Nanoscale magnesium hydroxide flame retardant, its preparation method and application

Abstract

The application discloses a kind of nanoscale magnesium hydroxide flame retardant and its preparation method and application, it is related to flame retardant technical field.The application utilizes magnesium salt and sodium hydroxide as raw material, is prepared nanometer magnesium hydroxide by nucleation, crystallization, then it is dispersed in ethanol, sequentially adding phosphate and amino silane is modified and handled to prepare composite modified nanometer magnesium hydroxide slurry, finally adding borate esterified oligomeric siloxane is reacted, and nanoscale magnesium hydroxide flame retardant is prepared.The application is sequentially modified and handled to nanometer magnesium hydroxide by utilizing phosphate, amino silane and borate esterified oligomeric siloxane, constructs composite interface on the surface of nanometer magnesium hydroxide, to reduce the oil absorption value of nanometer magnesium hydroxide flame retardant, enhances its interface bonding force with resin matrix, improves flame retardant performance.

Description

Technical Field

[0001] This invention relates to the field of flame retardant technology, and in particular to a nano-scale magnesium hydroxide flame retardant, its preparation method, and its application. Background Technology

[0002] Magnesium hydroxide (MH), as an inorganic flame retardant, operates on the following mechanism: upon heating, MH decomposes, absorbing a large amount of heat and releasing water vapor, thereby inhibiting flame propagation. Simultaneously, residual MgO forms a dense protective film on the surface of the combustion source, isolating oxygen, blocking heat transfer, and suppressing smoke generation. Compared to traditional halogenated flame retardants, MH offers advantages such as low smoke, low toxicity, high thermal stability, and environmental friendliness, and has been widely used in fields such as wire and cable, plastic modification, rubber products, new energy vehicle components, electronics, and building materials.

[0003] Currently, magnesium hydroxide flame retardants are commonly used as additives for the flame-retardant modification of thermoplastic polymers. However, magnesium hydroxide particles have strong hydrophilicity and polarity, while common resin matrices such as polyolefins, EVA, and rubber are mostly non-polar or weakly polar, exhibiting significant differences in surface properties compared to magnesium hydroxide. Therefore, when magnesium hydroxide is used for flame-retardant modification of polymers, the interfacial bonding between the two is weak, leading to high oil absorption, poor mechanical properties, and unsatisfactory flame-retardant effects in the polymer flame-retardant materials.

[0004] In existing technologies, magnesium hydroxide is often surface-modified to improve the interfacial compatibility between it and the resin matrix. For example, modifiers such as stearic acid and silane coupling agents are used to modify the surface of magnesium hydroxide, reducing its surface polarity and increasing its hydrophobicity, thereby enhancing the interfacial bonding between magnesium hydroxide and the resin matrix. However, stearic acid binds to magnesium hydroxide through physical adsorption or weak coordination, and is easily desorbed during washing, drying, and mixing. Silane coupling agents require hydrolysis and condensation processes, which are extremely sensitive to parameters such as moisture content and pH value. Furthermore, the competing hydrolysis-condensation reaction is difficult to control precisely, resulting in uneven coating of the silane coupling agent on the magnesium hydroxide surface.

[0005] Therefore, there is an urgent need to develop a composite modifier for surface modification of nano-magnesium hydroxide to improve the interfacial bonding between nano-magnesium hydroxide and the resin matrix, thereby improving the oil absorption value, mechanical properties and flame retardant effect of polymer flame retardant materials. This is of practical significance for promoting the flame retardant materials industry towards environmentally friendly and high-performance directions. Summary of the Invention

