STUDY OF VACUUM THERMAL AGING ON THE MECHANICAL AND DIELECTRIC PROPERTIES OF LIQUID SILICONE RUBBER

Liquid silicone rubber (LSR) is widely used in the cable joints, and the stability of which is key to the safe of cables. In the present study we performed a series of vacuum thermal ageing tests on LSR at the temperature of 80℃, 100℃ and 120℃ for 1000h, to investigate the ageing mechanism. The mechanical properties of the samples were studied by tensile test and Dynamic Mechanical Analysis (DMA) test, while the dielectric properties were measured by the broadband dielectric spectroscopy (BDS) and the Terahertz time-domain spectra (THz-TDS). Combining with the microstructure observation and the cross-linking density measurement, results were obtained that the vacuum thermal condition impacted on the mechanical and dielectric properties of LSR by causing the molecules motion and cross-linking. When the aging temperature is 80℃, the destruction of the original cross-linking points caused by the heat led the elongation at break and the permittivity increased. However, when the aging temperature was higher, except for the precipitation, the Si-OH on the nano SiO2 formed hydrogen bond with the main chains, making the cross-linking density higher, causing the elongation at break and the glass transition temperature increased while the permittivity decreased and the loss peak of steering polarization disappeared.