Graphite rubber-plastic composite flame-retardant material and preparation method thereof

Abstract

The invention relates to the technical field of rubber-plastic composite flame-retardant materials, and provides a graphite rubber-plastic composite flame-retardant material and a preparation method thereof.The preparation method comprises the following processes that nitrile rubber, polyvinyl chloride, dioctyl phthalate, modified expandable graphite, a stabilizer, sulfur and an anti-aging agent are added into a high-speed mixer and mixed to be uniform, and a premix is obtained; and feeding the premix into a double-screw extruder, and carrying out melt blending, extrusion and vulcanization to obtain the composite flame-retardant material. The preparation method has the beneficial effects that the modifier is combined with the expansible graphite and compounded with the nitrile rubber, the polyvinyl chloride and other base materials, so that the flame retardant property and the mechanical property of the prepared composite material are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite flame retardant material preparation, and in particular to a graphite rubber-plastic composite flame retardant material and a preparation method thereof. Background Art

[0002] In recent years, demand for flame-retardant rubber-plastic composite materials has been growing in applications such as construction, electronics, and transportation. Traditional flame-retardant materials primarily achieve their flame-retardant properties by adding halogenated flame retardants or inorganic fillers. However, halogenated flame retardants produce toxic gases and smoke during combustion, posing a threat to the environment and human health. While inorganic fillers such as aluminum hydroxide and magnesium hydroxide are environmentally friendly, they require high dosages to achieve the desired flame-retardant effect, often leading to a significant decrease in the material's mechanical properties, such as reduced tensile strength and toughness. Furthermore, expandable graphite, a highly effective flame retardant, has attracted attention for its ability to expand at high temperatures to form a dense carbon layer. However, its compatibility with rubber and plastic matrices is poor, leading to agglomeration and uneven dispersion, which in turn affects the material's flame retardancy and mechanical properties. Currently, some studies have attempted to modify expandable graphite through physical or chemical methods to improve its dispersibility, but physical modification has limited success. Conventional chemical modification methods, such as treatment with silane coupling agents, while partially improving interfacial bonding, still suffer from drawbacks such as the modifier's ease of decomposition at high temperatures or in complex environments, and insufficient flame retardancy.

[0003] Therefore, in order to solve the above problems, the present invention provides a graphite rubber-plastic composite flame retardant material and a preparation method thereof. Summary of the Invention

[0004] The present invention provides a graphite rubber-plastic composite flame retardant material and a preparation method thereof, which solves the defects in the related art.

[0005] The technical solutions of the present invention are as follows: A method for preparing a graphite rubber-plastic composite flame retardant material comprises the following steps: Step 1: Add expandable graphite and polymethylene diphenyl diisocyanate to xylene, stir at 25°C for 30-40 minutes, then add dibutyltin dilaurate, continue stirring at 80-90°C under nitrogen protection for 8-10 hours, filter under reduced pressure, wash, and dry to obtain isocyanate-treated expandable graphite; Step 2: Mix the isocyanate-treated expandable graphite, the modifier, and xylene, stir evenly, add dibutyltin dilaurate, raise the temperature to 80-90° C., react under nitrogen for 8-10 hours, filter, wash, and dry to obtain modified expandable graphite; Step 3: Add nitrile rubber, polyvinyl chloride, dioctyl phthalate, modified expandable graphite, stabilizer, sulfur, and antioxidant into a high-speed mixer, mix evenly to obtain a premix, and then feed the premix into a twin-screw extruder for melt blending, extrusion, and vulcanization to obtain a composite flame retardant material.

[0006] In the scheme, in xylene solvent, the isocyanate groups of polymethylene diphenyl diisocyanate undergo nucleophilic addition reaction with the hydroxyl groups on the surface of expandable graphite to form carbamate bonds. The unreacted isocyanate groups then remain on the graphite surface and further react with the amino groups in the modifier to obtain modified expandable graphite.

[0007] More optimally, the isocyanate-treated expandable graphite raw material comprises the following components: by weight, 15-20 parts of expandable graphite, 30-40 parts of polymethylene diphenyl diisocyanate, 80-90 parts of xylene, and 0.1-0.2 parts of dibutyltin dilaurate.

