Polymer structure and morphology of low density polyethylene filled with silica nanoparticles

The effect of silica nanoparticles on structure and morphology of low density polyethylene (LDPE) was investigated. To prepare the nanocomposites, SiO2 nanoparticles were dispersed in a LDPE with cryogenic high-energy ball milling (HEBM). Films of these nanocomposites with different loads (0%, 1.8%, 2.3%, 3.3%, 7.9%, 16.5% wt/wt) were obtained by hot pressing. Differential scanning calorimetry (DSC) was used to study the nonisothermal melting and crystallization of the films. The morphological characterization was done by atomic force microscopy (AFM). To determine the most representative periodical spacing associated to the LDPE crystallites, a new approach based on the first moment of the frequency distribution obtained from the fast Fourier transform of the AFM phase contrast images was used. Ultracryomicrotomed surfaces of the nanocomposites revealed an efficient dispersion of the nanoparticles throughout the polymer bulk. Although HEBM promotes the formation of the metastable monoclinic phase in the LDPE, nanocomposites in the form of films did not show important differences in their thermal and morphological characteristics, suggesting that there are not high interactions between the polar nanoparticles and the nonpolar polymer and that thermal treatment is enough to eliminate the specific microstructure induced by HEBM. POLYM. COMPOS., 33:20092021, 2012. (C) 2012 Society of Plastics Engineers