Deformation and failure of PP composites reinforced with lignocellulosic fibers: Effect of inherent strength of the particles

PP/wood composites were prepared from two lignocellulosic fibers with different particle size and aspect ratio in order to determine the effect of these factors on the deformation and failure mechanism as well as on the properties of the composites. Wood content was changed from 0 to 80 wt%. Maleinated polypropylene (MAPP) was added to improve interfacial adhesion. The MAPP/wood ratio was kept constant at 0.1. Mechanical properties were determined by tensile testing. Micromechanical deformation processes were followed by acoustic emission (AE) and volume strain (VOLS) measurements, and by the study of fracture surfaces. The results proved that micromechanical deformations change drastically both with decreasing particle size and changing interfacial adhesion. Less debonding, fiber pull out and fiber fracture occur in composites containing small particles. Hardly any change was observed in the mechanical properties of the composites with decreasing particle size, in spite of the drastic modification of the deformation mechanism. The apparently slight influence of particle size on composite strength results from the smaller aspect ratio of the small particles, which indicates that orientation and orientation distribution must have a strong effect on reinforcement. Further improvement in composite strength is possible only through the optimization of particle size, aspect ratio and the inherent strength of wood.     

Wood based PLA and PP composites: Effect of fibre type and matrix polymer on fibre morphology,dispersion and composite properties

This study presents a comparison of the effect of various wood fibre types in polylactic acid and polypropylene composites produced by melt processing. The study also reveals the reinforcing effect of pelletised wood fibres compared to conventionally used wood flour or refined fibres. Composites containing 30 wt.% of chemical pulps, thermomechanical pulp and wood flour were produced by compounding and injection moulding. Fibre morphologies were analysed before and after melt processing. The dispersion of the fibres and mechanical performance of the composites were also investigated. Fibre length was reduced during melt processing steps, reduction being higher with longer fibres. Wood fibres provided clearly higher plastic reinforcement than wood flour. Comparing the wood fibre types, TMP fibres provided the highest improvement in mechanical properties in polylactic acid composites with uniform fibre dispersion. In polypropylene composites, fibre selection is not as crucial.     

Die drawn wood polymer composites. II. Micromechanical modelling of tensile modulus

The Cox–Krenchel micromechanical model was applied to give predictions for the tensile moduli of isotropic and oriented wood polymer composites (WPC). The oriented WPC were produced by the Leeds die-drawing process using polypropylene filled with softwood and hardwood powders. The wood particles were extracted from the composites to determine their density and aspect ratio by dissolving in hot decalin. To measure particle shape and size, image analysis was employed. These experimental parameters were then introduced to the Cox–Krenchel model which was found to give prediction of tensile modulus in very good agreement with the experimental values.     

Biological performance of wood–plastic composites containing zinc borate: Laboratory and 3-year field test results

Six different formulations of wood–plastic composites (WPC) fabricated from wood and polypropylene (PP) were tested in the laboratory against decay and termites and in a protected above-ground field test in southern Japan. Variables examined included comparisons of untreated and zinc borate (ZnB) incorporated formulations, wood content ratio, wood particle size and increased surface area via surface grooves (channels) to promote moisture infusion. A standard method originally designed to test durability of solid wood was modified for testing WPC. Wood decay fungi and Formosan subterranean termite activity in laboratory and field tests resulted in different mass losses, post-decay moisture contents and field test ratings depending on their wood and ZnB content. The results show that as wood content increased, mass losses also increased. Addition of ZnB at 1% (w/w) retention level significantly decreased mass losses of wood–plastic composite when exposed to laboratory decay and termite tests. The effects of surface grooves and wood particle size were less important, compared to wood particle content. All WPC tested were highly resistant to fungal decay under protected above-ground field conditions during 36 months. Termite attack, on the other hand, started at earlier stage reducing mean ratings 1 year after the installation.     

