Single-step preparation of nanocomposite polyamide 6 hollow fiber membrane with integrally skinned asymmetric structure for organic solvent nanofiltration

An integrally skinned organic solvent-resistant membrane with asymmetric structure for organic solvent nano-filtration (OSN) application was developed via thermally induced phase separation (TIPS) of nanocomposite polyamide 6. The nanocomposite polyamide 6 contains intercalated silicate sheets, which could improve the mechanical properties of the resultant membrane, as well as mitigate swelling after exposure in solvent. The influence of nanocomposite polyamide 6 composition of the hollow fiber membrane and the subsequent thermal annealing was investigated in this study. Crystallinity data revealed that polyamide 6 crystal formed during the TIPS process was primarily alpha-phase type, but the use of nanocomposite polymer initiated the formation of gamma-type crystalline structure. Thermal annealing at 120 degrees C was also found to even promote a higher overall crystallinity of the membranes. The membranes were subjected for OSN operation with methanol (MeOH) as solvent and cyanocobalamin (vitamin B-12) as the solute. The intercalated silicate sheets in the nanocomposite polyamide 6 brought about the dense outer surface and sublayer formation, resulting in higher mechanical properties and stability in MeOH; however, the membranes formed with purely nanocomposite polyamide 6 suffered from very low permeance, primarily due to the dense outer surface and sublayer. The membrane whose composition is 50% nanocomposite polyamide 6 exhibited MeOH permeance of 0.1 L m(-2) h(-1) bar(-1) and vitamin B-12 rejection of over 99.0%. This work was able to provide how polymeric material, thermal annealing, and the resultant crystallinity could affect the membrane's mechanical properties and filtration performance with solvent resistance.