Self-repairing silicone rubber flame-retardant protective pad for high-temperature welding and preparation method thereof

Abstract

The invention belongs to the technical field of preparation of flame-retardant materials, and provides a self-repairing silicone rubber flame-retardant protective pad for high-temperature welding and a preparation method of the self-repairing silicone rubber flame-retardant protective pad. The preparation method comprises the following steps: reacting phosphonitrilic chloride trimer with pyridine to prepare ionic flame-retardant powder; the preparation method comprises the following steps: modifying mesoporous silica by using a silane coupling agent and preparing phosphazene mesoporous silica; modifying a molecular sieve with phosphoric acid, calcining at high temperature to form a phosphate molecular sieve, and mixing to prepare a composite flame retardant; secondly, constructing a boron ester cross-linked precursor with dynamic self-repairing capability through boric acid, introducing a furan group through furan formaldehyde to prepare a furanized methyl vinyl phenyl silicone rubber matrix, and further modifying the silicone rubber through reversible cross-linking reaction of N-maleimidohexanoic acid and the furan group to endow the silicone rubber with high-temperature self-repairing performance; and finally, mixing the modified methyl vinyl phenyl silicone rubber, a composite flame retardant, an inorganic filler, an auxiliary filler and the boron ester crosslinking precursor to obtain the self-repairing silicone rubber flame-retardant protective pad for high-temperature welding.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant material preparation, and relates to a self-repairing 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 used in aerospace, automobile 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 will not only pose a safety threat to operators, but may also damage surrounding equipment, environment and materials and even cause fires. Traditional high-temperature protective materials, such as glass fiber fabrics, ceramic fiber mats, etc., although they can isolate heat radiation and high-temperature molten droplets to a certain extent, are easy to decompose or burn under high temperature conditions, and cannot meet the flame retardant requirements in extreme environments. In addition, traditional materials are difficult to repair themselves after being damaged (such as cracks and melting) at high temperatures, which affects the service life and increases the replacement cost. Silicone rubber has gradually become the preferred material for high-temperature protection due to its excellent flexibility, heat resistance and chemical stability. However, single silicone rubber materials still have insufficient high-temperature flame retardant properties, especially under extreme conditions such as welding operations. It cannot meet actual needs. Therefore, it has become an important demand in the field of industrial safety to prepare a silicone rubber flame retardant protective pad for high-temperature welding that also has self-repairing ability. Summary of the invention

[0003] In view of the shortcomings of the prior art, 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 takes methyl vinyl phenyl silicone rubber as a matrix, chemically modifies it, introduces dynamic boron ester bonds and a reversible cross-linking network, thereby realizing the self-healing function of the material. At the same time, by preparing a multifunctional composite flame retardant, combining inorganic fillers and auxiliary fillers, the flame retardant properties and thermal stability of the material are improved to meet the needs of actual production.

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

[0005] In a first aspect, the present invention provides a method for preparing a self-repairing silicone rubber flame retardant protective pad for high temperature welding, the preparation method comprising:

[0006] Step A1, dispersing hexachlorocyclotriphosphazene in anhydrous acetonitrile, then adding pyridine to the anhydrous acetonitrile, heating to a first temperature for reflux reaction, cooling to room temperature after the reaction, adding acetone for filtration and washing to obtain a cationic cyclic phosphazene, dispersing the cationic cyclic phosphazene in anhydrous ethanol, then adding sodium hexametaphosphate to the anhydrous ethanol, heating to a second temperature for reaction under stirring, and distilling and drying under reduced pressure to obtain an ionic flame retardant powder;

[0007] Step A2, dispersing mesoporous silica in anhydrous ethanol, adding a silane coupling agent under stirring, heating to a first temperature, stirring and refluxing to react, filtering and washing after the reaction is completed, placing the product under vacuum drying at a second temperature to obtain epoxy mesoporous silica, dispersing hexachlorocyclotriphosphazene in anhydrous toluene to obtain a hexachlorocyclotriphosphazene solution, then dispersing epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, adding anhydrous triethylamine, heating to a third temperature, refluxing and stirring to react, filtering and washing after the reaction is completed, placing the product under vacuum drying at the second temperature to obtain phosphazene mesoporous silica;

[0008] Step A3, dispersing the molecular sieve in a phosphoric acid solution, heating to a third temperature, stirring to react, filtering and washing after the reaction is completed, placing the product under vacuum drying at a fourth temperature, transferring the dried product to a muffle furnace, and calcining at a fifth temperature to obtain a phosphate molecular sieve;

[0009] Step A4, placing the ionic flame retardant powder, phosphazene mesoporous silica and phosphate molecular sieve in a ball mill and mixing them evenly, adding the polyaryletherketone to anhydrous DMF, heating to a fourth temperature and stirring to dissolve, then adding the ball-milled mixture to the polyaryletherketone solution, adjusting the temperature to the third temperature, stirring evenly, placing the product under vacuum drying at a fourth temperature to obtain a solid composite, transferring the solid composite to a muffle furnace, heating to a fifth temperature and fully calcining to obtain a composite flame retardant.

