The role of polyvinyl butyral additive in forming desirable pore structure for thin film composite forward osmosis membrane

Abstract

A thin-film composite forward osmosis (TFC-FO) membrane was developed by combining a new substrate consisting of cellulose acetate butyrate (CAB) and polyvinyl butyral (PVB) with the conventional polyamide active layer. The incorporation of the PVB additive (0–4 wt%) was to improve the hydrophilicity and alter the pore formation mechanism of the substrate to reduce the internal concentration polarization (ICP) effect in FO. The results showed that promising structural parameters of the CAB/PVB substrate such as A value (1.08 L m−2 h−1 bar−1) and S value (363.5 μm) could be obtained for the M2 substrate with 2 wt% PVB, due to the combined effect of finger-like pores and high porosity with high pore connectivity. The evaluation of the TFC-FO membranes showed that the water flux of the TFC-M2 was up to 27.5 L m−2 h−1 with 1 M NaCl draw solution in active-layer facing draw solution (AL-DS) mode, which was 40% and 130% flux enhancement compared to the reported commercial CTA and pure CAB control TFC membrane, respectively, with lower specific salt flux Js/Jw (0.35 g/L). The fouling experiments using model feed containing BSA foulant showed that the TFC-M2 was almost unaffected (98%) by the dilutive ICP effect in the active-layer facing feed solution (AL-FS) mode; while it also exhibited the highest flux recovery of 88% in the AL-DS mode. Overall, the total mass transfer resistance Rt of the TFC-M2 was the lowest compared to all as-prepared TFC-FO membranes, indicating the key role of the PVB additive in tuning the CAB substrate structure for designing high performance FO membranes.