Fluoroelastomers hardness

Figures 10-14 illustrate the reductions obtained in hardness, 50% modulus, 100% modulus, elongation, and tensile strength, respectively, for a fluoroelastomer compound produced under normal production conditions. Table 1 shows the improvement obtained in detail.

Figure 10 Comparison of hardness 3 sigma variability ratings fluoroelastomer compound.

The description of the physical properties of fluoroelastomers is necessarily less precise than that of fluoroplastics because of the major effect of adding curatives and fillers to achieve useful cross-linked materials of a given hardness and specific mechanical properties Generally, two parameters are varied increasing cross-link density increases modulus and decreases elongation, and raising filler levels increases hardness and decreases solvent swell because of the decreased volume fraction of the elastomer In addition to these two major vanables, the major determinants of vulcanizate behavior are the chemical and thermal stabilities of its cross-links The selection of elastomer, of course, places limits on the overall resistance to fluids and chemicals and on its service temperature range... 

Liquid vulcanizable fluoroelastomers consisting of vinylidene fluoride, per-fluoro(methyl vinyl ether), and tetrafluoroethylene were prepared by Kojima [4] and Park [5] and used for molding materials of low hardness. 

Crosslinking the Ester-Containing Polymer. Crosslinking was brought about easily using a conventional fluoroelastomer hexamethyl-enediamine carbamate cure, or by using p-phenylenediamine. In the samples tested, vulcanizate properties (hardness, elongation) and re-... 

Uses Release coaling esp. designed for peroxide-cured fluoroelastomer and similar hard-lo-release compds. 

Fluoroelastomers are blended with fluorosilicones and other high-temperature polymers to meet engine compartment environments and cost/performance balance. Fine-particle sihca increases hardness, red iron oxide improves heat resistance, and zinc oxide improves thermal conductivity. Hardness ranges from about Shore 35 A to 70 A. Fluorosilicones are resistant to nonpolar and nominally polar solvents, diesel and jet fuel, and gasoline, but not to solvents such as ketones and esters. 

The fluorinated rubbers are exceptionally good for high-temperature service, but they are below silicones in this respect. They resist most of the lubricants, fuels, and hydraulic fluids encountered in aircraft a wide variety of chemicals, especially the corrosive variety and also most chlorinated solvents. They have good physical properties, somewhere near those of styrene butadiene rubber (SBR) at the higher hardness levels. FKM is valnable in automotive use for its extreme heat and oil resistance and is on a much higher level in this respect than the acrylic elastomers. It has weathering properties snperior to those of neoprene. However, fluoroelastomers are relatively expensive. 

In the evaluation commercial 90 Shore A hardness extrusion resistant compounds based on NBR were compared with fluoroelastomers, normally or originally considered to have poor resistance to extrusion. The formulations of the compounds evaluated are tabulated in Table 6. 

Comparison of NBR with Fluoroelastomers A paper by Du Pont published in 1984 compared nitrile elastomer with various fluoroelastomers. The results compared soft and hard seals at 150°C and 200°C, in various oil well fluids. 

Although not recorded in this chapter, the original reference shows the same data for hard (90-95) seals. The outcome was essentially the same except that all the fluoroelastomer grades were somewhat better in all fluids. 

Unfortunately several data points are missing. However, one can conclude that, as before, fluoroelastomers have excellent resistance to acid completion fluid even at this extreme temperature. FKMGF again provides good resistance to basic completion fluid and also appears to give fair to satisfactory performance in both NACE A and B fluids. The hard version of this compound, for some reason, is poor with NACE A fluid. 

The third period since mid 70s might be called as the era of functional polymers. The commercialized examples are membranes, a thermoplastic elastomer, weather resistant paints and some cyclopolymers. The thermoplastic fluoroelastomer developed by Daikin involves a quite interesting technology. This is a very unique block copolymer with hard and soft segments based on the specially designed iodine-containing living fluoropolymer (1). 

The first step is to select the right composition for the fluoroelastomer since httle can be achieved through compounding. Then, the right viscosity and the right type must be selected. Finally, the formulation will tackle properties such as hardness. 

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