Morphology and thermal properties of HDPE nanocomposites: Effect of spherical silica surface modification and compatibilizer

HDPE composites, filled with 6 wt.% of unmodified (SiO2) or modified spherical nanosilica, containing immobilized silver (Ag-SiO2) or copper (Cu-SiO2) nanoparticles, differing in filler particle size (30, 60 and 90 nm), were prepared by melt mixing using a twin-screw co-rotating extruder. Maleated HDPE (MHDPE) was used to enhance the interaction between silica and polymer matrix, which facilitated the dispersion of silica. The composites were analyzed using scanning and transmitting electron microscopy (SEM, TEM), dynamic-mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). SEM and TEM results revealed that silica nanoparticles aggregates were in general distributed homogenously. DSC results showed that the incorporation of silica nanoparticles could decrease the melting temperature but increase the crystallization temperature, and could lower the crystallinity degree of the HDPE. Moreover, the homogenous distribution of silica particles in the HDPE significantly affected the thermo-oxidative degradation of the composites. Cu-SiO2 particles of 60 nm dimension in the presence of MHDPE showed the best thermal stability, a maximum increment of 86 °C was obtained compared to the pure HDPE. DMTA results were in good agreement with the findings of the morphological and thermal studies.