Preparing highly porous chitosan/cellulose acetate blend hollow fibers as adsorptive membranes: Effect of polymer concentrations and coagulant compositions

In this work, we report the study on the effect of fabrication factors influencing the structures and morphologies of the chitosan and cellulose acetate blend hollow fibers as adsorptive membranes to achieve highly porous and macrovoids-free structures with different pore sizes. The factors investigated include chitosan (CS) and cellulose acetate (CA) concentrations in the spinning dope solutions, and the composition of the external and internal coagulants. For CA concentration at 12-18 wt% and CS concentration at up to 4 wt% in the spinning dope solutions, the blend hollow fibers were successfully prepared with outer surface pore sizes, specific surface areas and porosities in the range of 0.54-0.049 mu m, 10.4-14.5 m(2)/g and 80.6-70.4%, respectively, depending on the CA and CS amounts in the spinning dope solutions and the coagulants used. Water, a weaker coagulant, can be used as both the external and internal coagulants in the fabrication process and the resultant CS/CA blend hollow fibers showed spongy-like, macrovoids-free and relatively uniform porous structures which are desirable for adsorptive membranes. By increasing the alkalinity of the coagulants, the coagulation rate of the blend hollow fibers was increased and the hollow fibers were observed to form relatively denser surface layers and to have smaller surface pore sizes and slightly greater specific surface areas, due to the stronger coagulation effect. Particularly, when NaOH solutions (1-3 wt%) were examined as the internal coagulant, more and larger macrovoids were formed in the blend hollow fibers at the near lumen side with the increase of the NaOH concentrations at low CS concentrations (< 3 wt%), indicating the importance of coagulant compositions and polymer concentrations in the fabrication of adsorptive CS/CA blend hollow fibers with uniform porous structures. (c) 2006 Elsevier B.V. All rights reserved.