Functionalized recycling of waste polypropylene into low-carbon asphalt modifier towards circularity: From mechanochemical preparation to structural and performance evaluations

Waste polypropylene (WPP), a common solid waste, has proven effective as an asphalt modifier for improving pavement performance. However, the direct application faces challenges such as high processing temperatures, poor dispersion, and inconsistent performance, which limit widespread application. To overcome these issues, this study applied a mechanochemical treatment of WPP using varying dosages of dicumyl peroxide (DCP) and epoxy soybean oil (ESO) to produce a novel waste plastic asphalt modifier. The process is designed to disrupt the long molecular chains and crystalline structure of WPP by DCP, while utilizing ESO to undergo dynamic chemical grafting reaction, thereby generating degraded WPP containing oxygen-active functional groups. Some testing results show that the modifier prepared with 0.3 % DCP reduced the dissolution temperature in organic solvents by about 20 °C and significantly enhanced high temperature performance and adhesion of asphalt. The softening point increased from 46.5 °C to 58.6 °C, a 26 % improvement, and fracture energy rose from 3.7 J·m −3 to 6.7 J·m −3 , yielding an 81 % increase in adhesion. In addition, the water damage resistance of the modified asphalt has also been significantly improved. Overall, the proposed WPP modifier preparation method effectively mitigates high temperature and performance inconsistency issues of conventional WPP modified asphalt, demonstrating significant comprehensive benefits.