Structural and physicochemical investigation of ageing of ion-exchange membranes in electrodialysis for food industry

The ageing mechanism of ion-exchange membranes (IEMs) used in electrodialysis for food industry was investigated through the use of several analytical techniques. Structural and physicochemical properties of two different IEMs, i.e. a cation-exchange membrane (CEM) and an anion-exchange membrane (AEM) were studied. The comparison of conductivity, thickness, water uptake, ion-exchange capacity and contact angle values as well as SEM micrographs and energy dispersive X-ray (EDX) spectra between new and used samples showed a significant degradation of membranes after 2 years of use in an electrodialysis module. The CEM became denser and more hydrophobic, while the thickness of the AEM increased and the membrane became more hydrophilic. A significant degradation in the polymer matrix of both membrane types was found. The used membranes lost a part of their ion-exchange sites, and their specific electrical conductivity significantly decreases. To explain the important variations of equilibrium properties, we have applied the microheterogeneous model. (C) 2013 Elsevier B.V. All rights reserved.