Properties of interfaces in silicone rubber

A salt fog test and an inclined plane test have been combined in order to trace changes in electrical and mechanical properties as well as in chemical stability of high temperature cured silicone rubber (HTV) samples containing interfaces. The interfaces were created in two different ways. The first technique, named adding/curing, was based on pressing together an uncured HTV silicone plate towards a piece of already cured one, followed by curing at atmospheric pressure and high temperature. The second type of interface was made by joining two pieces of cured HTV rubber by silicone glue (RTV-1). Thereafter both types of samples were divided in two parts, one of which was additionally exposed to UV-radiation before testing. The combined salt fog inclined plane test did not reveal significant differences in the development of leakage currents, in the change of surface roughness, or in the degree of surface oxidation in comparison to reference samples of cured HTV rubber without interfaces. At the same time the leakage currents became lower on the UV-exposed samples. It is suggested that the reduction in leakage currents resulted from a combination of increased surface roughness and increased hydrophobicity. Reduction of mechanical properties of UV-exposed samples was also observed. The tensile testing showed that samples containing the adding/curing interfaces maintained their mechanical strength after ageing while the strength of the glued samples was significantly reduced, indicating that the adding/curing system has better long-term mechanical stability compared to the glued system