Beyond Mechanical Recycling: Giving New Life to Plastic Waste.

Increasing the stream of recycled plastic from currently 12 wt.% necessitates an approach beyond traditional low value recycling via melting and re-extrusion. Various chemical recycling processes have great potential to enhance recycling rates, because a higher variety of plastic waste streams can be recycled leading to a higher purity and quality product than melting and re-extrusion. But despite long-standing efforts, commercial processes are still not operated at the volumes to address the recycling necessity. In this review, a summary of the various chemical recycling routes and assessment via life cycle analysis is complemented by a list of processes developed by companies active in chemical recycling. We show that each of the currently available processes is applicable for specific plastic waste streams. Thus, only a combination of different technologies can address the plastic waste problem. While pyrolysis can handle relatively mixed waste streams, it works best with polyolefins, PS and PMMA. Contaminations including PVC, PET and PU and non-plastic additives like glass fiber cause operational problems. Multilayer plastics containing these materials are best separated into mono-streams by dissolution/precipitation. Pure polyester or polyamide waste streams can be recycled by solvolysis techniques with high monomer recovery. Research should focus on more realistic, more contaminated and mixed waste streams, while collection and sorting infrastructure will need to be improved, i.e. by stricter regulation. This review aims to inspire both science and innovation for the production of higher value and quality products from plastic recycling suitable for reuse or valorization to create the necessary economic and environmental push for a circular economy.