Preparation method and application of nano flame-retardant low-smoke halogen-free polyolefin material

Abstract

The invention provides a preparation method and application of a nano flame-retardant low-smoke halogen-free polyolefin material, and belongs to the field of materials. The transition metal oxide is loaded on the graphene nanosheet, the material is subjected to carbonization reaction when meeting high temperature, a continuous, compact and stable carbonization layer is formed on the surface of a polymer, combustible gas and heat are isolated, and volatilization of pyrolysis products is reduced. The valence-state-variable metal ions can also capture free radicals generated in the combustion process, the free radical chain reaction is inhibited, and the flame retardance of the material is improved. In addition, the graphene nanosheets are large in specific surface area and high in conductivity and tensile strength, and the mechanical performance of the material can be improved by adding the graphene nanosheets into polyolefin.

Description

Technical Field

[0001] The invention belongs to the field of materials and relates to a preparation method and application of a nano flame-retardant low-smoke halogen-free polyolefin material. Technical Background

[0002] Low-smoke, halogen-free, flame-retardant polyolefins have attracted much attention worldwide, especially in the wire and cable industry, where their safety and environmental protection have been widely recognized and developed. Today, researchers have conducted in-depth research on improving the flame retardant properties of polyolefin materials, reducing smoke production and reducing the release of toxic gases.

[0003] One of the keys to preparing efficient flame-retardant materials is the selection of flame retardants. Inorganic flame retardants, especially metal hydroxides, are non-toxic, non-corrosive, and inexpensive, and have broad application prospects in the field of flame retardant materials. Metal hydroxides decompose when heated, and the non-combustible gases produced can absorb heat and dilute combustible gases and combustion-supporting gases. In addition, the active metal oxides produced by decomposition have a high specific surface area and can form a dense protective layer covering the surface of the burning matrix, delaying further combustion inside the solid phase material. Active metal oxides can also catalyze polymer carbonization and prevent heat conduction and heat radiation. However, this type of flame retardant also has certain disadvantages. Its flame retardant effect increases with the increase in the amount added, but a large amount of filling is not conducive to the mechanical properties of the product. In addition, the affinity between inorganic flame retardants and organic polymers is poor. If inorganic flame retardants are directly added in large quantities, agglomerations and stress collection points will form due to uneven particle size, resulting in interface defects in composite materials. In order to take into account both the flame retardant efficiency and mechanical properties of flame retardant materials, they can be optimized through flame retardant nano-sizing, compounding and synergy. On the one hand, nano-scale flame retardants have small particle size, large specific surface area, and excellent thermal stability. When participating in the combustion reaction, they can quickly capture free radicals in the gas phase combustion zone, inhibit free radical chain reactions, and prevent the spread of flames. In addition, during the use of nano-flame retardants, the amount of flame retardant added can be reduced to achieve the flame retardant effect of the original quality additive required, so as to maintain or even improve the physical properties of the matrix. On the other hand, a single flame retardant is often difficult to meet the high requirements in the actual flame retardant process. Compounding flame retardants can combine the advantages of two or more flame retardants, making the performance complementary and synergistically improving the flame retardant properties and physical properties of the material.

[0004] Carbon materials have excellent physical and chemical properties, and have good thermal conductivity, electrical conductivity and thermal stability. The electrolysis reaction of carbon materials at high temperatures can effectively reduce the flame temperature. In addition, carbon materials undergo carbonization when they are burned in fire. The carbonized products formed after the volatilization of elements such as hydrogen, oxygen, and nitrogen can not only isolate oxygen and heat, but also absorb and convert heat, slowing down or preventing the combustion reaction. For example, graphene nanosheets are a two-dimensional continuous crystal composed of a single layer of carbon atoms, with a large specific surface area, high electrical conductivity and tensile strength. Adding it to polyolefins can improve the material's fire resistance and mechanical properties. Summary of the Invention

