Bitumen Modification 101The polymer modification of bitumen can be a complex process difficult to understand for many stakeholders. The Bitumen Modification 101 Series was developed to highlight the best practices and various aspects of using Kraton polymers in bituminous applications in an approachable, yet comprehensive way --- serving as a reliable resource to the entire bitumen (asphalt binder) industry. Using high loading levels of SBS may not always be feasible due to incompatible asphalt binder or high formulation viscosity. Fortunately, Kraton offers many specialized low-viscosity SBS grades with enhanced asphalt binder compatibility. Our global technical service and research team is available to provide formulation assistance. |
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Styrene-butadiene-styrene (SBS) is a class of polymers commonly used worldwide since the 1970s to enhance asphalt binder performance in the paving and roofing industries. The styrene and butadiene monomers, chemical precursors, are arranged in blocks of polystyrene and polybutadiene. This combination gives SBS polymers its unique properties. In SBS polymer, the blocks exist as separate phases that do not mix. Polystyrene (the grey cubes) is a hard, strong plastic. Polybutadiene (the orange springs) is resilient, soft and elastic.
SBS polymers are most effective as asphalt binder modifiers when they form a continuous polymer-rich network. When this happens, asphalt binder – originally a visco-plastic liquid – becomes a visco-elastic solid. The transition is accompanied by an order of magnitude improvement in asphalt binder toughness and durability performance. However, the performance improvement does not follow linearly with an increase in SBS loading. Rather, it follows an “S-curve.”
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Ultraviolet (UV) light microscope is a powerful tool to visualize the SBS polymeric network in asphalt binders. The microscope makes it possible to gain insight into the polymer and asphalt binder’s compatibility or the blend preparation process’s effectiveness. In asphalt binder, only maltenes – specifically aromatics (A) and resins(R) – produce strong fluorescence signals [1]. Coincidentally, SBS blends with asphalt binder by absorbing some aromatics and resins.
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