A high-strength flame-retardant aramid fiber composite material and its preparation method

Abstract

This invention belongs to the field of aramid fiber preparation technology, and provides a high-strength flame-retardant aramid fiber composite material and its preparation method. First, ortho-benzoxazole phosphoramide is prepared by reacting 2-aminobenzoxazole with phosphorus oxychloride. Second, polydimethylsiloxane is grafted and modified with formylphenylboronic acid to prepare borate ester-grafted polysiloxane, which imparts excellent flame-retardant properties to the material. Further, bisimidazole benzoxazole phosphoramide is prepared by reacting 2-chlorobenzoxazole with phosphorus pentachloride and combining it with 2-methylimidazole functionalization. In the fiber preparation stage, an aramid solution is prepared and ortho-benzoxazole phosphoramide, bisimidazole benzoxazole phosphoramide, borate ester-grafted polysiloxane and modified zinc borate are added. After high-pressure homogenization and dispersion, a spinning solution is prepared. The spinning solution is subjected to curing, soaking and pulping processes to obtain a high-strength flame-retardant aramid fiber composite material.

Description

Technical Field

[0001] This invention belongs to the field of aramid fiber preparation technology, and relates to a high-strength flame-retardant aramid fiber composite material and its preparation method. Background Technology

[0002] With the rapid development of industrialization and urbanization, modern engineering places increasingly stringent demands on the performance of materials. In the fields of aerospace, defense, rail transportation, and construction, materials not only need to possess high strength and high modulus, but also must have excellent flame retardant properties to ensure safe use. Due to its outstanding comprehensive performance, aramid fiber composite materials have gradually become one of the important directions in new material research and development.

[0003] Aramid fibers are a class of high-performance fiber materials based on aromatic polyamides, characterized by the presence of benzene rings and amide bonds in their molecular backbone. These fibers are widely used in aerospace, military protection, and high-performance composite materials due to their high specific strength and high specific modulus. However, the flame-retardant properties of traditional aramid fibers do not fully meet the requirements of certain stringent applications, especially in high-temperature or fire scenarios, where aramid fibers may undergo thermal degradation, leading to a decline in material performance or even failure. Chinese patent application CN109183177A discloses a high-strength, high-modulus para-aramid fiber, its preparation method, and its applications. The para-aramid fiber is obtained by modifying it by combining sodium pyruvate, iron acetylacetone, and sodium tripolyphosphate. However, this preparation method requires re-dissolving the treated para-aramid fiber in concentrated sulfuric acid and spinning it again, making the preparation process relatively complex. Chinese patent application CN106009667A discloses a high-temperature resistant and flame-retardant polyimide film and its preparation method. By adding inorganic raw materials such as calcium borate and organic raw materials such as furfural resin, the mixture acts as a heat-resistant modifier in the polyimide film, improving the material's high-temperature resistance, chemical resistance, and impact resistance. Similarly, by adding inorganic raw materials such as aluminum hypophosphite and organic raw materials such as hexachlorocyclopentadiene, the mixture acts as a flame-retardant modifier, giving the resulting material high flame retardancy and self-extinguishing properties. This prior art uses an additive method to achieve flame retardancy; however, additive flame retardants often suffer from drawbacks such as high dosage, poor dispersibility, and negative impacts on polymer properties. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention aims to provide a high-strength flame-retardant aramid fiber composite material and its preparation method. First, using 2-aminobenzoxazole as a raw material, a phosphoryl chloride intermediate is generated through a phosphorylation reaction with phosphorus oxychloride. This intermediate is then subjected to a nucleophilic substitution reaction with p-aminophenol to obtain an ortho-benzoxazole phosphoramide containing a phosphoramide bond. This product exhibits excellent thermal stability and flame-retardant properties due to its phosphoramide structure. Second, by condensing polydimethylsiloxane-amino with 4-formylphenylboronic acid and then reducing it with sodium cyanoborohydride, a borate ester-grafted polysiloxane is obtained. The synergistic effect of the borate ester and silicon-oxygen bonds introduced into its structure further enhances the flame retardancy and thermal stability of the material. Furthermore, by reacting 2-chlorobenzoxazole with phosphorus pentachloride to form a phosphoryl chloride intermediate, which is then reacted with 2-methylimidazole, a phosphoramide compound containing a bisimidazole benzoxazole structure is prepared. The presence of the imidazole ring in this compound significantly improves the mechanical strength and thermal stability of the material. In subsequent steps, these functional compounds are compounded with an aramid solution prepared using p-phenylenediamine and terephthaloyl chloride as monomers. A spinning solution is then formed using high-pressure homogenization dispersion technology. During spinning, the spinning solution undergoes processes such as curing, degassing, and coagulation to generate fiber materials, thereby meeting the needs of actual production.

