35 – García Fernández, F., de Palacios, P.,  García Esteban, L., García-Iruela, A., González-Adrados, J.R., López Alvarez, J.V. Sorption and thermodynamic properties of cork from the 35ºC and 50ºC isotherms. Bois et Forêt des Tropiques. 311(1): 63-74.

Abstract: Because of its characteristics, cork currently has no substitute in the bottle stopper industry for high quality wines and champagnes. Few studies have been conducted on water-cork relations, particularly the thermodynamic behaviour of cork. The hygroscopicity and thermodynamic properties of two cork samples of the same quality, harvested in 1968 and 2006, were studied to determine any differences in behaviour caused by the passing of time. The 35ºC and 50ºC isotherms were plotted following the saturated salts method and fitted using the GAB model. The isotherms were compared through the hysteresis coefficients. The infrared spectra were recorded to study the chemical changes in the cell wall, and the thermodynamic parameters were determined using the integration method of the Clausius-Clapeyron equation. No significant differences were observed between the equilibrium moisture content obtained in the two samples, although the monolayer saturation moisture content was significantly lower in the older cork. In both types of cork, as occurs in wood, the points of inflexion where multilayer sorption begins to predominate over monolayer sorption occurred at very similar values, around 31-35% RH. In terms of the thermodynamic properties, the net isosteric heat curves were similar to those obtained in wood, and the bond energy in the recently harvested cork was lower than in the older cork.