Positron annihilation in polyethylene and azidosilane-modified glass/polyethylene composites

Positron annihilation lifetime spectra were measured on glass bead-filled high density polyethylene, with a glass content ranging from 0 to 50% by volume. In some cases, the glass beads were surface-modified by different amounts of an azidofunctional alkoxysilane. A composite model for positron annihilation was proposed to account for the observed changes in the relative intensities with increasing amount of filler. A decrease in the intensity of the longest lifetime with increased amount of the silane coupling agent was observed. This suggests a reduction of the free volume in the interphase region between glass and polyethylene, despite a reduction in the crystallinity of the interphase.