A core-shell structure composite flame-retardant material and a preparation method and application thereof

Abstract

The application belongs to the technical field of flame retardants, and particularly relates to a core-shell structure composite flame-retardant material and a preparation method thereof. The core-shell structure composite flame-retardant material comprises a core and a shell from inside to outside, the core is a carboxylic acid compound containing phosphorus, nitrogen and boron, and the shell is boron-silicon modified ammonium polyphosphate. The core-shell structure composite flame-retardant material provided by the application not only realizes a nitrogen-phosphorus-boron-silicon four-element synergistic flame-retardant mechanism, reduces the addition in a polymer, but also has excellent dispersibility and compatibility in the polymer, does not reduce the mechanical properties of the polymer, and has excellent aging resistance.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant technology, specifically relating to a core-shell structured composite flame retardant material and its preparation method. Background Technology

[0002] Flame retardants have wide applications in polymer modification, coatings, and electronic packaging, especially in polymer modification. These applications include the modification of α-olefin ethylene copolymers, vinyl elastomers, metallocene polyolefins, high-performance polypropylene, polyisobutylene, poly4-methylpentene-1, ethylene-vinyl alcohol copolymers, highly branched polyolefins, polyvinyl chloride, polybutylene terephthalate, polyethylene terephthalate, polyethylene terephthalate-1,4-cyclohexanediol, polybutylene succinate, unsaturated polyesters, and biodegradable polyester plastics. The use of flame retardants has broadened their application scenarios. Flame retardants can be divided into halogenated flame retardants and halogen-free flame retardants. Although halogenated flame retardants have good flame retardant effects, they produce toxic gases and are gradually being phased out. Halogen-free flame retardants, due to their non-toxicity and low smoke, have become a research and development hotspot.

[0003] Halogen-free flame retardants typically include phosphorus-based, nitrogen-based, boron-based, silicon-based, and their composite systems. The flame retardant ability of a single halogen-free flame retardant is limited, and multi-component synergistic flame retardant systems have become a research trend.

[0004] The applicant has previously conducted preliminary research on multi-component composite flame retardants and applied for related patents, the publication number of which is CN119874774 A. This invention provides a flame retardant integrating N, P, and B, as well as its synthesis method and application. The provided flame retardant integrates the three flame retardant functions of nitrogen, phosphorus, and boron into the same product. The components work synergistically during combustion to form a glassy char layer and release inert gas, while inhibiting smoke generation and improving flame retardant efficiency and thermal stability of the material.

[0005] Chinese Patent CN119931068A discloses a Si-PNC quaternary hybrid flame-retardant system composition and its preparation method. The method involves adding a nitrogen-phosphorus flame retardant, a thermoplastic resin, and a silane coupling agent to a graphene oxide suspension. After a functionalization reaction, a graphene oxide-grafted nitrogen-phosphorus flame retardant and a graphene oxide-grafted thermoplastic resin are obtained. The graphene oxide-grafted nitrogen-phosphorus flame retardant and the graphene oxide-grafted thermoplastic resin are then mixed with modified wollastonite and a silane coupling agent to obtain the Si-PNC quaternary hybrid flame-retardant system composition. This technical solution, based on modified wollastonite, introduces a nitrogen-phosphorus flame retardant, a thermoplastic resin, and graphene oxide. This not only gives the system composition excellent compatibility with the polymer matrix, resulting in better mechanical and processing properties, but also demonstrates excellent flame-retardant performance due to the synergistic flame-retardant effect of Si, P, N, and C.

[0006] However, the flame retardant compositions obtained by the above technical solutions all have a high addition amount in polypropylene. The amount of flame retardant added will affect the dispersibility and compatibility of the polymer material, and thus affect its mechanical properties. Summary of the Invention

[0007] This invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial alternative. Specifically, this invention provides a core-shell structured composite flame retardant material and its preparation method. This invention uses tris(2-hydroxyethyl)isocyanuric acid as a starting material, reacting it sequentially with maleic anhydride, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and boric acid to obtain a nitrogen-phosphorus-boron ternary synergistic flame retardant compound as the core. Using ammonium polyphosphate as the base material, and borosilicate-modified ammonium polyphosphate obtained by modification with phenyltrimethoxysilane and boric acid as the core and shell, the resulting core-shell structured composite flame retardant material achieves a nitrogen-phosphorus-boron-silicon quaternary synergistic flame retardant mechanism.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a core-shell structured composite flame retardant material, comprising a core and a shell from the inside out, wherein the core is a carboxylic acid compound containing phosphorus, nitrogen, and boron, and the shell is borosilicate-modified ammonium polyphosphate.

