Halogen-free low-smoke flame-retardant power cable and preparation method thereof

Abstract

The invention discloses a halogen-free low-smoke flame-retardant power cable and a preparation method thereof, belongs to the technical field of cable material processing, and aims to solve the technical problems that the addition amount of a halogen-free flame retardant is large and the mechanical strength and the smoke suppression effect of a cable sheath layer need to be further improved in the processing process of the halogen-free flame-retardant power cable sheath layer in the prior art. A halogen-free low-smoke flame-retardant power cable comprises a plurality of cable cores, a wrapping layer and a sheath layer which are sequentially arranged from inside to outside. And the wrapping layer is obtained by wrapping a wrapping tape outside the plurality of cable cores. According to the invention, mutual fusion and uniform dispersion among modified polysiloxane, supported diatomite and low-density polyethylene are promoted by anhydride modified EVA, then under the action of an initiator and high temperature, intermolecular crosslinking is promoted, the mechanical strength of a cable sheath layer is improved, and the flame-retardant performance of the cable sheath layer is improved by optimizing the combination of halogen-free flame-retardant additives. The flame retardant property of the power cable material is improved; the generation of smoke during combustion is inhibited.

Description

Technical Field

[0001] The present invention relates to the technical field of cable material processing, and particularly relates to a halogen-free and low-smoke flame-retardant power cable and a preparation method thereof. Background Art

[0002] With the continuous improvement of the safety performance requirements of power cables in modern industries such as construction, transportation, and communication, as a key safety component, the performance of flame-retardant cables directly affects the stable operation of the power system and the safety of personnel's lives and property. Traditional flame-retardant cables mostly use halogen-containing flame retardants. Although they have a certain flame-retardant effect, they will release a large amount of toxic smoke and corrosive gases when burning, which will cause great obstacles to the evacuation of personnel and the fire fighting, and at the same time will cause serious environmental pollution.

[0003] Halogen-free and low-smoke flame-retardant power cables use halogen-free flame-retardant materials. Through special formulation and preparation processes, while achieving flame retardancy, the amount of smoke generated and toxicity during combustion are significantly reduced. At present, the insulation and sheath materials of halogen-free and low-smoke flame-retardant power cables mainly use low-smoke and halogen-free flame-retardant polyolefin materials. These materials are given excellent flame-retardant and low-smoke properties by adding additives such as flame retardants and smoke suppressants. However, the current halogen-free flame-retardant system mainly relies on metal oxides (such as Al2O3, MgO), phosphorus-based flame retardants or intumescent flame retardants. However, the addition amount of these materials is often relatively high, and it is necessary to reach about 50% to meet the flame-retardant standard, resulting in a significant decline in the mechanical properties (such as tensile strength and elongation at break) of the cable sheath. In addition, the smoke suppression effect of traditional halogen-free flame retardants is limited and it is difficult to meet the strict low-smoke requirements.

[0004] In view of the technical defects in this regard, a solution is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a halogen-free and low-smoke flame-retardant power cable and a preparation method thereof, which are used to solve the technical problems that in the processing of the sheath layer of halogen-free flame-retardant power cables in the prior art, the addition amount of halogen-free flame retardants is large, and the mechanical strength and smoke suppression effect of the cable sheath layer need to be further improved.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A halogen-free and low-smoke flame-retardant power cable includes a plurality of cable cores, a wrapping layer, and a sheath layer arranged in sequence from the inside out;

[0008] The wrapping layer is obtained by wrapping a wrapping tape around the outside of a plurality of cable cores;

[0009] The sheath layer comprises the following components by weight: 70-80 parts of low-density polyethylene, 10-15 parts of anhydride-modified EVA, 20-28 parts of modified polysiloxane, 25-40 parts of supported diatomite, 0.8-1.2 parts of dicumyl peroxide, and 2-3 parts of additives.

[0010] Further, the preparation method of the anhydride-modified EVA is as follows: Add EVA and maleic anhydride into a torque rheometer at a temperature of 160-170 °C and knead for 3 min. Add the initiator to the torque rheometer in batches, keep warm and mix for 8-12 min, and then perform post-treatment to obtain anhydride-modified EVA.

[0011] Further, the dosage ratio of the EVA, maleic anhydride, and initiator is 80 g: 1.2-1.5 g: 0.2-0.4 g. The initiator is dicumyl peroxide. The post-treatment includes: After crushing the grafted product, mix it with toluene at a ratio of 1 g: 8 mL. Raise the temperature of the reaction system to 85-95 °C, keep warm and stir until the system dissolves. Remove the heating, add acetone to the reaction system, and a large amount of solid will precipitate. Filter by suction, wash the filter cake with acetone twice and then drain it. Transfer the filter cake to a drying oven at a temperature of 50-60 °C and vacuum dry it to constant weight to obtain anhydride-modified EVA.

[0012] Further, the modified polysiloxane is obtained by the following steps:

[0013] A1. Under the protection of an inert atmosphere, mix melamine and N,N-dimethylformamide and stir until the system dissolves. Raise the temperature of the reaction system to 50-60 °C, and dropwise add a 1-dimethoxy(methyl)silylmethyl isocyanate solution to the reaction system. After the dropping is completed, keep warm and react for 80-110 min, and then perform post-treatment to obtain modified triazine;

[0014] The synthesis reaction formula of modified triazine is:

[0015]

[0016] The synthesis reaction mechanism of modified triazine is:

[0017] During the reaction, the amino group on the melamine molecule condenses with the isocyanate group on the 1-dimethoxy(methyl)silylmethyl isocyanate molecule, and a modified triazine modified with dimethoxymethylsilane is formed on the triazine molecule.

[0018] A2. Mix the modified triazine, D4, and tetramethyltetravinylcyclotetrasiloxane and stir. Raise the temperature of the reaction system to 120-130 °C, add a catalyst to the reaction system, keep warm and react for 4-6 h, add a capping agent, and keep warm and react for 2-3 h, and then perform post-treatment to obtain crosslinked polysiloxane;

[0019] The synthesis reaction formula of crosslinked polysiloxane is as follows:

[0020]

[0021] In the formula:

[0022]

[0023] The synthesis reaction mechanism of crosslinked polysiloxane is as follows:

[0024] During the reaction process, under the action of a catalyst, the D4 and tetramethyltetravinylcyclotetrasiloxane molecules undergo ring-opening and condensation reactions with the silanol groups formed by the hydrolysis of the siloxane bonds on the modified triazine molecules, forming a long polysiloxane crosslinked network with triazine as the connecting axis. The end-capping agent is used for end-capping modification of chain termination. It hydrolyzes under the condition of the catalyst to form n-propylamine modified with silanol at one end, and forms amino modification on the long polysiloxane crosslinked network, and the crosslinked polysiloxane is prepared.

