Name: poly(ether-ether-ketone)
Abbreviation: PEEK
Long-term Operating Temperature: 260℃

 

Polyetheretherketone is an aromatic semicrystalline linear thermoplastic polymer. Its molecular chain contains benzene rings, ether bonds, and carbonyl groups, with paraphenylene groups connected by oxygen bridges (ether and ketone). This unique chemical structure gives PEEK stable physical and chemical properties, resulting in excellent properties such as heat resistance, radiation resistance, chemical resistance, and high mechanical strength.

The key to synthesizing polyetheretherketone lies in preparation of monomer 4,4-difluorobenzophenone. There are six methods for synthesizing 4,4-difluorobenzophenone: benzene condensation, halogen exchange, catalytic carbonylation, dichloroethylene oxidation, Friedel-Crafts alkylation, and diazotization. Friedel-Crafts alkylation and diazotization are the most commonly used methods. Following synthesis equation uses Friedel-Crafts alkylation method:

 

PEEK resin is primarily derived from polycondensation reaction of 4,4-difluorobenzophenone and sodium hydroquinone using diphenyl sulfone as solvent. Synthesis equation is as follows:

 

Polyetheretherketone prepared by this method exhibits very stable thermal properties.

Heat Resistance: PEEK resin is a semi-crystalline polymer. Its glass transition temperature (Tg) is 143℃ and its melting point (Tm) is 334℃. While heat deflection temperature of pure resin is only 152℃, it can reach 300℃ when reinforced with 30% glass fiber (GF) or carbon fiber (CF).
Mechanical Properties: It exhibits high strength and high modulus, with tensile strength exceeding 100 MPa, excellent flexural strength and modulus, as well as good toughness and impact resistance. It maintains high strength even at high temperatures, resulting in overall mechanical properties superior to other thermoplastic resins.
Flame Retardancy: PEEK is self-extinguishing. Unflammable PEEK with a thickness of 0.8-1.6 mm achieves UL94 V-0 rating. It also produces very little smoke under forced combustion and produces no toxic gases.
Hot Water Resistance: Hot water and steam resistance are among PEEK's most significant characteristics. After immersion in 80℃ hot water for 800 hours, its tensile strength and elongation at break remain essentially unchanged. In steam at 200℃, its tensile strength and appearance remain unchanged, allowing it to be used in steam for extended periods. Among all engineering plastics, PEEK has the highest steam resistance.
Electrical Properties: PEEK resin has a volume resistivity of 1016 Ω.cm and a low dielectric loss tangent at high frequencies. It maintains excellent electrical insulation properties even in harsh environments such as high temperature, high pressure, and high humidity.
Radiation Resistance: PEEK exhibits strong radiation resistance. Its resistance to gamma rays is the best among all engineering plastics. PEEK begins to become brittle after absorbing a gamma-ray dose of 1.0-1.2 × 107 Gy; it is unaffected by beta-rays of 0.1-12 × 106 Gy.
Self-lubricating Properties: PEEK has very high self-lubricating properties, making it suitable for applications requiring a low coefficient of friction and high wear resistance. PEEK modified with carbon fiber, graphite, or PTFE exhibits exceptional wear resistance.
Biocompatibility: PEEK is inherently non-toxic, safe, and non-allergenic, with excellent physiological compatibility. Implantable-grade PEEK has undergone comprehensive biocompatibility testing at an independent international testing facility in strict accordance with ISO 10993 requirements. Results demonstrate excellent biocompatibility and no side effects.
Easy Processing: It exhibits excellent high-temperature fluidity and a high thermal decomposition temperature. It can be processed using a variety of methods, including injection molding, extrusion, compression molding, blow molding, melt spinning, rotational molding, and powder coating, to produce components with complex geometries.

Easy Processing: It exhibits excellent high-temperature fluidity and a high thermal decomposition temperature. It can be processed using a variety of methods, including injection molding, extrusion, compression molding, blow molding, melt spinning, rotational molding, and powder coating, to produce components with complex geometries.

PEEK is commonly used in three forms: granules, powder, and fine powder. Granular PEEK is generally used for injection molding, extrusion of monofilaments, wire coatings, and profiles. Powder is used for composite extrusion granulation for reinforcement and filling, and compression molding often uses fine powder PEEK.
▶ Injection Molding
Injection molding is a commonly used PEEK polyetheretherketone (PEEK) molding process. Injection molding involves heating and melting PEEK powder or granules, then injecting molten material into a mold using an injection molding machine. Injection molding can produce a variety of shapes, such as parts, pipes, and plates.

▶ Extrusion Molding
Extrusion molding involves heating and melting PEEK polyetheretherketone (PEEK) and then extruding molten material through an extruder to form various shapes, such as plates, rods, and pipes. Extrusion molding is suitable for mass production of large, complex parts of same shape.
Unstretched PEEK film has a low degree of crystallinity. However, after stretching and heat treatment, its melting point rises significantly, and its mechanical strength is greatly improved. Its performance is between that of PET film and Kapton, a polyimide film, and it is classified as a Class C insulation material. PEEK film has excellent transparency. According to data from PEEK film produced by Sumitomo Chemical Industries, Ltd. in Japan, its light transmittance can reach approximately 85%.

▶ Pressing Molding
Pressing molding involves placing PEEK (polyetheretherketone) powder or granules into a mold, melting them under high temperature and high pressure, and then pressing them into shape. Pressing molding is suitable for manufacturing complex-shaped parts or small-batch production.
▶ Extrusion Molding
Spraying molding involves heating and melting PEEK granules, then spraying them onto a substrate using a spraying machine to form a coating. Spraying molding involves spraying a PEEK (polyetheretherketone) solution onto mold surface, drying it to form a thin film, then hot pressing it into shape. Spraying molding is suitable for manufacturing complex-shaped parts, thin-walled structures, surface coatings, films, and other products.

The most critical type of PEEK modification is reinforced products with glass and carbon fibers. This reinforcement significantly enhances PEEK's mechanical strength, rigidity, and temperature resistance. Following introduces new PEEK grades and PEEK alloys that have been developed in recent years.
▶ Conductive PEEK
In recent years, materials used in the manufacturing of semiconductors, LCD glass substrates, and integrated circuit wafer holders must not only possess high toughness, dimensional stability, and lightweight properties, but also possess antistatic properties during high-temperature processing. To meet these stringent requirements, Mitsui Tosu Chemicals Co., Ltd. of Japan has successfully developed a new conductive PEEK material, KNE5010. This material significantly reduces PEEK's surface resistivity from 1016Ω to 108-1010Ω while retaining many of PEEK's inherent excellent properties.

Performance of Conductive PEEK Grades
▶ High-Strength PEEK
In 1994, Mitsui Tosu Chemicals Co., Ltd. of Japan successfully developed a new high-strength PEEK grade, PKU-CF30. This new material, a composite reinforced with specially treated carbon fibers, boasts exceptional mechanical strength and modulus. Its tensile strength reaches 284 MPa, only slightly lower than that of aluminum alloys, while its specific strength, at 206 MPa, far exceeds that of aluminum alloys.

Comparison of Performance of High-Strength PEEK PKU-CF30 with Other Materials
Injection-molded impellers for automotive turbines made with PKU-CF30 can reduce their weight by half compared to those made with aluminum alloys. Furthermore, resulting product boasts high strength, excellent heat resistance, and excellent fatigue resistance. It is a high-performance yet affordable injection-molded product and is currently used in Nissan's flagship turbine vehicles.
▶ PEEK Alloys
PEEK resin is relatively expensive. For a heat-resistant polymer, its glass transition temperature (143℃) is somewhat low. Above glass transition temperature, its strength and modulus decrease rapidly, and glass fiber reinforcement or alloying are often used to improve it. PEEK can be blended with non-crystalline, high-glass-transition-temperature resins such as PSF, PEI (polyetherimide), and PES to create alloys with higher glass transition temperatures. For example, a polymer alloy made by blending PEEK and PEI at a 50/50 (by mass) ratio achieves a glass transition temperature of 180℃, 37℃ higher than PEEK. While absolute crystallinity and crystallization rate of PEEK decrease at this point, crystallinity remains. For PEI, addition of PEEK improves its solvent resistance.
Blending PEEK with PPS not only improves fluidity of PEEK melt and raises its glass transition temperature, but also reduces costs.
Different varieties of polyaryletherketones can be blended to form polymer alloys, such as PEEK and PEK. Melting points and glass transition temperatures can be adjusted by varying ratio of ether to ketone in their molecular structures. Polymer alloys formed with PEEK and LCP (liquid crystal polymer) significantly suppress loss of strength and modulus above glass transition temperature of PEEK. Compared to PEEK, PEEK/LCP alloys exhibit increased helical flow length and improved formability.

PEI processing does present numerous challenges. While unique properties of plastics offer certain advantages, these characteristics also present several considerations that must be addressed to ensure optimal results.

 

 

▶ Aerospace
Applications: Aircraft engine components, wing structures, satellite parts, etc.
Purpose: Due to its excellent weather resistance and high-temperature resistance, PEEK is widely used in aircraft radar components, radomes, and engine parts, ensuring reliability in extreme climates and high-temperature environments. Carbon fiber or glass fiber reinforced PEEK is also used to manufacture door handles, cabin panels, control levers, and helicopter tails for aircraft and spacecraft, significantly improving strength and durability of these critical components.

