Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2002
Publication Date: 11/1/2003
Citation: Taylor, M.M., Liu, C., Marmer, W.N., Brown, E.M. 2003. Enzymatic modification of hydrolysis products from collagen using a microbial transglutaminase. III. preparation of films with improved mechanical properties. Journal of American Leather Chemists Assocation. 98(11):435-444. Interpretive Summary: Gelatin can be obtained from the processing of tannery waste, but that gelatin needs further processing to serve as a commercially useful material. We had shown that films prepared from commercial gelatins that had been modified using environmentally benign enzymes had improved strength, were tougher and less soluble in water than unmodified gelatin films. In the present study, we attempted to further improve these films. Stretching the films in one direction during drying has been described as a method to improve mechanical properties and we found that the strength improved significantly when this stretching took place on either unmodified or enzyme-modified gelatin films. We further demonstrated that the temperature of drying affects mechanical properties in that drying at or near room temperature gave products with significantly higher strength over those products that had been dried at a higher temperature. Finally, we demonstrated that when polyvinyl alcohol, a biodegradable plastic compound that has been routinely used in preparation of gelatin composites, was added to the gelatin mixture, products were obtained that had good strength and were tough. In all studies, it was found that by modifying the gelatin with enzymes, the resulting products were superior and still almost totally biodegradable. These studies will help to identify potential markets for waste products from the tanning industry.
Technical Abstract: Previous work from this laboratory demonstrated that films prepared from gelatins that had been enzymatically modified with microbial transglutaminase had improved tensile strength and toughness, were less soluble in water than gelatin alone and had improved hydrophilic properties. In the present study, our goal was to further enhance functional properties of the enzymatically prepared films and at the same time determine if biodegradability is retained. Orienting films has been described as a method to improve mechanical properties. We found that tensile strength, maximum strain, and Young's Modulus improved significantly when orientation took place on either unmodified or crosslinked dry gelatin films or on films that were swollen in water and then were subsequently dried in the strained position. We further demonstrated that the temperature of drying affects mechanical properties; drying at ambient temperature gives products with significantly higher tensile strength and reduced strain over those products that had been dried at a higher temperature. Furthermore, we found that mechanical properties of strained and unstrained films, dried at ambient temperature, will give similar tensile strengths, thus indicating the importance of careful drying in film preparation. Finally, when polyvinyl alcohol was added to the gelatin mixture, films with improved tensile strength and maximum strain were obtained. In all studies, not only was biodegradability demonstrated but it was also found that by enzymatically modifying the gelatin, the resulting products were superior.