A method for preparing a nanocellulose-reinforced silica aerogel composite

Abstract

The application discloses a preparation method of a nanocellulose casting reinforced silica aerogel composite material and belongs to the field of composite materials.The composite material comprises a silica aerogel as a matrix, nanocellulose extracted from straws as a reinforcing body, and is formed by using a casting method.The nanocellulose reinforced silica aerogel composite material is simple to prepare, has higher strength while keeping low thermal conductivity, reduces the phenomena of slagging and powdering, is lower in cost, and achieves the effects of waste utilization, environmental protection and saving.

Description

TECHNICAL FIELD

[0001] The application discloses a preparation method of a nanocellulose cast reinforced silica aerogel composite material and belongs to the field of composite materials. BACKGROUND

[0002] Aerogel refers to a kind of nanoscale porous solid material formed by replacing liquid phase in a gel with gas through a sol-gel method and a certain drying method. Aerogel is a new kind of low-density amorphous material with super high porosity, and has a three-dimensional network structure. For example, about 95% of SiO2 aerogel is composed of air, and the remaining 5% is composed of cross-linked three-dimensional network silica nanoparticles. The high porosity of aerogel leads to its extremely low thermal conductivity, and the low thermal conductivity makes it have good heat preservation and insulation performance. Meanwhile, the unique structure also makes it have low refractive index, low elastic modulus, low dielectric constant, low acoustic impedance and other properties. These physical properties make aerogel have good development prospects in many fields such as aerospace, automobile manufacturing, sound insulation and heat insulation materials, super capacitors, electrode batteries, catalysis and military industry.

[0003] However, since the gel contains a large amount of alcohol and water, the surface tension is large, and the microstructure is prone to collapse during the drying process, resulting in fragility and easy residue dropping. Therefore, in addition to modification, embedding fibers into silica aerogel can prevent shrinkage during the drying process to a great extent, improve the mechanical properties, and prevent residue and powder dropping. SUMMARY

[0004] The application aims to solve the problem of using nanocellulose to reinforce silica aerogel, using nanocellulose to enhance the mechanical strength and toughness of silica aerogel, and achieving the effect of waste utilization and environmental protection.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0006] A nanocellulose reinforced silica aerogel composite material, wherein silica aerogel is used as a matrix, a macroscopic fiber network of nanocellulose framework is used as a reinforcing body, tetraethyl orthosilicate is used as a silicon source of the silica aerogel, and the matrix and the reinforcing body are combined together by using a casting method to form the nanocellulose reinforced silica aerogel composite material.

[0007] The preparation method of the nanocellulose reinforced silica aerogel composite material in the application comprises the following specific steps:

[0008] 1) The tetraethyl orthosilicate, anhydrous ethanol and deionized water are mixed according to a molar ratio of 1:(6-10):4 to obtain a precursor solution;

[0009] 2) adding acid solution to the precursor solution to perform second mixing, adjusting pH to be between 3 and 4, and stirring for 60 min with a magnetic stirrer, placing in a water bath, and allowing sufficient hydrolysis to obtain a silica sol;

[0010] 3) performing layering on the prepared nanocellulose to obtain a loose cellulose layer;

[0011] 4) adding ammonia water to the silica sol obtained in step 2) to adjust pH to be between 7 and 8, and then slowly pouring into the cellulose layer prepared in step 3) to allow the silica sol to be fully filled into the fiber layer, and sealing and standing at room temperature to allow the silica sol to gel, thereby obtaining a cellulose-reinforced silica wet gel;

[0012] 5) standing the cellulose-reinforced silica wet gel prepared in step 4) in the precursor solution to perform aging;

[0013] 6) immersing the cellulose-reinforced silica wet gel subjected to aging in step 5) in n-hexane to perform solution exchange and hydrophobic modification;

[0014] 7) finally performing precooling and freeze drying in a freeze dryer to obtain the nanocellulose-reinforced silica aerogel.

[0015] Preferably, the acid solution in step 2) is 0.5 mol / L hydrochloric acid, and the hydrolysis is performed at a constant temperature in a 25℃ water bath for 6-8 h.

[0016] Preferably, the nanocellulose in step 3) is extracted from hemp straw, and the layering is performed in an orthogonal direction.

[0017] Preferably, the ammonia water in step 4) has a concentration of 1 mol / L.

