CN103754886A - Preparation method for composite silica aerogel with ultra high strength and high specific surface area - Google Patents

Abstract

The invention belongs to the technical field of airgel materials, and in particular relates to a method for preparing composite silica airgel with ultrahigh strength and high specific surface area. The present invention adopts a sol-gel-organic-inorganic hybrid method, that is, a mixed silicon source containing a silane coupling agent is used to form a wet gel through a sol-gel method, and then the isocyanate is used as an organic reinforcing material to compound the wet gel. Combined with the supercritical drying process, a high-strength diisocyanate composite silica airgel material was prepared. The invention has the characteristics of easy-to-obtain raw materials, simple reaction process, etc., and the obtained material has a nanoscale multi-level microstructure, and the maximum specific surface area can reach more than 400m ² /g, which solves the problem of the fragility of conventional silica airgel. Features such as low strength.

Description

A preparation method of ultra-high strength, high specific surface area composite silica airgel

technical field

The invention belongs to the technical field of preparing porous materials with high strength and high specific surface area, and in particular relates to a general method for silica airgel materials widely used in aerospace deep space exploration, light weight, high strength heat insulation and the like.

Background technique

Isocyanates can be used to synthesize a series of polyurethane foam plastics, rubber, elastic fibers, coatings, adhesives, synthetic leather, artificial wood, etc. with excellent properties. Aerogels are a class of nanoporous functional materials with hierarchical fractal structures. Due to the combination of macroscopic properties and nano-effects, it exhibits many unique properties and has broad application prospects. However, the extremely poor mechanical properties are the biggest obstacle to the widespread use of aerogels. The elastic modulus of pure silica airgel is usually 10 ⁵ -10 ⁷ Pa, and the compressive strength of silica airgel with a density of 120mg/cm ³ is 31kPa. The composite material obtained by hybridizing organic matter and inorganic matter has the properties of both components in nature-good mechanical properties, high temperature resistance, etc.

The organic-inorganic hybrid airgel prepared by the sol-gel method uses a bifunctional silane coupling agent-one end has a self-hydrolyzable alkoxy group, which participates in the sol-gel reaction with the non-polar precursor to form SiO ₂ The other end of the gel is a polymeric group, which reacts with organic matter to form a polymer shell and seal the inorganic SiO network. After being dried by supercritical fluid, it becomes aerogel.

Contents of the invention

The object of the present invention is to provide a kind of preparation method of diisocyanate composite _SiO2 airgel material with high strength and high specific surface area, which has wide application range, low cost, short reaction cycle and possible industrial scale-up. The basic idea is to add a bifunctional silane coupling agent to hydrolyze and polycondense together with other silicon sources to form a SiO ₂ gel, and use methyltrimethoxysilane and isocyanate monomers to strengthen the bond between the gel and the organic compound. The wettability makes the reaction more complete, and the polymer is wrapped in the outer layer of the gel to realize the preparation of organically reinforced SiO ₂ airgel with high strength and high specific surface area, the improvement of formability and the regulation of microstructure. The specific content is as follows:

The present invention proposes a method for preparing composite silica airgel with ultra-high strength and high specific surface area, which adopts a sol-gel-organic-inorganic hybrid method, and the specific steps are as follows:

(1) Dissolve the mixed silicon source in an organic solvent to form a solution A, and mix water and an organic solvent to form a solution B;

(2) Mix solution A and solution B in step (1) at -60 to -70 degrees Celsius, stir evenly, and obtain a gel after standing; wherein, the addition of the mixed silicon source, organic solvent, and deionized water The ratio is 10-20ml: 25-45ml: 5-15ml;

(3) After aging the gel obtained in step (2), put it into an organic solution with a mass fraction of diisocyanate of 10% and a temperature of 70-80 degrees Celsius for 60-80 hours;

(4) aging the gel obtained in step (3) at room temperature and then drying to obtain the desired organically reinforced SiO ₂ airgel material.

In the present invention, the mixed silicon source in step (1) is composed of methyl silicate (TMOS), methyltrimethoxysilane (MTMS) and 3-aminopropyltriethoxysilane (APTES), methyl silicate Ester, methyltrimethoxysilane and 3-aminopropyltriethoxysilane volume ratio: 4-12ml:1-6ml:2.5-10ml.

In the present invention, the organic solvent in step (1) and step (3) is acetonitrile.

In the present invention, the diisocyanate in step (3) is hexamethylene diisocyanate (HDI).

In the present invention, the drying method described in step (4) is any one of methods such as supercritical fluid drying, freeze drying, heating degassing drying or normal pressure natural drying.

The organically reinforced _SiO2 airgel prepared by the present invention has high strength, high specific surface area and multi-level fractal nanoporous network structure, which successfully solves the problem that the pure _SiO2 nanoporous airgel is brittle and fragile, and the comparative area after organic enhancement The low problem is of great significance in the fields of aerospace deep space exploration, light weight and high strength heat insulation and other fields.

