## 3 Results and Discussion
### Mechanical and Dynamic Mechanical Analysis
The loss factor and loss modulus curves of each composite are comparable. To distinguish the samples, two relaxations can be seen in the loss factor vs. temperature and loss modulus vs. temperature curves of PP composites reinforced with glass fiber or a mixture of glass fiber and treated fly ash. Another relaxation can be seen in Figure 5d exclusively on the curves for composites containing elastomer, PP-25G-E and PP-25G-C-E \({}^{\prime\prime}\) peak 1 is only found in PP-25G-E and PP-25G-C-E because it corresponds to the Tg of the elastomer (olefin block) [52], whereas E\({}^{\prime\prime}\) peak 2 is associated with the glass transition of PP (Tg) and E\({}^{\prime\prime}\) peak 3 is associated with the lamellar slip and rotation in the crystalline phase of PP [53]. The tan \(\delta\) curves of the samples exhibit three distinct relaxation peaks that correspond to the peaks of the loss modulus. The loss modulus curve's highest peak, which corresponds to Tg, is seen for PP-30G at approximately 13.4 \({}^{\circ}\)C, whereas the peak for PP-25G was found at approximately 11 \({}^{\circ}\)C. Table 6 indicates that PP-25G-E and PP-25G-C-E exhibited Tg values that were 0.1-1.7 \({}^{\circ}\)C higher than PP-25G. This suggests that there was an improvement in the viscous properties due to good component interaction. The PP glass transition temperature (Tg) of 17 \({}^{\circ}\)C was determined from the tan \(\delta\) vs. temperature plot, while a second peak at around 95 \({}^{\circ}\)C is associated with lamellar slip and rotation in the crystalline phase of PP. Glass transitions of elastomer can be seen in Figure 5 (d) at \(-\)52.6 \({}^{\circ}\)C and \(-\)50.7 \({}^{\circ}\)C only for PP-25G-E and PP-25G-C-E. Composites with elastomer have the lowest values for Tg (from tan delta) and the highest tan delta peak heights. These results mean lower thermal stability for these samples, but higher impact strength. The DMA results correlate very well with mechanical impact tests (Figure 5a) and with the TGA results (Table 3). Figure 5e shows the storage moduli of the studied composites as a function of temperature. Sample PP-30G has the highest stiffness of all samples due to having the highest concentration of incorporated glass fiber in neat PP [54]. PP-25G-C has higher stiffness compared to PP-25G due to the presence of well dispersed ash powder and compatibilizing agent in the PP system. Such an enhancement was pointed out in a study by [PERSON] et al. [41], where more effectively dispersed silica particles and the presence of PP-MA compatibilizing agent caused stronger interactions and increases in the elastic moduli of the materials. A similar effect with the introduction of well-dispersed ash powder and compatibilizing agent into recycled PP was observed in a previous study by [PERSON] et al. [12]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Tensile Stress** & **Young’s Modulus** & **Axial Strain at Break** & **Impact Strength** \\  & **at Tensile Strength (MPa)** & **(MPa)** & **(\%)** & **(KJ/m\({}^{2}\))** \\ \hline PP-25G & 71 \(\pm\) 2 & 4576 \(\pm\) 575 & 2.8 \(\pm\) 0.3 & 9 \(\pm\) 0.3 \\ PP-30G & 80 \(\pm\) 3 & 4905 \(\pm\) 435 & 2.9 \(\pm\) 0.3 & 10 \(\pm\) 0.5 \\ PP-25G-C & 62 \(\pm\) 0.5 & 4162 \(\pm\) 199 & 2.5 \(\pm\) 0.2 & 7 \(\pm\) 0.3 \\ PP-25G-E & 59 \(\pm\) 1.2 & 3258 \(\pm\) 262 & 3.9 \(\pm\) 0.3 & 13 \(\pm\) 0.5 \\ PP-25G-C-E & 48 \(\pm\) 0.5 & 3238 \(\pm\) 115 & 4.6 \(\pm\) 0.3 & 11 \(\pm\) 0.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Mechanical properties of PP-25G, PP-30G, PP-25G-E, PP-25G-C and PP-25G-C-E composites.