The effect of asphaltene concentration on polymer modification of bitumen with SBS copolymers

This paper describes the competing mechanism between polymer and asphaltenes for the maltene phase during polymer modification of bitumen. Polymer modified bitumen (PMBs) were produced using bitumen with different asphaltene concentrations and two different styrene–butadiene–styrene (SBS) copolymer at a fixed polymer contents (4.5% w/w). Rheological and microscopic evaluation was carried out to assess the impact of different asphaltene contents on the physical properties and morphology of the resultant PMB. The results of the investigation indicate that the PMB with a lower content of asphaltenes exhibited better compatibility but demonstrated lower improvement in elasticity. As the asphaltene content increased the elasticity of the PMB improved as indicated by the increase in the relaxation time. The storage stability of the PMB worsened as the asphaltene content in the bitumen used to prepare the PMB increased indicating that the compatibility between the polymer and the maltene phase reduced with an increase in asphaltene content. The increase in the asphaltene content of the bitumen used to prepare a PMB results in a reduction of the available maltene phase for the polymer to solvate. The reduction in available maltene fraction for polymer solvation could then potentially result in a confined polymer morphology that results in an improvement in elasticity. Model PMB systems were used to verify the above hypothesis. The results from this work highlight the importance of the asphaltene content of bitumen with respect to PMB performance. Manufacturers should account for bitumen variability when producing PMBs to target polymer concentrations.