Effect of gamma radiation on the specific volume of polytetrafluoroethylene from −80°C. to +40°C

Abstract

AbstractSpecific volume vs. temperature relationships for γ‐irradiated polytetrafluoroethylene (PTFE) samples (1/2 in. diameter rods) have been studied over the −80 to +40°C. temperature range for radiation doses up to 890 Mrads. At low doses, the overall specific volume decreases with increasing dose. Between 100 and 300 Mrads the effect reverses, and the specific volume increases with dose up to 890 Mrads. As reported in the literature, an inflection point associated with the first‐order crystalline transition appears in the specific volume curve near 19°C. for unirradiated PTFE. This inflection point loses definition and shifts to lower temperatures with increasing radiation dose. At 890 Mrads the inflection point has decreased about 50°C. to near −33°C. Effects noted in irradiated PTFE are attributed to chain scission, changes in per cent crystallinity, and eventual disordering of the crystallites with increasing radiation dose. No significant difference in results are detected between samples irradiated in air and samples irradiated in vacuum‐sealed containers.