Poly-ethylene tetrafluoroethylene-based

The significant contribution of Nafion or perfluorosulfonic membranes to the cost of the fuel cells stacks and the high alcohol crossover levels that affect the fuel efficiency, prompted the development of radiation grafted proton exchange membranes based on poly(ethylene-tetrafluoroethylene) (ETFE) [172-178], PVdF [175], andPTFE [179]. The peroxy radicals produced on the base polymer by y-ray, electron- or proton-beam, react with styrene to form a co-polymer that is then sulphonated. 

Screening tests were conducted on potential construction materials. The candidate materials evaluated included the following polytetrafluoroethylene (PTFE, TFE), fluorinated ethylene-propylene copolymer (FEP), perfluoroalkoxy-alkanes (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (E-CTFE), poly vinylidene fluoride (PVDF), polypropylene (PP), and polyvinyl chloride (PVC). These materials were chosen based on cost, availability, and information from manufacturers on compatibility with acid solutions. 

Examples of fluoroplastics include polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), ethylene—chlorotrifluoroethylene (ECTFE), ethylene—tetrafluoroethylene (ETFE), poly(vinylidene fluoride) (PVDF), etc (see Fluorine compounds, organic). These polymers have outstanding electrical properties, such as low power loss and dielectric constant, coupled with very good flame resistance and low smoke emission during fire. Therefore, in spite of their relatively high price, they are used extensively in telecommunication wires, especially for production of plenum cables. Plenum areas provide a convenient, economical way to run electrical wires and cables and to interconnect them throughout nonresidential buildings (14). Development of special flame-retardant low smoke compounds, some based on PVC, have provided lower cost competition to the fluoroplastics for indoors application such as plenum cable, Riser Cables, etc. 

H.P. Brack, H.G. Buhrer, L. Bonorand, and G.G. Scherer. Grafting of pre-irradiated poly(ethylene-alt-tetrafluoroethylene) films with styrene Influence of base polymer film properties and processing parameters. Journal of Materials Chemistry 10, 1795-1803 2000. 

To prepare PSSA-grafted fluoropolymers, poly(vinylidene fluoride-co-hexafluoropropylene), poly (ethylene-co-tetrafluoroethylene) and poly(tetrafluoroethylene-co-hexafluoropropylene) were used as base polymers. Each polymer was molded into a film (200-300 pm thick) and irradiated with y-ray at room temperature at the rate of 6.8 kGyh using a cobalt-60 source to obtain a total absorbed dose of 50 kGy. The irradiated film was immersed in nitrogen-purged styrene at 70°C for 8 h for... 

Brack HP, Biichi FN, Huslage J, Rota M, Scherer GG (2000) Development of radiation grafted membranes for fuel cell applications based on poly(ethylene-aZt-tetrafluoroethylene). In Pinnau I, Freeman BD (eds) Membrane formation and modification. ACS symposium series 744. Oxford University Press, New York, p 174 Brack HP, Scherer GG (1997) Macromol Symp 126 25 Brack HP, Biihrer HG, Bonorand L, Scherer GG (2000) J Mater Chem 10 1795 Walsby N, Sundholm F, KaUio T, Sundholm G (2001) J Polym Sci A 39 3008 Lee W, Shibasaki A, Saito K, Sugita K, Okuyama K, Suyo T (1996) J Electrochem Soc 143 2795... 

The acid-base Nafion composite membranes include blends of Nafion with polypyrrole (PPy) [98-104], polybenzimidazole (PBI) [105-107], poly (propyleneoxide) (PPO) [108, 109], polyfurfuryl alcohol (PFA) [110], poly(vinyl alcohol) (PVA) [111-115], sulfonated phenol-formaldehyde (sPF) [116], polyvinylidene fluoride (PVdF) [117-122], poly(p-phenylene vinylene) (PPV) [123], poly(vinyl pyrrolidone) (PVP) [124] polyanifine (PANI) [125-128], polyethylene (PE) [129], poly(ethylene-terephtalate) [130], sulfated p-cyclodextrin (sCD) [131], sulfonated poly(ether ether ketone) (sPEEK) [132-135], sulfonated poly(aryl ether ketone) (sPAEK) [136], poly(arylene ether sulfone) (PAES) [137], poly(vinylimidazole) (PVl) [138], poly(vinyl pyridine) (PVPy) [139], poly (tetrafluoroethylene) (PTFE) [140-142], poly(fluorinated ethylene-propylene) [143], sulfonated polyhedral oligomeric silsesquioxane (sPOSS) [144], poly (3,4-ethylenedioxythiophene) (PEDT) [145, 146], polyrotaxanes (PR) [147], purple membrane [148], sulfonated polystyrene (PSSA) [149, 150], polystyrene-b-poly(ethylene-ran-butylene)-bpolystyrene (SEES) [151], poly(2-acrylamido-2-methyl-l-propanesulphonic acid-co-l,6-hexanediol propoxylate diacrylate-co-ethyl methacrylate) (AMPS) [152], and chitosan [31]. A binary PVA/chitosan [153] and a ternary Nafion composite with PVA, polyimide (PI) and 8-trimethoxy silylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS) has also been reported [154]. 

