Flame-retardant modified expandable graphite and preparation method thereof

Abstract

The invention relates to the technical field of flame-retardant high polymer materials, in particular to flame-retardant modified expandable graphite and a preparation method thereof.The method comprises the steps that firstly, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is prepared into a dichloromethane solution, then a catalyst and a silane coupling agent are added, the mixture is stirred for a reaction, and the flame-retardant modified expandable graphite is obtained; and finally, carrying out rotary evaporation to obtain a modified oxide, preparing an ethanol solution from the modified oxide, adjusting the pH value to 3-4, carrying out stirring reaction on the ethanol solution and the ethanol solution of the expandable graphite, and filtering and drying to obtain the modified expandable graphite. According to the method, the thermal stability and the charring capacity of the expandable graphite are improved, the problem of non-uniform distribution of the flame retardant is avoided, more carbon layers can be promoted to be generated in the combustion process, and the flame-retardant purpose is achieved; the method is simple to operate and mild in reaction condition, the phosphorus flame retardant and the expansible graphite have a synergistic effect, and the modified expansible graphite is good in thermal stability and high in high-temperature carbon residue amount.

Description

Technical Field

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

[0002] Polymer materials are widely used in electronics, transportation, building materials and household products, and have become an indispensable part of modern life. However, most polymer materials are easy to burn, which can easily cause the fire to spread in a fire, causing casualties and property losses. Therefore, flame retardant treatment of polymer materials is crucial to reduce their fire safety risks.

[0003] Expandable graphite is one of the most commonly used inorganic flame retardants. Its volume can expand hundreds of times at high temperatures. The expanded product has excellent oxidation resistance and high temperature resistance, and can form a carbon layer to block the combustion of polymer materials. However, the worm-like carbon layer produced by expandable graphite during high-temperature combustion is relatively loose and has serious fly ash, resulting in a small amount of carbon layer with thermal oxygen barrier effect formed on the polymer surface, and a single flame retardant effect is not good. In order to improve its flame retardant effect, it is often used in combination with other organic flame retardants such as phosphorus or nitrogen to improve the flame retardant effect through synergistic effects. Conventional organic flame retardants are mostly small molecular components. However, when multiple flame retardants are added to the matrix material in a blended manner, the distribution between the flame retardants is not uniform, affecting the long-term stability of the overall flame retardant effect of the material.

[0004] Chemical grafting modification is a method to improve the flame retardancy and carbon-forming ability of expandable graphite. Phosphorus-based flame retardants are combined with expandable graphite through chemical grafting. Grafting a small amount of phosphorus-based flame retardants can improve the carbon-forming ability and avoid the problem of uneven distribution of multiple flame retardants. However, the grafting modification process of expandable graphite often involves harsh conditions such as high temperature and strong acid, and there are certain safety risks.

[0005] Therefore, it is necessary to make corresponding improvements to the existing problems of expandable graphite in the flame retardant of polymer materials. Summary of the invention

[0006] The purpose of the present invention is to solve the above-mentioned problems existing in the current expandable graphite flame retardant, and to provide a modified expandable graphite and a preparation method thereof. The method is simple to operate and has mild reaction conditions. By grafting a phosphorus-based flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide on the surface of the expandable graphite, the phosphorus-based flame retardant is chemically combined with the expandable graphite, and the small molecule flame retardant component is effectively anchored in the polymer matrix, thereby improving the dual-phase synergistic flame retardant effect and the stability of the flame retardant performance, and promoting the formation of a carbon layer, thereby having the beneficial effect of improving the flame retardancy and thermal stability of the polymer material.

[0007] In order to solve the above technical problems, the solution adopted by the present invention is as follows: A method for preparing flame retardant modified expandable graphite comprises the following steps: Step (1): dissolving 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in dichloromethane at room temperature to prepare a dichloromethane solution with a concentration of 1-2 mol / L, then adding a catalyst, and adding an isocyanate silane coupling agent dropwise while stirring within 2-3 hours. After the addition is completed, stirring and reacting for 6-10 hours, and finally rotary evaporating to obtain a modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; Step (2): dissolving the modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide obtained in step (1) in 90% ethanol solution to prepare an ethanol solution with a concentration of 10-20 mg / mL, adjusting the pH to 3-4, and stirring the solution at 65-70° C. to obtain a modified solution; stirring and dispersing expandable graphite in 90% ethanol solution, heating to 65-70° C., adding the modified solution, continuing to stir the reaction for 3-4 hours, filtering, and drying to obtain modified expandable graphite.

