Specific volume studies of γ‐irradiated polytetrafluoroethylene from 40 to 150°C

Abstract

The effect of γ‐irradiation and post‐irradiation heat treatment on the specific volume versus temperature relationships of polytetrafluoroethylene (PTFE) samples (1/2‐in. diameter rods) have been studied over the 40–150°C. temperature range for radiation doses up to 8.9 X 10⁸ rad. At low doses the specific volume at any temperature decreased with dose, but above about 10⁸ rad it increased with dose. Similarly, the rate of volumetric expansion initially decreased with dose, while, at very high doses (8.9 X 10⁸ rad) the rate of expansion at temperatures above 100°C. exceeded that of the unirradiated PTFE. Heating at 150°C. for 100 hr. produced a substantial decrease in the specific volume and a decrease in the rate of expansion for the irradiated samples. Irradiation effects in PTFE are considered to be a result of such factors as radiation‐induced chain scission, increased crystallinity, and increased void content. Changes resulting from post‐irradiation heat treatment can be attributed to increased crystallinity, decreased void content, and weight loss.