Fluoropolymers

Fluoropolymers have excellent heat, chemical and corrosion resistance. The most common is polytetrafluoroethylene (PTFE), often known by the Dupont trademark, Teflon . Other tradenames include Dyneon (3M) and Fluon (Asahi Glass). The invention of PTFE is often used as an example of serendipity, but it was actually a combination of serendipity, curiosity, and hard work. Roy Plunkett was working on experimental refrigerants when a cylinder that had been filled withtetrafluoroethylene (TFE) gas did not deliver gas when the valve was opened. Often, when something does not occur as planned, people discard the results and move on, but Plunkett was curious. When the cylinder was cut open, a white lubricious solid was discovered. Further investigation revealed the solid to be a polymer of tetrafluoroethylene [28]. 

Consumers know PTFE because it is used as a coating material in non-stick cookware. The excellent chemical resistance makes it suitable for coating reactors and piping that are exposed to aggressive chemicals. The extremely low coefficient of friction makes it usefiil for bearings and gears. Specialty bullets are coated with PTFE to reduce wear on a rifle barrel. 

PTFE is available either as the homopolymer or modified with small amounts (typically less than 1% by weight) of a comonomer. The comonomer can have the benefit of improving processability by decreasing the molecular weight. Crystallization is also inhibited. The modifier is used at a low enough level that the desirable PTFE properties are maintained. 

The PTFE chain adopts a slowly twisting hehx with an outer sheath of fluorine atoms encompassing a carbon-based core. There is mutual repulsion of the fluorine atoms. These cylinders can slip past each other and this can lead to cold flow or creep [32]. Creep is permanent deformation of a plastic due to the prolonged application of stress. An example is a plastic strap that is holding a weight and over time permanently stretches and is elongated even after the weight is removed. PTFE is more susceptible to creep than many other polymers. 

Porous PTFE, also known as expanded PTFE (ePTFE) can be highly porous while retaining excellent strength. Fluorocarbons are hydrophobic so the combination of porosity and hydrophobicity makes ePTFE excellent for waterproof clothing. This technology is the basis for the outdoor clothing made from Gore-Tex [33-35]. 

New additives based on fluoropolymers have been introduced by DuPont and by Dyneon, to promote free flowing in polyolefins for extrusion and blown film production. They appear to act by coating the interior surface of the extrusion die with a microscopically thin non-stick film, which reduces friction at the resin/die interface and allows the extrusion compound to flow freely and more rapidly through the die opening. The non-stick properties also prevent accumulation of resin particles at the exit of the die, so eliminating the major cause of die build-up. The coating is continuously renewed by the additive through the extrusion process. 

The DuPont product is named Viton FreeFlow SC and RC and, unlike earlier types of fluoropolymer additives, they can be mixed into many pigmented masterbatches, with less interaction. The Dyneon grades are marketed as Dynamar PPA. The latest fluorocarbons comply with most world food contact legislation. 

As well as improved output, processors gain extended use of equipment and greater flexibility in speed, temperature, pressure, and gauge control, with a wider choice of blend ratios. There is less downtime for cleaning die apertures and start-up is also easier. The latest types can also be mixed into many pigmented masterbatches with less interaction. 

The effects become apparent after the additive has coated the metallic surfaces of the equipment, requiring 15-60 minutes conditioning time , depending on 

Resin PPA type Apparent viscosity (Pa) Melt fracture 

The commercial production of polymers containing fluorine is very small compared to the output of many other synthetic polymers. Nevertheless, several fluoropolymers are used in various important specialized applications. The principal commercial fluoropolymers at the present time are the homopolymers of tetrafluoroethylene (I), chlorotrifluoroethylene (II), vinyl fluoride (III) and vinylidene fluoride (IV) and vinylidene fluoride-chlorotrifluoroethylene, vinyli-dene fluoride-hexafluoropropylene (V) and tetrafluoroethylene-hexafluoropro-pylene copolymers. These materials, together with a few other fluoropolymers of interest, form the contents of this chapter. 

