Continuous fiber-reinforced aromatic polyimide 3D printing composite material and preparation method thereof

Abstract

The application belongs to the technical field of 3D printing of composite materials, and particularly relates to a continuous fiber reinforced aromatic polyimide 3D printing composite material and a preparation method thereof. The method adopts aromatic polyimide prepolymer solution to impregnate continuous fiber filaments or tapes, adjusts glue content and filament / tape shape through a glue extrusion mechanism, removes solvents and completely solidifies resins through a heat flow channel, adjusts the cross-sectional shape of the consumables through a shaping mechanism, and obtains 3D printing consumables after cooling. The printing consumable structure comprises 10%-80% of continuous fiber filaments or tapes in terms of volume percentage, and 20%-90% of completely solidified aromatic polyimide resins, and has good plasticity, and can be printed through 3D printing technologies such as fused deposition or automatic filament laying and automatic tape laying without relying on thermoplastic plastics as an adhesive. The continuous fiber reinforced resin-based composite material obtained by printing the above consumables has excellent mechanical, heat-resistant and chemical-resistant properties, and can be degraded and recycled under special conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of 3D printing of composite materials, in particular to a continuous fiber reinforced aromatic polyimide 3D printing composite material and a preparation method thereof. BACKGROUND

[0002] 3D printing is an advanced manufacturing technology that uses digital driving to stack materials layer by layer. The printing consumables are the material basis of 3D printing, mainly divided into powder, liquid, sheet and filament. The commonly used 3D printing filaments are mainly pure plastic filaments (such as nylon filaments, polylactic acid filaments, polycarbonate filaments) and short-cut fiber reinforced composite plastic filaments (such as short-cut carbon fiber reinforced nylon filaments). When printing composite materials with high mechanical performance requirements using the above filaments, it is found that there are obvious defects such as weak bearing capacity, poor interlayer performance, and low tensile strength, which seriously limit the further application and development of composite materials. Patent applications US20150165691 and US2022001587A1 disclose a composite material 3D printing technology using continuous carbon fiber filaments as reinforcing materials and thermoplastic plastics as resin matrix. During the printing process, the viscosity of the plastic is relatively high, resulting in poor wettability of the carbon fiber filaments and low fiber volume content. However, during the printing process, the plastic is melted by heat, and good adhesion can be formed between the filaments and the interlayers, and the interlayer shear strength is relatively high. The use of thermoplastic plastic as the resin matrix can make the composite material recyclable. Patent applications US2020283591A1 and CN111163921A disclose a composite material 3D printing technology using continuous carbon fiber reinforced epoxy resin as a printing filament and thermoplastic plastic as an adhesive. The wettability of the resin to the carbon fiber filaments is improved, the fiber volume content and the mechanical properties of the composite material are improved, but the use of traditional thermosetting resin to wet the carbon fiber results in the composite material being non-recyclable. In addition, the thermosetting epoxy resin cannot be melted by heat, and the filaments and the interlayers must rely on the melted thermoplastic plastic as an adhesive to form good adhesion. Compared with thermoplastic plastic, traditional thermosetting resin generally forms a prepolymer first, and the latent functional groups continue to react to form a crosslinked body structure during molding, which is irreversible. When heated, it cannot be melted and plasticized, and it is not soluble in solvents, making it difficult to recycle the composite material. Waste is usually used as filler, buried as garbage or incinerated, which not only causes great waste of resources, but also causes serious environmental pollution. SUMMARY

[0003] The application aims to provide a continuous fiber reinforced aromatic polyimide 3D printing consumable, a composite material and a preparation method thereof. By utilizing the dynamic covalent bond structure of aromatic imine contained in the special thermosetting aromatic polyimide resin, the consumable is endowed with good plasticity similar to that of thermoplastic plastic under printing conditions, so that the continuous fiber reinforced thermosetting resin-based composite material printed by using the 3D technology can be degraded and recycled under special conditions.

[0004] The application achieves the above-mentioned purpose by the following technical solutions.

