Life cycle assessment of wood-plastic composites: Analysing alternative materials and identifying an environmental sound end-of-life option

In the drive towards a sustainable Bioeconomy, a growing interest in the development of composite materials made of plastics compounded with wood particles, known as wood-plastic composites (WPC), can be observed. Wood is seen as one of the cornerstones for sustainable economic growth, while the use of thermoplastics from hydrocarbon fossil resources and additives for WPC potentially cause severe environmental impacts along the entire life cycle. In this study, the life cycle stages of raw material supply and end-of-life pathways of WPC were assessed environmentally from different perspectives with life cycle assessment (LCA). The utilization of alternative raw materials reflected the WPC producer’s point of view. Harmonized product LCA standards were applied and combined with physical parameters of actually produced composites to give credit to substitution potentials in terms of resource quality. The downstream pathways of post-consumer WPC products reflected the recycler’s perspective. A system LCA approach was needed where systems with equal functions were generated to secure a comparison of end-of-life (EoL) treatment systems. Results showed that WPC produced from secondary materials is the ecologically and technically superior alternative. Recycling of the composites would be the ecologically preferable pathway, but the recycled WPC content in novel WPC is a sensitive issue when comparing both EoL treatment systems. Yet, incineration of the composites is the predominant EoL pathway due to current recycling directives and lack of markets for secondary WPC material.