Effects of SBS on phase morphology of iPP/aPS blends

The supermolecular structure of binary isotactic polypropylene/poly(styrene‐b‐butadiene‐h‐styrene) (iPP/SBS) and isotactic polypropylene/atactic polystyrene (iPP/aPS) compression molded blends and that of ternary iPP/aPS/SBS blends were studied by optical microscopy, scanning and transmission electron microscopy, wide‐angle X‐ray diffraction and differential scanning calorimetry. Nucleation, crystal growth, solidification and blend phase morphology are affected by the addition of amorphous components (SBS and aPS). As a compatiblizer in immiscible iPP/aPS blends, SBS formed interfacial layer between dispersed honeycomb‐like aPS/SBS particles and the iPP matrix, thus influencing the crystallization process in iPP. The amount of SBS and aPS, and compatibilizing efficiency of SBS, determine the size of dispersed aPS, SBS, and aPS/SBS particles and, consequently, the final blend phase morphologies: well‐developed spherulitic morphology, cross‐hatched structure with blocks of sandwich lamellae and co‐continuous morphology. The analysis of the relationship between the size of spherulites and dispersed particles gave the criterion relation, which showed that, in the case of a well‐developed spherulitization, the spherulites should be about fourteen times larger than the incorporated dispersed particles; i.e. to be large enough to engulf dispersed inclusions without considerable disturbing of the spherulitic structure.