International Journal of Material Forming

, Volume 11, Issue 5, pp 717–727 | Cite as

The role of microcrystalline structure on optical scattering characteristics of semi-crystalline thermoplastics and the accuracy of numerical input for IR-heating modeling

  • Sinan Boztepe
  • Rémi Gilblas
  • Olivier de Almeida
  • Christian Gerlach
  • Yannick Le Maoult
  • Fabrice Schmidt
Original Research


Infrared (IR) heating is widely used for thermoforming of thermoplastic polymers. The key benefit of radiation heating is that a significant amount of the radiative energy penetrates into the polymers thanks to their semi-transparency. For the case of heating unfilled semi-crystalline polymers, the relation between their microcrystalline structure and optical properties is the key to develop a predictive IR-heating model as microcrystalline structure introduces an optically heterogeneous medium. In this study, a relation between the microcrystalline structure of a polyethylene (PE) and its effect on the thermo-optical properties was experimentally analyzed considering a two-step analysis. At very first step, the relation was analyzed considering samples with identical thicknesses and different morphologies, characterized here in terms of degree of crystallinity (Xc (%)). Using Fourier Transform Infrared (FT-IR) spectroscopy and integrating sphere, optical characteristics of the PE samples were analyzed in near-infrared (NIR) and middle-infrared (MIR) spectral ranges. The analyses showed that a slight variation in Xc (%) has a great effect on the optical characteristics of PE, particularly the transmission characteristics in NIR range. The wavelength-dependent effect of Xc (%) on the transmission behaviors opened a discussion about the fact that the microcrystalline structures -in particular spherulites or their substructures such as lamellae- are responsible for optical scattering. Using the optical properties obtained from the two-step experimental analyses, two different thermo-optical properties were calculated, namely extinction and absorption coefficients, and used as a numerical input for the parametric numerical studies. The numerical studies were performed using an in-house developed radiation heat transfer algorithm -RAYHEAT-. Both the experimental and numerical analyses demonstrated the importance of the optical scattering regarding the identification of thermo-optical properties, used as a numerical input for radiation heat transfer models.


Infrared heating Semi-crystalline thermoplastics Thermo-optical properties Optical scattering Crystallinity Radiation heat transfer modeling 



The authors declare that they have no conflict of interest.


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Copyright information

© Springer-Verlag France SAS, part of Springer Nature 2017

Authors and Affiliations

  • Sinan Boztepe
    • 1
  • Rémi Gilblas
    • 1
  • Olivier de Almeida
    • 1
  • Christian Gerlach
    • 2
  • Yannick Le Maoult
    • 1
  • Fabrice Schmidt
    • 1
  1. 1.Institut Clément Ader (ICA), Université de Toulouse, CNRS, IMT Mines Albi, INSA, ISAE-SUPAERO, UPS, Campus Jarlard, 81013 Albi CT Cedex 09, FranceAlbiFrance
  2. 2.Procter & Gamble Services NV, Brussels Innovation CenterStrombeek BeverBelgium

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