[0006] To address the aforementioned limitations of existing technologies, the present invention aims to provide a nano-scale magnesium hydroxide flame retardant, its preparation method, and its applications. Using magnesium salts and sodium hydroxide as raw materials, nano-magnesium hydroxide is prepared through nucleation and crystallization. This nano-magnesium hydroxide is then dispersed in ethanol, and phosphate esters and aminosilanes are added sequentially for modification to obtain a composite-modified nano-magnesium hydroxide slurry. Finally, borosilicate-treated oligomeric siloxanes are added for reaction to obtain the nano-scale magnesium hydroxide flame retardant. This invention utilizes phosphate esters, aminosilanes, and borosilicate-treated oligomeric siloxanes to sequentially modify nano-magnesium hydroxide, constructing a composite interface on the surface of the nano-magnesium hydroxide. This reduces the oil absorption value of the nano-magnesium hydroxide flame retardant, enhances its interfacial bonding with the resin matrix, and improves its flame retardant performance.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a nano-sized magnesium hydroxide flame retardant, comprising the following steps: (1) After mixing magnesium salt solution and sodium hydroxide solution, nucleation reaction was carried out, followed by heating for crystallization. After the reaction, the mixture was filtered, the solid was collected, and washed to obtain nano magnesium hydroxide. (2) After mixing nano-magnesium hydroxide and ethanol solution, a slurry is obtained; phosphate ester is added to the slurry for the first reaction. After the reaction is completed, aminosilane is added to the system after the reaction for the second reaction to obtain composite modified nano-magnesium hydroxide slurry. (3) Add borate-esterified oligosiloxane to the composite modified nano magnesium hydroxide slurry, react under heating, filter after the reaction is completed, collect the solid, wash and dry to obtain nano-sized magnesium hydroxide flame retardant.

[0008] Preferably, in step (1), the magnesium salt is one or more of magnesium chloride, magnesium nitrate, and magnesium sulfate, the mass fraction of the magnesium salt solution is 15%-16%, and the mass fraction of the sodium hydroxide solution is 16%-18%.

[0009] Preferably, in step (1), the mass ratio of magnesium salt solution to sodium hydroxide solution is (4-5):(3-4).

[0010] Preferably, in step (1), the temperature during crystallization is 120-140℃, the rotation speed is 500-700r / min, and the reaction time is 6-10h.

[0011] Preferably, in step (2), the ethanol solution is prepared by mixing ethanol and water in a mass ratio of (8-9):(1-2).

[0012] Preferably, in step (2), the solid content in the slurry is 8%-12%.

[0013] Preferably, in step (2), the phosphate ester is one or more of 2-methacryloyloxyethyl phosphate, hydroxyethyl methacrylate phosphate, and allyl phosphate.

[0014] Preferably, in step (2), the aminosilane is γ-aminopropyltriethoxysilane.

[0015] Preferably, the mass ratio of nano-magnesium hydroxide, phosphate ester, aminosilane, and borate esterified oligosiloxane is 100:(0.6-1.0):(0.2-0.6):(1.5-2.5).

[0016] Preferably, in step (2), the reaction temperature is 50-60℃, the pH is 7.5-8.5, and the reaction time is 30-50 min during the first reaction.

[0017] Preferably, in step (2), during the second reaction, the reaction temperature is 60-70℃, the pH is 8.0-9.0, and the reaction time is 50-60min.

[0018] Preferably, in step (3), the borate-esterified oligosiloxane is prepared by the following method: After preheating the hydroxyl-terminated polydimethylsiloxane to 75-85℃, tributyl borate and catalyst were added with stirring. The reaction was carried out at 95-110℃ for 2-4 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was distilled under reduced pressure to obtain borate-esterified oligosiloxane.

[0019] Furthermore, the catalyst is tetrabutyl titanate or tetraisopropyl titanate.

[0020] Furthermore, the mass ratio of hydroxyl-terminated polydimethylsiloxane, tributyl borate, and catalyst is 10:(1.0-1.2):(0.01-0.02).

[0021] Preferably, in step (3), the heating temperature is 70-80℃ and the reaction time is 1-2h.

[0022] Preferably, in step (3), the drying temperature is 80-100℃ and the drying time is 6-10h.

[0023] In a second aspect, the present invention provides a nano-sized magnesium hydroxide flame retardant prepared by the above-described preparation method.

[0024] A third aspect of the present invention provides the application of the above-mentioned nano-sized magnesium hydroxide flame retardant in the preparation of flame retardant resins.

[0025] Preferably, the flame-retardant resin is prepared by the following method: Heat the internal mixer to 130-150℃, add EVA resin at 50-70r / min and mix for 1-2min; then add antioxidant 1010 and EBS and continue mixing for 1-2min; finally add the above-mentioned nano-grade magnesium hydroxide flame retardant and continue mixing for 4-6min. After mixing, cool to obtain flame retardant resin.

[0026] Furthermore, the mass ratio of EVA resin, nano magnesium hydroxide flame retardant, antioxidant 1010 and EBS is 100:(140-160):(0.2-0.4):(0.4-0.6).

