Modified aramid fiber, method for preparing the same, and use thereof

Abstract

The application discloses a modified aramid fiber and a preparation method and application thereof. The modified aramid fiber comprises aramid fibers and carbon nanotubes, the aramid fibers and the carbon nanotubes are connected through an amide bond, the length of the carbon nanotubes is 1-5 microns, and the surface of the carbon nanotubes is grafted with a polymer containing an amino group. The modified aramid fiber of the application has the surface grafted with the carbon nanotubes with the length of 1-5 microns, the surface roughness of the aramid fiber is improved, mechanical locking action is generated between the aramid fiber and epoxy resin. Further, covalent bonding occurs between the amino group on the surface of the modified aramid fiber and the epoxy resin, and the bonding force between the fiber and the resin is further improved. In addition, the modulus of the introduced interface layer is between the resin and the aramid fiber, and defects at the interface of the fiber composite under working conditions can be reduced. Meanwhile, the modified aramid fiber can be produced continuously, the treatment process is simple, efficient and green, and is beneficial to industrial amplification.

Description

Technical Field

[0001] The present invention belongs to the technical field of aramid fibers, and in particular relates to a modified aramid fiber and a preparation method and application thereof. Background Art

[0002] Aramid fiber, also known as aromatic polyamide fiber, is approximately 20% lighter than carbon fiber and has a density of approximately 60% of that of equivalent glass fiber. It possesses properties such as high modulus, high strength, high temperature resistance, low hysteresis loss, fatigue resistance, and a low linear expansion coefficient, and can be used as a primary reinforcement material for resins and rubbers. However, due to the high crystallinity, smooth surface, and chemical inertness of the aramid fiber surface, the interfacial adhesion with the resin or rubber matrix is ​​poor, resulting in poor mechanical performance of the aramid fiber. Therefore, surface modification of aramid fibers to enhance the interfacial adhesion properties of aramid fiber composites is of great significance and application value.

[0003] In recent years, a variety of fiber surface modification methods have been developed, which are mainly divided into physical modification and chemical modification. The most common physical modification is coating treatment, that is, coating the fiber surface with a resin with functional groups to improve the mechanical properties of fiber composites by inhibiting the expansion of cracks. Chemical modification refers to the replacement or hydrolysis of amide bonds on the fiber surface under certain conditions to generate functional groups such as hydroxyl and carboxyl groups on its surface. Although the chemical modification process is complicated, the modification effect is often better than physical coating modification. Studies have shown that small molecules such as dopamine, latex, and coupling agents can be uniformly bound to the fiber surface through strong physical adhesion or chemical reaction, and increase the roughness and surface polarity of the fiber through grafting or self-polymerization reaction, thereby enhancing the bonding strength between the fiber and the matrix material.

[0004] Existing technologies can improve fiber surface polarity and surface roughness to a certain extent through the use of small molecule modifiers, significantly enhancing the performance of aramid fiber composites. However, the use of acids or bases is unavoidable during the modification process, and the corrosion of these acids and bases often damages the fiber surface structure, resulting in a reduction in the fiber's inherent strength. Furthermore, this process is time-consuming, making it impractical for industrial continuous production. Therefore, it is of great significance to find a suitable process that combines physical surface coating and chemical grafting reactions to produce modified aramid fibers with excellent performance. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides an aramid fiber and a preparation method and application thereof.

[0006] The invention provides a modified aramid fiber, comprising aramid fiber and carbon nanotubes, wherein the aramid fiber and the carbon nanotubes are connected via amide bonds, the carbon nanotubes are 1 to 5 μm in length, and a polymer containing amino groups is grafted onto the surface of the carbon nanotubes.

[0007] According to one embodiment of the present invention, based on the total molar weight of atoms on the surface of the modified aramid fiber being 100%, the amino content on the surface of the modified aramid fiber is 8-40%.

[0008] According to another embodiment of the present invention, based on the total mass of the modified aramid fiber being 100%, the mass content of the carbon nanotubes in the modified aramid fiber is 0.2-5%.

