Submitted to: Bio Environmental Polymer Society
Publication Type: Abstract only
Publication Acceptance Date: 10/17/2007
Publication Date: 10/17/2007
Citation: Shogren, R.L. 2007. Effect of orientation on the physical properties of amylose and high amylose starch films [abstract]. Bio Environmental Polymer Society. Paper No. 67. Interpretive Summary:
Technical Abstract: There has been much interest in starch-based materials since starch is made from a renewable agricultural feedstock, is inexpensive, and is biodegradable. Starch films are, however, rather brittle and water sensitive and this limits their usefulness for many applications. A flexible, semi-water resistant starch film or fiber could have applications in numerous areas such as consumer packaging, personal hygiene articles, paper, etc. Orientation is known to result in improvement in strength and flexibility of many types of polymer films and fibers. 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 example, birefringence of oriented amylose films was approximately 0.04 compared to about 0.004 for oriented high amylose corn starch films. For amylose films, orientation resulted in two and three fold increases in tensile strength and elongation, respectively, 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% as 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.