Degradation in silicone rubber used for outdoor insulator by UV radiation

We investigate the aging by UV radiation of silicone rubber used for outdoor insulators. Results from the measurement of surface potential decay by corona charging and of contact angle show a change of surface electrostatic properties and a slow decrease of contact angle under UV irradiation. For changes in the micro-morphological and chemical structure of the UV-treated silicone rubber, we utilize several analytical techniques such as SEM, ATR-FTIR, and XPS. From this study, it is shown that chemical reactions, such as scissoring of side chain Si-CH₃, cross-linking and branching, occur on the surface of silicone rubber during the UV irradiation. Also, we observe the results of the depletion of low molecular weight chains by cross-linking and oxidation reactions. From the results of inclined plane tracking resistance tests and the above experiments, we propose that surface charging has an effect on the tracking resistance of insulating materials