Modification of Wood Flour Surfaces by Esterification with Acid Chlorides: Use in HDPE/Wood Flour Composites

Modification of wood fiber/flour (WF) surfaces can improve their compatibility with hydrophobic plastic matrices and reduce composite water uptake. WF was esterified with octanoyl chloride and palmitoyl chloride. Modified WF was analyzed by FT-IR. More extensive esterification occurred in highly polar dimethylformamide (DMF) than in much less polar CHCl₃ or methyl tert-butyl ether (MTBE). DMF penetrates into the fiber far more than CHCl₃ or MTBE, making more –OH groups available for esterification. Increasing the acid chloride chain length from C₈ to C₁₆ decreased the mole fraction of esterification. Longer chains cover surface –OH groups, retarding reactions with nearby hydroxyls after esterification. Longer chain acid chlorides also have lower reactivity and penetrate into the hydrophilic wood fiber more slowly. Modified wood flour surfaces were covered by a hydrophobic layer of ester groups (SEM). Modified wood flour surfaces and WF/HDPE composite fracture surfaces were studied by SEM. C₈-modified wood flour (60 wt%)/HDPE composites exhibited far less water absorption after 24 h and 216 h immersions compared with unmodified WF (60 wt%)/HDPE composites. Water absorption continues over the 216 h period. Esterified WF/HDPE composites exhibited lower flexural strengths and moduli. In contrast to C₈-esterification, the addition of maleated polypropylene (MAPP) to WF/HDPE composites improved composite mechanical performance and gave similar water absorption properties to C₈-esterified WF composites.     

Thermorheological Properties and Thermal Stability of Polyethylene/Wood Composites

The thermal stability, flame retardancy, thermorheological, and mechanical properties of polyethylene/wood flour (PE/WF) composites were characterized. By time–temperature superposition treatment, addition of WF was found to lead to a complexity in the thermorheological behaviors in low-density PE/wood composites. However, high-density PE/wood counterparts showed no obvious thermorheological complexity. The effects of WF and ammonium polyphosphate contents on the thermorheological behavior and thermal stability were also studied. The current work should be of practical significance for the optimization of wood/plastic composite) formulae, as well as for further investigations on correlations between processing and performance of polymer composites.     

Properties of Natural Rubber Vulcanizates/Nanosilica Composites Prepared Based on the Method of In-situ Generation and Coagulation

Using the characteristics of silica sol dispersing well in water and easy formation of silica gel when the silica sol is heated, by mixing a system of concentrated natural rubber latex and silica sol, the silica sol can in-situ generate SiO₂ particles when heated. After coagulation of the mixed system, natural rubber/nanosilica composites C(NR/nSiO₂) were obtained. The composites C(NR/nSiO₂) and their vulcanizates were studied using a rubber processing analyzer (RPA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The influence of silica contents on the C(NR/nSiO₂) vulcanizates mechanical properties, cross-linking degree, Payne effect, dissipation factor (tanδ), and the particle size and dispersion of SiO₂ in NR were investigated. The results obtained were compared with the NR/SiO₂ composites based on traditional dry mixing of bale natural rubber and precipitated silica (white carbon black). The results showed that when using a sulfur curing system with a silica coupling agent (Si69) in C(NR/nSiO₂), the vulcanizate had better mechanical properties, higher wet resistance, and lower rolling resistance than those without Si69. In the composites C(NR/nSiO₂) and their vulcanizates, the SiO₂ particles’ average grain diameter was 60 nm, and the good-dispersion of the in-situ generated SiO₂ in the rubber matrix were a significant contribution to the satisfactory properties of C(NR/nSiO₂) composites and their vulcanizates.     

Moisture Absorption Behavior of Wood/Plastic Composites Made with Ultrasound-Assisted Alkali-Treated Wood Particulates

The combined effects of alkali and ultrasound treatment of wood flour on the moisture absorption behavior of polypropylene-based wood/plastic composites (WPCs) were examined. FT-IR measurements confirmed that the alkali treatment removed both hemicellulose and lignin from the wood, and there was an increase in the number of hydroxyl groups on the cellulose surface. This process was promoted by ultrasound treatment. Particle size analysis of treated wood fibers revealed that alkali treatment reduced the particle size slightly, and the particle size was further reduced by the assistance of ultrasound. Moisture absorption measurements revealed the interplay between the presence of relative amounts of cellulose, hemicellulose and lignin in the wood and the amount of coupling agent added. It was found that appropriate alkali treatment and an optimum amount of added coupling agent could simultaneously improve composite mechanical properties and reduce both the rate and the maximum amount of moisture absorbed. Further improvements require preferential removal of hemicellulose from the wood and conditions that promote covalent bonding between the coupling agent and the wood reinforcement.     

