New polypropylene supported chitosan NF-membrane for desalination application Mahesh Padaki a , Arun M. Isloor a, ⁎, Jenifer Fernandes b , K. Narayan Prabhu c a Membrane Technology Division, Department of Chemistry, National Institute of Technology-Karnataka, Surathkal, Mangalore 575 025, India b Department of Chemical Engineering, National Institute of Technology-Karnataka, Surathkal, Mangalore 575 025, India c Department of Metallurgical and Materials Engineering, National Institute of Technology-Karnataka, Surathkal, Mangalore 575 025, India abstract article info Article history: Received 27 March 2011 Received in revised form 10 May 2011 Accepted 5 June 2011 Available online 3 September 2011 Keywords: Chitosan Water flux Salt rejection Polypropylene support In the present study, a new NF membrane was prepared by coating chitosan on polypropylene fiber support, by the dissolution of chitosan in 2% acetic acid solution. The resulting membrane was characterized by thermo gravimetric analysis, water absorption, contact angle measurement and scanning electron microscopy. Prepared membrane showed two Tg peaks, one at ~90 °C that was due to chitosan and the other peak at ~ 170 °C that was corresponding to the supporting polypropylene membrane. The membrane showed a low swelling ratio at pH 7, 9, and 11 as compared with pH 5. The performance of the membrane was assessed out using dead end cell. Water flux was studied at different pressures. The salt rejection study was done using NaCl solution and the effect of pH on performance of the membrane was also examined. Newly prepared membrane showed improved water flux, and % of rejection is highest in acidic pH and lowest in basic pH. Hydrulic permeability coefficient and the dielectric constant confirms that the prepared membrane is nanofiltration membrane. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Chitosan is a significant biomaterial that has been known from a long time. It is a polysaccharide mainly composed of the b(1–4)-2-amino-2- deoxy-D-lucopyranose (D-glucosamine) repeating unit and includes a small amount ( b 20%) of N-acetyl-D-glucosamine (GlcNAc) residues. The material is natural and environmentally safe. Its applications are being found in the fields of health care, food, beverages, cosmetics, toiletries, agriculture, waste and water treatment, product separation, recovery and immobilization and also for cell culture. Membranes prepared from chitosan have been developed for solution filtering, which can improve the qualities of feed solution. Chitosan membranes are being used in separation techniques such as ultrafiltration and reverse osmosis [1,2]. The membrane process is governed by a size exclusion mechanism, solute-solute and solute-membrane interactions that are dependent on membrane surface characteristics such as hydrophilic/hydrophobic balance, electrostatic charges on both membranes, and on the solute [2,3]. Chitosan in the acidic pH range is positively charged due to protonation of –NH 2 groups [4]. However the protonation leads to the dissolution of the material in the organic acid at low pH. In ammonia atmosphere, de-protonation of the polymeric chain occurs. Chitosan causes the fine sediment particles to bind together and is subsequently removed with the sediment during sand filtration. Chitosan also removes phosphorus, heavy minerals, and oil from the water. It is an important additive in the filtration process. Sand filtration apparently can remove up to 50 % of the turbidity alone, while the chitosan with sand filtration removes up to 99% turbidity. Previous researchers [5] have discovered that the lower hydro- philic property of chitosan often leads to problems in performance such as mechanical strength. To further enhance the performance of chitosan membranes, chondroitin sulfate (CS) was utilized to modify the chitosan membranes for preparing composite membranes with better hydrophilicity and biological compatibility [5]. Chemical modification of chitosan is not a easier process because of its insoluble nature in most of the solvents. In membrane technology, membranes with high tolerance to mechanical strain are very desirable. Chitosan membrane with suitable support is much preferred in membrane technology for the filtration applications, instead of chitosan mem- brane alone due to its high tolerance to mechanical stress. These findings have prompted us to study more about preparation and properties of polypropylene supported chitosan membrane for better water desalination. We studied the effect of feed solution pH on the performance of membrane. Contact angle measurement, water uptake study (to have an idea about the hydrophilicity of the membrane), morphology, water flux and dielectric characterization of the membrane are discussed. 2. Experimental 2.1. Membrane preparation Chitosan (degree of Deacytylation75%) from Sigma Aldrich (M w = 20000 Da) and polypropylene support were used for the membrane preparation. Polypropyle support was Cranemat KC, which Desalination 280 (2011) 419–423 ⁎ Corresponding author. Fax: + 91 824 2474033. E-mail address: isloor@yahoo.com (A.M. Isloor). 0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.06.032 Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal