A flame-retardant rubber and its preparation method

Abstract

This invention discloses a flame-retardant rubber and its preparation method. The flame-retardant rubber, by weight, comprises: 45-65 parts of ethylene-vinyl acetate copolymer; 12-20 parts of ethylene propylene diene monomer (EPDM) rubber; 3-6 parts of maleic anhydride-grafted ethylene-vinyl acetate copolymer; 8-12 parts of phosphorus-modified nanocellulose; 2-5 parts of submicron zinc borate; 2-4 parts of melamine polyphosphate; 0.5-2.5 parts of graphene; 1-2.5 parts of phosphorus-containing flame-retardant plasticizer; and 1-4 parts of multifunctional acrylate crosslinking agent. This application replaces traditional melamine with melamine polyphosphate (MPP). MPP has higher thermal stability, its decomposition temperature matches the char formation window of P-NC more closely, and it has its own phosphorus source, enabling a complementary and continuous phosphoric acid supply with P-NC on both the time and temperature axes, thus solving the problem of insufficient phosphorus catalysis after reducing the amount of P-NC alone.

Description

Technical Field

[0001] This application relates to the field of rubber materials technology, specifically to a flame-retardant rubber suitable for automotive parts and its preparation method. Background Technology

[0002] With the rapid development of the automotive industry, especially the popularization of new energy vehicles, the internal electrical systems of automobiles are becoming increasingly complex, placing higher demands on wiring harness protection, battery pack sealing, and the safety of components in the engine compartment. Rubber wiring harness sleeves, shock absorbers, buffer blocks, and sealing strips, as key automotive components, not only need to possess excellent resistance to aging and high and low temperatures, but must also meet strict flame retardant standards to prevent the spread of fire in the event of an electrical fault, ensuring the safety of passengers.

[0003] Currently, the industry commonly uses halogenated or phosphorus-nitrogen-based flame retardants to impart flame-retardant properties to rubber. However, to achieve high flame-retardant standards such as UL94 V-0, traditional formulations often require the addition of large amounts of flame retardants (typically 20-25 parts by weight per 100 parts by matrix). While this high filler content solves the flame-retardant problem, it also brings significant side effects: the addition of a large amount of inorganic flame-retardant powder disrupts the continuity of the rubber matrix, leading to a significant increase in material hardness and decreased flexibility. For components such as automotive wiring harness sleeves and sealing strips that require frequent bending, installation, and are located in confined spaces, excessively hard materials not only increase assembly difficulty but are also prone to cracking due to stress concentration during use. For shock absorbers and buffer blocks, the high modulus resulting from high filler content weakens the material's shock absorption capacity, affecting the overall NVH (noise, vibration, and harshness) performance of the vehicle.

[0004] Therefore, how to significantly reduce the amount of flame retardant added while ensuring that the flame retardant performance is not reduced, thereby restoring the inherent flexibility and elasticity of rubber materials, has become a technical problem that urgently needs to be solved in the field of automotive rubber parts. Summary of the Invention

[0005] To address the issues of decreased mechanical properties due to excessive flame retardant addition and low efficiency of existing synergistic systems in the prior art, this application provides a flame-retardant rubber and its preparation method.

[0006] The first aspect of this application provides a flame-retardant rubber, comprising, by weight: 45-65 parts of ethylene-vinyl acetate copolymer; 12-20 parts of ethylene propylene diene monomer (EPDM) rubber; 3-6 parts of maleic anhydride-grafted ethylene-vinyl acetate copolymer; 8-12 parts of phosphorus-modified nanocellulose; 2-5 parts of submicron zinc borate, wherein the median particle size D50 of the submicron zinc borate is <500 nm; 2-4 parts of melamine polyphosphate; 0.5-2.5 parts of graphene; 1-2.5 parts of phosphorus-containing flame-retardant plasticizer; and 1-4 parts of multifunctional acrylate crosslinking agent.

