Synthesis of castor oil-based polyurethane (PU) containing different disulfide contents and self-healing properties of the PU modified asphalt

Developing modifiers with self-healing properties can significantly extend the service life of asphalt pavements. This study utilized castor oil and MDI-100 as the primary raw materials to synthesize three distinct polyurethanes containing disulfide bonds. The successful preparation of these polyurethanes was confirmed through Fourier-transform infrared spectroscopy and Raman spectroscopy analyses. A comprehensive series of tests, including swelling tests, DMA, TG, SEM, and mechanical performance assessments, were conducted to characterize the properties of the synthesized polyurethanes. The results indicated that the polyurethane of S0.85 exhibited the most favorable self-healing performance. Utilizing polyurethane of S0.85 as a modifier, modified asphalt containing dynamic covalent bonds was prepared. Fluorescence microscopy tests demonstrated that the modifier was uniformly dispersed within the asphalt, indicating good compatibility between the two components. The binder bond strength (BBS) test results reveal that the modified asphalt's self-healing capability is significantly superior to that of the base asphalt, and the presence of disulfide bonds positively influences the healing performance through dynamic exchange. This study presents a promising approach for applying bio-based polyurethane-modified asphalt containing dynamic covalent bonds and encourages the utilization of bio-based materials.