Melt rheology and morphology of nitrile rubber and ethylene-vinyl acetate copolymer blends

The melt rheological behavior of nitrile rubber (NBR)/ethylene-vinyl acetat e (EVA) copolymer blends was studied with special reference to the effect o f the blend ratio, cross-linking systems, and shear rate using a capillary rheometer. At a given shear stress at 90 degrees C, the viscosities of the blends vary slightly with composition. The effect of cross-linking systems [viz., sulfur (S), peroxide (DCP) and mixed (S+DCP) systems] on the viscosi ty of NBR/EVA blends is negligible. The melt viscosity of the blends decrea ses with increasing shear rate, showing pseudoplastic behavior. The flow be havior index values also support the pseudoplastic nature of these blends. Various theoretical models were used to predict the melt viscosity of the b lends. Parameters such as die swell, principal normal stress difference, re coverable shear strain, and shear modulus were calculated to characterize t he melt elasticity of these blends. The melt elasticity of the system was i ncreased by the addition of NBR to EVA. The extrudate deformation at differ ent shear rates was also studied. It was observed that as the shear rate in creases, the extrudate surface exhibits a higher degree of deformation. The morphology of the extrudates of the blends at different shear rates has be en examined by a scanning electron microscope. The morphology was found to be dependent on the blend ratio and shear rate.