Water vapor transport parameters of a cast wheat gluten film

Understanding the mode of transport of water vapor through the film is important for improving the moisture barrier properties of wheat gluten (WG) films. Effective permeability ( P eff), solubility ( S eff), and diffusion ( D eff) coefficients of a hydrophilic cast WG film were determined at 25°C within the relative humidity (RH) range of 0–84% (with a 9–13% RH gradient between upstream and downstream water vapor flux). P eff, S eff, and D eff increased substantially as the RH gradient moved upwards in the RH spectrum. P eff increased by four orders of magnitude from the lowest RH condition of 0–11% (3.8×10 −11 g·m/m 2·s·Pa) to the highest RH condition of 75–84% (4.1×10 −7 g·m/m 2·s·Pa). A moisture sorption isotherm of the film at 25°C was constructed. Both the Guggenheim–Anderson–DeBoer (GAB) and the Kuhn moisture sorption isotherm models showed a good fit to the experimental adsorption data. Testing of WG films at the expected conditions of actual use is necessary to quantify the water vapor permeation through the films.