[0005] A preparation method of a continuous fiber reinforced aromatic polyimide 3D printing composite material, comprising the following steps:

[0006] (1) uniformly dissolving aromatic aldehyde and aromatic amine in an aprotic solvent, stirring and reacting at 30-90 DEG C for 10-90 minutes to obtain an aromatic polyimide prepolymer solution;

[0007] (2) impregnating continuous fiber filaments or tapes with the aromatic polyimide prepolymer solution obtained in step (1), adjusting the glue content and the shape of the filaments or tapes through a glue extrusion mechanism, removing the solvent and completely curing the aromatic polyimide resin through a hot flow channel, adjusting the cross-sectional shape of the consumable through a shaping mechanism, and winding after cooling to obtain a 3D printing consumable;

[0008] (3) printing the continuous fiber reinforced aromatic polyimide 3D printing composite material by using the 3D printing consumable obtained in step (2) through a 3D printing technology.

[0009] Preferably, the aromatic aldehyde in step (1) is at least one of aromatic dialdehyde, aromatic trialdehyde, aromatic tetraaldehyde and aromatic hexaldehyde, and the aromatic amine is at least one of aromatic diamine and aromatic triamine; the reactants contain at least one of aromatic trialdehyde, aromatic tetraaldehyde, aromatic hexaldehyde and aromatic triamine; and the number of moles of aldehyde groups in the structure of the aromatic aldehyde is equal to that of primary amine groups in the structure of the aromatic amine.

[0010] Preferably, the aromatic aldehyde is one or more than two of the following structures:

[0011]

[0012]

[0013] The aromatic amine is one or more than two of the following structures:

[0014]

[0015]

[0016] Preferably, the continuous fiber yarn or tape in step (2) is impregnated by a glue dipping device, the glue dipping speed is 0.1-5 m / min; the temperature range of the hot flow channel is divided into three sections, the temperature of each section is 60-160, 180-300, 40-80℃ respectively; the heating temperature of the shaping mechanism is 200-300℃, and the shaping mechanism is located between the second and third sections of the hot flow channel.

[0017] Preferably, the aprotic solvent in step (1) is one or more of N-methyl pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, dichloromethane, ethyl acetate; the volume of solvent added per gram of reactant is 0.5-10 ml.

[0018] Preferably, the continuous fiber yarn or tape in step (2) is one or more of continuous carbon fiber yarn or tape, continuous glass fiber yarn or tape, continuous quartz fiber yarn or tape, continuous basalt fiber yarn or tape, continuous aramid fiber yarn or tape, continuous boron fiber yarn or tape, with axial thermal conductivity less than 35 W / m·K.

[0019] A continuous fiber reinforced aromatic polyimide 3D printing composite material, composed of continuous fiber yarn or tape and aromatic polyimide resin matrix, the volume percentage of continuous fiber yarn or tape in the composite material is 10%-80%, the volume percentage of the matrix in the composite material is 20%-90%; the structure formula of the matrix is as follows:

[0020]

[0021] wherein, R1 and R2 are aromatic structures containing benzene rings.

[0022] Preferably, the composite material can be degraded and recycled; the degradation and recycling method is: soaking with a strong acid / solvent mixed solution, separating the fiber from the degradation acid solution, cleaning with acid solution, water, alkali solution, water, and then drying to obtain the fiber; the degradation acid solution is neutralized by alkali solution, precipitated, filtered, washed with water, and dried to obtain the resin synthesis raw materials aromatic amine and aromatic aldehyde.

[0023] Preferably, the strong acid is sulfuric acid and hydrochloric acid, the alkali solution is a saturated solution of sodium carbonate or sodium bicarbonate; the amount of the strong acid / solvent mixed solution is 5-30 ml per gram of the composite material, the concentration of the strong acid is 0.1-10 mol / L, the solvent is one or more than two of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, dichloromethane, tetrahydrofuran, 2,5-dimethylfuran and hexamethylphosphoramide, the soaking temperature is 20-100 DEG C, and the soaking time is 0.5-48 hours.

