Influence of grade of natural rubber on reversion behaviour
1991
Bristow, G. M.
The reversion behaviour of fifty samples of natural rubber, compounded in a conventional cure system (2.5 p.p.h.r. sulphur, 0.5 p.p.h.r. CBS) has been studied by oscillating disc rheometry at 160° C - 180° C. Over all the samples, the reversion rate varied by a factor of ca. 1.8. Further, while there was considerable scatter, on an average field coagulum grades, such as TSR 20, reverted some 14% faster than grades such as RSS and SMR CV which are prepared by the acid coagulation of latex. The same feature was evident in more limited studies at 100°C - 120°C. The dependence of reversion rate on temperature conforms to the Arrhenius relation with an activation energy of ca. 104 kJ/mol, independent of grade. This value is ca. 10% greater than the activation energy for vulcanisation for which published values are ca. 95 kJ/mol. The rate of reversion decreases with time and the activation energy depends on the extent of reversion. Hence, like vulcanisation, reversion is presumably a complex process. The possibility is mooted that reversion rate assessed in this manner could be used as a further measure of natural rubber quality.
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