a simple melting extrusion. An effective approach was developed to clean and modify the surface of as-received CNT with nitric acid and then with a silane coupling agent. The mechanical evaluation demonstrated that a significant reinforcement was achieved for POM/CNT composites due to the improved interfacial adhesion between CNT and the matrix. The thermal stabilities of the composites were also improved in the presence of CNT. The studies on crystallization behaviors showed that CNT acted as a nucleation agent for the crystallization of POM domain in composites, and therefore, the crystallization rate and nucleation density increased remarkably due to the heterogeneous nucleating effect of CNT.
The automotive industry has great interest in designing and producing lightweight high-performance components using fiber-reinforced polymers (FRPs), primarily due to their high specific strengths. Injection molding of FRP is one of the preferred processes to meet low-cost, high-volume objectives. It is imperative to account for shrinkage and warpage while designing the tools for injection molding. However, predicting shrinkage and warpage of injection-molded FRP parts remains a challenge. This is because both the structural and thermal properties depend on the condition of the fibers in the resin, that is, variation in the orientation, length, and concentration throughout the part. Additional challenges come from the fact that the material properties of polymers are a function of temperature, which varies as the parts cool. In this study, we are presenting a finite element-based semiempirical approach to address both these challenges and predict warpage due to cooling for a fiber-reinforced resin component in solid phase. The approach is demonstrated to predict warpage of an injection-molded flat plaque made of glass fiber-reinforced polypropylene, cooled from 160°C to room temperature of 23°C. First, the fiber orientation in the plaque is estimated. Next the material properties for the combined material, that is, glass and resin, are measured as a function of temperature. Then the combined material properties and calculated fiber orientations are used to estimate the ‘in-mold’ condition resin properties using reverse engineering. Finally, the warpage of the plaque is predicted using the estimated resin properties and fiber orientations. Warpage predictions using this method compare well with the measured experimental results. Our study demonstrates that valid predictions for shrinkage and warpage of injection-molded fiber-reinforced thermoplastic parts in solid phase can be made if accurate material properties are used.
The present study seeks to investigate the effect of beverage storage carton (Tetra Pak™) waste and maleic anhydride-grafted polyethylene (MAPE), coordinated to light polyethylene on the mechanical properties of wood–plastic composites. Four levels of Tetra Pak™ (0%, 10%, 20%, and 30%) and two levels MAPE (0% and 3%) were used. At first, the materials were mixed in a Haake internal mixer and then the samples were made through the injection molding method. The results showed that the composites containing 30% of Tetra Pak™ and 3% MAPE have the highest strength and tensile modulus. Moreover, the sample Tetra Pak™ and containing 3% of MAPE has the highest impact resistance. These results have been confirmed by scanning electron microscopy.
Experimental studies were made on isotropic cylindrical skew panels made of Aluminum 7075-T6 and laminated composite cylindrical skew panels under uniaxial compression. The experimental values of the critical buckling load (P cr) were determined using five different methods. The values of P cr were also determined using MSC/Nastran and CQUAD8 finite element. The experimental values of the P cr obtained by different methods were compared with the finite element solution. The effects of the skew angle and aspect ratio on the critical buckling load of isotropic cylindrical skew panels made of Aluminum 7075-T6 were studied. The effects of the skew angle, aspect ratio, and the laminate stacking sequence on the critical buckling load of laminated composite cylindrical skew panels were also studied. It is found that the method IV (based on a plot of applied load (P) vs. average axial strain) yields the highest value for P cr and method III (based on a plot of P vs. square of out-of-plane-deflection) the lowest value for P cr. The experimental values given by method IV are seen to be closest to the finite element solution, the discrepancy being in the range of 5–23% for laminated composite cylindrical skew panels. For isotropic panels, it is found that the value P cr initially increases with an increase in the skew angle and later decreases as the skew angle increases beyond 15°. For laminated composite panels, the P cr value decreases as the aspect ratio increases for all laminate stacking sequences.
Void consolidation of high-performance thermoplastic composites strongly depends not only on average void content but also on the distributions of void size, shape, and location within the prepreg materials. High-resolution 3-D X-ray microcomputed tomography shows that voids in carbon/poly(ether ether ketone) (AS4/APC2) prepreg are rodlike with major axis along the fiber axial direction. In order to accurately characterize the void microstructure, a detailed study was conducted to quantify the statistical distribution of void content, void length, equivalent void diameter, and void aspect ratio. Resolution of 1.48 μm/pixel provided a balance of measurement accuracy and inspection time. Suitable statistical distribution functions were found to describe the void length, diameter, and aspect ratio. For each void property, a sub-statistical representative volume element (SRVE) was determined. The SRVE of the overall void microstructure is defined as the maximum dimensions of the sub-SRVEs. In case of AS4/APC2 tape, the SRVE was found to be 6.1 mm in length (fiber direction), 27 mm in width (transverse to fiber direction), and 0.18 mm of full prepreg thickness.
The torque rheological properties of plastic wood composites are important to practical processing, but the research in this field is rare. In present, a Brabender plastrograph torque rheometer was used to analyse the rheological behavior of polypropylene (PP)/cocoa pod husk (CPH) composites. The effect of processing parameter, filler content, and addition of maleated polypropylene (MAPP) on torque rheological properties was investigated. The torque rheological data found that the processing torque increased with the increases of rotor speed, filler content, and addition of MAPP. The PP/CPH composites melt behavior as pseudoplastics and shear thinning occurred at higher shear rate. The decrease of power law index (n) evidenced the pseudoplasticity of PP/CPH composites increased at higher filler content and presence of MAPP. The increase of viscosity on PP/CPH was due to filler–filler interaction at higher filler content and strong filler–matrix adhesion after addition of MAPP. The activation energy of PP/CPH composites also increased with higher amount of CPH and addition of MAPP.
The aim of this study is to simultaneously improve the mechanical strength and fracture toughness properties of recycled poly(ethylene terephthalate) (r-PET). For this purpose, Joncryl® was used as chain extender and Lotader® was used as impact modifier. The combined effect of chain extender and impact modifier on the chemical, fractural, mechanical, and thermal properties of r-PET was investigated. Fourier transformed infrared spectroscopy (FTIR) analysis, EWF analysis, tensile test, and differential scanning calorimetry (DSC) analysis were performed. FTIR analysis revealed that all the epoxy groups in the Joncryl® were consumed during the compounding. EWF results showed that while toughness of r-PET decreased with the addition of Joncryl®, toughness was increased with addition of impact modifier Lotader®. It was found that 2.5% Lotader® usage at the same time with Joncryl® increased the tensile strength of r-PET as well as toughness. It was observed from DSC analysis that chain extender and impact modifier addition did not change the thermal transition temperatures of r-PET.
Nitrile butadiene rubber (NBR) particles as impact modifier mixed with treated ceramic fillers (aluminum oxide, yttria-stabilized zirconia, and silicon dioxide) were used to reinforce poly(methyl methacrylate) (PMMA) denture base material. The powder components are PMMA, benzoyl peroxide, NBR (5, 7.5, and 10 wt%), and ceramic fillers (5 wt%) treated with silane. The liquid components are 90% methyl methacrylate and 10% ethylene glycol dimethacryate. Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy analyses confirmed that the ceramic fillers were successful. The morphology of fracture surfaces of specimens was characterized using field emission scanning electron microscopy. The impact strength (IS) and fracture toughness (K IC) improved significantly. IS increased to 56% (8.26 kJ m–2) and 73% (2.77 MPa m1/2) for K IC when compared with unreinforced PMMA matrix. Statistical analyses of data results were significantly improved (p < 0.005). PMMA denture base reinforced by NBR particles mixed with treated ceramic fillers are ideally suited for dentistry applications with the ability to withstand high mastication forces.
This work is devoted to investigate the available agricultural Tunisian waste: the date pits as reinforcing filler for thermoplastic matrix. The chemical composition of this reinforcing filler is found to be comparable to nonwood plants: its content comprises of 13% of extractibles, 22% of lignin, and 61% of holocellulose. Then, the lignocellulosic filler was used to prepare different composites films using Brabender mixing device. A series of composite film was established by different loadings of the date pits waste with 10–50% of the filler in 10% as an interval. The ensuing composites materials were then characterized by several techniques such as the morphology of the composites, which was investigated using scanning electron microscopy. The thermal properties of prepared materials were studied using differential scanning calorimetry and thermogravimetric analysis. Finally, the mechanical and water absorption properties were involved. The obtained results indicated that date pits–based particles enhanced the thermomechanical properties of the thermoplastic matrix and demonstrated that this available lignocellulosic biomass can be considered to be a promising filler material.
This article deals with the investigation of electrical and mechanical properties of styrene–butadiene–styrene tri-block copolymer (SBS) nanocomposites containing SBS-grafted graphene oxide (SBS-g-GO) nanofillers dispersed in the SBS matrix through a solution processing method. In order to improve the compatibility of graphene oxide in SBS, graphene oxide was modified by maleic anhydride-grafted SBS to SBS-g-GO. The SBS-g-GO were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and thermogravimetric analysis. The results showed that the SBS molecules were homogeneously bonded onto the surface of the GO, leading to an improvement of the mechanical and electrical properties of SBS/SBS-g-GO composites due to the excellent interfacial adhesion and dispersion of SBS-g-GO in SBS.
Poly(lactic acid)/sugarcane bagasse fiber (PLA/SCBF) composites were prepared using melt compounding followed by compression molding. Epoxidized soybean oil (ESO) was selected as plasticizer for the PLA/SCBF composites. SCBF was alkali-treated and ground into powder form with the size of approximately 100 μm (hereafter designated as SCBFP). The properties of the PLA composites were assessed using impact tests, field-emission scanning electron microscopy, and dynamic mechanical analysis (DMA). DMA results showed that the addition of SCBF increased the storage modulus of PLA and the effect is more pronounced for the one containing SCBFP. The impact strength of PLA/SCBF composites was improved significantly by the addition of ESO.
A new type of biocomposite, bamboo flour/copolyester (BFCP) composite for selective laser sintering (SLS™) was studied in this article. The bamboo flour was made from the bamboo residual of the bamboo production collected from a chopsticks factory. The BFCP composites of three mixture ratios (20/80, 25/75, and 30/70 (wt/wt)) were processed by SLS™. The proper processing parameters were determined by single-layer sintering methods. The mechanical properties of test specimens made from BFCP composites of three mixture ratios have been investigated. The results demonstrated that the mechanical properties of the specimens made by BFCP composite of 20/80 (wt/wt) were the best among those of the three mixture ratios and the average tensile strength, flexural strength, and impact strength of the specimens made from BFCP composite of 20/80 (wt/wt) were up to 4.14 MPa, 11.02 MPa, and 0.84 kJ m–2, respectively. The mechanical properties of specimens are extremely improved through infiltrating epoxy resin.
The present investigation reports about the solid particle erosion behavior of randomly oriented short date palm leaf (DPL) fiber-reinforced polyvinyl pyrrolidone composites. The erosion rates of these composites have been evaluated at different impingement angles (15–90°) and impact velocities (48–109 m/s). The neat polyvinyl pyrrolidone shows maximum erosion rate at 30° impingement angle, whereas, PVA/DPL composites exhibit maximum erosion rate at 45° impingement angle irrespective of fiber loading showing semi-ductile behavior. Erosion efficiency () values (2.83–15.29%) indicate micro-ploughing and micro-cutting as dominant wear mechanisms. The morphology of eroded surfaces was examined by scanning electron microscopy. Possible erosion mechanisms are discussed.
Powder-mixed polypropylene (PP)–graphite binary composites exhibit an electrical percolation threshold at 10 wt% graphite signifying insulator-semiconductor transition. Three conducting fillers such as carbon black (CB), sonicated expanded graphite (s-ExGr), and carbon nanofiber (CNF) are mixed with PP-7 wt% graphite binary composites. The electrical percolation threshold has been found to have inverse relation to the aspect ratio of second conducting fillers in hybrid composites. The aspect ratio of second conducting fillers varies in the order CB < ExGr < CNF. The electrical percolation threshold is found to vary for the hybrid composites as 2.2 wt% for CB addition, 0.75 wt% for ExGr addition, and 0.2 wt% for CNF addition in the PP-7 wt% graphite binary composites. When the aspect ratio of second conducting fillers increases, they reduce the barrier for the charge transport. The second conducting fillers occupy the interspace of graphite and alternating current studies show that the effective dielectric constant increases with the concentration of second conducting filler in the hybrid composites. The composites are characterized by transmission electron microscopy and scanning electron microscopy. Melt-crystallized PP-7 wt% graphite-CNF composites exhibit higher percolation threshold due to decrease in the polymer viscosity which increases the interparticulate distance.
Thermoplastic vulcanizates (TPVs) based on ethylene–vinyl acetate copolymer (EVA)/ethylene–vinyl acetate rubber (EVM) were prepared by dynamic vulcanization. Mechanical properties, morphology, and Mullins effect of the TPVs were investigated. The results showed that the EVA/EVM TPV with 40/60 weight ratio had excellent mechanical properties. There was no obvious phase separation on the fracture surface of the TPV. Mullins effect could be observed in the stress–strain curves of TPVs during the uniaxial loading–unloading cycles. Compared with TPV with 20/80 weight ratio, the TPV with 40/60 weight ratio had the relatively larger maximum stress, residual deformation, and internal friction loss at specific strain.
In this research, transparent titania (TiO2) thin films were deposited on a glass microscope slide and on a flexible polyethylene terephthalate (PET) substrate under a high vacuum condition by means of the thermionic vacuum arc (TVA) method in a very short period of time (60 s). Optical properties and surface properties of the coated TiO2 surfaces are related to the structural changes of the coated layers due to ion energies and substrate effect. But obtained results are closely linked to literature values. Our analysis showed that the TVA method is an alternative method for low-temperature coatings and the produced films present important advantages for optical and industrial applications.
This study reports the results of experimental and numerical investigations on the thermophysical properties and the process of melting of a phase-change composite material. The proposed phase-change composite material based on epoxy resin with spherical shape paraffin wax (RT27) was used as a new thermal storage system. Thermal characterization was performed using a transient guarded hot plate technique. The results revealed the importance of thermal storage by latent heat. The numerical analysis is realized using numerical COMSOL® Multiphysics 4.3b. The effect of various parameters of the numerical solution on the results is examined: in particular, the term describing the mushy zone in the momentum equation and the influence of temperature melting range. The findings of the experimental investigation compare favorably with the numerical results.
"Sea-island" structure silver/polyaniline (Ag/PANI) nanocomposites were synthesized through sonication of an aqueous solution with silver nitrate and aniline at the temperature of 20 ± 1°C under nitrogen atmosphere. The nanocomposites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet–visible absorption spectroscopy,field emission scanning electron microscopy, and energy dispersive spectrometry, respectively. Furthermore, Ag/PANI nanocomposites were immobilized on the surface of glassy carbon electrode (GCE) and electroactivity behavior was investigated by cyclic voltammetry and differential pulse voltammetry. The obtained sea-island structured Ag/PANI nanocomposite-modified GCE showed high electrocatalytic activity for the oxidation of
The aim of this research was to investigate the interaction of electron beam irradiation on the different valence of copper (I) and copper (II) oxides (Cu2O and CuO) added low-density polyethylene (LDPE) composites. The results showed the increasing of Cu2O loading level in replacing the CuO has significantly reduced the gel content (or degree of cross-linking networks) in LDPE matrix. This is due to the poorer effect of Cu2O in inducing the polymeric free radicals. Meanwhile, the application of low irradiation dosage (≤100 kGy) has significantly increased the crystallite size for crystallite peak (110) of all LDPE composites. However, further increment in irradiation dosages from 100 to 300 kGy has gradually reduced the crystallite size of deflection peak (110). The tensile strength of all LDPE composites was gradually decreased with increasing of Cu2O loading level due to agglomeration of Cu2O and CuO particles in LDPE matrix. In addition, the increasing of irradiation dosages on all Cu2O /CuO added LDPE composites has gradually increased the tensile strength by inducing the formation of the cross-linking networks in LDPE matrix. Nevertheless, the increasing of irradiation dosage has gradually decreased the elongation at break of all Cu2O /CuO added LDPE composites. This is due to the higher degree of cross-linking networks in LDPE matrix could restrict the mobility of LDPE macromolecular chains when subjected to straining stress.
Composites were prepared from recycled polypropylene (RPP), oil palm empty fruit bunch (EFB) and/or glass fibre (GF) using extrusion and injection moulding techniques. Two types of maleic anhydride-grafted polypropylene such as Polybond 3200 and Fusabond P 613 were used to improve the interfacial adhesion between fibres and matrix. The EFB: GF ratio was fixed as 70:30 and fibre loading was considered as 40 wt%. Microwave was used to treat the EFB fibre, which was soaked in a fixed mass concentration (12.5%) of alkali solution at different temperatures (70, 80 and 90°C) for a fixed period of time (60 min) and for different times (60, 90 and 120 min) at a fixed temperature (90°C). A magnetron controller was developed to control the time and temperature accurately for the treatment of fibre. Various characterization techniques such as density, melt flow index, tensile, Izod impact, flexural, field-emission scanning electron microscopy and water uptake testing were performed for the composites. Besides, thermogravimetric analysis and differential scanning calorimetry were also used to evaluate the thermal and crystalline properties of the composites, respectively. Result analyses revealed that microwave-treated fibre-based composites showed improved mechanical and thermal properties. EFB fibres treated at 90°C for 90 min were found to be suitable for better reinforcement into the composite in terms of mechanical, thermal and crystalline properties. Moreover, onset degradation temperature and water absorption properties were also found to be changed apparently due to treatment.
This article investigates three-layer co-extruded blown film comprised of low-density polyethylene (LDPE)/ethylene–vinyl alcohol (EVOH)/LDPE without adhesion layers. Various thicknesses of pure EVOH were sandwiched by outer LDPE layers blended with linear low-density polyethylene-grafted-maleic anhydride (LLDPE-g-MAH) as compatibilizer in concentrations from 0 wt% to 2.0 wt%. The study found that a mere 3-μ EVOH layer can achieve a 180 times improvement of oxygen barrier properties as compared to the control sample. When the EVOH loading is 10–15 wt% of the total film mass, the addition of LLDPE-g-MAH into the outer layers indicated a positive synergistic effect by enhancing barrier properties. In contrast, when the EVOH loadings are at 5 wt% and 7.5 wt%, the barrier properties of the film was reduced. Layer-to-layer interaction between the LDPE and EVOH was notably improved as demonstrated by a 26–42% increase of interlaminate peel strength in the presence of 0.5–2 wt% LLDPE-g-MAH in all samples. Congruently, the introduction of the LLDPE-g-MAH into the outer LDPE layers also resulted in an increased dart impact toughness and tensile strength for the film. The EVOH crystallinity showed a reduction after adding LLDPE-g-MAH, particularly apparent for the lower EVOH concentrations.
The intercalation complex marked as KAA was a modified kaolinite (KA) with potassium acetate as an intercalating agent, which was used as a reinforcement to prepare polyamide 1010 (PA1010) matrix nanocomposites (PKAA) by melt compounding. X-Ray diffraction results indicated that the interlayer basal spacing increased from 0.720 nm (KA) to 1.411 nm (KAA), after an intercalation process with an intercalation ratio of 99.7%. The nanocomposite with 2 wt% KAA exhibited the best comprehensive mechanical properties, including tensile strength, elongation at break, and notched impact strength. Furthermore, the thermal performance of these nanocomposites could be effectively improved, which manifested as the elevated glass transition temperature and thermal decomposition temperature in the test results of the dynamic mechanical thermal analysis and thermogravimetric analysis (TGA). The melting point and crystallization behavior of PKAA were also increased due to results from the differential scanning calorimetry. Besides, the bilayer inserting model was simulated by Materials Studios software to further understand the structure-function relationship of PKAA.
Biodegradable films from hydroxypropyl distarch phosphate (HPDSP)/poly(vinyl alcohol) (PVA) and cationic starch/PVA blends were obtained by extrusion blowing at ratios of 100:0, 95:5, 90:10, 85:15, and 80:20. The morphology, X-ray patterns, transparency, mechanical properties, thermal properties, and water vapor permeability (WVP) of the films were measured and compared. Scanning electron microscopic micrographs of the films showed continuous matrix texture as well as better compatibility between modified starches and PVA. X-Ray diffraction indicated the formation of ordered crystalline structures in the films during extrusion blowing. The addition of PVA to modified starches significantly increased their tensile strength (TS, 3.92 MPa) while decreasing their water vapor permeability (WVP, 3.23 x 10–10 g m–1 s–1 Pa–1). The starch/PVA composite films did not show phase separation.
In this study, microstructural features and physical properties of thermoplastic polyurethane (TPU)/organoclay nanocomposites films prepared via melt blending (MB) and solution mixing (SM) methods were investigated in detail. Amount of organoclay into the composition varied in the range of 2 and 8 wt%. Microstructural properties of samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) methods. It was found that the organoclay layers exhibited better dispersion, exfoliated, and semi-exfoliated structure in the MB samples than the SM counterparts. Viscoelastic properties of samples were also studied by measuring the rheological behaviors of bulk samples in an oscillatory rheometer in the melt state and measuring of the time-dependent nonlinear creep behaviors of film samples in a dynamic mechanical analyzer in the solid state. Gas and water vapor permeability (WVP) values of nanocomposite films were measured. Based on the melt rheology measurements, it was found that the MB samples showed characteristic solid-like behavior and higher improvement in storage modulus at low-frequency region. Creep behaviors of samples were also quantified with the four-element Burger model. It was found that the introducing of organoclay into the composition via MB method yielded more improvement in the creep resistance, gas, and WVP values of films than the SM counterparts, possibly due to the better dispersion of organoclay layers into the TPU structure. Based on the improvement in permeability and mechanical properties of the samples and also SEM and TEM observations, the average aspect ratio value (A f) of organoclay stacks was estimated in the range of 15–20 for the MB samples.
In the present work, a different green coupling agent (GCA) was developed from virgin coconut oil (GCA-C). The GCA-C were a kind of glycidyl fatty acid ester which are reactive to natural filler. A comparison between GCA made from palm oil (GCA-P) and coconut oil (GCA-C) was studied. The results indicated the tensile strength and tensile modulus of composites increased with increasing the GCA content, and the 3 wt% of GCA content was the optimum content to achieve maximum improvement. Meanwhile, the increased GCA content slightly reduced the elongation at break of composites, but the elongation at break increased at 5 wt% of GCA content. The GCA-C had better performance in improving interfacial adhesion compared to GCA-P due to different fatty acid content. The micrographs of scanning electron microscope evidenced that the modified cocoa pod husk (CPH) with 3 wt% GCA had better filler–matrix adhesion with polypropylene matrix.
Three types of surfactants, specifically cationic, anionic, and nonionic, at different weight percentages were added into high-density polyethylene/low-density polyethylene/cellulose (HDPE/LDPE/cellulose) biocomposites via melt mixing. The cationic and anionic surfactants which are hexadecyltrimethylammonium bromide (HTAB) and sodium stearate (SS), respectively, were added from 4 to 20 wt%, whereas the nonionic surfactant which is sorbitan monostearate (SM) was added from 1 to 5 wt%. The mechanical testing results exhibited that the addition of HTAB increased tensile strength and tensile modulus, while SS deteriorated mechanical properties, while SM increased impact strength and tensile extension of the biocomposites. Based on the mechanical properties results, optimum weight percentages of HTAB and SM were 12 wt% and 4 wt%, respectively. The scanning electron microscopic micrographs displayed that the amount of cellulose fillers pullout decreased with the addition of HTAB, followed by SM, but it increased with SS. Fourier transform infrared spectra, X-ray diffractometer patterns, thermogravimetric analysis results, and differential scanning calorimetry thermograms have confirmed the presence of physical interactions only with the addition of HTAB and SM. Based on the results, compatibilizing effect was found in HTAB, whereas SM has not showed compatibilizing effect but instead plasticizing effect. However, neither compatibilizing nor plasticizing effect was exhibited by SS.
Flame-retardant properties of ammonium polyphosphate (APP) and its two microcapsules, APP with a shell of melamine–formaldehyde (MF) resin (MFAPP) and APP with a shell of epoxy resin (EPAPP), were studied in styrene–butadiene–styrene (SBS). The results indicate that APP after the microencapsulation leads to an increase in limiting oxygen index in SBS compared with APP. When dipentaerythritol is incorporated into the SBS composites containing the APP microcapsules, a further improvement in flame retardancy of the composites is observed. The microencapsulation does not result in much improvement of mechanical properties. Moreover, the effect of a compatibilizer (SBS grafted with maleic anhydride) on flame-retardant and mechanical properties of SBS/APP composites was investigated.
Kinetics of non-isothermal crystallization of isotactic polypropylene (iPP)/nucleating agent blends was studied for the nucleation mechanism. Avrami, Jeziorny, and correctional Friedman methods were applied to analyze the non-isothermal crystallization of the iPP/aryl heterocylic aluminum phosphate/sodium laurate (iPP/AHP-Al/L-Na) blends. For a given cooling rate of 10°C min–1, the onset temperature (T o) and crystallization temperature (T c) of the iPP/AHP-Al/L-Na blends increased by 4.19°C and 3.57°C, respectively, compared to iPP/L-Na. The T o and T c of iPP/AHP-Al/L-Na blends increased by 2.13°C and 1.79°C, respectively, compared to iPP/AHP-Al, when the AHP-Al mass fraction reached 1.2. The effective activation barrier (E) for non-isothermal crystallization was the least when the AHP-Al mass fraction was 0.8. The value of the initial slope of the exotherm increased with the addition of AHP-Al monotonically. All these findings indicated that AHP-Al could improve the initial crystallization rate and also that the addition of AHP-Al/L-Na reduced the E for non-isothermal crystallization. It is speculated that an ion exchange reaction between AHP-Al and L-Na occurs during the mixing process and could be possible that this results in the generation of a more efficient nucleating agent.
Use of organic biomass, industrial waste lignin, was considered interesting due to its easy availability, polymeric nature, and ample scope to modify with an aim to replace conventional metal oxides to achieve improved properties of the blend when blended with polyolefins. To study the effect of chemical modification of lignin on the thermal, structural, and mechanical properties of polypropylene (PP)/modified lignin blends, purified industrial waste lignin was modified by two different chemical methods and blended in various proportions in PP matrix. The thermal stability of the blends was studied by thermogravimetric analysis, whereas melting and crystallization behavior of blends was studied by non-isothermal differential scanning calorimetry. The results show improved thermal stability of blends with increasing modified lignin proportion in the PP matrix. More depression in melting point was observed in PP/alkylated lignin blends than PP/arylated lignin blends, whereas addition of alkylated lignin shows polymorphism in PP matrix. Intermolecular interactions between blend components have been evaluated by applying several mathematical models to experimental mechanical property data. In most of the cases, good agreement has been obtained between the predictions made by using mathematical models and interpretations done on the basis of experimental data, showing the suitability of these models for predicting the mechanical properties of PP/modified lignin blends.
In the present article, a highly heat-resistant composite with a high fiber volume fraction (Vf > 60%) was successfully manufactured using engineering plastic Nylon66 as matrix and carbon fabric as reinforcement by a solution impregnation molding method. The mechanical properties of the composite were investigated using a tensile measuring device. Mechanical analysis revealed the superior mechanical properties of the composite relative to those of previously reported carbon fiber-reinforced thermoplastics (CFRTPs). The cross section and fracture surface of the composite were characterized by scanning electron microscopy. The resin successfully impregnated the fiber bundles and the bonding strength of the fiber–resin interface was excellent. Dynamic mechanical analysis was used to evaluate the heat-resistant property of the composite. The composite exhibited a better heat-resistant property relative to that of the carbon fiber-reinforced crystalline co-polyester composite. To further verify the versatility of this method, super engineering plastic polyetherimide with a higher molecular weight was successfully employed as matrix to prepare CFRTP.
The aim of the work was to investigate the effect of recycling on the mechanical behaviour of polypropylene composites reinforced with glass fibres (GFs), starting from a material already used in automotive for vehicle components, obtained by injection moulding. Formerly specimens of pristine composites were subjected to tensile and flexural tests, then the specimens were grinded, reprocessed and recycled only once. The recycled composites showed a slight decrease in the elastic modulus and tensile and flexural strength values. Morphological investigations, carried out by scanning electron microscopy and optical microscopy, were also performed to study the microstructure and the fibre–polymer interfaces, together with the GFs’ orientation and distribution within the polymeric matrix before and after the mechanical recycling. The results revealed that the mechanical recycling had no significant effect on the final microstructure and performance of the fully recycled composites, which can be still successfully used for structural applications in the automotive field.
In this work, a kinetic study on the thermal degradation of films prepared from high-density polyethylene (HDPE), poly(
The aim of the work is to prepare the halogenated methacrylate-based polymer nano-aluminum oxide (Al2O3) composites and to study the effect of incorporated nano-Al2O3 on morphological and thermal studies. A functional 2,4,6-tribromophenyl methacrylate-co-glycidyl methacrylate copolymer microspheres (poly(TBPMA-co-GMA); pTG) by emulsion solvent evaporation techniques, whereas (2,4,6-tribromophenyl methacrylate-co-glycidyl methacrylate)-Al2O3 nanocomposites (pTG-Al2O3 nanocomposites) were prepared by solution mixing techniques. The pTG and its Al2O3 nanocomposites were structurally characterized by Fourier transform infrared (FTIR) spectroscopy. Thermal studies of pTG and its Al2O3 nanocomposites were carried out by thermogravimetric analysis and differential scanning calorimetry . The molecular weight of the pTG was determined by gel permeation chromatography. The size distribution and morphology of the pTG and its Al2O3 nanocomposites were determined by scanning electron microscopy (SEM). The FTIR results reveal that there is no significant interaction between the polymer matrix and Al2O3 nanoparticle. The significant increase in the initial decomposition temperature and glass transition temperature of pTG-Al2O3 nanocomposites compared to its polymer was due to the incorporation of nano-Al2O3 in the polymer matrix. The SEM observation provides the information about the morphological changes that arise in polymer matrix due to the incorporation of nano-Al2O3.
In this work, isotactic polypropylene (iPP) nanocomposites were prepared containing silver nanoparticles (Ag-NPs) with a novel and easy method, using polyethylene glycol (PEG) as reducing agent and surface modifier. Ag-NPs were prepared using different amounts in weight of silver nitrate into PEG to induce the formation of Ag-NPs. PP/Ag nano compounds were prepared by melt blend method: single-screw extruder and internal Brabender mixer. The effects of Ag-NPs and PEG on the crystallization, morphology, thermal, and mechanical properties were evaluated. Ag-NPs with a particle size of 80 nm and typical growth of the β-form in iPP were observed. The presence of PEG in samples of PP/Ag-NPs was detected by infrared spectrometry and the peak characteristic of Ag-NPs by ultraviolet–visible analysis. X-Ray diffraction patterns and differential scanning calorimetry thermograms showed the β-phase formation in both of the dispersion methods, but Brabender mixer showed higher percentages of crystallinity (31% of β-phase). The elongation at break was increased and it was directly dependent on the relative amount of crystalline β-phase. PEG is an excellent precursor to get Ag-NPs and a good interface modifier of iPP.
The present research investigates the morphology and rheological behavior of poly(butylene terephthalate)/polypropylene (PBT/PP) blends containing hydrophilic and hydrophobic organoclays. The distribution of nanoclays and morphology of nanocomposites were analyzed using X-ray diffraction (XRD) and transmission and scanning electron microscopies. The XRD patterns show that the level of intercalation structure in nanocomposites reinforced by hydrophilic nanoclay is significantly higher than nanocomposites filled by hydrophobic one. According to morphological analysis, both types of nanocomposites indicate the reduction of droplet size, whereas hydrophilic nanoparticles illustrate more compatibilization efficiency than hydrophobic. According to transmission electron microscopy, hydrophilic nanoclays are mainly localized in the PBT matrix and at the interface, whereas hydrophobic nanoparticles are confined in the PP-dispersed phase and at the interface. From the rheological point of view, the results show that nanocomposites with hydrophilic nanoclay show stronger pseudoplasticity, higher viscosity, and more elasticity than nanocomposites with the hydrophobic one. The localization of hydrophilic organoclay in the PBT matrix aids to finer morphology of the PBT/PP blend, whereas hydrophobic one resists the breakup of droplets by confinement in dispersed phase.
Two diblock copolymers of poly(methyl methacrylate)-block-poly(styrene) with chlorine as terminal group (PMMA-b-PS-Cl) were synthesized via two-step atom transfer radical polymerization. The structures of the block copolymers were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and gel permeation chromatography. Thermal properties including glass transition temperature (T g) and thermal stability were studied by differential scanning calorimetry and thermogravimetric analysis (TGA), respectively. The block copolymers of PMMA-b-PS-Cl exhibited two glass transitions, which were attributed to the T gs of PMMA and PS segments, respectively. According to TGA, thermal decompositions of PMMA macro-initiator and PMMA-b-PS-Cl block copolymers had two stages. The weight loss ratio in the second stage was more significant than that in the first stage, which may be attributed to the separation of the halogen atom from the terminal group and the formation of a double bond. The breaking down of the backbone dominates in the second stage in which the weight loss ratio was more than 70%, represented the main stage of pyrolysis. It was found that the introduction of the PS chain remarkably enhanced the thermal stability of the copolymer, thus endowing the block copolymers high activation energy for thermal decomposition. On the other hand, the remaining two pyrolysis procedures further indicated that thermodynamic mechanism didn’t change due to the introduction of PS segments.
In this attempt, we have designed novel poly(ester–urethane) (PEU) using poly(di(ethylene glycol)/trimethylolpropane-alt-adipic acid), tolylene-2,4-diisocyanate, and novel diol. Later, PEU has been employed for the fabrication of nanocomposites and foams with hydroxyl-modified montmorillonite (MMT-OH) via in situ polymerization. Afterward, structure and physical properties of PEU/MMT-OH nanocomposites and foams have been explored using various techniques. Physical characteristics of nanocomposites and foams seemed to be dependent upon polyurethane structure, modification of layered silicate and physical interaction between matrix and organoclay platelets. Field emission scanning electron microscopy revealed distorted honeycomb morphology of PEU/MMT-OH 1–5 foams, while PEU/MMT-OH 1–5 nanocomposites depicted dispersed MMT-OH in the matrix. Increased cell density in nanocomposite foams was also observed relative to pure PEU foam. PEU/MMT-OH 5 (5 wt% MMT-OH) foam showed improved tensile strength of 58.1 MPa relative to PEU/MMT-OH 1 foam (56.8 MPa). The density of the foams was also increased (0.7–1.7 g cm– 1) with clay loading. The 10% thermal decomposition temperature of PEU/MMT-OH 1–5 foams measured by thermogravimetric analysis was in the range of 431–465°C. Percentage of water absorption was also measured for the foam materials. Dynamic mechanical thermal analysis of PEU/MMT-OH 5 foam with 5 wt% nanofiller showed higher glass transition temperature (T g) of 129°C relative to PEU/MMT-OH 1 (T g 116°C). UL 94 and limiting oxygen index results showed that PEU/MMT-OH 1–5 foam had increased nonflammability (V-0 rating) with the clay loading. Silicate layers of MMT-OH were well exfoliated in PEU matrix due to chemical reaction between the hydroxyl of MMT-OH and functional groups of PEU. The morphology, mechanical, thermal, and flame retardant properties of PEU/MMT-OH 1–5 foams were found to be superior to those of PEU/MMT-OH 1–5 nanocomposites.
Composite sandwich structures show promising lightweight properties for the aviation industry. Nowadays time-consuming manufacturing methods still prevent an extensive application of composite sandwiches, which can be overcome by the use of thermoplastic polymers in skins and core. During manufacturing of thermoplastic composite (TPC) sandwich structures, the joining of skins and core is a critical step. Therefore, several skin–core joining methods have been under investigation and development in the published literature, which can be categorized into adhesive bonding or fusion bonding. Fusion bonding by means of vacuum moulding, compression moulding or in situ foaming shows great potential for joining sandwich skins and core. Although various phenomena such as core collapsing or skin deconsolidation challenge the processes. This article aims to present an overview of research that has been done in the area of manufacturing TPC sandwich structures and will serve as a baseline and aid for further research and development efforts.
The aim of this work is to investigate the degradation of low molar mass poly(ethylene terephthalate) (PET)/organically modified montmorillonite (OMMT) clay nanocomposites prepared by melt processing. The rheological behavior in combination with transmission electron microscopic images suggests an intercalation and therefore a percolating network. Furthermore, the results indicate that the increase of organoclay content caused a degradation of PET during processing of PET/OMMT nanocomposites, once it was observed the PET molar mass decreases. The effect mentioned could be attributed to an increase of Brønsted acidic sites on the platelet surface, which is produced by the Hofmann elimination reaction of ammonium, and also the presence of residual metal compounds on clay surface might possibly favored the polymer matrix degradation process.
In addition to fiber properties, the fabric structure plays an important role in determining ballistic performance of composite body armor textile. Textile structures used in ballistic protection are woven fabrics, unidirectional (UD) fabric structures, and nonwoven fabrics. In this article, an analytical model based on wave propagation and energy balance between the projectile and the target is developed to analyze hybrid fabric panels for ballistic protection. The hybrid panel consists of two types of structure: woven fabrics as the front layers and UD material as the rear layers. The model considers different cross sections of surface of the target in the woven and UD fabric of the hybrid panel. Also the model takes into account possible shear failure by using shear strength together with maximum tensile strain as the failure criteria. Reflections of deformation waves at interface between the layers and also the crimp of the yarn are modeled in the woven part of the hybrid panel. The results show greater efficiency of woven fibers in front layers (more shear resistance) and UD yarns in the rear layers (more tensile resistance), leading to better ballistic performance. Also modeling the yarn crimp results in more trauma at the backface of the panel producing data closer to the experimental results. It was found that there is an optimum ratio of woven to UD materials in the hybrid ballistic panel.
This article holds significance in preparing nanocomposites with reasonably good strength and flexibility. Nanohydroxyapatite (nHA) and polypropylene glycol-coated nHA (PPG-nHA) were synthesized by sol–gel technique. Nanocomposites derived from immiscible blends of thermoplastic polyurethane (TPU) and polydimethylsiloxane (PDMS) rubber with nHA as the nanofiller were prepared by melt mixing technique and characterized. Transmission electron microscopic images display a significant extent of dispersion of modified and unmodified nHA in the blend matrices. Scanning electron microscopy results show that the incorporation of PPG-nHA leads to a reduction in the particle size of PDMS in the blends. Dynamic storage modulus against strain sweep study reveals the interaction between the polymer matrix and the filler increased by the surface coating of nHA with PPG. Surface coating of nHA with PPG led to the enhancement of physicomechanical properties of the blend nanocomposites. Thermogravimetric analysis shows the incorporation of PPG-nHA increases the degradation temperature of TPU-PDMS blends. Melt rheological studies of the blends and the blend nanocomposites reveal the shear-thinning behavior of the nanocomposites at all different filler loadings, and this shear thinning effect is more prominent in the case of composites at higher loading of the nanofiller.
Poly(lactic acid) (PLA) and wood flour/PLA composites were prepared and blended with two antimicrobial agents, triclosan and silver-substituted zeolite (Zeomic), using a twin-screw extruder. The mechanical and thermal properties, antimicrobial activity, and biodegradation performance were investigated. The addition of wood and Zeomic was found to increase the Young’s modulus of the composites, whereas the tensile strength, elongation at break, and impact strength dropped. However, the mechanical properties of PLA and wood/PLA loaded with triclosan did not show any definite trends. Differential scanning calorimetry data indicated that the glass transition temperature value of neat PLA was 63°C, whereas those of wood/PLA composites were lower. When wood and Zeomic were incorporated, PLA exhibited double melting peaks. Triclosan (1.0 and 1.5 wt%) demonstrated antibacterial activity against Staphylococcus aureus, as determined by plate count agar technique, whereas Zeomic did not. Biodegradation tests of neat PLA and wood/PLA composites showed that after a 60-day incubation period, the biodegradation rate of wood/PLA was higher than that of PLA. PLA and wood/PLA-containing Zeomic were found to degrade more quickly, suggesting that wood and Zeomic acted as biodegradation promoters. On the other hand, triclosan could be considered a biodegradation retarder since no biodegradation was observed for any triclosan-loaded samples during the initial 20 days of incubation, while neat PLA and wood/PLA composites began to degrade within the first few days.
The current study details on the moisture absorption behavior and its effect on the hybrid bionanocomposites of polylactic acid (PLA). In order to improve the compatibility between PLA and fiber, silanization was performed on fiber as well as C30B nanoclay was used as the secondary reinforcing filler. Silanization was confirmed through Fourier transform infrared study. In addition, thermogravimetric analysis (TGA) of fiber proved that hydrophilicity of fiber could decrease after silane treatment. Bionanocomposites of PLA were prepared using melt blending technique followed by injection molding. Samples were immersed in distilled water for 30 days at room temperature to analyze the moisture absorption behavior and its kinetic parameter. The results from moisture study revealed that PLA/fiber/nanoclay bionanocomposites have higher moisture resistance than PLA/fiber biocomposites. Further, the changes in mechanical as well as thermal properties of PLA and its composites during moisture absorption have been carried out. With increase in percentage of moisture absorption, the mechanical strength and modulus of composites decreased significantly, however, the unnotched impact strength and elongation at break found to improve. TGA of PLA and its composites revealed that thermal stability of composites decreased after moisture absorption. The morphology of the composites was monitored during moisture absorption, and the result revealed that moisture absorption has severely damaged the matrix–fiber interface.
This study demonstrated that poly(styrene-co-N-maleimide isobutyl polyhedral oligosilsesquioxane (POSS)) (P(S-co-NMIP)) was successfully prepared using free radical polymerization. For this purpose, firstly, N-maleimide isobutyl POSS (NMIP) was synthesized using aminopropyllsobutyl POSS (POSS-NH2) and maleic anhydride. Secondly, P(S-co-NMIP) was synthesized using styrene, NMIP, and 2,2-azobis(isobutyronitrile) as initiator in tetrahydrofuran for 24 h at 75°C to give copolymer. The synthesized polymer and compounds were characterized by proton nuclear magnetic resonance, gel permeation chromatography, and Fourier transform infrared spectroscopy. Thermal behaviors of P(S-co-NMIP) were analyzed using thermogravimetric and differential scanning calorimetric analyses. The apparent activation energies (Es) for thermal degradation of P(S-co-NMIP) were obtained by integral methods (Flynn–Wall–Ozawa (FWO) and Kissinger). P(S-co-NMIP) was heated thermogravimetrically under various heating rates such as 5, 10, 15, and 20°C min–1 at a temperature range of 30–1000°C to determine their thermal degradation mechanisms. The values of E for P(S-co-NMIP) were found to be 127.5 ± 2.3 and 134.4 ± 14.8 kJ mol–1 for FWO and Kissinger methods, respectively. Also, the values of E of synthesized copolymer (P(S-co-NMIP)) were compared with styrene-co-maleic anhydride copolymer in literature.
The ultra-high molecular weight polyethylene (UHMWPE) fibers, as the fibrous morphology of polyethylene (PE), were first used to reinforce thermoplastic starch (TPS) by a twin screw extruder. The influence of the UHMWPE content on the mechanical and dynamic mechanical thermal properties, thermal stability, contact angle, torque rheological properties, and fractured surface morphology of the UHMWPE/TPS composites was studied in detail. We found that the UHMWPE fibers were well dispersed in the TPS matrix, and the mechanical properties and water resistance of the composites improved significantly. Especially, the incorporation of UHMWPE fibers at a content of 2 wt% generated a composite with better performance (tensile strength of 8.78 MPa and contact angle of 80.2°).
The friction and wear behaviours of carbon fibre (CF)- and carbon nanotube (CNT)-filled styrene–butadiene rubber (SBR) composite was investigated in a ring-on-block wear tester. Ti6Al4V alloy ring (with a diameter of 28 mm) was selected as the counter body in this study. It was found that the detachment of particles, ripples and ploughs were observed under higher load. The addition of CNT efficiently improves the interfacial adhesion of CF/SBR composite. Both the friction coefficient and wear increased with load, and the CNT-filled one showed lower friction coefficient and wear.
Fibre-reinforced thermoplastic composite materials can be manufactured rapidly using a thermoforming process. The assortment of thermoplastic matrix systems is manifold and starts from bulk plastic like polypropylene (PP) up to high-performance systems like polyether ether ketone. High-performance thermoplastic polymers have durable properties but relatively high raw material costs. For structural application, engineering methods are needed to ensure the availability for use over the full range of the life cycle of parts. This equates to at least 15 years under exposure to varying climatic conditions for an automobile component. Bulk plastics have complex viscoelastic behaviour, which means that advanced methods are needed to ensure the long-term behaviour of both the pure plastic or fibre-reinforced materials with such a matrix system. In the following study, the creep behaviour of a glass fibre-reinforced PP material is investigated using different uniaxially loaded creep tests at different load and temperature levels. Starting from this empirical base, two characteristic creep functions are derived using a modified Burgers approach. To transfer the results of uniaxial creep situations to a three-dimensional multiaxial stress state, a method to interpolate the experimental creep curves is presented. This developed creep model is integrated into the implicit non-linear finite element program SAMCEF/Mecano and used to predict the creep behaviour of a complex laminate. The results are then validated against the performed experiments.
The end of life of carbon fibre-reinforced polymer (CFRP) structures represents a major challenge to the aerospace industry, as new European regulations are demanding recycling solutions that can be complicated and expensive to apply. This study aims to address new practical ways to recycle CFRP materials. CFRP materials with a polyether ether ketone (PEEK) matrix were fragmented via electrodynamical fragmentation, which exhibits several benefits compared to mechanical shredding processes, especially for composites commonly found in the aerospace industry. The fragments are characterized and reused to produce new CFRP aerospace parts. Structural testing of recycled composite parts revealed a 17% decrease of the mechanical properties compared to the novel material. The combination of these manufacturing and recycling techniques closes the cradle to cradle loop of thermoplastic CFRP.
Poly(lactic acid)/halloysite nanoclay (PLA/HNC) nanocomposites with N,N'-ethylenebis(stearamide) (EBS) were produced by melt mixing. Water absorption behaviors of the PLA nanocomposites were studied at three different temperatures, that is, 30, 40, and 50°C. The water absorption kinetics of PLA/HNC nanocomposites conform to Fickian diffusion behavior at immersion temperatures of 30 and 40°C due to the diffusional exponent (n) values that were close to 0.5 for all specimens. However, the hydrolysis of PLA occurred for longer time deviations at 50°C. Activation energy of water diffusion (E a) for PLA nanocomposites were found to be affected by the HNC and EBS contents. The glass transition temperature (T g), cold crystallization temperature (T cc), and melting temperature (T m) of the PLA sample were shifted to lower temperature after subjected to immersion temperature of 50°C. The carbonyl index of all PLA specimens increased after water absorption at 40 and 50°C due to the formation of higher amount of carboxylic acid end groups during the hydrolysis process.
