PEEK vs PEKK: Which High Performance Material Should You Choose?

PEEK and PEKK are high performance polymers, known for their strength and thermal properties, that are increasingly used in additive manufacturing industry. PEEK and PEKK demonstrate sufficient mechanical strength at temperatures over 250°C, and can resist deformation well above the limits of common plastics such as nylon, ABS, or PC. Because of this, these tough materials are often used in place of metal, when users want to reduce waste, prevent corrosion, and allow for more complex designs. When it comes to AM, PEEK and PEKK are compatible with material extrusion (FDM) and selective laser sintering. But what are the differences between these two high-performance thermoplastics? Which one should you choose?

PEEK and PEKK are considered high performance polymers

Composition and Characteristics

When comparing two high performance polymers, it is important to start with their composition and properties. This will help you understand how they will perform during the manufacturing process, which can be a determining factor in your choice. These two materials belong to the PAEK family, a group of high-performance semi-crystalline and amorphous thermoplastics. In this family, the most commonly used polymer is PEEK, which is formed by a molecular structure of 1 ketone and 2 ethers.

PEKK, on the other hand has an inverse molecular structure: it has 2 ketones and 1 ether. The ketone bonds are more flexible, which increases the flexibility of the polymer in question. This means that the glass transition temperature (the temperature at which the polymer starts to soften) and the melting temperature are higher with PEKK.

Both materials have high mechanical strength, high temperature resistance, fatigue resistance and low flammability. PEKK is more resistant to chemical fluids, has good dielectric stability and does not emit toxic fumes. PEEK has excellent mechanical properties and a good strength-to-weight ratio, making it a good substitute for some metals. Both polymers can be sterilized, facilitating their use in healthcare applications.

PEKK 3D printed parts. (Photo Credit: Weerg)

The main distinction between PEEK and PEKK is their degree of crystallinity and the speed of crystallisation. This concept refers to the total number of crystalline regions present in a polymer, and is represented as a percentage. Both materials are semi-crystalline elements, but their degree of crystallinity depends on how they are processed. In general, when we talk about the 3D printing process, PEEK can achieve a high level of crystallization, while PEKK has a much weaker crystal structure. The crystallinity affects the properties of the final piece, while the speed of crystalization and the rheological properties have an impact on the ease of printing.

Ease of Printing

To use high performance polymers like PEEK and PEKK, you need a 3D printer that meets certain temperature requirements. When using PEEK for 3D printing, you need a machine with an extruder that can reach 752°F (400°C), as well as a chamber heated to 248°F (120°C) and a building plate that can go up to 446°F (230°C), so that the layers can adhere to it and to remove it without problems (thus preventing issues with warping).

In the case of amorphous PEKK, the requirements will be very similar, but not as stringent. The extrusion temperature will typically be between 644 and 680°F (340 and 360°C). Additionally, it also requires both a heated build plate and a heated chamber.

PEEK is durable, biocompatible polymer ideal for medical implants. (Photo Credit: 3D Systems)

As the extruded filament solidifies, a partial alignment of the polymer molecular chains occurs. Based on the crystallization nuclei, the molecular chains fold up and form ordered regions. Therefore, the lower the percentage of crystallization nuclei in the polymer, the faster the cooling process will be, and the layers will have a better adhesion to each other. This prevents warping.

In other words, if the cooling and solidification process is too fast, the molecular chains will not bend properly, which will directly affect the adhesion of the part to the print bed, as well as its final mechanical properties.

As mentioned, PEKK has a lower degree of crystallization than PEEK. This means that it will be less affected by the cooling process once the part is 3D printed. Therefore, in terms of ease of 3D printing, PEEK will be more complex and technical to use, as it requires specific knowledge that will allow the user to control the extrusion and cooling steps.

Additionally, the choice of build plate is important when printing PEEK or PEKK. It must be able to operate at high temperatures, typically between 120 and 160°C. This allows the bottom layers to bond securely, preventing warping.

When it comes to selective laser sintering (SLS) technology, the polymer behaves differently depending on the size of the parts you want to manufacture. This means that warping deformations will be much smaller or non-existent for smaller models, but the larger the part to be created, the more difficult it will be to control the printing parameters.

