Self-healing silicone rubber flame retardant protective pad for high-temperature welding and its preparation method

Abstract

The present invention belongs to the technical field of the preparation of flame-retardant materials, and provides a self-healing silicone rubber flame-retardant protective pad for high-temperature welding and a preparation method thereof. First, hexachlorocyclotriphosphazene reacts with pyridine to prepare an ionic flame-retardant powder; mesoporous silica is modified with a silane coupling agent to prepare phosphazene mesoporous silica; molecular sieves are modified with phosphoric acid and calcined at high temperature to form phosphate molecular sieves, and a composite flame retardant is prepared by mixing; secondly, a borate crosslinking precursor with dynamic self-healing ability is constructed through boric acid, a furanized methylvinylphenyl silicone rubber matrix is prepared by introducing furan groups through furfuraldehyde, and the silicone rubber is further modified through the reversible crosslinking reaction between N-maleimidecaproic acid and furan groups to endow it with high-temperature self-healing performance; finally, the modified methylvinylphenyl silicone rubber, the composite flame retardant, inorganic fillers, auxiliary fillers and the borate crosslinking precursor are mixed to obtain a self-healing silicone rubber flame-retardant protective pad for high-temperature welding.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame retardant material preparation, and relates to a self-healing silicone rubber flame retardant protective pad for high-temperature welding and a preparation method thereof. Background Art

[0002] With the rapid development of industrial manufacturing, high-temperature operations such as welding and cutting have been widely applied in fields such as aerospace, automotive manufacturing, construction, and shipbuilding industries. However, a large amount of heat radiation, sparks, molten droplets, and metal slag are inevitably generated in high-temperature working environments. These high-temperature heat sources not only pose a safety threat to operators but also may damage the surrounding equipment, environment, and materials, and even cause fires. Traditional high-temperature protective materials, such as fiberglass fabrics and ceramic fiber mats, can to a certain extent isolate heat radiation and high-temperature molten droplets, but are prone to decomposition or combustion under high-temperature conditions and cannot meet the flame retardant requirements in extreme environments. Moreover, traditional materials are difficult to self-repair after being damaged (such as cracks and corrosion) at high temperatures, which affects the service life and increases the replacement cost. Silicone rubber has gradually become the preferred high-temperature protective material due to its excellent flexibility, heat resistance, and chemical stability. However, a single silicone rubber material still has deficiencies in high-temperature flame retardant performance and cannot meet the actual needs, especially under extreme conditions such as welding operations. Therefore, the preparation of a silicone rubber flame retardant protective pad for high-temperature welding with self-healing ability has become an important requirement in the field of industrial safety. Summary of the Invention

[0003] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a self-healing silicone rubber flame retardant protective pad for high-temperature welding and a preparation method thereof. The present invention uses methyl vinyl phenyl silicone rubber as the matrix, and through its chemical modification, dynamic borate bonds and reversible crosslinking networks are introduced to achieve the self-healing function of the material. At the same time, by preparing a multifunctional composite flame retardant and combining inorganic fillers and auxiliary fillers, the flame retardant performance and thermal stability of the material are improved to meet the actual production needs.

[0004] To achieve this purpose, the present invention adopts the following technical solutions:

[0005] In the first aspect, the present invention provides a preparation method of a self-healing silicone rubber flame retardant protective pad for high-temperature welding, and the preparation method is as follows:

[0006] Step A1: Disperse hexachlorocyclotriphosphazene in anhydrous acetonitrile, then add pyridine to the anhydrous acetonitrile, heat up to the first temperature for reflux reaction, after the reaction is completed, cool to room temperature, add acetone for filtration and washing to obtain cationic cyclic phosphazene. Disperse the cationic cyclic phosphazene in anhydrous ethanol, then add sodium hexametaphosphate to the anhydrous ethanol, heat up to the second temperature and react under stirring conditions, and carry out reduced pressure distillation and drying to obtain ionic flame retardant powder;

[0007] Step A2: Disperse mesoporous silica in absolute ethanol, add a silane coupling agent under stirring conditions, heat up to the first temperature, stir and reflux for reaction. After the reaction is completed, filter and wash, and place the product in vacuum drying at the second temperature to obtain epoxy mesoporous silica. Disperse hexachlorocyclotriphosphazene in anhydrous toluene to obtain a hexachlorocyclotriphosphazene solution. Then disperse the epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, add anhydrous triethylamine, heat up to the third temperature, and reflux and stir for reaction. After the reaction is completed, filter and wash, and place the product in vacuum drying at the second temperature to obtain phosphazene mesoporous silica;

[0008] Step A3: Disperse the molecular sieve in a phosphoric acid solution, heat up to the third temperature, stir for reaction. After the reaction is completed, filter and wash, and place the product in vacuum drying at the fourth temperature. Transfer the dried product to a muffle furnace and calcine at the fifth temperature to obtain a phosphate molecular sieve;

[0009] Step A4: Place the ionic flame retardant powder, phosphazene mesoporous silica and phosphate molecular sieve in a ball mill and mix evenly. Add polyaryletherketone to anhydrous DMF, heat up to the fourth temperature and stir to dissolve. Then add the ball-milled mixed material to the polyaryletherketone solution, adjust the temperature to the third temperature, stir evenly, place the product in vacuum drying at the fourth temperature to obtain a solid composite. Transfer the solid composite to a muffle furnace, heat up to the fifth temperature and fully calcine to obtain a composite flame retardant.

[0010] Step S1: Add boric acid and polyethylene glycol - 400 to anhydrous DMF, heat up to the third temperature, stir for reaction. After the reaction is completed, place it in vacuum drying at the second temperature to obtain a borate cross-linked precursor;

[0011] Step S2: Disperse methyl vinyl phenyl silicone rubber and furfural in anhydrous toluene, add tetrabutylammonium bromide, adjust the temperature to the third temperature, stir for reaction to obtain a furanized methyl vinyl phenyl silicone rubber matrix solution. Dissolve N - maleimidocaproic acid in anhydrous toluene and then add it to the furanized methyl vinyl phenyl silicone rubber matrix solution, and continue the reaction at the third temperature. After the reaction is completed, perform vacuum drying to obtain modified methyl vinyl phenyl silicone rubber;

[0012] Step S3: Mix the modified methyl vinyl phenyl silicone rubber, composite flame retardant, inorganic filler, auxiliary filler and borate cross-linked precursor evenly, and press to obtain a self - repairing silicone rubber flame retardant protective pad for high - temperature welding.

