Chitosan derivatives with thickening properties obtained by reductive alkylation

Chitosan derivatives were prepared by reductive alkylation using glutaraldehyde and 3-amino-1-propanol. The reducing agent used was sodium borohydride. Tests of solubility, stability and viscosity were performed to evaluate the effect of the molar ratio of the reactants and the presence of nitrogen in the reaction system. The 1H NMR characterization of chitosan derivatives confirmed the presence of hydrophobic groups grafted onto the chitosan backbone. The rheological behavior of the polymers was studied as a function of polymer concentration, temperature and ionic strength of the medium. It was observed that the chemical modification of chitosan resulted in derivatives with thickening action, and the polymer solubility in acetic acid aqueous solution decreased with the increase of the glutaraldehyde and 3-amino-1-propanol molar ratio in relation to chitosan. The atmosphere of nitrogen and a larger amount of reducing agent in the reaction system contributed to the increase in solubility, stability and viscosity of the polymer in solution. The chitosan derivative solutions were significantly more viscous than the chitosan solution and showed higher thermal stability in the presence of salt, which could be explained by the hydrophobic groups grafted onto the chitosan backbone.