PTFE Polytetrafluoroethylene

PTFE is marketed under the tradename of Teflon by DuPont and the tradename Halon by Ausimont USA. It is a fully fluorinated thermoplastic 

PTFE has an operating temperature range of from — 20°F to + 430°C (— 29°C to + 212°C). This temperature range is based on the physical and mechanical properties of PTFE. When handling aggressive chemicals, it may be necessary to reduce the upper temperature limit. 

PTEE is unique in its corrosion resistance properties. It is virtually inert in the presence of most materials. There are very few chemicals that will attack PTEE at normal use temperatures. Among materials that will attack PTFE are the most violent oxidizing and reducing agents known. Elemental sodium removes fluorine from the molecule. The other alkali metals (potassium, lithium, etc.) act in a similar manner. 

Eluorine and related compounds (e.g., chlorine trifluoride) are absorbed into PTEE resin to such a degree that the mixture becomes sensitive to a source of ignition such as impact. These potent oxidizers should be only handled with great care and a recognition of the potential hazards. 

The handling of 80% sodium hydroxide, aluminum chloride, ammonia, and certain amines at high temperatures have the same effect as elemental sodium. Slow oxidation attack can be produced by 70% nitric acid imder pressure at 480°F (250°C). 

PTFE does not melt like a true thermoplastic but sinters . As with other fluoroplastics, PTFE is relatively inert chemically. It is prepared for bonding by the techniques described in Chapter 6. 

Polytetrafluoroethylene (PTFE) is a crystalline translucent solid polymer with a high molecular weight ranging between 10 and 10 g mol. It is prepared from the monomer C2F4 by polymerization in aqueous medium and is obtained as fine powder. A number of trade names exist for PTFE. Thus it is often referred to as Teflon (DuPont), Hostaflon (Dyneon), Fluon (ICI), Hahn (AUied Chemical) or Fluoroplast (Ftoroplastoviye Tekhnohgii JSC) [1, 2]. 

Metal-Fluorocarhon Based Energetic Materials, First Edition. Ernst-Christian Koch. 

Studies on the rate of degradation of PTFE in air at 410 C, 125 C and 450 C have shown [9] that the quantity of the volatile decomposition products is approximately the same as in vacuo. The thermo-oxidative degradation of PTFE at 470 °C leads to volatile products to a greater extent than thermal degradation under vacuum. 

PTFE degradation at 350-380 C in the presence of oxygen leads to the appearance of considerable quantities of carbon monoxide (18% mol) and carbon dioxide (63% mol) among the volatile products, indicating defluorination. 

One may predict the accelerating action of oxygen during the degradation of PTFE to be insignificant because the production of hydroperoxides in this polymer is impossible. Clearly, the following equations are the basic ones in the thermal degradation of PTFE [10]  

The Equations 4.1-4.6 show that oxygen promotes recombination of the macro radicals and, consequently, the rate of chain scission increases in its presence. This would enable structurisation of the involatile residue from PTFE. However, Equations 4.4-4.6 show that the recombination of the secondary peroxide radicals results in the formation of radicals which readily isomerise with cleavage of the macromolecules. For this reason, restructuring of the final residue of PTFE is observed only at the late stages of its thermal oxidation. 

In an inert atmosphere, no further reaction would be anticipated. However, in air, the following was postulated  

The basic monomer unit is a totally fluorinated ethylene molecule (—CF —CF —). It is well known under its common trade name Teflon. It was discovered in 1938 by Roy J. Plunkett a DuPont scientists. Industrially, polytetrafluoroethylene is obtained from several consecutive of steps. First, chloroform reacts with hydrofluoric acid to yield chlorodifluoromethane. The chlorodifluoromethane is then pyrolized at 800-1000 C to yield the monomer, i.e., tetra-fluoroethylene (CF2=CF2, TFE) which is purified and polymerized in aqueous emulsion or suspension using organic peroxides, persulfates or hydrogen peroxide as catalysts. The simple polymerization reaction is as follows. 

The fluorinated ethylene propylene (FEP) macromolecule consist mainly of a linear chain with the basic monomer unit [—(CFJ,—CF(CF3)—] .This translucent fluorocarbon is flexible and more workable than PTFE, and like PTFE it resists to all known chemicals except molten alkali metals, elemental fluorine, fluorine precursors, and concentrated perchloric acid. It withstands temperatures up to 200 C and may be sterilized by all known chemical and thermal methods. Certain carefully prepared films of FEP can be used as windows in equipment when necessary. The product has found extensive use as a pipe fitting liner as well as a liner in small vessels. 

Polytetrafluoroethylene is a fluoropolymer. The market for fluoropolymers worldwide is reported to be around 100,000 tonnes of which approximately 40% is consumed in the US and approximately 10% is consumed in Japan. PTFE accounts for some 70% of total demand for fluoropolymers which are increasingly being used because of their outstanding qualities. 

