Journal of Thermoplastic Composite Materials

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.

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.

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.

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.

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.

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 (K _C) 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 (K _C) values increased from 1.7 MPa m^1/2 (virgin epoxy) to 2.5 MPa m^1/2 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.

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 γ-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 ν_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 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 (T _m) and melting enthalpy (ΔH _m) of the HDPE phase of the nanocomposites are lower than those of the neat EVA/HDPE blend. Although crystallization temperature (T _c) 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.

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.

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).