A bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material and its preparation method and application

Abstract

The present invention relates to a bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material and its preparation method and application, belonging to the technical field of flame retardant material synthesis. The composite material is prepared from nylon 6, bimetallic layered hydroxide and phytic acid. Wherein, the phosphate functional group in the phytic acid can chelate with the metal ion in the bimetallic layered hydroxide, thereby forming a novel flame retardant. When combustion occurs, the layered structure and thermal decomposition products such as metal oxides, metal phosphates, and carbon-containing aromatic network structure substances in the flame retardant help to suppress the release of smoke and toxic gases, and the release of metal ions and phosphorus-containing free radicals helps to suppress the spread of fire. Compared with pure nylon 6, the peak heat release rate and total heat release rate of the composite material are greatly reduced, the limiting oxygen index is greatly increased, and the vertical combustion test reaches V-0 level. At the same time, the raw material sources in the preparation method of the composite material are abundant, the operation is simple, and it is suitable for scaled-up production.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant material synthesis, and relates to a bimetallic layered hydroxide / phytic acid synergistic flame retardant nylon 6 composite material, a preparation method and an application thereof. Background Art

[0002] Nylon 6 fiber products are widely used in various industries due to their high strength, good wear resistance, and excellent elasticity. However, like most chemical fiber products, nylon 6 produces molten dripping when heated or burned. When the molten drippings, carrying the heat from the combustion, separate from the substrate, there is a potential for ignition of nearby flammable materials, further posing a greater risk of fire expansion or spread, making them extremely dangerous in practical applications. With growing awareness of safety, the development and application of flame-retardant nylon 6 composites have become a research priority for major scientific research institutions and R&D companies. Flame retardant nylon 6 is often achieved by adding flame retardants. Common flame retardants include halogen-based flame retardants, phosphorus-based flame retardants, boron-based flame retardants, nitrogen-based flame retardants, silicon-based flame retardants, halogen-phosphorus-based flame retardants, phosphorus-nitrogen-based flame retardants, and bio-based flame retardants. Halogenated flame retardants inevitably produce toxic gases that are harmful to health during use. While other flame retardants offer advantages such as low toxicity and smoke, they still suffer from issues such as low flame retardancy and deterioration in thermal stability and mechanical properties. Therefore, the development of a new flame retardant is crucial.

[0003] Phytic acid (PA) is a bio-based phosphorus-based flame retardant monomer and an environmentally friendly flame retardant found primarily in grains, soybeans, and oilseeds. The PA structure contains six phosphate functional groups, with a phosphorus content of up to 28% by weight. These functional groups have a wide range of functions, including participating in acid-base neutralization reactions to form salts, interacting with positively charged molecules, and chelating metal ions. This ability to chelate metal ions can be exploited to construct chelates with metal ions in bimetallic layered hydroxides. Due to their layered structure, bimetallic layered hydroxides act as a physical barrier during combustion, inhibiting the release of smoke and toxic gases. Once released, the phosphorus-containing groups in PA can capture active free radicals, thereby preventing the spread of combustion. Therefore, chelating PA and bimetallic layered hydroxides together is expected to combine the advantages of both substances to form a new flame retardant. Although CN113666427A discloses a phytic acid-modified transition metal layered double hydroxide, which reacts the highly chelating phosphate groups in PA with the metal ions in the transition metal layered double hydroxide to form a Metal-OP bond, the resulting PA-modified transition metal layered double hydroxide is used as a water oxidation electrocatalyst in electrocatalytic water splitting. However, research on using phytic acid-modified nickel-cobalt layered double hydroxide as a flame retardant for nylon 6 has not yet been reported. Summary of the Invention

[0004] In view of this, one of the objects of the present invention is to provide a method for preparing a bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material; a second object of the present invention is to provide a bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material; a third object of the present invention is to provide an application of a bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material in textiles and clothing, food packaging or automotive parts.

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

[0006] 1. A method for preparing a bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material, the preparation method being as follows:

[0007] (1) Preparation of double metal layered hydroxide / phytic acid: The double metal layered hydroxide was dissolved in anhydrous ethanol, and then ultrasonicated to form a uniform suspension. Phytic acid and water were added to the suspension at a rate of 1.5 ml / min, and then reacted at 200-30°C for 102 h to obtain a reaction solution. The reaction solution was filtered, and the precipitate was collected and rinsed with anhydrous ethanol 305 times, and dried at 800-100°C for 100-16 h.

