Structural and molecular insights into diisocyanate functionalized lignosulfonate for improving asphaltic aging...

Lignosulfonate (LS) is used to improve asphaltic aging resistance owing to absorbing ultraviolet (UV) light and trapping free radicals. However, excessive addition of LS disrupts uniform dispersion in the asphaltic matrix due to polarity mismatch, causing aggregation, phase separation, and matrix hardening, which collectively reduces anti-aging effectiveness. Herein, we demonstrate a strategy of diisocyanate to enhance LS on asphaltic compatibility with asphalt by synergistically reducing hydrophilic groups and surface free energy. In detail, three diisocyanate functionalized LSs (DFLSs) were prepared via covalent binding of hydroxyl and isocyanate groups, and their structural properties were characterized using various techniques. The results indicated that DFLS had larger particle sizes, greater hydrophobicity, and improved UV absorption than LS. Subsequently, DFLS was utilized to modify asphalt (DFLS-MA), demonstrating superior aging resistance compared to LS-modified asphalt (LS-MA) and pristine asphalt (PA). Beyond the compatibility test, the interaction between DFLS and asphalt was elucidated using molecular simulations (MS). Through functioning of diisocyanates, the surface energy value of LS declined from 34.034 to 8.470 mJ/m² maximumly, stating that the aggregation of LS was inhibited markedly. Meanwhile, Binding energy calculations revealed that DFLS exhibited higher absolute values than LS, indicating that the functionalization of improved LS dispersion in asphalt and contributed valid aging protection. Furthermore, 4,4'-diphenylmethane diisocyanate (MDI) illustrating the most effective enhancement among all, highlighting that the introduction of benzene ring was pivotal in improving LS compatibility with asphalt. This finding presents a novel approach to enhancing asphalt aging resistance through the structural organization of lignin materials.