Reactive mixing enables enzymatic depolymerization of recalcitrant or unsortable polyester wastes.

Abstract

Enzyme-catalyzed depolymerization allows efficient recycling of poly(ethylene terephthalate) (PET) bottles, which are easy to sort and made of slowly crystallizing PET. However, because crystalline phases are recalcitrant to enzymatic hydrolysis, this technology fails for rapidly crystallizing polyester wastes such as poly(butylene terephthalate) (PBT), unsortable mixed polyesters, or heterogeneous formulated PET waste streams. We show that melt transesterification and vitrimerization of mixtures of rapidly crystallizing polyester wastes, leveraging catalysts already present, produce copolyesters that crystallize slowly and are readily depolymerized. For example, reactive blending of a rapidly crystallizing postindustrial PET nonwoven waste with PBT improves depolymerization yields from 20% (PET nonwoven) and 1% (PBT) to 90%. Synergistic mixing can replace sorting, extending the scope of enzymatic recycling to recalcitrant, heterogeneous, and unsortable wastes.