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Propriétés mécaniques, structure interne et mécanismes de transfert de l'oxygène dans le liège

Abstract : During the post bottling aging, premature oxidation reactions could occur and the oxygen barrier properties of the stopper are often pointed out. Nowadays, the internal structure of this material or the effect of hydration on its mechanical properties are still undetermined. Moreover, regarding the barrier properties, the limiting step of the oxygen transfer was not yet fully understood as well as the effect of compression or the role of the glass/cork interface in a bottleneck. The study of the internal structure of cork stopper allowed us to visualize the macroporosity of the material and conclude that there is no interconnectivity between lenticels, for the two qualities studied. The effect of hydration on the mechanical properties of cork was also investigated. The results shown that the rigidity of the material was not significantly affected for relative humidity < 50 %. Above this hydration level, the Young’s moduli decrease due to clusters formation of water molecules. Comparing the natural cork behavior to other stoppers, an effect of the particle size and the ratio cork/additives used in these stoppers was also highlighted. Regarding the transport mechanism of gas through cork, the limiting step was clearly determined: it’s the diffusion through the cell wall according to a Fickian mechanism. The compression of the stopper does not have a significant impact on the effective diffusion coefficient of oxygen. However, the role of the glass/cork interface is really important and seems to govern the gas transfer from the surrounding atmosphere into the bottle.
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Aurélie Lagorce-Tachon. Propriétés mécaniques, structure interne et mécanismes de transfert de l'oxygène dans le liège. Alimentation et Nutrition. Université de Bourgogne, 2015. Français. ⟨NNT : 2015DIJOS073⟩. ⟨tel-01375902⟩

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