[0005] To achieve this objective, the present invention adopts the following technical solution:

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

[0007] S1, in an ice-salt bath, 2-aminobenzoxazole and phosphorus oxychloride are mixed and the temperature is adjusted to room temperature to react and obtain an intermediate. In an ice-water bath, the intermediate, p-aminophenol and pyridine are dispersed in anhydrous tetrahydrofuran and reacted. After the reaction solution is concentrated, column chromatography is performed to collect the Rf fraction and obtain ortho-benzoxazole phosphoramide.

[0008] S2, polydimethylsiloxane-amino, 4-formylphenylboronic acid and p-toluenesulfonic acid are dispersed in toluene and reacted. The reaction system is cooled to the freezing point, sodium cyanoborohydride is added, the reaction is adjusted to room temperature, and the reaction is quenched with hydrochloric acid solution to obtain borate ester grafted polysiloxane.

[0009] S3, 2-chlorobenzoxazole and PCl5 are dispersed in hexamethylphosphoric acid triamine to react and obtain phosphoric acid chloride intermediate. The phosphoric acid chloride intermediate and 2-methylimidazole are dispersed in DMF, potassium carbonate is added, and the reaction is carried out to obtain bisimidazole benzoxazole phosphoramide.

[0010] S4, calcium chloride is dispersed in anhydrous NMP, and then p-phenylenediamine and terephthaloyl chloride are added to obtain an aramid solution. Ortho-benzoxazole phosphoramide, bisimidazole benzoxazole phosphoramide, borate ester grafted polysiloxane and modified zinc borate are added to the aramid solution in sequence to obtain a spinning solution. The spinning solution is subjected to aging, soaking, pulping and washing processes 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 then extruded from a spinneret. After extrusion, it enters a coagulation bath to solidify and form a composite material. After washing, drying and oiling, a high-strength flame-retardant aramid fiber composite material is obtained.

[0011] Specifically, it includes:

[0012] A1. Zinc borate was mixed with a silane coupling agent, anhydrous ethanol was added, ball milled for 4 hours, centrifuged and vacuum dried to obtain modified zinc borate.

[0013] S1, under ice-salt bath conditions, 2-aminobenzoxazole and phosphorus oxychloride were mixed and stirred at room temperature. After the reaction was completed, the intermediate was obtained by vacuum distillation. Under ice-water bath conditions, the intermediate, p-aminophenol and pyridine were dispersed in anhydrous tetrahydrofuran and the reaction was carried out at the first temperature. After the reaction solution was concentrated, column chromatography was performed to collect specific Rf components and vacuum drying to obtain ortho-benzoxazole phosphoramide.

[0014] S2, polydimethylsiloxane-amino, 4-formylphenylboronic acid and p-toluenesulfonic acid are dispersed in toluene, the temperature is adjusted to the second temperature and refluxed, the reaction system is cooled to the freezing point, sodium cyanoborohydride is added, the temperature is adjusted to room temperature and the reaction is quenched with hydrochloric acid solution, after separation, the organic phase is washed with saturated sodium bicarbonate solution, dried with anhydrous magnesium sulfate, and rotary evaporated to obtain borate ester grafted polysiloxane;

[0015] S3, 2-chlorobenzoxazole and PCl5 are dispersed in hexamethylphosphoric acid triamine, the temperature is adjusted to the third temperature under nitrogen atmosphere, and the reaction is carried out by vacuum distillation to obtain phosphoric acid chloride intermediate. The phosphoric acid chloride intermediate is dispersed in DMF with 2-methylimidazole, potassium carbonate is added, the temperature is adjusted to the second temperature, the reaction is carried out by hot filtration, concentration and recrystallization to obtain bisimidazole benzoxazole phosphoramide.

[0016] In a nitrogen atmosphere (S4), calcium chloride is dispersed in anhydrous NMP. 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 dissolves, the reaction system is cooled to the fourth temperature, and terephthaloyl chloride is added. The mixture is stirred until gelation occurs, and then stirring is stopped to obtain an aramid solution. Ortho-benzoxazole phosphoramide and diimidazole benzoxazole phosphoramide are added to the aramid solution in sequence. After complete dispersion, borate ester-grafted polysiloxane and modified zinc borate are added. After high-pressure homogenization, a spinning solution is obtained. The spinning solution undergoes aging, soaking, pulping, washing, and drying processes 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, filtered, and the temperature is adjusted to the fifth temperature. The solution is extruded from a spinneret and then solidified in a coagulation bath. After washing, drying, and oiling, a high-strength flame-retardant aramid fiber composite material is obtained.

