Flame-retardant polypropylene sheath material for cable and preparation method of flame-retardant polypropylene sheath material

Abstract

The invention discloses a flame-retardant polypropylene sheath material for a cable and a preparation method of the flame-retardant polypropylene sheath material, and relates to the technical field of cable sheath materials. The flame-retardant polypropylene sheath material for the cable at least comprises the following raw materials in parts by mass: 100 parts of polypropylene, 20-35 parts of ethylene propylene diene monomer, 2-8 parts of ethylene propylene diene monomer grafted maleic anhydride, 15-22 parts of an intumescent flame retardant, 10-20 parts of modified glass fibers, 10-15 parts of modified aramid fibers, 0.5-1.3 parts of an inorganic filler, 1.1-1.5 parts of calcium stearate and 2-3 parts of an antioxidant. Wherein the modified glass fiber is a Fe2O3 nano particle-glass fiber wrapped by polyphosphazene; the modified aramid fibers are aramid fibers wrapped by polyphosphazene. The flame-retardant polypropylene sheath material for the cable has the advantages of good mechanical property, excellent flame retardant property and long service life.

Description

Technical Field

[0001] The present invention relates to the technical field of cable sheath materials, and particularly relates to a flame-retardant polypropylene sheath material for cables and a preparation method thereof. Background Art

[0002] At present, with the development of social economy, the consumption of wires and cables has increased rapidly. The basic structure of power cables consists of four parts: a conductor core, an insulating layer, a shielding layer, and an outer sheath. The conductor core is the conductive part of the power cable, used to transmit electrical energy, and is the main part of the power cable. The insulating layer electrically isolates the conductor core from the ground and from conductor cores of different phases, ensuring the transmission of electrical energy, and is an indispensable part of the power cable structure. Power cables of 15 kV and above generally have a conductor shielding layer and an insulation shielding layer. The function of the outer sheath protective layer is to protect the power cable from the intrusion of external impurities and moisture, and to prevent direct damage to the power cable by external forces. The role of the outer sheath is particularly important in the use of cables. In the prior art, the protective effect of power cable outer sheath materials is often not ideal, and the comprehensive functions are poor.

[0003] Polypropylene has the following advantages: it is the resin with the lowest density among all general-purpose plastics, and its products are light in weight; it has excellent heat resistance and can be continuously used at a temperature of 120 °C without easy softening, and it is the cheapest high-temperature general-purpose plastic; it has excellent physical and mechanical properties such as tensile and impact properties, and has relatively high strength; it has good chemical corrosion resistance and environmental stress cracking resistance. At room temperature, except for a small amount of low-molecular-weight aliphatic hydrocarbons and aromatic hydrocarbons that can soften or swell, other solvents are basically insoluble; it has relatively high wear resistance, its product surface is not easily worn, and it is scratch-resistant; it is not easily absorbent, has good thermal stability, is not easily decomposed during production and processing, will not corrode the mold, and can extend the service life of the mold. At present, it has been widely used in cable sheath materials. However, the oxygen index of polypropylene is very low and it is easy to burn. The flame retardancy of existing polypropylene cable sheath materials cannot meet the needs of society, and polypropylene needs to be modified. To improve the flame retardancy performance, the traditional method is to add intumescent flame retardants. However, the addition amount is generally relatively high, which will deteriorate the mechanical properties of polypropylene. Therefore, existing flame-retardant polypropylene sheath materials for cables have defects such as poor mechanical properties and low flame retardancy, which severely limit the use of this technology. Summary of the Invention

[0004] The purpose of the present invention is to provide a flame-retardant polypropylene sheath material for cables and a preparation method thereof, and solve the following technical problems: Existing polypropylene composites used for cable sheath materials have problems of poor flame retardancy and low flame retardant performance.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A flame-retardant polypropylene sheath material for cables, comprising at least the following raw materials in parts by mass: 100 parts of polypropylene, 20 - 35 parts of ethylene propylene diene monomer (EPDM), 2 - 8 parts of EPDM grafted maleic anhydride, 15 - 22 parts of intumescent flame retardant, 10 - 20 parts of modified glass fiber, 10 - 15 parts of modified aramid fiber, 0.5 - 1.3 parts of inorganic filler, 1.1 - 1.5 parts of calcium stearate, 2 - 3 parts of antioxidant; Among them, the modified glass fiber is polyphosphazene - wrapped Fe 2 O 3 nanoparticle - glass fiber; the modified aramid fiber is polyphosphazene - wrapped aramid fiber.