[0007] This application achieves a significant reduction in the total amount of flame retardant by reconstructing the synergistic mechanism of flame retardant components. Specifically, melamine polyphosphate (MPP) is used to replace traditional melamine. MPP has higher thermal stability, its decomposition temperature matches the char formation window of P-NC more closely, and it has its own phosphorus source, enabling it to form a complementary and continuous phosphoric acid supply with P-NC on both the time and temperature axes, thus solving the problem of insufficient phosphorus catalysis after reducing the amount of P-NC alone. Simultaneously, the zinc borate is submicronized (D50 < 500 nm), significantly increasing its specific surface area. This allows the ZnO generated during combustion to provide highly efficient Lewis acid catalytic sites, forming a Brønsted-Lewis dual-acid relay catalysis with the polyphosphoric acid released from P-NC, significantly improving char formation efficiency and char layer quality. Furthermore, a phosphorus-containing flame retardant plasticizer is introduced to replace part of the traditional combustible plasticizer, which not only acts as a plasticizer but also eliminates the combustible burden and supplements the phosphorus source. The addition of graphene further constructs a physical barrier layer, which, together with the cross-linking network formed by the cross-linking agent, enables the material to maintain excellent flame retardant and mechanical properties even with a 25%-30% reduction in the total amount of flame retardant.

[0008] Furthermore, the phosphorus-modified nanocellulose and graphene are subsequently combined to form a composite filler system. Through the pre-composite process, the graphene sheets and phosphorus-modified nanocellulose fibers form an interpenetrating structure at the nanoscale, which not only improves the dispersion of both in the matrix but also enhances the interfacial bonding force, resulting in a denser and more continuous char layer, further improving the flame retardant effect.

[0009] Furthermore, the surface of the submicron zinc borate is coated with an aluminate coupling agent, the amount of which is 3-5% of the mass of the zinc borate. The aluminate coupling agent not only improves the dispersibility of the submicron zinc borate in the rubber matrix, but the Al³⁺ ions it introduces are also Lewis acids, capable of forming a dual Lewis acid catalytic system with ZnO, further enhancing the catalytic char formation efficiency.

[0010] Furthermore, the surface of the melamine polyphosphate is coated with an aminosilane coupling agent. This surface modification treatment improves the compatibility of MPP with the organic rubber matrix, enhances the interfacial state, and is beneficial for improving mechanical properties.

[0011] Furthermore, the phosphorus loading rate of the phosphorus-modified nanocellulose is 10-12 wt%. This loading rate range ensures the high-concentration phosphoric acid catalytic ability while retaining sufficient free hydroxyl groups on the surface of the nanocellulose, maintaining its nano-reinforcing effect and interaction with the matrix.

[0012] Furthermore, the phosphorus-containing flame-retardant plasticizer is resorcinol bis(diphenyl phosphate) (RDP). RDP exerts its plasticizing effect at room temperature and decomposes at high temperatures to release phosphoric acid and phenolic free radical quenchers, achieving a functional reversal from "flammability burden" to "flame-retardant contributor".

[0013] Furthermore, it also includes 2-3 parts of citrate ester plasticizer. An appropriate amount of citrate ester plasticizer helps adjust the viscosity of the system and optimize processing performance.

[0014] Furthermore, it also includes processing aids, including at least one of calcium stearate, zinc stearate, paraffin wax, and antioxidants. These aids are used to improve the processing flowability and aging resistance of the material.

[0015] The second aspect of this application provides a method for preparing the above-mentioned flame-retardant rubber, comprising the following steps: preparing phosphorus-modified nanocellulose: dispersing nanocellulose in dimethyl sulfoxide, adding triethylamine under nitrogen protection, cooling and then adding phosphorus oxychloride dropwise, reacting at a higher temperature, and then post-processing to obtain phosphorus-modified nanocellulose powder; preparing submicron-modified zinc borate: wet ball milling zinc borate to D50 < 500 nm, and adding an aluminate coupling agent to an ethanol / water system for surface modification; preparing modified melamine polyphosphate: coupling an aminosilane... After hydrolysis of the crosslinking agent, the melamine polyphosphate powder is surface-treated; composite filler is prepared by dispersing the phosphorus-modified nanocellulose in a solvent, adding graphene, and then drying after ultrasonic and high-shear dispersion to obtain the composite filler; mixing: ethylene-vinyl acetate copolymer, ethylene propylene diene monomer (EPDM) rubber, and maleic anhydride-grafted ethylene-vinyl acetate copolymer are melted, and plasticizer, the composite filler, submicron-modified zinc borate, modified melamine polyphosphate, crosslinking agent, and processing aids are added sequentially for mixing; extrusion molding; and irradiation crosslinking.

