Mechanical properties of extruded high density polyethylene and polypropylene wood flour decking boards

In this study, mechanical properties of high density polyethylene (HDPE) and polypropylene (PP)-wood flour composite (WFC) decking boards were evaluated and the effect of maleated polypropylene (MAPP) as a coupling agent was investigated. Decking boards were manufactured using Davis-Standard (R) WT-94 Woodtruder (TM). Flexural, tensile and impact properties of the decking boards were evaluated. Fractured surface of samples were also studied using scanning electron microscope. Results showed that PP-WFC decking boards provided higher tensile and flexural properties than HDPE-WFC decking boards. The use of maleated polypropylene (MAPP) coupling agent significantly increased the tensile strength and tensile modulus of both HDPE-WFC and PP-WFC composite decking boards. In the case of flexural properties, MAPP coupling agent slightly increased the flexural strength of HDPE-WFC but did not affect the flexural modulus of HDPE-WFC, and flexural strength and flexural modulus of PP-WFC decking boards. This study showed that MAPP coupling agent can effectively be used as a coupling agent for HDPE base resin. It is believed that this performance is due to the base resin used in this study since it is a narrow molecular weight hexene copolymer HDPE. Both HDPE-WFC and PP-WFC decking boards, even with no coupling agent, provided flexural properties required by the ASTM standard for polyolefin-based plastic lumber decking boards. In the case Izod impact strength, addition of VIAPP coupling agent significantly reduced the notched Izod impact strength of the all decking boards. In addition, morphological study showed that compatibility between the wood flour and the plastic matrix were improved with the use of MAPP coupling agent.