(Re)processing effects on linear low-density polyethylene/silica nanocomposites

A linear low density polyethylene matrix was melt compounded with a given amount (2 vol.%) of both untreated (hydrophilic) and surface treated (hydrophobic) fumed silica nanoparticles with the aim to investigate the influence of the time under processing conditions on the microstructure and thermo-mechanical properties of the resulting materials. Crosslinking reactions induced by thermal processing caused a remarkable increase of the melt viscosity, as revealed by the melt flow index values of both neat matrix and nanocomposites. Thermal oxidation of the matrix was slightly reduced by the introduction of fumed silica nanoparticles, especially for long compounding times. Differential scanning calorimetry evidenced how silica nanoparticles had a nucleating effect on the matrix, while both the melting temperature and the relative crystallinity were decreased by the compounding process. Nanosilica addition promoted a general improvement of the tensile properties, that progressively decreased with the processing time.