[0025] A3. Under the protection of an inert atmosphere, polyethylene oxide and N,N-dimethylformamide are mixed, the temperature of the reaction system is raised to 70 - 80 °C, and stirred until the system dissolves. Isophorone diisocyanate is added to the reaction system, and the reaction is carried out under insulation for 40 - 60 min. Crosslinked polysiloxane is added to the reaction system, and the reaction is carried out under insulation for 80 - 100 min, and then post-treated to obtain modified polysiloxane.

[0026] The synthesis reaction formula of modified polysiloxane is as follows:

[0027]

[0028] In the formula:

[0029] ;

[0030] .

[0031] The synthesis reaction mechanism of modified polysiloxane is as follows:

[0032] During the reaction process, the hydroxyl group on the polyethylene oxide molecule undergoes a condensation reaction with one isocyanate group on the isophorone diisocyanate molecule to form an intermediate modified with isocyanate group on polyethylene oxide. The isocyanate group on the intermediate molecule then undergoes a condensation reaction with the amino group on the crosslinked polysiloxane molecule to form modified polysiloxane with polyethylene oxide modifying crosslinked polysiloxane.

[0033] Further, in step A1, the dosage ratio of melamine to N,N-dimethylformamide is 1 g: 3 mL. The 1-dimethoxy(methyl)silylmethyl isocyanate solution consists of 1-dimethoxy(methyl)silylmethyl isocyanate and N,N-dimethylformamide in a ratio of 1 g: 1 mL. The dosage ratio of melamine to 1-dimethoxy(methyl)silylmethyl isocyanate is 1 mol: 3 mol. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, absolute ethanol is added to the reaction system, filtration is carried out, the filter cake is washed three times with absolute ethanol and then dried by suction, the filter cake is transferred to a drying oven at 50-60 °C, and vacuum dried to constant weight to obtain modified triazine.

[0034] Further, in step A2, the dosage ratio of the modified triazine, D4, tetramethyltetravinylcyclotetrasiloxane, catalyst and terminator is 1-2 g: 5-7 g: 3-4 g: 0.3 g: 0.5-0.8 g. The catalyst is 90-98 wt% sulfuric acid, and the terminator is 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, 0.1 mol / L aqueous sodium carbonate solution is added to the reaction system to adjust the pH of the system to 7, standing for liquid separation, the upper layer liquid is washed 3 times with purified water and then transferred to a rotary evaporator at 80-90 °C, and low-boiling substances are removed under reduced pressure to obtain crosslinked polysiloxane.

[0035] Further, in step A3, the dosage ratio of polyethylene oxide, N,N-dimethylformamide and crosslinked polysiloxane is 1 g: 7 mL: 3 g. The molar amount of isophorone diisocyanate is the same as the molar amount of hydroxyl groups in polyethylene oxide. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is raised to 110-120 °C, and low-boiling substances are removed under reduced pressure to obtain modified polysiloxane.

[0036] Further, the preparation method of the supported diatomite is: mixing biochar-modified diatomite and a loading solution, ultrasonically dispersing at room temperature for 30-50 min, adding sodium hydroxide solution to the reaction system to adjust the pH of the system to 9-10, raising the temperature of the reaction system to 50-60 °C, adding a 5-hexenyltriethoxysilane solution to the reaction system, and carrying out a heat preservation reaction for 60-80 min, followed by post-treatment to obtain the supported diatomite.

[0037] The synthesis reaction mechanism of the supported diatomite is:

[0038] Metal nitrates in the loading solution hydrolyze to form metal ions. Through ultrasonic dispersion, the metal ions and biochar-modified diatomaceous earth are uniformly dispersed. By adjusting the pH of the reaction system, metal ions hydrolyze to form hydroxide precipitates. The porous structure of biochar-modified diatomaceous earth provides a good carrier for the metal hydroxide precipitates. The siloxane bonds on the 5-hexenyltriethoxysilane molecules hydrolyze to form silanols, which react with the active functional groups on the surface of biochar-modified diatomaceous earth to form chemical bonds, thus preparing a supported diatomaceous earth with an olefin double bond-modified metal hydroxide-loaded biochar-modified diatomaceous earth.

[0039] Furthermore, the dosage ratio of the biochar-modified diatomaceous earth, the loading solution, and the 5-hexenyltriethoxysilane solution is 3 g: 10 mL: 15 mL. The loading solution is composed of bismuth nitrate, magnesium nitrate, aluminum nitrate, and deionized water in a ratio of 1 g: 2 g: 2 g: 20 mL. The 5-hexenyltriethoxysilane solution is composed of 5-hexenyltriethoxysilane and tetrahydrofuran in a ratio of 1 g: 10 mL. The post-treatment includes: after the reaction is completed, filtration is carried out, and the filter cake is transferred to an oven at a temperature of 70 - 80 °C and dried to a constant weight to obtain the supported diatomaceous earth.

[0040] Furthermore, the biochar-modified diatomaceous earth is processed by the following steps:

[0041] B1. Place the plant powder in a sodium hydroxide solution, stir, and boil for 30 - 50 min, followed by post-treatment to obtain a pretreated powder;

[0042] B2. Mix the pretreated powder, diatomaceous earth, and the modification solution, and perform ultrasonic dispersion for 60 - 80 min, followed by post-treatment to obtain a modified mixed powder;

[0043] B3. After calcining the modified mixed powder, perform post-treatment to obtain the biochar-modified diatomaceous earth.

[0044] The synthesis reaction mechanism of the biochar-modified diatomaceous earth is as follows:

[0045] During the reaction process, the plant powder is treated with an alkali to promote the hydrolysis of the ester bonds of lignin and hemicellulose in the plant powder, destroy its cross-linked structure, and the high-temperature boiling of the sodium hydroxide solution accelerates the reaction, removes low-molecular organic substances and impurities in the plant powder, and forms a porous skeleton structure, providing active sites for subsequent loading of metal ions; the hydrophilic segments of polyethylene glycol form hydrogen bonds with the surface hydroxyl groups of diatomite and the pretreated powder, prevent particle aggregation, form a micelle structure in ultrasonic dispersion, and guide the uniform loading of zinc chloride on diatomite and the pretreated powder; in a high-temperature environment under an inert gas atmosphere, the plant powder in the modified mixed powder undergoes pyrolysis carbonization reaction, and the molten zinc chloride reacts with the carbon skeleton to form a rich microporous-mesoporous composite structure through dehydration and condensation. The biochar fills the pores of diatomite to form a "carbon-silicon" double-network structure, and then the residual metal compounds are removed by pickling to form a multi-porous biochar-modified diatomite.

