Viscose-polyacrylonitrile-based carbon fiber thermal insulation carbon felt and preparation method thereof

Abstract

The invention provides a viscose-polyacrylonitrile-based carbon fiber thermal insulation carbon felt 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 and polyacrylonitrile staple fibers in a mixed aqueous solution to obtain mixed staple fiber slurry; carrying out wet molding on the mixed short fiber slurry, and drying to obtain a mixed short fiber preform; the mixed short fiber preform is sequentially subjected to primary dipping, primary drying, primary hot-pressing curing, primary heat treatment, secondary dipping, secondary drying, secondary hot-pressing curing and secondary heat treatment, and the viscose-polyacrylonitrile-based carbon fiber heat preservation and insulation carbon felt is obtained. The viscose-polyacrylonitrile-based carbon fiber thermal insulation carbon felt prepared by the invention has the advantages of low density, high thermal insulation, high temperature resistance, good mechanical performance and the like, can effectively balance the thermal insulation performance and the mechanical performance, and has excellent comprehensive performance, and related products and equipment can show an excellent thermal protection effect in an actual high-temperature application scene.

Description

Technical Field

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

[0002] Thermal insulation materials play a crucial role in key areas such as high-temperature industries and aerospace. The continued development of key industries involving high-temperature protection is driving the ever-increasing demand for high-temperature thermal protection materials. Traditional thermal insulation materials may experience performance degradation, failure, and reduced service life under high-temperature environments, leading to increased energy consumption and maintenance costs. Carbon-based insulation materials, due to their chemical composition and structural advantages, possess advantages such as high melting point, low thermal conductivity, small coefficient of thermal expansion, lightweight, and excellent thermal stability, better meeting the actual needs of high-temperature thermal protection equipment for stable, lightweight, and long-lasting insulation materials. Currently, the commonly used carbon fiber types on the market include pitch-based, polyacrylonitrile (PAN)-based, and viscose-based. Among them, viscose-based carbon fiber products have the characteristics of wide availability of raw materials, excellent thermal insulation performance, and high product purity; polyacrylonitrile-based carbon fiber products have better mechanical properties, excellent comprehensive performance, and more mature large-scale production technology. Therefore, the development of these two types of carbon fibers for the field of thermal insulation materials has considerable prospects. However, using carbon fiber as a raw material still presents problems such as high cost, complex preparation process and high energy consumption. These factors restrict the large-scale application and promotion of carbon fiber reinforced thermal insulation materials.

[0003] Patent CN202211081268.3 provides a method for preparing a carbon fiber thermal insulation board. The method involves uniformly mixing and dispersing carbon fiber filaments obtained by mixing and crushing viscose-based carbon fiber and PAN-based carbon fiber in water, followed by casting, phenolic resin impregnation, and heat curing to obtain a non-delaminating carbon fiber insulation board with good heat resistance. However, the cost of the carbon fiber raw materials is too high, and the product lacks high-temperature heat treatment, resulting in polymers in the system that are limited by high temperatures, making the product unsuitable for extreme applications. Patent CN202410945552.3 mixes chopped viscose-based carbon fiber and acrylate in water, shapes it, and after curing, impregnates it with resin and then carbonizes it to obtain a viscose-based insulation board. The patent describes a carbon fiber insulation material that can be applied to high-temperature scenarios and has good thermal insulation performance. However, the product has insufficient mechanical properties, and the viscose-based carbon fiber is difficult to disperse in water, resulting in a long preparation process and high cost. Patents CN201610758751.9 and CN202410772711.4 describe mixing short-cut carbon fibers (at least one of viscose-based, polyacrylonitrile-based, or pitch-based carbon fibers) with resin in water, followed by curing, demolding, and heat treatment to obtain low-density short-cut carbon fiber insulation felt with good thermal insulation properties. However, the method of mixing the resin and fiber before molding can easily cause uneven fiber dispersion, and the high cost of carbon fiber as a raw material limits its large-scale promotion.

