The determination of isosteric heats of sorption of leather: Experimental and mathematical investigations

Knowledge of sorption isotherms of leather products is necessary to control rehydration/dehydration and storage processes and it is valuable tool for prediction of the stability and shelf life of products but the impact of the controlled climate on moisture sorption isotherms of leather remains unclear. The aim of this work is to predict moisture desorption isotherms of leather of bovine variety. The static gravimetric method was used to determine sorption isotherms at four temperatures (30, 40, 50 and 60 °C) and the equilibrium moisture content of leather samples was measured within the range of 5–90% relative. All the curves exhibited type II behavior, according to Brunauer’s classification. Equilibrium moisture contents are observed to drop as the temperature is enhanced. Many models available in the literature were used to describe the experimental data. The agreement between experimental and calculated sorption isotherms is seen to be satisfactory (correlation coefficients from 0.93 to 0.99). Furthermore, DENT model is found to be the most appropriate for describing the relationship between the equilibrium moisture content, the water activity and temperature. On the other hand, the isosteric heats of desorption were determined from sorption isotherms and then correlated with corresponding equilibrium moisture contents. Besides, the isosteric heats of desorption decreased continuously with increasing of the equilibrium moisture content.