A transparent flexible double-crosslinked silicon-based modified cellulose aerogel and a preparation method thereof

Abstract

The application provides a transparent flexible double-crosslinked silicon-based modified cellulose aerogel and a preparation method thereof. Vinyl silane and methyl silane are used as precursors, a double-crosslinked method of radical polymerization / hydrolysis polycondensation is adopted, a polysiloxane homogeneous sol is prepared, a cellulose gel is immersed in the homogeneous sol, and finally the supercritical drying process is performed to prepare the aerogel of the application. Due to the double-crosslinked structure of radical polymerization and hydrolysis polycondensation, the aerogel has good transparency and strength. Meanwhile, the introduction of methyl silane and the unique characteristics of cellulose endow the aerogel with good hydrophobic property and excellent flexibility. In addition, the aerogel material has an extremely low thermal conductivity, and the heat preservation and insulation performance is far superior to that of traditional heat preservation materials, so that the aerogel has a broad application prospect in the fields of heat preservation and insulation and transparent glass.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of aerogel materials, and relates to a transparent flexible double-crosslinked silicon-based modified cellulose aerogel and a preparation method thereof. BACKGROUND

[0002] Cellulose is a natural linear macromolecule, is widely available and renewable, and is a recognized green biomaterial. Meanwhile, cellulose aerogels prepared from cellulose have attracted widespread attention in the fields of thermal insulation, heat preservation, adsorption, purification, etc. due to their renewable, biodegradable, environmentally friendly, high transparency and good flexibility.

[0003] The practical application of cellulose aerogels is mainly limited by the heat resistance and hydrophilicity of cellulose. In order to better exert the unique advantages of cellulose aerogels, surface modification technology of cellulose aerogels has always been a research hotspot.

[0004] Patent CN117126449A discloses a silicon-based modified cellulose aerogel, and the preparation method comprises the following steps: cellulose is added to an ionic liquid, after heating and stirring, the cellulose sol is placed in a vacuum drying oven for vacuum deaeration treatment to obtain treated cellulose sol; the treated cellulose sol is prepared into a cellulose sol film by a film forming process; then an ionic liquid aqueous solution is added to the cellulose sol film to form a cellulose wet gel film; after solvent replacement, a cellulose alcohol gel film is obtained; the cellulose alcohol gel film is placed in a silica sol solution for standing to obtain a cellulose / silica composite wet gel film; the composite wet gel film is placed in an oven for aging to obtain a cellulose / silica composite alcohol gel film; finally, the composite alcohol gel film is subjected to supercritical drying to obtain a flexible transparent silicon-based modified cellulose aerogel film with a thickness of 0.1-0.5 mm. The silicon-based modified cellulose aerogel has high transparency, but its flexibility and hydrophobicity need to be further improved.

[0005] Patent CN111499919A discloses a biomass fiber hybrid polyorganosiloxane aerogel glass, which is prepared by using vinyl alkoxy silane as a precursor and introducing biomass cellulose through five process links of free radical polymerization, hydrolysis polycondensation, aging, solvent replacement and drying. The aerogel prepared by the method has high light transmittance and high flexibility, but its hydrophobicity cannot be effectively improved, which greatly limits the application of transparent flexible aerogel in the field of thermal insulation glass.

[0006] The present application aims to overcome the shortcomings of the prior art, and provides a transparent flexible double-crosslinked silicon-based modified cellulose aerogel, which has high strength, high light transmittance, good hydrophobicity and good flexibility, and has an extremely low thermal conductivity. SUMMARY

[0007] The present application aims to provide a transparent flexible double crosslinking silicon-based modified cellulose aerogel and a preparation method thereof, and overcomes the poor thermal insulation performance of existing glass and the poor hydrophobicity, low transparency and low flexibility of aerogels.

[0008] A transparent flexible double crosslinking silicon-based modified cellulose aerogel is prepared from vinyl silane, methyl silane and cellulose as raw materials.

[0009] The viscous liquid obtained by radical polymerization of the vinyl silane is mixed with the methyl silane at a mass ratio of (5-10):1, and a hydrolysis-polycondensation reaction is performed.

[0010] The vinyl silane is one or more of vinyl trimethoxysilane, vinyl triethoxysilane, vinyl methyl dimethoxysilane or vinyl ethyl diethoxysilane.

[0011] The methyl silane is one or more of methyl trimethoxysilane or methyl triethoxysilane.

[0012] The cellulose is one or more of carboxymethyl cellulose, carboxypropyl methyl cellulose or hydroxy cellulose.

