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

Abstract

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 crosslinking is the dominant radiolysis mechanism that occurs when this material is exposed to gamma irradiation in air.

Gamma radiation effect of polymethylvinylphenylsiloxane rubbers under different temperatures

“…The new noticeable absorption peak near 1652 cm −1 in the spectra of irradiated samples can be attributed to the carbonyl group. Irradiation can induce polymer chain‐scission reaction and oxidation reaction . The intensity of hydroxyl and carbonyl absorption peaks could be regarded as a determination of the oxidation degradation degree.…”

“…The sample extracts obtained from aged and pristine PMVPS rubbers were evaluated by liquid‐state 1 H NMR spectroscopy to detect if there were some low‐molecular‐weight radiolysis products generated after gamma radiation . Figure shows the 1 H NMR spectra of the extractable part of the samples.…”

“…Crosslink density is an important parameter for rubbers which would affect the crucial properties of materials, such as elastic modulus, elongation at break, and crystallinity. Previous work performed on polysiloxane rubbers have shown that increasing the absorbed dose resulted in increase in the crosslink density of the polymer no matter in nitrogen or in air atmosphere . In this study, solvent swelling experiments were used to measure the crosslink density of PMVPS rubbers before and after irradiation.…”

“…This result can well explain the DSC thermograms. Increase in crosslinking density reduces the degree of crystallization, either by hindering the ability of the macromolecular chains to reorganize or by decreasing the size of the crystalline domains . So the heat of fusion decreased gradually with increasing absorbed dose.…”

“…Over the past 50 years, the effect of radiation on silicone rubbers has been widely studied . In the previous studies, the influences of absorbed dose and radiation atmosphere (irradiated in air or nitrogen environment) on the performance of polymer materials have been investigated . Radiation‐induced chain‐scission, crosslinking, and oxidation reaction are found to occur.…”