2.6.3. Water Vapor Permeability (WVP)

The WVP of the zein fiber and bilayer films was performed according to the standard ASTM E 96/E 96M-16 [38]. Thus, the samples were sealed in permeation cells containing anhydrous calcium chloride and stored in desiccators with a relative humidity of 50% at room temperature. The permeation cells were weighed on the first day and after seven days to determine the calcium chloride mass gain. The results were quantified using Equation (2) and expressed as g m⁻¹ Pa⁻¹ s⁻¹.

where, Wa is the amount of absorbed water (g), t is the total analysis time (s), l is the average film thickness (m), A is the area of the exposed film surface (m²), and ΔP is the partial vapor pressure difference across the samples (Pa).