An Efficient Polymerization of MHET to PET via a Stepwise Heating Strategy

Polyethylene terephthalate (PET) plays a critical role in the global plastics industry due to its outstanding properties. However, the continuously growing demand for PET not only challenges production capacity but also leads to substantial waste accumulation. Herein, we innovatively integrate enzymatic depolymerization with an efficient synthesis process to achieve the sustainable development of PET. Using mono(2-hydroxyethyl) terephthalate (MHET), which is a key intermediate derived from enzymatic depolymerization of PET, as the raw material, a stepwise heating esterification process is developed to synthesize PET under low ethylene glycol (EG) usage. Under the optimal conditions, the molar ratio of MHET to EG is reduced to 1:0.2-0.4, while the esterification and polycondensation times are shortened to approximately 3-3.5 h and 1-1.5 h, respectively. Moreover, the synthesized PET demonstrates excellent thermal and mechanical properties, which are comparable to those of commercially available PET, along with the melting point of 252.5°C, the initial decomposition temperature of 388.8°C, the maximum decomposition temperature of 424.8°C, tensile strength of 79.2 MPa. This approach significantly reduces EG consumption while shortening the total polymerization reaction time for esterification and polycondensation, providing a new direction for the efficient synthesis and recycling of PET.