Anchoring polyamide active layer to improve the thermal stability of polyacrylonitrile composite forward osmosis membrane through interfacial enthalpic effect

Abstract

Traditional composite polymer membranes suffer from deteriorated rejection when operation temperature exceed 60 °C, which is attributed to the decrease in glass transition temperature of polymer in cross-linked active layer. To address this issue and fabricate thermally stable composite membranes, primary amino group was successfully introduced to polyacrylonitrile (PAN) through reaction between cyan group and diethylenetriamine to firmly anchor polymer chains of active layer on surface of support layer. This not only restrained the movement of polymer chains in the active layer but also the movement of polymer chains in the cross-linked support layer. The resulting thermally stable membrane was used to improve water flux of forward osmosis (FO) process. All the modified FO membranes exhibited substantial thermal stability compared to FO membrane based on original PAN support layer. Taking 1 mol/L NaCl as draw solution and deionized water as feed solution, the water flux of PAN-C3 reached 103.0 ± 8.2 L/(m2·h) at 90 °C, which was three times the value at 25 °C, with a constant JS/JW of 0.35 g/L. Furthermore, the rejection was stable at 93.4 %. This method can be further applied to fabricate thermally stable reverse osmosis and nanofiltration membranes.