A chemical method to upcycle waste polypropylene into bitumen compatible modifier by polyol grafting through reactive extrusion

Abstract

Recently, the utilization of waste plastics in asphalt pavement construction has gained increasing interest for both waste recycling and pavement performance enhancement. However, most existing methods to recycle waste plastics are physical, and their effectiveness was limited by the severe phase separation in waste plastic modified bitumen. Alternatively, chemical recycling approaches show promise to address this concern but have not been sufficiently studied yet. Hence, this study aims to develop an innovative chemical recycling approach to solve the poor storage issue of waste plastic modified bitumen. The approach involved grafting polar functional groups, maleic anhydride (MA) and flexible polyol chains onto recycled polypropylene (PP) thorough reactive extrusion. The infrared spectroscopy and thermal analyses confirmed the partial degradation of PP and the successful production of PP grafted by MAH (PP-g-MAH) and PP-g-MAH grafted by polyol (PP-g-MAH-g-Polyol) modifiers. Performance tests showed that extruded PP modifiers exhibited superior workability and could preserve the excellent high-temperature properties of the plastic modified bitumen without significantly affecting the viscosity-temperature susceptibility. And the storage stability and dynamic shear rheology (DSR) tests revealed that PP-g-MAH-g-Polyol had a more pronounced positive impact on the storage stability compared with PP-g-MAH, due to its improved polarity and similarity in aromatic structures with bitumen. Overall, the proposed chemical recycling method can effectively address the storage challenges of the waste PP modified binder while maintaining excellent high-temperature performance, showing high potential for applications.