[0004] Viscose-based carbon fiber reinforced products possess good thermal insulation capabilities, but their mechanical properties are often insufficient. Products made from polyacrylonitrile-based carbon fibers exhibit better mechanical properties, but their thermal insulation performance often requires optimization. How to overcome the shortcomings of different types of carbon fiber systems, effectively leverage the performance advantages of different types of carbon fibers, and balance the thermal insulation and mechanical properties of carbon felt products is an urgent issue to be addressed. Therefore, developing technologies with wider raw material sources, lower costs, lower production energy consumption, and simpler processes to prepare thermal insulation carbon felts with better overall performance in terms of thermal insulation and mechanical properties has significant practical value. Summary of the Invention

[0005] The purpose of this invention is to provide a viscose-polyacrylonitrile-based carbon fiber thermal insulation felt and its preparation method.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing viscose-polyacrylonitrile-based carbon fiber thermal insulation felt, comprising the following steps: 1) Viscose staple fibers and polyacrylonitrile staple fibers are dispersed in a mixed aqueous solution to obtain a mixed staple fiber slurry; the mixed aqueous solution contains a dispersant, a surfactant, 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 drying, one hot pressing curing, one heat treatment, a second impregnation, a second drying, a second hot pressing curing, and a second heat treatment in sequence to obtain viscose-polyacrylonitrile-based carbon fiber thermal insulation felt.

[0007] Preferably, in step 1), the lengths of the viscose short fibers and polyacrylonitrile short fibers are independently 1-15 mm, the total mass fraction of the viscose short fibers and polyacrylonitrile short fibers in the mixed aqueous solution is 0.1-1.0%, and the mass ratio of the viscose short fibers to the polyacrylonitrile short fibers is 0.5-5:1; 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 fiber and polyacrylonitrile staple fiber 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 0.5-5.0%; 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 drainage method in the wet molding process of step 2) is vacuum dehydration and / or pressure filtration, and the drainage pressure is 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; Step 3) The temperature for the primary drying and the secondary drying are independent, and the time is independent, which is 60~120min.

[0012] 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.

[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 viscose-polyacrylonitrile-based carbon fiber thermal insulation carbon felt.

[0016] The beneficial effects of this invention are: 1) This invention uses viscose-based fiber filaments and polyacrylonitrile-based fiber filaments as reinforcing fiber raw materials during molding, instead of directly using carbon fiber. Compared with methods that directly use carbon fiber filaments as reinforcing materials, this invention has a wide range of raw material sources and a complete supply chain, resulting in significant advantages in raw material costs and energy consumption during the process. The technical route of this invention is mature, the process is simple, and the reaction is controllable, making it suitable for large-scale industrial production and widespread application.

[0017] 2) This invention uses viscose-based fiber and polyacrylonitrile-based fiber precursors directly as raw materials for wet molding, followed by resin impregnation and high-temperature heat treatment to obtain a lightweight thermal insulation carbon felt with uniform system, good thermal insulation and perfect comprehensive performance, providing a new idea for the development and promotion of carbon fiber thermal insulation materials.

[0018] 3) The viscose-polyacrylonitrile-based carbon fiber thermal insulation felt of this invention features randomly interwoven and disordered short fibers that extend the heat transfer pathway, thereby reducing thermal conductivity. The numerous pores generated during the carbonization process of the viscose and polyacrylonitrile short fibers due to shrinkage further enhance the material's thermal insulation capabilities. Simultaneously, the small-sized microcrystalline structure and high defect density of the viscose-based carbon fiber itself contribute to better thermal insulation performance, while the introduction of polyacrylonitrile-based carbon fiber effectively enhances mechanical properties. The viscose-polyacrylonitrile-based carbon fiber thermal insulation felt prepared by this invention possesses advantages such as low density, high thermal insulation, high temperature resistance, and excellent mechanical properties. It effectively balances thermal insulation and mechanical properties, exhibiting excellent overall performance. Related products and equipment can demonstrate outstanding thermal protection effects in practical high-temperature application scenarios. Attached Figure Description

