A method for preparing a phosphorus-containing triazine-based covalent organic framework flame retardant and its application in epoxy resins.

Abstract

This invention discloses a method for preparing a phosphorus-containing triazine-based covalent organic framework flame retardant and its application in epoxy resins. The flame retardant is prepared by a Pudovik addition reaction between a triazine-based covalent organic framework and diphenylphosphine oxide. After being introduced into epoxy resin, it is dispersed, mixed, and cured to obtain a flame-retardant composite material. This material can significantly improve the flame retardancy and thermal stability of epoxy resins, reduce the peak heat release rate and total heat release, and also possess good mechanical properties, even at relatively low addition levels.

Description

Technical Field

[0001] This invention belongs to the field of polymer flame retardant materials technology, specifically relating to a method for preparing a phosphorus-containing triazine-based covalent organic framework flame retardant and its application in epoxy resin, applicable to the field of high-performance fireproof materials. Background Technology

[0002] Epoxy resins are widely used in electronics, construction, aerospace, and adhesives and composite materials due to their excellent mechanical properties, electrical insulation, and chemical resistance. However, their inherent flammability severely limits their application in scenarios with high fire safety requirements. They are highly susceptible to causing fires, and their combustion process releases large amounts of dense smoke, carbon monoxide, and volatile organic compounds, causing serious environmental pollution and directly threatening human lives. In the past, halogenated flame retardants were commonly used in industry to inhibit combustion, but these release highly toxic and persistent pollutants such as hydrogen halides and dioxins during production, use, and disposal (especially during combustion), and are subject to strict restrictions under the Stockholm Convention RoHS Directive and other requirements.

[0003] Covalent organic frameworks (COFs), as emerging porous crystalline materials, have attracted widespread attention in the fields of chemistry, physics, and materials science. COFs are a class of crystalline porous polymers formed by organic molecules linked by covalent bonds. Their core characteristic lies in the effective integration of the primary structure built by covalent bonds with non-covalent interactions, resulting in a highly ordered network system. COFs possess high designability; by pre-selecting building blocks with different symmetries and functions, the framework and pore structures can be precisely controlled, thereby obtaining regular and predictable two-dimensional or three-dimensional topologies and permanent channels with specific sizes, shapes, and chemical environments. This atomic-level precision control gives COFs significant advantages in terms of structural and functional tunability. Triazine-based COFs, as a novel porous organic material with unique properties and broad application prospects, have also garnered significant attention in materials science. The triazine units, constructed by strong covalent bonds, not only endow the material with excellent chemical stability but also give it a rich nitrogen content. Compared with traditional inorganic fillers or small-molecule flame retardants, COFs possess unique advantages in constructing multifunctional synergistic flame retardant systems due to their designable framework, tunable pore structure, and high thermal stability. A few studies have shown that triazine-based COFs can simultaneously reduce heat release and smoke emission in various polymer matrices and improve mechanical properties. However, current research on COF applications mainly focuses on gas adsorption, catalysis, energy storage, and sensing, with extremely limited exploration in polymer flame retardancy. Most COFs only contain carbon, hydrogen, and nitrogen elements, lacking an effective combination of synergistic flame-retardant elements, resulting in poor or even non-existent flame-retardant effects. Furthermore, the addition of some COF structures may lead to uneven dispersion in the polymer matrix due to agglomeration, or damage to the polymer's mechanical properties due to poor interfacial compatibility. Therefore, developing a covalent organic framework material with good structural stability, phosphorus-nitrogen synergistic effect, and good dispersion characteristics, and applying it to the flame-retardant modification of epoxy resins, is of great significance for achieving efficient flame retardancy and synergistic improvement of mechanical properties. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned deficiencies of the prior art and to provide a method for preparing a phosphorus-containing triazine-based covalent organic framework flame retardant and its application in epoxy resin.

