CN107051339B - Fiber composite toughened SiO2Aerogel and preparation method thereof - Google Patents

Abstract

The invention discloses fiber toughened SiO₂Aerogel and a preparation method thereof, belonging to the technical field of aerogel. The preparation method comprises the steps of preparing fiber composite SiO by a sol-gel method₂Wet gel, aging, replacing residual reaction medium by solvent exchange, surface modification, and drying under normal pressure to obtain fiber composite toughened SiO₂Aerogels, respectively polyacrylonitrile toughened SiO₂Aerogel and aramid fiber toughened SiO₂Aerogel and polypropylene toughened SiO₂An aerogel. The preparation method has the advantages of simplification, safety and low cost of the preparation process, and can realize large-scale production, and the fiber composite toughened SiO prepared by the preparation method₂The wet gel has good compressibility.

Description

Fiber composite toughened SiO2Aerogel and preparation method thereof

Technical Field

The invention belongs to the technical field of aerogel, and particularly relates to fiber composite toughened SiO₂Aerogel and a preparation method thereof.

Background

SiO₂The aerogel is a novel amorphous solid porous material which is formed by gathering nano-scale particles and takes air as a dispersion medium, has very special and excellent performances in the aspects of thermology, electricity, acoustics, optics, chemistry and the like due to a series of characteristics of low density, high porosity, high specific surface area, low thermal conductivity, low sound wave propagation rate, low dielectric constant and the like, has a very wide application field, and particularly has a wide application prospect in the aspects of heat preservation and insulation (serving as a super heat-insulating material), chemical catalysis (serving as a novel efficient catalyst and a catalyst carrier), environmental management (serving as an adsorption material of toxic harmful gas and heavy metal ions) and the like, and plays an important role in realizing industrial energy conservation and emission reduction and building a conservation-oriented society.

Whereas conventionally SiO₂The preparation of the aerogel adopts a supercritical drying process, which not only consumesHigh energy, expensive equipment and high cost, and because high temperature and high pressure have certain dangerousness, continuous and large-scale production is difficult to carry out, thereby limiting the commercial application of the high-temperature high-pressure high-temperature high-pressure high-. To give full play to SiO₂The excellent performance of the aerogel is firstly to solve the problem of SiO₂The main objectives of the aerogel preparation process are to simplify, secure and reduce the cost of the preparation process, so that the aerogel can be produced on a large scale. In addition to this, due to SiO₂The aerogel has the defects of low strength, poor toughness, easy breakage and the like, and limits the practical application of the product to a certain extent, so that the preparation of the flexible SiO₂Aerogels are of great importance.

Disclosure of Invention

In order to overcome the problems in the prior art, the invention provides fiber composite toughened SiO₂Aerogel and a method for preparing the same, the method being simple, safe and low cost, and being capable of mass production, the fiber-toughened SiO prepared by the method₂Aerogels have some flexibility.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

fiber composite toughened SiO₂The preparation method of the aerogel comprises the steps of preparing fiber composite SiO by a sol-gel method₂Wet gel, aging, replacing residual reaction medium by solvent exchange, surface modification, and drying under normal pressure to obtain fiber composite toughened SiO₂An aerogel.

Further, the sol-gel method is used for preparing fiber composite SiO₂The specific method of the wet gel is as follows:

firstly, weighing a certain amount of surfactant, adding the surfactant into a reaction container, then adding methanol and glacial acetic acid solution in proportion, stirring to dissolve the surfactant, then adding a precursor and N, N-dimethylformamide in proportion, placing the mixture in a constant-temperature magnetic stirrer, stirring for 0.5-1h at 20-40 ℃ to fully hydrolyze the mixture, then adding ammonia water to adjust the pH value to 8.5, stirring to fully mix the ammonia water with the solution, then taking out a rotor, adding clean fibers, and placing the mixture in a constant-temperature water bath kettle at 40 ℃ until gel is formed.

Further, the surfactant is cetyl trimethyl ammonium bromide.

Further, the amount ratio of the surfactant, the methanol and the glacial acetic acid substance is 0.002:1: 6.

