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PEEK (Polyetheretherketone): A Comprehensive Guide

Polyetheretherketone (PEEK) is an advanced engineering thermoplastic widely recognized for its outstanding overall performance, making it the material of choice in demanding environments across various industries. From aerospace to medical implants, PEEK’s applications are extensive and significant, with its high-temperature performance, mechanical strength, and chemical stability excelling in high-end applications.
This article will explore in depth the definition, characteristics, production process, and key applications of PEEK in various industries, providing a comprehensive understanding of this high-performance polymer.

What Is PEEK?

peek powder

Polyetheretherketone (PEEK) is a high-performance engineering thermoplastic from the polyaryletherketone (PAEK) family, renowned for its outstanding comprehensive properties, making it suitable for various demanding applications across industries. PEEK is a semi-crystalline, colorless organic polymer known for its excellent mechanical, thermal, and chemical resistance, maintaining its properties even at high temperatures.

What Is the Origin of PEEK Material?

The origin of PEEK material dates back to the 1960s with the first patent related to PEEK. It was developed by the British company ICI (Imperial Chemical Industries). The patent for PEEK was officially filed in 1978, marking a significant milestone in the development of this high-performance polymer.

How Is PEEK Produced?

PEEK, or polyetheretherketone, is produced through a process known as step-growth polymerization. This process involves the dialkylation of bisphenol salts, where monomers such as 4,4′-difluorobenzophenone and hydroquinone react in the presence of alkali carbonates to form high molecular weight polymers. This controlled polymerization ensures the material’s uniformity and consistency.

What Are the Key Features of PEEK?

The main characteristics of PEEK include:

  • High-temperature performance: PEEK operates at temperatures up to 260°C (480°F) with a melting point around 341°C (646°F). It maintains high physical properties, such as flexural and tensile strength, even in harsh environments.
  • Exceptional mechanical strength and toughness: PEEK offers great mechanical strength, including high tensile strength and fatigue resistance. It also exhibits resistance to bending and compressive stresses, making it suitable for applications requiring stability.
  • Outstanding chemical resistance: PEEK withstands a variety of chemicals, including acids, bases, organic solvents, and other agents, making it ideal for use in harsh chemical environments.
  • Wear resistance: PEEK exhibits excellent wear resistance and abrasion resistance, ideal in many engineering fields, including applications requiring low friction coefficients, such as bearings and sliding bearings.
  • Stability in aqueous environments: PEEK retains its properties in hot water or steam, making it very suitable for high temperature and high pressure applications.
  • Dimensional stability: PEEK’s unique chemical structure provides excellent dimensional stability under load and in harsh environments.
  • Biocompatibility: PEEK is biocompatible, suitable for direct contact with human tissue, thus used in medical implants.
  • Radiolucency: In medical applications, PEEK’s radiolucency allows for clear post-surgical imaging without interference.
  • Low thermal conductivity: PEEK’s low thermal conductivity is advantageous in applications requiring thermal insulation, such as in fused filament fabrication (FFF) printing, where it thermally separates the hot end from the cool end.
  • Flame retardant: PEEK has inherent flame retardant properties, reaching a V-0 burning rate in flammability tests without the need for additives.
  • Hydrolysis resistance: PEEK and its composites are not chemically affected by water and high-pressure steam, maintaining excellent performance even in high temperature and high pressure environments continuously.

What Is the Color of PEEK?

PEEK’s natural color is a very light brown or tan. However, depending on the specific formulation and the addition of pigments or dyes, it is available in various colors, including black, white, yellow, blue, blue-gray, light gray, and navy blue.

What Are the Common Grades of PEEK?

Common grades of PEEK include:

  1. Unfilled PEEK: This general-purpose grade has the highest elongation and toughness among all PEEK grades. It is available in natural (light brown or tan) and black colors and is known for its excellent chemical resistance, extremely low moisture absorption, and good wear resistance. It has been approved by the U.S. Food and Drug Administration (FDA) for food contact applications.
  2. 30% Glass-Filled PEEK: This grade contains glass fibers, which reduce the expansion rate and increase the flexural modulus, making it very suitable for structural applications requiring increased strength, stiffness, or stability, especially at temperatures above 150°C (300°F).
  3. 30% Carbon-Filled PEEK: The addition of carbon fibers enhances compressive strength and stiffness, significantly reduces expansion rate, and increases thermal conductivity by 3.5 times compared to unfilled PEEK. This grade is very suitable for applications requiring the best wear resistance and load-bearing capacity.
  4. Bearing Grade PEEK (Ketron HPV): This grade offers low friction, low wear, high limit PV values, low mating part wear, and ease of machining. It is typically black or dark gray and is used for bearings and other applications requiring high friction resistance and durability.
  5. High-Temperature PEEK (PEEK HT): Designed for applications requiring mechanical performance at higher temperatures than typical PEEK materials can withstand.
  6. Semitron ESd 480: An electrostatic dissipative grade, designed for electronic manufacturing applications requiring electrostatic dissipative (ESD) properties.
  7. Ceramic Filled PEEK: Offers better wear resistance and thermal performance.
  8. Medical Grade: Such as PEEK-LSG, PEEK-CA30 LSG, PEEK-GF30 LSG, and PEEK-CLASSIX LSG, designed specifically for medical applications.