[0005] To achieve the above-mentioned objective, in a first aspect, the present invention provides a method for preparing a phosphorus-containing group-grafted triazine-based covalent organic framework flame retardant, comprising:

[0006] Preparation of nitrogen / phosphorus triazine-containing covalent organic frameworks;

[0007] In one embodiment, a method for preparing a nitrogen / phosphorus triazine-containing covalent organic framework is as follows:

[0008] 2,4,6-Tris(4-aminophenyl)-1,3,5-triazine (TFPT) and p-phenylenediamine were ultrasonically dispersed in a mixed solvent of trimethylbenzene and 1,4-dioxane, respectively. Zinc(II) bis(trifluoromethanesulfonyl)imine was added as a catalyst during the ultrasonic dispersion of the TFPT suspension. Subsequently, a p-phenylenediamine solution was added dropwise to the TFPT suspension at room temperature for approximately 30 minutes, with vigorous stirring throughout. After the addition was complete, the system was heated to 80°C and slowly stirred under a nitrogen atmosphere for 24 hours. The resulting black turbid liquid was filtered and washed successively with N,N-dimethylformamide, methanol, and ethanol, with the filtrate gradually becoming nearly colorless. During subsequent washing, the filter cake was appropriately squeezed and transferred to a flask, where an appropriate amount of N,N-dimethylformamide was added for further ultrasonic dispersion to dissolve residual impurities as much as possible. Filtration continued until the filtrate was completely colorless. After drying at 60°C, a lightweight powder of triazine-based covalent organic framework material was obtained.

[0009] The above-mentioned brown triazine-based covalent organic framework material powder was reacted with a tetrahydrofuran solution of diphenylphosphine oxide at 50°C under a N2 atmosphere for 30 min. The mixture was then filtered, the solid was washed with ethanol, and dried at 60°C under forced-air drying to finally obtain a brownish-yellow nitrogen / phosphorus-containing triazine-based covalent organic framework flame retardant (also known in this invention as a phosphorus-grafted triazine-based covalent organic framework flame retardant, or simply a nitrogen / phosphorus-containing triazine-based covalent organic framework, see below). Figure 1 )powder.

[0010] The nitrogen / phosphorus triazine-based covalent organic framework flame retardant is a porous network crystal structure formed by covalently connecting phosphorus-containing monomers and nitrogen-containing monomers, and its structure contains both P=O bonds and nitrogen-containing heterocyclic structures.

[0011] Secondly, the present invention provides the application of the phosphorus-containing group-grafted triazine-based covalent organic framework flame retardant prepared by the above-mentioned method in epoxy resin.

[0012] In one embodiment, it is used to prepare a flame-retardant epoxy resin.

[0013] In one embodiment, the nitrogen / phosphorus triazine-based covalent organic framework flame retardant obtained above is dispersed in E51 type epoxy resin by mechanical stirring to obtain a uniform mixture. Then, the mixture is reacted at 100°C for a period of time, and 4,4'-diaminodiphenylmethane curing agent is added and stirred until a uniform epoxy resin mixture solution is obtained. Finally, the epoxy resin mixture solution is vacuumed to remove excess air bubbles, and then poured into a preheated mold for thermosetting. After curing, it is allowed to cool to room temperature. Finally, a flame-retardant epoxy resin composite material is prepared.

[0014] In one embodiment, the mass ratio of the nitrogen / phosphorus triazine-based covalent organic framework flame retardant to E51 type epoxy resin is 2 to 6:100.

[0015] In one embodiment, the reaction temperature of the nitrogen / phosphorus triazine-based covalent organic framework flame retardant and the E51 type epoxy resin is 100°C, and the reaction time is 30 to 60 minutes.

[0016] Furthermore, the application is characterized in that the peak heat release rate (pHRR) of the flame-retardant epoxy resin composite material is reduced by 27% or more.

[0017] Furthermore, the application is characterized in that the total heat release of the flame-retardant epoxy resin composite material is reduced by 32% or more.

[0018] Furthermore, the application is characterized in that the limiting oxygen index of the flame-retardant epoxy resin composite material is 31.3%.

[0019] The advantages and beneficial effects of this invention compared to the prior art are as follows:

[0020] (1) The nitrogen / phosphorus triazine-based covalent organic framework flame retardant provided by the present invention is simple to prepare and can significantly improve the flame retardant performance of epoxy resin under low addition conditions.

