The structural changes in butyl and halogenated butyl elastomers during gamma irradiation

Ionizing radiation induces various changes in the molecular structure of elastomers; consequently, the macroscopic properties of the irradiated elastomers will be modified. The newly formed products and the alteration of the initial chemical structure are the result of free-radical reactions which provide the crosslinking and/or the depolymerization of the tested materials and destructive simultaneous processes involving diffused aggressive agents. This paper describes the behavior of butyl and chlorinated and brominated butyl elastomers under the action of gamma radiation for total doses up to 0.5 MGy. The experimental data provided by several procedures emphasize a complex chemistry circumstance consisting of the simultaneous crosslinking and scission of the macromolecular chains and consecutive processes involving free radicals. Evaluation of the studied changes was via gel content, oxidation level, unsaturation, and halogen distribution as dependent on the total radiation dose. The mechanism of the degradation and a relationship between the crosslinking/scission ratio and the absorbed dose are discussed. © 1996 John Wiley & Sons, Inc.