Can I please have feedback on my PTFE report

LeNom · 28 July 2022 23:10

History/development of technology

Polytetrafluoroethylene (PTFE) was discovered on April 6th, 1938, by Dr Roy Plunkett. Like polyethylene, PTFE was discovered by accident. Working for the company DuPont, Plunkett was assigned to work on synthesising various forms of refrigerant, to find a non-toxic alternative to sulphur dioxide/ammonia. Plunket and his assistant were experimenting with a potential alternative refrigerant, tetrafluoroethylene (TFE), and they created around one hundred pounds of TFE gas and stored it in small cylinders. However, upon opening the valve of one of these previously frozen cylinders, nothing came out, despite the fact that it seemed to be full based on its weight. The two decided to cut the cylinder open to further investigate and discovered that that the TFE gas had polymerised into a waxy white powder, PTFE resin. Plunkett ran some tests on the substance and found that it has an extremely high melting point, was chemically stable, non-corrosive, and extremely slippery. Because these properties were deemed interesting, the study of PTFE was transferred to DuPont’s Central Research Department. Three years later the substance was copyrighted as Teflon.

The Central Research department concluded that PTFE takes a long time to form, and is an expensive polymer to make, so further development seemed unlikely. However, soon after its properties were discovered, PTFE was brought to the attention of Leslie Groves, director of the Manhattan project. The chemicals used in the nuclear weapons involved in the Manhattan project corroded most materials, however not PTFE, so this substance could be used to coat valves and seals in the pipes holding uranium hexafluoride.

At this point, PTFE was not yet used in household products, as DuPont was concerned about lawsuits regarding the PFTE creating potentially harmful gasses. However, 1954, after seeing her husband coat fishing gear with Teflon, Collette Gregoire suggested that it could be used to prevent food from sticking to her cooking pans. Her husband, Marc Gregoire, experienced difficulties of getting the PTFE to bond to the pan, however overcome this by etching the Aluminium pan with acid, and then heating PTFE powder on the surface. The couple began to sell this Teflon coated cookware under the brand name ‘Tefal.’ In the 1990s, chemical engineers found that when Teflon is above its melting point in an oxygen free environment, it could be cross linked with radiation. This causes it to have improved radiation resistance in a radiation field.

How PTFE is made:

Methane reacts with chlorine to produce chloroform, with a by-product of hydrochloric acid. This can be executed in the liquid phase or vapour phase.
Chloroform reacts with anhydrous hydrogen fluoride to produce chlorodifluoro- methane with a by-product of hydrochloric acid.
Chlorodifluoromethane is then pyrolyzed (heated in the absence of air) to create TFE. Since it is explosive, TFE is produced immediately before polymerisation is to occur, minimising storage time.
The TFE must then quickly be cooled to avoid explosive decomposition.
TFE must then polymerised to produce PTFE through addition polymerization. The covalent double C=C bond in TFE is broken, forming a covalent C-C bond, with each carbon atom having 2 fluorine atoms attached. These molecules then join up to form PTFE. For this reaction to be carried out, TFE is fed into a container with water and a radical polymer (such as ammonium persulfate.) This polymer acts as a catalyst and provides the necessary energy for polymerisation to occur. The container is heated to 327 °C

Properties of PTFE:

High melting point:

Fluorine is the most electronegative element, so the polymer strands of the PTFE are very strong and close together. This means that a large amount of energy is required to break the bonds, so PTFE can be heated without degrading. (Melting point of 327 °C.) This allows PTFE to be used safely in cooking equipment and hair products that will reach high temperatures.

Extremely low coefficient of friction:

PTFE has a friction coefficient of 0.04, meaning it is very slippery, and a good lubricant. This allows it to be used for constantly moving parts like gears and windscreen wipers.

Chemically inert:

Since the covalent bonds between the carbon and fluorine atoms in PTFE are very strong, the PTFE polymer is unreactive and chemically inert. Additionally, the three lone pairs of electrons on the fluorine atoms repel other molecules. This allows PTFE to be used to hold corrosive nuclear compounds, such as in the Manhattan project, and also as a waterproof coating.

Insulator:

PTFE has a high dielectric strength and breakdown voltage, meaning it is a good insulator. This means that it can be used in cables and wiring and can be used to create printed circuit boards.

Non-corrosive:

Due to the extremely high electronegativity that is common in most fluorocarbons, the C-F and C-C covalent bonds in PTFE are very strong; too strong for the fluorine atoms to be removed or replaced, so there will not be any other chemical bonding (except for very rare cases). This means that it can be used to coat pipes against highly corrosive metals.

Bibliography

History

The History of Teflon™ Fluoropolymers

Roy J. Plunkett | Science History Institute

This Month in Physics History (aps.org)

Discovery and History of Fluoropolymers - ScienceDirect

Teflon a History (fluoroprecision.co.uk)

How is PTFE (Teflon®) Made? | Orion Industries, Ltd. (orioncoat.com)

PTFE - Teflon (Polytetrafluoroethylene) Suspension - Techno Ad

How teflon is made (madehow.com)

PTFE: Properties, Processing, and Applications - Matmatch

Production Process of PTFE Polymer (standard-ptfe.com)