Two kinds of multiwalled carbon nanotubes/silica nanohybrids (CNTs/SiO2) were synthesized via a sol–gel method by coating SiO2 on the surfaces of CNTs that had been functionalized with poly(sodium-p-styrenesulfonate) (PSS). The influence of the nanohybrids on the thermal properties of poly(vinyl alcohol) (PVA) and polyurethane (PU) composites was investigated. Characterization of CNTs/SiO2 nanohybrids, elucidated with scanning electron microscopy and X-ray diffraction, showed that PSS played a key role in the final morphology and resulted in a "core/shell" and "candied haws on a stick"-like structure. The thermal degradation and thermo-oxidation of PVA and PU composites evaluated by thermogravimetic analyses suggested that the thermal properties of PVA/(CNTs/SiO2) composites were improved at relative high temperature range when compared with pure PVA, and the improvement mainly depended on the loading fraction of the nanohybrids, while for PU/(CNTs/SiO2) composites, a small fraction of the nanohybrids increased the materials thermal properties, but the improvements were influenced by the type of CNTs/SiO2 nanohybrids.
An important material for making composites is the scrap of multilayer films. Using plant fibers in these composites can further contribute to reduce their environmental impact. We prepared, by extrusion and injection molding, composites of this scrap reinforced with 20 wt% of curauá fibers. These were characterized using scanning electron microscopy (SEM); optical microscopy; tensile, flexural, and notched impact strength tests; differential scanning calorimetry; carbonyl index (CI) by Fourier transform infrared spectroscopy; reflectance ultraviolet–visible spectroscopy; and water absorption measurements. The fiber promoted an increase in the flexural and tensile moduli strengths. SEM showed good fiber/matrix adhesion, dispersion of the fibers in the matrix and their fibrillation. Weathering of the surface of the composite during environmental aging was evidenced by CI, degree of crystallinity, melting temperature, and the formation of cracks caused by chemi-crystallization. Despite the environmental degradation of the exposed composite surface, the mechanical properties and interfacial adhesion did not change significantly.
Polypropylene (PP)/ethylene acrylic acid (EAA)/maleic anhybride-grafted PP (PP-g-MA)/organoclay nanocomposites were prepared using the melt mixing technique, and PP-g-MA and EAA were employed as the compatibilizers. The sodium montmorillonite (MMT) were pretreated with high-speed airflow pulverization method and then grafted using -glycidoxypropyltrimethoxysilane, followed by modification using trihexyltetradecylphosphonium chloride cation with supercritical carbon dioxide as the reaction medium (the obtained product was abbreviated as OGMMT). The modification of MMT was characterized by thermogravimetric analysis, X-ray diffraction (XRD), and scanning electron microscopy. The effect of organoclay content on microstructure and mechanical properties of PP/EAA/PP-g-MA/OGMMT nanocomposites was investigated by XRD, transmission electron microscopy, dynamic mechanical analysis, tensile strength, notched impact strength, flexural strength, and flexural modulus. The results show that the OGMMT has a high weight loss, a large d-spacing increment, and exfoliation predomination structure. The addition of compatibilizers benefited the formation of exfoliated structure and the dispersion of OGMMT in PP matrix, and hence, enhanced the storage modulus (G') below the glass transition temperature (T g), storage modulus (G''), T g, tensile strength, flexural strength, and flexural modulus of the nanocomposites. Furthermore, with the increasing OGMMT content, the nanocomposites exhibited very inconsiderable alteration in the clay dispersion level and enhanced G' below the T g, G'', tensile strength, flexural strength, and flexural modulus of the nanocomposites, whereas the T g was invariant. As a whole, the introduction of compatibilizers and OGMMT led to the reduction of notched impact strength, which also nearly linearly decreased with increasing clay content.
Nanofluids, which are formed by suspending nanoparticles into conventional fluids, exhibit anomalously high thermal conductivity. Renovated Maxwell model was developed by Choi in which the presence of very thin nanolayer surrounding the solid particles was considered, which can measurably increase the effective thermal conductivity of nanofluids. A new model is proposed by introducing a fitting parameter in the renovated Maxwell model, which accounts for nanolayer, nonuniform sizes of filler nanoparticles together with aggregation. The model shows that the effective thermal conductivity of nanofluids is a function of the thickness of the nanolayer, the nanoparticle size, the nanoparticle volume fraction and the thermal conductivities of suspended nanoparticles, nanolayer and base fluid. The validation of the model is done by applying the results obtained by the experiments on nanofluids, other theoretical models, and artificial neural network technique. The uncertainty of the present measurements is estimated to be within 5% for the effective thermal conductivity.
In the furniture, automotive and contruction industries, there is increased demand for cost-effective and lightweight biocomposites. The objective of this work was to develop new natural fibre-based composites with specific properties. Palm and pineapple leaf fibres were chosen in association with polypropylene (PP). The first step was to investigate the effect of these natural fibres as reinforcement for PP. The evolution of chemical structure and crystallinity was proposed with infrared spectroscopy measurements and differential scanning calorimetry thermograms, respectively. The assessments of mechanical properties with tensile tests and melt viscoelastic behaviour were also investigated. The study enabled to distinguish the influence of fibre content. The second step in our work was to assess the composite durability after ultraviolet exposure or thermal ageing. The oxidation level was calculated. The long-term evolution of thermal and mechanical properties was also proposed. As a result, the PP/pineapple leaf composite revealed a promising biocomposite.
Graphene/zinc oxide (ZnO) hybrid was prepared using biosafe
To reveal the deformation, strength, and failure modes of woven textile sandwich composites (WTSCs), test methods suggested by national standards were referenced and discussed to carry out flatwise and edgewise compression experiments, uniaxial stretching experiments, and three-point bending experiments according to the structural characteristics of WTSC. Strength and failure modes of WTSCs in flatwise compression and uniaxial tension were acquired. Anisotropy and size dependency of strength and failure modes of WTSC panels in edgewise compression were revealed. Strength of weft-compressed panels has few variations when the length is smaller than 60 mm and then decreases obviously when the length is over 60 mm, accompanying with the failure modes turning from crushing, fracture to buckling. Progressive crushing and bending fracture are two observed post-failure modes. Two competing shear failure modes and facesheet failure were observed in three-point bending experiments. Shear strength of the woven core of WTSC was deduced by beam flexure. To acquire facesheet failure mode by long beam flexure, the span should be above 36 times the thickness of the panel.
Flame-retardant polyurethane elastomers (PUEs) have been prepared using trichloroethyl phosphate (TCEP) as flame retardant. The combustion performances and thermal decomposition properties of PUEs were studied using cone calorimetry test and thermogravimetric analysis, respectively. Kissinger method and Flynn–Wall–Ozawa (FWO) method were adopted to discuss the pyrolysis kinetics of PUEs. The experimental results showed that TCEP has good flame-retardant effect for PUE. With the increase of TCEP, the peak heat release rate and total heat release values decrease. A good diagram of linear regression can be obtained from both Kissinger and FWO methods. The activation energy values of flam- retardant PUE can be calculated from FWO method at different conversion rates.
The focus of this work was to study the effect of multiwalled carbon nanotubes (MWCNTs) on morphology, mechanical, and thermal properties of high-density polyethylene (HDPE) nanocomposites. MWCNTs/HDPE nanocomposites were prepared using submerged friction stir processing (SFSP) technique. The pristine MWCNTs without any pretreatment were blended with HDPE at a fixed traverse speed of 30 mm min–1 and various rotational speeds ranging from 1200 r min–1 to 2100 r min–1. The effect of rotational speed on MWCNTs dispersion in HDPE matrix was assessed using scanning electron microscopy. The experimental results showed the rotational speed affected the disperision of the MWCNTs. The mechanical properties of the composites were measured, and the results indicated that the tensile strength increased at first and then decreased with the increase of the rotation speed. The thermal properties of MWCNTs-filled HDPE nanocomposites were studied by differential scanning calorimetry, and the crystalline content of the prepared composites by the SFSP technology was increased. From the experimental research, it was found that the SFSP technique was a practical way to fabricate polymeric composites.
In this study, acoustic emission (AE) technique is used to investigate different time-to-failure mechanisms of delamination in glass/epoxy composite laminates. Woven and unidirectional layups were subjected to the double cantilever beam, end notch flexure, and mixed-mode bending tests and the generated AE signals were captured. Discrimination of the AE events, caused by different types of the damage mechanisms, was performed using wavelet packet transform (WPT) and fuzzy clustering method (FCM) associated with a principal component analysis (PCA). The FCM and WPT analyses identified three dominant damage mechanisms. Furthermore, different interface layups and different GII/GT modal ratio values (ratio of mode II strain energy release rate per total strain energy release rate) indicated different time-to-failure mechanisms incidence. Additionally, the damaged mechanisms were observed using scanning electron microscopic (SEM) analysis. The results showed that the dominant damage mechanisms in all the specimens are matrix cracking and fiber–matrix debonding. Besides, some fiber breakage appeared during the tests, and the percentage of this damage mechanism in the unidirectional specimens and mode I condition was higher than those in the woven specimens and mode II. SEM observations were also in good agreement with the obtained results. It was found that the presented methods can be utilized to improve the characterization and discrimination of damage mechanisms in the actual occurring modes of delamination in composite structures.
The polyfluorinated ethylene propylene (FEP)/polypropylene (PP) blend was compounded at melt state in a twin-screw extruder. The melt dynamic viscoelasticity of FEP/PP blends was measured using a Bohlin rheometer with the extended temperature option under experimental conditions with temperature scope from 270°C to 280°C and shear frequency () varying from 10–2 to 101 s–1. The results showed that the shear storage modulus (G') and shear loss modulus (G'') increased nonlinearly, while the dynamic complex viscosity (*) decreased slightly with increasing . The G' and G'' were an exponential function of . The G', G'', and * of the blend melts decreased with an addition of the PP weight fraction
Concerns about environmental waste problems caused by non-biodegradable petrochemical-based plastic packaging materials as well as consumer demand for high-quality food products have led to increased interest in the development of biodegradable packaging materials using annually renewable natural biopolymers. Inherent shortcomings of natural polymer-based packaging materials such as low mechanical properties and low barrier properties can be recovered by applying nanocomposite technology. Polymer nanocomposites, especially natural biopolymer-layered silicate nanocomposites, exhibit markedly improved packaging properties due to large nanoparticle surface area and their significant aspect ratios. Additionally, natural biopolymer is susceptible to microorganisms, resulting in good biodegradability, which is one of the most promising aspects of its incorporation in packaging materials and industries. The present review article explains the various categories of nanoclay and bio-based polymer-based composites with particular regard to their application as packaging materials. It also gives an overview of the most recent advances and emerging new aspects of nanotechnology for development of composites for environmentally compatible food packaging materials.
Poly(ethylene-co-vinyl acetate-co-carbon monoxide) (EVACO)/halloysite nanotube (HNT) nanocomposite films were solution cast. Dispersion of HNTs in the matrix was analyzed by elemental mapping and the role of HNTs on crystallizability, flammability and thermal, mechanical, and electrical properties of the polymer was evaluated. The nature of interaction between the EVACO matrix and HNTs was studied using Fourier transform infrared spectroscopy. The highest tensile strength was observed for the composite with 1% filler loading, whereas the highest crystallinity was observed for that with 3% filler loading. The decay in the tensile properties at higher filler loading was due to agglomeration of HNTs and debonding of polymer–filler interface. The electrical volume resistivity of the composites decreased with HNT loading because of the ionic charge transfer. The direct current electrical resistivity study of the composites proves that the addition of HNT can improve the antistatic properties of the polymer.
The effect of perforated interlayers on the stress wave transmission of multilayered materials was investigated both experimentally and numerically using the Split Hopkinson pressure bar (SHPB) testing. The multilayer combinations consisted of a ceramic face plate and a glass/epoxy backing plate with a laterally constrained low modulus solid or perforated rubber and Teflon interlayer. The perforations on rubber interlayer delayed the stress rise time and reduced the magnitude of the transmitted stress wave at low strains, while the perforations allowed the passage of relatively high transmitted stresses at large strains similar to the solid rubber interlayer. It was concluded that the effect of perforations were somewhat less pronounced in Teflon interlayer configuration, arising from its relatively low Poisson’s ratio. It was finally shown that SHPB testing accompanied with the numerical simulations can be used to analyze the effect of compliant interlayer insertion in the multilayered structures.
Usage of discontinuous glass fibers in injection- and compression-molded resin components is rapidly increasing to improve their mechanical properties. Since added fiber contributes to more strength along the fiber direction compared with transverse direction, the mechanical properties of such components strongly depend on the fiber orientation. Therefore, it is important to estimate the fiber orientation distribution in such materials. In this article, we are presenting a recently developed method to estimate fiber orientation using micro computerized tomography (CT) scan-generated three-dimensional (3-D) image of fibers. However, the large size of the CT scan-generated 3-D image often makes it difficult to separate each fiber and extract end point information. In this article, a novel method to address this challenge is presented. The micro-CT images were broken into finite volume, reducing data size, and then each fiber was reduced to its own centerline, using Mimics® Innovation Suite (Materialise NV), further reducing the data size. These 3-D centerlines were then used to quantify the second-order orientation tensor. The results from the proposed method are compared with the measurements using well-established industry standard approach called the method of ellipses for validation. The key challenges in estimating the fiber orientation are identified and future improvements are proposed.
Photonic crystals were fabricated using self-assembled polystyrene (PS) submicrospheres with different content of nanospheres with different glass transition temperatures (T g: 100 to –54°C) and their opalescent and mechanical properties were investigated. PS spheres (185.4 nm) and nanospheres were prepared by soap-free emulsion polymerization. Nanospheres were prepared using one or two types of monomers, styrene, n-butyl methacrylate, and butyl acrylate with sodium p-styrenesulfonate. Surface morphology, particle size (D n), and wavelength () of photonic crystals were determined from scanning electron microscopy (SEM), effective refractive index equation, and modified Bragg’s law, respectively. The reflection wavelength ( max) was measured from ultraviolet-visible spectroscopy. SEM results showed that hard nanospheres were distributed around PS spheres in their photonic crystals. On the other hand, soft nanospheres were coated onto PS spheres in their photonic crystals. With increasing weight fraction of hard or soft nanospheres in the photonic crystals, Dn and were increased. The value of max corresponded to that of . The mechanical property of the photonic crystals was measured by the pencil hardness (PH) test. The result showed that by decreasing the T g and increasing the weight fraction of nanospheres, PH was increased. The opal film prepared from PS spheres with 20% N-54 nanospheres had the highest PH (H).
The damage formation in a multilayered armor system without and with an interlayer (rubber, Teflon, and aluminum foam) between the front face ceramic layer and the composite backing plate were investigated experimentally and numerically. The projectile impact tests were performed in a low-velocity projectile impact test system and the numerical studies were implemented using the nonlinear finite element code LS-DYNA. The results of numerical simulations showed that the stress wave transmission to the composite backing plate decreased significantly in Teflon and foam interlayer armor configurations. Similar to without interlayer configuration, the rubber interlayer configuration led to the passage of relatively high stress waves to the composite backing plate. This was mainly attributed to the increased rubber interlayer impedance during the impact event. The numerical results of reduced stress wave transmission to the backing plate and the increased damage formation in the ceramic front face layer with the use of Teflon and foam interlayer was further confirmed experimentally.
The waterborne polyurethane/nano-silica composites (WPU/nano-silica, WPUS) and WPU composites modified by polyethersiloxanediol (WPUPES) were prepared, respectively. The properties of WPUS and WPUPES were investigated by various characterizations. The results showed both WPUS and WPUPES had better waterproof property and thermal stability than neat WPU. However, WPUPES has a lower elongation at break due to the higher micro-phase separation. This is ascribed to migration and aggregation of siloxane segments during the film formation. The tensile strength of WPUS was higher than that of neat WPU. This is attributed to the WPUS chain restriction caused by the network and physical cross-link points of nano-silica particles. Moreover, the glass transition temperature of WPUS shifted to higher temperature region while that of WPUPES shifted to lower temperature region.
N,N'-Dicyclohexyl-2,6-naphthalenedicarboxamide (NU100), a commercial β-nucleating agent (NA) for isotactic polypropylene (iPP), is found dissolvable in iPP melt. Various heating temperatures (T hs) of iPP/NU100 cause different solubilities of NA, resulting in various aggregation morphologies of NU100 in the melt. Moreover, nucleation efficiency of NA NU100 on iPP changes with the T h of iPP/NU100. In this article, the effects of T h on nucleation behaviors of iPP nucleated with different concentrations of NU100 were systematically studied. The results indicated nucleation efficiency of NU100 depended not only on concentration of NA but also on T h of nucleated iPP. With the increase of T h, crystallization peak temperature (T cp) of nucleated iPP decreased remarkably. The whole process that T cp shifted from 126.8°C to 120.8°C was obtained by investigating the nucleation behavior of iPP/0.1 wt% NU100. Polarized optical microscopy observation confirmed lower T cp, representing the crystallization of iPP nucleated by dissolved–recrystallized NA NU100. Further, diverse aggregation morphologies of NA in iPP melt during crystallization were observed. A schematic diagram was proposed illustrating the morphologies formed during recrystallization process of NU100 melted at different T hs.
This article deals with an experimental and numerical study of the inductive heating of glass fibre (GF)-reinforced thermoplastics with susceptors made of stainless steel that are embedded in them. The objective of this article is to examine the links between individual process and system parameters and the heating behaviour of fibre-reinforced plastics. Two different susceptor designs were tested in relation to their heating capability. Furthermore, it was possible to experimentally study the dependency of the space between the specimens and inductors and therefore the impact of the generator output of the induction system and inductor attachments differing in their geometric shapes in terms of heating. Moreover, it was possible to use numerical simulation to examine the heating behaviour at different frequencies. These findings indicate that it is possible to heat GF-reinforced semi-finished products by fibre-shaped susceptors. Finally, it was possible to demonstrate that the heating process can be designed by means of the frequency of the induction system and directly controlled using the generator output.
This research focuses on utilization of kapok husk (KH) as a natural filler in linear low-density polyethylene (LLDPE) ecocomposites. The effect of KH content and coupling agent on tensile properties, thermal properties, water absorption behavior, and morphology of ecocomposites were studied. The addition of KH had increased tensile modulus and water absorption of ecocomposites, whereas tensile strength and elongation at break decreased. However, the polyethylene-grafted acrylic acid (PEAA) was used as a polymeric-coupling agent to enhance the properties of LLDPE/KH ecocomposites. The incorporation of PEAA improved the tensile strength, tensile modulus, crystallinity, and thermal stability as well as reduced the water absorption of LLDPE/KH ecocomposites. The improvement of those properties was caused by the enhanced interfacial bonding, which was evidenced by scanning electron microscopy. The Fourier transmission infrared spectra also confirmed the presence of ester linkage between PEAA and KH.
Early stage crystallization kinetics of polypropylene (PP)/clay composites is studied using rheometery. Relaxation modulus of composites is measured at low frequencies near liquid–solid transition. Small amplitude oscillating shear flow is applied at low frequencies to obtain relaxation modulus. Relaxation modulus of polymeric materials at the liquid–solid transition follows
In this work, styrene/methyl methacrylate (St/MMA) copolymer particles were synthesized by suspension polymerization process with different copolymer compositions to study the visual batch foaming dynamics. The visualization system consisted of the self-sealing observation cell equipped to the pressure and temperature controller. The synthesized copolymer particles were impregnated by n-pentane, followed by recording of particle expansion. The cell structure of foams was studied by scanning electron microscopy. The effect of different foaming conditions on the expansion behavior of copolymers was examined. It was concluded that sorption pressure and temperature have contradictory effects on the foaming ratio of the synthesized copolymers at lower and higher sorption pressures, and the results were confirmed with the foams’ cell structure. Furthermore, it was shown that, at different temperatures and pressures, the expansion behavior change dramatically with increasing of MMA content in the copolymer.
Natural fiber-reinforced composite materials are finding wide acceptability in various engineering applications. A substantial increase in the volume of production of these composites necessitates high-quality cost-effective manufacturing. Drilling of holes is an important machining operation required to ascertain the assembly operations of intricate composite products. In the present experimental investigation, natural fiber (sisal and Grewia optiva fiber)-reinforced polylactic acid-based green composite laminates were developed using hot compression through film stacking method. The drilling behavior of green composite laminates was evaluated in terms of drilling forces (thrust force and torque) and drilling-induced damage. The cutting speed, feed rate, and the drill geometry were taken as the input process parameters. It was concluded that all the three input process parameters affect the drilling behavior of green composite laminates. The drill geometry was established as an important input parameter that affects the drilling forces and subsequently the drilling-induced damage.
This article presents the results of acoustic emission (AE) monitoring of crack propagation in 2024-T3 clad aluminum panels repaired with adhesively bonded octagonal and elliptical boron/epoxy composite patches using FM-73 adhesive under tension–tension fatigue loading. Two crack propagation gages and four broadband AE sensors were used to monitor crack initiation and propagation, respectively. The acquired AE signals were processed in time and frequency domain to identify sensor features correlated with fatigue cycle and crack propagation, which were used to train neural networks for predicting crack length. The results show that AE events are correlated with crack propagation, and crack propagation signals can be differentiated from signals due to matrix cracking, fiber breakage, and shear of the composite patch. Three back-propagation cascade feed-forward networks were trained to predict crack length using number of fatigue cycles, number of AE events, and number of fatigue cycles and number of AE events together as inputs, respectively. It was found that network with fatigue cycles as input gave good results, while the network with just AE events as input gave greater error. However, the network using both fatigue cycles and number of AE events as inputs to predict crack length gave much better results.
Wood–plastic composite (WPC) material has been developed rapidly and used widely to replace wood production in recent years. The cutting process of WPC material is the key to directly affect the efficiency of utilization and processing. The infrared thermal imaging system and numerical control machine tool were used in this article to analyze the cutting temperature under different cutting parameters, which was further compared with massoniana wood cutting procedure to provide theoretical basis for WPC material processing. Under certain conditions, the cutting depth was the most important factor on the cutting temperature, followed by spindle speed, while cutting width was the least affected. In the cases of similar processing parameters, although cutting temperature for massoniana wood is always higher than WPCs, the change trends of their cutting temperature are similar. Besides, shear heat moderately affected the cutting temperature during cutting.
Non-isothermal crystallization kinetics of virgin polypropylene (PP) and its nanocomposites have been evaluated using differential scanning calorimetric technique. The nanocomposites were prepared using melt intercalation method. It is observed that the crystallization peak temperature of nanocomposite is marginally higher than virgin PP at various cooling rates. The non-isothermal crystallization melt data were analysed using Avrami, Ozawa and Mos models. The half-time for crystallization decreased with incorporation of clay nanoparticles. The values of crystallization rate constant and cooling rate at unit crystallization time showed that the crystallization rate increased with the increasing of cooling rates for virgin PP and nanocomposite, but the crystallization rate of nanocomposite was faster than that of PP at a given cooling rate. The activation energy for non-isothermal crystallization of virgin polymer and nanocomposites based on Kissinger method has been determined to be 186 and 196 kJ mol–1, respectively. The polarized micrographs showed that the number of effective nuclei increased in the PP-clay nanocomposite, where the clay acts as a heterogeneous nucleating agent during the crystallization of the nanocomposite.
Starch platelets of micro particle size in the range of 10–100 µm were extracted from potato by acid hydrolysis. Two types of starch-reinforced composites, one with poly(vinyl alcohol) (PVA) and the other with poly(lactic acid) (PLA), were prepared by solvent casting and hot press molding methods, respectively. Mechanical properties of the starch/PVA and the starch/PLA composites were determined, and the maximum tensile and yield strength obtained were around 19.7 MPa for 6% starch/PVA composite and around 7.2 MPa for 6% starch/PLA composite, correspondingly. The structure of both the composites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis (differential thermal analysis/differential thermogravimetric analysis), thermomechanical analysis, and scanning electron microscopy. Finally, antimicrobial test was conducted to assess the potentiality of both the composites to be used for biomedical applications and only starch/PVA composite was observed to inhibit microbial growth against both a gram-positive (Bacillus subtillis) and a gram-negative (Escherichia coli) bacteria.
Fly ash, a waste generated from thermal power plant, can be used as reinforcing agent for polymer composite applications due to its fine particle size and abundant availability. This article highlights the experimental findings of modification of fly ash to convert its size from micro to nano and its nanocomposites preparation through melt blending technique based on acrylonitrile butadiene styrene (ABS) as matrix material. The nanostructured fly ash (NFA) developed through mechanical milling is characterized to understand its viability toward the filler material in polymer composites. The study showed that the NFA produced after 40 h of milling has a broken rougher surface with improved amorphous nature. Further, a detailed study on the properties of ABS nanocomposites reinforced with NFA has been conducted. ABS/NFA composites at 7 wt% loading have showed better thermomechanical properties. These results are further supported with the fractured surface analysis of nanocomposite using various morphological techniques. The outcome of this study suggests the potential use of nano fly ash to develop sustainable polymer nanocomposites for high-end industrial applications.
Adding fillers of high thermal conductivity to the base polymer materials is a solution to make composites of high thermal conductivity. Expanded graphite sheets have been recognized as an economic and efficient filler material to make composite polymers of high conductivity. However, the prediction of the effective thermal conductivity of the composite materials is a difficult task due to the random nature in fillers distribution. The anisotropic properties of the sheet fillers make the heat transfer analysis difficult. In this study, a conjugate heat conduction model considering the random distribution nature of fillers is set up and numerically solved. A validated commercial software FLUENT and finite volume method was used in the analysis. Then an experiment is done to validate the model. The numerical results are used to summarize a correlation for the prediction of the effective thermal conductivity of the composite materials. It is found that the filler height to thickness ratio plays an important role in intensifying the heat conduction in the composite materials. At a given filler content, the graphite sheets should be fabricated thin enough to have higher height to thickness ratios and consequently higher performance in effective conductivity.
Poly(butylene terephthalate)/polycarbonate (PBT/PC) binary blend was reprocessed by repeated injection moulding process to explore whether recycling is possible for this polymer blend. In the current study, PBT/PC blends were reprocessed until five processing cycles and the mechanical, chemical, thermal, and rheological properties of recycled PBT/PC blends were evaluated after each reprocessing cycle. The recycling of the glass-fibre-reinforced PBT/PC composites was also investigated in this study. From the experimental results, it was concluded that recycled glass-fibre-reinforced PBT/PC (PBT/PC-GF) composites showed better mechanical properties in comparison to virgin PBT/PC binary blends and fifth recycled PBT/PC-GF composite could be used instead of virgin PBT/PC. It was also found that PBT/PC binary blend was a suitable material for the recycling process and this polymer blend did not suffer any significant deterioration.
The present work was developed to utilize kapok husk (KH) as filler in recycled polypropylene (rPP) green composites. Stearic acid (SA) was used as surface modifier in rPP/KH composites. It was found that the modified KH with SA was reduced the stabilization torque of composites. The addition of KH in rPP decreased the tensile strength and elongation at break but increased tensile modulus of composites. The modified KH with SA improved the tensile strength, tensile modulus, crystallinity, and thermal stability of composites. The scanning electron microscopic micrograph provd that the interfacial interaction and adhesion was improved by SA modification.
The lightweight economical bipolar plates for proton exchange membrane fuel cells were fabricated by using vinyl ester resin as matrix material, graphite powder as reinforcement and conducting polymer as additive. Effects of various contents of graphite and its particle size on electrical conductivity, physical and mechanical properties of the composite were investigated. The optimum composition of composite plates was determined at 55% graphite, 40% resin and 5% poly(1,4-phenylene sulphide) based on measurements of physical, electrical and mechanical properties with various graphite contents. The plate molded with 2.93 mm thickness gives density of 1.81 g cm–3 and compressive strength of 73 MPa, which is in consonance with reported standard. Thermogravimetric analysis–differential thermal analysis–derivative thermogravimetry of the composite was carried out in air atmosphere to find out mode of degradation and basis of its stability. The study reveals that composite is less stable than resin and graphite, but much more stable than operational fuel cell which works at 80–100°C.
The photodegradation behavior of poly(vinyl chloride) (PVC) nanocomposites containing different amounts of synthesized titanium dioxide (TiO2) nanoparticles and commercial rutile powder is investigated via the formation of carbonyl compounds, peroxides, and polyenes propagation over 5112 h exposure, as a function of irradiation wavelength and intensity. All the PVC/TiO2 nanocomposites are found to exhibit lower concentration of mentioned species compared with the composite samples. The results show that added TiO2 nanoparticles can retard the photodegradation processes, wherein increasing the amounts of these nanoparticles yields more reduction. With an increase in irradiation intensity the rate of formation of investigated groups increases, although in cases with raised temperature range, this pattern is not observed. An evaluation on the irradiation wavelength effect also shows that more photon energy provides more degradation. The loss of weight analysis shows a tremendous and novel result on evaluating a point of meaningful weight loss.
To address the industrial need for manufacturing advanced thermoplastic composite parts with less energy, waste, and time and at lower cost, the feasibility of automated fiber placement using ultrasonic consolidation (UC) is investigated as an alternative to hot gas torch, laser, and infrared (IR) heating. The flexural stiffness and strength of simple flat parts made using UC and also thermal pressing per manufacturer’s specifications are measured by three-point bending and compared. Whereas UC proved to be more effective in welding polyethylene terephthalate/carbon prepreg tape than thermal pressing for both unidirectional and quasi-isotropic layups, the opposite was true for high-density polyethylene/glass, although optimal welding process parameters may not have been used. Finally, a simple transient conduction model is used to predict temperature rise in the thickening laminate and is compared to experimental measurements.
The aim of this study was to investigate the dimensional stability, mechanical and biological performance and thermal degradation of wood–plastic composites made from high-density polyethylene and recycled wood treated with chromated copper arsenate (CCA), a commonly used wood preservative chemical. Virgin pine wood samples were also prepared with and without a coupling agent and used as the control group. Samples of CCA-treated Scots pine (Pinus sylvestris L.) with varying wood content were produced by adding different ratios of the coupling agent. The recycled CCA-treated wood-filled composites exhibited better flexural and tensile strength properties and dimensional stability than the control group, whilst their impact strength was less. Biological test values showed improved durability against termites and fungus with the recycled CCA-treated wood-filled composites. In addition, the leaching of heavy metals was significantly diminished when the coupling agent was utilized at a level of 5% (w/w), thus presenting a much lower impact on the environment.
The accelerated aging effects on mechanical properties of carbon fiber-reinforced polyetherketoneketone (PEKK) thermoplastic composites are reported. Ultraviolet (UV) radiation and moisture absorption may induce property changes that weaken the polymeric matrix and/or deteriorate the matrix fiber interface by debonding or microcracking. The aim of the present work is to correlate the influence of the accelerated aging effects on compression and shear properties of carbon fiber-reinforced PEKK thermoplastic composite manufacturing by hot compression molding. The hot compression molding process was shown to be a good alternative for producing the thermoplastic composite, with an appropriate impregnation. The UV radiation/condensation conditioning effect did not show significant influence on shear strength properties. However, the most significant change was observed in the compression and shear strength after the specimens were submitted to the hygrothermal conditioning, which presented a marked increase. This behavior suggests an antiplasticization effect.
In this article, the polypropylene (PP) nanocomposites containing nanoclay particles and basalt fiber (BF) are prepared in the presence of maleic anhydride grafted PP (PP-g-MA) as compatibilizing agent. The Charpy impact behavior of PP/PP-g-MA/clay nanocomposites and PP/PP-g-MA/Clay/BF nanocomposites at room temperature (25°C), cryogenic temperature (–196°C), and high temperature (120°C) is presented. The BFs prevented the PP matrix from plastic deformation, but the impact strength improvement of nanocomposites is obtained when nanoclay in the PP matrix resists the propagation of cracks. The fracture surfaces are examined with scanning electron microscopy (SEM).
To enhance biodegradability of plastics and to utilize Centella spent (CTS) gainfully, green composites were prepared using high-density polyethylene (HDPE) and CTS. The green composites were fabricated by extrusion, followed by injection molding. HDPE/CTS composites were fabricated with 10, 20, and 30 wt% of CTS using maleic anhydride-grafted-polyethylene (MA-g-PE) as compatibilizer. The fabricated composites were tested for physicomechanical and tribological properties, which included water absorption, density, tensile properties, and three-body abrasive wear test. Tensile modulus of composites increased from 579 MPa to 950 MPa (64% improvement) with increase in filler addition from 0% to 30%. The experimentally obtained tensile property values including tensile strength, tensile modulus, and tensile elongation at break were compared with theoretical model values. The effects of 150, 300, 450, and 600 m abrading distances and 23.5 and 33.5 N normal loads at 200 r/min on the abrasive wear characteristics were studied using dry sand/rubber wheel abrasive test rig. Incorporation of CTS filler lowered the abrasion resistance of HDPE/CTS composites. The surface morphology of tensile-fractured specimens and worn surface features of composite specimens were examined by scanning electron microscopy.
Cocoa pod husk (CPH)-filled polypropylene (PP) composites were prepared via melt compounding. The effect of filler content and chemical treatment using 3-mercaptopropyltrimethoxysilane (MPS) and sodium dodecyl sulfate (SDS) on properties of composites were investigated. The results indicated that the treated composites with MPS and SDS improved the tensile strength, tensile modulus, thermal stability, stabilization torque, water resistivity, and crystallinity of composites. The treated composites with SDS show better tensile properties and water resistivity than composites treated with MPS. Scanning electron microscopic results show that the interfacial bonding between CPH and PP matrix improved with the presence of MPS or SDS.
An investigation was reported on the effect of foaming parameters on the microstructure, mechanical properties, and thermal conductivity of low-density polyethylene (LDPE) foams containing various amount of ultrahigh-molecular-weight-polyethylene (UHMWPE) as a reducer of chemical cross-linking. Azodicarbonamide (ADCA) and dicumyl peroxide (DCP) were used as foaming agent and cross-linking agent, respectively. The LDPE/UHMWPE blends were prepared in an internal mixer and foamed using a single-stage compression molding technique. Considering various parameters and their levels, optimization of Taguchi experimental design was carried out, an L9 orthogonal standard array was selected and the efficient levels for different variables were calculated using analysis of variance (ANOVA) of the results. Also due to different objective functions investigated in this process, optimization of overall evaluation criteria (OEC) method was used. The results revealed that addition of UHMWPE leads to a significant increase in the storage modulus and complex viscosity of melt as well as a considerable decrease in gel content of blend foams compared to neat LDPE foam containing the same amount of DCP was observed. Also in presence of UHMWPE, the foam cell size was decreased compared to previous studies in the same condition. A linear relationship between relative density and thermal conductivity as well as cell size and thermal conductivity was observed. ANOVA results revealed that foaming temperature is the most effective parameter on foam properties and OEC results suggested 10 phr ADCA, 0.6 phr DCP, foaming temperature of 180°C, and 4 min soak time at foaming temperature are the optimum levels of parameters.
Intumescent fire-retardant epoxy (IFR-EP) coatings including ammonium polyphosphate (APP), pentaerythritol (PER), melamine (MEL), magnesium hydroxide (MH), epoxy resin (EP) and polyamide resin (PA) were prepared. Thermal decomposition processes of the pure EP-PA, APP, PER, MEL and MH by thermogravimetric analysis (TGA) technique indicate that the decomposition temperature ranges of EP-PA, APP, PER and MEL are properly consistent with the intumescent mechanism of flame retardants. Thermal decomposition of IFR-EP coatings shows that 15 parts per hundred parts of resin MH is more appropriate to be selected in the formulation of IFR-EP coatings. Kinetic analysis of the TGA data based on the Kissinger methods revealed that activation energy could be used as an important parameter to judge the thermal decomposition process. The conversion dependencies of the activation energy plot show the complex effect of MH content on the thermal decomposition process of IFR-EP coatings.
Composites have gained wide acceptance because of their unique properties. Drilling is a prerequisite operation for composite materials to form assemblies. Poor hole quality can affect tensile strength, structural integrity in long-term usages. The parameters to predict machinability of a good-quality hole are lower specific cutting energy, minimum drilling-induced damages like peel up at entrance and push out delamination. In this article, effect of different tool geometries, speeds and feeds are investigated during drilling on a composite plate having different chemical composition for specific cutting energy, peel up at entrance and push out delamination. A series of experiments was established based on the techniques of Taguchi. Statistical tools like signal-to-noise ratio, the analysis of variance and regression analysis are used to investigate effect on specific cutting energy and delamination. Conclusions show that proper selection of tool and cutting parameters influence specific cutting energy and delamination.
Isotactic polypropylene (iPP) composites with carbon nanotube (CNT) networks at relatively high loadings could have various applications such as electromagnetic interference shielding and thermal conductivity. The crystallization behavior of iPP inside CNT networks could be very much related to the above properties, which was found to be quite different from that of neat iPP in this work. In CNT networks, CNTs not only act as effective heterogeneous nucleating agents to noticeably increase the onset temperature (more than 18°C) of iPP crystallization but also bring strong confinement on the mobility of iPP chains and then reduce the overall crystallization rate of iPP matrix. It is interesting to find that CNT networks, especially in the case of ultrahigh loading (90 wt%), have remarkable confinement effect on crystallization of iPP, overcoming the heterogeneous nucleation of CNTs, resulting in a decline of crystallization rate of iPP. The nonisothermal crystallization kinetics of iPP in the dense CNT network quite fits to the modified Avrami mode by Jeziorny, even more satisfactorily than the case of neat iPP. When confinement effect is dominated during crystallization, we found that the perfection and size of crystallites are extremely decreased at ultrahigh loading, leading to a very low melting point of iPP (approximately 140°C).
In this article, a three-dimensional (3D) finite elements method has been developed for predicting the effective thermal conductivity (ETC) of a conductive hollow tube polymer composite. 3D Representative Volume Element (3D-RVE) was used to represent the composite material. Governing heat transfer equations in both transverse and longitudinal directions for predicting the effective thermal conductivities of composites are used. ETC was numerically calculated using COMSOLTM software. The guarded hot plate method was used to measure the composites conductivities consisting of epoxy resin matrix filled with metallic hollow tube. A comparison between the numerically calculated thermal conductivities, measured and analytical ones for various samples was made. A satisfactory agreement between numerical and experiment takes place.
This study evaluates the influence of hybridization on the flammability, thermal, dynamic mechanical and impact properties of bamboo–glass hybrid polypropylene composites. Flammability tests using cone calorimetry show that the hybrid composites performed better than the glass–polypropylene (GPP) composites, exhibiting a minimum reduction of 19% on the heat release rate (HRR) and smoke release as well as taking longer to ignite. Thermogravimetric analysis (TGA) reveals that the hybrid composites are thermally more stable before starting to degrade at 275°C and fully degraded at 400°C. The dynamic mechanical analysis shows an increase in the storage modulus indicating higher stiffness and lower damping ratio in the case of hybrid composites. The charpy impact strength of the hybrid composites was increased to 1129.2 J m–1 compared to 530.9 J m–1 of bamboo–polypropylene composites. These results indicate that, by replacing several layers of glass with bamboo fabric in GPP composites, a hybrid concept is feasible for developing an excellent and economical lightweight composite.
The self-reinforced composites based on poly(ethylene terephthalate) (PET) are relatively new materials, competitive to composites based on polymers from the group of polyolefins. The use of PET as a base material should be another step forward for this technology, taking into account the properties, price, and the recycling possibility of proposed composites. In this research work, the main subject was to assess the impact of processing conditions on the final properties of the PET self-reinforced composites (srPET). The examined samples were prepared by hot-compaction technique under variable thermal conditions. The input material was composed of PET resin and low-melting copolymer (LPET). The high tenacity PET fibers were used as reinforcement for PET copolymer matrix. Initially both materials were in the form of continuous fiber; they were woven into a hybrid yarn wherein the proportion of PET and LPET fibers was 50/50. The properties of this hybrid yarn were investigated by differential scanning calorimetry (DSC) analysis, where the hot-compaction process conditions were simulated. Composite samples were investigated using the dynamic mechanical analysis (DMA) and static tension tests. The structure of the composite was observed using the optical microscope. The obtained mechanical properties of such a composite are not comparable to commercially made composite sheets, in which overall properties are mostly higher.
A thermal power station fly ash (FA) was mechanochemically activated by high-energy ball milling that yielded nanostructured FA. This nanostructured FA was incorporated into biodegradable poly(vinyl alcohol) (PVA) matrix by solution mixing and ultrasonication. Transmission electron micrographs revealed that the smooth spherical particles of FA were changed into irregular and rough ones; in addition, the particle size of FA was reduced to a few hundred nanometers, and its specific surface area value increased after the high-energy milling process. All these factors, in turn, led to a thermodynamically favorable interaction between the mechanochemically activated FA and PVA as evidenced by Fourier transform infrared spectroscopy. The incorporation of a very small amount of the nanostructured FA led to an increase in crystallinity of the polymer matrix. The glass transition temperature of the PVA matrix increased by about 18°C when 5 wt% of the nanostructured FA was used as the reinforcement.
The objective of the investigation described in this work was to study the reprocessing effects on the alfa fiber reinforced polyvinylchloride composites with and without maleic anhydride-grafted polyvinyl chloride used as compatibilizer. The material was characterized after each extrusion using tensile tests, scanning electron microscopy (SEM), dynamic mechanical, and thermal analysis. Results indicated that generally after four cycles, the recycled composites had considerably higher modulus as compared with the original composites, which were attributed to changes in physical and chemical properties of the composites induced by the recycling process. This effect was enhanced for the compatibilized samples. Increase of the modulus strength of the poly(vinyl chloride) (PVC) matrix is detected due to the molecular chain cross-linking resulting from degradation. In addition, it was found that the reprocessing cycles increase in glass transition temperature of PVC and PVC/alfa composites.
A macroinitiator was prepared by copolymerization of styrene (St) with 7-methacryloyloxy-4-chloromethylcoumarone (MAOCMC). Grafting studies of coumarone with methyl methylacrylate were carried out in the presence of the macroinitiator poly(7-methacryloyloxy-4-chloromethylcoumarone-co-styrene) and with the catalyst of copper(I) bromide/2,2'-bipyridyne at 110°C. The activation energy valuations of graft copolymers acquired by Coats–Redfern, Tang and Flynn–Wall–Ozawa methods were designated to be 212.69, 214.44 and 223.57 kJ mol–1, respectively. For the outcomes were compared with these valuation differential methods and discrepant integral were used. In terms of experiential outcomes, the reaction mechanism was a dimensional diffusion (Dn) deceleration type in the transformation range worked.
This article reports a study on the erosion response of polypropylene (PP) composites filled with micro-sized Linz-Donawitz (LD) slag particles. LD slag is a major solid waste generated in huge quantities during steel making. It comes from slag formers such as burned lime/dolomite and from oxidation of silica, iron etc. while refining the iron into steel in the LD furnace. In this work, composites with different LD slag content (0, 7.5, 15, 22.5, 30 wt%) in a thermoplastic PP matrix base are prepared by injection molding technique. The composites are characterized with regard to their density, porosity, micro-hardness and strength properties. Solid particle erosion trials, as per ASTM G 76 test standards, are conducted on the composite samples following a well-planned experimental schedule based on Taguchi design of experiments. An air jet type erosion test rig capable of creating reproducible erosive wear situations is used for this purpose. Significant process parameters predominantly influencing the rate of erosion are identified. The study reveals that the LD slag content and impact velocity in the composites are most significant among various factors influencing the wear rate.
Microscopic and physico-chemical methods were used for a comprehensive surface characterization of different extruded polypropylene- and polyethylene-based wood–plastic composite (WPC) formulations. The surfaces were analysed using stereophotogrammetry, high-resolution scandisk confocal microscopy and scanning electron microscopy, resulting in detailed information about the topography and surface morphology. In addition, dynamic water contact angle measurements were carried out to characterize the wettability of the samples. The effects of polymer type, polymer content, additive content and processing method on the resulting topography and wetting were investigated. The correlation between topography and wetting resulted in a conceptual model of WPC surface morphology and wetting, which may be applied to optimize adhesion properties of this composite material.
Mixed-mode fracture characteristics of epoxy-based biocomposite reinforced with 20 wt% walnut shell particle and 10 wt% coconut fibres are investigated. The biocomposite is fabricated using the squeeze casting method. The positive aspect of hybrid combination of fibre and particle reinforcement is advocated by comparing mode I, mode II and mixed-mode I/II fracture surfaces under a scanning electron microscope. An edge-cracked semicircular arc specimen subjected to symmetric three-point bend (TPB) loading is suggested for fracture toughness testing of biocomposite material. A series of fracture tests are conducted on hybrid biocomposite using the proposed semicircular bend (SCAB) specimen geometry, TPB and four-point bend (FPB) specimens. The average mode I and II fracture toughness obtained from semicircular arc bend (SCAB) specimen are 1.319 MPa and 1.219 MPa
A series of polyimides (PIs) was synthesized by reacting a nitrile-containing aromatic diamine, 3,5-diaminobenzonitrile, with various dianhydrides to yield poly(amic acid)s that were then cyclized to yield PIs by a thermal imidization method. The samples were characterized using thermal analysis, tensile testing, optical transparency analysis, and gas permeability analysis. The cast films exhibited good thermal stability with glass transition temperatures of 204–243°C and none exhibited significant decomposition at temperatures below 480°C. These PI films showed coefficient of thermal expansion values in the range 41.68–106.16 ppm/°C. The oxygen transmission rate values of the films containing various dianhydride monomers were in the range 0.93–27.40 cc m–2 day–1. The PI films containing various dianhydride monomers showed tensile strengths of 47–128 MPa, initial moduli of 2.16–3.23, and elongations at break of 1–7%. Moreover, the PI films possessed a transmittance of 58–82% at 500 nm and had a yellowish color with a yellow index of 12.17–59.61.
The surface functionalization of titanium dioxide (TiO2) was used to modify the surface of carbon fiber (CF). The objective of this study is to improve the interlaminar shear strength and impact properties of the composites by mixing high-density polyethylene (HDPE) resin and modifying CFs. The Izod impact strength of the CF/HDPE composites increases with increasing CF content because of the high impact strength of the CF, whereas incorporation of the TiO2 increased the impact strength of the CF/HDPE composites, which may be attributed to the reinforcing effect of the TiO2 particles. Especially the surface treatment of TiO2 increases the interfacial adhesion and the thermal stability of the CF/TiO2/HDPE composite.
