Thermally-induced phase change intelligent wave-absorbing paper based on VO2 coating and preparation process of thermally-induced phase change intelligent wave-absorbing paper

Abstract

The invention relates to the cross technical field of special papermaking and carbon fiber material preparation, in particular to thermally induced phase change intelligent wave-absorbing paper based on a VO2 coating and a preparation technology thereof.The preparation technology comprises the following steps that S1, aramid precipitation A, pitch-based carbon fibers B and a PAM dispersing agent serve as raw materials, and a mixture A is prepared; preparing pitch-based carbon fiber aramid paper E by adopting a wet forming process; s2, impregnating the pitch-based carbon fiber aramid paper E in a phenolic resin-ethanol blending system F, and then performing vacuum drying and hot-pressing finishing to obtain carbon fiber paper H; and S3, coating the carbon fiber paper H with a VO2 dispersion liquid, and then performing drying and hot-pressing finishing to obtain the thermally induced phase change intelligent wave-absorbing paper. The problem that the mechanical property and the wave absorbing property of the microwave absorbing material are difficult to consider at the same time is solved through aramid precipitation auxiliary interweaving, low-concentration resin impregnation, viscose preparation and surface coating.

Description

Technical Field

[0001] The present invention relates to the technical field of special papermaking and carbon fiber material preparation, and specifically relates to a thermo-induced phase change intelligent absorbing paper based on VO2 coating and a preparation process thereof. Background Art

[0002] As the core functional material of electromagnetic compatibility, the core function of microwave absorbing materials is to convert incident electromagnetic waves into heat or other forms of energy through the energy dissipation mechanism, thereby achieving electromagnetic interference suppression. However, current technologies face many key bottlenecks. As an intelligent phase change material, VO2's wave absorption performance is highly dependent on the interfacial bonding strength with the substrate. The surface of traditional paper-based materials has weak hydrophilicity and low roughness, which makes the VO2 coating easy to fall off, especially in hot and humid environments, where the durability is poor. Although existing modification technologies can temporarily improve adhesion, the process is complex and the cost is high, making it difficult to meet the needs of industrial production. In order to improve mechanical strength, traditional processes require high-concentration resin impregnation or composite polymer materials, but the resin is prone to form a rigid network after curing, which significantly increases the brittleness of the material. This contradiction makes it difficult for the material to balance wave absorption performance and flexibility, limiting its application in dynamic environments. Furthermore, the electromagnetic properties of existing absorbing material systems are determined by the intrinsic properties of the materials, making it difficult to achieve real-time adjustment of the dielectric constant and magnetic permeability through external field control. Although nano-absorbing materials can adjust the absorption frequency band to the terahertz range, their environmental stability is insufficient, and the absorption efficiency is severely attenuated in high temperature or high humidity environments. Traditional multi-layer composite structures can expand the absorption frequency band, but the parameters of each layer are fixed and cannot adapt to the dynamic changes in complex electromagnetic environments. In addition, multifunctional collaborative optimization technology has not yet broken through the performance balancing dilemma. Existing research has contradictions in absorbing performance and lightweight, high temperature resistance and broadband absorption, and lacks systematic solutions for the integrated design of electromagnetic compatibility, thermal management, mechanical protection and other functions. These technical bottlenecks have seriously restricted the in-depth application of absorbing materials in fields such as 5G communications and hypersonic aircraft.

[0003] To develop composite materials with enhanced microwave absorption performance, scientists use fiber composites as a base material and then compound them with conductive fillers in resins to create microwave absorbing materials. For example, the BN fiber nanocomposite absorber developed in patent CN119287669A combines high-temperature stability with broadband absorption through the synergistic effect of boron nitride fibers and polyaniline. Patent CN119253288A proposes a multi-spectrum compatible absorber that utilizes a composite structure of an ITO transparent conductive layer and a dielectric layer to simultaneously achieve microwave, infrared, and visible light absorption camouflage. Patent CN116284898A dissolves a polymer matrix material, adds an ionic liquid and nano-vanadium dioxide, mixes thoroughly, and then dries and hot-presses to create a recyclable, reshapeable, transparent, intelligent absorber for military and civilian applications in transparent electromagnetic protection. Patent CN115322442A uses vanadium dioxide as a functional material, compounded with a matrix material, to create a temperature-responsive electromagnetic shielding composite material. However, these approaches still suffer from challenges in balancing mechanical properties and flexibility, and weak microwave absorption efficiency. Domestic microwave absorbing materials started late, resulting in a gap between their manufacturing technology and that of foreign countries. High-performance products rely on imports, which affects the widespread application of this material in the field of microwave absorption. Summary of the Invention

[0004] In view of the problems in the existing technology of electromagnetic shielding composite materials such as difficulty in balancing the mechanical properties and flexibility of the materials and weak microwave absorption efficiency, the present invention provides a thermally induced phase change intelligent absorbing paper based on VO2 coating and a preparation process thereof. The carbon fiber aramid absorbing paper is prepared by using asphalt-based carbon fiber as the skeleton and aramid precipitation as the auxiliary fiber forming method, and is reinforced by low-concentration phenolic resin impregnation and vanadium dioxide coating to solve the contradiction between the mechanical properties and microwave absorption performance of the composite fiber material.

