Highly flame retardant ceramifiable silicone rubber and method for its preparation

Abstract

The application relates to the field of flame-retardant silicone rubber, and particularly discloses high-flame-retardant ceramifiable silicone rubber and a preparation method thereof. The high-flame-retardant ceramifiable silicone rubber comprises the following raw materials in parts by weight: 100 parts of silicone rubber, 10-20 parts of hydroxyl silicone oil, 5-10 parts of a vulcanizing agent, 20-40 parts of low-melting-point glass powder, 3-5 parts of a plasticizer, 2-7 parts of a coupling agent, 10-20 parts of a ceramifiable aid, 15-25 parts of white carbon black, 10-30 parts of modified expandable graphite, and 10-20 parts of hydrophobic modified silica aerogel; the silicone rubber comprises methyl vinyl silicone rubber and liquid silicone rubber at a mass ratio of 1:0.5; and the modified expandable graphite comprises expandable graphite, halloysite, dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide at a mass ratio of 10:1-2:0.1-0.2:0.1-0.2. The ceramifiable silicone rubber disclosed by the application has good high-temperature resistance, strong flame-retardant capacity and high ceramic strength.

Description

Technical Field

[0001] This application relates to the field of flame-retardant silicone rubber, and more specifically, it relates to a highly flame-retardant ceramicized silicone rubber and its preparation method. Background Technology

[0002] With the development of technology, new energy vehicles are accounting for an increasingly larger proportion of the market. However, the safety of battery pack materials for new energy vehicles remains a significant challenge. To improve their safety performance, silicone rubber can be used as a material for battery packs. Silicone rubber itself has good thermal stability. When burned in a flame, the Si-O structure of silicone rubber transforms into a continuous, oxidation-resistant, and insulating network of silica ash covering the surface, effectively preventing further burning and providing a material basis for the ceramization of composite materials, thus greatly reducing the amount of ceramic filler added. At the same time, silicone rubber is a semi-organic and semi-inorganic material with a low heat release rate and low total heat release, resulting in a low fire index. Ceramicized silicone rubber can sinter into a ceramic-like object under flame, thus preventing high temperature damage to the interior. Furthermore, ceramicized silicone rubber materials do not contain halogen elements, have low smoke, are non-toxic, and corrosion-resistant, making them a high-performance fire-resistant material.

[0003] To improve the flame retardant properties and ceramic-forming effect of silicone rubber, flame retardants are generally added to the silicone rubber. For example, Chinese invention patent application CN2018112662152 discloses a method for preparing flame-retardant ceramicized silicone rubber. It uses methyl vinyl silicone rubber as the main material and nano magnesium hydroxide and nano aluminum hydroxide as flame retardants. First, the methyl vinyl silicone rubber is internally mixed, and then vulcanizing agent, modified glass powder, nano magnesium hydroxide, nano aluminum hydroxide, zinc borate, modified dispersant, coupling agent and plasticizer are added and mixed. The mixture is then molded into sheets and cold-pressed to obtain flame-retardant ceramicized silicone rubber.

[0004] Regarding the aforementioned technologies, the inventors discovered that while using magnesium hydroxide and aluminum hydroxide as flame retardants offers advantages such as low price, non-toxicity, smokelessness, and good thermal stability, their poor compatibility with the matrix material leads to agglomeration when mixed with the matrix, thereby affecting the flame retardant effect and mechanical strength of silicone rubber. Summary of the Invention

[0005] To improve the flame retardancy and mechanical strength of silicone rubber, this application provides a highly flame-retardant ceramicized silicone rubber and its preparation method.

[0006] In a first aspect, this application provides a highly flame-retardant ceramicized silicone rubber, employing the following technical solution:

[0007] A highly flame-retardant ceramicized silicone rubber comprises the following raw materials in parts by weight: 100 parts silicone rubber, 10-20 parts hydroxyl silicone oil, 5-10 parts vulcanizing agent, 20-40 parts low melting point glass powder, 3-5 parts plasticizer, 2-7 parts coupling agent, 10-20 parts ceramicizing agent, 15-25 parts silica, 10-30 parts modified expandable graphite, and 10-20 parts hydrophobic modified silica aerogel.

[0008] The silicone rubber comprises methyl vinyl silicone rubber and liquid silicone rubber in a mass ratio of 1:0.5;

[0009] The modified expandable graphite comprises expandable graphite, halloysite, dodecyltrimethylammonium bromide, and hexadecyltrimethylammonium bromide in a mass ratio of 10:1-2:0.1-0.2:0.1-0.2.

[0010] By adopting the above technical solution, silica aerogel is a porous material with a three-dimensional spatial network structure, possessing extremely low density, large specific surface area, high porosity, and extremely low thermal conductivity. Its nanoporous structure gives it a near-vacuum thermal insulation effect, significantly reducing heat transfer. When silica aerogel is combined with silicone rubber, it forms an effective thermal barrier, preventing flame and heat from transferring into the silicone rubber, thereby improving flame retardant performance. Furthermore, hydrophobically modified silica aerogel, added as a reinforcing filler to silicone rubber, can fill the gaps between silicone rubber molecular chains, forming a denser network structure. This structure restricts the movement of silicone rubber molecular chains, thereby improving its mechanical strength. The silanol groups (Si-OH) on the surface of hydrophobically modified silica aerogel can improve its compatibility with silicone rubber. The interaction between the silanol groups and the terminal hydroxyl groups in silicone rubber can enhance the interfacial interaction between silica aerogel and silicone rubber, further improving the mechanical strength of silicone rubber. After hydrophobic modification, good dispersion and compatibility in silicone rubber are ensured, giving full play to the reinforcing effect of silica aerogel, improving the dispersion of silica aerogel in silicone rubber, and thus more effectively improving its mechanical strength.