[0006] As a further solution of the present invention: The preparation method of the modified glass fiber includes the following steps: Adding the pretreated glass fiber into a mixed solution of Fe(NO 3 ) 3 ˙9H 2 O and urea, reacting, drying, and calcining to obtain composite glass fiber; Dispersing the composite glass fiber in ethanol, adding a 4,4'-diaminodiphenyl sulfone / triethylamine / acetonitrile mixed solution, and then adding a hexachlorocyclotriphosphazene / acetonitrile mixed solution, reacting and drying to obtain modified glass fiber.

[0007] As a further solution of the present invention: The mass ratio of the glass fiber, the Fe(NO 3 ) 3 ˙9H 2 O and the urea is 10:0.25 - 0.35:0.2 - 0.3.

[0008] As a further solution of the present invention: The addition ratio of the composite glass fiber, the 4,4'-diaminodiphenyl sulfone, the triethylamine, the hexachlorocyclotriphosphazene and the acetonitrile is 10g:0.2 - 0.6g:5 - 20mL:0.10 - 0.3g:230 - 300mL.

[0009] As a further solution of the present invention: The preparation method of the modified aramid fiber includes the following steps: Pre - treating the aramid fiber and dispersing it in ethanol, adding a 4,4'-diaminodiphenyl sulfone / triethylamine / acetonitrile mixed solution, and then adding a hexachlorocyclotriphosphazene / acetonitrile mixed solution, reacting and drying to obtain modified aramid fiber.

[0010] As a further solution of the present invention: the addition ratio of the aramid fiber, the 4,4'-diaminodiphenyl sulfone, the triethylamine, the hexachlorocyclotriphosphazene and the acetonitrile is 10 g: 0.4 - 0.5 g: 10 - 15 mL: 0.15 - 0.22 g: 230 - 240 mL.

[0011] As a further solution of the present invention: the length of the aramid fiber is 3 - 6 mm and the diameter is 12 - 16 μm, and the length of the glass fiber is 3 - 5 mm and the diameter is 10 - 15 μm.

[0012] As a further solution of the present invention: the intumescent flame retardant is ammonium polyphosphate, pentaerythritol and melamine, and the mass ratio of the ammonium polyphosphate, the pentaerythritol and the melamine is 4 - 5: 2 - 3: 1 - 2.

[0013] As a further solution of the present invention: the inorganic filler is one or a mixture of talc powder, mica powder, kaolin, montmorillonite, silica white, and the antioxidant is a mixture of antioxidant 1076 and antioxidant 168.

[0014] A preparation method of a flame-retardant polypropylene sheath material for cables at least includes the following preparation steps: Weigh each component according to the raw material formula. First, add polypropylene, ethylene-propylene-diene monomer rubber, and ethylene-propylene-diene monomer rubber grafted with maleic anhydride into a high-speed mixer and mix at high speed for 20 - 25 min. Then, add the intumescent flame retardant, modified glass fiber, modified aramid fiber, inorganic filler, calcium stearate and antioxidant and continue to mix for 20 - 25 min to obtain a mixture. Add the mixture into a twin-screw extruder. The screw speed of the twin-screw extruder is 100 - 150 r / min, and the processing temperature is 160 - 170 °C. After extrusion granulation and cooling, a flame-retardant polypropylene sheath material for cables is obtained.

