Effect of Functional Grafting Modification on Dielectric Properties of Polypropylene Insulation—Part 1: Frequency Domain Spectroscopy

This series of papers investigates the effect of functional grafting modification on the dielectric properties of polypropylene (PP) insulation, of which this article focuses on the frequency domain spectroscopy (FDS) characteristics varying with temperature. The Fourier transform infrared spectroscopy (FT-IR) confirms the successful grafting of functional monomers on PP. The oxidative induction time (OIT) test results indicate that PP grafting with AO3052 has enhanced oxidant resistance compared to PP and those grafted with dibenzylidene acetone and
$2^{\prime} $
-hydroxychalcone, due to the hindered phenolic group can eliminate free radicals. The Havriliak–Negami (H–N) model is employed to analyze the FDS variation of grafted-PP samples with temperatures and to analyze the
$\alpha $
and
$\delta $
relaxation. The results show that the
$\alpha $
relaxation strength (
$\Delta \varepsilon _{\alpha }{)}$
corresponding to the strength of orientational polarization of grafted-PP samples has increased compared with PP since the intermolecular interaction factor (
${g}{)}$
and the average dipole moment (
$\mu {)}$
are increased. As carrier hopping polarization, the
$\delta $
relaxation strength (
$\Delta \varepsilon _{\delta }{)}$
of grafted-PP samples decreases compared with PP since the barrier height that the carrier hop needs to overcome (
$\Phi {)}$
is increased. The
$\Phi $
of PP-g-3 is larger than that of PP-g-1 and PP-g-2, resulting in better inhibition of carrier hop. In summary, PP grafting with AO3052 can enhance its antioxidant performance and improve its ability to inhibit carrier hopping, thereby improving the direct current (dc) insulation performance of PP.