[0013] Hexachlorocyclotriphosphazene is a six-membered cyclic compound. In its structure, three phosphorus atoms and three nitrogen atoms are arranged alternately in sequence, forming a P-N conjugate system. The phosphorus atoms are connected to chlorine atoms through P-Cl bonds with relatively strong polarity. The strong electronegativity of chlorine makes the P-Cl bonds have significant polarity, and the phosphorus atoms carry partial positive charges. Due to the participation of the lone pair electrons of nitrogen atoms in the weak conjugate effect on the ring, hexachlorocyclotriphosphazene as a whole exhibits electron-deficient characteristics, and the phosphorus atoms show high reactivity towards nucleophiles. The pyridine molecule contains a nitrogen atom with a lone pair of electrons, which can act as a nucleophile to react with the electron-deficient phosphorus atoms. The lone pair of electrons on the nitrogen atom of pyridine attacks the phosphorus atoms of hexachlorocyclotriphosphazene. At the same time, the electron cloud of the P-Cl bond shifts towards the chlorine atom. Subsequently, the P-Cl bond breaks, and the chloride ion leaves as a leaving group, generating a phosphorus-nitrogen bond. Due to the nucleophilic attack of the pyridine molecule, some of the chlorine in hexachlorocyclotriphosphazene is replaced by pyridine, and the product is a cationic cyclic phosphazene compound. After the reaction, pyridine is connected to the phosphazene ring as a substituent. At the same time, due to the basicity of the pyridine nitrogen atom and the symmetry of the molecular structure, the generated compound carries a positive charge and shows cationic properties. The cationic phosphazene compound has good solubility and reactivity, providing a basis for the subsequent reaction with sodium hexametaphosphate. Sodium hexametaphosphate is a cyclic polyphosphate, which is composed of six phosphate units connected by P-O-P bonds. The molecule contains six sodium cations and a polyphosphate anion. The polyphosphate anion has a high negative charge and strong coordination ability, and can form ionic bond interactions or electrostatic attractions with positively charged compounds. The positive charge center of the cationic phosphazene combines with the polyphosphate anion of sodium hexametaphosphate through electrostatic interactions, generating an ionic bond network of a supramolecular structure. The positive charges in the cationic phosphazene act through electrostatic attraction with the polyphosphate anion. Multiple cationic phosphazene molecules interact with one polyphosphate anion, forming an ionic network system. This ionic network structure is further stabilized by electrostatic forces and weak hydrogen bonds.

[0014] The polyphosphate anion has a cyclic structure, in which six phosphorus atoms are connected to oxygen atoms through P-O-P bonds, forming a stable polyanion system. Due to its cyclic polyphosphorus-oxygen bond structure, the polyphosphate anion exhibits good thermal stability. When the temperature rises continuously, the anion will gradually break, releasing small-molecule phosphate compounds (such as metaphosphoric acid HPO3 and orthophosphoric acid H3PO4). These decomposition products can further participate in dehydration and condensation reactions under high-temperature conditions. Metaphosphoric acid is a compound containing P=O and P-OH groups, with high hydrophilicity and thermal instability, and is prone to further dehydration condensation at high temperatures, losing water molecules to form polyphosphoric acid with a higher degree of polymerization, and polyphosphoric acid has excellent thermal stability. At the same time, phosphate compounds exhibit a catalytic effect at high temperatures, capable of promoting the dehydration and carbonization reactions of organic materials. Phosphate compounds are strong acidic substances and can act as dehydration catalysts to promote the dehydration reaction of hydroxyl groups and hydrogen atoms in organic materials. The dehydration reaction will lead to the formation of more conjugated double bonds or aromatic compounds in the molecular structure of the material, thereby improving the thermal stability of the material; phosphate compounds can also catalyze the carbonization reaction of the material. The dehydration effect of phosphate compounds removes the volatile groups in the material, reducing the release of flammable gases. Carbon atoms gradually aggregate at high temperatures and form a dense carbonaceous layer, covering the surface of the material, forming a barrier to isolate the entry of oxygen and heat, and preventing the further progress of combustion. And hexachlorocyclotriphosphazene decomposes at high temperatures to generate phosphorus oxide intermediates (such as PO·, PO2·), which can capture the active free radicals in the combustion chain. Through the reaction with free radicals, phosphorus oxides reduce the free radical concentration in the combustion chain reaction, lower the flame propagation speed, and delay or prevent combustion. The ionic supramolecular network is formed by the combination of cationic phosphazene compounds and polyphosphate anions through electrostatic interactions and ionic bonds. The ionic network structure has strong stability at high temperatures, is not easily decomposed or damaged, and can maintain the overall function of the flame retardant during the combustion process. The stable network structure can provide continuous release of phosphoric acid or phosphorus oxides or avoid premature decomposition or volatilization of the flame retardant.

[0015] In an ethanol solution, the methoxy part of the silane coupling agent KH-560 hydrolyzes to form silanol groups, which then undergo a condensation reaction with the hydroxyl groups on the surface of silica to form Si-O-Si covalent bonds. The epoxy groups activate the surface of the mesoporous silica, providing reaction sites for subsequent reactions with hexachlorocyclotriphosphazene. At the same time, the electron-deficient nature of hexachlorocyclotriphosphazene makes it prone to undergo a ring-opening reaction with the epoxy groups. Triethylamine acts as a basic catalyst to promote the ring-opening of the epoxy groups, and the phosphorus atoms in hexachlorocyclotriphosphazene undergo further nucleophilic reactions with the hydroxyl groups after ring-opening to generate phosphazene-modified mesoporous silica. The high specific surface area and uniform distribution of the phosphazene mesoporous silica enable it to come into full contact with the matrix material, effectively catalyzing the dehydration and carbonization reactions of the matrix material during the carbonization process. The resulting carbonaceous material can uniformly cover the surface of the mesoporous silica, forming a dense carbonized layer. Moreover, the regular pore structure of the mesoporous silica causes the carbonaceous material to deposit along the pores at high temperatures, forming a continuous carbon network inside and outside the pores, improving the overall strength and thermal stability of the carbonized layer. The templating effect of the mesoporous silica makes the carbonized layer have higher density and consistency, thereby preventing heat conduction and oxygen diffusion, significantly improving the heat insulation and flame retardant properties of the material. At high temperatures, the phosphoric acid compounds (H3PO4, HPO3) generated by the decomposition of the phosphazene groups further catalyze the carbonization reaction of the matrix material, synergistically with the templating effect of the mesoporous silica, to generate a denser carbonized layer.

[0016] ZSM-5 is a silicoaluminate molecular sieve, whose framework is formed by connecting silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra through oxygen bridges (Si-O-Al) to form a three-dimensional pore structure. Under heating conditions, the hydroxyl groups of H3PO4 undergo a condensation reaction with the acidic hydroxyl groups on the surface of ZSM-5, forming Si-O-P bonds and releasing water molecules. The pore system of ZSM-5 provides efficient adsorption sites for phosphoric acid molecules, and the phosphoric acid molecules are adsorbed in the molecular sieve pores through hydrogen bonding or electrostatic interactions. During the calcination stage, the adsorbed phosphoric acid molecules may further dehydrate and condense to form metaphosphoric acid or polyphosphoric acid coating layers. And under acidic conditions, phosphoric acid may have a certain etching effect on the surface structure of ZSM-5, partially dissolving the Si-O-Si bonds and exposing more active sites, enhancing the chemical activity of the molecular sieve and its compatibility with the polymer matrix. During the high-temperature calcination process, the phosphoric acid substances further dehydrate and condense to generate thermally stable phosphate molecular sieves. Phosphoric acid loses water to form metaphosphoric acid or polyphosphoric acid, and the metaphosphoric acid or polyphosphoric acid further condenses with the surface hydroxyl groups of the molecular sieve to form stable phosphate bonds. The calcination stage evenly distributes the phosphate on the surface and in the pores of ZSM-5, forming a "phosphate modification layer", which improves the thermal stability of the molecular sieve and its ability to capture combustion free radicals. The formation of the phosphate layer significantly improves the thermal stability of the molecular sieve, making it not easily decomposed under high-temperature conditions. The phosphoric acid compounds released during the decomposition of the phosphate further catalyze the dehydration and carbonization of the matrix material, improving the flame retardancy of the material. At the same time, the porous structure of ZSM-5 helps the phosphate to be evenly distributed, improving the dispersibility and synergy of the flame retardant in the polymer matrix. The phosphate is embedded in the pores of ZSM-5, further enhancing the adsorption ability of the molecular sieve for volatile combustible products and reducing the flammability of the combustion products. Polyaryletherketone is a typical highly heat-resistant polymer, whose basic structure consists of aromatic rings, ether bonds and ketone groups. The ether bonds and ketone groups on the polyaryletherketone molecular chain are polar groups, which can form hydrogen bonds with other polar groups (such as Si-OH, P=O), enhancing the interfacial binding force between polyaryletherketone and the flame retardant, thereby improving the overall thermal stability and mechanical properties of the material. During the calcination process, the pore structure of mesoporous silica or ZSM-5 may induce partial molecular chains of polyaryletherketone to dehydrate and carbonize at high temperatures, promoting the orderly formation of the polyaryletherketone carbonized layer, thereby improving the density, strength and heat insulation of the carbonized layer.

