Study of the characteristics and the performance of self-made nanoporous polyethersulfone membranes

Polyethersulfone (PES) membranes were prepared in this study by using the DIPS technique (diffusion induced phase separation) in view of a better insight into the performance of commercial polyethersulfone membranes and a verification for the limited information given by the manufacturer. During this process, a lot of conditions influence the final membrane structure. Beside the choice of the solvent (dimethylformamide (DMF) or N-methyl-pyrrolidone (NMP)), it was shown that the concentration of the polymer and the relative air humidity are the most crucial ones. Optimizing these factors led to reproducible membranes, which were characterized for hydrophobicity, roughness, surface charge and molecular weight cut-off (MWCO). The performance was studied by doing cross-flow filtration experiments with aqueous solutions of uncharged and charged component. Although the self-made membranes were characterized by a larger MWCO in comparison with commercial polyethersulfone nanofiltration membranes, the retention for the self-made membranes was almost equal to or even higher than the commercial membranes in the case of filtrating negatively, respectively, positively charged component. The high retention of the self-made membranes for positively charged component can be explained by adsorption experiments or by surface charge measurements before and after filtration.