Preparation method and application of high-temperature-resistant thermoplastic sizing agent for aramid fiber

Abstract

The application relates to a preparation method and application of a high-temperature-resistant thermoplastic sizing agent for aramid fibers, and relates to a preparation method and application of a high-temperature-resistant thermoplastic sizing agent. The application designs a high-temperature-resistant sizing agent for AF to solve the interface problem of an AF / PEEK composite material in view of a thermoplastic resin PEEK. The method comprises the following steps: one, preparing a polyimide sizing agent; two, preparing a carboxylated carbon nanotube / aramid nanofiber composite particle aqueous solution; and three, preparing a high-temperature-resistant thermoplastic sizing agent. The high-temperature-resistant thermoplastic sizing agent for aramid fibers is used for improving the interface of the AF / PEEK composite material. In the application, the flexible filamentous nanofiber ANF plays a bridging role at the interface, the rigid CNT-COOH forms an effective armor on the fiber surface, and the two form a rigid-flexible composite structure at the interface, the structure can reduce stress concentration, improve stress transmission efficiency, and further disperse external stress action.

Description

Technical Field

[0001] This invention relates to a method for preparing a high-temperature thermoplastic sizing agent and its application. Background Technology

[0002] Thermoplastic resins and their fiber-reinforced composites have advantages over thermosetting composites, such as good thermal stability, high toughness, short molding cycle, recyclability, good impact and fatigue resistance, long service life, and reduced use of traditional equipment and high-temperature resistant additives. They can significantly reduce manufacturing costs compared to thermosetting composites, have considerable advantages in processing efficiency and environmental protection, and also have better impact resistance.

[0003] Among commonly used high-performance thermoplastic resin matrices, polyetheretherketone (PEEK) boasts the best overall performance. It is a semi-crystalline polymer containing benzene rings, ether bonds, and ketone bonds in its structure. The benzene rings in the main chain provide PEEK with high chemical stability and strength, while the ether bonds allow for flexible rotation, giving it good processability and flexibility. PEEK's tensile strength can reach 90 MPa, allowing for long-term use at a working temperature of 250°C. However, PEEK's high melt viscosity and near insolubility in any solvent make the preparation of continuous fiber-reinforced PEEK resin matrix composites a persistent challenge.

[0004] In recent years, scholars have frequently used carbon fiber (CF) and PEEK to prepare composites, and have designed a series of CF sizing agents to improve the overall mechanical properties of CF / PEEK. However, aramid fiber (AF) has poor wettability with PEEK due to its high crystallinity and smooth surface. Furthermore, research on AF-reinforced resin composites has mainly focused on thermosetting resins as the matrix. Currently, no scholars have addressed the interface problem between AF and PEEK. Additionally, due to PEEK's high melting point, its molding temperature is above 350℃. At this molding temperature, the epoxy sizing agent on the surface of AF will decompose at high temperatures, forming defects such as bubbles and voids at the interface. Therefore, preparing a high-temperature resistant thermoplastic sizing agent is crucial for solving the preparation and interface problems of AF / PEEK composites. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing and applying a high-temperature resistant thermoplastic sizing agent for aramid fibers.

[0006] This invention designs a high-temperature resistant sizing agent for AF (aluminum oxide) based on thermoplastic resin PEEK to solve the interface problem of AF / PEEK composite materials.

[0007] A method for preparing a high-temperature resistant thermoplastic sizing agent for aramid fibers is specifically carried out according to the following steps:

[0008] I. Preparation of polyimide sizing agent:

[0009] Polyimide resin powder is dissolved in an organic solvent and ultrasonically treated for a period of time to obtain a polyimide sizing agent;

[0010] II. Preparation of aqueous solution of carboxylated carbon nanotube / aramid nanofiber composite particles:

[0011] ① The carboxylated carbon nanotube aqueous solution was ultrasonically dispersed to obtain an ultrasonically dispersed carboxylated carbon nanotube aqueous solution;

[0012] ② The aqueous solution of aramid nanofibers was ultrasonically dispersed to obtain an ultrasonically dispersed aqueous solution of aramid nanofibers;

[0013] ③ Mix the ultrasonicated carboxylated carbon nanotube aqueous solution with the ultrasonicated aramid nanofiber aqueous solution, and disperse by ultrasonication to obtain an aqueous solution of carboxylated carbon nanotube / aramid nanofiber composite particles.

[0014] III. Preparation of high-temperature resistant thermoplastic sizing agents:

[0015] Aqueous solutions of carboxylated carbon nanotubes / aramid nanofibers were mixed with a polyimide sizing agent and ultrasonically stirred to obtain a high-temperature thermoplastic sizing agent for aramid fibers.

[0016] A high-temperature resistant thermoplastic sizing agent for aramid fibers is used to improve the interface of AF / PEEK composite materials.

[0017] The interface modification mechanism in this invention can be summarized as follows:

[0018] (1) CNT-COOH has a high specific surface area and active functional groups. As an active site, it will play a riveting role, improving the effective contact area and physical interlocking effect between the fiber and the resin matrix.

[0019] (2) The introduction of active groups induces hydrogen bonding between nanoparticles and π-π conjugation between nanoparticles and PI, which makes the sizing agent adhere firmly and uniformly to the fiber surface and increases the interaction of the interface.

[0020] (3) There is a π-π interaction between PI and PEEK, which has good compatibility and wettability, which is conducive to its synergistic effect with nanoparticles;

[0021] (4) The flexible filamentous nanofibers ANF act as bridges at the interface, while the rigid CNT-COOH forms an effective armor on the fiber surface. The two form a rigid-flexible composite structure at the interface, which can reduce stress concentration, improve stress transmission efficiency, and further disperse the effects of external stress. In summary, the synergistic effect promotes the formation of a stable intermediate region by various sizing agent components. This highly efficient buffer can effectively improve interfacial bonding, thereby improving the overall mechanical properties of AF / PEEK.

