Rules of supermolecular structure formation in sheared isotactic polypropylene melts

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Abstract

Shear-induced crystallization of isotactic polypropylene (iPP) homo-, block, and random copolymers was studied and compared to that in quiescent melt. It was evidenced by means of the thermo-optical technique that melt-shearing, caused by fiber pulling, is associated with the development of α-row-nuclei. The surface of the in situ formed α-row-nuclei may induce the growth of the β-modification of iPP resulting in a cylindrite of polymorphous composition. The polymorphous composition is controlled by the temperature-dependent relative growth rate of the α- and β-iPP for which a model explanation was given. The β-nucleation ability of the α-row-nuclei is lost by melt-shearing at high temperature or remelting. This was attributed to a coverage of the β-nuclei by the α-phase. The structural memory of the supermolecular structures was studied in repeated melting and crystallization cycles and discussed. It was found that the quality of the fiber did not influence the mechanisms concluded. The shear-induced crystallization of propylene block copolymers was highly analogous to the homopolymers. In case of the random copolymers, however, crystallization in sheared melt resulted in an α-cylindritic structure, because for propylene random copolymers the growth rate of the α-modification is always higher than that of the β. It was also demonstrated that the mechanism of shear-induced crystallization was unaffected when the crystallizing PP melt contained selective β-nucleants.

Original languageEnglish
Pages (from-to)657-670
Number of pages14
JournalJournal of Polymer Science, Part B: Polymer Physics
Volume34
Issue number4
Publication statusPublished - Mar 1996

Fingerprint

Polypropylenes
Crystallization
polypropylene
crystallization
copolymers
nuclei
Copolymers
shear
propylene
shearing
Shearing
Propylene
melting
Remelting
fibers
Fibers
pulling
Homopolymerization
block copolymers
Chemical analysis

Keywords

  • α-polypropylene
  • β-polypropylene
  • Crystallization
  • Cylindrite
  • Isotactic polypropylene
  • Melting
  • Nucleation
  • Quiescent melt
  • Sheared melt
  • Supermolecular structure
  • Thermo-optical study
  • Transcrystallization

ASJC Scopus subject areas

  • Materials Chemistry
  • Polymers and Plastics

Cite this

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title = "Rules of supermolecular structure formation in sheared isotactic polypropylene melts",
abstract = "Shear-induced crystallization of isotactic polypropylene (iPP) homo-, block, and random copolymers was studied and compared to that in quiescent melt. It was evidenced by means of the thermo-optical technique that melt-shearing, caused by fiber pulling, is associated with the development of α-row-nuclei. The surface of the in situ formed α-row-nuclei may induce the growth of the β-modification of iPP resulting in a cylindrite of polymorphous composition. The polymorphous composition is controlled by the temperature-dependent relative growth rate of the α- and β-iPP for which a model explanation was given. The β-nucleation ability of the α-row-nuclei is lost by melt-shearing at high temperature or remelting. This was attributed to a coverage of the β-nuclei by the α-phase. The structural memory of the supermolecular structures was studied in repeated melting and crystallization cycles and discussed. It was found that the quality of the fiber did not influence the mechanisms concluded. The shear-induced crystallization of propylene block copolymers was highly analogous to the homopolymers. In case of the random copolymers, however, crystallization in sheared melt resulted in an α-cylindritic structure, because for propylene random copolymers the growth rate of the α-modification is always higher than that of the β. It was also demonstrated that the mechanism of shear-induced crystallization was unaffected when the crystallizing PP melt contained selective β-nucleants.",
keywords = "α-polypropylene, β-polypropylene, Crystallization, Cylindrite, Isotactic polypropylene, Melting, Nucleation, Quiescent melt, Sheared melt, Supermolecular structure, Thermo-optical study, Transcrystallization",
author = "J. Varga and J. Karger-Kocsis",
year = "1996",
month = "3",
language = "English",
volume = "34",
pages = "657--670",
journal = "Journal of Polymer Science, Part B: Polymer Physics",
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publisher = "John Wiley and Sons Inc.",
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TY - JOUR

T1 - Rules of supermolecular structure formation in sheared isotactic polypropylene melts

AU - Varga, J.

AU - Karger-Kocsis, J.

PY - 1996/3

Y1 - 1996/3

N2 - Shear-induced crystallization of isotactic polypropylene (iPP) homo-, block, and random copolymers was studied and compared to that in quiescent melt. It was evidenced by means of the thermo-optical technique that melt-shearing, caused by fiber pulling, is associated with the development of α-row-nuclei. The surface of the in situ formed α-row-nuclei may induce the growth of the β-modification of iPP resulting in a cylindrite of polymorphous composition. The polymorphous composition is controlled by the temperature-dependent relative growth rate of the α- and β-iPP for which a model explanation was given. The β-nucleation ability of the α-row-nuclei is lost by melt-shearing at high temperature or remelting. This was attributed to a coverage of the β-nuclei by the α-phase. The structural memory of the supermolecular structures was studied in repeated melting and crystallization cycles and discussed. It was found that the quality of the fiber did not influence the mechanisms concluded. The shear-induced crystallization of propylene block copolymers was highly analogous to the homopolymers. In case of the random copolymers, however, crystallization in sheared melt resulted in an α-cylindritic structure, because for propylene random copolymers the growth rate of the α-modification is always higher than that of the β. It was also demonstrated that the mechanism of shear-induced crystallization was unaffected when the crystallizing PP melt contained selective β-nucleants.

AB - Shear-induced crystallization of isotactic polypropylene (iPP) homo-, block, and random copolymers was studied and compared to that in quiescent melt. It was evidenced by means of the thermo-optical technique that melt-shearing, caused by fiber pulling, is associated with the development of α-row-nuclei. The surface of the in situ formed α-row-nuclei may induce the growth of the β-modification of iPP resulting in a cylindrite of polymorphous composition. The polymorphous composition is controlled by the temperature-dependent relative growth rate of the α- and β-iPP for which a model explanation was given. The β-nucleation ability of the α-row-nuclei is lost by melt-shearing at high temperature or remelting. This was attributed to a coverage of the β-nuclei by the α-phase. The structural memory of the supermolecular structures was studied in repeated melting and crystallization cycles and discussed. It was found that the quality of the fiber did not influence the mechanisms concluded. The shear-induced crystallization of propylene block copolymers was highly analogous to the homopolymers. In case of the random copolymers, however, crystallization in sheared melt resulted in an α-cylindritic structure, because for propylene random copolymers the growth rate of the α-modification is always higher than that of the β. It was also demonstrated that the mechanism of shear-induced crystallization was unaffected when the crystallizing PP melt contained selective β-nucleants.

KW - α-polypropylene

KW - β-polypropylene

KW - Crystallization

KW - Cylindrite

KW - Isotactic polypropylene

KW - Melting

KW - Nucleation

KW - Quiescent melt

KW - Sheared melt

KW - Supermolecular structure

KW - Thermo-optical study

KW - Transcrystallization

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VL - 34

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JO - Journal of Polymer Science, Part B: Polymer Physics

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