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Polyether ether ketone
View on Wikipediafrom Wikipedia
 | |
| Identifiers | |
|---|---|
PubChem CID
|
|
| Properties | |
| (C19H12O3)n | |
| Molar mass | 288.3 g/mol |
| Density | 1.32 g/cm3 |
| Melting point | 343 °C (649 °F; 616 K) |
| Related compounds | |
Related compounds
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|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
| Polyether ether ketone | |
|---|---|
| Physical properties | |
| Density (ρ) | 1.32 g/cm3 |
| Water absorption—over 24 hours | 0.1% |
| Mechanical properties | |
| Young's modulus (E) | 3.6 GPa |
| Tensile strength (σt) | 90–100 MPa |
| Elongation (ε) at break | 50% |
| Notch test | 55 kJ/m2 |
| Thermal properties | |
| Melting temperature (Tm) | 343 °C |
| Glass transition temperature (Tg) | 143 °C |
| Thermal conductivity (k) | 0.25 W/(m⋅K) |
| [1] | |
Polyether ether ketone (PEEK) is a beige coloured organic thermoplastic polymer in the polyaryletherketone (PAEK) family, used in engineering applications. It was invented in November 1978[2] and brought to market in the early 1980s by part of Imperial Chemical Industries (ICI), the PEEK division was acquired through a management buyout, giving rise to Victrex PLC.[3]
Synthesis
[edit]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 sulfone.[4][5]
Properties
[edit]PEEK is a semicrystalline thermoplastic with excellent mechanical and chemical resistance properties that are retained to high temperatures. The processing conditions used to mould 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.[6] 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).[4] The thermal conductivity increases nearly linearly with temperature between room temperature and solidus temperature.[7] It is highly resistant to thermal degradation,[8] 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
[edit]PEEK is used to fabricate items for 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, and chemical industries.[9] PEEK is used in medical implants, for example in creating a partial replacement skull in neurosurgical applications.
PEEK is used in spinal fusion devices and reinforcing rods.[10] It is radiolucent, but it is hydrophobic causing it to not fully fuse with bone.[9][11] PEEK seals and manifolds are commonly used in fluid applications. PEEK also performs well in high temperature applications (up to 260 °C/500 °F).[12] Because of this and its low thermal conductivity, it is also used in fused filament fabrication (FFF) printing to thermally separate the hot end from the cold end.
Processing options
[edit]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.[13][14] PEEK filaments have been demonstrated for producing medical devices up to class IIa.[15] 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 a high-performance polymer, but its high price, due to its complex production process, restricts its use to only the most demanding applications.[16]
Shape-memory PEEK in biomechanical applications
[edit]PEEK is not traditionally a shape-memory polymer; however, recent advances in processing have allowed shape-memory behaviour in PEEK with mechanical activation. This technology has expanded to applications in orthopaedic surgery.[17]
References
[edit]- ^ van der Vegt, A.K.; Govaert, L.E. (2003). Polymeren, van keten tot kunstof (in Dutch) (5th ed.). DUP Blue. ISBN 90-407-2388-5.
- ^ "Victrex celebrates 40 years of PEEK success". Victrex. Retrieved 2021-11-01.
- ^ "Why PEEK?". drakeplastics.com. Retrieved 23 April 2018.
- ^ a b 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. doi:10.1002/14356007.a21_449.pub3. ISBN 978-3527306732. (subscription required)
- ^ Kemmish, David (2010). Update on the Technology and Applications of PolyArylEtherKetones. ISmithers. ISBN 978-1-84735-408-2.
- ^ Material Properties Data: Polyetheretherketone (PEEK), www.makeitfrom.com.
- ^ Blumm, J.; Lindemann, A.; Schopper, A. (2008). "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. pp. 306–8. ISSN 0911-1743.
- ^ 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.
- ^ a b "PEEK (Polyether Ether Ketone)". www.scientificspine.com. Retrieved 2020-05-06.
- ^ Lauzon, Michael (May 4, 2012). "Diversified Plastics Inc., PEEK playing role in space probe". PlasticsNews.com. Crain Communications Inc. Retrieved May 6, 2012.
- ^ "10 Porous TLIF cages to Know...!". SPINEMarketGroup. 2020-02-01. Retrieved 2020-05-06.
- ^ "Properties of PEEK Material". www.uplandfab.com.
- ^ Newsom, Michael (24 March 2014). "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.
