CONTROL OF PORE SIZES IN MACROPOROUS CHITOSAN AND CHITIN MEMBRANES

A novel method for the preparation of macroporous chitosan and chitin membranes is suggested, which employs silica particles as porogen. The macroporous chitosan membranes were prepared by (1) casting an acidic chitosan solution that contains silica particles, (2) removing the so lvent by evaporation, and (3) dissolving the silica particles by immer sing the membranes into an alkaline solution. This simple method provi des chitosan membranes with high porosity and satisfactory mechanical strength, the pore sizes of which can be easily controlled by varying the size of silica particles. The effects of various evaporation condi tions and amount of silica on the flow rate of water through the membr anes were investigated. In order to prevent their dissolution in acidi c solutions, the chitosan membranes were cross-linked under alkaline c onditions, using epichlorohydrin as the cross-linking agent. Macroporo us chitin membranes were prepared by acetylating the chitosan membrane s with acetic anhydride in methanol. In contrast to the uncross-linked chitosan membranes, which are soluble in dilute acidic solutions and insoluble in alkaline solutions, the chitin membranes are insoluble bo th in acidic and basic solutions. Both kinds of membranes can be emplo yed in affinity or ion-exchange bioseparations.