CN114907591A

CN114907591A - Reduced graphene oxide coated carbon fiber reinforced nylon 12 composite material for MJR3D printing and preparation method and application thereof

Info

Publication number: CN114907591A
Application number: CN202210583774.6A
Authority: CN
Inventors: 郑玉婴; 陆祖辉
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2022-05-27
Filing date: 2022-05-27
Publication date: 2022-08-16

Abstract

The invention discloses a reduced graphene oxide coated carbon fiber reinforced nylon 12 composite material used for MJR3D printing and a preparation method thereof. In order to improve the interface bonding between Carbon Fiber (CF) and nylon 12 (PA 12), the thermal reduction graphene oxide is directly synthesized on the surface of the pretreated carbon fiber to prepare the carbon fiber composite material so as to reinforce the interface between the carbon fiber and the matrix. Firstly, carbon fibers are pretreated by nitric acid, lac is directly converted into RGO through single-step low-temperature annealing, a conformal and firm RGO coating is formed on the surface of CF, and the RGO @ CF composite material is obtained, so that hydrogen bonds and mechanical interlocking are formed on the interface of the composite material. And finally adding the RGO and PA12 particles into absolute ethyl alcohol, simultaneously adding calcium stearate with the mass fraction of 0.5 percent of nylon and an antioxidant 1010, and then transferring the mixture into a high-temperature high-pressure reaction kettle to obtain RGO @ CF reinforced nylon 12 composite powder for a MJR3D printer.

Description

Reduced graphene oxide coated carbon fiber reinforced nylon 12 composite material for MJR3D printing and preparation method and application thereof

Technical Field

The invention belongs to the field of additive manufacturing, and particularly relates to a reduced graphene oxide coated carbon fiber reinforced nylon 12 composite material used for MJR3D printing, and a preparation method and application thereof.

Background

Carbon Fiber (CF) is excellent in properties such as high strength, high modulus, high temperature resistance, corrosion resistance, fatigue resistance, creep resistance, good electrical conductivity, excellent heat conductivity and low thermal expansion coefficient. Therefore, the carbon fiber and the composite material thereof are widely applied to the fields of aerospace, sports and leisure products, automobiles, wind power generation blades and the like as structural materials and functional materials. The carbon fiber reinforced resin matrix composite material is a novel structural material which is prepared by taking carbon fibers as a reinforcing material and synthetic resin as a matrix material and adopting various molding processes, and is one of the most advanced composite materials at present. However, the CF surface is non-polar and has chemically active groups, which results in CF having poor wettability and adsorptivity in most substrates, and thus the interfacial bonding strength between CF and substrates is weak, and load cannot be effectively transferred from the substrates to CF. The carbon fibers should be surface treated before use. Various methods have been developed to modify surfaces, including thermal treatment, wet chemistry, electrochemical oxidation, plasma treatment, gas phase oxidation, radiation treatment, coating treatment, and the like. The purpose of these surface treatments is to increase the surface energy, chemically active functional groups and to change the microstructure of the CF surface.

The nylon 12 matrix material can be modified by adding the filler to obtain materials with different mechanical properties, so that the material is suitable for different application occasions, no document reports about the content of the fiber material reinforced nylon 12 at present, and no research on the application of the fiber material reinforced nylon 12 in MJR exists at home.

Based on the carbon fiber/nylon 12 composite material coated with reduced graphene oxide for MJR3D printing, the preparation method and the application thereof, the home-made carbon fiber/nylon 12 composite powder is developed, and the monopoly abroad is broken.

Disclosure of Invention

The invention aims to solve the problems of material shortage in the existing 3D printing technology, insufficient mechanical property of pure nylon 3D printing and the like, provides a carbon fiber reinforced nylon 12 composite material coated with reduced graphene oxide and used for MJR3D printing and a preparation method thereof, and aims to improve the interface combination of Carbon Fiber (CF) and nylon 12 (PA 12), and the Carbon Fiber (CF) composite material is prepared by directly synthesizing thermally Reduced Graphene Oxide (RGO) on the surface of pretreated carbon fiber so as to reinforce the interface of the carbon fiber and a matrix.

