Morphology Control of Polysulfone Membranes in Filtration Processes: a Critical Review Amira Abdelrasoul [1],* , Huu Doan [1] , Ali Lohi [1] , Chil-Hung Cheng [1] www.ChemBioEngRev.de ª 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ChemBioEng Rev 2015, 2, No. 1, 22–43 22 Abstract Polysulfone (PSU) membranes have been widely ap- plied in microfiltration and ultrafiltration processes due to their excellent properties, such as chemical inertness across the entire pH range, compressive strength, and thermal stability. Despite these advan- tages, the application of PSU membranes in filtra- tion processes has often been restricted due to their hydrophobic nature, which results in serious mem- brane fouling and a reduced permeate flux. More- over, PSU membranes suffer from several disadvan- tages, including bulky structure, low binding force between fibers, and poor mechanical properties. The key factor in the development and application of polymeric membranes is the control of its poly- meric morphology due to the significant influence of membrane morphology on the membrane perfor- mance. Effective techniques of controlling PSU membrane morphology are accessed, and the effects of the morphological control on mechanical proper- ties, chemical stability, membrane performance, and membrane fouling are investigated. Findings from various individual studies were analyzed and dis- cussed in order to provide a critical review of this subject. The results emphasized that the membrane pore size and surface porosity mostly governs PSU membrane morphology, which enhances membrane performance and reduces membrane fouling. Keywords: Polysulfone membrane, Morphology, Pore size, Porosity, Performance, Fouling Received: October 17, 2014; revised: November 18, 2014; accepted: November 19, 2014 DOI: 10.1002/cben.201400030 1 Introduction Polysulfone (PSU) has numerous excellent properties, such as chemical inertness on the entire pH range, compressive strength, thermal stability (150–170 °C), and mechanical strength (fracture, flexure, torsion), and as such is one of the most popular synthetic polymer materials used for the fabrica- tion of membranes [1–2]. In the recent past, PSU membranes have been widely applied to micro-/ultra-filtration, gas separa- tion, pervaporation, hemodialysis, plasma separators, mem- brane oxygenators, cell culture, and bio artificial organs [3–6]. The market share for the PSU membrane use is continuously increasing, for instance, the PSU is the most widely used mem- brane for CO 2 /CH 4 separation process due to its low price, chemical stability, and mechanical strength. The world market for natural gas is estimated at approximately US-$ 22 billion annually and as it keeps growing, the market for PSU mem- brane technology will be increasing as well [7]. Compared to cellulose acetate, PSU has lower CO 2 permeability and CO 2 / CH 4 selectivity but higher plasticization pressure, the pressure at which the permeability starts to increase with increasing the penetrant concentration or pressure [7]. Plasticization pressure becomes important in practice due to its effect on membrane selectivity with high CO 2 feed concentration or on high operat- ing pressure [7]. Nevertheless, applications of the PSU mem- branes in the filtration of aqueous solutions are often limited because of their hydrophobic nature which results in a low per- meate flux and significant membrane fouling. Moreover, PSU membranes suffer from a number of disadvantages, such as bulky structure, low binding force between fibers, and poor mechanical properties. The thermodynamic, rheological and adsorptive properties have been found to significantly change with its surface modification [8–9]. The surface modification and post-treatment of PSU mem- branes has become a popular subject for discussion among re- searchers. In particular, there are three different directions in the process of modification and post-treatment. First, to introduce the hydrophilic group to the surface layer by coating, adsorp- tion, plasma treatment, pH treatment, and surface grafting poly- merization, so as to increase the hydrophilicity of PSU mem- branes [10–13]. Second, to promote the performance of the PSU membrane by adding the hydrophilic substance into the PSU preparation solution to gain a hydrophilic blend membrane ————— [1] Dr. Amira Abdelrasoul (corresponding author), Prof. Huu Doan, Prof. Ali Lohi, Prof. Chil-Hung Cheng Department of Chemical Engineering, Ryerson University, 350 Vic- toria Street, Toronto, Ontario, M5B 2K3, Canada. E-Mail: amira.abdelrasoul@ryerson.ca