Crystallization behavior, crystal transformation, and morphology of polypropylene/polybutene-1 blends

The effects of composition on crystallization behavior, crystal transformation, and morphology of crystalline/crystalline PP/PB-1 blends are complicated. The crystallization rate of PP decreases with increasing PB-1 content in the cooling or isothermal crystallization process. Avrami constants of the PP crystallization are, however, insignificantly dependent on the PB-1 content. The crystallization rate and spherulite size of PB-1 are both enhanced by PP in PB-1-rich blends. As prepared by the solution–precipitation method, pure PB-1 exhibits crystal forms I′ (or III) and II, whereas the PB-1 in the blends exhibits only crystal form I′; pure PP and PP in the blends both exhibit only crystal form α. Crystal transformation from form I′ to form II for PB-1 in the blends can occur upon dynamic heating and cooling, but the transformation is retarded with increasing PP content. The crystal form II of PB-1 can be transformed to form I upon aging at room temperature, and this transformation can be facilitated by the PP in PB-1-rich blends. The similar helix conformation, of crystal form α of PP and of crystal forms I′ and I of PB-1, is found to be a driving force in preventing crystal form I′ of PB-1 in PP-rich blends from transforming to form II upon dynamic heating and cooling, and in facilitating crystal transformation from form II to form I for PB-1 in PB-1-rich blends upon aging at room temperature.