THE EFFECTS OF SPINNING CONDITIONS ON ASYMMETRIC 6FDA 6FDAM POLYIMIDEHOLLOW FIBERS FOR AIR SEPARATION/

We have found that the chemistries of inner and external coagulants, g elation bath temperature, and air gap distance have profound effects o n 6FDA-polyimde hollow-fiber morphology and performance. This 6FDA-pol yimide is made of 50 mol % 2,2'-bis(3,4'-dicarboxyphenyl) hexafluoro p ropane dianhydride (6FDA) and 50 mol % 2,2'-bis(S-aminophenyl)hexafluo ro propane (4,4' GF-diamine)(6FDAM). An increase in air gap distance t ends to induce three-dimensional open-cell pore formation. Raising bat h temperature has a similar effect. Multilayer finger-void structure c an be completely eliminated if one properly chooses a bore-fluid flow rate and a gelation bath temperature. Experimental data demonstrate th at the location of the dense layer can be shifted from the inner skin to the outer skin based on the chemistry (solubility parameter) of coa gulants. The location of finger voids is also dependent on the chemist ry of coagulants, and the dense layer location may shift from the inne r surface to the external surface or appear in both surfaces dependent on the differences in solubility and coagulation rate. A defect-free 6FDA/6FDAM polyimide fiber with a selectivity of 4.73 and a permeance of 38.1 GPU is produced. (C) 1997 John Wiley & Sons, Inc.