Preparation method of flexible carbon fiber film aerogel converted from silk

Abstract

The present application relates to a kind of preparation method of silkworm silk conversion flexible carbon fiber film aerogel, with silkworm silk as raw material, the process method of carbon fiber aerogel prepared by high temperature carbonization and later multilayer stacking.The segmented high temperature carbonization procedure presented in the present application is beneficial to the retention of fiber film flexibility, so that the final carbon fiber aerogel has excellent compression elastic performance;The multilayer fiber film stacking mode of "absorption layer+reflection layer" and the corresponding high temperature carbonization method presented in the present application are beneficial to the impedance matching and multiple reflection of multilayer fiber film aerogel to electromagnetic wave, and finally have excellent wave-absorbing type electromagnetic shielding performance.The method is simple and easy to operate, and the performance of the prepared product is stable, and the finally obtained self-supporting carbon fiber aerogel is an excellent wave-absorbing type electromagnetic shielding material, and has excellent characteristics such as low density, good compression recovery performance, good heat insulation performance, etc., and has very excellent practical value.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a silk-transformed flexible carbon fiber film aerogel with wave-absorbing electromagnetic shielding properties, belonging to the cross technical field of electromagnetic wave-absorbing / shielding materials and biological transformation carbon fiber materials. BACKGROUND

[0002] With the continuous development and innovation of information technology in modern society, electromagnetic wave interference and electromagnetic radiation have been affecting the normal operation of electronic equipment and the health of people. Therefore, it is of great practical significance to develop high-performance electromagnetic protection materials. Electromagnetic shielding materials can effectively isolate the influence of external electromagnetic waves on the internal objects, and are widely used as electromagnetic protection materials. For example, the most commonly used high-conductive metal-based and carbon-based materials can reflect most of the incident electromagnetic waves through impedance mismatching effect, thereby protecting the internal structure. However, this kind of "reflective" electromagnetic shielding material cannot fundamentally eliminate electromagnetic waves, and the reflected electromagnetic waves will also cause "secondary electromagnetic pollution" to the environment. Therefore, developing "wave-absorbing" electromagnetic shielding materials and related preparation technologies is a more effective electromagnetic protection scheme, which has important significance for expanding the application range and practical efficiency of electromagnetic shielding materials.

[0003] According to the different microstructures, wave-absorbing electromagnetic shielding materials can be divided into two categories: composite film type and porous type. The composite film type mainly realizes electromagnetic wave absorption by constructing a multi-layer gradient structure. For example, Kim et al. (Nano Letters. 21(2), 1132-1140 (2021)) developed an Al / Al2O3 multi-gradient film material, which realized near-zero reflection electromagnetic shielding (reflection shielding effectiveness <0.04 dB), but the preparation process of this material is complex and the yield is very low, which greatly reduces its practicability. In addition, using this principle, other scholars also developed PDMS / rGO / SWCNT nanocomposite film (ACS appl. Mater. Interfaces. 10(31), 26723-26732 (2018)), TPU / CIP / Ni composite film (Chem. Eng. J. 428, 131167 (2022)), BiFeO3 / BaFe7(MnTi) 2.5 O 19Multi-gradient electromagnetic shielding materials such as composite films (J. Alloy. Compd. 772, 99-104 (2019)) and the like, however, these materials have complex structures and relatively low absorption coefficients (A) (about 0.8). On the other hand, porous electromagnetic absorbing materials such as foam materials (Carbon. 173, 932-940 (2021); J Mater Chem A. 8(18), 9146-9159), sponge materials (Carbohyd. Polym. 276(15), 118799 (2021)) and aerogel materials (Chem. Eng. J. 369, 1068-1077 (2019); Compos. Part. B: Eng. 217, 108853 (2021)) and the like mainly rely on their rich internal porous structure and specific surface area to rely on interface polarization and multiple reflection and other mechanisms to dissipate the energy of the incident electromagnetic waves. However, the complex preparation process and material cost of making electromagnetic wave-absorbing porous materials limit their further application and mass production.

[0004] Silk fiber has excellent mechanical properties and flexibility, and is a widely used natural fiber material. After simple degumming treatment of silkworm pupa raw materials, soft silk fiber can be obtained. After high-temperature carbonization treatment, carbonized silk fiber has excellent electrical conductivity and relatively low cost, and has been applied in the fields of catalyst template materials (Electrochim. Acta 2016, 215, 223-230), gas adsorbents (Prog. Polym. Sci. 2015, 46, 86-110), biosensors (Biosens. Bioelectron. 2010, 25, 2189-2193; Adv. Mater. 2016, 28, 6640-6648), supercapacitors (J. Energy Chem. 2018, 27, 161-166), fuel cells (Nano Energy 2017, 32, 382-388) and the like. However, the research on continuous carbonized silk fiber as electromagnetic wave-absorbing or electromagnetic shielding material is less reported so far. The applicant has proved in the previous research (ACS Sustainable Chem. Eng. 2021, 9, 12747-12754) that carbonized silk fiber has excellent electromagnetic wave-absorbing performance. However, the carbonized silk prepared in this study can only be encapsulated in a silica gel matrix as a wave-absorbing agent, and cannot be self-supporting, and the flexibility needs to be further improved. SUMMARY

[0005] The application aims to improve the deficiencies of the prior art and provides a simple and low-cost preparation method of flexible carbon fiber film aerogel converted from silk, excellent flexible carbonized silk fiber film with excellent mechanical properties and adjustable electrical conductivity is obtained, and finally a self-supporting carbon fiber aerogel with excellent wave-absorbing electromagnetic shielding material is obtained by using the template, combining impedance matching and multi-layer structure design, and the self-supporting carbon fiber aerogel has the characteristics of low density, good compression recovery performance, good heat insulation performance and excellent practical value.

[0006] The technical scheme of the application is a preparation method of flexible carbon fiber film aerogel converted from silk, and the specific steps are as follows:

[0007] (1) Silk degumming pretreatment: natural cocoon is soaked in NaCO3 aqueous solution and heated to boiling, after the cocoon is softened, it is transferred to water for cleaning and removal of internal silkworm pupae, the silk is arranged into a shape and dried in an oven to constant weight to obtain pretreated silk fiber film;

[0008] (2) Carbonization treatment: the pretreated silk fiber film is placed in a gas atmosphere furnace, and after high-temperature carbonization and high-temperature carbonization at two different temperatures in a protective gas (argon or nitrogen), an absorbing layer carbon fiber film and a reflecting layer carbon fiber film are obtained respectively;

[0009] (3) Carbon fiber aerogel construction: the absorbing layer carbon fiber film and the reflecting layer carbon fiber film are stacked in order, and a high-temperature resistant adhesive solution is used to bond between each layer, then the multi-layer stacked fiber film is placed in an oven to crosslink and solidify the adhesive, and a carbon fiber film aerogel is obtained.

[0010] Preferably, the mass concentration of the NaCO3 aqueous solution in step (1) is 0.1-1.0%; and the silkworm pupae is continuously soaked for 0.5-1h after the aqueous solution is boiled.

[0011] Preferably, the procedure for preparing the absorbing layer carbon fiber film by high-temperature carbonization in step (2) is as follows: 1) the temperature is raised from room temperature to T1 of 120-180℃ at a rate of 5-10℃ / min and kept for 0.5-1h; 2) the temperature is raised from T1 to T2 of 300-400℃ at a rate of 1-3℃ / min and kept for 1-3h; 3) the temperature is raised from T2 to carbonization temperature T3 of 600-800℃ at a rate of 0.5-2℃ / min and kept for 1-4h; 4) the temperature is lowered from carbonization temperature T3 to T2 at a rate of 0.5-2℃ / min; 5) the temperature is lowered from T2 to room temperature at a rate of 5-10℃ / min.

[0012] The high-temperature carbonization in step (2) is preferably prepared by the following procedure: 1) increasing the temperature from room temperature to T1 of 120-180℃ at a rate of 5-10℃ / min and maintaining the temperature for 0.5-1h; 2) increasing the temperature from T1 to T2 of 300-400℃ at a rate of 1-3℃ / min and maintaining the temperature for 1-3h; 3) increasing the temperature from T2 to carbonization temperature T3 of 1300-1500℃ at a rate of 0.5-2℃ / min and maintaining the temperature for 1-4h; 4) decreasing the temperature from carbonization temperature T3 to T2 at a rate of 0.5-2℃ / min; and 5) decreasing the temperature from T2 to room temperature at a rate of 5-10℃ / min.

