Development of Neem Oil Ester Modified With Reduced Graphene Oxide and TiO₂ for Distribution Transformers

This article aims to develop an environmentally friendly insulating fluid using nonedible esters, specifically neem oil (NMO). Initially, NMO is modified by degumming at 80 °C with 2% water and 0.025 wt% phosphoric acid. The synthesis of modified NMO (MNMO) involves using NMO and biodegradable materials, reduced graphene oxide (rGO), and titanium dioxide (TiO2), as heterogeneous catalysts. Optimal reaction conditions, including a molar ratio of 1:12, 1.5 wt% catalyst at 65 °C, and a 3-h reaction time, achieved a yield of 91.49% for MNMO. Quantification of esters using Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) confirmed the presence of fatty acid methyl ester (FAME) in MNMO. MNMO exhibited superior dielectric breakdown voltage (62.2 kV) compared to raw neem oil (RNMO) (30 kV), and its lower viscosity of 13 cSt at 40 °C (RNMO shows 62.26 cSt) demonstrated inherent shear stress of 14.298 Pa. RNMO’s dielectric constant increased with temperature due to C = O and C-O bonds, while MNMO’s showed steady behavior. UV spectrometry revealed carbonyl C = O transitions with absorbance intensity (2.75 versus 1.05) in RNMO and MNMO, respectively. These favorable properties position MNMO as a promising natural ester for distribution transformers.