[0021] (2) The nitrogen / phosphorus triazine-based covalent organic framework flame retardant provided by the present invention is a flame retardant epoxy resin. The covalent organic framework material has good structural tunability and can achieve performance optimization by controlling the monomer structure. It is suitable for flame retardant modification of various polymer systems.

[0022] (3) The nitrogen / phosphorus triazine-based covalent organic framework flame retardant provided by the present invention retards epoxy resin. During the combustion process, the flame retardant inhibits the chain reaction of combustible free radicals in the gas phase and promotes the dehydration and carbonization of the matrix in the condensed phase to form a stable and dense carbon layer, thereby achieving multi-mechanism synergistic flame retardancy.

[0023] (4) The nitrogen / phosphorus triazine-based covalent organic framework flame retardant provided by the present invention has good compatibility with epoxy resin matrix, has little impact on the mechanical properties of the material, and has a positive effect on mechanical properties in a certain proportion, and has good application prospects.

[0024] (5) This invention discloses the preparation of a nitrogen / phosphorus triazine-based covalent organic framework composite material and its application in the field of flame-retardant epoxy resin. A green and environmentally friendly flame-retardant epoxy resin is prepared by using the nitrogen / phosphorus triazine-based covalent organic framework as a filler in epoxy resin and curing it. This nitrogen / phosphorus triazine-based covalent organic framework not only inhibits the intense heat release in the initial stage of epoxy resin combustion but also effectively slows down secondary combustion caused by char layer rupture or continuous release of combustible volatiles in the later stages. Furthermore, it reduces the contribution of total combustible components that can be converted into heat throughout the combustion process, helping to slow the spread of fire. Attached Figure Description

[0025] Figure 1 The infrared spectra of the nitrogen / phosphorus triazine-based covalent organic framework material, TFPT, p-phenylenediamine, diphenylphosphine oxide, and triazine-based covalent organic framework material obtained in Example 1 are shown below.

[0026] Figure 2 The powder X-ray diffraction patterns of the nitrogen / phosphorus triazine covalent organic framework and the triazine covalent organic framework obtained in Example 1 are shown below.

[0027] Figure 3 Thermogravimetric analysis (TGA) curve of nitrogen-containing / phosphorus triazine-based covalent organic framework material obtained in Example 1;

[0028] Figure 4 The graph shows the heat release rate of the flame-retardant epoxy resin containing nitrogen / phosphorus covalent organic framework obtained in Experiment Example 3.

[0029] Figure 5 The graph shows the total heat release of the flame-retardant epoxy resin obtained from the nitrogen / phosphorus triazine-based covalent organic framework flame retardant in Experiment Example 3.

[0030] Figure 6 The graph shows the carbon dioxide generation rate of the flame-retardant epoxy resin obtained from the nitrogen / phosphorus triazine-based covalent organic framework flame retardant in Experiment Example 3. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0032] To achieve the aforementioned objectives of the invention, in the first aspect,

[0033] This invention provides a method for preparing a nitrogen / phosphorus triazine-based covalent organic framework flame retardant (also known as a phosphorus-grafted triazine-based covalent organic framework flame retardant, or simply a nitrogen / phosphorus triazine-based covalent organic framework), comprising the following steps:

[0034] Preparation of nitrogen / phosphorus triazine-containing covalent organic frameworks;

[0035] In one embodiment, a method for preparing a nitrogen / phosphorus triazine-containing covalent organic framework is as follows:

[0036] 2,4,6-Tris(4-aminophenyl)-1,3,5-triazine (TFPT) and p-phenylenediamine were ultrasonically dispersed in a mixed solvent of trimethylolpropene and 1,4-dioxane to obtain TFPT suspension and p-phenylenediamine solution, respectively. Zinc(II) bis(trifluoromethanesulfonyl)imine was added as a catalyst during the ultrasonic dispersion of the TFPT suspension. Subsequently, the p-phenylenediamine solution was added dropwise to the TFPT suspension at room temperature for approximately 30 min, with vigorous stirring throughout. After the addition was complete, the system was heated to 80°C and slowly stirred under a nitrogen atmosphere for 24 h. The resulting black turbid liquid was filtered and washed successively with N,N-dimethylformamide, methanol, and ethanol, with the filtrate gradually becoming nearly colorless. During subsequent washing, the filter cake was appropriately squeezed and transferred to a flask, where an appropriate amount of N,N-dimethylformamide was added for further ultrasonic dispersion to dissolve residual impurities as much as possible. Filtration continued until the filtrate was completely colorless. After drying at 60℃, a lightweight powder of triazine-based covalent organic framework material can be obtained.