[0024] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0025] (1) The continuous fiber reinforced aromatic polyimide 3D printing consumables prepared by the present application have a fiber volume percentage content in the range of 10% to 80% and can be adjusted at will, the matrix resin has good wettability to the fiber, the matrix resin is completely cured, and the filaments and tapes have excellent mechanical properties. The printing consumables have good plasticity, can be printed without relying on thermoplastic plastics as an adhesive, and can be printed by 3D printing technologies such as fused deposition or automatic fiber laying, automatic tape laying, etc. alone.

[0026] (2) The continuous fiber reinforced aromatic polyimide special thermosetting resin-based 3D printing composite material prepared by the present application has excellent mechanical, heat-resistant and chemical-resistant properties, and can be degraded and recycled under special conditions. DETAILED DESCRIPTION

[0027] The present application will be further described below in combination with specific examples, but the content of the present application is not limited to the following examples.

[0028] Example 1

[0029] Aromatic polyimide prepolymer solution was obtained by dissolving 4 mol of tris[(4-formylphenoxy)-methyl]ethane and 6 mol of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane in 5 L of N-methylpyrrolidone at 50 °C with stirring for 30 min. The prepolymer solution was poured into a dipping tank, and continuous carbon fiber filaments (T300-1k, fiber axial thermal conductivity of about 10 W / (m·K)) were dipped through the tank at a speed of 1 m / min. The filament shape and the content of the glue were adjusted by a glue extrusion mechanism, and the solvent and the aromatic polyimide resin were removed by passing through heat flow channels at 100, 270, and 60 °C, respectively. The shape of the consumable was adjusted by a shaping mechanism with a 0.4 mm diameter round hole at 280 °C, and a continuous linear printing filament was obtained after cooling. The filament diameter was about 0.40 mm, the fiber content was about 51%, the filament tensile strength was about 1486 MPa, and the filament axial thermal conductivity was 5.1 W / (m·K). Using this filament, a unidirectional composite material plate was printed by a 3D printer, and the printing head temperature was set to 280 °C. The fiber volume content in the composite material was about 48%. The tensile strength of the composite material was 1285 MPa (determined according to the ASTM D638-14 standard), the interlaminar shear strength of the composite material was 79 MPa (determined according to the ASTM D2344 / D2344M-2016 standard), the heat distortion temperature of the composite material was 235 °C (determined according to the ASTM D648-07 standard), the 5 wt% thermal decomposition temperature of the composite material was 481 °C, and the thermal conductivities of the composite material in the out-of-plane, in-plane perpendicular to the fiber direction, and in-plane parallel to the fiber direction were 0.33, 0.51, and 4.9 W / (m·K), respectively (determined according to the ISO22007-2 standard). The composite material could withstand corrosion of acid solutions, alkali solutions, salt solutions, and solvents except concentrated sulfuric acid and concentrated nitric acid. After 1 g of the composite material was immersed in 20 ml of a mixed solution of hydrochloric acid / water / tetrahydrofuran (tetrahydrofuran content of 80%) with a concentration of 1 mol / L at room temperature for 36 hours, the composite material was completely degraded. The carbon fiber filaments were taken out of the acid solution, washed with 0.5 mol / L hydrochloric acid, water, saturated sodium carbonate solution, and water, and then dried to recover the carbon fiber filaments, with a recovery rate of 99.7%. After the acid solution was neutralized by saturated sodium carbonate solution, precipitated, filtered, washed with water, and dried, tris[(4-formylphenoxy)-methyl]ethane and 2,2'-bis[4-(4-aminophenoxyphenyl)]propane were obtained, with a recovery rate of 95.8%.

