A flame-retardant polyethylene sheath material for extra-high voltage cables and a preparation method thereof

Abstract

The application relates to the technical field of cable materials, and particularly discloses a kind of fire-retardant polyethylene sheath material for super-high voltage cable and a preparation method thereof.The fire-retardant polyethylene sheath material for super-high voltage cable provided by the application uses low-density polyethylene as a main base material, the molecular structure of the low-density polyethylene has more long branches, which endows the material with excellent flexibility and elasticity, and meanwhile, by adding composite fillers and additives, the prepared polyethylene sheath material has excellent mechanical properties, high and low temperature resistance and fire-retardant properties.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cable materials, in particular to a kind of flame-retardant polyethylene sheath material for super-high voltage cable and preparation method thereof. BACKGROUND

[0002] Super-high voltage cable refers to the power cable used for transmission of 110kv or above, generally as the hub in large power transmission system, and belongs to a kind of high-voltage cable with higher technical content, mainly used for long-distance power transmission. Due to the special working conditions, the performance requirements of the sheath material are relatively high, such as elongation at break, breaking strength, flame retardant performance, etc.

[0003] The sheath material for super-high voltage cable basically adopts polyethylene sheath material, but polyethylene material still has significant defects in key performance. On the one hand, the high temperature resistance of polyethylene is insufficient. When the temperature rises due to current load or external heat source during cable operation, the sheath is easy to soften, deform or even melt, which exposes the internal conductor and significantly increases the risk of short circuit and electrical fire. On the other hand, the inherent flame retardant performance of polyethylene material is poor, which makes it difficult to effectively prevent the spread of fire along the cable when a fire occurs, and cannot gain valuable time for personnel evacuation and fire rescue, posing a serious threat to life and property safety.

[0004] For example, Chinese patent document CN202310413407.6 discloses a halogen-free low-smoke flame-retardant polyolefin sheath material and its preparation process, which comprises the following steps: step 1: preparation of halogen-free flame retardant; step 2: preparation of flame retardant synergist: disperse montmorillonite in N,N-dimethylformamide, modify with octadecyl isocyanate to obtain flame retardant synergist; step 3: mix ethylene-octene copolymer elastomer, high-density polyethylene, ethylene-octene copolymer grafted maleic anhydride copolymer, halogen-free flame retardant, flame retardant synergist, lubricant and organic peroxide by stirring, mixing, mixing and extruding to obtain polyolefin sheath material. The mechanical properties and flame retardant properties of the prepared sheath material are improved to a certain extent, but further improvement is still needed. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application aims to provide a flame-retardant polyethylene sheath material for super-high voltage cable and a preparation method thereof.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] The application discloses a fire-retardant polyethylene sheath material for extra-high voltage cables, which comprises the following components in parts by weight: low-density polyethylene 40-60 parts, ethylene-propylene-diene rubber 8-12 parts, PE grafted maleic anhydride 10-15 parts, composite filler 15-20 parts, lubricant 2-4 parts, antioxidant 1-3 parts, ultraviolet absorber 1-2 parts and thermal stabilizer 0.2-0.5 parts.

[0008] In the technical scheme disclosed by the application, the composite filler is prepared by the following method:

[0009] S1, preparing a composite mica material

[0010] Carboxymethyl chitosan is added into deionized water and stirred and dissolved, then mica powder is added into the solution and uniformly dispersed through ultrasonic treatment, and then the composite mica material is obtained through filtration, drying, calcination and grinding.

[0011] In this step, the mass ratio of the mica powder and the carboxymethyl chitosan is 10-15:3-6, and in some embodiments of the application, for example, the mass ratio can be 10:3, 10:4, 10:5, 10:6, 12:3, 12:5, 12:6, 15:3, 15:5 or 15:6, but is not limited to the listed values, and other values in the range also apply.

[0012] In this step, the calcination is carried out under a nitrogen atmosphere, the calcination temperature is 400-500 DEG C, and the calcination time is 2-3 h.

