In situ PEGylation of polyamide network of thin film composite membrane by inter-polymer H-bond complex formation

Abstract

Fouling propensity of membranes is a bottleneck problem. PEGylation is an effective approach to improve the antifouling property of a polyamide (PA) thin film composite (TFC) membrane. However, reactive PEG involves in the covalent network formation with PA leading to the increase of network pore size and lowers the rejection efficiency of the membranes. Post-surface modification by reactive PEG leads to lowering of permeates flux. End-functional (reactive) PEG samples are costly and prepared by multi-step process. Herein, the high pKa value of the fraction of –COOH groups of PA network is utilized for the formation of stable complex with PEG. Addition of linear PEG into the aqueous solution of m-phenylenediamine during interfacial polymerization leads to grafting of polyamide network by PEG through the formation of interpolymer H-bond complex of ether oxygen of PEG and –COOH groups of cross-linked PA network. PEG in the PA network increases the hydrophilicity, permeate flux, rejection efficacy and antifouling property of the membranes. The PEG chains remain stable in the PA network in the pH window of acidic to ≤8 as confirmed by the ATR-IR, wetting behavior, model spectroscopic experiments and X-Ray photoelectron spectroscopy. A PEGylated membrane prepared by the in situ addition of PEG (molecular weight 2000 g mol−1, 1% w v−1) into the MPD solution shows 20–30% higher permeate water flux, superior salt rejection efficiency and fouling resistant property than that of a pristine membrane. This approach is simple, cost-effective and easy to implicate.