[0011] Dodecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide enable the uniform dispersion of expandable graphite and halloysite in silicone rubber. The layered structure of expandable graphite and halloysite can form a directional filling network in silicone rubber. Expandable graphite expands rapidly when heated, forming a physical barrier that prevents flame and heat from contacting the substrate, thereby improving the flame retardant properties of the material. The introduction of halloysite can improve the thermal stability of silicone rubber, making it less prone to decomposition at high temperatures and delaying the combustion process. Moreover, after halloysite burns, it can form a dense and compact residue layer on the surface of silicone rubber. This residue layer has a good thermal barrier effect, which can further prevent the spread of flame and the transfer of heat. In addition to flame retardant properties, halloysite and expandable graphite can also play a reinforcing role in ceramicized silicone rubber, thereby improving its mechanical properties such as tensile strength and elongation at break.

[0012] Preferably, the modified expandable graphite is prepared by the following method:

[0013] Halloysite was treated with acid, washed until neutral, and dried to obtain acid-treated halloysite. Cellulose nanospheres were added to distilled water to prepare a treatment solution with a concentration of 2-3 wt%. The acid-treated halloysite and expandable graphite were added, stirred and dispersed, and then dried to obtain pretreated expanded graphite. The mass ratio of cellulose nanospheres to halloysite was 0.5-1:1.

[0014] Dodecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide were added to deionized water and stirred for 10-20 minutes. The pretreated expanded graphite was then added, and the mixture was sonicated for 30-60 minutes and dried.

[0015] By employing the above technical solution, halloysite is a tubular nanomaterial composed of 1:1 layered aluminosilicate. Its inner wall has an aluminum-oxygen structure exhibiting a positive charge, while the outer wall has a silicon-oxygen structure exhibiting a negative charge. Cellulose nanospheres, a non-toxic and harmless natural substance used as a bio-based intumescent flame retardant, contain a large number of hydroxyl groups. When halloysite is acid-treated, the inner cavity of the tube is first eroded, gradually increasing the inner diameter and thinning the tube wall. Hydrogen ions in the acid react with the aluminum-oxygen structure on the surface of halloysite to form cations such as Al3+. These cations remain in the inner cavity of the halloysite nanotubes, thereby increasing the positive charge on the inner surface. Meanwhile, the hydroxyl groups on the surface of the cellulose nanospheres exhibit negative charge, allowing the cellulose nanospheres to bind to the acidified halloysite surface. Utilizing cellulose nanospheres to modify the surface of halloysite allows for the construction of a three-dimensional flame-retardant system with expanded graphite, reducing the popcorn effect of expanded graphite when heated and improving its flame-retardant effect. Halloysite, being tubular, can form a char layer after combustion. The three-dimensional network structure provides support for the expanded graphite carbon layer. Cellulose nanospheres are a novel type of nanocellulose with a nano-sized spherical morphology. Spherical nanocellulose particles have the characteristics of being lightweight, high strength, and high thermal stability. Their nano-size leads to an increased carbonization effect, which can form a dense carbon layer during combustion, thereby hindering heat transfer and oxygen diffusion, and playing a flame-retardant role. As a carbon source, cellulose nanospheres improve the density of the expanded graphite carbon layer after carbonization. Dodecyltrimethylammonium bromide is a cationic surfactant. Its positive surface charge can interact with the negative charge on the surface of expandable graphite, halloysite, and cellulose nanospheres through electrostatic adsorption and hydrogen bonding, adsorbing onto the modified halloysite surface and reducing the hydrophilicity of pretreated expanded graphite. Hexadecyltrimethylammonium bromide and dodecyltrimethylammonium bromide are compounded through electrostatic adsorption to obtain CS alkyl chains. CS alkyl chains are adsorbed onto pretreated expanded graphite through hydrogen bonding, improving the dispersibility and compatibility of expanded graphite in silicone rubber.

[0016] Optionally, the cellulose nanospheres undergo the following pretreatment:

[0017] Cellulose nanospheres were dispersed in ethylene glycol and water, sonicated for 20-30 min, and then chloroplatinic acid aqueous solution was added. The mixture was stirred at 120-130℃ for 2-3 h, centrifuged, washed, and dried at 60-70℃ to constant weight to obtain platinum-loaded cellulose nanospheres.

[0018] Platinum-loaded cellulose nanospheres and PAN nanofibers were mixed and added to a magnesium sulfate solution with a concentration of 2-3 wt%. After ultrasonic dispersion for 20-30 min, ammonia water was added, and the mixture was reacted at 30-40℃ for 2-3 h. The mixture was then filtered, heated to 200-220℃, and kept at that temperature for 8-10 h. The mass ratio of platinum-loaded cellulose nanospheres and PAN nanofibers to magnesium sulfate solution was 1:0.2-0.4:1-1.5.

