抄録
It has been pointed out that free volumes in polymer materials are related to their microscopic structure, and thus it is considered that degradation mechanism of polymer materials will be well understood if correlations among free volumes and various characteristics of polymer materials are clarified. Recently, positron annihilation spectroscopy has been applied to evaluate free volumes in polymer materials. In this study, six types of polyethylene with different densities and cross-linked polyethylene were selected as typical polymer materials, and their free volumes were evaluated by the positron annihilation technique. Then, their relationships among free volumes and material characteristics such as thermal expansion and tensile strength were investigated. As a result, it was found that the estimated free volume radius and number density decreased with the increase in the material density, and their estimated average free volume radii were about 0.3nm. We proposed a parameter which is related to both of the volume and the number density and referred to it as relative free volume. The relative free volume decreased with the material density. Moreover, it increased with the increase in the coefficient of thermal expansion and with the decrease in the tensile strength. The correlations among the relative free volume and these material characteristics were confirmed to be strong.