[0027] The beneficial effects of this invention are: 1. This invention utilizes magnesium salts and sodium hydroxide as raw materials to obtain nano-magnesium hydroxide through nucleation and crystallization. Then, it is dispersed in ethanol, and phosphate esters and aminosilanes are added sequentially for modification treatment to obtain composite modified nano-magnesium hydroxide slurry. Finally, borate-esterified oligomeric siloxanes are added for reaction to obtain nano-scale magnesium hydroxide flame retardant.

[0028] 2. This invention utilizes phosphate esters, aminosilanes, and borate-esterified oligomeric siloxanes to sequentially modify nano-magnesium hydroxide, constructing a composite interface on the surface of the nano-magnesium hydroxide. This reduces the oil absorption value of the nano-magnesium hydroxide flame retardant, enhances its interfacial bonding with the resin matrix, and improves its flame retardant performance. Specifically: First, phosphate esters are used to modify nano-magnesium hydroxide. The phospho groups in the phosphate esters can coordinate, adsorb, or interact with the magnesium active sites on the surface of nano-magnesium hydroxide, thus anchoring the phosphate esters to the surface of magnesium hydroxide to form a stable chemisorption layer. This layer has good bonding strength, which can reduce the risk of desorption of the modifier during washing, drying, or high-temperature mixing, and provides an interfacial bonding basis for subsequent aminosilane bridging.

[0029] Then, aminosilane is used for modification. The aminosilane is hydrolyzed to generate Si-OH, which can condense or adsorb with the hydroxyl groups on the surface of magnesium hydroxide. At the same time, the amino group can form hydrogen bonds or acid-base interactions with the phosphate ester adsorption layer, thereby forming a stable phosphate ester-silane composite interface on the surface of nano magnesium hydroxide.

[0030] Finally, borosilicated oligosiloxanes are introduced for modification, which can form a hydrophobic coating layer containing siloxane segments on the surface of magnesium hydroxide. This hydrophobic coating layer can reduce the surface polarity of nano-magnesium hydroxide, reduce its adsorption of oily components, and thus achieve the effect of reducing the oil absorption value.

[0031] Meanwhile, borate-esterified oligosiloxanes can form inorganic or semi-inorganic residues containing Si-O, BO, or Si-OB structures during combustion. These residues can form an inorganic barrier layer together with MgO produced by the decomposition of magnesium hydroxide, thereby improving the flame retardant effect. Attached Figure Description

[0032] Figure 1 XRD pattern of nano-sized magnesium hydroxide flame retardant prepared in Example 1; Figure 2 Electron micrograph of the nano-sized magnesium hydroxide flame retardant prepared in Example 1. Detailed Implementation

[0033] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0034] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0035] The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0036] In this invention, the CAS number of 2-methacryloyloxyethyl phosphate is 52628-03-2, the CAS number of γ-aminopropyltriethoxysilane is 919-30-2, the CAS number of hydroxyl-terminated polydimethylsiloxane is 70131-67-8, the CAS number of tributyl borate is 688-74-4, and the CAS number of tetrabutyl titanate is 5593-70-4.

[0037] The EVA resin was purchased from Ningbo Qihuida Materials Technology Co., Ltd., and the product name is Ateva 2810A, with a VA content of 28%.