In order to realize the purpose, the invention adopts the following technical scheme:

the carbon fiber reinforced nylon 12 composite material is prepared by firstly pretreating carbon fibers with nitric acid, directly converting lac into RGO through single-step low-temperature annealing, and forming a conformal and firm RGO coating on the surface of CF to obtain the RGO @ CF composite material, so that hydrogen bonds and mechanical interlocking are formed on the interface of the composite material. And finally, adding the RGO @ CF composite material and PA12 particles into absolute ethyl alcohol, simultaneously adding calcium stearate with the mass fraction of 0.5% of nylon and an antioxidant 1010, and then transferring the mixture into a high-temperature high-pressure reaction kettle to obtain RGO @ CF reinforced nylon 12 composite powder for a MJR3D printer. The preparation method comprises the following steps:

(1) carbon Fiber (CF) pretreatment

CF and concentrated nitric acid are sequentially added into the flask, heated to 120 ℃ and refluxed for 8 h. Then the suspension is diluted, filtered, cooled to room temperature and repeatedly washed to neutrality. Finally, the carbon fibers are dried in a vacuum oven for standby.

(2) Preparation of Shellac (SF) solution

Dissolving shellac in isopropanol solution, stirring in 60 deg.C water bath for 1 hr, and ultrasonic treating for 0.5 hr to dissolve shellac in isopropanol solution.

(3) Preparation of RGO @ CF composite

Fully and uniformly stirring the carbon fiber pretreated in the step (1) and the violet glue solution prepared in the step (2), and then transferring the solution to a 65 ℃ oven for drying for 12 hours; and then annealing the dried SF @ CF composite material in a tubular furnace at different temperatures for 30min at the heating rate of 3 ℃/min, and grinding to obtain the RGO @ CF composite material.

(4) Firstly, adding RGO @ CF powder and PA12 particles into 100ml of absolute ethyl alcohol, simultaneously respectively adding 0.5 percent of calcium stearate and 0.5 percent of antioxidant 1010 with the mass fraction of nylon 12, transferring the raw materials into a high-temperature high-pressure reaction kettle, heating the temperature from room temperature to 150 ℃, violently stirring, and preserving the temperature for 2 h; then the temperature is rapidly reduced to 110 ℃, so that the nylon 12 takes RGO @ CF as a core for heterogeneous nucleation, and finally the RGO @ CF/PA12 composite powder is obtained by washing with deionized water, suction filtration, drying and grinding.

(5) The prepared RGO @ CF/PA12 composite powder is used for MJR3D printing, printing and forming, a fluxing agent is selectively sprayed on a powder layer according to layer printing data, and the fluxing agent absorbs infrared light to convert the infrared light into heat after infrared illumination, so that the modified nylon 12 powder is melted and shaped; after the first layer is printed, the powder bed is lowered by one layer height (lowered height: powder layer thickness), and then the steps of powder laying, preheating, flux spraying and the like are repeated to print the second layer. And the required 3D printing spline is finally printed by analogy.

Further, the ratio of the mass of the carbon fiber to the volume of the concentrated nitric acid in the step (1) is 1 g: 60 mL; in the step (2), the volume ratio of the lac mass to the isopropanol is 1 g: 30 ml; the ratio of the mass of the carbon fiber powder to the volume of the lac solution pretreated in the step (3) is 1: 20ml of the solution; the annealing conditions in the step (4) are as follows: the vacuum condition is 0.12 mbar, and the annealing is performed at a heating rate of 3 ℃/min at 300-700 ℃ for 30min, preferably at 500-600 ℃ and more preferably at 500 ℃.

Among various nanomaterials, Reduced Graphene Oxide (RGO) is widely used to reinforce the interface between CF and a matrix in a Carbon Fiber (CF) -based composite material, and its oxygen-containing polar group not only improves the surface wettability of CF and the matrix, but also can generate a covalent bond during the curing process. However, the disadvantages of toxic raw materials, long processing time and complicated process required by this method of RGO synthesis make the synthesized RGO @ CF composite material environmentally hazardous and costly. In addition, the weak adhesion of RGO and CF synthesized by the above method results in poor binding force of RGO @ CF composite material, thereby severely limiting the practical application thereof.