[0046] Further, in step B1, the dosage ratio of the plant powder to the sodium hydroxide solution is 1 g:10 mL. The plant powder is one or more of coconut shell powder, apricot shell powder, and straw powder. The particle size of the plant powder is 5-15 mm. The concentration of the sodium hydroxide solution is 6-8 mol / L. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is reduced to room temperature, filtered by suction, the filter cake is washed with purified water until neutral and then dried by suction, the filter cake is transferred to a drying oven at 60-70 °C, and vacuum dried to constant weight to obtain the pretreated powder.

[0047] Further, in step B2, the dosage ratio of the pretreated powder, diatomite, and the modification liquid is 0.6-0.8 g:1 g:10 mL. The modification liquid is composed of zinc chloride, PEG-800, and deionized water in a ratio of 1 g:0.1 g:10 mL. The post-treatment includes: after the reaction is completed, filtered by suction, the filter cake is transferred to a drying oven at 60-70 °C and dried to constant weight to obtain the modified mixed powder.

[0048] Further, in step B3, the calcination temperature is 680-750 °C. The post-treatment includes: after the calcination is completed, the calcined powder is washed 3 times with 1-2 mol / L hydrochloric acid and then washed with purified water until neutral. The solid is placed in a drying oven at 60-70 °C and dried to constant weight to obtain the biochar-modified diatomite.

[0049] A preparation method of a halogen-free and low-smoke flame-retardant power cable includes the following steps:

[0050] S1. Place a plurality of cable cores parallel to each other, use a wrapping tape to wrap and fix the plurality of cable cores together to form a wrapping layer outside the cable cores;

[0051] S2. Add low-density polyethylene, acid anhydride-modified EVA, modified polysiloxane, supported diatomite, dicumyl peroxide and additives into an extruder, melt and mix for 6 - 9 min, then extrude and coat the outside of the lapped layer, cool down and solidify to form a sheath layer outside the lapped layer, thus obtaining a power cable.

[0052] Further, the additives are composed of a dispersant, a lubricant, a plasticizer, an antioxidant and a stabilizer in a ratio of 5:2:4:2:1. The dispersant is a stearate, the lubricant is any one of butyl stearate, oleamide and ethylene bisstearamide, the plasticizer is a phthalate, the antioxidant is any one of antioxidant AW, antioxidant DNP and antioxidant CPPD, the stabilizer is a calcium-zinc stabilizer. The temperatures of the 5 temperature zones of the extruder from the feed end to the discharge end are 170 °C, 175 °C, 180 °C, 180 °C and 185 °C in sequence.

[0053] The present invention has the following beneficial effects:

[0054] 1. For the halogen-free low-smoke flame-retardant power cable of the present invention, acid anhydride-modified EVA promotes the uniform dispersion of modified polysiloxane and supported diatomite with low-density polyethylene. Then, under the action of an initiator and high temperature, intermolecular crosslinking is promoted to improve the mechanical strength of the cable sheath layer. When preparing supported diatomite, diatomite is modified by biochar. The porous structures of diatomite and biochar provide loading sites for metal ions. Moreover, the porous and rigid diatomite and biochar are dispersed in the LDPE matrix as rigid fillers to form physical crosslinking points, restricting the slippage of polyethylene molecular chains, thereby improving the tensile strength. By modifying olefin double bonds on its surface, the long-chain olefin ends are combined with the low-density polyethylene molecular chains through winding or co-crystallization, improving the compatibility between the filler and the matrix, reducing interface defects, and enhancing the mechanical strength of the sheath layer material. At the same time, the porous structure of diatomite and the layered carbon structure of biochar form a dense carbon layer during combustion, isolating the transfer of oxygen and heat. The loaded metal compounds catalyze the oxidative decomposition of the sheath layer at high temperature to generate a carbon layer, reducing smoke generation. The dense and porous carbon layer formed by diatomite and biochar can reduce the release of volatile organic compounds, reduce the soot particles generated by incomplete combustion, improve its flame-retardant performance, and reduce the concentration of flue gas.

[0055] 2. The halogen-free and low-smoke flame-retardant power cable of the present invention constructs a three-dimensional cross-linked network by cooperating with D4 and tetramethyltetravinylcyclotetrasiloxane with modified triazine as the matrix. This cross-linked network serves as a physical reinforcement phase in the polyethylene matrix, restricting the slippage of polyethylene molecular chains, thereby improving the tensile strength. Then, polyethylene oxide is modified on the cross-linked polysiloxane molecules, enabling them to bind to polyethylene molecular chains through hydrogen bonds or van der Waals forces, enhancing the interfacial bonding force between the two phases, reducing stress concentration, promoting the uniform dispersion of polysiloxane in low-density polyethylene, and further improving the tensile strength of the material. The flexibility of the polysiloxane main chain and the elasticity of the polyethylene oxide chain segments can absorb part of the energy during the stretching process, increasing the elongation at break of the material. The triazine in the modified polysiloxane molecules decomposes at high temperatures to release nitrogen, diluting the concentration of combustible gases and inhibiting the combustion chain reaction. At the same time, the cross-linked polysiloxane decomposes during combustion to form silicon dioxide, which cooperates with the supported diatomite to inhibit the release of organic volatiles, reduce smoke particles, and further reduce the smoke release amount while improving the flame-retardant performance of the material.

[0056] 3. The halogen-free and low-smoke flame-retardant power cable of the present invention modifies EVA with anhydride, modifies a strongly polar anhydride matrix on the EVA molecules, and uses the anhydride-modified EVA as a bridge to improve the compatibility of low-density polyethylene with modified polysiloxane and supported diatomite, enhancing the overall tensile strength. Moreover, the high reactivity of maleic anhydride groups can promote the branching and entanglement of low-density polyethylene molecular chains, forming a denser molecular network. The anhydride modified on EVA decomposes at high temperatures to generate carboxylic acid groups, which cooperate with the metal compounds supported on the supported diatomite to further catalyze the carbonization of the sheath layer to form a dense protective layer, isolating oxygen and heat, and improving the flame-retardant performance of the material. When preparing the sheath layer, intermolecular cross-linking is promoted by a free radical initiator between its molecules, reducing the melting and dripping during combustion and prolonging the carbon layer protection time, enhancing the flame-retardant performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0058] Figure 1 It is a three-dimensional structural schematic diagram of the whole of the present invention.

[0059] In the figure: 1. Cable core; 2. Wrapping layer; 3. Sheath layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0060] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work belong to the scope of protection of the present invention.

[0061] In this application, D4 is octamethylcyclotetrasiloxane, and its CAS number is 556-67-2;

[0062] In this application, polyethylene oxide is selected from Hubei Langbowan Biopharmaceutical Co., Ltd., with a CAS number of 8441-17-8 and a molecular weight of 1000;

[0063] In this application, PEG-800 is polyethylene glycol 800, selected from Jining Fangyu Chemical Co., Ltd., with a CAS number of 25322-68-3;

[0064] In this application, EVA is ethylene-vinyl acetate copolymer, in which the content of vinyl acetate is 12-16%, and its CAS number is 24937-78-8;

[0065] In this application, the calcium-zinc stabilizer is selected from Shijiazhuang Zhongdao Chemical Technology Co., Ltd., and the model is 808;

[0066] In this application, the low-density polyethylene brand is Sinopec Yanshan, the grade is LD605, the melt flow rate is 6 g / 10 min, and the density is 0.922 g / cm 3 .

