Surface characteristics of ionically crosslinked chitosan membranes

In this study, homogenous dense chitosan membranes were prepared by solution-casting procedure. Then the membranes were ionically crosslinked by sulfu- ric acid. The surfaces of chitosan membranes before and after crosslinking were characterized by using FTIR-ATR, X-ray photoelectron spectroscopy (XPS), and atomic-force microscopy (AFM) techniques. The XPS data suggest that the surface composition of crosslinked membrane does not change significantly with respect to uncrosslinked membrane and the most important evidence is a certain amount of sulfur, coming from the crosslinker. The resultINTRODUCTIONChitosan is a copolymer of b-(1?4)-linked 2-acet- amido-2-deoxy-D-glucopyranose and 2-amino-2-deoxy- D-glucopyranose.1 This polysaccharide polymer has re- active hydroxyl and amino groups for various chemical modifications.2 In recent years, chitosan is receiving attention as a pervaporation membrane material as the active skin layer due to its high affinity to water, good membrane forming properties, easy modification, and good chemical stability.3–5 The pervaporation perform- ance for alcohol dehydration3–6 and dimethyl carbonate (DMC) separation7 have been investigated using chito- san and modified chitosan membranes. In those applica- tions, membrane modifications have been reported including crosslinking,6–8 blending,9 multilayer cast- ing,10 and chemical modification.11,12 Among these, crosslinking is one of the most effective approach for improving membrane stability and increasing separa-from FTIR-ATR data shows the effectiveness of the cross- linking procedure by the shift in amide I and amide II bands. The investigation of membrane surfaces by AFM indicates that the crosslinking procedure modifies the surface morphology of chitosan. After crosslinking, the surface topography becomes more homogenous and rela- tively flat.