Effects of fiber characteristics on the physical and mechanical properties of wood plastic composites

We investigated the effects of fiber variability, size, and content on selected mechanical and physical properties of wood plastic composites. HDPE and fibers were compounded into pellets by twin-screw extrusion and test specimens were prepared by injection molding. All tested properties vary significantly with fiber origin. Higher fiber size produces higher strength and elasticity but lower energy to break and elongation. The effect of fiber size on water uptake is minimal. Increasing fiber load improves the strength and stiffness of the composite but decreases elongation and energy to break. Water uptake increases with increasing fiber content.     

SiC颗粒-SiC晶须混杂填料/双马来酰亚胺树脂导热复合材料的制备与性能

以双马来酰亚胺树脂(BMI)为树脂基体,二烯丙基双酚A(DABA)为增韧剂,γ-缩水甘油醚氧丙基三甲氧基硅烷(KH-560)表面改性的SiC颗粒-SiC晶须(SiCP-SiCW)为复配导热填料,浇注成型制备SiC_P-SiC_W/BMI导热复合材料,分析研究SiC形状、用量、质量比及表面改性对SiC_P-SiC_W/BMI导热复合材料的导热性能、介电性能、力学性能和热性能的影响。结果表明,当改性SiC_P-SiC_W用量为40wt%且SiC_P∶SiC_W质量比为1∶3时,SiC_P-SiC_W/BMI导热复合材料具有最佳的综合性能,导热系数λ为1.125W(m·K)~(-1),介电常数ε为4.12,5%热失重温度为427℃。     

Effects of formulation variables on surface properties of wood plastic composites

Degree of surface quality of wood plastic composites (WPCs) is a function of both raw material characteristics and the manufacturing variables. The WPC panels comprised of different panel densities (800, 950, 1000, and 1080 kg/m³), wood flour contents (50, 60, 70, and 80 wt.%), wood flour sizes (<0.5, ?0.5 to <0.8, 0.8–1, and >1 mm), and hot-pressing temperatures (190 and 210 °C) were manufactured using a dry blend/flat-pressing method under laboratory conditions. The surface smoothness of the WPC panels improved with increasing WPC density, plastic content, and hot-pressing temperature while it deteriorated with increasing wood flour size. The reduction in the particle size of the WF resulted in a more compact structure on the WPC surface. In general, the wettability of the samples increased by increasing surface roughness.     

Effects of chemical preservative treatments on durability of wood flour/HDPE composites

The main objective of this study was to determine the durability of chemical preservatives treated wood flour/high density polyethylene (HDPE) composites to white-rot fungus (Coriolus versicolor). Specimens, containing treated and untreated poplar wood flour (PF, 60%), were mixed with HDPE (38%) as polymer matrix and maleic anhydride grafted polyethylene (MAPE, 2 wt.%) as coupling agent. Two fungicide materials, namely 3-iodo-2-propynyl butylcarbamate (IPBC, 0.3, 0.6 and 0.9 wt.%) and 2 thiazol-4-yl-1H-benzoimidazole (TBZ, 0.3, 0.6 and 0.9 wt.%) were used in preparation of wood plastic composites (WPCs). Then, treated and untreated composites were exposed to the fungal decay for 12 weeks according to the European Union (EN) 113 standard. Mechanical and physical properties of the composites were evaluated before and after fungal incubation. The experimental results indicated that treated composites were more resistant to decay, with strength losses significantly lower than the untreated (control) sample. Physical properties in terms of water absorption and thickness swelling were improved by the incorporation of fungicide agents, but no significant differences were observed between the treaded samples. Weight losses for the various treated composites ranged from 1.1% to 4.5%. In addition, IPBC treated samples showed slightly lower weight loss compared with the treated composites with TBZ. The highest weight loss corresponds to the control. Accordingly, IPBC and TBZ can be effectively used as preservatives for WPC. However, IPBC showed superior results compared to the TBZ and it is recommended for the WPCs preservation.     

The utilization of bamboo charcoal enhances wood plastic composites with excellent mechanical and thermal properties

In order to enhance the mechanical properties and thermal properties of wood plastic composites (WPCs), bamboo charcoal (BC) was used as reinforcing filler of WPC, and a series of BC-WPC composites were prepared. The effect of BC and water treatment on water absorptions, morphologies, mechanical properties, the effect of water treatment on mechanical properties and thermal properties of the composites were investigated. The results showed that BC could have strong interfacial interaction in the WPC. The water resistance, flexural properties, tensile properties and thermal properties of BC-WPC were higher than WPC. The flexural and tensile properties were reduced and the impact strength was increased after water treatment. The presence of BC resists the influence of water absorption on composites mechanical properties.     

