Halogen-free flame-retardant polyolefin material and its use in the production of nuclear power cable materials

Abstract

The application discloses a kind of halogen-free flame-retardant polyolefin materials and its application in nuclear power cable material preparation.The halogen-free flame-retardant polyolefin material of the present application, the side group grafting polyethylene of flame-retardant unit can not only improve the physical properties of polyolefin itself by grafting different flame-retardant structure units to polyethylene-vinyl acetate hydrolysis, but also can improve the flame-retardant performance and flame-retardant grade of polyolefin;In addition, the halogen-free flame-retardant polyolefin material provided by the present application has excellent heat aging life and anti-radiation effect, which can significantly improve the comprehensive properties of polyolefin cable material for nuclear power plant, such as flame-retardant performance, anti-radiation performance, heat aging life and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high polymer materials, and particularly relates to a halogen-free flame-retardant polyolefin material and application thereof in preparation of nuclear power cable materials. BACKGROUND

[0002] At present, the most advanced high-temperature gas cooled reactor, CAP1400 nuclear power cable with high safety and its core key materials, including power, control, instrument, high-temperature, network communication, coaxial cable and insulation, sheath, filling and other series of key materials. Due to the rich raw materials, low price, easy processing, good electrical insulation performance and excellent comprehensive performance, polyolefin is widely used in nuclear power cable materials. The high safety performance of nuclear power cable is reflected in long service life (≥60 years) at 90℃, high radiation dose resistance (≥2500kGy), functional integrity under design accident conditions, and also meets the mechanical properties, electrical properties, flame retardant properties, acid and alkali medium resistance and other properties.

[0003] The new generation of nuclear power requires that the cable still has good elongation after being irradiated by 2500kGy high-energy rays, but the radiation resistance of general high molecular materials is poor. In order to improve the radiation stability of polymer, radiation protectants can be added to the polymer, thereby prolonging the service life of the material in the strong radiation field. The first kind is sacrificial anti-radiation agent. This kind of protective agent is mainly some free radical trapping agents, which accept radiation energy from the irradiated material, protect the irradiated material and decompose themselves. The second kind is sponge type anti-radiation agent. This kind of protective agent has naphthalene, anthracene, phenanthrene, o-phenol and the like rich in benzene ring structure, which can transfer the radiation energy absorbed by the main components of the irradiated polymer to itself, and then release it in the form of light or heat, and the polymer itself only produces small damage. However, these two kinds of anti-radiation agents are easy to migrate to the environment and cause physical loss in high temperature use environment due to their small molecular weight, and too large addition amount will affect the comprehensive properties of the cable material.

[0004] The service life of nuclear power cable at 90℃ is required to be greater than 60 years. Antioxidants are widely used in nuclear power cables to improve their thermal aging life. However, antioxidants are consumed during service, either due to chemical loss caused by antioxidant activity or due to physical loss caused by their migration to the environment, both of which lead to degradation of the polymer. Among them, the migration of antioxidants has always been a major problem affecting the service life of nuclear power cables. Macromolecularization or immobilization of antioxidants is an effective method to solve the above problems, which limits the migration of synthetic antioxidants.

[0005] In order to obtain better flame retardant performance, it is necessary to add a higher content of flame retardant in nuclear power cable material. Today's flame retardant trend is halogen-free and environmentally friendly, and halogen-free flame retardants are increasingly used in cable materials. The commonly used aluminum hydroxide and magnesium hydroxide flame retardants in cable materials have the problems of poor dispersibility, non-dense carbon layer, poor carbon layer shell performance and large use amount. Intrinsic flame retardant, also called reactive flame retardant, refers to the addition of a reaction system during the polymerization reaction of the high polymer, which participates in the reaction in the form of monomer, becomes a part of the polymer through chemical bonding, has little effect on the physical and mechanical properties of the polymer, and has persistent flame retardant performance. However, there are few reports on intrinsic flame retardant polyolefins.

[0006] Studies have shown that phosphite containing +3 valence state phosphorus is a commonly used flame retardant antioxidant, and its mechanism is to act as a hydrogen peroxide decomposer, which can reduce the hydrogen peroxide released by the high polymer into alcohol, and itself is oxidized into phosphate. Phosphorus compounds are a class of excellent flame retardants. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO, phosphorus is +1 valence state) and diphenyl phosphinic chloride (DC, phosphorus is +1 valence state) are a new type of flame retardant intermediate. Low-valence phosphorus-containing flame retardants mainly improve the flame retardant performance through the gas phase flame retardant mechanism. In addition, anthracene carboxylic acid (ACA) contains a benzene ring structure and has the effects of promoting carbonization and flame retardation. These substances not only can effectively scavenge free radicals to play an antioxidant role, but also have certain flame retardant and anti-radiation effects. There is no research report on grafting low-valence phosphorus-containing flame retardants and multi-benzene ring compounds on the main chain of polyolefins. Therefore, grafting DOPO, DC containing low-valence phosphorus elements and benzene ring structures and anthracene carboxylic acid containing multi-benzene ring structures on polyolefins for preparing halogen-free flame-retardant polyolefin materials for nuclear power stations has very important significance to improve the flame retardant performance, anti-radiation performance and thermal aging life of polyolefin composites. SUMMARY

[0007] The present application provides a halogen-free flame-retardant polyolefin material and its application in the preparation of nuclear power cable materials. The present application not only can endow the polyolefin cable material with good flame retardant properties, but also can solve the problem of long-term thermal aging and radiation durability of nuclear power polyolefin cable materials.

[0008] The raw materials of the halogen-free flame-retardant polyolefin material according to the present application consist of the following components in parts by mass:

[0009] Polyolefin 5-45 parts, flame-retardant unit side group grafted polyethylene 40-95 parts, multi-functional crosslinking agent 0.5-5 parts, antioxidant 0.5-4 parts.

[0010] The polyolefin is selected from one or more of polyethylene, maleic anhydride grafted polyethylene, polypropylene, maleic anhydride grafted polypropylene, ethylene-vinyl acetate copolymer, maleic anhydride grafted ethylene-vinyl acetate copolymer, polyethylene-octene copolymer, maleic anhydride grafted polyethylene-octene copolymer, ethylene-propylene-diene terpolymer, maleic anhydride grafted ethylene-propylene-diene terpolymer, styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, or maleic anhydride grafted hydrogenated styrene-butadiene-styrene block copolymer, in any proportion.

[0011] The antioxidant is selected from one or more of a phenolic antioxidant, a phosphorus-containing antioxidant, a sulfur-containing antioxidant, or a copper corrosion inhibitor, in any proportion.

