Adsorptive fouling of modified and unmodified commercial polymeric ultrafiltration membranes (original) (raw)
1999, Journal of Membrane Science
The fouling tendency, due to adsorption on the pore walls, of two pairs of modi®ed and unmodi®ed ultra®ltration membranes, with similar observed retentions determined by dextran and gel permeation chromatography, was studied. The membranes investigated were made of modi®ed and unmodi®ed polyaramide (PA) and modi®ed and unmodi®ed polyvinylidene¯uoride (PVDF). The PVDF membrane was surface-modi®ed and the PA membrane was made from a modi®ed polymer solution. Membrane modi®cation was used to reduce fouling by adsorption. Octanoic acid was used as the fouling substance, representing a large number of small, hydrophobic compounds. It is demonstrated in this investigation that membrane modi®cation is not always successful. It was determined that at lower concentrations of octanoic acid, the modi®ed PA membrane exhibits a smaller fouling tendency than the unmodi®ed PA membrane, while the result is reversed for concentrations above 60% of the saturation concentration. The fouling tendency of the unmodi®ed PVDF membrane is much lower than that of the modi®ed PVDF membrane at all concentrations. The cross-sections of the membranes were visually examined with scanning electron microscopy, but no difference could be observed between the modi®ed and unmodi®ed membranes. The membranes were also examined with Fourier transform infrared spectroscopy. The spectra of the two PA membranes were different, while no difference was observed for the unmodi®ed and surface-modi®ed PVDF membranes. Remains of octanoic acid were found in the membranes, although they had been thoroughly rinsed with deionized water and the initial pure water¯ux was recovered.
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