[0030] Example 2

[0031] The aromatic polyimide prepolymer solution was obtained by dissolving 1 mol of tetra[(4-formylphenoxy)methylene]methane, 3 mol of p-xylylene glycol and 5 mol of 4,4'-diaminodiphenyl ether in 3 L of N,N-dimethylformamide at 80 °C for 15 minutes. The prepolymer solution was poured into a dipping tank, and continuous carbon fiber filaments (T300-3k, fiber axial thermal conductivity of about 10 W / (m·K)) were dipped through the tank at a speed of 0.5 m / min. The glue content and filament shape were adjusted by a glue extrusion mechanism, and the solvent was removed and the aromatic polyimide resin was completely cured by passing through 120, 280 and 80 °C heat flow channels. The shape of the consumable was adjusted by a 0.8 mm diameter round hole shaping mechanism at 260 °C, and the continuous linear printing filament was obtained after cooling. The filament diameter was about 0.80 mm, the fiber content was about 76%, the filament tensile strength was about 2017 MPa, and the filament axial thermal conductivity was 7.5 W / (m·K). Using this filament, a unidirectional composite material plate was printed by a 3D printer, and the printing head temperature was set to 260 °C. The fiber volume content in the composite material was about 74%. The tensile strength of the composite material was 1746 MPa (tensile properties were determined according to ASTM D638-14 standard); the interlaminar shear strength of the composite material was 73 MPa (interlaminar shear test was determined according to ASTM D2344 / D2344M-2016 standard); the heat distortion temperature of the composite material was 218 °C (determined according to ASTM D648-07 standard); the 5 wt% thermal decomposition temperature of the composite material was 476 °C; and the thermal conductivities of the composite material in the out-of-plane, in-plane perpendicular to the fiber direction, and in-plane parallel to the fiber direction were 0.53, 0.69 and 7.2 W / (m·K), respectively (determined according to ISO22007-2 standard). The composite material could withstand corrosion of acid solutions, alkali solutions, salt solutions and solvents except concentrated sulfuric acid and concentrated nitric acid. After 20 ml of 1 mol / L sulfuric acid / water / tetrahydrofuran mixed solution (tetrahydrofuran volume content of 60%) was immersed in 1 g of composite material at 80 °C for 3 hours, the composite material was completely degraded, the carbon fiber filaments were taken out of the acid solution, washed with 0.5 mol / L sulfuric acid, water, saturated sodium carbonate solution and water, and then dried, and the carbon fiber filaments were recovered, with a recovery rate of 99.9%. After the acid solution was neutralized by saturated sodium carbonate solution, precipitated, filtered, washed with water and dried, tetra[(4-formylphenoxy)methylene]methane, p-xylylene glycol and 4,4'-diaminodiphenyl ether were obtained, with a recovery rate of 94.8%.

[0032] Example 3

[0033] Aromatic polyimide prepolymer solution was obtained by dissolving 3 mol of isophthaldehyde, 1 mol of tris[(4-formylphenoxy)-methyl]ethane, 3 mol of 4,4-diaminodiphenyl methane, and 1 mol of 1,3,5-tris(4-aminophenoxy)benzene in 3 L of N-methylpyrrolidone and 3 L of dimethyl sulfoxide, respectively, and stirring at 60 °C for 40 min. The prepolymer solution was poured into a dipping tank, and 30 continuous carbon fiber filaments (T300-1k, fiber axial thermal conductivity of about 10 W / (m·K)) were dipped through the tank at a speed of 0.5 m / min. The content of the glue and the shape of the belt were adjusted by a glue extrusion mechanism, and the solvent and the aromatic polyimide resin were removed by passing through 130, 280, and 70 °C heat flow channels, respectively. The shape of the consumable was adjusted by a 10 mm long and 0.2 mm wide rectangular shaping mechanism at 280 °C, and a continuous printing belt was obtained after cooling. The belt had a width of about 10 mm, a thickness of about 0.2 mm, a fiber content of about 63%, a belt tensile strength of about 1754 MPa, and a parallel fiber direction thermal conductivity of 6.2 W / (m·K). Using the belt, a unidirectional composite material plate was printed by a 3D printer, and the printing head temperature was set to 270 °C. The fiber volume fraction in the composite material was about 60%. The tensile strength of the composite material was 1542 MPa (determined according to ASTM D638-14 standard), the interlaminar shear strength of the composite material was 84 MPa (determined according to ASTM D2344 / D2344M-2016 standard), the heat distortion temperature of the composite material was 223 °C (determined according to ASTM D648-07 standard), the 5 wt% thermal decomposition temperature of the composite material was 486 °C, and the out-of-plane, in-plane perpendicular to the fiber direction, and in-plane parallel to the fiber direction thermal conductivities of the composite material were 0.42, 0.61, and 6.0 W / (m·K), respectively (determined according to ISO22007-2 standard). The composite material could withstand corrosion of acid solutions, alkali solutions, salt solutions, and solvents except concentrated sulfuric acid and concentrated nitric acid. After 30 ml of 1 mol / L hydrochloric acid / water / tetrahydrofuran mixed solution (tetrahydrofuran volume content of 80%) was used to soak 1 g of the composite material at 60 °C for 12 hours, the composite material was completely degraded, the carbon fiber filaments were taken out of the acid solution, washed with 0.5 mol / L hydrochloric acid, water, saturated sodium carbonate solution, and water, and then dried, and the carbon fiber filaments were recovered with a recovery rate of 99.6%. After the acid solution was neutralized by saturated sodium carbonate solution, precipitated, filtered, washed with water, and dried, isophthaldehyde, tris[(4-formylphenoxy)-methyl]ethane, 4,4-diaminodiphenyl methane, and 1,3,5-tris(4-aminophenoxy)benzene were obtained with a recovery rate of 93.8%.

