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

• Ageing mechanism of 2 IEMs used for 2 years in ED for food industry was investigated.
• Used IEMs lost some ion-exchange sites, and their conductivity decreases sharply.
• CEM became denser and more hydrophobic; AEM became thicker and more hydrophilic.
• Significant degradation in the polymer matrix of both membrane types was found.
• Microheterogeneous model was applied to explain the IEMs ageing mechanism.

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.