Macro-initiator mediated surface selective functionalization of ultrafiltration membranes with anti-fouling hydrogel layers applicable to ready-to-use capillary membrane modules

• Novel macro-initiator enables selective grafting modification of hidden surfaces.
• Protective polyzwitterionic hydrogel layers reduce fouling of capillary membranes for water treatment.
• Surface-selective functionalization of ultrafiltration membranes in ready-to-use modules is feasible.

A new process for surface selective graft modification of ultrafiltration (UF) membranes with protective hydrogel layers was developed. The process uses a random copolymer of n-butylmethacrylate and N,N-dimethylaminoethylmethacrylate as a redox co-initiator (“macro-initiator”). Due to its molecular weight, the macro-initiator is completely rejected by the used Multibore® polyethersulfone UF membranes. Zwitterionic [3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl) ammonium hydroxide and bifunctional N,N′-methylenebis(acrylamide) were used as monomers for “macro-initiator”-mediated, surface selective cross-linking polymerization toward anti-fouling hydrogel layers. The functionalization comprises two main steps; i) adsorption of the macro-initiator to the barrier layer surface of the membrane, e.g. during a short ultrafiltration; ii) grafting of the hydrogel layer after bringing the membrane in contact with a solution containing monomer(s) and a dissolved initiator (here ammonium persulfate) which is complementary to the co-initiator for a predetermined reaction time at room temperature. Hydrogel-grafted flat sheet and capillary UF membranes showed dextran sieving curves shifted to lower molecular weight values, increased total organic carbon rejection and improved anti-fouling behaviour in filtration tests with flower soil extract as model foulant. Furthermore, stability tests with sodium hydroxide and hydrogen peroxide solutions showed good chemical stability of graft-functionalized membranes. The obtained results are very promising for future applications, since the presented technique can be applied in ready-to-use membrane modules and capillary membranes easily.

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