A flame-retardant and thermally conductive styrene-butadiene rubber composite material and its preparation method

Abstract

This invention discloses a flame-retardant and thermally conductive styrene-butadiene rubber (SBR) composite material and its preparation method, comprising the following raw materials by weight: 100 parts SBR; 15 parts expandable graphite microcapsules; 45-55 parts reinforcing agent; 1-2 parts sulfur; 2-4 parts accelerator; 1-2 parts stearic acid; 2-10 parts zinc oxide; and 1-1.5 parts antioxidant RD. This invention uses expandable graphite as the core and hydroxyethyl methacrylate phosphate monomer as the shell material, selecting thermally conductive and insulating boron nitride-doped shells. Expandable graphite microcapsules containing organic phosphate esters and inorganic boron nitride are prepared through in-situ polymerization. Blending these microcapsules with SBR as the base material for tires can significantly improve the flame-retardant and thermally conductive properties of the SBR composite material.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant and thermally conductive materials, specifically to a flame-retardant and thermally conductive styrene-butadiene rubber composite material and its preparation method. Background Technology

[0002] Styrene-butadiene rubber (SBR) possesses excellent physical and chemical properties and is widely used in products such as tires and conveyor belts. However, SBR is extremely flammable and has low thermal conductivity, which limits its application range. Therefore, developing a SBR composite material with flame-retardant and thermally conductive properties is of great significance.

[0003] Expandable graphite, as an intumescent flame retardant additive, boasts advantages such as low smoke and low cost, and is widely used in flame retardant applications for materials like rubber, plastics, and coatings. During combustion, expandable graphite rapidly expands upon heating, forming a large, worm-like expanded char layer, thereby improving the flame retardant properties of the composite material. However, on the one hand, the char layer formed by the thermal expansion of expandable graphite is too porous, limiting its flame retardant performance; on the other hand, the hydrophobicity of expandable graphite and its poor compatibility with the matrix severely affect the mechanical properties of the composite material. Coating expandable graphite with organic polymers can increase its compatibility with natural rubber. However, existing coating technologies often use organic polymers with low thermal conductivity as wall materials. While this improves the compatibility between expandable graphite and natural rubber, it also degrades the thermal conductivity of natural rubber, increasing the risk of fire due to heat accumulation. Summary of the Invention

[0004] Based on the problems existing in the prior art, the purpose of this invention is to develop a flame-retardant and thermally conductive styrene-butadiene rubber composite material. By selecting hydroxyethyl methacrylate phosphate monomer as the shell material and selecting thermally conductive and insulating boron nitride-doped shell, expandable graphite microcapsules with excellent flame-retardant and thermally conductive properties are prepared, thereby improving the flame-retardant and thermally conductive properties of the styrene-butadiene rubber composite material.

[0005] To achieve its objectives, the present invention employs the following technical solution:

[0006] A flame-retardant and thermally conductive styrene-butadiene rubber composite material, comprising the following raw materials in parts by weight:

[0007] 100 parts of styrene-butadiene rubber;

[0008] 15 portions of expandable graphite microcapsules;

[0009] 45-55 parts of reinforcing agent;

[0010] 1-2 parts sulfur;

[0011] Accelerator 2-4 parts;

[0012] 1-2 parts stearic acid;

[0013] 2-10 parts zinc oxide;

[0014] Anti-aging agent RD 1-1.5 parts.

[0015] Furthermore, the expandable graphite microcapsules are formed by in-situ polymerization of expandable graphite as the core and hydroxyethyl methacrylate phosphate monomer as the shell material on the surface of expandable graphite, with boron nitride doping occurring simultaneously during the in-situ polymerization. The specific preparation method of the expandable graphite microcapsules is as follows:

[0016] Boron nitride was dispersed in a solution of hydroxyethyl methacrylate phosphate containing azobisisobutyronitrile, and then expandable graphite was added and stirred until homogeneous to obtain a reaction solution. The reaction solution was transferred to deionized water containing sodium dodecyl sulfate and magnetically stirred for 1-3 hours to form a pre-emulsion. The pre-emulsion was sonicated for 1-3 hours to form a microemulsion. Finally, the microemulsion was reacted in an oil bath at 70-110°C for 6-10 hours, centrifuged, washed and dried to obtain expandable graphite microcapsules.

