PEKK
A PAEK polymer for aerospace and printing
Typical values for the temper in the title
PEKK belongs to the PAEK family, like PEEK, but with more ketone groups. So its Tg is higher (about 160 °C versus about 143 in PEEK). The melting point (about 305–358 °C) and crystallization rate are set by the T/I isomer ratio.
Slow-crystallizing grades can be processed as nearly amorphous material and crystallized later. So PEKK is common in FDM printing for aerospace, thermoplastic composites, and parts needing excellent chemical and flame resistance.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | ≈95–110 MPa | |
| Modulus of elasticity E | 3.0–3.6 GPa | |
| Density ρ | 1.29 g/cm³ | |
| Max continuous service temperature | ≈240–260°C | |
| Machinability | 55% | relative rating in the site database |
Structure and family
| Feature | Value | Meaning |
|---|---|---|
| Family | PAEK (ketone-ketone) | |
| Tg | about 160–165 °C | higher than PEEK |
| Tm | about 305–358 °C | by T/I ratio |
Typical values per producer data sheets.
Grades and versions
In PEKK the grade is chosen by T/I ratio: more T gives a higher melt and fast crystallization, more I gives slow crystallization and easier processing.
| Version | Properties | When to choose it |
|---|---|---|
| T/I 60:40 | slow crystallization | FDM, composites |
| T/I 70:30 | moderate crystallization | injection molding |
| T/I 80:20 | fast crystallization, high Tm | structural parts |
Applications
- Aerospace and space parts
- FDM printing
- Thermoplastic composites
- Chemical-resistant parts
- Flame-retardant parts
Fabrication
Machining
Use very sharp tools, a feed that does not overheat the material, and good support (the material is flexible and deforms under clamping). For precision parts, stress-relief annealing before final machining is sometimes performed.
Thermal expansion
The expansion coefficient of an unfilled polymer is several times that of a metal. In a precision part or an assembly with metal, design clearances accordingly.
Printing
In slow grades, printing is simpler than PEEK, and the part can be crystallized afterwards by heating.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| PEEK | 100 MPa | Ultrasonic / Laser | PEEK: the most common of the family, lower Tg · material page |
| PEI (Ultem) | 105 MPa | Ultrasonic | PEI: amorphous, cheaper · material page |
| PEEK CF30 | 212 MPa | — | PEEK CF30: carbon-fiber reinforced · material page |
Common mistakes
Switching T/I grade without checking
Grades differ widely in melting and crystallization.
Designing above Tg under load
Above about 160 °C stiffness drops.
Choosing PEKK where PEEK is enough
It is expensive and less available.
Equivalents, standards and supply
| ISO | PEKK |
|---|---|
| Standards | Producer specification (Arkema Kepstan) |
| Forms | sheet · rod · pellets |
| Producers | Arkema (Kepstan) · Solvay |
Learn more
Values are typical for an unfilled grade (unless stated otherwise) and for comparison only. In polymers, properties depend on grade, filler, temperature, moisture and load duration. For design, rely on the producer data sheet for the specific grade. Sources: ASTM classification standards (D8033, D5205, D5204, D6394, D4067 and others), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026