Furthermore, the precursor is formed by mixing methyltrimethoxysilane and dimethyldimethoxysilane according to the mass ratio of 1: 0.6.

Furthermore, the mass ratio of the added precursor, methanol, glacial acetic acid solution and N, N-dimethylformamide is 1:8:12: 0.5.

Further, the molar concentration of the glacial acetic acid is 0.01 mol/L.

Further, the fiber is one of polyacrylonitrile, aramid fiber and polypropylene, and the adding amount of the fiber is 1.5% of the mass of the aerogel.

Further, firstly aging for 6h, then adding isopropanol for aging for 6h, pouring out the liquid after aging, and replacing for 6h under normal hexane solvent;

the normal pressure drying is to pour out the residual liquid, put the sample into a constant temperature air-blast drying oven at 30 ℃ for drying for 12h, and then put into a constant temperature air-blast drying oven at 40 ℃ for drying for 24 h.

Fiber composite toughened SiO prepared by the preparation method₂An aerogel.

Has the advantages that: compared with the prior art, the fiber composite toughened SiO provided by the invention₂The preparation method of the aerogel is to prepare the fiber composite SiO by a sol-gel method₂Aging wet gel, replacing residual reaction medium by solvent exchange, performing surface modification, drying at normal pressure, replacing liquid in the wet gel with air, and keeping the skeleton network structure of the gel unchanged, thereby obtaining the fiber composite toughened SiO₂An aerogel; the preparation method has the advantages of simplification, safety and low cost of the preparation process, and can realize large-scale production; fiber composite toughened SiO prepared by the preparation method₂Wet coagulationThe glue has good compressibility.

Further, methyltrimethoxysilane (MTMS) is selected as a precursor to prepare SiO₂The aerogel is easy to dissolve in an organic solvent, high-dispersion and high-uniformity sol is easy to obtain, chemical proportion is easy to realize, and unnecessary byproducts can be avoided.

Further, methanol is selected as a solvent in the sol-gel reaction process, so that the reaction process is simple.

Further, an acid-base two-step catalysis method is adopted, glacial acetic acid solution is used for catalyzing hydrolysis, ammonia water is used for catalyzing polycondensation, the reaction time is shortened, and when the polycondensation rate is greater than the hydrolysis rate, gel formed by condensation polymerization of silicic acid monomers has a network structure with strong cross-linked branched chains, so that the structural strength is high.

Further, the final result of the aging process coarsens and smoothes the gel network and improves strength.

Furthermore, n-hexane with low surface tension is selected as a displacement solvent and a drying medium, so that the surface tension and the contact angle between the solvent and the aerogel network structure can be reduced, and the capillary pressure is reduced, so that the aerogel shrinkage is reduced.

Furthermore, the method of drying under normal pressure is low in cost, continuous in production process and suitable for large-scale production.

Drawings

FIG. 1 is a diagram of fiber composite toughened SiO₂The aerogel preparation flow diagram;

FIG. 2 shows different fiber composite toughened SiO₂Scanning electron micrographs of aerogels;

FIG. 3 shows different fiber composite toughened SiO₂An infrared spectrum of the aerogel;

FIG. 4 shows different fiber composite toughened SiO₂Thermogravimetric analysis of aerogels;

FIG. 5 shows different fiber composite toughened SiO₂Pressure strain curve of aerogel.

Detailed Description

The invention is further elucidated with reference to the figures and embodiments.

Fiber composite toughened SiO₂The preparation method of the aerogel comprises the steps of preparing fiber composite SiO by a sol-gel method₂Aging wet gel, replacing residual reaction medium by solvent exchange, performing surface modification, drying at normal pressure, replacing liquid in the wet gel with air, and keeping the skeleton network structure of the gel unchanged, thereby obtaining the fiber composite toughened SiO₂An aerogel.

