Halogen-free flame-retardant EPDM composite foamed material and preparation method thereof

Abstract

The application discloses a kind of halogen-free flame-retardant EPDM composite foamed materials and preparation method thereof, belong to high polymer composite foam material field.It is with melamine, concentrated phosphoric acid as raw material preparation melamine polyphosphate flame retardant, and using aluminium hydroxide and magnesium hydroxide to melamine polyphosphate coating treatment, obtain a core-shell structure flame retardant, again with polyphenylene sulfide fiber compound formation melamine polyphosphate / aluminium hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant, the obtained composite flame retardant with EPDM using double roll mill, mould pressing foaming method is prepared a kind of halogen-free flame-retardant EPDM composite foamed material.The obtained halogen-free flame-retardant EPDM composite foamed material has excellent mechanical property, thermal stability and flame-retardant performance, it can realize surface rapidly carbonization when burning test, with strong smoke suppression effect, and melt drop phenomenon is greatly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of high polymer composite foam materials, and particularly relates to a halogen-free flame-retardant EPDM composite foam material and a preparation method thereof. BACKGROUND

[0002] Ethylene propylene diene monomer (EPDM) is a copolymer of ethylene, propylene and a small amount of a third monomer after curing and granulation, and belongs to a kind of ethylene propylene rubber. According to the different third monomers, the ethylene propylene diene monomer can be divided into the following three types: 1,4-hexadiene type (HD-EPDM), dicyclopentadiene type (DCPD-EPDM) and ethylidenenorbornene type (ENB-EPDM). The molecular structure is linear and a double bond is introduced in the side chain, so that sulfur can be used for vulcanization and peroxide such as dicumyl peroxide can also be used for vulcanization; according to the different propylene content in the ethylene propylene diene monomer, it can be divided into high propylene, medium propylene and low propylene, and the higher the propylene content in the main body, the more the elasticity and mechanical properties of the ethylene propylene diene monomer vulcanized rubber decrease. The high molecular main chain is composed of soft segment and hard segment. Among many synthetic rubber materials, the ethylene propylene diene monomer (EPDM) exhibits high elasticity of traditional rubber at room temperature, and has plasticity of ordinary plastic at high temperature, and has the characteristics of plastic and rubber. The production efficiency of EPDM is high, and it can use the common processing technology of thermoplastic plastic, such as melt blending extrusion molding. EPDM has excellent chemical stability, electrical insulation, aging resistance and waterproof performance, good ductility, high strength and high filling plasticizing capacity, and other excellent properties. Now it has been widely used in automobile engineering, building engineering, air conditioning, refrigeration and other industries.

[0003] However, EPDM has a fatal defect in use, and its oxygen index is usually only 18-23%, and toxic gases such as CO are released during combustion, and serious dripping phenomenon occurs during combustion, accompanied by heavy black smoke. The flammability of the material itself needs to be improved to make it more convenient to use. The material needs to be modified by flame retardant functionalization to make it difficult to burn. The addition of flame retardant can make the ethylene propylene diene monomer material extinguish faster during combustion, slow down the decomposition of the material itself, greatly reduce the release amount of flammable gas and toxic ingredients, and reasonable use can reduce fire loss.

[0004] Commonly used flame-retardant elements are halogen elements, N, P, B, Al, etc., among which commercially available flame retardants are mainly halogen-based flame retardants. However, halogen-based flame retardants will release toxic gases and a large amount of smoke when ignited by open flame at high temperature, which will cause serious pollution to the environment. Therefore, developing a new type of high-efficiency, non-toxic and environmentally friendly flame retardant has become the development direction of the flame retardant field. SUMMARY

[0005] The purpose of the present application is to provide a halogen-free flame-retardant EPDM composite foaming material which has good flame-retardant effect and processing performance.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A halogen-free flame-retardant EPDM composite foaming material, the halogen-free flame-retardant EPDM composite foaming material comprises, in terms of weight fraction: 100 parts of EPDM particles, 5-15 parts of melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant, 5-10 parts of carbon black, 2 parts of zinc oxide, 2 parts of stearic acid, 6 parts of foaming agent azodicarbonamide, 0.5 parts of crosslinking agent dicumyl peroxide, and 2-4 parts of talc.