[0010] Step S1, adding boric acid and polyethylene glycol-400 to anhydrous DMF, heating to a third temperature, stirring for reaction, and placing under vacuum drying at a second temperature after the reaction is completed to obtain a boron ester cross-linking precursor;

[0011] Step S2, dispersing methyl vinyl phenyl silicone rubber and furan formaldehyde in anhydrous toluene, adding tetrabutylammonium bromide, adjusting the temperature to a third temperature, stirring to react, obtaining a furanized methyl vinyl phenyl silicone rubber matrix solution, dissolving N-maleimidocaproic acid in anhydrous toluene, adding the solution to the furanized methyl vinyl phenyl silicone rubber matrix solution, maintaining the third temperature to continue the reaction, and vacuum drying after the reaction to obtain the modified methyl vinyl phenyl silicone rubber;

[0012] Step S3, uniformly mixing the modified methyl vinyl phenyl silicone rubber, the composite flame retardant, the inorganic filler, the auxiliary filler and the boron ester cross-linking precursor, and pressing to obtain a self-healing silicone rubber flame retardant protective pad for high temperature welding.

[0013] Hexachlorocyclotriphosphazene is a six-membered cyclic compound. Three phosphorus atoms and three nitrogen atoms are arranged alternately in its structure to form a PN conjugated system. The phosphorus atom is connected to the chlorine atom through a P-Cl bond with strong polarity. The strong electronegativity of chlorine makes the P-Cl bond have significant polarity. The phosphorus atom carries a partial positive charge. Since the lone pair of electrons of the nitrogen atom participates in the weak conjugation effect of the ring, the hexachlorocyclotriphosphazene exhibits electron-deficient characteristics as a whole, and the phosphorus atom shows high reactivity to nucleophilic reagents. The pyridine molecule contains a nitrogen atom with a lone pair of electrons, which can react with an electron-deficient phosphorus atom as a nucleophile. The lone pair of electrons on the nitrogen atom of pyridine attacks the phosphorus atom of hexachlorocyclotriphosphazene. At the same time, the electron cloud of the P-Cl bond shifts to the chlorine atom. Subsequently, the P-Cl bond breaks, and the chloride ion is detached as a leaving group to generate a phosphorus-nitrogen bond. Due to the nucleophilic attack of the pyridine molecule, part of the chlorine in the 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 has a positive charge and is cationic. The cationic phosphazene compound has good solubility and reactivity, which provides a basis for the subsequent reaction with sodium hexametaphosphate. Sodium hexametaphosphate is a cyclic polyphosphate composed of six phosphate units connected by POP bonds. The molecule contains six sodium cations and one polyphosphate anion. The polyphosphate anion has a high degree of negative charge and strong coordination ability, and can undergo ionic bonding or electrostatic attraction with positively charged compounds. The positive charge center of the cationic phosphazene combines with the polyphosphate anion of sodium hexametaphosphate through electrostatic action to generate an ionic bond network of a supramolecular structure. The positive charge in the cationic phosphazene reacts with the polyphosphate anion through electrostatic attraction. Multiple cationic phosphazene molecules interact with one hexametaphosphate anion to form an ionic network system. This ionic network structure is further stabilized by electrostatic forces and weak hydrogen bonds.

[0014] Polyphosphate anion is a cyclic structure, which is composed of six phosphorus atoms and oxygen atoms connected by POP bonds to form a stable polyanion system. Polyphosphate anion has good thermal stability due to its cyclic polyphosphorus oxygen bond structure. When the temperature continues to rise, the anion will gradually break and release small molecular phosphoric acid compounds (such as metaphosphate HPO 3 and orthophosphate H 3 PO 4). 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. It has high hydrophilicity and thermal instability. It is easy to further dehydrate and condense at high temperature, losing water molecules to generate polyphosphoric acid with a higher degree of polymerization. Polyphosphoric acid has excellent thermal stability. At the same time, phosphoric acid compounds show catalytic effects at high temperatures and can promote the dehydration and carbonization reactions of organic materials. Phosphoric acid compounds are strong acidic substances and can act as dehydration catalysts to promote the dehydration reactions 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; phosphoric acid compounds can also catalyze the carbonization reaction of the material. The dehydration of phosphoric acid compounds removes volatile groups in the material and reduces the release of combustible 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 prevent further combustion. And hexachlorocyclotriphosphazene decomposes at high temperatures to generate phosphorus oxide intermediates (such as PO·, PO 2 ·), can capture active free radicals in the combustion chain, phosphorus oxides react with free radicals, reduce the free radical concentration in the combustion chain reaction, reduce 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 action and ionic bonds. The ionic network structure has strong stability at high temperatures, is not easy to decompose or destroy, 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 ethanol solution, the methoxy part of the silane coupling agent KH-560 is hydrolyzed to generate silanol groups, which then undergo 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 mesoporous silica, providing reaction sites for the subsequent reaction with hexachlorocyclotriphosphazene. At the same time, the electron deficiency of hexachlorocyclotriphosphazene makes it easy to undergo ring-opening reaction with epoxy groups. Triethylamine, as an alkaline catalyst, promotes the ring-opening of epoxy groups. The phosphorus atoms in hexachlorocyclotriphosphazene undergo further nucleophilic reaction with the hydroxyl groups after ring-opening to generate phosphazene-modified mesoporous silica. The high specific surface area and uniform distribution of phosphazene mesoporous silica enable it to fully contact with the matrix material, effectively catalyzing the dehydration and carbonization reaction of the matrix material during the carbonization process. The generated carbonaceous material can evenly cover the surface of the mesoporous silica to form a dense carbonized layer. The regular pore structure of the mesoporous silica allows the carbonaceous material to be deposited along the pores at high temperatures, and forms a continuous carbon network inside and outside the pores, thereby improving the overall strength and thermal stability of the carbonized layer. The template effect of the mesoporous silica gives the carbonized layer a higher density and consistency, thereby preventing heat conduction and oxygen diffusion, and significantly improving the thermal insulation and flame retardant properties of the material. At high temperatures, the phosphoric acid compounds (H 3 PO 4 , HPO 3 ) further catalyzes the carbonization reaction of the matrix material and cooperates with the template effect of mesoporous silica to generate a denser carbonization layer.

[0016] ZSM-5 is an aluminosilicate molecular sieve whose skeleton is composed of silicon-oxygen tetrahedrons and aluminum-oxygen tetrahedrons connected by oxygen bridges (Si-O-Al) to form a three-dimensional pore structure. 3 PO 4The hydroxyl groups of ZSM-5 react with the acidic hydroxyl groups on the surface of ZSM-5 to form Si-OP bonds and release water molecules. The pore system of ZSM-5 provides efficient adsorption sites for phosphoric acid molecules. Phosphoric acid molecules are adsorbed in the pores of the molecular sieve through hydrogen bonds or electrostatic effects. During the calcination stage, the adsorbed phosphoric acid molecules may further dehydrate and condense to form a metaphosphoric acid or polyphosphoric acid coating layer. In addition, under acidic conditions, phosphoric acid may have a certain etching effect on the surface structure of ZSM-5, partially dissolving Si-O-Si bonds, exposing more active sites, and enhancing the chemical activity of the molecular sieve and its compatibility with the polymer matrix. During the high-temperature calcination process, phosphoric acid substances further dehydrate and condense to form a thermally stable phosphate molecular sieve. Phosphoric acid loses water to form metaphosphoric acid or polyphosphoric acid. Metaphosphoric acid or polyphosphoric acid further condenses with the surface hydroxyl groups of the molecular sieve to form a stable phosphate bond. During the calcination stage, the phosphate is evenly distributed on the surface and pores of ZSM-5 to form 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 difficult to decompose under high temperature conditions. The phosphoric acid compounds released when the phosphate decomposes further catalyze the dehydration and carbonization of the matrix material, improving the flame retardant properties 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 molecular sieve's adsorption capacity for volatile combustible products and reducing the flammability of the combustion products. Polyaryletherketone is a typical highly heat-resistant polymer, and its basic structure is composed 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), thereby enhancing the interfacial bonding force between polyaryletherketone and 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 some molecular chains of polyaryletherketone to dehydrate and carbonize at high temperature, promoting the orderly formation of the carbonized layer of polyaryletherketone, thereby improving the density, strength and thermal insulation of the carbonized layer.

[0017] The boric acid molecule contains three hydroxyl groups connected to the central boron atom. Due to its electron defect, the boron atom exhibits Lewis acidity and can accept electron pairs to react chemically with hydroxyl groups or other nucleophilic groups. The hydroxyl groups of boric acid react with the hydroxyl groups of hydroxyl-containing compounds (polyethylene glycol-400) under anhydrous conditions to form boron ester bonds. The boron ester bond is a strong covalent bond with a high dissociation energy. It can remain stable at high temperatures and is not easy to decompose. At the same time, the cross-linked structure of the boron ester bond limits the free movement of the molecular chain, increases the glass transition temperature and thermal decomposition temperature of the material, and can also serve as a physical cross-linking point to form a dynamic cross-linking network, giving the material a certain self-healing ability and heat resistance. A three-dimensional network is formed in silicone rubber through cross-linking of silicon-oxygen bonds. The boron atoms in the boranoic acid cross-linking precursor can act as Lewis acid catalysts to promote the cross-linking reaction of silicon-oxygen bonds. The BOC bonds in the boranoic acid cross-linking precursor work synergistically with the Si-O bonds of silicone rubber to form a denser cross-linking network, which significantly improves the thermal stability and mechanical properties of the material. The physical cross-linking characteristics of the boranoic acid bonds give silicone rubber a certain self-healing ability, and the boranoic acid precursor inhibits the thermal decomposition of silicone rubber through cross-linking. At the same time, the generated boron oxide forms a protective thermal insulation layer at high temperature, further improving the flame retardant properties 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 methylvinylphenyl 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 methylvinylphenyl silicone rubber to form a stable ring structure, providing a new cross-linking point for the silicone rubber matrix. In addition, 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, which further cross-links the silicone rubber molecular chains to form a three-dimensional cross-linking network. The addition reaction of the furan group and the maleimide group forms new cross-linking points between the silicone rubber molecular chains, which significantly increases the cross-linking density. The higher cross-linking density restricts the free movement of the molecular chains and improves the mechanical strength of the material. The aldehyde group of furan carboxaldehyde combines with the vinyl group of methyl vinyl phenyl silicone rubber through an addition reaction to form silicone rubber containing furan groups; the furan ring of furan carboxaldehyde 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 furan carboxaldehyde reacts with the imide group of maleimide anhydride to form a cross-linked network. The cycloaddition product and imide group generated by the reaction give the material a higher thermal decomposition temperature, thereby enhancing the high-temperature stability of the material. At the same time, the thermal reversibility of the reaction provides the material with dynamic adjustment capabilities at high temperatures, while giving the material a certain self-healing function.

