Abstract
Equilibrium water sorption isotherms were obtained for ethylene-vinyl alcohol copolymers (EVA) with a wide variety of hydroxyl contents to examine the sorptive capacity of EVA polymers as a function of hydroxyl content. The state of water molecules sorbed by EVA was investigated using the clustering function.
The larger was the hydroxyl content of EVA, the higher was the sorptive affinity toward water. The molar ratio of water sorbed to hydroxyl content varied linearly with hydroxyl content over the whole range of relative humidity studied. The BET sorption mechanism was obeyed by this EVA-water system in the relative humidities ranging from about 20 to 44%.
At low humidities, the clustering function was larger than -1 for each EVA. This indicates that there is a tendency for water molecules to cluster in these polymers. The clustering function showed a minimum at about 30% relative humidity where the amount of water sorbed by EVA is equal to that required for monolayer to be formed.
