Abstract
In order to inhibit the outward-migrations of photo-initiator molecules in the ultraviolet-initiated crosslinking process and simultaneously improve the crosslinking degree and dielectric properties of crosslinked polyethylene (XLPE) materials, we have specifically developed surface-modified-SiO2/XLPE nanocomposites with the silica nanofillers that have been functionalized through chemical surface modifications. With the sulfur-containing silanes and 3-mercaptopropyl trimethoxy silane (MPTMS), the functional monomers of auxiliary crosslinker triallyl isocyanurate (TAIC) have been successfully grafted on the silica surface through thiol–ene click chemistry reactions. The grafted functional groups are verified by molecular characterizations of Fourier transform infrared spectra and nuclear magnetic resonance hydrogen spectra. Scanning electronic microscopy (SEM) indicates that the functionalized silica nanoparticles have been filled into polyethylene matrix with remarkably increased dispersivity compared with the neat silica nanoparticles. Under ultraviolet (UV) irradiation, the high efficient crosslinking reactions of polyethylene molecules are facilitated by the auxiliary crosslinkers that have been grafted onto the surfaces of silica nanofillers in polyethylene matrix. With the UV-initiated crosslinking technique, the crosslinking degree, insulation performance, and space charge characteristics of SiO2/XLPE nanocomposites are investigated in comparison with the XLPE material. Due to the combined effects of the high dispersion of nanofillers and the polar-groups of TAIC grafted on the surfaces of SiO2 nanofillers, the functionlized-SiO2/XLPE nanocomposite with an appropriate filling content represents the most preferable crosslinking degree with multiple improvements in the space charge characteristics and direct current dielectric breakdown strength. Simultaneously employing nanodielectric technology and functional-group surface modification, this study promises a modification strategy for developing XLPE nanocomposites with high mechanical and dielectric performances.
Highlights
Crosslinked polyethylene (XLPE) is a representative insulating material of thermo-setting homopolymers derived from polyethylene, which inherits the excellent electrical insulation performances of polyethylene and acquires a higher heat resistance and better physical-mechanical properties [1]
We develop XLPE nanocomposites with the nanofillers functionalized by auxiliary crosslinkers to prevent the outward-migration and volatilization of small molecular photo-initiation system in UV-initiated crosslinking process and simultaneously improve the crosslinking degree, space charge characteristics and breakdown electric field of high-voltage
◦ C can be attributed to the small molecules, while the weight loss at higher temperatures of 250~800 molecules in Figure 4a, the measured peak positions of the synthesis products exactly coincide with decomposition of organic groups on nanosurfaces
Summary
Crosslinked polyethylene (XLPE) is a representative insulating material of thermo-setting homopolymers derived from polyethylene, which inherits the excellent electrical insulation performances of polyethylene and acquires a higher heat resistance and better physical-mechanical properties [1]. SiO2 /methacrylate have been comprehensively developed to improve the mechanical and electrical properties of polymers [21,22,23] This is a valid strategy of exploiting the inorganic SiO2 nanoparticles in polyethylene crosslinking reactions to improve the insulation performances of UV-XLPE insulating materials. SiO2 /UV-XLPE nanocomposites with the functionalized SiO2 nanofillers are essentially developed by combining the photon-initiated crosslinking technology of polymers and the surface modification schemes of nanodielectrics, which can render various novel features of crosslinking configuration and effectively improve dielectric properties of UV-XLPE insulation materials. We develop XLPE nanocomposites with the nanofillers functionalized by auxiliary crosslinkers to prevent the outward-migration and volatilization of small molecular photo-initiation system in UV-initiated crosslinking process and simultaneously improve the crosslinking degree, space charge characteristics and breakdown electric field of high-voltage. The crosslinking degree, space charge characteristics and dielectric breakdown strength of these SiO2 /XLPE nanocomposites with surface-modified hybrid nanofillers are investigated by testing and analyzing the nuclear magnetic resonance, infrared spectrum, scanning electron microscopy, dielectric breakdown strength and space charge distribution
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