Coextrusion is a process in which two or more polymer materials are extruded and converged upon a single feedblock or die to form a single multilayer structure(e.g.,flat, annular, or core-shell profiles). It has become one of the most advanced plastic processing technologies in creating multilayer composites with different complementary layer characteristics and in making properties of final products highly " tunable", For example, target composite properties such as oxygen and moisture bariier, shading and insulation, and mechanical properties can be adhibited by incorporating one or more layers with target properties. In addition, coextrusion can signifcantly reduce material and production costs, and help recycle the used material.
Because of those advantages, coextrusion technology is widely uesd in plastic composite films and sheets, coated tubes and pipe. However, the potential of applying coextrusion technology to wood plastic composites(WPCs) is just being recognized, and the work focused on this aspects is very limited. Few published studies include virgin polyvinyl(PVC) and high density polyethylene(HDPE) based WPC with a core-shell structure. It was reported that coextruded HDPE-wood composite had reduced moisture uptake rate, increase flexural strength, and decreased flexural modulus compared with regular HDPE-wood control samples. Coextruded HDPE-wood composites also had improved moisture resistance and color stability. However, mechanical performance of composite system was less understood from the published studies. Several commercial coextruded HDPE-wood composites are currently available.
In recent years, most comercial WPCs use recycled, commingled plastic blends as their base resin system. It is an environmentally beneficial and economically competitive approach for the WPC industry. Howevre, the utilization of multicomponent commingled, recycled plastics was a significant challenge in miantaining target composite properties. It was due to the incompatibility among different plastics which limits their recycling used WPC material often suffers large strength loss due to degradation from moisture and weathering, which limits its direct use in making new WPC. Coextrusion with its ability to create a layered structure may offer a pratical solution to the use of recycled WPC material. In this study, we simulated industrial manufacturing process and produced coextruded WPC, and to investigate the influences of wood loading and thickness of the shell layer and core quality on mechanical and water absortion properties of the resultant compositions