Evaluation of number-average molecular weight of poly(tetrafluoroethylene) irradiated with γ rays

The number-average molecular weight of poly(tetrafluoroethylene) (PTFE) irradiated from a 60Co source in air at room temperature has been estimated from the experimental results of tensile creep measurements and electron microscopy. The viscoelastic method which makes use of the maximum relaxation time was used for samples with low radiation doses. The mean chain length of highly irradiated samples, which can form fully extended chain crystals upon crystallization from the melt, was obtained from the bandwidth distribution on micrographs of the fracture surfaces. The dependence of the average molecular weight on the radiation dose is derived on the basis of a statistical treatment in which effects of cages in the process of chain scission and of molecules evolved out of the specimen, together with random decomposition of polymer backbone chains, are considered. Good agreement between the experimental and calculated results is attained over a wide range of radiation doses