[0017] Boric acid molecules contain three hydroxyl groups connected to the central boron atom. Due to its electron deficiency, the boron atom exhibits Lewis acidity, can accept electron pairs, and undergoes chemical reactions with hydroxyl groups or other nucleophilic groups. The hydroxyl groups of boric acid and the hydroxyl groups of hydroxyl-containing compounds (polyethylene glycol - 400) form borate bonds through dehydration condensation reactions under anhydrous conditions. Borate bonds are strong covalent bonds with high dissociation energy, can remain stable at high temperatures, and are not easily decomposed. At the same time, the borate bond cross-linked structure restricts the free movement of molecular chains, increases the glass transition temperature and thermal decomposition temperature of the material, and can also serve as physical cross-linking points to form a dynamic cross-linked network, endowing the material with certain self-healing ability and heat resistance. In silicone rubber, a three-dimensional network is formed through the cross-linking of silicon-oxygen bonds. The boron atoms in the borate cross-linking precursor can act as Lewis acid catalysts to promote the cross-linking reaction of silicon-oxygen bonds. The B-O-C bonds in the borate cross-linking precursor and the Si-O bonds in silicone rubber act synergistically to form a denser cross-linked network, significantly improving the thermal stability and mechanical properties of the material. The physical cross-linking characteristics of borate bonds endow silicone rubber with certain self-healing ability, and the borate precursor inhibits the thermal decomposition of silicone rubber through cross-linking. At the same time, the generated boron oxides form a protective heat-insulating layer at high temperatures, further improving the flame retardancy of the composite material.

[0018] Furfural is a compound containing a furan ring and an aldehyde group. The aldehyde group in furfural can undergo an addition reaction with the vinyl group in methyl vinyl phenyl silicone rubber to form a new carbon-carbon bond. At the same time, the furan ring in furfural undergoes an addition reaction with the phenyl group in methyl vinyl phenyl silicone rubber to form a stable ring structure, providing new cross-linking points for the silicone rubber matrix. And N-maleimidocaproic acid undergoes an addition reaction with the furan group introduced by furfural through its imide group to generate a stable six-membered ring structure, further cross-linking the silicone rubber molecular chains to form a three-dimensional cross-linked network. The addition reaction between the furan group and the maleimide group forms new cross-linking points between the silicone rubber molecular chains, significantly increasing the cross-linking density. The higher cross-linking density restricts the free movement of molecular chains and improves the mechanical strength of the material. The aldehyde group of furfural combines with the vinyl group of methyl vinyl phenyl silicone rubber through an addition reaction to form a silicone rubber containing furan groups; the furan ring of furfural combines with the phenyl group in methyl vinyl phenyl silicone rubber through an addition reaction to further cross-link and modify the silicone rubber matrix. And the furan group introduced by furfural undergoes an addition reaction with the imide group of maleimide anhydride to form a cross-linked network. The cycloaddition product and imide group generated by the reaction endow the material with a higher thermal decomposition temperature, enhancing the high-temperature stability of the material. At the same time, the thermoreversibility of the reaction provides the material with dynamic adjustment ability at high temperatures and endows the material with certain self-healing functions.

[0019] As a preferred technical solution of the present invention, in step A1, the mass-volume ratio of the hexachlorocyclotriphosphazene to anhydrous acetonitrile is 1 g: 15 mL.

[0020] In some alternative examples, the mass ratio of the hexachlorocyclotriphosphazene to pyridine is 2:(1.3 - 1.5). For example, it can be 2:1.3, 2:1.4, or 2:1.5, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0021] In some alternative examples, the first temperature is 60 - 80 °C. For example, it can be 60.0 °C, 62.0 °C, 64.0 °C, 66.0 °C, 68.0 °C, 70.0 °C, 72.0 °C, 74.0 °C, 76.0 °C, 78.0 °C, or 80.0 °C, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0022] In some alternative examples, the reflux reaction time is 12 - 13 h. For example, it can be 12.0 h, 12.1 h, 12.2 h, 12.3 h, 12.4 h, 12.5 h, 12.6 h, 12.7 h, 12.8 h, 12.9 h, or 13.0 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0023] In some alternative examples, the mass - to - volume ratio of the cationic cyclic phosphazene to absolute ethanol is 1 g:15 mL.

[0024] In some alternative examples, the mass ratio of the cationic cyclic phosphazene to sodium hexametaphosphate is 2:(3.3 - 3.5). For example, it can be 2:3.3, 2:3.4, or 2:3.5, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0025] In some alternative examples, the second temperature is 50 - 60 °C. For example, it can be 50.0 °C, 51.0 °C, 52.0 °C, 53.0 °C, 54.0 °C, 55.0 °C, 56.0 °C, 57.0 °C, 58.0 °C, 59.0 °C, or 60.0 °C, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0026] In some alternative examples, the stirring reaction time at the second temperature is 2 - 3 h. For example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h, or 3.0 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0027] As a preferred technical solution of the present invention, in step A2, the mass - to - volume ratio of the mesoporous silica to absolute ethanol is 1 g:25 mL.

[0028] In some alternative examples, the silane coupling agent is KH-560, and the mass ratio of the mesoporous silica to the silane coupling agent is 1:1.

[0029] In some alternative examples, the reflux reaction time after adding the silane coupling agent is 6 - 7 h. For example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h or 7.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0030] In some alternative examples, the drying time after the reaction with the silane coupling agent is 12 - 14 h. For example, it can be 12.0 h, 12.2 h, 12.4 h, 12.6 h, 12.8 h, 13.0 h, 13.2 h, 13.4 h, 13.6 h, 13.8 h or 14.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0031] In some alternative examples, the mass-to-volume ratio of the hexachlorocyclotriphosphazene to the anhydrous toluene is 1 g:50 mL.

[0032] In some alternative examples, the mass ratio of the hexachlorocyclotriphosphazene to the epoxy mesoporous silica is 1:2.

[0033] In some alternative examples, the mass-to-volume ratio of the epoxy mesoporous silica to the anhydrous triethylamine is 2 g:1 mL.

[0034] In some alternative examples, the third temperature is 80 - 90 °C. For example, it can be 80.0 °C, 81.0 °C, 82.0 °C, 83.0 °C, 84.0 °C, 85.0 °C, 86.0 °C, 87.0 °C, 88.0 °C, 89.0 °C or 90.0 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0035] In some alternative examples, the reflux reaction time after adding the anhydrous triethylamine is 8 - 9 h. For example, it can be 8.0 h, 8.1 h, 8.2 h, 8.3 h, 8.4 h, 8.5 h, 8.6 h, 8.7 h, 8.8 h, 8.9 h or 9.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0036] In some alternative examples, the drying time after adding anhydrous triethylamine is 12 - 14 h. For example, it can be 12.0 h, 12.2 h, 12.4 h, 12.6 h, 12.8 h, 13.0 h, 13.2 h, 13.4 h, 13.6 h, 13.8 h, or 14.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0037] As a preferred technical solution of the present invention, in step A3, the molecular sieve is ZSM-5, and the mass-volume ratio of the molecular sieve to the phosphoric acid solution is 4 g : 30 mL.

