Morphology,mechanical properties,and dimensional stability of wood particle/high density polyethylene composites: Effect of removal of wood cell wall composition

Variation in the chemical composition of wood cell walls has a significant influence on the properties of wood plastic composites (WPCs). This study investigated the effect of removal of hemicellulose and/or lignin on the mechanical properties and dimensional stability of WPCs. Four types of wood particles with various compositions including native wood flour (WF), hemicellulose-removed particle (HR), holocellulose (HC), and α-cellulose (αC) were prepared and compounded with high density polyethylene (HDPE) in an extruder, both with and without maleated polyethylene. Injection molding was used to make test specimens. The HR-based composites exhibited the best water resistance. The HC-based composites obtained a greater tensile modulus but a lower water resistance. The highest values for tensile strength, elongation at brake, toughness, and impact strength were achieved by the composites filled with αC.     

Effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of unidirectional hemp/epoxy composites

The objective of this study was to investigate the effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of hemp fibre/epoxy composites. Pectin removal by EDTA and endo-polygalacturonase (EPG) removed epidermal and parenchyma cells from hemp fibres and improved fibre separation. Hemicellulose removal by NaOH further improved fibre surface cleanliness. Removal of epidermal and parenchyma cells combined with improved fibre separation decreased composite porosity factor. As a result, pectin removal increased composite stiffness and ultimate tensile strength (UTS). Hemicellulose removal increased composite stiffness, but decreased composite UTS due to removal of xyloglucans. In comparison of all fibre treatments, composites with 0.5% EDTA + 0.2% EPG treated fibres had the highest tensile strength of 327 MPa at fibre volume content of 50%. Composites with 0.5% EDTA + 0.2% EPG → 10% NaOH treated fibres had the highest stiffness of 43 GPa and the lowest porosity factor of 0.04.     

Utilization of natural montmorillonite modified with dimethyl,dehydrogenated tallow quaternary ammonium salt as reinforcement in almond shell flour–polypropylene bio-nanocomposites

The main goal of this work was to evaluate the technical feasibility of almond shell flour (ASF) as wood substitute in the production of wood–plastic composites (WPCs). The effects of organically modified montmorillonite (OMMT), as reinforcing agent, on the mechanical and physical properties were also investigated. In order to improve the poor interfacial interaction between the hydrophilic Lignocellulosic material and hydrophobic polypropylene matrix, maleic anhydride grafted polypropylene (MAPP) was added as a coupling agent to all the composites studied. In the sample preparation, OMMT and ASF contents were used as variable factors. The morphology of the specimens was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The results of mechanical properties measurements indicated that when 3 wt.% OMMT were added, tensile and flexural properties reached their maximum values. At high level of OMMT loading (5 wt.%), increased population of OMMT lead to agglomeration and stress transfer gets blocked. The addition of OMMT filler decreased the water absorption and thickness swelling of composites. SEM study approved the good interaction of the almond shell flour with the polymer as well as the effectiveness of OMMT in improvement of the interaction. TEM study revealed better dispersion of silicate layers in WPCs loaded with 3 wt.% of OMMT. The improvement of physico-mechanical properties of composites confirmed that OMMT has good reinforcement and the optimum synergistic effect of OMMT and ASF was achieved at the combination of 3 and 50 wt.%, respectively. The findings indicated that almond shell as agro-waste material is a valuable renewable natural resource for composite production and could be utilized as a substitute for wood in composite industries.     

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.     

Lignin particle- and wood flour-reinforced phenolic foams: Friability,thermal stability and effect of hygrothermal aging on mechanical properties and morphology

In the present work, the effect of lignin particles and wood flour weight fractions incorporated on friability and thermal stability of a phenolic foam was determined. In addition, the effect of hygrothermal aging on compressive mechanical properties and cell size of the materials was studied. The incorporation of lignin particles decreased friability of the phenolic foam; whereas, wood flour increased it. The influence of both reinforcements on thermal stability of the material was very low. Although the reduction in mechanical properties of reinforced foams was higher than for the unreinforced material after hygrothermal aging, modulus and strength of the reinforced foams were still superior to those of the unreinforced material. Hygrothermal aging did not influence cell size of the foams studied. The material which exhibits the best combination of features was 8.5 wt.% lignin particle-reinforced phenolic foam.     

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.     

