Structure control of hydrophilized PVDF hollow-fiber membranes using amphiphilic copolymers: PMMA-co-P (HEMA-co-MEA)

Highly Effective Anti-Organic Fouling Performance of a Modified PVDF Membrane Using a Triple-Component Copolymer of P(Stx-co-MAAy)-g-fPEGz as the Additive

In this study, a triple-component copolymer of P(St_x-co-MAA_y)-g-fPEG_z containing hydrophobic (styrene, St), hydrophilic (methacrylic acid, MAA), and oleophobic (perfluoroalkyl polyethylene glycol, fPEG) segments was synthesized and used as an additive polymer to prepare modified PVDF membrane for enhanced anti-fouling performance. Two compositions of St:MAA at 4:1 and 1:1 for the additive and two blending ratios of the additive:PVDF at 1:9 and 3:7 for the modified membranes were specifically examined. The results showed that the presence of the copolymer additive greatly affected the morphology and performance of the modified PVDF membranes. Especially, in a lower ratio of St to MAA (e.g., St:MAA at 1:1 versus 4:1), the additive polymer and therefore the modified PVDF membrane exhibited both better hydrophilic as well as oleophobic surface property. The prepared membrane can achieve a water contact angle at as low as 48.80° and display an underwater oil contact angle at as high as 160°. Adsorption experiments showed that BSA adsorption (in the concentration range of 0.8 to 2 g/L) on the modified PVDF membrane can be reduced by as much as 93%. From the filtration of BSA solution, HA solution, and oil/water emulsion, it was confirmed that the obtained membrane showed excellent resistance to these organic foulants that are often considered challenging in membrane water treatment. The performance displayed slow flux decay during filtration and high flux recovery after simple water cleaning. The developed membrane can therefore have a good potential to be used in such applications as water and wastewater treatment where protein and other organic pollutants (including oils) may cause severe fouling problems to conventional polymeric membranes.

Antifouling enhancement of polyacrylonitrile-based membrane grafted with poly(sulfobetaine methacrylate) layers

In this work, zwitterionic polyacrylonitrile (PAN)-based membranes were synthesized via surface grafting strategy for improving the antifouling properties. The copolymer membrane consisting of PAN and poly(hydroxyethyl methacrylate) segments, was cast via nonsolvent induced phase separation, and then treated with acryloyl chloride to tether with carbon-carbon double bonds. Zwitterionic poly(sulfobetaine methacrylate) (PSBMA) layers were grafted onto membrane surface via concerted reactions of radical grafting copolymerization and quaternization with 2-(dimethylamino)ethyl methacrylate) and 1, 3-propanesultone (1, 3-PS) as the monomers. The grafting degree (GD) of PSBMA layers increases with the incremental content of monomers, leading to the enhancement in membranes surface hydrophilicity. The permeation experiments show that the flux of the zwitterionic membrane increases and then decreases with the increasing GD value, because of the surface coverage of PSBMA layers. The zwitterionic membrane has excellent separation efficiency for oil-in-water emulsion, with the rejection of a higher value than 99%. The irreversible membrane fouling caused by oil adsorption has been suppressed, as proved by the cycle-filtration tests. These outcomes confirm that oil-fouling resistances of membranes are improved obviously by the surface grafting of zwitterionic PSBMA layers.