[0008] Preferably, in step (1), the catalyst is triethylamine, and the added amount is 4-5% of the molar number of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0009] Preferably, the isocyanate silane coupling agent in step (1) is isocyanate propyl trimethoxy silane or isocyanate propyl ethoxy silane.

[0010] Preferably, in step (1), the molar ratio of the isocyanate silane coupling agent to the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:1.

[0011] Preferably, the stirring speed in step (1) is 400-600 rpm; and the rotary evaporation temperature is 30°C.

[0012] Preferably, the concentration of the 90% ethanol dispersion of expandable graphite in step (2) is 50 mg / mL, and the volume ratio of the modified liquid to the dispersion is 0.5-1.5:1.

[0013] Preferably, the stirring speed in step (2) is 400-600 rpm; and the drying condition is 80-90° C. for 8-12 h.

[0014] A flame retardant modified expandable graphite, characterized in that it is prepared by the preparation method described in any one of claims 1 to 7.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The modifier and expandable graphite used in the present invention have a flame retardant synergistic effect, and the two are combined into a whole by a chemical grafting method to improve the thermal stability and carbon-forming ability of the expandable graphite itself; It avoids the problem of uneven distribution of flame retardants, can improve the overall flame retardant effect of composite materials, and can promote the generation of more carbon layers during the combustion process to achieve the purpose of flame retardancy; The preparation method of the modified expandable graphite of the present invention is simple to operate, and the reaction conditions are mild. The phosphorus flame retardant used has a synergistic effect with the expandable graphite, and the modified expandable graphite has good thermal stability and a high amount of high-temperature residual carbon. The carbonization amount during polymer combustion can be increased, and the purpose of flame retardancy can be achieved by generating more carbon layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the modification process of expandable graphite in the present invention.

[0017] Figure 2 This is the infrared spectrum of modified expandable graphite.

[0018] Figure 3 This is the thermogravimetric curve of modified expandable graphite.

[0019] Figure 4 This is the thermogravimetric curve of polyurethane foam. DETAILED DESCRIPTION

[0020] The technical scheme of the present invention is further described in detail below through specific embodiments. In the present invention, unless otherwise specified, the methods in the following embodiments are all conventional methods in the art.

[0021] like Figure 1 As shown, Figure 1 The figure is a schematic diagram of the modification process of the modified expandable graphite. According to this process, the specific steps are as follows: A method for preparing flame retardant modified expandable graphite, specifically comprising the following steps: Step (1): dissolving 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in dichloromethane at room temperature to prepare a dichloromethane solution with a concentration of 1-2 mol / L, then adding a catalyst, and adding an isocyanate silane coupling agent dropwise while stirring within 2-3 hours. After the addition is completed, stirring is continued for 6-10 hours at a stirring speed of 400-600 rpm, and finally rotary evaporation is performed to obtain a modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; the rotary evaporation temperature is 30°C; in: The catalyst is triethylamine, and the added amount is 4-5% of the molar number of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; The isocyanate silane coupling agent is isocyanate propyl trimethoxy silane or isocyanate propyl ethoxy silane; The molar ratio of the isocyanate silane coupling agent to the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:1; Step (2): dissolving the modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide obtained in step (1) in 90% ethanol solution to prepare an ethanol solution with a concentration of 10-20 mg / mL, adjusting the pH to 3-4, and stirring the solution at 65-70° C. to obtain a modified solution; stirring and dispersing expandable graphite in 90% ethanol solution at a speed of 400-600 rpm, heating to 65-70° C. and then adding the modified solution, continuing to stir the reaction for 3-4 hours, filtering, and drying at 80-90° C. for 8-12 hours to obtain modified expandable graphite; Wherein: the concentration of the 90% ethanol dispersion of expandable graphite is 50 mg / mL, and the volume ratio of the modified liquid to the dispersion is 0.5-1.5:1.

[0022] According to the above method, a specific flame retardant modified expandable graphite is prepared, and the prepared flame retardant modified expandable graphite is used to prepare a corresponding foam material to test its performance.

[0023] Embodiment 1: A flame retardant modified expandable graphite, the preparation process is as follows: Step (1): 6.48 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was dissolved in 30 mL of dichloromethane, 0.12 g of triethylamine was added, and 7.41 g of isocyanate propylethoxysilane was added dropwise at room temperature with stirring at a stirring rate of 400 rpm. After the addition was completed within 2 h, the reaction was continued for 6 h. After rotary evaporation at 30 ° C, modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was obtained; Step (2): 12 g of the modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide prepared in step (1) was dissolved in 600 mL of 90% ethanol solution, the pH of the solution was adjusted to 3 with glacial acetic acid, and the solution was stirred and dissolved at 70°C and a stirring rate of 400 rpm to obtain a modified solution; 50 g of expandable graphite was stirred and dispersed in 500 mL of 90% ethanol solution at a speed of 400 rpm, and after heating to 70°C, 500 mL of the modified solution was added thereto, and the reaction was continued by stirring for 4 h, and then filtered, and dried at 80°C for 8 h to obtain modified expandable graphite.

