Study On Hydrophilic Modification And Antifouling Property Of Ultrafiltration Membrane Surfaces

As a green and energy-efficient separation technology, ultrafiltration exhibits a vast prospect of application in bioseparation, while membrane fouling still constitutes a bottleneck of its development. Membrane materials show great impact on membrane fouling. Major approaches for fouling reduction include exploitation of novel hydrophilic membrane materials and hydrophilic modification of membrane materials applied. In this dissertation, with the aim of reducing membrane fouling during biosepration, preparation and hydrophilc modification of ultrafiltration membranes were investigated.Poly (vinyl butyral) (PVB) ultrafiltration membranes were prepared via the phase inversion process and modified through an acid catalyzed hydrolysis process. XPS and water contact angle results indicated the increase of hydroxyl groups at membrane surface and the enhancement of surface hydrophilicity, and SEM suggested that modified membranes remained asymmetric structure; meanwhile, the mechanical property and porosity were close to the values of control PVB membranes.Ultrafiltration results showed that separation performance was affected to some extent by chemical modification. The systematical analysis of membrane fouling confirmed that chemical modification could effectively improve the antifouling property of PVB membranes. When treated with 1.0 M HCl solution for 4 h, the flux loss ratio was decreased from 45.1% to 38.1% while the flux recovery ratio was increased from 58.8% to 78.5%.Polyethersulfone (PES) ultrafiltration membrane was modified through adsorption to introduce the hydrophilic poly (vinyl alcohol) (PVA) chains to the hydrophobic membrane surface. The modified membranes were characterized and evaluated. XPS results confirmed the presence of PVA at membrane surface, and the value of water contact angle indicated the hydrophilicity enhancement. The membrane structure had no significant changes according to SEM. Ultrafiltration results showed that adsorption would reduce membrane flux, but it had effectively improved the antifouling property of PES membranes. When PVA concentration was 0.5 wt% and adsorption cycle was 3, the total and irreversible fouling ratio of modified membranes were 0.38 and 0.22, respectively, much lower than control PES membrane, of which the value were 0.61 and 0.47. The flux recovery ratio was increased from 53.1% to 78.2%, while the long term ultrafiltration experiment showed an ideal stability of modification.A comb copolymer PS-b-PEG, which contained hydrophilic poly (ethyl glycol) (PEG) chains, was blended with PES to fabricate ultrafiltration membrane, and the blend membranes were characterized and evaluated. The PEG segments were spontaneously segregated to the membrane surface and the surface hydrophilicity was correspondingly enhanced, which was confirmed by the water contact angle and XPS results. The membrane structure had no significant changes and the mechanical property could still well meet the need of ultrafiltration. The protein adsorption experiments indicated the blend membranes had excellent protein adsorption resistance; the lowest adsorption amount reached 0.5μg/cm2. Ultrafiltration results showed that the blend membranes had a little higher flux, which was due to the pore-forming effect of the copolymer. The fouling investigation confirmed the antifouling property improvement of PES membrane through blending; the total and irreversible fouling were both remarkably reduced.