[0016] The preparation method features a stable process flow. Through stepwise modification and pre-composite treatment, it ensures the uniform dispersion and functional performance of each functional component in the matrix. The specific order of feeding utilizes the low viscosity window created by the plasticizer, which is beneficial to the dispersion of nanoscale fillers, thereby ensuring the consistent performance of the final product.

[0017] Furthermore, the irradiation dose for crosslinking is 8-10 Mrad. This moderate irradiation dose constructs a high-density crosslinked network, restricting chain segment movement and the escape of combustible debris, reducing combustible gas release at the source, and compensating for potential mechanical property losses due to reduced flame retardant content.

[0018] The present invention has the following beneficial effects: (1) This invention solves the problem of insufficient phosphorus catalysis after the reduction of flame retardant by introducing MPP, RDP and P-NC to construct a multi-source phosphorus supply system, and achieves a 25%-30% reduction in the total amount of flame retardant while maintaining UL94 V-0 flame retardant performance. (2) By introducing submicron modified zinc borate, its high specific surface area and Lewis acid catalytic properties are utilized to form a relay with the Brønsted acid catalysis of P-NC, which significantly improves the carbonization efficiency and carbon layer quality. (3) The use of RDP to replace part of the flammable plasticizer eliminates the flammable burden in the system and contributes additional flame retardant effect; (4) Particularly suitable for automotive parts: Due to the reduction in the total amount of flame retardant, the binding of rigid fillers on the rubber molecular chains is reduced, allowing the material to maintain high strength while having better flexibility and elongation at break. This characteristic makes it particularly suitable for manufacturing automotive wiring harness sleeves (easy to install, resistant to bending), shock absorbers (low modulus, high resilience) and sealing strips (small compression deformation), solving the problem of traditional flame retardant rubber being too hard, leading to assembly difficulties or shock absorption failure. Detailed Implementation

[0019] To facilitate understanding of this application, a more complete description will be provided below. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0020] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0023] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0024] Unless otherwise specified, the percentage content mentioned in this application refers to mass percentage for solid-liquid mixtures and solid-phase-solid mixtures, and volume percentage for liquid-phase-liquid mixtures.

[0025] Unless otherwise specified, all percentage concentrations mentioned in this application refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0026] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.

[0027] The term "particle" as used in this application, or a substance with a defined particle size distribution, is not necessarily spherical in shape; it may be irregular and can be either primary or secondary particles. The particle size of irregular particles is calculated as the average of their maximum and minimum diameters.

[0028] In the specific implementation of this invention, those skilled in the art can make appropriate adjustments to the formulation parameters according to actual application needs. In some preferred embodiments, the content of the ethylene-vinyl acetate copolymer (EVA) can be selected from any value among 45 parts, 50 parts, 55 parts, 60 parts, and 65 parts; preferably, the content of vinyl acetate (VA) in the EVA is 25-30 wt%, for example, 28 wt%.

[0029] In some preferred embodiments, the content of the ethylene propylene diene monomer (EPDM) rubber can be selected from any value among 12 parts, 15 parts, 16 parts, 18 parts, and 20 parts.

[0030] In some preferred embodiments, the grafting rate of the maleic anhydride-grafted ethylene-vinyl acetate copolymer (MAH-g-EVA) is 0.8-1.2 wt%, for example, 1.0 wt%.

[0031] In some preferred embodiments, the phosphorus loading rate of the phosphorus-modified nanocellulose can be selected from any value among 10 wt%, 11 wt%, and 12 wt%.

[0032] In some preferred embodiments, the median particle size D50 of the submicron zinc borate can be selected from any value among 100nm, 200nm, 300nm, 400nm, and 500nm, as long as D50 < 500nm.

