## 3 Results of the Investigation of the Foaming Agents
### The Thermal and Morphological Properties of CBAs, TGA, TGA-FTIR, DSC
It is important to note that the type of effective gas also has an effect on the final foam structure. CO\({}_{2}\) has higher solubility (20 wt%) in the PLA matrix compared to N\({}_{2}\) (2 wt%). As a result, CO\({}_{2}\) effectively lowers melt pressure during extrusion and increases the percentage of crystalline fraction [25]. The reaction range of CBAs was also analysed with a DSC test. Figure 5 below contains the measurement results. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **dTG Range** & **Mass Reduction** & **dTG Range** & **Mass Reduction at** \\  & **N\({}_{2}\)** & **at 190 \({}^{\circ}\)C N\({}_{2}\)** & **Air** & **190 \({}^{\circ}\)C Air** \\ \hline
**[-]** & [\({}^{\circ}\)C] & **[\%]** & [\({}^{\circ}\)C] & **[\%]** \\ \hline Tracel3170 & 145–239 & 7.5 & 147–212 & 2.8 \\ Tracel4200 & 145–188, 204–245 & 6.9 & 147–187, 196–232 & 6.5 \\ Hyd\_3168 & 186–237 & 0.1 & 193–237 & 0.1 \\ \hline Luv\_9537 & 136–168, 168–225 & 4.8 & 137–165, 174–214 & 3.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The decomposition range of CBAs (dTG ranges relevant from the aspect of PLA extrusion processing) and mass reduction at 190 \({}^{\circ}\)C.  
Figure 3: Thermogravimetric analysis (TGA) results of foaming agents in nitrogen and air (**a**) mass reduction as a function of temperature (50–800 \({}^{\circ}\)C), (**b**) the rate of mass reduction as a function of temperature (50–800 \({}^{\circ}\)C). The broken line indicates the nitrogen atmosphere, while the continuous line indicates air. Figure 4: The Fourier transform infrared (FTIR) spectrum of foaming agents (in the 600–4000 cm\({}^{-1}\) range). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Foaming Agent**} & \multicolumn{2}{c}{**Absorbance Maximums [-]**} & \multirow{2}{*}{**Type of Gas Generated**} \\ \cline{2-3} \cline{5-4}  & **Wave Number [cm\({}^{-1}\)]** & & **Temperature [\({}^{\circ}\)C]** \\ \hline \multirow{3}{*}{Tracel3170} & 600–750, 2250–2350, 3600–3750 & 183 & CO\({}_{2}\) \\  & 2050–2250 & 183 & CO \\  & 750-1250, 1450–1800, 3200–3500 & 183 & NH\({}_{3}\) \\ \hline \multirow{3}{*}{Tracel4200} & 600–750, 2250–2350, 3600–3750 & 168 & CO\({}_{2}\) \\  & 1600–1700, 3500–3700 & 168 & H\({}_{2}\)O \\ \hline \multirow{3}{*}{Luv\_9537} & 2050–2250 & 147 & CO \\  & 600–750, 2250–2350, 3600–3750 & 147 & CO\({}_{2}\) \\ \hline \multirow{3}{*}{Hyd\_3168} & 2050–2250 & 225 & CO \\  & 600–750, 2250–2350, 3600–3750 & 225 & CO\({}_{2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The results of the TGA-FTIR measurement (10 \({}^{\circ}\)C/min, nitrogen measuring atmosphere). Figure 5: Differential scanning calorimetry (DSC) results of foaming agents (50–250\({}^{\circ}\)C, first heating, 10 \({}^{\circ}\)C/min). We compared the absorbance spectrum of generated effective gases with the intensity peaks of the spectra of materials in the IR database of the National Institute of Standards and Technology [26]. Figure 5 shows that Tracel3170 has an exothermic conversion peak, while in the case of Tracel4200, Luv_9537 and Hyd_3168, more endothermic reaction occurred. The conversion temperatures measured by DSC can be compared to the temperature ranges measured by TGA and this provides more accurate information concerning the temperature range of the decomposition process. Table 4 contains these data. The initial chemical change temperature of DSC is nearly the same as the beginning of the decomposition range measured by TGA but the end of the decomposition range (according to dTG) falls a little after the end of the changing temperature range registered by DSC. This is because the DSC data describe the changing process of the foaming agent and only the beginning part of this process is the same as TGA. TGA, on the other hand, does not show the energy change before and after the start of decomposition; it only registers the mass reduction effect of the decomposition product released in the gas phase, which continues after the reaction, as well.