[0017] Furthermore: the mass ratio of boron nitride to hydroxyethyl methacrylate phosphate solution is 1:2-4, the mass of expandable graphite is 2-4 times the total mass of boron nitride and hydroxyethyl methacrylate phosphate solution; the volume ratio of expandable graphite to deionized water is 12-40g:400mL.

[0018] Further: In the hydroxyethyl methacrylate phosphate solution, the mass percentage of azobisisobutyronitrile is 1-2 wt.%. In the deionized water containing sodium dodecyl sulfate, the mass percentage of sodium dodecyl sulfate is 2-4 wt.%.

[0019] Further: the reinforcing agent is selected from one or more mixtures of carbon black, calcium carbonate, silica, and carbon fiber. The accelerator is selected from one or more mixtures of accelerator NS and accelerator M.

[0020] The preparation method of the flame-retardant and thermally conductive styrene-butadiene rubber composite material of the present invention is as follows: Styrene-butadiene rubber, stearic acid, zinc oxide, antioxidant RD, expandable graphite microcapsules, reinforcing agent, accelerator, and sulfur are added sequentially to a Banbury mixer. After uniform mixing, the mixture is pressed into sheets on an open mill and vulcanized using a flat vulcanizing machine to obtain the flame-retardant and thermally conductive styrene-butadiene rubber composite material. The vulcanization conditions are: temperature 155-165℃, pressure 5-8MPa, and time 15-20min.

[0021] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0022] This invention uses expandable graphite as the core and hydroxyethyl methacrylate phosphate monomer as the shell material, with thermally conductive and insulating boron nitride-doped shell, to prepare expandable graphite microcapsules through in-situ polymerization. The expandable graphite microcapsules contain organic phosphate esters and inorganic boron nitride. When blended with styrene-butadiene rubber (SBR) as a tire substrate, they can significantly improve the flame retardant and thermal conductivity of SBR composites: on the one hand, the flame retardant properties of SBR are improved synergistically by expandable graphite and organic phosphate esters; on the other hand, the boron nitride-doped microcapsules form thermally conductive pathways in the matrix, improving the thermal conductivity of SBR and preventing heat accumulation during tire use. Attached Figure Description

[0023] Figure 1 This is a SEM image of the expandable graphite microcapsules prepared in Example 2.

[0024] Figure 2 In the middle (A) and (B), the HRR curves and THR curves of sample three and sample four are respectively. Detailed Implementation

[0025] The present invention will be further described below with reference to the embodiments.

[0026] Example 1

[0027] This embodiment prepares styrene-butadiene rubber composite material according to the following steps:

[0028] 1. Preparation of expandable graphite microcapsules

[0029] 2g of hexagonal boron nitride nanosheets were dispersed in 4g of hydroxyethyl methacrylate phosphate (containing 1wt.% azobisisobutyronitrile) solution, and then 12g of expandable graphite was added and stirred until homogeneous to obtain a reaction solution. The reaction solution was transferred to 400mL of deionized water (containing 2wt.% sodium dodecyl sulfate) and magnetically stirred for 1h to form a preemulsion. The preemulsion was sonicated for 1h to form a microemulsion. Finally, the microemulsion was transferred to a three-necked flask and reacted in an oil bath at 110℃ for 6h. After centrifugation, washing and drying, expandable graphite microcapsules were obtained.

[0030] 2. Preparation of styrene-butadiene rubber composite materials

[0031] According to the sample formulation in Table 1, styrene-butadiene rubber, stearic acid, zinc oxide, antioxidant RD, expandable graphite microcapsules, reinforcing agent, accelerator and sulfur were added sequentially in an internal mixer. After being mixed evenly, the mixture was pressed into sheets on an open mill and vulcanized using a flat vulcanizing machine to obtain styrene-butadiene rubber composite material samples. The vulcanization conditions were: temperature 155℃, pressure 8MPa, time 20min.

[0032] Table 1. Formulation of Sample 1 and Sample 2 (parts by weight)

[0033] Sample name / parts by weight Sample 1 Sample 2 Styrene-butadiene rubber 100 100 Reinforcing agent silica 55 55 Anti-aging agent RD 1 1 stearic acid 1 1 Zinc oxide 5 5 Accelerator NS 2 2 sulfur 1.5 1.5 Expandable graphite microcapsules \ 15

[0034] The following performance tests were performed on the rubber composite material: the limiting oxygen index (LOI) was tested according to GB 10707-2008; the thermal conductivity was tested at room temperature using a TC3100 thermal conductivity meter. Table 2 shows the limiting oxygen index (LOI) and thermal conductivity of sample one and sample two. It can be seen that the rubber composite material with expandable graphite microcapsules added in this invention has good flame retardant and thermal conductivity properties.