Filler networking is considered as the most important parameter in controlling the mechanical and rheological properties of highly filled systems. Besides, the interparticle distance as a function of filler size and concentration seems to be the main parameter to govern the filler network strength or filler–filler interaction. In this article, considering the importance of filler networking, estimation of the interparticle distance for different values of filler size and concentration, investigation of the architecture of filler network in the nanocomposite for various filler sizes as well as analysis of the effects of filler size and concentration on the dynamic behavior of the filler networks are discussed and atomic force microscopic imaging is used to investigate the filler network parameters. In addition to the proposed filler network structure, the results suggest that the rheological properties of nanocomposites in the linear region could be related to the interparticle distance independent of filler size and concentration. On the other hand, by studying the linear and nonlinear viscoelastic properties of these highly filled systems, the results indicate that an increase in loss and storage modulus would occur by increasing the filler concentration and reducing the filler size.
The surface treatment of poly(p-phenylene benzobisoxazole) (PBO) fiber is to improve the interfacial adhesion of the PBO fiber-reinforced high-density polyethylene (HDPE) composite. The surface characteristics of untreated and treated PBO fiber were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The interfacial shear strength between HDPE and PBO fiber was analyzed by measuring three-point bending properties of the composite. TPB exhibited different results due to the PBO fiber surface treatment. The results showed that the treatment of PBO fiber improved the interfacial adhesion as compared to the untreated one. The effects of PBO fiber content on tribological properties of the HDPE composites were investigated. The worn surface morphologies of HDPE composites were examined by scanning electron microscopy and the wear mechanisms were discussed. Results show that all treated PBO/HDPE have superior tribological characteristics to unfilled ones.
Silaned nano-silicon dioxide (SiO2) was used to improve the adhesion properties of carbon fiber/polyoxymethylene (CF/POM) composites. The CF and nano-SiO2 were treated and the changes on the surface properties of the treated and untreated composites were studied by impact, three-point bending tests, and scanning electron microscopic analysis. The measurement showed that the fracture toughness increases with the increase of CF content, while very high content of CF did not further cause the increase of the toughness of CF/POM composite. The impact strength of treated specimens is still higher than those of the untreated ones. The modified composite with the good matrix/fiber adhesion possessed 20% higher interlaminar shear strengths compared to the composite having weak interface.
In this article, the different chemical modifications of natural fiber on the physical and mechanical properties of polypropylene (PP)/wood flour (WF)/nanoclay hybrid composites were studied. To meet this objective, the chemical treatments on WF, namely alkali, acetylation, and benzoylation, were carried out. Then, the composites were prepared through the melt mixing of WF and PP at 50% weight ratios, with various amounts of nanoclay (0, 3, and 6 per hundred compounds (phc)) in Haake internal mixer and the test specimens were prepared by injection molding. The amount of coupling agent was fixed at 2 phc for all formulations. The tensile strength, impact strength, and water uptake of these composites were analyzed and the reinforcing properties of the chemically treated composites were compared with those of untreated composites. The chemical modification efficiency was verified by Fourier transform infrared (FTIR) analysis, and the dispersion state of nanoclay in the composites was examined using X-ray diffractometer and transmission electron microscopy. The results showed that the tensile modulus, tensile strength, and impact strength of the composites increased by applying chemical treatments. Modified composites had lower water absorption (WA) and thickness swelling than unmodified ones. Furthermore, the highest mechanical properties and the lowest water uptake were observed in the composite modified with acetic anhydride. FTIR spectra show that the intensity of O–H bond at 3444.2 cm–1 and formation of ester bond at 1741.4 cm–1 were indications of changes in the chemical structure of the fibers. The tensile modulus and strength increased with increase of nanoclay up to 3 phc and then decreased. However, the impact strength and WA decreased with increase of nanoclay loading. The morphological findings showed that the samples containing 3 phc of nanoclay had higher order of intercalation and better dispersion.
In this study, the direct melt impregnation of unidirectional glass fiber tapes in an injection molding process is investigated. The simple textile structures were used for a load-adapted reinforcement of injection-molded parts, determining the impregnation quality by mechanical tests. A sandwich layer construction was made with an outer unidirectional fiber layers and an inner injection-molded layer with pure or additionally short fiber-reinforced polypropylene (PP). The glass fiber tapes were produced in a continuously working fiber–foil process where the aligned fiber bundles have been fixed with one side on a PP foil under temporarily acting pressure and temperature. A special bundle spreading device reduced the number of individual fiber layers, which ensured the direct melt impregnation in the injection molding process. The mechanical properties of the sandwich structures were determined using a three-point bending flexural test as well as Charpy and puncture impact tests to investigate the energy absorption. The results were compared to unreinforced and globally short fiber-reinforced test samples. The local reinforcement, designed for bending stiffness and energy absorption, led to a considerable reinforcement effect with minimal mass increase in comparison with the short fiber-reinforced samples. The fiber masses required to achieve commensurable properties were significantly reduced. Thus, when using the fiber tapes, only one-third of the fiber mass necessary for reinforcement with short glass fibers was required.
Montmorillonite (MMT)/rice husk (RH) hybrid filler-filled low-density polyethylene (LDPE) nanocomposite films, containing 0, 2, 3, 4, 5, and 6 wt% MMT (based on the total weight) were prepared by extrusion blown film. The films were characterized by morphological, mechanical, oxygen (O2) barrier, and thermal properties. The delamination of MMT layers evidenced from X-ray diffraction results suggests an increase in the interlayer distance and shows intercalated structure of the nanocomposites. Adding MMT did not adversely affect the interfacial morphology, as confirmed by scanning electron microscopy. Addition of MMT into the LDPE/RH system improved the mechanical and O2 barrier properties. For instance, tensile strength, tensile modulus, and tear strength increased by 8, 10, and 5%, respectively, with the addition of 3 wt% MMT. Further, the O2 barrier of the composite films improved more than twofold by adding 4 wt% MMT. Initial degradation temperature of LDPE/RH composites increased with the incorporation of MMT suggesting that the nanocomposites are more thermally stable than LDPE/RH composites.
In this study, the preparation of nylon 6/talc nanocomposites was studied by melt blending in a co-rotating twin-screw extruder having length/diameter ratio of 32:1 at a screw rotation speed of 100 r min–1. Concentration of nanotalc was varied from 1 phr to 5 phr in nylon 6. The composite samples were subjected to a series of three extrusion cycles, and the effect of reprocessing on the structural properties of materials was investigated. Properties such as mechanical (tensile flexural and impact), thermal (differential scanning calorimetry), morphological (scanning electron microscopy), rheological (viscosity vs. shear rate), and colour spectrophotometry were investigated. This study would enrich the knowledge about the recycling of nylon 6, with the additional aspect of the use of collected data from more complex system, that is, composite materials, where the nanotalc particles play a role in the interactions initiated by repeated extrusion processing. Mechanical, thermal, rheological and colour properties improved with the increase in nanotalc in nylon 6 and remained nearly unchanged up to second extrusion processing. However, all the properties decreased on third extrusion processing due to the degradation of nylon 6 matrix.
Recycled carbon fiber (RCF) was employed as a reinforcing material to prepare polyoxymethylene (POM)-based composites through a simple melting extrusion. An effective approach was developed to clean and modify the surface of the as-received RCF with nitric acid and then with a silane coupling agent. The mechanical evaluation demonstrated that a significant reinforcement was achieved for POM/RCF composites due to the improved interfacial adhesion between the fibers and the matrix. The thermal stabilities of the composites were also improved in the presence of RCF. The morphological observation of impact fracture surfaces indicated that the RCF gained a homogeneous dispersion in POM matrix due to good interfacial boding between fibers and matrix. The studies on nonisothermal and isothermal crystallization behaviors showed that RCF acted as a nucleation agent for the crystallization of POM domain in composites; therefore, the crystallization rate and nucleation density increased remarkably due to the heterogeneous nucleating effect of RCF. These crystallization features may be advantageous for the enhancement of mechanical performance and processability of POM-based composites.
Mechanical strength of phenylenebenzobisoxazole (PBO) fibers and cross-linked polyethylene (XLPE) matrix composites were studied with particular interest on the effects of oxygen cold plasma-treated fibers. PBO fibers were treated in a radio frequency plasma reactor using oxygen for different treatment times to increase the interface adhesion. Tensile tests on PBO fibers showed that plasma treatment caused an increase in average tensile strength compared with untreated fibers. Fracture analysis confirmed the increase in interfacial adhesion due to oxygen plasma treatment.
This article is concerned with the effects of the silane surface treatment of silicon dioxide (SiO2) on the tribological properties of the SiO2-reinforced polymethyl methacrylate (PMMA) (SiO2/PMMA) composites filled with carbon fiber (CF). Silane treatment and CF bring positive effect to improve friction reduction and antiwear properties of SiO2/PMMA composites. Fourier transform infrared analysis shows that SiO2 has been oxidized and etched by silane treatment. The presence of active groups increases the polarity of SiO2, and so the bonding property between the particle and the matrix improves. The scanning electron microscopy (SEM) observation revealed that this hybrid reinforcement could be interpreted in terms of a positive rolling effect of the particles between the two sliding surfaces, which protected the short CFs from being pulled out of the PMMA matrix.
In this article, an attempt is made to improve the filler-loading capacity of fly ash (FA) by its surface modification with zinc hydroxide and calcium hydroxide. In the modification reaction, FA to calcium hydroxide weight ratio was maintained constant at 5:1, while that of FA to zinc hydroxide was varied as 5:0.4, 5:0.6, and 5:0.8 and the optimized composition was utilized as filler in nylon 6. Modified FA was found to have formed hemimorphite on to its surface, giving rise to spine-structured surface morphology. FA surface modified with 5:0.6 weight ratio of FA to zinc hydroxide (FaZn6Ca) provided FA with the highest level of spine-structured surface morphology and thus was determined to the optimized composition to be utilized as filler in nylon 6. Concentration of FaZn6Ca was varied up to 40 phr in nylon 6. Prepared composites were characterized for mechanical, thermal, rheological, crystallinity, and morphological properties. Melting and crystallization temperatures remained approximately constant; tensile strength, flexural strength, crystallinity, tensile modulus, flexural modulus, enthalpy of melting (H m), and enthalpy of crystallization increased, whereas elongation at break and impact strength decreased with increase in FaZn6Ca concentration in nylon 6. Spine-structured surface morphology formed on the surface of FA increased the filler-loading capacity of FaZn6Ca in nylon 6; while the improvement in the properties were caused due to better interactions happening between nylon 6 and FaZn6Ca due to the hydrophilic nature of both the materials. Since FA is obtained as waste from thermal power plant, the use of this material as a filler in nylon 6 would help ease the solid waste disposal problem which will benefit the environment.
The C–O, C=O, and C(=O)O groups were introduced onto high-density polyethylene (HDPE) chains by ultraviolet irradiation in air and the groups’ content increased with increase in the irradiation time. When they irradiated for 16 h, gels were formed in the irradiated HDPE, and the content of the gels increased with increase in the irradiation time. Compared with HDPE, the crystal form of the irradiated HDPE did not change and still retained the orthorhombic structure, and its melting temperature decreased, while its crystallinity increased. The irradiated HDPE was added in HDPE/CaCO3 composites as a compatibilizer, and HDPE/irradiated HDPE/CaCO3 composites were obtained. Compared with those in HDPE/CaCO3 composites, the dispersion of the CaCO3 and interfacial interaction between CaCO3 and HDPE matrix in HDPE/irradiated HDPE/CaCO3 composites improved due to compatibilization of the irradiated HDPE, and its mechanical properties (especially impact strength), thus, showed remarkable enhancement. With increase in irradiation time, the tensile strength of HDPE/irradiated HDPE/CaCO3 composites enhanced and its impact strength increased during irradiation time of 16 h and then decreased slightly. In the same irradiation time, the tensile strength and impact strength of HDPE/irradiated HDPE/CaCO3 composites increased with increase in the content of the irradiated HDPE.
First, some groups of C=O and C–O were introduced onto high-density polyethylene (HDPE) chains by ultraviolet irradiation for short time in ozone atmosphere. The content of the groups was increased with increasing the irradiation time. The irradiated HDPE was blended with calcium carbonate (CaCO3) to prepare the composites. The melting temperature and crystallinity of HDPE in irradiated HDPE/CaCO3 composites were lower than the HDPE in HDPE/CaCO3 composites. Compared with the HDPE/CaCO3 composites, the dispersion of CaCO3 and the interfacial interaction between CaCO3 and HDPE in the irradiated HDPE/CaCO3 composites increased respectively. With increasing the irradiation time, the mechanical properties (especially impact strength) of the irradiated HDPE/CaCO3 composites were markedly enhanced, while their thermal stability decreased slightly. For example, the tensile strength and impact strength of the irradiated (20 min) HDPE/CaCO3 composites increased from 25.7 MPa and 72 J m–1 to 30.3 MPa and 416 J m–1, respectively, compared with those of the HDPE/CaCO3 composites, and stiffened and toughened HDPE composites were obtained.
The goals of this work are to obtain thermoplastic starch (TPS) with different glycerol/water ratios, verify its characterization by different techniques, and study the influence of addition of cellulose nanofibers in the matrix of TPS. The general procedure for processing starchy materials involves granular alteration with the combination of temperature, shear, and plasticizers. Distilled water and glycerol are used as plasticizers, and the influence of both of them has been studied in tensile properties. By infrared spectroscopy analysis, the addition of plasticizers created new physical links (hydrogen bonds) with starch molecules thereby shifting the characteristic peaks of native corn starch to higher wave number. The most suitable composition for the elaboration of bionanocomposites has been determined and bionanocomposites with different content of cellulose nanofibers have been obtained and their mechanical properties have been studied.
An epoxy macromolecular chain extender, polymethyl methacrylate-co-glycidyl methacrylate (PMMA-co-GMA), was synthesized by continuous random free radical polymerization, which was introduced into poly(ethylene terephthalate) (PET) and PET blends. The modified PET blends exhibited higher torque with increasing the content and the polymerization degree of PMMA-co-GMA. The rise of torque after initial melting period was observed, which indicated the occurrence of reaction between the epoxy group of PMMA-co-GMA and hydroxyl or carboxyl end groups of PET. The melting temperature, crystallization temperature, and crystallization degree of PET blends decreased. The chain extender was introduced in PET/ethylene–propylene–diene monomer (EPDM)-graft-GMA (EPDM-g-GMA) blends with the composition of 85/15, which exhibited brittle fracture behavior. The blends, in which the chain extender content in PET was over 8 wt%, exhibited ductile fracture behavior. EPDM-g-GMA was used to toughen PET with 8 wt% chain extender. The brittle–ductile transition took place between the rubber content of 10 wt% and 15 wt%. The transition was in advance when compared with PET/EPDM-g-GMA blends. The content of chain extender in PET showed little influence on the compatibility of PET blends. The macromolecular chain extender was an effective extender for PET. The introduction of macromolecular chain extender showed contribution for the toughening PET.
Filler treatment is one of the recognized methods that can be implemented to improve the mechanical properties of composite materials. However, no research has examined this particular issue from the dynamic perspective. Hence in this study, both untreated and treated polypropylene (PP)/muscovite (M)-layered silicate composites were tested under static and dynamic loadings of up to 1100 s–1, using a universal testing machine and split Hopkinson pressure bar apparatus, respectively. M particles were treated with lithium nitrate and cetyltrimethylammonium bromide as a surfactant, through an ion exchange treatment. This treatment process was successfully proven, using Fourier transform infrared, X-ray diffraction, and transmission electron microscopy analyses. Results show that the treated PP/M specimens with a fine state of dispersion level show better mechanical performances under a wide range of strain rates that were investigated, when compared with the untreated PP/M specimens. In addition, the mechanical properties of both the tested PP/M-layered silicate composites also show great dependency on the strain rate applied, where yield stress, compression modulus, ultimate compressive strength, and absorbed energy steadily increased when the strain rate was increased. However, the yield strain shows a contrary trend. Postdamage analyses were found to be consistent with the mechanical results for both tested specimens.
This study examined the effect of titanium dioxide (TiO2) dispersion on the tribological properties of carbon fiber (CF)-reinforced–polyimide (PI) matrix (CF/PI) composites. Nanocomposites were prepared through compression molding as milled CF/PI mixtures without further melt mixing. The incorporation of TiO2 leads to a significant improvement in friction and wear properties of the CF/PI composite. The scratches on the worn surface of the CF/PI composite filled with TiO2 are considerably reduced. We can see a relatively smooth, uniform, and compact worn surface, which is in good agreement with the considerably increased wear resistance of the CF/PI composite.
Wood–plastic composite foams (WPCFs), consisting of polypropylene and bagasse as wood fiber, were produced using tandem extrusion. The simultaneous effects of different material parameters including bagasse loading and particle size, melt viscosity of the used thermoplastic, type and content of chemical blowing agent on the microstructure, and physical properties of the obtained composite foams have been evaluated. Special sandwich morphology has been observed for these foams. Void fraction of WPCFs was measured and optimized using an experimental design method, response surface methodology. The maximum determined void fraction of the prepared WPCFs was 54%, which was obtained at the middle values of blowing agent content and bagasse particle size. Employing a mixture of endothermic–exothermic blowing agents has also caused the optimum amount of void fraction. Moreover, thermal behavior of wood–plastic composites was studied and the effects of all material parameters on decomposition behavior of polymer and bagasse fibers were investigated. The results verify that both bagasse content and bagasse particle size considerably influence the thermal stability of the microcomposites.
Carbon fiber (CF)-reinforced polyimide (PI) has been widely used in many engineering fields because of its high specific strength and stiffness. However, PI does not adhere well with CFs because it has low free surface energy. In addition, high viscosity in the melted phase causes poor impregnation. In this study, surface treatment methods, that is, coupling agents (CAs) with plasma treatment on CFs, were applied to increase the interfacial strength between the CFs and the PI matrix. The modified CF surfaces were analyzed by X-ray photoelectron spectroscopy and scanning electron microscopy. To analyze the effectiveness of the surface treatment method, the interlaminar shear strength (ILSS) was measured using the three-point bending test. From the test results, the ILSS of the specimens treated with the silane CA after the plasma treatment increased by 48.7% compared with the untreated specimens.
The aim of this work is to evaluate the effects of oxidation treatment and the addition of silicon dioxide (SiO2) on the mechanical properties of carbon nanotube (CNT)/polytetrafluoroethylene (PTFE) composite film. A powder impregnation process with integrated inline continuous oxidation of CNTs was used to produce CNT/PTFE composite. CNT/PTFE composite was processed into test laminates by compression molding, and interface-dominated composite properties were studied. The tensile strength of composites-containing SiO2 and oxidation-treated CNT improved obviously.
In the last decades, poly(methyl methacrylate) (PMMA) has been widely studied due to its outstanding mechanical, chemical, and physical properties. In this article, the PMMA composites doped with an excited state intramolecular proton transfer (ESIPT) compound 3-hydroxy-2-naphthoic acid (3HNA) are reported. The 3HNA-doped PMMA composites were synthesized by in situ polymerization and characterized by Fourier transform infrared spectra, ultraviolet absorption spectra, fluorescence spectra, and thermogravimetric analysis. The effect of 3HNA and various solvents on the fluorescent properties of the PMMA composites was systematically investigated. The results indicated that the emission spectra of the 3HNA-doped PMMA composites exhibited 3HNA dual emission. A violet emission was observed in 3HNA-doped PMMA composites containing nonpolar solvents or weak polar solvents, whereas the composites containing strong polar solvents exhibited a large Stokes-shifted green fluorescence, which was attributed to the ESIPT of 3HNA.
The effect of β-hydroxynaphthoic acid (β-HNA) addition on electrical and mechanical properties of multiwalled carbon nanotubes (MWCNTs)–polystyrene (PS) composite at a fixed amount of MWCNTs (0.85 wt%) are delineated. Obtained electrical, mechanical, morphological, and Fourier transform infrared results showed that addition of β-HNA up to 1 wt% to MWCNTs-PS composite enhanced the dispersion of MWCNTs in the neat PS, formation of MWCNTs-PS network, relative permittivity, dielectric loss, and the electrical conductivity increased by about three orders of magnitude for the prepared composite. Dielectric relaxation results showed that at the domain frequency range, the relaxation process below 1.0 wt% β-HNA was mostly due to polymer molecular relaxation process, while at 1.0 wt% β-HNA, the composite relaxation behavior was mostly due to charge conductivity relaxation. Mechanical results showed that addition of β-HNA to composite system up to 1.0 wt% increased the elastic modulus, yield stress, and tensile strength of the composites by about 12.2, 17.1, and 10.0%, respectively, which indicated that the addition of β-HNA to composite system improved MWCNTs dispersion in PS matrix and enhanced the interfacial bond in the β-HNA-MWCNTs-PS network.
Polyolefin elastomer-grafted multiwalled carbon nanotubes (POE-MWCNTs) were incorporated in a polyimide (PI) matrix. The POE shell formed on the MWCNTs improved the dispersion of MWCNTs and enhanced the interfacial adhesion between the PI matrix and MWCNTs, leading to improvements in storage modulus and the glass transition temperature of the composites and enhancement of the electrical properties of PI. Thus, composites with 4–5 wt% POE-MWCNTs showed increased electrical properties by about 60–70% and retained the high impact strength when compared with the neat PI.
Poly(methyl)methacrylate (PMMA) composites with various contents of titanium dioxide (TiO2) were prepared. The effects of fiber content and modification on the mechanical properties and thermal behavior of PMMA composite film were studied. The use of organosolv lignin and acrylic acid together as a binary modifying agent for TiO2 filler increased both the strength and the ultimate strain of treated PMMA composites as compared to the untreated ones. The higher temperature dramatically increased the weight loss of all three sample categories. The organosolv lignin and acrylic acid mixture was more effective than a single modifying agent in reducing the thermal decomposition of PMMA/TiO2 composites.
Different concentrations of fillers such as manganese dioxide (MnO2) and magnetite (Fe3O4) were incorporated into acrylonitrile butadiene rubber (NBR)-interlinked composites. The prepared composite systems were irradiated by electrons at a constant dose of 50 kGy to induce radiation cross-linking under atmospheric conditions. The effect of different contents of fillers and temperature variations on direct current (DC) electrical conductivity, DC, in NBR/MnO2 and NBR/Fe3O4 mixture systems was investigated. The calculated activation energy, E DC, from DC was found to be highly affected by both the type and concentration of the fillers, while the dielectric properties namely dielectric constant, dielectric loss, and the alternating current (AC) electrical conductivity ( AC), were measured as functions of frequency and temperature and for different filler concentrations of MnO2 and Fe3O4. The AC value was calculated from dielectric measurements and by employing a simple relationship. The analysis of the AC results shows that the conductivity increases up to a temperature of about 330 K. Further increase of temperature reduces the conductivity of Fe3O4 samples, while the conductivity of MnO2 samples tends to show almost constant values after this temperature. Mechanical properties, tensile strength (TS), tensile modulus at 100% elongation, and hardness were established as a function of different concentrations of fillers MnO2 and Fe3O4. It was found that filler incorporation into the NBR matrix is one of the major factors that enhance the TS as well as hardness resistance, while the elongation at break shows an adverse behavior by increasing the content of MnO2 and Fe3O4 fillers.
This article presents the nonlinear dynamic response of functionally graded (FG) shallow spherical shells in thermal environments subjected to low-velocity impact by an elastic ball. The material properties of a FG shallow spherical shell vary continuously through the thickness according to a power law distribution of the volume fraction of the constituents. The temperature field is considered to vary along the thickness direction due to the steady state heat transfer. Based on the higher order shear deformation theory, the governing equations of motion for the shell, which account for geometric nonlinearity is obtained using Hamilton’s principle. The contact force between the shell and the impactor is relative to local deformation and calculated using a numerical method. Then, the governing equations of motion are solved numerically by the Chebyshev collocation method and Newmark scheme. This is a complete model that can not only fully model the dynamic behavior of the shell but also fully model the impactor’s dynamic behavior. In the numerical example, the effects of material properties, temperature, initial impact velocity and mass of the impactor on the dynamic behavior of the shells, and contact force are discussed in detail.
Long glass fiber-reinforced polypropylene composites (LGFPP) are widely used in the industrial field, especially in automotive applications, due to their excellent mechanical properties and low cost. This article focuses on obtaining optimal mechanical properties of LGFPP for different objectives. The primary objective is to minimize the cost of the composite. The other objective is to obtain specific, desired properties of the composite (irrespective of the composite cost). The latter case is useful in designing products where quality of the composite cannot be compromised (while the cost of the composite is secondary). The properties that were optimized include tensile Young’s modulus, flexural Young’s modulus, and notched Izod impact. Surrogate models were obtained and used to predict these properties as functions of corresponding compositions of the composites. Furthermore, optimization framework that employs these models either as constraints or as objective functions was developed with the aim of developing tailored fiber-reinforced polypropylene. All simulations are programmed using MATLAB version 7.10.0 (R2010a).
In the current work, the influence of filler particle size on the performance of the composites was studied. Some physical parameters were measured for linear low-density polyethylene (LLDPE) films reinforced with silicon dioxide (SiO2) powder. Samples filled with SiO2 of different particle sizes and concentrations were prepared. It was found that fillers with small size caused an increase in mechanical properties of LLDPE at lower concentration than that of particles with bigger size. This was confirmed experimentally by measuring different physical parameters such as yield strength, coefficient of thermal expansion, thermal conductivity, melting temperature, and structural morphology. Therefore, filler sizes ranged from nano to micro could help in reducing the amount of the usage of filler, which could overcome the recycling problems of the filled polymers without affecting the end-use properties of the composite. Illustrations are given using figures, images, and tables.
The aim of this study was to investigate the effects of foaming on the electrical properties of carbon nanotube (CNT)-reinforced polystyrene (PS). A pseudo-three-dimensional (3D) model based on random walk simulation was developed for predicting the electrical properties of CNT nanocomposites. The electromagnetic interference shielding effectiveness (EMI SE) of foamed PS/CNT composites was also studied through a network analyzer, measuring the EMI SE of specimens through reflection and absorption mechanisms. Six types of nanocomposites, including foamed and nonfoamed PS/CNT composites with a CNT loading of 2.1 vol% and different void contents, were manufactured using compression molding and leaching techniques. To realize the effects of foaming on the electrical conductivity of PS/CNT composites, electrochemical impedance spectroscopy analyses were carried out and compared with the pseudo-3D model. We also found that foaming via the leaching method improved the EMI shielding properties of the composites up to 24%.
There are different stress–strain definitions to measure the elastic modulus of hydrogel materials. However, there is no agreement as to which stress–strain definition should be employed. This study is aimed to carry out a comparative study on different results that are given by the various definitions of stress–strain and to recommend a specific definition when testing hydrogel materials. The prepared gelatin hydrogels are subjected to a series of compression tests to measure their mechanical properties. Three stress definitions (second Piola–Kirchhoff stress, engineering stress, and true stress) and four strain definitions (Almansi–Hamel strain, Green–St Venant strain, engineering strain, and true strain) are used to determine the elastic modulus and maximum stress and strain. The highest nonlinear stress–strain relation is observed for the Almansi–Hamel strain definition and, as a result, it may overestimate the elastic modulus at different stress definitions (second Piola–Kirchhoff stress, engineering stress, and true stress). The Green–St Venant strain definition fails to address the nonlinear stress–strain relation using different definitions of stress and invokes an underestimation of the elastic modulus values. Engineering stress and strain definitions are only valid for small strains and displacements which make them impractical when large deformation is expected. The results also show that the effect of varying the stress definition on the maximum stress measurements is significant but not when calculating the elastic modulus. It is of vital importance to consider which stress–strain definition is employed when characterizing the mechanical properties of hydrogel materials. The results suggest the application of the true stress–true strain definition for characterization of the hydrogel material mechanics since it gives more accurate measurements of the material’s response using instantaneous values.
Poly(benzimidazole/ether/siloxane/amide) (PBESA) having siloxane and ether groups in the backbone has been prepared using 4-(3,4-diaminophenoxy)benzene-1,2-diamine, bis(carboxypropy)tetramethyldisiloxane, and 4,4'-oxydianiline via polyphosphoric acid processes with heating up to 160°C. The sulfonation of polystyrene (PS-S) was conducted using 98% sulfuric acid. Afterward, a series of hybrid membranes using PBESA/PS-S/silica nanoparticles (SiNPs) have been developed with 0.1–2 wt% nanofiller. Later, the membranes were doped with phosphoric acid and subjected to various characterization techniques. Field emission scanning electron micrographs (FESEMs) showed gyroid-like patterning of nanoporous membranes with uniform ionic pathways. Fine water retention capability and higher proton conductivity of new hybrids, owing to consistent porous membrane structure, were observed. Increasing the amount of nanoparticles (0.1–2 wt%) also enhanced the tensile stress of acid-doped PBESA/PS-S/SiNPs nanocomposites from 64.9 to 68.1 MPa. There existed a relationship between nanofiller loading and thermal stability of the membranes. The glass transition temperature of phosphoric acid–doped PBESA/PS-S/SiNPs nanocomposites increased from 202 to 214°C. The membranes also had fine ion exchange capacity (IEC) of around 2.5–3.7 mmol g–1. Novel membranes with high IEC value achieved high proton conductivity of 1.26–2.74 S cm–1 in a wide range of humidity values at 80°C, which was higher than that for perfluorinated Nafion® 117 membrane (1.1 x 10–1 S cm–1 at 80°C, 94% relative humidity (RH)). The fuel cell (hydrogen/oxygen) using PBESA/PS-S/SiNPs 2 (IEC 3.7 mmol g–1) showed better performance than that of Nafion® 117 at 40°C (30% RH).
This study tended to modify polyvinylidene fluoride (PVDF) microfiltration membranes by the addition of nanomagnesium oxide (nano-MgO) particles via fabrication of the phase inversion method. The detailed structure and properties of these composite membranes were characterized. The findings showed that the membrane hydrophilicity was significantly improved with the addition of nano-MgO content increasing from 0% to 1%. The improved hydrophilicity and decrease in roughness of the composite membrane enhanced the antifouling performance during the reclaimed water treatment.
A new kind of polyamide-6,6/mobile crystalline material (PA66/MCM-41) hybrid composites were prepared by in situ polymerization. The crystal structural and physical properties of these composites were investigated by Fourier transform infrared and nitrogen adsorption/desorption measurements. The nonisothermal crystallization behavior of PA66/MCM-41 was studied through differential scanning calorimetry measurements. Ozawa, Mo, and Kissinger models were used to analyze the kinetics of the nonisothermal crystallization process. It was found that MCM-41 acting as a nucleating agent in composites accelerated the crystallization rate; the Ozawa method failed to describe the nonisothermal crystallization behavior of PA66/MCM-41 composites. However, the Mo model was able to describe the nonisothermal crystallization process fairly well.
In this study, the thermal behavior of modified urea–formaldehyde (UF) resin with nanosilica (nano-SiO2), wood flour (WF), and their mixture of SiO2/WF was investigated. Five modified UF hybrid composite materials with 0.8 F/U ratio with different filler were synthesized using the same procedure. The thermal behavior of materials was studied using nonisothermal thermogravimetric analysis, differential thermal gravimetry (DTG), and differential thermal analysis and supported by data from infrared spectroscopy. The shift of DTG peaks to a high temperature indicates the increase in thermal stability of modified UF resin with hybrid SiO2/WF fillers, which is confirmed by the data obtained from the Fourier transform infrared spectroscopic study. It was estimated that the UF/WF samples based on nano-SiO2 have better thermal stability.
Nanocopper (nano-Cu)/poly(acetoacetoxyethyl methacrylate (AAEM)–styrene (St)) (P(AAEM-St)) composites were synthesized by reducing copper acetate solution in AAEM and St monomer by ultrasonic technique without adding emulsifier. The morphology, structure, thermal stability, and the interaction between Cu nanoparticles (NPs) and P(AAEM-St) matrix of the composites were characterized using ultraviolet–visible spectroscopy, X-ray diffractometer, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA), respectively. The results show that Cu NPs possessed face-centered cubic structure, and they were homogeneously dispersed in P(AAEM-St) matrix. XPS and FTIR analyses reveal the interaction between Cu NPs and C=O of the acetoacetoxy in the copolymer of AAEM and St. TGA proves that the thermal stability of the pure P(AAEM-St) is higher than that of the nano-Cu/P(AAEM-St) composites.
Polyoxymethylene (POM) composites with various contents of cellulose fibres (CFs) were prepared. The effects of fibre content and ionic liquid surface treatment on the tribological behaviour of POM composites were studied under different nominal pressures ranging from 50 N to 300 N. The tribological mechanisms were discussed based on scanning electron microscopy inspections of the worn surfaces. The surface treatment of CFs improves the tribological performance of the neat polymer matrix. Differential scanning calorimetric study showed that CFs played the role of nucleating agents.
In this work, a structural reactive injection moulding process using reactive anionic polyamide 6 (APA-6) is studied. Semi-empirical equations for the prediction of the APA-6 reaction kinetics and an advection equation for void transport are used in the numerical scheme. A complex numerical simulation of reactive injection of -caprolactam was developed for a three-dimensional industrial part. The validity of the approach is demonstrated for determining an effective injection strategy, including the position of vents and gates and the most effective parameter values for minimum mould filling time without the formation of voids.
Polypropylene (PP)/calcium carbonate (CaCO3) nanocomposites were prepared from masterbatch by melt blending in a twin-screw extruder. The effect of three different nano-CaCO3 loadings (5, 10, and 15 wt%) on the rheological/viscoelastic and mechanical properties of the nanocomposites was investigated. A scanning electron microscopy was used to study the morphology of the nanocomposites, whereas a differential scanning calorimetry was used to analyze the thermal properties. The rheological properties were characterized using an oscillatory rheometer, and the mechanical properties were characterized by a tensile test machine. In the melt rheological study, a frequency sweep test showed that the complex viscosity
In this study, within the scope of experiments, two kinds of biaxial weft-knitted (BWK) fabrics with aramid (AR) and polyamide 66 (PA66) stitch fibers were used as reinforcement systems to fabricate thermoplastic composites with PA66 resin yarn. Then final composite became BWK with AR stitch yarn and cross-ply. The mechanical properties of composites were investigated by conducting tensile and three-point bending tests on specimens. In all specimens, PA66 was commingled with AR yarn. AR was used as reinforcement. In preliminary studies, AR unidirectional composites with AR/PA66 commingled fibers and with various twisting angles were produced and appropriate twisting angle was found by conducting tensile and three-point bending impact tests on specimens. Because of the higher volume fraction of the cross-ply composites, tensile and three-point bending properties of the cross-ply composite structures had higher than the BWK composites with the AR stitch yarn.
In this study, the thermally stable poly(amide–imide) (PAI)/cupric oxide (CuO) nanocomposites (NCs) containing 4, 6 and 8 wt% of CuO nanoparticles (NPs) were prepared by ultrasonic technique. At first, the optically active PAI was synthesized from the polymerization of a chiral monomer, N-trimellitylimido-
Nanocomposites (NCs) of poly(vinyl alcohol) (PVA) with chiral-modified magnesium–aluminum-layered double hydroxides (LDHs) were prepared by solution intercalation method. A novel chiral organomodified LDH was synthesized from the coprecipitation reaction of the aluminum (III) nitrate nonahydrate, magnesium (II) nitrate hexahydrate, and bioactive N-trimellitylimido-
In this work, the wear behavior of cross-linked ultra-high-molecular weight polyethylene (UHMWPE) is discussed. The UHMWPE specimens are molded through injection molding techniques by varying the parameters of melting temperature (MT). The cross linking of UHMWPE was carried out by iridium 192 isotopes, where the specimen received 25 kGy energy. The wear tests were conducted on a hip joint simulator that was designed and fabricated in the laboratory. The contact loads are varied from 50 N to 100 N. The study revealed that MT has influenced the hardness and wear properties such as coefficient of friction and wear rate, respectively. -Irradiated UHMWPE has better wear and friction resistances than unirradiated UHMWPE. The worn out surfaces were examined with the help of scanning electron microscope, and it revealed the presence of wear mechanisms such as ironing, scratching, ploughing, plastic deformation, and fatigue wear.
Poly(amic acid) (PAA) was prepared by the reaction of 4,4'-(hexafluoro isopropylidene) diphthalic anhydride with 2,2'-bis(trifluoromethyl) benzidine in N, N-dimethylacetamide. Hybrid films were obtained from blended solutions of the precursor polymer and saponite (SPT) or organically modified hectorite (STN) clays, and the clay content was varied from 0 to 40 wt%. The cast film of PAA was heat treated at different temperatures to create polyimide (PI) hybrid films. The nanostructure of the hybrid films was observed using transmission electron microscopy, which showed that the clay layers were well dispersed into the matrix polymer, although some clusters or agglomerated particles were also detected. The addition of SPT was more effective than the addition of STN with regard to improving the thermal properties, whereas the addition of STN was more effective with regard to improving the optical transparency and gas barrier characteristics of the PI matrix.
The effects of the wool fiber as reinforcement in the friction materials on the friction and wear properties were investigated in this study. The contents of the wool fiber in the friction materials tested were 0, 3, and 4 wt%. The friction tests were conducted with a constant friction tester at a temperature range of 100, 150, 200, 250, 300, and 350°C. The friction coefficient and wear rate were recorded. The friction coefficient of the friction materials reinforced with the wool fiber of 3 wt% was steady, and the wear rate was low. As the temperature increased, the stability of the friction coefficient of friction materials was improved. The Rockwell hardness decreased and the impact strength increased as the content of wool fibers was increased. The morphology of the worn surfaces was examined using scanning electron microscopy. The results indicated that the adhesive wear and abrasive wear were dominant in the friction materials reinforced with wool fiber.
This study is aimed at utilizing the gramineae to reinforced polyethylene (PE). The interface modification was performed by treatment of silvergrass (SV) fibers with sodium hydroxide (NaOH) and polymeric methylene diphenyldiisocyanate (PMDI). The modified fibers were characterized by Fourier transform infrared spectroscopy. Composites were fabricated with different fiber loadings (10%, 20%, 30%, 40%, 50%, and 60%) of SV fibers by injection molding. The properties of the composites were studied by mechanical property, thermogravimetric analysis, and differential scanning calorimetry. The mechanical properties of the treated composites were compared well with those of untreated composites. A marked improvement of 49.0% in tensile strength and 47.35% in flexural strength for 40% SV fibers-reinforced high-density PE composites was noticed. It is also found that the treated fiber is acting as a nucleating agent. It can be deduced that the thermal stability of the wood–plastic composites can be improved when SV fibers were treated by NaOH and PMDI.
Biodegradable nanocomposites comprising of organically modified montmorillonite-reinforced polylactic acid (PLA) and polyhydroxybutyrate (PHB) were assessed. This study investigates different nanocomposites mixing techniques as methods of achieving exfoliation. The incorporation of reverse flow mixing sections resulted in an increase in exfoliation of nanoclay platelets in PLA nanocomposites. PHB nanocomposites were shown to be more sensitive to thermal degradation and therefore benefited from a reduction in the number of processing steps utilised. Further development of the process was observed with the incorporation of compatibilisers for both polymers which led to considerable improvements in terms of mechanical properties exhibiting superior flexural properties. It was shown using x-ray diffraction that improvements in intercalation was observed which affected the compostability of both composites. Composites with increased interlayer spacing degraded faster and the nanocomposites in general degraded at a faster rate than the virgin polymers.
Poly(4-methyl-1-pentene) (PMP)/elastomer (ethylene–propylene–diene monomer (EPDM), polyolefin elastomer (POE), and styrene–butadiene–styrene (SBS)) blends with various mass fraction were prepared using a twin-screw extruder in the melt state. Mechanical properties, the fracture morphology, melting and crystallization behavior, and melt flow rate of PMP and PMP/elastomer blends were investigated by universal testing machine, differential scanning calorimeter, scanning electron microscopy, and melt flow indexer. The effect of elastomer and their content on the microstructure and properties of the PMP/elastomer blends were discussed. The results showed that EPDM, POE, and SBS all had good effect on PMP toughening. Therein, PMP/POE blends had the best comprehensive property, which was attributed to the comprehensive effects of phase morphology, molecular chains tangle, and the degree of crystallinity of PMP phase.
Optical and electrical properties of conductive polymer composites made of polystyrene (PS) containing ultrafine iron particles of size 2 μm were studied under different measuring conditions: iron filler concentrations (0, 5, 10, 20, and 30 wt.%), ultraviolet radiation wavelength, temperature range (30–90°C), and applied frequency range (50 kHz–1.5 MHz). The absorption spectra from the composites were measured using a spectrophotometer. The analysis of the optical results showed that the electronic transitions are direct in the k-space. The optical energy gap and the energy tails were determined as a function of iron particles’ content. It was found that optical energy gap decreased and energy tails increased with iron content. The determined refractive index (n) and the extinction coefficient (k) increased with iron concentration. The alternating current (AC) conductivity and dielectric properties were determined using impedance measurements. The collected impedance data were analyzed and showed that the dielectric constant (') and dielectric loss ('') of the composites are increasing as iron concentration increases and decreasing as the applied frequency increases. It was found that the AC conductivity increases with increasing frequency, temperature, and iron concentration. Some theoretical and empirical models are used to describe the observed optical and electrical behavior of the prepared PS composites.
Hybrid composites composed of polypropylene (PP) or high-density polyethylene (HDPE), different flax fibers (unidirectional, biaxial, and twill2 x 2), and silicon dioxide (SiO2) were produced by hot-press technique. The ternary polymer composite was effectively fabricated by spraying SiO2 solvents onto the surface of flax fiber. The dispersion of SiO2 particles and flax in the composites was studied by scanning electron microscopy. The related PP- and HDPE-based composites were subjected to instrumented falling weight impact test. The thermal and mechanical properties of the composites were determined by thermogravimetric analysis, dynamic mechanical thermal analysis, creep and stress relaxation tests, respectively. It was found that thermal decomposition temperature of the PP or HDPE/flax composites increased by the addition of SiO2 particles. The impact energy, stiffness, creep resistance, and relaxation modulus value of all flax composites increased markedly compared with the PP and HDPE matrix. Time–temperature superposition was applied to estimate the creep and relaxation modulus of the composites as a function of time in the form of a master curve. The activation energies for all the PP and HDPE composites systems studied were also calculated using the Arrhenius equation. The generalized Maxwell model was fairly applicable to the stress relaxation results.
Within the scope of experiments, five kinds of biaxial weft-knitted (BWK) fabrics with various loop lengths (8.0, 9.2, 10.5, 11.9, and 13.5 mm) were used as reinforcement systems to fabricate thermoplastic composites with polypropylene (PP) resin yarn. Then, the final composite became BWK composite with various loop lengths. The mechanical properties of the composites were investigated by conducting tensile, three-point bending, and three-point bending impact tests on specimens. In all specimens, PP was commingled with glass yarn. Glass was used as the reinforcement material. Fiber volume fraction of weft fibers with the 8.0 mm loop length was the highest compared with the other four types of specimens. Because of the higher volume fraction of the BWK composites with the 8.0 mm loop lengths, tensile, three-point bending, and three-point bending impact properties of the 8.0 mm loop were higher than the other four types (9.2, 10.5, 11.9, and 13.5 mm) of composite structures.
The mechanical properties of biomaterials under different strain rates play an important role in their application as potential implant material for replacement and repair of soft tissues, that is, liver and kidney. The biomaterials being implanted for the human soft tissues should have the physical and mechanical properties as close as possible to those of the tissues being replaced. Polyvinyl alcohol (PVA) is a biocompatible biomaterial with suitable mechanical properties which is in widespread use in biomedical and pharmaceutical areas as well as in tissue engineering applications. However, so far the effect of strain rate on the mechanical properties of this versatile biomaterial remains poor. In this study, the nonlinear mechanical behavior of a fabricated PVA sponge is investigated experimentally and computationally under different strain rates. A series of tension tests with the strain rates of 1, 20, and 100 mm/min are carried out for the PVA sponge. The Yeoh strain energy density function (SEDF), which is indicated to be the most suitable material model for spongy biomaterials, is calibrated using the experimental data. The general prediction ability of Yeoh SEDF is verified using finite element simulations of PVA tensile experiments. The elastic modulus and maximum stress of PVA sponge with the strain rate of 20 mm/min are almost 48 and 3.22 times higher than that of 1 mm/min. Results also revealed that Yeoh materials model can suitably capture the nonlinear mechanical behavior of PVA sponge biomaterial which can be used in future biomechanical simulations of the spongy biomaterials. These results can be utilized to understand the nonlinear mechanical behavior of PVA sponges and has implications for wound healing and tissue engineering purposes.
Hessian cloth-reinforced urethane acrylate-based thermoset composites were prepared by compression molding. The composition of the matrix solution was formulated with different concentrations of urethane acrylate ((F1: 55%, F2: 65%, F3: 75%, F4: 85%, and F5: 95%) in solvent methanol (44.5, 34.5, 24.5, 14.5, and 4.5%) along with thermal photoinitiator benzyl peroxide (0.5%). Mechanical properties of the composites were examined. It was found that F4 with 85% urethane acrylate-based composite showed the best results. The maximum value of tensile strength (TS), bending strength (BS), tensile modulus (TM), bending modulus (BM), and elongation at break (Eb%) were found to be 47 MPa, 61 MPa, 1250 MPa, 1550 MPa, and 9.38%, respectively, for F4-treated composites. Different intensities of radiation (100–500 krad) were applied on F4-soaked hessian cloth-reinforced composites. The mechanical properties of the irradiated composites were found to increase significantly compared with those of nonirradiated composites. The maximum TS, BS, TM, and BM for the treated composites were found to be 66 MPa, 84 MPa, 1882 MPa, and 2250 MPa, respectively, at 300 krad dose. Water uptake and soil degradation test of the composites were also performed.
Polypropylene/polycarbonate (PP/PC), PP/poly(styrene-b-(ethylene-co-butylene)-b-styrene) (PP/SEBS) binary blends, and PP/PC/SEBS ternary blend were produced via melt blending in a co-rotating twin-screw extruder. The phase morphology, tensile, and impact behaviors of the blends were studied. Transmission optical microscopy and atomic force microscopy investigations of the necking region in tensile tests and scanning electron microscopy of tensile fractured surfaces were performed to characterize the fracture mechanism. In the PP/PC/SEBS ternary blend, core–shell morphology (PC particles as a core and the SEBS phase as a shell) was formed. Analysis of micromechanical deformation suggested that crazing occurred in PP and shear yielding did not occur during tensile tests. Rubber particles cavitation, shear yielding, and crazing occurred in both the PP/SEBS binary blend and PP/PC/SEBS ternary blend. Results showed that Corté and Leibler’s theory was unable to describe the effect of core–shell particles in these blends.