Polymerization of fluorine-containing olefins was first described in 1934 in a patent to I. G. Farbenindustrie (Germany) which related to poly chlorotrifluoroethylene. However, this polymer was of limited value and it was not until 1938, when Plunkett in the United States prepared poly tetrafluoroethylene, that commercial interest quickened. This polymer has found a great number of uses and probably accounts for at least 90% of the current ouput of fluoropolymers. The first pilot plant for poly tetrafluoroethylene came into operation in 1943 and large scale production began in 1950 (E.I. du Pont de Nemours and Co.) (U.S.A.). In addition to poly tetrafluoroethylene, many other fluoropolymers have been investigated and a few have reached commercial status. In these investigations, attention has centered particularly on copolymers with rubbery characteristics. 

Tetrafluoroethylene is currently prepared from chloroform by the following route  

Ethylene is treated with an excess of chlorine at 300—350°C in the presence of activated charcoal to give hexachloroethane. This product is then treated with hydrogen fluoride in the presence of antimony pentachloride to yield trichloro-trifluo roe thane. Dechlorination in the liquid phase with zinc dust and ethanol 

Vinyl fluoride may be obtained from acetylene by either of the two following routes  

The mechanical properties of carbon fibre PVF composites have been studied by Vidhate and co-workers [66]. 

Shelestova and co-workers [68], studied the effects of modification of carbon fibres on the thermo-physical properties of carbon filled PTFE. 

Zhonghai and co-workers [154] studied the mechanical properties of carbon fibre reinforced films of this polymer as a function of the degree of crosslinking with triethylenetetramine. In general, an improvement in mechanical properties resulted in little or no effect on the electrical properties of this polymer, which is a strong candidate for the fabrication of lithium battery electrodes. 

fluoropolymer family consists of polymers produced from alkenes in which one or more hydrogens have been replaced by fluorine. The most important members of this family are pol3ftetrafluoroethylene (PTFE) (XLVII), polychlorotrifluoroethylene (PCTFE) (XLVIII), poly(vinyl fluoride) (PVF) (XLIX), poly(vinylidene fluoride) (PVDF) (L) copolymers of 

Trade names for fiuoropolymers include Aflon, Fluon, Halar, Hostaflon, Kel-F, Kynar, Polyflon, Tedlar, Teflon, and Tefzel. 

PC can be processed by injection molding, extrusion, coextrusion, and blow molding. Coextrusions with EVOH or polyamides are carried out with the help of adhesives. PC can be laminated or coextruded to PP, PE, PET, PVC, and PVDC. PC is a hydrophilic polymer, and at ambient conditions can reach moisture levels of 0.35%. 

Fluoropolymers are a family of polymers containing C-F bonds. Polytetrafluoro-ethylene (PIPE) has the following structure  

FIFE was first commercialized by DuPont, under the brand name Teflon. PTFE is a very highly crystalline polymer, extremely inert, an excellent barrier, and exhibits a very low coefficient of friction. Its glass transition temperature (Tg) is about -100°C, and its melt temperature is about 327 C (621°F). Flowever, its very high viscosity makes it very difficult to process. PTFE is used most often as a component in packaging equipment, such as providing a nonstick surface on heat sealers, rather than in packages themselves. 

The stereochemically random presence of the Cl atom limits the crystallinity. In commercial resins, it is generally further modified by copolymerization, resulting in a semicrystalline material, with a glass transition temperature about 45°C and a melt temperature of about 190°C. It is sold by Allied Corp. under the name Aclar. PCTFE can be melt processed, though not easily. Its main advantage is its extremely good water vapor barrier, which is the best of any plastic film available. The WVTR at 38°C and 90% RH is 9.8-17.7 g pm/m2 d (0.025-0.045 g mil/100 in2 24 h). 

The more halogen is replaced by hydrogen, the more a plastic material resembles PVC [599]. 

---

Electromagnetic flow meters ate avadable with various liner and electrode materials. Liner and electrode selection is governed by the corrosion characteristics of the Hquid. Eor corrosive chemicals, fluoropolymer or ceramic liners and noble metal electrodes are commonly used polyurethane or mbber and stainless steel electrodes are often used for abrasive slurries. Some fluids tend to form an insulating coating on the electrodes introducing errors or loss of signal. To overcome this problem, specially shaped electrodes are avadable that extend into the flow stream and tend to self-clean. In another approach, the electrodes are periodically vibrated at ultrasonic frequencies. 

Ausimont SpA Milan, Italy SFg, fluoropolymer fluids, fluoromonomers, F2 gas large... 

