The Mechanism of the Depolymerization of Polytetrafluoroethylene With Pyrolytic and Radiolytic Initiation

The rate of decomposition of polytetrafluoroethylene, exposed to gamma radiation in a flowing helium atmosphere, was studied in the range of temperatures 330 to 450 °C, dose rates 0.1 to 7.6 MR/h, and sample thicknesses 0.0006 to 0.01 cm. Rate measurements were made with a thermal conductivity cell in the exit stream, which recorded essentially the difference between the thermal and radiation-induced rate, in total molecules of volatiles per second. At temperatures below about 400 °C, the volatile products were a complex mixture. Above 400 °C, tetrafluoroethylene was the major product, and the radiation-induced rate had an activation energy* of 70 to 84 kJ/mol. The radiation-induced rate is proportional to square root of dose rate, after appropriate allowance for the thermal initiation is made. Analysis of the results suggests that the rate of the thermal initiation has a very high preexponential factor, 10²⁸ to 10³⁰ s-¹. The activation energy for termination is large, E reaction may be important. The thermal decomposition mechanism seems clearly to consist of random initiation, termination by bimolecular recombination and a short kinetic chain (13 at 480 °C).