Oriented gelatin - A new source for high-performance materials

Two types of gelatin with different gel-forming capabilities (''bloom values'') were used in a novel processing technique to improve their mechanical properties when in the form of films. Networks consisting of the water-soluble gelatin chains were prepared by diisocyanate crosslinking in 2,2,2-trifluoroethanol-in which gelatin forms no collagen folds (physical junctions) at room temperature. The liquid-crystalline behavior of both the uncrosslinked gelatin and its networks were studied with regard to the effects of molecular weight and nature of the solvent. Mechanical property measurements indicated dramatic increases in tensile strength, tensile modulus, and toughness after drying the swollen films under stain, both uniaxial and equi-biaxial. The improvements in mechanical properties were determined as a function of polymer concentration at stretching, elongation during drying, and molecular weight of the gelatin. In all cases the improvements increased monotonically with the increase of elongation during drying. Furthermore, equi-biaxial orientation resulted in almost twofold improvements in tensile strength and modulus compared to those from uniaxial orientation (at essentially the same extension ratio during drying). Additional characterization, in terms of the extent of ordering in these oriented networks, was obtained from birefringence measurements. In overall performance the oriented gelatin films can be described as tough plastics, with tensile strengths between 65 and 140 MPa and elongations at break of 15-20%.