# Novel Hybrid PETG Composites for 3D Printing
## 3 Results
### Properties of Virgin PETG with Expanded Graphite
The high thermal conductivity of the EG could result in better heat transfer in the polymer matrix, and it also depends on homogeneous dispersion of filler inside the matrix. A carbon layer was probably formed on the surface of the filament, which served as an insulating carbon barrier. Therefore, several opposite effects led to ambiguous trends. The wettability analysis (Table 6) showed that the addition of EG to PETG resulted in reduced contact angle values. It was expected due to the contact angle value of pure expanded graphite, which was significantly lower, \(-\)49.4\({}^{\circ}\)[21]. A similar situation was also found in the literature, where the contact angle decreased with increasing content of EG [22]. The opposite effect was found in the case of density. The density of the prepared composite materials increased with increasing content of EG (Table 6). This trend was clear because the density of the pure expanded graphite was higher than the PETG density. The value of pure filler was 1.5 g\(\cdot\)cm\({}^{-3}\). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & \(\mathbf{E}\) **(MPa)** & \(\sigma_{\mathbf{Y}}\) **(MPa)** & \(\sigma_{\mathbf{B}}\) **(MPa)** & \(\epsilon_{\mathbf{B}}\) **(\%)** & \(\mathbf{E_{r}}\) **(GPa)** & **\(\mathbf{H}\) **(GPa)** \\ \hline
**A** & 1600 \(\pm\) 90 & 58.3 \(\pm\) 2.1 & 59.7 \(\pm\) 5.5 & 362.5 \(\pm\) 10.9 & 2.59 \(\pm\) 0.50 & 0.13 \(\pm\) 0.03 \\
**AG-1** & 1970 \(\pm\) 120 & 57.7 \(\pm\) 4.4 & 57.6 \(\pm\) 4.3 & 4.4 \(\pm\) 0.4 & 2.80 \(\pm\) 0.10 & 0.14 \(\pm\) 0.01 \\
**AG-2** & 2040 \(\pm\) 75 & 55.1 \(\pm\) 1.9 & 53.5 \(\pm\) 3.9 & 4.5 \(\pm\) 0.6 & 2.88 \(\pm\) 0.36 & 0.13 \(\pm\) 0.02 \\
**AG-3** & 2150 \(\pm\) 225 & 54.1 \(\pm\) 3.3 & 53.1 \(\pm\) 2.3 & 4.4 \(\pm\) 0.5 & 3.07 \(\pm\) 0.13 & 0.14 \(\pm\) 0.01 \\
**AG-4** & 2190 \(\pm\) 40 & 55.4 \(\pm\) 5.2 & 53.6 \(\pm\) 6.6 & 4.4 \(\pm\) 0.8 & 3.07 \(\pm\) 0.17 & 0.14 \(\pm\) 0.01 \\
**AG-5** & 2250 \(\pm\) 70 & 54.6 \(\pm\) 3.9 & 53.4 \(\pm\) 4.0 & 4.5 \(\pm\) 0.9 & 3.29 \(\pm\) 0.17 & 0.14 \(\pm\) 0.01 \\
**AG-10** & 2630 \(\pm\) 90 & 32.1 \(\pm\) 2.2 & 32.2 \(\pm\) 1.8 & 2.4 \(\pm\) 0.2 & 3.86 \(\pm\) 0.20 & 0.14 \(\pm\) 0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mechanical properties of virgin PETG filled with expanded graphite. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & \(\mathbf{T_{10}}\) **(\({}^{\circ}\)C)** & \(\mathbf{T_{50}}\) **(\({}^{\circ}\)C)** & \(m_{550}\) **(\%)** & \(\mathbf{\alpha}\) **(10\({}^{-6}\) K\({}^{-1}\))** \\ \hline
**A** & 402.1 & 431.8 & 9.0 & 60.12 \\
**AG-1** & 401.6 & 426.2 & 9.2 & 60.70 \\
**AG-2** & 402.6 & 427.5 & 9.7 & 62.06 \\
**AG-3** & 402.1 & 428.5 & 9.2 & 64.85 \\
**AG-4** & 403.3 & 430.5 & 10.0 & 52.07 \\
**AG-5** & 402.9 & 431.7 & 10.9 & 51.23 \\
**AG-10** & 404.3 & 432.5 & 12.4 & 55.14 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Thermal properties of the prepared composite materials–virgin PETG and expanded graphite. Figure 1 represents the cross-section of the prepared filament. As can be seen on the AG-5 sample from a scanning electron microscope at a 708\(\times\) magnification under the electron beam, the EG was evenly dispersed and no visible agglomerates of the filler were present.