[0012] The phenolic antioxidant is selected from one or more of tetrakis[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate]pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyethyl-β-(3,5-di-tert-butyl-4-hydroxyphenyl)propio- nylacetate, 3,5-di-tert-butyl-4-hydroxyphenyl stearate, N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxy- phenyl)propionyloxyethyl)urea, or N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy- ethyl)oxamide, in any proportion. phenyl ) propionic acid The phenolic antioxidant is selected from one or more of tetrakis[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate]pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyethyl-β-(3,5-di-tert-butyl-4-hydroxyphenyl)propio- nylacetate, 3,5-di-tert-butyl-4-hydroxyphenyl stearate, N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxy- phenyl)propionyloxyethyl)urea, or N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy- ethyl)oxamide, in any proportion.

[0013] The phosphorus-containing antioxidant is selected from one or more of tris[2.4-di-tert-butylphenyl] phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, or tetra(2,4-di-tert-butylphenyl)- 4,4'-diphenyldiphosphite, in any proportion. phosphite

[0014] The sulfur-containing antioxidant is selected from one or more of dilauryl thiodipropionate, distearyl thiodipropionate, 4,4'-thio(bis)(6-tert-butyl-3-methylphenol), 2,2'-thiobis[3-(3,5-di-tert- butyl-4-hydroxyphenyl)propionate], 6,6'-di-tert-butyl-2,2'-thiodi-p-cresol, or pentaerythritol tetrakis(3- laurylthiopropionate), in any proportion.

[0015] The copper corrosion inhibitor is selected from N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine.

[0016] The multifunctional crosslinking agent is selected from one or more of triallyl cyanurate, triallyl isocyanurate, trimethylolpropane trimethacrylate, trihydroxymethyl triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, in any proportion.

[0017] ​The flame-retardant unit side group grafted polyethylene is an ethylene-vinyl acetate copolymer EVA hydrolysis grafted with different flame-retardant structural units, wherein the flame-retardant structural unit is a phosphorus-containing or benzene ring structure flame retardant; the grafting amount of the flame-retardant structural unit is 15-35%.

[0018] The flame-retardant structural unit is selected from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), diphenyl phosphinic chloride (DC) or anthracene carboxylic acid (ACA) and the like. The corresponding structural formula is as shown below:

[0019]

[0020] The flame-retardant unit side group grafted polyethylene is prepared by a method comprising the following steps:

[0021] Step 1: EVA is added to a solvent and stirred, and heated to 40℃, after EVA is completely dissolved, sodium hydroxide ethanol solution is added and hydrolysis is carried out at this temperature for 2-5h, then hydrochloric acid solution is added for neutralization reaction for 5-10min; after the reaction is completed, the reaction liquid is poured into distilled water and stirred constantly until all the precipitates are separated out, filtered and washed, the precipitates are cut into pieces and placed in an 80℃ oven for drying for 12h to obtain EVA-OH product.

[0022] Step 2: EVA-OH is grafted with a flame retardant containing a flame-retardant structural unit, including the following three ways:

[0023] Way one: EVA-OH is added to a solvent and stirred, and heated to 40℃, after EVA-OH is completely dissolved, diphenyl phosphinic chloride is added to the system, nitrogen is bubbled for 12h, anhydrous methanol is washed and dried to obtain flame-retardant unit side group DC grafted polyethylene (EVA-DC).

[0024] Way two: EVA-OH is added to a solvent and stirred, and heated to 40℃, after EVA-OH is completely dissolved, anthracene carboxylic acid chloride ACA-Cl is added dropwise to the above solution, nitrogen is bubbled for 12h, anhydrous methanol is washed and dried to obtain flame-retardant unit side group ACA grafted polyethylene (EVA-ACA).

[0025] Wherein the anthracene carboxylic acid chloride is prepared by the following method: taking anthracene carboxylic acid as raw material, dichlorosulfoxide and chloroform are added to the reaction system, heated to 40-60℃ under nitrogen atmosphere; after the reaction is completed, the temperature is lowered to room temperature, the solvent is recovered by rotary evaporation to obtain a viscous liquid product, which is anthracene carboxylic acid chloride ACA-Cl.

[0026] Method three: EVA-OH and DOPO are stirred in a solvent, and the temperature is raised to 40℃. After EVA-OH and DOPO are completely dissolved, carbon tetrachloride is added to the above solution, nitrogen is blown for 12 hours, and then the mixture is washed with anhydrous methanol and dried to obtain a flame-retardant unit side group DOPO grafted polyethylene (EVA-DOPO).

[0027] In the method one, the raw materials are composed of the following mass fractions:

[0028] Ethylene-vinyl acetate copolymer EVA 65-85 parts, ethanol 50-200 parts, sodium hydroxide 0.5-1.5 parts, 1 mol / L HCl solution 50-100 parts, solvent 200-300 parts, diphenyl phosphinic chloride 15-35 parts.

[0029] In the method two, the raw materials are composed of the following mass fractions:

[0030] Ethylene-vinyl acetate copolymer EVA 65-85 parts, ethanol 50-200 parts, sodium hydroxide 0.5-1.5 parts, 1 mol / L HCl solution 50-100 parts, solvent 200-300 parts, anthracene formic acid 15-35 parts, dichlorosulfoxide 15-35 parts.

[0031] In the method three, the raw materials are composed of the following mass fractions:

[0032] Ethylene-vinyl acetate copolymer EVA 65-85 parts, ethanol 50-200 parts, sodium hydroxide 0.5-1.5 parts, 1 mol / L HCl solution 50-100 parts, solvent 200-300 parts, DOPO 15-35 parts, carbon tetrachloride 15-35 parts.

[0033] The solvent is selected from any one or more of ethanol, N,N-dimethylformamide, tetrahydrofuran, dichloromethane, chloroform, and 1,4-dioxane. The mass fraction of the above-mentioned solvent is the total amount of solvent used in the preparation process.

[0034] The preparation method of the halogen-free flame-retardant polyolefin material comprises the following steps:

[0035] The polyolefin and the flame-retardant unit side group grafted polyethylene are weighed according to the proportioning amount, mixed in a banbury mixer at 140℃-200℃ for 5-20 minutes, then the multifunctional crosslinking agent and the antioxidant are added, and the mixture is uniformly mixed and then extruded and granulated at 140℃-200℃ to obtain granules.

[0036] The application of the halogen-free flame-retardant polyolefin material in the preparation of a cable conductive core insulating layer for a nuclear power station.

[0037] The granules are used as a coating material for the cable conductive core insulation layer, and are subjected to irradiation cross-linking treatment. Specifically, the irradiation cross-linking treatment is performed under a 10KW, 10MeV electron beam, and the irradiation dose is 100KGy-2400KGy.