[0013] In this step, the carboxymethyl chitosan is first dissolved in deionized water, the carboxymethyl chitosan molecules contain a large number of hydroxyl groups, and the carboxymethyl chitosan is loaded on the surface and interlayer of the mica powder through hydrogen bonding, and then the calcination is carried out under a nitrogen atmosphere, the carboxymethyl chitosan forms a dense carbon layer, which can isolate oxygen and prevent heat transfer, thereby improving the fire-retardant property of the mica powder.

[0014] S2, preparing a double bond modified composite material

[0015] The composite mica material is dispersed in an ethanol aqueous solution, then vinyltriethoxysilane is added into the solution, and the double bond modified composite material is obtained through filtration, washing and drying.

[0016] In this step, the mass ratio of the composite mica material and the vinyltriethoxysilane is 10-15:2-4, and in some embodiments of the application, for example, the mass ratio can be 10:2, 10:3, 10:4, 12:2, 12:3, 12:4, 15:2, 15:3 or 15:4, but is not limited to the listed values, and other values in the range also apply.

[0017] In this step, the double bond is introduced into the composite mica material, which is beneficial to the subsequent reaction.

[0018] S3, preparing the composite filler

[0019] The double bond modified composite material is dispersed in an organic solvent, then 1,4-butenediol, phosphonic acid-B-styryl ester and benzoyl peroxide are added thereto, heated and stirred to react, then 1,3-bis(4'-glycidyl ether phenyl)adamantane and triethylamine are added thereto to continue the reaction, after the reaction is completed, the composite filler is obtained through filtration, washing and drying.

[0020] In this step, the mass ratio of the double bond modified composite material, 1,4-butenediol, phosphonic acid-B-styryl ester, benzoyl peroxide, 1,3-bis(4'-glycidyl ether phenyl)adamantane and triethylamine is 10-15:3-6:3-6:0.05-0.1:4-8:2-4.

[0021] In this step, the temperature of the heated and stirred reaction is 60-80℃, for example, 60℃, 65℃, 70℃, 75℃ or 80℃ can be selected, and the time of the heated and stirred reaction is 3-5h, for example, 3h, 3.5h, 4h, 4.5h or 5h can be selected, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0022] In this step, through the addition reaction between the double bonds, 1,4-butenediol and phosphonic acid-B-styryl ester copolymerize to form a composite copolymer, the molecular structure of phosphonic acid-B-styryl ester contains a benzene ring structure and a phosphonic acid group, the benzene ring structure can improve the thermal stability of the molecular chain, so that the material is not easy to decompose at high temperature, thereby improving the heat resistance of the material, and the phosphonic acid group has good flame retardancy, thereby improving the flame retardant performance of the material; the alkyl flexible long chain structure in 1,4-butenediol improves the low-temperature impact resistance of the material, then the hydroxyl group in 1,4-butenediol reacts with the epoxy group in 1,3-bis(4'-glycidyl ether phenyl)adamantane, through the introduction of adamantyl structure, the thermal stability of the material is further improved, the adamantyl structure can also disperse stress and reduce the expansion of cracks, thereby improving the impact resistance of the polyethylene sheath material, in addition, the unreacted epoxy group in 1,3-bis(4'-glycidyl ether phenyl)adamantane can also form a network structure through crosslinking reaction with the anhydride in PE grafted maleic anhydride, thereby further improving the mechanical properties of the polyethylene sheath material.

[0023] In the technical solution disclosed in the present application, the lubricant is selected from any one of calcium stearate, polyethylene wax, stearic acid and stearic acid monoglyceride.

[0024] In the technical solution disclosed in the present application, the antioxidant is selected from antioxidant 1010 or antioxidant 1076.

[0025] In the technical scheme disclosed in the present application, the ultraviolet absorber is selected from one or more of titanium dioxide, UV328, UV327 and UV326.