What Is the Price of PEEK?

PEEK is 5 to 8 times more expensive than other high-end polymers, with a price of $4,500 per pound.

What Are the Physical Properties of PEEK Material?

The physical properties of PEEK material include:

  1. Density: PEEK has a density of about 1.32 g/cm³.
  2. Water Absorption: Extremely low water absorption, typically about 0.1% within 24 hours.
  3. Melting Point: PEEK melts at about 343°C (649.4°F).
  4. Glass Transition Temperature: PEEK’s glass transition temperature is around 143°C (289°F).

What Are the Chemical Properties of PEEK Material?

The chemical properties of PEEK include:

  1. Chemical Resistance: PEEK withstands hydrocarbons, acids, and solvents. It maintains its integrity when exposed to harsh chemical environments without significant degradation.
  2. Hydrolysis Resistance: PEEK does not undergo hydrolysis, meaning it can withstand thousands of hours in steam or high-pressure water without significantly reducing its performance. This makes it suitable for applications involving hot water or steam.
  3. Insolubility: It is insoluble in all common solvents, thus exhibiting excellent chemical stability and tolerance.
  4. Biodegradability Resistance: PEEK has strong resistance to biodegradation, ensuring long-term durability and reliability in various applications.
  5. Stability in Concentrated Sulfuric Acid: Although PEEK tolerates most chemicals, it is soluble in concentrated sulfuric acid at room temperature. However, dissolution takes a long time unless the polymer has a high surface area to volume ratio, such as fine powder or thin film.

What Are the Applications of PEEK Material?

PEEK is a versatile high-performance thermoplastic with excellent mechanical properties, chemical resistance, and thermal stability, widely used across various industries. Key applications of PEEK material include:

  1. Aerospace Industry:
    • PEEK is used for critical engine components, aircraft exterior parts resistant to rain erosion, and internal components due to its inherent flame retardancy, low smoke, and toxic gas emissions. It is also used in the manufacture of coiled tubing to protect aircraft electrical systems’ wires and optical fibers.
  2. Automotive Industry:
    • In the automotive industry, PEEK is used to manufacture under-the-hood piston assemblies, seals, washers, bearings, and various active components for transmission, braking, and air conditioning systems. Its properties help improve fuel efficiency and reduce noise.
  3. Medical Industry:
    • As an advanced biomaterial with biocompatibility and hydrolysis resistance, PEEK is used for medical implants, including reinforcement rods, spinal fusion devices, surgical instruments, and can withstand up to 3,000 high-pressure sterilization cycles. PEEK is also used in dental instruments, endoscopes, and dialyzers.
  4. Electronics and Semiconductor Industry:
    • Due to its excellent electrical insulation properties, PEEK is used in mobile phones, laptops, gaming devices, and semiconductor manufacturing equipment. It is also used to produce wafer clamps, suction cups, and other components requiring high purity and low outgassing performance.
  5. Food Industry:
    • PEEK meets stringent food contact material requirements, thus suitable for food packaging and processing equipment. It is used in components requiring resistance to extreme temperatures and chemicals, such as oven parts and other components.
  6. Oil and Gas Industry:
    • In the oil and gas industry, PEEK’s chemical resistance and ability to withstand high temperatures and pressures are essential. Its applications include seals, washers, and various components used during drilling and extraction processes.
  7. General Industrial Applications:
    • PEEK is used for various industrial applications, including bearings, piston parts, pumps, high-performance liquid chromatography columns, compressor plate valves, and cable insulation. Its durability, wear resistance, and resistance to harsh environments make it suitable for multiple industrial uses.

What Are the Benefits of PEEK Material?

PEEK material offers a wide range of advantages, making it a favored polymer in various high-performance applications:

  1. High-Temperature Resistance: PEEK has excellent high-temperature resistance, maintaining superior mechanical strength and stability even at high temperatures. This characteristic makes it particularly suitable for applications in the aerospace, automotive, and electrical industries that require high-temperature resistance.
  2. Chemical Resistance: Polyetheretherketone offers outstanding resistance to acids, solvents, and hydrocarbons. This chemical resistance ensures the material’s durability and integrity in harsh chemical environments, making PEEK suitable for chemical processing, oil and gas, and medical industries.
  3. Mechanical Strength: PEEK has excellent mechanical properties, including high rigidity, toughness, and wear resistance. Even under heavy loads and harsh conditions, it exhibits low friction and excellent dimensional stability, making it ideal for gears, bearings, seals, and structural components.
  4. Electrical Insulation: Polyetheretherketone is an excellent electrical insulator, widely used in the electrical and electronics fields. Its electrical properties remain stable across a broad temperature range, allowing it to perform reliably in challenging environments.
  5. Fuel Reduction and Extended Part Life: Compared to metals, PEEK helps reduce fuel and has a longer service life, making it a cost-effective and durable choice for various applications.
  6. Safety: Due to its low conductivity, PEEK reduces heat buildup, thus enhancing safety in applications requiring high electrical insulation and thermal resistance.
  7. Wear Resistance: PEEK’s wear and abrasion resistance are beneficial for applications involving moving parts, such as bearings and gears.
  8. Low Moisture Absorption: PEEK’s extremely low moisture absorption ensures excellent dimensional stability and performance in humid environments.
  9. Biocompatibility: PEEK is biocompatible, making it suitable for medical implants and devices. When in contact with body tissue, it does not produce adverse reactions.
  10. Resistance to Biodegradation: PEEK has strong resistance to biodegradation, ensuring long-term durability and reliability in various applications.
  11. Machinability: Despite its high melting point, polyetheretherketone can still be machined to produce precision parts with tight tolerances through processes such as CNC machining.

