A flame retardant, its preparation method and its use in polyvinyl chloride

Abstract

The application relates to the field of flame retardants, and particularly discloses a flame retardant, a preparation method thereof and application of the flame retardant in polyvinyl chloride. The flame retardant comprises the following raw materials in parts by weight: 2.8-3.6 parts of carboxymethyl chitosan microcapsules, 2.5-4 parts of hydroxyapatite-coated aluminum magnesium hydrotalcite, 3.5-4.5 parts of tricresyl phosphate, 0.7-0.9 parts of expandable graphite and 3-5 parts of polyvinyl butyral. The core of the carboxymethyl chitosan microcapsules is magnesium hydroxide loaded with bismuth stannate, the wall is carboxymethyl chitosan, and the mass ratio of the carboxymethyl chitosan to the magnesium hydroxide loaded with bismuth stannate is 4-5:1. The flame retardant can be used in polyvinyl chloride, has the advantages of good flame-retardant and smoke-suppression effects, and can effectively improve the mechanical strength of the PVC.

Description

Technical Field

[0001] This application relates to the field of flame retardant technology, and more specifically, to a flame retardant, its preparation method, and its application in polyvinyl chloride. Background Technology

[0002] As is well known, polyvinyl chloride (PVC) has experienced rapid development due to its excellent performance and processing properties. However, its widespread application is limited by the significant loss of life and property caused by the large amounts of smoke and toxic gases it produces when burning. To improve the flame retardant and smoke-suppressing properties of PVC materials, flame retardants are often added directly to the PVC resin.

[0003] Flame retardants have flame-retardant and smoke-suppressing effects on PVC materials. Directly adding flame retardants to PVC resin is the most economical and effective way to prepare flame-retardant PVC. Additive flame retardants are divided into organic and inorganic types. Organic flame retardants mainly include phosphate esters, ammonium polyphosphate, and melamine. They are characterized by low dosage but high price and weak smoke suppression effect, thus their application in PVC is relatively limited. In contrast, inorganic flame retardants have advantages over organic flame retardants, such as good thermal stability, environmental friendliness, and low production cost, and are therefore widely used in PVC. Currently, commonly used inorganic flame retardants mainly include aluminum hydroxide, magnesium hydroxide, antimony-based flame retardants, and zinc hydroxystannate (ZHS). Inorganic flame retardants are popular in industrial applications due to their low cost, high thermal stability, low toxicity, and thermal insulation effect. However, to achieve the desired flame retardant effect, inorganic flame retardants need to be added at more than 50% of the weight of polyvinyl chloride. But inorganic flame retardants have higher surface energy, while polyvinyl chloride has lower surface energy. This energy difference results in poor compatibility between inorganic flame retardants and polyvinyl chloride, thereby reducing the mechanical properties of polyvinyl chloride materials. Summary of the Invention

[0004] In order to improve the dispersibility of inorganic flame retardants in PVC, thereby enhancing the mechanical, smoke-suppressing and flame-retardant properties of PVC, this application provides a flame retardant, its preparation method and its application in polyvinyl chloride.

[0005] In a first aspect, this application provides a flame retardant, which adopts the following technical solution:

[0006] A flame retardant comprising the following raw materials in parts by weight: 2.8-3.6 parts carboxymethyl chitosan microcapsules, 2.5-4 parts hydroxyapatite-coated aluminum magnesium hydrotalcite, 3.5-4.5 parts tricresyl phosphate, 0.7-0.9 parts expandable graphite, and 3-5 parts polyvinyl butyral.

[0007] The core of the carboxymethyl chitosan microcapsule is magnesium hydroxide-supported bismuth stannate, and the capsule wall is carboxymethyl chitosan. The mass ratio of carboxymethyl chitosan to magnesium hydroxide-supported bismuth stannate is 4-5:1.

[0008] By adopting the above technical solution, using carboxymethyl chitosan as the capsule wall and magnesium hydroxide loaded with bismuth stannate as the core, some hydroxyl groups on the surface of magnesium hydroxide can react with carboxymethyl chitosan, thereby forming a relatively smooth network film on the surface of magnesium hydroxide, improving the dispersibility of bismuth stannate loaded on magnesium hydroxide. The carboxymethyl chitosan coating improves the compatibility of magnesium hydroxide in PVC, increasing the tensile strength and elongation at break of the PVC material, and further enhancing its mechanical strength. In addition, carboxymethyl chitosan undergoes a ring-opening reaction before PVC decomposes, self-aggregating in PVC to form an aromatic ring cross-linked structure, thereby accelerating the decomposition of the PVC matrix, i.e., dehydration and carbonization, increasing char formation and thus exerting a condensed phase flame retardant mechanism. Moreover, as a nitrogen-containing compound, carboxymethyl chitosan exhibits good combustion properties. It can produce non-toxic gases such as ammonia and nitrogen, which can dilute the concentration of oxygen and combustible gases, inhibit combustion, and exert a gas-phase flame retardant mechanism. On the other hand, it can also promote the expansion of the carbon layer, better enhance the flame retardant effect of the condensed phase, and increase the smoke suppression effect. Magnesium hydroxide decomposes at high temperature, producing a dehydration reaction. The crystal water obtained by hydrolysis absorbs heat and turns into water vapor, which reduces the concentration of gaseous combustibles, inhibits the temperature rise of the burning material, and prevents further combustion. At the same time, the dispersed product magnesium oxide protective film has good fire resistance, covers the surface of the burning material, prevents the burning material from continuing to contact oxygen, and hinders the heat transfer capacity, thus achieving a flame retardant effect. The tin in the bismuth stannate loaded on its surface has a catalytic carbonization effect, promotes the cross-linking of PVC chains, forms a dense protective carbon layer, and inhibits the release of heat.

[0009] Hydroxyapatite itself is non-combustible, and its high phosphorus content makes it suitable as a novel inorganic flame retardant. Aluminum-magnesium hydrotalcite (ALH) is a layered bimetallic hydroxide. Functionalizing ADH with hydroxyapatite enhances the thermal stability of the inner ADH layer upon heating. During the initial stages of PVC degradation, the hydroxyapatite coating dehydrates to generate water vapor, diluting flammable gases. It also reacts with HCl released during PVC degradation to form Ca5(PO4)3Cl, further reducing HCl release. The inner ADH layer continues to dehydrate at high temperatures, generating water vapor and the flame-retardant gas carbon dioxide, which dilutes oxygen and flammable gases in the air. Simultaneously, it absorbs heat, lowering the temperature of the burning material and preventing or delaying thermal decomposition. Furthermore, the metal oxides produced during decomposition have high melting points, forming a dense protective layer on the material surface, preventing further intrusion of oxygen and heat and slowing the combustion rate. The combined action of hydroxyapatite and ADH alters the properties of PVC. The pyrolysis process generates more condensed phase carbon layers, which more effectively protects the resin matrix beneath the carbon layers.

