Blends of bitumen with polymers having a styrene component

The properties of a 100 penetration grade bitumen are modified considerably , and in a number of ways by the addition of 10 to 40 parts per hundred (pp h) of a homopolystyrene and graft, block and random copolymers of styrene w ith butadiene and acrylonitrile. At low temperatures some blends have a sim ilar stiffness to or even lower stiffness than the bitumen, but generally t he blends are more than one order of magnitude stiffer, even when a rubber is added. The contrasting behavior is displayed by a polystyrene and a high impact polystyrene, similar to3% to 4% of grafted rubber on the latter bei ng sufficient to cause the enhancement, even at the 10 pph level, by two di fferent random styrene-butadiene copolymers, and also by blends consisting of different amounts of SBS block copolymer. Some polymers apparently trigg er a Hartley inversion of the micellar structure of the asphaltene micelles . High law temperature stiffness correlates roughly with a lower Tg, as mea sured by the peak maximum in the E " plots of the dynamic mechanical therma l analysis (DMTA) and by the steps in the differential scanning calorimetry (DSC) curves at temperatures below 0 degreesC. Tan delta maxima and DSC tr aces detected the glass transition in the continuous phase and in the dispe rsed phases, but none of these amorphous polymers formed a crystalline phas e, though the DSC traces of the polystyrene and the SBS blends suggested th at the polymer-rich phases underwent an aging/ordering process on cooling. Our SBS blends differ in phase inversion behavior and the pattern of loss p rocesses from others that had a smaller asphaltene component.