[0024] The modified expandable graphite prepared above is used to prepare expandable graphite flame retardant polyurethane foam, and the specific method is as follows: Step (1): weigh 100 g of polyether polyol 4110, 1 g of water, 1 g of AK 8805, 0.1 g of N,N-dimethylcyclohexylamine, 0.1 g of dibutyltin dilaurate and 40 g of modified expandable graphite and mix them uniformly to obtain S1; weigh 80 g of TDI-80 as S2; Step (2): Add S2 to S1 and stir thoroughly for 20 seconds, then pour into a mold, cure at room temperature for 30 minutes, take out, and continue to mature for 8 hours to obtain a modified expandable graphite flame-retardant polyurethane foam.

[0025] Embodiment 2: A flame retardant modified expandable graphite, the preparation process is as follows: Step (1): dissolving 12.56 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in 60 mL of dichloromethane, adding 0.3 g of triethylamine, and adding 14.82 g of isocyanate propylethoxysilane dropwise at room temperature with stirring at a rate of 600 rpm. After the addition is completed within 2 h, the reaction is continued for 8 h. After rotary evaporation at 30 ° C, modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is obtained; Step (2): Take 20 g of the modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide prepared in step (1) and dissolve it in 1000 mL of 90% ethanol solution, adjust the pH of the solution to 4 with glacial acetic acid, and stir and dissolve it at 70°C and a stirring rate of 600 rpm to obtain a modified solution; stir and disperse 60 g of expandable graphite in 600 mL of 90% ethanol solution at a speed of 600 rpm, heat it to 70°C, take 900 mL of the modified solution and add it thereto, continue the reaction for 4 hours, filter it, and dry it at 85°C for 12 hours to obtain modified expandable graphite.

[0026] The modified expandable graphite prepared above is used to prepare expandable graphite flame retardant polyurethane foam, and the specific method is as follows: Step (1): weigh 100 g of polyether polyol 4110, 1 g of water, 1 g of AK 8805, 0.1 g of N,N-dimethylcyclohexylamine, 0.1 g of dibutyltin dilaurate and 50 g of modified expandable graphite and mix them uniformly to obtain S1; weigh 80 g of TDI-80 as S2; Step (2): Add S2 to S1 and stir thoroughly for 20 seconds, then pour into a mold, cure at room temperature for 30 minutes, take out, and continue to mature for 8 hours to obtain a modified expandable graphite flame-retardant polyurethane foam.

[0027] Embodiment 3: A flame retardant modified expandable graphite, the preparation process is as follows: Step (1): 6.48 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was dissolved in 30 mL of dichloromethane, 0.12 g of triethylamine was added, and 6.15 g of isocyanate propylmethoxysilane was added dropwise at room temperature with stirring at a stirring rate of 400 rpm. After the addition was completed within 2 h, the reaction was continued for 6 h. After rotary evaporation at 30 ° C, modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was obtained; Step (2): 12 g of the modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide prepared in step (1) was dissolved in 600 mL of 90% ethanol solution, the pH of the solution was adjusted to 4 with glacial acetic acid, and the modified solution was dissolved by stirring at 70°C and a stirring rate of 400 rpm; 50 g of expandable graphite was dispersed in 500 mL of 90% ethanol solution by stirring at 400 rpm, and 500 mL of the modified solution was added thereto after the temperature was raised to 70°C, the reaction was continued for 4 h, and then the solution was filtered and dried at 80°C for 8 h to obtain the modified expandable graphite.

[0028] The modified expandable graphite prepared above is used to prepare expandable graphite flame retardant polyurethane foam, and the specific method is as follows: Step (1): weigh 100 g of polyether polyol 4110, 1 g of water, 1 g of AK 8805, 0.1 g of N,N-dimethylcyclohexylamine, 0.1 g of dibutyltin dilaurate and 40 g of modified expandable graphite and mix them uniformly to obtain S1; weigh 80 g of TDI-80 as S2; Step (2): Add S2 to S1 and stir thoroughly for 20 seconds, then pour into a mold, cure at room temperature for 30 minutes, take out, and continue to mature for 8 hours to obtain a modified expandable graphite flame-retardant polyurethane foam.