[0019] By employing the above technical solutions, platinum loading reduces the initial thermal decomposition temperature and char residue of cellulose nanospheres. Furthermore, platinum can induce the breakage of Si-CH3 and the coupling of free radicals in silicone rubber at lower temperatures, forming crosslinking points and promoting crosslinking of the silicone rubber. Platinum loading enables the cellulose nanospheres to form a denser and higher char layer after combustion, and the silicone rubber to form a ceramic layer with higher density and ceramicization degree after combustion, thus exhibiting better flame retardant effects. Using ammonia as a precipitant, magnesium sulfate is converted into magnesium hydroxide, which adheres to PAN nanofibers and platinum-loaded cellulose nanospheres. The linear macromolecules of polyacrylonitrile form more cyclic structures through cyclization reactions, and the triple bond C≡N portion is reduced to C=N double bonds, thereby transforming polyacrylonitrile from thermoplastic to thermosetting. Therefore, after coating with magnesium hydroxide, heating... Heat treatment induces cyclization, hydrogenation, and oxidation reactions in PAN nanofibers. The cyclization reaction transforms the linear PAN chains into a cyclic ladder structure. Dehydrogenation removes hydrogen atoms from the molecules in the form of water. The oxidation reaction removes hydrogen from the intermolecular hydrogen and generates oxygen-containing groups, making the fibers more stable. Coating with magnesium hydroxide improves the thermal stability of PAN nanofibers and cellulose nanospheres. PAN is a polymer, and cellulose nanospheres are plant cellulose. Improving the thermal stability of both can avoid introducing new combustion sources when incorporating expandable graphite. Therefore, adding platinum-loaded cellulose nanospheres and PAN nanofibers, and coating them with magnesium hydroxide, can create an expanded carbon layer on the surface of silicone rubber and promote the formation of a cross-linked network in silicone rubber during combustion, thus improving the flexural strength after ceramicization.

[0020] Optionally, the hydrophobic modified silica aerogel is prepared as follows:

[0021] Prepare a dispersion of MXene nanosheets with a concentration of 5-10 mg / ml, add polyethylene glycol, sonicate for 10-20 min, remove air bubbles by vacuuming, and obtain a spraying solution;

[0022] The coating liquid is evenly sprayed onto the polyester fiber and dried at 50-60℃ for 20-24 hours to obtain the modified polyester fiber. The mass ratio of polyester fiber to coating liquid is 1:0.2-0.3.

[0023] Water glass and deionized water were mixed at a mass ratio of 1:10, the pH was adjusted to 3, modified polyester fiber was added dropwise, and ammonia was added dropwise. The mixture was then soaked in anhydrous ethanol for 24 hours for solvent exchange, and then soaked in a solution of perfluorochlorosilane in isopropanol for 20-24 hours. The mixture was dried under normal pressure to obtain hydrophobic modified silica aerogel. The amount of modified polyester fiber added was 2-2.5 wt% of the amount of water glass.

[0024] By adopting the above technical solution, the introduction of polyethylene glycol molecular chains improves the dispersibility of MXene nanosheets, allowing MXene nanosheets to be embedded in the polyethylene glycol molecular chains and form a strong bond. Simultaneously, the oxygen-containing functional groups in the molecular chains and the abundant -OH and -F surface functional groups on the MXene nanosheets can generate covalent bonds such as ether bonds, producing hydrogen bonding and various chemical and physical forces such as electrostatic adsorption. Therefore, under the action of polyethylene glycol, MXene nanosheets form a protective film on polyester fibers. When burned, MXene nanosheets can form a complete layered structure, obtaining a uniform brick-wall structure. Therefore, when added to silica aerogel, it can form an interwoven overlapping structure within the silica network structure. Silica particles are tightly entangled with fibers as the skeleton, resulting in a uniform particle structure and a distinct porous network structure. This effectively combines the polyester fibers and aerogel, effectively improving the toughness of the silica aerogel and thus improving the mechanical strength of the silicone rubber.

[0025] Optionally, the ceramic forming aid is selected from at least one of boric acid, zinc borate, sodium borate, mica powder, and kaolin.

[0026] By adopting the above technical solution, as the temperature rises, the ceramic additives continuously melt, making the contact between the fillers closer. When the temperature drops, a hard ceramic structure is formed, and the mechanical properties are improved accordingly.

[0027] Optionally, the coupling agent is selected from any one of titanate coupling agents, silane coupling agents, or aluminate coupling agents.

[0028] Optionally, the plasticizer is selected from any one of di-n-octyl phthalate, dibutyl phthalate, or dimethyl phthalate.

[0029] Optionally, the vulcanizing agent is selected from one of dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, and 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, preferably at least one of 2,4-dichlorobenzoyl peroxide.

[0030] Secondly, this application provides a method for preparing highly flame-retardant ceramicized silicone rubber, employing the following technical solution:

[0031] A method for preparing highly flame-retardant ceramicized silicone rubber includes the following steps:

[0032] S1. Knead the silicone rubber at 70-90℃ for 3-6 minutes, add modified expandable graphite and hydrophobic modified silica aerogel, white carbon black and hydroxyl silicone oil, and mix for 20-30 minutes to obtain the mixture.

[0033] S2. Add coupling agent, low melting point glass powder, ceramic forming agent and plasticizer to the mixture obtained in S1, and mix for 60-120 minutes.

[0034] S3. Vacuum treatment is performed on the product obtained in S2, and after cooling, a vulcanizing agent is added and the mixture is kneaded for 10-20 minutes.

[0035] S4. The product obtained in S3 is subjected to primary and secondary vulcanization to obtain highly flame-retardant ceramicized silicone rubber.

[0036] By adopting the above technical solution, various raw materials are mixed, kneaded, vulcanized and other processes to produce ceramicized silicone rubber with good flame retardancy and high ceramic strength.

[0037] Optionally, the primary vulcanization temperature is 140-180℃, the time is 20-40 min, and the pressure is 10-15 MPa; the secondary vulcanization temperature is 180℃-200℃, and the time is 60-180 min.

[0038] In summary, this application has the following beneficial effects:

[0039] 1. This application uses raw materials such as silicone rubber, low-melting-point glass powder, and ceramic additives, and utilizes modified expandable graphite and hydrophobic modified silica aerogel as flame retardants. The modified expandable graphite is made of expandable graphite, halloysite, dodecyltrimethylammonium bromide, and hexadecyltrimethylammonium bromide. Dodecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide can uniformly disperse the expanded graphite and halloysite in the silicone rubber, thereby forming a directional filling network, which can achieve excellent flame retardant effect, prevent the spread of flame and heat transfer, and further improve the mechanical strength of silicone rubber.