The lac is a natural biopolymer with low cost and environmental protection, has a long aliphatic (C-C) main chain and a lower thermal decomposition temperature, and is beneficial to graphitization at a low temperature. This low graphitization temperature allows the shellac to be directly converted to RGO on the CF surface without destroying the CF internal structure, thereby contributing to a strong adhesion between CF and the directly converted RGO, which plays a key role in the strong adhesion between RGO and CF given that a large fraction of the oxygen-containing functional groups are converted to covalent bonds at high temperatures.

Here, the present invention uses a single-step, environmentally friendly and cost-effective method to grow RGO directly on the surface of carbon fiber, thereby improving the mechanical strength of RGO @ CF/PA12 composite. The annealing temperature range did not affect the internal structure of the CF and successfully converted the shellac into a robust RGO protective coating on its surface, and the RGO content and RGO @ CF/PA12 interface characteristics could be easily adjusted by controlling the annealing temperature of the CF surface. The tensile strength and impact strength of the composite further demonstrate a significant increase in the interfacial bond strength between the matrix with the RGO coating and the CF. There are currently methods of forming reduced graphene oxide coatings on the surfaces of metal sheets and glass. However, the direct one-step synthesis of RGO on the surface of CF is not reported, and the RGO @ CF composite material obtained by synthesizing RGO on the surface of CF is used as a heterogeneous nucleation center, so that the prepared RGO @ CF/PA12 composite powder has certain innovativeness when being used in the MJR3D printing technology.

The invention has the beneficial effects that:

the invention discloses a reduced graphene oxide coated carbon fiber reinforced nylon 12 composite material used for MJR3D printing and a preparation method thereof. Among the numerous nanomaterials, Reduced Graphene Oxide (RGO) is widely used in CF-based composites to enhance the interface of CF and the matrix. The oxygen-containing polar groups not only improve the surface wettability of CF and a substrate, but also can generate covalent bonds in a curing stage. However, the adhesion of RGO to CF is weak, resulting in poor reliability of RGO-CF composites, severely limiting their practical applications. The lac is a low-cost natural biopolymer, has a longer aliphatic (C-C) skeleton and a lower thermal decomposition temperature, and is beneficial to graphitization at a low temperature. This lower graphitization temperature allows the shellac to be converted directly to RGO on the surface of the carbon fibers without destroying them, thus allowing strong adhesion between the carbon fibers and the RGO produced therefrom.

Drawings

FIG. 1 is an SEM image of a carbon fiber of the present invention before and after treatment;

FIG. 2 is an SEM image of an RGO @ CF composite of the present invention;

FIG. 3 is an SEM image of an RGO @ CF/PA12 composite powder prepared in accordance with the present invention at 500 ℃ annealing;

FIG. 4 is a Raman diagram of an RGO @ CF composite of the present invention;

FIG. 5 is a DSC of RGO @ CF/PA12 composite powder at 500 ℃ anneal as used in the present invention;

FIG. 6 is a sample graph printed in Experimental examples 1-5 and comparative example 1 of the present invention.

Detailed Description

The present invention will be further described with reference to the following examples, but the present invention is not limited to these examples.

Experimental example 1

(1) Carbon Fiber (CF) pretreatment

5g of CF and 300ml of concentrated nitric acid were added to the flask in this order, heated to 120 ℃ and refluxed for 8 hours. Then the suspension is diluted, filtered, cooled to room temperature and repeatedly washed to neutrality. Finally, the carbon fibers are dried in a vacuum oven for standby.

(2) Preparation of Shellac (SF) solution

Dissolving 10g of shellac in 300ml of isopropanol solution, stirring in a 60 deg.C water bath for 1h, and then subjecting to ultrasonic treatment for 0.5h to dissolve shellac in the isopropanol solution sufficiently.

