Recycled carbon fiber-viscose-based carbon fiber thermal insulation material and preparation method thereof

Abstract

The invention provides a recycled carbon fiber-viscose-based carbon fiber thermal insulation material and a preparation method thereof, and belongs to the technical field of thermal insulation materials. The method comprises the following steps: dispersing chopped recycled carbon fibers and viscose staple fibers in a mixed aqueous solution, carrying out wet molding on the obtained mixed staple fiber slurry, and drying to obtain a mixed staple fiber preform; the mixed short fiber preform is sequentially subjected to primary dipping, primary hot-pressing curing, primary heat treatment, secondary dipping, secondary hot-pressing curing and secondary heat treatment, and the recycled carbon fiber-viscose-based carbon fiber heat preservation and insulation material is obtained. The short carbon fibers disorderly distributed in the thermal insulation material prolong the phonon transmission path and reduce the thermal conductivity of the system; the viscose-based fiber precursor generates a large number of pore structures due to shrinkage in the carbonization process, and the recycled carbon fiber plays a structural supporting role in the system, so that the porosity of the system is further increased, and the final thermal insulation capability of the product is enhanced.

Description

Technical Field

[0001] This invention relates to the field of thermal insulation materials, and in particular to a recycled carbon fiber-viscose-based carbon fiber thermal insulation material and its preparation method. Background Technology

[0002] In critical fields such as aerospace and high-temperature thermal engineering, thermal insulation materials play an irreplaceable role. The demand for high-temperature thermal protection materials continues to grow with technological advancements and industry expansion. However, when operating under sustained high-temperature environments, traditional thermal insulation materials are prone to performance degradation, shortened lifespan, or functional failure, potentially leading to increased maintenance costs and energy consumption for thermal protection equipment. Carbon-based thermal insulation materials, with their advantages of high-temperature resistance, low density, good thermal insulation, excellent thermal stability, and low coefficient of thermal expansion, can meet the increasingly diverse extreme high-temperature operating environments and better satisfy the growing demands of high-temperature protection equipment for lightweight, high-insulation, and high-stability thermal insulation materials. Therefore, developing a low-cost, environmentally friendly carbon fiber thermal insulation material and its preparation method is of significant practical importance.

[0003] Invention patent CN202411093313.6 describes a method for obtaining a viscose-based thermal insulation composite material by pretreating viscose fibers, followed by carbonization and chopping, then secondary pretreatment, phenolic resin mixing and curing, and high-temperature heat treatment. This method can produce thermal insulation materials with good thermal insulation performance, but the carbonization process of the secondary pretreatment of viscose fibers makes the preparation process cumbersome and significantly increases energy consumption. Invention patents CN201910290913.4 and CN202210571216.8 describe a method for obtaining a thermal insulation material by pulverizing, washing, and drying short carbon fibers recovered from pyrolysis. The recycled carbon fiber insulation material is obtained after being mixed with resin, molded and cured in a mold, and then demolded and carbonized. This method can effectively utilize recycled short-cut carbon fibers, but the relatively high viscosity of the resin in the slurry can easily lead to uneven system performance when mixed with the fiber. Invention patent CN202410226169.2 controls the size of the recycled carbon fiber after crushing to the micron level, and then mixes the crushed carbon fiber with resin. After curing and carbonization, a lightweight porous carbon brick is obtained. This method improves the uniformity of the system, but the excessively small fiber size can easily lead to insufficient mechanical properties.

[0004] Viscose-based carbon fiber and its derivatives possess excellent thermal insulation properties and high purity, making them frequently used in the development of thermal protection materials. However, the production of virgin carbon fiber is complex and energy-intensive, resulting in persistently high costs. Furthermore, the use and promotion of virgin carbon fiber inevitably increases resource consumption and greenhouse gas emissions, hindering the large-scale application and widespread adoption of carbon fiber and its derivatives. In addition, with the increasing prevalence of carbon fiber products, the disposal of carbon fiber and its derivatives after their service life has become a growing concern, leading to increasing emphasis on the recycling and reuse of carbon fiber.

