Closed-Loop Upcycling of Waste Nylon Plastic under Hydrothermal Clean Water Atmosphere

The extensive use and longevity of nylon plastics pose substantial challenges for plastic management, recycling, and pollution control. Depolymerization and monomer recycling are potential solutions for valorizing waste plastics, but they often rely on complex and costly catalysts. Additionally, various additives in nylon plastics can negatively impact the catalyst efficiency. To address these issues, we proposed a novel method of hydrothermal clean water depolymerization without any catalysts. In this study, high-purity monomers were successfully recovered from nylon plastics by utilizing the reversibility and hydrophilicity of amide bonds, with hydrothermal amphoteric hydrolysis applied as the method. On this basis, repolymerization of the monomer was completed, and new nylon was generated by one-pot solution polycondensation, thereby achieving a closed-loop recycling process. A depolymerization model was established for nylon in a hydrothermal system at both macro- and micro levels, revealing a unique mechanism of simultaneous surface and internal depolymerization. This process enables the closed-loop upcycling of nylon, transforming waste back into its starting materials, reducing carbon emissions, and promoting sustainability.