Halogen-free flame-retardant rubber based on phosphorus-nitrogen-silicon synergism and preparation method thereof

Abstract

The invention relates to phosphorus-nitrogen-silicon synergistic halogen-free flame-retardant rubber and a preparation method thereof, and belongs to the technical field of rubber preparation. The flame-retardant rubber comprises the following raw materials in parts by weight: 100 parts of a rubber matrix, 5-15 parts of modified graphene, 10-20 parts of ammonium polyphosphate, 2-6 parts of modified nano silicon dioxide, 1-3 parts of a peroxide vulcanizing agent and 0.5-2 parts of a vulcanizing aid. The modified graphene is formed by taking nitrogen-doped graphene as a core and titanium dioxide as a shell and modifying by a silane coupling agent. The product provided by the invention has good flame retardance, good mechanical properties and good processing fluidity.

Description

Technical Field

[0001] This invention belongs to the field of rubber preparation technology, and relates to a halogen-free flame-retardant rubber based on phosphorus-nitrogen-silicon synergy and its preparation method. Background Technology

[0002] Rubber materials are widely used in wires and cables, conveyor belts, seals, and automotive parts due to their excellent properties such as high elasticity, wear resistance, and electrical insulation. However, most rubber materials are flammable and will burn rapidly in the event of a fire, releasing large amounts of heat and toxic fumes, posing a serious threat to people's lives and property.

[0003] Traditional flame-retardant modification of rubber mainly uses halogenated flame retardants (such as decabromodiphenyl ether and tetrabromobisphenol A). Although these have high flame-retardant efficiency, they release large amounts of toxic and corrosive hydrogen halide gases during combustion, causing secondary hazards. Furthermore, they have been subject to strict restrictions from EU RoHS and other environmental regulations in recent years. Halogen-free flame retardants such as aluminum hydroxide and magnesium hydroxide are environmentally friendly, but they have low flame-retardant efficiency and typically require high addition levels to achieve the desired flame-retardant effect. This severely deteriorates the mechanical properties and processing flowability of rubber, limiting its application in high-end fields.

[0004] To overcome the aforementioned shortcomings, existing technologies attempt to introduce intumescent flame retardants (such as ammonium polyphosphate / melamine / pentaerythritol systems) or nanoparticles (such as layered silicates, graphene, and carbon nanotubes) for synergistic modification. However, these systems still suffer from problems such as poor compatibility between the flame retardant and the rubber matrix, easy migration of flame retardant components during combustion, and insufficient char layer strength, making it difficult to simultaneously achieve excellent flame retardant properties and good mechanical properties at low addition levels. Therefore, flame retardant modification of rubber materials has significant practical implications. Summary of the Invention

[0005] The purpose of this invention is to provide a halogen-free flame-retardant rubber based on phosphorus-nitrogen-silicon synergy and its preparation method, the resulting rubber having strong flame retardancy and good mechanical properties.

[0006] The objective of this invention can be achieved through the following technical solutions: In a first aspect, the present invention provides a halogen-free flame-retardant rubber comprising the following raw materials in parts by weight: Rubber matrix: 100 parts; Modified graphene: 5-15 parts; Ammonium polyphosphate: 10-20 parts; Modified nano-silica: 2-6 parts; Peroxide vulcanizing agent: 1-3 parts; Vulcanizing aid: 0.5-2 parts; The modified graphene is obtained by coating nitrogen-doped graphene with titanium dioxide and then modifying it with a silane coupling agent.

[0007] As used in this text, "modified graphene" refers to a composite material with nitrogen-doped graphene as the core, titanium dioxide as the shell, and surface modified with a silane coupling agent. Nitrogen-doped graphene, through the introduction of nitrogen atoms under hydrothermal conditions, forms pyridine nitrogen, pyrrole nitrogen, or graphitic nitrogen in the graphene lattice. This not only retains graphene's excellent physical barrier and thermal conductivity but also endows it with the ability to release non-combustible gases (NH3, N2) during combustion, creating a synergistic dual gas source effect with ammonium polyphosphate. Titanium dioxide transforms into a dense ceramic protective layer at high temperatures, enhancing the thermal stability and mechanical strength of the carbon layer.

[0008] Preferably, the silane coupling agent is γ-methacryloxypropyltrimethoxysilane or vinyltriethoxysilane. Silane coupling agents not only improve the compatibility between flame retardants and the rubber matrix, but their unsaturated double bonds can also participate in the rubber crosslinking reaction during peroxide vulcanization, chemically anchoring the entire core-shell structure within the rubber network and effectively preventing the migration and precipitation of flame retardant components during processing and use.

