Extrusion process fiber membranes

The formation of the hollow fiber membrane via TIPS process has not been studied very much. Kim et al. [13] prepared poypropylene hollow fiber membrane from polypropylene/soybean oil mixture. The membrane was formed by the TIPS process and subsequent cold-stretching. The hollow fiber became more oriented by increasing the melt-draw ratio defined as the ratio of take-up speed to the extrusion of the polymer solution. The cold-stretching of the hollow fiber membranes remarkably increased the membrane porosity. 

The selection of the polymer material for the production of dialysis membranes has significant implications on the quality of hemodialysis therapy. Only a limited number of polymers are suitable for the spinning and extrusion process involved in the manufacture of capillary membranes. The selection was originally based on experiences from textile fiber production. Further, biochemical and physical properties that may result from the membrane formation process, determine the selection of a polymer. The ideal polymer family should allow the production of biocompatible dialysis membranes and possess a stable physical stability. The latter guarantees an easy production process and sterilization without problems. 

Besides the abovementioned advantages, ceramic hollow-fiber membranes unveil further superiorities over other ceramic membranes. In addition to a substantially higher surface area/volume ratio due to the smaller radius, the unique microchannels inside the membrane wall play an important role in lowering mass transfer resistance and elevate the accessible geometric and specific surface areas. Such a structure is formed due to the concurrence of several process phenomena during the membrane fabrication, which is different from the conventional ram-extrusion-based process where only a simple symmetric structure can be delivered. 

Commercially PTFE is available in granular and fine powder resin forms and aqueous dispersions. The granular form of PTFE resin is prepared by suspension polymerization process in an aqueous mediiun with little or no dispersing agent. These forms of PTFE resins are mainly used for compression molding and ram extrusion. The fine PTFE powder is prepared by controlled emulsion polymerization and it is useful for paste extrusion into tapes, tubes, pipe liners, insulation layer of wires, gas-liquid separation membranes and fibers. 

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