Preparation method of aramid fiber sandwich panel containing graphene coating and short aramid fibers

Abstract

This invention discloses a method for preparing an aramid fiber sandwich panel containing a graphene coating and short aramid fibers, belonging to the field of composite material sandwich panel preparation technology. The method includes the following steps: S1: preparing uniformly dispersed flocculent chopped fibers; S2: preparing an aramid fiber cloth with a graphene coating on its surface; S3: preparing an aramid fiber cloth with uniformly dispersed flocculent chopped fibers on the graphene coating surface; S4: preparing an intermediate layer of aramid fiber cloth; S5: preparing an outer layer of aramid fiber cloth; S6: polishing the upper and lower surfaces of the aluminum honeycomb sandwich layer; S7: laying one outer layer of aramid fiber cloth, fourteen intermediate layer aramid fiber cloths, and one outer layer of aramid fiber cloth from top to bottom in the order [0 / 45 / -45 / 90] on the polished aluminum honeycomb sandwich layer, and performing hot pressing and curing to obtain an aramid fiber sandwich panel containing a graphene coating and short aramid fibers. This invention greatly improves the interfacial toughness of composite materials and can effectively resist their cohesive failure.

Description

Technical Field

[0001] This invention belongs to the field of composite sandwich panel preparation technology, specifically relating to a method for preparing aramid fiber sandwich panels containing graphene coating and short aramid fibers. Background Technology

[0002] Aramid fiber sandwich panels are a type of composite material that is lightweight, high-strength, heat-insulating, fire-resistant, corrosion-resistant, insulating, and easy to clean. They are widely used in military protective equipment and aerospace equipment.

[0003] Because aramid fibers have a smooth surface structure, high crystallinity, few chemically active genes, and a chemically inert surface, they have poor adhesion to most matrix materials when making aramid fiber sandwich panels. This limits their interfacial properties, making them prone to delamination when subjected to impact, thus weakening their impact resistance.

[0004] Currently, to address the aforementioned issues, a technique for modifying the surface of aramid fibers has been proposed to improve the adhesion between the aramid fibers and the matrix material, thereby enhancing the interfacial properties of sandwich panels. Existing modification techniques mainly fall into three categories: physical etching, chemical etching, and surface grafting. Physical etching and chemical etching damage the fiber surface, creating grooves and increasing roughness. This is essentially a slight form of surface damage, and the degree of etching is difficult to control, potentially impairing the mechanical properties of the aramid fibers later on. Surface grafting introduces reactive groups onto the aramid fiber surface to improve the interfacial adhesion between the material and the matrix. However, surface grafting is technically challenging, typically requiring high temperature and pressure conditions, placing significant demands on equipment, and making mass production difficult.

[0005] In addition, aramid fiber sandwich panels need to be tested regularly during use to determine their deterioration effect. The existing testing method is to detect the resistance change by embedding the panels. However, due to the insulating properties of aramid fibers, it is difficult to perform in-situ testing of ordinary aramid fiber sandwich panels by embedding them.

[0006] In view of this, a method for preparing aramid fiber sandwich panels containing graphene coating and short aramid fibers is designed to solve the above problems. Summary of the Invention

[0007] To address the problems mentioned in the background section, this invention provides a method for preparing aramid fiber sandwich panels containing a graphene coating and short aramid fibers, which significantly improves interfacial toughness and allows for the detection of damage levels using resistance changes.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing an aramid fiber sandwich panel containing a graphene coating and short aramid fibers, comprising the following steps:

[0009] S1: After cutting the aramid fiber cloth into short fibers, place it in a mixer with a blunt head structure and stir continuously to form evenly dispersed flocculent short fibers.

[0010] S2: Use a CO2 laser engraving machine to irradiate aramid fiber cloth to form a graphene coating on its surface;

[0011] S3: Spread the flocculent short-cut fibers evenly onto the aramid fiber cloth with a graphene coating on the surface;

[0012] S4: Immerse the aramid fiber cloth with uniformly laid flocculent short chopped fibers and a graphene coating on the surface into an epoxy resin mixture until it is fully immersed and removed to obtain the intermediate layer aramid fiber cloth.

[0013] S5: Place the aramid fiber cloth with flocculent short chopped fibers evenly spread and graphene coating on the surface onto silicone paper. Use a scraper to evenly apply epoxy resin mixture along the texture direction of one side of the aramid fiber cloth until one side of the aramid fiber cloth is completely wetted to obtain the outer aramid fiber cloth.

[0014] S6: Use coarse sandpaper to polish the upper and lower surfaces of the aluminum honeycomb sandwich layer;

[0015] S7: Lay one outer aramid fiber cloth, fourteen middle aramid fiber cloths, and one outer aramid fiber cloth from top to bottom in the order of [0 / 45 / -45 / 90] on the polished aluminum honeycomb sandwich panel, and perform hot pressing and curing to obtain an aramid fiber sandwich panel containing graphene coating and short aramid fibers.

[0016] Furthermore, in step S1, the length of the cut short fibers is 6mm.

[0017] Furthermore, in step S1, the stirring speed of the stirrer is 2000 r / min, and the stirring time is 1 min.

[0018] Furthermore, in step S2, the laser power of the CO2 laser engraving machine is 6.5W, and the writing speed is 50mm·s. -1 .

[0019] Furthermore, in step S3, the density of the flocculent short-cut fibers is 6 g / m³. 2 .

[0020] Furthermore, in steps S4 and S5, the epoxy resin mixture is formed by thoroughly mixing epoxy resin and retarder, wherein the mass ratio of epoxy resin to retarder is 5:1.

[0021] Furthermore, in step S7, the hot pressing curing is divided into three stages. In the first stage, the hot pressing temperature is raised from 25°C to 50°C within 10 minutes and then kept at that temperature for 30 minutes. In the second stage, the hot pressing temperature is raised from 50°C to 70°C within 10 minutes and then kept at that temperature for 30 minutes. In the third stage, the temperature is lowered to 25°C within 1.5 hours and then allowed to cool naturally.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. This invention combines short aramid toughening with graphene conductivity detection. Short aramid can improve the adhesion between aramid fibers and other materials, and improve the interfacial toughening performance. The graphene coating, on the one hand, makes the aramid fiber sandwich panel conductive, and damage detection can be achieved by measuring its resistance change after energization. On the other hand, the graphene coating has a microscopic porous structure, which can form a microscopic "interlocking" structure, which can enhance the interfacial toughness to a certain extent. In addition, the microscopic interlocking structure can provide more attachment points for the short aramid fibers, so that the aramid fiber cloth and the short chopped aramid fibers used for toughening are better bonded, thereby forming a more reliable "bridging" structure at the interface. The graphene coating can not only toughen by utilizing its own structure, but also provide assistance for the toughening of short fibers. The two interfacial toughening methods can toughen independently, and can also promote the toughening effect of each other. To a certain extent, it greatly improves the interfacial toughness of the composite material and can effectively resist its cohesive failure.

[0024] 2. The graphene coating of this invention is formed by CO2 laser engraving machine, which has low environmental requirements and can complete the surface modification of aramid fibers in an indoor environment without heating or pressurizing. It causes less damage to the aramid fibers themselves and will not cause significant damage to their mechanical properties in the later stage.

[0025] 3. This invention does not require complex operating techniques to improve the mechanical and electrical properties of aramid fiber sandwich panels in both directions, and can be mass-produced. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope image of the fiber used in this invention.

[0027] Figure 2 This is a scanning electron microscope image of the graphene coating of this invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Please see Figure 1-2 The present invention provides the following technical solution: a method for preparing an aramid fiber sandwich panel containing a graphene coating and short aramid fibers, comprising the following steps:

[0030] S1: After cutting the aramid fiber cloth into 6mm short fibers, place it in a mixer with a blunt head structure and stir continuously at 2000r / min for 1min to form uniformly dispersed flocculent short fibers.

