Fireproof flame-retardant power cable

Abstract

The invention relates to the technical field of cables, and provides a fireproof flame-retardant power cable and a preparation method thereof. The fireproof flame-retardant power cable comprises a conductor, an insulating layer and a flame-retardant outer sheath layer, the flame-retardant outer sheath layer is prepared from the following raw materials in parts by weight: 40 to 50 parts of ethylene-vinyl acetate copolymer, 20 to 30 parts of high-density polyethylene, 12 to 16 parts of low-density polyethylene, 8 to 12 parts of maleic anhydride grafted polyethylene, 10 to 15 parts of hydrophobic modified porous magnesium oxide, 10 to 12 parts of modified expanded graphite, 3 to 5 parts of zinc borate, 0.5 to 1 part of antioxidant, 0.8 to 1.2 parts of polyethylene wax and 0.5 to 0.9 part of calcium stearate. And 0.3-0.5 part of an ultraviolet light absorber. According to the fire-resistant flame-retardant power cable prepared in the invention, the fire resistance of the material to a high-temperature environment is improved, and the moisture absorption condition of the material in a humid environment is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cables, and in particular to a fire-resistant and flame-retardant power cable. Background Art

[0002] Fire-resistant and flame-retardant power cables are cables that, under specified test conditions, can maintain normal power supply for a specified period of time after exposure to flames and self-extinguish after the flames have dissipated. These cables are capable of maintaining safe operation for a specified period of time in the event of a fire, ensuring the evacuation of personnel, power supply to firefighting equipment, and the emergency operation of critical equipment. They are key equipment for ensuring the reliable operation of power systems in extreme situations such as fires.

[0003] Currently, in the field of refractory materials, although some common materials such as magnesium hydroxide and aluminum hydroxide have certain fire resistance properties, these materials still have some limitations in practical applications. Specifically, the fire resistance of these materials is not sufficient to meet the needs of all high-temperature environments. At the same time, although inorganic refractory materials such as magnesium oxide perform well in terms of fire resistance temperature and have high fire resistance, they also have a significant disadvantage, which is their strong hygroscopicity. This means that in a humid environment, these inorganic refractory materials easily absorb moisture from the air, resulting in an increase in the moisture content inside the material. This moisture absorption will have a negative impact on the electrical performance of the cable, especially reducing its insulation resistance. The decrease in insulation resistance will make the cable more prone to leakage when transmitting current, thereby affecting the safety and reliability of the entire electrical system. Therefore, when selecting refractory materials, it is necessary to comprehensively consider factors such as its fire resistance and hygroscopicity to ensure the performance stability and safety of the material in practical applications. In order to solve the above technical problems, the present invention proposes a new fire-resistant and flame-retardant power cable. Summary of the Invention

[0004] The present invention provides a fire-resistant and flame-retardant power cable and a preparation method thereof, which enhances the fire resistance of the material in high-temperature environments and improves the moisture absorption condition of the material in humid environments.

[0005] The technical solutions of the present invention are as follows: In a first aspect, the present invention provides a fire-resistant and flame-retardant power cable, comprising a conductor, an insulation layer and a flame-retardant outer sheath layer, wherein the flame-retardant outer sheath layer is composed of the following raw materials in parts by weight: 40-50 parts of ethylene-vinyl acetate copolymer, 20-30 parts of high-density polyethylene, 12-16 parts of low-density polyethylene, 8-12 parts of maleic anhydride grafted polyethylene, 10-15 parts of hydrophobically modified porous magnesium oxide, 10-12 parts of modified expanded graphite, 3-5 parts of zinc borate, 0.5-1 part of antioxidant, 0.8-1.2 parts of polyethylene wax, 0.5-0.9 parts of calcium stearate, and 0.3-0.5 parts of ultraviolet absorber.

[0006] As a further technical solution, the preparation method of the hydrophobically modified porous magnesium oxide includes: adding MgCl2 solution to K2CO3 solution, stirring at 300-350rpm to form a white precipitate mixture, adding citric acid, stirring in a water bath at 70-80°C to form a transparent sol, then performing a hydrothermal reaction at 180-190°C for 2-3 hours, washing and drying to obtain a basic magnesium carbonate precursor; then heating the basic magnesium carbonate precursor to 500-600°C at 5°C / min and keeping it warm for 2-3 hours; dispersing the magnesium oxide obtained after calcination in toluene, adding octadecyltrichlorosilane solution, refluxing at 100-110°C under nitrogen protection for 5-6 hours, washing, and drying to obtain the product.