[0013] A preparation method of a transparent flexible double crosslinking silicon-based modified cellulose aerogel includes the following steps:

[0014] (1) Preparation of homogeneous sol:

[0015] A radical initiator is added to the vinyl silane, the reaction system is sealed and replaced with an inert gas, and a transparent viscous liquid is obtained by reaction; the methyl silane is added to the viscous liquid, mixed thoroughly, and then the solvent, deionized water and catalyst are sequentially added, and a homogeneous sol is obtained by mixing, wherein the mass ratio of the viscous liquid to the methyl silane is (5-10):1.

[0016] Preparation of cellulose alcohol gel film:

[0017] The cellulose is mixed with the ionic liquid, and after heating and stirring, vacuum degassing and film formation, a cellulose sol film is obtained; the cellulose sol film is regenerated in an ionic liquid aqueous solution to obtain a cellulose wet gel film; and the cellulose wet gel film is subjected to solvent replacement to obtain a cellulose alcohol gel film.

[0018] (2) The cellulose alcohol gel film obtained in step (1) is placed in the homogeneous sol, and a cellulose / silicon composite wet gel is obtained by standing; the composite wet gel is sequentially subjected to aging and supercritical drying to obtain a transparent flexible double crosslinking silicon-based modified cellulose aerogel.

[0019] The reaction temperature of step (1) is 100-140 DEG C, and the reaction time is 4-48 h; the free radical initiator is one or more of di-tert-butyl peroxide, azobisisobutyronitrile or azobisisoheptyl nitrile; and the molar ratio of vinylsilane to free radical initiator is (5-15):1.

[0020] The solvent of step (1) is one or more of methanol, ethanol, n-butanol or t-butanol; the catalyst is one or more of tetramethylammonium hydroxide, ammonium fluoride or ammonia; the molar ratio of methylsilane to solvent, deionized water and catalyst is 1:(1-5):(1-5):(0.01-0.1); the ionic liquid is one or more of EmimCl, EmimBr, EmimF, EmimAc, AmimCl, AmimBr or AmimF, the mass fraction of ionic liquid used for regeneration of the cellulose sol film is 20 wt%; and the cellulose sol film is prepared by mixing cellulose and ionic liquid at a molar ratio of 1:(30-60).

[0021] The solvent replacement of step (1) is performed once every 12 h, and the replacement is performed 2-4 times; the aging temperature of step (2) is 40-60 DEG C, and the aging time is 12-48 h; and the supercritical drying is carbon dioxide supercritical fluid drying, the pressure is 5-20 MPa, the temperature is 30-60 DEG C, and the drying time is 24-72 h.

[0022] A transparent flexible double-crosslinked silicon-based modified cellulose aerogel is used in the field of thermal insulation and serves as transparent glass interlayer.

[0023] The present application has the following advantages:

[0024] The double-crosslinked silicon-based structure prepared by using vinylsilane effectively improves the transparency and mechanical strength of the cellulose aerogel, and the introduction of methylsilane effectively improves the hydrophobicity and flexibility of the cellulose, and the bending strength reaches 0.28 MPa, the light transmittance is 93%, and the contact angle is 138 DEG.

[0025] The transparent flexible double-crosslinked silicon-based modified cellulose aerogel prepared by the present application has excellent thermal insulation performance, and the thermal conductivity is as low as 0.02 W·(mk) -1 .

[0026] The transparent flexible double-crosslinked silicon-based modified cellulose aerogel prepared by the present application is easy to degrade and is a new green and environmentally friendly material. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A real object diagram of the transparent silicon-based modified cellulose aerogel prepared in Example 1. DETAILED DESCRIPTION

[0028] The embodiments of the present application will be described in detail below with examples, which are only used to illustrate the present application and should not be considered as limiting the scope of the present application.

[0029] Example 1

[0030] The di-tert-butyl peroxide and vinyltrimethoxysilane were added into a reaction kettle, and after nitrogen replacement, they were heated at 125℃ for 6h to obtain a transparent viscous liquid, wherein the molar ratio of di-tert-butyl peroxide to vinyltrimethoxysilane was 1:10.

[0031] The methyltrimethoxysilane was added into the transparent viscous liquid, and after mixing well, the ethanol, deionized water and tetramethylammonium hydroxide were added in sequence, and the mixture was fully mixed to obtain a homogeneous sol, wherein the mass ratio of methyltrimethoxysilane to the viscous transparent liquid was 1:10, and the molar ratio of methyltrimethoxysilane to ethanol, deionized water and tetramethylammonium hydroxide was 1:2:3:0.01.

