## 3 Results and Discussion
### Mechanical and Dynamic Mechanical Analysis  
Glass fiber-reinforced thermoplastic composites offer advantages such as high mechanical strength, hardness and unlimited shelf life together with a positive environmental impact, as shown in a study by [PERSON] et al. [47]. The variation in mechanical properties can mainly depend on the fiber shortening and breaking that takes place during the extrusion and injection molding processes. It is well known that glass fiber greatly increases the strength and stiffness of neat thermoplastic polymers [48; 49; 50]. In Figure 5a and Table 5, composite PP-25G-C-E, which contains glass fiber and elastomer as well as fly ash, is competing in its mechanical properties with both PP-25G and PP-30G. A key aspect that determines whether a material is suitable or not for an application in the automotive industry is its balance of mechanical properties, because by greatly improving one property, we risk downgrading another one. Therefore, for many automotive applications, the important properties for reinforced thermoplastic composites are improved toughness (impact strength and axial strain) in addition to high strength and stiffness. By looking at the variation in properties in Figure 5a,b as well as in Table 5, we see that while the introduction of elastomer leads to 25-39% higher impact strength, the values for stiffness (Young's modulus and storage modulus E) are reduced by approximately 30%. With the addition of 5% ash, the composite PP-25G-C-E has higher impact strength value than PP-25G of approximately 17%, than PP-30G of approximately 8%, as well as higher axial strain value of approximately 41% and 38%, respectively, as seen in Figure 5c. A particular case can be observed in the stress vs. strain curves that indicates a lower tensile strength for PP-25G-C-E compared to PP-25G-E while having higher axial strain. [PERSON] et al. [23] reported in their study that the presence of elastomer may improve a composite's toughness (expressed by axial strain and impact strength) at the cost of tensile strength. Their study also showed that various ratios between a PP matrix, a layered silicate and elastomer may lead to variations in mechanical properties where a decrease in tensile strength and increase in axial strain are observed. Their argument is that good particle dispersion and interactions between the components may lead to percolated structures that improved the mechanical properties of neat PP. It is possible that a similar effect might have occurred in our study. These results prove good dispersion and interaction among the components in PP-25G-C-E. A study by [PERSON] et al. [44] showed similar results and explained that the maleic anhydride functional group improves the interfacial adhesion between SEBS and glass fiber, thus improving its impact strength. Figure 5: Mechanical and dynamic mechanical properties of PP-25G, PP-30G, PP-25G-E, PP-25G-and PP-25G-C-E composites. (**a**) Tensile and impact properties; (**b**) Young’s moduli and storage moduli at 25 °C; (**c**) stress vs. strain curves; (**d**) loss moduli and loss factors; (**e**) storage moduli. Through DMA analysis, the impact of ash powder and elastomer on the viscoelastic behavior of glass fiber-reinforced PP was analyzed. This allowed for an evaluation of the stiffness and elastic behavior via the storage modulus (E\({}^{\prime}\)) and the viscous characteristic through the loss modulus (E\({}^{\prime\prime}\)) for the studied composites. Furthermore, the loss factor (tan \(\delta\)) was obtained for assessing the impact resistance of the composites as well as the weight of the elastic and viscous phases [51]. Figure 5b displays the comparison of the storage modulus at 30 \({}^{\circ}\)C to [PERSON]'s modulus, while Figure 5d reveals the loss modulus and loss factor of the PP composites as a function of temperature. E\({}^{\prime}\) of PP-25G-C-E decreases by 25-33% compared to PP-25G and PP-30G, respectively, and these values are consistent with their [PERSON]'s modulus values (Figure 5b).