[0013] The total thickness of the multi-layer stacked fiber film in step (3) is preferably 9-14mm, and the thickness ratio of the absorbing layer to the reflecting layer is 2-3:1. The stacking sequence from top to bottom is "absorbing layer + reflecting layer".

[0014] The solvent in the high-temperature resistant adhesive solution in step (3) is preferably any one or two of water, ethanol or ethylene glycol; the high-temperature resistant adhesive is preferably one of Al(H2PO4)3, Mg(H2PO4)2, Cr(H2PO4)3 or Zr(H2PO4)4; and the mass concentration of the high-temperature resistant adhesive solution is preferably 2-15%.

[0015] The amount of the adhesive used in the adhesive solution in step (3) is preferably 70-120μL per square centimeter on the surface of each layer of the fiber film, and then the next layer is stacked in the same way.

[0016] The cross-linking and curing temperature is preferably 80-100℃, and the cross-linking and curing time is preferably 12-24h.

[0017] Advantages: The present application discloses a process for preparing carbon fiber aerogel from silk as raw material through high-temperature carbonization and later multi-layer stacking. The segmented high-temperature carbonization procedure is beneficial to the retention of the flexibility of the fiber film, and the final carbon fiber aerogel has excellent compression resistance and elasticity. The multi-layer fiber film stacking mode of "absorbing layer + reflecting layer" and the corresponding high-temperature carbonization method are solutions optimized for electromagnetic wave absorption characteristics, which are beneficial to the impedance matching and multiple reflection of the multi-layer fiber film aerogel to electromagnetic waves, and finally have excellent wave-absorbing electromagnetic shielding performance. The method is simple and easy to implement, and the prepared product has stable performance. The final lightweight and elastic fiber aerogel has excellent wave-absorbing electromagnetic shielding performance, and the average electromagnetic wave energy absorption coefficient in the X-Ku band is greater than 0.97. It also has excellent compression resistance and heat insulation performance. The present application provides a simple and low-cost process for preparing lightweight and efficient wave-absorbing electromagnetic shielding fiber materials. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 : Flow chart of preparation of silk transformed carbon fiber aerogel in Example 1;

[0019] Figure 2 : Flexibility display chart of silk transformed carbon fiber aerogel in Example 1;

[0020] Figure 3 : Electromagnetic wave energy coefficient chart (reflection coefficient R, absorption coefficient A and transmission coefficient T) of multi-layer stacked silk transformed carbon fiber aerogel in Example 1 at 8-18 GHz;

[0021] Figure 4 : Stress-strain curve chart of silk transformed carbon fiber aerogel in Example 1 (a) under different compression strains; (b) after different cycle times. DETAILED DESCRIPTION

[0022] The present application will be further described in conjunction with examples:

[0023] Example 1:

[0024] According to the flow chart Figure 1 , the specific preparation method flow is as follows:

[0025] (1) 1L of 0.1% NaCO3 aqueous solution was measured and poured into 10 glass beakers with a capacity of 100mL, and the beakers were placed in a water bath to heat to boiling; 20 natural silkworm chrysalis were taken and immersed in the beakers in batches, each for 1h, and then transferred to deionized water for cleaning and removal of internal silkworm chrysalis; the cleaned silk was arranged into shape and placed in an oven for drying.

[0026] (2) The silk fibers of step (1) were divided into 2 groups and laid flat in 2 Al2O3 crucible boats, and the two crucibles were sent into two high-temperature atmosphere furnaces (A and B), and after three times of repeated Ar gas pumping, the heating program was prepared.

[0027] (3) The heating program of high-temperature atmosphere furnace A in step (2) was set: the temperature was raised from room temperature to 120℃ at a rate of 5℃ / min and kept for 0.5h; the temperature was raised from 120℃ to 300℃ at a rate of 1℃ / min and kept for 1h; the temperature was raised from 300℃ to 700℃ at a rate of 0.5℃ / min and kept for 1h; the temperature was lowered from 700℃ to 300℃ at a rate of 0.5℃ / min; the temperature was lowered from 300℃ to room temperature at a rate of 5℃ / min.

[0028] (4) Set the heating program of high-temperature atmosphere furnace B in step (2): increase the temperature from room temperature to 120°C at a rate of 5°C / min and keep for 0.5 h; increase the temperature from 120°C to 300°C at a rate of 1°C / min and keep for 1 h; increase the temperature from 300°C to 1300°C at a rate of 0.5°C / min and keep for 1 h; decrease the temperature from 1300°C to 300°C at a rate of 0.5°C / min; decrease the temperature from 300°C to room temperature at a rate of 5°C / min.

[0029] (5) Stack the 700°C carbonized fiber films obtained in step (3) layer by layer into 10 mm thick as an absorption layer, and stack the 1300°C carbonized fiber films obtained in step (4) layer by layer into 2 mm thick as a reflection layer; use 2% (mass fraction) Al(H2PO4)3 alcohol solution as an adhesive between each layer of fiber films, and uniformly apply the adhesive at a density of 120 μL per square centimeter for bonding. The stacking sequence from top to bottom is “6 mm absorption layer + 3 mm reflection layer”.

[0030] (6) Place the stacked fiber films in a 100°C oven for 12 h to dry and crosslink the adhesive, and finally obtain carbon fiber film aerogel.

[0031] Figure 1 Preparation flowchart. Figure 2 Silk converted carbon fiber aerogel flexibility display, it can be seen that after bending and compression, the aerogel material can still restore to the original state. Figure 3 Silk converted carbon fiber aerogel electromagnetic wave energy coefficient (reflection coefficient R, absorption coefficient A and transmission coefficient T) in 8-18 GHz, it can be seen that after multilayer design and stacking, the material as a whole shows excellent electromagnetic wave absorption characteristics, the absorption coefficient A is greater than 0.9 in the full frequency band of 8-18 GHz, and the average absorption coefficient is greater than 0.97. Figure 4 Silk converted carbon fiber aerogel (a) stress-strain curve diagram under different compression strain; (b) stress-strain curve diagram after different cycle times, it can be seen that after different compression strain tests, the aerogel material can all restore to the original position, and after 1000 cycle loading-unloading tests, it still maintains more than 90% compression stress.

[0032] Example 2:

[0033] (1) Measure 1 L of 1% NaCO3 aqueous solution, and pour it into 10 glass beakers with a capacity of 100 mL, and heat the beakers in a water bath to boiling; take 20 natural silkworm chrysalis, and immerse each in the beaker in batches and boil for 0.5 h, and then transfer to deionized water for cleaning and remove the internal silkworm chrysalis; arrange the cleaned silk into a shape and place it in an oven for drying.

[0034] (2) The silk fibers of step (1) were divided into two groups and laid flat in two Al2O3 crucible boats, respectively. The two crucibles were then placed in two high-temperature atmosphere furnaces (A and B), respectively. After three times of repeated Ar gas pumping and supplying, the heating program was started.

[0035] (3) The heating program of high-temperature atmosphere furnace A in step (2) was set as follows: the temperature was raised from room temperature to 180°C at a rate of 10°C / min and maintained for 1 h; the temperature was raised from 180°C to 400°C at a rate of 3°C / min and maintained for 3 h; the temperature was raised from 400°C to 700°C at a rate of 2°C / min and maintained for 4 h; the temperature was lowered from 700°C to 400°C at a rate of 2°C / min; and the temperature was lowered from 400°C to room temperature at a rate of 10°C / min.

[0036] (4) The heating program of tube furnace B in step (2) was set as follows: the temperature was raised from room temperature to 180°C at a rate of 10°C / min and maintained for 1 h; the temperature was raised from 180°C to 400°C at a rate of 3°C / min and maintained for 3 h; the temperature was raised from 400°C to 1300°C at a rate of 2°C / min and maintained for 4 h; the temperature was lowered from 1300°C to 400°C at a rate of 2°C / min; and the temperature was lowered from 400°C to room temperature at a rate of 10°C / min.

[0037] (5) The 700°C carbonized fiber thin films obtained in step (3) were stacked layer by layer to a thickness of 6 mm as an absorption layer, and the 1300°C carbonized fiber thin films obtained in step (4) were stacked layer by layer to a thickness of 3 mm as a reflection layer. A 2% by mass Mg(H2PO4)2 aqueous solution was used as an adhesive between each layer of fiber thin films, and the adhesive was uniformly applied at a density of 120 μL / cm2 for bonding. The stacking order from top to bottom was “6 mm absorption layer + 3 mm reflection layer”.

[0038] (6) The stacked fiber thin films were placed in a 100°C oven for 12 h to dry and crosslink the adhesive, and finally a carbon fiber thin film aerogel was obtained.

