A modified magnesium hydroxide flame retardant and its preparation method and application

Abstract

The present invention provides a modified magnesium hydroxide flame retardant, a preparation method and application thereof, and relates to the technical field of flame retardant materials. The modified magnesium hydroxide flame retardant provided by the present invention comprises magnesium hydroxide and silicon dioxide coated on the surface of the magnesium hydroxide. Compared with magnesium hydroxide, the modified magnesium hydroxide flame retardant provided by the present invention has good flame retardant effect and high flame retardant efficiency. In the process of preparing polymer flame retardant composite materials, the amount added to the polymer material can be reduced, thereby ensuring the good physical and mechanical properties of the polymer material. The present invention provides a preparation method for the modified magnesium hydroxide flame retardant described in the above technical scheme. The preparation method provided by the present invention can ensure the uniform coating of silicon dioxide on the surface of magnesium hydroxide, improve the compatibility of the flame retardant in the polymer substrate, and thereby improve the comprehensive performance of the polymer flame retardant composite material; and the preparation method provided by the present invention is simple to operate, low in cost, and easy to mass produce.

Description

Technical Field

[0001] The invention relates to the technical field of flame retardant materials, and in particular to a modified magnesium hydroxide flame retardant and a preparation method and application thereof. Background Art

[0002] Polymer materials are widely used, but most of them are flammable, which limits their application areas. Therefore, it is very necessary to modify them to be flame retardant. In order to avoid the rapid spread of fire, reduce the occurrence of fire, and reduce the release of toxic smoke, adding flame retardants directly to polymer materials is a common method. This method is simple, easy and economical.

[0003] Magnesium hydroxide is a classic filling flame retardant. It releases bound water when the material is thermally decomposed during combustion, absorbs a large amount of latent heat, and reduces the surface temperature of the synthetic material it fills in the flame. It has the effect of inhibiting the decomposition of polymer materials and cooling the generated combustible gases. In addition, the magnesium oxide generated by the decomposition of magnesium hydroxide is a good refractory material. Covering the surface of the burning material, it can also help improve the fire resistance of the synthetic material. At the same time, the water vapor released by magnesium hydroxide can also be used as a smoke suppressant. Therefore, magnesium hydroxide is recognized as an excellent flame retardant with the triple functions of flame retardancy, smoke suppression and filling. It is widely used in polymer materials such as rubber, plastics, unsaturated polyesters, paints, and coatings. However, as an inorganic flame retardant, magnesium hydroxide has low flame retardant efficiency. In order to ensure the flame retardant properties of polymer materials, the amount of magnesium hydroxide required will be very large, and the large amount of magnesium hydroxide added will significantly reduce the physical and mechanical properties of polymer materials. Summary of the invention

[0004] In view of this, the present invention aims to provide a modified magnesium hydroxide flame retardant and a preparation method and application thereof. The modified magnesium hydroxide flame retardant provided by the present invention can improve the flame retardant efficiency of magnesium hydroxide, reduce its addition amount in polymer materials, and improve the compatibility with polymer matrix resins.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a modified magnesium hydroxide flame retardant, comprising magnesium hydroxide and silicon dioxide coated on the surface of the magnesium hydroxide.

[0007] Preferably, the particle size of the modified magnesium hydroxide flame retardant is 0.1-3 μm; the mass ratio of magnesium hydroxide to silicon dioxide in the modified magnesium hydroxide flame retardant is 99.9-90:0.1-10.

[0008] The present invention provides a method for preparing the modified magnesium hydroxide flame retardant described in the above technical solution, comprising the following steps:

[0009] Mixing magnesium hydroxide with water to obtain magnesium hydroxide slurry;

[0010] The magnesium hydroxide slurry is mixed with sodium silicate and subjected to a first wet grinding to obtain a mixed slurry;

[0011] The mixed slurry is adjusted to a pH value of 4 to 7 and then subjected to a second wet grinding process to obtain a modified magnesium hydroxide precursor slurry;

[0012] The modified magnesium hydroxide precursor slurry is sequentially washed, solid-liquid separated and solid-phase heated and dried to obtain a modified magnesium hydroxide primary product;

[0013] The modified magnesium hydroxide primary product is mixed with a surfactant, and surface modified at 100-150° C. to obtain the modified magnesium hydroxide flame retardant.