[0009] In some preferred embodiments, the phosphorus-nitrogen-boron-containing carboxylic acid compound contains an isocyanurate ring, a phosphorus-phenanthrene group, and a boric acid group in its molecular structure.

[0010] The phosphorus, nitrogen, and boron-containing carboxylic acid compounds described in this invention can be referenced to the preparation method of the phosphorus, nitrogen, and boron-containing carboxylic acid compounds disclosed in Chinese Patent Publication No. CN 111732607 B.

[0011] Specifically, the raw materials for the phosphorus, nitrogen, and boron-containing carboxylic acid compounds include tris(2-hydroxyethyl) isocyanurate, maleic anhydride, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and boric acid in a molar ratio of 1:2-2.1:2-2.1:1-1.05.

[0012] Furthermore, the method for preparing the phosphorus-, nitrogen-, and boron-containing carboxylic acid compound includes the following steps: (1) Esterification reaction: tris(2-hydroxyethyl) isocyanurate, maleic anhydride and solvent a, heat to 85-95℃, and stir continuously for 2-4 hours under nitrogen atmosphere; (2) Addition reaction: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and solvent a are added in batches to the reaction solution of step (1), the temperature is raised to 100-110℃ and the reaction is carried out for 8-9 hours; (3) Esterification reaction: Dissolve boric acid in solvent a and add it to the mixture in step (2), and then continue the reaction for 2-3 hours; (4) Purification: Remove solvent a from the solution after the reaction in step (3), and wash and dry the crude product to obtain a white solid product.

[0013] Furthermore, in steps (1)-(4), solvent a is dioxane, and there is no special limitation on the amount of solvent a used, as long as the reaction proceeds smoothly.

[0014] Furthermore, in step (4), the crude product is washed with deionized water.

[0015] In some preferred embodiments, the raw materials for the borosilicate-modified ammonium polyphosphate include ammonium polyphosphate, phenyltrimethoxysilane, and boric acid.

[0016] Furthermore, the mass ratio of ammonium polyphosphate, phenyltrimethoxysilane, and boric acid is 35-45:5-8:0.8-1.5.

[0017] Furthermore, the mass ratio of ammonium polyphosphate, phenyltrimethoxysilane, and boric acid is 40:6.9:1.1.

[0018] In some preferred embodiments, the mass ratio of the total mass of the phosphorus-nitrogen-boron-containing carboxylic acid compound and the borosilicate-modified ammonium polyphosphate raw material is 1:0.5-1.5.

[0019] The core and shell components of a core-shell composite flame-retardant material have the most direct impact on the flame-retardant effect. However, it is impossible to predict whether the core and shell components will achieve a flame-retardant effect of 1+1=2 or 1+1>2. One of the key points of this invention is to use a carboxylic acid compound containing phosphorus, nitrogen, and boron as the core and borosilicate-modified ammonium polyphosphate as the shell. When the borosilicate-modified ammonium polyphosphate is phenyltrimethoxysilane and boric acid-modified ammonium polyphosphate, the core releases non-flammable gas through nitrogen to dilute the concentration of flammable gas, phosphorus generates PO· free radicals in the gas phase to interrupt the combustion chain reaction, and boron promotes char formation in the condensed phase and improves the quality of the char layer. The phosphate groups in the shell further promote char formation, and the silicon-oxygen network forms a dense SiO2 protective layer. The boron component enhances the density and thermal stability of the char layer through the B2O3-SiO2 glass phase. Experimental verification has shown that a synergistic flame-retardant effect of nitrogen, phosphorus, boron, and silicon quaternary components has been achieved.

[0020] Secondly, the present invention provides a method for preparing the above-mentioned core-shell structured composite flame-retardant material, comprising the following steps: S1. The core is pretreated with a silane coupling agent to obtain a pretreated core. S2. Mix the pretreated core, ammonium polyphosphate, emulsifier and solvent b. Under acidic conditions, add a mixture of phenyltrimethoxysilane and boric acid dropwise at a first temperature. React at a second temperature. After the reaction is complete, the mixture is obtained by rotary evaporation, washing and vacuum drying.

