Viscose-based carbon fiber thermal insulation material and preparation method thereof

Abstract

The invention provides a 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 viscose staple fibers in a mixed aqueous solution, carrying out wet molding on the obtained viscose staple fiber slurry, and drying to obtain a wet molded preform; and sequentially carrying out primary dipping, primary drying, primary hot-pressing curing, primary heat treatment, secondary dipping, secondary drying, secondary hot-pressing curing and secondary heat treatment on the wet-process molded preform. According to the viscose-based carbon fiber heat-preservation composite material, the disordered step-by-step and randomly staggered short fibers in the viscose-based carbon fiber heat-preservation composite material prolong a heat transfer path, so that the heat conductivity is reduced; meanwhile, the viscose fibers generate a large number of pore structures due to shrinkage in the carbonization process, so that the thermal insulation capability of the material is further enhanced; the viscose-based carbon fiber thermal insulation material has the advantages of light weight, low thermal conductivity, high temperature resistance and the like, so that the viscose-based carbon fiber thermal insulation material has a good effect in high-temperature service of thermal protection equipment.

Description

Technical Field

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

[0002] Thermal insulation materials play an irreplaceable role in key fields such as aerospace technology and high-temperature industries. The continuous development of key industry technologies is driving the increasing demand for these materials. Traditional insulation materials are more prone to functional failure, performance degradation, and shortened service life under high-temperature environments, leading to increased wear and maintenance costs during equipment operation. Carbon fiber reinforced carbon-based insulation materials possess advantages such as high melting point, low thermal conductivity, low coefficient of thermal expansion, and excellent thermal stability, better meeting the needs of equipment operating in high-temperature environments for lightweight, highly stable, and long-life insulation materials. Among the mainstream carbon fiber products currently on the market, viscose-based carbon fiber products have the advantages of outstanding thermal insulation performance and high product purity, making them more suitable for material development in the insulation field. However, the high price, complex manufacturing process, and high energy consumption of viscose-based carbon fiber restrict the promotion and large-scale application of this type of carbon fiber reinforced insulation material. Furthermore, the current process of forming long filaments for carbon fiber composites is cumbersome and can easily lead to the formation of phonon transmission pathways within the material system, thus affecting the insulation effect in actual use. Therefore, developing a process method with low raw material cost and simple procedure to prepare carbon fiber insulation materials with excellent thermal insulation and mechanical properties is of great practical significance.

[0003] The invention patent with application number CN202410945552.3 provides a method for preparing carbon fiber reinforced carbon-based thermal insulation material using chopped viscose-based carbon fiber as raw material. It involves uniformly mixing chopped viscose-based carbon fiber with acrylate in water and molding, then impregnating with phenolic resin after curing and curing again, followed by carbonization to obtain the carbon fiber thermal insulation material. The invention patent with application number CN202411093313.6 pre-treats viscose-based fibers, then carbonizes and chops them, followed by secondary pre-treatment, phenolic resin mixing and curing, and high-temperature heat treatment to obtain a viscose-based thermal insulation composite material. The invention patent with application number CN202410772711.4 blends viscose-based chopped carbon fiber with resin in water, and after curing, demolding, and heat treatment, prepares a low-density chopped carbon fiber thermal insulation felt with good thermal insulation properties. However, the method of mixing the short fibers and resin before molding poses a challenge to the uniformity of fiber dispersion. All of the above methods use short-cut viscose-based carbon fibers as raw materials. However, the process of processing viscose-based precursor fibers into viscose-based carbon fibers is long and energy-intensive. Furthermore, due to the surface inertness of carbon fibers, they are difficult to disperse evenly in the solution. The one-step molding method of resin and fiber poses a significant challenge to maintaining product uniformity and process stability. At the same time, the resin shrinks while the fiber does not, resulting in poor interfacial bonding and overall material mechanical properties.

[0004] Therefore, how to develop a method with a wider range of raw material sources, lower energy consumption, lower production costs, more stable processes, and shorter procedures to prepare a carbon fiber insulation material with good system uniformity and excellent thermal insulation performance is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a viscose-based carbon fiber thermal insulation material and its preparation method. The method uses low-cost and widely available viscose fiber as raw material and a simple wet molding process to obtain a lightweight, uniform, and thermally insulating viscose-based carbon fiber thermal insulation material.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a viscose-based carbon fiber thermal insulation material, comprising the following steps: 1) Viscose staple fibers are dispersed in a mixed aqueous solution to obtain a viscose staple fiber slurry; the mixed aqueous solution contains a dispersant, a surfactant, a binder, and water; 2) The viscose short fiber slurry is wet-molded and then dried to obtain a wet-molded preform; 3) The wet-formed preform is subjected to a series of processes in sequence: one impregnation, one drying, one hot-press curing, one heat treatment, a second impregnation, a second drying, a second hot-press curing, and a second heat treatment to obtain a viscose-based carbon fiber insulation material. Step 2) The drainage method in the wet molding process is vacuum dehydration and / or pressure filtration, with a drainage pressure of 0.02~1MPa.

