Antimicrobial films produced from chitosan.

Antimicrobial films were prepared by dissolving chitosan into hydrochloric, formic, acetic, lactic and citric acid solutions. Below 40 degrees C, the counter ions could be classified into two groups based on their effect on zero-shear-rate viscosity in 2% solutions of organic acids. Chloride and citrate produced solutions with much lower viscosities than formate, acetate and lactate. At higher temperatures, these differences vanished, and the activation energies of viscous flow were all similar between 40 and 60 degrees C. Films prepared from these solutions were evaluated in tension for Young's modulus, stress and elongation at yield and break points. Films made from hydrochloric, formic and acetic acids were hard and brittle, whereas those from lactic and citric acids were soft and could be stretched. Good correlation was found between Young's modulus and volume of the counter ion. Film properties are essentially governed by the volume of the counter ion and not by the interactions between this counter ion and the macromolecule. Results suggest that acetate has the maximum molecular volume above which the film strength decreases very rapidly.