A recyclable flame-retardant carbon fiber / epoxy resin composite material and its preparation method

Abstract

The invention relates to the technical field of composite materials and discloses a recyclable flame-retardant carbon fiber / epoxy resin composite material and a preparation method thereof. The composite material comprises, by weight, 15-30% of an aldehyde-containing epoxy compound, 15-30% of an amino-containing cyclotriphosphazene compound curing agent, and 40-70% of carbon fiber. In the invention, the aldehyde-containing epoxy compound and the amino-containing cyclotriphosphazene compound are used as curing agents, and the two are combined to form an epoxy resin containing a Schiff base structure. Since both the cyclotriphosphazene and the Schiff base structure have flame-retardant properties and the Schiff base structure is easily degradable, the composite material ultimately has both flame-retardant and degradable properties and relatively excellent mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and in particular to a recyclable flame-retardant carbon fiber / epoxy resin composite material and a preparation method thereof. Background Art

[0002] Carbon fiber-reinforced resin-based composites, characterized by their lightweight, high specific strength and modulus, have been widely used in aerospace, transportation, electronics, and other fields. Epoxy resin is one of the most widely used and mature thermosetting resin matrices. However, once cured, epoxy resin forms an insoluble, infusible cross-linked network, making it difficult to recycle and reuse. Furthermore, epoxy resin is also prone to flammability. Therefore, improving its flame retardant properties and expanding its application areas are of great significance. With the increasing awareness of environmental protection and sustainable development, the efficient recycling and reuse of discarded high-performance carbon fiber composites has become a research hotspot.

[0003] To improve the flame retardancy of carbon fiber / epoxy resin composites, a common method is to add flame retardants to the epoxy resin system. However, due to the large amount of flame retardants added and their poor compatibility with the resin matrix, the mechanical properties of the material are reduced. Currently developed methods for recycling carbon fiber composites include mechanical pulverization, thermal decomposition, and solvent recovery.

[0004] Although the mechanical crushing method is simple, it destroys the fiber size and is often used as a filler for secondary use, which greatly reduces the value of the carbon fiber; the pyrolysis method can recycle continuous carbon fiber, but the high-temperature oxidation conditions will cause certain damage to the carbon fiber, and the performance of the recycled carbon fiber will be reduced; the supercritical fluid method can also recycle continuous carbon fiber, but it has very high requirements on equipment and the recycling cost is high.

[0005] For example, CN110857341A discloses a degradation solvent for a carbon fiber resin-based composite material and a method for recovering carbon fiber by catalytic pyrolysis of a carbon fiber resin-based composite material. The method adopts a pyrolysis method to recover carbon fiber, wherein the carbon fiber composite material and the degradation solvent are mixed and added to a reactor; the reactor is heated to 150-300°C and kept warm for 30-120 minutes; the degradation product is removed from the reactor, ultrasonically cleaned in water for 10 minutes, and then dried to obtain the recovered carbon fiber.

[0006] CN115505240A discloses a recyclable carbon fiber / epoxy resin prepreg, composite material, preparation method, and application. The prepreg is prepared by reacting an amino acid latent curing agent with a glycidyl ester epoxy resin to form an epoxy resin matrix. The hydrolyzable ester bonds in the resulting epoxy network are then used to degrade the epoxy resin matrix, enabling lossless recycling of the carbon fibers. However, epoxy resins containing ester bonds exhibit lower glass transition temperatures and mechanical strength.

[0007] However, further research is still needed to obtain carbon fiber / epoxy resin composites with both excellent flame retardant properties and biodegradable properties. Summary of the Invention

[0008] The present invention addresses the shortcomings of existing epoxy resin-based carbon fiber composites, which are difficult to recycle and easy to burn, and provides a recyclable flame-retardant carbon fiber / epoxy resin composite material. The composite material adopts an aldehyde-containing epoxy compound and an amino-containing cyclotriphosphazene compound as a curing agent. The two are combined to form an epoxy resin containing a Schiff base structure, achieving both flame retardant and biodegradable properties.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] A recyclable flame-retardant carbon fiber / epoxy resin composite material, comprising raw materials by mass: 15-30% of an aldehyde-containing epoxy compound, 15-30% of an amino-containing cyclotriphosphazene compound curing agent, and 40-70% of carbon fiber;

[0011] The aldehyde-containing epoxy compound includes a compound having any of the following structures:

[0012]

[0013] The amino-containing cyclotriphosphazene compound curing agent includes a compound having any of the following structures:

[0014]

[0015] In the present invention, an aldehyde-containing epoxy compound and an amino-containing cyclotriphosphazene compound are used as curing agents, and the two are combined to form an epoxy resin containing a Schiff base structure. Since both the cyclotriphosphazene and the Schiff base structure have flame retardant properties, the epoxy resin matrix and the composite material thereof have excellent flame retardant properties. In addition, since the Schiff base structure is unstable in an acidic solution and easily breaks, the resin-based carbon fiber composite material containing the Schiff base structure can be degraded when immersed in an acidic solution, thereby achieving lossless carbon fiber recovery. The epoxy resin containing the Schiff base structure can obtain a high glass transition temperature and mechanical properties, ultimately making the composite material both flame retardant and degradable, and also having relatively excellent mechanical properties.

[0016]

[0017] The raw materials for synthesizing the above structure are abundant and cheap, and the mechanical properties of the epoxy resin obtained are relatively high.

[0018] Preferably, the amino-containing cyclotriphosphazene compound curing agent includes a compound having any of the following structures:

[0019]

[0020] Likewise, the raw materials for the above structure synthesis are abundant and cheap, and the mechanical properties of the epoxy resin obtained are relatively high.

[0021] The molar ratio of the aldehyde-containing epoxy compound to the amino-containing cyclotriphosphazene compound curing agent is 1:0.25-0.5.

[0022] The active groups in the aldehyde-containing epoxy compound include epoxy groups and aldehyde groups, wherein the reaction molar ratio of the epoxy group to the amino group is 2:1, and the reaction molar ratio of the aldehyde group to the amino group is 1:1; the raw material ratio is appropriately adjusted according to the difference in the active groups of the epoxy compound and the amino structure in the cyclotriphosphazene compound.

[0023] The recyclable flame-retardant carbon fiber / epoxy resin composite material of the present invention has excellent flame retardant and mechanical properties, and its vertical combustion rating is UL 94V0; the oxygen index is 35% to 45%; for example, the composite material prepared based on T700 grade carbon fiber has a tensile strength higher than 2100MPa, a tensile modulus higher than 100GPa, a flexural strength higher than 1000MPa, a flexural modulus higher than 90GPa, and an interlaminar shear strength higher than 60MPa.

[0024] Preferably, 3-methoxy-4-(oxiran-2-ylmethoxy)benzaldehyde epoxy compound and hexa(4-amino-2-vinylphenoxy)cyclotriphosphazene curing agent are used to prepare unidirectional carbon fiber prepreg and composite materials. The flame retardant grade of the carbon fiber composite material can reach UL 94V0, and its tensile strength is 2216.5MPa, tensile modulus is 126.2GPa, flexural strength is 1298.8MPa, flexural modulus is 110.6GPa, and interlaminar shear strength is 75.1MPa. About 1.2g of the composite material is placed in 60mL of 0.2mol HCl / THF / H2O (V THF / V H2O =9 / 1) in an acidic solution at 50°C for 3 hours, the resin matrix is completely degraded to obtain damage-free carbon fibers, thereby realizing the recovery of damage-free carbon fibers.

[0025] The recyclable flame-retardant carbon fiber / epoxy resin composite material also has an excellent biodegradable effect. It can be dissolved in an acidic degradation solution at a solid-liquid mass ratio of 1:0.5 to 1:50 (g / g) at room temperature for more than 48 hours and completely degraded; it can be dissolved in 40-60°C for more than 3 hours and completely degraded at 80-100°C for more than 1 hour, thereby achieving the recycling of lossless carbon fiber.

[0026] The acidic degradation solvent includes hydrochloric acid, an organic solvent and water; the molar concentration of the hydrochloric acid is 0.1 to 1 mol / L, and the volume ratio of the organic solvent to water is 5 / 5 to 9 / 1; the organic solvent includes any one or more of tetrahydrofuran, acetone, methanol, ethanol, dioxane and N-methylformamide.