[0007] Preferably, in step 1), the length of the viscose short fiber is 1-15 mm, and the mass fraction of the viscose short fiber in the mixed aqueous solution is 0.1-1.0%; in the mixed aqueous solution, the mass fraction of the dispersant is 0.05-0.5%, the mass fraction of the surfactant is 0.01-0.2%, and the mass fraction of the binder is 0.01-0.5%.

[0008] Preferably, the dispersant in step 1) comprises one or more of polyacrylamide, hydroxymethyl cellulose, hydroxyethyl cellulose, polyvinylpyrrolidone, sodium carboxymethyl cellulose, sodium polyacrylate, and polyethylene oxide; the surfactant comprises one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, and polyethylene glycol; and the binder comprises one or more of polyvinyl alcohol, waterborne polyurethane, and modified starch.

[0009] Preferably, the viscose staple fibers are sequentially acid-washed, water-washed, and then dispersed in a mixed aqueous solution; the acid solution used for acid washing includes one or more of hydrochloric acid, sulfuric acid, acetic acid, and oxalic acid solutions, and the mass fraction of the acid solution is 0.1-5.0%; the acid washing time is 10-30 minutes, the number of water washings is 3-5 times, and the time of each water washing is 5-20 minutes.

[0010] 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.

[0011] Preferably, the temperature for the primary drying and the secondary drying in step 3) are independently 80~100℃, and the time is independently 60~120min.

[0012] Preferably, in step 3), the temperatures for the primary and secondary hot-press curing are independently 120~180℃, the time is independently 60~180min, the pressure is independently 0.1~1.8MPa, and the rates of heating to the primary and secondary hot-press curing temperatures are independently 1~10℃ / min.

[0013] 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.

[0014] 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.

[0015] The present invention also provides a method for preparing the aforementioned viscose-based carbon fiber thermal insulation material, resulting in a viscose-based carbon fiber thermal insulation material.

[0016] The beneficial effects of this invention are: 1) This invention prepares viscose-based carbon fiber insulation materials through wet molding, resin impregnation, hot pressing curing, and heat treatment. The process route is simple, the technology is mature, the reaction conditions are mild, and the thickness of the carbon fiber insulation material is controllable, making it suitable for large-scale industrial production. Compared to commonly used methods that use carbon fiber filaments as reinforcing materials, this invention uses viscose-based precursor fibers as reinforcing fiber materials, offering advantages such as a shorter process flow, more uniform product system, lower energy consumption, and lower cost.

[0017] 2) The viscose-based carbon fiber thermal insulation composite material prepared by this invention features disordered, stepwise, and randomly interwoven short fibers that extend the heat transfer pathway, thereby reducing thermal conductivity. Simultaneously, the numerous pores generated during the carbonization process of the viscose fibers due to shrinkage further enhance the material's thermal insulation capabilities. Furthermore, the small-sized microcrystals and high defect density structure of the viscose-based carbon fibers themselves endow the system with even better thermal insulation performance. Viscose-based carbon fiber thermal insulation materials possess advantages such as lightweight, low thermal conductivity, and high-temperature resistance, enabling them to demonstrate excellent performance in high-temperature applications of thermal protection equipment. Attached Figure Description

[0018] Figure 1 SEM image of the viscose-based carbon fiber thermal insulation material prepared in Example 1; Figure 2 This is a high-magnification SEM image of the viscose-based carbon fiber thermal insulation material prepared in Example 1. Figure 3SEM image of the viscose-based carbon fiber thermal insulation material prepared in Example 2; Figure 4 SEM image of the viscose-based carbon fiber thermal insulation material prepared in Example 3; Figure 5 SEM image of carbon fiber insulation material prepared from commercially available short-cut carbon fibers, for Comparative Example 1. Detailed Implementation