[0007] As a further technical solution, the concentration of the MgCl2 solution is 0.4-0.6 mol / L; the concentration of the K2CO3 solution is 0.7-0.9 mol / L; and the usage ratio of the MgCl2 solution, K2CO3 solution and citric acid is 100 mL:120-130 mL:10-11 g.

[0008] As a further technical solution, the octadecyltrichlorosilane solution is a toluene solution with a concentration of 5-7 wt% octadecyltrichlorosilane; the usage ratio of the magnesium oxide, toluene, and octadecyltrichlorosilane solution is 10 g: 180-220 mL: 45-55 mL.

[0009] As a further technical solution, the preparation method of the modified expanded graphite includes: acid-washing graphite and then drying it to obtain pretreated graphite, mixing it with sulfuric acid, potassium permanganate and ammonium phosphate with a mass concentration of 70%-80%, stirring and reacting at a temperature of 40±2°C and 200-250rpm for 50-60min, washing with water and then vacuum drying to obtain the obtained graphite.

[0010] As a further technical solution, the pickling step includes: impregnating the graphite with hydrochloric acid having a mass concentration of 5-10%, washing with water until neutral, and then drying at a temperature of 55-65°C for 2-3 hours.

[0011] As a further technical solution, the weight ratio of the pretreated graphite, sulfuric acid, potassium permanganate and ammonium phosphate is 10:25-35:1.5-2.5:4-5.

[0012] As a further technical solution, the antioxidant is antioxidant 1010, and the ultraviolet absorber is ultraviolet absorber UV-531.

[0013] In a second aspect, the present invention provides a method for preparing a fire-resistant and flame-retardant power cable, comprising the following steps: mixing ethylene-vinyl acetate copolymer, high-density polyethylene, low-density polyethylene and maleic anhydride grafted polyethylene at a temperature of 85-95°C for 2-4 minutes, adding hydrophobically modified porous magnesium oxide and modified expanded graphite, mixing for 2-3 minutes, adding zinc borate, calcium stearate and an antioxidant, and mixing for 3-5 minutes while maintaining the temperature at 85-95°C; raising the temperature to 100-120°C, adding polyethylene wax and an ultraviolet absorber, continuing to mix at this temperature for 4-6 minutes, and standing at room temperature for 24 hours for aging to obtain a flame-retardant outer sheath layer rubber mixture, melt-extruding the mixture through a twin-screw extruder to coat the conductor to form an outer sheath layer with a thickness of 1.5-3.5 mm, and winding the mixture after cooling and shaping to obtain the fire-resistant and flame-retardant power cable.

[0014] As a further technical solution, the temperature of the first zone of the twin-screw extruder is 115-125°C, the temperature of the second zone is 135-145°C, the temperature of the third zone is 155-165°C, and the die head temperature is 145-155°C.

[0015] The working principle and beneficial effects of the present invention are: The present invention achieves a synergistic improvement in flame retardancy, moisture and heat resistance, and mechanical strength through a preparation process of hydrophobically modified porous magnesium oxide. First, a basic magnesium carbonate precursor is synthesized by a citric acid-assisted hydrothermal method, and a porous magnesium oxide skeleton is formed after high-temperature calcination. Its highly porous structure provides abundant reaction sites for subsequent hydrophobic modification. Further, through the silanization reaction of octadecyltrichlorosilane, long-chain alkyl groups are grafted on the surface of magnesium oxide to form a hydrophobic layer, which effectively blocks the penetration of water molecules and solves the problem that traditional inorganic flame retardants are prone to moisture absorption, resulting in a decrease in flame retardant properties. From the perspective of the synergistic mechanism, the combination of porous structure and hydrophobic modification achieves dual functional complementarity: porosity improves flame retardant efficiency, and hydrophobicity ensures environmental stability. The two together give the material long-term and stable flame retardant properties in a hot and humid environment. In addition, the endothermic decomposition characteristics of magnesium oxide can reduce the temperature of the combustion area, forming a synergistic flame retardant effect with the physical barrier effect of the hydrophobic layer on combustible gases, which significantly improves the limiting oxygen index of the material.