- ^ Thryft, Ann. "3D Printing High-Strength Carbon Composites Using PEEK, PAEK". Design News. Archived from the original on 2 February 2016. Retrieved 27 January 2016.
- ^ Press release Indmatec PEEK MedTec[permanent dead link].
- ^ Yin, Jun; Zhang, Aiqing; Liew, Kong Yong; Wu, Lihua (2008). "Synthesis of poly(ether ether ketone) assisted by microwave irradiation and its characterization". Polymer Bulletin. 61 (2): 157–163. doi:10.1007/s00289-008-0942-6. ISSN 1436-2449. S2CID 97563069.
- ^ 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.
Polyether ether ketone
View on Grokipediafrom Grokipedia
Polyether ether ketone (PEEK) is a semi-crystalline, high-performance thermoplastic polymer in the polyaryletherketone (PAEK) family, featuring a linear structure composed of aromatic rings connected by ether (-O-) and ketone (C=O) linkages in the repeating unit (C19H14O3)n.[1][2] This organic polymer, with a density of approximately 1.3 g/cm³, is prized for its exceptional balance of mechanical toughness, thermal stability, and chemical inertness, enabling it to replace metals in rigorous engineering contexts.[3][1]
Invented in November 1978 by researchers at Imperial Chemical Industries (ICI) in the United Kingdom through nucleophilic aromatic substitution of hydroquinone with 4,4'-difluorobenzophenone, PEEK was first commercialized in 1981 by ICI under the Victrex brand. The PEEK business was spun off from ICI in 1993 to form Victrex plc.[4][3][5] Over the subsequent decades, its production has expanded globally, with Victrex maintaining a capacity of over 8,000 tonnes annually across facilities in the UK, US, and Asia, supporting innovations like filled grades (e.g., carbon or glass fiber-reinforced) and specialized forms such as films, fibers, and additive manufacturing powders.[4][6] These developments have driven PEEK's integration into billions of components worldwide, from medical devices to industrial machinery.[4]
PEEK's defining properties stem from its highly aromatic backbone, which confers a glass transition temperature of 143°C, a melting point of 343°C, and suitability for continuous use at up to 260°C without significant degradation.[2][3] Mechanically, unfilled PEEK offers a tensile strength of 78-100 MPa, flexural strength of 125-170 MPa, and elastic modulus of 3.7-4.0 GPa, while exhibiting low creep and high fatigue resistance; reinforced variants can achieve tensile strengths up to 330 MPa.[2][1] Chemically, it resists most acids, bases, hydrocarbons, and organic solvents, though it is susceptible to concentrated sulfuric or nitric acids, and it maintains dimensional stability under steam sterilization for over 1,000 hours.[1] Additionally, PEEK is biocompatible, electrically insulating (dielectric strength of 584 V/mil), and hydrolytically stable, making it ideal for sterile and high-voltage environments.[3][1]
In applications, PEEK excels in sectors requiring lightweight, durable materials under extreme conditions. In aerospace, it forms engine components, seals, and piston parts that withstand jet fuel and high temperatures.[2] The automotive industry employs it in transmission gears and bearings for enhanced fuel efficiency and wear resistance.[2] Medical uses include implants, prosthetics, and dental instruments, leveraging its biocompatibility and sterilizability, and used in millions of devices worldwide.[3][4] In oil and gas, PEEK seals and downhole tools endure harsh chemicals and pressures, while electronics and food processing benefit from its insulating and FDA-compliant grades.[2][1] Overall, as of 2024, PEEK's versatility has fueled its growth across more than 100 million industrial machines and 500 million automotive parts globally.[4][7]
Overview and history
Chemical structure
Polyether ether ketone (PEEK) features a repeating unit with the molecular formula . This unit consists of three 1,4-disubstituted aromatic phenylene rings interconnected by two ether () linkages and one ketone () bridge, arranged in the sequence , where all linkages are in the para position to provide linearity and rigidity to the polymer chain.[8] Commercial grades of PEEK are produced with number-average molecular weights typically ranging from 20,000 to 120,000 g/mol, allowing for variations in processability and performance across different applications.[9] PEEK is a semi-crystalline thermoplastic, possessing both amorphous regions that impart ductility and crystalline domains that enhance strength and thermal stability. The degree of crystallinity in processed PEEK usually falls between 25% and 45%, depending on cooling rates and processing conditions, which directly influences the material's structural heterogeneity.[10] Among the polyaryletherketone (PAEK) family, PEEK is distinguished by its 2:1 ratio of ether to ketone groups per repeating unit, in contrast to polyetherketone (PEK) with a 1:1 ratio and polyetherketoneketone (PEKK) with a 1:2 ratio.[11]Discovery and commercialization
