High-flame-retardant organic silicon foam sheet and preparation method thereof

Abstract

The invention discloses a high-flame-retardant organic silicon foam sheet and a preparation method thereof, and belongs to the technical field of organic silicon. The foam sheet is prepared from polydimethylsiloxane, methyltriethoxysilane, nano-modified zinc borate, an intumescent flame retardant, pretreated graphene oxide, polyethylene glycol, azodiisobutyronitrile and a catalyst. The preparation method comprises the following steps: mixing polydimethylsiloxane with methyltriethoxysilane, sequentially adding a modified flame retardant system, pretreated graphene oxide and an auxiliary agent, heating and uniformly stirring, and then adding a foaming agent and a catalyst; according to the modified flame retardant system, a glass layer and an expanded carbon layer are formed through the synergistic effect of nano-modified zinc borate and an intumescent flame retardant, and the flame retardance and dispersity are enhanced through pretreated graphene oxide. The tensile strength of the product reaches 0.52-0.71 MPa, the compression strength reaches 0.60-0.65 MPa, the oxygen index is 38-40, the vertical combustion reaches V-0, the foam expansion is 15-17, and the product has efficient flame retardance, excellent mechanical properties and light weight.

Description

Technical Field

[0001] The present invention relates to the technical field of silicone, and particularly to a highly flame-retardant silicone foam sheet and a preparation method thereof. Background Art

[0002] As a lightweight, porous, and high-temperature-resistant material, silicone foam sheets have been widely used in fields such as construction, aerospace, and electronic devices due to their excellent physical properties and chemical stability. In recent years, with the continuous increase in the demand for fire safety, the research and development of highly flame-retardant silicone foams have become a research hotspot in this field. The development of related technologies has evolved from the physical doping of single flame retardants to the design of composite flame-retardant systems. Early technologies mainly improved the flame-retardant performance of materials by adding inorganic flame retardants (such as aluminum hydroxide and magnesium hydroxide) or organic flame retardants (such as phosphate esters). Subsequently, a synergistic flame-retardant mechanism was gradually introduced, for example, combining intumescent flame retardants with charring agents to form a denser heat-insulating carbon layer. In addition, with the progress of nanotechnology, nano-fillers such as graphene and montmorillonite have also been tried to enhance the flame retardancy and thermal stability of foams. At the same time, significant progress has been made in the optimization of the preparation process. For example, by controlling the crosslinking density and pore structure during the foaming process, the mechanical properties and flame-retardant effect of the material are further improved. However, although the above technologies have improved the flame-retardant performance of silicone foams to a certain extent, their development is still limited by challenges such as flame-retardant efficiency, durability, and processing complexity.

[0003] Although the existing technologies have achieved certain achievements in the field of highly flame-retardant silicone foams, their deficiencies are still significant, especially in terms of flame-retardant efficiency, where there is still much room for improvement. Taking borate as an example, as a common flame retardant, its application in silicone foams is limited due to its low flame-retardant efficiency. Borate mainly inhibits combustion by releasing crystal water to absorb heat and forming a glassy protective layer, but its action mechanism is relatively single and difficult to effectively cope with continuous thermal decomposition and oxygen penetration at high temperatures, resulting in an unsatisfactory flame-retardant effect. Summary of the Invention

[0004] Although the existing technologies have achieved certain achievements in the field of highly flame-retardant silicone foams, their deficiencies are still significant, especially in terms of flame-retardant efficiency, where there is still much room for improvement. Taking borate as an example, as a common flame retardant, its application in silicone foams is limited due to its low flame-retardant efficiency. Borate mainly inhibits combustion by releasing crystal water to absorb heat and forming a glassy protective layer, but its action mechanism is relatively single and difficult to effectively cope with continuous thermal decomposition and oxygen penetration at high temperatures, resulting in an unsatisfactory flame-retardant effect.

[0005] The present application provides a preparation method for a highly flame-retardant silicone foam sheet, including the following technical steps:

[0006] Step S1. In a stirring device, mix polydimethylsiloxane and methyltriethoxysilane at a mixed stirring speed. Sequentially add the modified flame retardant system, pretreated graphene oxide, and additives. Heat and stir to ensure uniform dispersion of the components. Add the foaming agent and catalyst, and continue stirring to obtain a mixed material.

[0007] Step S2. Pour the mixed material into a mold and place it in a foaming furnace to allow the mixed material to fully expand to form a porous structure. Transfer the foamed material to a curing furnace to form a stable crosslinked network.

[0008] Step S3. Take out the cured foam sheet, naturally cool it to room temperature, and trim it to the required size with cutting equipment to obtain a highly flame-retardant silicone foam sheet.

