Characteristics of chitosan membranes modified by argon plasmas

Dense chitosan membranes were prepared and studied for surface modification using argon plasma produced at low pressures from 6.67–133.3 Pa with RF frequencies at a power ranging from 6–90 W. Glutaraldehyde and sulfuric acid in methanol were used as linking reagents before the plasma treatment. When the plasma density was fixed at conditions of 6 W and 49 W at 66.7 Pa, the membrane wettability was measured as a decrease in contact angle between the water drop and the membrane surface. Water swelling properties were increased in glutaraldehyde cross-linked membrane. It was found that the ionic permeability of the membranes did not depend linearly on the plasma density used. The density at 6 W was smaller than that produced at 49 W, but it increased the Cl− to K+ permeability ratio of the membranes by 1.4–1.8 times, with the maximum increase found in glutaraldehyde cross-linked membranes. Results from AFM showed that plasma treatment caused roughness at the membrane surface, and consequently, the hydraulic permeability of the membranes was reduced. Moreover, results from ATR-FTIR showed a major increase in the absorption spectra of CO, C–H, and C–O functional groups. The results were similar for the sulfuric acid cross-linked and the control membrane. In contrast, a glutaraldehyde cross-linked membrane was not affected greatly by plasma treatment. This study indicates that surface modification by argon plasma leads to changes in filtration characteristics and ionic permeability of chitosan membranes.