High-flame-retardant EVA foaming material and preparation method thereof

Abstract

The invention discloses a high-flame-retardant EVA (Ethylene Vinyl Acetate) foaming material and a preparation method thereof, and relates to the technical field of high polymer materials. The high-flame-retardant EVA foaming material is prepared from a coated functional filler, a nitrogen-doped graphene-like carbon / cobalt nano composite material, EVA, stearic acid, zinc stearate, zinc oxide, a foaming agent AC and dicumyl peroxide, a core-shell combined filler composed of a coated functional filler and a nitrogen-doped graphene-like carbon / cobalt nano composite material is uniformly distributed in an EVA three-dimensional network cross-linked matrix to form a porous material with a uniform closed cell structure, so that the flame retardant property is improved by virtue of a physical barrier effect and a catalytic carbon formation mechanism, and an efficient and stable conductive network is also constructed; the antistatic performance is optimized, and the application range of the EVA foaming material is widened.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically referring to a highly flame-retardant EVA foam material and its preparation method. Background Technology

[0002] Ethylene-vinyl acetate copolymer (EVA) is an important thermoplastic elastomer, copolymerized from ethylene monomers and vinyl acetate monomers. The introduction of vinyl acetate monomers reduces the crystallinity of the material, giving it good processability, flexibility, low-temperature toughness, resistance to environmental stress cracking, and weather resistance. As a result, it is widely used in packaging, construction, and automotive industries. However, the high flammability of EVA poses safety hazards in many applications. Therefore, it is particularly important to develop efficient flame retardants to improve the flame retardant properties of EVA.

[0003] The existing technology currently suffers from the following main problems:

[0004] In the application of EVA foam materials, there are still common problems with insufficient flame retardant and antistatic properties, which limits their wider and safer use. Summary of the Invention

[0005] In view of the above situation and to overcome the defects of the prior art, the present invention proposes a high flame retardant EVA foam material, comprising the following components in parts by weight: 40-50 parts of coated functional filler, 8-10 parts of nitrogen-doped graphene-like carbon / cobalt nanocomposite material, 200-300 parts of EVA, 2.5-2.7 parts of stearic acid, 2.5-2.7 parts of zinc stearate, 6.0-6.5 parts of zinc oxide, 12.5-13.5 parts of foaming agent AC, and 2.5-2.7 parts of dicumyl peroxide.

[0006] The coated functional filler is made from the following components in parts by weight: 10-20 parts of silane-modified grafted ammonium polyphosphate and 0.8-1.0 parts of dopamine hydrochloride.

[0007] The preparation method of the coated functional filler specifically includes the following steps:

[0008] (1) Add 3-glycidyl etheroxypropyltrimethoxysilane to 200-250 mL of 90% ethanol solution, and adjust the pH to 4.0-5.0 with acetic acid. Stir for 30-50 min in an oil bath at 40-50℃ to obtain a hydrolysate. Add 80.0-100.0 g of piperazine pyrophosphate to the hydrolysate in 5 portions, and disperse by ultrasonication for 15-20 min. Then, stir and react at 70℃ for 2-3 h under a nitrogen atmosphere. Centrifuge and wash the precipitate repeatedly with anhydrous ethanol until the eluent is dry and free of residue and the pH is neutral. Finally, dry the washed product in a vacuum drying oven at 60℃ for 10-12 h. A three-dimensional network of organosilicon polymer shells with Si-O-Si as the framework and anchored by Si-OP bonds is formed on the surface of piperazine phosphate particles. The core flame-retardant components are anchored in the polymer network, which can remain in the expanded char layer for a longer time during combustion to continuously play a role, suppressing dripping and thus improving the quality and stability of the char layer. At the same time, it also improves the compatibility with the EVA matrix, which can not only make the flame-retardant particles uniformly dispersed in the matrix to avoid the island structure caused by agglomeration, but also form a denser and more uniform filler network in the EVA matrix, thereby building an ion-conducting pathway inside the material, improving the flame-retardant performance and antistatic performance, resulting in silane-modified grafted ammonium polyphosphate.

[0009] (2) Weigh 10.0-20.0g of the silane-modified grafted ammonium polyphosphate described in step (1) and add it to 400mL of 30% ethanol solution. Sonicate for 30-40min. Add dopamine hydrochloride and 2.0-2.5g of tris(hydroxymethyl)aminomethane hydrochloride under stirring. Adjust the pH of the mixture to 8.5 with ammonia before completely adding dopamine hydrochloride. Stir the reaction at room temperature for 30-36h. After the reaction is complete, centrifuge and wash the precipitate with deionized water until the supernatant is colorless. Freeze-drying, with polydopamine coating as the outermost layer, anchors the core flame retardant at the combustion site through adhesion, preventing it from falling off and failing prematurely. It also slows down the transfer of heat and decomposition products through a dense physical barrier, thus synergistically enhancing the flame retardant performance. At the same time, the abundant hydrophilic groups on the surface of polydopamine can also strongly adsorb water molecules in the environment, forming a thin hydrated layer on the surface of the filler. This layer provides a moisture-based ion conduction channel as a charge carrier, thereby improving the antistatic performance and resulting in a coated functional filler.

[0010] Preferably, in step (1), the amount of 3-glycidyl etheroxypropyltrimethoxysilane added is 3.0-4.0g. As an organosilicon component, 3-glycidyl etheroxypropyltrimethoxysilane can promote the formation of a more stable silicon-carbon-phosphorus composite carbon layer during combustion, thereby enhancing the heat insulation and oxygen barrier capabilities of the carbon layer.

[0011] Preferably, in step (2), the amount of dopamine hydrochloride added is 0.8-1.0g. The polydopamine coating formed by oxidation and self-polymerization not only serves as a high-quality carbon source and foaming agent, but also reacts strongly with the polyphosphoric acid produced by the decomposition of piperazine pyrophosphate during combustion, catalyzing the dehydration of itself and the EVA matrix into carbon. The carbon layer formed by polydopamine also has higher thermal stability and continuity, wrapping and reinforcing the brittle phosphate carbon layer catalyzed by piperazine pyrophosphate, making it denser and stronger, and less likely to be dispersed by the flame airflow, thereby greatly improving the heat insulation and oxygen barrier effect.

[0012] This invention also provides a method for preparing a highly flame-retardant EVA foam material, specifically including the following steps:

[0013] S1. 2,2'-Bipyridine-5,5'-dicarboxylic acid was suspended in 200 mL of 50% ethanol solution. While stirring at 200 rpm, 1 mol / L potassium hydroxide aqueous solution was slowly added to adjust the pH to 8.5-9.5. Then, 8.5 g of cobalt chloride hexahydrate was added, and the mixture was stirred for 0.5-1 h. The mixture was then transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted at 110-120 °C for 24 h. After centrifugation, the precipitate was washed three times alternately with deionized water and methanol, and dried in a vacuum drying oven at 60 °C for 12 h. The resulting precursor was placed in a tube furnace and heat-treated at 500-600 °C for 1-2 h under nitrogen protection. Cobalt ions act as the catalytic center, strongly catalyzing the surrounding... Organic ligands are carbonized and directed to graphitization, forming a nitrogen-doped graphene-like carbon matrix. At the same time, cobalt ions uniformly distributed in the precursor are reduced in situ to metallic cobalt nanoparticles. Due to their initial atomic-level dispersion in the coordination polymer, they are effectively confined in the carbon layer, avoiding severe aggregation at high temperatures. The cobalt nanoparticles can catalyze the cross-linking and dehydration reactions of EVA molecular chains, significantly improving the carbonization rate. In the EVA matrix, the highly dispersed cobalt nanoparticles and their encapsulated / connected conductive carbon network together construct a highly efficient three-dimensional percolation conductive network. Electrons can migrate through tunneling or direct contact, thereby obtaining stable and durable antistatic properties, resulting in a nitrogen-doped graphene-like carbon / cobalt nanocomposite material.

