Applicability of positron annihilation spectroscopy to evaluation of polymer materials

Free volumes of six types of polyethylene with different densities and one type of cross-linked polyethylene were evaluated by the positron annihilation technique, and relationships between free volumes and material characteristics such as material density and mechanical characteristics were investigated. As a result, it was found that the estimated free volume radius and its number density decreased with an increase in the material density, and the free volume radius was estimated to be about 0.3nm. We proposed a parameter related to both the volume and number density of free volumes and referred to it as the relative free volume. The relative free volume decreased with an increase in the material density and increased with a decrease in the yield and tensile strength.