Preparation method and application of halogen-free composite flame retardant for natural rubber

Abstract

The application discloses a preparation method and application of a halogen-free composite flame retardant for natural rubber, and successfully prepares a high-performance halogen-free composite flame retardant by screening a specific functional grinding aid (PT-103), designing a special modifier formula, constructing a "ultrafine magnesium hydroxide + ultrafine silicon powder + TGD" three-component synergistic system, and matching a unique proportion of a composite dispersant. When the addition amount of the flame retardant in the natural rubber is only 30-50 parts, excellent flame-retardant effects with an oxygen index of greater than or equal to 24.1% can be achieved, while good mechanical properties with a tensile strength of greater than or equal to 22.5 MPa and an elongation at break of greater than or equal to 545% are maintained. The technical pain points of the existing halogen-free flame retardant, such as "high addition amount, low flame-retardant efficiency and poor mechanical properties", are solved, the whole preparation process is environment-friendly and non-toxic, the product is halogen-free, smoke-free and non-toxic gas-releasing, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of composite flame retardant preparation technology, and in particular to a method for preparing and applying a halogen-free composite flame retardant for natural rubber, specifically applicable to the production of natural rubber products where high requirements are placed on flame retardant efficiency, mechanical properties and environmental friendliness. Background Technology

[0002] In recent years, rubber materials have been widely used in various fields such as daily life, medical and health care, transportation, industrial production, and meteorological measurement due to their excellent properties. Natural rubber, as the most widely used general-purpose rubber, is mainly composed of 91-94% polyisoprene rubber hydrocarbon, with the remaining less than 10% consisting of non-rubber substances such as proteins, fatty acids, ash, and sugars. Due to its molecular structure, natural rubber is highly flammable. The oxygen index of pure natural rubber is only about 17%, and its combustion process is a violent and complex thermal oxidation reaction, characterized by the emission of dense smoke or intense flames. During combustion, natural rubber first undergoes a free radical chain degradation reaction with oxygen in the air, producing volatile combustibles. When these combustibles reach a certain concentration and temperature, they ignite and burn. The heat released during combustion further accelerates rubber degradation, producing even more flammable gases, greatly reducing the probability of escape in a fire and posing a serious threat to life and property safety. Therefore, flame-retardant modification of natural rubber has become a research hotspot both domestically and internationally.

[0003] Currently, there are two main methods to improve the flame retardancy of natural rubber: one is to introduce flame-retardant units to achieve inherent flame retardancy. However, due to the lack of suitable reactive flame-retardant monomers and the complexity of the synthesis reaction, this method is greatly limited in actual production and difficult to apply industrially. The second method is to add flame retardants. Commonly used additive flame retardants include halogenated flame retardants, metal oxides, phosphorus and nitrogen-based flame retardants, and nano-flame retardants. Among these, although halogenated flame retardants have good flame retardant effects and are inexpensive, they produce a large amount of toxic and corrosive gases and fumes when burning, seriously endangering human health and the ecological environment. With the increasing awareness of environmental protection and safety, the replacement of halogenated flame retardants with halogen-free flame retardants has become an inevitable trend.

[0004] Inorganic flame retardants (such as magnesium hydroxide and aluminum hydroxide) are widely used in flame retardancy of rubber and plastic materials due to their advantages of low smoke, low toxicity, and low price. However, they suffer from a key drawback: low flame retardancy efficiency. Typically, large amounts (generally ≥60%) are required to achieve the desired flame retardant effect. High addition levels significantly damage the mechanical properties of the material (such as decreased tensile strength and elongation at break), limiting their application in high-end fields. While existing technologies have attempted to improve the performance of inorganic flame retardants through ultrafine processing, surface modification, or compounding, several shortcomings remain: for example, single ultrafine processing cannot completely solve the dispersion problem; conventional modifiers (such as common silane coupling agents) have limited surface modification effects on magnesium hydroxide, failing to effectively improve its compatibility with the rubber matrix; compound systems are mostly two-component (such as magnesium hydroxide + silica, magnesium hydroxide + zinc borate), lacking multi-component synergistic design, resulting in limited improvement in flame retardancy efficiency and poor balance of mechanical properties; some compound formulations use flame retardants with problems such as easy migration and poor flame retardant durability.