[0034] Example 4

[0035] Aromatic polyimide prepolymer solution was obtained by dissolving 4 mol of tris[(4-formylphenoxy)-methyl]ethane and 3 mol of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2 mol of tris(4-aminophenyl)methane in 5 L of N-methylpyrrolidone successively, and stirring at 50 °C for 30 min. The prepolymer solution was poured into a sizing tank, and continuous alkali-free glass fiber yarn (E8, fiber axial thermal conductivity of about 1 W / (m·K)) was sized at a speed of 3 m / min by passing through the sizing tank, the sizing content and the filament shape were adjusted by the sizing extrusion mechanism, and the solvent was removed, the aromatic polyimide resin was completely cured by passing through the 130, 280, 80 °C hot air channels, respectively, the shape of the consumable was adjusted by passing through the 0.8 mm diameter round hole shaping mechanism at 270 °C, and the continuous linear printing filament was obtained after cooling. The filament diameter was about 0.80 mm, the fiber content was about 35%, the filament tensile strength was about 1265 MPa, and the filament axial thermal conductivity was 0.58 W / (m·K). Using this filament, a unidirectional composite material plate was printed by a 3D printer, and the printing head temperature was set to 270 °C. The fiber volume content in the composite material was 32%. The tensile strength of the composite material was 1046 MPa (the tensile properties were determined according to ASTM D638-14 standard); the interlaminar shear strength of the composite material was 71 MPa (the interlaminar shear test was determined according to ASTM D2344 / D2344M-2016 standard); the heat distortion temperature of the composite material was 231 °C (determined according to ASTM D648-07 standard); the 5 wt% thermal decomposition temperature of the composite material was 493 °C; and the thermal conductivities of the composite material in the out-of-plane, in-plane perpendicular to the fiber direction, and in-plane parallel to the fiber direction were 0.25, 0.29, and 0.55 W / (m·K), respectively (determined according to ISO22007-2 standard). The composite material can withstand corrosion of acid solutions, alkali solutions, salt solutions, and solvents except concentrated sulfuric acid and concentrated nitric acid. After each gram of the composite material was immersed in 15 ml of a mixed solution of hydrochloric acid / water / tetrahydrofuran (tetrahydrofuran content of 80%) with a concentration of 1 mol / L at room temperature for 40 hours, the composite material was completely degraded, the glass fiber filament was taken out of the acid solution, washed with 0.5 mol / L hydrochloric acid, water, saturated sodium carbonate solution, and water, and then dried, and the glass fiber filament was recovered, with a recovery rate of 98.6%. After the acid solution was neutralized by saturated sodium carbonate solution, precipitated, filtered, washed with water, and dried, tris[(4-formylphenoxy)-methyl]ethane, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, and tris(4-aminophenyl)methane were obtained, with a recovery rate of 92.4%.

