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Material · Synthetic

PEEK

The plastic that behaves like a metal — 250 °C continuous service, near-total chemical resistance, and a price to match.

PEEK is the top of the thermoplastic hierarchy. It runs continuously at around 250 °C, resists essentially every solvent and most acids, is stiff and strong for a polymer, wears well, and is inherently flame retardant with low smoke emission.

It is also expensive — an order of magnitude or more above engineering plastics like nylon and acetal, and enough that it appears only where the alternative is a metal part that is too heavy, too conductive, or corroding.

It is one of very few polymers whose properties are usually described against metals rather than against other plastics, because that is what it is competing with.

Processing

Injection moulded and extruded, at melt temperatures around 400 °C, which puts it beyond ordinary tooling — the machine, the hot runners and the mould all have to be specified for it.

Also a 3D printing material at the demanding end, needing a heated chamber to control crystallinity: cooled too fast it stays largely amorphous and loses much of the temperature resistance it was chosen for. And it is machined from stock, which is how most low-volume parts are made.

Uses

Aerospace brackets, clips and cable insulation, where displacing aluminium saves weight and avoids galvanic corrosion against carbon fibre. Downhole oil and gas seals and connectors. Semiconductor wafer handling, where its purity and low outgassing matter more than its strength. Pump and valve components in aggressive chemical service.

In medicine it is a spinal and orthopaedic implant material. Its stiffness is far closer to bone than titanium's, so it does not shield the bone from load and cause the resorption a titanium implant can, and it is radiolucent — a surgeon can see the healing on an X-ray through the implant.

History

Developed at ICI in the late 1970s and commercialised in 1981. It arrived alongside carbon fibre composites and found much of its market in the same aircraft, as the polymer that could survive next to them and be bonded to them.

The spinal implant use is a later and largely unforeseen market, and now a substantial one.

Environmental impact

A thermoplastic, and genuinely reprocessable — offcuts and machining swarf are recovered and remelted, because the material is valuable enough to make collection worthwhile. That is the inverse of the usual polymer recycling problem, and it is entirely a matter of price rather than of chemistry.

Its production is energy intensive per kilogram. Whether that matters depends on the part: a PEEK component that removes a kilogram from an aircraft for twenty years is a straightforward net saving.

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 · aromatic rings throughout, which is where the thermal stability comes from
  • Hydrogen — element · on the rings
  • Oxygen — element · in the ether links between rings, which give the chain just enough flexibility to be processable at all

is produced by

  • Polymerisation — process · a step-growth polymerisation between aromatic monomers at high temperature in a polar solvent

is an input to

  • Injection moulding — process · at melt temperatures around 400 °C, which puts the tooling and the machine beyond ordinary specification

is used as

  • Additive manufacturing — application · at the demanding end, needing a heated chamber — cooled too fast it stays amorphous and loses the temperature resistance it was chosen for

is used in

  • Semiconductor manufacturing — industry · wafer handling components, where purity and low outgassing matter more than strength
  • Aerospace manufacture — industry · brackets, clips and cable insulation, displacing aluminium for weight and to avoid galvanic corrosion against carbon fibre
  • Medical devices — industry · spinal cages, where the stiffness is close enough to bone not to shield it from load, and which are radiolucent

is an alternative to

  • Polytetrafluoroethylene — 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

belongs to the group

  • Plastic — material · the top of the thermoplastic hierarchy, and priced accordingly

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 PEEK 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

  • PEEK → is produced by (a step-growth polymerisation between aromatic monomers at high temperature in a polar solvent) → 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
  • PEEK → is produced by (a step-growth polymerisation between aromatic monomers at high temperature in a polar solvent) → 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
  • PEEK → is produced by (a step-growth polymerisation between aromatic monomers at high temperature in a polar solvent) → 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
  • PEEK → is produced by (a step-growth polymerisation between aromatic monomers at high temperature in a polar solvent) → 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
  • PEEK → is produced by (a step-growth polymerisation between aromatic monomers at high temperature in a polar solvent) → 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
  • PEEK → is produced by (a step-growth polymerisation between aromatic monomers at high temperature in a polar solvent) → 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. PEEK can be traced through others besides.

Downstream — what it becomes

  • PEEK → is an input to (at melt temperatures around 400 °C, which puts the tooling and the machine beyond ordinary specification) → Injection moulding
  • PEEK → is used as (at the demanding end, needing a heated chamber — cooled too fast it stays amorphous and loses the temperature resistance it was chosen for) → Additive manufacturing
  • PEEK → is used in (wafer handling components, where purity and low outgassing matter more than strength) → Semiconductor manufacturing
  • PEEK → is used in (brackets, clips and cable insulation, displacing aluminium for weight and to avoid galvanic corrosion against carbon fibre) → Aerospace manufacture
  • PEEK → is used in (spinal cages, where the stiffness is close enough to bone not to shield it from load, and which are radiolucent) → Medical devices