Composite membranes porous polytetrafluoroethylene

J. Xu et al. [283] have shown that immobilization of enzymes can be done using a specially designed composite membrane with a porous hydrophobic layer and a hydrophilic ultrafiltration layer. A polytetrafluoroethylene (PTFE) membrane with micrometer pores as an excellent hydrophobic support for immobilization was employed for the porous hydrophobic layer, and a biocompatible material of polyvinyl alcohol (PVA) which provided a favourable environment to retain the lipase activity was used to prepare the hydrophilic... 

More recently, W. L. Gore Associates, Inc. [31] have used expanded polytetrafluoroethylene (ePTFE) porous films and PFSA resin solutions to produce a composite membrane. In this process, the PFSA solution was brushed onto both sides of the ePTFE film so as to impregnate and substantially occlude the interior volume of the film a nonionic surfactant (5%, w/v) was then added into the PFSA solution as a penetrant. The surfactant was removed by soaking in isopropanol after drying at 140 °C (this procedure was repeated several times so as to fully occlude the interior... 

Yang, L., Li, H., Ai, F., Chen, X., Tang, J., Zhu, Y, Wang, C., Yuan, W.Z., Zhang, Y, and Zhang, Y. (2013) A new method to prepare high performance fluorinated sulfonic acid ionomer/porous expanded polytetrafluoroethylene composite membranes based on perfluorinated suHonyl fluoride polymer solution, J. Power Sourc., 243, 392-396. 

The selective layer of a membrane should be as thin as possible since the flux is inversely proportional to the membrane thickness. Thus, membranes for industrial applications are composite structures with a thin selective dense layer (0.5-5 micron) on a porous and mechanically stable support (Figure 20.2a) [20, 21]. This issue is particularly important for a soft and elastic material such as PDMS. The nature of the support can be organic (e.g., cellulose acetate, polysul-fone, polytetrafluoroethylene, polyvinylidine fluoride, etc.) or inorganic (e.g., alumina, titania). The support is often backed by a highly porous non-woven layer. In principle, the role of the support on the mass transport should be negligible, but it could be predominant in some cases [22]. 

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