Crystallization of high temperature vulcanized silicone rubber: Effect of ATH concentration

High temperature vulcanized silicone rubber (HTVSR) insulators have been widely used on transmission lines. To improve the tracking and erosion resistance and flame retardant of HTVSR, a great of amount of aluminium hydroxide (ATH) is added. It inevitably influences the crystallization characteristics which are important since HTVSR insulators operate below the crystallization temperature. In this paper, to analyze influence of ATH on crystallization of HTVSR, differential scanning calorimeter (DSC), polarized optical microscopy (POM), and broadband dielectric spectroscopy (BDS) were used. A complete crystallization process has been observed by POM. DSC showed that ATH accelerated the crystallization and improved the melting temperature, which meaned that stability of crystal was enhanced. From the isochronal plot of dielectric permittivity, it was found that, with increase of ATH, the temperature of glass transition was lower and the temperature range during glass transition became wider, which indicated that ATH increased the cooperative rearrangement and inhomogeneity in amorphous region. These indicated that two phases (crystal and amorphous region) were more distinct due to ATH.