PEKK (Polyetherketoneketone): Aerospace-Grade PAEK — FST-Compliant, Out-of-Autoclave Processable
Published: 2026-05-31
Polyetherketoneketone (PEKK) is the aerospace-optimized member of the PAEK family, distinguished from PEEK by a higher ketone-to-ether ratio (2:1 in PEKK vs 1:2 in PEEK by the 'KK' vs 'EK' nomenclature). This difference has profound processing...
Polyetherketoneketone (PEKK) is the aerospace-optimized member of the PAEK family, distinguished from PEEK by a higher ketone-to-ether ratio (2:1 in PEKK vs 1:2 in PEEK by the 'KK' vs 'EK' nomenclature). This difference has profound processing and performance implications: PEKK crystallizes significantly more slowly than PEEK (lower Tc, broader processing window), enabling out-of-autoclave (OOA) thermoplastic composite processing (vacuum-bag-only consolidation, automated fiber placement with in-situ consolidation) that is not achievable with PEEK due to its rapid crystallization freezing in porosity. PEKK is the matrix material of choice for thermoplastic carbon-fiber composites in next-generation single-aisle aircraft (Airbus Wing of Tomorrow, Boeing TTBW truss-braced wing demonstrators) and urban air mobility (UAM/eVTOL) structures where 100× higher production rates than autoclave-thermoset composites are required.
The terephthalic:isophthalic (T:I) isomer ratio in PEKK is a unique tunable parameter — it controls melting point (Tm ranges from 305°C at 60:40 T:I to 360°C at 100:0 T:I), crystallization rate, and crystalline content. Higher T:I ratio = higher Tm, faster crystallization, higher crystallinity, better solvent resistance, but narrower processing window. This tunability means PEKK can be 'dialed in' for specific manufacturing processes — a capability unmatched by any other thermoplastic.
Technical Properties
| Density | 1.30 g/cm³ |
|---|---|
| Tensile Strength | 110 MPa (unfilled) |
| Melting Point | 338-360 °C (tunable by terephthalic:isophthalic ratio) |
| Shrinkage Rate | 1.0% |
| Flexural Modulus | 4.6 GPa |
| Hdt | 170 °C at 1.82 MPa |
| Continuous Service Temp | 260 °C |
Engineering Tool: Shrinkage & Cost Estimator
Calculate part weight, mold cavity dimensions accounting for shrinkage, and material cost — all locally in your browser.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Arkema Kepstan | |
| Solvay NovaPEKK | |
| Victrex AE 250 |
Frequently Asked Questions
How does PEKK compare to PEEK for aerospace composites?
PEKK's slower crystallization enables out-of-autoclave processing — the key advantage. In automated fiber placement (AFP) with in-situ consolidation, PEEK crystallizes so rapidly upon cooling from the melt that the interface between plies freezes with trapped porosity, requiring a post-consolidation autoclave step that eliminates the cost and throughput advantage of AFP. PEKK's slower crystallization allows the polymer chains at ply interfaces to interdiffuse (reptation across the interface) before the morphology locks, achieving autoclave-equivalent interlaminar shear strength without an autoclave. PEKK also has higher notched Izod impact and compression-after-impact (CAI) strength — the dominant design drivers for damage-tolerant composite structures — and lower equilibrium moisture absorption (0.2% vs 0.3% for PEEK — maintaining hot/wet Tg). The tradeoff: PEKK costs approximately 1.5-2× PEEK per kg and has 10-15% lower tensile strength.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org