注塑级聚烯烃塑木复合材料性能研究

制备了注塑级塑木复合材料,研究了木粉添加量对塑木注塑成型复合材料流变性能、弯曲性能和熔融结晶性能的影响。结果表明:随木粉添加量的增加,塑木注塑成型复合材料弯曲强度、弯曲模量和熔融峰温度均出现先增加再降低的现象,当木粉添加量在30份时,复合材料弯曲强度达到30.85MPa,弯曲模量达到3065.21MPa,熔融峰温度也达到最高。     

Electrical and thermal properties of polyamide 12 composites with hybrid fillers systems of multiwalled carbon nanotubes and carbon black

Hybrid filler systems of multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) were incorporated into two types of polyamide 12 (PA12) using small-scale melt mixing in order to identify potential synergistic effects on the interaction of these two electrical conductive fillers. Although no synergistic effects were observed regarding the electrical percolation threshold, at loadings well above the percolation threshold higher volume conductivities were obtained for samples containing both, MWCNT and CB, as compared to single fillers. This effect was more pronounced when using a higher viscous PA12 matrix. The formation of a co-supporting network can be assumed. The combined use of CB and MWCNTs improved the macrodispersion of MWCNT agglomerates, which can be assigned as a synergistic effect. DSC measurements indicated an effect of the nanofiller on crystallisation temperatures of PA12; however this was independent of the kind or amount of the carbon nanofiller.     

Effects of carbon nanotubes and its functionalization on the thermal and flammability properties of polypropylene/wood flour composites

In this article, pristine carbon nanotubes (CNTs) and hydroxylated CNTs (CNT-OH) were employed to enhance the thermal stability and flame retardancy of polypropylene (PP)/wood flour composites (WPC) compatibilzed by maleic anhydride-grafted polypropylene (PP-g-MA). Incorporating 10 wt% PP-g-MA only enhanced the mechanical and thermal properties to some extent, but did not improve the flame retardancy of WPC. Thermogravimetric analysis (TGA) showed that the thermal stability of WPC was further increased with the addition of CNTs or CNT-OH and the increase of their loading level. Cone calorimeter measurements suggested that CNTs and CNT-OH could effectively reduce the peak heat release rate (PHRR) of WPC, and the flame retardancy properties reached the optimum value when both of their loading was 1.0 wt%, for instance, a reduction in PHRR by 16.7% and 25% for CNTs and CNT-OH, respectively. In addition, CNT-OH conferred better flame retardancy on WPC relative to pristine CNTs due to the better interfacial adhesion with wood flour and PP matrix, which was evidenced by scanning electron microscopy (SEM) observations.     

高热导率无机填料／硅橡胶复合绝缘材料的电性能

分别添加不同含量的微米Al2O3（0．5～3μm）、微米Si3N4（O．3～3μm）和纳米Al2O3（13nm）,利用共混法制备了具有不同导热性能的无机填料／硅橡胶复合材料。填料体积分数为30％时,通过改变微米Si3N4和纳米Al2O3体积比,发现微米Si3N4和纳米Al2O3共填充的硅橡胶复合材料的热导率较微米Si3...     

Effects of hydrophobation treatments of wood particles with an amino alkylsiloxane co-oligomer on properties of the ensuing polypropylene composites

In this study an amino alkylsiloxane co-oligomer was used to treat the wood particles to weight percent gains of 1.5%, 4.5%, and 7.0%, respectively, and coupling effects on the properties of the ensuing wood polypropylene composites were determined. The n-propyl-trimethoxysilane (alkylsilane) and 3-amino-propyltriethoxysilane (aminosilane) were also used for comparison. Compared to composites filled with untreated particles, composites treated with co-oligomer exhibited greater reduction in both the rates of water uptake and dimensional swelling than those treated with the other two silanes. Both, the flexural- and Charpy impact strengths of the composites, were moderately reduced but the tensile strength increased up to 23% due to treatment with the co-oligomer. The different effects by the silanes were also evidenced by dynamic mechanical analysis and microscopy. These results show that use of the co-oligomer can create a highly hydrophobic composite and any improvement in the mechanical properties is comparable to that with aminosilane.     

