CN113860848A - Modified carbon fiber/SiO2Preparation method of aerogel composite material - Google Patents

Modified carbon fiber/SiO2Preparation method of aerogel composite material Download PDF

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CN113860848A
CN113860848A CN202111170001.7A CN202111170001A CN113860848A CN 113860848 A CN113860848 A CN 113860848A CN 202111170001 A CN202111170001 A CN 202111170001A CN 113860848 A CN113860848 A CN 113860848A
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carbon fiber
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CN113860848B (en
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秦舒浩
罗丹
龙丽娟
向宇姝
单春燕
张凯
何敏
于杰
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Guizhou Material Industrial Technology Research Institute
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Abstract

The invention provides a modified carbon fiber/SiO2The preparation method of the aerogel composite material comprises the following steps: desizing carbon fibers, oxidizing the carbon fibers by nitric acid, and then performing surface modification grafting treatment on the carbon fibers by using silane coupling agents KH-550 and KH-560 to obtain modified carbon fibers; and (3) uniformly stirring and dispersing the modified carbon fiber and the silicon dioxide wet gel, drying, aging, performing hydrophobic modification, soaking, and freeze-drying. The preparation method of the aerogel composite material adopts the modified carbon fiber to reinforce SiO2Compared with the prior physical combination mode, the aerogel has better mechanical property due to the chemical crosslinking combination of the two,the whole operation method is simple, the operation condition is mild, the steps are closely connected, and the prepared material has good performance.

Description

Modified carbon fiber/SiO2Preparation method of aerogel composite material
Technical Field
The invention relates to the field of aerogel preparation, and particularly relates to modified carbon fiber/SiO2A method for preparing aerogel composite material.
Background
Silicon dioxide (SiO)2) The aerogel is a nano porous solid material which is formed by gathering colloidal particles or nano particles by taking gas as a dispersion medium, and has the excellent characteristics of ultra-light weight, ultra-low heat conductivity, high light transmission, high specific surface area and the like. SiO 22The aerogel has wide application prospect in the fields of heat insulation, adsorption, aerospace and the like. However, SiO2Aerogels have the defects of low strength, poor toughness, fragility, easy moisture absorption and the like, and the application of the aerogels in different fields is limited.
At present, to strengthen SiO2The mechanical properties of the aerogel are that research personnel adopt various fiber materials (mullite fiber, glass fiber and the like) and SiO2And performing composite modification on the aerogel. The aerogel skeleton strength can be improved by doping glass fiber, carbon fiber and ceramic fiber, high polymer, nano particles and the like, and the aerogel composite material meeting certain performance requirements is prepared. The aerogel felt/block is prepared by taking a fiber felt body or reinforcing materials such as short fibers, whiskers, carbon nanotubes and the like as a framework.
However, direct use of fibers with SiO2The bonding is only physical bonding, chemical bond bonding is not generated, serious 'powder falling' phenomenon exists, and the powder falling can cause environmental pollution.
Patent 201110339659.6 reports a method for preparing a silica aerogel composite material from SiO2Aerogel as matrix, glass fibres or fibresThe vinylon is used as a reinforcement, and hydrochloric acid or a silane coupling agent is used as a fiber surface treatment agent. Soaking the glass fiber or the glass wool in a hydrochloric acid solution, slowly stirring for 0.5-2 hours, then taking out, rinsing with water, then carrying out heat treatment at 110 ℃ for 1-5 hours, and cooling at room temperature for later use, or putting the glass fiber or the glass wool after acid treatment into a silane coupling agent treatment solution, slowly stirring for 1-5 hours, then carrying out heat treatment at 110 ℃ for 1-5 hours, and cooling at room temperature for later use. The silane coupling agent is one or more of KH550, KH560 and KH570, the mass ratio of the silane coupling agent to the fibers is 1: 10-1000, and the volume ratio of the silane coupling agent to the solvent is 1: 50-2000. It can be found that the modification method of the silane coupling agent reported in the patent is to complete the modification of the glass fiber by a one-step method. The composite material prepared by the method has general mechanical properties, and the bonding capability between the fiber and the matrix is weak.
