Modified Nano-SiO₂ Synergistic Carnauba Wax Reinforced Polyurethane Composite with Enhanced Hydrophobicity, Wear Resistance, and Vibration Damping for Underwater Equipment

The wear and vibration challenges of water-lubricated polymer components in mechanical systems remain critical. In this study, a polyurethane composite reinforced with modified nano-SiO 2 and carnauba wax via casting (PUCW-SiO 2 ) was developed, and its properties were explored. With merely 0.5% additive content of modified SiO 2, the optimized composite of PUCW-0.5%SiO 2 exhibited a low water swelling rate (0.157% after 7 days), enhanced mechanical properties (compressive elastic modulus is 410.39 MPa and compressive strength is 89.12 MPa), reduced wear loss (0.01 g in water), effective vibration damping (vibration acceleration signal is reduced to −4–4 m/s 2 in a stable wear stage in a pure water environment), and sand-water environmental tolerance (average friction coefficient is 0.351, average wear loss is 0.0253 g). The improvements stem from modified SiO 2 reinforcing the polyurethane matrix and synergizing with carnauba wax, facilitating the formation of a hydrophobic surface and continuous lubricating film that collectively mitigate wear and vibration.