[0014] S2. Weigh 8.0-10.0g of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material described in step S1 and place it in 150mL of deionized water. Add 1.2g of sodium dodecyl sulfate and ultrasonically disperse for 50-60min to form a dispersion for later use. Dry 40.0-50.0g of the coated functional filler at 60℃ for 1-2h, then disperse it in 300mL of deionized water and ultrasonically treat it for 20-30min. Then, while stirring at 300-500rpm, add the dispersion. After complete addition, adjust the pH to 8.0-9.0 with ammonia water and react at room temperature for 12-24h. Centrifuge and use the precipitate first... Wash three times with hot water at 60-70℃, then wash twice with anhydrous ethanol, then dry, grind, and pass through an 80-100 mesh sieve to obtain a composite filler for later use. Place 200.0-300.0g EVA, 2.5-2.7g stearic acid, 2.5-2.7g zinc stearate, and 6.0-6.5g zinc oxide in a mixer and melt-blend for 2 minutes. Then add the composite filler in three batches and mix for 3.5-4.5 minutes. Add 12.5-13.5g foaming agent AC and mix for 1-2 minutes. Then add 2.5-2.7g dicumyl peroxide and mix for 1-2 minutes. Finally, extrude and granulate to obtain the masterbatch. The granules are dried at 50℃ for 5-6 hours, placed in a mold, and preheated in a flat vulcanizing machine at 100-120℃ for 2-3 minutes. A pressure of 5-10 MPa is applied and maintained for 2-3 minutes. Finally, the temperature is raised to 170-180℃ and foamed at 8-10 MPa for 2-3 minutes. The pressure is then released, the mixture is cooled, and demolded. In this process, under the action of dicumyl peroxide, a chemically cross-linked three-dimensional network matrix is ​​formed between the EVA molecular chains. The interior is uniformly dispersed with a special heterogeneous structure of filler composed of coated functional fillers (outer layer) and nitrogen-doped graphene-like carbon / cobalt nanocomposite materials (core), forming a uniform closed-cell structure. The porous composite material, with its uniformly dispersed composite filler, constructs a tortuous path within the material and the char layer formed during combustion. This effectively blocks heat transfer to the material interior, the outward diffusion of combustible volatile products, and the inward penetration of oxygen, significantly improving flame retardant performance. Furthermore, the encapsulated functional filler, acting as a carrier, prevents excessive agglomeration of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material and helps it to be better dispersed and positioned during the mixing process. As a result, the composite filler as a whole forms a denser distribution of points in the material, which is conducive to the efficient construction and stabilization of the conductive network, achieving a durable and reliable antistatic function, and obtaining a highly flame-retardant EVA foam material.

[0015] Preferably, in step S1, the amount of 2,2'-bipyridine-5,5'-dicarboxylic acid added is 8.7g. After pyrolysis, 2,2'-bipyridine-5,5'-dicarboxylic acid is directly converted into highly graphitized, nitrogen-doped carbon sheets, which can form a continuous, highly conductive carbon network on the EVA matrix, thereby optimizing the antistatic performance.

[0016] Preferably, in step S2, during the melt blending process, the temperature of the feeding section is 120-140℃, the temperature of the melting section is 150-160℃, the temperature of the discharging section is 140-150℃, and the rotation speed is 80-100 rpm. The setting of parameters for each zone is conducive to achieving the ideal state of uniform dispersion, complete network and strong interface of the combined filler in the EVA matrix.

[0017] The beneficial effects achieved by this invention are as follows:

[0018] This invention utilizes a core-shell composite filler, composed of a coated functional filler and a nitrogen-doped graphene-like carbon / cobalt nanocomposite material, uniformly distributed within a three-dimensional network cross-linked matrix of EVA. This forms a porous material with a uniform, closed-cell structure, enhancing flame retardant performance through physical barrier effects and catalytic carbonization mechanisms. Furthermore, it constructs a highly efficient and stable conductive network, optimizing antistatic properties and broadening the application range of EVA foam materials. In the coated functional filler, a three-dimensional network of organosilicon polymer shell with a Si-O-Si framework and Si-OP bonds anchored is first generated on the surface of piperazine pyrophosphate particles, followed by the coating of silane-modified grafted ammonium polyphosphate. The polydopamine coating not only anchors the core flame-retardant components at the combustion site through adhesion, preventing premature detachment and failure, but also delays the transfer of heat and decomposition products through a dense physical barrier, synergistically enhancing flame-retardant performance. Furthermore, polydopamine possesses a unique π-π conjugated electron system and abundant polar functional groups, giving it semiconductor-like properties. Within the EVA matrix, the polydopamine shells approach each other, forming an interfacial conductive / polarized network throughout the material, thereby reducing surface resistivity and improving antistatic properties. In the nitrogen-doped graphene-like carbon / cobalt nanocomposite material, cobalt ions serve as the catalytic center. The nitrogen-doped graphene-like carbon matrix is ​​strongly catalyzed to carbonize and guide the surrounding organic ligands to graphitization, forming a nitrogen-doped graphene-like carbon matrix. Simultaneously, cobalt ions uniformly distributed in the precursor are reduced in situ to metallic cobalt nanoparticles. These cobalt nanoparticles, acting as highly efficient catalysts, further strongly catalyze the cross-linking and dehydration reactions of the EVA molecular chains, promoting the formation of a denser and more stable carbon layer. During combustion, the nitrogen-doped graphene-like carbon network integrates into the carbon layer formed by the EVA, serving as a robust framework that greatly enhances the mechanical strength, continuity, and thermal stability of the carbon layer. This makes it less prone to breakage under high temperatures and airflow impacts, thus providing a more durable thermal and thermal insulation effect. Within the EVA matrix, a highly distributed graphene-like carbon network... Dispersed cobalt nanoparticles and their encapsulated / connected conductive carbon network together construct a highly efficient three-dimensional percolation conductive network, allowing electrons to migrate through tunneling or direct contact, thereby achieving stable and durable antistatic properties. The uniformly dispersed cobalt particles act as anchor points, improving the interfacial bonding between the filler and the matrix, further enhancing flame retardant and antistatic properties. This invention uses coated functional fillers, nitrogen-doped graphene-like carbon / cobalt nanocomposites, EVA, stearic acid, zinc stearate, zinc oxide, foaming agent AC, and dicumyl peroxide to prepare a highly flame-retardant EVA foam material, significantly improving the material's flame retardant and antistatic properties. Attached Figure Description

[0019] Figure 1 The limiting oxygen index results are shown in the figures for Examples 1-4 and Comparative Examples 1-3 of the present invention.

[0020] Figure 2The figures show the volume resistivity results of Examples 1-4 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0023] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; unless otherwise specified, the experimental materials used in the following embodiments are all purchased from commercial channels.

[0024] Example 1

[0025] This embodiment proposes a highly flame-retardant EVA foam material, comprising the following components in parts by weight: 45 parts of coated functional filler, 9 parts of nitrogen-doped graphene-like carbon / cobalt nanocomposite material, 250 parts of EVA, 2.6 parts of stearic acid, 2.6 parts of zinc stearate, 6.25 parts of zinc oxide, 13.0 parts of foaming agent AC, and 2.6 parts of dicumyl peroxide.

[0026] The coated functional filler is made from the following components in parts by weight: 15 parts of silane-modified grafted ammonium polyphosphate and 0.9 parts of dopamine hydrochloride.

