Fluorocarbons, combustion

It has good weathering resistance and does not support combustion. It is resistant to most chemicals and solvents and has greater strength, wear resistance, and creep resistance than the preceding three fluorocarbon resins. 

In contrast to past environmental problems associated with fluorocarbon refrigerants, the exceptional properties of fluorine in polymers have great environmental value. Some fluoropolymers are enabling green technologies such as hydrogen fuel cells for automobiles and oxygen-selective membranes for cleaner diesel combustion. 

A liquid perfluorocarbon was being used as solvent in an oxidation by oxygen under pressure more energy was released than expected [1], It is cautioned that fluorocarbons are not inert to oxidation, presumably to carbonyl fluoride. An explosion has been experienced with perfluorotoluene in like circumstances [2], A correspondent reports that perfluorotoluene is flammable in air, more saturated perfluorocarbons in pure oxygen [3], Another detailed the combustion performance of polytetrafluoroethylene 148 kcal/mole ignition temperature not below 465°C at 7000 psi of oxygen [4], the product is mostly carbonyl fluoride. Other oxidants may also present a risk in extreme circumstances. 

Koch, E.-C., Metal-Fluorocarbon Pyrolants IV Thermochemical and Combustion Behavior of Magnesium/Teflon/ Viton (MTV), Propellants, Explosives, Pyrotechnics, Vol. 27, 2002, pp. 340-351. 

The copolymer of vinyl ferrocene (VF) and butadiene has also been reported in the literature for use as a binder for composite propellants. It does not require any burn-rate (BR) accelerator because of the presence of iron (Fe) in vinyl ferrocene which is converted to finely divided Fe203 (a well-known BR accelerator) during combustion. A few groups of scientists have also studied fluorocarbon polymers as binders for composite propellants because of their excellent compatibility with oxidizers and fuels coupled with high density. Accordingly, Kel-F elastomer (a copolymer of vinylidene fluoride and chlorotrifluoroethylene, trade name of 3M, USA) and Viton-A (copolymer of hexafluoropropylene and vinylidene fluoride, trade name of Du Pont, USA) have also been reported for this purpose. The structures of Kel-F 800 [Structure (4.13)] and Viton-A [Structure (4.14)] are ... 

Thus, Tokuyama Soda KK have patented [149] a piece of technology for the combustion of the hydrogen gas with the fluorocarbons produced in the ECF reaction with the objective of recovering HF which would otherwise be lost. 

It should not be thought, however, that perfluorocarbons are completely inert toward combustion. Even the very inert perfluorocarbon polymer polytetrafluoroethylene [PTFE, Du Pont s Teflon F(CF2CF2)nF] is thermodynamically unstable in oxygen with respect to CO2 and CF4 (Exercise 12.6) and can burn in a 95% 02/5% N2 mixture at 0.1 MPa, although combustion is hard to initiate because of the nonvolatility of PTFE and the resistance of the thermal degradation products to oxidation. Conflagrations involving more reactive, volatile fluorocarbons such as perfluoro-toluene have been reported.15... 

ETFE resins do not support combustion in air and have typical limiting oxygen index (LOI) about 30 to 31. LOI depends on monomer ratio in the polymer and it increases gradually as the fluorocarbon content is increased to the alternating composition and then increases more rapidly to the LOI values for FIFE.68... 

The combustion behaviour of freons and fluorocarbons has been reviewed by Fletcher [142(b)]. 

Fluoroarsenates are notoriously difficult to analyze because of the kinetic stability of AsF ", which persists even in aqueous solution in the presence of H2S reagent. In addition the C-F bond is a very stable one and conventional combustion analysis cannot normally be applied to such fluorocarbon materials as these. 

Plastics in general (including all forms) are sensitive to high temperatures, among the more resistant being fluorocarbon resins, nylon, phenolics, polyim-ides, and silicones, though even these soften or melt above 260C. Other types (cellulosics, polyethylene, acrylic polymers, polystyrene) are combustible when exposed to flame for a short time and still others (polyurethane) burn with evolution of toxic fumes. 

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