EFFECT OF BLEND RATIO ON MOONEY SCORCH TIME OF RUBBER BLENDS

The Mooney scorch times of three rubber blends [ epoxidized natural ru bber (ENR) 50/SMR L, ENR 50/styrene butadiene rubber(SBR), and Standar d Malaysian Rubber SMR L/SBR] were studied in the temperature range of 120-160 degrees C using an automatic Mooney viscometer. N-Cyclohexyl- 2-benzothiazyl sulfenamide was used as the accelerator, and the rubber formulation was based on the conventional vulcanization system. Resul ts for the blends investigated indicate that a negative deviation of s corch time from the interpolated value was observed, especially for te mperatures lower than 130 degrees C. This observation was attributed t o the induction effect of the ENR 50 in the ENR 50/SMR L and ENR 50/SB R blends to produce more activated precursors to crosslinks, thus enha ncing interphase crosslinking. To a lesser extent, SMR L also exhibite d such an induction effect in the SMR L/SBR blend. At 120 degrees C, m aximum induction effect occurred at around a 40% blend ratio of ENR 50 and SMR L in the respective blends. For the filled stock at 140 degre es C, carbon black exhibited less effect on the scorch property of the blends compared to silica. (C) 1998 John Wiley & Sons, Inc.