[0005] The present invention is achieved through the following technical solutions: A preparation process of a thermally induced phase change intelligent absorbing paper based on VO2 coating comprises the following steps: S1, using aramid precipitate A, pitch-based carbon fiber B and PAM dispersant as raw materials, a wet forming process was used to prepare pitch-based carbon fiber aramid paper E; S2, impregnating the asphalt-based carbon fiber aramid paper E in the phenolic resin-ethanol blend system F, and then vacuum drying and hot pressing to obtain the carbon fiber paper H; S3, coating the carbon fiber paper H with VO2 dispersion, and then drying and hot pressing to obtain the thermo-induced phase change smart absorbing paper.

[0006] Preferably, in S1, the specific process of preparing the aramid paper is: S11, adding aramid precipitate A to water, dispersing and dispersing to obtain aramid precipitate slurry, then adding pitch-based carbon fiber B to the aramid precipitate slurry and mixing evenly, and then adding PAM dispersant to dispersing and dispersing to obtain mixed fiber slurry C; S12, homogenizing and dehydrating the mixed fiber slurry C to obtain a wet paper web D; S13, absorbing moisture from both sides of the wet paper web D, and then vacuum drying to obtain aramid carbon fiber paper E.

[0007] Preferably, in S11, the added asphalt-based carbon fiber and aramid precipitated absolute dry mass ratio is 30% to 60%: 40% to 70%.

[0008] Preferably, in S2, the preparation method of the phenolic resin-ethanol blend system F is: dissolving phenolic resin powder in ethanol to obtain the phenolic resin-ethanol blend system F, wherein the solid content of the phenolic resin powder is 1 wt% to 2 wt%.

[0009] Preferably, in S2, during the impregnation, the asphalt-based carbon fiber aramid paper E is completely immersed in the phenolic resin-ethanol blend system F, and the impregnation time is 5 to 10 minutes; During vacuum drying, the vacuum degree is 0.096~0.098MPa, the temperature is 95~115℃, and the time is 0.5~1h; During hot pressing finishing, the temperature is 140~150℃, the pressure is 9~10MPa, and the time is 5~8min.

[0010] Preferably, in S3, the preparation method of the VO2 dispersion is: VO2 powder and phenolic resin powder are shaken and mixed evenly, anhydrous ethanol solution is added, and stirring is continued until a colloidal system is obtained, which is the VO2 dispersion.

[0011] Preferably, the amount of VO2 powder used is 1-3 g, and the amount of phenolic resin powder used is 3-9 g.

[0012] Preferably, in S3, during drying, the temperature is 140-150°C, the pressure is 9-10 MPa, and the time is 0.5-1 h; During hot pressing finishing, the temperature is 140~150℃, the pressure is 9~10MPa, and the time is 5~8min.

[0013] A thermo-induced phase-change intelligent absorbing paper obtained according to the preparation process of the thermo-induced phase-change intelligent absorbing paper based on VO2 coating.

[0014] An application of the thermoinduced phase change intelligent absorbing paper in the field of microwave absorption.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention proposes a process for preparing thermally induced phase-change intelligent microwave-absorbing paper based on a VO2 coating. This process utilizes pitch-based carbon fibers as a framework, aramid precipitation as an auxiliary fiber forming agent, and low-concentration phenolic resin impregnation and metal oxide coating as reinforcements. This process produces carbon fiber aramid paper with high microwave absorption performance, resolving the conflict between the mechanical and microwave absorption properties of carbon fiber aramid paper. Compared to previously published process solutions, the raw material components have been optimized. Firstly, the invention introduces aramid precipitated fibers, which, through the excellent dispersion after aramid precipitation and brooming, improves the uniformity of the carbon fiber base paper and promotes fiber interweaving. Secondly, low-concentration phenolic resin impregnation and bonding promotes the crosslinking of the fiber molecular structure. In this structure, the introduced aramid pulp molecular structure is composed of alternating benzene rings and amide bonds, and the molecular structure has a high carbon content. The introduced phenolic resin main molecular structure is phenol and formaldehyde, and the molecular structure has a high carbon content. After hot pressing, the degree of molecular cross-linking is further improved, and a richer conductive network is formed between the original fiber interwoven network, which is conducive to obtaining paper with higher conductivity, improving the comprehensive conductive properties of paper, and improving dielectric loss performance by enhancing interface polarization and conduction loss.