[0021] When a core-shell structured composite flame retardant material is added to a polymer, poor dispersibility and compatibility with the polymer can affect the polymer's mechanical properties and resistance to heat and oxygen aging. Another key aspect of this invention is the preparation method of the core-shell structured composite flame retardant material. This method has two crucial points: First, a silane coupling agent is used to pre-treat the core surface, enhancing its surface activity and facilitating in-situ coating of borosilicate-modified polyphosphate while preventing hydrolysis of the core during the coating process. Second, an in-situ coating method is used to achieve the in-situ generation of borosilicate-modified polyphosphate on the surface of a phosphorus-nitrogen-boron-containing carboxylic acid compound, forming a dense coating structure. This prevents the migration and aggregation of flame retardant components, achieving a synergistic flame retardant effect of the nitrogen-phosphorus-boron-silicon quaternary structure. Furthermore, the borosilicate-modified polyphosphate on the surface of the phosphorus-nitrogen-boron-containing carboxylic acid compound improves the dispersibility and compatibility of the core-shell structured composite flame retardant material in the polymer matrix, thereby preventing a decline in the polymer's mechanical properties and resistance to heat and oxygen aging.

[0022] In some preferred embodiments, the silane coupling agent is selected from at least one of KH550, KH560, KH570 and KH590.

[0023] Furthermore, the silane coupling agent is KH550.

[0024] In some preferred embodiments, the surface pretreatment method is as follows: mixing the core, silane coupling agent and ethanol, and performing heat treatment to obtain the pretreated core.

[0025] Furthermore, the mass ratio of the core, silane coupling agent, and ethanol is 8-12:0.05-0.1:15-20.

[0026] Furthermore, the heat treatment temperature is 60-80℃, and the heat treatment time is 5-15 minutes.

[0027] Furthermore, the particle size of the pretreated core is 1-10µm.

[0028] In some preferred embodiments, the ammonium polyphosphate has a phosphorus content of 30-32.5% and a nitrogen content of 14-15%.

[0029] In some preferred embodiments, the emulsifier is selected from at least one of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and fatty acid polyoxyethylene ether.

[0030] Furthermore, the emulsifier is an alkylphenol polyoxyethylene ether.

[0031] Furthermore, the alkylphenol polyoxyethylene ether is OP-9 and / or OP-10.

[0032] In some preferred embodiments, the amount of emulsifier added is 1-1.5% of the mass of the mixture of phenyltrimethoxysilane and boric acid.

[0033] In some preferred embodiments, solvent b is diethylene glycol dimethyl ether.

[0034] In some preferred embodiments, the amount of solvent b added is 10-30% of the mass of ammonium polyphosphate.

[0035] In some preferred embodiments, the pH of the acidic conditions is 1-3.

[0036] In some preferred embodiments, the first temperature is 60-80°C.

[0037] In some preferred embodiments, the second temperature is 120-140°C.

[0038] In some preferred embodiments, the reaction time at the second temperature is 4-6 hours.

[0039] Thirdly, the present invention provides the application of the above-mentioned core-shell structured composite flame-retardant material in polymer modification, coatings and electronic packaging.

[0040] Compared with the prior art, the present invention has the following beneficial effects: 1. The core-shell structured composite flame retardant material provided by this invention has excellent flame retardant properties: UL-94 V-0 rating can be achieved when 10% is added to the polymer; 2. The core-shell structured composite flame retardant material provided by this invention has good compatibility and dispersibility in polymers, thus avoiding the decline in the mechanical properties of polymers; 3. The core-shell composite flame retardant material provided by this invention has good resistance to thermo-oxidative aging, thus avoiding the decline in the mechanical properties of the polymer after thermo-oxidative aging. Attached Figure Description

[0041] Figure 1 The infrared spectrum of the core-shell structured composite flame-retardant material of Embodiment 1 of the present invention is shown. Detailed Implementation

[0042] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0043] Unless otherwise specified, the raw materials, reagents or apparatus used in the following examples and comparative examples are available from conventional commercial sources or can be obtained by existing known methods.

[0044] Polypropylene resin: Yanshan Petrochemical PP-R B8101; Ammonium polyphosphate, with a phosphorus content of 30-32.5% and a nitrogen content of 14-15%: Zhejiang Xusen Flame Retardant Co., Ltd. XS-APPII-040; Alkylphenol polyoxyethylene ether OP-9: Haian Petrochemical Plant, Jiangsu Province.