[0015] The beneficial effects of the present invention: The flame-retardant polypropylene sheath material for cables provided by the present invention is prepared by reacting polypropylene and ethylene-propylene-diene monomer (EPDM) as resin raw materials, and simultaneously adding a compatibilizer, an intumescent flame retardant, an antioxidant, a lubricant, an inorganic filler, modified glass fiber, and modified aramid fiber. Adding EPDM toughens polypropylene, greatly improving the low-temperature impact strength of polypropylene while retaining its rigidity, achieving the purpose of toughening. EPDM grafted with maleic anhydride acts as a compatibilizer in the system, improving the compatibility between polypropylene and EPDM and the mechanical properties of the flame-retardant polypropylene sheath material, thereby enhancing the strength and toughness of the cable. The modified flame retardant and modified glass fiber can synergistically improve the flame-retardant performance of the flame-retardant outer sheath, reducing the use of the intumescent flame retardant, thus inhibiting the "wick effect". Moreover, the addition of modified aramid fiber to the system improves the reduction in mechanical strength caused by the addition of EPDM and modified glass fiber, while enhancing the aging resistance of the composite material. In the present invention, using the polypropylene composite material as the sheath material for the cable, the obtained cable has the advantages of high strength, good mechanical properties, excellent flame-retardant performance, and long service life.

[0016] In the present invention, the modified glass fiber is a composite material of polyphosphazene-coated Fe 2 O 3 nanoparticle-glass fiber. The addition of glass fiber can improve the tensile strength and flexural strength of the polypropylene composite material. Although modifying the glass fiber reduces the improvement of the mechanical properties of the composite material, it greatly enhances the flame-retardant performance of the composite material. The Fe 2 O 3 nanoparticles loaded on the glass fiber can be used as a catalytic charring agent to improve the flame-retardant performance of the flame-retardant polypropylene sheath material. Growing Fe 2 O 3 nanoparticles on the surface of the glass fiber increases the surface roughness of the glass fiber, which will lead to interfacial carbonization. During the combustion process, the intumescent flame retardant decomposes into phosphorus- and nitrogen-containing small molecules and incombustible gases, forming an expanded carbon layer, effectively inhibiting the heat release rate and reducing the combustion rate. The modified glass fiber and the intumescent flame retardant have a synergistic effect, promoting the formation of residual carbon and increasing the amount of residual carbon, thereby improving the flame-retardant performance of the polypropylene composite material. At the same time, the silicon element in the modified glass fiber will improve the thermal stability of the carbon layer, enabling it to fully play the role of heat insulation and gas isolation, so that the flame-retardant outer sheath has excellent flame-retardant effect.

[0017] The present invention also uses polyphosphazene for Fe 2 O 3A composite material of nanoparticles and glass fibers, and aramid fibers are used for wrapping and modification treatment. Due to its high crosslinking density, polyphosphazene can form a stable three-dimensional network structure, which not only endows the material with excellent mechanical strength and heat stability, but also, because of its high content of phosphorus and nitrogen elements, these two elements themselves are efficient flame retardant elements, which can effectively inhibit the free radical chain reaction during combustion and further improve the flame retardant performance. Aramid fibers themselves have high strength and modulus, play a skeleton role in the composite material, can bear and absorb a large amount of impact energy, so that the entire composite material can withstand higher energy and improve the notched impact performance. At the same time, the fibers have a heterogeneous nucleation effect, which can promote the crystallization of polypropylene and improve the strength of polypropylene itself. By combining inorganic nanoparticles with organic flame retardants, not only can a synergistic flame retardant effect be achieved, but also the dispersion of the flame retardant in the polymer matrix can be improved, avoiding agglomeration, and striving to improve the mechanical properties and thermal stability of the material while reducing the smoke density and the emission of toxic gases. Detailed implementation mode

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0019] Example 1 The preparation method of modified glass fibers includes the following steps: Put 100 g of glass fibers into a high-temperature muffle furnace, calcine at 500 °C for 90 min. After cooling, immerse the glass fibers in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3 for 1 h, wash 3 times with distilled water, and place in an 80 °C oven until completely dry to obtain pretreated glass fibers; Put 2.5 g of Fe(NO 3 ) 3 ˙9H 2 O and 2.2 g of urea into 500 mL of deionized water and mix evenly. Add the above pretreated glass fibers, and place them in a high-pressure reaction kettle. Then slowly pour the prepared solution into the high-pressure reaction kettle, fully react in an 80 °C oven for 4 h, wash after cooling, and then place in an 80 °C oven for 12 h, and calcine in a high-temperature muffle furnace at 350 °C for 2 h to obtain composite glass fibers.