Post-Processing of PEEK and PEKK

PEEK and PEKK post-processing is not the easiest of tasks. It is possible to anneal 3D printed PEEK or PEKK parts, that is, reheating them in a controlled way after printing, to improve the fusion between layers and increase the part’s crystallinity, which in turn boosts its final mechanical characteristics. Some 3D printers integrate this annealing step directly into the machine, as is the case with the miniFactory Ultra 2.

Parts printed in PEEK can also be finished using traditional machining methods like drilling or milling, for example to add precise holes or threads that are difficult to achieve directly through printing. Because PEEK retains heat poorly during machining, cooling and proper tool selection (diamond tooling is often used for reinforced grades) are important to avoid deformation.

Finally, PEEK parts can be metalized, meaning coated with a thin layer of metal through electroplating, to add properties the raw plastic doesn’t have on its own, such as electromagnetic shielding or added durability. This is mostly used in aerospace and defense applications where parts need to meet strict performance standards.

3DGence printing support is compatible with high performance materials (Photo Credits: 3DGence)

PEEK and PEKK Applications

PEEK and PEKK have similar applications. Aerospace, automotive, and aviation industries tend to adopt the materials the most, due to the materials’ mechanical and high-pressure resistance, lightness, and heat resistance. Being biocompatible, they are also often used in the medical sector. PEEK has properties that facilitate osseointegration, i.e. the direct, structural and functional connection between a bone and the surface of an implant under functional load. PEKK has better resistance to chemical fluids, which is why it will be used more in the oil and gas industry. It can also be fire/smoke certified for the railway industry.

PEKK is used more in the oil and gas sector (photo credit: Kimya)

The Cost of PEEK and PEKK

As you can imagine, PEEK and PEKK are more expensive than most polymers on the market due to their properties and characteristics. On average, a 500 gram roll of PEEK will cost you between €300 and 350 (about $350 to 420), while the same amount of PEKK will cost you between €350 and 400 (about $415 to 48). Of course, if you buy a high-performance, carbon-fiber reinforced polymer, the price will be even higher.

For PEKK powder, count on the price being about €500 for one kilogram ($597.06 for about 2.2lbs). A 3D SLS print can therefore quickly become expensive if we consider that an EOS P800 machine requires about 100 kilos of powder, based on its dimensions. Even if about 50% of the unused powder can be recycled, SLS printing jobs with high performance materials are quite expensive compared to nylon. So you’ll need to make sure that the 3D file is perfect with the correct printing parameters – mistakes can be expensive!

Parts 3D printed with PEKK via a powder sintering process (photo credits: Arkema)

Manufacturers

As explained above, PEEK and PEKK are mainly available as filaments, but there are also powders for sintering, though this is only possible with PEKK. Looking first at PEEK, the main producers of the material are chemists such as Victrex, Evonik, or Solvay. Most of them have developed their own range of filaments; Victrex, for example, offers its Low Melt PAEK (LMPAEK) and works with high-performance machine manufacturers such as Intamsys and 3DGence; Evonik has developed its VESTAKEEP® range for 3D printing of implants.

Beyond the chemists, there are several 3D printing material manufacturers that offer PEEK: 3DXTECH, 3D4Makers, W2 Polymer and OPM. Machine manufacturers are also getting in on the act, such as Zortrax with its Z-PEEK.

For PEKK, the French chemical company Arkema remains the largest manufacturer, whether in powder or granular form. Its PEKK Kepstan® range meets the needs of many manufacturers. The company Lehvoss also offers its LUVOCOM 3F PEKK 50082 NT in granulated form. Finally, Oxford Performance Materials offers a PEKK powder, particularly for the medical sector. As for PEKK filament manufacturers, some of the most prominent are the French brand Kimya, the Dutch company 3D4Makers, the American 3DXTECH or Nanovia.

Do you use PEEK or PEKK in additive manufacturing? Let us know in a comment below or on our LinkedIn and Facebook pages! Don’t forget to sign up for our free weekly Newsletter here, the latest 3D printing news straight to your inbox! You can also find all our videos on our YouTube channel.