[0036] Example 5

[0037] Aromatic polyimide prepolymer solution was obtained by dissolving 2 mol of tris[(4-formylphenoxy)-methyl]ethane, 3 mol of 2,2-(1,6-hexanediyl dioxy)dibenzaldehyde, and 3 mol of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, and 3 mol of 4,4'-diaminodiphenyl ether in 6 L of N-methylpyrrolidone successively at 60 °C for 30 min. The prepolymer solution was poured into a dipping tank, and continuous aramid fiber yarn (Kevlar 49, fiber axial thermal conductivity of about 5 W / (m·K)) was dipped through the tank at a speed of 2 m / min. The content of the glue and the shape of the yarn were adjusted by a glue extrusion mechanism, and the solvent was removed and the aromatic polyimide resin was completely cured by passing through 100, 260, and 50 °C heat flow channels, respectively. The shape of the consumable was adjusted by a 0.3 mm diameter round hole shaping mechanism at 260 °C, and a continuous linear printing filament was obtained after cooling. The filament diameter was about 0.31 mm, the fiber content was about 48%, the tensile strength of the filament was about 1127 MPa, and the axial thermal conductivity of the filament was 2.7 W / (m·K). Using this filament, a unidirectional composite material plate was printed by a 3D printer, and the printing head temperature was set to 250 °C. The fiber volume content in the composite material was about 46%. The tensile strength of the composite material was 983 MPa (tensile properties were determined according to ASTM D638-14 standard); the interlaminar shear strength of the composite material was 65 MPa (interlaminar shear test was determined according to ASTM D2344 / D2344M-2016 standard); the heat distortion temperature of the composite material was 196 °C (determined according to ASTM D648-07 standard); the 5 wt% thermal decomposition temperature of the composite material was 463 °C; and the thermal conductivities of the composite material in the out-of-plane, in-plane perpendicular to the fiber direction, and in-plane parallel to the fiber direction were 0.26, 0.43, and 2.5 W / (m·K), respectively (determined according to ISO22007-2 standard). The composite material could withstand corrosion of acid solutions, alkali solutions, salt solutions, and solvents except concentrated sulfuric acid and concentrated nitric acid. After each gram of the composite material was immersed in 20 ml of a mixed solution of hydrochloric acid / water / tetrahydrofuran (tetrahydrofuran content of 80%) with a concentration of 1 mol / L at room temperature for 24 hours, the composite material was completely degraded, the carbon fiber yarn was taken out of the acid solution, washed with 0.5 mol / L hydrochloric acid, water, saturated sodium carbonate solution, and water, and then dried, and the carbon fiber yarn was recovered with a recovery rate of 99.5%. After the acid solution was neutralized by saturated sodium carbonate solution, precipitated, filtered, washed with water, and dried, tris[(4-formylphenoxy)-methyl]ethane, 2,2-(1,6-hexanediyl dioxy)dibenzaldehyde, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, and 4,4'-diaminodiphenyl ether were obtained with a recovery rate of 93.3%.

[0038] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principles of the present application should be equivalent replacement manners and should be included in the protection scope of the present application.