[0035] Table 2 Performance test data of Sample 1 and Sample 2

[0036] sample LOI (%) Thermal conductivity (W / m·K) Sample 1 19.4 0.3691 Sample 2 27.1 0.6833

[0037] Example 2

[0038] This embodiment prepares styrene-butadiene rubber composite material according to the following steps:

[0039] 1. Preparation of expandable graphite microcapsules

[0040] 2g of hexagonal boron nitride nanosheets were dispersed in 6g of hydroxyethyl methacrylate phosphate solution (containing 1wt.% azobisisobutyronitrile), and then 15g of expandable graphite was added and stirred until homogeneous to obtain a reaction solution. The reaction solution was transferred to 400mL of deionized water (containing 3wt.% sodium dodecyl sulfate) and magnetically stirred for 1.5h to form a preemulsion. The preemulsion was sonicated for 1.5h to form a microemulsion. Finally, the microemulsion was transferred to a three-necked flask and reacted in an oil bath at 90℃ for 8h. After centrifugation, washing, and drying, expandable graphite microcapsules were obtained.

[0041] 2. Preparation of styrene-butadiene rubber composite materials

[0042] According to the sample formulation in Table 3, styrene-butadiene rubber, stearic acid, zinc oxide, antioxidant RD, expandable graphite microcapsules, reinforcing agent, accelerator and sulfur were added sequentially in an internal mixer. After being mixed evenly, the mixture was pressed into sheets on an open mill and vulcanized using a flat vulcanizing machine to obtain styrene-butadiene rubber composite material samples. The vulcanization conditions were: temperature 160℃, pressure 6.5MPa, time 18min.

[0043] Table 3. Formulation of Samples 3 and 4 (parts by weight)

[0044] Sample name / parts by weight Sample 3 Sample 4 Styrene-butadiene rubber 100 100 Reinforcing agent carbon black 50 50 Anti-aging agent RD 1 1 stearic acid 1.5 1.5 Zinc oxide 7.5 7.5 Accelerator M 3 3 sulfur 1 1 Expandable graphite microcapsules \ 15

[0045] The following performance tests were performed on the rubber composite material: the limiting oxygen index test was conducted according to GB 10707-2008; the thermal conductivity was tested at room temperature using a TC3100 thermal conductivity meter; the heat release test of the sample was conducted using a cone calorimeter from Nanjing Jiangning Analytical Instrument Co., Ltd. according to ISO5660-1:2002 standard; the mechanical property test was conducted according to GB / T6344-2008 standard, and the tensile rate of the sample was 500 mm / min.

[0046] Table 4 shows the limiting oxygen index (LOI), thermal conductivity, peak heat release ratio (PHRR), total heat release (THR), tensile strength, and elongation at break for samples three and four. It is evident that the rubber composite material with expandable graphite microcapsules added in this invention possesses excellent flame retardant properties, thermal conductivity, and mechanical properties.

[0047] Table 4 Performance test data of Sample 3 and Sample 4

[0048]

[0049]

[0050] Example 3

[0051] This embodiment prepares styrene-butadiene rubber composite material according to the following steps:

[0052] 1. Preparation of expandable graphite microcapsules

[0053] 2g of hexagonal boron nitride nanosheets were dispersed in 8g of hydroxyethyl methacrylate phosphate (containing 1wt.% azobisisobutyronitrile) solution, and then 40g of expandable graphite was added and stirred until homogeneous to obtain a reaction solution. The reaction solution was transferred to 400mL of deionized water (containing 4wt.% sodium dodecyl sulfate) and magnetically stirred for 2h to form a preemulsion. The preemulsion was sonicated for 2h to form a microemulsion. Finally, the microemulsion was transferred to a three-necked flask and reacted in an oil bath at 110℃ for 6h. After centrifugation, washing and drying, expandable graphite microcapsules were obtained.

[0054] 2. Preparation of styrene-butadiene rubber composite materials

[0055] According to the sample formulation in Table 5, styrene-butadiene rubber, stearic acid, zinc oxide, antioxidant RD, expandable graphite microcapsules, reinforcing agent, accelerator and sulfur were added sequentially in an internal mixer. After being mixed evenly, the mixture was pressed into sheets on an open mill and vulcanized using a flat vulcanizing machine to obtain styrene-butadiene rubber composite material samples. The vulcanization conditions were: temperature 165℃, pressure 5MPa, time 15min.

