DEGRADATION OF HYDROGENATED NITRILE RUBBER

Studies of low temperature degradation were carried out on hydrogenated (HNBR), highly saturated (HSN) nitrile rubber and nitrile rubber (NBR) in the temperature range 75°C to 150°C in the presence of air and high-temperature degradation in the presence of nitrogen from room temperature to 800°C. The molecular weight of HSN initially increased with ageing time and decreased again after an optimum ageing time. In the case of NBR the molecular weight first decreased at higher temperature and then there was an upturn, after which, on prolonged ageing, it again decreased. The contact angle for HSN and NBR decreased with ageing time. There was gel formation in the case of NBR but not with HSN even after long ageing times. IR studies showed that both HSN and NBR generated {A figure is presented} and -COOR functionality on oxidation. ESCA studies indicated that the oxidation in HSN took place through CN, which was converted to CNH. It was observed from thermogravimetric analysis that the temperature at which the degradation was maximum (Tmax) was much higher in the case of HNBR than of NBR, which showed two Tmaxs. TG curves were analysed using the Freeman and Carrol method and the energies of activation for degradation were 220 kJ/mole, 350 kJ/mole and 175 kJ/mole for HSN. HNBR and NBR, respectively. The order of the reaction for HSN and HNBR was unity. The mechanism of the degradation of HNBR could be predicted easily from these studies. © 1990.