Chemical interactions and yellowing in chitosan-treated cellulose

The chemical interactions between cellulose and chitosan were studied in chitosan-treated celluloses using diffuse reflectance spectroscopic techniques (UV–Vis and FTIR) and fluorescence spectroscopy. The materials were obtained by treating pure cotton cellulose with chitosan in dilute acetic acid solutions of different concentration, and some samples were exposed to different thermal treatments in air. Other related materials, including cellulose treated with benzyl amine and chitosan-treated with acetaldehyde, were also prepared and studied as models for chitosan-treated celluloses. The spectra of the treated celluloses showed new absorption and emission bands that revealed the existence of chemical interactions. These bands were assigned to conjugated imines produced in the reaction of the chitosan amino groups with cellulose carbonyl groups. The reaction is strongly amplified at temperatures above 100 °C, causing the intense yellowing of chitosan-treated celluloses.