Characteristic of natural rubber composites absorbing X-radiation

Radiopaque polymers can be used in medicine. Conventional protective shields against radiation X contain harmful lead compounds that are heavy and fragile. The aim of this work was to study the check the properties of selected fillers as X-radiation absorbing substance and them use in natural rubber (NR) composites. Fillers and simultaneously active substances were bismuth (III) oxide (Bi₂O₃), gadolinium (III) oxide (Gd₂O₃), tungsten (III) oxide (WO₃) and antimony (III) oxide (Sb₂O₃). The polymeric matrix consisted of NR and sulfuric cross-linking system was applied. The properties of the fillers were determined from zeta potential and particle size measurements. X-ray absorption measurements were carried out using isotopic source ⁵⁷Co (122?keV). The mechanical properties of the thin 1?mm composite plates were examined.     

Effect of Carbon Nanotubes on the Mechanical Properties of Polypropylene/Wood Flour Composites: Reinforcement Mechanism

Maleic anhydride grafted polypropylene (PP-g-MA) was employed as the compatibilizer and carbon nanotubes (CNTs) or hydroxylated CNTs as reinforcements for polypropylene/wood flour composites. The results showed that when the PP-g-MA loading level was 10 wt%, the bending strength, tensile strength, Izod notched impact strength, and elongation at break of PP-wood composites were enhanced by 85% (66.3 MPa), 93% (33.7 MPa), 5.8% (2.01 kJ/m²), and 64% (23%), respectively, relative to the uncompatibilized composites. The introduction of pristine CNTs only improved slightly the overall mechanical properties of the compatibilized composites due to poor interfacial compatibility. Unlike CNTs, incorporating hydroxylated CNTs (CNT-OH) could significantly improve all of the mechanical properties; for instance, at 0.5 wt% CNT-OH loading, the flexural strength and tensile strength reached 68.5 MPa, and 40.4 MPa about 6.6% higher than that for the composites with the same CNT loading. Furthermore, CNT-OH also remarkably enhanced the storage modulus. Contact angle and morphology observations indicated that the increases in mechanical properties could be attributed to the improvements of interfacial interactions and adhesions of CNTs with the matrix and fillers.     

Influence of particle size on electromagnetic behavior and microwave absorption properties of Z-type Ba-ferrite/polymer composites

The electromagnetic and microwave absorption properties of the Z-type Ba-ferrite/polymer composites were investigated. The results showed that particle size of the Ba-ferrite fillers has a significant influence on the effective properties of the two-phase composites. The relative dielectric constant and initial permeability of such composites are about 95 and 5.2 at high frequency under certain combination of ferrite fillers with different particle size, respectively. Microwave absorption properties of the composites are simultaneously influenced due to the strong correlation between reflection loss and electromagnetic parameters of the ferrite/polymer composites.     

Natural fibre composites from polyethylene waste and hazelnut shell: dimensional stability,physical, mechanical and thermal properties

Within the framework of this study, the physical modification of high-density polyethylene waste foil was performed using finely ground hazelnut flour to produce a composite whose physical, mechanical and flammable properties make it possible to use inside and outside of buildings. Three mixtures were produced with filler shares of 11, 26 and 42 vol.% using equipment that is normally used in polymer processing, and no refining additives were applied. The produced materials were analysed for their processing (mass flow ratio), physical (density and moisture content) and mechanical properties (tensile strength, elongation at break and dynamic thermal analysis) and resistance to environmental factors (swelling and water absorption, thermogravimetric analysis and combustion heat). The particle size distribution of the filler and morphological properties of the composites (scanning electron microscopy) were also investigated. It was vital to obtain an inexpensive material with low absorptivity. The resulting materials are characterised by a low density, acceptable low absorptive and good mechanical properties; also, they can constitute an important fuel once their practical properties have been exploited.     