[0037] The above-mentioned brown triazine-based covalent organic framework material lightweight powder was reacted with a tetrahydrofuran solution of diphenylphosphine oxide at 50°C under a N2 atmosphere for 30 min. After filtration and washing the solid with ethanol, the solid was dried at 60°C by forced air drying to finally obtain a brownish-yellow nitrogen / phosphorus-containing triazine-based covalent organic framework flame retardant (also known in this invention as phosphorus-containing group-grafted triazine-based covalent organic framework flame retardant) powder.

[0038] The nitrogen / phosphorus triazine-based covalent organic framework flame retardant is a porous network crystal structure formed by covalently connecting phosphorus-containing monomers and nitrogen-containing monomers, and its structure contains both P=O bonds and nitrogen-containing heterocyclic structures.

[0039] Secondly, the present invention provides the application of the nitrogen / phosphorus triazine-based covalent organic framework flame retardant prepared by the above-mentioned method (i.e., the phosphorus-grafted triazine-based covalent organic framework flame retardant, also referred to as the nitrogen / phosphorus triazine-based covalent organic framework flame retardant).

[0040] Furthermore, it is used to prepare flame-retardant epoxy resins.

[0041] Furthermore, the obtained nitrogen / phosphorus triazine-based covalent organic framework flame retardant was dispersed in E51 epoxy resin by mechanical stirring to obtain a uniform mixture. Then, the mixture was reacted at 100°C for a period of time, and 4,4'-diaminodiphenylmethane curing agent was added. The mixture was stirred until a uniform epoxy resin mixture solution was obtained. Finally, the epoxy resin mixture solution was vacuumed to remove excess air bubbles, and then poured into a preheated mold for thermosetting. After curing, it was allowed to cool to room temperature. Finally, a flame-retardant epoxy resin composite material was prepared.

[0042] Furthermore, the mass ratio of the nitrogen / phosphorus triazine-based covalent organic framework flame retardant to E51 type epoxy resin is 2 to 6:100, for example, 3:100, 4:100, 6:100, etc. Within this range, the mass ratio of the nitrogen / phosphorus triazine-based covalent organic framework flame retardant to E51 type epoxy resin can not only effectively improve the flame retardant properties of epoxy resin composites, but also avoid the reduction of mechanical properties of epoxy resin composites due to excessive flame retardant dosage.

[0043] Furthermore, the reaction temperature of the nitrogen / phosphorus triazine-based covalent organic framework flame retardant and E51 type epoxy resin is 100℃; the reaction time is 30-60 minutes, for example, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 60 minutes, etc.; the optimal reaction conditions are selected according to the ratio of nitrogen / phosphorus triazine-based covalent organic framework flame retardant and E51 type epoxy resin, and the reaction temperature and reaction time are reasonably controlled to obtain a hot epoxy resin solution that is uniformly mixed with the flame retardant.

[0044] According to experiments, the optimal conditions are a mass ratio of 6:75.2:18.8 for nitrogen / phosphorus triazine-based covalent organic framework flame retardant, E51 type epoxy resin, and 4,4'-diaminodiphenylmethane curing agent, and when these components are uniformly mixed at 100°C for 40 minutes, an epoxy resin composite material with the highest flame retardant efficiency and the best mechanical properties can be obtained.

[0045] This invention has undergone numerous experiments, and some of the experimental results are presented here for reference to further describe the invention in detail. The following is a detailed description in conjunction with specific embodiments.

