Neutron irradiation effect on dielectic loss of bi-stretched polyethylene naphthalate .

Abstract

In the present work, the study of the evolution of the β∗ process in both pristine and neutron irradiated bi-stretched polyethylene naphthalate films, is realized at a constant temperature and in the frequencies domain comprised between 102 and 106 Hz by using the impedance spectroscopy technique. The results show the presence of dielectric loss peak determined in 105 to 106Hz frequency range, where the shape, position and the intensity are affected by morphological damage due to the large quantity of neutron beam energy transferred to the polymeric molecules that were highlighted by different structural analysis such as the Fourier transform infrared spectroscopy (FTIR) and the polarized light optical microscopy (PLOM). At room temperature, the FTIR technique showed an increase in the quantity of the carbonyl and naphthalene groups responsible of the presence of the Sub-Tg dielectric relaxation in the volume of the irradiated BSPEN (IR-BSPEN) film due to the amorphization phenomena traduced, respectively, by the absence and presence of the absorption bands characteristics of crystalline and amorphous phases. The PLOM characterization, revealed change in the texture of the IR-BSPEN surface indicating by the appearance of microcracks which contribute to the oxidation of macromolecular chains. The study of the effect of temperature on the dielectric behavior of non irradiated BSPEN film, in β∗ region, showed that the dielectric parameters such as the maximum of dielectric losses and its position are thermally activated. This dielectric response has not identified in the case of irradiated BSPEN film, for which the evolution of losses with temperature change above T = 333K