| Low temperature plasma polymers of methane, air and acrylic acid were used to modify the surfaces of commercially available 10,000 Dalton molecular weight cut-off polysulfone membranes. The objective of using plasma polymerization was to reduce fouling by imparting a hydrophilic character to the membranes while retaining the bulk properties of the membranes. The plasma modified surfaces were characterized by conducting Atomic Force Microscopy, Fourier Transform Infra Red Spectroscopy, Transmission Electron Microscopy and Contact angle measurement studies on the membrane surfaces. The processing abilities of the membranes were tested using whey. All plasma treatments substantially increased surface hydrophilicity as compared to the unmodified membranes. The durability of the plasma polymerized membranes was assessed by measuring the change in hydrophilicity over a year of storage. The modified membranes retained their hydrophilicty indicating that hydrophilic groups attached on the membrane surface were “locked in” on the membrane surface. No discernible changes in membrane structure attributable to the modification process were detected Membrane performance is assessed in terms of (i) difference in flux rates between plasma polymerized and unpolymerized membranes, (ii) cleanability and flux recovery, (iii) processing abilities, and (iv) differences in protein retention. Whey was used as the test medium. The plasma polymerized membranes were observed to have higher whey permeate fluxes and enhanced separation abilities, while exhibiting excellent chemical stability to cleaning chemicals and extreme pH conditions. Fractional flux changes were used to study fouling characteristics. Chromatographic analyses of permeate and retentate streams were used to study protein retention. The results of this study clearly establish that surface modification of ultrafiltration membranes using low temperature plasma can significantly improve membrane performance and reduce fouling. |
