Abstract
Impact loads under extreme conditions pose serious threats to personnel and equipment, driving the urgent need for impact-resistant materials that combine high strength and toughness. Inspired by the hierarchical structures of biological materials, this study proposes a novel biomimetic design strategy for impact-resistant elastomers. By employing supramolecular chemistry, nanocellulose and linear polyurethane molecular chains are simultaneously tailored and expanded to construct high-performance composites through multiple hydrogen bonding interactions. In this work, 2-ureido-4[1H]-pyrimidinone (UPy), which contains quadruple hydrogen bonds, was used as a chain extender for polyurethane prepolymers and simultaneously employed to modify cellulose nanofibers (CNF). This approach established a hierarchical hydrogen bonding network between the matrix and the filler, effectively inhibiting excessive crystallization of the polycaprolactone (PCL) soft segments and promoting uniformly distributed microphase separation. At an optimal UPy-CNF loading of 0.5 wt%, the resulting composite elastomer (SPU-CNF-0.5) achieved a remarkable fracture strength of 47.5 MPa and an exceptional elongation at break of 974.2%, representing a 121% increase in strength compared to the neat SPU elastomer. Low-field NMR and variable-temperature FTIR analyses confirmed the presence of multiple hydrogen bonds (urethane double hydrogen bonds, carboxyl double hydrogen bonds, and UPy quadruple hydrogen bonds) and their reversible dissociation and reassociation under mechanical stress, which are key to the material's high energy dissipation and self-reinforcement capabilities. In summary, through the synergistic combination of rigid nanocellulose reinforcement and dynamic UPy supramolecular networks, this study successfully developed a biomimetic elastomer integrating high strength, high toughness, and superior impact resistance, offering a promising strategy for advanced protective materials.