Processability,morphology and mechanical properties of wood flour reinforced high density polyethylene composites

Abstract

Wood flour reinforced high density polyethylene (HDPE) composites have been prepared and their rheological properties measured. The melt viscosity decreased as the processing temperature increased and the wood flour content decreased. A power law model was used to describe the pseudoplasticity of these melts. Adding wood flour to HDPE produced an increase in tensile strength and modulus. Composites compounded in a twin screw extruder and treated with a coupling agent (vinyltrimethoxysilane) or a compatibliser (HDPE grafted with maleic anhydride) exhibited better mechanical properties than the corresponding unmodified composites because of improved dispersion and good adhesion between the wood fibre and the polyalkene matrix. Scanning electron microscopy of the fracture surfaces of these composites showed that both the coupling agent and compatibiliser gave superior interfacial strength between the wood fibre and the polyalkene matrix.     

Glass fiber/wood flour modified high density polyethylene composites

Composites of high density polyethylene (HDPE) with the reinforcements of glass fiber (GF) and wood flour (WF) have been studied in this work. High‐density polyethylene‐grafted maleic hydride (HDPE‐g‐MAH) was used as a compatibilizer. In particular, the effect of GF, WF, and HDPE‐g‐MAH on the overall properties of GF/WF/HDPE composites (GWPCs in short form) was systematically studied. The results indicate that HDPE‐g‐MAH as a compatibilizer can effectively promote the interfacial adhesion between GF/WF and HDPE. By the incorporations of GF/WF, the heat deflection temperature can reach above 120°C, and the water absorption can be below 0.7%, also the tensile strength, flexural strength, and impact strength of GWPCs can surpass 55.2 Mpa, 69.4 Mpa, and 11.1 KJ/m², respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Rheological properties of teak wood flour reinforced HDPE and maize starch composites

Teak wood flour reinforced high density polyethylene and maize starch composites were prepared by using maleic anhydride grafted polyethylene as a compatibilizer. The mechanical properties (tensile and flexural) of all the composites increased after addition of 10%–40% teak wood flour into HDPE matrix. The complex viscosity (η*) was higher for all the composites at the low frequency, but decreased with increasing frequencies indicating a shear thinning behavior of the composites. The storage modulus and loss modulus increased for the composites compared to the HDPE at low frequencies. Damping factor peak of HDPE and composites showed high below 1 Hz, but the peak start decreasing with increasing above 1 Hz. The relaxation behavior of HDPE and the composites after incorporating teak wood flour, maize starch, and compatibilizer was obtained by Han plot. Biodegradability was enhanced with the incorporation of teak wood flour, maize starch into the composites. Appreciable water uptake and the thickness swelling for the composites indicating it's potential for interior, automobile and packaging applications.     

Thermal and mechanical characterization of linear low‐density polyethylene/wood flour composites

A linear low‐density polyethylene (LLDPE) matrix was modified with an organic peroxide and by a reaction with maleic anhydride (MAn) and was simultaneously compounded with untreated wood flour in a twin‐screw extruder. The thermal and mechanical properties of the modified LLDPE and the resulting composites were evaluated. The degree of crystallinity was reduced in the modified LLDPE, but it increased with the addition of wood flour for the formation of the composites. Significant improvements in the tensile strength, ductility, and creep resistance were obtained for the MAn‐modified composites. This enhancement in the mechanical behavior could be attributed to an improvement in the compatibility between the filler and the matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2775–2784, 2003     

HDPE/竹粉复合材料的界面演变及流变特性

采用扫描电子显微镜-X射线能谱仪跟踪硅烷偶联剂中Si元素在高密度聚乙烯(HDPE)基竹塑共混体系界面处的分布,并结合旋转流变仪研究了共混体系加工过程中的界面演变过程。发现随着加工时间的延长,界面处Si元素的含量相对增加,体系的动态模量、黏度升高。表明偶联剂连接的竹粉与HDPE分子链间的相互作用增强,界面层厚度增加。共混体系的动态流变测试结果表明,竹粉填充体系在低频末端区的线性黏弹行为显著不同于HDPE基体,表现出"类固体"特性,动态流变测试对偶联剂的加入所引起的体系的黏弹行为及结构变化响应较敏感。Cole-Cole曲线可反映竹粉粒子网络结构及竹粉与HDPE基体界面相关的松弛信息,体现体系界面性质及竹粉与分子链间网络结构的变化。     

