Cylindritic structures of isotactic polypropylene molded by sequential co-injection molding

  • Guang-Long Wang
  • Ying-Guo Zhou
  • Song-Jie Wang
  • Jing-Bo Chen
  • Xiao-Li Zhang
  • Sheng Lu
Original Paper


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.


Morphology 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.


  1. 1.
    Yong SS, White JL, Clark ES, Oyanagi Y (1980) A basic experimental study of sandwich injection molding with sequential injection [J]. Polym Eng Sci 20:798–804CrossRefGoogle Scholar
  2. 2.
    Seldon R (2000) Co-injection molding: effect of processing on material distribution and mechanical properties of a sandwich molded plate [J]. Polym Eng Sci 40(5):1165–1176CrossRefGoogle Scholar
  3. 3.
    Nagaoka T, Ishiaku US, Tomari T, Hamada H, Takashima S (2005) Effect of molding parameters on the properties of PP/PP sandwich injection moldings [J]. Polym Test 24:1062–1070CrossRefGoogle Scholar
  4. 4.
    Turng L, Wang V (1991) Simulation of co-injection and gas-assisted injection molding [C]. SPE-ANTEC 37:297–299Google Scholar
  5. 5.
    Chen S, Hsu K, Jeng M (1993) Numerical simulation and experimental studies of the co-injection molding process [C]. SPE-ANTEC 39:82–86Google Scholar
  6. 6.
    Ilinca F, Hétu JF, Derdouri A (2006) Numerical investigation of the flow front behaviour in the co-injection moulding process [J]. Int J Numer Methods Fluids 50(12):1445–1460CrossRefGoogle Scholar
  7. 7.
    Karacs G (2002) Internal structure of co-injection molded PP/PP specimen [J]. J Macromol Sci B Phys B41(4–6):1279–1289Google Scholar
  8. 8.
    Kadota M, Cakmak M, Hamada H (1999) Structureal hierarchy developed in co-injection molded polystyrene/polypropylene parts [J]. Polymer 40:3119–3145CrossRefGoogle Scholar
  9. 9.
    Cheng CC, Ono Y, Jen CK (2007) Real-time diagnosis of co-injection molding using ultrasound [J]. Polym Eng Sci 47(9):1491–1500CrossRefGoogle Scholar
  10. 10.
    Zhang K, Liu Z, Yang B, Yang W, Lu Y, Wang L, Sun N, Yang M (2011) Cylindritic structures of high-density polyethylene molded by multi-melt multi-injection molding [J]. Polymer 52(17):3871–3878CrossRefGoogle Scholar
  11. 11.
    Gomes M, Martino D, Pontes AJ, Viana JC (2011) Co-injection molding of immiscible polymers: skin-core structure and adhesion studies [J]. Polym Eng Sci 51(12):2398–2407CrossRefGoogle Scholar
  12. 12.
    Pantani R, Coccorullo I, Speranza V, Titomanlio G (2005) Modeling of morphology evolution in the injection molding process of thermoplastic polymers [J]. Prog Polym Sci 30:1185–1222CrossRefGoogle Scholar
  13. 13.
    Lin X, Caton-Rose F, Ren D, Wang K (2013) Shear-induced crystallization morphology and mechanical property of high density polyethylene in micro-injection molding [J]. J Polym Res 20:122–133CrossRefGoogle Scholar
  14. 14.
    Guo X, Isayev AI, Guo L (1999) Crystallinity and microstructure in injection moldings of isotactic polypropylenes. Part 1: a new approach to modeling and model parameters [J]. Polym Eng Sci 39(10):2096–2114CrossRefGoogle Scholar
  15. 15.
    Fujiyama M, Masada I, Mitani K (2000) Melting and crystallization behaviors of injection-molded polypropylene[J]. J Appl Polym Sci 78:1751–1762CrossRefGoogle Scholar
  16. 16.
    Viana JC, Cunha AM, Billon N (2001) The effect of the skin thickness and spherulite size on the mechanical properties of injection mouldings [J]. J Mater Sci 36:4411–4418CrossRefGoogle Scholar
  17. 17.
    Viana JC, Cunha AM, Billon N (2002) The thermomechanical environment and the microstructure of an injection moulded polypropylene copolymer [J]. Polymer 43:4185–4196CrossRefGoogle Scholar
  18. 18.
    Viana JC (2004) Development of the skin layer in injection moulding: phenomenological model [J]. Polymer 45:993–1005CrossRefGoogle Scholar
  19. 19.
    Shen C, Zhou Y, Chen J, Li Q (2008) Numerical simulation of crystallization morphological evolution under non-isothermal condition [J]. Polym Plast Technol Eng 47(7):708–715CrossRefGoogle Scholar
  20. 20.
    Zhu PW, Edward G (2004) Distribution of Shish-Kebab structure of isotactic polypropylene under shear in the presence of nucleating agent [J]. Macromolecules 37:2658–2660CrossRefGoogle Scholar