Fluoropolymers are unique amongst polymers in respect of their chemical and thermal stability, biocompatibility, water resistance and superb dielectric properties, having a dielectric constant of 2.1. Other members of the Teflon family include a polymer of tetrafluoroethylene and hexafluoropropylene (FEP) and a polymer of tetrafluoroethylene and perfluorovinylether (PEA). The 327 °C melting point of PTFE is reputed to be one of the highest in organic polymer chemistry. The melting points of FEP and PEA are 260 C and 305 °C, respectively. 

PTFE is used in connectors and printed circuits, especially in hostile environments calling for heavy duty models. It can also be used to produce computer chip packages and shielding gaskets where it can be used in an expanded form. 

The selection of PCB material is determined by the end use application, and to achieve the required performance, ceramic filled PTFE composites, with or without the addition of woven or non-woven glass fibre, may be used. PTFE may also be used in heavy duty electrical connectors. It can also be used when connectors are moulded on to cables. 

Peak Notation Assignment of Main Peaks Molecular WeIgM Retention Index Relative Intensity 

4) Lonfei, J. Jingling, W. Shuman, X. 7. Anal Appl Pyrolysis 1986,10, 99. 

Compatible showed no visible attack up to the boiling point 

15-25 9 Resistant little or no change in weight small effect on mechanical properties generally suitable for practical use Fluorosint Quadrant EPP 

Woishnis and Ebnesajjad. Chemical Resistance of Specialty Thermoplastics. DOI http //dx.doi.org/10.1016/B978-l-4557-3110-7.00006-3 

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A recent innovation in IR sample preparation is the use of disposable sample cards made from thin sheets of either polyethylene (PE) or polytetrafluoroethylene (PTFE). 

Dry chlorine has a great affinity for absorbing moisture, and wet chlorine is extremely corrosive, attacking most common materials except HasteUoy C, titanium, and tantalum. These metals are protected from attack by the acids formed by chlorine hydrolysis because of surface oxide films on the metal. Tantalum is the preferred constmction material for service with wet and dry chlorine. Wet chlorine gas is handled under pressure using fiberglass-reinforced plastics. Rubber-lined steel is suitable for wet chlorine gas handling up to 100°C. At low pressures and low temperatures PVC, chlorinated PVC, and reinforced polyester resins are also used. Polytetrafluoroethylene (PTFE), poly(vinyhdene fluoride) (PVDE), and... 

Polytetrafluoroethylene (PTFE) provides the most satisfactory electrical insulation. Concentric rings of PTFE and PTFE impregnated with calcium fluoride are used for the packing glands which support the anode and cathode posts. Rubber is used as the gasket material to form a seal between the cover... 

Aqueous hydrogen fluoride of greater than 60% maybe handled in steel up to 38°C, provided velocities are kept low (<0.3 m/s) and iron pickup in the process stream is acceptable. Otherwise, mbber or polytetrafluoroethylene (PTFE) linings are used. For all appHcations, PTFE or PTEE-lined materials are suitable up to the maximum use temperature of 200°C. PTEE is also the material of choice for gasketing. AHoy 20 or Monel is typically used for valve and pump appHcations. Materials unacceptable for use in HE include cast iron, type 400 stainless steel, hardened steels, titanium, glass, and siHcate ceramics. 

In some cases particles have been added to electrical systems to improve heat removal, for example with an SF -fluidized particulate bed to be used in transformers (47). This process appears feasible, using polytetrafluoroethylene (PTFE) particles of low dielectric constant. For a successful appHcation, practical problems such as fluidizing narrow gaps must be solved. 

Steric Factors. Initially, most of the coUisions of fluorine molecules with saturated or aromatic hydrocarbons occur at a hydrogen site or at a TT-bond (unsaturated) site. When coUision occurs at the TT-bond, the double bond disappears but the single bond remains because the energy released in initiation (eq. 4) is insufficient to fracture the carbon—carbon single bond. Once carbon—fluorine bonds have begun to form on the carbon skeleton of either an unsaturated or alkane system, the carbon skeleton is somewhat stericaUy protected by the sheath of fluorine atoms. Figure 2, which shows the crowded hehcal arrangement of fluorine around the carbon backbone of polytetrafluoroethylene (PTFE), is an example of an extreme case of steric protection of carbon—carbon bonds (29). 

Peifluorinated ethylene—piopjiene (FEP) lesin [25067-11-2] is a copolymer of tetiafluoioethylene [116-14-3] (TFE) and hexafluoiopiopylene [116-15-4] (HEP) thus its blanched stmctuie contains units of —CF2—CF2— and units of —CF2—CF(CF2)—. It retains most of the desirable characteristics of polytetrafluoroethylene (PTFE) but with a melt viscosity low enough for conventional melt processing. The introduction of hexafluoropropylene lowers the melting point of PTFE from 325°C to about 260°C. 