Further, the sol-gel method is used for preparing fiber composite SiO₂The specific method of the wet gel is as follows:

firstly, weighing a certain amount of surfactant, adding the surfactant into a reaction container, then adding methanol and glacial acetic acid solution in proportion, stirring to dissolve the surfactant, then adding a precursor and N, N-dimethylformamide in proportion, placing the mixture in a constant-temperature magnetic stirrer, stirring for 0.5-1h at 20-40 ℃ to fully hydrolyze the mixture, then adding ammonia water to adjust the pH value to 8.5, stirring to fully mix the ammonia water with the solution, then taking out a rotor, adding clean fibers, and placing the mixture in a constant-temperature water bath kettle at 40 ℃ until gel is formed.

Further, the surfactant is cetyl trimethyl ammonium bromide.

Further, the amount ratio of the surfactant, the methanol and the glacial acetic acid substance is 0.002:1: 6.

Furthermore, the precursor is formed by mixing methyltrimethoxysilane and dimethyldimethoxysilane according to the mass ratio of 1: 0.6.

Furthermore, the mass ratio of the added precursor, methanol, glacial acetic acid solution and N, N-dimethylformamide is 1:8:12: 0.5.

Further, the molar concentration of the glacial acetic acid is 0.01 mol/L.

Further, the fiber is one of polyacrylonitrile, aramid fiber and polypropylene, and the adding amount of the fiber is 1.5% of the mass of the aerogel.

Further, firstly aging for 6h, then adding isopropanol for aging for 6h, pouring out the liquid after aging, and replacing for 6h under normal hexane solvent;

the normal pressure drying is to pour out the residual liquid, put the sample into a constant temperature air-blast drying oven at 30 ℃ for drying for 12h, and then put into a constant temperature air-blast drying oven at 40 ℃ for drying for 24 h.

Fiber composite toughened SiO prepared by the preparation method₂An aerogel.

Example 1

1. Polyacrylonitrile toughened SiO₂Method for producing aerogels

Referring to fig. 1, a certain amount of surfactant (cetyl trimethyl ammonium bromide) is first weighed into a beaker, and then methanol and glacial acetic acid solution are added in proportion, wherein the ratio of the amount of the surfactant, the methanol and the glacial acetic acid is 0.002:1: 6. Stirring to dissolve surfactant, adding MTMS (methyl trimethoxy silane), DMMS (dimethyl dimethoxy silane) and DMF (N, N-dimethylformamide) according to a certain proportion, placing in a constant temperature magnetic stirrer, stirring at 30 ℃ for 1h to fully hydrolyze, adding ammonia water to adjust pH value to 8.5, stirring for 5min to fully mix ammonia water with the solution, taking out a rotor, adding cleaned 10mm short-cut polyacrylonitrile fiber with 1.5% of aerogel mass, placing in a constant temperature water bath kettle at 40 ℃ until the solution forms gel, aging for 6h after the gel, adding isopropanol to age for 6h, pouring out the liquid after aging, adding a certain amount of N-hexane to replace the solvent for 6h, pouring out the liquid in a beaker, placing the beaker in a constant temperature drying oven at 30 ℃ to dry for 12h, then placing in a constant temperature drying oven at 40 ℃ to dry for 24h, the preparation is finished. Wherein the precursor (MTMS: DMDMMS is 1: 0.6), methanol: water (acetic acid c is 0.01mol/L) and DMF are mixed and stirred according to the mass ratio of 1:8:12: 0.5.

2. Polyacrylonitrile toughened SiO₂Aerogel

Toughening prepared polyacrylonitrile SiO₂The aerogels were subjected to various characterizations, the results of which are referenced in fig. 2-5.