Polyether ether ketone (PEEK) was invented in November 1978 by researchers John Brewster Rose and Philip Anthony Staniland at Imperial Chemical Industries (ICI), from which Victrex was spun off in 1993, through a nucleophilic aromatic substitution polycondensation reaction involving hydroquinone and 4,4'-difluorobenzophenone.[12][4] The first experimental batch was produced on November 19, 1978, at ICI's Wilton site in the UK, marking the initial synthesis of this high-performance thermoplastic.[13] This development built on earlier research into polyaryletherketones (PAEKs) dating back to the 1960s, but PEEK's specific structure provided superior crystallinity, thermal stability, and mechanical strength, distinguishing it from prior variants.[2] Commercialization began in the early 1980s, with ICI launching the first Victrex PEEK polymers, including unreinforced, glass-filled, and carbon-filled grades, under the Victrex brand in 1981.[4][13] Key intellectual property was secured through patents like European Patent EP0001879, filed by ICI in 1978 and granted in 1989, which covered the polymer's composition and preparation method.[12] Initial production capacity was modest at around 1,000 tonnes per year, focused on high-value sectors. While ICI retained primary production, similar PAEK materials were independently developed by competitors like DuPont, fostering broader industry adoption without direct licensing for PEEK itself.[14] The drive for commercialization stemmed from the aerospace industry's need for lightweight, heat-resistant materials to replace metals in components like brackets and insulators, where PEEK's high strength-to-weight ratio and continuous use temperature up to 260°C offered significant advantages. By the mid-1980s, PEEK entered the automotive sector, enabling lighter engine parts, seals, and bearings that improved fuel efficiency and durability under high-temperature conditions.[15] A major milestone came in the late 1990s when PEEK received U.S. Food and Drug Administration (FDA) approval for medical implants, paving the way for its use in orthopedic devices and spinal cages due to its biocompatibility and radiolucency.[16] These early adoptions established PEEK as a versatile engineering material, with Victrex spinning off from ICI via management buyout in 1993 to focus on its expansion.[5]Synthesis and production
Monomer preparation
The primary monomers used in the synthesis of polyether ether ketone (PEEK) are 4,4'-difluorobenzophenone (DFBP) and hydroquinone.[17][1] The preparation of DFBP typically begins with the Friedel-Crafts acylation of fluorobenzene using acetyl chloride in the presence of a Lewis acid catalyst such as aluminum chloride or boron trifluoride, yielding 4-fluoroacetophenone as the intermediate product.[18] This ketone is then subjected to oxidation of the methyl group, often using potassium permanganate or chromic acid, to form 4-fluorobenzoic acid, which is subsequently converted to 4-fluorobenzoyl chloride via reaction with thionyl chloride or oxalyl chloride. Finally, the acid chloride undergoes a second Friedel-Crafts acylation with fluorobenzene under similar Lewis acid conditions to produce DFBP.[19] This multi-step route ensures the para-substituted product predominates due to the directing effects of the fluorine substituent.[20] Alternative synthetic routes for DFBP include the direct acylation of fluorobenzene with p-fluorobenzotrichloride or the halogen exchange reaction starting from 4,4'-dichlorobenzophenone using potassium fluoride, which can offer cost advantages in large-scale production.[21][22] Hydroquinone, a commercially available diol, requires no specialized preparation but is typically purified by recrystallization from water or ethanol to meet monomer standards.[23] Monomers for PEEK synthesis must exhibit high purity, generally exceeding 99% and often reaching 99.9%, to minimize side reactions such as branching or discoloration during subsequent processing; impurities below this threshold can disrupt polymer chain regularity and reduce crystallinity in the final material.[24][25]Polymerization processes
