Polyaryletherketones (PAEKs) are a class of semi-crystalline high performance engineering thermoplastics having a unique combination of thermal stability, chemical resistance, and excellent mechanical properties over a wide temperature range. This class of polymers has also good resistance to combustion and good electrical performance.
The high thermal stability is provided by the diphenylene ketone groups which impart high strength and high resistance to oxidation, but make the polymer rigid. Flexibility in the polymer backbone is provided by ether linkages which also add to the thermal stability. Some types, like PEEK, are extremely tough and have very high impact strength. Due to the semi-crystalline nature of these polymers, a high degree of mechanical properties is retained close to their melting temperature. They also have very low tendency to creep and good sliding and wear properties. These properties are retained over a wide temperature range.
Polyetherketones are known for their excellent chemical resistance to many organic and inorganic chemicals and exceptionallly good resistance to hydrolysis in hot water. However, they exhibit poor or only moderate resistance to weathering due to damage caused by UV radiation1, whereas resistance to beta, gamma and X-rays is good.
Some grades of PAEKs show good resistance to combustion, and when they burn, they produce fewer toxic and corrosive gases than many other high performance polymers.
Most grades can be fabricated by conventional thermoplastic processing methods, such as extrusion and compression molding. PEKs can be also used as matrix resins for high performance reinforced composites.
Commercial grades of unfilled and glass-reinforced polyetherketones are available from Raychem Corp., Evonik, Solvay, and SABIC. The unfilled grades are available in a range of melt viscosities.
|Polyetherketone||Structure of Repeat Unit||Trade Name|
|Polyetherketone (PEK)||G-PAEK®, Ultrapek®1, RTP|
|Polyetheretherketone (PEEK)||LNP™, VESTAKEEP®, Zeniva® PEEK, LUVOCOM®|
|Polyetherketoneketone (PEKK)||KEPSTAN®, RTP, Cypec®, Oxpekk®|
PAEKs and polyethersulfones are often used in similar applications. However, PAEKs have better solvent resistance than polyethersulfones because they are semicrystalline wheras the later are amorphous polymers which makes them more prone to solvent attack. The excellent solvent resistance can be a critical factor in many demanding applications.
Like polyethersulfones, polyetherketones are usually not attacked by prolonged exposure to (sea) water or steam, which makes them ideal candidates for use in applications such as medical components, subsea equipment, and valve components.
Because of their good wear resistance and mechanical properties, including high stiffness and long-term creep and fatigue properties, mechanical parts made of PAEKs can replace steel in many applications. Examples are high-speed rotors, intricate bearing shells, aircraft landing gear hubcaps and aerospace P-clamps.
Due to their semi-crystalline nature, PAEKs retain a high degree of their mechanical properties close to their melting temperature. Some PAEKs have a continuous service temperature rating of more than 250°C (480°F).
- PEK - Poly(ether ketone)
- PEEK - Poly(ether ether ketone)
- PEKK - Poly(ether ketone ketone)
1Carbon filled grades provide improved UV stability and can be used in certain applications where greater UV resistance is required.