[0008] Further, the preparation of the melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant comprises the following steps:

[0009] (1) Melamine polyphosphate is added to 200 mL of deionized water, and ultrasonic oscillation is performed at 25°C until uniform dispersion is achieved, and then the solution is transferred to a 60°C water bath and subjected to continuous magnetic stirring;

[0010] (2) Aluminum hydroxide and magnesium hydroxide are slowly added to the solution obtained in step (1) in batches, and after stirring and reacting in a water bath for 4 h, the solution is placed at room temperature for continuous stirring for 4 h and then left to stand overnight;

[0011] (3) The precipitate obtained by centrifugation of the reaction solution obtained in step (2) is dried to obtain a melamine polyphosphate / aluminum hydroxide / magnesium hydroxide microspherical core-shell flame retardant;

[0012] (4) The melamine polyphosphate / aluminum hydroxide / magnesium hydroxide microspherical core-shell flame retardant obtained in step (3) and polyphenylene sulfide fibers are added to a mortar and ground and mixed uniformly to obtain a melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant.

[0013] Further, the preparation method of the melamine polyphosphate is: 12.6g of melamine is added into 200mL of deionized water at 95℃, stirred for 10min to disperse, then 11.5mL of 85wt.% concentrated phosphoric acid is slowly added in batches, continue to stir for 1.5h until the reaction is complete, filter after the reaction is cooled to room temperature, wash the filter cake with deionized water, then place it in a vacuum drying oven at 80℃ and dry for 4h to obtain melamine polyphosphate.

[0014] Further, the mass ratio of melamine polyphosphate, aluminum hydroxide and magnesium hydroxide is 8:1:1.

[0015] Further, the temperature of the water bath in step (2) is 60℃.

[0016] Further, the temperature of the drying in step (3) is 60℃, and the time is 10h.

[0017] Further, the mass ratio of melamine polyphosphate / aluminum hydroxide / magnesium hydroxide microspherical core-shell flame retardant to polyphenylene sulfide fiber in step (4) is 9:1.

[0018] The application also provides a preparation method of the above-mentioned flame-retardant EPDM composite foaming material, which comprises the following steps:

[0019] (1) uniformly mix EPDM, melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant, carbon black, zinc oxide, stearic acid, foaming agent, crosslinking agent and talc powder using a preheated two-roll open mill for 10-20min, the heating temperature is 50-60℃, after the glue is completely mixed and uniform, pass it through the mill 4-6 times to obtain a glue sheet with a thickness of 2-4mm;

[0020] (2) place the glue sheet obtained in step (2) in the mold cavity of a preheated flat plate mold press after it is placed for 4-6h, mold and foam under the condition of 175℃ and 10MPa for 450s, then obtain a halogen-free flame-retardant EPDM composite foaming material after cooling.

[0021] The application has the following beneficial effects:

[0022] (1) The application uses melamine and phosphoric acid as raw materials to prepare melamine polyphosphate, and through the method of co-precipitation, the melamine polyphosphate is made into melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant together with aluminum hydroxide, magnesium hydroxide and polyphenylene sulfide fiber and applied in EPDM composite foaming material, the formula is scientific and reasonable, the process flow is practical and simple, and the melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant is prepared by using a green and environmentally friendly method, so that the prepared EPDM composite foaming material has the benefits of health and environmental protection.

[0023] (2) The melamine polyphosphate prepared by the present application contains rich N and P elements in the structure. The N-containing part is decomposed by heat to release non-combustible NH3 and N2, etc., which can dilute the concentration of oxygen and combustible gas. Meanwhile, the P-containing part can migrate to the surface of the polymer to catalyze the formation of carbon and enhance the surface carbon layer. Moreover, the introduction of the cyclic structure improves the compatibility with the EPDM matrix, overcomes the shortcomings of the traditional nitrogen-based flame retardant, such as easy aggregation in the matrix and poor compatibility with the matrix, and maintains good flame retardant performance.

[0024] (3) The melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant prepared by the present application has a nitrogen ring structure that is attracted to inorganic materials and forms a core-shell structure with the hydroxide. The melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant can be used as a flame retardant and a reinforcing agent due to the combination of the components. The polyphenylene sulfide fiber, which is a short rod-shaped fiber, can be uniformly dispersed in the EPDM matrix with the help of the core-shell structure, which makes the stress distribution uniform and improves the tensile strength of the EPDM composite foam material. The combination of the melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant and carbon black forms a new synergistic flame retardant system, which can overcome the shortcomings of EPDM foam material, such as flammability, dripping, and smoke generation during combustion. When the EPDM composite foam material containing 15% of the flame retardant system burns, the polymer can quickly form carbon on the surface without combustion. After the fire is removed, the material can quickly self-extinguish and has strong smoke suppression effect. The flame retardant system significantly improves the flame retardant performance of the EPDM composite foam material while maintaining the original mechanical properties of the material.

