Characterization of a non-fouling ultrafiltration membrane

This report describes the properties of surface-modified poly(vinylidene fluoride) (PVDF) membranes. These membranes were created by coating hydrophilic polymers on the support PVDF membrane to reduce the tendency to protein fouling. The modified membranes with different molecular weight cut-off (MWCO) were characterized by filtration studies using bovine serum albumin (BSA) and an enzyme solution as test media, and the membranes exhibited the non-fouling property. The surface chemistry of the unmodified and modified PVDF membranes was characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). These surface sensitive techniques were used to confirm the successful surface modification. ToFSIMS imaging visualizes the distribution of the coating layer on the PVDF membrane. Furthermore, the amount of protein adsorption onto the membrane surfaces was determined by the radio labeling technique. For the protein adsorption experiments, we have developed a method, which ensures that protein molecules only adsorb on the membrane surface, and that no adsorption on the pore walls of the porous sub-layer takes place.

We have investigated the performance of the surface-modified PVDF membranes, ETNA01PP and ETNA10PP, by filtration studies. The filtration of BSA and the enzyme solution suggests that the modified membranes (ETNA01PP and ETNA10PP) exhibit non-fouling properties, whereas the polysulfone or polyethersulfone membranes GR81PP, GR61PE and PES1 showed severe fouling problems. Due to the antifouling properties, the ETNA membranes could be cleaned without using cleaning agents, which is advantageous from an economical as well as from an environmental point of view. The coating layer of the modified membranes, ETNA01PP and ETNA10PP, was characterized by two surface analytical methods, i.e. XPS and ToF-SIMS. Both methods indicate that the PVDF membrane was coated with a thin layer, which confirms the successful surface modification. ToF-SIMS imaging was applied to study the homogeneity of the coating layer. The negative ion imaging showed that that the coating layer was nearly homogeneous. The antifouling properties of the modified membrane ETNA01PP were further demonstrated by the fibrinogen adsorption test. The amount of protein adsorption was quantified by the radio labeling technique, and the data of protein adsorption also suggest that the modified PVDF has much better antifouling properties than the unmodified PVDF membrane and the PES membrane.