Key Factors Affecting the Manufacture of Hydrophobic Ultrafiltration Membranes for Surface Water Treatment Huyen T. Dang, 1 Dipak Rana, 2 Roberto M. Narbaitz, 1 Takeshi Matsuura 2 1 Department of Civil Engineering, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5 2 Department of Chemical and Biological Engineering, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5 Received 27 July 2009; accepted 7 November 2009 DOI 10.1002/app.31739 Published online 27 January 2010 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: As part of the development of poly(ether sulfone) (PES) membranes whose surface is modified by the incorporation of a newly synthesized hydrophobic sur- face modifying macromolecule (nSMM) additive, this study investigates the impact of four key membrane prep- aration factors. They are concentration of PES, concentra- tion of nSMM, casting thickness, and casting speed. The synthesis and characterizations of nSMM by nuclear mag- netic resonance, gel permeation chromatography, differen- tial scanning calorimeter, and elemental analysis have been presented. The changes in characteristics and per- formance of the membranes have been evaluated via Fou- rier transform infrared spectroscopy, contact angle analysis, scanning electron microscopy, and solute trans- port tests. The addition of 0.5 wt % of nSMM increased the contact angle of PES membranes by 20  ; however, higher nSMM concentrations did not increase the hydro- phobicity any further. Only the additive concentration had a statistically significant impact on flux reduction and dis- solved organic carbon rejection. Even though other factors such as membrane thickness may alter the pore character- istics, their effect on membrane performance was mar- ginal. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2626– 2637, 2010 Key words: polymeric membranes; hydrophobic additive; key modification factors; solute rejection; mathematical model INTRODUCTION Porous integrally asymmetric membranes are often made by the phase inversion method. 1,2 This method is applied mainly in the preparation of membranes for dialysis, microfiltration (MF), and ultrafiltration (UF). Most commercial UF membranes are cast via this technique using a multicomponent solution con- taining polymer(s), solvent(s), and nonsolvent(s) or additive(s). In many cases, the pore characteristics (porosity and pore size) and skin layer morphology are modified by blending additives to the casting so- lution. 3 The additives can be inorganic salts (e.g., LiNO 3 , LiCl, and ZnCl 2 ), organic polymers (e.g., poly(vinyl pyrrolidone) (PVP), poly(ethylene glycol) (PEG), sulfonated poly(ether ether ketone), metha- cryloyloxyethylphosphorylcholine (MPC) copolymer, and poly(amide imide) (PAI)), or nanoparticles (e.g., TiO 2 and Al 2 O 3 ). 4–12 Although PVP or PEG acts as a surface modifying additive, their effects are tempo- rary because they are water soluble and eventually leach out from the modified membrane. Since the 1990s, our research group has been involved in the development of different types of hydrophobic sur- face modifying macromolecules (SMMs) to modify the membrane surface more permanently. Earlier studies with a hydrophobic SMM incorporation 13–15 did not result in a significant impact on membrane performance for drinking water treatment probably because of insufficiently migration of the particular SMM additive. A more rapidly migrating SMM has been developed (called as nSMM) for the prepara- tion of pervaporation membranes. 16 The lead author’s doctoral research plan included a compari- son of the impact of hydrophobic/hydrophilic sur- face modification on the effectiveness of membrane cleaning. This manuscript however reports solely the preparation and performance of the more hydropho- bic PES-nSMM membranes. It is reported in the literature that the formation of membranes made by phase inversion technique depends on a number of material- and process-spe- cific parameters including type and amount of base polymers, solvents, type and amount of additives, casting thickness, casting speed, post-treatment, con- ditions (temperature and composition) of the coagu- lation bath, and drying conditions. 17 This article investigates the impact of four key preparation fac- tors including concentration of PES, concentration of Correspondence to: R. M. Narbaitz (narbaitz@uottawa.ca). Contract grant sponsors: Vietnam Government (Vietnamese Overseas Scholarship Programs-VOSP), Natural Sciences and Engineering Research Council of Canada (NSERC), Ministry of the Environment (MOE), Ontario, Canada. Journal of Applied Polymer Science, Vol. 116, 2626–2637 (2010) V C 2010 Wiley Periodicals, Inc.