[0005] To address the aforementioned technical challenges, this invention optimizes the raw material pretreatment process, screens specific functional additives, and designs a synergistic "inorganic-organic" three-component system. This achieves simultaneous reduction in flame retardant addition and improvement in flame retardant and mechanical properties, providing a superior halogen-free composite flame retardant for natural rubber. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing halogen-free flame retardants in the application of natural rubber, namely "high addition amount, low flame retardant efficiency, and poor mechanical properties". This invention provides a halogen-free composite flame retardant for natural rubber that is simple to prepare, environmentally friendly and non-toxic. When the addition amount of this composite flame retardant is only 40 parts or less, it can make the oxygen index of natural rubber ≥25.3%, while maintaining excellent tensile strength (≥22MPa) and elongation at break (≥548%), achieving a synergistic effect of "low addition, high flame retardancy, and excellent mechanical properties".

[0007] A method for preparing a halogen-free composite flame retardant for natural rubber, comprising the following specific steps:

[0008] Step 1: Preparation of ultrafine magnesium hydroxide powder: Select high-purity magnesium hydroxide ore with a magnesium hydroxide content ≥96% and crush it twice to an average particle size of 20mm. Add 0.7% (by weight) of inorganic powder grinding aid PT-103 to the ball mill and perform ultrafine wet grinding at 3000r / min for 2h to obtain ultrafine magnesium hydroxide powder with a D50 of 0.8-1.2μm.

[0009] Step 2: Surface modification of ultrafine magnesium hydroxide powder: The ultrafine magnesium hydroxide powder is fed into a continuous modifier, and a modifier accounting for 0.8-1.5% of the powder mass is added. The modification is carried out at 70℃ for 30 min. The modifier is composed of 15% silane coupling agent KH171, 70% ethanol, 2.5% emulsifier SDS, 1% initiator KPS, and 31.5% butyl acrylate by mass fraction.

[0010] Step 3: Preparation of ultrafine silica powder: Select 80-mesh silica powder with a silica content ≥99%, feed it into a ball mill and dry ball mill at 3500 r / min for 2 h to obtain ultrafine silica powder with D50 of 1.8-2.2 μm;

[0011] Step 4: Surface modification of ultrafine silica powder: The ultrafine silica powder is fed into a high-speed mixer, and sodium methylsilane modifier accounting for 0.8% of the powder mass is added. The mixture is modified at 80°C for 20 minutes.

[0012] Step 5: Compounding and molding of composite flame retardant: Surface-treated ultrafine magnesium hydroxide, ultrafine silica powder and flame retardant TGD are compounded in a mass ratio of 6-10:1-3:1-3. A composite dispersant accounting for 1% of the total mass of the composite flame retardant is added. The mixture is mixed at high speed at 80℃ for 20 minutes, dried and packaged to obtain the finished product. The composite dispersant is composed of sodium dodecylbenzenesulfonate: sodium oleate: sodium vinyl acetate-maleic anhydride copolymer = 5:3:2 in mass ratio. The TGD is synthesized by a controlled ring-opening addition reaction of 1,3,5-triglycidyl isocyanurate and DOPO.

[0013] Preferably, in step 2, the amount of the modifier is 1.2% of the mass of the ultrafine magnesium hydroxide powder.

[0014] Preferably, in step 5, the mass ratio of the ultrafine magnesium hydroxide, ultrafine silicon powder and flame retardant TGD is 8:3:2.

[0015] This invention also provides an application of a halogen-free composite flame retardant for natural rubber, characterized in that the halogen-free composite flame retardant is used to prepare natural rubber products and is an environmentally friendly flame retardant material with low additive content and high flame retardant performance.

[0016] Preferably, the amount of the composite flame retardant added to the natural rubber system is 30-50 parts by weight, based on 100 parts by weight of natural rubber.

[0017] Preferably, the amount of the composite flame retardant added is 40 parts by weight. Based on 100 parts by weight of natural rubber, the oxygen index of the natural rubber after addition is ≥27.0%, the tensile strength is ≥22.85MPa, and the elongation at break is ≥561.98%.

[0018] Preferably, the natural rubber product production system further includes one or more of zinc oxide, antioxidant, stearic acid, silica, carbon black, vulcanizing agent, and accelerator.