[0026] In the technical scheme disclosed in the present application, the heat stabilizer is selected from calcium-zinc heat stabilizer CZ-113 or calcium-zinc heat stabilizer CZ-116.

[0027] The present application also provides a preparation method of the flame-retardant polyethylene sheath material for super-high voltage cables, which comprises the following steps: adding low-density polyethylene, ethylene-propylene-diene rubber, PE grafted maleic anhydride, composite filler, lubricant, antioxidant, ultraviolet absorber and heat stabilizer into a high-speed mixer according to the formula amount, mixing for 30-60 min, and then adding into a twin-screw extruder, setting the temperature at 160-180 DEG C and the screw rotation speed at 150-300 r / min, and then melt-extruding and granulating to obtain the flame-retardant polyethylene sheath material for super-high voltage cables.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] (1) The flame-retardant polyethylene sheath material for super-high voltage cables provided by the present application uses low-density polyethylene as the main base material, and the molecular structure of the low-density polyethylene has more long branches, which endows the material with excellent flexibility and elasticity, and through the addition of composite fillers and additives, the prepared polyethylene sheath material has excellent mechanical properties, high and low temperature resistance and flame-retardant properties.

[0030] (2) In the present application, the carboxymethyl chitosan is loaded on the surface and interlayer of the mica powder, and then calcined under a nitrogen atmosphere, so that the carboxymethyl chitosan forms a dense carbon layer, which can isolate oxygen and prevent heat transfer, thereby improving the flame-retardant properties of the mica powder.

[0031] (3) 1,4-Butanediol and phosphonic acid-B-styryl ester are copolymerized by addition reaction between double bonds to form a complex copolymer, the molecular structure of the phosphonic acid-B-styryl ester contains a benzene ring structure and a phosphonic acid group, the benzene ring structure can improve the thermal stability of the molecular chain, so that the material is not easy to decompose at high temperature, thereby improving the heat resistance of the material, and the phosphonic acid group has good flame retardancy, thereby improving the flame retardant performance of the material; the alkyl flexible long chain structure in 1,4-butanediol improves the low-temperature impact resistance of the material, and then the hydroxyl group in 1,4-butanediol reacts with the epoxy group in 1,3-bis(4'-glycidyl ether phenyl) adamantane, by introducing adamantyl structure, the thermal stability of the material is further improved, the adamantyl structure can also disperse stress and reduce crack propagation, thereby improving the impact resistance of the polyethylene sheath material, in addition, the unreacted epoxy group in 1,3-bis(4'-glycidyl ether phenyl) adamantane can also form a network structure with the anhydride in PE grafted maleic anhydride through crosslinking reaction, further improving the mechanical properties of the polyethylene sheath material. DETAILED DESCRIPTION

[0032] The application will be further described in detail below through specific preferred embodiments, but the application is not limited to the following embodiments only.

[0033] It should be noted that, unless otherwise specified, the chemical reagents involved in the application are purchased through commercial channels.

[0034] The brand of the low-density polyethylene used in the embodiments of the application is VL8005; the brand of the ethylene-propylene-diene rubber is Dow 4725P; the brand of the PE grafted maleic anhydride is DuPont 40E529; the CAS of the phosphonic acid-B-styryl ester is 1707-08-0; and the mesh number of the mica powder is 400 mesh.

[0035] Example 1

[0036] A preparation method of a flame-retardant polyethylene sheath material for ultra-high voltage cables, comprising the following steps:

[0037] 50 parts of low-density polyethylene, 10 parts of ethylene-propylene-diene rubber, 12 parts of PE grafted maleic anhydride, 18 parts of a composite filler, 3 parts of a lubricant stearic acid, 2 parts of an antioxidant 1010, 1 part of an ultraviolet absorber UV328 and 0.3 parts of a calcium-zinc thermal stabilizer CZ-113 are added into a high-speed mixer, mixed for 45 min, and then added into a double-screw extruder, the temperature is set to 170℃, and the screw rotation speed is set to 200 r / min, and then melt extrusion granulation is performed, to obtain the flame-retardant polyethylene sheath material for ultra-high voltage cables.

