# Novel Hybrid PETG Composites for 3D Printing
## 3 Results
### Characterization of the Properties of Recycled PETG Filled with EG, CFs, and Their Combination  
Because the price of filament is one of the crucial requirements for mass production of 3D printing we tried to replaces commercial virgin PETG with cheaper recycled PETG whose price is ten times lower. The usage of recycled PETG is also an important part of the circular economy that is on the rise for industrial scales. Also, it significantly helps to protect the planet. The results of the mechanical properties of pure recycled PETG (sample B) and three prepared composite materials from recycled PETG are summarized in Table 13. As can be seen from the table, the values of the \(E\) and \(\sigma_{Y}\) for all prepared materials based on recycled PETG with consideration of the standard deviation, are comparable with the equivalent composites based on virgin PETG, and only the sample BF-5 had a slightly lower \(\sigma_{Y}\). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Density (g-cm\({}^{-3}\))** & **Contact Angle (\({}^{\circ}\))** \\ \hline
**A** & 1.27 & 86.9 \(\pm\) 2.6 \\
**AGF-8-2** & 1.29 & 89.9 \(\pm\) 3.6 \\
**AGF-6-4** & 1.21 & 85.5 \(\pm\) 6.7 \\
**AGF-5-5** & 1.20 & 81.3 \(\pm\) 6.8 \\
**AGF-4-6** & 1.20 & 80.2 \(\pm\) 5.4 \\
**AGF-2-8** & 1.17 & 79.3 \(\pm\) 5.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: The densities of prepared PETG composites with EG and CFs at the total loading of 10 wt.%. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & \(\mathbf{T_{10}}\) **(\({}^{\circ}\)C)** & \(\mathbf{T_{50}}\) **(\({}^{\circ}\)C)** & \(\mathbf{m_{550}}\) **(\%)** & \(\mathbf{\alpha}\) **(10\({}^{-6}\) K\({}^{-1}\))** \\ \hline
**A** & 402.1 & 431.8 & 9.0 & 60.12 \\
**AGF-8-2** & 400.9 & 430.1 & 12.0 & 48.86 \\
**AGF-6:4** & 401.5 & 431.7 & 15.6 & 48.68 \\
**AGF-5:5** & 402.1 & 431.8 & 14.8 & 34.83 \\
**AGF-4:6** & 403.6 & 431.9 & 16.8 & 36.61 \\
**AGF-2:8** & 401.7 & 431.7 & 14.9 & 40.37 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Thermal properties of the prepared composite materials–vrigin PETG with EG and CF. The \(\sigma_{B}\) and \(\varepsilon_{B}\) of the prepared recycled PETG composites were comparable with the values for virgin PETG composites. Again, the sample BF-5 had a \(\sigma_{B}\) slightly lower than the AF-5 sample. Deterioration of mechanical properties was observed from nanoindentation measurements when all parameters decreased except \(E_{r}\) for BF-5 sample. Nevertheless, all mechanical properties were eligible for reinforced PETG filament with regard to the significant reduction of the final price. The thermal properties are summarized in Table 14. Recycled PETG reached \(T_{50}\) about 5 \({}^{\circ}\)C lower than \(T_{50}\) of virgin PETG. The differences between the virgin PETG and recycled PETG composites were not significant after the addition of the filler. This could be caused by the good thermal conductivity of both carbon fillers. The same effect was also observed in case of linear thermal expansion coefficient \(\alpha\), when carbon fillers decreased their values, but the absolute value of recycled PETG composites was slightly higher than the value for virgin PETG composites due to the higher initial value of pure recycled PETG. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & \(E\) **(MPa)** & \(\sigma_{Y}\) **(MPa)** & \(\sigma_{B}\) **(MPa)** & \(\varepsilon_{B}\) **(\%)** & \(E_{r}\) **(GPa)** & \(H\) **(GPa)** \\ \hline
**B** & \(1690\pm 45\) & \(58.4\pm 4.6\) & \(55.1\pm 1.4\) & \(326.2\pm 52.8\) & \(2.41\pm 0.13\) & \(0.11\pm 0.01\) \\
**BG-5** & \(2115\pm 120\) & \(53.6\pm 1.8\) & \(52.8\pm 1.4\) & \(4.8\pm 0.7\) & \(2.87\pm 0.25\) & \(0.11\pm 0.01\) \\
**BF-5** & \(2500\pm 265\) & \(67.4\pm 3.0\) & \(66.8\pm 2.7\) & \(4.9\pm 0.6\) & \(3.14\pm 0.38\) & \(0.11\pm 0.01\) \\
**BGF-5:5** & \(3110\pm 190\) & \(64.5\pm 4.3\) & \(63.2\pm 3.3\) & \(4.3\pm 0.4\) & \(2.47\pm 0.3\) & \(0.11\pm 0.02\) \\ \hline \hline \end{tabular}
\end{table}