[0027] The preparation method of the coated functional filler includes the following steps:

[0028] (1) 3-Glycidyl etheroxypropyltrimethoxysilane was added to 225 mL of 90% ethanol solution. The amount of 3-glycidyl etheroxypropyltrimethoxysilane added was 3.5 g. As an organosilicon component, 3-glycidyl etheroxypropyltrimethoxysilane can promote the formation of a more stable silicon-carbon-phosphorus composite carbon layer during combustion, thereby enhancing the heat insulation and oxygen barrier capacity of the carbon layer. The pH was adjusted to 4.5 with acetic acid. The mixture was stirred for 40 min in an oil bath at 45 °C to obtain a hydrolysate for later use. 90.0 g of piperazine pyrophosphate was added to the hydrolysate in 5 portions and ultrasonically dispersed for 17.5 min. Then, the mixture was stirred and reacted at 70 °C for 2.5 h under a nitrogen atmosphere. After centrifugation, the precipitate was repeatedly washed with anhydrous ethanol until the eluent was dry and free of residue and the pH was normal. H is neutral. Finally, the washed product was dried in a vacuum drying oven at 60℃ for 11 hours, forming a three-dimensional network of organosilicon polymer shells with Si-O-Si as the framework and anchored by Si-OP bonds on the surface of piperazine pyrophosphate particles. The core flame retardant components are anchored in the polymer network, which can remain in the expanded char layer for a longer time during combustion to continuously play a role, suppressing dripping and thus improving the quality and stability of the char layer. At the same time, it also improves the compatibility with the EVA matrix, which can not only make the flame retardant particles uniformly dispersed in the matrix to avoid the island structure caused by agglomeration, but also form a denser and more uniform filler network in the EVA matrix, thereby building an ion-conducting pathway inside the material, improving the flame retardant and antistatic properties, and obtaining silane-modified grafted ammonium polyphosphate.

[0029] (2) Weigh 15.0g of the silane-modified grafted ammonium polyphosphate described in step (1) and add it to 400mL of 30% ethanol solution. Sonicate for 35min. Add dopamine hydrochloride and 2.25g of tris(hydroxymethyl)aminomethane hydrochloride under stirring. The amount of dopamine hydrochloride added is 0.9g. The polydopamine coating formed by oxidative self-polymerization not only serves as a high-quality carbon source and foaming agent, but also reacts strongly with the polyphosphoric acid produced by the decomposition of piperazine pyrophosphate during combustion, catalyzing the dehydration of itself and the EVA matrix into carbon. The carbon layer formed by polydopamine also has higher thermal stability and continuity, wrapping and reinforcing the brittle phosphate carbon layer catalyzed by piperazine pyrophosphate, making it denser and stronger, and less likely to be dispersed by the flame gas flow. This greatly enhances the heat insulation and oxygen barrier effects. Before fully adding dopamine hydrochloride, the pH of the mixture is adjusted to 8.5 with ammonia water. The mixture is stirred and reacted at room temperature for 33 hours. After the reaction, the mixture is centrifuged, and the precipitate is washed with deionized water until the supernatant is colorless. The mixture is then freeze-dried. The polydopamine coating, as the outermost layer, anchors the core flame retardant at the combustion site through adhesion, preventing it from falling off and failing prematurely. It also slows down the transfer of heat and decomposition products through a dense physical barrier, thus synergistically enhancing the flame retardant performance. At the same time, the abundant hydrophilic groups on the surface of polydopamine can also strongly adsorb water molecules in the environment, forming a thin hydrated layer on the surface of the filler. This layer provides a moisture-based ion conduction channel as a charge carrier, thereby improving the antistatic performance and resulting in a coated functional filler.

[0030] This embodiment provides a method for preparing a highly flame-retardant EVA foam material, specifically including the following steps:

[0031] S1. 2,2'-Bipyridine-5,5'-dicarboxylic acid was suspended in 200 mL of 50% ethanol solution. The amount of 2,2'-bipyridine-5,5'-dicarboxylic acid added was 8.7 g. After pyrolysis, 2,2'-bipyridine-5,5'-dicarboxylic acid directly transforms into highly graphitized, nitrogen-doped carbon sheets, which can form a continuous, highly conductive carbon network on the EVA matrix, thereby optimizing the antistatic properties. Under stirring at 200 rpm, 1 mol / L potassium hydroxide aqueous solution was slowly added to adjust the pH to 9.0, followed by the addition of 8.5 g of cobalt chloride hexahydrate. The mixture was stirred for 0.75 h, then transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted at 115 °C for 24 h. After centrifugation, the precipitate was washed three times alternately with deionized water and methanol, and dried in a vacuum drying oven at 60 °C for 12 h. The obtained precursor was then placed... In a tube furnace, under nitrogen protection, the mixture was heat-treated at 550℃ for 1.5h. Cobalt ions, acting as the catalytic center, strongly catalyzed the carbonization and graphitization of surrounding organic ligands, forming a nitrogen-doped graphene-like carbon matrix. Simultaneously, the uniformly distributed cobalt ions in the precursor were reduced in situ to metallic cobalt nanoparticles. Due to their initial atomic-level dispersion in the coordination polymer, they were effectively confined in the carbon layer, avoiding severe agglomeration at high temperatures. The cobalt nanoparticles catalyzed the crosslinking and dehydration reactions of EVA molecular chains, significantly improving the carbonization rate. In the EVA matrix, the highly dispersed cobalt nanoparticles and their encapsulated / connected conductive carbon network together constructed a highly efficient three-dimensional percolation conductive network. Electrons could migrate through tunneling or direct contact, thereby obtaining stable and durable antistatic properties, resulting in a nitrogen-doped graphene-like carbon / cobalt nanocomposite material.

[0032] S2. Weigh 9.0 g of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material described in step S1 and place it in 150 mL of deionized water. Add 1.2 g of sodium dodecyl sulfate and ultrasonically disperse for 55 min to form a dispersion for later use. Dry 45.0 g of the coated functional filler at 60 °C for 1.5 h, then disperse it in 300 mL of deionized water and ultrasonically treat for 25 min. Next, add the dispersion while stirring at 400 rpm. After complete addition, adjust the pH to 8.5 with ammonia water and react at room temperature for 18 h. Centrifuge, wash the precipitate three times with 65 °C hot water, then wash twice with anhydrous ethanol, then dry, grind, and pass through 9... The composite filler was obtained through a 0-mesh sieve and set aside for later use. 250.0g EVA, 2.6g stearic acid, 2.6g zinc stearate, and 6.25g zinc oxide were placed in an internal mixer and melt-blended for 2 minutes. During the melt-blending process, the feed temperature was 130℃, the melting temperature was 155℃, and the discharge temperature was 145℃, with a rotation speed of 90 rpm. These parameters were set to ensure uniform dispersion, a complete network, and a strong interface in the EVA matrix. The composite filler was then added in three batches and mixed for 4.0 minutes each. 13.0g of foaming agent AC was added and mixed for 1.5 minutes. Finally, 2.6g of dicumyl peroxide was added. The mixture was kneaded for 1.5 minutes, then extruded and granulated. The resulting masterbatch was dried at 50°C for 5.5 hours, placed in a mold, and preheated at 110°C for 2.5 minutes in a flat vulcanizing machine. A pressure of 7.5 MPa was applied and held for 2.5 minutes. Finally, the temperature was raised to 175°C and foamed at 9 MPa for 2.5 minutes. The pressure was released, the mixture was cooled, and demolded. In this process, under the action of dicumyl peroxide, a chemically cross-linked three-dimensional network matrix was formed between the EVA molecular chains. The interior was uniformly dispersed with a special heterogeneous structure combination filler composed of coated functional fillers (outer layer) and nitrogen-doped graphene-like carbon / cobalt nanocomposite materials (core), forming uniform closed pores. The porous composite material with a uniformly dispersed composite filler creates a tortuous path within the material and the char layer formed during combustion. This effectively blocks heat transfer to the material interior, the diffusion of combustible volatile products to the outside, and oxygen penetration to the inside, significantly improving flame retardant performance. Furthermore, the coated functional filler acts as a carrier, preventing excessive agglomeration of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material and helping it to better disperse and position itself during the mixing process. As a result, the composite filler forms a denser distribution of points within the material, which is beneficial for the efficient construction and stabilization of the conductive network, achieving a durable and reliable antistatic function, and resulting in a highly flame-retardant EVA foam material.