[0045] Preparation example: Preparation of carboxylic acid compounds containing phosphorus, nitrogen, and boron: In a three-necked round-bottom flask equipped with a mechanical stirrer, reflux condenser, and thermometer, 78.3 g of tris(2-hydroxyethyl) isocyanurate, 58.8 g of maleic anhydride, and 60 mL of dioxane were added and stirred at a constant speed. The mixture was heated to 90 °C under a nitrogen atmosphere and reacted for 2 h. Then, within 30 min, 129.6 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 100 mL of dioxane were added to the reaction solution in three batches. The mixture was further heated to reflux (100 °C) and maintained for 8 h. Then, a solution of 20 mL of dioxane containing 18.5 g of boric acid was added to the reactants, and the reaction was continued for 3 h. After the reaction was completed, the solution was distilled to remove dioxane. The crude product was then washed with deionized water and dried under vacuum to obtain a carboxylic acid compound containing phosphorus, nitrogen, and boron.

[0046] Example 1: Preparation of Core-Shell Structure Composite Flame Retardant Material S1. Mix 48g of a phosphorus, nitrogen and boron-containing carboxylic acid compound, 0.48g of silane coupling agent KH550 and 96g of ethanol, and heat treat at 70℃ for 10min to obtain a pretreated core. Control the particle size of the pretreated core to be 5µm. S2. Add 40g of ammonium polyphosphate, 0.12g of alkylphenol polyoxyethylene ether OP-9 and 8g of diethylene glycol dimethyl ether to the pretreated core from step S1, mix well, adjust the pH to 2 with hydrochloric acid, and add a mixture of 6.9g of phenyltrimethoxysilane and 1.1g of boric acid dropwise over 30 minutes at 70°C. Increase the temperature to 130°C and react for 5 hours. After the reaction is completed, the core-shell structured composite flame retardant material is obtained by rotary evaporation, washing with deionized water and vacuum drying.

[0047] The infrared image of the core-shell structured composite flame-retardant material obtained in this embodiment is as follows: Figure 1 As shown, at 3445cm -1 1742 and 1681cm -1 1463cm -1 1149cm -1 1042cm-1 1349cm -1 1082cm -1 961cm -1 799cm -1 The characteristic peaks are for NH, C=O, BOC, P=O, PO, BO, Si-O-Si, Si-OB, and Si-O bonds, respectively.

[0048] Example 2: Preparation of Core-Shell Structured Composite Flame Retardant Material S1. Mix 48g of a phosphorus, nitrogen and boron-containing carboxylic acid compound, 0.48g of silane coupling agent KH550 and 96g of ethanol, and heat treat at 70℃ for 10min to obtain a pretreated core. Control the particle size of the pretreated core to be 5µm. S2. Add 20g of ammonium polyphosphate, 0.06g of alkylphenol polyoxyethylene ether OP-9 and 4g of diethylene glycol dimethyl ether to the pretreated core from step S1, mix well, adjust the pH to 2 with hydrochloric acid, and add a mixture of 3.45g of phenyltrimethoxysilane and 0.55g of boric acid dropwise over 30 minutes at 70°C. Increase the temperature to 130°C and react for 5 hours. After the reaction is completed, the core-shell structured composite flame retardant material is obtained by rotary evaporation, washing with deionized water and vacuum drying.

[0049] Example 3: Preparation of Core-Shell Structured Composite Flame-Retardant Material S1. Mix 48g of a phosphorus, nitrogen and boron-containing carboxylic acid compound, 0.48g of silane coupling agent KH550 and 96g of ethanol, and heat treat at 70℃ for 10min to obtain a pretreated core. Control the particle size of the pretreated core to be 5µm. S2. Add 60g of ammonium polyphosphate, 0.18g of alkylphenol polyoxyethylene ether OP-9 and 12g of diethylene glycol dimethyl ether to the pretreated core from step S1, mix well, adjust the pH to 2 with hydrochloric acid, and add a mixture of 10.35g of phenyltrimethoxysilane and 1.65g of boric acid dropwise over 30 minutes at 70°C. Increase the temperature to 130°C and react for 5 hours. After the reaction is completed, the core-shell structured composite flame retardant material is obtained by rotary evaporation, washing with deionized water and vacuum drying.

