POLYTETRAFLUOROETHYLENEFluorinated Polymers have extraordinary properties as well as high cost. Because of its expensiveness, Teflon is used when other technopolymers can’t satisfy needed application requirements, such as in chemically aggressive environments or in presence of highest temperatures. Main feature of fluorinated polymers is that the majority of chemical bonds is of C – F Type (Carbon – Fluorine). The direct result is very high molecular stability, excellent thermal, chemical as well as stress resistance, more than other polymers. The ancestor of fluorinated polymers is polytetrafluoroethylene (PTFE) that was accidentally discovered in 1938 during tests on chlorofluorocarbon refrigerant. That new polymer showed unique features: excellent chemical resistance: it was inert to almost all known chemicals; it was so slippery that no material can stick on it; it was completely water repellent; its melting point is very high, it could be exposed to the sunlight without degrading and it didn’t flow at temperatures higher than melting point. It was undestood immediately that PTFE could be shaped at will using the same technology used in the machining of metallurgical powders: they created blocks machinable with tools. So Teflon was born (Dupont registered trademark), it was traded from 40s and it is still the polymer with the best succesful application. Indeed PTFE is considered a “high – tech and a high performance” material.
(known as TEFLON)
- Non-stick properties: PTFE has a very low energy surface, this means that it is non-stick and anti-adhesive.
- Atmospheric agents resistance: PTFE is very resistant to UV rays as well as to oxidation and it maintains its properties even at low temperatures; furthermore fluorinated polymers resist to microorganism attacks and they are totally non-biodegradable.
- Absence of contaminating agents: fluorinated polymers are inherently pure so they don’t cause chemical pollution.
- Corrosion resistance: they resist to chemical agents in the long term
- Heat resistance: fluorinated polymers can work at continuous operating temperatures of around 260 ° C, with higher peack for short terms.
PTFE has a low heat tranfer coefficient so it has good thermal insulation properties; it is non – flammable and it conserves its stability even for long-period up to 260°C.
PTFE is inert to almost all known chemicals, except for alkaline metals in their elemental form, for elemental fluorine at high temperature and pressure and for chlorine trifluoride. PTFE is insoluble in any solvents up to 300° C. Only the use of highly fluorinated oil at a temperature near the melting point of ptfe, could reinflate or melt it.
Unadhesiveness and low coefficient of frictions – espacially under light load - are the main mechanical features of PTFE. The elongation at break value is more than 100%.
Using appropriate methods is necessary to maintain dimensional stability of PTFE. Because of its transition temperature near to 20° C, using specific precaution becomes necessary, especially when poor tolerances are required.
PTFE has excellent dielectric strength at various temperatures and frequencies. It is completely water repellent. Atmospheric agents does not affect its properties, even after lon periods of time.
PTFE properties can be further improved by adding special filler. The so – called filled PTFE are obtained by adding special additive powders to the polymer tath enhance all the features desribed above: glass, carbon, graphite, molybdenum disulfide, bronze, ceramic and mixture of more than one aboved substances.
- improve the resistance to compression
- improve the resistance to wear
- reduce the thermal expansion coefficient
- improve surface and volume resistivity
- enhance the hardness
PTFE is largely used in mechanical industry in making gaskets subjected to static and dynamics stress, pistons, gears, coverings. All these mechanical parts can be obtained by tubes, rods and sheets.