The effect of pluronic composition on the structure and performance of thin film composite polyphenyl sulfone/polyamide membranes for nanofiltration

Abstract

The novel thin film composite polyphenylsulfone (PPSU)/polyamide (PA) nanofiltration membranes were developed. Due to the high chemical and thermo stability, as well as oxidation, polymers of polysulfone group are very perspective as ultrafiltration membrane materials. However, rather high surface hydrophobicity limits their application. There are a lot of techniques for modification of such polymers and increase of their hydrophilicity. One of the most effective is the addition of hydrophilic additive into the casting solution. Block copolymers of polyethylene glycol (PEG) and polypropylene glycol (PPG) are promising modifying additives for polymer matrices due to their amphiphilic nature. There are various trademarks of PEG and PPG block copolymers which differ in their molecular weight, hydrophilic-lipophilic balance, and molecular architecture. It is known that the addition of polymeric additives to the casting solution significantly affects membrane's structure and performance, and allows the adjustment of porosity, pore size, roughness, and hydrophilicity of the membrane selective layer. The formation of the selective layer by interfacial polymerization (IP) is highly dependent on the properties of the substrate membrane. Pore size, porosity, hydrophilicity, wettability, and affinity to amine monomer of the membrane substrate are known to influence the velocity of amine monomer release from membrane substrate to reaction interface. It influences thickness and structure of the polyamide (PA) selective layer formed via IP. Increasing the surface hydrophilicity can lead to a more uniform distribution of the amine while the formation of a polyamide layer obtained by interfacial polymerization. This may result in formation of denser and thinner polyamide layer with high salt retention.