[0010] Trimethylbenzene phosphate is a colorless or pale yellow oily liquid, insoluble in water. It is also a flame-retardant plasticizer with good flame retardancy with PVC. After thermal decomposition, it produces phosphoric acid substances, which catalyze the charring of PVC, thereby preventing heat release. Moreover, it works synergistically with bismuth stannate in the core to inhibit the heat release of PVC and reduce smoke production. In particular, phosphoric acid and tin can catalyze the conversion of toxic fumes such as CO into non-toxic gases such as CO2. In the event of a fire, this can protect the safety of victims and reduce casualties. Therefore, it can synergistically improve the graphitization degree of the char residue, increase the density of the char residue, prevent the release of heat during PVC combustion, and prevent the release of toxic gases, thus achieving a flame-retardant and smoke-suppressing effect.

[0011] Expandable graphite expands when heated, forming a carbon layer structure that isolates heat and combustible gases. It also provides some reinforcement. Furthermore, the carbon atoms on the surface of expandable graphite can be oxidized into carboxyl active groups, improving the mechanical properties of polyvinyl chloride. Hydroxyapatite and tricresyl phosphate decompose when heated to produce phosphates, which not only promote the dehydration and carbonization of carboxymethyl chitosan wall materials but also interact with the carbon layer structure formed by expandable graphite, filling the pores left by the expandable graphite and forming a more stable condensed phase intercalated carbon layer structure. This greatly reduces the transfer of heat and combustible gases, achieving a flame-retardant effect.

[0012] Polyvinyl butyral has good compatibility with PVC, which can improve the affinity between expandable graphite and PVC matrix, enhance the compatibility between PVC matrix and various raw materials, and reduce the impact of raw material addition on the mechanical properties of PVC.

[0013] Optionally, the capsule wall of the carboxymethyl chitosan microcapsule further contains melamine-modified calcium hydroxystannate, with a mass ratio of carboxymethyl chitosan to melamine-modified calcium hydroxystannate of 1:0.1-0.3.

[0014] By adopting the above technical solution, melamine phosphate, belonging to the phosphorus-nitrogen flame retardant system, can effectively inhibit the thermal decomposition and combustion propagation of PVC. Furthermore, its modification of calcium hydroxystannate improves its thermal stability. Additionally, melamine phosphate has good compatibility with polyvinyl chloride, improving the compatibility between calcium hydroxystannate and PVC and reducing its impact on mechanical strength. Calcium hydroxystannate catalyzes the rapid cross-linking of PVC near the flame end into char, and under high-temperature conditions, it continuously dehydrates to generate water vapor, diluting combustible gases. The dehydrated calcium stannate further adsorbs and reacts with free HCl in the air, and the resulting calcium chloride and tin tetrachloride undergo a series of redox reactions with carbon monoxide, producing tin chloride and calcium stanide while reducing smoke toxicity. Moreover, tin chloride and... Calcium stannate can also have a more significant thermal barrier effect with the char layer; calcium hydroxystannate has a good flame-retardant synergistic effect with hydroxyapatite and tricresyl phosphate, which can improve the graphitization degree and density of the char residue, prevent the release of heat during PVC combustion, prevent the release of toxic gases, and improve the smoke suppression and flame retardant effect. Phosphoric acid produced by the thermal decomposition of hydroxyapatite and tricresyl phosphate, as well as tin ions produced by calcium hydroxystannate, promote the char formation of PVC. Calcium chloride and tin chloride produced by the decomposition of calcium hydroxystannate further react with the phosphoric acid produced by hydroxyapatite and tricresyl phosphate to generate phosphate substances. These inorganic salts greatly help the formation of a dense char layer. The formed char layer prevents the dissipation of heat and the release of harmful gases, achieving a good flame retardant and smoke suppression effect.

[0015] Optionally, the mass ratio of melamine phosphate to calcium hydroxystannate in the melamine phosphate modified calcium hydroxystannate is 3:1.4-1.6.

[0016] By adopting the above technical solution and using an appropriate ratio of melamine phosphate to calcium hydroxystannate, melamine phosphate can effectively improve the dispersibility and compatibility of calcium hydroxystannate with PVC. At the same time, melamine phosphate can also significantly improve the thermal decomposition performance of PVC, enhance the natural properties of PVC, and inhibit the release of smoke during combustion.

[0017] Optionally, the mass ratio of the carboxymethyl chitosan microcapsules, tricresyl phosphate, and expandable graphite is 4:5:1.

[0018] By adopting the above technical solution, the three substances, when in a specific mass ratio, form a continuous insulating carbon layer with the best synergistic effect, strong gas isolation ability, and the most obvious smoke suppression and flame retardant effects.

[0019] Optionally, the expandable graphite is phytic acid-coated expandable graphite.

[0020] By adopting the above technical solution, phytic acid, a flame-retardant bio-based compound containing six phosphate groups, produces a large number of phosphate derivatives during pyrolysis, which capture flammable free radicals, absorb heat, and inhibit flame spread. After combustion, it cross-links with the char layer to form aliphatic and aromatic POC bonds. Excessive phytic acid combustion forms a circular structure that adheres to the char layer surface, reinforcing the originally loose and fragile char layer, reducing the gaps between char layer sheets, making it difficult for smoke and toxic gases to escape, and simultaneously blocking heat dissipation and propagation, thus improving the flame-retardant performance of the material. Furthermore, the phytic acid coating increases the compatibility between expandable graphite and PVC, which is beneficial for improving mechanical strength. Moreover, the phosphate groups of phytic acid can coordinate with calcium ions in hydroxyapatite. On the other hand, the hydroxyl and amino groups in carboxymethyl chitosan can also react chemically with the phosphate groups in phytic acid to form stable chemical bonds. Therefore, phytic acid can improve the interaction between carboxymethyl chitosan microcapsules and hydroxyapatite-coated aluminum-magnesium hydrotalcite.

[0021] Optionally, phytic acid-coated expandable graphite is prepared by adding phytic acid and silane coupling agent KH-550 to an 85% ethanol solution and stirring at 60°C for 3 hours. The expandable graphite and the mixed solution are repeatedly filtered, washed with ethanol, centrifuged, and dried at 70°C to constant weight.