[0016] The present invention prepares modified expanded graphite through an acidification-oxidation intercalation process, achieving synergistic optimization of flame retardancy and mechanical strength. First, ammonium phosphate is used as an intercalation agent, synergistically acting with sulfuric acid and potassium permanganate to introduce phosphorus- and nitrogen-containing oxidized groups between graphite layers. This reduces the interlayer binding energy of the graphite, allowing it to expand more easily at high temperatures to form a dense carbon layer. The modified expanded graphite rapidly expands during combustion, forming a porous carbon layer that exhibits dual flame retardancy: physically, the carbon layer's low thermal conductivity effectively isolates heat transfer; chemically, the phosphorus- and nitrogen-containing groups catalyze the carbonization reaction, generating a stable cross-linked carbon layer that inhibits the release of combustible gases. Synergy with hydrophobically modified porous magnesium oxide is demonstrated in that the magnesium oxide particles produced by the decomposition of magnesium oxide fill the pores of the expanded graphite carbon layer, enhancing its compactness. The carbon layer structure of the expanded graphite provides a support for the dispersion of the magnesium oxide, preventing its aggregation and the resulting decrease in flame retardancy. The two together construct a three-dimensional flame retardant network of "physical barrier + chemical catalysis", which significantly improves the strength retention rate of the material after thermal aging.

[0017] This invention achieves synergistic benefits through the formulation of the flame-retardant outer sheath. The flexibility of ethylene-vinyl acetate copolymer (EVA) as the matrix compensates for the impairment of material toughness caused by inorganic fillers. The combination of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) ensures the material's processing fluidity while also enhancing its mechanical strength through the formation of a microphase-separated structure due to differences in crystallinity. Maleic anhydride-grafted polyethylene, a compatibilizer, significantly improves the interfacial bonding between the inorganic fillers (magnesium oxide and expanded graphite) and the organic matrix, addressing the strength loss caused by uneven filler dispersion. Based on the synergistic principle, the endothermic decomposition of MgO and the carbon barrier of expanded graphite form a dual "gas-condensed phase" flame retardant mechanism. The addition of zinc borate further catalyzes the formation of the carbon layer while simultaneously lowering the combustion temperature by releasing water of crystallization. The combination of antioxidant 1010 and UV absorber UV-531 ensures the material's long-term stability against both thermal and photoaging, preventing degradation-induced flame retardancy. This formula design achieves a balance of flame retardancy, moisture and heat resistance, mechanical strength and processing performance through the synergy of multiple components. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0019] It should be noted that the ethylene-vinyl acetate copolymer in the present invention, CAS No.: 24937-78-8, MDL No.: MFCD00133996, Article No.: P815474, was purchased from Maclean Reagent; high-density polyethylene was purchased from Utop Technology Suzhou Co., Ltd., p77512; low-density polyethylene was purchased from PetroChina Jilin Petrochemical Company, brand DFDA-7042; maleic anhydride grafted polyethylene was purchased from Nanjing Sutai Polymer Technology Co., Ltd., brand PE-12LL; magnesium oxide was purchased from Shandong Yuanbang New Materials Co., Ltd.; polyethylene wax was purchased from Guangzhou Binlong Chemical Co., Ltd., model D1100.

[0020] Example 1 This embodiment provides a fire-resistant and flame-retardant power cable, including a conductor, an insulation layer, and a flame-retardant outer sheath layer. The flame-retardant outer sheath layer is composed of the following raw materials in parts by weight: 45 parts of ethylene-vinyl acetate copolymer, 25 parts of high-density polyethylene, 14 parts of low-density polyethylene, 10 parts of maleic anhydride grafted polyethylene, 12 parts of hydrophobically modified porous magnesium oxide, 11 parts of modified expanded graphite, 4 parts of zinc borate, 0.8 parts of antioxidant 1010, 1 part of polyethylene wax, 0.7 parts of calcium stearate, and 0.4 parts of ultraviolet absorber UV-531.

