Effects of polymerized sulfur on rheological properties, morphology and stability of SBS modified asphalt

Abstract

The objective of this study was to investigate effects of polymerized sulfur on viscosity functions, morphology and storage stability of SBS modified asphalt, as compared to elemental sulfur. Viscosity functions including complex viscosity, steady flow viscosity and dynamic viscosity were measured by dynamic shear rheometer (DSR) and Brookfield viscosity rheometer. The morphology and microstructure of modified asphalt were observed using fluorescence microscopy and Fourier Transform Infrared spectroscopy (FTIR). The results revealed that the increment in viscosity of modified asphalt containing polymerized sulfur was slower than that of elemental sulfur. Vulcanization rate decreases with the increase of polymerized sulfur, i.e. delayed vulcanization effect. In morphology, large polymer domains progressively transform to the fine dispersed SBS phase with smaller dimensions as the elongation of mixing time; whereas a fine polymer phase was found for elemental sulfur at the initial stage of mixing, which is significant evidence of delayed vulcanization. Moreover, the FTIR results verify the decrease of unsaturation of poly-butadiene block and the formation of CS bond. Viscosities of asphalt with polymerized sulfur were always lower than those of elemental sulfur and decreased with the increase of polymerized sulfur content. SBS phase domain vulcanized by polymerized sulfur is larger than that of elemental sulfur and tends to become larger with the increase of polymerized sulfur content. Lastly, SBS modified asphalt with higher level of polymerized sulfur shows the improved storage stability.