Material Extrusion 3D Printing of PEEK-Based Composites

High-performance thermoplastics like polyetheretherketone (PEEK), with their outstanding
thermal stability, mechanical properties and chemical stability, have great potential for various structural
applications. Combining with additive manufacturing methods extends further PEEK usage,
e.g., as a mold insert material in polymer melt processing like injection molding. Mold inserts must
possess a certain mechanical stability, a low surface roughness as well as a good thermal conductivity
for the temperature control during the molding process. With this in mind, the commercially available
high-performance thermoplastic PEEK was doped with small amounts of carbon nanotubes (CNT,
6 wt%) and copper particles (10 wt%) targeting enhanced thermomechanical properties and a higher
thermal conductivity. The composites were realized by a commercial combined compounder and
filament maker for the usage in a material extrusion (MEX)-based 3D-printer following the fused filament
fabrication (FFF) principle. Commercial filaments made from PEEK and carbon fiber reinforced
PEEK were used as reference systems. The impact of the filler and the MEX printing conditions like
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printing temperature, printing speed and infill orientation on the PEEK properties were characterized
comprehensively by tensile testing, fracture imaging and surface roughness measurements. In
addition, the thermal conductivity was determined by the laser-flash method in combination with
differential scanning calorimetry and Archimedes density measurement. The addition of fillers did
not alter the measured tensile strength in comparison to pure PEEK significantly. The fracture images
showed a good printing quality without the MEX-typical voids between and within the deposited
layers. Higher printing temperatures caused a reduction of the surface roughness and, in some cases,
an enhanced ductile behavior. The thermal conductivity could be increased by the addition of the
CNTs. Following the given results, the most critical process step is the compounding procedure,
because for a reliable process–parameter–property relationship, a homogeneous particle distribution
in the polymer matrix yielding a reliable filament quality is essential.