Crystallization and melting behavior of HDPE in HDPE/teak wood flour composites and their correlation with mechanical properties

The nonisothermal crystallization behavior and melting characteristics of high‐density polyethylene (HDPE) in HDPE/teak wood flour (TWF) composites have been studied by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) methods. Composite formulations of HDPE/TWF were prepared by varying the volume fraction (?_f) of TWF (filler) from 0 to 0.32. Various crystallization parameters evaluated from the DSC exotherms were used to study the nonisothermal crystallization behavior. The melting temperature (T_m) and crystallization temperature (T_p) of the composites were slightly higher than those of the neat HDPE. The enthalpy of melting and crystallization (%) decrease with increase in the filler content. Because the nonpolar polymer HDPE and polar TWF are incompatible, to enhance the phase interaction maleic anhydride grafted HDPE (HDPE‐g‐MAH) was used as a coupling agent. A shift in the crystallization and melting peak temperatures toward the higher temperature side and broadening of the crystallization peak (increased crystallite size distribution) were observed whereas crystallinity of HDPE declines with increase in ?_f in both DSC and WAXD. Linear correlations were obtained between crystallization parameters and tensile and impact strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Rheological behavior and mechanical properties of wood flour/high density polyethylene blends: Effects of esterification of wood with citric acid

This study explored the modifying effects of wood flour (WF) with citric acid (CA) on the rheological and mechanical properties of WF/high density polypropylene (HDPE) composites. WF was treated with CA, which acts a cross‐linking agent and melt‐blended with HDPE with a twin‐screw extruder. Injection molding was used to make tensile and impact tests samples. The rheological properties of the blends were characterized using a Haake microcompounder, torque‐, capillary‐, and rotational‐rheometer, respectively. Results show that the thermal stability of WF decreased after treatment. Compared with those of untreated composites, the tensile strength, elongation‐at‐break, and impact strength of the composites treated with 5% CA were reduced by 6%, 14%, and 16%, respectively. This reduction was attributed to embrittlement of WF, which may negatively influence the mechanical properties of the resulting composites. Scanning electron microscopy revealed better dispersion of CA‐treated WF in the composites than the untreated WF. For composites treated with 5% CA, the melt torque, viscosity, moduli, and shear stress decreased significantly, indicating an improvement in processibility. This improvement is attributed to uniform dispersion of the modified WF, as well as to better interfacial adhesion between WF and the matrix. Results suggest that treating WF with CA shows promise for improving the processibility of highly filled thermoplastic composites via extrusion/injection molding processing. POLYM. COMPOS., 37:553–560, 2016. © 2014 Society of Plastics Engineers     

Preparation of highly filled wood flour/recycled high density polyethylene composites by in situ reactive extrusion

Highly filled wood flour/recycled high density polyethylene (WF/RHDPE) composites were directly prepared by in situ reactive extrusion using a twin‐screw/single‐screw extruder system. The effects of dicumyl peroxide (DCP) content on extrusion pressure, rheological behavior, mechanical properties, fractured surface morphology of the composites, and melting temperature of RHDPE in the composites were investigated. The extrusion pressure and torque of WF/RHDPE composite melt increased with DCP content. Mechanical property tests and scanning electron microscopy analysis results confirmed that the interfacial interaction of the composites was improved by in situ reaction. The composites show lower melting peak temperature (T_m) than RHDPE. The cooling in profile extrusion shortened the crystallization time, resulting in decrease of crystalline order of RHDPE in the composites. There are no noticeable changes of T_m values with increasing DCP content. Comparative study on composites with maleic anhydride grafted polyethylene as compatibilizer demonstrated that mechanochemical treatment with DCP and maleic anhydride was an effective method to improve interfacial adhesion for WF/RHDPE composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Wood‐thermoplastic composites from wood flour and high‐density polyethylene

