Abstract
The geometry of polymeric hollow fibers for hemodialysis or desalination is a key factor determining their performance. Deformations are frequently observed, but they are rather random. Here we were able to exactly control the shape evolution of the internal channels or lumens of polymeric hollow fibers, leading to polygonal geometries with increasing number of sides. The elasticity of the incipient channel skin and instabilities during fiber formation are affected by the internal coagulant fluid composition and flow rate; and highly influence the polygonal shape. We propose a holistic explanation by analyzing the thermodynamic, kinetic and rheological aspects involved in the skin formation and their synergy.
Highlights
Instabilities in polymeric fiber spinning might primarily determine the overall process economics in terms of fiber quality and fiber production rate
Hollow fibers for hemodialysis or water treatment are commonly manufactured by solution processes using an spinneret
Longitudinal instability in fiber spinning mainly occurs when one applies a normal stress on the incipient fibers, at certain fiber collection speeds
Summary
The geometry of polymeric hollow fibers for hemodialysis or desalination is a key factor determining their performance. The three primary instabilities during polymeric fiber spinning are: (i) local instabilities in polymer-lean regions in the polymer bulk flow, (ii) longitudinal instability under fiber collection and (iii) circumferential instability caused by radial/normal stresses Understanding their fundamental mechanisms is crucial to control or overcome these instabilities. Compared to the two other instabilities above, which have been widely studied and understood, circumferential instability is less analyzed and contradictory experimental observations were obtained in various reports[14,15,16] This type of spinning instability leads to fiber deformation, where its wall thickness is non-uniform and its cross-sectional shape is not circular. To understand the underlying instability that causes fiber deformation and the reasons of controversial experimental observations, for the first time we analyzed thermodynamic, rheological and kinetic aspects of the polymer system and hollow fibers preparation. Regular shapes of fiber inner contour were achieved and their corresponding interpretations are more representative
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