## 3 Results  
### Physical Properties  
Table 2 shows the physical properties of the asphalt binder. The softening point increased in all of the modified samples regarding the pristine asphalt; therefore, all these mixtures will be less susceptible to permanent deformations. The softening point behaved analogously to the viscosity since these two properties are closely related, this is consistent with the fact that asphalts with a high softening point are more viscous than those with a low softening point. Additionally, the processing conditions of the composites (prepared at 80 \({}^{\circ}\)C and 50 or 70 rpm, respectively) do not seem to significantly affect the physical properties of the asphalt modified with those composites (M5 and M6). On the other hand, the addition sequence of the additives into the asphalt (as shown by the properties of the samples M3 and M4) has a greater effect on the physical properties of the asphalt blends, which indicates that the addition order determines the way in which CFP interacts with the heavy fractions of the asphalt through intermolecular forces, resulting in a high softening point and low phase separation and penetration values. However, the improvement of the physical properties of the modified asphalts is not as good as in the samples modified just with SBS or only with CFP (samples M1 and M2). As can be observed in Table 2, the best results correspond to those of the asphalt modified using just CFP (M2), a natural waste that was not subjected to any chemical process. This implies that the size reduction of the chicken feathers is sufficient for promoting the use of CFP as an efficient modifier of the physical properties of the asphalt. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Code**} & **Softening Point, R\&B (\({}^{\circ}\)C)** & **Phase Separation R\&B (\({}^{\circ}\)C)** & **Penetration (dmm)** & **Rotational Viscosity, 135 \({}^{\circ}\)C (Pa.s)** \\ \hline
**Asphalt** & 52 & 0 & 44 & 0.545 \\ \hline
**M1** & 63 & 2.3 & 39.6 & 1.46 \\ \hline
**M2** & 64 & 0.5 & 28.0 & 1.533 \\ \hline
**M3** & 54.2 & 10 & 41.1 & 1.275 \\ \hline
**M4** & 60 & 7.5 & 36.5 & 1.430 \\ \hline
**M5** & 60 & 2.5 & 39.8 & 1.290 \\ \hline
**M6** & 60 & 4.5 & 41.6 & 1.202 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Effect of SBS/CF composite and CF on the physical properties of asphalt binder. The softening temperature values after the phase separation test exhibited that the largest difference between the top and bottom parts of the collapsible tube, clearly corresponds to that of the asphalt binder modified with SBS and CFP in that addition order (M3). The incorporation of only CFP in the mixture causes a narrowing of the difference between the properties of the upper and lower regions of the tube; the difference fits into the range of the storage-stable mixtures as shown by the value of less than 1 \({}^{\circ}\)C for asphalt modified with only CFP (M2), the lowest value among all the tested materials, followed by 2.3 \({}^{\circ}\)C, shown by the asphalt modified with SBS (M1). The rest of the asphalts presented higher temperature gaps. This behavior indicates that the asphalt blend prepared with raw CFP was the most homogeneous. This behavior is attributed to the interaction between the amino acid groups of the keratin structure and the polar compounds of the asphalt, such as resins and asphaltenes. These interactions can be explained by the presence of three different mechanisms: (1) existence of rigid inclusions, (2) filler-asphal interfacial effects and (3) reinforcement due to the filler volume produced by particle interaction [8; 22]. Keratin has a complex structure that leads to an increased mechanical stability in the asphalt blend [23]. Similar behavior between polar particles has already been reported, e.g., nanoclays and asphalt heavy fractions [22] as well as oyster shell, which are mainly composed of calcium carbonate [8]. However, in the case of CFP, a better response in softening temperature and penetration was achieved.