Reprocessable bio-based rubber with hierarchical hydrogen bonding: A sustainable solution for high strength, superior extensibility, and recyclability

Covalent Adaptive Networks (CANs), especially when assisted by sacrificial bonds or fillers, present a compelling strategy to achieve simultaneous high-performance and recyclability in rubbers. However, CAN-based rubbers often suffer from limited extensibility. Weak interactions acting as crosslinking points have shown surprising performance reversal in thermalplastic elastomers, but the design of non-covalently crosslinked rubbers with high mechanical strength remains a significant challenge. In this study, we present an effective approach totally depending on weak interactions to develop a bio-based epoxidized natural rubber (ENR), modified with carboxylic acid-functionalized 2-ureido-4-pyrimidinone (UPy-COOH), which forms a hierarchical hydrogen bonding network (ENR-UPy). The cohesive energy, energy dissipation, and dynamic responsiveness provided by the hierarchical hydrogen bonding network, coupled with strain-induced crystallization (SIC) of ENR, enable ENR with exceptional extensibility, surpassing CANs-based rubbers while maintaining robust mechanical strength. The optimized ENR-UPy exhibits outstanding elongation of 1190 % at break and toughness of 62.00 MJ/m 3 while maintaining high tensile strength of 11.87 MPa. More importantly, the dynamic nature of this hierarchical hydrogen bonding network enables reprocessed ENR-UPy to recover 99 % and 96 % tensile strength and elongation respectively, remarkably superior to reprocessability of CANs-based rubbers, and totally different from the non-renewable characteristics of conventional vulcanized rubbers. This work highlights the potential of hierarchical hydrogen bonds in creating reprocessable rubbers, offering a sustainable solution to the challenges of rubber waste and advancing green fabrication technologies.