[0027] Preferably, according to the solid-liquid mass ratio of 1:5 to 1:20, the composite material is THF / V H2O =9 / 1) In an acidic solution, the resin matrix is completely degraded over 48 hours at room temperature; over 3 hours at 50°C; and over 1 hour at 90°C; all without damaging the carbon fiber, thus enabling the recovery of non-destructive carbon fiber.

[0028] The present invention also provides a method for preparing the recyclable flame-retardant carbon fiber / epoxy resin composite material, which is characterized by comprising the steps of:

[0029] Step 1, dissolving an aldehyde-containing epoxy compound and an amino-containing cyclotriphosphazene compound curing agent in a volatile solvent to form a resin mixed solution;

[0030] Step 2: impregnating carbon fiber in the resin mixed solution, and removing the solvent and water generated by the reaction in vacuum at 50-60° C. to obtain a carbon fiber prepreg, which is then cured to obtain a recyclable flame-retardant carbon fiber / epoxy resin composite material.

[0031] After the carbon fiber is impregnated with the resin mixed solution, under vacuum conditions of 50-60°C, while removing the organic solvent, the aldehyde group in the aldehyde-containing epoxy compound will first react with the amino group in the amino-containing cyclotriphosphazene compound curing agent to form a Schiff base structure. However, the epoxy group and the amino group will not undergo a curing reaction under these conditions, thereby obtaining a carbon fiber prepreg.

[0032] Preferably, the mass concentration of the reaction raw materials in the resin mixed solution of step 1 is 10-15%. The resin content of the prepreg can be regulated by the concentration of the resin mixed solution. Generally, a low solution concentration results in a low prepreg resin content, requiring multiple dip coatings. A high solution concentration results in a high prepreg resin content, and the solvent trapped in the resin is difficult to remove completely, which can easily increase the porosity of the composite material and reduce the mechanical properties of the composite material. Here, the reaction raw materials are an aldehyde-containing epoxy compound and an amino-containing cyclotriphosphazene compound curing agent.

[0033] The volatile solvent includes any one or more of acetone, tetrahydrofuran, dioxane, and N-methylformamide.

[0034] Preferably, the vacuum condition in step 2 is lower than -0.1 MPa. In the present invention, the prepreg is first subjected to a vacuum treatment, mainly to remove the solvent and water generated by the reaction.

[0035] The mass content of the resin coated on the carbon fiber prepreg in step 1 is 30-60%.

[0036] The curing conditions are: 0.5-2h at 70-90℃, 1-3h at 100-130℃, and 1-3h at 140-160℃.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention adopts an aldehyde-containing epoxy compound and an amino-containing cyclotriphosphazene compound as curing agents, and simultaneously introduces a degradable group and a flame retardant group into the epoxy resin system to obtain a carbon fiber / epoxy resin composite material. The composite material has excellent flame retardancy, mechanical properties and degradability, can be degraded under mild conditions, and can achieve lossless recycling and reuse of the carbon fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is the NMR spectrum of 3-methoxy-4-(oxiran-2-ylmethoxy)benzaldehyde prepared in Example 1.

[0040] Figure 2 This is the NMR spectrum of the hexa(4-aminophenoxy)cyclotriphosphazene curing agent prepared in Example 1.

[0041] Figure 3 This is the DSC curing curve of the epoxy resin matrix of the prepreg in Example 1. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art will make modifications or equivalent substitutions based on understanding the technical solution of the present invention, without departing from the spirit and scope of the technical solution of the present invention, and all should be encompassed within the protection scope of the present invention.

[0043] The raw materials used in the following specific embodiments were purchased from the market. The epoxy compounds containing aldehyde groups and the cyclotriphosphazene compounds containing amino groups were synthesized according to conventional methods reported in the literature and were homemade when used.

