A flame-retardant polypropylene sheath material for cables and its preparation method

Abstract

The present invention discloses a flame-retardant polypropylene sheath material for cables and a preparation method thereof, which relates to the technical field of cable sheath materials. The flame-retardant polypropylene sheath material for cables of the present invention comprises 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, and 2-3 parts of antioxidant; wherein, the modified glass fiber is polyphosphazene-coated Fe2O3 nanoparticle-glass fiber; and the modified aramid fiber is polyphosphazene-coated aramid fiber. The flame-retardant polypropylene sheath material for cables prepared by the present invention has the advantages of good mechanical properties, excellent flame retardant properties, 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 being an essential component in the structure of power cables. Power cables of 15 kV and above generally have a conductor shielding layer and an insulating shielding layer. The function of the outer sheath protection 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 unsatisfactory, and the comprehensive functions are relatively poor.

[0003] Polypropylene has the following advantages: It is the resin with the lowest density among all general-purpose plastics, and its products are lightweight; it has excellent heat resistance and can be continuously used at a temperature of 120 °C without easy softening, being the cheapest high-temperature general-purpose plastic; it has excellent physical and mechanical properties such as tensile and impact properties, with 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, and the surface of its products is not easily worn and scratched; it is not easily water-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. Currently, 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 application 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:

[0005] When existing polypropylene composites are used as cable sheath materials, there are problems of poor flame retardancy and low flame retardant performance.

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

[0007] A flame-retardant polypropylene sheath material for cables, comprising at least the following raw materials in parts by mass:

[0008] 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;

[0009] Among them, the modified glass fiber is polyphosphazene-coated Fe2O3 nanoparticles - glass fiber; the modified aramid fiber is polyphosphazene-coated aramid fiber.

[0010] As a further scheme of the present invention: The preparation method of the modified glass fiber includes the following steps:

[0011] Add the pretreated glass fiber into the mixed solution of Fe(NO3)3·9H2O and urea, react, dry, and calcine to obtain composite glass fiber;

[0012] Disperse the composite glass fiber in ethanol, add 4,4'-diaminodiphenyl sulfone / triethylamine / acetonitrile mixed solution, and then add hexachlorocyclotriphosphazene / acetonitrile mixed solution, react and dry to obtain modified glass fiber.

[0013] As a further scheme of the present invention: 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.

[0014] As a further scheme 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.

[0015] As a further scheme of the present invention: The preparation method of the modified aramid fiber includes the following steps:

[0016] Pretreat the aramid fiber and disperse it in ethanol, add 4,4'-diaminodiphenyl sulfone / triethylamine / acetonitrile mixed solution, and then add hexachlorocyclotriphosphazene / acetonitrile mixed solution, react and dry to obtain modified aramid fiber.

[0017] As a further scheme of the present invention: The addition ratio of the aramid fiber, the 4,4'-diaminodiphenyl sulfone, the triethylamine, the hexachlorocyclotriphosphazene, and the acetonitrile is 10g:0.4 - 0.5g:10 - 15mL:0.15 - 0.22g:230 - 240mL.

[0018] As a further solution of the present invention: the length of the aramid fiber is 3-6 mm, the diameter is 12-16 μm, the length of the glass fiber is 3-5 mm, and the diameter is 10-15 μm.

[0019] As a further solution of the present invention: the intumescent flame retardant is ammonium polyphosphate, pentaerythritol and melamine, and the mass ratio of ammonium polyphosphate, pentaerythritol and melamine is 4-5:2-3:1-2.

[0020] As a further solution of the present invention: the inorganic filler is one or a mixture of talc powder, mica powder, kaolin, montmorillonite, white carbon black, and the antioxidant is a mixture of antioxidant 1076 and antioxidant 168.

[0021] A preparation method of a flame-retardant polypropylene sheath material for cables comprises at least the following preparation steps:

[0022] Weigh each component according to the raw material formula. First, add polypropylene, ethylene propylene diene monomer (EPDM), and EPDM grafted 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 mixed material.

[0023] Add the mixed material 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. After extrusion granulation and cooling, a flame-retardant polypropylene sheath material for cables is obtained.

[0024] The beneficial effects of the present invention:

[0025] The flame-retardant polypropylene sheath material for cables provided by the present invention is made of polypropylene and ethylene propylene diene monomer (EPDM) as resin raw materials, and is reacted by adding a compatibilizer, an intumescent flame retardant, an antioxidant, a lubricant, an inorganic filler, a modified glass fiber, and a modified aramid fiber. Adding EPDM toughens polypropylene, greatly improving the low-temperature impact strength of polypropylene while retaining the rigidity of polypropylene, achieving the purpose of toughening. EPDM grafted 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 the 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". The addition of the modified aramid fiber to the system improves the reduction of mechanical strength caused by the addition of EPDM and the modified glass fiber, and at the same time improves the aging resistance of the composite material. In the present invention, using the polypropylene composite material as the sheath material of the cable, the obtained cable has the advantages of high strength, good mechanical properties, excellent flame retardant performance and long service life.

