The investigation of irregular inner skin morphology of hollow fiber membranes at high-speed spinning and the solutions to overcome it

In the fabrication of hollow fiber membranes, a high-speed spinning is important to maximize the productivity and minimize the production cost. However, the high-speed spinning process has been shown to influence the morphology of the resultant fibers, especially inner layer of the fibers. For the first time, we report that the increase in the take-up speed results in the deformation of inner shapes of the fibers. This phenomenon is not desirable as it results in the formation of low mechanical strength fibers. It is hypothesized that the phenomenon occurs due to the formation of vacuum condition in the lumen side of the fiber, which may be due to rapid formation of dense skin inner layer. With increasing take-up speed the inner surface becomes denser leading to insufficient bore fluid supply which promotes more vacuum condition in the lumen side. Four possible solutions were proposed to eliminate the inner layer deformation phenomena, i.e. (1) by increasing the bore fluid flow rate, (2) by chemical modification of the bore fluid, (3) by simultaneously increasing dope and bore flow rates while maintaining a constant ratio between them and (4) by simultaneously increasing bore and dope flow rates in the same order with the increase in take-up speed.