[0008] (2) Preparation of a bimetallic layered hydroxide / phytic acid / nylon 6 composite material: The bimetallic layered hydroxide / phytic acid and nylon 6 in step (1) were melt-mixed at 2450-270° C., and then extruded through a twin-screw extruder.

[0009] Preferably, in step (1), the mass ratio of the double metal layered hydroxide to phytic acid is 0.5:0.209:2; and the volume ratio of the phytic acid to water is 1:1.

[0010] Preferably, the double metal layered hydroxide in step (1) is prepared according to the following method:

[0011] Ultrasonic dispersion of a metal organic framework material and a water-soluble metal salt in anhydrous ethanol to form a mixed solution, stirring the mixed solution to obtain a stirred liquid, transferring the stirred liquid to a high-pressure reactor, reacting at 900-120° C. for 100-14 hours, obtaining a reaction product after completion of the reaction, centrifuging the reaction product to remove the supernatant and leaving a precipitate, washing the precipitate 305 times with ethanol and water respectively, and then drying at 800-120° C. for 100-16 hours;

[0012] The metal in the metal organic framework material and the metal in the water-soluble metal salt are of different types.

[0013] Preferably, the water-soluble metal salt is any one of a soluble cobalt salt or a soluble aluminum salt; and the mass ratio of the metal-organic framework material to the water-soluble metal salt is 0.6:1.203:6.

[0014] Preferably, the preparation method of the metal organic framework material is as follows:

[0015] A water-soluble divalent metal salt and 2-methylimidazole are ultrasonically dispersed in methanol to form a mixed solution, the mixed solution is stirred at 220-26°C, and then the supernatant is removed by centrifugation to leave a precipitate, the precipitate is washed with methanol 305 times, and dried at 800-100°C for 408 hours.

[0016] Preferably, the water-soluble divalent metal salt is any one of a divalent nickel salt, a divalent cobalt salt and a divalent magnesium salt; the mass ratio of the water-soluble divalent metal salt to 2-methylimidazole is 0.5:0.803.0:3.6.

[0017] Preferably, in step (2), the mass ratio of the double metal layered hydroxide / phytic acid to nylon 6 is 1:99010:90; and the screw speed of the twin-screw extruder is 20060 rpm.

[0018] 2. The double metal layered hydroxide / phytic acid synergistic flame retardant nylon 6 composite material prepared by the method.

[0019] 3. Application of the bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material in the preparation of textile clothing, food packaging or automotive parts.

[0020] The present invention provides a bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material. The composite material is prepared from nylon 6, bimetallic layered hydroxide, and phytic acid. The phosphate functional groups in the phytic acid can chelate with the metal ions in the bimetallic layered hydroxide, thereby forming a novel flame retardant. During combustion, the catalytically active metal ions in the bimetallic layered hydroxide portion catalyze the carbonization of the nylon 6, forming a protective carbonaceous layer on its surface, effectively inhibiting the expansion and spread of the fire. Furthermore, its unique layered structure acts as a physical barrier during nylon 6 combustion, suppressing the release of smoke and toxic gases. During combustion and decomposition, the phytic acid portion produces compounds such as phosphoric acid and pyrophosphate, which readily capture free radicals and also catalyze carbonization, helping to block the spread of combustion. Furthermore, upon thermal decomposition, the flame retardant can generate metal oxides, metal phosphates, and substances with a carbon aromatic network structure, further forming a dense carbon layer that suppresses the emission of smoke and toxic gases. Compared with pure nylon 6, the nylon 6 composite material formed by adding a certain amount of bimetallic layered hydroxide / phytic acid flame retardant to nylon 6 has a significant decrease in its peak heat release rate (pHRR) and total heat release rate (THR), a greatly improved limiting oxygen index (LOI), and a vertical burning test (UL-94) reaching V-0 level, which shows that the flame retardant properties of the composite material are very excellent.

[0021] The present invention also provides a preparation method of a bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material. The preparation method has abundant raw material sources, is simple to operate, and is suitable for scale-up production.

[0022] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0024] Figure 1 is the XRD pattern of the NiCo-LDH@PA / nylon 6 composite material in Example 1;

[0025] Figure 2 1 is a pHHR trend diagram of pure nylon 6 and the NiCo-LDH@PA / nylon 6 composite material in Example 103;

[0026] Figure 3 This is the THR trend diagram of pure nylon 6 and the NiCo-LDH@PA / nylon 6 composite material in Example 103. DETAILED DESCRIPTION

[0027] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the features in the following embodiments and embodiments can be combined with each other without conflict.

