Influence of the blend composition on the properties and separation performance of novel solvent resistant polyphenylsulfone/polyimide nanofiltration membranes

In this study, the preparation of novel solvent resistant nanofiltration membranes made of polyphenylsulfone (Radel-R® – PPSU) and polyimide (Matrimid®(MI)) in blends with three different compositions of PPSU/MI (75/25, 50/50, 25/75 wt%) in NMP was investigated. Scanning electron microscopy (SEM) was used to investigate the morphological characteristics and the structure of asymmetric membranes. The prepared membranes had a typical asymmetric structure with a dense skin layer and a porous substructure. Macro-voids were observed in the membrane substructures for all compositions. The permeation of different organic solvents was measured for all prepared membranes in dead-end filtration cells. The flux of organic solvents through these membranes was found to depend directly on the blend composition. The highest flux for alcohol and alkanes was achieved for a 50/50 wt% blend while for acetone and methyl ethyl ketone the highest permeability was measured for a 75/25 wt% blend of PPSU/MI. A higher permeability of alkyl acetates was observed for the membrane made of 25/75 wt% PPSU/MI. Solvent stability of the membranes has been tested by measuring the methanol permeability and Sudan II rejection before and after solvent treatment. Except for pure PPSU, all membranes were stable in the examined solvents. The results confirm that the membranes prepared from these blends are promising to be used for organic solvent nanofiltration. For better insight into the phase behaviour of the PPSU/MI blend, dense reference membranes were prepared by solution casting and solvent evaporation, followed by pure liquid sorption, differential scanning calorimetry and gas permeation measurements.