[0032] The carboxymethyl cellulose was added into the EmimCl ionic liquid, and heated and stirred at 70℃ until the cellulose was completely dissolved to obtain a uniform transparent cellulose sol, and the vacuum was extracted in a vacuum oven at 70℃ for 1h, wherein the molar ratio of carboxymethyl cellulose to ionic liquid was 1:50. The above cellulose sol was poured into a mold to form a film and stand, a 20wt% EmimCl aqueous solution was poured into the mold, and the solution was 2mm higher than the cellulose sol, and after the gel was condensed, it was removed and taken out, and the ethanol was sequentially replaced, and the replacement was performed every 12h for 2 times to obtain a cellulose alcohol gel film. The cellulose alcohol film was immersed in the prepared homogeneous sol with stirring, and the stirring speed was controlled at 200r / min. After standing at room temperature for 12h, the composite gel film was aged in a 60℃ oven for 12h, and finally the composite gel film was subjected to carbon dioxide supercritical drying, the temperature was controlled at 50℃, the pressure was 10 MPa, the air release rate was 1L / min, and the drying was performed for 48h to obtain a 1mm transparent silicon-based modified cellulose aerogel film, and the actual photo is shown in Figure 1

[0033] It was found through characterization that the composite aerogel film had a bending strength of 0.22MPa, a light transmittance of 90%, a contact angle of 135°, and a thermal conductivity of 0.021W·(mk) -1 .

[0034] Example 2

[0035] The di-tert-butyl peroxide and vinyltrimethoxysilane were added into a reaction kettle, and after nitrogen replacement, they were heated at 125℃ for 6h to obtain a transparent viscous liquid, wherein the molar ratio of di-tert-butyl peroxide to vinyltrimethoxysilane was 1:10.

[0036] ​Methyl triethoxysilane was added to the viscous transparent liquid, mixed well, then ethanol, deionized water, ammonia were added in turn, and the homogeneous sol was obtained after mixing well, wherein the mass ratio of methyl triethoxysilane to the viscous transparent liquid was 1:5, and the molar ratio of methyl triethoxysilane to ethanol, deionized water, ammonia was 1:2:3:0.01.

[0037] Hydroxyl cellulose was added to EmimCl ionic liquid, heated and stirred at 70°C until the cellulose was completely dissolved, and a uniform transparent cellulose sol was obtained. The cellulose sol was poured into a mold to form a film and placed in a vacuum oven at 70°C for 1h to degas. The molar ratio of hydroxyl cellulose to ionic liquid was 1:50. A 20wt% EmimCl aqueous solution was prepared and poured into the mold, and the solution was 2mm higher than the cellulose sol. After the gel was removed, it was replaced with ethanol in sequence, and replaced every 12h for 2 times to obtain a cellulose alcohol gel film. The cellulose film was immersed in the homogeneous sol prepared before, with a stirring speed of 200r / min. After standing at room temperature for 12h, it was aged in a 60°C oven for 12h. Finally, the composite gel film was subjected to carbon dioxide supercritical drying, with a temperature of 50°C, a pressure of 10 MPa, and a gas release rate of 1L / min. The drying time was 48h, and a 0.8mm transparent silicon-based modified cellulose aerogel film was obtained.

[0038] Characterization showed that the composite aerogel film had a bending strength of 0.21MPa, a light transmittance of 88%, a contact angle of 128°, and a thermal conductivity of 0.024W·(mk) -1 .

[0039] Example 3

[0040] Azo diisobutyronitrile and vinylmethyl dimethoxysilane were added to a reaction kettle, and after nitrogen replacement, they were heated at 125°C for 6h to obtain a viscous transparent liquid. The molar ratio of azo diisobutyronitrile to vinylmethyl dimethoxysilane was 1:10.

[0041] Methyl triethoxysilane was added to the viscous transparent liquid, mixed well, then ethanol, deionized water, ammonia were added in turn, and the homogeneous sol was obtained after mixing well, wherein the mass ratio of methyl triethoxysilane to the viscous transparent liquid was 1:5, and the molar ratio of methyl triethoxysilane to ethanol, deionized water, ammonia was 1:2:3:0.01.

