Morphology control of waste polyesters for enhanced glycolysis reactivity and minimization of side reactions

Abstract

Effective pretreatment routes using dimethyl sulfoxide (DMSO) as solvent were accomplished to enhance the polyethylene terephthalate (PET) glycolysis rate. Highly ordered structure PET flakes were dissolved in DMSO at high temperatures, followed by solid-liquid separation using two different methods to generate micro-sized powders. Under identical glycolysis conditions, the reaction time of pretreated PET powders was gradually reduced by approximately five times that of PET flakes. During the glycolysis of PET with ethylene glycol (EG), diethylene glycol-containing terephthalate compounds (DCTC) are formed as undesired byproducts at high temperatures. These byproducts significantly affect the overall quality of BHET. Consequently, pretreated PET degradation under mild conditions was employed as a preventive measure against EG dehydration, leading to the production of DCTC. PET powders with controlled morphology exhibit outstanding performance and achieve a 100 % PET conversion at 180 degrees C to DCTC-free bis(2-hydroxyethyl) terephthalate (BHET). The purity of the obtained BHET was characterized using proton-NMR spectroscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The utilization of this technology presents a potential solution for overcoming the technical and economic challenges associated with current PET upcycling methodologies.