[0033] Example 2

[0034] This embodiment proposes a highly flame-retardant EVA foam material, comprising the following components in parts by weight: 50 parts of coated functional filler, 10 parts of nitrogen-doped graphene-like carbon / cobalt nanocomposite material, 300 parts of EVA, 2.7 parts of stearic acid, 2.7 parts of zinc stearate, 6.5 parts of zinc oxide, 13.5 parts of foaming agent AC, and 2.7 parts of dicumyl peroxide.

[0035] The coated functional filler is made from the following components in parts by weight: 20 parts of silane-modified grafted ammonium polyphosphate and 1.0 part of dopamine hydrochloride.

[0036] The preparation method of the coated functional filler includes the following steps:

[0037] (1) 3-Glycidyl etheroxypropyltrimethoxysilane was added to 250 mL of 90% ethanol solution. The amount of 3-glycidyl etheroxypropyltrimethoxysilane added was 4.0 g. As an organosilicon component, 3-glycidyl etheroxypropyltrimethoxysilane can promote the formation of a more stable silicon-carbon-phosphorus composite carbon layer during combustion, thereby enhancing the heat insulation and oxygen barrier capacity of the carbon layer. The pH was adjusted to 5.0 with acetic acid. The mixture was stirred for 50 min in an oil bath at 50 °C to obtain a hydrolysate for later use. 100.0 g of piperazine pyrophosphate was added to the hydrolysate in 5 portions and ultrasonically dispersed for 20 min. Then, the mixture was stirred and reacted at 70 °C for 3 h under a nitrogen atmosphere. After centrifugation, the precipitate was repeatedly washed with anhydrous ethanol until the eluent was dry and free of residue and the pH was adjusted. To neutralize the product, the washed product was dried in a vacuum drying oven at 60°C for 12 hours, forming a three-dimensional network of organosilicon polymer shells with Si-O-Si as the framework and anchored by Si-OP bonds on the surface of piperazine pyrophosphate particles. The core flame-retardant components were anchored in the polymer network, which can remain in the expanded char layer for a longer time during combustion to continuously play a role, suppressing dripping and thus improving the quality and stability of the char layer. At the same time, it also improved the compatibility with the EVA matrix, which can not only make the flame-retardant particles uniformly dispersed in the matrix to avoid the island structure caused by agglomeration, but also form a denser and more uniform filler network in the EVA matrix, thereby building an ion-conducting pathway inside the material, improving the flame-retardant and antistatic properties, and obtaining silane-modified grafted ammonium polyphosphate.

[0038] (2) Weigh 20.0g of the silane-modified grafted ammonium polyphosphate described in step (1) and add it to 400mL of 30% ethanol solution. Sonicate for 40min. Add dopamine hydrochloride and 2.5g of tris(hydroxymethyl)aminomethane hydrochloride under stirring conditions. The amount of dopamine hydrochloride added is 1.0g. The polydopamine coating formed through oxidative self-polymerization not only serves as a high-quality carbon source and foaming agent, but also reacts strongly with the polyphosphoric acid produced by the decomposition of piperazine pyrophosphate during combustion, catalyzing the dehydration of itself and the EVA matrix into carbon. The carbon layer formed by polydopamine also has higher thermal stability and continuity, encapsulating and reinforcing the brittle phosphate carbon layer catalyzed by piperazine pyrophosphate, making it denser and stronger, and less easily dispersed by the flame flow. To significantly improve the heat insulation and oxygen barrier effects, the pH of the mixture was adjusted to 8.5 with ammonia before the complete addition of dopamine hydrochloride. The mixture was stirred and reacted at room temperature for 36 hours. After the reaction, the mixture was centrifuged, and the precipitate was washed with deionized water until the supernatant was colorless. The mixture was then freeze-dried. The polydopamine coating, as the outermost layer, anchors the core flame retardant at the combustion site through adhesion, preventing it from falling off and failing prematurely. It also slows down the transfer of heat and decomposition products through a dense physical barrier, thus synergistically enhancing the flame retardant performance. At the same time, the abundant hydrophilic groups on the surface of polydopamine can also strongly adsorb water molecules in the environment, forming a thin hydrated layer on the surface of the filler. This layer provides a moisture-based ion conduction channel as a charge carrier, thereby improving the antistatic performance and resulting in a coated functional filler.

[0039] This embodiment provides a method for preparing a highly flame-retardant EVA foam material, specifically including the following steps:

[0040] S1. 2,2'-Bipyridine-5,5'-dicarboxylic acid was suspended in 200 mL of 50% ethanol solution. The amount of 2,2'-bipyridine-5,5'-dicarboxylic acid added was 8.7 g. After pyrolysis, 2,2'-bipyridine-5,5'-dicarboxylic acid directly transforms into highly graphitized, nitrogen-doped carbon sheets, which can form a continuous, highly conductive carbon network on the EVA matrix, thereby optimizing the antistatic properties. Under stirring at 200 rpm, 1 mol / L potassium hydroxide aqueous solution was slowly added to adjust the pH to 9.5, followed by the addition of 8.5 g of cobalt chloride hexahydrate. The mixture was stirred for 1 h, then transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted at 120 °C for 24 h. After centrifugation, the precipitate was washed three times alternately with deionized water and methanol, and dried in a vacuum drying oven at 60 °C for 12 h. The obtained precursor was placed in... In a tube furnace, under nitrogen protection, the mixture was heat-treated at 600℃ for 2 hours. Cobalt ions, acting as the catalytic center, strongly catalyzed the carbonization of surrounding organic ligands and guided them to graphitization, forming a nitrogen-doped graphene-like carbon matrix. Simultaneously, the cobalt ions uniformly distributed in the precursor were reduced in situ to metallic cobalt nanoparticles. Due to their initial atomic-level dispersion in the coordination polymer, they were effectively confined in the carbon layer, avoiding severe agglomeration at high temperatures. The cobalt nanoparticles could catalyze the cross-linking and dehydration reactions of EVA molecular chains, significantly improving the carbonization rate. In the EVA matrix, the highly dispersed cobalt nanoparticles and their encapsulated / connected conductive carbon network together constructed a highly efficient three-dimensional percolation conductive network. Electrons could migrate through tunneling effects or direct contact, thereby obtaining stable and durable antistatic properties, resulting in a nitrogen-doped graphene-like carbon / cobalt nanocomposite material.