[0038] In some alternative examples, the mass ratio of phosphoric acid to deionized water in the phosphoric acid solution is 2 : 15.

[0039] In some alternative examples, the stirring reaction time is 6 - 7 h. For example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h, or 7.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0040] In some alternative examples, the fourth temperature is 100 - 110 °C. For example, it can be 100.0 °C, 101.0 °C, 102.0 °C, 103.0 °C, 104.0 °C, 105.0 °C, 106.0 °C, 107.0 °C, 108.0 °C, 109.0 °C, or 110.0 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0041] In some alternative examples, the drying time at the fourth temperature is 12 - 14 h. For example, it can be 12.0 h, 12.2 h, 12.4 h, 12.6 h, 12.8 h, 13.0 h, 13.2 h, 13.4 h, 13.6 h, 13.8 h, or 14.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0042] In some alternative examples, the fifth temperature is 300 - 350 °C. For example, it can be 300.0 °C, 305.0 °C, 310.0 °C, 315.0 °C, 320.0 °C, 325.0 °C, 330.0 °C, 335.0 °C, 340.0 °C, 345.0 °C, or 350.0 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0043] In some alternative examples, the calcination time is 4 - 5 h. For example, it can be 4.0 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h or 5.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0044] As a preferred technical solution of the present invention, in step A4, the mass ratio of the ionic flame retardant powder, phosphazene mesoporous silica and phosphate molecular sieve is 5:2:3.

[0045] In some alternative examples, the mass ratio of the ionic flame retardant powder to polyaryletherketone is 1:2.

[0046] In some alternative examples, the mass - to - volume ratio of polyaryletherketone to anhydrous DMF is 1 g:5 mL.

[0047] In some alternative examples, the stirring time for heating to the third temperature is 6 - 7 h. For example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h or 7.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0048] In some alternative examples, the vacuum drying time is 12 - 14 h. For example, it can be 12.0 h, 12.2 h, 12.4 h, 12.6 h, 12.8 h, 13.0 h, 13.2 h, 13.4 h, 13.6 h, 13.8 h or 14.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0049] In some alternative examples, the calcination time is 6 - 7 h. For example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h or 7.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0050] As a preferred technical solution of the present invention, in step S1, the mass ratio of boric acid to polyethylene glycol - 400 is 1:2.

[0051] In some alternative examples, the mass - to - volume ratio of boric acid to anhydrous DMF is 1 g:10 mL.

[0052] In some alternative embodiments, the stirring reaction time is 1 - 2 h, for example, it can be 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2.0 h, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0053] In some alternative embodiments, the vacuum drying time is 6 - 8 h, for example, it can be 6.0 h, 6.2 h, 6.4 h, 6.6 h, 6.8 h, 7.0 h, 7.2 h, 7.4 h, 7.6 h, 7.8 h or 8.0 h, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0054] As a preferred technical solution of the present invention, in step S2, the mass ratio of the methyl vinyl phenyl silicone rubber to furfural is 20:1.

[0055] In some alternative embodiments, the mass - volume ratio of the methyl vinyl phenyl silicone rubber to anhydrous toluene is 1 g:1 mL.

[0056] In some alternative embodiments, the mass ratio of the methyl vinyl phenyl silicone rubber to tetrabutylammonium bromide is 200:1.

[0057] In some alternative embodiments, the stirring reaction time is 2 - 3 h, for example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0058] In some alternative embodiments, the mass ratio of the methyl vinyl phenyl silicone rubber to N - maleimidocaproic acid is 25:2.

[0059] In some alternative embodiments, the mass - volume ratio of N - maleimidocaproic acid to anhydrous toluene is 2 g:25 mL.

[0060] In some alternative embodiments, the reaction time after adding N - maleimidocaproic acid is 4 - 5 h, for example, it can be 4.0 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h or 5.0 h, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0061] As a preferred technical solution of the present invention, in step S3, the inorganic filler is iron powder, graphene, ceramic powder, lithium carbonate, ammonium metavanadate, calcium fluoride and alumina, and the mass ratio is 8:30:6:2:1:6:90.

[0062] In some alternative examples, the auxiliary filler is ascorbic acid, polybutylene terephthalate, 1,2-dimethylimidazole, potassium citrate, dipropylene glycol, 1,1-di-tert-butylperoxycyclohexane, methyl silicone oil, zinc stearate and methyl vinyl organopolysiloxane, and the mass ratio is 1:22:2:2:1:4:38:1:50.

[0063] In some alternative examples, the mass ratio of the modified methyl vinyl phenyl silicone rubber, the composite flame retardant, the inorganic filler, the auxiliary filler and the borate crosslinking precursor is 100:25:143:121:15.

[0064] In a second aspect, a self-healing silicone rubber flame retardant protective pad for high-temperature welding prepared by using the preparation method described in the first aspect.

[0065] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0066] (1) Introduce boric acid to react with polyethylene glycol to generate a dynamic borate bond crosslinking precursor, endowing the material with dynamic reorganizability under high-temperature conditions, enabling the protective pad to achieve self-healing through dynamic crosslinking after being damaged, and reacting the methyl vinyl phenyl silicone rubber modified with furfuraldehyde with N-maleimide hexanoic acid to construct a thermally reversible crosslinking network, further enhancing the self-healing ability and high-temperature performance of the material;

[0067] (2) By preparing ionic flame retardant powder, improve the thermal shielding ability and flame retardant efficiency of the flame retardant, epoxy modify mesoporous silica through a silane coupling agent, and further introduce phosphazene groups to prepare phosphazene mesoporous silica, thereby enhancing the thermal stability and carbonization ability of the material. Prepare phosphate molecular sieve through phosphoric acid modification and high-temperature calcination, endowing the material with good flame retardant performance and endothermic characteristics of high-temperature decomposition, and calcine to form a composite flame retardant to improve the flame retardant performance of the material;

[0068] (3) By combining the modified silicone rubber matrix with the composite flame retardant, inorganic filler and auxiliary filler, a multi-component synergistic system is constructed. While improving the flame retardant performance of the material, the combination of dynamic chemical bonds and the composite flame retardant system enables the material to have comprehensive properties of flame retardancy, high-temperature stability and self-healing in high-temperature scenarios such as welding. Description of the Drawings

[0069] Figure 1 It is the SEM image of the phosphazene mesoporous silica prepared in Example 1 of the present invention;

[0070] Figure 2 SEM image of the phosphate molecular sieve prepared in Example 1 of the present invention (scale bar: 1 μm);

[0071] Figure 3 SEM image of the phosphate molecular sieve prepared in Example 1 of the present invention (scale bar: 500 nm);

[0072] Figure 4 SEM image of the phosphate molecular sieve prepared in Example 1 of the present invention (scale bar: 500 nm). Detailed implementation manners

[0073] The technical solutions of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific specific implementation manners of the present invention and are used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary, and should not be construed as limiting the implementation manners of the present invention and the protection scope of the present invention. Except for the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of the present application. These technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0074] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products and have not been further purified.

