Wood/plastic composites co‐extruded with multi‐walled carbon nanotube‐filled rigid poly(vinyl chloride) cap layer

Wood/plastic composites (WPCs) can absorb moisture in a humid environment due to the hydrophilic nature of the wood in the composites, making products susceptible to microbial growth and loss of mechanical properties. Co‐extruding a poly(vinyl chloride) (PVC)‐rich cap layer on a WPC significantly reduces the moisture uptake rate, increases the flexural strength but, most importantly, decreases the flexural modulus compared to uncapped WPCs. A two‐level factorial design was used to develop regression models evaluating the statistical effects of material compositions and a processing condition on the flexural properties of co‐extruded rigid PVC/wood flour composites with the ultimate goal of producing co‐extruded composites with better flexural properties than uncapped WPCs. Material composition variables included wood flour content in the core layer and carbon nanotube (CNT) content in the cap layer of the co‐extruded composites, with the processing temperature profile for the core layer as the only processing condition variable. Fusion tests were carried out to understand the effects of the material compositions and processing condition on the flexural properties. Regression models indicated all main effects and two powerful interaction effects (processing temperature/wood flour content and wood flour content/CNT content interactions) as statistically significant. Factors leading to a fast fusion of the PVC/wood flour composites in the core layer, i.e. low wood flour content and high processing temperature, were effective material composition and processing condition parameters for improving the flexural properties of co‐extruded composites. Reinforcing the cap layer with CNTs also produced a significant improvement in the flexural properties of the co‐extruded composites, insensitive to the core layer composition and the processing temperature condition. Copyright © 2009 Society of Chemical Industry     

Effect of highly degraded high‐density polyethylene (HDPE) on processing and mechanical properties of wood flour‐HDPE composites

The influence of highly degraded high‐density polyethylene (HDPE) on physical, rheological, and mechanical properties of HDPE‐wood flour composites was studied. For this purpose, the virgin HDPE was subjected to accelerated weathering under controlled conditions for 200 and 400 h. The virgin and exposed HDPE and pine wood flour were compounded to produce wood flour‐HFPE composites. The results showed that the accelerated weathering highly degraded HDPE. Degradation created polar functional carbonyl groups and also produced extensive cross‐linking in HDPE and consequently poor processibility. The interruptions in the flow characteristics of the degraded HDPE potentially caused processing hurdles when using them for extrusion or injection molding manufacturing as only small part (10%) of virgin HDPE could be replaced by highly degraded HDPE for wood flour‐HDPE composite manufacturing. The mechanical properties of composites containing highly degraded HDPEs were similar to the composites with virgin HDPE and in some cases they exhibited superior properties, with the exception being with the impact strength. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Waste pine cones as a source of reinforcing fillers for thermoplastic composites

In this study, we evaluated some physical and mechanical properties of polypropylene (PP) composites reinforced with pine‐cone flour and wood flour. Five types of wood–plastic composites (WPCs) were prepared from mixtures of cone flour, wood flour, PP, and a coupling agent. The water resistance and flexural properties of the composites were negatively affected by an increase in cone‐flour content. Extractives in the cone flour had a significant effect on the flexural properties of the WPCs. However, the flexural properties and water resistance of the WPC samples were not significantly affected by the addition of 10 wt % of the cone flour when compared to the WPC samples made from wood flour. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Properties of flat‐pressed wood plastic composites containing fire retardants

This study investigated physical, mechanical, and fire properties of the flat‐pressed wood plastic composites (WPCs) incorporated with various fire retardants (FRs) [5 or 15% by weight (wt)] at 50 wt % of the wood flour (WF). The WPC panels were made from dry‐blended WF, polypropylene (PP) with maleic anhydride‐grafted PP (2 wt %), and FR powder formulations using a conventional flat‐pressing process under laboratory conditions. The water resistance and strength values of the WPC panels were negatively affected by increasing the FR content as compared to the WPC panels without FR. The WPC panels incorporated with zinc borate (ZB) gave an overall best performance in both water resistance and strength values followed by the panels containing magnesium hydroxide (MH) and ammonium polyphosphate (APP). For these three FR's, the best fire resistance as measured in the cone calorimeter was obtained with the 15 wt % APP treatment and then followed by 15 wt % ZB, or 15 wt % MH formulations. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Abiotic and biotic degradation of post‐consumer polypropylene/ethylene vinyl acetate: Wood flour composites exposed to natural weathering