[0056] Table 5. Formulations (parts by weight) for Samples 5 and 6

[0057] Sample name / parts by weight Sample 1 Sample 2 Styrene-butadiene rubber 100 100 Calcium carbonate as a reinforcing agent 45 45 Anti-aging agent RD 1.5 1.5 stearic acid 2 2 Zinc oxide 10 10 Accelerator NS 4 4 sulfur 2 2 Expandable graphite microcapsules \ 15

[0058] The following performance tests were performed on the rubber composite material: the limiting oxygen index (LOI) was tested according to GB 10707-2008; the thermal conductivity was tested at room temperature using a TC3100 thermal conductivity meter. Table 6 shows the limiting oxygen index (LOI) and thermal conductivity of samples five and six. It can be seen that the rubber composite material with expandable graphite microcapsules added in this invention has good flame retardant and thermal conductivity properties.

[0059] Table 6 Performance test data for samples 5 and 6

[0060]

[0061]

[0062] The above embodiments are typical embodiments of the present invention and are not intended to limit the present invention in any way. Any adjustments and modifications made by those skilled in the art to the described technical solutions, as long as they do not deviate from the inventive concept or exceed the scope defined in the claims, shall fall within the protection scope of the present invention.

Claims

1. A flame retardant heat conductive styrene butadiene rubber composite material characterized by, Including the following raw materials by weight: 100 parts of styrene-butadiene rubber; 15 portions of expandable graphite microcapsules; 45-55 parts of reinforcing agent; 1-2 parts sulfur; Accelerator 2-4 parts; 1-2 parts stearic acid; 2-10 parts zinc oxide; Anti-aging agent RD 1-1.5 parts; The expandable graphite microcapsules are formed by in-situ polymerization of expandable graphite as the core and hydroxyethyl methacrylate phosphate as the shell material on the surface of expandable graphite, with boron nitride doping occurring simultaneously during the in-situ polymerization. The preparation method of the expandable graphite microcapsules is as follows: Boron nitride was dispersed in a solution of hydroxyethyl methacrylate phosphate containing azobisisobutyronitrile, and then expandable graphite was added and stirred until homogeneous to obtain a reaction solution. The reaction solution was transferred to deionized water containing sodium dodecyl sulfate and magnetically stirred for 1-3 h to form a pre-emulsion. The pre-emulsion was sonicated for 1-3 h to form a microemulsion. Finally, the microemulsion was reacted in an oil bath at 70-110℃ for 6-10 h, centrifuged, washed, and dried to obtain expandable graphite microcapsules. The mass ratio of boron nitride to hydroxyethyl methacrylate phosphate solution was 1:2-4, and the mass of expandable graphite was 2-4 times the total mass of boron nitride and hydroxyethyl methacrylate phosphate solution. The volume ratio of expandable graphite to deionized water was 12-40 g:400 mL.

2. The flame retardant heat conductive SBR composite material of claim 1, wherein: The mass percentage of azobisisobutyronitrile in the hydroxyethyl methacrylate phosphate solution is 1-2 wt.%.

3. The flame retardant heat conductive SBR composite material of claim 1, wherein: The deionized water containing sodium dodecyl sulfate has a sodium dodecyl sulfate content of 2-4 wt.%.

4. The flame retardant heat conductive styrene butadiene rubber composite of claim 1, wherein: The reinforcing agent is selected from one or more mixtures of carbon black, calcium carbonate, silica, and carbon fiber.

5. The flame retardant heat conductive styrene butadiene rubber composite of claim 1, wherein: The accelerator is selected from one or more mixtures of accelerator NS and accelerator M.

6. A process for the preparation of the flame retardant heat conductive styrene butadiene rubber composite material according to any one of claims 1 to 5, characterized by: Styrene-butadiene rubber, stearic acid, zinc oxide, antioxidant RD, expandable graphite microcapsules, reinforcing agent, accelerator and sulfur are added sequentially to a mixer. After being mixed evenly, the mixture is pressed into sheets on an open mill and vulcanized with a flat vulcanizing machine to obtain a flame-retardant and thermally conductive styrene-butadiene rubber composite material.

7. The production method according to claim 6, characterized by, The vulcanization conditions are: temperature 155-165℃, pressure 5-8MPa, and time 15-20 min.

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