What is Polytetrafluoroethylene Fibers (PTFE)?
Polytetrafluoroethylene (PTFE) is a high-performance synthetic fiber made from tetrafluoroethylene (TFE). It is widely known under the brand name Teflon, introduced by DuPont. Polytetrafluoroethylene (PTFE) was first synthesized in 1938 by the American chemist Roy Plunkett. In 1954, DuPont launched the first filament yarns and staple fibers made of PTFE. PTFE fibers have a very low coefficient of friction (0.01–0.04), so the transition from rest to movement is smooth.
Polytetrafluoroethylene, otherwise known as PTFE, is often sold under the trademark of Teflon. It is made from calcium chloride that has been treated with sulphuric acid to form hydrogen fluoride. This compound reacts with chloroform, and it is heated in the presence of a catalyst to produce a powder form of tetrafluoroethylene. The resin is washed, dried and formed into a viscous polymer which is then extruded and coagulated in hydrochloric acid. Ultimately, it is heated rapidly to get the particles to fuse into the filament and then drawn to three or four times its original length. This article explores the properties, production methods, and industrial applications of polytetrafluoroethylene fibers.
Properties of Polytetrafluoroethylene Fibers
PTFE fibers are known for their unique combination of chemical, thermal, and physical properties that make them ideal for specialized industrial uses. The PTFE has an extraordinary resistance to chemicals and is attacked only by molten alkali metals, chlorine trifluoride and fluorine gas, hot and at high pressure. There is no known solvent for the polymer at normal temperatures, and it withstands elevated temperatures much better than any other organic plastic. It begins to decompose at about 300°C without melting. It is practically undyeable. They are tan to light brown as it is manufactured but can be bleached to white using oxidizing strong mineral acids and are very strong and having high density due to its structure – close packing of fluorine atoms around carbon atoms.
The major properties of the polytetrafluoroethylene fiber is summarized below:
- Stain-Resistant
- Excellent resistance to chemicals, mildew, bacteria and insects.
- PTFE does not absorb moisture
- Sunlight resistant
- Heat-Resistant (melts at 288⁰c)
- Hydrophobic
- Oleophobic (lacks an affinity for oils)
- Breathable
- Water resistant
- Easy care
- Flammability: Nonflammable; melts with decomposition
- Tenacity, cN/tex (g/den) dry, wet: 10.6–12.4 (1.2–1.4), 10.6–12.4 (1.2–1.4)
- Tensile strength, kg/cm2: 2205–2625
- Elongation, %, dry (wet): 15–32 (15–32)
- Specific gravity: 2.1
- Effect of alkalis: They completely inert even to all strong, hot alkalis
- Effect of acids: PTFE fiber is completely inert, even to boiling sulphuric acid, to fuming nitric acid or to aqua regia
- Effect of organic solvents: The only known solvents for PTFE are certain perfluorinated organic liquids at temperatures above 299°C.
- Thermal properties: They have best thermal stability, flexible, tough and chemical-resistant. PTFE fiber loses its fiber properties 327°C. It retains a useful strength up to 205°C, and perform at temperatures as high as 288°C.
Production Method of Polytetrafluoroethylene Fibers
Polytetrafluoroethylene fibers can be produced in various ways. Mostly the matrix wet spinning process is used. For this, a solution of 60% PTFE and 8% viscose is suspended together with alkyl or acrylic polyglycol ether, filtered, spun out at 20°C through the spinneret into a spinning bath. This consists of 10% sulfuric acid, 16% sodium sulfate, 10% zinc sulfate and water. After coagulation, the filaments are washed and dried. This is followed by drawing on hot godets (360–390°C) by a factor of 7 (below Figure 1). In the process, the cellulose burns and the PTFE is sintered to form a multifilament yarn. The resulting yarns are yellow-brown in color, which can be bleached by treatment in boiling sulfuric acid with the addition of nitric acid. Fibers produced in this way have a strength of 10–20 cN/tex, an elongation at break of approx. 18%, shrink relatively strongly at high temperatures (10–20%) and have a continuous service temperature of 250°C.
Alternatively, PTFE fibers can also be paste-extruded. For this purpose, PTFE is combined with a lubricant (15–25% by mass). Through the combination of the process steps extrusion and rapid hot stretching, the fiber expands and cracks and a fine network of fibrils and pores is formed. The pore size is 300–800 μm depending on the stretching temperature (250–300°C). The proportion of pores can be up to 96%. The strength of these so-called ePTFE fibers is significantly higher than that of standard PTFE fibers and ranges from 10–60 cN/tex, the elongation at break is 3–5%, as is the shrinkage. The density of ePTFE is about 0.2–2.2 g/cm³, depending on the pore size, and the thermal conductivity is 0.1–0.3 W/mK. The continuous service temperature of 260°C is somewhat higher than for PTFE. The LOI is 95, which is one of the highest values ever for polymers. Both PTFE staple fibers and PTFE filaments are available. Gore-Tex™ membranes are also produced using this process. Water vapor can escape through the pores from the inside, but they are so small that no water in liquid form can penetrate from the outside.
Industrial Uses
The PTFE is an inert polymer in all conditions and medium and therefore it has numerous high-tech and industrial applications. Industrial and technical materials where toughness and resistance to corrosion and heat are required. It is also used as a coating to fabrics, such as school uniforms, to help them resist stains. Teflon surrounds the fiber, creating an invisible barrier that is safe, gentle, and effective. Teflon does not harm the environment because it does not contain CFCs. It makes fabrics water resistant, stain-resistant, breathable and easy to care for. PTFE used in the coating in non-stick frying pans and other cookware, braided packing, filtration fabrics, gaskets, laundry pads, conveyor belt, electrical tapes, corrosion resistance cordage, electrical insulator, and water-repellent composites. Teflon fibers are also used in the aerospace and aviation industry.
Conclusion
Polytetrafluoroethylene (PTFE) fibers represent a remarkable advancement in technical textiles. PTFE fibers are versatile materials with superior chemical, thermal, and mechanical properties, produced through specialized polymerization and fiber-forming techniques. Though it is expensive but their outstanding resistance to heat, chemicals, and wear makes them suitable for demanding industrial applications. As technology continues to advance, PTFE fibers will play an increasingly vital role in industries that demand reliability under extreme conditions.
References
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