[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 optional examples, the mass ratio of 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 it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] In some optional instances, 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, and other unlisted values ​​within the numerical range are also applicable.

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

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

[0024] In some optional 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 it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] In some optional instances, 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, and other unlisted values ​​within the numerical range are also applicable.

[0026] In some optional examples, the second temperature stirring reaction time is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

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

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

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

[0030] In some optional examples, the drying time after the addition of the silane coupling agent is 12-14 hours, for example, it can be 12.0 hours, 12.2 hours, 12.4 hours, 12.6 hours, 12.8 hours, 13.0 hours, 13.2 hours, 13.4 hours, 13.6 hours, 13.8 hours or 14.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

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

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

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

[0034] In some optional instances, 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

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

[0036] In some optional examples, the drying time after adding anhydrous triethylamine is 12-14h, for example, it can be 12.0h, 12.2h, 12.4h, 12.6h, 12.8h, 13.0h, 13.2h, 13.4h, 13.6h, 13.8h or 14.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also 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 4g:30mL.

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

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

[0040] In some optional instances, 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] In some optional examples, the fourth temperature drying time is 12-14h, for example, it can be 12.0h, 12.2h, 12.4h, 12.6h, 12.8h, 13.0h, 13.2h, 13.4h, 13.6h, 13.8h or 14.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] In some optional instances, the fifth temperature is 300-350°C, for example, it may 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] In some optional examples, the calcination time is 4-5h, for example, it can be 4.0h, 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h or 5.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also 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 optional examples, the mass ratio of the ionic flame retardant powder to the polyaryletherketone is 1:2.

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

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

[0048] In some optional examples, the vacuum drying time is 12-14 hours, for example, it can be 12.0 hours, 12.2 hours, 12.4 hours, 12.6 hours, 12.8 hours, 13.0 hours, 13.2 hours, 13.4 hours, 13.6 hours, 13.8 hours or 14.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

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

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

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

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

[0053] In some optional examples, the vacuum drying time is 6-8h, for example, it can be 6.0h, 6.2h, 6.4h, 6.6h, 6.8h, 7.0h, 7.2h, 7.4h, 7.6h, 7.8h or 8.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also 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 optional examples, the mass volume ratio of the methyl vinyl phenyl silicone rubber to anhydrous toluene is 1 g:1 mL.

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

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

[0058] In some optional examples, the mass ratio of the methylvinylphenyl silicone rubber to N-maleimidocaproic acid is 25:2.

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

[0060] In some optional examples, the reaction time after adding N-maleimidocaproic acid is 4-5h, for example, it can be 4.0h, 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h or 5.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also 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 aluminum oxide, and the mass ratio is 8:30:6:2:1:6:90.

[0062] In some optional examples, the auxiliary filler is ascorbic acid, polybutylene terephthalate, 1,2-dimethylimidazole, potassium citrate, dipropylene glycol, 1,1-di-tert-butyl peroxide cyclohexane, 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 optional examples, 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 cross-linking 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 is prepared by the preparation method described in the first aspect.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] (1) Boric acid is introduced to react with polyethylene glycol to generate a dynamic boron ester bond cross-linking precursor, which gives the material dynamic reconfigurability under high temperature conditions, so that the protective pad can achieve self-repair through dynamic cross-linking after being damaged. Methyl vinyl phenyl silicone rubber modified with furan formaldehyde is reacted with N-maleimidocaproic acid to construct a thermally reversible cross-linking network, further enhancing the material's self-repair ability and high-temperature performance;

[0067] (2) By preparing ionic flame retardant powder, the heat shielding ability and flame retardant efficiency of the flame retardant are improved, the mesoporous silica is epoxy-modified by a silane coupling agent, and phosphazene groups are further introduced to prepare phosphazene mesoporous silica, thereby enhancing the thermal stability and carbonization ability of the material, and the phosphate molecular sieve is prepared by phosphoric acid modification and high-temperature calcination, giving the material good flame retardant properties and high-temperature decomposition endothermic characteristics, and calcining to form a composite flame retardant to improve the flame retardant properties of the material;

[0068] (3) A multi-component synergistic system was constructed by combining the modified silicone rubber matrix with a composite flame retardant, an inorganic filler and an auxiliary filler. While improving the flame retardant properties 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. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0072] Figure 4 This is a SEM image of the phosphate molecular sieve prepared in Example 1 of the present invention (scale: 500 nm). DETAILED DESCRIPTION

[0073] The technical solution of the present invention is described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific embodiments of the present invention, which are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limitations on the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments recorded herein.

[0074] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products without any further purification treatment.

