(168d) Controlled Graft Polymerization as a Tool for Membrane Surface Modification

Two methods of grafting hydrophilic chains onto the membrane surface were investigated. In Bulk method membranes were transferred into the solutions of the oxidizing agent, monomer and chain transfer agent respectively for the modification to take place. In the other method called drop method membrane was held flat and above mentioned solutions were added to the membrane sheet in a drop-wise manner so that entire membrane is exposed to reagents and thereby results in the formation of a modified surface. Performance of the membranes modified by the above methods and the virgin membrane are compared. With respect to flux decline, during operation, the initial fluxes for the virgin, bulk-modified and drop-modified membranes averaged 75, 81 and 95 L/sq.m-hr, respectively. While all membranes experienced a decline in flux during the 6-hour Dextran operation time, the drop-modified reached a steady flux that was higher than the initial flux of either the virgin or the bulk-modified membranes. Therefore, the drop modification produced a superior membrane with respect to transport properties. It is hypothesized that the increase in flux for both modification methods was due to the increase in hydrophilicity (i.e. PEG addition). We believe that the drop method keeps modification to the surface of the membrane only instead of pores, which accounts for greater effects.