[0022] Advantages of this invention:

[0023] I. This invention selects a soluble, high-temperature resistant thermoplastic polyimide resin powder (PI) Matrimid 5218 as the solute for the sizing agent. This PI can be dissolved in the organic solvent N-methylpyrrolidone (NMP), eliminating the harsh conditions and cumbersome process of using the precursor polyamic acid to convert polyimide at high temperatures when coating the fiber surface. It also avoids the adverse effects of bubbles and pores caused by water, a byproduct of polyamic acid in the formation of polyimide, on the performance of the composite material.

[0024] II. Polyimide resin powder (PI) Matrimid 5218, carboxylated carbon nanotubes (CNT-COOH), and aramid nanofibers (ANF) all exhibit good high-temperature resistance. Furthermore, after sizing, they can form a rigid-flexible composite nanonetwork at the interface, improving the wettability and interfacial bonding between the fibers and the resin. The modified AF / PEEK composite material showed a 132.90% increase in flexural strength and a 182.97% increase in interlaminar shear strength compared to the unmodified material.

[0025] This invention provides a high-temperature resistant thermoplastic sizing agent for aramid fibers. Attached Figure Description

[0026] Figure 1 The figure shows the thermogravimetric curves of the sizing agent components. In the figure, ANF is aramid nanofiber, CNTS-COOH is carboxylated carbon nanotube, Matrimid 5218 is polyimide resin powder, and PEEK is polyetheretherketone.

[0027] Figure 2 The images show scanning electron microscope (SEM) images of aramid fiber woven fabric before and after modification. In the images, a) is the aramid fiber woven fabric without desizing (EAF), b) is the aramid fiber woven fabric after desizing (BAF), c) is the aramid fiber woven fabric after activation (AAF), d) is the aramid fiber woven fabric modified with PI / NMP sizing agent prepared in Comparative Example 1 (PI-AF), and e) is the aramid fiber woven fabric modified with high-temperature thermoplastic sizing agent prepared in Example 4 (PI / 0.7AC-AF).

[0028] Figure 3 Infrared spectral analysis of aramid fiber woven fabric before and after modification, and the composition of sizing agent;

[0029] Figure 4 The XPS full spectrum and C1s fine spectrum fitting spectra of the fiber surface before and after modification of aramid fiber woven fabric are shown in the figure. a) is the full spectrum of BAF, PI-AF and PI / 1AC-AF; b) is the C1s peak diagram of BAF; c) is the C1s peak diagram of PI-AF; d) is the C1s peak diagram of PI / 1AC-AF.

[0030] Figure 5 The flexural strength of EAF / PEEK, BAF / PEEK, PI-AF / PEEK, PI / 0.1AC-AF / PEEK, PI / 0.25AC-AF / PEEK, PI / 0.5AC-AF / PEEK, PI / 0.7AC-AF / PEEK and PI / 1AC-AF / PEEK composites;

[0031] Figure 6 The flexural modulus of EAF / PEEK, BAF / PEEK, PI-AF / PEEK, PI / 0.1AC-AF / PEEK, PI / 0.25AC-AF / PEEK, PI / 0.5AC-AF / PEEK, PI / 0.7AC-AF / PEEK and PI / 1AC-AF / PEEK composites;

[0032] Figure 7 Interlaminar shear strength of EAF / PEEK, BAF / PEEK, PI-AF / PEEK, PI / 0.1AC-AF / PEEK, PI / 0.25AC-AF / PEEK, PI / 0.5AC-AF / PEEK, PI / 0.7AC-AF / PEEK and PI / 1AC-AF / PEEK composites;

[0033] Figure 8 Storage modulus of EAF / PEEK, BAF / PEEK, PI-AF / PEEK, PI / 0.1AC-AF / PEEK, PI / 0.25AC-AF / PEEK, PI / 0.5AC-AF / PEEK, PI / 0.7AC-AF / PEEK and PI / 1AC-AF / PEEK composites;

[0034] Figure 9The damping factor is the composite material of EAF / PEEK, BAF / PEEK, PI-AF / PEEK, PI / 0.1AC-AF / PEEK, PI / 0.25AC-AF / PEEK, PI / 0.5AC-AF / PEEK, PI / 0.7AC-AF / PEEK and PI / 1AC-AF / PEEK. Detailed Implementation

[0035] Specific Implementation Method 1: This implementation method describes a method for preparing a high-temperature resistant thermoplastic sizing agent for aramid fibers, which is specifically completed according to the following steps:

[0036] I. Preparation of polyimide sizing agent:

[0037] Polyimide resin powder is dissolved in an organic solvent and ultrasonically treated for a period of time to obtain a polyimide sizing agent;

[0038] II. Preparation of aqueous solution of carboxylated carbon nanotube / aramid nanofiber composite particles:

[0039] ① The carboxylated carbon nanotube aqueous solution was ultrasonically dispersed to obtain an ultrasonically dispersed carboxylated carbon nanotube aqueous solution;

[0040] ② The aqueous solution of aramid nanofibers was ultrasonically dispersed to obtain an ultrasonically dispersed aqueous solution of aramid nanofibers;

[0041] ③ Mix the ultrasonicated carboxylated carbon nanotube aqueous solution with the ultrasonicated aramid nanofiber aqueous solution, and disperse by ultrasonication to obtain an aqueous solution of carboxylated carbon nanotube / aramid nanofiber composite particles.

