# Thermoforming Process Effect on Performances of Thermoplastic/Recycled Carbon Fiber Composites
## 3 Results and Discussion
### Effect of Molding Process on Crystallinity  
Since the properties of composites based on semicrystalline polymers are partly determined by the crystalline structure and the degree of crystallinity of the thermoplastic matrix, it was necessary to study the effect of the recovery process, in particular the molding, on the degree of crystallinity. Measuring the melting enthalpy of a polymer allows for estimating its degree of crystallinity. The amorphous or semi-crystalline nature affects the melting enthalpy value and, consequently, the degree of crystallinity (\(Xc\)). In particular, the \(Xc\) can be estimated using the following equation [36]:  
\[X_{\mathrm{C}}=\frac{\Delta H_{m}-\Delta H_{c}}{\Delta H_{m}^{0}}.100\;[\%] \tag{4}\]  
where \(\Delta H_{m}\) is the enthalpy of neat resin obtained by normalizing the weight of the tested sample on the percentage of fiber content; \(\Delta H_{c}\) is the enthalpy associated with the cold crystallization phenomenon, and \(\Delta H_{m}^{0}\) is the melting enthalpy of a perfect crystal.  
The melting enthalpy of 100% crystallized PA6 is 230 J/g [37; 38]. Table 5 reports the enthalpy values of the two heating cycles of DSC and the respective crystallinities calculated using Equation (4) for the manufactured PA6/60 panels. Additionally, the difference between the two crystallinity values was determined by subtracting the crystallinity of the second cycle from that of the first cycle. The data analysis shows that for Carbiso TM-PA6/60, Method 1 leads to a greater crystallinity reduction than Method 2, resulting in more amorphous material.  
The melting enthalpy of 100% crystallized PP is 209 J/g [39; 40]. In Table 6, the results of the DSC analysis of MAPP/60 panels and the respective crystallinity are reported. The results highlight that the Carbiso TM-MAPP/60 lamination process leads to lower crystallinity with respect to the one-shot method. This result is opposite to that of PA6/60.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Description** & **E\({}^{\prime}\) @ 20 \({}^{\circ}\)C** & **E\({}^{\prime\prime}\) @ 20 \({}^{\circ}\)C** & **Tans @ 20 \({}^{\circ}\)C** \\  & **[GPa]** & **[GPa]** & **[-]** \\ \hline MAPP/60 1L & 11.2 \(\pm\) 1.41 & 0.2 \(\pm\) 0.03 & 0.021 \(\pm\) 0.0003 \\ MAPP/60 2 LM1 & 10.8 \(\pm\) 1.36 & 0.3 \(\pm\) 0.05 & 0.027 \(\pm\) 0.0014 \\ MAPP/602 LM2 & 16.7 \(\pm\) 0.57 & 0.4 \(\pm\) 0.02 & 0.021 \(\pm\) 0.0007 \\ MAPP/60 3 LM1 & 15.4 \(\pm\) 0.40 & 0.3 \(\pm\) 0.01 & 0.022 \(\pm\) 0.0009 \\ MAPP/60 3 LM2 & 14.7 \(\pm\) 1.31 & 0.3 \(\pm\) 0.03 & 0.023 \(\pm\) 0.0011 \\ \hline \end{tabular}
\end{table}
Table 4: Results of DMA analysis at 20 \({}^{\circ}\)C.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Description** & **1 st Reaction** & **2 nd Reaction** & **1 st DOC** & **2 nd DOC** & **\(\Delta\) DOC** \\  & **[J/g]** & **[J/g]** & **[\%]** & **[\%]** & **[\%]** \\ \hline PA6/60 1L & 74.5 \(\pm\) 1.0 & 63.4 \(\pm\) 1.2 & 32.4 & 27.6 & 4.8 \\ PA6/60 2 LM1 & 73.1 \(\pm\) 1.4 & 58.2 \(\pm\) 1.6 & 31.8 & 25.3 & 6.5 \\ PA6/60 2 LM2 & 71.0 \(\pm\) 1.3 & 64.2 \(\pm\) 1.8 & 30.9 & 27.9 & 3.0 \\ PA6/60 3 LM1 & 72.1 \(\pm\) 1.2 & 65.1 \(\pm\) 1.2 & 31.3 & 28.3 & 3.0 \\ PA6/60 3 LM2 & 70.0 \(\pm\) 1.1 & 66.4 \(\pm\) 1.0 & 30.4 & 28.9 & 1.6 \\ \hline \end{tabular}
\end{table}
Table 5: Results of DSC and crystallinity analysis of PA6/60 panels.