Improved wood–plastic composites through better processing

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.