[0009] It should be noted that in Step S1, polydimethylsiloxane and methyltriethoxysilane are mixed and stirred to form a crosslinked precursor. The hydrolysis and condensation reaction of methyltriethoxysilane provides the basis for the subsequent network. After adding the modified flame retardant system (nano-modified zinc borate and intumescent flame retardant), the borate glass layer and intumescent carbon layer mechanisms synergistically retard combustion. The pretreated graphene oxide delays the penetration of heat and oxygen through the two-dimensional barrier effect. The additives improve the dispersibility. The foaming agent and catalyst regulate the pore generation and curing rate to ensure the uniformity of the mixed material. In Step S2, the high temperature in the foaming furnace causes the decomposition of the foaming agent, and it expands to form a porous structure. The crosslinking reaction is completed in the curing furnace to construct a stable network, enhancing the mechanical and flame-retardant properties. Step S3 ensures the practicality of the material through cooling and trimming. This process achieves the balance between high-efficiency flame retardancy and lightness through chemical crosslinking and physical structure optimization.

[0010] As a preferred technical solution for the preparation method of a highly flame-retardant silicone foam sheet, the preparation method of the modified flame retardant system includes: Take zinc borate, add an ethanol solution according to a mass ratio of 1:5, add 3-8 wt% trimethyl phosphate, stir at 60 °C for 2 hours, ultrasonically disperse for 30 minutes, filter, and dry at 80 °C for 4 hours to obtain nano-modified zinc borate; Dry mix melamine triazine and cyanuric acid in a mass ratio of 1:2 for 10 minutes, add 20 wt% water and stir into a paste, pre-react at 50 °C for 30 minutes, dry at 100 °C for 2 hours, and grind to obtain an intumescent flame retardant; Mix the two in a ratio of 2:1 and stir at 300 rpm for 20 minutes to obtain the modified flame retardant system.

[0011] It should be noted that when preparing nano-modified zinc borate, zinc borate is dispersed in an ethanol solution at a mass ratio of 1:5 to increase surface exposure. Subsequently, 3-8 wt% of trimethyl phosphate is added, and the mixture is stirred at 60 °C for 2 hours to graft phosphate groups through an esterification reaction, enhancing the surface activity. Ultrasonic dispersion is carried out for 30 minutes to break up agglomerates, reducing the particle size and increasing the specific surface area. Drying is performed at 80 °C for 4 hours to solidify the modified layer. This modification makes it easier for zinc borate to decompose to generate boric acid and be converted into boron oxide (B2O3), forming a dense glass layer that isolates oxygen and heat, while absorbing heat to lower the temperature. Secondly, when preparing the intumescent flame retardant, melamine tris(2,4,6-triaminotriazine) and cyanuric chloride are dry-mixed at a ratio of 1:2 for 10 minutes for uniform contact, 20 wt% of water is added and stirred into a paste, and pre-reaction is carried out at 50 °C for 30 minutes to promote preliminary interaction. Drying is performed at 100 °C for 2 hours and then ground into fine particles. Finally, the two are mixed at a ratio of 2:1 and stirred at 300 rpm for 20 minutes to ensure dispersion. The cyanuric acid generated by cyanuric chloride and melamine tris(2,4,6-triaminotriazine) form carbon together. The hydroxyl group of cyanuric acid and the amino group of melamine tris(2,4,6-triaminotriazine) form a denser carbon layer structure during dehydration crosslinking, providing a uniform attachment matrix for the glass layer of zinc borate and enhancing the barrier stability. In addition, the large amounts of gases (N2, NH3) released by melamine tris(2,4,6-triaminotriazine) and cyanuric chloride and the water vapor decomposed from zinc borate act together to promote the rapid expansion of the carbon layer, forming a porous heat-insulating structure to further isolate heat and oxygen.

[0012] As a preferred technical solution of a preparation method of a high-flame-retardant silicone foam sheet, in step S1, the average particle size of the zinc borate is 1 to 5 μm.

[0013] It should be noted that the particle size within this range ensures that zinc borate has a high specific surface area in the matrix, facilitating the graft modification of trimethyl phosphate, enhancing the surface activity, promoting the decomposition at high temperature to generate boric acid and boron oxide, and forming a dense glass layer to isolate oxygen. If the particle size is too small, it is easy to agglomerate and reduce the dispersibility; if it is too large, the reaction contact area will be reduced and the flame retardant efficiency will decline.

[0014] As a preferred technical solution of a preparation method of a high-flame-retardant silicone foam sheet, in step S1, the preparation steps of the pretreated graphene oxide include: taking graphene oxide, adding deionized water at 1-5 mg / mL, performing ultrasonic dispersion for 30 minutes, dissolving KH-550 in ethanol / water at a ratio of 1:10, adjusting the pH to 4-5, stirring for 10 minutes, adding the suspension to the silane solution with a mass ratio of 1:1, stirring at 50 °C for 2 hours, centrifuging, washing 3 times with ethanol and water, drying in vacuum at 50 °C for 6 hours, grinding through a 200-mesh sieve to obtain pretreated graphene oxide.