Effects of chemical modification of wood particles with glutaraldehyde and 1,3-dimethylol-4,5-dihydroxyethyleneurea on properties of the resulting polypropylene composites

Both glutaraldehyde (GA) and 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) can crosslink the cell wall polymers and dimensionally stabilize wood particles and the treated wood particles are thus expected to enhance the properties of the resulting wood particle/polypropylene composites. Compared to the composites filled with untreated particles, treatments of wood particles with both GA and DMDHEU showed a great reduction in water uptake and dimensional swelling of the resulting composites up to 39% and 46%, respectively. Both the flexural and tensile moduli increased due to wood particles treatments with GA and DMDHEU. Treatments of wood particles improved the tensile strength but moderately weakened the flexural strength and Charpy impact strength of the composites. Dynamic mechanical analysis and microscopy suggested an improved interfacial compatibility between wood particles and matrix due to GA and DMDHEU treatments. Chemical treatment resulted in smaller particle sizes and altered microscopic fracture appearance after composite production as compared to untreated particles. Morphological changes were attributed to embrittlement of wood particles, which may negatively influence the mechanical properties of the resulting composites.     

Activating relaxation-controlled diffusion mechanisms for tailored moisture resistance of gelatin-based bioadhesives for engineered wood products

The feasibility of tailoring the moisture resistance of bioadhesives by activating relaxation-controlled diffusion mechanisms is demonstrated herein using gelatin, a hydrophilic biopolymer, as a model biobased resin for engineered wood products. The effect of gelatin-to-water concentration and tannin addition on the governing kinetics of water transport in gelatin-based bioadhesives was investigated in this work. Time-dependent flexural mechanical properties of laminated (a) gelatin and (b) gelatin–tannin wood veneer composites conditioned at both moderate and high humidity were characterized and compared to oriented strand board and plywood. Results indicate that increases in both gelatin and tannin content not only decrease rates of water uptake, volumetric swelling, and maximum moisture contents of gelatin-based resins, but also increasingly induce relaxation-controlled moisture diffusion behavior, which implies short-term moisture resistance and long-term moisture affinity. This behavior could be leveraged to address both in-service (i.e., strength, stiffness) and out-of-service (i.e., rapid biodegradation) requirements for engineered wood products.     

Influence of refiner fibre quality and fibre modification treatments on properties of injection-moulded beech wood–plastic composites

Thermo-mechanical pulp (TMP) fibres made from beech wood were produced using increasing refiner gap widths and thus with increasing fibre length and coarseness. Fibres (60% by weight) were compounded in an internal kneading mixer using high-density polyethylene as the matrix and injection-moulded. Fibre lengths and length/width ratios were determined (a) before processing and (b) after injection-moulding and Soxhlet extraction using the optical FibreShape system. An increase in fibre length resulted in a decrease in water absorption and an improvement in flexural strength and modulus of elasticity of the wood–plastic composites (WPC). However, flexural strength of the WPC with TMP fibres was not improved compared to WPC with wood flour when maleic anhydride-grafted polyethylene (MAPE) was used as a coupling agent. After injection-moulding, differences in length of the various TMP fibre types were minor. Fibre geometry before processing strongly influences the water absorption and flexural properties of the composite. Fibre treatment with emulsified methylene diphenyl diisocyanate (EMDI) resin before compounding was shown to be equally efficient in reducing water absorption and improving flexural strength as the addition of MAPE during the compounding step.     

Micromechanical deformation processes in PP/wood composites: Particle characteristics,adhesion, mechanisms

Polypropylene (PP) was reinforced with four natural fillers having different particle characteristics. Interfacial adhesion was changed by the introduction of maleated polypropylene (MAPP). The properties of the studied PP/wood composites depended strongly on interfacial adhesion and on the particle characteristics of the wood. Coupling with functionalized polymer is necessary for the preparation of composites with acceptable properties if the size of the particles is large and their aspect ratio is small. The effect of adhesion is smaller for particles with large aspect ratio. Several micromechanical deformation processes may occur in PP/wood composites including matrix yielding, debonding, fiber pull-out and fiber fracture both parallel and perpendicular to the fiber axis. The processes are competitive and may take place simultaneously and/or consecutively. The inherent properties of the reinforcement may limit the improvement of composite strength. Micromechanical deformation processes determine composite properties irrespectively of their mechanism.     

