Temperature effect on the moisture sorption isotherms for methylcellulose and ethylcellulose films

Moisture sorption isotherms were obtained at 9°C, 15°C, 20°C, 25°C and 35°C for methylcellulose (MC) and ethylcellulose (EC) films following the normalized microclime method. Cast MC and EC film samples were equilibrated to 0.22, 0.44, 0.57, 0.75, and 0.90 aw values. MC films had an equilibrium moisture content about five times higher than the EC films. The Guggenheim–Anderson–deBöer (GAB) and Brunauer–Emmett–Teller (BET) equations were fitted to the experimental data using nonlinear regression. The regression coefficient (R2) used to evaluate model fit showed a best fit for the GAB model. The monolayer moisture content (xm) decreased with temperature and correlated better with values calculated using the BET equation.