[0038] The preparation method of the composite filler is as follows:

[0039] S1, 3g carboxymethyl chitosan is added to 100mL deionized water, stirred and dissolved, then 10g mica powder is added and uniformly dispersed by ultrasonic, filtered, dried, calcined at 400℃ for 3h under nitrogen atmosphere, ground through a 400 mesh sieve to obtain a composite mica material;

[0040] S2, 10g of the composite mica material is dispersed in 100mL of an ethanol aqueous solution (volume ratio of ethanol to water is 3:1), then 2g of vinyl triethoxysilane is added and stirred for 2h, filtered, washed and dried to obtain a double bond modified composite material;

[0041] S3, 10g of the double bond modified composite material is dispersed in 100mL of an organic solvent DMF, then 3g of 1,4-butenediol, 3g of phosphonic acid-B-styryl ester and 0.05g of benzoyl peroxide are added and heated and stirred at 80℃ for 3h, then 4g of 1,3-bis(4'-glycidyl ether phenyl)adamantane and 2g of triethylamine are added and the reaction is continued at 80℃ for 2h, after the reaction is completed, the product is filtered, washed and dried to obtain a composite filler.

[0042] Example 2

[0043] A preparation method of a flame-retardant polyethylene sheath material for ultra-high voltage cables, comprising the following steps:

[0044] 40 parts of low-density polyethylene, 8 parts of ethylene-propylene-diene rubber, 10 parts of PE grafted maleic anhydride, 15 parts of a composite filler, 2 parts of a lubricant stearic acid, 1 part of an antioxidant 1076, 1 part of an ultraviolet absorber UV328 and 0.2 parts of a calcium-zinc thermal stabilizer CZ-113 are added to a high-speed mixer and mixed for 45min, then added to a twin-screw extruder, the temperature is set to 170℃ and the screw rotation speed is set to 200r / min, and the product is melt-extruded and granulated to obtain a flame-retardant polyethylene sheath material for ultra-high voltage cables.

[0045] The preparation method of the composite filler is as follows:

[0046] S1, 3g carboxymethyl chitosan is added to 100mL deionized water, stirred and dissolved, then 10g mica powder is added and uniformly dispersed by ultrasonic, filtered, dried, calcined at 400℃ for 3h under nitrogen atmosphere, ground through a 400 mesh sieve to obtain a composite mica material;

[0047] S2, 10g of the composite mica material is dispersed in 100mL of an ethanol aqueous solution (volume ratio of ethanol to water is 3:1), then 2g of vinyl triethoxysilane is added and stirred for 2h, filtered, washed and dried to obtain a double bond modified composite material;

[0048] S3, 15g of the double bond modified composite material was dispersed in 100mL of organic solvent DMF, then 6g of 1,4-butenediol, 6g of phosphonic acid-B-styryl ester and 0.1g of benzoyl peroxide were added thereto, and heated and stirred at 80℃ for 3h, then 8g of 1,3-bis(4'-glycidyl ether phenyl)adamantane and 4g of triethylamine were added thereto, and the reaction was continued at 80℃ for 2h, after the reaction was completed, filtration, washing and drying were performed to obtain the composite filler.

[0049] Example 3

[0050] A preparation method of a flame-retardant polyethylene sheath material for super-high voltage cables, comprising the following steps:

[0051] 60 parts of low-density polyethylene, 12 parts of ethylene-propylene-diene rubber, 15 parts of PE grafted maleic anhydride, 20 parts of composite filler, 4 parts of lubricant stearic acid, 3 parts of antioxidant 1076, 2 parts of ultraviolet absorber UV328 and 0.5 parts of calcium-zinc thermal stabilizer CZ-113 were added into a high-speed mixer and mixed for 45min, then added into a twin-screw extruder, the temperature was set to 170℃, and the screw rotation speed was set to 200r / min, and then melt extrusion granulation was performed, thereby obtaining the flame-retardant polyethylene sheath material for super-high voltage cables.

