Accelerated aging investigation of silicone rubber/silica composites for coating of high-voltage insulators

Room temperature vulcanized silicone rubber (RTV-SiR) is a prominent polymeric material for coating of high-voltage insulators. Like other polymeric materials, silicone rubber also exhibits aging in outdoor applications. Silica is one of the most effective additives for properties’ enhancement of polymeric materials. To analyze the effect of silica on the aging behavior of RTV-SiR, we prepared its two silica-based composites with 10% micro \(+\)5% nano and 15% microsilica. Prepared samples are subjected to accelerated stresses such as ultraviolet radiation, acid rain, heat, and fog for 9000 h in a specially fabricated chamber. For timely analysis of the samples, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), leakage current monitoring and Swedish Transmission Research Institute hydrophobicity analyses are used along with continuous visual inspection. In the course of time, all samples showed gradual decrease in transparency. Increase in leakage current was highest in case of the neat SiR (SiR-0) and lowest in case of the hybrid composite (SiR-2). Initial values of leakage current for SiR-0, SiR-1 and SiR-2 were 0.5, 0.5 and 0.3 \(\upmu \)A, respectively, and after aging the increased leakage current values were 0.9, 0.8 and 0.6 \(\upmu \)A. From FTIR, the lowest decrease in the intensities of absorption peaks of important groups in SiR-2 were recorded. In SiR-0, the peaks of symmetric C–H stretching of \(\hbox {CH}_{3}\) and Si–\(\hbox {CH}_{3}\) symmetric bending after 9000 h were 91.7 and 94.6% of virgin, respectively. In SiR-1 and SiR-2, symmetric C–H stretching of \(\hbox {CH}_{3}\) exhibited an increase which was 120 and 110%, respectively, while Si–\(\hbox {CH}_{3}\) symmetric bending remained 95% of virgin in SiR-1 and nearly 97% in SiR-2 after 9000 h. Final hydrophobicities of SiR-0 and SiR-1 were HC-2, while comparatively SiR-1 had higher hydrophobicity class of HC-1. SEM results also exposed least changes in the surface of hybrid composite. Silica revealed great impact on the aging behavior of silicone rubber which was highest in the case of the hybrid composite.