Radiochemical ageing of butyl rubbers for space applications

An increase of the tensile strength of the material was observed during ageing. This increase of the mechanical properties is due to a modification of the rubber network structure. This hypothesis was confirmed by swelling measurements done before and after ageing at various irradiation doses associated with an estimation of the crosslink density by the Flory-Rehner equation. Crosslinking and chains scission reactions occurred under irradiation and the contribution of both processes was estimated thanks to the Charlesby-Pinner equation. The high level of carbon blacks in the butyl rubber formulation plays also an important role in the degradation process. Correlations between mechanical properties and crosslink density are also presented. The modification of the rubber mechanical properties underlines that the degradation mechanism is strongly influenced by the temperature especially at high irradiation doses. At 25 °C, the chain crosslinking process predominates over the chain scission reactions whereas the two phenomena are in competition at the ageing temperature of 70 °C.