[0005] In order to optimize the flame retardancy of low-smoke halogen-free materials, reduce the material preparation cost, and improve the mechanical properties and environmental performance of flame-retardant polyolefins, the first object of the present invention is to provide a nano flame-retardant low-smoke halogen-free polyolefin material, and the raw material composition of the nano flame-retardant low-smoke halogen-free polyolefin material is as follows:

[0006] 55 - 70 parts of EVA;

[0007] 15 - 25 parts of PE;

[0008] 5 - 10 parts of elastomer;

[0009] 5 - 10 parts of compatibilizer;

[0010] 150 - 180 parts of flame retardant;

[0011] 5 - 8 parts of graphene-supported transition metal oxide composite;

[0012] 4 - 8 parts of lubricant;

[0013] 0.5 - 2 parts of antioxidant;

[0014] 1 - 2 parts of coupling agent;

[0015] The preparation method of the graphene-supported transition metal oxide composite is to mix a transition metal salt, graphene powder, and an 80% ethanol solution according to a mass ratio of (0.2 - 2):(0.8 - 8):100, perform solvothermal treatment at 180 - 200 °C, centrifuge, wash, and dry, and then place it in an inert atmosphere for high-temperature calcination at 600 - 800 °C.

[0016] Transition metal oxides have rich and adjustable surface functional groups, can accept electron pairs to form coordination bonds, and polymers with negatively charged groups can pair with them. During high-temperature combustion, they can catalyze esterification crosslinking to form carbon, forming a continuous, dense, and stable carbonized layer on the polymer surface, reducing the volatilization of pyrolysis products and reducing the generation of combustible gases. Metal ions with variable valence states can also capture free radicals generated during combustion, inhibit free radical chain reactions, and improve the flame retardancy of the material.

[0017] In addition, the boiling point of organic solvents is relatively low. The reaction system is above the critical substance concentration and critical pressure, and comprehensively has the dissolution characteristics of liquids and the transfer characteristics of gases. Based on the above principles, the solvothermal method uses organic solvents to surround the reactants to form uniformly dispersed reaction groups, which helps to obtain transition metal oxides with good crystal forms and uniform sizes. High-temperature calcination can tightly load high-purity transition metal oxides with a uniform particle size distribution onto graphene nanosheets to form a composite material, and then compound it synergistically with inorganic flame retardants, which can not only reduce the usage amount of traditional hydroxides, but also help the uniform dispersion of flame retardants in the material, comprehensively improving the flame retardancy and mechanical properties of the material.

[0018] In one embodiment, the PE is metallocene linear low-density polyethylene mLLDPE, and its melt index is 0.5 - 20 g / 10 min;

[0019] The elastomer is POE, that is, a copolymer of ethylene and α-olefin, and its melt index is 0.5 - 10 g / 10 min;

[0020] The compatibilizer is polyethylene-grafted maleic anhydride PE-g-MAH, wherein the melt index of polyethylene PE is 0.5 - 20 g / 10 min.

[0021] In one embodiment, the flame retardant is a mixture of aluminum hydroxide and magnesium hydroxide with a mass ratio of 4:1, and the particle size D50 is 1 - 2 μm;

[0022] The lubricant is a mixture of polyethylene wax and silicone masterbatch with a mass ratio of (1 - 5):(2 - 10);

[0023] The antioxidant is a mixture of pentaerythritol ester antioxidant 1010 and phosphate ester antioxidant 168 with a mass ratio of 1:1;

[0024] The coupling agent is at least one of chromium complexes, silanes, and titanates.

[0025] In one embodiment, the specific method of centrifugal water washing and drying is to place the sample in a high-speed centrifuge, centrifuge at a speed of 5000 rpm for 10 min, rinse with deionized water repeatedly for 3 times, and dry at 80 °C.

[0026] In one embodiment, the conditions for high-temperature calcination under an inert atmosphere are heating at a heating rate of 2 - 10 °C / min under a nitrogen atmosphere and carbonizing for 2 - 4 h.

