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All You Need to Know About PEKK

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.

Overview

PEKK, the multi-use polymer (image via ptonline)
  • 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: ArkemaVeloxRTP 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

Unique Qualities

  • 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.”

Real-world Applications

Medical

A patient-specific OsteoFab cranial implant 3D-printed by OPM. (Image courtesy of OPM.)

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.

Aerospace

The 3D manufactured part — a black bracket holding the instrument’s fiber-optic cables (Image courtesy of NASA)

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.

Military

Military uses can be plentiful thanks to its robust structure (image via 3dprint.com)

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.

Kepstan 6001 PF powder

Like PEEK, the transition material played a key role throughout the PEKK extrusion process.

Extruding the filament on the Advanced Level Extruder

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).

The finished result!

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.

Year and a Half Later – Setting the standard with PEEK

Year and a Half Later – Setting the standard with PEEK
A year and a half ago, we began testing the prototype of what is today referred to as the Next 1.0 Advanced Level desktop filament extruder.
Taking forward the same commitment to quality and innovation, we focused on our next experiment – working with a semi-crystalline thermoplastic with mechanical and chemical properties ideal for sustaining high temperatures. This thermoplastic is known as PEEK (Polyether Ether Ketone).
Working with PEEK has presented interesting challenges, chief among which involved extruding it in the correct temperature range, while factoring in internal pressure, and without affecting the material’s crystallinity. It has been a good start, and our first trials turned out to be easier than expected.
But first, a bit about PEEK. And its key applications.

PEEK test result 1.75mm 3devo filament
PEEK test result 1.75mm 3devo filament – done by Apium Additive Technologies GmbH http://apiumtec.com/en/3d-printer/

PEEK finds its main uses in the Aerospace, Automotive and Medical industries.

Aerospace industry: Being strong, lightweight, and durable in a wide range of temperatures, PEEK is evolving into a popular choice of material in the aerospace industry. Its low price point does not hurt either.

Aerospace part
Aerospace part
Source: www.roboze.com

Automotive industry: Besides the primary advantages of its high strength (safety), low weight, and durability in a wide range of temperatures, PEEK is also energy efficient and has the intrinsic ability to reduce vibrations. This makes it a perfect fit for the fast developing automotive industry.

Gear Pump Source: www.Apiumtec.com
Gear Pump
Source: http://apiumtec.com/en/3d-printer/

Medical industry: 3D printing has already established itself as an invaluable asset to the medical and dental industries, bringing a whole new level of freedom and accuracy to the process of printing unique parts and components. PEEK (or PEKK for dental industry) extends the scope of 3D printing, having similar properties as the human bone, and thus being one of the few materials that the body does not resist.

Implants Source: www.pkm.kit.edu
Implants
Source: www.pkm.kit.edu

Recent PEEK tests with the Next 1.0 Advanced Level desktop filament extruder
Switching from PLA to PEEK presented an unique challenge: building up the temperature inside the Advanced Level extruder to PEEK’s high melting point of 343 degrees.
We went about it in phases, using 2 cleaning compounds as transition materials. First, we slowly raised the temperature from 170 to 300 degrees with the first transition material. Once temperatures had crossed 300 degrees, we switched to the second transition material, and worked on reaching 390 degrees. This was the final stage in our trial, where we could proceed to extrude PEEK.
Because of PEEK’s steady flow and relatively quick cooling properties, extruding it to the desired thickness (2.85mm or 1.75mm) was easier than expected. Winding it on a spool was a different ballgame, though. Due to the strength of the material we had to tape the first part of the filament on the spool, so as to wind it correctly and prevent it from popping out of the spool.

3devo PEEK Filament 2.85mm
3devo PEEK Filament 2.85mm

Transition materials and PEEK
The transition material played a key role throughout our PEEK extrusion process. We first mixed the PEEK with the transition material, and then gradually lowered the temperature range while increasing the amount of transition material in the mix.

PEEK and purging compound @3devo
PEEK and purging compound @3devo

Phase 1

Image: 3devo BV - phase 1 extruding PEEK
Image: 3devo BV – phase 1 extruding PEEK

Phase 2

Image: 3devo BV - phase 2 extruding PEEK
Image: 3devo BV – phase 2 extruding PEEK

Extruding your own PEEK – The main advantages
Buying PEEK granulate will only set you back by around 100 Euros per kg, as opposed to a filament spool that will cost you to the tune of 1000 Euros per spool.
In addition to this, you can try creating custom composites with PEEK granules, by adding in different materials such as carbon fiber.

Do you have one of our Advanced Level extruders?
Contact sales@3devo.com for the profile settings to start extruding PEEK.