Mechanical Properties of Cork : Effect of Hydration
Résumé
The use of cork as sealing for wine bottles is due to its low permeability to liquids and gases, imputrescibility and good mechanical properties, in particular its remarkable elasticity [1]. We focused in this study on the compression properties of cork along the radial or the tangential direction at 298 K when cork is stored under various relative humidity environments, from 0 to 100 %.
All stress-strain curves were characterized by an elastic region up to approximately 5 % strain, followed by a large plateau up to 60 % strain caused by the progressive buckling of cell walls.
Firstly, it is worthy to note that the direction of compression significantly affects the Young modulus, with a higher value in radial compression, as already reported by Anjos and Pereira [2,3]. This corresponds to the orientation of the lenticels, which reinforces the rigidity of the material when the strain is applied along their growth direction.
More surprising is the effect of water sorption in cork on its mechanical properties. Both radial and tangential direction exhibit the same behavior, characterized by an increase in the Young modulus up to around 50 % relative humidity and followed by a decrease in rigidity. Maximum observed values are 46.9±8.1 MPa and 22.1±2.0 MPa for radial and tangential directions, respectively. Below that point, the increase in water content leads an antiplasticizing effect while above it gives a more classical plasticizing effect. This is in favor of the existence of an amorphous fraction in cork which goes across the glass transition in this relative humidity range.
1. Mano, J.F. 2002. The viscoelastic properties of cork. Journal of Membrane Science. 37(2), 257-263.
2. Anjos, O., Pereira, H., Rosa, M.E. 2008. Effect of quality, porosity and density on the compression properties of cork. European Journal of Wood and Wood Products. 66(4), 295-301.
3. Pereira, H., Graca, J., Baptista, C. 1992. The effect of growth-rate on the structure and compressive properties of cork. Iawa Bulletin? 13(4), 389-396.
Domaines
Ingénierie des aliments
Origine : Fichiers produits par l'(les) auteur(s)