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     

Foam extrusion of high density polyethylene/wood‐flour composites using chemical foaming agents

A one‐way analysis of variance and thermal analysis were performed in this study to examine the influences of the contents, types (exothermic vs. endothermic), and forms (pure vs. masterbatch) of chemical foaming agents (CFAs), as well as the use of coupling agents, on the density reduction (or void fraction) and cell morphology of extrusion‐foamed neat high density polyethylene (HDPE) and HDPE/wood‐flour composites. The CFA types and forms did not affect the void fractions of both the neat HDPE and HDPE/wood‐flour composites. However, a gas containment limit was observed for neat HDPE foams whereas the average cell size achieved in the HDPE/wood‐flour composite foams remained insensitive to the CFA contents, irrespective of the foaming agent types. The experimental results indicated that the use of coupling agent in the formulation was required to achieve HDPE/wood‐flour composite foams with high void fraction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3139–3150, 2003     

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.     

Synergistic compatibilization and reinforcement of HDPE/wood flour composites

Multi‐monomer grafted copolymers, high‐density polyethylene‐grafted‐maleic anhydride‐styrene (HDPE‐g‐(MAH‐St)) and polyethylene wax‐grafted‐ maleic anhydride ((PE wax)‐g‐MAH), were synthesized and applied to prepare high‐performance high‐density polyethylene (HDPE)/wood flour (WF) composites. Interfacial synergistic compatibilization was studied via the coordinated blending of high‐density polyethylene‐grafted‐maleic anhydride (MPE‐St) and polyethylene wax‐grafted‐ maleic anhydride (MPW) in the high‐density polyethylene (HDPE)/wood flour (WF) composites. Scanning electron microscopy (SEM) morphology and three‐dimensional WF sketch presented that strong interactive interface between HDPE and WF, formed by MPE‐St with high graft degree of maleic anhydride (MAH) together with the permeating effect of MPW with a low molecular weight. Experimental results demonstrated that HDPE/WF composites compatibilized by MPE‐St/MPW compounds showed significant improvement in mechanical properties, rheological properties, and water resistance than those compatibilized by MPE, MPE‐St or MPW separately and the uncompatibilized composites. The mass ratio of MPE‐St/MPW for optimizing the HDPE/WF composites was 5:1. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42958.     

The effect of maleic anhydride grafting efficiency on the flexural properties of polyethylene composites

Many authors have reported on the property enhancements possible by compounding high density polyethylene (HDPE) with fillers to produce composites. It is accepted that polyethylene combined with materials such as nanoclay or wood flour will not yield favorable properties unless a compatibilizing material is used to form a link. In this work, compatibilized HDPE was produced by grafting maleic anhydride (MA) to its backbone in a twin screw extruder using a peroxide initiated reactive process. Fourier transform infrared spectroscopy (FTIR) was used to examine the effects of varying peroxide and MA levels on the grafting percentage and it was found that a high percentage could be achieved. The gel content of each HDPE‐g‐MA batch was determined and twin bore rheometry analysis was carried out to examine the effects of crosslinking and MA grafting on the melt viscosity. These HDPE‐g‐MA compatibilizers were subsequently compounded with nanoclay and wood flour to produce composites. The composite materials were tested using a three point bending apparatus to determine the flexural modulus and strength and were shown to have favorable mechanical properties when compared with composites containing no compatibilizer. X‐ray diffraction (XRD) was used to examine the effects of grafted MA content on the intercalation and exfoliation levels of nanoclay composites. The results from XRD scans showed that increased intercalation in polymer nanoclay composites was achieved by increasing the grafted MA content. This was confirmed using a scanning electron microscope, where images produced showed increased levels of dispersion and reductions in nanoclay agglomerates. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of chemical modification of wood flour on the rheological properties of high‐density polyethylene blends

Chemical modification of lignocellulosic fibers can improve interfacial adhesion and dimensionally stabilize the resulting plastic composites. This study examined the rheological properties of wood flour/high density polyethylene (HDPE) melts after poplar wood flour was modified with glutaraldehyde (GA, mainly cell wall cross‐linking) and 1,3‐dimethylol‐4,5‐dihydroxyethyleneurea (DMDHEU, mainly poly‐condensation). Results show improvement in both the dispersibility of treated wood flour in the HDPE and its interfacial compatibility. Treatment with GA decreased melt viscosity, moduli, and shear stress as evidenced by rheometry. However, the modifying effects of DMDHEU were not observed, which was mainly due to reduced HDPE content. This study indicates that chemical modification of wood flour is a promising approach to improve the processability of highly filled wood thermoplastic composites via extrusion/injection molding processing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41200.     

