Fundamental Properties of Fluoropolymers

The basic properties of fluoropol5miers arise from the atomic stmcture of fluorine, carbon, and their co- 

The size of the fluorine atom allows the formation of a uniform and continuous sheath around the carbon-carbon bonds and protects them from attack, thus imparting chemical resistance and stability to the molecule. The fluorine sheath is also responsible for the low surface energy (18 dynes/cm)[ i and low coefficient of friction (0.05-0.08, static)[ i of PTFE. Another attribute of the imiform fluorine sheath is the electrical inertness (or non-polarity) of the PTFE molecule. Electrical fields impart only slight polarization to this molecule, so volume and surface resistivity are high. Table 1.1 summarizes the fundamental properties of PTFE, which represents the ultimate polymer among all fluoroplastics. 

The basic properties of perfluoropolymers provide beneficial attributes with high commercial value (Table 1.2). 

High melting point, 342°C High thermal stability 

Useful mechanical properties at extremely low and high temperatures 

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A fundamental property of fluoropolymers is their resistance to organic and inorganic chemicals (Fig. 12.1). Increased content of fluorine enhances the chemical resistance of the polymer. The overwhelming majority of the applications of fluoropolymers take advantage of their inertness to chemicals. Chemical properties of fluoropolymers are not affected by fabrication conditions. Another aspect of the interaction of these plastics with chemicals is permeation. Even though a reagent may not react with a fluoropolymer, it may be able to permeate through the polymer structure. The extent and rate of permeation is dependent upon the structure and properties of the plastic article as well as the type and concentration of permeant. Temperature and pressure usually influence the permeation process. This chapter reviews chemical compatibility of fluoropolymers and their permeation behavior towards different chemicals. 

Monomers for commercially important large-volume fluoropolymers and their basic properties are shown in Table 1.1. These can be combined to yield homopolymers, copolymers, and terpolymers. The resulting resins range from rigid resins to elastomers with unique properties not achievable by any other polymeric materials. Details about the basic chemistry and polymerization methods are included in Chapter 2, fundamental properties of the resulting products are discussed in Chapter 3, and processing and applications in Chapter 4. 

As shown in the previons section, many of the fundamental properties of the polymers depend on their structure, mainly on the nature of monomeric units composing them. This section concentrates on the specific properties of individual fluoropolymers— more specifically fluoroplastics—and how they relate to their utility in practical applications. The properties of fluoroelastomers are discussed in Chapter 5. 

One of the underlying assumptions of this analysis is that there is only a single failure mechanism occurring. This is generally true of the vinyl polymers and also for the fluoropolymers, but may not be true depending on the basic material properties of poly-ethylenes, polypropylenes, and cross-linked poly-ethylenes. Polyolefin materials will exhibit a change in tile failure mode from a ductile failure to a britfle or slit-type failure, depending on the fundamental... 

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. 

There are two approaches to characterizing fluoropolymers for injection molding. The more fundamental methodology centers around the measurement of physical properties such as melt viscosity and thermal diffusivity to generate data for mathematical modeling (simulation) of injection molding processes. 

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