Low molecular weight of fluid in an alloy of EPDM/SIR [insulator applications]

Ethylene propylene diene rubber (EPDM), silicone rubber (SIR) and their alloys have good performance when used as outdoor insulators. The hydrophobicity of the surface is maintained in wet and polluted conditions as a result of the presence of silicone fluid on the surface. This is sustained by the diffusion of low molecular weight (LMW) fluid from the bulk to the surface. The amount of LMW fluid on the surface and in the bulk of the material determines the hydrophobicity during the lifetime of the alloy of EPDM/SIR used as insulators. A study of the amount, loss and generation of the LMW fluid in an alloy of EPDM/SIR used for outdoor insulators has been performed as a function of temperature in order to simulate the effects of the heat generated by the dry band arcing on the surface. From an infrared (IR) spectroscopy study, the LMW fluid extracted from the virgin specimen is found to be composed of two kinds of fluids, one comes from the EPDM and the other comes from the SIR components of the alloy. The component of the fluid from the SIR initially decreases with sequential heating at 200°C for 32 h in air and extraction by immersion in hexane at 44°C for 96 h, but then the component of the fluid from EPDM finally becomes predominant.