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Tailoring microstructure and mechanical properties of injection molded isotactic–polypropylene via high temperature preshear
Author(s) -
Chang Baobao,
Wang Bo,
Zheng Guoqiang,
Dai Kun,
Liu Chuntai,
Shen Changyu
Publication year - 2015
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.24078
Subject(s) - materials science , tacticity , composite material , crystallinity , izod impact strength test , microstructure , nucleation , spherulite (polymer physics) , polypropylene , molding (decorative) , core (optical fiber) , polymer , ultimate tensile strength , polymerization , chemistry , organic chemistry
In this work, isotactic–polypropylene (iPP) specimens were prepared by a modified injection molding machine, in which high temperature preshear (HTPS) can be imposed on the molten polymer during the plasticizing stage. The effect of HTPS on the microstructure and mechanical property of iPP was investigated. It was found that spherulite size in core region of iPP part decreased steadily with the increasing HTPS duration, indicating that HTPS could substantially enhance iPP nucleation. Moreover, β ‐iPP formation correlated strongly with HTPS duration. That is, in the absence of HTPS, β ‐iPP existed only in intermediate region; with moderate HTPS duration, β ‐iPP could be unexpectedly formed in core region; however, long HTPS duration inhibited β ‐iPP formation in both intermediate region and core region. Based on the relationship between β ‐iPP formation and HTPS duration, metastable nuclei, instead of α ‐row nuclei, were proposed to be responsible for the development of β ‐iPP. Notched Izod impact test showed that moderate HTPS duration enhance the impact strength of injection molded iPP by decreasing the thickness of shear region and elevating β ‐iPP crystallinity in core region. Dynamic mechanical test indicated that with the increase of HTPS duration, the storage modulus of injection‐molded iPP improves drastically. POLYM. ENG. SCI., 55:2714–2721, 2015. © 2015 Society of Plastics Engineers