A novel method for one-step preparation of antifouling ultrafiltration membranes via a non-solvent induced phase separation (NIPS) technique is proposed. It involves using aqueous 0.05–0.3 wt.% solutions of cationic polyelectrolyte based on a copolymer of acrylamide and 2-acryloxyethyltrimethylammonium chloride (Praestol 859) as a coagulant in NIPS. A systematic study of the effect of the cationic polyelectrolyte addition to the coagulant on the structure, performance and antifouling stability of polysulfone membranes was carried out. The methods for membrane characterization involved scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), contact angle and zeta-potential measurements and evaluation of the permeability, rejection and antifouling performance in human serum albumin solution and surface water ultrafiltration. It was revealed that in the presence of cationic polyelectrolyte in the coagulation bath, its concentration has a major influence on the rate of “solvent–non-solvent” exchange and thus also on the rate of phase separation which significantly affects membrane structure. The immobilization of cationic polyelectrolyte macromolecules into the selective layer was confirmed by FTIR spectroscopy. It was revealed that polyelectrolyte macromolecules predominately immobilize on the surface of the selective layer and not on the bottom layer. Membrane modification was found to improve the hydrophilicity of the selective layer, to increase surface roughness and to change zeta-potential which yields the substantial improvement of membrane antifouling stability toward natural organic matter and human serum albumin.

Surface modification of polysulfone ultrafiltration membranes was performed via addition of an anionic polymer flocculant based on acrylamide and sodium acrylate (PASA) to the coagulation bath upon membrane preparation by non-solvent induced phase separation (NIPS). The effect of PASA concentration in the coagulant at different coagulation bath temperatures on membrane formation time, membrane structure, surface roughness, hydrophilic-hydrophobic balance of the skin layer, surface charge, as well as separation and antifouling performance was studied. Scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, contact angle and zeta potential measurements were utilized for membrane characterization. Membrane barrier and antifouling properties were evaluated in ultrafiltration of model solutions containing human serum albumin and humic acids as well as with real surface water. PASA addition was found to affect the kinetics of phase separation leading to delayed demixing mechanism of phase separation due to the substantial increase of coagulant viscosity, which is proved by a large increase of membrane formation time. Denser and thicker skin layer is formed and formation of macrovoids in membrane matrix is suppressed. FTIR analysis confirms the immobilization of PASA macromolecules into the membrane skin layer, which yields improvement of hydrophilicity and change of zeta potential. Modified membrane demonstrated better separation and antifouling performance in the ultrafiltration of humic acid solution and surface water compared to the reference membrane.

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The effect of degree of saturation of casting solutions (α*-the ratio of the nonsolvent amount added to the polymer solution to the non-solvent amount which causes phase separation) and nonsolvent power on the structure and performance of membranes prepared from system "Polyethersulfone (PES)non-solvent-solvent" have been studied. Nonsolvent power has been characterized in terms of precipitation number (PN), i.e., the amount of nonsolvent that leads to phase separation of 100 mL of a 1% PES solution. Glycerol (PN = 27.8 g/dL), polyethylene glycol 400 (PN > 1000 g/dL), and their mixtures have been used as a nonsolvent additive to the casting solution. It has been shown that membranes with a nice spongy structure are formed in the case of using casting solutions located near the binodal line. In this case, the membrane flux depends on the nonsolvent power: the higher the PN of the nonsolvent, the higher the membrane flux. The highest flux is exhibited by membranes prepared from casting solutions with a degree of saturation of α* = 0.52-0.81 depending on the PN of the nonsolvent. In this case, macrovoids are present in the structure of the supporting layer of the membranes; the size and shape of the macrovoids also depend on the PN of the nonsolvent: the higher the PN, the larger the macrovoid size in the membrane supporting layer. The results have made it possible to propose a new approach to obtaining PES membranes with a desired structure and properties.

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