STATES OF SOLVENTS ABSORBED IN SEMICRYSTALLINE FILMS IN POLYVINYL-ALCOHOL .1. SWELLING IN WATER

Poly(vinyl alcohol) films of various crystallinities were swollen to different degrees by water and studied in DSC. At low swelling (<24%), the absorbed water cannot be frozen. On further swelling, there was first a solvent phase freezing at lower temperature than the normal freezing point of water, then a solvent phase freezing in a similar manner as liquid water. The latter phase would correspond to liquid-like water confined in dynamic pores. Non-freezable water appears only when about one water molecule was bound to every hydroxyl site in the amorphous region. The equilibrium swelling decreases drastically with increasing crystallinity of the film, indicating that the crystalline regions are impermeable and are capable of acting as physical cross-links.