Oriented polymer crystal growth from flowing solutions
Spevacek, John Anthony
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https://hdl.handle.net/2142/22099
Description
Title
Oriented polymer crystal growth from flowing solutions
Author(s)
Spevacek, John Anthony
Issue Date
1990
Doctoral Committee Chair(s)
McHugh, Anthony J.
Department of Study
Chemical 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, Materials Science
Language
eng
Abstract
The kinetics of dilute solution flow-induced crystallization in a tubular flow geometry have been quantified for several polymer systems using digital image processing to observe and monitor the birefringence of the crystallizing fiber. Three molecular weights of polyethylene were studied in 0.01 wt% xylene solutions as well as solutions of polypropylene in decalin and solutions of polystyrene in xylene. Crystallization was studied over a range of temperatures and flowrates and was found to always occur by a two-step process with a highly concentrated amorphous polymer phase forming first, followed later by crystallization. The kinetics were observed to follow the Avrami equation. The time exponent, n, was found to have values around 2, while the constant, k/X$\sb\infty$, was found to show the predicted temperature dependency for nucleation and growth kinetics, i.e. proportionality to exp($-$T$\sb\infty$/T$\sb{\rm x}\Delta$T). It was found that the melting point elevation predicted from theories of strain-induced crystallization could not be used to explain the rapid kinetics of crystallization. Consequently, a theory was developed which allowed the observed solution velocity effects to be included into the Avrami equation thereby yielding a quantitative explanation for the role of flow in the crystal nucleation and growth process. Work with amorphous polystyrene showed the initial unoriented phase separation step occurring, although the phase appeared to be a swollen gel. Further work on the precursor and its formation is crucial to advancing knowledge in this area.
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