# Thermoforming Process Effect on Performances of Thermoplastic/Recycled Carbon Fiber Composites
## 3 Results and Discussion
### Viscoelastic Characterization  
The viscoelastic behavior of the sample with a temperature from \(-\)70 to 180 \({}^{\circ}\)C is reported in Figure 7. Figure 7d shows a scanning electron microscopy (SEM) image of the fractured surface of the PA6/60 one-layer panel. The microstructure reveals a heterogeneous distribution of recycled carbon fibers embedded in the PA6 matrix. The image displays clear interfacial bonding between the matrix and the fibers, although some fiber pull-outs and voids are visible, indicating localized debonding or porosity.  
DMA experiments were performed in the linear viscoelastic deformation range to investigate how the molding process influences the storage modulus, loss modulus and tan\(\delta\) of the manufactured panels, the number of overlapping layers and the porosity.  
Table 3, instead, shows the results of DMA at 50 \({}^{\circ}\)C for the PA6/60 panels. The selected temperature was chosen close to the glass transition temperature of the hosting matrices to compare both materials under the same mobility conditions.  
Figure 7: The first row shows the DMA curves of the panels manufactured using the first method, specifically: (**a**) PA6/60 single layer; (**b**) PA6/60 2 LM1; (**c**) PA6/60 3 LM1. The second row presents (**d**) SEM image of a PA6/60 one-layer panel near a porosity and the DMA curves of the panels manufactured using the second method: (**e**) PA6/60 2 LM2; (**f**) PA6/60 3 LM2.  
The viscoelastic behavior of the sample with a temperature from \(-70\) to \(120\)\({}^{\circ}\)C is reported in Figure 8. Figure 8d presents an SEM image of the fracture surface of an MAPP/60 one-layer panel. Several fibers appear to be well embedded, while others exhibit pull-out features, suggesting partial debonding or fiber-matrix interfacial failure. The presence of voids and resin-rich areas can also be observed, indicating heterogeneities likely introduced during the compression-molding process. These morphological characteristics are consistent with the mechanical behavior observed in the DMA results, particularly in terms of storage modulus and damping performance.  
DMA experiments were performed in the linear viscoelastic deformation range to investigate how the molding process influences the storage modulus, loss modulus and  
Figure 8: The first row shows the DMA curves of the panels manufactured using the first method, specifically (**a**) MAPP/60 single layer; (**b**) MAPP/60 2 LM1; (**c**) MAPP/60 3 LM1. The second row presents (**d**) a micrograph of a MAPP/60 one-layer panel and the DMA curves of the panels manufactured using the second method: (**e**) MAPP/60 2 LM2; (**f**) MAPP/60 3 LM2.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Description** & **E\({}^{\prime}\) @ 50 \({}^{\circ}\)C** & **E\({}^{\prime\prime}\) @ 50 \({}^{\circ}\)C** & **Tans @ 50 \({}^{\circ}\)C** \\  & **[GPa]** & **[GPa]** & **[-]** \\ \hline PA6/60 1L & 16.2 \(\pm\) 1.10 & 0.40 \(\pm\) 0.03 & 0.025 \(\pm\) 0.0029 \\ PA6/60 2 LM1 & 10.0 \(\pm\) 1.06 & 0.36 \(\pm\) 0.04 & 0.036 \(\pm\) 0.0029 \\ PA6/60 2 LM2 & 15.2 \(\pm\) 1.06 & 0.34 \(\pm\) 0.05 & 0.023 \(\pm\) 0.0014 \\ PA6/60 3 LM1 & 11.4 \(\pm\) 1.22 & 0.32 \(\pm\) 0.05 & 0.028 \(\pm\) 0.0020 \\ PA6/60 3 LM2 & 11.6 \(\pm\) 0.31 & 0.32 \(\pm\) 0.01 & 0.028 \(\pm\) 0.0005 \\ \hline \end{tabular}
\end{table}
Table 3: Results of DMA analysis at 50 \({}^{\circ}\)C.  
tan\(\delta\) of the manufactured panels, the number of overlapping layers and the porosity. Table 4, instead, shows the results of DMA at 20 \({}^{\circ}\)C for the MAPP/60 panels. This temperature was chosen because it is near the glass transition temperature of the maleic anhydride-grafted polypropylene (MAPP).