Characterization and biodegradability of polypropylene composites using agricultural residues and waste fish

The objective of this research was to study the potential of waste agricultural residues such as rice-husk fiber (RHF), bagasse fiber (BF), and waste fish (WF) as reinforcing and biodegradable agents for thermoplastic composites. Addition of maleic anhydride grafted polypropylene (MAPP) as coupling agent was performed to promote polymer/fiber interfacial adhesion. Several composites with various polypropylene (PP) as polymer matrix, RHF, BF, WF, and MAPP contents were fabricated by melt compounding in a twin-screw extruder and then by injection molding. The resulting composites were evaluated through mechanical properties in terms of tensile, flexural, elongation at break and Izod notched impact following ASTM procedures. Biodegradability of the composites was measured using soil burial test in order to study the rates of biodegradation of the composites. In general, the addition of RHF and BF promoted an increase in the mechanical properties, except impact strength, compared with the neat PP. According to the results, WF did not have reinforcing effect on the mechanical properties, while it could considerably improve the biodegradation of the composites. It was found that the composites with high content of WF had higher degradation rate. Except impact strength, all mechanical properties were found to enhance with increase in cellulosic fiber loading In addition, mechanical properties and biodegradability of the composites made up using RHF was superior to those of the composites fabricated with BF, due to its morphological (aspect ratio) characteristics.     

Influence of wood flour moisture content on the degree of silane-crosslinking and its relationship to structure–property relations of wood–thermoplastic composites

The objective of this work was to examine how the moisture content of wood flour affects the degree of crosslinking when producing silane-crosslinked wood–thermoplastic composites. Crosslinked composites were produced by adding a silane solution to the compounding process of wood flour and polyethylene. Crosslinked composites of pre-dried as well as non-dried wood flour were prepared and their degree of crosslinking at various storage conditions was determined. Mechanical properties and the creep response of the crosslinked composites were tested in order to establish structure–properties relations. The results showed that all crosslinked composites displayed higher strengths and lower creep responses compared with non-crosslinked control samples. However, the degree and rate of crosslinking proved to be lower when a larger amount of moisture was present in the compounding process. It was concluded that the silane-grafting yield was lower when wood flour of a higher moisture content was used.     

A comparative study on the effects of Coriolus versicolor on properties of HDPE/wood flour/paper sludge composites

In this study, the effects of white-rot fungus (Coriolus versicolor) on the properties of high density polyethylene (HDPE)/wood flour/paper sludge composites were examined. In addition, the effectiveness of using coupling agent on the durability of decayed and undecayed WPCs was investigated. Two different types of sludge materials, namely paper making waste water sludge (PS) and ink-eliminated sludge (IES) were used. The mechanical properties, morphology, and water absorption of fabricated composites were investigated. At a similar wood flour loading, except for modulus of elasticity, the fungi treated composites showed lower mechanical properties (such as modulus of rupture and unnotched Izod impact strength), and higher water absorption compared to untreated composites. According to the results, addition of wood flour decreased the resistance of the composites to moisture and fungal environment. The exposure of the composites to a 4-cycle (2, 24, 48 and 72 h) water immersion caused serious damage to the interfacial adhesion between wood flour and polymer matrix due to contraction and swelling stresses developed during the cyclic exposure. The detrimental effect of fungal treatment on the water uptake of the composites could be explained by the degradation of lignin which made the cellulose content more accessible. Further, it makes chains of cavities that accelerate water absorption. However, the weight losses of all cases of treated composites were low (less than 2.5%), while PS filled composites were more susceptible to white-rot fungi. The addition of coupling agent during the compounding of wood flour and HDPE prevented the colonization and proliferation of fungus on the surface of the composites, and had an advantageous effect on the water uptake and mechanical properties of both treated and untreated composites.     

