Polyvinylamine-grafted polyamide reverse osmosis membrane with improved antifouling property

• PVAm was covalently grafted to the commercial RO membrane surface.
• PVAm grafting had small influence on the membrane permselectivity.
• Three PVA-coated antifouling RO membranes were used for comparisons.
• PVAm-grafted membrane generally exhibited the best antifouling property.

It is known that some commercially antifouling reverse osmosis (RO) membranes are coated with polyvinyl alcohol (PVA) layers. In this work, a new antifouling RO membrane was prepared by surface grafting of a commercial RO membrane (RE4021-TE from Woongjin, without a PVA layer) with the positively charged and hydrophilic polyvinylamine (PVAm) which was synthesized in lab. To determine the similarities and differences between the PVAm-grafted and PVA-coated membranes, one lab-prepared PVA-coated membrane (also coating on the TE membrane) and two typical commercially antifouling RO membranes with PVA coating layers (BW30FR from Filmtec and LFC3 from Hydranautics) were used for comparisons. Successful synthesis of PVAm was confirmed by the results of the ATR-FTIR and 1H-NMR analyses. ATR-FTIR, XPS and zeta potential measurements of the membranes together indicated that the PVAm was successfully grafted onto the TE membrane surface. The membrane surface became more hydrophilic and smoother after the PVAm grafting. More importantly, for the TE membrane, the membrane surface charge climbed from negative to positive values after the grafting of PVAm with increasing concentrations, while the surface was still negatively charged after the PVA coating though the charge density was reduced. Besides, the PVAm grafting had smaller influence on the membrane permselectivity than the PVA coating: after the PVAm grafting (with a concentration of 0.20 w/v%) the salt rejection was slightly increased and the water flux decreased by 12.4%, but after the PVA coating the salt rejection was slightly declined and the water flux decreased by 35.4%. Fouling behaviors of the membrane grafted with 0.20 w/v% PVAm and the other three membranes with PVA coating layers were investigated and compared using two proteins (bovine serum albumin (BSA) and lysozyme), one polysaccharide (sodium alginate, SA), one surfactant (dodecyltrimethylammonium bromide, DTAB) and one colloid (colloidal ferric hydroxide, Fe(OH)3) as model foulants. The results showed that the PVAm-grafted membrane exhibited better antifouling property than the two commercially antifouling RO membranes with PVA coating layers. In addition, fouling behavior of the lab-prepared PVA-coated membrane indicated that lower initial water flux resulted in less initial flux decline in the fouling process. This work provides a new potential strategy for improvement of antifouling property of commercial RO membranes besides the traditional PVA coating process.