Example 2

1. Polyacrylonitrile toughened SiO₂Method for producing aerogels

Referring to fig. 1, a certain amount of surfactant (cetyl trimethyl ammonium bromide) is first weighed into a beaker, and then methanol and glacial acetic acid solution are added in proportion, wherein the ratio of the amount of the surfactant, the methanol and the glacial acetic acid is 0.002:1: 6. Stirring to dissolve surfactant, adding MTMS (methyl trimethoxy silane), DMMS (dimethyl dimethoxy silane) and DMF (N, N-dimethylformamide) according to a certain proportion, placing in a constant temperature magnetic stirrer, stirring at 20 deg.C for 1h to fully hydrolyze, adding ammonia water to adjust pH to 8.5, stirring for 5min to fully mix ammonia water with the solution, taking out a rotor, adding cleaned 10mm short-cut polyacrylonitrile fiber with 1.5% of aerogel mass, placing in a constant temperature water bath at 40 deg.C until the solution forms gel, aging for 6h after the gel, adding isopropanol, aging for 6h, pouring out the liquid after aging, adding a certain amount of N-hexane for solvent replacement for 6h, pouring out the liquid in a beaker, placing the beaker in a constant temperature drying oven at 30 deg.C for drying for 12h, then placing in a constant temperature drying oven at 40 deg.C for drying for 24h, the preparation is finished. Wherein the precursor (MTMS: DMDMMS is 1: 0.6), methanol: water (acetic acid c is 0.01mol/L) and DMF are mixed and stirred according to the mass ratio of 1:8:12: 0.5.

Example 3

1. Aramid fiber toughened SiO₂Method for producing aerogels

Referring to fig. 1, a certain amount of surfactant (cetyl trimethyl ammonium bromide) is first weighed into a beaker, and then methanol and glacial acetic acid solution are added in proportion, wherein the ratio of the amount of the surfactant, the methanol and the glacial acetic acid is 0.002:1: 6. Stirring to dissolve a surfactant, adding MTMS (methyl trimethoxy silane), DMMS (dimethyl dimethoxy silane) and DMF (N, N-dimethylformamide) according to a proportion, placing in a constant-temperature magnetic stirrer, stirring for 1h at 30 ℃ to fully hydrolyze the surfactant, adding ammonia water to adjust the pH value to 8.5, stirring for 5min to fully mix the ammonia water with the solution, taking out a rotor, adding cleaned 6mm short-cut aramid fibers accounting for 1.5% of the mass of aerogel, placing in a constant-temperature water bath at 40 ℃ until the solution forms gel, aging for 6h after the gel, adding isopropanol to age for 6h, pouring the liquid out after the aging, adding a certain amount of N-hexane to replace the solvent for 6h, pouring out the liquid in a beaker, placing the beaker in a constant-temperature drying air blowing box at 30 ℃ to dry for 12h, then placing in a constant-temperature drying air blowing box at 40 ℃ to dry for 24h, the preparation is finished. Wherein the precursor (MTMS: DMDMMS is 1: 0.6), methanol: water (acetic acid c is 0.01mol/L) and DMF are mixed and stirred according to the mass ratio of 1:8:12: 0.5.

2. Aramid fiber toughened SiO₂Aerogel

Prepared aramid fiber toughened SiO₂The aerogels were subjected to various characterizations, the results of which are referenced in fig. 2-5.

Example 4

1. Aramid fiber toughened SiO₂Method for producing aerogels

Referring to fig. 1, a certain amount of surfactant (cetyl trimethyl ammonium bromide) is first weighed into a beaker, and then methanol and glacial acetic acid solution are added in proportion, wherein the ratio of the amount of the surfactant, the methanol and the glacial acetic acid is 0.002:1: 6. Stirring to dissolve the surfactant, adding MTMS (methyl trimethoxy silane), DMMS (dimethyl dimethoxy silane) and DMF (N, N-dimethylformamide) according to a proportion, placing in a constant temperature magnetic stirrer, stirring for 0.5h at 40 ℃ to fully hydrolyze, adding ammonia water to adjust pH value to 8.5, stirring for 5min to fully mix ammonia water with the solution, taking out a rotor, adding cleaned 6mm short cut aramid fiber with 1.5% of aerogel mass, placing in a constant temperature water bath kettle at 40 ℃ until the solution forms gel, aging for 6h after the gel, adding isopropanol to age for 6h, pouring out the liquid after the aging, adding a certain amount of N-hexane to perform solvent replacement for 6h, pouring out the liquid in a beaker, placing the beaker in a constant temperature blast drying oven at 30 ℃ to dry for 12h, then placing in a constant temperature blast drying oven at 40 ℃ to dry for 24h, the preparation is finished. Wherein the precursor (MTMS: DMDMMS is 1: 0.6), methanol: water (acetic acid c is 0.01mol/L) and DMF are mixed and stirred according to the mass ratio of 1:8:12: 0.5.