[0025] (4) The melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant used as an additive for EPDM composite foam material has good compatibility with the EPDM matrix, is easy to disperse, and has excellent mechanical properties and flame retardant performance. The EPDM composite foam material has the advantages of light weight, small density, and good elasticity. The present application also provides a new method for preparing composite flame retardants and foam materials and has great social and economic benefits and development prospects in practical applications. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 SEM image of the melamine polyphosphate prepared by the present application.

[0027] Figure 2 FTIR image of the melamine polyphosphate prepared by the present application.

[0028] Figure 3 SEM image of melamine polyphosphate / aluminum hydroxide / magnesium hydroxide prepared according to the present application.

[0029] Figure 4 SEM image of melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant prepared according to the present application.

[0030] Figure 5 SEM image of Example 3 of the flame-retardant EPDM foam prepared according to the present application. DETAILED DESCRIPTION

[0031] In order to make the content of the present application more convenient to understand, the technical solutions described in the present application will be further described below in combination with specific embodiments, but the present application is not limited thereto.

[0032] A preparation of melamine polyphosphate includes the following steps:

[0033] At 95°C, 200 mL of deionized water and 12.6 g of melamine were added to a three-necked flask, stirred for 10 min until highly dispersed, then 11.5 mL of concentrated phosphoric acid (85 wt.%) was slowly added in batches, and stirring was continued for 1.5 h until the reaction was complete. After the reaction was cooled to room temperature, the filter cake was washed with deionized water and placed in a vacuum drying oven at 80°C for 4 h to obtain white crystals of melamine polyphosphate.

[0034] Figure 1 SEM image of melamine polyphosphate prepared according to the present application, which can be seen that the prepared melamine polyphosphate presents a morphology of agglomeration and stacking. Figure 2 FTIR image of melamine polyphosphate prepared according to the present application, 619 cm -1 is the deformation vibration absorption peak of NH2, 1654 cm -1 , 1550 cm -1 , 1467 cm -1 and 1404 cm -1 are ring stretching vibration absorption peaks; NH symmetric and antisymmetric stretching vibration absorption peaks appear at 3419 cm -1 and 3135 cm -1 , 1350 cm -1 appears P-OH symmetric stretching vibration peak, indicating that melamine polyphosphate is successfully synthesized.

[0035] A preparation of melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant includes the following steps:

[0036] (1) Take 8g melamine polyphosphate, add to a 200mL beaker of deionized water, ultrasonically shake at 25°C until uniformly dispersed, transfer the beaker to a 60°C water bath, and continuously stir magnetically;

[0037] (2) Take 1g aluminum hydroxide and 1g magnesium hydroxide, slowly add to the mixture prepared in step (1) in batches, continue to stir and react at 60°C in the water bath for 4h, then take the beaker out of the water bath and continue to stir for 4h, then stand overnight;

[0038] (3) Centrifuge the completed reaction mixture to obtain white precipitate, place the white precipitate obtained in a 60°C vacuum drying oven for 10h to obtain melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant.

[0039] Figure 3 SEM image of melamine polyphosphate / aluminum hydroxide / magnesium hydroxide prepared by the present application.

[0040] Example 1

[0041] A method for preparing a flame-retardant EPDM composite foam material, comprising the following steps:

[0042] 1) Mix 100 parts of EPDM particles, 5 parts of melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant, 10 parts of carbon black, 2 parts of zinc oxide, 2 parts of stearic acid, 6 parts of foaming agent AC (azodicarbonamide), 0.5 parts of crosslinking agent DCP (dicumyl peroxide), and 4 parts of talc using a preheated two-roll mill at 50°C for 20min, until all the raw materials are uniformly mixed, then press the mixed raw materials into 4mm sheets using a two-roll mill, and dry the raw material sheets in a forced air drying oven for 5h;

[0043] 2) Place the sheets prepared in step 1) in the film cavity of a preheated flat vulcanizing machine, and mold and foam at 10MPa and 175°C for 450s, then take out, to obtain a halogen-free flame-retardant composite foam material.