[0050] Comparative Example 1: Preparation of Core-Shell Structured Composite Flame Retardant Material (Carboxylic Acid Compounds Containing Phosphorus, Nitrogen, and Boron Not Pretreated) 48g of a phosphorus, nitrogen, and boron-containing carboxylic acid compound (particle size 5µm) was mixed with 40g of ammonium polyphosphate, 0.12g of alkylphenol polyoxyethylene ether OP-9, and 8g of diethylene glycol dimethyl ether. The mixture was then adjusted to pH 2 with hydrochloric acid. A mixture of 6.9g of phenyltrimethoxysilane and 1.1g of boric acid was added dropwise over 30 minutes at 70℃. The temperature was raised to 130℃ and the reaction was carried out for 5 hours. After the reaction was completed, the core-shell structured composite flame retardant material was obtained by rotary evaporation, washing with deionized water, and vacuum drying.

[0051] Comparative Example 2: Preparation of core-shell structured composite flame-retardant material (by replacing boric acid with an equal mass of phenyltrimethylsilane). S1. Mix 48g of a phosphorus, nitrogen and boron-containing carboxylic acid compound, 0.48g of silane coupling agent KH550 and 96g of ethanol, and heat treat at 70℃ for 10min to obtain a pretreated core. Control the particle size of the pretreated core to be 5µm. S2. Add 40g of ammonium polyphosphate, 0.12g of alkylphenol polyoxyethylene ether OP-9 and 8g of diethylene glycol dimethyl ether to the pretreated core from step S1, mix well, adjust the pH to 2 with hydrochloric acid, add 8g of phenyltrimethoxysilane dropwise over 30 minutes at 70℃, raise the temperature to 130℃ and react for 5 hours. After the reaction is completed, the core-shell structured composite flame retardant material is obtained by rotary evaporation, washing with deionized water and vacuum drying.

[0052] Comparative Example 3: Preparation of core-shell structured composite flame retardant material (by replacing phenyltrimethylsilane and boric acid with an equal mass of silane coupling agent KH550). S1. Mix 48g of a phosphorus, nitrogen and boron-containing carboxylic acid compound, 0.48g of silane coupling agent KH550 and 96g of ethanol, and heat treat at 70℃ for 10min to obtain a pretreated core. Control the particle size of the pretreated core to be 5µm. S2. Add 40g of ammonium polyphosphate, 0.12g of alkylphenol polyoxyethylene ether OP-9 and 8g of diethylene glycol dimethyl ether to the pretreated core from step S1, mix well, adjust the pH to 2 with hydrochloric acid, and add 8g of silane coupling agent KH550 dropwise over 30 minutes at 70℃. Increase the temperature to 130℃ and react for 5 hours. After the reaction is completed, the core-shell structured composite flame retardant material is obtained by rotary evaporation, washing with deionized water and vacuum drying.

[0053] Comparative Example 4: Preparation of core-shell structured composite flame-retardant material (phenyltrimethylsilane was replaced with an equal mass of vinyltrimethoxysilane). S1. Mix 48g of a phosphorus, nitrogen and boron-containing carboxylic acid compound, 0.48g of silane coupling agent KH550 and 96g of ethanol, and heat treat at 70℃ for 10min to obtain a pretreated core. Control the particle size of the pretreated core to be 5µm. S2. Add 40g of ammonium polyphosphate, 0.12g of alkylphenol polyoxyethylene ether OP-9 and 8g of diethylene glycol dimethyl ether to the pretreated core from step S1, mix well, adjust the pH to 2 with hydrochloric acid, and add a mixture of 6.9g of vinyltrimethoxysilane and 1.1g of boric acid dropwise over 30 minutes at 70°C. Increase the temperature to 130°C and react for 5 hours. After the reaction is completed, the core-shell structured composite flame retardant material is obtained by rotary evaporation, washing with deionized water and vacuum drying.

[0054] Comparative Example 5: Preparation of Core-Shell Structured Composite Flame-Retardant Material (with Adjusted Preparation Method) S1. Mix 48g of a phosphorus, nitrogen and boron-containing carboxylic acid compound, 0.48g of silane coupling agent KH550 and 96g of ethanol, and heat treat at 70℃ for 10min to obtain a pretreated core. Control the particle size of the pretreated core to be 5µm. S2, 6.9g phenyltrimethoxysilane, 1.1g boric acid and 8g diethylene glycol dimethyl ether were mixed, and the pH was adjusted to 3 with hydrochloric acid. The mixture was reacted at 80℃ for 6h. Then, a pretreated core, 40g ammonium polyphosphate, 0.12g alkylphenol polyoxyethylene ether OP-9 and 8g diethylene glycol dimethyl ether were added and mixed evenly. The mixture was stirred for 40min. After the reaction was completed, the core-shell structured composite flame retardant material was obtained by rotary evaporation, washing with deionized water and vacuum drying.

