Microstructure of Melt Blended Polymer Systems

Abstract

Two thermodynamically incompatible polymers were melt blended. The resulting microstructure and, consequently, the physical properties were dependent on the blending conditions and the rheological properties of the components. In this study the blending conditions were held constant while the rheological properties were varied and correlated with dispersion characteristics of the phases and the physical properties of the composite. A series of five atactic polystyrenes (weight average molecular weight from 75,000 to 400,000) and five linear polyethylenes (weight average molecular weight from 43,000 to 347,000) were used. The blending was done over a range of composition ratios in a normal stress extruder. Viscosity and normal stress of each pure component were measured in torsional flow. The mixed extrudates were examined by light interference microscopy, scanning electron microscopy, and solvent leaching. The nature and the fineness of the microstructure were interpreted in terms of the composition ratios, mixing history, and the melt rheological properties of the components. It was concluded that the fineness of the minor phase in a shear mixing process is a function of the difference between both the viscous and elastic behavior of the components.