[0005] Therefore, developing an environmentally friendly technical route that has a wide range of raw material sources, low cost and energy consumption, simple process, and can reduce greenhouse gas emissions, to prepare carbon fiber thermal insulation materials with excellent comprehensive performance is of great value and practical significance. Summary of the Invention

[0006] The purpose of this invention is to provide a recycled carbon fiber-viscose-based carbon fiber thermal insulation material and its preparation method. The carbon fiber thermal insulation material prepared by this invention has the advantages of uniform system, lightweight, and excellent thermal insulation performance, providing a new approach for low-cost and controllable preparation of carbon fiber thermal insulation materials, improving resource utilization, and effectively promoting the green circular ecological construction of carbon-based materials. This invention can effectively recycle recycled carbon fibers, solve the problem of uneven dispersion in short fiber molding, and overcome the problems of high raw material prices and process costs, excessive energy consumption, and cumbersome production processes that are common in the current preparation of carbon fiber reinforced thermal insulation materials.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing recycled carbon fiber-viscose-based carbon fiber thermal insulation material, comprising the following steps: 1) Short-cut recycled carbon fibers and viscose staple fibers are dispersed in a mixed aqueous solution to obtain a mixed staple fiber slurry; the mixed aqueous solution contains a dispersant, a binder, and water; 2) The mixed short fiber slurry is wet-molded and then dried to obtain a mixed short fiber preform; 3) The mixed short fiber preform is subjected to one impregnation, one hot-press curing, one heat treatment, a second impregnation, a second hot-press curing, and a second heat treatment in sequence to obtain recycled carbon fiber-viscose-based carbon fiber thermal insulation material.

[0008] Preferably, in step 1), the length of the chopped recycled carbon fiber is 1-10 mm, the length of the viscose short fiber is 1-15 mm, the total mass fraction of the chopped recycled carbon fiber and viscose short fiber in the mixed aqueous solution is 0.1-1.0%, and the mass ratio of the chopped recycled carbon fiber to the viscose short fiber is 0.5-4:1; in the mixed aqueous solution, the mass fraction of the dispersant is 0.05-0.5%, and the mass fraction of the binder is 0.01-0.5%.

[0009] Preferably, the dispersant in step 1) comprises one or more of polyacrylamide, sodium polyacrylate, sodium carboxymethyl cellulose, polyethylene oxide, hydroxymethyl cellulose, hydroxyethyl cellulose, and polyvinylpyrrolidone, and the binder comprises one or more of polyvinyl alcohol, waterborne polyurethane, and modified starch.

[0010] Preferably, the drainage method in the wet molding process of step 2) is vacuum dehydration and / or pressure filtration drainage, with a drainage pressure of 0.02~1MPa.

[0011] Preferably, the impregnation solution used for the first and second impregnation in step 3) is a phenolic resin solution, wherein the mass fraction of phenolic resin in the phenolic resin solution is 5-25%, and the solvent is one or more of anhydrous ethanol, methanol, acetone and ethyl acetate. The first impregnation time is 10~60min, the second impregnation is atmospheric pressure impregnation or vacuum impregnation, the temperature of the second impregnation is 25~50℃, the time is 10~120min, and the pressure of vacuum impregnation is -1~-0.08MPa.

[0012] Preferably, in step 3), after the first immersion, a first drying is performed, and after the second immersion, a second drying is performed. The temperature for the first drying and the second drying are independently 80~100℃, and the time is independently 60~120min.

[0013] Preferably, in step 3), the temperatures for the primary and secondary hot-press curing processes are independently 120~180℃, the time is independently 60~180min, and the pressure is independently 0.1~2MPa; the rates of heating to the primary hot-press curing temperature and heating to the secondary hot-press curing temperature are independently 1~10℃ / min.

[0014] Preferably, the heat treatment in step 3) is either a low-temperature heat treatment or a high-temperature heat treatment. The low-temperature heat treatment is carried out in an air atmosphere, with a temperature of 200~350℃ and a time of 10~60min. The high-temperature heat treatment is carried out in a nitrogen atmosphere, with a temperature of 350~1000℃ and a time of 10~20min. The heating rates to the low-temperature heat treatment temperature and to the high-temperature heat treatment temperature are independent and are 1~10℃ / min.

[0015] Preferably, the secondary heat treatment in step 3) is carried out in two stages under a protective atmosphere. The temperature of the first stage heat treatment is 1000~1500℃, the time is 10~30min, and the rate of heating to the temperature of the first stage heat treatment is 1~10℃ / min. The temperature of the second stage heat treatment is 1500~2200℃, the time is 15~60min, and the rate of heating to the temperature of the second stage heat treatment is 1~5℃ / min. The protective atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0016] The present invention also provides a method for preparing the recycled carbon fiber-viscose-based carbon fiber thermal insulation material, resulting in a recycled carbon fiber-viscose-based carbon fiber thermal insulation material.

[0017] The beneficial effects of this invention are: 1) The raw materials used in this invention are chopped recycled carbon fiber and viscose-based precursor fiber. Both types of fiber raw materials have the advantage of low cost compared to expensive virgin carbon fiber. The raw material sources are relatively wide, which effectively reduces energy consumption. Furthermore, the application and promotion of recycled carbon fiber helps to realize the recycling and reuse of carbon fiber waste resources, thereby effectively promoting the green and circular ecological construction of the carbon fiber material industry.