Description of drawings

Fig. 1 The photograph of embodiment 1 sample;

The Fourier transform infrared spectrogram of Fig. 2 embodiment 1 sample;

The scanning electron micrograph of Fig. 3 embodiment 1 sample;

The nitrogen adsorption-desorption curve of Fig. 4 embodiment 1 sample;

Fig. 5 embodiment 1 pore size distribution figure;

Fig. 6 Example 1 stress-strain curve.

Detailed ways

The present invention will be further specifically described below through the examples and accompanying drawings. (All raw materials are commercially available raw materials, and the purity is chemically pure or analytically pure grade unless otherwise specified).

Embodiment 1 : high strength, high specific surface area diisocyanate composite SiO ₂ preparation of airgel

Select the mixed silicon source (methyl silicate: methyltrimethoxysilane: 3-aminopropyltriethoxysilane volume ratio: 4:1:2.5), the volume ratio of organic solvent and deionized water is: 10ml: 25ml: 5ml Methyl silicate (TMOS), acetonitrile, methyltrimethoxysilane, 3-aminopropyltriethoxysilane, mixed into 18ml solution A, deionized water and acetonitrile mixed into 22 solution B . Cool solution A to about -70°C, pour into solution B, stir rapidly, and gel at room temperature. After 24 hours, the solution was replaced with acetonitrile for 3 times, 8-12 hours each time. Soak the gel in an acetonitrile solution with a mass fraction of 10% hexamethylene diisocyanate for 24 hours, put it in a fresh acetonitrile solution, and place it in an oven at 70°C for 3*24 hours. The gel was placed in fresh acetonitrile solution for 3 replacements, each time 8-12h. Finally, supercritical drying was carried out to obtain a reinforced aerogel with a density of 330 mg/cm ³ . Its physical photos are shown in Figure 1.

Embodiment 2 : choose the volume ratio of mixed silicon source (methyl silicate: methyltrimethoxysilane: 3-aminopropyltriethoxysilane volume ratio: 12:6:10), organic solvent, deionized water For: 20ml:45ml:15ml. Methyl silicate Methyl silicate (TMOS), acetonitrile, methyltrimethoxysilane, 3-aminopropyltriethoxysilane, mixed into 35ml A solution, deionized water and acetonitrile mixed into 45ml B solution. Cool solution A to about -60°C -70°C, pour into solution B, stir rapidly, and gel at room temperature. After 24 hours, the solution was replaced with acetonitrile for 3 times, 8-12 hours each time. Soak the gel in an acetonitrile solution with a mass fraction of 10% hexamethylene diisocyanate for 24 hours, put it in fresh acetonitrile solution, and place it in an oven at 70°C for 3*24 hours. The gel was placed in fresh acetonitrile solution for 3 replacements, each time 8-12h. Finally, supercritical drying was carried out.

As shown in Figure 2, the Fourier transform infrared spectrum of the sample shows that the Si-O-Si network structure is obtained through the hydrolysis-polycondensation reaction of the mixed silicon source, and the amine group reacts with the organic hexamethylene diisocyanate to finally form a polymer shell. The scanning electron micrographs in Figure 3 show that the material has an interpenetrating porous structure composed of nanoscale networks. The nitrogen adsorption and desorption and pore size distribution diagrams in Figures 4 and 5 further prove that the material also has a fine structure of about 20 nm, and the specific surface area of the sample is as high as 446.3 m ² /g. The stress-strain curves in Figure 6 indicate the mechanical properties of the material. Comprehensive test results show that the material is a high-strength, high-specific-surface-area diisocyanate-composite _SiO2 airgel with a multi-level structure.

Claims (5)

1. a preparation method for superstrength, high-specific surface area dioxide composite silica aerogel, is characterized in that adopting the method for collosol and gel-organic inorganic hybridization, and concrete steps are as follows:

(1) mixing silicon source is dissolved in to organic solvent wiring solution-forming A, by deionized water and organic solvent mixing wiring solution-forming B;

(2) by mixing under the be placed in-60--70 of solution A and solution B of step (1) gained degree Celsius, stir, obtain gel after standing; Wherein, the adding proportion of mixing silicon source, organic solvent, deionized water is 10-20ml:25-45ml:5-15ml;

(3) gel step (2) being obtained, after aging, is put into vulcabond massfraction and is 10%, temperature is that the organic solution of 70-80 degree Celsius is soaked 60-80 hour;

(4) step (3) gained gel is aging rear dry at normal temperatures, obtain required organic enhancing SiO ₂nanoporous aerogel material.

2. preparation method according to claim 1, it is characterized in that the mixing silicon source in step (1) is comprised of methyl silicate, methyltrimethoxy silane and 3-amine propyl-triethoxysilicane, methyl silicate, methyltrimethoxy silane and 3-amine propyl-triethoxysilicane volume ratio: 4-12ml:1-6ml:2.5-10ml.

3. preparation method according to claim 1, is characterized in that the organic solvent described in step (1) and step (3) is acetonitrile.

4. preparation method according to claim 1, is characterized in that the vulcabond described in step (3) is hexamethylene diisocyanate.

5. preparation method according to claim 1, it is characterized in that drying means described in step (4) is supercritical fluid drying, lyophilize, heat de-airing is dry or normal pressure seasoning mode in any.

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