Mechanical Reinforcement of Polymer Nanocomposites with Different Network Structure of Polymer Grafted Nanoparticles

Abstract

In this work, the melt reinforcement behavior of polyethylene grafted silica (PE-g-SiO₂) and polypropylene grafted silica (PP-g-SiO₂) filled polymer nanocomposites (PNCs) was investigated by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and linear rheology from small-amplitude oscillatory shear (SAOS) measurements. The effects of nanoparticle loading (Φ) and dispersion state on the rheological behavior of PNCs were examined. Compared with unmodified nanoparticles, polymer grafted nanoparticles exhibit better dispersibility in both PE and PP PNCs. The TEM and SAXS results show that the dispersibility of PE-g-SiO₂ systems is worse than that of PP-g-SiO₂ systems, which originates from the lower grafting molecular weight of PE-g-SiO₂ systems. Both the HDPE14K/HDPE1K-g-SiO₂ system and the PP370K/PP90K-g-SiO₂ system show the deviation from the Guth-Gold model when Φ reaches 5 wt.%. SAOS results reveal that once Φ exceeds the percolation threshold, nanoparticles form interconnected networks, thereby significantly enhancing the mechanical performance of PNCs. Due to the different conformation structures of the grafting chains on the surface of silica, the nanoparticles contact each other by brush chains and bridge into a polymer-mediated nanoparticle network in HDPE14K/HDPE1K-g-SiO₂ PNCs, resulting in a more significant modulus reinforcement than that of PP370K/PP90K-g-SiO₂ PNCs with a soft interfacial structure of grafted chains.