[0019] Figure 1 SEM image of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt prepared in Example 1; Figure 2 SEM image of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt prepared in Example 1 at a high magnification. Figure 3 SEM image of the adhesive-based thermal insulation carbon felt in Comparative Example 1; Figure 4 SEM image of the polyacrylonitrile short fiber thermal insulation carbon felt of Comparative Example 2. Figure 5 The image shows a SEM image of the short fiber thermal insulation carbon felt in Comparative Example 3. Detailed Implementation

[0020] This invention provides a method for preparing viscose-polyacrylonitrile-based carbon fiber thermal insulation felt, comprising the following steps: 1) Viscose staple fibers and polyacrylonitrile staple fibers are dispersed in a mixed aqueous solution to obtain a mixed staple fiber slurry; the mixed aqueous solution contains a dispersant, a surfactant, 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 drying, one hot pressing curing, one heat treatment, a second impregnation, a second drying, a second hot pressing curing, and a second heat treatment in sequence to obtain viscose-polyacrylonitrile-based carbon fiber thermal insulation felt.

[0021] In this invention, the lengths of the viscose short fibers and polyacrylonitrile short fibers in step 1) are preferably 1-15 mm, more preferably 3-10 mm, and even more preferably 5-8 mm. The total mass fraction of the viscose short fibers and polyacrylonitrile 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%. The mass ratio of the viscose short fibers to the polyacrylonitrile short fibers is preferably 0.5-5:1, more preferably 1-4:1, and even more preferably 2-3:1. 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 surfactant is preferably 0.01-0.2%, more preferably 0.02-0.15%, and even more preferably 0.05-0.1%. 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%.

[0022] In this invention, the length of viscose short fibers and the mass fraction of polyacrylonitrile short fibers in the aqueous solution make them more uniformly dispersed in water. The composite system after wet molding has a certain porosity and mechanical strength, which is conducive to obtaining a heat insulation carbon felt product with uniform system and excellent comprehensive performance.

[0023] 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.

[0024] In this invention, the viscose staple fiber and polyacrylonitrile staple fiber are preferably sequentially acid-washed, water-washed, and then dispersed in a mixed aqueous solution; the acid solution used for acid washing preferably contains one or more of hydrochloric acid, sulfuric acid, acetic acid, and oxalic acid solutions, and the mass fraction of the acid solution is preferably 0.5-5.0%, 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.

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

[0026] This invention involves wet forming in a wet forming equipment, which separates short fibers from water and forms them in the initial stage.

[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 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. Step 3) The temperature for the primary and secondary drying processes is 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.

[0028] 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 0.1-2 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.

[0029] 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.

[0030] 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.

[0031] The present invention also provides a method for preparing the viscose-polyacrylonitrile-based carbon fiber thermal insulation carbon felt.

[0032] 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.

[0033] 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; and the viscosity of hydroxymethyl cellulose was 100,000, mainly supplied by Shanghai Yuanye Biotechnology Co., Ltd. The viscose staple fiber was purchased from Tangshan Sanyou Group Co., Ltd., model FR-W. The polyacrylonitrile staple fiber was prepared in the laboratory. For the specific process method, please refer to Example 1 of the application number CN202210651788.7, invention titled "A Polyacrylonitrile-based Carbon Fiber Provenance and Its Preparation Method". 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.

[0034] Example 1

[0035] 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 short fibers and polyacrylonitrile short fibers, each 5–10 mm in length, were immersed in 1.0% sulfuric acid at room temperature for 20 min. The acid-washed viscose short fibers and polyacrylonitrile short fibers were then rinsed four times with deionized water for 10 min each time, yielding pretreated viscose short fibers and pretreated polyacrylonitrile short fibers. The pretreated viscose short fibers and pretreated polyacrylonitrile short fibers, in a 1:1 mass ratio, were added to the mixed aqueous solution, with a total mass fraction of 0.5% for the short fibers. The fibers were mechanically stirred in the solution to fully disperse them, obtaining a uniformly dispersed mixed short fiber slurry.

[0036] The wet molding process is adopted. The mixed short fiber slurry is transferred to the wet molding equipment. The water in the slurry is removed by vacuum drainage at a pressure of 0.6MPa. The wet mat is formed on the drainage filter screen. The wet mat is then fully dried at 80℃ and demolded to obtain the mixed short fiber preform.

