The Supermolecular Structure of Isotactic Polypropylene/Atactic Polystyrene Blends

The supermolecular structure of binary isotactic polypropylene/atactic polystyrene (iPP/PS) injection-molded blends were studied by wide-angle X-ray diffraction, differential scanning calorimetry, and optical microscopy. The combination of different methods gives a possibility of analysis of relation between the phase transformation in polypropylene and crystallization parameters. Effect of compatibilization of poly(styrene-b-ethylene-co-butylene-b-styrene) grafted with maleic anhydride (SEBS-g-MA) block copolymers in the iPP/PS blends on the structure, nucleation, crystal growth, solidification, and the phase morphology was analyzed. We found that the beta-crystallization tendency of polypropylene matrix can be enhanced by adding atactic polystyrene. However, the incorporation of SEBS-g-MA into iPP/PS blends resulted in an important decrease in beta-content of iPP. It is evident that the presence of compatibilizing agent caused a very significant reduction of the alpha-spherulite growth rates and the crystal conversion as well as increases of half-time crystallization in comparison with the iPP/PS systems. The relation between kinetic parameters of crystallization process and polymorphic structure of iPP in blend systems has been satisfactorily explained. Moreover, a strong effect of processing parameters on the beta-phase formation was observed. The results clearly show that at a higher temperature of mold and lower injection speed, the amount of beta-phase of iPP matrix slightly decreases. POLYM. ENG. SCI., 51:2505-2516, 2011. (C) 2011 Society of Plastics Engineers