Disclosure of Invention
The invention aims to provide an aerogel block composite material, which is reinforced by using modified carbon fibers to reinforce SiO2Compared with the prior physical combination mode, the aerogel has better mechanical properties due to the chemical crosslinking combination of the two, and can obtain SiO2The whole operation method of the block composite material of the aerogel is simple, the operation condition is mild, the steps are connected tightly, and the prepared material has good performance.
In order to achieve the above purpose of the present invention, the following technical solutions are adopted:
the invention provides a preparation method of an aerogel composite material, which comprises the following steps:
desizing carbon fibers, oxidizing the carbon fibers by nitric acid, and then sequentially adopting silane coupling agents KH-550 and KH-560 to perform surface modification grafting treatment on the carbon fibers to obtain modified carbon fibers;
and (3) uniformly stirring and dispersing the modified carbon fiber and the silicon dioxide wet gel, drying, aging, performing hydrophobic modification, soaking, and freeze-drying.
Carbon fibers have many excellent characteristics, but are difficult to be well combined with a matrix material due to smooth surfaces, and the dispersion condition of the fibers in the matrix is an important problem to be solved. The reported literature at present mainly adopts carbon fiber felt, and few reports exist on the preparation of aerogel block composite materials by directly using carbon fibers.
Based on the prior art, the invention provides a modified carbon fiber/SiO2A novel method for preparing aerogel composite material.
The preparation method of the aerogel composite material provided by the invention comprises the steps of firstly modifying carbon fibers by adopting a silane coupling agent, then the modified carbon fiber is mixed with the silica wet gel, thereby achieving the effect of improving the relevant performance of the aerogel material, firstly, silane coupling agent gamma-aminopropyl triethoxy silane KH-550 is adopted for modification, then the modified silane coupling agent gamma-glycidoxypropyltrimethoxysilane KH-560 is adopted for modification, that is, the whole modification step not only needs to adopt a specific silane coupling agent, but also needs to pay attention to the sequence of the modification and the specific operation steps of the modification, because-OH on the surface of the carbon fiber can react with Si-OH of KH550 to generate Si-O-Si combination, and simultaneously, the surface of the carbon fiber is provided with-NH.2Introducing KH560, utilizing epoxy group of KH560 and-NH on carbon fiber surface2The reaction is carried out, so that Si-OH is carried on the surface of the carbon fiber, the Si-OH reacts with Si-OH of the silica sol to form Si-O-Si crosslinking, and in addition, a carbon long chain is formed on the surface of the silica sol, so that the performance of a crosslinked network is improved, and the modification step and the specific operation step of the modification are required to be operated and executed according to the scheme of the invention.
Figure BDA0003292773350000031
Preferably, as a further practicable aspect, the step of modifying with the silane coupling agent KH-550 comprises:
soaking carbon fiber in KH-550 modified solution at 40-70 deg.C for more than 24 hr, washing with deionized water, and drying at 80-90 deg.C for more than 8 hr.
Preferably, as a further practicable aspect, the step of modifying with the silane coupling agent KH-560 comprises:
soaking the carbon fiber modified by KH-550 in KH-560 modified solution for more than 24h at 40-70 ℃, washing with deionized water for multiple times, and drying at 80-90 ℃ for more than 8 h.
Preferably, as a further practicable embodiment, the KH-550 modification solution is prepared by a method comprising:
mixing 75% by volume of ethanol and 25% by volume of deionized water in sequence, adjusting pH to 2-4 with acetic acid, adding 25% by volume of KH-550, and stirring at 50 deg.C for 30min to obtain KH-550 modified solution.
Preferably, as a further practicable embodiment, the KH-560 modification solution is prepared by a method comprising:
mixing 80% by volume of ethanol and 10% by volume of deionized water in sequence, adjusting pH to 2-4 with acetic acid, adding 10% by volume of KH-560, and stirring at 50 deg.C for 30min to obtain KH-560 modified solution.
Preferably, as a further practicable aspect, in the process of uniformly stirring and dispersing the modified carbon fiber and the silica wet gel, the added mass of the modified carbon fiber is 0.5 to 2 wt% of the total mass. It is required to be controlled within this mass percentage range because it is found in practice that if the amount added is further reduced, a block material cannot be formed, and if the amount is too large, not only is there no improvement in properties, but also the density is increased to deteriorate the heat insulating properties, so that the most excellent range is controlled to be between 0.5 and 2 wt%.