[0038] The raw materials of the halogen-free flame-retardant polyolefin material according to the present application are composed of the following components in parts by mass:

[0039] Polyolefin 10-30 parts, flame-retardant unit side group grafted polyethylene 25-40 parts, microencapsulated halogen-free flame retardant 40-50 parts, multifunctional flame-retardant synergist 1-5 parts, multifunctional crosslinking agent 1-3 parts, lubricant 0.5-2 parts, antioxidant 1-4 parts.

[0040] The polyolefin, the flame-retardant unit side group grafted polyethylene, the multifunctional crosslinking agent, and the antioxidant are defined as above.

[0041] The microencapsulated halogen-free flame retardant is composed of a shell material and a core flame retardant.

[0042] The shell material is selected from one of a silica gel, a hyperbranched charring agent, and a polyphosphazene; and the core flame retardant is selected from one or more of aluminum hydroxide, magnesium hydroxide, magnesium-aluminum double hydroxide, zinc-aluminum double hydroxide, magnesium-iron double hydroxide, zinc-iron double hydroxide, nickel-iron double hydroxide, ammonium polyphosphate, pentaerythritol, melamine, melamine phosphate, melamine cyanurate, inorganic aluminum hypophosphite, organic aluminum hypophosphite, triazine charring agent, piperazine pyrophosphate, zinc borate, zinc aluminate, zinc stannate, and low-melting-point glass powder, which are mixed in any proportion.

[0043] The mass ratio of the shell material to the core flame retardant is (10-30):(70-90).

[0044] The microencapsulated flame retardant can be prepared into a microencapsulated flame retardant with a shell of a hyperbranched charring agent or a silica gel according to the methods disclosed in Chinese Patent 201410016870.8 and Chinese Patent 200810156885.9.

[0045] The multifunctional flame-retardant synergist is composed of a nanoparticle anti-radiation agent and graphene. The nanoparticle anti-radiation agent is selected from one or more of tungsten oxide, bismuth oxide, bismuth carbonate, rare earth metal oxide, and nano-silicon dioxide, which are mixed in any proportion. The rare earth metal in the rare earth metal oxide is one of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, and europium.

[0046] Further, the preparation method of the multifunctional flame-retardant synergist comprises the following steps:

[0047] The graphene is mixed with water and ultrasonically treated for 20-40 min, then the corresponding precursor of the nanoparticle anti-irradiation agent is added, under nitrogen protection and stirring, the alkaline adjusting agent is added dropwise to make the pH of the system 9-11, after dropwise addition is completed, the system is heated to react, after reaction is completed, centrifugal separation, water washing, alcohol washing and drying are carried out, and the graphene loaded with the nanoparticle anti-irradiation agent is obtained, that is, the multifunctional flame-retardant synergist.

[0048] The corresponding precursor of the nanoparticle anti-irradiation agent is tungsten chloride, bismuth chloride, a rare earth metal salt or tetraethyl orthosilicate.

[0049] The mass ratio of the graphene, the corresponding precursor of the nanoparticle anti-irradiation agent and water is 3:(2-5):300.

[0050] The alkaline adjusting agent is a 25wt% ammonia water solution or a 1mol / L sodium carbonate solution.

[0051] The heating reaction can be water bath heating to 80℃ for 24h, or the system is transferred to a hydrothermal reaction kettle for hydrothermal reaction at 180℃ for 12h.

[0052] The lubricant is selected from one or more of silicone powder, zinc stearate, paraffin wax and PE wax.

[0053] The preparation method of the halogen-free flame-retardant polyolefin material comprises the following steps:

[0054] The polyolefin and the flame-retardant unit side group grafted polyethylene are weighed according to the proportioning amount, mixed and kneaded in a banbury mixer at 140℃-200℃ until uniform, then the microencapsulated halogen-free flame retardant, the multifunctional flame-retardant synergist, the multifunctional crosslinking agent, the antioxidant and the lubricant are added, and after uniform mixing and kneading, the system is extruded and pelletized at 140℃-200℃ to obtain the granules.

[0055] The application of the halogen-free flame-retardant polyolefin material in preparing the outer sheath layer of a cable conductive core for nuclear power plants.

[0056] The obtained granules are used as the outer sheath material of a cable conductive core, and the cable conductive core is subjected to irradiation crosslinking treatment.

[0057] Compared with the prior art, the excellent effects of the present application are embodied in:

[0058] (1) The application selects the graft polyethylene with flame-retardant unit side group as an important component of the base material, and the high grafting rate and high benzene ring content of the resin, so as to endow the polyolefin insulation material and the sheath material with excellent anti-radiation performance; the multifunctional flame-retardant synergist is the graphene hybrid loaded with nano-particle anti-radiation agent, the graphene loaded with nano-particle anti-radiation agent is hybridized together by a hydrothermal method or a coprecipitation method, and is uniformly mixed with the resin material in a molten state in a banbury mixer or an extruder, and the purpose is to realize the exfoliation or intercalation nanocomposite dispersion state of the graphene in the multifunctional flame-retardant synergist in the sheath material, which is beneficial to play the effect of the graphene and the nano-particle anti-radiation agent on the barrier of radiation rays; the application disperses the hybrid graphene multifunctional additive with high anti-radiation performance in the polyolefin material in a nanocomposite state, improves the anti-radiation performance of the sheath material of the nuclear power station.

[0059] (2) The graphene in the functional flame-retardant synergist is dispersed in the polymer base in an exfoliated or intercalated state, and can play the effect of the barrier of the layer and the labyrinth effect; the sheath material is soaked in different chemical medium materials, the chemical medium penetrates into the internal path of the sheath material, the path is lengthened, and the migration rate is slowed down, so that the medium resistance of the sheath material can be improved.

[0060] (3) The graft polyethylene with flame-retardant unit side group selected as an important component of the base material endows the polyolefin insulation material with an oxygen index of up to 24%, reaches the V-2 level of vertical combustion, and the graft polyethylene with flame-retardant unit side group can significantly improve the flame-retardant performance, mechanical properties and insulation resistance of the polyolefin insulation material.

