State-of-the-art of industrial PET mechanical recycling: technologies, impact of contaminations and guidelines for decision-making

Abstract

Poly(ethylene terephthalate) (PET) waste streams are of a high societal and commercial value, with complementary mechanical and chemical recycling technologies enabling a circular implementation for many generations and life cycles, in case the multi-scale characteristics of polyester synthesis and recycling are properly quantified. In the present contribution, it is highlighted which challenges the PET mechanical recycling industry faces, connecting (i) variations at the molecular scale (e.g. degradation reactions), co-defining the material and ultimately the application properties, with (ii) variables at the plant scale (e.g. pre-treatment efficiencies). It is explained why both a polymer reaction engineering (PRE) analysis for the key processing (e.g. extrusion and solid state modification) units, and a life cycle assessment (LCA) analysis at the process level (e.g. energy calculations) from the field of environmental engineering science (EES), acknowledging changes in contamination (e.g. non-intentially added substances (NIAS)) levels and PET supply, are necessary. Per unit in the production plant the main influencing factors are discussed, and it is put forward how the overall performance is affected by the performance of each unit, from collection to relaunching of the PET product on the market. It is also elaborated how model-based design and data analysis can support the overall process and energy optimization. General guidelines are formulated, facilitating the combined molecular and process scale driven assessment of the feasibility of mechanical recycling technology. This in turn allows to initialize a more fundamentally based framework for the decision-making regarding preferred recycling technologies, including both the PET mechanical and recycling route.