[0028] Example 1

[0029] A NiCo-LDH@PA synergistic flame-retardant nylon 6 composite material is prepared by, by weight percentage, 98% nylon 6, 1.8% NiCo-LDH, and 0.2% PA. The specific preparation method is as follows:

[0030] (1) Preparation of Ni-ZIF: 2.0 g of Ni(NO3)2·6H2O and 2.4 g of 2-methylimidazole were ultrasonically dispersed in 120 ml of methanol. After mixing, the mixture was magnetically stirred at 25°C for 1 h. The supernatant was removed by centrifugation to retain the precipitate. The precipitate was washed five times with methanol and dried in an oven at 80°C for 5 h to obtain Ni-ZIF.

[0031] (2) Preparation of NiCo-LDH: 2 g Ni-ZIF and 4 g Co(NO3)2·6H2O were ultrasonically dispersed in 400 ml of anhydrous ethanol. After magnetic stirring for 30 min, the stirred solution was transferred to a high-pressure reactor and reacted at 120°C for 10 h. After the reaction was completed, the product was centrifuged to remove the supernatant and retain the precipitate. The precipitate was washed three times with ethanol and three times with water, and then dried in a vacuum oven at 80°C for 12 h to obtain the final product, NiCo-LDH.

[0032] (3) Preparation of NiCo-LDH@PA: 3.4 g of NiCo-LDH was dissolved in 120 ml of anhydrous ethanol and ultrasonicated for 1 h to form a uniform suspension. 50 ml of PA and 50 ml of water were added to the suspension at a rate of 1.5 ml / min. The suspension was reacted at 30 °C for 1 h and the precipitate was collected by filtration. The precipitate was rinsed with anhydrous ethanol four times and dried in a vacuum oven at 80 °C for 12 h to obtain the NiCo-LDH@PA product.

[0033] (4) Preparation of NiCo-LDH@PA / nylon 6 composite material: 2 g of NiCo-LDH@PA and 98 g of nylon 6 were melt-mixed at 245 °C, then extruded through a twin-screw extruder at a screw speed of 40 rpm, and finally pelletized to produce 4 × 5 × 2 mm nylon 6 composite materials containing 2% NiCo-LDH@PA.

[0034] The NiCo-LDH@PA / nylon 6 composite material in Example 1 was characterized by XRD powder diffraction. The experimental results are as follows: Figure 1 As shown. Figure 1 It can be seen that the prepared material is NiCo-LDH@PA / nylon 6 composite material.

[0035] Example 2

[0036] A NiCo-LDH@PA synergistic flame-retardant nylon 6 composite material is prepared by, by weight percentage, 97% nylon 6, 2.7% NiCo-LDH, and 0.3% PA. The specific preparation method is as follows:

[0037] (1) Preparation of Ni-ZIF: 2.4 g of Ni(NO3)2·6H2O and 2.8 g of 2-methylimidazole were ultrasonically dispersed in 160 ml of methanol. After mixing, the mixture was magnetically stirred at 25°C for 1 h. The supernatant was removed by centrifugation to retain the precipitate. The precipitate was washed four times with methanol and dried in an oven at 80°C for 5 h to obtain Ni-ZIF.

[0038] (2) Preparation of NiCo-LDH: 2.4 g Ni-ZIF and 4.8 g Co(NO3)2·6H2O were ultrasonically dispersed in 460 ml of anhydrous ethanol. After magnetic stirring for 30 min, the stirred solution was transferred to a high-pressure reactor and reacted at 120°C for 10 h. After the reaction was completed, the product was centrifuged to remove the supernatant and leave the precipitate. The precipitate was washed three times with ethanol and three times with water, and then dried in a vacuum oven at 80°C for 12 h to obtain the final product, NiCo-LDH.

[0039] (3) Preparation of NiCo-LDH@PA: 3.6 g of NiCo-LDH was dissolved in 140 ml of anhydrous ethanol and ultrasonically treated for 1 h to form a uniform suspension. 75 ml of PA and 75 ml of water were added to the suspension at a rate of 1.5 ml / min. The mixture was reacted at 30°C for 1 h and the precipitate was collected by filtration. The precipitate was rinsed with anhydrous ethanol five times and dried in a vacuum oven at 80°C for 12 h to obtain the NiCo-LDH@PA product.

