Rheological modification of bitumen with maleic anhydride and dicarboxylic acids

Abstract

The rheological properties of roading bitumens, modified through reaction (6 h, 150°C) with maleic anhydride (MAH), succinic anhydride (SAH) and various straight chain dicarboxylic acids, were investigated using capillary viscometry, penetration and dynamic shear rheometry (DSR). Chemical properties of the reaction products/blends were measured by gas chromatography, infrared spectroscopy and gel permeation chromatography. Consistent with previous work, bitumen–MAH reaction products were found to have reduced temperature sensitivity (in terms of the ratio of the complex modulus ( G*) at 5°C to that at 50°C) and be more elastic in character (decreased tan δ), compared to the control. Although only 40–50% of the MAH had reacted irreversibly with the bitumen (probably by a Diels–Alder mechanism), the increase in G* and reduction in G* 5/ G* 50 was greater than that achieved using SAH. For both MAH and SAH, the anhydride ring was observed to open almost immediately so that the effect on binder rheology was attributed to the resulting dicarboxylic acids. Longer chain dicarboxylic acids were also found to increase G* and decrease tan δ, the magnitude of the effects increasing with chain length. Values of G* 5/ G* 50 for the dicarboxylic acids were slightly reduced, however, the reduction in temperature sensitivity, achieved with the long chain di-acids, was similar to that obtained with SAH, but less than that achieved with (covalently bound) acid groups from MAH. In contrast, decanoic acid (a monocarboxylic acid) markedly increased tan δ relative to the control, G* 5/ G* 50 also increased. The results can be interpreted in terms of the formation (or enhancement of existing) transient networks of bitumen species, linked by hydrogen bonding and dipole–dipole interactions with the dicarboxylic acids (two acid groups are necessary).