[0041] S2. Weigh 10.0 g of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material described in step S1 and place it in 150 mL of deionized water. Add 1.2 g of sodium dodecyl sulfate and ultrasonically disperse for 60 min to form a dispersion for later use. Dry 50.0 g of the coated functional filler at 60 °C for 2 h, then disperse it in 300 mL of deionized water and ultrasonically treat for 30 min. Next, add the dispersion while stirring at 500 rpm. After complete addition, adjust the pH to 9.0 with ammonia water and react at room temperature for 24 h. Centrifuge, wash the precipitate three times with 70 °C hot water, then wash twice with anhydrous ethanol, then dry and grind. The composite filler was obtained by passing it through a 100-mesh sieve. 300.0g EVA, 2.7g stearic acid, 2.7g zinc stearate, and 6.5g zinc oxide were placed in an internal mixer and melt-blended for 2 minutes. During the melt-blending process, the feed temperature was 140℃, the melting temperature was 160℃, the discharge temperature was 150℃, and the rotation speed was 100rpm. These parameters were set to ensure uniform dispersion, a complete network, and a strong interface in the EVA matrix. The composite filler was then added in three batches and mixed for 4.5 minutes. 13.5g of foaming agent AC was added and mixed for 2 minutes, followed by the addition of 2.7g of zinc peroxide. Cumene peroxide was mixed for 2 minutes, then extruded and granulated. The resulting masterbatch was dried at 50°C for 6 hours, placed in a mold, and preheated at 120°C for 3 minutes in a flat vulcanizing machine. A pressure of 10 MPa was applied and held for 3 minutes. Finally, the temperature was raised to 180°C and foamed at 10 MPa for 3 minutes. The pressure was released, the mixture was cooled, and demolded. In this process, under the action of dicumyl peroxide, a chemically cross-linked three-dimensional network matrix was formed between the EVA molecular chains. The interior was uniformly dispersed with a special heterogeneous structure of filler composed of coated functional fillers (outer layer) and nitrogen-doped graphene-like carbon / cobalt nanocomposite materials (core), forming a uniform closed-cell structure. The porous composite material, with its uniformly dispersed composite filler, constructs a tortuous path within the material and the char layer formed during combustion. This effectively blocks heat transfer to the material interior, the outward diffusion of combustible volatile products, and the inward penetration of oxygen, significantly improving flame retardant performance. Furthermore, the encapsulated functional filler, acting as a carrier, prevents excessive agglomeration of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material and helps it to better disperse and position itself during the mixing process. Consequently, the composite filler as a whole forms a denser distribution of points within the material, which is conducive to the efficient construction and stabilization of the conductive network, achieving a durable and reliable antistatic function, resulting in a highly flame-retardant EVA foam material.

[0042] Example 3

[0043] This embodiment proposes a highly flame-retardant EVA foam material, comprising the following components in parts by weight: 40 parts of coated functional filler, 8 parts of nitrogen-doped graphene-like carbon / cobalt nanocomposite material, 200 parts of EVA, 2.5 parts of stearic acid, 2.5 parts of zinc stearate, 6.0 parts of zinc oxide, 12.5 parts of foaming agent AC, and 2.5 parts of dicumyl peroxide.

[0044] The coated functional filler is made from the following components in parts by weight: 10 parts of silane-modified grafted ammonium polyphosphate and 0.8 parts of dopamine hydrochloride.

[0045] The preparation method of the coated functional filler includes the following steps:

[0046] (1) 3-Glycidyl etheroxypropyltrimethoxysilane was added to 200 mL of 90% ethanol solution. The amount of 3-glycidyl etheroxypropyltrimethoxysilane added was 3.0 g. As an organosilicon component, 3-glycidyl etheroxypropyltrimethoxysilane can promote the formation of a more stable silicon-carbon-phosphorus composite carbon layer during combustion, thereby enhancing the heat insulation and oxygen barrier capacity of the carbon layer. The pH was adjusted to 4.0 with acetic acid. The mixture was stirred for 30 min in an oil bath at 40 °C to obtain a hydrolysate for later use. 80.0 g of piperazine pyrophosphate was added to the hydrolysate in 5 portions and ultrasonically dispersed for 15 min. Then, the mixture was stirred and reacted at 70 °C for 2 h under a nitrogen atmosphere. After centrifugation, the precipitate was repeatedly washed with anhydrous ethanol until the eluent was dry and free of residue and the pH was 4.0. After washing, the product was dried in a vacuum drying oven at 60℃ for 10 hours, forming a three-dimensional network of organosilicon polymer shells with Si-O-Si as the framework and anchored by Si-OP bonds on the surface of piperazine pyrophosphate particles. The core flame retardant components were anchored in the polymer network, which can remain in the expanded char layer for a longer time during combustion to continuously play a role, suppressing dripping and thus improving the quality and stability of the char layer. At the same time, it also improved the compatibility with the EVA matrix, which can not only make the flame retardant particles uniformly dispersed in the matrix to avoid the island structure caused by agglomeration, but also form a denser and more uniform filler network in the EVA matrix, thereby building an ion-conducting pathway inside the material, improving the flame retardant and antistatic properties, and obtaining silane-modified grafted ammonium polyphosphate.

[0047] (2) Weigh 10.0g of the silane-modified grafted ammonium polyphosphate described in step (1) and add it to 400mL of 30% ethanol solution. Sonicate for 30min. Add dopamine hydrochloride and 2.0g of tris(hydroxymethyl)aminomethane hydrochloride under stirring conditions. The amount of dopamine hydrochloride added is 0.8g. The polydopamine coating formed through oxidative self-polymerization not only serves as a high-quality carbon source and foaming agent, but also reacts strongly with the polyphosphoric acid produced by the decomposition of piperazine pyrophosphate during combustion, catalyzing the dehydration of itself and the EVA matrix into carbon. The carbon layer formed by polydopamine also has higher thermal stability and continuity, encapsulating and reinforcing the brittle phosphate carbon layer catalyzed by piperazine pyrophosphate, making it denser and stronger, and less easily dispersed by the flame flow. To significantly improve the heat insulation and oxygen barrier effects, the pH of the mixture was adjusted to 8.5 with ammonia before the complete addition of dopamine hydrochloride. The mixture was stirred and reacted at room temperature for 30 hours. After the reaction, the mixture was centrifuged, and the precipitate was washed with deionized water until the supernatant was colorless. The mixture was then freeze-dried. The polydopamine coating, as the outermost layer, anchors the core flame retardant at the combustion site through adhesion, preventing it from falling off and failing prematurely. It also slows down the transfer of heat and decomposition products through a dense physical barrier, thus synergistically enhancing the flame retardant performance. At the same time, the abundant hydrophilic groups on the surface of polydopamine can also strongly adsorb water molecules in the environment, forming a thin hydrated layer on the surface of the filler. This layer provides a moisture-based ion conduction channel as a charge carrier, thereby improving the antistatic performance and resulting in a coated functional filler.

[0048] This embodiment provides a method for preparing a highly flame-retardant EVA foam material, specifically including the following steps:

[0049] S1. 2,2'-Bipyridine-5,5'-dicarboxylic acid was suspended in 200 mL of 50% ethanol solution. The amount of 2,2'-bipyridine-5,5'-dicarboxylic acid added was 8.7 g. After pyrolysis, 2,2'-bipyridine-5,5'-dicarboxylic acid directly transforms into highly graphitized, nitrogen-doped carbon sheets, which can form a continuous, highly conductive carbon network on the EVA matrix, thereby optimizing the antistatic properties. Under stirring at 200 rpm, 1 mol / L potassium hydroxide aqueous solution was slowly added to adjust the pH to 8.5, followed by the addition of 8.5 g of cobalt chloride hexahydrate. The mixture was stirred for 0.5 h, then transferred to a high-pressure reactor lined with polytetrafluoroethylene (PTFE). The reaction was carried out at 110 °C for 24 h. After centrifugation, the precipitate was washed three times alternately with deionized water and methanol, and then dried in a vacuum drying oven at 60 °C for 12 h. The obtained precursor was placed... In a tube furnace, under nitrogen protection, the mixture was heat-treated at 500℃ for 1 hour. Cobalt ions, acting as the catalytic center, strongly catalyzed the carbonization and graphitization of surrounding organic ligands, forming a nitrogen-doped graphene-like carbon matrix. Simultaneously, the cobalt ions uniformly distributed in the precursor were reduced in situ to metallic cobalt nanoparticles. Due to their initial atomic-level dispersion in the coordination polymer, they were effectively confined in the carbon layer, avoiding severe agglomeration at high temperatures. The cobalt nanoparticles catalyzed the crosslinking and dehydration reactions of EVA molecular chains, significantly improving the carbonization rate. In the EVA matrix, the highly dispersed cobalt nanoparticles and their encapsulated / connected conductive carbon network together constructed a highly efficient three-dimensional percolation conductive network. Electrons could migrate through tunneling or direct contact, thereby obtaining stable and durable antistatic properties, resulting in a nitrogen-doped graphene-like carbon / cobalt nanocomposite material.

