Cellulose Nanocrystal-Reinforced Waterborne Polyurethane Composites with Excellent Dynamic Impact Resistance

To address the high-efficiency energy dissipation requirements of flexible protective materials, this study developed cellulose nanocrystal (CNC)-reinforced waterborne polyurethane (WPU) nanocomposites through an interface hydrogen bond regulation strategy. Utilizing the strong interfacial interactions between WPU chains and surface hydroxyl groups of CNC, a CNC/WPU system with a homogeneous dispersion structure was fabricated by the solution casting method. Fourier transform infrared spectroscopy results confirmed the formation of a high-density hydrogen-bonded crosslinked network between CNC and WPU. Dynamic mechanical analysis revealed that CNC predominantly interacted with hard segments of WPU through hydrogen bonding. Split Hopkinson pressure bar tests demonstrated that the composite containing 0.5 wt.% CNC exhibited optimal dynamic impact performance: elastic modulus increased by 59.6% to 5.57 ± 0.46 GPa, energy absorption improved 29.9% to 165.2 ± 6.7 MJ·m −3 , and maximum engineering stress grew by 36.2% to 545.5 ± 17.5 MPa. This enhancement originated from the well-dispersed CNC and robust hydrogen-bonded networks in CNC/WPU nanocomposites, which forced molecular chain orientation during dynamic impact and induced remarkable strain-hardening behavior.