Carbon fiber / polylactic acid composite material with gradient interface structure and preparation method thereof

Abstract

The invention relates to the technical field of 3D printing composite materials, in particular to a carbon fiber / polylactic acid composite material with a gradient interface structure and a preparation method of the carbon fiber / polylactic acid composite material. A polymer flexible layer and a carbon-based rigid layer are sequentially constructed on the surface of the continuous carbon fiber through a stepwise chemical grafting technology, a rigid-flexible gradient interface structure is formed, and the modified continuous carbon fiber is obtained; then, the modified continuous carbon fiber and polylactic acid are subjected to melt blending, granulation and extrusion to prepare a composite wire, and finally, 3D printing forming is performed. The gradient interface design ensures effective stress redistribution and modulus stable conversion at the interface, and the mechanical properties (strength and toughness) of the obtained composite material are remarkably improved. The carbon fiber with the rigid-flexible alternating structure constructed on the surface is successfully applied to the field of 3D printing, and an effective way is provided for preparing a high-performance composite material component.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printing composite materials, and in particular to a carbon fiber / polylactic acid composite material with a gradient interface structure and a preparation method thereof. Background Art

[0002] AI Model Additive Manufacturing (AM) is a technology driven by digital models that creates three-dimensional (3D) parts by depositing materials layer by layer. With advantages such as high design flexibility, cost-effectiveness, and rapid production capabilities, AM has been widely used in various fields such as automotive, aerospace, packaging, and biomedicine. Among them, fused deposition modeling (FDM) is considered one of the most promising 3D printing technologies due to its wide material compatibility, relatively simple operation process, good adaptability, and rapid prototyping capabilities.

[0003] However, due to the layer-by-layer deposition process characteristics of FDM, the components manufactured by it generally have poor interlayer bonding, which fundamentally limits the mechanical strength and dimensional stability of the components. At the same time, polylactic acid (PLA), a commonly used printing material, has a medium strength that makes it difficult to meet the diverse needs of industrial applications. Therefore, modifying the PLA matrix through reinforcing materials has become a key research direction. Carbon fiber (CF) has become the preferred reinforcement solution to break through this technical bottleneck due to its excellent lightweight properties, high specific strength, and excellent impact and fatigue resistance.

[0004] However, the surface of carbon fiber is non-polar and chemically inert, while the PLA matrix is ​​a polar material. There is a lack of effective chemical binding sites between the two, and the intermolecular force is weak, resulting in poor interfacial bonding performance. Interfacial bonding failure will affect the mechanical properties (such as strength and toughness) and long-term reliability of the composite material. To solve this problem, surface modification has become a key strategy to improve the strength and toughness of the interface between carbon fiber and PLA matrix. In existing studies, the introduction of rigid materials at the interface can enhance mechanical strength, but it is easy to cause stress concentration and brittle damage; the introduction of flexible materials can disperse stress, but it is difficult to achieve modulus matching between the fiber and the matrix. Summary of the Invention

[0005] The purpose of the present invention is to address the problem that surface modification technology in the existing technology is difficult to strike a balance between strength and toughness, and to provide a carbon fiber / polylactic acid composite material with a gradient interface structure and a preparation method thereof. Through gradual chemical grafting technology, a polymer flexible layer and a carbon-based rigid layer are sequentially constructed on the surface of continuous carbon fibers to form a "rigid-flexible" gradient interface structure, ultimately significantly improving the mechanical properties (strength, toughness) of the resulting composite material.

[0006] To achieve the above object, the present invention provides a method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure, comprising the following steps:

[0007] S1. A polymer flexible layer and a carbon-based rigid layer are sequentially constructed on the surface of a continuous carbon fiber to form a gradient interface structure to obtain a modified continuous carbon fiber;

[0008] S2. The modified continuous carbon fiber and polylactic acid are melt blended and granulated to obtain chopped carbon fiber / polylactic acid composite particles;

[0009] S3. The chopped carbon fiber / polylactic acid composite particles are extruded to obtain a composite wire;

[0010] S4. The composite filament is 3D printed to obtain a carbon fiber / polylactic acid composite material with a gradient interface structure.

[0011] Preferably, in S1, sequentially constructing a polymer flexible layer and a carbon-based rigid layer on the surface of the continuous carbon fiber to form a gradient interface structure includes:

[0012] (1) immersing continuous carbon fibers in a polymer solution to obtain continuous carbon fibers having a polymer flexible layer;

[0013] (2) The continuous carbon fiber constructed with the polymer flexible layer is immersed in a carbon source solution to obtain a modified continuous carbon fiber.

[0014] Preferably, in step (1), the polymer comprises polyethyleneimine, and the mass concentration of the polymer solution is 0.5 mg / mL-1.5 mg / mL;

[0015] In step (1), the soaking time is 22h-26h.