Preferably, as a further practicable scheme, the modified carbon fiber is cut into a length of 1-2mm, and then is uniformly dispersed with silica wet gel by stirring.
Preferably, as a further practicable aspect, the temperature of drying after stirring and dispersing uniformly is 40 to 60 ℃.
Preferably, as a further implementable solution, the step of aging comprises: soaking in ethanol, aging for more than 24h, and changing the ethanol solution every 10-12 h.
Preferably, as a further implementable solution, the freeze-drying time is 12-24 h.
According to the invention, each parameter in the preparation method of the aerogel block material is regulated and controlled within a proper range, so that the performance of each aspect of the prepared material is optimal.
In practical operation, the optimal operation mode of the preparation method of the aerogel composite material can be carried out according to the following steps:
step 1: carbon fiber modification:
(1) desizing:
selecting a carbon fiber (Dongli T700 CF) fiber section with the length of 2m, and carrying out vacuum oven drying treatment on the carbon fiber to obtain a dry carbon fiber precursor. The carbon fiber is then desized, placed in a mixed solution of acetone and ethanol (volume ratio of 1:1) and subjected to ultrasonic desizing for 6h, wherein the solution temperature is kept below 56 ℃ (the boiling point of acetone is 56.53 ℃). After desizing is finished, washing the acetone solution on the surface of the carbon fiber with ethanol, and then putting the carbon fiber into a vacuum drying oven for drying treatment, wherein the temperature of the oven is 80 ℃, and the drying time is 6 h.
(2) Surface oxidation:
after the surface of the carbon fiber is subjected to desizing treatment, placing a carbon fiber bundle at the bottom of a flask, pouring 100ml of concentrated nitric acid into the flask and enabling the carbon fiber bundle to pass through the flask, starting an oil bath kettle, setting the temperature to be 70 ℃, carrying out nitric acid acidification treatment on the desized carbon fiber, and reacting for 4 hours, thereby laying a foundation for the next carbon fiber surface grafting modification work. And after the nitric acid oxidation experiment on the surface of the carbon fiber is finished, the carbon fiber after the concentrated nitric acid oxidation treatment is placed in an oven for drying treatment for 8 hours, the temperature is set to be 85 ℃, and the carbon fiber is taken out after the drying treatment and is placed in a sample sealing bag for use.
(3) Surface grafting
Carrying out surface grafting treatment on the carbon fibers after surface oxidation by using silane coupling agents KH-550 and KH-560; firstly preparing KH-550 modified liquid, mixing 75% by volume of ethanol and 25% by volume of deionized water, then adjusting the pH value to 3 by using acetic acid, then adding 25% KH-550, then stirring the mixed solution at 50 ℃ for 30min to obtain the KH-550 modified liquid, then soaking the oxidized carbon fiber bundle in the modified liquid for 24h at 50 ℃, washing the carbon fiber bundle with deionized water after the modification is finished, and then drying the carbon fiber bundle in a vacuum drying box at 85 ℃ for 8 h.
Modifying a carbon fiber bundle by using KH-550, then modifying again by using an ethanol solution of KH-560, mixing 80 volume percent of 10 volume percent of ethanol and deionized water, then adjusting the pH value to 4 by using acetic acid, then adding 10 volume percent of KH-550, then stirring the mixed solution at 50 ℃ for 30min to obtain a KH-560 modified solution, then soaking the oxidized carbon fiber bundle in the modified solution at 50 ℃ for 24h, washing the carbon fiber bundle with deionized water after the modification is finished, then drying the carbon fiber bundle in a vacuum drying oven at 85 ℃ for 8h, taking out the carbon fiber bundle after the drying is finished, and putting the carbon fiber bundle in a self-sealing bag for later use.
Step 2: preparing a modified carbon fiber/silicon dioxide aerogel composite material:
(1) preparation of pure silica aerogel
Dispersing a silicon source in a mixed solution of an organic solvent and deionized water, wherein the silicon source is Tetraethoxysilane (TEOS) or silica sol, the organic solvent is absolute ethyl alcohol, and the proportion of Tetraethoxysilane (TEOS), absolute ethyl alcohol and deionized water is 1:4: 5.
And adjusting the pH value of the mixed solution to 2-3 by adding acid. The acid is hydrochloric acid.
The solution was heated to 80 ℃ and stirred for a period of time to allow sufficient hydrolysis of the TEOS.
