Evaluation of Scratch Resistance of Polyether Ether Ketone (PEEK) Nanocomposite Coatings Reinforced With Ceria—Effect of Composition and Ultraviolet (UV) Exposure

Scratch and UV-resistance of a polyether ether ketone (PEEK) coating reinforced with ceria (CeO₂) nanoparticles are investigated. Using an electrostatic spray technique, PEEK-based nanocomposite coatings containing ceria at 0.5, 1.5, and 3 wt% concentrations were applied to mild steel substrates. The process achieved a consistent film thickness of ~100 ± 5 μm. The surface characteristics and mechanical properties were evaluated through water contact angle (WCA) measurements, x-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and scratch tests. Among all compositions, the PEEK/1.5 wt% ceria coating exhibited the most outstanding scratch resistance, enduring a maximum applied load of 30 N without showing signs of failure. In addition, after 500 h of ultraviolet (UV) exposure, this concentration also illustrated significantly better UV durability than the pristine PEEK coating. The PEEK/1.5 wt% ceria coating retained a higher WCA (43° ± 3°), compared to the significant drop observed in pristine PEEK (from 80° ± 3° to 28° ± 3°). FTIR analysis revealed that the PEEK/1.5 wt% ceria coating experienced minimal photodegradation compared to the pristine PEEK coating. Scratch testing on UV-exposed samples showed that the pristine PEEK failed at a much lower load of 12 N, whereas the PEEK/1.5 wt% ceria variant withstood loads up to 30 N without failure, highlighting its excellent resistance to UV-induced deterioration.