[0029] Comparative Example 1: Step (1): weigh 100 g of polyether polyol 4110, 1 g of water, 1 g of AK 8805, 0.1 g of N,N-dimethylcyclohexylamine, and 0.1 g of dibutyltin dilaurate, and mix them uniformly to obtain S1; weigh 80 g of TDI 80 as S2; Step (2): Add S2 to S1 and stir thoroughly for 20 seconds, then pour into a mold, cure at room temperature for 30 minutes, and continue to mature for 8 hours before taking out to obtain a polyurethane foam.

[0030] Comparative Example 2: Step (1): weigh 100 g of polyether polyol 4110, 1 g of water, 1 g of AK 8805, 0.1 g of N,N-dimethylcyclohexylamine, 0.1 g of dibutyltin dilaurate and 40 g of expandable graphite and mix them uniformly to obtain S1; weigh 80 g of TDI-80 as S2; Step (2): Add S2 to S1 and stir thoroughly for 20 seconds, then pour into a mold, cure at room temperature for 30 minutes, take out, and continue to mature for 8 hours to obtain expandable graphite flame-retardant polyurethane foam.

[0031] Comparative Example 3: Step (1): weigh 100 g of polyether polyol 4110, 1 g of water, 1 g of AK 8805, 0.1 g of N,N-dimethylcyclohexylamine, 0.1 g of dibutyltin dilaurate, 39.2 g of expandable graphite and 0.8 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and mix them uniformly to obtain S1; weigh 80 g of TDI-80 as S2; Step (2): Add S2 to S1 and stir thoroughly for 20 seconds, then pour into a mold, cure at room temperature for 30 minutes, take out, and continue to mature for 8 hours to obtain expandable graphite compounded flame-retardant polyurethane foam.

[0032] The modified expandable graphite prepared in Examples 1-3 of the present invention was subjected to infrared spectroscopy and thermogravimetric tests.

[0033] The foam samples prepared in the embodiments of the present invention and the comparative examples were subjected to thermogravimetric test and flame retardant performance test, wherein the flame retardant performance test was carried out according to the following standards: The limiting oxygen index test is carried out according to GB / T 2406.2-2009; The vertical burning test is carried out according to GB / T 2408-2021; Cone calorimetry testing was performed according to ISO 5660-1.

[0034] About the preparation process of the present invention: Figure 1 As shown, Figure 1Schematic diagram of the modification process of modified expandable graphite. Expandable graphite (EG) is prepared into modified expandable graphite (MEG) by the reaction between the PH bond on 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and the -NCO of the coupling agent, and the reaction between the silanol (Si-OH) after Si-OR hydrolysis and the hydroxyl (-OH) of expandable graphite.

[0035] The stability of the flame retardant modified expandable graphite prepared by the present invention is specifically as follows.

[0036] like Figure 2 As shown, Figure 2 The infrared spectrum of the modified expandable graphite is shown in Figure 2. The modified expandable graphite (MEG) prepared from expandable graphite (EG) has an infrared spectrum of 754 cm -1 A new PC peak appeared at 1450–1435 cm -1 The peak of P-phenyl vibration is at 1581 cm -1 The benzene ring skeleton vibration peak appeared at 3400 cm -1 The -OH peak at 40° is weakened, indicating that the -OH on the surface of EG is consumed by reaction, resulting in a decrease in the peak intensity. The appearance and changes of the above peaks indicate that 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is successfully grafted onto expandable graphite, and expandable graphite is successfully modified.

[0037] Figure 3 This is the thermogravimetric curve of modified expandable graphite, and its main data are shown in the following table: In the above table, T 5% and T 30% are the temperatures at which the sample mass loss reaches 5% and 30%, respectively; Mass is the mass percentage of the sample at 600℃.

[0038] From the above data analysis, it can be seen that in nitrogen atmosphere, the T of MEG 5% 217℃, T 30% The temperature difference between the two is 108℃, which is significantly higher than the temperature difference of EG, indicating that the thermal decomposition rate of the modified sample slows down; while the mass percentage of MEG at 600℃ increases from 46.64% of EG to 60.56%, and the residual carbon content of the sample increases. The data show that the grafting of phosphorus flame retardant helps to improve the thermal stability and carbon-forming ability of expandable graphite itself, and the residual carbon content increases significantly at high temperature.

[0039] The flame retardant effect of the flame retardant modified expandable graphite prepared by the present invention is specifically as follows.

[0040] Figure 4This is the thermogravimetric curve of flame retardant polyurethane foam. Its main data, limiting oxygen index and vertical combustion test results are shown in the following table: In the above table, T 5% and T 50% are the temperatures at which the sample loses 5% and 50% of its mass respectively; Mass is the mass percentage of the sample at 600°C; LOI is the limiting oxygen index value; UL-94 represents the vertical burning rating.