Among the failure modes of composite materials, delamination is the most striking one. It may result in the reduction of stiffness and long-term performance of composite materials. The initiation stage is very crucial in delamination. This is because initiation stage requires higher amount of force, and after this stage, there is a stable propagation of delamination that requires little force and causes the failure of the structure. Initiation of delamination consists of two main stages including minor initiation and major initiation. These two stages are vital stages in the delamination process. Understanding the delamination behavior and their internal micro events in these stages may lead to better design and result in enhanced strength against crack initiation. This article proposes a combined method to discriminate various fracture mechanisms in the initiation of delamination. The combination of sentry function analysis and frequency analysis of acoustic emission (AE) waveforms are used to analyze crack initiation and to discriminate its internal micro failures during mode I delamination. Discrimination process is derived from the power spectrum density of AE waveform in distinct frequency intervals. Scanning electron microscopy (SEM) observation was used to determine different fracture mechanisms and associate these observed fracture mechanisms and their equivalent AE signal frequency range. It is shown that this combined method is a powerful device to study the behavior of the initiation of delamination.
The coeffect of β-nucleating agent (β-NA) and different core–shell particles (CSPs) on improving the mechanical properties and thermal stability of polypropylene random copolymer (PPR) composites were investigated. Different CSPs, that is, the regular POE/nano-calcium carbonate (CaCO3) and the novel PE/nano-CaCO3 CSP were prepared through melt blending. The transmission electron microscopic micrograph demonstrated that the core–shell structure was successfully prepared and the CSP dispersed homogeneously in the PPR matrix. β-NA was also introduced into the PPR matrix to control the crystalline structure. The results of differential scanning calorimetry, wide-angle x-ray diffraction, and polarization optical microscopy showed that the relative content of β-form crystal was greatly enhanced in the presence of β-NA. The results of the mechanical tests and thermal gravimetric analysis indicated that the comprehensive mechanical properties and thermal stability were all greatly improved, especially for the sample with the incorporation of both β-NA and PE/nano-CaCO3 CSP.
Within the scope of experiments, two kinds of biaxial weft-knitted (BWK) fabrics with aramid (AR) and polyamide (PA) 66 stitch fibers were used as reinforcement systems to fabricate thermoplastic composites with PA66 resin yarn. Then, the final composite became BWK with AR stitch yarn and cross-ply. The mechanical properties of composites were investigated by conducting tensile and three-point bending impact tests on specimens. In all specimens, PA66 was commingled with AR yarn. AR was used as reinforcement. In preliminary studies, AR unidirectional composites with AR/PA66 commingled fibers and with various twisting angles were produced and appropriate twisting angle was found out by conducting tensile test on specimens. Due to the random multiple cracks that changed the fracture behavior of BWK composites with AR stitch, the tensile properties of the BWK composites with AR stitch became lower compared with the cross-ply. However, the three-point bending impact properties of the BWK composites with AR stitch fiber were higher compared with the cross-ply.
Well-aligned poly(azo-naphthyl-imide) (PANI) fibers and PANI/multi-walled carbon nanotube (MWCNT) nanofibers-based nanocomposite were produced via self-reinforcement. High-molecular-weight 31 x 103 g mol-1 PANI has been fabricated in this study. Scanning electron microscopy and transmission electron microscopy showed that the electrospun PANI/MWCNT nanofibers were uniformly aligned and almost free of defects. The as-prepared well-aligned electrospun nanofibers were then utilized as homogeneous reinforcement to enhance the tensile strength and toughness of films. Compared with neat 3 wt% PANI nanofibers (304.6 MPa), the tensile strength for the film reinforced with 3 wt% PANI/MWCNT nanofibers (245.9 MPa) was considerably increased. The significant enhancement in the overall tensile properties of the PANI/MWCNT nanofibers-reinforced polyimide films was ascribed to good compatibility between the electrospun nanofibers and the matrix as well as high nanofiber orientation in the matrix. The thermal stability of PANI/MWCNT nanofibers-reinforced polyimide was also superior having 10% gravimetric loss of 599–625°C and glass transition temperature of 243–261 °C relative to the neat polymer and PANI nanofiber-based system. High-performance polyimide nanocomposites via self-reinforcement can act as potential contenders for light-weight aerospace materials.
In this research work, the possibility of defect detection in wood–plastic composites (WPCs) by shearography method has been assessed. Shearography is one of the practical nondestructive test methods that has been commonly used for detecting defects in polymer-based composites. In this experimental work, first, a defect (hole) was intentionally drilled on one side of the extruded WPC and then the shearography test and analysis was performed on it. This preliminary step was performed to evaluate the application of the test and calibration. Subsequently, the injection-molded WPCs with different volume fraction of wood content were assessed via shearography test for detection of the probable defects in their structures. The results indicated that shearography method can be effectively used for defect revelation in wood–plastic composites.
Within the scope of experiments, five kinds of biaxial weft-knitted (BWK) fabrics with various knitting techniques (plain, interlock, tuck, tuck-miss, and interlock2) were used as reinforcement systems to fabricate thermoplastic composites with polypropylene (PP) resin yarn. Then, the final composite became BWK composites with various knitting types. The mechanical properties of composites were investigated by conducting tensile, three-point bending, and three-point bending impact tests on specimens. In all specimens, PP was commingled with glass yarn. Glass was used as reinforcement. Fiber volume fraction (V f) of weft fibers of the interlock2 was the highest, and the length of straight part of loop shape was the longest in the interlock2 compared with the other four types of specimens. Because of the higher V f of the BWK composites with the interlock2, tensile, three-point bending, and three-point bending impact properties of the interlock2 was higher than the other four types (plain, interlock, tuck, and tuck-miss) of composite structures.
Improvement in the tribological properties of the polyamide 6 (PA6) with various fillers, for example, talc, glass fiber (GF), combined solid lubricants such as graphite, and ultrahigh-molecular-weight polyethylene was systematically studied. The results revealed that GF could reduce the coefficient of friction (COF) and wear rate of pure PA6 more efficiently than talc, and the optimum content was 15 wt%. The COF and wear rate increased with the increase of load, except the wear rate of the composite with 20 and 25 wt% GF, which decreased with the increase of load. The incorporation of combined solid lubricants to PA6 contributed to increases in COF and wear rate. Further addition of 15 wt% GF enhanced the tribological properties remarkably. To further understand the wear mechanism, the worn surfaces were examined using scanning electron microscopy.
Maleated thermoplastic starches (MTPS) were prepared by reactive extrusion, with corn starch as raw material, glycerol as the plasticizer, and maleic anhydride (MAH) as esterification agent. The influence of the amount of MAH on MTPS properties was studied. With thermoplastic starch (TPS) as contrasting sample, Fourier transform infrared spectroscopy results displayed that esterification reaction successfully occurs between corn starch and MAH. The degree of substitution (DS) results showed that the DS of MTPS increased along with the increasing amount of MAH. X-Ray diffractometry results showed that esterification reaction resulted in the decrease of crystallinity of TPS, indicating that the thermoplastic property of starch was improved. The greater the proportion of MAH, the more decreased is the degree of crystallinity of MTPS. Differential scanning calorimetric results showed that the melting temperature and enthalpy of melting decreased with increasing the amount of MAH. The thermal weight loss initial temperature of MTPS was below TPS, and thermal weight loss rate was greater than TPS. The contact angle of MTPS was greater than TPS, while the water absorption of MTPS was less than TPS. Further, with increasing of MAH content, the contact angle increased, while water absorption decreased, which indicated that the hydrophobic was gradually improved.
Thermoplastic elastomers (TPEs) based on polypropylene (PP)/waste ethylene–propylene–diene terpolymer powder (WEPDMP) composites were prepared by melt compounding, and the composites were compatibilized by styrene–butadiene–styrene block copolymer (SBS). The effects of SBS compatibilizer on mechanical, morphological properties, and the Mullins effect of the TPEs were investigated systematically. Experimental results indicate that SBS had a good compatibilization effect on the PP/WEPDMP composites. Compared with PP/WEPDMP composites, the tensile strength and the elongation at break went through a maximum value at an SBS content of 6 phr, which were improved by 49.4 and 170.3%, respectively. Morphology study shows that the interface interaction of the PP/WEPDMP composites compatibilized by SBS was strong, which contributed to the significantly improved mechanical properties. Mullins effect results show that the softening obviously appeared after the second loading–unloading cycle, while the maximum stress decreased slightly at the later cycles and the internal friction loss of PP/SBS/WEPDMP composites was lower than that of PP/WEPDMP composites, indicating the elasticity of PP/WEPDMP TPE is improved by the incorporation of SBS.
A series of the long glass fiber–reinforced thermoplastic polyurethane elastomers and acrylonitrile–butadiene–styrene (LGF/TPU/ABS) composites with different content of LGFs were prepared using self-designed impregnation device. Dynamic mechanical properties of the LGF/TPU/ABS composites have been investigated using dynamic mechanical thermal analysis. The results indicated that the content of LGFs and scanning frequency have some effect on the dynamic mechanical properties and glass transition of LGF/TPU/ABS composites. In the meantime, the Arrhenius relationship has been used to calculate the activation energy of α-transition of the LGF/TPU/ABS composites. The thermogravimetric analysis thermograms of the LGF/TPU/ABS composites were found to decrease in two steps. The good dispersion of the LGFs in the matrix resins is obtained from scanning electron micrographs. In addition, effects of the LGF contents on mechanical properties of LGF/TPU/ABS composites were investigated.
Poly(ethylene glycol) (PEG) was mixed at various weight percentage with biodegradable poly(lactic acid) (PLA) via direct melt compounding method. Nanocomposites of PLA/PEG, with two types of organoclay namely, cloisite 93A (C93A) and cloisite 30B (C30B) were also prepared by melt blending method. The crystallization behaviors of PLA/PEG and PLA/PEG/organoclay were studied using differential scanning calorimetry (DSC). The isothermal crystallization kinetics has been investigated using the Avrami’s equation. In PLA/PEG, the PLA crystallized first followed by crystallization of PEG during the cooling. The viscoelastic behavior of the PLA/PEG and PLA/PEG/organoclay were investigated by dynamic mechanical analysis where the nanocomposites showed higher magnitude of storage modulus. The plasticizing effect of PEG acts predominantly in the mechanical performance of PLA/PEG, which shows increased percentage elongation and impact strength in the blend. The sample with 20 wt% PEG showed optimum impact strength. Again, the nanocomposite with 3 wt% C30B exhibited better tensile strength and modulus than the sample with C93A. The characterization of fractured surface of the matrix polymer and the blend were compared through scanning electron microscopy. The rheological and compostability study of the system were further investigated.
Solution-blended hybrid composites with carbon black (CB) as the second conducting filler in polyethersulfone (PES)-graphite have been prepared by first dissolving PES in dichloro methane. Addition of 1 wt% CB to solution-blended PES-7 wt% graphite results in decrease in the direct current electrical resistivity by four orders compared to the addition of 0 wt% CB. The particle size of graphite is reduced from few micron to nano level as evidenced by transmission electron microscopy analysis resulting in better dispersion. Without the addition of CB, the binary composite namely PES-7 wt% graphite exhibits finite conductivity due to increase in the contact between graphite particles as a result of reduction in the particle size. Comparison of electrical conductivity of PES-7 wt% graphite-2 wt% CB composites prepared by both solution-blending and powder-mixing routes proves the above-mentioned point. The alternating current behaviour, both conductance and effective dielectric constant studies shows that solution-blended composites exhibit higher value of conductance and effective dielectric constant at 0.01 Hz. This can only be attributed to better graphite dispersion in solution-blended composites. The enhancement is due to only particle size reduction of graphite that decreases the interparticular distance as the solution-blended binary composites with CB act as insulators up to 10 wt%. The charge transport at low concentrations of CB in solution-blended hybrid composites is dominated by the interfacial barriers and capacitance effects, while at higher concentrations it is mainly of hopping type at room temperature. The interfacial capacitance increases from 37.6 pF with 0 wt% CB addition to 96 pF with 2 wt% CB addition in PES-7 wt% graphite. Differential scanning calorimetry result suggests that more than 10°C enhancement in the glass transition temperature of PES is obtained for PES-7 wt% graphite-1 wt% CB.
Fiber-reinforced polymer composites are nowadays used in numerous applications due to their good tribological, mechanical, and thermal properties. In the present investigation, the tribological behavior of polyether ether ketone (PEEK) and PEEK reinforced with glass fiber (GF) has been investigated using the pin-on-disk wear tester under dry sliding condition at different applied loads, speeds, and sliding distance. Modeling and optimization of tribological parameters is carried out using response surface methodology (RSM)-based D-optimal design. Tribological parameters such as load, sliding speed, and sliding distance are chosen as numerical factor, and the weight percentage of GF content is considered as the categorical factor. An experimental plan of four-factor (three numerical + one categorical) D-optimal design based on the RSM is employed to carry out the experimental study. The wear performances of PEEK matrix composites are evaluated using the performance indicators such as specific wear rate and coefficient of friction. The morphologies of the worn surfaces are observed using scanning electron microscopy and atomic force microscopy.
The present study aims to investigate the moisture absorption of polypropylene (PP)/rubberwood flour (RWF) composites and its effects on dimensional stability. The compositions included different grades of plastic, and the amounts of wood flour, maleic anhydride-grafted polypropylene (MAPP), and ultraviolet (UV) stabilizer were varied. The composite materials were manufactured into panels by a twin-screw extruder. Long-term water absorption (WA), long-term thickness swelling (TS), and degradation of flexural properties of the composites were studied for a range of water immersion times. The WA and TS of the samples increased with RWF content and immersion time. Recycled PP gave higher WA and TS than virgin PP, for the composites with 45 wt% RWF. Increasing MAPP content from 3 to 5 wt% had no significant effect on WA and TS, whereas the addition of 1 wt% UV stabilizer increased them. A MAPP content of 3 wt% is recommended for moisture resistance, while the amount of UV stabilizer should be kept as low as possible. Flexural strength and modulus of composites also decreased with moisture uptake; however, <3% WA did not significantly affect the flexural strength. In contrast, the maximum strain of composites consistently increased with WA.
Composites of acid-functionalized multi-walled carbon nanotubes (MWCNTs) that reinforced poly(amide–imide) (PAI) were developed. The obtained composites containing 5, 10, and 15 wt% MWCNT–COOH exhibited a relatively good dispersion on the macroscopic scale. MWCNT/PAI composite films have been prepared by casting a solution of precursor polymer containing MWCNTs into a thin film, and its tensile properties were examined. The mechanical and thermal properties of the composites were investigated. The incorporation of MWCNTs–COOH improved the mechanical properties of the composites compared with that of neat PAI. An improvement in thermal properties of the MWCNT/PAI composites was also observed. Fourier transform infrared spectroscopy, powder x-ray diffraction, scanning and transmission electron microscopies were also used to evaluate the MWCNT/PAI composite system.
The present article studies the effect of treatment of 0.5, 1.5, and 2.5% titanate-coupling agent (LICA 38) on various properties of fly ash–filled polypropylene (PP) composites. The fly ash content varied from 0 to 30 wt%. The mechanical and thermal properties of the composite material were evaluated, and microstructure investigated through scanning electron microscopy. Experimental results were compared with various existing models. Experimental data for tensile yield strength showed good fit to the existing models. Adhesion parameter or interfacial interaction was also evaluated though Pukanszky model. The values of yield stress and breaking strength of treated fly ash–based composites showed higher values compared to that of untreated fly ash–filled PP composites at corresponding filler content. The overall mechanical properties of fly ash–filled composites are essentially decided by wettability of the filler. It is also found that Vicat softening point improved with the addition of fly ash filler. Morphological studies of the tensile fracture surfaces of the composites revealed that the presence of titanate-coupling agent increased the interfacial interaction between fly ash and PP. It also improved the dispersion of fly ash in PP matrix. Thus, the treatment resulted in improvement in mechanical and thermal properties of the composites as compared to untreated fly ash–filled composites. The overall results showed that fly ash dispersion and interfacial adhesion are greatly affected by the amount of the coupling agent.
Superabsorbent hydrogels based on natural polymer, carboxymethyl cellulose (CMC)/sodium alginate (SA) were prepared by 60Co radiation as a source of initiation of cross-linking. The effect of different ratios of SA (20, 30, 40, and 50%) on the physical properties of the CMC/SA hydrogel such as gel fraction percentage (GF%), and swelling percentage (SW%) were investigated. It was found that the GF % decreases with increasing SA content in the hydrogel. While the SW% of CMC/SA hydrogel tends to increase with increasing SA content in the hydrogel at constant irradiation dose (2.5 kGy). Morphology of the hydrogels was examined using scanning electron microscopy, which indicates compatibility between CMC and SA. Thermal properties were also investigated using thermogravimetric analysis. It was found that the thermal properties of the hydrogel having different composition were almost the same. The results obtained from ultraviolet–visible spectrophotometric analysis show that the prepared hydrogels can be used in the removal of heavy metals from waste water. The ability to absorb these heavy metals is of great importance from the point of view of environmental pollution.
In order to improve the waste sludge dewaterability of polyacrylamide (PAM), composite conditioner of cationic PAM/montmorillonite (CPAM/MMT) was synthesized by in situ polymerization. The structure and property of the composite were studied in terms of intermolecular hydrogen bonding, melting behavior, intercalation behavior, and dewaterability of the waste sludge. The results revealed that the molecular weight and cationic degree of CPAM/MMT composites decreased with the increase of MMT content. The hydrogen bonding between –OH groups of MMT and –NH groups of CPAM was confirmed by Fourier transform infrared spectroscopic analysis, which led to a relatively high elastic modulus values and low tan values at 5 wt% MMT content, indicating the possible formation of a physically cross-linked network in aqueous solution for the composite. The melting temperature of the composites presented decreasing trend first and then became higher as the content of MMT increased. The MMT platelets dispersed well with an intercalated state in CPAM matrix as indicated by x-ray diffraction analysis and transmission electron microscopic observation. The addition of MMT reduced the specific resistance to filtration of the waste sludge, with a minimum value being achieved at 5 wt% MMT content, while the ultraviolet transmittance of the supernatant of the waste sludge was also improved, and the turbidity was reduced. This synergistic effect of the two components in the composite through charge neutrality and bridging action of CPAM as well as the adsorption capacity of MMT resulted in an enhanced dewaterability of waste sludge.
Thermoplastic vulcanizates (TPVs) based on acrylonitrile–butadiene–styrene terpolymer (ABS)/nitrile butadiene rubber (NBR) blends were prepared by dynamic vulcanization where ABS matrix was plasticized by dioctyl phthalate (DOP), and the influences of DOP plasticizer dosage on mechanical properties, Mullins effect, and morphological properties of the TPVs were investigated systematically. Experimental results indicated that the mechanical properties of ABS/NBR TPVs were improved significantly with the incorporation of DOP. Compared with ABS/NBR TPVs, the tensile strength and the elongation at break went through maximum values at a plasticizer content of 10 phr, while the Shore A hardness was decreased apparently. Mullins effect results showed that the TPVs incorporated with DOP had relatively lower stress-softening effect, residual deformation, and internal friction loss than that of the ABS/NBR TPVs, indicating the improvement of elasticity. Morphology studies showed that the fracture surface of ABS/NBR/DOP TPVs was relatively smoother, indicating the significantly improved elastic resilience ability.
Shear and extensional properties of high-density polyethylene (HDPE) and poly(butylene succinate) (PBS) blends were measured using capillary rheometers to investigate the influences of processing conditions and mixing ratios on flow behaviors, and the predictive abilities of extensional master curve, back propagation neural network model, and constitutive equation were analyzed for the extensional flow. The results showed that the shear flow of blend melts obeyed the power law, and the influence of PBS content on shear-thinning behavior was obvious. The extensional viscosity of the blends decreased with extensional strain rate, extrusion rate, and PBS content increasing. The extensional master curve was applied for HDPE/PBS blends, and scaling factor reduced with the increasing extrusion rate. In addition, the approach of back propagation neural network model was an effective approach to predict extensional viscosity for the purposes of polymer processing control and monitoring.
In an attempt to maximize the beneficial effect of irradiation, the influence of multifunctional acrylates (MFAs) such as trimethylol propane triacrylate, ethylene glycol dimethacrylate, trimethylol propane trimethacrylate, and tripropylene glycol diacrylate on the 90/10 ethylene vinyl acetate/waste tire dust (EVA/WTD) were studied. The 90/10 EVA/WTD and EVA-containing 4 phr MFA prepared using a Haake mixer at 140°C and 50 r min-1 rotor speed. The blends were then irradiated using a 3.0-MeV electron beam machine. Results on gel fraction revealed that EVA/WTD blends were cross-linked by electron beam irradiation. Among the MFA employed in this studies, TPGDA was found to render highest tensile strength with the best retention in elongation at break and increased heat of fusion and crystallinity of blends upon irradiation. The changes in the properties of EVA/WTD blends upon irradiation are attributed to the cross-linking of the EVA matrix. The changes in crystallinity and crystalline melting temperatures of EVA/WTD blends upon irradiation are discussed in detail.
Leather shavings, the by-products of leather industry, are usually treated by the landfill, which probably makes them hazardous to the human health and the environment due to the oxidation of the containing chromium (Cr) (III) to toxic Cr (VI). Therefore, efficient and environment-friendly reusing of leather shavings is not only of great interest but is also a huge challenge. This article reported a reuse method of leather shavings by combing two novel technologies, that is, the solid state shear milling (S3M) to mechanochemically pulverize and activate leather shavings, and the thermal processing of poly (vinyl alcohol) (PVA) to make them filled with PVA. The related mechanism, the structure, and properties of the obtained composites were investigated. The results showed that S3M method could efficiently pulverize and activate leather shavings through very strong shearing and compressing forces, promoting the formation of more hydrogen bonds and the chelation in the interfaces between PVA and leather shavings, and consequently enhancing their compatibility. In this way, PVA/leather shaving composites with pretty good performances, for example, better mechanical properties, thermal stability, and water resistance as compared with neat PVA, were obtained. This is a convenient, cost-efficient, and environment-friendly technology to recycle hazardous chrome-containing leather shavings.
The interlaminar shear strength (ILSS) of polytetrafluoroethylene (PTFE) fiber-reinforced polymethyl methacrylate (PMMA) composites enhanced by filled silicon dioxide (SiO2) is studied. The PMMA blends were prepared by combining the techniques of high-speed mechanical stirring. Experimental results showed that ILSS and impact properties of PMMA composites were improved. The largest improvement in ILSS and impact strength were obtained with 7 vol % loading of SiO2. ILSS and impact strength were improved by 15 and 50%, respectively, compared with the composite without SiO2. The fracture and surface morphologies of the composite specimens were characterized using scanning electron microscopy. This PTFE fiber-reinforced composite can be applied to bioengineering and fabrics.
Polypropylene (PP)/nano-calcium carbonate (nCC) composites modified with methacrylic acid (MA) with and without dicumyl peroxide (DCP) were prepared by a twin-screw extruder. The effects of nCC and MA on the mechanical, thermal, and rheological properties of PP/nCC composites were investigated. The mechanical tests indicating that nCC could simultaneously reinforce and toughen PP. In addition, incorporation of MA further increased the mechanical properties of the composites. In the presence of DCP, a small amount of MA could increase markedly the mechanical properties of PP/nCC composites. Differential scanning calorimetry results indicate that the addition of nCC increased the crystallization temperature (T c) as a result of heterogeneous nucleation effect of nCC on PP and can induce β-phase PP. The addition of MA can further increase the T c of PP and the intensity of β-phase PP. The results of rheological property analysis indicated that the viscosity increased with increasing amount of the filler, especially at low shear rates. The addition of MA improved the dispersion of nCC resulting in the increasing of apparent viscosity.
After separation of metals from printed circuit boards (PCBs), they are sent to recycling process; however, significant amounts of useless nonmetallic particles are also included. Recycling useful materials from used PCBs is a major challenging problem that must be solved in China renewable resource industries through harmless and feasible processes. In this article, a novel β-polypropylene (PP)/nonmetals composite was prepared and evaluated. The nonmetallic particles were treated with calcium pimelate (PA, a β-nucleating agent for PP) and then compounded with PP through melt blending method. The results show that when cooling and crystallizing from the melt, β-PP are formed because of the surface effects of PA. This observation is assumed as the source of good rigidity and toughness of prepared PP composites. In the composite containing 10 wt % nonmetallic particles treated with 5 wt % PA, the content of β-PP was found to be larger than 90% and the impact strength and flexural modulus of PP composite increased by 205.3 and 61.8%, respectively, compared with those of neat PP. Although the addition of PA-modified nonmetals slightly increased the tensile strength of PP, considering all factors, the optimal mass ratio of PP/nonmetals/PA composites to reach optimum mechanical properties was observed as 100/10/0.5. Thus, the application of treated nonmetals to prepare nonmetals/β-PP composites provides a promising way to recycle PCBs waste and produce useful PP composites.
In this study, the effect of multi-walled carbon nanotubes (MWCNTs) and maleic anhydride-grafted polyethylene (MAPE) on the physical and mechanical properties of composites based on wood flour (WF) and high-density polyethylene (HDPE) was investigated. To meet this objective, MWCNTs, as a reinforcing agent, in 4 levels of 0, 1, 3, and 5 wt% and MAPE, as a compatibilizer, in 2 levels of 0 and 3 wt% were used. The amount of WF was fixed at 50 wt% for all formulations. First, the materials were prepared by melt compounding process in an internal mixer (Brabender® Plasti-Corder®), and then the samples were manufactured by injection molding method. The morphology of the specimens was characterized using scanning electron microscopy (SEM) technique. The results showed that when the contents of the MWCNTs were increased from 0 to 3 wt%, the tensile strength and modulus of the samples increased to 41.7% and 24.3%, respectively, and the water absorption values of the samples decreased to 58.8%. Similar results were also observed for the thickness swelling values. Both mechanical and physical properties of samples were improved by adding MAPE up to 3 wt%. The nanocomposites having 3 wt% MWCNTs and 3 wt% MAPE exhibited the highest impact and tensile strength values, while tensile modulus and physical properties reached their maximum when 5 wt% of MWCNT and 3 wt% of MAPE were used. Also, SEM micrographs showed that CNTs can fill the voids of wood–plastic composites, and the addition of MAPE and MWCNTs enhanced the interaction between the components.
An experimental study was carried out to investigate the effect of temperature on the mechanical properties and the fracture mechanism of wood–plastic composites (WPCs) under tension. The specimens were prepared via injection molding of various weight fractions of pine wood particles and high-density polyethylene (with and without coupling agent, maleic anhydride-grafted polyethylene (MAPE)). The deformation and fracture behaviors of the samples at different temperatures were studied using a portable microscope setup during the test. The results indicated the significant effect of the test temperature on the fracture mechanism of WPC specimens. At room temperature, the dominant fracture mechanism for the samples without MAPE was debonding, whereas wood cracking was the dominant fracture mechanism in the presence of MAPE. At high temperatures, debonding was prominent over wood cracking in all samples (with and without MAPE), whereas at low temperatures (below 0°C) wood cracking was the dominant fracture mechanism.
Long-fiber thermoplastic (LFT) composite materials are rapidly expanding in automotive, transportation, and recreational industry. Most of these materials are natural or black in color with a need for secondary painting of the manufactured products. Standard organic pigments and dyes are not stable above 250°C and degrade during processing. Alternatively, inorganic pigments are thermally stable to at least 800°C. High-performance inorganic pigments offer resistance to outdoor weathering, chemicals, and acids. However, in fiber-reinforced composites, the pigment causes fiber attrition and thereby shows reduction in strength. This work explores colored inorganic-pigmented LFT composites. The ability to integrate the color in the manufacturing steps eliminates the need for secondary painting. Pigment variables such as particle size, distribution, chemistry, and coatings have been investigated. The article presents the processing and performance envelopes of colored inorganic-pigmented LFTs in comparison with unpigmented standard LFTs.
In recent years, there has been increasing interest in the development of wood–plastic composites (WPC) for use as building materials. Using wood as natural reinforcement in composite materials, instead of mineral reinforcements, has several advantages such as low density, low cost, and less abrasive finish. The natural reinforcements are also non-toxic and recyclable. The wide variety of WPCs makes it difficult to discuss the performance of these composites. In this research, the bubble inflation technique, introduced by Joye et al., is used to study the behaviour of biocomposite materials in cold temperatures. The results of experiments with high-density polyethylene and WPC membranes with 20, 30, 40, 50 and 60 wt% of wood fibre, under the combined effect of temperature and pressure are presented. The membranes are tested under the maximum pressure of 18 psi within the temperature range of -50C to +50°C with 25°C increments.
In this article, a newly developed model is utilized to simulate the strain-rate-dependent constitutive equation of graphene/polypropylene nanocomposites, using the mechanical properties of the constituent materials of nanocomposites. The model is a combination of the micromechanics and Goldberg models called strain-rate-dependent micromechanics (SRDM) model. The Johnson-Cook material model is used by the explicit finite element code LS-DYNA to simulate the strain-rate-dependent mechanical behavior of the standard tensile test specimen made of graphene/polypropylene nanocomposites under dynamic loading and its constants are calculated by the SRDM model. Polypropylene reinforced with 0.5, 1.0, and 2.0 wt% graphene sheets were prepared via coating polypropylene with graphene particles. Then, by melt blending in a twin-screw extruder followed by an injection molding process, the nanocomposite samples are manufactured. Good enhancements of Young’s modulus and yield stress at very low graphene contents are achieved. To evaluate the current model, the results are compared with the experimental result of the standard tensile test specimen. A good agreement between the experimental data and the SRDM model is achieved.
Thermoplastic tape placement opens the possibility of a fully automated composite production. The resulting quality is highly dependent on the thermal history during consolidation. This article focuses on the thermal modelling of a tape placement system employing a near-infrared laser. A nonlinear two-dimensional finite element model is presented for a carbon fibre reinforced thermoplastic (AS4/PEEK) composite placement process using a conformable roller. The relative influence of roller geometry, roller temperature and thermal contact resistance was studied. Temperature measurements were performed using thermocouples welded to the substrate. The model predictions show good correlation in terms of timing of the irradiation, shadow and consolidation regions. The roller temperature was found to have the most significant impact on the bond line temperature distribution.
Carbon particle-reinforced polyamides (PAs) are finding increasing applications in many engineering fields. Machining of these materials is needed for obtaining near net shape and precision fit. In this work, application of fuzzy logic technique along with the Taguchi’s orthogonal array is used in turning of PA6 to develop a model for predicting surface roughness. There are many factors affecting the surface roughness. Among these factors the machining parameters that play a dominant role are cutting speed, feed, and depth of cut. The adequacy of the fuzzy rule-based model is verified through coefficient of determination. The correlation that exists between the experimental value and the fuzzy model is on the higher side; hence, the fuzzy logic technique can be effective when estimating the surface roughness in turning of PA6.
An efficiently brominated flame-retardant system which is composed of decabromodiphenyl oxide (DB) and antimonous oxide (AO) was used for long glass fiber-reinforced polypropylene (LGFPP), and the thermal stability, flame retardancy, and mechanical properties of DB-AO/LGFPP composites were investigated. When 12 wt% of DB-AO flame retardant was added into LGFPP, the limiting oxygen index of composites could reach 24.8 and pass the V-0 rating in UL-94 test. The results showed that DB and AO improved the flame retardancy of LGFPP more efficiently which could be proved by thermogravimetric test that had less effect on mechanical properties than widely used intumescent flame retardant to flame-retardant LGFPP. What’s more, analysis of cone calorimeter tests data indicated that gas phase flame-retardant mechanism exists in the DB-AO/LGFPP composites.
Short-term creep behavior of wheat straw composites made with either polypropylene homopolymer or impact-modified copolymer was studied at elevated temperatures (50–90°C). Various mineral fillers were tried to enhance creep resistance in the composite materials among which wollastonite was found to be the most effective one. All formulations exhibited higher creep deformations at higher temperatures where the effect of temperature was more pronounced for composites containing the impact-modified copolymer as the matrix. Short-term creep was successfully modeled using a three-parameter power law and Burgers model, and the dependence of the power law model parameters on temperature was evaluated to quantify temperature dependence of creep behavior. Long-term creep at 50°C was predicted based on the short-term data using the time–temperature superposition (TTS) principle, the power law model, and the Burgers model, and the results were compared with actual long-term data. While TTS was found to be the best method to accurately extrapolate short-term data, the failure of the two other methods was found to be related to the time scale of the deformation in short-term creep tests. The results of this study will provide a basis for the design of natural fiber thermoplastic composites to be used in under the hood applications in auto industry.
The aim of the research was to utilize cocoa pod husk (CPH) in polypropylene (PP) biocomposites. Maleated polypropylene (MAPP) was used as coupling agent to improve the properties of PP/CPH biocomposites. The addition of MAPP had increased the stabilization torque of PP/CPH biocomposites. The tensile strength and modulus of PP/CPH with MAPP were higher compared to PP/CPH biocomposites without MAPP, except the elongation at break decreased. The crystallinity and thermal stability of PP/CPH biocomposites with MAPP increased. These improvements were due to the enhanced interfacial bonding between CPH and PP matrix, which were proved by SEM analysis.
In this article, a new model was developed to predict the fatigue life and stiffness reduction in thermoplastics filled with two-dimensional nanoparticles. The established model is a combination of micromechanics model and the normalized stiffness degradation approach. It was assumed that under fatigue loading condition, only stiffness of thermoplastic resin was degraded due to the temperature rise and thermal softening phenomena, while the stiffness of the nanofillers remains unchanged. The developed model is capable of predicting the fatigue life of thermoplastic nanocomposites based on the experimental data of the neat thermoplastic resin without nanofillers. The results obtained by the new model are in very good agreement with the experimental data of polyamide-6 pellets and hectorite clay nanocomposites under constant stress amplitudes fatigue loading conditions.
Thermoplastics with and without fiber-reinforced plastic reinforcement are currently being used in waterfront applications, for example, in piers instead of timber and reinforced concrete pilings. Although the use of thermoplastics as the compression members exists, they have not been used as the flexural members in civil engineering structures such as bridges or building. To be able to safely use these materials as flexural elements in structures, the suitability of the design procedures needs to be investigated. In this study, ultimate strength design procedure similar to the one used in concrete structures was developed for thermoplastic beams. Experimental data were also provided for comparison. Although the needed coefficients used in the procedure need modifications by more experiments, the developed procedure shall be valuable for practicing engineer using familiar procedures of reinforced concrete design.
The thermo-oxidative decomposition behavior of polypropylene (PP) and polyethylene (PE) filled with carbon nanotube (CNT) and organo montmorillonite (OMMT) as a heat stabilizing filler was comparatively investigated using nonisothermal- and isothermal–thermogravimetric (TG) analyses. The isoconversional method was employed to evaluate the kinetic parameters (Ea, lnA, and n) under dynamic heating in air. OMMT and CNT exhibited respective lowest and highest thermo-oxidative stability as revealed from the lowest and highest Tonset values, respectively, whereas thermo-oxidative stability of PE was better than PP. The TG profiles and calculated kinetic parameters strongly depended on the sorts of fillers and polyolefins. From TG data and calculated kinetic parameters, the incorporation of CNT and OMMT into PP and PE significantly improved the thermo-oxidative stability of the composites. The highest relative Ea value was observed for CNT-containing composites in the conversion extent region of 0.10–0.45. Simultaneous differential scanning calorimetry thermograms revealed that the degradation processes for the neat polyolefins and their composites were exothermic in air. By adding the same filler, the thermo-oxidative stability of the PE-containing composite system under isothermal heating at 320°C was much higher than that of PP composite systems. The obtained results of nonisothermal and isothermal investigations and morphological observation of the samples after heating suggested the improved thermo-oxidative stability of polyolefins modified by CNT over that by OMMT.
This work aimed to study the effects of radiation on the properties of ethylene propylene diene terpolymer/chlorosulfonated polyethylene rubber blend reinforced with 50 phr of carbon black and cross-linked either with sulfur/tetramethylthiuram disulfide or dicumyl peroxide. Irradiation doses were 100, 200, and 400 kGy. It was observed that doses higher than 200 kGy practically destroy the assessed properties of all obtained elastomeric materials, irrespective of used curing system. However, samples cured with sulfur showed a pronounced decrease in mechanical properties.
Poly(butylene adipate-co-terephthalate) (PBAT)/nano-alumina (NA) composite films were prepared using extrusion and compression moulding processes. The aim of this work is to improve the performance property of PBAT. Concentration of NA varied from 0.1 to 5 wt% in PBAT. The prepared films were characterised for mechanical (tensile strength (TS), tensile modulus (TM) and elongation at break (PEB)), thermal (melting temperature (Tm) and enthalpy of melting (Hm)), rheological (viscosity vs. shear rate), morphological (SEM), barrier (water vapour permeability (WVP) and oxygen permeability(OP)) and crystallinity (x-ray diffraction) properties. PEB and crystallinity decreased, whereas, TS and Tm remained unaffected on addition of NA in PBAT, as the addition of NA decreased the crystallinity of PBAT. Nevertheless, significant reduction in WVP and OP of 59 and 33% were obtained for 3 wt% addition of NA in PBAT. Hm and viscosity of PBAT decreased with increase in concentration of NA, due to the thermally conducting nature of NA. Considering the obtained properties, PBAT containing 3 wt% NA can be a potential material for food and pharmaceutical packaging applications.
Polypropylene (PP) thermoplastic composites were fabricated using recycled carbon fibres (rCFs; recovered from composite parts) and waste CFs (wCFs; generated during post-manufacturing processes). Both staple CFs (average 60 mm long) were blended with staple PP resin fibres (60 mm long) and then converted into yarns prior to the composite fabrication using hot-pressed moulding technique. It is found that the composites fabricated from wCFs contained longer CFs (40 mm long) and exhibited better electrical and mechanical properties (conductivity: 10.75 x 103 S m-1; tensile strength 160 MPa and modulus 45 GPa) compared with the composites fabricated from rCFs. It was concluded and recommended that both composite materials could be used as cost-effective and heating elements in lightweight applications.
The tribological behavior of the sliding surfaces is dependent on the frictional heating. Surface and near surface temperatures may become high enough to cause changes in structure and properties of the sliding surfaces. It can also cause oxidation and even melting. Wear and frictional behavior of materials above ambient (25°C) conditions would become critical for polymers as the operating temperature bands of polymers are always limited. In the present study, tribological studies on two-phase and three-phase polystyrene composites at temperatures of 45 and 60°C have been reported. It is found that with increase in temperature the wear rate increases, whereas the friction coefficient decreases. Polymer–ceramic composite exhibited higher friction coefficient than other composites. At temperature of 45°C, the wear rate of the neat polymer increases exponentially whereas at 60°C it decreased. However, addition of fillers into polystyrene brought in drastic reduction in the wear rate of polymer composites. Scanning electron microscopic pictures revealed melting, flowing, and glazing after wear test. Higher pressure velocity resulted in higher wear coefficient.
The present article reports the preparation and characterization of polypropylene (PP) composite with pulque (Agave cantala) leaf fibres treated with sodium hydroxide or sodium chlorite. PP composite material of untreated fibres was also prepared for comparison. The composite samples prepared by hot press-moulding machine were analyzed using Fourier transform infrared, scanning electron microscopy (SEM), thermogravimetric analysis and tensile mechanical tests. SEM analysis pointed out that in the case of PP composite with alkali-treated fibre (AF), the multi-cellular nature of fibre filament appeared more clearly, and the fibre surface became rough as compared to other composite systems that may be the cause of better interlocking between PP matrix and fibres. Consequently, the PP composite with AF (i.e. PP/AF 80/20) exhibited higher values of elastic modulus than other composite systems. The composite of PP with alkali-treated pulque fibres also displayed higher thermal resistance than the composite of PP with raw or bleached fibres.
An investigation was carried out on the noncross-linked low-density polyethylene (LDPE) nanocomposite foams with polyethylene graft maleic anhydride (PE-g-MA) compatibilizer. Nanocomposite foams with similar densities were produced by extrusion method, and the effect of organophilic montmorillonite (OMMT) nanoclay (closite20A) content on cell microstructure, mechanical properties, thermal conductivity, and flame retardancy of samples were studied. X-ray diffraction (XRD) was used to investigate the nanoclay dispersion in LDPE matrix. In XRD patterns of LDPE nanocomposite foams, closite20A characteristic peak was not observed as an evidence of nanoclay intercalation–exfoliation in the polymer matrix. For increasing the compatibility of PE and nanoclay, PE-g-MA compatibilizer was used. Due to the presence of compatibilizer in the nanocomposite foams and decreasing the cell nucleation energy around the nanoclay, the average cell size was reduced, but the cell density and microstructure uniformity increased. Furthermore, the compatibilized nanocomposites showed lower thermal conductivity and burning rate than that of the nanocomposites without PE-g-MA compatibilizer and neat LDPE foams, which can be attributed to the cell size reduction as well as distribution of cells of narrow size in nanocomposite foams.
A novel self-designed dynamic injection molding machine by screw axial vibration introduced in plasticizing process was used in the preparation of polypropylene (PP) standard specimens. Under other process and same conditions, the vibration frequency and amplitude are changed in plasticizing process. The whole energy consumption in the molding process, the tensile stress, impact stress, density, and differential scanning calorimetric results of the specimens were measured. Furthermore, the effects of vibration parameters of plasticizing process on dispersion were studied with the mixture of PP and nano-calcium carbonate (CaCO3) materials using scanning electron microscopy (SEM). The experimental results showed that the maximum increment of tensile stress and impact stress of the specimens are 9.8and 13.8%, respectively, by screw axial vibration introduced in plasticizing process. The maximum increment of density is 0.3%. The melt point of specimens has a significant increase of 3°C and the energy consumption of the whole processing decreases 6.6% at maximum. The SEM micrographs show that the dispersion of nano-CaCO3 became more homogeneous compared with the steady specimens.
Filling materials are used in root end surgery to seal the cavities of teeth and protecting teeth from saliva and bacterial leakage. This study fabricates nonwoven nets using low-melting point polylactic acid (PLA) fibers. Intermediate restorative material (IRM®, a temporary filling material) is made of zinc oxide powder and eugenol solvent with a 3:1 ratio. IRM is then added with PLA fibers or nets to form the fiber-reinforced composite filling material (FFM) or net-reinforced composite filling material (NFM), respectively. FFM and NFM are tested in terms of setting time, compressive strength, solubility, and microleakage to compare the difference between the addition of fibers or nets. The results show that FFM with 2% PLA fibers demonstrates an optimal reinforcing effectiveness and does not cause leaking beyond 40 days after being tested. In addition, it also has better compressive strength than IRM and thus provides greater reinforcement.
The focus of this study is to investigate the effects of oxidative functionalized carbon nanotubes (f-CNTs) and aminosilanized carbon nanotubes (s-CNTs) on the mechanical and thermal properties of polyamide 6 nanocomposites. Oxidation of nanotube surfaces was conducted with sulfuric acid/nitric acid mixture and then aminosilanization was carried out with -aminopropyltriethoxysilane. Nanocomposites were compounded by melt mixing technique and shaped by injection molding. Scanning electron microscopy images revealed that f-CNTs and s-CNTs were dispersed more evenly due to increased interactions with the matrix. Tensile tests indicated that yield strength and Young’s modulus of nanocomposites increased 20 and 23%, respectively, with the addition of only 1 wt% s-CNTs due to very efficient load transfer from the matrix to covalently bonded CNTs. Both dynamic mechanical analysis and thermogravimetric analysis showed that surface-modified CNTs improve all thermal properties due to decreased matrix mobility and physical barrier formation. For example, increases in the storage modulus values were as much as 25%, while the increase in the thermal degradation temperatures were as much as 5°C in the specimens with only 1 wt% s-CNTs.
Linear and nonlinear (in both steady and transient shear flows) rheological properties of polyamide 6/acrylonitrile–butadiene–styrene (PA6/ABS) nanocomposite blends have been investigated. Characterization of nanocomposite samples morphology by scanning electron microscopy revealed that with increasing nanoclay loading, size of dispersing phase droplets decreases significantly and their uniformity improved considerably. Transmission electron microscopy observations clearly display a coexistence of intercalate and exfoliate structure for nanoclay in the polymer-blend nanocomposite. On the other hand, we see that the tactoids are collected of a few silicate layers and possibly also of a single silicate. In other words, the results on rheological properties indicated that overshoots were observed for the start-up tests after different shear rates and delay times. Also, the results showed that the height of these overshoots increased with the applied shear rate and delay time. In addition, the overshoots are highly dependent on the network structure of the blends, and the magnitude of the overshoots increases with increasing nanoclay content. Hence, at very short delay time, the transient shear viscosity does not display any overshoot, while with increment in the delay time, the overshoot appears and increases as the delay time increases. Presented results revealed that increment in the preshearing rate decreases elastic and increases viscose behavior of nanocomposite samples.
Paulownia wood flour (PWF), a by-product of milling lumber, was employed as a biofiller and blended with high-density polyethylene (HDPE) via extrusion. Paulownia wood (PW) shavings were milled through a 1-mm screen and then separated via shaking into various particle fractions (600–≤74 µm) using sieves (#30–>#200 US Standards). The influence of a commercial coupling agent, maleated polyethylene (MAPE), used at various concentrations (0, 1, 3, 5, or 10% w/w) with HDPE and wood particles obtained from a #50-mesh sieve, is examined. Incorporation of high concentrations of MAPE (approximately 5%) in HDPE-PWF blends improved tensile strength compared to lower MAPE concentrations (≤3%). Particle size of wood significantly influenced the mechanical properties of the biocomposite. HDPE-MAPE blends containing smaller wood particles (<180 µm) had higher tensile strength than neat HDPE or blends containing larger particles (>300 µm). Young’s modulus for all HDPE-PWF-MAPE blends was 14–27% higher than that of neat HDPE. Generally, incubation of tensile bars of various HDPE-PWF blends in 95% humidity for 28 days reduced the mechanical properties approximately by 5%. Differential scanning calorimetry analysis showed a slight reduction in the percentage crystallinity among various HDPE-PW blends.
This work focused on the utilization of waste fly ash (FA) as filler in the reinforcement of chlorinated styrene–butadiene rubber (CSBR) with reference to their processing characteristics, morphological, thermal, and mechanical properties, solvent resistance, and electrical resistivity measurements. Rheometric properties such as optimum cure time and scorch time decreases with increase in filler content, whereas maximum torque increases up to 30 phr for FA particles. An appreciable increase in glass transition temperature has been observed from differential scanning calorimetric study. The mechanical properties such as tensile and tear strength, modulus, hardness, compression set, and heat buildup increases, whereas elongation at break and resilience decreases with loading of filler. The observed variation in mechanical properties has been supported by the fractography of the composites obtained by scanning electron microscopy. Variation in the bound rubber formation in CSBR/FA composite has been studied. The bound rubber content decreases with increasing extraction temperature, and its activation energy is also calculated from the Arrhenius plot. The electrical properties such as alternating current conductivity, dielectric constant, and dissipation factor are higher than that of CSBR, and the values increase with increase in the content of FA in the composites.
