Elevated Temperature Rheological Properties of Styrene-Butadiene-Modified Binders: Role of Molecular Structure

Polymer-modified binders are heated to the elevated temperatures during storage, transportation, and pavement construction. This study evaluates the role of molecular structure (linear, branched, high vinyl, and diblock) and concentration (2-7 wt%) of styrene-butadiene polymer on the rheological properties of the modified binder at elevated temperature. The rheological analysis was performed between 120 and 170 degrees C in rotational and oscillatory deformation modes in a dynamic shear rheometer. The results show that the molecular structure of the styrene-butadiene (SB) polymer significantly affects the elevated temperature rheological properties of the SB-modified binders (SB-MBs). The combination of radial branches and higher molecular weight in branched SB polymer results in SB-MBs with a stronger interconnected network. Consequently, compared to the other three SB polymers, the viscosity of the branched SB-MBs binders was 2-5 times higher at elevated temperatures, while the phase angle values were lower. Above 3 wt% of SB content, the influence of molecular structure becomes more prominent. Hence, at a fixed SB content, the modified binder with branched SB polymer needs to be maintained at higher temperatures during pavement construction related to the additional three SB polymers. On the other hand, diblock structure and lower molecular weight in diblock SB polymer result in SB-MBs with the lowest viscosity. In all the cases, two distinct rheological behavior was observed from the temperature sweep measurements, one between 120 and 140 degrees C and another between140 and 170 degrees C. The findings from the study are practically relevant while using SB-modified binders for pavement construction.