[0044] Example 2

[0045] A method for preparing a flame-retardant EPDM composite foam material, comprising the following steps:

[0046] 1) EPDM particles 100 parts, melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant 10 parts, carbon black 10 parts, zinc oxide 2 parts, stearic acid 2 parts, foaming agent AC (azodicarbonamide) 6 parts, crosslinking agent DCP (dicumyl peroxide) 0.5 parts, talc 4 parts are mixed using a double roller mill preheated to 50°C for 20 min until all the raw materials are uniformly mixed, after the raw materials are thoroughly mixed, the mixed raw materials are pressed into 4 mm sheets using a double roller mill, and the raw material sheets are placed in a forced air drying oven for drying for 5 hours;

[0047] 2) The sheets prepared in step 1) are placed in the film cavity of a preheated flat vulcanizing machine, and after 450 s of molding and foaming at 10 MPa and 175°C, they are taken out, and a halogen-free flame-retardant composite foamed material is obtained.

[0048] Example 3

[0049] A method for preparing a flame-retardant EPDM composite foamed material, comprising the following steps:

[0050] 1) EPDM particles 100 parts, melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant 15 parts, carbon black 10 parts, zinc oxide 2 parts, stearic acid 2 parts, foaming agent AC (azodicarbonamide) 6 parts, crosslinking agent DCP (dicumyl peroxide) 0.5 parts, talc 4 parts are mixed using a double roller mill preheated to 50°C for 20 min until all the raw materials are uniformly mixed, after the raw materials are thoroughly mixed, the mixed raw materials are pressed into 4 mm sheets using a double roller mill, and the raw material sheets are placed in a forced air drying oven for drying for 5 hours;

[0051] 2) The sheets prepared in step 1) are placed in the film cavity of a preheated flat vulcanizing machine, and after 450 s of molding and foaming at 10 MPa and 175°C, they are taken out, and a halogen-free flame-retardant composite foamed material is obtained.

[0052] Comparative Example 1

[0053] A method for preparing an EPDM composite foamed material, comprising the following steps:

[0054] 1) EPDM particles 100 parts, carbon black 10 parts, zinc oxide 2 parts, stearic acid 2 parts, foaming agent AC (azodicarbonamide) 6 parts, crosslinking agent DCP (dicumyl peroxide) 0.5 parts, talc 4 parts are mixed using a double roller mill preheated to 50°C for 20 min until all the raw materials are uniformly mixed, after the raw materials are thoroughly mixed, the mixed raw materials are pressed into 4 mm sheets using a double roller mill, and the raw material sheets are placed in a forced air drying oven for drying for 5 hours;

[0055] 2) Put the sheet prepared in step 1) into the membrane cavity of the preheated flat vulcanizing machine, and take out after molding and foaming at 10 MPa and 175℃ for 450s, to obtain the halogen-free flame-retardant composite foaming material.

[0056] Comparative Example 2

[0057] A preparation method of an EPDM composite foaming material, comprising the following steps:

[0058] 1) uniformly mix 100 parts of EPDM particles, 10 parts of melamine polyphosphate, 10 parts of carbon black, 2 parts of zinc oxide, 2 parts of stearic acid, 6 parts of foaming agent AC (azodicarbonamide), 0.5 parts of crosslinking agent DCP (dicumyl peroxide), and 4 parts of talc using a double roller mill, press mix the mixed raw materials using a double roller mill preheated to 50℃ for 20 min until all the raw materials are uniformly mixed, and press the mixed raw materials into 4mm sheets using a double roller mill, and dry the raw material sheets in a forced air drying oven for 5 hours;

[0059] 2) put the sheet prepared in step 1) into the membrane cavity of the preheated flat vulcanizing machine, and take out after molding and foaming at 10 MPa and 175℃ for 450s, to obtain the halogen-free flame-retardant composite foaming material.

[0060] Comparative Example 3

[0061] A preparation method of an EPDM composite foaming material, comprising the following steps:

[0062] 1) uniformly mix 100 parts of EPDM particles, 10 parts of melamine, 10 parts of carbon black, 2 parts of zinc oxide, 2 parts of stearic acid, 6 parts of foaming agent AC (azodicarbonamide), 0.5 parts of crosslinking agent DCP (dicumyl peroxide), and 4 parts of talc using a double roller mill preheated to 50℃ for 20 min, press the mixed raw materials into 4mm sheets using a double roller mill after sufficient mixing of the raw materials, and dry the raw material sheets in a forced air drying oven for 5 hours;

[0063] 2) put the sheet prepared in step 1) into the membrane cavity of the preheated flat vulcanizing machine, and take out after molding and foaming at 10 MPa and 175℃ for 450s, to obtain the halogen-free flame-retardant composite foaming material.

