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Shear‐Induced Skin‐Core Structure of Molten Isotactic Polypropylene and the Formation of β‐Crystal
Author(s) -
Pan Yamin,
Guo Xiaobei,
Zheng Guoqiang,
Liu Chuntai,
Chen Qiang,
Shen Changyu,
Liu Xianhu
Publication year - 2018
Publication title -
macromolecular materials and engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.913
H-Index - 96
eISSN - 1439-2054
pISSN - 1438-7492
DOI - 10.1002/mame.201800083
Subject(s) - tacticity , materials science , shearing (physics) , shear rate , crystallization , crystallinity , composite material , shear (geology) , crystallization of polymers , shear flow , spherulite (polymer physics) , polypropylene , melt flow index , polymer , crystal (programming language) , rheology , chemical engineering , thermodynamics , polymerization , copolymer , physics , computer science , engineering , programming language
The study of crystallization behavior and crystalline morphology of polymer melt under shear flow is of great interest due to the strong effect of flow field on the final properties of polymer products in the practical processing. In this respect, the shearing hot stage provides a unique tool which monitors sensitively the changes in crystalline structure induced by precise experimental conditions. Herein, the impacts of both melting temperature and shear rate on the crystallization behavior of isotactic polypropylene (iPP) melt are investigated. Under static conditions, there are only random spherulite structures. Once shear is involved, the cylindrite‐layers appear near both surfaces of the sample, which is consistent with the skin‐core structure in the injection molded parts. Meanwhile, the β‐crystals can be developed and are related to the molecular orientation, depending on the applied melting temperatures and shear rates. More interestingly, the crystallinity of β‐crystal in the pure iPP can reach 15%. The above results indicate that the melting temperature and shear rate are important factors in determining the β‐form crystal development of iPP matrix.