Mechanical properties with respect to water content of gelatin films in glassy state

Changes on the structural and molecular level of gelatin films induced by hydration below 25±3% water content (glass-rubbery transition at ambient temperature) were identified with DSC and FTIR spectroscopy. Three main stages of hydration were distinguished: (I) water bound by high-energy sorption centres; (II) structural water; (III) polymolecular layer water. The mechanical behaviour of gelatin films at each stage of hydration was characterized. Relaxation of the films during hydration was taken into account in the analysis of results. Hydrated gelatin films were characterized as brittle below the glass-rubbery transition at ambient temperature, however some improvement of mechanical properties related to a higher renaturation level was showed between 7 and 14% of water content in stage II (structural water).