Thermodynamics of Moisture Vapor Sorption and Mechanical Characterization of Methylcellulose and Ethylcellulose Based Films

The thermodynamic parameters of moisture sorption isotherms and the mechanical behavior of ethylcellulose and methylcellulose based films were studied. The GAB equation was used to describe the sorption isotherms. The thermodynamic analysis showed that the minimum integral entropy value was found in the 0.1–0.6 range of water activity (aw) in both types of films, being the lower range for methylcellulose. Compensation enthalpy–entropy theory showed that the water vapor sorption was mainly driven by entropy at low aw values. Mechanical analysis of films equilibrated under different aw conditions (0.22–0.90) showed constant values of tensile strength and elongation to break for films in the region where the minimum of entropy was reached, indicating that thermodynamic properties could be used as one criterion to describe the mechanical stability of films intended for food packaging applications.