And adding ammonia water to adjust the pH value of the solution to 6-7, pouring the solution into a mold, sealing and standing for gelation.
(2) Preparation of modified carbon fiber/silicon dioxide aerogel composite material
Pouring the silica sol with certain viscosity prepared in the step (1) into a mold, adding chopped carbon fibers (with the length of 1-2 mm), stirring to uniformly disperse the carbon fibers (the mass fraction of the carbon fibers is 0.5-2 percent respectively), putting the carbon fibers into a 50-DEG C oven, aging and hardening the carbon fibers, adding ethanol, soaking and aging the carbon fibers for 24 hours (replacing the ethanol solution every 12 hours), and then adding n-hexane and ethanol in a volume ratio of 1:1 for 12 hours, transferring the mixture to a mixed solution of n-hexane and trimethylchlorosilane in a volume ratio of 10:1 for 24 hours, after the surface modification is finished, soaking the mixed solution for 36 hours by using normal hexane (changing the normal hexane solution every 12 hours), after the solvent replacement is finished, freezing and drying the wet gel to obtain dry gel, wherein the drying step is specifically; and (3) completely freeze-drying the wet gel block in liquid nitrogen, and then putting the wet gel block into a freeze dryer for vacuum drying for 12-24 hours to obtain the aerogel block.
Compared with the prior art, the invention has the beneficial effects that:
(1) according to the invention, the carbon fiber is modified, so that the content of functional groups and the length of carbon chains on the surface of the carbon fiber are increased, and the method is favorable for improving the related performance of the composite material after the carbon fiber is subsequently crosslinked and compounded with aerogel.
(2) The surface of the modified carbon fiber contains Si-OH, which is beneficial to the Si-O-Si crosslinking reaction with the hydroxyl on the surface of the silicon dioxide.
(3) The composite material of the invention strengthens SiO by adopting modified carbon fiber2Compared with the traditional physical combination mode, the aerogel has better mechanical properties due to the chemical crosslinking combination of the two, the whole operation method is simple, the operation condition is mild, the steps are closely connected, and the prepared material has good properties.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings.
FIG. 1 is a sample view of a composite material provided in example 1 of the present invention;
FIG. 2 is a sample view of a composite material provided in example 2 of the present invention;
FIG. 3 is a sample view and SEM image of a composite material provided in example 3 of the present invention;
FIG. 4 is a sample diagram of a pure silica aerogel provided in comparative example 1 of the present invention;
fig. 5 is a sample view and SEM image of the composite material provided in comparative example 2 of the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
Example 1
The preparation method of the aerogel composite material comprises the following steps:
step 1: carbon fiber modification:
(1) desizing:
selecting a carbon fiber (Dongli T700 CF) fiber section with the length of 2m, and carrying out vacuum oven drying treatment on the carbon fiber to obtain a dry carbon fiber precursor. The carbon fiber is then desized, placed in a mixed solution of acetone and ethanol (volume ratio of 1:1) and subjected to ultrasonic desizing for 6h, wherein the solution temperature is kept below 56 ℃ (the boiling point of acetone is 56.53 ℃). After desizing is finished, washing the acetone solution on the surface of the carbon fiber with ethanol, and then putting the carbon fiber into a vacuum drying oven for drying treatment, wherein the temperature of the oven is 80 ℃, and the drying time is 6 h.
(2) Surface oxidation:
after the surface of the carbon fiber is subjected to desizing treatment, placing a carbon fiber bundle at the bottom of a flask, pouring 100ml of concentrated nitric acid into the flask and enabling the carbon fiber bundle to pass through the flask, starting an oil bath kettle, setting the temperature to be 70 ℃, carrying out nitric acid acidification treatment on the desized carbon fiber, and reacting for 4 hours, thereby laying a foundation for the next carbon fiber surface grafting modification work. And after the nitric acid oxidation experiment on the surface of the carbon fiber is finished, the carbon fiber after the concentrated nitric acid oxidation treatment is placed in an oven for drying treatment for 8 hours, the temperature is set to be 85 ℃, and the carbon fiber is taken out after the drying treatment and is placed in a sample sealing bag for use.
