SYNTHESIS AND THERMAL-STABILITY OF BITUMEN POLYMER IONOMERS

Road bitumens, when combined with polymers such as styrene-butadiene-styrene (SBS) block copolymers, show improved mechanical properties. The corresponding blends, however, are thermodynamically unstable, and phase separation quickly occurs at higher temperatures. A solution is proposed for improving the thermal stability of these blends: It is based on the formation of reversible, ionic interactions between the bitumen and the SBS, thereby leading to a mixed, ionomeric network. Both compounds are first chemically modified by the grafting of carboxylic acid groups, then mixed, and, finally, the available acid groups are partially or totally neutralized by adding zinc acetate dihydrate to the blends. Comparison of the thermal stability of the resulting ionomeric blends with that of the untreated blends is discussed. The use of ion-ion interactions to enhance miscibility, which, for the first time, has been extended to bitumen-polymer systems, is shown to be a means of obtaining stable blends.