Rheological properties of molten polymers. II. Two-phase systems



A study is carried out for characterizing two-phase systems of molten polymers by their viscous and elastic properties. The two-phase systems chosen for study are blends of polystyrene and polypropylene, and blends of polystyrene and high-density polyethylene. For the study, measurements of wall normal stresses are made by use of a capillary melt rheometer described in part I of this series. The concept of the “exit pressure” is used to determine the elastic properties of the two-phase polymer systems. The present study shows anomalous viscous and elastic properties of two-phase systems, which are difficult to predict from knowing the viscous and elastic properties of their individual components. A detailed discussion is given on the state of dispersion of two incompatible polymer systems in the molten state, by presenting pictures of the microstructure of the extrudate samples. The state of dispersion appears to vary depending on the blending ratio, extrusion temperature, melt viscosities of individual components, and blending method.