Perfluoroplastics

Polyurethane-based FTPEs are produced by reacting fluorinated polyether diols with aromatic disocyanates. The resulting block copolymers contain fluorinated polyether soft segments.68 Another possible method of preparation of fluorinated TPE is dynamic vulcanization. Examples are a blend of a perfluoroplastic and a perfluoroelastomer containing curing sites or a combination of VDF-based fluo-roelastomers and thermoplastics, such as polyamides, polybutylene terephtalate, and polyphenylene sulhde.69 70... 

Amorphous perfluoroplastics developed by DuPont (Teflon AF) and Asahi Glass (Cytop) contain bulky structures that are responsible for the absence of crystallinity. When Teflon AF was irradiated by low-energy x-rays, it was found that the inclusion of the dioxole monomer not only improves the optical properties but also increases the radiation tolerance of the homopolymer [43]. 

Figure 3.118 shows the effect of y radiation on the break elongation of PVF, PVDF, ETFE, FEP, and PFA. It can be seen that the impact on PVF, PVDF, and ETFE is smaller than the radiation impact on FEP and PFA FEP fares better than PFA. Figure 3.119 provides a comparison of the radiation resistance of several fluoroplastics as a function of radiation dose, as expressed by the retained elongation as percent of initial break elongation of the pol5mier. FEP is the most radiation resistant of the perfluoro-polymers while PTFE is the most susceptible. ETFE has far superior radiation resistance to all the perfluoroplastics shown in Fig. 3.119. 

Perfluoroplastics have a multitude of useful properties. Any one of these properties may possibly be found in certain hydrocarbon-containing polymers, metals, or other materials. However, it is in the applications that require a combination of two or more of these properties where the perfluoroplastic finds unique utility. The unique properties and performance of perfluoroplastics are highly related to their structure. 

Perfluoroplastics are nonpolar with a symmetrical arrangement that centers the charge balance in the middle of the polymer chain. The lack of polarity leads to exceptional electrical performance with a low dielectric constant and dissipation factor. Perfluoroplastics further benefit from the rigid, linear chain which maintains consistent dielectric properties across a wide temperature range [2],... 

The van der Waals interactions in perfluoroplastics are extremely low. As a result, polytetrafluoroethylene (PTFE) has the lowest coefficient of friction of any known polymer. This property is due to the chemistry and structure described above which also give rise to the excellent electrical properties, thermal stability and chemical inertness. 

Foamed fluoroplastics have been used in coaxial cables since the 1960s, but they are receiving increased interest for twisted-pair applications since the dielectric performance of all solids can be improved by the uniform addition of voids. Current efforts focus on smaller and more uniform voids that can be incorporated into thin-walled products such as micro coaxial cables and twisted pair cables. The use of advanced foamed perfluoroplastic resins provides the cable designer with options for improving cable performance and/or reducing cable weight [14,15]. 

High MW PTFE tends to be favored in applications where the potential for extreme temperatures, harsh chemicals, and other extremely aggressive environments exist. This is particularly true when combined with high frequency requirements such as coaxial cable applications where the excellent dielectric properties are also required. Unfortunately, such FITE cannot be processed by conventional melt processing techniques. With the recent developments in foamed perfluoroplastic products, economical cables with properties very near to those of expanded PTFE are possible. 

The melt processible fluoroplastics are often desired due to the cost benefits of melt extrusion over paste extrusion. FEP, PEA and specially formulated melt processible perfluoroplastics are used in many of these applications however, in some of these applications, perfluoroplastics may not be the ideal choice. In cases where high cut-through resistance and better tensile properties are required, it is often desirable to employ a partially fluorinated polymer such as ETFE (ethylene-tetrafluoroethylene). ETFE is the copolymer of ethylene and TEE [16] that normally includes an additional termonomer to increase the flexibility required in commercial applications [17]. The increased physical and electronic interactions of the ETFE polymer chain are responsible for the comparatively enhanced physical properties. Additionally, the partially fluorinated polymers may be cross-linked to further improve physical properties. These benefits, however, are obtained at the expense of the unique properties of perfluoroplastics discussed in the Introduction and Overview. 

Excellent chemical resistance combined with the broad temperature rating makes perfluoroplastics a natural fit for wiring in the chemical process industry (CPI). The... 

Compounding can assist with the limited combustible requirements mentioned above. Although j ackets made with perfluoroplastic have been around since the advent of the plenum specifications, their market share has declined due to low productivity and relatively high cost. New products that combine compounding technology with the inherently low fuel load of perfluorinated polymers promise to open new windows for jacket compounds that possess the low flammability of perfluorinated resins combined with improved processibility. 

The incorporation of nanoparticles into polymers has generated considerable excitement and activity since the interfacial effects at that scale can impart significant physical property improvements [18], The low surface energy of perfluoroplastics increases the difficulty of producing fully exfoliated nanocomposites. The incorporation is easier with partially fluorinated compounds such as polyvinylidene fluoride (PVDF) or fluoroelastomers [ 19], but even PTFE compounds have been produced for wire and cable applications [20],... 

The melt processible perfluoroplastics highlighted in the above sections are often polymerized in totally aqueous media and are therefore available as aqueous dispersions of perfluoroplastic particles with a mean volumetric particle size of 150 to... 

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