Production of hydrogen fluoride from reaction of Cap2 with sulfuric acid is the largest user of fluorspar and accounts for approximately 60—65% of total U.S. consumption. The principal uses of hydrogen fluoride are ia the manufacture of aluminum fluoride and synthetic cryoHte for the Hall aluminum process and fluoropolymers and chlorofluorocarbons that are used as refrigerants, solvents, aerosols (qv), and ia plastics. Because of the concern that chlorofluorocarbons cause upper atmosphere ozone depletion, these compounds are being replaced by hydrochlorofluorocarbons and hydrofluorocarbons. 

Another impetus to expansion of this field was the advent of World War 11 and the development of the atomic bomb. The desired isotope of uranium, in the form of UF was prepared by a gaseous diffusion separation process of the mixed isotopes (see Fluorine). UF is extremely reactive and required contact with inert organic materials as process seals and greases. The wartime Manhattan Project successfully developed a family of stable materials for UF service. These early materials later evolved into the current fluorochemical and fluoropolymer materials industry. A detailed description of the fluorine research performed on the Manhattan Project has been pubUshed (2). 

High temperature resistance of ETEE and other fluoropolymers ia automotive fuels and their permeation resistance have been discussed (28,29). 

Stripes may be appHed to wire coated with ETEE fluoropolymer over DuLite 817-5002 fluoropolymer clear enamel or other bases. Thermally stable pigments are required. Stripes may be appHed by gravure-wheel-type appHcators and oven-cured in-line. 

The success of many appHcations depends on the abiHty of ETEE fluoropolymer to be economically assembled. 

The Du Pont HaskeU Laboratory for Toxicology and Industrial Medicine has conducted a study to determine the acute inhalation toxicity of fumes evolved from Tefzel fluoropolymers when heated at elevated temperatures. Rats were exposed to decomposition products of Tefzel for 4 h at various temperatures. The approximate lethal temperature (ALT) for Tefzel resins was deterrnined to be 335—350°C. AH rats survived exposure to pyrolysis products from Tefzel heated to 300°C for this time period. At the ALT level, death was from pulmonary edema carbon monoxide poisoning was probably a contributing factor. Hydrolyzable fluoride was present in the pyrolysis products, with concentration dependent on temperature. 

Technical Information, No. 11, Processing Guidelinesfor Du Pont Fluoropolymer Fotocasting Powders ofTef l and Teflon PFA, E. I. du Pont de Nemours Co., Inc., Wilmington, Del., 1982. 

Because of its excekent combination of properties, processibkity, and relatively low price compared to other fluoropolymers, PVDF has become the largest volume fluoropolymer after PTFE consumption in the United States has grown from zero in 1960 to about 6200 metric tons in 1991 (186). About 49% of the consumed volume is PVDF modified by copolymerization with 5—12-wt % HFP to enhance flexibkity. In 1992, Hst price for homopolymer powders was 15.32/kg, and for pekets 15.42/kg the reported market price was 14.09—14.22/kg (187). In the United States, almost ak PVDF is suppHed by Ausimont USA, Inc., Elf Atochem North America, Inc., and Solvay Polymers, Inc. Ausimont and Elf Atochem are producers Solvay is an importer of the resin. Smak amounts of resin are imported from Germany by Huls America, Inc, and from Japan by Kureha Chemical Industry Co., Ltd. PVDE producers and their trademarks are Hsted in Table 4. 

After 10 years of unabated rapid growth in the plenum wire and cable market, fluoropolymers including PVDE, primarily the flexible VDE/HEP copolymer, are beginning to lose market share to lower priced PVC-akoys. The loss of market share in the plenum market probably wkl be compensated by growth of PVDE in other fields thus during the mid-1990s the total volume of PVDE may not grow (188). 

Other sources of by-product HCl include allyl chloride, chlorobenzenes, chlorinated paraffins, linear alkylbenzene, siHcone fluids and elastomers, magnesium, fluoropolymers, chlorotoluenes, benzyl chloride, potassium sulfate, and agricultural chemicals. 

The PVC formulations shown in Table 2 represent typical compounds used by the wine and cable industry. PVC compounders have developed new PVC-based formulations with very good fire and smoke properties (can pass the UL 910 Steiner Tunnel test) that compete with the more expensive fluoropolymers. These can be used in fabricating telecommunication cables usable for plenum area appHcations. 

