## 3 Results and Discussion
### Extrusion of Filament from Polyvinyl Butryal Granulates  
Before filament fabrication starts, it is necessary to ensure the proper extrudepreviously previously previously used. This step is crucial for the resulting quality of the produced filament. As was suggested before, proper material drying before extrusion is an essential part of the whole process. Based on the experiment, we recommend drying the material for at least three hours. If these steps are successfully performed, it is possible to start the extrusion process [28]. The extruder has to be heated up at the required temperature. Filament yarns were extruded at different temperatures to reveal the optimal extrusion temperature for the chosen material. The first group of specimens was made at a temperature of 175 \({}^{\circ}\)C for extrusion. Then subsequent groups were made at 160 \({}^{\circ}\)C, 155 \({}^{\circ}\)C, and 150 \({}^{\circ}\)C, and the last group of specimens was extruded at a temperature of 140 \({}^{\circ}\)C. Figure 6 represents the process of filament production and measurements taken using a thermocamera. These measurements consisted of stabilizing the nozzle temperature at 175 \({}^{\circ}\)C and gradually lowering it, stabilizing it, and measuring it until the material breaks. In this case, the temperature of 155 \({}^{\circ}\)C appeared ideal for extruding fibers from this material. The temperature of 140 \({}^{\circ}\)C was already too low, the diameter of the material was not constant, and there was clogging of the nozzle and even fiber breakage. The subsequent verification of the established temperature was carried out using microscopic images. For this purpose, two sets of samples were selected. The first series consists of the following extremes: the highest and lowest extrusion temperatures [22,27]. These were intended to demonstrate the additional negative impact observable in cases of negative or positive temperature extremes. The second series of samples comprise temperatures of 160, 155, and 150 \({}^{\circ}\)C, which appeared ideal upon simple visual inspection during and after extrusion. Considering that the filament itself, with a diameter of 1.75 mm, cannot be processed to a level at which individual defects are observable at the required level, the samples were prepared in advance--preparation involved embedding the samples into a casting resin commonly used for materials microscopy [28]. Three types of casting resins were gradually selected. Two of them were excluded due to insufficient filament visibility or defects arising during casting and a chemical reaction with the PVB material, resulting in material dissolution before the solidification of the casting resin. Figure 6 shows the preparation process of PVB filament samples, which were cold-hardened into acrylic resin Durocit. Samples were cold-hardened for better manipulation and stability during the observation under the microscope (Figure 7). For a successful series of prepared samples, it is possible to declare the samples visible in Figure 8. The casting material Durocit-3 was utilized for this purpose. The material did not chemically react with the material used, and sufficient color contrast was ensured between the observed sample and the casting material [27]. Given these results, the prepared samples were utilized to generate microscopic images. The Keyence VH-ZST device was employed to create microscopic images. As depicted in Figure 8, two images of the deformation of the extruded filament in the longitudinal direction were initially generated. These clearly illustrate two types of deformations in the case of incorrect extrusion temperature settings. Figure 8 displays a sample created at a temperature of  
Figure 6: Thermovision diagnostics of filament extrusion. Figure 7: Preparation of PVB filament samples embedded in Durocit-3 material. 140 \({}^{\circ}\)C. Across the entire surface of the sample, visible irregularities are caused by the low extrusion temperature and discontinuous material feeding from the nozzle.