[0018] Preferably, the aging in step 5) is performed for 6-8 h.

[0019] Preferably, the immersion in n-hexane in step 6) is performed for 24 h.

[0020] Preferably, the precooling in step 7) is performed for 12 h in the freeze dryer, and the freeze drying is performed for 24 h.

[0021] Advantages of the present application:

[0022] 1. The cellulose itself has mechanical strength, low price, wide source, environmental protection and easy degradation,

[0023] 2. The cellulose-reinforced silica aerogel composite material enhances the aerogel skeleton, so that the composite material has better mechanical strength, better formability, and higher porosity, lower density and thermal conductivity.

[0024] 3. Cellulose-reinforced silica aerogel composite materials have greatly improved the phenomenon of slagging and powdering. Attached Figure Description

[0025] Figure 1 This is a schematic flowchart of the preparation method of the nanocellulose-reinforced silica aerogel composite material in this invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0027] Example 1

[0028] 1) After thoroughly mixing tetraethyl orthosilicate, anhydrous ethanol, and deionized water in a molar ratio of 1:8:4, add 0.5 mol / L hydrochloric acid solution to adjust the pH to 4, place in a 25°C water bath, and stir with a magnetic stirrer for 60 min to allow for complete hydrolysis, thus obtaining silica sol.

[0029] 2) Lay out the pre-made nanocellulose in mutually orthogonal directions to obtain a loose cellulose layer.

[0030] 3) Add the silica sol from step 1) to 1 mol / L ammonia water, adjust the pH value to 8, and then slowly pour it into the fiber layer that was pre-laid in step 2) so that the silica sol can fully fill the fiber layer. Let it stand to gel and obtain cellulose-reinforced silica wet gel.

[0031] 4) The cellulose-reinforced silica wet gel prepared in step 3) was placed in the precursor solution and aged in a water bath at 25°C for 8 hours.

[0032] 5) Soak the aged wet gel from step 4) in n-hexane for 24 hours for solution exchange and hydrophobic modification.

[0033] 6) The nanocellulose-reinforced silica aerogel is obtained by pre-cooling in a freeze dryer for 12 hours and vacuum drying for 24 hours.

[0034] Example 2

[0035] 1) After thoroughly mixing tetraethyl orthosilicate, anhydrous ethanol, and deionized water in a molar ratio of 1:6:4, a precursor solution is obtained. Then, 0.5 mol / L hydrochloric acid solution is added to adjust the pH to 4, and the solution is placed in a 50°C water bath and stirred with a magnetic stirrer for 60 min to allow it to fully hydrolyze and obtain silica sol.

[0036] 2) The pre-prepared nanocellulose is laid in the mutually orthogonal direction to obtain a loose cellulose layer.

[0037] 3) The silica sol in step 1) is added to 1 mol / L ammonia water to adjust the pH value to 8, and then slowly poured into the pre-laid fiber layer in step 2) to fully fill the silica sol into the fiber layer, and the gel is left to stand to obtain a cellulose-reinforced silica wet gel.

[0038] 4) The cellulose-reinforced silica wet gel prepared in step 3) is left to stand in the precursor solution and aged in a water bath at 50°C for 8h.

[0039] 5) The obtained wet gel is soaked in n-hexane for 24h for solution exchange and hydrophobic modification.

[0040] 6) Precooling in a freeze dryer for 12h and vacuum drying for 24h to obtain the nanocellulose-reinforced silica aerogel.

[0041] Example 3

[0042] 1) The tetraethyl orthosilicate, anhydrous ethanol and deionized water are fully mixed according to the molar ratio of 1:10:4 to obtain a precursor solution; 0.5 mol / L hydrochloric acid solution is added to adjust the pH to 4, and placed in a 30°C water bath, stirred with a magnetic stirrer for 60 min, and fully hydrolyzed to obtain a silica sol.

[0043] 2) The pre-prepared nanocellulose is laid in the mutually orthogonal direction to obtain a loose cellulose layer.

[0044] 3) The silica sol in step 1) is added to 1 mol / L ammonia water to adjust the pH value to 8, and then slowly poured into the pre-laid fiber layer in step 2) to fully fill the silica sol into the fiber layer, and the gel is left to stand to obtain a cellulose-reinforced silica wet gel.