[0019] This invention provides a method for preparing a viscose-based carbon fiber thermal insulation material, comprising the following steps: 1) Viscose staple fibers are dispersed in a mixed aqueous solution to obtain a viscose staple fiber slurry; the mixed aqueous solution contains a dispersant, a surfactant, a binder, and water; 2) The viscose short fiber slurry is wet-molded and then dried to obtain a wet-molded preform; 3) The wet-formed preform is subjected to a series of processes in sequence: one impregnation, one drying, one hot-press curing, one heat treatment, a second impregnation, a second drying, a second hot-press curing, and a second heat treatment to obtain a viscose-based carbon fiber insulation material. Step 2) The drainage method in the wet molding process is vacuum dehydration and / or pressure filtration, with a drainage pressure of 0.02~1MPa.

[0020] In this invention, the length of the viscose short fibers in step 1) is preferably 1-15 mm, more preferably 3-10 mm, and even more preferably 5-8 mm; the mass fraction of the viscose short fibers in the mixed aqueous solution is preferably 0.1-1.0%, more preferably 0.3-0.8%, and even more preferably 0.5%; 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 surfactant is preferably 0.01-0.2%, more preferably 0.02-0.15%, and even more preferably 0.05-0.1%; and 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%.

[0021] In this invention, the length of the viscose short fibers and their mass fraction in the aqueous solution make them more uniformly dispersed in water, while ensuring that the fibers in the system have a certain bonding strength after molding, thereby obtaining a carbon fiber thermal insulation material with a uniform system and good mechanical strength.

[0022] In this invention, the dispersant in step 1) preferably comprises one or more of polyacrylamide, hydroxymethyl cellulose, hydroxyethyl cellulose, polyvinylpyrrolidone, sodium carboxymethyl cellulose, sodium polyacrylate, and polyethylene oxide; the surfactant preferably comprises one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, and polyethylene glycol; and the binder preferably comprises one or more of polyvinyl alcohol, waterborne polyurethane, and modified starch.

[0023] In this invention, the viscose staple fibers are preferably sequentially acid-washed, water-washed, and then dispersed in a mixed aqueous solution; the acid solution used for acid washing preferably includes one or more of hydrochloric acid, sulfuric acid, acetic acid, and oxalic acid solutions, and the mass fraction of the acid solution is preferably 0.1-5.0%, more preferably 1.0-4.0%, and even more preferably 2.0-3.0%, and the acid washing is carried out at room temperature; the acid washing time is preferably 10-30 min, more preferably 15-25 min, and even more preferably 20 min; the number of water washings is preferably 3-5 times, more preferably 4 times, and the time for each water washing is preferably 5-20 min, and even more preferably 10-15 min.

[0024] In this invention, the drainage pressure during the wet molding process in step 2) is preferably 0.02~1MPa, more preferably 0.05~0.5MPa, and even more preferably 0.1~0.4MPa.

[0025] 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 8-20%, and even more preferably 10-18%. The solvent is preferably one or more of anhydrous ethanol, methanol, acetone, and ethyl acetate. The first impregnation time is preferably 10-60 min, more preferably 20-50 min, and even more preferably 30-40 min. The first impregnation is carried out at room temperature and pressure. The second impregnation is preferably atmospheric pressure impregnation or vacuum impregnation. The temperature of the second impregnation is preferably 25-50℃, more preferably 30-45℃, and even more preferably 35-40℃. The time is preferably 10-120 min, more preferably 30-100 min, and even more preferably 50-70 min. The pressure of the vacuum impregnation 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.

[0026] In this invention, the temperatures for the primary and secondary drying processes in step 3) are preferably 80-100°C, more preferably 85-95°C, and even more preferably 90°C. The time for the primary and secondary drying processes is preferably 60-120 min, more preferably 70-100 min, and even more preferably 80-90 min.

[0027] 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 time is preferably 60-180 min, more preferably 80-150 min, and even more preferably 100-130 min; the pressure is preferably 0.1-1.8 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.

[0028] 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 is preferably 200~350℃, more preferably 250~300℃, and the time 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 is preferably 350~1000℃, more preferably 450~800℃, and more preferably 550~700℃, and the time 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 independently preferably 1~10℃ / min, more preferably 3~8℃ / min, and more preferably 5~6℃ / min.

