DSC and TGA studies of the behavior of water in native and crosslinked gelatin

Water molecules absorbed into gelatin are found to be only partially crystallizable. The fraction of noncrystallizable water depends on whether the gelatin is native or crosslinked, and on the crosslinking conditions as well. This dependence is explained by the Tg-regulation effect newly proposed by Rault and coworkers for water-swollen gelatin cooled below 0°C. According to this effect, a part of the frozen water cannot crystallize because during the cooling the amorphous gelatin–water phase becomes glassy before the water crystallization temperature is reached. During the heating of water-plasticized gelatin samples in a TGA cell, the crystallizable water separates from the gelatin, mainly in the temperature interval 50–100°C, whereas the noncrystallizable water leaves the gelatin gradually over the entire temperature interval investigated, up to 300°C.