[0027] The second object of the present invention is to provide a preparation method of a nano flame-retardant low-smoke halogen-free polyolefin material, and the preparation method is as follows: drying all raw materials in an oven at 80 °C, and then placing them in a mixer to mix evenly to obtain a compound nano flame-retardant polyolefin copolymer. Transfer the copolymer to a two-roll mill to initially press it into a sheet, and then hot-press it into a sheet through a flat vulcanizer. After cooling to room temperature, a compound nano flame-retardant low-smoke halogen-free polyolefin material is obtained.

[0028] In one embodiment, the processing temperature of the mixer is 130-150 °C, the rotation speed is 40 rpm, and the mixing processing time is 15-25 min.

[0029] In one embodiment, the temperature of the two-roll mill is 135-140 °C.

[0030] In one embodiment, the sheet pressing temperature of the flat vulcanizer is 180-200 °C, and the sheet pressing time is 15-20 min.

[0031] The third object of the present invention is to provide the application of the above nano flame-retardant low-smoke halogen-free polyolefin material or the nano flame-retardant low-smoke halogen-free polyolefin material prepared by the above method in the field of wire and cable.

[0032] Beneficial effects:

[0033] The present invention uses an efficient solvothermal method combined with high-temperature calcination to prepare a transition metal oxide with high purity and stable crystal form, and then tightly load it on graphene nanosheets. When the prepared composite material encounters high temperature, the material undergoes a carbonization reaction, forming a continuous, dense and stable carbonized layer on the surface of the polymer, isolating combustible gas and heat, and reducing the volatilization of pyrolysis products. The metal ions with variable valence states can also capture free radicals generated during combustion, inhibit the free radical chain reaction, and improve the flame retardancy of the material. In addition, graphene nanosheets have a large specific surface area, high conductivity and tensile strength. Adding them to polyolefins can improve the mechanical properties of the material.

[0034] The present invention compounded nano-scale flame retardants to promote the performance complementarity between different flame retardants. During use, the addition amount of the flame retardant can be reduced to achieve the flame retardant effect of the original required quality additives, and the flame retardant performance and mechanical properties of the material can be synergistically improved.

[0035] The present invention has a simple formula and is easy to implement. It provides a preparation method of a compound nano flame-retardant low-smoke halogen-free polyolefin material, which helps to optimize the flame retardant effect of the low-smoke halogen-free material, reduce the material preparation cost, improve the mechanical properties and environmental protection performance of the flame-retardant polyolefin. Specific embodiments

[0036] It should be noted that the raw materials used in the present invention are all ordinary commercially available products, and no specific limitation is made on their sources.

[0037] Example 1

[0038] Weigh cobalt nitrate, graphene powder and 80% ethanol solution according to the mass ratio of 1:4:100. After mixing, place them at 180 °C and carry out high-temperature solvothermal reaction for 18 h. Place the mixture in a high-speed centrifuge and centrifuge at a speed of 5000 rpm for 10 min. Rinse it repeatedly with deionized water for 3 times and dry it at 80 °C. Immediately heat the prepared powder to 800 °C at a heating rate of 5 °C / min in a nitrogen atmosphere and carbonize it for 2 h to obtain a nano-composite material of cobalt oxide supported on graphene.

[0039] This example provides a compound nano-flame-retardant low-smoke and halogen-free polyolefin material. By weight, the material formula includes 62 parts of EVA, 20 parts of mLLDPE, 8 parts of POE, 8 parts of PE-g-MAH, 170 parts of a flame retardant (a mixture of aluminum hydroxide and magnesium hydroxide with a mass ratio of 4:1), 8 parts of the nano-composite material of cobalt oxide supported on graphene, 6 parts of a lubricant (a mixture of polyethylene wax and silicone masterbatch with a mass ratio of 2:10), 1 part of an antioxidant (a mixture of pentaerythritol ester antioxidant 1010 and phosphate antioxidant 168 with a mass ratio of 1:1), and 1 part of a silane coupling agent (Chisso S230, Japan). Dry the above raw materials in an oven at 80 °C, then place them in a mixer and mix and knead them at 140 °C and 40 rpm for 20 min to obtain a compound nano-flame-retardant polyolefin copolymer. Transfer the copolymer to a two-roll mill at 135 °C, preliminarily press it into a sheet, and then use a flat vulcanizer to hot-press it into a sheet at 180 °C for 20 min. After cooling to room temperature, a compound nano-flame-retardant low-smoke and halogen-free polyolefin material is obtained.

