Compatibility and storage stability of styrene-butadiene-styrene copolymer modified bitumens

Abstract

The compatibility and storage stability of styrene-butadiene-styrene copolymer (SBS) modified bitumens were studied using fluorescence microscopy and dynamic mechanical analysis. Chemical characteristics of base bitumens and SBS polymers were determined by means of thin layer and gel permeation chromatography, respectively. The results showed that the morphology and phase separation of the modified binders varied with the characteristics of bitumens and polymers and were influenced by polymer content. At a given polymer content, the modified binders produced from bitumens with a higher content of aromatics exhibited better compatibility and higher storage stability. An increase in asphaltenes was observed to adversely affect storage stability. When mixing a small amount of polymer with bitumen, the modified binder showed dispersed polymer particles. At relatively high polymer content, depending on the base bitumens used, a continuous SBS phase was observed. On the other hand, the storage stability of modified binders decreased with increasing SBS content. Compared with branched SBS polymer, linear SBS displayed a finer dispersion in modified binder, and consequently, a lower phase separation was observed during hot storage. The degree of SBS dispersion in bitumen influenced storage stability and the rheological properties of modified binders; however, no definite relationships among them could be established.