Submitted to: Biomacromolecules
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/27/2007
Publication Date: 11/1/2007
Citation: Shogren, R.L. 2007. Effect of orientation on the physical properties of amylose and high amylose starch films. Biomacromolecules. 8:3641-3545. Interpretive Summary: There has been considerable interest recently in developing starch-based fibers and films for use as biodegradable packaging and hygiene products. Such biobased products are desirable since they are made from a renewable, agricultural commodity produced in the U.S. (corn) rather than imported oil. However, starch based materials are typically brittle and rather water sensitive. This research has demonstrated that stretching starch films so that the starch molecules are pointed in one direction (oriented) gives films that are much more flexible. An easy method to assess the degree of orientation was also developed. In addition, it was found that treating the starch films under hot, humid conditions gives much improved water resistance. These results should help companies and university scientists develop new starch-based materials for disposable consumer products.
Technical Abstract: The effect of orientation on the properties of amylose and starch films was studied in order to determine if film strength, flexibility and water resistance could be improved. Potato amylose and high (70%) amylose cornstarch were peracetylated, cast into films, stretched in hot glycerol 1-6 times the original length and deacetylated. Molecular orientation of amylose films was much higher than for high amylose starch films as determined by optical birefringence. For amylose films, orientation resulted in large increases in tensile strength and elongation but little change in modulus. For high amylose starch films, tensile strength and modulus did not change with draw ratio but elongation to break increased from about 8% to 27% draw ratio increased from 1 to 5. Scanning electron micrographs revealed many small crazes in the drawn starch films, suggesting that the improved film toughness was due to energy dissipation during deformation of the crazes. Annealing of drawn films at 100% humidity resulted in partial crystallization and improved wet strength.