[0042] III. Preparation of high-temperature resistant thermoplastic sizing agents:

[0043] Aqueous solutions of carboxylated carbon nanotubes / aramid nanofibers were mixed with a polyimide sizing agent and ultrasonically stirred to obtain a high-temperature thermoplastic sizing agent for aramid fibers.

[0044] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the polyimide resin powder mentioned in step one is polyimide resin powder Matrimid 5218. The other steps are the same as in Specific Implementation Method One.

[0045] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the organic solvent mentioned in step one is N-methylpyrrolidone, dichloromethane, tetrahydrofuran, N,N-dimethylformamide, or chloroform; the mass ratio of the polyimide resin powder to the volume of the organic solvent mentioned in step one is 2g:200mL. Other steps are the same as in Specific Implementation Method One or Two.

[0046] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step one, the polyimide resin powder is dissolved in an organic solvent and ultrasonically sonicated for 1 to 2 hours using an ultrasonic cell disruptor, with an ultrasonic power of 100W to 1000W. The other steps are the same as in Specific Implementation Methods One to Three.

[0047] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the mass fraction of carboxylated carbon nanotubes in the aqueous solution of carboxylated carbon nanotubes in step two① is 0.12% to 0.30%; and the ultrasonic dispersion time in step two① is 1 to 2 hours. Other steps are the same as in Specific Implementation Methods One to Four.

[0048] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the mass fraction of aramid nanofibers in the aramid nanofiber aqueous solution described in step two ② is 0.1% to 0.24%; and the ultrasonic dispersion time described in step two ② is 1 to 2 hours. The other steps are the same as in Specific Implementation Methods One to Five.

[0049] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: in step two, the mass ratio of carboxylated carbon nanotubes to aramid nanofibers in the aqueous solution of the carboxylated carbon nanotube / aramid nanofiber composite particles is 5:4; and the ultrasonic dispersion time in step two, three is 1 to 2 hours. Other steps are the same as in Specific Implementation Methods One to Six.

[0050] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that the total mass of carboxylated carbon nanotubes and aramid nanofibers in the high-temperature resistant thermoplastic sizing agent for aramid fibers described in step three accounts for 0.1% to 1% of the mass fraction of the sizing agent. The other steps are the same as in Specific Implementation Methods One to Seven.

[0051] Specific Implementation Method Nine: This implementation method is a high-temperature resistant thermoplastic sizing agent for aramid fibers used to improve the interface of AF / PEEK composite materials.

[0052] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One through Nine in that: the improvement of the interface of the AF / PEEK composite material using a high-temperature resistant thermoplastic sizing agent for aramid fibers is specifically accomplished through the following steps:

[0053] I. Soxhlet extraction and desizing:

[0054] The undesized aramid fiber woven fabric EAF was cut into 150mm×100mm pieces and placed in a Soxhlet extractor. The extraction temperature was set to 80℃ and extracted in acetone for 24h. After extraction, the woven fabric was washed 3 to 5 times with deionized water and anhydrous ethanol respectively, and then dried in a vacuum drying oven at 80℃ for 24h to obtain the desized aramid fiber woven fabric BAF.

[0055] 2. Use oxygen plasma to etch the aramid fiber woven fabric after Soxhlet extraction and desizing for 5 min to 10 min to obtain the activated aramid fiber woven fabric.

[0056] 3. The activated aramid fiber woven fabric is immersed in a high-temperature resistant thermoplastic sizing agent for aramid fibers for 1h to 3h, and then vacuum dried at 80℃ to 100℃ for 12h to 24h to obtain the aramid fiber woven fabric modified by the high-temperature resistant thermoplastic sizing agent.

[0057] IV. Preparation of AF / PEEK composite materials:

[0058] ① Cut the PEEK resin film into 150mm×100mm pieces, wash the PEEK resin film in anhydrous ethanol 3 to 5 times, and then dry it in an 80℃ oven for 12 hours to obtain the cleaned PEEK resin film.

[0059] ② Alternately lay aramid fiber woven fabric modified with high-temperature thermoplastic sizing agent and washed PEEK resin film in a [0 / 90] 8s layering pattern. Then, under a pressure of 5MPa, first raise the temperature from room temperature to 200℃ and hold for 30min, then raise the temperature to 370℃ and hold for 30min, then lower the temperature from 370℃ to 300℃ and hold for 30min, and finally allow it to cool naturally to room temperature in air to obtain the AF / PEEK composite material. Other steps are the same as in specific embodiments one to nine.

[0060] The beneficial effects of the present invention are verified using the following embodiments:

[0061] Example 1: A method for preparing a high-temperature resistant thermoplastic sizing agent for aramid fibers, specifically comprising the following steps:

[0062] I. Preparation of polyimide sizing agent:

[0063] 2.0g of polyimide resin powder Matrimid 5218 (PI) was dissolved in 200mL of NMP and sonicated for 1h using an ultrasonic cell disruptor to obtain a polyimide sizing agent.

[0064] The ultrasonic power mentioned in step one is 300W;

[0065] II. Preparation of aqueous solution of carboxylated carbon nanotube / aramid nanofiber composite particles:

[0066] ① The carboxylated carbon nanotubes (CNTS-COOH) aqueous solution was ultrasonically dispersed for 1 hour to obtain the ultrasonically dispersed carboxylated carbon nanotube aqueous solution;

[0067] The mass fraction of carboxylated carbon nanotubes in the aqueous solution of carboxylated carbon nanotubes mentioned in step 2① is 0.25%.