[0016] Preferably, in step (2), the carbon source includes graphene oxide, and the mass concentration of the carbon source solution is 0.2 mg / mL-0.6 mg / mL;

[0017] In step (2), the soaking time is 3h-9h.

[0018] Preferably, in step (1), before immersing the continuous carbon fibers in the polymer solution, the method further comprises activating the continuous carbon fibers in an oxygen-containing functional group treatment solution;

[0019] The oxygen-containing functional group treatment liquid includes an ethanol solution of McBride's acid, wherein the ratio of the mass of McBride's acid to the volume of ethanol in the ethanol solution of McBride's acid is 1g-2g:80mL-120mL;

[0020] The activation temperature is 20°C-30°C, and the activation time is 2h-4h.

[0021] Preferably, in S2, the mass fraction of the modified continuous carbon fibers in the chopped carbon fibers / polylactic acid composite particles is 3%-12%;

[0022] In S2, the temperature of melt blending is 180° C.-210° C., the feed rate of melt blending is 3 r / min-8 r / min, and the screw speed of melt blending is 180 r / min-240 r / min.

[0023] Preferably, in S2, the particle size of the chopped carbon fiber / polylactic acid composite particles is 2 mm to 3 mm.

[0024] Preferably, in S3, the extrusion barrel temperature is 170°C-190°C, the extrusion nozzle head temperature is 190°C-200°C, and the extrusion screw speed is 30r / min-70r / min;

[0025] In S3, the diameter of the composite wire is 1.7 mm to 1.8 mm.

[0026] Preferably, in S4, the nozzle temperature of 3D printing is 210°C-230°C, the bed temperature of 3D printing is 50°C-70°C, the nozzle diameter of 3D printing is 0.3mm-0.5mm, the interlayer spacing of 3D printing is 0.3mm-0.5mm, and the print head movement speed of 3D printing is 30mm / s-50mm / s.

[0027] The present invention also provides a carbon fiber / polylactic acid composite material with a gradient interface structure, which is prepared according to the preparation method of the carbon fiber / polylactic acid composite material with a gradient interface structure.

[0028] The beneficial effects of the present invention are:

[0029] The present invention provides a method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure, comprising the following steps: sequentially constructing a polymer flexible layer and a carbon-based rigid layer on the surface of a continuous carbon fiber to form a gradient interface structure to obtain a modified continuous carbon fiber; melt-blending and granulating the modified continuous carbon fiber and polylactic acid to obtain chopped carbon fiber / polylactic acid composite particles; extruding the chopped carbon fiber / polylactic acid composite particles to obtain a composite filament; and 3D printing the composite filament to obtain a carbon fiber / polylactic acid composite material with a gradient interface structure. The present invention uses a step-by-step chemical grafting technique to sequentially construct a polymer flexible layer and a carbon-based rigid layer on the surface of a continuous carbon fiber to form a "rigid-flexible" gradient interface structure to obtain a modified continuous carbon fiber; subsequently, melt-blending, granulating, and extruding the modified continuous carbon fiber with polylactic acid to obtain a composite filament, which is finally formed by 3D printing. The gradient interface design ensures effective stress redistribution and smooth modulus conversion at the interface, significantly improving the mechanical properties (strength, toughness) of the resulting composite material. The present invention successfully applies carbon fibers with a rigid-flexible alternating structure on the surface to the field of 3D printing, providing an effective way to prepare high-performance composite components. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is the SEM characterization diagram of different continuous carbon fiber materials of the present invention, Figure 1 a in the figure is the SEM characterization image of the continuous carbon fiber after pretreatment in Example 1. Figure 1 b is the SEM characterization picture of the continuous carbon fiber after activation in Example 1, Figure 1 c is a SEM characterization image of the continuous carbon fiber with a polymer flexible layer constructed in Example 1, Figure 1 d in the figure is a SEM characterization image of the continuous carbon fiber with a carbon-based rigid layer constructed in Comparative Example 4. Figure 1 e in the figure is the SEM characterization image of the modified continuous carbon fiber in Example 1;

[0031] Figure 2 is a graph characterizing the shear strength of different composite materials of the present invention;

[0032] Figure 3 is a graph of tensile and bending properties of different composite materials of the present invention, Figure 3 a in the figure is the tensile strength diagram of different composite materials. Figure 3 b in the figure is the tensile modulus diagram of different composite materials. Figure 3 c in the figure is the bending strength diagram of different composite materials. Figure 3 d in the figure is the bending modulus diagram of different composite materials;

[0033] Figure 4 It is a characterization diagram of the impact strength of different composite materials of the present invention. DETAILED DESCRIPTION

[0034] The present invention provides a method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure, comprising the following steps:

[0035] S1. A polymer flexible layer and a carbon-based rigid layer are sequentially constructed on the surface of a continuous carbon fiber to form a gradient interface structure to obtain a modified continuous carbon fiber;

[0036] S2. The modified continuous carbon fiber and polylactic acid are melt blended and granulated to obtain chopped carbon fiber / polylactic acid composite particles;

[0037] S3. The chopped carbon fiber / polylactic acid composite particles are extruded to obtain a composite wire;

[0038] S4. The composite filament is 3D printed to obtain a carbon fiber / polylactic acid composite material with a gradient interface structure.

