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Extensional Flow-Induced Dynamic Phase Transitions in Isotactic Polypropylene.

Jianzhu Ju1, Zhen Wang1, Fengmei Su1

  • 1National Synchrotron Radiation Lab, CAS Key Laboratory of Soft Matter Chemistry, University of Science and Technology of China, Hefei, 230029, China.

Macromolecular Rapid Communications
|July 5, 2016
PubMed
Summary
This summary is machine-generated.

Flow-induced crystallization (FIC) in isotactic polypropylene (iPP) was studied. Above the melting point, flow induces β and α crystal formation, with kinetics favoring the metastable β phase over the stable α phase.

Keywords:
crystallizationmeltpolypropylenereal-time X-ray scattering

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Area of Science:

  • Polymer Science
  • Materials Science
  • Crystallization

Background:

  • Flow-induced crystallization (FIC) is crucial for polymer properties.
  • Understanding phase transitions under flow is essential for material processing.

Purpose of the Study:

  • To investigate the flow-induced crystallization (FIC) of isotactic polypropylene (iPP).
  • To construct a flow phase diagram and analyze phase competitions under varying conditions.

Main Methods:

  • Utilized a fast extension rheometer and in situ synchrotron radiation ultra-fast small- and wide-angle X-ray scattering.
  • Studied iPP crystallization at temperatures below and above the melting point of α crystals (Tmα).

Main Results:

  • A flow phase diagram was constructed, identifying melt, non-crystalline shish, α, and α&β coexistence regions.
  • Above Tmα, flow induced FIC of β and α crystals as a dynamic phase transition.
  • Kinetic rates, not thermodynamic stability, favored metastable β over stable α crystals with increasing temperature or strain rate.

Conclusions:

  • Flow conditions dictate phase transitions and crystallization pathways in iPP.
  • Kinetic factors play a dominant role in the competition between α and β crystal formation.
  • Extreme conditions can lead to non-crystalline shish formation, hindering crystallization.