Copolymers of Tetrafluoroethylene and Hexafluoropropylene FEP

Polytetrafluoroethylene (PTFE Teflon) was discovered accidently by PlunkettCZ nd commercialized by DuPont in the 1940 s. This polymer has a solubility parameter of about 6H and a high melting point of 327°C and is not readily moldable. Poly-chlorotrifluoroethylene (CTFE, Kel-F), the copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), polyvinylidene fluoride (PVDF, Kynar), the copolymer of tetrafluoroethylene and ethylene (ETFE), the copolymer of vinylidene fluoride and hexafluoroisobutylene (CM-1), perfluoroalkoxyethylene (PFA) and polyvinyl fluoride (PVF, Tedlar) are all more readily processed than PTFE. However, the lubricity and chemical resistance of these fluoropolymers is less than that of PTFE. 

Table 5.23. Effect of End-Capping Treatment on the End Groups of a Copolymer of Tetrafluoroethylene and Hexafluoropropylene (FEP) ...

Examples of three copolymers of tetrafluoroethylene and hexafluoropropylene (FEP) have been de-scribedl l to illustrate the effect of shearing on the removal of unstable polymer links. Table 5.26 shows a summary of the polymer characteristics and the extrusion conditions. The color (indicated by %Green) in the pellets indicated that they still contained some unstable end groups. 

Materials compatibility. We use scrupulously clean and scratch-free FEP (FEP is the acronym for the copolymer of tetrafluoroethylene and hexafluoropropylene) tubing for handling our mixtures of fluorine and nitrogen at ambient temperature. Corrugated FEP tubing is convenient for making strain-free assemblies. We have found that Monel is excellent for use with dry molten KF-2HF. Mild steel corrodes slowly and stainless steels corrode rapidly. Kel-F polychlorotrifluoroethylene is satisfactory for use with HF and with KF-2HF polypropylene and polymethylpentene are not satisfactory. 

The processability of fluorine-containing polymers is improved by replacement of one or more of the fluorine atoms. Replacing one of the eight fluorine atoms with a trifluoromethyl group gives a product called FEP or Viton, actually a copolymer of tetrafluoroethylene and hexafluoropropylene (Equation 6.53). Polytrifluoromonochloroethylene (PCTFE, Kel F) (Equation 6.54), in which one fluorine atom has been replaced by a chlorine atom, has a less regular structure and is thus more easily processed. Poly(vinylidene fluoride) (PVDF, Kynar) (Equation 6.55) is also more easily processable but less resistant to solvents and corrosives. 

Teflon. The Teflon TFE polymer is prepared from tetrafluoroethylene by Du Pont it is white and nearly opaque except in thin sheets. Teflon FEP is a copolymer of tetrafluoroethylene and hexafluoropropylene, which is more readily molded and is translucent. The FEP polymer has more limited chemical... 

Several plastics, with high resistance to chemical attack and high temperatures, deserve special mention for process designers of inherently safer plants. For example, tetrafluoroethylene (TFE), commonly called Teflon brand TFE, is practically unaffected by all alkalies and acids except fluorine and chlorine gas at elevated temperatures, and molten metals. It retains its properties at temperatures up to 260°C. Other plastics that have similarly excellent properties (but are different enough that they each have their niche) include chlorotrifluoroethylene (CTFE) Teflon FEP, a copolymer of tetrafluoroethylene and hexafluoropropylene polyvinylidene fluoride (PVF2) (also... 

Crystallinity of never-melted PTFE is in the range of 92-98%, consistent with an unbranched chain structure while FEP, a copolymer of tetrafluoroethylene and hexafluoropropylene, has an as-polymerized crystallinity of 40-50%. In FEP, the pendent CF3 group is bonded to a tertiary carbon that is less thermally stable than primary and secondary carbon atoms. Degradation curves (Fig. 3) indicate degradation onset temperatures of 300°C for FEP (0.02% weight loss) and 425°C for PTFE (0.03%i weight loss). 

Chem. Descrip. FEP resin (copolymer of tetrafluoroethylene and hexafluoropropylene)... 

Copolymers. Fluorinated ethylene propylene (FEP) is a copolymer of tetrafluoroethylene and hexafluoropropylene. It has properties similar to PTFE but with a melt viscosity suitable for molding with conventional toermoplastic processing techniques. The improved processabUity is obtained by replacing one of the fluorine groups on PTFE with a trifluoromethyl group as shown in Fig. 2.4. ... 

Fig. 10. True stress-true strain behavior of polymers. Delrin is an acetal resin Lexan, a polycarbonate Teflon TFE designates the tetrafluoroethylene homopolymer Teflon FEP is a copolymer of tetrafluoroethylene and hexafluoropropylene (17). To convert MPa to psi, multiply by 145. Courtesy of Polymer Engineering and Science.

Fluorinated Ethylene-Propylene Resin (FEP, PFEP) This member of the fluorocarbon family is a copolymer of tetrafluoroethylene and hexafluoropropylene, possessing most of the desirable properties of PTFE, yet truly meltable and, therefore, processable in conventional extrusion and injection-molding equipment. It is available in pellet form for those operations and as dispersions for spraying and dipping. 

