Effect of partially crosslinked nanoparticle cluster networks in dispersed rubber phase on the toughness and stiffness of polypropylene composites

To achieve a balance between toughness and stiffness in polypropylene (PP) composites and to explore the underlying mechanisms, this study employed modified nano-silica particles (S-SP) by a cross-linkable modifier (Si69) as reinforcing fillers. PP composites toughened with ethylene–propylene–diene monomer (EPDM) reinforced by S-SP were prepared and compared with those reinforced by unmodified and methyl-trimethoxy-silane (MTMS)-modified silica particles. The results showed that when the S-SP content reached 30 wt% (relative to reinforced EPDM), the notched impact strength of the PP composite at room temperature reached 75 kJ/m 2 , while the tensile yield strength and Young's modulus were 23 ± 2 MPa and 670 ± 20 MPa, respectively, only 32.3 % and 34 % lower than those of pure PP. Mechanistic analysis revealed that the modified nanoparticles with cross-linking ability played a key role in constraining the rubber phase size, enhancing its modulus, rigidifying the particle networks, and improving the interface adhesion. These factors were essential in mitigating the loss of modulus and stiffness of the composites. Additionally, they significantly improve the notch impact strength of the composites by promoting the cavitation of the rubber phase into many slender fibrils and micro-voids, and inducing intense shear deformation of the PP matrix ligaments.