[0050] S2. Weigh 8.0g of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material described in step S1 and place it in 150mL of deionized water. Add 1.2g of sodium dodecyl sulfate and ultrasonically disperse for 50min to form a dispersion for later use. Dry 40.0g of the coated functional filler at 60℃ for 1h, then disperse it in 300mL of deionized water and ultrasonically treat for 20min. Then, while stirring at 300rpm, add the dispersion. After complete addition, adjust the pH to 8.0 with ammonia water and react at room temperature for 12h. Centrifuge, wash the precipitate three times with 60℃ hot water, then wash it twice with anhydrous ethanol, then dry and grind. The mixture was passed through an 80-mesh sieve to obtain a composite filler for later use. 200.0g EVA, 2.5g stearic acid, 2.5g zinc stearate, and 6.0g zinc oxide were placed in an internal mixer and melt-blended for 2 minutes. During the melt-blending process, the feed section temperature was 120℃, the melting section temperature was 150℃, and the discharge section temperature was 140℃, with a rotation speed of 80 rpm. These parameters were set to ensure the composite filler achieved uniform dispersion, a complete network, and a strong interface within the EVA matrix. The composite filler was then added in three batches and mixed for 3.5 minutes each. 12.5g of foaming agent AC was added and mixed for 1 minute, followed by the addition of 2.5g of zinc peroxide. Cumene peroxide was mixed for 1 minute, then extruded and granulated. The resulting masterbatch was dried at 50°C for 5 hours, placed in a mold, and preheated at 100°C for 2 minutes in a flat vulcanizing machine. A pressure of 5 MPa was applied and held for 2 minutes. Finally, the temperature was raised to 170°C and foamed at 8 MPa for 2 minutes. The pressure was released, the mixture was cooled, and demolded. In this process, under the action of dicumyl peroxide, a chemically cross-linked three-dimensional network matrix was formed between the EVA molecular chains. The interior was uniformly dispersed with a special heterogeneous structure of filler composed of coated functional fillers (outer layer) and nitrogen-doped graphene-like carbon / cobalt nanocomposite materials (core), forming a uniform closed-cell structure. The porous composite material, with its uniformly dispersed composite filler, constructs a tortuous path within the material and the char layer formed during combustion. This effectively blocks heat transfer to the material interior, the outward diffusion of combustible volatile products, and the inward penetration of oxygen, significantly improving flame retardant performance. Furthermore, the encapsulated functional filler, acting as a carrier, prevents excessive agglomeration of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material and helps it to better disperse and position itself during the mixing process. Consequently, the composite filler as a whole forms a denser distribution of points within the material, which is conducive to the efficient construction and stabilization of the conductive network, achieving a durable and reliable antistatic function, resulting in a highly flame-retardant EVA foam material.

[0051] Example 4

[0052] This embodiment proposes a highly flame-retardant EVA foam material, comprising the following components in parts by weight: 40 parts of coated functional filler, 10 parts of nitrogen-doped graphene-like carbon / cobalt nanocomposite material, 300 parts of EVA, 2.7 parts of stearic acid, 2.7 parts of zinc stearate, 6.5 parts of zinc oxide, 13.5 parts of foaming agent AC, and 2.7 parts of dicumyl peroxide.

[0053] The coated functional filler is made from the following components in parts by weight: 10 parts of silane-modified grafted ammonium polyphosphate and 1.0 part of dopamine hydrochloride.

[0054] The preparation method of the coated functional filler includes the following steps:

[0055] (1) 3-Glycidyl etheroxypropyltrimethoxysilane was added to 250 mL of 90% ethanol solution. The amount of 3-glycidyl etheroxypropyltrimethoxysilane added was 4.0 g. As an organosilicon component, 3-glycidyl etheroxypropyltrimethoxysilane can promote the formation of a more stable silicon-carbon-phosphorus composite carbon layer during combustion, thereby enhancing the heat insulation and oxygen barrier capacity of the carbon layer. The pH was adjusted to 5.0 with acetic acid. The mixture was stirred for 50 min in an oil bath at 50 °C to obtain a hydrolysate for later use. 100.0 g of piperazine pyrophosphate was added to the hydrolysate in 5 portions and ultrasonically dispersed for 20 min. Then, the mixture was stirred and reacted at 70 °C for 3 h under a nitrogen atmosphere. After centrifugation, the precipitate was repeatedly washed with anhydrous ethanol until the eluent was dry and free of residue and the pH was adjusted. To neutralize the product, the washed product was dried in a vacuum drying oven at 60°C for 12 hours, forming a three-dimensional network of organosilicon polymer shells with Si-O-Si as the framework and anchored by Si-OP bonds on the surface of piperazine pyrophosphate particles. The core flame-retardant components were anchored in the polymer network, which can remain in the expanded char layer for a longer time during combustion to continuously play a role, suppressing dripping and thus improving the quality and stability of the char layer. At the same time, it also improved the compatibility with the EVA matrix, which can not only make the flame-retardant particles uniformly dispersed in the matrix to avoid the island structure caused by agglomeration, but also form a denser and more uniform filler network in the EVA matrix, thereby building an ion-conducting pathway inside the material, improving the flame-retardant and antistatic properties, and obtaining silane-modified grafted ammonium polyphosphate.

[0056] (2) Weigh 10.0g of the silane-modified grafted ammonium polyphosphate described in step (1) and add it to 400mL of 30% ethanol solution. Sonicate for 40min. Add dopamine hydrochloride and 2.5g of tris(hydroxymethyl)aminomethane hydrochloride under stirring conditions. The amount of dopamine hydrochloride added is 1.0g. The polydopamine coating formed through oxidative self-polymerization not only serves as a high-quality carbon source and foaming agent, but also reacts strongly with the polyphosphoric acid produced by the decomposition of piperazine pyrophosphate during combustion, catalyzing the dehydration of itself and the EVA matrix into carbon. The carbon layer formed by polydopamine also has higher thermal stability and continuity, encapsulating and reinforcing the brittle phosphate carbon layer catalyzed by piperazine pyrophosphate, making it denser and stronger, and less easily dispersed by the flame flow. To significantly improve the heat insulation and oxygen barrier effects, the pH of the mixture was adjusted to 8.5 with ammonia before the complete addition of dopamine hydrochloride. The mixture was stirred and reacted at room temperature for 36 hours. After the reaction, the mixture was centrifuged, and the precipitate was washed with deionized water until the supernatant was colorless. The mixture was then freeze-dried. The polydopamine coating, as the outermost layer, anchors the core flame retardant at the combustion site through adhesion, preventing it from falling off and failing prematurely. It also slows down the transfer of heat and decomposition products through a dense physical barrier, thus synergistically enhancing the flame retardant performance. At the same time, the abundant hydrophilic groups on the surface of polydopamine can also strongly adsorb water molecules in the environment, forming a thin hydrated layer on the surface of the filler. This layer provides a moisture-based ion conduction channel as a charge carrier, thereby improving the antistatic performance and resulting in a coated functional filler.

