Ageing of polyethersulfone ultrafiltration membranes under long-term exposures to alkaline and acidic cleaning solutions Enrique Antón a , José R. Álvarez a , Laura Palacio b , Pedro Prádanos b , Antonio Hernández b , Arto Pihlajamäki c , Susana Luque a,n a Department of Chemical and Environmental Engineering, University of Oviedo, 33071 Oviedo, Spain b Surfaces and Porous Materials (SMAP), UA-UVA-CSIC, University of Valladolid, 47071 Valladolid, Spain c Laboratory of SeparationTechnology, Lappeenranta University of Technology, 53850 Lappeenranta, Finland HIGHLIGHTS  Six PES UF membranes were aged with NaOH and HNO 3 solutions at 50 1C.  PES UF membranes were more resistant to acid than alkali in all tested conditions.  Changes in membrane performance mainly took place in the first 10 days of exposure.  Support layer material must be taken into account in membrane resistance.  Temperature played a significant role for the least resistant membranes. article info Article history: Received 2 December 2014 Received in revised form 8 April 2015 Accepted 13 April 2015 Available online 28 April 2015 Keywords: Cleaning Ageing Ultrafiltration (UF) Polyethersulfone (PES) membranes abstract Six commercial ultrafiltration membranes made of polyethersulfone from Microdyn Nadir, Koch Membrane Systems and GE Osmonics were exposed to 0.01, 0.1 and 1.0 M nitric acid (HNO 3 ) and sodium hydroxide (NaOH) solutions at 50 1C for 150 days. Water permeability, molecular weight cut-off curves, ATR-FTIR, SEM- EDS, AFM and contact angle measurements were employed to evaluate membrane ageing. All membranes showed a high resistance to acidic solutions keeping their chemical and morphological properties almost invariant. The alkaline ageing did not induce any substantial change in the Nadir membranes but, the stability of Koch and GE Osmonics support layers was compromised at high NaOH concentrations, leading to even the complete degradation of these supports in some cases. This was confirmed by ATR-FTIR, SEM and GC–MS analysis. The Nadir membrane resistance to alkaline conditions was found to be in the support layer material composition (mixture of polyethylene and polypropylene). Koch and GE Osmonics membranes support material (polyethylene terephthalate) broke down into its monomers under strong alkaline conditions via hydrolysis reaction. Almost all membranes showed changes in membrane performance which were attributed to their conditioning or their degradation. Regardless of the cause, those changes took place mainly in the first 10 days of exposure. The influence of temperature on the ageing was also studied under the strongest alkaline condition. Its effect on chemically stable membranes were negligible whereas for the others, higher temperatures led to faster support layer degradation. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction Ultrafiltration (UF) is a pressure driven membrane process in which pore size is usually between 10 and 1000 Å (Kulkarni et al., 1992). Therefore, UF membranes are able to retain species with molecular weights (MW) from 0.3 to 500 kDa and have a wide range of applications. Among those are the purification of biotechnology products, whey protein recovery, juice clarification, waste water treatment, water desalination, and the separation of lignin compounds from effluents in the pulp and paper industry (Koivula et al., 2013; Mondal et al., 2011; Strathmann et al., 2006; van Reis and Zydney, 2007; Zydney, 1998). One of the most important limiting factors for the industrial application of UF is membrane fouling which is the result of Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science http://dx.doi.org/10.1016/j.ces.2015.04.023 0009-2509/& 2015 Elsevier Ltd. All rights reserved. n Corresponding author: Tel.: þ34 985 10 29 98; fax: þ34 985 10 27 78. E-mail address: sluque@uniovi.es (S. Luque). Chemical Engineering Science 134 (2015) 178–195