PBI-BuI and PAN-PSSALi based UF membranes: Effects of solute and membrane surface interactions on rejection and flux Deepti Bhagat 1 , Bhavana Mule 1 , Neeraj Mandlekar 1 , Kiran Pandare 1 , Ulhas Kharul ⁎ Polymer Science and Engineering Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India HIGHLIGHTS • Ultrafiltration type of porosity generated in PBI-BuI based membranes • H-bonding interactions between PEG and PBI led to considerable fouling and flux reduction. • Presence of PEG on PBI membrane surface was established by different tools. • PAN-PSSALi membrane surface showed lower PEG-membrane interactions. abstract article info Article history: Received 21 August 2013 Received in revised form 16 November 2013 Accepted 19 November 2013 Available online 15 December 2013 Keywords: Ultrafiltration Polybenzimidazole Rejection Gel permeation chromatography Solute adsorption Ultrafiltration membrane using tert-butylpolybenzimidazole (PBI-BuI) was prepared and characterized for flux and rejection performance using Gel Permeation Chromatography (GPC). Polyethylene glycol (PEG) and polyeth- ylene oxide (PEO) with different molecular weights were used as the solutes. While using feed solution contain- ing mixture of PEGs, higher rejection was observed than using individual PEG. The water flux of PBI-BuI membrane after passing individual PEG solutions showed considerable (~36%) reduction, which could be attrib- utable to the PEG adsorption on the membrane pore surface. PEG adsorption was further substantiated by SEM, IR and TGA. The amphoteric nature of PBI-BuI could cause H-bonding between membrane surface and PEG mole- cules, leading to PEG adsorption on the membrane and pore surface. To ascertain this postulation, a study with PAN-PSSALi (which does not contain H-bonding) based UF membrane containing negatively charged \SO3 - group was done. It was found that PEG adsorption in this case is not as predominant as in earlier case. This mem- brane showed marginal reduction in water flux of 8%, vis-à-vis 36% reduction shown by PBI-BuI based mem- brane. This indicated that H-bonding present in PBI-BuI is mainly responsible for the PEG adsorption on its membrane and pore surface, in spite of PEG being a neutral molecule. © 2013 Elsevier B.V. All rights reserved. 1. Introduction In porous membranes, especially of ultrafiltration and nanofiltration type, flux and rejection properties are primarily governed by pore size, their density and surface morphology. Chemical nature of polymer used for making the membrane plays a key role in governing these pa- rameters. It has been well documented in the literature that water- soluble macromolecules adsorb readily on the polymeric ultrafiltration membranes [1]. Polybenzimidazole (PBI) to be used as a membrane ma- terial is attracting considerable attention due to its excellent thermo- chemical and mechanical stability [2–4]. Although polybenzimidazole based membranes are known in the literature, they are mostly nanofiltration (NF) type [2,5,6]. Rejection analysis of these membranes was carried out using neutral solutes with the help of Total Organic Carbon (TOC) analysis as an analytical tool [2,5,6]. Recently, Xing et al. could obtain PBI-based ultrafiltration membrane while casting mem- brane at elevated temperature. The rejection analysis of these mem- branes was done using TOC [7]. The determination of rejection/molecular weight cut off (MWCO) is one of the popular methods to characterize the membrane pore size. The MWCO is obtained by plotting rejection of selected solutes versus their molar mass [8]. The solutes have to satisfy certain criteria such as minimal interactions with the membrane surface, availability of incre- mental molar masses, good solubility in the solvent used for membrane characterization (usually water) and narrow molecular weight distribu- tion. Various solutes and methods have been suggested for the determi- nation of MWCO of porous membranes [9]. These need to be employed under different analytical conditions, depending upon the nature of the solutes used. Commonly used solutes are polyethylene glycols (PEGs) [8], dextrans [9], proteins [10], cephalexin [2] etc.; while majorly used analytical tools are UV spectroscopy [10], Gel Permeation Chromatogra- phy (GPC) [9,11], HPLC with evaporative light scattering detection [12], Desalination 333 (2014) 45–51 ⁎ Corresponding author. Tel.: +91 20 2590 3015; fax: +91 20 2590 2615. E-mail address: uk.kharul@ncl.res.in (U. Kharul). 1 Tel.: +91 20 2590 3015; fax: +91 20 2590 2615. 0011-9164/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.desal.2013.11.036 Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal