PEEK properties
Polyetheretherketone (PEEK) is a high-performance semi-crystalline thermoplastic belonging to the polyaryletherketone (PAEK) family. Its exceptional combination of mechanical strength, thermal stability, and chemical resistance makes it the material of choice in demanding sectors such as aerospace, medical, oil & gas, and semiconductor manufacturing. With a density of approximately 1,32 g/cm³ and a tensile strength that can exceed 100 MPa, PEEK maintains its properties at elevated temperatures where other polymers have failed. Its dielectric strength, low outgassing, and biocompatibility further broaden its application horizons.
Chemical composition
Section titled “Chemical composition”PEEK is synthesized via step-growth polymerization from 4,4’-difluorobenzophenone and the disodium salt of hydroquinone, in a polar aprotic solvent such as diphenyl sulfone at approximately 300 °C. Its molecular structure consists of ether-ether-ketone repeating units, with the chemical formula (C₁₉H₁₂O₃)ₙ and a molar mass of 288,3 g/mol per repeating unit.
| Component | Structural formula |
|---|---|
| Repeating unit | -O-(C₆H₄)-O-(C₆H₄)-C(O)-(C₆H₄)- |
| Molecular formula | (C₁₉H₁₂O₃)ₙ |
| Molar mass (per unit) | 288,3 g/mol |
Mechanical properties
Section titled “Mechanical properties”The mechanical properties of PEEK vary significantly depending on the grade (unreinforced, glass fiber or carbon fiber reinforced) and processing conditions, which determine the degree of crystallinity. At 23 °C, a typical unreinforced grade exhibits an elongation at break of up to 50%.
| Property | Value (Metric / Imperial) |
|---|---|
| Tensile strength | 70,3 - 103 MPa / 10,2 - 14,9 ksi |
| Young’s modulus (Tension) | 3,6 - 3,95 GPa / 0,522 - 0,573 x 10⁶ psi |
| Elongation at break | 30 - 50 % |
| Compressive strength | 118 - 130 MPa / 17,1 - 18,9 ksi |
| Flexural strength (Modulus of rupture) | 105 - 116 MPa / 15,2 - 16,8 ksi |
| Shear modulus | 1,36 - 1,43 GPa / 0,197 - 0,207 x 10⁶ psi |
| Hardness (Indentation) | 261 - 285 MPa / 37,9 - 41,3 ksi |
| Fracture toughness | 2,73 - 4,30 MPa·m¹/² / 2,49 - 3,91 ksi·in¹/² |
| Fatigue strength (Endurance limit) | 28,1 - 41,2 MPa / 4,1 - 6,0 ksi |
| Poisson’s ratio | 0,38 - 0,39 |
| Resilience (Charpy impact, unnotched) | 55 kJ/m² / 26,2 ft·lb/in² |
| Bulk modulus | 5,48 - 5,75 GPa / 0,794 - 0,834 x 10⁶ psi |
Physical properties
Section titled “Physical properties”The density of PEEK at 23 °C is in the range of 1,30 to 1,32 Mg/m³ (81,2 to 82,4 lb/ft³), making it significantly lighter than most engineering metals. It exhibits very low water absorption, typically reaching 0,1% by weight during a 24-hour immersion.
| Property | Value (Metric / Imperial) |
|---|---|
| Density | 1,30 - 1,32 Mg/m³ / 81,2 - 82,4 lb/ft³ |
| Water absorption (24 h) | 0,1 % |
| Loss coefficient (Damping) | 0,0101 - 0,0106 |
| Abrasion resistance (Factor 1-5) | 3 (Good) |
| Natural color | Beige |
Thermal properties
Section titled “Thermal properties”PEEK exhibits a crystalline melting temperature of approximately 322 to 346 °C (611 to 655 °F), while its glass transition temperature ranges from 143 to 199 °C (269 to 390 °F). Its maximum continuous service temperature can reach 260 °C (500 °F), maintaining excellent resistance to thermal degradation.
| Property | Value (Metric / Imperial) |
|---|---|
| Glass transition temperature (Tg) | 416 - 472 K / 143 - 199 °C / 289 - 390 °F |
| Melting temperature (Tm) | 595 - 619 K / 322 - 346 °C / 611 - 655 °F |
| Maximum service temp. | 512 - 533 K / 239 - 260 °C / 462 - 500 °F |
| Minimum service temp. | 150 - 200 K / -123 to -73 °C / -190 to -100 °F |
| Thermal conductivity | 0,24 - 0,26 W/m·K / 0,45 - 0,49 BTU·ft/h·ft²·°F |
| Specific heat | 1443 - 1501 J/kg·K / 1,12 - 1,16 BTU/lb·°F |
| Coefficient of thermal expansion | 72 - 194 x 10⁻⁶ /K / 130 - 350 x 10⁻⁶ /°F |
Electrical properties
Section titled “Electrical properties”As a high-performance electrical insulator, PEEK has a very high dielectric strength of 16,7 to 20,0 MV/m (423 to 508 V/mil) and an extraordinarily high volume resistivity, typically greater than 10²¹·10⁻⁸ Ω·m.
