Effects of dope compositions on morphologies and separation performances of PMDA-ODA polyimide hollow fiber membranes in aqueous and organic solvent systems

摘要

Hollow fibers (HFs) fabricated with organo-insoluble polyimides are rarely adopted in the application of organic solvent nanofiltration (OSN), since the insolubility limits their processability. To deal with it, its precursor polyamic acid (PAA) is selected to fabricate HFs, but the slow phase inversion nature of PAA may lead to filament breaking during spinning. In an earlier study, we have successfully addressed the processing of spinning PMDA-ODA PAA HFs with regular cross-sections, but the membrane's separation performances is not shown. Here for optimal performances, we investigate the effects of dope compositions including polymer concentration, ethanol (EtOH) and TiO2 additives on the pore size and pore size distributions, hydrophilicities, and separation properties of PMDA-ODA PI HF membranes in both aqueous and organic solvent systems. The results showed that polymer dopes with high concentrations of PAA or EtOH led to high rejections but sacrificing permeability. Interestingly, just adding 1.1 wt% TiO2 in dope solutions significantly increased membrane porosities, hydrophilicities and decreased membrane surface charges. Therefore, membrane water fluxes were doubled and rejections to negatively charged dyes increased. At last, the PMDA-ODA PI HF membranes showed good separation performance in organic solvents also. The optimal permeability and rejection in DMF solution was 2.51 L m(-2) h(-1) bar(-1) and 90.6% for FG (Fast Green, MW = 808 Da) dye. Hence, the PMDA-ODA PI HF membranes are suitable for applications in both aqueous and organic systems.