[0039] In the present invention, in S1, sequentially constructing a polymer flexible layer and a carbon-based rigid layer on the surface of the continuous carbon fiber to form a gradient interface structure includes:

[0040] (1) immersing continuous carbon fibers in a polymer solution to obtain continuous carbon fibers having a polymer flexible layer;

[0041] (2) The continuous carbon fiber constructed with the polymer flexible layer is immersed in a carbon source solution to obtain a modified continuous carbon fiber.

[0042] In the present invention, in step (1), the polymer includes polyethyleneimine, and the mass concentration of the polymer solution is 0.5 mg / mL-1.5 mg / mL.

[0043] In the present invention, in step (1), the soaking temperature is 20° C.-30° C., and the soaking time is 22 h-26 h.

[0044] In the present invention, in step (1), after soaking, washing and drying are carried out in sequence; the number of washings is ≥ 2 times; the drying temperature is 60° C.-100° C., and the drying time is 5 h-7 h.

[0045] In the present invention, in step (2), the carbon source includes graphene oxide, and the mass concentration of the carbon source solution is 0.2 mg / mL-0.6 mg / mL.

[0046] In the present invention, in step (2), the soaking temperature is 20° C.-30° C., and the soaking time is 3 h-9 h.

[0047] In the present invention, in step (2), after soaking, washing and drying are carried out in sequence; the number of washings is ≥ 2 times; the drying temperature is 60° C.-100° C., and the drying time is 5 h-7 h.

[0048] In the present invention, in step (1), before immersing the continuous carbon fibers in the polymer solution, the method further comprises activating the continuous carbon fibers in a treatment solution containing oxygen functional groups.

[0049] In the present invention, the oxygen-containing functional group treatment liquid includes an ethanol solution of McBurney's acid, wherein the ratio of the mass of McBurney's acid to the volume of ethanol in the ethanol solution of McBurney's acid is 1g-2g:80mL-120mL; the activation temperature is 20℃-30℃, and the activation time is 2h-4h.

[0050] In the present invention, after activation, water washing and drying are carried out in sequence, the number of water washing is ≥5 times, and drying is carried out under vacuum conditions, the drying temperature is 80° C.-120° C., and the drying time is 5 h-7 h.

[0051] In the present invention, before the continuous carbon fibers are activated in the oxygen-containing functional group treatment solution, the continuous carbon fibers are further cleaned and dried.

[0052] In the present invention, the cleaning comprises acetone cleaning and water cleaning performed sequentially, the acetone cleaning is performed under ultrasonic conditions, and the acetone cleaning time is 10 hours to 14 hours.

[0053] In the present invention, in S2, before melt-blending the modified continuous carbon fiber and polylactic acid, the modified continuous carbon fiber and polylactic acid are further dried separately; the drying temperature is 60° C.-100° C., and the drying time is 3 h-5 h.

[0054] In the present invention, in S2, the mass fraction of the modified continuous carbon fibers in the chopped carbon fiber / polylactic acid composite particles is 3%-12%.

[0055] In the present invention, in S2, melt blending is carried out using a twin-screw extruder and melt blending is achieved through a dual feeding system, the main feed port is used for adding polylactic acid, and the dedicated fiber feed port is used for adding modified continuous carbon fiber.

[0056] In the present invention, in S2, the temperature of melt blending (temperature setting range from feeder to mold) is 180°C-210°C; during melt blending, the temperature from feeder to mold is set to 190°C, 180°C, 190°C, 200°C, 200°C, 200°C, 200°C and 210°C in sequence.

[0057] In the present invention, in S2, the feed rate of melt blending is 3 r / min-8 r / min, and the screw speed of melt blending is 180 r / min-240 r / min.

[0058] In the present invention, in S2, the particle size of the chopped carbon fiber / polylactic acid composite particles is 2 mm to 3 mm.

[0059] In the present invention, the chopped carbon fiber / polylactic acid composite particles obtained in S2 are dried before S3; the drying temperature is 40° C.-60° C., and the drying time is 5 h-7 h.

[0060] In the present invention, in S3, extrusion is performed using a single-screw extruder, the extrusion barrel temperature is 170°C-190°C, the extrusion nozzle head temperature is 190°C-200°C, and the extrusion screw speed is 30r / min-70r / min.

[0061] In the present invention, in S3, the diameter of the composite wire is 1.7 mm to 1.8 mm.

