Study On Performance Influence Factors And Interfacial Characteristic Of Pe Wood Plastic Composite

Nearly, wood plastic composite (WPC) has been a hot spot in the field of wood science and polymer material science. There are lots of achievements in the processing of raw materials, formula and process improvement, modifier development, and interface mechanism research. But the interface mechanism of WPC is not good enough. And the whole process from raw materials analysis to the WPC products performance study still need be further researched.The WPCs were prepared from rice husk flour, pine flour, poplar flour, or bamboo flour with high density polyethylene (HDPE) or low density polyethylene (LDPE) by extrusion molding in this study. Mechanical test, water absorption test, degradation test, mildew test, and UV aging test were employed to study the effect of raw materials and formula, process improvement, and modifier treatment on the appearance, physical, mechanical, water absorption, and weather resistance properties of WPC. Thermal analysis, infrared analysis, X-ray diffraction (XRD) analysis, contact angle analysis, X-ray photoelectron spectroscopy (XPS) analysis, dynamic thermal mechanical analysis (DMA) and scanning electron microscope (SEM) analysis were used to explain the interfacial characteristic of WPC and the modified mechanism of WPC treated by modifier. The main conclusions were summarized as followed:(1) The effect of ethylene-vinyl acetate copolymer (EVA) on the properties of WPC is significant:(a) The process ability, mechanical properties and weather resistance of WPC with EVA are improved and the water absorption capabilities of WPC with EVA are reduced. The best EVA content should be15%. The mechanical properties of WPC are increasing with vinyl acetate (VA) content raise and melt index reducing. (b) The number of hydroxyl groups of the wood flour treated with EVA is reduced by XPS analysis. The polar of wood flour is reduced. The wood flour treated EVA is coated completely with plastic by SEM analysis. The properties of WPC are improved.(2) The performance influence factors of WPC:(a) Plant fiber form, moisture content, the ratio of wood flour to plastic, and process technology have significant impacts on the appearance property of WPC.(b) Plastic hardness and plant fiber content have significant impacts on the hardness of WPC. The ratio of wood flour to plastic and filler content have decisive impacts on the density of WPC. The hardness of HDPE is53.83%higher than that of LDPE. So the hardness of WPCs from rice husk flour, pine flour, poplar flour or bamboo flour with HDPE are28.93%,21.45%,14.46%and20.72%higher than those of WPCs with LDPE.(c) Mechanical strength of plastic, fiber length of plant fiber, and the surface free energy and the non-polar surface free energy of raw materials have significant impacts on the mechanical properties of WPC. The surface free energy and the non-paler surface free energy of pine flour, poplar flour and bamboo flour are higher than those of rice husk flour. Flexural strength of WPCs from pine flour, poplar flour or bamboo flour with HDPE are25.57%,19.93%, and18.38%higher than those of WPCs from rice husk flour.(d) The number of active hydroxyl of plant fiber and the surface polarity of raw materials have significant impact on the water uptake property of WPC. Pine flour has the highest surface polarity and poplar flour has the lowest surface polarity in the four kinds of plant Fibers. Water absorption of WPCs from pine flour, bamboo flour, and rice husk flour with HDPE are126.36%,88.18%and63.64%higher than those of WPCs from poplar flour.(3) The interfacial characteristics and the mixing mechanism of WPC:All the components can affect the performances of WPC. The most important impact factors are material usage and evenness of mixing. When the materials are incompletely mixed, the contact angle of WPC is unstable. Adding EVA can improve the mixing of plant fiber and plastic and enhance the mechanical properties of WPC.