Effect of sodium acetate and drying temperature on physicochemical and thermomechanical properties of gelatin films

The aim of this work was to evaluate the effect of sodium acetate (NaOAc) on the physicochemical properties of gelatin films with different leveling of triple helical structure. Films were obtained by casting method and dried at two temperatures (25 and 35 °C). Drying at 25 °C improved physical properties and increased the formation content of triple helix. The plasticizing effect of NaOAc was shown from typical stress–strain curves with the features of ductile materials. Dynamic mechanical thermal analysis (DMTA) also confirmed the thermomechanical properties of the films and revealed the decrease of glass transition temperature (Tg) with increasing NaOAc content. The increase of moisture content or decrease in intermolecular forces because of the existence of NaOAc might be attributed to the plasticizing effect. Films with NaOAc showed a higher capacity to absorb water compared to those without NaOAc at higher relative humidity (75% and 97%). All these gelatin films exhibited dominant elastic behavior (than viscous behavior) over the entire frequency range (0.1–100 Hz) at any loading content of NaOAc but the compactness of films was changed. X-ray diffraction (XRD) and water contact angle (WCA) revealed that the NaOAc crystals were dissolved in the gelatin matrix. These results may cause the extensive concern for the effects of salts (organic or inorganic) on films because salts exist widely.