[0040] Example 2

[0041] Weigh cobalt nitrate, graphene powder and 80% ethanol solution according to the mass ratio of 2:6:100. After mixing, place them at 200 °C and carry out high-temperature solvothermal reaction for 15 h. Place the mixture in a high-speed centrifuge and centrifuge at a speed of 5000 rpm for 10 min. Rinse it repeatedly with deionized water for 3 times and dry it at 80 °C. Immediately heat the prepared powder to 600 °C at a heating rate of 2 °C / min in a nitrogen atmosphere and carbonize it for 4 h to obtain a nano-composite material of cobalt oxide supported on graphene.

[0042] This embodiment provides a compounded nano flame-retardant low-smoke halogen-free polyolefin material. By weight, the material formula includes 60 parts of EVA, 25 parts of mLLDPE, 6 parts of POE, 8 parts of PE-g-MAH, 160 parts of a flame retardant (a mixture of aluminum hydroxide and magnesium hydroxide with a mass ratio of 4:1), 8 parts of a nano composite material of graphene supported cobalt oxide, 6 parts of a lubricant (a mixture of polyethylene wax and silicone masterbatch with a mass ratio of 2:10), 1 part of an antioxidant (a mixture of pentaerythritol ester antioxidant 1010 and phosphate ester antioxidant 168 with a mass ratio of 1:1), and 1 part of a silane coupling agent (Chisso S230 from Japan). The above raw materials are dried in an oven at 80°C, and then placed in a mixer and mixed and kneaded at 140°C and 40 rpm for 20 minutes to obtain a compounded nano flame-retardant polyolefin copolymer. The copolymer is transferred to a two-roll mill at 135°C and preliminarily pressed into sheets, and then formed into sheets by a flat vulcanizer at 180°C under hot pressing for 20 minutes. After cooling to room temperature, a compounded nano flame-retardant low-smoke halogen-free polyolefin material is obtained.

[0043] Example 3

[0044] Weigh cobalt carbonate, graphene powder, and 80% ethanol solution according to a mass ratio of 1:6:100, mix them, and place them at 190°C for high-temperature solvothermal reaction for 16 hours. Place the mixture in a high-speed centrifuge and centrifuge at a speed of 5000 rpm for 10 minutes, and rinse it with deionized water repeatedly for 3 times, and dry it at 80°C. Immediately, the prepared powder is heated to 800°C at a heating rate of 10°C / min in a nitrogen atmosphere and carbonized for 3 hours to obtain a nano composite material of graphene supported cobalt oxide.

[0045] This embodiment provides a compounded nano flame-retardant low-smoke halogen-free polyolefin material. By weight, the material formula includes 66 parts of EVA, 18 parts of mLLDPE, 6 parts of POE, 8 parts of PE-g-MAH, 160 parts of a flame retardant (a mixture of aluminum hydroxide and magnesium hydroxide with a mass ratio of 4:1), 6 parts of a nano composite material of graphene supported cobalt oxide, 8 parts of a lubricant (a mixture of polyethylene wax and silicone masterbatch with a mass ratio of 2:10), 1 part of an antioxidant (a mixture of pentaerythritol ester antioxidant 1010 and phosphate ester antioxidant 168 with a mass ratio of 1:1), and 1 part of a silane coupling agent (Chisso S230 from Japan). The above raw materials are dried in an oven at 80°C, and then placed in a mixer and mixed and kneaded at 130°C and 40 rpm for 25 minutes to obtain a compounded nano flame-retardant polyolefin copolymer. The copolymer is transferred to a two-roll mill at 135°C and preliminarily pressed into sheets, and then formed into sheets by a flat vulcanizer at 180°C under hot pressing for 20 minutes. After cooling to room temperature, a compounded nano flame-retardant low-smoke halogen-free polyolefin material is obtained.

