Upcycling waste PET into high-purity bis(4-hydroxybutyl) terephthalate via repeated transesterification and purification

초록

Poly(butylene adipate-co-terephthalate) (PBAT) is a biodegradable polyester with promising applications, but its mechanical limitations hinder broader adoption. To overcome these limitations, we investigated bis(4-hydroxybutyl) terephthalate (BHBT)-a symmetrical monomer that favors the formation of alternating rather than random PBAT copolymers-as a building block for high-performance materials. In this study, a repeated transesterification process was developed to synthesize BHBT from poly(ethylene terephthalate) (PET) using 1,4-butanediol (BDO) as both the depolymerizing and transesterifying agent. The effects of the PET-to-BDO molar ratio and catalyst loading on product composition were systematically evaluated. Repeated transesterification combined with deionized water (DW)-induced precipitation progressively enriched BHBT content, reaching 84.7 mol% in the final reaction product, with BHBT dimer as the main impurity. To achieve high purity, a temperature-controlled DW extraction at 40 degrees C was performed, followed by liquid-liquid extraction using dichloromethane (DCM), selected for its high partition coefficient and favorable phase separation, enabling efficient separation of BHBT from BHBT dimer. The final BHBT product achieved a chemical purity of 98.2 +/- 1.6%, as confirmed by quantitative 1H NMR. This scalable process enables the selective production of high-purity BHBT from waste PET, providing a viable monomer platform for synthesizing alternating PBAT copolymers with superior mechanical strength and thermal stability compared to conventional random PBAT.

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