# Effect of Chemical Composition of Bio- and Petroleum-Based Modifiers on Asphalt Binder Rheology
## 4 Discussion  
### Summary of Modifier Chemistry  
The Elemental analysis showed that modifiers G and C had higher nitrogen content (9% and 3.5%, respectively), while E and K had some sulfur (0.33% and 0.98%, respectively) compared to other modifiers. Modifier G has significantly low carbon (47.9%) and high oxygen (33.1%) content.  
FTIR spectra further validated the presence of nitrogen in modifiers C and G with peaks in the ranges of 1000-1250 cm\({}^{-1}\) and 3100-3500 cm\({}^{-1}\) which are characteristic of C-N stretching and N-H stretching (from secondary amines), respectively. A distinct peak at 2860 cm\({}^{-1}\) and a small peak at 1650 cm\({}^{-1}\) further validate the presence of nitrogen, as these peaks are representative of amine salt and amides, respectively. Modifiers A, C, D, and E show the presence of carbonyl functionality, which was observed from the carbonyl peaks at 1742 cm\({}^{-1}\).  
Molecular weight analysis showed that modifiers A, C, D, and E have average molecular weights in a similar range, modifier G has the lowest weight and K has the highest. In addition, modifier K possesses significantly high PDI indicating a wide variation of molecular species presence. Modifiers,  
Figure 8: Black space diagrams showing G* vs phase angle (8) at reference temperature of 15 °C and reduced frequency of 0.005 rad/s for all aging conditions for **(a)** modifiers A, C, D, and E compared to unmodified binder S5; and **(b)** modifiers G and K compared to unmodified binder S5.  
however, have different molecular size distributions, with some modifiers having multiple peaks (A, C, D, and K) and hence, are composed of distinct molecules. On the other hand, others (E and G) had single peak which means they are composed of single molecular size.  
Modifier G has a distinct chemical composition compared to other modifiers. It is significantly high on nitrogen and oxygen and relatively low on carbon compared to others. The presence of nitrogen was validated by the FTIR spectra. Peaks corresponding to amine salt and primary and secondary amines were observed. It was found that the molecular weight of G was the lowest single peak distribution. Additionally, modifier C showed relatively higher content of elemental nitrogen in the form of secondary amines which was verified by the FTIR spectrum.  
SARA analysis of G was inconclusive and additional characterization with a different method is required to evaluate the chemical characteristics of modifier G. Moreover, its solubility in water requires additional investigation of the AC's susceptibility to moisture. Modifiers C and E are largely composed of resins and asphaltenes with limited or no saturates and aromatics. While A and D have some aromatics and asphaltenes along with a majority of resins. Modifier K has large amount of insoluble residue with high saturate content and limited resins with traces of aromatics.  
Furthermore, modifier A shows similar chemical functional groups, molecular weight and molecular weight distribution to modifier D, which indicates that modifier A may belong to bio-oil category.