Fluoropolymer membranes blending

Yi et al. reported a new type of PVDF membrane prepared by blending two very different polymers, a PVDF fluoropolymer such as Kynar with a sulfonated poly-electrolyte. The new membrane is inexpensive and displayed good performance and durability based on 1,000-h test data. 

To enhance membrane mechanical and hydro-thermal stability, Jiang et al. prepared a blend of side-chain sulfonated PFCB block copolymer and a PVDF fluoropolymer [129]. The chemical structure of the side-chain sulfonated PFCB ionomer is shown in Scheme 6.32. They evaluated the membrane s fiandamental properties, such as proton conductivity, gas permeability, water uptake, and... 

To realize the long-term hydrophilicity of the blend polymer membranes, the key point is to improve the stability of the hydrophilic component on the membrane surface and matrix. To this end, amphiphilic polymers have been adopted to replace linear hydrophilic PEG and PVP in membrane preparation. Theoretically, improved interactions among the hydrophobic segments in amphiphilic polymers and the fluoropolymer can improve the compatibility of the blend, and thus enhance the stability of amphiphilic polymer in the membrane matrix. Three kinds of amphiphilic polymers, viz., triblock copolymer of poly(ethylene oxide)-( -poly(propylene oxide)-ft-poly(ethylene oxide) (EPE), comb-like copolymer of polysiloxane with poly(ethylene oxide) and poly(propylene oxide) side chains (ACPS), and the hyperbranched star copolymer of polyester-g-methoxyl poly(ethylene glycol) (HPE-g-MPEG), have been... 

As a substimte to Nafion impregnation into a fluoropolymer matrix, solution cast films have been prepared from blends of Nafion and vinylidene fluoride-hex-afluoropropylene copolymer [16]. Upon addition of 20 60% vinylidene copolymer, a steep decrease in proton conductivity was observed, from 10 " S cm to 10 -10 S cm , which was accompanied by a significant decrease in methanol permeability. In a more recent paper [27], Si et al. solution cast membranes composed of Nafion and poly(vinylidene fluoride), henceforth denoted as PVDF, where characterized where the PVDF content was varied from 0 to 65 wt%. As expected, the conductivity and methanol permeability decreased with inaeasing PVDF content, with a much more dramatic drop in transport parameters when the PVDF content was >50%. From proton conductivity and methanol permeability data, the relative selectivity can be determined ... 

Due to the unacceptably high methanol permeability of commercial Nafion, most DMFC tests are performed with relatively dilute aqueous methanol feed solutions (typically, 0.5 or 1 M). A Nafion-PBI membrane (5 wt% PBI with Nafion polymer that was 40% in the protonated form) performed well at low (1 M) and high (5 M) methanol feed concentrations, as shown in Fig. 14.19. As was the case for the Nafion-FEP and Nafion-PFA blends discussed previously, PBI-doped Nafion films contain much less fluoropolymer (2-A times less) as compared with commercial 117 membranes from DuPont, yet their performance is equal or superior to any Nafion material in a DMFC. 

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