[0042] Carboxypropyl cellulose was added into EmimCl ionic liquid, heated and stirred at 70℃ until the cellulose was completely dissolved, obtaining a uniform transparent cellulose sol, vacuum degassing in a vacuum oven at 70℃ for 1h, wherein the molar ratio of carboxypropyl cellulose and ionic liquid was 1:50. The above cellulose sol was poured into a mold to form a film and stand, a 20wt% EmimCl aqueous solution was prepared and poured into the mold, the solution was 2mm higher than the cellulose sol, after the gel was removed, the ethanol was sequentially replaced, every 12h, for 2 times, obtaining a cellulose alcohol gel film. The cellulose film was immersed in the homogeneous sol prepared before, stirring at a speed of 200r / min. After standing at room temperature for 12h, aging in a 60℃ oven for 12h, finally the composite gel film was supercritical dried by carbon dioxide, the temperature was controlled at 50℃, the pressure was 10 MPa, the air release rate was 1L / min, and the drying time was 48h, obtaining a 1.2mm transparent silicon-based modified cellulose aerogel film.

[0043] After characterization, it was found that the composite aerogel film had a bending strength of 0.17MPa, a light transmittance of 85%, a contact angle of 125°, and a thermal conductivity of 0.026W·(mk) -1 .

[0044] Example 4

[0045] Di-tert-butyl peroxide, vinyl trimethoxysilane were added into the reaction kettle, after nitrogen replacement, heated at 125℃ for 6h, obtaining a viscous transparent liquid, wherein the molar ratio of di-tert-butyl peroxide and vinyl trimethoxysilane was 1:10.

[0046] Methyl trimethoxysilane was added into the viscous transparent liquid, after mixing well, ethanol, deionized water, tetramethylammonium hydroxide were added in turn, and after fully mixing, a homogeneous sol was obtained, wherein the mass ratio of methyl trimethoxysilane and viscous transparent liquid was 1:5, and the molar ratio of methyl trimethoxysilane, ethanol, deionized water and tetramethylammonium hydroxide was 1:2:3:0.01.

[0047] Carboxymethyl cellulose was added into EmimCl ionic liquid, heated and stirred at 70℃ until the cellulose was completely dissolved, obtaining a uniform transparent cellulose sol, and the cellulose sol was poured into a mold to form a film and placed, a 20wt% EmimCl aqueous solution was prepared and poured into the mold, the solution was 2mm higher than the cellulose sol, and after the gel was removed, the ethanol was sequentially replaced, and the replacement was performed every 12h for 2 times, obtaining a cellulose alcohol gel film. The cellulose film was immersed in the homogeneous sol prepared before, and the stirring speed was controlled at 200r / min. After standing at room temperature for 12h, the composite gel film was aged in a 60℃ oven for 12h, and finally the composite gel film was subjected to carbon dioxide supercritical drying, the temperature was controlled at 50℃, the pressure was 10 MPa, the air release rate was 1L / min, and the drying was performed for 48h, obtaining a 1mm transparent silicon-based modified cellulose aerogel film.

[0048] It was found through characterization that the composite aerogel film had a bending strength of 0.28MPa, a light transmittance of 93%, a contact angle of 138°, and a thermal conductivity of 0.020W·(mk) -1 .

[0049] Comparative Example 1

[0050] The same as Example 4, except that the mass ratio of methyltrimethoxysilane to viscous transparent liquid was 1:1.

[0051] It was found through characterization that the composite aerogel film had a bending strength of 0.12MPa, a light transmittance of 80%, a contact angle of 128°, and a thermal conductivity of 0.048W·(mk) -1 .

[0052] Comparative Example 2

[0053] The same as Example 4, except that the cellulose was nanocellulose.

[0054] It was found through characterization that the composite aerogel film had a bending strength of 0.11MPa, a light transmittance of 82%, a contact angle of 94°, and a thermal conductivity of 0.038W·(mk) -1 .

[0055] Comparative Example 3

[0056] The same as Example 4, except that the methylsilane was replaced with dimethyldimethoxysilane.

[0057] It was found through characterization that the composite aerogel film had a bending strength of 0.12MPa, a light transmittance of 79%, a contact angle of 107°, and a thermal conductivity of 0.041W·(mk) -1 .