[0029] 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℃, more preferably 1300~1400℃, and the time is preferably 10~30min, more preferably 15~25min, more preferably 20min. The rate of heating to the temperature of the first stage heat treatment is preferably 1~10℃ / min, more preferably 2~8℃ / min, more preferably 5~6℃ / min. The temperature of the second stage heat treatment is preferably 1500~2200℃, more preferably 1600~2000℃, more preferably 1800~1900℃, and the time is preferably 15~60min, more preferably 20~50min, more preferably 30~40min. The rate of heating to the temperature of the second stage heat treatment is preferably 1~5℃ / min, more preferably 2~4℃ / min, more preferably 3℃ / min. The protective atmosphere is preferably a nitrogen atmosphere or an argon atmosphere.

[0030] The present invention also provides a method for preparing the aforementioned viscose-based carbon fiber thermal insulation material, resulting in a viscose-based carbon fiber thermal insulation material.

[0031] 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.

[0032] 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. The viscose staple fiber was purchased from Tangshan Sanyou Group Co., Ltd., model FR-W; the wet forming equipment was purchased from Guangdong Fuaibo Fiber Technology Research Co., Ltd., specifically the intermittent fiber composite material forming machine, model SheetFormer 200F.

[0033] Example 1

[0034] Polyacrylamide, sodium dodecyl sulfate, and polyvinyl alcohol were sequentially added to deionized water and magnetically stirred at 500 rpm until fully dissolved, yielding a mixed aqueous solution with a mass fraction of 0.2% for polyacrylamide, 0.1% for sodium dodecyl sulfate, and 0.1% for polyvinyl alcohol. Viscose staple fibers with a length of 5–10 mm were soaked in 1.0% sulfuric acid at room temperature for 20 min. The acid-washed viscose staple fibers were then rinsed four times with deionized water for 10 min each time, yielding pretreated viscose staple fibers. The pretreated viscose staple fibers (0.5% by mass) were added to the mixed aqueous solution and stirred at 300 rpm until fully dispersed, obtaining a uniformly dispersed viscose staple fiber slurry.

[0035] The viscose short fiber slurry is transferred to a wet forming equipment using a wet forming process. The water is filtered out under a pressure of 0.5 MPa, and a wet felt is formed on the filter screen. The wet felt is then fully dried at 80°C and demolded to obtain viscose fiber felt.

[0036] At room temperature and pressure, viscose fiber mat was initially impregnated in a phenolic resin solution (solvent: anhydrous ethanol, phenolic resin content: 10% by mass) 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 subjected to a pressure of 0.2 MPa for initial hot-press curing for 120 min to obtain viscose fiber cured mat. The viscose fiber cured mat was then subjected to preliminary heat treatment in an air atmosphere, with the temperature increased from room temperature to 200℃ at a rate of 5℃ / min and held for 15 min; then increased to 250℃ at a rate of 5℃ / min and held for 20 min; finally, the temperature was increased to 300℃ at a rate of 5℃ / min and held for 20 min to obtain pre-oxidized mat. The pre-oxidized felt 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 viscose-based carbon fiber insulation material.

[0037] The density of the viscose-based carbon fiber insulation material in this embodiment is 0.168 g / cm³. 3 The thermal conductivity is 0.117 W / (m·K), and the compressive strength is 0.621 MPa. The SEM image of the viscose-based carbon fiber insulation material prepared in Example 1 is shown below. Figure 1 As shown, the SEM image at a higher magnification is as follows: Figure 2 As shown, by Figure 1 and Figure 2 It is known that the viscose-based carbon fiber insulation material system has good uniformity and a large number of pore structures inside, which makes the insulation material lightweight and has excellent thermal insulation performance. At the same time, due to the good bonding between the fiber and the resin, the synergistic effect of the matrix and the reinforcing carbon fiber together forms a relatively complete network structure, which endows the viscose-based carbon fiber insulation material with good mechanical properties.

[0038] Example 2

[0039] 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.

[0040] The density of the viscose-based carbon fiber insulation material in this embodiment is 0.128 g / cm³. 3 The thermal conductivity is 0.094 W / (m·K), and the compressive strength is 0.551 MPa. The SEM image of the viscose-based carbon fiber insulation material prepared in Example 2 is shown below. Figure 3 As shown, by Figure 3 It is known that viscose-based carbon fiber insulation materials have higher porosity, but the amount of resin carbon used as the matrix connecting fiber is reduced, which enhances thermal insulation performance, but also weakens mechanical properties.

[0041] Example 3

[0042] The mass fraction of phenolic resin in the phenolic resin solution of Example 1 was changed from 10% to 18%, while other processes remained the same as in Example 1.

