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

The variations of the permeation rate of ethanol in ethanol-water mixt ures through poly(vinylalcohol) membranes of different crystallinities were studied in the transient regime. We observed an anomalous two-wa ve kinetics, which was accounted for in terms of a model postulating t wo diffusion-pathways for ethanol molecules in the polymer. One wave c orresponds to the permeation of ethanol through the amorphous polymer matrix, which occurs whatever the water content in the mixture. The ot her 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 molecul es through clusters formed with the water molecules sorbed on the hydr oxyl sites.