Reutilization of waste polymer plastics: a molecular dynamics study on toughness enhancement and interfacial mechanisms in SBS-modified asphalt

Plastics are widely used as modifiers to enhance asphalt pavement performance due to their distinctive molecular structure. However, there is still limited theoretical analysis of the effect of plastics on the aging behavior of SBS-modified asphalt on a molecular scale. Therefore, in this study, molecular dynamics software was used to establish aging behavior of SBS-modified asphalt with different types of plastics (polyethylene (PE), polypropylene (PP), and poly acrylic (PA)). The thermodynamic parameters, mean square displacement (MSD), radial distribution function (RDF), free volume fraction (FFV), and relative concentration, and mechanical parameters were analyzed to evaluate the diffusion behavior of plastics in aged SBS-modified asphalt and their effects on its properties. The results indicate that the polymer molecules representing plastics are dispersed around the asphaltene components in aged SBS-modified asphalt, disrupting asphaltene aggregation and enhancing its dispersion, ultimately improving asphalt's thermal stability. Additionally, the surface energy values of PE, PP, and PMA were found to be 33.47 mJ m^-3, 28.56 mJ m^-3, and 29.47 mJ m^-3, respectively, representing increases of 27.02%, 7.74%, and 11.84% compared to aged SBS-modified asphalt. These findings suggest that the incorporation of plastics enhances the crack resistance of aged SBS-modified asphalt, with PE exhibiting the most significant improvement compared to PP and PMA. This study provides novel insights and theoretical foundations for the efficient utilization of waste plastics and the molecular-level improvement in the aging behavior of SBS-modified asphalt performance.