| Fouling-resistant ultrafiltration polymer-modified ceramic (PMC) membranes were prepared by graft polymerization of poly(vinyl pyrrolidone) (PVP) chains from activated surface sites on carbon-supported zirconia ultrafiltration (UF) membranes. PMC membranes were prepared at different grafting conditions to vary polymer chain density and length of the covalently attached brush layer. Membrane performance (i.e., solute rejection and permeate flux) was studied via UF of well-characterized synthetic oil-in-water (o/w) microemulsions and commercial cutting oil emulsion. Membrane properties such as, surface roughness and pore size and their relation to membrane fouling were investigated by scanning electron microscope images of membrane surface and by hydraulic permeability measurements. Polymer-modified surrogate substrates (i.e., particles and wafers) were also used to assess the properties of the grafted surfaces (i.e., graft yield, chain length and density, surface wetting characteristics and hydrophilicity) employing various methods such as, atomic force microscopy (AFM), contact angle measurements, thermogravimetric analysis, and adsorption studies.; The native zirconia membrane was irreversibly fouled due to adsorption of foulants on the membrane surface, from both the synthetic and commercial cutting o/w emulsions. Irreversible fouling was not observed for the different PMC membranes, despite differences in their surface hydrophilicity. Adsorption and filtration studies identified the anionic surfactant in the o/w microemulsions as the irreversible foulant for the native membrane. Higher oil rejection (of more than 2-fold) for the PMC membrane, relative to the native membrane, was attributed to pore size reduction of membrane defects (i.e., ‘pin-holes’) by the grafted polymer chains. However, both native and modified membranes allowed desirable passage of recyclable amphiphiles. Flux decline analysis suggested that fouling due to pore blockage occurred during the initial stages of filtration. Finally, contact angle analysis of modified surfaces along with membrane UF studies revealed that the fouling-resistant attribute of the PMC membranes is due to the alteration of surface chemistry regardless of the native membrane roughness. |
