PTFE: when no other plastic can withstand the chemicals

PTFE has almost universal chemical resistance and the lowest coefficient of friction of any plastic. Here’s how to use the material correctly. When other plastics are broken down by chemicals or heat, PTFE is often the last option left.

Almost all chemicals

PTFE is a fluoroplastic with a level of chemical resistance that most other plastics cannot match. It withstands acids, bases, solvents and aggressive gases at temperatures up to around 260 °C.

Only a handful of chemicals affect PTFE, including certain molten alkali metals and elemental fluorine at high temperatures. For the vast majority of industrial processes, PTFE is therefore a safe choice when other materials fail.

PTFE is also hydrophobic, meaning that it does not absorb water. This makes the material suitable for applications where dirt and liquids need to be repelled.

The lowest coefficients of friction

PTFE has a very low dynamic coefficient of friction against most materials. This makes it the standard choice for seals, gaskets, plain bearings and guide strips for conveyor belts where nothing must become stuck.

The disadvantage is that PTFE has low mechanical strength and is prone to creep under load. It is therefore often used in a form filled with glass fibre, carbon, graphite or bronze to improve wear resistance and load-bearing capacity. Filled grades have a higher load-bearing capacity but slightly higher friction than pure PTFE.

When choosing a filler, you should consider the mating surface. For example, bronze filler may be unsuitable for use against soft metal surfaces as the filler can cause scratching. Glass fibre provides good wear resistance but is harder on the mating surface than carbon or graphite.

How to process PTFE

PTFE cannot be machined in the usual way. Instead, the material is sintered from powder. Pre-formed semi-finished products are pressed and sintered into sheets, tubes and rods. It can be turned, milled and cut, but the material is soft and requires sharp tools.

As PTFE is relatively porous compared with, for example, PEEK or PVDF, it is not suitable for components that must be completely gas-tight without special processing. For seals and gaskets, however, it works excellently as the material conforms to the surface.

PTFE can also be expanded to produce sealing tapes that are soft and pliable. Such tapes are used in the pipework and ventilation industries to seal flanges and joints.

PTFE in pipework and ventilation

In the pipework and ventilation sectors, PTFE is used for gaskets, coatings and components that need to withstand aggressive gases. The material’s combination of chemical resistance and temperature resistance makes it suitable for valves, pumps and flanges.

Pure PTFE is soft and can deform under high loads. For this reason, filled or reinforced variants are often used in pipework systems where pressure and mechanical stress are high.

Next step

Are you looking for PTFE in sheet, rod, tube or as a finished component? See PTFE in the materials guide, search our range or contact us for advice.

Filled grades and properties

Fillers in PTFE are selected to improve mechanical properties without compromising too much of the material’s chemical resistance. Glass fibre increases wear resistance and dimensional stability. Carbon reduces friction and improves thermal conductivity. Graphite makes the material self-lubricating.

Bronze fillers are used for higher load-bearing capacity and better heat dissipation. They are well suited to plain bearings and seals, but may be too hard for soft mating surfaces.

Quality and certification

PTFE for food and medical applications requires the correct certification. Pure PTFE for industrial use has different requirements. Always check that you are ordering the correct grade for your application.

The material should be supplied with certificates detailing its composition and properties. This is particularly important in regulated sectors such as food, pharmaceuticals and semiconductors.

How to machine PTFE

PTFE is soft and ductile compared to many other engineering plastics. This makes the material easy to shape into moulded and sintered components, but more difficult to machine with high precision. The surface is often soft and can become deformed under mechanical stress.

To improve mechanical properties, filled grades are available with glass fibre, carbon fibre, graphite or bronze. These fillers increase wear resistance and dimensional stability, whilst also potentially altering friction and chemical resistance slightly.

When ordering PTFE, you should select the dimensions based on the end use. Thick sheets and large tubes are often available as extruded semi-finished products. Smaller components can be manufactured by injection moulding or compression moulding.

Summary

PTFE is the obvious choice when chemical resistance and low friction are more important than mechanical strength. For tougher mechanical loads, filled grades are available that retain the excellent chemical properties.

Choose the right grade, dimensions and processing method for your application. Please contact us if you need help choosing between different PTFE variants.

Frequently asked questions

Why is PTFE so resistant to chemicals? PTFE has a very strong carbon-fluorine bond, which makes the material inert to most chemical substances.

Is PTFE hard? No, PTFE is relatively soft and leaves an impression easily. Filled grades are harder and more wear-resistant.

Can PTFE be used at high temperatures? Yes, PTFE can withstand continuous temperatures of up to approximately 260 degrees Celsius.