Electrical properties fluoroplastics

Fluoroplastic FPs have superior heat and chemical resistance, excellent electrical properties, but only moderate strength. Variations include PTFE, FEP, PFA, CTFE, ECTFE, ETFE, and PVDF. Used for bearings, valves, pumps handling concentrated corrosive chemicals, skillet linings, and as a film over textile webs for inflatables such as pneumatic sheds. Excellent human-tissue compatibility allows its use for medical implants. 

More recently, modified fluoroplastics such as fluorinated ethylene/propylene copolymer, polychlorotrifluoroethylene, and polyvinylidene fluoride have been offered by DuPont, Allied Chemical, 3M, and Pennwalt respectively, to provide improved processability and mechanical strength at some sacrifice in heat-resistance, electrical properties, and chemical resistance and at prices of 3.70-7.15 these have also been finding appropriate if smaller markets. 

Examples of fluoroplastics include polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), ethylene—chlorotrifluoroethylene (ECTFE), ethylene—tetrafluoroethylene (ETFE), poly(vinylidene fluoride) (PVDF), etc (see Fluorine compounds, organic). These polymers have outstanding electrical properties, such as low power loss and dielectric constant, coupled with very good flame resistance and low smoke emission during fire. Therefore, in spite of their relatively high price, they are used extensively in telecommunication wires, especially for production of plenum cables. Plenum areas provide a convenient, economical way to run electrical wires and cables and to interconnect them throughout nonresidential buildings (14). Development of special flame-retardant low smoke compounds, some based on PVC, have provided lower cost competition to the fluoroplastics for indoors application such as plenum cable, Riser Cables, etc. 

HTE fluoroplastic exhibits exceptional balance of tensile strength, good electrical properties, good resistance to permeation of vapors and fuels, as well as excellent chemical resistance. Because of its relatively low melting temperature, it is easy to process and can be processed on equipment without the high level of corrosion protection usually required by many other fluoroplastics. HTE is suitable for wire and cable insulation and for extruded Aims used for chemically resistant linings, release layers, and other applications. A summary of properties of the two current grades of HTE is shown in Table 3.13. 

ETFE is a fluoroplastic with excellent electrical and chemical properties. It also has excellent mechanical properties. ETEE is especially suited for uses requiring high mechanical strength, chemical, thermal, and/or electrical properties. The mechanical properties of ETEE are superior to those of PTEE and EEP. ETFE has ... 

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. 

Copolymers of chlorotrifluoroethylene and ethylene were introduced by Allied Chemicals under the trade name Halar in the early 1970s. This is essentially a 1 1 alternating copolymer compounded with stabilising additives. The polymer has mechanical properties more like those of nylon than of typical fluoroplastic, with low creep and very good impact strength. Furthermore the polymers have very good chemical resistance and electrical insulation properties and are resistant to burning. They may be injection moulded or formed into fibres. 

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. 

Ethylene chlorotrifluoroethylene copolymer (ECTFE, E/CTFE) n. A fluoroplastic with good mechanical, thermal, electrical, processing, and resistance properties. 

Fluoroplastics Excellent electrical, chemical, and thermal properties. CFCI3 lowest MVTR of any transparent film, LOX (liqnid oxygen) compatible and flexible at cryogenictemperatnres nses packaging of hygroscopic pharmacenticals. 

Every plastic manifests a limited shear resistance, determined as the permissible shear rate exceeding this value causes mechanical destruction and tearing of molecules of the plastic as a result of excessive internal friction, which has a bearing on the mechanical, electrical or thermal properties of the moulded part. The plastics with the greatest shear resistance are those of low viscosity, e.g., readily fluid versions of PP and PE, PA, etc. Low shear resistance is a feature of plastics like PP (of a high viscosity), PC, PSU and PPS. PVC, CA, CAB, EVA, POM and fluoroplastics have a particularly low shear resistance. 

Perfluorocyclobutane (PFCB) polyaryl ethers are one such class of partially fluorinated polymers which combine the processability and durability of engineering thermoplastics with the optical, electrical, thermal, and chemical resistant properties of traditional fluoroplastics. Developed originally at The Dow Chemical Company" in Freeport, TX, PFCB polymers are prepared by the radical mediated thermal cyclopolymerization of trifluorovinyl ethers (Figure 1) and have, to date, provided a variety of thermoplastic and thermosetting materials possessing a tunable range of... 

PTFE Fluoroplastic n Polytetrafluoroethylene is prepared by free radical polymerization of tetrafluor-oethylene in aqueous systems with persulphate or peroxide initiators to give granular or dispersion polymers. The polymers have exceptionally high thermal and thermo-oxidative stability and are completely solvent resistant. PTFEs are tough, relatively flexible materials which have outstandingly good electrical insulation properties as well as unusually low coefficients of friction. 

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