Towards bio-upcycling of polyethylene terephthalate

TLDR

Over 359 million tons of plastics were produced worldwide in 2018, and the rapid growth of plastic production poses a global end‑of‑life management challenge, while recent discoveries of enzymes that can degrade previously non‑biodegradable plastics open opportunities for biotechnological recycling. The study demonstrates a sequential conversion of post‑consumer polyethylene terephthalate (PET) into a medium‑chain‑length polyhydroxyalkanoate (PHA) and a novel bio‑based poly(amide urethane) (bio‑PU). PET films are hydrolyzed by a thermostable polyester hydrolase to yield terephthalate and ethylene glycol, which are fed to an evolved *Pseudomonas umsongensis* GO16 that produces PHA and secretes hydroxyalkanoyloxy‑alkanoates (HAAs) used as monomers for chemo‑catalytic synthesis of bio‑PU. The resulting value chain upcycles PET without costly monomer purification, providing technological flexibility for global plastic end‑of‑life management.

Abstract

Over 359 million tons of plastics were produced worldwide in 2018, with significant growth expected in the near future, resulting in the global challenge of end-of-life management. The recent identification of enzymes that degrade plastics previously considered non-biodegradable opens up opportunities to steer the plastic recycling industry into the realm of biotechnology. Here, the sequential conversion of post-consumer polyethylene terephthalate (PET) into two types of bioplastics is presented: a medium chain-length polyhydroxyalkanoate (PHA) and a novel bio-based poly(amide urethane) (bio-PU). PET films are hydrolyzed by a thermostable polyester hydrolase yielding highly pure terephthalate and ethylene glycol. The obtained hydrolysate is used directly as a feedstock for a terephthalate-degrading Pseudomonas umsongensis GO16, also evolved to efficiently metabolize ethylene glycol, to produce PHA. The strain is further modified to secrete hydroxyalkanoyloxy-alkanoates (HAAs), which are used as monomers for the chemo-catalytic synthesis of bio-PU. In short, a novel value-chain for PET upcycling is shown that circumvents the costly purification of PET monomers, adding technological flexibility to the global challenge of end-of-life management of plastics.