  21. 21.
    Wang Y, Na B, Fu Q, Men YF (2004) Shear induced shish–kebab structure in PP and its blends with LLDPE [J]. Polymer 45:207–215CrossRefGoogle Scholar
  22. 22.
    Ludwig HC, Fischer G, Becker H (1995) A quantitative comparison of morphology and fiber orientation in push-pull processed and conventional injecion-molded parts [J]. Compos Sci Technol 53:235–239CrossRefGoogle Scholar
  23. 23.
    Waschitschek K, Kech A, Christiansen JC (2002) Influence of push-pull injection molding on fibers and matrix of fibre reinforced polypropylene [J]. Compos A: Appl Sci Manuf 33:735–744CrossRefGoogle Scholar
  24. 24.
    Somani RH, Yang L, Zhu L, Hsiao BS (2005) Flow-induced shish-kebab precursor structures in entangled polymer melts [J]. Polymer 46:8587–8623CrossRefGoogle Scholar
  25. 25.
    Na B, Li Z, Lv R (2011) Oriented re-crystallization of polypropylene through partial melting and its dramatic influence on mechanical properties [J]. J Polym Res 18:2103–2108CrossRefGoogle Scholar
  26. 26.
    Zhou Y, Turng L, Shen C (2010) Morphological evolution and orientation development of stretched iPP films: influence of draw ratio [J]. J Polymer Sci, Part B: Polymer Phys 48(11):1223–1234CrossRefGoogle Scholar
  27. 27.
    Varga J, Karger-Kocsis J (1996) Rules of supermolecular structure formation in sheared isotactic polypropylene melts [J]. J Polymer Sci, Part B: Polymer Phys 34:657–670CrossRefGoogle Scholar
  28. 28.
    Li H, Zhang X, Kuang X, Wang J, Wang D, Li L, Yan S (2004) A scanning electron microscopy study on the morphologies of Isotactic Polypropylene induced by its own fibers [J]. Macromolecules 37(8):2847–2853CrossRefGoogle Scholar
  29. 29.
    Somani RH, Yang L, Sics I, Hsiao BS, Pogodina NV, Winter HH, Agarwal P, Fruitwala H, Tsou A (2002) Orientation-induced crystallization in isotactic polypropylene melt by shear deformation [J]. Macromol Symp 185:105–117CrossRefGoogle Scholar
  30. 30.
    Zhang CG, Hu HQ, Wang DJ, Yan SK, Han CC (2005) In situ optical microscope study of the shear-induced crystallization of isotactic polypropylene [J]. Polymer 46:8157–8161CrossRefGoogle Scholar
  31. 31.
    Zhou Q, Liu F, Guo C, Fu Q, Shen K, Zhang J (2011) Shish–kebab-like cylindrulite structures resulted from periodical shear-induced crystallization of isotactic polypropylene [J]. Polymer 52(13):2970–2978CrossRefGoogle Scholar
  32. 32.
    Bai H, Luo F, Zhou T, Deng H, Wang K, Fu Q (2011) New insight on the annealing induced microstructural changes and their roles in the toughening of β-form polypropylene [J]. Polymer 52:2351–2360CrossRefGoogle Scholar
  33. 33.
    Luo F, Wang J, Bai H, Wang K, Deng H, Zhang Q, Chen F, Fu Q, Na B (2011) Synergistic toughening of polypropylene random copolymer at low temperature: β-Modification and annealing [J]. Polymer 528(22–23):7052–7059Google Scholar
  34. 34.
    Lotz B (1998) α and β phases of isotactic polypropylene a case of growth kinetics ‘phase reentrency’ in polymer crystallization [J]. Polymer 39(19):4561–4567CrossRefGoogle Scholar
  35. 35.
    Lu Q, Dou Q (2009) β-Crystal formation of isotactic polypropylene induced by N, N’-dicyclohexylsuccinamide [J]. J Polym Res 16:555–560CrossRefGoogle Scholar
  36. 36.
    Wenig W, Herzog F (1993) Injection molding of polypropylene: x-ray investigation of the skin–core morphology [J]. J Appl Polym Sci 50(12):2163–2171CrossRefGoogle Scholar
  37. 37.
    Varga J, Karger-Kocsis J (1993) Direct evidence of row-nucleated cylindritic crystallization in glass fiber-reinforced polypropylene composites [J]. Polym Bull 30:105–110CrossRefGoogle Scholar
  38. 38.
    Ziabicki A (2005) Nucleation-controlled multiphase transitions [J]. J Chem Phys 103:123–174Google Scholar
  39. 39.
    Bassett DC (2006) Linear nucleation of polymers [J]. Polymer 47:5221–5227CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  1. 1.National Engineering Research Center for Advanced Polymer Processing TechnologyZhengzhou UniversityZhengzhouPeople’s Republic of China
  2. 2.School of Materials Science and EngineeringJiangsu University of Science and TechnologyZhenjiangPeople’s Republic of China

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