# Novel Hybrid PETG Composites for 3D Printing
## 3 Results
### Properties of Virgin PETG Filled with Carbon Fibers  
The tensile mechanical properties of the prepared composite material of the PETG filled with CFs are summarized in Table 7. Samples were prepared from 2 mm long CFs in the concentration range 1-20 wt.%. The mechanical properties were enhanced more significant in case of CFs than EG filling. The AF-10 sample reached about 30% higher value of [PERSON]'s modulus as the AG-10 sample. The AF-20 sample had a 124% higher \(E\) than the pure polymer matrix. As the increase in CF content also increased the tensile stress, the material became more resistant to permanent (plastic) deformation, while the addition of EG caused the \(\sigma_{\rm Y}\) and \(\sigma_{B}\) slight decrease. The decrease in the \(\varepsilon_{B}\) of the prepared CF composites is comparable with the effect of EG, although absolute values of \(\varepsilon_{B}\) of CF composites are double the values for EG composites. The same effect was observed for nanoindentation measurements. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **Density (g\(\cdot\)cm\({}^{-3}\))** & **Contact Angle (\({}^{\circ}\))** \\ \hline
**A** & 1.27 & 86.9 \(\pm\) 2.6 \\
**AG-1** & 1.30 & 78.8 \(\pm\) 3.8 \\
**AG-2** & 1.30 & 76.9 \(\pm\) 3.6 \\
**AG-3** & 1.31 & 75.1 \(\pm\) 2.4 \\
**AG-4** & 1.31 & 73.3 \(\pm\) 4.1 \\
**AG-5** & 1.32 & 71.3 \(\pm\) 3.5 \\
**AG-10** & 1.32 & 70.9 \(\pm\) 5.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The densities and contact angles of the prepared virgin PETG composite materials with the EG. Figure 1: SEM micrograph of cross-section filament–virgin PETG composite containing 5 wt.% of the expanded graphite. The \(E_{r}\) was increased with increasing loading with CF up to 150% comparing to pure polymer matrix but H remained constant at the same value as for EG composites--about 140 MPa. Here it is necessary to note that nanoindentation reinforcement (\(E_{r}\)) was not as significant as in the case of EG composites. The results of the thermogravimetric analysis are summarized in Table 8, where the temperature information \(T_{10}\), \(T_{50}\), and \(m_{550}\) are demonstrated. Similar results to EG composite materials were observed and it can be concluded that thermogravimetric properties are independent of the carbon filler. However, a significant difference was observed for dilatometry. As can be seen from Table 8, \(\alpha\) for CF composites sharply decreased with increasing loading of filler. It is a very positive property in case of 3D printing when thermal shrinkage is one of the limiting factors for high-volume printing. The relationship of the contact angle to the CF content is shown in Table 9. The contact angle dropped, and the effect was the same in case EG composites. Opposite trends, as for the EG filaments, were observed for the density of CF filaments when density was decreasing with increasing loading up to 88% of density pure polymer matrix (sample AF-20). It was caused by the low density of pure CFs since the manufacturer reported the value of 1.80 g-cm-3. In Figure 2A, which was obtained with a scanning electron microscope at a 75\(\times\) magnification, the cross-section of the filament is visible. Homogeneous distribution of CFs in the whole fracture