Teflon® is one of the trade names for polytetrafluoroethylene (PTFE). Fluorinated polymers perform outstandingly but are offset by their high cost. Therefore, they are used when other engineering polymers cannot meet application requirements, for example, in chemically aggressive environments or at high temperatures.
The main characteristic of Teflon is that most of the chemical bonds are C-F (Carbon-Fluorine). As a result, the molecules are very stable and can withstand high thermal stress and chemical aggression more than other polymers. These materials are used when no other polymer can meet high to extreme application requirements.
The forefather of fluorinated polymers is polytetrafluoroethylene (PTFE), which was discovered in 1938 by chance as experiments were carried out on fluorinated refrigerants. The characteristics of the new polymer showed that it was this material had unique properties. More precisely, it was practically not attacked by any chemical reagent, its surface was so slippery that no material could adhere to it, and it was hydrophobic. Moreover, it did not degrade when exposed to light and had a very high melting point. In addition, unlike known thermoplastic resins, the polymer did not flow at temperatures above its melting point. Experts soon realised that this new material could have numerous application possibilities. They also realised that it could be transformed into the desired shape using a technology conceptually similar to that of powder metallurgy, i.e. obtaining blocks by sintering that could then be machined with a tool. The result was Teflon (registered trademark of DuPont), marketed since the 1940s and still one of the most successful polymers today.
We can summarise the main characteristics of fluoropolymers can as follows:
PTFE has a low heat transfer coefficient and is therefore considered a thermal insulator, is non-flammable and is stable for indefinitely long periods up to 260°.
Teflon (PTFE) is inert to virtually all known chemical reagents.
It is attacked only by elemental alkali metals, chlorotrifluoride and elemental fluorine at high temperature and pressure. PTFE is insoluble in any solvent at temperatures up to 300°C.
Certain highly fluorinated oils can swell and dissolve only at temperatures close to the crystalline melting point.
The mechanical properties of PTFE are its non-adhesivity and its low coefficient of friction, particularly under pretty high loads.
Elongation at break is greater than 100%. Shrinkage after processing is high.
For the dimensional control of PTFE products, it is necessary to use suitable techniques suggested by the nature of the product. The existence of the transition point at around 20°C means that special precautions must be taken when very tight tolerances are required. In such cases,
standard control procedures should be established.
PTFE has excellent dielectric properties over a wide range of temperatures and frequencies. Since there is practically no water absorption, the properties remain unchanged even after prolonged exposure to atmospheric agents, and the dielectric strength is virtually unaffected by the operating temperature.
Adding special additives can further improve the properties of PTFE. In such cases, the so-called “filled” types are used, in which the introduction of appropriate additive powders modifies the characteristics mentioned above of the PTFE into the polymer: these include glass fibres, carbon, graphite, molybdenum disulphide, bronze, ceramic powder and even mixtures of two or more of the fillers mentioned above.
These additional fillers can :
increase hardness.
It is used in mechanical engineering for the production of seals subject to static and dynamic stress, pistons and other machine parts, linings and casings and gears made from semi-finished products such as tubes, drilled bars, solid rounds and sheets.
PTFE + carbon
PTFE + bronze
PTFE + glass
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