(3) Surface grafting
Carrying out surface grafting treatment on the carbon fibers after surface oxidation by using silane coupling agents KH-550 and KH-560; firstly preparing KH-550 modified liquid, mixing 75% by volume of ethanol and 25% by volume of deionized water, then adjusting the pH value to 3 by using acetic acid, then adding 25% KH-550, then stirring the mixed solution at 50 ℃ for 30min to obtain the KH-550 modified liquid, then soaking the oxidized carbon fiber bundle in the modified liquid for 24h at 50 ℃, washing the carbon fiber bundle with deionized water after the modification is finished, and then drying the carbon fiber bundle in a vacuum drying box at 85 ℃ for 8 h.
Modifying a carbon fiber bundle by using KH-550, then modifying again by using an ethanol solution of KH-560, mixing 80 volume percent of 10 volume percent of ethanol and deionized water, then adjusting the pH value to 4 by using acetic acid, then adding 10 volume percent of KH-550, then stirring the mixed solution at 50 ℃ for 30min to obtain a KH-560 modified solution, then soaking the oxidized carbon fiber bundle in the modified solution at 50 ℃ for 24h, washing the carbon fiber bundle with deionized water after the modification is finished, then drying the carbon fiber bundle in a vacuum drying oven at 85 ℃ for 8h, taking out the carbon fiber bundle after the drying is finished, and putting the carbon fiber bundle in a self-sealing bag for later use.
Step 2: preparing a modified carbon fiber/silicon dioxide aerogel composite material:
(1) preparation of pure silica aerogel
Dispersing a silicon source in a mixed solution of an organic solvent and deionized water, wherein the silicon source is Tetraethoxysilane (TEOS) or silica sol, the organic solvent is absolute ethyl alcohol, and the proportion of Tetraethoxysilane (TEOS), absolute ethyl alcohol and deionized water is 1:4: 5.
And adjusting the pH value of the mixed solution to 2-3 by adding acid. The acid is hydrochloric acid.
The solution was heated to 80 ℃ and stirred for a period of time to allow sufficient hydrolysis of the TEOS.
And adding ammonia water to adjust the pH value of the solution to 6-7, pouring the solution into a mold, sealing and standing for gelation.
(2) Preparation of modified carbon fiber/silicon dioxide aerogel composite material
Pouring the silica sol with certain viscosity prepared in the step (1) into a mold, adding chopped carbon fibers (with the length of 1-2 mm), stirring to uniformly disperse the carbon fibers (the mass fraction of the carbon fibers accounts for 0.5 wt% of the total mass of the carbon fibers and the silica gel), putting into a 50 ℃ oven, aging and hardening, adding ethanol, soaking and aging for 24 hours (replacing the ethanol solution every 12 hours), and then putting into a mold, wherein the volume ratio of n-hexane to ethanol is 1:1 for 12 hours, transferring the mixture to a mixed solution of n-hexane and trimethylchlorosilane in a volume ratio of 10:1 for 24 hours, after the surface modification is finished, soaking the mixed solution for 36 hours by using normal hexane (changing the normal hexane solution every 12 hours), after the solvent replacement is finished, freezing and drying the wet gel to obtain dry gel, wherein the drying step is specifically; and (3) completely freeze-drying the wet gel block in liquid nitrogen, freeze-drying the wet gel block in a freeze dryer for 12-24 hours to obtain the gel block, wherein a specifically prepared sample picture is shown in figure 1.
Example 2
The other operating steps correspond to those of example 1, with the difference that: the mass fraction of the carbon fiber accounts for 2 wt% of the total mass of the carbon fiber and the silica gel, and a specific sample diagram is shown in figure 2.
Example 3
The other operating steps correspond to those of example 1, with the difference that: the mass fraction of the carbon fiber accounts for 1 wt% of the total mass of the carbon fiber and the silica gel, and a specific sample diagram and an SEM diagram are shown in a figure 3.
Example 4
The other operating steps correspond to those of example 1, with the difference that:
surface grafting of step 1 (3):
carrying out surface grafting treatment on the carbon fibers after surface oxidation by using silane coupling agents KH-550 and KH-560; firstly preparing KH-550 modified liquid, mixing 75% by volume of ethanol and 25% by volume of deionized water, then adjusting the pH value to 2 by using acetic acid, then adding 25% KH-550, then stirring the mixed solution at 50 ℃ for 30min to obtain the KH-550 modified liquid, then soaking the oxidized carbon fiber bundle in the modified liquid for 30h at 40 ℃, washing the carbon fiber bundle with deionized water after the modification is finished, and then drying the carbon fiber bundle in a vacuum drying box at 90 ℃ for 10 h.
