Nanostructural and Nanomechanical Properties of LDPE-Modified Binders

Abstract

The main objective of this study is to explore the effects of various asphalt binder modifiers, including styrene–butadiene–styrene (SBS), elemental sulfur, reactive ethylene terpolymer (Elvaloy), and polyphosphoric acid (PPA) polymers on the nanostructural and nanomechanical (elastic and viscoelastic) properties of low-density polyethylene (LDPE)-modified binders. The study also aims to investigate the effect of aging on the nanoproperties of such blends. To this end, we used the PeakForce quantitative nanomechanical mapping (PFQNM) test and the nanoscale dynamic mechanical analysis (nDMA) test by means of atomic force microscopy. We further utilized the nanoscale results to better understand and interpret the bulk scale properties obtained using the dynamic shear rheometer (DSR). The nDMA results indicated an increase in stiffness and an enhancement in the elastic behavior of the blends after modification. Moreover, the blends exhibited a stiffer and more elastic behavior at the nanoscale when compared with the bulk DSR test results. Using Elvaloy and Elvaloy+PPA greatly enhanced the bond between LDPE and the binder. Both blends also showed resistance to heat-induced polymer separation and aging. Furthermore, the addition of SBS+sulfur enhanced LDPE dispersion within the binder. It was demonstrated that the use of elemental sulfur showed high efficacy in stabilizing LDPE-modified binders by inducing physical interaction between LDPE and the binder. Lastly, we concluded that the nanoscale measurements are very useful in understanding the local interactions, explaining the main aspects of the response at the bulk scale, and in the design of asphalt blends with improved properties.