Single-Stage PET Waste Upcycling into Copolymers: Study of Thermal Properties and Crystallization

The transesterification of polyester with hydroxyl-terminated oligoesters represents a promising route for the chemical upcycling of polyethylene terephthalate waste. The single-stage melt process under investigation yielded value-added PET-based copolyesters containing up to 15 mol.% diethylene glycol and triethylene glycol units. The effect of comonomer content on the thermal properties and crystallization of the copolymers was studied. It was found that an increase in the number of oxyethylene groups in the comonomer leads to a greater decrease in the glass transition temperature and the isothermal crystallization rate. Diethylene glycol was shown to lower the equilibrium melting temperature more than triethylene glycol. Thus, during PET upcycling, the glass transition temperature decreased from 80 to 50 °C, and the melting temperature from 280 to 250 °C.