993 resultados para fragment size


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Nylon 10 10 crystals, which isothermally crystallized from the molten state and cold crystallized from melt-quenched samples at various temperatures, were investigated by using temperature-variable wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS). No Brill transition occurred for the melt-crystallized crystals. However, this transition was easily observed for the cold-crystallized nylon 10 10, and the transition temperature is pertinent to the crystallization temperature. The sizes of these crystals was determined by SAYS and correlated with the Brill transition temperatures (T-B). It was found that the T-B had a linear relationship with the size of crystals, which was used to predict the T-B for those crystals with thick lamella and to calculate the crystal size showing T-B below room temperature. Nylon 10 10 crystal will possess the gamma form (pseudohexagonal form) rather than the a phase at room temperature if its size becomes small enough.

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The effects of CaCO3 on the crystallization behavior of polypropylene (PP) were studied by means of DSC and WAXD. The average sizes of the CaCO3 powders used were 0.1 mum (UC) and 0.5 mum (GC), respectively. The PP/CaCO3 composites at compositions of 1 phr and 10 phr were investigated. The results showed that the addition of CaCO3 reduced the supercooling, the rate of nucleation and the overall rate of crystallization (except for the 10 phr UC/PP sample). The crystallinity of PP was increased and the size distribution of the crystallites of alpha -PP; was: broadened. On the other hand,the crystallization rate of 10 phr UC/PP is 1.5 times higher than that of neat PP. It has an overall rate of crystallization 2 times as much as that of the neat PP and has the maximum crystallinity. The sizes of crystallites and the unit cell parameters of alpha -PP were varied by the addition of CaCO3. beta -PP was formed by addition of Ge and was not detected by addition of UC. The differences of crystallization behaviors of PP might be attributed to the combined effects of the content and size of CaCO3 filled.

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By using different catalyst systems, two trans-1,4-polybutadiene (TPBD) samples with different tr trans-content and molecular weight were synthesized. The phase transition of two samples from monoclinic form to hexagonal phase was revealed by differential calorimeter scanning and X-ray, respectively. The small-angle X-ray scattering measurements showed the remarkable discrepancy of phase transition and melting point between the two samples was attributed to the different lamellar thickness of crystals: The crystals with different crystalline morphology and lamellar thickness were developed by casting different concentration TPBD solutions. Transmission electron microscopy morphology observations proved that annealing the specimen at the temperature above the phase transition point for different times resulted in the different lamellae thickening of monoclinic form. It means that annealing the TPBD in its hexagonal phase will also slightly favor the increase of both the phase transition temperature and melting point of hexagonal phase. (C) 2001 Elsevier Science Ltd. All rights reserved.