Polyether ether ketone

Polyether ether ketone (PEEK) is a colourless organic thermoplastic polymer in the polyaryletherketone (PAEK) family, used in engineering applications. It was originally introduced by Victrex PLC, then Imperial Chemical Industries (ICI) in the early 1980s.[2]

Polyether ether ketone
Density 1320 kg/m3
Young's modulus (E)3.6 GPa
Tensile strength (σt) 90–100 MPa
Elongation @ break50%
notch test 55 kJ/m2
Glass temperature 143 °C
melting point343 °C
Thermal conductivity0.25 W/(m·K)
Water absorption, 24 hours (ASTM D 570)0.1%
source:[1]

Synthesis

PEEK polymers are obtained by step-growth polymerization by the dialkylation of bisphenolate salts. Typical is the reaction of 4,4'-difluorobenzophenone with the disodium salt of hydroquinone, which is generated in situ by deprotonation with sodium carbonate. The reaction is conducted around 300 °C in polar aprotic solvents - such as diphenyl sulphone.[3][4]

Properties

PEEK is a semicrystalline thermoplastic with excellent mechanical and chemical resistance properties that are retained to high temperatures. The processing conditions used to mold PEEK can influence the crystallinity and hence the mechanical properties. Its Young's modulus is 3.6 GPa and its tensile strength is 90 to 100 MPa.[5] PEEK has a glass transition temperature of around 143 °C (289 °F) and melts around 343 °C (662 °F). Some grades have a useful operating temperature of up to 250 °C (482 °F).[3] The thermal conductivity increases nearly linearly with temperature between room temperature and solidus temperature.[6] It is highly resistant to thermal degradation,[7] as well as to attack by both organic and aqueous environments. It is attacked by halogens and strong Brønsted and Lewis acids, as well as some halogenated compounds and aliphatic hydrocarbons at high temperatures. It is soluble in concentrated sulfuric acid at room temperature, although dissolution can take a very long time unless the polymer is in a form with a high surface-area-to-volume ratio, such as a fine powder or thin film. It has high resistance to biodegradation.

Applications

Because of its robustness, PEEK is used to fabricate items used in demanding applications, including bearings, piston parts, pumps, High-performance liquid chromatography columns, compressor plate valves, and electrical cable insulation. It is one of the few plastics compatible with ultra-high vacuum applications, which makes it suitable for aerospace, automotive, teletronic, and chemical industries.[8] PEEK is considered an advanced biomaterial used in medical implants, e.g., use with a high-resolution magnetic resonance imaging (MRI), for creating a partial replacement skull in neurosurgical applications.

PEEK is finding increased use in spinal fusion devices and reinforcing rods.[9] It offers optimal bone growth and is radiolucent, but it is hydrophobic causing it to not fully fuse with bone.[8] [10] PEEK seals and manifolds are commonly used in fluid applications. PEEK also performs well in applications where continuous high temperatures (up to 500 °F/260 °C) are common.[11] Because of this and its low thermal conductivity, it is also used in FFF printing to thermally separate the hot end from the cold end.

Processing options

PEEK melts at a relatively high temperature (343 °C / 649.4 °F) compared to most other thermoplastics. In the range of its melting temperature it can be processed using injection moulding or extrusion methods. It is technically feasible to process granular PEEK into filament form and 3D printing parts from the filament material using fused deposition modeling – FDM (or fused filament fabrication – FFF) technology.[12][13] PEEK filaments have been demonstrated for producing medical devices up to class IIa.[14] With this new filament, it is possible to use the FFF method for different medical applications like dentures.

In its solid state PEEK is readily machinable, for example, by (CNC) milling machines and is commonly used to produce high-quality plastic parts that are thermostable and both electrically and thermally insulating. Filled grades of PEEK can also be CNC machined, but special care must be taken to properly manage stresses in the material.

PEEK is considered a high-performance polymer, that is to say, its high price restricts its use to the most demanding applications only.

Shape-memory PEEK in biomechanical applications

PEEK is not traditionally a shape-memory polymer; however, recent advances in processing have allowed shape-memory behavior in PEEK with mechanical activation. This technology has expanded to applications in orthopedic surgery.[15]

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References
  1. A. K. van der Vegt & L. E. Govaert, Polymeren, van keten tot kunstof, ISBN 90-407-2388-5.
  2. "Why PEEK?". drakeplastics.com. Retrieved 23 April 2018.
  3. David Parker; Jan Bussink; Hendrik T. van de Grampe; Gary W. Wheatley; Ernst-Ulrich Dorf; Edgar Ostlinning; Klaus Reinking (15 April 2012). Polymers, High-Temperature. Ullmann's Encyclopedia of Industrial Chemistry (online Version). doi:10.1002/14356007.a21_449.pub3. ISBN 978-3527306732. (subscription required)
  4. David Kemmish "Update on the Technology and Applications of PolyArylEtherKetones" 2010. ISBN 978-1-84735-408-2.
  5. Material Properties Data: Polyetheretherketone (PEEK), www.makeitfrom.com.
  6. J. Blumm, A. Lindemann, A. Schopper, "Influence of the CNT content on the thermophysical properties of PEEK-CNT composites", Proceedings of the 29th Japan Symposium on Thermophysical Properties, October 8–10, 2008, Tokyo.
  7. Patel, Parina; Hull, T. Richard; McCabe, Richard W.; Flath, Dianne; Grasmeder, John; Percy, Mike (May 2010). "Mechanism of thermal decomposition of poly(ether ether ketone) (PEEK) from a review of decomposition studies" (PDF). Polymer Degradation and Stability. 95 (5): 709–718. doi:10.1016/j.polymdegradstab.2010.01.024.
  8. "PEEK (Polyether Ether Ketone)". www.scientificspine.com. Retrieved 2020-05-06.
  9. Lauzon, Michael (May 4, 2012). "Diversified Plastics Inc., PEEK playing role in space probe". PlasticsNews.com. Crain Communications Inc. Retrieved May 6, 2012.
  10. "10 Porous TLIF cages to Know...!". SPINEMarketGroup. 2020-02-01. Retrieved 2020-05-06.
  11. "Properties of PEEK Material". www.uplandfab.com.
  12. Newsom, Michael. "Arevo Labs announces Carbon Fiber and Nanotube-reinforced High Performance materials for 3D Printing Process". Solvay Press Releases. LouVan Communications Inc. Retrieved 27 January 2016.
  13. Thryft, Ann. "3D Printing High-Strength Carbon Composites Using PEEK, PAEK". Design News. Retrieved 27 January 2016.
  14. Press release Indmatec PEEK MedTec.
  15. Anonymous. "Surgical Technologies; MedShape Solutions, Inc. Announces First FDA-cleared Shape Memory PEEK Device; Closing of $10M Equity Offering". Medical Letter on the CDC & FDA.
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