The aqueous dispersion was coagulated by agitation until a particulate coagulum was obtained which was then separated from water by filtration, rinsed with water, and dried. The dry powder was spread on aluminum trays to a depth of 5 cm and heated for 3 hours at 350°C. The product was a mass of copolymer of tetrafluoroethylene and hexafluoropropylene. It had a melting point of280°C, melt viscosity of 7 x 10" poise. A sample of FEP was chopped into small pieces and... 

The most chemical-resistant plastic commercially available today is tetrafluoroethylene or TFE (Teflon). This thermoplastic is practically unaffected by all alkahes and acids except fluorine and chlorine gas at elevated temperatures and molten metals. It retains its properties up to 260°C (500°F). Chlorotrifluoroethylene or CTFE (Kel-F, Plaskon) also possesses excellent corrosion resistance to almost all acids and alkalies up to 180°C (350°F). A Teflon derivative has been developed from the copolymerization of tetrafluoroethylene and hexafluoropropylene. This resin, FEP, has similar properties to TFE except that it is not recommended for continuous exposures at temperatures above 200°C (400°F). Also, FEP can be extruded on conventional extrusion equipment, while TFE parts must be made by comphcated powder-metallurgy techniques. Another version is poly-vinylidene fluoride, or PVF2 (Kynar), which has excellent resistance to alkahes and acids to 150°C (300°F). It can be extruded. A more recent development is a copolymer of CTFE and ethylene (Halar). This material has excellent resistance to strong inorganic acids, bases, and salts up to 150°C. It also can be extruded. 

The need for highly fluorinated thermoplastic polymers that, unlike PTFE, could be fabricated by conventional melt-processing methods led to the development of a group of resins that are copolymers of tetrafluoroethylene (TFE) with other perflu-orinated monomers. Commercially, the copolymer of TFE and hexafluoropropylene (HFP) is commonly known as fluorinated ethylene propylene (FEP). Copolymerization of TFE with perfluoropropylvinyl ether (PPVE) leads to PFA resins, and copolymerization of TFE with perfluoromethylvinyl ether (PMVE) produces MFA resins. 

FEP polymers are fully fluorinated and melt processible. They have chemical resistance comparable to polytetrafluoroethylene (PTFE). Melt viscosity of FEP is over one million times lower than PTFE. Fluorinated ethylene propylene resins are in general copolymers of tetrafluoroethylene with hexafluoropropylene and possibly one or more other comonomers. Commercial examples of the latter include perfluoroalkyl vinyl ether (PAVE), such perfluoroethyl vinyl ether (PEVE). FEP... 

Fluorinated ethylene propylene (FEP), copolymer of tetrafluoroethylene (TEE) and hexafluoropropylene (HFP) has physical and chemical properties similar to those of PTFE but differs from it in that FEP can be processed by standard melt-processing techniques. 

Fluorinated ethylene-propylene (FEP) is a copolymer of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP). It has a branched structure containing units of -CF2-CF2- and -CF2-CF (CF3)-. It retains most of the favorable properties of PTFE but its melt viscosity is low enough for conventional melt-processing. The introduction of HFP reduces the melting point of polytetrafluoroethylene from 325°C (617°F) to about 260°C (500°F).26... 

FEP, a copolymer of tetrafluoroethylene ( IFF) and hexafluoropropylene (HFP), is essentially PTFE with an occasional methyl side group attached. The methyl groups have effect as defects in crystallites and therefore reduce the melting point. These side groups also impede the slipping of the polymer chains past each other, thus reducing the cold flow. 

Note ETFE, copolymer of ethylene and tetrafluoroethylene MFA, copolymer of perfluoromethylvi-nylether and tetrafluorethylene PFA, copolymer of perfluoropropylvinylether and tetrafluoroethylene FEP, fluorinated ethylene-propylene copolymer PCTFE, poly(chlorotrifluoroethylene) PVDF, poly(vinylidene fluoride) VDF-HFP, copolymer of vinylidene fluoride and hexafluoropropylene. 

Copolymers of tetrafluoroethylene were developed in attempts to provide materials with the general properties of PTFE and the melt process-ability of the more conventional thermoplastics. Two such copolymers are tetrafluoroethylene-hexafluoropropylene (TFE-HFP) copolymers (Teflon FEP resins by Du Pont FEP stands for fluorinated ethylene propylene) with a melting point of 290°C and tetrafluoroethylene-ethylene (ETFE) copolymers (Tefzel by Du Pont) with a melting point of 270°C. These products are melt processable. A number of other fluorine containing melt processable polymers have been introduced. 

A phase transition occurs in Teflon at 19°C, and this involves a change in the degree of helical structure. It may be observed [59] as a spectral change in a weak doublet-type Raman band at 598 and 577 cm A few copolymers of tetrafluoroethylene exist, including tetrafluor-oethylene-hexafluoropropylene (FEP), tetrafluoroethylene-perfluoroalkyl-vinylether (PFA), and tetrafluoroethylene-hexafluoropropylene-perfluo-roalkylvinylether (EPE). An example of the IR and Raman spectra of EPE is provided in Reference Spectrum 24. Although these three copolymers have similar IR spectra, the bands around 990 cm are used to distinguish these copolymers [60]. The hexafluoropropylene moiety of FEP produces a band at 982 cm while the perfluoroalkyl vinylether moiety of PFA has a band at 993 cm As expected, EPE exhibits both the 993 and the 982 cm bands. The IR spectrum in Reference Spectrum 24 shows the 993 cm band as a shoulder on the 982 cm band. 

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