[0075] Example 1

[0076] This embodiment provides a method for preparing a self-repairing silicone rubber flame retardant protective pad for high temperature welding, and the preparation method specifically comprises the following steps:

[0077] Step A1, dispersing 1 g of hexachlorocyclotriphosphazene in 15 mL of anhydrous acetonitrile, adding 0.7 g of pyridine to the anhydrous acetonitrile, heating to 63° C. and reflux reaction for 12.3 h, cooling to room temperature after the reaction, adding acetone to filter and wash to obtain a cationic cyclic phosphazene, dispersing 2 g of the cationic cyclic phosphazene in 30 mL of anhydrous ethanol, adding 3.3 g of sodium hexametaphosphate to the anhydrous ethanol, heating to 60° C. and reacting for 2.6 h under stirring conditions, and distilling and drying under reduced pressure to obtain an ionic flame retardant powder;

[0078] Step A2, dispersing 2g of mesoporous silica in 50mL of anhydrous ethanol, adding 2g of silane coupling agent KH-560 under stirring, heating to 67°C, stirring and refluxing for 6.3h, filtering and washing after the reaction, placing the product at 52°C in vacuum and drying for 12.3h to obtain epoxy mesoporous silica, dispersing 1g of hexachlorocyclotriphosphazene in 50mL of anhydrous toluene to obtain a hexachlorocyclotriphosphazene solution, and then dispersing 2g of epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, and then adding 1mL of anhydrous triethylamine, heating to 87°C, refluxing and stirring for 8.7h, filtering and washing after the reaction, and placing the product at 54°C in vacuum and drying for 13.4h to obtain phosphazene mesoporous silica;

[0079] Step A3, dispersing 4 g of molecular sieve ZSM-5 in 30 mL of phosphoric acid solution, heating to 87° C., stirring and reacting for 6.3 h, filtering and washing after the reaction is completed, placing the product under vacuum drying at 109° C. for 12.9 h, transferring the dried product to a muffle furnace, and calcining at 320° C. for 4.6 h to obtain a phosphate molecular sieve;

[0080] Step A4, place 5g of ionic flame retardant powder, 2g of phosphazene mesoporous silica and 3g of phosphate molecular sieve in a ball mill and mix evenly, add 10g of polyaryletherketone into 50mL of anhydrous DMF, heat to 106°C and stir to dissolve, then add the ball-milled mixture to the polyaryletherketone solution, adjust the temperature to 84°C, stir evenly for 6.3h, place the product at 100°C and vacuum dry for 12.6h to obtain a solid composite, transfer the solid composite to a muffle furnace, heat to 340°C and fully calcine for 6.3h to obtain a composite flame retardant.

[0081] Step S1, adding 6 g of boric acid and 12 g of polyethylene glycol-400 to 60 mL of anhydrous DMF, heating to 84° C., stirring for reaction for 1.6 h, and after the reaction is completed, placing under vacuum drying at 57° C. for 6.7 h to obtain a boron ester cross-linking precursor;

[0082] Step S2, dispersing 10g of methyl vinyl phenyl silicone rubber and 0.5g of furan formaldehyde in 10mL of anhydrous toluene, adding 0.05g of tetrabutylammonium bromide, adjusting the temperature to 87°C, stirring and reacting for 2.6h to obtain a furanized methyl vinyl phenyl silicone rubber matrix solution, dissolving 0.8g of N-maleimidocaproic acid in 10mL of anhydrous toluene, and then adding it to the furanized methyl vinyl phenyl silicone rubber matrix solution, maintaining 89°C and continuing the reaction for 4.9h, and vacuum drying after the reaction to obtain a modified methyl vinyl phenyl silicone rubber;

[0083] Step S3, 100g modified methyl vinyl phenyl silicone rubber, 25g composite flame retardant, 8g iron powder, 30g graphene, 6g ceramic powder, 2g lithium carbonate, 1g ammonium metavanadate, 6g calcium fluoride, 90g aluminum oxide, 1g ascorbic acid, 22g polybutylene terephthalate, 2g 1,2-dimethylimidazole, 2g potassium citrate, 1g dipropylene glycol, 4g 1,1-di-tert-butyl peroxide cyclohexane, 38g methyl silicone oil, 1g zinc stearate, 50g methyl vinyl organopolysiloxane and 15g boron ester cross-linked precursor are mixed evenly, and pressed to obtain a self-healing silicone rubber flame retardant protective pad for high temperature welding.

[0084] Figure 1 This is a SEM image of the phosphazene mesoporous silica prepared in Example 1 of the present invention; Figure 2 This is a SEM image of the phosphate molecular sieve prepared in Example 1 of the present invention; Figure 3 This is a 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 the particles are relatively uniform; Figure 4 This is a SEM image of the phosphate molecular sieve prepared in Example 1 of the present invention.

[0085] Example 2

[0086] This embodiment provides a method for preparing a self-repairing silicone rubber flame retardant protective pad for high temperature welding, and the preparation method specifically comprises the following steps:

[0087] Step A1, dispersing 2 g of hexachlorocyclotriphosphazene in 30 mL of anhydrous acetonitrile, adding 1.45 g of pyridine to the anhydrous acetonitrile, heating to 60° C. and reflux reaction for 12.0 h, cooling to room temperature after the reaction, adding acetone to filter and wash to obtain a cationic cyclic phosphazene, dispersing 2 g of the cationic cyclic phosphazene in 30 mL of anhydrous ethanol, adding 3.4 g of sodium hexametaphosphate to the anhydrous ethanol, heating to 50° C. and reacting for 2.0 h under stirring conditions, and distilling and drying under reduced pressure to obtain an ionic flame retardant powder;