[0022] By adopting the above technical solution, phytic acid, a highly efficient bio-based flame retardant, is grafted onto the surface of expandable graphite through a silane coupling agent. Phytic acid binds the expandable graphite together, allowing it to form a dense network and mesh-like cross-linked structure after combustion. This enhances the density and strength of the char layer, and better blocks heat and combustible gases.

[0023] Optionally, the raw materials for the hydroxyapatite-coated aluminum-magnesium hydrotalcite include calcium phosphate-coated gel and aluminum-magnesium hydrotalcite in a mass ratio of 1:0.5-1.

[0024] The above-mentioned technical solutions include hydrothermal synthesis, electrochemical deposition, sol-gel synthesis, and plasma spraying. In this application, calcium phosphate coated gel and aluminum-magnesium hydrotalcite are used to prepare hydroxyapatite-coated aluminum-magnesium hydrotalcite via the sol-gel method. Calcium phosphate precursors are dispersed in an organic solvent and subjected to chemical reactions such as hydrolysis and condensation to form a stable transparent sol system in the solution. The sol is then aged and slowly polymerized between the gel particles to form a three-dimensional network structure gel. After drying and sintering, the desired hydroxyapatite is obtained. The above-mentioned amounts of calcium phosphate coated gel and aluminum-magnesium hydrotalcite enable hydroxyapatite to be uniformly coated on the surface of aluminum-magnesium hydrotalcite, improving the compatibility of aluminum-magnesium hydrotalcite with PVC while enhancing the flame retardancy of PVC.

[0025] Optionally, the calcium-phosphorus coated gel is prepared by adding an anhydrous ethanol solution of phosphorus pentoxide to an anhydrous ethanol solution of calcium nitrate tetrahydrate, adjusting the pH to 9.5-10.5 with ammonia water, and then aging at room temperature.

[0026] By adopting the above technical solution, phosphorus pentoxide and calcium nitrate tetrahydrate are used as raw materials for calcium phosphorus coating gel. The gel can produce a certain degree of adhesion with aluminum magnesium hydrotalcite. After sintering, a hydroxyapatite coating layer can be obtained on the surface of aluminum magnesium hydrotalcite.

[0027] Secondly, this application provides a method for preparing a flame retardant, which adopts the following technical solution:

[0028] A method for preparing a flame retardant includes the following steps:

[0029] Expandable graphite was dispersed in deionized water, ultrasonicated to homogenize, and then carboxymethyl chitosan microcapsules were added. After homogenization, the mixture was pre-frozen and freeze-dried to obtain an aerogel matrix.

[0030] Polyvinyl butyral was dissolved, and hydroxyapatite-coated aluminum magnesium hydrotalcite and tricresyl phosphate were added and mixed evenly to obtain a blend.

[0031] The flame retardant is prepared by immersing the aerogel matrix in a blending solution, vacuuming and impregnating, and then drying at 70-90℃.

[0032] By employing the above technical solution, expandable graphite and carboxymethyl chitosan microcapsules are mixed under the dispersion of deionized water, and then freeze-dried to form an aerogel matrix with a porous framework. The carboxymethyl chitosan microcapsules can provide a certain support for the expandable graphite. Then, a blend of polyvinyl butyral, tricresyl phosphate, and hydroxyapatite-coated aluminum-magnesium hydrotalcite is vacuum impregnated to fill and support the porous framework, increasing the structural stability, structural strength, and structural integrity of the three-dimensional porous framework of the aerogel. The addition of flame retardants to PVC resin results in more air layers in the PVC material, effectively blocking the contact between combustibles and oxygen, reducing the combustion rate. Moreover, the aerogel has an extremely low thermal conductivity, which can delay heat transfer and limit the generation and diffusion of smoke.

[0033] Thirdly, this application provides the application of a flame retardant in polyvinyl chloride.

[0034] By adopting the above technical solution, the flame retardant prepared in this application can be used in polyvinyl chloride (PVC) to not only effectively improve the flame retardant and smoke suppression effects of PVC, but also improve its mechanical strength.

[0035] Optionally, the amount of flame retardant used is 3-5 wt% of the amount of polyvinyl chloride used.

[0036] By adopting the above technical solution, excellent flame retardant and smoke suppression effects can be achieved by adding flame retardant to polyvinyl chloride in a lower quantity.

[0037] In summary, this application has the following beneficial effects:

[0038] 1. Because this application uses carboxymethyl chitosan microcapsules, hydroxyapatite-coated aluminum magnesium hydrotalcite, tricresyl phosphate, and expandable graphite as raw materials to prepare flame retardants, the carboxymethyl chitosan microcapsules have carboxymethyl chitosan as the capsule wall and magnesium hydroxide-loaded bismuth stannate as the capsule core. Carboxymethyl chitosan can effectively improve the compatibility and dispersibility of the capsule core in PVC. Hydroxyapatite can also improve the compatibility of aluminum magnesium hydrotalcite with PVC. Trisyl phosphate and polyvinyl butyral have good compatibility with PVC. Expandable graphite can achieve a certain synergistic effect with tricresyl phosphate and carboxymethyl chitosan microcapsules. Thus, the flame retardant can not only effectively improve the flame retardancy and smoke suppression ability of PVC, but also enhance the mechanical strength of PVC.

[0039] 2. In this application, a certain amount of melamine phosphate-modified calcium hydroxystannate is preferably added to the carboxymethyl chitosan capsule wall. Melamine phosphate can improve the compatibility of calcium hydroxystannate with PVC. Melamine phosphate and calcium hydroxystannate also have certain flame retardant effects. Moreover, calcium hydroxystannate can form phosphate substances with hydroxyapatite and phosphoric acid produced by the thermal decomposition of tricresyl phosphate, thereby increasing the density of the char layer and enhancing the flame retardant and smoke suppression effects.

[0040] 3. In this application, phytic acid is used to modify expandable graphite, which can increase the compatibility and dispersibility of expandable graphite with PVC, reduce the impact of the addition of expandable graphite on the mechanical strength of PVC, and at the same time, the phosphoric acid derivatives produced by the thermal decomposition of phytic acid can also have a synergistic effect with bismuth stannate, calcium stannate, etc., further enhancing the smoke suppression and flame retardant effect. Detailed Implementation

[0041] The following embodiments provide a further detailed description of this application.

