Thermal Cycling Induced Aging on Polypropylene/Elastomer Blends for DC Cable Insulation

Abstract

This paper reports on the ageing phenomenon of the polypropylene (PP) /elastomer blends that are used as DC cable insulation. The elastomers employed are propylene-based elastomer (PBE) and ethylene-octene copolymer elastomer (EOC), which are blended into the PP to form the test samples. The samples go through thermal cycling treatment with temperatures from -30 to 150 °C, after which the trap distribution and the DC breakdown strength are measured. Structural changes in the samples are estimated through Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and differential scanning calorimetry (DSC) measurements. The test results indicate that, with the growth of the thermal cycling number, the trap center decreases whereas the trap density increases, and the DC breakdown strength tends to be reduced. The appearance of oxidation product, loose structure and decreased crystallinity with the thermal cycling ageing should be responsible for the encouragement in charge transport and the reduction in the breakdown strength. The degradation of PP/EOC is more obvious than that of PP/PBE due to its worse compatibility, the PP/PBE exhibits better resistance to the thermal cycling ageing.