High-strength flame-retardant aramid fiber composite material and preparation method thereof

Abstract

The invention belongs to the technical field of aramid fiber preparation, and provides a high-strength flame-retardant aramid fiber composite material and a preparation method thereof. The preparation method comprises the following steps: firstly, reacting 2-aminobenzoxazole with phosphorus oxychloride to prepare ortho-benzoxazole phosphamide; secondly, polydimethylsiloxane and formylphenylboronic acid are subjected to graft modification, boric acid ester grafted polysiloxane is prepared, and the material is endowed with excellent flame retardant property; further reacting 2-chlorobenzoxazole with phosphorus pentachloride, and combining with functionalization of 2-methylimidazole, so as to prepare bis-imidazole benzoxazole phosphamide; in the fiber preparation stage, an aramid fiber solution is prepared, ortho-benzoxazole phosphamide, bis-imidazole benzoxazole phosphamide, boric acid ester grafted polysiloxane and modified zinc borate are added, a spinning solution is prepared after high-pressure homogeneous dispersion, and the high-strength flame-retardant aramid fiber composite material is obtained after the spinning solution is subjected to the processes of curing, soaking, pulping and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of aramid fiber preparation, and relates to a high-strength flame-retardant aramid fiber composite material and a preparation method thereof. Background Art

[0002] With the rapid development of industrialization and urbanization, modern engineering is placing increasingly stringent demands on material performance. In the fields of aerospace, defense, rail transportation, and construction, materials must not only possess high strength and modulus, but also excellent flame retardancy to ensure safe use. Aramid fiber composites, due to their superior comprehensive properties, are becoming a key area of ​​research and development for new materials.

[0003] Aramid fiber is a type of high-performance fiber material based on aromatic polyamides, characterized by the presence of benzene rings and amide bonds in its molecular backbone. Due to its advantages such as high specific strength and high specific modulus, this type of fiber is widely used in aerospace, military protection, and high-performance composite materials. However, the flame retardant properties of traditional aramid fibers do not fully meet the requirements of certain demanding applications. In particular, in high-temperature or fire scenarios, aramid fibers may thermally degrade, resulting in a decrease in material performance or even failure. A Chinese patent application with publication number CN109183177A discloses a high-strength and high-modulus para-aramid fiber, a preparation method, and applications. The para-aramid fiber is obtained by compounding sodium pyruvate, ferric acetylacetonate, and sodium tripolyphosphate, followed by a modification treatment of the para-aramid fiber. However, this preparation method requires the treated para-aramid fiber to be re-dissolved in concentrated sulfuric acid and spun again, resulting in a relatively complex preparation process. Chinese patent application publication number CN106009667A discloses a high-temperature-resistant, highly flame-retardant polyimide film and its preparation method. Inorganic raw materials such as colemanite interact with organic raw materials such as furfural resin to act as heat-resistant modifiers in the polyimide film, improving the material's high-temperature resistance, chemical resistance, and impact resistance. Inorganic raw materials such as aluminum hypophosphite interact with organic raw materials such as hexachlorocyclopentadiene to act as flame-retardant modifiers in the polyimide film, imparting high flame retardancy and self-extinguishing properties. This prior art utilizes additive technology to achieve flame retardancy, but additive flame retardants often suffer from drawbacks such as large dosages, poor dispersibility, and degradation of polymer properties. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention aims to provide a high-strength flame-retardant aramid fiber composite material and a preparation method thereof. First, 2-aminobenzoxazole is used as a raw material, and a phosphoryl chloride intermediate is generated by a phosphorylation reaction with phosphorus oxychloride, which is then subjected to a nucleophilic substitution reaction with p-aminophenol to obtain an o-benzoxazole phosphoramide containing a phosphoramide bond. The product has excellent thermal stability and flame retardant properties due to its phosphoramide structure. Secondly, polydimethylsiloxane-amino is condensed with 4-formylphenylboronic acid, and then reduced with sodium cyanoborohydride to obtain a borate-grafted polysiloxane. The borate and silicon-oxygen bonds introduced in its structure act synergistically, further enhancing the flame retardancy and thermal stability of the material. In addition, a phosphoryl chloride intermediate is formed by reacting 2-chlorobenzoxazole with phosphorus pentachloride, which is then reacted with 2-methylimidazole to prepare a phosphoramide compound containing a biimidazole benzoxazole structure. The compound significantly improves the mechanical strength and thermal stability of the material due to the presence of the imidazole ring. In subsequent steps, these functional compounds are compounded with an aramid solution prepared from p-phenylenediamine and terephthaloyl chloride. High-pressure homogenization and dispersion technology is used to form a spinning solution. During the spinning process, the solution undergoes aging, degassing, and coagulation to produce fiber materials that meet actual production needs.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a high-strength flame-retardant aramid fiber composite material, the preparation method comprising:

[0007] S1, mixing 2-aminobenzoxazole and phosphorus oxychloride in an ice-salt bath, adjusting the temperature to room temperature for reaction to obtain an intermediate, dispersing the intermediate, p-aminophenol, and pyridine in anhydrous tetrahydrofuran in an ice-water bath for reaction, concentrating the reaction solution and subjecting it to column chromatography to collect the Rf fraction to obtain o-benzoxazole phosphamide;

[0008] S2, dispersing polydimethylsiloxane-amino, 4-formylphenylboronic acid, and p-toluenesulfonic acid in toluene for reaction, cooling the reaction system to freezing point, adding sodium cyanoborohydride, adjusting the temperature to room temperature for reaction, and quenching with hydrochloric acid solution to obtain borate grafted polysiloxane;

[0009] S3, dispersing 2-chlorobenzoxazole and PCl5 in hexamethylphosphoric triamide to react to obtain a phosphorus oxychloride intermediate, dispersing the phosphorus oxychloride intermediate and 2-methylimidazole in DMF, adding potassium carbonate, and reacting to obtain bisimidazolebenzoxazolephosphamide;

[0010] S4, dispersing calcium chloride in anhydrous NMP, then adding p-phenylenediamine and terephthaloyl chloride to obtain an aramid solution, sequentially adding o-benzoxazole phosphamide, bisimidazole benzoxazole phosphamide, borate grafted polysiloxane and modified zinc borate to the aramid solution to obtain a spinning solution, the spinning solution is subjected to aging, soaking, beating and washing processes to obtain pulp-like fibers, and then the pulp-like fibers are dispersed in concentrated sulfuric acid to obtain a spinning solution, the spinning solution is degassed and filtered, and then extruded from a spinneret, and after extrusion, enters a coagulation bath for coagulation and molding, and then washed, dried and oiled to obtain a high-strength flame-retardant aramid fiber composite material.