[0021] Among them, the preparation method of hydrophobically modified porous magnesium oxide includes: adding 100 mL of 0.5 mol / L MgCl2 solution to 125 mL of 0.8 mol / L K2CO3 solution, stirring at 325 rpm to form a white precipitate mixture, adding 10.5 g of citric acid, and stirring in a water bath at 75°C until a transparent sol is formed; then hydrothermal reaction at 185°C for 2.5 hours, washing with deionized water and ethanol alternately three times, and vacuum drying at 60°C for 12 hours to obtain a basic magnesium carbonate precursor; then heating the basic magnesium carbonate precursor to 550°C at 5°C / min and keeping it warm for 2.5 hours; dispersing 10 g of the magnesium oxide obtained after calcination in 200 mL of toluene, adding 50 mL of 6 wt% octadecyltrichlorosilane toluene solution, reflux at 105°C under nitrogen protection for 5.5 hours, washing with toluene three times, and vacuum drying at 80°C for 24 hours to obtain the obtained product; The preparation method of modified expanded graphite includes: impregnating graphite with 7% hydrochloric acid for 30 minutes, washing with water until neutral, and drying at 60°C for 2.5 hours to obtain pretreated graphite, mixing with 75% sulfuric acid aqueous solution, potassium permanganate, and ammonium phosphate, stirring at 40°C and 225 rpm for 55 minutes, washing with water until neutral, and vacuum drying at 100°C for 12 hours to obtain the pretreated graphite; the weight ratio of the pretreated graphite, sulfuric acid, potassium permanganate, and ammonium phosphate is 10:30:2:4.5; The preparation method of the fire-resistant and flame-retardant power cable comprises the following steps: Ethylene-vinyl acetate copolymer, high-density polyethylene, low-density polyethylene and maleic anhydride grafted polyethylene are mixed at a temperature of 90°C for 3 minutes, hydrophobically modified porous magnesium oxide and modified expanded graphite are added and mixed for 2.5 minutes, zinc borate, calcium stearate and an antioxidant are added and mixed for 4 minutes while maintaining the temperature at 90°C; the temperature is raised to 110°C, polyethylene wax and ultraviolet absorber are added, and mixing is continued at this temperature for 5 minutes, and the mixture is left at room temperature for 24 hours for aging to obtain a flame-retardant outer sheath layer compound, which is melt-extruded through a twin-screw extruder to coat the conductor to form an outer sheath layer with a thickness of 2 mm, and is rolled up after cooling and shaping to obtain a fire-resistant and flame-retardant power cable, wherein the temperature of the first zone of the twin-screw extruder is 120°C, the temperature of the second zone is 130°C, the temperature of the third zone is 160°C, and the temperature of the die head is 150°C.

[0022] Example 2 This embodiment provides a fire-resistant and flame-retardant power cable, including a conductor, an insulation layer, and a flame-retardant outer sheath layer. The flame-retardant outer sheath layer is composed of the following raw materials in parts by weight: 40 parts of ethylene-vinyl acetate copolymer, 20 parts of high-density polyethylene, 12 parts of low-density polyethylene, 8 parts of maleic anhydride grafted polyethylene, 10 parts of hydrophobically modified porous magnesium oxide, 10 parts of modified expanded graphite, 3 parts of zinc borate, 0.5 parts of antioxidant 1010, 0.8 parts of polyethylene wax, 0.5 parts of calcium stearate, and 0.3 parts of ultraviolet absorber UV-531.

[0023] Among them, the preparation method of hydrophobically modified porous magnesium oxide includes: adding 100 mL of 0.4 mol / L MgCl2 solution to 120 mL of 0.7 mol / L K2CO3 solution, stirring at 300 rpm to form a white precipitate mixture, adding 10 g of citric acid, and stirring in a water bath at 70°C until a transparent sol is formed; then performing a hydrothermal reaction at 180°C for 2 hours, washing alternately with deionized water and ethanol three times, and vacuum drying at 60°C for 12 hours to obtain a basic magnesium carbonate precursor; then heating the basic magnesium carbonate precursor to 500°C at 5°C / min and keeping it warm for 2 hours; dispersing 10 g of the magnesium oxide obtained after calcination in 180 mL of toluene, adding 45 mL of 5 wt% octadecyltrichlorosilane toluene solution, refluxing at 100°C under nitrogen protection for 5 hours, washing with toluene three times, and vacuum drying at 80°C for 24 hours to obtain the obtained product; The preparation method of modified expanded graphite includes: impregnating graphite with 5% hydrochloric acid for 30 minutes, washing with water until neutral, and drying at 55°C for 2-3 hours to obtain pretreated graphite; mixing with 70% sulfuric acid aqueous solution, potassium permanganate, and ammonium phosphate, stirring at 40°C and 200 rpm for 50 minutes, washing with water until neutral, and vacuum drying at 100°C for 12 hours to obtain the pretreated graphite; the weight ratio of the pretreated graphite, sulfuric acid, potassium permanganate, and ammonium phosphate is 10:25:1.5:4; The preparation method of the fire-resistant and flame-retardant power cable comprises the following steps: Ethylene-vinyl acetate copolymer, high-density polyethylene, low-density polyethylene and maleic anhydride grafted polyethylene are mixed at a temperature of 85°C for 2 minutes, hydrophobically modified porous magnesium oxide and modified expanded graphite are added and mixed for 2 minutes, zinc borate, calcium stearate and an antioxidant are added and mixed at a temperature maintained at 85°C for 3 minutes; the temperature is raised to 100°C, polyethylene wax and ultraviolet absorber are added, and mixing is continued at this temperature for 4 minutes. The mixture is left to mature at room temperature for 24 hours to obtain a flame-retardant outer sheath layer rubber compound, which is melt-extruded through a twin-screw extruder to coat the conductor to form an outer sheath layer with a thickness of 1.5 mm. After cooling and shaping, the mixture is wound up to obtain a fire-resistant and flame-retardant power cable. The temperature of the first zone of the twin-screw extruder is 115°C, the temperature of the second zone is 135°C, the temperature of the third zone is 155°C, and the temperature of the die head is 145°C.

