## 3 Results
### Thermogravimetric Analysis (TGA)  
The thermal analysis has proven to be an important tool for evaluating the decomposition process of asphalt, through the analysis of curves of weight loss and derivative Thermogravimetry (DTG) [25].  
Figure 2 shows TGA thermograms of the prepared asphalt blends. Raw CFP and SBS were tested independently for comparison. As observed, the CFP decomposition curve shows a weight loss stage at the range of 50-250 \({}^{\circ}\)C attributed to the beginning of thermal decomposition of keratin [26], a second one at the range of 250-400 \({}^{\circ}\)C consistent with the keratin denaturation and disulfide bonds breakdown, and finally, a residue (about 18%) at 1000 \({}^{\circ}\)C [20]. The SBS thermogram showed a single decomposition stage ranging from 400 to 500 \({}^{\circ}\)C, which is typical of this kind of material [20].  
Figure 1: Fluorescence microscopy images: (**a**) M1, (**b**) M2, (**c**) M3, (**d**) M4, (**e**) M5, (**f**) M6.  
Asphalt blends prepared with CFP presented a weight loss stage from 250 \({}^{\circ}\)C to 500 \({}^{\circ}\)C with a residue of about 15%, which is quite similar to that of raw CFP. In this region, the decomposition of asphaltenes has been reported before [27]. The multiple decomposition stages have also been reported for asphalt binders [28]. Given that the decomposition temperatures of the CFP and the asphalt are quite similar, the derivative weight loss curve (DTG) was obtained to determine the point corresponding to the most significant weight loss. A derivative weight loss curve can be used to indicate the point at which weight loss is most apparent and the temperature of the peak in the DTG corresponds to the temperature at which maximum degradation takes place. In addition, its quotient allows to determine the blend susceptibility to decomposition. In Figure 3, from the DTG curve it can be observed that the total decomposition of the asphalt blends takes place in a single stage around 480 \({}^{\circ}\)C, far beyond the blending temperature and similar to the SBS decomposition temperature [29]. Even if the decomposition temperature of the modified asphalts is technically the same, their quotient shows slight variations, which indicates their susceptibility to degradation. The CFP-modified asphalt shows a lower quotient compared to the rest of the modified asphalts, which means that it is the least likely to suffer thermal weight loss; this may be due to the physical interactions between CFP and the heavy fractions of asphalt, which require more energy to break the bonding. Based on the results of this study, CFP by itself is the best modification agent for increasing the stability to decomposition at the same temperature, in contrast with either SBS or SBS/CFP composites. Additionally, these results confirm the compatibility between CFP and the asphalt [26]. This behavior can be attributed to the keratin structure, which makes the asphalt more resistant to temperature, even if its decomposition begins before SBS [29]. The addition order has a similar effect on the thermal stability, showing an improved behavior compared with that of the asphalt modified either only with SBS or with the SBS/CFP composites.  
Figure 2: SDT (DSC/TGA) thermograms for SBS, CF, and modified asphalts M1–M6.