[0026] In the present invention, the modified glass fiber is a composite material of polyphosphazene-coated Fe2O3 nanoparticles and glass fiber. The addition of glass fiber can improve the tensile strength and flexural strength of the polypropylene composite material. Although the modification of glass fiber reduces the improvement of the mechanical properties of the composite material, it greatly improves the flame retardancy of the composite material. The Fe2O3 nanoparticles loaded on the glass fiber can be used as a catalytic charring agent to improve the flame retardancy of the flame-retardant polypropylene sheath material. Growing Fe2O3 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 small molecules containing phosphorus and nitrogen and non-combustible 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 retardancy 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 barrier, so that the flame-retardant outer sheath has excellent flame retardant effect.

[0027] The present invention also uses polyphosphazene to wrap and modify the composite material of Fe2O3 nanoparticles and glass fiber, as well as aramid fiber. Due to its high cross-linking density, polyphosphazene can form a stable three-dimensional network structure, which not only endows the material with excellent mechanical strength and heat resistance stability, but also because of its high content of phosphorus and nitrogen elements, these two elements themselves are highly efficient flame retardant elements, which can effectively inhibit the free radical chain reaction during the combustion process and further improve the flame retardancy. Aramid fiber itself has very high strength and modulus, plays 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 fiber has 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 the 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. Specific embodiments

[0028] 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 the 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.

[0029] Example 1 The preparation method of the modified glass fiber includes the following steps:

[0030] Put 100 g of glass fiber into a high-temperature muffle furnace, calcine it 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 it 3 times with distilled water, and place it in an 80 °C oven until completely dry to obtain pretreated glass fiber;

[0031] Add 2.5 g of Fe(NO3)3·9H2O and 2.2 g of urea to 500 mL of deionized water and mix evenly. Add the above pretreated glass fiber and place it in a high-pressure reaction kettle. Then slowly pour the above-prepared solution into the high-pressure reaction kettle, react fully in an 80 °C oven for 4 h, wash it after cooling, and then place it in an 80 °C oven for 12 h, and calcine it in a high-temperature muffle furnace at 350 °C for 2 h to obtain composite glass fiber.

[0032] Disperse 100 g of the above 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 and drop it into the above suspension, and react at 50 °C for 6 h. After the reaction is completed, wash and dry to obtain modified glass fiber.

[0033] Example 2 The preparation method of the modified glass fiber includes the following steps:

[0034] Put 100 g of glass fiber into a high-temperature muffle furnace, calcine it 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 it 3 times with distilled water, and place it in an 80 °C oven until completely dry to obtain pretreated glass fiber;

[0035] Add 3.2 g of Fe(NO3)3·9H2O and 2.9 g of urea to 500 mL of deionized water and mix evenly. Add the above pretreated glass fiber and place it in a high-pressure reaction kettle. Then slowly pour the above-prepared solution into the high-pressure reaction kettle, react fully in an 80 °C oven for 4 h, wash it after cooling, and then place it in an 80 °C oven for 12 h, and calcine it in a high-temperature muffle furnace at 350 °C for 2 h to obtain composite glass fiber.

[0036] Disperse 100 g of the above 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 and drop it into the above suspension, and react at 50 °C for 6 h. After the reaction is completed, wash and dry to obtain modified glass fiber.

[0037] Example 3 The preparation method of the modified aramid fiber comprises the following steps:

[0038] Soak 100 g of aramid fiber in a 0.5% sodium hydroxide solution for 1 h, then soak it in an acetone solution for 12 h. After washing and drying, the surface-treated aramid fiber is obtained;

[0039] Disperse the surface-treated glass fiber mentioned above in 1500 ml of ethanol solution, add 4 g of 4,4'-diaminodiphenyl sulfone, 100 ml of triethylamine and 1500 ml of acetonitrile, and ultrasonically disperse for 0.5 h to form a suspension. Dissolve 2 g of hexachlorocyclotriphosphazene in 90 ml of acetonitrile and drop it into the above suspension, and react at 50 °C for 6 h. After the reaction is completed, wash and dry to obtain the modified aramid fiber.

[0040] Example 4 A flame-retardant polypropylene sheath material for cables and its preparation method are made by the following method:

[0041] Add 100 parts by mass of polypropylene, 25 parts by mass of ethylene-propylene-diene monomer rubber, and 5 parts by mass of ethylene-propylene-diene monomer rubber grafted with maleic anhydride to 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 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 mixture;

[0042] Add the mixture to 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.

[0043] Example 5 A flame-retardant polypropylene sheath material for cables and its preparation method are made by the following method:

[0044] Add 100 parts by mass of polypropylene, 25 parts by mass of ethylene-propylene-diene monomer rubber, and 5 parts by mass of ethylene-propylene-diene monomer rubber grafted with maleic anhydride to 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 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 mixture;

[0045] 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.