[0067] Example 1

[0068] This example provides a preparation method of a modified polysiloxane for halogen-free and low-smoke flame-retardant power cables, including the following steps:

[0069] A1. Preparation of modified triazine

[0070] Mix 48.4 g of 1-dimethoxy(methyl)silylmethyl isocyanate and 48.4 mL of N,N-dimethylformamide evenly to obtain a 1-dimethoxy(methyl)silylmethyl isocyanate solution;

[0071] Weigh: 12.6 g of melamine and 37.8 mL of N,N-dimethylformamide are added to a 250 mL reaction flask protected by argon and stirred. The temperature of the reaction flask is raised to 50 °C. After stirring until the system becomes clear, the 1-dimethoxy(methyl)silylmethyl isocyanate solution prepared above is added dropwise to the reaction flask. After the addition is complete, keep the temperature for reaction for 80 min. Then the temperature of the reaction flask is lowered to room temperature. 200 mL of absolute ethanol is added to the reaction flask, and filtration is carried out. The filter cake is washed three times with absolute ethanol and then dried by suction. The filter cake is transferred to a drying oven at 50 °C, and the vacuum is pumped to a negative pressure of 0.1 MPa, and vacuum drying is carried out until constant weight to obtain modified triazine.

[0072] A2. Preparation of crosslinked polysiloxane

[0073] Weigh: 10 g of modified triazine, 50 g of D4, and 30 g of tetramethyltetravinylcyclotetrasiloxane are added to a 250 mL reaction flask and mixed and stirred. The temperature of the reaction flask is raised to 120 °C. 3 g of 90 wt% sulfuric acid is added to the reaction flask, and the temperature is kept for reaction for 4 h. 5 g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is added, and the temperature is kept for reaction for 2 h. Then the temperature of the reaction flask is lowered to room temperature. 0.1 mol / L sodium carbonate aqueous solution is added to the reaction flask to adjust the pH of the system to 7. Let it stand for liquid separation. The upper layer liquid is washed 3 times with purified water and then transferred to a rotary evaporator at 80 °C. The vacuum is pumped to a negative pressure of 0.1 MPa, and low-boiling substances are removed under reduced pressure to obtain crosslinked polysiloxane.

[0074] A3. Preparation of modified polysiloxane

[0075] Weigh: 20 g of polyethylene oxide and 140 mL of N,N-dimethylformamide are added to a 250 mL reaction flask protected by argon and stirred. The temperature of the reaction flask is raised to 70 °C. After stirring until the system is dissolved, isophorone diisocyanate is added to the reaction flask according to the calculation amount of N 聚氧化乙烯-OH / N 异佛尔酮二异氰酸酯-NCO =1:2. Keep the temperature for reaction for 40 min. 30 g of crosslinked polysiloxane is added to the reaction flask, and the temperature is kept for reaction for 80 min. The temperature of the reaction flask is raised to 110 °C. The vacuum is pumped to a negative pressure of 0.1 MPa, and low-boiling substances are removed under reduced pressure to obtain modified polysiloxane.

[0076] Example 2

[0077] This example provides a preparation method of modified polysiloxane for halogen-free and low-smoke flame-retardant power cables, including the following steps:

[0078] A1. Preparation of modified triazine

[0079] Mix 48.4 g of 1-dimethoxy(methyl)silylmethyl isocyanate and 48.4 mL of N,N-dimethylformamide evenly to obtain a 1-dimethoxy(methyl)silylmethyl isocyanate solution;

[0080] Weigh: 12.6 g of melamine and 37.8 mL of N,N-dimethylformamide, add them to a 250 mL reaction flask protected by argon and stir. The temperature of the reaction flask rises to 55 °C. After stirring until the system becomes clear, add the above-prepared 1-dimethoxy(methyl)silylmethyl isocyanate solution dropwise to the reaction flask. After the addition is complete, keep the temperature for reaction for 95 min. Then lower the temperature of the reaction flask to room temperature. Add 200 mL of absolute ethanol to the reaction flask, filter by suction. Wash the filter cake three times with absolute ethanol and then dry by suction. Transfer the filter cake to a drying oven at 55 °C, evacuate to a negative pressure of 0.1 MPa, and dry under vacuum until constant weight to obtain modified triazine.

[0081] A2. Preparation of crosslinked polysiloxane

[0082] Weigh: 15 g of modified triazine, 60 g of D4, and 35 g of tetramethyltetravinylcyclotetrasiloxane, add them to a 250 mL reaction flask and mix and stir. The temperature of the reaction flask rises to 125 °C. Add 3 g of 94 wt% sulfuric acid to the reaction flask, keep the temperature for reaction for 5 h. Then add 7 g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, keep the temperature for reaction for 2.5 h. Lower the temperature of the reaction flask to room temperature. Add 0.1 mol / L sodium carbonate aqueous solution to the reaction flask to adjust the pH of the system to 7. Let it stand and separate the liquid. Wash the upper layer liquid 3 times with purified water and then transfer it to a rotary evaporator at 85 °C. Evacuate to a negative pressure of 0.1 MPa and reduce the pressure to remove low-boiling substances to obtain crosslinked polysiloxane.

[0083] A3. Preparation of modified polysiloxane

[0084] Weigh: 20 g of polyethylene oxide and 140 mL of N,N-dimethylformamide, add them to a 250 mL reaction flask protected by argon and stir. The temperature of the reaction flask rises to 75 °C. After stirring until the system dissolves, add isophorone diisocyanate to the reaction flask according to the calculation amount of N 聚氧化乙烯-OH / N 异佛尔酮二异氰酸酯-NCO =1:2. Keep the temperature for reaction for 50 min. Add 30 g of crosslinked polysiloxane to the reaction flask, keep the temperature for reaction for 9 min. Raise the temperature of the reaction flask to 115 °C, evacuate to a negative pressure of 0.1 MPa, and reduce the pressure to remove low-boiling substances to obtain modified polysiloxane.