Date palm wood flour/glass fibre reinforced hybrid composites of recycled polypropylene: Mechanical and thermal properties

Recycled polypropylene (RPP) based hybrid composites of date palm wood flour/glass fibre were prepared by different weight ratios of the two reinforcements. Mixing process was carried out in an extruder and samples were prepared by injection molding machine. Recycled PP properties were improved by reinforcing it by wood flour. The tensile strength and Young’s modulus of wood flour reinforced RPP increased further by adding glass fibre. Glass fibre reinforced composites showed higher hardness than other composites. Morphological studies indicated that glass fiber has good adhesion with recycled PP supporting the improvement of the mechanical properties of hybrid composites with glass fiber addition. Addition of as little 5 wt% glass fibre to wood flour reinforced RPP increases the tensile strength by about 18% relative to the wood flour reinforcement alone. An increase in wood particle content in the PP resulted in a decrease in the degree of crystallinity of the polymer. The tensile strength of the composites increased with an increase in the percentage of crystallinity when adding the glass fibre. The improvement in the mechanical properties with the increase in crystallinity percentage (and with the decrease of the lamellar thicknesses) can be attributed to the constrained region between the lamellae because the agglomeration is absent in this case.     

Fatigue properties of wood and wood composites

An overview of the state of fatigue research for wood and wood products is presented. The extreme lack of a satisfactory data base and the persistent neglect of fatigue characteristics in wood material design is emphasized. Some theoretical considerations are presented to point out the difficulties met when attempting to model the behavior of wood products exposed to cyclic loading phenomena.A major conclusion of the work is the need for the entire materials science community to consider wood as a valuable and rewarding material upon which to focus research efforts. As wood is the world's primary renewable structural resource, a concerted effort must be made to understand its fatigue performance and the degree of accuracy in predicting life expectancy.

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Résumé On présente une revue générale des recherches dans le domaine de la fatigue du bois et des produits à base de bois. On fait remarques l'extrème pauvreté de bases de données satisfaisantes et la négligence persistante avec laquelle les caractéristiques de fatigue sont prises en considération dans la conception à partir de matériaux en bois. On présente quelques considérations théoriques exprimant les difficultés rencontrées lorsqu'il s'agit de modéliser le comportement des produits ligneux exposés au phénomène de mise en charge cyclique.Une conclusion importante du travail vise à sensibiliser la communauté des sciences des matériaux à considérer le bois comme un matériau valable et prometteur sur lequel un effort de recherche doit être concentré. Comme le bois est la ressource structurelle première entièrement renouvelable de ce monde, un effort concerté doit être entrepris afin de comprendre ses performances à la fatigue et le degré d'exactitude des prévisions de vie.

     

Alfa fibres for unsaturated polyester composites reinforcement: Effects of chemical treatments on mechanical and permeation properties

In this study, composite materials were prepared using unsaturated polyester resins reinforced by Alfa fibres. The fibres were previously modified by chemical treatments, maleic anhydride (MA), styrene (S), acrylic acid (AA) and acetic anhydride (Ac). The Ac and the S treatments allowed an increase in the moisture resistance and the mechanical properties of the fibres. The preliminary S or MA treatment of the fibres allowed a decrease of the water permeability of the composite. A slight increase of the stiffness of the composite was observed due to the presence of the fibres (treated or not), whereas the resistance (breaking strength and strain) was not improved. The mechanical behaviour of the composites appeared similar whatever the treatment of the fibres except with S treatment which seemed to improve the breaking strength.     

Effect of wood species on property and weathering performance of wood plastic composites

The effects of wood species on mechanical, thermal and accelerated weathering behaviors of high-density polyethylene based wood plastic composites (WPC) were investigated. The selected wood species are poplar, Douglas-fir, black locust, white oak, and ponderosa pine. Hybrid poplar and Douglas-fir based composite ranked highly in flexural properties. Thermogravimetric analysis indicated that thermal stability of the WPC is species dependent. The final decomposition of hemicelluloses in the hardwoods occurred at higher temperatures compared to that of softwoods. Color and chemical changes that occurred due to accelerated weathering were monitored using colorimetry and Fourier transform infrared spectroscopy. Weathered WPCs showed that color change and lightness increased with exposure time; degree of increase depends on wood species. WPC oxidation by weathering was assessed by carbonyl group concentration and was shown to increase with exposure. Hybrid poplar and ponderosa pine were shown to have good color stability among the wood species examined for WPC.     

Investigation of physical and chemical properties of polypropylene hybrid nanocomposites

Hybrid nanocomposites fabricated based on an optimized physical and chemical properties modified polypropylene (PP)/polypropylene grafted maleic anhydride (PP-g-MA) with varied concentrations (1–7 wt% at a step of 2 wt%) of organoclay, montmorillonite (MMT). The morphology of the nanocomposites was studied by scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). It was found that partly intercalated and partly exfoliated structure (intercalated–exfoliated structures) existed in the system. The degree of exfoliation is a key factor to determine the reinforcement efficiency. The ratio of exfoliation to intercalation plays an important role in determining the properties of PP nanocomposites and only completely exfoliated silicate layers can significantly improve the properties. PP hybrid nanocomposites showed good thermal stability in the thermogravimetric analysis (TGA). Introduction of ∼3% MMT in the nanocomposites increased the onset temperature of degradation by 27.5 °C compared to that of pure PP, while the 5 wt% MMT resulted the maximum hardness in these nanocomposites. The solvent resistance of PP hybrid nanocomposites slightly increased with increasing the clay content.     

