DIFFERENTIAL PERMEATION .2. BEHAVIORS OF POLYVINYLALCOHOL FILMS IN TRANSIENT PERMEATION

The variations of the permeation rate of ethanol in ethanol-water mixtures through poly(vinylalcohol) membranes of different crystallinities were studied in the transient regime. We observed an anomalous two-wave kinetics, which was accounted for in terms of a model postulating two diffusion-pathways for ethanol molecules in the polymer. One wave corresponds to the permeation of ethanol through the amorphous polymer matrix, which occurs whatever the water content in the mixture. The other wave appears only when the water content in the mixture exceeds a threshold. The higher the crystallinity, the higher the value of this threshold. This wave is attributed to the diffusion of ethanol molecules through clusters formed with the water molecules sorbed on the hydroxyl sites.