[0085] Example 3

[0086] This example provides a preparation method of modified polysiloxane for halogen-free and low-smoke flame-retardant power cables, including the following steps:

[0087] A1. Preparation of Modified Triazine

[0088] Mix 48.4 g of 1-dimethoxy(methyl)silylmethyl isocyanate and 48.4 mL of N,N-dimethylformamide evenly to obtain a 1-dimethoxy(methyl)silylmethyl isocyanate solution;

[0089] Weigh: 12.6 g of melamine and 37.8 mL of N,N-dimethylformamide, add them to a 250 mL reaction flask protected by argon and stir. Raise the temperature of the reaction flask to 60 °C. After stirring until the system becomes clear, add the above-prepared 1-dimethoxy(methyl)silylmethyl isocyanate solution dropwise to the reaction flask. After the addition is complete, keep the temperature for reaction for 110 min. Lower the temperature of the reaction flask to room temperature. Add 200 mL of absolute ethanol to the reaction flask, filter by suction. Wash the filter cake three times with absolute ethanol and then drain it by suction. Transfer the filter cake to a drying oven at 60 °C, evacuate to a negative pressure of 0.1 MPa, and dry under vacuum until constant weight to obtain modified triazine.

[0090] A2. Preparation of Crosslinked Polysiloxane

[0091] Weigh: 20 g of modified triazine, 70 g of D4, and 40 g of tetramethyltetravinylcyclotetrasiloxane, add them to a 250 mL reaction flask and mix and stir. Raise the temperature of the reaction flask to 130 °C. Add 3 g of 98 wt% sulfuric acid to the reaction flask, keep the temperature for reaction for 6 h. Add 8 g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, keep the temperature for reaction for 3 h. Lower the temperature of the reaction flask to room temperature. Add 0.1 mol / L sodium carbonate aqueous solution to the reaction flask to adjust the pH of the system to 7. Let it stand for liquid separation. Wash the upper layer liquid three times with purified water and then transfer it to a rotary evaporator at 90 °C. Evacuate to a negative pressure of 0.1 MPa and reduce the pressure to remove low-boiling substances to obtain crosslinked polysiloxane.

[0092] A3. Preparation of Modified Polysiloxane

[0093] Weigh: 20 g of polyethylene oxide and 140 mL of N,N-dimethylformamide, add them to a 250 mL reaction flask protected by argon and stir. Raise the temperature of the reaction flask to 80 °C. After stirring until the system dissolves, add isophorone diisocyanate to the reaction flask according to the calculation amount of N 聚氧化乙烯-OH / N 异佛尔酮二异氰酸酯-NCO =1:2. Keep the temperature for reaction for 60 min. Add 30 g of crosslinked polysiloxane to the reaction flask, keep the temperature for reaction for 100 min. Raise the temperature of the reaction flask to 120 °C. Evacuate to a negative pressure of 0.1 MPa and reduce the pressure to remove low-boiling substances to obtain modified polysiloxane.

[0094] Example 4

[0095] This embodiment provides a method for preparing a supported diatomite for a halogen-free and low-smoke flame-retardant power cable, comprising the following steps:

[0096] B1. Prepare the pretreated powder

[0097] Weigh: 100 g of coconut shell powder with a particle size of 5 - 15 mm and 1000 mL of 6 mol / L sodium hydroxide solution, add them to a 3 L reaction flask and stir. Heat the reaction flask until the system refluxes, maintain the boiling state for 30 min, then lower the temperature of the reaction flask to room temperature, perform suction filtration. Wash the filter cake with purified water until it is neutral and then drain it. Transfer the filter cake to a drying oven at 60 °C, evacuate to a negative pressure of 0.1 MPa, and vacuum dry until constant weight to obtain the pretreated powder.

[0098] B2. Prepare the modified mixed powder

[0099] Mix zinc chloride, PEG - 800 and deionized water evenly at a ratio of 1 g:0.1 g:10 mL to obtain a modified solution for standby;

[0100] Weigh: 60 g of the pretreated powder, 100 g of diatomite, and 1000 mL of the modified solution, add them to a 3 L reaction flask and mix. Perform ultrasonic dispersion for 60 min, then perform suction filtration. Transfer the filter cake to a drying oven at 60 °C and dry until constant weight to obtain the modified mixed powder.

[0101] B3. Prepare the biochar-modified diatomite

[0102] Transfer the modified mixed powder to a tubular furnace under a nitrogen atmosphere. Heat the tubular furnace to 680 °C and calcine for 3 h. Then lower the temperature of the tubular furnace to room temperature. Wash the calcined powder 3 times with 1 mol / L hydrochloric acid and then wash it with purified water until it is neutral. Place the solid in a drying oven at 60 °C and dry until constant weight to obtain the biochar-modified diatomite.

[0103] B4. Prepare the supported diatomite

[0104] Mix bismuth nitrate, magnesium nitrate, aluminum nitrate and deionized water evenly at a ratio of 1 g:2 g:2 g:20 mL to obtain a loading solution;

[0105] Mix 5-hexenyltriethoxysilane and tetrahydrofuran evenly at a ratio of 1 g:10 mL to obtain a 5-hexenyltriethoxysilane solution;

[0106] Weigh: 90 g of biochar-modified diatomite and 300 mL of the loading solution are added to a 3-L reaction flask and mixed. Ultrasonic dispersion is carried out for 30 min at room temperature. 1 mol / L sodium hydroxide solution is added to the reaction flask to adjust the system pH to 9. The temperature of the reaction flask is raised to 50 °C. 450 mL of 5-hexenyltriethoxysilane solution is added to the reaction flask, and the reaction is carried out under insulation for 60 min. The temperature of the reaction flask is lowered to room temperature, and then filtration is carried out. The filter cake is transferred to an oven at 70 °C and dried to a constant weight to obtain the supported diatomite.

[0107] Example 5

[0108] This example provides a preparation method of supported diatomite for halogen-free and low-smoke flame-retardant power cables, including the following steps:

[0109] B1. Prepare the pretreated powder

[0110] Weigh: 100 g of apricot shell powder with a particle size of 5 - 15 mm and 1000 mL of 7 mol / L sodium hydroxide solution are added to a 3-L reaction flask and stirred. The temperature of the reaction flask is raised to the system reflux, and the boiling state is maintained for 40 min. The temperature of the reaction flask is lowered to room temperature, and then filtration is carried out. The filter cake is washed with purified water until neutral and then dried by suction. The filter cake is transferred to an oven at 65 °C, and the vacuum is pumped to a negative pressure of 0.1 MPa, and vacuum drying is carried out to a constant weight to obtain the pretreated powder.

[0111] B2. Prepare the modified mixed powder

[0112] Zinc chloride, PEG-800 and deionized water are mixed evenly according to 1 g: 0.1 g: 10 mL to obtain the modified solution for standby;

[0113] Weigh: 70 g of the pretreated powder, 100 g of diatomite and 1000 mL of the modified solution are added to a 3-L reaction flask and mixed. Ultrasonic dispersion is carried out for 70 min, and then filtration is carried out. The filter cake is transferred to an oven at 65 °C and dried to a constant weight to obtain the modified mixed powder.

