View source for Polytetrafluoroethylene

{| class="toccolours" border="1" style="float: right; clear: right; margin: 0 0 1em 1em; border-collapse: collapse;"
! {{chembox header}} | Polytetrafluoroethylene
|-
| align="center" colspan="2" bgcolor="#ffffff" | [[image:teflon.bmp]]
|-
! {{chembox header}} | General 
|- 
| Other Names
| Poly(tetrafluoroethylene)<br/>PTFE<br/>Teflon
|-
| Molecular Formula
|  (CF<sub>2</sub>-CF<sub>2</sub>)<sub>n</sub><br/>C<sub>2</sub>F<sub>4</sub>
|-
| Molar Mass
| 100.015612
|-
| Appearance and odour
| white powder<br/>white solid<br/>no odour
|-
| CAS Number
| 9002-84-0
|-
| {{chembox header}} | Mechanical properties
|-
| Tensile strength
| 2.500 - 4.000 (psi)
|-
| Elongation
| 200 - 400 (%)
|-
| Flexural Modulus
| 27.000 (psi)
|-
| Folding Endurance
| >10<sup>6</sup> ((MIT) cyles)
|-
| Coefficient of friction<br/> dynamic
| <0.1 (<3m/min)
|-
| {{chembox header}} | Thermal properties
|-
| Melting Point
| 327 (°C)
|-
| upper service temperature<br/> (20,000hr)
| 260 (°C)
|-
| Boiling Poing
| 400 °C
|-
| Limitibng oxygen index
| >95%
|-
| {{chembox header}} | Electrical properties
|-
| Dielectric constant
| 2.1 (MHz)
|-
| Dissipation factor
| 0.0001 (MHz)
|-
| Arc Resistnace
| >300 (sec)
|-
| Volume resistivity
| 10<sup>18</sup> (Ohm-cm)
|-
| Surface resistivity
| 10<sup>18</sup> (Ohm/sq cm)
|-
| {{chembox header}} | Other properties
|-
| Density
| 1.5<br/>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.

[[image:P_25904990_1580696.jpg|thumb|non-stick frying pan]]
==Synthesis==
The complete synthesis actually takes the following steps:

CaF<sub>2</sub> + H<sub>2</sub>SO<sub>4</sub> --> CaSO<sub>4</sub> + 2HF

CH<sub>4</sub> + 3Cl<sub>2</sub> --> CHCl<sub>3</sub> + 3HCl

CHCl<sub>3</sub> + 2HF --> CHClF<sub>2</sub> + 2HCl

2CHClF<sub>2</sub> --> CF<sub>2</sub>CF<sub>2</sub> + 2HCl

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

[[image:Ptfe04.gif]]


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:

[[image:Fluorination_of_polyethylene.gif]]
==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