Study On The Water Absorption Of WPC And Its Influences

The wood plastic composites (WPC) were prepared by extrusion using wood powder and recycled high density poly(ethylene)(HDPE) as main raw materials, and some additives. Both water absorption of WPC and its effects were systematically investigated. The strategy to reduce water absorption of WPC are proposed on the basis of the results of the effects of modification of plastic, lubricant and content of plastic on water absorption and properties of WPC.The results of study on water absorption of WPC show that although much lower than that of wood, the water absorption of WPC is still obvious. With increasing the immersion time in water, water absorption of WPC increases rapidly at first and then slows down. When the immersion time is long enough, the water absorption of WPC reaches an equilibrium and remains constant. Flexural strength of WPC reduces at first over the immersion time, and the flexural strength of WPC becomes stable when the equilibrium is reached. The oxidation induction time (OIT) of WPC is decreased over the immersion time. The WPC expansion in length, width and thickness directions are all increased with increasing the water absorption, and then become stable after the WPC were saturated with water.By using the modified HDPE which was grafted silane coupling agent, it is expected that the interfacial compatibility of wood/plastic in WPC can be improved, and in turn the water absorption of the WPC can be reduced and the strength can be increased effectively. With increasing the amount of the modified HDPE, the flexural strength of WPC is significantly increased, and both the water absorption and the expansion rate of WPC are reduced. The experiments of immersion in water, outdoor exposure and xenon lamp aging show that the OIT and strength of the WPC with modified HDPE are reduced less than that of WPC without modified HDPE. Both freezing-thawing resisting and color stability are improved by adding the modified HDPE in WPC.The results of study on the effect of content of plastic on WPC water absorption shows that both the water absorption and the expansion rate caused by the water absorption at three directions are reduced with increasing the content of plastic in WPC. The flexural strength of WPC increases with increasing the content of plastic, but the flexural strength is less than that of the WPC prepared with adding the HDPE grafted with silane coupling agents.The results of study on the effect of lubricant on WPC water absorption shows that the formation of ester linkage between MAPE and hydroxyl groups on wood powder surface will be hindered if the lubricant contains stearic acid salts, Thus, the introduction of this kind of lubricant will influence the interfacial compatibility of WPC. As a result, the water absorption of the WPC is increased and the flexural strength decreases with the addition of the lubricant with stearic acid salts. The WPCs prepared using the lubricant without stearic acid salts have a relatively lower water absorption, higher flexural strength and smaller expansion after absorbing water.