Influence of γ‐irradiation on the transition temperatures of crystalline polytetrafluorethylene

Abstract

The influence of γ‐irradiation on the melting and two solid‐solid transitions, occurring near 19° and 30°C, of polytetrafluorethylene was studied by differential scanning calorimetry. A continuous depression of all three transition temperatures, with increasing dose was observed in a first scan of highly crystalline samples at a heating rate of 20°C/min. Additional information was obtained about the accompanying heats of transition. Values for the number of CF₂ units excluded from the crystal lattice per 100 eV energy deposition were calculated by using an equation for the depression of the melting point by chemical impurities. The value obtained of G(–units) = 3.3 ± 0.3 is in agreement with a value of G(chemically damaged units) = 3.0 ± 0.1 previously reported on the basis of scavenging techniques. It is concluded that chemical radiation‐induced damage in this polymer may be estimated by reference to changes in the melting temperature. A value of G(–units) = 1.6 ± 0.2 was obtained by reference to the 19°C transition.