Cylindritic structures of isotactic polypropylene molded by sequential co-injection molding
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In this study, isotacitc polypropylene (iPP) samples were prepared by conventional injection molding (CIM) and sequential co-injection molding (SCIM), in which two kinds of polymer melt were injected into the mold cavity one after the other. The morphological structure of the samples was investigated by polarized light microscopy (PLM) and scanning electron microscopy (SEM). Results show that the structures of the samples prepared by CIM have a typical skin-core structure. This structure could be divided into three layers along the thickness direction of the samples: skin layer, transition region and core layer. However, the morphologies of the samples prepared by SCIM have a fascinating supermolecular structure that can not be roughly divided into three layers. A region of cylindritic structures, which is rare in CIM, is formed between the skin layer and the core layer of the second injected material. In particular, the cylindritic structures are more easily found when the melt temperature is relatively lower and the delay time is longer. The results were further interpreted based on the analysis and comparison of the thermo-mechanical history imposed on the melt during the CIM and SCIM processes.
KeywordsMorphology Semi-crystalline polymer Skin-core Sequential co-injection molding (SCIM) Isotactic polypropylene (iPP) Cylindrite
The authors would like to express their gratitude to Natural Science Foundation of China (No. 11172272), The Research Fund for the Doctoral Program of Higher Education (No. 20104101110002), Innovation Scientists and Technicians Troop Construction Projects of Henan Province (No. 114200510018), the Natural Science Foundation of Jiangsu Province (No. BK2011519), the Natural Science Fund for Colleges and Universities in Jiangsu Province (No. 10KJB430007), and Jiangsu Provincial Key Laboratory of Optics and Photonics (No. GZ201102) for financial support. The authors also thank Prof. Lih-Sheng Turng at the University of Wisconsin-Madison and Prof. Chang-Yu Shen at Dalian University of Technology for their helpful suggestions.
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