# 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 is in agreement with the results in Figure 4: the carbonyl groups for the neat saturates disappeared for A-RBs saturates. This reflected the influence of rubber on decreasing the carbonyl components and thus enhancing aging resistance [13]. A further contributing factor was the redistribution of \(I_{CO}\) into more polar fractions, especially the resins, with A-RB 190-600 demonstrating a  
Figure 7: FTIR spectra of asphaltene: (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. value of 0.08. For A-RB 190-3000 resins, the \(I_{\text{CC}}\) had a value near zero (0.0018), concurring with the qualitative results displayed in Figure 6. For this sample, the hydrogen bonding or chemical interaction caused the O-H peak at 3300 cm\({}^{-1}\) to be broadened and the C=O peak at 1700 cm\({}^{-1}\) peak to disappear. In Figure 8b, the COV values for \(I_{SO}\) ranged from 0.84 to 52.92%. \(I_{SO}\) was the highest in the neat saturates and aromatics, while the AR-B saturates and aromatics had the lowest values. Furthermore, the resin fraction of A-RB 190-3000 revealed the highest \(I_{SO}\) (0.65), while its saturate and aromatic values had the lowest \(I_{SO}\) values. These findings suggested the absorbance of S=O components from saturates and aromatics into the rubber or rearrangement into more polar fraction (e.g., resins). Figure 8c shows the \(I_{CC}\) with COV values ranging from 1.92 to 29.14%. From saturates to asphaltenes, a general trend revealed an increase in the unsaturated components for neat binder and A-RBs. However, the general trend was different for the aliphatic components in Figure 8d, highlighting a decrease in the \(I_{CH}\) values as the fractions progressed from saturates to asphaltenes. These trends were expected, because asphaltenes are rich in aromatic rings with short aliphatic chains, and saturates mostly consist of nonpolar linear, cyclic, and branched saturated hydrocarbons (e.g., naphthene and paraffin) [55; 56]. The \(I_{CC}\) was the highest for A-RB 190-600 aromatics, with a value of 0.16, which corresponds with the qualitative analysis in Figure 5, where a C=C aromatic peak developed at 1560 cm\({}^{-1}\). Nevertheless, for A-RB 190-3000 saturates, it had the highest \(I_{CC}\), which agrees with the qualitative analysis in Figure 4. A C=C aromatic peak at 1571 cm\({}^{-1}\) appeared in Figure 4 for the A-RB 190-3000 saturates and was absent in the aromatics of the same sample shown  
Figure 8: FTIR indices: (**a**) \(I_{\text{CO}}\); (**b**) \(I_{\text{SO}}\); (**c**) \(I_{\text{CC}}\); and (**d**) \(I_{\text{CH}}\). in Figure 4:0 This reveals that the lower interaction speed (600 min\({}^{-1}\)) promoted the rubber unsaturated components to migrate into the aromatics, while the higher speed (3000 min\({}^{-1}\)) shifted their migrations into the saturates. Figure 8d shows the \(I_{CH}\) with COV values ranging from 0.46 to 10.77%. Most of the A-RBs fractions had higher \(I_{CH}\) values than the neat fractions. The A-RB 190-600 saturates had the highest \(I_{CH}\) in Figure 8d, reaching a value of 0.95, higher than the neat binder value by 32%. The intensity of the aliphatic peaks for this sample was the highest, as depicted in Figure 4, which supported migration of the rubber aliphatic hydrocarbon chains into saturates. For the A-RB 190-3000 saturates, the \(I_{CH}\) was lower than the value of A-RB 190-600 saturates. However, in the aromatics, this trend was reversed, suggesting that changing the interaction speed from 600 to 3000 min\({}^{-1}\) altered the rubber's aliphatic migration into aromatics. At 3000 min\({}^{-1}\), rubber particles absorbed more aliphatic components, swelled more, partially dissolved more--as confirmed by the dissolved rubber percentage--and released more aliphatics back into the aromatics fraction.