Catalyst-Free Upcycling of Poly(ethylene terephthalate) (PET) Waste into Degradable PET-Based Engineering Plastics via the Solvothermal Method

Poly(ethylene terephthalate) (PET) is widely used as an engineering plastic due to its excellent mechanical properties and reasonable thermal stability. PET waste is commonly degraded into terephthalic acid for disposal. This work aims to employ a simple solvothermal method to chemically convert PET waste into PET-based engineering plastics (PEPGs) with excellent mechanical strength by soil burial degradation. The inherently excellent mechanical properties of PET waste molecular chains could be harnessed to create a new molecular structure composed of PET and poly(vinyl alcohol) (PVA) units through dehydration condensation, transforming PET waste into PEPGs. This macromolecular reaction can be easily performed under solvothermal conditions without the need for high temperatures or catalysts, resulting in PEPGs with enhanced tensile strength of up to 78 MPa. When subjected to tensile forces or impact, the shape of the PEPGs remained largely unchanged, demonstrating their good durability. The activation energies (Ea) of PET waste and PEPGs were 206.67 and 155.38 kJ·mol–1, respectively, as determined using Kissinger kinetics. The addition of the PVA units changed the molecular chain properties of PET waste, effectively reducing the Ea and allowing the PEPGs to exhibit degradation properties. This work offers a new approach to converting PET waste into degradable, PET-based engineering plastics with excellent mechanical properties and durability.