Effects of hybrid fillers based on micro- and nano-sized silver particles on the electrical performance of epoxy composites

In the present study, electrically conductive adhesives produced from hybrid fillers based on micro- and nano-sized silver (Ag) was developed. The influence of the hybrid filler composition on the electrical properties of the hybrid system was studied. The electrical conductivity of the epoxy composites filled with micro- and nano-silver was correlated with their morphologies. A positive effect was observed in the electrical conductivity result when the composition of micro- and nano-sized Ag particles reached a 50:50 weight ratio. The nano-sized Ag particles became interconnecting particles in the interstitial spaces between micro-sized particles. Micrograph scanning shows that the particles were well distributed and dispersed, the separation between lumps of Ag filler by the insulating matrix was significantly reduced, leading to the formation of continuous linkages. The increased electrical conductivity resulted in a charge around the particle distribution, which led to the high capacity. Hence, these particles increased the conductivity of the system.     

Effect of MWCNTs/ZnO inorganic fillers on the electrical,mechanical and thermal properties of SiR-based composites

Rubber insulation materials were widely used in the fields of electrical and electronic engineering, especially, which have excellent nonlinear electrical conductivity and can be employed to homogenize the electric field distribution of cable accessories. To enable the rubber materials, such as silicon rubber (SiR), to possess excellent nonlinear electrical conductivity has been a hot issue. In this paper, MWCNTs/ZnO inorganic fillers were prepared by mixing a small amount of multi-wall carbon nanotubes (MWCNTs) with zinc oxide (ZnO) nanosheets, and MWCNTs/ZnO/SiR composites were prepared. The macroscopical properties results show that the nonlinear electrical conductivity characteristics can be induced by filling appropriate content of MWCNTs/ZnO fillers, and the threshold field strength corresponding to the nonlinear conductivity gradually decreases with the increase of MWCNTs filling content, which further decreases with the increase of measured temperature. The COMSOL simulation results also verify that MWCNTs/ZnO/SiR composite with nonlinear conductivity can effectively reduce the electric field strength at the stress cone of cable accessories. In addition, the thermal conductivity and tensile strength for MWCNTs/ZnO/SiR composite are also improved comparing to pristine SiR. This work demonstrates MWCNTs/ZnO/SiR composites possess outstanding overall properties and have good potential to be used in the cable accessory.

     

Effects of chitosan as biopolymer coupling agent on the thermal and rheological properties of polyvinyl chloride/wood flour composites

Chitosan (CS) was opted as a novel biopolymer coupling agent for wood flour polyvinyl chloride composites (WF/PVC) to improve interfacial adhesion. This study mainly aimed at investigating the effects after adding CS of different addition amounts and particle sizes on the thermal and rheological properties of WF/PVC composites by the analyses of vicat softening temperature test (VST), differential scanning calorimetry (DSC), thermogravimetry (TGA) and torque rheometry. The results indicated that an optimum addition amount (30 phr) with the particle size (180–220 mesh) could elevate heat resistance capacity, glass transition temperature of composites as well as thermal stability at the early stage of degradation more effectively. In the aspect of rheological characteristics, longer fusion time, lower fusion torque and higher fusion temperature were showed as the CS addition amount increased and the particle size declined. In order to obtain sufficient compaction and ensure proper blending to compounds during extrusion, the higher pressure needed to be supplied when the addition amount of CS exceeded 20 phr.     

Enhanced thermal conductivity and retained electrical insulation for polyimide composites with SiC nanowires grown on graphene hybrid fillers

Polyimide (PI) composites containing one-dimensional SiC nanowires grown on two-dimensional graphene sheets (1D–2D SiC_NWs-GSs) hybrid fillers were successfully prepared. The PI/SiC_NWs-GSs composites synchronously exhibited high thermal conductivity and retained electrical insulation. Moreover, the heat conducting properties of PI/SiC_NWs-GSs films present well reproducibility within the temperature range from 25 to 175 °C. The maximum value of thermal conductivity of PI composite is 0.577 W/mK with 7 wt% fillers loading, increased by 138% in comparison with that of the neat PI. The 1D SiC nanowires grown on the GSs surface prevent the GSs contacting with each other in the PI matrix to retain electrical insulation of PI composites. In addition, the storage modulus and Young’s modulus of PI composites are remarkably improved in comparison with that of the neat PI.