[0011] Specifically include:

[0012] A1, mixing zinc borate and a silane coupling agent, adding anhydrous ethanol, ball milling for 4 hours, centrifuging, and vacuum drying to obtain modified zinc borate;

[0013] S1, under ice-salt bath conditions, 2-aminobenzoxazole and phosphorus oxychloride are mixed, the mixture is uniformly mixed, the temperature is adjusted to room temperature, and the reaction is stirred. After the reaction is completed, vacuum distillation is performed to obtain an intermediate. Under ice-water bath conditions, the intermediate, p-aminophenol, and pyridine are dispersed in anhydrous tetrahydrofuran, the temperature is adjusted to a first temperature, and the reaction is carried out. The reaction solution is concentrated and subjected to column chromatography to collect a specific Rf component, and vacuum drying is performed to obtain o-benzoxazole phosphamide;

[0014] S2, dispersing polydimethylsiloxane-amino, 4-formylphenylboronic acid and p-toluenesulfonic acid in toluene, adjusting the temperature to a second temperature for reflux reaction, cooling the reaction system to freezing point, adding sodium cyanoborohydride, adjusting the temperature to room temperature for reaction, quenching with hydrochloric acid solution, and after separation, washing the organic phase with saturated sodium bicarbonate solution, drying over anhydrous magnesium sulfate, and rotary evaporation to obtain borate grafted polysiloxane;

[0015] S3, dispersing 2-chlorobenzoxazole and PCl5 in hexamethylphosphoric triamide, adjusting the temperature to a third temperature under a nitrogen atmosphere for reaction, and performing reduced pressure distillation to obtain a phosphorus oxychloride intermediate, dispersing the phosphorus oxychloride intermediate and 2-methylimidazole in DMF, adding potassium carbonate, adjusting the temperature to a second temperature for reaction, hot filtration, concentration, and recrystallization to obtain bisimidazolebenzoxazolephosphoramide;

[0016] S4, in a nitrogen atmosphere, calcium chloride is dispersed in anhydrous NMP, and the temperature is adjusted to the second temperature. After the calcium chloride is evenly dispersed, the temperature is lowered to room temperature and p-phenylenediamine is added. After the p-phenylenediamine is dissolved, the reaction system is cooled to the fourth temperature, terephthaloyl chloride is added, and the stirring is stopped until gelation occurs to obtain an aramid solution. Ortho-benzoxazole phosphamide and bisimidazole benzoxazole phosphamide are added to the aramid solution in sequence. After complete dispersion, borate grafted polysiloxane and modified zinc borate are added, and high-pressure homogenization is performed to obtain a spinning solution. The spinning solution is subjected to processes such as aging, soaking, beating, and washing, and is dried to obtain pulp-like fibers. The pulp-like fibers are then dispersed in concentrated sulfuric acid to obtain a spinning solution. The spinning solution is degassed and filtered, and the temperature is adjusted to the fifth temperature. The spinning solution is extruded from a spinneret, and after extrusion, it enters a coagulation bath for coagulation and molding, and is then washed, dried, and oiled to obtain a high-strength flame-retardant aramid fiber composite material.

[0017] The amino group in the 2-aminobenzoxazole molecule has a lone pair of electrons, can be used as a nucleophilic reagent to attack the phosphorus atom of phosphorus oxychloride, and the phosphorus atom presents strong electrophilicity due to the chlorine atoms with higher electronegativity connected to three, prompting the lone pair of electrons of the amino group to form a coordination bond with the phosphorus atom, generating an unstable tetrahedral intermediate. Chloride ion then breaks away from as a leaving group, forming a phosphorus oxychloride intermediate (the amino group on the benzoxazole ring is substituted by -POCl2 groups). In this process, POCl3 excessive use ensures the complete phosphorylation of the amino group, and pyridine, as an acid binding agent, is released by the combined reaction of the HCl, preventing the hydrolysis side reaction or equipment corrosion caused by an acidic environment. After completing phosphorylation, a condensation reaction occurs in the phosphorus oxychloride intermediate and p-aminophenol, and the amino group of p-aminophenol, as a new nucleophilic reagent, attacks the phosphorus atom of the phosphorus oxychloride intermediate. The phosphorus atom, bound to two chlorine atoms, remains highly reactive, prompting the amino group to replace one of the chlorine atoms, forming a phosphoramide bond (-PN-). The ortho-selectivity of this step is determined by both the electronic effect and steric hindrance of the benzoxazole ring: the oxygen atom ortho to the C2 amino group stabilizes the transition state through conjugation, while the steric hindrance created by the phosphoryl group and the planar structure of the benzoxazole ring forces the reaction to preferentially occur at the ortho position. HCl released by the condensation reaction is neutralized again by pyridine, driving the reaction toward the product. In the resulting ortho-benzoxazolephosphoramide molecule, the phosphoramide group forms an extended conjugated system with the benzoxazole ring, enhancing its thermal stability. The presence of the phosphorus atom not only imparts flame retardancy but also, through its lone pair of electrons, forms hydrogen bonds or coordination bonds with the amino groups in the aramid matrix, enhancing interfacial interactions. The rigid structure of the phosphoryl group restricts the free rotation of the molecular segments, resulting in a more ordered microstructure in the composite. During the purification process, the ortho-substituted product has a lower overall molecular polarity due to the conjugation effect between the phosphoryl group and the benzoxazole ring. On the silica gel stationary phase, its interaction with the eluent (ethyl acetate / petroleum ether mixed system) is weak and the migration rate is fast. Possible by-products, such as meta-substituted products or diphosphorylated products, form stronger hydrogen bonds with the silanol groups on the silica gel surface due to the destruction of molecular symmetry or the increase of polar groups, resulting in delayed elution.

