Optimization of solvent resistant nanofiltration membranes prepared by the in-situ diamine crosslinking method

Diamine crosslinked polyimide membranes are well known for their excellent performance in pervaporation, gas separation and solvent resistant nanofiltration, as well as for the use as support layers. The generally used post-synthesis crosslinking method involves a second processing step, plus the use of methanol, an environmentally hazardous compound. The recently developed in-situ crosslinking method avoids the use of methanol by introducing the diamine crosslinker as an additive in the coagulation bath containing water. In this study, the effect of the presence of the crosslinker in the coagulation bath on the structure and performance of the membranes is investigated. Starting from different membrane compositions, the influence of the type of crosslinker and its concentration are investigated. Based on these results, a parameter-by-parameter optimization of the phase inversion parameters was done for this crosslinking method. The membranes were characterized by scanning electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy and solvent resistant nanofiltration experiments. In DMF, the optimal membranes show 10 times higher fluxes than the commercial Duramem® series at equal rejections.