# Novel Hybrid PETG Composites for 3D Printing
## 3 Results
### Properties of Virgin PETG Filled with EG and CFs  
Because both the above-mentioned carbon fillers have their own advantages for 3D filaments, we tried to combine them to prepared hybrid composites. CFs are better for reinforcing and eliminating thermal expansion, while EG decreases surface roughness of filament and supports the rheology during 3D printing. For better comparison, the concentration of filler was kept constant at 10 wt.% and the ratio of EG to CFs was varied between 8:2, 6:4, 5:5, 4:6, and 2:8, respectively. The results of the mechanical properties of the hybrid virgin PETG composites are summarized in Table 10. In the case of EG composite materials, increasing the concentration of the filler increased Young's modulus. An even more pronounced increase in Young's modulus was recorded in CF composites. It is understandable that in the case of hybrid composite materials containing a combination of EG and CFs, Young's modulus will grow with an increasing of CFs content. From the AG-1 to AG-10 samples, the \(\sigma_{Y}\) decreased with an increasing concentration of EG, and in the AF-1 to AF-20 samples there was an increase in the \(\sigma_{Y}\) with an increasing concentration of CFs. In the case of a combination of fillers, the \(\sigma_{Y}\) and \(\sigma_{B}\) can be assumed as constant, but higher than for the pure polymeric matrix. Since the addition of EG and CFs caused a significant drop in \(\varepsilon_{B}\), it also occurred when both fillers were used simultaneously. \(E_{r}\) decreased with an increasing ratio of CFs; however for all cases it was above the value for pure polymer matrix. The hardness from nanoindentation measurements seemed to be constant. \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
**A** & \(1600\pm 90\) & \(58.3\pm 2.1\) & \(59.7\pm 5.5\) & \(362.5\pm 10.9\) & \(2.59\pm 0.50\) & \(0.13\pm 0.03\) \\
**AGF-8:2** & \(2646\pm 170\) & \(63.4\pm 2.7\) & \(58.6\pm 2.3\) & \(4.6\pm 0.8\) & \(4.02\pm 0.24\) & \(0.16\pm 0.02\) \\
**AGF-6:4** & \(3364\pm 190\) & \(66.9\pm 5.9\) & \(65.7\pm 5.8\) & \(4.2\pm 0.8\) & \(3.76\pm 0.28\) & \(0.15\pm 0.01\) \\
**AGF-5:5** & \(3054\pm 235\) & \(66.2\pm 1.1\) & \(62.4\pm 5.8\) & \(4.9\pm 1.6\) & \(3.26\pm 0.38\) & \(0.14\pm 0.02\) \\
**AGF-4:6** & \(3095\pm 370\) & \(66.4\pm 4.1\) & \(63.9\pm 3.9\) & \(5.1\pm 1.2\) & \(3.49\pm 0.21\) & \(0.14\pm 0.01\) \\
**AGF-2:8** & \(3330\pm 480\) & \(69.1\pm 7.4\) & \(66.3\pm 1.3\) & \(4.5\pm 1.6\) & \(3.35\pm 0.25\) & \(0.14\pm 0.01\) \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Mechanical properties of virgin PETG filled with EG and CFs. Figure 2: SEM micrograph of the fracture surface of the prepared AF-5 composite material. (**A**) shows the cross-section of the entire string at 75 magnification, and (**B**) shows a fracture area at 1228\(\times\) magnification. The results of the thermogravimetric analysis are summarized in Table 11. The same trends were present for filaments with individual fillers. Only a slight effect on the temperature of degradation and a significant decrease for the coefficient of thermal expansion were observed, which were caused by the presence of CFs. In composite materials with EG, an increase in the concentration of the filler resulted in a reduction in contact angle values. A similar trend was also found in CF composite materials when the contact angle was reduced with increasing CF concentration. As can be seen from Table 12, the combination of these two fillers decreased the contact angle with an increasing concentration of CF. The contact angle of the prepared composites was higher than the contact angle of samples AG-10 and AF-10. The densities recorded in Table 12 had a relatively expected progression as EG PETG composites grew densities with increasing EG content and CF composites density dropped with an increasing CF content.