Cold mastication of hydrogenated nitrile rubbers

The study of cold mastication of hydrogenated nitrile rubbers containing fr om 34 to 43 wt.-% of acrylonitrile showed that these rubbers undergo signif icant degradation due to action of mechanical shearing forces. The prolonga ted mastication time results in limited molecular weight of rubber M-n,M-li m = 58,5 to 66,5 kg/mol. Both the degradation rate and the resulting degrad ation level or degradation degree determined by the decrease of the average molecular weight are almost not affected by the concentration of residual double bonds or bound acrylonitrile content in HNBR as well. The decrease o f molecular weight of all rubbers studied can be described by the same firs t order rate constant k(1) = 4,80 (+/- 0,22) 10(-4) s(-1). The cold mastica tion of HNBR is accompanied by the decrease both of Mooney viscosity and by the narrowing of the molecular weight distribution, From GPC studies it fo llows that the degradation of rubber chains occuring due to cold masticatio n of hydrogenated nitrile rubber is not a statistical process.