Modular self-wiping co-rotating twin screw extruders have been widely used in polymers blending and compounding over the past four decades since they were first commercialized by Werner and Pfleiderer [1]. Despite its importance in the polymer processing industry, studies of the initial mixing process ina modular co-rotating twin screw extruder of binary polymer blends have received little attention until the last three years [2 to 9]. Among the various factors controlling the mixing of thermoplastic blends, the viscosity characteristics are a major determinant the degree of deformation of a disperse phase domain depends greatly upon the viscosity ratio. When one component of the mixing system has a very low viscosity, and there is an extremely large viscosity ratio, it is well known to be very difficult to mix [10 to 12].