Creation Of Highly Stable Porous Polyacrylonitrile Membranes Using Infrared Heating

Highly stable porous membranes made of commercial polyacrylonitrile (PAN) were developed for high pressure application in aprotic solvents. The membranes prepared by NIPS method from the casting solution with PAN concentration of 15 or 18 wt% in DMSO demonstrated good mechanical stability towards the transmembrane pressure of 30 bar and MWCO of 22 and 14.5 kg/mol, respectively; whereas the lower polymer concentration (12 wt%) led to collapsing of porous structure based on SEM data. By adjustment of treatment time and temperature, it was shown that the porous PAN membranes became insoluble in aprotic solvents such as DMSO, DMF, DMAc, and NMP after 5 min of infrared heating at 170 degrees C. The analysis of the data obtained by SEM, liquid liquid displacement porosimetry, solvent filtration, and MWCO revealed that such IR treatment did not noticeably change the membrane structure and properties originally formed during the membrane casting. Replacement of conventional heating reported in the literature by IR heating allowed to reduce the treatment time from 6 h at 250 degrees C down to 5 min at 170 degrees C (estimated energy saving by a factor of 6.5). The mechanism of the transformation of PAN into insoluble form was proposed based on the data of FTIR analysis. The hypothesized role of adsorbed water molecules in accelerating cross-linking of PAN upon the near-IR heating was considered and discussed. IR treated PAN membranes can be employed as porous supports for solvent resistant nanofiltration membranes or directly as ultrafiltration membranes for non-aqueous applications.