Polyketones are partially crystalline engineering thermoplastics that can be used at high temperatures. They also have excellent chemical resistance, high strength, and excellent resistance to burning. Although they require high melt temperatures, polyketones can be extruded and injection molded with standard processing equipment.
Commercially available polyketones are:
- Polyaryletherketones (PAEK or PEK), repeating ether and ketone groups combined by phenyl rings.
- Polyetherketoneketones(PEEK), repeating monomers of two ether groups and a ketone group.
- Polyetherketoneketones (PEKK), repeating monomers of one ether group and two ketone groups.
In addition, other materials with various combinations of the ether and ketone groups are designed to provide a balance of high heat resistance and good processibility, e.g. poly [ether][ketone] [ether] [ketone] [ketone].
Polyketone resins are available as natural resins and glass or carbon -fiber-reinforced and mineral-filled grades.
Suppliers of polyketone resins are: Amoco (Kadel), BASF (Ultrapek PAEK), Du Pont (Areton PEKK), Hoechst Celanese (Hostatec), and ICI (Victrex PEK and PEEK).
Properties: Glass transition temperatures (T,) and melting temperatures (T.) for polyketones depend on the ratio of ketone to ether groups. With increasing ether groups, both temperatures decrease. With increasing ketone groups, the temperatures go up. PEEK's T, is 289°F and its T. is 635°F; PAEK's Tg is 375°F and its T. 718° F; and PEKEKK has a T,, of 350°F and a T. of 707 °F.
Polyketones are stronger and more rigid than most other engineering plastics. They are tough and impact resistant over a wide range of temperatures. Polyketones have very high fatigue strength. Both coefficients of friction and wear rates for polyketones are very low.
The thermal oxidative stability of polyketones is excellent. Typically, continuous use temperatures are above 480°F (i.e., 50% of strength and rigidity are retained up to this temperature).
Moduli of polyketones remain almost constant until the temperature is close to the T, Polyketones have comparatively low thermal coefficient of linear expansion.
Polyketones have excellent resistance to buming and very low flame spread (they are typically rated as V-0 per UL 94). Further, their smoke density is extremely low.
These materials have good dielectric properties, with high volume and surface resistivities, and high dielectric strength.
Polyketones are extremely resistant to numerous inorganic and organic chemicals. They are dissolved or decomposed by concentrated, anhydrous, or strong oxidizing acids. Common solvents do not attack polyketones even at elevated temperatures. They have very good resistance to hydrolysis, even in hot water.
Like most plastics composed of aromatic building blocks, polyketones are affected by UV radiation. Polyketones have extremely high resistance to beta-rays, gamma-rays, and X-rays over a wide range of temperatures.
Processing: Applicable processing methods are injection molding, extrusion, rotational molding, and powder coating. Conventional injection-molding machines can be used with polyketones. Melt temperatures for polyketones vary depending on the resin type. PEK melt temperatures range from 735 to 805°F; for PEEK, the range is 715 to 750° F. Mold temperatures from 355 to 420 °F are recommended for molding PEK, and 355 to 375°F for PEEK. Parts for high-temperature applications should be molded at the high end of the temperature range.
Polyketones can be extruded to form sheet, cast-film, stock for machining, and wire coatings. Typical melt temperatures for extrusion are 750 to 805 °F.
Polyketone parts can be assembled using various adhesives and welding techniques. The adhesives can be epoxies, cyanoacrylates, polyurethanes, or silicones. Welding techniques include heated-tool welding (750 to 1,000F for 10 to 90 sec); spin welding; hot-air welding (840 to 930 ° F); and ultrasonic welding.