A study of transient flow-induced crystallization of polymer melts
Bushman, Alexander Craig
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https://hdl.handle.net/2142/21649
Description
Title
A study of transient flow-induced crystallization of polymer melts
Author(s)
Bushman, Alexander Craig
Issue Date
1995
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)
Chemistry, Polymer
Engineering, Chemical
Language
eng
Abstract
Flow-induced crystallization of several polymer systems has been studied using a four-roll mill device, coupled with optical polarimetry, to provide an in-situ technique for monitoring the transformation kinetics both during and following flow. The use of a crystallizable droplet phase, suspended within a non-crystallizable carrier phase, prevents die blockage and allows for direct measure of the droplet phase kinematics. Both birefringence and dichroism are used to investigate the crystallinity development within the deforming droplet. Birefringence studies suggest that the initial rate of crystallization is a function of both the induced stress and strain within the deformed material. Pre-crystallinity during the flow regime, prior to flow cessation, is required to achieve reproducible stress-strain behavior. Unlike birefringence studies, the dichroism studies allowed the study of the transient crystallization occurring during the flow regime. Induction times to crystallinity were found to correlate with the extension rate during the deformation. Rheological studies of the polymer systems were performed, wherein viscoelastic data and relaxation time constants were determined. A theoretical model for flow-induced crystallization was developed using a modified strain-induced crystallization model, coupled with the Hamiltonian Bracket formalism, to account for the dynamics of flow. A variety of flow kinematics and their effect on flow-induced crystallization are modeled. A non-linear force factor is incorporated to account for the finite extensibility of the molecule. The model is compared to experimental data and does predict qualitatively the effects of the flow field on crystallization.
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