Journal of Membrane Science 326 (2009) 627–634 Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci Effect of preparation variables on morphology and pure water permeation flux through asymmetric cellulose acetate membranes Ehsan Saljoughi, Mohtada Sadrzadeh, Toraj Mohammadi ∗ Research Centre for Membrane Separation Processes, Faculty of Chemical Engineering, Iran University of Science and Technology (IUST), Narmak, Tehran, Iran article info Article history: Received 19 July 2008 Received in revised form 28 October 2008 Accepted 29 October 2008 Available online 5 November 2008 Keywords: Cellulose acetate Ultrafiltration membranes PEG additive Phase inversion Taguchi abstract In this study, cellulose acetate (CA) ultrafiltration (UF) membranes were prepared using the phase inver- sion method. Effects of CA and polyethylene glycol (PEG) concentrations in the casting solution and coagulation bath temperature (CBT) on morphology of the synthesized membranes were investigated. Based on L 9 orthogonal array of Taguchi experimental design 18 membranes were synthesized (with two replications) and pure water permeation flux through them were measured. It was found out that increasing PEG concentration in the casting solution and CBT, accelerate diffusional exchange rate of solvent 1-methyl-2-pyrrolidone (NMP) and nonsolvent (water) and consequently facilitate formation of macrovoids in the membrane structure. Increasing CA concentration, however, slows down the demix- ing process. This prevents instantaneous growth of nucleuses in the membrane structure. Hence, a large number of small nucleuses are created and distributed throughout the polymer film and denser mem- branes are synthesized. Rate of water flux through the synthesized membranes is directly dependent on the size and number of macrovoids in the membrane structure. Thus, maximum value of flux is obtained at the highest levels of PEG concentration and CBT (10 wt.% and 23 ◦ C, respectively) and the lowest level of CA concentration (13.5wt.%). Analysis of variance (ANOVA) showed that all parameters have significant effects on the response. However, CBT is the less influential factor than CA and PEG concentrations on the response (flux). © 2008 Elsevier B.V. All rights reserved. 1. Introduction Membrane separation processes offer a number of advantages in terms of less energy requirements, environmental impacts and capital investments. The processes are also simple and easy to operate and need compact equipment. Hence, they have recently demonstrated a significant industrial role in terms of economical considerations and been used in a wide range of applications such as supply of high quality water, removal or recovery of toxic or valu- able components from various industrial effluents and also food and pharmaceutical industries [1–3]. The most important part of a membrane separation process is the membrane itself and polymeric membranes are the most com- mon ones used in the membrane processes. In fact, all polymers can be used as barrier or membrane material but the chemical and physical properties differ so much that only a limited number are used in practice [4]. Among the different polymeric materials, cel- lulose acetate (CA) is very convincing, with characteristics such as good toughness, high biocompatibility, good desalting, high poten- ∗ Corresponding author. Tel.: +98 21 77240496; fax: +98 21 77240495. E-mail address: torajmohammadi@iust.ac.ir (T. Mohammadi). tial flux and relatively low cost [5–8], thus it has been widely used for reverse osmosis, ultrafiltration (UF), microfiltration and gas sep- aration. Also CA membranes have excellent hydrophilicity that is very important in minimizing fouling [9–13]. There are several ways to prepare porous polymeric membranes, such as solution casting, sintering, stretching, track etching and phase inversion. The final morphology of the membrane obtained varies greatly, depending on the properties of materials and the process conditions utilized [14]. The phase inversion process induced by immersion precipita- tion is a well-known technique to prepare asymmetric polymeric membranes [15–19]. By immersion of a substrate in a coagulation bath, solvent in the casting solution film is exchanged with non- solvent in the precipitation media and phase separation occurs. This process results in an asymmetric membrane with a dense top layer and a porous sublayer. The sublayer formation is con- trolled by numerous variables in the polymer dope solutions such as composition, coagulant temperature and organic/inorganic additives. To attain a desired membrane morphology and perfor- mance, the phase inversion process must be carefully controlled [20]. In this study, effects of CA and polyethylene glycol (PEG) concentrations and coagulation bath temperature (CBT) on the 0376-7388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2008.10.044