[0037] At room temperature and pressure, the mixed short fiber pre-fabricated felt 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 initially hot-pressed at 150℃ and 0.2 MPa pressure for 120 min to obtain the composite short fiber cured felt. The composite short fiber cured felt was then subjected to preliminary heat treatment in 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, increased to 300℃ at a rate of 5℃ / min and held for 20 min to obtain the pre-oxidized felt. 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 conducted in two stages under an argon atmosphere. The first stage involves heating to 1300℃ at a rate of 5℃ / min and holding for 10 min; the second stage involves heating to 2000℃ at a rate of 5℃ / min and holding for 20 min to obtain a viscose-polyacrylonitrile-based carbon fiber thermal insulation felt.

[0038] The density of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt in this embodiment is 0.219 g / cm³. 3 The thermal conductivity is 0.151 W / (m·K), and the compressive strength is 1.213 MPa. The SEM image of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt 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 viscose-polyacrylonitrile-based carbon fiber thermal insulation felt has a large number of pores, which makes the product lightweight and has good thermal insulation performance. At the same time, the mixed fibers are evenly distributed and can be well combined with resin carbon. The synergistic effect between viscose-based carbon fiber and polyacrylonitrile carbon fiber, and between matrix and reinforcing fiber in the composite system, together form a perfect network structure, which gives it good mechanical strength, thus making the thermal insulation felt have excellent comprehensive performance.

[0039] Example 2

[0040] The mass ratio of pretreated viscose short fibers to pretreated polyacrylonitrile short fibers in Example 1 was changed from 1:1 to 2:1, while other processes remained the same as in Example 1.

[0041] The density of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt in this embodiment is 0.181 g / cm³. 3It has a thermal conductivity of 0.129 W / (m·K) and a compressive strength of 0.877 MPa.

[0042] Example 3

[0043] The mass ratio of pretreated viscose short fibers to pretreated polyacrylonitrile short fibers in Example 1 was changed from 1:1 to 0.5:1, while other processes remained the same as in Example 1.

[0044] The density of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt in this embodiment is 0.247 g / cm³. 3 It has a thermal conductivity of 0.174 W / (m·K) and a compressive strength of 1.411 MPa.

[0045] Example 4

[0046] 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.

[0047] The density of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt in this embodiment is 0.176 g / cm³. 3 It has a thermal conductivity of 0.137 W / (m·K) and a compressive strength of 0.912 MPa.

[0048] Example 5

[0049] 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.

[0050] The density of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt in this embodiment is 0.293 g / cm³. 3 It has a thermal conductivity of 0.201 W / (m·K) and a compressive strength of 1.781 MPa.

[0051] Example 6

[0052] In Example 1, the temperature of the first stage of the secondary heat treatment was changed from 1300℃ to 1100℃, and the temperature of the second stage was changed from 2000℃ to 1800℃. Other processes were the same as in Example 1.

[0053] The density of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt in this embodiment is 0.218 g / cm³. 3 It has a thermal conductivity of 0.152 W / (m·K) and a compressive strength of 1.128 MPa.

[0054] Example 7

[0055] In Example 1, the temperature of the first stage of the secondary heat treatment was changed from 1300℃ to 1500℃, and the temperature of the second stage was changed from 2000℃ to 2200℃. Other processes were the same as in Example 1.

[0056] The density of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt in this embodiment is 0.221 g / cm³. 3 It has a thermal conductivity of 0.155 W / (m·K) and a compressive strength of 1.286 MPa.

[0057] Example 8

[0058] The mass fraction of polyacrylamide in the mixed aqueous solution of Example 1 was changed from 0.2% to 0.1%, the mass fraction of sodium dodecyl sulfate was changed from 0.1% to 0.05%, and the mass fraction of polyvinyl alcohol was changed from 0.1% to 0.05%. Other processes were the same as in Example 1.

[0059] The density of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt in this embodiment is 0.225 g / cm³. 3 It has a thermal conductivity of 0.157 W / (m·K) and a compressive strength of 1.205 MPa.

