187 / 2018-08-30 13:21:25

A Comparative Study on the Temperature Resistance of High Temperature Vulcanized Silicone Rubber and Liquid Silicone Rubber

temperature resistance；high temperature vulcanized silicone rubber; liquid silicone rubber

High temperature vulcanized silicone rubber (HTV) insulators have been widely used in transmission systems for more than 60 years for their excellent anti-contamination performance, low weight, low maintenance cost, and easy installation. Liquid silicone rubber (LSR), another kind of silicone rubber insulators, is also widely used in Europe, North Africa, Emirates, Japan, Australia, etc. Most silicone rubber insulators operate outdoors, which means that they are subjected not only to high electric and mechanical stresses, but also to harsh conditions. In Inner Mongolia, the lowest temperature is -55℃, which is close to crystallization temperature of silicone rubber. The mechanical and electrical properties of silicone rubber change dramatically at crystallization temperature. In Qinghai Tibet Plateau, the temperature difference between day and night is as high as 35℃. Therefore, the temperature resistance is important for silicone rubber insulators. However, the comparative study of temperature resistance between HTV and LSR is rather lacking. In this paper, glass transition temperature (Tg), crystallization temperature (Tc), isothermal crystallization process, and thermal stability of HTV and LSR were compared by dynamic mechanical thermal analysis (DMA), differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA). Tg of HTV and LSR are -117℃ and -114℃ respectively. Tc of HTV and LSR are -61.01℃ and -65.27℃, which indicates that LSR is more suitable to use in low temperature regions in consideration of actual environmental temperature in North China. Besides, the isothermal crystallization kinetics of HTV and LSR has been described by the Avrami equation. The Avrami exponent, n for LSR at -65℃ is in the range of 2–3, which means that LSR is likely to produce truncated spherical crystals. Moreover, the crystallization rate constant of LSR at -65℃, 0.83 min-1, is also calculated. The high fillers loadings in HTV accelerate the crystallization process, which result in crystallization completed in the cooling process before the preset temperature is reached. Therefore, isothermal crystallization curve of HTV is hard to capture. In nitrogen atmosphere, there is only one decomposition process (thermal decomposition of silicone rubber) in LSR. Peak temperature of decomposition in TGA differential (DTG) is 630.6℃ and the residual is 58.72%. Two decomposition processes (ATH decomposition and silicone rubber decomposition) exist in HTV. Two decomposition peak temperatures in DTG of HTV are 345.4℃ and 480.2℃ respectively. Besides, the residual mass is 49.55%. In oxygen atmosphere, LSR presents two decomposition stages. Two decomposition peak temperatures are 465.7℃ and 536.4℃. The residual mass is 54.80%. For HTV, the two decomposition peak temperatures are 353.9℃and 477.5℃. 49.85% of mass is left. It is obvious that oxygen promotes the decomposition of LSR but influences the decomposition of HTV a little. However, the thermal stability of LSR is still more excellent than that of HTV. Finally, the conclusion can be drawn that LSR is more excellent than HTV in temperature resistance. LSR insulators can be applied in some cold regions and areas with large temperature changes.