Polytetrafluoroethylen applications

The high thermal stability of the carbon-fluorine bond has led to considerable interest in fluorine-containing polymers as heat-resistant plastics and rubbers. The first patents, taken out by IG Farben in 1934, related to polychlorotri-fluoroethylene (PCTFE) (Figure 13.1 (a)), these materials being subsequently manufactured in Germany and the United States. PCTFE has been of limited application and it was the discovery of polytetrafluoroethylene (PTFE) (Figure... 

A need for single-phase polymers in some applications, e.g., polytetrafluoroethylene, VHMWPE, light-sensitive polymers, etc. 

Besides the spontaneous, complete wetting for some areas of application, e.g., washing and dishwashing, the rewetting of a hydrophobic component on a solid surface by an aqueous surfactant solution is of great importance. The oil film is thereby compressed to droplets which are released from the surface. Hydrophobic components on low-energy surfaces (e.g., most plastics) are only re wetted under critical conditions. For a complete re wetting of a hydrophobic oil on polytetrafluoroethylene (PTFE) by an aqueous solution, the aqueous solution-oil interface tension must be less than the PTFE-oil interface tension... 

Ethylene vinyl acetate has also found major applications in drug delivery. These copolymers used in drug release normally contain 30-50 wt% of vinyl acetate. They have been commercialized by the Alza Corporation for the delivery of pilocarpine over a one-week period (Ocusert) and the delivery of progesterone for over one year in the form of an intrauterine device (Progestasert). Ethylene vinyl acetate has also been evaluated for the release of macromolecules such as proteins. The release of proteins form these polymers is by a porous diffusion and the pore structure can be used to control the rate of release (3). Similar nonbiodegradable polymers such as the polyurethanes, polyethylenes, polytetrafluoroethylene and poly(methyl methacrylate) have also been used to deliver a variety of different pharmaceutical agents usually as implants or removal devices. 

Oxygen reduction can be accelerated by an application of electrodes with high surface area, e.g. the porous electrodes [9, 13]. The porous electrodes usually consist of catalysts, hydrophobic agent (polytetrafluoroethylene-PTFE) and conductive additive. Electrode kinetics on the porous electrodes is complicated by the mass and charge transfer in the pores and is called the macrokinetics of electrode processes . 

Polytetrafluoroethylene (PTFE), 72 211, 217-218 74 228 78 288, 329. See also PTFE entries Teflon entries absorption, permeation, and interactions of, 78 297-298 applications of, 78 305-306 asbestos substitute, 3 314t... 

The investigation of free radicals formed by high energy irradiation of polytetrafluoroethylene is an example of an early application of EPR to polymer radicals. 

The success of this and the other operations derives from the correct application of back-pulse filtration principles, in particular the back-pulse step itself in which the filter cloths are cleaned and made ready for further filtration. The properties of the GORE-TEX membrane, composed of expanded polytetrafluoroethylene, give rise to the desirable results of these brine filtrations, in particular ... 

ISO 7258 1984 Polytetrafluoroethylene (PTFE) tubing for aerospace applications -Methods for the determination of the density and relative density ISO 7313 1984 Aircraft - High temperature convoluted hose assemblies in polytetrafluoroethylene (PTFE)... 

Xing, D. M., Yi, B. L., Liu, F. Q., Fu, Y. Z. and Zhang, H. M. 2005. Characterization of sulfonated poly (ether ether ketone)/polytetrafluoroethylene composite membranes for fuel cell applications. Fuel Cells 5 406M11. 

When a glass plate which is heated e.g. at 130°C is rubbed with a polytetrafluoroethylene (PTFE) briquette, a highly oriented thin film (2— 100 nm thick) of PTFE can be made on the plate such a film is termed a friction-transfer layer [24]. This method is applicable to make thin oriented layers of other polymers. Various kinds of organic compormds can be oriented on the PTFE friction-transfer layer from vapor phase, from solutions and from the melts [24]. 

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 ... 

Another field of application of fluorinated biomaterials is connected to lesions or evolving disease pathology of blood vessels. In particular, arteries may become unable to insure an adequate transport of the blood to organs and tissues. Polytetrafluoroethylene (PTFE) and expanded e-PTFE are the preferred materials for vascular prostheses. The interactions of blood cells and blood plasma macromolecules with both natural and artificial vessel walls are discussed in terms of the mechanical properties of the vascular conduit, the morphology, and the physical and chemical characteristics of the blood contacting surface. 

Researchers are now seeking practical ways to fluorinate the surfaces of diamond films, as the resulting surfaces are expected to have very low coefficients of friction (cf. non stick polytetrafluoroethylene or Teflon, Section 12.3) and hence have applications in low-friction tools. Direct flu-orination with elemental fluorine is impractical, but photodecomposition of fluoroalkyl iodides chemically absorbed on the diamond surface looks promising.4... 

Related to the fixation of C02, electrochemical carbon , which is prepared by converting carbon halides (e.g. polytetrafluoroethylene) to carbon, is recently attracting attention for its technological applicabilities. Non-aqueous electrolyte solutions are often used in the electrochemical carbonization processes [13]. The use of non-aqueous electrolyte solutions is also popular in electrochemical organic syntheses, as is apparent in Ref. [14], although not dealt with in this book. 

Plastics. Almost all commercial plastics find some use both dry and lubricated for sliding at low speeds and light loads the most commonly used thermoplastics are nylon, acetal resins, and polytetrafluoroethylene (PTFE). Typical thermosetting resins for bearing applications are phenolics, polyesters, and polyimides. Table 8 compares the characteristics of plastic bearing materials with those of graphite, wood, and rubber which find use in somewhat similar applications. 

Esveld et a/.81,82 developed a continuous dry media reactor (CDMR) for pilot-scale applications. It consisted of a multi-modal tunnel microwave cavity operating at a frequency of 2.45 GHz with a power range from 0 to 6 kW irradiated on a surface of 0.6 m2. Temperatures of up to 250°C were achieved. A web conveyor travelling at 17 cm min-1 transported the solid-phase reaction mixture to the oven in low, open Pyrex supports closely packed on a polytetrafluoroethylene (PTFE)-coated glass fibre. An open flat bed process was employed to facilitate easy evaporation. 

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. 

D. Fluorocarbon Polymers. Four different fluorocarbons account for the bulk of the laboratory applications polytetrafluoroethylene, Teflon PTFE po-ly(chlorotrifluoroethylene), KEL-F tetrafluoroethylene-hexafluoropropylene copolymer, Teflon FEP and tetrafluoroethylene-perfluorovinyl ether copolymer, PFA. These polymers are inert with most chemicals and solvents at room temperature and exceptionally inert with oxidizing agents. They also have an exceptional resistance to temperature extremes. However, they are decomposed by liquid alkali metals, solutions of these metals in liquid ammonia, and carban-ion reagents such as butyllithium. Teflon retains some of its compliance at liquid hydrogen temperature. The maximum temperature which is recommended for continuous service is 260°C for Teflon PTFE and PFA, and about 200°C for Kel-F and Teflon FEP. 

Surface treatments involving alkali metals are sometimes used to eliminate the characteristic surface properties and promote the adhesion between polytetrafluoroethylene and other substances (Doban Nelson, Kilduff, and Benderly Purvis and Beck Rappaport). It has been shown that these treatments produce a marked increase in the polarity of the surface as measured by the contact angle with various liquids (Allan, 1957). They also increase the coefficient of friction. One interesting application of surface properties of polytetrafluoroethylene was reported by Bowden (1953, 1955) who applied the polymer to the bottoms of his skiis and thereby reduced the friction between the skiis and the snow. 

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... 

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