[0031] S2: Using a CO2 laser engraving machine with a laser power of 6.5W and a wavelength of 50mm·s -1 The writing speed is used to irradiate aramid fiber cloth, forming a graphene coating on its surface. This graphene layer gives the aramid fiber cloth a conductive function, which facilitates damage detection by measuring resistance changes later. At the same time, the surface of the graphene layer has a microporous structure, which can improve the poor adhesion of aramid fibers.

[0032] S3: Cut the flocculent short fibers at 6g / m 2 The density is evenly spread onto the aramid fiber cloth that forms a graphene coating on the surface;

[0033] S4: Immerse the aramid fiber cloth with uniformly spread flocculent short chopped fibers and graphene coating on the surface into an epoxy resin mixture formed by adding epoxy resin and retarder in a mass ratio of 5:1 and stirring thoroughly until fully immersed and removed to obtain the intermediate layer aramid fiber cloth.

[0034] S5: Place the aramid fiber cloth with flocculent short chopped fibers evenly spread and graphene coating on the surface onto silicone paper. Use a scraper to evenly spread the epoxy resin mixture formed by adding epoxy resin and retarder in a mass ratio of 5:1 along the texture direction of one side of the aramid fiber cloth until one side of the aramid fiber cloth is completely wetted to obtain the outer aramid fiber cloth.

[0035] S6: Use coarse sandpaper to polish the upper and lower surfaces of the aluminum honeycomb sandwich layer to create a rough surface;

[0036] S7: Lay one outer aramid fiber cloth, fourteen middle aramid fiber cloths, and one outer aramid fiber cloth from top to bottom in the order of [0 / 45 / -45 / 90] on the polished aluminum honeycomb sandwich panel, and then perform hot pressing and curing. Here, [0 / 45 / -45 / 90] refers to the laying directions of the outer aramid fiber cloth, fourteen middle aramid fiber cloths, and one outer aramid fiber cloth being 0°, 45°, -45°, 90°, 0°, 45°, -45°, and 90° respectively. The hot-pressing curing process is divided into three stages: 0°, 45°, -45°, 90°, 0°, 45°, -45°, and 90°. In the first stage, the hot-pressing temperature is raised from 25° to 50° within 10 minutes and then held for 30 minutes. In the second stage, the hot-pressing temperature is raised from 50° to 70° within 10 minutes and then held for 30 minutes. In the third stage, the temperature is lowered to 25° within 1.5 hours and then allowed to cool naturally, thus producing an aramid fiber sandwich panel containing a graphene coating and short aramid fibers.

[0037] To understand the toughening mechanism of graphene coating and aramid short fibers, scanning electron microscopy (SEM) was used to observe aramid fiber sandwich panel specimens prepared with graphene coating and aramid short fibers. The instrument used for SEM was a Phillips XL30 scanning electron microscope with a magnification of 40–1000x and a voltage acceleration of 15 kV. (See attached image.) Figure 1-2 As shown in the image, the observation images of the resin-rich area of ​​a typical cross-section of the specimen show that the aramid fibers are exposed outside the resin and have obvious end-branching and thinning characteristics. This indicates that during the interfacial fracture process, the aramid fibers first peel off and pull out from the resin-rich area of ​​the other side of the specimen, forming a bridging structure connecting the panel and the core. The graphene layer also has the same characteristics. Subsequently, due to the further opening of the interfacial crack, the aramid fiber bridging structure is subjected to tensile failure. The cross-sectional features of the other side of the specimen also show the pull-out and fracture characteristics of the aramid short fibers. In addition, the peeling traces of neatly and densely arranged carbon fibers can also be observed, indicating that the cracks extend in a tortuous manner within the interface. Furthermore, another morphology exhibited by the interfacial layer of the specimen is the appearance of "composite material rounded corners" near the pore walls of the core. This "rounded corner" structure is due to the fact that during the preparation of the specimen structure, some aramid short fibers flow with the resin and are affected by surface tension, resulting in a resin-rich area near the pore walls of the porous core. In the "composite material rounded corner" area, a large number of uniformly and randomly distributed aramid short fibers, as well as traces of aramid short fiber fracture, can also be observed.

