Enzymatic depolymerization of highly crystalline polyethylene terephthalate enabled in moist-solid reaction mixtures

Abstract

Significance Although polyethylene terephthalate (PET) is the most recycled plastic, its recycling typically involves thermomechanical means, producing a plastic of lower quality that cannot be recycled again. In contrast, breaking PET down to its building blocks allows for repolymerization into high-quality PET. Chemical depolymerization of PET requires hazardous chemicals and conditions. Enzymes are environmentally benign, renewable catalysts that work under mild conditions. Several enzymes capable of depolymerizing low-crystallinity PET have been reported; however, efficient depolymerization of highly crystalline forms of PET typically found in consumer products has remained elusive. Here, we report that, in moist-solid reaction mixtures, the cutinase from Humicola insolens can efficiently hydrolyze highly crystalline PET to terephthalic acid with a 50% yield, without any amorphization or pretreatment of PET.