[0033] In some preferred embodiments, the amount of the aluminate coupling agent can be selected from any value among 3.0%, 3.5%, 4.0%, 4.5%, and 5.0% of the mass of zinc borate.

[0034] In some preferred embodiments, the irradiation dose for the irradiation crosslinking can be selected from any value among 8 Mrad, 8.5 Mrad, 9 Mrad, 9.5 Mrad, and 10 Mrad.

[0035] Example 1: A flame-retardant rubber and its preparation method This embodiment provides a flame-retardant rubber, the formulation of which is detailed in Table 1, and its preparation method is as follows: (1) Preparation of phosphorus-modified nanocellulose (P-NC): 100 g of nanocellulose (diameter 10-50 nm, length 0.5-2 μm) was added to 1000 mL of dimethyl sulfoxide (DMSO) and mechanically stirred at 500 rpm for 2 h at room temperature. Under nitrogen protection, 370 g of triethylamine (TEA) was added, and the mixture was cooled to 0-5 °C. 280 g of phosphorus oxychloride (POCl3) was slowly added dropwise, controlling the temperature to not exceed 5 °C, over a period of 1.5 h. After the addition was complete, the temperature was raised to 65 °C and the reaction was allowed to proceed for 18 h. After cooling, the reaction mixture was poured into 3 L of anhydrous ethanol, stirred for 30 min, and then filtered. The filter cake was washed successively with anhydrous ethanol and deionized water until neutral, and then freeze-dried at -50 °C for 24 h to obtain P-NC powder (phosphorus loading approximately 11 wt%).

[0036] (2) Preparation of submicron modified zinc borate: 100g of zinc borate (2ZnO·3B2O3·3.5H2O) was added to a planetary ball mill jar. ZrO2 grinding beads (0.5mm in diameter) were used as the grinding medium at a ball-to-particle ratio of 10:1. 200mL of anhydrous ethanol was added, and the mixture was ball-milled at 400rpm for 8 hours to obtain a slurry (D50≈400nm). 200mL of an ethanol / water (95:5 volume ratio) mixed solvent was prepared, and 4g of aluminate coupling agent DL-411 was added and dissolved. The ball-milled slurry was added to the coupling agent solution, stirred at 50℃ for 3 hours, filtered, washed, and dried at 80℃ for 6 hours to obtain submicron modified zinc borate powder.

[0037] (3) Preparation of modified melamine polyphosphate (MPP): Prepare 200 mL of ethanol / water (90:10 v / v) mixed solvent, adjust the pH to 4.5 with glacial acetic acid, add 2 g of γ-aminopropyltriethoxysilane (KH-550) and hydrolyze for 1 h. Add 100 g of melamine polyphosphate (MPP) powder, stir at 60 °C for 2 h, filter, and dry at 80 °C for 4 h to obtain modified MPP powder.

[0038] (4) Preparation of P-NC / graphene composite filler: 105g of the P-NC powder obtained in step (1) was added to 1000mL of anhydrous ethanol and stirred to disperse. 15g of few-layer graphene (1-5 layers, lateral size 1-5μm) was added and ultrasonically treated for 30min (power 400W). Subsequently, it was dispersed under high shear at 10000rpm for 15min. The dispersion was vacuum dried at 60℃ for 12h to obtain the P-NC / graphene composite filler.

[0039] (5) Secret refining: Set the internal mixer temperature to 120℃ and the rotor speed to 60rpm.

[0040] First, add EVA, EPDM, and MAH-g-EVA, and mix for 3 minutes until completely melted; Add tributyl citrate and RDP, and mix for 2 minutes; Add the P-NC / graphene composite filler obtained in step (4) (containing 10.5 parts of P-NC and 1.5 parts of graphene) and mix for 5 minutes; Add the submicron modified zinc borate obtained in step (2) and the modified MPP obtained in step (3), and mix for 3 min; Add PETIA, calcium stearate, zinc stearate, paraffin wax, and antioxidant 1010, and mix for 2 minutes.

