Apparent Water Vapor Permeability (WVP)
The WVP metal cups received from Kansas State Univ.
with an open mouth area of 33 cm2 were filled with distilled
water with an air gap of 2.5 cm from the film specimen. Film
samples were placed over the open mouth of metal cups and
tightly sealed symmetrically with six screws onto the cups.
Cup weights were recorded fifteen times at 30 min intervals
for seven hours in a Mettler AE 163 balance. WVP was measured
in chamber at 23 8C, and at 55% relative humidity. The
linear regression-derived slopes were used to estimate water
vapor transmission rate and WVP measurements were performed
as described