The effects of natural weathering on the visual appearance and chemical changes of wood plastic composite (WPC) formulations based on post‐consumer polypropylene/ethylene vinyl acetate (PP‐EVA) matrix were investigated. The WPC composition used was 70/30 (w/w) (recycled PP‐EVA/wood flour). Besides, the effectiveness of using coupling agent on adhesion of WPC and its influence in degradation were evaluated. Colorimetry, scanning electron microscopy, Fourier transform infrared spectroscopy, mechanical test, and biodegradation in simulated soil after natural weathering were used in this research. The results showed the samples with longer exposure time to natural weathering presented significant color change, increased in carbonyl index, and wood loss on weathered WPC surfaces. Weathered WPC exhibited decreased in mechanical properties, higher mass loss after biodegradation test when compared with no weathering WPC, reaching to 15.0% mass loss against 3.7%, respectively. Climatic conditions directly affect the characteristics of all composites, thus indicating a significant photo‐oxidation of the samples with a longer time of exposure to weathering, and this natural ageing has facilitated the WPC biodegradation . POLYM. COMPOS., 38:571–582, 2017. © 2015 Society of Plastics Engineers     

Compression wood as a source of reinforcing filler for thermoplastic composites

Compression wood (CW) is a reaction wood formed in gymnosperms in response to various growth stresses. Many of the anatomical, chemical, physical, and mechanical properties of CW differ distinctly from those of normal wood. Because of different properties, the CW is much less desirable than normal wood. This study was conducted to investigate the suitability of CW flour obtained from black pine (Pinus nigra Arnold) in the manufacture of wood plastic composite (WPC). Polypropylene (PP) and CW flour were compounded into pellets by twin‐screw extrusion, and the test specimens were prepared by injection molding. WPCs were manufactured using various weight percentages of CW flour/PP and maleic anhydride‐grafted PP (MAPP). Water absorption (WA), modulus of rupture (MOR), and modulus of elasticity (MOE) values were measured. The results showed that increasing of the CW percentage in the WPC increased WA, MOR, and MOE values. Using MAPP in the mixture improved water resistance and flexural properties. CW flour of black pine can be used for the manufacturing of WPC as a reinforcing filler. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical and water absorption behaviors of corn stalk/sisal fiber‐reinforced hybrid composites

In this study, corn stalk flour (CSF) was used as filler instead of wood flour (WF) to prepare poly(vinyl chloride) (PVC) based wood plastic composite (WPC). In order to enhance the mechanical properties of the WPC, sisal fiber (SF) was introduced as reinforcer. The mechanical and the water absorption behaviors of WPC were investigated in detail. The results indicated that the chemical structure of CSF proved by FTIR was similar to that of WF. The effect of the hybridization of SF and CSF on the mechanical and water absorption behaviors of CSF/SF/PVC composite was studied. It was found that the introduction of SF of 5 mm in length resulted in improvement of the mechanical properties and had little effect on water absorption behavior. Scanning electron microscopy was carried out to observe the fracture surface of the composite. The distribution of CSF and SF in PVC was analyzed. Meanwhile, the hybrid enhancement mechanism of SF in PVC matrix was discussed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46405.     

Bleached extruder chemi‐mechanical pulp fiber‐PLA composites: Comparison of mechanical,thermal, and rheological properties with those of wood flour‐PLA bio‐composites

An environmentally friendly bleached extruder chemi‐mechanical pulp fiber or wood flour was melt compounded with poly(lactic acid) (PLA) into a biocomposite and hot compression molded. The mechanical, thermal, and rheological properties were determined. The chemical composition, scanning electron microscopy, and Fourier transform infrared spectroscopy results showed that the hemicellulose in the pulp fiber raw material was almost completely removed after the pulp treatment. The mechanical tests indicated that the pulp fiber increased the tensile and flexural moduli and decreased the tensile, flexural, and impact strengths of the biocomposites. However, pulp fiber strongly reinforced the PLA matrix because the mechanical properties of pulp fiber‐PLA composites (especially the tensile and flexural strengths) were better than those of wood flour‐PLA composites. Differential scanning calorimetry analysis confirmed that both pulp fiber and wood flour accelerated the cold crystallization rate and increased the degree of crystallinity of PLA, and that this effect was greater with 40% pulp fiber. The addition of pulp fiber and wood flour modified the rheological behavior because the composite viscosity increased in the presence of fibers and decreased as the test frequency increased. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44241.     

Effects of vinyltrimethoxy silane on thermal properties and dynamic mechanical properties of polypropylene–wood flour composites

The viability of vinyltrimethoxy silane was investigated as a coupling agent for the manufacture of wood–plastic composites (WPC). The effect of silane pretreatment of the wood flour on the thermal and the dynamic mechanical properties and thermal degradation properties of the composites were studied. Moreover, the effect of organosilane on the properties of composites was compared with the effect of maleated polypropylene (MAPP). DSC studies indicated that the wood flour acts as a PP-nucleating agent, increasing the PP crystallization rate. In general, pretreatment with small amounts of silane improved this behavior in all the WPCs studied. Thermal degradation studies of the WPCs indicated that the presence of wood flour delayed degradation of the PP. Silane pretreatment of the wood flour augmented this effect, though without significantly affecting cellulose degradation. Studies of dynamic mechanical properties revealed that the wood flour (at up to 30 wt %) increased storage modulus values with respect to those of pure PP; in WPCs with a higher wood flour amount, there was no additional increase in storage modulus. Pretreatment of the wood flour with silane basically had no effect on the dynamic mechanical properties of the WPC. These results show that with small amounts of vinyltrimethoxy silane similar properties to the MAPP are reached. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of material parameters on the diffusion and sorption properties of wood‐flour/polypropylene composites

Composites of wood in a thermoplastic matrix (wood–plastic composites) are considered a low maintenance solution to using wood in outdoor applications. Knowledge of moisture uptake and transport properties would be useful in estimating moisture‐related effects such as fungal attack and loss of mechanical strength. Our objectives were to determine how material parameters and their interactions affect the moisture uptake and transport properties of injection‐molded composites of wood‐flour and polypropylene and to compare two different methods of measuring moisture uptake and transport. A two‐level, full‐factorial design was used to investigate the effects and interactions of wood‐flour content, wood‐flour particle size, coupling agent, and surface removal on moisture uptake and transport of the composites. Sorption and diffusion experiments were performed at 20°C and 65 or 85% relative humidity as well as in water, and diffusion coefficients were determined. The wood‐flour content had the largest influence of all parameters on moisture uptake and transport properties. Many significant interactions between the variables were also found. The interaction between wood‐flour content and surface treatment was often the largest. The diffusion coefficients derived from the diffusion experiments were different from those derived from the sorption experiments, suggesting that different mechanisms occur. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 752–763, 2007     

Procedure effect on the physical and mechanical properties of the extruded wood plastic composites

This article investigates the effect of raw material preparation on the mechanical and physical properties in wood‐plastic composite (WPC) production. Four possible procedures in material preparation to obtain a determined level of wood content are: (i) to use and feed raw materials in the same ratio of the desired composition (single stage), (ii) to use the batch of granules of the same composition (two‐stage), (iii) to add wood to the batch of granules having a lower wood content, (iv) to add polymer to the batch of granules having a higher wood content. The main question then is that, while it is economically attractive to use granules of a fixed wood content in all productions, whether there are noticeable differences in final properties of the products. The examined compositions were 50, 60, and 70 wt% of wood content which are considered as highly filled WPCs and mainly used in the WPC markets. Thus, 12 sets of WPC profiles were manufactured and the processing conditions (temperature, pressure, and outlet velocity) recorded. The flexural properties, impact strength, density, and water uptake were measured. Results revealed that in the production of WPCs with 50 and 70 wt% of wood content, using the WPC granules with the same composition yields better physical and mechanical properties. However, for producing WPC with 60 wt% of wood content, using WPC granules with 70 wt% of wood and adding appropriate amount of polymer exhibit better results. POLYM. COMPOS. 34:1349–1356, 2013. © 2013 Society of Plastics Engineers     

Surface microencapsulated ammonium polyphosphate with beta‐cyclodextrin and its application in wood‐flour/polypropylene composites

In order to improve the hydrophilicity of ammonium polyphosphate (APP), as well as its compatibility with composite matrix, in this research, beta‐cyclodextrin (β‐CD) was crosslinked by polydiphenylmethane diisocyanate (PMDI) and used as clothing to prepare microencapsulated APP (MCAPP) via polymerization in situ . Then, APP and MCAPP were mixed with wood‐flour and polypropylene to manufacture wood‐flour/polypropylene composites (WPCs) by hot pressing. Both APP and MCAPP were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), water solubility tests, and water contact angle (WCA) tests. Limiting oxygen index (LOI) and cone calorimetry tests were used to investigate the flame retardancy of WPCs. Moreover, laser Raman spectroscopy and real‐time FTIR (RT‐FTIR) were used to explore the flame retardant mechanism. Results indicated that APP was successfully coated by the crosslinked β‐CD. MCAPP showed lower water solubility and better surface hydrophobicity, and WPC/MCAPP performed better flame retardnacy and mechanical properties. POLYM. COMPOS., 38:2312–2320, 2017. © 2015 Society of Plastics Engineers     