[0040] 2. In this application, it is preferred to add cellulose nanospheres to modified expandable graphite, which can further increase the density of the char layer formed after the expansion graphite and halloysite are burned, and improve the flame retardant effect. Moreover, the cellulose nanospheres are pretreated with chloroplatinic acid, and platinum is loaded on their surface. Then, they are mixed with PAN nanofibers and magnesium sulfate and heat-treated to form magnesium hydroxide on the platinum-loaded cellulose nanospheres and PAN nanofibers. After heat treatment, the PAN nanofibers undergo cyclization and other reactions, which improves their heat resistance and stability. Therefore, the pretreatment of cellulose nanospheres with platinum, PAN nanofibers, magnesium sulfate, etc. can further improve the flame retardant effect of cellulose nanospheres and avoid introducing new combustion sources.

[0041] 3. In this application, hydrophobically modified silica aerogel containing MXene nanosheets and polyester fibers is preferred. The MXene nanosheets are uniformly dispersed under the action of polyethylene glycol and attached to the polyester fibers. Then, the polyester fibers overlap each other in the silica aerogel, which improves the mechanical strength of the silica aerogel, while the MXene nanosheets further improve the flame retardant effect of the polyester fibers. Detailed Implementation

[0042] The present application will be further described in detail below with reference to the embodiments.

[0043] Preparation Examples of Modified Expandable Graphite 1-10

[0044] Preparation Example 1: (1) 100g halloysite was added to 300ml concentrated hydrochloric acid, stirred at 50℃ for 1h, cooled to room temperature, washed with deionized water until neutral, filtered and dried at 105℃ to obtain acid-treated halloysite.

[0045] (2) Add 10g dodecyltrimethylammonium bromide and 10g hexadecyltrimethylammonium bromide to 1000g deionized water, stir and mix for 20min, add acid-treated halloysite and expanded graphite, sonicate for 30min, and dry at 80℃ for 20h.

[0046] Preparation Example 2: The difference from Preparation Example 1 is that an equal amount of deionized water is used instead of dodecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide.

[0047] Preparation Example 3: The difference from Preparation Example 1 is that halloysite was not added.

[0048] Preparation Example 4: (1) 100g halloysite was added to 300ml of concentrated hydrochloric acid, stirred at 50°C for 1h, cooled to room temperature, washed with deionized water until neutral, filtered and dried at 105°C to obtain acid-treated halloysite.

[0049] (2) 100g of cellulose nanospheres were added to distilled water to prepare a treatment solution with a concentration of 3wt%. Acid-treated halloysite and 1000g of expandable graphite were added. After stirring for 30min, the solution was dried at 80℃ to obtain pretreated expanded graphite. The mass ratio of cellulose nanospheres to halloysite was 1:1. Preparation of cellulose nanospheres: Short cotton lint paperboard was cut into pieces, soaked in a sodium hydroxide solution with a concentration of 18wt% for 24h, washed with deionized water until neutral, and dried at 60℃ to obtain pretreated cellulose. The mass ratio of short cotton lint paperboard to sodium hydroxide solution was 1:40. The pretreated cellulose and a phosphoric acid solution with a concentration of 85wt% were mixed at a mass ratio of 1:50. The mixture was heated to 50℃ and stirred in a water bath for 10h. After adding 10 times the mass of deionized water to the mixture, it was allowed to stand. The supernatant was removed, the precipitate was centrifuged, dialyzed until neutral, and then freeze-dried.

[0050] (3) Add 10g dodecyltrimethylammonium bromide and 10g hexadecyltrimethylammonium bromide to 1000g deionized water, stir and mix for 20min, add pretreated expanded graphite, sonicate for 30min, and dry at 80℃ for 20h.

[0051] Preparation Example 5: (1) 200g halloysite was added to 300ml concentrated hydrochloric acid, stirred at 50°C for 1h, cooled to room temperature, washed with deionized water until neutral, filtered and dried at 105°C to obtain acid-treated halloysite.

[0052] (2) 100g of cellulose nanospheres were added to distilled water to prepare a treatment solution with a concentration of 2wt%. Acid-treated halloysite and 1000g of expandable graphite were added. After stirring for 30min, the solution was dried at 80℃ to obtain pretreated expanded graphite. The mass ratio of cellulose nanospheres to halloysite was 0.5:1. Preparation of cellulose nanospheres: Short cotton lint paperboard was cut into pieces, soaked in a sodium hydroxide solution with a concentration of 18wt% for 24h, washed with deionized water until neutral, and dried at 60℃ to obtain pretreated cellulose. The mass ratio of short cotton lint paperboard to sodium hydroxide solution was 1:40. The pretreated cellulose and a phosphoric acid solution with a concentration of 85wt% were mixed at a mass ratio of 1:50. The mixture was heated to 50℃ and stirred in a water bath for 10h. After adding 10 times the mass of deionized water to the mixture, it was allowed to stand. The supernatant was removed, the precipitate was centrifuged, dialyzed until neutral, and then freeze-dried.

[0053] (3) Add 20g dodecyltrimethylammonium bromide and 20g hexadecyltrimethylammonium bromide to 1000g deionized water, stir and mix for 10min, add pretreated expanded graphite, sonicate for 60min, and dry at 80℃ for 20h.