[0020] Disperse 100 g of the above-mentioned composite glass fiber in 1500 ml of ethanol solution, add 4 g of 4,4'-diaminodiphenyl sulfone, 100 ml of triethylamine and 1500 ml of acetonitrile, ultrasonically disperse for 0.5 h to form a suspension, dissolve 2 g of hexachlorocyclotriphosphazene in 90 ml of acetonitrile, dropwise add it to the above suspension, and react at 50 °C for 6 h. After the reaction is completed, wash and dry to obtain modified glass fiber.

[0021] Example 2 The preparation method of the modified glass fiber comprises the following steps: Put 100 g of glass fiber into a high-temperature muffle furnace, calcine at 500 °C for 90 min, after cooling, immerse the glass fiber in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3 for 1 h, wash 3 times with distilled water, and place it in an 80 °C oven until completely dry to obtain pretreated glass fiber; Put 3.2 g of Fe(NO 3 ) 3 ˙9H 2 O and 2.9 g of urea into 500 mL of deionized water, mix evenly, add the above-mentioned pretreated glass fiber, and place it in a high-pressure reactor, then slowly pour the above-prepared solution into the high-pressure reactor, fully react in an 80 °C oven for 4 h, cool and wash, and then place it in an 80 °C oven for 12 h, and calcine in a high-temperature muffle furnace at 350 °C for 2 h to obtain composite glass fiber.

[0022] Disperse 100 g of the above-mentioned composite glass fiber in 1500 ml of ethanol solution, add 4.5 g of 4,4'-diaminodiphenyl sulfone, 120 ml of triethylamine and 1500 ml of acetonitrile, ultrasonically disperse for 0.5 h to form a suspension, dissolve 2.5 g of hexachlorocyclotriphosphazene in 100 ml of acetonitrile, dropwise add it to the above suspension, and react at 50 °C for 6 h. After the reaction is completed, wash and dry to obtain modified glass fiber.

[0023] Example 3 The preparation method of the modified aramid fiber comprises the following steps: Immerse 100 g of aramid fiber in 0.5% sodium hydroxide solution for 1 h, then immerse it in acetone solution for 12 h, wash and dry to obtain surface-treated aramid fiber; Disperse the above surface-treated glass fiber in 1500 ml of ethanol solution, add 4 g of 4,4'-diaminodiphenyl sulfone, 100 ml of triethylamine and 1500 ml of acetonitrile, ultrasonically disperse for 0.5 h to form a suspension, dissolve 2 g of hexachlorocyclotriphosphazene in 90 ml of acetonitrile, dropwise add it to the above suspension, and react at 50 °C for 6 h. After the reaction is completed, wash and dry to obtain modified aramid fiber.

[0024] Example 4 A flame-retardant polypropylene sheath material for cables and its preparation method are made by the following method: Add 100 parts by mass of polypropylene, 25 parts by mass of ethylene-propylene-diene monomer (EPDM), and 5 parts by mass of EPDM grafted maleic anhydride into a high-speed mixer and mix at high speed for 20 - 25 min. Then, add 8 parts by mass of ammonium polyphosphate, 4 parts by mass of pentaerythritol, 4 parts by mass of melamine, 18 parts by mass of the modified glass fiber prepared in Example 1, 12 parts by mass of the modified aramid fiber prepared in Example 3, 0.8 part by mass of the inorganic filler silica, 1.2 parts by mass of calcium stearate, 1 part by mass of antioxidant 1076, and 1 part by mass of antioxidant 168 and continue to mix for 20 - 25 min to obtain a mixed material; Add the mixed material into a twin-screw extruder. The screw speed of the twin-screw extruder is 100 - 150 r / min, and the processing temperature is 160 - 170 °C. After extrusion and pelletization, it is cooled to obtain a flame-retardant polypropylene sheath material for cables.

