Expanded graphite synergistic halogen-free flame-retardant silicone rubber and preparation method thereof

Abstract

The invention discloses expanded graphite synergistic halogen-free flame-retardant silicone rubber and a preparation method thereof, and belongs to the technical field of silicone rubber materials. Comprising the following raw materials in parts by weight: 50 parts by weight of silica gel, 35 parts by weight of expanded graphite, 10 parts by weight of aluminum hydroxide, 5 parts by weight of zinc borate, 0.5-1.5 parts by weight of dimethyl silicone oil and 0.1-0.3 part by weight of 2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane. The expanded graphite, the aluminum hydroxide and the zinc borate are reasonably compounded to play a synergistic effect in the silicone rubber, so that the flame retardant property and the environment-friendly function of the silicone rubber are improved.

Description

Technical Field

[0001] This invention belongs to the field of silicone rubber material technology, specifically relating to a halogen-free flame-retardant silicone rubber with synergistic effect of expanded graphite and its preparation method. Background Technology

[0002] Silicone rubber is a polymeric elastic material with silicon-oxygen bonds as the main chain and organic groups as side chains. It combines the properties of both inorganic and organic materials, exhibiting strong resistance to water, oil, and most chemical reagents, and is not prone to swelling or degradation. Its outstanding properties, including resistance to high and low temperatures, electrical insulation, chemical corrosion resistance, ozone, ultraviolet radiation, and oxidative aging, as well as long service life in outdoor or harsh environments, have led to its widespread application in electronics, electrical engineering, aerospace, and many other fields. However, it is important to note that silicone rubber is inherently flammable with a low oxygen index. In the event of a fire, it will not only burn violently but also release a large amount of heat and smoke, seriously threatening life and property safety and limiting its application in fields with high flame-retardant requirements. Currently, the main way to improve the flame-retardant properties of silicone rubber is by adding flame retardants. While traditional halogenated flame retardants perform well in flame retardancy, they release large amounts of toxic and harmful gases during combustion, causing serious harm to the environment and human health. With increasingly stringent environmental protection requirements, the development of halogen-free flame-retardant silicone rubber has become a research hotspot in this field, and related research is progressing towards richer details and more comprehensive perspectives.

[0003] Patent CN102876045B describes a novel flame-retardant silicone rubber prepared using ammonium polyphosphate as a flame retardant, combined with magnesium aluminum hydrotalcite, magnesium hydroxide, α,ω-dihydroxypolydimethylsiloxane, silicone oil, and nano-calcium carbonate. However, ammonium polyphosphate slowly decomposes at 150°C and begins to degrade above 240°C, with the degradation product being polyphosphoric acid. This significantly affects the mechanical properties of the silicone rubber during prolonged use in high-temperature environments, making it difficult to achieve good heat resistance at high temperatures. Furthermore, the silicone rubber with added ammonium polyphosphate forms an expansion layer after high-temperature combustion, which may cause tracking under high voltage conditions, leading to high-temperature corrosion. The presence of this expansion layer also continuously damages the structure of the silicone rubber, making it unsuitable for applications such as insulating sheaths.

[0004] In summary, achieving high flame retardancy in the preparation process of silicone rubber, and obtaining halogen-free flame-retardant silicone rubber that combines excellent flame retardancy with environmental protection, is a key problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a halogen-free flame-retardant silicone rubber with synergistic effects of expanded graphite and its preparation method. By rationally compounding expanded graphite, aluminum hydroxide, and zinc borate, among other halogen-free flame retardants, they exert a synergistic effect in the silicone rubber, improving its flame-retardant properties while also considering environmental protection, thereby solving the problems mentioned in the background art. Specifically, the technical solution of this invention includes the following: One objective of this invention is to provide a halogen-free flame-retardant silicone rubber with synergistic effects of expanded graphite, characterized in that the halogen-free flame-retardant silicone rubber comprises the following raw materials in parts by weight: 50 parts by weight of silica gel, 35 parts by weight of expanded graphite, 10 parts by weight of aluminum hydroxide, 5 parts by weight of zinc borate, 0.5 to 1.5 parts by weight of dimethyl silicone oil, and 0.1 to 0.3 parts by weight of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

[0006] Furthermore, the silicone rubber includes methyl vinyl silicone rubber, wherein the vinyl content of the methyl vinyl silicone rubber is 0.12 mol%, and the number average molecular weight of the methyl vinyl silicone rubber is 700 kDa.