[0046] Example 1

[0047] The preparation of a nitrogen / phosphorus triazine-based covalent organic framework flame retardant includes the following steps:

[0048] 0.88 g of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TFPT) and 0.345 g of p-phenylenediamine were ultrasonically dispersed in a mixed solvent of 20 mL of trimethylbenzene and 30 mL of 1,4-dioxane, respectively, to obtain a TFPT suspension and a p-phenylenediamine solution. While the TFPT suspension was ultrasonically dispersed, 0.13 g of zinc (II) bis(trifluoromethanesulfonyl)imine was added as a catalyst. Subsequently, the p-phenylenediamine solution was added dropwise to the TFPT suspension containing the catalyst at room temperature for approximately 30 min, with vigorous stirring throughout. The temperature of the reaction system after the addition was raised to 80 °C, and the mixture was slowly stirred under a nitrogen atmosphere for 24 h. The resulting black turbid liquid was filtered and washed successively with N,N-dimethylformamide, methanol, and ethanol; the filtrate gradually became nearly colorless. In the subsequent washing process, the filter cake was appropriately squeezed and transferred to a flask. An appropriate amount of N,N-dimethylformamide was added, and ultrasonic dispersion was continued to dissolve residual impurities as much as possible. Filtration continued until the filtrate was completely colorless. The obtained colorless filtrate was dried at 60°C by forced air drying to obtain a brown triazine-based covalent organic framework material lightweight powder.

[0049] The above-mentioned 1.0 g brown triazine covalent organic framework material powder was reacted with a tetrahydrofuran solution containing 2.0 g diphenylphosphine oxide at 50 °C under a N2 atmosphere for 30 min. After filtration and washing the solid with ethanol, the solid was dried at 60 °C by forced air drying to finally obtain a brownish-yellow nitrogen / phosphorus triazine covalent organic framework flame retardant powder.

[0050] Infrared spectroscopy was performed on the nitrogen / phosphorus triazine-based covalent organic framework material obtained in Example 1, TFPT, p-phenylenediamine, diphenylphosphine oxide, and the triazine-based covalent organic framework material. The obtained infrared spectra are shown below. Figure 1 ;

[0051] The powder containing nitrogen / phosphorus triazine covalent organic framework and triazine covalent organic framework material obtained in Example 1 was subjected to X-ray diffraction analysis, and the X-ray diffraction pattern is shown below. Figure 2 ;

[0052] The nitrogen- / phosphorus triazine-based covalent organic framework material obtained in Example 1 was subjected to nitrogen thermogravimetric analysis (TGA). The obtained nitrogen TGA chromatogram is shown below. Figure 3 .

[0053] Experimental Example 1

[0054] Two parts by weight of the nitrogen / phosphorus triazine-based covalent organic framework flame retardant prepared in Example 1 were dispersed in 78.4 parts by weight of E51 type epoxy resin by mechanical stirring. The mixture was then heated to 100°C and reacted for 60 minutes. Subsequently, 19.6 parts by weight of 4,4'-diaminodiphenylmethane curing agent were added, and the mixture was stirred until a stable and homogeneous epoxy resin solution was obtained. Finally, the epoxy resin solution was vacuum-sealed to remove excess air bubbles, then poured into a preheated mold, and cured at 100°C for half an hour, 120°C for 2 hours, and 150°C for 2 hours. After curing, the mixture was allowed to cool naturally to room temperature and demolded to obtain the flame-retardant epoxy resin composite material.

[0055] The prepared flame-retardant epoxy resin samples were subjected to cone calorimetry testing. The cone calorimetry sample dimensions were 100 mm × 100 mm × 3 mm. The results showed that the addition of a nitrogen / phosphorus triazine-based covalent organic framework flame retardant effectively reduced the heat release rate of the epoxy resin composite. Compared with pure epoxy resin, the peak heat release rate of the epoxy resin composite decreased from 1004 kW / m³. 2 Decreased to 727 kW / m 2 The decline rate was 27.5%.