[0041] From the data in the analysis table, it can be seen that the limiting oxygen index value of the sample after adding the flame retardant is increased from 17.2 to more than 25.0, which is a significant improvement. At 40 parts of flame retardant added, the limiting oxygen index value of Comparative Example 3 is higher than that of Comparative Example 2, but lower than that of Example 1 and Example 3; at the same time, the vertical combustion of Comparative Example 2 cannot reach the rating, while Comparative Example 3 and each embodiment can reach the V0 level. It can be seen that the addition of phosphorus flame retardant effectively improves the flame retardant properties of the foam material, and compared with the method of mixing and adding two flame retardants in Comparative Example 3, the modified flame retardant has a higher limiting oxygen index.

[0042] In terms of the thermal stability of the foam samples, the T 5% The initial decomposition temperature of the foam increased from 191°C to 231°C. The higher initial decomposition temperature helps to improve the flame retardancy of the sample in the early stage. 50% The temperature is higher than that of Example 1 and Comparative Example 2. The reason is that the synergistic efficiency between the phosphorus flame retardant and the expandable graphite is improved after grafting, the uneven distribution problem caused by direct mixing is avoided, and its ability to promote decomposition into carbon is improved; at 600°C, the mass percentage of the foam in Example 1 is increased from 0.04% of Comparative Example 1 to 16.6%, and is higher than that of Comparative Example 2 and Comparative Example 3, indicating that the carbonization amount of the sample increases after adding MEG, and its carbonization effect is greater than the simple mixing of EG and two flame retardants alone.

[0043] In summary, the present invention uses 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and isocyanate coupling agent to graft-modify expandable graphite, and the prepared flame-retardant modified expandable graphite has high thermal stability and carbon-forming ability, and can produce good synergistic effects with the grafted phosphorus flame retardant to improve the flame retardant efficiency; at the same time, the method is simple to operate, the reaction conditions are mild, and the safety of the preparation process is improved. The modified expandable graphite is applied to the flame retardancy of polyurethane foam, and the limiting oxygen index value of the obtained flame retardant material can reach 26.7%, the vertical combustion level reaches V0 level, the carbonization amount at high temperature increases, and the flame retardant performance is excellent. The flame retardant modified expandable graphite prepared by the present invention is halogen-free and non-corrosive. It is an environmentally friendly and flame-retardant material that can meet the flame retardant requirements of polymer materials.

[0044] It is obvious to those skilled in the art that the above embodiments are not intended to be exhaustive or limit the embodiments to the specific precise forms disclosed. It is obvious to those skilled in the art that certain modifications, combinations and variations can be made based on the above teachings.

Claims

1. A method for preparing flame retardant modified expandable graphite, characterized in that: The following steps are involved: Step (1): dissolving 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in dichloromethane at room temperature to prepare a dichloromethane solution with a concentration of 1-2 mol / L, then adding a catalyst, and adding an isocyanate silane coupling agent dropwise while stirring within 2-3 hours. After the addition is completed, stirring and reacting for 6-10 hours, and finally rotary evaporating to obtain a modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; Step (2): dissolving the modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide obtained in step (1) in 90% ethanol solution to prepare an ethanol solution with a concentration of 10-20 mg / mL, adjusting the pH to 3-4, and stirring the solution at 65-70° C. to obtain a modified solution; The expandable graphite is stirred and dispersed in a 90% ethanol solution, and the modified liquid is added after the temperature is raised to 65-70°C. The reaction is continued by stirring for 3-4 hours, and then filtered. After drying, the modified expandable graphite is obtained.

2. The preparation method according to claim 1, characterized in that: In step (1), the catalyst is triethylamine, and the added amount is 4-5% of the molar number of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

3. The preparation method according to claim 1, characterized in that: The isocyanate silane coupling agent in step (1) is isocyanate propyl trimethoxy silane or isocyanate propyl ethoxy silane.

4. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of the isocyanate silane coupling agent to the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:

1.

5. The preparation method according to claim 1, characterized in that: The stirring speed in step (1) is 400-600 rpm; and the rotary evaporation temperature is 30°C.

6. The preparation method according to claim 1, characterized in that: Step (2) The concentration of the 90% ethanol dispersion of expandable graphite is 50 mg / mL, and the volume ratio of the modified liquid to the dispersion is 0.5-1.5:

1.

7. The preparation method according to claim 1, characterized in that: The stirring speed in step (2) is 400-600 rpm; and the drying condition is 80-90° C. for 8-12 h.

8. A flame retardant modified expandable graphite, characterized in that: The product is prepared by the preparation method described in any one of claims 1 to 7.

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