[0068] The ultrasonic dispersion power mentioned in step 2① is 300W;

[0069] ② The aqueous solution of aramid nanofibers (ANF) was ultrasonically dispersed for 1 hour to obtain the ultrasonically dispersed aqueous solution of aramid nanofibers.

[0070] The aramid nanofiber aqueous solution mentioned in step 2② has a mass fraction of aramid nanofibers of 0.2%.

[0071] The ultrasonic dispersion power mentioned in step 2② is 300W;

[0072] ③ Mix the ultrasonicated carboxylated carbon nanotube aqueous solution with the ultrasonicated aramid nanofiber aqueous solution, and ultrasonically disperse for 1 hour to obtain an aqueous solution of carboxylated carbon nanotube / aramid nanofiber composite particles.

[0073] In step 2③, the mass ratio of carboxylated carbon nanotubes to aramid nanofibers in the aqueous solution of carboxylated carbon nanotube / aramid nanofiber composite particles is 5:4.

[0074] The ultrasonic dispersion power mentioned in step 2③ is 300W;

[0075] III. Preparation of high-temperature resistant thermoplastic sizing agents:

[0076] Aqueous solutions of carboxylated carbon nanotubes / aramid nanofibers were mixed with polyimide sizing agent and ultrasonically stirred to obtain a high-temperature resistant thermoplastic sizing agent (PI / 0.1AC-AF) for aramid fibers.

[0077] In step three, the total mass of carboxylated carbon nanotubes and aramid nanofibers in the high-temperature resistant thermoplastic sizing agent for aramid fibers accounts for 0.1% of the mass fraction of the sizing agent.

[0078] Example 2: The difference between this example and Example 1 is that the total mass of carboxylated carbon nanotubes and aramid nanofibers in the high-temperature resistant thermoplastic sizing agent for aramid fibers in step three accounts for 0.25% of the mass fraction of the sizing agent; thus, a high-temperature resistant thermoplastic sizing agent for aramid fibers (PI / 0.25AC-AF) is obtained.

[0079] Example 3: The difference between this example and Example 1 is that the total mass of carboxylated carbon nanotubes and aramid nanofibers in the high-temperature resistant thermoplastic sizing agent for aramid fibers in step three accounts for 0.5% of the mass fraction of the sizing agent; thus, a high-temperature resistant thermoplastic sizing agent for aramid fibers (PI / 0.5AC-AF) is obtained.

[0080] Example 4: The difference between this example and Example 1 is that the total mass of carboxylated carbon nanotubes and aramid nanofibers in the high-temperature resistant thermoplastic sizing agent for aramid fibers described in step 3 accounts for 0.7% of the mass fraction of the sizing agent; thus, a high-temperature resistant thermoplastic sizing agent for aramid fibers (PI / 0.7AC-AF) is obtained.

[0081] Example 5: The difference between this example and Example 1 is that the total mass of carboxylated carbon nanotubes and aramid nanofibers in the high-temperature resistant thermoplastic sizing agent for aramid fibers described in step three accounts for 1% of the mass fraction of the sizing agent; thus, a high-temperature resistant thermoplastic sizing agent for aramid fibers (PI / 1AC-AF) is obtained.

[0082] Comparative Example 1: The PI / NMP sizing agent was prepared according to the following steps:

[0083] I. Preparation of polyimide sizing agent:

[0084] 2.0g of polyimide resin powder Matrimid 5218 (PI) was dissolved in 200mL of NMP and sonicated for 1h using an ultrasonic cell disruptor to obtain PI / NMP sizing agent.

[0085] The power of the ultrasound in step one is 300W.

[0086] Example 6: The preparation method of EAF / PEEK composite material is carried out according to the following steps:

[0087] ① Cut the undesized aramid fiber woven fabric (EAF) into 150mm×100mm pieces;

[0088] ② Cut the PEEK resin film into 150mm×100mm pieces, wash the PEEK resin film 5 times in anhydrous ethanol, and then dry it in an 80℃ oven for 12 hours to obtain the cleaned PEEK resin film.

[0089] ③ Alternately lay up the undesizing aramid fiber woven fabric (EAF) and the cleaned PEEK resin film in a [0 / 90] 8s layering pattern. Then, under a pressure of 5MPa, first heat up from room temperature to 200℃ and hold for 30min, then heat up to 370℃ and hold for 30min, then cool down from 370℃ to 300℃ and hold for 30min, and finally allow it to cool naturally to room temperature in the air to obtain the EAF / PEEK composite material.

[0090] Example 7: The preparation method of BAF / PEEK composite material is carried out according to the following steps:

[0091] ① Soxhlet extraction and desizing:

[0092] Undesized aramid fiber woven fabric (EAF) was cut into 150mm×100mm pieces and placed in a Soxhlet extractor. The extraction temperature was set to 80℃ and extracted in acetone for 24 hours. After extraction, the woven fabric was washed 5 times with deionized water and anhydrous ethanol respectively, and then dried in a vacuum drying oven at 80℃ for 24 hours to obtain desized aramid fiber woven fabric (BAF).

[0093] ② Cut the PEEK resin film into 150mm×100mm pieces, wash the PEEK resin film 5 times in anhydrous ethanol, and then dry it in an 80℃ oven for 12 hours to obtain the cleaned PEEK resin film.

[0094] ③ Alternately lay the desized aramid fiber woven fabric (BAF) and the washed PEEK resin film in a [0 / 90] 8s manner. Then, under a pressure of 5MPa, first raise the temperature from room temperature to 200℃ and hold for 30min, then raise the temperature to 370℃ and hold for 30min, then lower the temperature from 370℃ to 300℃ and hold for 30min, and finally allow it to cool naturally to room temperature in the air to obtain the BAF / PEEK composite material.

