Evaluation of silicone rubber hydrophobicity after different periods of accelerated photo-ageing

In recent years, due to the advantages of silicone rubber (SR) insulators such as low cost, light weight, high mechanical strength, hydrophobic surface and good dielectric properties compared with porcelain and glass insulators, they have been widely used over the world for electrical power transmission and distribution systems. These materials are prone to decomposition under different environmental conditions, the main deleterious factors leading to the elastomer´s degradation include solar radiation, humidity, temperature cycles and pollution, acting simultaneously and in various degrees, depending on the environment, making the study and the forecast of life span of the silicone rubber based equipments rather complex. In an attempt to contribute to this important problem we underwent a systematic study of the photodegradation of SR in simulated environment. Samples were subjected to accelerated weathering in a Weather-Ometer chamber for 4500 hours. During this time, were evaluated the hydrophobicity, topography by Atomic Force Microscopy and the element composition on the surface by Energy Dispersive Spectrometer. The results indicate that hydrophobicity increases for all composites after the weathering, probably due to increase in surface roughness of composites, which could be attributed to the exposure of the fillers, such as silica and aluminum trihydrate. In addition, it has been observed micron-sized crackles formation on the surface which may be facilitate the diffusion of low molecular weight (LMW) compounds from the bulk sample to surface, which are one of the responsible factors for the hydrophobic surface of SR.