[0019] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention fundamentally solves the pain points of traditional halogen-free flame retardants, which suffer from high addition levels, low flame retardancy, and poor mechanical properties. It achieves breakthroughs in performance and application from multiple dimensions, with significant beneficial effects: First, it achieves high flame retardancy with low addition levels, with an oxygen index ≥24.1% at 30-50 parts by weight and 27.0% at 40 parts, far superior to the flame retardant effect of traditional single modified magnesium hydroxide at 80 parts; Second, it balances flame retardancy with mechanical properties, achieving a tensile strength ≥22.5MPa and an elongation at break ≥545% across the entire addition range, with minimal loss of mechanical properties; Third, it achieves triple synergistic flame retardancy + The formula features optimized interface, excellent flame retardancy and durability, no component migration issues, and superior performance stability. Fourthly, it is a completely halogen-free formula, releasing no toxic or corrosive substances during preparation and combustion, meeting environmental and safety standards. Fifthly, the preparation process is simple, requiring no special equipment, and can be directly integrated into the conventional natural rubber production system, exhibiting strong adaptability. The low addition amount also reduces industrialization costs and facilitates large-scale promotion. Sixthly, the powder dispersibility and interfacial compatibility are significantly improved, effectively avoiding local performance defects in products and enhancing the overall quality of natural rubber products. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the present invention;

[0021] Figure 2 Tables and graphs showing the performance test results for Examples 1-7;

[0022] Figure 3 Tables and graphs showing the performance test results for comparison;

[0023] Figure 4 The table shows the performance test results for the comparative and blank groups. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] Preparation of ultrafine magnesium hydroxide powder:

[0026] High-purity magnesium hydroxide ore with a magnesium hydroxide content of ≥96% is selected and subjected to secondary crushing to obtain small ore with an average particle size of 20mm, ensuring subsequent grinding efficiency and powder purity;

[0027] Small ore is fed into a ball mill, and 0.7% (by weight) of inorganic powder grinding aid PT-103 (an organosilicon grinding aid, which, unlike conventional grinding aids, has a unique inorganic powder shape repair function that can promote the transformation of particles into uniform spherical shapes, significantly narrow the particle size distribution, and at the same time weaken the polar adsorption between particles, thus avoiding agglomeration) is added.

[0028] Ultrafine wet milling was performed at a speed of 3000 r / min for 2 h to obtain ultrafine magnesium hydroxide powder with a D50 of 0.8-1.2 μm. This particle size range was verified by experiments to minimize the impact on the mechanical properties of rubber while ensuring flame retardant efficiency.

[0029] Surface modification of ultrafine magnesium hydroxide powder:

[0030] The above-mentioned ultrafine magnesium hydroxide powder is fed into a continuous modifier, and a modifier with a specific formulation is added. The mass fraction of each component of the modifier is as follows: silane coupling agent KH171 15%, ethanol 70%, emulsifier SDS 2.5%, initiator KPS 1%, and butyl acrylate 31.5%.

[0031] The modifier is used at 0.8-1.5% (preferably 1.2%) of the powder mass, and the modification is carried out at 70℃ for 30 min.

[0032] This modifier formulation achieves efficient surface modification of magnesium hydroxide through synergistic effects: silane coupling agent KH171 provides organic groups compatible with the rubber matrix, butyl acrylate forms a flexible interface layer, emulsifier SDS and initiator KPS ensure the uniformity of the modification reaction, and ethanol is used as a solvent to adjust the viscosity of the system, ultimately resulting in surface-treated ultrafine magnesium hydroxide powder with significantly improved compatibility with the rubber matrix.

[0033] Preparation of ultrafine silica powder:

[0034] 80-mesh silica powder with a silica content of ≥99% was selected and fed into a ball mill for dry ball milling at a speed of 3500 r / min for 2 hours to obtain ultrafine silica powder with a D50 of 1.8~2.2μm. This particle size forms a reasonable gradation with ultrafine magnesium hydroxide powder, which is conducive to building a dense flame-retardant barrier.

[0035] Surface modification of ultrafine silica powder:

[0036] The ultrafine silicon powder was fed into a high-speed mixer, and 0.8% of sodium methylsilane modifier by weight of the powder was added. The mixture was then modified at 80°C for 20 minutes.

[0037] Compared to conventional silane modifiers, sodium methylsilane has a higher reactivity with the hydroxyl groups on the surface of silica powder, which can significantly reduce the surface polarity of silica powder, improve its dispersibility in the rubber matrix, and enhance the interfacial bonding with other flame retardant components.

