THE INFLUENCE OF A LOW-MOLECULAR HYDROPHOBIC SOLUTE ON THE FLUX OF POLYSULFONE ULTRAFILTRATION MEMBRANES WITH DIFFERENT CUTOFF

In this study the influence of a low-molecular hydrophobic solute on t he Bur of a hydrophilic regenerated cellulose membrane and hydrophobic polysulphone membranes with different nominal molecular weight cut-of f, NMWCO, was investigated. Octanoic acid was used as a model substanc e because it is considerably smaller than the NMWCO of all the membran es used in the investigation. Octanoic acid was found to decrease the flux of the polysulphone membranes considerably. The decrease was depe ndent on the NMCWO, although in all cases the NMWCO is many times larg er than the size of the octanoic acid molecules. It is also shown that the Bur of the hydrophilic membrane, with a NMWCO of the same size as one of the denser hydrophobic membranes, is unaffected by the octanoi c acid. The cross-sections of both used and unused membranes were exam ined in a scanning electron microscope (SEM). No visual difference was observed between the used and unused membrane samples. Analysis of th e membranes with Fourier transform infrared spectroscopy (FTIR) showed that octanoic acid remained in the membranes even after thorough clea ning.