[0062] In the present invention, in S4, 3D printing is performed using an FDM (fused deposition modeling) printer, the printing direction of 3D printing is 0°, the nozzle temperature of 3D printing is 210°C-230°C, the bed temperature of 3D printing is 50°C-70°C, the preheating time of the bed is 3min-7min, the nozzle diameter of 3D printing is 0.3mm-0.5mm, the interlayer spacing of 3D printing is 0.3mm-0.5mm, and the print head movement speed of 3D printing is 30mm / s-50mm / s.

[0063] In the present invention, the filling pattern for 3D printing is a concentric circle pattern.

[0064] The present invention also provides a carbon fiber / polylactic acid composite material with a gradient interface structure, which is prepared according to the preparation method of the carbon fiber / polylactic acid composite material with a gradient interface structure.

[0065] The present invention is further described below with reference to the accompanying drawings and examples. Unless otherwise defined, technical or scientific terms used herein shall have the same meanings as those commonly understood by persons of ordinary skill in the art to which the present invention pertains. The above-mentioned features or features described in the specific examples of the present invention may be combined in any manner. These specific examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention.

[0066] In the following embodiments and comparative examples of the present invention, continuous carbon fiber (model T300, tow specification 3K, diameter about 7 μm) was provided by Yixing Siweiqi Carbon Fiber Products Co., Ltd.; polyethyleneimine (molecular weight 10,000) was from Adamas Reagent Co., Ltd.; graphene oxide was from Suzhou Tanfeng Graphene Technology Co., Ltd.; and polylactic acid (4032D, Ingeo biopolymer) was provided by Nature Works.

[0067] Example 1

[0068] This embodiment provides a method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure, comprising the following steps:

[0069] The continuous carbon fiber was wound on a stainless steel frame, then immersed in acetone for ultrasonic cleaning for 12 hours, taken out, washed with water, and finally dried to obtain the pretreated continuous carbon fiber.

[0070] The pretreated continuous carbon fibers were immersed in an ethanol solution of McBride's acid (the ratio of the mass of McBride's acid to the volume of ethanol in the ethanol solution of McBride's acid was 1.5 g:100 mL) for activation. The activation temperature was set to 25°C and the activation time was 3 h. After the activation was completed, the fibers were washed with water 6 times and then vacuum dried at 100°C for 6 h to obtain the activated continuous carbon fibers.

[0071] The activated continuous carbon fibers were immersed in a polyethyleneimine solution (the mass concentration of polyethyleneimine in the polyethyleneimine solution was 1 mg / mL) at 25°C for 24 hours. After the immersion, they were washed with water three times and then dried at 80°C for 6 hours to obtain continuous carbon fibers with a polymer flexible layer.

[0072] The continuous carbon fiber constructed with a polymer flexible layer was immersed in a graphene oxide solution (the mass concentration of graphene oxide in the graphene oxide solution was 0.4 mg / mL) at 25°C for 6 hours. After the soaking, it was washed with water three times and then dried at 80°C for 6 hours to obtain a modified continuous carbon fiber.

[0073] The modified continuous carbon fiber and polylactic acid were dried at 80°C for 4h respectively; the two were melt-blended using a twin-screw extruder (dual feeding system, the main feed port is used for adding polylactic acid, and the special fiber feed port is used for adding modified continuous carbon fiber), and the temperatures from the feeder to the mold were set to 190°C, 180°C, 190°C, 200°C, 200°C, 200°C, 200°C and 210°C, respectively. The feed rate was 8r / min, and the screw speed was 200r / min. After the end, granulation was carried out to obtain short-cut carbon fiber / polylactic acid composite particles with a particle size of 2.5mm. The mass fraction of modified continuous carbon fiber in the short-cut carbon fiber / polylactic acid composite particles was 9%.

[0074] The composite particles were dried at 50°C for 6 h and extruded using a single-screw extruder with the barrel temperature set at 180°C, the nozzle head temperature set at 195°C, and the screw speed set at 50 r / min to obtain a composite wire with a diameter of 1.75 mm.

[0075] The composite filament was 3D printed using an FDM printer. The printing direction of the 3D printing was set to 0°, the nozzle temperature was 220°C, the bed temperature was 60°C, the bed preheating time was 5 min, the nozzle diameter was 0.4 mm, the interlayer spacing was 0.4 mm, the print head movement speed was 40 mm / s, and the concentric circle pattern was selected as the filling pattern to obtain a carbon fiber / polylactic acid composite material with a gradient interface structure.

[0076] Example 2

[0077] This embodiment provides a method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure, which is basically the same as Example 1, except that the mass fraction of the modified continuous carbon fiber in the chopped carbon fiber / polylactic acid composite particles is modified to 3%.

[0078] Example 3

[0079] This embodiment provides a method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure, which is basically the same as Example 1, except that the mass fraction of the modified continuous carbon fiber in the chopped carbon fiber / polylactic acid composite particles is modified to 6%.

