Dry-RO membranes from blends of ionogenic and nonionogenic polymers

Abstract

In earlier studies it was shown that the performance characteristics of Dry-RO membranes could be improved by the addition of quaternary ammonium groups to the cellulose acetate (CA) from which the membranes were fabricated. The initial approach employed only modified CA with ion exchange capacities (I.E.C.s) between 0.1 and 0.2 meq/g and carried with it the related disadvantages of high cost and poor reproducibility. These problems have now been overcome by blending polymers with I.E.C.s ⪢ 0.2 meq/g with neutral CA to yield membranes with an average I.E.C. of 0.2 meq/g. Although certain noncellulosic ionogenic polymers such as the quaternized polycaprolactone polyols were found to be compatible with CA, the best practical membranes to date are those in which the triethylammonium salt of CA 11-bromoundecanoate is utilized as the ionoqenic polymer in the blend.