[0040] (4) Preparation of NiCo-LDH@PA / nylon 6 composite material: 3 g of NiCo-LDH@PA and 97 g of nylon 6 were melt-mixed at 245 °C, then extruded through a twin-screw extruder at a screw speed of 40 rpm, and finally pelletized to prepare 4 × 5 × 2 mm nylon 6 composite materials containing 3% NiCo-LDH@PA.

[0041] Example 3

[0042] A NiCo-LDH@PA synergistic flame-retardant nylon 6 composite material is prepared by, by weight percentage, 95% nylon 6, 4.6% NiCo-LDH, and 0.4% PA. The specific preparation method is as follows:

[0043] (1) Preparation of Ni-ZIF: 2.8 g of Ni(NO3)2·6H2O and 2.8 g of 2-methylimidazole were ultrasonically dispersed in 200 ml of methanol. After mixing, the mixture was magnetically stirred at 25°C for 1 h. The supernatant was removed by centrifugation to retain the precipitate. The precipitate was washed five times with methanol and dried in an oven at 80°C for 5 h to obtain Ni-ZIF.

[0044] (2) Preparation of NiCo-LDH: 2.8 g Ni-ZIF and 5.6 g Co(NO3)2·6H2O were ultrasonically dispersed in 500 ml of anhydrous ethanol. After magnetic stirring for 30 min, the stirred solution was transferred to a high-pressure reactor and reacted at 120°C for 10 h. After the reaction was completed, the product was centrifuged to remove the supernatant and retain the precipitate. The precipitate was washed three times with ethanol and three times with water, and then dried in a vacuum oven at 80°C for 12 h to obtain the final product, NiCo-LDH.

[0045] (3) Preparation of NiCo-LDH@PA: 4.0 g of NiCo-LDH was dissolved in 150 ml of anhydrous ethanol and ultrasonicated for 1 h to form a uniform suspension. 100 ml of PA and 100 ml of water were added to the suspension at a rate of 1.5 ml / min. The mixture was reacted at 30 °C for 1 h and the precipitate was collected by filtration. The precipitate was rinsed with anhydrous ethanol five times and dried in a vacuum oven at 80 °C for 12 h to obtain the NiCo-LDH@PA product.

[0046] (4) Preparation of NiCo-LDH@PA / nylon 6 composite material: 5 g of NiCo-LDH@PA and 95 g of nylon 6 were melt-mixed at 245 °C, then extruded through a twin-screw extruder at a screw speed of 40 rpm, and finally pelletized to prepare 4 × 5 × 2 mm nylon 6 composite materials containing 5% NiCo-LDH@PA.

[0047] The peak heat release rate (pHRR) and total heat release rate (THR) of nylon 6 composite materials with different NiCo-LDH@PA contents in Example 10 and Example 3 were tested, and the experimental results were as follows: Figure 2 and Figure 3 shown. Figure 2 The pHHR trend diagram of pure nylon 6 and NiCo-LDH@PA / nylon 6 composite material in Example 103 is shown in FIG. Figure 2 It can be seen that compared with pure nylon, as the addition amount of NiCo-LDH@PA in nylon 6 increases, the corresponding pHRR decreases continuously. When 2.0wt.%, 3.0wt.%, and 5.0wt.% NiCo-LDH@PA are added to nylon 6, the peak heat release rate (pHRR) of the corresponding composites decreases by 39.2%, 43.3%, and 48.6%, respectively, compared with pure nylon. Figure 3 The THR trend diagram of pure nylon 6 and NiCo-LDH@PA / nylon 6 composite material in Example 103 is shown in FIG. Figure 3 It can be seen that, compared to pure nylon, increasing the amount of NiCo-LDH@PA added to nylon 6 also results in a decreasing total heat release rate (THR) compared to pure nylon. When 2.0 wt.%, 3.0 wt.%, and 5.0 wt.% NiCo-LDH@PA were added to nylon 6, the total heat release rate (THR) of the corresponding composites decreased by 15.6%, 16.8%, and 19.2%, respectively, compared to pure nylon. Furthermore, the limiting oxygen index (LOI) for pure nylon 6, nylon 6 containing 2.0 wt.% NiCo-LDH@PA, nylon 6 containing 3.0 wt.% NiCo-LDH@PA, and nylon 6 containing 5.0 wt.% NiCo-LDH@PA was calculated to be 21.0%, 27.2%, 28.5%, and 30.2%, respectively. The increasing LOI indicates that the addition of NiCo-LDH@PA to nylon 6 makes it less flammable. At the same time, the vertical combustion test (UL-94) corresponding to the nylon 6 composite materials with different addition amounts can all reach V-0 level. In summary, the composite materials of the present invention have excellent flame retardant properties.