[0042] Preparation Examples I-II of Melamine Phosphate Modified Calcium Hydroxystannate

[0043] Preparation Example I: ① Preparation of calcium hydroxystannate: 0.555 g of calcium chloride and 1.333 g of Na2SnO3·3H2O were dissolved in 50 mL of deionized water to prepare a 0.1 mol / L solution; the pH of the calcium chloride solution was adjusted to 10 using a 0.5 mol / L sodium hydroxide solution and used as the mother liquor. Under magnetic stirring, the Na2SnO3 solution was poured into the mother liquor and reacted for 5 minutes. A large amount of white precipitate was rapidly produced in the clear solution. The precipitate was washed three times by centrifugation with deionized water and dried at 60 °C for 12 h.

[0044] ② Add 1.4g of calcium hydroxystannate and 3g of melamine phosphate to 350ml of deionized water, stir at 50℃ for 5h, centrifuge, and then dry at 60℃ for 8h.

[0045] Preparation Example II: ① Preparation of calcium hydroxystannate: 0.555 g of calcium chloride and 1.333 g of Na2SnO3·3H2O were dissolved in 50 mL of deionized water to prepare a 0.1 mol / L solution; the pH of the calcium chloride solution was adjusted to 10 using a 0.5 mol / L sodium hydroxide solution and used as the mother liquor. Under magnetic stirring, the Na2SnO3 solution was poured into the mother liquor and reacted for 5 minutes. A large amount of white precipitate was rapidly produced in the clear solution. The precipitate was washed three times by centrifugation with deionized water and dried at 60 °C for 12 h.

[0046] ② Add 1.6g of calcium hydroxystannate and 3g of melamine phosphate to 350ml of deionized water, stir at 50℃ for 5h, centrifuge, and then dry at 60℃ for 8h.

[0047] Preparation Examples of Carboxymethyl Chitosan Microcapsules 1-9

[0048] Preparation Example 1: (1) Preparation of magnesium hydroxide-supported bismuth stannate in the core: 6g of bismuth stannate was ultrasonically dispersed in 60ml of deionized water, 6.4g of magnesium chloride was added to 10mL of deionized water, the temperature was raised to 90℃ and added to the above solution, and then 10ml of magnesium sulfate solution with a concentration of 0.3mol / l was added. The mixture was stirred and ammonia was added dropwise to adjust the pH to 11. The mixture was cooled to room temperature, the precipitate was washed with deionized water and dried at 60℃. The bismuth stannate was selected from Shanghai Yuanye Biotechnology, product number B81050;

[0049] (2) Preparation of carboxymethyl chitosan microcapsules: 5g of carboxymethyl chitosan was dissolved in 100ml of deionized water and stirred at 75℃ to obtain a capsule wall solution. 1g of magnesium hydroxide-loaded bismuth stannate was added to 100ml of anhydrous ethanol and ultrasonically dispersed for 30min to obtain a suspension. The suspension was poured into the capsule wall solution, refluxed at 130℃ and stirred for 15h, centrifuged, and the centrifuged precipitate was dissolved with deionized water. The precipitate was washed three times alternately with deionized water and anhydrous ethanol, frozen at -10℃ for 18h, pre-frozen in liquid nitrogen for 0.5h and then freeze-dried at -65℃ for 20h. The carboxymethyl chitosan was selected from Shifeng Biotechnology, catalog number A2308.

[0050] Preparation Example 2: (1) Preparation of magnesium hydroxide-supported bismuth stannate in the core: 6g of bismuth stannate was ultrasonically dispersed in 60ml of deionized water, 6.4g of magnesium chloride was added to 10mL of deionized water, the temperature was raised to 90℃ and added to the above solution, and then 10ml of magnesium sulfate solution with a concentration of 0.3mol / l was added. The mixture was stirred and ammonia was added dropwise to adjust the pH to 11. The mixture was cooled to room temperature, the precipitate was washed with deionized water and dried at 60℃. The bismuth stannate was selected from Shanghai Yuanye Biotechnology, product number B81050;

[0051] (2) Preparation of carboxymethyl chitosan microcapsules: 4g of carboxymethyl chitosan was dissolved in 100ml of deionized water and stirred at 75℃ to obtain a capsule wall solution. 1g of magnesium hydroxide-loaded bismuth stannate was added to 100ml of anhydrous ethanol and ultrasonically dispersed for 30min to obtain a suspension. The suspension was poured into the capsule wall solution, refluxed at 130℃ and stirred for 15h, centrifuged, and the centrifuged precipitate was dissolved with deionized water. The precipitate was washed three times alternately with deionized water and anhydrous ethanol, frozen at -10℃ for 18h, pre-frozen in liquid nitrogen for 0.5h and then freeze-dried at -65℃ for 20h. The carboxymethyl chitosan was selected from Shifeng Biotechnology, catalog number A2308.

[0052] Preparation Example 3: The difference from Preparation Example 1 is that in step (2), the amount of magnesium hydroxide-supported bismuth stannate in the core is 0.5g.

[0053] Preparation Example 4: The difference from Preparation Example 1 is that in step (2), the amount of magnesium hydroxide loaded with bismuth stannate in the core is 2g.

[0054] Preparation Example 5: Compared with Preparation Example 1, magnesium hydroxide was used as the capsule core. The specific method was as follows: 4g of carboxymethyl chitosan was dissolved in 100ml of deionized water and stirred at 75℃ to obtain a capsule wall solution. 1g of magnesium hydroxide was added to 100ml of anhydrous ethanol and ultrasonically dispersed for 30min to obtain a suspension. The suspension was poured into the capsule wall solution, refluxed at 130℃ and stirred for 15h, centrifuged, and the centrifuged precipitate was dissolved with deionized water. The precipitate was washed three times alternately with deionized water and anhydrous ethanol, frozen at -10℃ for 18h, pre-frozen in liquid nitrogen for 0.5h, and then freeze-dried at -65℃ for 20h. The carboxymethyl chitosan was selected from Shifeng Biotechnology, catalog number A2308.

[0055] Preparation Example 6: The difference from Preparation Example 1 is that bismuth stannate is used as the capsule core. The specific method is as follows: 4g of carboxymethyl chitosan is dissolved in 100ml of deionized water and stirred at 75℃ to obtain a capsule wall solution. 1g of bismuth stannate is added to 100ml of anhydrous ethanol and ultrasonically dispersed for 30min to obtain a suspension. The suspension is poured into the capsule wall solution, refluxed at 130℃ and stirred for 15h, centrifuged, and the centrifuged precipitate is dissolved with deionized water. It is washed three times alternately with deionized water and anhydrous ethanol, frozen at -10℃ for 18h, pre-frozen in liquid nitrogen for 0.5h, and then freeze-dried at -65℃ for 20h. The bismuth stannate is selected from Shanghai Yuanye Biotechnology, product number B81050, and the carboxymethyl chitosan is selected from Shifeng Biotechnology, catalog number A2308.

