Effect of Draw Ratio on the Morphology of Polysulfone Hollow Fiber Membranes
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ct of Draw Ratio on the Morphology of Polysulfone Hollow Fiber Membranes D. N. Matveeva, *, K. A. Kutuzova, and V. P. Vasilevskya aTopchiev
Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected] Received July 15, 2020; revised August 1, 2020; accepted August 11, 2020
Abstract—The draw ratio (DR) is an important parameter in the process of spinning hollow fiber membranes, by which their separation and performance characteristics can be controlled over a wide range of values. For the first time, a method for determining the DR using a roller movable in the vertical direction is described, which makes it possible to establish the ratio of the dope extrusion linear flow rate to the take-up speed. In the course of the work, polysulfone hollow-fiber membranes were obtained at various DR values. The influence of the draw ratio on the morphology and geometric and gas transport properties of the resulting polysulfone hollow fiber membranes has been examined. Keywords: hollow fiber membrane, dry-jet wet forming, postspinning drawing, polysulfone DOI: 10.1134/S2517751620060074
INTRODUCTION Polymer hollow fiber membranes were first described in 1966 [1]; however, improving their fabrication methods is still a demanding task [2–7]. The hollow fiber membrane configuration provides a large separation surface area due to a high packing density of the membrane in a module compared to flat and tubular membranes. A porous asymmetric hollow fiber membrane is an anisotropic structure with a denser (finely porous) selective layer, which is located on the porous substrate of the same material. The porous substrate may or may not contain macropores of various configurations, most often finger-shaped. The selective layer can be located both outside and in the bore of the hollow fiber [5]. The porosity and thickness of the selective layer depend primarily on the composition of the dope solution and on the conditions for making the hollow fiber membrane. By varying the spinning parameters of hollow fibers and the composition of the dope solution, it is possible to control the characteristics of the membrane and optimize its properties for specific separation tasks [4, 5]. Hollow fiber membranes can be fabricated by dry or wet spinning processes, or by a combination thereof, that is, a dry-jet wet process. During membrane spinning in the hollow fiber form, phase inversion—a phase separation process in which a liquid polymer solution is transformed into its solid state— occurs [3]. Despite various processes for fabricating hollow fiber membranes, in all cases, the polymer
solution is extruded through a special device, a spinneret. Dry-jet wet spinning is most widely used to obtain membranes for various purposes [3, 5]. This method for fabricating hollow fiber membranes is characterized by the presence of an air gap between the spinneret and the coagulation bath. At the spinneret outlet, we have the so-called nascent hollow fiber membrane. During its residence in the air gap, parti
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