Claims

1. A continuous fiber-reinforced aromatic polyimide 3D printing composite material, characterized in that, It is composed of continuous fiber filaments or tapes and an aromatic polyimide resin matrix. The volume percentage of the continuous fiber filaments or tapes in the composite material is 10%~80%, and the volume percentage of the matrix in the composite material is 20%~90%. The matrix structure is as follows: Among them, R1 and R2 are aromatic structures containing benzene rings; The continuous fiber-reinforced aromatic polyimide 3D printing composite material was prepared by the following method: (1) Dissolve aromatic aldehydes and aromatic amines uniformly in an aprotic solvent and stir at 30~90℃ for 10~90 minutes to obtain an aromatic polyimide prepolymer solution; (2) Impregnate the continuous fiber filament or tape with the aromatic polyimide prepolymer solution obtained in step (1), adjust the adhesive content and tape shape through the adhesive extrusion mechanism, remove the solvent through the hot flow channel, completely cure the aromatic polyimide resin, adjust the cross-sectional shape of the consumable through the shaping mechanism, and roll it up after cooling to obtain 3D printing consumable. The continuous fiber filaments or tapes mentioned in step (2) are impregnated by an impregnation device at a speed of 0.1~5m / min; the temperature range of the hot flow channel is divided into three sections, with temperatures of 60~160℃, 180~300℃, and 40~80℃ respectively; the heating temperature of the shaping mechanism is 200~300℃, and the shaping mechanism is located between the second and third sections of the hot flow channel; (3) Using the 3D printing consumables obtained in step (2), a continuous fiber-reinforced aromatic polyimide 3D printing composite material is printed by 3D printing technology.

2. The continuous fiber-reinforced aromatic polyimide 3D printing composite material according to claim 1, characterized in that, The aromatic aldehyde in step (1) is at least one of aromatic dialdehyde, aromatic trialdehyde, aromatic tetraaldehyde, and aromatic hexaaldehyde; the aromatic amine is at least one of aromatic diamine and aromatic triamine; the reactants contain at least one of aromatic trialdehyde, aromatic tetraaldehyde, aromatic hexaaldehyde, and aromatic triamine; the amount of aldehyde group in the aromatic aldehyde structure is equal to the amount of primary amine group in the aromatic amine structure.

3. The continuous fiber-reinforced aromatic polyimide 3D printing composite material according to claim 1, characterized in that, The aromatic aldehyde is one or more of the following structures: ； The aromatic amine is one or more of the following structures: 。 4. The continuous fiber-reinforced aromatic polyimide 3D printing composite material according to claim 1, characterized in that, The aprotic solvent mentioned in step (1) is one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, dichloromethane, and ethyl acetate; the volume of solvent added to each gram of reactant is 0.5 to 10 ml.

5. The continuous fiber-reinforced aromatic polyimide 3D printing composite material according to claim 1, characterized in that, The continuous fiber filament or tape mentioned in step (2) is one or more of the following: continuous carbon fiber filament or tape, continuous glass fiber filament or tape, continuous quartz fiber filament or tape, continuous basalt fiber filament or tape, continuous aramid fiber filament or tape, and continuous boron fiber filament or tape with an axial thermal conductivity of less than 35 W / m·K.

6. The continuous fiber-reinforced aromatic polyimide 3D printing composite material according to claim 1, characterized in that, The shaping mechanism mentioned in step (2) is a circle with a diameter of 0.1~1mm, or a rectangle with a length of 1mm~5cm and a width of 0.1mm~1mm; the 3D printing technology mentioned in step (3) is fused deposition modeling or automatic filament placement and automatic tape placement.

7. The continuous fiber-reinforced aromatic polyimide 3D printing composite material according to claim 1, characterized in that, The composite material is degradable and recyclable. The degradation and recycling methods are as follows: the fiber is separated from the degradation acid solution by soaking in a strong acid / solvent mixed solution, and then dried after washing with acid solution, water, alkali solution and water to recover the fiber. The degradation acid solution is then neutralized with alkali solution, precipitated, filtered, washed with water and dried to obtain the resin synthesis raw materials aromatic amine and aromatic aldehyde.

8. The continuous fiber-reinforced aromatic polyimide 3D printing composite material according to claim 7, characterized in that, The strong acid is sulfuric acid and hydrochloric acid; the alkaline solution is a saturated solution of sodium carbonate or sodium bicarbonate; the amount of the strong acid / solvent mixture is 5-30 ml per gram of composite material, the concentration of the strong acid is 0.1-10 mol / L, the solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, dichloromethane, tetrahydrofuran, 2,5-dimethylfuran and hexamethylphosphoramide, the soaking temperature is 20-100℃ and the time is 0.5-48 hours.

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