[0075] Example 1

[0076] This example provides a preparation method of a self-healing silicone rubber flame retardant protective pad for high-temperature welding. The preparation method specifically includes the following steps:

[0077] Step A1: Disperse 1 g of hexachlorocyclotriphosphazene in 15 mL of anhydrous acetonitrile, then add 0.7 g of pyridine to the anhydrous acetonitrile, heat up to 63 °C and reflux for 12.3 h. After the reaction is completed, cool to room temperature, add acetone and filter and wash to obtain cationic cyclic phosphazene. Disperse 2 g of cationic cyclic phosphazene in 30 mL of anhydrous ethanol, then add 3.3 g of sodium hexametaphosphate to the anhydrous ethanol, heat up to 60 °C and react under stirring for 2.6 h, and dry by vacuum distillation to obtain ionic flame retardant powder;

[0078] Step A2: Disperse 2 g of mesoporous silica in 50 mL of absolute ethanol. Under stirring conditions, add 2 g of silane coupling agent KH-560, heat up to 67 °C, and stir and reflux for 6.3 h. After the reaction is completed, filter and wash, and place the product in a vacuum dryer at 52 °C for 12.3 h to obtain epoxy mesoporous silica. Disperse 1 g of hexachlorocyclotriphosphazene in 50 mL of absolute toluene to obtain a hexachlorocyclotriphosphazene solution. Then disperse 2 g of epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, add 1 mL of absolute triethylamine, heat up to 87 °C, and reflux and stir for 8.7 h. After the reaction is completed, filter and wash, and place the product in a vacuum dryer at 54 °C for 13.4 h to obtain phosphazene mesoporous silica;

[0079] Step A3: Disperse 4 g of molecular sieve ZSM-5 in 30 mL of phosphoric acid solution, heat up to 87 °C, and stir and react for 6.3 h. After the reaction is completed, filter and wash, and place the product in a vacuum dryer at 109 °C for 12.9 h. Transfer the dried product to a muffle furnace and calcine at 320 °C for 4.6 h to obtain phosphate molecular sieve;

[0080] Step A4: Place 5 g of ionic flame retardant powder, 2 g of phosphazene mesoporous silica, and 3 g of phosphate molecular sieve in a ball mill and mix evenly. Add 10 g of polyaryletherketone to 50 mL of absolute DMF, heat up to 106 °C and stir to dissolve. Then add the ball-milled mixed material to the polyaryletherketone solution, adjust the temperature to 84 °C, and stir evenly for 6.3 h. Place the product in a vacuum dryer at 100 °C for 12.6 h to obtain a solid complex. Transfer the solid complex to a muffle furnace, heat up to 340 °C, and fully calcine for 6.3 h to obtain a composite flame retardant.

[0081] Step S1: Add 6 g of boric acid and 12 g of polyethylene glycol-400 to 60 mL of absolute DMF, heat up to 84 °C, and stir and react for 1.6 h. After the reaction is completed, place it in a vacuum dryer at 57 °C for 6.7 h to obtain a borate cross-linked precursor;

[0082] Step S2: Disperse 10 g of methyl vinyl phenyl silicone rubber and 0.5 g of furfural in 10 mL of absolute toluene, add 0.05 g of tetrabutylammonium bromide, adjust the temperature to 87 °C, and stir and react for 2.6 h to obtain a furanized methyl vinyl phenyl silicone rubber matrix solution. Dissolve 0.8 g of N-maleimidocaproic acid in 10 mL of absolute toluene, and then add it to the furanized methyl vinyl phenyl silicone rubber matrix solution, and continue to react at 89 °C for 4.9 h. After the reaction is completed, vacuum dry to obtain modified methyl vinyl phenyl silicone rubber;

[0083] Step S3: Mix 100 g of modified methyl vinyl phenyl silicone rubber, 25 g of composite flame retardant, 8 g of iron powder, 30 g of graphene, 6 g of ceramic powder, 2 g of lithium carbonate, 1 g of ammonium metavanadate, 6 g of calcium fluoride, 90 g of alumina, 1 g of ascorbic acid, 22 g of polybutylene terephthalate, 2 g of 1,2-dimethylimidazole, 2 g of potassium citrate, 1 g of dipropylene glycol, 4 g of 1,1-di-tert-butylperoxycyclohexane, 38 g of methyl silicone oil, 1 g of zinc stearate, 50 g of methyl vinyl organopolysiloxane and 15 g of boron ester crosslinking precursor evenly, and press to obtain a self-healing silicone rubber flame retardant protection pad for high-temperature welding.

[0084] Figure 1 SEM image of the phosphazene mesoporous silica prepared in Example 1 of the present invention; Figure 2 SEM image of the phosphate molecular sieve prepared in Example 1 of the present invention; Figure 3 SEM image of the phosphate molecular sieve prepared in Example 1 of the present invention. It can be seen that the surface of the molecular sieve is relatively smooth, without obvious cracks or defects, indicating that the molecular sieve has good crystallinity and relatively uniform particles; Figure 4 SEM image of the phosphate molecular sieve prepared in Example 1 of the present invention.

[0085] Example 2

[0086] This example provides a preparation method of a self-healing silicone rubber flame retardant protection pad for high-temperature welding. The preparation method specifically includes the following steps:

[0087] Step A1: Disperse 2 g of hexachlorocyclotriphosphazene in 30 mL of anhydrous acetonitrile, then add 1.45 g of pyridine to the anhydrous acetonitrile, heat up to 60 °C and reflux for 12.0 h. After the reaction is completed, cool to room temperature, add acetone for filtration and washing to obtain cationic cyclic phosphazene. Disperse 2 g of cationic cyclic phosphazene in 30 mL of anhydrous ethanol, then add 3.4 g of sodium hexametaphosphate to the anhydrous ethanol, heat up to 50 °C and react under stirring for 2.0 h, and dry by vacuum distillation to obtain ionic flame retardant powder;

[0088] Step A2: Disperse 3 g of mesoporous silica in 75 mL of anhydrous ethanol, add 3 g of silane coupling agent KH-560 under stirring, heat up to 74 °C, and stir and reflux for 6.7 h. After the reaction is completed, filter and wash, and place the product in a vacuum dryer at 50 °C for 13.6 h to obtain epoxy mesoporous silica. Disperse 1.5 g of hexachlorocyclotriphosphazene in 75 mL of anhydrous toluene to obtain a hexachlorocyclotriphosphazene solution, then disperse 3 g of epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, add 1.5 mL of anhydrous triethylamine, heat up to 90 °C, and reflux and stir for 8.3 h. After the reaction is completed, filter and wash, and place the product in a vacuum dryer at 50 °C for 13.0 h to obtain phosphazene mesoporous silica;

[0089] Step A3: Disperse 4 g of zeolite ZSM-5 in 30 mL of phosphoric acid solution, heat up to 81 °C, stir and react for 6.7 h. After the reaction is completed, filter and wash, place the product in a vacuum dryer at 103 °C for 13.4 h, transfer the dried product to a muffle furnace, and calcine at 350 °C for 4.1 h to obtain phosphate molecular sieve;

[0090] Step A4: Place 2.5 g of ionic flame retardant powder, 1 g of phosphazene mesoporous silica and 1.5 g of phosphate molecular sieve in a ball mill and mix evenly. Add 5 g of polyaryletherketone to 25 mL of anhydrous DMF, heat up to 102 °C and stir to dissolve. Then add the mixed material after ball milling to the polyaryletherketone solution, adjust the temperature to 80 °C, stir evenly for 6.0 h, place the product in a vacuum dryer at 109 °C for 13.2 h to obtain a solid complex. Transfer the solid complex to a muffle furnace, heat up to 330 °C and calcine sufficiently for 6.8 h to obtain a composite flame retardant.

