Recycling of Wood–Plastic Composites—A Reprocessing Study

Wood–plastic composites, consisting of wood particles and a thermoplastic matrix, are common composites often used in buildings as decking boards or for similar non-load-carrying applications. As these are usually semi-finished products, a certain amount of material is available after cutting these to size, in the factory and also at installation sites. Especially for in-house waste streams in factories, the question remains whether these materials can be reprocessed without any negative influence on the materials’ properties. Therefore, the aim of this work is to investigate the influence of reprocessing on the property profile of polypropylene based wood–plastic composites. Two base formulations with 40 wt% of wood particles and two different polypropylene grades were investigated for their mechanical properties, wood particle size, color, weathering stability and water uptake. We found that most of the wood–plastic composites’ properties were not negatively influenced by the multiple processing steps; the most pronounced effect beside particle size reduction is color degradation, as the composites darken with increasing number of processing steps. In our opinion this shows, that wood–plastic composites can be recycled, especially if these are only reprocessed in smaller shares together with virgin materials.