Effect of Curing Systems on Selected Physical Properties of Natural Rubber Vulcanizates

Abstract

Abstract Selected physical tests were made on natural rubber vulcanizates prepared with six levels of each of six different curing systems. These combinations produced different types of crosslinks which were subjected to analysis using a combination of swelling measurements and lithium aluminum hydride reduction analyses. The effect of crosslink type or length was reflected in stress-strain measurements. One might reasonably look to crystallization measurements on such vulcanizates for a more complete explanation of the effects of crosslink type on stress-strain measurements. The ability of polysulfide crosslinks to exchange to form new links as the sample is strained should also be examined. When subjected to stress, especially when hot, polysulfide crosslinks are more susceptible to rupture than monosulfide or carbon-to-carbon crosslinks. This crosslink rupture may or may not be compensated for by subsequent formation of new polysulfide or monosulfide crosslinks in a deformed state. Under suitable experimental conditions, as in our compression set measurements, no net change in total crosslinks may take place. Under sufficiently severe test conditions, as in our blowout tests, degradation is severe and total crosslinks measured by swelling decrease. Under some circumstances, it is possible to follow changes in both the quantity and type of crosslinks by the analytical methods used in this study.