[0039] Example 3:

[0040] (1) 1 L of a 0.5% by mass NaCO3 aqueous solution was measured and poured into 10 glass beakers with a capacity of 100 mL, respectively. The beakers were placed in a water bath and heated to boiling. 20 natural silkworm cocoons were immersed in the beakers one by one in batches and boiled for 0.5 h. After the silkworm cocoons were softened, they were transferred to deionized water for cleaning and removal of the internal silkworm pupae. The cleaned silk was arranged into a shape and placed in an oven for drying.

[0041] (2) The silk fibers of step (1) were divided into 2 groups and laid flat in 2 Al2O3 crucible boats, and the two crucibles were sent into two high-temperature atmosphere furnaces (A and B), respectively. After three times of repeated Ar gas pumping and sending, the heating program was prepared to be started.

[0042] (3) The heating program of high-temperature atmosphere furnace A in step (2) was set as follows: the temperature was raised from room temperature to 180°C at a rate of 5°C / min and kept for 1 h; the temperature was raised from 180°C to 400°C at a rate of 3°C / min and kept for 3 h; the temperature was raised from 400°C to 650°C at a rate of 1°C / min and kept for 2 h; the temperature was lowered from 650°C to 400°C at a rate of 1°C / min; and the temperature was lowered from 400°C to room temperature at a rate of 5°C / min.

[0043] (4) The heating program of high-temperature atmosphere furnace B in step (2) was set as follows: the temperature was raised from room temperature to 180°C at a rate of 5°C / min and kept for 1 h; the temperature was raised from 180°C to 400°C at a rate of 3°C / min and kept for 3 h; the temperature was raised from 400°C to 1500°C at a rate of 1°C / min and kept for 2 h; the temperature was lowered from 1500°C to 400°C at a rate of 1°C / min; and the temperature was lowered from 400°C to room temperature at a rate of 5°C / min.

[0044] (5) The 650°C carbonized fiber thin films obtained in step (3) were stacked layer by layer to a thickness of 12 mm as an absorption layer, and the 1500°C carbonized fiber thin films obtained in step (4) were stacked layer by layer to a thickness of 2 mm as a reflection layer; a bonding agent of 4% Cr(H2PO4)3 ethanol + water solution (volume ratio 1:1) was used between each layer of fiber thin films, and the bonding agent was uniformly applied at a density of 100 μL per square centimeter for bonding. The stacking sequence from top to bottom was “10 mm absorption layer + 4 mm reflection layer”.

[0045] (6) The stacked fiber thin films were placed in an 80°C oven for 12 h to dry and crosslink the bonding agent, and finally the carbon fiber thin film aerogel was obtained.

[0046] Example 4:

[0047] (1) 1 L of 0.5% NaCO3 aqueous solution was measured and poured into 10 glass beakers with a capacity of 100 mL, and the beakers were placed in a water bath and heated to boiling; 15 natural silkworm chrysalis were taken and immersed in the beakers one by one for boiling for 1 h, and after the silkworm chrysalis were softened, they were transferred to deionized water for cleaning and removal of the internal silkworm chrysalis; the cleaned silk was arranged into a shape and placed in an oven for drying for standby use.

[0048] (2) The silk fibers of step (1) are divided into 3 groups and laid flat in 3 Al2O3 crucible boats, and the three crucibles are sent into three high-temperature atmosphere furnaces (A, B and C), respectively. After three times of repeated N2 gas pumping and sending, the heating program is prepared to be started.

[0049] (3) The heating program of high-temperature atmosphere furnace A in step (2) is set as follows: the temperature is raised from room temperature to 160°C at a rate of 8°C / min and kept for 1 h; the temperature is raised from 160°C to 350°C at a rate of 2°C / min and kept for 2 h; the temperature is raised from 350°C to 600°C at a rate of 1°C / min and kept for 2 h; the temperature is lowered from 600°C to 350°C at a rate of 1°C / min; and the temperature is lowered from 350°C to room temperature at a rate of 8°C / min.

[0050] (4) The heating program of high-temperature atmosphere furnace B in step (2) is set as follows: the temperature is raised from room temperature to 160°C at a rate of 8°C / min and kept for 1 h; the temperature is raised from 160°C to 350°C at a rate of 2°C / min and kept for 2 h; the temperature is raised from 350°C to 800°C at a rate of 1°C / min and kept for 2 h; the temperature is lowered from 800°C to 350°C at a rate of 1°C / min; and the temperature is lowered from 350°C to room temperature at a rate of 8°C / min.