[0044] UL-94 vertical burning rating test standard: ASTM D3801-20; test specimen thickness is 2±0.5mm

[0045] Composite material oxygen index test standard: ISO 4589-2;

[0046] Composite material tensile properties test standard: ASTM D3039 / D3039M-17;

[0047] Composite material flexural properties test standard: ASTM D7264 / D7264M-15;

[0048] Composite material interlaminar shear strength test standard: ASTM D2344 / D2344M-16.

[0049] Example 1

[0050] Synthesis method of 3-methoxy-4-(oxiran-2-ylmethoxy)benzaldehyde epoxy compound:

[0051] 3-Methoxy-4-hydroxybenzaldehyde (152 g, 1 mol), epichlorohydrin (159 g, 1.5 mol) and tetrabutylammonium bromide (4.67 g, 0.014 mol) were placed in a round-bottom flask equipped with a constant pressure funnel and a magnetic stirrer and maintained at 80°C for 2 hours. After cooling, a 50 wt% aqueous NaOH solution (80 g, 2 mol NaOH) was added dropwise over 15 minutes, followed by a reaction at a temperature of approximately 16°C for 3 hours. The mixture was washed with deionized water until neutral, then dried over anhydrous magnesium sulfate, and then precipitated with petroleum ether and dried at 80°C for 2 hours to obtain 155 g of a light yellow solid product with a yield of 74.5%. The reaction formula is as follows:

[0052]

[0053] The NMR spectrum of the product 3-methoxy-4-(oxiran-2-ylmethoxy)benzaldehyde epoxy compound is as follows Figure 1As shown, the structure was correct after analysis and the compound was successfully synthesized.

[0054] Synthesis method of hexa(4-aminophenoxy)cyclotriphosphazene curing agent:

[0055] Hexachlorocyclotriphosphazene (69.6 g, 0.2 mol), an acid-binding agent, anhydrous potassium carbonate (110.4 g, 0.8 mol), and 1200 mL of acetone were placed in a round-bottom flask equipped with a constant pressure funnel and a magnetic stirrer and stirred at 65°C. p-Nitrophenol (194.6 g, 1.4 mol) was then dissolved in acetone and slowly added dropwise to the flask, followed by stirring at 65°C for 6 hours. The precipitate was washed with deionized water until neutral, then with ethanol until white. After filtering, the white precipitate was dried at 80°C for 10 hours to obtain 185.2 g of hexa(4-nitrophenoxy)cyclotriphosphazene (white powder) with a yield of 96.1%.

[0056] Hexa(4-nitrophenoxy)cyclotriphosphazene (173.52 g, 0.18 mol), palladium-carbon catalyst (21.6 g), and 2800 mL of tetrahydrofuran were placed in a round-bottom flask equipped with a constant pressure funnel and a magnetic stirrer and stirred at 75°C. Hydrazine hydrate (350 mL) was slowly added dropwise to the flask. After the addition was complete, stirring was continued at 75°C for 6 hours. The reaction solution was concentrated by rotary evaporation and added to deionized water. A white precipitate was precipitated by stirring. The precipitate was washed three times with deionized water, filtered, and dried at 80°C for 10 hours to obtain 128.6 g of hexa(4-aminophenoxy)cyclotriphosphazene (white powder) with a yield of 91.1%. The reaction formula is as follows:

[0057]

[0058] The NMR spectrum of the product hexa(4-aminophenoxy)cyclotriphosphazene is as follows Figure 2 As shown, the analysis shows that the structure has been successfully synthesized.

[0059] Example 2

[0060] Step 1: Dissolve 124.8 g (0.6 mol) of the 3-methoxy-4-(oxiran-2-ylmethoxy)benzaldehyde epoxy compound prepared in Example 1 and 117.6 g (0.15 mol) of a hexakis(4-aminophenoxy)cyclotriphosphazene curing agent in acetone to form a mixed solution having a concentration of 10% by mass of the reaction raw materials;

[0061] In step 2, after impregnating a 300 mm × 300 mm unidirectional carbon fiber fabric with the mixed solution, the solvent and the water generated by the reaction are removed under vacuum conditions of 50°C and -0.1 MPa to obtain a carbon fiber prepreg, wherein the resin mass content of the prepreg is approximately 40%; further, 12 layers of prepreg are placed in a mold for hot pressing and curing, and the curing system is 1 hour at 80°C, 2 hours at 120°C, and 2 hours at 150°C to obtain a recyclable flame-retardant carbon fiber / epoxy resin composite material. Figure 3 This is the DSC curing curve of the epoxy resin matrix of the prepreg in Example 1.