[0056] Preparation Example 7: The difference from Preparation Example 1 is that calcium hydroxystannate is added to the capsule wall. The specific method is as follows: (1) Preparation of bismuth stannate loaded with magnesium hydroxide in the capsule core: 6g of bismuth stannate is ultrasonically dispersed in 60ml of deionized water, 6.4g of magnesium chloride is added to 10mL of deionized water, the temperature is raised to 90℃, and added to the above solution. Then, 10ml of magnesium sulfate solution with a concentration of 0.3mol / l is added, stirred and ammonia is added dropwise, the pH is adjusted to 11, cooled to room temperature, the precipitate is washed with deionized water, and dried at 60℃. The bismuth stannate is selected from Shanghai Yuanye Biotechnology, product number B81050;

[0057] (2) Preparation of carboxymethyl chitosan microcapsules: 5g of carboxymethyl chitosan was dissolved in 100ml of deionized water and stirred at 75℃. 1.5g of calcium hydroxystannate was added to obtain a capsule wall solution. 1g of magnesium hydroxide-loaded bismuth stannate was added to 100ml of anhydrous ethanol and ultrasonically dispersed for 30min to obtain a suspension. The suspension was poured into the capsule wall solution, refluxed at 130℃ and stirred for 15h, centrifuged, and the centrifuged precipitate was dissolved with deionized water. The precipitate was washed three times alternately with deionized water and anhydrous ethanol, frozen at -10℃ for 18h, pre-frozen in liquid nitrogen for 0.5h and then freeze-dried at -65℃ for 20h. Calcium hydroxystannate was prepared according to the method in Preparation Example I. Carboxymethyl chitosan was selected from Shifeng Biotechnology, catalog number A2308.

[0058] Preparation Example 8: (1) Preparation of magnesium hydroxide-supported bismuth stannate: 6g of bismuth stannate was ultrasonically dispersed in 60ml of deionized water, 6.4g of magnesium chloride was added to 10mL of deionized water, the temperature was raised to 90℃ and added to the above solution, and then 10ml of magnesium sulfate solution with a concentration of 0.3mol / l was added. The mixture was stirred and ammonia was added dropwise to adjust the pH to 11. The mixture was cooled to room temperature, the precipitate was washed with deionized water and dried at 60℃. The bismuth stannate was selected from Shanghai Yuanye Biotechnology, product number B81050;

[0059] (2) Preparation of carboxymethyl chitosan microcapsules: 5g of carboxymethyl chitosan was dissolved in 100ml of deionized water and stirred at 75℃. 1.5g of melamine phosphate-modified calcium hydroxystannate was added to obtain a capsule wall solution. 1g of magnesium hydroxide-loaded bismuth stannate was added to 100ml of anhydrous ethanol and ultrasonically dispersed for 30min to obtain a suspension. The suspension was poured into the capsule wall solution, refluxed at 130℃ and stirred for 15h, centrifuged, and the centrifuged precipitate was dissolved with deionized water. The precipitate was washed three times alternately with deionized water and anhydrous ethanol, frozen at -10℃ for 18h, pre-frozen in liquid nitrogen for 0.5h, and then freeze-dried at -65℃ for 20h. The melamine phosphate-modified calcium hydroxystannate was prepared by Preparation Example I, and the carboxymethyl chitosan was selected from Shifeng Biotechnology, catalog number A2308.

[0060] Preparation Example 9: (1) Preparation of magnesium hydroxide-supported bismuth stannate: 6g of bismuth stannate was ultrasonically dispersed in 60ml of deionized water, 6.4g of magnesium chloride was added to 10mL of deionized water, the temperature was raised to 90℃ and added to the above solution, and then 10ml of magnesium sulfate solution with a concentration of 0.3mol / l was added. The mixture was stirred and ammonia was added dropwise to adjust the pH to 11. The mixture was cooled to room temperature, the precipitate was washed with deionized water and dried at 60℃. The bismuth stannate was selected from Shanghai Yuanye Biotechnology, product number B81050;

[0061] (2) Preparation of carboxymethyl chitosan microcapsules: 5g of carboxymethyl chitosan was dissolved in 100ml of deionized water and stirred at 75℃. 0.5g of melamine phosphate-modified calcium hydroxystannate was added to obtain a capsule wall solution. 1g of magnesium hydroxide-loaded bismuth stannate was added to 100ml of anhydrous ethanol and ultrasonically dispersed for 30min to obtain a suspension. The suspension was poured into the capsule wall solution, refluxed at 130℃ and stirred for 15h, centrifuged, and the centrifuged precipitate was dissolved with deionized water. The precipitate was washed three times alternately with deionized water and anhydrous ethanol, frozen at -10℃ for 18h, pre-frozen in liquid nitrogen for 0.5h, and then freeze-dried at -65℃ for 20h. The melamine phosphate-modified calcium hydroxystannate was prepared by Preparation Example II, and the carboxymethyl chitosan was selected from Shifeng Biotechnology, catalog number A2308.

[0062] Preparation Examples of Hydroxyapatite-Coated Alumina-Magnesium Hydrotalcite 10-11

[0063] Preparation Example 10: 1.42 g of phosphorus pentoxide was dissolved in 30 ml of anhydrous ethanol, and 7.88 g of calcium nitrate tetrahydrate was dissolved in 30 ml of anhydrous ethanol. The anhydrous ethanol solution of phosphorus pentoxide was added to the anhydrous ethanol solution of calcium nitrate tetrahydrate. The pH was adjusted to 10 with ammonia. After stirring evenly at room temperature, the mixture was allowed to stand at room temperature for 24 h to obtain calcium phosphorus coated gel.

[0064] 10g of calcium phosphate coated gel was mixed with 10g of aluminum magnesium hydrotalcite, stirred at room temperature for 1 hour, and then treated at 550℃ for 2 hours. The aluminum magnesium hydrotalcite was selected from Shanghai Jizhi Biochemical Technology Co., Ltd., model H41520-100g.

[0065] Preparation Example 11: 1.42 g of phosphorus pentoxide was dissolved in 30 ml of anhydrous ethanol, and 7.88 g of calcium nitrate tetrahydrate was dissolved in 30 ml of anhydrous ethanol. The anhydrous ethanol solution of phosphorus pentoxide was added to the anhydrous ethanol solution of calcium nitrate tetrahydrate. The pH was adjusted to 10 with ammonia. After stirring evenly at room temperature, the mixture was allowed to stand at room temperature for 24 h to obtain calcium phosphorus coated gel.

