What is PTFE (Polytetrafluoroethylene)? | The Complete Guide

PTFE or polytetrafluoroethylene is a high-performance, and versatile fluoropolymer made up of carbon and fluorine atoms. A fluoropolymer is a group of plastics offering a wide array of properties and benefits. PTFE is one such fluoropolymer, and its discovery reformed the fluoropolymer group forever and paved the way for several applications.

One of the common applications for PTFE material includes non-stick coatings for kitchen cookware. Thanks, to its non-reactive nature, partly because of the strength of carbon-fluorine bonds, it is often utilized for making pipeworks and containers for reactive and corrosive chemicals.

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How is PTFE Made?

The making of PTFE is quite similar to any other polymer. It is manufactured by the free-radical polymerization technique in an aqueous media using the addition polymerization of TFE in a batch process.

The chemical structure of PTFE is identical to polyethylene; the only major difference is that the hydrogen atoms are completely replaced by fluorine. However, the preparation methods for PE and PTFE are drastically different from each other.

The size of the fluorine atom is huge, and that forms a uniform and continuous sheath around carbon-carbon bonds and hence provides good chemical resistance, electrical inertness, and stability to the molecule.

The Interesting History of PTFE –

Like many other great discoveries, PTFE was found accidentally. Roy J. Plunkett first discovered it in 1938. At the time, he was working in new jersey for Dupont. Plunkett’s original purpose was to make a new chlorofluorocarbon refrigerant. However, the tetrafluoroethylene gas in its pressure bottle stopped flowing before the bottle’s weight had gone to the point signaling “empty.”

But as Plunkett measured the amount of gas used by weighing the bottle, he became interested in the source of weight and finally decided to split the bottle apart.

He found the interior of the bottle coated with a white waxy and slippery material. Later it was named polymerized perfluoroethylene, and the iron from the container’s inside acted as a catalyst.

The new material was patented by kinetic chemicals in 1941 as new fluorinated plastic and registered the Teflon trademark in 1945. Fast forward, the year 1961 was when the first US-made PTFE-coated pan was marketed in the United States as “The Happy Pan.” Since then, there is no looking back and non-stick cookware has been one of the most common household products produced by thousands of manufacturers and available worldwide.

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Characteristics and Properties of PTFE –

PTFE is mainly available in three forms – granule, water-based dispersions, and fine powder.

The granular PTFE materials are produced by suspension polymerization in an aqueous medium with a meager or no dispersing agent. The granule PTFE material is mainly used in compression, isostatic, and ram extrusion methods.
Water-based PTFE dispersions using the same aqueous polymerization using more amount of dispersing agents with agitation. Water-based dispersions are mostly used in coatings ad film casting methods.
The fine powder PTFE are small, white particles made by controlled emulsion polymerization. Fine PTFE powders can be processed into thin sections by paste extrusion or additives to improve wear resistance.

Other salient properties of PTFE are excellent high and low heat resistance, electrical insulation properties, chemical inertness, low coefficient of friction (static 0.08 and dynamic 0.01), and non-stickiness over a wide range of temperatures (260 to 260°C).

PTFE is one of the most reliable materials in terms of chemical resistance. It is only attacked by molten alkali metals, organic halogenated compounds like chlorine trifluoride (ClF3) and oxygen difluoride (OF2), and gaseous fluorine at high temperatures.
The mechanical property of PTFE is also impressive but interior to other engineering plastics at room temperature. The addition of fillers has been proved as a successful way to overcome that obstacle. In its normal temperature range, PTFE exhibits some useful mechanical properties. Those properties are also hindered by processing variables such as sintering temperature, preform pressure, cooling rate, etc. Polymer attributes like molar mass particle size and particle size distribution can negatively impact mechanical properties.

Polytetrafluoroethylene has outstanding electrical insulating properties, low dielectric constant, and insulation pressure. The very low dielectric constant (2.0) is a result of a sophisticatedly symmetric structure of macromolecules.
PTFE material also shows good thermal properties without obvious degradation below 440 °C.
It is also attacked by air degradation and radiation, which begins at a dose of 0.02 Mrad.

Below is a table showing the typical properties and value of PTFE.

Property	Unit
Melting Temperature (°C)	320 to 340
Elongation at Break (%)	300-550
Tensile Modulus (MPa)	550
Surface Energy (Dynes/g)	18
Dynamic Coefficient of Friction	0.04
Dielectric Constant	2
Refractive Index	1.35
Dielectric strength (kV/mm)	19.7
Appl. Temperature (°C)	260

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Disadvantages of PTFE Material –

The traditional PTFE material doesn’t come without some drawbacks. Here are they:

Creep and abrasion sensitive
It can’t be processed in molten state processing methods, and the suitable methods can often come as unconventional and expansive.
Joining difficulties
High dimensional variation around glass transition temperature.
Low radiation resistance
Corrosive and prone to toxic fumes.

Importance of Fillers and Additives for PTFE –

The addition of fillers and additives can significantly improve PTFE’s mechanical properties, specifically creep and wear rate. The common fillers used are steel, carbon, glass fiber carbon fiber, graphite, bronze, steel, etc.