[0080] Example 4

[0081] This embodiment provides a method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure, which is basically the same as Example 1, except that the mass fraction of the modified continuous carbon fiber in the chopped carbon fiber / polylactic acid composite particles is modified to 12%.

[0082] Comparative Example 1

[0083] This comparative example provides a method for preparing a carbon fiber / polylactic acid composite material, comprising the following steps:

[0084] The continuous carbon fiber was wound on a stainless steel frame, then immersed in acetone for ultrasonic cleaning for 12 hours, taken out, washed with water, and finally dried to obtain the pretreated continuous carbon fiber.

[0085] The pretreated continuous carbon fiber and polylactic acid were dried at 80°C for 4h respectively; the two were melt-blended using a twin-screw extruder (dual feeding system, the main feed port is used for adding polylactic acid, and the special fiber feed port is used for adding pretreated continuous carbon fiber), and the temperatures from the feeder to the mold were set to 190°C, 180°C, 190°C, 200°C, 200°C, 200°C, 200°C and 210°C, respectively. The feed rate was 8r / min, and the screw speed was 200r / min. After the end, granulation was carried out to obtain short-cut carbon fiber / polylactic acid composite particles with a particle size of 2.5mm. The mass fraction of the pretreated continuous carbon fiber in the short-cut carbon fiber / polylactic acid composite particles was 9%.

[0086] The composite particles were dried at 50°C for 6 h and extruded using a single-screw extruder with the barrel temperature set at 180°C, the nozzle head temperature set at 195°C, and the screw speed set at 50 r / min to obtain a composite wire with a diameter of 1.75 mm.

[0087] The composite filament was 3D printed using an FDM printer. The printing direction of the 3D printing was set to 0°, the nozzle temperature was 220°C, the bed temperature was 60°C, the bed preheating time was 5 min, the nozzle diameter was 0.4 mm, the interlayer spacing was 0.4 mm, the print head moving speed was 40 mm / s, and the concentric circle pattern was selected as the filling pattern to obtain a carbon fiber / polylactic acid composite material.

[0088] Comparative Example 2

[0089] This comparative example provides a method for preparing a carbon fiber / polylactic acid composite material, comprising the following steps:

[0090] The continuous carbon fiber was wound on a stainless steel frame, then immersed in acetone for ultrasonic cleaning for 12 hours, taken out, washed with water, and finally dried to obtain the pretreated continuous carbon fiber.

[0091] The pretreated continuous carbon fibers were immersed in an ethanol solution of McBride's acid (the ratio of the mass of McBride's acid to the volume of ethanol in the ethanol solution of McBride's acid was 1.5 g:100 mL) for activation. The activation temperature was set to 25°C and the activation time was 3 h. After the activation was completed, the fibers were washed with water 6 times and then vacuum dried at 100°C for 6 h to obtain the activated continuous carbon fibers.

[0092] The activated continuous carbon fiber and polylactic acid were dried at 80°C for 4 hours respectively; the two were melt-blended using a twin-screw extruder (dual feeding system, the main feed port is used for adding polylactic acid, and the special fiber feed port is used for adding the activated continuous carbon fiber), and the temperatures from the feeder to the mold were set to 190°C, 180°C, 190°C, 200°C, 200°C, 200°C, 200°C and 210°C, respectively. The feed rate was 8r / min, the screw speed was 200r / min, and granulation was carried out after completion to obtain short-cut carbon fiber / polylactic acid composite particles with a particle size of 2.5 mm. The mass fraction of the activated continuous carbon fiber in the short-cut carbon fiber / polylactic acid composite particles was 9%.

[0093] The composite particles were dried at 50°C for 6 h and extruded using a single-screw extruder with the barrel temperature set at 180°C, the nozzle head temperature set at 195°C, and the screw speed set at 50 r / min to obtain a composite wire with a diameter of 1.75 mm.

[0094] The composite filament was 3D printed using an FDM printer. The printing direction of the 3D printing was set to 0°, the nozzle temperature was 220°C, the bed temperature was 60°C, the bed preheating time was 5 min, the nozzle diameter was 0.4 mm, the interlayer spacing was 0.4 mm, the print head moving speed was 40 mm / s, and the concentric circle pattern was selected as the filling pattern to obtain a carbon fiber / polylactic acid composite material.

[0095] Comparative Example 3

[0096] This comparative example provides a method for preparing a carbon fiber / polylactic acid composite material, comprising the following steps:

[0097] The continuous carbon fiber was wound on a stainless steel frame, then immersed in acetone for ultrasonic cleaning for 12 hours, taken out, washed with water, and finally dried to obtain the pretreated continuous carbon fiber.

