A recyclable process between a monomer and polyester with a natural catalyst

Abstract

Polylactide (PLA) is a biodegradable polyester with wide applications, and it degrades readily into CO₂ and H₂O. Although PLA paves the way for a circular economy with ‘neutral’ carbon footprint in the ecosystem, its complete degradation and the loss of lactic units are inevitable. Therefore, it is highly desirable to develop an efficient and economical recycling method among end-of-life options. In this work, a novel closed-loop process is constructed: L-ascorbic acid (vitamin C, VC) and sodium L-ascorbate (VCNa), two natural catalysts, were applied for the ring-opening polymerization (ROP) of lactide (LA) to PLA. More importantly, VCNa could catalyze the upcycling of PLA to alkyl lactate. Alkyl lactate could be converted back to LA by VCNa, providing an opportunity for a closed-loop process. The ROP of other lactones and copolymerization of lactide and lactone were also investigated. The relationship between the degradation rate and stereo-regularity of PLA was also explored for the first time.