[0007] Furthermore, the method for preparing the expanded graphite includes the following steps: High-purity graphite (LC300-99.99), sulfuric acid solution, and nitric acid solution were mixed in a mass ratio of 10:50:5 and heated to 30-60℃ with stirring for 40-80 minutes to obtain modified graphite. After being rinsed with deionized water, the modified graphite is dried at 60-100℃ for 6-12 hours and then expanded at 800-1000℃ for 10-60 seconds to obtain expanded graphite. Nitric acid solution acts as a strong oxidizing agent, oxidizing some of the carbon atoms in the graphite layers to form positively charged carbon layers between the graphite layers. Sulfuric acid solution acts as an intercalating agent, entering the oxidized graphite layers to form interlayer compounds. At the same time, sulfuric acid solution also acts as an acidic medium and a dehydrating agent.

[0008] Furthermore, the sulfuric acid solution comprises a sulfuric acid solution with a mass fraction of 98%, and the nitric acid solution comprises a nitric acid solution with a mass fraction of 65%.

[0009] Furthermore, the modified graphite is rinsed with deionized water until the pH of the rinse water is 7.

[0010] Furthermore, the viscosity of the dimethyl silicone oil includes 350 mPa·s.

[0011] The second objective of this invention is to provide a method for preparing halogen-free flame-retardant silicone rubber with synergistic effects of expanded graphite, the preparation method comprising the following steps: After silicone is plasticized in a thin pass, expanded graphite, aluminum hydroxide, zinc borate and dimethyl silicone oil are added in sequence and mixed to obtain a compound; Halogen-free flame-retardant silicone rubber was obtained by vulcanizing the compound with 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

[0012] Furthermore, the thin-pass plasticizing process includes a thin-pass process and a plasticizing process. The conditions of the thin-pass process include a thin-pass roller gap of 2-3 mm and a thin-pass number of 3-5 passes. The plasticizing process includes a plasticizing roller gap of 5-6 mm, a plasticizing temperature of 50-60℃, and a plasticizing time of 5-10 min.

[0013] Furthermore, the mixing process includes first adding expanded graphite and mixing for 5-8 minutes at 60°C, then adding aluminum hydroxide and mixing for 5-7 minutes, then adding zinc borate and mixing for 3-5 minutes, and finally adding dimethyl silicone oil and mixing for 5-8 minutes.

[0014] Furthermore, the conditions for the mixed vulcanization treatment include a vulcanization temperature of 180~200℃, a vulcanization pressure of 10~15MPa, and a vulcanization treatment time of 10~20min.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Significant flame retardant effect: Expanded graphite rapidly expands at high temperature to form a dense porous carbon layer, which covers the surface of silicone rubber, isolating oxygen and heat transfer, and can also adsorb smoke particles; aluminum hydroxide decomposes when heated to absorb heat and release water vapor; zinc borate can form a glassy covering layer at high temperature, isolating oxygen and heat, and can also promote the formation and stability of the expanded graphite carbon layer; the three work together to significantly improve the oxygen index of silicone rubber and enhance the overall flame retardant performance, while inhibiting smoke and reducing the release of toxic gases.

[0016] (2) Halogen-free and environmentally friendly: The silicone rubber prepared by this invention adopts a halogen-free flame retardant system, does not contain toxic and harmful substances, and will not produce toxic and harmful gases when burning. It meets environmental protection requirements, is harmless to the environment and human health, and can be widely used in fields with high environmental protection requirements. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below through embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Unless otherwise stated, all raw materials and reagents used in this invention are commercially available or can be prepared by known methods.

