Abstracts - peq / coppe / ufrj

Conductivity (mS/cm)Contact angle (°)Permeability (10 -9 m 2 *s -1 )By means of SEM images and the BET specific surface area (Sp) it was possible toacknowledge that membrane porosity increased gradually with the time of operation. Thisexplains the increase in permeability by the appearance of new pores which form channelsfor non-selective electrolyte transfer.9.28.88.48.07.67.26.86.46.00 20 40 60 80 100Lifetime (%) Water content (%)282624222018• Thickness (mm)0.190.180.170.160.150.140.130.1210090807060503,02,52,01,51,00,50,00 20 40 60 80 100Lifetime (%)Fig. 1. Physico-chemical properties of AEM samples in function of their lifetime. Conductivity,water uptake, thickness and contact angle (right). 0.1M NaCl permeability (left)Via Soxhlet extraction with THF, 44% of the new membrane was recovered as extractable.This decreased gradually up to 11.4 for the membrane at 100% of lifetime. Extractable wasrecognized by FTIR we as PVC. Accordingly, new pores in the membrane were created by theloss of PVC washed out from the membrane during the cleaning-in-place process in ED.These new pores contribute not only to increasing electrolyte permeability, but also togrowing conductivity in the last stage of ED. The latter is due to the fact that there is asubstitution of non-conductive regions occupied by PVC for pores filled with electrolytesolution apparently containing also organic components of whey.The new AEM sample presented a combination of the mechanical properties associated withthe two polymeric components, i.e. the rigidity of PS-DVB and the toughness of PVC.However, the loss of PVC had severe consequences in the mechanical properties of the AEM.As it was seen in the stress-strain curves, the Young Modulus, which indicates the rigidity ofa material, decreased by 20% from A0 to A3. The breaking strength, which represents themembrane plasticity, decreased by 45% and the area under the stress-strain curvedecreased of almost 80%, which strongly indicated a loss of the material toughness.ConclusionWe have found that there are several events accompanying the process of membraneageing. Fouling occurs from the beginning of the operation leading to a decrease in thecounterion mobility. The following phases of membrane deterioration are apparently due tothe loss of PVC which results in formation of non-charged pores within the membranematrix, available for electroneutral electrolyte solution and for large molecules coming fromwhey. In addition, membrane toughness decreases. Gradually the AEM membraneconverted from rigid and tough to rigid and brittle material. This caused formation of cracksand tears leading to membrane final failure in the ED stack.