Systematic Investigation of UV-Curable Unsaturated Polyester Resin Nanocomposite Coatings Reinforced with Fe/Al Layered Double Oxide Nanoparticles

This study presents a systematic evaluation of unsaturated polyester resin-based polymer nanocomposite coatings, formulated as UV_bUPR-curable systems. A novel UV_bUPR resin was synthesized and modified with Fe/Al layered double oxide nanoparticles, prepared by calcination of Fe/Al layered double hydroxides. These nanoparticles served as multifunctional fillers and nano-modifiers for the resin. Thin coatings were applied to Al L3005 alloy substrates, with filler loadings between 1 and 5 wt.% to investigate dispersion, stabilization, and performance. Comprehensive characterization was conducted using structural, chemical, and mechanical analyses. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy confirmed the chemical stability of the lab-made resin and its successful modification with layered double oxide fillers. Mechanical testing revealed elastic–plastic behaviour dependent on indenter geometry and applied load. Optimal reinforcement was achieved at 3 wt.% layered double oxide, yielding a 14% increase in adhesion and a maximum microhardness of 95.6 MPa, attributed to ideal particle dispersion and effective load transfer across the matrix–filler interface. Surface roughness introduced variability in nanohardness and modulus values, highlighting microstructural imperfections. Hydrophilicity decreased slightly with filler loading, with surface energy dropping from 41.16 to 36.78 mN/m. At higher loadings (3–5 wt.%), the coatings exhibited significant improvements: storage modulus increased to 1270–1283 MPa, glass transition temperature (T g ) shifted to 95–97 °C, damping decreased and elastic response improved. The addition of Fe/Al LDO up to 5 wt.% did not significantly influence the thermal degradation behaviour of the UV-cured bUPR matrix, indicating good thermal compatibility of the filler with the polymer network. Conversely, low loading (1 wt.%) disrupted the network and reduced stiffness. Overall, Fe/Al layered double oxide nanoparticles effectively reinforced UV_bUPR coatings, advancing the design of UV-curable nanocomposites with enhanced mechanical performance, adhesion, and durability for protective and functional applications.