Membranes PTFE reinforcement

PFSA lonomer and PTFE Reinforcement at Asahi Kasei Aciplex Membranes.794... 

The molecular structure of a conventional polymer used for a PFSA membrane is shown in Fig. 1. Membranes registered as Nafion (DuPont), Flemion , (Asahi Glass), and Aciplex (Asahi Chemical) have been commercialized for brine electrolysis and they are used in the form of alkali metal salt. Figure 4 shows a schematic illustration of a membrane for chlor-alkali electrolysis. The PFSA layer is laminated with a thin perfluorocarboxylic acid layer, and both sides of the composite membrane are hydrophilized to avoid the sticking of evolved hydrogen and chlorine. The membrane is reinforced with PTFE cloth. The technology was applied to PEFC membranes with thickness of over 50 xm [14]. 

Wang L, Yi B, Zhang H, Liu Y, Xing D, Shao ZG, et al. Sulfonated polyimide/PTFE reinforced membrane for PEMFCs. J Power Sources 2007 167(l) 47-52. 

Figure 10.3.18 illustrates the structure of the electrode/membrane system where the membrane (e.g., Nafion 900 Series) is reinforced by a nonconductive polytetrafluoroethylene (PTFE) fabric. Note that the current flux deforms around the PTFE reinforcement, leading to an increase in the voltage drop through the membrane. Therefore, the arrangement of the PTFE reinforcement must be optimized for mechanical strength and voltage drop. 

The porous PTFE reinforced QNPSU (QNPSU/PTFE) composite membrane was prepared by surface activation of porous PTFE (thickness 30 pm) as described in Sect. 12.2.3 [69]. The activated PTFE-ca was used for preparing the QNPSU/PTFE-ca composite membrane following the scheme as shown in Fig. 12.21. 

Lu S, Xiu R, Xu X et al (2014) Polytetrafluor-oethylene (PTFE) reinforced poly(ether sulfone)-poly(vinyl pyrrolidone) composite membrane for high temperature fuel cells. J Membr Sci 464 1-7... 

Zhang Y Zhang H, Zhu X, Gang L, Bi C etal. (2007c), Fabrication and characterization of a PTFE-reinforced integral composite membrane for self-humidifying PEMFC , J. Power Sources, 165, 786-792. 

Zhu X, Zhang H, Liang Y, and Zhang Y (2006), A novel PTFE-reinforced multilayer self-humidifying composite membrane for PEM fuel cells , Electrochem. Solid-State Lett., 9,A49-A52. 

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. 

Perfluorinated membranes reinforced with woven PTFE, such as Nafion 324 or Nafion 417, are used in many industrial electrochemical processes. Unfortunately, the relatively coarse weave of the woven PTFE reinforcement results in membranes that are much too thick for high electrochemical performance. Some non-woven PTFE/perfluorinated ionomer composite membranes have been formulated for ion transport studies and for investigation of other properties relevant to chlor-alkaU and fuel cell applications. Advancements in materials and processing technology have resulted in the introduction of PTFE/perfluorinated ionomer composite membranes claimed by Gore and Associates, Inc. under the Gore Select trademark. Most types of ion exchange membranes contain some type of reinforcement because they are weak and tend to swell substantially as they incorporate a solvent onto their structure. This reinforcement can be a macro reinforcement or a micro reinforcement . 

Water uptake and swelling of reinforced PEMs have also been studied. It has been found that water uptake and water flux of Nafion/porous PTFE PEMs increases with increased ionomer loading and that the rate of water uptake as a function of temperature is actually higher for the reinforced membrane in comparison to Nation 112.2 However, it was also seen that the actual water uptake of a similar reinforced membrane was about half as much as a Nation 1135 sample with a commensurate lower degree of swelling.2 ... 

A few studies have reported the embedding of an MIP film between two membranes as a strategy for the construction of composite membranes. For example, a metal ion-selective membrane composed of a Zn(II)-imprinted film between two layers of a porous support material was reported [253]. The imprinted membrane was prepared by surface water-in-oil emulsion polymerisation of divinylbenzene as polymer matrix with 1,12-dodecanediol-0,0 -diphenylphosphonic acid as functional host molecule for Zn(II) binding in the presence of acrylonitrile-butadiene rubber as reinforcing material and L-glutamic acid dioleylester ribitol as emulsion stabiliser. By using the acrylonitrile-butadiene rubber in the polymer matrix and the porous support PTFE, an improvement of the flexibility and the mechanical strength has been obtained for this membrane. 

Table IV indicates the degree of elongation found for membranes reinforced with PTFE fabric.

Table IV. Elongation of Perfluoro Ionomer Membrane Reinforced with PTFE Fabric.

Membrane Fabrication, Lamination and Reinforcement. The thermoplastic copolymer of TFE and PVEX monomer can be extruded or molded into a thin film by conventional methods. Extrusion is most appropriate for continuous production of large membranes because it facilitates control of film thickness. Lamination can be performed with a roll press to obtain multilayer membrane. To improve their mechanical properties, membranes are generally reinforced with an inert material such as fabric made of PTFE (67, 68), fibriled PTFE (69), or wire netting (70). 

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