Comparative Damages in RTV Silicone Rubber Exposed to Mineral and Natural Ester Oil

Room-temperature vulcanized (RTV) silicone rubber is widely used as a protective coating for power transformer bushings due to its exceptional hydrophobicity, hydrophobicity recovery, and superior anti-pollution flashover properties. However, the performance of silicone rubber may experience significant deterioration when exposed to transformer mineral and ester oil. There is a lack of literature that addresses the comparative degradation behavior of silicone rubber when exposed to mineral and natural ester oil. Therefore, in the present work, RTV silicone rubber specimens are subjected to thermal aging in mineral and soyabean-based natural ester oil at a temperature of 70 °C for a duration of 200 h. Surface morphology and micro and macro properties are analyzed using scanning electron microscopy (SEM), 3-D microscopy, hydrophobicity retention and recovery characteristics, Fourier transform infrared (FTIR) spectroscopy, hardness, infrared (IR) thermography, thermogravimetric analysis, ac breakdown voltage (BDV), and inclined plane tracking and erosion test (IPT). Results show greater degradation and physiochemical changes in specimens aged in mineral oil compared to natural ester oil. The experimental outcomes are correlated with observed functional group changes through FTIR investigation to provide insights into the degradation dynamics of the aged specimens.