Blends and interpenetrating polymer networks of polypropylene and polystyrene‐block‐poly(ethylene‐stat‐butylene)‐block‐polystyrene. 2: Melt flow and injection molding properties

Injection molding and melt flow properties of a set of blends prepared by mixing the triblock thermoplastic elastomer polystyrene‐block‐poly(ethylene‐stat‐buty‐lene)‐block‐polystyrene with polypropylene and a processing oil are reported. Despite the high viscosity of the thermoplastic elastomer, the melt viscosity of the blends was similar to or lower than that of the pure polypropylene. The rheological behavior of the molten blends seems to be dominated by a low‐viscosity melt phase containing mainly polypropylene and oil. The surface of solidified extrudates from the capillary rheometer was rich in polypropylene and free from large domains of the thermoplastic elastomer. Injection molded plates had a similar surface morphology, although in this case, larger domains of the elastomeric phase were found in narrow, band‐shaped surface regions. These local surface heterogeneities were probably caused by flow‐induced phase segregation during mold filling. Weld lines in injection molded test pieces prepared from blends within the composition range giving interpenetrating network structures had no noticeable effect on either stress‐strain behavior or falling dart impact strength.