Super-selective polysulfone hollow fiber membranes for gas separation: rheological assessment of the spinning solution

A polysulfone spinning solution used recently to produce enhanced selectivi ty gas separation hollow fiber membranes was theologically assessed using a rotational rheometer and an optical shear cell. Effects of temperature and shear rate on viscosity, power law behavior and normal force provided some clues regarding phase inversion and molecular orientation. At relatively l ow temperatures, phase inversion may occur in the absence of a shear held. At moderately low temperatures, phase inversion may be induced by applied s hear. At higher temperatures, phase inversion is not induced by shear but r ather shear induces molecular orientation. The results suggest that, unless spinning at low temperature, extrusion she ar does not directly induce demixing during membrane formation but, instead , is linked indirectly to phase inversion through induced molecular orienta tion which, in turn, affects the subsequent dry or ever precipitation stage s in spinning. This work is a step towards the construction of phase diagra ms and determining their distortion in shear fields. Such knowledge, couple d with deeper insights into induced polymer molecule orientation, would ena ble further improvements in spinning techniques and membrane performance. ( C) 2001 Elsevier Science Ltd. Ail rights reserved.