Abstract
Water in polymer gels is known to remain sometimes unfrozen during cooling to turn into a glassy state, and to crystallise during subsequent warming. As the behaviour is likely to be influenced by the change in the polymer network, i.e., by the density of crosslinks, and freezing and drying are both dehydration processes from around the polymer moieties besides, drying and water adsorption of crosslinked dextran gels were investigated from the viewpoint of their dependency on the density of crosslinks. The adsorption isotherm indicated that the amount of adsorbed water is more for gels with lower crosslink density, and lay below the desorption isotherm. The extent of the hysteresis was more remarkable with gels with lower crosslink density. The rate of drying was slower with gels with lower crosslink density around the water content of 50 wt%. These results can be explained by considering that the polymer network in gels with lower crosslink density is more flexible than those with higher crosslink density and change easily during water adsorption or drying, and that water in gels with lower crosslink density is trapped readily by the polymer network as a result of its change during drying.
