PTFE Polytetrafluoroethylene is a high-performance, versatile fluoropolymer composed of carbon and fluorine atoms. Fluoropolymers are a group of plastics that possess a wide range of properties and benefits. PTFE is one such fluoropolymer whose discovery revolutionized the fluoropolymer group forever and paved the way for a wide variety of applications.
One of the common applications of PTFE materials includes non-stick coatings for kitchen cookware. Due to its non-reactive nature, partly due to the strength of the carbon-fluorine bond, it is often used to make pipes and containers for reactive and corrosive chemicals.
How is PTFE made?
Image The manufacturing of PTFE is very similar to any other polymer. It is manufactured by free radical polymerization techniques using addition polymerization of TFE in a batch process in an aqueous medium.
The chemical structure of PTFE is identical to that of polyethylene; the only major difference is that the hydrogen atoms are completely replaced by fluorine. However, the methods of making PE and PTFE are very different.
The fluorine atoms are huge in size and form a uniform and continuous sheath around the carbon-carbon bonds, which provides the molecule with good chemical resistance, electrical inertness, and stability.
Like many other great discoveries, polytetrafluoroethylene was discovered by accident. Roy J. Plunkett first discovered it in 1938. At the time, he was working for Dupont in New Jersey. Plunkett's original intention was to create a new chlorofluorocarbon refrigerant. However, the flow of polytetrafluoroethylene gas in the pressure bottle stopped before the weight of the pressure bottle reached the "empty" signal.
But when Plunkett measured the amount of gas used by weighing the bottle, he became interested in the source of the weight and finally decided to take the bottle apart.
He found that the inside of the bottle was coated with a white waxy smooth material. Later it was named polymerized perfluoroethylene, and the iron inside the container acted as a catalyst.
The new material was patented by Kinetic Chemical Company in 1941 as a new fluorinated plastic, and the Teflon trademark was registered in 1945. By 1961, the first American-made PTFE-coated pan was available in the U.S., called "The Happy Pan." Since then, non-stick cookware has become one of the most common household products produced by thousands of manufacturers around the world.
Properties and Performance of PTFE –
PTFE is available in three main forms – granules, water-based dispersions, and fine powders.
Granular PTFE materials are produced by suspension polymerization in an aqueous medium with little or no dispersant. Granular PTFE materials are primarily used in compression, isostatic pressing, and ram extrusion methods.
Water-based PTFE dispersions use the same aqueous polymerization, with more dispersant and stirring. Water-based dispersions are primarily used in coatings and film casting methods.
Fine powder PTFE is small white particles made by controlled emulsion polymerization. Fine PTFE powder can be processed into flakes by paste extrusion or with additives to improve wear resistance.
Other notable properties of PTFE include excellent high and low temperature resistance, electrical insulation properties, chemical inertness, low coefficient of friction (static 0.08 and dynamic 0.01), and non-stick properties over a wide temperature range (-260 to 260°C).
PTFE is one of the most reliable materials in terms of chemical resistance. It is attacked only by molten alkali metals, organic halides such as chlorine trifluoride (ClF3) and oxygen difluoride (OF2), and gaseous fluorine at high temperatures.
PTFE's mechanical properties are also impressive, but not as good as other engineering plastics at room temperature. The addition of fillers has proven to be a successful way to overcome this obstacle. Within its normal temperature range, PTFE exhibits some useful mechanical properties. These properties are also hampered by processing variables such as sintering temperature, preform pressure, cooling rate, etc. Polymer properties such as molar mass particle size and particle size distribution can negatively affect mechanical properties.
PTFE has outstanding electrical insulation properties, low dielectric constant and dielectric withstand voltage. The very low dielectric constant (2.0) is a result of the complex symmetrical structure of the macromolecules.
PTFE material also shows good thermal properties, with no significant degradation below 440 °C.
It is also subject to degradation in air and attack by radiation, starting at a dose of 0.02 Mrad.
