Soutenance de thèse de Thomas Schatzmayr Welp Sa

Thomas Schatzmayr Welp Sa soutiendra sa thèse de doctorat intitulée “Impact d'un traitement d'ignifugation sur les propriétés acoustiques des laines isolantes d'origine végétale : du laboratoire à la production à l'échelle pilote” le vendredi 21 novembre 2025 à 13h30 dans l'Amphithéâtre Clugnet (Bâtiment Coriolis) ENPC - Cité Descartes, 8 Av. Blaise Pascal 77420 Champs-sur-Marne.

Composition du jury :

• Rodolphe SONNIER, IMT Mines Alès (Rapporteur)
• Nicolas Dauchez, UTC Compiègne (Rapporteur)
• Céline Perlot Bascoules, Université de Pau et des Pays de l’Adour (Examinatrice)
• Lily Deborde, CAVAC Biomatériaux (Examinatrice)
• M’hamed Yassin Rajiv da Gloria, Federal University of Rio de Janeiro, Brésil (Examinateur)
• Fouad Laoutid, Materia Nova, Belgique (Co-encadrant de thèse)
• Clément Piegay, UMRAE, Cerema, Université Gustave Eiffel (Co-encadrant de thèse)
• Sandrine Marceau, Université Gustaveeiffel, MAST-CPDM (Directrice de thèse)

Résumé :

Vegetal wools have very interesting multi-functional properties that reinforce their use as a building insulation alternative to traditional insulation materials, such as excellent acoustic absorption properties, high thermal insulation, and a hygroscopic nature for humidity regulation. However, their high flammability imposes limitations on their application in constructions, requiring the use of flame-retardants. For vegetal wools, the flame-retardants need to be in agreement with the bio-based nature of the material and comply with the manufacturing process. Furthermore, the fireproof treatment should not cause changes in the structure of the fibers and in their properties, since the acoustic and thermal performances of the material depends on them. Therefore, the goal of this thesis is to reduce the flammability of vegetal wools while taking into account their manufacture, application processes, and bio-based nature, as well as to evaluate their performance as acoustic and thermal insulators.
The study was conducted on different scales of the hemp wool panels development, starting from bulk hemp fibers, passing to hemp wool prototypes and ending with hemp wool panels produced on a pilot scale. In the first step, phytic acid and urea were chosen as flame retardants, due to their bio-based origin and accessibility, respectively. Then, two different application methods were tested, immersion and pulverization, aiming for an efficient and scalable treatment. The treatment was able to graft phosphorus molecules into the hemp fibers, which significantly reduced their flammability. A slight reduction in the fibers’ sound absorption capacity was observed, linked to a small increase in the estimated fiber radius from the Tarnow model. No significant changes were observed in the thermal conductivity of these samples.
At the prototype scale, small hemp wool panels, containing hemp and synthetic fibers as binder, were produced using a simplified method. Four different concentrations of flame retardants and two treatment methods were tested: by treating all fibers before the panel’s fabrication, or only their surfaces after the panel’s fabrication. It was observed that the surface treatment was not enough to significantly reduce the flammability of the hemp wools, as their interior still burned intensely. Therefore, the chosen treatment method consisted of hemp wools treated before panel production with 5% phytic acid and 15% urea, which were used in the production of a fireproof treated hemp wool at an industrial scale. In the acoustic side, the characteristic parameters of the pore network of the hemp wools were obtained by direct measurements or by the inversion of the JCAL model. A reduction in porosity, airflow resistivity, and slight changes in the thermal characteristic parameters of the pore geometry led to a reduction in their sound absorption performance.
In conclusion, the production of fireproof treated hemp wools is feasible, and a significant reduction in their flammability can be achieved by the use of phytic acid and urea. A slight reduction in sound absorption is observed, however, they remain excellent absorbers suitable for acoustic correction. The thermal conductivity did not significantly change directly with the treatment, but rather indirectly due to changes in the apparent density.