[0016] The aramid fibrids introduced in this invention, with their unique structure of alternating benzene rings and amide bonds, can form efficient conductive pathways within the paper structure, significantly improving the paper's overall conductivity and successfully balancing the conflicting strength, flexibility, and conductivity of carbon fibers. Furthermore, the amount of aramid fibrids added was determined through repeated experimental optimization. Excessive aramid fibrid content will impair the formation of the carbon conductive network and compromise the conductivity of the finished paper.

[0017] Furthermore, the present invention, based on the introduction of aramid precipitation assistance, realizes the bonding and strengthening of the interweaving points between carbon fibers, carbon fibers and aramid precipitation, and aramid precipitation through ultra-low concentration phenolic resin impregnation; the concentration of phenolic resin is the result of process optimization. At a lower concentration, it not only ensures the replenishment of insufficient fiber contact points, which is beneficial to the subsequent vanadium dioxide coating, but also realizes the transmission of stress during the stretching process, which can improve the mechanical strength and ensure the realization of paper performance.

[0018] Furthermore, the preferred aramid precipitated terminal groups in the present invention contain rich amino groups, have good compatibility and self-binding ability with phenolic resin, and ensure high efficiency at low concentration. The principle is that the aramid precipitated terminal groups can form extensive hydrogen bonds with the resin, and the curing of the phenolic resin can cross-link the aramid precipitated chemical fiber, so the two achieve high-strength bonding through the combined action of chemistry and physics.

[0019] Furthermore, the present invention adds a vanadium dioxide coating process to the phenolic resin impregnation process. In the areas where the raw material fibers are not in sufficient contact, the phenolic resin is infiltrated, bonded and solidified to form a tight network. After hot pressing and finishing, a richer conductive network is constructed, thereby improving the comprehensive conductive properties of the carbon fiber paper. The amount of vanadium dioxide used in the vanadium dioxide coating process is the result of process optimization. If the amount is too low, the vanadium dioxide is difficult to adhere to the surface of the paper. If the amount is too high, a large amount of vanadium dioxide penetrates into the gaps in the paper, which easily leads to increased brittleness of the paper, affecting the structural properties of the paper itself, reducing the strength, and failing to maintain good paper morphology and mechanical properties.

[0020] Furthermore, the pulp decomposition speed, fiber addition order, drying temperature, hot pressing finishing temperature, hot pressing finishing pressure, and insulation temperature of the carbonization process in the present invention are all the results of process optimization. For example, the pulp decomposition speed ensures that the paper will not break under high dispersion, the drying temperature ensures energy saving under high efficiency, and the finishing temperature ensures that the phenolic resin will not flow and block under curing. These are all the results of long-term process optimization. The technical effect is to improve paper quality and save energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of a process for preparing a thermally induced phase change intelligent absorbing paper based on a VO2 coating according to the present invention; Figure 2 This is a detailed flow chart of a process for preparing a thermally induced phase change intelligent absorbing paper based on a VO2 coating according to the present invention; Figure 3 This is the surface SEM image of the carbon fiber aramid absorbing paper in Example 5 at 10.4 mm × 30 LM; Figure 4 This is the surface SEM image of the carbon fiber aramid absorbing paper in Example 5 under 0.4 mm × 1.10k SE; Figure 5 This is a cross-sectional SEM image of the carbon fiber aramid absorbing paper in Example 5; Figure 6 This is a test diagram of the microwave absorption performance of the absorbing paper obtained in Experimental Example 1 under the electric + magnetic mode; Figure 7 This is a test diagram of the microwave absorption performance of the absorbing paper obtained in Experimental Example 2 under the electric + magnetic mode; Figure 8 This is a test diagram of the microwave absorption performance of the absorbing paper obtained in Experimental Example 3 under the electric + magnetic mode; Figure 9 This is a test diagram of the microwave absorption performance of the absorbing paper obtained in Experimental Example 4 under the electric + magnetic mode; Figure 10 This is a test diagram of the microwave absorption performance of the absorbing paper obtained in Experimental Example 5 under the electric + magnetic mode; Figure 11This is a test diagram of the microwave absorption performance of the absorbing paper obtained in Experimental Example 6 under the electric + magnetic mode. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0023] The present invention discloses a preparation process of a thermo-induced phase change intelligent absorbing paper based on VO2 coating, referring to Figure 1 、 2 , including the following steps: Step 1: Select aramid precipitate A, dissolve it in water at 15,000-20,000 rpm, and then evenly disperse it to obtain aramid precipitate slurry; Pitch-based carbon fiber B with a length of 7 mm, a diameter of 13 μm, a resistivity of 2.0 μΩ·m, a tensile strength of 2.3 GPa, and an elongation at break of 0.25% was selected. The pitch-based carbon fiber was added according to the absolute dry mass ratio of 30%-60% of the pitch-based carbon fiber to aramid pulp: 40%-70%. Then, 10-12 mL of a PAM dispersion with a concentration of 6-7 g / L was added. The mixture was dispersed uniformly at 15,000-20,000 rpm to obtain a mixed fiber slurry C. The mixed fiber slurry C is then poured into a paper sheet former to form a wet paper web D. Finally, wool felt was spread on both sides to absorb moisture, and then dried in a paper dryer at 95-115°C and vacuum for 10-15 minutes with a vacuum degree of 0.096-0.098 MPa to obtain pitch-based carbon fiber aramid paper E. Step 2: dissolving 3 g of phenolic resin powder in 200-300 ml of anhydrous ethanol to obtain a phenolic resin-ethanol blend system F; Then, the prepared asphalt-based carbon fiber aramid paper E was impregnated in a phenolic resin-ethanol blend system F for 5-10 minutes, and then placed in an oven and dried at 95-115°C for 0.5-1 hour to obtain a resin-impregnated asphalt-based carbon fiber aramid base paper G. The prepared resin-impregnated carbon fiber paper G was then hot-pressed on a flat vulcanizer at 140-150° C. and 9-10 MPa for 5-8 min to obtain a hot-pressed carbon fiber aramid paper H.

