Shear‐Enhanced Nucleation of Isotactic Polypropylene in Limited Space

Autor: Daisuke Yuya, Toshinori Kikuchi, Yoshitaka Iwai, Tadashi Inoue, Akiyoshi Kawaguchi
Rok vydání: 2006
Předmět:
Zdroj: Journal of Macromolecular Science, Part B. 45:85-103
ISSN: 1525-609X
0022-2348
DOI: 10.1080/00222340500407939
Popis: The nucleation rate was measured by directly counting the number of nuclei, which were developed while an isotactic polypropylene melt was flowing under shear in a thin film. The nucleation rate was enhanced with an increased rate of shear, e.g., by a factor of 10 larger at the rate of shear of 14 s−1 compared with the quiescent state, at 134°C. The ratio of the shear‐enhanced nucleation rate to the nucleation rate in the quiescent state was larger at a higher temperature of crystallization, i.e., about 10 times at 134°C to 590 times at 140°C. The increase of the nucleation rate under shear flow was explained by a reduction of the lateral and end (fold) surface free energies; the product σ s 2 σ e decreased to 3.2×10−7 for the sheared melt, from 6.0×10−7 (J m−2)3 for the isotropic state. The free energy reduction was caused by transition of the nucleus formation mode from three‐dimensional folded chain nuclei to two‐dimensional bundle nuclei, in which chains lie down on the glass substrate, aligning paral...
Databáze: OpenAIRE
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