The effect of prevulcanization on the rheological behavior of natural rubber (NR), styrene butadiene rubber (SBR) latices, and their blends was studied with special reference to shear rate, blend ratio, vulcanizing systems, prevulcanization time, and accelerator systems. The NR latex showed a sharp increase in viscosity with increase in prevulcanization time due to high extent of crosslinking. However, SBR latex showed marginal effect on viscosity with prevulcanization time due to its low dry rubber content and low degree of unsaturation. Blends showed variations in viscosity according to the change in composition. The use of a single accelerator was found to have marked influence on the viscosity of the blends compared with a combination of accelerators. Swelling experiments were carried out in order to determine the crosslink density of the blends. The viscosity changes have been correlated with the crosslinking density of the latices and their blends. 0 1996 John Wiley & Sons, Inc.
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Several investigations have been made in the past few years in the field of blenling of Blending is used extensively to improve the processing characteristics as well as the properties of the end-products. The influence of blending variations on viscosity of the blends has been ~t u d i e d . ~ Shundo, Imoto, and Minoura' found out a relation between the properties of unvulcanized and vulcanized blends of NR and SBR prepared by means of solution blending, latex blending, roll blending, and Banbury mixer blending. Additionally, NR/SBR blends showed a direct relation to their blend ratio, regardless of blending method used. In most cases, latex blending results in a good degree of dispersion, which cannot be achieved by other blending techn i q u e ~. ~~~ Excellent reports regarding latex blends exist in the l i t e r a t ~r e . ~-' ~ Matsumoto et a1.l' found that dual-phase electrolytes, those having high ionic conductivity S/cm) and good mechanical strength, can be prepared by mixing NBR and SBR latices. Okikura" conducted a series of studies on * To whom correspondence should be addressed.