[0052] The preparation method of the composite filler is as follows:

[0053] S1, 5g of carboxymethyl chitosan was added to 100mL of deionized water and stirred and dissolved, then 12g of mica powder was added thereto and ultrasonically dispersed uniformly, then filtered, dried, calcined at 400℃ for 3h under nitrogen atmosphere, and ground through a 400 mesh sieve to obtain a composite mica material;

[0054] S2, 12g of the composite mica material was dispersed in 100mL of an ethanol aqueous solution (the volume ratio of ethanol to water was 3:1), then 3g of vinyltriethoxysilane was added thereto and stirred for 2h, then filtered, washed and dried to obtain a double bond modified composite material;

[0055] S3, 12g of the double bond modified composite material was dispersed in 100mL of organic solvent DMF, then 4g of 1,4-butenediol, 6g of phosphonic acid-B-styryl ester and 0.1g of benzoyl peroxide were added thereto, and heated and stirred at 80℃ for 3h, then 6g of 1,3-bis(4'-glycidyl ether phenyl)adamantane and 3g of triethylamine were added thereto, and the reaction was continued at 80℃ for 2h, after the reaction was completed, filtration, washing and drying were performed to obtain the composite filler.

[0056] Comparative Example 1

[0057] A preparation method of a flame-retardant polyethylene sheath material for super-high voltage cables, comprising the following steps:

[0058] 50 parts of low density polyethylene, 10 parts of ethylene-propylene-diene rubber, 12 parts of PE grafted maleic anhydride, 18 parts of the composite filler, 3 parts of lubricant stearic acid, 2 parts of antioxidant 1010, 1 part of ultraviolet absorber UV328 and 0.3 parts of calcium-zinc heat stabilizer CZ-113 are added into a high-speed mixer, mixed for 45 min, and then added into a twin-screw extruder, with the temperature set to 170℃ and the screw rotation speed set to 200r / min, and then melt-extruded and granulated to obtain the flame-retardant polyethylene sheath material for ultra-high voltage cables.

[0059] The preparation method of the composite filler is as follows:

[0060] S1, 10g of mica powder is dispersed in 100mL of an ethanol aqueous solution (the volume ratio of ethanol to water is 3:1), and then 2g of vinyl triethoxysilane is added thereto, stirred for 2h, filtered, washed and dried to obtain double bond modified mica powder;

[0061] S2, 10g of the double bond modified mica powder is dispersed in 100mL of an organic solvent DMF, and then 3g of 1,4-butenediol, 3g of phosphonic acid-B-styryl ester and 0.05g of benzoyl peroxide are added thereto, heated and stirred at 80℃ for 3h, and then 4g of 1,3-bis(4'-glycidyl ether phenyl)adamantane and 2g of triethylamine are added thereto, and the reaction is continued at 80℃ for 2h, and after the reaction is completed, the product is filtered, washed and dried to obtain the composite filler.

[0062] In the comparative example 1, the mica powder is not treated with carboxymethyl chitosan.

[0063] Comparative example 2

[0064] A preparation method of a flame-retardant polyethylene sheath material for ultra-high voltage cables, comprising the following steps:

[0065] 50 parts of low density polyethylene, 10 parts of ethylene-propylene-diene rubber, 12 parts of PE grafted maleic anhydride, 18 parts of the composite filler, 3 parts of lubricant stearic acid, 2 parts of antioxidant 1010, 1 part of ultraviolet absorber UV328 and 0.3 parts of calcium-zinc heat stabilizer CZ-113 are added into a high-speed mixer, mixed for 45 min, and then added into a twin-screw extruder, with the temperature set to 170℃ and the screw rotation speed set to 200r / min, and then melt-extruded and granulated to obtain the flame-retardant polyethylene sheath material for ultra-high voltage cables.