Effect of solvent on the characteristics of nanostructured composites of poly (1-naphthylamine) with poly (vinyl alcohol)

Efficient utilization of inherently conducting polymers in nano technological applications faces the challenge to assemble them into highly ordered structures which may yield novel properties. The present study reports for the first time the synthesis and characterization of nanostructured poly (1-naphthylamine) (PNA) dispersed polyvinyl alcohol (PVA) composites. The composites were prepared by loading PNA from 2 wt% to 10 wt% in PVA in aqueous as well as nonaqueous media. The composites were characterized by UV–visible spectroscopy, TEM, stress–strain studies, electrical conductivity measurements and moisture absorption studies under controlled humidity. A discrete but uniform distribution of nanoparticles was obtained in PNA/PVA composites synthesized in water having particle size between 5 and 30 nm. A self assembled network of nanostructured PNA particles was obtained in case of PNA/PVA composites synthesized in N-methylpyrolidone (NMP) with particle sizes between 10 and 65 nm. The variation in the nanostructured morphology of PNA particles in PVA matrix in the two cases resulted from the pronounced interaction of PVA with NMP through hydrogen bonding. This leads to the formation of a homogeneous matrix that facilitates the formation of a self assembled network of PNA nano particles. In case of PNA/PVA composites synthesized in water, lower affinity of PVA towards water was responsible for a discrete, agglomerate free distribution of PNA particles. We have found that the PNA/PVA nano composite synthesized in water exhibited good mechanical properties and electrical conductivity (8.1 × 10⁻¹ S/cm) as well as lowest moisture absorption (4 wt%) which holds potential for use in semiconductor and biomedical devices.     

Influence of Ethylene-Butyl Acrylate-Glycidyl Methacrylate Terpolymer on Compatibility of Ethylene Vinyl Acetate Copolymer/Olive Husk Flour Composites

The paper reports some results of an experimental study on ethylene vinyl acetate (EVA) copolymer/olive husk flour (OHF) composites incorporated at various filler ratios (15, 30 and 45 wt%) in the absence and the presence of ethylene-butyl acrylate-glycidyl methacrylate (EBAGMA) terpolymer used as a compatibilizer. The composite samples have been prepared by melt blending and their chemical structure, as well as morphological, mechanical and water absorption properties investigated. It is shown that the compatibility of EVA/OHF composites is improved by the addition of EBAGMA terpolymer. Indeed, FT-IR analysis shows that chemical interactions have occurred between the compatibilizer and the base blend components. Morphological results from SEM shows better dispersion of the wood particles in the EVA matrix and the resulting composite samples exhibit better tensile properties at break and lower water absorption than the uncompatibilized ones. Moreover, the results indicate that the loading concentrations of both OHF and EBAGMA have an effect on the composite properties.     

Influence of particle size on the electromagnetic and microwave absorption properties of FeSi/paraffin composites

The electromagnetic and microwave absorption properties of the composites employing FeSi alloy powders with different particle sizes as absorbent and paraffin as matrix were investigated. The results showed that the particle size had significant influence on the electromagnetic and microwave absorption properties of the composites in the 2-7 GHz frequency range. By decreasing the particle size of FeSi alloy powders, both the complex permittivity and permeability of the composites increased to a certain extent. In addition, the microwave absorption properties were improved, and the frequency of absorption peak shifted towards lower frequency range. In other words, the micron-grade FeSi alloy powders with smaller particle size were more suitable to be used as absorbent in measured frequency region.     

Design of Some Oxide/Metal Composite Supports and Catalysts

Textural, mechanical and catalytic properties of porous composite materials Al₂O₃/Al, MeO _x (Me)/Al₂O₃/Al with metal particles homogeneously distributed in the alumina matrix were studied. These materials were prepared by mixing the powdered components with aluminum followed by hydrothermal treatment and calcination. The macroporous structure was shown to be controlled by the size of large (>microns) particles in starting blends. The mesoporous structure is primarily determined by the properties of alumina formed by dehydration of hydroxide produced in turn via aluminum oxidation by water. The mechanical strength of porous cermets is determined by the number and properties of contacts between micron-size components of composites. Improved catalytic performance of composites is ensured by the developed macroporous structure providing enhanced mass transfer inside the cermet granules.     