[0056] Experimental Example 2

[0057] Four parts by weight of the nitrogen / phosphorus triazine-based covalent organic framework flame retardant prepared in Example 1 were dispersed in 76.8 parts by weight of E51 type epoxy resin by mechanical stirring. The mixture was then heated to 100°C and reacted for 60 minutes. Subsequently, 19.2 parts by weight of 4,4'-diaminodiphenylmethane curing agent were added, and the mixture was stirred until a stable and homogeneous epoxy resin solution was obtained. Finally, the epoxy resin solution was vacuum-sealed to remove excess air bubbles, then poured into a preheated mold, and cured at 100°C for half an hour, 120°C for 2 hours, and 150°C for 2 hours. After curing, the mixture was allowed to cool naturally to room temperature and demolded to obtain the flame-retardant epoxy resin composite material.

[0058] The prepared flame-retardant epoxy resin samples were subjected to cone calorimetry testing. The cone calorimetry sample dimensions were 100 mm × 100 mm × 3 mm. The results showed that, compared to pure epoxy resin, the peak heat release rate of the epoxy resin composite material increased from 1004 kW / m³. 2 Decreased to 621 kW / m 2 The decline rate was 38.1%.

[0059] Experimental Example 3

[0060] Six parts by weight of the nitrogen / phosphorus triazine-based covalent organic framework flame retardant prepared in Example 1 were dispersed in 75.2 parts by weight of E51 type epoxy resin by mechanical stirring. The mixture was then heated to 100°C and reacted for 60 minutes. Subsequently, 18.8 parts by weight of 4,4'-diaminodiphenylmethane curing agent were added, and the mixture was stirred until a stable and homogeneous epoxy resin solution was obtained. Finally, the epoxy resin solution was vacuum-sealed to remove excess air bubbles, then poured into a preheated mold, and cured at 100°C for half an hour, 120°C for 2 hours, and 150°C for 2 hours. After curing, the mixture was allowed to cool naturally to room temperature and demolded to obtain the flame-retardant epoxy resin composite material.

[0061] The prepared flame-retardant epoxy resin specimens were subjected to cone calorimetry testing. The cone calorimetry specimens were 100mm × 100mm × 3mm in size. The peak heat release rate of the flame-retardant epoxy resin obtained in Experimental Example 3 is as follows: Figure 4 As shown, the total heat release curve is as follows: Figure 5 As shown, the peak carbon dioxide generation rate is as follows Figure 6 As shown. The results indicate that the flame-retardant epoxy resin composite containing a nitrogen / phosphorus triazine covalent organic framework has a peak heat release rate that is 1004 kW / m³ higher than that of pure epoxy resin. 2 Decreased to 551 kW / m 2 The decrease rate was 45.1%; the total heat release decreased from 58.1 MJ / m³ for pure epoxy resin. 2 It dropped to 44.6 MJ / m 2 The peak carbon dioxide generation rate decreased by 23.2% from 0.52 g / s for pure epoxy resin to 0.23 g / s, a reduction of 55.8%.

[0062] Compare with Example 1

[0063] 80 parts by weight of E51 type epoxy resin and 20 parts by weight of 4,4'-diaminodiphenylmethane curing agent were mechanically stirred at 100°C until homogeneous to obtain an epoxy resin solution. Finally, the epoxy resin solution was vacuum-sealed to remove excess air bubbles, then poured into a preheated mold, and cured at 100°C for half an hour, 120°C for 2 hours, and 150°C for 2 hours. After curing, it was allowed to cool naturally to room temperature and demolded to obtain the reference epoxy resin.

[0064] The prepared epoxy resin specimens were subjected to cone calorimetry testing. The cone calorimetry specimens were 100mm × 100mm × 3mm in size.