[0018] The primary amino group at the amino terminal of polydimethylsiloxane undergoes a nucleophilic addition-elimination reaction with the aldehyde group of 4-formylphenylboronic acid to generate an imine. The lone pair of electrons of the amino group attacks the carbonyl carbon atom of the aldehyde group to form a tetrahedral intermediate. The carbonyl oxygen atom exhibits strong electronegativity due to the conjugation effect of the lone pair of electrons and the carbon-oxygen double bond, which makes the carbon atom an electrophilic center. The hydroxyl group in the tetrahedral intermediate is protonated under acidic conditions to form an easily leaving water molecule. As the water molecule leaves, the carbon-nitrogen double bond is formed, completing the construction of the imine structure. The generated imine is reduced to a secondary amine under the action of sodium cyanoborohydride. The BH3 in sodium cyanoborohydride -The group acts as a hydrogen ion donor to attack the carbon-nitrogen double bond of the imine. The carbon atom is partially positive because it is connected to the nitrogen atom with higher electronegativity, and preferentially accepts H - A carbon-hydrogen bond is formed. After the addition of the hydride ion, the lone electron pair on the nitrogen atom undergoes proton transfer with the adjacent hydrogen atom, forming a stable secondary amine structure. The selectivity of the reduction stage is reflected in both functional group selectivity and stereoselectivity: NaBH3CN preferentially reduces the imine bond while having no significant effect on the boronic acid group in phenylboronic acid. The planar structure of the imine allows the hydride ion to attack from a less sterically hindered direction, resulting in a thermodynamically more stable trans-addition product. The resulting secondary amine and the phenylboronic acid group form a stable six-membered ring structure through a boronate ester bond. Under weakly acidic conditions, the hydroxyl group in the phenylboronic acid group partially deprotonates to form a negatively charged borate ion. The nitrogen atom of the secondary amine acts as a Lewis base, donating its lone electron pair to coordinate with the empty p orbital of the boron atom, forming a coordination bond. This coordination induces intramolecular dehydration, and the hydroxyl group undergoes esterification with the adjacent methylene group to form a six-membered cyclic boronate ester. This ring structure is stabilized by the synergistic effect of covalent and coordination bonds: the covalent bond provides a rigid skeleton, while the coordination bond reduces ring strain through electron delocalization. In the molecular structure of the final product, the rigidity of the six-membered borate ring complements the flexibility of the siloxane chain, resulting in a higher glass transition temperature than unmodified polydimethylsiloxane-amino. The borate decomposes at high temperatures to form a B2O3 glass layer, isolating oxygen and inhibiting the diffusion of combustible gases. The high-temperature resistance of the siloxane backbone slows thermal degradation of the material. The borate groups bind to the polar groups in the aramid matrix through hydrogen bonds or coordination, improving the composite's interfacial compatibility.

[0019] 2-Chlorobenzoxazole reacts with phosphorus pentachloride to form a phosphorus oxychloride intermediate. Phosphorus pentachloride, as a strong chlorinating agent, partially dissociates into PCl4 in a polar solvent. + and Cl - , among which PCl4 + As an electrophilic reagent, it attacks the chlorine substitution site on the benzoxazole ring. The chlorine atom of the benzoxazole ring activates the adjacent carbon atom through the electron-withdrawing effect, making it the target of electrophilic attack. + After attacking the carbon atom, a tetracoordinate phosphorus intermediate is formed, which then releases Cl- and reconstructs the aromatic ring to generate a phosphorus oxychloride compound containing a P-Cl bond. Subsequently, the phosphorus oxychloride intermediate undergoes a nucleophilic substitution condensation reaction with 2-methylimidazole. The nitrogen atom of 2-methylimidazole acts as a nucleophile to attack the phosphorus center of phosphorus oxychloride, forming a pentacoordinate transition state. The phosphorus atom exhibits strong electrophilicity due to being connected to two chlorine atoms with higher electronegativity, which promotes the attack of the nucleophile. With the formation of the nitrogen-phosphorus bond, a Cl - As a leaving group, it leaves and generates a monosubstituted phosphoramide intermediate. The second 2-methylimidazole molecule repeats the above process and replaces another Cl -, ultimately forming a bisimidazole phosphamide product. Potassium carbonate acts as a base to neutralize the HCl released in the reaction to maintain the pH of the system and prevent the protonation of imidazole, which leads to a decrease in nucleophilicity. The selectivity of the reaction is controlled by both steric and electronic effects. The methyl group of 2-methylimidazole limits the attack direction through steric hindrance, ensuring that substitution occurs preferentially at the axial position of phosphorus oxychloride; the electron-withdrawing property of the P=O double bond in phosphorus oxychloride activates the phosphorus center through a conjugation effect, enhancing its ability to accept nucleophilic attack. The molecular function of bisimidazole benzoxazole phosphamide is closely related to its performance. In terms of flame retardancy, the N2 and NH3 released by the decomposition of imidazole dilute oxygen and combustible gases, achieving gas-phase flame retardancy; the phosphoramide bond decomposes at high temperature to form polyphosphoric acid, which catalyzes the formation of a carbon layer. Bisimidazole enhances the crystal packing density through intermolecular hydrogen bonds, further delaying thermal degradation.

[0020] In terms of mechanical properties, the rigid conjugated structure of o-benzoxazole phosphamide and bisimidazole benzoxazole phosphamide (benzoxazole ring and phosphamide bond) binds to the aramid backbone through π-π stacking and hydrogen bonding, forming an intermolecular physical crosslinking network. The planar rigidity of the benzoxazole ring restricts the local bending vibration of the aramid molecular chain, while the polarity of the phosphamide bond enhances the interchain binding energy through dipole-dipole interactions. Furthermore, the surface modification of zinc borate with a silane coupling agent enhances interfacial compatibility with the aramid matrix, promoting a uniform distribution of crystal nuclei. This effect refines the size of the crystalline domains, forming a dense "nanocrystalline-amorphous" alternating structure. The fine-grained structure hinders dislocation motion through grain boundary strengthening, while the nanoparticles inhibit local relaxation of the molecular chains, further enhancing the fiber's stiffness and modulus. In addition, the flexible long chains of polydimethylsiloxane-amino form an interpenetrating network with the aramid molecular chains through physical entanglement. Under the action of external load, the slip and extension of the siloxane chain segments absorb part of the energy, while the rigid skeleton of the aramid main chain maintains the stability of the overall structure, thereby improving the modulus while maintaining toughness.

[0021] As a preferred technical solution of the present invention, in A1, the mass ratio of the zinc borate to the silane coupling agent is 100:(3-5), for example, it can be 100:(3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8 or 5.0), but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] In some optional embodiments, the silane coupling agent is KH-560.