A self-made vibration-assisted injection molding machine (VAIM) was developed to generate oscillation injection pressure during filling and packing The cavity pressure changes sinusoidal with time during filling and packing in VAIM. The filling time can be shortened with the introduction of oscillation injection pressure. The melt peak of the parts become wider and the melt point move to high temperature with the increase in piston rod vibration amplitude/frequency.
Thermoplastic vulcanizates (TPVs) based on isotactic polypropylene (iPP) and oil-free/oil-extended ethylene propylene diene monomer (EPDM) rubber were prepared by dynamic vulcanization. Their rheological and tensile properties as well as morphological peculiarities were examined and compared with those of uncured blends. Vulcanization was performed using two types of cross-linking agents: phenolic resin and sulfur-accelerating systems. Dynamic vulcanization was shown to change the melt viscosity of oil-free and oil-extended iPP/EPDM blends. These changes were found to depend on both rubber content and type of vulcanizing agent. For identical composition, the melt viscosity of TPVs cured by sulfur system was higher than that of blends cured by phenolic resin system (PRS). Dynamic vulcanization by PRS decreased tensile properties of TPVs in comparison with sulfur vulcanization. Morphology of iPP/EPDM blends studied by atomic force microscope was found to be dependent on the ratio of components, type of elastomer, and nature of vulcanizing system.
Mechanical properties and deformation mechanism of polypropylene (PP) filled with different weight percentage of ethylene–octene copolymer (EOC) and fibrillar silicate attapulgite (ATP) clay were investigated under uniaxial cyclic loading at constant crosshead speed to evaluate plasticity/damage coupling behavior. With increasing EOC and clay content, PP exhibited typical plastics response with marked stress drop at yield followed by steady state plastics region up to rupture. The addition of 3 wt% ATP clay to the PP/EOC blend shows enhanced impact strength up to four times compared to PP with decrease in yield strength by 24% implied synergistic toughening effect. Volume strain, which characterizes deformation damage, steadily increased over the whole plastics stage up to 5.2 for axial strain of 0.30 after a critical tensile strain of 0.05. The small energy value observed for large volume strain revealed matrix shear deformation as the controlling factor for energy dissipation without crazing. Fractography observation using scanning electron microscopy revealed formation of debonding and cavitations on the surface of PP matrix, contributing increase in the volume of all compositions.
Shape-memory polyurethane (SMPU) having segmented structure, with 4,4-diphenylmethane diisocyanate as hard segment, poly caprolactone diol 4000 as soft segment, and 1,4-butane diol as chain extender was synthesized using two-step polymerization technique. This pure SMPU was blended with unmodified and modified multiwalled nanotubes (MWNTs), using twin screw extruder and melt spinning technique. X-Ray diffraction, differential scanning calorimetry, morphological analysis, and shape-memory behavior results for the SMPUs are presented in this study. An improvement in the thermal stability and degradation temperature of the SMPU was observed especially in the soft segments, upon 0.1% loading of MWNT. Slight decrease in crystallinity was recorded for MWNT/SMPU as compared to virgin SMPU. The recovery ratio of SMPU fiber increased to 90% with 0.1 wt% loading of MWNT, but the spinnability decreased due to reduced crystallinity and viscosity with an addition of nanotubes to the polyurethane matrix.
Chemically treated sawdust-reinforced recycled polyethylene composites were fabricated by the injection molding method, and the effect of fiber treatment on the physicomechanical properties of the composites were examined. Upon treatment with sodium hydroxide and benzoyl chloride, the hydrophilic nature of sawdust was significantly reduced. The physical properties of the composites such as water absorption, thickness swelling, and biodegradation behavior revealed that upon fiber surface modification, the composites have attained significant resistance to moisture absorption and microbial attacks. The mechanical properties of the chemically treated sawdust-reinforced composites were found to be improved compared to those of the untreated ones, suggesting that better fiber–matrix interfacial adhesion has occurred upon treatment of sawdust. This was further supported by surface morphology of the tensile-fractured surfaces of the composites captured by scanning electron microscopy that showed much less microvoids and interfacial flaws compared to those of the untreated ones.
By combining carbon woven fabric with thermoplastics, a thermostamping process was proposed to form composite parts with complex double curvatures in one step and to implement affordable application of fiber-reinforced composites in automotive industry. In the proposed process, a laminated carbon woven fabrics with thermoplastic grains were heated, then transferred rapidly to a preheated mold for thermostamping, and cooled down to form the composite part. Various thermoplastics including polyamide 6, polypropylene, and acrylonitrile butadiene styrene were used as matrix materials. It is demonstrated that high-quality parts can be achieved with the proposed forming process and defects are controllable. The experiment results show that the rheological characteristics of thermoplastic resin, the fixed method of mold, and the yarn orientation of the composite blank are very important factors in the thermostamping process. With the proposed process, it is feasible to implement the high-volume and low-cost manufacturing of fiber-reinforced composite parts.
Poly(vinylidene chloride-co-acrylonitrile)-based gel polymer electrolytes are obtained using solution casting technique. The ionic conductivity and thermal behavior of polymer electrolytes have been investigated as a function of wt% of ethylene carbonate (EC). The thermal decompositions of polymer electrolytes have been determined by thermogravimetry and differential thermal analysis in the temperature range between 30 and 800°C. All the polymer complexes can be operated upto 170°C. This range well includes the operating temperature range of the lithium polymer batteries incorporating these materials. Bulk resistance of the electrolyte from alternating current (AC) impedance analysis gives the optimal EC ratio as 80 wt% for maximum ionic conductivity.
This article presents an experimental investigation on the effect of glass fiber length on the mechanical properties of hybrid wood–plastic composites (HWPCs) manufactured via an extrusion process. There is a substantial interest in enhancing the mechanical performance of WPCs. Incorporation of glass fibers has been found to be an effective remedy in this regard. Theoretically, it is expected that mechanical properties can be improved via applying longer fibers. Three different lengths, 5, 15, and 25 mm of glass fibers were added to the WPC compounds to reinforce WPCs in an extrusion process. In addition, continuous glass fibers were also embedded into the extruded WPC with 70 wt% wood content, utilizing a special equipment in extrusion. Mechanical tests showed that applying noncontinuous glass fibers only marginally improved the mechanical strengths. In contrast, continuous fibers did significantly enhance the final properties of the produced profiles. The glass fiber size was also measured after extrusion, and it was observed that severe fiber breakages occurred during the process, which is the main reason for the inefficiency of noncontinuous fibers. The flexural, tensile, and impact strengths were improved up to 14%, 50%, and seven times in the continuously glass fibers reinforced WPC.
Isotactic poly(4-methyl-1-pentene) (PMP) is a semicrystalline polyolefin with many unique properties. The crystallization theory of pure PMP had been well studied based on its molecular structure. In this study, the crystallization behavior and compatibility of PMP/polypropylene (PP) blends were investigated by differential scanning calorimetry, x-ray diffraction, scanning electron microscopy (SEM), and mechanical testing. It was found that the PP crystallization behavior was strongly affected by the presence of PMP in the blend: first, PMP crystallized and then acted as nucleating agent during the crystallization process of PP at lower temperature. In contrast, the influence of PP on the crystallization of PMP was relatively small due to the wide disparity of the melting temperatures of PMP and PP. The fracture morphology observed by SEM showed that there was no obvious phase separation structure in the blends; but the mechanical properties of PP/PMP blends are not good as expected for an ideal homogenous mixture.
Thermoplastic vulcanizates (TPVs) based on high-impact polystyrene (HIPS)/styrene–butadiene rubber (SBR) blends were prepared by dynamic vulcanization technique, and the TPVs were compatibilized by styrene–butadiene–styrene block copolymer (SBS). Experimental results indicate that SBS had a good compatibilization effect on the HIPS/SBR TPVs. A rubber process analyzer reveals that elastic modulus increased with increasing frequency and increasing SBR content in the TPVs led to obvious decrease in elastic modulus. A softening phenomenon could be observed in the stress–stretch curves of HIPS/SBR and HIPS/SBS/SBR TPVs during the uniaxial loading–unloading cycles. Compatibilized HIPS/SBR TPV had the relatively lower stress and internal friction loss.
This study uses coir from agricultural waste, electromagnetic shielding carbon fiber, impact-resistant polypropylene (PP), and methylmaleic anhydride-grafted PP (MA-g-PP) to make wood plastic composites (WPCs). According to the experimental results, when coir and carbon fiber are at a ratio of 3:12, the resulting WPC exhibits an maximum electromagnetic shielding effectiveness (EMSE) of -25 dB, which reaches the protective grade of staple merchandise. At fibers ratio of 3:12, the tensile strength is improved by 10% more than at ratio of 15:0; and the increased flexural strength is by 20% accordingly. A multiblending process is used to simulate the recycling and explores its thermodestruction of the resulting WPC. With a ratio of 3:12, the WPC still has an EMSE of -25 dB at nine cycles of multiblending; however, its tensile and flexural strengths both decrease by 10%.
This study presents a simple approach to the preparation of hollow silica spheres via template-sacrificial techniques. The hard poly(styrene) (PS) template was prepared by soap-free emulsion polymerization in the boiling state for a specified period, followed by introduction of silane into the reaction system to generate the core–shell PS/silicon dioxide (SiO2) spheres without the use of structure-directing agents or surface modification. The SiO2 shell was constructed by co-hydrolysis/condensation of mixed silane containing various weight ratios of tetraethyl orthosilicate (TEOS) and triethoxymethylsilane. The degree of compatibility between PS and SiO2 was shown to be affected by the composition of the silane mixture, and increasing the proportion of TEOS in the silane mix enhanced the mechanical robustness of the SiO2 shell. Based on the residual weight percentage from thermogravimetric analysis, the portion of SiO2 in the PS/SiO2 spheres prepared using various compositions of silane was about 10 wt%. Furthermore, hollow SiO2 spheres were obtained by calcination of the PS/SiO2 spheres prepared using an appropriate formulation of silane at 400°C. Scanning electron microscopy analysis indicated that the size of the hollow spheres was about 200 nm, and the spheres displayed a high degree of monodispersity. Observation of certain cavities on the surface of the spheres also demonstrated the hollow structure of the SiO2 spheres.
Melt centrifugal spinning has been used to successfully produce nanofibres from compounds of polypropylene (PP) and multi-walled carbon nanotubes (MWNTs) at a concentration of 1%. The compounds were prepared either via twin screw compounding or by dissolution in decalin with sonication. Nanofibre production was conducted by centrifugal spinning in a Forcespinner™, a technology capable of producing nanofibres with a high material throughput. Processing via dissolution resulted in a reduction in the size of the MWNT agglomerations in the polymer, which led to a more uniform fibre morphology and a reduced incidence of bead defects as compared to products produced from the melt extrusion compound. The addition of a nonionic surfactant (Triton X-100) to the compound solution aided dispersion of the MWNTs as determined by optical light microscopy of thin cast films and produced fibres with the lowest mean diameter. The mean fibre diameter in the as-spun webs prepared by dissolution of PP in decalin with sonication was found to decrease with increasing spinneret speed; however, a similar trend was not observed for fibres generated from the melt compounded material.
The interest towards wood-plastic composites (WPCs) is growing due to growing interest in materials with novel properties, which can replace more traditional materials, such as wood and plastic. The use of recycled materials in manufacture is also a bonus. However, the application of WPCs has been limited because of their often poor mechanical and barrier properties, which can be improved by incorporation of the reinforcing fillers. Nano-sized fillers, having a large surface area, can significantly increase interfacial interactions in the composite on molecular level, leading to materials with new properties. The review summarizes the development trends in the use on nanofillers for WPC design, which were reported in accessible literature during the last decade. The effect of the nanofillers on the mechanical properties, thermal stability, flammability and wettability of WPC is discussed.
This article presents a study of the tribological properties of short carbon/polyamide (PA)/polytetrafluoroethylene hybrid composites. Their wear rate and the coefficient of friction were examined as a function of operating conditions (load and sliding distance) under dry and lubricated conditions. In addition, the hybrid composites with varying carbon to PA volume ratio were tested to assess hybrid effects. It was found that the friction and wear rate decreased with sliding distance and then leveled off under dry sliding conditions. Different changing patterns with normal load were observed under dry sliding conditions. Furthermore, it was noted that the hybrid effects on the wear resistance and the friction coefficient were identified for the current hybrid system. The composite with a carbon fiber content of 30 vol% was found to have the least wear and friction among all hybrid composites studied. Worn surfaces were observed by scanning electron microscope and wear mechanisms were discussed in this study.
Sisal fibers (SFs) were pretreated by heat treatment (HT). The SFs were mixed with a biodegradable material, polylactide (PLA), and the composites were prepared by hot press molding. The effects of the HT temperature and time on the mechanical properties of the composites were investigated, and the HT mechanism was studied by scanning electron microscopy and infrared, x-ray photoelectron, and nuclear magnetic resonance spectroscopies. The results show that an appropriate HT can remove strongly hydrophilic materials such as hemicelluloses from the fibers, and thus decrease their hydrophilicity, thereby improving the retting between the fibers and the matrix. This improves fiber–matrix interfacial adhesion, which can improve the mechanical properties of the composites. The HT also influences the fiber strength to some extent and affects the mechanical properties of composites.
This is a study on evaluating the effect of nano-calcium carbonate (CaCO3) particles on the mechanical properties of thermoplastic casts, which were performed by mechanical tests, such as scanning electron microscopy and energy dispersive spectroscopy. Composites loaded with a mass rate of 1–2 wt% of nano-CaCO3 particles in polyethersulphone (PES) showed the most excellent mechanical function. The increase in the rate of compressive strength, the maximum compressive modulus and the flexural modulus increases is 47%, 51% and 32% in contrast to neat thermoplastic resin, respectively. The improvement in mechanical properties is attributed to the nanocomposites based on the modified nano-CaCO3 fillers that perform higher modulus and lower Poisson’s ratio than neat PES resin.
A series of composite films consisting of bisphenol A polycarbonate (BAPC) and carbon black (CB) as nanofillers were prepared by solution mixing followed by film casting. The influence of both CB content and temperature on thermal and dielectric properties of BAPC was investigated. X-Ray diffraction patterns show semicrystalline nature of the prepared films. The thermal and dielectric properties were carried out as a function of frequency in the range from 20 Hz to 3 MHz, temperature in the range from 20 to 80°C for concentrations 0, 1, 3, 5, 7, 10, and 15 wt% CB. Differential scanning calorimetric results show a decrease in the glass transition temperature and apparent activation energy at decomposition temperature when the CB content increases. The dielectric measurements show that the dielectric constant (') and alternating current conductivity increase with CB content and also with the temperature. However, the ' and dissipation factor decrease with frequency. The increase in ' with temperature is due to the formation of new dipoles or accumulation of charge carriers in a nanoparticle–polymer interface. Parameters relating to thermal and dielectric properties of these composites can be controlled by adjusting the CB nanoparticles content in the BAPC matrix and temperature. It could be concluded that the obtained composites should be desirable candidates for high ' materials in embedded capacitor applications.
The long-term stress-accelerated photothermal oxidative aging behavior of polyamide 6 (PA6) was studied in terms of the creep behavior, mechanical properties, chemical structure, crystallization, and orientation behavior. It was found that the creep deformation of PA6 under stress with ultraviolet (UV) irradiation was lower than that of the sample aging without UV irradiation. Due to stress-induced orientation, the tensile strength of PA6 aging under stress was higher than that of the sample aging without stress. For samples aging with stress, the variation in the content of gel tended to slow down, and the reduced viscosity was lower than that of the sample aging without stress. The oxidation of PA6 can be inhibited by orientation, leading to a relatively low content of carboxylic group; however, stress would accelerate the degradation of PA6, resulting in the strengthening of UV absorption. A decrease in crystallinity of PA6 after aging was observed, which was generated by chain scission in crystalline region and the cross-linking of PA6. Stress would accelerate the degradation of PA6, resulting in further decrease in crystallinity. The orientation factor increased obviously in the case of PA6 aged with stress indicating that a clear orientation of molecules induced by stress formed.
Rare earth solution (RES) surface modification and acid treatment methods were used to functionalize carbon nanotubes (CNTs). CNT composite thin films were prepared on hydroxylated glass substrates by a self-assembling process from specially formulated solution. Atomic force microscopy, x-ray photoelectron spectrometry, and scanning electron microscopy were used to characterize the thin films. Tribological properties of the CNT thin films sliding against a steel ball were evaluated on a friction and wear tester. The experimental results showed that the friction coefficient of the glass substrate was reduced from 0.85 to 0.1 after the formation of CNT composite self-assembled film on its surface, and the film exhibited good wear resistant property. The superior friction reduction and wear resistance of CNT composite films were attributed to the improvement of load-bearing capacity afforded by the chemical bond between CNTs and the films as well as good adhesion of the films to the substrate.
A new penetration equation for ballistic limit analysis (BLA) of a projectile–target pair is developed and presented. A critical review of the classic BLA (CBLA) has identified that the CBLA penetration equations do not satisfy the conservation of momentum and energy principles simultaneously and completely. It has also been found that the classic definition of residual velocity of the projectile does not quantify the instantaneous rigid body velocity of the projectile at ballistic limit. A new definition of the projectile relative velocity with respect to the target in contact (and in motion) is defined, and this new definition is used to define the projectile instantaneous velocity at ballistic limit. With this new definition of the projectile instantaneous velocity, the new penetration equation is derived satisfying both the conservation of momentum and energy principles simultaneously. A general functional form of the new penetration equation is used in analyzing experimental data and the results are found to match well with the experiments. The new equation is shown to be able to explain projectile residual velocity at and around ballistic limit, can predict the jump velocity at ballistic limit (if any), and is applicable to experimental ballistic data of a wide range of thin and thick targets. The present work sets the background for further development of theoretical penetration models incorporating material properties and parameters of the projectile–target pair.
The rheological and electrical percolation threshold of single-walled carbon nanotube (SWNT)-reinforced thermoplastic elastomer based on polypropylene/ethylene–propylene–diene monomer (PP/EPDM; 80/20) nanocomposite was investigated by melt-mixing process. The rheological properties revealed that the addition of SWNT increased the shear stress and shear viscosity. Both PP/EPDM and its nanocomposites exhibited non-Newtonian behavior. It was also found that the materials experience a fluid–solid transition at 0.5 wt% SWNT. The steady shear behaviors and die swell decreased with increasing temperature. The maximum flow activation energy corresponding to the minimum die swell was also observed. The scanning electron microscopic morphology of the PP/EPDM/SWNT nanocomposites showed that the EPDM particles were dispersed through PP and the size of dispersed phase decreased with the introduction of SWNT to 0.5 wt%. The electrical percolation threshold was formed at approximately 1 wt% of SWNT. In addition, difference between electrical and rheological percolation thresholds was observed due to the nanotube–nanotube distance after the formation of the percolating network.
The measured mechanical properties of carbon fiber/polyamide 6 (CF/PA6) laminates decreased with exposure time at 60°C and 100% relative humidity. Both the bending stiffness and the strength degraded to a level of about 65%, whereas interlaminar shear strength (ILSS) dropped to about 87% of the property values of the unexposed material. The bending stiffness and strength at -45°C are about 87% of the properties at room temperature, whereas at 115°C, the stiffness drops to 75% and the strength drops to 60% of the properties at room temperature. The ILSS values also drop to about 75% at both -45°C and 115°C. Extreme temperatures and longtime exposure to humidity of quasi-isotropic CF/PA6 laminates can thus reduce the bending stiffness and strength by up to 35% and the ILSS by up to 25%.
The polyetheretherketone (PEEK) composites are high-performance materials. These composites have potential applications in various structural components. It is necessary to investigate the cutting parameters of PEEK composites. In this article, an attempt is made to investigate the effect of cutting parameters on the cutting force of carbon and glass fiber-doped PEEK and compare it with unreinforced PEEK when cutting with polycrystalline diamond (PCD) or cemented carbide (K15) tools. The results of statistical analyses highlight that each machining force (Fx, Fy, and Fz) is influenced by the main factors (cutting tools (A), material type (B), feed rate (C), and cutting speed (D)) and some of the interactions (AB, AC, BC, BD, and CD). For the main factors, the material type has a higher effect on Fx and Fy, while Fz is influenced more by feed rate. Cutting tools have no significant effect on Fx and Fy. The regression models used fit 99.56, 92.75, and 90.65% of Fz, Fx, and Fy, respectively. Developed models show that the feed rate has a higher effect on machining force than the cutting speed. The model graphs illustrate that reinforced PEEK has a higher machining force compared with unreinforced PEEK when cutting with PCD or K15. Furthermore, machining with K15 tools increases the cutting force of PEEK-reinforced carbon, while it decreases that of PEEK-reinforced glass and unreinforced PEEK. The investigation of the interaction with the machining force shows that Fx is more influenced by AB, BC, and BD interactions. Fy shows similar results as Fx, but it is also influenced by AC interaction. However, Fz is influenced by all the interactions except BD.
Nanosilver/poly(2-acrylamido-2-methylpropanesulfonate sodium) (nano-Ag/PAMPS) composites were synthesized by a microwave synthesis method. The mechanism of catalytic reduction of Ag ion by atomic nitrogen (from PAMPS) was explored. The composites were characterized by the ultraviolet–visible spectroscopy, x-ray diffractometry, transmission electron microscopy, x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and thermogravimetric analysis (TGA). The results show that Ag nanoparticles (AgNPs) possessed face-centered cubic structure and they were homogeneously dispersed in PAMPS matrix. XPS analysis reveals the interaction between AgNPs and PAMPS matrix. TGA proves that the thermal stability of the pure PAMPS was higher than that of the nano-Ag/PAMPS composites.
The flammable and the mechanical effects of silica (SiO2) on the halogen-free, flame-retarded ethylene–octene copolymer (POE)/polypropylene (PP) composites were investigated. Through the thermal stability analysis and the combustion test, it was found that the SiO2 had a synergistic effect on the intumescent flame retardant (IFR), especially when the SiO2 content was 3 wt%. According to the results of mechanical properties, the tensile strength of composites increased with the rising SiO2 content and most of the impact strength is retained. The fracture morphology showed the state of SiO2/IFR particles in the POE/PP blends, which reflected that with the increasing SiO2 content and the decreasing IFR content, the aggregates became less compact and the size of aggregates became smaller.
The thermomechanical properties of Graphene Nanoplatelets (GNPs)/low-density polyethylene (LDPE) composites were investigated and characterised to understand the effect of nanoscaled reinforcement in the thermoplastic matrix. Results show that the presence of the filler does not produce a change in the microscopic structure of the polymer. However, on a macroscopic scale, graphene platelets limit the mobility of the polymer chains, resulting in an increase in stiffness and in some cases, strength of the composite. Orientation of Graphene Nanoplatelets in the LDPE matrix was evaluated by testing composites made with two different manufacturing techniques (compression moulding and blown extrusion). A comparison between experimental data and predictions using the Halpin–Tsai model shows that the orientation of the nanoplatelets due to the extrusion process leads to better mechanical properties than those obtained with the randomly oriented graphene resulting from the compression moulding technique.
An experimental investigation of resistance welding of thermoplastic composite double lap shear (DLS) joints is presented. DLS specimens consisting of unidirectional carbon fibre/polyetheretherketone (CF/PEEK), carbon fibre/polyetherketoneketone (CF/PEKK), carbon fibre/polyetherimide (CF/PEI) and 8-harness satin weave fabric glass fibre/polyetherimide (GF/PEI) composites were resistance welded using a stainless steel mesh heating element. The welded specimens were tested under static and fatigue loadings, and the quality of the welds was examined using optical and scanning electron microscopy. Weld strengths of 53, 49, 45 and 34 MPa were obtained for CF/PEEK, CF/PEKK, CF/PEI and GF/PEI DLS joints, respectively. Indefinite fatigue lives were obtained between 20 and 30% of the ultimate static failure loads of the joints. Performances of the resistance-welded DLS and single lap shear (SLS) joints were compared. It was shown that the effect of joint geometry, that is, DLS versus SLS, on the mechanical performance of the resistance-welded joints is minimal, indicating a good resistance of welded joints to peel stresses.
In this article, we investigated the properties of thermoplastic starch (TPS) with pineapple leaf fiber (PALF)/poly(lactic acid) (PLA) composite compared to both TPS with a PALF composite and TPS/PLA blend. The composite is prepared by a single-screw extruder. It appears that the TPS with PALF/PLA composite gives better mechanical properties and water resistance than the TPS/PLA blend, but it presents the same flow behavior (based on the power law index) as the PLA alone.
This work focuses on the combination of the complementary physical properties of multiwalled carbon nanotubes (MWCNTs) and poly(3-octylthiophene) (P3OT)/polystyrene (PS) polymer blend. The characterization of MWCNTs/P3OT/PS hybrid system performed by Fourier transform infrared spectroscopy, ultraviolet (UV)–visible absorption, and electrical measurements show interesting effects. Optical results demonstrate that the addition of MWCNT to P3OT/PS matrix blend will enhance the UV–visible absorption and insignificantly affect the optical energy gap of P3OT/PS matrix; this can be explained in terms of a reduced photo-induced charge transfer in such composite system. This study shows that incorporation of 5 wt% functionalized MWCNTs onto P3OT/PS polymer blend will convert this material from insulator to conductor and at this level of MWCNTs content, MWCNTs will form a network inside blend matrix with low capacitor element and high resistor element effects.
The present work is to predict the fracture behaviour of biocomposites from the tensile properties of its components. In this work, a direct numerical simulation was realized for fracture behaviour of random short spruce fibre-reinforced composites. For calculations, wood fibres were considered as linear elastic bodies and polypropylene matrix as an elastic–plastic material. Then, the numerical results were compared with the experimental results obtained by digital image correlation (DIC). This comparison indicates that random fibre finite element (FE) model can be able to fairly reflect the influence of random fibre microstructure on the fracture behaviour of the composites. The calculation and comparison show that in a region in the front of the crack tip, the average values of J-integral of both random fibre and homogeneous FE model are in good agreement with that of DIC experiment under the same extension load.
A highly crystalline aliphatic segmented polyurethane (PU) elastomer with 40 wt% hard segment (HS) content, based on 1,6-hexamethylene diisocyanate and 1,4-butanediol as the HS, and a block copolymer of hexamethylene carbonate and polycaprolactone as the soft segment (SS), has been used as the matrix to prepare carbon nanofiller/PU composites by solution casting. Composite films with different loadings of solvent-exfoliated graphene (G)/nanographite, graphene oxide (GO) obtained by the so-called modified Hummers method, and acid-treated multiwalled carbon nanotubes (MWCNT) were obtained and characterised. Tensile test results show that the effectiveness of increasing PU strength follows the trend MWCNT > GO > G. The ductility reduction in all the cases is related to the large sizes of nanofillers in relation to PU hard domains and the hindrance to allow plastic flow of PU SSs by larger fillers.
The U.S. Army Engineer Research and Development Center (ERDC) executed a load test and verification simulation on a novel thermoplastic composite bridge, T-8518, located on Tuckers Road in Camp Mackall, North Carolina. The bridge was made with 94% recycled plastic material, primarily recycled high-density polyethylene. An M1 Abrams battle tank and a loaded dump truck were used as a live load to determine the appropriate military load classification (MLC) and civilian load rating for the bridge superstructure. The bridge was designed to support the M1 Abrams battle tank with a gross weight of 63.5 tones to replace a dilapidated timber bridge that, because of its condition, was limited to a maximum load of 4.26 tones. A finite element analysis (FEA) of the entire superstructure based on the load test results indicated that the bridge exceeded design specifications and performed in a normal linear–elastic manner with relatively small viscoelastic responses for all loads.
New Schiff-base polyesters were prepared from a dihydroxy monomer (E)-1-(5-(4-hydroxy-3-chlorobenzylidene)thiocarbamoylaminonaphthyl)-3-(4-hydroxy-3-chlorobenzyli-dene)thiourea. The processable pyridine or thiophene-based poly(azomethine–ester)s (PAEs) possess high molar mass of 111 x 103–127 x 103 g mol-1. The 10% weight loss (521–527°C) and glass transition temperature (287–291°C) depicted high thermal stability. Polyaniline (PAN) doped with dodecylbenzenesulfonic acid (PAN/DBSA), prepared by in situ doping polymerization, was blended in solution/melt with PAEs. Field emission scanning electron microscopy of melt blended PAEs/PAN/DBSA showed nanolevel homogeneity of microstructure accountable for superior electrical conductivity (1.9–2.8 S cm-1). The miscible nanoblends also exhibited high heat stability (T10; 500–507°C) and mechanical strength (45.51–48.17 MPa) relative to reported azomethine/PAN-based structures.
The polypropylene–long glass fiber (PP/LGF) composites were prepared using self-designed impregnation device. The mechanical properties and dynamic mechanical properties of PP/LGF composites with two different compatibilizers including PP grafted with glycidyl methacrylate (PP-g-GMA) and maleic anhydride-grafted PP copolymer (PP-g-MA) were investigated on injection molding standard bars. The experimental results demonstrated that the addition of PP-g-GMA led to decrease in mechanical properties and storage modulus. However, it is found that the maximum mechanical properties and storage modulus are reached for the PP/LGF composites when PP-g-MA are 7 wt%. Moreover, PP-g-MA is better than PP-g-GMA in the PP/LGF composites.
The surface of micro and nanoparticles of calcium carbonate (CaCO3) was modified by 3-mercaptopropyl trimethoxysilane and polymethylhydrogensiloxane. Fourier transform infrared spectra of extracted CaCO3 particles revealed interfacial bonding between coupling agents and CaCO3 particles. Poly(vinyl chloride) (PVC)/surface-modified CaCO3 with different mass ratios of (micro/nano)-CaCO3 particles were melt blended using a Brabender torque rheometer and kept with a constant content of CaCO3. The impact strength, tensile strength, elongation at break, and Young’s modulus of the composites were considerably enhanced at 9/6 mass ratio of (micro/nano)-CaCO3. The mechanical properties were improved relative to the pure PVC due to the interfacial bonding between the filler and the matrix. Scanning electron microscopic images of fractured surfaces of the test specimens showed larger voids with nonsmooth edge around the cavities, as compared with the nano-CaCO3/PVC composite, which is more pronounced by the increase in the micro particles contents.
To study the effect of sample width and inclined angle on flame spread across expanded polystyrene (EPS) surface, a series of laboratory-scale experiments were conducted in the Lhasa plateau and the Hefei plain. Surface flame height, flame spread rate and preheating zone length were obtained. The dimensionless surface flame height varied as the -n power of the sample width and 0.7 < n < 0.9. As angle of incline increased, the surface flame height first rose and then dropped. The surface flame height difference between maximum and minimum width became smaller with the increase in angle of incline. With an increase in sample width, the flame spread rate first dropped and then rose where the angle of incline was small, while the trend was reverse for samples with larger angle of incline. For EPS at 15°and 30°, the trend of flame spread rate versus sample width in Lhasa was inverse, compared with the results obtained in Hefei. The variation trend of preheating zone length with sample width and inclined angle was different from the flame spread rate trend. However, a linear relationship of vf/w and ph/w was found in Lhasa plateau. The surface flame height, flame spread rate and preheating zone length in Hefei plain were larger than the results obtained in Lhasa plateau. The experimental results agreed well with theoretical analysis.
A novel β-nucleating agent of isotactic polypropylene (iPP), the potassium salt of 1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid (CA-19), was found and its effects on the mechanical properties, content of β-crystal, and crystallization behavior of iPP were investigated. The results showed the content of β-crystals of nucleated iPP (kβ value) can reach 46.3% with 0.25 wt% CA-19. The impact strength and crystallization peak temperature of nucleated iPP greatly increased. Compared with pure iPP, the impact strength of nucleated iPP shows two times increase, and the crystallization peak temperature (Tp) of nucleated iPP increased by 7°C. The spherulite size of the nucleated iPP dramatically decreased compared with that of pure iPP. The Caze et al. method was used to investigate the nonisothermal crystallization kinetics of nucleated iPP and the crystallization activation energy was obtained by the Kissinger method.
In this work, novel optically active poly(amide-imide)/zinc oxide bionanocomposites (PAI/ZnO BNCs) containing <sc>l</sc>-valine moiety in the main chain were prepared via a simple and inexpensive ultrasonic irradiation process. Chiral PAI was synthesized by direct polycondensation reaction of N,N'-(pyromellitoyl)-bis-valine with 3,5-diamino-N-(thiazol-2-yl)benzamide in the tetrabutyl ammonium bromide/triphenylphosphite as a green solvent system. Due to the high surface energy and the tendency for agglomeration, the surface of ZnO nanoparticles (NPs) was modified with -aminopropyltriethoxysilane. PAI/ZnO BNCs containing 4, 8, and 12% of NPs were successfully fabricated through ultrasonic irradiation technique. The obtained BNCs were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), x-ray diffraction, ultraviolet–visible spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy (TEM) techniques. TGA data indicated an increase in thermal stability of the BNCs when compared with the pure polymer. From the TEM image of PAI/ZnO BNCs, it can be found that the surface-modified ZnO NPs, with a diametric size of less than 35 nm, are uniformly dispersed in the PAI matrix.
Pre-consolidated carbon fibre-reinforced polyphenylene sulphide (CF/PPS) laminates were thermoformed into V-shaped parts via designed out of autoclave thermoforming experiments. The different processing conditions tested in the experiment have resulted in final part angles whose differences ranged from 2.087 to 3.431° from the original mould angle. The test results show that processing conditions influenced finished part dimensions as the final sample angles were found to decrease relative to the tooling dimensions, as mould temperature increases. Higher mould temperature conditions produce thinner parts due to the thermal expansion of mould tools. The mould temperature of 170°C, which can produce parts with high degree of crystallinity as well as small size of crystal, has been established as the optimal thermoforming condition for CF/PPS composites.
Recycled poly(ethylene terephthalate) (R-PET) was partially replaced with halloysite nanotubes (HNTs) as fillers in natural rubber (NR) composites. The composites were prepared by incorporating hybrid filler into NR using a laboratory size two-roll mill. The total amount of hybrid filler in each formulation was kept constant at 20 phr. Results revealed that scorch time, cure time, maximum torque, cross-link density and thermal stability increased with the replacement of R-PET by HNTs. Due to its reinforcing effect and ductility of the HNTs, the moduli, tensile strength, elongation at break and fatigue life were found to increase consecutively with increasing HNTs content. Morphological study of the tensile fracture surfaces of the composites exhibited that HNTs has better adhesion and is well-dispersed in NR matrix as compared to R-PET particles. However, R-PET exhibited positive effect by reducing the curing time of the hybrid NR composites.
Single layer graphene oxide (GO)–polyamide 6 (PA6) nanocomposites were produced via the in situ polymerization of -caprolactum dissolved in a water-based dispersion of single layer GO. As prepared GO and nanocomposites containing 0, 0.035, 0.076, 0.44 and 0.65 wt% GO in PA6 were characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Raman thermal analysis and tensile testing. XPS, AFM and TEM analyses confirmed that the modified Hummers method used to prepare the GO resulted in sheets of oxidized single layer graphene. It was observed using AFM that the in situ polymerization resulted in an efficient poly chain grafting and a reduction in the lateral dimensions of the sheets. The GO/PA6 nanocomposites showed an increased degradation temperature relative to neat PA6, which is an indicative of high levels of interfacial interaction and dispersion. It was observed that the addition of GO reduced the average PA6 molecular weight and acted as nucleation agent for α-form crystallinity while suppressing the formation of -form crystals. Mechanical reinforcement was also observed, with a tensile strength of 60.6 MPa recorded for PA6, rising incrementally with increased GO loading to 64.9 MPa at 0.65 wt%.
The present study aimed at exploiting the unfavorable changes of thermally modified shellac with the idea of developing starch/shellac-based composites intended for food contact applications. On baking shellac samples at 200°C for different time intervals (0–20 min), functional groups and linkages were drastically modified, especially anhydride formation, polyesterification, and ether/acetyl linkage occurrences. These processes caused a marked increase in the glass transition temperatures (from about 33 to 60°C) and melting temperatures (from 175 to about 230°C) but a decreased solubility in ethanol (from 95 to 9%). The addition of shellac into a starch-based formulation for producing shaped bodies in combination with heat could significantly strengthen the composite materials and drastically reduce the water uptake after soaking in both cold water and hot water. Furthermore, application of a food-grade biodegradable coating showed remarkable improvement in terms of water resistance and mechanical strength of the composites. The first attempt at making chopsticks was successful and showed promising results. Nevertheless, forming processes and mold designs of such articles—long narrow tubes—need further study.
The article reports on the successful processing of flax-reinforced poly(lactic acid) (PLA) profiles by thermoplastic pultrusion into ‘sandwich’ structures consisting of commingled yarns as outer layers and layers of nonwoven material in the core section. The results showed that a good quality matrix impregnation was obtained. The profiles produced from only commingled yarns had higher impact strengths due to yarns in the middle of the profiles; the matrix of which did not melt during pultrusion. The flexural properties of the composites improved with increasing nonwoven layers. Good PLA impregnation improved the flexural properties. The tensile strength of the ‘sandwich’ structures was much lower than that of commingled yarn-based composites, this being attributed to the poor distribution of flax fibres and poor interfacial adhesion leading to poor stress transfer from matrix to fibres. Crystallinity decreased as the number of nonwoven layers increased presumably due to blockage of nucleating sites essential for crystal growth. The storage modulus of composites reinforced with commingled yarns was greater than that of the composites reinforced with ‘sandwich’ material, confirming effective transfer of stress from matrix to the commingled flax yarns and indicating that increasing nonwoven layers decreased adhesion between reinforcement and the matrix. The effects of a wide range of pultrusion process parameters on the mechanical properties of resulting profiles were investigated. Higher die temperatures (290°C) and lower pulling speeds (0.5 m min-1) improved the mechanical properties due to better melting and lower viscosity of the matrix, enabling increased penetration within the reinforcement. Flexural and tensile properties of microwave-heated samples were very low due to fibre degradation. Scanning electron microscopic images showed that fibre impregnation was good in ‘sandwich’ systems, but fibre distribution remained a challenge.
Montmorillonite-rich local bentonite was modified with four different quaternary alkyl salts: hexadecyltrimethylammonium bromide ((HMA)(Br)), tetra(kis)decylammonium bromide ((TKA)(Br)), tetrabutylammonium tetrafluoroborate ((TBA)(BF4)), and tetrabutylphosphonium tetrafluoroborate ((TBP)(BF4)) to produce organoclays. The organoclays produced were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), and x-ray diffraction (XRD). The XRD results indicate that the d-spacing of the organoclays increased as a consequence of the exchange of Na+ ions in the clay galleries with the cation of the surfactants with long alkyl tails. The d-spacing of the bentonite increased from 1.2 nm to 1.78 nm, 2.56 nm, 1.48 nm, and 1.64 nm after modification with HMA, TKA, TBA, and TBP cations, respectively. TGA analysis of the organoclays showed that the decomposition temperatures of the organoclays were higher than the melt processing temperature of polypropylene (PP), permitting the use of these organoclays in melt processing of PP. Ternary composites of PP/PP-grafted maleic anhydride/organoclays were prepared using a twin screw extruder followed by injection molding for characterization. Transmission electron microscopy analysis of the composites showed intercalated structures as well as microcomposite formations. Mechanical properties of pure PP were improved through ternary composite formation.
This work presents how the optimization of polymer conductive composites constituting the semi-crystalline polymer matrix (low-density polyethylene (LDPE) and isotactic polypropylene (it-PP)) and carbon black (CB) by melt-mixing process, has an important influence not only in diminishing the resistivity of the composite but also in reducing the critical concentration of CB. The experimental procedure consists of studying the influence of processing parameters such as mixing temperature, time, and speed on the electrical resistivity values. Optimal parameters are considered as those obtained with the lowest standard deviation for electrical resistivity and a reduction in resistivity in comparison with the arbitrary conditions established as preliminary or reference. The control of those parameters allows in attaining an important reduction (7%) in the critical CB concentration at threshold percolation in both the studied composites in comparison with those obtained under unfavorable conditions or even with those obtained under reference conditions.
A recently developed frequency-modulated thermal wave imaging (FMTWI) has been applied for subsurface defect detection of jute fibre-reinforced polypropylene (PP) matrix composite. Composites are subject to manufacturing and in-service defects like voids, delamination, cracks and so on. Active thermography like lock-in thermography (LT) and pulsed thermography (PT) has been widely used for non-destructive testing of composites and laminates. FMTWI may be viewed as a superposed LT, wherein multiple frequency response is obtained through single measurement. It is very much suitable for newly developed material for which the thermal properties are not well established, thereby impeding the choice of appropriate frequency for conventional LT. In this article, FMTWI is applied to detect and characterize artificially generated subsurface defects in jute–PP composite. The measurements also show the effect of frequency on the depth of defect detection and accuracy.
The disposal problems associated with the conventional plastic have imposed a long-standing quest of developing the degradable material. Indeed, blending of conventional plastic with renewable resources as the base materials is an attempt of imparting some level of biodegradability on the resulting composites. Thus, for this study, the effect of plasticized sago starch (plasticized) incorporation on the properties of low-density polyethylene (LDPE)-reinforced with kenaf core fiber (KCF) was evaluated. The ratio of LDPE/KCF was fixed at 80/20 and blended with the thermoplastic sago starch (TPSS) content ranging from 10 to 40 wt%. The blended samples were characterized by means of mechanical performance, Fourier transform infrared analysis, thermogravimetric and differential scanning calorimetry behavior, water uptake, and morphological properties. The experimental result shows that there is a gradual decrease in tensile strength, modulus, and elongation at break with an increase in TPSS loading. The degree of dispersion and adhesion of TPSS in LDPE/KCF composites revealed by scanning electron micrograph supports the findings of tensile properties. The thermal stability of the composite was clearly improved with the addition of TPSS. However, water uptake and hydrophilic character of the composite system tended to augment as the TPSS imparted to the composites.
Blast furnace slag (BFS) is a major solid waste in iron industries that results from the fusion of fluxing stone with coke and the siliceous and aluminous residues remaining after the reduction and separation of iron from the ore. Using this BFS in different proportions (0, 10, 20, and 30 wt%) in thermoplastic polypropylene matrix base, hybrid composites are prepared with and without 20 wt% short glass fiber reinforcement, by injection-molding route. The composites are characterized in regard to their physical and mechanical properties and their dry sliding wear characteristics are studied experimentally. For this, a standard pin on-disk test set-up and Taguchi’s orthogonal arrays are used. Taguchi’s experimental design method eliminates the need for repeated experiments and thus saves time, materials, and cost. It identifies the significant control factors predominantly influencing the wear rate. From the experimental findings, optimal combinations of control factors are obtained for minimum wear rate and on that basis, predictive correlations are proposed. The morphology of worn surfaces is then examined by scanning electron microscopy and possible wear mechanisms are discussed. Furthermore, a model based on artificial neural networks (ANN) for the prediction of sliding wear properties of these thermoplastic polymer composites is implemented. The ANN prediction profiles for the characteristic wear properties exhibit very good agreement with the measured results demonstrating that a well-trained network has been created. The simulated results explaining the effect of significant process variables on the wear rate indicate that the trained neural network possesses enough generalization capability of predicting wear rate even beyond the experimental range.
Biodegradable polymer nanocomposites have received great attention due to their synergistic properties of good mechanical and barrier properties; yet, they are biodegradable. In this research, prior to compression into thin sheets, polylactic acid (PLA), tapioca starch, glycerol and maleic anhydride (MA) were compounded with different loadings of montmorillonite (MMT) through a twin screw extruder. MMT was added to improve the mechanical and barrier properties of PLA/starch blend. The effects of MMT loadings on tensile property, morphology and biodegradability were studied. X-Ray diffraction analysis showed that samples with MMT loadings below 6 phr exhibited exfoliated structure, while samples that contained MMT above 6 phr (5.66 wt%) exhibited intercalated structure. The exfoliated-type structure was observed using transmission electron microscopy. These effects were manifested in the tensile results, which showed an increase in modulus, tensile strength and elongation at break. However, for the modulus, the MMT content was limited to 4 phr (3.85 wt%). Beyond that, the modulus decreased. It was thought that above 4 phr, the MMT particles agglomerated, thus reducing the modulus of the samples. This argument was supported by field emission scanning electron microscopic images, which showed big lump when MMT loadings were at 6 and 8 phr (7.41 wt%). Meanwhile, the addition of MMT has improved the water barrier property and hastened the rate of biodegradation. The nanosized MMT particles disturb the continuity of PLA/starch chain, which formed pathways for microorganisms to enter and attack the chain, thus increasing the biodegradation rate. The particle is also able to block a tortuous pathway for water to enter the starch chain, thus reducing the water uptake and improving the physical barrier of nanocomposite.
The thermal degradation of short-time heated carbon fiber (CF)-reinforced polyetheretherketone (PEEK, CF/PEEK) and high-density polyethylene (HDPE), in the range of 10 ms up to 3 min, was investigated by various detection methods such as differential scanning calorimetry, gravimetric analysis, and Fourier transform infrared spectroscopy (FTIR). Therefore, the polymers were heated by extrinsic and intrinsic heating methods, including induction heating, infrared heating, and laser heating, which provides the highest heat flux. The short-time heated polymers revealed thermal degradation after several milliseconds of laser irradiation as well as after several seconds of induction heating. CF/PEEK exhibited a decrease in crystallinity and melting extrapolated onset temperature with an increase in irradiation time and power. The FTIR results indicated that random chain scissoring started at the phenyl ring bonding, the ether bonding, and the aromatic hydrogen bonding, whether some new nonaromatic hydrogen bonding occurred. HDPE showed a decrease in melting peak temperature and some changes in the methylene stretching bonding.
In the lay-up process of thermoplastic composite tape, the thermal conditions have great influence on the end quality and performance of composites. In the lay-up process of thermoplastic matrix composites, a semi-infinite solid model is used to analyse the heat transfer by simulating the heating of hot gas torch. Temperature of the control volume is calculated based on the model. A dynamic finite element model is developed to obtain the transient temperature field. The birth–death element strategy in ANSYS was used to simulate the movement of lay-up head during dynamic loading and laying-up prepreg onto the composite substrate. The simulation results of using the transient heat transfer model and the finite element model were compared well. The bonding temperature increases linearly with the heater temperature and is closely related to the moving speed of the roller. The bonding temperature changed slowly when the roller moved faster.
The most popular use of wood–plastic composite (WPC) members in the United States has been as outdoor decking material in residential construction. If the use of these products expands into more structural applications, such as beams and joists, it is imperative that the material’s mechanical behavior be understood. Since most of the potential structural uses of this material are as flexural members, it is particularly important that the response to this mode of loading is well characterized. Like many filled polymers, WPCs are anisotropic and bimodal, and thus their shear and two axial moduli (tension and compression) must be determined separately. This study determined the shear and axial moduli of six WPC formulations (mainly polypropylene, high-density polyethylene, and low-density polyethylene) by testing prismatic members in bending at multiple span-to-depth ratios. The initial moduli were determined from constant strain rate tests, and their time dependencies were found using creep tests. The resulting axial-to-shear moduli ratios were shown to be greater than 25 for all formulations. The ratios were relatively constant over time at low stress levels, while decreasing over time at high stress levels.