(3) Preparation of RGO @ CF composite

Fully and uniformly stirring 3g of the pretreated carbon fiber and 60ml of lac solution, and then transferring the solution to a 65 ℃ oven for drying for 12 hours; and then annealing the dried SF @ CF composite material for 30min at 300 ℃ under the vacuum condition of 0.12 mbar and at the heating rate of 3 ℃/min in a tube furnace, and grinding to obtain the RGO @ CF composite material.

(4) Preparation of RGO @ CF/PA12 composite powder

Firstly, adding 2g of GO @ CF powder and 8gPA12 particles into 100ml of absolute ethyl alcohol, simultaneously adding 0.04g of calcium stearate and 0.04g of antioxidant 1010 respectively, transferring the raw materials into a high-temperature high-pressure reaction kettle, raising the temperature from room temperature to 150 ℃, violently stirring, and preserving the heat for 2 hours; then rapidly cooling to 110 ℃ to ensure that the nylon 12 takes RGO @ CF as a core to carry out heterogeneous nucleation, and finally washing with deionized water, carrying out suction filtration, drying and grinding to obtain RGO @ CF/PA12 composite powder.

(5) MJR3D preparation of printed RGO @ CF/PA12 composite

The prepared RGO @ CF/PA12 composite powder is used for MJR3D printing, printing and forming, a fluxing agent is selectively sprayed on a powder layer according to layer printing data, and the fluxing agent absorbs infrared light to convert the infrared light into heat after infrared illumination, so that the modified nylon 12 powder is melted and shaped; after the first layer is printed, the powder bed is lowered by one layer (lowering height: powder layer thickness), and then the steps of powder laying, preheating, flux spraying and the like are repeated to print out the second layer. And the required 3D printing spline is finally printed by analogy.

Example 2

(1) Carbon Fiber (CF) pretreatment

(2) Preparation of Shellac (SF) solution

Dissolving 10g of shellac in 300ml of isopropanol solution, stirring in a 60 deg.C water bath for 1h, and then sonicating for 0.5h to dissolve the shellac sufficiently in the isopropanol solution.

(3) Preparation of RGO @ CF composite

Fully and uniformly stirring 3g of the pretreated carbon fiber and 60ml of lac solution, and then transferring the solution to a 65 ℃ oven for drying for 12 hours; and then annealing the dried SF @ CF composite material for 30min at 400 ℃ under the vacuum condition of 0.12 mbar and at the heating rate of 3 ℃/min in a tubular furnace, and grinding to obtain the RGO @ CF composite material.

(4) Preparation of RGO @ CF/PA12 composite powder

Firstly, adding 2g of GO @ CF powder and 8gPA12 particles into 100ml of absolute ethyl alcohol, simultaneously adding 0.04g of calcium stearate and 0.04g of antioxidant 1010 respectively, transferring the raw materials into a high-temperature high-pressure reaction kettle, raising the temperature from room temperature to 150 ℃, violently stirring, and preserving the heat for 2 hours; then the temperature is rapidly reduced to 110 ℃, so that the nylon 12 takes RGO @ CF as a core for heterogeneous nucleation, and finally the RGO @ CF/PA12 composite powder is obtained by washing with deionized water, suction filtration, drying and grinding.

(5) MJR3D preparation of printed RGO @ CF/PA12 composite

Example 3

(1) Carbon Fiber (CF) pretreatment

(2) Preparation of Shellac (SF) solution

(3) Preparation of RGO @ CF composite

Fully and uniformly stirring 3g of the pretreated carbon fiber and 60ml of lac solution, and then transferring the solution to a 65 ℃ drying oven for drying for 12 hours; and then annealing the dried SF @ CF composite material for 30min at 500 ℃ under the vacuum condition of 0.12 mbar and at the heating rate of 3 ℃/min in a tube furnace, and grinding to obtain the RGO @ CF composite material.