Example 5

1. Polypropylene toughened SiO₂Method for producing aerogels

Referring to fig. 1, a certain amount of surfactant (cetyl trimethyl ammonium bromide) is first weighed into a beaker, and then methanol and glacial acetic acid solution are added in proportion, wherein the ratio of the amount of the surfactant, the methanol and the glacial acetic acid is 0.002:1: 6. Stirring to dissolve surfactant, adding MTMS (methyl trimethoxy silane), DMMS (dimethyl dimethoxy silane) and DMF (N, N-dimethylformamide) according to a certain proportion, placing in a constant temperature magnetic stirrer, stirring at 30 deg.C for 1h to fully hydrolyze, adding ammonia water to adjust pH to 8.5, stirring for 5min to fully mix ammonia water with the solution, taking out a rotor, adding cleaned 3mm short-cut polypropylene with 1.5% of aerogel mass, placing in a constant temperature water bath at 40 deg.C until the solution forms gel, aging for 6h after the gel, adding isopropanol, aging for 6h, pouring out the liquid after aging, adding a certain amount of N-hexane for solvent replacement for 6h, pouring out the liquid in a beaker, placing the beaker in a constant temperature drying oven at 30 deg.C for drying for 12h, then placing in a constant temperature drying oven at 40 deg.C for drying for 24h, the preparation is finished. Wherein the precursor (MTMS: DMDMMS is 1: 0.6), methanol: water (acetic acid c is 0.01mol/L) and DMF are mixed and stirred according to the mass ratio of 1:8:12: 0.5.

2. Polypropylene toughened SiO₂Aerogel

Toughening the prepared polypropylene with SiO₂The aerogels were subjected to various characterizations, the results of which are referenced in fig. 2-5.

Characterization analysis

1. Scanning electron micrographs and analysis of aerogels

Referring to fig. 2, wherein fig. 2-a is a scanning electron microscope photograph of the aramid fiber toughened aerogel, fig. 2-b is a scanning electron microscope photograph of the polypropylene fiber toughened aerogel, and fig. 2-c is a scanning electron microscope photograph of the polyacrylonitrile fiber toughened aerogel. From FIG. 2, SiO can be seen₂The aerogel sample has small shape difference, shows a continuous nano porous network structure, is full of gaps inside, has a spongy shape, has a loose framework and uniform particle size, and three fibers are well dispersed in SiO₂Air condensationIn the gel, the fibers act as a framework in the aerogel, and the aerogel particles completely wrap the fibers, indicating that the fibers and the aerogel are effectively compounded together.

2. Infrared spectral analysis of aerogels

And carrying out comparative analysis on the aerogels toughened and modified by different fibers.

Referring to fig. 3, the infrared spectrograms of three fiber toughened aerogels are shown, wherein fig. 3-a is an infrared spectroscopic analysis of the aramid fiber toughened aerogel, fig. 3-b is an infrared spectroscopic analysis of the polypropylene fiber toughened aerogel, and fig. 3-c is an infrared spectroscopic analysis of the polyacrylonitrile fiber toughened aerogel. 2964.66cm^-1Small peak of (A) is-CH₃Absorption peak of 1401.81cm^-1Small peak of (a) corresponds to Si-CH₃The antisymmetric deformation peak of (a). 1260cm^-1Absorption peak of (A) is Si-CH₃The symmetric deformation vibration peak of (1). 1014.42cm^-1The strong transmission peak is the vibration absorption peak of the Si-O-Si bond. 779.13cm^-1The large peak corresponds to a Si-C strong absorption peak, 853.88cm^-1The small peak corresponds to a weak Si-C absorption peak. From the figure, it can be seen that the three fiber toughened aerogel particles are 2964.66cm^-1And 1260cm^-1There is a significant variation, mainly due to the different fibers containing different groups, which does not have much influence on the properties of the aerogel itself.

