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A Complete Guide on Polyetheretherketone (PEEK)

Polyetheretherketone (PEEK): A Complete Guide on High-Heat Engineering Plastic

Polyetheretherketone (PEEK) is a high-performance, engineering thermoplastic characterized by an unusual combination of properties. These properties range from high temperature performance to mechanical strength and excellent chemical resistance. But, what are the key characteristics which make PEEK a high-performance plastic? What it is made up of? Get all the technical information on Polyetheretherketone, explore what are its key properties and benefits in detail! Also, learn about popular application (aerospace, automotive, medical...) and processing conditions for this polymer.

Overview

What is PEEK – Polyetheretherketone?

What is PEEK – Polyetheretherketone?

Polyetheretherketone (PEEK) is a semi-crystalline, high-performance engineering thermoplastic. This rigid opaque (grey) material offers a unique combination of mechanical properties, resistance to chemicals, wear, fatigue and creep as well as exceptionally high temperature resistance, up to 260°C (480°F).

The polymer belongs to polyketone family of polymers (PEK, PEEK, PEEKK, PEKK, PEKEKK) and amongst them, PEEK is the most widely used and manufactured in large scale.

Polyetheretherketone (PEEK): A Complete Guide on High-Heat Engineering Plastic

PEEK [CAS: 29658-26-2; Chemical Name: poly(oxy-1,4-phenyene-oxy-1, 4-phenyene)] has:


PEEK can be processed by conventional methods such as injection molding, extrusion, compression molding etc.

Thanks to these properties, PEEK and its composites are widely used in aerospace, automotive, structural, high temperature electrical and biomedical applications.

Despite high price of the polymer, the added value that PEEK materials bring by offering the possibility of manufacturing parts include lightweight, strength or toughness and able to survive longer in harsh environments.

PEEK is fully recyclable plastic. PEEK has been commercially available from ICI since early 1980s.


Key Properties of Polyetheretherketone (PEEK)

Key Properties of Polyetheretherketone (PEEK)

  1. PEEK exhibits exceptional tensile properties. When reinforced with carbon fibers, tensile strength of 29000psi can be achieved with excellent properties retained at 299°C
  2. The polymer also exhibits excellent creep resistance. When combined with flexural & tensile characteristics, it provides an excellent balance of properties where the material is required to withstand high loadings for long periods at high temperature without permanent deformations
  3. Its flexural modulus at very high temperatures can further be improved with glass- or carbon-reinforcement. (Reinforcement also increases creep and fatigue resistance, thermal conductivity of the polymer as well as heat distortion temperature)


  4. Polymer Matrix Selection for Very High Temperature Composites

  5. The polymer exhibits high volume resistivity and surface resistivity. It can maintain good insulating properties in a broad temperature range and environmental changes
  6. PEEK has V0 flammability rating down to 1.45 mm and an LOI of 35%. Its smoke and toxic gas generation are extremely low
  7. Crystallinity imparts excellent resistance to wide range if liquids and superb fatigue performance
  8. PEEK is insoluble in all common solvents. It does not undergo hydrolysis and can be used for thousands of hours in steam or high-pressure water without significant property degradation
  9. More properties of PEEK include:
    • Low friction
    • Good dimensional stability
    • Exception insulation properties
    • Excellent sterilization resistance at high temperature
    • Biocompatible
    • Long life
    • Inherent purity


Neat PEEK vs Other Polymers

Neat PEEK vs Other Polymers

Below table lists the properties of unfilled, 30% glass fiber-reinforced, 30% carbon fiber-reinforced PEEK grades:

Property Unfilled 30% carbon fiber 30% glass fiber
Dielectric Constant 3.2 3.2 - 3.4 3.3 - 4.2
Dielectric Strength (kV/mm) 20 18.5 - 19 15 - 24
Volume Resistivity (x 1015 Ohm.cm) 16 - 17 1 - 8 15 - 16
Elongation at Break (%) 30 - 150 1 - 3 2 - 3
Flexibility (Flexural Modulus) (GPa) 3.7 - 4 13 - 19 9 - 10
Young Modulus (GPa) 3.5 - 3.9 13 - 22.3 9 - 11.4
Toughness (Notched Izod Impact at Room Temperature) (J/m) 80 - 94 85 - 120 95 - 130
Density (g/cm3) 1.26 - 1.32 1.4 - 1.44 1.49 - 1.54
Thermal Insulation (Thermal Conductivity) (W/m.K) 0.25 0.9 - 0.95 0.43