[0024] Step 3: Mix 1.5 g of VO2 powder and 6-10 g of phenolic resin powder, add 10 ml of anhydrous ethanol solution, and continue stirring until the solution becomes viscous to obtain a colloidal system I.

[0025] The hot-pressed carbon fiber aramid paper was flattened and the surface was evenly coated with colloidal system I with a brush to a thickness of 1-2 mm. The paper was then placed in an oven and dried at 95-115°C for 0.5-1 h. The paper was then hot-pressed on a flat vulcanizer at 140-150°C and 9-10 MPa for 5-8 min to obtain the thermally induced phase change smart absorbing paper.

[0026] The present invention provides a thermo-induced phase-change intelligent absorbing paper based on a VO2 coating and a preparation process thereof. First, aramid precipitate A and asphalt-based carbon fiber B are wet-formed to obtain aramid paper. The asphalt-based carbon fiber aramid paper is then impregnated with phenolic resin, dried, and finished to obtain asphalt-based carbon fiber base paper. Finally, VO2 and phenolic resin viscose are applied to the surface of the asphalt-based carbon fiber aramid base paper, dried, and finished to obtain the thermo-induced phase-change intelligent absorbing paper. A novel method for preparing carbon fiber aramid paper with absorbing properties involves wet-forming a mixed slurry, resin impregnation reinforcement, hot pressing finishing, and metal oxide surface coating and hot pressing finishing. This method, through aramid precipitate-assisted interweaving, low-concentration resin reinforcement, and metal oxide coating and compounding, addresses the difficulty in balancing the mechanical and absorbing properties of microwave absorbing materials. This method provides a thermo-induced phase-change intelligent absorbing paper based on a VO2 coating and a preparation process thereof.

[0027] The deflaker, paper sheet former, dryer, oven, hot press, etc. used in the process scheme of the present invention are all conventional equipment, the solvents are tap water and ethanol, and the process links are environmentally friendly, which lays a good foundation for the industrialization and scale-up of the technology of the present invention and has a high market competitive advantage.

[0028] The present invention also discloses a thermo-induced phase-change intelligent absorbing paper obtained by a thermo-induced phase-change intelligent absorbing paper based on a VO2 coating and a preparation process thereof.

[0029] Example 1 Step 1, selecting aramid precipitate A, dispersing it in water at 15000 rpm and then uniformly dispersing it to obtain aramid precipitate slurry; Pitch-based carbon fiber B with a length of 7 mm, a diameter of 13 μm, a resistivity of 2.0 μΩ·m, a tensile strength of 2.3 GPa, and an elongation at break of 0.25% was selected. The pitch-based carbon fiber was added according to the absolute dry mass ratio of the pitch-based carbon fiber to the aramid pulp of 35%:65%, and then 10 mL of a PAM dispersion with a concentration of 6 g / L was added. The mixture was dispersed uniformly at 15,000 rpm to obtain a mixed fiber slurry C. The mixed fiber slurry C is then poured into a paper sheet former to form a wet paper web D. Finally, wool felt was placed on both sides to absorb moisture, and then dried in a paper dryer at 105°C and a vacuum degree of 0.096 MPa for 10 min to obtain pitch-based carbon fiber aramid paper E; Step 2, dissolving 3 g of phenolic resin powder in 250 ml of anhydrous ethanol to obtain a phenolic resin-ethanol blend system F; The prepared asphalt-based carbon fiber aramid paper E was then impregnated in a phenolic resin-ethanol blend system F for 5 minutes, and then placed in an oven and dried at 115°C for 1 hour to obtain a resin-impregnated asphalt-based carbon fiber aramid base paper G. The prepared resin-impregnated carbon fiber paper G was hot-pressed on a flat vulcanizer at 150° C. and 10 MPa for 5 min to obtain a hot-pressed carbon fiber aramid paper H.

