Effect of a post‐annealing process on microstructure and mechanical properties of high‐density polyethylene/silica nanocomposites

ABSTRACT High‐density polyethylene (HDPE) and nanosilica nanocomposites were prepared for SiO2 content up to 15 wt%. Microstructural characterization evidenced a homogenous distribution of silica aggregates with a mean size increasing with the filler content finally resulting in a rheological percolation between 7.5 and 10 wt%. Nanoparticles did not induce any significant impact on the matrix crystallinity but led to a real improvement on elastic properties accompanied with a large embrittlement above the percolation threshold. The effect of annealing near HDPE melting temperature was studied. Differential scanning calorimetry, X‐ray diffraction, and small‐angle X‐ray scattering analyses showed a significant change in the HDPE microstructure after annealing at 125°C. A large increase in the crystallinity (from 68 to 76%) and a clear improvement of Young's modulus (by 55%) were observed prior to polymer degradation. A valuable impact of silica particles on thermal stability was also obvious regarding the evolution of elastic properties for extended exposure times (850–1,200 h). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 535–546 High Density Polyethylene/silica nanocomposites were prepared. A homogenous distribution of silica aggregates was observed at low filler content, whereas a rheological percolation was evidenced between 7.5 and 10 wt% fillers. Nanoparticles did not induce any significant impact on the matrix crystallinity, but did lead to a real improvement of Young's modulus. Annealing at 125°C led to a significant change in the HDPE microstructure and a clear improvement of the Young's modulus prior to polymer degradation. A valuable impact of silica particles on thermal stability was also obvious regarding the evolution of elastic properties for extended exposure times.