Hello and welcome to the Part 2C of our High Performance Thermoplastics selection blog series. Today we discuss the Ether-Ketone Polymer family (PAEK and PEEK), their chemistry and production processes, their main properties, processing methods, and applications.
Overview - 6 major high performance thermoplastics families (“the magnificent six”)
In this blog post series we discuss six major high performance thermoplastics families (“the magnificent six”) which are outlined in the following enumeration
1. Introduction to High Performance Polymers
2. Short profile of the "magnificent six" families:
-Part 2C: Polyether (PPE, PAEK, PEEK, PEKK)
-Part 2D: Liquid Crystal Polymers (LCP) and High-performance Polyesters (Polycyclohexylene terephthalate - PCT)
-Part 2E: Semi- and Fully Aromatic Polyamides (PARA, PPA, Aramid)
-Part 2F: Polyhalogenolefins (PTFE, PCTFE, FEP, PVDF, ECTFE)
3. Key properties and design data for selection
4. Polymer Material Selection 4-stage funnel methodology (POMS-Funnel-Method)
5. Examples for Ultra- and high performance polymer selection
1. Introduction to Polyaryletherketones
Screening the patent literate regarding the invention of Polyaryletherketones, it was reported independently by Imperial Chemical Industries (ICI) and DuPont. Polyetheretherketone (PEEK) was first produced in 1978 by scientists at ICI in the UK, with the first batch made on November 19, 1978, by John B. Rose and Philip A. Staniland's team. ICI commercialized it as Victrex PEEK in the early 1980s, initially for demanding defense and aerospace uses, becoming a high-performance thermoplastic known for its strength, temperature resistance, and chemical inertness.
In general, the aromatic ether ketone polymer family, including Polyetheretherketone (PEEK), Polyaryletherketone (PAEK), and Polyetherketoneketone (PEKK) are high-performance thermoplastics valued for their outstanding mechanical, thermal, and chemical properties. Recent research and industry trends are increasingly focusing on PAEK blends to further tailor and enhance performance for demanding applications.
2. Chemistry and Production
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Chemical Structure:All three are aromatic polyketones with ether and ketone groups.
- PEEK: Regular ether/ketone sequence.
- PAEK: Family with variable ether/ketone ratios, allowing for property tuning.
- PEKK: Higher ketone content, affecting crystallinity and processing.
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PEEK Polycondensation Process:
- Mechanism: PEEK is produced via a high-temperature polycondensation reaction, typically through nucleophilic aromatic substitution.
- Monomers: The main industrial method (patented by Victrex PLC in the late 1970s) uses 4,4'-difluorobenzophenone (or 4,4'-dichlorobenzophenone) and hydroquinone (1,4-benzenediol or bisphenol).
- Solvent & Catalysts: The reaction occurs in a high-boiling polar aprotic solvent, diphenyl sulfone (DPS), with a mixture of potassium and sodium carbonate as the base.
- Process Steps:
- Salt Formation: Hydroquinone reacts with alkali metal carbonates to form a bisphenate salt, releasing water and CO₂.
- Polycondensation: The bisphenate salt reacts with 4,4'-difluorobenzophenone, displacing fluorine atoms and forming ether linkages, with potassium and sodium fluoride as byproducts.
- Purification: The resulting high-molecular-weight PEEK powder is cooled, crushed, and washed with hot water and organic solvents (e.g., acetone) to remove residual salts and solvent.
- Drying: The purified polymer is dried, often under vacuum at ~120°C.
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PAEK Blends:
- Produced by blending PAEK with other polymers or additives to achieve specific property profiles, such as improved toughness, flexibility, or processability.
The ether/ketone ratio impacts the thermal transitions of ether-ketone polymers. Table 1 illustrates the influence of the ether/ketone ratio on the thermal transitions of various Polyaryletherketones. As the ether/ketone ratio increases from 1.0 to 3.0, both the glass transition temperature (Tg) and the melting temperature (Tm) of the polymers decrease. Specifically, PEK (ether/ketone ratio 1.0) exhibits the highest Tg and Tm, while PEEEK (ratio 3.0) shows the lowest values. This trend demonstrates that increasing the ether content in the polymer backbone reduces the thermal transitions of Polyaryletherketones by enhancing chain flexibility and increasing the free volume between polymer chains.
For anyone working with high-performance materials, understanding these trends is key to selecting the optimal polymer for demanding applications.
