Hollow fiber membrane lumen modified by polyzwitterionic grafting Ngoc Lieu Le a , Mathias Quilitzsch b , Hong Cheng a , Pei-Ying Hong a , Mathias Ulbricht b,n , Suzana P. Nunes a,nn , Tai-Shung Chung a,c,n a King Abdullah University of Science and Technology (KAUST), Biological and Environmental Science and Engineering Division (BESE), Thuwal 23955-6900, Saudi Arabia b Lehrstuhl für Technische Chemie II, Universität Duisburg-Essen, 45117 Essen, Germany c Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore article info Article history: Received 2 May 2016 Received in revised form 13 August 2016 Accepted 21 August 2016 Available online 22 August 2016 Keywords: Fouling Poly(sulfobetaine) Zwitterionic Grafting Pressure-retarded osmosis abstract In this study, we demonstrate an effective way to modify the lumen of polyetherimide hollow fibers by grafting zwitterionic poly(sulfobetaine) to increase the membrane resistance to fouling. Surface-selective grafting of the protective hydrogel layers has been achieved in a facile two-step process. The first step is the adsorption of a macromolecular redox co-initiator on the lumen-side surface of the membrane, which in the second step, after flushing the lumen of the membrane with a solution comprising monomers and a complementary redox initiator, triggers the in situ cross-linking copolymerization at room temperature. The success of grafting reaction has been verified by the surface elemental analyses using X-ray photoelectron spectroscopy (XPS) and the surface charge evaluation using zeta potential measurements. The hydrophilicity of the grafted porous substrate is improved as indicated by the change of contact angle value from 44° to 30°, due to the hydration layer on the surface produced by the zwitterionic poly(sulfobetaine). Compared to the pristine polyetherimide (PEI) substrate, the poly(sul- fobetaine) grafted substrates exhibit high fouling resistance against bovine serum albumin (BSA) ad- sorption, E. coli attachment and cell growth on the surface. Fouling minimization in the lumen is im- portant for the use of hollow fibers in different processes. For instance, it is needed to preserve power density of pressure-retarded osmosis (PRO). In high-pressure PRO tests, a control membrane based on PEI with an external polyamide selective layer was seriously fouled by BSA, leading to a high water flux drop of 37%. In comparison, the analogous membrane, whose lumen was modified with poly(sulfobetaine), not only had a less water flux decline but also had better flux recovery, up to 87% after cleaning and hydraulic pressure impulsion. Clearly, grafting PRO hollow fiber membranes with zwitterionic polymeric hydrogels as a protective layer potentially sustains PRO performance for power generation. & 2016 Elsevier B.V. All rights reserved. 1. Introduction Membrane fouling is a major obstacle to the practical applica- tions of membrane-based techniques such as ultrafiltration, na- nofiltration, reverse osmosis, forward osmosis and pressure-re- tarded osmosis. While inorganic scaling by calcium salts on membrane surfaces can be managed by controlling pH and using antiscalants [1], membrane fouling by organic compounds is more challenging and generally requires an intensive pretreatment step. To prevent organic fouling, surface modification with hydrophilic polymers has been identified as a potential strategy because many organic foulants are hydrophobic in nature. A thin layer of hy- drophilic polymers can be attached on membrane surfaces through coating or grafting techniques. The latter is more efficient in long-term operations because the grafted layer is anchored on the surfaces and hence no delamination occurs. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science http://dx.doi.org/10.1016/j.memsci.2016.08.038 0376-7388/& 2016 Elsevier B.V. All rights reserved. Abbreviations: AIBN, 2,2´-azobis(2-methylpropionitrile); APS, ammonium per- sulfate; BMA, butylmethacrylate; BSA, bovine serum albumin; BSA-FITC, fluorescein isothiocyanate-conjugated bovine serum albumin; DEG, diethylene glycol; DMAE- MA-co-BMA, (2-dimethyl amino) ethyl methacrylate-co-butyl methacrylate; DMAEMA, 2-(dimethylamino)ethylmethacrylate; DMF, dimethylformamide; FES- EM, field emission scanning electron microscope; MBAA, N,N-methylene bisacry- lamide; NMP, N-methyl-pyrrolidone; NMR, nuclear magnetic resonance; PDI, polydispersity index; PEG, poly(ethyleneglycol); PEI, polyetherimide; PES, poly- ethersulfone; PRO, pressure-retarded osmosis; SPP, 3-((3-methacrylamidopropyl) dimethylammonio)propane-1-sulfonate; TFC, thin film composite; XPS, X-ray photoelectron spectroscopy n Corresponding authors. nn Correspondence to: King Abdullah University of Science and Technology (KAUST), Biological and Environmental Science and Engineering Division (BESE), Thuwal 23955-6900, Saudi Arabia. E-mail addresses: mathias.ulbricht@uni-essen.de (M. Ulbricht), suzana.nunes@kaust.edu.sa (S.P. Nunes), chencts@nus.edu.sg (T.-S. Chung). Journal of Membrane Science 522 (2017) 1–11