[0018] 2) This invention uses short fiber wet molding and wet-molded composite short fiber preform structure to prepare environmentally friendly carbon fiber reinforced thermal insulation material through resin impregnation, hot pressing curing and heat treatment. The method of this invention has low energy consumption, low cost, simple process and good reaction controllability, which helps to effectively reduce costs and promote large-scale industrial production and application.

[0019] 3) The recycled carbon fiber-viscose-based carbon fiber thermal insulation material of this invention features randomly arranged and interwoven short fibers. This disordered distribution of short carbon fibers extends the phonon transmission path, thus reducing the system's thermal conductivity. During carbonization, the viscose-based fiber precursors shrink, creating numerous porous structures. The presence of recycled carbon fibers maintains the basic structural morphology of the system, providing structural support and further increasing its porosity, thereby enhancing the final thermal insulation capability of the product. The multi-defect and small-sized microcrystalline structure of the viscose-based carbon fibers reduces heat conduction pathways, thus imparting superior thermal insulation performance to the material. The recycled carbon fiber-viscose-based carbon fiber thermal insulation material prepared by this invention is lightweight, high-temperature resistant, and possesses excellent thermal insulation properties. While contributing to the technological development in the field of high-temperature thermal protection, it can effectively drive the improvement of the upstream and downstream industrial chain of carbon fiber resource recycling and reuse, thus providing new ideas for developing novel green and environmentally friendly carbon fiber thermal insulation materials. Attached Figure Description

[0020] Figure 1SEM image of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material prepared in Example 1; Figure 2 This is a high-magnification SEM image of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material prepared in Example 1. Figure 3 SEM image of the short-cut recycled carbon fiber composite material prepared in Comparative Example 1; Figure 4 SEM image of the viscose short fiber composite material prepared in Comparative Example 2; Figure 5 SEM image of the composite material prepared from the short-cut virgin carbon fibers of Comparative Example 3. Detailed Implementation

[0021] This invention provides a method for preparing recycled carbon fiber-viscose-based carbon fiber thermal insulation material, comprising the following steps: 1) Short-cut recycled carbon fibers and viscose staple fibers are dispersed in a mixed aqueous solution to obtain a mixed staple fiber slurry; the mixed aqueous solution contains a dispersant, a binder, and water; 2) The mixed short fiber slurry is wet-molded and then dried to obtain a mixed short fiber preform; 3) The mixed short fiber preform is subjected to one impregnation, one hot-press curing, one heat treatment, a second impregnation, a second hot-press curing, and a second heat treatment in sequence to obtain recycled carbon fiber-viscose-based carbon fiber thermal insulation material.

[0022] In this invention, the length of the chopped recycled carbon fiber in step 1) is preferably 1-10 mm, more preferably 3-8 mm, and even more preferably 4-6 mm; the length of the viscose short fiber is preferably 1-15 mm, more preferably 3-10 mm, and even more preferably 5-8 mm; the total mass fraction of the chopped recycled carbon fiber and viscose short fiber in the mixed aqueous solution is preferably 0.1-1.0%, more preferably 0.3-0.8%, and even more preferably 0.5-0.6%; the mass ratio of the chopped recycled carbon fiber to the viscose short fiber is preferably 0.5-4:1, more preferably 1-3:1, and even more preferably 2-2.5:1; in the mixed aqueous solution, the mass fraction of the dispersant is preferably 0.05-0.5%, more preferably 0.1-0.4%, and even more preferably 0.2-0.3%; the mass fraction of the binder is preferably 0.01-0.5%, more preferably 0.02-0.4%, and even more preferably 0.1-0.3%.

[0023] In this invention, the length of the chopped recycled carbon fibers and the mass fraction of viscose short fibers in the aqueous solution make them more uniformly dispersed in water. The composite fiber system after wet molding has both a certain mechanical strength and a porous structure, which helps to produce carbon fiber thermal insulation materials with complete structure, uniform system and good comprehensive performance.

[0024] In this invention, the dispersant in step 1) preferably comprises one or more of polyacrylamide, sodium polyacrylate, sodium carboxymethyl cellulose, polyethylene oxide, hydroxymethyl cellulose, hydroxyethyl cellulose and polyvinylpyrrolidone, and the binder preferably comprises one or more of polyvinyl alcohol, waterborne polyurethane and modified starch.

[0025] In this invention, the drainage method in the wet molding process described in step 2) is preferably vacuum dehydration and / or pressure filtration drainage, and the drainage pressure is preferably 0.02~1MPa, more preferably 0.05~0.5MPa, and even more preferably 0.1~0.4MPa.

