Polyetheretherketone (PEEK)
Key Takeaways
- Continuous service around 250°C, with short-term capability considerably higher.
- Exceptional chemical resistance — including resistance to hydrolysis and repeated steam sterilisation.
- It marks well under a fiber laser, because the aromatic backbone chars readily without an additive.
- The same inertness defeats adhesives, so bonding requires aggressive pretreatment.
Polyetheretherketone (PEEK)
Polyetheretherketone is a semi-crystalline high-performance thermoplastic built from aromatic rings linked by ether and ketone groups, offering continuous service temperatures around 250°C together with outstanding chemical, hydrolysis, wear and fatigue resistance. It sits at the top of the engineering thermoplastic hierarchy in both capability and cost, and it is specified where a metal would otherwise be required.
That rigid aromatic backbone is responsible for essentially every property PEEK is bought
for. It resists thermal degradation, it resists chemical attack, and it holds mechanical
properties at temperatures where most engineering plastics have long since softened. It also
makes the polymer expensive to produce and demanding to process.
PEEK Against the Alternatives
| Polymer | Continuous service | Relative cost | Why choose it over PEEK |
|---|---|---|---|
| PEEK | Around 250°C | Very high | The benchmark: best combination of temperature, chemical resistance, toughness, wear and fatigue |
| PPS | Around 200–240°C | Moderate | Much cheaper, inherently flame retardant, dimensionally excellent — if brittleness is acceptable |
| PEI (polyetherimide) | Around 170–180°C | High | Transparency, easier processing, good dielectric properties, lower cost |
| PEKK and PAEK variants | Comparable to PEEK | Very high | Tailored crystallisation behaviour, particularly for additive manufacturing |
| PPSU | Around 180°C | High | Transparency and excellent repeated steam sterilisation at lower cost |
| LCP | Around 200–240°C | High | Very thin wall flow and minimal warpage for fine-pitch parts |
The honest position is that PEEK is frequently over-specified. Where the requirement is
temperature and chemical resistance without extreme toughness or wear demands, PPS delivers a
large fraction of the capability at a fraction of the price.
Processing Requirements
- Very high melt temperature, typically around 360–400°C, which
requires machines and tooling rated for it. Standard equipment will not process PEEK. - Hot tooling is essential. Mould temperature governs crystallinity, and
crystallinity governs the chemical and mechanical performance the part was specified for. An
undercooled tool produces a part that looks correct and underperforms. - Drying before processing, despite low moisture uptake in service.
- Annealing is often specified to complete crystallisation and relieve
stress, particularly for machined components and for parts facing thermal cycling. - Machining generates heat that can locally alter crystallinity; sharp
tooling and adequate cooling matter more than on commodity resins.
Marking and Bonding PEEK
| Operation | Behaviour | Practical guidance |
|---|---|---|
| Fiber laser marking | Good — the aromatic backbone chars readily | Marks dark without an additive. Restrain energy; PEEK marks easily enough that over-marking is the usual error. |
| Marking filled grades | Glass and carbon fillers alter the result | Carbon-filled grades are already dark, limiting contrast range. Glass fibre emergence occurs as in other filled resins. |
| Adhesive bonding | Poor without pretreatment | Chemical inertness leaves adhesives little to react with. Cold gas plasma or Pyrosil are the practical routes. |
| Printing and coating | Poor without pretreatment | As bonding. Verify with contact angle rather than assuming treatment succeeded. |
| Welding | Possible but demanding | The high melt temperature narrows the process window considerably. |
| Sterilisation | Excellent | Withstands repeated steam autoclave, gamma and ethylene oxide, which is central to its medical use. |
Where It Is Specified
- Medical implants and instruments — biocompatible grades, radiolucency, and survival of repeated autoclaving. Spinal implants are a signature application.
- Aerospace interior and structural components, where the strength-to-weight ratio and flame behaviour justify the cost.
