Influence of Carbon Nanotubes on Morphology of Asphalts Modified with Styrene–Butadiene–Styrene

Abstract

The main challenge of asphalt modified with styrene–butadiene–styrene (SBS) during storage and application is the phase separation of SBS-rich phases and asphaltene-rich phases. These phases have a close relationship with the morphology of SBS-modified asphalt [SBS–polymer-modified binders (PMBs)]. Carbon nanotubes (CNTs) were selected in this paper to provide different morphology of SBS-PMBs with CNTs. The morphology was composed of SBS-rich phases, asphaltene-rich phases, and their interphase, captured from fluorescence microscopy (FM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The components and morphologies of the interface on a molecular scale were obtained by molecular dynamic simulation. The results from FM images showed an increase in the relative content of SBS-rich phases as the amount of CNTs increased, highlighting CNTs’ positive role in the compatibility of SBS and asphalt. Mixing CNTs with a mechanical stirrer provided a larger size of SBS-rich phases than that of SBS-PMBs in AFM images using an ultrasound performed on an interpenetration network of AFM and FM images, whereas mixing with an extruding machine resulted in an orange-skin morphology in FM images. The results from SEM demonstrated that CNTs changed the interface of SBS-PMBs by pullout behaviors. The results from the molecular dynamic simulation showed that SBS intertwined or surrounded CNTs to improve their interaction. Saturate, aromatic, and resin were absorbed into the tube of CNTs. Therefore, CNTs had a positive action on the interaction between SBS and asphalt because they acted as a bridge to link the different phases, finally reinforcing the interface of SBS-PMBs.