2.4.4. Water vapor permeability (WVP) measurement
The gravimetric method based on the ASTM method E96-
95 (1995) with some modifications (McHugh, Avena-Bustillas, &
Krochta, 1993) was employed to determine WVP. Each film sample
without defects was sealed over a circular opening of 0.0032 m2 in
a permeation cell (inner diameter = 63.5 mm, height = 25 mm) that
was stored at 25 ◦C in a glass chamber. In order to maintain a 75%
RH gradient across the film, anhydrous CaCl2 (0% RH) was placed
inside the cell and a saturated NaCl solution (75% RH) was added to
the glass chamber. The RH inside the cell was always maintained
lower than outside, and water vapor transport was determined
from the weight gain of the permeation cell. At steady-state conditions
(after 2 h) permeation cells were weighed for the first time
and at regular time intervals over a 24-h period. The water vapor
permeability of the samples was determined in triplicate with the
following equation: