Electrical Properties
Tefzel exhibits high resistivity and low losses. Tefzel has a dielectric constant of 2.5- 2.6 at frequencies below 10MHz. At higher frequencies, the value decreases to approximately 2.3 at 10GHz. Te dissipation factor is below 0.001 at a low frequencies but gradually increases to a peak at about 0.023 at approximately 100 MHz, after which it decreases to below 0.01 at 10GHz.
Figure 4 shows the typical performance of dielectric constant over a wide range of frequencies, up to and including the high gigahertz values. Teflon® has the lowest known dielectric constant of any plastic material. The dissipation factor of Teflon® AF remains low over this same range of frequencies, as shown in Figure 5.
Strength and resistance to deformation under load is unusual for most fluoropolymers.
TECHNICAL DESCRIPTION OF TEFLON
History of Teflon
The story of Teflon® began April 6, 1938, at DuPont's Jackson Laboratory in New Jersey. DuPont chemist, Dr. Roy J. Plunkett, was working with gases related to Freon® refrigerants, another DuPont product. Upon checking a frozen, compressed sample of tetrafluoroethylene, he and his associates discovered that the sample had polymerized spontaneously into a white, waxy solid to form polytetrafluoroethylene (PTFE).
PTFE is inert to virtually all chemicals and is considered the most slippery material in existence. These properties have made it one of the most valuable and versatile technologies ever invented, contributing to significant advancements in areas such as aerospace, communications, electronics, industrial processes and architecture. As DuPont registered trademark Teflon®, it has become a familiar household name, recognized worldwide for the superior non-stick properties associated with its use as a coating on cookware and as a soil and stain repellant for fabrics and textile products.
The Teflon® trademark was coined by DuPont and registered in 1945; the first products were sold commercially under the trademark beginning in 1946. Applications and product innovations snowballed quickly. Today, the family of Teflon® fluoropolymers from DuPont consists of: PTFE, the original resin; FEP, introduced in 1960; Tefzel® ETFE in 1970; and PFA, in 1972.
The invention of PTFE has been described as "an example of serendipity, a flash of genius, a lucky accident ... even a mixture of all three." Whatever the exact circumstances of the discovery, one thing is certain: PTFE revolutionized the plastics industry and, in turn, gave birth to limitless applications of benefit to mankind. In 1990, U.S. President George Bush presented the National Medal of Technology to DuPont for the company's pioneering role in the development and commercialization of man-made polymers over the last half century. The citation lists Teflon® fluoropolymer resin as one of these special products.
Dr. Roy Plunkett (1911-1994) has been recognized the world over by scientific, academic and civic communities. He was inducted into the Plastics Hall of Fame in 1973, and, in 1985, into the National Inventors' Hall of Fame joining such distinguished scientists and innovators as Thomas Edison, Louis Pasteur and the Wright Brothers.
The spirit of invention with DuPont fluoropolymers that was led by Dr. Plunkett is commemorated globally with the DuPont For Innovation With Teflon®.
General Properties
Teflon® mechanical properties are low compared to other plastics, but its properties remain at a useful level over a wide temperature range of -100°F to +400°F (-73°C to 204°C). Mechanical properties are often enhanced by adding fillers (see paragraph below). It has excellent thermal and electrical insulation properties and a low coefficient of friction. PTFE is very dense and cannot be melt processed -- it must be compressed and sintered to form useful shapes.
Filled Grades
PTFE's mechanical properties can be enhanced by adding fillers such as glass fibers, carbon, graphite, molybdenum disulphide, and bronze. Generally, filled PTFE's maintain their excellent chemical and high temperature characteristics, while fillers improve mechanical strength, stability, and wear resistance.
The properties of 25% glass-filled and 25% carbon-filled PTFE grades are shown below for comparison purposes. There are literally dozens of different filled PTFE products and grades -- too many to be listed here. Please contact Boedeker Plastics for more information about other filled PTFE.
It has an extremely low surface energy in the solid state, thus providing an excellent antistick, nonwetting contact surface. Conversely, when these resins are in a molten state, they become low surface-tension liquids, ideal for high-performance, hot-melt adhesives. Teflon is extremely resistant to oxidation, surface fouling, discoloration, and embrittlement, as proven by tests conducted in Florida for periods of up to 20 years. It is inert to enzymic and microbiological attack because the pure polymer does not provide nourishment or porosity for these growths. Fluoropolymers are chemically inert and pure. They generally contain no additives—plasticizers, stabilizers, lubricants, or antioxidants—which could contaminate process fluids. They are resistance to even the most aggressive organic and inorganic chemicals and solvents over a broad temperature range. It is remarkably resistance to high temperatures and flames because of very high melting points and auto-ignition temperatures, as well as exceptional thermal degradation thresholds. Flame propagation characteristics, such as rate of heat release and smoke generation, are very low. It has one of the lowest coefficients of friction of any solid material. It’s abrasion resistance is adaptable to demanding environments by using inorganic fillers, such as glass fiber, graphite, and powdered metals. Property retention after exposure to temperatures beyond the limit of almost all other thermoplastics and elastomers. Depending on the end-use requirements, these resins are often rated for continuous service at temperatures as high as 260°C (500°F). In certain cases, they can also withstand short excursions to higher temperatures. In under floor heating temperatures may rise to a maximum of 30 to 40 degrees. It is extremely hydrophobic and completely resistant to hydrolysis. It has good barriers to water permeation; its typical properties and dimensional stability remain unchanged even after year-long immersion in water. It has an outstanding retention of properties after aging, even at high temperatures and in the presence of solvents, oils, oxidizing agents, ultraviolet light, and other environmental agents. Because they do not use any leachable or degradable stabilizing additives, fluoropolymers offer an important safety advantage when designing products for long service life.
PTFE is an extaordinary material. Some say that it is the most useful material known to man. This is because it has a combination of properties that are very hard to find. Its four great properties are: 1. very low coefficient of friction, 2. highly inert, 3. high melting point, 4. wonderful electrical properties. These properties are due to its unique molecular structure.
As you can see, PTFE is composed of carbon and fluorine. Carbon-fluorine and carbon-carbon bonds are among the strongest in single bond organic chemistry. This accounts for many of its properties. Because of the strong bonds, much thermal energy must be used to break down the material. It is also nonpolar; this leads to its chemical inertness, as the diagram demonstrates, and the fact that its electrical resistance is over 1018 . The low coefficient of friction of Teflon results from low interfacial forces between its surface and another material and the comparatively low force to deform.
Biography
Speedheat International: Underfloor Heating Company. Manufacturers of heating element
Warm Up: Underfloor Heating Company
Du Pont: Manufacturers of Tefzel and Teflon which is a registered Trademark
American Wire Suppliers LTD
Hoch Tief GMBH
