Dielectric Properties of Gamma-Irradiated Tetrafluoroethylene-Hexafluoropropylene Copolymers (Special Issue on Physical, Chemical and Biological Effects of Gamma Radiation, VIII)

The effect of gamma-irradiation on dielectric properties in copolymers of tetrafluoroethylene and hexafluoropropylene (TFE-HFP copolymer) has been investigated in connection with possible change in the structure of this copolymer.The dielectric constant and loss were measured on irradiated TFE-HFP copolymers with different irradiation doses at frequencies from 1 to 300 kHz over a temperature range of -40 to +180°C.In accordance with the dielectric constant versus temperature relation the coefficient of thermal expansion in the copolymers exhibited a small change at about 60°C, indicating the existence of a transition.The changes in both the dielectric constant and the expansion coefficient were obscured for a highly irradiated copolymer.The sizes of the a and r relaxations found for unirradiated copolymers were influenced by gamma irradiation : With increasing the irradiation dose the magnitude of the r loss peak increased and the a loss peak showed a considerable change at the dose of 10MR.The r relaxation was dependent also on the degree of crystallinity.The activation enthalpy and entropy for the a relaxation were reduced with raising the irradiation dose, while these activation parameters in the ; one showed a gradual increase.The results were discussed in relation to the chain scission of the copolymer by gamma-irradiation. * / iFMk , rk*ff ( 97 )