[0095] Example 8: The preparation method of PI-AF / PEEK composite material is carried out according to the following steps:

[0096] I. Soxhlet extraction and desizing:

[0097] Undesized aramid fiber woven fabric (EAF) was cut into 150mm×100mm pieces and placed in a Soxhlet extractor. The extraction temperature was set to 80℃ and extracted in acetone for 24 hours. After extraction, the woven fabric was washed 5 times with deionized water and anhydrous ethanol respectively, and then dried in a vacuum drying oven at 80℃ for 24 hours to obtain desized aramid fiber woven fabric (BAF).

[0098] 2. The aramid fiber woven fabric after Soxhlet extraction and desizing was etched with oxygen plasma for 10 minutes to obtain the activated aramid fiber woven fabric (AAF).

[0099] 3. The activated aramid fiber woven fabric was immersed in the PI / NMP sizing agent prepared in Comparative Example 1 for 2 hours, and then vacuum dried at 80°C for 24 hours to obtain the aramid fiber woven fabric modified with high temperature resistant thermoplastic sizing agent (PI-AF).

[0100] IV. Preparation of PI-AF / PEEK composite materials:

[0101] ① Cut the PEEK resin film into 150mm×100mm pieces, wash the PEEK resin film 5 times in anhydrous ethanol, and then dry it in an 80℃ oven for 12 hours to obtain the cleaned PEEK resin film.

[0102] ② The aramid fiber woven fabric modified with high temperature resistant thermoplastic sizing agent and the cleaned PEEK resin film are alternately laid in a [0 / 90] 8s manner. Then, under a pressure of 5MPa, the temperature is first raised from room temperature to 200℃ and held for 30min, then raised to 370℃ and held for 30min, then lowered from 370℃ to 300℃ and held for 30min. Finally, the temperature is naturally cooled to room temperature in the air to obtain the AF / PEEK composite material.

[0103] Example 9: The difference between this example and Example 8 is that the PI / NMP sizing agent prepared in Comparative Example 1 in step 3 of Example 8 is replaced with the PI / 0.1AC-AF prepared in Example 1. Other steps and parameters are the same as in Example 8, and PI / 0.1AC-AF / PEEK composite material is obtained.

[0104] Example 10: The difference between this example and Example 8 is that the PI / NMP sizing agent prepared in Comparative Example 1 in step 3 of Example 8 is replaced with the PI / 0.25AC-AF prepared in Example 2. The other steps and parameters are the same as in Example 8, and the PI / 0.25AC-AF / PEEK composite material is obtained.

[0105] Example 11: The difference between this example and Example 8 is that the PI / NMP sizing agent prepared in Comparative Example 1 in step 3 of Example 8 is replaced with the PI / 0.5AC-AF prepared in Example 3. The other steps and parameters are the same as in Example 8, and the PI / 0.5AC-AF / PEEK composite material is obtained.

[0106] Example 12: The difference between this example and Example 8 is that the PI / NMP sizing agent prepared in Comparative Example 1 in step 3 of Example 8 is replaced with the PI / 0.7AC-AF prepared in Example 4. The other steps and parameters are the same as in Example 8, and the PI / 0.7AC-AF / PEEK composite material is obtained.

[0107] Example 13: The difference between this example and Example 8 is that the PI / NMP sizing agent prepared in Comparative Example 1 in step 3 of Example 8 is replaced with the PI / 1AC-AF prepared in Example 5. The other steps and parameters are the same as in Example 8, and the PI / 1AC-AF / PEEK composite material is obtained.

[0108] The thermal stability of the resin matrix PEEK and the sizing agent components PI, CNT-COOH, and ANF was tested in N2, ranging from room temperature to 800℃, with a heating rate of 10℃ / min. The thermogravimetric curves are shown below. Figure 1 As shown;

[0109] from Figure 1 It can be seen that the curve drop before 200℃ can be attributed to moisture loss due to physical absorption. Test results show that CNTS-COOH hardly decomposes at 370℃, but loses 2.82% of its weight at 800℃, which is due to the thermal decomposition of the carboxyl functional groups on the CNTS-COOH surface. ANF loses 6.01% of its weight at 370℃; Matrimid 5218 decomposes by 3.37% at 370℃, both exhibiting excellent thermal stability and suitable for use as sizing agents on fiber surfaces. The resin matrix PEEK begins to undergo high-temperature decomposition of the main chain at 540℃-600℃, with a mass loss reaching 40%.

[0110] Figure 2 The images show scanning electron microscope (SEM) images of aramid fiber woven fabric before and after modification. In the images, a) is the aramid fiber woven fabric without desizing (EAF), b) is the aramid fiber woven fabric after desizing (BAF), c) is the aramid fiber woven fabric after activation (AAF), d) is the aramid fiber woven fabric modified with PI / NMP sizing agent prepared in Comparative Example 1 (PI-AF), and e) is the aramid fiber woven fabric modified with high-temperature thermoplastic sizing agent prepared in Example 4 (PI / 0.7AC-AF).

[0111] from Figure 2 It can be seen that the surface of the aramid fiber woven fabric (EAF) without desizing has obvious small white particles. These are the original sizing agent and impurities that were coated on the surface of the fiber when it left the factory. After desizing, the particles will be removed. Figure 2 b) The surface is smooth and clean with some shallow grooves, which indicates that the desizing process has effectively removed the original sizing agent and impurity molecules from the surface. Figure 2 c) Plasma treatment for 10 minutes deepens the grooves on the fiber surface and causes some protrusions to appear; Figure 2 In d), the PI-AF surface after sizing was clearly and successfully coated with a layer of polyimide resin film, while the sizing agent filled the grooves on the fiber surface. Figure 2 e) The surface of the PI / AC-AF fiber is clearly coated with nanoparticles, which is direct evidence that polyimide, CNT-COOH and ANF are coated on the fiber surface.

