Challenges for Wood–Plastic Composites: increasing wood content and internal compatibility

Wood–plastic composites (WPCs) are interesting materials as the bio-based content is determined by the inclusion of wood particles regenerated from residual wood sources of biomass products. At present, the aim is to increase the wood content in WPCs above 60 %, while it is currently limited to around 40 %. The rationale behind this is based on the increase in performance of the WPC, the relatively cheap price of wood and the aim to augment the biobased content. Most studies are presently carried out with a maximum of 50 % wood particles (preferably ranging around 30 – 40 %), while there are only very few sources where the wood concentration was increased to 70 %, but the formulations were not yet optimized and there were problems in interface compatibility, leading to weak mechanical properties. Problems in augmentation of the wood content have to be controlled, e.g., aggregation, dimensional stability and water absorption. Alternative approaches for the treatment of the wood chips before (or during) compounding with the polymer matrix should be developed. As water resistance is mainly related to control of the surface properties of the hydroscopic wood particles, possible solutions should consider better protection of the individual wood particles' surface against water ingress, better development of the wood–polymer interface and the hindrance of the formation of a continuous network with contacting wood particles. Therefore, this presentation gives an overview of the technological feasibility of various processing routes together with economic feasibility potential based on various sources from the literature, including the effects of compatibilizers and additives, spray-coating of wood particles, chemical pretreatment, physical modifications and thermal treatment of the wood fillers.