[0088] Step A2, dispersing 3g of mesoporous silica in 75mL of anhydrous ethanol, adding 3g of silane coupling agent KH-560 under stirring, heating to 74°C, stirring and refluxing for 6.7h, filtering and washing after the reaction, placing the product at 50°C in vacuum and drying for 13.6h to obtain epoxy mesoporous silica, dispersing 1.5g of hexachlorocyclotriphosphazene in 75mL of anhydrous toluene to obtain a hexachlorocyclotriphosphazene solution, and then dispersing 3g of epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, and then adding 1.5mL of anhydrous triethylamine, heating to 90°C, refluxing and stirring for 8.3h, filtering and washing after the reaction, and placing the product at 50°C in vacuum and drying for 13.0h to obtain phosphazene mesoporous silica;

[0089] Step A3, dispersing 4 g of molecular sieve ZSM-5 in 30 mL of phosphoric acid solution, heating to 81° C., stirring and reacting for 6.7 h, filtering and washing after the reaction is completed, placing the product under vacuum drying at 103° C. for 13.4 h, transferring the dried product to a muffle furnace, and calcining at 350° C. for 4.1 h to obtain a phosphate molecular sieve;

[0090] Step A4, place 2.5g of ionic flame retardant powder, 1g of phosphazene mesoporous silica and 1.5g of phosphate molecular sieve in a ball mill and mix evenly, add 5g of polyaryletherketone into 25mL of anhydrous DMF, heat to 102°C and stir to dissolve, then add the ball-milled mixture to the polyaryletherketone solution, adjust the temperature to 80°C, stir evenly for 6.0h, place the product at 109°C and vacuum dry for 13.2h to obtain a solid composite, transfer the solid composite to a muffle furnace, heat to 330°C and fully calcine for 6.8h to obtain a composite flame retardant.

[0091] Step S1, adding 4 g of boric acid and 8 g of polyethylene glycol-400 to 40 mL of anhydrous DMF, heating to 80° C., stirring for reaction for 1.1 h, and after the reaction is completed, placing under vacuum drying at 59° C. for 7.3 h to obtain a boron ester cross-linking precursor;

[0092] Step S2, dispersing 20g of methyl vinyl phenyl silicone rubber and 1g of furan formaldehyde in 20mL of anhydrous toluene, adding 0.1g of tetrabutylammonium bromide, adjusting the temperature to 83°C, stirring and reacting for 2.1h to obtain a furanized methyl vinyl phenyl silicone rubber matrix solution, dissolving 1.6g of N-maleimidocaproic acid in 20mL of anhydrous toluene, and then adding it to the furanized methyl vinyl phenyl silicone rubber matrix solution, maintaining 84°C and continuing the reaction for 4.1h, and vacuum drying after the reaction to obtain a modified methyl vinyl phenyl silicone rubber;

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

[0094] Example 3

[0095] This embodiment provides a method for preparing a self-repairing silicone rubber flame retardant protective pad for high temperature welding, and the preparation method specifically comprises the following steps:

[0096] Step A1, dispersing 4 g of hexachlorocyclotriphosphazene in 60 mL of anhydrous acetonitrile, adding 2.8 g of pyridine to the anhydrous acetonitrile, heating to 74° C. and reflux reaction for 13.0 h, cooling to room temperature after the reaction, adding acetone to filter and wash to obtain a cationic cyclic phosphazene, dispersing 2 g of the cationic cyclic phosphazene in 30 mL of anhydrous ethanol, adding 3.5 g of sodium hexametaphosphate to the anhydrous ethanol, heating to 52° C. and reacting for 2.4 h under stirring conditions, and distilling and drying under reduced pressure to obtain an ionic flame retardant powder;

[0097] Step A2, dispersing 4g of mesoporous silica in 100mL of anhydrous ethanol, adding 4g of silane coupling agent KH-560 under stirring, heating to 80°C, stirring and refluxing for 6.0h, filtering and washing after the reaction, placing the product at 56°C in vacuum and drying for 14.0h to obtain epoxy mesoporous silica, dispersing 2g of hexachlorocyclotriphosphazene in 100mL of anhydrous toluene to obtain a hexachlorocyclotriphosphazene solution, and then dispersing 4g of epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, and then adding 2mL of anhydrous triethylamine, heating to 84°C, refluxing and stirring for 8.0h, filtering and washing after the reaction, and placing the product at 58°C in vacuum and drying for 14.0h to obtain phosphazene mesoporous silica;

[0098] Step A3, dispersing 4 g of molecular sieve ZSM-5 in 30 mL of phosphoric acid solution, heating to 84° C., stirring and reacting for 7.0 h, filtering and washing after the reaction is completed, placing the product under vacuum drying at 110° C. for 12.1 h, transferring the dried product to a muffle furnace, and calcining at 340° C. for 4.9 h to obtain a phosphate molecular sieve;

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

[0100] Step S1, adding 6 g of boric acid and 12 g of polyethylene glycol-400 to 60 mL of anhydrous DMF, heating to 90° C., stirring for reaction for 1.9 h, and after the reaction is completed, placing under vacuum drying at 53° C. for 8.0 h to obtain a boron ester cross-linking precursor;

