Abstract/Details

Shear-induced crystallization of model polymers


2005 2005

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Abstract (summary)

The properties of a product made of semi-crystalline polymers strongly depend on both molecular parameters and on the processing conditions applied. This dissertation is focused on flow-induced structure formation correlating the material and crystallization time scales with the structure development in isotactic polypropylene (iPP) after a temperature quench. Morphological changes during the quiescent (no flow prior to crystallization) and shear-induced (with flow prior to crystallization) isothermal crystallization have been monitored with optical microscopy, light scattering and rheology. The experiments have the purpose to identify the effects of shear rate, total strain, molar mass and high molecular weight fraction on the crystallization of iPP. Dimensionless quantities are introduced to correlate the characteristic time scales with structure development; namely, the Weissenberg number ( We), consisting of the product of the applied shear rate and a material characteristic relaxation time ([special characters omitted]) is introduced to demonstrate the transition from spherulitic to oriented structure. A dimensionless characteristic crystallization time scale (τ), defined as the ratio of the experimental time and a characteristic crystallization time, and allows for comparison of crystallization patterns of samples with different molecular specifications (molecular weight, molecular weight distribution) and at different thermo-mechanical conditions. Wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) show the characteristics of the crystalline populations present in the cooled samples after completion of crystallization.

Indexing (details)


Subject
Chemical engineering;
Polymers;
Plastics
Classification
0542: Chemical engineering
0495: Polymers
0795: Plastics
Identifier / keyword
Applied sciences; Pure sciences; Crystallization; Polypropylene; Quenching
Title
Shear-induced crystallization of model polymers
Author
Elmoumni, Aadil
Number of pages
100
Publication year
2005
Degree date
2005
School code
0118
Source
DAI-B 66/02, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
0496976389, 9780496976386
Advisor
Winter, H. Henning
University/institution
University of Massachusetts Amherst
University location
United States -- Massachusetts
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3163664
ProQuest document ID
304997729
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/304997729
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