Effects of polyacrylonitrile carboxylation on pore structure and performance of thermally crosslinked organic solvent nanofiltration membrane

In this work, polyacrylonitrile (PAN) membranes were hydrolyzed with NaOH solution, and then hydrolyzed PAN (HPAN) membranes were used to prepare organic solvent nanofiltration (OSN) membranes with thermal crosslinking method. The chemical structure and pore structure evolutions of membrane during hydrolysis and thermal crosslinking were systematically investigated. The influences of hydrolysis carboxylation on permeation performances of membranes were studied in detail. Benefiting from the carboxylic groups generated by hydrolysis reaction of nitrile groups, the cyclization reaction of HPAN molecular chains was more easily initiated by ionic mechanism at a lower temperature, and the pore structure fusion of thermally crosslinked membranes was effectively inhibited. The permeances of the thermally crosslinked membranes derived from HPAN membranes were greatly improved. Furthermore, the thermally crosslinked membrane showed stable OSN performance due to the generation of ladder structure during thermal crosslinking. Therefore, the OSN membranes prepared in this work have great potential for practical applications.