INFLUENCE OF THE MEMBRANE MATERIAL ON THE ADSORPTIVE FOULING OF ULTRAFILTRATION MEMBRANES

The hydrophilic/hydrophobic properties of the membrane material have a n important influence on the membrane flux reduction when treating sol utions containing hydrophobic solutes. Different methods of measuring the hydrophobic properties of membranes have been evaluated; measureme nt of the contact angle being the most commonly used method. In this i nvestigation the flux reduction of eight membranes of approximately th e same cut-off, but of different materials, was determined and related to the contact angle. A low-molecular weight hydrophobic solute (octa noic acid) was used as foulant. The flux of the hydrophilic membrane w as only marginally reduced, whereas the flux reduction of hydrophobic membranes was significant. Membranes of polyvinylidene fluoride had th e lowest flux reduction of the hydrophobic membranes. Differences betw een membranes of the same material (polyethersulfone), but from differ ent manufacturers, were observed. No relation was found between the fl ux reduction and the contact angle of the membrane, the initial pure w ater flux or the retention of a hydrophilic macromolecule (PEG20). The pure water flux of two of the hydrophobic membranes increased signifi cantly during the experiments, whereas the pure water flux of the othe r hydrophobic membranes decreased. A membrane of polyaramide, with a c ontact angle of the same order of magnitude as the other hydrophobic m embranes, behaved as a hydrophilic membrane, with no influence on the flux at concentrations below the solubility limit of the hydrophobic s olute, but experienced the most severe flux decline of all the membran es included in the investigation at the solubility limit. Two modified membranes were included in the investigation. The flux reduction of t hese membranes was not significantly lower than for the corresponding unmodified membranes of the same materials.