Fluoropolymers extreme properties

This chapter examines why fluoropolymers exhibit extreme properties. It focuses on the reasons that replacement of hydrogen with fluorine in hydrocarbon macromolecules improves their thermal stability, chemical resistance, electrical properties, and coefficient of friction. Understanding the role of fluorine in determining the properties of a polymer will contribute to a more in depth appreciation of some of the other information in this book. It will also allow the readers to make more informed judgments about fluoropolymers and their applications. 

Curiously, fluorine incorporation can result in property shifts to opposite ends of a performance spectrum. Certainly with reactivity, fluorine compounds occupy two extreme positions, and this is true of some physical properties of fluoropolymers as well. One example depends on the combination of the low electronic polarizability and high dipole moment of the carbon-fluorine bond. At one extreme, some fluoropolymers have the lowest dielectric constants known. At the other, closely related materials are highly capacitive and even piezoelectric. 

As was noted above, functional fluoropolymers produced by copolymerization of fluoroolefins with functional PFAVE have several unique properties, with the main disadvantage of these materials being the extremely high cost of functional monomers and the resulting high cost of the functional polymers produced from them. The fact that they are so expensive limits their wider industrial application in other fields such as catalysis and membrane separation, except for chlorine-alkali electrolysis and fuel cells, where the only suitable materials are fully fluorinated polymers because of the extreme conditions associated with those processes. 

Fluoropolymers. These form one of our oldest and most spectacular families of engineering plastics. Polytetrafluoroethylene was developed by DuPont over two decades ago, and more recently by Allied Chemical, Hoechst, ICI, Pennwalt, and other manufacturers as well. It combines unusually low adhesion and friction, high temperature and flame resistance, excellent electrical properties, and extreme chemical inertness. Its high melting point and melt viscosity make thermoplastic processing extremely difficult, so that many... 

Halar ECTFE (ethylenechlorotrifluoroethylene) This material is an alternating copolymer of ethylene and chlorotrifluroethylene. This fluoropolymer withstands continuous exposure to extreme temperatures and maintains excellent mechanical properties across this entire range (from cryogenic temperatures to 180°C). It has excellent electrical properties and chemical resistance, having no known solvent at 121°C. It is also nonbuming and radiation-resistant. Its ease of processing affords a wide range of products. 

This section presents information and data related to thermal stability of resins and basic properties as a function of temperature. Thermal stability of fluoropolymers has special importance because of the high processing temperatures required by these thermoplastics and the toxic and corrosive nature of their degradation products. Fluoroplastics have useful properties at temperature extremes above and below ambient conditions. 

The volume resistivity of fluoropolymers is about 10 2 cm and the surface resistivity is about 10 2 per square (measured by ASTM D257). These extremely high values make them good electrical insulation materials. These properties are not affected by time and temperature. 

Hydrated nitrile rubber (HNBR) reliably withstands extreme temperature under the hood, as well as the effects of oils and fuels. HNBR grades exceed previous resistance ratings. They close the gap between oil-resistant nitrile rubbers and the extremely heat-resistant, but very expensive fluoropolymers. At the same time, the classic rubber properties of nitrile rubbers are maintained, especially its low-temperature flexibility. 

The first part of the book deals with definitions and fundamental subjects surrounding the polymerization of fluoropol)miers. Basic subjects such as the identification of fluoropolymers, their key properties, and some of their everyday uses are addressed. The main monomer, tetrafluoroethylene, is extremely flammable and explosive. Consequently, safe polymerization of this monomer requires special equipment and technology. Molecular forces within these polymers are reviewed and coimected to macro properties. Monomer and polymer synthesis techniques and properties are described. Part One ends with a detailed list of advertised commercial grades of fluoroplastics. 

Surface and volume resistivity (measured by ASTM D257) of fluoropolymers is extremely high and they make good electrical insulation material. Neither properties are affected by time and temperature and are about 10 Q cm (volume resistivity) and 10 Q per square (surface resistivity). 

The unique properties of fluoropolymers are due to the strong bond between carbon and fluorine and shielding of the carbon backbone by fluorine atoms. Fluoropolymers exhibit excellent physicochemical properties such as high thermal and oxidative stability, good weather stability, extreme resistance to chemical attack, low surface energy, low coefficient of friction and low dielectric constant. Fluoropolymers, with unrivaled combination of properties, showed solutions to several industrial problems and facilitated several technological developments in our way of life. This review addresses only popular industrial fluoropolymers with their chemistry, properties and general applications. 

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