[0025] Example 5 A flame-retardant polypropylene sheath material for cables and its preparation method are made by the following method: Add 100 parts by mass of polypropylene, 25 parts by mass of ethylene-propylene-diene monomer (EPDM), and 5 parts by mass of EPDM grafted maleic anhydride into a high-speed mixer and mix at high speed for 20 - 25 min. Then, add 8 parts by mass of ammonium polyphosphate, 4 parts by mass of pentaerythritol, 4 parts by mass of melamine, 18 parts by mass of the modified glass fiber prepared in Example 2, 12 parts by mass of the modified aramid fiber prepared in Example 3, 0.8 part by mass of the inorganic filler silica, 1.2 parts by mass of calcium stearate, 1 part by mass of antioxidant 1076, and 1 part by mass of antioxidant 168 and continue to mix for 20 - 25 min to obtain a mixed material; Add the mixed material into a twin-screw extruder. The screw speed of the twin-screw extruder is 100 - 150 r / min, and the processing temperature is 160 - 170 °C. After extrusion and pelletization, it is cooled to obtain a flame-retardant polypropylene sheath material for cables.

[0026] Example 6 A flame-retardant polypropylene sheath material for cables and its preparation method are made by the following method: Add 100 parts by mass of polypropylene, 30 parts by mass of ethylene-propylene-diene monomer (EPDM), and 8 parts by mass of EPDM grafted maleic anhydride into a high-speed mixer and mix at high speed for 20 - 25 min. Then, add 10 parts by mass of ammonium polyphosphate, 4 parts by mass of pentaerythritol, 3 parts by mass of melamine, 20 parts by mass of the modified glass fiber prepared in Example 1, 10 parts by mass of the modified aramid fiber prepared in Example 3, 0.8 part by mass of the inorganic filler silica, 1.4 parts by mass of calcium stearate, 1 part by mass of antioxidant 1076, and 1 part by mass of antioxidant 168 and continue to mix for 20 - 25 min to obtain a mixed material; Add the mixture into a twin-screw extruder. The screw speed of the twin-screw extruder is 100 - 150 r / min, and the processing temperature is 160 - 170 °C. After extrusion granulation, cool it to obtain the flame-retardant polypropylene sheath material for cables.

[0027] Example 7 A flame-retardant polypropylene sheath material for cables and its preparation method are made by the following method: Add 100 parts by mass of polypropylene, 30 parts by mass of ethylene propylene diene monomer (EPDM), and 8 parts by mass of EPDM grafted maleic anhydride into a high-speed mixer and mix at high speed for 20 - 25 min. Then, add 10 parts by mass of ammonium polyphosphate, 4 parts by mass of pentaerythritol, 3 parts by mass of melamine, 20 parts by mass of the modified glass fiber prepared in Example 2, 10 parts by mass of the modified aramid fiber prepared in Example 3, 0.8 part by mass of inorganic filler silica, 1.4 parts by mass of calcium stearate, 1 part by mass of antioxidant 1076, and 1 part by mass of antioxidant 168 and continue to mix for 20 - 25 min to obtain a mixture. Add the mixture into a twin-screw extruder. The screw speed of the twin-screw extruder is 100 - 150 r / min, and the processing temperature is 160 - 170 °C. After extrusion granulation, cool it to obtain the flame-retardant polypropylene sheath material for cables.

[0028] Comparative Example 1 Compared with Example 4, in Comparative Example 1, the modified glass fiber prepared in Example 1 is replaced with the composite glass fiber prepared in Example 1 in equal mass, and the modified aramid fiber prepared in Example 3 is replaced with the untreated aramid fiber in equal mass. The remaining components and preparation method are completely the same as those in Example 4.

