Progress in upcycling polylactic acid waste as an alternative carbon source: A review

Polylactic acid (PLA) is currently the highest production of all bio-based plastics globally. Its production will increase year by year to replace part of petroleum-based plastics to reduce environmental pollution and curb carbon emissions. However, the raw materials for synthesizing PLA mainly come from sugary foods, and mass production will pose a threat to food security. In addition, the degradation rate of PLA is slow, and a large amount of waste PLA accumulation still causes pollution. As a high-quality carbon source, compared with direct degradation, recycling PLA is a more green and environmentally friendly method. Because PLA can not only be depolymerized into raw materials for synthesizing PLA but also can be upcycled to chemicals required by various industries, which helps to reduce the use of petroleum resources. In addition, the recycling of PLA helps to reduce CO₂ emissions, because the source of PLA does not consume petroleum resources, but rather fixes CO₂ in the air. This review summarizes the works of upcycling waste PLA as an alternative carbon source for energy and other chemicals from the perspectives of tertiary and quaternary recycling, which provides a reference for the proper treatment of a large amount of waste PLA.