[0009] The present invention also provides a method for preparing the modified aramid fiber, comprising: S1, treating the aramid fiber with oxygen plasma to generate carboxyl groups on the surface of the aramid fiber; S2, using carbon nanotubes with a length of 1 to 5 μm and having carboxyl groups on the surface of the carbon nanotubes, and then grafting a polymer containing amino groups onto the surface of the carbon nanotubes to form amino-modified carbon nanotubes; S3, grafting the amino-modified carbon nanotubes onto the surface of the aramid fiber.

[0010] According to one embodiment of the present invention, in step S1, the aramid fiber is plasma treated in an oxygen atmosphere at a power range of 150 to 700 W.

[0011] According to another embodiment of the present invention, in the step S2, based on the total molar weight of carbon nanotube surface atoms with carboxyl groups as 100%, the content of carboxyl groups on the surface of the carbon nanotubes is 3-30%.

[0012] According to another embodiment of the present invention, in step S2, the polymer containing amino functional groups is one or more of polyetheramine, polyallylamine, polyacrylamide, polyethyleneimine and polyamidoamine, and the weight average molecular weight of the polymer is greater than 2,000 and less than 20,000.

[0013] According to another embodiment of the present invention, in the step S3, the aramid fiber treated with oxygen plasma is passed through an amino-treated carbon nanotube aqueous dispersion and reacted at a temperature of 60°C to 300°C for 2 minutes to 40 minutes, so that the amino group reacts with the carboxyl group on the surface of the aramid fiber to form a covalent bond.

[0014] The present invention further provides an aramid fiber resin composite material, comprising the modified aramid fiber.

[0015] According to one embodiment of the present invention, the composite material further comprises epoxy resin, and amino groups on the surface of the modified aramid fiber are covalently bonded to the epoxy resin.

[0016] The modified aramid fiber of the present invention has carbon nanotubes with a length of 1 to 5 μm grafted onto its surface, which increases the surface roughness of the aramid fiber. This allows it to combine with epoxy resin to form a mechanical locking effect with the epoxy resin. The amino groups on the surface of the aramid fiber can produce covalent bonds with the epoxy resin, thereby increasing the bonding strength between the fiber and the resin. In addition, the modulus of the introduced interface layer (carbon nanotube layer) is between that of the resin and the aramid fiber, which can reduce defects at the interface of the fiber composite material under working conditions. The use of the modified aramid fiber can significantly improve the interface properties and comprehensive mechanical properties of the aramid fiber composite material. The continuous production method is simple, efficient, and green, and is conducive to industrial scale-up. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic flow chart of a method for preparing modified aramid fiber according to one embodiment of the present invention.

[0018] Figure 2 It is a schematic diagram of the preparation process of modified aramid fiber according to another embodiment of the present invention.

[0019] Figure 3 is an electron microscope photograph of the untreated aramid fiber in Example 1.

[0020] Figure 4 This is an electron microscope photograph of the aramid fiber after oxygen plasma treatment in Example 1.

[0021] Figure 5 This is an electron microscope photograph of the amino-grafted carbon nanotube aramid fiber in Example 1.

[0022] Figure 6 This is an electron microscope photograph of aramid fibers after being pulled out from a composite material formed by untreated aramid fibers.

[0023] Figure 7 This is an electron microscope photograph of aramid fibers after being pulled out from a composite material formed by aramid fibers treated with oxygen plasma.

[0024] Figure 8 This is an electron microscope photograph of the aramid fiber after being pulled out from the composite material formed by the modified aramid fiber prepared in Example 1. DETAILED DESCRIPTION

[0025] The present invention will be described in detail below with reference to specific embodiments.

[0026] The modified aramid fiber of the present invention comprises aramid fiber and carbon nanotubes. The aramid fiber and carbon nanotubes are connected through amide bonds (-CO-NH-). The carbon nanotubes (CNTs) are 1 to 5 μm in length, and a polymer containing amino groups is grafted onto the surface of the carbon nanotubes. The surface roughness of the aramid fiber is increased due to the grafting of carbon nanotubes with a length of 1 to 5 μm, which creates a mechanical locking effect between the fiber and the resin, thereby improving the bonding strength between the fiber and the resin. Furthermore, the surface of the carbon nanotubes is grafted with a polymer containing amino groups, that is, the amino groups on the surface of the modified aramid fiber can covalently bond with the epoxy resin, further enhancing the bonding strength between the aramid fiber and the resin. This further improves the interfacial properties and mechanical properties of the aramid fiber composite material. In addition, the introduced interfacial layer modulus is between that of the resin and the aramid fiber, which can reduce defects at the interface of the fiber composite material under working conditions. The use of the modified aramid fiber can significantly improve the interfacial properties and comprehensive mechanical properties of the aramid fiber composite material.

