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Material · Synthetic

Polytetrafluoroethylene

Carbon wrapped in fluorine, which almost nothing sticks to and almost nothing attacks — the non-stick pan, the plumber's tape and the seal in the chemical plant.

Insulator

PTFE is a carbon chain with every available position occupied by fluorine, and that sheath is what gives it its properties. The carbon–fluorine bond is among the strongest in organic chemistry and the fluorine atoms are packed tightly enough to shield the chain completely, so there is nothing for a reagent to attack and almost nothing for another molecule to grip.

The result has the lowest coefficient of friction of any solid material and is inert to nearly every chemical there is — including aqua regia, which dissolves gold. Molten alkali metals and elemental fluorine at temperature are the short list of things that attack it.

Processing

Being inert makes it difficult to manufacture with. PTFE does not flow when melted — it becomes a gel rather than a liquid — so it cannot be injection moulded or extruded like other thermoplastics, and is instead compacted from powder and sintered, in a process closer to powder metallurgy than to plastics processing.

Getting it to stick to a pan is the same problem inverted. The surface has to be roughened, or primed, or chemically etched, because the property being sold is precisely that nothing adheres to it.

It was found by accident in 1938: Roy Plunkett opened a cylinder of tetrafluoroethylene that had polymerised itself into a white waxy solid, and weighed the cylinder rather than discarding it.

Economic significance

The non-stick pan is the famous use and a small one. PTFE's industrial value is in gaskets, seals, linings and valve seats for chemical plant, in thread-sealing tape, in bearings that run without lubricant, and as the dielectric in coaxial cable where its low loss at high frequency is hard to substitute.

Its reputational problem is not the polymer but the processing aid once used to make it. PFOA is persistent, bioaccumulative and has been phased out under regulatory pressure and litigation; the finished PTFE contains none of it and is not itself bioavailable. The distinction is real and gets lost constantly, partly because both belong to the same broad family of fluorinated compounds now under scrutiny.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

contains

  • Carbon — element · the chain, entirely shielded — there is nothing for a reagent to reach
  • Fluorine — element · every available position on it, and the whole of the material's behaviour: the strongest bond in organic chemistry, packed tightly enough that nothing sticks and nothing attacks

is produced by

  • Polymerisation — process · found by accident when a cylinder of tetrafluoroethylene polymerised itself, and made deliberately the same way since

is an alternative to

  • Polypropylene — material · as a chemically resistant lining, where PTFE is the answer when polypropylene is not enough and cost stops being the deciding factor
  • PEEK — material · both survive chemistry that defeats everything else. PEEK is stiff, strong and structural; PTFE is soft, creeps under load, and is more chemically inert still

is used as

  • Sealing and gasketing — application · where the chemistry defeats every elastomer, at the cost of having no elasticity to recover with

is used in

  • Chemical manufacture — industry · linings and gaskets where the chemistry defeats every elastomer

belongs to the group

  • Plastic — material · the one nothing sticks to, and the one nothing attacks

Sources

  • Material World
    Our own writing
  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)

Questions this page answers

Where it comes from, and what it becomes

Follow Polytetrafluoroethylene back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Polytetrafluoroethylene → is produced by (found by accident when a cylinder of tetrafluoroethylene polymerised itself, and made deliberately the same way since) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as the brine the cell electrolyses, and as the source of the hydrogen that comes off the cathode) → Water → is sourced from (by desalination, where energy is cheap and coastline available — the only route that adds fresh water rather than moving it) → Seawater
  • Polytetrafluoroethylene → is produced by (found by accident when a cylinder of tetrafluoroethylene polymerised itself, and made deliberately the same way since) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is produced by (electrolysis of potassium bifluoride, which is molten and conducts — there is no chemical oxidant strong enough to displace fluorine from a compound, so electricity is the only route and always has been) → Molten salt electrolysis → takes as input (after concentration, as one of the two routes to lithium chloride) → Lepidolite
  • Polytetrafluoroethylene → is produced by (found by accident when a cylinder of tetrafluoroethylene polymerised itself, and made deliberately the same way since) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is extracted from (by electrolysis of brine, which yields chlorine and sodium hydroxide together) → Halite
  • Polytetrafluoroethylene → is produced by (found by accident when a cylinder of tetrafluoroethylene polymerised itself, and made deliberately the same way since) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is extracted from (the only significant source; hydrofluoric acid is made from it and everything fluorinated follows) → Fluorite
  • Polytetrafluoroethylene → is produced by (found by accident when a cylinder of tetrafluoroethylene polymerised itself, and made deliberately the same way since) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (the largest single use of salt, and the process the whole chlorine and caustic soda industry rests on) → Salt → is produced by (in the solar route — the same process, read from the other end) → Brine evaporation
  • Polytetrafluoroethylene → is produced by (found by accident when a cylinder of tetrafluoroethylene polymerised itself, and made deliberately the same way since) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite

These are the most distinct paths back. Polytetrafluoroethylene can be traced through others besides.

Downstream — what it becomes