[0030] Step 3: Mix 1.5 g of VO2 powder and 6 g of phenolic resin powder evenly, add 10 ml of anhydrous ethanol solution, and continue stirring until the solution becomes viscous to obtain a colloidal system I.

[0031] The hot-pressed carbon fiber aramid paper was flattened and the surface was evenly coated with colloidal system I with a coating thickness of 1 mm using a brush. The paper was then placed in an oven and dried at 115°C for 1 hour. The paper was then hot-pressed on a flat-plate vulcanizer at 150°C and 10 MPa for 5 minutes to obtain a thermally induced phase change smart absorbing paper.

[0032] The smart absorbing paper prepared in this embodiment has a basis weight of 95g / m 2 The ratio of carbon fiber to aramid precipitation is 35%:65%. At a temperature of 70°C, the minimum reflection loss reaches -59.09dB, and the maximum absorption bandwidth is 6.39GHz, which has microwave absorption characteristics.

[0033] Example 2 Step 1, selecting aramid precipitate A, dispersing it in water at 15000 rpm and then uniformly dispersing it to obtain aramid precipitate slurry; Pitch-based carbon fiber B with a length of 7 mm, a diameter of 13 μm, a resistivity of 2.0 μΩ·m, a tensile strength of 2.3 GPa, and an elongation at break of 0.25% was selected. The pitch-based carbon fiber was added according to the absolute dry mass ratio of the pitch-based carbon fiber to the aramid pulp of 35%:65%, and then 10 mL of a PAM dispersion with a concentration of 6 g / L was added. The mixture was dispersed uniformly at 15,000 rpm to obtain a mixed fiber slurry C. The mixed fiber slurry C is then poured into a paper sheet former to form a wet paper web D. Finally, wool felt was placed on both sides to absorb moisture, and then dried in a paper dryer at 105°C and a vacuum degree of 0.096 MPa for 10 min to obtain pitch-based carbon fiber aramid paper E; Step 2, dissolving 3 g of phenolic resin powder in 250 ml of anhydrous ethanol to obtain a phenolic resin-ethanol blend system F; The prepared asphalt-based carbon fiber aramid paper E was then impregnated in a phenolic resin-ethanol blend system F for 5 minutes, and then placed in an oven and dried at 115°C for 1 hour to obtain a resin-impregnated asphalt-based carbon fiber aramid base paper G. The prepared resin-impregnated carbon fiber paper G was hot-pressed on a flat vulcanizer at 150° C. and 10 MPa for 5 min to obtain a hot-pressed carbon fiber aramid paper H.

[0034] Step 3: Mix 1.5 g of VO2 powder and 6 g of phenolic resin powder evenly, add 10 ml of anhydrous ethanol solution, and continue stirring until the solution becomes viscous to obtain a colloidal system I.

[0035] The hot-pressed carbon fiber aramid paper was flattened and the surface was evenly coated with colloidal system I with a coating thickness of 1 mm using a brush. The paper was then placed in an oven and dried at 115°C for 1 hour. The paper was then hot-pressed on a flat-plate vulcanizer at 150°C and 10 MPa for 5 minutes to obtain a thermally induced phase change smart absorbing paper.

[0036] The smart absorbing paper prepared in this embodiment has a basis weight of 95g / m 2 The ratio of carbon fiber to aramid precipitation is 35%:65%. At a temperature of 25°C, the minimum reflection loss reaches -27.60dB, and the maximum absorption bandwidth is 5.60GHz, which has microwave absorption characteristics.

[0037] Example 3 Step 1, selecting aramid precipitate A, dispersing it in water at 15000 rpm and then uniformly dispersing it to obtain aramid precipitate slurry; Pitch-based carbon fiber B with a length of 7 mm, a diameter of 13 μm, a resistivity of 2.0 μΩ·m, a tensile strength of 2.3 GPa, and an elongation at break of 0.25% was selected. The pitch-based carbon fiber was added according to the absolute dry mass ratio of the pitch-based carbon fiber to the aramid pulp of 43%:57%. Then, 10 mL of a PAM dispersion with a concentration of 6 g / L was added. The mixture was dispersed uniformly at 15,000 rpm to obtain a mixed fiber slurry C. The mixed fiber slurry C is then poured into a paper sheet former to form a wet paper web D. Finally, wool felt was placed on both sides to absorb moisture, and then dried in a paper dryer at 105°C and a vacuum degree of 0.096 MPa for 10 min to obtain pitch-based carbon fiber aramid paper E; Step 2, dissolving 3 g of phenolic resin powder in 250 ml of anhydrous ethanol to obtain a phenolic resin-ethanol blend system F; The prepared asphalt-based carbon fiber aramid paper E was then impregnated in a phenolic resin-ethanol blend system F for 5 minutes, and then placed in an oven and dried at 115°C for 1 hour to obtain a resin-impregnated asphalt-based carbon fiber aramid base paper G. The prepared resin-impregnated carbon fiber paper G was hot-pressed on a flat vulcanizer at 150° C. and 10 MPa for 5 min to obtain a hot-pressed carbon fiber aramid paper H.

