"Rigid-Flexible" interpenetrating network: Performance regulation & multi-scale mechanism of lignin – Polyurethane composite asphalt

Traditional polyurethane-modified road asphalt (PU-RA) relies on fossil resources and has high costs, and bio-based materials provide a new path for its green development. This study prepared lignin-polyurethane modified road asphalt (LPU-RA) using sodium lignosulfonate (LS) as a bio-based alternative component, aimed at clarifying how LS regulates LPU-RA performance and its core mechanism. FTIR, FM and AFM were used to characterize chemical structure and micromorphology, combined with molecular dynamics (MD) simulation to analyze intermolecular interactions. The results show that LPU-RA achieves optimal comprehensive performance when LS replaces 10% polyols, with its core properties including high/low-temperature resistance and rutting resistance significantly improved compared with PU-RA. LS’s rigid benzene rings covalently bond with polyurethane (PU) flexible chains via urethane bonds, forming a "rigid-flexible" interpenetrating network to inhibit microphase separation. MD simulation confirms that PU/LS group enrichment improves surface free energy, and hydrogen bonds between LS and asphaltenes strengthen molecular binding, jointly optimizing performance. The clarified "bio-based component-microstructure-macro-performance" mechanism and optimal LS ratio provide theoretical support for directional design of bio-based modified asphalt.