# Thermoforming Process Effect on Performances of Thermoplastic/Recycled Carbon Fiber Composites
## 3 Results and Discussion
### Effect of Porosity on the Storage Modulus  
The intricate relationship between porosity and the mechanical properties of composite materials is a critical factor in assessing their performance. The presence of pores within the polymer matrix can drastically impact both stiffness and viscoelastic behavior, making it essential to understand this dynamic. Generally, increased porosity leads to a reduction in the storage modulus and an elevated damping factor. This underlines the importance of selecting optimal hot-pressing methodology and processing parameters to effectively control porosity, influencing the material's properties and potential for advanced structural applications. Figure 9 illustrates the correlation between the elastic modulus and porosity in PA6/60 panels. As porosity rises, the storage modulus (E\({}^{\prime}\)) value declines. Notably, for samples obtained by two layers and compression-molded with Method 2 emerged as the better choice, overcoming Method 1. The 2 LM1 sample achieved an average E\({}^{\prime}\) value of 10 GPa, while the 2 LM2 sample excelled with a remarkable 15.2 GPa. This striking contrast in modulus values is directly linked to the higher porosity of the one-shot process (13.2%) compared to the lamination process (9.9%), highlighting the significance of compression molding process parameters. However, as the number of layers increases, the differences in compaction methodologies decrease. In the case of three-layer panels, the storage modulus for the 3 LM1 sample reaches 14.4 GPa, while the 3 LM2 sample holds at 11.6 GPa. Additionally, porosity values begin converging at approximately 14% for the first sample and 16.7% for the second, emphasizing the complex interplay between processing conditions and material performance. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Description**} & **1 st Reaction** & **2 nd Reaction** & \multirow{2}{*}{**1 st DOC**} & **2 nd DOC** & \multirow{2}{*}{**\(\Delta\) DOC**} \\  & **Enthalpy** & **[/g]** & **[/g]** & **[\%]** & **[\%]** & **[\%]** \\ \hline MAPP/60 1L & 108.0 \(\pm\) 1.6 & 92.2 \(\pm\) 1.1 & 51.7 & 44.1 & 7.6 \\ MAPP/60 2 LM1 & 109.6 \(\pm\) 1.0 & 97.6 \(\pm\) 1.2 & 52.4 & 46.7 & 5.7 \\ MAPP/602 LM2 & 104.1 \(\pm\) 1.2 & 93.2 \(\pm\) 1.5 & 49.8 & 44.6 & 5.2 \\ MAPP/60 3 LM1 & 105.8 \(\pm\) 1.3 & 94.2 \(\pm\) 1.7 & 50.6 & 45.1 & 5.6 \\ MAPP/60 3 LM2 & 103.1 \(\pm\) 1.1 & 92.9 \(\pm\) 1.3 & 49.3 & 44.5 & 4.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Result of DSC and crystallinity analysis of MAPP/60 panels. Figure 9: Relationship between [PERSON]’s modulus and porosity for various PA6/60 composite configurations. The graph shows a strong negative correlation (R\({}^{2}\) = 0.979), with a linear regression equation of y = \(-45.89\times\) + 19.29. Error bars represent the measurement uncertainties for each data point. Figure 10 shows the microscopic analysis on a PA6/60 2 LM1 sample in proximity of a porosity, while Figure 11 is the same analysis for a PA6/60 2 LM2 sample. The defect in the sample made with Method 1 has an average thickness of 44.7 \(\upmu\)m, while the defect in the sample produced with Method 2 has an average thickness of 39.2 \(\upmu\)m. Micrographs confirm that the samples prepared according to Method 1 (M1) reproduce samples with a higher degree of porosity and weak materials. Figure 11: Defect analysis by image analysis, sample rCF-PA6/2 LM2. Figure 10: Defect analysis by image analysis, sample rCF-PA6/2 LM1. Figure 12 illustrates the variation of Elastic modulus as a function of porosity for the MAPP/60 panels. Consistent with previous findings, Method 2 yielded better results for the two-layer panels. Specifically, the elastic modulus for the 2 LM2 sample is 16.7 GPa, compared to 10.8 GPa for the 2 LM1 sample. This difference is linked to the variation in porosity between the two methods, which is 4.1% for the lamination process and 8.0% for the one-shot method.