Study On Accelerated Aging Properties Of Wood Plastic Composites

Wood-plastic composite (WPC) is promoted as an environment-friendly material because of the raw materials of WPC are waste plastic and wood derived from the renewable resources. With the fast development of technology of WPC, outdoor applications of it become more and more widespread, such as floor plate in the park, exterior building wall and so on. Therefore, the research on the aging properties and improving methods of WPC are very important.Based on previous studies about photo-oxidation performance of polymer and wood, photo-oxidation theory of WPC was studied. WPC experienced color change, as well as flexural property loss after accelerated weathering. Scanning electron microscopy (SEM) analysis suggested that there were small cracks appeared on the surface. Reduction of surface contact angle of weathered WPC suggested that there were more wood flour appeared on the surface. Moreover, the fact that surface of weathered WPC experienced oxidation were determined by XPS; and the fact that carbonyl index and vinyl index increased significantly, while the crystallinity increased firstly and decreased lastly were determined by FTIR and DSC.After master the weathering performance of WPC, this paper identifies three main factors that influence WPC weathering. Three methods are presented to improve the aging properties of WPC according to above factors:adding stabilizer, optimizing processing conditions, improving using environment.Effects of different stabilizers of the same class on aging properties of HDPE/WF composites were studied. As to improving color and flexural propertie loss of WPC, a benzotriazole ultraviolet absorber(UVA) is better than benzophenone one; a high molecular weight hindered amine light stabilizer is better than low one; black class pigment is better than yellow one.In this paper, effects of incorporating different concentrations of an UVA, HALS and/or pigment into WPC by fractional factorial experiment were studied. Optimum formulations of stabilizers on decreasing the loss of color and flexural property of HDPE/WF composites were determined as UV-327:1.0%, GW-944:0.5%, brown iron oxide:1.0%.Injection molding conditions of WPC were studied by single-factor and response surface methodology experiment. Optimum injection molding conditions on improving the color fading of LDPE/WF composites were determined as barrel temperature:145℃, injection pressure:65MPa, injection speed:89mm/s. After optimizing the processing conditions,ΔE of weathered WPC is 0.99. It decreased 32% to 1.45 which were determined before optimizing.The influence of weathering environment (UV radiation, with or without water spray) on the aging properties of HDPE/WF composites was determined. The presence of water accelerated aging properties, such as changes of color and flexural property and interfacial compatibility of wood flour and polymer. As a result, measures should be applying to protect WPC when it is used in moisture environment.