[0066] The preparation method of the composite filler is as follows:

[0067] S1, 3g carboxymethyl chitosan is added to 100mL deionized water, stirred and dissolved, then 10g mica powder is added, ultrasonic dispersion is uniform, filtration, drying, calcination under nitrogen atmosphere at 400℃ for 3h, grinding through 400 mesh sieve, to obtain composite mica material;

[0068] S2, 10g composite mica material is dispersed in 100mL ethanol aqueous solution (volume ratio of ethanol and water is 3:1), then 2g vinyl triethoxysilane is added, stirring for 2h, filtration, washing, drying, to obtain double bond modified composite material;

[0069] S3, 10g double bond modified composite material is dispersed in 100mL organic solvent DMF, then 3g 1,4-butenediol and 0.05g benzoyl peroxide are added, heating and stirring at 80℃ for 3h, then 4g 1,3-bis(4'-glycidyl ether phenyl)adamantane and 2g triethylamine are added, continuing to react at 80℃ for 2h, after the reaction is completed, filtration, washing, drying, to obtain composite filler.

[0070] Comparative example 2 and example 1 are compared, without adding phosphonic acid-B-styryl ester.

[0071] Comparative example 3

[0072] A preparation method of a flame-retardant polyethylene sheath material for ultra-high voltage cable, comprising the following steps:

[0073] 50 parts of low-density polyethylene, 10 parts of ethylene-propylene-diene rubber, 12 parts of PE grafted maleic anhydride, 18 parts of composite filler, 3 parts of lubricant stearic acid, 2 parts of antioxidant 1010, 1 part of ultraviolet absorber UV328 and 0.3 parts of calcium-zinc heat stabilizer CZ-113 are added into a high-speed mixer, mixed for 45min, then added into a double-screw extruder, the temperature is set to 170℃, the screw speed is set to 200r / min, melt extrusion and granulation, to obtain the flame-retardant polyethylene sheath material for ultra-high voltage cable.

[0074] The preparation method of the composite filler is as follows:

[0075] S1, 3g carboxymethyl chitosan is added to 100mL deionized water, stirred and dissolved, then 10g mica powder is added, ultrasonic dispersion is uniform, filtration, drying, calcination under nitrogen atmosphere at 400℃ for 3h, grinding through 400 mesh sieve, to obtain composite mica material;

[0076] S2, 10g composite mica material is dispersed in 100mL ethanol aqueous solution (volume ratio of ethanol and water is 3:1), then 2g vinyl triethoxysilane is added, stirring for 2h, filtration, washing, drying, to obtain double bond modified composite material;

[0077] S3, 10 g of the double bond modified composite material was dispersed in 100 mL of organic solvent DMF, then 3 g of 1,4-butenediol, 3 g of phosphonic acid-B-styryl ester and 0.05 g of benzoyl peroxide were added thereto, and the reaction was stirred at 80°C for 3 h. After the reaction was completed, the composite filler was obtained by filtration, washing and drying.

[0078] Comparative Example 3 does not add 1,3-bis(4'-glycidyl ether phenyl)adamantane compared with Example 1.

[0079] The polyethylene sheath material prepared in Examples 1-3 and Comparative Examples 1-3 was prepared into samples in accordance with the test standards, and then the performance tests were carried out, as follows:

[0080] Tensile strength test: tested according to GB / T 1040.1-2018 standard, the tensile speed was 100 mm / min;

[0081] Oxygen index test: tested according to GB / T 2406.2-2009 standard;

[0082] Heat aging resistance test: heat aging was carried out in a heat aging oven according to standard GBT 7141-2008, the heat aging condition was 135°C, 168 h, and then the tensile strength retention rate was tested;

[0083] Unnotched impact strength test: tested according to GB / T 1843-2008 standard, the temperature was -40°C;

[0084] The test results are shown in Table 1.