[0046] Example 6 A flame-retardant polypropylene sheath material for cables and its preparation method are made by the following method:

[0047] 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 mixture.

[0048] 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.

[0049] Example 7 A flame-retardant polypropylene sheath material for cables and its preparation method are made by the following method:

[0050] 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 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 mixture.

[0051] 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.

[0052] Comparative Example 1 Compared with Example 4, in Comparative Example 1, the modified glass fiber prepared in Example 1 was replaced with the composite glass fiber prepared in Example 1 in equal mass, and the modified aramid fiber prepared in Example 3 was replaced with the untreated aramid fiber in equal mass. The remaining components and preparation method were exactly the same as those in Example 4.

[0053] Comparative Example 2 Compared with Example 4, in Comparative Example 2, the modified glass fiber prepared in Example 1 was not added, and the other components and preparation method were exactly the same as those in Example 4.

[0054] Comparative Example 3 Compared with Example 4, in Comparative Example 3, the modified aramid fiber prepared in Example 3 was not added, and the other components and preparation method were exactly the same as those in Example 4.

[0055] Comparative Example 4 Compared with Example 4, in Comparative Example 4, the modified glass fiber prepared in Example 1 was replaced with untreated glass fiber of equal mass, and the other components and preparation method were exactly the same as those in Example 4.

[0056] Performance Testing

[0057] Tensile property: The tensile strength was tested according to the method of GB / T 1040.1. Using injection-molded dumbbell-shaped tensile standard specimens, the tensile speed was set at 50 mm·min -1 , and the test was carried out under the constant temperature condition of 23°C; the test results are shown in Table 1;

[0058] Flexural property: 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°C; the test results are shown in Table 1;

[0059] Impact property: The cantilever beam impact strength was tested according to the method of GB / T 1843-2008. Using injection-molded long-strip standard specimens, and a V-notch was made with a notch maker within 4 h after injection molding. A pendulum with an appropriate energy was selected, and the test was carried out under the constant temperature condition of 23°C; the test results are shown in Table 1;

[0060] 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, by observing its combustion characteristics, a series of experiments were carried out at different oxygen concentrations to estimate the lowest oxygen concentration, that is, the limiting oxygen index. The experiment was carried out under the constant temperature condition of 23°C. 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

[0061] 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, its combustion behavior was evaluated by measuring the afterflame and afterglow time, range, and particle dripping. 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;

[0062] Table 1: Statistical table of performance test data of polypropylene sheath materials in Examples 4-7 and Comparative Examples 1-4

[0063]

[0064] As can be seen from Table 1, the flame-retardant polypropylene sheath material 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 enhance the flame-retardant property. 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 property 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 property decreased, indicating that the modification of glass fiber would 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 situation of the decrease in mechanical properties was improved.

[0065] The above has described in detail an embodiment of the present invention, but the content described 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 should still fall within the scope covered by the patent of the present invention.

Claims

1. A flame-retardant polypropylene sheath material for cables, characterized in that, 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 - coated Fe2O3 nanoparticle - glass fiber; the modified aramid fiber is polyphosphazene - coated aramid fiber.

2. The flame retardant polypropylene sheath material for cables according to claim 1, characterized in that, The preparation method of the modified glass fiber comprises the following steps: Adding the pretreated glass fiber into a mixed solution of Fe(NO3)3·9H2O 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 the modified glass fiber.

3. The flame-retardant polypropylene sheath material for cables 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 cables according to claim 2, characterized in that, The preparation method of the modified aramid fiber comprises the following steps: Pretreating 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 the modified aramid fiber.

5. A flame-retardant polypropylene sheath material for cables according to claim 4, characterized in that, The length of the aramid fiber is 3 - 6 mm, and the diameter is 12 - 16 μm; the length of the glass fiber is 3 - 5 mm, and the diameter is 10 - 15 μm.

6. The flame-retardant polypropylene sheath material for cables according to claim 1, wherein, 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.

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

8. A method for preparing a flame-retardant polypropylene sheath material for cables as described in any one of claims 1-7, characterized in that, At least comprising the following preparation steps: Weighing each component according to the raw material formula. First, adding polypropylene, EPDM, and EPDM grafted maleic anhydride into a high - speed mixer and mixing at high speed for 20 - 25 min. Then, adding the intumescent flame retardant, modified glass fiber, modified aramid fiber, inorganic filler, calcium stearate, and antioxidant and continuing to mix for 20 - 25 min to obtain a mixture; Adding the mixture into a twin - screw extruder, with the screw speed of the twin - screw extruder being 100 - 150 r / min and the processing temperature being 160 - 170 °C, extruding and pelletizing, and then cooling to obtain the flame - retardant polypropylene sheath material for cables.

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