Sandra R, Scagliusi
Bromobutyl rubber (BIIR) is an isobutylene/isoprene copolymer, containing 1.9% to 2.1% bromine content. Halogenated butyl rubbers have their major applications in tires without inner tubes, various types of seals, membranes, hoses for chemical products conveying and stoppers for pharmaceutical uses. When butyl rubbers are subjected to high-energy radiation, they form easy free radicals that initiate various chemical reactions. These reactions alter the molecular distribution of irradiated rubbers by crosslinking or scission affecting their physical and mechanical properties. The aim of this work is the analysis of effect induced by gamma exposure on the crosslinking density in butyl rubbers (pristine or modified IIR by chlorination and bromination) by swelling measurements accomplished before and after irradiation at 5, 25, 50, 100, 150 and 200 kGy allowing the evaluation of crosslinking density according with Flory-Rehner equation. Rheometric tests were also carried out to complete the characterization of radiation effects in this rubber structures. It can be noticed that the modification in material structure by the formation of new three-dimensional network changes the features of studied rubbers. This evolution was confirmed by swelling measurements on all -exposed butyl rubbers at various doses. The estimation of crosslinking density by Flory-Rehner equation is a proper procedure for the qualification of radiation resistance. The decrease in the damaging rate is properly described by the modification in crosslink number. However, the consistency of results indicates the predominance of chain scission in gamma processed butyl rubbers. The change in crosslinking density of butyl rubber compounds emphasizes that the mechanism of degradation is strongly influenced mainly by irradiation dose for doses above 50 kGy, since the process of chain scission predominates over the crosslinking reaction.
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