# Thermoforming Process Effect on Performances of Thermoplastic/Recycled Carbon Fiber Composites
## 3 Results and Discussion  
### Thermal Characterization  
The thermogravimetric analysis (TGA) of the PA6/60 and MAPP/60 samples, shown in Figure 5a,b, highlights the two materials' thermal behavior as a temperature function. Both materials exhibit significant weight loss between 350 \({}^{\circ}\)C and 500 \({}^{\circ}\)C, indicating the thermal decomposition of the main polymer. However, the degradation profile differs between the two samples. PA6/60 shows the main decomposition phase with a peak in the derivative thermogravimetry curve around 460 \({}^{\circ}\)C, characteristic of polyamide 6 (PA6). On the other hand, MAPP/60 displays a primary decomposition occurring at slightly lower temperatures, with a DTG peak around 430 \({}^{\circ}\)C. This is likely due to the presence of maleic anhydride-grafted polypropylene (MAPP), which degrades at lower temperatures than PA6. Additionally, the solid residue at high temperatures (600 \({}^{\circ}\)C) is around 40% for both materials, a value consistent with the material datasheet [32]. Table 1 reports the weight loss of the examined materials from room temperature up to 250 \({}^{\circ}\)C and the maximumdegradation temperature observed. PA6/60 shows a higher weight loss at 250 \({}^{\circ}\)C, which could indicate the presence of components that volatilize or degrade at this temperature. The differential scanning calorimetry (DSC) analysis of the PA6/60 and MAPP/60 samples, shown in Figure 6a,b, allows for the identification of key thermal transitions, including the glass transition temperature (Tg) and melting point (Tm). For PA6/60, the first heating cycle shows a glass transition temperature around 50-60 \({}^{\circ}\)C, indicated by a slight shift in the baseline of the heat flow. The primary melting peak is observed at approximately 220-225 \({}^{\circ}\)C, with a well-defined area characteristic of the crystalline phase of polyamide 6 (PA6). Additionally, in the second heating cycle, a similar glass transition is observed, confirming the stability of Tg after the first thermal treatment. The crystallization temperature during cooling (Tc) is identified around 180-190 \({}^{\circ}\)C, indicating the material's ability to recrystallize after melting. Instead, MAPP exhibits two transitions in the \(-\)50 \({}^{\circ}\)C to 100 \({}^{\circ}\)C range. The first transition at around 0 \({}^{\circ}\)C is \(\beta\)-relaxation, and it is associated with the glass-rubber transition of the fully amorphous phase. The temperature transition between 40 and 60 \({}^{\circ}\)C is \(\alpha\)-relaxation [33]. The Tg associated with \(\alpha\)-relaxation was selected for inclusion in Table 2. The melting peak (Tm) appears between 160 and 170 \({}^{\circ}\)C, characteristic of polypropylene. The second heating cycle confirms these values, indicating good reproducibility of the material's thermal structure. The crystallization temperature (Tc) is around 120 \({}^{\circ}\)C, reflecting the material's recrystallization behavior. In the first heating cycle, all the analyzed samples show two melting peaks (Figure 6b). The peak on the left is associated with the melting of the \(\beta\)-phase, while the one on the right corresponds to the \(\alpha\)-phase [34]. After \begin{table}
\begin{tabular}{c c c} \hline \hline
**Description** & **Weight Loss @ 250 \({}^{\circ}\)C** & **T@ Maximum** \\  & **[\%]** & **Decomposition** \\  & & [\({}^{\circ}\)C] \\ \hline PA6/60 & 1.7 \(\pm\) 0.5 & 440.9 \(\pm\) 0.5 \\ MAPP/60 & 0.5 \(\pm\) 0.2 & 425.4 \(\pm\) 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Results of TGA analyses. Figure 5: TGA thermograms, weight (%) in solid line and derivative weight (%/\({}^{\circ}\)C) in dotted one, for (**a**) PA6/60 and (**b**) MAPP/60.