Studying On The Preparation And Properties Of High Density Polyethylene/Poplar Wood Flour Composites

Wood-plastic composites (WPCs) have attracted more and more attention in both commercial applications and scientific research due to their excellent biodegradability and renewability, low cost as well as relatively high mechanical properties. In this paper, HDPE/PWF composites were prepared by melt blending and injection moulding techniques, using high density polyethylene (HDPE) as matrixes and poplar wood flour (PWF) as filler. The additives such as modifiers and antioxidant were added as well.Firstly, the content of PWF and different additives on the properties of HDPE/PWF composites was investigated. At low content, the flexural strength of the composites increase with the adding of rigid PWF. While the content of PWF exceed about 40%, the flexural strength of the composites gradually decrease. The incompatibility between polymer matrix and wood flour lead the tensile strength, impact strength and elongation at break decrease with the adding of wood flour. The adding of interface modifier improved the compatibility between wood flour and polymer matrix and enhanced the mechanical properties of WPCs in some degree. But the reinforcing effect was slight when the small molecular coupling agent y-aminopropyltriethoxysilane (y-APS), polymeric compatibilizer polyethylene-grafted glycidyl methacrylate (HDPE-g-GMA) and ethylene-octene copolymer-grafted glycidylmethacrylate (POE-g-GMA) was used separately.Secondly, to further improve the compatibility between the wood flour and polymer matrix, the small molecular coupling agent γ-APS and polymeric compatibilizer HDPE-g-GMA was used in combination, with the expectation that the two modifiers could play the advantages of both and improve the coupling effectiveness. The scanning electron microscopy(SEM) showed that a stronger interfacial adhesion was formed between the wood flour and HDPE matrixes when the combined using of y-APS and HDPE-g-GMA, while the X-ray photoelectron spectroscopy(XPS) results show that the more HDPE chains linked to the surface of PWF through the formation of chemical bonding in the presence of y-APS and HDPE-g-GMA, so the HDPE-g-GMA and y-APS showed a synergistic effect on the improvement of compatibility between the PWF and HDPE matrixes, and the better mechanical properties of WPCs were obtained.At last, in order to slove the problem that the dramatical decreasing in impact property due to the introducing of brittle PWF, ethylene-octene copolymer-grafted glycidyl methacrylate (POE-g-GMA) and γ-APS were chosen as toughening agents and compatibilizers as well. It was observed that POE-g-GMA and y-APS showed a synergistic effect on the improvement of mechanical properties of HDPE/PWF composites, especially with the notched and unnotched impact strength increased to 135% and 350%, as compared to pristine one. The SEM and rheological tests showed that good interfacial situation was formed when the combination of y-APS and POE-g-GMA was used. The synergistic effect of y-APS and POE-g-GMA was contributed to the synergistic modified effect on PWF as investigated by XPS. Better coupling effect was obtained with more POE chains linked to the surface of PWF through the formation of chemical bonding in the presence of y-APS and POE-g-GMA, thus forming core-shell encapsulation around the PWF, giving the composites improved compatibility and better toughness.