Modeling Flow-Induced Crystallization

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• 关键词：Compressibility ; Dilatometry ; Flow induced crystallization ; Lamellar branching ; Non ; isothermal ; Nonlinear viscoelasticity ; Polymer Processing ; Polymorphism ; Polypropylene ; Shish ; kebab
• 刊名：Advances in Polymer Science
• 出版年：2017
• 出版时间：2017
• 年：2017
• 卷：277
• 期：1
• 页码：243-294
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• 作者单位：Peter C. Roozemond (22) (23)
  Martin van Drongelen (22)
  Gerrit W. M. Peters (22)
  
  22. Department of Mechanical Engineering, Eindhoven University of Technology, 513, 5600 MB, Eindhoven, The Netherlands
  23. DSM Ahead Materials Science Center, 18, 6160 MD, Geleen, The Netherlands
  
• 丛书名：Polymer Crystallization II
• ISBN：978-3-319-50684-5
• 卷排序：277

文摘

A numerical model is presented that describes all aspects of flow-induced crystallization of isotactic polypropylene at high shear rates and elevated pressures. It incorporates nonlinear viscoelasticity, including viscosity change as a result of formation of oriented fibrillar crystals (shish), compressibility, and nonisothermal process conditions caused by shear heating and heat release as a result of crystallization. In the first part of this chapter, the model is validated with experimental data obtained in a channel flow geometry. Quantitative agreement between experimental results and the numerical model is observed in terms of pressure drop, apparent crystallinity, parent/daughter ratio, Hermans’ orientation, and shear layer thickness. In the second part, the focus is on flow-induced crystallization of isotactic polypropylene at elevated pressures, resulting in multiple crystal phases and morphologies. All parameters but one are fixed a priori from the first part of the chapter. One additional parameter, determining the portion of β-crystal spherulites nucleated by flow, is introduced. By doing so, an accurate description of the fraction of β-phase crystals is obtained. The model accurately captures experimental data for fractions of all crystal phases over a wide range of flow conditions (shear rates from 0 to 200 s−1, pressures from 100 to 1,200 bar, shear temperatures from 130°C to 180°C). Moreover, it is shown that, for high shear rates and pressures, the measured γ-phase fractions can only be matched if γ-crystals can nucleate directly on shish.