Effect of Thermal Aging on the Dielectric Properties of Polypropylene/Elastomer Cable Insulation

This paper focuses on the effect of thermal aging on the properties of polypropylene (PP) and thermoplastic polyolefin (TPO) blending system cable insulation. The PP/TPO samples are subjected to an accelerated thermal aging test at 135 ℃ for 168, 336, 720, and 1440 hours in an incubator. The Fourier transform infrared spectroscopy (FT-IR) test is applied to analyze the changes in functional groups in the PP/TPO insulation. The result of FI-IR indicates that the carbonyl group increases after aging. The Scanning Electron Microscope (SEM) shows that the average area of TPO increases. In the initial stage of the PP/TPO insulation, the fragmented spherulites will undergo recrystallization, making the fragmented spherulites perfect, leading to an increase in melting enthalpy and an increase in the resistivity of PP/TPO insulation. In the later stage of the PP/TPO insulation, the molecular chain of PP/TPO insulation is broken seriously, leading to the broken of the spherulites, thus decreasing the resistivity. The break of the chain of the PP/TPO insulation makes the low-density area increase, thus reducing the breakdown strength of PP/TPO insulation. The increasing average area of TPO makes the stress more concentrated in PP/TPO insulation, leading to a decrease in the mechanical characteristics.