Glass Fiber: Its addition will improve the creep performance and wear attributes of PTFE by affecting its low and high temperatures. Furthermore, Glass-filled compounds perform exceptionally well in oxidizing environments.

Carbon Fiber: Carbon fibers are essential in lowering creep, raising hardness, increasing flex, and a compressive modulus. The PTFE blended with carbon fiber compounds has high thermal conductivity, and a lowers coefficient of thermal expansion. Carbon fiber is inert to strong bases and hydrofluoric acids (Glass fiber can withstand both). These parts are perfect for making automotive parts like shock absorbers.

Carbon: Carbon as an additive will help in reducing creep, increasing hardness, and improving the thermal conductivity of PTFE. The same results can also be achieved by blending PTFE and graphite with elevating the wear resistance of carbon-filled compounds. These blends are ideal for non-lubricated applications like piston rings found in compression cylinders.

Bronze-filled PTFE: This compound exhibits outstanding thermal and electrical conductivity making it perfectly suited for applications where apart is subjected to extreme loads and temperatures.

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Advantages of Incorporating Fillers –

Fillers/additives are crucial for increasing the porosity of PTFE compounds and thus affect electrical properties – it decreases the dielectric strength while increasing the dielectric constant and dissipation factor.
Fillers can improve the properties of PTFE substantially in both high and low temperatures.
The changes in chemical property can highly depend on the type of additive used, but. in general, it also leaves positive results.

PTFE Applications –

In general, fluorinated thermoplastics are utilized for high-performance applications with high heat, high purity, low temperatures, chemical inertness, non-sticking, and self-lubricating properties. Below are some of the most common PTFE uses:

Engineering – bearing, non-stick surfaces, seats, plugs, fittings, valve, and pump parts.

Medical – heart patches, cardiovascular grafts, ligament replacement.

Chemical Industry – pumps, diaphragms, impellers, Coatings for heat exchangers, autoclaves, reaction vessels, tanks, containers, etc.

Automotive – valve stem seals, shaft seals, gaskets, O-rings, linings for fuel hoses, power steering, and transmission, etc.

Electrical & Electronics – flexible printed circuit boards, electrical insulation, etc.

Best Techniques to Process PTFE –

PTFE’s rigid polymer chain structure makes it extremely difficult to process conventional methods like injection molding and extrusion. Still, it’s very high melt viscosity and high melting temperature also don’t help at all. Processing technologies ideally dealing with powder metallurgy are well suited for PTFE.

Sintering, compression molding, pressing, ram or paste extrusion, hot stamping, machining, extrusion of pre-sintered powders on special machines.
Paste extrusion, which blends PTGE with hydrocarbons, is used to fabricate PTFE into tapes, tubes, and wire insulation. The hydrocarbon will vaporize before the part is sintered.
Operating range -200°C to 260°C.

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The Future of PTFE Material –

According to a leading market research company ResearchAndMarkets, the global polytetrafluoroethylene market will see a CAGR of 5.13% during the forecast period of 2019-2024.

However, the road will be full of hurdles because of the Covid-19 pandemic. As of writing this piece, the world has re-opened again after a prolonged lockdown, and a vaccine is also making the rounds of the world, but the prolonged shutdown effect will be long felt as the global economy is seeing its worst economic recession in the history of humanity.

Having said that, it’s not all doom and gloom, as the vaccine has been made and people are getting vaccinated rapidly, things can catch up faster than previously anticipated. The same can be said about the PTFE market, let alone the plastic processing industry.

The key for rapid growth lies in the Asian market; China is already the world’s largest consumer of PTFE and still has immense growth potential. Apart from China, countries like India, Indonesia, Japan, Korea, and Bangladesh hold significant potential for future growth thanks to rising household incomes and favorable government policies to trim down the economic adversities caused by the Covid-19 pandemic.

FAQs –

1. Is PTFE carcinogenic?

Ans. It has been proven that PTFE is toxic to human health because it contains a carcinogenic substance called PFOA. However, there is no need to worry as PTFE non-stick coatings do not include that substance anymore.

2. What is PTFE tubing used for?

Ans. PTFE tubing is most commonly used as laboratory tubing, where chemical resistance and purity are the most important. PTFE has an extremely low coefficient of friction and is known as one of the most “slippery” substances known.

3. What type of plastic is PTFE?

Ans. PTFE is a thermoplastic polymer belonging to a fluoropolymer made up of carbon and fluorine atoms.

4. What are PTFE sheets used for?

Ans. PTFE sheets are used in various applications, such as PTFE envelope gaskets and PTFE packings. It comes with an exceptional ability to resist gases, water, chemicals, fuels, and oil.

5. Is PTFE FDA approved?

Ans. PTFE is FDA approved thus used in the food processing and service industry as insulators and bearings.

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Final Thoughts –

That was all I has to say about PTFE plastics. Polytetrafluoroethylene, with its salient properties, should be a good choice for plastic manufactures. Only powder form processing might be a drawback for many, but it doesn’t come without its perks.

Thanks for reading. Kindly share your thoughts in the comment box.

Have a Fantastic Day.