[0043] The density of the viscose-based carbon fiber insulation material in this embodiment is 0.222 g / cm³. 3 The thermal conductivity is 0.155 W / (m·K), and the compressive strength is 0.802 MPa. The SEM image of the viscose-based carbon fiber insulation material prepared in Example 3 is shown below. Figure 4 As shown, the porosity of the viscose-based carbon fiber insulation material is reduced, but the amount of resin carbon used as the matrix connecting fiber is increased, resulting in enhanced mechanical properties compared to Example 1, but weakened thermal insulation properties.

[0044] Example 4

[0045] 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.

[0046] The density of the viscose-based carbon fiber insulation material in this embodiment is 0.169 g / cm³. 3 It has a thermal conductivity of 0.119 W / (m·K) and a compressive strength of 0.613 MPa.

[0047] Example 5

[0048] 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.

[0049] The density of the viscose-based carbon fiber insulation material in this embodiment is 0.170 g / cm³. 3 It has a thermal conductivity of 0.124 W / (m·K) and a compressive strength of 0.643 MPa.

[0050] Example 6

[0051] The length of the viscose staple fiber in Example 1 was changed from 5~10mm to 3~5mm, and the other processes were the same as in Example 1.

[0052] The density of the viscose-based carbon fiber insulation material in this embodiment is 0.156 g / cm³. 3 It has a thermal conductivity of 0.113 W / (m·K) and a compressive strength of 0.553 MPa.

[0053] Example 7

[0054] The mass fraction of polyacrylamide in the mixed aqueous solution of Example 1 was changed from 0.2% to 0.05%, the mass fraction of sodium dodecyl sulfate was changed from 0.1% to 0.025%, and the mass fraction of polyvinyl alcohol was changed from 0.1% to 0.025%. Other processes were the same as in Example 1.

[0055] The density of the viscose-based carbon fiber insulation material in this embodiment is 0.169 g / cm³. 3 It has a thermal conductivity of 0.122 W / (m·K) and a compressive strength of 0.619 MPa.

[0056] Example 8

[0057] Polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, and aqueous polyurethane were sequentially added to deionized water and magnetically stirred at 500 rpm until fully dissolved, yielding a mixed aqueous solution with a mass fraction of 0.3% for polyvinylpyrrolidone, 0.15% for sodium dodecylbenzenesulfonate, and 0.15% for aqueous polyurethane. Viscose short fibers with a length of 8–12 mm were immersed in 3.0% hydrochloric acid at room temperature for 20 min. The acid-washed viscose short fibers were then rinsed five times with deionized water for 10 min each time, yielding pretreated viscose short fibers. The pretreated viscose short fibers (0.3% by mass) were added to the mixed aqueous solution and stirred at 300 rpm until fully dispersed, obtaining a uniformly dispersed viscose short fiber slurry.

[0058] The viscose short fiber slurry is transferred to a wet forming equipment using a wet forming process. The water is filtered out under a pressure of 0.2 MPa, and a wet felt is formed on the filter screen. The wet felt is then fully dried at 80°C and demolded to obtain viscose fiber felt.

[0059] At room temperature and pressure, viscose fiber mat is initially impregnated in a phenolic resin solution (acetone solvent, phenolic resin mass fraction in the solution is 15%) for 40 min. After impregnation, it is dried at 95℃ for 70 min, then heated to 170℃ at a heating rate of 8℃ / min and subjected to a pressure of 0.8MPa for initial hot-press curing for 80 min to obtain viscose fiber cured mat. The viscose fiber cured mat is then subjected to preliminary heat treatment in a nitrogen atmosphere, with the temperature increased from room temperature to 500℃ at a rate of 8℃ / min and held for 20 min to obtain pre-carbonized mat. The pre-carbonized mat undergoes secondary resin impregnation, secondary drying, and secondary hot-press curing (process parameters are the same as the initial resin impregnation, initial drying, and initial hot-press curing, the only difference being that the secondary impregnation is carried out under vacuum at 40℃ and -0.5MPa negative pressure) to obtain secondary cured mat. The secondary curing felt was subjected to a secondary heat treatment, which was carried out in two stages under a nitrogen atmosphere. In the first stage, the temperature was increased to 1100℃ at 8℃ / min and held for 20min. In the second stage, the temperature was increased to 1700℃ at 3℃ / min and held for 40min to obtain viscose-based carbon fiber thermal insulation material.

