A General Strategy for Upcycling Plastic Commodity Waste to Self-Healable and Fully-Recyclable Materials

The rapid expansion of the plastic industry has led to significant environmental and ecological harm due to plastic waste. Considering the drawbacks of traditional recycling methods, as most of the plastic wastes are down-cycled into low-value products such as garden furniture or pots, upcycling has garnered increased attention for transforming plastic waste into high-value products. This study presents a general strategy to upcycle commodity plastic waste to a class of fully recyclable and self-healable polymers. Coumarin and its derivatives are light-sensitive and can self-react when triggered by ultraviolet (UV) light at varying wavelengths. Upon exposure to 365 nm UV light, coumarin undergoes dimerization and forms a cyclobutene ring. Conversely, exposure to 254 nm UV light results in the cleavage of the ring and a reversion to its original state. We demonstrate that after embedding the coumarin groups into our polymer matrix, thanks to the photodimerization and photocleavage occurring on the coumarin group C=C bonds under 254 nm and 365 nm UV light, our materials exhibit four distinct properties: light-tunable mechanics, reprocessing ability, light-activated self-healing, and recyclability. We show our strategy is universal to various commodity plastic wastes, such as PS, PP, PET, and PE. This transition from plastic waste to multifunctional materials offers a new strategy for upcycling various plastic wastes into a category of high-value products.