[0026] The mixed short fiber slurry of the present invention is wet-formed in a wet forming equipment to separate the short fibers from water and form a preliminary shape.

[0027] In this invention, the impregnation solution used for the first and second impregnation in step 3) is preferably a phenolic resin solution. The mass fraction of phenolic resin in the phenolic resin solution is preferably 5-25%, more preferably 8-22%, and even more preferably 10-20%. The solvent is preferably one or more of anhydrous ethanol, methanol, acetone, and ethyl acetate. The first immersion time is preferably 10-60 min, more preferably 20-50 min, and even more preferably 30-40 min. The first immersion is carried out at room temperature and pressure. The second immersion is preferably atmospheric pressure immersion or vacuum immersion. The temperature of the second immersion is preferably 25-50℃, more preferably 30-45℃, and even more preferably 35-40℃. The time of the second immersion is preferably 10-120 min, more preferably 30-100 min, and even more preferably 50-70 min. The pressure of the vacuum immersion is preferably -1 to -0.08 MPa, more preferably -0.8 to -0.095 MPa, and even more preferably -0.6 to -0.2 MPa.

[0028] In this invention, after the first impregnation in step 3), it is preferable to perform a first drying, and after the second impregnation, it is preferable to perform a second drying. The temperature of the first drying and the second drying is preferably 80~100℃, more preferably 85~95℃, and more preferably 90℃. The time of the first drying and the second drying is preferably 60~120min, more preferably 70~100min, and more preferably 80~90min.

[0029] In this invention, the temperatures for the primary and secondary hot-press curing in step 3) are preferably 120-180°C, more preferably 130-160°C, and even more preferably 140-150°C; the times for the primary and secondary hot-press curing are preferably 60-180 min, more preferably 80-150 min, and even more preferably 100-130 min; the pressure is preferably 0.1-2 MPa, more preferably 0.5-1.2 MPa, and even more preferably 0.8-1 MPa; and the rates of heating to the primary and secondary hot-press curing temperatures are preferably 1-10°C / min, more preferably 3-8°C / min, and even more preferably 5-6°C / min.

[0030] In this invention, the primary heat treatment in step 3) is preferably a low-temperature heat treatment or a high-temperature heat treatment. The low-temperature heat treatment is preferably carried out in an air atmosphere, and the temperature of the low-temperature heat treatment is preferably 200~350℃, more preferably 250~300℃. The time of the low-temperature heat treatment is preferably 10~60min, more preferably 15~50min, and more preferably 20~40min. The high-temperature heat treatment is preferably carried out in a nitrogen atmosphere, and the temperature of the high-temperature heat treatment is preferably 350~1000℃, more preferably 450~800℃, and more preferably 550~700℃. The time of the high-temperature heat treatment is preferably 10~20min, more preferably 12~18min, and more preferably 15~16min. The rates of heating to the low-temperature heat treatment temperature and heating to the high-temperature heat treatment temperature are independent and preferably 1~10℃ / min, more preferably 3~8℃ / min, and more preferably 5~6℃ / min.

[0031] In this invention, the secondary heat treatment in step 3) is preferably carried out in two stages under a protective atmosphere. The temperature of the first stage heat treatment is preferably 1000~1500℃, more preferably 1200~1450℃, and even more preferably 1300~1400℃. The time of the first stage heat treatment is preferably 10~30 min, more preferably 15~25 min, and even more preferably 20 min. The rate of heating to the first stage heat treatment temperature is preferably 1~10℃ / min, more preferably 2~8℃ / min, and even more preferably 5~6℃ / min. The temperature of the second stage heat treatment is preferably 1500~2200℃, more preferably 1600~2000℃, and even more preferably 1700~1800℃. The time of the second stage heat treatment is preferably 15~60min, more preferably 20~50min, and even more preferably 30~40min. The rate of heating to the second stage heat treatment temperature is preferably 1~5℃ / min, more preferably 2~4℃ / min, and even more preferably 3℃ / min. The protective atmosphere is preferably a nitrogen atmosphere or an argon atmosphere.

[0032] The present invention also provides a method for preparing the recycled carbon fiber-viscose-based carbon fiber thermal insulation material, resulting in a recycled carbon fiber-viscose-based carbon fiber thermal insulation material.