[0098] The pretreated continuous carbon fibers were immersed in an ethanol solution of McBride's acid (the ratio of the mass of McBride's acid to the volume of ethanol in the ethanol solution of McBride's acid was 1.5 g:100 mL) for activation. The activation temperature was set to 25°C and the activation time was 3 h. After the activation was completed, the fibers were washed with water 6 times and then vacuum dried at 100°C for 6 h to obtain the activated continuous carbon fibers.

[0099] The activated continuous carbon fibers were immersed in a polyethyleneimine solution (the mass concentration of polyethyleneimine in the polyethyleneimine solution was 1 mg / mL) at 25°C for 24 hours. After the immersion, they were washed with water three times and then dried at 80°C for 6 hours to obtain continuous carbon fibers with a polymer flexible layer.

[0100] The continuous carbon fiber and polylactic acid with a polymer flexible layer were dried at 80°C for 4 hours respectively; the two were melt-blended using a twin-screw extruder (dual feeding system, the main feed port is used for adding polylactic acid, and the special fiber feed port is used for adding continuous carbon fiber with a polymer flexible layer), and the temperature from the feeder to the mold was set to 190°C, 180°C, 190°C, 200°C, 200°C, 200°C, 200°C and 210°C in sequence, the feed rate was 8r / min, the screw speed was 200r / min, and granulation was carried out after completion to obtain short-cut carbon fiber / polylactic acid composite particles with a particle size of 2.5mm. The mass fraction of continuous carbon fibers with a polymer flexible layer in the short-cut carbon fiber / polylactic acid composite particles was 9%.

[0101] The composite particles were dried at 50°C for 6 h and extruded using a single-screw extruder with the barrel temperature set at 180°C, the nozzle head temperature set at 195°C, and the screw speed set at 50 r / min to obtain a composite wire with a diameter of 1.75 mm.

[0102] The composite filament was 3D printed using an FDM printer. The printing direction of the 3D printing was set to 0°, the nozzle temperature was 220°C, the bed temperature was 60°C, the bed preheating time was 5 min, the nozzle diameter was 0.4 mm, the interlayer spacing was 0.4 mm, the print head moving speed was 40 mm / s, and the concentric circle pattern was selected as the filling pattern to obtain a carbon fiber / polylactic acid composite material.

[0103] Comparative Example 4

[0104] This comparative example provides a method for preparing a carbon fiber / polylactic acid composite material, comprising the following steps:

[0105] The continuous carbon fiber was wound on a stainless steel frame, then immersed in acetone for ultrasonic cleaning for 12 hours, taken out, washed with water, and finally dried to obtain the pretreated continuous carbon fiber.

[0106] The pretreated continuous carbon fibers were immersed in an ethanol solution of McBride's acid (the ratio of the mass of McBride's acid to the volume of ethanol in the ethanol solution of McBride's acid was 1.5 g:100 mL) for activation. The activation temperature was set to 25°C and the activation time was 3 h. After the activation was completed, the fibers were washed with water 6 times and then vacuum dried at 100°C for 6 h to obtain the activated continuous carbon fibers.

[0107] The activated continuous carbon fibers were immersed in a graphene oxide solution (the mass concentration of graphene oxide in the graphene oxide solution was 0.4 mg / mL) at 25°C for 6 hours. After the immersion, the fibers were washed with water three times and dried at 80°C for 6 hours to obtain continuous carbon fibers with a carbon-based rigid layer.

[0108] The continuous carbon fiber and polylactic acid with a carbon-based rigid layer were dried at 80°C for 4 hours respectively; the two were melt-blended using a twin-screw extruder (dual feeding system, the main feed port is used for adding polylactic acid, and the special fiber feed port is used for adding continuous carbon fiber with a carbon-based rigid layer), and the temperature from the feeder to the mold was set to 190°C, 180°C, 190°C, 200°C, 200°C, 200°C, 200°C and 210°C in sequence, the feed rate was 8r / min, the screw speed was 200r / min, and granulation was carried out after completion to obtain short-cut carbon fiber / polylactic acid composite particles with a particle size of 2.5mm. The mass fraction of continuous carbon fiber with a carbon-based rigid layer in the short-cut carbon fiber / polylactic acid composite particles was 9%.

[0109] The composite particles were dried at 50°C for 6 h and extruded using a single-screw extruder with the barrel temperature set at 180°C, the nozzle head temperature set at 195°C, and the screw speed set at 50 r / min to obtain a composite wire with a diameter of 1.75 mm.

[0110] The composite filament was 3D printed using an FDM printer. The printing direction of the 3D printing was set to 0°, the nozzle temperature was 220°C, the bed temperature was 60°C, the bed preheating time was 5 min, the nozzle diameter was 0.4 mm, the interlayer spacing was 0.4 mm, the print head moving speed was 40 mm / s, and the concentric circle pattern was selected as the filling pattern to obtain a carbon fiber / polylactic acid composite material.