[0009] Preferably, the preparation of the modified graphene includes the following steps: (a) Nitrogen-doped graphene was dispersed in anhydrous ethanol, tetrabutyl titanate and glacial acetic acid were added, and the mixture was reacted at 50-80°C for 4-6 hours. After centrifugation, washing and drying, the core-shell composite was obtained. (b) The core-shell complex was dispersed in anhydrous ethanol, a silane coupling agent was added, the pH was adjusted to 4-5, the reaction was carried out at 60-80℃ for 4-6 hours, and the mixture was centrifuged, washed and dried to obtain modified graphene.

[0010] Preferably, the mass ratio of tetrabutyl titanate to nitrogen-doped graphene in step (a) is (3-8):1. This fully utilizes the ceramic-enhancing effect of titanium dioxide without compromising the physical barrier function of the graphene core due to an excessively thick shell.

[0011] Preferably, the modified nano-silica is nano-silica modified with a silane coupling agent containing double bonds. The unsaturated double bonds on its surface can participate in rubber crosslinking during peroxide vulcanization, forming chemical bonds. Simultaneously, the silica particles react with ammonium polyphosphate during combustion, enhancing the thermal stability and mechanical strength of the char layer.

[0012] Preferably, the preparation of modified nano-silica includes the following steps: Nano-silica was dispersed in anhydrous ethanol, KH570 silane coupling agent was added, and the mixture was refluxed at 60-80℃ for 4-6 hours. After centrifugation, washing and drying, modified nano-silica was obtained.

[0013] Preferably, the rubber matrix is ​​at least one of EPDM rubber, natural rubber, styrene-butadiene rubber, and silicone rubber.

[0014] Preferably, the peroxide sulfiding agent is dicumyl peroxide or 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane.

[0015] Preferably, the mass ratio of modified graphene, ammonium polyphosphate, and modified nano-silica is 5-10: 12-18: 3-5. Modified graphene serves as the char-forming framework and physical barrier layer; ammonium polyphosphate acts as an acid and gas source, providing catalytic char formation and foaming expansion; and modified nano-silica acts as a synergist, enhancing the strength of the char layer. During combustion, these three components form a multi-layered protective char layer with a graphene framework for support, ammonium polyphosphate for catalytic expansion, and silica for enhanced density, achieving a synergistic flame-retardant effect.

[0016] Secondly, the present invention provides a method for preparing halogen-free flame-retardant rubber, comprising the following steps: (1) Add rubber matrix, then add modified graphene, ammonium polyphosphate, modified nano silica and vulcanizing agent in sequence, mix evenly, and control the temperature at 100-120℃. (2) Add peroxide vulcanizing agent, mix evenly, and vulcanize at 150-180℃ for 15-25 minutes on a flat vulcanizing machine to obtain halogen-free flame retardant rubber.

[0017] The preparation method of this invention employs a stepwise mixing process. First, highly thermally stable flame-retardant fillers (modified graphene, ammonium polyphosphate, and modified nano-silica) are mixed with the rubber matrix at 100-120°C to ensure sufficient dispersion of the fillers. The peroxide vulcanizing agent is added later in the mixing process to prevent premature decomposition and scorching during high-temperature mixing. During the vulcanization stage, a flat-plate vulcanizing machine is used at 150-180°C for 15-25 minutes, allowing the rubber molecular chains and the unsaturated double bonds on the flame retardant surface to undergo a simultaneous cross-linking reaction, forming a chemically bonded synergistic flame-retardant network.

[0018] The beneficial effects of this invention are: This invention constructs a modified graphene and combines it with ammonium polyphosphate and modified nano-silica to form a synergistic flame-retardant system. The unsaturated double bonds on the surfaces of the modified graphene and modified nano-silica participate in the rubber cross-linking reaction during peroxide vulcanization, chemically anchoring the flame-retardant components within the rubber network, thus improving the problems of easy migration and poor compatibility of traditional flame retardants. Simultaneously, during combustion, the nitrogen-doped graphene in the core layer releases non-combustible gases to dilute oxygen and form a char layer framework, while the outer layer of titanium dioxide transforms into a dense ceramic protective layer. Ammonium polyphosphate catalyzes char formation, and the modified nano-silica reacts with ammonium polyphosphate to enhance the strength of the char layer. The synergistic effect of these components forms a multi-layered, dense, ceramicized char layer. Detailed Implementation

[0019] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0020] Example 1 The preparation of a halogen-free flame-retardant rubber includes: The following raw materials are in parts by weight: 100 parts EPDM rubber, 8 parts modified graphene, 15 parts ammonium polyphosphate, 4 parts modified nano silica, 2 parts dicumyl peroxide, and 1 part TAIC vulcanizing agent.

[0021] In a two-roll mill, EPDM rubber is added, followed by modified graphene, ammonium polyphosphate, modified nano-silica, and the vulcanizing agent TAIC. The mixture is thoroughly mixed, with the actual compound temperature controlled at 105-110℃. Dicumyl peroxide is then added, and the mixture is further mixed thoroughly before passing through a thin sheet four times. The sheet is then sheeted and vulcanized at 160℃ for 20 minutes on a flat vulcanizing machine to obtain halogen-free flame-retardant rubber.

