Water state in chemically and physically crosslinked chitosan membranes

Chemically and physically crosslinked chitosan membranes were prepared by treating chitosan (Ch) with glutaraldehyde (GA) and sulfuric acid (SA). FTIR and XRD results were employed to confirm the formation of covalent and ionic crosslinks between Ch, GA, and SA. The states of water in non-crosslinked and covalently and ionically crosslinked chitosan membranes containing different amount of water were investigated by low temperature differential scanning calorimetry measurements. The equilibrium swelling in water was examined gravimetrically. Two types of water were found in the polymer samples, i.e., freezing water and non-freezing water. The effect of crosslinking process on water state and water uptake was analyzed. The water uptake decreased after chitosan crosslinking with GA, but significantly increased after later crosslinking with SA. The amount of non-freezing water was generally smaller in crosslinked membranes. An impact of molecular and supermolecular structure on water uptake and state of water in non-crosslinked and crosslinked chitosan membranes was discussed. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1707-1715, 2013