[0061] In addition, the microencapsulated halogen-free flame retardant is selected as the main flame retardant, and due to the protection of the high molecular shell layer, the dispersibility and compatibility of the core flame retardant can be improved, so that the comprehensive performance of the sheath material is improved; the shell material and the core flame retardant can play a synergistic flame-retardant effect when burning, and further improve the flame-retardant effect of the flame retardant; the graft polyethylene with flame-retardant unit side group is also selected in the polyolefin sheath material, and plays a synergistic flame-retardant effect with the microencapsulated flame retardant, the graft polyethylene with flame-retardant unit side group can play the gas phase flame-retardant effect of low-valence phosphorus, the added halogen-free flame retardant plays the condensed phase flame-retardant effect, and the two flame-retardant mechanisms synergize to reduce the flame spread rate and heat release, and improve the flame-retardant performance; the graphene multifunctional additive dispersed in the sheath material in a nanometer state can further play a multi-component synergistic flame-retardant effect with the microencapsulated flame retardant, and further improve the flame-retardant performance of the polyolefin sheath material; the graft polyethylene with flame-retardant unit side group, the microencapsulated halogen-free flame retardant and the multifunctional flame-retardant synergist synergize to reduce the addition amount of the flame retardant when reaching the same flame-retardant level, so as to improve the comprehensive properties of the polyolefin sheath material.

[0062] (4)The present application disperses the graphene loaded with nano-particle anti-radiation agent in the sheath material in exfoliated or intercalated state, which is beneficial to slow down the migration rate of the antioxidant and prolong the migration path, thus slowing down the loss rate of the antioxidant and keeping excellent thermal aging effect for a long time, when high temperature thermal aging occurs; the low valence (+1 valence) phosphorus element in the flame-retardant unit side group grafted polyethylene can play the role of auxiliary antioxidant, as a hydrogen peroxide decomposer, it can reduce the hydrogen peroxide released by the polymer material into alcohol, and itself is oxidized into phosphate; the benzene ring structure in the flame-retardant unit side group grafted polyethylene can not only effectively remove the free radicals generated by aging in the polyolefin material, play the role of antioxidant, but also improve the temperature resistance grade, long-term aging resistance and thermal aging life of the polyolefin composite material. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 Phosphorus spectrum (a) and hydrogen spectrum (b) of DOPO and EVA-DOPO.

[0064] Figure 2 HRR and THR curves of EVA and EVA-DOPO.

[0065] Figure 3 Hydrogen spectrum of EVA-OH (a) and EVA-ACA (b).

[0066] Figure 4 Hydrogen spectrum (a) and phosphorus spectrum (b) of EVA-DC. DETAILED DESCRIPTION

[0067] In order to further illustrate the technical solutions of the present application, the preferred embodiments of the present application are described below in combination with examples, however, it should be understood that these descriptions are only for further illustrating the features and advantages of the present application, and are not limitations of the claims of the present application. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0068] Example 1:

[0069] a, Preparation of EVA-OH

[0070] Take 500ml three-port bottle, first 25g of EVA dissolved in tetrahydrofuran solution, then slowly drop 40ml sodium hydroxide / ethanol solution (0.5mol / L), and apply reflux condenser device, under the condition of mechanical stirring, at 60℃ for 5h. After the reaction is finished, add 22.5ml HCl solution (1mol / L) to neutralize the mixed solution, stir for 10 minutes, stop the reaction. Pour into 500ml distilled water, stir until the precipitate is precipitated, filter, wash, cut the precipitate to dry the product at 60℃ for 12h to obtain EVA-OH.

[0071] b. Preparation of EVA-DOPO

[0072] Take 500ml three-port bottle, add 20g EVA-OH, 3g DOPO and 200ml dichloromethane, stir to warm to 40℃, after the reaction is completely dissolved, add 7.94g carbon tetrachloride, nitrogen stirring for 12h. After the reaction is finished, pour into 500ml distilled water, stir until the precipitate is precipitated, filter, wash, cut the precipitate to dry the product at 60℃ for 12h to obtain EVA-DOPO.

[0073] c. Preparation of ACA-Cl

[0074] Add 4.44g (0.02mol) anthracene carboxylic acid (ACA) to a 250ml three-port bottle, add 100ml chloroform to dissolve it, slowly drop 4ml dichloro sulfoxide under nitrogen protection, react at 50℃ for 5h, after the reaction is finished, remove the solvent and unreacted dichloro sulfoxide by reduced pressure distillation, finally obtain anthracene carboxylic acid chloride (ACA-Cl).

[0075] d. Preparation of EVA-ACA

[0076] Take 500ml three-port bottle, add 20g EVA-OH and 200ml chloroform, stir to warm to 60℃, after the reaction is completely dissolved, slowly drop 5g ACA-Cl, nitrogen stirring for 12h. After the reaction is finished, pour into 500ml distilled water, stir until the precipitate is precipitated, filter, wash, cut the precipitate to dry the product at 60℃ for 12h to obtain EVA-ACA.

[0077] e. Preparation of EVA-DC

[0078] Take 500ml three-port bottle, add 20g EVA-OH and 200ml tetrahydrofuran, stir to warm to 60℃, after the reaction is completely dissolved, slowly drop 6g DC, nitrogen stirring for 12h. After the reaction is finished, pour into 500ml distilled water, stir until the precipitate is precipitated, filter, wash, cut the precipitate to dry the product at 60℃ for 12h to obtain EVA-DC.

[0079] Example 2

[0080] An insulating material for nuclear power plant cable comprises the following components by weight:

[0081] Polyolefin: polyethylene 35 parts, maleic anhydride grafted polyethylene 5 parts;

[0082] Flame-retardant unit side group grafted polyethylene EVA-ACA 58.4 parts;

[0083] Polyfunctional crosslinking agent: trimethylolpropane triacrylate 1.5 parts;

[0084] Antioxidant: tetra[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate] pentaerythritol ester 0.75 parts, tri[2.4-di-t-butylphenyl] phosphite 0.45 parts, dilauryl thiodipropionate 0.3 parts, N,N'-bis[β-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine 0.1 parts.

[0085] The preparation method of the above-mentioned inner insulating material for nuclear power plant cable is as follows: the polyolefin and the flame-retardant unit side group grafted polyethylene EVA-ACA are weighed according to the above-mentioned formula, mixed in a 150°C mixing mill for 10 minutes, then the polyfunctional crosslinking agent and the antioxidant are added and mixed uniformly, and then extruded and granulated at 140°C to prepare insulating granules.

[0086] The prepared inner insulating granules are used for extrusion coating on the 1.5mm 2 The conductive wire core is irradiated and crosslinked by an electron beam with a power of 10KW and an energy of 10MeV, and the irradiation dose is 120KGy.

[0087] Comparative Example 2

[0088] The insulating material of the present comparative example is the same as that of Example 2, except that the 58.4 parts of flame-retardant unit side group grafted polyethylene EVA-ACA in Example 2 is replaced by polyethylene, and the other formula components and preparation methods are the same.

