Probing oxidative aging in natural ester nanofluids using FTIR and frequency domain spectroscopy

Natural ester insulating liquids are promising alternatives to mineral oils due to their biodegradability and lower environmental impact. Oxidation is less problematic in sealed systems; however, under conditions where oxygen exposure or elevated temperatures are present, the aging behavior of natural esters still warrants attention. In this study, oxidative aging in a canola-based natural ester and its nanoparticle-enhanced variants was monitored using Fourier Transform Infrared Spectroscopy (FTIR) and Frequency Domain Spectroscopy (FDS). Nanofluids were prepared with SiO 2 and TiO 2 nanoparticles of varying sizes (5–30 nm) and concentrations (0.05–0.25 wt%) using a two-step dispersion method. Oxidative aging was induced following the ASTM D2440 protocol. FTIR analysis revealed a superior molecular stability in oxidation-related functional groups in nanofluids containing TiO 2 , particularly at 5 nm, indicating improved resistance to chemical degradation. Complementary FDS measurements showed lower conductivity and dissipation factors in aged TiO 2 -based nanofluids, confirming enhanced dielectric stability at the molecular level. These spectroscopic diagnostics demonstrate the effectiveness of TiO 2 nanoparticles in mitigating oxidation pathways and preserving dielectric integrity under thermal-oxidative stress. The results highlight the value of FTIR and FDS as non-destructive monitoring tools and contribute to the design of more durable, high-performance natural ester insulating fluids for advanced power systems.