Mechanical and physical stability of polyhydroxyalkanoate (PHA)-based wood plastic composites (WPCs) under natural weathering

This study investigated the effects of natural weathering on the physical and mechanical properties of biodegradable composites based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and wood flour (WF). Composite samples with three different wood contents (0, 20 and 50 wt%), as well as polylactic acid (PLA) and polyethylene (PE) composites containing 50 wt% of WF, were placed on an outdoor inclined rack for 12 months. Neat PHBV and the 20% WF samples showed minimal mould growth and little loss in mechanical properties over the 12-month period. By contrast, the tensile strength of the composites (of all polymer types) made with 50% WF dropped gradually. This decrease was interpreted to be due to the evolution of surface/bulk defects brought about by the degradation of wood particles from moisture-induced fungal (mould) attack. Overall, the wood content and the accessibility of wood particles inside the matrix control the stability of the composites under natural weathering.