Joachim Wolff

Tailoring of ultrafiltration membranes by plasma treatment and their application for the desalination and concentration of water-soluble organic substances

Abstract Commercially available asymmetric ultrafiltration membranes (M.W. cut-off: 8000 and 20,000) were treated in a bell jar reactor with a resistively coupled audiofrequency plasma. Using NH 3 as discharge gas NH 2 groups were created on the membrane skin. These NH 2 groups were converted with acylating agents (e.g. trichlorotriazine derivatives). For the concentration and desalination of water-soluble organic substances (M.W. ≤ 1000) which tend to form associates in solution this conversion was carried out by association-inducing derivatives of trichlorotriazine. This modification yields ultrafiltration membranes with higher retention and higher solvent flux than untreated membranes, allows real dry handling of the membrane (without pore fillers), decreases compaction, but leaves salt permeation unchanged. The formation of a secondary membrane by associated solute molecules supported by the fixed association-inducing groups is assumed to be responsible for the improved membrane performance.