Isothermal Crystallization Kinetics of Highly Filled Wood Plastic Composites: Effect of Wood Particles Content and Compatibilizer

The isothermal crystallization behavior and crystal structure of the polypropylene (PP) component in wood plastic composites (WPC) with respect to wood particle content and maleic anhydride-grafted polypropylene (MAHPP) compatibilizer were studied by means of polarized optical microscopy, scanning electron microscopy, x-ray diffraction, and differential scanning calorimetry. It was found that under the experimental conditions of this research, the speed of crystallization of PP was faster in WPC with MAHPP than in composites without MAHPP. This is ascribed to the difference in undercooling due to the change in the equilibrium melting temperatures (T ⁰ _m ) of the PP component in WPC due to the addition of wood flour and MAHPP compatibilizer. T ⁰ _m decreased with the increase of wood particle content, and it decreased more severely with the addition of wood flour than the addition of compatibilizer. The half-crystallization time was the smallest in PP/wood composites, intermediate in PP/wood/compatibilizer system, and the largest in pure PP under the same undercooling. The fast crystallization in PP/wood composites is ascribed to the heterogeneous nucleation effects of wood particles, which could be hindered by the MAHPP compatibilizers; this was verified by the higher fold surface free energy in WPC with compatibilizer than in WPC without compatibilizer.     

Fabrication of Tb0.3Dy0.7Fe2/epoxy composites: Enhanced uniform magnetostrictive and mechanical properties using a dryprocess

To improve the uniformity of the magnetostrictive properties of Terfenol-D composites along the field direction, a dry method is developed in the present study. We examined the compaction pressure, particle volume fraction, particle size and composite configuration as factors that affected the magnetostrictive properties of the composites. The experimental results indicated that the magnetostrictive properties were improved with the increase of compaction pressure and particle volume fraction. In addition, larger average particle size was shown to result in more pronounced magnetostrictive properties. The particle alignment due to the orientation field is beneficial for the promotion of the magnetostrictive properties. The largest saturation magnetostriction and the maximum piezo-magnetic coefficient in the absence of a mechanical preload was obtained at 1005 ppm and 4.08 nm/A, respectively, for the aligned composite including a particle volume fraction of 77% and an average particle size of 210 μm.     

Electrical Conductivities and Physical and Mechanical Properties of Carbon Fiber (CF) and Carbon Nano-Tube (CNT) Filled Polyolefin Nano-Composites

Carbon nano-tube (CNT)- and carbon fiber (CF)-filled polyolefin nano-composites were prepared by melt blending. The water absorption, expansion ratio, electrical conductivities, and physical and mechanical properties of the prepared nano-composites were extensively investigated. The experimental results showed that the water absorption increased with the elapsed time from the starting point when the samples were immersed into the water. The linear expansion ratios of the composites were found to increase gradually with time till reaching an equilibrium value. Composites with excellent dielectric properties could be obtained when the filler content was above the percolation threshold. The addition of CNT and CF resulted in no obvious improvement in mechanical properties in the present study, but both Shore hardness and Vicat softening temperature (VST) of the composites increased with increasing filler content. The present work will be of practical importance to the CNT/CF filler composites design, and optimization of processing variables, as well as the further exploration of the “processing-structure-property” relationship of polyolefin materials.     

Fiber-optic pH sensor based on sol-gel film immobilized with neutral red

In this study, we developed a fiber-optic pH sensor based on a sol-gel film immobilized with neutral red (NR). A solgel film was prepared by mixing tetramethylorthosilicate (TMOS), trimethoxymethylsilane (MTMS), ethanol (EtOH), distilled water (H₂O), and NR powder. Accordingly, the thin pH sol-gel film was fabricated through a sol-gel process with a dip-coating method. The thickness and diameter of the fabricated pH sol-gel film are 0.11 and 0.6 mm, respectively. We measured the optical absorbance and the light intensity with the spectra of reflected light, which change with the color variation of the pH sol-gel film in the fiber-optic sensing probe. From the experimental results, we demonstrated that the proposed fiber-optic pH sensor has good reversibility, reproducibility, and a fast response time, in which the optical properties of the NR-based pH sol-gel film change with the pH value.     

