Cheap organocatalyst diphenyl phosphate for efficient chemical recycling of poly(lactic acid), other polyesters and polycarbonates

Abstract

Bioplastics are regarded as a sustainable alternative to traditional petroleum-based plastics, particularly poly(lactic acid) (PLA). However, due to the slow biodegradation of PLA and the lack of an overall recycling strategy, its large-scale use could make it an acute source of future plastic pollution. Herein, we find that diphenyl phosphate (DPP), a cheap organocatalyst, can efficiently catalyze PLA hydrolysis into valuable oligomers/lactic acid. Without pressure and organic solvents, under mild conditions with 3.5 wt% DPP and a little water (160 °C, 1.5 h), commercial PLA pellets/products are rapidly converted into oligomers with molecular weight below 500 g/mol by random hydrolysis. DPP can catalyze at least 10 batches of PLA without compromising its catalytic performance, and kilogram-scale PLA degradation is facilely achieved. The DPP-containing oligomers can be used directly to synthesize lactide, and subsequently high-quality PLA is obtained using a well-established industrial route to achieve closed-loop recycling. Meanwhile, an aqueous lactic acid solution with comparable commercial quality and intact configuration retention is harvested. Moreover, DPP can also effectively catalyze the hydrolysis of other polyesters and polycarbonates. Overall, this study is expected to address the environmental and engineering challenges associated with plastic waste disposal, in particular fostering a PLA-based green circular bio-economy.