[0112] Figure 3 Infrared spectral analysis of aramid fiber woven fabric before and after modification, and the composition of sizing agent;

[0113] from Figure 3It can be seen that the NH bending vibration peak (1540 cm⁻¹) was observed in BAF, PI-AF, and PI / 0.7AC-AF. -1 C=O tensile vibration (1637cm) -1 and 823cm -1 ) and CN and OH synergistic tensile vibration (1308cm) -1 3308cm -1 The characteristic peaks are due to the amide bonds in the AF fiber molecular chain. A symmetrically stretched region (1723 cm⁻¹) of the imide carbon group appears in the PI-AF spectrum. -1 728cm -1 ) and the stretching vibration absorption peak of the CN bond (1398 cm⁻¹) -1 This indicates that the PI layer has been successfully coated on the fiber surface. The surface chemical structure of PI / 0.7AC-AF after CNT-COOH / ANF sizing did not change significantly in its spectrum. This is because ANF and AF have the same chemical structure, and the amount of nanoparticles added is not large. Therefore, further analysis of the functional groups on the fiber surface before and after modification using X-ray photoelectron spectroscopy is needed to confirm whether the rigid-flexible nanoparticle composite structure has been successfully constructed on the fiber surface.

[0114] Figure 4 The XPS full spectrum and C1s fine spectrum fitting spectra of the fiber surface before and after modification of aramid fiber woven fabric are shown in the figure. a) is the full spectrum of BAF, PI-AF and PI / 1AC-AF; b) is the C1s peak diagram of BAF; c) is the C1s peak diagram of PI-AF; d) is the C1s peak diagram of PI / 1AC-AF.

[0115] from Figure 4It can be seen that the AF surface contains C, O, and N elements before and after modification. After plasma activation and sizing, the elemental content on the fiber surface changed. After C1s peak separation, there were five synthetic peaks: CC (284.48-284.9 eV), CN / CO (285.48-285.7 eV), C=O (287.93-288.1 eV), O=C-OH (289.38 eV), and π-π interaction (290.3 eV). The PI-AF surface has 1.48% carboxyl groups, indicating that oxygen plasma introduced a certain amount of oxygen-containing active groups to the fiber surface. The increased CN / CO functional group content indicates that the PI coating was successfully applied to the fiber surface. After adding CNT-COOH / ANF, the carboxyl content on the AF surface increased to 1.56%, indicating that the surface active functional groups increased after fiber modification. This is attributed to the contribution of carboxyl groups contained in the two nanoparticles, which shows that CNT-COOH / ANF is effectively constructed on the fiber surface. The π-π interaction peaks appearing in the C1s spectrum of PI / 1AC-AF are attributed to the π-π interactions between CNT-COOH and ANF or between PI and CNT-COOH / ANF.

[0116] Table 1. Percentage of different elements on the fiber surface in XPS

[0117] Fiber samples CC CN / CO C=O COOH π-π BAF 62.92 27.37 9.71 / / PI-AF 61.94 27.75 8.83 1.48 / PI / 1AC-AF 73.28 16.31 7.80 1.56 1.04

[0118] According to the testing standard (ASTM D7264), the prepared composite laminates treated with eight different sizing agents—EAF / PEEK, BAF / PEEK, PI-AF / PEEK, PI / 0.1AC-AF / PEEK, PI / 0.25AC-AF / PEEK, PI / 0.5AC-AF / PEEK, PI / 0.7AC-AF / PEEK, and PI / 1AC-AF / PEEK—were cut into specimens of a certain size. For each type, the flexural strength and flexural modulus of five specimens were tested, and the average values ​​were plotted in a bar chart as shown below. Figure 5 and Figure 6 As shown;

[0119] Figure 5 The flexural strength of EAF / PEEK, BAF / PEEK, PI-AF / PEEK, PI / 0.1AC-AF / PEEK, PI / 0.25AC-AF / PEEK, PI / 0.5AC-AF / PEEK, PI / 0.7AC-AF / PEEK and PI / 1AC-AF / PEEK composites;

[0120] Figure 6The flexural modulus of EAF / PEEK, BAF / PEEK, PI-AF / PEEK, PI / 0.1AC-AF / PEEK, PI / 0.25AC-AF / PEEK, PI / 0.5AC-AF / PEEK, PI / 0.7AC-AF / PEEK and PI / 1AC-AF / PEEK composites;