[0015] It should be noted that graphene oxide is added to deionized water at 1-5 mg / mL and ultrasonically dispersed for 30 minutes. The mechanical energy of ultrasonic waves is used to exfoliate the lamellae, exposing the surface hydroxyl and carboxyl groups, and increasing the reaction activity. Then, the silane coupling agent KH-550 (γ-aminopropyltriethoxysilane) is dissolved in an ethanol / water mixed solvent at a ratio of 1:10, the pH is adjusted to 4-5 and stirred for 10 minutes. KH-550 hydrolyzes to form silanol groups (-Si-OH), and the acidic environment optimizes the hydrolysis rate. The graphene oxide suspension and the silane solution are mixed at a mass ratio of 1:1 and stirred at 50 °C for 2 hours. The silanol groups undergo dehydration condensation reactions with the hydroxyl groups on the surface of graphene oxide: GO-OH + HO-Si-R → GO-O-Si-R + H2O. The grafting of aminopropyl groups improves the compatibility with the matrix. After centrifugal separation, it is washed 3 times with ethanol and water to remove unreacted substances, and vacuum-dried at 50 °C for 6 hours to cure the modified layer, and ground through a 200-mesh sieve to ensure uniform particle size. The pretreated graphene oxide enhances the flame retardancy and dispersibility through the two-dimensional barrier effect and surface modification.

[0016] As a preferred technical solution of a preparation method of a highly flame-retardant silicone foam sheet, the auxiliary agent is polyethylene glycol.

[0017] It should be noted that polyethylene glycol can improve the uniform dispersion of components in the polydimethylsiloxane matrix. At the same time, the hydrophilicity of polyethylene glycol and the hydrophobicity of silicone form an interfacial bridge, improving the compatibility between the filler and the matrix and reducing interfacial defects. In addition, it can act as a trace lubricant during the foaming process, optimizing the consistency of the formation of the pore structure, and ultimately enhancing the flame retardancy efficiency and mechanical properties of the foam.

[0018] As a preferred technical solution of a preparation method of a highly flame-retardant silicone foam sheet, the foaming agent is azobisisobutyronitrile.

[0019] It should be noted that azobisisobutyronitrile decomposes when heated to about 60 to 80 °C, releasing nitrogen and forming free radicals. Nitrogen, as an inert gas, expands rapidly at a high temperature of about 80 to 120 °C in the foaming furnace, pushing the polydimethylsiloxane matrix to form a uniform porous structure, improving the lightness of the foam. The free radicals generated by decomposition can initiate a small amount of cross-linking reactions, synergizing with methyltriethoxysilane to enhance the network stability.

[0020] As a preferred technical solution of a preparation method of a highly flame-retardant silicone foam sheet, in step S3, the temperature of the foaming furnace is controlled at 80-120 °C, the foaming time is 10-15 minutes, the temperature of the curing furnace is 150-180 °C, and the curing time is 30-60 minutes.

[0021] It should be noted that the foaming temperature and time ensure the efficient decomposition of the foaming agent and the uniform expansion of nitrogen to form a porous structure, taking into account both lightness and flame retardancy; the curing temperature and time promote the complete cross-linking reaction, generate a stable Si-O-Si network, and improve mechanical strength and thermal stability; the process parameter matching optimizes the synchronization of foaming and curing, uniform structure, extended flame retardant time, and improved overall flame retardant efficiency.

[0022] In addition, the present invention provides a highly flame-retardant silicone foam sheet prepared by the above preparation method, which includes, by mass: 50 to 70 parts of polydimethylsiloxane, 5 to 10 parts of methyltriethoxysilane, 5 to 10 parts of nano-modified zinc borate, 10 to 20 parts of intumescent flame retardant, 2 to 5 parts of pretreated graphene oxide, 1 to 3 parts of auxiliary agent, 3 to 8 parts of foaming agent and 0.5 to 2 parts of catalyst.

[0023] It should be noted that 50 to 70 parts of polydimethylsiloxane provide flexibility and high temperature resistance as a matrix. 5 to 10 parts of methyltriethoxysilane form a cross-linked network through hydrolysis and condensation to improve structural stability. 5 to 10 parts of nano-modified zinc borate decompose at high temperature to generate boric acid and boron oxide, forming a glass layer to isolate oxygen. 10 to 20 parts of intumescent flame retardant release nitrogen and catalyze carbonization to form an intumescent carbon layer, which cooperates with zinc borate to flame retardant. 2 to 5 parts of pretreated graphene oxide blocks heat transfer with a two-dimensional structure. 1 to 3 parts of auxiliary agent polyethylene glycol improves dispersibility through hydrogen bonding. 3 to 8 parts of foaming agent azobisisobutyronitrile decompose to produce nitrogen and construct a porous structure. 0.5 to 2 parts of dibutyltin dilaurate catalyze the cross-linking of siloxane to ensure synchronization of foaming and curing, and optimize flame retardancy and mechanical properties.

