Syndiotactic polystyrene/high-density polyethylene blends compatibilized with SEBS copolymer: thermal, morphological, tensile, dynamic-mechanical, and ultrasonic characterization

A series of syndiotactic polystyrene (sPS)/high-density polyethylene (HDPE) binary blends were prepared in the melt and then compression molded. Afterwards the blends were characterized by means of DSC, SEM and TEM microscopy, tensile tests, DMTA and acoustic measurements. The morphological, thermal and dynamic-mechanical analyses carried out on the binary blends evidence a clear phase separation between the components at all compositions and a lack of adhesion at the interface. Coherently, tensile tests show no improvement in the toughness of sPS when blended with HDPE. Upon addition of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) copolymer to the binary blends as compatibilizer, a fine dispersion of HDPE within the sPS matrix and a good adhesion at the interface is found. Although the good adhesion is confirmed by DMTA, tensile tests reveal no improvement of the mechanical properties of these ternary blends. This result is explained by assuming that the crystallization of sPS at the interface favors the disentanglement of polystyrene end-groups of SEBS out of the sPS domain and therefore a weakening of the interfacial bonding strength.