[0046] Comparative Example 1

[0047] This comparative example provides a flame-retardant low-smoke halogen-free polyolefin material containing graphene. By weight, the material formula includes 62 parts of EVA, 20 parts of mLLDPE, 8 parts of POE, 8 parts of PE-g-MAH, 160 parts of a flame retardant (a mixture of aluminum hydroxide and magnesium hydroxide with a mass ratio of 4:1), 6 parts of graphene powder, 6 parts of a lubricant (a mixture of polyethylene wax and silicone masterbatch with a mass ratio of 2:10), 1 part of an antioxidant (a mixture of pentaerythritol ester antioxidant 1010 and phosphate ester antioxidant 168 with a mass ratio of 1:1), and 1 part of a silane coupling agent (Chisso S230, Japan). The above raw materials are dried in an 80°C oven and then placed in a mixer at 140°C and 40 rpm for 20 minutes of mixing and kneading to obtain a compounded nano flame-retardant polyolefin copolymer. The copolymer is transferred to a two-roll mill at 135°C for preliminary sheet pressing, and then hot-pressed into sheets at 180°C for 20 minutes using a flat vulcanizer. After cooling to room temperature, a compounded nano flame-retardant low-smoke halogen-free polyolefin material is obtained.

[0048] Comparative Example 2

[0049] Weigh cobalt nitrate and 80% ethanol solution according to a mass ratio of 1:20, mix them and place them at 180°C for 18 hours of high-temperature solvothermal reaction. Place the mixture in a high-speed centrifuge and centrifuge at 5000 rpm for 10 minutes, and rinse it with deionized water three times repeatedly, then dry it at 80°C. Immediately heat the prepared powder to 800°C at a heating rate of 5°C / min in a nitrogen atmosphere and carbonize it for 2 hours to obtain cobalt oxide nanoparticles.

[0050] This comparative example provides a flame-retardant low-smoke halogen-free polyolefin material containing cobalt oxide nanoparticles. By weight, the material formula includes 62 parts of EVA, 20 parts of mLLDPE, 8 parts of POE, 8 parts of PE-g-MAH, 160 parts of a flame retardant (a mixture of aluminum hydroxide and magnesium hydroxide with a mass ratio of 4:1), 6 parts of cobalt oxide nanoparticles, 6 parts of a lubricant (a mixture of polyethylene wax and silicone masterbatch with a mass ratio of 2:10), 1 part of an antioxidant (a mixture of pentaerythritol ester antioxidant 1010 and phosphate ester antioxidant 168 with a mass ratio of 1:1), and 1 part of a silane coupling agent (Chisso S230, Japan). The above raw materials are dried in an 80°C oven and then placed in a mixer at 140°C and 40 rpm for 20 minutes of mixing and kneading to obtain a compounded nano flame-retardant polyolefin copolymer. The copolymer is transferred to a two-roll mill at 135°C for preliminary sheet pressing, and then hot-pressed into sheets at 180°C for 20 minutes using a flat vulcanizer. After cooling to room temperature, a compounded nano flame-retardant low-smoke halogen-free polyolefin material is obtained.

[0051] Comparative Example 3

[0052] This comparative example provides a flame-retardant low-smoke halogen-free polyolefin material. By weight, the material formula includes 62 parts of EVA, 20 parts of mLLDPE, 8 parts of POE, 8 parts of PE-g-MAH, 160 parts of a flame retardant (a mixture of aluminum hydroxide and magnesium hydroxide with a mass ratio of 4:1), 6 parts of a lubricant (a mixture of polyethylene wax and silicone masterbatch with a mass ratio of 2:10), 1 part of an antioxidant (a mixture of pentaerythritol ester antioxidant 1010 and phosphate ester antioxidant 168 with a mass ratio of 1:1), and 1 part of a silane coupling agent (Chisso S230 from Japan). The above raw materials are dried in an 80°C oven and then placed in a mixer and mixed and kneaded at 140°C and 40 rpm for 20 minutes to obtain a compounded nano flame-retardant polyolefin copolymer. The copolymer is transferred to a two-roll mill at 135°C and preliminarily pressed into sheets, and then formed into sheets by a flat vulcanizer at 180°C and hot-pressed for 20 minutes. After cooling to room temperature, a compounded nano flame-retardant low-smoke halogen-free polyolefin material is obtained.