[0033] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0034] In the examples and comparative examples, the polyacrylamide was anionic polyacrylamide with a molecular weight of 10 million, purchased from Shanghai Titan Technology Co., Ltd.; the polyvinyl alcohol was type 1788 with a monomer molecular weight of 44.05, purchased from Aladdin Biochemical Technology Co., Ltd.; the phenolic resin was thermosetting phenolic resin, model Ron RH804391; the waterborne polyurethane was anionic waterborne polyurethane with a molecular weight of 20,000, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; and the polyvinylpyrrolidone was model K30 with a molecular weight of 50,000, purchased from Shanghai Titan Technology Co., Ltd. Viscose staple fiber was purchased from Tangshan Sanyou Group Co., Ltd., model FR-W; chopped recycled carbon fiber was purchased from Nantong Woyuan New Material Technology Co., Ltd., model OY-T300. The wet molding equipment was purchased from Guangdong Fuaibo Fiber Technology Research Co., Ltd., specifically named an intermittent fiber composite material molding machine, model Sheet Former 200F.

[0035] Example 1

[0036] Polyacrylamide and polyvinyl alcohol were sequentially added to deionized water under magnetic stirring at 500 rpm. After stirring for 12 hours, the mixture was fully dissolved to obtain a mixed aqueous solution with a polyacrylamide mass fraction of 0.3% and a polyvinyl alcohol mass fraction of 0.15%. Short-cut recycled carbon fibers (3-6 mm in length) and viscose short fibers (5-10 mm in length) in a mass ratio of 1:1 were added to the mixed aqueous solution, with a total mass fraction of 0.4% for the mixed short fibers. The mixed short fibers were stirred in the solution at 300 rpm to fully disperse them, obtaining a mixed short fiber slurry.

[0037] The mixed short fiber slurry is transferred to a wet molding equipment. The wet molding process is used to remove water from the slurry under a pressure of 0.5 MPa. After the mixed short fibers are initially formed on the filter screen, they are fully dried at 80°C and demolded to obtain a chopped recycled carbon fiber-viscose fiber preform.

[0038] At room temperature and pressure, the chopped recycled carbon fiber-viscose fiber preform was initially impregnated in a phenolic resin solution (anhydrous ethanol as solvent, with a phenolic resin mass fraction of 10%) for 30 min. After impregnation, it was dried at 90℃ for 90 min, then heated to 150℃ at a heating rate of 5℃ / min, and initially hot-pressed at 150℃ and 0.2 MPa for 120 min to obtain a composite short fiber cured material. The composite short fiber cured material was then subjected to preliminary heat treatment in air atmosphere, with a heating rate of 5℃ / min. The temperature was increased from room temperature to 200℃ and held for 15 min, then increased to 250℃ and held for 20 min, and finally increased to 300℃ and held for 20 min to obtain a pre-oxidized material. The pre-oxidized material undergoes secondary resin impregnation, secondary drying, and secondary hot-press curing (process parameters are the same as the initial impregnation, initial drying, and initial hot-press curing, the only difference being that the secondary impregnation is carried out under vacuum at 35℃ and -0.8MPa negative pressure) to obtain a secondary cured felt. The secondary cured felt is then subjected to a secondary heat treatment, which is carried out in two stages under an argon atmosphere. In the first stage, the temperature is increased to 1300℃ at a rate of 5℃ / min and held for 10 min; in the second stage, the temperature is increased to 2000℃ at a rate of 5℃ / min and held for 20 min to obtain a recycled carbon fiber-viscose-based carbon fiber thermal insulation material.

[0039] The density of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material in this embodiment is 0.126 g / cm³. 3 The thermal conductivity is 0.109 W / (m·K), and the compressive strength is 0.589 MPa. The SEM image of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material prepared in Example 1 is shown below. Figure 1 As shown, the SEM images at higher magnification are as follows: Figure 2 As shown, by Figure 1 and Figure 2 It is known that the recycled carbon fiber-viscose-based carbon fiber thermal insulation material is composed of recycled carbon fiber and viscose-based carbon fiber. The two types of short fibers are evenly distributed and interwoven with each other. The two types of short fibers are connected to each other through resin carbon and can be well bonded with the resin carbon. The synergistic effect between the recycled carbon fiber and viscose-based carbon fiber, as well as between the short fibers and the resin carbon, constitutes a complete network structure. The disordered network structure gives the system a high porosity. The recycled carbon fiber plays the role of supporting structure in the system. After carbonization, the viscose fiber can further increase the porosity of the material on the basis of this supporting structure. While ensuring its mechanical strength, it can also maintain excellent thermal insulation ability. Thus, the prepared environmentally friendly composite chopped carbon fiber thermal insulation material has excellent comprehensive performance and helps to promote the recycling of carbon fiber resources.

[0040] Example 2

[0041] In Example 1, the mass ratio of chopped recycled carbon fiber to viscose staple fiber was changed from 1:1 to 0.5:1, while other processes remained the same as in Example 1.

[0042] The density of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material in this embodiment is 0.124 g / cm³. 3 It has a thermal conductivity of 0.115 W / (m·K) and a compressive strength of 0.672 MPa.

