Separation-free upcycling of emerging PET/PEF waste streams into high-performance PEFT copolymers via direct melt transesterification

초록

The increasing consumption of poly(ethylene terephthalate) (PET) and the emerging adoption of bio-based poly(ethylene furanoate) (PEF) pose new challenges for polyester recycling systems. However, PEF's limited ductility and the current lack of effective recycling strategies create problematic mixed PET/PEF waste streams. Conventional sorting and mechanical blending are often costly and degrade the overall material performance. Herein, a separation-free upcycling strategy is developed to produce poly(ethylene furanoate-co-terephthalate) (PEFT) copolymers through direct melt processing. Two distinct chemical routes were comprehensively evaluated: polycondensation (P series) and direct transesterification (T series). The mechanical performance can be tailored by the synthetic route and composition; specifically, the P series at a 50 : 50 ratio achieves a tensile strength of 101 MPa, whereas the T series with 20% PEF incorporation yields an exceptional elongation of 378%, both exceeding the mechanical performance of conventional bottle-grade PET. PEFT maintains a high glass transition temperature while exhibiting a notably lower melting temperature, which improves thermal processability. Furthermore, the incorporation of furan units reduces gas permeability by over 50% compared to conventional PET. Life cycle assessment confirms that the direct transesterification route (0.83 kg CO2 eq.) reduces greenhouse gas emissions by 53% compared to conventional recycled PET, highlighting the environmental benefits of the simplified transesterification process. This scalable upcycling platform offers a practical and sustainable pathway for mixed polyester waste toward circular packaging and carbon neutrality.

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