[0064] Comparative Example 4

[0065] A preparation method of an EPDM composite foaming material, comprising the following steps:

[0066] 1) Mix 100 parts of EPDM granules, 10 parts of flame retardant (obtained by mixing 8 parts of melamine polyphosphate, 1 part of aluminum hydroxide, 1 part of magnesium hydroxide, and 1 part of polyphenylene sulfide fiber), 10 parts of carbon black, 2 parts of zinc oxide, 2 parts of stearic acid, 6 parts of foaming agent AC (azodicarbonamide), 0.5 parts of crosslinking agent DCP (dicumyl peroxide), and 4 parts of talc powder using a two-roll mill preheated to 50°C for 20 minutes to achieve uniform mixing. After the raw materials are fully mixed, press the mixed raw materials into 4mm thin sheets using a two-roll mill and dry the raw material sheets in a forced-air drying oven for 5 hours.

[0067] 2) Place the sheet prepared in step 1) into the preheated flat vulcanizing machine cavity, and mold it for 450 seconds at 10MPa and 175℃. Then take it out to obtain the halogen-free flame-retardant composite foam material.

[0068] Comparative Example 5

[0069] A method for preparing an EPDM composite foam material includes the following steps:

[0070] 1) Mix 100 parts of EPDM granules, 10 parts of melamine polyphosphate / aluminum hydroxide / magnesium hydroxide microsphere core-shell flame retardant, 10 parts of carbon black, 2 parts of zinc oxide, 2 parts of stearic acid, 6 parts of foaming agent AC (azodicarbonamide), 0.5 parts of crosslinking agent DCP (dicumyl peroxide), and 4 parts of talc powder evenly using a two-roll mill. After the raw materials are fully mixed, press the mixture in a two-roll mill preheated to 50°C for 20 minutes until all raw materials are evenly mixed. After the raw materials are fully mixed, press the mixture into 4mm thin sheets using a two-roll mill and dry the raw material sheets in a forced-air drying oven for 5 hours.

[0071] 2) Place the sheet prepared in step 1) into the preheated flat vulcanizing machine cavity, and mold it for 450 seconds at 10MPa and 175℃. Then take it out to obtain the halogen-free flame-retardant composite foam material.

[0072] The samples obtained from the examples and comparative examples were subjected to performance tests, and the results are shown in Table 1.

[0073] Table 1 Sample performance test results

[0074]

[0075] The data in Table 1 show that when the addition amount of melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant reaches 15 parts, the limiting oxygen index of the sample can reach 29.5, and the UL-94 rating is V-0. And with the increase of the addition amount of the composite flame retardant, the tensile strength and elongation at break of the sample also increase to a certain extent, which shows that the composite flame retardant used in the application can also effectively improve the mechanical properties of the sample. Compared with the comparative example 1 without adding the composite flame retardant, the comparative example 2 adding only 10 parts by weight of melamine polyphosphate, and the comparative example 4 adding 10 parts by weight of the doped flame retardant (obtained by mixing 8 parts of melamine polyphosphate, 1 part of aluminum hydroxide, 1 part of magnesium hydroxide and 1 part of polyphenylene sulfide fiber), the flame retardant effect of the EPDM composite foaming material prepared in the example 2 is significantly improved, which shows that the prepared melamine polyphosphate / aluminum hydroxide / magnesium hydroxide core-shell microsphere flame retardant and polyphenylene sulfide fiber play a synergistic flame-retardant effect, that is, 1+1>2. And the polyphenylene sulfide fiber itself is a short rod-shaped fiber which can be uniformly dispersed in the EPDM matrix with the help of the core-shell structure, so that the stress distribution is uniform, thereby improving the tensile strength of the EPDM composite foaming material (comparative example 5). The application uses melamine polyphosphate, magnesium hydroxide and aluminum hydroxide to prepare a core-shell flame retardant material MMA, instead of simply stacking several raw materials, and adds polyphenylene sulfide fiber to the synthesized core-shell material instead of simply using polyphenylene sulfide granular resin, and the combination of the two obtains a composite flame retardant, wherein the polyphenylene sulfide fiber undertakes the improvement of the toughening and part of the flame retardant performance, and the core-shell flame retardant MMA shows better flame-retardant effect than the ordinary doped flame retardant due to its special inner and outer spherical structure, Figure 4 The electron microscope image of the synthesized core-shell structure flame retardant can further enhance the mechanical properties of the foamed matrix material due to the use of the "ball-rod" additive shape. In addition, the comparative example 3 adding only 10 parts by weight of melamine has a flame retardant effect worse than that of the example 2 and the comparative example 2, which shows that the melamine polyphosphate prepared in the application can achieve better flame retardant effect. It can be clearly seen from Figure 5 that the prepared composite flame retardant can be well dispersed in the EPDM composite foaming material, so that the final product prepared has excellent flame-retardant effect and mechanical properties.