[0019] Preparation Example 1: The preparation method of expanded graphite specifically includes the following steps: 10g of high-purity graphite of grade LC300-99.99 was placed in a reaction vessel, and 50g of sulfuric acid solution with a mass fraction of 98% and 5g of nitric acid solution with a mass fraction of 65% were added. The mixture was heated and stirred in a water bath at 30℃ for 80min to obtain modified graphite. The modified graphite was rinsed with deionized water until the pH of the rinsing solution reached neutral. The washed modified graphite was then placed in an oven and dried at 60°C for 12 hours to remove moisture, thus obtaining the dried modified graphite. The dried modified graphite was placed in a high-temperature furnace and heated to 800°C at a heating rate of 20°C / min. It was then treated at this temperature for 60 seconds and then allowed to cool naturally to room temperature to obtain expanded graphite.

[0020] Preparation Example 2: The preparation method of expanded graphite specifically includes the following steps: 15g of high-purity graphite of grade LC300-99.99 was placed in a reaction vessel, and 75g of sulfuric acid solution with a mass fraction of 98% and 7.5g of nitric acid solution with a mass fraction of 65% were added. The mixture was heated and stirred in a water bath at 45℃ for 60min to obtain modified graphite. The modified graphite was rinsed with deionized water until the pH of the rinsing solution reached neutral. The washed modified graphite was then placed in an oven and dried at 80°C for 9 hours to remove moisture, thus obtaining the dried modified graphite. The dried modified graphite was placed in a high-temperature furnace and heated to 900°C at a heating rate of 20°C / min. It was then treated at this temperature for 35 seconds and then allowed to cool naturally to room temperature to obtain expanded graphite.

[0021] Preparation Example 3: The preparation method of expanded graphite specifically includes the following steps: 20g of high-purity graphite of grade LC300-99.99 was placed in a reaction vessel, and 100g of sulfuric acid solution with a mass fraction of 98% and 10g of nitric acid solution with a mass fraction of 65% were added. The mixture was heated and stirred in a water bath at 60℃ for 40min to obtain modified graphite. The modified graphite was rinsed with deionized water until the pH of the rinsing solution reached neutral. The washed modified graphite was then placed in an oven and dried at 100°C for 6 hours to remove moisture, thus obtaining the dried modified graphite. The dried modified graphite was placed in a high-temperature furnace and heated to 1000°C at a heating rate of 20°C / min. It was then treated at this temperature for 10 seconds and then allowed to cool naturally to room temperature to obtain expanded graphite.

[0022] Example 1: A preparation process for a halogen-free flame-retardant silicone rubber with synergistic effects of expanded graphite includes the following steps: Preheat the open mill to 60°C and adjust the roll gap to 2 mm. Add 50 parts by weight of methyl vinyl silicone rubber (the vinyl content of this rubber is 0.12 mol%, and the number average molecular weight is 700 kDa) to the open mill and pass it through the mill three times. Then widen the roll gap to 5 mm and plasticize for 5 min. After plasticizing, add 35 parts by weight of expanded graphite obtained in Preparation Example 1 and mix at 60°C for 5 min until there are no obvious graphite particles on the surface of the rubber compound. Then add 10 parts by weight of aluminum hydroxide and continue to mix at 60°C for 5 min. Then add 5 parts by weight of zinc borate and mix at 60°C for 5 min. Finally, add 0.5 parts by weight of dimethyl silicone oil (viscosity is 350 mPa·s) and mix at 60°C for 5 min to obtain the compound. The flat vulcanizing machine is preheated to 120°C. The above-obtained compound and 0.3 parts by weight of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane are added to the preheated flat vulcanizing machine. The temperature is then raised to 180°C, and the pressure of the flat vulcanizing agent is controlled at 15 MPa. The pressure vulcanization treatment is carried out for 20 minutes. After vulcanization, the product is naturally cooled to room temperature, demolded, and the burrs are removed to obtain halogen-free flame-retardant silicone rubber.