[0014] Preferably, the particle size of the magnesium hydroxide is 0.1-10 μm; and the solid content of the magnesium hydroxide slurry is 60-80 wt %.

[0015] Preferably, the mass ratio of the sodium silicate to the magnesium hydroxide in the magnesium hydroxide slurry is 1:5 to 1:100; and the time of the first wet grinding is 1 to 3 hours.

[0016] Preferably, the reagent used to adjust the pH value is an acid reagent, and the acid reagent includes one or more of hydrochloric acid, sulfuric acid, phosphoric acid, formic acid and acetic acid; the time of the second wet grinding is 1 to 8 hours.

[0017] Preferably, the temperature of the solid phase heating drying is 100-150° C.; and the water content of the modified magnesium hydroxide primary product is less than 0.4%.

[0018] Preferably, the surfactant includes γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, aminopropylsilane hydrolyzate, γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, NN diethylaminopropyltrimethoxysilane, NN dimethylaminopropyltrimethoxysilane, N-β-(aminoethyl)-aminopropyltrimethoxysilane, One or more of N-β-(aminoethyl)-aminopropyltriethoxysilane, γ-diethylenetriaminopropylmethyldimethoxysilane, γ-diethylenetriaminopropyltrimethoxysilane, bis-(γ-trimethoxysilylpropyl)amine, bis-(γ-triethoxysilylpropyl)amine, γ-piperazinylpropylmethyldimethoxysilane, N-phenylaminomethyltriethoxysilane and γ-diethylaminomethyltriethoxysilane; the mass ratio of the surfactant to magnesium hydroxide is 1:10 to 1:1000.

[0019] Preferably, the surface modification time is 5 to 20 minutes.

[0020] The present invention provides the use of the modified magnesium hydroxide flame retardant described in the above technical solution or the modified magnesium hydroxide flame retardant prepared by the preparation method described in the above technical solution in the preparation of a polymer flame retardant composite material.

[0021] The present invention provides a modified magnesium hydroxide flame retardant, comprising magnesium hydroxide and silicon dioxide coated on the surface of the magnesium hydroxide. By coating magnesium hydroxide with silicon dioxide, the present invention can utilize the cross-linking effect of silicon element in silicon dioxide when burning to form carbon, while maintaining the flame retardant effect of magnesium hydroxide, thereby improving the thermal stability of magnesium hydroxide and the carbon forming ability of polymer materials when burning, and enhancing the strength of the carbon layer; in addition, by coating magnesium hydroxide with silicon dioxide, the difference in refractive index between silicon dioxide and magnesium hydroxide can be utilized to improve the covering power of magnesium hydroxide. Compared with magnesium hydroxide, the modified magnesium hydroxide flame retardant provided by the present invention has good flame retardant effect and high flame retardant efficiency. In the process of preparing polymer flame retardant composite materials, the amount of magnesium hydroxide added in the polymer material can be reduced, thereby ensuring the good physical and mechanical properties of the polymer material.

[0022] The present invention provides a method for preparing the modified magnesium hydroxide flame retardant described in the above technical solution. The present invention uses sodium silicate as a raw material, converts sodium silicate into silicic acid by adjusting the pH value and uniformly coats it on the surface of magnesium hydroxide, and then dehydrates it by heating and drying, thereby obtaining silicon hydroxide uniformly coated with silicon dioxide; and, the present invention performs surface modification on the magnesium hydroxide coated with silicon dioxide by a surfactant, which can reduce the agglomeration and overlap of the flame retardant particles, enhance the powder fluidity of the flame retardant particles, and improve the dispersibility of the particles in the polymer matrix. The preparation method provided by the present invention can ensure the uniform coating of silicon dioxide on the surface of magnesium hydroxide, improve the compatibility of the flame retardant in the polymer substrate, and thus enhance the comprehensive performance of the polymer flame-retardant composite material; and, the preparation method provided by the present invention is simple to operate, low in cost, and easy to scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a SEM microscopic morphology image of the modified magnesium hydroxide flame retardant prepared in Example 1. DETAILED DESCRIPTION