Microencapsulated red phosphorus (MRP)-filled polypropylene (PP) composites were prepared using a twin-screw extruder. The effects of load and temperature as well as the dispersion or distribution of the filler particles in the matrix on the melt volume flow rate (MVR) and melt density (m) of the PP/MRP composites were investigated using a melt flow indexer and a scanning electron microscope. The temperatures and loads were varied from 180 to 205°C and from 2.16 to 12.5 kg, respectively. The results showed that the MVR of the composites increased nonlinearly with increase in temperature and load. The sensitivity of MVR of the composite melts to temperature was significant. The MVR of the composites also decreased slightly with an increase in the MRP weight fraction. However, the values of m of the composites varied slightly with increase in load, temperature, and MRP weight fraction. The findings can provide useful information for optimum processing of these composites.
The nanocomposite blends of ultra-high-molecular-weight polyethylene (UHMWPE) and high-density PE (HDPE) reinforced with 1 wt% of multi-wall carbon nanotube (MWCNT) were prepared by melt mixing at different compositions in an internal mixer. Two different grades of HDPE were used in this research to improve the processability of UHMWPE. Rheological, thermal, morphological, and mechanical properties were investigated for both (UHMWPE/HDPE) blends and their nanocomposites. The results confirmed the reduction in melt viscosity and improvement in the processability of UHMWPE by the addition of HDPE. Differential scanning calorimetry (DSC) results showed a single melting and crystallization peak, and the broadness of these peaks in blends compared to pure components indicated that two components form separate crystals. The effect of incorporating MWCNT to the blend samples on mechanical properties was studied, and the samples prepared with HDPE 5218 exhibited slight improvement in mechanical properties. Incorporating MWCNT into the blend of UHMWPE (20 wt%) accelerated crystallization; but in higher contents of UHMWPE, crystallization of the composites was slightly delayed. Rheological data exhibited lower complex viscosity and storage modulus and therefore lower elasticity for UHMWPE/HDPE/MWCNT nanocomposites compared to their blends. Drop in viscosity and storage modulus as well as tensile strength of nanocomposites compared to their blends was attributed to adsorption of higher molar mass polyethylene chains onto MWCNT surface. The morphology of nanocomposites was analyzed by scanning electron microscopy (SEM) and phase separation, and probably localization of MWCNT predominantly into HDPE matrix and HDPE/UHMWPE interface was concluded. X-ray diffraction (XRD) patterns indicated that MWCNT was well distributed and dispersed in HDPE matrix.
Different national resources like nut shells and residual wood flours (WFs) are being used as filler materials of polymer composites. It is possible to obtain proper composites from high percentage addition of different sized wood chips to the polymer raw material. This article investigates the effects of three different-dimensioned beech flours as additives on the morphological and mechanical properties of the polymer composite materials. At lower particle sizes, loading of certain concentrations of WF results in better mechanical properties and morphological improvements in composites are experienced.
The effects of -caprolactam on tensile properties, morphology, thermal degradation, and swelling behavior of recycled high-density polyethylene–chicken feather fiber composites (r-HDPE/CFF) were studied. The r-HDPE/CFF composites were prepared using Brabender Plasticorder at 160°C and a rotor speed of 50 r min-1 for 6 min. The r-HDPE/CFF/-caprolactam composites exhibit higher tensile strength, modulus of elasticity, and final decomposition temperature, but lower mass swell percentage and elongation at break than r-HDPE/CFF composites. Scanning electron microscopic morphology showed that the CFF was more widely dispersed in the r-HDPE matrix with the addition of -caprolactam as a coupling agent. It was also found that the addition of -caprolactam offers better thermal stability in r-HDPE/CFF/caprolactam composites than r-HDPE/CFF composites.
The thermal decomposition behavior of poly(ether imide) (PEI)/carbon fiber composites used in aeronautical field was studied using thermogravimetric analysis in an inert atmosphere, at several heating rates between 2 and 10°C min-1. The activation energies (Ea) were determined by Flynn–Wall–Ozawa (FWO) and Kissinger methods, and the preexponential factor (A) was calculated by the FWO method. The obtained data were used in order to predict the thermal lifetime of the material under the established temperature range and 5% mass loss criterion. Overall, the results represented PEI’s good thermal stability. Furthermore, it was concluded that the material can be safely applied for aeronautical use.
In order to investigate the combined action of temperature, humidity, and ultraviolet (UV) radiation, polyphenylene sulfide (PPS)–carbon fiber composite specimens were exposed to environmental degradation through two different techniques: water immersion and UV climatic chamber. The moisture weight gain curves of the composites were compared with those of the neat matrix in order to determine the interface effect on moisture absorption. Fourier-transform infrared spectroscopy of UV-weathered samples presented oxidation formation. Compressive tests and dynamic mechanical thermal analysis (DMA) revealed that the weathered materials gained in stiffness, nevertheless a small deterioration in strength was found after long periods of UV radiation exposure.
Basalt-reinforced composites are recently developed materials. Basalt fiber (BF) as inorganic filler and polyamide-6 (PA6) as organic filler are characterized by mechanical properties analysis and morphology examination for polytetrafluoroethylene (PTFE) matrix blends. Effects of different filler content on tensile strength and impact strength are proposed. It is observed from scanning electron microscopic studies that addition of BF and PA6 are beneficial in increasing mechanical strength via increasing the interface-dispersed phase. The optimum tensile properties of BF content were at 10 wt% for PTFE composite. The optimum impact properties of PTFE/PA6/BF composite on melt mixing conditions were obtained at PA6 content was 4 wt% for PTFE/PA6/BF composite. The results showed a significant improvement in mechanical properties of PTFE/PA6/BF ternary blend composite, and it is useful for the development of an applicable theoretical constitutive composite materials model.
In this article, a commercial grade of polypropylene (PP) was reinforced with short poly(ethylene terephthalate) (PET) fibres up to 30 wt%. In order to have a reactive interface, two different compatibilizers, glycidyl methacrylate (GMA)-grafted PP and maleic anhydride (MA)-grafted PP, were used. To choose an optimized fibre length for the PET fibre in PP/PET composites, critical PET fibre length was evaluated applying stress analysis and Von Mises yield criterion. PP/PET fibre pre-pegs were prepared by melt impregnation technique using an internal mixer followed by the compression moulding. Tensile and flexural properties were investigated. Morphological studies were carried out by scanning electron microscopy technique. It was observed that the addition of PET fibres enhanced flexural modulus compared with that of pure PP, which was higher for GMA-modified composites. The tensile modulus results also showed enhancement by the addition of PET fibres. However, the tensile modulus of unmodified specimens versus fibre load was little greater than that of unmodified samples up to 15 wt% of fibres due to higher crystallinity. The flexural strength results of modified composites versus fibre wt% also showed enhancement that was higher for those of GMA-modified ones. The fibre to matrix bonding was better in the presence of GMA than that of MA, as revealed by scanning electron micrographs of tensile fracture surfaces. Halpin–Tsai, Pan and Cox–Krenchel equations were applied to predict the tensile modulus of random PET fibre-reinforced PP composites, among which the Pan’s model had the best prediction. To evaluate relative reinforcement at different fibre loads, fibre efficiency factor was calculated for GMA-modified composites.
The effects of aqueous solutions were evaluated on the properties of regenerated cellulosic nanofibers prepared from pure cellulose fibers in various formulations of aqueous solutions. Thermoplastic composites were prepared with reinforcement of the regenerated cellulosic nanofibers. The regenerated cellulosic fibers from cellulosic woody biomass were obtained from dissolved cellulose solutions by coagulating with sulfuric acid and water for phase separation. The properties of the regenerated cellulosic fibers were characterized using Fourier-transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (WAXRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy, and tensile testing. The TGA, WAXRD, and FTIR spectra indicated that the regenerated nanofibers possessed cellulosic crystal type II. The micrographs of regenerated cellulosic fibers showed a dense composite structure and lower crystallinity than controlled fibers. The tensile strength of regenerated cellulosic fiber-reinforced polymer composites reached 30 MPa, which was 70% higher than the control fiber-reinforced composites. The composites prepared from regenerated fibers with sodium hydroxide (NaOH)/urea and NaOH/urea/thiourea aqueous solutions provided the best results. This work also provides a potential promising method to efficiently obtain nanocellulosic fibers as reinforcement materials in bio-based nanocomposites.
Chlorosulfonated polyethylene rubber (CSM) was blended with chlorinated natural rubber (CNR) with various formulations and blend ratios (CSM/CNR: 100/0; 75/25; 50/50; 25/75; 0/100) keeping the total waste rubber powder (WRP) content constant at 50 phr (parts per 100 rubber). Rheological, mechanical, dynamic mechanical and thermal aging properties as well as irradiation resistance were used as characterization of the blends. The amount of CNR in blends significantly affected the properties of the blends. The CSM/CNR/WRP rubber blend (50/50/50) possessed higher tensile strength compared with pure CSM and CNR rubber even after irradiation or thermal aging. Modulus, tensile strength and hardness of the blends appeared to increase, but elongation at break decreased progressively with increasing CNR content. These properties decreased in rubber blends after thermal aging. After irradiation, hardness, modulus and tensile strength increased up to 200 kGy and then decreased significantly for the blends with high CNR content, whereas no change in modulus was observed. CNR and CSM showed damping peaks at about 65 and -45°C, respectively, and these values correlate with the glass transition temperatures (Tgs) of CNR and CSM, respectively. The shift in the Tg values was observed after blending, suggesting an interfacial interaction between the two phases probably caused by the covulcanization in CSM/CNR blends.
Carbon fiber composites were prepared in order to study the influence of fillers (polyamide 6; PA6) on the tensile and tribological properties of polypropylene (PP) composites. Tensile fracture mechanism was discussed based on the tensile test results. Tribological tests were conducted on a Mobile Remote Handler-3 (MRH-3) friction and wear tester using a block-on-ring arrangement. It was observed that the carbon fiber (CF) played a main role in the tensile-resistant and wear-resistant properties of the CF/PP composites. The tensile properties were ruled by the fiber–matrix adhesion. Moreover, the excellent tribological performance of the CF/PA6/PP composite is consistent with the worn surface morphology shown.
The present investigation deals with the preparation and characterization of nanocomposites of poly(ether ether ketone) (PEEK) containing nanosized nickel filler up to 3 wt% loading. Characterization of the developed nanocomposites has been carried out by various advanced analytical techniques. Thermogravimetric analysis study depicts that the prepared nanocomposites exhibit enhanced thermal stability. Dynamic mechanical analysis (DMA) technique has been utilized to investigate the viscoelastic deformation of nanocomposites. From DMA studies, it has been demonstrated that with the increase in nano-nickel content, the stiffness of nanocomposites decreases and a very minute change in glass transition temperature (Tg) has been noticed. The resulting nanocomposites show the optimum improvement in Young’s modulus, tensile strength, flexural strength and flexural modulus. Scanning electron microscopy study reveals that he dispersion of nano-nickel particulates is uniform throughout the PEEK matrix.
High-density polyethylene–low-density polyethylene (HDPE-LDPE) blends involving HDPE-LDPE (50/50 wt%) with dialkyl peroxide (DAP; 0.05 wt%) containing different amounts (5, 10 and 15 wt%) of nanocalcium carbonate (nCC) were prepared by melt blending followed by compression molding. The effect of addition of nCC on the morphology, mechanical and crystallization behaviors of HDPE-LDPE blends with and without DAP was also evaluated. The measurements of the mechanical properties showed that the impact strength of the nanocomposites increased at first and then decreased with the addition of nanofillers, and the tensile strength was reduced at the same time. With the addition of a small amount of DAP, the mechanical properties of the obtained nanocomposites increased. Scanning electron microscopy observation showed that the addition of DAP improved the dispersion of the nanofiller in the HDPE-LDPE blends. Differential scanning calorimetric results indicated that the addition of DAP increased the crystallization temperature as a result of heterogeneous nucleation effect of nCC on HDPE-LDPE blends.
Polypropylene (PP)/recycled acrylonitrile butadiene rubber (NBRr)/rice husk powder (RHP) composites were fabricated with silane and acetic anhydride (Ac) treatment agent. The in situ formed RHP-filled PP/NBRr composites were prepared by melt mixing technique. The mechanical properties of both the treatment methods were investigated with Instron mechanical analysis and Fourier transform infrared. The results indicated that Ac treatment was found to exhibit better mechanical properties of RHP-filled PP/NBRr composites treated with silane. This was due to good compatibility and stronger interaction between anhydride moieties with PP/NBRr.
In this study, nano-montmorillonite (NMMT) was incorporated in alumina trihydrate (ATH) added low-density polyethylene–ethylene vinyl acetate (LDPE-EVA) for enhancing the mechanical and electrical properties of the hybrid blends. The Young’s modulus of 50 phr ATH added LDPE-EVA (LE) blends has improved significantly, when the NMMT loading level increased from 5 to 15 phr. This is because the intercalation of NMMT particles reduces the cavities while enhancing the interfacial adhesion between the particle surface and LE matrix as observed via morphology analysis. The good interfacial adhesion could effectively transfer the stress from polymer matrix to filler’s particles during straining and improved the mechanical properties. On the other hand, the volume resistivity of 5 phr added LE blends was gradually decreased as the loading level of ATH has increased from 50 to 150 phr. The surface and volume resistivity of LE blends exhibited that high polarity of ATH and NMMT molecules could increase the mobility of charges in passages through polymer matrix and surface. Thus, the incorporation of ATH and NMMT could reduce the electrical resistance of LE blends. In addition, the increasing of ATH loading level also improved fire resistivity of LE blends as indicated by the promising limiting oxygen index. This is because the endothermic reaction of ATH during combustion process could reduce the temperature of polymer blends while releasing water vapour and the formation of alumina char. Furthermore, the increasing of NMMT loading level in ATH-added LE blends was found to slightly increase the fire retardancy. This is due to the addition of NMMT that could promote the dripping characteristics and charring effect during combustion and subsequently improve the fire retardancy of ATH added LE blends.
A new organic coupling agent called coconut oil coupling agent (COCA) was produced from coconut oil. The effects of filler content and COCA on mechanical, thermal, and morphological properties of corn cob (CC)-filled polylactic acid (PLA) eco-composites were studied. The results show that the addition of CC decreased the tensile strength and elongation at break but increased the modulus of elasticity of PLA/CC eco-composites. However, the presence of COCA improved the tensile strength, elongation at break, and modulus of elasticity of PLA/CC eco-composites. Meanwhile, the glass transition temperature (Tg) of PLA/CC eco-composites was increased by increasing the CC content and COCA treatment. The peak crystallization temperature (Tc) in PLA/CC eco-composites indicated the nucleating effect of CC and the Tc of PLA/CC eco-composites decreased at 40 php of CC content. The addition of CC increased the melting temperature (Tm) of PLA/CC eco-composites but reduced the crystallinity of PLA/CC eco-composites. The COCA treatment enhanced the mechanical properties and the crystallization process of PLA/CC eco-composites. The Tc and Tm of PLA/CC eco-composites were not significantly affected by COCA treatment. The presence of COCA improved the adhesion and interaction between CC and PLA matrix.
A series of the thermal conductive polyamide 66 (PA66) composites were prepared by two methods, including extrusion method (EM) and solution method (SM). The thermal conductivity, mechanical properties, thermal stability, and electric property of PA66 composites were investigated. The results showed that the maximum value of thermal conductivity of carbon fiber/PA66 composites containing 40 wt% carbon fiber prepared by SM achieves 2.537 W/m·K, which was superior to that of carbon fiber/PA66 composites prepared by EM at the same carbon fiber content. Moreover, its value was eight times more than that of pure PA66. The orientation of carbon fiber in process of injection had an influence on thermal conductivity of carbon fiber/PA66 composites, and the perpendicular distribution of carbon fibers helped in improving the thermal conductivity of composites. The carbon fiber/PA66 composites had good heat conducting performance but also had good material properties and electrical properties.
Polypropylene (PP) composites reinforced with down feather whisker (DFW) with and without surface modification were prepared and characterized through a series of tensile tests. The reaction of isopropyl tri(dioctylpyrophosphate) titanate (NDZ-201) on the surface of DFW was investigated to improve the compatibility between PP and DFW. The chemical reaction between DFW and NDZ-201 was characterized using the attenuated total reflection attachment on the Fourier transform infrared spectroscopy. PP/modified DFW (MDFW) composites showed more uniform whisker dispersion in the PP matrix, higher compatibility and good tensile strength than pure PP and PP/DFW composites. It was worth noting that the Young’s modulus of PP/DFW composites was higher than that of pure PP but lower than that of PP/MDFW composites. Furthermore, the effects of DFW and MDFW on the microstructural and thermal properties of different composites were also investigated, respectively. These results indicated that DFW could be a potential natural reinforcement for the PP matrix achieved with the use of NDZ-201.
The effects of kenaf (KNF) loading and 3-aminopropyltriethoxysilane (APTES) on processing torque, tensile properties and morphological properties of KNF-filled polypropylene (PP)/waste tire dust (WTD) composites were investigated. In this research, PP/WTD served as a matrix and KNF as a filler and the composites were prepared using a Thermo Haake Polydrive internal mixer, where different KNF loadings (0, 5, 10, 15 and 20 parts per hundred parts of resin) were used. The results revealed that the stabilization torque and tensile modulus increased with increasing KNF loading but tensile strength and elongation at break were found to decrease. The composites with APTES exhibited higher stabilization torque, tensile strength and tensile modulus but lower elongation at break than composites without APTES. The presence of APTES had enhanced the interfacial adhesion between PP/WTD matrix and KNF, which had resulted in higher tensile strength and modulus of the composites. These findings were supported by the morphological study on the tensile fractured surfaces of the composites.
Disposal of Chinese herbal residues (CHRs) during Chinese herbal medicine production and processing has become a problem that requires attention. In this study, CHRs were pretreated by steam explosion or pulverization and composites were prepared by mixing pretreated CHRs with polylactic acid. The mechanical properties of composites of CHRs pretreated by two different methods were compared, the main compositions of CHRs were analyzed, and the morphology of various CHRs and brittle fracture surfaces of composites were observed by scanning electron microscopy. The results show that the mechanical properties of the composites are closely related to the herbal species and pretreatment methods. The mechanical properties of CHR composites pretreated by steam explosion are superior to those pretreated by pulverization. Choosing CHRs with large fiber cell wall–lumen ratio, high lignin and cellulose contents, low contents of hetero cells and hemicellulose are helpful in making composites with good comprehensive performance.
Polylactic acid nanocomposite was prepared by melt blending polylactic acid (PLA) and transition metal ion (TMI)-modified montmorillonite (MMT; TMI-MMT) using a co-rotating conical twin-screw microcompounder attached with a mini injection moulder. MMT was modified by ion exchange reaction using TMI. Intercalation morphology of TMI on MMT was investigated by x-ray diffraction (XRD) and transmission electron microscopic analyses. XRD patterns indicated penetration of the metal ions into the MMT interlayer and formation of intercalated structure. In order to increase the adsorbed amount of Zn2+ and Cu2+ ions, MMT was previously intercalated with ethylene diamine. Thermogravimetric analysis indicated an increase in the onset of degradation temperature of nanocomposites when compared with virgin PLA. The isothermal cold crystallization kinetics of PLA/TMI-MMT nanocomposites was investigated by differential scanning calorimetry in the temperature range of 100–120°C and the development of relative crystallinity with the crystallization time was analyzed by the Avrami equation. PLA nanocomposites reinforced with TMI-MMT showed a significant increase in tensile and flexural modulus and impact strength when compared with virgin PLA. The flammability studies of PLA/TMI-MMT nanocomposites displayed slow rate of burning and enhanced carbonaceous char formation when compared with virgin PLA matrix.
Sandwich structures have been studied extensively for planar structures; however, the use of composite tubing, manufactured by pultrusion, in a bending situation where a core material can contribute to take shear stresses, can find many applications in modern structures made of composite materials. The objective of this article is to develop analytical solutions for axial effective modulus and major Poisson’s ratio of a pultruded unidirectional composite tubing filled with a core material. In this work, the unidirectional composite tubing and its core are considered to have transversely isotropic and isotropic properties, respectively. For the validation of the results, the obtained exact analytical solutions are reduced to a case where both the materials are isotropic and compared to the existing solutions for an isotropic material filling in an isotropic tube. Further validations of our exact analytical solutions for the transversely isotropic tubing and isotropic core are carried out employing a finite element analysis of the same structure, where the results show excellent agreements between the analytical solutions and the numerical results. Finally, a parametric study is conducted to investigate the variations in the effective properties of the two-phase composite cylinder based on the variations in the skin and/or core geometries and their material properties.
Silaned nano-silicon dioxide (SiO2) was used to improve the adhesion properties of carbon fibre/polyethylene (CF/PE) composites. The nano-SiO2 were treated by silane under different discharge time. And the changes on the surface properties of the treated and untreated composites were studied by impact, three-point bending tests and scanning electron microscopic analysis. The measurement showed that CF increases fracture toughness with the increase in CF content. Too much high content of CF did not further cause the increase in the toughness of CF/PE composite. The impact strength of silaned specimens is still higher than those of the unsilaned ones. The modified composite with the good matrix/fibre adhesion possessed 20% higher interlaminar shear strengths than the composite having weak interface.
Composites including short and randomly arranged Phormium tenax fibres in a polypropylene (PP) matrix (fibre content of 20, 30 and 40 wt%) were produced by twin-screw compounding and injection moulding. They have been characterised by tensile testing, scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results indicated that tensile modulus has been increased by reinforcing the matrix with growing amounts of fibres, whilst the effect on tensile strength had lower evidence. Fracture surface characterisation by SEM indicated that debonding and pull-out are prevalent, which suggests the need to optimise the interfacial bonding. Thermal characterisation results have shown that the main degradation peak for PP was slightly shifted to higher temperatures with the increasing fibre contents, thus improving the thermal stability of the composites. The introduction of fibres did not result in a significant variation in the position of the peaks for calorimetric analysis, except for the melting peak, which appeared lower for the composites with respect to the neat matrix. A slight increase in crystallinity was also measured.
Biodegradable polymer nanocomposites of poly(lactic acid) and nanoclay (Cloisite 30B) samples were prepared with compositions of 0%, 1%, 2%, 3%, 4%, and 5% (by mass) nanoclay using extrusion followed by injection molding. An exfoliated morphology was observed using x-ray diffraction. The nanocomposites were investigated for their mechanical properties using dynamic mechanical analysis (DMA) and tensile testing. The combination with 3% nanoclay was found to be optimum as a result of having the greatest mechanical strength. The fracture surfaces of the samples were also observed with the help of a scanning electron microscopy, and the images obtained complied with the experimental values attained for the samples, indicating more ductile fractures for those samples with greater mechanical strength. The thermal properties of the composites were studied with the help of differential scanning calorimetry and DMA data, and it was found that the trend followed by the glass transition temperature values obtained by both the methods was the same.
Self-reinforced composite (SRC) has gained significant interest due to its lightweight and good recyclability. In the present work, SRCs were prepared from woven polypropylene tapes. The woven tapes were further stitched by lock stitch and its effects on flexural and impact properties of the composites were studied. Flexural and impact results show that stitching parameters such as stitches per inch, sewing yarn count and the direction of stitching have a significant effect on the improvement of mechanical properties compared with the control sample (unstitched sample) without stitching. The morphological studies were carried out using optical microscopy and failure mechanism was analysed.
In the present investigation, novel optically active poly(amid–imide) (PAI)/organoclay (OC)/titanium dioxide (TiO2) bionanocomposite (BNC) films were prepared by solution intercalation method. These BNCs were synthesized by blending the chiral OC and modified TiO2 nanoparticles (NPs) with the PAI solution. An optically active PAI containing <sc>l</sc>-phenylalanine amino acid was synthesized via direct polycondensation reaction of N,N'-(pyromellitoyl)-bis-phenylalanine diacid 4 with 4,4'-diaminodiphenylsulfone 5 in the presence of molten tetrabutylammonium bromide as a green solvent. This polymer was end capped with amine end groups of diamine in the final polymerization process. Cloisite Na+ and protonated form of <sc>l</sc>-phenylalanine amino acid were used for the preparation of the chiral OC via ion-exchange reaction. The surface of TiO2 NPs was fictionalized by KH550 (-aminopropyltriethoxyl) coupling agent under ultrasonic irradiation. Finally, PAI/OC/TiO2 BNC films containing 5 wt% of the OC and 5, 10 and 15 wt% of modified TiO2 were prepared via solution intercalation technique. The resulting hybrid materials were subjected to Fourier transform infrared spectroscopy, thermogravimetric analysis techniques and x-ray diffraction. The morphology of the obtained materials was examined by transmission electron microscopy and field emission scanning electron microscopy techniques.
Organic hybrid composites based on carboxylated nitrile rubber and nylon-12 reinforced with mercerized and diisocyanated lignocellulose residue (LCR) was prepared. The influence of the LCR on the viscoelastic properties of these organic hybrids was investigated by dynamic mechanical analysis and thermal analysis (differential scanning calorimetry (DSC)). It is found that either the position of the damping peak was shifted to higher values or the intensity of the damping peak was significantly increased with LCR. These results could imply that the LCR enhanced the damping properties of the composites. The thermal stability of the composites was evaluated with the mean values obtained using thermogravimetrical analysis. The decomposition rate was investigated using differential thermal gravimetry. The crystallization behavior of the prepared composites was checked by DSC.
The influence of spherical (titanium dioxide (TiO2)) and platelet-like (Closite20A) nanofillers on the physical properties of polyethylene terephthalate (PET) nanocomposites was investigated. PET nanocomposites were prepared by melt blending of PET and nanofillers. Differential scanning calorimetry showed that PET nanocomposites had higher crystallinity than the neat PET, possibly due to the nucleating role of the nanoparticles. It was observed that the influence of nanoclays on crystallization of PET is more considerable than TiO2 nanoparticles. For PET/TiO2 and PET/clay nanocomposites, the highest value of crystallinity observed at 3 wt% and 1 wt% loading level of TiO2 and Closite20Ananoparticles, respectively. Scanning electron microscopic micrographs showed that uniform distribution and good dispersion of TiO2 through PET matrix were achieved at 1 and 3 wt% loadings but at higher loadings up to 5 wt%, nanoparticles tend to accumulate. Transmission electron microscopy and wide angle X-ray diffraction showed that the dominant structure of PET nanocomposites containing 1 wt% nanoclays was exfoliation while at higher loading levels, the shift in peak to lower angles and subsequent increase in platelet spacing suggest intercalated structure. The addition of TiO2 nanoparticles caused noticeable enhancement of PET ductility, while the incorporation of nanoclays into PET matrix developed a fragile structure with lower ductility.
Ultrasonic welding is a very fast joining technique well suited for thermoplastic composites, which does not require the use of foreign materials at the welding interface for either carbon or glass fibre-reinforced substrates. Despite very interesting investigations carried out by several researchers on different aspects of the process, ultrasonic welding of thermoplastic composite parts is not well understood yet. This article presents a deep experimental analysis of the transformations and heating mechanisms at the welding interface and their relationship with the dissipated power and the displacement of the sonotrode as provided by a microprocessor-controlled ultrasonic welder. The main aim of this research is to build up the knowledge to enable straightforward monitoring of the process and ultimately of the weld quality through the feedback provided by the ultrasonic welder.
The mechanical properties of composites from recycled waste plastic and waste sawdust are of interest in trying to convert these waste streams to useful products. The development of these composites from natural fiber is therefore receiving widespread attention due to the growing environmental awareness. The effects of compositions were investigated including different grades of plastic (virgin and recycled) and amounts of wood flour, coupling agent, and ultraviolet (UV) stabilizer on mechanical and physical properties of polypropylene/rubberwood flour (RWF) composites. Virgin polypropylene gave better mechanical properties than recycled (recycled polypropylene (rPP)), both in composites and as unfilled plastic. RWF content exceeding 25 wt% enhanced the strength of RWF-reinforced rPP composites. The modulus and hardness of composites increased linearly with wood flour loadings. Maleic anhydride-grafted polypropylene (MAPP) as a coupling agent increased the strength, modulus, and hardness of the composites. However, addition of 1 wt% UV stabilizer degraded the mechanical properties. Therefore, 4 wt% MAPP content is recommended to achieve good mechanical properties of rPP/RWF composites, while the amount of UV stabilizer should be as small as possible to avoid its negative influence.
Neat poly(trimethylene terephthalate) (PTT) and PTT/modified organoclay nanocomposite with various amounts of clay were synthesized by a two-step procedure. Terephthalic acid (TPA) was reacted with 1,3-propanediol (1,3-PDO) in the esterification step. Then, polycondensation reaction resulted in the formation of PTT in the presence of tetra buthyl titanate (Ti(OC4H9)4) as a catalyst. Commercially available organoclay (Cloisite 30B) was modified using 3-aminopropyltriethoxysilane via a silylation reaction. Thermal stability of modified clay was studied by means of thermal gravimetric analysis (TGA) that showed 10% less weight loss than Cloisite 30B. PTT/organoclay nanocomposites with 0.5, 1 and 2 wt% of modified organoclay were prepared by in situ polymerization. Synthesized polyesters were characterized by Fourier-transform infrared spectroscopy and proton-nuclear magnetic resonance spectroscopy (1H-NMR). Number average molecular weights were determined by 1H-NMR and a new Mark–Houwink equation is reported for highly pure dichloroacetic acid as solvent at 25°C. Polymer’s morphology was examined with x-ray diffraction and transmission electron microscopy. It was observed that clay layers were not accumulated. Thermal properties and crystallization behavior were investigated by differential scanning calorimetry and TGA. Crystallization temperature (Tc) of nanocomposites increased about 6°C compared to neat PTT that reflects greater overall crystallization. Modified Averami Equation was used to describe crystallization kinetics and crystal size was studied using polarized optical microscopy. It was observed that crystal size reduces with nanoclay content. PTT mostly is used as polymeric fiber. Hence, dyeability of neat PTT and nanocomposites was investigated using a spectrophotometer. About 32% increase in color uptake was determined.
In this work, the mechanical behavior of polyhyroxyalkanoate (PHA)/poly(lactic acid) (PLA) blends is investigated in a wide range of compositions. The mechanical properties can be optimized by varying the PHA contents of the blend. The flexural and tensile properties were estimated by different models: the rule of mixtures, Kerner–Uemura–Takayanagi (KUT) model, Nicolai–Narkis model and Béla–Pukánsky model. This study was aimed at investigating the adhesion between the two material phases. The results anticipate a good adhesion between both phases. Nevertheless, for low levels of incorporation of PHA (up to 30%), where PLA is expectantly the matrix, the experimental data seem to deviate from the perfect adhesion models, suggesting a decrease in the adhesion between both polymeric phases when PHA is the disperse phase. For the tensile modulus, a linear relationship is found, following the rules of mixtures (or a KUT model with perfect adhesion between phases) denoting a good adhesion between the phases over the composition range. The incorporation of PHA in the blend leads to a decrease in the flexural modulus but, at the same time, increases the tensile modulus. The impact energy of the blends varies more than 157% over the entire composition. For blends with PHA weight fraction lower than 50%, the impact strength of the blend is higher than the pure base polymers. The highest synergetic effect is found when the PLA is the matrix and the PHA is the disperse phase for the blend PHA/PLA of 30/70. The second maximum is found for the inverse composition of 70/30. PLA has a heat-deflection temperature (HDT) substantially lower than PHA. For the blends, the HDT increases with the increment in the percentage of the incorporation of PHA. With up to 50% PHA (PLA as matrix), the HDT is practically constant and equal to PLA value. Above this point (PHA matrix), the HDT of the polymer blends increases linearly with the percentage of addition of PHA.
In this article, polypropylene/styrene–ethylene–butylene–styrene grafted with maleic anhydride (PP/SEBS-g-MA) triblock copolymer blends and their samples containing various amounts of organo-modified montmorillonite (1–5 phr) are prepared through melt compounding in an internal mixer. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) are used to evaluate the dispersion of nanoclay particles in the blends. The measurements of mechanical and thermal properties of all the samples are carried out by means of standard methods. XRD and TEM results show existence of exfoliated and intercalated structures in the samples. Furthermore, the measurements of mechanical properties of the samples show that despite the decrease in tensile strength and Young’s modulus of PP in the presence of SEBS-g-MA as a toughening agent, addition of clay as the reinforcing filler improves these properties. So, a good balance between strength/stiffness and toughness/ductility is obtained with the addition of SEBS-g-MA and clay simultaneously and controlling their contents. Finally, thermal studies reveal that addition of clay has no significant influence on the structure and stability of the PP crystals formed.
Resistance welding is one of the most suitable and mature welding techniques for thermoplastic composites. It uses the heat generated at the welding interface when electric current flows through a resistive element, mostly a metal mesh. Closed-loop resistance welding relies on indirect temperature feedback from the weld line for process control. Its implementation is more complex than the most common open-loop welding, but on the contrary, it does not, in principle, require the definition of processing windows for each welding configuration and it allows for constant-temperature welding. The temperature at the welding interface can be indirectly monitored through the resistance of the heating element. The relationship between resistance and temperature, expected to be approximately linear for a metal mesh heating element, can then be used to translate the welding temperature into a target resistance value for the process-control routine. Despite the apparent straightforwardness of this procedure, the research results presented in this article prove that different types of characterization tests yield different resistance versus temperature relations for a metal mesh heating element, which can lead to significant temperature deviations when used in closed-loop processes.
Nanocomposites containing nano-calcium carbonate (nano-CaCO3) in the range of 0.25–1.5% (w/w) were prepared via in situ polymerization of urethane methacrylate pre-polymer derived from poly(ethylene glycol) (PEG 400), polymeric diphenylmethane diisocyanate and 2-hydroxyethyl methacrylate. Incorporation of nano-CaCO3 into poly (urethane methacrylate) matrix was confirmed by Fourier transform infrared spectroscopy and wide-angle x-ray diffraction studies. Density studies indicated that nanocomposites containing 0.75 wt% nano-CaCO3 had more condensed microstructure. Tensile strength, abrasion resistance, heat deflection temperature and shore hardness of nanocomposites were found to be higher than that of pristine polymer. Impact strength decreased with an increase in the nano-CaCO3 content. Thermal studies indicated single-step degradation under a nitrogen atmosphere. Scanning electron microscopy studies confirmed the uniform distribution of nano-CaCO3 at lower loading of nano-CaCO3 and microcracking occurred during wearing.
Present study deals with the effect of variation in melt flow index (MFI) of maleic anhydride–grafted polypropylene (PP-g-MAH) as a polymeric compatibilizing agent on various properties of fly ash (FA)-filled polypropylene (PP) composites. The FA content was varied from 0 to 40 wt%. The effect of polymeric compatibilizing agents with different MFI and very high maleic anhydride (MAH) content on interfacial adhesion between filler and matrix and filler dispersion were studied. The mechanical and thermal properties of the composite material were evaluated, and the microstructure was investigated through scanning electron microscopy. The values of yield stress and breaking strength of compatibilized PP/PP-g-MAH/FA-based composites showed higher values compared to that of untreated FA-filled PP composites at corresponding filler content. Incorporation of FA into PP led to stiffer materials, as tensile modulus increased significantly. Tensile and impact properties varied with varying molecular weight of PP in PP-g-MAH and are essentially decided by wettability of the filler. It is also found that heat-deflection temperature and vicat softening point improved with the addition of FA filler. The use of PP-g-MAH as polymeric coupling agent provides improvement in mechanical and thermal properties of filled polymers. The higher effect of compatibilization is obtained using high-molecular-weight PP in PP-g-MAH as a polymeric compatibilizing agent and low-molecular-weight PP in PP-g-MAH resulted in better dispersion of FA in PP matrix. The overall results showed that FA dispersion and interfacial adhesion are greatly affected by the kind of PP-g-MAH.
Composites composed of polylactide (PLA), modified PLA and woven flax fiber textiles (flax weave style of 2 x 2 twill and 4 x 4 hopsack) were produced by hot press technique. Two structurally different additives were used to modify PLA. The dispersion of the flax in the composites was studied by scanning electron microscopy and computed microtomography system (µCT). The PLA composites were subjected to water absorption and instrumented falling weight impact tests. The thermomechanical and creep properties of the composites were determined using thermogravimetric analysis, dynamic-mechanical thermal analysis and short-time creep tests. It was found that the modified PLA and its composite increased the impact resistance compared with the unmodified PLA. Incorporation of flax decreased resistance to thermal degradation and increased water uptake. The impact energy and stiffness value of PLA/flax composites were markedly higher than that of PLA but reflect the effects of composite structures and flax content. The storage modulus master curves were constructed by applying the time–temperature superposition principle. From the master curve data, the effect of modified PLA on the storage modulus was more pronounced in the low frequency range.
Manufacturing of thermoplastic composite based on textile preforms made from hybrid yarns is well suited for the production of fiber-reinforced plastic (FRP) in medium- and large-scale production runs. Especially, the consolidation of thermoplastic FRP is currently complicated by the high viscosity of molten material. Woven multilayered and z-reinforced NCF-preforms are very interesting for FRP supposed to withstand three-dimensional loading and impact stress. These preforms with z-directional reinforcement improve the FRP delamination behavior and out-of-plane characteristics. The well-known composite parameters are essential to ensure the use of these materials in a wide range of applications.
Monomer casting (MC) nylon-6 was a polymeric modified by grafting 4-amion-2,2,6,6-tetramentylniperidine (TEMP) as reactive-hindered amine onto its chain so as to improve the compatibility and stability of the stabilizer in the polymer matrix. The structure of the reactive stabilizer was confirmed by Fourier transform infrared and proton nuclear magnetic resonance spectroscopic analyses. The effect of TEMP on the thermal stability of MC nylon-6 was studied. It was found that with the increase in TEMP dosage, the thermal weight loss of the samples first decreased and then increased and the preferred dosage of TEMP was about 0.2 mol%. The residual weight percentage (R) of all the samples decreased with heating time, and it does much more slowly for the grafting sample than that of pure one. The thermal degradation characteristic temperatures of MC nylon-6 were improved by grafting TEMP. The long-term aging of MC nylon-6 indicated that the carboxylic acid concentration of the grafting sample was lower than that of the pure sample, and its end amine group concentration was relatively higher during the whole aging process, presenting more stable chemical structure. Ultraviolet absorption and gel content of MC nylon-6 were also reduced by grafting TEMP. The crystallinity (Xc) of MC nylon-6 increased, and the crystallization growth rate and melt temperature (Tm) decreased with aging time, resulting from the annealing process at high temperature and the small molecular products during aging.
The properties of injection-moulded polylactic acid (PLA) and recycled carbon fibre composites are examined in this study. Measurement of tensile, flexural, and impact resistance properties quantify the mechanical properties of the composites with increased fibre loading. Tensile strength and modulus of PLA and 30 wt% carbon fibre composite were found to increase by 73% and 438%, while flexural strength and modulus of carbon fibre composite increased by 53% and 400% compared to neat PLA. Consequently, storage modulus measured by dynamic mechanical analysis also improved with the addition of carbon fibre. Mechanical properties were correlated with the Hirsch model. Composite morphological study through scanning electron microscopy (SEM) showed pullout and partial wetting of fibre by matrix along with agglomeration. Differential scanning calorimetry study of the composites showed minor increase in relative crystallinity and crystallization temperature, while melting and cold crystallization temperatures were found to decrease due to the high-thermal conductivity of carbon fibre.
Although wood–plastic composites (WPCs) are materials widely used in the construction industry, their durability constitutes a serious issue especially when used for outdoor applications. Therefore, this work gives account on the effect of biotic and abiotic degradation agents on two different WPCs prepared from recycled high-density polyethylene (HDPE) and pinewood residues. Two aspects were evaluated, namely mechanical properties and aesthetics. Compression-molded samples obtained from two different formulations based on 40% of wood and 60% of HDPE, containing 0 and 5% of coupling agent with respect to wood content, were subjected to 0, 1000 and 2000 h of accelerated weathering (AW), using an ultraviolet-type accelerated tester equipped with UVA-340 fluorescent lamps. Afterward, the aged specimens were exposed to attack by termites (TA) of the species Nasutitermes nigriceps for 15 and 30 days. Tensile properties after AW and TA were assessed using an Instron 5500R (1125) universal tester. Similarly, the aesthetic aspect was studied to evaluate the color changes on the specimens’ surfaces using a Minolta CR-200 Chroma Meter. The results of this work show drops in the mechanical properties of both composites that were not significant, even after being exposed to 2000 h of AW in combination with 30 days of TA. However, their aesthetics was seriously affected by both degradation agents, as reflected by the variations registered on the total color change and relative lightness of the tested samples.
In this study, highly oriented self-reinforced wood–polymer composite (WPC) rods were produced by stable and continuous solid-state extrusion through a conical die. Polypropylene, softwood flour and inorganic filler were used at 50%, 40% and 10% weight concentration, respectively. The properties and morphology of the samples were studied by differential scanning calorimetry analyses, scanning electron microscopy observation and mechanics performance testing. Compared to a conventional extruded rod, the self-reinforced WPC rod profile exhibited a fibrillar structure largely parallel to the direction of extrusion, which contributed to the significantly high strength and modulus of the product as well as improved thermal properties and good dimensional stability. With the increase in draw ratio, the melting peak moved to high temperature, modulus (from 2200 to 5800 MPa) and strength (from 20.7 to 81.6 MPa) were greatly increased.
This study explores the thermomechanical behavior of steel fiber-reinforced high-density polyethylene matrix thermoplastic composite (TPC) discs possessing distinct fiber arrays and the influence of circular hole diameter, upon exposure to convective air cooling loading. The discs were manufactured and their thermomechanical properties were assessed. Models of the discs for different D/W ratios (where D is the circular hole diameter and W is the disc width) were constructed and analyzed. Two parameters, the circular-hole diameter and the fiber array configuration, were varied. Thermal stresses generated during the cooling of each disc were then determined. Residual thermal stress and equivalent plastic strain for each respective D/W ratio were presented in graphical form, enabling evaluation and comparison. A parametric study was conducted to identify the influence of both circular hole diameter and distinct fiber reinforcement upon residual thermal stress and plastic deformation for steel fiber/TPC discs subjected to thermal loading.
In order to create polymer composites that can shield machine and instrument casings from electromagnetism and to reclaim waste material, this study melt-blended impact-resistant polypropylene (PP) chips, carbon fibers (CFs; 5, 10, 15, or 20 wt%), and glass fibers (GFs; 0, 5, 7 wt%). This process used a single-screw extruder to make electrically conductive composites. The resulting composites were then evaluated in terms of mechanical properties, electromagnetic shielding effectiveness (EMSE), and surface resistivity. According to experimental results, an increase in CF content increased PP/CF composites’ tensile strength to 29.31 MPa and flexural strength to 38.93 MPa but decreased the impact strength to 49.04 MPa. When the CFs were increased to 15 wt%, the EMSE and surface resistivity of PP/CF composites were above 20 db and 3.3 x 103 /square. For PP/CF/GF composites, with an increase in GF content, the EMSE decreased and the surface resistivity increased.
Commingled composites of polylactide (PLA) and seed flax fibers were prepared by carding and needle pressing of PLA and flax fibers to nonwoven mats followed by compression molding. The nonwoven mats were treated using two different types of cellulolytic enzymes, namely cellobiohydrolases and endoglucanases. Both the enzymes changed the properties of the seed flax fibers surface. The resulting composites were studied using scanning electron microscopy, mechanical testing and thermal analysis. The effects of these modifications were minor on the thermal and mechanical properties measured. However, in the scanning electron micrographs, a difference in the fiber pull-out behavior of the untreated and treated fibers was observed. Treated seed flax fibers showed an improvement in adhesion with PLA.
Thermoplastic elastomers (TPEs) based on high-density polyethylene (HDPE)/waste ground rubber tire (WGRT) powder composites were prepared by melt compounding, and the composites were compatibilized by styrene–butadiene–styrene block copolymer (SBS). The effects of the SBS compatibilizer on mechanical properties, morphological properties and the Mullins effect of the composites were investigated systemically. Experimental results indicated that SBS had a good compatibilization effect on the HDPE/WGRT composites. Compared with HDPE/WGRT composites, the tensile strength and the elongation at break went through maximum values at a compatibilizer resin content of 12 phr. Morphological study showed that the interface interaction of the HDPE/WGRT composites compatibilized by SBS was strong, which contributed to the significantly improved mechanical properties. The Mullins effect results showed that the softening appeared after the first loading of the HDPE/WGRT and HDPE/SBS/WGRT composites, the maximum stress decreased at the later cycles, and the residual deformations in uniaxial loading–unloading cycles of the HDPE/SBS/WGRT sample were lower than those of the HDPE/WGRT sample, indicating that the elasticity of the HDPE/SBS/WGRT TPE was improved.
In this study, the effect of nanoclay on the rheological and morphological properties of polyamide 6 (PA6)/acrylonitrile–butadiene–styrene (ABS) blends was investigated. The scanning electron microscopy micrographs showed that with increment in the nanoclay content, the dispersed phase droplets size and their polydispersity index decreased, and the finer and more uniform dispersed phase was obtained. The transmission electron microscopy micrographs of nanocomposites indicated well-dispersed nanoclay tactoids in the polymer matrix produced by exfoliation of the nanoclay in the polymeric blends. Dynamic strain sweep experiments showed that the extent of the linear viscoelastic region is sensitive to the nanoclay content and compatibilizer. With increasing nanoclay content in the blend, the extent of the linear viscoelastic region decreased. On the other hand, the rheological measurements revealed that the nanoclay content has a significant effect on the moduli and complex viscosity of the blends. These results have indicated that with increasing nanoclay content the storage modulus (G'), loss modulus (G'') and complex viscosity (*) increased. In addition, the results of creep experiments revealed that with the addition of compatibilizer (polyethylene octene elastomer grafted with maleic anhydride) and nanoclay to PA6/ABS blends, creep and recovery strain, over time, decreased remarkably and the recovery percentage increased. It was concluded that there is a good conformity between the results obtained from morphological and rheological investigations.
The thermal degradation behaviors of poly(vinyl alcohol) (PVA) and PVA/zinc oxide (ZnO) composite are investigated using differential thermal analysis (DTA). The degradation activation energy (Ed), frequency factor (ko) and Avrami exponent (n) as thermal kinetic parameters are calculated from the DTA results. The calculated values of Ed are 80.94 and 148.58 kJ mol-1 for PVA and PVA/ZnO composite, respectively, indicating the enhancement of the PVA thermal stability as ZnO nanoparticles are filled in PVA matrix. The n values are evaluated from the shape analyses of degradation peaks. From estimated n values, the degradation mechanisms are determined for both the complexes under investigation.
