Precipitation of Nylon 6 membranes using compressed carbon dioxide

Membrane formation using a compressed antisolvent is analogous to conventio nal immersion precipitation using liquid nonsolvents and introduces pressur e as an additional variable for tailoring the membrane microstructure. Thin films of a semicrystalline polyamide, Nylon 6, were precipitated from 2,2, 2-trifluoroethanol by exposing the incipient membrane to compressed CO2 ant isolvent at 35 degreesC and variable pressures up to 173.4 bar. Membrane st ructures dominated by liquid-liquid (L-L) and solid-liquid (S-L) demixing p rocesses were observed as a function of precipitation conditions. Interpret ation of the resulting membrane morphologies was based on structural featur es observed for traditional phase inversion processes and reflected the rel ative rates of L-L and S-L demixing as a function of the pressure-dependent strengths of the solvent and antisolvent. The ability to tailor the morpho logy of a semicrystalline membrane using compressed antisolvent suggests an alternative to current CO2-based polymer impregnation techniques, which re quire solute solubility in CO2, for the generation of composite thin films and membranes. (C) 2001 Elsevier Science Ltd. All rights reserved.