[0038] In summary, the addition of graphene coating and aramid short fibers results in short fiber bridging structures connecting the two ends of the interface after interfacial cracking. This increases the critical load for interfacial crack propagation and dissipates energy through fiber pull-out and fiber breakage, thereby improving the critical energy release rate for interfacial crack propagation. Furthermore, the short fiber-toughened interface can form a "rounded corner" reinforcement structure near the pore walls of the porous core. This microstructure increases the contact area of ​​the interface, thereby improving interfacial adhesion. These observations reveal the microscopic toughening mechanism of aramid short fibers.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an aramid fiber sandwich panel containing a graphene coating and short aramid fibers, characterized in that, Includes the following steps: S1: After cutting the aramid fiber cloth into short fibers, place it in a mixer with a blunt head structure and stir continuously to form a uniformly dispersed flocculent short fiber. S2: Use a CO2 laser engraving machine to irradiate aramid fiber cloth to form a graphene coating on its surface; S3: Spread the flocculent short-cut fibers evenly onto the graphene coating of the aramid fiber cloth on the surface of the graphene coating. S4: The aramid fiber cloth with uniformly spread flocculent short chopped fibers and a graphene coating on the surface is immersed in an epoxy resin mixture until it is fully immersed and then removed to obtain the intermediate layer aramid fiber cloth. S5: Place the aramid fiber cloth with uniformly spread flocculent short chopped fibers and graphene coating on the surface onto silicone paper, and use a scraper to evenly apply epoxy resin mixture along the texture direction of one side of the aramid fiber cloth until one side of the aramid fiber cloth is completely wetted to obtain the outer aramid fiber cloth. S6: Use coarse sandpaper to polish the upper and lower surfaces of the aluminum honeycomb sandwich layer; S7: A layer of outer aramid fiber cloth, fourteen layers of middle aramid fiber cloth, and another layer of outer aramid fiber cloth are laid on the polished aluminum honeycomb sandwich layer in the order of [0° / 45° / -45° / 90°] from top to bottom, and then hot-pressed and cured to obtain an aramid fiber sandwich panel containing graphene coating and short aramid fibers.

2. The method for preparing an aramid fiber sandwich panel containing a graphene coating and short aramid fibers according to claim 1, characterized in that: In step S1, the length of the cut short fibers is 6mm.

3. The method for preparing an aramid fiber sandwich panel containing a graphene coating and short aramid fibers according to claim 1, characterized in that: In step S1, the stirring speed of the stirrer is 2000 r / min, and the stirring time is 1 min.

4. The method for preparing an aramid fiber sandwich panel containing a graphene coating and short aramid fibers according to claim 1, characterized in that: In step S2, the laser power of the CO2 laser engraving machine is 6.5W, and the writing speed is 50mm•s. -1 .

5. The method for preparing an aramid fiber sandwich panel containing a graphene coating and short aramid fibers according to claim 1, characterized in that: In step S3, the density of the flocculent short-cut fibers is 6 g / m³. 2 .

6. The method for preparing an aramid fiber sandwich panel containing a graphene coating and short aramid fibers according to claim 1, characterized in that: In steps S4 and S5, the epoxy resin mixture is formed by thoroughly mixing epoxy resin and retarder, wherein the mass ratio of epoxy resin to retarder is 5:

1.

7. The method for preparing an aramid fiber sandwich panel containing a graphene coating and short aramid fibers according to claim 1, characterized in that: In step S7, the hot pressing curing is divided into three stages. In the first stage, the hot pressing temperature is raised from 25°C to 50°C within 10 minutes and then kept at that temperature for 30 minutes. In the second stage, the hot pressing temperature is raised from 50°C to 70°C within 10 minutes and then kept at that temperature for 30 minutes. In the third stage, the temperature is lowered to 25°C within 1.5 hours and then allowed to cool naturally.

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