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Shear-Enhanced Crystallization in Isotactic Polypropylene. 1. Correspondence between in Situ Rheo-Optics and ex Situ Structure Determination

Kumaraswamy, Guruswamy and Issaian, Ani M. and Kornfield, Julia A. (1999) Shear-Enhanced Crystallization in Isotactic Polypropylene. 1. Correspondence between in Situ Rheo-Optics and ex Situ Structure Determination. Macromolecules, 32 (22). pp. 7537-7547. ISSN 0024-9297. https://resolver.caltech.edu/CaltechAUTHORS:20180719-145939318

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Abstract

The effects of “short term shearing” on the subsequent crystallization of a polydisperse Ziegler−Natta isotactic polypropylene are observed using in situ optical measurements and ex situ microscopy. Imposition of brief intervals of shear (0.25−20 s, less than a thousandth of the quiescent crystallization time) can reduce the crystallization time by 2 orders of magnitude (e.g., at 141 °C with a wall shear stress of 0.06 MPa). With increasing shearing time, the crystallization time saturates and highly anisotropic growth ensues. This transition to oriented growth correlates with changes in the transient behavior during flow and the semicrystalline morphology observed ex situ. During flow, we observe the generation of long-lived, highly oriented structures (evident in the transient birefringence) under all conditions that induce subsequent growth of highly oriented crystallites. In turn, the development of oriented crystallites observed in situ after cessation of flow correlates with development of a “skin-core” morphology (highly oriented skin on a spherulitic core) observed ex situ. Interestingly, the long-lived structures generated during flow appear at shorter times with increasing temperature (at fixed shear stress), the opposite of the trend one would expect on the basis of the temperature dependence of quiescent crystallization.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://dx.doi.org/10.1021/ma990772jDOIArticle
ORCID:
AuthorORCID
Kornfield, Julia A.0000-0001-6746-8634
Additional Information:© 1999 American Chemical Society. Received May 18, 1999; Revised Manuscript Received July 15, 1999. We would like to acknowledge financial support from P&G, the Cargill-NIST ATP, NSF-DMR 9901403, and the Schlinger fund that made this project possible. One of the authors (K.G.) would like to acknowledge support from a Landau fellowship. We are very grateful to Dr. A. Prasad (Quantum Chemical) for providing us with the commercial grade polypropylene, PP8004MR (“PP-300/6”), for our experiments. We are grateful to Dr. R. L. Sammler (The Dow Chemical Co.) for providing us with the atactic polypropylene sample. We would also like to acknowledge help from Joanna Dodd for preliminary characterization of PP-300/6.
Funders:
Funding AgencyGrant Number
Procter and GambleUNSPECIFIED
Cargill, Inc.UNSPECIFIED
National Institute of Standards and Technology (NIST)UNSPECIFIED
NSFDMR-9901403
Schlinger Fund, CaltechUNSPECIFIED
Landau fellowshipUNSPECIFIED
Issue or Number:22
Record Number:CaltechAUTHORS:20180719-145939318
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180719-145939318
Official Citation:Shear-Enhanced Crystallization in Isotactic Polypropylene. 1. Correspondence between in Situ Rheo-Optics and ex Situ Structure Determination Guruswamy Kumaraswamy, Ani M. Issaian, and Julia A. Kornfield Macromolecules 1999 32 (22), 7537-7547 DOI: 10.1021/ma990772j
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88022
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:19 Jul 2018 22:13
Last Modified:03 Oct 2019 20:02

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