As seen before, the exit zone of the reactor does not exhibit many of these optical features. Therefore, the exit zone was not investigated, but additionally the virgin material was analyzed as reference. The regions for the Raman analysis of the three different sample locations can be seen as microscopic images in Figure . Please note, these images are normal light microscopic images with two-dimensional information. The virgin materials (before use) have a characteristic surface structuring, which is originating from the different material processing during manufacturing of the tubing. The PTFE surface has some sort of striations, while the PFA surface is exhibiting a crater structure on the surface, likely due to the different extrusion methods as mentioned previously (see 2.1.1). The used material of the inlet and catalyst zone keep some of the characteristic surface structures, but additionally exhibit deposits in fiber form and some fragments, which might also originate from the fibers.