[0024] The highly flame-retardant organic silicon foam sheet and the preparation method thereof provided by the present invention have significant beneficial effects. By optimizing components such as polydimethylsiloxane, nano-modified zinc borate, intumescent flame retardant and pretreated graphene oxide and their synergistic effects, and combining precise foaming and curing processes, a foam sheet having excellent flame retardant properties (oxygen index 38-40, vertical combustion V-0), mechanical properties (tensile strength 0.52-0.71MPa, compressive strength 0.60-0.65MPa) and lightness (foaming multiple 15-17) is prepared; the nano-modified zinc borate and the intumescent flame retardant form a dual flame retardant mechanism of a glass layer and an intumescent carbon layer, the pretreated graphene oxide enhances the two-dimensional barrier effect and dispersibility, and the polyethylene glycol improves the compatibility, significantly improving the flame retardant efficiency, durability and processing stability, and is suitable for the fields of construction, aerospace and electronic equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 The influence of the mass ratio of nano-modified zinc borate and intumescent flame retardant on the oxygen index. Specific embodiments

[0027] To make the above objects, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention will be described in detail below in conjunction with the embodiments of the specification.

[0028] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar promotions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0029] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure or characteristic that can be included in at least one implementation manner of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it an embodiment that is separate or selectively exclusive of other embodiments.

[0030] Preparation examples

[0031] Preparation example 1

[0032] The preparation steps of the pretreated graphene oxide include: taking graphene oxide, adding deionized water at 1-5 mg / mL, ultrasonic dispersing for 30 minutes, dissolving KH-550 in ethanol / water at a ratio of 1:10, adjusting the pH to 4-5, stirring for 10 minutes, adding the suspension to the silane solution with a mass ratio of 1:1, stirring at 50 °C for 2 hours, centrifuging, washing 3 times with ethanol and water, vacuum drying at 50 °C for 6 hours, grinding through a 200-mesh sieve to obtain pretreated graphene oxide.

[0033] Preparation example 2

[0034] The preparation method of the modified flame retardant system includes:

[0035] Taking zinc borate, adding an ethanol solution at a mass ratio of 1:5, adding 3-8 wt% trimethyl phosphate, stirring at 60 °C for 2 hours, ultrasonic dispersing for 30 minutes, filtering, drying at 80 °C for 4 hours to obtain nano-modified zinc borate;

[0036] Dry-mixing melamine tris (2,4,6-triaminotriazine) and cyanuric acid at a mass ratio of 1:2 for 10 minutes, adding 20 wt% water and stirring into a paste, pre-reacting at 50 °C for 30 minutes, drying at 100 °C for 2 hours, grinding to obtain an intumescent flame retardant;

[0037] Mixing the two at a ratio of 2:1 and stirring at 300 rpm for 20 minutes to obtain a modified flame retardant system.

[0038] Example

[0039] Example 1

[0040] Embodiment 1 provides a highly flame-retardant silicone foam sheet and a preparation method thereof, wherein:

[0041] A highly flame-retardant silicone foam sheet, comprising, by weight: 50 parts of polydimethylsiloxane, 8 parts of methyltriethoxysilane, 5 parts of nano-modified zinc borate, 10 parts of intumescent flame retardant, 3 parts of pretreated graphene oxide, 1 part of auxiliary agent (polyethylene glycol), 5 parts of foaming agent (azobisisobutyronitrile) and 0.5 parts of catalyst (dibutyltin dilaurate);

[0042] The preparation method of the flame retardant silicone foam sheet comprises the following technical steps:

[0043] Step S1. In a stirring device, 50 parts of polydimethylsiloxane and 8 parts of methyltriethoxysilane were mixed at a stirring speed of 200 rpm for 10 minutes, 15 parts of a modified flame retardant system (Preparation Example 2), 3 parts of pretreated graphene oxide (Preparation Example 1) and 1 part of an auxiliary agent were added in sequence, the temperature was raised to 40°C, and high-speed stirring (500 rpm) was performed for 20 minutes to ensure that the components were evenly dispersed, 5 parts of a blowing agent and 0.5 parts of a catalyst were added, and stirring was continued for 5 minutes to obtain a mixture;

[0044] Step S2. Pour the mixture into a mold, place it in a foaming furnace, control the temperature to 100°C, and foam for 15 minutes to allow the mixture to fully expand to form a porous structure. Transfer the foamed material to a curing furnace and cure it at 180°C for 30 minutes to form a stable cross-linked network.

[0045] Step S3. Take out the solidified foam sheet, cool it naturally to room temperature, and trim it into a desired size using a cutting device to obtain a highly flame-retardant silicone foam sheet.

[0046] Example 2

[0047] Embodiment 2 provides a highly flame-retardant silicone foam sheet and a preparation method thereof, wherein:

[0048] A highly flame-retardant silicone foam sheet, comprising, by weight: 70 parts of polydimethylsiloxane, 10 parts of methyltriethoxysilane, 8 parts of nano-modified zinc borate, 16 parts of an intumescent flame retardant, 2 parts of pretreated graphene oxide, 3 parts of an auxiliary agent (polyethylene glycol), 3 parts of a foaming agent (azobisisobutyronitrile) and 1 part of a catalyst (dibutyltin dilaurate);

[0049] The preparation method of the flame retardant silicone foam sheet comprises the following technical steps:

[0050] Step S1. In a stirring device, mix 70 parts of polydimethylsiloxane with 10 parts of methyltriethoxysilane at a stirring speed of 200 rpm for 10 minutes. Then, successively add 24 parts of the modified flame retardant system (Preparation Example 2), 2 parts of pretreated graphene oxide (Preparation Example 1), and 3 parts of the additive. Heat the mixture to 40°C and stir at a high speed (500 rpm) for 20 minutes to ensure uniform dispersion of the components. Add 3 parts of the blowing agent and 1 part of the catalyst, and continue stirring for 5 minutes to obtain a mixed material.