[0101] Step S2, dispersing 20g of methyl vinyl phenyl silicone rubber and 1g of furan formaldehyde in 20mL of anhydrous toluene, adding 0.1g of tetrabutylammonium bromide, adjusting the temperature to 80°C, stirring and reacting for 3.0h to obtain a furanized methyl vinyl phenyl silicone rubber matrix solution, dissolving 1.6g of N-maleimidocaproic acid in 20mL of anhydrous toluene, and then adding it to the furanized methyl vinyl phenyl silicone rubber matrix solution, maintaining 80°C and continuing the reaction for 4.6h, and vacuum drying after the reaction to obtain a modified methyl vinyl phenyl silicone rubber;

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

[0103] Example 4

[0104] This embodiment provides a method for preparing a self-repairing silicone rubber flame retardant protective pad for high temperature welding, and the preparation method specifically comprises the following steps:

[0105] Step A1, dispersing 2 g of hexachlorocyclotriphosphazene in 30 mL of anhydrous acetonitrile, adding 1.37 g of pyridine to the anhydrous acetonitrile, heating to 80° C. and reflux reaction for 12.7 h, cooling to room temperature after the reaction, adding acetone to filter and wash to obtain a cationic cyclic phosphazene, dispersing 2 g of the cationic cyclic phosphazene in 30 mL of anhydrous ethanol, adding 3.4 g of sodium hexametaphosphate to the anhydrous ethanol, heating to 57° C. and reacting for 3.0 h under stirring conditions, and distilling and drying under reduced pressure to obtain an ionic flame retardant powder;

[0106] Step A2, dispersing 2g of mesoporous silica in 50mL of anhydrous ethanol, adding 2g of silane coupling agent KH-560 under stirring, heating to 62°C, stirring and refluxing for 7.0h, filtering and washing after the reaction, placing the product at 60°C in vacuum and drying for 12.9h to obtain epoxy mesoporous silica, dispersing 1g of hexachlorocyclotriphosphazene in 50mL of anhydrous toluene to obtain a hexachlorocyclotriphosphazene solution, and then dispersing 2g of epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, and then adding 1mL of anhydrous triethylamine, heating to 80°C, refluxing and stirring for 9.0h, filtering and washing after the reaction, and placing the product at 60°C in vacuum and drying for 12.3h to obtain phosphazene mesoporous silica;

[0107] Step A3, dispersing 4 g of molecular sieve ZSM-5 in 30 mL of phosphoric acid solution, heating to 90° C., stirring and reacting for 6 h, filtering and washing after the reaction is completed, placing the product under vacuum drying at 101° C. for 14 h, transferring the dried product to a muffle furnace, and calcining at 310° C. for 5 h to obtain a phosphate molecular sieve;

[0108] Step A4, place 5g of ionic flame retardant powder, 2g of phosphazene mesoporous silica and 3g of phosphate molecular sieve in a ball mill and mix evenly, add 10g of polyaryletherketone into 50mL of anhydrous DMF, heat 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 7.0h, place the product at 103°C and vacuum dry for 12.1h to obtain a solid composite, transfer the solid composite to a muffle furnace, heat to 310°C and fully calcine for 6.0h to obtain a composite flame retardant.

[0109] Step S1, adding 8 g of boric acid and 16 g of polyethylene glycol-400 to 80 mL of anhydrous DMF, heating to 87° C., stirring and reacting for 1.4 h, and after the reaction is completed, placing under vacuum drying at 50° C. for 6.1 h to obtain a boron ester cross-linking precursor;

[0110] Step S2, dispersing 10g of methyl vinyl phenyl silicone rubber and 0.5g of furan formaldehyde in 10mL of anhydrous toluene, adding 0.05g of tetrabutylammonium bromide, adjusting the temperature to 90°C, stirring and reacting for 2.4h to obtain a furanized methyl vinyl phenyl silicone rubber matrix solution, dissolving 0.8g of N-maleimidocaproic acid in 10mL of anhydrous toluene, and then adding it to the furanized methyl vinyl phenyl silicone rubber matrix solution, maintaining 83°C and continuing the reaction for 4.3h, and vacuum drying after the reaction to obtain a modified methyl vinyl phenyl silicone rubber;

[0111] Step S3, 100g modified methyl vinyl phenyl silicone rubber, 25g composite flame retardant, 8g iron powder, 30g graphene, 6g ceramic powder, 2g lithium carbonate, 1g ammonium metavanadate, 6g calcium fluoride, 90g aluminum oxide, 1g ascorbic acid, 22g polybutylene terephthalate, 2g 1,2-dimethylimidazole, 2g potassium citrate, 1g dipropylene glycol, 4g 1,1-di-tert-butyl peroxide cyclohexane, 38g methyl silicone oil, 1g zinc stearate, 50g methyl vinyl organopolysiloxane and 15g boron ester cross-linked precursor are mixed evenly, and pressed 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 method for preparing 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. The 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 method for preparing 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, and the 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 method for preparing 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, and the 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 method for preparing 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, and the 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 embodiment and the comparative example was tested according to GB / T 10295-2008; the limiting oxygen index of the silicone rubber protective pads prepared in each embodiment and the comparative example was tested according to GB / T 10707-2008; and the UL94 test of the silicone rubber protective pads prepared in each embodiment and the comparative example was performed according to GB / T 2408-2021. The test results are shown in Table 1.