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 appHcations are phenoHcs, polyesters, and polyimides. Table 8 compares the characteristics of plastic bearing materials with those of graphite, wood, and mbber which find use in somewhat similar appHcations. 

About 90% of the chloroform produced goes into the production of HCFC-22 (chlorodifluoromethane [75-45-6]). Of this 90% about 70% is used as a refrigerant and about 30% is used as a starting material in the production of fluoropolymers, such as polytetrafluoroethylene (PTFE). Of the remaining 10% of the chloroform production about 8% is exported and 2% is used in other ways. 

Composites. Another type of electro deposit in commercial use is the composite form, in which insoluble materials are codeposited along with the electro-deposited metal or alloy to produce particular desirable properties. Polytetrafluoroethylene (PTFE) particles are codeposited with nickel to improve lubricity (see Lubrication and lubricants). SiHcon carbide and other hard particles including diamond are co-deposited with nickel to improve wear properties or to make cutting and grinding tools (see Carbides Tool materials). 

Blends of the polysulfone tesia have been made with ABS, poly(ethylene terephthalate), polytetrafluoroethylene (PTFE), and polycarbonate. These ate sold by Amoco under the Miadel trademark. Additional materials ate compounded with mineral filler, glass, or carbon fiber to improve properties and lower price. 

The use of chemical mapping is demonstrated in the following example involving the delamination of a silicone primer and polytetrafluoroethylene (PTFE) material. The positive mass spectrum acquired from the delaminated interface contains peaks known to be uniquely characteristic of PTFE (CF3 at mass 69) and the silicone primer (Si(CH3)3 at mass 73). Figures 6 and 7 are secondary ion im es of the CF3 and (Si(CH3)3 fragments taken from a 1-mm area of the delaminated interface. These maps clearly indicate that the PTFE and the silicone primer exist in well-defined and complementary areas. 

New materials also emerged. Nylon, developed brilliantly by W. H. Carothers and his team of research workers for Du Pont as a fibre in the mid-1930s, was first used as a moulding material in 1941. Also in 1941 a patent taken out by Kinetic Chemical Inc. described how R. J. Plunkett had first discovered polytetrafluoroethylene. This happened when, on one occasion, it was found that on opening the valve of a supposedly full cylinder of the gas tetrafluoroethylene no gas issued out. On subsequently cutting up the cylinder it was found that a white solid, polytetrafluoroethylene (PTFE), had been deposited on the inner walls of the cylinder. The process was developed by Du Pont and, in 1943, a pilot plant to produce their product Teflon came on stream. 

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... 

It has recently been reported that a molecule, claimed to contain a high concentration of conjugated alkyne units, can be prepared by electrochemical reduction of polytetrafluoroethylene (PTFE) [32,33]. The reduction is carried out using magnesium and stainless steel as anode and cathode respectively. The electrolyte solution contains THE (.30 cm ), LiCI (0.8 g) and FeCl2 (0.48 g). A 10 X 10 nm PTFE film, covered with solvent, is reduced to carbyne (10 V for 10 h)... 

Shock-resistant, flexible hose (Figure 40.32) assemblies are required to absorb the movements of mounted equipment under both normal operating conditions and extreme conditions. They are also used for their noiseattenuating properties and to connect moving parts of certain equipment. The two basic hose types are synthetic rubber and polytetrafluoroethylene (PTFE), such as DuPont s Teflon fluorocarbon resin. 

Some authors have suggested the use of fluorene polymers for this kind of chromatography. Fluorinated polymers have attracted attention due to their unique adsorption properties. Polytetrafluoroethylene (PTFE) is antiadhesive, thus adsorption of hydrophobic as well as hydrophilic molecules is low. Such adsorbents possess extremely low adsorption activity and nonspecific sorption towards many compounds [109 111]. Fluorene polymers as sorbents were first suggested by Hjerten [112] in 1978 and were tested by desalting and concentration of tRN A [113]. Recently Williams et al. [114] presented a new fluorocarbon sorbent (Poly F Column, Du Pont, USA) for reversed-phase HPLC of peptides and proteins. The sorbent has 20 pm in diameter particles (pore size 30 nm, specific surface area 5 m2/g) and withstands pressure of eluent up to 135 bar. There is no limitation of pH range, however, low specific area and capacity (1.1 mg tRNA/g) and relatively low limits of working pressure do not allow the use of this sorbent for preparative chromatography. 

Polytetrafluoroethylene (PTFE) Poor significantly damaged. The others show... 

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... 

It has been a dream for a tribologiest to create a motion with a super low friction or even no friction between two contact surfaces. In order to reduce friction, great efforts have been made to seek materials that can exhibit lower friction coefficients. It is well known that friction coefficients of high quality lubricants, e.g., polytetrafluoroethylene (PTFE), graphite, molybdenum disulphide (M0S2), etc., are hardly reduced below a limit of 0,01,... 

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