[0023] Example 2: A preparation process for a halogen-free flame-retardant silicone rubber with synergistic effects of expanded graphite includes the following steps: Preheat the open mill to 55°C, adjust the roll gap to 3 mm, add 50 parts by weight of methyl vinyl silicone rubber (the vinyl content of this rubber is 0.12 mol%, and the number average molecular weight is 700 kDa) into the open mill, pass it through the mill 4 times, and then widen the roll gap to 6 mm and plasticize for 8 min; after plasticizing, add 35 parts by weight of expanded graphite obtained in Preparation Example 2, and mix at 60°C for 7 min until there are no obvious graphite particles on the surface of the rubber compound, then add 10 parts by weight of aluminum hydroxide, and continue to mix at 60°C for 6 min, then add 5 parts by weight of zinc borate, and mix at 60°C for 7 min, and finally add 1 part by weight of dimethyl silicone oil (viscosity is 350 mPa·s) and mix at 60°C for 6 min to obtain the compound; The flat vulcanizing machine is preheated to the set temperature of 120°C. The above-obtained compound and 0.2 parts by weight of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane are added to the preheated flat vulcanizing machine. The temperature is then raised to 190°C, and the pressure of the flat vulcanizing agent is controlled at 13 MPa. The pressure vulcanization treatment is carried out for 15 minutes. After vulcanization, the product is naturally cooled to room temperature, demolded, and the burrs are removed to obtain halogen-free flame-retardant silicone rubber.

[0024] Example 3: A preparation process for a halogen-free flame-retardant silicone rubber with synergistic effects of expanded graphite includes the following steps: Preheat the open mill to 60°C and adjust the roll gap to 2 mm. Add 50 parts by weight of methyl vinyl silicone rubber (the vinyl content of this rubber is 0.12 mol%, and the number average molecular weight is 700 kDa) to the open mill and pass it through the mill three times. Then widen the roll gap to 5 mm and plasticize for 5 min. After plasticizing, add 35 parts by weight of expanded graphite obtained in Preparation Example 3 and mix at 60°C for 5 min until there are no obvious graphite particles on the surface of the rubber compound. Then add 10 parts by weight of aluminum hydroxide and continue to mix at 60°C for 5 min. Then add 5 parts by weight of zinc borate and mix at 60°C for 5 min. Finally, add 0.5 parts by weight of dimethyl silicone oil (viscosity is 350 mPa·s) and mix at 60°C for 5 min to obtain the compound. The flat vulcanizing machine is preheated to the set temperature of 120°C. The above-obtained compound and 0.1 parts by weight of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane are added to the preheated flat vulcanizing machine. The temperature is then raised to 200°C, and the pressure of the flat vulcanizing agent is controlled at 10 MPa. The pressure vulcanization treatment is carried out for 10 minutes. After vulcanization, the product is naturally cooled to room temperature, demolded, and the burrs are removed to obtain halogen-free flame-retardant silicone rubber.

[0025] Comparative Example 1: A preparation process for a halogen-free flame-retardant silicone rubber with synergistic effects of expanded graphite includes the following steps: High-purity graphite of grade LC300-99.99 was used instead of the expanded graphite obtained in Preparation Example 1, and the rest of the process was the same as in Example 1.

[0026] Comparative Example 2: A preparation process for a halogen-free flame-retardant silicone rubber with synergistic effects of expanded graphite includes the following steps: Zinc oxide was used instead of zinc borate, and the rest of the process was the same as in Example 1.

[0027] Comparative Example 3: A preparation process for a halogen-free flame-retardant silicone rubber with synergistic effects of expanded graphite includes the following steps: Magnesium hydroxide was used instead of aluminum hydroxide, and the rest of the process was the same as in Example 1.

[0028] (1) According to the vertical burning test in GB / T2408-2021, the flame retardant rating of the halogen-free flame retardant silicone rubbers obtained in Examples 1-3 and Comparative Examples 1-3 was tested, and the results are shown in Table 1.

[0029] Table 1 Flame retardant performance test results

[0030] (2) The oxygen index of the halogen-free flame-retardant silicone rubbers obtained in Examples 1-3 and Comparative Examples 1-3 was tested according to GB / T2406.2-2009, and the results are shown in Table 2.

