Polytetrafluoroethylene membrane composition

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... 

Xing, D. M., Yi, B. L., Liu, F. Q., Fu, Y. Z. and Zhang, H. M. 2005. Characterization of sulfonated poly (ether ether ketone)/polytetrafluoroethylene composite membranes for fuel cell applications. Fuel Cells 5 406M11. 

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... 

For areas with special application requirements, specifically modified polyester fabrics, as well as fabrics from aramid fibres, fluorine polymers and arylamides like Kevlar (ref. DuPont), have proved to be satisfactory. The membranes show different characteristics depending on the coatings used. Fluorine polymers such as PVDF (polyvinylidene fluoride) are used on PES fabrics (refs Mehler and Ferrari) a PTFE (polytetrafluoroethylene) coating is very suitable for fibreglass fabrics (ref Verseidag) and there is a newly developed composite membrane with THV (ret Dyneon), a polymeric blend of tetrafluoroethylene, hexafluoropropylene and vinylidenefluorine, used as a coating on PES fabrics, of which VALMEX vivax (ret Mehler) is one example. 

Asymmetric and composite membranes commercially known as HYFLON AD are obtained from copolymers of tetrafluoroethylene (TFE) and 2,2,4-trifluoro-5-trifluoromethoxy-l,3-dioxole (TTD) these membranes show a high hydrophobic character with contact angles to water greater than 120° (Arcella et al. 1999). Hydrophobic membranes from copolymers of polytetrafluoroethylene (PTFE) and polyvinylidenefluoride (PVDF) were prepared by a phase inversion process (Feng et al. 2004) these membranes exhibit excellent mechanical properties and good hydrophobicity (contact angle to water of about 87°). 

Yang L, Li H, Ai F et al (2013) A new method to prepare high performance fluorinated sulfonic acid ionomer4>orous expanded polytetrafluoroethylene composite membranes based on perfluorinated sulfo-nyl fluoride polymer solution. J Power Sources 243 392-3%... 

The biggest application for fiuorinated ionomers currently is as unreinforced membranes for fuel cells, or polytetrafluoroethylene (PTFE) fiber-reinforced composite membranes for electrolytic baths. The membranes can be fabricated by the extrusion method or the solution-cast method. 

Fig. 8.4 CNT nanocomposite membrane process, (a) Schematic membrane fabrication process. Step h The functionalized CNTs are dispersed in THF solution. Step 2 The CNTs/THF solution is filtered through 0.2 pm pore size hydrophobic polytetrafluoroethylene (PTFE) membrane filter. Step 3 The CNTs/PTFE membrane is spin coated with a dilute PS solution. Some nanotube tips are embedded in polymer matrix, (b) Side-view SEM image of CNTs standing vertically on a membrane filter, (c) Side-view SEM image of aligned nanotube/PS nanocomposite membrane after spin-coating. Polymer coating is so thin that some CNT tips are exposed on top of the surface, (d) Side-view SEM image of aligned nanotube/PS/PDMS composite membrane with a protective PDMS coating of 4 pm. (From [8])...

Xing, D., He, G., Hou, Z., Ming, P, and Song, S. (2013) Properties and morphology of Nafion/polytetrafluoroethylene composite membrane fabricated by a solution-spray process, Int. J. Hydrogen Energ., 38, 8400-8408. 

Recently, they fabricated the polytetrafluoroethylene (PTFE)-reinforced SPEEK composite membranes to improve their chemical stability and ion selectivity in VRB applications. Compared to pristine SPEEK membranes, the composite membranes exhibited the lower swelling ratio and higher mechanical stability due to the PTFE reinforcement. As expected, the SPEEK/PTFE membranes showed much higher coulombic efficiency and energy efficiency than those of SPEEK membrane. In addition, the composite membranes exhibited much better stability than pristine SPEEK under VRB operating conditions. 

Wang, X. Li, M. Golding, B. T. Sadeghi, M. Cao, Y Yu, E. H. Scott, K., A polytetrafluoroethylene-quatemary l,4-diazabicyclo-[2.2.2]-octane polysulfone composite membrane for alkaline anion exchange membrane fuel cells. International Journal of Hydrogen Energy 2011, 36(16), 10022-10026. 

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]. 

Recently, PVDF has become a more popular material to produce hydrophobic membranes through phase inversion processes, mainly for membrane contactor and MD applications. It is preferred to other more hydrophobic polymers, such as polypropylene and polytetrafluoroethylene, because of its excellent combination of properties and its solubility in common organic solvents. Furthermore, the excellent thermal stability of PVDF has made it interesting as a membrane material in a wide range of industrial applications. In addition, unlike other crystalline polymers, PVDF exhibits thermodynamic compatibility with other polymers, such as poly(methyl methacrylate) (PMM A), over a wide range of blend compositions, which can be useful in the fabrication of membrane with desired properties. PVDF can be further chemically modified to obtain specific functions. In addition, it can be cross-linked when subjected to electron beam radiation or gamma radiation. 

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