Two different techniques were used to photochemically modify 50 kDa poly(ether sulfone) (PES) membranes with the monomer N-vinyl-2-pyrrolidinone (NVP) to increase surface wettability and decrease adsorptive fouling during the constant volume diafiltration of 0.1 wt % bovine serum albumin (BSA). The filtration performance of the modified membranes was compared to that of a commercially available PES membrane and a regenerated cellulose membrane. Both the dip and immersion modification techniques produced membranes with essentially the same wettability as regenerated cellulose, a wettability increase of 30% over the base PES membrane. There was a substantial decrease in the irreversible adsorptive fouling of the base membrane as measured by the permanent flux drop after water cleaning with respect to the initial buffer flux using either modification (from 0.42 to 0-0.09). The immersion-modified membrane with the best performance exhibited no adsorptive fouling, similar permeability, and higher rejection than the regenerated cellulose membrane. Both modification techniques sharply decreased membrane permeability at high monomer concentrations due to pore blockage by grafted polymer chains. The dip-modified membranes exhibited simultaneous loss of BSA rejection and permeability, which suggested that although radiation cleaved PES bonds and enlarged the pores, the high degree of grafted polymer chains on the surface blocked the pores and decreased the permeability. The immersionmodified membranes retained their rejection because the monomer NVP solution was found to absorb up to 88% of the emitted energy, depending on its concentration, thereby protecting the pore structure from intense irradiation. Thus, the dip and immersion techniques are useful for applications where high protein transmission and retention are desired, respectively.

Low protein fouling 50 kDa poly(ether sulfone) ultrafiltration membranes were produced by UV-assisted graft polymerization of the monomer 1-vinyl-2-pyrrolidinone by using a dip modification technique without loss of protein rejection. UV lamps with an emission wavelength maximum of 300 nm and two specially selected UV light filters, benzene and an aromatic polyester film, were used to filter out 254 nm wavelength light which was found to be responsible for severe loss of protein rejection. The modified membranes that performed the best were prepared by using 300 nm lamps and the benzene filter. With increasing degree of grafting, these membranes exhibited up to 20% higher surface wettability (cos ϑ = 0.83−0.89) than the base membrane (cos ϑ = 0.74), which translated into lower irreversible flux loss (−0.05 to 0.03 compared with 0.42). While the protein rejection remained unchanged after modification, the permeability of the membranes decreased from 6.5 to 0.3 l m-2 h-1 (kPa)-1 with increasing degree of grafting as a result of pore plugging by the grafted chains. These membranes exhibited similar irreversible flux loss (0.03 vs ∼0), similar permeability (1.2 vs 1.8 l m-2 h-1 (kPa)-1), and higher rejection (97.4 vs 93.4%) as compared with a 50 kDa regenerated cellulose membrane.