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Shear-Enhanced Crystallization in Isotactic Polypropylene. In-Situ Synchrotron SAXS and WAXD

Kumaraswamy, Guruswamy and Verma, Ravi K. and Kornfield, Julia A. and Yeh, Fengji and Hsiao, Benjamin S. (2004) Shear-Enhanced Crystallization in Isotactic Polypropylene. In-Situ Synchrotron SAXS and WAXD. Macromolecules, 37 (24). pp. 9005-9017. ISSN 0024-9297.

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In-situ synchtrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) are used to follow the isothermal crystallization (lamellar thickness, crystallinity, orientation, and parent-to-daughter ratio) of a polydisperse isotactic polypropylene subjected to “short term shearing” as a function of imposed shear stress, shearing duration, and crystallization temperature. The X-ray data are interpreted in view of the real-space morphological information from ex-situ microscopy. Under “mild” shearing conditions (shear stress less than a critical value and shearing duration less than a critical time), needlelike nuclei are induced during shear but are so far apart that crystallites splay substantially as they grow to form somewhat distorted spherulites; the X-ray results show weakly oriented growth on a time scale that is rapid compared to quiescent crystallization and show that the orientation distribution broadens as crystallization progresses. Stronger shearing leads to the elaboration of these nuclei into threadlike structures that template the formation of highly oriented crystals with fiberlike orientation. The parent-to-daughter ratio is influenced by both temperature and flow. As expected, increasing the crystallization temperature leads to fewer daughter crystals relative to the parents. Shear also enhances the formation of parents relative to daughters:  as parent crystals form with their chain axis along the flow direction, the epitaxial daughter crystals have their chain axis in an unfavorable direction, perpendicular to the flow.

Item Type:Article
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URLURL TypeDescription Information
Kornfield, Julia A.0000-0001-6746-8634
Additional Information:© 2004 American Chemical Society. Received 4 December 2003. Published online 27 October 2004. Published in print 1 November 2004. Support for this research was provided by the NSF (DMR-9901403 and DMR-0216491). X-ray experiments were performed at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the Department of Energy, Division of Materials Sciences (DE-AC02-98CH10886 and DE-FG02-99ER45760). We are very grateful to Prof. Buckley Crist for detailed comments on the manuscript.
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-98CH10886
Department of Energy (DOE)DE-FG02-99ER45760
Issue or Number:24
Record Number:CaltechAUTHORS:20170724-073123746
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Official Citation:Shear-Enhanced Crystallization in Isotactic Polypropylene. In-Situ Synchrotron SAXS and WAXD Guruswamy Kumaraswamy, Ravi K. Verma, Julia A. Kornfield, Fengji Yeh, and Benjamin S. Hsiao Macromolecules 2004 37 (24), 9005-9017 DOI: 10.1021/ma035840n
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79283
Deposited By: Ruth Sustaita
Deposited On:24 Jul 2017 16:39
Last Modified:03 Oct 2019 18:18

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