[0017] The amino group in the 2-aminobenzoxazole molecule possesses a lone pair of electrons, which can act as a nucleophile to attack the phosphorus atom of phosphorus oxychloride. The phosphorus atom, due to its connection with three highly electronegative chlorine atoms, exhibits strong electrophilicity, prompting the lone pair of electrons in the amino group to form a coordinate bond with the phosphorus atom, generating an unstable tetrahedral intermediate. Subsequently, the chloride ion dissociates as a leaving group, forming a phosphoryl chloride intermediate (the amino group on the benzoxazole ring is replaced by a -POCl2 group). During this process, the excess of POCl3 ensures complete phosphorylation of the amino group, while pyridine acts as an acid-binding agent, binding the released HCl to prevent hydrolysis side reactions or equipment corrosion caused by an acidic environment. After phosphorylation, the phosphoryl chloride intermediate undergoes a condensation reaction with p-aminophenol, where the amino group acts as a new nucleophile, attacking the phosphorus atom of the phosphoryl chloride intermediate. The phosphorus atom, bonded 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 effects and steric hindrance of the benzoxazole ring: the oxygen atom adjacent to the C2 amino group of the benzoxazole ring stabilizes the transition state through a conjugation effect, while the steric hindrance created by the planar structure of the phosphoryl group and the benzoxazole ring forces the reaction to preferentially occur at the ortho position. The HCl released in the condensation reaction is again neutralized by pyridine, driving the reaction toward the product. In the final ortho-benzoxazole phosphoramide molecule, the phosphoramide group forms an extended conjugated system with the benzoxazole ring. This conjugation enhances the molecule's thermal stability. The presence of the phosphorus atom not only endows the molecule with flame-retardant activity but also enhances interfacial interactions by forming hydrogen bonds or coordinate bonds with the amino group in the aramid matrix through its lone pair electrons. The rigid structure of the phosphoryl group restricts the free rotation of molecular chain segments, thereby forming a more ordered microstructure in the composite material. During the purification process, ortho-substituted products have lower overall molecular polarity due to the conjugation effect between the phosphoryl group and the benzoxazole ring. On the silica gel stationary phase, their interaction with the eluent (ethyl acetate / petroleum ether mixture) is weaker, and their migration rate is faster. However, potential byproducts, such as meta-substituted products or diphosphorylated products, form stronger hydrogen bonds with the silanol groups on the silica gel surface due to the disruption of molecular symmetry or the increase of polar groups, resulting in elution lag.

[0018] The primary amino group at the amino terminus of polydimethylsiloxane undergoes a nucleophilic addition-elimination reaction with the aldehyde group of 4-formylphenylboronic acid to generate an imine. The lone pair electrons of the amino group attack the carbonyl carbon atom of the aldehyde group, forming a tetrahedral intermediate. The carbonyl oxygen atom exhibits strong electronegativity due to the conjugation of the lone pair electrons with the carbon-oxygen double bond, making the carbon atom an electrophilic center. The hydroxyl group in the tetrahedral intermediate is protonated under acidic conditions, forming a readily leaving water molecule. As the water molecule detaches, the carbon-nitrogen double bond forms, completing the construction of the imine structure. The generated imine is reduced to a secondary amine by sodium cyanoborohydride. The BH3 in sodium cyanoborohydride... -The group acts as a hydride anion donor, attacking the carbon-nitrogen double bond of the imine. The carbon atom, being partially positively charged due to its bond with the more electronegative nitrogen atom, preferentially accepts the hydride ion. - After the formation of carbon-hydrogen bonds and the addition of hydride ions, the lone pair electrons on the nitrogen atom undergo proton migration with the neighboring 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 borate group in phenylboronic acid; the planar structure of the imine allows the hydride ion to attack from the direction with less steric hindrance, generating a more thermodynamically stable trans-addition product. The secondary amine generated by reduction forms a stable six-membered ring structure with the phenylboronic acid group through a borate ester bond. Under weakly acidic conditions, the hydroxyl group in the phenylboronic acid group partially deprotonates to form a negatively charged borate anion. The nitrogen atom of the secondary amine, acting as a Lewis base, provides a lone pair electron to coordinate with the empty p orbital of boron, forming a coordinate bond. The coordination effect induces intramolecular dehydration, and the hydroxyl group undergoes an esterification reaction with the neighboring methylene group to generate a six-membered cyclic borate ester. This cyclic structure is stabilized through the synergistic effect of covalent and coordinate bonds: the covalent bonds provide a rigid framework, and the coordinate bonds reduce ring strain through electron delocalization. In the final product's molecular structure, the rigid structure of the borate ester's six-membered ring complements the flexibility of the siloxane chain, resulting in a higher glass transition temperature compared to unmodified polydimethylsiloxane-amino. At high temperatures, the borate ester decomposes to form a B2O3 glass layer, isolating oxygen and inhibiting the diffusion of combustible gases. The high-temperature resistance of the siloxane backbone delays the material's thermal degradation. Furthermore, the borate ester groups bind to polar groups in the aramid matrix through hydrogen bonding or coordination, improving the composite material's interfacial compatibility.