[0055] Comparative Example 6: Preparation of Composite Flame Retardant Materials 40g of ammonium polyphosphate, 0.12g of alkylphenol polyoxyethylene ether OP-9 and 8g of diethylene glycol dimethyl ether were mixed evenly, and the pH was adjusted to 2 with hydrochloric acid. A mixture of 6.9g of phenyltrimethoxysilane and 1.1g of boric acid was added dropwise over 30 minutes at 70℃. The temperature was raised to 130℃ and the reaction was carried out for 5 hours. After the reaction was completed, the composite flame retardant material was obtained by rotary evaporation, washing with deionized water and vacuum drying.

[0056] Comparative Example 7: Preparation of Composite Flame Retardant Materials S1, 40g ammonium polyphosphate, 0.12g alkylphenol polyoxyethylene ether OP-9 and 8g diethylene glycol dimethyl ether were mixed evenly, and the pH was adjusted to 2 with hydrochloric acid. A mixture of 6.9g phenyltrimethoxysilane and 1.1g boric acid was added dropwise over 30min at 70℃. The temperature was raised to 130℃ and reacted for 5h. After the reaction was completed, the modified ammonium polyphosphate was obtained by rotary evaporation, washing with deionized water and vacuum drying. S2. Mix 48g of a phosphorus-nitrogen-boron-containing carboxylic acid compound and 48g of modified ammonium polyphosphate evenly to obtain a composite flame retardant material.

[0057] Application example: Preparation of flame-retardant polypropylene The flame-retardant polypropylene formulation, by weight, is as follows: 100 parts polypropylene resin, 0.2 parts calcium stearate, 0.1 parts antioxidant 1010, 0.1 parts antioxidant 168, and 10 parts flame retardant (core-shell structured composite flame-retardant materials of Examples 1-3, Comparative Examples 1-5, composite flame-retardant materials of Comparative Examples 6-7, and the phosphorus-nitrogen-boron carboxylic acid compound of the preparation example).

[0058] The preparation method is as follows: polypropylene resin, calcium stearate, antioxidant and flame retardant are blended and melt-blended and extruded at 200°C.

[0059] The flame-retardant polypropylene obtained from the above application example was subjected to performance testing: Test Example 1 Flame retardancy: Tested according to UL94 standard; Limiting oxygen index: Tested according to GB / T 2406.2-2009 standard; Tensile yield strength and elongation at break: tested according to GB / T 1040.1-2018 standard; results are shown in Table 1.

[0060] Table 1

[0061] Test Example 2 The flame-retardant polypropylene obtained was aged at 120℃ and with an oxygen content of 50% for 48 hours, and tensile strength and elongation at break were tested. The results are shown in Table 2.

[0062] Table 2

[0063] Results analysis: As can be seen from Tables 1 and 2: A comparison of Examples 1-3 shows that a V-0 flame retardant rating and a high limiting oxygen index can be achieved at an addition amount of 10%. However, as the shell thickness increases, the mechanical properties and resistance to thermo-oxidative aging of polypropylene decrease. As can be seen from the comparison of Example 1 and Comparative Example 1, when the carboxylic acid compound containing phosphorus, nitrogen and boron is pretreated with a silane coupling agent, the V-0 flame retardant rating cannot be achieved at an addition amount of 10%, the limiting oxygen index decreases, and the mechanical properties and thermo-oxidative aging resistance of polypropylene decrease. Comparing Example 1 and Comparative Example 2, it can be seen that when boric acid is replaced with the same mass of phenyltrimethylsilane, the V-0 flame retardant rating cannot be achieved at an addition amount of 10%, the limiting oxygen index decreases, the mechanical properties of polypropylene are not significantly affected, but the resistance to thermo-oxidative aging decreases. Comparing Example 1 and Comparative Example 3, it can be seen that when phenyltrimethylsilane and boric acid are replaced with the same mass of silane coupling agent KH550, the flame retardant rating can only reach V-2 flame retardant rating at a 10% addition amount, the limiting oxygen index decreases significantly, and the mechanical properties and thermo-oxidative aging resistance of polypropylene also decrease. Comparing Example 1 and Comparative Example 4, it can be seen that replacing phenyltrimethylsilane with the same mass of vinyltrimethoxysilane at a 10% addition level cannot achieve the V-0 flame retardant rating, the limiting oxygen index decreases, the mechanical properties of polypropylene are not significantly affected, but the resistance to thermo-oxidative aging decreases. As can be seen from the comparison of Example 1 and Comparative Example 5, the preparation method not only significantly affects the flame retardant performance and limiting oxygen index of the core-shell structure composite flame retardant material, but also affects the mechanical properties and thermo-oxidative aging resistance of polypropylene. Comparisons of Examples 1, 6, and 7 with added phosphorus, nitrogen, and boron carboxylic acid compounds show that using a single phosphorus, nitrogen, and boron carboxylic acid compound, borosilicate-modified ammonium polyphosphate, or a direct mixture of both, at a 10% addition level, cannot achieve a V-0 flame retardant rating, significantly reduces the limiting oxygen index, and also affects the mechanical properties and thermo-oxidative aging resistance of the polymer.

