Optimization of Dielectric Properties and Energy Storage Characteristics of Sulfur-Containing Functional Monomer Grafted Polypropylene via Melt Grafting

This study takes polypropylene (PP) as the matrix material, and introduces the sulfur-containing functional monomer furfuryl methyl sulfide (FMT) into the PP molecular chain through melt grafting technology to prepare modified polypropylene composites with excellent dielectric properties and thermal stability. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{1} \mathrm{H}$</tex>NMR) characterization confirm that FMT is successfully grafted onto the PP main chain. X-ray diffraction (XRD) results show that the grafting reaction does not significantly damage the crystallinity integrity of PP. The study finds that the introduction of FMT enhances the molecular polarization ability, significantly improves the stability of the dielectric constant in the broadband range <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left(10^{2}-10^{6} ~\text{Hz}\right)$</tex>, and reduces the dielectric loss by about 38%. Meanwhile, the presence of thioether bonds improves the thermal stability of the material. The thermal decomposition temperature of modified PP increases from 310°C to 345°C, and the breakdown strength reaches <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$398 \text{kV} / \text{mm}$</tex>, which is 32% higher than that of unmodified PP. In addition, the energy storage density of modified PP increases from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.1 ~\mathrm{J} / \text{cm}^{3}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3.6 ~\mathrm{J} / \text{cm}^{3}$</tex> under an electric field of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{4 0 0 ~ M V} / \mathbf{m}$</tex>, demonstrating good energy storage potential.