[0024] The present invention provides a modified magnesium hydroxide flame retardant, comprising magnesium hydroxide and silicon dioxide coated on the surface of the magnesium hydroxide. In the present invention, the particle size (D 50The particle size) is preferably 0.1 to 3 μm; the mass ratio of magnesium hydroxide to silicon dioxide in the modified magnesium hydroxide flame retardant is preferably 99.9 to 90: 0.1 to 10. The present invention coats magnesium hydroxide with silicon dioxide, while maintaining the flame retardant effect of magnesium hydroxide, can utilize the cross-linking effect of silicon element in silicon dioxide when burning to form carbon, improve the thermal stability of magnesium hydroxide and the carbonization ability of polymer materials when burning, enhance the strength of the carbon layer, and improve the flame retardant effect; in addition, by coating magnesium hydroxide with silicon dioxide, the difference in refractive index between silicon dioxide and magnesium hydroxide can be utilized to improve the covering power of magnesium hydroxide.

[0025] The present invention provides a method for preparing the modified magnesium hydroxide flame retardant described in the above technical solution, comprising the following steps:

[0026] Mixing magnesium hydroxide with water to obtain magnesium hydroxide slurry;

[0027] The magnesium hydroxide slurry is mixed with sodium silicate and subjected to a first wet grinding to obtain a mixed slurry;

[0028] The mixed slurry is adjusted to a pH value of 4 to 7 and then subjected to a second wet grinding process to obtain a modified magnesium hydroxide precursor slurry;

[0029] The modified magnesium hydroxide precursor slurry is sequentially washed, solid-liquid separated and solid-phase heated and dried to obtain a modified magnesium hydroxide primary product;

[0030] The modified magnesium hydroxide primary product is mixed with a surfactant, and surface modified at 100-150° C. to obtain the modified magnesium hydroxide flame retardant.

[0031] In the present invention, unless otherwise specified, the raw materials involved are commercially available products well known to those skilled in the art.

[0032] The present invention mixes magnesium hydroxide with water to obtain magnesium hydroxide slurry. In the present invention, the particle size of the magnesium hydroxide is preferably 0.1 to 10 μm; the present invention has no special requirements for the magnesium hydroxide, and magnesium hydroxide well known to those skilled in the art can be used. The present invention has no special requirements for the water, and water well known to those skilled in the art can be used. In the present invention, the solid content of the magnesium hydroxide slurry is preferably 60 to 80 wt%, more preferably 60 to 70 wt%.

[0033] After obtaining the magnesium hydroxide slurry, the present invention mixes the magnesium hydroxide slurry with sodium silicate for a first wet grinding to obtain a mixed slurry. In the present invention, the mass ratio of the sodium silicate to the magnesium hydroxide in the magnesium hydroxide slurry is preferably 1:5 to 1:100, more preferably 1:20 to 1:50. In the present invention, the time of the first wet grinding is preferably 1 to 3 hours, more preferably 1 to 2 hours; during the first wet grinding, the sodium silicate is coated on the surface of the magnesium hydroxide.

[0034] After obtaining the mixed slurry, the present invention adjusts the pH value of the mixed slurry to 4-7 and then performs a second wet grinding to obtain a modified magnesium hydroxide precursor slurry. In the present invention, the pH value is preferably 4-5; the reagent used to adjust the pH value is preferably an acid reagent, and the acid reagent preferably includes one or more of hydrochloric acid, sulfuric acid, phosphoric acid, formic acid and acetic acid, and more preferably hydrochloric acid. The present invention converts the sodium silicate in the mixed slurry into silicic acid by adjusting the pH value of the mixed slurry to 4-7. In the present invention, the time of the second wet grinding is preferably 1-8h, more preferably 3-5h; after the second wet grinding, a uniform silicate film is formed on the surface of the magnesium hydroxide to obtain a modified magnesium hydroxide precursor.