This work is focused on the modification of montmorillonite by hexadecyl trimethyl ammonium bromide (HDTMA) as a surfactant by cation exchange reaction. HDTMA-modified layered silicate (HDTMA-MLS) was compounded with polylactide (PLA) by melt extrusion technique for making nanocomposites. These nanocomposites were subjected to morphological, rheological, thermal and mechanical analyses. Variations in mechanical properties, plasticity and thermal stability with the addition of modified nanoclays in PLA were investigated. The presence of HDTMA in clay minerals was confirmed by Fourier-transform infrared (FTIR) analysis that shows two absorption bands at 2927 cm-1 and 2860 cm-1 that corresponds to the asymmetric and symmetric stretching vibrations of C–CH2 of alkyl chain, respectively, and the band at about 1470 cm-1 was assigned to the vibration of trimethyl ammonium quaternary group C–N(CH3)3. Melt rheology of virgin PLA and nanocomposites performed by small amplitude oscillation shear measurement. Incorporation of HDTMA-MLS (1–7 wt%) into PLA matrix yields significant improvements in the elastic modulus (G') of nanocomposites due to intercalation at high temperature. X-Ray diffraction (XRD) and transmission electron microscopy determined that PLA/HDTMA-MLS nanocomposites were intercalated. Nanocomposite prepared using 5 wt% HDTMA-MLS exhibited optimum mechanical performance with an increase in the tensile and flexural modulus and impact strength as compared to virgin PLA, which confirms intercalation morphology. Dynamic mechanical analysis study revealed an increase in the storage modulus (G') confirming a strong interaction between the modified clays and PLA. Differential scanning calorimetry and thermogravimetric analysis showed improved thermal properties. Heat deflection temperature of the matrix also increases in the presence of nanoclays.
The present work investigates the effect of organomodified nanoclay (ZW1) and butadiene–acrylonitrile copolymer terminated with amine group (ATBN copolymer) on the properties of epoxy resin (EP). The impact strength (IS) and the critical stress intensity factor (KC) values of EP containing 1% nanoclay increased approximately by 200% and 75%, respectively, in relation to neat EP. Moreover, hybrid composites containing 1% or 2% nanoclay and ATBN showed improved mechanical properties in relation with unmodified EP. The magnification and analysis of the Fourier-transform infrared spectra showed an increase in the peak height of 3338 cm-1 due to polymeric modifier incorporation. This finding might be explained by the reaction between modifier or hardener amine groups and the unreacted part of EP cured at room temperature. Hybrid composite containing 2% Nanobent ZW1 and 5% ATBN exhibited synergistic effect in terms of tensile adhesive strength toward composites with one modifier. Moreover, scanning electron micrographs showed more elongated and leaf-like structure for hybrid compositions, explaining the enhancement of IS and KC values of the tested composites.
Mass production of tires and their subsequent storage after use is a serious environmental problem that is tried to be solved in various ways. One of these ways is the mixture of these old used tires (ground tire rubber (GTR)) with various thermoplastic and thermostable polymers. These blends are made by modifying the pretreatment the GTR is subjected to, the degree of devulcanization, the mixing or pressing conditions, etc. Later the mixtures are analyzed structurally and mechanically, looking for possible industrial applications for them. The present work aims to obtain materials suitable for the electric industry from the mixture of polyamide with old used tires (GTR), starting from the requirement of minimum recycling costs, that is using vulcanized GTR without any prior treatment but acting on the particle sizes with a simple and inexpensive screening. A novelty of this study is the large number of compounds analyzed, and the deep analysis these have been submitted to dielectric, mechanical, thermal and microstructure analyses to get a large number of variables in each test. Compounds were categorized as the three GTR particle sizes (p < 200 μm, 200 < p < 500 μm and p > 500 μm) and seven concentrations of GTR (0%, 5%, 10%, 20%, 40%, 50% and 70%), resulting in a total of 21 new compounds. In addition, in order to have the dielectric tests as much exhaustive as possible and to show the behavior of the compound under widely changing conditions, a wide range of temperatures (30–120°C) and frequencies (1 x 10-2 Hz to 3 x 106 Hz) were taken into consideration. All these data have provided an accurate characterization of the properties of the new compounds, and according to these results, possible electrical applications have been explored, with the requirement that they must comply with official regulations.
In this article, low-density polyethylene (LDPE) rubber and silica (SiO2) particles were employed to modify polytetrafluorethylene (PTFE) simultaneously. The distribution and dispersion of LDPE and SiO2 particles in PTFE matrix can be adjusted by the wettability of SiO2 particles toward PTFE and LDPE, so as to achieve a simultaneous enhancement of toughness and modulus of PTFE. A unique structure with the majority of PTFE surrounded by SiO2 particles was first observed using maleic anhydride (MAH)-grafted LDPE, resulting in a dramatical increase in Izod impact strength as the rubber content in the range of brittle–ductile transition (4–16 wt%). The friction and wear properties were obviously improved with the addition of MAH-grafted LDPE regardless of the content of SiO2.
Poly(ethylene terephthalate) (PET) from off grades of industrial manufacturer was partially and thoroughly depolymerized using excess glycol to synthesize PET oligomers and bis(hydroxyethyl) terephthalate (BHET), respectively. Design of experiments and analysis of variance were applied for optimization of samples. Effects of reaction time, volume of glycol, catalyst concentrations and particle size of off grade PET on the yield of products were investigated based on the design of experiments. Thermal analysis of glycolyzed products is performed by differential scanning calorimetry. The optimum samples were also well characterized by Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy (proton nuclear magnetic resonance spectroscopy and carbon nuclear magnetic resonance spectroscopy). The optimal conditions to synthesize PET oligomers were glycol/PET molar ratio of 2 with no catalyst using granule-shape PET for a 120-min glycolysis reaction time. Desired oligomer repeating units were 3–8. On the other hand, a reaction time of 180 min, weight ratio (catalyst to PET) of 0.25 wt% and glycol/PET molar ratio of 5 were obtained as the suitable conditions of BHET production. Then, end capped PET oligomers, as a compatiblizer for preparing PET nanocomposites, were produced via reaction between maleic anhydride and phthalic anhydride (MA/PhA) composition. The combination of reaction time of 106 min and PhA/MA molar ratio of 0.85 produced the best results based on d-spacing and peak intensity of nanocomposite samples. Moreover, the reaction of MA and BHET from glycolyzation of PET was successfully performed at 160°C and 190°C for 8 h.
Poly(ethylene terephthalate) (PET) containing 3 wt% of organo-montmorillonite (OMMT) was prepared using twin-screw extruder followed by injection molding. Maleic anhydride-grafted styrene–ethylene/butylene–styrene (SEBS-g-MAH) and N,N'-ethylenebis(stearamide) (EBS) were used as impact modifier and dispersing agent. The reprocessing ability of PET/OMMT nanocomposites was studied through three cycles of extrusion. Properties of the reprocessed PET nanocomposites were characterized using intrinsic viscosity measurements, impact tests, thermogravimetric analysis, differential scanning calorimetry, x-ray diffraction (XRD) and scanning electron microscopy. The enhanced intercalation of the OMMT silicate layers in the PET was confirmed using XRD. The intrinsic viscosity, impact strength and thermal stability of PET nanocomposites were reduced after subjecting to three cycles of extrusion. Nevertheless, the retention ability in mechanical and thermal properties of PET/OMMT/EBS nanocomposites was higher than that of PET/OMMT/SEBS-g-MAH counterparts.
The aim of this study was to understand the stick–slip (Sk-Sp) properties of para-aramid woven fabrics. For this reason, pullout test was conducted on para-aramid Twaron CT® 716 (CT716) and Twaron CT® 716 (CT714) woven fabrics. The Sk-Sp region and accumulative retraction force region were defined based on the single- or multiple-yarn pullout force–displacement curve. It was found that Sk-Sp force and accumulative retraction force depend on the fabric density and the number of pulled ends in the fabric. Sk-Sp force in the multiple-yarn pullout test was higher than that of the single-yarn pullout test. Sk-Sp force in single- and multiple-yarn pullout tests in the dense CT716 fabric was higher than that of the loose CT714 fabric. In addition, long fabric samples showed high Sk-Sp force compared to that of the short fabric samples. On the other hand, the amount of Sk-Sp force was related to the number of interlacement points in the fabric, whereas the amount of accumulative retraction force was related to fabric structural response.
The effects of polytetrafluoroethylene (PTFE) on the tensile and tribological properties of carbon fiber–reinforced poly(methyl methacrylate) (PMMA) composites were studied. Tribological tests were conducted on an Amsler friction and wear tester using a block-on-ring arrangement. It was observed that the PTFE played a main role in the tensile-resistant and wear-resistant properties of the PMMA composites. The tensile properties were ruled by the fiber–matrix adhesion. And the excellent tribological performance of the PTFE fillers improved the tribological properties of PMMA composites.
Poly-p-phenylenebenzobisoxazole (PBO)-filled polytetrafluoroethylene (PTFE) has been successfully prepared at different compositions in a corotating twin-screw extruder, where PTFE acts as the polymer matrix and PBO as the dispersed phase. The morphology and impact properties of these blends were investigated using scanning electron microscopy. The presence of PBO particles dispersed in the PTFE continuous phase exhibited a coarse morphology. Increasing PBO contents in the blend improved the impact properties at weak deformation. It was found that the interfacial adhesion played an important role in the creation of an interphase that was formed by the interaction between the PTFE and the PBO. This induced an improvement in impact properties. In addition, the optimum impact properties were obtained when the content of PBO is 30 vol%.
A novel water-swellable rubber (WSR) has been prepared by dynamically vulcanized ethylene–vinyl acetate copolymer (EVA)/chlorinated polyethylene (CPE)/nitrile butadiene rubber (NBR) blends where the cross-linked poly(sodium acrylate) (CPNaAA) was used as a super water-absorbent resin and dispersed in the NBR rubber. The mechanical properties, water-swelling behavior, weight loss and crystallization behavior of the prepared WSRs were investigated systemically. When the CPNaAA content was 20 phr above, the increase in CPNaAA dosage contributed to the decrease in mechanical properties. However, the WSRs showed strong water-swelling behaviors and the water-swelling ratio of WSRs with 50 phr CPNaAA was 669.3% at 120 h. The WSRs with 60 phr CPNaAA showed high water-swelling rate and achieved the equilibrium swelling at about 566.3% in 23 h. The secondary and third water-swelling behaviors of WSRs showed significantly rapid equilibrium swelling and remarkable decrease in weight loss. X-ray diffraction results revealed the increase in CPNaAA content would result in the reduction of crystalline structure content in EVA. Morphological study of etched surface showed that the CPNaAA particles were dispersed evenly in the WSRs and coated with cross-linked NBR rubber; moreover, field-emission scanning electron microscopic graphs showed the crystalline structure of EVA and clusters of flakes were dispersed on the etched surface of WSRs.
Addition of measured amounts of fillers into a polymer matrix is expected to improve the desired properties of the composites. Also the ease of processability of the matrix and reinforcement is always desired. Use of powder fillers in the polymer matrix at ambient conditions would make the processing much easier. This will help in in situ applications. In the present work, polymer–matrix composites are prepared with polystyrene as the matrix using metal (copper/aluminum/steel) and ceramic (alumina) fillers at ambient conditions. The composites with metallic and ceramic fillers in the ratio of 50:25:25 wt% (polymer:filler 1:filler 2) designated as three-phase composites were investigated for tribological applications. Both copper and aluminum fillers were considered for comparison in terms of their contribution to tribological behavior because of their thermal conductivity, specific heat and density.
Polystyrene is filled with metal powder (copper, aluminum or steel) and alumina in equal proportion and subjected to wear and friction tests. The polymer steel–ceramic composite has the least with the other two composites having almost the same values of friction coefficient. The polymer aluminum–ceramic composite has the least wear at all operating conditions. Polymer aluminum–ceramic composite was found to have better wear behavior among the three-phase composites. This may be attributed to the favorable value of density of aluminum, moderate thermal conductivity and excellent specific heat.
Polylactic acid (PLA) nanocomposites were prepared using melt blending technique. Two different commercially available nanoclays, Cloisite 93A (C93A) and Cloisite 30B (C30B) at various wt%, have been used to prepare the nanocomposites. The mechanical properties of the nanocomposites have been studied to evaluate the effect of the nanoclay within the matrix polymer. Mechanical tests revealed an increase in the mechanical properties with the incorporation of organically modified nanoclays as compared with PLA matrix. PLA/C30B nanocomposites exhibited optimum tensile modulus at 3 wt% of clay loading. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies were also performed to evaluate the thermal behavior of the nanocomposites. Further, viscoelastic behavior in the nanocomposites has been investigated using dynamic mechanical analysis (DMA) to study the damping behavior of the materials. Also the morphological study was carried out through X-ray diffraction analysis, and a better exfoliation or dispersion of C30B clay with PLA matrix was observed. The interaction between the clays and PLA matrix has also been studied using transmission electron microscopy (TEM).
The structure of polysodium acrylate (PSA) hydrogel was modified using N,N-methylenebisacrylamide and cellulose microfibrils (CMFs) as a cross-linker and filler, respectively. CMF was obtained from banana fiber by acid hydrolysis process. The resulting structure and morphology of CMF and PSA/CMF hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD) analysis and scanning electron microscopy. From the FTIR and XRD spectra, the formation of CMF from banana fiber is confirmed. Differential scanning calorimetric study was carried out on the swollen PSA/CMF hydrogels to determine the state and quantification of water present inside the hydrogels. The mechanical characterization of PSA/CMF hydrogels was studied in brief by dynamic mechanical analysis technique.
A series of blend fibers based on a certain weight polypropylene (PP) and poly(butyl methacrylate-co-hydroxyethyl methacrylate) (PBMA-co-HEMA) were prepared via melt spinning in a corotating twin screw extruder. The morphology and structure of the blend fiber was studied by stereoscopic microscopy, polarized optical microscopy, wide-angle x-ray diffraction and field emission scanning electronic microscopy. Thermal properties were carried out by means of differential scanning calorimetry and melt flow index. The results demonstrated that the crystalline structure is proven to be greatly destroyed owing to the entanglement and cross-linking of molecular chains caused by hydrogen bond network of the copolymer in the blend. Oil absorbency decreases with increasing mass fraction of PP in the blend fiber. Moreover, the enthalpy of crystallization and supercooling temperature decrease as the content of PBMA-co-HEMA component increases.
The objective of this work is to improve the interlaminar shear strength (ILSS) of the composites by surface coating of carbon fibers (CFs). The effect of polypyrrole (PPy) coating on CF composites was studied. The morphologies of untreated and treated CFs were characterized by scanning electron microscope and x-ray photoelectron spectroscopy, respectively. Surface analysis showed that the surface of CFs chemisorbed oxygen-containing groups and active carbon as well as increased wettability after surface treatment with PPy. The mechanical properties show that the treated CF composites can possess excellent interfacial properties with polytetrafluoroethylene matrix, and ILSS of the composites is up to 106 MPa.
Polystyrene (PS)–poly(lactic acid) (PLA)–PS triblock copolymer is prepared with PLA and styrene (St) via atom transfer radical polymerization (ATRP). The structure and thermal properties of the copolymer are analyzed by infrared spectroscopy, gel permeation chromatography, nuclear magnetic resonance, thermogravimetry, differential scanning calorimetry and alcoholysis. The ATRP of St using bromine-terminated PLA as the initiator exhibits first-order kinetics and a low-molecular-weight distribution (Mw/Mn 1.5). The thermal stability of PLA is improved by copolymerization. Both the initial temperature of thermal decomposition and glass transition temperature are increased with an increasing length of PS block.
In this study, low-density polyethylene (LDPE)–thermoplastic corn starch blends containing various amounts of organomodified montmorillonite (OMMT, 0.5–3 part per hundred (phr) resins) were prepared using a twin screw extruder. A 3-wt% LDPE-grafted maleic anhydride was used as a compatibilizer. The tensile, flow and water absorption properties of all the samples were measured by means of standard methods. Intercalated structures were achieved in all the samples, based on the x-ray diffraction and transmission electron microscopic results. Increasing levels of clay also led to the higher gallery distance of silicate layers (i.e. 32.5–34.5 Å). Furthermore, increment in ultimate tensile strength (UTS) and Young’s modulus (E) as well as decrement in elongation at break (b) were obtained with increase in clay loading. The sample containing 1 phr nanoparticles showed 20% and 63% increase in UTS and E when compared with the reference sample, respectively. However, b of this sample decreased by 17%. In addition, the flow property measurements indicated that as shear rate and the clay content increased, the apparent viscosity of all the samples decreased and increased, respectively. Finally, the presence of OMMT led to decrease in the melt flow index (MFI) of the samples. The MFI values also decreased with increasing the OMMT concentration. It is believed that the samples prepared in this work may biodegrade after exposure to the environment.
Laboratory-scale research had shown the potential of using cotton burr/stem (CBS) as fiber filler in thermoplastic composites. This study evaluates the potential of using waste materials from cotton harvesting/ginning operations, CBS and cotton module wraps (CMWs), as a filler and substrate in thermoplastic composites at commercial scale. The study also compares the effect of scale-up from laboratory to commercial scale on the properties of the thermoplastic composite materials. Two separate commercial trials were conducted to manufacture thermoplastic composite boards with (a) 0, 12.5, 25 and 37.5% by weight of CBS and (b) up to 30% by weight of CMW. Testing of these samples showed that commercial-scale samples with 12.5% CBS had all properties comparable to those made with wood filler. At higher substitution rates, CBS tended to increase water absorption and coefficient of thermal expansion, and increase nail-holding capacity (NHC) and hardness in commercial-scale samples. This study also showed that CMW can be substituted by up to 30% by weight without deterioration of properties in comparison with a commercially available product. Scaling of the process had significant influence on all properties tested, expect NHC. In general, all commercial-scale samples exhibited physicomechanical properties within the range of properties reported for commercially available wood–plastic composite decking materials.
Carbon fiber (CF) and nano-silica (nano-SiO2) particles were employed simultaneously to modify polyoxymethylene (POM). Our goal was to control the distribution and dispersion of CF and nano-SiO2 particles in POM matrix using an appropriate processing method and adjusting the dispersion of nano-SiO2 particles toward CF and POM, so as to achieve a simultaneous enhancement of toughness and modulus of POM. The results of tribological tests showed that the POM with 3 vol% nano-SiO2 presented better tribological properties. When the content of nano-SiO2 was not more than 3 vol%, the CF/POM/nano-SiO2 samples presented lower friction coefficients and smaller wear volumes. However, higher contents of nano-SiO2 than 3 vol% were very disadvantageous to the tribological performances.
In this research, we have investigated the effects of addition of different percentages of nanoclay on the decay resistance and physicomechanical properties of natural fiber-reinforced plastic composites against white-rot fungi (Trametes versicolor). To meet this objective, the beech wood flour was mixed with polypropylene (PP) at 50% by weight fiber loading. The samples were prepared by melt compounding and injection molding. The concentration varied as 0, 1, 2, 3, 4, and 5 per hundred compounds (phc) for nanoclay. The amount of maleic anhydride-grafted PP (PP-g-MA) as a coupling agent was fixed at 2 phc for all formulations. Physical and mechanical properties of all the specimens were determined prior to and after incubation with the fungus for 8 weeks at 25°C and 75% relative humidity. Weight losses of the specimens were also determined after incubation. The results indicated that the flexural strength and modulus increased with an increase in nanoclay up to 3 phc and then decreased. However, the impact strength and water absorption were decreased with an increase in nanoclay loading. Furthermore, the lowest weight loss and the highest hardness were observed in the composite containing 5 phc nanoclay. The morphological findings showed that the samples containing 3 phc of nanoclay had higher order of intercalation and better dispersion.
The tribological properties of high temperature resistant thermoplastic composites, polyetherimide (PEI), reinforced with graphite and short carbon fiber (SCF), were investigated in dry sliding conditions. Friction and wear experiments were conducted on a pin-on-disc apparatus, using composite pins against polished steel counterparts. It was found that SCF could effectively enhance both the wear resistance and the load-carrying capacity of the base polymers. With the addition of SCF, the frictional coefficient and wear rate of the composites were further reduced especially. On the basis of microscopic observation of worn surfaces, dominant wear mechanisms are discussed.
To improve the friction and wear behavior of hydrogenated nitrile butadiene rubber (HNBR) composites, graphite and silane-treated Silicon carbon (SiC) were incorporated. The tribological properties of the resulting composites were investigated systematically on a model ball-on-block test rig. The friction and wear mechanisms of the composites were studied through analyzing the worn surfaces by a scanning electron microscopy. Experimental results showed that the friction and wear behavior of the filled composites were improved greatest when graphite and silane-treated SiC were added together, indicating that there was a synergistic effect between them.
In this study, the effects of gamma irradiation on the tribological behaviors of high-density polyethylene (HDPE)-filled ultrahigh-molecular-weight polyethylene (UHMWPE) composites were investigated. The tribological changes were evaluated by friction and wear tests as well as scanning electron microscopic analysis of the worn surfaces. It was found that the irradiation induced the degradation of UHMWPE molecular chains and the interfacial cross-linking was formed. The addition of HDPE significantly increased the wear resistance of UHMWPE composites. Friction and wear tests indicated that HDPE improved the tribological properties of the materials before and after irradiation. HDPE and irradiation exhibited a good synergistic effect for improving the wear resistant and tribological properties of UHMWPE material.
To further improve and enhance the performances and properties of polyvinyl acetate (PVAc), montmorillonite (MMT) and N-hydroxymethyl acrylamide (NMA) were introduced together to polymerize with vinyl acetate (VAc). The exfoliated nanocomposite of PVAc–NMA–MMT was prepared through different synthesis precursors. Linear macromolecular chains of PVAc–NMA were formed in MMT layers. MMT was exfoliated into layers or sheets of nanoparticles and dispersed randomly in PVAc–NMA matrix. Both PVAc–NMA and MMT had small particles with a diameter of 50–100 nm. They dispersed together randomly. PVAc–NMA–MMT was a pseudo-plastic non-Newtonian fluid and possessed the normal stress effect (or Weissenberg effect from the pole-climbing phenomenon. With the change of different synthesis precursors and the increase of NMA content and MMT content in the synthesis system, the molecular weight of PVAc–NMA–MMT increased. PVAc–NMA–MMT had good dispersion, excellent storage stability and high static tensile at 6.47–6.85 MPa.
The organically modified montmorillonite (OMMT)-filled polyamide 6 (PA6) nanocomposites were toughened with epoxidized natural rubber (ENR). The PA6, ENR (15–30 wt%) and OMMT (4 parts per hundered (phr)) were melt compounded using counterrotating twin-screw extruder followed by the injection molding. X-ray diffraction (XRD) results indicated that the OMMT platelets in PA6/ENR/OMMT nanocomposites were well dispersed. The Fourier transform infrared (FT-IR) spectra showed graft esterification reaction between PA6 and ENR during processing. It was found that the addition of ENR (up to 20% wt) increased the impact strength and elongation at break of the nanocomposites. Scanning electron microscopy (SEM) images revealed well-dispersed ENR particles. Differential scanning calorimetry (DSC) results showed that the presence of ENR and OMMT had negligible effect on the glass transition of PA6 with a slight decrease in crystallization temperature and crystallinity in PA6/ENR/OMMT nanocomposites.
In this study, we evaluated dimensional stability and some mechanical properties of polypropylene composites filled with chestnut shell flour (CSF). To meet this objective, CSF was compounded with polypropylene with and without coupling agent in a twin screw corotating extruder and then were manufactured by injection molding process. The thickness swelling and water absorption of the samples increased with increasing CSF content. The flexural and tensile modulus improved with increasing CSF content, while the flexural and tensile strengths of the samples decreased. The use of maleic anhydride polypropylene had a positive effect on the dimensional stability and mechanical properties of the polypropylene composites filled with CSF. This work showed that the composites treated with maleated polypropylene could be efficiently used as decking products, due to high-dimensional stability and satisfactory mechanical properties of the composites.
In this study, composites were produced using alkali-treated kenaf fibre and recycled polypropylene to improve the interfacial bonding between them. Maleic anhydride grafted polypropylene was used at a ratio of 1:10 to the fibre as a coupling agent. Blends are mixed together by means of a twin screw extruder and test specimens for mechanical testing were prepared through injection moulding machine. Fibre density, tensile property, elemental analysis, structural and morphological changes due to treatment was observed and their effects on the properties of the formulated composites were analyzed. Characterization of the composites was done by the tensile, flexural, impact and melt flow index tests. Thermogravimetric analysis and differential scanning calorimetry analysis were carried out to evaluate the thermal properties of the composites. Experiment showed that best tensile strength (TS) was found at 40% loading of fibre and alkali treatment of fibre enhanced the TS by 57%. Activation energies were calculated through Broido’s equation. It was also found that recycled polypropylene degrades at one stage, while composites degrade at two stages. Incorporating fibres decrease the activation energies of the composites but both coupling agent and treatment of fibres in that case enhance activation energies by 11 kJ mol-1 and 29 kJ mol-1, respectively, in the second stage. Field emission scanning electron microscope of the fractured surface showed that treatment of fibre improves the interfacial bonding between fibres and matrix. Density and water uptake of the composites were also studied in this study.
Chitosan-reinforced starch-based biodegradable composite films were prepared by solution casting. The chitosan content in the films was varied from 20% to 80% (w/w). Tensile strength (TS) and tensile modulus (TM) of the starch-based composites were improved significantly with the addition of chitosan. Water vapor permeability (WVP) and oxygen transmission rate (OTR) of chitosan-reinforced starch-based films showed a significant reduction compared to native chitosan film and indicated better barrier properties to water vapor and oxygen. The water uptake of the films pointed out better hydrophobic character due to the incorporation of chitosan in starch-based films. Thermal stability was also found to increase with the addition of chitosan in starch-based films and was confirmed by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Fourier transform infrared (FT-IR) spectroscopy supported the molecular interactions due to the reinforcement of chitosan in starch-based films. Surface and interface morphologies of chitosan film and starch/chitosan composite film were examined by scanning electron microscope (SEM) and suggested sufficient homogenization of starch and chitosan in the biodegradable composite films.
Polymer blending has attracted wide concern for modification of polymer materials especially in the tribological field. In this article, the structure, mechanical and tribological properties were investigated carefully for the polyamide-6-based composites blended with polyphenylene sulfide (PA6-PPS). It was found that the composites were partially miscible, and the modulus of PA6 was improved apparently with the addition of PPS. The average friction coefficient of PA6-PPS composites decreased as the content of PPS increased at the stable stage. The friction coefficients and wear rate of the PA6-PPS composites increased under higher load, while the friction coefficient decreased and the wear rate increased at higher sliding speed. Besides, scanning electron micrograph of worn surface morphology revealed the primary wear mechanism of PA6-PPS composites gradually transformed from the micro-cutting wear to adhesive wear and abrasive wear.
This study presents the experimental characterization of new thermoplastic elastomers that comprised polypropylene and waste tire rubber (WTR). The processing was investigated to obtain standard tensile test samples. Particles and matrix compatibilization has been examined and the melt flow index was found to be a suitable way to determine the best ratio of compatibilizer. Additionally, standard mechanical tests were done on selected blends that have convenient compatibilizer concentration. Dynamic mechanical analysis tests have been carried out and storage modulus and loss factor were drawn as function of temperature. Influence of WTR concentration has been examined through quasistatic tensile tests ( = 10-4, 10-3, 10-2 s-1). X-Ray tomography has been used to visualise the postmortem fracture surfaces as well as the internal microstructure of the samples. Image analyses have been performed via an in situ device in order to follow the damage process of the samples occurring under tensile stress in this type of composite.
Composite materials are produced using thermoplastic starch reinforced with cellulose microfibrils. The cellulose microfibrils are isolated from two different sources and their reinforcement capacity was evaluated. Vegetable cellulose (VC) microfibrils are isolated from vascular bundles of banana rachis, while bacterial cellulose (BC) microfibrils are produced by Gluconacetobacter genus bacteria using pineapple peel juice as the culture media. For this study, both the materials were obtained from Colombian agroindustrial wastes. Composite films were characterized using different techniques, including mechanical tensile testing, attenuated total reflection Fourier transform infrared spectroscopy, and thermogravimetric analysis. The purpose of this study is to assess the effect of different processing methods and cellulose microfibrils content in the composite material behavior. The results showed that the mechanical properties were increased when cellulose microfibrils were added before gelatinization. Significant increments in Young’s modulus and tensile strength of both VC and BC composites were obtained with respect to starch matrix.
Biopolymers and their composites are one of the best alternatives for replacing petroleum-based plastic commodities. The main drawback of biopolymer is its high cost that restricts its applications; however, biopolymers filled with natural fibers are able to reduce cost but suffer lower impact strength and fracture toughness. Nanoclay which has a very high aspect ratio shows a significant effect on mechanical and thermal properties. This article concentrates on hybridization of nanoclay and natural fibers. Mechanical properties show that with the addition of nanoclay, impact strength increases more than 50%; however, other mechanical properties are also increased, which are proved by fractography analysis. Thermal analysis shows that hybrid biocomposite exhibits higher storage modulus, decomposition temperature and higher percentage of crystallinity. Fourier-transform infrared (FT-IR) analysis confirms formation of new bond between nanoclay and polymer matrix which is the main reason for improving thermal and mechanical properties of the hybrid biocomposite.
Shape-memory polymer–magnetite (Fe3O4) composite samples were prepared by extrusion compounding and injection molding. Thermal diffusivity, conductivity and specific heat capacity were measured from 290 K to 340 K. Increasing filler fraction decreases specific heat capacity and increases thermal diffusivity. Experimental results show a good agreement with Agari–Uno and Hashin–Shtrikman models but not with Bruggeman model. The interconnectivity of the particles is very poor. Agari–Uno model leads to a high influence of polymer on thermal properties. Below 350 K mainly the polymer and above 350 K mainly the Fe3O4 influences specific heat capacity that shows drastic changes around 310 K (recovery temperature) and 357 K.
This article presents an experimental study on the effect of polymeric matrix flow behavior on the properties of the reprocessed wood–plastic composites (WPC) of high-density polyethylene (HDPE) and wood sawdust. WPCs are considered as sustainable materials due to their durability in the environmental conditions and recyclability. Three grades of HDPE were utilized as polymeric matrix with different melt flow indices (MFIs). Composites containing 60 wt% of sawdust were manufactured via a twin-screw extruder to produce 15 mm rod-shaped profiles (named here as virgin WPCs). In reprocessing, the produced WPC profiles were then ground to obtain WPC granules and then reprocessed (reextruded) via the same extruder. The mechanical properties of both the virgin and the reprocessed profiles were obtained from the bending tests and tensile tests, and the physical tests including water uptake and density measurements were also carried out. Interestingly, reprocessed composites produced with the low and middle MFI HDPE showed an increase in mechanical properties compared with the virgin ones, while for the composites with the high MFI HDPE, opposite result was observed. Water uptake measurement also indicated the best performance of the composites produced with the middle MFI HDPE.
Conductive polymer composites are at the forefront of composites science research because of the huge number of applications that have been developed around their interesting and unique properties. The present article is focused on the fabrication of natural rubber/polyaniline (NR/PANI) compounds for electromagnetic wave shielding applications at microwave frequency. Their microstructures were examined by means of scanning electron microscopy and thermogravimetric analyses. The as-fabricated NR/PANI composite was mechanically characterized to investigate the effect of dispersion of PANI on NR matrix composite. The dielectric spectroscopy, absorption loss, and reflection loss of NR/PANI composite in the frequency range from 1 to 12 GHz have been performed. The total electromagnetic interference shielding effectiveness by absorption and reflection loss depends on PANI content in the composite. Results show that the NR/PANI composite represents a new class of conducting lightweight material that makes the NR/PANI with good electromagnetic shielding effectiveness that is suitable for use in industrial application such as electronic conducting composite in polymer package and for radar absorbing materials.
This article presents a comparative study on the effects of using nano α-alumina (Al2O3) on toughening mechanisms and structural behaviors of polypropylene (PP) nanocomposites. The role of using dispersant in nanocomposite preparation was also investigated. For nanocomposite preparation, mixing of the elements was performed using a Haake Poly Drive blending machine at 175°C and the rotor speed of 50 rpm. The notched Izod impact energy obtained for PP was about 27 J/m and by the addition of nano α-Al2O3 (4 wt%) to PP, the notched Izod impact energy increases up to ~43 J/m. However, higher concentration of nano α-Al2O3 in the nanocomposite resulted in the reduction of Izod impact property due to nano α-Al2O3 agglomeration. Fourier transform infrared spectroscopy (FTIR) spectra of pure PP and PP/nano α-Al2O3 composites demonstrated Al–O bond at 568 cm-1 for nanocomposite spectrum that indicates the creation of nano α-Al2O3 particles. The x-ray diffraction patterns and FTIR spectra of PP/nano α-Al2O3 composites showed that the intensity of the peaks when dispersant was used slightly increased and the arrangement of the peaks are normalized. This observation is attributed to homogeneous dispersion of nano α-Al2O3 filler in the matrix when dispersant was used. Scanning electron micrograph of impact fractured surface showed that the fracture surface of PP/nano α-Al2O3 composite becomes rougher with increasing the content of filler.
Thin films of poly(ethylene oxide) (PEO) doped with sodium iodide (NaI) were prepared by casting method. The films have an average thickness of 70 µm and contain different NaI concentrations, that is 1, 2, 4, 6, 8, 10, and 15% by weight (wt%). The dielectric constant, alternating current (AC)-conductivity, and thermal conductivity of the electrolytic composites were studied as a function of applied frequency, temperature, and NaI concentration. The AC conductivity and dielectric constants were determined from the impedance data, and the thermal conductivity was measured using the transient electric pulse method. It was found that the dielectric constants and AC conductivity increase with increasing temperature and NaI concentration. The percolation threshold of the observed AC conductivity occurs at about 1 wt% NaI dispersed in the PEO matrix. The charge transfer in the electrolytic films is dominated by ions transport and creation of more localized energy states due to high amorphous phase in the solid electrolyte. The formed iodide complexes also contribute in increasing the AC quantities. It was found that the thermal conductivity of the polymer electrolyte films increases with both temperature and NaI concentration. Empirical models were used to describe the dependence of electrical and thermal conductivities on the dopant content, frequency, and temperature.
The possibility of assembling through welding is one of the major features of thermoplastic composites and it positively contributes to their cost-effectiveness in manufacturing. This article presents a comparative evaluation of ultrasonic, induction and resistance welding of individual carbon fibre-reinforced polyphenylene sulphide (PPS) thermoplastic composite samples that comprises an analysis of the static and dynamic mechanical behaviour of the joints as well as of the main process variables. The induction welding process as used in this research benefitted from the conductive nature of the reinforcing fibres. Hence, no susceptor was placed at the welding interface. Resistance welding used a fine-woven stainless-steel mesh as the heating element and low welding pressures and times were applied to prevent current leakage. Triangular energy directors moulded on a separate tape of PPS resin were used to concentrate ultrasonic heat at the welding interface. The static single-lap shear strength of the joints was found similar for induction and ultrasonic welding. A 15% drop in the static mechanical properties of the resistance welded joints was attributed to incomplete welded overlaps following current leakage prevention. However, the fatigue performance relative to the static one was similar for the three sorts of joints. A comparative analysis of process variables such as welding time, required power and energy was also carried out.
In this article, Hansen solubility parameters (HSP) have been used to evaluate the dispersion state and interfacial strain transfer ability of purified, nitric acid-functionalized and octadecylamine-functionalized single-walled carbon nanotubes (SWNTs) as the reinforcing materials in a poly(vinylidene fluoride) (PVDF) matrix. Composites were prepared by solution blending of PVDF and SWNTs and injection molding. The observations of the dispersion were obtained by dynamic light scattering and light optical microscopy and compared with the HSP results. The interfacial strain transfer between the polymer matrix and the carbon nanotubes in SWNTs/PVDF composite was studied by measuring the shift of the Raman two-dimensional peak position under tension. It was found that the strain transfer is affected by the degree of homogeneity of the fillers in the composites, the carbon nanotube bundle size and the affinities between two materials.
In this study, the effect of organomodified montmorillonite (OMMT) on the acoustic properties and clay dispersion of polypropylene (PP)/wood flour (WF) composites was investigated. To meet this objective, the blend composites were prepared through the melt mixing of PP/WF at 50% weight ratios, with various amounts of OMMT (0, 3, and 6 per hundred compounds (phc)) in hake internal mixer then the samples made by injection molding. The amount of coupling agent was fixed at 2 phc for all formulations. The acoustic properties such as speed of sound propagation, time of sound propagation, and sound energy absorbance were evaluated. Results indicated that the time of sound propagation and sound energy absorbance of composites increased with increase in OMMT. However, the speed of sound propagation decreased with the increase in OMMT loading. Also, the biggest improvement of the tensile modulus can be achieved for the nanoclay loading at 3 phc. X-Ray diffraction patterns and transmission electron microscopy revealed that the nanocomposites formed were intercalated. Also, morphological findings showed that samples containing 3 phc of OMMT had higher order of intercalation.
The generation of wear particles from the ultra-high-molecular-weight polyethylene (UHMWPE) counter-face of metal sliding pair is relatively high. These polyethylene wear particles lead to osteolysis and that result in the failure of the implant made with the sliding pair. Hence, an investigation has been carried out to enhance the wear resistance of UHMWPE by argon plasma surface modification of UHMWPE. Results show the argon plasma-treated UHMWPE gains high crosslink, which provides less adhesive force interactions between the materials. Thus, a lower value of steady state coefficient of friction can be obtained.
Mechanical and tribological properties of polymethyl methacrylate (PMMA) composites filled with titanium oxide (TiO2) were studied with particular interest on the HCl surface treatment. Increasing the TiO2 content in the PMMA matrix from 1 wt% to 7 wt% resulted in improved tensile strength and then decreased. The tensile and tribological properties show the optimum TiO2 content is obtained at 3 wt%. HCl treatment largely improved the friction and wear of TiO2/PMMA composites. Scanning electron microscope (SEM) investigation of worn surfaces of PMMA composites showed that HCl-treated TiO2/PMMA composite had strong interfacial adhesion and smooth worn surface under given load.
Binary and ternary composites composed of high-density polyethylene (HDPE), boehmite alumina (BA) and different kinds of natural and animal fibers, such as flax, sponge gourd, palm and pig hair (PH), were produced by hot press technique. Aqueous BA suspensions were sprayed on the HDPE/flax mat to prepare nanoparticle/natural fiber–reinforced ternary polymer composites followed by drying. The dispersion of the natural and animal fibers and BA particles in the composites was studied by scanning electron microscopy and discussed. The thermomechanical and stress relaxation properties of the composites were determined by the thermogravimetric analysis, dynamic-mechanical thermal analysis and short-time stress relaxation tests (performed at various temperatures), respectively. The HDPE-based composites were subjected to water absorption and instrumented falling weight impact tests. It was found that all the composite systems increased the stiffness and stress relaxation and reduced the impact toughness. The stress relaxation modulus of natural and animal fiber composites was higher compared with that of the neat HDPE. This modulus increased greatly with incorporation of BA. The relaxation master curves were constructed by applying the time–temperature superposition principle. The inverse of Findley power law could be fairly applicable to describe the relaxation modulus versus time traces for all systems studied. Incorporation of BA particles enhanced the thermal resistance, which started to degrade at higher temperature compared with the HDPE/flax mat composite. The HDPE/flax mat/BA composite could reduce the water uptake.
In order to improve the tribological properties of poly(methyl methacrylate) (PMMA) frictional parts, nano-silica (SiO2) and -titanium dioxide (TiO2) particle-reinforced PMMA composites were prepared by hot press. The tribological behavior and wear mechanisms of the composite were investigated in dry friction condition. The results show that great strengthening effects are obtained using nano-SiO2 and -TiO2 particles to reinforce PMMA composite. The composite exhibits excellent tribological properties. The wear mechanisms change from microcutting wear, multiplastic deformation wear and adhesive wear into abrasive wear and brittle fracture wear.
The objective of this work is to improve the interlaminar shear strength and tribological properties of the high-density polyethylene (HDPE) composites by oxidation treatment method of carbon fiber (CF) and ultraviolet irradiation of HDPE. The morphologies of untreated and treated CFs were characterized by x-ray photoelectron spectroscopy. Surface analysis showed that after treatment, the surface of CFs chemisorbed oxygen-containing groups, active carbon atom, the surface roughness, and wetting ability were increased. The results show that the treated CF composites can possess excellent interfacial properties and tribological properties accordingly after treatment.
Wood–plastic composites (WPCs) have been proposed as an alternative to natural wood due to their physical and mechanical properties. Development of these composites from natural fibers is receiving widespread attention partly because of growing environmental awareness. To dispose of produced waste from industry, low-value fiber resources could be converted into high-value products. This research studies the combination of polyvinyl chloride (PVC) to rubberwood (RBW) fiber, to palm oil trunk fiber, and to palm oil shell (POS) fiber. Composite performance optimization, material option comparison, basic engineering performance improvement, and durability of WPCs have been investigated. A two-stage process consisting of compounding and forming to produce WPCs using 40%–60% natural fiber reinforcements was carried out. Physical and mechanical properties of the WPCs were studied. The results showed that WPCs consisting of 60% RBW fiber and 40% PVC yielded the highest modulus of elasticity and modulus of rupture, which are approximately 90,130 MPa and 433 MPa, respectively. The ultimate compressive strength with a value of approximately 316 MPa was achieved from 60% POS fiber and 40% PVC. Reinforcing 40% POS fiber in 60% PVC exhibited the lowest water absorption rate. The overall result indicates an improvement of engineering performance, making better use of industrial wastes and indirectly assists environmental conservation endeavor along the process.
Spherical iron silicon (FeSi) particles and irregular shaped magnetite (Fe3O4) particles with particle sizes ≤146 μm and varying volume filler fractions up to x = 0.7 (70 vol%) were mixed with polypropylene (PP) matrix. The samples were prepared by kneading and injection moulding and show particle–particle interaction at elevated filler fraction of x ≥ 0.5. Thermal and magnetic properties of the composites were characterized and show a significant increase at filler fractions of x ≥ 0.3. The thermal conductivity of PP (0.176 W/(m K)) was increased up to seven times to 1.239 W/(m K) at x = 0.7. FeSi-filled composites show slightly higher values of thermal conductivity than Fe3O4-filled composites. The magnetic permeability of the composites rise from 1 for PP to a maximum value of 23.1 for PP/FeSi composites at x = 0.7. The nonlinear increase in the thermal conductivity corresponds with the lower boundary of the Hashin–Shtrikman model. The Bruggeman model can be applied to describe the nonlinear increase in the magnetic permeability. Magnetic permeability increases with mean particle diameter as well as magnetic coercivity and loss dissipation increases with inverse mean particle diameter.
The results of in-plane shear tests performed on 5-hardness satin woven carbon/polyphenylene sulphide and polyetheretherketone thermoplastic prepregs are described in this article. The experimental analyses are based on bias-extension tests performed in an environmental chamber. The results are given for different temperatures on both sides of the melting point. This range of temperature is that of the part during a thermoforming process. The effect of displacement rate is also investigated. The results are given both as load versus displacement curves and as shear-moment versus shear-angle curves. The latter data can be directly used in a thermoforming simulation code. It is shown on a forming simulation example that the temperature and the related change of the shear behaviour have strong consequences on the final composite part. In particular, wrinkles can develop when the process temperature is too low.
Styrene butadiene rubber (SBR) friction materials containing different carbon fiber (CF) content were prepared using molding process. The effects of CF content on mechanical property, friction performance and wear rate were studied. Worn surfaces of samples were analyzed by scanning electron microscope. The results show that with increasing fiber content, the tensile strength decreases first and then presents an increment trend. Both the friction coefficient and wear increased with load, and the low molecular weight polybutadiene liquid rubber graft maleic anhydride (LMPB-g-MAH)-treated fiber shows lower friction coefficient and wear. LMPB-g-MAH-treated CF/SBR composite was used for some components or parts of machines in chemical engineering, textile engineering, food processing, paper making industry, pharmacy, transportation engineering, agricultural engineering as well as coal and ceramic production.
Development of novel injection moldable materials that are thermally conductive but electrically insulative are important for the continuous advancement in modern electronics. In this context, this article details the fabrication and characterization of polymer–matrix composites (PMC), which consists of linear low-density polyethylene matrix, and filled with either silicon carbide or hexagonal boron nitride. Experimental results indicated that the addition of ceramic fillers not only promoted the PMCs’ effective thermal conductivity without compromising their electrical resistivity but also resulted in the reduction of coefficient of thermal expansion and improved mechanical properties.
A novel dry phantom nanoconducting composite that can simulate the effect of electromagnetic wave on human tissues composed of graphite/nickel (GN) nanoparticles and polyvinyl chloride (PVC) was successfully fabricated. The morphology of as-synthesized graphite nanosheets and PVC/GN composites was investigated by means of scanning electron microscope. Dielectric parameters such as relative permittivity, imaginary permittivity, and alternating current conductivity are evaluated in the frequency range of 0.5–12 GHz. The results are compared with the in vitro equivalent human tissue data and good agreement is reported. The absorption and reflection coefficient as a function of frequency of nanocomposites were also studied. The novel PVC/GN nanocomposites have potential applications for dry phantom and the coupling media in microwave medical imaging.
In this work, the fracture and thermal behaviour of environmentally friendly composites based on polypropylene (PP), an olefin block copolymer (OBC) and ash from biomass combustion was investigated. PP/OBC/ash composites with different ash contents and 10 wt% OBC were prepared by extrusion followed by compression moulding. Ash particles were treated with a silane coupling agent before blending to promote interfacial adhesion between polymer matrix, OBC and ash. An approach to fracture mechanics was investigated and showed that the fracture parameters increased when OBC was used. Fracture surface analysis by scanning electron microscope revealed that the presence of OBC promotes the material ductile failure and that one of the main failure mechanisms was fibrillised debonding of ash particles encapsulated by OBC from the matrix and its subsequent elongation around them. Free OBC inclusions distributed within the PP matrix would have also induced toughening in the composites investigated. The crystalline state of PP analysed by differential scanning calorimetry is clearly modified by the presence of ash particles, increasing the crystallisation rate and the crystallinity degree of the matrix due to the nucleating effect of the filler. However, the presence of the copolymer counteracted these effects and the PP crystalline state remained practically unchanged in the composites with OBC. Finally, environmentally friendly composites with significantly higher toughness than the matrix or binary PP/ash composites were obtained by introducing an OBC copolymer in the formulation.
