Non-conventional method of crosslinking of butadiene-acrylonitrile rubber
Heating of butadiene—acrylonitrile rubber (NBR) affects the formation of elastomer networks comprising both covalent and complex-type crosslinks.The covalent crosslinks are formed in thermo-oxidative reactions and in the cyclization and polymerization reactions of butadiene mers and nitrile groups, these processes being probably facilitated by ZnCl2. Complex type crosslinks comprise -CN groups as ligands, whereas their cores are formed by domains of zinc chloride. ZnCl2 accelerates sulphur vulcanization of elastomers and enhances the yield of crosslinking. Vulcanizates comprising complex-type crosslinks exhibit a considerable rate of mechanical relaxation (cf. Figs. 4 and 5). In such vulcanizates there is active a mechanism of dissipation of critical stresses resulting in an increase in their mechanical strength, the strength values being several times higher than those of vulcanizates with covalent crosslinks (cf. Fig. 7). ZnCl2-contaming NBR sorbs a considerable amount of water, what results in a decrease of vulcanizate strength (cf. Fig. 8).
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