# Novel Hybrid PETG Composites for 3D Printing
## 3 Results
### Properties of Virgin PETG with Expanded Graphite  
The mechanical properties from tensile test and nanoindentation of the prepared virgin PETG composite filled with EG are summarized in Table 4. Table 4 shows the varying values of [PERSON]'s modulus of elasticity of the prepared composite materials. With increasing content of EG, the \(E\) increases, so that the material becomes stiffer. Tensile stress at yield (\(\sigma_{Y}\)) and tensile stress at break (\(\sigma_{B}\)) did not change significantly with the addition of EG, but for the highest concentration of filler (sample AG-10) dropped sharply. In order for the filler to increase the strength of the material, the maximum adhesion to the matrix-filler interface is needed. In the case of the AG-10 sample, the addition of a large amount of expanded graphite caused weakening interactions between the polymer chains and fillers and prevailing of shear forces between expanded graphite particles. This idea is also confirmed by decreasing \(\varepsilon_{B}\). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \(E\) (MPa) & \(\sigma_{Y}\) (MPa) & \(\sigma_{B}\) (MPa) & \(\varepsilon_{B}\) (\%) & \(T_{10}\) & \(T_{50}\) & \(m_{550}\) & **Contact** & \(\rho\) \\  & & & & (\({}^{\circ}\)C) & (\({}^{\circ}\)C) & (\%) & **Angle (\({}^{\circ}\))** & **(g\(\cdot\)cm\({}^{-3}\))** \\ \hline
**A** & 1600 \(\pm\) 90 & 58.3 \(\pm\) 2.1 & 59.7 \(\pm\) 5.5 & 362.5 \(\pm\) 10.9 & 402.1 & 431.8 & 9.0 & 86.9 \(\pm\) 2.6 & 1.27 \\
**B** & 1690 \(\pm\) 40 & 58.4 \(\pm\) 4.6 & 55.1 \(\pm\) 1.4 & 326.2 \(\pm\) 52.8 & 401.9 & 426.5 & 9.2 & 83.3 \(\pm\) 2.6 & 1.32 \\ \hline \hline \end{tabular}
\begin{tabular}{c} \(E\)—Young’s modulus, \(\sigma_{Y}\)—tensile stress at yield, \(\sigma_{B}\)—tensile stress at break, \(\varepsilon_{B}\)—elongation at break, \(T_{10}\)—the temperature at which 10% weight loss was recorded, \(T_{50}\)—the temperature at which 50% weight loss was recorded, \(m_{550}\)—char yield at 550\({}^{\circ}\)C, \(\rho\)—density. \\ \end{tabular}
\end{table} 
Table 3: Experimental properties of virgin PETG (sample A) and recycled PETG (sample B). The same effect was confirmed from nanoindentation measurements. Reduced Young's modulus (\(E_{r}\)) was increased with increasing concentration of filler, but hardness (\(H\)) was not significantly changed with average value about 140 MPa. It is necessary to notice that the nanoindentation test does not observe a significant drop of properties for the highest concentration of filler. The results of thermal properties are summarized in Table 5. It provides information about the \(T_{10}\) temperature (the temperature at which the sample quantity dropped to 90% of the original sample quantity), \(T_{50}\) (the temperature at which the sample quantity dropped to 50% of the original sample quantity), \(m_{550}\) (unburnt weight with respect to original weight at 550 \({}^{\circ}\)C) from thermogravimetric analysis, and linear thermal expansion coefficient (\(\alpha\)) from dilatometry. From the measured temperatures \(T_{10}\) and \(T_{50}\) it can be seen there was only a small effect of filler on the final thermal stability of polymer composites compared to pure virgin PETG. The value of \(T_{10}\) was almost unchanged; the value \(T_{50}\) was more dependent on the concentration of filler; however, there was no uniform trend. First, it decreased with an increasing amount of filler about 4 \({}^{\circ}\)C then it was increased up to the values of neat PETG. In the case of char yield at 550 \({}^{\circ}\)C, the trend was clear with assumptions and it increased with an increased amount of EG. It was obvious that EG was not subject to thermal degradation. Nevertheless, the value for the thermal expansion coefficient slightly decreased from the value for virgin PETG, \(\sim\)60 \(\times\) 10\({}^{-6}\) K\({}^{-1}\) up to \(\sim\)51 \(\times\) 10\({}^{-6}\) K\({}^{-1}\).