Modifying a carbon fiber bundle by using KH-550, then modifying again by using an ethanol solution of KH-560, mixing 80 volume percent of ethanol and 10 volume percent of deionized water, then adjusting the pH value to 4 by using acetic acid, then adding 10 volume percent of KH-550, then stirring the mixed solution at 50 ℃ for 30min to obtain a KH-560 modified solution, then soaking the oxidized carbon fiber bundle in the modified solution at 50 ℃ for 30h, washing the carbon fiber bundle with deionized water after the modification is finished, then drying the carbon fiber bundle in a vacuum drying oven at 80 ℃ for 8h, taking out the carbon fiber bundle after the drying is finished, and putting the carbon fiber bundle in a self-sealing bag for later use.
Example 5
The other operating steps correspond to those of example 1, with the difference that:
surface grafting of step 1 (3):
carrying out surface grafting treatment on the carbon fibers after surface oxidation by using silane coupling agents KH-550 and KH-560; firstly preparing KH-550 modified liquid, mixing 75% by volume of ethanol and 25% by volume of deionized water, then adjusting the pH value to 4 by using acetic acid, then adding 25% KH-550, then stirring the mixed solution at 50 ℃ for 30min to obtain the KH-550 modified liquid, then soaking the oxidized carbon fiber bundle in the modified liquid for 30h at 40 ℃, washing the carbon fiber bundle with deionized water after the modification is finished, and then drying the carbon fiber bundle in a vacuum drying box at 90 ℃ for 10 h.
Modifying a carbon fiber bundle by using KH-550, then modifying again by using an ethanol solution of KH-560, mixing 80 volume percent of 10 volume percent of ethanol and deionized water, then adjusting the pH value to 2 by using acetic acid, then adding 10 volume percent of KH-550, then stirring the mixed solution at 50 ℃ for 30min to obtain a KH-560 modified solution, then soaking the oxidized carbon fiber bundle in the modified solution at 50 ℃ for 30h, washing the carbon fiber bundle with deionized water after the modification is finished, then drying the carbon fiber bundle in a vacuum drying oven at 90 ℃ for 10h, taking out the carbon fiber bundle after the drying is finished, and putting the carbon fiber bundle in a self-sealing bag for later use.
Comparative example 1
Pure silica aerogel material:
dispersing a silicon source in a mixed solution of an organic solvent and deionized water, wherein the silicon source is Tetraethoxysilane (TEOS), the organic solvent is absolute ethyl alcohol, and the ratio of Tetraethoxysilane (TEOS), absolute ethyl alcohol and deionized water is 1:4: 5.
And adjusting the pH value of the mixed solution to 2-3 by adding acid. The acid is hydrochloric acid.
The solution was heated to 80 ℃ and stirred for a period of time to allow sufficient hydrolysis of the TEOS.
Adding ammonia water to adjust the pH value of the solution to 6-7, pouring the solution into a mold, sealing and standing for gelation, and specifically preparing a sample shown in figure 4.
Comparative example 2
TEOS is dispersed in a mixed solution of absolute ethyl alcohol and deionized water, and the proportion of Tetraethoxysilane (TEOS), absolute ethyl alcohol and deionized water is 1:4: 5.
And adjusting the pH value of the mixed solution to 2-3 by adding hydrochloric acid.
The solution was heated to 80 ℃ and stirred for 1h to fully hydrolyze the TEOS.
And adding ammonia water to adjust the pH value of the solution to 6-7, pouring the solution into a mold, sealing and standing.