[0024] Example 3 This embodiment provides a fire-resistant and flame-retardant power cable, including a conductor, an insulation layer, and a flame-retardant outer sheath layer. The flame-retardant outer sheath layer is composed of the following raw materials in parts by weight: 50 parts of ethylene-vinyl acetate copolymer, 30 parts of high-density polyethylene, 16 parts of low-density polyethylene, 12 parts of maleic anhydride grafted polyethylene, 15 parts of hydrophobically modified porous magnesium oxide, 12 parts of modified expanded graphite, 5 parts of zinc borate, 1 part of antioxidant 1010, 1.2 parts of polyethylene wax, 0.9 part of calcium stearate, and 0.5 part of ultraviolet absorber UV-531.

[0025] Among them, the preparation method of hydrophobically modified porous magnesium oxide includes: adding 100 mL of 0.6 mol / L MgCl2 solution to 130 mL of 0.9 mol / L K2CO3 solution, stirring at 350 rpm to form a white precipitate mixture, adding 11 g of citric acid, and stirring in a water bath at 80°C until a transparent sol is formed; then performing a hydrothermal reaction at 190°C for 3 hours, washing with deionized water and ethanol alternately three times, and vacuum drying at 60°C for 12 hours to obtain a basic magnesium carbonate precursor; then heating the basic magnesium carbonate precursor to 600°C at 5°C / min and keeping it warm for 3 hours; dispersing 10 g of the magnesium oxide obtained after calcination in 220 mL of toluene, adding 55 mL of 7 wt% octadecyltrichlorosilane toluene solution, reflux at 110°C under nitrogen protection for 6 hours, washing with toluene three times, and vacuum drying at 80°C for 24 hours to obtain the obtained product; The preparation method of modified expanded graphite includes: impregnating graphite with 10% hydrochloric acid for 30 minutes, washing with water until neutral, and drying at 65°C for 3 hours to obtain pretreated graphite; mixing with 80% sulfuric acid aqueous solution, potassium permanganate, and ammonium phosphate, stirring at 40°C and 250 rpm for 60 minutes, washing with water until neutral, and vacuum drying at 100°C for 12 hours to obtain the pretreated graphite; the weight ratio of the pretreated graphite, sulfuric acid, potassium permanganate, and ammonium phosphate is 10:35:2.5:5; The preparation method of the fire-resistant and flame-retardant power cable comprises the following steps: Ethylene-vinyl acetate copolymer, high-density polyethylene, low-density polyethylene and maleic anhydride grafted polyethylene are mixed at a temperature of 95°C for 4 minutes, hydrophobically modified porous magnesium oxide and modified expanded graphite are added and mixed for 3 minutes, zinc borate, calcium stearate and an antioxidant are added and mixed at a temperature maintained at 95°C for 5 minutes; the temperature is raised to 120°C, polyethylene wax and ultraviolet absorber are added, and mixing is continued at this temperature for 6 minutes. The mixture is left at room temperature for 24 hours for aging to obtain a flame-retardant outer sheath layer rubber compound, which is melt-extruded through a twin-screw extruder to coat the conductor to form an outer sheath layer with a thickness of 3.5 mm. After cooling and shaping, the mixture is wound up to obtain a fire-resistant and flame-retardant power cable. The temperature of the first zone of the twin-screw extruder is 125°C, the temperature of the second zone is 145°C, the temperature of the third zone is 165°C, and the temperature of the die head is 155°C.