木粉含量对木粉-淀粉/聚乳酸复合材料性能的影响

以杨木粉、玉米淀粉和聚乳酸(PLA)为原料,甘油为相容剂,利用熔融挤出法制备了木粉-淀粉/PLA复合材料。研究了木粉含量对复合材料界面相容性、热性能、力学性能、流变性能以及吸水率的影响。结果表明:随着木粉含量的增加,PLA与木粉之间的界面相容性下降,木粉-淀粉/PLA复合材料的热稳定性下降,储能模量、损耗模量和复数黏度逐渐增加;随着木粉含量的增加,木粉-淀粉/PLA复合材料的拉伸强度和弯曲强度呈现先增大后减小的趋势,当木粉含量为18wt%时,复合材料的拉伸强度和弯曲强度均达到最大值,最大值分别为40.65 MPa和60.91 MPa;随木粉含量的增加,复合材料的断裂伸长率由9.64%减小到5.97%,而吸水率由5.38%增大到13.43%。     

硅烷偶联剂改性的木粉/P34HB复合包装材料的制备

目的研究硅烷偶联剂KH550含量对木粉/P34HB复合包装材料性能的影响。采用KH550改性木粉,提高与聚(3-羟基丁酸酯-4-羟基丁酸酯)(P34HB)的结合强度,改善复合材料的力学性能和界面相容性。方法以KH550为改性剂,木粉和P34HB为原料,利用共混热压工艺制备改性木粉/P34HB复合材料;通过对复合材料的形貌进行观察,以及傅里叶变换红外光谱(FTIR)、热重分析(TGA)和力学性能分析,研究KH550质量分数不同时对复合材料界面相容性、力学性能和热性能的影响。结果添加KH550后,复合材料的的界面相容性得到改善;FTIR分析表明,KH550已经成功接枝到木粉中;适量的KH550提高了复合材料的热稳定性;复合材料的储能模量增加;复合材料的力学性能也有所提高。此外还得到了最佳的KH550添加量,即质量分数为0.5%。结论 KH550不仅使得木粉与P34HB的相容性得到改善,同时也增强了复合包装材料的力学性能和热性能。     

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.     

Wood cellulose biocomposites with fibrous structures at micro- and nanoscale

High-strength composites from wood fiber and nanofibrillated cellulose (NFC) were prepared in a semi-automatic sheet former. The composites were characterized by tensile tests, dynamic mechanical thermal analysis, field-emission scanning electron microscopy, and porosity measurements. The tensile strength increased from 98 MPa to 160 MPa and the work to fracture was more than doubled with the addition of 10% NFC to wood fibers. A hierarchical structure was obtained in the composites in the form of a micro-scale wood fiber network and an additional NFC nanofiber network linking wood fibers and also occupying some of the micro-scale porosity. Deformation mechanisms are discussed as well as possible applications of this biocomposites concept.     

Poly(vinyl chloride)–wood flour press mould composites: The influence of raw materials on performance properties

In this paper is described an approach to the study of the influence of the nature and the composition on the performance properties of wood flour/poly(vinyl chloride)(PVC) composites. The raw materials were mixed on a two-roll mill. The final composites were obtained by controlled press moulding. The results indicate that properties such as surface tension and flexibility do not change significantly with the composition in the chosen composition range. The colour is easily controlled by variation in the content and the type of wood flour. A thermal and morphological study has been performed on the raw materials and on the composites to assess the effect of wood flour on the stability of the composites. The inclusion of wood flour into PVC leads to poorer tensile properties. This effect is related to the lack of association between the wood flour and the PVC.     

Lignocellulosic fibre mediated rubber composites: An overview

The rising concern towards the reduction in the use of petroleum-based, non-renewable resources and the need for more versatile polymer-based composite materials have led to increasing interests on natural polymer composites filled with natural organic fillers, i.e. coming from renewable and biodegradable sources. This paper reviews wood flour and other lignocellulosic fibres filled rubber composites, including cellulosic rubber composites, cellulosic thermoplastic elastomers, nanocellulose based rubber nanocomposites, with the aims at providing the most state of the art information for directing further scientific research, possible commercialization and design of cellulosic rubber composites. It has been found that 1) the surface properties of natural cellulose, hence the compatibility and interface of the natural cellulose and matrix rubber/plastics, are crucial for the successful development of the composites, such, physical and chemical modification and additives have been widely attempted to improve the incompatibility and poor interfacial adhesion between the filler and matrix; 2) the curing characteristics, mechanical properties, thermal stability and morphologies of the composites are complex but closely related to not only the interfacial properties, but also the compositions (e.g. the concentration of cellulosic materials) and other processing parameters; 3) the nature of hydrophilic cellulosic and hydrophobic matrix rubber and/or plastics requires an accurate introduction of coupling agent, one end of its structure shall be compatible to hydrophilic and the other to hydrophobic. The reviews on the main paths and results of study on the advanced nanocellulose reinforced rubber nanocomposites and sandwiches indicate much potentials and needs for further in-depth studies.     

Effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites

The effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites was evaluated. Alkali treatment of the fibers and reaction with organosilanes as coupling agents were applied to improve fiber–matrix adhesion. Fiber loadings of 1, 3, 5, and 7 wt% were incorporated to the phenolic matrix and tensile, flexural, morphological and thermal properties of the resulting composites were studied. In general, mechanical properties of the composites showed a maximum at 3% of fiber loading and a uniform distribution of the fibers in such composites was observed. Silane treatment of the fibers provided derived composites with the best thermal and mechanical properties. Meanwhile, NaOH treatment improved thermal and flexural properties, but reduced tensile properties of the materials. Therefore, the phenolic composite containing 3% of silane treated cellulose fiber was selected as the material with optimal properties.     

玻璃纤维含量对竹粉/高密度聚乙烯复合材料性能的影响

为利用玻璃纤维提高木塑复合材料的综合性能,探讨玻璃纤维含量对竹粉/高密度聚乙烯(HDPE)复合材料性能的影响规律,首先,采用A-171硅烷偶联剂对竹粉表面进行了改性,并加入了一定量的玻璃纤维;然后,采用热压成型工艺制备了玻璃纤维-竹粉/HDPE复合材料;最后,考察了玻璃纤维含量对复合材料力学性能、热学性能及摩擦学性能的影响,并利用SEM观察材料的断面和磨损表面形貌。结果表明:当玻璃纤维含量为3wt%时,能显著提高竹粉/HDPE复合材料的拉伸强度和弯曲强度,与未添加玻璃纤维的复合材料相比,添加玻璃纤维后复合材料的拉伸强度和弯曲强度分别提高了19.41%和23.54%;在30~60℃温度范围内,复合材料长度-宽度方向上的线膨胀系数随着玻璃纤维含量的增加而明显减小,而同一复合材料的线膨胀系数随温度的升高而逐步增大;在氮气气氛下,随玻璃纤维含量的增加,竹粉/HDPE复合材料的摩擦系数先逐渐增大,而后基本保持不变,磨损率逐渐减小。所得结论显示玻璃纤维含量为3wt%~7wt%的木塑产品适用于建筑横梁(如凉亭或桥梁等),而玻璃纤维含量为7wt%~10wt%的木塑产品适用于高人流量场所(如公园或休闲绿道等)的地面铺装。      

Effect of TiO2 and nanoclay on the properties of wood polymer nanocomposite

High density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP) and poly(vinyl chloride) (PVC) with Phragmiteskarka wood flour (WF) and polyethylene-co-glycidyl methacrylate (PE-co-GMA) was used to develop wood polymer composite (WPC) by solution blending method. The effect of addition of nanoclay and TiO₂ on the properties of the composite was examined. The exfoliation of silicate layers and dispersion of TiO₂ nanopowder was studied by X-ray diffractometry and transmission electron microscopy. The improvement in miscibility among polymers due to addition of compatibilizer was studied by scanning electron microscopy (SEM). WPC treated with 3 phr each of clay and TiO₂ showed an improvement in thermal stability. Mechanical, UV resistance and flame retarding properties were also enhanced after the incorporation of clay/TiO₂ nanopowder to the composites. Both water and water vapor absorption were found to decrease due to inclusion of nanoclay and TiO₂ in WPC.     

Mechanical and interfacial properties of wood and bio-based thermoplastic composite

The aim of this investigation was to study a new family of wood polymer composites with thermoplastic elastomer matrix (pebax® copolymers) instead of commonly used WPC matrices. These copolymers are polyether-b-amide thermoplastic elastomers which present an important elongation at break and a melting point below 200 °C to prevent wood fibers degradation during processing. Moreover these polymers are synthesized from renewable resources and they present a hydrophilic character which allow them to interact with wood fibers. We have used two pebax® grade with different hardness and three types of wood fibers, so the influence of the matrix and wood fibers characteristics were evaluated. Composites were produced using a laboratory-size twin screw extruder to obtain composite pellets prior to injection moulding into tensile test samples. We have evaluated fibers/matrix interaction by differential scanning calorimetry (DSC), infrared spectroscopy (IRTF) and scanning electron microscopy (SEM). Then, the mechanical properties, through tensile test, were assessed. We also observed fibers dispersion into the matrix by tomography X. DSC, IRTF and SEM measurements confirmed the presence of strong interface interactions between polymer and wood. These interactions lead to good mechanical properties of the composites with a reinforcement effect of wood fibers due also to a good dispersion of fibers into the matrix without agglomerate.     