[0121] Table 1 Test results of self-repairing 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 (UL941.6mm) 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 combustion level 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 combustion level and limiting oxygen index are lower than those of Example 1. Sodium hexametaphosphate is a polyphosphate. In the present invention, the phosphate in sodium hexametaphosphate is combined with the cationic structure of the cationic phosphazene through an ionic bond 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, which plays 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 heat absorption and cooling, excessive sodium hexametaphosphate may cause the inorganic salt content in the material to be too high. Excessive inorganic salt particles may cause the appearance of microscopic pores or cracks in the material, which increases the heat conduction path, weakens the integrity and strength of the matrix, or causes the effective proportion of hexachlorocyclotriphosphazene in the material to decrease, thereby weakening the overall flame retardant synergistic effect, so the thermal conductivity increases, and the vertical combustion grade and limiting oxygen index decrease. In Comparative Example 2, there is less 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 produced by the decomposition of the material at high temperature is reduced, and the carbonization effect cannot be effectively promoted, resulting in insufficient formation of the carbon layer, so the thermal conductivity increases, and the vertical combustion grade and limiting oxygen index decrease.

[0124] N-maleimido caproic acid reacts with the furan group introduced by furan formaldehyde to form a thermally reversible dynamic cross-linked network, and N-maleimide groups react with furan groups to generate a cross-linking point of a six-membered ring structure. By distributing an appropriate amount of cross-linking points, the molecular chain movement of the material is restricted, and the mechanical strength and thermal stability of the material can be improved. The nitrogen and carbon structure in the N-maleimido 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-maleimido caproic acid can cause the cross-linking point to be too dense, so that the molecular chain of the material is over-restricted, the flexibility of the molecular chain decreases, and the high-density cross-linked structure may form a microscopic rigid region, increase the thermal conductivity of the material, and although N-maleimido caproic acid contains a functional group that contributes to carbonization, its excess can reduce the synergistic effect of other flame retardant components (such as furan groups or boron ester bonds). In Comparative Example 4, N-maleimidocaproic acid is insufficient, and the number of cross-linking points is reduced, which reduces the overall structural stability of the material. The molecular chains are more easily decomposed under high temperature conditions or cause the thermal oxidation stability of the cross-linked network in the material to decrease. Therefore, the thermal conductivity increases, and the vertical combustion grade and limiting oxygen index decrease.

[0125] The above description is only a specific implementation mode 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 are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a self-repairing silicone rubber flame retardant protective pad for high temperature welding, characterized in that: The preparation method is: Step S1, adding boric acid and polyethylene glycol-400 into anhydrous DMF, and heating the reaction to obtain a boron ester cross-linking precursor; Step S2, dispersing methyl vinyl phenyl silicone rubber and furan formaldehyde in anhydrous toluene, adding tetrabutylammonium bromide, reacting to obtain a furanized methyl vinyl phenyl silicone rubber matrix solution, dissolving N-maleimidocaproic acid in anhydrous toluene, and adding the solution to the furanized methyl vinyl phenyl silicone rubber matrix solution, reacting to obtain a modified methyl vinyl phenyl silicone rubber; Step S3, uniformly mixing the modified methyl vinyl phenyl silicone rubber, the composite flame retardant, the inorganic filler, the auxiliary filler and the boron ester cross-linking precursor, and pressing to obtain a self-healing silicone rubber flame retardant protective pad for high temperature welding.

2. The method for preparing a self-repairing silicone rubber flame retardant protective pad for high temperature welding according to claim 1, characterized in that: The preparation method of the composite flame retardant is: Step A1, dispersing hexachlorocyclotriphosphazene in anhydrous acetonitrile, adding pyridine to the anhydrous acetonitrile to react to obtain cationic cyclic phosphazene, dispersing the cationic cyclic phosphazene in anhydrous ethanol, adding sodium hexametaphosphate to the anhydrous ethanol to react to form an ionic bond network, and drying to obtain an ionic flame retardant powder; Step A2, dispersing mesoporous silica in anhydrous ethanol, adding a silane coupling agent, reacting to obtain epoxy mesoporous silica, dispersing hexachlorocyclotriphosphazene in anhydrous toluene to obtain a hexachlorocyclotriphosphazene solution, then dispersing epoxy mesoporous silica in the hexachlorocyclotriphosphazene solution, and then adding anhydrous triethylamine to react to obtain phosphazene mesoporous silica; Step A3, dispersing the molecular sieve in a phosphoric acid solution, transferring the dried product to a muffle furnace after the reaction, and calcining to obtain a phosphate molecular sieve; Step A4, mixing ionic flame retardant powder, phosphazene mesoporous silica and phosphate molecular sieve, adding polyaryletherketone into anhydrous DMF, adding the ball-milled mixture into the polyaryletherketone solution, and calcining the obtained solid composite to obtain a composite flame retardant.

3. The method for preparing a self-repairing 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.

4. The method for preparing a self-repairing 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 ratio of the methyl vinyl phenyl silicone rubber to N-maleimidocaproic acid is 25:2; 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 aluminum oxide, 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-butyl peroxide cyclohexane, 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 cross-linking precursor is 100:25:143:121:

15.

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

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

7. The method for preparing a self-repairing silicone rubber flame retardant protective pad for high temperature welding according to claim 2, 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 4g:30mL; The mass ratio of phosphoric acid to deionized water in the phosphoric acid solution is 2:15; The calcination time is 4-5h.

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

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

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