[0065] As can be seen from the above embodiments or experimental examples, the flame-retardant properties of the flame-retardant epoxy resin composite materials prepared by the present invention are significantly improved. With the introduction of nitrogen / phosphorus triazine-based covalent organic framework flame retardants into epoxy resin, the heat release rate, smoke production rate, carbon monoxide generation rate, and carbon dioxide generation rate during epoxy resin combustion can be effectively reduced, and the quality of the char layer is significantly improved. This indicates that nitrogen / phosphorus triazine-based covalent organic framework flame retardants can effectively inhibit the generation of heat, smoke, and harmful gases during epoxy resin combustion, and can form a stable heat insulation layer, better preventing external heat from entering the epoxy resin matrix. This suggests that nitrogen / phosphorus triazine-based covalent organic framework materials are promising candidates for epoxy resin flame retardants.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a phosphorus-containing triazine-based covalent organic framework flame retardant, characterized in that, Includes the following steps: 2,4,6-Tris(4-aminophenyl)-1,3,5-triazine (TFPT) and p-phenylenediamine were ultrasonically dispersed in a mixed solvent of trimethylolpropene and 1,4-dioxane to obtain TFPT suspension and p-phenylenediamine solution, respectively. While ultrasonically dispersing the TFPT suspension, zinc (II) bis(trifluoromethanesulfonyl)imine was added as a catalyst. Then, the p-phenylenediamine solution was added dropwise to the TFPT suspension with the zinc (II) bis(trifluoromethanesulfonyl)imine catalyst at room temperature for approximately 30 minutes, with vigorous stirring throughout. After the addition was complete, the reaction temperature was raised to 80°C, and the mixture was slowly stirred for 24 minutes under a nitrogen atmosphere. h; The resulting black turbid liquid was filtered and washed successively with N,N-dimethylformamide, methanol, and ethanol. The filtrate gradually became nearly colorless. During subsequent washing, the filter cake was squeezed and transferred to a flask. An appropriate amount of N,N-dimethylformamide was added and ultrasonically dispersed to dissolve residual impurities as much as possible. Filtration was continued until the filtrate was completely colorless. The above colorless filtrate was dried at 60°C to obtain a brown triazine-based covalent organic framework material lightweight powder. The above-mentioned brown triazine covalent organic framework material powder was reacted with a tetrahydrofuran solution of diphenylphosphine oxide at 50°C and under a N2 atmosphere for 30 min. The solid was then filtered and washed with ethanol. After drying in a forced-air environment at 60°C, a brownish-yellow nitrogen / phosphorus triazine covalent organic framework flame retardant powder was finally obtained. The nitrogen / phosphorus covalent triazine-based organic framework flame retardant is a porous network crystal structure formed by phosphorus-containing monomers and nitrogen-containing monomers connected by covalent bonds, and its structure contains both P=O bonds and nitrogen-containing heterocyclic structures.

2. The application of the phosphorus-containing group-grafted triazine-based covalent organic framework flame retardant prepared by the method of claim 1.

3. The application according to claim 2, characterized in that, Used to prepare flame-retardant epoxy resins.

4. The application according to claim 3, characterized in that, The nitrogen / phosphorus triazine covalent organic framework flame retardant obtained by the preparation method of the phosphorus-containing group-grafted triazine covalent organic framework flame retardant according to claim 1 is dispersed in E51 type epoxy resin by mechanical stirring to obtain a uniform mixture. Then, the mixture is reacted at 100°C for a period of time, and 4,4'-diaminodiphenylmethane curing agent is added and stirred until a uniform epoxy resin mixture solution is obtained. Finally, the epoxy resin mixture solution is vacuumed to remove excess air bubbles, and then poured into a preheated mold for thermosetting. After curing, it is allowed to cool to room temperature. Finally, a flame-retardant epoxy resin composite material is prepared.

5. The application according to claim 4, characterized in that, The mass ratio of the nitrogen- / phosphorus triazine-based covalent organic framework flame retardant to E51 type epoxy resin is 2-6:

100.

6. The application according to claim 4, characterized in that, The reaction temperature of the nitrogen / phosphorus triazine-based covalent organic framework flame retardant and the E51 type epoxy resin is 100℃, and the reaction time is 30-60 minutes.

7. The application according to any one of claims 4-6, characterized in that, The peak heat release rate (pHRR) of the flame-retardant epoxy resin composite material is reduced by 27% or more.

8. The application according to any one of claims 4-6, characterized in that, The peak carbon dioxide generation rate of the flame-retardant epoxy resin composite material is reduced by 31% or more.

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