[0038] Compounding and molding of composite flame retardants:

[0039] The above-mentioned surface-treated ultrafine magnesium hydroxide, ultrafine silica powder, and flame retardant TGD are compounded in a mass ratio of 6~10:1~3:1~3 (preferably 8:3:2); wherein, TGD is a novel flame retardant synthesized by a controlled ring-opening addition reaction of 1,3,5-triglycidyl isocyanurate (TGIC) and DOPO. It is different from traditional phosphorus and nitrogen flame retardants. It is halogen-free, smokeless, non-toxic, and does not migrate easily. It has better flame retardant durability and can form a synergistic flame retardant effect with inorganic flame retardant components.

[0040] A composite dispersant is added, with the mass ratio of sodium dodecylbenzenesulfonate: sodium oleate: sodium vinyl acetate-maleic anhydride copolymer = 5:3:2. This ratio has been verified by experiments to maximize the dispersion uniformity of the three components and avoid local agglomeration.

[0041] The dispersant dosage is 1% of the total mass of the composite flame retardant. The mixture is high-speed mixed at 80℃ for 20 minutes, and then dried and packaged to obtain the final composite flame retardant product.

[0042] Explanation of the synergistic flame retardant mechanism

[0043] The composite flame retardant of this invention achieves a performance breakthrough through "triple synergistic flame retardancy + interface optimization":

[0044] When heated, ultrafine magnesium hydroxide decomposes, absorbing heat from the burning surface and releasing a large amount of moisture, diluting the oxygen concentration. The active magnesium oxide generated by the decomposition adheres to the surface of the combustible material to form a physical barrier, playing a basic flame-retardant role of cooling and oxygen isolation.

[0045] Ultrafine sodium silane modified silica powder has excellent heat resistance. During combustion, it can enhance the density and firmness of the carbon layer, prevent the carbon layer from falling off, effectively block the transfer of heat and oxygen, and form a "physical barrier synergy" with magnesium hydroxide.

[0046] When TGD burns, it forms a complete and dense phosphorus-rich carbon layer, which further blocks the combustion chain reaction. At the same time, its organic structure can improve the interfacial compatibility between inorganic components and rubber matrix, forming a "chemical-physical synergistic flame retardant" with inorganic components.

[0047] The specific formulation of modifiers and composite dispersants ensures that the three components are uniformly dispersed in the rubber matrix, avoiding excessive local concentrations that could lead to a decrease in mechanical properties, and achieving a synergistic improvement in flame retardant properties and mechanical properties.

[0048] Example 1

[0049] This embodiment verifies the superiority of the technical solution of the present invention by adjusting key parameters such as the amount of modifier, the compounding ratio, and the amount of flame retardant added. Comparative experiments were also conducted (with different grinding aids, different modifiers, and different compounding systems). All experiments used natural rubber samples prepared according to the basic formulation in Table 1 (excluding the flame retardant), and tensile strength, elongation at break, hardness, and oxygen index were tested. The results are as follows: Figures 2-4 As shown.

[0050] Table 1 Basic Application Formulation (parts by weight)

[0051] Components Dosage Components Dosage NR (Natural Rubber) 100 vulcanizing agent 1.6 Zinc oxide 7.0 NOBS (accelerator) 1.5 Anti-aging agents 2.0 TMTD (Accelerator) 1.0 stearic acid 1.5 Flame retardant Variables (30 / 40 / 50) precipitate 15 - - carbon black 4 - -

[0052] Example 1

[0053] Preparation of ultrafine magnesium hydroxide: Following the technical procedure, powder with D50 of 0.8-1.2 μm was obtained;

[0054] Magnesium hydroxide modification: Modifier dosage 0.8%, other parameters according to the technical plan;

[0055] Preparation and modification of ultrafine silica powder: Follow the technical plan.

[0056] Compound ratio: ultrafine magnesium hydroxide: ultrafine silica powder: TGD = 6:2:1;

[0057] Flame retardant dosage: 30 parts;

[0058] The remaining steps, following the technical solution, yielded the composite flame retardant product. The test results of the sample performance are shown below. Figure 2 .

[0059] Example 2

[0060] Difference from Example 1: 40 parts of flame retardant were added;

[0061] The remaining steps are the same; performance test results can be found in [link to relevant documentation]. Figure 2 .

[0062] Example 3

[0063] Differences from Example 1: Modifier dosage 1.2%, flame retardant addition 40 parts;

[0064] The remaining steps are the same; performance test results can be found in [link to relevant documentation]. Figure 2 .

[0065] Example 4

[0066] Differences from Example 1: Modifier dosage 1.5%, compounding ratio 8:3:1, flame retardant addition 40 parts;

[0067] The remaining steps are the same; performance test results can be found in [link to relevant documentation]. Figure 2 .

