3.3. Water Vapor Permeability (WVP), Sorption and Diffusion

The water vapor permeability of the obtained films was determined by the gravimetric method (Debeaufort, Martin-Polo and Voilley, 1993) [55]. An RH difference of (50–100%) at a temperature of 25 ± 1 °C was used. At least three replicates were performed for each film type, and the WVP was determined at steady state and from the change in the cell mass as a function of time.

The water vapor sorption kinetics were measured after 0.5, 1, 3, 6, 9, 12, 24, 48, 72, 96 and 120 h under constant temperature of 25 °C and relative humidity of 75.3%. For each type of film, at least 3 repetitions were performed. The kinetic curves were plotted as graphs showing the dependence of the change in the amount of adsorbed water on the time of the process.

The water vapor diffusion coefficient was estimated by approximation and valid for the used testing conditions only according to the method described by Galus et al. [56] based on Fick’s second law (Crank, 1975) [57].