The effect of crystallinity and aging enthalpy on the mechanical properties of gelatin films

In this study the mechanical properties of gelatin films were evaluated for gelatin with varying amounts of structural gelatin (crystallinity) and aging enthalpy, which results from drying gelatin solutions under different conditions. The mechanical properties of a gelatin film were measured by the uniaxial tensile testing and the optical microscopy of the fractured films. Differential scanning calorimetry was used to measure crystallinity, and aging enthalpy was obtained from the thermogramic peak area of the corresponding transition. Gelatin films with crystallinity of less than 5 J/g failed predominantly by brittle cracking fracture regardless of its aging enthalpy. However, for gelatin films with crystallinity of around 10 J/g, shear yielding was the dominant deformation mechanism for small aging enthalpy (<3 J/g) while samples with larger aging enthalpy deformed by brittle cracking. For gelatin films with the largest crystallinity (>15 J/g), deformation was caused predominantly by shear yielding irrespective of the aging enthalpy. A fracture mechanism map based on its crystallinity and aging enthalpy for gelatin films was constructed.