Polytetrafluoroethylene melting point

Tetrafluoroethylene. Emulsion polymerisation of tetrafluoroethylene, catalysed by oxygen, yields polytetrafluoroethylene (Tejlon) as a very tough horn-hke material of high melting point. It possesses excellent electrical insulation properties and a remarkable inertness towards all chemical reagents, including aqua regia. 

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. 

Hence at room temperature there are no solvents for polyethylene, polypropylene, poly-4-methyl-pentene-l, polyacetal or polytetrafluoroethylene, but at temperatures of about 30°C below their melting point solvents of... 

Fluoropolymers. These form one of our oldest and most spectacular families of engineering plastics. Polytetrafluoroethylene was developed by DuPont over two decades ago, and more recently by Allied Chemical, Hoechst, ICI, Pennwalt, and other manufacturers as well. It combines unusually low adhesion and friction, high temperature and flame resistance, excellent electrical properties, and extreme chemical inertness. Its high melting point and melt viscosity make thermoplastic processing extremely difficult, so that many... 

Polytetrafluoroethylene is a linear polymer of the general formula -(CF2 CF2) — Its molecular weight (106 to 107) and its melting point (327 °C) are extremely high The usable temperature range of PTFE extends from below... 

Starkweather, H. W. A comparison of the rheological properties of polytetrafluoroethylene below its melting point with certain low-molecular weight smectic states. J. Polymer Sci., Polymer Phys. Ed. 17, 73 (1979)... 

In Gee s (1957) Tilden Lecture he quotes entropies of fusion calculated in the case of polytetrafluoroethylene from the effect of pressure on the melting point... 

Polytetrafluoroethylene represents in many respects the extreme of known polymers. Among its most notable properties are its high crystalline melting point (327° C), its high melt viscosity (about 1011 poises at For paper I see this Journal 1, 75—113 (1958). 

Above its melting point of 327° C, polytetrafluoroethylene has some properties more like a rubber than a liquid. The instantaneous Young s modulus is 2—3 X 107 dynes/cm2, and the melt viscosity is about 10u poises at 380° C (Nishioka and Watanabe). Because of this very high melt viscosity, it is not feasible to process the polymer by conventional extrusion or injection molding. Instead, techniques similar to those of powder metallurgy are employed. These involve three basic steps. 

Polytetrafluoroethylene powders can be extruded but not by the methods applied to conventional thermoplastics. The polymer must not be subjected to excessive mechanical working above the melting point or cracking of the finished piece will result. For this reason, the polymer is worked while it is still cold. The powder is compacted with the aid of a screw or a ram and forced through a hot die in which it is sintered (James). This method is used to fabricate rods or heavy wall tubing or to apply heavy coatings to electrical conductors. 

Matsumae, K., M. Watanabe, A. Nishioka and T. Ichimiya Viscosity and elasticity of gamma-irradiated polytetrafluoroethylene resin above the melting point. J. Polymer Sci. 28, 653—655 (1958). 

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... 

Fluoropolymers are used for the manufacture of coatings for frying pans, pots, fryers and other cooking equipment and utensils. Polytetrafluoroethylene with a melting point of approximately 327 °C is mostly used but polymer mixtures with perfluoro-alkylvinyl ether and hexafluoropropylene can also be used. 

Sintering A process in which polytetrafluoroethylene (PTFE) particles are heated above the melting point they soften and coalesce, thus forming a continuous film or a solid body. 

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. 

Polytetrafluoroethylene is a completely fluorinated polymer manufactured by free-radical polymerization of tetrafluoroethylene. With a linear molecular structure of repeating -CF2—CF2- units, PTFE is a crystalline polymer with a melting point of 326.7°C. Its specific gravity is 2.13—2.19. Polytetrafluoroethylene has exceptional resistance to chemicals. Its dielectric constant (2.1) and loss factor are low and stable across a wide range of temperature. It has useful mechanical properties from myogenic temperatures to 260°C. In the United States, PTFE is sold as Halon, Algoflon, Teflon, Fluon, Hostaflon, and Polyflon. ... 

The melting of a semierystalline or crystalline pol mier exhibits itself as an endothermic peak. The peak temperature is correspondent to the actual melting point of the pol mier. As in DSC, the area under the peak is proportional to the crystalline fraction of the sample. Mixtures of polymers can be characterized by DTA because the melting points of individual pol miers are, for the most part, unaffected by the mixture. Similar pol miers, such as high and low density, are distinguishable by DTA while infrared spectroscopy would not be able to easily resolve such subtle differences. Figure 10.29 shows a thermogram of a mixture of polytetrafluoroethylene (PTFE) and perfluoroalkoxy polymer (PFA). 

Hot Stamping - This is a process for obtaining a specific geometry in a polytetrafluoroethylene stock shape. Hot stamping is conducted using a stamp which is heated well above (>360°C) the pol5mier melt point. Pressure and time are the other variables that can be manipulated to obtain the desired pattern. 

---