Polyether ether ketone (PEEK) is synthesized primarily through a step-growth polymerization mechanism involving nucleophilic aromatic substitution (SNAr), where the phenoxide ions from the diphenol displace fluoride ions from the activated dihalide monomer.[26] This process typically employs 4,4'-difluorobenzophenone (DFBP) as the dihalide and hydroquinone as the diphenol, with potassium carbonate (K₂CO₃) serving as the base to deprotonate the hydroquinone and facilitate the substitution.[1] The reaction occurs in a dipolar aprotic solvent such as diphenyl sulfone (DPS), which maintains liquidity at elevated temperatures, at 300–350 °C to drive the equilibrium toward high molecular weight polymer formation.[1][26] The balanced reaction equation for the ideal polymerization is: This equation represents the formation of the repeating PEEK unit, where the ether linkages are created via SNAr at the para positions activated by the ketone group.[26] The process requires precise stoichiometric control of monomers to achieve desired molecular weights, as imbalances can lead to low conversion or excess reactive ends.[27] Variations of the standard solution polymerization include melt polymerization, which eliminates the need for solvents and reduces production costs by simplifying purification and recovery steps.[1] In melt processes, the monomers are heated directly to 350–400 °C under inert atmosphere, relying on the base to initiate substitution without a liquid medium, though this demands robust equipment to handle the high viscosity.[1] Molecular weight is further tuned in both methods by adjusting monomer ratios or incorporating monofunctional end-cappers, such as fluorobenzene derivatives, to terminate chain growth and avoid crosslinking.[27] Key challenges in PEEK polymerization arise from the high temperatures, which can promote side reactions like hydrolysis of the monomers or ether exchange in the polymer chains, potentially degrading yield and product quality.[27] The use of anhydrous conditions and mild bases like K₂CO₃ minimizes hydrolysis, while end-capping strategies prevent gelation by quenching residual phenoxide or fluoride ends that could initiate unintended branching.[27] These measures ensure the production of linear, high-performance PEEK with controlled polydispersity.[26]Physical and chemical properties
Mechanical properties
Polyether ether ketone (PEEK) exhibits robust mechanical performance that makes it suitable for demanding engineering environments, characterized by high strength, stiffness, and resilience under various loading conditions. For unfilled PEEK, the tensile strength typically ranges from 90 to 100 MPa at yield, reflecting its ability to withstand significant axial loads without permanent deformation. The Young's modulus, a measure of stiffness, falls between 3.6 and 4.0 GPa, indicating that PEEK deforms elastically under stress similar to some engineering thermoplastics but with far superior thermal endurance. These properties are derived from standardized testing on grades like VICTREX PEEK 450G, ensuring consistency across industrial applications.[28][29] Impact resistance further underscores PEEK's toughness, with a notched Izod value of approximately 8.0 kJ/m² at room temperature, demonstrating good energy absorption before fracture in the presence of stress concentrators. Under cyclic loading, PEEK displays favorable fatigue behavior, maintaining structural integrity over millions of cycles due to its semi-crystalline microstructure, which resists crack propagation. This fatigue endurance is particularly notable at elevated temperatures, where PEEK outperforms many polymers by sustaining performance without significant degradation.[30] Creep resistance is another hallmark of PEEK, with minimal deformation observed even under sustained loads at elevated temperatures. This low creep is attributed to PEEK's rigid aromatic backbone, enabling reliable dimensional stability in load-bearing scenarios.[29] The degree of crystallinity in PEEK significantly influences its mechanical profile: higher crystallinity levels, achievable through controlled annealing, enhance stiffness and tensile strength by promoting denser molecular packing, but they concurrently reduce toughness and impact resistance due to decreased ductility. For instance, as crystallinity increases from amorphous to fully crystalline states, the Young's modulus rises proportionally, while elongation at break diminishes, highlighting a trade-off central to material optimization. Seminal studies confirm that crystallinity degrees around 30-40% balance these attributes optimally for most uses.[31][32] For carbon fiber reinforced variants of PEEK (CFR-PEEK) with 30-60% carbon fiber reinforcement, the Young's modulus can be tuned to approximately 18-23 GPa depending on fiber type (e.g., PAN-based fibers yielding around 18.5 GPa versus pitch-based at 12.5 GPa), fiber length, and orientation. This tunability is particularly valuable in biomedical applications, where matching the modulus of cortical bone (around 18 GPa) helps mitigate stress shielding. Standard commercial grades, such as VICTREX PEEK 450CA30 with 30% carbon fiber, exhibit a tensile modulus of 28 GPa.[33][34]| Property | Value (Unfilled PEEK) | Test Standard | Source |
|---|---|---|---|
| Tensile Strength (Yield) | 90–100 MPa | ISO 527 | Victrex TDS |
| Young's Modulus | 3.6–4.0 GPa | ISO 527 | Victrex Properties Guide |
| Notched Izod Impact | 8.0 kJ/m² | ISO 180/A | Victrex Datasheet |