Visible light–triggered co-upcycling of polypropylene and polyethylene terephthalate using waste chlorinated solvents

Abstract

The chemical incompatibility of mixed plastics poses a fundamental barrier to their circularity. Polypropylene (PP) and polyethylene terephthalate (PET), among the highest-volume manufactured polyolefin and polyester, are particularly difficult to process together due to their divergent structures and stabilities. Here, we demonstrate a synergistic photo-induced strategy that concurrently converts both polymers into valuable products by employing waste chlorinated solvents as a sustainable chlorine radical source. Under visible-light irradiation, chlorine radicals generated in situ from these discarded solvents selectively abstract tertiary hydrogens from PP, triggering an oxygen-mediated chain scission that produces terminal methyl ketone-functionalized polypropylene with lower-molecular-weight (OPP)—a material exhibiting strong performance as a hot-melt adhesive. The hydrogen chloride released during this process simultaneously drives efficient PET depolymerization into terephthalic acid with 1,2-dichloroethane. This coupled reaction not only enables compatible valorization of mixed plastic waste but also upgrades hazardous chlorinated solvents into functional reagents, establishing a triple-waste valorization paradigm with potential for further scale-up and process optimization for sustainable materials management. Processing poly(propylene) and poly(ethylene terephthalate) together is difficult, hindering the recycling of their mixed waste. Here, the authors co-upcycle PP and PET in waste chlorinated solvent via a light-driven process to produce terephthalic acid and a functionalised polypropylene hot-melt adhesive.