[0064] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A core-shell structured composite flame-retardant material, characterized in that, It includes a core and a shell from the inside out, wherein the core is a carboxylic acid compound containing phosphorus, nitrogen, and boron, and the shell is borosilicate-modified ammonium polyphosphate; The phosphorus-nitrogen-boron-containing carboxylic acid compound contains an isocyanurate ring, a phosphorus-phenanthrene group, and a boric acid group in its molecular structure. The method for preparing the phosphorus-nitrogen-boron-containing carboxylic acid compound includes the following steps: (1) Esterification reaction: tris(2-hydroxyethyl) isocyanurate, maleic anhydride and solvent a, heat to 85-95℃, and stir continuously for 2-4 hours under nitrogen atmosphere; (2) Addition reaction: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and solvent a are added in batches to the reaction solution of step (1), the temperature is raised to 100-110℃ and the reaction is carried out for 8-9 hours; (3) Esterification reaction: Dissolve boric acid in solvent a and add it to the mixture in step (2), and then continue the reaction for 2-3 hours; (4) Purification: Remove solvent a from the solution after the reaction in step (3), and wash and dry the crude product to obtain a white solid product; The solvent a is dioxane; The raw materials for the borosilicate-modified ammonium polyphosphate include ammonium polyphosphate, phenyltrimethoxysilane, and boric acid.

2. The core-shell structured composite flame-retardant material according to claim 1, characterized in that, The mass ratio of ammonium polyphosphate, phenyltrimethoxysilane, and boric acid is 35-45:5-8:0.8-1.

5.

3. The core-shell structured composite flame-retardant material according to claim 2, characterized in that, The mass ratio of the total mass of the phosphorus-nitrogen-boron-containing carboxylic acid compound and the borosilicate-modified ammonium polyphosphate raw material is 1:0.5-1.

5.

4. The method for preparing the core-shell structured composite flame-retardant material according to any one of claims 1-3, characterized in that, Includes the following steps: S1. The core is pretreated with a silane coupling agent to obtain a pretreated core. S2. Mix the pretreated core, ammonium polyphosphate, emulsifier and solvent b. Under acidic conditions, add a mixture of phenyltrimethoxysilane and boric acid dropwise at the first temperature. React at the second temperature. After the reaction is completed, the mixture is obtained by rotary evaporation, washing and vacuum drying. Solvent b is diethylene glycol dimethyl ether.

5. The method for preparing the core-shell structured composite flame-retardant material according to claim 4, characterized in that, The silane coupling agent is selected from at least one of KH550, KH560, KH570 and KH590.

6. The method for preparing the core-shell structured composite flame-retardant material according to claim 4, characterized in that, The surface pretreatment method is as follows: mix the core, silane coupling agent and ethanol, and perform heat treatment to obtain the pretreated core.

7. The method for preparing the core-shell structured composite flame-retardant material according to claim 4, characterized in that, The ammonium polyphosphate has a phosphorus content of 30-32.5% and a nitrogen content of 14-15%.

8. The application of the core-shell structured composite flame retardant material according to any one of claims 1-3 or the core-shell structured composite flame retardant material prepared by the preparation method according to any one of claims 4-7 in polymer modification, coatings and electronic packaging.

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