超高填充聚丙烯基木塑复合材料高低温性能

为了充分降低成本,增加环境友好性并获得良好的木质感,以杨木纤维和毛竹纤维为原料,通过挤出成型制备超高填充聚丙烯基木塑复合材料(UH-WPCs)。基于聚丙烯基体含量的大幅降低,对比分析了填充量和木质纤维种类对UH-WPCs高低温力学性能、高低温蠕变性能、热膨胀性能、尺寸稳定性及吸水性能的影响。结果表明,随着填充量从75wt%增加到90wt%,其线性热膨胀系数大幅降低,蠕变应变逐渐减小而在90wt%时增大;拉伸模量和弯曲模量随填充量的增加先升高而后在90wt%时下降;拉伸强度、弯曲强度和冲击强度随着填充量的增加逐渐降低;在低温?30℃时UH-WPCs的拉伸和弯曲性能较高,高温60℃时冲击韧性较好。温度、湿度及含水率变化均导致UH-WPCs尺寸变化,其中厚度方向尺寸变化率最大,其次为宽度方向,长度方向最小,表现出明显的各向异性;湿度对UH-WPCs的尺寸稳定性的影响远大于温度的作用。杨木基UH-WPCs综合性能优于毛竹基UH-WPCs,这与杨木纤维具有更大的长径比及良好的界面结合有关。UH-WPCs的研究为降低WPCs生产成本和拓宽其应用领域提供了理论依据。      

Wood–plastic composites formulated with virgin and recycled ABS

It is demonstrated that wood–plastic composites (WPCs) having desirable mechanical properties can be formulated using acrylonitrile butadiene styrene (ABS) as the matrix polymer. This is accomplished by compounding the polymer with 50 wt.% wood particulates using a twin-screw extruder; both virgin resin and polymer recovered from computer monitors and keyboards were utilized for this purpose. It was found that, while the impact strength and ductility of the virgin and recycled polymers were significantly different, the composite properties differed only slightly from each other. These properties could be improved with the use of coupling agents, but the extent of improvement depended on the chemical nature of the coupling agent employed. In view of this, ABS recovered from post-consumer applications can be recycled into high-value composites without going through the expense of separating out impurities from the polymer.     

木粉/聚丙烯木塑复合泡沫材料吸能特性

采用模压法制备木粉/聚丙烯复合泡沫材料,并对不同木粉含量的泡沫材料进行静态压缩、循环压缩、压缩蠕变、动态热机械分析的测试,探讨了不同木粉含量的木粉/聚丙烯复合泡沫材料的能量吸收效果。结果表明: 随着木粉含量的增加,木粉/聚丙烯木塑复合泡沫材料的能量吸收量、能量吸收效率参数、松弛率、循环损耗量、动态力学性能等均呈先升后降的趋势,在木粉质量比为30%时泡沫材料吸能性能达到最佳。     

Dynamic particle analysis for the evaluation of particle degradation during compounding of wood plastic composites

A dynamic image analysis method was applied for particle characterisation to study the effect of different process conditions during twin-screw compounding of WPC. The use of distributions based on different types of quantity is discussed with respect to their sensitivity to reveal the effects of different process conditions on particle degradation. Distributions based on length proved to be most suitable to represent the initially broad length distribution of the particles before processing. Sensitivity was strong enough to show differences in particle size after processing depending on process conditions. Particle size was reduced by more than 97% compared to initial size. Degradation was stronger with increasing wood content and when the screw design contained more mixing elements. The effect of screw speed and feed rate was dependent on filler content and screw design.     

