Mechanical properties of wood-plastic composites made from various wood species with different compatibilisers

Wood-plastic composites (WPCs) were prepared containing wood from six different tree species invasive to South Africa, low density polyethylene (LDPE) and three different compatibilisers, namely poly(ethylene-co-vinyl alcohol) (EVOH), polyethylene-graft maleic anhydride (PE-g-MA) and thermally degraded LDPE (dPE). Tensile modulus, tensile strength, elongation at break and impact strength were determined. The tensile modulus of compatibilised composites was high with PE-g-MA and low for EVOH for all the species, while it increased significantly with increasing wood load for most uncompatibilised composites. Composites containing PE-g-MA and dPE had a high tensile strength, whereas composites containing EVOH proved to be inferior. Composites with PE-g-MA as compatibiliser showed the lowest elongation at break compared to other composites, for all wood species but pine. The addition of compatibilisers improved the impact strength of most of the composites. The mechanical performance of the composites improved when PE-g-MA or dPE compatibilisers were added, whereas EVOH as compatibiliser tended to yield inferior results. The study proved that the investigated invasive wood species-mostly hardwoods-can be incorporated into WPCs. It was shown that dPE, a novel and inexpensive compatibiliser that can be sourced from waste materials, is an effective adhesion promoter in WPCs independent of the wood species used.