[0114] B3. Prepare the biochar-modified diatomite

[0115] The modified mixed powder is transferred to a tubular furnace under a nitrogen atmosphere. The temperature of the tubular furnace is raised to 715 °C and calcined for 4 h. The temperature of the tubular furnace is lowered to room temperature. The calcined powder is washed 3 times with 1.5 mol / L hydrochloric acid and then washed with purified water until neutral. The solid is placed in an oven at 65 °C and dried to a constant weight to obtain the biochar-modified diatomite.

[0116] B4. Prepare the supported diatomite

[0117] Bismuth nitrate, magnesium nitrate, aluminum nitrate and deionized water are mixed evenly according to 1 g: 2 g: 2 g: 20 mL to obtain the loading solution;

[0118] Mix 5-hexenyltriethoxysilane and tetrahydrofuran evenly at a ratio of 1 g:10 mL to obtain a 5-hexenyltriethoxysilane solution;

[0119] Weigh: 90 g of biochar-modified diatomite and 300 mL of loading solution, add them to a 3 L reaction flask and mix. Ultrasonically disperse for 40 min at room temperature. Add 1 mol / L sodium hydroxide solution to the reaction flask to adjust the system pH to 9.5. Raise the temperature of the reaction flask to 55 °C. Add 450 mL of the 5-hexenyltriethoxysilane solution to the reaction flask, keep the temperature for reaction for 70 min. Lower the temperature of the reaction flask to room temperature, filter by suction. Transfer the filter cake to a drying oven at 75 °C and dry to constant weight to obtain the supported diatomite.

[0120] Example 6

[0121] This example provides a preparation method of supported diatomite for halogen-free and low-smoke flame-retardant power cables, including the following steps:

[0122] B1. Prepare the pretreated powder

[0123] Weigh: 100 g of straw powder with a particle size of 5 - 15 mm and 1000 mL of 8 mol / L sodium hydroxide solution, add them to a 3 L reaction flask and stir. Raise the temperature of the reaction flask to the system reflux temperature, keep it boiling for 50 min. Lower the temperature of the reaction flask to room temperature, filter by suction. Wash the filter cake with purified water until neutral and then drain it. Transfer the filter cake to a drying oven at 70 °C, evacuate to a negative pressure of 0.1 MPa, and vacuum dry to constant weight to obtain the pretreated powder.

[0124] B2. Prepare the modified mixed powder

[0125] Mix zinc chloride, PEG-800 and deionized water evenly at a ratio of 1 g:0.1 g:10 mL to obtain a modified solution for standby;

[0126] Weigh: 80 g of the pretreated powder, 100 g of diatomite, and 1000 mL of the modified solution, add them to a 3 L reaction flask and mix. Ultrasonically disperse for 80 min, filter by suction. Transfer the filter cake to a drying oven at 70 °C and dry to constant weight to obtain the modified mixed powder.

[0127] B3. Prepare the biochar-modified diatomite

[0128] Transfer the modified mixed powder to a tube furnace under a nitrogen atmosphere. Raise the temperature of the tube furnace to 750 °C and calcine for 5 h. Lower the temperature of the tube furnace to room temperature. Wash the calcined powder with 2 mol / L hydrochloric acid three times and then wash it with purified water until neutral. Place the solid in a drying oven at 70 °C and dry to constant weight to obtain the biochar-modified diatomite.

[0129] B4. Preparation of Supported Diatomite

[0130] Mix bismuth nitrate, magnesium nitrate, aluminum nitrate and deionized water evenly at a ratio of 1 g: 2 g: 2 g: 20 mL to obtain a loading solution;

[0131] Mix 5-hexenyltriethoxysilane and tetrahydrofuran evenly at a ratio of 1 g: 10 mL to obtain a 5-hexenyltriethoxysilane solution;

[0132] Weigh: 90 g of biochar-modified diatomite and 300 mL of the loading solution, add them to a 3 L reaction flask and mix. Ultrasonically disperse for 50 min at room temperature. Add 1 mol / L sodium hydroxide solution to the reaction flask to adjust the system pH to 10. Raise the temperature of the reaction flask to 60 °C. Add 450 mL of the 5-hexenyltriethoxysilane solution to the reaction flask, keep the temperature for reaction for 80 min. Lower the temperature of the reaction flask to room temperature, filter by suction. Transfer the filter cake to a drying oven at 80 °C and dry to constant weight to obtain the supported diatomite.

[0133] Example 7

[0134] This example provides a preparation method of a halogen-free and low-smoke flame-retardant power cable, including the following steps:

[0135] Step 1. Preparation of Anhydride-Modified EVA

[0136] Weigh: 800 g of EVA and 12 g of maleic anhydride, add them to a torque rheometer at 160 °C and knead for 3 min. Add 2 g of dicumyl peroxide to the torque rheometer in batches, keep the temperature for mixing for 8 min. After crushing the grafted product, add it to a reaction flask with toluene at a ratio of 1 g: 8 mL and mix. Raise the temperature of the reaction flask to 85 °C, keep stirring until the system dissolves. Remove the heating. Add acetone to the reaction system according to acetone / toluene = 3:1, and a large amount of solid precipitates. Filter by suction. Wash the filter cake with acetone twice and then drain it. Transfer the filter cake to a drying oven at 50 °C and vacuum dry to constant weight to obtain the anhydride-modified EVA.

[0137] Step 2. Wrapping of Cable Core

[0138] Select a copper core cable with an outer coating of insulating rubber as Cable Core 1;

[0139] Place several Cable Cores 1 parallel to each other and use a polyester wrapping tape to wrap and fix the several Cable Cores 1 together to form a wrapping layer 2 on the outside of the Cable Cores 1.

[0140] Step 3. Preparation of Power Cable

[0141] Mix zinc stearate, butyl stearate, dibutyl phthalate, antioxidant AW and calcium-zinc stabilizer evenly at a ratio of 5: 2: 4: 2: 1 to obtain an additive;

[0142] Weigh by parts by weight: 70 parts of low-density polyethylene, 10 parts of acid anhydride-modified EVA, 20 parts of the modified polysiloxane prepared in Example 1, 25 parts of the supported diatomaceous earth prepared in Example 4, 0.8 part of dicumyl peroxide, and 2 parts of additives, and add them to a twin-screw extruder. The temperatures of the 5 temperature zones of the extruder from the feeding end to the discharging end are 170 °C, 175 °C, 180 °C, 180 °C, and 185 °C in sequence. After melting and mixing in the twin-screw extruder for 6 min, it is extruded and coated outside the wrapping layer 2, cooled and solidified, and a sheath layer 3 is formed outside the wrapping layer 2 to obtain a power cable.