[0019] 2-Chlorobenzoxazole reacts with phosphorus pentachloride to form a phosphoric acid chloride intermediate. Phosphorus pentachloride, as a strong chlorinating agent, partially dissociates into PCl4 in polar solvents. + and Cl - PCl4 + As an electrophile, PCl4 attacks the chlorine substitution sites on the benzoxazole ring. The chlorine atom in the benzoxazole ring activates the adjacent carbon atom through an electron-withdrawing effect, making it a target for electrophilic attack. + Attacking the carbon atom forms a four-coordinate phosphorus intermediate, which then releases Cl- and reconstructs the aromatic ring, generating a phosphoryl chloride compound containing a p-Cl bond. Subsequently, the phosphoryl chloride intermediate undergoes a nucleophilic substitution condensation reaction with 2-methylimidazole. The nitrogen atom of the 2-methylimidazole acts as a nucleophile, attacking the phosphorus center of the phosphoryl chloride, forming a five-coordinate transition state. The phosphorus atom, due to its connection with two highly electronegative chlorine atoms, exhibits strong electrophilicity, promoting the nucleophilic attack. With the formation of the nitrogen-phosphorus bond, a Cl-... - As a leaving group, it decomposes to generate a monosubstituted phosphoramide intermediate. The second 2-methylimidazole molecule repeats the above process, replacing another Cl group. -Ultimately, the product, bisimidazole phosphoramide, is formed. Potassium carbonate acts as a base, neutralizing the HCl released during the reaction to maintain the pH of the system and prevent protonation of imidazole from reducing nucleophilicity. The selectivity of the reaction is controlled by both steric hindrance and electronic effects. The methyl group of 2-methylimidazole restricts the direction of attack through steric hindrance, ensuring that substitution preferentially occurs at the axial position of the phosphoryl chloride. The electron-withdrawing property of the P=O double bond in the phosphoryl chloride activates the phosphorus center through conjugation, enhancing its ability to accept nucleophilic attack. The molecular function of bisimidazole benzoxazole phosphoramide 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 generate polyphosphoric acid, catalyzing the formation of a char layer; and bisimidazole enhances the crystal packing density through intermolecular hydrogen bonds, further delaying thermal degradation.

[0020] In terms of mechanical properties, the rigid conjugated structure (benzoxazole ring and phosphoramide bond) of ortho-benzoxazole phosphoramide and bisimidazole benzoxazole phosphoramide binds to the aramid backbone through π-π stacking and hydrogen bonding, forming an intermolecular physical cross-linking network. The planar rigidity of the benzoxazole ring restricts the local bending vibration of the aramid molecular chain, while the polarity of the phosphoramide bond enhances the interchain bonding energy through dipole-dipole interactions. Simultaneously, the zinc borate surface, after modification with a silane coupling agent, exhibits enhanced interfacial compatibility with the aramid matrix, promoting uniform distribution of crystal nuclei. This effect refines the crystal size, forming a dense alternating "nanocrystalline-amorphous" structure. The fine-grained structure hinders dislocation movement through grain boundary strengthening, while the nanoparticles suppress local relaxation of the molecular chain, further enhancing the fiber's rigidity and modulus. Furthermore, the flexible long chains of polydimethylsiloxane-amino form an interpenetrating network with the aramid molecular chains through physical entanglement. Under external load, the slippage and extension of the siloxane chain segments absorb some 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 embodiment of the present invention, in A1, the mass ratio of zinc borate to 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 it is not limited to the listed values, and other unlisted values ​​within this 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 4-5 hours, for example, 4.0 hours, 4.1 hours, 4.2 hours, 4.3 hours, 4.4 hours, 4.5 hours, 4.6 hours, 4.7 hours, 4.8 hours, 4.9 hours, or 5.0 hours, and the ball-to-material ratio is 5:1, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0024] As a preferred embodiment of the present invention, in S1, the mass-to-volume ratio of 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. 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 not limited to the listed values; other unlisted values ​​within this range also apply.

[0025] In some optional embodiments, the room temperature stirring reaction time is 6-7 hours, for example, 6.0 hours, 6.1 hours, 6.2 hours, 6.3 hours, 6.4 hours, 6.5 hours, 6.6 hours, 6.7 hours, 6.8 hours, 6.9 hours, or 7.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

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

[0027] In some alternative 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, other unlisted values ​​within this range are also applicable.