[0060] Example 9

[0061] Hydroxymethyl cellulose, polyethylene glycol 400, and polyvinyl alcohol were sequentially added to deionized water and magnetically stirred at 500 rpm until fully dissolved, yielding a mixed aqueous solution with 0.3% hydroxymethyl cellulose, 0.15% polyethylene glycol 400, and 0.15% polyvinyl alcohol by mass. Viscose short fibers and polyacrylonitrile short fibers, each 3–8 mm in length, were soaked in 3.0% acetic acid at room temperature for 20 min. The acid-washed viscose and polyacrylonitrile short fibers were then rinsed five times with deionized water for 10 min each time, yielding pretreated viscose and polyacrylonitrile short fibers. These pretreated viscose and polyacrylonitrile short fibers, in a mass ratio of 4:1, were added to the mixed aqueous solution, with a total short fiber mass fraction of 0.4%. The fibers were mechanically stirred to fully disperse them in the solution, resulting in a uniformly dispersed mixed short fiber slurry.

[0062] The wet molding process is adopted. The mixed short fiber slurry is transferred to the wet molding equipment. The water in the slurry is removed by vacuum drainage at a pressure of 0.2MPa. The wet mat is formed on the drainage filter screen. The wet mat is then fully dried at 80℃ and demolded to obtain the mixed short fiber preform.

[0063] At room temperature and pressure, the mixed short fiber pre-fabricated felt was initially impregnated in a phenolic resin solution (acetone solvent, phenolic resin mass fraction in the solution was 15%) for 40 min. After impregnation, it was dried at 95℃ for 70 min, and then heated to 170℃ at a heating rate of 8℃ / min. It was then initially hot-pressed and cured at 170℃ and 0.8MPa pressure for 80 min to obtain the composite short fiber cured felt. The composite short fiber cured felt was pre-heat-treated in a nitrogen atmosphere, and the temperature was increased from room temperature to 500℃ at a rate of 8℃ / min and held for 20 min to obtain the pre-carbonized felt. The pre-carbonized felt underwent secondary resin impregnation, secondary drying, and secondary hot-pressing curing (process parameters were the same as the primary resin impregnation, primary drying, and primary hot-pressing curing, the only difference being that the secondary impregnation was carried out under vacuum impregnation at 40℃ and -0.5MPa negative pressure) to obtain the secondary cured felt. 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 1200℃ at 8℃ / min and held for 25min. In the second stage, the temperature was increased to 1600℃ at 3℃ / min and held for 50min to obtain viscose-polyacrylonitrile-based carbon fiber thermal insulation felt.

[0064] The density of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt in this embodiment is 0.241 g / cm³. 3 It has a thermal conductivity of 0.176 W / (m·K) and a compressive strength of 1.374 MPa.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that the viscose staple fibers and polyacrylonitrile staple fibers, both with a length of 5-10 mm, are replaced with only viscose staple fibers. The other processes are the same as in Example 1.

[0067] The density of the viscose-based thermal insulation carbon felt prepared in this comparative example is 0.177 g / cm³. 3 The thermal conductivity is 0.119 W / (m·K), and the compressive strength is 0.663 MPa. The SEM image of the viscose-based thermal insulation carbon felt in Comparative Example 1 is shown below. Figure 3 As shown, by Figure 3 It can be seen that, compared with Example 1, the viscose-based thermal insulation carbon felt has a higher internal porosity and thus a lower overall density. This results in a lower thermal conductivity and improved thermal insulation, but significantly reduced mechanical properties. In Example 1, PAN fibers significantly enhance the mechanical properties of the product.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 1 is that the viscose short fibers and polyacrylonitrile short fibers, both with a length of 5~10mm, are replaced with only polyacrylonitrile short fibers. The other processes are the same as in Example 1.

