Polyether ether ketone (PEEK) is a high-performance thermoplastic material with unique combination of properties and widely used in various markets and applications including medical, aerospace, automotive, oil and gas and industrial applications.
As shown in the table below, there are several polymers in the family of Polyaryletherketones exist and among them Polyetheretherketone (PEEK) is widely used and manufactured in large scale. PEEK materials were initially made in 1977 by Imperial Chemical Industries ICI and now it is manufactured and marketed as Victrex PEEK by Victrex. Other well-known manufacturers of PEEK raw material are Solvay and Evonik.
| Polymer | Chemical Name | Chemical Structure | Tm°C | Tg°C |
|---|---|---|---|---|
| PEK | Polyetherketone |  | 163 | 361 |
| PEEK | Polyetherether ketone |  | 144 | 344 |
| PEEKK | Polyetheretherketone ketone |  | 154 | 358 |
| PEKK | Polyetherketone ketone |  | 165 | 384-391 |
Chemical Structure:
As evident from the chemical structure, PEEK contains relatively stiff aromatic polymer backbone and remains as a reason for very high thermal transitions. As a results, these polymers are having continuous use temperature of around 240-250°C, even in hot water or steam. PEEK material possesses very good mechanical properties and outstanding chemical resistance, equivalent to fluoropolymer.
PEEK is an aromatic polymer and presence of ether linkage gives the melt processability in conventional techniques such as injection moulding, compression moulding and extrusion. The rigid and stiff chemical structure affects the crystallisability of PEEK and allowing up to 48% as maximum achievable crystallinity.
Achieving VL 0 classifications, OSU heat release test and extremely low smoke emission makes PEEK as one of the best material in flame resistance characteristics. The softening temperatures of unfilled PEEK is around the Tg of PEEK but after filling with glass fiber or carbon fiber, the softening temperature increases significantly reaching close to the melting the point , i.e around 315-320°C.
Typical Material Properties:
Some of the properties for unfilled PEEK are listed below. These values to be considered as indicative rather than accurate.
| Material Property | Unit | Indicative Value |
|---|---|---|
| Mechanical Properties | ||
| Tensile Strength | MPa | 95 |
| Tensile Elongation at Break | % | 78 |
| Tensile Modulus | MPa | ~3500 |
| Density | g/cm3 | 1.30 |
| Izod Impact strength (Notched) | J/m | 91 |
| Shore Hardness | D | 88 |
| Thermal Properties | ||
| Typical Melting Range | °C | 340-345 |
| Glass Transition Temperature Tg | °C | 150 |
| Heat Deflection Temperature (HDT) 1.8 Mpa | °C | 157 |
| Service Temperature | °C | Maximum of 250 |
| Thermal Conductivity | W/m/k | 0.24 |
| CTE (-50 to +50°C) | cm/cm/°C | 4.3 x 10-5 |
| Electrical Properties | ||
| Dielectric Constant at 60Hz | 3.06 | |
| Dissipation Factor Tan δ at 60Hz | 1 x 10-3 | |
| Dielectric Strength | 17 | |
| Volume Resistivity | 1.6 x 1017 | |
| Surface Resistance | Above 1.9 x 1017 | |
Typical Processing Methods:
- Injection moulding
- Extrusion
- Compression moulding
- Thermoforming
- Fibre spinning
- Composites moulding techniques: Prepreg moulding, AFP and ATL
- Welding
- Coating
- 3D printing
Unique Properties of PEEK:
- High temperature resistance: Depending on application requirement and loading conditions, PEEK could be used up to 240-250°C as continuous use temperature.
- Tribological properties: Excellent wear and surface properties: Around 50% of applications are because of its wear and other surface properties. PEEK is normally blended with additives for applications demanding good wear and other surface properties.
- Very good fatigue resistance.
- Outstanding hydrolytic stability and radiation resistance
- Good material for aggressive environment. PEEK is being used in nuclear environments, Oil and geothermal wells, chemical industries, and high-pressure valves.
- Ideal material for metal replacement applications mainly because of outstanding corrosion resistance, strength, durability, wear resistance and high temperature stability.
- Food grade approval: With food grade approval PEEK materials finds its application in food processing industry mainly as a bearings and seals for food processing equipment’s.
- Material properties of PEEK could be easily modified via blending with various fillers (carbon, graphite, lubricant, minerals, etc) and reinforcements (carbon fibre, glass fibre, etc) to improve mechanical, thermal and tribological properties.
Limitations of PEEK:
- Opaque material and may not be a material of choice where transparency is required.
- Very expensive
- Very high processing temperature. PEEK materials are processed at around 380-420°C demanding high end processing equipment
- PEEK is very hard material and could be aggressive against soft mating components in tribological applications.
- Poor microwave resistance at high temperature.
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