Polymer Data File:
Polyether ether ketone
- PEEK
Polymer Data File:Polyether ether ketone
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Introduction
PEEK was one of the first of the 'new generation' of engineering thermoplastics introduced and was developed by ICI in 1977 and first marketed in 1978. The material is one of the polyaryletherketone family - a group of partially crystalline polymers that are suitable for use at high temperatures. The polyether ether ketones have repeating monomers of two ether and ketone groups and PEEK is one of the highest rated thermoplastic materials in terms of heat resistance. The useful properties of the material are retained at temperatures as high as 315oC.
The materials have excellent chemical resistance, high strength and good resistance to burning but equally the high cost of these materials makes applications limited to those where the properties are very necessary.
Typical
Applications
Automotive: Piston components, bearing linings.
Electrical engineering: Wire insulation for extremely high temperature applications, cable couplings and connectors.
Appliances: Handles, cooking equipment.
Medicine: Prosthetics, instruments.
Others: Aircraft parts and wire insulation, pump casings and impellers, monofilament for production of woven products for filters, belting and meshes.
Physical
and Mechanical Properties
General physical properties
PEEK is has greater strength and rigidity than many of the engineering thermoplastics and is tough and impact resistant over a wide range of temperatures.
Mechanical properties
PEEK has good mechanical properties and these are retained over a wide temperature range. The co-efficient of friction and wear rate are low over a wide temperature range.
Property
Approximate Value
Tensile strength (@23oC)
97 MN/m2
Tensile Modulus ( @ 1% strain @ 23oC)
3.5 GN/m2
Elongation at Break (@23oC)
Up to 60 %
Flexural Strength (@23oC)
170 MN/m2
Notched Impact Strength (@23oC)
7.5 kJ/m2
Specific Heat (Melt)
2.16 kJ/kgoC
Glass Transition Temperature
143 oC
Heat Distortion Temperature
152 oC
Coefficient of Thermal Expansion
< Tg 4.7 x 10-5 / oC
> Tg 10.8 x 10-5 / oC
Long Term Service Temperature
Up to 260 oC
Specific Gravity
1.32
Mould Shrinkage
0.01 - 0.02 m/m
Water Absorption
Up to 0.5 % (50% rh)
Transparency
Opaque
Thermal,
Electrical and Optical Properties
Thermal properties
The thermal oxidative stability of PEEK is excellent and the material has a UL rated continuous operating temperature of around 250oC
Fire behaviour
PEEK has excellent resistance to burning and very low flame spread being rated as UL 94 V-0 for thicknesses down to 2 mm. The LIO (Limiting Oxygen Index) is 35%) and even when burning the material has very low smoke generation.
Electrical properties
Good dielectric properties with high volume and surface resistivities and good dielectric strength. These properties are retained at temperatures as high as 200oC.
Optical properties
N/A
Natural colour
Grey/brown
Chemical
Resistance Properties
General
PEEK has excellent chemical resistance and is extremely resistant to many organic and inorganic chemicals. It is dissolved or decomposed only by concentrated anhydrous or strong oxidizing agents.
The material has exceptionally good resistance to hydrolysis in hot water and remains unaffected after several thousand hours at more than 250oC in pressurised water.
Weathering resistance
PEEK is not greatly resistant to UV radiation but has good resistance to beta, gamma and X-rays.
Advantages and
Limitations
Advantages
Limitations
1. Excellent high temperature performance for all mechanical properties
1. Extremely high cost (even for engineering polymers) but the properties can sometimes justify this when it becomes almost the only polymer capable of being used.
2. Excellent electrical performance at high temperatures.
2. Limited supplier base.
3. High rigidity at high temperatures.
4. Excellent gamma radiation resistance.
5. Excellent hydrolysis resistance.
Processing
PEEK can be processed on standard processing equipment and the only concern is that the processing temperatures required are quite high.
Material should be pre-dried at 150oC for 3 hours before processing.
Injection moulding
Injection moulding is best screws with an L/D ratio of 18 to 22. Melt temperatures should be in the range 370 to 400oC. Mould temperatures should be in the range 160 to 215oC.
Injection pressure is 1500 bar, decreasing to 1000 bar for the second stage. Injection speed can be high because the material does not suffer from degradation due to shearing. Screw speed can also be high.
Mouldings do not require any thermal post-treatment.
Extrusion
Extrusion is best with 3 section screws and an L/D ratio of 22 to 30. Melt temperatures in the range 400 to 430oC and feed temperatures of at least 425oC are recommended.
Can be reprocessed at up to 30%.
Processing Method
Applicable
Injection Moulding
Yes.
Extrusion
Yes
Extrusion Blow Moulding
Yes
Rotational Moulding
Yes
Thermoforming
Yes
Casting
Yes
Bending and joining
Yes
Finishing
Machining
PEEK can be machined easily and accurately.
Surface treatment
PEEK can be printed, hot-foiled or treated with most common methods.
Welding
PEEK can be welded by most common thermoplastic welding techniques.
Bonding
PEEK can be bonded using epoxies, cyanoacrylates, polyurethanes or silicones
Health
and Safety
Health and Safety
PEEK has no significant Health and Safety implications.
Other
Information
Identification
Material has a hard, stiff feel and cannot be cut easily. The high density (1.2 - 1.4) means it sinks in water. Natural colour is grey/brown and colours are sometimes dulled by this base colour.
Flame is slightly orange with yellow edges. Low smell and small amounts of smoke.
Last edited: 14/11/2005
© Tangram Technology Ltd. 2001
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