[0038] Example 1: Preparation method of nano-sized magnesium hydroxide flame retardant (1) A magnesium chloride solution with a mass fraction of 15.8% was prepared by mixing MgCl2·6H2O and deionized water at a mass ratio of 162.64:320; a sodium hydroxide solution with a mass fraction of 16.7% was prepared by mixing sodium hydroxide and deionized water at a mass ratio of 64:320. Magnesium chloride solution and sodium hydroxide solution were mixed at a mass ratio of 482:384 and placed in a rotating liquid film reactor for nucleation reaction. After the reaction stopped producing precipitate, the nucleation reaction system was placed at 130℃ and 600r / min for 8h to crystallize. After the reaction was completed, the mixture was filtered, the solid was collected, and washed to obtain nano magnesium hydroxide. (2) Anhydrous ethanol and deionized water were mixed at a mass ratio of 85:15 to obtain an ethanol solution; nano magnesium hydroxide and ethanol solution were mixed to obtain a slurry with a solid content of 10%. 2-Methacryloxyethyl phosphate was added to the slurry and reacted at 55°C and pH 8.0 for 40 min. After the reaction was completed, γ-aminopropyltriethoxysilane was added to the system and reacted at 65°C and pH 8.5 for 60 min to obtain the composite modified nano magnesium hydroxide slurry. (3) The hydroxyl-terminated polydimethylsiloxane was preheated to 80°C, and tributyl borate and tetrabutyl titanate (catalyst) were added under stirring. The reaction was carried out at 105°C for 3 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was subjected to vacuum distillation at -0.09 MPa and 100°C for 25 minutes to remove butanol and unreacted tributyl borate, and borate-esterified oligosiloxane was obtained. The mass ratio of hydroxyl-terminated polydimethylsiloxane, tributyl borate and tetrabutyl titanate was 10:1.1:0.015. Boron-esterified oligomeric siloxane was added to the composite modified nano magnesium hydroxide slurry, and the mixture was heated to 75°C and reacted for 1.5 h. After the reaction was completed, the mixture was cooled, filtered, and the precipitate was collected. It was then washed with deionized water and ethanol solution in sequence, and finally dried under vacuum at 90°C for 8 h to obtain nano-sized magnesium hydroxide flame retardant.

[0039] The mass ratio of nano-magnesium hydroxide, 2-methacryloyloxyethyl phosphate, γ-aminopropyltriethoxysilane, and borate-esterified oligosiloxane is 100:0.8:0.4:2.0.

[0040] The structure of the nano-sized magnesium hydroxide flame retardant prepared in this application was characterized, and the results are as follows: Figures 1-2 As shown.

[0041] Depend on Figure 1 It can be seen that obvious diffraction peaks appear at 2θ of approximately 18.56°, 32.80°, 38.00°, 50.81°, 58.64°, 62.06° and 68.21°. These diffraction peaks correspond to the characteristic diffraction peaks of magnesium hydroxide, indicating that the inorganic main crystalline phase in the nano-sized magnesium hydroxide flame retardant prepared in Example 1 is magnesium hydroxide, and the modification treatment did not destroy the main crystalline phase of nano-magnesium hydroxide.

[0042] Depend on Figure 2It can be seen that the nano-sized magnesium hydroxide flame retardant prepared by the present invention has a hexagonal plate structure with clear plate outlines and the lateral size of the particles is at the nanoscale; some hexagonal plate particles are superimposed on each other along the plate direction to form a loose layered aggregate.

[0043] Comparative Example 1: The difference between this comparative example and Example 1 is that only aminosilane was used to modify the nano-magnesium hydroxide. Specifically: Nano-sized magnesium hydroxide and ethanol solution were prepared according to the method of Example 1; after mixing the nano-sized magnesium hydroxide and ethanol solution, a slurry with a solid content of 10% was prepared. γ-aminopropyltriethoxysilane was added to the slurry and reacted at 65℃ and pH 8.5 for 60 min to obtain modified nano magnesium hydroxide slurry. After filtration, the solid was collected and washed successively with deionized water and ethanol solution. Finally, it was vacuum dried at 90℃ for 8 h to obtain nano-sized magnesium hydroxide flame retardant. The mass ratio of nano-magnesium hydroxide to γ-aminopropyltriethoxysilane is 100:0.4.

[0044] Comparative Example 2: The difference between this comparative example and Example 1 is that the nano-magnesium hydroxide is modified using phosphate esters and aminosilanes. Specifically: Nano-sized magnesium hydroxide and ethanol solution were prepared according to the method in Example 1. After mixing the nano-sized magnesium hydroxide and ethanol solution, a slurry with a solid content of 10% was obtained. 2-Methacryloxyethyl phosphate was added to the slurry and reacted at 55℃ and pH 8.0 for 40 min. After the reaction was completed, γ-aminopropyltriethoxysilane was added to the system and reacted at 65℃ and pH 8.5 for 60 min to obtain a composite modified nano magnesium hydroxide slurry. The precipitate was collected after filtration and washed with deionized water and ethanol solution in sequence. Finally, it was vacuum dried at 90℃ for 8 h to obtain nano-sized magnesium hydroxide flame retardant. The mass ratio of nano-magnesium hydroxide, 2-methacryloyloxyethyl phosphate, and γ-aminopropyltriethoxysilane is 100:0.8:0.4.