What Are the Limitations of PEEK Material?

The limitations of PEEK material include:

  1. High Processing Temperature: PEEK requires high temperatures for processing, complicating the manufacturing process and increasing production costs.
  2. Cost: Expensive, making it less suitable for applications where budget limitations or cost-effectiveness are key factors.
  3. Degradation at Specific Temperatures: PEEK degrades at temperatures between its glass transition and melting temperatures. This degradation could occur within the body, posing risks for biomedical applications.
  4. Low Surface Energy: Polyetheretherketone’s low surface energy reduces cell adhesion, a significant drawback for medical implants requiring tissue integration.
  5. Chemical Sensitivity: Although PEEK withstands a variety of chemicals, it is vulnerable to certain acids, such as concentrated sulfuric acid, limiting its use in some chemical environments.
  6. Manufacturing Challenges: The characteristics that make it an ideal material also present manufacturing challenges, such as the need for specialized equipment and processes due to its high melting point.
  7. Biological Inertness: PEEK’s hydrophobic surface leads to its biological inertness, which may cause poor bone integration with the host bone tissue in orthopedic applications, leading to complications such as implant displacement and pseudoarthrosis.

Is PEEK Stronger Than Steel?

No, PEEK is not stronger than steel. Although polyetheretherketone has excellent mechanical properties, including high tensile strength and wear resistance, its strength and durability do not surpass steel. Stainless steel, in particular, has much greater toughness, able to withstand greater impact forces without breaking or bending.

Is PEEK Plastic Toxic?

No, PEEK plastic is not toxic. Even when heated, it does not produce significant smoke or harmful fumes, and contact with any form of PEEK does not pose serious health risks. The only known health issue is the risk of burns from high temperatures or molten PEEK during processing, which is treated like other thermal burns, with no special considerations beyond typical burn treatment protocols.

PEEK vs PEK vs PTFE

When comparing PEEK, PEK, and PTFE, it is essential to understand their different properties and applications to determine which material is best suited for a specific use. Here is a detailed comparison based on the provided information:

PEEK (Polyetheretherketone)

  • Properties: PEEK is a semi-crystalline thermoplastic with excellent chemical resistance, extremely low moisture absorption, excellent mechanical strength, and good dimensional stability across a wide temperature range. It is strong, has good rigidity, and excellent creep resistance. In demanding high-pressure and high-temperature (HPHT) environments, PEEK maintains its properties.
  • Applications: Commonly used in chemical processing, semiconductor manufacturing, oil and gas applications, medical implants, healthcare equipment, and various electronic devices. Its reliability under high temperature and pressure conditions makes it valuable in industrial bearings, pistons, pumps, oilfield and gas equipment, and other applications.

PEK (Polyetherketone)

  • Properties: PEK is similar to PEEK but can operate more reliably at temperatures up to 30˚C higher while maintaining dimensional stability and performance properties. It has good resistance to material fatigue and creep, making it suitable for electrical applications requiring reduced thermal expansion and enhanced chemical resistance.
  • Applications: Ideal for applications under vibration or cyclic load conditions, where components must withstand high mechanical loads at high temperatures over long periods, such as in the aerospace and automotive industries for gears, shafts, bushings, bearings, and precision parts.

PTFE (Polytetrafluoroethylene)

  • Properties: Polytetrafluoroethylene differs from polyetherketone, belonging to the fluoropolymer family. It has excellent chemical resistance, particularly to strong acids, very low friction coefficient, low moisture absorption, and high electrical resistance. Compared to PEEK and PEK, it is softer and more elastic at low temperatures.
  • Applications: Used for specialty seals, bearings, bushings, various market electrical components, and high-purity grade fluid handling systems in semiconductor manufacturing. Polytetrafluoroethylene is popular in applications requiring operating temperatures from -350F to 500F and is known for its self-lubricating properties, making it the preferred choice in high-wear applications.

In summary, the choice between PEEK, PEK, and PTFE depends on the specific requirements of the application, including temperature resistance, mechanical strength, chemical resistance, and cost factors. PEEK and PEK are more suitable for high-strength, high-temperature applications, while PTFE is favored for its chemical inertness and low friction in non-high mechanical load applications.

Conclusion

PEEK stands out as a versatile and high-performance material with a broad range of applications across various industries. Its exceptional properties such as high-temperature resistance, chemical resistance, mechanical strength, and biocompatibility make it an ideal choice for challenging environments.
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