[0053] Comparative Example 4

[0054] Weigh cobalt nitrate, graphene powder, and deionized water according to a mass ratio of 1:4:100. After mixing at 60°C and 300 rpm using a magnetic stirrer and drying at 80°C, a nano composite material of graphene-supported cobalt oxide prepared by a one-step method is obtained.

[0055] This example provides a compounded nano flame-retardant low-smoke halogen-free polyolefin material. By weight, the material formula includes 62 parts of EVA, 20 parts of mLLDPE, 8 parts of POE, 8 parts of PE-g-MAH, 170 parts of a flame retardant (a mixture of aluminum hydroxide and magnesium hydroxide with a mass ratio of 4:1), 8 parts of a nano composite material of one-step graphene-supported cobalt oxide, 6 parts of a lubricant (a mixture of polyethylene wax and silicone masterbatch with a mass ratio of 2:10), 1 part of an antioxidant (a mixture of pentaerythritol ester antioxidant 1010 and phosphate ester antioxidant 168 with a mass ratio of 1:1), and 1 part of a silane coupling agent (Chisso S230 from Japan). The above raw materials are dried in an 80°C oven and then placed in a mixer and mixed and kneaded at 140°C and 40 rpm for 20 minutes to obtain a compounded nano flame-retardant polyolefin copolymer. The copolymer is transferred to a two-roll mill at 135°C and preliminarily pressed into sheets, and then formed into sheets by a flat vulcanizer at 180°C and hot-pressed for 20 minutes. After cooling to room temperature, a compounded nano flame-retardant low-smoke halogen-free polyolefin material is obtained.

[0056] The mechanical properties and flame retardancy of Examples 1 - 3 and Comparative Examples 1 - 4 were tested according to national standards. As shown in Tables 1 - 2, Table 1 shows the mechanical property test results, and Table 2 shows the flame retardancy test results.

[0057] Table 1 Mechanical Property Results of Examples 1 - 3 and Comparative Examples 1 - 3

[0058] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Tensile strength / MPa 14.5 14.1 13.9 12.6 11.4 10.5 11.0 Elongation at break / % 220 200 200 190 180 170 180

[0059] Table 2 Flame Retardant Performance Results of Examples 1-3 and Comparative Examples 1-3

[0060]

[0061] It can be found through the comparison between the examples and the comparative examples that, compared with the polyolefin materials containing only aluminum hydroxide and magnesium hydroxide, when cobalt oxide nanoparticles or graphene powder are applied to flame-retardant polyolefins, both the mechanical strength and the flame-retardant performance of the materials are improved. Especially for the graphene-supported cobalt oxide nanocomposite prepared by the solvothermal method combined with high-temperature calcination, after being compounded with traditional flame retardants, the mechanical properties of the examples are better, the oxygen index is increased, the smoke density, the maximum heat release rate and the total heat release are significantly reduced, and the ignition time of the materials is prolonged. This shows that loading transition metal oxides on graphene nanosheets can not only improve the mechanical properties of the materials, but also produce an efficient synergistic flame-retardant effect with aluminum hydroxide and magnesium hydroxide, and can more effectively improve the charring behavior in the condensed phase during combustion, thus improving the flame-retardant and smoke-suppressing performance of the materials.

