(449bc) Micro-Computed Tomography of Swollen Heterogeneous Ion-Exchange Membranes

Heterogeneous ion-exchange membranes are widely used in electro-separation processes such as e. g. electrodialysis or electrodeionization. Their optimal electrochemical characteristics are thus of utmost importance for ideal performance of large-scale industrial units. Two of the parameters that strongly affect their characteristics are their composition and the surface and volume structure. Heterogeneous ion-exchange membranes consist of three major components: (i) finely ground ion-exchange resin providing the functionality, (ii) polyethylene or polypropylene used as a binder, and (iii) polymeric fibers (polyester or polyamide) providing mechanical strength to the membranes. The membranes are made in the form of large sheets which one produces by laminating slightly melted blend of the ion-exchange resin and the binder. In this process, only control over the composition (how much of each component is in the membrane) is possible. Spatial distribution of ion-exchange resin within the binder is completely random and irregular.

One can measure integral electrochemical characteristics of these membranes after their production and therefore optimize their properties in a trial-and-error method.

In this project we set out to develop techniques that should help to accelerate the trial-and-error method. Our technique allows (i) to analyze the structure of heterogeneous ion-exchange membranes after their preparation and (ii) to characterize these membranes by means of electrochemical measurements. This contribution will focus on micro-computed tomography of swollen membranes. We will present our devised method for scanning of swollen membranes. This technique is based on scanning the membranes in an environment saturated with water vapors to prevent their drying and drying accompanying changes in membrane volume. Simple immersion of membranes in water solutions causes strong attenuation of the signal resulting in poor quality of obtained data. The next part of the presentation will be devoted to a parametrical study investigating the effect of ionic strength of the external solution on swelling/shrinking of the membranes and irreversible changes of the membrane caused by repeatable swelling and shrinkage.