[0066] 10g of calcium phosphate coated gel was mixed with 5g of aluminum magnesium hydrotalcite, stirred at room temperature for 1 hour, and then treated at 550℃ for 2 hours. The aluminum magnesium hydrotalcite was selected from Shanghai Jizhi Biochemical Technology Co., Ltd., model H41520-100g. Example

[0067] Example 1: A flame retardant, the raw material amounts of which are shown in Table 1, wherein the capsule wall of the carboxymethyl chitosan microcapsule is carboxymethyl chitosan, the core is magnesium hydroxide-supported bismuth stannate, the mass ratio of carboxymethyl chitosan to magnesium hydroxide-supported bismuth stannate is 5:1, the carboxymethyl chitosan microcapsules are prepared from Preparation Example 1, the hydroxyapatite-coated aluminum magnesium hydrotalcite is prepared from Preparation Example 10, and the density of expandable graphite is 2.25 g / cm³. 3 The scale size is 100mm, and the mass ratio of expandable graphite, carboxymethyl chitosan and tricresyl phosphate is 1:4:5. Polyvinyl butyral is selected from Kuraray, model B60H.

[0068] The preparation method of the above flame retardant includes the following steps:

[0069] Expandable graphite was dispersed in 10 times its mass of deionized water, ultrasonically dispersed for 30 min, then carboxymethyl chitosan microcapsules were added, ultrasonically treated for 10 min, homogenized for 30 min, frozen in liquid nitrogen for 2 h, and freeze-dried at -65℃ and below 5 Pa for 72 h to obtain an aerogel matrix.

[0070] Polyvinyl butyral was dissolved in methanol at 1.25 times its mass, and hydroxyapatite-coated aluminum magnesium hydrotalcite and tricresyl phosphate were added and mixed evenly to obtain a blend.

[0071] The aerogel matrix was immersed in a blend solution, vacuumed and impregnated, and vacuum impregnated at 80°C for 12 hours. Then the temperature was raised to 90°C and dried to constant weight to obtain the flame retardant.

[0072] Table 1. Raw material dosage of flame retardants in Examples 1-6

[0073]

[0074] Example 2: A flame retardant, the raw material amounts of which are shown in Table 1, wherein the capsule wall of the carboxymethyl chitosan microcapsule is carboxymethyl chitosan, the core is magnesium hydroxide-supported bismuth stannate, the mass ratio of carboxymethyl chitosan to magnesium hydroxide-supported bismuth stannate is 4:1, the carboxymethyl chitosan microcapsules are prepared in Preparation Example 2, the hydroxyapatite-coated aluminum magnesium hydrotalcite is prepared in Preparation Example 11, and the density of expandable graphite is 2.25 g / cm³. 3 The scale size is 100mm, and the mass ratio of expandable graphite, carboxymethyl chitosan and tricresyl phosphate is 1:4:5. Polyvinyl butyral is selected from Kuraray, model B60H.

[0075] The preparation method of the above flame retardant includes the following steps:

[0076] Expandable graphite was dispersed in 10 times its mass of deionized water, ultrasonically dispersed for 60 min, then carboxymethyl chitosan microcapsules were added, ultrasonically treated for 10 min, homogenized for 40 min, frozen in liquid nitrogen for 2 h, and freeze-dried at -65℃ and below 5 Pa for 72 h to obtain an aerogel matrix.

[0077] Polyvinyl butyral was dissolved in 1.5 times its weight of methanol, and hydroxyapatite-coated aluminum magnesium hydrotalcite and tricresyl phosphate were added and mixed evenly to obtain a blend.

[0078] The aerogel matrix was immersed in a blend solution, vacuumed and impregnated, and vacuum impregnated at 80°C for 12 hours. Then the temperature was raised to 70°C and dried to constant weight to obtain the flame retardant.

[0079] Example 3: A flame retardant, the amount of raw materials used is shown in Table 1, and the rest is the same as in Example 1.

[0080] Example 4: A flame retardant, which differs from Example 1 in that the raw material amounts are shown in Table 1, wherein the mass ratio of expandable graphite, carboxymethyl chitosan and tricresyl phosphate is 1:4:3.89.

[0081] Example 5: A flame retardant, which differs from Example 1 in that the raw material amounts are shown in Table 1, wherein the mass ratio of expandable graphite, carboxymethyl chitosan and tricresyl phosphate is 1:3.11:5.

[0082] Example 6: A flame retardant, which differs from Example 1 in that the raw material amounts are shown in Table 1, wherein the mass ratio of expandable graphite, carboxymethyl chitosan and tricresyl phosphate is 1:3.11:3.89.

[0083] Example 7: A flame retardant, which differs from Example 1 in that the carboxymethyl chitosan microcapsules are prepared in Example 7.

[0084] Example 8: A flame retardant, which differs from Example 1 in that the carboxymethyl chitosan microcapsules are prepared in Example 8.

[0085] Example 9: A flame retardant, which differs from Example 1 in that the carboxymethyl chitosan microcapsules are prepared in Example 9.

[0086] Example 10: A flame retardant, differing from Example 9 in that the expandable graphite is phytic acid-coated expandable graphite. The method for preparing phytic acid-coated expandable graphite is as follows:

[0087] Add 10 ml of phytic acid and 1 g of silane coupling agent KH-550 to 200 ml of 85% ethanol solution, stir at 60 °C for 3 h to obtain a mixed solution. Filter 20 g of expandable graphite and the mixed solution repeatedly, wash with ethanol, centrifuge, and dry at 70 °C to constant weight.

[0088] Comparative Example

[0089] Comparative Example 1: A flame retardant, which differs from Example 1 in that the mass ratio of carboxymethyl chitosan in the capsule wall to magnesium hydroxide-loaded bismuth stannate in the core of the carboxymethyl chitosan microcapsule is 5:0.5, and the carboxymethyl chitosan microcapsule is prepared by Preparation Example 3.

[0090] Comparative Example 2: A flame retardant, which differs from Example 1 in that the mass ratio of carboxymethyl chitosan in the capsule wall to magnesium hydroxide-loaded bismuth stannate in the core of the carboxymethyl chitosan microcapsule is 5:2, and the carboxymethyl chitosan microcapsule is prepared by Example 4.

[0091] Comparative Example 3: A flame retardant, which differs from Example 1 in that the core of the carboxymethyl chitosan microcapsules is magnesium hydroxide, and the carboxymethyl chitosan microcapsules are prepared by Example 5.

