The crystallization and thermal behaviour of crystallizable random propene/ethene copolymers (P-co-E) was systematically investigated. Index of crystallinity and, index of y-form, enthalpy and entropy of fusion, equilibrium melting temperature, spherulite growth rate, and overall kinetic rate constant were determined and correlated with the overall ethene content and with the concentration of specific chemical defects as determined by "C NMR analysis (PEP, EPP, EPE triads). The samples of the copolymers, obtained with very-high-yield Ziegler-Natta catalysts, were characterized by IR, 13C NMR, wide angle X-ray scattering, and differential scanning calorimetry.

ABSTRACT:Isotactic polypropylene/organoclay nanocomposites were prepared by a solution methodology and characterized by structural, morphological, and mechanical analysis. X-ray and microscopic analyses (SEM) have revealed a homogeneous dispersion of the nanoclay in the iPP matrix and good adhesion between the two phases, especially in nanocomposites containing lower organoclay amounts ( 1% and 3%) . Particularly it was observed that the sample with 1% clay content maintains the exfoliated structure during processing, while the sample with 3% clay evolves from an intercalated structure toward an exfoliated structure when processed by compression molding. The influence of the modified organoclay nanoparticles on the iPP crystallization process was also investigated. The results have shown that while the nanoparticles increase the rate of crystallization there is a delay in the onset of the solidification process. A regime II-III transition temperature was also observed which decreases with increasing organoclay content. C 2005 Wiley Periodicals,

The morphology, the crystallization and thermal behaviour of isotactic polypropylene (iPP) in its blends with two different samples of low density polyethylene (LDPE) was investigated at temperatures high enough to prevent any solidification of LDPE. It is found that pre-existing liquid LDPE domains are incorporated in intra-spherulitic regions during the isothermal crystallization of iPP. The radial growth rate of spherulites is almost unaffected by the LDPE content. The overall rate of crystallization of iPP, on the contrary, is strongly depressed by the addition of LDPE. A depression of the equilibrium melting temperature of iPP, due to kinetic and morphological effects, is also observed. The depression of the overall kinetic rate constant is accounted for by the negative effect (decrease in the number of nuclei) that the addition of LDPE has on the primary nucleation process of iPP.

The isothermal crystallization from the melt of isotactic polypropylene in the presence of Kevlar 49 fibers has been investigated. The nucleating ability of the fibers was demonstrated, and the presence of extensive transcrystalline regions was related to crystallization parameters, such as crystallization temperature, melt precrystallization temperature, and residence time at precrystallization temperature. The results are discussed in terms of the presence of heterogeneities in the bulk and preformed self‐seeded nuclei located in the anfractuosities of fiber surfaces.