Closed-Loop Upcycling\nof Waste Nylon Plastic under\nHydrothermal Clean Water Atmosphere

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