Dimensional stability and mechanical behaviour of wood–plastic composites based on recycled and virgin high-density polyethylene (HDPE)

This paper investigated the stability, mechanical properties, and the microstructure of wood–plastic composites, which were made using either recycled or virgin high-density polyethylene (HDPE) with wood flour (Pinus radiata) as filler. The post-consumer HDPE was collected from plastics recycling plant and sawdust was obtained from a local sawmill. Composite panels were made from recycled HDPE through hot-press moulding exhibited excellent dimensional stability as compared to that made from virgin HDPE. The tensile and flexural properties of the composites based on recycled HDPE were equivalent to those based on virgin HDPE. Adding maleated polypropylene (MAPP) by 3–5 wt% in the composite formulation significantly improved both the stability and mechanical properties. Microstructure analysis of the fractured surfaces of MAPP modified composites confirmed improved interfacial bonding. Dimensional stability and strength properties of the composites can be improved by increasing the polymer content or by addition of coupling agent. This project has shown that the composites treated with coupling agents will be desirable as building materials due to their improved stability and strength properties.     

Effect of glass fiber hybridization on properties of sisal fiber–polypropylene composites

Natural fiber reinforced polymer composites became more attractive due to their light weight, high specific strength, and environmental concern. However, some limitations such as low modulus, poor moisture resistance were reported. This study aimed to investigate the effect of glass fiber hybridization on the physical properties of sisal–polypropylene composites. Polypropylene grafted with maleic anhydride (PP-g-MA) was used as a compatibilizer to enhance the compatibility between the fibers and polypropylene. Incorporating glass fiber into the sisal–polypropylene composites enhanced tensile, flexural, and impact strength without having significant effect on tensile and flexural moduli. In addition, adding glass fiber improved thermal properties and water resistance of the composites.     

Effect of coating on the microstructure and thermal conductivities of diamond-Cu composites prepared by powder metallurgy

Diamond-Cu composites from the direct combination of diamond and Cu show low thermal conductivities due to weak interface and high thermal resistance as a result of chemical incompatibility. In this paper, a new method is proposed to strengthen interfacial binding between diamond and Cu by coating strong carbide-forming elements, e.g., Ti or Cr on the surface of the diamond through vacuum micro-deposition. Interfacial thermal resistance of diamond-Cu composites is greatly decreased when diamond particles are coated by a Cr or Ti layer of a certain thickness before combining with Cu. Thermal conductivity is also increased several times. Cr coating can reduce more effectively interface thermal resistance between diamond and Cu than Ti coating. Moreover, it has a smaller negative impact on the thermal conductivity of the Cu matrix, resulting in higher thermal conductivity of Cr-coated diamond-Cu composites. Through the vacuum micro-deposition technology, Cr on the diamond particle surface is present in the form Cr₇C₃ near diamond and a pure Cr outer layer at 2:1. The optimum thickness is within 0.6-0.9 μm; at this depth, the thermal conductivities of 70 vol% diamond-Cu composites can be increased four times and reach as high as 657 W/m K. In this work, an original theoretical model is proposed to estimate the thermal conductivities of composite materials with an interlayer of a certain thickness. The predicted values from this model are in good agreement with the experimental values.     

Mechanical properties of elastomeric composite membranes made from the porous biaxially drawn ultrahigh-molecular-weight polyethylene film and polyether polyurethane materials

Fibrous composites are commonly found in soft tissue but few man-made composites are used for soft tissue replacement. In this study, fibrous composites, made from biaxially drawn ultra-high molecular-weight polyethylene (BD-UHMWPE) and polyether polyurethane materials, were fabricated by solution casting and heat compaction. The effects of processing conditions on tensile properties of the composites were evaluated, in terms of the molecular structures of the polyurethane materials, thermal behavior of the UHMWPE, and the microstructures of the as-made composites. The results indicated that composites of improved tensile properties were constructed in the form of interpenetration of polyurethane through the stacks of the BD-UHMWPE. The tensile strength and modulus of the composites (made from Toyobo TM5 and Solupor™ 7P03) are approximately 69 and 210 MPa. The as-made composite has a significant improvement on its toughness, about 5 times increase in the tensile toughness if compared to that of the BD-UHMWPE. A possible interlocking structure was suggested for those polyurethane materials (Toyobo TM5) that might be recrystallized during heat compaction. The polyurethane like Tecoflex 80A, not indicating a symptom of annealing crystallization, has no impact on increasing the tensile properties but a decrease with plasticizing the materials.