Among plastic materials, polyetheretherketone (PEEK) is a very special engineering plastic. Its high-temperature resistance, corrosion resistance, wear resistance, and hydrolysis resistance make it highly sought after in aerospace, automotive, medical, energy, and power, as well as machinery. Below, we explain in detail what PEEK plastic is.
Definition of Polyetheretherketone Material
Polyetheretherketone, or PEEK, is a thermoplastic polymer that is only partially crystalline. It has aromatic rings, ether linkages, and ketone groups. It is the most commercially successful member of the polyaryletherketone (PAEK) family. The ether bonds (-O-) and ketone groups (-C(O)-) that connect its molecular chains form a very organized crystalline structure that gives it great mechanical and thermal stability. Victrex bought the related company from ICI in 1981, making it the most popular high-performance engineering plastic in the world. ICI first made it in the UK in 1978.
Benefits of Molecular Structure
The ether link makes the molecule more flexible, while the benzene ring makes it more stiff. The ketone group makes the intermolecular forces stronger. These three things work together to keep PEEK's structure stable at a melting point of 343°C and a long-term operating temperature of up to 260°C. This unusual structure lets it keep more than 90% of its original strength, even in very hot places like the nacelles of aircraft engines.
Rules for naming chemicals
The full name "Polyetheretherketone" describes the molecular chain structure: Poly (polymer) + ether (ether bond) × 2 + ketone (ketone group).
This naming scheme makes it clear what the chemical makeup is, and it is a common way to name things in materials science.
Core performance parameters of polyetheretherketone material
Physical and Mechanical Properties
| Property | Value Range | Technical Significance |
|---|---|---|
| Density | 1.3-1.35 g/cm³ | Only half the density of aluminum, significantly reducing equipment weight |
| Tensile Strength | 90-100 MPa (unfilled resin) | Comparable to aluminum alloy (6061-T6 has a tensile strength of 290 MPa) |
| Flexural Modulus | 3.6 GPa (unfilled resin) | Can reach 20 GPa with carbon fiber reinforcement, outperforming most engineering plastics |
| Elongation at Break | 30%-150% | Combines rigidity and toughness, capable of withstanding complex stresses |
Thermal Performance
Glass Transition Temperature (Tg): 143°C, higher than common engineering plastics (e.g., POM, which is -60°C).
Heat Deflection Temperature (HDT): 157°C (under a load of 1.8 MPa). Improved crystallinity after injection molding can push the HDT above 200°C.
Temperature Resistance: Withstands short-term temperatures of 300°C and can operate continuously at 250°C for 10,000 hours without significant degradation.
Chemical and Environmental Resistance
Corrosion Resistance: Completely inert to 98% of organic solvents (e.g., acetone, toluene) and acidic and alkaline solutions (pH 1-14), except concentrated sulfuric acid. No swelling after immersion in a 30% KOH solution for three years.
Hydrolysis Resistance: Withstood 3,000 sterilization cycles at 134°C with autoclave steam, with a weight loss of < 0.1%, far exceeding the standard for medical-grade stainless steel.
Flame retardant properties: It can achieve UL 94 V-0 rating without adding flame retardants, and the amount of smoke released when burning is only 1/5 of that of traditional plastics.
Manufacturing and processing technology of polyetheretherketone material
Polymerization Reaction Mechanism
A nucleophilic substitution polycondensation method is used, using 4,4'-difluorobenzophenone and sodium bisphenol A as raw materials. High-temperature polymerization is carried out in diphenyl sulfone solvent under the catalysis of anhydrous potassium carbonate. Note that this reaction requires a strictly controlled anhydrous environment (moisture content < 50 ppm). Microwave-assisted polymerization can shorten the reaction time from 24 hours in the traditional reflux method to 3 hours.
Key Molding Process Parameters
Injection Molding:
Mold Temperature: 160-190°C (to promote crystallization)
Melt Temperature: 370-420°C (to avoid thermal decomposition)
Injection Pressure: 70-140 MPa (to ensure filling of complex structures)
Note: The shrinkage of unfilled grades is 1.2-2.4%, while that of carbon fiber-reinforced grades can be reduced to 0.1-1.1%.
3D Printing Technology:
When using FDM, the nozzle temperature should be controlled between 360-400°C, and the heated bed maintained at 120°C to minimize warping.
The use of polyetheretherketone material
Aerospace
The Airbus A350 cargo hold drainage system uses Victrex PEEK composite material instead of aluminum alloy, reducing weight by 50%. It also withstands extreme temperature fluctuations from -50°C to 120°C and has passed 100,000 cycle fatigue testing. Its low smoke and low toxicity (SDR ≤ 15) meet FAR 25.853 fire protection standards, making it the preferred material for next-generation passenger aircraft interiors.
Medical
Orthopedics:
The elastic modulus of carbon fiber-reinforced PEEK interbody fusion cages (8-12 GPa) closely matches that of human cortical bone (10-30 GPa), effectively reducing stress shielding. The US FDA has approved it for use in over 20 types of implants, including those in the cervical and lumbar spine.