[0023] In some optional embodiments, the ball milling 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, and the ball-to-material ratio of ball milling is 5:1, but it is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0024] As a preferred technical solution of the present invention, in S1, the mass volume ratio of the 2-aminobenzoxazole, phosphorus oxychloride, p-aminophenol and pyridine is (50-55) g:120 mL: (40-43) g: (30-33) mL, for example, it can be (50.0, 50.5, 51.0, 51.5, 52.0, 52.5, 53.0, 53.5, 54.0, 54.5 or 55.0) g:120 mL: (40.0, 40.3, 40.6, 40.9, 41.2, 41.5, 41.8, 42.1, 42.4, 42.7 or 43.0) g: (30.0, 30.3, 30.6, 30.9, 31.2, 31.5, 31.8, 32.1, 32.4, 32.7 or 33.0) mL, but is not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0025] In some optional embodiments, the reaction time of stirring at room 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.

[0026] In some optional embodiments, the volume ratio of pyridine to anhydrous tetrahydrofuran is 1:5.

[0027] In some optional embodiments, the first temperature is 40-45°C, for example, it can be 40.0°C, 40.5°C, 41.0°C, 41.5°C, 42.0°C, 42.5°C, 43.0°C, 43.5°C, 44.0°C, 44.5°C or 45.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] In some optional embodiments, the time of the first temperature reaction is 10-12h, for example, it can be 10.0h, 10.2h, 10.4h, 10.6h, 10.8h, 11.0h, 11.2h, 11.4h, 11.6h, 11.8h or 12.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In some optional embodiments, the Rf is Rf=0.3.

[0030] In some optional embodiments, the silica gel for column chromatography is 200-300 mesh, the eluent gradient for column chromatography is 1:4 to 1:2, and the eluent is ethyl acetate / petroleum ether.

[0031] As a preferred technical solution of the present invention, in S2, the mass volume ratio of the polydimethylsiloxane-amino, 4-formylphenylboronic acid, p-toluenesulfonic acid, toluene and sodium cyanoborohydride is (50-54) g: (15-17) g: 5 g: 150 mL: (5-7) g, for example, it can be (50.0, 50.4, 50.8, 51.2, 51.6, 52.0, 52.4, 52.8, 53.2, 53.6 or 54.0)g: (15.0, 15.2, 15.4, 15.6, 15.8, 16.0, 16.2, 16.4, 16.6, 16.8 or 17.0)g: 5g: 150mL: (5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, 6.4, 6.6, 6.8 or 7.0)g, but is not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0032] In some optional embodiments, the second temperature is 80-90°C, for example, it can be 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] In some optional embodiments, the reflux reaction time 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.

[0034] In some optional embodiments, the room temperature reaction time is 11-12 hours, for example, it can be 11.0 hours, 11.1 hours, 11.2 hours, 11.3 hours, 11.4 hours, 11.5 hours, 11.6 hours, 11.7 hours, 11.8 hours, 11.9 hours or 12.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] In some optional embodiments, the mass fraction of the hydrochloric acid solution is 5-7wt.%, for example, it can be 5.0wt.%, 5.2wt.%, 5.4wt.%, 5.6wt.%, 5.8wt.%, 6.0wt.%, 6.2wt.%, 6.4wt.%, 6.6wt.%, 6.8wt.% or 7.0wt.%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0036] As a preferred technical solution of the present invention, in S3, the mass ratio of 2-chlorobenzoxazole, PCl5, 2-methylimidazole and potassium carbonate is (15-17): (25-28): (20-23): (41-44), for example, it can be (15.0, 15.2, 15.4, 15.6, 15.8, 16.0, 16.2, 16.4, 16.6, 16.8 or 17.0): (25.0, 25.3, 25.6, 25.9, 26.2, 26. 5, 26.8, 27.1, 27.4, 27.7 or 28.0): (20.0, 20.3, 20.6, 20.9, 21.2, 21.5, 21.8, 22.1, 22.4, 22.7 or 23.0): (41.0, 41.3, 41.6, 41.9, 42.2, 42.5, 42.8, 43.1, 43.4, 43.7 or 44.0), but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] In some optional embodiments, the third temperature is 110-120°C, for example, it can be 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C or 120°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In some optional embodiments, the time of the third temperature reaction 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.

[0039] In some optional embodiments, the second temperature reaction time is 24-25h, for example, it can be 24.0h, 24.1h, 24.2h, 24.3h, 24.4h, 24.5h, 24.6h, 24.7h, 24.8h, 24.9h or 25.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] As a preferred technical solution of the present invention, in S4, the mass volume ratio of the calcium chloride, anhydrous NMP, p-phenylenediamine and terephthaloyl chloride is (8.9-9.2) g:100 mL: (3.7-4) g: (7-7.3) g, for example, it can be (8.90, 8.93, 8.96, 8.99, 9.02, 9.05, 9.08, 9.11, 9.14, 9.17 or 9.20) g: 100mL: (3.70, 3.73, 3.76, 3.79, 3.82, 3.85, 3.88, 3.91, 3.94 or 4.00)g: (7.00, 7.03, 7.06, 7.09, 7.12, 7.15, 7.18, 7.21, 7.24, 7.27 or 7.30)g, but are not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0041] In some optional embodiments, the mass ratio of the aramid solution, o-benzoxazole phosphamide, bisimidazole benzoxazole phosphamide, borate grafted polysiloxane and modified zinc borate is (82-85): (7-9): (4-5): (5-6): (2-3), for example, it can be (82.0, 82.3, 82.6, 82.9, 83.2, 83.5, 83.8, 84.1, 84.4, 84.7 or 85.0): (7.0, 7.2, 7.4, 7.6, 7.8, 8.0, 8.2, 8. 4.5, 4.6, 4.7, 4.8, 4.9 or 5.0): (5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9 or 6.0): (2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.0), but are not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0042] In some optional embodiments, the fourth temperature is -15°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] In some optional embodiments, the aging temperature is 60°C and the aging time is 5-6 hours, for example, it can be 5.0 hours, 5.1 hours, 5.2 hours, 5.3 hours, 5.4 hours, 5.5 hours, 5.6 hours, 5.7 hours, 5.8 hours, 5.9 hours or 6.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] In some optional embodiments, the mass volume ratio of the pulp-like fiber to concentrated sulfuric acid is 1 g:200 mL.

