| Insulation layer is an important part of high voltage direct current cable,which affects the service life of the cable.Therefore,in order to develop high performance insulating materials,this paper prepared crosslinked polyethylene(XLPE)and its composite materials by mechanical blending method.These composite materials are the master materials for the preparation of high voltage direct current cable insulating materials,and crosslinked polyethylene and its composite materials by hot pressing crosslinking method.The effects of the type of crosslinking agent and nano filler on the electrical properties of crosslinked polyethylene were discussed.First,low density polyethylene(LDPE)was crosslinked by diisopropylbenzene peroxide(DCP)and double tert-butylisopropylbenzene peroxide(BIPB),respectively.The effects of the amount of peroxy and content of crosslinking agent on the electrical properties of crosslinked polyethylene were studied.Then,TS-1/XLPE nanocomposites were prepared by hydrothermal synthesis of titano-silicon molecular sieve(TS-1).The effects of TS-1 content on the properties of the composites were studied.Finally,TS-1 was treated with alkali for 12 hours and 24 hours respectively to make it have different pore sizes.TS-1 nanoparticles were added to crosslinked polyethylene for different alkali treatment times,and the effects of the content and morphology of nanoparticles on the electrical properties of the composites were studied.1.Using diisopropylbenzene peroxide(DCP)containing one peroxy group and double tert-butylisopropylbenzene peroxide(BIPB)containing two peroxy groups,cross-linked polyethylene samples with different crosslinking agents and a series of concentrations were prepared through mixing and hot pressing.The cross-linking efficiency of BIPB is greater than that of DCP.When the mass fraction of DCP and BIPB is 1.5 wt%,the cross-linking degree of crosslinked polyethylene reaches 75.96 % and88.28 % respectively.When the mass fraction of DCP is 2.5wt %,the cross-linking efficiency of crosslinked polyethylene reaches 75.96 % and 88.28 % respectively.The degree of crosslinking reached 89.39 %.The DC voltage breakdown test,resistivity measurement and space charge measurement were carried out on the crosslinked polyethylene sample to study the influence of the quantity of peroxy group and the content of crosslinking agent on the electrical properties of crosslinked polyethylene material.The results show that when BIPB is used as the crosslinking agent,the DC breakdown field strength and resistivity of the crosslinking polyethylene sample are larger than that when DCP is used as the crosslinking agent.The maximum DC breakdown field strength can reach 330 k V/mm,and the maximum resistivity can reach7.9*1014 Ω/m.When BIPB is used as the crosslinking agent,the content of space charge in the crosslinked polyethylene sample is also greatly reduced.2.Titanosilicate(TS-1)nanoparticles with uniform particle size were synthesized by hydrothermal method,and their morphology was characterized by TEM.Different kinds of crosslinking agents were added to LDPE,and TS-1 nanoparticles were uniform Ly added to polyethylene matrix under different crosslinking agents by mechanical blending.TS-1/XLPE nanocomposites were prepared by hot-pressing crosslinking method.The DC breakdown voltage test,dielectric property measurement,DC resistivity measurement,thermal conductivity measurement and space charge measurement of TS-1/XLPE nanocomposites were carried out.The effects of the type of crosslinking agent and the content of TS-1 nanoparticles on the performance of crosslinked polyethylene were discussed respectively.It is found that TS-1 nanoparticles are uniform Ly dispersed in XLPE matrix,which improves the DC breakdown field strength of XLPE and the resistivity of XLPE matrix to a certain extent.When TS-1content is small,the crosslinking agent has a great effect on the electrical properties of composites,but when TS-1 mass fraction exceeds 0.6 wt%,The type of crosslinking agent has negligible effect on the nanocomposites,and the content of TS-1 nanoparticles plays a major role.Meanwhile,the addition of TS-1 inhibits the injection and accumulation of space charge in the composites.TS-1/XLPE nanocomposites have the highest DC breakdown field strength,thermal conductivity and resistivity when TS-1content is 1.5 wt%.3.In order to investigate the effect of the pore size of the filler on the electrical properties of the composites,the TS-1 nanoparticles were treated with sodium hydroxide(Na OH)to make them have different pore sizes.With DCP concentration of 1.5wt %,TS-1/XLPE nanocomposites with different TS-1 contents were prepared by adding two TS-1 nanoparticles to LDPE matrix by mechanical blending and hot pressing crosslinking methods.The DC breakdown voltage test,DC resistivity,dielectric properties and space charge measurements of TS-1/XLPE nanocomposites were carried out,and the effect of the pore size of TS-1 nanoparticles on the electrical properties of the nanocomposites was studied.It was found that the pore sizes of TS-1 nanoparticles treated with alkali for 12 hours and 24 hours were about 10 nm and 50 nm,respectively,and the two TS-1 nanoparticles were uniform Ly dispersed in the polymer matrix.The breakdown field and resistivity of XLPE were increased after alkali treatment for 12 hours.It also inhibits the injection and accumulation of space charge in the composite because the existence of aperture limits the occurrence of electron avalanche inside the material.TS-1/XLPE nanocomposites showed the highest DC breakdown field and resistivity when the content of TS-1 nanoparticles was 1.5 wt% after 12 h alkali treatment.Due to the large pore size of TS-1 nanoparticles treated with alkali for 24 hours,it is easy for electrons to be transferred within the material,thus reducing the DC breakdown field strength and resistivity of the composites,and also promoting the injection and accumulation of space charge in the materials. |
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