Electrosurgical Instruments:
Solvay's KetaSpire® PEEK powder is sprayed onto the surface of metal cannulas, achieving a coating thickness of only 0.0645mm. It withstands voltages exceeding 10kV and 1,000 cycles of ethylene oxide sterilization. It is already used in core components of the da Vinci surgical robot.
Food Processing Machinery Components
Polyetheretherketone (PEEK) is a material that is resistant to cleaning and disinfection (releasing no harmful substances), exhibits low surface migration and abrasion resistance, and complies with food contact standards. Typical applications include valve cores in dairy production lines, conveyor belt links in bakery equipment, and filter support frames in juice presses.
Bushings, Bearings, Seals, and Support Rings
Polyetheretherketone (PEEK) is replacing metal and traditional plastics in moving parts thanks to its combined advantages of low friction, high load capacity, and corrosion resistance.
Bushings and Bearings: Carbon fiber-reinforced PEEK boasts a coefficient of friction as low as 0.15 (dry friction conditions), 40% lower than bronze bearings. At a load of 10 MPa and an environment of 150°C, its wear rate is only 0.001 mm³/(N·m), making it suitable for chemical pump bushings and automotive transmission bearings.
Seals and Support Rings: In the acidic environment of crude oil extraction (containing H₂S and CO₂), PEEK V-rings offer a sealing life 10 times that of nitrile rubber. A hydraulic equipment manufacturer employed PEEK support rings to overcome the creep failure problem of traditional PTFE rings at 30 MPa pressure, extending their service life from 3,000 hours to 15,000 hours.
Comparison between Polyetheretherketone Material and Similar Materials
| Performance Indicator | PEEK | PTFE | PEI | PI |
|---|---|---|---|---|
| Long-term Service Temperature | 260°C | 250°C | 210°C | 300°C |
| Tensile Strength | 90-100 MPa | 25-35 MPa | 100-110 MPa | 80-100 MPa |
| Coefficient of Friction | 0.35-0.45 | 0.03-0.05 | 0.25-0.35 | 0.2-0.3 |
| Dielectric Strength | 50 kV/mm | 50-150 kV/mm | 30-40 kV/mm | 20-30 kV/mm |
| Processing Cost | Extremely high | Moderate | Moderate | Extremely high |
Recommended Selection:
For high-temperature and high-pressure applications: PEEK (heat and hydrolysis resistance) is preferred.
For ultra-low friction requirements: PTFE is preferred, but strength is compromised.
For high-frequency insulation: PEI offers a more cost-effective option, but its temperature resistance is limited.
FAQ
Q: Can PEEK be recycled?
A: Currently, the recycling rate is less than 10%, primarily due to the high energy consumption of high-temperature processing and a 30% degradation in the properties of the recycled material. Victrex is developing closed-loop recycling technology that uses supercritical fluid depolymerization to increase the recycling rate to 85%.
Q: How is PEEK bonded to metal?
A: Chemical anchors (such as 3M DP460 epoxy adhesive) or physical inserts (molded metal inserts) can be used. An automotive manufacturer uses a PEEK piston unit with an interference fit in an aluminum alloy cylinder, which has operated at 200°C for 10,000 hours without loosening.
Q: What are the limitations of PEEK in the semiconductor industry?
A: Although it can achieve 99.999% purity, particle release (>0.1μm) must be controlled to <100 particles/g. Currently, it is only used in non-critical processes such as wafer carriers. Toray Industries' newly developed ultra-clean grade PEEK, with a particle content of less than 10 particles/g, has entered testing on 14nm chip production lines.
Q: Is PEEK suitable for long-term outdoor use?
A: Pure PEEK has average UV resistance and may suffer from surface chalking (approximately 10% degradation over 5 years) after prolonged exposure to sunlight. However, the addition of carbon black or UV absorbers can improve weather resistance by 3-5 times, making it suitable for high-temperature connectors in photovoltaic power plants and outdoor high-voltage switchgear.
Q: Can PEEK be welded? What are some common welding methods?
A: Yes, it can be welded. Common methods include: ① Hot plate welding (suitable for flat components, with weld strength reaching 80% of the parent material); ② Laser welding (with accuracy up to 0.1mm, suitable for sterile seams in medical devices); and ③ Ultrasonic welding (highly efficient, used for electronic component packaging). The welding temperature must be controlled between 343-380°C (above the melting point but below the decomposition temperature).
Q: What is the difference between food-grade PEEK and standard PEEK?
A: Food-grade PEEK must pass stringent migration tests (such as EU Directive 10/2011, which stipulates a full migration limit of < 10mg/dm²). Heavy metal catalysts are prohibited during production, and the purity is higher (ash content < 0.01%). Ordinary PEEK may not be suitable for food contact applications due to residual additives.
Q: Will the performance of recycled PEEK material degrade?
A: The tensile strength of recycled PEEK will decrease by 15-20%, and its crystallinity by 5-8%, primarily due to molecular chain breakage caused by heavy processing at high temperatures. Currently, recycled material is only used in non-critical structural parts (such as protective covers and brackets). High-end applications (such as medical and aviation) still require virgin material.