[0027] In an alternative embodiment, the amino content of the modified aramid fiber surface is 8-40%, based on the total molar weight of atoms on the modified aramid fiber surface as 100%. The amino groups in the modified aramid fiber can form covalent bonds with the epoxy resin, enhancing interfacial bonding strength. Therefore, those skilled in the art can reasonably select any value within the above range for the amino content of the modified aramid fiber based on actual needs, such as, but not limited to, 8%, 10%, 15%, 20%, 25%, 30%, 35%, and 40%.

[0028] In an alternative embodiment, the mass content of carbon nanotubes on the surface of the modified aramid fiber is 0.2-5%, based on the total mass of the modified aramid fiber being 100%. The carbon nanotube content in the modified aramid fiber determines the surface roughness of the fiber and the amount of amino-containing polymers that can be grafted. Those skilled in the art can select any value within the above range for the carbon nanotube content based on actual needs, such as, but not limited to, 0.2%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%.

[0029] The following combination Figure 1 The following describes a method for preparing modified aramid fibers according to one embodiment of the present invention. The method comprises: S1, treating aramid fibers with oxygen plasma to generate carboxyl groups on the surface of the aramid fibers; S2, providing carbon nanotubes having a length of 1 to 5 μm and surface carboxyl groups, and then grafting a polymer containing amino groups onto the surface of the carbon nanotubes to form amino-containing carbon nanotubes; and S3, grafting the amino-containing carbon nanotubes onto the surface of the aramid fibers.

[0030] In step S1, the aramid fiber surface is treated to impart a large number of carboxyl groups. Specific parameters for the oxygen plasma treatment include plasma treatment of the aramid fiber in an oxygen atmosphere at a power range of 150 to 700 W. In the present invention, oxygen plasma treatment of the aramid fiber is employed to control the atmosphere, power, and movement rate, thereby enabling control of the fiber surface roughness and carboxyl content. Simultaneously, carboxyl groups can be generated on the aramid fiber surface, effectively increasing the number of amino-containing carbon nanotubes subsequently grafted onto the aramid fiber surface. Furthermore, oxygen plasma treatment of aramid fibers can be performed continuously, with stable results and minimal damage to the fibers.

[0031] In step S2, a polymer containing amino groups is grafted onto the surface of the carbon nanotubes. The amino-containing polymer reacts with carbon nanotubes with carboxyl groups, i.e., the amino groups in the polymer react with the carboxyl groups on the surface of the carbon nanotubes to form amide bonds, thereby grafting the amino-containing polymer onto the surface of the carbon nanotubes to obtain amino-modified carbon nanotubes.

[0032] In an alternative embodiment, the carboxyl content of the carbon nanotubes in this step is 3-30%, based on the total molar weight of carbon nanotube surface atoms bearing carboxyl groups as 100%. As previously described, the amino-containing polymer reacts with the carboxyl groups on the carbon nanotube surface to form an amide bond, thereby grafting the amino-containing polymer onto the carbon nanotube surface. Therefore, the carboxyl content on the carbon nanotube surface can determine the amount of polymer that can be grafted onto the carbon nanotube surface. Therefore, those skilled in the art can select an appropriate carboxyl content in the carbon nanotubes according to actual needs, such as, but not limited to, 3%, 10%, 15%, 20%, 25%, and 30%.

