Mapping the Strength–Ductility Landscape of Recycled Polypropylene Blends Through Automated Compounding

ABSTRACT The increasing use of recycled polypropylene (rPP) in engineering applications is limited by reduced ductility and material variability. In this study, a systematic experimental and statistical analysis approach was used to investigate polypropylene (PP) blends combining virgin PP (vPP), rPP, and elastomeric modifiers. A single commercial talc‐filled rPP grade containing approximately 30% mineral filler was used throughout, so that recycled polymer content and filler content vary together, and all quantitative results reported here refer to this specific material system. A systematic compositional matrix was explored using automated compounding, varying rPP content (0–100 wt%), elastomer type (EPDM and EPDM‐g‐MA), and elastomer loading (10–30 wt%). Results demonstrate that rPP significantly increases stiffness due to residual mineral filler but severely reduces ductility, raising the tensile modulus from 3155 to 6993 MPa (+122%) while lowering elongation at break from 80% to 8.5% (−89%). Elastomer addition promotes a brittle‐to‐ductile transition, accompanied by losses in strength and modulus; 30 wt% EPDM in the virgin matrix increases elongation at break to 554% at the cost of 77% of the modulus and 29% of the yield stress. Statistical analysis reveals strong interaction effects between composition variables, while Pareto frontier analysis identifies formulations that balance strength and ductility. The individual property trends follow the established behavior of talc‐filled and elastomer‐modified PP. The contribution of this work lies in the combination of automated compounding, a complete and balanced formulation matrix, and statistical analysis into a scalable screening workflow, and in the empirical models derived from it, which are specific to the grades investigated.