Abstract
Polyetheretherketone (PEEK), an attractive matrix for highly loaded parts in terms of temperature and mechanical performance, is applied in many engineering applications. However, its improvement in the mechanical properties by, for example, nanoparticles is sometimes necessary to fulfill actual requirements. In this case, the nanoparticles need to be deagglomerated, wetted by the polymer matrix, and equally distributed. Excellent results can be achieved by a second extrusion step applied on the masterbatch. Theoretical calculations of processing parameters (e.g., shear energy) explain the reason for a better dispersion and distribution of nanoparticles inside the matrix for the multipass extrusion process. PEEK compounds reinforced with 15 nm titanium dioxide (TiO2) nanoparticles are compared with PEEK reinforced with 300 nm particles. The incorporation of the nanoparticles into the PEEK matrix was realized by a corotating twin screw extruder (ZE25x44, Berstorff GmbH) with 10 heating barrels. The mechanical and thermal properties of the materials were characterized at room temperatures by tensile and impact testing, differential scanning calorimetry, and dynamic mechanical thermoanalysis. The important distribution quality of the nano-sized particles and corresponding fracture surfaces are shown in high-resolution scanning and transmission electron microscopy micrographs. It becomes visible that the 15 nm particles enhance the polymer properties much better than the 300 nm particles. The 15 nm particles improve the stiffness and the strength as a function of filler content. Highest values of impact energy can be achieved at a filler content of 2.2 vol. %.