Modification of chitosan films with environmentally benign reagents for increased water resistance

Abstract

Chitosan is a non-toxic, renewable, abundant natural material with excellent film-forming properties. It is shown here that water absorption by chitosan films can be decreased by chemical modification with the bio-based reagents citric acid and glycerol. Infrared spectroscopy showed that citric acid reacted with chitosan amine groups to form an acyclic amide structure. Glycerol imparted flexibility and water repellency to the films. When soaked in water for six hours, a chitosan–citric acid–glycerol (1:1:9) film absorbed 44% water by weight after initial exposure and remained unchanged for the duration of the experiment. In comparison, a pure chitosan membrane initially absorbed 70% water and gradually increased to 96%. After soaking, the modified film swelled by only 11% compared to 42% for pure chitosan. Similar results were observed for water contact angle with the film surfaces. For the modified film, change in contact angle over time could be attributed solely to evaporation, whereas the pure chitosan film absorbed the droplets. These results show that the properties of chitosan can be improved using environmentally benign reagents in accordance with green chemistry principles.