[0048] Example 4

[0049] A CoAl-LDH@PA synergistic flame-retardant nylon 6 composite material is prepared from 96% nylon 6, 3.7% CoAl-LDH, and 0.3% PA by weight. The specific preparation method is as follows:

[0050] (1) Preparation of Co-ZIF: 2.8 g of CoCl2·6H2O and 2.8 g of 2-methylimidazole were ultrasonically dispersed in 200 ml of methanol. After mixing, the mixture was magnetically stirred at 25°C for 1 h. The supernatant was removed by centrifugation to retain the precipitate. The precipitate was washed five times with methanol and dried in an oven at 80°C for 5 h to obtain Co-ZIF.

[0051] (2) Preparation of CoAl-LDH: 2.8 g of Co-MOF and 5.6 g of Al(NO3)3 were ultrasonically dispersed in 500 ml of anhydrous ethanol. After magnetic stirring for 30 min, the stirred solution was transferred to a high-pressure reactor and reacted at 120°C for 10 h. After the reaction was completed, the product was centrifuged to remove the supernatant and leave the precipitate. The precipitate was washed three times with ethanol and water respectively, and then dried in a vacuum oven at 80°C for 12 h to obtain the final product CoAl-LDH.

[0052] (3) Preparation of CoAl-LDH@PA: 3.6 g of CoAl-LDH was dissolved in 140 ml of anhydrous ethanol and sonicated for 1 h to form a uniform suspension. 75 ml of PA and 75 ml of water were added to the suspension at a rate of 1.5 ml / min. The mixture was reacted at 30°C for 1 h and the precipitate was collected by filtration. The precipitate was rinsed with anhydrous ethanol five times and dried in a vacuum oven at 80°C for 12 h to obtain the CoAl-LDH@PA product.

[0053] (4) Preparation of CoAl-LDH@PA / nylon 6 composite material: 4 g of CoAl-LDH@PA and 96 g of nylon 6 were melt-mixed at 245 °C, then extruded through a twin-screw extruder at a screw speed of 40 rpm, and finally pelletized to prepare 4 × 5 × 2 mm nylon 6 composite materials containing 4% CoAl-LDH@PA.

[0054] Example 5

[0055] A MgAl-LDH@PA synergistic flame-retardant nylon 6 composite material is prepared from 98% nylon 6, 1.8% MgAl-LDH, and 0.2% PA by weight. The specific preparation method is as follows:

[0056] (1) Preparation of Mg-ZIF: 2.0 g of Mg(NO3)2 and 2.4 g of 2-methylimidazole were ultrasonically dispersed in 120 ml of methanol. After mixing, the mixture was magnetically stirred at 25°C for 1 h. The supernatant was removed by centrifugation to retain the precipitate. The precipitate was washed five times with methanol and dried in an oven at 80°C for 5 h to obtain Mg-ZIF.

[0057] (2) Preparation of MgAl-LDH: 2 g of Mg-ZIF and 4 g of Al(NO3)3 were ultrasonically dispersed in 400 ml of anhydrous ethanol. After magnetic stirring for 30 min, the stirred solution was transferred to a high-pressure reactor and reacted at 120°C for 10 h. After the reaction was completed, the product was centrifuged to remove the supernatant and retain the precipitate. The precipitate was washed three times with ethanol and three times with water, and then dried in a vacuum oven at 80°C for 12 h to obtain the final product, MgAl-LDH.

[0058] (3) Preparation of MgAl-LDH@PA: 3.4 g of MgAl-LDH was dissolved in 120 ml of anhydrous ethanol and ultrasonicated for 1 h to form a uniform suspension. 50 ml of PA and 50 ml of water were added to the suspension at a rate of 1.5 ml / min. The mixture was reacted at 30°C for 1 h and the precipitate was collected by filtration. The precipitate was rinsed with anhydrous ethanol four times and dried in a vacuum oven at 80°C for 12 h to obtain the MgAl-LDH@PA product.

[0059] (4) Preparation of MgAl-LDH@PA / nylon 6 composite material: 2 g of MgAl-LDH@PA and 98 g of nylon 6 were melt-mixed at 245 °C, then extruded through a twin-screw extruder at a screw speed of 40 rpm, and finally pelletized to produce 4 × 5 × 2 mm nylon 6 composite materials containing 2% MgAl-LDH@PA.