- Oil and gas seals, backup rings and connectors facing hot aggressive fluids under pressure.
- Semiconductor manufacturing, where purity and chemical resistance matter more than the price of the part.
- Bearings, bushings and wear parts, exploiting the fatigue and wear resistance that distinguishes PEEK from PPS.
- Additive manufacturing, increasingly, though crystallinity control in printed parts remains the central technical difficulty.
Diagnosing PEEK Processing Problems
| Symptom | Likely cause | Correction |
|---|---|---|
| Part meets dimensions but underperforms in chemical exposure | Insufficient crystallinity from an undercooled tool | Raise mould temperature, or anneal. The part will look entirely correct while falling short of its datasheet. |
| Dimensions shift after the part sees service temperature | Crystallisation continuing in service | Anneal to complete crystallisation before machining or final inspection. |
| Adhesive bond fails at the PEEK interface | Chemical inertness — nothing for the adhesive to react with | Pretreat with cold gas plasma or Pyrosil, and verify by contact angle rather than assuming the treatment worked. |
| Machined parts distort or crack later | Machining heat altering local crystallinity, plus relieved stress | Sharp tooling, adequate cooling, and anneal before final machining. |
| Mark over-burnt at settings that suit PPS | PEEK chars readily; the recipe is too aggressive | Reduce energy and raise speed. Restraint rather than power is the requirement. |
| Little contrast available on a carbon-filled grade | The substrate is already dark | Expected. Consider a light foamed mark rather than a dark carbonized one, or relocate to an unfilled area. |
| Cost overruns against the business case | PEEK specified where PPS or PEI would serve | Revisit the binding constraint. PEEK earns its premium on toughness, wear, fatigue and hydrolysis resistance specifically. |
Related Terms and Reading
- Polyphenylene sulfide (PPS)
- Surface energy
- Laser marking high-temperature plastics
- Pharmaceutical and medical manufacturing
Applying this in production
The Sabreen Group provides independent engineering support for high-performance polymer marking, bonding and surface preparation. If you are specifying a process, qualifying a material or troubleshooting a production problem, our engineering services team can help. Contact us to discuss your application.
Frequently Asked Questions
Does PEEK need a laser additive to mark?
No. The aromatic backbone chars readily, so PEEK gives good dark contrast under a fiber laser unaided. The practical difficulty is the reverse of the polyolefin problem: it marks easily enough that energy has to be restrained, and carbon-filled grades are already dark, which limits the available contrast range regardless of parameters.
Why is PEEK so difficult to bond?
The chemical inertness that makes it valuable in service leaves adhesives very little to react with, and its surface energy is low relative to what most adhesive systems need. Aggressive pretreatment is required — low-pressure cold gas plasma or a deposited silicate layer such as Pyrosil are the practical routes — and the result should be verified by contact angle rather than assumed.
When is PPS the better choice than PEEK?
Frequently. Where the requirement is high temperature and chemical resistance without extreme toughness, wear or fatigue demands, PPS delivers a large fraction of the capability at a fraction of the cost, and it is inherently flame retardant. PEEK earns its premium on toughness, wear, fatigue and hydrolysis resistance; where those are not the binding constraints, it is often over-specified.
Why does mould temperature matter so much for PEEK?
Because it controls crystallinity, and crystallinity controls the chemical resistance, dimensional stability and mechanical performance the part was specified for. A tool that runs too cool produces a part that looks entirely correct while underperforming against its datasheet, and the shortfall may only appear in service. Annealing is often specified to complete crystallisation, particularly on machined parts.
Can PEEK be repeatedly sterilised?
Yes, and this is one of its defining advantages. It withstands repeated steam autoclave, gamma irradiation and ethylene oxide without meaningful property loss, which is why it dominates reusable surgical instruments and implantable applications. Where a mark is applied for identification, that mark should still be re-graded across the validated cycle count rather than assumed to age as well as the substrate does.