Reinforcing mechanism of a novel hydrophilic nano-carbon black in natural rubber latex

Novel water-dispersible carbon nanoparticles (PNASS-CBs) were produced by radical polymerization of sodium 4-styrenesulfonate (NASS) on the surface of carbon black (CB) in the solid state. Scanning electron microscopy (SEM) and the Payne effect results showed that the modified CBs were less likely to form particle networks and thus dispersed better in the natural rubber (NR) matrix, with an average size of 90 nm that was much less than that of the aggregated pristine CBs. We propose that the appropriate modification of CBs mitigates filler-filler interaction and enhances the filler-rubber interaction, which can also be proved by the higher bound rubber contents of the NRL/PNASS-CB composites. When a NRL/PNASS-CB composite is subjected to an outside force, e.g. tensile, more physically absorbed rubber chains (bound rubber) slip and self-adjust their absorbed spots on the CBs’ surface (stress redistribution) in order to jointly share the applied stress. This has a positive effect on the resistance to damage of the rubber molecular chains. Therefore, the addition of the hydrophilic CBs in NR latex leads to significant improvements in the mechanical properties of the NRL/PNASS-CB composites.     

Effect of Polyethylene Functionalization on Mechanical Properties and Morphology of PE/SiO2 Composites

In this study composites of high density polyethylene (HDPE) with various SiO₂ content were prepared by melt compounding using maleic anhydride grafted polyethylene (PE-g-MAH) as a compatibilizer. The composites containing 2, 4 and 6% by weight of SiO₂ particles were melt-blended in a co-rotating twin screw extruder. In all composites, polyethylene-graft-maleic anhydride copolymer (PE-g-MAH, with 0.85% maleic anhydride content) was added as a compatibilizer in the amount of 2% by weight. Morphology of inorganic silica filler precipitated from emulsion media was investigated. Mechanical properties and composite microstructure were determined by tensile tests and scanning electron microscopy technique (SEM). Tensile strength, yield stress, Young's modulus and elongation at break of PE/SiO₂ composites were mainly discussed against the properties of PE/PE-g-MAH/SiO₂ composites. The most pronounced increase in mechanical parameters was observed in Young's modulus for composites with polyethylene grafted with maleic anhydride. The increase in the E-modulus of PE/PE-g-MAH/SiO₂composites was associated with the compatibility and improvement of interfacial adhesion between the polyethylene matrix and the nanoparticles, leading to an increased degree of particle dispersion. This finding was verified on the basis of SEM micrographs for composites of PE/PE-g-MAH/4% by weight of SiO₂. The micrographs clearly documented that addition of only 2 wt% of the compatibilizer changed the composite morphology by reducing filler aggregates size as well as their number. Increased adhesion between the PE matrix and SiO₂ particles was interpreted to be a result of interactions taking place between the polar groups of maleic anhydride and silanol groups on the silica surface. These interactions are responsible for reduction of the size of silica aggregates, leading to improved mechanical properties.     

Effect of Processing Parameters on the Interlaminar Shear Strength of Carbon Fiber/Epoxy Composites

The objective of this work was to improve the interlaminar shear strength of carbon fiber/epoxy composites by determining the effect on it of the processing parameters of the cured composites system, i.e., temperature, content of curing agent, and heating rate. Taguchi methodology and analysis of variance were applied for optimizing and statistically determining the significant factors that influenced the mechanical properties of the composites. It was found that the temperature and content of curing agent were equally the primary significant factors in controlling the interlaminar shear strength of the composites. Also, the correlation between water absorption and mechanical properties of the composites was investigated.     

Synthesis and stabilization of ZnS nanoparticles embedded in silica nanospheres

The silica-coated ZnS nanocomposites have been synthesized by a seeded-growth procedure in iso-propanol. The results of XRD, HRTEM and UV absorption show that the ZnS nanoparticles can be incorporated in the silica nanospheres without changing the particle size, and the composites are of multi-core structure. UV absorption and emission spectra have been performed to check the character of the composites, which show that the silica shell not only increases the PL intensity, but also greatly improves the anti-oxidation ability and thermal stability. PACS 81.05.Dz; 81.16.Be; 81.65.Rv; 78.55.Et; 78.66.Hf