[0035] After obtaining the modified magnesium hydroxide precursor slurry, the present invention sequentially washes, solid-liquid separates and solid-phase heats and dries the modified magnesium hydroxide precursor slurry to obtain a modified magnesium hydroxide primary product. In the present invention, the detergent used for the washing is preferably water; the method for solid-liquid separation is preferably centrifugal separation. In the present invention, the temperature of the solid-phase heating and drying is preferably 100-150°C, more preferably 120-145°C; the present invention dehydrates the solid product after solid-liquid separation by the solid-phase heating and drying, and in the process, silicic acid is converted into silicon dioxide to form magnesium hydroxide uniformly coated with silicon dioxide, i.e., the modified magnesium hydroxide primary product. In the present invention, the moisture content of the modified magnesium hydroxide primary product dehydrated by silicate is preferably less than 0.4%, more preferably less than 0.3%.

[0036] After obtaining the modified magnesium hydroxide primary product, the present invention mixes the modified magnesium hydroxide primary product with a surfactant, performs surface modification at 100 to 150° C., and obtains the modified magnesium hydroxide flame retardant. In the present invention, the surfactant preferably includes γ-aminopropyl triethoxysilane, γ-aminopropyl trimethoxysilane, γ-aminopropyl methyl diethoxysilane, aminopropyl silane hydrolyzate, γ-aminopropyl methyl dimethoxysilane, N-phenyl-γ-aminopropyl trimethoxysilane, N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxysilane, NN diethylaminopropyl trimethoxysilane, NN dimethylaminopropyl trimethoxysilane, N-β-(aminoethyl)-aminopropyl trimethoxysilane, N-β-(aminoethyl)- One or more of aminopropyl triethoxysilane, γ-diethylene triaminopropyl methyl dimethoxysilane, γ-diethylene triaminopropyl trimethoxysilane, bis-(γ-trimethoxysilyl propyl) amine, bis-(γ-triethoxysilyl propyl) amine, γ-piperazine propyl methyl dimethoxysilane, N-phenylaminomethyl triethoxysilane and γ-diethylaminomethyl triethoxysilane, more preferably γ-aminopropyl trimethoxysilane, NN diethylaminopropyl trimethoxysilane and N-phenylaminomethyl triethoxysilane. One or more. In the present invention, the mass ratio of the surfactant to magnesium hydroxide is preferably 1:10 to 1:1000, more preferably 0.5:100 to 3:100, and further preferably 1:100 to 3:100. In the present invention, the mixing method is preferably high-speed dispersion, and the rate of the high-speed dispersion is preferably 300 to 2000rpm. In the present invention, the temperature of the surface modification is 100-150°C, preferably 120-145°C, and more preferably 130-140°C. At the temperature, the surfactant reacts chemically with the surface of the modified magnesium hydroxide primary product, thereby anchoring the surfactant on the particle surface; the surface modification time is preferably 5-20 minutes, more preferably 8-12 minutes, and further preferably 10 minutes. The present invention uses a surfactant to modify the surface of the magnesium hydroxide coated with silicon dioxide, which can reduce the agglomeration and overlap of the flame retardant particles, enhance the powder fluidity of the flame retardant particles, and improve the dispersibility of the particles.