  • In comparison to fluoropolymers, PEEK show superior tensile strength, HDT, operating temperature, bonding, processing and toxic gas emission; but they are inferior in terms of chemical resistance, cost, toughness and UV weathering
  • As compared to PPS, PEEK has markedly superior thermal resistance, toughness and flashing
  • PEEK has much higher temperature performance, wear resistance, chemicals resistance and fatigue performance as compared to PES

PEEK is not normally blended with other polymers. However, it forms miscible blends with a range of other polyketones and PEI.

PEEK/PEI blends have higher Tg. And, its blends with PES and PPS are highly compatible.


Limitation of PEEK

Limitation of PEEK

  1. Expensive, applicable for highly demanding application
  2. Processing at high temperatures
  3. Attached by some acids, such as conc. Sulphuric, Nitric, Chromic… and is attacked by halogens and sodium
  4. Low resistance to UV light


How PEEK is Manufactured?

How PEEK is Manufactured?

PEEK polymers are obtained by step-growth polymerization by the dialkylation of bisphenolate salts. It involves reaction of 4,4’-difluorobenzophenone or 1,4-bis(4-fluorobenzoyl) benzene with hydroquinone in the presence of alkali carbonates. The polymer is then isolated by removal of alkali metal fluoride and the polymerization solvent.

Molecular Structure of PEEK
Molecular Structure of PEEK

Because of its relatively stiff aromatic polymer backbone, the polymer exhibits some of the highest thermal transitions among several other commercial polymers and hence can be used at temperatures as high as 240°C.


Processing Conditions for PEEK Polymers

Processing Conditions for PEEK Polymers

PEEK can be processed by conventional methods such as injection molding, extrusion, compression molding etc. However, the processing conditions used to mold PEEK can influence the crystallinity, and hence the mechanical properties.

As a linear thermoplastic, Polyetheretherketone can be melt processed in the temperature range of 370 to 420°C. While processing Polyetheretherketone, no corrosive gases are evolved.




Before processing Polyetheretherketone, drying is recommended for 3 hours at 150°C or 2 hours at 180°C. This is done to avoid any molding defects.

Polyetheretherketone can be processed by injection molding and extrusion. These processes with their processing guidelines are described below:


Injection Molding


  • A mold temperature of 160-190°C is recommended to obtain good crystallization and minimize warping.
  • Post crystallization at 200°C is possible but it is not recommended for applications requiring high dimensional stability.
  • PEEK is suitable for injection of very small parts with tight dimensional tolerances.
  • Injection pressure: 70-140 Mpa
  • Mold shrinkage: Unfilled – 1.2-2.4%, Filled – 0.1-1.1%


Extrusion


  • Cooling temperature have a strong influence on crystallinity and then on performances.
  • For film and sheet extrusion, cooling cylinders at 50°C lead to transparent amorphous material.
  • Cooling cylinders at 170°C lead to opaque and highly crystalline material.
  • It is also possible to produce oriented or bioriented films by the process of extrusion.


3D printing


Thanks to its unique properties, 3D printing of PEEK allows construction of almost any complex design geometry, which cannot be manufactured using other technologies. Fused deposition modeling – FDM (or fused filament fabrication – FFF) methods are used for 3D Printing with PEEK filaments.
  • Nozzle temperature: 360-400 degrees Celsius
  • Heated bed: 120 degrees Celsius

It is an excellent candidate for FFF due to its low moisture absorption as opposed to other common FFF materials, such as Acrylonitrile Butadiene Styrene (ABS).

» Find Suitable PEEK Grade for your Next 3D Printing Development



Find Suitable Polyetheretherketone (PEEK) Grade

View a wide range of polyetheretherketone (PEEK) grades available in the market today, analyze technical data of each product, get technical assistance or request samples.

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