Performance of PTMEG/CO composite polyurethane and modification mechanism of polyurethane-modified asphalt

Polyurethane (PU) is recognized as a promising material for asphalt modification due to its tunable physicochemical properties. To reduce reliance on petroleum-based polyols, this study employed bio-derived castor oil (CO) combined with polytetrahydrofuran (PTMEG), diphenylmethane diisocyanate (MDI), and 1,4-butanediol (BDO) as raw materials. Polyether-type PU (PTMEG-MDI) and polyether/castor oil composite PU (PTMEG/CO-MDI) were successfully synthesized through controlled hard segment content ( C h ) and isocyanate index ( r ), followed by application in asphalt modification. The structure-property relationships were investigated using FTIR, TGA, DSC, and mechanical testing systems. The results demonstrated that the incorporation of CO significantly enhanced the comprehensive performance of PU composites. Compared to the single polyether-type PU, the PTMEG/CO composite PU exhibited better thermal stability, mechanical strength, and elongation at break. Increasing C h continuously improved the Shore hardness and tensile strength of PU, while reducing its thermal stability and elongation at break. When r reached 1.2, the PU molecular chains attained an optimal stability equilibrium state. FTIR analysis confirmed chemical reactions between the -NCO groups in PU and active components of asphalt, forming characteristic urethane absorption peaks, thereby achieving chemical bonding modification. In terms of asphalt modification performance, the PTMEG/CO-MDI system notably enhanced high-temperature stability while maintaining favorable low-temperature performance. This research establishes fundamental correlations between PU molecular design parameters ( C h and r ) and asphalt modification performance, providing theoretical guidance for developing eco-friendly high-performance asphalt modifiers.