[0111] Comparative Examples 5-7

[0112] Comparative Examples 5-7 respectively provide a method for preparing a carbon fiber / polylactic acid composite material, which is basically the same as Comparative Example 1, except that the mass fraction of the pretreated continuous carbon fiber in the chopped carbon fiber / polylactic acid composite particles is modified to 3% (Comparative Example 5), 6% (Comparative Example 6), and 12% (Comparative Example 7).

[0113] Comparative Examples 8-10

[0114] Comparative Examples 8-10 respectively provide a method for preparing a carbon fiber / polylactic acid composite material, which is basically the same as Comparative Example 2, except that the mass fraction of the activated continuous carbon fiber in the chopped carbon fiber / polylactic acid composite particles is modified to 3% (Comparative Example 8), 6% (Comparative Example 9), and 12% (Comparative Example 10).

[0115] Comparative Examples 11-13

[0116] Comparative Examples 11-13 respectively provide a method for preparing a carbon fiber / polylactic acid composite material, which is basically the same as Comparative Example 3, except that the mass fraction of the continuous carbon fiber with a polymer flexible layer constructed in the chopped carbon fiber / polylactic acid composite particles is modified to 3% (Comparative Example 11), 6% (Comparative Example 12), and 12% (Comparative Example 13).

[0117] Comparative Examples 14-16

[0118] Comparative Examples 14-16 respectively provide a method for preparing a carbon fiber / polylactic acid composite material, which is basically the same as Comparative Example 4, except that the mass fraction of the continuous carbon fiber with a carbon-based rigid layer constructed in the chopped carbon fiber / polylactic acid composite particles is modified to 3% (Comparative Example 14), 6% (Comparative Example 15), and 12% (Comparative Example 16).

[0119] Experimental Example 1

[0120] The pretreated continuous carbon fibers, activated continuous carbon fibers, continuous carbon fibers with a polymer flexible layer, and modified continuous carbon fibers in Example 1, and the continuous carbon fibers with a carbon-based rigid layer in Comparative Example 4 were characterized by SEM, respectively, to obtain SEM characterization images of different continuous carbon fiber materials, as shown in FIG. Figure 1 shown. Figure 1 a in the figure is the SEM characterization image of the continuous carbon fiber after pretreatment in Example 1. Figure 1 b is the SEM characterization picture of the continuous carbon fiber after activation in Example 1, Figure 1 c is a SEM characterization image of the continuous carbon fiber with a polymer flexible layer constructed in Example 1, Figure 1 d in the figure is a SEM characterization image of the continuous carbon fiber with a carbon-based rigid layer constructed in Comparative Example 4. Figure 1 e in the figure is the SEM characterization picture of the modified continuous carbon fiber in Example 1. Figure 1 It can be seen that the surface roughness of the modified continuous carbon fiber is significantly increased, indicating that the polymer flexible layer and the carbon-based rigid layer have been successfully loaded on its surface.

[0121] Experimental Example 2

[0122] The carbon fiber / polylactic acid composite materials with a gradient interface structure prepared in Example 1 and the carbon fiber / polylactic acid composite materials prepared in Comparative Examples 1 to 4 were respectively characterized for interfacial shear strength using a single fiber pullout tester (Model: YG163, Wenzhou Jigao Testing Instrument Co., Ltd., China). The interfacial strength and adhesion (IFSS) was used as the evaluation standard. The formula for calculating the IFSS value (in MPa) is as follows: Where F is the maximum load recorded, d is the diameter of a single fiber, and l is the embedded length. The shear strength characterization diagram of different composite materials is obtained, as shown in Figure 2 As shown. Figure 2 It can be seen that the carbon fiber / polylactic acid composite material with a gradient interface structure has higher interface shear strength, and the interface performance between carbon fiber and polylactic acid is better.

[0123] Experimental Example 3

[0124] The carbon fiber / polylactic acid composite materials with gradient interface structures prepared in Examples 1 to 4 and the carbon fiber / polylactic acid composite materials prepared in Comparative Examples 1 to 16 were respectively subjected to tensile and flexural properties tests using a universal tensile testing machine (CMT100GD, Shanghai Xieqiang Instrument Manufacturing Co., Ltd.). The tensile and flexural properties tests were conducted in accordance with ISO-527 and ISO 178 standards, respectively, at a test speed of 1 mm / min. The tensile and flexural properties graphs of different composite materials were obtained, as shown in FIG. Figure 3 shown. Figure 3 a in the figure is the tensile strength diagram of different composite materials. Figure 3 b in the figure is the tensile modulus diagram of different composite materials. Figure 3 c in the figure is the bending strength diagram of different composite materials. Figure 3 The d in the figure is the bending modulus of different composite materials. Figure 3 It can be seen that the carbon fiber / polylactic acid composite material with gradient interface structure has better tensile and bending properties.

