# FTIR Characterization of Asphalt SARA Fractions in Response to Rubber Modification
## 3 Results and Discussion
### FTIR Spectral Comparisons of Neat Binder and A-RB Fractions
This reveals the existence of rubber unsaturated components in the aromatics at 190 \({}^{\circ}\)C and 600 min\({}^{-1}\); however, at 190 \({}^{\circ}\)C and 3000 min\({}^{-1}\), a similar peak emerged in the saturates (Figure 4). This highlights that increasing the interaction speed from 600 to 3000 min\({}^{-1}\) urged the unsaturated components to migrate into the saturate (non-polar) fraction. Figure 6 shows the FTIR spectra of resins fractions extracted from neat binder and A-RBs. The aliphatic C-H stretching vibrations between 2955 and 2850 cm\({}^{-1}\) intensified for A-RB resins compared to the neat resin, highlighting the migration of aliphatic components from rubber into resins. The broad O-H stretching peak at 3300 cm\({}^{-1}\) was intense for the neat binder resin; however, for A-RB 190-3000, this peak was extremely broadened. This could be related to hydrogen bonding or chemical interaction that broadened the O-H peak at 3300 cm\({}^{-1}\) and disappeared the C=O peak at 1700 cm\({}^{-1}\)[50]. However, the O-H and C=O peaks for the A-RB 220-3000 increased again due to oxidation and degradation of rubber components (e.g., depolymerization and excessive devulcanization). Contrary to saturates and aromatics, the spectra of resins did not show C=C stretching vibrations in  
Figure 4: FTIR spectra of saturates: (**a**) 4000–600 cm\({}^{-1}\) and (**b**) 2000–600 cm\({}^{-1}\). The purple box delineates the fingerprint region, magnified on the right to illustrate specific chemical alterations. aromatics at 1560 or 1571 cm\({}^{-1}\). Thus, the aromatics in rubber migrated into aromatics or saturates rather than resins. Figure 5: FTIR spectra of aromatics: (**a**) 4000–600 cm\({}^{-1}\) and (**b**) 2000–600 cm\({}^{-1}\). The purple box delineates the fingerprint region, magnified on the right to illustrate specific chemical alterations. Figure 6: FTIR spectra of resins: (**a**) 4000–600 cm\({}^{-1}\) and (**b**) 2000–600 cm\({}^{-1}\). The purple box delineates the fingerprint region, magnified on the right to illustrate specific chemical alterations. Figure 7 shows the FTIR spectra of asphaltenes fractions extracted from neat binder and A-RBs. During the interaction between rubber and asphalt at 3000 min\({}^{-1}\) and 190 \({}^{\circ}\)C, the rubber polymeric components were absorbed with the asphaltene as a polar- and aromatic-rich asphalt fraction [51]. These rubber components were detected at 971 cm\({}^{-1}\) (extending from 983 to 959 cm\({}^{-1}\)) and 735 cm\({}^{-1}\) (extending from 752 to 718 cm\({}^{-1}\)), which were related to the C-H out-of-plane bending of trans-alkene in PB and out-of-plane bending of the C-H in the monosubstituted aromatic ring in PS, respectively [52; 53]. These peaks were not detected in the asphaltenes of the neat binder and the A-RB 190-600. Moreover, the PB peak had higher intensity at A-RB 190-3000 than 220-3000, with areas of 4.38 and 1.98%.cm\({}^{-1}\), respectively. The PS peak at 735 cm\({}^{-1}\) for A-RB 190-3000 had an area of 10.62%.cm\({}^{-1}\); however, at 220 \({}^{\circ}\)C, this peak disappeared, which was related to the depolymerization that occurred at 220 \({}^{\circ}\)C. The C-H stretching vibrations at 2925 and 2850 cm\({}^{-1}\) were more intense in A-RBs than in neat asphaltene, showing deeper transmittance values. These peaks were related to the vibrations of aliphatic hydrocarbon groups [54] that intensified from the low-molecular-weight rubber products. Figure 8 illustrates the FTIR indices of SARA fractions: \(I_{CO}\) in Figure 8a, \(I_{SO}\) in Figure 8b, \(I_{CC}\) in Figure 8c, and \(I_{CH}\) in Figure 8d. In Figure 8a, the COV values for \(I_{CO}\) ranged from 15.03 to 37.68%. The neat saturates had the highest \(I_{CO}\) value (0.23), which concurred with the results presented in Figure 4: neat saturates showed carbonyl groups at 1723 and 1753 cm\({}^{-1}\). For A-RBs saturates, the \(I_{CO}\) decreased reaching the lowest values for A-RBs 190-600 and 190-3000, hitting values of zero.