Mixing of the printing material and catalyst as well as extrusion of the filament was conducted in a single process step. Although this approach seemed to be straightforward, our own experiments showed a poor quality of the resulting filaments due to poor mixing between both components. The resulting filament strings contained brittle areas with agglomerations of TiO2 that could cause clogging during the 3D-printing process. The probability of clogging is higher if more filament is needed for the 3D-printing part and thus increases with the size of the specimen. In many studies the composite filament was only applied for small scale test bodies or reactors but no extended structures such as static mixers or dedicated reactor inserts that demand a higher material input. To intensify the mixing of both solids, i.e. PP and TiO2, and to provide an as uniform photocatalyst distribution as possible, additional mixing steps were introduced. This resulted in the following procedure involving 3 different machines: a heated extruder with downstream water bath, a commercial filament extruder with integrated spooling device and a commercial filament shredder with integrated granulator.