[0143] Example 8

[0144] This example provides a preparation method of a halogen-free and low-smoke flame-retardant power cable, including the following steps:

[0145] Step 1. Prepare acid anhydride-modified EVA

[0146] Weigh: 800 g of EVA and 13.5 g of maleic anhydride, add them to a torque rheometer at a temperature of 165 °C, mix for 3 min, add 3 g of dicumyl peroxide to the torque rheometer in batches, keep warm and mix for 10 min, crush the grafted product, and add it to a reaction flask with toluene at a ratio of 1 g:8 mL and mix. Raise the temperature of the reaction flask to 90 °C, keep warm and stir until the system dissolves, remove the heating, add acetone to the reaction system according to acetone / toluene = 3:1, a large amount of solid precipitates, filter by suction, wash the filter cake with acetone twice and then drain it, transfer the filter cake to a drying oven at a temperature of 55 °C, and vacuum dry to constant weight to obtain acid anhydride-modified EVA.

[0147] Step 2. Cable core wrapping

[0148] Select a copper core cable with an outer coating of insulating rubber as the cable core 1;

[0149] Place several cable cores 1 parallel to each other, and use a polyester wrapping tape to wrap and fix several cable cores 1 together to form a wrapping layer 2 outside the cable cores 1.

[0150] Step 3. Prepare a power cable

[0151] Mix calcium stearate, oleamide, diisobutyl phthalate, antioxidant DNP, and calcium-zinc stabilizer evenly according to 5:2:4:2:1 to obtain additives;

[0152] Weigh by parts by weight: 75 parts of low-density polyethylene, 13 parts of anhydride-modified EVA, 24 parts of the modified polysiloxane prepared in Example 2, 27 parts of the supported diatomite prepared in Example 5, 1.0 part of dicumyl peroxide, and 2.5 parts of additives, and add them to a twin-screw extruder. The temperatures of the 5 temperature zones of the extruder from the feeding end to the discharging end are 170 °C, 175 °C, 180 °C, 180 °C, and 185 °C in sequence. After melt mixing in the twin-screw extruder for 7.5 min, it is extruded and coated outside the wrapping layer 2, cooled and solidified, and a sheath layer 3 is formed outside the wrapping layer 2 to obtain a power cable.

[0153] Example 9

[0154] This example provides a method for preparing a halogen-free and low-smoke flame-retardant power cable, which includes the following steps:

[0155] Step 1: Prepare anhydride-modified EVA

[0156] Weigh: 800 g of EVA and 15 g of maleic anhydride, add them to a torque rheometer at a temperature of 170 °C and mix for 3 min. Add 4 g of dicumyl peroxide to the torque rheometer in batches, keep warm and mix for 12 min. After crushing the grafted product, add it to a reaction flask with toluene at a ratio of 1 g:8 mL and mix. Raise the temperature of the reaction flask to 95 °C, keep warm and stir until the system dissolves. Remove the heating, add acetone to the reaction system according to acetone / toluene = 3:1, a large amount of solid precipitates, filter by suction, wash the filter cake with acetone twice and then drain it. Transfer the filter cake to a drying oven at a temperature of 60 °C and vacuum dry to constant weight to obtain anhydride-modified EVA.

[0157] Step 2: Wrap the cable core

[0158] Select a copper core cable with an outer coating of insulating rubber as the cable core 1;

[0159] Place several cable cores 1 parallel to each other, and use a polyester wrapping tape to wrap and fix the several cable cores 1 together to form a wrapping layer 2 outside the cable core 1.

[0160] Step 3: Prepare a power cable

[0161] Mix magnesium stearate, ethylene bisstearamide, diisooctyl phthalate, antioxidant CPPD, and calcium-zinc stabilizer evenly according to 5:2:4:2:1 to obtain additives;

[0162] Weigh by parts by weight: 80 parts of low-density polyethylene, 15 parts of anhydride-modified EVA, 28 parts of the modified polysiloxane prepared in Example 3, 40 parts of the supported diatomite prepared in Example 6, 1.2 parts of dicumyl peroxide, and 3 parts of an additive, and add them to a twin-screw extruder. The temperatures of the 5 temperature zones of the extruder from the feed end to the discharge end are 170 °C, 175 °C, 180 °C, 180 °C, and 185 °C in sequence. After melt mixing in the twin-screw extruder for 9 minutes, it is extruded and coated outside the wrapping layer 2, cooled and solidified, and a sheath layer 3 is formed outside the wrapping layer 2 to obtain a power cable.

[0163] Comparative Example 1

[0164] The difference between this comparative example and Example 9 is that when the modified polysiloxane is prepared, step A1 is cancelled, and the modified triazine is not added in step A2.

[0165] Comparative Example 2

[0166] The difference between this comparative example and Example 9 is that when the modified polysiloxane is prepared, step A3 is cancelled, and the crosslinked polysiloxane in step A2 is used to replace the modified polysiloxane in step three.

[0167] Comparative Example 3

[0168] The difference between this comparative example and Example 9 is that when the supported diatomite is prepared, step B1 is cancelled, and the pretreatment powder is not added in step B2.

[0169] Comparative Example 4

[0170] The difference between this comparative example and Example 9 is that step one is cancelled, and the EVA in step one is used to replace the anhydride-modified EVA in step three.

[0171] Performance test:

[0172] Refer to the standard GB / T 32129-2015 "Halogen-free low-smoke flame-retardant cable materials for wire and cable" to measure the tensile strength, elongation at break, oxygen index, and smoke density of the sheath layers of the power cable specimens prepared in Examples 7-9 and Comparative Examples 1-4;

[0173] The specific test results are shown in Table 1 below.

[0174] Table 1 - Performance test data table of specimens

[0175]

[0176] Data analysis:

[0177] Comparing and analyzing the data in Table 1 above, the tensile strength of the sheath layer of the power cable sample prepared by the present invention reaches 15.2 MPa, the elongation at break reaches 330%, the oxygen index reaches 37%, the smoke density during flaming combustion is reduced to 118, and the smoke density during non-flaming smoldering is reduced to 48. All performance parameters are superior to those of the comparative example. This shows that by promoting the uniform dispersion of the modified polysiloxane, supported diatomaceous earth and low-density polyethylene through acid anhydride-modified EVA, and then promoting intermolecular crosslinking under the action of an initiator and high temperature, the mechanical strength of the cable sheath layer is improved, while the flame retardant performance of the power cable material is improved and the generation of smoke during combustion is inhibited.

[0178] The above content is only an example and explanation of the structure of the present invention. Those skilled in the art of this technology can make various modifications, supplements or use similar methods to replace the specific embodiments described, as long as they do not deviate from the structure of the invention or exceed the scope defined by this claim book, they should fall within the protection scope of the present invention.

[0179] In the description of this specification, the description with reference to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0180] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not elaborate all the details, nor limit the present invention to only the specific implementation manners. Obviously, many modifications and variations can be made according to the content of this specification. The present specification selects and specifically describes these embodiments to better explain the principle and practical application of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claim book and its full scope and equivalents.