[0060] Similarly, the peak heat release rate (pHRR), total heat release rate (THR), limiting oxygen index (LOI) and vertical burning test (UL-94) were measured for the composite material in Example 405. The experimental results obtained showed the same trend as the composite material in Example 103, indicating that the addition of double metal layered hydroxides such as CoAl-LDH@PA and MgAl-LDH@PA to nylon 6 can also improve the flame retardant properties of the material.

[0061] In summary, the present invention provides a bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material. Compared to pure nylon 6, by adding a certain amount of bimetallic layered hydroxide / phytic acid flame retardant to nylon 6, the resulting composite material significantly reduces both the peak heat release rate (pHRR) and the total heat release rate (THR), while significantly increases the limiting oxygen index (LOI), and can achieve V-0 in the vertical burning test (UL-94). This demonstrates that the composite material exhibits excellent flame retardancy.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material, characterized by: The preparation method is as follows: (1) Preparation of double metal layered hydroxide / phytic acid: The double metal layered hydroxide is dissolved in anhydrous ethanol, and then ultrasonically formed into a uniform suspension. Phytic acid and an aqueous solution mixed in a volume ratio of 1:1 are added to the suspension at a rate of 1.5 ml / min, and then reacted at 20-30°C for 1-2 hours to obtain a reaction solution. The reaction solution is filtered, and the precipitate is collected and rinsed with anhydrous ethanol for 3-5 times, and dried at 80-100°C for 10-16 hours to chelate the phosphate functional groups in the phytic acid with the metal ions in the double metal layered hydroxide. (2) Preparation of a bimetallic layered hydroxide / phytic acid / nylon 6 composite material: The bimetallic layered hydroxide / phytic acid and nylon 6 prepared in step (1) were melt-mixed at 245-270° C., and then extruded through a twin-screw extruder.

2. The method for preparing a composite material according to claim 1, wherein: The mass ratio of the double metal layered hydroxide to phytic acid in step (1) is 0.5:0.2~9:

2.

3. The method for preparing a composite material according to claim 1, wherein: The double metal layered hydroxide in step (1) is prepared according to the following method: Ultrasonic dispersion of a metal organic framework material and a water-soluble metal salt in anhydrous ethanol to form a mixed solution, stirring the mixed solution to obtain a stirred liquid, transferring the stirred liquid to a high-pressure reactor, reacting at 90-120° C. for 10-14 hours, obtaining a reaction product after completion of the reaction, centrifuging the reaction product to remove the supernatant and leaving a precipitate, washing the precipitate with ethanol and water for 3-5 times each, and then drying at 80-120° C. for 10-16 hours; The metal in the metal organic framework material and the metal in the water-soluble metal salt are of different types.

4. The method for preparing a composite material according to claim 3, wherein: The water-soluble metal salt is any one of a soluble cobalt salt or a soluble aluminum salt; the mass ratio of the metal organic framework material to the water-soluble metal salt is 0.6:1.2~3:

6.

5. The method for preparing a composite material according to claim 3, wherein: The preparation method of the metal organic framework material is as follows: A water-soluble divalent metal salt and 2-methylimidazole are ultrasonically dispersed in methanol to form a mixed solution, the mixed solution is stirred at 22-26° C., and then centrifuged to remove the supernatant and retain the precipitate. The precipitate is washed with methanol 3-5 times and dried at 80-100° C. for 4-8 hours.

6. The method for preparing a composite material according to claim 5, wherein: The water-soluble divalent metal salt is any one of a divalent nickel salt, a divalent cobalt salt and a divalent magnesium salt; the mass ratio of the water-soluble divalent metal salt to 2-methylimidazole is 0.5:0.8~3.0:3.

6.

7. The method for preparing a composite material according to claim 1, wherein: The mass ratio of the double metal layered hydroxide / phytic acid to nylon 6 in step (2) is 1:99-10:90; the screw speed of the twin-screw extruder is 20-60 rpm.

8. A double metal layered hydroxide / phytic acid synergistic flame retardant nylon 6 composite material prepared by the method according to any one of claims 1 to 7.

9. Use of the bimetallic layered hydroxide / phytic acid synergistic flame-retardant nylon 6 composite material according to claim 8 in the preparation of textiles and clothing, food packaging or automotive parts.

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