[0037] The present invention provides the use of the modified magnesium hydroxide flame retardant described in the above technical solution or the modified magnesium hydroxide flame retardant prepared by the preparation method described in the above technical solution in the preparation of polymer flame-retardant composite materials. In the present invention, the polymer matrix in the polymer flame-retardant composite material is preferably polyethylene, polypropylene, polyvinyl chloride, polystyrene, nylon, polyester, epoxy resin or phenolic resin; the amount of the modified magnesium hydroxide flame retardant added to the polymer flame-retardant composite material is preferably 20-60wt%, more preferably 30-40%, which is 5-10wt% lower than the amount of magnesium hydroxide added. The present invention has no special requirements for the application method of the modified magnesium hydroxide flame retardant in the preparation of polymer flame-retardant composite materials, and the application method familiar to those skilled in the art can be used. The modified magnesium hydroxide flame retardant provided by the present invention has good flame retardant effect and high flame retardant efficiency. In the process of preparing polymer flame-retardant composite materials, the amount added to the polymer material can be reduced, thereby ensuring the good physical and mechanical properties of the polymer material.

[0038] The modified magnesium hydroxide flame retardant provided by the present invention and its preparation method and application are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0039] Example 1

[0040] Magnesium hydroxide with a particle size of 0.1 to 10 μm is added with water to form a slurry with a solid content of 60 wt%, sodium silicate is added (the mass of sodium silicate is 1% of the mass of magnesium hydroxide), and ground for 1 hour to obtain a mixed slurry; hydrochloric acid is added to the mixed slurry, the pH value is adjusted to 5, and wet grinding is performed again for 3 hours to obtain a modified magnesium hydroxide precursor slurry; the modified magnesium hydroxide precursor slurry is washed with water, centrifugally dehydrated, and then dried (heating temperature is 130° C.) until the water content is less than 0.3 wt% to obtain a silicon dioxide-coated magnesium hydroxide sample (i.e., a modified magnesium hydroxide primary product); finally, γ-aminopropyltrimethoxysilane (the mass of γ-aminopropyltrimethoxysilane is 1% of the mass of magnesium hydroxide) is added to the silicon dioxide-coated magnesium hydroxide sample as a surface modifier, and surface modification is performed by high-speed dispersion at 120° C. for 10 minutes to obtain a modified magnesium hydroxide flame retardant finished product.

[0041] Figure 1 The SEM microscopic morphology of the prepared modified magnesium hydroxide flame retardant is Figure 1 It can be seen that there are a large number of small particles on the surface of magnesium hydroxide, indicating that silicon dioxide is coated on the surface of magnesium hydroxide relatively evenly.

[0042] According to the above scheme, three parallel samples of modified magnesium hydroxide flame retardant were prepared, which were recorded as parallel sample 1, parallel sample 2 and parallel sample 3 respectively. The performance of each parallel sample was tested. The test results are shown in Table 1:

[0043] Table 1 Performance data of the finished modified magnesium hydroxide flame retardant prepared in Example 1

[0044]

[0045] The modified magnesium hydroxide flame retardant prepared in Example 1 was added to polypropylene (PP) and the flame retardant performance was compared with that of unmodified magnesium hydroxide. Test results: When 60wt% unmodified magnesium hydroxide (particle size is about 2μm) was added to PP, the oxygen index value was 26.2%; when the same amount of the modified magnesium hydroxide flame retardant of this example was added, the oxygen index value was 28.5%, the carbon residue after combustion increased by 9.5%, and the flame retardant performance was significantly improved.

[0046] Example 2

[0047] Magnesium hydroxide with a particle size of 0.1 to 10 μm is added with water to form a slurry with a solid content of 70 wt%, sodium silicate is added (the mass of sodium silicate is 1% of the mass of magnesium hydroxide), and ground for 1 hour to obtain a mixed slurry; hydrochloric acid is added to the mixed slurry, the pH value is adjusted to 5, and wet grinding is performed again for 3 hours to obtain a modified magnesium hydroxide precursor slurry; the modified magnesium hydroxide precursor slurry is washed with water, centrifugally dehydrated, and then dried (heating temperature is 120° C.) until the water content is less than 0.3 wt% to obtain a silicon dioxide-coated magnesium hydroxide sample (i.e., a modified magnesium hydroxide primary product); finally, NN diethylaminopropyl trimethoxysilane (the mass of NN diethylaminopropyl trimethoxysilane is 0.5% of the mass of magnesium hydroxide) is added to the silicon dioxide-coated magnesium hydroxide sample as a surface modifier, and surface modification is performed at 130° C. by high-speed dispersion for 12 minutes to obtain a modified magnesium hydroxide flame retardant finished product. According to the above method, three parallel samples of modified magnesium hydroxide flame retardant were prepared, which were recorded as parallel sample 1, parallel sample 2 and parallel sample 3 respectively. The performance of each parallel sample was tested. The test results are shown in Table 2:

