RHEOLOGICAL BEHAVIOR OF BLENDS OF NATURAL-RUBBER AND STYRENE-BUTADIENE RUBBER LATICES

The theological behavior of blends of natural rubber (NR) and styrene- butadiene rubber (SBR) latices has been studied with reference to the effects of blend ratio, shear rate, surface-active agents (casein and sodium carboxymethyl cellulose), and temperature. When the SBR content was less than 50%, the viscosities of the blends appeared to be a non additive function of the viscosities of the constituent homopolymers; i.e., a positive deviation was observed. This was due to the structura l buildup of the SBR domains. The SBR domains underwent agglomeration and consequently so-called microflocculation took place. The viscositi es of all the blends were found to decrease with increase of temperatu re and shear rate. The increase in temperature and shear rate marginal ly weakened the structural buildup as evidenced by the lowering of vis cosity. As the SBR content in the system increased, the pseudoplastici ty of the blend increased. Even in the presence of surface-active agen ts the blends showed composition-dependent positive deviation. However , surface-active agents marginally reduced the extent of structural bu ildup by reducing the microflocculation behavior of SBR domains. (C) 1 995 John Wiley and Sons, Inc.