[0008] More optimally, the modified expandable graphite raw material comprises the following components: by weight, 15-20 parts of isocyanate-treated expandable graphite, 20-22 parts of a modifier, 80-90 parts of xylene, and 0.1-0.2 parts of dibutyltin dilaurate.

[0009] More optimally, the composite flame retardant material includes the following components: by weight, 40-60 parts of nitrile rubber, 30-40 parts of polyvinyl chloride, 20-30 parts of dioctyl phthalate, 20-30 parts of modified expandable graphite, 2-5 parts of stabilizer, 1-3 parts of sulfur, and 1-2 parts of antioxidant.

[0010] More optimally, the preparation process of the modifier is: S1: 2-amino-1,3,4-thiadiazole was mixed with ethanol, the temperature was raised to 90°C, and refluxed with stirring for 2-3 minutes. Then, p-hydroxybenzaldehyde was added, and refluxed with stirring at the same temperature for 10-12 hours. Then, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was added, and the reaction was continued at 90°C for 10-12 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain intermediate A. S2: paraformaldehyde, ethylenediamine and isopropanol were mixed and stirred at room temperature, and then intermediate A was added. The temperature was raised to 100-110°C and refluxed for 4-5 hours. After the reaction was completed, the mixture was cooled to room temperature and post-treated to obtain a modifier.

[0011] In the scheme, the amino group of 2-amino-1,3,4-thiadiazole reacts with the aldehyde group of p-hydroxybenzaldehyde to form an imine bond, which then undergoes a nucleophilic addition reaction with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to form intermediate A. The specific reaction process is shown below:

[0012] More optimally, the intermediate A raw material includes the following components: by weight, 10-12 parts of amino-1,3,4-thiadiazole, 100-120 parts of ethanol, 12-15 parts of p-hydroxybenzaldehyde, and 23-25 ​​parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0013] In this scheme, paraformaldehyde and ethylenediamine undergo a Mannich reaction to form a methylene-bridged amine structure, after which the active hydroxyl group of intermediate A further reacts with it to obtain a modifier. The specific reaction process is shown below:

[0014] More optimally, the modifier raw material includes the following components: by weight, 25-28 parts of paraformaldehyde, 6-8 parts of ethylenediamine, 40-42 parts of intermediate A, and 100-120 parts of isopropanol.

[0015] Compared with the prior art, the present invention has the following advantages: The present invention significantly improves the flame retardancy and mechanical properties of the prepared composite material by combining a modifier with expandable graphite and compounding it with a base material such as nitrile rubber and polyvinyl chloride. The details are as follows: First, the chemically synthesized modifier in this proposal can capture key free radicals in the combustion chain under high-temperature conditions, terminating the oxidation reaction chain. Simultaneously, nitrogen releases ammonia, and sulfur releases sulfur dioxide and other non-combustible gases, diluting the oxygen and combustible gas concentrations in the combustion zone and reducing combustion intensity. Furthermore, when combined with expandable graphite, phosphorus further catalyzes the formation of a continuous, dense carbon layer, while sulfur promotes cross-linking of carbon chains through free radicals, increasing the density and strength of the carbon layer.

[0016] Second, in this approach, large steric groups are introduced onto the surface of modified expandable graphite through chemical grafting. These bulky molecular structures form a spatial barrier between the graphite sheets, effectively preventing restacking and agglomeration. Simultaneously, the grafted polar groups form hydrogen bonds or chemical bonds with the rubber / plastic matrix, enhancing interfacial adhesion. This structure not only improves the uniform dispersion of the graphite within the matrix but also optimizes stress transfer efficiency, significantly enhancing the mechanical properties of the composite material. Furthermore, the modification of the expandable graphite further enhances its thermal stability, preventing premature expansion during processing that could compromise its flame retardant effectiveness. DETAILED DESCRIPTION

