Characterization of cross-links introduced in gelatin

Abstract

A method for the determination of the effectiveness of gelatin hardeners was proposed. Formaldehyde (FA) and 1,3-bis (vinylsulfonyl)-2-propanol (BVSP) were used as cross-linking agents for the hardening of gelatin. The cross-linked gelatin showed a typical rubber elasticity in a swollen state with a mixed solution composed of concentrated aqueous LiBr and diethylene glycol monoalkyl ether. The energy components to total retractive forces were below 0.3. The amount of intermolecular cross-links was estimated by applying an usual rubber elasticity theory for the swollen samples. The number of cross-linking sites was also determined by the amino acid analysis of BVSP cross-linked gelatin. The cross-linking efficiency for the reaction of BVSP occurring in a casting film with less swelling conditions was about four times higher than in a swollen gel. Approximately 92% or more of BVSP used was reacted with the free amino groups of lysine and arginine residues. There was a significant difference between the reactivities of these amino groups. The amino groups of lysine residues were more reactive than those of arginine in a gel state; the reactivities, however, reversed in a thin layer of wet film. The effectiveness of FA was extremely low. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1879–1892, 1997