[0089] Example 3

[0090] An insulating material for nuclear power plant cable comprises the following components by weight:

[0091] Polyolefin: ethylene-vinyl acetate copolymer 5 parts, maleic anhydride grafted hydrogenated styrene-butadiene-styrene block copolymer 5 parts;

[0092] Flame-retardant unit side group grafted polyethylene EVA-DOPO 85.9 parts;

[0093] Polyfunctional crosslinking agent: triallyl isocyanurate 3 parts;

[0094] Antioxidant: β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid n-octadecyl ester 0.5 parts, pentaerythritol tetrakis(3-laurylthiopropionate) 0.5 parts, N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine 0.1 part.

[0095] The preparation method of the above-mentioned inner insulation material for nuclear power plant cables is as follows: the polyolefin and the flame-retardant unit side group grafted polyethylene EVA-DOPO are weighed according to the above-mentioned formula, mixed in a mixer at 170 ℃ for 10 min, then the multifunctional crosslinking agent and the antioxidant are added and mixed uniformly, and then extruded and granulated at 170 ℃ to prepare insulation granules.

[0096] The prepared inner insulation granules are used for extrusion coating on the cable 2.5 mm 2 The conductive wire core is irradiated and crosslinked as an insulation material under a power of 10 KW and an energy of 10 MeV electron beam, and the irradiation dose is 160 KGy.

[0097] Comparative Example 3:

[0098] The insulation material of the present comparative example is the same as that of Example 3, except that the 85.9 parts of flame-retardant unit side group grafted polyethylene EVA-DOPO in Example 3 is replaced by ethylene-vinyl acetate copolymer, and the other formula composition and preparation method are completely the same.

[0099] Example 4:

[0100] An insulation material for nuclear power plant cables, comprising the following components by weight:

[0101] Polyolefin: maleic anhydride grafted polyethylene-octene copolymer 5 parts;

[0102] Flame-retardant unit side group grafted polyethylene EVA-DC 92.4 parts;

[0103] Multifunctional crosslinking agent: trimethylol triacrylate 1.5 parts;

[0104] Antioxidant: tetra[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionic acid] pentaerythritol ester 0.5 parts, tri[2.4-di-tert-butylphenyl] phosphite 0.25 parts, dilauryl thiodipropionate 0.25 parts, N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl] hydrazine 0.1 part.

[0105] The preparation method of the above-mentioned inner insulation material for nuclear power plant cables is as follows: the polyolefin and the flame-retardant unit side group grafted polyethylene EVA-DC are weighed according to the above-mentioned formula, mixed in a mixer at 140 ℃ for 10 min, then the multifunctional crosslinking agent and the antioxidant are added and mixed uniformly, and then extruded and granulated at 140 ℃ to prepare insulation granules.

[0106] The obtained inner insulation granules were used for extrusion coating on the cable 1.5mm 2 The conductive wire core was irradiated and cross-linked as the inner insulation material under the power and energy of 10KW and 10MeV electron beam respectively, and the irradiation dose was 180KGy.

[0107] Comparative Example 4:

[0108] The insulation material of the present comparative example was the same as that of Example 4, except that the 92.4 parts of flame-retardant unit side group grafted polyethylene EVA-DC in Example 4 was completely replaced by polyethylene-octene copolymer, and the other formulation components and preparation methods were completely the same.

[0109] Example 5:

[0110] A halogen-free flame-retardant polyolefin sheath material for nuclear power plants comprises the following components by weight:

[0111] Polyolefin: ethylene-octene copolymer 16 parts, maleic anhydride grafted polyethylene-octene copolymer 5 parts;

[0112] Flame-retardant unit side group grafted polyethylene: EVA-ACA 25 parts;

[0113] Microencapsulated halogen-free flame retardant: polyphosphazene microencapsulated zinc aluminum double hydroxide 40 parts, polyphosphazene microencapsulated inorganic aluminum hypophosphite 7 parts, polyphosphazene microencapsulated zinc aluminate 23 parts;

[0114] Multifunctional flame retardant synergist: graphene hybrid loaded with bismuth carbonate nanoparticles anti-radiation agent 1 part;

[0115] Multifunctional crosslinking agent: pentaerythritol triacrylate 2 parts;

[0116] Lubricant: silicone powder 0.8 parts, PE wax 0.2 parts;

[0117] Antioxidant: N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine 0.5 parts, bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite 0.3 parts, 2,2'-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] 0.1 parts, N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine 0.1 parts.

[0118] The preparation method of the microencapsulated flame retardant is as follows:

[0119] Preparation of polyphosphazene microencapsulated zinc-aluminum double hydroxide: under ice water bath conditions, 200 parts by mass of pyridine, 10 parts by mass of melamine, 20 parts by mass of 4,4'-diamino diphenyl ether and 100 parts by mass of the core flame retardant, zinc-aluminum double hydroxide, were added to a reactor equipped with a stirrer, reflux condenser and dry nitrogen, and stirred uniformly to obtain a mixed solution A; 20 parts by mass of hexachlorotriphosphazene was dissolved in 50 parts by mass of pyridine to form a mixed solution B; the mixed solution B was added dropwise to the mixed solution A at a speed of 3mL / min, and after the dropwise addition was completed, the temperature was raised from the ice water bath to 80℃ and reacted for 12h; after the reaction was completed, the product was sequentially filtered, washed with water and dried to obtain a microencapsulated flame retardant with a polyphosphazene shell and a zinc-aluminum double hydroxide core;

[0120] The preparation method of polyphosphazene microencapsulated inorganic aluminum hypophosphite or polyphosphazene microencapsulated zinc aluminate is the same as that of polyphosphazene microencapsulated zinc-aluminum double hydroxide, except that the core is replaced by inorganic aluminum hypophosphite or zinc aluminate.

[0121] The preparation method of the multifunctional flame-retardant synergist is as follows:

[0122] Under room temperature conditions, 250 parts by mass of distilled water, 3 parts by mass of graphene and 3 parts by mass of the precursor bismuth chloride of the nanoparticle anti-radiation agent were added to a reaction vessel equipped with a stirrer, reflux condenser and dry nitrogen, and ultrasonicated for 30 minutes at room temperature, then 1mol / L sodium carbonate solution was added dropwise to adjust the pH to 10 and stirred, and after the dropwise addition was completed, it was transferred to a hydrothermal reaction kettle and hydrothermally reacted at 180℃ for 12 hours; after the reaction was completed, the product was centrifuged, washed with water, washed with ethanol and dried in a vacuum oven at 80℃ to obtain graphene loaded with bismuth carbonate nanoparticle anti-radiation agent.