甲基化木粉与PE-g-MAH对木粉/HDPE复合材料力学性能的协同作用研究

主要研究了木粉表面甲基化改性和增容剂马来酸酐接枝聚乙烯(PE-g-MAH)对木粉/高密度聚乙烯(HDPE)复合材料力学性能的协同作用。木粉经表面甲基化处理后,与10%PE-g-MAH协同使用,甲基化木粉/PE-g-MAH/HDPE复合材料的拉伸强度、弯曲强度和冲击强度均明显高于未改性木粉/PE-g-MAH/HDPE复合材料,其原因在于在PE-g-MAH的作用下,甲基化木粉在聚合物基体中分布更加均匀,两者的界面作用力更高,即甲基化木粉和PE-g-MAH对提升木粉/HDPE复合材料的力学性能具有良好的协同作用。     

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     

Effectiveness of functionalized polyolefins as compatibilizers for polyethylene/wood flour composites

The effects of various types of compatibilizers on the mechanical properties of high‐density polyethylene/wood flour (HDPE/WF) composite were investigated. Functionalized polyolefins such as maleated and acrylic acid grafted polyethylenes, maleated polypropylene (PPgMA) and styrene‐ethylene/butylene‐styrene triblock copolymer (SEBSgMA) were incorporated to reduce the interfacial tension between the polyethylene matrix and the wood filler. Among them, it was found that maleated linear low‐density polyethylene (LLDPEgMA) gave maximum tensile and impact strength of the composites, presumably because of better compatibility with the HDPE matrix. Similar but less enhanced improvements in the mechanical properties, depending on the compatibilizer loading, were seen for the SEBSgMA system. Whereas acrylic acid grafted high‐density polyethylene (HDPEgAA) and maleated polypropylene (PPgMA) only slightly improved tensile modulus and tensile strength; and they both increased with increasing loadings of compatibilizers. A scanning electron microscopic study was employed to reveal the interfacial region and confirm these findings. In addition, dynamical mechanical thermal measurements also revealed the interaction between filler and matrix, and FTIR spectroscopy was used to assign the chemical fixation and the various chemical species involved at the surface of the wood fillers before and after surface treatment.     

木粉粒径对木塑复合材料性能的影响

采用不同粒径的木粉填充高密度聚乙烯制备木塑复合材料，研究了木粉粒径对木塑复合材料力学性能和加工流动性的影响。结果表明：木粉粒径对复合材料性能的影响十分明显，较大粒径的木粉有利于复合材料弯曲性能和冲击强度的提高。木粉粒径从100μm增加到850μm，复合材料弯曲强度增加10．4％，弯曲模量增加56．3％，冲击强度增加14．6％。随木粉粒径的增大，拉伸强度呈现先上升后下降的趋势，在200μm时出现最大值。木粉粒径对熔体流动速率（MFR）和密度的影响十分明显，大粒径的木粉使复合材料具有较高的MFR和较低的密度。     

Preparation of HDPE/SEBS‐g‐MAH and its effect on mechanical properties of HDPE/wood flour composites

In this article, high density polyethylene/styrene‐ethylene‐butylene‐styrene block copolymer blends (HDPE/SEBS) grafted by maleic anhydride (HDPE/SEBS‐g‐MAH), which is an effective compatibilizer for HDPE/wood flour composites was prepared by means of torque rheometer with different contents of maleic anhydride (MAH). The experimental results indicated that MAH indeed grafted on HDPE/SEBS by FTIR analysis and the torque increased with increasing the content of maleic anhydride and dicumyl peroxide (DCP). Styrene may increase the graft reaction rate of MAH and HDPE/SEBS. When HDPE/SEBS MAH was added to HDPE/wood flour composites, tensile strength and flexural strength of composites can reach 25.9 and 34.8 MPa in comparison of 16.5 and 23.8 MPa (without HDPE/SEBS‐g‐MAH), increasing by 157 and 146%, respectively. Due to incorporation of thermoplastic elastomer in HDPE/SEBS‐g‐MAH, the Notched Izod impact strength reached 5.08 kJ m^?2, increasing by 145% in comparison of system without compatibilizer. That HDPE/SEBS‐g‐MAH improved the compatibility was also conformed by dynamic mechanical measurement. Scanning electron micrographs provided evidence for strong adhesion between wood flour and HDPE matrix with addition of HDPE/SEBS‐g‐MAH. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Structure and properties of phase change materials based on HDPE,soft Fischer‐Tropsch paraffin wax,and wood flour

Phase‐change materials based on high density polyethylene (HDPE), soft Fischer‐Tropsch paraffin wax (M3), and alkali‐treated wood flour (WF) were investigated. The blend and composite samples were prepared by melt mixing using a Brabender Plastograph, followed by melt pressing. They were characterized in terms of their morphology, as well as thermal, mechanical, thermo‐mechanical, and water absorption properties. Although SEM micrographs showed some evidence of intimate contact between the WF particles and the HDPE matrix as a result of alkali treatment, poor filler dispersion, and interfacial adhesion were also observed. Partial immiscibility of the HDPE and the M3 wax was noticed, with the WF particles covered by wax. There was plasticization of the HDPE matrix by the wax, as well as partial cocrystallization, inhomogeneity and uneven wax dispersion in the polymer matrix. The HDPE/WF/M3 wax composites were more homogeneous than the blends. The presence of wax reduced the thermal stability of the blends and composites. Both the presence of M3 wax and WF influenced the viscoelastic behavior of HDPE. The HDPE/M3 wax blends showed an increase in the interfacial amorphous content as the wax content increases, which resulted in the appearance of a β‐relaxation peak. The presence of M3 wax in HDPE reduced the mechanical properties of the blends. For the composites these properties varied with WF content. An increase in wax content resulted to a decrease in water uptake by the composites, probably because the wax covered the WF particles and penetrated the pores in these particles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of nanoclay on properties of HDPE/wood composites

