Photoinduced grafting of ultrafiltration membranes: comparison of poly(ether sulfone) and poly(sulfone)

Using UV-assisted graft polymerization of three hydrophilic monomers, N-vin yl-2-pyrrolidinone (NVP), 2-acrylamidoglycolic acid monohydrate (AAG) and 2 -acrylamido-2-methyl-1-propanesulfonic acid (AAP), both poly(ether sulfone) (PES) and poly(sulfone) (PSf) 50 kDa ultrafiltration (UF) membranes were m odified using, the dip method with 300 nm wavelength lamps. The concentrati on of monomer and irradiation energy supplied to the membranes was varied. The modified membranes were characterized physicochemically by their degree of grafting using attenuated total reflection-Fourier transform infrared s pectra (ATR-FTIR) and by their wettability using a captive air bubble techn ique. They were also characterized by their filtration performance with a 0 .1 wt.% bovine serum albumin (BSA) solution in phosphate buffered saline (P BS) at 20 TIC and at pH 7.4. The filtration protocol gave several measures of performance including the initial water permeability, the protein soluti on permeability and the water permeability after flushing with DI water. Four different modification conditions were found that gave modified UF mem branes with superior filtration performance than the base unmodified PES, t he base unmodified PSf, or a regenerated cellulose (RC) control membrane. S lightly compromised protein solution permeabilities were compensated for wi th low fouling modified membranes that exhibited excellent cleaning charact eristics. All the best cases were at the highest monomer concentrations (5 wt.%) and lowest irradiation energy (< 65 mJ/cm(2) for PES and < 130 mJ/cm( 2) for PSf). This work also suggests that low degrees of grafting (DG < 0.5 3) and intermediate wettabilities (0.74 < cos theta < 0.82) were sufficient to obtain attractive non-fouling membranes. Since BSA is strongly negative ly charged at pH 7.4, it is not surprising that AAP was the monomer that ex hibited best performance for two of the four best cases. An important findi ng was that PES is far more sensitive to UV-assisted graft polymerization a nd, thus, requires far less energy to attain a desired degree of grafting t han PSf. (C) 2001 Elsevier Science B.V. All rights reserved.