Fabrication of cation exchange membrane with excellent stabilities for electrodialysis: A study of effective sulfonation degree in ion transport mechanism

Composite cation exchange membranes (CEMs) based on sulfonated polyether sulfone (SPES) with low sulfonation degree (DS) have been prepared in our previous studies. The results provided an approach for the preparation of CEM with low cost, environment-friendly technology, and ideal properties. On the basis of the previous research, the first purpose of this study was aimed to explore more suitable hydrophilic additives to further improve CEM properties. Hydrophilic polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) with different molecular weight (Mw) were used as hydrophilic additives, while SPES was still used as the matrix material. The results showed that PEG was not a suitable additive for CEMs due to the low MW, while stability was clearly improved with increased PVP MW. Hence, for researchers, there is no need to waste time on PEG as a hydrophilic agent of CEM prepared with this method in the future. The second purpose of this study, which was the further optimization of the CEM performance, was achieved in the research of suitable hydrophilic additives. The results of stability and electrodialysis showed that SPES blended with PVP K90 was the best prepared CEM. The third purpose was the investigation of mechanism of synergistic effects between sulfonated groups and hydrophilicity on membrane properties. In this part, an innovative concept of effective DS was put forward. This innovative concept will directly impact on ion transport mechanism, and have a very important influence on the preparation idea of CEM. In conclusion, this study is of great significance for selection of CEM materials, improvement of membrane stability and further study of ion transport mechanism.