[0057] This embodiment provides a method for preparing a highly flame-retardant EVA foam material, specifically including the following steps:

[0058] S1. 2,2'-Bipyridine-5,5'-dicarboxylic acid was suspended in 200 mL of 50% ethanol solution. The amount of 2,2'-bipyridine-5,5'-dicarboxylic acid added was 8.7 g. After pyrolysis, 2,2'-bipyridine-5,5'-dicarboxylic acid directly transforms into highly graphitized, nitrogen-doped carbon sheets, which can form a continuous, highly conductive carbon network on the EVA matrix, thereby optimizing the antistatic properties. Under stirring at 200 rpm, 1 mol / L potassium hydroxide aqueous solution was slowly added to adjust the pH to 9.5, followed by the addition of 8.5 g of cobalt chloride hexahydrate. The mixture was stirred for 1 h, then transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted at 120 °C for 24 h. After centrifugation, the precipitate was washed three times alternately with deionized water and methanol, and dried in a vacuum drying oven at 60 °C for 12 h. The obtained precursor was placed in... In a tube furnace, under nitrogen protection, the mixture was heat-treated at 600℃ for 2 hours. Cobalt ions, acting as the catalytic center, strongly catalyzed the carbonization of surrounding organic ligands and guided them to graphitization, forming a nitrogen-doped graphene-like carbon matrix. Simultaneously, the cobalt ions uniformly distributed in the precursor were reduced in situ to metallic cobalt nanoparticles. Due to their initial atomic-level dispersion in the coordination polymer, they were effectively confined in the carbon layer, avoiding severe agglomeration at high temperatures. The cobalt nanoparticles could catalyze the cross-linking and dehydration reactions of EVA molecular chains, significantly improving the carbonization rate. In the EVA matrix, the highly dispersed cobalt nanoparticles and their encapsulated / connected conductive carbon network together constructed a highly efficient three-dimensional percolation conductive network. Electrons could migrate through tunneling effects or direct contact, thereby obtaining stable and durable antistatic properties, resulting in a nitrogen-doped graphene-like carbon / cobalt nanocomposite material.

[0059] S2. Weigh 10.0 g of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material described in step S1 and place it in 150 mL of deionized water. Add 1.2 g of sodium dodecyl sulfate and ultrasonically disperse for 60 min to form a dispersion for later use. Dry 40.0 g of the coated functional filler at 60 °C for 2 h, then disperse it in 300 mL of deionized water and ultrasonically treat for 30 min. Next, add the dispersion while stirring at 500 rpm. After complete addition, adjust the pH to 9.0 with ammonia water and react at room temperature for 24 h. Centrifuge, wash the precipitate three times with 70 °C hot water, then wash twice with anhydrous ethanol, then dry and grind. The composite filler was obtained by passing it through a 100-mesh sieve. 300.0g EVA, 2.7g stearic acid, 2.7g zinc stearate, and 6.5g zinc oxide were placed in an internal mixer and melt-blended for 2 minutes. During the melt-blending process, the feed temperature was 140℃, the melting temperature was 160℃, the discharge temperature was 150℃, and the rotation speed was 100rpm. These parameters were set to ensure uniform dispersion, a complete network, and a strong interface in the EVA matrix. The composite filler was then added in three batches and mixed for 4.5 minutes. 13.5g of foaming agent AC was added and mixed for 2 minutes, followed by the addition of 2.7g of zinc peroxide. Cumene peroxide was mixed for 2 minutes, then extruded and granulated. The resulting masterbatch was dried at 50°C for 6 hours, placed in a mold, and preheated at 120°C for 3 minutes in a flat vulcanizing machine. A pressure of 10 MPa was applied and held for 3 minutes. Finally, the temperature was raised to 180°C and foamed at 10 MPa for 3 minutes. The pressure was released, the mixture was cooled, and demolded. In this process, under the action of dicumyl peroxide, a chemically cross-linked three-dimensional network matrix was formed between the EVA molecular chains. The interior was uniformly dispersed with a special heterogeneous structure of filler composed of coated functional fillers (outer layer) and nitrogen-doped graphene-like carbon / cobalt nanocomposite materials (core), forming a uniform closed-cell structure. The porous composite material, with its uniformly dispersed composite filler, constructs a tortuous path within the material and the char layer formed during combustion. This effectively blocks heat transfer to the material interior, the outward diffusion of combustible volatile products, and the inward penetration of oxygen, significantly improving flame retardant performance. Furthermore, the encapsulated functional filler, acting as a carrier, prevents excessive agglomeration of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material and helps it to better disperse and position itself during the mixing process. Consequently, the composite filler as a whole forms a denser distribution of points within the material, which is conducive to the efficient construction and stabilization of the conductive network, achieving a durable and reliable antistatic function, resulting in a highly flame-retardant EVA foam material.

[0060] Comparative Example 1

[0061] This comparative example provides a highly flame-retardant EVA foam material, which differs from Example 1 in that the coated functional filler does not contain 3-glycidyl etheroxypropyltrimethoxysilane; the preparation method of the coated functional filler does not include step (1); the preparation method of the highly flame-retardant EVA foam material is the same as that of Example 1.

[0062] Comparative Example 2

[0063] This comparative example provides a highly flame-retardant EVA foam material, which differs from Example 1 in that the coated functional filler does not contain dopamine hydrochloride; the preparation method of the coated functional filler does not include step (2); the preparation method of the highly flame-retardant EVA foam material is the same as that of Example 1.

[0064] Comparative Example 3

[0065] This comparative example provides a highly flame-retardant EVA foam material, which differs from Example 1 in that the nitrogen-doped graphene-like carbon / cobalt nanocomposite material does not contain 2,2'-bipyridine-5,5'-dicarboxylic acid; the preparation method of the coating functional filler is the same as that of Example 1; and 2,2'-bipyridine-5,5'-dicarboxylic acid is not added in step S1 of the preparation method of the highly flame-retardant EVA foam material.

[0066] Experimental Example 1

[0067] Flame retardancy test

[0068] Test samples: High flame-retardant EVA foam materials prepared in Examples 1-4 and Comparative Examples 1-3.

[0069] Test method: The test sample is prepared into a standard sample strip (100mm×10mm×10mm) by injection molding machine, and then the limiting oxygen index is tested according to the standard GB / T2406.2-2009 "Determination of burning behavior of plastics by oxygen index method". The higher the limiting oxygen index (%), the better the flame retardancy.

[0070] Figure 1The graph shows the limiting oxygen index (LOI) results for Examples 1-4 and Comparative Examples 1-3. As shown, the LIOI for Examples 1-4 is 30-33%, indicating good flame retardancy; the LIOI for Comparative Examples 1-3 is 22-27%, indicating average or poor flame retardancy. The coating-type functional filler in Comparative Example 1 does not contain 3-glycidyl etheroxypropyltrimethoxysilane, which is detrimental to improving compatibility with the EVA matrix. Furthermore, the absence of the silane interlayer also hinders the uniform coating of polydopamine, thus reducing flame retardancy during combustion. The flammable agent detaches and cannot form a continuous char layer, resulting in poor flame retardancy. The coating-type functional filler in Comparative Example 2 does not contain dopamine hydrochloride, so it cannot anchor the core flame-retardant component to the combustion site through adhesion, causing it to detach and fail prematurely, resulting in mediocre flame retardancy. The nitrogen-doped graphene-like carbon / cobalt nanocomposite material in Comparative Example 3 does not contain 2,2'-bipyridine-5,5'-dicarboxylic acid, so it cannot guide the formation of atomically dispersed precursors. The lack of cobalt catalyst and nitrogen-doped carbon skeleton results in mediocre flame retardancy.

[0071] Experiment Example 2

[0072] Antistatic test

[0073] Test samples: High flame-retardant EVA foam materials prepared in Examples 1-4 and Comparative Examples 1-3.

[0074] Test method: The test sample is prepared into a specimen with a size of 100mm×100mm×10mm and tested according to GB / T1410-2006 "Test method for volume resistivity and surface resistivity of solid insulating materials" to obtain the volume resistivity (Ω·cm). The smaller the volume resistivity, the better the antistatic performance.