[0125] Experimental Example 4

[0126] The carbon fiber / polylactic acid composite material with a gradient interface structure prepared in Example 1 and the carbon fiber / polylactic acid composite materials prepared in Comparative Examples 1 to 4 were subjected to Charpy impact tests (PTM7000, Shenzhen Sansi Zongheng Technology Co., Ltd.) for impact strength characterization. Following ISO 179, the test specimens were rectangular in shape with a length of 80 mm, a width of 10 mm, and a thickness of 4 mm. Characterization graphs of the impact strength of different composite materials were obtained, as shown in FIG. Figure 4 As shown. Figure 4 It can be seen that the carbon fiber / polylactic acid composite material with gradient interface structure has higher impact strength.

[0127] Therefore, the present invention adopts the above-mentioned method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure. Through a step-by-step chemical grafting technique, a polymer flexible layer and a carbon-based rigid layer are sequentially constructed on the surface of the continuous carbon fiber to form a "rigid-flexible" gradient interface structure, thereby obtaining a modified continuous carbon fiber. The modified continuous carbon fiber is then melt-blended with polylactic acid, pelletized, and extruded to produce a composite filament, which is finally formed by 3D printing. The gradient interface design ensures effective stress redistribution and smooth modulus conversion at the interface, significantly improving the mechanical properties (strength and toughness) of the resulting composite material.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure, characterized in that: The following steps are involved: S1. A polymer flexible layer and a carbon-based rigid layer are sequentially constructed on the surface of a continuous carbon fiber to form a gradient interface structure to obtain a modified continuous carbon fiber; S2. The modified continuous carbon fiber and polylactic acid are melt blended and granulated to obtain chopped carbon fiber / polylactic acid composite particles; S3. The chopped carbon fiber / polylactic acid composite particles are extruded to obtain a composite wire; S4. The composite filament is 3D printed to obtain a carbon fiber / polylactic acid composite material with a gradient interface structure.

2. The method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure according to claim 1, characterized in that: In S1, a polymer flexible layer and a carbon-based rigid layer are sequentially constructed on the surface of the continuous carbon fiber to form a gradient interface structure, including: (1) immersing continuous carbon fibers in a polymer solution to obtain continuous carbon fibers having a polymer flexible layer; (2) The continuous carbon fiber constructed with the polymer flexible layer is immersed in a carbon source solution to obtain a modified continuous carbon fiber.

3. The method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure according to claim 2, characterized in that: In step (1), the polymer includes polyethyleneimine, and the mass concentration of the polymer solution is 0.5 mg / mL-1.5 mg / mL; In step (1), the soaking time is 22h-26h.

4. The method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure according to claim 2 or 3, characterized in that: In step (2), the carbon source includes graphene oxide, and the mass concentration of the carbon source solution is 0.2 mg / mL-0.6 mg / mL; In step (2), the soaking time is 3h-9h.

5. The method for preparing the carbon fiber / polylactic acid composite material with a gradient interface structure according to claim 2, characterized in that: In step (1), before immersing the continuous carbon fibers in the polymer solution, the method further comprises activating the continuous carbon fibers in an oxygen-containing functional group treatment solution; The oxygen-containing functional group treatment liquid includes an ethanol solution of McBride's acid, wherein the ratio of the mass of McBride's acid to the volume of ethanol in the ethanol solution of McBride's acid is 1g-2g:80mL-120mL; The activation temperature is 20°C-30°C, and the activation time is 2h-4h.

6. The method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure according to claim 1, characterized in that: In S2, the mass fraction of the modified continuous carbon fiber in the chopped carbon fiber / polylactic acid composite particles is 3%-12%; In S2, the temperature of melt blending is 180° C.-210° C., the feed rate of melt blending is 3 r / min-8 r / min, and the screw speed of melt blending is 180 r / min-240 r / min.

7. The method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure according to claim 1 or 6, characterized in that: In S2, the particle size of the chopped carbon fiber / polylactic acid composite particles is 2 mm to 3 mm.

8. The method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure according to claim 1, characterized in that: In S3, the extrusion barrel temperature is 170°C-190°C, the extrusion nozzle head temperature is 190°C-200°C, and the extrusion screw speed is 30r / min-70r / min; In S3, the diameter of the composite wire is 1.7 mm to 1.8 mm.

9. The method for preparing a carbon fiber / polylactic acid composite material with a gradient interface structure according to claim 1, characterized in that: In S4, the nozzle temperature of 3D printing is 210℃-230℃, the bed temperature of 3D printing is 50℃-70℃, the nozzle diameter of 3D printing is 0.3mm-0.5mm, the interlayer spacing of 3D printing is 0.3mm-0.5mm, and the print head movement speed of 3D printing is 30mm / s-50mm / s.

10. A carbon fiber / polylactic acid composite material with a gradient interface structure, characterized in that: It is prepared according to the preparation method of the carbon fiber / polylactic acid composite material with a gradient interface structure according to any one of claims 1 to 9.

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