[0092] Comparative Example 4: A flame retardant, which differs from Example 1 in that the core of the carboxymethyl chitosan microcapsules is bismuth stannate, and the carboxymethyl chitosan microcapsules are prepared by Example 6.

[0093] Comparative Example 5: A flame retardant, which differs from Example 1 in that an equal amount of magnesium hydroxide is used instead of carboxymethyl chitosan microcapsules.

[0094] Comparative Example 6: A flame retardant that differs from Example 1 in that it uses expandable graphite in place of tricresyl phosphate, i.e., the mass ratio of expandable graphite to carboxymethyl chitosan microcapsules is 5:5.

[0095] Comparative Example 7: A flame retardant, which differs from Example 1 in that it does not contain expandable graphite.

[0096] Comparative Example 8: A flame retardant, which differs from Example 1 in that an equal amount of aluminum-magnesium hydrotalcite is used to replace hydroxyapatite in coating the aluminum-magnesium hydrotalcite. The aluminum-magnesium hydrotalcite is selected from Shanghai Jizhi Biochemical Technology Co., Ltd., model H41520-100g.

[0097] Comparative Example 9: A flame retardant, which differs from Example 1 in that it is prepared by the following method: polyvinyl butyral is dissolved in methanol at 1.25 times its mass, hydroxyapatite-coated aluminum magnesium hydrotalcite, tricresyl phosphate, expandable graphite and carboxymethyl chitosan microcapsules are added, mixed evenly, heated to 90°C, and dried to constant weight to obtain the flame retardant.

[0098] Application examples

[0099] Application Example 1: Application of a flame retardant in polyvinyl chloride (PVC). The specific method is as follows: 36g of PVC and 1.8g of the flame retardant prepared in Example 1 are mixed together. Plasticizer (dioctyl phthalate), 0.18g of stearic acid, 0.18g of calcium stearate and 0.35g of silane coupling agent KH550 are added and mixed evenly. The mixture is then kneaded at 140°C for 8 minutes, then hot-pressed at 150°C and 7.5MPa for 8 minutes, and cold-pressed at room temperature for 8 minutes. The mixture is then cut into the required size. The PVC resin is selected from Tianjin LG Dagu, model TL-1000.

[0100] Application Example 2: Application of a flame retardant in polyvinyl chloride (PVC). The specific method is as follows: 36g of PVC and 1.08g of the flame retardant prepared in Example 1 are mixed together. Plasticizer (dioctyl phthalate), 0.18g of stearic acid, 0.18g of calcium stearate, and 0.35g of silane coupling agent KH550 are added and mixed evenly. The mixture is then kneaded at 140°C for 8 minutes, followed by hot pressing at 150°C and 7.5MPa for 8 minutes, and cold pressing at room temperature for 8 minutes. The mixture is then cut into PVC resin of the required size. The resin is selected from Tianjin LG Dagu and the model is TL-1000.

[0101] Application Examples 3-10: The difference from Application Example 1 is that the flame retardants prepared in Examples 3-10 are used respectively.

[0102] Application Examples 11-19: The difference from Application Example 1 is that the flame retardants prepared by Comparative Examples 1-9 are used respectively.

[0103] Application Example 20: PVC resin, selected from Tianjin LG Dagu, model TL-1000.

[0104] Performance testing

[0105] The performance of the PVC composite materials prepared according to the following methods for the corresponding use cases was tested, and the test results were recorded in Table 2.

[0106] 1. Limiting Oxygen Index: Under room temperature conditions, the limiting oxygen index of polyvinyl chloride materials prepared according to the corresponding test case was tested using a JF-3 oxygen index tester. The test standard was GB / T2406.2-2009, and the sample size was 120mm×6.5mm×3mm.

[0107] 2. Combustion performance: The CCT cone calorimeter was used for testing. The reference standard was GB / T16172-2007. The sample size was 100mm×100mm×10mm. The sample thermal radiation power was 35kW / m2. The total smoke release was tested at 400s.

[0108] 3. Tensile strength and elongation at break: According to GB / T1040.1-2006 standard, the tensile strength and elongation at break were measured by a UTM4204 universal tensile tester. Five parallel tests were performed and the average value was taken. The tensile speed was 2 mm / min, the sample size was 100 mm × 6 mm × 3 mm, and the gauge length was 30 mm.

[0109] Table 2 Performance test results of polyvinyl chloride containing flame retardants

[0110]

[0111] Based on the data in Table 2 and the raw material dosage in Example 1, it can be seen that the mass ratio of expandable graphite, carboxymethyl chitosan microcapsules, and tricresyl phosphate in Example 1 is 1:4:5. Furthermore, the addition of hydroxyapatite-coated aluminum-magnesium alloy results in a flame retardant that, when added to PVC resin, not only exhibits good flame retardancy and smoke suppression capabilities but also improves the mechanical strength of PVC to a certain extent. In Examples 2 and 3, the raw material dosages were adjusted, but the mass ratio of expandable graphite, carboxymethyl chitosan microcapsules, and tricresyl phosphate remained at 1:4:5, resulting in flame retardant and smoke suppression effects similar to those in Example 1.

[0112] Compared with Example 1, Examples 4-6 show that the mass ratio of expandable graphite, carboxymethyl chitosan microcapsules, and tricresyl phosphate was adjusted, while the other components remained unchanged. It can be seen that the flame retardant prepared and used in polyvinyl chloride exhibited a slight decrease in flame retardancy and smoke suppression capabilities.

[0113] In Example 7, the carboxymethyl chitosan microcapsules prepared in Preparation Example 7 were used. Compared with Preparation Example 1 in Example 1, Preparation Example 7 also added calcium hydroxystannate to the capsule wall. The data in Table 2 show that the flame retardant prepared in this way, when added to PVC resin, further improved the flame retardant and smoke suppression effects, but the tensile strength and elongation at break decreased slightly.

[0114] Examples 8 and 9 used carboxymethyl chitosan microcapsules prepared in Examples 8 and 9, respectively. Compared with Example 1 in Example 1, melamine phosphate was added to the wall material to improve calcium hydroxystannate. It can be seen that the oxygen index of the PVC materials prepared in Examples 8 and 9 increased, the total smoke release decreased, and the tensile strength was also slightly improved. This indicates that the flame retardant and smoke suppression effects of the flame retardant are enhanced, and its addition can reduce the impact on the mechanical strength of PVC and improve the mechanical properties of the composite material.