Pouring the prepared silica sol with certain viscosity into a mold, adding unmodified chopped carbon fibers (with the length of 1-2 mm), stirring to uniformly disperse the carbon fibers (the mass fraction of the carbon fibers is 1 wt%), putting the carbon fibers into a 50-DEG C oven, aging and hardening the carbon fibers, adding ethanol, soaking and aging for 24 hours (changing an ethanol solution every 12 hours), and then adding n-hexane and ethanol in a volume ratio of 1:1 for 12 hours, transferring the mixture to a mixed solution of n-hexane and trimethylchlorosilane in a volume ratio of 10:1 for 24 hours, after the surface modification is finished, soaking the mixed solution for 36 hours by using normal hexane (changing the normal hexane solution every 12 hours), after the solvent replacement is finished, freeze-drying the wet gel to obtain dry gel, wherein the drying step is specifically; and (3) completely freeze-drying the wet gel block in liquid nitrogen, and then putting the wet gel block into a freeze dryer for vacuum drying for 12-24 hours to obtain the aerogel block. The image of the sample prepared specifically and the SEM image are shown in fig. 5.
TABLE 1 mechanical Properties of modified carbon fiber silica aerogels
Figure BDA0003292773350000121
The data in table 1 show that the best mechanical property effect is example 3, it can be seen that the mechanical property is facilitated when the addition quality of the carbon fiber is appropriate, and other examples compare with example 3, the mechanical property of the material is better, and the thermal conductivity coefficient reaches the lowest. Comparative example 1 due to pure SiO2The aerogel is powder and has no mechanical property. Comparative example 2 unmodified carbon fiber SiO2The surface of the aerogel composite material block has large cracks and is crushed basically once being pressed. Therefore, the mechanical property and the heat-insulating property of the composite material can be obviously improved after the composite material is modified by adopting the specific modification method.
While particular embodiments of the present invention have been illustrated and described, it would be obvious that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims (10)

1. Modified carbon fiber/SiO2The preparation method of the aerogel composite material is characterized by comprising the following steps of:
desizing carbon fibers, oxidizing the carbon fibers by nitric acid, and then sequentially adopting silane coupling agents KH-550 and KH-560 to perform surface modification grafting treatment on the carbon fibers to obtain modified carbon fibers with long carbon chain structures;
and after uniformly stirring and dispersing the modified carbon fiber and the silicon dioxide wet gel, drying, aging, performing hydrophobic modification and soaking, and freeze-drying to form the aerogel with a cross-linked structure.
2. The method according to claim 1, wherein the step of modifying with silane coupling agent KH-550 comprises:
soaking carbon fiber in KH-550 modified solution at 40-70 deg.C for more than 24 hr, washing with deionized water, and drying at 80-90 deg.C for more than 8 hr.
3. The method according to claim 1, wherein the step of modifying with the silane coupling agent KH-560 comprises:
soaking the modified carbon fiber in KH-550 in KH-560 modifying solution at 40-70 deg.C for over 24 hr, washing with deionized water, and drying at 80-90 deg.C for over 8 hr.
4. The method for preparing the KH-550 modified solution, according to claim 2, wherein the method for preparing the KH-550 modified solution comprises the following steps:
mixing 75% by volume of ethanol and 25% by volume of deionized water in sequence, adjusting pH to 2-4 with acetic acid, adding 25% by volume of KH-550, and stirring at 50 deg.C for 30min to obtain KH-550 modified solution.
5. The preparation method according to claim 3, wherein the KH-560 modified solution is prepared by a method comprising:
mixing 80% by volume of ethanol and 10% by volume of deionized water in sequence, adjusting pH to 2-4 with acetic acid, adding 10% by volume of KH-560, and stirring at 50 deg.C for 30min to obtain KH-560 modified solution.
6. The production method according to claim 1, wherein the added mass of the modified carbon fiber is 0.5 to 2 wt% of the total mass in the process of uniformly stirring and dispersing the modified carbon fiber and the silica wet gel.
7. The preparation method according to claim 6, wherein the modified carbon fiber is cut into a length of 1-2mm, and then uniformly dispersed with the silica wet gel by stirring.
8. The method according to claim 1, wherein the drying temperature is 40 to 60 ℃ after the uniform dispersion by stirring.
9. The method of claim 1, wherein the step of aging comprises: soaking and aging with ethanol for more than 24h, changing the ethanol solution every 10-12h, and then soaking with a mixed solution of n-hexane and ethanol at a volume ratio of 1:1 for 12 h;
after the aging is finished, transferring the mixture into a mixed solution of n-hexane and trimethylchlorosilane in a volume ratio of 10:1 for hydrophobic modification, and then soaking the mixture for 12 hours by using the n-hexane.
10. The method of claim 1, wherein the freeze-drying time is 12-24 hours.
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