INJECTION AND COMPRESSION MOLDING OF POLYSTYRENE HIGH-DENSITY POLYETHYLENE BLENDS - PHASE MORPHOLOGY AND TENSILE BEHAVIOR/

Processing and compatibilization effects on the phase morphology and t he tensile behavior of blends of polystyrene and high-density polyethy lene (PS/HDPE) were investigated. As predicted by theory, high shear r ates encountered during extrusion blending led to efficient minor phas e emulsification in immiscible PS/HDPE blends for which the viscosity ratio approaches unity. Consequently, the emulsifying effect of a styr ene/ethylene-butylene/styrene (SEBS) compatibilizer was found to be ne gligible. In the subsequent molding process, disintegration, shape rel axation and coarsening of the minor phase domains were found to be res ponsible for the morphological evolution. In the compression molding p rocess, morphological observations showed that the rate of minor phase coarsening followed the predictions of the Ostwald ripening theory, i n agreement with the rheological analysis. In the injection molding pr ocess, minor phase coarsening was attributed to shear coalescence. Ten sile tests performed on compression molded and injection molded blends showed that the mechanical behavior of PS/HDPE blends depend strongly upon the matrix orientation as well as the dispersed phase morphology and orientation. In both postforming operations, compatibilization ef fects on the morphological stability and the tensile behavior of PS/HD PE blends were found to be dependent upon the composition and the rheo logical behavior of the blend. Evidence of adhesion between the PS and HDPE phases was observed in the presence of SEBS in HDPE-rich blends.