[0022] The preparation of modified graphene includes: 1 g of nitrogen-doped graphene was dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed for 30 minutes. 5 g of tetrabutyl titanate and 1 mL of glacial acetic acid were added, and the mixture was stirred for 30 minutes. 2 mL of water was slowly added dropwise, and the mixture was heated to 60 °C and reacted for 5 hours. The mixture was centrifuged (8000 rpm, 10 minutes), washed three times with anhydrous ethanol, and dried under vacuum at 60 °C for 6 hours to obtain the composite.

[0023] The above-mentioned complex was dispersed in 100 mL of anhydrous ethanol, and 0.5 g of KH570 silane coupling agent was added. The pH was adjusted to 5 with glacial acetic acid, and the mixture was refluxed at 70 °C for 5 hours. After centrifugation, the mixture was washed three times with anhydrous ethanol and dried under vacuum at 50 °C for 12 hours to obtain KH570 modified graphene.

[0024] The preparation of modified nano-silica includes: 10g of nano-silica was dispersed in 200mL of anhydrous ethanol and ultrasonically dispersed for 30 minutes. 2g of KH570 silane coupling agent was added, and the pH was adjusted to 5 with glacial acetic acid. The mixture was then refluxed at 70℃ for 6 hours. After centrifugation, the nano-silica was washed three times with anhydrous ethanol and dried under vacuum at 50℃ for 12 hours to obtain KH570 modified nano-silica.

[0025] Example 2 The preparation of a halogen-free flame-retardant rubber includes: The following raw materials are in parts by weight: 100 parts natural rubber, 10 parts modified graphene, 18 parts ammonium polyphosphate, 5 parts modified nano silica, 2.5 parts 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and 1 part TAIC vulcanizing agent.

[0026] In a two-roll mill, natural rubber is added, followed by modified graphene, ammonium polyphosphate, modified nano-silica, and the vulcanizing agent TAIC. The mixture is thoroughly mixed, with the actual compound temperature controlled at 100-105℃. Then, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane is added, and the mixture is thoroughly mixed before passing through a thin sheet three times. The sheet is then sheeted and vulcanized at 170℃ for 20 minutes on a flat vulcanizing machine to obtain halogen-free flame-retardant rubber.

[0027] The preparation of modified graphene and modified nano-silica is the same as in Example 1.

[0028] Example 3 The preparation of a halogen-free flame-retardant rubber includes: The following raw materials are in parts by weight: 100 parts styrene-butadiene rubber, 6 parts modified graphene, 12 parts ammonium polyphosphate, 3 parts modified nano silica, 2.5 parts dicumyl peroxide, and 1 part TAIC vulcanizing agent.

[0029] In a two-roll mill, styrene-butadiene rubber (SBR) is added, followed by modified graphene, ammonium polyphosphate, modified nano-silica, and the vulcanizing agent TAIC. The mixture is thoroughly mixed, with the actual compound temperature controlled at 110-115℃. Dicumyl peroxide is then added, and the mixture is thoroughly mixed before passing through a thin sheet five times. The sheet is then sheeted and vulcanized at 160℃ for 18 minutes on a flat vulcanizing machine to obtain halogen-free flame-retardant rubber.

[0030] The preparation of modified graphene and modified nano-silica is the same as in Example 1.

[0031] Example 4 The preparation of a halogen-free flame-retardant rubber includes: Prepared from the following raw materials in parts by weight: 100 parts methyl vinyl silicone rubber, 8 parts modified graphene, 15 parts ammonium polyphosphate, 4 parts modified nano silica, 1.5 parts dicumyl peroxide, and 1 part TAIC vulcanizing agent.

[0032] In a two-roll mill, silicone rubber is added, followed by modified graphene, ammonium polyphosphate, modified nano-silica, and the vulcanizing agent TAIC. The mixture is thoroughly mixed, with the actual temperature of the compound controlled at 115-120℃. Dicumyl peroxide is then added, and the mixture is thoroughly mixed before passing through a thin sheet three times. The sheet is then sheeted and vulcanized at 170℃ for 20 minutes on a flat vulcanizing machine to obtain a first-stage vulcanized product. The first-stage vulcanized product is placed in an oven and held at 200℃ for 4 hours for a second-stage vulcanization. After cooling, halogen-free flame-retardant silicone rubber is obtained.

[0033] The preparation of modified graphene and modified nano-silica is the same as in Example 1. Comparative Example 1 Flame-retardant rubber was obtained by replacing the modified graphene with unmodified ordinary graphene, and otherwise the same as in Example 1.