[0031] Table 2 Oxygen Index Test Results

[0032] As can be seen from Tables 1-2, the flame retardant grades of the halogen-free flame-retardant silicone rubbers prepared by Examples 1-3 all reached FV-0. The oxygen index was also significantly improved compared with the halogen-free flame-retardant silicone rubbers prepared by Comparative Examples 1-3. The higher the oxygen index, the less likely the material is to burn. At high temperatures, the flame retardant properties and oxygen index of silicone rubber can be improved more significantly due to the synergistic effect of expanded graphite forming a dense porous carbon coating layer, aluminum hydroxide decomposing and releasing water vapor, and zinc borate forming a glassy coating layer.

[0033] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A synergistic halogen-free flame-retardant silicone rubber with expanded graphite, characterized in that, The halogen-free flame-retardant silicone rubber comprises the following raw materials by weight: 50 parts by weight of silica gel, 35 parts by weight of expanded graphite, 10 parts by weight of aluminum hydroxide, 5 parts by weight of zinc borate, 0.5-1.5 parts by weight of dimethyl silicone oil and 0.1-0.3 parts by weight of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

2. The synergistic intumescent halogen-free flame-retardant silicone rubber according to claim 1, characterized in that, The silica gel comprises methyl vinyl silicone rubber, the content of vinyl in the methyl vinyl silicone rubber is 0.12 mol%, and the number average molecular weight of the methyl vinyl silicone rubber is 700 kDa.

3. The synergistic intumescent halogen-free flame-retardant silicone rubber according to claim 1, characterized in that, The preparation method of the expanded graphite comprises the following steps: high-purity graphite with a brand of LC300-99.99, a sulfuric acid solution and a nitric acid solution are mixed in a mass ratio of 10:50:5 and heated to 30-60 DEG C for stirring reaction for 40-80 min to obtain modified graphite; the modified graphite is washed by deionized water and then dried at 60-100 DEG C for 6-12 h, and finally expanded at 800-1000 DEG C for 10-60 s to obtain expanded graphite.

4. The intumescent graphite synergistic halogen-free flame retardant silicone rubber according to claim 3, characterized in that, The sulfuric acid solution comprises a sulfuric acid solution with a mass fraction of 98%, and the nitric acid solution comprises a nitric acid solution with a mass fraction of 65%.

5. The synergistic intumescent halogen-free flame retardant silicone rubber according to claim 1, characterized in that, The viscosity of the dimethyl silicone oil comprises 350 mPa.s.

6. A method for preparing the synergistic halogen-free flame-retardant silicone rubber with expanded graphite according to any one of claims 1-5, characterized in that, The preparation method comprises the following steps: The silica gel is thin-pass plasticized, and then expanded graphite, aluminum hydroxide, zinc borate and dimethyl silicone oil are added in sequence to mix and knead to obtain a mixed rubber; the mixed rubber is mixed with 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane for vulcanization treatment to obtain a halogen-free flame-retardant silicone rubber.

7. The method according to claim 6, wherein the method is characterized by, The thin-pass plasticizing comprises a thin-pass process and a plasticizing process, the conditions of the thin-pass process comprise a thin-pass roll gap of 2-3 mm and a thin-pass frequency of 3-5 times, and the plasticizing process comprises a plasticizing roll gap of 5-6 mm, a plasticizing temperature of 50-60 DEG C and a plasticizing time of 5-10 min.

8. The method according to claim 6, wherein the method is characterized by, The mixing comprises adding expanded graphite at 60 DEG C first for mixing and kneading for 5-8 min, then adding aluminum hydroxide for mixing and kneading for 5-7 min, then adding zinc borate for mixing and kneading for 3-5 min, and finally adding dimethyl silicone oil for mixing and kneading for 5-8 min.

9. The method according to claim 6, wherein the method is characterized by, The conditions of the mixing vulcanization treatment comprise a vulcanization temperature of 180-200 DEG C, a vulcanization pressure of 10-15 MPa and a vulcanization treatment time of 10-20 min.

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