3. Thermogravimetric analysis of aerogels

As can be seen from FIG. 4, pure SiO exists between 20 ℃ and 300 DEG C₂Aerogel, 1.5 percent of polyacrylonitrile fiber, 1.5 percent of aramid fiber and 1.5 percent of polypropylene toughened SiO₂The weight loss rates of the aerogel are respectively about 3%, 5%, 15% and 10%, and the main reason is that SiO is₂The aerogel contains a certain amount of water, alcohol, normal hexane and volatile and partial decomposition of unreacted organic matters; at 300-500 deg.c, pure SiO₂Aerogel, 1.5% of polyacrylonitrile fiber, 1.5% of aramid fiber and 1.5% of polypropylene toughened SiO₂The weight loss rates of the aerogel are respectively about 10%, 15%, 40% and 20%, and the toughened aerogel is obviously less than that of the modified SiO₂The weight loss rate of the aerogel mainly changes the structure of the aerogel by adding fibers; after 600 deg.CTwo kinds of SiO₂No further loss of quality occurred in the aerogel. By contrast, the aramid fiber toughened SiO₂The heat resistance of the aerogel is relatively good.

4. Analytical study of aerogel BET

Table 1 aerogel mercury intrusion test results

Through carrying out mercury intrusion instrument test to the aerogel that prepares, survey the aerogel pore volume that prepares and show in table 1, because the pore volume of the aerogel that prepares, the aperture is on a large side, show that it is applicable to very much and adsorbs the oil of macromolecule, have better adsorption efficiency.

5. Study on mechanical properties of aerogels

Referring to FIG. 5, for SiO₂The aerogel axially applies bearable pressure, when the external force is removed, the sample achieves 100 percent of rebound, and the SiO is proved to be contained₂Good compressibility of the aerogel; as can be seen from FIG. 5, SiO₂The stress-strain curve of the aerogel has a phenomenon of hysteresis elasticity when SiO₂When the elastic deformation of the aerogel is 80%, the pressure born by the polypropylene is 180Mpa, the pressure born by the aramid fiber is 280Mpa, and the pressure born by the polyacrylonitrile is 160 Mpa.

Claims (3)

1. Fiber composite toughened SiO₂The preparation method of the aerogel is characterized by comprising the following steps: the preparation method comprises the steps of preparing fiber composite SiO by a sol-gel method₂Wet gel, aging, replacing residual reaction medium by solvent exchange, surface modification, and drying under normal pressure to obtain fiber composite toughened SiO₂An aerogel;

wherein, the sol-gel method is used for preparing fiber composite SiO₂The specific method of the wet gel is as follows:

firstly, weighing a certain amount of surfactant, adding the surfactant into a reaction container, then adding methanol and glacial acetic acid solution in proportion, stirring to dissolve the surfactant, then adding a precursor and N, N-dimethylformamide in proportion, stirring for 0.5h at 40 ℃ to fully hydrolyze the surfactant, then adding ammonia water to adjust the pH value to 8.5, stirring to fully mix the ammonia water and the solution, then taking out a rotor, adding clean fibers, and placing the rotor in a constant-temperature water bath kettle at 40 ℃ until gel is formed; the amount ratio of the surfactant to the methanol to the glacial acetic acid is 0.002:1: 6; the added precursor is as follows: methanol: water in glacial acetic acid solution: the mass ratio of N, N-dimethylformamide is 1:8:12: 0.5;

the precursor is formed by mixing methyltrimethoxysilane and dimethyldimethoxysilane according to the mass ratio of 1: 0.6;

the fibers are aramid fibers, and the adding amount of the fibers is 1.5% of the mass of the aerogel;

the specific operations of aging and replacement are as follows: firstly, aging for 6h, adding isopropanol, aging for 6h, pouring out liquid after aging, and replacing for 6h under normal hexane solvent;

the normal pressure drying is to pour out the residual liquid, put the sample into a constant temperature air-blast drying oven at 30 ℃ for drying for 12h, and then put into a constant temperature air-blast drying oven at 40 ℃ for drying for 24 h.

2. The fiber composite toughened SiO of claim 1₂The preparation method of the aerogel is characterized by comprising the following steps: the surfactant is cetyl trimethyl ammonium bromide.

3. Fiber composite toughened SiO prepared by the preparation method of claim 1 or 2₂An aerogel.

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