Mechanical properties of poly(3‐hydroxybutyrate‐ co ‐3‐hydroxyvalerate)/wood flour composites: Effect of interface modifiers

A fully biodegradable and biobased wood plastic composite based on a microbial biopolyester matrix, poly(3‐hydroxybutyrate‐ co ‐3‐hydroxyvalerate) (PHBV), and a lignocellulosic filler, pine wood flour (WF), was manufactured using extrusion at industry‐standard level of wood content. The effects of three compatibilization techniques on the mechanical properties of the composites were investigated. Techniques include silicone fiber treatment using Sigmacote, maleic anhydride (MA) grafting of PHBV matrix, and the addition of polymethylene diphenyl‐diisocyanate (pMDI). Results showed that Sigmacote treatment resulted in a 20 ± 5% decrease in tensile strength of the composite. The use of MA‐grafted PHBV, independent of content, enhanced slightly the composites tensile strength (5 ± 3%) and impact strength (10 ± 4%). The addition of 2 wt % of pMDI improved the tensile strength of the composite by 25 ± 6%, but the strength level returned to the original state when 4 wt % was added. Processing conditions had a more significant effect on the composite properties giving a 40 ± 5% reduction in tensile strength and 45 ± 6% in impact strength when a higher shear extrusion configuration was used. The modeling of the mechanical data suggested that PHBV/WF composites have achieved better interfacial interactions without compatibilization when compared to other composite systems.