[0045] 4) The cellulose-reinforced silica wet gel prepared in step 3) is left to stand in the precursor solution and aged in a water bath at 30°C for 8h.

[0046] 5) The wet gel aged in step 4) is soaked in n-hexane for 24h for solution exchange and hydrophobic modification.

[0047] 6) Precooling in a freeze dryer for 12h and vacuum drying for 24h to obtain the nanocellulose-reinforced silica aerogel.

[0048] Effect verification

[0049] The density, porosity, contact angle and bending strength of examples 1-3 are tested, and the data are shown in Table 1.

[0050] Table 1

[0051] Density Porosity Contact angle Bending strength Example 1 0.31 g / cm 3 ]] 81％ 133° 2.98 MPa Example 2 0.42 g / cm 3 ]] 76％ 128° 2.03 MPa Example 3 0.38 g / cm 3 ]] 80％ 130° 2.64 MPa

[0052] Through test comparison, the cellulose-reinforced silica aerogel composite material prepared by the application has lower density and higher porosity, wherein the material performance in Example 1 is the best, the density is 0.31 g / cm 3 , the porosity of the aerogel is 81%, the contact angle is 135°, and the hydrophobicity is good. The application reinforces the skeleton of the aerogel by cellulose, improves the falling residue and powder phenomenon of the traditional aerogel with low density and high porosity, and significantly improves the strength.

Claims

1. A method for the preparation of nanocellulose-reinforced silica aerogel composites, characterized by, The specific steps of the method are as follows: 1) The first mixing is performed according to the molar ratio of 1: (6-10): 4 of tetraethyl orthosilicate, anhydrous ethanol and deionized water to obtain a precursor solution; 2) The second mixing is performed by adding an acid solution to the precursor solution to adjust the pH to 3-4, and stirring for 60 min with a magnetic stirrer, and placing in a water bath to allow sufficient hydrolysis to obtain a silica sol; 3) The pre-prepared nanocellulose is layered to obtain a loose cellulose layer; 4) Ammonia is added to the precursor solution in step 2) to adjust the pH to 7-8, and then slowly poured into the pre-prepared fiber layer in step 3) to allow the silica sol to be fully filled into the fiber layer, and sealed at room temperature to allow the silica sol to gel, to obtain a cellulose-reinforced silica wet gel; 5) The cellulose-reinforced silica wet gel prepared in step 4) is aged in the precursor solution; 6) The cellulose-reinforced silica wet gel aged in step 5) is soaked in n-hexane for solution exchange and hydrophobic modification; 7) Finally, precooling and freeze-drying are performed in a freeze-drying machine to obtain the nanocellulose-reinforced silica aerogel.

2. The method of producing a nanocellulose-reinforced silica aerogel composite according to claim 1, characterized in that, The acid solution in step 2) is 0.5 mol / L hydrochloric acid.

3. The method of producing a nanocellulose-reinforced silica aerogel composite according to claim 1, characterized in that, The hydrolysis in step 2) is constant temperature hydrolysis at 25°C for 6-8 h.

4. The method of producing a nanocellulose-reinforced silica aerogel composite according to claim 1, characterized in that, The nanocellulose in step 3) is extracted from Hanfasheng.

5. The method of producing a nanocellulose-reinforced silica aerogel composite material according to claim 1, characterized in that, The layering in step 3) is performed in the orthogonal direction.

6. The method of producing a nanocellulose-reinforced silica aerogel composite material according to claim 1, characterized in that, The ammonia in step 4) is 1 mol / L.

7. The method of producing a nanocellulose-reinforced silica aerogel composite material according to claim 1, characterized in that, The aging time in step 5) is 6-8 h.

8. The method of producing a nanocellulose-reinforced silica aerogel composite material according to claim 1, characterized by, The soaking time in n-hexane for solution exchange and hydrophobic modification in step 6) is 24 h.

9. The method of producing a nanocellulose-reinforced silica aerogel composite material according to claim 1, characterized in that, The precooling time in step 7) is 12 h, and the freeze-drying time is 24 h.

10. A nanocellulose-reinforced silica aerogel composite material prepared by the method of any one of claims 1 to 9, characterized in that, The nanocellulose-reinforced silica aerogel composite material is formed by the combination of the silica aerogel as the matrix and the macroscopic fiber network of the nanocellulose framework as the reinforcing body.

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