Spinning of hollow porous fibres via the TIPS mechanism

Hollow porous fibres have been spun from solutions of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) in cyclohexanol. This solution exhibits liquid-liquid phase separation upon cooling and two different cooling ways were used in the continuous process employed: spinning into the open air (dry spinning) and quenching in a water bath (air-gap spinning). In the first process the temperature of the spinneret was used as a parameter, while in the dry-wet spinning process the air-gap length was altered. The fibres could be used for the separation of oxygen and nitrogen and the selectivity was perfect, however the permeability was too low. In order to analyze the influence of different cooling histories across the fibre thickness, and the final local morphology, calculations were performed on cooling rates occurring in fibre spinning and specimens were prepared under a wide range of controlled cooling circumstances and analyzed using SEM. Now it is principally possible to optimize the process in order to reach asymmetric hollow fibres with an open, porous inner structure and a closed thin skin, in order to combine good selectivity with high permeability.