Composite membranes reinforcement

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. 

Figure 14. Strain-to-failure versus number of cycles for two types of MEAs one with a reinforced composite membrane (Gore-5510) and the other with regular PFSA membrane (N- 111). The samples are cycled from 30 to 80% RH and from 80 to 120% RH.37...

For industrial applications, where the membrane sizes are larger, reinforcement of the thin skin membrane by an appropriate support is required to maintain dimensional stability. This type of membrane consisting of a skin layer (perm-selective layer) supported by a suitable support is called a composite membrane. 

The main driving force for the development of reinforced composite membranes has been the possibility of increasing both mechanical strength and dimensional stability, leading to the feasible production of very thin membranes. As mentioned in Section 10.2.2, as the cell resistance increases proportionally to the thickness, an improvement in PEMFC performance could easily be achieved by using thin, reinforced composite membranes. From a cost perspective, such thin reinforced composites would contain much less of the expensive ionomer resin than conventional membranes. 

A novel, thin, three-layer reinforced and self-humidifying composite membrane,... 

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]. 

Before fabrication of the membranes, the terminal group is converted to a more stable form, sulfonyl fluoride or methyl carboxylate. Then the copolymer is extruded to form a membrane. The extmded films can be further processed to achieve a variety of membrane properties. They can be laminated with PTFE fabric to produce a reinforced membrane, and membranes made of polymers with different values of m, n, p or q can be laminated to form composite membranes with desired properties. After fabrication is complete, the X group is converted by hydrolysis to SO3 or COO". 

Referring to microbial cellulose applications, bacterial nanocellulose has proven to be a remarkably versatile biomaterial with use in paper products, electronics, acoustic membranes, reinforcement of composite materials, membrane filters, hydraulic fracturing fluids, edible food packaging films, and due to its unique nanostructure and properties, in numerous medical and tissue-engineered applications (tissue-engineered constructs, wound healing devices, etc). 

Figure 17. SEM micrographs for the PVA/PAA composite polymer membrane reinforced with sulfonated PP/PE separator (a) top surface and (b) cross-section.

Liu YH, Yi BL, Shao ZG, Xing DM, Zhang HM, Carbon nanotubes reinforced Nation composite membrane for fuel cell applications. Electrochem Solid-State Lett 2006 9 A356-9. 

Nafion-112, and Nafion-212, use the thicker membrane Nafion-117 in DMFCs. The use of crosslinked PVA electrospun nano-fiber film supported Nafion composite membranes (Nafion/ PVA-fiber, thickness 50 pm) in DMFCs has been reported to exhibit a much better DMFC performance than Nafion-117 and Nafion/PVA blended PEMs [26-31]. Several researchers blended the Nafion PEMs with low methanol compatible PVA to reduce the methanol crossover in the PEMs [32-35]. However, these modified Nafion membranes had thicknesses greater than 175 pm, which were similar to (or higher than) that of the neat Nafion-117 membrane. Although there was a decrease in the methanol crossover from these Nafion/PVA blended membranes, the proton transfer resistance of these membranes increased, resulting in a lower DMFC performance. The advantage of applying the thin Nafion/PVA-fiber PEMs to the DMFCs is that the methanol crossover can be reduced without increasing the area specific resistance (i.e., Lla) because of low membrane thickness. Table 12.1 summarizes the thickness, proton conductivity, and Lja of the fiber reinforced Nafion composite membranes obtained from literature reports. The mechanical properties of the composite membranes reported in literature are also listed in Table 12.2. 

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