[0062] The aldehyde group of 3-methoxy-4-(oxiran-2-ylmethoxy)benzaldehyde and the amino group of hexa(4-aminophenoxy)cyclotriphosphazene curing agent are dehydrated at 50°C to form an epoxy compound containing a Schiff base structure. The reaction formula is as follows:

[0063]

[0064] During curing, the epoxy structure in 3-methoxy-4-(oxiran-2-ylmethoxy)benzaldehyde further reacts with a hexakis(4-aminophenoxy)cyclotriphosphazene curing agent to produce a cured epoxy resin containing both Schiff base and cyclotriphosphazene structures. Because both the cyclotriphosphazene and Schiff base structures possess flame retardancy, the epoxy resin matrix and its composite material possess excellent flame retardancy. Furthermore, because the Schiff base structure is unstable and prone to breakage in acidic solutions, the resin-based carbon fiber composite containing the Schiff base structure can be degraded by immersion in an acidic solution, enabling the non-destructive recycling of the carbon fibers.

[0065] The performance of the prepared composite material was tested, and its oxygen index was 40%; the flame retardant grade of vertical burning was UL94V0, its tensile strength was 2241.6MPa, tensile modulus was 118.6GPa, its flexural strength was 1233.8MPa, flexural modulus was 105.2GPa, and interlaminar shear strength was 72.2MPa.

[0066] The biodegradability of the composite material was tested by placing 1.2 g of the composite material in 60 mL of 0.2 mol HCl / THF / H2O (V THF / V H2O =9 / 1) In acidic solutions, the epoxy resin matrix was found to completely degrade within 48 hours at room temperature, within 3 hours at 50°C, and within 1 hour at 90°C. All of these conditions left the carbon fibers intact, enabling the recovery of intact carbon fibers. (Complete degradation is determined by removing the fibers from the degradation solution, ultrasonically washing them three times with acetone, and drying them. If the fibers remain fluffy and their weight remains unchanged, this indicates complete resin degradation.)

[0067] Example 3

[0068] 4-(Oxiran-2-ylmethoxy)benzaldehyde epoxy compound was synthesized using 4-hydroxybenzaldehyde as raw material according to the experimental method of Example 1.

[0069]

[0070] Unidirectional carbon fiber prepreg and composite materials were prepared by using 4-(oxiran-2-ylmethoxy)benzaldehyde epoxy compound and the hexa(4-aminophenoxy)cyclotriphosphazene curing agent prepared in Example 1 according to the experimental method of Example 2.

[0071] The performance of the material was tested, and the results showed that its flame retardant grade can reach UL 94V0, the oxygen index is 42%, its tensile strength is 2205.2MPa, tensile modulus is 112.2GPa, its flexural strength is 1112.6MPa, flexural modulus is 100.5GPa, and its interlaminar shear strength is 65.8MPa.

[0072] Degradation effect: About 1.2g of the composite material was placed in 60mL of 0.2mol HCl / THF / H2O (V THF / V H2O =9 / 1) in an acidic solution at 50°C for 3 hours, the resin matrix is completely degraded to obtain damage-free carbon fibers, thereby realizing the recovery of damage-free carbon fibers.

[0073] Example 4

[0074] Using 4-nitro-2-vinylphenol as a raw material, hexa(4-amino-2-vinylphenoxy)cyclotriphosphazene curing agent was synthesized according to the experimental method of Example 1. The reaction formula is as follows.

[0075]

[0076] The 3-methoxy-4-(oxiran-2-ylmethoxy)benzaldehyde epoxy compound prepared in Example 1 and the hexa(4-amino-2-vinylphenoxy)cyclotriphosphazene curing agent were used to prepare unidirectional carbon fiber prepreg and composite materials according to the experimental method of Example 2.