[0054] Preparation Example 6: The difference from Preparation Example 4 is that the cellulose nanospheres were pretreated according to the following method:

[0055] 1 g of cellulose nanospheres were dispersed in 300 ml of ethylene glycol and 200 ml of water, sonicated for 20 min, and then 1 ml of 0.0386 mol / L chloroplatinic acid aqueous solution was added. The mixture was stirred at 120 °C for 3 h, centrifuged, washed three times with deionized water, and dried at 60 °C to constant weight to obtain platinum-loaded cellulose nanospheres.

[0056] 10g of platinum-loaded cellulose nanospheres and 4g of PAN nanofibers were mixed and added to 15g of 3wt% magnesium sulfate solution. After ultrasonic dispersion for 30min, 5ml of ammonia water was added and reacted at 30℃ for 3h. After filtration, the temperature was raised to 200℃ and kept at 20h for 10h. The PAN nanofibers had a diameter of 500nm and a length of 2μm.

[0057] Preparation Example 7: The difference from Preparation Example 4 is that the cellulose nanospheres were pretreated according to the following method:

[0058] 1 g of cellulose nanospheres were dispersed in 300 ml of ethylene glycol and 200 ml of water, sonicated for 30 min, and then 1 ml of 0.0386 mol / L chloroplatinic acid aqueous solution was added. The mixture was stirred at 130 °C for 2 h, centrifuged, washed three times with deionized water, and dried at 70 °C to constant weight to obtain platinum-loaded cellulose nanospheres.

[0059] 10g of platinum-loaded cellulose nanospheres and 2g of PAN nanofibers were mixed and added to 10g of 2wt% magnesium sulfate solution. After ultrasonic dispersion for 20min, 4ml of ammonia water was added and reacted at 40℃ for 2h. After filtration, the temperature was raised to 220℃ and kept at 8h. The PAN nanofibers had a diameter of 500nm and a length of 2μm.

[0060] Preparation Example 8: The difference from Preparation Example 6 is that no aqueous solution of chloroplatinic acid was added.

[0061] Preparation Example 9: The difference from Preparation Example 6 is that magnesium sulfate solution and ammonia were not added. Platinum-loaded cellulose nanospheres and PAN nanofibers were mixed and kept at 220°C for 8 hours.

[0062] Preparation Example 10: The difference from Preparation Example 6 is that PAN nanofibers, magnesium sulfate solution and ammonia were not added. Instead, 1g of cellulose nanospheres were dispersed in 300ml of ethylene glycol and 200ml of water, sonicated for 20min, and then 1ml of 0.0386mol / l chloroplatinic acid aqueous solution was added. The mixture was stirred at 120℃ for 3h, centrifuged, washed 3 times with deionized water, and dried at 60℃ to constant weight.

[0063] Preparation Examples of Hydrophobically Modified Silica Aerogels 11-14

[0064] Preparation Example 11: (1) 5 ml of water and 15 ml of hydrochloric acid were added to a polytetrafluoroethylene beaker and stirred. 1 g of LiF was added and waited for 5 min. MAX precursor was added (added in batches over 30 min). The beaker was covered and stirred for 24 h. The mixture was centrifuged at 4000 r / min for 5 min. After the pH of the supernatant of the final solution was greater than 6, the bottom precipitate was freeze-dried to obtain multi-layer MXene. After ultrasonic vibration and centrifugation, single-layer MXene was obtained. MXene nanosheets were dispersed in deionized water to prepare an MXene nanosheet dispersion with a concentration of 10 mg / ml. Polyethylene glycol with a mass ratio of 1:1 to MXene nanosheets was added. The mixture was ultrasonically treated for 20 min and vacuumed for 10 min to remove bubbles to obtain a spraying solution.

[0065] (2) Spray 3g of spray liquid evenly onto 10g of polyester fiber and dry it at 60℃ for 20h to obtain modified polyester fiber with a length of 3mm and a diameter of 20D.

[0066] (3) Mix 50g of water glass and deionized water at a mass ratio of 1:10, adjust the pH to 3 with concentrated sulfuric acid, add modified polyester fiber dropwise, add ammonia water dropwise, soak in anhydrous ethanol for 24h for solvent exchange, then soak in a mixed solution of 1g perfluorochlorosilane and 250ml isopropanol for 24h, and dry under normal pressure to obtain hydrophobic modified silica aerogel. The amount of modified polyester fiber added is 2.5wt% of the amount of water glass.

[0067] Preparation Example 12: (1) 5 ml of water and 15 ml of hydrochloric acid were added to a polytetrafluoroethylene beaker and stirred. 1 g of LiF was added and waited for 5 min. MAX precursor was added (added in batches over 30 min). The beaker was covered and stirred for 24 h. The mixture was centrifuged at 4000 r / min for 5 min. After the pH of the supernatant of the final solution was greater than 6, the bottom precipitate was freeze-dried to obtain multi-layer MXene. After ultrasonic vibration and centrifugation, single-layer MXene was obtained. MXene nanosheets were dispersed in deionized water to prepare an MXene nanosheet dispersion with a concentration of 5 mg / ml. Polyethylene glycol with a mass ratio of 1:1 to MXene nanosheets was added. The mixture was ultrasonically treated for 10 min and vacuumed for 15 min to remove bubbles to obtain a spraying solution.

[0068] (2) Spray 2g of spray liquid evenly onto 10g of polyester fiber and dry at 50℃ for 24h to obtain modified polyester fiber with a length of 3mm and a diameter of 20D.

[0069] (3) Mix 50g of water glass and deionized water at a mass ratio of 1:10, adjust the pH to 3 with concentrated sulfuric acid, add modified polyester fiber and then add ammonia water, soak in anhydrous ethanol for 24h for solvent exchange, then soak in a mixed solution of 1g perfluorochlorosilane and 250ml isopropanol for 20h, and dry under normal pressure to obtain hydrophobic modified silica aerogel. The amount of modified polyester fiber added is 2wt% of the amount of water glass.