[0026] Comparative Example 1 In this comparative example, the hydrophobically modified porous magnesium oxide was replaced by porous magnesium oxide without modification by octadecyltrichlorosilane. The rest was the same as in comparative example 1, and the preparation steps were the same as in comparative example 1.

[0027] Comparative Example 2 In this comparative example, the hydrophobically modified porous magnesium oxide is replaced by commercially available magnesium oxide, and the rest is the same as in comparative example 1, and the preparation steps are the same as in comparative example 1.

[0028] Comparative Example 3 In this comparative example, the hydrophobically modified porous magnesium oxide was replaced by an equal mass of modified expanded graphite, and the rest was the same as in comparative example 1, and the preparation steps were the same as in comparative example 1.

[0029] Comparative Example 4 In this comparative example, the modified expanded graphite is replaced by pretreated graphite without modification. The rest is the same as in comparative example 1, and the preparation steps are the same as in comparative example 1.

[0030] Comparative Example 5 In this comparative example, the modified expanded graphite is replaced by an equal mass of hydrophobically modified porous magnesium oxide, and the rest is the same as in comparative example 1, and the preparation steps are the same as in comparative example 1.

[0031] Comparative Example 6 In this comparative example, the hydrophobically modified porous magnesium oxide was replaced by porous magnesium oxide without modification with octadecyltrichlorosilane, and the modified expanded graphite was replaced by pretreated graphite without modification. The rest was the same as in comparative example 1, and the preparation steps were the same as in comparative example 1.

[0032] Test Example 1: The fire-resistant and flame-retardant power cables prepared in the above Examples 1-4 and Comparative Examples 1-6 were subjected to the following tests: Limiting Oxygen Index (LOI): Tested in accordance with GB / T 2406.2-2009 standard; Tensile strength: tested in accordance with GB / T1040.2-2006 standard; Thermal aging performance: Tested in accordance with GB / T 2951.12-2008 standard, the specimens were hung in an aging chamber and aged at 135°C for 168 hours; Resistance to heat and humidity aging: 85°C, 85% RH for 168h, test the limiting oxygen index; The flame retardant performance test results are shown in Table 1 below: Table 1

[0033] Combined with the above, Examples 1-3 all exhibit excellent overall performance: a limiting oxygen index of 36.7% to 37.8%; a tensile strength of 16.8 to 17.5 MPa, and a strength retention rate of >89% after heat aging. After humidity and heat cycling, the LOI decreased by only 1.4 to 3.4%, demonstrating stable flame retardancy. Hydrophobically modified porous magnesium oxide effectively improves flame retardancy, humidity and heat resistance, and mechanical strength.

[0034] Comparative Example 1: Unmodified magnesium oxide: LOI and wet heat LOI decreased. The lack of hydrophobicity leads to moisture absorption, which easily renders the flame retardant ineffective. Comparative Example 2: Replaced with commercially available standard magnesium oxide: LOI and strength decreased. The non-porous structure results in poor dispersibility and low flame retardant efficiency. Comparative Example 3: Replaced magnesium oxide with an equal amount of modified expanded graphite: LOI and strength decreased. The heat absorption and smoke suppression properties of magnesium oxide are lost, destroying the synergistic flame retardant effect. Comparative Example 4: Unmodified expanded graphite: LOI and wet heat LOI decreased. Unmodified graphite: Inadequate barrier properties prevent effective charring at high temperatures. Comparative Example 5: Replaced expanded graphite with an equal amount of hydrophobic magnesium oxide: LOI and strength decreased. Excessive magnesium oxide accumulation impairs dispersion, and the absence of expanded graphite results in an incomplete carbon layer. Comparative Example 6: Double omissions: LOI and strength decreased. The flame retardant system completely fails, demonstrating the essential nature of both.

[0035] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A fire-resistant and flame-retardant power cable, characterized in that: The invention comprises a conductor, an insulating layer and a flame-retardant outer sheath layer. The flame-retardant outer sheath layer is composed of the following raw materials in parts by weight: 40-50 parts of ethylene-vinyl acetate copolymer, 20-30 parts of high-density polyethylene, 12-16 parts of low-density polyethylene, 8-12 parts of maleic anhydride grafted polyethylene, 10-15 parts of hydrophobically modified porous magnesium oxide, 10-12 parts of modified expanded graphite, 3-5 parts of zinc borate, 0.5-1 part of antioxidant, 0.8-1.2 parts of polyethylene wax, 0.5-0.9 part of calcium stearate and 0.3-0.5 part of ultraviolet absorber.

