Gamma irradiation and oxidative degradation of a silica-filled silicone elastomer

The radiation oxidative degradation of a commonly used silica-filled silicone elastomer DC745 was investigated by a series of experimental techniques. This elastomer is known to be chemically and thermally stable, but insufficient data exist on its radiation resistance. In the present work, gamma doses up to 200 kGy were applied under air at room temperature and 1 Gy/s. Chemical changes due to radiation were investigated by NMR, FT-IR, resonance Raman, and mass spectroscopy. DSC and TGA experiments probed thermal transitions and thermal stability changes with exposure dose. SEM probed variations on the surface of the elastomer, and changes in the polymer network were investigated using solvent swelling methods. Electron paramagnetic resonance (EPR) was employed to detect and identify free radicals. Uniaxial compression load tests at variable temperatures were performed to assess changes in the material's mechanical response as a function of radiation dose. Results demonstrate that, with increasing exposure, DC745 undergoes changes in chemistry that lead to an increase in thermal stability and cross-link density, formation of free radical species, decrease in heat of fusion and increase in stiffness at low temperatures. Taken together, these results indicate that oxidative cross-linking is the dominant radiolysis mechanism that occurs when this material is exposed to gamma irradiation in air.