Advancing sustainable hybrid bitumen systems: A compatibilization solution by functionalized polyolefins for enhanced crumb rubber content in bitumen

Polymer waste pollution has a profound effect on the environment and, consequently, on the lifestyle of humankind. The massive production and disposal of cross-linked polymers clearly exemplify the challenges of recycling. Increasing efforts are being undertaken to introduce recycled polymers, especially crumb rubber (CR), into asphalt formulations. Due to the rather poor processability and phase separation associated with CR-modified bitumen (CRMB) compositions, a broader implementation of such concept is challenging unless an efficient compatibilizer is applied. Results from the study on usage of In-Reactor-Functionalized Polyolefins viz. poly(propylene-co-hex-1-ene-co-hex-5-en-1-ol) (FPP), demonstrated excellent compatibilizing ability in CRMB, allowing incorporation of up to 10 wt% of CR. This represents a significant improvement when compared to the best-in-class solutions. The FPP-containing products exhibit superior bulk, nanomechanical and rheological properties, as well as stability during binder annealing. Furthermore, the bitumen surface morphology is significantly improved. The polar groups present in the FPP create a thermo-reversible interpenetrating cross-linked network that provides mechanical integrity and contributes to the adhesion to different components of the modified bitumen at service temperatures, enhancing its processability. The exceptional compatibility of FPP in CRMB resulted in a significant increase in the Performance Grade of the hybrid system by 5 classes (88) compared to neat bitumen (58). Moreover, the best-performing composition fulfilled the low-temperature ductility specifications, withstanding deformation without fracturing or breaking up to a 400 mm elongation.