[0115] Compared with Example 9, Example 10 also uses phytic acid to pretreat expandable graphite. It can be seen that the PVC composite material made in Example 10 has a higher oxygen index, a lower total smoke emission, and improved flame retardant and smoke suppression effects.

[0116] In Application Examples 11 and 12, flame retardants prepared by Comparative Examples 1 and 2 were used, respectively. In Comparative Examples 1 and 2, carboxymethyl chitosan microcapsules prepared by Preparation Examples 3 and 4 were used, respectively. Compared with Preparation Example 1, Preparation Examples 3 and 4 reduced and increased the amount of core material, respectively. In Comparative Example 1, the amount of core material was reduced. Although the carboxymethyl chitosan wall material could effectively improve the compatibility between the core material and PVC and the mechanical strength did not change much, its flame retardant and smoke suppression capabilities were significantly reduced. In Comparative Example 2, the amount of core material was increased. Carboxymethyl chitosan could not effectively improve the compatibility between the core material and PVC, resulting in a decrease in mechanical strength. Furthermore, because the core material could not form a good dispersion in the PVC resin, its flame retardant effect was affected, and the improvement in flame retardant effect was not obvious.

[0117] In Application Examples 13 and 14, flame retardants prepared by Comparative Examples 3 and 4 were used, respectively. Compared with Example 1, Comparative Examples 3 and 4 used carboxymethyl chitosan microcapsules prepared by Preparation Examples 5 and 6, respectively. In Preparation Example 5, magnesium hydroxide was used as the core, and in Preparation Example 6, bismuth stannate was used as the core. It can be seen that in Application Examples 13 and 14, the oxygen index of the PVC material decreased and the total smoke release increased, but the tensile strength did not change much. This indicates that using magnesium hydroxide or bismuth stannate as the core alone does not significantly improve the flame retardant and smoke suppression effect of PVC as much as using magnesium hydroxide-loaded bismuth stannate as the core material.

[0118] In Application Example 15, the flame retardant prepared in Comparative Example 5 was used. Compared with Example 1, Comparative Example 5 used magnesium hydroxide instead of carboxymethyl chitosan, that is, bismuth stannate was not loaded on magnesium hydroxide and carboxymethyl chitosan wall material was not coated. It can be seen that the flame retardant prepared not only has a reduced flame retardant effect, but also causes the mechanical properties of the material, such as tensile strength, to be worse than those of pure PVC resin.

[0119] In Application Example 16, the flame retardant prepared in Comparative Example 6 was used. Compared with Example 1, Comparative Example 6 used expandable graphite in place of tricresyl phosphate by mass. It can be seen that the flame retardant and smoke suppression capabilities of the PVC material prepared in Comparative Example 6 were not as good as those in Example 1. Moreover, the increased amount of expandable graphite made it easy to generate agglomeration, which led to a decrease in the mechanical properties of PVC.

[0120] Compared with Application Example 1, Application Example 17 used the flame retardant prepared in Comparative Example 7, which did not contain expandable graphite. It can be seen that the flame retardant prepared in Application Example 17 had a lower flame retardant ability and a higher smoke release compared with Application Example 1.

[0121] In Application Example 18, the flame retardant prepared in Comparative Example 8 was used. Compared with Example 1, Comparative Example 8 used aluminum magnesium hydrotalcite instead of hydroxyapatite to coat aluminum magnesium hydrotalcite. It can be seen that the flame retardant prepared in Comparative Example 8 did not significantly improve the flame retardant ability and smoke suppression effect of PVC as much as in Example 1.

[0122] In Application Example 19, the flame retardant prepared by Comparative Example 9 was compared with that in Example 1. The flame retardant prepared by blending the raw materials in Application Example 9 showed that the oxygen index of the PVC composite material decreased and the smoke production increased. This indicates that the flame retardant prepared by direct blending is not as effective as that in Example 1 in improving the flame retardant and smoke suppression effect of PVC.

[0123] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A flame retardant, characterized in that, The raw materials include the following parts by weight: 2.8-3.6 parts carboxymethyl chitosan microcapsules, 2.5-4 parts hydroxyapatite-coated aluminum magnesium hydrotalcite, 3.5-4.5 parts tricresyl phosphate, 0.7-0.9 parts expandable graphite, and 3-5 parts polyvinyl butyral. The core of the carboxymethyl chitosan microcapsule is magnesium hydroxide-loaded bismuth stannate, and the capsule wall is composed of carboxymethyl chitosan and melamine phosphate-modified calcium hydroxystannate. The mass ratio of carboxymethyl chitosan to magnesium hydroxide-loaded bismuth stannate is 4-5:1, and the mass ratio of carboxymethyl chitosan to melamine phosphate-modified calcium hydroxystannate is 1:0.1-0.

3. The expandable graphite is phytic acid-coated expandable graphite. The method for preparing the flame retardant, The process includes the following steps: dispersing expandable graphite in deionized water, ultrasonicating to homogenize it, adding carboxymethyl chitosan microcapsules, homogenizing, pre-freezing, and freeze-drying to obtain an aerogel matrix; Polyvinyl butyral was dissolved, and hydroxyapatite-coated aluminum magnesium hydrotalcite and tricresyl phosphate were added and mixed evenly to obtain a blend. The flame retardant is prepared by immersing the aerogel matrix in a blending solution, vacuuming and impregnating, and then drying at 70-90℃.

2. The flame retardant according to claim 1, characterized in that: The mass ratio of melamine phosphate to calcium hydroxystannate in the melamine phosphate modified calcium hydroxystannate is 3:1.4-1.

6.

3. The flame retardant according to claim 1, characterized in that: The mass ratio of the carboxymethyl chitosan microcapsules, tricresyl phosphate, and expandable graphite is 4:5:

1.

4. The flame retardant according to claim 1, characterized in that: The raw materials for the hydroxyapatite-coated aluminum-magnesium hydrotalcite include calcium phosphate-coated gel and aluminum-magnesium hydrotalcite in a mass ratio of 1:0.5-1.

5. The flame retardant according to claim 4, characterized in that: The calcium-phosphorus coated gel was prepared by adding an anhydrous ethanol solution of phosphorus pentoxide to an anhydrous ethanol solution of calcium nitrate tetrahydrate, adjusting the pH to 9.5-10.5 with ammonia water, and then aging at room temperature.

6. The use of the flame retardant as described in any one of claims 1-5 in polyvinyl chloride.

7. The application of the flame retardant according to claim 6 in polyvinyl chloride, characterized in that: The amount of flame retardant used is 3-5 wt% of the amount of polyvinyl chloride used.

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