Claims

1. A halogen-free and low-smoke flame-retardant power cable, characterized in that, It includes several cable cores (1), a wrapping layer (2) and a sheath layer (3) which are arranged from inside to outside in sequence; The wrapping layer (2) is obtained by wrapping a wrapping tape around the outside of several cable cores (1); The sheath layer (3) comprises the following components by weight: 70-80 parts of low-density polyethylene, 10-15 parts of anhydride-modified EVA, 20-28 parts of modified polysiloxane, 25-40 parts of supported diatomite, 0.8-1.2 parts of dicumyl peroxide and 2-3 parts of additives.

2. A halogen-free and low-smoke flame-retardant power cable according to claim 1, characterized in that, The preparation method of the anhydride-modified EVA is as follows: EVA and maleic anhydride are added into a torque rheometer at a temperature of 160-170 °C and kneaded for 3 min, initiator is added into the torque rheometer in batches, kept warm and mixed for 8-12 min, and then post-treated to obtain anhydride-modified EVA.

3. The halogen-free and low-smoke flame-retardant power cable according to claim 2, characterized in that, The dosage ratio of the EVA, maleic anhydride and initiator is 80 g: 1.2-1.5 g: 0.2-0.4 g, and the initiator is dicumyl peroxide.

4. A halogen-free and low-smoke flame-retardant power cable according to claim 1, characterized in that The modified polysiloxane is obtained by the following steps: A1. Under the protection of an inert atmosphere, melamine and N,N-dimethylformamide are mixed and stirred until the system is dissolved, the temperature of the reaction system is raised to 50-60 °C, a solution of 1-dimethoxy(methyl)silylmethyl isocyanate is added dropwise to the reaction system, after the addition is completed, the reaction is kept warm for 80-110 min, and then post-treated to obtain modified triazine; A2. The modified triazine, D4 and tetramethyltetravinylcyclotetrasiloxane are mixed and stirred, the temperature of the reaction system is raised to 120-130 °C, a catalyst is added to the reaction system, the reaction is kept warm for 4-6 h, a capping agent is added, and the reaction is kept warm for 2-3 h, and then post-treated to obtain crosslinked polysiloxane; A3. Under the protection of an inert atmosphere, polyethylene oxide and N,N-dimethylformamide are mixed, the temperature of the reaction system is raised to 70-80 °C, stirred until the system is dissolved, isophorone diisocyanate is added to the reaction system, the reaction is kept warm for 40-60 min, crosslinked polysiloxane is added to the reaction system, and the reaction is kept warm for 80-100 min, and then post-treated to obtain modified polysiloxane.

5. A halogen-free and low-smoke flame-retardant power cable according to claim 4, characterized in that, In step A1, the dosage ratio of melamine to N,N-dimethylformamide is 1 g: 3 mL. The 1-dimethoxy(methyl)silylmethyl isocyanate solution is composed of 1-dimethoxy(methyl)silylmethyl isocyanate and N,N-dimethylformamide at a ratio of 1 g: 1 mL. The dosage ratio of melamine to 1-dimethoxy(methyl)silylmethyl isocyanate is 1 mol: 3 mol. In step A2, the dosage ratio of the modified triazine, D4, tetramethyltetravinylcyclotetrasiloxane, catalyst, and end-capping agent is 1-2 g: 5-7 g: 3-4 g: 0.3 g: 0.5-0.8 g. The catalyst is 90-98 wt% sulfuric acid, and the end-capping agent is 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. In step A3, the dosage ratio of polyethylene oxide, N,N-dimethylformamide, and crosslinked polysiloxane is 1 g: 7 mL: 3 g. The molar amount of isophorone diisocyanate is the same as the molar amount of hydroxyl groups in polyethylene oxide.

6. The halogen-free and low-smoke flame-retardant power cable according to claim 1, wherein The preparation method of the supported diatomite is as follows: Mix the biochar-modified diatomite and the loading solution, and ultrasonically disperse them at room temperature for 30-50 min. Add a sodium hydroxide solution to the reaction system to adjust the pH of the system to 9-10. Raise the temperature of the reaction system to 50-60 °C. Add a 5-hexenyltriethoxysilane solution to the reaction system, and keep the reaction at a constant temperature for 60-80 min. Perform post-treatment to obtain the supported diatomite.

7. A halogen-free and low-smoke flame-retardant power cable according to claim 6, characterized in that, The dosage ratio of the biochar-modified diatomite, the loading solution, and the 5-hexenyltriethoxysilane solution is 3 g: 10 mL: 15 mL. The loading solution is composed of bismuth nitrate, magnesium nitrate, aluminum nitrate, and deionized water at a ratio of 1 g: 2 g: 2 g: 20 mL. The 5-hexenyltriethoxysilane solution is composed of 5-hexenyltriethoxysilane and tetrahydrofuran at a ratio of 1 g: 10 mL.

8. A halogen-free and low-smoke flame-retardant power cable according to claim 6, characterized in that, The biochar-modified diatomite is processed through the following steps: B1. Place the plant powder in a sodium hydroxide solution and stir. Boil for 30-50 min, and perform post-treatment to obtain the pretreated powder. B2. Mix the pretreated powder, diatomite, and the modification solution, and ultrasonically disperse them for 60-80 min. Perform post-treatment to obtain the modified mixed powder. B3. After roasting the modified mixed powder, perform post-treatment to obtain the biochar-modified diatomite.

9. A halogen-free and low-smoke flame-retardant power cable according to claim 8, characterized in that, In step B1, the dosage ratio of the plant powder to the sodium hydroxide solution is 1 g: 10 mL. The plant powder is one or more of coconut shell powder, apricot shell powder, and straw powder. The particle size of the plant powder is 5-15 mm, and the concentration of the sodium hydroxide solution is 6-8 mol / L. In step B2, the dosage ratio of the pretreated powder, diatomite, and the modification solution is 0.6-0.8 g: 1 g: 10 mL. The modification solution is composed of zinc chloride, PEG-800, and deionized water at a ratio of 1 g: 0.1 g: 10 mL. In step B3, the roasting temperature is 680-750 °C.

10. A method for preparing a halogen-free and low-smoke flame-retardant power cable according to any one of claims 1-9, characterized in that, It includes the following steps: S1. Place a plurality of cable cores (1) parallel to each other, and use a wrapping tape to wrap and fix the plurality of cable cores (1) together to form a wrapping layer (2) on the outside of the cable cores (1). S2. Add low-density polyethylene, acid anhydride-modified EVA, modified polysiloxane, supported diatomaceous earth, dicumyl peroxide and additives into an extruder, melt and mix them for 6-9 minutes, then extrude and coat them outside the lapping layer (2), cool and solidify to form a sheath layer (3) outside the lapping layer (2), thus obtaining a power cable.

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