[0045] In some optional embodiments, the fifth temperature is 60-65°C, for example, it can be 60.0°C, 60.5°C, 61.0°C, 61.5°C, 62.0°C, 62.5°C, 63.0°C, 63.5°C, 64.0°C, 64.5°C or 65.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] In a second aspect, the present invention provides a high-strength flame-retardant aramid fiber composite material prepared by the preparation method described in the first aspect.

[0047] Compared with the prior art, the present invention has the following beneficial effects: (1) ortho-benzoxazole phosphamide integrates the flame retardant element with the rigid skeleton through the conjugated structure of the benzoxazole ring and the phosphamide bond. Compared with traditional flame retardants, the rigidity of the benzoxazole ring enhances the interaction between the aramid molecular chains through π-π stacking, thereby improving the modulus. The phosphamide bond decomposes at high temperature to generate polyphosphoric acid, catalyzes carbonization and releases free radicals to quench the flame, and is bonded to the aramid main chain, thereby avoiding the precipitation problem in the use of small molecule flame retardants and improving the long-term flame retardant stability. (2) Bisimidazole benzoxazole phosphamide integrates the flame retardant element with the rigid skeleton through the conjugated structure of the benzoxazole ring and the phosphamide bond. In synergy with the phosphoramide bond, imidazole decomposes to release N2 and NH3 to dilute oxygen, and phosphorus catalyzes the formation of a dense carbon layer, which is more efficient than single phosphorus flame retardants. The π-π stacking of imidazole rings and aramid benzene rings forms physical crosslinking points, inhibiting molecular chain slippage and achieving modulus improvement; (3) Borate-grafted polysiloxane solves the contradiction between interface bonding and brittleness through dynamic covalent bonds and flexible chain segment design. The reversible fracture-recombination characteristics of borate bonds make stress uniformly distributed, repair microcracks, and improve fatigue resistance; the flexibility of the siloxane chain buffers external impact and avoids brittle fracture of high modulus materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is an SEM image of the pulp-like fibers provided in Example 1 of the present invention;

[0049] Figure 2 This is an SEM image of the high-strength flame-retardant aramid fiber composite material provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0050] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be understood as limiting the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments described 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 described herein.

[0051] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products and have not been subjected to any further purification treatment.

[0052] Example 1

[0053] This embodiment provides a high-strength flame-retardant aramid fiber composite material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0054] A1: Mix 100 g of zinc borate and 3 g of KH-560, add 3 L of anhydrous ethanol, and use a ball-to-material ratio of 5:1. Ball mill for 4 h, centrifuge, and vacuum dry to obtain modified zinc borate.

[0055] S1, under ice-salt bath conditions, 50 g of 2-aminobenzoxazole and 120 mL of phosphorus oxychloride were mixed, the mixture was adjusted to room temperature and stirred for 6.2 h, and after the reaction was completed, the intermediate was distilled under reduced pressure to obtain the intermediate. Under ice-water bath conditions, the intermediate, 40 g of p-aminophenol, and 30 mL of pyridine were dispersed in 150 mL of anhydrous tetrahydrofuran, the temperature was adjusted to 44° C., and the reaction was carried out for 10.0 h. The reaction solution was concentrated and subjected to column chromatography. The silica gel for the column chromatography was 200-300 mesh. The eluent for the column chromatography was ethyl acetate / petroleum ether in a gradient of 1:4 to 1:2. The fraction with Rf=0.3 was collected and dried under vacuum to obtain o-benzoxazole phosphamide;

[0056] S2, 50 g of polydimethylsiloxane-amino, 15 g of 4-formylphenylboronic acid and 5 g of p-toluenesulfonic acid were dispersed in 150 mL of toluene, the temperature was adjusted to 88° C. and refluxed for 8.3 h, the reaction system was cooled to freezing point, 5.2 g of sodium cyanoborohydride was added, the temperature was adjusted to room temperature and the reaction was continued for 11.5 h, and the reaction was quenched with 5.0 wt.% hydrochloric acid solution. After separation, the organic phase was washed with saturated sodium bicarbonate solution, dried over anhydrous magnesium sulfate, and rotary evaporated to obtain borate grafted polysiloxane;

[0057] S3, 15g of 2-chlorobenzoxazole and 25g of PCl5 were dispersed in 200mL of hexamethylphosphoric triamide, the temperature was adjusted to 110°C under nitrogen atmosphere, and the reaction was carried out for 6.3h. The phosphorus oxychloride intermediate was obtained by distillation under reduced pressure. The phosphorus oxychloride intermediate and 20g of 2-methylimidazole were dispersed in 300mL of DMF, 41g of potassium carbonate was added, the temperature was adjusted to 88°C, and the reaction was carried out for 24.2h. The mixture was hot filtered, concentrated, and recrystallized to obtain bisimidazolylbenzoxazole phosphoramide;

[0058] S4, in a nitrogen atmosphere, 890g of calcium chloride was dispersed in 10L of anhydrous NMP, and the temperature was adjusted to 88°C. After the calcium chloride was evenly dispersed, the temperature was lowered to room temperature and 370g of p-phenylenediamine was added. After the p-phenylenediamine was dissolved, the reaction system was cooled to -15°C, 700g of terephthaloyl chloride was added, and the stirring was stopped until gelation occurred to obtain an aramid solution. 700g of o-benzoxazole phosphamide and 400g of bisimidazole benzoxazole phosphamide were added to 8.2kg of the aramid solution in sequence. After the dispersion was complete, 500 g of borate grafted polysiloxane and 200 g of modified zinc borate are added, and after high-pressure homogenization and dispersion, a spinning solution is obtained. The spinning solution is aged at 60° C. for 5.0 h, soaked, beaten, washed, and dried to obtain pulp-like fibers. The pulp-like fibers are then dispersed in concentrated sulfuric acid to obtain a spinning solution. The spinning solution is degassed and filtered, and the temperature is adjusted to 65° C. The solution is extruded from a spinneret and then placed in a coagulation bath for coagulation and molding. The solution is then washed, dried, and oiled to obtain a high-strength flame-retardant aramid fiber composite material.

[0059] Figure 1 This is an SEM image of the pulp-like fibers provided in this embodiment; Figure 2 This is a SEM image of the high-strength flame-retardant aramid fiber composite material provided in this embodiment. The aramid fibers are uniform in thickness, smooth in surface, and have no obvious cracks.