[0076] The above only describes the preferred embodiments of the application, and any equivalent changes and modifications made within the scope of the application should be included in the scope of the application.

Claims

1. A halogen-free flame-retardant EPDM composite foam material, characterized in that: The halogen-free flame-retardant EPDM composite foaming material comprises, in parts by weight: 100 parts of EPDM particles, 5-15 parts of melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant, 5-10 parts of carbon black, 2 parts of zinc oxide, 2 parts of stearic acid, 6 parts of foaming agent azodicarbonamide, 0.5 parts of crosslinking agent dicumyl peroxide, and 2-4 parts of talc. The preparation of the melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant comprises the following steps: (1) Melamine polyphosphate is added to 200 mL of deionized water, and ultrasonic oscillation is performed at 25°C until uniform dispersion is achieved. Then, the solution is transferred to a 60°C water bath and subjected to continuous magnetic stirring; (2) Aluminum hydroxide and magnesium hydroxide are slowly added to the solution obtained in step (1) in batches, and stirring is performed under water bath for 4 h. Then, the solution is placed at room temperature for continuous stirring for 4 h and then left to stand overnight; (3) The precipitate obtained by centrifugation of the reaction solution obtained in step (2) is dried to obtain a melamine polyphosphate / aluminum hydroxide / magnesium hydroxide microspherical core-shell flame retardant; (4) The melamine polyphosphate / aluminum hydroxide / magnesium hydroxide microspherical core-shell flame retardant obtained in step (3) is mixed with polyphenylene sulfide fibers in a mortar to obtain a melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant.

2. The halogen-free flame-retardant EPDM composite foamed material according to claim 1, characterized in that: The preparation method of the melamine polyphosphate comprises the following steps: 12.6 g of melamine is added to 200 mL of deionized water at 95°C, and stirring is performed for 10 min until dispersion is achieved. Then, 11.5 mL of 85 wt.% concentrated phosphoric acid is slowly added in batches, and stirring is continued for 1.5 h until the reaction is complete. After the reaction is cooled to room temperature, the reaction product is filtered, the filter cake is washed with deionized water, and then placed in a vacuum drying oven at 80°C for drying for 4 h to obtain melamine polyphosphate.

3. The halogen-free flame-retardant EPDM composite foamed material according to claim 1, characterized in that: The mass ratio of melamine polyphosphate, aluminum hydroxide, and magnesium hydroxide is 8:1:

1.

4. The halogen-free flame-retardant EPDM composite foamed material according to claim 1, characterized in that: The temperature of the water bath in step (2) is 60°C.

5. The halogen-free flame-retardant EPDM composite foamed material according to claim 1, characterized in that: The drying temperature in step (3) is 60°C, and the drying time is 10 h.

6. The halogen-free flame retardant EPDM composite foam material according to claim 1, characterized in that: In step (4), the mass ratio of the melamine polyphosphate / aluminum hydroxide / magnesium hydroxide microspherical core-shell flame retardant to the polyphenylene sulfide fibers is 9:

1.

7. The process for preparing a halogen-free flame-retardant EPDM composite foam material according to claim 1, characterized in that: The method comprises the following steps: (1) EPDM, melamine polyphosphate / aluminum hydroxide / magnesium hydroxide / polyphenylene sulfide composite flame retardant, carbon black, zinc oxide, stearic acid, foaming agent, crosslinking agent, and talc are uniformly mixed using a preheated two-roll open mill for 10-20 min, and the heating temperature is 50-60°C. After the rubber compound is uniformly mixed, it is passed through the mill 4-6 times to obtain a rubber sheet with a thickness of 2-4 mm; (2) The rubber sheet obtained in step (2) is left to stand for 4-6 h, and then placed in the mold cavity of a preheated flat plate mold press. Foaming is performed at 175°C and 10 MPa for 450 s, and then cooled to obtain a halogen-free flame-retardant EPDM composite foaming material.

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