The effect of the temperature of preparation on the mechanical properties and structure of gelatin films

Gelatin films prepared by evaporation from aqueous solution at temperatures of 60°C and above differ considerably in structure and mechanical properties from films dried slowly at 20°C, when gelling precedes dehydration. In the high-temperature preparation dehydration precedes the formation of a continuous structure, and X-ray and other evidence indicates that the molecular chains are in a disordered contracted state not far removed from their condition in the sol. The high-temperature film is characterized by low strength and high recoverable extension under conditions of high relative humidity. In the low-temperature preparation the greater degree of crystallization has partially extended the molecular chains, and the unidirectional contraction of the film on drying has oriented them in the plane of the film. This film exhibits thermal contraction in hot methanol, and is stronger, but at high humidity is much less extensible, than the high-temperature preparation.