PEEK

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Polyetheretherketones (PEEK), also referred to as polyketones, are obtained from aromatic dihalides and bisphenolate salts by nucleophilic substitution. The bisphenolate salt is formed in situ from bisphenol and either added sodium or added alkali metal carbonate or hydroxide.

PEEK is a thermoplastic with extraordinary mechanical properties. The Young's modulus is 3.6 GPa (522,000 psi) and its tensile strength 170 MPa (25,000 psi).

PEEK is partially crystalline, and is highly unusual in exhibiting two glass transition temperatures at around 140°C (284°F) and around 275ºC (527°F), depending on cure cycle and precise formulation. PEEK melts at around 350°C (662°F) and is highly resistant to thermal degradation. The material is also resistant to both organic and aqueous environments, and is used in bearings, piston parts, pumps, compressor plate valves, and cable insulation applications. It is one of the few plastics compatible with ultra-high vacuum applications.

PEEK is considered an advanced biomaterial used in medical implants, often in reinforced format using biocompatible fibre fillers such as carbon. Also in carbon fibre reinforced form, PEEK has come under consideration as an aerospace structural material due to its high strength-to-weight ratio. Electronic circuitry also has a high demand for PEEK's large temperature range.

Chemical resistance

PEEK also exhibits good chemical resistance in many environments, including alkalis (i.e. sodium, potassium and ammonium hydroxides), aromatic hydrocarbons, alcohols (i.e. ethanol, propanol), greases, oils and halogenated hydrocarbons.

However, its performance in acids is very dependent on the type of acid - PEEK shows poor resistance in concentrated sulfuric, nitric, hydrochloric, hydrobromic and other mineral acids (though performance may be adequate for short term use with these acids in very dilute form). Its resistance to hydrofluoric acid and oleum is very poor. PEEK shows good resistance to phosphoric acid and organic acids (acetic, citric, oxalic, tartaric etc.), but varying resistance in the presence of halogens. PEEK is resistant to dissolution by some aldehydes and ketones such as acetone, but not (at higher temperature) methylethyl ketone.

References

1. ^ A.K. vam der Vegt & L.E. Govaert, Polymeren, van keten tot kunstof, ISBN 90-407-2388-5