[0051] (5) The heating program of high-temperature atmosphere furnace C in step (2) is set as follows: the temperature is raised from room temperature to 160°C at a rate of 8°C / min and kept for 1 h; the temperature is raised from 160°C to 350°C at a rate of 2°C / min and kept for 2 h; the temperature is raised from 350°C to 1400°C at a rate of 1°C / min and kept for 2 h; the temperature is lowered from 1400°C to 350°C at a rate of 1°C / min; and the temperature is lowered from 350°C to room temperature at a rate of 8°C / min.

[0052] (6) The 600°C carbonized fiber thin films obtained in step (3) are stacked layer by layer to a thickness of 6 mm as an absorption layer A, the 800°C carbonized fiber thin films obtained in step (4) are stacked layer by layer to a thickness of 4 mm as an absorption layer B, and the 1400°C carbonized fiber thin films obtained in step (5) are stacked layer by layer to a thickness of 4 mm as a reflection layer; a Zr(H2PO4)4 alcohol + water solution (volume ratio 2:1) with a mass fraction of 8% is used as an adhesive between each layer of fiber thin films, and the adhesive is uniformly applied at a density of 80 μL per square centimeter for bonding. The stacking order from top to bottom is “4 mm absorption layer A + 4 mm absorption layer B + 4 mm reflection layer”.

[0053] (7) The stacked fiber thin films are placed in an 80°C oven for drying for 24 h to cross-link and solidify the adhesive, and finally a carbon fiber thin film aerogel is obtained.

[0054] Example 5:

[0055] (1) Measure 1 L of 0.5% NaCO3 aqueous solution, and pour into 10 glass beakers with a capacity of 100 mL, and put the beakers into a water bath to heat to boiling; take 15 natural silkworm chrysalis, and immerse in the beakers in batches for 0.5 h, and then transfer to deionized water to clean and remove the internal silkworm chrysalis; after cleaning, the silk is arranged into a shape and dried in an oven for standby.

[0056] (2) The silk fibers of step (1) are divided into 3 groups and laid flat in 3 Al2O3 crucible boats, and the three crucibles are sent into three high-temperature atmosphere furnaces (A, B and C), and after three times of repeated N2 gas suction and supply, the heating program is prepared to be started.

[0057] (3) Set the heating program of high-temperature atmosphere furnace A in step (2): increase the temperature from room temperature to 150°C at a rate of 5°C / min and keep for 1 h; increase the temperature from 150°C to 350°C at a rate of 2°C / min and keep for 2 h; increase the temperature from 350°C to 650°C at a rate of 1°C / min and keep for 2 h; decrease the temperature from 650°C to 350°C at a rate of 1°C / min; decrease the temperature from 350°C to room temperature at a rate of 5°C / min.

[0058] (4) Set the heating program of high-temperature atmosphere furnace B in step (2): increase the temperature from room temperature to 150°C at a rate of 5°C / min and keep for 1 h; increase the temperature from 150°C to 350°C at a rate of 2°C / min and keep for 2 h; increase the temperature from 350°C to 700°C at a rate of 1°C / min and keep for 2 h; decrease the temperature from 700°C to 350°C at a rate of 1°C / min; decrease the temperature from 350°C to room temperature at a rate of 5°C / min.

[0059] (5) Set the heating program of high-temperature atmosphere furnace C in step (2): increase the temperature from room temperature to 150°C at a rate of 5°C / min and keep for 1 h; increase the temperature from 150°C to 350°C at a rate of 2°C / min and keep for 2 h; increase the temperature from 350°C to 1500°C at a rate of 1°C / min and keep for 2 h; decrease the temperature from 1500°C to 350°C at a rate of 1°C / min; decrease the temperature from 350°C to room temperature at a rate of 5°C / min.

[0060] (6) The 650℃ carbonized fiber films obtained in step (3) were stacked layer by layer to a thickness of 5 mm as an absorption layer A, the 700℃ carbonized fiber films obtained in step (4) were stacked layer by layer to a thickness of 5 mm as an absorption layer B, and the 1500℃ carbonized fiber films obtained in step (5) were stacked layer by layer to a thickness of 4 mm as a reflection layer. An aqueous solution of Al(H2PO4)3 with a mass fraction of 5% was used as the binder between each layer of fiber film, and the binder was uniformly applied at a density of 100 μL per square centimeter for bonding. The stacking sequence from top to bottom was "5 mm absorption layer A + 5 mm absorption layer B + 4 mm reflection layer".