[0077] The performance test of the composite material showed that the flame retardant grade of its carbon fiber composite material can reach UL 94V0, the oxygen index is 38%, its tensile strength is 2216.5MPa, the tensile modulus is 126.2GPa, the flexural strength is 1298.8MPa, the flexural modulus is 110.6GPa, and the interlaminar shear strength is 75.1MPa.

[0078] Degradation effect: About 1.2g of the composite material was placed in 60mL of 0.2mol HCl / THF / H2O (V THF / V H2O=9 / 1) in an acidic solution at 50°C for 3 hours, the resin matrix is completely degraded to obtain damage-free carbon fibers, thereby realizing the recovery of damage-free carbon fibers.

[0079] Examples 2 and 3 use the same hexakis(4-aminophenoxy)cyclotriphosphazene curing agent. The 3-methoxy-4-(oxiran-2-ylmethoxy)benzaldehyde epoxy compound in Example 2 has only one more methoxy group than the 4-(oxiran-2-ylmethoxy)benzaldehyde epoxy compound in Example 3. However, the mechanical properties of the composite material in Example 2 are slightly higher than those of the composite material in Example 3. This is because the methoxy group in the epoxy compound in Example 2 forms hydrogen bonds with the hydroxyl group generated by the epoxy ring opening. Therefore, the mechanical properties of the resin matrix in Example 2 are higher than those in Example 3, and the corresponding composite material also has better mechanical properties. However, due to the additional methoxy group in the 3-methoxy-4-(oxiran-2-ylmethoxy)benzaldehyde epoxy compound, its oxygen index is slightly lower.

[0080] Example 4 uses the same 3-methoxy-4-(oxiran-2-ylmethoxy)benzaldehyde epoxy compound as Example 2. The hexa(4-amino-2-vinylphenoxy)cyclotriphosphazene curing agent in Example 4 has an additional vinyl group compared to the hexa(4-aminophenoxy)cyclotriphosphazene curing agent. Because the vinyl group readily undergoes cross-linking reactions even at high temperatures, the crosslink density of the resin matrix in Example 4 is higher than that in Example 2. Consequently, the mechanical properties of the epoxy resin in Example 4 are superior to those in Example 2, and the corresponding composite material also exhibits superior mechanical properties. However, the additional vinyl group in the hexa(4-amino-2-vinylphenoxy)cyclotriphosphazene curing agent reduces its oxygen index, indicating that different structures can lead to differences in epoxy performance.

[0081] Comparative Example 1

[0082] The commercially available bisphenol A epoxy resin E51 / E20 (65 / 35) was uniformly mixed at 90°C using a vacuum planetary mixer, and then a curing agent, methyl nadic anhydride, and an accelerator, 2-ethyl-4-methylimidazole, were added, wherein the mass ratio of the mixed epoxy resin: curing agent: accelerator was 100:50:2, and further uniformly mixed using a vacuum planetary mixer. Then, an epoxy resin film was prepared on a hot melt film machine, and its surface density was 30g / m 2 .

[0083] A hot melt adhesive film prepreg machine was used to prepare the prepreg by double-sided dipping with a resin content of 40%. The prepreg was placed in a mold for hot pressing and curing. The curing system was 80°C for 1h, 120°C for 2h, and 150°C for 2h to obtain a carbon fiber / epoxy resin composite material.

[0084] The mechanical properties of the composite material are as follows: tensile strength 2100MPa, tensile modulus 110.6GPa, flexural strength 998.6MPa, flexural modulus 91GPa, and interlaminar shear strength 62.5MPa. In addition, the composite material is flammable, has no flame retardant grade for vertical combustion, and has an oxygen index of 27%.

[0085] The material was also placed in a degradable acid solution to observe its degradability, and it was found that the resin did not degrade in the acidic solution.

