Physical foaming of 25% post-industrial recycled TPU using the supercritical foaming technology
Francesco MACIARIELLO, Giovanni LUCCHETTA, Marco SORGATO
Abstract. The production of recyclable TPU foams has seen rising interest due to the requirement for a green alternative to chemical foams. While extensive research has been conducted on batch foaming and microcellular injection molding of TPU, the processing of recycled TPU (rTPU) remains largely unexplored. This paper investigated the foaming process of 25% post-industrial recycled TPU using the microcellular method and nitrogen as the physical blowing agent. Rectangular specimens with a thickness of 14 mm and a density of 0.22 g/cm3 were molded. Gas counterpressure was utilized to favor the uniform foaming of the component. Average cell size and cell number analyses were performed, demonstrating that in the core region of the specimen, the recycled TPU foams exhibited similar properties as the foams manufactured using virgin material. In the skin region, rTPU samples showed an improved morphology when compared to the non-recycled foams. The processing temperature of rTPU proved to have a great impact on the properties of the material, with lower temperatures being favorable to avoid excessive degradation.
Keywords
Sustainability, Thermoplastics, Foaming
Published online 9/10/2025, 8 pages
Copyright © 2025 by the author(s)
Published under license by Materials Research Forum LLC., Millersville PA, USA
Citation: Francesco MACIARIELLO, Giovanni LUCCHETTA, Marco SORGATO, Physical foaming of 25% post-industrial recycled TPU using the supercritical foaming technology, Materials Research Proceedings, Vol. 57, pp 311-318, 2025
DOI: https://doi.org/10.21741/9781644903735-36
The article was published as article 36 of the book Italian Manufacturing Association Conference
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 license. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
References
[1] D. I. Alves, Ó. Carvalho, N. A. Fernandes, L. T. Cosentino, A. C. Paula Junior, R. Fangueiro, D. P. Ferreira, Upcycling of industrial footwear waste into nonwoven fibrous structures with thermal and acoustic insulation properties, J. Environ. Manag. 363 (2024), 121363. https://doi.org/10.1016/j.jenvman.2024.121363
[2] M. L. Van Rensburg, S. L. Nkomo, N. M. Mkhize, Life cycle and End-of-Life management options in the footwear industry: A review, Waste Manag Res 38 (2020) 599–613. https://doi.org/10.1177/0734242X20908938
[3] W. Zhai, J. Jiang, C. B. Park, A review on physical foaming of thermoplastic and vulcanized elastomers, Polym. Rev. 62 (2022) 95–141. https://doi.org/10.1080/15583724.2021.1897996
[4] E. Di Maio, E. Kiran, Foaming of polymers with supercritical fluids and perspectives on the current knowledge gaps and challenges, J. Supercrit. Fluids 134 (2018) 157–166. https://doi.org/10.1016/j.supflu.2017.11.013
[5] S.-C. Chen, K.-H. Lee, C.-W. Chang, T.-J. Hsu, C.-T. Feng, Using Gas Counter Pressure and Combined Technologies for Microcellular Injection Molding of Thermoplastic Polyurethane to Achieve High Foaming Qualities and Weight Reduction, Polymers 14 (2022) 2017. https://doi.org/10.3390/polym14102017
[6] G. Wang, G. Zhao, G. Dong, Y. Mu, C. B. Park, G. Wang, Lightweight, super-elastic, and thermal-sound insulation bio-based PEBA foams fabricated by high-pressure foam injection molding with mold-opening, Eur. Polym. J. 103 (2018) 68–79. https://doi.org/10.1016/j.eurpolymj.2018.04.002
[7] H.-P. Heim, M. Tromm, General aspects of foam injection molding using local precision mold opening technology, Polymer 56 (2015) 111–118. https://doi.org/10.1016/j.polymer.2014.10.070
[8] J. W. S. Lee, C. B. Park, Use of Nitrogen as a Blowing Agent for the Production of Fine‐Celled High‐Density Polyethylene Foams, Macromol. Mater. Eng. 291 (2006) 1233–1244. https://doi.org/10.1002/mame.200600203
[9] X. Sun, H. Kharbas, L. Turng, Fabrication of highly expanded thermoplastic polyurethane foams using microcellular injection molding and gas‐laden pellets, Polym. Eng. Sci. 55 (2015) 2643–2652. https://doi.org/10.1002/pen.24157
[10] A. Voda, K. Beck, T. Schauber, M. Adler, T. Dabisch, M. Bescher, M. Viol, D. E. Demco, B. Blümich, Investigation of soft segments of thermoplastic polyurethane by NMR, differential scanning calorimetry and rebound resilience, Polym. Test. 25 (2006) 203–213. https://doi.org/10.1016/j.polymertesting.2005.10.007
[11] J. Jiang, M. Zhou, Y. Li, B. Chen, F. Tian, W. Zhai, Cell structure and hardness evolutions of TPU foamed sheets with high hardness via a temperature rising foaming process, J. Supercrit. Fluids 188 (2022) 105654. https://doi.org/10.1016/j.supflu.2022.105654
[12] B. Wölfel, A. Seefried, V. Allen, J. Kaschta, C. Holmes, D. Schubert, Recycling and Reprocessing of Thermoplastic Polyurethane Materials towards Nonwoven Processing, Polymers 12 (2020) 1917. https://doi.org/10.3390/polym12091917
[13] M. Nofar, E. Büşra Küçük, B. Batı, Effect of hard segment content on the microcellular foaming behavior of TPU using supercritical CO2, J. Supercrit. Fluids 153 (2019) 104590. https://doi.org/10.1016/j.supflu.2019.104590
[14] S.-K. Yeh, R. Rangappa, T.-H. Hsu, S. Utomo, Effect of extrusion on the foaming behavior of thermoplastic polyurethane with different hard segments, J. Polym. Res. 28 (2021) 244. https://doi.org/10.1007/s10965-021-02604-z