[0048] Table 2 Performance data of the finished modified magnesium hydroxide flame retardant prepared in Example 2

[0049]

[0050] The modified magnesium hydroxide flame retardant prepared in Example 2 was added to low-density polyethylene (LDPE) and flame retardant performance was compared with that of unmodified magnesium hydroxide. Test results: When 40wt% unmodified magnesium hydroxide (particle size is about 2μm) was added to LDPE, the oxygen index value was 22.6%; when the same amount of the modified magnesium hydroxide flame retardant of this example was added, the oxygen index value was 24.2%, the residual carbon after combustion increased by 6.9%, and the flame retardant performance was significantly improved.

[0051] Example 3

[0052] Magnesium hydroxide with a particle size of 0.1 to 10 μm is added with water to form a slurry with a solid content of 80 wt%, sodium silicate is added (the mass of sodium silicate is 1% of the mass of magnesium hydroxide), and the mixture is ground for 1 hour to obtain a mixed slurry; hydrochloric acid is added to the mixed slurry, the pH value is adjusted to 5, and wet grinding is performed again for 3 hours to obtain a modified magnesium hydroxide precursor slurry; the modified magnesium hydroxide precursor slurry is washed with water, centrifugally dehydrated, and then dried (heating temperature is 145° C.) until the water content is less than 0.3 wt% to obtain a silicon dioxide-coated magnesium hydroxide sample (i.e., a modified magnesium hydroxide primary product); finally, N-phenylaminomethyltriethoxysilane (the mass of N-phenylaminomethyltriethoxysilane is 3% of the mass of magnesium hydroxide) is added to the silicon dioxide-coated magnesium hydroxide sample as a surface modifier, and the surface is modified by high-speed dispersion at 140° C. for 8 minutes to obtain a modified magnesium hydroxide flame retardant finished product. According to the above method, three parallel samples of modified magnesium hydroxide flame retardant were prepared, which were recorded as parallel sample 1, parallel sample 2 and parallel sample 3, and the performance of each parallel sample was tested. The test results are shown in Table 3:

[0053] Table 3 Performance data of the finished modified magnesium hydroxide flame retardant prepared in Example 3

[0054]

[0055] The modified magnesium hydroxide flame retardant prepared in Example 3 was added to polyvinyl chloride (PVC) and the flame retardant performance was compared with that of unmodified magnesium hydroxide. Test results: When 60 parts by mass of unmodified magnesium hydroxide (particle size of about 2 μm) was added to 100 parts by mass of PVC, the oxygen index value was 25.6%; when the same amount of the modified magnesium hydroxide flame retardant of this example was added, the oxygen index value was 27.5%, the residual carbon after combustion increased by 5.3%, and the flame retardant performance was significantly improved.

[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A modified magnesium hydroxide flame retardant, It is characterized in that It comprises magnesium hydroxide and silicon dioxide coated on the surface of the magnesium hydroxide; The preparation method of the modified magnesium hydroxide flame retardant comprises the following steps: Mixing magnesium hydroxide with water to obtain magnesium hydroxide slurry; The magnesium hydroxide slurry is mixed with sodium silicate and subjected to a first wet grinding to obtain a mixed slurry; the first wet grinding time is 1 to 3 hours; The mixed slurry is adjusted to a pH value of 4 to 5 and then subjected to a second wet grinding process to obtain a modified magnesium hydroxide precursor slurry; the second wet grinding process lasts for 1 to 8 hours; The modified magnesium hydroxide precursor slurry is sequentially washed, solid-liquid separated and solid-phase heated and dried to obtain a modified magnesium hydroxide primary product; the temperature of the solid-phase heating and drying is 100-150° C.; The modified magnesium hydroxide primary product is mixed with a surfactant, and surface modification is performed at 100-150° C. to obtain the modified magnesium hydroxide flame retardant.