High‐density polyethylene/wood flour (HDPE/WF) composites were prepared by a twin‐screw extruder. The effects of WF, silane coupling agents, polymer compatibilizers, and their content on the comprehensive properties of the WF/HDPE composites have been studied in detail, including the mechanical, thermal, and rheological properties and microstructure. The results showed that both silane coupling agents and polymer compatibilizers could improve the interfacial adhesion between WF and HDPE, and further improve the properties of WF/HDPE composites, especially with AX8900 as a compatibilizer giving higher impact strength, and with HDPE‐g‐MAH as a compatibilizer giving the best tensile and flexural properties. The resultant composite has higher strength (tensile strength = 51.03 MPa) and better heat deflection temperature (63.1°C). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Incorporation effect of enzymatic hydrolysis lignin on the mechanical and rheological properties of the resulting wood flour/high‐density polyethylene composites

Enzymatic hydrolysis lignin (EHL) from ethanol production was used as an additive to incorporate in the wood flour/high‐density polyethylene (HDPE) composite during the melt extrusion, and the incorporating effects on the mechanical and rheological properties of the resulting composites were investigated. The addition of EHL caused an improvement in both the tensile strength and impact strength, and a reduction in the complex viscosity of the composites as evidenced by the rotational rheometry, which suggests an increased flowability of the composite melt due to incorporation of EHL. The water absorption and swelling of the composites decreased with increasing EHL content during water immersion test. The scanning electron microscopy micrographs of EHL incorporated wood flour/high‐density polyethylene composites showed a homogeneous dispersion of wood flour and EHL in the HDPE matrix. POLYM. COMPOS., 37:379–384, 2016. © 2014 Society of Plastics Engineers     

Compressive mechanical properties of sawdust/high density polyethylene composites under various strain rate loadings

This article is concerned with the static and dynamic mechanical properties of high‐density polyethylene (HDPE) reinforced with sawdust (SD) at a strain rate of up to 10³ s^?1. In this study, the static and dynamic properties of HDPE/SD composites with different filler loadings of 5, 10, 15, 20, and 30 wt% SD were deliberated at different levels of strain rates (0.001, 0.01, 0.1, 650, 900, and 1100 s^?1) using a conventional universal testing machine and the split Hopkinson pressure bar apparatus. The results showed that the stress–strain curves, yield behavior, stiffness, and strength properties of the HDPE/SD composites were strongly affected by both the strain rate and the filler loadings. Furthermore, the rate sensitivityof the HDPE/SD composites showed a great dependency on the applied strain rate, increasing as the strain rate increased. However, the thermal activation values showed a contrary trend. Meanwhile, for the postdamage analysis, the results showed that the applied strain rates influenced the deformation behavior of the tested HDPE/SD composites. Moreover, for the fractographic analysis at dynamic loading, the composites showed that all the specimens underwent a severe catastrophic deformation. J. VINYL ADDIT. TECHNOL., 24:162–173, 2018. © 2016 Society of Plastics Engineers     

The impact of silane chemistry conditions on the properties of wood plastic composites with low density polyethylene and high wood content

Silane chemistry was implemented on various formulations of wood/thermoplastic polymer composites (WPCs) with low density polyethylene (LDPE) and high wood content (60 wt%). Taguchi analysis was used to evaluate the impact of vinyltrimethoxysilane content (VTMS), dicumyl peroxide content (DCP), and processing temperature on the rheological, morphological, and dynamic mechanic properties of WPCs. The torque power was measured by a Haake torque rheometer and indicated that the VTMS content and temperature most significantly impacted the rheological properties related to silane reactions. Differential scanning calorimetry also showed a larger depression in LDPE melting point and crystallinity index when a high VTMS content (35 phr), high DCP content (0.5 phr), and a high compounding temperature (200°C) were used. With dynamic mechanical analysis (DMA), it was shown that the compounded formulations had a higher storage modulus over a wide range of temperature whereas the β transition temperature increased with higher content in silane reactants. Interestingly, the high humidity/temperature conditioning step aimed at crosslinking resulted in a drop of dynamic moduli compared to the freshly compounded formulations. This was explained by the fact that during compounding of LDPE with high wood content and silane reactants, significant amounts of matrix and interfacial silane crosslinking already occurred. Subsequent conditioning in a high humidity and temperature environment was proposed to hydrolyze the interfacial siloxane bonds resulting in a degradation of mechanical properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Comparative mechanical,fire‐retarding,and morphological properties of high‐density polyethylene/(wood flour) composites with different flame retardants