[0062] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A nano flame-retardant low-smoke halogen-free polyolefin material, characterized in that The raw material composition of the nano flame-retardant low-smoke halogen-free polyolefin material is as follows: 55 - 70 parts of EVA; 15 - 25 parts of PE; 5 - 10 parts of elastomer; 5 - 10 parts of compatibilizer; 150 - 180 parts of flame retardant; 5 - 8 parts of graphene-supported transition metal oxide composite; 4 - 8 parts of lubricant; 0.5 - 2 parts of antioxidant; 1 - 2 parts of coupling agent; The preparation method of the graphene-supported transition metal oxide composite is to mix transition metal salt, graphene powder, and 80% ethanol solution according to the mass ratio of (0.2 - 2):(0.8 - 8):100, perform solvothermal treatment at 180 - 200 °C, centrifuge, wash with water, and dry, and then place it in an inert atmosphere for high-temperature calcination at 600 - 800 °C.

2. The nano flame-retardant low-smoke halogen-free polyolefin material according to claim 1, wherein The PE is metallocene linear low-density polyethylene mLLDPE, and its melt index is 0.5 - 20 g / 10 min; The elastomer is POE, that is, a copolymer of ethylene and α-olefin, and its melt index is 0.5 - 10 g / 10 min; The compatibilizer is polyethylene grafted with maleic anhydride PE-g-MAH. Among them, the melt index of polyethylene PE is 0.5 - 20 g / 10 min.

3. A nano flame-retardant low-smoke halogen-free polyolefin material according to claim 1, characterized in that, The flame retardant is a mixture of aluminum hydroxide and magnesium hydroxide with a mass ratio of 4:1, and the particle size D50 is 1 - 2 μm; The lubricant is a mixture of polyethylene wax and silicone masterbatch with a mass ratio of (1 - 5):(2 - 10); The antioxidant is a mixture of pentaerythritol ester antioxidant 1010 and phosphate antioxidant 168 with a mass ratio of 1:1; The coupling agent is at least one of chromium complexes, silanes, and titanates.

4. A nano flame retardant low-smoke halogen-free polyolefin material according to claim 1, characterized in that, The specific method of centrifuging, washing with water, and drying is to place the sample in a high-speed centrifuge, centrifuge at a speed of 5000 rpm for 10 min, rinse with deionized water 3 times repeatedly, and dry at 80 °C.

5. A nano flame-retardant low-smoke halogen-free polyolefin material according to claim 1, characterized in that, The conditions for high-temperature calcination in an inert atmosphere are in a nitrogen atmosphere, with a heating rate of 2 - 10 °C / min for heating and carbonization for 2 - 4 h.

6. The preparation method of any one of the nano flame-retardant low-smoke halogen-free polyolefin materials according to claims 1-5, characterized in that, The preparation method is as follows: Dry all raw materials in an 80 °C oven, then place them in a mixer to mix evenly to obtain a compound nano flame-retardant polyolefin copolymer. Transfer the copolymer to a two-roll mill to be preliminarily pressed into sheets, and then hot-press into sheets through a flat vulcanizer. After cooling to room temperature, a compound nano flame-retardant low-smoke halogen-free polyolefin material is obtained.

7. The preparation method of a nano flame-retardant low-smoke halogen-free polyolefin material according to claim 6, characterized in that, The processing temperature of the mixer is 130 - 150 °C, the rotation speed is 40 rpm, and the mixing processing time is 15 - 25 min.

8. The preparation method of a nano flame-retardant low-smoke halogen-free polyolefin material according to claim 6, characterized in that, The temperature of the two-roll mill is 135 - 140 °C.

9. The preparation method of a nano flame-retardant low-smoke halogen-free polyolefin material according to claim 6, characterized in that, The sheet pressing temperature of the flat vulcanizer is 180 - 200 °C, and the sheet pressing time is 15 - 20 min.

10. Application of a nano flame-retardant low-smoke halogen-free polyolefin material as described in any one of claims 1 - 5 or a nano flame-retardant low-smoke halogen-free polyolefin material prepared by the method as described in any one of claims 6 - 9 in the field of wire and cable.

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