How is PTFE (TeflonŽ) Made?
PTFE Coating Overview
Polytetrafluoroethylene (PTFE), commonly known as Teflon®, is a fluoropolymer made of tetrafluoroethylene (TFE) molecules. PTFE has with some exceptional properties which makes it a widely used compound for numerous applications.
PTFE is hydrophobic (it is not wet by water or any substances containing water due to the high electronegativity of fluorine), highly non-reactive, and has one of the lowest friction rates found in solids. PTFE coatings are one of the world's most sought after non-stick products. It has outstanding release capabilities and can withstand a maximum use temperature of 500°F. This coating is typically applied to a thickness of 0.0003" - 0.0008".
PTFE has a whopping worldwide annual production of around 200,000 tons. The many industrial and niche applications of PTFE coatings, include:
- Cable insulations
- Machinery components where its low friction coefficient helps reduce wear and energy consumption.
- Reactor and plant equipment where its non-reactive property helps to avoid corrosion by highly corrosive reactants or products
- Non-stick domestic utensils like frying pans, woks and saucepans
- Medical industry coatings for catheters and graft material
The PTFE Coating Origin Story
In 1938, Roy Plunkett, a young scientist at Du Pont, accidentally discovered PTFE when trying to create a new chlorofluorocarbon refrigerant. Plunkett hoped to create the new refrigerant by reacting hydrochloric acid with tetrafluoroethylene (TFE). He stored the TFE gas in metal cans and during his tests used the weight of the cans to measure of the amount of TFE used in each experiment. On April 6, 1938 Plunkett discovered that although the weight of the gas pressure bottle didn't signal that it was empty, no gas flowed out of it. Out of curiosity he decided to examine the source of the weight and eventually resorted to sawing the metal can apart. What he found was a white and flaky powder on the interior of the pressure bottle. The TFE had polymerized overnight with the iron from the inside of the can acting as a catalyst. This new polymer was later registered as Teflon®.
How Are PTFE Coatings Made?
Polytetrafluoroethylene, also known as Teflon®, is made with four ingredients -- fluorspar, hydrofluoric acid, chloroform, and water, which are combined in a chemical reaction chamber heated to between 1094-1652°F (590-900°C). Creating PTFE involves 2 main phases and a series of reactions.
- The TFE must be synthesized out of chloroform (trichloromethane), hydrofluoric acid, and fluorspar. These ingredients are combined in a process known as pyrolysis. TFE is highly flammable and its transportation is very risky. Therefore, this step must be performed on-site where the final product (PTFE) is created.
- Next, the TFE is polymerized into PTFE by radical polymerization, with the help of small amounts of initiators like disuccinic acid peroxide or ammonium persulfate. The other key ingredient of the polymerization process is water.
The key steps of producing PTFE can be summed up as follows:
Production of chloroform (trichloromethane)
Chloroform can be produced by reacting methane with a mixture of hydrogen chloride and chlorine. This can be executed in the liquid phase or alternatively in the vapor phase. The chemical reaction is:
CH4(g) + 3Cl2(g) --> CHCl3(g) + 3HCl(g)
Production of chlorodifluoromethane
By reacting chloroform with anhydrous hydrogen fluoride, chlorodifluoromethane is created. The chemical reaction is:
CHCl3(g) + 2HF(g) --> CHCIF2(g) + 2HCl(g)
Production of tetrafluoroethylene (TFE)
Since TFE is highly explosive, it is produced on-site, when and where the polymerization will occur, minimizing storage time. Heating chlorodifluoromethane in the absence of air, a process known as pyrolysis, yields tetrafluoroethylene (TFE). The chemical reaction formula is:
2CHClF2(g) --> C2F4(g) + 2HCl(g)
Once created, TFE must be cooled rapidly to avoid reverse reaction and explosive decomposition.
Polymerization of TFE (Creating PTFE out of TFE)
While many details of the polymerization process of TFE are industrial secrets of famous brands, there are two well-known main methods of producing PTFE: the suspension polymerization and the dispersion polymerization methods. The first method creates grains of PTFE that can be processed into pellets which can be molded. The latter method produces PTFE in the form of a milky paste that can be processed into a fine powder.