[0070] The density of the polyacrylonitrile short fiber thermal insulation carbon felt prepared in this comparative example is 0.251 g / cm³. 3 The thermal conductivity is 0.232 W / (m·K), and the compressive strength is 2.556 MPa. The SEM image of the polyacrylonitrile short fiber thermal insulation carbon felt prepared in Comparative Example 2 is shown below. Figure 4 As shown, the porosity of the polyacrylonitrile short fiber thermal insulation carbon felt is reduced, and the resin carbon of the reinforcing fibers in the connecting system is increased under the same conditions, resulting in an increase in overall density. Therefore, the mechanical properties are significantly enhanced compared to Example 1, but the thermal insulation performance is worse, because the addition of viscose fiber in Example 1 helps to further improve the thermal insulation performance of the product.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that the viscose short fibers and polyacrylonitrile short fibers with a length of 5-10 mm are replaced with 6 mm commercial short-cut carbon fibers (TORAY-T700SC), while the other processes are the same as in Example 1.

[0073] The density of the short-fiber thermal insulation carbon felt prepared in this comparative example is 0.121 g / cm³. 3 The thermal conductivity is 0.165 W / (m·K), and the compressive strength is 0.529 MPa. The SEM image of the short-fiber thermal insulation carbon felt prepared in Comparative Example 3 is shown below. Figure 5 As shown, by Figure 5 It is known that direct molding of short carbon fibers has better regularity than carbonization after molding of viscose short fibers and polyacrylonitrile short fibers. The system with direct carbon fiber molding has higher porosity and can maintain better thermal insulation performance. However, the interaction between carbon fibers with high regularity is weakened, and the amount of resin carbon loading of connecting fibers is reduced under the same conditions, thereby weakening the mechanical properties of the molded carbon fiber composite material. Moreover, due to the relatively expensive price of fiber raw materials, it has no cost advantage.

[0074] Comparative Example 4

[0075] 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.

[0076] The density of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt in this comparative example is 0.191 g / cm³. 3 The thermal conductivity is 0.144 W / (m·K), and the compressive strength is 0.851 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 result in an imperfect structure after molding of the viscose-polyacrylonitrile-based carbon fiber thermal insulation material, thus affecting the material's apparent mechanical properties. Therefore, a secondary impregnation process is a necessary step to improve the system's structure.

[0077] The examples and comparative examples demonstrate that the preparation method of the viscose-polyacrylonitrile-based carbon fiber thermal insulation felt of the present invention, based on low-cost, widely available fiber raw materials and a mature wet process route, produces a thermal insulation carbon felt with a uniform system, low density, excellent thermal insulation performance, and outstanding mechanical strength. This effectively solves the problems of imperfect performance of single fiber systems and excessively high cost of carbon fiber raw materials, and helps to promote the large-scale production and widespread application of low-energy-consumption, low-cost thermal insulation carbon felt.

[0078] 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-polyacrylonitrile-based carbon fiber thermal insulation felt, characterized in that, It includes the following steps: 1) Viscose staple fibers and polyacrylonitrile staple fibers are dispersed in a mixed aqueous solution to obtain a mixed staple fiber slurry; the mixed aqueous solution contains a dispersant, a surfactant, 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 drying, one hot pressing curing, one heat treatment, a second impregnation, a second drying, a second hot pressing curing, and a second heat treatment in sequence to obtain viscose-polyacrylonitrile-based carbon fiber thermal insulation felt.

2. The preparation method according to claim 1, characterized in that, Step 1) The viscose short fibers and polyacrylonitrile short fibers have independent lengths of 1~15mm, the total mass fraction of viscose short fibers and polyacrylonitrile short fibers in the mixed aqueous solution is 0.1~1.0%, and the mass ratio of viscose short fibers to polyacrylonitrile short fibers is 0.5~5:1; in the mixed aqueous solution, the mass fraction of dispersant is 0.05~0.5%, the mass fraction of surfactant is 0.01~0.2%, and the mass fraction of 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 staple fiber and polyacrylonitrile staple fiber 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 0.5-5.0%. 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 2) The drainage method in the wet molding process is vacuum dehydration and / or pressure filtration, with a drainage pressure of 0.02~1MPa.

6. The preparation method according to claim 4 or 5, 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; 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 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 viscose-polyacrylonitrile-based carbon fiber thermal insulation felt prepared by the method according to any one of claims 1 to 9.

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