AGING PHENOMENON OF 6FDA-POLYIMIDE POLYACRYLONITRILE COMPOSITE HOLLOWFIBERS/

We have observed time-dependent drifts in permeability and selectivity for two types of composite hollow fibers used for air separation. One was PVP [poly(4-vinyl pyridine)]/ 6FDA-durene/polyacrylonitrile (PAN) composite hollow fiber, and the other was 6FDA-3,5-diaminobenzonitril e/6FDA-durene/PAN composite hollow fiber. Their permeabilities dropped 50 to 70% after 3 to 5 months, while selectivities for O-2/N-2 deteri orated slightly with time. A systematic study was carried out to inves tigate the causes of this creep behavior. Various composite fibers, su ch as polyimide/Celgard and polyimide siloxane/PAN, were fabricated to simulate the aging process. We conclude that the aging phenomenon obs erved for these two 6FDA-durene/PAN composite fibers was not due to th e structure change of the PAN substrate, but mainly to the densificati on effect of the 6FDA-durene gutter layer on composite fibers. (C) 199 6 John Wiley & Sons, Inc.