What Is PAEK?
Poly(aryl ether ketone)s (PAEKs) are a family of high-performance thermoplastic polymers characterized by excellent thermal stability, chemical resistance, and mechanical properties. They consist of aromatic backbones interconnected by ether and ketone linkages. The two most common members of the PAEK family are:
- Polyether ether ketone (PEEK): A semi-crystalline polymer with recurring units of :
- Polyether ketone ketone (PEKK): A semi-crystalline polymer with recurring units of :
The ratio and sequence of ether and ketone groups in the polymer backbone determine the glass transition temperature (Tg) and melting point (Tm) of the material. Generally, a higher ketone content results in a more rigid polymer chain, leading to higher Tg and Tm values.
Properties of PAEK
Thermal and Crystallization Properties
- Glass transition temperatures (Tg) typically >155°C
- Melting temperatures (Tm) range from ~300°C to ~400°C, depending on composition
- Exhibit slow crystallization kinetics, with crystallization half-times >12 min at 280°C
- Crystallinity and crystallization rate influenced by thermal history and presence of fillers
Mechanical Properties
- High tensile strength (e.g. 42.6 MPa for photocured PAEK )
- Excellent dimensional stability and creep resistance
- Stiffness and strength can be tailored by varying composition and crystallinity
- Carbon fiber-reinforced PAEK composites exhibit exceptional strength-to-weight ratios
Other Key Properties
- Excellent chemical and solvent resistance
- Low flammability and smoke emission
- Good biocompatibility for medical implants
- The high free volume enables good gas separation performance
Production of PAEK
PAEK Production Methods
PAEKs, particularly PEEK, can be manufactured by nucleophilic polycondensation of bisphenols with organic dihalide compounds in a suitable solvent in the presence of alkali metal carbonates and/or bicarbonates or alkaline earth metal carbonates and/or bicarbonates. This process is described in patents like EP0001879A, EP0182648A, EP0244167A, and EP3049457A. WO2018055384 also discloses a method for manufacturing PAEKs.
PAEK Powder Processing for Additive Manufacturing
For additive manufacturing applications, PAEK powders undergo annealing treatment at a temperature exceeding the glass transition temperature by at least 20 °C for at least 30 minutes before being used as a construction material. This treatment makes the powder suitable for layer-wise manufacturing of three-dimensional objects.
Additive Manufacturing of PAEK Composite
Additive manufacturing systems can print 3D objects using a combination of at least one PAEK polymer and at least one poly(aryl ether sulfone) (PAES). The part material can incorporate PAEK and PAES in the form of filaments or spherical particles.
Pros and Cons of PAEK material
Advantages of PAEK Materials
- Excellent Thermal and Chemical Resistance: PAEK materials, including PEEK and PEKK, exhibit exceptional thermal stability and resistance to a wide range of chemicals. They can withstand temperatures up to 300 °C and are resistant to hydrolysis, radiation, and various solvents, making them suitable for demanding applications in aerospace, automotive, and oil and gas industries.
- Superior Mechanical Properties: PAEKs possess high strength, stiffness, and toughness, comparable to metallic materials. They have a tensile strength ranging from 90 to 100 MPa and a flexural modulus of around 4 GPa, enabling their use in load-bearing applications. Additionally, PAEKs exhibit excellent fatigue resistance and dimensional stability.
- Biocompatibility and Sterilizability: PAEK materials, particularly PEEK, are biocompatible and can be sterilized using various methods, including gamma radiation, ethylene oxide, and steam autoclaving. This makes them suitable for medical applications, such as implants, surgical instruments, and drug delivery systems.
Disadvantages of PAEK Materials
- Poor Adhesion to Metals: PAEKs generally exhibit poor adhesion to metal substrates, which limits their use in applications where metal-polymer bonding is crucial, such as wire coatings and automotive components. However, surface treatments and the development of PAEK-based composites can improve adhesion.
- Anisotropic Properties in Additive Manufacturing: Parts manufactured using additive manufacturing techniques, such as selective laser sintering (SLS), can exhibit anisotropic mechanical properties, with lower strength in the out-of-plane (Z-axis) direction compared to the in-plane (XY) direction.
- Limited Recyclability: PAEK materials have limited recyclability, as the use of recycled PAEK powder can cause degradation and affect the mechanical properties of the final parts. However, recent research has explored methods to improve the recyclability of PAEK materials for additive manufacturing processes.
Applications of PAEK material
Aerospace and Automotive Applications
The high-performance characteristics of PAEK polymers, including their low density, high thermal stability, and excellent mechanical properties, make them suitable for use in the aerospace and automotive industries. PAEK materials can replace metals in various components due to their lightweight yet durable nature.
Biomedical Applications
PAEKs exhibit good biocompatibility and chemical resistance, enabling their use in medical devices and implants. Their mechanical properties are comparable to human bone, making them viable alternatives to metal-based implants. Applications include orthopedics, craniofacial and cardiothoracic surgery, cardiovascular devices, dental prostheses, and tissue engineering.
Additive Manufacturing
PAEKs are increasingly being used in additive manufacturing (AM) processes, such as selective laser sintering and fused filament fabrication. AM facilitates the rapid development of customized PAEK products with complex structures and functionalities. However, challenges related to crystallization kinetics and layer adhesion need to be addressed.
Electronics and Other Applications
The chemical stability, low dielectric constant, and high-temperature performance of PAEKs make them suitable for applications in the electronics industry. They are also used in offshore drilling, wind power, sporting goods, and construction due to their excellent mechanical properties and chemical resistance.
Application Cases
| Product/Project | Technical Outcomes | Application Scenarios |
|---|---|---|
| PAEK Aerospace Components | PAEK materials offer high thermal stability, low density, and excellent mechanical properties, enabling lightweight yet durable components that can replace metals in aerospace applications, leading to reduced weight and improved fuel efficiency. | Aircraft components such as engine parts, structural components, and interior fittings. |
| PAEK Biomedical Implants | PAEK polymers exhibit excellent biocompatibility, chemical resistance, and mechanical properties comparable to human bone, making them suitable alternatives to metal-based implants with reduced risk of adverse reactions and improved integration with surrounding tissues. | Orthopedic implants, craniofacial and cardiothoracic surgery, cardiovascular devices, dental prostheses, and tissue engineering applications. |
| PAEK 3D Printed Parts | Additive manufacturing processes like selective laser sintering and fused filament fabrication enable the rapid production of customized PAEK components with complex geometries, reducing lead times and facilitating on-demand manufacturing. | Prototyping, small-batch production, and customized components for various industries, including aerospace, automotive, and medical. |
| PAEK Membrane Filters | PAEK materials exhibit excellent chemical resistance, thermal stability, and mechanical strength, making them suitable for use in membrane filters for harsh environments, enabling efficient separation and purification processes with extended service life. | Industrial filtration systems, water treatment plants, chemical processing facilities, and pharmaceutical manufacturing. |
| PAEK Electrical Insulation | PAEK polymers possess outstanding dielectric properties, high heat resistance, and dimensional stability, making them suitable for electrical insulation applications, ensuring reliable and safe operation of electrical systems in demanding environments. | Insulation for high-voltage cables, motors, generators, and other electrical equipment in harsh environments such as aerospace, automotive, and industrial applications. |
Latest innovations in PAEK material
Improved Processability and Crystallization
New PAEK polymer compositions with significantly increased crystallization rates have been developed, particularly polyetherketoneketone (PEKK) compositions. Incorporating liquid crystal polymers (LCPs) promotes crystal nucleation, accelerating crystallization and improving the moldability and dimensional stability of the final product. Inorganic nucleating agents and reinforcing fillers can also enhance crystallization kinetics.
Advanced Manufacturing Techniques
Additive manufacturing (AM) techniques like selective laser sintering (SLS) are being explored for PAEK materials. Optimizing powder characteristics like particle size distribution improves the surface finish and accuracy of SLS-printed PAEK parts. Carbon fiber-reinforced low-melt PAEK composites in tape and filament form enable AM of high-performance parts, though challenges like void formation and fiber breakage need to be addressed.
High-Performance Composites
Reinforcing PAEK with fillers like glass fibers, polyphenylsulfone, and polyethersulfone yields composites with improved mechanical properties like strength and toughness. Tailoring the PAEK matrix, reinforcement type/content, and processing allows optimizing performance for demanding applications in the aerospace, automotive, and energy sectors.
Technical Challenges
| Improving Crystallisation Rate of PAEK Polymers | Developing PAEK polymer compositions with significantly increased crystallisation rates, particularly by incorporating liquid crystal polymers (LCPs), inorganic nucleating agents, or reinforcing fillers to promote crystal nucleation and accelerate crystallisation kinetics. |
| Enhancing Processability of PAEK Polymers | Optimising the powder characteristics, such as particle size distribution, of PAEK polymers for additive manufacturing techniques like selective laser sintering (SLS) to improve surface finish and accuracy of printed parts. |
| Improving Biocompatibility of PAEK Implants | Developing strategies to enhance osseointegration and biocompatibility of PAEK implants, such as surface modifications or incorporating bioactive agents, to promote bone growth and integration with the host tissue. |
| Developing High-Performance PAEK Composites | Formulating PAEK polymers with reinforcing fillers, such as carbon fibres, to produce high-performance composites with improved mechanical properties, strength, and toughness for various applications. |
| Enhancing Melt Viscosity of PAEK Polymers | Developing PAEK polymer compositions with reduced melt viscosity to enable processing of thin-walled components and facilitate high-volume manufacturing techniques like surface mount technology (SMT). |
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