Crystallization Behavior of Immiscible Blends

The properties of these systems depend on the composition and the morphological characteristics, which in turn are affected by the crystallization conditions. Generally, because in the melt the two polymer phases are 

When the crystallization of the matrix polymer takes place in the presence of a molten dispersed phase, the crystallization behavior is comparable to that of crystalline/amorphous blends in which the amorphous component is the dispersed phase. However, a different behavior may be observed when the crystallization of the matrix occurs in the presence of a crystallized dispersed phase. Coincident crystallization of the components has been reported for blends in which the matrix phase has a crystallization temperature lower than that of the dispersed component, and this latter does not crystallize at its usual undercooling, owing to its very fine dispersion into the blend, which causes a lack of heterogeneities that is able to initiate the crystallization of the droplets at their characteristic T. In such case, as reported for PVDF/polyamide-6 (PA6) and PVDF/PBT blends 

1 Polyethylene/PolypropyleneBlends Blends of polyolefins represent one of the most studied polymer systems in the field of immiscible blends. Studies on blends of iPP with crystallizable and/or amorphous polyolefins, such as polyethylenes (PEs) of various density (HD PE, ED PE, LLDPE), atactic PP, propylene-etylene elastomers, and polyisobutylene, have shown that their properties depend strongly on the crystalline morphology, crystallization conditions, and composition 

Studies on the crystallization kinetics of iPP/HDPE and iPP/LDPE blends showed that the overall crystallization rate of iPP matrix was largely depressed by the presence of the dispersed PE phase [40, 84]. Since the growth rate G of iPP spherulites (in the same range) 

Similar effects were reported for iPP/HDPE blends crystallized at temperatures higher than 127°C [78]. In order to verify the hypothesis of the migration of nuclei and its effect on the primary nucleation of the spherulites, crystallization experiments were carried out on iPP/HDPE blends containing nucleating agents—that is sodium benzoate and magnesium sulphate—active for the crystallization of polypropylene (PP) (at higher T ) 

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The immiscible semicrystalline polymer blends may be classified in terms of crystalline/crystalline systems in which both components are crystallizable and crystalline/amorphous systems in which only one component can crystallize, being either the matrix or the dispersed phase (Utracki 1989). Numerous authors have been investigating the crystallization behavior of immiscible blends. In Tables 3.14 and 3.15, an overview is given of a number of important immiscible crystallizable blend systems. 

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