[0051] Step S2. Pour the mixed material into a mold and place it in a foaming furnace. Control the temperature at 80°C and the foaming time at 15 minutes to allow the mixed material to fully expand and form a porous structure. Transfer the foamed material to a curing furnace and cure it at 150°C for 60 minutes to form a stable crosslinked network.

[0052] Step S3. Take out the cured foam sheet, naturally cool it to room temperature, and trim it to the required size using cutting equipment to obtain a highly flame-retardant silicone foam sheet.

[0053] Example 3

[0054] Example 3 provides a highly flame-retardant silicone foam sheet and a preparation method thereof. Among them,

[0055] The highly flame-retardant silicone foam sheet, by mass, includes: 65 parts of polydimethylsiloxane, 7 parts of methyltriethoxysilane, 9 parts of nano-modified zinc borate, 18 parts of intumescent flame retardant, 3 parts of pretreated graphene oxide, 1 part of additive (polyethylene glycol), 8 parts of blowing agent (azobisisobutyronitrile), and 0.5 part of catalyst (dibutyltin dilaurate);

[0056] The preparation method of the flame-retardant silicone foam sheet includes the following technical steps:

[0057] Step S1. In a stirring device, mix 65 parts of polydimethylsiloxane with 7 parts of methyltriethoxysilane at a stirring speed of 200 rpm for 10 minutes. Then, successively add 27 parts of the modified flame retardant system (Preparation Example 2), 3 parts of pretreated graphene oxide (Preparation Example 1), and 1 part of the additive. Heat the mixture to 40°C and stir at a high speed (500 rpm) for 20 minutes to ensure uniform dispersion of the components. Add 8 parts of the blowing agent and 0.5 part of the catalyst, and continue stirring for 5 minutes to obtain a mixed material.

[0058] Step S2. Pour the mixed material into a mold and place it in a foaming furnace. Control the temperature at 120°C and the foaming time at 10 minutes to allow the mixed material to fully expand and form a porous structure. Transfer the foamed material to a curing furnace and cure it at 160°C for 50 minutes to form a stable crosslinked network.

[0059] Step S3. Take out the cured foam sheet, naturally cool it to room temperature, and trim it into the required size with a cutting device to obtain a highly flame-retardant silicone foam sheet.

[0060] Example 4

[0061] Example 4 provides a highly flame-retardant silicone foam sheet and its preparation method, wherein,

[0062] The highly flame-retardant silicone foam sheet, by mass, comprises: 60 parts of polydimethylsiloxane, 6 parts of methyltriethoxysilane, 7 parts of nano-modified zinc borate, 14 parts of intumescent flame retardant, 2 parts of pretreated graphene oxide, 3 parts of an auxiliary agent (polyethylene glycol), 5 parts of a foaming agent (azobisisobutyronitrile), and 0.5 part of a catalyst (dibutyltin dilaurate);

[0063] The preparation method of the flame-retardant silicone foam sheet comprises the following technical steps:

[0064] Step S1. In a stirring device, mix 60 parts of polydimethylsiloxane with 6 parts of methyltriethoxysilane at a stirring speed of 200 rpm for 10 minutes. Then, successively add 21 parts of the modified flame retardant system (Preparation Example 2), 2 parts of pretreated graphene oxide (Preparation Example 1), and 3 parts of the auxiliary agent, heat up to 40 °C, and stir at a high speed (500 rpm) for 20 minutes to ensure uniform dispersion of the components. Add 5 parts of the foaming agent and 0.5 part of the catalyst, and continue stirring for 5 minutes to obtain a mixture;

[0065] Step S2. Pour the mixture into a mold, place it in a foaming furnace, control the temperature at 100 °C, and foam for 10 minutes to allow the mixture to fully expand to form a porous structure. Transfer the foamed material to a curing furnace and cure it at 180 °C for 60 minutes to form a stable crosslinked network

[0066] Step S3. Take out the cured foam sheet, naturally cool it to room temperature, and trim it into the required size with a cutting device to obtain a highly flame-retardant silicone foam sheet.