[0121] from Figure 5 and Figure 6 It can be seen that the flexural strength and flexural modulus of EAF / PEEK are 20.14% and 1.11% higher than those of BAF / PEEK, respectively. This may be because the epoxy resin sizing agent on its surface provides some interfacial bonding strength. However, since the thermosetting sizing agent is incompatible with the thermoplastic resin PEEK, it has a certain negative effect during high-temperature molding. After plasma activation treatment and PI sizing modification, the flexural strength and flexural modulus of PI-AF / PEEK increased by 52.27% and 51.16%, respectively. The significant improvement can be attributed to the fact that the activated AF surface has more oxygen-containing functional groups, which allows the high molecular weight PI to form a uniform and dense sizing coating on the fiber surface. The PI film, which has good compatibility with PEEK, provides more interaction sites between AF and PEEK. However, the flexible resin interfacial layer is not enough to withstand high loads, so its improvement effect is still limited. Therefore, the addition of CNT-COOH / ANF rigid-flexible composite nanonetwork forms a composite nanolayer with higher strength, further improving the flexural strength and modulus of the composite material. With the increase of the mass fraction of composite nanoparticles, the flexural strength and flexural modulus also showed an upward trend. When 0.7 wt% CNT-COOH / ANF was added, the flexural strength (220.97 MPa) and flexural modulus (12.80 GPa) of PI / 0.7AC-AF / PEEK reached the highest, increasing by 132.60% and 99.00%, respectively. This may be attributed to the good film-forming properties of ANF, which allows ANF and CNT-COOH to effectively adhere to the fiber surface, forming a loosely arranged network of rigid nanoparticles interacting with flexible nanofibers. The rigid-flexible interface forms a buffer pad, which can transfer external stress from the matrix to the fiber, further reducing structural damage to the composite material. At the same time, the synergistic effect of the higher nanoparticle content network and the high molecular weight PI is conducive to the formation of a denser bridging network structure, which is beneficial to the penetration of PEEK resin, thereby enhancing the mechanical interlocking effect between the fiber and the resin matrix. When the content increases to 1.0 wt%, the flexural strength and flexural modulus of PI / 1AC-AF / PEEK decrease slightly. This may be because the content of interfacial nanoparticles is too high, forming a dense nano-network with small pores that are not conducive to the penetration of PEEK resin. This leads to fiber breakage under shear load, resulting in stress concentration at the interface and reduced stress transfer efficiency at the interface.

[0122] Figure 7 Interlaminar shear strength of EAF / PEEK, BAF / PEEK, PI-AF / PEEK, PI / 0.1AC-AF / PEEK, PI / 0.25AC-AF / PEEK, PI / 0.5AC-AF / PEEK, PI / 0.7AC-AF / PEEK and PI / 1AC-AF / PEEK composites;

[0123] from Figure 7 Consistent with the trend observed in the flexural strength test results, the interlaminar shear strength of the composite material significantly improved after PI sizing and CNT-COOH / ANF composite nanoparticle sizing modification. After plasma activation and 1.0 wt% PI sizing, the interlaminar shear strength (ILSS) of PI-AF / PEEK increased by 54.66% (7.30 MPa), indicating that the high molecular weight PI significantly improved the poor interfacial bonding between AF and PEEK. Furthermore, the addition of a CNT-COOH / ANF rigid-flexible composite interfacial layer further significantly increased the ILSS of the composite material. This is attributed to the interaction between ANF and CNT-COOH, which possesses good film-forming properties, forming a stable bridging network region between AF and PEEK. The flexible nanofibers, wrapped around the rigid carboxylated carbon nanotubes, jointly reinforced the interface. At a CNT-COOH / ANF mass fraction of 0.7 wt%, the ILSS of PI / 0.7AC-AF / PEEK reached its maximum value (13.36 MPa), representing a 182.97% improvement compared to desizing AF. As the concentration of composite nanoparticles increases, the ILSS of PI / 1AC-AF / PEEK decreases. This may be because excessive sizing due to high nanoparticle concentration leads to poor PEEK penetration, reduced stress transfer efficiency at the interface, and thus decreased interfacial bonding strength.

[0124] DMA investigated the thermomechanical properties of the composite material using a single cantilever mode test over a temperature range from room temperature to 300 °C. The results for its storage modulus and damping factor are as follows: Figure 8 As shown;

[0125] Figure 8 Storage modulus of EAF / PEEK, BAF / PEEK, PI-AF / PEEK, PI / 0.1AC-AF / PEEK, PI / 0.25AC-AF / PEEK, PI / 0.5AC-AF / PEEK, PI / 0.7AC-AF / PEEK and PI / 1AC-AF / PEEK composites;

[0126] Storage modulus indicates a material's ability to resist deformation and store energy, and can be used to characterize a material's rigidity and interfacial compatibility. At room temperature, after surface sizing with PI, the E' of PI-AF / PEEK increased by 22.3% compared to BAF / PEEK. Further construction of the rigid-flexible composite particle interface resulted in a gradual increase in E' with increasing mass fraction, with PI / 0.7AC-AF / PEEK showing an 82.7% increase in E'. As temperature increased, the E' of the composite material generally showed a decreasing trend, but its effect on temperature was relatively small before Tg, indicating that AF / PEEK maintains good stability within its operating temperature range. The storage modulus increases with increasing material rigidity, which is largely due to its strong relationship with the compatibility between the resin and the interface. After surface sizing, the interfacial relationship between the fiber and resin was significantly improved. This is because the good interfacial structure of the rigid-flexible composite structure, through physical entanglement and similar compatibility, effectively transfers stress to the reinforcing fibers, allowing the composite material to withstand higher loads under the same conditions. Meanwhile, the addition of a large number of active groups to the fiber surface interacts with the matrix to form a relatively attractive interface and chemical bonds, which also helps to improve the compatibility of the interface.

[0127] Figure 9 The damping factor is the composite material of EAF / PEEK, BAF / PEEK, PI-AF / PEEK, PI / 0.1AC-AF / PEEK, PI / 0.25AC-AF / PEEK, PI / 0.5AC-AF / PEEK, PI / 0.7AC-AF / PEEK and PI / 1AC-AF / PEEK.

[0128] from Figure 9 It can be seen that the loss factor of the surface-modified composite material gradually decreases, while its peak temperature gradually increases. The decrease in tanδ is due to the improved interfacial bonding between the fiber and resin resulting from the addition of PI and CNT-COOH / ANF. In particular, the construction of the rigid-flexible composite nanostructure with a high specific surface area leads to an increase in the effective contact area between the fiber and resin, which corresponds to its high storage modulus. The increase in Tg can be explained by the greater difficulty in untangling the polymer molecular chains of the composite material with good interfacial bonding, thus requiring more energy. Therefore, it is further demonstrated that PI / CNT-COOH / ANF can effectively improve the interfacial bonding of the composite material.