[0060] The density of the viscose-based carbon fiber insulation material in this embodiment is 0.193 g / cm³. 3 It has a thermal conductivity of 0.147 W / (m·K) and a compressive strength of 0.713 MPa.

[0061] Comparative Example 1

[0062] The difference between this comparative example and Example 1 is that the viscose staple fiber is replaced with 6mm commercially available short-cut carbon fiber (TORAY-T700SC), while the other processes are the same as in Example 1.

[0063] The density of the carbon fiber insulation material in this comparative example is 0.115 g / cm³. 3 The thermal conductivity is 0.166 W / (m·K), and the compressive strength is 0.536 MPa. The SEM image of the carbon fiber insulation material prepared in Comparative Example 1 is shown below. Figure 5 As shown, by Figure 5 It is known that commercially available short-cut carbon fibers have better regularity and higher porosity after molding compared to carbonized viscose-based carbon fibers. However, the interaction between carbon fibers with higher regularity is weaker, and the carbon loading of the resin is reduced under the same conditions, thereby weakening the mechanical properties of the carbon fiber composite material after molding. In addition, the raw material cost of using carbon fiber molding is relatively high.

[0064] Comparative Example 2

[0065] 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.

[0066] The density of the viscose-based carbon fiber insulation material in this comparative example is 0.151 g / cm³. 3 The thermal conductivity is 0.119 W / (m·K) and the compressive strength is 0.431 MPa. Single resin impregnation is difficult to penetrate into the thick felt, resulting in system shrinkage and unevenness between the inside and outside. Single resin impregnation and heat treatment lead to imperfect structure of viscose-based carbon fiber insulation material after molding, thus affecting the apparent mechanical properties of the material.

[0067] As can be seen from the examples and comparative examples, the present invention can prepare viscose-based carbon fiber insulation materials with excellent thermal insulation performance, lightweight, good system uniformity and good mechanical properties by using low-cost raw materials and simple process routes. The method of the present invention has low technical requirements, can effectively reduce raw material and process input, save energy consumption, and can effectively solve the problems of high raw material and technology costs and complex preparation processes of existing carbon fiber insulation materials, providing a new idea for low-cost and large-scale production of thermal insulation materials.

[0068] 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 a viscose-based carbon fiber thermal insulation material, characterized in that, It includes the following steps: 1) Viscose staple fibers are dispersed in a mixed aqueous solution to obtain a viscose staple fiber slurry; the mixed aqueous solution contains a dispersant, a surfactant, a binder, and water; 2) The viscose short fiber slurry is wet-molded and then dried to obtain a wet-molded preform; 3) The wet-formed preform is subjected to a series of processes in sequence: one impregnation, one drying, one hot-press curing, one heat treatment, a second impregnation, a second drying, a second hot-press curing, and a second heat treatment to obtain a viscose-based carbon fiber insulation material. Step 2) The drainage method in the wet molding process is vacuum dehydration and / or pressure filtration, with a drainage pressure of 0.02~1MPa.

2. The preparation method according to claim 1, characterized in that, Step 1) The length of the viscose short fiber is 1~15mm, and the mass fraction of the viscose short fiber in the mixed aqueous solution is 0.1~1.0%; in the mixed aqueous solution, the mass fraction of the dispersant is 0.05~0.5%, the mass fraction of the surfactant is 0.01~0.2%, 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, hydroxymethyl cellulose, hydroxyethyl cellulose, polyvinylpyrrolidone, sodium carboxymethyl cellulose, sodium polyacrylate, and polyethylene oxide; the surfactant comprises one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, and polyethylene glycol; 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, The viscose short fibers are sequentially acid-washed, water-washed, and then dispersed in a mixed aqueous solution. The acid solution used for acid washing contains one or more of hydrochloric acid, sulfuric acid, acetic acid, and oxalic acid solutions, and the mass fraction of the acid solution is 0.1-5.0%. The acid washing time is 10-30 minutes, and the water washing is performed 3-5 times, with each water washing lasting 5-20 minutes.

5. The preparation method according to claim 3, 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) The temperature for the primary drying and the secondary drying are independent, and the time is independent, which is 60~120min.

7. The preparation method according to claim 6, characterized in that, Step 3) The temperature for the first hot-press curing and the second hot-press curing are 120~180℃, the time is 60~180min, the pressure is 0.1~1.8MPa, and the rate of heating to the first hot-press curing temperature and the rate of heating to the second hot-press curing temperature are 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 viscose-based carbon fiber thermal insulation material prepared by the method of any one of claims 1 to 9.

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