2.7. Water vapor permeability
Water vapor permeability (WVP) was gravimetrically measured according to a modified standard method [27],
and was corrected for the stagnant air gap inside test cups according to the equations of Gennadios et al. [28]. Special
glass cups with wide rims were used to determine WVP. Anhydrous calcium chloride (80 g) was used as the desiccant.
Briefly, circles (with an area of 28.27 cm2) without pinholes or defects were cut from the films and sealed to
the cup mouths using molten paraffin wax. Each cup was placed in a desiccator and maintained at 75% RH with a
sodium chloride saturated solution. This difference in RH corresponds to a driving force of 1753.55 Pa, expressed as
water vapor partial pressure. After mounting the specimens, the weight gain of the whole assembly was recorded
every 1 h during the first 9 h and finally after 24 h (with an accuracy of 0.0001 g). The cups were horizontally shaken
after every weighing. The slope of weight versus time plot (the lines’ regression coefficients were >0.998)was divided
by the effective film specimen area to obtain the water