SORPTION AND TRANSPORT OF WATER-VAPOR IN ALGINIC ACID, SODIUM ALGINATE, AND ALGINATE-COBALT COMPLEX FILMS

The sorption and the transport of water vapor in films of alginic acid (G1), sodium alginate (G1Na), and alginate-cobalt complex (G1Co) were studied at 30-degrees-C by employing the weighing method. Sorption isotherms for all films of G1, G1Na, and G1Co were to type II in the Brunauer's classification. The integral absorption from, and desorption to, zero pressure were non-Fickian type for all films studied. The mean permeability coefficient PBAR, which was determined by the cup method, increased with the increase of vapor pressure, especially in the low vapor pressure region. PBAR for G1Na was much higher than that for G1, which mainly reflects more hygroscopic nature of G1Na than that of G1. The values of PBAR for G1Co were lower than those for G1 at lower pressures and then approached those for G1 at higher vapor pressures. Integral diffusion coefficient DBAR evaluated as PBAR/S, where the solubility coefficient S was evaluated from sorption isotherms, increased rapidly with increasing water concentration and then leveled off. In the concentration region studied, the magnitude of DBAR and its dependence on concentration for H2O-G1Na system did not differ much from those for H2O-G1 system. DBAR for H2O-G1Co system was much lower than that for H2O-G1 system. (C) 1994 John Wiley & Sons, Inc.