The effect of the presence of silica nanoparticles on the structure, thermal stability and dynamics of low density polyethylene, LDPE, has been studied. Different loads of nanoparticles were dispersed within a LDPE matrix using high energy ball milling (HEBM) as a preliminary processing step to ensure a uniform dispersion of nanofiller to obtain nanocomposites in the form of films by hot pressing. The monitoring of the FTIR-ATR spectra of the samples as a function of the temperature has proven as a convenient method to study the interactions at a molecular scale between the polyethylene chains and the nanofiller. Band splitting observed in the bending and rocking modes of the ethylene groups indicated formation of crystalline phases whereas the analysis of absorbance band ratios from the stretching vibrations of PE accounted for the behavior of the polymer bulk. No evidence of strong polymer-filler interactions were found with the exception of a thermal relaxation process observed at 55 degrees C. Structural, morphological and thermal characterization of the nanocomposites did not reveal remarkable changes at low loads of filler, indicating that in the case of LDPE-silica nanocomposites, where weak interactions between the polymer and filler occur, the volume fraction of nanoparticles must be relatively high in order to produce changes in the bulk properties.