[0091] Step S1: Add 4 g of boric acid and 8 g of polyethylene glycol-400 to 40 mL of anhydrous DMF, heat up to 80 °C, stir and react for 1.1 h. After the reaction is completed, place it in a vacuum dryer at 59 °C for 7.3 h to obtain a borate cross-linked precursor;

[0092] Step S2: Disperse 20 g of methyl vinyl phenyl silicone rubber and 1 g of furfural in 20 mL of anhydrous toluene, then add 0.1 g of tetrabutylammonium bromide, adjust the temperature to 83 °C, stir and react for 2.1 h to obtain a furanized methyl vinyl phenyl silicone rubber matrix solution. Dissolve 1.6 g of N-maleimidocaproic acid in 20 mL of anhydrous toluene, and then add it to the furanized methyl vinyl phenyl silicone rubber matrix solution, and continue to react at 84 °C for 4.1 h. After the reaction is completed, vacuum dry to obtain modified methyl vinyl phenyl silicone rubber;

[0093] Step S3: Mix 100 g of modified methyl vinyl phenyl silicone rubber, 25 g of composite flame retardant, 8 g of iron powder, 30 g of graphene, 6 g of ceramic powder, 2 g of lithium carbonate, 1 g of ammonium metavanadate, 6 g of calcium fluoride, 90 g of alumina, 1 g of ascorbic acid, 22 g of polybutylene terephthalate, 2 g of 1,2-dimethylimidazole, 2 g of potassium citrate, 1 g of dipropylene glycol, 4 g of 1,1-di-tert-butylperoxycyclohexane, 38 g of methyl silicone oil, 1 g of zinc stearate, 50 g of methyl vinyl organopolysiloxane and 15 g of borate cross-linked precursor evenly, and press to obtain a self-healing silicone rubber flame retardant protective pad for high-temperature welding.

[0094] Example 3

[0095] This embodiment provides a preparation method of a self-healing silicone rubber flame-retardant protective pad for high-temperature welding. The preparation method specifically includes the following steps:

[0096] Step A1: Disperse 4 g of hexachlorocyclotriphosphazene in 60 mL of anhydrous acetonitrile, then add 2.8 g of pyridine to the anhydrous acetonitrile, heat up to 74 °C and reflux for 13.0 h. After the reaction is completed, cool to room temperature, add acetone for filtration and washing to obtain cationic cyclic phosphazene. Disperse 2 g of cationic cyclic phosphazene in 30 mL of anhydrous ethanol, then add 3.5 g of sodium hexametaphosphate to the anhydrous ethanol, heat up to 52 °C and react under stirring for 2.4 h, and then perform vacuum distillation and drying to obtain ionic flame-retardant powder.

[0097] Step A2: Disperse 4 g of mesoporous silica in 100 mL of anhydrous ethanol, add 4 g of silane coupling agent KH-560 under stirring, heat up to 80 °C, and stir and reflux for 6.0 h. After the reaction is completed, filter and wash, and place the product in a vacuum dryer at 56 °C for 14.0 h to obtain epoxy mesoporous silica. Disperse 2 g of hexachlorocyclotriphosphazene in 100 mL of anhydrous toluene to obtain a hexachlorocyclotriphosphazene solution, then disperse 4 g of epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, add 2 mL of anhydrous triethylamine, heat up to 84 °C, and reflux and stir for 8.0 h. After the reaction is completed, filter and wash, and place the product in a vacuum dryer at 58 °C for 14.0 h to obtain phosphazene mesoporous silica.

[0098] Step A3: Disperse 4 g of molecular sieve ZSM-5 in 30 mL of phosphoric acid solution, heat up to 84 °C, and stir for 7.0 h. After the reaction is completed, filter and wash, and place the product in a vacuum dryer at 110 °C for 12.1 h. Transfer the dried product to a muffle furnace and calcine at 340 °C for 4.9 h to obtain phosphate molecular sieve.

[0099] Step A4: Place 10 g of ionic flame-retardant powder, 4 g of phosphazene mesoporous silica, and 6 g of phosphate molecular sieve in a ball mill and mix evenly. Add 20 g of polyaryletherketone to 100 mL of anhydrous DMF, heat up to 110 °C and stir to dissolve, then add the ball-milled mixed material to the polyaryletherketone solution, adjust the temperature to 89 °C, and stir evenly for 6.7 h. Place the product in a vacuum dryer at 106 °C for 13.9 h to obtain a solid composite. Transfer the solid composite to a muffle furnace, heat up to 300 °C and fully calcine for 6.2 h to obtain a composite flame retardant.

[0100] Step S1: Add 6 g of boric acid and 12 g of polyethylene glycol-400 to 60 mL of anhydrous DMF, heat up to 90 °C, and stir for 1.9 h. After the reaction is completed, place it in a vacuum dryer at 53 °C for 8.0 h to obtain a borate crosslinking precursor.

[0101] Step S2: Disperse 20 g of methyl vinyl phenyl silicone rubber and 1 g of furfural in 20 mL of anhydrous toluene, then add 0.1 g of tetrabutylammonium bromide, adjust the temperature to 80 °C, and stir and react for 3.0 h to obtain a furanized methyl vinyl phenyl silicone rubber matrix solution. Dissolve 1.6 g of N-maleimidocaproic acid in 20 mL of anhydrous toluene, and then add it to the furanized methyl vinyl phenyl silicone rubber matrix solution. Keep reacting at 80 °C for 4.6 h. After the reaction, perform vacuum drying to obtain modified methyl vinyl phenyl silicone rubber;

[0102] Step S3: Mix 100 g of modified methyl vinyl phenyl silicone rubber, 25 g of composite flame retardant, 8 g of iron powder, 30 g of graphene, 6 g of ceramic powder, 2 g of lithium carbonate, 1 g of ammonium metavanadate, 6 g of calcium fluoride, 90 g of alumina, 1 g of ascorbic acid, 22 g of polybutylene terephthalate, 2 g of 1,2-dimethylimidazole, 2 g of potassium citrate, 1 g of dipropylene glycol monoether, 4 g of 1,1-di-tert-butylperoxycyclohexane, 38 g of methyl silicone oil, 1 g of zinc stearate, 50 g of methyl vinyl organopolysiloxane and 15 g of boron ester crosslinking precursor evenly, and press to obtain a self-healing silicone rubber flame retardant protective pad for high-temperature welding.

[0103] Example 4

[0104] This example provides a preparation method of a self-healing silicone rubber flame retardant protective pad for high-temperature welding. The preparation method specifically includes the following steps:

[0105] Step A1: Disperse 2 g of hexachlorocyclotriphosphazene in 30 mL of anhydrous acetonitrile, then add 1.37 g of pyridine to the anhydrous acetonitrile, heat up to 80 °C and reflux for 12.7 h. After the reaction, cool to room temperature, add acetone for filtration and washing to obtain cationic cyclic phosphazene. Disperse 2 g of cationic cyclic phosphazene in 30 mL of anhydrous ethanol, then add 3.4 g of sodium hexametaphosphate to the anhydrous ethanol, heat up to 57 °C and react under stirring for 3.0 h, and perform reduced pressure distillation and drying to obtain ionic flame retardant powder;

[0106] Step A2: Disperse 2 g of mesoporous silica in 50 mL of anhydrous ethanol, add 2 g of silane coupling agent KH-560 under stirring conditions, heat up to 62 °C, and stir and reflux for 7.0 h. After the reaction, filter and wash, and place the product in a vacuum dryer at 60 °C for 12.9 h to obtain epoxy mesoporous silica. Disperse 1 g of hexachlorocyclotriphosphazene in 50 mL of anhydrous toluene to obtain a hexachlorocyclotriphosphazene solution, then disperse 2 g of epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, add 1 mL of anhydrous triethylamine, heat up to 80 °C, and reflux and stir for 9.0 h. After the reaction, filter and wash, and place the product in a vacuum dryer at 60 °C for 12.3 h to obtain phosphazene mesoporous silica;

[0107] Step A3: Disperse 4 g of molecular sieve ZSM-5 in 30 mL of phosphoric acid solution, heat up to 90 °C, stir and react for 6.0 h. After the reaction is completed, filter and wash. Place the product in a vacuum dryer at 101 °C for 14.0 h. Transfer the dried product to a muffle furnace and calcine at 310 °C for 5.0 h to obtain a phosphate molecular sieve.