[0043] Example 3

[0044] In Example 1, the mass ratio of chopped recycled carbon fiber and viscose staple fiber was changed from 1:1 to 2:1, while other processes remained the same as in Example 1.

[0045] The density of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material in this embodiment is 0.131 g / cm³. 3 It has a thermal conductivity of 0.106 W / (m·K) and a compressive strength of 0.587 MPa.

[0046] Example 4

[0047] The mass fraction of phenolic resin in the phenolic resin solution of Example 1 was changed from 10% to 20%, while other processes remained the same as in Example 1.

[0048] The density of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material in this embodiment is 0.169 g / cm³. 3 It has a thermal conductivity of 0.154 W / (m·K) and a compressive strength of 0.722 MPa.

[0049] Example 5

[0050] The mass fraction of phenolic resin in the phenolic resin solution of Example 1 was changed from 10% to 5%, while other processes remained the same as in Example 1.

[0051] The density of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material in this embodiment is 0.102 g / cm³. 3 It has a thermal conductivity of 0.099 W / (m·K) and a compressive strength of 0.459 MPa.

[0052] Example 6

[0053] In Example 1, the temperature of the first stage of the secondary heat treatment was changed from 1300℃ to 1400℃, and the temperature of the second stage was changed from 2000℃ to 2100℃. Other processes were the same as in Example 1.

[0054] The density of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material in this embodiment is 0.127 g / cm³. 3 It has a thermal conductivity of 0.112 W / (m·K) and a compressive strength of 0.591 MPa.

[0055] Example 7

[0056] In Example 1, the temperature of the first stage of the secondary heat treatment was changed from 1300℃ to 1200℃, and the temperature of the second stage was changed from 2000℃ to 1900℃. Other processes were the same as in Example 1.

[0057] The density of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material in this embodiment is 0.125 g / cm³. 3 It has a thermal conductivity of 0.111 W / (m·K) and a compressive strength of 0.586 MPa.

[0058] Example 8

[0059] The mass fraction of polyacrylamide in the mixed aqueous solution of Example 1 was changed from 0.3% to 0.1%, and the mass fraction of polyvinyl alcohol was changed from 0.15% to 0.05%. Other processes were the same as in Example 1.

[0060] The density of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material in this embodiment is 0.124 g / cm³. 3 It has a thermal conductivity of 0.116 W / (m·K) and a compressive strength of 0.594 MPa.

[0061] Example 9

[0062] Polyvinylpyrrolidone (PVP) and aqueous polyurethane were sequentially added to deionized water under magnetic stirring at 500 rpm. After stirring for 12 hours, the mixture was fully dissolved to obtain a mixed aqueous solution with a mass fraction of 0.4% for PPV and 0.3% for aqueous polyurethane. Short-cut recycled carbon fibers (5-7 mm in length) and viscose short fibers (3-7 mm in length) in a mass ratio of 3:1 were added to the mixed aqueous solution, with a total mass fraction of 0.7% for the mixed short fibers. The mixed short fibers were stirred in the solution at 300 rpm to fully disperse them, obtaining a mixed short fiber slurry.

[0063] The mixed short fiber slurry is transferred to a wet molding equipment. The wet molding process is used to remove water from the slurry under a pressure of 0.7 MPa. After the mixed short fibers are initially formed on the filter screen, they are fully dried at 80°C and demolded to obtain a chopped recycled carbon fiber-viscose fiber preform.

[0064] At room temperature and pressure, short-cut recycled carbon fiber-viscose fiber preforms were initially impregnated in a phenolic resin solution (acetone solvent, phenolic resin mass fraction in the solution was 15%) for 20 min. After impregnation, they were dried at 85℃ for 100 min, and then heated to 170℃ at a heating rate of 7℃ / min. The preforms were then initially hot-pressed at 170℃ and 1MPa pressure for 80 min to obtain a composite short fiber cured material. The composite short fiber cured material was then pre-heat-treated in a nitrogen atmosphere at a heating rate of 3℃ / min, from room temperature to 600℃ and held for 15 min to obtain a pre-oxidized material. The pre-oxidized material underwent secondary resin impregnation, secondary drying, and secondary hot-pressing curing (process parameters were the same as the initial impregnation, drying, and hot-pressing curing, the only difference being that the secondary impregnation was performed under vacuum at 30℃ and -0.5MPa negative pressure) to obtain a secondary cured felt. The secondary curing felt was subjected to a secondary heat treatment, which was carried out in two stages under an argon atmosphere. In the first stage, the temperature was increased to 1400℃ at 8℃ / min and held for 20min. In the second stage, the temperature was increased to 1800℃ at 3℃ / min and held for 40min to obtain recycled carbon fiber-viscose-based carbon fiber thermal insulation material.

