Investigating the heat resistance of peroxide-cured silicone rubber for shelf and service life considerations.

The heat aging resistance of a peroxide-cured silicone rubber (VMQ) in the temperature range from 75 to 225 °C was investigated. Activation energies for the degradation process were calculated in order to understand the durability and lifetime of the rubber. The hardness, tensile stress at 10% elongation, and chemical cross-link density measured by solvent swell and double-quantum nuclear magnetic resonance increase as a function of thermal aging. The increase is due to the prevalence of cross-linking reactions over chain scission events which was confirmed by FTIR analysis. The unaged monomodal cross-link distribution becomes more heterogeneous with heat aging as its distribution significantly widens toward higher cross-link densities. Calculated activation energies for the heat-induced degradation process were between 70 and 101 kJ/mol. Activation energies depended on the experimental test used to probe the system. The FTIR analysis confirmed the loss of –CH bonds and gain of Si–O–Si linkages during thermal aging. Oxidative products were extracted and characterized from the degraded VMQ. Aerobic and non-aerobic degradation mechanisms have been proposed to explain the presence of cross-linking and chain scission reactions. Given the lack of data change during low-temperature aging, the results are suitable for use to predict the performance of VMQ in applications between 100 and 225 °C. [ABSTRACT FROM AUTHOR]