2. A fire-resistant and flame-retardant power cable according to claim 1, characterized in that: The preparation method of the hydrophobically modified porous magnesium oxide comprises: adding an MgCl2 solution to a K2CO3 solution, stirring at 300-350 rpm to form a white precipitate mixture, adding citric acid, stirring in a water bath at 70-80°C until a transparent sol is formed, then performing a hydrothermal reaction at 180-190°C for 2-3 hours, washing, and drying to obtain a basic magnesium carbonate precursor; then heating the basic magnesium carbonate precursor to 500-600°C at a rate of 5°C / min and keeping the temperature for 2-3 hours; dispersing the magnesium oxide obtained after calcination in toluene, adding an octadecyltrichlorosilane solution, refluxing at 100-110°C under nitrogen protection for 5-6 hours, washing, and drying to obtain the hydrophobically modified porous magnesium oxide.

3. A fire-resistant and flame-retardant power cable according to claim 2, characterized in that: The concentration of the MgCl2 solution is 0.4-0.6 mol / L; the concentration of the K2CO3 solution is 0.7-0.9 mol / L; the usage ratio of the MgCl2 solution, K2CO3 solution and citric acid is 100 mL:120-130 mL:10-11 g.

4. A fire-resistant and flame-retardant power cable according to claim 2, characterized in that: The octadecyltrichlorosilane solution is a toluene solution of octadecyltrichlorosilane with a concentration of 5wt%-7wt%; the usage ratio of the magnesium oxide, toluene, and octadecyltrichlorosilane solution is 10g:180-220mL:45-55mL.

5. The fire-resistant and flame-retardant power cable according to claim 1, characterized in that: The preparation method of the modified expanded graphite includes: acid-washing and then drying graphite to obtain pretreated graphite, mixing it with sulfuric acid, potassium permanganate and ammonium phosphate with a mass concentration of 70%-80%, stirring and reacting at a temperature of 40±2°C and 200-250rpm for 50-60min, washing with water and then vacuum drying to obtain the modified expanded graphite.

6. The fire-resistant and flame-retardant power cable according to claim 5, characterized in that: The pickling step comprises: impregnating the graphite with hydrochloric acid having a mass concentration of 5%-10%, washing with water until neutral, and then drying at a temperature of 55-65° C. for 2-3 hours.

7. The fire-resistant and flame-retardant power cable according to claim 5, characterized in that: The weight ratio of the pretreated graphite, sulfuric acid, potassium permanganate and ammonium phosphate is 10:25-35:1.5-2.5:4-5.

8. The fire-resistant and flame-retardant power cable according to claim 1, characterized in that: The antioxidant is antioxidant 1010, and the ultraviolet absorber is ultraviolet absorber UV-531.

9. A method for preparing a fire-resistant and flame-retardant power cable according to any one of claims 1 to 8, characterized in that the steps include: Ethylene-vinyl acetate copolymer, high-density polyethylene, low-density polyethylene and maleic anhydride grafted polyethylene are mixed at a temperature of 85-95°C for 2-4 minutes, hydrophobically modified porous magnesium oxide and modified expanded graphite are added and mixed for 2-3 minutes, zinc borate, calcium stearate and an antioxidant are added and mixed for 3-5 minutes while maintaining the temperature at 85-95°C; the temperature is raised to 100-120°C, polyethylene wax and an ultraviolet absorber are added, and mixing is continued at this temperature for 4-6 minutes, and the mixture is left to mature at room temperature for 24 hours to obtain a flame-retardant outer sheath layer rubber mixture, which is melt-extruded through a twin-screw extruder to coat the conductor to form an outer sheath layer with a thickness of 1.5-3.5 mm, and the mixture is cooled and shaped before being rolled up to obtain the fire-resistant flame-retardant power cable.

10. The method for preparing a fire-resistant and flame-retardant power cable according to claim 9, characterized in that: The temperature of the first zone of the twin-screw extruder is 115-125°C, the temperature of the second zone is 135-145°C, the temperature of the third zone is 155-165°C, and the die head temperature is 145-155°C.

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