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The Difference Between 3D Printing PEEK and PEKK


Understanding of PEEK


PEEK is a member of the PAEK (polyaryletherketone) family, which is known for its high thermo-mechanical performance. If we look at the pyramid of different polymers in the industry, Polyetheretherketone is located at the top, belonging to the category of high-performance polymers. It was first introduced to the market in the late 1970s and quickly adopted by industries such as aerospace or electronics for its performance. If we look at its structure, note that it is a semi-crystalline polymer, so when it melts, its molecules arrange themselves in a certain order under the heat until the material solidifies completely. This enables it to maintain its mechanical properties as the temperature rises.


What are the differences between 3D printing PEEK and PEKK?


If you look at the main chains of these two polymers, you can notice that compared to PEEK, PEKK has an extra ketone replacing an ether. This ketone increases the glass transition temperature, as it is a harder bond than the ether bond. The main difference between 3D printed parts of the two main members of the PAEK family, PEKK (polyetherketoneketone) and PEEK, lies in their crystallinity. Due to the lower crystallization rate of PEKK, it is usually considered as an amorphous polymer, depending on the production process.


On the other hand, PEEK has a higher crystallization rate, which allows for crystalline parts to be obtained using additive manufacturing processes under appropriate conditions. The difference can be seen by the naked eye: crystalline polyetheretherketone is a dull beige color, while amorphous Polyetheretherketone is a more translucent brown color.


3D printing PEKK: 


Although semi-crystalline materials have higher heat and chemical resistance, temperature-controlled production environments can minimize the impact factors during solidification, allowing the polymer melt to cool slowly. PEKK is usually printed at lower chamber temperatures in its amorphous form because it does not have enough time to crystallize during the printing process due to its slow crystallization rate. Material morphology also affects printing behavior. For example, the use temperature of untreated amorphous PEKK is about 150℃, and compared to PEEK, it exhibits chemical inertness to a narrower range of chemicals. The semi-crystalline version has better properties but requires a lot of post-processing, which increases the complexity of the production process;


3D printed PEEK: 


After PEEK is melted and extruded, it begins to cool and forms crystalline parts in the deposited plastic. At the microscopic level, the formation of these ordered domains is opposite to the random arrangement of molecules in the amorphous part, resulting in up to 2% shrinkage, which makes printing difficult. This difficulty occurs during the solidification stage of the material, where the different shrinkage between the semi-crystalline and amorphous regions causes distortion and separation of the part from the printing platform.

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