Preparation and Tribological Properties of Onion-like Carbon/ Waterborne Polyurethane Coatings

Rice husk powder was used as a carbon source in a high-temperature carbonization reaction for the production of rice husk ash (RHA). Under the catalysis of ferric nitrate, onion-like carbon (OLC) nanomaterial with a particle size of approximately 200 nm was successfully prepared and incorporated into waterborne polyurethane (WPU). The tribological properties of the coatings were determined using a controlled-atmosphere tribometer (WMT-2E) under dry-friction conditions. Following the friction test, the friction mechanism was investigated by characterizing the abrasive spot surfaces of the test samples using 3D laser microscopy and scanning electron microscopy/energy dispersive spectrometer. The final results demonstrated that the thermal stability of WPU composite coatings containing various concentrations of OLC nanoparticles was significantly enhanced, binding forces between coatings and steel sheets increased, and hardness improved compared to pure WPU coatings. Tribological tests revealed a notable enhancement in the anti-wear properties of WPU coatings due to the presence of OLC particles. Specifically, the wear rate of the 1.5%OLC/WPU coating was reduced by 45.3%. The coating's anti-wear mechanism was attributed to the improvement in the mechanical properties of WPU due to OLC, as well as OLC's participation in the formation of a transfer film under induced friction, which protected the matrix.