2. The modified magnesium hydroxide flame retardant according to claim 1, It is characterized in that The particle size of the modified magnesium hydroxide flame retardant is 0.1-3 μm; the mass ratio of magnesium hydroxide to silicon dioxide in the modified magnesium hydroxide flame retardant is 99.9-90:0.1-10.

3. The preparation method of the modified magnesium hydroxide flame retardant according to claim 1, It is characterized in that The following steps are involved: Mixing magnesium hydroxide with water to obtain magnesium hydroxide slurry; The magnesium hydroxide slurry is mixed with sodium silicate and subjected to a first wet grinding to obtain a mixed slurry; the first wet grinding time is 1 to 3 hours; The mixed slurry is adjusted to a pH value of 4 to 5 and then subjected to a second wet grinding process to obtain a modified magnesium hydroxide precursor slurry; The second wet grinding time is 1 to 8 hours; The modified magnesium hydroxide precursor slurry is sequentially washed, solid-liquid separated and solid-phase heated and dried to obtain a modified magnesium hydroxide primary product; the temperature of the solid-phase heating and drying is 100-150° C.; The modified magnesium hydroxide primary product is mixed with a surfactant, and surface modification is performed at 100-150° C. to obtain the modified magnesium hydroxide flame retardant.

4. The preparation method according to claim 3, It is characterized in that The particle size of the magnesium hydroxide is 0.1-10 μm; the solid content of the magnesium hydroxide slurry is 60-80 wt %.

5. The preparation method according to claim 3, It is characterized in that The mass ratio of the sodium silicate to the magnesium hydroxide in the magnesium hydroxide slurry is 1:5 to 1:

100.

6. The preparation method according to claim 3, It is characterized in that The reagent used to adjust the pH value is an acid reagent, and the acid reagent includes one or more of hydrochloric acid, sulfuric acid, phosphoric acid, formic acid and acetic acid.

7. The preparation method according to claim 3, It is characterized in that The water content of the modified magnesium hydroxide primary product is less than 0.4%.

8. The preparation method according to claim 3, It is characterized in that The surfactant includes γ-aminopropyl triethoxysilane, γ-aminopropyl trimethoxysilane, γ-aminopropyl methyl diethoxysilane, aminopropyl silane hydrolyzate, γ-aminopropyl methyl dimethoxysilane, N-phenyl-γ-aminopropyl trimethoxysilane, N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxysilane, NN diethylaminopropyl trimethoxysilane, NN dimethylaminopropyl trimethoxysilane, N-β-(aminoethyl)-aminopropyl trimethoxysilane, N- One or more of β-(aminoethyl)-aminopropyltriethoxysilane, γ-diethylenetriaminopropylmethyldimethoxysilane, γ-diethylenetriaminopropyltrimethoxysilane, bis-(γ-trimethoxysilylpropyl)amine, bis-(γ-triethoxysilylpropyl)amine, γ-piperazinylpropylmethyldimethoxysilane, N-phenylaminomethyltriethoxysilane and γ-diethylaminomethyltriethoxysilane; the mass ratio of the surfactant to magnesium hydroxide is 1:10~1:1000.

9. The preparation method according to claim 3 or 8, It is characterized in that The surface modification time is 5 to 20 minutes.

10. Use of the modified magnesium hydroxide flame retardant according to any one of claims 1 to 2 or the modified magnesium hydroxide flame retardant prepared by the preparation method according to any one of claims 3 to 9 in the preparation of a polymer flame retardant composite material; the amount of the modified magnesium hydroxide flame retardant added to the polymer flame retardant composite material is 20 to 60 wt%.

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