Processing-microstructure-fracture toughness relationships in PP/EPDM/SiO2 blend-nanocomposites: Effect of mixing sequence

This study investigates the mechanical properties and fracture behavior of polypropylene (PP)-based blend-nanocomposites comprising 30 wt.% ethylene-propylene-diene monomer (EPDM) and 5 wt.% SiO2 nanoparticles. Different mixing sequences were employed to prepare the nanocomposites, and the resulting morphology development and dispersion states of modifiers were analyzed. Mechanical performance of the nanocomposites was evaluated through quasi-static and high-speed dynamic fracture tests. The dispersion and distribution of SiO2 nanoparticles within the nanocomposites were significantly influenced by the mixing protocol. In impact fracture tests, the presence of nanoparticles exhibited a beneficial efffect on fracture energy, demonstrating a synergistic toughening effect of the soft EPDM and rigid SiO2 particles. Conversely, adverse effects were observed in quasi-static tests. Essential work of fracture (EWF) parameters indicated an increase in the yielding component and a decrease in the necking-to-tearing component with SiO2 incorporation into the PP/EPDM blends. During impact loadings, the highest improvement in crack propagation resistance was observed in nanocomposites with nanoparticles localized around the rubbery domains forming a network-like structure of EPDM/SiO2-nanoparticles. Morphologies where rubber domains and nanoparticles were separately distributed in the PP matrix resulted in the lowest fracture parameters. Energy dissipation mechanisms were elucidated, revealing multiple void formation followed by matrix shear yielding as the primary source under both quasi-static and impact fracture conditions. In the latter case, stress-concentrating percolated structures in the PP matrix facilitated the nucleation of dilatational bands evolving into highly stretched void-fibrillar structures upon further loading. These findings contribute valuable insights into tailoring nanocomposite morphologies for enhanced mechanical performance in different loading scenarios. Highlights Fracture behavior of PP/EPDM/SiO(2 )ternary systems was evaluated by EWF methodology and Izod impact test. Rubber particles surrounded by silica nanoparticles led to a percolated morphology and as a result to superior impact resistance. EWF parameters were mostly controlled by the tearing-related parts regardless of phase morphology. The impact toughness was mainly controlled by the dispersion and distribution characteristics of the SiO2 nanoparticles.