[0017] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0018] Example 1: A method for preparing a graphite rubber-plastic composite flame retardant material, comprising the following steps: Step 1: Add 15 parts of expandable graphite and 30 parts of polymethylene diphenyl diisocyanate to 80 parts of xylene, stir at 25°C for 30 minutes, then add 0.1 parts of dibutyltin dilaurate, continue stirring at 80°C under nitrogen protection for 8 hours, filter under reduced pressure, wash, and dry to obtain isocyanate-treated expandable graphite; Step 2: 15 parts of isocyanate-modified expandable graphite, 20 parts of modifier, and 80 parts of xylene were mixed and stirred evenly, 0.1 parts of dibutyltin dilaurate was added, the temperature was raised to 80° C., and the mixture was reacted under nitrogen for 8 hours. The mixture was filtered, washed, and dried to obtain modified expandable graphite; Step 3: adding 40 parts of nitrile rubber, 30 parts of polyvinyl chloride, 20 parts of dioctyl phthalate, 20 parts of modified expandable graphite, 2 parts of stabilizer, 1 part of sulfur, and 1 part of antioxidant into a high-speed mixer, mixing uniformly to obtain a premix, and then feeding the premix into a twin-screw extruder, melt blending, extruding, and vulcanizing to obtain a composite flame retardant material; Wherein, the preparation process of the modifier is: S1: 10 parts of 2-amino-1,3,4-thiadiazole were mixed with 100 parts of ethanol, the temperature was raised to 90°C, and the mixture was refluxed with stirring for 2 minutes. Subsequently, 12 parts of p-hydroxybenzaldehyde were added, and the mixture was refluxed with stirring for 10 hours at the same temperature. Subsequently, 23 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added, and the reaction was continued at 90°C for 10 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain intermediate A; S2: 25 parts of paraformaldehyde, 6 parts of ethylenediamine and 100 parts of isopropanol were mixed and stirred at room temperature. Then 40 parts of intermediate A were added and the temperature was raised to 100°C. The mixture was reacted for 4 hours. After the reaction was completed, the mixture was cooled to room temperature and post-treated to obtain a modifier.

[0019] Example 2: A method for preparing a graphite rubber-plastic composite flame retardant material, comprising the following steps: Step 1: Add 20 parts of expandable graphite and 40 parts of polymethylene diphenyl diisocyanate to 90 parts of xylene, stir at 25°C for 40 minutes, then add 0.2 parts of dibutyltin dilaurate, continue stirring at 90°C under nitrogen protection for 10 hours, filter under reduced pressure, wash, and dry to obtain isocyanate-treated expandable graphite; Step 2: 20 parts of isocyanate-modified expandable graphite, 22 parts of modifier, and 90 parts of xylene were mixed and stirred evenly, 0.2 parts of dibutyltin dilaurate was added, the temperature was raised to 90° C., and the mixture was reacted under nitrogen for 10 hours. The mixture was filtered, washed, and dried to obtain modified expandable graphite; Step 3: adding 60 parts of nitrile rubber, 40 parts of polyvinyl chloride, 30 parts of dioctyl phthalate, 30 parts of modified expandable graphite, 5 parts of stabilizer, 3 parts of sulfur, and 2 parts of antioxidant into a high-speed mixer, mixing uniformly to obtain a premix, and then feeding the premix into a twin-screw extruder, melt blending, extruding, and vulcanizing to obtain a composite flame retardant material; Wherein, the preparation process of the modifier is: S1: 12 parts of 2-amino-1,3,4-thiadiazole were mixed with 120 parts of ethanol, the temperature was raised to 90°C, and refluxed with stirring for 3 minutes. Subsequently, 15 parts of p-hydroxybenzaldehyde were added, and refluxed with stirring at the same temperature for 12 hours. Subsequently, 25 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added, and the reaction was continued at 90°C for 12 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain intermediate A; S2: 28 parts of paraformaldehyde, 8 parts of ethylenediamine and 120 parts of isopropanol were mixed and stirred at room temperature. Then 42 parts of intermediate A were added and the temperature was raised to 110°C. The reaction was allowed to proceed for 5 hours. After the reaction was completed, the mixture was cooled to room temperature and post-treated to obtain a modifier.