Claims

1. A recyclable flame-retardant carbon fiber / epoxy resin composite material, characterized in that: The raw materials include: 15-30% of epoxy compound containing aldehyde group, 15-30% of cyclotriphosphazene compound curing agent containing amino group, and 40-70% of carbon fiber by mass content; The aldehyde-containing epoxy compound includes a compound having any of the following structures: The amino-containing cyclotriphosphazene compound curing agent includes a compound having any of the following structures: The preparation method of the recyclable flame-retardant carbon fiber / epoxy resin composite material comprises the following steps: Step 1, dissolving an aldehyde-containing epoxy compound and an amino-containing cyclotriphosphazene compound curing agent in a volatile solvent to form a resin mixed solution; Step 2: impregnating carbon fibers in the resin mixed solution, and removing the solvent and water generated by the reaction under vacuum at 50-60° C. to obtain a carbon fiber prepreg, which is then cured to obtain a recyclable flame-retardant carbon fiber / epoxy resin composite material; The curing conditions are: 0.5-2h at 70-90℃, 1-3h at 100-130℃, and 1-3h at 140-160℃.

2. The recyclable flame-retardant carbon fiber / epoxy resin composite material according to claim 1, characterized in that: The aldehyde-containing epoxy compound includes a compound having any of the following structures: The amino-containing cyclotriphosphazene compound curing agent includes a compound having any of the following structures:

3. The recyclable flame-retardant carbon fiber / epoxy resin composite material according to claim 1, characterized in that: The molar ratio of the aldehyde-containing epoxy compound to the amino-containing cyclotriphosphazene compound curing agent is 1:0.25-0.

5.

4. The recyclable flame-retardant carbon fiber / epoxy resin composite material according to claim 1, characterized in that: Its vertical combustion rating is UL94 V0; the oxygen index is 35% to 45%; When the carbon fiber is T700, the tensile strength of the composite material is higher than 2100MPa, the tensile modulus is higher than 100GPa, the flexural strength is higher than 1000MPa, the flexural modulus is higher than 90GPa, and the interlaminar shear strength is higher than 60MPa.

5. The recyclable flame-retardant carbon fiber / epoxy resin composite material according to claim 1, characterized in that: The recyclable flame-retardant carbon fiber / epoxy resin composite material is completely degraded by dissolving in an acidic degradation solution at a solid-liquid mass ratio of 1:0.5 to 1:50 for more than 48 hours at room temperature; completely degraded by dissolving at 40-60°C for more than 3 hours; and completely degraded by dissolving at 80-100°C for more than 1 hour.

6. The recyclable flame-retardant carbon fiber / epoxy resin composite material according to claim 5, characterized in that: The acidic degradation solvent includes hydrochloric acid, an organic solvent and water; the molar concentration of the hydrochloric acid is 0.1 to 1 mol / L, and the volume ratio of the organic solvent to water is 5 / 5 to 9 / 1; the organic solvent includes any one or more of tetrahydrofuran, acetone, methanol, ethanol, dioxane and N-methylformamide.

7. The method for preparing the recyclable flame-retardant carbon fiber / epoxy resin composite material according to any one of claims 1 to 6, characterized in that: Including steps: Step 1, dissolving an aldehyde-containing epoxy compound and an amino-containing cyclotriphosphazene compound curing agent in a volatile solvent to form a resin mixed solution; Step 2: impregnating carbon fiber in the resin mixed solution, and removing the solvent and water generated by the reaction in vacuum at 50-60° C. to obtain a carbon fiber prepreg, which is then cured to obtain a recyclable flame-retardant carbon fiber / epoxy resin composite material.

8. The method for preparing the recyclable flame-retardant carbon fiber / epoxy resin composite material according to claim 7, characterized in that: The mass concentration of the reaction raw materials in the resin mixed solution in step 1 is 10-30%; the volatile solvent includes any one or more of acetone, tetrahydrofuran, dioxane, and N-methylformamide.

9. The method for preparing the recyclable flame-retardant carbon fiber / epoxy resin composite material according to claim 7, characterized in that: The vacuum condition in step 2 is lower than -0.1 MPa; the mass content of the resin in step 1 coated on the carbon fiber prepreg is 30-60%.

10. The method for preparing the recyclable flame-retardant carbon fiber / epoxy resin composite material according to claim 7, characterized in that: The curing conditions are: 0.5-2h at 70-90℃, 1-3h at 100-130℃, and 1-3h at 140-160℃.

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