Kumaraswamy, Guruswamy and Verma, Ravi K. and Kornfield, Julia A. (1999) Novel flow apparatus for investigating shear-enhanced crystallization and structure development in semicrystalline polymers. Review of Scientific Instruments, 70 (4). pp. 2097-2104. ISSN 0034-6748 http://resolver.caltech.edu/CaltechAUTHORS:KUMrsi99
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An instrument to study the effects of shearing on the crystallization process in semicrystalline polymers is described. It can impose transient stresses similar to those encountered in polymer processing and provides in situ monitoring of microstructure development during and after cessation of flow. Box-like wall shear stress profiles (rise and fall times under 50 ms with maximum wall shear stress on the order of 0.1 MPa) can be applied for controlled durations. A unique feature of our device is that it accommodates a wide variety of real-time probes of structure such as visible and infrared polarimetry and light and x-ray scattering measurements. The design also allows us to retrieve the sample for ex situ optical and electron microscopy. Data are acquired with millisecond resolution enabling us to record the extent of shear deformation of the polymer melt during the pressure pulse. Our device works with small sample quantities (as little as 5 g; each experiment takes ~ 500 mg) as opposed to the kilogram quantities required by previous instruments capable of imposing comparable deformations. This orders-of-magnitude reduction in the sample size allows us to study model polymers and new developmental resins, both of which are typically available only in gram-scale quantities. The compact design of the shear cell makes it possible to transport it to synchrotron light sources for in situ x-ray scattering studies of the evolution of the crystalline structure. Thus, our device is a valuable new tool that can be used to evaluate the crystallization characteristics of resins with experimental compositions or molecular architectures when subjected to processing-like flow conditions. We demonstrate some of the features of this device by presenting selected results on isotactic polypropylenes.
|Additional Information:||©1999 American Institute of Physics. (Received 6 October 1998; accepted 12 January 1999) The authors would like to acknowledge financial support from Procter & Gamble and the Schlinger fund that made this project possible. One of the authors (G.K.) would like to acknowledge support from a Landau fellowship. The authors are very grateful to Dr. A. Prasad (Equistar Chemical) for providing the commercial grade polypropylene, PP8004MR (PP-300/6), and to Dr. R. L. Sammler and Dr. C. P. Bosnyak (The Dow Chemical Company) for supplying the narrow polydispersity isotactic polypropylene (Dow developmental resin, PP-186/2.1). Dr. R. L. Sammler also gave a critical reading of the manuscript and very useful comments. Dr. G. Smedley and Professor R. C. Flagan (Caltech) gave valuable advice regarding the design of the instrument.|
|Subject Keywords:||polymer melts; shear deformation; shear flow; crystallisation; channel flow; polymer structure|
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|Deposited By:||Archive Administrator|
|Deposited On:||13 Feb 2006|
|Last Modified:||26 Dec 2012 08:45|
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