 

French Rafale fighter fuselage skin

 

US stealth helicopter LHX rotor and missile shell

 

US V-22 Osprey aircraft front landing gear door

 

F117B stealth bomber fully automatic tail

 

U. S. C-130 transport aircraft fuselage belly panel

APC-2 composite material made from PEEK by UK-based ICI company boasts significantly greater toughness than traditional epoxy composites, exceeding 10 times. This material has a wide range of applications, including large components such as space stations and aircraft wings, as well as other products, and can replace epoxy resins. ICI also uses glass-fiber-reinforced PEEK (PEEK) through injection molding to manufacture rocket igniter tubes. This new material not only reduces costs but is also particularly well-suited for intense ignition and launch environments of rockets, replacing traditional metal materials.
▶ Medical Devices
Applications: Manufacturing artificial joints, spinal implants, dental restorations, etc.
Benefits: PEEK material has excellent biocompatibility and does not provoke an immune response in human body. Compared to traditional metal implant materials, PEEK has a lower elastic modulus and mechanical properties closer to those of human bone, reducing stress shielding and promoting bone tissue growth and healing.

 

Spinal surgery interbody PEEK fusion cage

 

Spinal surgery PEEK suture rivets
As the largest PEEK material manufacturer, Victrex has been researching and developing PEEK medical implants since 1989 and holds relevant patent [DE69032928D1]. Over time, many companies around the world have invested in research on PEEK biomedical materials, and a variety of PEEK biomedical materials are now commercially available. Following are some of main PEEK biomedical materials and their characteristics:
Victrex's PEEK-OPTIMA® series of materials: Produced by Victrex's subsidiary Invibio, these materials are widely used in medical field due to their excellent biocompatibility and mechanical properties.
Solvay's Solviva series of biomaterials: Solvay has launched the Solviva series, which includes Zeniva, a material with high strength, stiffness, toughness, fatigue resistance, and biostability, meeting ASTM F2026-07 standard for PEEK for surgical implants.
Evonik's VESTAKEEP® implantable-grade PEEK: Evonik's VESTAKEEP® implantable-grade PEEK has demonstrated excellent biocompatibility and no side effects in domestic and international testing, making it another PEEK material used in medical field.
▶ Automotive Manufacturing
Applications: Engine inner covers, bearings, gaskets, seals, clutch rings, and other automotive parts.
Purpose: PEEK's excellent friction resistance and mechanical properties make it a suitable alternative to metal in manufacturing of automotive parts.

 

▶ Electronics and Electrical
Applications: Wire sheathing, magnetic wire sheathing, high-temperature terminal blocks, motor insulation, integrated circuit wafer holders, etc.: ① Wire sheathing; ② Magnetic wire sheathing; ③ High-temperature terminal blocks; ④ Motor insulation; ⑤ Integrated circuit wafer holders.
Purpose: PEEK offers excellent dimensional stability, high purity, high mechanical properties, and superior electrical properties, making it used in manufacture of various high-performance components in electronics and electrical industries.

 

Circuit Board

 

Electronic Connectors
▶ Energy
Applications: Nuclear industry components, oil and gas extraction equipment, etc.
Purpose: PEEK meets high-performance material requirements of these industries, such as radiation resistance, excellent electrical properties at high temperatures, and outstanding mechanical strength.
▶ Semiconductor Industry
Applications: High-performance plastic parts such as CMP retaining rings, wafer carriers, and wafer clamps.
Purpose: PEEK can withstand temperatures up to 260℃ and corrosion from various chemicals, reducing wafer cooling time, improving production efficiency, and increasing wafer yield.

 

CMP Retaining Ring

 

Semiconductor Test Socket

 

Global PEEK market is projected to grow from 4.9 billion yuan in 2022 to 8.4 billion yuan in 2027, achieving a compound annual growth rate of 11.38%. In China, PEEK market demand is expected to exceed 5,000 tons by 2027, reaching a market size of 2.838 billion yuan (market size growth). National policies are increasingly supporting new materials industry. For example, National Raw Materials Industry Symposium held in June 2024 proposed building new growth engines such as new materials. As a key new material, PEEK is expected to benefit from these policies and receive increased support for R&D and industrialization (policy support). With continued expansion of PEEK's application in emerging fields such as humanoid robots, its market demand is expected to grow further. Humanoid robots' requirements for lightweight, high strength, and high precision are highly compatible with PEEK's performance. Domestic manufacturers have already incorporated PEEK into humanoid robot components such as joints, bearings, and gears, forming a supporting production chain (emerging field expansion).