PVDF and FEP based materials were not stable enough to be tested in fuel cells, but the authors prepared a similar AEM by electron-beam grafting of VBC onto poly (ethylene-co-tetrafluoroethylene) (ETFE) that has been used to prepare a MEA for ADMFC [204]. 

T. Tran Duy, S.I. Sawada, S. Hasegawa, Y. Katsumura, Y. Maekawa, Poly(ethylene-co-tetrafluoroethylene)(ETFE)-based graft-type polymer electrolyte membranes with different ion exchange capacities relative humidity dependence for fuel cell applications, J. Membr. Sci. 447 (2013) 19-25. 

H.P. Brack, F.N. Btichi, M. Rota and G.G. Scherer, Development of radiation-grafted membranes for fuel ceU applications based on poly(ethylene-alt-tetrafluoroethylene), Polym. Mater. Sci. Eng. 77, 368 (1997). 

Varcoe, J.R., Slade, R.C., Lam How Yee, E., Poynton, S.D., Driscoll, D.J., Apperley, D. C. (2007) Poly(ethylene-co-tetrafluoroethylene)-derived radiation-grafted anion-exchange membrane with properties specifically tailored for application in metal-cat-ion-free alkaline polymer electrolyte fuel cells. Chemistry of Materials, 19, 2686-2693. Slade, R.C., Varcoe, J.R. (2005) Investigations of conductivity in FEP-based radiation-grafted alkaline anion-exchange membranes. Solid State Ionics, Y16, 585-597. 

The most chemical-resistant plastic commercially available today is tetrafluoroethylene or TFE (Teflon). This thermoplastic is practically unaffected by all alkahes and acids except fluorine and chlorine gas at elevated temperatures and molten metals. It retains its properties up to 260°C (500°F). Chlorotrifluoroethylene or CTFE (Kel-F, Plaskon) also possesses excellent corrosion resistance to almost all acids and alkalies up to 180°C (350°F). A Teflon derivative has been developed from the copolymerization of tetrafluoroethylene and hexafluoropropylene. This resin, FEP, has similar properties to TFE except that it is not recommended for continuous exposures at temperatures above 200°C (400°F). Also, FEP can be extruded on conventional extrusion equipment, while TFE parts must be made by comphcated powder-metallurgy techniques. Another version is poly-vinylidene fluoride, or PVF2 (Kynar), which has excellent resistance to alkahes and acids to 150°C (300°F). It can be extruded. A more recent development is a copolymer of CTFE and ethylene (Halar). This material has excellent resistance to strong inorganic acids, bases, and salts up to 150°C. It also can be extruded. 

The inability to process PTFE by conventional thermoplastics techniques has nevertheless led to an extensive search for a melt-processable polymer but with similar chemical, electrical, non-stick and low-friction properties. This has resulted in several useful materials being marketed, including tetrafluoro-ethylene-hexafluoropropylene copolymer, poly(vinylidene fluoride) (Figure 13.1(d)), and, most promisingly, the copolymer of tetrafluoroethylene and perfluoropropyl vinyl ether. Other fluorine-containing plastics include poly(vinyl fluoride) and polymers and copolymers based on CTFE. 

Poly(hexafluoropropylene-co-vinylidene fluoride) n. 1,1,2,3,3,3-hexafluoro-l-propene-co-l,l-difluoroethene a fully fluorinated polymer based on gas CF3 CF=CF2, not commercial. However, the co-polymers of hexafluoropropylene and tetrafluoroethylene make up the family of fluorinated ethylene propylene resins (See image). 

Several other thermoplastic powders are available based on specialty polymers such as ethylene-chlorotrifluoroethylene [25101-45-5], poly(phenylene sulfide) [25212-74-2], and tetrafluoroethylene-ethylene [68258-85-5] copolymers. Such powders are used in functional applications where resistance to corrosion and elevated temperatures are required. They are usually applied by fluidized-bed coating techniques but can also be applied by electrostatic techniques to a heated substrate (15). Extremely high application temperatures in the range of 250-350°C are required for these polymers because of high melting point and high melt viscosity. 

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