[0065] The density of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material in this embodiment is 0.141 g / cm³. 3 It has a thermal conductivity of 0.136 W / (m·K) and a compressive strength of 0.673 MPa.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is that the short-cut recycled carbon fibers with a length of 3-6 mm and the viscose staple fibers with a length of 5-10 mm are replaced with only short-cut recycled carbon fibers with a length of 3-6 mm. The other processes are the same as in Example 1.

[0068] The density of the short-cut recycled carbon fiber composite material prepared in this comparative example is 0.134 g / cm³. 3 The thermal conductivity is 0.103 W / (m·K), and the compressive strength is 0.323 MPa. The SEM image of the short-cut recycled carbon fiber composite material prepared in Comparative Example 1 is shown below. Figure 3 As shown, by Figure 3 It is known that the short-cut recycled carbon fiber composite material is composed of single fibers, with a relatively denser fiber arrangement and a reduced internal porosity. Therefore, its density is slightly increased compared to the mixed fiber system. However, due to the more ordered fiber arrangement, the interaction between them is weakened, resulting in less network structure. Consequently, the mechanical properties are reduced compared to Example 1.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that the short-cut recycled carbon fibers with a length of 3-6 mm and the viscose staple fibers with a length of 5-10 mm are replaced with viscose staple fibers with a length of 5-10 mm. The other processes are the same as in Example 1.

[0071] The density of the viscose short fiber composite material prepared in this comparative example is 0.162 g / cm³. 3 The thermal conductivity is 0.119 W / (m·K), and the compressive strength is 0.637 MPa. The SEM image of the viscose short fiber composite material prepared in Comparative Example 2 is shown below. Figure 4 As shown, by Figure 4 It can be seen that, compared with Comparative Example 1, the viscose-based carbon fiber composite material has a larger scale and a more disordered morphology, making it easier for the fibers to connect with each other to form a network. At the same time, the denser network increases the carbon loading of the resin, thus enhancing the density and mechanical properties of the system. However, compared with the composite system of Example 1, the density of the viscose-based carbon fiber single system is significantly increased, and the thermal insulation performance is weakened.

[0072] Comparative Example 3

[0073] The difference between this comparative example and Example 1 is that the 3-6 mm long chopped recycled carbon fibers and the 5-10 mm long viscose staple fibers are replaced with 6 mm long commercial chopped carbon fibers (TORAY-T700SC), while the other processes are the same as in Example 1.

[0074] The density of the short-cut virgin carbon fiber reinforced composite material prepared in this comparative example is 0.122 g / cm³. 3 The thermal conductivity is 0.168 W / (m·K), and the compressive strength is 0.536 MPa. The SEM image of the composite material prepared from the short-cut virgin carbon fibers in Comparative Example 3 is shown below. Figure 5 As shown, by Figure 5 It is known that commercially available chopped carbon fiber has a more regular shape than composite fiber systems when directly molded. After molding, its higher porosity ensures that the system has thermal insulation capabilities. Moreover, virgin carbon fiber has fewer defects than recycled carbon fiber. However, the single system results in weaker mechanical properties, and due to its relatively high price, it has no cost advantage.

[0075] Comparative Example 4

[0076] The initial resin impregnation, initial drying, and initial hot-press curing of Example 1 are omitted, and the other processes are the same as in Example 1.

[0077] The density of the recycled carbon fiber-viscose-based carbon fiber thermal insulation material in this comparative example is 0.123 g / cm³. 3The thermal conductivity is 0.122 W / (m·K), and the compressive strength is 0.361 MPa. Single resin impregnation is insufficient to penetrate the thick felt, leading to system shrinkage and unevenness between the internal and external surfaces. Single resin impregnation and heat treatment may result in imperfect structure of the molded recycled carbon fiber-viscose-based carbon fiber insulation material, thus affecting the material's mechanical strength. Therefore, a secondary impregnation process is necessary to improve the system's structure.

[0078] The examples and comparative examples demonstrate that this invention, through green, recyclable, low-cost raw materials and a simple process route, prepares recycled carbon fiber-viscose-based carbon fiber thermal insulation materials with good mechanical properties and excellent thermal insulation performance. This invention can effectively solve the problems of high raw material prices and process costs, excessive energy consumption, and cumbersome production processes that are common in the development of existing carbon fiber reinforced thermal insulation materials, such as the recycling and reuse of carbon fiber resources. It provides a broader approach for the low-cost, large-scale production of thermal insulation materials and the construction of a green circular industrial chain for the carbon fiber materials industry.