Preparation,structure, and property of wood flour incorporated polypropylene composites prepared by a solid‐state mechanochemical method

In this article, a solid‐state mechanochemical method based on a pan‐mill equipment was used to prepare 60 wt % loading of wood flour (WF) incorporated polypropylene (PP) wood–plastic composite (WPC) with good comprehensive performance. The particle size distribution, crystallization, microstructure, and properties of the prepared WPC were accordingly investigated. The results show that under co‐effects of the strong shear force field of pan milling and the compatibilization of PP grafted maleic anhydride (PP‐g‐MAH), the mixture of PP and WF is effectively pulverized and homogeneously mixed. Meanwhile, the WF particles are adequately activated by exposure of their characteristic functional groups, which is beneficial to the interfacial mechanochemical reaction. PP‐g‐MAH and PP prove to be in situ grafted onto WF particles surface during pan milling, thus resulting in the substantial enhancement in both the dispersion of the added WF fillers in PP matrix and the interfacial bonding. The mechanochemical effects of pan milling could also remarkably promote the heterogeneous nucleation effect of WF particles on PP crystallization and influence the dynamic mechanical behavior of composite. Compared with the unmilled and uncompatibilized composite, the milled and compatibilized WPC material possesses greatly enhanced mechanical performance and shows good application prospects. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43108.     

Biodegradability and mechanical properties of agro‐flour–filled polybutylene succinate biocomposites

The objective of this study was the production of rice husk flour (RHF) and wood flour (WF) filled polybutylene succinate (PBS) biocomposites as alternatives to cellulosic material filled conventional plastic (polyolefins) composites. PBS is one of the biodegradable polymers, made from the condensation reaction of 1,4‐butanediol and succinic acid that can be naturally degraded in the natural environment. We compared the mechanical properties between conventional plastics and agro‐flour–filled PBS biocomposites. We evaluated the biodegradability and mechanical properties of agro‐flour–filled PBS biocomposites according to the content and filler particle size of agro‐flour. As the agro‐flour loading was increased, the tensile and impact strength of the biocomposites decreased. As the filler particle size decreased, the tensile strength of the biocomposites increased but the impact strength decreased. The addition of agro‐flour to PBS produced a more rapid decrease in the tensile strength, notched Izod impact strength, and percentage weight loss of the biocomposites during the natural soil burial test. These results support the application of biocomposites as environmentally friendly materials. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1513–1521, 2005     

异氰酸酯对木塑力学性能与疏水性的影响

将木粉表面的羟基分别与异氟尔酮二异氰酸酯(IPDI)、甲苯二异氰酸酯(TDI)反应,再与聚乙烯(PE)通过挤出混合,挤出成型制备出了不同处理效果的木塑复合材料(WPC)。在不同种类和不同浓度的条件下,异氰酸酯改性木粉对木塑复合材料(WPC)的力学性能以及吸水率具有不同的影响。红外光谱(FTIR)和接触角测试表明,异氰酸酯成功接枝到木粉上。采用场发射扫描电子显微镜(FESEM)观察木粉与聚乙烯(PE)的相容性变化,通过微机控制电子万能试验机测试不同处理条件下的木塑复合材料力学性能,并参照GB/T 1462—2005计算了木塑吸水率。结果表明,在质量比为TDI∶木粉=5∶100条件下,木塑的力学性能和疏水效果最佳,拉伸强度达到27.8±0.7 MPa,浸入水中48 h吸水率达到0.45%。     

Preparation and cell morphology of ethylene‐vinyl acetate copolymer (EVA)/wood‐flour foams with low density

The main objective of this study is to obtain ethylene‐vinyl acetate copolymer (EVA)/wood‐flour foams with low density (< 0.2 g/cm³) using chemical blowing agent. Stearic acid was used as a compatibilizer to improve not only the compatibility between wood‐flour and EVA but also the compatibility between moisture and EVA in this study. The effects of wood‐flour content on the density and mechanical properties of EVA/wood‐flour foams were studied. Also, the effects of content of stearic acid on the cell morphology of EVA/wood‐flour foams were investigated. The shape of EVA/wood‐flour foams with 20% wood‐flour content becomes more uniform with increasing content of stearic acid. The most stabilized shape of the foams is obtained with 5 wt % stearic acid content. The density of EVA/wood‐flour foams with 20% wood‐flour and 5 wt % stearic acid is 0.11 g/cm³. With increasing content of stearic acid, more gas remains in the EVA matrix and consequently, average cell size and density increase. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40894.     

