Cure and mechanical properties of filled SMR L/ENR 25 and SMR L/SBR blends

The effect of blend ratio of natural rubber/epoxidized natural rubber (SMR L/ENR 25) and natural rubber/styrene-butadiene rubber (SMR L/SBR) blends on scorch time (t(2)), cure time (t(90)), resilience, hardness, and fatigue p roperties were studied in the presence of car bon black and silica. An acce lerated sulfur vulcanization system was used throughout the investigation. The scorch and cure times of the rubber compound were assessed by using a M oving-Bie Rheometer (MDR 2000). Resilience, hardness, and fatigue life were determined by using a Wallace Dunlop Tripsometer, a Wallace Bead Load Hard ness Tester, and a Fatigue to Failure Tester, respectively. The results ind icate that t(2) and t(90) decrease with increasing ENR 25 composition in th e SMR L/ENR 25 blend whereas both values increase with increasing SBR conte nt in the SMR L/SBR blend. This observation is attributed to faster cure in ENR 25 and higher saturation in SBR. Resilience decreases with increase in % ENR and % SBR but hardness shows the reverse behavior in their respectiv e blends. The fatigue life increases with % ENR, but it passes through a ma ximum with % SBR in the respective blends. In all cases, aging lowers the f atigue life, a phenomenon that is caused by the breakdown of crosslinks in the vulcanizate. Differences in all the observed values between carbon blac k-filled and silica-filled blends ar e associated with the varying degrees of interaction and dispersion of the two fillers in the rubber blend matrix . (C) 2001 John Wiley & Sons, Inc.