[0123] The preparation method of the above-mentioned halogen-free flame-retardant sheath material for nuclear power plants is as follows:

[0124] The polyolefin, the flame-retardant unit side group grafted polyethylene, the microencapsulated halogen-free flame retardant, the multifunctional flame-retardant synergist, the multifunctional crosslinking agent, the antioxidant and the lubricant were weighed according to the formula, mixed uniformly in a banbury mixer at 140℃, then extruded and pelletized at 140℃ to prepare the sheath granules.

[0125] The prepared sheath granules are used for the outer sheath layer of the cable conductive core, and when the sheath granules are used as the coating material of the cable conductive core insulation layer, they need to be irradiated and crosslinked under the power and energy of 10KW and 10MeV electron beam respectively, and the irradiation dose is 240KGy.

[0126] Comparative Example 5:

[0127] The sheath material of the present comparative example is the same as that of Example 5, except that the flame-retardant unit side group grafted polyethylene EVA-ACA 25 parts in Example 5 is all replaced by polyethylene-octene copolymer, and other formulation compositions and preparation methods are completely the same.

[0128] Example 6:

[0129] A halogen-free flame-retardant sheath material for nuclear power plants comprises the following components by weight:

[0130] Polyolefin: ethylene-vinyl acetate copolymer 10 parts, maleic anhydride grafted ternary ethylene-propylene rubber 5 parts;

[0131] Flame-retardant unit side group grafted polyethylene EVA-DOPO 40 parts;

[0132] Microencapsulated halogen-free flame retardant: the following microencapsulated flame retardant is prepared according to the method of Example 1 disclosed in Chinese patent 201410016870.8, microencapsulated core magnesium hydroxide 25 parts, microencapsulated core ammonium polyphosphate 8 parts, microencapsulated core zinc stannate 2 parts;

[0133] Multifunctional flame-retardant synergist: graphene hybrid loaded with lanthanum oxide nanoparticles anti-radiation agent 5 parts;

[0134] Multifunctional crosslinking agent: trimethylolpropane trimethacrylate 3 parts;

[0135] Lubricant: silicone powder 0.4 parts, zinc stearate 0.1 parts;

[0136] Antioxidant: β-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate 0.8 parts, distearyl thiodipropionate 0.3 parts, pentaerythritol tetrakis(3-laurylthiopropionate) 0.3 parts, N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl] hydrazine 0.1 parts.

[0137] The preparation method of the multifunctional flame-retardant synergist is as follows:

[0138] Under room temperature conditions, 200 parts by mass of distilled water, 3 parts of graphene, and 4 parts of nanoparticle anti-radiation agent precursor lanthanum chloride are added to a reaction vessel equipped with a stirrer, a reflux condenser, and a nitrogen gas inlet, and ultrasonic treatment is performed for 30 minutes at room temperature. Then, 25wt% ammonia solution is added dropwise to adjust the pH to 10 and stirring is performed. After the dropwise addition is completed, the temperature is increased to 80°C and the reaction is performed for 24 hours. After the reaction is completed, the product is centrifuged, washed with water and ethanol, and dried in a vacuum oven at 80°C to obtain graphene loaded with lanthanum oxide nanoparticles anti-radiation agent.

[0139] The preparation method of the halogen-free flame-retardant sheath material for nuclear power station:

[0140] The polyolefin, the flame-retardant unit side group grafted polyethylene, the microencapsulated halogen-free flame retardant, the multifunctional flame-retardant synergist, the multifunctional crosslinking agent, the antioxidant, and the lubricant are weighed according to the formula, mixed in a mixer at 180°C until uniform, and then extruded and granulated at 180°C to prepare the sheath granules.

[0141] The prepared sheath granules are used for the outer sheath layer of the cable conductive core, and the inner insulation granules are used as the coating material of the cable conductive core inner insulation layer, which needs to be irradiated and crosslinked at a power of 10 KW and an energy of 10 MeV electron beam, and the irradiation dose is 100 KGy.

[0142] Comparative Example 6:

[0143] The sheath material of the present comparative example is the same as that of Example 6, except that the 40 parts of the flame-retardant unit side group grafted polyethylene EVA-DOPO in Example 6 is all replaced by polyethylene-vinyl acetate copolymer, and the other formula compositions and preparation methods are completely the same.

[0144] Example 7:

[0145] A halogen-free flame-retardant sheath material for nuclear power station, comprising the following components by weight:

[0146] Polyolefin: 10 parts of terpolymer ethylene-propylene rubber, 5 parts of maleic anhydride grafted terpolymer ethylene-propylene rubber;

[0147] Flame-retardant unit side group grafted polyethylene EVA-DC 40 parts;

[0148] Microencapsulated halogen-free flame retardant: the following microencapsulated flame retardant is prepared according to the method of Example 1 disclosed in Chinese patent 200810156885.9, 25 parts of silicon gel shell microencapsulated core nickel-iron double hydroxide, 15 parts of silicon gel shell microencapsulated core melamine polyphosphate;

[0149] Multifunctional flame-retardant synergist: graphene hybrid loaded with silica nanoparticles anti-irradiation agent 2 parts;

[0150] Multifunctional crosslinking agent: 2.5 parts of trihydroxymethyl acrylate;

[0151] Lubricant: 0.5 parts of silicone powder, 0.2 parts of PE wax;

[0152] Antioxidant: Tetra [methylene-3-(3', 5'-di-t-butyl-4'-hydroxyphenyl) propionic acid] pentaerythritol ester 1 part, bis (2, 4-di-t-butyl phenol) pentaerythritol diphosphite 0.4 parts, 6, 6'-di-t-butyl-2, 2'-thiobis-p-cresol 0.3 parts, N, N'-bis [beta-(3, 5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine 0.1 parts.

[0153] The preparation method of the multifunctional flame-retardant synergist is as follows:

[0154] Under room temperature conditions, 180 parts by mass of distilled water, 3 parts by mass of graphene, and 5 parts by mass of the precursor tetraethyl orthosilicate of the nano-particle anti-radiation agent were added to a reaction container equipped with a stirrer, a reflux condenser, and a nitrogen inlet, and then ultrasonic treatment was performed for 30 minutes at room temperature. Then, 25 wt% of an ammonia water solution was added dropwise to adjust the pH to 10 and stirring was performed. After the dropwise addition was completed, the temperature was increased to 80°C and reaction was performed for 24 hours. After the reaction was completed, the product was centrifuged, washed with water and ethanol, and dried in a vacuum oven at 80°C to obtain graphene loaded with nano-particle anti-radiation agent.

