Thermodynamic of moisture vapor sorption and mechanical properties of methylcellulose and ethylcellulose based films to predict its stability

Abstract

The thermodynamic parameters of moisture adsorption isotherms and the mechanical behavior of ethylcellulose (EC) and metylcellulose (MC) polymer-based films were studied. The experimental isotherms were well fitted using the GAB equation with E < 10%. 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 values for MC. Pore radius values of the films ranged from 0.49 to 352.56 nm, which corresponds to the micropores and mesopores classification. As the moisture content and temperature increased, the pore radius also increased. Compensation enthalpy-entropy in films showed that the water vapor adsorption phenomena was driven by entropy at low aw values. Mechanical analysis of films equilibrated at different aw conditions (0.11–0.90) showed constant values of tensile strength and elongation to break for films at aw values between 0.1 and 0.6, where also the minimum of entropy was reached, confirming that thermodynamic properties could be used to predict the stability of films. The study of thermodynamic water adsorption and the mechanical properties allows understanding the preparation process of stable films with adequate parameters intended for food packaging materials.