Thermodynamic properties and modeling of sorption isotherms for longer storage of Urtica urens leaves

Moisture equilibrium data of Urtica urens leaves by desorption and adsorption were determined at 30, 40, and 50°C. The isotherms were determined by a static gravimetric method for various temperature and humidity conditions. Five mathematical models were used to fit the experimental data. A nonlinear least-squares regression program was used to evaluate the constants of the five desorption and adsorption isotherm models GAB and Modified Halsey models were adequate to describe the sorption characteristics of the samples. Isosteric heats of desorption and adsorption were calculated by applying the Clausius-Clapeyron equation to the sorption isotherms at different temperatures. It decreased with increasing moisture content. We recognized the linear relation exists between the enthalpy and entropy of the sorption reaction.