Positron annihilation lifetime study of irradiated and deformed low density polyethylene

Abstract

Positron annihilation lifetime spectroscopy has been used to study the free volume hole properties of unirradiated and irradiated low density polyethylene (LDPE) as a function of deformation in the range from 0 to 110%. Deconvolution of the lifetime spectra into three components reflected three different morphologies of the polymer structure. The variation of positron annihilation parameters with deformation shows three stages; the elastic range, strain-softening region, and plastic region. The free volume was probed using ortho-positronium (o-Ps) pick-off annihilation lifetime parameters as a measure of electron density and the mean free volume hole radius. For unirradiated sample, the average of the free volume hole increases with deformation in the elastic region, remains unchanged within the strain softening region, and finally tends to increase in the plastic region. A reduction in the size of the free volume holes and concentrations has been observed in the case of irradiated sample which is due to a structural change. The distribution of the free volume for unirradiated sample shifts from a small to large size as the deformation increases and has very similar Gaussian-like distribution. For irradiated one, the distribution becomes broader and has an asymmetric appearance. The results show that positron lifetime is a sensitive means to probe the microstructural change of polymers during deformation.