[0033] In step S2, carbon nanotubes of a specific length and a specific carboxyl content can be formed by any appropriate means. For example, but not limited to, carbon nanotubes that meet the requirements can be purchased commercially, or the carbon nanotubes can be chopped and surface carboxylated to achieve the desired length and carboxyl content. In the present invention, in order to ensure the mechanical strength of the surface-modified aramid fiber, it is necessary to control the length of the carbon nanotubes to be 1 to 5 μm. If the carbon nanotubes are too short (less than 1 μm), it is difficult to wrap around the fiber surface. If the carbon nanotubes are too long (greater than 5 μm), they will entangle with each other, resulting in poor dispersion, and it is difficult for the carbon nanotubes to be evenly grafted onto the aramid fiber surface.

[0034] The polymer containing amino functional groups is one or more of polyetheramine, polyallylamine, polyacrylamide, polyethyleneimine, and polyamidoamine. Preferably, the weight-average molecular weight of the polymer is between 2,000 and 20,000. A polymer weight-average molecular weight within the above range ensures that the amino group content is within a certain range, while also ensuring that the polymer length is not too large, thereby preventing steric hindrance that would affect its grafting onto the carbon nanotube surface. Those skilled in the art can select a polymer with any molecular weight within the above weight-average molecular weight range based on practical needs, such as, but not limited to, 2,000, 5,000, 10,000, 15,000, or 20,000. The specific grafting reaction process can be as follows: carbon nanotubes and polymer are added to methanol, the mixture is treated with an ultrasonic system for 10 minutes to 2 hours to uniformly disperse the two in the methanol, and the dispersion system is then reacted at 50-100°C for 5-24 hours to graft the polymer onto the CNT surface, thereby obtaining amino-modified carbon nanotubes.

[0035] There is no order requirement for steps S1 and S2. The two steps can be performed simultaneously or one after the other (i.e., either step S1 or S2 can be performed first).

[0036] In step S3, the aramid fiber with carboxyl groups on its surface reacts with a polymer grafted with amino groups. The carboxyl groups and amino groups form amide bonds, attaching the carbon nanotubes to the aramid fiber surface. The specific process can include adding the prepared amino-treated carbon nanotubes to water to form an aqueous carbon nanotube dispersion. The treated aramid fiber is then passed through the amino-treated carbon nanotube dispersion at a temperature of 60°C to 300°C for 2 to 40 minutes, allowing the amino groups to react with the carboxyl groups on the aramid fiber surface to form covalent bonds. Because the amino-containing polymer is grafted onto the carbon nanotubes, it effectively improves the dispersibility of the carbon nanotubes. This dispersion can be stable and well-dispersed without the need for a surfactant. This process is simple, environmentally friendly, and conducive to industrialization. The aqueous carbon nanotube dispersion can be formed by adding the amino-treated carbon nanotubes to water and ultrasonically treating them using a cell disruptor (e.g., at a processing power of 600W to 1600W, for a processing time of 5 to 120 minutes, and with a mass ratio of water to amino-treated carbon nanotubes of 100:0.05 to 1) to obtain the dispersion. The reaction conditions of the S3 step are mild and have little effect on the fiber and polymer structure. The amino content on the surface of the modified aramid fiber is 8%-40%, which is the basis for improving the mechanical properties of the composite material.

[0037] It can be seen from the above process flow that the preparation method of the present invention is suitable for continuous production. Figure 2 .like Figure 2As shown, the aramid fiber to be treated is first unwound and allowed to move forward. An oxygen plasma treatment device is placed in the aramid fiber's path. As the aramid fiber moves forward through the oxygen plasma device, its surface is treated with carboxyl groups. The oxygen plasma-treated aramid fiber then passes through a guide roller and into a dispersion of amino-treated carbon nanotubes. The aramid fiber then continues forward through a heating device, where the amino-treated carbon nanotubes on its surface covalently bond with the carboxyl groups on the aramid fiber's surface, grafting the carbon nanotubes onto the aramid fiber surface. The amino-treated carbon nanotube dispersion and heating device steps can be repeated, depending on the specific situation. The number of repetitions can be adjusted appropriately. These two steps can also be omitted. Finally, the modified aramid fiber is rewound, completing the continuous production process. This continuous production method is simple, efficient, and environmentally friendly, making it suitable for industrial scale-up.

