Sustainable Upcycling of Waste PET into High-Performance Biobased PEICT Copolyesters with Life Cycle Assessment

Abstract Polyethylene terephthalate (PET) is the most widely utilized polyester globally; yet, its poor degradability and inefficient recycling have resulted in severe waste accumulation, posing a major threat to environmental sustainability. Chemical upcycling of waste PET into high-value chemicals and materials is therefore critical for advancing a circular economy and alleviating the carbon footprint of plastics. Herein, the environmentally benign ionic liquid 1-butyl-3-methylimidazolium (L)-lactate ([Bmim][Lact]) was utilized as the catalytic medium for the glycolysis of PET. After systematic parameter optimization, this protocol was successfully scaled up to a 2 L batch reactor, affording bis(2-hydroxyethyl) terephthalate (BHET) with up to 88.3% yield. The recycled BHET was further copolymerized with biobased isosorbide (ISB) to synthesize value-added poly(ethylene-co-isosorbide-co-1,4-cyclohexanedimethylene terephthalate) (PEICT) copolyesters. The PEICT copolyesters exhibited a high glass transition temperature (Tg) of 103.7 °C, showing excellent heat resistance for high-performance engineering applications. Mechanical tests demonstrated that PEICT copolymerized from recycled BHET exhibited comparable mechanical properties to the control sample synthesized from petroleum-based terephthalic acid monomers, with yield strength ranging from 50.6 to 52.2 MPa and elongation at break ranging from 170.4% to 239.0%. Life cycle assessment (LCA) indicated that, within the PEICT copolyester series studied here, increasing the incorporation of chemically recycled BHET reduced fossil resource dependence and lowered the global warming potential.