[0155] The preparation method of the halogen-free flame-retardant sheath material for nuclear power plants is as follows:

[0156] The polyolefin, the flame-retardant unit side group grafted polyethylene, the microencapsulated halogen-free flame retardant, the multifunctional flame-retardant synergist, the multifunctional crosslinking agent, the antioxidant, and the lubricant were weighed according to the formula, mixed in a mixer at 160°C until uniform, and then extruded and granulated at 160°C to obtain sheath granules.

[0157] The sheath granules were used as the outer sheath layer of the cable conductive core. When the inner insulation granules were used as the coating material of the cable conductive core inner insulation layer, the inner insulation granules needed to be subjected to irradiation crosslinking treatment under power and energy of 10 KW and 10 MeV electron beams, respectively, and the irradiation dose was 160 KGy.

[0158] Comparative Example 7:

[0159] The sheath material of the present comparative example was the same as that of Example 7, except that the flame-retardant unit side group grafted polyethylene EVA-DC 40 parts in Example 7 was replaced by ethylene propylene terpolymer rubber, and the other formula compositions and preparation methods were completely the same.

[0160] The insulation materials of Examples 2-3-4 and Comparative Examples 2-3-4 were made into sheets according to the irradiation crosslinking treatment in the corresponding examples, and the mechanical properties, thermal aging life, and radiation resistance of the insulation materials were tested. The test results are shown in Table 1.

[0161] Table 1 Properties of nuclear polyolefin insulation materials of Examples 2-3-4 and Comparative Examples 2-3-4

[0162]

[0163]

[0164] The results show that the Example 2, Example 3 and Example 4 using flame retardant unit side group grafted polyethylene have better flame retardant performance, radiation resistance and longer thermal aging life than the commercial polyolefin comparative experimental formulation.

[0165] The sheath materials of Example 5-6-7 and the sheath materials of Comparative Example 5-6-7 are made into sheets according to the radiation crosslinking treatment in the corresponding examples, and the performance of the sheath materials is tested, and the test results are shown in Table 2.

[0166] Table 2 Performance of nuclear power polyolefin sheath materials of Example 5-6-7 and Comparative Example 5-6-7

[0167]

[0168]

[0169] The results show that the Example 5, Example 6 and Example 7 using flame retardant unit side group grafted polyethylene have better flame retardant performance, medium resistance, radiation resistance and longer thermal aging life than the commercial polyolefin comparative experimental formulation.

Claims

1. A halogen-free flame-retardant polyolefin material, which is obtained by mixing and processing raw materials in the following mass fractions: 5-45 parts of polyolefin, 40-95 parts of flame-retardant unit side group grafted polyethylene, 0.5-5 parts of multifunctional crosslinking agent, and 0.5-4 parts of antioxidant; the multifunctional crosslinking agent is selected from one or more of triallyl cyanurate, triallyl isocyanurate, trimethylolpropane tri-methacrylate, trihydroxymethyl triacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate in any proportion; the flame-retardant unit side group grafted polyethylene is hydrolysis grafted with flame-retardant structure units of ethylene-vinyl acetate copolymer (EVA), wherein the flame-retardant structure units are flame retardants containing phosphorus or benzene ring structure, and the grafting amount of the flame-retardant structure units is 15-35%; the flame-retardant unit side group grafted polyethylene is prepared by a method comprising the following steps: Step 1: adding EVA into a solvent and stirring, and heating to 40℃, after EVA is completely dissolved, adding sodium hydroxide ethanol solution and stirring at this temperature for 2-5h for hydrolysis, and then adding hydrochloric acid solution for neutralization reaction; after the reaction is completed, the reaction liquid is poured into distilled water and continuously stirred until all the precipitates are separated out, filtered, washed and dried to obtain EVA-OH product; Step 2: adding EVA-OH into a solvent and stirring, and heating to 40℃, after EVA-OH is completely dissolved, adding diphenyl phosphinic chloride into the system, stirring for 12h under nitrogen, and washing with anhydrous methanol and drying to obtain flame-retardant unit side group DC grafted polyethylene; alternatively, the flame-retardant unit side group grafted polyethylene is prepared by a method comprising the following steps: Step 1: adding EVA into a solvent and stirring, and heating to 40℃, after EVA is completely dissolved, adding sodium hydroxide ethanol solution and stirring at this temperature for 2-5h for hydrolysis, and then adding hydrochloric acid solution for neutralization reaction; after the reaction is completed, the reaction liquid is poured into distilled water and continuously stirred until all the precipitates are separated out, filtered, washed and dried to obtain EVA-OH product; Step 2: using anthracene carboxylic acid as raw material, adding dichlorosulfoxide and solvent into the reaction system, and heating to 40-60℃ under nitrogen atmosphere for reaction; after the reaction is completed, the temperature is lowered to room temperature, the solvent is recovered by rotary evaporation to obtain viscous liquid product, which is anthracene carboxylic chloride ACA-Cl; adding EVA-OH into a solvent and stirring, and heating to 40℃, after EVA-OH is completely dissolved, adding anthracene carboxylic chloride ACA-Cl dropwise into the above solution, stirring for 12h under nitrogen, and washing with anhydrous methanol and drying to obtain flame-retardant unit side group ACA grafted polyethylene; alternatively, the flame-retardant unit side group grafted polyethylene is prepared by a method comprising the following steps: Step 1: adding EVA into a solvent and stirring, and heating to 40℃, after EVA is completely dissolved, adding sodium hydroxide ethanol solution and stirring at this temperature for 2-5h for hydrolysis, and then adding hydrochloric acid solution for neutralization reaction; after the reaction is completed, the reaction liquid is poured into distilled water and continuously stirred until all the precipitates are separated out, filtered, washed and dried to obtain EVA-OH product. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Step 2: EVA-OH and DOPO are stirred in a solvent and warmed to 40℃. After EVA-OH and DOPO are completely dissolved, carbon tetrachloride is added dropwise to the above solution, and nitrogen is bubbled for 12 hours. After drying with anhydrous methanol, the flame-retardant unit side group DOPO grafted polyethylene is obtained.

2. Use of the halogen-free flame-retardant polyolefin material of claim 1 in the preparation of a cable conductor core insulating layer for nuclear power plants.

3. Use according to claim 2, characterized in that The method comprises the following steps: The polyolefin and the flame-retardant unit side group grafted polyethylene are weighed according to the proportioning amount, mixed in a mixer at 140-200℃ for 5-20 minutes, then the multifunctional crosslinking agent and the antioxidant are added, and after being uniformly mixed, the mixture is extruded and granulated at 140-200℃ to obtain granules; the granules are used as a coating material for the cable conductor core insulating layer, and the coating material is subjected to irradiation crosslinking treatment.

