STATES OF SOLVENTS ABSORBED IN SEMICRYSTALLINE FILMS IN POLYVINYL-ALCOHOL .2. SWELLING IN WATER-ETHANOL MIXTURES

Poly(vinyl alcohol) (PVA) films of various crystallinities were swollen to equilibrium by water ethanol, water-1-butanol and water-1-octanol mixtures and studied by DSC. At low crystallinities, PVA films may be so swollen in the range of 60-90 wt% of water in mixtures with ethanol that they become completely dissolved. At very high crystallinities, the swelling ratio was limited and no maximum was observed. This behaviour is attributed to the impermeability of the crystallites, together with their cross-linking action. Depending on the swelling ratio, there may be up to three states of the sorbed liquid: viz. non-freezable liquid and two types of freezable liquids with one type probably in the same state as the liquid mixture in equilibrium with the films. The same PVA film, especially when its crystallinity is low, may show different swellings in the two liquid phases in thermodynamic equilibrium; again, sorbed liquid which is identical to the liquid mixture was found, indicating that there is in the swollen polymer a liquid phase which has penetrated the films without selectivity (or interactions with the polymer chains).