Continuous Rapid Depolymerization Process to Upcycle Polyethylene Terephthalate into Polyols

Polyethylene terephthalate (PET) is one of the most widely used polymers in the world. This extensive adoption has led to issues involving disposal of PET products after usage. Mechanical recycling has become the default option for most recycling efforts. However, such processes often result in products with substandard properties, reducing the overall value of downcycled PET. Chemical recycling for the full depolymerization of PET into monomers has also been targeted as a method. Unfortunately, achieving full depolymerization requires a complex series of processes, which often involve the usage of high temperatures, pressures, and chemical solvents. All of these factors can limit the mass-scale adoption of such processes. This study presents the development of a novel continuous extrusion-based depolymerization process for PET into an oligomeric feedstock for upcycling without the need for toxic chemicals. Following optimization of the cleaving agent and temperature, the successful depolymerization of both pure PET and actual PET textile waste was achieved, together with the demonstration of upcycling of extrudates into reprocessable vitrimer films to function as a recyclable adhesive. The developed process is one that is straightforward and efficient with good scalability. As such, the process has great potential to have a large impact, not only on the sustainable usage of PET but also on other polycondensation polymers.