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| Table 1: Aromatic Ether-Ketone Polymers - influence of the ether/ketone ration on thermal transitions. |
- PEEK has high thermal stability (max. continuous use temperature UL746B = 260°C; max short-term use temperature: 310°CHDT 1.8 MPa = 160°C), mechanical strength (tensile modulus = 4000 MPa; tensile strength = 110 MPa), inherent flame retardant (UL94 V0), and high chemical resistance.
- Blends:
- Blending ketone-polymers with other polymers (e.g., polyetherimide, polyphenylene sulfide, liquid crystal polymers, or elastomers) can improve processability, impact strength, and tailor crystallinity.
- Nanofiller or fiber-reinforced PAEK blends offer enhanced mechanical, thermal, and tribological properties.
- PEKK has a slower crystallization rate which makes it good for 3D printing.
- Injection Molding, Extrusion, Compression Molding, Machining, 3D Printing.
- PAEK Blends:
- Improved processability and lower processing temperatures compared to pure PAEK.
- Blends can be tailored for compatibility with specific manufacturing techniques.
- Recycling of PEEK: Regrind of spure, gates and faulty parts can be used without problem up to a level of 25%. Important is to blend the regrind with virgin PEEK pellets to ensure uniform processing and use consistent amount of regrind.
- Aerospace: PEEK was originally developed for the aerospace industry. Its high strength-to-weight ratio, flame retardancy (meeting FST standards), and resistance to aerospace fluids like jet fuel are highly valued for improving fuel efficiency and safety:
- Structural components: Lightweight brackets, clamps, and clips can replace heavier aluminum parts without compromising strength.
- Engine components: Seals, bearings, and insulation in turbine systems that withstand high temperatures and pressures.
- Interior components: Used in seat frames and cabin panels due to its flame-retardant properties and durability.
- Electrical insulation: Cable insulation and various electrical connectors due to its high dielectric strength.
- Automotive:
- Engine & Transmission: Thrust washers, seal rings, bushings, and gears in transmission and engine systems, where they endure high temperatures and mechanical stress.
- Braking Systems: Components in ABS/ESC brake systems and brake wear sensors.
- Fuel Systems: Seals, O-rings, and valve seats in fuel injection systems and pumps, due to resistance to various fuels and oils.
- Traction motors: magnet wire coating by using direct extrusion on copper wire.
- Electronics
- Medical: Surgical equipment and long-term implantable devices, because of its biocompatibility, radiolucency (transparent to X-rays), and ability to withstand repeated sterilization. Applications include handles for reusable surgical instruments, sterilization trays, and components in fluid transfer systems and pumps (e.g., in dialysis equipment).
- Oil & Gas: In the demanding high-pressure, high-temperature (HPHT) and corrosive environments of the oil and gas industry, PEEK's resistance to hydrocarbons, steam, and aggressive chemicals is crucial. Applications include sealing systems, downhole tools, Valve and Pump Components.
- 3D Printing.
- PAEK Blends:
- Used where a balance of toughness, chemical resistance, and processability is required.
- Fiber- or nanoparticle-reinforced blends are ideal for lightweight, high-strength parts in aerospace and automotive sectors.
- Cost:High compared to engineering and other high-performance polymers, however blends can sometimes reduce costs by enabling easier processing or using less expensive co-polymers.
- Value:Blends offer tailored solutions, potentially reducing total cost of ownership through improved performance and manufacturability.
- PEEK: Victrex (VICTREX 450G™), Syensqo (KetaSpire®), Evonik (VESTAKEEP®), Zhejiang Pfluon Chemical (PFLUON®), Zhongyan Polymer Materials Co (ZYPEEK).
- PAEK: Victrex (LMPAEK™), Syensqo (AvaSpire® PAEK).
- PEKK: Arkema (Kepstan®), Syensqo (APC and Cypek).
- Ether/Ketone Blends: Offered by major suppliers and custom compounders; specific formulations may be proprietary.
Thanks for reading & #findoutaboutplastics
Greetings,
Literature:
[1] https://pmc.ncbi.nlm.nih.gov/articles/PMC10575340/#polymers-15-03943-f004
[2] https://www.vink-kunststoffe.de/produkte/peek/technisches-datenblatt-peek.pdf
[3] https://link.springer.com/chapter/10.1007/978-94-011-7073-4_18
[4] https://www.syensqo.com/en/brands/ketaspire-peek
[5] https://www.victrex.com/en/products/polymers/peek-polymers
[6] https://www.findoutaboutplastics.com/2020/11/plastic-part-failure-part-2-antidote.html
