Understanding the physico-chemical properties of thermally aged natural ester oil adopting fluorescent technique

The molecular level changes in natural ester oil due to thermal aging are studied. Accelerated thermal aging of natural ester oil at 180°C is performed and the subsequent effect on oil matrix is studied using corona inception voltage (CIV) variation under AC and DC voltage. Various physico-chemical diagnostic techniques such as UV-Vis absorbance, FT-IR, fluorescence microscope, DLS, and TEM were used to study the thermally aged natural ester oil. Thermal aging leads to the reduction in corona inception voltage as observed in the present work. The CIV is much higher under DC voltage than AC voltage but its variation is not much under positive/Negative DC voltage. Spectrum analyzer measurement indicates that burst type discharges occur under negative DC voltages. Thermal aging induces degradation of natural ester oil, resulting in the formation of carbonaceous particles. As these carbonaceous particles are fluorescent in nature, a facile fluorescence based analysis is developed to understand and monitor its degradation. 3D excitation emission matrix (EEM) fluorescence data are modeled with parallel factor analysis (PARAFAC).