[0038] Step 3: Mix 1.5 g of VO2 powder and 6 g of phenolic resin powder evenly, add 10 ml of anhydrous ethanol solution, and continue stirring until the solution becomes viscous to obtain a colloidal system I.

[0039] The hot-pressed carbon fiber aramid paper was flattened and the surface was evenly coated with colloidal system I with a coating thickness of 1 mm using a brush. The paper was then placed in an oven and dried at 115°C for 1 hour. The paper was then hot-pressed on a flat-plate vulcanizer at 150°C and 10 MPa for 5 minutes to obtain a thermally induced phase change smart absorbing paper.

[0040] The smart absorbing paper prepared in this embodiment has a basis weight of 95g / m 2 The ratio of carbon fiber to aramid precipitation is 43%:57%. At a temperature of 70°C, the minimum reflection loss reaches -44.73dB, and the maximum absorption bandwidth is 4.81GHz, which has microwave absorption characteristics.

[0041] Example 4 Step 1, selecting aramid precipitate A, dispersing it in water at 15000 rpm and then uniformly dispersing it to obtain aramid precipitate slurry; Pitch-based carbon fiber B with a length of 7 mm, a diameter of 13 μm, a resistivity of 2.0 μΩ·m, a tensile strength of 2.3 GPa, and an elongation at break of 0.25% was selected. The pitch-based carbon fiber was added according to the absolute dry mass ratio of the pitch-based carbon fiber to the aramid pulp of 43%:57%. Then, 10 mL of a PAM dispersion with a concentration of 6 g / L was added. The mixture was dispersed uniformly at 15,000 rpm to obtain a mixed fiber slurry C. The mixed fiber slurry C is then poured into a paper sheet former to form a wet paper web D. Finally, wool felt was placed on both sides to absorb moisture, and then dried in a paper dryer at 105°C and a vacuum degree of 0.096 MPa for 10 min to obtain pitch-based carbon fiber aramid paper E; Step 2, dissolving 3 g of phenolic resin powder in 250 ml of anhydrous ethanol to obtain a phenolic resin-ethanol blend system F; The prepared asphalt-based carbon fiber aramid paper E was then impregnated in a phenolic resin-ethanol blend system F for 5 minutes, and then placed in an oven and dried at 115°C for 1 hour to obtain a resin-impregnated asphalt-based carbon fiber aramid base paper G. The prepared resin-impregnated carbon fiber paper G was hot-pressed on a flat vulcanizer at 150° C. and 10 MPa for 5 min to obtain a hot-pressed carbon fiber aramid paper H.

[0042] Step 3: Mix 1.5 g of VO2 powder and 6 g of phenolic resin powder evenly, add 10 ml of anhydrous ethanol solution, and continue stirring until the solution becomes viscous to obtain a colloidal system I.

[0043] The hot-pressed carbon fiber aramid paper was flattened and the surface was evenly coated with colloidal system I with a coating thickness of 1 mm using a brush. The paper was then placed in an oven and dried at 115°C for 1 hour. The paper was then hot-pressed on a flat-plate vulcanizer at 150°C and 10 MPa for 5 minutes to obtain a thermally induced phase change smart absorbing paper.

[0044] The smart absorbing paper prepared in this embodiment has a basis weight of 95g / m 2 The ratio of carbon fiber to aramid precipitation is 43%:57%. At a temperature of 25°C, the minimum reflection loss reaches -53.41dB, and the maximum absorption bandwidth is 5.60GHz, which has microwave absorption characteristics.