| Property | Value (Metric / Imperial) |
|---|---|
| Dielectric strength | 16,7 - 20,0 MV/m / 423 - 508 V/mil |
| Dielectric constant | 3,1 - 3,3 |
| Volume resistivity | 3,3 x 10¹³ to 3 x 10¹⁴ Ω·m |
Applications by industry
Section titled “Applications by industry”The versatility of PEEK allows it to be processed by injection molding, extrusion, and machining, covering applications ranging from deep space to inside the human body.
| Industry | Typical applications |
|---|---|
| Aerospace | Structural brackets, clamps, engine components, and electrical insulators replacing aluminum to reduce weight. |
| Medical / Healthcare | Spinal implants (interbody cages), osteosynthesis screws, dental prostheses, and external fixators due to radiolucency and biocompatibility. |
| Oil & Gas | Seals, couplings, valve seats, and pipe supports operating in environments with high pressure, temperature, and exposure to aggressive chemicals. |
| Semiconductors | Retaining rings, wafer carriers, and connectors requiring low outgassing, high purity, and resistance to process chemicals. |
| Automotive | Bearings, gears, oil pump components, and under-hood parts exposed to high temperature and friction areas. |
| Chemical processing | Pump bodies, valves, and high-performance liquid chromatography (HPLC) components. |
Comparison with similar materials
Section titled “Comparison with similar materials”PEEK competes directly with other high-performance thermoplastics such as PEI (polyetherimide), PPS (polyphenylene sulfide), and PAI (polyamide-imide). Its strength lies in its ability to operate continuously at temperatures above 240 °C while maintaining mechanical integrity.
| Property | PEEK (Unreinforced) | PEI (Ultem 1000) | PPS (Ryton R-7) | PAI (Torlon 4203L) |
|---|---|---|---|---|
| Tensile strength | 100 MPa / 14,5 ksi | 105 MPa / 15,2 ksi | 86 MPa / 12,5 ksi | 152 MPa / 22,0 ksi |
| Glass transition temp. | 143 °C / 289 °F | 217 °C / 423 °F | 85 °C / 185 °F | 275 °C / 527 °F |
| Max. service temp. | 260 °C / 500 °F | 170 °C / 338 °F | 220 °C / 428 °F | 260 °C / 500 °F |
| Wear resistance | Excellent | Good | Good | Excellent |
| Relative cost (indicative) | High | Medium | Medium | Very high |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum service temperature of PEEK?
Section titled “What is the maximum service temperature of PEEK?”PEEK can withstand a continuous service temperature of up to 260 °C / 500 °F, with short-term peaks above 300 °C / 572 °F without significant loss of properties.
Is PEEK suitable for food contact and medical applications?
Section titled “Is PEEK suitable for food contact and medical applications?”Yes, specific grades of PEEK comply with FDA and USP Class VI regulations, being biocompatible and suitable for direct contact with food and bodily fluids in applications such as surgical implants and food processing components.
How does PEEK compare to metals in terms of weight and performance?
Section titled “How does PEEK compare to metals in terms of weight and performance?”With a density of approximately 1,32 g/cm³, PEEK is about 85 % lighter than steel and 50 % lighter than aluminum. Its strength-to-weight ratio is exceptional, allowing direct replacement of metals in structural and friction components.
Can PEEK be sterilized without degrading its properties?
Section titled “Can PEEK be sterilized without degrading its properties?”Absolutely. PEEK withstands hundreds of sterilization cycles via autoclave (steam at 134 °C / 273 °F), gamma radiation, and hydrogen peroxide plasma without degradation, making it an ideal material for reusable surgical instruments and implants.
What are the differences between virgin PEEK and fiber reinforced grades?
Section titled “What are the differences between virgin PEEK and fiber reinforced grades?”Carbon fiber (CF30) or glass fiber (GF30) reinforced grades dramatically increase stiffness (modulus of elasticity up to 20 GPa / 2,9 × 10⁶ psi) and wear resistance, but reduce elongation at break to less than 3 %. Virgin PEEK offers greater ductility and excellent base chemical resistance.
How is PEEK machined to produce precision parts?
Section titled “How is PEEK machined to produce precision parts?”PEEK is easily machined with conventional CNC equipment and carbide or diamond tools. It is crucial to use abundant coolant to dissipate heat and avoid local thermal stresses. Post-machining annealing at 250 °C / 482 °F is often necessary to relieve internal stresses and dimensionally stabilize the final part.
Sources Consulted
Section titled “Sources Consulted”- azom.com: https://www.azom.com/properties.aspx?ArticleID=1882
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/
- steelnumber.com: https://www.steelnumber.com/en/search_form_eu.php