Claims

1. A transparent flexible dual-crosslinked silica-based modified cellulose aerogel, characterized in that, The cellulose is one or more of carboxymethyl cellulose, carboxypropyl methyl cellulose or hydroxyl cellulose. The preparation method comprises the following steps: (1) preparation of a homogeneous sol: A free radical initiator is added to the vinyl silane, the reaction system is closed and replaced with an inert gas, and a transparent viscous liquid is obtained by reaction; methyl silane is added to the viscous liquid, mixed thoroughly, and then solvent, deionized water and catalyst are sequentially added, and a homogeneous sol is obtained by mixing, wherein the mass ratio of the viscous liquid to methyl silane is (5-10):1; Preparation of a cellulose alcohol gel film: The cellulose is mixed with an ionic liquid, heated and stirred, vacuum degassed and then formed into a film to obtain a cellulose sol film; the cellulose sol film is regenerated in an ionic liquid aqueous solution to obtain a cellulose wet gel film; and the cellulose wet gel film is subjected to solvent replacement to obtain a cellulose alcohol gel film; (2) the cellulose alcohol gel film obtained in step (1) is placed in the homogeneous sol, and a cellulose / silicon composite wet gel is obtained by standing; the composite wet gel is sequentially aged and supercritically dried to obtain a transparent flexible double-crosslinked silicon-based modified cellulose aerogel. The vinyl silane is one or more of vinyl trimethoxysilane, vinyl triethoxysilane, vinyl methyl dimethoxysilane or vinyl ethyl diethoxysilane. The methyl silane is one or more of methyl trimethoxysilane or methyl triethoxysilane.

2. The transparent flexible dual-crosslinked silicate-based modified cellulose aerogel according to claim 1, characterized in that, The viscous liquid obtained by radical polymerization of the vinyl silane is mixed with the methyl silane at a mass ratio of (5-10):1, and hydrolysis-polycondensation reaction is carried out.

3. The transparent flexible dual-crosslinked silicate-based modified cellulose aerogel according to claim 1, wherein, The cellulose is one or more of carboxymethyl cellulose, carboxypropyl methyl cellulose or hydroxyl cellulose.

4. The process for the preparation of transparent flexible dual-crosslinked siliceous modified cellulose aerogels according to any one of claims 1-3, characterized in that, The preparation method comprises the following steps: (1) preparation of a homogeneous sol: A free radical initiator is added to the vinyl silane, the reaction system is closed and replaced with an inert gas, and a transparent viscous liquid is obtained by reaction; methyl silane is added to the viscous liquid, mixed thoroughly, and then solvent, deionized water and catalyst are sequentially added, and a homogeneous sol is obtained by mixing, wherein the mass ratio of the viscous liquid to methyl silane is (5-10):1; Preparation of a cellulose alcohol gel film: The cellulose is mixed with an ionic liquid, heated and stirred, vacuum degassed and then formed into a film to obtain a cellulose sol film; the cellulose sol film is regenerated in an ionic liquid aqueous solution to obtain a cellulose wet gel film; and the cellulose wet gel film is subjected to solvent replacement to obtain a cellulose alcohol gel film; (2) the cellulose alcohol gel film obtained in step (1) is placed in the homogeneous sol, and a cellulose / silicon composite wet gel is obtained by standing; the composite wet gel is sequentially aged and supercritically dried to obtain a transparent flexible double-crosslinked silicon-based modified cellulose aerogel.

5. The process for the preparation of transparent flexible dual-crosslinked siliceous modified cellulose aerogels as claimed in claim 4, wherein, The reaction temperature of the viscous liquid in step (1) is 100-140℃, and the reaction time is 4-48 h; the free radical initiator is one or more of di-t-butyl peroxide, azobisisobutyronitrile or azobisisoheptyl nitrile; and the molar ratio of the vinyl silane to the free radical initiator is (5-15):

1.

6. The process for preparing transparent flexible dual-crosslinked siliceous modified cellulose aerogels as claimed in claim 4, wherein, The solvent in step (1) is one or more of methanol, ethanol, n-butanol or t-butanol; the catalyst is one or more of tetramethylammonium hydroxide, ammonium fluoride or ammonia; the molar ratio of methylsilane to solvent, deionized water and catalyst is 1:(1-5):(1-5):(0.01-0.1); the ionic liquid is one or more of EmimCl, EmimBr, EmimF, EmimAc, AmimCl, AmimBr or AmimF, and the mass fraction of the ionic liquid used for regeneration of the cellulose sol film is 20wt%; the cellulose sol film is prepared by mixing cellulose and ionic liquid at a molar ratio of 1:(30-60).

7. The process for preparing transparent flexible dual-crosslinked siliceous modified cellulose aerogels as claimed in claim 4, wherein, The solvent in step (1) is replaced every 12h, and the replacement is performed 2-4 times; the aging temperature in step (2) is 40-60℃, and the aging time is 12-48h; the supercritical drying is carbon dioxide supercritical fluid drying, the pressure is 5-20MPa, the temperature is 30-60℃, and the drying time is 24-72h.

8. Use of transparent flexible dual-crosslinked siliceous modified cellulose aerogels according to any one of claims 1 to 3, characterized in that, Used in the field of thermal insulation as transparent glass interlayer.

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