Abstract
A commercial styrene-butadiene block copolymer (SBS) with lamellar type phase separations was injection and compression molded, and resultant mechanical properties and morphology of the moldings were examined. Compression moldings showed excellent notched Izod impact strength although inferior to injection moldings in tensile, flexural properties and heat deflection temperature. The polybutadiene (PB) phase and the polystyrene (PS) phase in the both moldings formed alternating quasi-layers with thicknesses of 150-200Å and 200-250Å, respectively. However, it was found that such lamellar structure consisted of large aspect ratio of the PB phase surrounded by the PS matrices and that there was great difference both in aspect ratio of the PB phase and in lamellar orderliness between the two moldings. Compression moldings would preferably dissipate a large amount of impact energy since highly ordered lamellae deformed with the extensive shear yielding development. Better tensile and flexural properties of injection moldings would be due to the closer networks of the PS matrices with the smaller aspect ratio of the PB phase. Compression moldings showed the appreciable mechanical anisotropy which cound be correlated with the SBS lamellar disorder and microstructural aniotropy formed on cooling.