[0060] Example 2

[0061] This embodiment provides a high-strength flame-retardant aramid fiber composite material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0062] A1: Mix 100 g of zinc borate and 4 g of KH-560, add 3 L of anhydrous ethanol, and use a ball-to-material ratio of 5:1. Ball mill the mixture for 4.6 h, centrifuge, and vacuum dry to obtain modified zinc borate.

[0063] S1, under ice-salt bath conditions, 55 g of 2-aminobenzoxazole and 120 mL of phosphorus oxychloride were mixed, the mixture was adjusted to room temperature and stirred for 6.0 h, and after the reaction was completed, the intermediate was distilled under reduced pressure to obtain the intermediate. Under ice-water bath conditions, the intermediate, 43 g of p-aminophenol, and 33 mL of pyridine were dispersed in 165 mL of anhydrous tetrahydrofuran, the temperature was adjusted to 45° C., and the reaction was carried out for 12.0 h. The reaction solution was concentrated and subjected to column chromatography. The silica gel for the column chromatography was 200-300 mesh. The eluent for the column chromatography was ethyl acetate / petroleum ether in a gradient of 1:4 to 1:2. The fraction with Rf=0.3 was collected and dried under vacuum to obtain o-benzoxazole phosphamide;

[0064] S2, 53 g of polydimethylsiloxane-amino, 17 g of 4-formylphenylboronic acid and 5 g of p-toluenesulfonic acid were dispersed in 150 mL of toluene, the temperature was adjusted to 80° C. and refluxed for 8.4 h, the reaction system was cooled to freezing point, 5.0 g of sodium cyanoborohydride was added, the temperature was adjusted to room temperature and the reaction was continued for 11.0 h, and the reaction was quenched with 7.0 wt.% hydrochloric acid solution. After separation, the organic phase was washed with saturated sodium bicarbonate solution, dried over anhydrous magnesium sulfate, and rotary evaporated to obtain borate grafted polysiloxane;

[0065] S3, 16g of 2-chlorobenzoxazole and 28g of PCl5 were dispersed in 200mL of hexamethylphosphoric triamide, the temperature was adjusted to 118°C under nitrogen atmosphere, and the reaction was carried out for 6.7h. The phosphorus oxychloride intermediate was obtained by distillation under reduced pressure. The phosphorus oxychloride intermediate and 23g of 2-methylimidazole were dispersed in 300mL of DMF, 43g of potassium carbonate was added, the temperature was adjusted to 80°C, and the reaction was carried out for 24.0h. The mixture was hot filtered, concentrated, and recrystallized to obtain bisimidazolylbenzoxazole phosphoramide;

[0066] S4, in a nitrogen atmosphere, 900g of calcium chloride was dispersed in 10L of anhydrous NMP, and the temperature was adjusted to 90°C. After the calcium chloride was evenly dispersed, the temperature was lowered to room temperature and 400g of p-phenylenediamine was added. After the p-phenylenediamine was dissolved, the reaction system was cooled to -15°C, 730g of terephthaloyl chloride was added, and the stirring was stopped until gelation occurred to obtain an aramid solution. 900g of o-benzoxazole phosphamide and 500g of bisimidazolyl benzoxazole phosphamide were added to 8.4kg of the aramid solution in sequence. After the dispersion was complete, the mixture was added. 600 g of borate grafted polysiloxane and 240 g of modified zinc borate are added, and after high-pressure homogenization and dispersion, a spinning solution is obtained. The spinning solution is aged at 60° C. for 6.0 h, soaked, beaten, washed, and dried to obtain pulp-like fibers. The pulp-like fibers are then dispersed in concentrated sulfuric acid to obtain a spinning solution. The spinning solution is degassed and filtered, and the temperature is adjusted to 62° C. The solution is extruded from a spinneret and then placed in a coagulation bath for coagulation and molding. The solution is then washed, dried, and oiled to obtain a high-strength flame-retardant aramid fiber composite material.

[0067] Example 3

[0068] This embodiment provides a high-strength flame-retardant aramid fiber composite material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0069] A1: Mix 100 g of zinc borate and 5 g of KH-560, add 3 L of anhydrous ethanol, and use a ball-to-material ratio of 5:1. Ball mill for 5.0 h, centrifuge, and vacuum dry to obtain modified zinc borate.

[0070] S1, under ice-salt bath conditions, 52 g of 2-aminobenzoxazole and 120 mL of phosphorus oxychloride were mixed, the mixture was adjusted to room temperature and stirred for 7.0 h, and after the reaction was completed, the intermediate was distilled under reduced pressure to obtain the intermediate. Under ice-water bath conditions, the intermediate, 42 g of p-aminophenol, and 31 mL of pyridine were dispersed in 155 mL of anhydrous tetrahydrofuran, the temperature was adjusted to 40° C., and the reaction was carried out for 11.6 h. The reaction solution was concentrated and subjected to column chromatography. The silica gel for the column chromatography was 200-300 mesh. The eluent for the column chromatography was ethyl acetate / petroleum ether in a gradient of 1:4 to 1:2. The fraction with Rf=0.3 was collected and dried under vacuum to obtain o-benzoxazole phosphamide;

[0071] S2, 54 g of polydimethylsiloxane-amino, 16 g of 4-formylphenylboronic acid and 5 g of p-toluenesulfonic acid were dispersed in 150 mL of toluene, the temperature was adjusted to 82° C. and refluxed for 9.0 h, the reaction system was cooled to freezing point, 7.0 g of sodium cyanoborohydride was added, the temperature was adjusted to room temperature and the reaction was continued for 12.0 h, and the reaction was quenched with 6.0 wt.% hydrochloric acid solution. After separation, the organic phase was washed with saturated sodium bicarbonate solution, dried over anhydrous magnesium sulfate, and rotary evaporated to obtain borate grafted polysiloxane;

[0072] S3, 17g 2-chlorobenzoxazole and 26g PCl5 were dispersed in 200mL hexamethylphosphoric triamide, the temperature was adjusted to 120°C under nitrogen atmosphere and the reaction was carried out for 7.0h, and the phosphorus oxychloride intermediate was obtained by distillation under reduced pressure. The phosphorus oxychloride intermediate and 22g 2-methylimidazole were dispersed in 300mL DMF, 44g potassium carbonate was added, the temperature was adjusted to 83°C and the reaction was carried out for 25.0h, hot filtration and concentration were carried out, and recrystallization was carried out to obtain bisimidazolylbenzoxazole phosphoramide;