Heat treated wood–nylon 6 composites

Heat treatment is a relatively benign modification method that is growing as an industrial process to improve hygroscopicity, dimensional stability and biological resistance of lignocellulosic fillers. There also has been increased interest in the use of lignocellulosic fillers in numerous automotive applications. This study investigated the influence of untreated and heat treated wood fillers on the mechanical and rheological properties of wood filled nylon 6 composites for possible under-the-hood applications in the automobile industry where conditions are too severe for commodity plastics to withstand. In this study, exposure of wood to high temperatures (212 °C for 8 h) improved the thermal stability and crystallinity of wood. Heat treated pine and maple filled nylon 6 composites (at 20 wt.% loading) had higher tensile strengths among all formulations and increased tensile strength by 109% and 106% compared to neat nylon 6, respectively. Flexural modulus of elasticity (FMOE) of the neat nylon 6 was 2.34 GPa. The FMOE increased by 101% and 82% with the addition of 30 wt.% heat treated pine and 20 wt.% heat treated maple, where it reached maximum values of 4.71 GPa and 4.27 GPa, respectively. The rheological properties of the composites correlated with the crystallinity of wood fillers after the heat treatment. Wood fillers with high crystallinity after heat treatment contributed to a higher storage modulus, complex viscosity and steady shear viscosity and low loss factor in the composites. This result suggests that heat treatment substantially affects the mechanical and rheological properties of wood filled nylon 6 composites. The mechanical properties and thermogravimetric analysis indicated that the heat treated wood did not show significant thermal degradation under 250 °C, suggesting that the wood-filled nylon composites could be especially relevant in thermally challenging areas such as the manufacture of under-the-hood automobile components.     

Die drawn wood polymer composites. I. Mechanical properties

Oriented wood polymer composites (WPC) have been prepared by the Leeds die drawing process. Softwood and hardwood powder were used at 40% weight concentration (32% volume concentration) and in both cases materials with significantly increased stiffness (from 1.9 to 8.2 GPa) and strength (from 13 to 127 MPa) were obtained. Although the moduli of the drawn filled composites were lower than the equivalent unfilled polypropylene, the specific moduli, which take into account the lower density of the die drawn materials due to void formation were very similar. The type of wood particles and the use of polypropylene grafted with maleic anhydride had only a marginal influence on the mechanical properties of the die drawn composites. The morphology of the wood composites was studied by electron microscopy.     

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.     

Polybutene as a matrix for wood plastic composites

This study examined the feasibility of using polybutene-1 (PB-1), a ductile plastic, as a matrix for manufacturing wood plastic composites (WPCs) with improved toughness and ductility compared to currently commercialized WPCs. The processability, tensile, flexural, and impact properties of injection molded PB-1/wood-flour composite samples with varying proportions of wood flour were characterized. Analysis also included the morphology of fractured samples surface and adhesion between the polymer and wood flour using SEM. Comparisons of the mechanical properties and adhesion in the PB-1 composites to those of HDPE and PP-based WPCs found the composites made with PB-1 matrix significantly inferior in strength and stiffness (both in tensile and flexural) than their counterparts made of HDPE and PP matrices. In contrast, the processability, elongation at break, impact strength and adhesion in PB-1/wood-flour composites, superior to those of HDPE and PP, confirmed their suitability for use as a matrix in composites intended for applications subjected to high impacts.     

Design analysis of three-layered structural composites based on post-consumer recycled plastics and wood residues

Three-layered structural composites were produced from municipal plastic wastes and wood flour residues to investigate the effects of design parameters on their flexural and impact performance. The studied parameters include wood content, thickness of individual composite layers, as well as stacking sequence and configuration (symmetric and asymmetric structures). The results indicate that the core layer has a lower influence on the flexural properties of structural beams in comparison with the skins. But depending on beam configuration (stacking sequence), different flexural characteristics can be obtained using the same composite layers. The classical beam theory was used to predict the flexural modulus with high precision. In addition, performance of the beams under impact tests was shown to be independent from their stacking sequences and layer thicknesses for each configuration.