[0045] Comparative Example 3: The difference between this comparative example and Example 1 is that the nano-magnesium hydroxide is modified using aminosilane and borate-esterified oligosiloxane. Specifically: Nano-sized magnesium hydroxide, ethanol solution, and borate-esterified oligosiloxane were prepared according to the method of Example 1. After mixing the nano-sized magnesium hydroxide and ethanol solution, a slurry with a solid content of 10% was obtained. γ-aminopropyltriethoxysilane was added to the slurry and reacted at 65°C and pH 8.5 for 60 min to obtain modified nano-magnesium hydroxide slurry. Boron esterified oligomeric siloxane was added to the slurry and heated to 75°C for 1.5 h. After the reaction was completed, the mixture was cooled, filtered, and the precipitate was collected and washed successively with deionized water and ethanol solution. Finally, it was vacuum dried at 90°C for 8 h to obtain nano-sized magnesium hydroxide flame retardant.

[0046] The mass ratio of nano-magnesium hydroxide, γ-aminopropyltriethoxysilane, and borate-esterified oligosiloxane is 100:0.4:2.0.

[0047] Test Example 1: Oil Absorption Value Detection The oil absorption values ​​of the flame retardants prepared in Example 1 and Comparative Examples 1-3 were tested according to the method in GB / T 5211.15-2014, and the results are shown in Table 1.

[0048] Table 1. Oil absorption values ​​of the flame retardants prepared in Example 1 and Comparative Examples 1-3 As shown in Table 1, the oil absorption value of the nano-magnesium hydroxide flame retardant prepared by modifying with only aminosilane (Comparative Example 1) is 54.8 mL / 100g. Based on aminosilane, the nano-magnesium hydroxide flame retardant prepared by introducing phosphate ester (Comparative Example 2) and borosilicated oligosiloxane (Comparative Example 3) for composite modification yields oil absorption values ​​of 49.6 mL / 100g and 45.9 mL / 100g, respectively. In contrast, the present invention uses phosphate ester, aminosilane, and borosilicated oligosiloxane for modification, resulting in an oil absorption value of 36.5 mL / 100g for the nano-magnesium hydroxide flame retardant.

[0049] Therefore, it can be seen that the present invention can significantly reduce the oil absorption value of nano-magnesium hydroxide particles by sequentially modifying them with phosphate ester, aminosilane and borate esterified oligosiloxane.

[0050] Experimental Example 2: This experimental example utilizes nano-magnesium hydroxide flame retardant and EVA resin as raw materials to prepare flame-retardant resin. The mechanical and flame-retardant properties of the flame-retardant resin are investigated to determine the interfacial bonding force between the nano-magnesium hydroxide flame retardant and EVA resin. The specific steps are as follows: EVA resin was dried at 60°C for 4 hours to remove surface adsorbed moisture. The nano-magnesium hydroxide flame retardants prepared in Example 1 and Comparative Examples 1-3 were dried at 105°C for 2 hours. After preheating the internal mixer to 140°C, EVA resin was added at a speed of 60 r / min and the mixture was internally mixed for 2 minutes. Then, antioxidant 1010 and EBS were added to the internal mixer and the mixture was continued to be mixed for 1 minute. Finally, the nano-magnesium hydroxide flame retardant was added and the mixture was mixed for 5 minutes. After the mixing was completed, the melt blend was taken out and placed in a hot press. It was hot-pressed at 10 MPa for 7 minutes and then cold-pressed at the same pressure for 6 minutes to obtain a flame retardant resin sheet with a thickness of 2 mm. The mass ratio of EVA resin, nano magnesium hydroxide flame retardant, antioxidant 1010 and EBS is 100:150:0.3:0.5.

[0051] The mechanical properties (tensile strength and elongation at break) of the flame-retardant resin sheets were tested according to GB / T 1040.1-2025; the limiting oxygen index of the flame-retardant resin sheets was tested according to GB / T 2406.2-2009, and the results are shown in Table 2.

