Thermo-mechanochemical recycling of waste polypropylene into degradation products as modifiers for cleaner production and properties enhancement of bitumen

Abstract

Recycled polypropylene (rPP) wastes have been used to improve the high-temperature performance of asphalt. However, the high melting temperature of rPP does not match the conventional mixing temperature of bitumen, resulting in more energy consumption and emissions. Therefore, this study adopted dicumyl peroxide (DCP) to chemically degrade the rPP through a melt-shear processing method to obtain the corresponding modifiers (rPPM) with better flowability at a lower temperature. Torque rheology, melt flow rate (MFR) and thermogravimetry analysis (TGA) characteristics of rPPM incorporated with different dosages (1‰, 3‰, and 5‰) of DCP were compared to that of rPP. Correspondingly, the rPPM modified asphalt (rPPMA) were characterized by penetration, softening point, viscosity, and the dynamic shear rheology (DSR) tests. The TGA test showed that the rPPMs have a lower thermal stability as compared to rPP, and the MFR of rPPM can be up to 1900% larger than that of the rPP. The rPPMs can contribute to increasing the softening point and reducing by almost 50% penetration of virgin binder, which are reflected that they can improve the high-temperature performance of virgin binder. The DSR results stated that rPPM can provide a slightly improved deformation resistance and a lower anti-fatigue characteristic, comparative capacities, as well as a relatively lower deformation resistance and higher fatigue failure to the virgin binder, respectively. Accordingly, 3‰ DCP is optimally recommended to degrade rPP to obtain the modifier for the cleaner production and enhancement of modified binders.