Frontiers of Mechanical Engineering

, Volume 13, Issue 1, pp 96–106 | Cite as

Microcellular injection molding process for producing lightweight thermoplastic polyurethane with customizable properties

  • Thomas Ellingham
  • Hrishikesh Kharbas
  • Mihai Manitiu
  • Guenter Scholz
  • Lih-Sheng TurngEmail author
Research Article
Part of the following topical collections:
  1. Near-net Shaping Technology


A three-stage molding process involving microcellular injection molding with core retraction and an “out-of-mold” expansion was developed to manufacture thermoplastic polyurethane into lightweight foams of varying local densities, microstructures, and mechanical properties in the same microcellular injection molded part. Two stages of cavity expansion through sequential core retractions and a third expansion in a separate mold at an elevated temperature were carried out. The densities varied from 0.25 to 0.42 g/cm3 (77% to 62% weight reduction). The mechanical properties varied as well. Cyclic compressive strengths and hysteresis loss ratios, together with the microstructures, were characterized and reported.


thermoplastic polyurethane microcellular injection molding cavity expansion compressive strength hysteresis loss ratio 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.



The authors would like to acknowledge the support of the Kuo K. and Cindy F. Wang Professorship, the Vilas Distinguished Achievement Professorship, the Wisconsin Distinguished Graduate Fellowship, the 3M Fellowship, and the Wisconsin Institute for Discovery.


  1. 1.
    Colton J S, Suh N P. The nucleation of microcellular thermoplastic foam with additives: Part I: Theoretical considerations. Polymer Engineering and Science, 1987, 27(7): 485–492CrossRefGoogle Scholar
  2. 2.
    Ames K A. Elastomers for shoe applications. Rubber Chemistry and Technology, 2004, 77(3): 413–475CrossRefGoogle Scholar
  3. 3.
    Colton J S, Suh N P. Nucleation of microcellular foam: Theory and practice. Polymer Engineering and Science, 1987, 27(7): 500–503CrossRefGoogle Scholar
  4. 4.
    Lakes R S. Viscoelastic Materials. Cambridge: Cambridge University Press, 2009, 359–360CrossRefGoogle Scholar
  5. 5.
    Engels H W, Pirkl H G, Albers R, et al. Polyurethanes: Versatile materials and sustainable problem solvers for today’s challenges. Angewandte Chemie International Edition, 2013, 52(36): 9422–9441CrossRefGoogle Scholar
  6. 6.
    Okamoto K T. Microcellular Processing. Cincinnati: Hanser Publication, 2003Google Scholar
  7. 7.
    Anson M, Ko J M, Lam E S S. Advances in Building Technology. Amsterdam: Elsevier, 2002Google Scholar
  8. 8.
    Xu J. Microcellular Injection Molding. Hoboken: Wiley, 2011Google Scholar
  9. 9.
    Kharbas H A. Developments in microcellular injection molding technology. Dissertation for the Doctoral Degree. Madison: University of Wisconsin-Madison, 2003Google Scholar
  10. 10.
    Sun X, Turng L S. Novel injection molding foaming approaches using gas-laden pellets with N2, CO2, and N2 + CO2 as the blowing agents. Polymer Engineering and Science, 2014, 54(4): 899–913CrossRefGoogle Scholar
  11. 11.
    Shaayegan V, Mark L H, Park C B, et al. Identification of cellnucleation mechanism in foam injection molding with gas-counter pressure via mold visualization. American Institute of Chemical Engineers, 2016, 62(11): 4035–4046CrossRefGoogle Scholar
  12. 12.
    Rizvi S J, Alaei M, Yadav A, et al. Quantitative analysis of cell distribution in injection molded microcellular foam. Journal of Cellular Plastics, 2014, 50(3): 199–219CrossRefGoogle Scholar
  13. 13.
    Moon Y, Cha S W, Seo J. Bubble nucleation and growth in microcellular injection molding processes. Polymer-Plastics Technology and Engineering, 2008, 47(4): 420–426CrossRefGoogle Scholar
  14. 14.
    Nellis G, Klein S. Heat Transfer. Cambridge: Cambridge University Press, 2009, 137zbMATHGoogle Scholar
  15. 15.
    Sun X, Turng L. Foam injection molding using nitrogen and carbon dioxide as co-blowing agents. Society of Plastics Engineers: Plastics Research Online, 2013, 2–4Google Scholar
  16. 16.
    Sun X, Kharbas H, Peng J, et al. A novel method of producing lightweight microcellular injection molded parts with improved ductility and toughness. Polymer, 2015, 56: 102–110CrossRefGoogle Scholar
  17. 17.
    Sun X, Kharbas H, Turng L S. Fabrication of highly expanded thermoplastic polyurethane foams using microcellular injection molding and gas-laden pellets. Polymer Engineering and Science, 2015, 55(11): 2643–2652CrossRefGoogle Scholar
  18. 18.
    Kharbas H A. Manufacturing highly expanded thermoplastic polyurethane foams using novel injection molding foaming technologies. Dissertation for the Doctoral Degree. Madison: University of Wisconsin-Madison, 2016Google Scholar
  19. 19.
    Qi H J J, Boyce M C C. Stress-strain behavior of thermoplastic polyurethanes. Mechanics of Materials, 2005, 37(8): 817–839CrossRefGoogle Scholar
  20. 20.
    Gong L, Kyriakides S, Triantafyllidis N. On the stability of Kelvin cell foams under compressive loads. Journal of the Mechanics and Physics of Solids, 2005, 53(4): 771–794CrossRefzbMATHGoogle Scholar

Copyright information

© Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  • Thomas Ellingham
    • 1
    • 2
  • Hrishikesh Kharbas
    • 1
    • 2
  • Mihai Manitiu
    • 3
  • Guenter Scholz
    • 3
  • Lih-Sheng Turng
    • 1
    • 2
    Email author
  1. 1.Department of Mechanical EngineeringUniversity of Wisconsin-MadisonMadisonUSA
  2. 2.Wisconsin Institute for DiscoveryUniversity of Wisconsin-MadisonMadisonUSA
  3. 3.BASF CorporationWyandotteUSA

Personalised recommendations