## 3 Results and Discussion
### Thermal Properties  
The DSC second heating curves of the neat mPPO and the GF/mPPO composites are shown in Figure 7, and the glass transition temperatures (T\({}_{\rm g}\)) are listed in Table 4. The curves show no melting peaks, indicating that mPPO is an amorphous polymer. In addition, a single transition region explains the miscibility between the PS and PPO. The small endothermic peak near 120 \({}^{\circ}\)C may be the LDPE added by the manufacturer as a lubricant [19]. The slight decrease in the T\({}_{\rm g}\) in the GF/mPPO composites could be attributed to the thermal degradation of the mPPO during the preparation of the GF/mPPO masterbatch. The molten polymer was exposed to air when it was fed into the second  
Figure 6: Fracture morphologies of the GF/mPPO composites; (**a**) GF/mPPO 30, (**b**) GF/mPPO 40, and (**c**) GF/mPPO 50.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **GF/mPPO 30** & **GF/mPPO 40** & **GF/mPPO 50** \\ \hline \(\lambda_{\sigma}\) & 0.126 & 0.129 & 0.113 \\ \(\lambda_{E}\) & 0.544 & 0.587 & 0.604 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The fiber efficiency factor for tensile strength and modulus of GF/mPPO composites.  
extruder from the first extruder (Figure 1), leading to the thermal degradation of the mPPO in the masterbatch. This phenomenon has been reported in the GF/PA composite manufactured by the two extruders system, similar to the one in this study [20]. The Tg of the degraded polymer chain is able to move easily at a relatively low temperature due to chain scission.  
From the TGA analyses, the weight loss curve and the derivative thermogravimetric (DTG) curve are shown in Figure 7, and the temperatures corresponding to the weight losses of 5 (T5%) and T (10%) are listed in Table 4. The GF enhances the thermal stability of the matrix because it has a higher thermal stability compared to the neat matrix [21]. Although the degradation of the mPPO occurred during the preparation of the GF/mPPO masterbatch, both decomposition temperatures (T5% and T10%) increased with increasing GF content. This indicates that the thermal stability of the GF/mPPO composite was improved by the GF. In the DTG curve of the neat mPPO, two peaks before and after approximately 430 \({}^{\circ}\)C were superimposed (Figure 8). Because PS is less thermally stable than PPO, the peak before 430 \({}^{\circ}\)C corresponds to PS, and the peak after 430 \({}^{\circ}\)C corresponds to PPO [22]. The PS peak was reduced more than the PPO peak with increasing GF content. This indicates that the thermal degradation of PS occurred intensively during the preparation of the GF/mPPO masterbatch because of its low thermal stability. The significant thermal degradation of PS may have additional negative effects on the impact strength among the mechanical properties because high-impact PS was reduced during the manufacturing processes.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Glass Transition** & \multicolumn{2}{c}{**Decomposition Temperature**} \\ \cline{2-4}  & **Temperature**, **Tg** (\({}^{\circ}\)C) & **T5\%** (\({}^{\circ}\)C) & **T10\%** (\({}^{\circ}\)C) \\ \hline Neat mPPO & 142.45 & 387.16 & 399.44 \\ GF/mPPO 30 & 141.53 & 393.81 & 405.71 \\ GF/mPPO 40 & 140.85 & 394.90 & 407.52 \\ GF/mPPO 50 & 140.58 & 397.21 & 410.00 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Thermal analysis results of neat mPPO and GF/mPPO composites.  
Figure 7: The 2 nd heating curves of neat mPPO and GF/mPPO composites.