[0038] The modified aramid fiber of the present invention has abundant amino groups on its surface that can form covalent bonds with epoxy resin, thereby enhancing the bonding strength between the aramid fiber and the resin. Furthermore, the carbon nanotubes increase the surface roughness of the aramid fiber, allowing for mechanical locking between it and the epoxy resin. The introduced interfacial layer modulus is between that of the resin and the aramid fiber, which can reduce defects at the interface of the fiber composite material under working conditions. The use of modified aramid fibers can significantly improve the interfacial properties and comprehensive mechanical properties of aramid fiber composite materials. Therefore, composite materials using the modified aramid fiber resin of the present invention have stronger interfacial bonding and therefore better mechanical properties.

[0039] The present invention is further described below by way of specific examples. However, these examples are merely exemplary and do not constitute any limitation on the scope of the present invention. In the following examples and comparative examples, the reagents, materials, and instruments used are all commercially available unless otherwise specified.

[0040] Example 1

[0041] The aramid fiber was treated with oxygen plasma. The oxygen plasma atmosphere used was oxygen. The aramid fiber was passed through the oxygen plasma nozzle at 500W at a speed of 1m / min. The SEM images of the aramid fiber before and after oxygen plasma treatment were as follows: Figure 3 and 4 As shown. Figure 3 and Figure 4 It can be seen that the surface roughness of the aramid fibers increased after treatment. Functional group content was characterized using X-ray photoelectron spectroscopy (XPS), and surface roughness was characterized using atomic force microscopy (AFM). The surface functional group content and surface roughness data of the aramid fibers before and after treatment are shown in Table 1.

[0042] CNTs were pretreated with a 50% HNO3 solution and then sonicated for 3 hours using a cell disruptor to reduce the average length of the CNTs to 1 μm. The CNTs were treated with a 30% HNO3 solution for 12 hours to impart a high number of carboxyl groups to their surfaces. An excess of 10,000-weight-average molecular weight polyethyleneimine (PEI) was mixed with carbon nanotubes in methanol and dispersed using an ultrasonic cell disruptor for 30 minutes to graft the PEI onto the CNT surface, producing PNH2-CNTs.

[0043] PNH2-CNTs were added to water and sonicated for 20 minutes using a cell crusher to achieve uniform dispersion. The dispersion was then poured into a water tank. Aramid fibers treated with oxygen plasma were passed through the dispersion and heated at 200°C for 10 minutes, allowing amino groups on the PNH2-CNT surfaces to react with carboxyl groups on the aramid fiber surface, forming a covalent bond. By controlling the fiber's immersion time in the dispersion and the dispersion concentration, the carbon nanotube mass fraction on the modified fiber surface was controlled to 1 wt%, resulting in surface-modified aramid fibers. Figure 5 The following is an electron microscope photograph of the prepared modified aramid fiber. It can be seen from the photograph that the roughness of the fiber surface is further increased. The surface functional group content and surface roughness data of the modified aramid fiber are shown in Table 1.

[0044] Table 1

[0045]

[0046] As can be seen from the data in Table 1, after the aramid fiber is treated with oxygen plasma, more carboxyl groups are generated on the surface of the aramid fiber. The amino carbon nanotubes are grafted to the surface of the aramid fiber after the oxygen plasma treatment through the carboxyl groups on the aramid surface, thereby preparing a modified aramid fiber. The carboxyl content on the surface of the modified aramid fiber is reduced, and the amino content is increased. At the same time, due to the surface grafting of carbon nanotubes, the roughness of the fiber surface is also improved. From the changes in the test data of the carboxyl content, amino content and roughness at different stages of the fiber surface, it can be seen that the method of the present invention can connect the amino-containing polymer to the surface of the aramid fiber by bonding with the carboxyl groups on the fiber surface. Therefore, the modified aramid fiber prepared by the method of the present invention has a large number of amino groups and a higher roughness, and therefore significantly improves its binding force with the epoxy resin.

[0047] The modified aramid fiber was used to prepare a modified aramid fiber / epoxy resin composite material. The preparation of the aramid fiber multifilament and the tensile strength test of the dipped yarn were carried out according to the standard "GJB 348A-2018". The sample preparation process is as follows:

[0048] (1) Fiber drying treatment: Place the fiber in an electric blast drying oven and dry it at a temperature of 70±2℃ for not less than 8 hours.

