Degradation of Hydrogenated Nitrile-butadiene Rubber in Aqueous Solutions of H2S or HCl

The degradation of hydrogenated nitrile-butadiene rubber(HNBR) soaped in aqueous solutions of H₂S and HCl was investigated. The samples unexposed and exposed to different solutions were characterized by ¹³C nuclear magnetic resonance(¹³C NMR), X-ray photoelectron and infrared spectroscopies. In contrast to those of unexposed samples and samples soaped in HCl solution, the mechanical properties of samples exposed to H₂S solution significantly deteriorated, in which the new groups of C(=O)―NH₂, C―S―C and C=S emerged. The mechanism of C=S and C―S―C formation was speculated, except for that of the formation of group C(=O)―NH₂, which was widely discussed in acidic condition such as HCl solution. The formation of C―S―C was due to radical reaction initiated by mercapto radical and that of C=S was due to nucleophilic reaction initiated by mercapto cations. This finding is helpful to understanding the seal failure of HNBR in working environment containing H₂S.