Abstract
The homogeneous primary nucleation of spherulitic crystallization in isotactic polypropylene (iPP) and its blends with atactic polypropylene (aPP) was studied. Bulk samples of iPP and iPP/aPP blends were crystallized isothermally under high undercoolings (∼ 100°C) using a specially designed crystallization cell. In crystallized samples the fifth-order average spherulite radius was determined on the basis of small-angle light scattering measurements. The parameters for homogeneous primary nucleation were obtained from the fitting of curves calculated on the basis of theoretical predictions for regime III to the experimental data. For that purpose the theoretical background for homogeneous nucleation in polymer blends and for small-angle light scattering by an assembly of impinged spherulites was developed. The results obtained for homogeneous nucleation in plain iPP are in very good agreement with theoretical predictions. For iPP/aPP blends it was found that the main reason for depression of nucleation in blends is the additional energy barrier connected with the separation of components of a homogeneous blend during crystallization of one of the components (iPP).
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