[0034] Comparative Example 2 Without adding ammonium polyphosphate, the rest is the same as in Example 1, resulting in flame-retardant rubber.

[0035] Comparative Example 3 Without adding modified nano-silica, the rest is the same as in Example 1, resulting in flame-retardant rubber.

[0036] Performance testing The performance of the rubber materials prepared in the examples and comparative examples was tested according to the following standards: Oxygen Index (OI): Tested according to GB / T 2406.2-2009. The sample is vertically fixed in the combustion chamber, and the oxygen concentration is gradually adjusted from low to high. The combustion behavior of the sample after ignition is observed, and the lowest oxygen concentration at which the sample just maintains combustion is recorded.

[0037] Vertical flammability rating: Tested according to GB / T 2408-2008. The sample is fixed vertically, and a Bunsen burner is applied to the lower end of the sample for 10 seconds. After removing the flame, the afterflame time is recorded. This process is repeated twice. The flame retardancy rating is evaluated based on indicators such as afterflame time and whether dripping material ignites cotton. The flame retardancy ratings from highest to lowest are V-0, V-1, and V-2.

[0038] Tensile strength and elongation at break: Tested according to GB / T 528-2009, dumbbell-shaped specimens, tensile speed of 500 mm / min, tensile strength and elongation at break.

[0039] Table 1 Performance Test Results

[0040] The above results confirm that the three-layer core-shell structure modified graphene, ammonium polyphosphate, and modified nano-silica of this invention exhibit a significant synergistic effect. Compared with existing technologies, this invention ensures good halogen-free flame retardancy, good mechanical properties, and good processing flowability while reducing the amount of flame retardant added.

[0041] Those skilled in the art should understand that, without affecting the technical effect of the present invention, conventional additives such as antioxidants, stearic acid, and plasticizers may be added as needed.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A halogen-free flame-retardant rubber, characterized in that, It contains the following ingredients by weight: Rubber matrix: 100 parts; Modified graphene: 5-15 parts; Ammonium polyphosphate: 10-20 parts; Modified nano-silica: 2-6 parts; Peroxide vulcanizing agent: 1-3 parts; Vulcanizing aid: 0.5-2 parts; The modified graphene is obtained by coating nitrogen-doped graphene with titanium dioxide and then modifying it with a silane coupling agent.

2. The halogen-free flame-retardant rubber according to claim 1, characterized in that, The silane coupling agent is γ-methacryloxypropyltrimethoxysilane or vinyltriethoxysilane.

3. The halogen-free flame-retardant rubber according to claim 1, characterized in that, The preparation of the modified graphene includes the following steps: (a) Nitrogen-doped graphene was dispersed in anhydrous ethanol, tetrabutyl titanate and glacial acetic acid were added, and the mixture was reacted at 50-80°C for 4-6 hours. After centrifugation, washing and drying, the core-shell composite was obtained. (b) The core-shell complex was dispersed in anhydrous ethanol, a silane coupling agent was added, the pH was adjusted to 4-5, the reaction was carried out at 60-80℃ for 4-6 hours, and the mixture was centrifuged, washed and dried to obtain modified graphene.

4. The halogen-free flame-retardant rubber according to claim 3, characterized in that, In step (a), the mass ratio of tetrabutyl titanate to nitrogen-doped graphene is (3-8):

1.

5. The halogen-free flame-retardant rubber according to claim 1, characterized in that, The modified nano-silica is nano-silica modified with a silane coupling agent containing double bonds.

6. The halogen-free flame-retardant rubber according to claim 5, characterized in that, The preparation of modified nano-silica includes the following steps: Nano-silica was dispersed in anhydrous ethanol, KH570 silane coupling agent was added, and the mixture was refluxed at 60-80℃ for 4-6 hours. After centrifugation, washing and drying, modified nano-silica was obtained.

7. The halogen-free flame-retardant rubber according to claim 1, characterized in that, The rubber matrix is ​​at least one of EPDM rubber, natural rubber, styrene-butadiene rubber, and silicone rubber.

8. The halogen-free flame-retardant rubber according to claim 1, characterized in that, The peroxide sulfiding agent is dicumyl peroxide or 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane.

9. The halogen-free flame-retardant rubber according to claim 1, characterized in that, The mass ratio of the modified graphene, ammonium polyphosphate, and modified nano-silica is 5-10: 12-18: 3-5.

10. A method for preparing the halogen-free flame-retardant rubber according to any one of claims 1-9, characterized in that, Includes the following steps: (1) Add rubber matrix, then add modified graphene, ammonium polyphosphate, modified nano silica and vulcanization aid in sequence, mix evenly, and control the material temperature at 100-120℃. (2) Add peroxide vulcanizing agent, mix evenly, and vulcanize at 150-180℃ for 15-25 minutes on a flat vulcanizing machine to obtain halogen-free flame retardant rubber.

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