[0070] Preparation Example 13: The difference from Preparation Example 11 is that the coating liquid containing MXene nanosheets was not sprayed onto the polyester fiber.

[0071] Preparation Example 14: The difference from Preparation Example 11 is that no modified polyester fiber was added.

[0072] Example

[0073] Example 1: A high flame-retardant ceramicized silicone rubber, the raw material amounts are shown in Table 1, wherein the silicone rubber includes methyl vinyl silicone rubber and liquid silicone rubber in a mass ratio of 1:0.5. The methyl vinyl silicone rubber is selected from Shenzhen Anchengxing Technology, model 110-1, and the liquid silicone rubber is selected from Shandong Dinghong New Materials, model 107, item number 325. The vulcanizing agent is dicumyl peroxide, the low melting point glass powder is selected from Foshan Chuangguo Chemical, model BL-55, the plasticizer is di-n-octyl phthalate, the coupling agent is silane coupling agent KH550, the ceramicizing aid is zinc borate, the modified expandable graphite is prepared from Preparation Example 1, and the hydrophobic modified silica aerogel is prepared from Preparation Example 11.

[0074] The preparation method of the above-mentioned high flame-retardant ceramicized silicone rubber includes the following steps:

[0075] S1. Knead the silicone rubber at 90°C for 3 minutes, add modified expandable graphite and hydrophobic modified silica aerogel, fumed silica and hydroxyl silicone oil, and continue to mix at 90°C for 20 minutes to obtain the mixture.

[0076] S2. Add coupling agent, low melting point glass powder, ceramic forming agent and plasticizer to the mixture obtained in S1, and mix at 90°C for 60 minutes.

[0077] S3. The product obtained in S2 is subjected to vacuum treatment, and after cooling, a vulcanizing agent is added. The mixture is then kneaded at 30°C for 20 minutes. The vacuum treatment temperature is 90°C, the vacuum degree is -0.06MPa, and the vacuum treatment time is 20 minutes.

[0078] S4. The product obtained in S3 is subjected to primary and secondary vulcanization to obtain high flame-retardant ceramicized silicone rubber. The primary vulcanization temperature is 180℃, the time is 20min, and the pressure is 15MPa. The secondary vulcanization temperature is 180℃, the pressure is 12MPa, and the time is 180min.

[0079] Table 1. Raw material dosage of high flame-retardant ceramicized silicone rubber in Examples 1-3

[0080]

[0081] Example 2: A high flame-retardant ceramicized silicone rubber, the raw material amounts are shown in Table 1, wherein the silicone rubber includes methyl vinyl silicone rubber and liquid silicone rubber in a mass ratio of 1:0.5. The methyl vinyl silicone rubber is selected from Shenzhen Anchengxing Technology, model 110-1, and the liquid silicone rubber is selected from Shandong Dinghong New Materials, model 107, item number 325. The vulcanizing agent is 2,4-dichlorobenzoyl peroxide, the low melting point glass powder is selected from Foshan Chuangguo Chemical, model BL-55, the plasticizer is dibutyl phthalate, the coupling agent is silane coupling agent KH550, the ceramicizing aid is mica powder, the modified expandable graphite is prepared from Preparation Example 1, and the hydrophobic modified silica aerogel is prepared from Preparation Example 12.

[0082] The preparation method of the above-mentioned high flame-retardant ceramicized silicone rubber includes the following steps:

[0083] S1. Knead the silicone rubber at 70°C for 6 minutes, add modified expandable graphite and hydrophobic modified silica aerogel, fumed silica and hydroxyl silicone oil, and continue to knead at 70°C for 30 minutes to obtain the mixture.

[0084] S2. Add coupling agent, low melting point glass powder, ceramic forming agent and plasticizer to the mixture obtained in S1, and mix at 70°C for 120 min.

[0085] S3. The product obtained in S2 is subjected to vacuum treatment, and after cooling, a vulcanizing agent is added. The mixture is then kneaded at 30°C for 20 minutes. The vacuum treatment temperature is 110°C, the vacuum degree is -0.03MPa, and the vacuum treatment time is 30 minutes.

[0086] S4. The product obtained in S3 is subjected to primary and secondary vulcanization to obtain high flame-retardant ceramicized silicone rubber. The primary vulcanization temperature is 140℃, the time is 30min, and the pressure is 10MPa. The secondary vulcanization temperature is 200℃, the pressure is 18MPa, and the time is 60min.

[0087] Example 3: A high flame retardant ceramicized silicone rubber, which differs from Example 1 in that the amount of raw materials used is shown in Table 1.

[0088] Example 4: A highly flame-retardant ceramicized silicone rubber, which differs from Example 1 in that the hydrophobically modified silica aerogel is prepared by Example 13.

[0089] Example 5: A highly flame-retardant ceramicized silicone rubber, which differs from Example 1 in that the hydrophobically modified silica aerogel is prepared by Example 14.

[0090] Example 6: A highly flame-retardant ceramicized silicone rubber, which differs from Example 1 in that the modified expandable graphite is prepared from Preparation Example 4.

[0091] Example 7: A highly flame-retardant ceramicized silicone rubber, which differs from Example 1 in that the modified expandable graphite is prepared from Preparation Example 5.

[0092] Example 8: A highly flame-retardant ceramicized silicone rubber, which differs from Example 6 in that the modified expandable graphite is prepared from Preparation Example 6.

[0093] Example 9: A highly flame-retardant ceramicized silicone rubber, which differs from Example 6 in that the modified expandable graphite is prepared from Preparation Example 7.