Examples of thermoplastic coatings an fluoropolymers, eg. Teflon or polyamides, eg, nylon. Thermosetting coatings are more resistant to ... 

Commonly used materials for cable insulation are poly(vinyl chloride) (PVC) compounds, polyamides, polyethylenes, polypropylenes, polyurethanes, and fluoropolymers. PVC compounds possess high dielectric and mechanical strength, flexibiUty, and resistance to flame, water, and abrasion. Polyethylene and polypropylene are used for high speed appHcations that require a low dielectric constant and low loss tangent. At low temperatures, these materials are stiff but bendable without breaking. They are also resistant to moisture, chemical attack, heat, and abrasion. Table 14 gives the mechanical and electrical properties of materials used for cable insulation. 

The anode and cathode chambers are separated by a cation-permeable fluoropolymer-based membrane (see Membrane technology). Platinum-electroplated high surface area electrodes sold under the trade name of TySAR (Olin) (85,86) were used as the anode the cathode was formed from a two-layer HasteUoy (Cabot Corp.) C-22-mesh stmcture having a fine outer 60-mesh stmcture supported on a coarse inner mesh layer welded to a backplate. The cell voltage was 3.3 V at 8 kA/m, resulting ia a 40% current efficiency. The steady-state perchloric acid concentration was about 21% by weight. 

Among the preformed polymers cured by minor additions of aHyl ester monomers and catalysts followed by heat or irradiation are PVC cured by diallyl fumarate (82), PVC cured by diallyl sebacate (83), fluoropolymers cured by triaHyl trimeUitate (84), and ABS copolymers cured by triaUyl trimeUitate (85). 

Core technical competencies may be composed of a number of core or key technologies. The competencies in turn can support product families, platforms, or core products, which then support individual products. These products may ultimately be found in a number of forms or shapes. For example, a key technology such as polymer characterization may support a competency in polymer synthesis and architecture, which in turn supports the platform of fluoropolymers and the product family of Teflon (DuPont) fluoropolymer resins that can be found as films, fibers, or in other forms. 

Chrome-complexed fluorochemicals, as weU as fluoropolymers, are widely used products. The compositions are proprietary. Fluorochemicals provide a high degree of water repeUency as weU as repeUency to aqueous stains, oUs, grease, and oilhorne stains. TraditionaUy, treatments are appUed duting a dmm process ia which about 30 min are required for flUl penetration of the leather to occur. Products are also avaUable for appUcation with sprayiag equipment and roU coaters. 

OU- and water-resistant treatments have been reported which iavolve blends of fluoropolymers and alkoxysUane or alkoxysUoxane materials, dehvered as 100% actives (90) or from solvent or emulsion (91), fluotinated alkoxysUoxane emulsions (92), and self-emulsifying fluotinated alkoxysUane-based concentrates (93). 

Materials of Construction. Glass has excellent corrosion-resistance to wet or dry bromine. Lead is very usefiil for bromine service if water is less than 70 ppm. The bromine corrosion rate increases with concentrations of water and organics. Tantalum and niobium have excellent corrosion-resistance to wet or dry bromine. Nickel has usefiil resistance for dry bromine but is rapidly attacked by wet bromine. The fluoropolymers Kynar, Halar, and Teflon are highly resistant to bromine but are somewhat permeable. The rate depends on temperature, pressure, and stmcture (density) of fluoropolymer (63). 

Electrical Applications. Plastics are used for electrical insulation, conduit and enclosures, lighting fixtures, and mechanical devices. The most widely used plastic for wire and cable insulation is flexible, plasticized PVC, which constitutes well over half the market in insulating wires for buildings, automobiles, appHances, and power and control lines. Polyethylene is also a factor. Higher performance plastics such as nylon and fluoropolymers also play a smaller role in this area. 

This high projected growth rate is driven by the expected strong growth of the HCFC-22 and fluoropolymer markets, which account for 90% of the total chloroform market. HCFC-22 is a substitute for some apphcations currendy using CFC-11 and CFC-12. It is restricted by the Montreal Protocol but will not be phased out until much later. This demand pushed chloroform production up 10% in both 1988 and 1989 (32). 

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. 

---