[0041] The material is discharged and pressed into tablets three times on an open mill.

[0042] (6) Extrusion molding: The compounded rubber strips are extruded in a single-screw extruder with a screw diameter of 65 mm, a length-to-diameter ratio of 25:1, and temperature settings of 100℃ for the feeding section, 110℃ for the compression section, 120℃ for the metering section, and 115℃ for the die head. The screw speed is 35 rpm, and the die head clearance / diameter ratio is 0.06.

[0043] (7) Irradiation crosslinking: Electron beam irradiation at an energy of 1.5 MeV and an irradiation dose of 9 Mrad was used, with the tube rotating through the irradiation zone. Examples 2-4: A flame-retardant rubber and its preparation method. The specific formula is detailed in Table 1. The preparation method is basically the same as in Example 1, with the only difference being: In Example 2, the NC:POCl3 weight ratio was 1:2.5 during P-NC preparation, and the phosphorus loading rate was approximately 10%.

[0044] In Example 3, the NC:POCl3 weight ratio was 1:3.0 during P-NC preparation, and the phosphorus loading rate was approximately 12%.

[0045] Example 4: Irradiation dose was 10 Mrad.

[0046] Comparative Examples 1-5 The specific formula is detailed in Table 1. The preparation method is basically the same as in Example 1, with the following differences: Comparative Example 1: Melamine was used to replace modified MPP.

[0047] Comparative Example 2: Conventional micron-sized zinc borate (D50≈5μm) was used, with a coupling agent dosage of 1.5%, and wet ball milling was not performed.

[0048] Comparative Example 3: No RDP was used, and all plasticizers used were tributyl citrate.

[0049] Comparative Example 4: P-NC and graphene were added directly during the mixing process without P-NC / graphene pre-composite.

[0050] Comparative Example 5: Using existing technology and formulation, P-NC uses the original process (NC:POCl3=1:2.3, reaction 15h), without using MPP, submicron zinc borate and RDP.

[0051] 1. Flame retardant performance test The UL94 vertical burning test standard (referencing GB / T 2408-2008) was adopted. The sample size was 125mm × 13mm × 3mm, and the test was conducted after conditioning at 23℃ and 50%RH for 48 hours. The first afterflame time t1, the second afterflame time t2, and the afterglow time t3 were recorded. The V-0 rating criteria were: single afterflame time ≤ 10s, total afterflame time ≤ 50s, and no burning drips igniting cotton.

[0052] Simultaneously, the limiting oxygen index (LOI) test (refer to GB / T 2406.2-2009) was used, with a sample size of 80mm × 10mm × 4mm, to determine the minimum oxygen concentration that just sustains combustion.

[0053] 2. Mechanical property testing According to GB / T 528-2009 standard, dumbbell-shaped type 2 specimens were used, with a tensile rate of 500 mm / min and an ambient temperature of 23±2℃. The tensile strength and elongation at break were recorded.

[0054] 3. Gel content determination Following ASTM D2765, the xylene reflux extraction method was used. Approximately 0.3 g of sample was weighed and refluxed in xylene at 140 °C for 24 h. The percentage of the dried residual mass after extraction to the original mass was calculated.

[0055] 4. Observation of carbon layer morphology The microstructure of the combustion residue of the sample after UL94 testing was observed using scanning electron microscopy (SEM) to analyze the compactness, pore structure and surface element distribution of the char layer.

