Green Synthesis of Alkyd Resins from Rubber Seed Oil Functionalized with Metal Oxide Nanoparticles and Garlic Extract: Characterization and Enhanced Antibacterial Activity

Abstract

This study presents the synthesis, characterization, and antibacterial evaluation of bio-based alkyd resins derived from rubber seed oil. The fatty acid composition was analyzed using Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography–Mass Spectrometry (GC-MS), while physicochemical properties were determined following Association of Official Analytical Chemists (AOAC) standard methods. Refined rubber seed oil (RRO) showed enhanced qualities over crude oil, with iodine value (96 g I₂/100 g), acid value (0.9 mg KOH/g), saponification value (195.74 mg KOH/g), refractive index (1.48), viscosity (100), and density (0.91). Alkyd resins were synthesized via alcoholysis and polyesterification and classified into short, medium, and long oil types. Acid values decreased during polymerization, with the long oil resin having the lowest (7.60 ± 0.40 mg KOH/g), the medium oil resin achieved the highest degree of polymerization (Dp = 4.15) and functional group conversion (76%). Nanoparticles (CuO, ZnO, TiO₂) at 2% and 4% (wt/wt) were incorporated and further functionalized with garlic extract to improve antimicrobial performance. Long oil alkyd resins with hybrid nanoparticles and garlic showed the strongest antibacterial activity, with inhibition zones reaching 40.5 mm against Staphylococcus aureus. These results support the development of green, multifunctional coatings for applications in biomedical, packaging, and environmental sectors.