Facile synthesis of Kevlar nanofibrous membranes via regeneration of hydrogen bonds for organic solvent nanofiltration

Polymeric organic solvent nanofiltration (OSN) membranes have gained increasing attention in OSN for their relatively low cost and ease of scaling up. However, fabrication processes are still complex, consume a large amount of aggressive solvents and sometimes even pose a safety risk in fabrication, resulting in a negative environmental impact and still having potential to lower the fabrication cost further. In this study, thin Kevlar nanofibrous organic solvent nanofiltration membranes were fabricated through a facile and green thermal treatment by using greener solvent. Instead of corrosive concentrated H2SO4, a greener solvent, i.e., a DMSO-KOH/water mixture was used to prepare a dope solution containing Kevlar nanofibers. Then, hydrogel ultrafiltration membranes were obtained from this dope solution by phase inversion. Subsequently, a facile thermal treatment in an oven was applied to transform the hydrogel ultrafiltration membrane into a solvent resistant nanofiltration membrane without consuming additional solvents and crosslinking agents by the regeneration of hydrogen bonds. The obtained nanofibrous membrane (M2%-200) has a Rose Bengal rejection of 95.4% and an ethanol permeation of 2.9 L/(m(2) bar h), outperforming most other polymeric pristine OSN membranes prepared by phase inversion. This gives the Kevlar membrane a high baseline for further modification in order to increase the performance. In addition, Kevlar nanofiltration membranes maintain a relatively constant dye rejection during the filtration of a dye solution for 6 h and retain a dye rejection over 94% after being treated by different solvents for 7 days, indicating a very good solvent resistance. Moreover, this study not only provides a facile way of synthesizing Kevlar OSN membranes from a dope solution containing nanofibers, but also enables the fabrication and application of Kevlar threads in membranes by a non-corrosive and greener solvent, which may open up new insights and strategies to develop Kevlar into nanofiltration membranes.