[0068] Example 5

[0069] Differences from Example 1: Modifier dosage 1.5%, compounding ratio 8:3:2, flame retardant addition 40 parts;

[0070] The remaining steps are the same; performance test results can be found in [link to relevant documentation]. Figure 2 .

[0071] Example 6

[0072] Differences from Example 1: Modifier dosage 1.5%, compounding ratio 10:3:2, flame retardant addition 40 parts;

[0073] The remaining steps are the same; performance test results can be found in [link to relevant documentation]. Figure 2 .

[0074] Example 7

[0075] Difference from Example 5: 50 parts of flame retardant were added;

[0076] The remaining steps are the same; performance test results can be found in [link to relevant documentation]. Figure 2 .

[0077] Comparative experimental group

[0078] Comparative Experiment 1 (Different Grinding Aids)

[0079] The difference from Example 5 is that the PT-103 grinding aid is replaced with a conventional silane grinding aid, while the other parameters remain the same.

[0080] Performance test results can be found Figure 3 .

[0081] Comparative Experiment 2 (Different Modifier Formulations)

[0082] The difference from Example 5 is that the modifier formulation is adjusted to 15% silane coupling agent KH550, 70% ethanol, 2.5% emulsifier OP-10, 1% initiator KPS, and 31.5% butyl acrylate, with the remaining parameters remaining the same;

[0083] Performance test results can be found Figure 3 .

[0084] Comparative Experiment 3 (Two-component compound system)

[0085] The difference from Example 5 is that TGD is removed and the compounding ratio is adjusted to ultrafine magnesium hydroxide: ultrafine silica powder = 11:3 (total mass remains unchanged), while the other parameters are the same.

[0086] Performance test results can be found Figure 3 .

[0087] Existing comparative examples 1-3 (retained, with additional variables added).

[0088] Comparative Example 1

[0089] Only prepare ultrafine magnesium hydroxide powder (according to step 1 of the technical solution), without modification, without adding silica powder and TGD, and add 40 parts of flame retardant;

[0090] Performance test results can be found Figure 4 .

[0091] Comparative Example 2-1

[0092] Surface-treated ultrafine magnesium hydroxide powder (modifier dosage 1.2%) was prepared without adding silica powder and TGD, and 40 parts of flame retardant were added.

[0093] Performance test results can be found Figure 4 .

[0094] Comparative Example 2-2

[0095] Prepare surface-treated ultrafine magnesium hydroxide powder (modifier dosage 1.2%) without adding silica powder and TGD, and add 80 parts of flame retardant;

[0096] Performance test results can be found Figure 4 .

[0097] Comparative Example 3

[0098] A compound surface-treated ultrafine magnesium hydroxide and ultrafine silica powder (ratio 8:3) are combined, without TGD, and the amount of flame retardant added is 40 parts;

[0099] Performance test results can be found Figure 4 .

[0100] Blank control group

[0101] Prepare samples according to the basic formulation in Table 1 without adding any flame retardants;

[0102] Performance test results can be found Figure 4 .

[0103] Performance Test Results and Analysis

[0104] Figure 2 Performance test results of Examples 1-7

[0105] Figure 3 Comparative test performance test results

[0106] Figure 4 Comparative and blank group performance test results

[0107] Effect of Addition Amount: A comparison of Examples 1 (30 parts), 5 (40 parts), and 7 (50 parts) shows that the composite flame retardant of the present invention achieves an oxygen index of 24.1% with an addition amount of 30 parts, increases to 27.0% with 40 parts, and reaches 27.8% with 50 parts, while maintaining a tensile strength of over 22.5 MPa and an elongation at break of ≥545%. In contrast, Comparative Example 2-2 requires the addition of 80 parts of single modified magnesium hydroxide to achieve an oxygen index of 25.5%, and the tensile strength is only 18.36 MPa. This demonstrates that the composite flame retardant of the present invention has significant advantages of "low addition, high flame retardancy" while minimizing mechanical property loss.

[0108] Effectiveness of innovation:

[0109] Comparative experiment 1 shows that PT-103 grinding aid can increase tensile strength by 7.0% and oxygen index by 7.1% compared with conventional grinding aids, verifying its unique role in optimizing particle morphology and improving dispersibility.

[0110] Comparative experiment 2 shows that the specific modifier formulation of the present invention can increase tensile strength by 4.9% and oxygen index by 5.9%, demonstrating the importance of the synergistic effect of each component of the modifier on interfacial compatibility and flame retardant efficiency.