[0045] Example 5 Step 1, selecting aramid precipitate A, dispersing it in water at 15000 rpm and then uniformly dispersing it to obtain aramid precipitate slurry; Pitch-based carbon fiber B with a length of 7 mm, a diameter of 13 μm, a resistivity of 2.0 μΩ·m, a tensile strength of 2.3 GPa, and an elongation at break of 0.25% was selected. The pitch-based carbon fiber was added according to the absolute dry mass ratio of the pitch-based carbon fiber to the aramid pulp of 51%:49%. Then, 10 mL of a PAM dispersion with a concentration of 6 g / L was added. The mixture was dispersed uniformly at 15,000 rpm to obtain a mixed fiber slurry C. The mixed fiber slurry C is then poured into a paper sheet former to form a wet paper web D. Finally, wool felt was placed on both sides to absorb moisture, and then dried in a paper dryer at 105°C and a vacuum degree of 0.096 MPa for 10 min to obtain pitch-based carbon fiber aramid paper E; Step 2, dissolving 3 g of phenolic resin powder in 250 ml of anhydrous ethanol to obtain a phenolic resin-ethanol blend system F; The prepared asphalt-based carbon fiber aramid paper E was then impregnated in a phenolic resin-ethanol blend system F for 5 minutes, and then placed in an oven and dried at 115°C for 1 hour to obtain a resin-impregnated asphalt-based carbon fiber aramid base paper G. The prepared resin-impregnated carbon fiber paper G was hot-pressed on a flat vulcanizer at 150° C. and 10 MPa for 5 min to obtain a hot-pressed carbon fiber aramid paper H.

[0046] Step 3: Mix 1.5 g of VO2 powder and 6 g of phenolic resin powder evenly, add 10 ml of anhydrous ethanol solution, and continue stirring until the solution becomes viscous to obtain a colloidal system I.

[0047] The hot-pressed carbon fiber aramid paper was flattened and the surface was evenly coated with colloidal system I with a coating thickness of 1 mm using a brush. The paper was then placed in an oven and dried at 115°C for 1 hour. The paper was then hot-pressed on a flat-plate vulcanizer at 150°C and 10 MPa for 5 minutes to obtain a thermally induced phase change smart absorbing paper.

[0048] The smart absorbing paper prepared in this embodiment has a basis weight of 95g / m 2 The carbon fiber and aramid precipitation ratio is 51%:49%. At a temperature of 70°C, the minimum reflection loss reaches -25.77dB, and the maximum absorption bandwidth is 6.56GHz. It has microwave absorption characteristics and has good social and economic benefits. Figure 3 、 4 , it can be seen that VO2 powder particles are attached to the surface of the paper. Figure 5 , VO2 is coated on the surface of the paper to form a metal oxide coating.

[0049] Example 6 Step 1, selecting aramid precipitate A, dispersing it in water at 15000 rpm and then uniformly dispersing it to obtain aramid precipitate slurry; Pitch-based carbon fiber B with a length of 7 mm, a diameter of 13 μm, a resistivity of 2.0 μΩ·m, a tensile strength of 2.3 GPa, and an elongation at break of 0.25% was selected. The pitch-based carbon fiber was added according to the absolute dry mass ratio of the pitch-based carbon fiber to the aramid pulp of 51%:49%. Then, 10 mL of a PAM dispersion with a concentration of 6 g / L was added. The mixture was dispersed uniformly at 15,000 rpm to obtain a mixed fiber slurry C. The mixed fiber slurry C is then poured into a paper sheet former to form a wet paper web D. Finally, wool felt was placed on both sides to absorb moisture, and then dried in a paper dryer at 105°C and a vacuum degree of 0.096 MPa for 10 min to obtain pitch-based carbon fiber aramid paper E; Step 2, dissolving 3 g of phenolic resin powder in 250 ml of anhydrous ethanol to obtain a phenolic resin-ethanol blend system F; The prepared asphalt-based carbon fiber aramid paper E was then impregnated in a phenolic resin-ethanol blend system F for 5 minutes, and then placed in an oven and dried at 115°C for 1 hour to obtain a resin-impregnated asphalt-based carbon fiber aramid base paper G. The prepared resin-impregnated carbon fiber paper G was hot-pressed on a flat vulcanizer at 150° C. and 10 MPa for 5 min to obtain a hot-pressed carbon fiber aramid paper H.

[0050] Step 3: Mix 1.5 g of VO2 powder and 6 g of phenolic resin powder evenly, add 10 ml of anhydrous ethanol solution, and continue stirring until the solution becomes viscous to obtain a colloidal system I.

[0051] The hot-pressed carbon fiber aramid paper was flattened and the surface was evenly coated with colloidal system I with a coating thickness of 1 mm using a brush. The paper was then placed in an oven and dried at 115°C for 1 hour. The paper was then hot-pressed on a flat-plate vulcanizer at 150°C and 10 MPa for 5 minutes to obtain a thermally induced phase change smart absorbing paper.

[0052] The smart absorbing paper prepared in this embodiment has a basis weight of 95g / m 2 The ratio of carbon fiber to aramid precipitation is 51%:49%. At a temperature of 25°C, the minimum reflection loss reaches -49.67dB, and the maximum absorption bandwidth is 4.11GHz, which has microwave absorption characteristics.

