Effect of syndiotactic polystyrene on the crystallization behavior of isotactic polypropylene/syndiotactic polystyrene blends with and without β-nucleating agent

Abstract

Blends of isotactic polypropylene (PP) and syndiotactic polystyrene (sPS) with and without β-nucleating agent were prepared using a twin-screw extruder at 290 °C. Blends of PP/sPS with β-nucleating agent mainly show β crystalline form, irrespective of high (20 °C min-1) or low (2 °C min-1) previous cooling rates. This suggests that the cooling rates have little effect on the polymorphic composition of PP in PP/sPS blends. The effect of sPS on the crystallization of PP is compared with that of polyamide 6 (PA6). The increase in crystallization temperature of PP is smaller in the presence of sPS than in the presence of PA6; the fold surface free energy of PP/sPS is larger than that of PP/PA6 blends. These results reveal that compared with PA6, sPS has much weaker α-nucleation effect on the crystallization of PP. The weak α-nucleation effect of sPS is attributed to the high lattice mismatch between PP and sPS crystals.© 2012 Society of Chemical Industry.