Preparation Of Functionalized Nano-SiO₂ And Its Effect On The Insulation Properties Of UV-crosslinked Polyethylene

Ultraviolet light cross-linked polyethylene（UV-XLPE）has excellent electrical insulation and mechanical properties,so it is widely used in the field of medium and low voltage submarine power cables.In order to improve the withstand voltage level of power cables,the method of doping nano-fillers is often used to modify the insulation layer.At the same time,a large number of studies have shown that the doping of nano-SiO₂ can significantly improve the electrical properties of polymer materials,but due to its large surface activity,it is prone to agglomeration in the polymer matrix,resulting in poor modification effects.In addition,in the production process of UV-XLPE,the auxiliary crosslinking agent of small molecules will undergo heat migration and evaporation due to its poor compatibility with polyethylene,resulting in the degree of crosslinking that cannot meet the requirements.Therefore,in order to solve the problem of cross-linking agent migration encountered in the production process of UV-XLPE power cables and to improve the voltage resistance of XLPE cables,a kind of nano-SiO₂ filler with cross-linking agent function is prepared and used to a certain extent.UV-XLPE nanocomposites were prepared by doping into polyethylene in a proportion,and the effect of functionalized nano-SiO₂on the electrical insulation properties of UV-XLPE was studied by experimental methods.Through the principle of sulfhydryl-double bond click chemistry and nano-SiO₂surface modification,nano-SiO₂ with cross-linking function is prepared,and then XLPE nanocomposites are prepared by ultraviolet cross-linking technology,and nano-SiO₂ is introduced into the cross-linked network structure of XLPE In the XLPE,the cross-linking degree of XLPE is improved while ensuring the dispersibility of nano-SiO₂ in the polymer matrix,thereby improving the electrical insulation properties of XLPE.In this paper,the functionalized nano-SiO₂ and XLPE nanocomposites are mainly used for structural characterization and corresponding electrical performance testing.The successful preparation of functionalized nano-SiO₂ was verified by hydrogen nuclear magnetic resonance spectrum and infrared spectroscopy;the thermal weight loss curve showed that functionalized nano-SiO₂ can still maintain good thermal stability at about 250℃.The gel content and scanning electron microscopy（SEM）test of the XLPE nanocomposite materials show that the gel content of XLPE prepared by functionalized nano-SiO₂ is slightly higher than that of XLPE prepared by small molecule auxiliary crosslinking agent,indicating that the functionalized nano SiO₂avoids the thermal migration and evaporation loss of the auxiliary cross-linking agent during the cross-linking process,and improves the cross-linking degree of the material;SEM results show that the functionalized nano-SiO₂ has relatively uniform dispersion in the XLPE matrix,which is conducive to the fullness of the nano-SiO₂ Take advantage of its small size effect.By comparing the AC and DC breakdown characteristics of the four materials in the test article under a certain temperature gradient and the tree resistance aging characteristics at room temperature,it can be concluded that functionalized nano-SiO₂ can significantly improve the electrical resistance of XLPE.Among them,the 1.5wt%TMPTA-s-SiO₂/XLPE nanocomposite has the highest characteristic breakdown field strength at each temperature;the electrical tree has the smallest size and shape,the fractal dimension is the largest,the water tree has the smallest size,and is resistant to tree aging The characteristics are the most excellent.The test results of space charge,electrical conduction current,and power frequency dielectric spectrum show that functionalized nano-SiO₂ can inhibit the injection of space charge,reduce electrical conduction current,and increase the electrical aging threshold field strength E_Ωof composite materials;increase the dielectric constant and loss Angle tangent.Thermal stimulation current（TSC）results show that functionalized nano-SiO₂ introduces a large number of deeper energy traps in the XLPE matrix,which is also the main reason for the excellent electrical properties of XLPE nanocomposites.