（Liaoning Key Laboratory of Polymer Science and Engineering, Liaoning High Performance Polymer Engineering Research Center, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China）
Sulfonated copoly(phthalazinone biphenyl ether sulfone)(SPPBES) coating solution were prepared with SPPBES as material and LiCl, NaCl and KCl as inorganic salt additives. SPPBES composite nanofiltration membranes were prepared with copoly(phthalazinone biphenyl ether sulfone)(PPBES) as ultrafiltration support membranes via dip coating method. The composite nanofiltration membranes prepared with LiCl, NaCl and KCl as inorganic salt additives were named as SPPBES-LiCl, SPPBES-NaCl and SPPBES-KCl, respectively. The effect of inorganic salt additives on the performance of composite nanofiltration membrane was studied. The composite nanofiltration membranes showed the rejection of inorganic salt in the order of Na2SO4>NaCl>MgSO4>MgCl2, which show the characteristic of negatively charged nanofiltration membranes. The flux of composite membrane increased with the increase in the radii of metal ion of inorganic salt additives, while the salt removing rate of composite membrane decreased. SPPBES-LiCl composite membrane showed highest salt removing rate while SPPBES-KCl composite membrane exhibited highest flux among the three membranes. The thermal stability, chemical stability and oxidative stability of composite membranes were investigated in detail. When the operating temperature increased from 20 to 95 ?C, the flux of SPPBES-LiCl membrane increased from 46 to 130 L·m-2·h-1 while the salt removing rate of composite membrane decreased by 3%. Compared to SPPBES-NaCl and SPPBES-KCl membrane, SPPBES-LiCl membrane showed the least change on membrane performance with the increasing temperature. After composite membranes were immersed into 0.2 g·L-1 NaClO solution for 8 days, the flux of SPPBES-LiCl composite membranes increased by 2% while the flux of SPPBES-NaCl membrane and SPPBES-KCl membrane increased about 8%. It was found that SPPBES composite membranes showed good high temperature resistance, excellent chemical stability and oxidation resistance. Besides, SPPBES-LiCl composite nanofiltration membrane showed better oxidative stability than SPPBES-NaCl membrane and SPPBES-KCl membrane. The effects of inorganic salt additive on morphology and hydrophilicity of composite membranes were investigated by SEM and contact angle. Composite membranes showed smooth surface and contact angle ranging from 55.5??to 58.6?, indicating that three kinds of composite membranes showed similar surface morphology and hydrophilicity.