[0108] Step A4: Place 5 g of ionic flame retardant powder, 2 g of phosphazene mesoporous silica, and 3 g of phosphate molecular sieve in a ball mill and mix evenly. Add 10 g of polyaryletherketone to 50 mL of anhydrous DMF, heat up to 104 °C and stir to dissolve. Then add the ball-milled mixture to the polyaryletherketone solution, adjust the temperature to 86 °C, stir evenly for 7.0 h. Place the product in a vacuum dryer at 103 °C for 12.1 h to obtain a solid complex. Transfer the solid complex to a muffle furnace, heat up to 310 °C and fully calcine for 6.0 h to obtain a composite flame retardant.

[0109] Step S1: Add 8 g of boric acid and 16 g of polyethylene glycol-400 to 80 mL of anhydrous DMF, heat up to 87 °C, stir and react for 1.4 h. After the reaction is completed, place it in a vacuum dryer at 50 °C for 6.1 h to obtain a borate cross-linked precursor.

[0110] Step S2: Disperse 10 g of methyl vinyl phenyl silicone rubber and 0.5 g of furfuraldehyde in 10 mL of anhydrous toluene, then add 0.05 g of tetrabutylammonium bromide, adjust the temperature to 90 °C, stir and react for 2.4 h to obtain a furanized methyl vinyl phenyl silicone rubber matrix solution. Dissolve 0.8 g of N-maleimidocaproic acid in 10 mL of anhydrous toluene and then add it to the furanized methyl vinyl phenyl silicone rubber matrix solution, keep reacting at 83 °C for 4.3 h. After the reaction is completed, vacuum dry to obtain a modified methyl vinyl phenyl silicone rubber.

[0111] Step S3: Mix 100 g of modified methyl vinyl phenyl silicone rubber, 25 g of composite flame retardant, 8 g of iron powder, 30 g of graphene, 6 g of ceramic powder, 2 g of lithium carbonate, 1 g of ammonium metavanadate, 6 g of calcium fluoride, 90 g of alumina, 1 g of ascorbic acid, 22 g of polybutylene terephthalate, 2 g of 1,2-dimethylimidazole, 2 g of potassium citrate, 1 g of dipropylene glycol, 4 g of 1,1-di-tert-butylperoxycyclohexane, 38 g of methyl silicone oil, 1 g of zinc stearate, 50 g of methyl vinyl organopolysiloxane, and 15 g of borate cross-linked precursor evenly, and press to obtain a self-healing silicone rubber flame retardant protective pad for high-temperature welding.

[0112] Comparative Example 1

[0113] This comparative example provides a preparation method for a self-healing silicone rubber flame-retardant protective pad for high-temperature welding. The difference from Example 1 is that the mass of sodium hexametaphosphate in step A1 is 6.3 g, which is 3 g more than that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0114] Comparative Example 2

[0115] This comparative example provides a preparation method for a self-healing silicone rubber flame-retardant protective pad for high-temperature welding. The difference from Example 1 is that the mass of sodium hexametaphosphate in step A1 is 0.3 g, which is 3 g less than that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0116] Comparative Example 3

[0117] The present invention provides a preparation method for a self-healing silicone rubber flame-retardant protective pad for high-temperature welding. The difference from Example 1 is that the mass of N-maleimidocaproic acid in step S2 is adjusted to 1.6 g, which is 0.8 g more than that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0118] Comparative Example 4

[0119] The present invention provides a preparation method for a self-healing silicone rubber flame-retardant protective pad for high-temperature welding. The difference from Example 1 is that the mass of N-maleimidocaproic acid in step S2 is adjusted to 0.1 g, which is 0.7 g less than that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0120] In the present invention, the thermal conductivity of the silicone rubber protective pads prepared in each example and comparative example was tested according to GB / T 10295-2008; the limiting oxygen index of the silicone rubber protective pads prepared in each example and comparative example was tested according to GB / T 10707-2008; the UL94 test was carried out on the silicone rubber protective pads prepared in each example and comparative example according to GB / T 2408-2021. The test results are shown in Table 1.

[0121] Table 1 Test results of self-healing silicone rubber flame-retardant protective pads for high-temperature welding prepared in Examples 1-4 and Comparative Examples 1-4

[0122] <![CDATA[Thermal conductivity (W·(m·K) -1 )]]> Vertical burning (UL94 1.6mm) Limiting oxygen index (%) Example 1 0.15 V-0 33.4 Example 2 0.16 V-0 32.6 Example 3 0.17 V-0 34.5 Example 4 0.15 V-0 32.1 Comparative Example 1 0.31 V-2 21.9 Comparative Example 2 0.33 V-2 21.3 Comparative Example 3 0.36 V-1 20.6 Comparative Example 4 0.39 V-2 21.1

[0123] As can be seen from Table 1, the thermal conductivity of Comparative Example 1 is higher than that of Example 1, and the vertical burning rating and limiting oxygen index are lower than those of Example 1; the thermal conductivity of Comparative Example 2 is higher than that of Example 1, and the vertical burning rating and limiting oxygen index are lower than those of Example 1. Sodium hexametaphosphate is a kind of polyphosphate. In the present invention, the phosphate groups in sodium hexametaphosphate are combined with the cationic structure of cationic phosphazene through ionic bonds to form an ionic network. At high temperatures, sodium hexametaphosphate decomposes to produce phosphoric acid, which further promotes the carbonization of the matrix to form a dense carbon layer, playing a role in heat insulation protection and oxygen isolation. At the same time, the high-temperature decomposition of sodium hexametaphosphate is an endothermic reaction, which can effectively reduce the temperature of the material surface, thereby slowing down the thermal decomposition rate of the material. In Comparative Example 1, there is too much sodium hexametaphosphate. Although sodium hexametaphosphate can promote carbonization and endothermic cooling, excessive sodium hexametaphosphate may lead to too high an inorganic salt content in the material. Excessive inorganic salt particles in the material may cause the appearance of microscopic pores or cracks, increasing the heat conduction paths, weakening the integrity and strength of the matrix, or causing a decrease in the effective proportion of hexachlorocyclotriphosphazene in the material, thereby weakening the overall flame retardant synergistic effect. Therefore, the thermal conductivity increases, and the vertical burning rating and limiting oxygen index decrease. In Comparative Example 2, there is too little sodium hexametaphosphate, and the formation of the ionic network in the material is incomplete, resulting in a decrease in the structural stability of the system. When sodium hexametaphosphate is insufficient, the amount of phosphoric acid and polyphosphoric acid generated by the decomposition of the material at high temperatures decreases, and the carbonization cannot be effectively promoted, resulting in insufficient formation of the carbon layer. Therefore, the thermal conductivity increases, and the vertical burning rating and limiting oxygen index decrease.

