Improved wood–plastic composites through better processing

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Abstract Wood–plastic composites (WPCs) undergo cyclic dimensional changes due to periodic absorption and desorption of moisture, and the resulting loss of mechanical integrity can be ameliorated using a coupling agent. Another solution is better processing. Here, we examine injection-molded, polypropylene (PP)-based wood–plastic composites and investigate why the rate of moisture absorption can be reduced by changing extruder operating conditions. At a given wood content, the mechanical properties were found to be similar, but the use of high screw rotation speeds, whether in the co-rotation or counter-rotation modes, and long residence times gave lower rates of moisture absorption even in the absence of a coupling agent.