[0020] Example 3: A method for preparing a graphite rubber-plastic composite flame retardant material, comprising the following steps: Step 1: Add 17.5 parts of expandable graphite and 35 parts of polymethylene diphenyl diisocyanate to 85 parts of xylene, stir at 25°C for 35 minutes, then add 0.15 parts of dibutyltin dilaurate, continue stirring at 85°C under nitrogen protection for 9 hours, filter under reduced pressure, wash several times, and dry to obtain isocyanate-treated expandable graphite; Step 2: 17.5 parts of isocyanate-modified expandable graphite, 21 parts of modifier, and 85 parts of xylene were mixed and stirred evenly, 0.15 parts of dibutyltin dilaurate were added, the temperature was raised to 85° C., and the mixture was reacted under nitrogen for 9 hours. The mixture was filtered, washed, and dried to obtain modified expandable graphite; Step 3: 50 parts of nitrile rubber, 35 parts of polyvinyl chloride, 25 parts of dioctyl phthalate, 25 parts of modified expandable graphite, 3.5 parts of stabilizer, 2 parts of sulfur, and 1.5 parts of antioxidant are added to a high-speed mixer and mixed evenly to obtain a premix, which is then fed into a twin-screw extruder for melt blending, extrusion, and vulcanization to obtain a composite flame retardant material; Wherein, the preparation process of the modifier is: S1: 11 parts of 2-amino-1,3,4-thiadiazole were mixed with 110 parts of ethanol, the temperature was raised to 90°C, and refluxed with stirring for 2.5 minutes. Subsequently, 13.5 parts of p-hydroxybenzaldehyde were added, and refluxed with stirring at the same temperature for 11 hours. Subsequently, 24 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added, and the reaction was continued at 90°C for 11 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain intermediate A; S2: 26.5 parts of paraformaldehyde, 7 parts of ethylenediamine and 110 parts of isopropanol were mixed and stirred at room temperature. Then 41 parts of intermediate A were added and the temperature was raised to 105°C. The reaction was carried out for 4.5 hours. After the reaction was completed, the mixture was cooled to room temperature and post-treated to obtain a modifier.

[0021] Comparative Example 1: The expandable graphite was not modified, and the rest was the same as Example 3, specifically as follows: 50 parts of nitrile rubber, 35 parts of polyvinyl chloride, 25 parts of dioctyl phthalate, 25 parts of expandable graphite, 3.5 parts of stabilizer, 2 parts of sulfur, and 1.5 parts of antioxidant are added to a high-speed mixer and mixed evenly to obtain a premix. The premix is ​​then fed into a twin-screw extruder, melt-blended, extruded, and vulcanized to obtain a composite flame retardant material.

[0022] Comparative Example 2: The expandable graphite was modified using a silane coupling agent. The rest was the same as in Example 3, specifically as follows: Dissolve γ-aminopropyltriethoxysilane in anhydrous ethanol to form a coupling agent solution, then add dry expandable graphite to the coupling agent solution and stir for 30 minutes, and finally dry to obtain coupling agent-modified expandable graphite; the mass percentage concentration of the coupling agent solution is 90%; 50 parts of nitrile rubber, 35 parts of polyvinyl chloride, 25 parts of dioctyl phthalate, 25 parts of coupling agent-modified expandable graphite, 3.5 parts of stabilizer, 2 parts of sulfur, and 1.5 parts of antioxidant are added to a high-speed mixer and mixed evenly to obtain a premix. The premix is ​​then fed into a twin-screw extruder, melt-blended, extruded, and vulcanized to obtain a composite flame retardant material.

[0023] Detection experiment: The oxygen index of the composite flame retardant materials prepared in the above embodiments and comparative examples was tested according to the standard ATSMD2863, and the tensile strength of the composite flame retardant materials prepared in the above embodiments and comparative examples was tested according to the standard GB / T528-2009. The obtained data are shown in the following table:

[0024] Table 1 Conclusion: This invention successfully prepared a high-performance graphite rubber-plastic composite flame retardant material by chemically modifying expandable graphite and compounding it with substrates such as nitrile rubber and polyvinyl chloride.

[0025] Experimental results demonstrate that the modification method of the present invention significantly improves the flame retardancy and mechanical properties of the material compared to unmodified expandable graphite (Comparative Example 1) and expandable graphite modified with a silane coupling agent (Comparative Example 2). Specifically, the oxygen index of Examples 1-3 all exceeded 43%, significantly higher than the 28.1% of Comparative Example 1 and the 32.2% of Comparative Example 2, demonstrating excellent flame retardancy. Furthermore, the tensile strength reached 21.4-22.5 MPa, significantly superior to the 12.5 MPa of Comparative Example 1 and the 18.9 MPa of Comparative Example 2, indicating enhanced interfacial bonding between the modified expandable graphite and the substrate, effectively improving the material's mechanical properties. Furthermore, the synergistic effects of the nitrogen, phosphorus, and sulfur elements in the modifier not only terminate the combustion chain reaction but also catalyze the formation of a dense carbon layer, further enhancing the flame retardancy.

