Experimental investigation of the degradation mechanism of silicone rubber exposed to heat and gamma rays

Cable-grade silicone rubber was aged thermally or by combining heat and gamma-ray radiation, and resultant changes in chemical, thermal, mechanical and electrical properties were examined. The experimental results obtained in these analyses are clearly consistent with the mechanism that silicone rubber is degraded by forming cross-linked structures via formation of abundant siloxane bonds. With further progress of degradation, decomposition becomes dominant. Reflecting these mechanisms, mechanical properties deteriorate dramatically by losing elasticity. Both the real and imaginary parts of complex permittivity decrease, which is a contrastive difference from typical ageing behaviour of organic insulating polymers. In addition, both the elongation at break and indenter modulus are good indicators of degradation of silicone rubber.