[0067] Example 5

[0068] Example 5 provides a highly flame-retardant silicone foam sheet and its preparation method, wherein,

[0069] The highly flame-retardant silicone foam sheet, by mass, comprises: 68 parts of polydimethylsiloxane, 6 parts of methyltriethoxysilane, 7.5 parts of nano-modified zinc borate, 7.5 parts of intumescent flame retardant, 2 parts of pretreated graphene oxide, 3 parts of an auxiliary agent (polyethylene glycol), 5 parts of a foaming agent (azobisisobutyronitrile), and 2 parts of a catalyst (dibutyltin dilaurate);

[0070] The preparation method of the flame-retardant silicone foam sheet comprises the following technical steps:

[0071] Step S1. In a stirring device, mix 68 parts of polydimethylsiloxane with 8 parts of methyltriethoxysilane at a stirring speed of 200 rpm for 10 minutes. Then, sequentially add 20 parts of the modified flame retardant system (Preparation Example 2), 2 parts of pretreated graphene oxide (Preparation Example 1), and 3 parts of an auxiliary agent. Heat the mixture to 40°C and stir at a high speed (500 rpm) for 20 minutes to ensure uniform dispersion of the components. Add 5 parts of a foaming agent and 2 parts of a catalyst, and continue stirring for 5 minutes to obtain a mixed material.

[0072] Step S2. Pour the mixed material into a mold and place it in a foaming furnace. Control the temperature at 120°C and the foaming time at 15 minutes to allow the mixed material to fully expand and form a porous structure. Transfer the foamed material to a curing furnace and cure it at 160°C for 30 minutes to form a stable cross-linked network.

[0073] Step S3. Take out the cured foam sheet, naturally cool it to room temperature, and trim it into the required size using cutting equipment to obtain a highly flame-retardant silicone foam sheet.

[0074] Example 6

[0075] Example 6 provides a highly flame-retardant silicone foam sheet and a preparation method thereof, wherein

[0076] The highly flame-retardant silicone foam sheet, by mass, comprises: 68 parts of polydimethylsiloxane, 6 parts of methyltriethoxysilane, 5 parts of nano-modified zinc borate, 10 parts of an intumescent flame retardant, 2 parts of pretreated graphene oxide, 3 parts of an auxiliary agent (polyethylene glycol), 5 parts of a foaming agent (azobisisobutyronitrile), and 2 parts of a catalyst (dibutyltin dilaurate);

[0077] The preparation method of the flame-retardant silicone foam sheet comprises the following technical steps:

[0078] Step S1. In a stirring device, mix 68 parts of polydimethylsiloxane with 8 parts of methyltriethoxysilane at a stirring speed of 200 rpm for 10 minutes. Then, sequentially add 20 parts of the modified flame retardant system (Preparation Example 2), 2 parts of pretreated graphene oxide (Preparation Example 1), and 3 parts of an auxiliary agent. Heat the mixture to 40°C and stir at a high speed (500 rpm) for 20 minutes to ensure uniform dispersion of the components. Add 5 parts of a foaming agent and 2 parts of a catalyst, and continue stirring for 5 minutes to obtain a mixed material.

[0079] Step S2. Pour the mixed material into a mold and place it in a foaming furnace. Control the temperature at 120°C and the foaming time at 15 minutes to allow the mixed material to fully expand and form a porous structure. Transfer the foamed material to a curing furnace and cure it at 160°C for 30 minutes to form a stable cross-linked network.

[0080] Step S3. Take out the solidified foam sheet, cool it naturally to room temperature, and trim it into a desired size using a cutting device to obtain a highly flame-retardant silicone foam sheet.

[0081] Example 7

[0082] Embodiment 7 provides a highly flame-retardant silicone foam sheet and a preparation method thereof, wherein:

[0083] A highly flame-retardant silicone foam sheet, comprising, by weight: 68 parts of polydimethylsiloxane, 6 parts of methyltriethoxysilane, 3.75 parts of nano-modified zinc borate, 11.25 parts of an intumescent flame retardant, 2 parts of pretreated graphene oxide, 3 parts of an auxiliary agent (polyethylene glycol), 5 parts of a foaming agent (azobisisobutyronitrile) and 2 parts of a catalyst (dibutyltin dilaurate);

[0084] The preparation method of the flame retardant silicone foam sheet comprises the following technical steps:

[0085] Step S1. In a stirring device, 68 parts of polydimethylsiloxane and 8 parts of methyltriethoxysilane were mixed at a stirring speed of 200 rpm for 10 minutes, 20 parts of a modified flame retardant system (Preparation Example 2), 2 parts of pretreated graphene oxide (Preparation Example 1) and 3 parts of an additive were added in sequence, the temperature was raised to 40°C, and high-speed stirring (500 rpm) was performed for 20 minutes to ensure that the components were evenly dispersed, 5 parts of a blowing agent and 2 parts of a catalyst were added, and stirring was continued for 5 minutes to obtain a mixture;

[0086] Step S2. Pour the mixture into a mold, place it in a foaming furnace, control the temperature to 120°C, and foam for 15 minutes to allow the mixture to fully expand to form a porous structure. Transfer the foamed material to a curing furnace and cure it at 160°C for 30 minutes to form a stable cross-linked network.

[0087] Step S3. Take out the solidified foam sheet, cool it naturally to room temperature, and trim it into a desired size using a cutting device to obtain a highly flame-retardant silicone foam sheet.