Aluminum hydroxide, magnesium hydroxide, and 1,2‐bis(pentabromophenyl) ethane were incorporated into high‐density polyethylene (HDPE) and wood flour composites, and their mechanical properties, morphology, and fire‐retardancy performance were characterized. The addition of flame retardants slightly reduced the modulus of elasticity and modulus of rupture of composites. Morphology characterization showed reduced interfacial adhesion among wood flour, HDPE, and flame retardants in the composites compared with control composites (HDPE and wood flour composites without the addition of flame retardants). The flame retardancy of composites was improved with the addition of the flame retardants, magnesium hydroxide and 1,2‐bis(pentabromophenyl) ethane, especially 1,2‐bis(pentabromophenyl) ethane, with a significant decrease in the heat release rate and total heat release. Char residue composition and morphology, analyzed by attenuated total reflectance, Fourier‐transform infrared spectroscopy, and scanning electron microscopy, showed that the char layer was formed on the composite surface with the addition of flame retardants, which promoted the fire performance of composites. The composites with 10 wt% 1,2‐bis(pentabromophenyl) ethane had good fire performance with a continuous and compact char layer on the composite surface. J. VINYL ADDIT. TECHNOL., 24:3–12, 2018. © 2015 Society of Plastics Engineers     

Dynamic mechanical properties of extruded nylon–wood composites

Dynamic mechanical properties determine the potential end use of a newly developed extruded nylon–wood composite in under‐the‐hood automobile applications. In this article, the dynamic mechanical properties of extruded nylon–wood composites were characterized using a dynamic mechanical thermal analyzer (DMTA) to determine storage modulus, glass transition temperature (T_g), physical aging effects, long‐term performance prediction, and comparisons to similar products. The storage modulus of the nylon–wood composite was found to be more temperature stable than pure nylon 66. The T_g range of the nylon–wood composite was found to be between 23 and 56°C, based on the decrease in storage modulus. A master curve was constructed based on the creep curves at various temperatures from 30 to 80°C. The results show that the relationship between shift factors and temperature follows Arrhenius behavior. Nylon–wood composites have good temperature‐dependent properties. Wood fillers reduced the physical aging effects on nylon in the wood composites. The comparison of the nylon–wood composite with other similar products shows that nylon–wood composites are a promising low cost material for industrial applications. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Effect of compatibilizing agents on the mechanical properties of high‐density polyethylene/olive husk flour composites

The main objective of this research was to investigate the effect on the thermal and mechanical properties of the addition of two different compatibilizing agents, malefic anhydride‐grafted polyethylene (PE) [synthesized in a solution state (MAPE) and commercial (XA255)], to olive husk flour, high‐density polyethylene (HDPE) composites. The composites contain 30 wt % of olive husk flour and a variable proportion of compatibilizer (3, 5, and 7 wt %). The grafting reaction was followed by Fourier transform infrared, and the grafting degree was evaluated by means of titration. The effect of grafting on the thermal properties of MAPE was observed by ATG/DTG. The mechanical and thermal properties of the composite were investigated. A morphological study of the composite reveals that there is a positive effect of compatibilizing agent on interfacial bonding. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical properties of teak wood flour‐reinforced HDPE composites