4. A halogen-free flame-retardant polyolefin material, which is obtained by mixing and processing the following raw materials in mass fractions: Polyolefin 5-30 parts, flame-retardant unit side group grafted polyethylene 25-40 parts, microencapsulated halogen-free flame retardant 40-50 parts, multifunctional flame-retardant synergist 1-5 parts, multifunctional crosslinking agent 1-3 parts, lubricant 0.5-2 parts, antioxidant 1-4 parts; The multifunctional crosslinking agent is selected from one or more of triallyl cyanurate, triallyl isocyanurate, trimethylolpropane tri(meth)acrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, or a mixture thereof in any proportion; The flame-retardant unit side group grafted polyethylene is an ethylene-vinyl acetate copolymer EVA hydrolyzed to graft a flame-retardant structural unit, wherein the flame-retardant structural unit is a phosphorus-containing or benzene ring structure flame retardant; the grafting amount of the flame-retardant structural unit is 15-35%; The flame-retardant unit side group grafted polyethylene is prepared by a method comprising the following steps: Step 1: EVA is stirred in a solvent and warmed to 40℃. After EVA is completely dissolved, sodium hydroxide ethanol solution is added and stirred at this temperature for 2-5 hours for hydrolysis, then hydrochloric acid solution is added for neutralization reaction; after the reaction is completed, the reaction liquid is poured into distilled water and continuously stirred until all the precipitates are separated out, then filtered, washed and dried to obtain EVA-OH product; Step 2: EVA-OH is stirred in a solvent and warmed to 40℃. After EVA-OH is completely dissolved, diphenyl phosphinic chloride is added to the system, and nitrogen is bubbled for 12 hours. After drying with anhydrous methanol, the flame-retardant unit side group DC grafted polyethylene is obtained; Alternatively, the flame-retardant unit side group grafted polyethylene is prepared by a method comprising the following steps: Step 1: EVA is stirred in a solvent and warmed to 40℃. After EVA is completely dissolved, sodium hydroxide ethanol solution is added and stirred at this temperature for 2-5 hours for hydrolysis, then hydrochloric acid solution is added for neutralization reaction; after the reaction is completed, the reaction liquid is poured into distilled water and continuously stirred until all the precipitates are separated out, then filtered, washed and dried to obtain EVA-OH product; Step 2: Anthracene carboxylic acid as raw material, dichlorosulfoxide and solvent are added to the reaction system, and the temperature is raised to 40-60℃ under nitrogen atmosphere; after the reaction is completed, it is cooled to room temperature, and the solvent is recovered by rotary evaporation to obtain a viscous liquid product, anthracene carboxylic acid chloride ACA-Cl; EVA-OH is added to the solvent and stirred, and the temperature is raised to 40℃; after EVA-OH is completely dissolved, anthracene carboxylic acid chloride ACA-Cl is added dropwise into the above solution, nitrogen is bubbled for 12h, and anhydrous methanol is washed and dried to obtain a flame-retardant unit side group ACA grafted polyethylene; Alternatively, the flame-retardant unit side group grafted polyethylene is prepared by a method comprising the following steps: Step 1: EVA is added to the solvent and stirred, and the temperature is raised to 40℃; after EVA is completely dissolved, sodium hydroxide ethanol solution is added and stirred at this temperature for 2-5h for hydrolysis, and then hydrochloric acid solution is added for neutralization reaction; after the reaction is completed, the reaction liquid is poured into distilled water and stirred constantly until all the precipitates are separated out, filtered, washed and dried to obtain EVA-OH product; Step 2: EVA-OH and DOPO are added to the solvent and stirred, and the temperature is raised to 40℃; after EVA-OH and DOPO are completely dissolved, carbon tetrachloride is added dropwise into the above solution, nitrogen is bubbled for 12h, and anhydrous methanol is washed and dried to obtain a flame-retardant unit side group DOPO grafted polyethylene; The microencapsulated halogen-free flame retardant is composed of a shell material and a core flame retardant; the shell material is selected from one of a silica gel, an over-branched charring agent and a polyphosphazene; the core flame retardant is selected from one or more of aluminum hydroxide, magnesium hydroxide, magnesium-aluminum double hydroxide, zinc-aluminum double hydroxide, magnesium-iron double hydroxide, zinc-iron double hydroxide, nickel-iron double hydroxide, ammonium polyphosphate, pentaerythritol, melamine, melamine phosphate, melamine cyanurate, inorganic aluminum hypophosphite, organic aluminum hypophosphite, triazine charring agent, piperazine pyrophosphate, zinc borate, zinc aluminate, zinc stannate and low-melting-point glass powder, which are mixed in any proportion; The multifunctional flame-retardant synergist is composed of a nanoparticle anti-radiation agent and graphene; the nanoparticle anti-radiation agent is selected from one or more of tungsten oxide, bismuth oxide, bismuth carbonate, rare earth metal oxide and nano-silicon dioxide, which are mixed in any proportion; the rare earth metal in the rare earth metal oxide is one of lanthanum, cerium, praseodymium, neodymium, promethium, samarium and europium.

5. The halogen-free flame retardant polyolefin material according to claim 4, characterized in that The preparation method of the multifunctional flame-retardant synergist comprises the following steps: The graphene is mixed with water and ultrasonically treated for 20-40min, then the corresponding precursor of the nanoparticle anti-radiation agent is added, under nitrogen protection and stirring, a basic regulator is added dropwise to make the pH of the system 9-11, after the dropwise addition is completed, the system is heated to react, after the reaction is completed, centrifugal separation, water washing, alcohol washing and drying are performed to obtain graphene loaded with the nanoparticle anti-radiation agent, which is the multifunctional flame-retardant synergist; The corresponding precursor of the nanoparticle anti-radiation agent is tungsten chloride, bismuth chloride, a chlorinated rare earth metal salt or tetraethyl orthosilicate.

6. Use of the halogen-free flame-retardant polyolefin material according to claim 4 or 5 in the preparation of a cable conductor core outer sheath layer for nuclear power plants.

7. Use according to claim 6, characterized in that comprising the following steps: The polyolefin, the flame-retardant unit side group grafted polyethylene, the microencapsulated halogen-free flame retardant, the multifunctional flame-retardant synergist, the multifunctional crosslinking agent, the antioxidant and the lubricant are weighed according to the proportioning amount, mixed in a mixer at 140-200 DEG C until uniform, then extruded and granulated at 140-200 DEG C to obtain granules; the obtained granules are used as the outer sheath material of the cable conductive core, and are subjected to irradiation crosslinking treatment.

Images