(4) Preparation of RGO @ CF/PA12 composite powder

(5) MJR3D preparation of printed RGO @ CF/PA12 composite

The prepared RGO @ CF/PA12 composite powder is used for MJR3D printing, printing and forming, a fluxing agent is selectively sprayed on a powder layer according to layer printing data, and the fluxing agent absorbs infrared light to convert the infrared light into heat after infrared illumination, so that the modified nylon 12 powder is melted and shaped; after the first layer is printed, the powder bed is lowered by one layer height (lowered height: powder layer thickness), and then the steps of powder laying, preheating, flux spraying and the like are repeated to print the second layer. And the required 3D printing spline is finally printed by analogy.

Example 4

(1) Carbon Fiber (CF) pretreatment

(2) Preparation of Shellac (SF) solution

(3) Preparation of RGO @ CF composite

Fully and uniformly stirring 3g of the pretreated carbon fiber and 60ml of lac solution, and then transferring the solution to a 65 ℃ oven for drying for 12 hours; and then annealing the dried SF @ CF composite material for 30min at 600 ℃ under the vacuum condition of 0.12 mbar in a tube furnace at the heating rate of 3 ℃/min, and grinding to obtain the RGO @ CF composite material.

(4) Preparation of RGO @ CF/PA12 composite powder

Firstly, adding 2g of GO @ CF powder and 8gPA12 particles into 100ml of absolute ethyl alcohol, simultaneously adding 0.04g of calcium stearate and 0.04g of antioxidant 1010 respectively, transferring the raw materials into a high-temperature high-pressure reaction kettle, heating the temperature from room temperature to 150 ℃, violently stirring, and keeping the temperature for 2 hours; then the temperature is rapidly reduced to 110 ℃, so that the nylon 12 takes RGO @ CF as a core for heterogeneous nucleation, and finally the RGO @ CF/PA12 composite powder is obtained by washing with deionized water, suction filtration, drying and grinding.

(5) MJR3D preparation of printed RGO @ CF/PA12 composite

Example 5

(1) Carbon Fiber (CF) pretreatment

(2) Preparation of Shellac (SF) solution

(3) Preparation of RGO @ CF composite

Fully and uniformly stirring 3g of the pretreated carbon fiber and 60ml of lac solution, and then transferring the solution to a 65 ℃ drying oven for drying for 12 hours; and then annealing the dried SF @ CF composite material for 30min at 700 ℃ under the vacuum condition of 0.12 mbar in a tube furnace at the heating rate of 3 ℃/min, and grinding to obtain the RGO @ CF composite material.

(4) Preparation of RGO @ CF/PA12 composite powder

(5) MJR3D preparation of printed RGO @ CF/PA12 composite

Comparative example 1

(1) Preparation of CF/PA12 composite powder

Firstly, adding 2g of pretreated CF powder and 8gPA12 particles into 100ml of absolute ethyl alcohol, simultaneously adding 0.04g of calcium stearate and 0.04g of antioxidant 1010 respectively, transferring the raw materials into a high-temperature high-pressure reaction kettle, raising the temperature from room temperature to 150 ℃, violently stirring, and preserving the heat for 2 h; then the temperature is rapidly reduced to 110 ℃, so that the nylon 12 takes CF as a core to carry out heterogeneous nucleation, and finally, the CF/PA12 composite powder is obtained by washing with deionized water, filtering, drying and grinding.

(2) MJR3 preparation of 3D printing CF/PA12 composite material

The prepared CF/PA12 composite powder is used for MJR3D printing and forming, a fluxing agent is selectively sprayed on the powder layer according to layer printing data, and the fluxing agent absorbs infrared light to convert the infrared light into heat after infrared illumination, so that the modified nylon 12 powder is melted and shaped; after the first layer is printed, the powder bed is lowered by one layer (lowering height: powder layer thickness), and then the steps of powder laying, preheating, flux spraying and the like are repeated to print out the second layer. And the required 3D printing spline is finally printed by analogy.

Performance testing

MJR3D printing forming main parameters are as follows: a printing mode: a fine printing mode; preheating temperature: 175 ℃; height of the powder layer: 110 microns; printing the spraying times of a spraying head of a powder layer: 4 pass; ink scraping distance of the nozzle: 15.8 inches, squeegee height: 6.0 inches, inking time: 4 s; negative pressure: 3.0Kpa, head voltage: 28V, spray head temperature: at 55 ℃.