[0111] Comparative experiment 3 shows that the addition of TGD can increase the oxygen index by 7.5%, verifying the superiority of the three-component synergistic flame retardant mechanism.

[0112] Significant synergistic effect: Compared with Comparative Example 3 (two-component compound), Example 5 showed an increase in oxygen index from 25.3% to 27.0%, and a slight increase in tensile strength, demonstrating the synergistic effect of TGD and inorganic components; compared with Comparative Example 2-1 (single modified magnesium hydroxide), the oxygen index increased from 24.0% to 27.0%, and the mechanical properties remained basically the same, reflecting the advantages of multi-component synergy.

[0113] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a halogen-free composite flame retardant for natural rubber, characterized in that, The specific steps are as follows: Step 1: Preparation of ultrafine magnesium hydroxide powder: Select high-purity magnesium hydroxide ore with a magnesium hydroxide content ≥96% and crush it twice to an average particle size of 20mm. Add 0.7% (by weight) of inorganic powder grinding aid PT-103 to the ball mill and perform ultrafine wet grinding at 3000r / min for 2h to obtain ultrafine magnesium hydroxide powder with a D50 of 0.8-1.2μm. Step 2: Surface modification of ultrafine magnesium hydroxide powder: The ultrafine magnesium hydroxide powder is fed into a continuous modifier, and a modifier accounting for 0.8-1.5% of the powder mass is added. The modification is carried out at 70℃ for 30 min. The modifier is composed of 15% silane coupling agent KH171, 70% ethanol, 2.5% emulsifier SDS, 1% initiator KPS, and 31.5% butyl acrylate by mass fraction. Step 3: Preparation of ultrafine silica powder: Select 80-mesh silica powder with a silica content ≥99%, feed it into a ball mill and dry ball mill at 3500 r / min for 2 h to obtain ultrafine silica powder with D50 of 1.8-2.2 μm; Step 4: Surface modification of ultrafine silica powder: The ultrafine silica powder is fed into a high-speed mixer, and sodium methylsilane modifier accounting for 0.8% of the powder mass is added. The mixture is modified at 80℃ for 20 min. Step 5: Compounding and molding of composite flame retardant: Surface-treated ultrafine magnesium hydroxide, ultrafine silica powder and flame retardant TGD are compounded in a mass ratio of 6-10:1-3:1-3. A composite dispersant accounting for 1% of the total mass of the composite flame retardant is added. The mixture is mixed at high speed at 80℃ for 20 minutes, dried and packaged to obtain the finished product. The composite dispersant is composed of sodium dodecylbenzenesulfonate: sodium oleate: sodium vinyl acetate-maleic anhydride copolymer = 5:3:2 in mass ratio. The TGD is synthesized by a controlled ring-opening addition reaction of 1,3,5-triglycidyl isocyanurate and DOPO.

2. The method for preparing a halogen-free composite flame retardant for natural rubber according to claim 1, characterized in that, In step 2, the amount of the modifier used is 1.2% of the mass of the ultrafine magnesium hydroxide powder.

3. The method for preparing a halogen-free composite flame retardant for natural rubber according to claim 1, characterized in that, In step 5, the mass ratio of the ultrafine magnesium hydroxide, ultrafine silica powder and flame retardant TGD is 8:3:

2.

4. The application of a halogen-free composite flame retardant for natural rubber as described in any one of claims 1-3, characterized in that, Halogen-free composite flame retardants are used to prepare natural rubber products and are environmentally friendly flame retardant materials with low additive content and high flame retardant performance.

5. The application of the halogen-free composite flame retardant for natural rubber according to claim 4, characterized in that, The amount of the composite flame retardant added to the natural rubber system is 30-50 parts by weight, based on 100 parts by weight of natural rubber.

6. The application of the halogen-free composite flame retardant for natural rubber according to claim 4, characterized in that, The composite flame retardant is added in an amount of 40 parts by weight. Based on 100 parts by weight of natural rubber, the oxygen index of the natural rubber after addition is ≥27.0%, the tensile strength is ≥22.85 MPa, and the elongation at break is ≥561.98%.

7. The application of the halogen-free composite flame retardant for natural rubber according to claim 5, characterized in that, The natural rubber product production system also includes one or more of the following: zinc oxide, antioxidant, stearic acid, silica, carbon black, vulcanizing agent, and accelerator.

Images