Compatibilizer Role of Styrene-butadiene-styrene Triblock Copolymer in Asphalt

Polymer modified asphalt (PMA) was prepared from mixtures of triblock copolymer poly (styrene- butadiene-styrene) (SBS) and asphalt. Physical and mechanical properties of the mixtures were characterized by differential scanning calorimeter (DSC), needle penetration and softening point methods, and tensile strength measurement. The glass transition temperatures of both blocks of SBS changed with the fraction of asphalt varied from 0 to 97%, which indicates the mixture system to be partially miscible at least. Maltene, the soluble fraction extracted from the asphalt by n-heptane, was found to interact preferentially with the polybutadiene unit of SBS, whereas asphaltene, insoluble fraction interacted predominantly with the polystyrene unit. Fraction dependence of viscosity, penetration and tensile strength of the mixtures showed the threshold at low SBS concentration (e.g., 5-10%) to increase markedly. A microstructure model for the PMA system with lower SBS is proposed. The small amount of SBS in PMA seem to act as compatibilizer and emulsify the two components of asphalt to make a mechanically stable network.