Co-upcycling of mixed polypropylene and polyesters†

Abstract

Mixed plastic waste management has long been a major challenge owing to complex compositions of plastic wastes and high sorting costs. Pyrolysis is the widely adopted method, but the requirement for constant high temperatures and the presence of oxygen element in polyester-containing mixed plastics often lead to low selectivity in the pyrolysis products. Herein, we developed a heating system that generated instantaneous temperature gradient heating (ITGH) to simultaneously achieve high efficiency and selectivity during the treatment of mixed polypropylene/polyethylene terephthalate (PP/PET) plastic wastes. This ITGH system exhibited remarkably rapid rates of heating and cooling, resulting in a temperature gradient over time. It effectively inhibited the occurrence of side reactions, which always occur under continuous heating and prolonged duration, and thus improved the selectivity for the ester thermal elimination of PET with a structure retention rate of 99% for monomer terephthalic acid (TPA). Moreover, it made the reaction highly efficient, and the degradation of mixed PP/PET plastic waste was achieved in just 5 min at 80 °C. This approach can be applied to other polyester-containing mixed plastic wastes and commercial plastics/textiles. It effectively resolves the issue of oxygen element interference in pyrolysis and promotes the sustainable management of mixed plastic wastes.