[0049] (2) Configuration of glue solution: add 27 g of p-p-phenylenediamine to 100 g of E-51 epoxy resin, and stir uniformly with acetone as the solvent.

[0050] (3) Glue solution immersion: pour the prepared glue solution into the glue tank, and after drying, the fiber is introduced into the glue tank through the yarn guide, tension controller, and guide wheel, and then wound on the sample holder through the glue scraping roller.

[0051] (4) Ensure that the tension remains unchanged, and the sample is placed for 20 h to allow the solvent to evaporate.

[0052] (5) Curing: place the sample holder with the immersed fiber on it into an electric hot air drying oven, and the curing program is: 90℃ / 2h+150℃ / 3h.

[0053] The fiber-wound reinforced composite material ring sample and NOL interlaminar shear strength test are carried out according to the standard "GB / T 1458-2023". The sample preparation process is as follows:

[0054] (1) Fiber drying treatment: place the aramid fiber in an oven at 105-120℃ for at least 2h.

[0055] (2) Glue solution preparation: add 27 g of molten p-p-phenylenediamine to 100 g of E-51 epoxy resin and stir uniformly for use.

[0056] (3) Mould preparation: apply release agent to the cleaned mould.

[0057] (4) Glue immersion: the fiber is introduced from the yarn ball, passes through the guide roller, and is introduced into the glue tank. After the fiber is pulled out of the glue tank, the excess glue solution is removed with a glue scraping plate.

[0058] (5) Yarn arrangement: the glued fiber is evenly wound on the mold (winding speed is not greater than 28 m / min).

[0059] (6) Curing: after the ring sample is wound, place the ring sample in an electric hot air drying oven, and the curing program is: 90℃ / 2h+150℃ / 3h.

[0060] The final fiber-wound reinforced composite material ring sample is prepared after curing.

[0061] The interfacial shear strength is tested by the micro-drop debonding method, and the sample preparation process is as follows:

[0062] (1) Fiber drying treatment: place the fiber in an electric hot air drying oven at a temperature of 70±2℃ for not less than 8h.

[0063] (2) Configuration of glue solution: add 1 g of polyether amine curing agent to 3 g of E-51 epoxy resin and stir uniformly.

[0064] (3) Loading droplets on the fiber surface: Control the droplet diameter on the fiber to be 130-150 μm.

[0065] (4) Curing: The fibers and droplets are left to stand at room temperature to completely cure.

[0066] (5) Test: Load the sample and fixture, place the blade of the fixture at the bottom of the droplet, and make the blade shear the resin on the fiber surface at 0.1mm / min. At the same time, record the force-displacement curve. When the droplet is completely separated from the resin, the test ends. Calculate according to the following formula:

[0067]

[0068] Where τ—composite material interface shear strength (MPa)

[0069] F—resin droplet debonding load (N)

[0070] d—fiber diameter (mm)

[0071] l—resin droplet embedding length (mm)

[0072] Sample preparation and testing methods for fiber nanoindentation Young's modulus, resin nanoindentation Young's modulus, and interface layer nanoindentation Young's modulus:

[0073] The cross section of the aramid fiber multifilament was sliced ​​into samples using an ultra-thin section method. Nanoindentation tests were performed on the fiber, interface, and resin of the fiber multifilament cross section to measure and record the nanoindentation Young's modulus.

[0074] For comparison, aramid fiber / epoxy resin composites were prepared using the same method using untreated aramid fiber. The mechanical properties of the aramid fiber / epoxy resin composites before and after surface modification are shown in Table 2.

[0075] Table 2

[0076]

[0077] As can be seen from the data in Table 2, the mechanical properties of the composite material formed by the modified aramid fiber of the present invention are significantly improved compared to the composite material formed by untreated aramid fiber. The introduced interfacial layer modulus is between that of the resin and the aramid fiber, which can reduce defects at the fiber composite interface under working conditions.