[0094] Example 10: A highly flame-retardant ceramicized silicone rubber, which differs from Example 9 in that the modified expandable graphite is prepared by Example 8.

[0095] Example 11: A highly flame-retardant ceramicized silicone rubber, which differs from Example 9 in that the modified expandable graphite is prepared from Preparation Example 9.

[0096] Example 12: A highly flame-retardant ceramicized silicone rubber, which differs from Example 9 in that the modified expandable graphite is made from Preparation Example 10.

[0097] Comparative Example

[0098] Comparative Example 1: A highly flame-retardant ceramicized silicone rubber, which differs from Example 1 in that the modified expandable graphite is prepared from Preparation Example 2.

[0099] Comparative Example 2: A highly flame-retardant ceramicized silicone rubber, which differs from Example 1 in that the modified expandable graphite is prepared from Preparation Example 3.

[0100] Comparative Example 3: A highly flame-retardant ceramicized silicone rubber, which differs from Example 1 in that an equal amount of expandable graphite is used instead of modified expandable graphite.

[0101] Comparative Example 4: A highly flame-retardant ceramicized silicone rubber, which differs from Example 1 in that an equal amount of hydrophobic modified silica aerogel is used instead of modified expandable graphite.

[0102] Performance testing

[0103] Ceramicized silicone rubber was prepared according to the methods in the examples and comparative examples, and its performance was tested according to the following methods. The test results are recorded in Table 2.

[0104] 1. Limiting oxygen index: The test is conducted in accordance with GB / T10707-2008, and the instrument is a JF-3 limiting oxygen index meter.

[0105] 2. Tensile strength and elongation at break: Tested in accordance with GB / T528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber".

[0106] 3. Bending strength after ablation: The test standard is GB / T6569-2006 "Test method for bending strength of fine ceramics". Silicone rubber is made into a sample of 80mm×10mm×3mm, placed in a tube furnace, heated to 800℃ at a rate of 10℃ / min, held for 30min, and tested using the "three-point bending method" with a loading rate of 2mm / min and a span of 60mm.

[0107] Table 2 Performance testing of high flame-retardant ceramicized silicone rubber

[0108]

[0109] As can be seen from the data in Table 2, the modified expandable graphite prepared by Preparation Example 1, the hydrophobic modified silica aerogel prepared by Preparation Examples 11-12, and the ceramicized silicone rubber prepared by silicone rubber, etc., have an oxygen index higher than 28%, have excellent flame retardant effect, and have a tensile strength greater than 6MPa, strong bending and tensile resistance, and high bending strength after being etched into ceramic.

[0110] In Example 4, the hydrophobic modified silica aerogel prepared in Preparation Example 13 was used. Compared with Preparation Example 11, Preparation Example 13 did not spray the coating liquid containing MXene nanosheets onto the polyester fiber. As can be seen in Table 2, the oxygen index of the ceramicized silicone rubber prepared in Example 4 was reduced, and the bending strength after ceramicization was reduced. It can be seen that MXene nanosheets can enhance the flame retardant effect of silica aerogel and enhance the ceramicization strength.

[0111] In Example 5, the hydrophobic modified silica aerogel prepared in Preparation Example 14 was used, in which polyester fibers with MXene nanosheets on the surface were not added. As can be seen in Table 2, the flame retardant effect of the ceramicized silicone rubber was weakened, and the tensile strength and other properties also decreased significantly.

[0112] Compared with Example 1, Examples 6 and 7 used modified expandable graphite prepared in Preparation Example 4 and Preparation Example 5, respectively. Compared with Preparation Example 1, a certain amount of cellulose nanospheres were also added. The data in Table 2 show that the ceramicized silicone rubber prepared in Examples 6 and 7 has better flame retardant effect, increased oxygen index, and greater bending strength after ablation.

[0113] In Examples 8 and 9, modified expandable graphite prepared in Preparation Examples 6 and 7 were used, respectively. Compared with Example 6 which used Preparation Example 4, the cellulose nanospheres in Examples 8 and 9 were further treated with platinum and PAN nanofibers, which shows that the flame retardant effect of the ceramicized silicone rubber prepared in Examples 8 and 9 is enhanced.

[0114] In Example 10, the modified expandable graphite prepared in Preparation Example 8 was used. Compared with Preparation Example 6 in Example 9, no aqueous solution of chloroplatinic acid was added, that is, no platinum was loaded on the cellulose nanospheres. It can be seen that its flame retardant effect was slightly reduced and its bending strength was reduced after ceramicization.

[0115] Compared with Example 9, Example 11 uses the modified expandable graphite prepared in Example 9, in which magnesium sulfate solution and ammonia were not added. Platinum-loaded cellulose nanospheres were mixed with PAN nanofibers and treated at high temperature to prepare modified expandable graphite. It can be seen that the flame retardant effect of the ceramicized silicone rubber prepared in this way is reduced.

[0116] In Example 12, the modified expandable graphite prepared in Preparation Example 10 was used. In Preparation Example 10, no PAN nanofibers and magnesium sulfate were added, and platinum was loaded only on cellulose nanospheres. As shown in Table 2, the tensile strength of the ceramicized silicone rubber prepared in Example 12 decreased and the ceramicized flexural strength weakened.

[0117] Comparative Examples 1 and 2 used modified expandable graphite prepared in Preparation Example 2 and Preparation Example 3, respectively. Preparation Example 2 did not add dodecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide, and Preparation Example 3 did not add halloysite. It can be seen that the tensile strength of the ceramicized silicone rubber prepared in Comparative Example 1 was significantly reduced and the flame retardant properties were weakened. Although the tensile strength of Comparative Example 2 did not change much, the flame retardant effect was weakened.