[0073] S4, in a nitrogen atmosphere, 920g of calcium chloride was dispersed in 10L of anhydrous NMP, and the temperature was adjusted to 80°C. After the calcium chloride was evenly dispersed, the temperature was lowered to room temperature and 390g of p-phenylenediamine was added. After the p-phenylenediamine was dissolved, the reaction system was cooled to -15°C, 720g of terephthaloyl chloride was added, and the stirring was stopped until gelation occurred to obtain an aramid solution. 800g of o-benzoxazole phosphamide and 430g of bisimidazole benzoxazole phosphamide were added to 8.5kg of the aramid solution in sequence. After the dispersion was complete, 550 g of borate grafted polysiloxane and 300 g of modified zinc borate are added, and after high-pressure homogenization and dispersion, a spinning solution is obtained. The spinning solution is aged at 60° C. for 5.4 h, soaked, beaten, washed, and dried to obtain pulp-like fibers. The pulp-like fibers are then dispersed in concentrated sulfuric acid to obtain a spinning solution. The spinning solution is degassed and filtered, and the temperature is adjusted to 60° C. The solution is extruded from a spinneret and then placed in a coagulation bath for coagulation and molding. The solution is then washed, dried, and oiled to obtain a high-strength flame-retardant aramid fiber composite material.

[0074] Example 4

[0075] This embodiment provides a high-strength flame-retardant aramid fiber composite material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0076] A1: Mix 100 g of zinc borate and 3 g of KH-560, add 3 L of anhydrous ethanol, and use a ball-to-material ratio of 5:1. Ball mill for 4.3 h, centrifuge, and vacuum dry to obtain modified zinc borate.

[0077] S1, under ice-salt bath conditions, 54 g of 2-aminobenzoxazole and 120 mL of phosphorus oxychloride were mixed, the mixture was adjusted to room temperature and stirred for 6.7 hours, and after the reaction was completed, the intermediate was distilled under reduced pressure to obtain the intermediate. Under ice-water bath conditions, the intermediate, 41 g of p-aminophenol, and 32 mL of pyridine were dispersed in 160 mL of anhydrous tetrahydrofuran, the temperature was adjusted to 42° C., and the reaction was carried out for 10.7 hours. The reaction solution was concentrated and subjected to column chromatography. The silica gel for the column chromatography was 200-300 mesh. The eluent for the column chromatography was ethyl acetate / petroleum ether in a gradient of 1:4 to 1:2. The fraction with Rf=0.3 was collected and dried under vacuum to obtain o-benzoxazole phosphamide;

[0078] S2, 51 g of polydimethylsiloxane-amino, 15 g of 4-formylphenylboronic acid and 5 g of p-toluenesulfonic acid were dispersed in 150 mL of toluene, the temperature was adjusted to 90° C. and refluxed for 8.0 h, the reaction system was cooled to freezing point, 6.4 g of sodium cyanoborohydride was added, and the temperature was adjusted to room temperature for 11.7 h, and quenched with 5.0 wt.% hydrochloric acid solution. After separation, the organic phase was washed with saturated sodium bicarbonate solution, dried over anhydrous magnesium sulfate, and rotary evaporated to obtain borate grafted polysiloxane;

[0079] S3, 16g of 2-chlorobenzoxazole and 27g of PCl5 were dispersed in 200mL of hexamethylphosphoric triamide, the temperature was adjusted to 114°C under nitrogen atmosphere, and the reaction was carried out for 6.0h. The phosphorus oxychloride intermediate was obtained by distillation under reduced pressure. The phosphorus oxychloride intermediate and 21g of 2-methylimidazole were dispersed in 300mL of DMF, 42g of potassium carbonate was added, the temperature was adjusted to 90°C, and the reaction was carried out for 24.7h. The mixture was hot filtered, concentrated, and recrystallized to obtain bisimidazolylbenzoxazole phosphoramide;

[0080] S4, in a nitrogen atmosphere, 910g of calcium chloride was dispersed in 10L of anhydrous NMP, and the temperature was adjusted to 84°C. After the calcium chloride was evenly dispersed, the temperature was lowered to room temperature and 380g of p-phenylenediamine was added. After the p-phenylenediamine was dissolved, the reaction system was cooled to -15°C, 710g of terephthaloyl chloride was added, and the stirring was stopped until gelation occurred to obtain an aramid solution. 840g of o-benzoxazole phosphamide and 480g of bisimidazole benzoxazole phosphamide were added to 8.3kg of the aramid solution in sequence. After the dispersion was complete, the reaction mixture was added. 570 g of borate grafted polysiloxane and 280 g of modified zinc borate were added, and high-pressure homogenization and dispersion were performed to obtain a spinning solution. The spinning solution was aged at 60° C. for 5.8 h, soaked, beaten, washed, and dried to obtain pulp-like fibers. The pulp-like fibers were then dispersed in concentrated sulfuric acid to obtain a spinning solution. The spinning solution was degassed and filtered, and the temperature was adjusted to 64° C. The solution was extruded from a spinneret and then placed in a coagulation bath for coagulation and molding. The solution was then washed, dried, and oiled to obtain a high-strength flame-retardant aramid fiber composite material.

[0081] Comparative Example 1

[0082] This embodiment provides a high-strength flame-retardant aramid fiber composite material and a preparation method thereof. The difference between this embodiment and Example 1 is that the mass of o-benzoxazolephosphamide in S4 is 200 g, which is 500 g less than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0083] Comparative Example 2

[0084] This embodiment provides a high-strength flame-retardant aramid fiber composite material and a preparation method thereof. The difference between this embodiment and Example 1 is that the mass of the bisimidazole benzoxazole phosphamide in S4 is 100 g, which is 300 g less than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0085] Comparative Example 3

[0086] This embodiment provides a high-strength flame-retardant aramid fiber composite material and a preparation method thereof. The difference between this embodiment and Example 1 is that the mass of the borate grafted polysiloxane in S4 is 100 g, which is 400 g less than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0087] The limiting oxygen index test method was GB / T 2406.2-2009; the flame retardancy test method was GB / T 2408-2021; and the tensile strength and elastic modulus test method was ASTM D7269. The test results are shown in Table 1.