[0052] Table 2. Mechanical and flame retardant properties of the flame-retardant resins corresponding to Example 1 and Comparative Examples 1-3. As shown in Table 2, the flame-retardant resin prepared using the nano-magnesium hydroxide flame retardant of the present invention exhibits excellent mechanical and flame-retardant properties. Specifically, the obtained flame-retardant resin has a tensile strength of 16.4 MPa, an elongation at break of 226%, and a limiting oxygen index of 35.6%. In contrast, the flame-retardant resins prepared using the nano-magnesium hydroxide flame retardants of Comparative Examples 1-3 have a tensile strength of 11.2-13.1 MPa, an elongation at break of 151%-186%, and a limiting oxygen index of 31.3%-32.9%. Therefore, the present invention, by sequentially modifying nano-magnesium hydroxide with phosphate ester, aminosilane, and borate-esterified oligomeric siloxane, can improve the interfacial bonding force between the nano-magnesium hydroxide flame retardant and the resin matrix (EVA resin), thereby achieving the effect of improving the mechanical and flame-retardant properties of the flame-retardant resin.

[0053] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a nano-sized magnesium hydroxide flame retardant, characterized in that, Includes the following steps: (1) After mixing magnesium salt solution and sodium hydroxide solution, nucleation reaction was carried out, followed by heating for crystallization. After the reaction, the mixture was filtered, the solid was collected, and washed to obtain nano magnesium hydroxide. (2) After mixing nano-magnesium hydroxide and ethanol solution, a slurry is obtained; phosphate ester is added to the slurry for the first reaction. After the reaction is completed, aminosilane is added to the system after the reaction for the second reaction to obtain composite modified nano-magnesium hydroxide slurry. (3) Add borate-esterified oligosiloxane to the composite modified nano magnesium hydroxide slurry, react under heating, filter after the reaction is completed, collect the solid, wash and dry to obtain nano-sized magnesium hydroxide flame retardant.

2. The preparation method of the nano-sized magnesium hydroxide flame retardant as described in claim 1, characterized in that, In step (1), the magnesium salt is one or more of magnesium chloride, magnesium nitrate, and magnesium sulfate, the mass fraction of the magnesium salt solution is 15%-16%, and the mass fraction of the sodium hydroxide solution is 16%-18%; the mass ratio of the magnesium salt solution to the sodium hydroxide solution is (4-5):(3-4). During the crystallization process, the temperature is 120-140℃, the rotation speed is 500-700r / min, and the reaction time is 6-10h.

3. The preparation method of the nano-sized magnesium hydroxide flame retardant as described in claim 1, characterized in that, In step (2), the ethanol solution is prepared by mixing ethanol and water in a mass ratio of (8-9):(1-2); the solid content in the slurry is 8%-12%.

4. The preparation method of the nano-sized magnesium hydroxide flame retardant as described in claim 1, characterized in that, In step (2), the phosphate ester is one or more of 2-methacryloyloxyethyl phosphate, hydroxyethyl methacrylate phosphate, and allyl phosphate; during the first reaction, the reaction temperature is 50-60℃, the pH is 7.5-8.5, and the reaction time is 30-50 min.

5. The preparation method of the nano-sized magnesium hydroxide flame retardant as described in claim 1, characterized in that, In step (2), the aminosilane is γ-aminopropyltriethoxysilane. During the second reaction, the reaction temperature is 60-70℃, the pH is 8.0-9.0, and the reaction time is 50-60 min.

6. The preparation method of the nano-sized magnesium hydroxide flame retardant as described in claim 1, characterized in that, In step (3), the borate-esterified oligosiloxane is prepared by the following method: After preheating the hydroxyl-terminated polydimethylsiloxane to 75-85℃, tributyl borate and catalyst were added with stirring. The reaction was carried out at 95-110℃ for 2-4 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was distilled under reduced pressure to obtain borate-esterified oligosiloxane. The catalyst is tetrabutyl titanate or tetraisopropyl titanate; the mass ratio of hydroxyl-terminated polydimethylsiloxane, tributyl borate and catalyst is 10:(1.0-1.2):(0.01-0.02).

7. The preparation method of the nano-sized magnesium hydroxide flame retardant as described in claim 1, characterized in that, In step (3), the heating temperature is 70-80℃ and the reaction time is 1-2h.

8. The preparation method of the nano-sized magnesium hydroxide flame retardant as described in claim 1, characterized in that, The mass ratio of nano-magnesium hydroxide, phosphate ester, aminosilane, and borate-esterified oligosiloxane is 100:(0.6-1.0):(0.2-0.6):(1.5-2.5).

9. The nano-sized magnesium hydroxide flame retardant prepared by the preparation method according to any one of claims 1-8.

10. The application of the nano-sized magnesium hydroxide flame retardant according to claim 9 in the preparation of flame retardant resin.

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