3D printing process: firstly, powder is paved on a powder bed of an MJR printer to obtain carbon fiber modified nylon 12 powder prepared in examples 1-5 and comparative example 1, then the temperature of the powder bed is raised to 175 ℃ (which is close to the melting point of the nylon 12 powder) to preheat the carbon fiber modified nylon 12 composite, a fluxing agent is selectively sprayed on the powder layer according to layer printing data, and the fluxing agent absorbs infrared light to convert the infrared light into heat after infrared illumination, so that the carbon fiber modified nylon 12 powder is melted and shaped; after the first layer is printed, the powder bed is lowered by one layer height (lowered height: powder layer thickness), and then the steps of powder laying, preheating, flux spraying and the like are repeated to print the second layer. And the required 3D printing spline is finally printed by analogy.

Table two shows the mechanical property data of the samples printed by the MJR3D printer from the powder materials prepared in each example and comparative example. From the above physical property test results, it is apparent that the RGO @ CF/PA12 composite exhibits a tendency to increase and then decrease in tensile strength, flexural strength and fracture impact toughness with increasing annealing temperature, and it is known that the dehydration of shellac occurs above a temperature of 150 ℃. At this temperature, the long hydrocarbon chain of the shellac, which has six-and five-membered carbocyclic rings in which the long aliphatic carbon chain is linked to the hydroxyl and carboxyl groups, decomposes with the formation of water vapor. When the temperature is gradually increased, a dehydrogenation reaction takes place, and the long carbon chains in the shellac precursor thermally dissociate into gaseous carbon building blocks, such as methyl or ethyl. Most shellac evaporated above 500 ℃, the quality dropped rapidly, and incomplete formation of graphene oxide was observed at an annealing temperature of 700 ℃. This may be due to insufficient energy to decompose and reform the precursor material required for graphene oxide formation. Therefore, when the temperature is higher than 500 ℃, the mechanical property of the RGO @ CF/PA12 composite material is reduced, and when the temperature is not high enough, the annealing time is not enough, the RGO growth on the CF surface is incomplete, and the mechanical property is lower than the annealing temperature of 500 ℃. From the comparative examples it appears that: the mechanical property of the nylon composite powder prepared by heterogeneous nucleation with unmodified carbon fibers as cores is lower than that of nylon composite powder prepared by heterogeneous nucleation by 1-5, and the condition that the surface appearance and roughness of the carbon fibers are obviously changed after the surfaces of the carbon fibers are wrapped by RGO (reduced oxygen radical) is shown, so that hydrogen bonds and mechanical interlocking are formed on a composite material interface, the interface property of a thermoplastic composite material can be enhanced, and the improvement of the mechanical property of the 3D printing composite powder is facilitated.

As can be seen from fig. 1, the (a) is untreated carbon fiber, and the (b) is acidified carbon fiber, which has many impurities on the surface compared with untreated carbon fiber, which is not favorable for combining with other matrix, and the impurities on the surface of the carbon fiber after being acidified are reduced.

As can be seen from FIG. 2, the microscopic morphology of the RGO @ CF composite material after annealing treatment at 500 ℃ is that the CF surface is uniformly wrapped by RGO. In addition, the RGO coating has better dispersity on the CF surface and increased surface roughness, and enhances the interface interaction between the CF and PA 12.

From FIG. 3, the microscopic morphology of the RGO @ CF/PA12 composite, with a nylon 12 matrix on the surface of the RGO @ CF, can be seen, indicating that RGO not only improves the interfacial strength of the composite at the molecular level through hydrogen bonds and covalent bonds, but also improves the interfacial strength of the composite at nano-and micro-scales through induced linkage effects.