[0028] In some alternative embodiments, the reaction time at the first temperature is 10-12 hours, for example, 10.0 hours, 10.2 hours, 10.4 hours, 10.6 hours, 10.8 hours, 11.0 hours, 11.2 hours, 11.4 hours, 11.6 hours, 11.8 hours, or 12.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

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

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

[0031] In a preferred embodiment of the present invention, in S2, the mass-to-volume ratio of 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 not limited to the listed values; other unlisted values ​​within this range also apply.

[0032] In some alternative 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, other unlisted values ​​within this range are also applicable.

[0033] In some alternative embodiments, the reflux reaction time is 8-9 hours, for example, 8.0 hours, 8.1 hours, 8.2 hours, 8.3 hours, 8.4 hours, 8.5 hours, 8.6 hours, 8.7 hours, 8.8 hours, 8.9 hours, or 9.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0034] In some optional embodiments, the room temperature reaction time is 11-12 hours, for example, 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; other unlisted values ​​within this range are also applicable.

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

[0036] In a preferred embodiment of the present invention, in S3, the mass ratio of 2-chlorobenzoxazole, PCl5, 2-methylimidazole to 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 not limited to the listed values; other unlisted values ​​within this range also apply.

[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, other unlisted values ​​within this range are also applicable.

[0038] In some alternative embodiments, the reaction time at the third temperature is 6-7 hours, for example, 6.0 hours, 6.1 hours, 6.2 hours, 6.3 hours, 6.4 hours, 6.5 hours, 6.6 hours, 6.7 hours, 6.8 hours, 6.9 hours, or 7.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

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

[0040] In a preferred embodiment of the present invention, in step S4, the mass-to-volume ratio of 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 not limited to the listed values; other unlisted values ​​within this range also apply.

[0041] In some optional embodiments, the mass ratio of the aramid solution, ortho-benzoxazole phosphoramide, diimidazole benzoxazole phosphoramide, borate ester-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, 8.6, 8.8 or 9.0): (4.0, 4.1, 4.2, 4.3, 4.4, 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 not limited to the listed values; other unlisted values ​​within this range also apply.

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

[0043] In some optional embodiments, the curing temperature is 60°C and the curing time is 5-6 hours, for example, 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 not limited to the listed values, other unlisted values ​​within this range are also applicable.

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

[0045] In some alternative 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, other unlisted values ​​within this 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 beneficial effects of the present invention are as follows: (1) The ortho-benzoxazole phosphoramide integrates the flame retardant element with the rigid skeleton through the conjugated structure of the benzoxazole ring and the phosphoramide bond. Compared with traditional flame retardants, the rigidity of the benzoxazole ring enhances the interaction force between aramid molecular chains through π-π stacking, thereby increasing the modulus. The phosphoramide bond decomposes at high temperature to generate polyphosphoric acid, which catalyzes the formation of carbon and releases free radicals to quench the flame. It is also bonded to the aramid main chain, avoiding the precipitation problem in the use of small molecule flame retardants and improving long-term flame retardant stability; (2) The bisimidazole benzoxazole phosphoramide integrates the flame retardant element with the rigid skeleton through the imidazole ring. 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 improves the efficiency compared with single phosphorus flame retardants. The π-π stacking of imidazole ring and aramid benzene ring forms physical cross-linking points, inhibiting molecular chain slippage and achieving modulus improvement; (3) Boronate grafted polysiloxane solves the contradiction between interface bonding and brittleness through dynamic covalent bond and flexible chain segment design. The reversible fracture-reorganization characteristics of boronate bond make stress uniformly distributed, repair microcracks, and improve fatigue resistance; the flexibility of siloxane chain buffers external impact and avoids brittle fracture of high modulus materials. Attached Figure Description

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

[0049] Figure 2 This is a SEM image of the high-strength flame-retardant aramid fiber composite material provided in Embodiment 1 of the present invention. Detailed Implementation

[0050] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0051] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment.

[0052] Example 1

[0053] This embodiment provides a high-strength flame-retardant aramid fiber composite material and its preparation method. The preparation method specifically includes the following steps:

[0054] A1. Mix 100g of zinc borate with 3g of KH-560, add 3L of anhydrous ethanol, ball mill at a ratio of 5:1 for 4.0h, centrifuge, and vacuum dry to obtain modified zinc borate.

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

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

[0057] S3, 15g of 2-chlorobenzoxazole and 25g of PCl5 were dispersed in 200mL of hexamethylphosphoric acid triamine, and the temperature was adjusted to 110℃ under nitrogen atmosphere and reacted for 6.3h. The phosphoric acid chloride intermediate was obtained by vacuum distillation. The phosphoric acid chloride intermediate was dispersed with 20g of 2-methylimidazole in 300mL of LDM, 41g of potassium carbonate was added, and the temperature was adjusted to 88℃ and reacted for 24.2h. The mixture was then concentrated by hot filtration and recrystallized to obtain bisimidazole benzoxazole phosphoramide.

