Valorization of Plastic Waste (PP-LDPE) from Moroccan Industry in Modification of Hybrid Bitumen: Application of the Mixture Design Methodology

This work aims to develop a prediction and optimization model using different types of recycled plastic wastes from the Moroccan industry, such as recycled low-density polyethylene (R-LDPE) and recycled polypropylene (R-PP) combined with styrene-butadiene-styrene (SBS) and styrene-ethylene-butylene-styrene (SEBS), as a commercial raw material for manufacturing a polymer-modified bitumen (PMB). The developed models will allow defining the most efficient formulation for bitumen and recycled plastic waste mixture to meet well-defined characteristic requirements, which, is going to give a considerable amount of value to the daily generated plastic waste in Morocco. The method of experimental design was used to validate the developed models. The control parameters adopted for this bitumen modification process and according to the Moroccan bitumen manufacturing industries practices are softening point, penetration, and elastic recovery. The effects of the added components on the mixture responses were described by Scheffe polynomial models, where a quadratic model was adopted for the softening point and penetration value, whereas, a special cubic model was adopted for the elastic recovery. All models were experimentally validated using ANOVA analysis. The diagnostics of the validated models indicated that the average absolute relative deviations were only 1.1%, 4.7%, and 3.3% for softening point, penetration, and elastic recovery, respectively. Using the developed models, an optimized composition of a polymer-modified bitumen was defined to satisfy the modified bitumen standards in Morocco. In conclusion, the models that have been developed can be used as an alternative optimization tool and method for the development of a hybrid polymer-modified bitumen formulation responding to a specific application. Further studies are going to be carried out to focus on the rheological properties of the hybrid polymer modified bitumen to evaluate the rutting and fatigue behavior of the mixture, as well as the storage stability with and without coupling agents. The numerical optimization models developed in this work were validated using real industrial-scale tests.