Properties of glycerin‐thermally modified wood flour/polypropylene composites

This study aimed to investigate the combination effect of glycerin treatment and thermal modification of wood flour on the physical, mechanical, thermal dynamic mechanical properties of wood flour/polypropylene (PP) composite. The morphological aspect was also investigated. The wood flour was first impregnated in the aqueous solution of glycerin, followed by heat treatment at 200°C for 1 h. Then the unmodified or modified wood flour was blended with PP at a weight ratio of 4:6 to prepare composites. Moisture adsorption experiment and X‐ray photoelectron spectroscopy analysis of wood flour demonstrated that the hygroscopicity and the free surface hydroxyl groups of wood flour decreased after glycerin‐thermal modification. Thickness swelling of the 10% wt glycerin‐thermally modified wood flour/PP composite was reduced by 42.8% after 96 h immersion as compared to unmodified control. Evaluation of mechanical properties in impact and flexure modes indicated that glycerin treatment alone had no significant effect, but the combination of glycerin and thermal treatment slightly decreased the strength, with the exception of 10% glycerin and heat modified sample. Dynamic mechanical analysis and scanning electron microscope illustrated the improved interfacial bonding between PP and wood flour modified by 10% glycerin and heat treatment. POLYM. COMPOS., 35:201–207, 2014. © 2013 Society of Plastics Engineers     

木粉疏水改性对HDPE基木塑复合材料性能的影响

采用一种操作简便且易于工业推广的方法对木粉进行疏水改性,具体过程为：将3种可热聚合的单体,即甲基丙烯酸甲酯（MMA）、甲基丙烯酸丁酯（BMA）和苯乙烯（St）均匀喷洒在木粉上,经过预热处理后,与配方中其他组分,如高密度聚乙烯（HDPE）和马来酸酐接枝聚乙烯（MAPE）等通过高速混合机混合均匀,采用双螺杆挤出机造粒后,注射制备木塑复合材料（WPC）样条,测试其力学性能。另外,考察了疏水改性对WPC接触角、维卡软化温度、洛氏硬度、吸水性能、热性能的影响规律。结果表明：疏水改性后WPC的接触角增大,木粉和HDPE的界面相容性改善,力学性能得到明显提高。其中,当MMA、BMA和St的添加量为3%时,WPC的力学性能最好,与疏水改性前相比,弯曲强度分别提高了17.3%、26.3%和27.5%,弯曲模量分别提高了24.4%、24.4%和26.0%,冲击强度分别提高了54.7%、57.7%和60.5%。 此外,疏水改性后WPC的维卡软化温度、洛氏硬度、耐水性和耐热性也得到改善。     

Characterization of UHMWPE/wood composites produced via dry‐blending and compression molding

In this study, composites made from wood flour and ultra‐high molecular weight polyethylene (UHMWPE) were produced and characterized. In particular, the composites were initially prepared using a simple dry mixing technique and then compression molded. The effect of wood content on the mechanical properties was determined up to 30wt%. Characterization included scanning electron microscopy to investigate wood dispersion and interfacial bonding quality, while the mechanical tests included tensile, torsion, and flexion. The results show that good dispersion and adhesion was achieved and wood flour addition increased substantially (up to 97%) all the moduli in the range of conditions tested. Finally, it was found that hardness increased by about 5 Shore D points by adding 30% wood flour in UHMWPE. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

木粉及聚磷酸铵对PE-HD木塑复合材料阻燃和力学性能的影响

以高密度聚乙烯(PE-HD)为基体,聚磷酸铵(APP)和木粉(WF)为膨胀型阻燃体系,制备了阻燃木塑复合材料(WPC)。通过极限氧指数、垂直燃烧UL 94、锥形量热分析、热失重分析、红外光谱分析、力学性能等对其进行性能表征。结果表明,与纯PE-HD相比,极限氧指数随着WF含量增加而提高,添加40 %WF时极限氧指数提高到30.5 %,UL 94可达V-0等级,热释放速率峰值和总热释放量降低;APP和WF燃烧过程中发生了化学作用,形成了保护炭层,提高了材料的热稳性,材料的拉伸和弯曲强度得到提高。