[0075] Figure 2 The figures show the volume resistivity results for Examples 1-4 and Comparative Examples 1-3; as shown, the volume resistivity of Examples 1-4 is 1.5 × 10⁻⁶. 7 -5.8×10 7 The volume resistivity is Ω·cm, indicating good antistatic properties; the volume resistivity of comparative examples 1-3 is 7.6 × 10⁻⁶. 9 -1.0×10 14The value of Ω·cm indicates that the antistatic properties are generally good or poor. In Comparative Example 1, the coated functional filler lacks 3-glycidyl etheroxypropyltrimethoxysilane, resulting in a lack of a silane layer to improve compatibility. The nitrogen-doped graphene-like carbon / cobalt nanocomposite material can be encapsulated within the agglomerated coated functional filler, failing to effectively connect into a conductive network, leading to poor antistatic properties. In Comparative Example 2, the coated functional filler lacks dopamine hydrochloride, preventing the auxiliary conductivity of polydopamine and hindering the anchoring of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material, thus reducing the efficiency of conductive network construction and resulting in generally good antistatic properties. In Comparative Example 3, the nitrogen-doped graphene-like carbon / cobalt nanocomposite material lacks 2,2'-bipyridine-5,5'-dicarboxylic acid, preventing the formation of a precursor. Consequently, the core component for constructing a three-dimensional conductive network, the nitrogen-doped graphene-like carbon / cobalt nanocomposite material, cannot be obtained through pyrolysis, resulting in poor antistatic properties.

[0076] The above experimental results show that the flame retardancy and antistatic properties of Examples 1-4 of the present invention are significantly better than those of Comparative Examples 1-3. Among them, Example 1, which uses coated functional filler and nitrogen-doped graphene-like carbon / cobalt nanocomposite material, has better flame retardancy and antistatic properties. The core-shell composite filler composed of coated functional filler and nitrogen-doped graphene-like carbon / cobalt nanocomposite material is uniformly distributed in the EVA three-dimensional network cross-linked matrix, forming a porous material with a uniform closed cell structure. It not only improves the flame retardancy performance by means of physical barrier effect and catalytic carbonization mechanism, but also constructs an efficient and stable conductive network and optimizes the antistatic performance.

[0077] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

[0078] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A highly flame-retardant EVA foam material, characterized in that: The high flame-retardant EVA foam material comprises the following components in parts by weight: 40-50 parts of coated functional filler, 8-10 parts of nitrogen-doped graphene-like carbon / cobalt nanocomposite material, 200-300 parts of EVA, 2.5-2.7 parts of stearic acid, 2.5-2.7 parts of zinc stearate, 6.0-6.5 parts of zinc oxide, 12.5-13.5 parts of foaming agent AC, and 2.5-2.7 parts of dicumyl peroxide; the coated functional filler is made from the following components in parts by weight: 10-20 parts of silane-modified grafted ammonium polyphosphate and 0.8-1.0 parts of dopamine hydrochloride.

2. A method for preparing a high flame-retardant EVA foam material according to claim 1, characterized in that: Specifically, the following steps are included: S1. 2,2'-bipyridine-5,5'-dicarboxylic acid was suspended in 200 mL of 50% ethanol solution. While stirring at 200 rpm, 1 mol / L potassium hydroxide aqueous solution was slowly added to adjust the pH to 8.5-9.

5. Then, 8.5 g of cobalt chloride hexahydrate was added and stirred for 0.5-1 h. The mixture was then transferred to a high-pressure reactor lined with polytetrafluoroethylene and reacted at 110-120 °C for 24 h. After centrifugation, the precipitate was washed three times alternately with deionized water and methanol and dried in a vacuum drying oven at 60 °C for 12 h. The resulting precursor was placed in a tube furnace and heat-treated at 500-600 °C for 1-2 h under nitrogen protection to obtain nitrogen-doped graphene-like carbon / cobalt nanocomposite material. S2. Weigh 8.0-10.0g of the nitrogen-doped graphene-like carbon / cobalt nanocomposite material described in step S1 and place it in 150mL of deionized water. Add 1.2g of sodium dodecyl sulfate and ultrasonically disperse for 50-60min to form a dispersion for later use. Dry 40.0-50.0g of the coated functional filler at 60℃ for 1-2h, then disperse it in 300mL of deionized water and ultrasonically treat for 20-30min. Then, while stirring at 300-500rpm, add the dispersion. After complete addition, adjust the pH to 8.0-9.0 with ammonia water and react at room temperature for 12-24h. Centrifuge, wash the precipitate three times with hot water at 60-70℃, then wash twice with anhydrous ethanol, then dry, grind, and pass through an 80-100 mesh sieve to obtain the combined filler for later use. Add 200.0-30g of... 0.0g EVA, 2.5-2.7g stearic acid, 2.5-2.7g zinc stearate, and 6.0-6.5g zinc oxide were melt-blended in an internal mixer for 2 minutes. Then, combined fillers were added in three batches and mixed for 3.5-4.5 minutes. 12.5-13.5g foaming agent AC was added and mixed for 1-2 minutes. Then, 2.5-2.7g dicumyl peroxide was added and mixed for 1-2 minutes. The mixture was then extruded and granulated. The resulting masterbatch was dried at 50℃ for 5-6 hours and placed in a mold. It was preheated in a flat vulcanizing machine at 100-120℃ for 2-3 minutes, and a pressure of 5-10MPa was applied and maintained for 2-3 minutes. Finally, the temperature was raised to 170-180℃ and the pressure was maintained at 8-10MPa for 2-3 minutes to foam. The pressure was released, the mixture was cooled, and the material was demolded to obtain a high flame-retardant EVA foam material.

3. The preparation method of the high flame-retardant EVA foam material according to claim 2, characterized in that: In step S1, the amount of 2,2'-bipyridine-5,5'-dicarboxylic acid added is 8.7 g.

4. The preparation method of the high flame-retardant EVA foam material according to claim 3, characterized in that: In step S2, during the melt blending process, the temperature of the feeding section is 120-140℃, the temperature of the melting section is 150-160℃, the temperature of the discharging section is 140-150℃, and the rotation speed is 80-100 rpm.

5. The method for preparing the high flame-retardant EVA foam material according to claim 4, characterized in that: The preparation method of the coated functional filler specifically includes the following steps: (1) Add 3-glycidyl etheroxypropyltrimethoxysilane to 200-250 mL of 90% ethanol solution and adjust the pH to 4.0-5.0 with acetic acid. Stir for 30-50 min in an oil bath at 40-50℃ to obtain hydrolysate for later use. Add 80.0-100.0 g piperazine pyrophosphate to the hydrolysate in 5 portions and disperse ultrasonically for 15-20 min. Then stir and react at 70℃ for 2-3 h under nitrogen atmosphere. Centrifuge and wash the precipitate repeatedly with anhydrous ethanol until the eluent is dry and free of residue and the pH is neutral. Finally, dry the washed product in a vacuum drying oven at 60℃ for 10-12 h to obtain silane-modified grafted ammonium polyphosphate. (2) Weigh 10.0-20.0g of the silane-modified grafted ammonium polyphosphate described in step (1) and add it to 400mL of 30% ethanol solution. Sonicate for 30-40min. Add dopamine hydrochloride and 2.0-2.5g of tris(hydroxymethyl)aminomethane hydrochloride under stirring. Adjust the pH of the mixture to 8.5 with ammonia before adding dopamine hydrochloride completely. Stir the reaction at room temperature for 30-36h. After the reaction is completed, centrifuge and wash the precipitate with deionized water until the supernatant is colorless. Freeze dry to obtain the coated functional filler.

6. The method for preparing the high flame-retardant EVA foam material according to claim 5, characterized in that: In step (1), the amount of 3-glycidyl etheroxypropyltrimethoxysilane added is 3.0-4.0 g.

7. The method for preparing the high flame-retardant EVA foam material according to claim 6, characterized in that: In step (2), the amount of dopamine hydrochloride added is 0.8-1.0g.

Images