[0078] Figure 6 、 Figure 7 and Figure 8The figure shows electron micrographs of untreated aramid fiber, aramid fiber treated with oxygen plasma, and the modified aramid fiber prepared in Example 1 after being pulled out of resin. Comparing the three images, it can be seen that the pulled-out portion of the untreated aramid fiber is the smoothest, while the pulled-out portion of the oxygen plasma-treated aramid fiber retains some resin. Furthermore, the modified aramid fiber prepared using the present invention exhibits a further enhanced bond with the resin, and a microdroplet debonding test allows the microfiber structure to be pulled out. These three images also demonstrate that the modified aramid fiber prepared using the present invention exhibits the strongest bond with the resin.

[0079] Example 2

[0080] The average length of CNT was controlled to 2 μm by controlling the HNO 3 treatment time. The other steps were the same as in Example 1 to prepare modified aramid fiber and interface-modified aramid fiber / epoxy resin composite materials.

[0081] Example 3

[0082] The average length of CNT was controlled to 5 μm by controlling the HNO 3 treatment time. The other steps were the same as in Example 1 to prepare modified aramid fiber and interface-modified aramid fiber / epoxy resin composite materials.

[0083] Example 4

[0084] By controlling the soaking time of the fiber in the dispersion and the concentration of the dispersion, the mass fraction of carbon nanotubes on the fiber surface was controlled to be 5 wt %. Other steps were the same as in Example 1 to prepare modified aramid fiber and interface-modified aramid fiber / epoxy resin composite materials.

[0085] Example 5

[0086] By controlling the soaking time of the fiber in the dispersion and the concentration of the dispersion, the mass fraction of carbon nanotubes on the fiber surface was controlled to be 0.2 wt %. Other steps were the same as in Example 1 to prepare modified aramid fiber and interface-modified aramid fiber / epoxy resin composite materials.

[0087] Comparative Example 1

[0088] Except that the aramid fiber was not subjected to oxygen plasma treatment, other steps were the same as those in Example 1 to prepare modified aramid fiber and interface-modified aramid fiber / epoxy resin composite materials.

[0089] Comparative Example 2

[0090] Except that the carbon nanotubes were not grafted onto the aramid fibers treated with oxygen plasma, other steps were the same as those in Example 1 to prepare modified aramid fibers and interface-modified aramid fiber / epoxy resin composite materials.

[0091] Comparative Example 3

[0092] The atmosphere during the plasma treatment was air, and other conditions were the same as those in Example 1. Modified aramid fibers and interface-modified aramid fiber / epoxy resin composite materials were prepared.

[0093] Table 3 shows the carboxyl and amino content of the aramid fiber surface after plasma treatment in air. For comparison, the carboxyl and amino content of the aramid fiber surface after plasma treatment in oxygen atmosphere in Example 1 is also listed in Table 3.

[0094] Table 3

[0095]

[0096] It can be seen from the data in Table 3 that, compared with air atmosphere, carboxyl groups are more easily generated after plasma treatment in oxygen atmosphere, and the surface amino content of carbon nanotube-grafted modified aramid fibers is also higher.

[0097] Comparative Example 4

[0098] Except that ethylenediamine was used instead of polyethyleneimine to be grafted on the CNT surface, other conditions were the same as those in Example 1 to prepare modified aramid fibers and interface-modified aramid fiber / epoxy resin composite materials.

[0099] Table 4 shows the amino content on the surface of the modified aramid fiber prepared in this comparative example and the average particle size of the carbon nanotube dispersion after amination. For comparison purposes, the amino content on the surface of the modified aramid fiber prepared in Example 1 and the average particle size of the carbon nanotube dispersion after amination are also listed in Table 4.

[0100] Table 4

[0101]

[0102] As can be seen from the data in Table 4, the modified aramid fibers obtained by grafting amino-containing polymers onto carbon nanotubes according to the present invention have a higher surface amino content than small-molecule amino-containing compounds, resulting in a stronger bond with the resin. Furthermore, the average particle size of the particles in the dispersion of the amino-containing carbon nanotubes according to the present invention is smaller. This is because the grafted polymer has longer molecular chains and contains a large number of amino groups, which prevents carbon nanotube agglomeration. Consequently, the particles in the dispersion are smaller, and the carbon nanotubes are better dispersed in the dispersion, forming a stable dispersion without the need for the addition of surfactants.

