Polytetrafluoroethylene electrical applications

The bulk (or volume)-specific resistance is one of the most useful general electrical properties. Specific resistance is a physical quantity that may vary more than 10 in readily available materials. This unusually wide range of conductivity allows wide variety of electrical applications. Conductive materials, such as copper, have specific resistance values of about 10 fl-cm, whereas good insulators such as polytetrafluoroethylene and LDPE have values of about 10 fl-cm. Specific resistance is calculated from the following equation where R is the resistance in ohms, a is the pellet area in square centimeters, t is the pellet thickness in centimeter, and P is the specific resistance in ohm-centimeter ... 

The excellent electrical insulation properties and chemical inertness over a wide temperature range account for the two main fields of use of polytetrafluoroethylene, namely electrical and chemical applications. Electrical applications include wire coatings, holders and spacers for use in aggressive conditions whilst chemical applications include gaskets, pump parts and laboratory equipment. Other uses include non-stick coverings for kitchen utensils, low-friction linings for hoppers, and diaphragms for low temperature equipment. 

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. 

Many important applications of polytetrafluoroethylene depend on its superb electrical properties tabulated in Table 3. These properties have been attributed to its highly symmetrical structure (Doban, Sperati, and Sandt). Complete fluorination of the carbon chain results in an exact balance of the electrical dipoles which is manifested in a very low dielectric constant and electrical loss factor. These two properties are virtually independent of the frequency from 60 to 109 cycles per second... 

PVDF is the third most widely used fluoropolymer, after polytetrafluoroethylene (PTFE) and fluorinated ethylene-propylene (FEP). The worldwide consumption of PVDF was approximately 15,000 metric tons in 2001 and is growing at an annual rate of 6-8%. PVDF applications have been expanded over the past 40 years because of its unique physical properties, and have over 30 years of proven and field performance data on thermal, chemical, radiation, and weathering applications. PVDF applications include, but are not limited to, chemical processing of pipes and components, semiconductor, architectural finishes and coatings, electrical plenum, cable jacketing. 

Polymers, which include synthetic materials such as plastics, vinyl, Nylon, polyester, and polytetrafluoroethylene (PTFE) and natural materials such as silk, cotton, starch and cellulose, are used in our lives every day. Since scientists began to control and manipulate polymers in the 19th Century, chemists have created hundreds of durable synthetic polymeric materials from just a few simple building blocks. Experimentation continues today with increasing polymer uses for applications in chemical, instrumentation, mechanical, electrical and electronic industries. 

Tapes. A great variety of tapes find application in electrical equipment. Some tapes contain filler materials in macroscopic form such as glass fibers, mica flakes, and cloth others have finely divided filler particles or no fillers at all. In the heavily filled materials the polymeric binders are present in small fractions, and the major emphasis may be on their adhesive capabilities rather than on their properties as dielectric materials. Most of the polymers used in tapes have already been mentioned in connection with other insulation applications, for example, polyesters, aromatic polyamides, polyimides, and polypropylene. Other polymers frequently used for electrical tapes are vinyls, including poly(vinyl fluoride) these are particularly well suited as conformable tapes. Polytetrafluoroethylene (Teflon TFE) has also been fabricated into tape constructions, frequently in combination with adhesives to provide a bondable material. 

Carbon reduces creep, increases hardness and elevates thermal conductivity of polytetrafluoroethylene. Wear resistance of carbon filled compounds improves, particularly when combined with graphite. Carbon-graphite compounds perform well in non-lubricated applications such as piston rings in compressor cylinders. Carbon-filled PTFE has some electrical conductivity. Close tolerances can be achieved... 

Major applications of unsintered polytetrafluoroethylene are as tape in thread sealing and wrapping electrical cables, and as rod and tape in packings. Important properties of PTFE like chemical resistance, broad service temperature, low friction, flexibility, high machine direction strength, and deformability in the cross direction make unsintered fine powder PTFE ideal for these applications. 

MAJOR APPLICATIONS Nylon 4,6 is often blended with glass fiber or polytetrafluoroethylene md is used in underhood automotive parts, gears, electrical parts, and bearings. 

Another requirement of a polymer for use in critical applications might be a combination of excellent continuous or maximum operating temperatme (see Table 4.6) and good electrical properties. It is seen in Table 5.8 that polyether ketone, polyphenylene sulfide, and polytetrafluoroethylene all meet the requirements. 

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