[0088] Table 1 Test results of high-strength flame-retardant aramid fiber composite materials of Examples 1-4 and Comparative Examples 1-3

[0089]

[0090]

[0091] As shown in Table 1, compared with Example 1, the limiting oxygen index, flame retardant grade, tensile strength, and elastic modulus of Comparative Example 1 all decreased; the limiting oxygen index, flame retardant grade, tensile strength, and elastic modulus of Comparative Example 2 all decreased; and the limiting oxygen index, flame retardant grade, tensile strength, and elastic modulus of Comparative Example 3 all decreased. This is because the o-benzoxazole phosphamide in Comparative Example 1 is insufficient, the amount of polyphosphoric acid generated at high temperatures is reduced, the thickness and density of the char layer decrease, and the oxygen and heat insulation effect is weakened, resulting in a decrease in the limiting oxygen index and flame retardant grade. The π-π stacking effect of the benzoxazole ring is weakened, and the bonding force between the molecular chains is reduced, resulting in a decrease in tensile strength and elastic modulus. In Comparative Example 2, the bisimidazole benzoxazole phosphamide is insufficient, and the amount of N2 and NH3 released by the bisimidazole structure at high temperatures is reduced. The concentration of combustible gases in the gas phase is relatively increased, the porosity of the char layer increases and the strength decreases, the flame retardant properties decrease, the π-π stacking effect between the imidazole ring and the aramid benzene ring is weakened, the molecular chain slip is aggravated, and the tensile strength and modulus decrease simultaneously. In Comparative Example 3, the borate grafted polysiloxane is insufficient, and the borate in the product is insufficient, which cannot be decomposed at high temperature to generate a sufficient B2O3 glass layer, resulting in reduced flame retardancy, reduced number of borate bonds, reduced stress transfer efficiency, and reduced tensile strength and elastic modulus.

[0092] The above description is only a specific embodiment 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 disclosure scope of the present invention.

Claims

1. A method for preparing a high-strength flame-retardant aramid fiber composite material, characterized in that: The preparation method comprises: S1, mixing 2-aminobenzoxazole and phosphorus oxychloride in an ice-salt bath, adjusting the temperature to room temperature for reaction to obtain an intermediate, dispersing the intermediate, p-aminophenol, and pyridine in anhydrous tetrahydrofuran in an ice-water bath for reaction, concentrating the reaction solution and subjecting it to column chromatography to collect the Rf fraction to obtain o-benzoxazole phosphamide; S2, dispersing polydimethylsiloxane-amino, 4-formylphenylboronic acid, and p-toluenesulfonic acid in toluene for reaction, cooling the reaction system to freezing point, adding sodium cyanoborohydride, adjusting the temperature to room temperature for reaction, and quenching with hydrochloric acid solution to obtain borate grafted polysiloxane; S3, dispersing 2-chlorobenzoxazole and PCl5 in hexamethylphosphoric triamide to react to obtain a phosphorus oxychloride intermediate, dispersing the phosphorus oxychloride intermediate and 2-methylimidazole in DMF, adding potassium carbonate, and reacting to obtain bisimidazolebenzoxazolephosphamide; S4, dispersing calcium chloride in anhydrous NMP, then adding p-phenylenediamine and terephthaloyl chloride to obtain an aramid solution, sequentially adding o-benzoxazole phosphamide, bisimidazole benzoxazole phosphamide, borate grafted polysiloxane and modified zinc borate to the aramid solution to obtain a spinning solution, the spinning solution is subjected to aging, soaking, beating and washing processes to obtain pulp-like fibers, and then the pulp-like fibers are dispersed in concentrated sulfuric acid to obtain a spinning solution, the spinning solution is degassed and filtered, and then extruded from a spinneret, and after extrusion, enters a coagulation bath for coagulation and molding, and then washed, dried and oiled to obtain a high-strength flame-retardant aramid fiber composite material.

2. The method for preparing a high-strength flame-retardant aramid fiber composite material according to claim 1, characterized in that: The preparation method of the modified zinc borate comprises: A1, mixing zinc borate and a silane coupling agent, adding anhydrous ethanol, ball milling, centrifugal separation, and vacuum drying to obtain modified zinc borate.

3. The method for preparing a high-strength flame-retardant aramid fiber composite material according to claim 1, characterized in that: In S1: The mass volume ratio of the 2-aminobenzoxazole, phosphorus oxychloride, p-aminophenol and pyridine is (50-55) g:120 mL: (40-43) g: (30-33) mL.

4. The method for preparing a high-strength flame-retardant aramid fiber composite material according to claim 1, characterized in that: In S1: The silica gel for the column chromatography was 200-300 mesh, and the eluent gradient for the column chromatography was 1:4 to 1:2, with the eluent being ethyl acetate / petroleum ether; The Rf is Rf=0.

3.

5. The method for preparing a high-strength flame-retardant aramid fiber composite material according to claim 1, characterized in that: In S2: The mass volume ratio of the polydimethylsiloxane-amino group, 4-formylphenylboronic acid, p-toluenesulfonic acid, toluene and sodium cyanoborohydride is (50-54) g: (15-17) g: 5 g: 150 mL: (5-7) g.

6. The method for preparing a high-strength flame-retardant aramid fiber composite material according to claim 1, characterized in that: In S3: The mass ratio of the 2-chlorobenzoxazole, PCl5, 2-methylimidazole and potassium carbonate is (15-17): (25-28): (20-23): (41-44).

7. The method for preparing a high-strength flame-retardant aramid fiber composite material according to claim 1, characterized in that: In S4: The mass volume ratio of the calcium chloride, anhydrous NMP, p-phenylenediamine and terephthaloyl chloride is (8.9-9.2) g:100 mL: (3.7-4) g: (7-7.3) g.

8. The method for preparing a high-strength flame-retardant aramid fiber composite material according to claim 1, characterized in that: In S4: The mass ratio of the aramid solution, o-benzoxazole phosphamide, bisimidazole benzoxazole phosphamide, borate grafted polysiloxane and modified zinc borate is (82-85): (7-9): (4-5): (5-6): (2-3); The mass volume ratio of the pulp-like fiber to concentrated sulfuric acid is 1 g:200 mL.

9. The method for preparing a high-strength flame-retardant aramid fiber composite material according to claim 2, characterized in that: In A1: The mass ratio of the zinc borate to the silane coupling agent is 100:(3-5); The silane coupling agent is KH-560; The ball-to-material ratio of the ball mill is 5:

1.

10. A high-strength flame-retardant aramid fiber composite material, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 9.

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