[0058] S4, under a nitrogen atmosphere, 890g of calcium chloride was dispersed in 10L of anhydrous NMP. The temperature was adjusted to 88℃. After the calcium chloride was evenly dispersed, the mixture was cooled to room temperature, and 370g of p-phenylenediamine was added. After the p-phenylenediamine dissolved, the reaction system was cooled to -15℃, and 700g of terephthaloyl chloride was added. Stirring was stopped when gelation occurred, resulting in an aramid solution. 700g of ortho-benzoxazole phosphoramide and 400g of diimidazole benzoxazole phosphoramide were added sequentially to 8.2kg of the aramid solution. After complete dispersion, [further steps were taken]. 500g of borate ester grafted polysiloxane and 200g of modified zinc borate were added and homogenized under high pressure to obtain a spinning solution. The spinning solution was then subjected to processes such as aging at 60℃ for 5.0h, soaking, pulping, and washing, 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, filtered, and then the temperature was adjusted to 65℃ before being extruded from a spinneret. After extrusion, the solution was coagulated in a coagulation bath and then washed, dried, and oiled to obtain a high-strength flame-retardant aramid fiber composite material.

[0059] Figure 1 This is a SEM image of pulp-like fibers provided in this embodiment; Figure 2 The image shows a SEM image of the high-strength flame-retardant aramid fiber composite material provided in this embodiment. The aramid fibers are of uniform thickness, have a smooth surface, and are free of obvious cracks.

[0060] Example 2

[0061] This embodiment provides a high-strength flame-retardant aramid fiber composite material and its preparation method. The preparation method specifically includes the following steps:

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

[0063] S1, under ice-salt bath conditions, 55g of 2-aminobenzoxazole was mixed with 120mL of phosphorus oxychloride. After mixing evenly, the temperature was adjusted to room temperature and stirred for 6.0h. After the reaction was completed, the intermediate was obtained by vacuum distillation. Under ice-water bath conditions, the intermediate, 43g of p-aminophenol and 33mL of pyridine were dispersed in 165mL of anhydrous tetrahydrofuran. The temperature was adjusted to 45℃ and the reaction was carried out for 12.0h. After the reaction solution was concentrated, column chromatography was performed. The silica gel for column chromatography was 200-300 mesh, and the eluent gradient for column chromatography was 1:4 to 1:2. The eluent was ethyl acetate / petroleum ether. The fraction with Rf = 0.3 was collected and dried under vacuum to obtain ortho-benzoxazole phosphoramide.

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

[0065] S3, 16g of 2-chlorobenzoxazole and 28g of PCl5 were dispersed in 200mL of hexamethylphosphoric acid triamine, and the temperature was adjusted to 118℃ under nitrogen atmosphere and reacted for 6.7h. The phosphoric acid chloride intermediate was obtained by vacuum distillation. The phosphoric acid chloride intermediate was dispersed with 23g of 2-methylimidazole in 300mL of LDM, 43g of potassium carbonate was added, and the temperature was adjusted to 80℃ and reacted for 24.0h. The mixture was then concentrated by hot filtration and recrystallized to obtain bisimidazole benzoxazole phosphoramide.

[0066] S4, under a nitrogen atmosphere, 900g of calcium chloride was dispersed in 10L of anhydrous NMP. The temperature was adjusted to 90℃. After the calcium chloride was evenly dispersed, the mixture was cooled to room temperature, and 400g of p-phenylenediamine was added. After the p-phenylenediamine dissolved, the reaction system was cooled to -15℃, and 730g of terephthaloyl chloride was added. Stirring was stopped when gelation occurred, resulting in an aramid solution. 900g of ortho-benzoxazole phosphoramide and 500g of diimidazole benzoxazole phosphoramide were added sequentially to 8.4kg of the aramid solution. After complete dispersion, [further steps were taken]. 600g of borate ester grafted polysiloxane and 240g of modified zinc borate were added and homogenized under high pressure to obtain a spinning solution. The spinning solution was then subjected to processes such as aging at 60℃ for 6.0h, soaking, pulping, and washing, and dried to obtain pulp-like fibers. The pulp-like fibers were then dispersed in concentrated sulfuric acid to obtain a spinning solution. After degassing and filtration, the spinning solution was adjusted to 62℃ and extruded from a spinneret. After extrusion, it was solidified in a coagulation bath and 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 its preparation method. The preparation method specifically includes the following steps:

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

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

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

[0072] S3, 17g of 2-chlorobenzoxazole and 26g of PCl5 were dispersed in 200mL of hexamethylphosphoric acid triamine, and the temperature was adjusted to 120℃ under nitrogen atmosphere and reacted for 7.0h. The phosphoric acid chloride intermediate was obtained by vacuum distillation. The phosphoric acid chloride intermediate was dispersed with 22g of 2-methylimidazole in 300mL of LDM, 44g of potassium carbonate was added, and the temperature was adjusted to 83℃ and reacted for 25.0h. The mixture was then concentrated by hot filtration and recrystallized to obtain bisimidazole benzoxazole phosphoramide.

