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Influence of shear on polypropylene crystallization kinetics
Hong Huo1, Yanfeng Meng, Hongfei Li
1State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 130022 Changchun, PRC.
The European Physical Journal. E, Soft Matter
|October 27, 2004
Summary
Shear enhances isothermal crystallization kinetics in polypropylene (iPP) melts, with relaxation playing a key role. Flow-induced ordering significantly impacts melt free energy, affecting crystallization rates.
Area of Science:
- Polymer Science
- Materials Science
- Rheology
Background:
- Understanding polymer crystallization under external fields is crucial for material properties.
- Isothermal crystallization kinetics are influenced by various factors, including temperature and flow.
- Polypropylene (iPP) is a widely used thermoplastic whose processing behavior is of significant industrial interest.
Purpose of the Study:
- To investigate the isothermal crystallization kinetics of iPP melts under shear.
- To elucidate the role of relaxation and shear rates on crystallization kinetics.
- To evaluate theoretical models for describing shear-induced crystallization.
Main Methods:
- Optical microscopy was employed to observe isothermal crystallization.
- iPP melts were subjected to varying shear conditions at different temperatures.
- Lauritzen-Hoffman theory and the DE-IAA model were applied for analysis.
Main Results:
- Shearing iPP melts from 200°C to crystallization temperatures significantly enhanced crystallization kinetics.
- Shear applied only at 200°C showed a less pronounced effect on kinetics.
- Spherulite growth rates increased with shear rates and were governed by relaxation processes.
- The degree of order increase due to flow effectively altered melt free energy.
Conclusions:
- Relaxation is a critical factor in shear-induced crystallization of iPP.
- The observed kinetics align well with predictions from the Lauritzen-Hoffman theory and the DE-IAA model.
- Flow-induced changes in melt free energy provide a framework for understanding shear effects on crystallization.