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Photoinitiated surface-selective graft copolymerization onto polypropylene (PP) microfiltration membranes was performed using two different methods for coating the photoinitiator, benzophenone (BP), on the membrane surface. An already established adsorption method and a novel method based on preswelling of the PP in heptane, subsequent solvent exchange, and thus entrapping of the BP in the surface layer of the PP had been evaluated. With acrylic acid (AA) as the monomer, functional polymer brush structures on the entire membrane pore surface were obtained. Further variations of the grafted layer had been achieved by copolymerization of AA with acryl amide (AAm) and methylene bisacrylamide (MBAA). Characterization had been done mainly by detailed measurements of membrane permeability including pH dependency as well as the reversible binding of a protein (lysozyme, Lys) under membrane chromatography conditions. Compared with BP adsorption, the BP entrapping method yielded a less dense grafted layer with longer PAA chains at the same degree of functionalization (DG). This was due to somewhat lower immobilized BP amounts, but also less side reactions via nonselective photoinitiated cross-linking by dissolved BP. Unexpected properties of the PAA-co-AAm brush layers were their even larger swelling/deswelling as a function of a pH change (above and below the pK a of PAA) as compared with the PAA brushes. Both PAA-co-AAm and cross-linked PAA-co-MBAA layers showed Lys binding capacitiessmore than 10 times higher than monolayer adsorption onto the unmodified PP membrane surfacesand quantitative recoveries similar to PAA of the same DG; and the highest efficiencies of protein binding (Lys amount relative to amount graft copolymer) were achieved with the membranes prepared by the entrapping method. In general, the more controlled BP entrapping method had distinct advantages in terms of the control of grafted layer structure leading to an improved membrane adsorber performance.

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Using diethylene glycol (DegOH) as non‐solvent additive (NSA) and N, N‐dimethylacetamide (DMAc) as solvent (S), polyethersulfone (PES) flat sheet membranes were prepared via immersion precipitation combined with the vapor induced phase separation (VIPS) process. Light transmittance was used to follow the precipitation rate during the immersion process as well as during the VIPS stage. As the addition of the NSA, the viscosity of casting solutions increased, which led to a slow precipitation rate. Though the precipitation rate decreased, the instantaneous demixing type was maintained. High flux membranes were obtained only at a high mass ratio of NSA/S; producing membranes had cellular pores on the top surface and sponge‐like structure on cross section. The VIPS process prior to immersion precipitation was important for the formation of cellular pore on the surface. With the increase in exposure time, the liquid–liquid phase separation took place on the surface of casting solution; nucleation and growth induced the formation of cellular pore on the top surface. Coagulation bath temperature also had large effect on the precipitation rate; high temperature on coagulation bath mainly accelerated the transfer of solvent and non‐solvent. Higher flux membrane with a porous skin layer could be obtained at a high coagulation bath temperature, but at the same time the mechanism properties were weakened. Copyright © 2007 John Wiley & Sons, Ltd.

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Microporous poly(ether sulfones) (PES) membranes were prepared via phase inversion using poly (ethylene glycol) (PEG) as additive and N,N-dimethylacetamide (DMAc) as solvent. Thermodynamic of the casting solutions was studied by coagulation value while precipitation rate was observed by light transmittance measurement. It was found that casting solution with PEG200 as additive was thermodynamically less stable than those with PEG400 and PEG600 as additive and easier to cause phase separation in exposure time. With the increase of PEG200 concentration, the casting solution became thermodynamically less stable and easier to cause phase separation in exposure time, but precipitation rate during immersion precipitation decreased because of the increased viscosities. ATR-FTIR spectra and TGA curves showed that the membranes prepared using PEG200 as additive had less PEG residual than those of PEG400 and PEG600, but it showed better permeation performance than that prepared using PEG400 and PEG600 as additive. With the increase of PEG200 concentration from 30 to 70 wt %, the cross section structure changed from macrovoid to sponge-like, micropores with a mean pore size around 0.1 lm began to form on the top surface. When the PEG200 concentration is 60 wt %, the pure water flux was 1845 L m 22 h 21 bar 21, which is the highest value. As the PEG200 concentration increased from 30 to 60 wt %, the contact angles decreased from 82.18 to 58.28. As the addition amount of PEG200 increased, the residual PEG made the prepared membranes more hydrophilic.