Aging Behavior of Polypropylene as Cable Insulation Under Gamma-Ray Irradiation

This article reports on aging behaviors of polypropylene (PP) and its composites that are used as nuclear cable insulation under gamma-ray irradiation. Isotactic PP (iPP), block PP (bPP), and iPP/elastomer blends are used to prepare the test samples. The samples are irradiated by a Cobalt-60 gamma source with a maximum dose of 1000 kGy, and then trap distribution and ac breakdown strength are measured. Structural changes in the samples are estimated by high-temperature gel permeation chromatograph (GPC), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR) measurements. The results indicate that as the total dose increases, the energy of trap centers becomes shallower and the ac breakdown strength tends to decrease. The molecular weight, crystallinity, and melting point of samples decrease, whereas the oxidation degree increases. It is suggested that the aging of samples is highly associated with the degradation of material structure caused by gamma-ray irradiation, and with the addition of elastomers, the irradiation resistance of PP is improved.