Here at 3Devo we really enjoy trying out new polymers. Most of them have different functions and qualities that make them unique. This week we had a look at PEKK, or Polyetherketoneketone. This semicrystalline polymer, shows off both a sound structural performance in high temperature and a strong chemical resistance. These positive qualities make it very useful in various fields, from medicine to aerospace.
Before 2011, PEKK’s main use was for the production of thermoplastic composites. It was sold in limited quantities to a few small compounding companies. These companies offered PEKK in various melting processes, as well as other specialty and composite processes. However, in 2011, Arkema began industrial PEKK production making it more accessible, so let us take a closer look into what makes this polymer so unique.
- PEKK is a part of the High Performance of Polyaryletherketone (PAEK) polymer family.
- Glass transition temperature of 162°C (323.6°F)
- The melting temperature for the PEKK homo-polymer is around 400°C
- Slow crystallization rate
- Manufacturers and distributors: Arkema, Velox, RTP and Cytec
- Brand names: Kepstan and RTP
PEEK vs PEKK
Unlike PEEK, PEKK displays both amorphous and crystalline material properties. This makes PEKK quite interesting. Thanks to its unique mechanical, physical and chemical properties, PEKK lends itself to a broader range of uses than PEEK:
- Up to 80% greater compression strength than PEEK
- Wider processing window of parameters than PEEK
- High strength and toughness
- Chemical resistance
- Easy processing
- Lower moulded-in stresses
- Greater dimensional stability
- Remains transparent even at higher operating temperatures
- Improved flow characteristics (due to an extremely slow rate of crystallisation)
According to Tim Spahr of Arkema’s Corporate Research in North America, “These properties allow for lower processing temperatures and the ability to process the Kepstan® 6000 Series (one of their products) copolymers polymers as either amorphous or semi-crystalline structures, depending on processing technologies and cooling conditions.” He also added, “They can be injection molded and extruded as an amorphous polymer without the need for quenching.”
Oxford Performance Materials, always popular with their advances in developing of applications, are now using PEKK to improve infections related to artificial hips, knees, and other implanted devices. In February 2014, OPM became the first company to receive FDA clearance. This was for the manufacturing of patient-specific 3D printed polymeric implants for a line of cranial prosthesis as shown above.
NASA is also not wanting to be left out of the 3D-printing world. They of course have many projects that involve 3D printing, but last year a 3D printed part received a lot of attention as part of their latest ICESat-2 project. The project aims to examine and measure changes in ice-sheet elevations, sea-ice thicknesses, and global vegetation in Greenland and the Antarctic. Stratasys had to develop a bracket for this project for the sole purpose of space travel. PEKK made its debut in space as part of the satellite, allowing for this central bracket component to be only the second 3D printed part to go into space so far.
The military will also be using PEKK’s heat and chemical resistance and its ability to withstand heavy mechanical weights for various uses out in the field. For example, a plastic guard that prevents light emitted from a flashlight from exposing a soldier’s location.
Our Tests with PEKK
We decided to use a bag of the Kepstan® 6000 series copolymers, as it offers offer a low melting point and has a slow crystallization rate. We used the Kepstan 6001 PF variant.
Like PEEK, the transition material played a key role throughout the PEKK extrusion process.
This time we used a different high temperature purging compound: Asaclean PX2 grade (280 Celcius up to 420 Celcius), to reach the desired temperature range for PEKK (330 Celcius up to 345 Celcius).
By pressure feeding the PEKK powder in the hopper of the Advanced Level Extruder, the cooling fans at 30% and the screw speed at 7RPM, we had a good time with the unique filament. Successfully we extruded 2.85mm, which will be tested any time soon by one of our clients. PEKK offers a lot of advantages to say PEEK or other polymers, but it truly stands out in real-world applications. Hopefully more industry sectors can see the potential of this useful polymer.