What is PTFE (polytetrafluoroethylene)

What is PTFE (Polytetrafluoroethylene) ?

PTFE Polytetrafluoroethylene is a high-performance multifunctional fluoropolymer composed of carbon atoms and fluorine atoms. Fluoropolymers are a group of plastics with a wide range of properties and benefits. PTFE is one such fluoropolymer whose discovery forever revolutionized the fluoropolymer group and paved the way for a variety of applications.

One of the common applications of PTFE materials includes non-stick coatings for kitchen cookware. Because of its non-reactivity, in part 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?

PTFE is manufactured much like any other polymer. It is manufactured by free radical polymerization technology using TFE addition polymerization in a batch process in aqueous media.

The chemical structure of PTFE is the same as Polyethylene; the only major difference is that the hydrogen atoms are completely replaced by fluorine. However, PE and PTFE are prepared in very different ways.

The large size of fluorine atoms forms a uniform, continuous sheath around carbon-carbon bonds, providing the molecule with good chemical resistance, electrical inertness, and stability.

Characteristics and performance of PTFE

PTFE comes in three main forms-granules, water-based dispersions, and fine powders.

Granular PTFE materials are produced by suspension polymerization in an aqueous medium using little or no dispersant. Granular PTFE materials are primarily used in compression, isostatic pressing and plunger extrusion methods.

Water-based PTFE dispersions use the same water-based polymerization with more dispersant and agitation. Water-based dispersions are primarily used in coatings and film casting methods.

Finely powdered PTFE is a small white particle produced by controlled emulsion polymerization. Fine PTFE powder can be processed into flakes through paste extrusion or additives to improve wear resistance.

Other notable properties of PTFE include excellent high and low temperature resistance, electrical insulating 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 when it comes to chemical resistance. It is only attacked 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. Adding fillers has proven to be a successful method of overcoming 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 impact mechanical properties.

PTFE has outstanding electrical insulation properties, low dielectric constant and insulation withstand voltage. The very low dielectric constant (2.0) is a result of the complex symmetrical structure of the macromolecules.

The PTFE material also shows good thermal properties, with no significant degradation below 440 °C.

It is also attacked by airborne degradation and radiation, starting at a dose of 0.02 Mrad.

Disadvantages of PTFE material

Traditional PTFE materials are not without some drawbacks. they are:

Creep and wear sensitive

It cannot be processed by molten state processing methods, and suitable methods can often be unconventional and scalable.

Difficulty in joining

High dimensional changes near the glass transition temperature.

Low radiation resistance

It is corrosive and can easily produce toxic fumes.

Importance of Fillers and Additives to PTFE

The addition of fillers and additives can significantly improve the mechanical properties of PTFE, especially creep and wear rates. Commonly used fillers include steel, carbon, glass fiber, carbon fiber, graphite, bronze, steel, etc.

Glass fiber: Its addition will improve the creep and wear properties of PTFE by affecting its low and high temperatures. Additionally, glass-filled compounds perform exceptionally well in oxidizing environments.

Carbon Fiber: Carbon fiber is essential to reduce creep, improve stiffness, increase flexibility and compressive modulus. PTFE blended with carbon fiber compounds has high thermal conductivity and a low coefficient of thermal expansion. Carbon fiber is inert to strong alkalis and hydrofluoric acid (glass fiber is resistant to both acids). These parts are ideal for manufacturing automotive parts such as shock absorbers.

Carbon: Carbon as an additive will help reduce creep, increase hardness, and improve the thermal conductivity of PTFE. The same results can be achieved by mixing PTFE and graphite and increasing the wear resistance of the carbon-filled compound. These mixtures are ideal for non-lubricated applications such as piston rings in compression cylinders.

Bronze-Filled PTFE: This compound has excellent thermal and electrical conductivity, making it ideal for applications that are subject to extreme loads and temperatures.

Advantages of adding fillers

Fillers/additives are essential to increase the porosity of the PTFE compound and therefore affect the electrical properties - it reduces the dielectric strength while increasing the dielectric constant and dissipation factor.

Fillers can significantly improve the performance of PTFE at both high and low temperatures.

Changes in chemical properties depend greatly on the type of additive used, however. Generally, it leaves positive results as well.

PTFE Applications

Typically, fluorinated thermoplastics are used in high-performance applications with high temperature resistance, high purity, low temperature, chemical inertness, non-stick and self-lubricating properties. Here are some of the most common uses for PTFE:

Engineering – Bearings, nonstick surfaces, valve seats, plugs, fittings, valves and pump parts.

Medical – Heart patches, cardiovascular grafts, ligament replacements.

Chemical industry - coating of pumps, diaphragms, impellers, heat exchangers, autoclaves, reaction vessels, storage tanks, vessels, etc.

Automotive – Stem seals, shaft seals, gaskets, O-rings, fuel hose liners, power steering, transmissions, and more.

Electrical and Electronics - Flexible Printed Circuit Boards, Electrical Insulation, etc.

Best Technologies for Processing PTFE

PTFE's rigid polymer chain structure makes it extremely difficult to process using traditional methods such as injection molding and extrusion. Still, its extremely high melt viscosity and high melting temperature don't help. The ideal processing technology for handling powder metallurgy is well suited for PTFE.

Sintering, compression molding, pressing, stamping or paste extrusion, hot stamping, machining, extrusion of pre-sintered powder on special machines.

Paste extrusion mixes PTFE with hydrocarbons, which are used to make it into tape, pipe and wire insulation. Hydrocarbons evaporate before the part is sintered.

Operating range -200°C to 260°C.

FAQ

1. Does polytetrafluoroethylene cause cancer?

answer. PTFE has been shown to be toxic to human health because it contains a carcinogen called PFOA. However, there is no need to worry as PTFE non-stick coatings no longer contain this substance.

2. What is PTFE pipe used for?

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

3. What kind of plastic is PTFE?

answer. PTFE is a thermoplastic polymer that is a fluoropolymer composed of carbon atoms and fluorine atoms.

4. What is the use of PTFE board?

answer. PTFE sheets are used in a variety of applications such as PTFE encapsulated gaskets and PTFE packing. It has excellent resistance to gases, water, chemicals, fuels and oils.