Polyurethanes (PURs) synthesized using hexamethylene diisocyanate (HDI) and polyethylene glycol with molecular weights of 400 g mol-1 and 600 g mol-1 (PUR 400 HDI and PUR 600 HDI) or polyoxypropylene diol (POPD) of molecular weights 1002 g mol-1 and 2002 g mol-1 (PUR 1002 HDI and PUR 2002 HDI) were used as modifiers for diglycidyl ether of bisphenol A. It was found that maximum improvement in impact strength and critical stress intensity factor (KC) values was obtained for compositions containing 15% PUR 400 and 5% PUR 1002. Such improvement in the resistance to crack propagation due to PUR incorporation might be related with the soft segments of polyethylene glycol and POPD. The critical stress intensity factor (KC) values increased from 1.7 MPa m1/2 (virgin epoxy) to 2.5 MPa m1/2 with the addition of 10% PUR 400. Fourier transform infrared spectra confirmed the formation of an interpenetrating polymer network structures with polymeric modifier. Scanning electron micrographs of epoxy resins (EPs) modified with PUR with longer chains (PUR 1002 and PUR 2002) exhibited a deformed leaf-like morphology with larger plastic deformation zones with the presence of microcracks. However, EP/PUR based on polyethylene glycol showed less deformed structure.
Wood polymer composite (WPC) was prepared using solution-blended high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), poly(vinyl chloride) (PVC), wood flour (WF) and polyethylene-co-glycidyl methacrylate (PE-co-GMA). The effect of nanoclay, SiO2 and ZnO addition on the properties of the composite was examined. The distribution of silicate layers, SiO2 and ZnO nanopowder was studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The improvement in miscibility among polymers was studied by scanning electron microscopy (SEM). Fourier transform infrared spectroscopic (FTIR) studies reveal the interaction between polymer, wood, clay, SiO2 and ZnO. WPC treated with 3 phr each of clay, SiO2 and ZnO showed an improvement in mechanical properties, thermal stability and a decrease in water uptake capacity.
Conducting polythiophene (PTP)/Na-montmorillonite (Na-MMT) composites have been prepared by intercalative polymerization. The synthesized composites are characterized by Fourier transform infrared spectroscopy, x-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM), and thermal analysis. XRD and TEM images showed that the PTP was intercalated into the clay layers. The thermogravimetric analysis and the differential thermal analysis revealed the introduction of Na-MMT results in thermal stability of composites with respect to pure PTP. Furthermore, adsorptive properties, the moisture retention, and water uptake values of composites were investigated. Conductivity behavior of composites was also studied.
A method is presented for qualitative assessment of nanoclay dispersion in a polymeric matrix, which is based on the effect of nanoclay dispersion on the thermal stability of polymer/nanoclay (PNC) systems. The method offers a fast, inexpensive macroscopic evaluation of nanoclay dispersion, which can be used for direct comparison of nanoclay dispersion in PNC samples. Using experimental design, it is also possible to discover material or process conditions that lead to desirable nanoclay dispersion. Furthermore, this method can be employed for confirmation purposes in support of other nanoclay dispersion assessment techniques. We proved this finding by means of six different independently obtained pieces of information on the quality of nanoclay dispersion in the samples, which are x-ray diffraction, atomic force microscopy, transmission electron microscopy, gas permeability, as well as mechanical and rheological measurements. We believe this method could be employed to study nanoclay dispersion in thermoset matrices as well, for which utilizing other techniques may be either unfeasible or difficult; therefore, this method could present an alternative for assessing nanoclay dispersion in this class of polymeric materials.
The mechanical and friction and wear behaviors of carbon fiber/polyphenylene sulfide (CF/PPS) composite and polyamide 6 (PA6)-filled CF/PPS (CF/PA6/PPS) composites were investigated. The addition of 2 vol%, 4 vol% and 6 vol% PA6 increases the bending strength of CF/PPS composite. In order to further understand the wear mechanisms, the worn surfaces of samples were analyzed by scanning electron microscopy (SEM). The experimental results indicated that the wear loss and the friction coefficient of CF/PPS composite decreased with the addition of PA6 particles. The main wear mechanisms under dry sliding condition are the plastic deformation and mechanical microploughing.
The ethylene vinyl acetate (EVA), high-density polyethylene (HDPE), compatibilizer (maleic anhydride-grafted polyethylene (MA-g-PE)) and organophilic montmorillonite (OMMT) clays were added in different sequences in a corotating twin screw extruder followed by injection molding. Montmorillonite clay was modified by octadecylamine and aminopropyltriethoxysilane to make it organophilic. The thermal behavior was characterized by thermogravimetric analysis and differential scanning calorimetry (DSC). The influence of blending HDPE with EVA on the thermal properties of EVA/HDPE blends was investigated. The effect of MA-g-PE and nanoclay on the thermal properties of EVA/HDPE blend and modified EVA/HDPE blends, respectively, were also investigated. The blends show two distinct unchanged melting peaks corresponding to the individual components of the blend. The addition of nanoclay improves the thermal properties of nanocomposites. The results of DSC behavior of the nanocomposites indicate that melting temperature (Tm) and melting enthalpy (Hm) of the HDPE phase of the nanocomposites are lower than those of the neat EVA/HDPE blend. Although crystallization temperature (Tc) of the nanocomposites is higher than the neat EVA/HDPE blend, it is observed that the incorporation of 4 phr clay loading into nanocomposites improves the thermal stability.
Two types of nanosilica-based urea–formaldehyde (UF) hybrid materials with formaldehyde to urea (F/U) ratio (0.8) were synthesized without (UF + SiO2) and with coumarin (4-chloro-3-nitro-2H-chromen-2-one). Obtained composites have been irradiated (50 kGy) and their radiation stability was evaluated on the basis of thermal behavior before and after irradiation. The thermal properties of materials were studied by nonisothermal thermogravimetric analysis, differential thermal gravimetry, differential thermal analysis and differential scanning calorimetry supported by data from infrared spectroscopy. The free formaldehyde percentage was determined for all prepared samples. The shift of temperature values for selected mass loss to a high temperature indicates the increase in thermal stability of materials with coumarin after -irradiation. The free formaldehyde percentage was reduced after irradiation from 15% to 3% for sample without coumarin and from 7% to 4% for sample with coumarin. The asymmetric stretching vibrations of –N–CH2–N– absorption band and as(Si–O) of siloxane or silicone in FTIR spectra of irradiated coumarin compound are shifted to higher wave number values and confirmed its higher thermal stability.
The effect of processing conditions, nucleating agent and compatibilizer on the crystallinity, mechanical property and oxygen permeability of polypropylene was studied using differential scanning calorimetry, x-ray diffraction, thermogravimetric analysis and universal tensile testing. The as received polymer had much lower extent of crystallinity, which was enhanced to 58% by the processing and molding using either slow cooling or fast cooling conditions. Although the overall crystallinity was not affected by the rate of cooling, the crystallization behavior was, however, affected as indicated by different onset and peak crystallization temperatures as well as different crystallite sizes indicated by the differences in oxygen permeation and mechanical performance of the polymer. Nucleating agent further enhanced the extent of crystallinity (crystal plane peaks were shifted and broadened) and tensile modulus, but the polymer was observed to become brittle and had higher gas permeation through it. The compatibilizer, on the other hand, reduced the tensile modulus, but enhanced the yield strain owing to matrix plasticization and retained the similar oxygen permeation as the polymer. The temperature used during processing also affected the oxygen permeation and mechanical property as the high temperature may induce partial polymer degradation resulting in the reduction of molecular weight and deteriorated properties.
Composites can be produced by combining different materials according to different targets. In this study, woven-type E-glass fiber with a 500 g/m2 unit-area weight has been used as a reinforcement material. Resin, hardener and accelerator have been used as the matrix materials. The dimensions of compression test sample molds were Ø50 mm x 100 mm. Starting from the center toward the outer diameter, spirally wound fibers have been placed into molds with intervals ranging from 1 mm to 9 mm. Composite materials have been prepared at room temperature by applying vibration to the casting method. Compression tests have been carried out on a total of 27 samples, as 3 samples per dimension. It has been determined that the compressive strengths of the polyester resin composites reinforced with spirally wound fiberglass changes per the spiral geometry. The highest compressive strength and density value have been obtained from the samples prepared with intervals of 1 mm. Compressive strength and density value curves have exhibited similar tendencies.
Five different maleic anhydride grafted polypropylene (PP) coupling agents (CAs) have been tested in wood polymer composites with wood contents of 40% and 60%. The tested CAs cover a wide range of backbone molecular weight (Mw 55–181 kDa) and also vary in MA graft level (0.5–1.5%). Furthermore, one PP copolymer-based product is among them. Mechanical properties (flexural strength, impact strength and heat deflection temperature) and water absorption (WA) have been evaluated as responses. Finally, dynamic rheological measurements on several compounds have been performed. The results show that the backbone polymer structure of the CA is the most important factor for its efficiency. Molecular weight seems to have an influence on WA properties. As regards to rheological measurements, a lubricant-like effect of a CA indicates a reduced capability for compatibilization at the interface.
This research explores the effects of chemical foaming agent and nanoclay on the long-term water absorption and cell morphology of wood–plastic nanocomposites. To meet this objective, the nanoclay, high-density polyethylene, and coupling agent were compounded and then granulated and were mixed with wood flour and blowing agent in a twin-screw extruder. Consequently, foaming process was completed in injection stage. The amount of wood flour was fixed at 50 wt% for all the samples. For nanoclay and chemical blowing agent, different levels of 0, 2 and 4 per hundred resins (phr) and 0, 0.5, 1 and 1.5 phr were considered, respectively. The long-term water absorptions of samples were evaluated by immersing them in water for several weeks, and water diffusion coefficients were also calculated by evaluating the water absorption isotherms. Results indicated that the water absorption, cell size, and average cell density of composites increased with increase in chemical foaming agent loadings. However, by the addition of nanoclay to wood–plastic composite foams, the water absorption and cell size decreased and their cell density increased. Scanning electron microscopy confirmed that the chemical foaming agent and nanoclay contents had significant influence on density reduction in foamed composites. X-Ray diffraction patterns revealed that the nanocomposites formed were intercalated. The mechanism of water absorption of the foamed wood–plastic nanocomposites under study followed the kinetics of a Fickian diffusion process.
Synergistic stabilizing effect of layered double hydroxides (LDHs) with micro- as well as nano-sized calcium carbonate (CaCO3) on thermal stability of polyvinyl chloride (PVC) was studied and evaluated. Nano-sized CaCO3 was prepared in the laboratory by matrix-mediated growth and controlled (in situ deposition) technique. Crystal size of nano-CaCO3 was estimated by studying x-ray diffraction pattern. The PVC composites were prepared using Brabender Plastograph instrument. Various formulations were prepared by taking fixed amount of LDH and varying the concentration of micro-/nano-sized CaCO3. PVC sheets of 1 mm thickness were prepared on compression molding machine. Thermal stability in terms of thermal degradation was studied by thermogravimetric analyzer. Surface morphology and mechanical property were studied using scanning electron microscopy and universal tensile machine. Increase in the onset temperature of the PVC sheets was considered as imparting a better thermal stability to PVC. Better synergistic effect on the stabilization of PVC was observed in case of LDH with nano-sized CaCO3 and compared with micro-sized CaCO3.
Monodisperse polystyrene (PS) nanoparticles with a size of 190 nm were first synthesized by emulsion polymerization. Then PS/titanium dioxide (TiO2; core/shell) nanocomposite particles were prepared by coating TiO2 nanoparticles on the surface of the PS nanoparticles using aqua ammonia/triethanolamine as the positive/negative catalyst pair. Roughness degree of the surface of the shell of the PS/TiO2 nanocomposite particles increased with increasing amounts of aqua ammonia or triethanolamine. Morphology of the surface of the TiO2 shell can be regulated by changing the amounts of aqua ammonia and triethanolamine synchronously. The PS/TiO2 nanocomposite particles obtained at 2.00 g/0.10 g, 3.00 g/0.20 g and 5.00g/0.40 g of aqua ammonia/triethanolamine showed good morphology of the surface of the TiO2 shell. Roughness on the surface of the TiO2 shell was remarkably heightened when the reaction temperature of the hydrolysis and condensation process was increased from 50°C to 70°C.
Blends of thermoplastic low-density polyethylene (LDPE) with bromobutyl rubber (BIIR) with varying ratios have been prepared. Vulcanization of prepared blends has been induced by gamma ionizing radiation of varying doses of up to 250 kGy. Physical properties, namely gel fraction percentage, and mechanical properties, namely tensile strength, tensile modulus at 50% elongation, percentage elongation at break, hardness and permanent set have been followed up as a function of irradiation dose and blend compositions. Moreover, measurements of thermogravimetric analysis and heat shrinking properties have been carried out. The results indicated that blending with LDPE has improved the properties of BIIR rubber. Moreover, the presence of BIIR enhances the heat shrinking properties of the obtained blends.
A prospective method for manufacturing thermoplastic composites involves commingling to produce hybrid yarn consisting of two components: reinforcement fibres and thermoplastic matrix. In this work, various types of commingled hybrid yarns were developed to improve blend uniformity and achieve homogeneous filament distribution in two-component hybrid yarns. An experiment was carried out to examine the distribution of filaments in a series of glass/polypropylene commingled hybrid yarns. The influence of changes in process parameters such as the degree of overfeeding, production speed, and air pressure on the filament distribution in the cross-section of commingled hybrid yarns was investigated. In this study, new technological approaches to achieve blend uniformity in commingled hybrid yarns are developed. The radial distribution index and a new blending coefficient were used to evaluate the blending uniformity of the yarns.
Polyethylene (PE)/clay nanocomposites were prepared by melt mixing using PE grafted with maleic anhydride (PEg) as compatibilizer. Concentrations between 2 and 15 wt% of an organophilic montmorillonite (MMT) and concentration ratios of 1:1, 2:1 and 3:1 of PEg/MMT were employed. The materials were characterized using X-ray diffraction, scanning electron microscopy (SEM) and thermogravimetry. The SEM images show that the presence of PEg results in a large degree of exfoliation at all clay concentrations. For 5 wt% MMT, the best degree of exfoliation is obtained for a 2:1 ratio of PEg/MMT. This ratio results in higher increase in the elastic modulus, mainly at low frequencies, with respect to that of the corresponding matrix. As the clay concentration increases, for a 2:1 ratio of PEg/MMT, the dynamic moduli increase showing pseudo solid-like behavior at clay concentrations higher than 8 wt%. Moreover, the nanocomposites show rheological properties that are affected by annealing at 200°C signaling further exfoliation or improved platelet and tactoid distributions. The oxygen permeability of PE decreases gradually with the clay concentration, reaching a maximum reduction of ~30% for 15 wt% MMT.
In this study, polypropylene (PP)/organoclay nanocomposites were prepared by melt-compounding PP with three levels of clay loading (3, 5 and 7 wt%), using two different compatibilizers with various contents (5, 10 and 15 wt %), maleic anhydride-grafted polypropylene (PPMA) and hexamethylenediamine-modified maleic anhydride-grafted polypropylene (PPHMA). Effects of structure, mechanical properties and crystallization behaviors of the compatibilizers on the clay dispersion and the amount of clay on the microstructure and mechanical properties of the nanocomposites were investigated. The PPHMA compatibilized system conferred higher mechanical properties than the PPMA compatibilized case. It was found that the PPHMA yielded better clay dispersion and more exfoliated structure compared with the PPMA. Microstructural characterization of the samples was also characterized by transmission electron microscopy. Differential scanning calorimetry results indicate that the addition of compatibilizer increased the crystallization temperature as a result of heterogeneous nucleation effect of clay on PP.
In this study, the filler–matrix interactions are assessed in two nanocomposites having different antibacterial activity. The two polymers used as matrix are poly(amide) 6 (PA6) and low-density poly(ethylene) (LDPE). The filler, zinc oxide (ZnO) nanoparticles, with a content as low as 1 w/w% in the polymers showed great antibacterial activity against Escherichia coli and Staphylococcus aureus. However, the bacterial slaying capability of composites was found better when ZnO was dispersed in PA6, where the efficiency is similar to pure ZnO particles. The dispersion of ZnO and its interactions with the matrix have been investigated by means of scanning electron microscope, rheology, thermogravimetric analysis and differential scanning calorimeter. This study shows stronger interactions of ZnO particles with LDPE, which could have an effect on final antibacterial properties.
In this article, the impact of laser-induced thermal damage on the static strength properties of consolidated continuous carbon fibre reinforced thermoplastics induced by high-power laser cutting is presented. Organic sheets based on a polyphenylene sulphide matrix are machined using a fibre laser providing a maximum output power of 6000 W. In this context, the influence of the applied laser power and the feed rate on the cut quality as well as the resulting tensile strength is discussed. In order to analyse the laser cutting edge through a quantitative evaluation of the damaged areas due to laser impact, optical micrographs are prepared. The results of tensile strength tests are compared with those measured from the specimens that were generated by a conventional processing technique (milling). A linear dependency between a specific part of the heat-influenced zone and the corresponding maximum tensile load is found. A reduced load bearing area, as a consequence of a modified fibre–matrix-structure due to laser impact, is identified as the responsible factor for reduced tensile strengths, especially for low feed rates.
Monodisperse core–shell poly(styrene) (poly(St))/poly(styrene-co-butyl methacrylate) spheres were fabricated from styrene (St) and butyl methacrylate (BMA) monomers by a two-step, soap-free emulsion polymerization process at the boiling point. The two-step process involves initial polymerization for a fixed period of time, followed by the addition of BMA monomer to generate the core–shell structure microsphere. Formation of the shell portion increased as the initial polymerization time period was decreased. Differential scanning calorimetric analysis showed that the core–shell microsphere exhibited glass transition temperatures (Tgs), when the monomer conversion during the initial St polymerization step was higher than 40%. The Tgs of the core and shell occurred at 107°C and 41.9–56.7°C, respectively. These core–shell structure spheres were used to fabricate a colloidal crystal film, the photonic band gap of which could be shifted from 455–631 nm by employing core–shell spheres of various sizes. These films having photonic band gaps in the visible region were obtained by self-assembly of the core–shell spheres at 30, 50, and 80°C. The pencil hardness of the films prepared using the core–shell spheres could be increased from 5B to HB by increasing the preparation temperature, whereas the hardness of the film prepared using simple poly(St) spheres was lower than 6B.
Polystyrene and its copolymers are a group of polymers with a wide field of applications. A major disadvantage among many of them is their high flammability. Previous research showed that one of the possibilities to reduce this negative property is to synergize conventional fire retardants and other types of fillers. Recent research showed that there is a synergy effect in clay-containing composites. This initial study is focused not only on the evaluation of synergy with modified or unmodified layered clay nanofillers but also on wide variety of other fillers such as clay nanotubes, melamine or magnesium hydroxide. All results are compared with pure polymer and polymer with conventional fire retardants. The samples were prepared in laboratory using Brabender Plasti-Corder kneader and analyzed by X-ray diffraction. Flammability was the most important property evaluated, and mechanical properties were also observed.
In this work, a novel polymer magnetic composite based on thermoplastic acrylate pressure-sensitive adhesive (acrylate PSA) filled with the nickel plating multiwall carbon nanotubes (Ni/MWNTs) were prepared using Ni/MWNTs obtained by electroless plating method. Then their morphology and properties were characterized by transmission electron microscope, scanning electron microscope (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and so on. Both SEM and XRD indicate that a large number of nickel particles are homogenously coated on the surface of MWNTs. SEM reveals that the Ni/MWNTs are homogeneously dispersed in thermoplastic acrylate PSA. The VSM show that the saturation magnetization (Ms) of the Ni/MWNTs is 92.0 emu/g and the increase in the Ni/MWNTs content could enhance the Ms of the thermoplastic acrylate PSA/Ni/MWNTs composites and decrease their coercivity (Hc). When the content of Ni/MWNTs is 10.0 wt%, the magnetic and mechanical properties of the thermoplastic acrylate PSA/Ni/MWNTs composites are optimum.
This article is concerned with the effects of the silane surface treatment of SiO2 on the tribological properties of the SiO2-reinforced poly(methyl methacrylate) (SiO2/PMMA) composites filled with graphite. Silane treatment and graphite bring positive effect on the improvement of friction reducing and antiwear of SiO2/PMMA composites. Fourier transform infrared spectroscopy analysis shows that the SiO2 has been oxidized and etched by the silane treatment. The presence of active groups increases the polarity of SiO2, and hence the bond property between the particle and matrix is improved.
Fly ash cenospheres are inexpensive, readily available from coal burning or heavy oil combustion, not an eco-friendly material. If ways can be found to use this, it will serve the twin purposes of facilitating applications for the ash bearing materials and at the same time reduce pollution. One way to achieve this task is to make ash-bearing composites having polymer matrices. The performance of filled polymers is generally determined on the basis of the interface attraction of filler and polymers. Fillers of widely varying particle size and surface characteristics are responsive to the interfacial interactions with the polymers. The present study deals with the effect of particle size (150 mesh, 100 mesh, and 300 mesh) variations in fly ash cenospheres, as a filler with different concentrations (0–40 wt%), on various properties of acrylonitrile butadiene styrene. The mechanical, thermal, and electrical properties of the composite material were evaluated, and the microstructure was investigated through scanning electron microscopy. The smaller particle size showed better properties in comparison with larger particle size. As increasing filler loading, the saturation level is influenced by the agglomeration of filler particles in the polymer matrix. Thus, the performance of polymer filled with fly ash cenosphere composites is the function of the particle size, the dispersion, and the interfacial interaction between the filler particles and the polymer matrix.
The objective of this study is to toughen organically modified montmorillonite (OMMT)-filled polypropylene (PP) nanocomposites with epoxidized natural rubber (ENR). PP, ENR (10–20 wt%), OMMT (6 wt%) and maleated PP (PP-g-MA; 10 wt%) were melt blended using counterrotating twin extruder, followed by injection molding to prepare test samples. X-ray diffraction results revealed that the OMMT platelets in PP/OMMT nanocomposites were intercalated and the incorporation of ENR into the nanocomposites further increased the d-spacing of OMMT layers. The Fourier transform infrared spectra showed that the maleic anhydride group in PP-g-MA reacted in situ with the epoxy groups of ENR, which demonstrates the occurrence of grafting reaction. With slight decrease in stiffness and strength, the addition of 20 wt% ENR increased the impact strength of PP/ENR/OMMT nanocomposites by 521% compared to PP/OMMT nanocomposites. Scanning electron microscopy images revealed that the ENR particle size increased with increasing ENR contents in PP/ENR/OMMT nanocomposites. Differential scanning calorimetry results revealed that the presence of ENR and OMMT had slightly increased the crystallization temperature as well as the degree of crystallinity of PP. Thermogravimetric analysis showed that the blending of ENR decreased the thermal stability of PP/OMMT nanocomposites.
This article addresses the experimental characterization of the abrasive wear of two woven fabric carbon fiber and glass fiber composite materials, taking into account the effect of moisture absorption. The composite materials were tested to three level loadings and two sliding speeds. The abrasive used was dry sand of size 0.6 µm, and the time of wear testing was 10 min. In order to study the effects of moisture on wear behavior, another series of samples was introduced into the tank of water during a period of 40 days at ambient temperature. The planning design experimentation approach was applied to obtain a mathematical model taking into account the influencing parameters on the wear behavior of the composites. The wear results have shown that for a higher turn speed and a load, the loss of matter increases. In the case of samples exposed to water absorption, the wear rate increases more than the dry samples. The micrographs of the surface of the samples tested were taken in order to characterize the wear mechanism.
Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanocomposites with different contents of nanoclays were prepared by melt mixing. The clays used included unmodified clays, a commercially available hydrophilic nanoclay based on bentonite (nanoclay 1) and organically modified clay based on montmorillonite (nanoclay 2). The nanocomposites obtained were analyzed by x-ray diffraction, differential thermal and differential scanning calorimetry analyses and their basic tensile and other characteristics were determined. The distribution of the filler throughout the matrix was found to be good for both the types of nanocomposite materials. Nanoclay 1 induced slight increase in the β-phase and higher deviation of the main diffractions (2 = 18.6° and 20.1° at 10 mass% filler). The degree of crystallinity of the materials containing nanoclay 2 decreased from 26.4 to 20.5% and from 23.9 to 18.7%, respectively, for the first and second heating. The tensile strength of the materials based on PVDF-HFP with nanoclays 1 and 2 was close to that of the initial copolymer or slightly increased with the addition of nanoclay 2. Young’s modulus was in the range of 215–265 MPa. The heat resistance by Vicat increased by 7°C compared with the initial copolymer.
The porous polyphenylene sulfide (PPS) self-lubricating composites with sweating effect were designed and fabricated, and the friction and wear behavior were evaluated. Results indicated that, porous PPS self-lubricating composite modified by 1 wt.% zeolite and impregnated with lithium-base grease in the pores showed the lowest friction coefficient and wear rate, which were recorded as 0.024 and 1.79 x 10-16 m3/Nm, respectively. Compared with pure PPS under dry condition, the friction coefficient reduced by 90% and wear resistance increased by 4.67 x 104 times. The wear resistant enhanced by 3.61 times than that of PPS/30 wt.% NaCl composites, so it showed synergistic effect on improving wear resistance. By means of scanning electron microscope, it was found that the pores of porous PPS composites with 1 wt.% zeolite were uniformly distributed and grease were well embedded in these orderly pores of PPS composites. Under the effect of load and temperature, grease squeezed from micropores and nanopores can provide the excellent lubrication effect, which are the main reason for the outstanding self-lubricating and wear resistance of PPS porous composites.
The thermal degradation of the polyamide 6,6 (abbreviated henceforth as PA 6,6) reinforced with different concentrations of carbon nanotubes (CNTs) was investigated by means of thermal analysis. In this study, the nanostructured composites were produced using 0.1, 0.5 and 1.0 wt% of CNT. X-ray diffraction analyses were performed in order to evaluate the crystallographic properties of nanostructured composite. The degradation kinetics of PA 6,6/CNT nanostructured composites were measured by thermogravimetric analysis at different heating rates under nitrogen flow. TGA experiments were performed to elucidate the thermal behavior and supply the data that characterize the degradation kinetic. The degradation parameter kinetics was determined using the Ozawa–Wall–Flynn (O-W-F) methods, which do not require knowledge of the reaction mechanism. In this work, the results show that the addition of CNT up to the amount of 0.5 wt% increases the thermal stability of PA 6,6.
The present work investigates the effect of epoxy resin (EP) modification with polyurethanes (PURs) based on polyethylene glycol and two different diisocyanates: 4,4'-diphenylmethane diisocyanate (MDI) and 2,4-toluene diisocyanate (TDI). The impact strength of the material based on 15 wt% PUR with TDI was enhanced by 130%, while the critical stress intensity factor and the flexural strength of epoxy composition based on 5 wt% PUR with MDI increased by approximately 140% in comparison with unmodified EP. Fourier transform infrared spectroscopy confirmed the occurrence of chemical reaction between the hydroxyl groups of EP and isocyanate groups of PUR, explaining the improvement in the mechanical properties of EP. Moreover, scanning electron micrographs showed a rough surface with plastic yielding and several microcracks in the compositions containing TDI-based PUR and deformed leaf-like morphology with more elongated structure for the EP modified with MDI-based PUR.
In this work, poly(vinyl alcohol) (PVA)/clay hydrogel based on various ratios of clay (20%, 50%, and 60%) were prepared using freezing and thawing techniques followed by electron beam (EB) irradiation at different irradiation doses (20, 25, and 30 kGy). The physicochemical property of such hydrogel in terms of gel fraction (%) and water uptake (%) was investigated. The structure and property of the hydrogel were investigated by x-ray diffraction (XRD) and scanning electron microscope (SEM). Thermal property was investigated using differential scanning calorimetry and thermogravimetric analysis. The results indicated that the gel fraction (%) increases on increasing the clay content in the hydrogel at all irradiation doses. The results obtained by XRD and SEM show an intercalation and exfoliation between PVA and clay. The occurrence of one Tg and Tm of the hydrogel indicates the presence of complete miscibility between PVA and clay. Also, the prepared hydrogel exhibit high thermal stability by increasing clay content in the hydrogel. It was found that the prepared PVA/clay hydrogel has a high water uptake, making it acceptable for the use in treatment of wastewater from heavy and toxic metal ions and dye wastes.
The structural and tribological behaviors sliding under different conditions of the novel polyamide (PA)-based composites blended by thermoplastic polyurethane (TPU) were investigated in this article. With a compatible structure shown by the fractured morphology and crystalline structure results, the toughness of the PA6-TPU composites was improved apparently. The friction coefficient of PA6-TPU composites would stabilize quickly at relatively low value, while their wear rate increased. Under a higher applied load condition, the friction coefficient and wear rate of the PA6-TPU composites increased apparently, attributing to lots of complex reasons. However, high sliding speed would be useful in the formation of thin and stable TPU transfer film, such that both the friction coefficient and wear rate of the PA6-TPU composites decreased at higher sliding speed. Morphology of worn surface of PA6-TPU composites revealed that the primary wear mechanism was adhesive wear and fatigue wear under the dry sliding condition. It is expected to provide some practical guidance for the application of polymer materials in the tribological field.
The mechanical properties of the coir fibers were evaluated in this study. Tensile strength (TS), Young’s modulus (YM) and elongation at break (Eb%) of virgin coir fibers were found to be 152 MPa, 5.3 GPa and 36%, respectively. Coir fibers were treated with ultraviolet (UV) radiation and were found to improve the mechanical properties significantly. Coir fiber-reinforced ethylene glycol dimethacrylate (EGDMA)-based composite was prepared and characterized. The surface of the coir fibers was modified with monomer EGDMA under UV radiation. Soaking time, monomer (EGDMA) concentration and radiation intensities were optimized over mechanical properties. The highest values of TS, YM, Eb and polymer loading (PL) were found for 50% EGDMA at 125th pass of UV radiation for 7 min soaking time. Pretreatment with UV radiation on the coir fiber was found to be more effective for the increment of its mechanical properties. The surface of the fiber was also mercerized (alkali treatment) using aqueous NaOH solutions (5–50%) at varied time and temperature. It was found that TS of the mercerized composites increased with the increase in NaOH solutions (up to 10%) and then decreased. The composites made using mercerized fibers treated with EGDMA showed further increase in TS. Pretreatment with mercerization + UV treatment of coir fiber showed significant improvement in the mechanical properties of the coir fiber-based composites.
In this study, an epoxy resin was dynamically cured in a polypropylene (PP)/maleic anhydride–grafted polypropylene (MAH-g-PP)/calcium carbonate (CaCO3) matrix to prepare dynamically cured PP/MAH-g-PP/CaCO3/epoxy composites. The torque measurement shows that the addition of epoxy resin into the PP/MAH-g-PP/CaCO3 composites results in a slight increase in the torque at equilibrium, and epoxy resin in the composites has been cured by 2-ethylene-4-methane-imidazole (EMI-2,4). Scanning electron microscopic analysis shows that dual compatibilizers composed of MAH-g-PP and an epoxy resin were demonstrated to effectively compatibilize the immiscible PP/CaCO3 composites. MAH-g-PP with a low MAH content is miscible with PP to make it quasi-functionalized, while the epoxy resin can react with MAH-g-PP and hydroxyl groups at the CaCO3 surface. Thus the formed MAH-g-PP-co-epoxy-co-CaCO3 copolymer at the interface is able to anchor along the interface and serve as an efficient compatibilizer. Dynamic cure of the epoxy resin can further increase the interaction adhesion in the PP/CaCO3 composites. The epoxy resin does not show compatibilization effects for the PP/CaCO3 composites without the presence of MAH-g-PP. The shift of crystallization peaks to the higher temperature suggests that the CaCO3 filler in the composites can act as a nucleating agent, accelerating the crystallization of PP component, and the PP/CaCO3 composites compatibilized by MAH-g-PP and the epoxy resin have higher crystallization peaks. This shows that an increase in the interaction adhesion between the CaCO3 and PP matrix, improving the nucleating activity of the filler and promoting crystallization of PP. Thermogravimetric analysis shows that the incorporation of the CaCO3 into the PP could improve the thermal stability of PP, and the addition of MAH-g-PP and the epoxy resin into the composites obviously could further improve the thermal stability. The mechanical properties of PP/MAH-g-PP/CaCO3 and PP/MAH-g-PP/CaCO3/epoxy composites are better than that of the PP/CaCO3 composites. The PP/MAH-g-PP/CaCO3/epoxy/EMI-2,4 composites have the best mechanical properties in all the PP/CaCO3 composites, which is attributed to the better interaction adhesion. The suitable content of epoxy resin is about 5 wt% in the presence of MAH-g-PP in the PP/CaCO3 composites, while an excess epoxy resin of above 5 wt% acts as an organic filler for PP.
With increasing environmental awareness and ecological risk, green composites have gained more and more research attention, as they have the potential to be attractive than the traditional petroleum-based composites which are toxic and nonbiodegradable. Because of their lightweight, friendly processing and acoustic insulation, green composites have been used widely ranging from aerospace sector to household applications. The end-of-life concern with many polymeric composites has also limited their application spectrum. The green composites not only replace the traditional materials such as steel and wood but also challenge certain nonbiodegradable polymer composites. The present research initiative aims at highlighting the issues and challenges in the development and characterization of poly lactic acid–based green composites. A few of these important composites and their mechanical properties (tensile, compressive, flexural, and impact strength) have been reported in this study. The focus is the identification of the possible areas for their novel applications. A study has been conducted to categorize the various types of green composites on the basis of their physical, chemical, and mechanical characteristics.
This study investigates the effect of nanoclay on the cell morphology and thickness swelling behavior in the extrusion foaming of wood flour/polyethylene composites with a chemical blowing agent. To meet this objective, the nanoclay, high-density polyethylene, and coupling agent were compounded and then the granules were mixed with wood flour and blowing agent in a twin-screw extruder. Consequently, foaming process was completed in the injection stage. The amount of wood flour was fixed at 50 wt% for all samples. For nanoclay and chemical blowing agent, different levels of 0, 2, 4 per hundred resins (phr) and 0, 0.5, 1, 1.5 phr were considered, respectively. The results indicate that the addition of clay generally reduces the cell size, increases the cell density, and facilitates foam expansion. Furthermore, the thickness swelling of the composite decreased with increase in nanoclay. The composites containing 1.5 phr of foaming agent exhibited higher thickness swelling value and swelling rate parameter (KSR) than those containing nanoclay. The swelling model provided a good predictor of the hygroscopic thickness swelling process of wood flour/polyethylene/nanoclay hybrid foamed composites.
The incorporation of zinc hydroxy stannate (ZHS), calcium borates (CBs), and NP-100 as flame-retardant fillers in polypropylene (PP) ethylene propylene diene monomer (EPDM) blends was investigated. The composites were prepared using an internal mixer and were molded using a compression mold to form test samples. Studies on the effect of filler loading (15, 30, 45, and 60 vol%) on the flame-retardant, thermal stability, and tensile properties were reviewed. A study on flame retardancy and thermal stability of ZHS, CB, and NP-100 fillers found that NP-100 has better flame retardancy compared with ZHS and CB even though NP-100 exhibits lower thermal stability compared with ZHS and CB. The mechanical properties of ZHS are the highest, followed by CB. NP-100 has the lowest mechanical properties. Tensile strength, Young’s modulus, and strain at break of 30 vol% ZHS are slightly higher compared with other loadings. In addition, 30 vol% CB has the highest mechanical properties for PP/EPDM/CB system but has slightly lower mechanical properties compared with 30 vol% ZHS-filled PP/EPDM composites.
A series of maleic anhydride grafted poly(lactic acid) (PLA-g-MAH) was prepared by mixing PLA, dicumyl peroxide (DCP) and maleic anhydride (MAH). Effects of DCP and MAH concentration on the grafting percentage were determined. PLA composites were prepared via melt mixing with halloysite clay (HNC; 3 wt%) and various amount of PLA-g-MAH (4–10 phr) using internal mixer followed by compression molding. Properties of the PLA composites were characterized using three-point bending flexural tests, scanning electron microscopy and differential scanning calorimetry. It was found that the grafting percentage of PLA-g-MAH was influenced by both DCP and MAH concentrations; however, DCP showed more profound effect. By the addition of PLA-g-MAH, the adhesion between PLA and HNC improved, which can be manifested by the enhancement in flexural properties. Degree of crystallinity of PLA/HNC increased significantly by the addition of PLA-g-MAH.
Maleic anhydride–grafted high-density polyethylene (HDPE; PE-g-MAH) was used to fill the interphase layer of silicon dioxide (SiO2)/polymethyl methacrylate (PMMA) composites. The mechanical, friction and wear properties of SiO2/PMMA/HDPE composites were investigated on a ring-on-ring friction and wear tester with AISI 1045 steel metallic ring counterface under dry friction conditions. Scanning electron microscopy (SEM) was utilized to study the worn surfaces of PMMA composites. Experimental results showed that the addition of HDPE decreased the friction coefficient of SiO2/PMMA composites slightly and reduced the wear volume loss of the PMMA composites obviously. SEM studies indicated that the addition of HDPE could reduce the abrasive wear of SiO2/PMMA composites. The dispersion of SiO2 in PMMA composites was also improved.
Wood-plastic composite (WPC) can be fine-cell processed to create a new class of low-weight composite material with improved mechanical properties that could broaden their applications. This study investigated the effects of a chemical blowing agent (CBA) and the drawdown ratio (DDR) on the surface quality, cell morphology, and mechanical properties of extruded foamed WPC profiles. The rectangular foamed WPC profiles were produced from high-density polyethylene and wood flour with different CBA contents and DDR values using a twin-screw extrusion line. The foam density, cell density, and their sizes and shapes were largely depended on the CBA content and the DDR. A foamed WPC profile with a 22% density reduction with cellular structure can be produced using an extrusion profile line.
To study the dynamic mechanical kinetics of exfoliated nanocomposites using dynamic mechanical analysis, polyvinyl acetate (PVAc)–montmorillonite (MMT)–dioctadecyl dimethyl ammonium bromide (DOAB) was synthesized through five different processes. Different synthesis processes and MMT-DOAB had little effect on the structure of PVAc-MMT-DOAB. MMT-DOAB lowered the glass transition temperature of PVAc, hence improving its low temperature resistance greatly. PVAc and PVAc-MMT-DOAB were homogeneous amorphous linear polymers and they appeared cold crystallized, and their glass transition and cold crystallization kinetics were analyzed using Agrawal integral equation.
The physical properties of polystyrene composites containing different concentrations of iron (0, 5, 10, 20 and 30 wt.%) were studied as a function of ultraviolet (UV) wavelength, iron concentration, temperature, and applied field frequency. The absorption spectra were collected using the UV-spectrophotometry, and the electrical results were determined using the alternating current (AC) impedance method. Analysis of the optical absorption spectra results showed that the transition of energy electrons is direct in k-space and the optical energy gap decreases with iron content. The impedance was measured in the frequency range 50 kHz–1 MHz and temperature range 30–110 C. It was found that the dielectric constant and the dielectric loss of the composites increase with iron concentration and decrease with the applied frequency. The AC conductivity of the composites increases with frequency, temperature, and iron concentration. The low value of the activation energies indicates that the composite of 30 wt.% of iron nearly becomes a conductive material.
This work addressed questions regarding the fate of wood pulp fibers in the composite manufacturing process, for instance whether the processing induced fiber damages, and the improved interfacial adhesion accelerated this function. A number of wood fibers were blended with various maleic anhydride-grafted polymers fully and partially to study their morphological changes. The fractured fibers were separated from wood composites with aromatic hydrocarbons and analyzed using Fiber quality analyses, Scanning electron microscope, Fourier transform infrared analysis and X-ray photoelectron spectroscopy to validate the degree of fiber fractures and the esterification reaction. The fiber damages were related to the maleic anhydride grafting degree, molecular weight and molecular structures of maleated polymers.
Wood–plastic composites (WPCs) and natural fiber composites (NFCs) are increasingly used in decking applications, where exterior exposure can lead to photodegradation and fungal deterioration. Since the fire retardancy is another proficiency concern of these composites, bagasse/polypropylene composites were produced by incorporation of commercially available additives including flame retardants, ultraviolet (UV) stabilizer, antifungal agent and color masterbatches. The addition of the flame retardant which decomposed at high temperature could result in NFC with significant decrease in burning rate (up to 98%) compared to the composite without flame retardant. Simultaneous effects of antifungal agent and green masterbatch lead to complete suppression of the fungal growth and reproduction on composites exposed to either Lentinus edodes, Pleurotus eryngii strain or each of them accompanied by Trichoderma sp. fungus. Durability performance followed by discoloration, mechanical properties loss and surface chemistry variation depended on all additives used. The results indicated that darker color pigment improved color stability and caused much lower fading for UV-stabilized NFC in comparison to the nonstabilized unpigmented composite.
The effect of chemical blowing agent on the cell morphology and long-term water absorption and thickness swelling of composites based on high-density polyethylene/rice husk flour were studied in this research. Composite materials containing high-density polyethylene, rice husk flour, chemical blowing agent and coupling agent were melt compounded using twin-screw extruder. Then, the samples were foamed via batch process using a compression molding machine. The results showed that the water absorption, thickness swelling, cell size and average cell density of composites increased by addition of chemical blowing agent. The mechanism of water absorption of the foamed wood plastic composites under study followed the kinetics of a Fickian diffusion process. Furthermore, adding the chemical blowing agent had effect on water diffusion coefficients and swelling rate parameter (KSR) of composites.
The melt flow behaviours of low-density polyethylene (LDPE)/palm kernel shell (PKS) composites were studied. Acrylic acid (AA) was used as a chemical modifier for PKS. The effect of filler loading and the presence of AA in melt flow behaviour of composites were determined. The melt flow index of the composites decreased with the increase in the filler loading. The apparent viscosity of the composites was found to exhibit linear relationship with reciprocal of the temperature. The study on the thermal properties showed that higher filler loading tend to reduce the onset temperature as the PKS possessed lower degradation temperature compared to the LDPE. The presence of the filler in LDPE polymeric matrix improved the thermal stability of the composites. The addition of AA provided better interfacial bonding between the LDPE matrix and the PKS filler, where higher onset temperature and lower weight loss were observed for LDPE/PKS composites with AA. The activation energy of the LDPE/PKS composites was increased with increasing filler loading. At similar filler loading, the addition of AA increased the activation energy of the LDPE/PKS composites.
The electrical properties of cement–polyvinyl alcohol were studied using the impedance measuring technique. The study has been carried out under different temperatures and frequencies. Some electrical quantities such as AC conductivity, dielectric constant, activation energy, and relaxation time of the conduction process were determined from collected impedance data, at a frequency range from 20 kHz to 1 MHz and temperatures of 30–105°C. It was found that the measured electrical quantities have frequency and temperature dependence. The dielectric constant and dielectric loss increase with increasing temperature and decrease with the applied frequency. The AC conductivity increases with increasing temperature and frequency. The calculated values of the activation energy and relaxation time vary with temperature and frequency. The observed enhancement in the electrical conductivity with increasing temperature may be due to electron hopping between the intrinsic localized states in composite composition. The increase in the dielectric constant with temperature is attributed to space charge, ions, and metallic inclusions existing in the cement structure.
In this study, the effect of -rays on the mechanical and thermal properties of polymer composites based on chlorinated isobutylene–isoprene rubber/chlorosulphonated polyethylene rubber blend with varying contents of carbon black (CB) filler was investigated. The samples were irradiated at ambient conditions with 100, 200 and 400 kGy radiation doses. Tensile strength and hardness are increasing with CB content and radiation dose is increasing, while elongation at break is decreasing. Loss of mass of 0.5, 10 and 30% was calculated for the samples from their respective thermogravimetric curves. The thermal stability of the nanocomposites was improved by both the degree of loading with filler and the cross-linking induced by -irradiation.
Effect of unmodified and surface-modified micro-/nano-calcium carbonate particles on the mechanical properties, crystallization behavior, and thermal properties of polypropylene (PP)/microscale calcium carbonate (micro-CaCO3 (mCC)) and PP/nanoscale calcium carbonate (nano-CaCO3 (nCC)) composites has been comparatively investigated via melt mixing. Mechanical tests indicated that PP/nCC composite with the addition of 5–10 wt% nCC is higher than that of virgin PP and even higher than that of PP/mCC composite with the addition of 5–15 wt% mCC. In addition, incorporation of titanate-coupling agent (isopropyl tri-(dioctylpyrophosphato) titanate (JN114)) further increased the mechanical properties of the composites. This improvement in the mechanical properties was evidenced by scanning electron microscopy. The addition of small amounts of JN114 into PP/mCC and PP/nCC induces the great change in crystallization behavior of PP matrix. Improved distribution of CaCO3, enhanced crystallization temperature, largely increased the degree of crystallinity, Xc (%), and the heat deformation temperature are achieved for PP/modified-nCC samples.
Pyridinium- and phosphonium-based filler surface modifications (tetraphenylphosphonium, hexadecylpyridinium and hexadecyltriphenylphosphonium), which are more thermally stable than the conventionally used ammonium modifications, were exchanged on the filler surface. Polypropylene nanocomposites with the modified fillers were prepared and characterized for gas barrier, mechanical, calorimetric and thermal properties. Mixed morphology consisting of single layers and tactoids of different thicknesses was observed in the composites. The developed morphology in the composites was a result of better thermal stability of the system as well as the nature of the surface modification. Though the completely aromatic surface modification was most thermally stable, it did not improve the composite properties significantly owing to poor interfacial intermixing with the polymer. On the other hand, impressive improvements in the gas barrier and mechanical properties were observed for the filler modifications which included long alkyl chains. These improvements were also better than the corresponding ammonium modifications. The incorporation of the filler led to enhanced thermal resistance of the composites.
The aim of this work was to study the effect of surface-modified calcium carbonate (CaCO3) nanoparticles in the mechanical properties and crystallization behavior of polypropylene (PP) homopolymer. Pimelic acid (Pa) was used as a surface modifier for nano-CaCO3 (nCC). Three compositions of PP/nCC composites were prepared in a corotational twin-screw extruder machine with nCC content of 5, 10, 15, and 20 wt%. The results of scanning electron microscopy showed that the Pa treatment enhanced the interfacial adhesion between the filler and the matrix, indicating the improvement in the compatibility between PP and nCC. The measurements of the mechanical properties showed that the elastic modulus (Ec) and impact strength (SIC) of the composites increased at first and then decreased with the addition of fillers, and the tensile yield stress (yc) was reduced at the same time. The crystallization properties of virgin PP and its composites were studied with differential scanning calorimetry. The results demonstrated that, in comparison with virgin PP and PP/nCC, the addition of the Pa-treated nCC fillers led to a higher crystallization temperature, and nucleation and crystallization were improved at the same time.