Claims

1. A method for preparing a high-temperature resistant thermoplastic sizing agent for aramid fibers, characterized in that... The preparation method is specifically carried out according to the following steps: I. Preparation of polyimide sizing agent: Polyimide resin powder is dissolved in an organic solvent and ultrasonically treated for a period of time to obtain a polyimide sizing agent; The polyimide resin powder mentioned in step one is polyimide resin powder Matrimid 5218; II. Preparation of aqueous solution of carboxylated carbon nanotube / aramid nanofiber composite particles: ① The carboxylated carbon nanotube aqueous solution was ultrasonically dispersed to obtain an ultrasonically dispersed carboxylated carbon nanotube aqueous solution; The mass fraction of carboxylated carbon nanotubes in the aqueous solution of carboxylated carbon nanotubes mentioned in step 2① is 0.12%~0.30%; ② The aqueous solution of aramid nanofibers was ultrasonically dispersed to obtain an ultrasonically dispersed aqueous solution of aramid nanofibers; The mass fraction of aramid nanofibers in the aqueous solution of aramid nanofibers mentioned in step 2② is 0.1%~0.24%; ③ Mix the ultrasonicated carboxylated carbon nanotube aqueous solution with the ultrasonicated aramid nanofiber aqueous solution, and disperse by ultrasonication to obtain an aqueous solution of carboxylated carbon nanotube / aramid nanofiber composite particles. In step 2③, the mass ratio of carboxylated carbon nanotubes to aramid nanofibers in the aqueous solution of carboxylated carbon nanotube / aramid nanofiber composite particles is 5:

4. III. Preparation of high-temperature resistant thermoplastic sizing agents: A high-temperature thermoplastic sizing agent for aramid fibers was obtained by mixing an aqueous solution of carboxylated carbon nanotube / aramid nanofiber composite particles with a polyimide sizing agent and ultrasonically stirring. In step three, the total mass of carboxylated carbon nanotubes and aramid nanofibers in the high-temperature resistant thermoplastic sizing agent for aramid fibers accounts for 0.1% to 1% of the mass fraction of the sizing agent.

2. The method for preparing a high-temperature resistant thermoplastic sizing agent for aramid fibers according to claim 1, characterized in that... The organic solvent mentioned in step one is N-methylpyrrolidone, dichloromethane, tetrahydrofuran, N,N-dimethylformamide, or chloroform; the mass ratio of the polyimide resin powder to the volume ratio of the organic solvent mentioned in step one is 2g:200mL.

3. The method for preparing a high-temperature resistant thermoplastic sizing agent for aramid fibers according to claim 1, characterized in that... In step one, the polyimide resin powder is dissolved in an organic solvent and ultrasonically sonicated for 1 to 2 hours using an ultrasonic cell disruptor with a power of 100W to 1000W.

4. The method for preparing a high-temperature resistant thermoplastic sizing agent for aramid fibers according to claim 1, characterized in that... The ultrasonic dispersion time mentioned in step 2① is 1h~2h.

5. The method for preparing a high-temperature resistant thermoplastic sizing agent for aramid fibers according to claim 1, characterized in that... The ultrasonic dispersion time mentioned in step 2② is 1h~2h.

6. The method for preparing a high-temperature resistant thermoplastic sizing agent for aramid fibers according to claim 1, characterized in that... The ultrasonic dispersion time mentioned in step 2③ is 1h~2h.

7. The application of a high-temperature resistant thermoplastic sizing agent for aramid fibers prepared by the preparation method according to claim 1, characterized in that... A high-temperature resistant thermoplastic sizing agent for aramid fibers is used to improve the interface of AF / PEEK composite materials.

8. The application of the high-temperature resistant thermoplastic sizing agent for aramid fibers according to claim 7, characterized in that... Improving the interface of AF / PEEK composite materials using a high-temperature resistant thermoplastic sizing agent for aramid fibers is accomplished through the following steps: I. Soxhlet extraction and desizing: The undesized aramid fiber woven fabric EAF was cut into 150mm×100mm pieces and placed in a Soxhlet extractor. The extraction temperature was set to 80℃ and extracted in acetone for 24h. After extraction, the woven fabric was washed 3 to 5 times with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 80℃ for 24h to obtain the desized aramid fiber woven fabric BAF.

2. Use oxygen plasma to etch the aramid fiber woven fabric after Soxhlet extraction and desizing for 5 min to 10 min to obtain the activated aramid fiber woven fabric.

3. Immerse the activated aramid fiber woven fabric in a high-temperature resistant thermoplastic sizing agent for aramid fibers for 1h~3h, take it out and vacuum dry it at 80℃~100℃ for 12h~24h to obtain the aramid fiber woven fabric modified by the high-temperature resistant thermoplastic sizing agent. IV. Preparation of AF / PEEK composite materials: ① Cut the PEEK resin film into 150mm×100mm pieces, wash the PEEK resin film in anhydrous ethanol 3-5 times, and then dry it in an 80℃ oven for 12 hours to obtain the cleaned PEEK resin film. ② The aramid fiber woven fabric modified with high temperature resistant thermoplastic sizing agent and the cleaned PEEK resin film are alternately laid in a [0 / 90] 8s manner. Then, under a pressure of 5MPa, the temperature is first raised from room temperature to 200℃ and held for 30min, then raised to 370℃ and held for 30min, then lowered from 370℃ to 300℃ and held for 30min. Finally, the temperature is naturally cooled to room temperature in the air to obtain the AF / PEEK composite material.

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