# Effect of ultrasound on the foaming of PMMA-based polymers

J A Villamil Jiménez, Barthelemy Alex, Margaux Haurat, Fabien Baillon, Martial Sauceau, Michel Dumon

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J A Villamil Jiménez, Barthelemy Alex, Margaux Haurat, Fabien Baillon, Martial Sauceau, et al. Effect of ultrasound on the foaming of PMMA-based polymers. EMSF 2023 - 19th European Meeting on Supercritical Fluids, University of Budapest, May 2023, Budapest, Hungary. hal-04960772

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Submitted on 21 Feb 2025

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Distributed under a Creative Commons Attribution 4.0 International License
Effect of ultrasound on the foaming of PMMA-based polymers

JA. Villamil Jiménez<sup>a</sup>, A. Barthelemy<sup>a</sup>, M. Haurat<sup>b</sup>, F. Baillon<sup>a</sup>, M. Sauceau<sup>a*,</sup> M. Dumon<sup>b,c</sup>

The development of porous and lightweight polymer structures is of major interest in many industrial fields. Indeed, these structures exhibit several advantages compared to a massive solid of similar chemical nature, with improved properties and material and energy savings. Among the different methods developed for the foaming of materials, supercritical carbon dioxide (sc-CO₂) as physical foaming agent has shown a high potential to develop various porous structures for a wide range of polymers [1,2]. However, the obtention of a large number of small pores remains a tackling problem. To solve this limitation, several techniques have been implemented by using either “internal” actions on the material (for instance enhancing the crystallinity) or “external” ones on the process. Among these, ultrasound US can be used to improve the cell nucleation during the foaming [3].

In the present work, we report the two-step solid-state sc-CO₂ batch foaming of PMMA-based materials assisted by US. These materials were selected because their foaming have already been studied [2, 4]. 2 small samples of the polymer were first impregnated with CO₂ in a high-pressure autoclave. After 24 h, the sample were recovered after a depressurisation profile chosen to avoid the foaming and to keep a maximum of the CO₂ into the sample. The impregnated samples were right after plunged into a distillate water bath at a controlled temperature for a certain duration, only one being exposed to ultrasound waves. For that, an ultrasounds probe was placed at 10 mm from the bottom of the bath and the sample were placed between the probe and the bath bottom. The two samples were then characterised to porosity (water pycnometry) and cellular morphology (SEM and image analysis)

Figure 1 shows the cell size distribution of different samples. The first observation to be made is that the lower the foaming temperature the higher the ultrasounds effect. Indeed, at lower temperature, exposing the samples to the ultrasounds results in a slight decrease of the mean cell size with a more homogeneous structure.

This work confirms that it is possible to master the cellular morphology of the polymer by using ultrasounds during the foaming step.

The next step will be to confirm the effect of ultrasound during a continuous foaming extrusion process [4].

<figure><img src="image_2.png" /><figcaption>Figure 1. Cell size distributions of PMMA samples foamed by sc-CO₂ without and with US</figcaption></figure>

References

[1] J.A Villamil Jiménez, N. le Moigne, J.C Bénézet, M. Sauceau, R. Sescousse, J. Fages, *Molecules* **2020**, *25*(15), 3408. DOI: https://doi.org/10.3390/molecules25153408

[2] M. Haurat, M. Dumon, *Molecules* **2020**, *25*(22), 5320. DOI: https://doi.org/10.3390/molecules25225320

[3] R. Dugad, G. Radhakrishna, A. Gandhi, *J. Polym. Res.* **2020**, *27*:182. DOI: https://doi.org/10.1007/s10965-020-02157-7

[4] M. Haurat, M. Sauceau, F. Baillon, L. Le Barbenchon, M. Pedros, M. Dumon, *J. Appl. Polym. Sci.* **2023**, e53277. DOI: https://doi-org.gorgone.univ-toulouse.fr/10.1002/app.53277

<footnote><sup>a</sup> Centre RAPSODEE, UMR CNRS 5302, IMT Mines Albi, Université de Toulouse, F-81013 Albi, France</footnote>

<footnote><sup>b</sup> Univ. Bordeaux, CNRS, Bordeaux INP, LCPO UMR 5629, F-33607 Pessac, France</footnote>

<footnote><sup>c</sup> Département Science et Génie des Matériaux -SGM, IUT, Université de Bordeaux, F-33170 Gradignan</footnote>

<footnote>* Corresponding author: martial.sauceau@mines-albi.fr</footnote>