[0085] Table 1 Performance test results of different groups

[0086]

[0087] Finally, it should be noted that the above examples do not limit the present application in any form. For those skilled in the art, some modifications and improvements can be made on the basis of the present application. Therefore, any modification or improvement made without departing from the spirit of the present application shall fall within the scope of the present application.

Claims

1. A flame-retardant polyethylene sheath material for an extra-high voltage cable, characterized by comprising, The components include the following weight parts: low-density polyethylene 40-60 parts, ethylene propylene diene rubber 8-12 parts, PE grafted maleic anhydride 10-15 parts, composite filler 15-20 parts, lubricant 2-4 parts, antioxidant 1-3 parts, ultraviolet absorber 1-2 parts, and thermal stabilizer 0.2-0.5 parts; The preparation method of the composite filler is as follows: S1, carboxymethyl chitosan is added to deionized water, stirred and dissolved, then mica powder is added and ultrasonically dispersed uniformly, filtered, dried, calcined, and ground to obtain a composite mica material; S2, the composite mica material is dispersed in an ethanol aqueous solution, then vinyltriethoxysilane is added and stirred, filtered, washed, and dried to obtain a double bond modified composite material; S3, the double bond modified composite material is dispersed in an organic solvent, then 1,4-butanediol, phosphonic acid-B-styryl ester, and benzoyl peroxide are added and heated and stirred to react, then 1,3-bis(4'-glycidyl ether phenyl)adamantane and triethylamine are added and continue to react, after the reaction is completed, the product is filtered, washed, and dried to obtain the composite filler.

2. The flame-retardant polyethylene jacketing material for extra-high voltage cables according to claim 1, characterized in that, In step S1, the mass ratio of mica powder to carboxymethyl chitosan is 10-15:3-6.

3. The flame-retardant polyethylene jacketing material for extra-high voltage cables according to claim 1, characterized in that, In step S2, the mass ratio of composite mica material to vinyltriethoxysilane is 10-15:2-4.

4. The flame-retardant polyethylene jacketing material for extra-high voltage cables according to claim 1, characterized in that, In step S3, the mass ratio of double bond modified composite material, 1,4-butanediol, phosphonic acid-B-styryl ester, benzoyl peroxide, 1,3-bis(4'-glycidyl ether phenyl)adamantane, and triethylamine is 10-15:3-6:3-6:0.05-0.1:4-8:2-4.

5. The flame-retardant polyethylene jacketing material for extra-high voltage cables according to claim 1, characterized in that, The lubricant is selected from any one of calcium stearate, polyethylene wax, stearic acid, and stearic acid monoglyceride.

6. The flame-retardant polyethylene jacketing material for extra-high voltage cables according to claim 1, characterized in that, The antioxidant is selected from antioxidant 1010 or antioxidant 1076.

7. The flame-retardant polyethylene jacketing material for extra-high voltage cables according to claim 1, characterized in that, The ultraviolet absorber is selected from one or more of titanium dioxide, UV328, UV327, and UV326.

8. The flame-retardant polyethylene jacketing material for extra-high voltage cables according to claim 1, characterized in that, The thermal stabilizer is selected from calcium-zinc thermal stabilizer CZ-113 or calcium-zinc thermal stabilizer CZ-116.

9. The process for the preparation of a flame-retardant polyethylene sheath compound for extra-high voltage cables according to any one of claims 1 to 8, characterized in that, The method comprises the following steps: low-density polyethylene, ethylene propylene diene rubber, PE grafted maleic anhydride, composite filler, lubricant, antioxidant, ultraviolet absorber, and thermal stabilizer are added to a high-speed mixer in the formula amount, mixed for 30-60 min, then added to a double-screw extruder, the temperature is set to 160-180℃, and the screw rotation speed is set to 150-300 r / min, and then melt extrusion granulation is performed to obtain the flame-retardant polyethylene sheath material for ultra-high voltage cables.

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