In the drive towards a sustainable bioeconomy, there is growing interest in the development of composite materials made of plastics compounded with wood particles, known as wood-plastic composites (WPC). The main use for WPC is as outdoor decking material. The market share of WPC decking compared to solid wood decking is small, but due to their promoted customer-friendliness in the use stage, WPC decking are likely to increase their share on the outdoor decking market. New products may soon be introduced to new markets as injection moulding and 3D printing of semi-finished WPC compounds or filaments are currently in an early stage. Recycling of post-consumer materials is promoted by political strategies and concepts, such as the European Bioeconomy Strategy and the Circular Economy to ensure a sustainable resource supply in the context of resource efficiency. The goal of the thesis was to identify resource efficiency potentials of WPC, in terms of the projected increase in WPC consumption and the resulting rise in post-consumer WPC in our society. The focus was on characterizing WPC produced from secondary materials from specific waste streams as well as assessing the environmental parameters of the product and end-of-life (EoL) stages of WPC. An extensive selection of methods was chosen comprising material flow and economic analysis, physical characterization of laboratory scaled WPC specimens, and life cycle assessment (LCA). Application considerations in context of normative standards and policy frameworks completed the holistic approach to be able to identify secondary material substitution potentials and an environmentally sound EoL treatment. Post-consumer mixed waste wood and recycled particleboard (both A II) could substitute virgin wood particles or wood co-products, but insufficient sorting of abrasive materials prevents their utilization in WPC. From an ecological point of view, wood co-products should be considered instead of recycled wood but, these materials in particular are facing a competing demand in context of energy purposes. From a physical perspective, however, using recycled wood in WPC achieved comparable results to WPC produced from virgin Norway spruce particles. Post-consumer thermoplastic polyolefins from packaging waste as well as polystyrene and acrylonitrile-butadiene-styrene from electronic waste were identified as substitutes for the virgin thermoplastics currently used in WPC. These secondary materials are readily available, as recyclers looking for new markets of their secondary materials, achieve comparable physical results and would benefit the environmental profile of WPC. Recycling to yield secondary WPC was identified as the environmentally best alternative compared to incineration with energy recovery by means of a system LCA.
University of Hamburg, Faculty of Mathematics, Informatics and Natural Sciences, Department of Biology
Prof. Dr. Andreas Krause