[0053] Table 1 Technical parameters of carbon fiber base paper prepared in Examples 1 to 6

[0054] Table 1 shows the technical parameters of the carbon fiber aramid paper prepared in the embodiment. Figures 6 to 11 The microwave absorption performance test graph of the absorbing paper obtained in Experiments 1 to 6 under the electric + magnetic mode. According to the data analysis, the carbon fiber aramid paper prepared by the process provided by the present invention has a minimum reflection loss within the range of -59.09 to -25.77 dB and a maximum absorption bandwidth within the range of 4.11 to 6.56 GHz. Figure 10 The microwave absorbing paper obtained in Example 5 exhibits excellent absorbing performance. This is because the carbon fiber and aramid precipitate are fully interwoven, and after being impregnated with phenolic resin and hot pressed, a rich conductive network is formed, which achieves higher conductivity and enhances interface polarization and conduction loss. At the same time, at a temperature of 70°C, VO2 reaches the phase transition temperature and transforms into a metallic state, significantly improving the dielectric loss, forming a "dual loss channel" with the magnetic loss mechanism, realizing "dielectric-magnetic loss coupling", and improving the absorbing performance.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and replacements, and these modifications and replacements are also within the scope of protection covered by the claims.

Claims

1. A process for preparing a thermally induced phase change intelligent absorbing paper based on VO2 coating, characterized in that: The following steps are involved: S1, using aramid precipitate A, pitch-based carbon fiber B and PAM dispersant as raw materials, a wet forming process was used to prepare pitch-based carbon fiber aramid paper E; S2, impregnating the asphalt-based carbon fiber aramid paper E in the phenolic resin-ethanol blend system F, and then vacuum drying and hot pressing to obtain the carbon fiber paper H; S3, coating the carbon fiber paper H with VO2 dispersion, and then drying and hot pressing to obtain the thermo-induced phase change smart absorbing paper.

2. The process for preparing the thermally induced phase change intelligent absorbing paper based on VO2 coating according to claim 1, characterized in that: In S1, the specific process of preparing aramid paper is as follows: S11, adding aramid precipitate A to water, dispersing and dispersing to obtain aramid precipitate slurry, then adding pitch-based carbon fiber B to the aramid precipitate slurry and mixing evenly, and then adding PAM dispersant to dispersing and dispersing to obtain mixed fiber slurry C; S12, homogenizing and dehydrating the mixed fiber slurry C to obtain a wet paper web D; S13, absorbing moisture from both sides of the wet paper web D, and then vacuum drying to obtain aramid carbon fiber paper E.

3. The process for preparing the thermally induced phase change intelligent absorbing paper based on VO2 coating according to claim 2, characterized in that: In S11, the absolute dry mass ratio of the added asphalt-based carbon fiber to the aramid precipitate is 30%~60%:40%~70%.

4. The process for preparing the thermally induced phase change intelligent absorbing paper based on VO2 coating according to claim 1, characterized in that: In S2, the preparation method of the phenolic resin-ethanol blend system F is: dissolving the phenolic resin powder in ethanol to obtain the phenolic resin-ethanol blend system F, wherein the solid content of the phenolic resin powder is 1 wt%~2 wt%.

5. The process for preparing the thermally induced phase change intelligent absorbing paper based on VO2 coating according to claim 1, characterized in that: In S2, during the impregnation, the asphalt-based carbon fiber aramid paper E was completely immersed in the phenolic resin-ethanol blend system F, and the impregnation time was 5-10 min; During vacuum drying, the vacuum degree is 0.096~0.098MPa, the temperature is 95~115℃, and the time is 0.5~1h; During hot pressing finishing, the temperature is 140~150℃, the pressure is 9~10MPa, and the time is 5~8min.

6. The process for preparing the thermally induced phase change intelligent absorbing paper based on VO2 coating according to claim 1, characterized in that: In S3, the VO2 dispersion is prepared by shaking and mixing the VO2 powder and the phenolic resin powder, adding anhydrous ethanol solution, and continuously stirring until a colloidal system is obtained, which is the VO2 dispersion.

7. The process for preparing the thermally induced phase change intelligent absorbing paper based on VO2 coating according to claim 6, characterized in that: The amount of VO2 powder used is 1~3g, and the amount of phenolic resin powder used is 3~9g.

8. The process for preparing the thermally induced phase change intelligent absorbing paper based on VO2 coating according to claim 1, characterized in that: In S3, during drying, the temperature is 140-150°C, the pressure is 9-10 MPa, and the time is 0.5-1 h; During hot pressing finishing, the temperature is 140~150℃, the pressure is 9~10MPa, and the time is 5~8min.

9. A thermo-induced phase change smart absorbing paper obtained by the preparation process of thermo-induced phase change smart absorbing paper based on VO2 coating according to any one of claims 1 to 8.

10. Use of the thermoinduced phase change intelligent absorbing paper according to claim 9 in the field of microwave absorption.

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