Radiation-induced deterioration of synthetic rubber vulcanizates containing chlorine

Three chlorine containing rubbers, i.e., polychloroprene (CR), polyepichlorohydrin (CHR), and epichlorohydrin-ethylene oxide copolymer (CHC) were chosen, and the vulcanizates of them were prepared using ethylenethiourea. The three vulcanizates were subject to solvent extraction to purify them, followed by the γ-ray irradiation in air at room temperature. The deterioration by γ-ray (0 - 20 Mrad) was investigated by the changes of tensile properties and solubility behaviors. CR vulcanizate suffered further crosslinking by the irradiation, consequently the increases of network-chain density (νe), tensile modulus, and hardness were observed. On the other hand, CHR and CHC were found to be degradation-type rubbers, i.e., νe, modulus and hardness decreased by the irradiation. By the Horikx theory, they are estimated to undergo random scission in their main chain. Polymer-solvent interaction parameters were found 0.414 for CR, 0.336 for CHR, and 0.357 for CHC. (author)