[0061] (7) The stacked fiber films were placed in an 80℃ oven for drying for 24 h to crosslink and solidify the binder, and finally the carbon fiber film aerogel was obtained.

[0062] The properties of the silk transformed carbon fiber aerogels obtained in the above examples are shown in Table 1.

[0063] Table 1 Properties of silk transformed carbon fiber aerogels in Examples 1-5

[0064]

Claims

1. A method for preparing a silk transformed flexible carbon fiber film aerogel, comprising the following steps: (1) silk degumming pretreatment: soaking natural cocoon in NaCO 3 aqueous solution and heating to boiling, after the cocoon is softened, transferring to water for cleaning and removing the internal pupa, arranging the silk into a shape, and drying in an oven to constant weight to obtain pretreated silk fiber film; (2) carbonization treatment: placing the pretreated silk fiber film in a gas atmosphere furnace, and after high temperature carbonization at 600-800℃ and high temperature carbonization at 1300-1500℃ in a protective atmosphere, respectively obtaining an absorbing layer carbon fiber film and a reflecting layer carbon fiber film; (3) carbon fiber aerogel construction: stacking the absorbing layer carbon fiber film and the reflecting layer carbon fiber film in order, using a high-temperature resistant adhesive solution to bond between each layer, and then placing the multi-layer stacked fiber film in an oven for crosslinking and curing to obtain a carbon fiber film aerogel. In step (1), the mass concentration of the NaCO 3 aqueous solution is 0.1-1.0%, and the pupa is continuously soaked for 0.5-1h after the aqueous solution is boiled. In step (2), the procedure for preparing the absorbing layer carbon fiber film by medium temperature carbonization is as follows: 1) increasing the temperature to T 1 of 120-180℃ at a rate of 5-10℃ / min and maintaining for 0.5-1h; 2) increasing the temperature from T 1 to T 2 of 300-400℃ at a rate of 1-3℃ / min and maintaining for 1-3h; 3) increasing the temperature from T 2 to carbonization temperature T 3 of 600-800℃ at a rate of 0.5-2℃ / min and maintaining for 1-4h; 4) decreasing the temperature from carbonization temperature T 3 to T 2 at a rate of 0.5-2℃ / min; and 5) decreasing the temperature from T 2 to room temperature at a rate of 5-10℃ / min. In step (2), the procedure for preparing the reflecting layer carbon fiber film by high temperature carbonization is as follows: 1) increasing the temperature to T 1 of 120-180℃ at a rate of 5-10℃ / min and maintaining for 0.5-1h; 2) increasing the temperature from T 1 to T 2 of 300-400℃ at a rate of 1-3℃ / min and maintaining for 1-3h; 3) increasing the temperature from T 2 to carbonization temperature T 3 of 1300-1500℃ at a rate of 0.5-2℃ / min and maintaining for 1-4h; 4) decreasing the temperature from carbonization temperature T 3 to T 2 at a rate of 0.5-2℃ / min; and 5) decreasing the temperature from T 2 to room temperature at a rate of 5-10℃ / min.

2. The method of claim 1, wherein: In step (3), the total thickness of the multi-layer stacked fiber film is 9-14mm, and the thickness ratio of the absorbing layer to the reflecting layer is 2-3:

1.

3. The method of claim 1, wherein: In step (3), when the adhesive solution is used for bonding, the amount of adhesive used is 70-120μL per square centimeter on the surface of each layer of fiber film.

4. The method of claim 1, wherein: The crosslinking and curing temperature is 80-100℃, and the crosslinking and curing time is 12-24h. ​ 5. The method of claim 1, wherein: ​ 6. The method of claim 1, wherein: The solvent in the high-temperature resistant adhesive solution in step (3) is any one or two of water, ethanol, or ethylene glycol; the high-temperature resistant adhesive is Al( H2 P O4)3 Mg( H2 P O4)2 Cr( H2 P O4)3 or Zr( H2 P O4)4 One of them; the mass concentration of the high-temperature resistant adhesive solution is 2-15%.

7. The method of claim 1, wherein: ​ 8. The method of claim 1, wherein: ​

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