Curing characteristics of nitrile and natural rubber blends

The dependence of Mooney scorch time and cure index on blend ratio of nitri le rubber/natural rubber (NBR/SMR L) and nitrile rubber/epoxidized natural rubber (NBR/ENR 25) blends were determined in the temperature range from 12 0 degreesC to 160 degreesC using a Monsanto automatic Mooney Viscometer. Se mi-efficient vulcanization system was used throughout the study. Results in dicate that scorch time decreases with increasing SMR L and ENR 25 contents , an observation which is attributed to the increasing solubility of sulfur , as SMR L and ENR 25 composition is increased, However, for temperature gr eater than 140 degreesC, the dependence of scorch time on blend ratio dimin ishes, as enough thermal energy is available to overcome the activation ene rgy of vulcanization. The cure index of NBR/SMR L blend passes through a ma ximum at 25% SMR L composition whereas in the case of NBR/ENR 25, generally it shows a gradual drop with increasing ENR 25 content. The differing obse rvation between the two blends in terms of cure index is explained by the c ompatibility factor of the respective blends. For the apparent activation e nergy of vulcanization of the two blends, similar dependence behavior on bl end ratio as that of cure index is obtained.