[0029] Comparative Example 2 Compared with Example 4, in Comparative Example 2, the modified glass fiber prepared in Example 1 is not added. The remaining components and preparation method are completely the same as those in Example 4.

[0030] Comparative Example 3 Compared with Example 4, in Comparative Example 3, the modified aramid fiber prepared in Example 3 is not added. The remaining components and preparation method are completely the same as those in Example 4.

[0031] Comparative Example 4 Compared with Example 4, in Comparative Example 4, the modified glass fiber prepared in Example 1 is replaced with the untreated glass fiber in equal mass. The remaining components and preparation method are completely the same as those in Example 4.

[0032] Performance testing Tensile property: The tensile strength is tested according to the method of GB / T 1040.1. Use an injection-molded dumbbell-shaped tensile standard specimen, and set the tensile speed to 50 mm·min -1 , and test under the constant temperature condition of 23 °C; the test results are shown in Table 1; Flexural properties: The flexural strength was tested according to the method of GB / T 9341-2008. Using injection-molded long strip standard specimens, the deflection was set at 6 mm and the test speed was 2 mm·min -1 , and the test was carried out under the constant temperature condition of 23℃; The test results are shown in Table 1; Impact properties: The Izod impact strength was tested according to the method of GB / T 1843-2008. Using injection-molded long strip standard specimens, a V-notch was cut with a notch cutter within 4 h after injection molding, and a pendulum with appropriate energy was selected for testing under the constant temperature condition of 23℃; The test results are shown in Table 1; Limiting oxygen index: The limiting oxygen index was tested according to the method of GB / T 2406.2-2009. Using injection-molded long strip standard specimens, a series of experiments were carried out at different oxygen concentrations by observing their combustion characteristics to estimate the lowest oxygen concentration, i.e., the limiting oxygen index. The experiment was carried out under the constant temperature condition of 23℃. Generally, when the limiting oxygen index is less than 22, it is flammable; when it is 22-27, it is combustible; when it is greater than 27, it is flame-retardant; The test results are shown in Table 1 Vertical burning: The vertical burning of the composite material was tested according to the method of GB / T2408—2021. Using injection-molded long strip standard specimens, the combustion behavior was evaluated by measuring the afterflame and afterglow time, range and particle dripping of its combustion. Generally, the vertical burning of materials can be divided into V-0, V-1 and V-2 grades; The test results are shown in Table 1; Table 1: Statistical table of performance test data of polypropylene sheath materials in Examples 4-7 and Comparative Examples 1-4

[0033] As can be seen from Table 1, the flame-retardant polypropylene sheath material for cables prepared by the present invention has mechanical properties and flame-retardant properties. In Comparative Example 1, the glass fiber and aramid fiber added were not wrapped with polyphosphazene, and the mechanical properties and flame-retardant properties of the obtained sheath material both decreased, indicating that the wrapping of polyphosphazene on glass fiber and aramid fiber can improve the dispersibility in the polypropylene substrate and also improve the flame-retardant properties. In Comparative Example 2, the modified aramid fiber was not added, and the mechanical properties of the obtained sheath material decreased significantly. In Comparative Example 3, the modified glass fiber was not added, and the flame-retardant properties of the obtained sheath material decreased significantly. In Comparative Example 4, the glass fiber added was not subjected to loading and coating treatment, and the obtained sheath material had good mechanical properties but the flame-retardant properties decreased, indicating that the modification of glass fiber will affect the improvement of the mechanical properties of the pure glass fiber on the polypropylene composite material, but after adding the modified aramid fiber, the decrease in mechanical properties was improved.

[0034] The above has described in detail an embodiment of the present invention, but the above content is only a preferred embodiment of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the application of the present invention shall still fall within the scope covered by the patent of the present invention.