[0124] N-maleimidocaproic acid reacts with the furan group introduced by furfuraldehyde to form a thermoreversible dynamic crosslinked network. The N-maleimide group and the furan group undergo a cycloaddition reaction to generate a crosslinking point with a six-membered ring structure. Through the appropriate distribution of crosslinking points, the movement of the molecular chains of the material is restricted, which can improve the mechanical strength and thermal stability of the material. The nitrogen and carbon structures in the N-maleimide group have good carbonization ability at high temperatures, forming a stable carbon layer to isolate heat and oxygen. In Comparative Example 3, too much N-maleimidocaproic acid will cause the crosslinking points to be too dense, resulting in excessive restriction of the molecular chains of the material, a decrease in the flexibility of the molecular chains, and the formation of microscopic rigid regions in the high-density crosslinked structure, increasing the thermal conductivity of the material. Although N-maleimidocaproic acid contains functional groups that contribute to carbonization, its excess will reduce the synergistic effect of other flame retardant components (such as furan groups or borate bonds). In Comparative Example 4, there is insufficient N-maleimidocaproic acid, and the reduction in the number of crosslinking points reduces the overall structural stability of the material. The molecular chains are more likely to decompose under high-temperature conditions or cause a decrease in the thermal oxidation stability of the crosslinked network in the material. Therefore, the thermal conductivity increases, and the vertical burning rating and limiting oxygen index decrease.

[0125] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a self-healing silicone rubber flame-retardant protective pad for high-temperature welding, characterized in that, The preparation method is as follows: Step S1: Add boric acid and polyethylene glycol-400 to anhydrous DMF, and after heating the reaction to completion, a borate cross-linking precursor is obtained. Step S2: Disperse methyl vinyl phenyl silicone rubber and furfural in anhydrous toluene, then add tetrabutylammonium bromide, and react to obtain a furanized methyl vinyl phenyl silicone rubber matrix solution. Dissolve N-maleimidocaproic acid in anhydrous toluene, and then add it to the furanized methyl vinyl phenyl silicone rubber matrix solution, and react to obtain modified methyl vinyl phenyl silicone rubber. Step S3: Mix the modified methyl vinyl phenyl silicone rubber, composite flame retardant, inorganic filler, auxiliary filler and borate cross-linking precursor evenly, and press to obtain a self-healing silicone rubber flame retardant protective pad for high-temperature welding. The preparation method of the composite flame retardant is as follows: Step A1: Disperse hexachlorocyclotriphosphazene in anhydrous acetonitrile, then add pyridine to the anhydrous acetonitrile, and react to obtain a cationic cyclic phosphazene. Disperse the cationic cyclic phosphazene in anhydrous ethanol, then add sodium hexametaphosphate to the anhydrous ethanol, and react to form an ionic bond network, and dry to obtain an ionic flame retardant powder. Step A2: Disperse mesoporous silica in anhydrous ethanol, add a silane coupling agent, and react to obtain epoxy mesoporous silica. Disperse hexachlorocyclotriphosphazene in anhydrous toluene to obtain a hexachlorocyclotriphosphazene solution, then disperse the epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, and then add anhydrous triethylamine, and react to obtain phosphazene mesoporous silica. Step A3: Disperse the molecular sieve in a phosphoric acid solution, transfer the dried product to a muffle furnace after the reaction, and calcine to obtain a phosphate molecular sieve. Step A4: Mix the ionic flame retardant powder, phosphazene mesoporous silica and phosphate molecular sieve. Add polyaryletherketone to anhydrous DMF, then add the ball-milled mixed material to the polyaryletherketone solution, and calcine the obtained solid composite to obtain a composite flame retardant. The mass ratio of the methyl vinyl phenyl silicone rubber to N-maleimidocaproic acid is 25:

2.

2. The preparation method of a self-healing silicone rubber flame retardant protective pad for high-temperature welding according to claim 1, characterized in that, In step S1, The mass ratio of the boric acid to polyethylene glycol-400 is 1:

2. The mass-volume ratio of the boric acid to anhydrous DMF is 1 g:10 mL.

3. The preparation method of a self-healing silicone rubber flame retardant protective pad for high-temperature welding according to claim 1, characterized in that, In step S2, The mass ratio of the methyl vinyl phenyl silicone rubber to furfural is 20:

1. The mass-volume ratio of the methyl vinyl phenyl silicone rubber to anhydrous toluene is 1 g:1 mL. The mass ratio of the methyl vinyl phenyl silicone rubber to tetrabutylammonium bromide is 200:

1. The mass-volume ratio of the N-maleimidocaproic acid to anhydrous toluene is 2 g:25 mL. In step S3, The inorganic filler is iron powder, graphene, ceramic powder, lithium carbonate, ammonium metavanadate, calcium fluoride and alumina, and the mass ratio is 8:30:6:2:1:6:

90. The auxiliary filler is ascorbic acid, polybutylene terephthalate, 1,2-dimethylimidazole, potassium citrate, dipropylene glycol, 1,1-di-tert-butylperoxycyclohexane, methyl silicone oil, zinc stearate and methyl vinyl organopolysiloxane, and the mass ratio is 1:22:2:2:1:4:38:1:

50. The mass ratio of the modified methyl vinyl phenyl silicone rubber, the composite flame retardant, the inorganic filler, the auxiliary filler and the boron ester crosslinking precursor is 100:25:143:121:

15.

4. The preparation method of a self-repairing silicone rubber flame retardant protective pad for high-temperature welding according to claim 1, characterized in that, In step A1, The mass-volume ratio of the hexachlorocyclotriphosphazene to the anhydrous acetonitrile is 1 g:15 mL; The mass ratio of the hexachlorocyclotriphosphazene to the pyridine is 2:(1.3 - 1.5); The mass-volume ratio of the cationic cyclic phosphazene to the anhydrous ethanol is 1 g:15 mL; The mass ratio of the cationic cyclic phosphazene to the sodium hexametaphosphate is 2:(3.3 - 3.5).

5. The preparation method of a self-repairing silicone rubber flame retardant protective pad for high-temperature welding according to claim 1, characterized in that, In step A2, The mass-volume ratio of the mesoporous silica to the anhydrous ethanol is 1 g:25 mL; The silane coupling agent is KH-560, and the mass ratio of the mesoporous silica to the silane coupling agent is 1:1; The mass-volume ratio of the hexachlorocyclotriphosphazene to the anhydrous toluene is 1 g:50 mL; The mass ratio of the hexachlorocyclotriphosphazene to the epoxy mesoporous silica is 1:2; The mass-volume ratio of the epoxy mesoporous silica to the anhydrous triethylamine is 2 g:1 mL.

6. The preparation method of a self-repairing silicone rubber flame retardant protective pad for high-temperature welding according to claim 1, characterized in that, In step A3, The molecular sieve is ZSM-5, and the mass-volume ratio of the molecular sieve to the phosphoric acid solution is 4 g:30 mL; The mass ratio of the phosphoric acid to the deionized water in the phosphoric acid solution is 2:15; The calcination time is 4 - 5 h.

7. The preparation method of a self-healing silicone rubber flame retardant protective pad for high-temperature welding according to claim 1, characterized in that, In step A4, The mass ratio of the ionic flame retardant powder, the phosphazene mesoporous silica and the phosphate molecular sieve is 5:2:3; The mass ratio of the ionic flame retardant powder to the polyaryletherketone is 1:2; The mass-volume ratio of the polyaryletherketone to the anhydrous DMF is 1 g:5 mL; The calcination time is 6 - 7 h.

8. A self-healing silicone rubber flame retardant protective pad for high-temperature welding obtained by the preparation method according to any one of claims 1 - 7.

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