A comprehensive evaluation of PVA enhanced polyamide nanofiltration membranes: Additive versus interlayer

Hydrophilic macromolecules represented by polyvinyl alcohol (PVA), either as aqueous additives or interlayers, are effective for enhancing polyamide (PA) thin film composite (TFC) membranes. Few of the previous reported works have comprehensively analyzed the different functions of PVA additives and PVA interlayers, which have profound influences on the PA layer thickness, nanostructures, chemical compositions, and surface properties. In this work, systematical characterizations and performance evaluations were conducted to analyze the differences of using PVA as additives or interlayers. The results prove that PVA additives can react with trimesoyl chloride (TMC) to form polyester to adjust the structure of the membrane, and the full interaction of high concentration of PVA and a small amount of PIP will make PIP diffuse more uniformly during interfacial polymerization, which is beneficial to construct a smooth and antifouling membrane. The PVA interlayer adjusts the surface properties of the membrane by changing the hydrophilicity of the support layer. The optimized membrane with 1.4% (mass) PVA as aqueous additive possesses an ultrathin PA selective layer of 13.5 nm, showing a water permeance of 32.4 L·m−2·h−1·bar−1 and a Na2SO4 rejection above 97%.