Perfluorinated fluoroplastics

Perfluorinated fluoroplastics have higher creep tendency than partially fluorinated fluoropol5miers. Polytetrafluoroethylene, comprised of 100% tet-rafluoroethylene monomer, has the highest tendency to exhibit cold flow. Copolymers of tetrafluoroeth-ylene containing small amounts (0.1% by weight) of certain other fluorinated monomers, also referred to as modifiers, have significantly lower creep. These modifiers form pendent groups in the polymer chain. 

Perfluorinated fluoroplastics have higher creep tendency than partially fluorinated fluoropolymers, due to their extreme neutrality and consequently weak in-termolecular interactions. Polytetrafluoroethylene,... 

Partially fluorinated fluoropolymers (PVDF, ETFE, ECTFE) are much more resistant to electron beam and y-radiation than perfluorinated fluoroplastics. Table 13.47 provides mechanical property data for ECTFE as a fiinction of Co radiation (y-rays). Figure 13.108 shows the effect ofy-rays on the break elongation and yield strength of PVDF. Exposure of... 

Perfluorinated fluoroplastics are chemically unaffected by nearly all commercial chemicals. An exception is highly oxidizing substances such as element forms of sodium, potassium, and other alkaline metals. This is the basis for sodium etching of fluoroplastic parts, which is described in this section. 

The era of fluoropolymers began with the serendipitous discovery of PTFE by Roy Plunkett of DuPont Companywhile conducting research to find new refrigerants. A number of fluoroplastics have been developed since the discovery of PTFE. They are divided into two classes of perfluorinated and partially fluorinated polymers. Perfluorinated fluoropolymers... 

Fluoropolymers are semicrystalline polymers most do not exhibit glass transition in the conventional sense during which all crystalline structures are converted to the amorphous. The glass transitions of fluoroplastics have been described as molecular relaxation (conformational disorder) that takes place in the amorphous phase of the polymer. These temperatures are also called second order transitions their value depends on the technique and the frequency of energy addition to the polymer sample. Table 3.61 presents these temperatures and melting points of perfluorinated and partially fluorinated fluoroplastics. 

Perfluroalkoxy polymer or PFA is one of the most important meltprocessible fluoroplastics due to its relative ease of processing and high service temperature equivalent to polytetrafluoroethylene (260°C). It also has the same excellent chemical resistance and low friction properties as PTFE. Perfluroalkoxy polymers are prepared by copolymerization of a perfluoroalkylvinyl ethers (Rf—O—CF=CF2, where Rj is a perfluorinated alkyl group) with tetrafluoroethylene. Examples of commercially utilized ethers include perfluoromethyl-vinyl ether (CFg—O—CF=CF2), perfluoroethylvinyl ether (C2F5—O—CF=CF2) and perfluoropropylvinyl ether (C3F7—O—CF=CF2). Several percent of ether is incorporated in a copolymer. 

The main driver for fluoroplastic foams has been the insulation for data transmission cables. An example is coaxial cables that have relatively thick insulation. Its low dielectric constant and dissipation factor are desirable electrical properties. Air has the ideal dielectric constant (1.0). The ideal dissipation factor for data-cable insulation is zero. Perfluoropolymers have low dielectric constant and dissipation factor values (Table 11.2, see Ch. 6 for additional data). Foaming perfluorinated fluoropolymers further reduces the dielectric constants toward 1.0 and moves the dissipation factors closer to zero because the resin is replaced with air-filled cells in the insulation. The decrease in the dielectric constant is proportional for example, FEP insulation with 60% void content had a dielectric constant of More uniform foam cell size and smaller cells yield foams with the best electrical properties. 

Carbon, fluorine, and hydrogen are the major elements that form the perfluorinated and partially fluori-nated fluoropolymers. The presence of fluorine is the main reason that these plastics have many special properties, which surpass those of most polymers. The desirable properties span across mechanical, tribological, electrical, and thermal characteristics of these polymers in addition to chemical resistance. Increased fluorine content of the fluoropolymers enhances these properties. Consequently, perfluoropolymers should be sought out when ultimate chemical resistance, electrical properties, etc., are required. This chapter concentrates on presenting the key properties of fluoropolymers. Properties of fluoroplastics films can be found in Ch. 6 and Appendix VI. 

Table 14.2 shows the effect of sodium etching on several fluoroplastics by Tetra-Etch on the surface composition and lap shear bond strength. In general, the data for various fluoroplastics indicate increase in the adhesive bond strength with increasing fluorine and chlorine content. Kinetics of treatment is more favorable to perfluorinated PTFE than PVF that contains one fluorine per monomer unit according to the data in Table 14.2. 

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