Properties of Fluorocarbons

Substitution of fluorine for hydrogen in an organic compound has a profound influence on the compound s chemical and physical properties. Several factors that are characteristic of fluorine and that underHe the observed effects are the large electronegativity of fluorine, its small size, the low degree of polarizabiHty of the carbon—fluorine bond and the weak intermolecular forces. These effects are illustrated by the comparisons of properties of fluorocarbons to chlorocarbons and hydrocarbons in Tables 1 and 2. 

Compression Set Resistant. One property of fluorocarbon elastomers that makes them uniquely valuable to the sealing industry is their extreme resistance to compression set. Figure 4 plots compression set vs time for compounds prepared especially for compression set resistance (O-ring grades). 

These unusual properties of fluorocarbons reflect theu nonpolar character, low polarizability, and overall relatively weak intermolecular attractions Saturated perfluoro-terr-ammes and -dialkyl ethers also closely resemble fluorocarbons rather than typical amines or ethers in their physical properties [4,... 

The X-ray diffraction peaks observed in the range of 3°-10° for the modified clays disappear in the rubber nanocomposites. photographs show predominantly exfoliation of the clays in the range of 12 4 nm in the BIMS. Consequently, excellent improvement in mechanical properties like tensile strength, elongation at break, and modulus is observed by the incorporation of the nanoclays in the BIMS. Maiti and Bhowmick have also studied the effect of solution concentration (5, 10, 15, 20, and 25 wt%) on the properties of fluorocarbon clay nanocomposites [64]. They noticed that optimum properties are achieved at 20 wt% solution. At the optimized solution concentration, they also prepared rubber/clay nanocomposites by a solution mixing process using fluoroelastomer and different nanoclays (namely NA, 10A, 20A, and 30B) and the effect of these nanoclays on the mechanical properties of the nanocomposites has been reported, as shown in Table 4 [93]. 

Electrooptical properties will be covered only briefly. Fluorocarbons find widespread utility in altering electrooptical properties of coatings. These properties are to be considered as derived from bulk properties of the fluorocarbon. In that regard, fluoropolymers are the most often selected. It is known from Eq. (2) that the electrooptical properties of fluorocarbons can be linked directly to the nature of the C—F bond (a oc n and e <=< n ). It is instructive to consider some relevant values. The dielectric constants e of PTFE, PE, and nylon-6,6 have been determined to be 2.1 (60 Hz-2 GHz), 2.2-2.3 (1 kHz), and 3.6-3.0 (100 Hz-1 GHz), respectively. The dielectric constants for PE and PTFE are comparable. The explanation can be found by comparing segmental polarizabilities a for groups with C—F bonds versus those with C—H bonds, as shown in Table 4.1. They are nearly identical. As e is related to a, it is not surprising that PE and PTFE have similar dielectric constants. The value of e for nylon-6,6 is included above for comparison. 

Table 1 Properties of fluorocarbon propellants and dimethyl ether s...

Pittman,A.G., Surface Properties of Fluorocarbon Polymers, Chapter 13, in "High Polymers, XXV. Fluoropolymers", ed. by Wall,. Wiley-Interscience (1972)... 

Cady, G. H., U. S. Atomic Energy Comm., MDDC-944 (1943). Preparation and Properties of Fluorocarbon Oils, Waxes, and Resins. 

Pittman, A. G. Surface Properties of Fluorocarbon Polymers. In Fluoropolymers Wall, L. A., Ed. Wiley-Interscience New York, 1972 pp 419-449. 

Several perfluoroalkyl and polyfluoroalkyl, and a number of perfluoro-vinyl and pentafluorophenyl compounds of tin have been prepared (Table II). Their study has added much to our knowledge of the chemical and spectroscopic properties of fluorocarbon-metal compounds. 

An article has been published by Shell [6] that discusses the fundamentals of grinding rubber at low temperatures. It covers a wide range of subjects including the nature of the product produced, its required storage conditions, the economics of the process and the management and quality systems that need to be installed. The article also includes data on the particle size distributions of hydrogenated nitrile rubber (HNBR) crumb and the properties of fluorocarbon rubber (FKM) and HNBR compounds containing different amounts of rubber crumb. 

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