[0073] S4, under a nitrogen atmosphere, 920g of calcium chloride was dispersed in 10L of anhydrous NMP. The temperature was adjusted to 80℃. After the calcium chloride was evenly dispersed, the mixture was cooled to room temperature, and 390g of p-phenylenediamine was added. After the p-phenylenediamine dissolved, the reaction system was cooled to -15℃, and 720g of terephthaloyl chloride was added. Stirring was stopped when gelation occurred, and an aramid solution was obtained. 800g of ortho-benzoxazole phosphoramide and 430g of diimidazole benzoxazole phosphoramide were added sequentially to 8.5kg of the aramid solution. After complete dispersion, [further steps were taken]. 550g of borate ester grafted polysiloxane and 300g of modified zinc borate were added and homogenized under high pressure to obtain a spinning solution. The spinning solution was then subjected to processes such as aging at 60℃ for 5.4h, soaking, pulping, and washing. After drying, pulp-like fibers were obtained. The pulp-like fibers were then dispersed in concentrated sulfuric acid to obtain a spinning solution. After degassing and filtration, the spinning solution was adjusted to 60℃ and extruded from a spinneret. After extrusion, it was solidified in a coagulation bath and 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 its preparation method. The preparation method specifically includes the following steps:

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

[0077] S1, under ice-salt bath conditions, 54g of 2-aminobenzoxazole was mixed with 120mL of phosphorus oxychloride. After mixing evenly, the temperature was adjusted to room temperature and the mixture was stirred for 6.7h. After the reaction was completed, the intermediate was obtained by vacuum distillation. Under ice-water bath conditions, the intermediate, 41g of p-aminophenol and 32mL of pyridine were dispersed in 160mL of anhydrous tetrahydrofuran. The temperature was adjusted to 42℃ and the reaction was carried out for 10.7h. The reaction solution was concentrated and then subjected to column chromatography. The silica gel for column chromatography was 200-300 mesh, and the eluent gradient for column chromatography was 1:4 to 1:2. The eluent was ethyl acetate / petroleum ether. The fraction with Rf = 0.3 was collected and dried under vacuum to obtain ortho-benzoxazole phosphoramide.

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

[0079] S3, 16g of 2-chlorobenzoxazole and 27g of PCl5 were dispersed in 200mL of hexamethylphosphoric acid triamine, and the temperature was adjusted to 114℃ under nitrogen atmosphere and reacted for 6.0h. The phosphoric acid chloride intermediate was obtained by vacuum distillation. The phosphoric acid chloride intermediate was dispersed with 21g of 2-methylimidazole in 300mL of LDM, 42g of potassium carbonate was added, and the temperature was adjusted to 90℃ and reacted for 24.7h. The mixture was then concentrated by hot filtration and recrystallized to obtain bisimidazole benzoxazole phosphoramide.

[0080] S4, under a nitrogen atmosphere, 910g of calcium chloride was dispersed in 10L of anhydrous NMP. The temperature was adjusted to 84℃. After the calcium chloride was evenly dispersed, the mixture was cooled to room temperature, and 380g of p-phenylenediamine was added. After the p-phenylenediamine dissolved, the reaction system was cooled to -15℃, and 710g of terephthaloyl chloride was added. Stirring was stopped when gelation occurred, and an aramid solution was obtained. 840g of ortho-benzoxazole phosphoramide and 480g of diimidazole benzoxazole phosphoramide were added sequentially to 8.3kg of the aramid solution. After complete dispersion, [further steps were taken]. 570g of borate ester grafted polysiloxane and 280g of modified zinc borate were added and homogenized under high pressure to obtain a spinning solution. The spinning solution was then subjected to processes such as aging at 60℃ for 5.8h, soaking, pulping, and washing, and dried to obtain pulp-like fibers. The pulp-like fibers were then dispersed in concentrated sulfuric acid to obtain a spinning solution. After degassing and filtration, the spinning solution was adjusted to 64℃ and extruded from a spinneret. After extrusion, it was solidified in a coagulation bath and 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 its preparation method. The difference between this embodiment and Example 1 is that the mass of ortho-benzoxazole phosphoramide in S4 is 200g, which is 500g less than that in Example 1. Other process parameters and operating conditions are exactly the same as in Example 1.