[0079] This invention prepares carbon fiber thermal insulation materials based on resource-recycling short-cut recycled carbon fibers, widely available viscose staple fibers, and mature and easy-to-implement wet molding technology. The short-cut recycled carbon fibers and viscose staple fibers used in this invention have the advantages of being both environmentally friendly and cost-effective. The wet molding technology employed is simple and energy-efficient, enabling the large-scale, low-cost preparation of thermal insulation materials. The resulting environmentally friendly carbon fiber thermal insulation materials have excellent thermal insulation capabilities and outstanding comprehensive performance, which aligns well with policy requirements for circular economy and green manufacturing, and has broad industrialization and application prospects in the field of thermal insulation composite materials.

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing recycled carbon fiber-viscose-based carbon fiber thermal insulation material, characterized in that, It includes the following steps: 1) Short-cut recycled carbon fibers and viscose staple fibers are dispersed in a mixed aqueous solution to obtain a mixed staple fiber slurry; the mixed aqueous solution contains a dispersant, a binder, and water; 2) The mixed short fiber slurry is wet-molded and then dried to obtain a mixed short fiber preform; 3) The mixed short fiber preform is subjected to one impregnation, one hot-press curing, one heat treatment, a second impregnation, a second hot-press curing, and a second heat treatment in sequence to obtain recycled carbon fiber-viscose-based carbon fiber thermal insulation material.

2. The preparation method according to claim 1, characterized in that, Step 1) The length of the chopped recycled carbon fiber is 1~10mm, the length of the viscose short fiber is 1~15mm, the total mass fraction of the chopped recycled carbon fiber and viscose short fiber in the mixed aqueous solution is 0.1~1.0%, and the mass ratio of the chopped recycled carbon fiber and viscose short fiber is 0.5~4:1; in the mixed aqueous solution, the mass fraction of the dispersant is 0.05~0.5%, and the mass fraction of the binder is 0.01~0.5%.

3. The preparation method according to claim 1 or 2, characterized in that, Step 1) The dispersant comprises one or more of polyacrylamide, sodium polyacrylate, sodium carboxymethyl cellulose, polyethylene oxide, hydroxymethyl cellulose, hydroxyethyl cellulose and polyvinylpyrrolidone, and the binder comprises one or more of polyvinyl alcohol, waterborne polyurethane and modified starch.

4. The preparation method according to claim 3, characterized in that, Step 2) The drainage method in the wet molding process is vacuum dehydration and / or pressure filtration drainage, with a drainage pressure of 0.02~1MPa.

5. The preparation method according to claim 4, characterized in that, Step 3) The impregnation solution used for the first and second impregnation is a phenolic resin solution. The phenolic resin solution has a mass fraction of 5-25% and the solvent is one or more of anhydrous ethanol, methanol, acetone and ethyl acetate. The first impregnation time is 10~60min, the second impregnation is atmospheric pressure impregnation or vacuum impregnation, the temperature of the second impregnation is 25~50℃, the time is 10~120min, and the pressure of vacuum impregnation is -1~-0.08MPa.

6. The preparation method according to claim 4 or 5, characterized in that, Step 3) After the first immersion, a first drying is performed, and after the second immersion, a second drying is performed. The temperature for the first drying and the second drying are independent, both at 80~100℃, and the time is independent, both at 60~120min.

7. The preparation method according to claim 5, characterized in that, Step 3) The temperatures for the first and second hot-press curing are independently 120~180℃, the time is independently 60~180min, and the pressure is independently 0.1~2MPa; the rates of heating to the first and second hot-press curing temperatures are independently 1~10℃ / min.

8. The preparation method according to claim 1 or 7, characterized in that, Step 3) The first heat treatment is either a low-temperature heat treatment or a high-temperature heat treatment. The low-temperature heat treatment is carried out in an air atmosphere, with a temperature of 200~350℃ and a time of 10~60min. The high-temperature heat treatment is carried out in a nitrogen atmosphere, with a temperature of 350~1000℃ and a time of 10~20min. The rates of heating to low-temperature heat treatment temperature and heating to high-temperature heat treatment temperature are independent, ranging from 1 to 10 °C / min.

9. The preparation method according to claim 8, characterized in that, Step 3) The secondary heat treatment is carried out in two stages under a protective atmosphere. The temperature of the first stage heat treatment is 1000~1500℃, the time is 10~30min, and the rate of heating to the first stage heat treatment temperature is 1~10℃ / min. The temperature of the second stage heat treatment is 1500~2200℃, the time is 15~60min, and the rate of heating to the second stage heat treatment temperature is 1~5℃ / min. The protective atmosphere is a nitrogen atmosphere or an argon atmosphere.

10. The recycled carbon fiber-viscose-based carbon fiber thermal insulation material prepared by the method of any one of claims 1 to 9.

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