As can be seen from the RGO @ CF Raman spectrum of FIG. 4, the two curves are at 1350cm ^-1 (corresponding to D band) and 1580cm ^-1 (corresponding to the G band) Two distinct characteristic peaks appear; their relative strength may represent the degree of order of the CF structure, i.e. from R = I _D / I _G The value (the ratio of the intensity of the D band to that of the G band) indicates that the larger the value, the larger the defect degree of the material and the lower the degree of order. R (I) of untreated CF _D / I _G ) R (I) with a value of 0.91, RGO @ CF _D / I _G ) The value is 0.75, which shows that the D band and the G band of the carbon fiber coated by the RGO are similar, but the D band is obviously weakened, and the RGO can reduce the defects of the CF material.

As can be seen from the DSC plot of RGO @ CF/PA12 at 500 ℃ treatment of FIG. 5, the composite powder has a higher crystallization peak temperature than the neat nylon 12 powder, indicating that the addition of RGO @ CF can aid in the crystallization of the nylon 12 powder.

The above description is only a preferred embodiment of the present invention, and all the equivalent changes and modifications made according to the claims of the present invention should be covered by the present invention.

Claims

1. A preparation method of a reduced graphene oxide coated carbon fiber reinforced nylon 12 composite material used for MJR3D printing is characterized by comprising the following steps:

(1) carbon fiber pretreatment

Mixing carbon fiber and concentrated nitric acid, heating to 120 ℃, keeping for 8 hours, then diluting, filtering, cooling to room temperature, repeatedly washing to be neutral, and drying in vacuum for later use;

(2) preparation of shellac solution

Dissolving the shellac in isopropanol solution, stirring in a water bath at 60 deg.C for 1h, and then ultrasonically treating for 0.5h to fully dissolve the shellac in the isopropanol solution to obtain shellac solution;

(3) preparation of RGO @ CF composite

Fully and uniformly stirring the pretreated carbon fibers and the lac solution, and then transferring the solution to a 65 ℃ oven for drying for 12 hours; then annealing the dried SF @ CF composite material, and grinding to obtain an RGO @ CF composite material;

(4) adding the RGO @ CF composite material obtained in the step (3) and nylon 12 particles into absolute ethyl alcohol, simultaneously adding calcium stearate and an antioxidant, transferring the raw materials into a high-temperature high-pressure reaction kettle, heating the temperature from room temperature to 150 ℃, violently stirring, and keeping the temperature for 2 hours; then the temperature is rapidly reduced to 110 ℃, so that the nylon 12 takes RGO @ CF as a core for heterogeneous nucleation, and finally the RGO @ CF/PA12 composite material is obtained by washing with deionized water, suction filtration, drying and grinding.

2. The method of claim 1, wherein: the ratio of the mass of the carbon fiber to the volume of the concentrated nitric acid in the step (1) is 1 g: 60 mL.

3. The method of claim 1, wherein: in the step (2), the volume ratio of the lac mass to the isopropanol is 1 g: 30 ml.

4. The method of claim 1, wherein: the ratio of the mass of the carbon fiber powder to the volume of the lac solution pretreated in the step (3) is 1: 20 ml.

5. The production method according to claim 1, characterized in that: the annealing conditions in the step (4) are as follows: the vacuum condition is 0.12 mbar, and the annealing is carried out for 30min at the temperature rising rate of 3 ℃/min and the temperature of 300 ℃ and 700 ℃.

6. A reduced graphene oxide-coated carbon fiber reinforced nylon 12 composite material for MJR3D printing prepared by the preparation method of any one of claims 1 to 5.

7. Use of the composition of claim 6 for MJR3D printing reduced graphene oxide-coated carbon fiber reinforced nylon 12, wherein: the carbon fiber reinforced nylon 12 composite material used for MJR3D printing, reduced graphene oxide wrapping is used for MJR3D printing, printing and forming, fluxing agents are selectively sprayed on powder layers according to layer printing data, and the fluxing agents absorb infrared light to convert the infrared light into heat after infrared illumination, so that the composite material is melted and shaped; and after the first layer is printed, the powder bed descends by one layer of height, then the steps of powder paving, preheating and fluxing agent spraying are repeated, the second layer is printed, and the required 3D printing sample strip is printed finally in the same way.