Closed-Loop Recycling and Upcycling of Fully Biobased Poly(thiourethane) Covalent Adaptable Networks

Abstract

Thermosetting polymers have been widely used in a variety of industrial applications due to their improved mechanical robustness, chemical inertness, and thermal stability. However, thermosetting waste, which is generally unrecyclable, has become a major cause of environmental pollution. Recently, research into dynamic bonding chemistries like transesterification and carbamate exchange has emerged, indicating covalent adaptable networks (CANs) as promising contenders for the recycling of cross-linked polymers. Herein, fully renewable CAN films based on poly(thiourethane) were synthesized using bioderived di(3-mercaptopropyl)sulfide, hexamercaptosqualene, and pentamethylene diisocyanate without using a metal-based catalyst. To enhance environmental sustainability, Cyrene, a cellulose-derived green solvent, was used as an alternative to the traditionally used toxic N,N-dimethylformamide. These novel poly(thiourethane) CAN films demonstrated good mechanical properties with tensile strength (23 MPa) and Young's modulus (433 MPa). Subsequent remolding and chemical recycling in ethanol and upcycling with PDI timer effectively regenerated the poly(thiourethane) CANs without significant loss of material properties, underscoring their durability and potential for sustainable material cycles.