Polytetrafluoroethylene

Polytetrafluoroethylene

General
Other Names	Poly(tetrafluoroethylene) PTFE Teflon
Molecular Formula	(CF₂-CF₂)_n C₂F₄
Molar Mass	100.015612
Appearance and odour	white powder white solid no odour
CAS Number	9002-84-0
Mechanical properties
Tensile strength	2.500 - 4.000 (psi)
Elongation	200 - 400 (%)
Flexural Modulus	27.000 (psi)
Folding Endurance	>10⁶ ((MIT) cyles)
Coefficient of friction dynamic	<0.1 (<3m/min)
Thermal properties
Melting Point	327 (°C)
upper service temperature (20,000hr)	260 (°C)
Boiling Poing	400 °C
Limitibng oxygen index	>95%
Electrical properties
Dielectric constant	2.1 (MHz)
Dissipation factor	0.0001 (MHz)
Arc Resistnace	>300 (sec)
Volume resistivity	10¹⁸ (Ohm-cm)
Surface resistivity	10¹⁸ (Ohm/sq cm)
Other properties
Density	1.5 2
Refractive index	1.35 - 0
Solubility in water	insoluble

General

Polytetrafluoroethylene (PTFE) is a fluoropolymer and was serendipitously discovered in 1938 by Roy J. Plunkett. It entered the commercial market in 1946 and is now much better know as Teflon, a brand name given by DuPont.

PTFE has the lowest known coefficiont of friction of any solid material, 0.1 or less. It is also very unreactive. This is why it is used as a non-stick coating for pans, general cookware, chemical containers and pipework. According to DuPont its melting point is 327 °C, but PTFE’s properties degrade above 260°C.

Uses

Some of PTFEs uses are to coat some hardened armourpiercing bullets. this is to reduce the wear on the inside of the firearms, when the bullets are fired.

Due to the fact that it has such a low coefficient of friction it is used a lot where parts slide over each other a lot, e.g. bearings, bushings, gears, slide plates, etc. The only problem here is that PTFE is quite susceptible to wear. Because PTFEs performance is so much better than for example acetal or nylon, mineral oils molybdenum disulfide are integrated into PTFEs structure to overcome the wear problem.

The most well know use for PTFE is for making nonstick pans. But it is also someimes used on carpets and fabrics, to make them extra stain resistant. Another big use for PTFE is in medicine. This is because bodies seldom reject it, so therefore it can be used for making artificial body parts.

Synthesis

The complete synthesis actually takes the following steps:

CaF₂ + H₂SO₄ --> CaSO₄ + 2HF

CH₄ + 3Cl₂ --> CHCl₃ + 3HCl

CHCl₃ + 2HF --> CHClF₂ + 2HCl

2CHClF₂ --> CF₂CF₂ + 2HCl

PTFE is synthesised form the monomer tetrafluoroethylene, using a process known as free radical vinyl polymerization; under pressure and using free radical catalysts:

another way for PTFE to be produced is by directly substituting the hydrogen atoms in polyethylene with fluorine. This is done in the gas pahse at 20 °C:

References

http://en.wikipedia.org/wiki/Polytetrafluoroethylene

http://physchem.ox.ac.uk/MSDS/PO/polytetrafluoroethylene.html

http://www.bocedwards.com/pdf/P120-09-025%20PTFE%20.pdf

http://www.teflon.com/

http://www.pslc.ws/mactest/ptfe.htm

http://www.sigmaaldrich.com/

http://www.chemexper.com/

Roberts, Royston M.; Serendipity: Accidental Discoveries in Science; John Wiley and Sons; New York; 1989.

http://www.eng.utah.edu/~nairn/mse/students/MSE3410/Teflon/synthesis.html