水道水残留塩素に侵されるNBRの劣化メカニズム

抄録

In order to elucidate the degradation behavior of NBR caused by residual chlorine in tap water, NBR diaphragms used in chlorine-contained tap water for about 4 and 9 years at an ambient temperature in Yokohama City and the unused product were analyzed by means of FT-IR, EPMA and XPS. NBR usually leads to hardening and degradation with increase of crosslinking density by heat or UV. However, NBR used in tap water softened and chlorine atom invaded into surface layer of NBR diaphragm. The degradation process of the NBR in the tap water is considered as follows: (1) the α-H of the butadiene double-bond of the NBR is susceptible to substitution by chlorine; (2) the chlorinated NBR reacted with other NBR and subtraction of the α-H produced the radical; (3) the radical subsequently produced hydroperoxide at the α-position and an aldehyde was formed by decomposition similar to that in the oxidation degradation mechanism of polybutadiene; (4) vulcanized points were cleaved simultaneously. These processes are expected to lower the molecular weight of the NBR and lead to softening and degradation.