# 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  
Figure 4 depicts the FTIR spectra of saturate fractions extracted from neat binder and A-RBs. The mutual exchange between rubber and saturates is confirmed via the FTIR spectral changes. The rubber low-molecular-weight components, aliphatic hydrocarbon chains, were migrated into saturates. This was highlighted in A-RB 190-600, showing a broader and higher intensity of C-H stretching vibrations for aliphatics (sp\({}^{3}\) hybrids) [19; 39] at 2955, 2925, and 2850 cm\({}^{-1}\) peaks compared to the neat saturates. For A-RB 190-3000, a peak that appeared at 1571 cm\({}^{-1}\) (extending from 1553 to 1590 cm\({}^{-1}\)) was related to C=C stretching vibrations in aromatics [44]. This reflects the migration of rubber aromatic components into saturates during the 190-3000 interaction. For this interaction, the rubber in the A-RB released both aromatic and aliphatic components in the saturates due to partial dissolution and thermal degradation of the rubber. Peaks at 1753 and 1723 cm\({}^{-1}\) related to C=O stretching vibrations of esters and ketones [45; 46] were noted for the saturates of the neat binder. Peaks at 1660 and 1627 cm\({}^{-1}\), corresponding to C=C stretching vibrations of aromatics [47; 48], were also observed for the neat saturates. However, these peaks disappeared in the A-RBs' saturates, reflecting the migration of unsaturated polar components, shifting saturates to a more aliphatic fraction. Two peaks appeared in the neat saturates at 816 cm\({}^{-1}\) (extending from 851 to 780 cm\({}^{-1}\)) and 1036 cm\({}^{-1}\) (extending from 1063 to 1006 cm\({}^{-1}\)), with areas of 15.24 and 8.67%.cm\({}^{-1}\), respectively. These peaks are related to C-H out-of-plane bending on aromatic rings and S=O stretching vibrations, respectively [16; 17]. For A-RB 19-600, the area at 816 and 1036 cm\({}^{-1}\) increased to 206.28 and 86.34%.cm\({}^{-1}\), respectively. However, for A-RB 190-3000, these areas had the lowest values, reaching 6.73 and 3.78%.cm\({}^{-1}\) at 816 and 1036 cm\({}^{-1}\), respectively. For A-RB 220-3000, these peaks' areas increased again at 220 \({}^{\circ}\)C, hitting values of 39.97 and 17.98%.cm\({}^{-1}\) at 816 and 1036 cm\({}^{-1}\), respectively. At 190 \({}^{\circ}\)C and 600 min\({}^{-1}\), rubber particles released aromatic and sulfur-containing components into saturates; however, at 190 \({}^{\circ}\)C and 3000 min\({}^{-1}\), the rubber absorbed these aromatic species from saturates and dissolved more, as explained later by the TGA analysis. Furthermore, at 220 \({}^{\circ}\)C, excessive rubber dissolution, detected by TGA, occurred, and rubber depolymerization and excess devulcanization caused the rubber particles to release these components back to the saturate fraction. This shows that the rubber in A-RB 190-3000 absorbed aromatic species at 816 cm\({}^{-1}\) and released other aromatic species at 1571 cm\({}^{-1}\), indicating mutual exchange. Figure 3: SARA fractions of neat binder and A-RBs. Figure 5 shows the FTIR spectra of aromatic fractions extracted from neat binder and A-RBs. The aliphatic C-H stretching vibrations between 2960 and 2850 cm\({}^{-1}\) for the A-RBs' aromatics were less intense than those in the neat aromatics. This reflects the decrease in the aliphatic chains of hydrocarbons, indicating the role of these components in the swelling of rubber particles. Another part of these aliphatic components could be thermally volatilized during the high-temperature interaction. At 220 \({}^{\circ}\)C, the intensities of these aliphatic components increased again due to depolymerization and excessive devulcanization of the rubber polymeric components. The C=C stretching vibrations peak at 1560 cm\({}^{-1}\)[49] emerged for the A-RB 190-600 aromatics and disappeared for the other two types of A-RB aromatics.