## 3 Results of the Investigation of the Foaming Agents  
### The Thermal and Morphological Properties of CBAs, TGA, TGA-FTIR, DSC  
First, we examined the decomposition temperature ranges of chemical foaming agents by TGA. The test showed the mass fraction of the CBAs, the fraction of the gas producer useful from the aspect of foaming and what is the proportion of carrier polymer and other residual materials. The samples were measured with two background gases, so it was possible to compare the processes occurring in the different media. We used a nitrogen (N\({}_{2}\)) atmosphere to get measurement results from an inert atmosphere, while air was used because that is what is present during extrusion; therefore, the measurement approximates real-life extrusion better. Figure 3 shows that the decomposition of CBAs occurred in several steps. In the case of Luv_9537, mass reduction starts at 136 \({}^{\circ}\)C, this CBA is followed by Tracel4200, then Tracel3170. While in the case of the exothermic Tracel3170, mass reduction occurs in one step up to 200 \({}^{\circ}\)C, the endothermic Tracel4200 and Luv_9537 exhibit mass reduction in two steps. Between 150-250 \({}^{\circ}\)C during the thermal decomposition of CBAs probably effective gases, taking an active part in foaming are released, above this temperature it is likely that the carrier materials decompose. In the case of Hyd_3168 and Luv_9537, a great reduction of mass can be observed at 300 \({}^{\circ}\)C and 444 \({}^{\circ}\)C, while in the case of Tracel3170 and 4200, an extended gradual decrease can be observed at low intensity. Comparing the same measurements in N\({}_{2}\) and air, we can conclude that gas formation occurs in the same temperature range. In air, the curve is continuously sloping, while in nitrogen the decomposition ranges separate; the degradation of the carrier polymer and the accompanying mass reduction only starts at around 400 \({}^{\circ}\)C. Table 2 contains the measurement results: the decomposition temperature ranges based on dTG and the percentage ratio of mass reduction at 190 \({}^{\circ}\)C. The data indicate that in the case of the investigated CBAs, in nitrogen and air atmosphere, at 190 \({}^{\circ}\)C, mass reduction was nearly the same. There is a greater difference only in the case of Tracel3170; in nitrogen mass reduction was 7.5%, while in air it was only 2.8%. The greatest mass reduction in nitrogen was observed in the case of Tracel3170 (7.5%), it is followed by Tracel4200 (6.9%), Luv_9537 (4.8%) and Hyd_3168 (0.1%). The data indicate that Hyd_3168 probably cannot produce a foam at 190 \({}^{\circ}\)C, the characteristic processing temperature of PLA. All four foaming agents produced residual mass at 800 \({}^{\circ}\)C, which is probably a nucleating agent. Figure 2: Measurement layout of measuring foam strength. We evaluated the gases released at the maximum intensity of decomposition with a TGA-FTIR measurement. The results can be seen in Figure 4. We determined the type of gases generated under the processing temperature (Table 3). The maximum intensity of gas generation in the case of the different CBAs: Tracel3170--183 \({}^{\circ}\)C, Tracel4200--168 \({}^{\circ}\)C, Lux_9537--147 \({}^{\circ}\)C, while in the case of Hyd_3168 there was no observable gas generation intensity maximum under 200 \({}^{\circ}\)C, the maximum occurred at 225 \({}^{\circ}\)C. Based on the spectrum measured by FTIR, in the case of Tracel3170, peaks indicating carbon dioxide have the highest intensity but carbon monoxide is also present with lower absorption. Also, a C=N bond appears as well, which indicates isocyanate (-2200-2350 cm\({}^{-1}\)), which is a typical decomposition product of azodicarbonamide. In the case of Tracel4200, a strong absorption carbon dioxide peak can be observed but no carbon monoxide. In the case of Luv_9537, the absorption wavelength of carbon dioxide can be observed. In the case of Hyd_3168, carbon dioxide appears as an effective gas but with a small intensity peak.