Preparation and characterization of vanillin-based self-healing polyurethane-modified asphalts based on acylhydrazone chemistry

The self-healing of asphalt pavement through extrinsic replenishment single is not sufficient for achieving sustainable healing and restoring excellent performance. Therefore, an intrinsic self-healing method based on acylhydrazone chemistry was proposed to enhance the healing ability and fatigue resistance of asphalt materials. Vanillin-based polyurethanes with tunable acylhydrazone bonds (V-PU1/V-PU2) were synthesized using self-emulsification, leading to the preparation of modified asphalts (VPMA1/VPEA1/VPEA2) containing 3 %, 6 %, 10 %, or 50 % of V-PU1/V-PU2. The comprehensive characterization results indicated that V-PU1 films achieved dynamic reversible healing under the motivations of 125 °C and acetic acid. Meanwhile, there was an activation energy of 48 kJ/mol and a tensile strength recovery rate of 81 % after self-healing. Compared to VPMA1-3 % and VPMA-6 %, V-PU1 and V-PU2 showed uniform phase distributions in VPEA1-10 %, VPEA1-50 %, VPEA2-10 % and VPEA2-50 %. The microscopic healing morphologies, complex viscosity curves and stress relaxation revealed that as the content of V-PU1/V-PU2 increased from 10 % to 50 %, the self-healing mechanism of VPEA1/VPEA2 transformed from the softening flow of asphalt phase in coordination with V-PU1/V-PU2 to dynamic reversible reactions. Furthermore, acylhydrazone bonds significantly contributed to fatigue resistance, which was verified by the fact that the fatigue healing index (HI) of VPEA1-50 % was 0.71 higher than that of VPEA2-50 %.