Ionic interactions between sulfuric acid and chitosan membranes

Treatment of chitosan with crosslinking agents is a common strategy for improving the performance of chitosan membranes in industrial applications. The preparation of sulfuric acid-crosslinked chitosan membranes was studied by infrared spectroscopy, elemental analysis, and X-ray diffraction, to better understand the mechanism of sulfuric acid treatment. The results indicated that first H2SO4 protonated the chitosan amine groups, then the SO42- anions slowly interacted with chitosan NH3+ groups to form ionic bridges between the polymer chains. Kinetic analysis showed that protonation was the rate-limiting factor in the adsorption of sulfuric acid by the membrane. The strong interactions between chitosan NH3+ groups and SO42- anions were related to changes in membrane crystallinity. Protonation of 10-mu m-thick chitosan membranes by 0.01 M sulfuric acid was accomplished within 5 min and complete ionic crosslinking required 30 min. The results of this study suggest better guidelines for treating chitosan membranes with divalent and multivalent acids. (C) 2008 Published by Elsevier Ltd.