Improving the pervaporation performance of the glutaraldehyde crosslinked chitosan membrane by simultaneously changing its surface and bulk structure

Preparation of CS-based membranes by pre-drying a chitosan/glutaraldehyde (CS/GA) solution for a certain time, followed by an acetone-immersion treatment, allowed the bulk characteristics of the resulting acetone-immersed CS (CSA) membranes to be changed. A decrease in pre-drying time resulted in that the degree of crystallinity was significantly decreased and the mobility of the polymer chains was less restricted. Pervaporation results indicated that the flux increased significantly and the water selectivity decreased with a decrease in pre-drying time. With an increase in relaxation time or degree of crystallinity, the activation energy of the pervaporation process (Ep) experienced an approximately linear increase. The permselectivity of the CSA membrane prepared with a shorter pre-drying time was further improved by introducing carboxyl groups onto its surface. For separating 90% ethanol/water mixtures at 60 °C, the surface-modified CSA membrane showed a separation factor of 500 and a flux of 400 g/m2 h, which are about 5 and 1.6 times greater, respectively, compared to the corresponding crosslinked CS membrane without bulk and surface modification. This indicates that the combination of bulk modification and surface functionalization is an effective approach for simultaneously improving the flux and selectivity of polymeric membranes.