[0088] Example 8

[0089] Embodiment 8 provides a highly flame-retardant silicone foam sheet and a preparation method thereof, wherein:

[0090] A highly flame-retardant silicone foam sheet, comprising, by weight: 68 parts of polydimethylsiloxane, 6 parts of methyltriethoxysilane, 3 parts of nano-modified zinc borate, 12 parts of an intumescent flame retardant, 2 parts of pretreated graphene oxide, 3 parts of an auxiliary agent (polyethylene glycol), 5 parts of a foaming agent (azobisisobutyronitrile) and 2 parts of a catalyst (dibutyltin dilaurate);

[0091] The preparation method of the flame retardant silicone foam sheet comprises the following technical steps:

[0092] Step S1. In a stirring device, 68 parts of polydimethylsiloxane and 8 parts of methyltriethoxysilane are mixed at a stirring speed of 200 rpm for 10 minutes. Then, 20 parts of the modified flame retardant system (Preparation Example 2), 2 parts of pretreated graphene oxide (Preparation Example 1), and 3 parts of an auxiliary agent are sequentially added. The temperature is raised to 40°C, and high-speed stirring (500 rpm) is carried out for 20 minutes to ensure uniform dispersion of the components. 5 parts of a foaming agent and 2 parts of a catalyst are added, and stirring is continued for 5 minutes to obtain a mixed material;

[0093] Step S2. The mixed material is poured into a mold and placed in a foaming furnace. The temperature is controlled at 120°C, and the foaming time is 15 minutes to allow the mixed material to fully expand to form a porous structure. The foamed material is transferred to a curing furnace and cured at 160°C for 30 minutes to form a stable cross-linked network

[0094] Step S3. The cured foam sheet is taken out, naturally cooled to room temperature, and trimmed to the required size using cutting equipment to obtain a highly flame-retardant silicone foam sheet.

[0095] Examples 6 to 8 are different from Example 5 in the mass ratio of nano-modified zinc borate and intumescent flame retardant, as shown in Table 1 below.

[0096] Table 1

[0097]

[0098] Control Example

[0099] Control Example 1

[0100] This Control Example 1 is different from Example 1 in that nano-modified zinc borate is replaced with an equal amount of polydimethylsiloxane.

[0101] Control Example 2

[0102] This Control Example 2 is different from Example 1 in that the intumescent flame retardant is replaced with an equal amount of polydimethylsiloxane.

[0103] Control Example 3

[0104] This control example is different from Example 1 in that pretreated graphene oxide is replaced with an equal amount of untreated graphene oxide.

[0105] Control Example 4

[0106] This control example is different from Example 1 in that nano-modified zinc borate is replaced with zinc borate.

[0107] Table 2

[0108]

[0109]

[0110] Note: In Comparative Example 3 in the table, there are 3 portions of un-pretreated graphene oxide, and in Comparative Example 4, there are 5 portions of zinc borate.

[0111] Performance detection test

[0112] Tensile strength: Tested in accordance with GB / T528 / 2009.

[0113] Oxygen index: Tested in accordance with GB / T2406.1-2008.

[0114] Vertical burning: Tested in accordance with UL94.

[0115] Foaming multiple: Tested in accordance with GB / T1410-2006.

[0116] Compressive strength: Tested in accordance with GB / T1041-2008.

[0117] Table 3 Experimental data of Examples 1 to 4 and Comparative Examples 1 to 4

[0118]

[0119] Combined with Examples 1 to 4 and Table 3, it can be seen that the preparation method of the highly flame-retardant silicone foam sheet provided by the present invention, by optimizing the components (such as polydimethylsiloxane, modified flame retardant system, pre-treated graphene oxide, etc.) and process parameters (such as foaming and curing conditions), successfully prepares a foam sheet with excellent performance, which has tensile strength (0.52 - 0.71 MPa), compressive strength (0.30 - 0.35 MPa at 40% compression, 0.60 - 0.65 MPa at 60% compression), flame retardant performance (oxygen index 38 - 40, vertical burning V-0) and foaming multiple (15 - 17).

[0120] Combined with Example 1, Comparative Example 1, Comparative Example 2 and Table 3, it can be seen that the oxygen index of the foam prepared in Example 1 is 38, and the vertical burning grade is V-0, which is significantly better than the oxygen index of 30 and vertical burning V-1 of Comparative Example 1, and the oxygen index of 32 and vertical burning V-1 of Comparative Example 2. This indicates that the synergistic effect of nano-modified zinc borate and intumescent flame retardant significantly increases the flame retardant effect of the foam.

[0121] It can be seen from Example 1, Comparative Example 3 and Table 3 that the foam prepared in Example 1 is superior to Comparative Example 3 in all properties. The tensile strength of Example 1 is 0.52 MPa, the 40% compressive strength is 0.30 MPa, the 60% compressive strength is 0.60 MPa, the oxygen index is 38, the vertical burning is V-0, and the foaming multiple is 15; while those of Comparative Example 3 are 0.41 MPa, 0.28 MPa, 0.55 MPa, 34, V-1 and 12 respectively. Example 1 uses pretreated graphene oxide, improves the dispersibility and compatibility through silane grafting, enhances the two-dimensional barrier effect, and improves the flame retardancy (the oxygen index is increased by 4 units and the combustion grade reaches V-0), while optimizing the mechanical properties and foaming structure. Comparative Example 3 uses untreated graphene oxide, and the agglomeration leads to a comprehensive decline in performance, verifying the necessity of pretreatment.

