A study of flow-induced crystallization in two-phase polymer melts
Guy, R. Kirk
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https://hdl.handle.net/2142/22112
Description
Title
A study of flow-induced crystallization in two-phase polymer melts
Author(s)
Guy, R. Kirk
Issue Date
1992
Doctoral Committee Chair(s)
McHugh, Anthony J.
Department of Study
Chemical and Biomolecular Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Language
eng
Abstract
The effects of shearing and elongational flows on flow induced crystallization in polymer melts were investigated for the two-phase system of high molecular weight polyethylene suspended in a linear low density polyethylene carrier phase. Shearing flow was produced by a counter-rotating couette device and elongational flow was produced by means of a four roller mill device. Deformation and bursting of droplets were observed in both of these flows, however, shearing flow was found unsuitable for quantitative studies, since the orientation of the optical axes in the carrier and suspended phases were not coaxial. Hot stage and dichroism studies indicated that crystallization occurs in the suspended phase in the four roller mill, at temperatures above which quiescent crystallization would occur. In-situ birefringence measurements were made and initial crystallization rates were determined and found to depend upon both stress and strain in the deforming droplet. This was very suggestive of a viscoelastic phenomenon, not simply, a nucleation and growth controlled mechanism, thus the separability, of flow effects and nucleation and growth crystallization, is brought into question by this complex behavior. A first order approximation based on molecular rheology has been used to gain qualitative and quantitative insights on the observed trends.
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