Thermal-and-mechanochemical recycling of waste polypropylene into maleated-epoxided degradation products as warm-mix asphalt modifier: Performance improvement and production mechanism analysis

Abstract

Polypropylene (PP) wastes do not easily mix with asphalt binder to reach a uniformly dispersed phase at a regular blending temperature as a result of its very high melting temperature and molecular nonpolar properties. With considering their use in asphalt applications, the melting temperature needs be reduced, together with improved polymer-asphalt compatibility using effective treating approaches. Therefore, this study proposes an innovative thermal-and-mechanochemical method to efficiently convert waste PP into maleated-epoxided degradation products as warm-mix asphalt modifiers (PPMs) through hybrid use of dicumyl peroxide (DCP), maleic anhydride (MAH), and epoxidized soybean oil (ESO), for modification and property enhancement of virgin binder. The modified asphalt (PPMA) binders with different treated PPMs and untreated PPM were prepared at blending temperatures of 140∼170 °C and 170–180 °C, respectively. Further, the viscosity, softening point, ductility, storage stability, and micro-morphology tests were characterized for the prepared PPM modified asphalts (PPMAs), while torque rheology, melt flow rate (MFR), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectra were measured for these PPMs, in order to analyze the performance improvement and cleaner production mechanisms. The results showed that the collective use of DCP, MAH, and ESO can cause a series of chemical reactions, including degradation and grafting, to PPM0 for the generation of maleated-epoxided degradation products with lower thermal stability and higher melt fluidity under thermal-and-mechanochemical treatment. Optimally, the maleated-epoxided PPM containing 5% ESO reduces the softening point difference of virgin binder by almost 70% due to the improved the modifier-asphalt compatibility, and its storage stability, softening point and viscosities are most improved. Overall, the designed processing method can promote waste PP to be upcycled into maleated-epoxided degradation products that can be used as warm-mix performance-enhancing modifiers.