[0103] Comparative Example 5

[0104] Except that the aramid fiber was not treated with plasma and carbon nanotubes were not grafted, other conditions were the same as those in Example 1 to prepare an untreated aramid fiber / epoxy resin composite material.

[0105] The mechanical properties of the interface-modified aramid fiber / epoxy resin composite materials prepared in Examples 2-5 and Comparative Examples 1-5 were tested using the same testing method as in Example 1. The test results are shown in Table 5.

[0106] Table 5

[0107]

[0108]

[0109] Comparing the data of Examples 1-3 in Table 5, it can be seen that the mechanical properties of the composite materials prepared decrease as the length of the carbon nanotubes increases. This is because the longer the carbon nanotubes are, the worse their dispersibility in water is, the smaller the specific surface area of ​​the fiber is, and the interaction with the epoxy resin will decrease, so the mechanical properties will decrease. It can be seen from the test data of Examples 1, 4 and 5 that when the content of carbon nanotubes is in the range of 0.2-5%, the mechanical properties of the fiber can be improved. The surface amino content of the modified aramid fibers prepared in Examples 1-5 is significantly higher than that of the control example, which can effectively enhance the bonding strength between the aramid fibers and the resin, thereby further improving the interface properties and mechanical properties of the aramid fiber composite materials.

[0110] Comparing the mechanical properties of the Examples and Comparative Examples in Table 5 shows that pre-treating aramid fibers can improve the mechanical properties of fiber-resin composites, with plasma treatment of aramid fibers in an oxygen atmosphere providing the most effective surface pre-functionalization. The mechanical enhancement achieved by grafting aramid fibers with carbon nanotubes modified with amino-containing polymers is superior to that achieved with small-molecule modification.

[0111] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing modified aramid fiber, characterized in that: include: S1, treating aramid fiber with oxygen plasma to generate carboxyl groups on the surface of the aramid fiber; S2, the carbon nanotubes used are 1 to 5 μm in length and have carboxyl groups on their surfaces, and then a polymer containing amino groups is grafted onto the surfaces of the carbon nanotubes to form amino-modified carbon nanotubes; S3, grafting the amino-modified carbon nanotubes onto the surface of the aramid fiber; In the step S2, the polymer containing amino groups is one or more of polyetheramine, polyallylamine, polyacrylamide, polyethyleneimine and polyamidoamine, and the weight average molecular weight of the polymer is 2,000 to 20,000.

2. The preparation method according to claim 1, characterized in that In the step S1, the aramid fiber is treated by plasma in an oxygen atmosphere at a power range of 150 to 700 W.

3. The preparation method according to claim 1, characterized in that In the step S2, based on the total molar weight of carbon nanotube surface atoms with carboxyl groups being 100%, the carboxyl content on the surface of the carbon nanotubes is 3-30%.

4. The preparation method according to claim 1, characterized in that In the step S3, the aramid fiber treated with oxygen plasma is passed through an amination-treated carbon nanotube aqueous dispersion and reacted at a temperature of 60° C. to 300° C. for 2 to 40 minutes, so that the amino groups react with the carboxyl groups on the surface of the aramid fiber to form covalent bonds.

5. A modified aramid fiber, characterized in that: Prepared by the preparation method according to any one of claims 1-4, comprising aramid fibers and carbon nanotubes, wherein the aramid fibers and the carbon nanotubes are connected by amide bonds, the carbon nanotubes are 1 to 5 μm in length, and a polymer containing amino groups is grafted onto the surface of the carbon nanotubes.

6. The modified aramid fiber according to claim 5, characterized in that Based on the total molar weight of atoms on the surface of the modified aramid fiber being 100%, the amino content on the surface of the modified aramid fiber is 8-40%.

7. The modified aramid fiber according to claim 5 or 6, characterized in that Based on the total mass of the modified aramid fiber being 100%, the mass content of the carbon nanotubes in the modified aramid fiber is 0.2-5%.

8. An aramid fiber resin composite material, characterized in that: The modified aramid fiber according to any one of claims 5 to 7.

9. The aramid fiber resin composite material according to claim 8, characterized in that: The composite material further comprises epoxy resin, and amino groups on the surface of the modified aramid fiber are covalently bonded to the epoxy resin.

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