WVTR was determined gravimetrically using a
modified ASTM Method E96-95. Film specimens were mounted
horizontally on poly(methylmethacrylate) cups filled with distilled
water up to 1 cm underneath the film.
The cups were placed in
an environmental chamber at 25 ◦C and 50% RH with air current
movement at 198 m/min. The cups were weighed every hour for a period of 8 h. The slopes of the steady-state (linear) portion of weight loss versus time curves were used to calculate WVTR.
In calculating WVP, effect of the resistance of the stagnant air layer
between the film undersides and the surface of the water in the
cups was corrected using the method of Gennadios and others
(1994).
Water contact angle (CA). The CA of water in air