[0026] In summary, the present invention solves the problems of low flame retardant efficiency and poor mechanical properties of traditional flame retardant materials by optimizing the modification process and formula, and provides an effective way to develop high-performance rubber-plastic composite flame retardant materials.

[0027] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a graphite rubber-plastic composite flame retardant material, characterized in that: The following steps are involved: Step 1: Add expandable graphite and polymethylene diphenyl diisocyanate to xylene, stir at 25°C for 30-40 minutes, then add dibutyltin dilaurate, continue stirring at 80-90°C under nitrogen protection for 8-10 hours, filter under reduced pressure, wash, and dry to obtain isocyanate-treated expandable graphite; Step 2: Mix the isocyanate-treated expandable graphite, the modifier, and xylene, stir evenly, add dibutyltin dilaurate, raise the temperature to 80-90° C., react under nitrogen for 8-10 hours, filter, wash, and dry to obtain modified expandable graphite; Step 3: Add nitrile rubber, polyvinyl chloride, dioctyl phthalate, modified expandable graphite, stabilizer, sulfur, and antioxidant into a high-speed mixer, mix evenly to obtain a premix, and then feed the premix into a twin-screw extruder for melt blending, extrusion, and vulcanization to obtain a composite flame retardant material.

2. The method for preparing a graphite rubber-plastic composite flame retardant material according to claim 1, characterized in that: The isocyanate-treated expandable graphite raw material comprises the following components: by weight, 15-20 parts of expandable graphite, 30-40 parts of polymethylene diphenyl diisocyanate, 80-90 parts of xylene, and 0.1-0.2 parts of dibutyltin dilaurate.

3. The method for preparing a graphite rubber-plastic composite flame retardant material according to claim 1, characterized in that: The modified expandable graphite raw material comprises the following components: by weight, 15-20 parts of isocyanate expandable graphite, 20-22 parts of a modifier, 80-90 parts of xylene, and 0.1-0.2 parts of dibutyltin dilaurate.

4. The method for preparing a graphite rubber-plastic composite flame retardant material according to claim 1, characterized in that: The composite flame retardant material comprises the following components: by weight, 40-60 parts of nitrile rubber, 30-40 parts of polyvinyl chloride, 20-30 parts of dioctyl phthalate, 20-30 parts of modified expandable graphite, 2-5 parts of stabilizer, 1-3 parts of sulfur, and 1-2 parts of antioxidant.

5. The method for preparing a graphite rubber-plastic composite flame retardant material according to claim 1, characterized in that: The preparation process of the modifier is: S1: 2-amino-1,3,4-thiadiazole was mixed with ethanol, the temperature was raised to 90°C, and refluxed with stirring for 2-3 minutes. Then, p-hydroxybenzaldehyde was added, and refluxed with stirring at the same temperature for 10-12 hours. Then, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was added, and the reaction was continued at 90°C for 10-12 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain intermediate A. S2: paraformaldehyde, ethylenediamine and isopropanol are mixed and stirred at room temperature, and then intermediate A is added. The temperature is raised to 100-110°C and the reaction is carried out for 4-5 hours. After the reaction is completed, the mixture is cooled to room temperature and post-treated to obtain a modifier.

6. The method for preparing a graphite rubber-plastic composite flame retardant material according to claim 5, characterized in that: The intermediate A raw material includes the following components: by weight, 10-12 parts of 2-amino-1,3,4-thiadiazole, 100-120 parts of ethanol, 12-15 parts of p-hydroxybenzaldehyde, and 23-25 ​​parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

7. The method for preparing a graphite rubber-plastic composite flame retardant material according to claim 5, characterized in that: The modifier raw material includes the following components: 25-28 parts of paraformaldehyde, 6-8 parts of ethylenediamine, 40-42 parts of intermediate A, and 100-120 parts of isopropyl alcohol, calculated by weight.

8. A composite flame retardant material obtained according to the method for preparing a graphite rubber-plastic composite flame retardant material according to any one of claims 1 to 7.

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