THERMAL-PROPERTIES OF WATER-INSOLUBLE ALGINATE FILMS CONTAINING DIVALENT AND TRIVALENT CATIONS

Water insoluble alginic acid (Alg) films were prepared by replacing th e sodium ions (Na+) of sodium alginate (NaAlg) with di- and trivalent cations, such as Cu2+, Al3+, Fe3+, etc. Dope concentration and degree of substitution (DS) were changed in order to prepare various types of alginate films. Glass transition temperature (T-g), heat capacity (C- p) and C-p difference at T-g (Delta C-p) of the Alg films in the dry s tate were investigated by differential scanning calorimetry (DSC). Wit h increasing ionic radius of cations, T-g of dry films decreased. In c ontrast, C-p's of alginate films in the glassy state and Delta C-p inc reased. The non-freezing water content (W-nf) in alginate films in the wet state was also estimated by DSC using enthalpies of melting and c rystallization of water. W-nf in the films increased with increasing i onic radius. These results indicated that alginate molecules form a mo re tightly cross linked structure with decreasing ionic radius. Struct ural change of alginate films during ion exchange was also investigate d based on the change of T-g, C-p and W-nf values as a function of DS.