[0056] Table 1. Formulation composition of Examples 1-4 and Comparative Examples 1-5 (unit: parts by weight) Components Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Matrix resin EVA 55 50 55 55 55 55 55 55 55 EPDM 16 18 16 16 16 16 16 16 16 MAH-g-EVA 4.5 4.5 5 4.5 4.5 4.5 4.5 4.5 4.5 Flame retardant system P-NC (phosphorus loading rate 10-12%) 10.5 11 9.5 10.5 10.5 10.5 10.5 10.5 10.6 Submicron modified zinc borate 3.5 3.5 4 3 3.5 - 3.5 3.5 - Micron-sized zinc borate - - - - - 3.5 - - 4.25 Modified MPP 3 2.5 3.5 3 - 3 3 3 - melamine - - - - 3 - - - 2.13 Functional packing Graphene (pre-composite) 1.5 2 1.5 1.5 1.5 1.5 1.5 - - Graphene (added directly) - - - - - - - 1.5 1.5 Crosslinking system PETIA 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Plasticizing system Tributyl citrate (TBC) 2.5 2 2.5 2 2.5 2.5 4 2.5 6 RDP 1.5 2 1.5 2 1.5 1.5 - 1.5 - Processing aids Calcium stearate 0.25 0.25 - 0.25 0.25 0.25 0.25 0.25 0.5 Zinc stearate 0.25 0.25 0.5 0.25 0.25 0.25 0.25 0.25 - paraffin 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Antioxidant 1010 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 process parameters Irradiation dose 9 10 9 10 9 9 9 9 8 Total amount of flame retardant 17 17 17 16.5 17 17 17 17 17 Table 2 Performance test results of the examples and comparative examples Test Project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Total amount of flame retardant (parts) 17 17 17 16.5 17 17 17 17 17 UL94 rating V-0 V-0 V-0 V-0 V-1 V-0 (marginal) V-0 (marginal) V-0 V-2 Longest single afterflame 3 4 3 5 15 10 8 6 25 LOI (%) 31.5 30.5 31.2 30.2 27.1 29.3 29 30.1 25 Tensile strength 26.5 25 25.8 26 24.5 23.5 25.2 24.8 24.2 Elongation at break (%) 420 390 405 395 415 395 418 390 435 Gel content (%) 70 72 71 73 70 70 70 70 60 As can be seen from the data in Table 2, Examples 1-4 all achieved the UL94 V-0 flame retardant standard when the total amount of flame retardant was reduced to 17 parts (a reduction of approximately 29%) and even 16.5 parts (Example 4), with the limiting oxygen index (LOI) remaining above 30%. In contrast, Comparative Example 5, with the same amount of flame retardant, only achieved a V-2 rating, with an LOI as low as 25% and an afterflame time as long as 25 seconds. This strongly demonstrates that this application successfully solved the technical problem of performance degradation caused by reducing the amount of flame retardant by reconstructing the synergistic system.

[0057] Comparative Example 1 data shows the most significant performance degradation, with the UL94 rating dropping to V-1 and the LOI decreasing by more than 4 percentage points. This indicates that replacing traditional melamine with melamine polyphosphate (MPP) is the most critical improvement in this application. Melamine sublimates at around 350°C, prematurely leaving the condensed phase reaction system, while the thermal decomposition temperature of MPP matches the catalytic char formation window of phosphorus-modified nanocellulose (P-NC) better, continuously providing phosphorus and nitrogen sources to form a stable expanded carbon layer.

[0058] Comparative Example 2 used micron-sized zinc borate instead of submicron-sized zinc borate. Although it barely achieved the V-0 level, the afterflame time was significantly prolonged, and the LOI decreased by about 2 percentage points. This verifies the importance of submicronization in improving the catalytic efficiency of zinc borate. Submicron particles have a larger specific surface area, and the ZnO generated during combustion can provide more Lewis acid catalytic sites, promoting the aromatization of the polyolefin skeleton into carbon, and improving the density and thermal insulation of the carbon layer.

[0059] The tensile strengths of Examples 1-4 were all higher than those of Comparative Examples 5 and 2. This is attributed to the reduction in the total amount of flame retardant, which decreased the disruption of matrix continuity caused by rigid particles, and the effective improvement in stress transfer through the three-layer interface design (MAH-g-EVA chemical compatibilization, graphene physical bridging, and irradiation locking). The elongation at break remained above 380%, meeting the application requirements of flexible materials. Example 1 exhibited the best mechanical properties, indicating that its formulation achieved an optimal balance between rigidity and toughness.

[0060] The gel content in Examples 1-4 was between 70% and 73%, significantly higher than the 60% in Comparative Example 5. The high-density cross-linked network restricted the thermal motion of polymer segments, reducing the release rate of flammable degradation products and playing a crucial auxiliary role in improving flame retardant properties. Simultaneously, the moderate cross-linking compensated for the potential modulus loss due to reduced filler content.