Claims

1. A flame retardant polypropylene sheath material for cable, characterized in that: At least the following raw materials by weight: 100 parts of polypropylene, 20-35 parts of EPDM rubber, 2-8 parts of EPDM grafted maleic anhydride, 15-22 parts of intumescent flame retardant, 10-20 parts of modified glass fiber, 10-15 parts of modified aramid fiber, 0.5-1.3 parts of inorganic filler, 1.1-1.5 parts of calcium stearate, 2-3 parts of antioxidant; Wherein, the modified glass fiber is polyphosphazene-wrapped Fe2O3 nanoparticle-glass fiber; and the modified aramid fiber is polyphosphazene-wrapped aramid fiber.

2. A flame retardant polypropylene sheath material for cable according to claim 1, characterized in that: The preparation method of the modified glass fiber comprises the following steps: The pretreated glass fiber is added into a mixed solution of Fe(NO3)3˙9H2O and urea, reacted, dried and calcined to obtain a composite glass fiber; The composite glass fiber is dispersed in ethanol, a mixed solution of 4,4'-diaminodiphenyl sulfone / triethylamine / acetonitrile is added, and then a mixed solution of hexachlorocyclotriphosphazene / acetonitrile is added, reacted and dried to obtain a modified glass fiber.

3. The flame retardant polypropylene sheath material for cable according to claim 2, characterized in that: The mass ratio of the glass fiber, the Fe(NO3)3˙9H2O and the urea is 10:0.25-0.35:0.2-0.

3.

4. The flame retardant polypropylene sheath material for cable according to claim 2, characterized in that: The addition ratio of the composite glass fiber, the 4,4'-diaminodiphenyl sulfone, the triethylamine, the hexachlorocyclotriphosphazene and the acetonitrile is 10 g: 0.2-0.6 g: 5-20 mL: 0.10-0.3 g: 230-300 mL.

5. The flame retardant polypropylene sheath material for cable according to claim 2, characterized in that: The preparation method of the modified aramid fiber comprises the following steps: The aramid fiber is pretreated and dispersed in ethanol, a mixed solution of 4,4'-diaminodiphenyl sulfone / triethylamine / acetonitrile is added, and then a mixed solution of hexachlorocyclotriphosphazene / acetonitrile is added, reacted and dried to obtain the modified aramid fiber.

6. The flame retardant polypropylene sheath material for cable according to claim 5, characterized in that: The addition ratio of the aramid fiber, the 4,4'-diaminodiphenyl sulfone, the triethylamine, the hexachlorocyclotriphosphazene and the acetonitrile is 10 g: 0.4-0.5 g: 10-15 mL: 0.15-0.22 g: 230-240 mL.

7. The flame-retardant polypropylene sheath material for cable according to claim 5, characterized in that: The aramid fiber has a length of 3-6 mm and a diameter of 12-16 μm, and the glass fiber has a length of 3-5 mm and a diameter of 10-15 μm.

8. The flame-retardant polypropylene sheath material for cable according to claim 1, characterized in that: The intumescent flame retardant is ammonium polyphosphate, pentaerythritol and melamine, and the mass ratio of the ammonium polyphosphate, the pentaerythritol and the melamine is 4-5:2-3:1-2.

9. The flame-retardant polypropylene sheath material for cable according to claim 1, characterized in that: The inorganic filler is one or a mixture of talcum powder, mica powder, kaolin, montmorillonite, and white carbon black, and the antioxidant is a mixture of antioxidant 1076 and antioxidant 168.

10. A method for preparing a flame-retardant polypropylene sheath material for a cable, characterized in that: The method comprises at least the following preparation steps: Weigh each component according to the raw material formula, first add polypropylene, EPDM rubber, and EPDM rubber grafted maleic anhydride into a high-speed mixer and mix at high speed for 20-25 minutes, then add intumescent flame retardant, modified glass fiber, modified aramid fiber, inorganic filler, calcium stearate and antioxidant and continue mixing for 20-25 minutes to obtain a mixture; The mixed material is added into a twin-screw extruder, the screw speed of the twin-screw extruder is 100-150 r / min, the processing temperature is 160-170° C., and the mixed material is cooled after extrusion granulation to obtain a flame-retardant polypropylene sheath material for cables.

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