[0118] Expandable graphite was used in Comparative Example 3, and hydrophobic modified silica aerogel was used to replace expandable graphite in Comparative Example 2. The data in Table 2 show that the flame retardant effect of the ceramicized silicone rubber prepared in Comparative Example 3 and Comparative Example 4 decreased significantly, and the ceramic strength and mechanical properties also decreased.

[0119] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A highly flame-retardant ceramicized silicone rubber, characterized in that, The raw materials include the following parts by weight: 100 parts silicone rubber, 10-20 parts hydroxyl silicone oil, 5-10 parts vulcanizing agent, 20-40 parts low melting point glass powder, 3-5 parts plasticizer, 2-7 parts coupling agent, 10-20 parts ceramic forming agent, 15-25 parts silica, 10-30 parts modified expandable graphite, and 10-20 parts hydrophobic modified silica aerogel. The silicone rubber comprises methyl vinyl silicone rubber and liquid silicone rubber in a mass ratio of 1:0.5; The modified expandable graphite comprises expandable graphite, halloysite, dodecyltrimethylammonium bromide, and hexadecyltrimethylammonium bromide in a mass ratio of 10:1-2:0.1-0.2:0.1-0.2; The method for preparing the modified expandable graphite is as follows: Halloysite was treated with acid, washed until neutral, and dried to obtain acid-treated halloysite. Cellulose nanospheres were added to distilled water to prepare a treatment solution with a concentration of 2-3 wt%. The acid-treated halloysite and expandable graphite were added, stirred and dispersed, and then dried to obtain pretreated expanded graphite. The mass ratio of cellulose nanospheres to halloysite was 0.5-1:

1. Dodecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide were added to deionized water and stirred for 10-20 minutes. The pretreated expanded graphite was then added, and the mixture was sonicated for 30-60 minutes and dried. The hydrophobic modified silica aerogel is prepared as follows: Prepare a dispersion of MXene nanosheets with a concentration of 5-10 mg / ml, add polyethylene glycol, sonicate for 10-20 min, remove air bubbles by vacuuming, and obtain a spraying solution; The coating liquid is evenly sprayed onto the polyester fiber and dried at 50-60℃ for 20-24 hours to obtain the modified polyester fiber. The mass ratio of polyester fiber to coating liquid is 1:0.2-0.

3. Water glass and deionized water were mixed at a mass ratio of 1:10, the pH was adjusted to 3, modified polyester fiber was added dropwise, and ammonia was added dropwise. The mixture was then soaked in anhydrous ethanol for 24 hours for solvent exchange, and then soaked in a solution of perfluorochlorosilane in isopropanol for 20-24 hours. The mixture was dried under normal pressure to obtain hydrophobic modified silica aerogel. The amount of modified polyester fiber added was 2-2.5 wt% of the amount of water glass.

2. The high flame-retardant ceramicized silicone rubber according to claim 1, characterized in that: The cellulose nanospheres underwent the following pretreatment: Cellulose nanospheres were dispersed in ethylene glycol and water, sonicated for 20-30 min, and then chloroplatinic acid aqueous solution was added. The mixture was stirred at 120-130℃ for 2-3 h, centrifuged, washed, and dried at 60-70℃ to constant weight to obtain platinum-loaded cellulose nanospheres. Platinum-loaded cellulose nanospheres and PAN nanofibers were mixed and added to a magnesium sulfate solution with a concentration of 2-3 wt%. After ultrasonic dispersion for 20-30 min, ammonia water was added, and the mixture was reacted at 30-40℃ for 2-3 h. The mixture was then filtered, heated to 200-220℃, and kept at that temperature for 8-10 h. The mass ratio of platinum-loaded cellulose nanospheres and PAN nanofibers to magnesium sulfate solution was 1:0.2-0.4:1-1.

5.

3. The high flame-retardant ceramicized silicone rubber according to claim 1, characterized in that: The ceramic forming additive is selected from at least one of boric acid, zinc borate, sodium borate, mica powder, and kaolin.

4. The high flame-retardant ceramicized silicone rubber according to claim 1, characterized in that: The coupling agent is selected from any one of titanate coupling agents, silane coupling agents, or aluminate coupling agents.

5. The high flame-retardant ceramicized silicone rubber according to claim 1, characterized in that: The plasticizer is selected from any one of di-n-octyl phthalate, dibutyl phthalate, or dimethyl phthalate.

6. The high flame-retardant ceramicized silicone rubber according to claim 1, characterized in that: The vulcanizing agent is selected from one of dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, and 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane.

7. The method for preparing the high flame-retardant ceramicized silicone rubber according to any one of claims 1-6, characterized in that: Includes the following steps: S1. Knead the silicone rubber at 70-90℃ for 3-6 minutes, add modified expandable graphite and hydrophobic modified silica aerogel, white carbon black and hydroxyl silicone oil, and mix for 20-30 minutes to obtain the mixture. S2. Add coupling agent, low melting point glass powder, ceramic forming agent and plasticizer to the mixture obtained in S1, and mix for 60-120 minutes. S3. Vacuum treatment is performed on the product obtained in S2, and after cooling, a vulcanizing agent is added and the mixture is kneaded for 10-20 minutes. S4. The product obtained in S3 is subjected to primary and secondary vulcanization to obtain highly flame-retardant ceramicized silicone rubber.

8. The method for preparing high flame-retardant ceramicized silicone rubber according to claim 7, characterized in that: The primary vulcanization temperature is 140-180℃, the time is 20-40 min, and the pressure is 10-15 MPa. The secondary vulcanization temperature is 180℃-200℃, and the time is 60-180 min.

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