[0061] Comparative Example 3, which did not use the phosphorus-containing flame retardant plasticizer RDP, resulted in a decrease in LOI and an increase in afterflame time. This indicates that RDP not only plays a plasticizing role, but the phosphoric acid and phenolic free radical quenchers released by its decomposition at high temperatures effectively participate in flame retardancy in both the gas phase and condensed phase, eliminating the flammability burden brought by traditional citrate plasticizers.

[0062] The data from Comparative Example 4 show that the pre-composite treatment of P-NC and graphene has a positive effect on improving the quality and dispersibility of the carbon layer. Direct addition will lead to uneven nano-dispersion and slightly affect the flame retardant efficiency.

[0063] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A flame-retardant rubber, characterized in that, By weight, it comprises: 45-65 parts of ethylene-vinyl acetate copolymer; 12-20 parts of ethylene propylene diene monomer (EPDM) rubber; 3-6 parts of maleic anhydride-grafted ethylene-vinyl acetate copolymer; 8-12 parts of phosphorus-modified nanocellulose; 2-5 parts of submicron zinc borate, wherein the median particle size D50 of the submicron zinc borate is <500 nm; 2-4 parts of melamine polyphosphate; 0.5-2.5 parts of graphene; 1-2.5 parts of phosphorus-containing flame retardant plasticizer; and 1-4 parts of multifunctional acrylate crosslinking agent.

2. The flame-retardant rubber according to claim 1, characterized in that, The phosphorus-modified nanocellulose and graphene are then combined to form a composite filler, which is introduced into the system.

3. The flame-retardant rubber according to claim 1, characterized in that, The submicron zinc borate surface is coated with an aluminate coupling agent, and the amount of the aluminate coupling agent is 3-5% of the mass of zinc borate.

4. The flame-retardant rubber according to claim 1, characterized in that, The melamine polyphosphate is coated with an aminosilane coupling agent.

5. The flame-retardant rubber according to claim 1, characterized in that, The phosphorus loading of the phosphorus-modified nanocellulose is 10-12 wt%.

6. The flame-retardant rubber according to claim 1, characterized in that, The phosphorus-containing flame retardant plasticizer is resorcinol bis(diphenyl phosphate).

7. The flame-retardant rubber according to claim 1, characterized in that, It also includes 2-3 parts of citrate plasticizer.

8. The flame-retardant rubber according to claim 1, characterized in that, It also includes processing aids, which include at least one of calcium stearate, zinc stearate, paraffin wax, and antioxidants.

9. A method for preparing flame-retardant rubber according to any one of claims 1-8, characterized in that, Includes the following steps: Preparation of phosphorus-modified nanocellulose: Nanocellulose was dispersed in dimethyl sulfoxide, triethylamine was added under nitrogen protection, phosphorus oxychloride was added dropwise after cooling, and the reaction was carried out at a higher temperature. After post-treatment, phosphorus-modified nanocellulose powder was obtained. Preparation of submicron modified zinc borate: Zinc borate was wet-milled to D50 < 500 nm, and aluminate coupling agent was added to an ethanol / water system for surface modification. Preparation of modified melamine polyphosphate: After hydrolyzing the aminosilane coupling agent, the melamine polyphosphate powder is surface treated; Preparation of composite filler: The phosphorus-modified nanocellulose was dispersed in a solvent, graphene was added, and the mixture was dispersed by ultrasound and high shear before drying to obtain the composite filler; Intensive mixing: Ethylene-vinyl acetate copolymer, ethylene propylene diene monomer (EPDM) rubber, and maleic anhydride-grafted ethylene-vinyl acetate copolymer are melted and then mixed with plasticizer, the composite filler, submicron modified zinc borate, modified melamine polyphosphate, crosslinking agent, and processing aids in sequence. Extrusion molding; Irradiation crosslinking.

10. The preparation method according to claim 9, characterized in that, The irradiation dose for the irradiation crosslinking is 8-10 Mrad.