Mechanical properties such as tensile and impact strength behavior of teak wood flour (TWF)‐filled high‐density polyethylene (HDPE) composites were evaluated at 0–0.32 volume fraction (Φ_f) of TWF. Tensile modulus and strength initially increased up to Φ_f = 0.09, whereas a decrease is observed with further increase in the Φ_f. Elongation‐at‐break and Izod impact strength decreased significantly with increase in the Φ_f. The crystallinity of HDPE also decreased with increase in the TWF concentration. The initial increase in the tensile modulus and strength was attributed to the mechanical restraint, whereas decrease in the tensile properties at Φ_f > 0.09 was due to the predominant effect of decrease in the crystallinity of HDPE. The mechanical restraint decreased the elongation and Izod impact strength. In the presence of coupling agent, maleic anhydride‐grafted HDPE (HDPE‐g‐MAH), the tensile modulus and strength enhanced significantly because of enhanced interphase adhesion. However, the elongation and Izod impact strength decreased because of enhanced mechanical restraint on account of increased phase interactions. Scanning electron microscopy showed a degree of better dispersion of TWF particles because of enhanced phase adhesion in the presence of HDPE‐g‐MAH. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dynamic mechanical properties of polystyrene/low density polyethylene blends

The dynamic mechanical properties of polystyrene/low density polyethylene blends and of polystyrene/polyethylene/di-block polystyrene-polyethylene copolymer blends have been investigated in the temperature range −160°C to +100°C. It is shown that anomalies in the low temperature shear modulus data of polystyrene-polyethylene blends are a consequence of non-adhesion between the components. From similar data of blends containing a partial di-block PS-PE copolymer it appears that only very small amounts of copolymer are needed to ensure adhesion between the polystyrene and polyethylene phase. Further it is shown that for modulus considerations of the blends, LDPE together with partial PS-PE copolymer can be treated as a single phase. In some cases the presence of copolymer causes formation of a continuous network throughout the polystyrene matrix, as reflected by a low value for the shear modulus of these blends. Phase reversal of polystyrene-polyethylene blends results in an increase of the loss modulus at 40°C which is ascribed to an increased friction caused by phase entanglements. This increase is more pronounced if an excess of polyethylene is present which is again a consequence of non-adhesion between the components.     

Decorated wood fiber/high density polyethylene composites with thermoplastic film as adhesives

It is difficult for wood fibers/high density polyethylene (WF/HDPE) composites to laminate with poplar (Populus tomentosa) wood veneer due to its nonpolar and imporous surface. In present study, four types of thermoplastic films, include two sorts of chlorinated polypropylene (CPP32 and CPP22) film and a mixture film of maleic anhydride grafted polyethylene (MAPE) and HDPE, were developed to glue poplar wood veneer onto WF/HDPE composite board under heat-pressing. The intermediate layer has well water resistance when used aforementioned films. Optical microscopy and scanning electron microscopy (SEM) results show that CPP32 with higher melt flow rate had the higher permeability into poplar wood and fitness with WF/HDPE surface than CPP22; accordingly, the bonding strength of CPP32 was higher than CPP22. MAPE/HDPE film formed the strongest bonding layer for the high compatibility with the WF/HDPE surface which confirmed using SEM, and the covalent bonding between the poplar veneer and MAPE were confirmed using fourier transform infrared (FTIR). Compared to the high heat-press temperature of MAPE/HDPE, CPP32 has the lower processing temperature and acceptable bonding strength. CPP32 and MAPE/HDPE film both suited as the bonding intermediary to substitute traditional adhesive to manufacture veneered wood-plastic composite boards.     

振动挤出HDPE管材的结构与力学性能

使用自制的电磁动态塑化挤出机和螺旋芯棒式机头挤出高密度聚乙烯(HDPE)管材.采用爆破压力测试,拉伸性能测试,差示扫描量热法分析等研究振动频率和振幅对HDPE管材结构与力学性能的影响.振动挤出的HDPE管材周向强度显著提高,实现了管材的双向自增强.与稳态相比,振动挤出的HDPE管材结晶度提高,熔点升高,结晶完善;爆破压力最大提高了34.2%,轴向拉伸屈服应力最大提高了5.3%.