[0122] It can be seen from Example 1, Comparative Example 4 and the data in Table 3 that the foam prepared in Example 1 is superior to Comparative Example 4 in all properties. The tensile strength of Example 1 is 0.52 MPa, the 40% compressive strength is 0.30 MPa, the 60% compressive strength is 0.60 MPa, the oxygen index is 38, the vertical burning is V-0, and the foaming multiple is 15; while those of Comparative Example 4 are 0.35 MPa, 0.27 MPa, 0.54 MPa, 33, V-1 and 14.8 respectively. Example 1 uses nano-modified zinc borate (modified by trimethyl phosphate), with enhanced surface activity and improved dispersibility, and decomposes to form a dense boron oxide glass layer, improving the flame retardancy (the oxygen index is 5 units higher and the combustion grade reaches V-0) and mechanical properties. Comparative Example 4 uses unmodified zinc borate, and the agglomeration leads to a decline in flame retardancy and mechanical properties, verifying the importance of modification.

[0123] Combined with Examples 5 to 8 and Figure 1 it can be seen that the mass ratio of nano-modified zinc borate to the intumescent flame retardant has a significant impact on the flame retardancy of the high-flame-retardant silicone foam sheet. When the mass ratio reaches 1:2, the oxygen index reaches the maximum value of 39. When the mass ratio continues to increase, the flame retardancy decreases significantly.

[0124] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a highly flame-retardant silicone foam sheet, characterized in that, It includes the following technical steps: Step S1. In a stirring device, mix polydimethylsiloxane and methyltriethoxysilane, stir at a mixing speed, successively add a modified flame retardant system, pretreated graphene oxide, and an auxiliary agent, raise the temperature and stir to ensure uniform dispersion of the components, add a foaming agent and a catalyst, and continue stirring to obtain a mixed material; Step S2. Pour the mixed material into a mold and place it in a foaming furnace to allow the mixed material to fully expand to form a porous structure. Transfer the foamed material to a curing furnace to form a stable cross-linked network. Step S3. Take out the cured foam sheet, naturally cool it to room temperature, and trim it into the required size with a cutting device to obtain a highly flame-retardant silicone foam sheet.

2. The preparation method of the highly flame-retardant silicone foam sheet according to claim 1, characterized in that, The preparation method of the modified flame retardant system includes: Take zinc borate, add an ethanol solution according to a mass ratio of 1:5, add 3-8 wt% trimethyl phosphate, stir at 60 °C for 2 hours, ultrasonically disperse for 30 minutes, filter, and dry at 80 °C for 4 hours to obtain nano-modified zinc borate; Dry-mix melamine cyanurate and cyanuric chloride in a mass ratio of 1:2 for 10 minutes, add 20 wt% water and stir into a paste, pre-react at 50 °C for 30 minutes, dry at 100 °C for 2 hours, and grind to obtain an intumescent flame retardant; Mix the two in a ratio of 2:1 and stir at 300 rpm for 20 minutes to obtain a modified flame retardant system.

3. The preparation method of the highly flame-retardant silicone foam sheet according to claim 2, characterized in that, In step S1, the average particle size of the zinc borate is 1 to 5 μm.

4. The preparation method of the highly flame-retardant silicone foam sheet according to claim 1, characterized in that In step S1, the preparation steps of the pretreated graphene oxide include: take graphene oxide, add deionized water at 1-5 mg / mL, ultrasonically disperse for 30 minutes, dissolve KH-550 in ethanol / water at a ratio of 1:10, adjust the pH to 4-5, stir for 10 minutes, add the suspension to a silane solution with a mass ratio of 1:1, stir at 50 °C for 2 hours, centrifuge, wash 3 times with ethanol and water, vacuum dry at 50 °C for 6 hours, grind through a 200-mesh sieve to obtain pretreated graphene oxide.

5. The preparation method of the highly flame-retardant silicone foam sheet according to claim 1, wherein, The auxiliary agent is polyethylene glycol.

6. The preparation method of the highly flame-retardant silicone foam sheet according to claim 1, characterized in that, The foaming agent is azobisisobutyronitrile.

7. The preparation method of the highly flame-retardant silicone foam sheet according to claim 1, characterized in that, In step S3, the temperature of the foaming furnace is controlled at 80-120 °C, the foaming time is 10-15 minutes, the temperature of the curing furnace is 150-180 °C, and the curing time is 30-60 minutes.

8. The high flame-retardant silicone foam sheet prepared by the preparation method according to claim 1, characterized in that, By mass, it includes: 50 to 70 parts of polydimethylsiloxane, 5 to 10 parts of methyltriethoxysilane, 5 to 10 parts of nano-modified zinc borate, 10 to 20 parts of intumescent flame retardant, 2 to 5 parts of pretreated graphene oxide, 1 to 3 parts of auxiliary agent, 3 to 8 parts of foaming agent, and 0.5 to 2 parts of catalyst.

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