[0083] Comparative Example 2

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

[0085] Comparative Example 3

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

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

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

[0089]

[0090]

[0091] As shown in Table 1, compared to Example 1, the limiting oxygen index, flame retardancy rating, tensile strength, and elastic modulus of Comparative Example 1 all decreased; the limiting oxygen index, flame retardancy rating, tensile strength, and elastic modulus of Comparative Example 2 all decreased; and the limiting oxygen index, flame retardancy rating, tensile strength, and elastic modulus of Comparative Example 3 all decreased. This is because, in Comparative Example 1, the amount of ortho-benzoxazole phosphoramide was insufficient, resulting in a reduction in the amount of polyphosphoric acid generated at high temperatures, a decrease in the thickness and density of the char layer, and a weakening of the oxygen and heat insulation effect, leading to a decrease in the limiting oxygen index and flame retardancy rating. The π-π stacking effect of the benzoxazole ring was also weakened, and the inter-chain bonding force decreased, resulting in a decrease in tensile strength and elastic modulus. In Comparative Example 2, the amount of bisimidazole benzoxazole phosphoramide was insufficient, resulting in a reduction in the amount of N2 and NH3 released by the decomposition of the bisimidazole structure at high temperatures, a relative increase in the concentration of combustible gases in the gas phase, an increase in the porosity of the char layer and a decrease in its strength, a decrease in flame retardancy, a weakening of the π-π stacking effect between the imidazole ring and the aramid benzene ring, and an intensification of molecular chain slippage, leading to a simultaneous decrease in tensile strength and modulus. In Comparative Example 3, the borate ester grafted polysiloxane was insufficient, resulting in an inadequate amount of borate ester in the product. Consequently, it was unable to decompose at high temperatures to generate a sufficient B2O3 glass layer, leading to a decrease in flame retardant properties, a reduction in the number of borate ester bonds, a decrease in stress transfer efficiency, and a reduction in 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 conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection 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 includes: S1, in an ice-salt bath, 2-aminobenzoxazole and phosphorus oxychloride are mixed and the temperature is adjusted to room temperature to react and obtain an intermediate. In an ice-water bath, the intermediate, p-aminophenol and pyridine are dispersed in anhydrous tetrahydrofuran and reacted. After the reaction solution is concentrated, column chromatography is performed to collect the Rf fraction and obtain ortho-benzoxazole phosphoramide. S2, polydimethylsiloxane-amino, 4-formylphenylboronic acid and p-toluenesulfonic acid are dispersed in toluene and reacted. The reaction system is cooled to the freezing point, sodium cyanoborohydride is added, the reaction is adjusted to room temperature, and the reaction is quenched with hydrochloric acid solution to obtain borate ester grafted polysiloxane. S3, 2-chlorobenzoxazole and PCl5 are dispersed in hexamethylphosphoric acid triamine to react and obtain phosphoric acid chloride intermediate. The phosphoric acid chloride intermediate and 2-methylimidazole are dispersed in DMF, potassium carbonate is added, and the reaction is carried out to obtain bisimidazole benzoxazole phosphoramide. S4, calcium chloride is dispersed in anhydrous NMP, and then p-phenylenediamine and terephthaloyl chloride are added to obtain an aramid solution. Ortho-benzoxazole phosphoramide, bisimidazole benzoxazole phosphoramide, borate ester grafted polysiloxane and modified zinc borate are added to the aramid solution in sequence to obtain a spinning solution. The spinning solution is subjected to aging, soaking, pulping and washing processes 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 then extruded from a spinneret. After extrusion, it enters a coagulation bath to solidify and form a composite material. After washing, drying and oiling, a high-strength flame-retardant aramid fiber composite material is obtained.

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 includes: A1. Zinc borate was mixed with a silane coupling agent, anhydrous ethanol was added, and the mixture was ball-milled, centrifuged, and vacuum dried 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-to-volume ratio of 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 used in the column chromatography is 200-300 mesh, the eluent gradient of the column chromatography is 1:4 to 1:2, and the eluent is 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, 4-formylphenylboronic acid, p-toluenesulfonic acid, toluene and sodium cyanoborohydride is (50-54)g:(15-17)g:5g:150mL:(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 2-chlorobenzoxazole, PCl5, 2-methylimidazole to 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-to-volume ratio of 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, ortho-benzoxazole phosphoramide, bisimidazole benzoxazole phosphoramide, borate ester grafted polysiloxane and modified zinc borate is (82-85):(7-9):(4-5):(5-6):(2-3); The mass-to-volume ratio of the pulp-like fiber to concentrated sulfuric acid is 1g:200mL.

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 zinc borate to silane coupling agent is 100:(3-5); The silane coupling agent is KH-560; The ball-to-material ratio in the ball mill is 5:

1.

10. A high-strength flame-retardant aramid fiber composite material, characterized in that, It is prepared according to any one of claims 1-9.

Images