Innovative valorization of low molecular weight lignin/SBS composite modifier for sustainable pavement construction: Antioxidant and rheological evolution during long-term aging

Lignin, a bio-renewable antioxidant resource derived from the pulp and paper industries, remains underutilized in pavement construction. For successful lignin valorization towards value-added asphalt modifiers, this study employed ethyl acetate to directly fractionate the low molecular weight (LMW) fraction from parent lignin, which was then introduced into the SBS system by hot-melt extrusion. LMW lignin fractions, lignin/SBS composite modifiers, and modified asphalt binders were studied by analytical chemistry, thermochemical, morphological, and rheology. The results indicated that the LMW fractions of lignin exhibited higher antioxidant activity, with the composite modifiers showing longer oxidation induction times and lower oxidation rates. Concurrently, SEM and FTIR confirmed the homogeneous dispersion of lignin within the SBS matrix and indicated that the hot-melt extrusion was primarily a physical process. Additionally, a comprehensive comparison based on the rheological indexes and their respective aging indexes demonstrated that, compared to parent lignin, LMW lignin enhanced high-temperature deformation resistance and low-temperature relaxation performance, but adversely affected fatigue performance. During long-term aging, although LMW lignin retards the aging of SBS modified asphalt, aging indexes under multivariate rheological performance encounter information redundancy issues, making it difficult to comprehensively characterize the aging degree of binders. Hence, principal component analysis (PCA) was conducted to capture the overall rheological evolution of the modified binders during thermo-oxidative aging. The established comprehensive aging index ( A Comprehensive ) indicated a lower aging degree of LMW lignin/SBS modified binders, providing critical insights for the development of sustainable asphalt pavements.