Understanding the effect of copolymer content on the processability and mechanical properties of polyhydroxyalkanoate (PHA)/wood composites

The present study investigates the effects of copolymer composition on the mechanical properties of extruded mixed culture poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB) copolymers and their composites with 50 wt% wood flour. The use of copolymers with a higher strain at break (i.e. 24 mol% 3-HV and 15 mol% 4-HB copolymers) for composite production resulted in a slight but promising improvement in strain at break at the cost of lower strength and modulus. The inclusion of 4-HB comonomer was more effective at improving the strain at break of the composites than for the 3-HV comonomer due to the inability of the 4-HB monomer unit to co-crystallise. However, unlike for the tensile properties, the matrix properties did not affect the composite impact strength. It is interpreted that the mechanical properties of the PHA-based WPCs with 50 wt% wood content are dominated by the rigid and brittle wood flour, with the matrix properties having limited influence on the bulk composite properties.