Composites based on high density polyethylene (HDPE), pine flour, and organic clay were made by melt compounding and then injection molding. The influence of clay on crystallization behavior, mechanical properties, water absorption, and thermal stability of HDPE/pine composites was investigated. The HDPE/pine composites containing exfoliated clay were made by a two‐step melt compounding procedure with the aid of a maleated polyethylene (MAPE). The use of 2% clay decreased the crystallization temperature (T_c), crystallization rate, and the crystallinity level of the HDPE/pine composites, but did not change the crystalline thickness. When 2% MAPE was added, the crystallization rate increased, but the crystallinity level was further lowered. The flexural and tensile strength of HDPE/pine composites increased about 20 and 24%, respectively, with addition of 1% clay, but then decreased slightly as the clay content increased to 3%. The tensile modulus and tensile elongation were also increased with the addition of 1% clay. The impact strength was lowered about 7% by 1% clay, but did not decrease further as more clay was added. The MAPE improved the state of dispersion in the composites. Moisture content and thickness swelling of the HDPE/pine composites was reduced by the clay, but the clay did not improve the composite thermal stability. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

高密度聚乙烯／木粉复合材料熔融性能及表面张力的研究

探讨了木粉及马来酸酐接枝聚乙烯(MAPE)对高密度聚乙烯(HDPE)/木粉复合材料熔融性能及表面张力的影响。结果表明:复合材料的起始熔融温度均略高于纯HDPE的,熔融峰的面积及形状介于纯木粉与纯HDPE之间,复合材料的表面张力及其极性组分均随木粉的质量分数逐渐增加。使用MAPE将提高复合材料熔融峰的面积,复合材料更难被熔化。质量分数为5%、10%的MAPE的复合材料的表面张力较低;而质量分数为15%及20%的MAPE的复合材料的表面张力与无MAPE的复合材料的基本相等。     

Mechanical properties of wood flake–polyethylene composites. II. Interface modification

This article discusses the methods of interface modification of composites based on raw wood flakes and high‐density polyethylene (HDPE) and the effects of these modifications on composite properties. An HDPE matrix was modified by a reaction with maleic anhydride (MA) in a twin‐screw extruder and then compounded with wood flakes to produce wood–polyethylene composites. Wood flakes were modified by a reaction with a silane coupling agent in an aqueous medium before being compounded with HDPE to produce silane‐modified WPCs. Differential scanning calorimetry and Fourier transform infrared spectroscopy data provide evidence for the existence of a polyethylene (PE)–silane‐grafted wood structure, which acts as a compatibilizer for wood flakes and PE. The results of MA‐modified composites indicate that some maleated HDPE is reacting with wood through esterification to form a compatibilizer for wood flakes and HDPE. Significant improvements in tensile strength, ductility, and Izod impact strength were obtained. Scanning electron micrographs provide evidence for strong interactions between the wood flakes and the matrix agent. The results indicate that 1–2 wt % MA modification on HDPE and 1–3 wt % silane treatment on wood flakes provide WPCs with the optimum properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2505–2521, 2002     

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     

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.     

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     

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.     

Effects of the accelerated freeze‐thaw cycling on physical and mechanical properties of wood flour‐recycled thermoplastic composites

This study investigated durability performance of wood‐plastic composites (WPCs) that were exposed to accelerated cycling of water immersion followed by freeze thaw (FT). The WPCs used in this study were made of high‐density polyethylene (HDPE) or polypropylene (PP) with radiata pine (Pinus radiata) wood flour using hot‐press molding. These two types of plastics included both recycled and virgin forms in the formulation. In the experiments, surface color, flexural properties, and dimensional stability properties (water absorption and thickness swelling) were measured for the FT cycled composites and the control samples. Interface microstructures and thermal properties of the composites were also investigated. The results show that the water absorption and the thickness swelling of the composites increased with the FT weathering. In the meantime, the flexural strength and stiffness decreased. Scanning electron microscopy (SEM) images of the fractured surfaces confirmed a loss of interface bonding between the wood flour and the polymer matrix. Differential scanning calorimetry (DSC) showed a decrease in crystallization enthalpy and crystallinity of the wood flour‐plastic composites as compared with the neat PP and HDPE samples. The crystallinity of the FT cycled composites using the virgin plastics (vPP and vHDPE) increased; however, the composites with the recycled plastics decreased in comparison with corresponding control samples. In general, the properties of the composites were degraded significantly after the accelerated FT cycling. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers