Synergistic low-temperature upcycling of post-consumer PET into engineering-grade PBT: Dual-activation by deep eutectic solvents and anisole-induced swelling

초록

Upcycling post-consumer poly(ethylene terephthalate) (PET) into high-value engineering plastics is essential for achieving a circular economy. However, chemical recycling via glycolysis using long-chain diols like 1,4-butane-diol remains technically challenging due to slow reaction kinetics and significant steric hindrance under mild conditions. Here, we report a synergistic low-temperature pathway for the direct conversion of PET into engineering-grade poly(butylene terephthalate) (PBT) using a choline chloride/zinc acetate (1:1) deep eutectic solvent (DES) catalyst and anisole as a swelling co-solvent. Under optimized conditions (150 degrees C, 4 h), the process achieved a high PET conversion of 94.5% and a bis(4-hydroxybutyl) terephthalate yield of 83.6% without requiring toxic halogenated solvents. NMR analysis reveals a dual-activation mechanism: the DES simultaneously enhances glycol nucleophilicity and ester carbonyl electrophilicity, while anisole promotes efficient polymer swelling through strong pi-pi interactions, overcoming internal diffusion barriers. The recycled PBT (r-PBT) exhibited a yield strength of 64 MPa and superior elongation of 290%, comparable to or exceeding that of commercial grades. Life cycle assessment confirms a 19% reduction in global warming potential and a 4% reduction in non-renewable energy use compared to conventional methanolysis-based recycling, highlighting the industrial feasibility of this sustainable upcycling strategy.

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