Lightweight thermal insulating cellulose nanofiber aerogel and method of making the same

Abstract

The application belongs to the technical field of functional aerogel, and provides lightweight thermal insulation cellulose nanofiber aerogel and a preparation method thereof.The method comprises the following steps: homogenizing cellulose nanofiber in water, freeze-drying cellulose nanofiber dispersion to obtain freeze-dried cellulose nanofiber aerogel; homogenizing the freeze-dried cellulose nanofiber aerogel in water, stirring and mixing secondary cellulose nanofiber dispersion, a crosslinking agent and silane, and then sequentially performing static pre-crosslinking, freeze-drying and crosslinking treatment to obtain lightweight thermal insulation cellulose nanofiber aerogel.The method for preparing lightweight thermal insulation cellulose nanofiber aerogel through secondary plastic shaping can maintain the fiber structure of cellulose nanofiber, reduce the mutual entanglement phenomenon between cellulose, and improve the mechanical properties, resilience and compression cycle performance of the aerogel, so that the prepared cellulose nanofiber aerogel has a good application prospect in the field of thermal insulation.

Description

Technical Field

[0001] The present invention relates to the technical field of functional aerogels, and in particular to a lightweight thermal insulating cellulose nanofiber aerogel and a preparation method thereof. Background Art

[0002] With the improvement of people's living standards, the thermal insulation function of traditional thermal insulation materials can no longer meet people's demand for quality of life. For example, the requirements of various industries for various types of thermal insulation materials are becoming increasingly diversified and focus on balancing multiple aspects. Thermal insulation materials not only need to ensure basic thermal insulation performance, but also need to be light, thin, highly elastic and breathable. Aerogel is a nanoporous material with ultra-low density and a highly cross-linked network structure. The liquid inside the wet gel is replaced by air, so the aerogel contains a large amount of air. Based on the above structural characteristics, aerogel has many advantages, such as high specific surface area, high porosity, low thermal conductivity, low density and 3D interconnected nanoporous network structure. It stands out among porous materials and is considered to be one of the thermal insulation materials with great application prospects. At present, aerogel used in the field of thermal insulation is mainly used as an interlayer between the substrate and coating of buildings, automobiles or electronic products, or ground into nanoparticles and sprayed on the surface of the substrate.

[0003] In the field of thermal insulation, aerogels generally suffer from shortcomings such as poor strength, poor toughness, and difficulty in processing. Cellulose, with its abundant raw materials, non-toxicity, ease of modification, and good biocompatibility, can be modified to impart improved mechanical properties and resilience, offering promising prospects in the field of thermal insulation. Developing insulating aerogels that are easy to process, have excellent mechanical properties, and are low in cost has become a top priority in current aerogel research and development in this field.

[0004] In addition, the cellulose nanofiber dispersion has a microstructure that is a typical 1D nanofiber structure. When the cellulose nanofiber dispersion is prepared by traditional freeze drying to obtain a cellulose nanofiber aerogel, the cellulose nanofibers will be entangled with each other, causing their microstructure to be changed from 1D nanofibers to a 2D sheet structure, which reduces the resilience and strength of the aerogel to a certain extent. Therefore, how to keep the cellulose nanofibers still in a 1D nanofiber structure during the freeze molding process, and then improve their mechanical properties, is a problem that needs to be solved urgently. CN118791781A discloses a thermal insulation material obtained by directly mixing oxidized cellulose with polyvinyl alcohol and freeze-drying. The material has high compressive strength and a simple and convenient preparation process. The disadvantage is that the cellulose is directly entangled with the polyvinyl alcohol into a sheet, the porosity is low, and the aerogel density is too large, which further reduces its thermal insulation performance.

[0005] Therefore, it is of great value to study a method for preparing a lightweight insulating cellulose nanofiber aerogel with good thermal insulation, mechanical properties and resilience. SUMMARY

[0006] The present application aims to provide a light thermal insulation cellulose nanofiber aerogel and a preparation method thereof to overcome the deficiencies of the prior art and solve the technical problems of poor flexibility and low strength of current thermal insulation aerogels.

[0007] To achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0008] The present application provides a preparation method of a light thermal insulation cellulose nanofiber aerogel, comprising the following steps:

[0009] 1) Homogenizing cellulose nanofibers in water to obtain a cellulose nanofiber dispersion, and freeze-drying the cellulose nanofiber dispersion to obtain freeze-dried cellulose nanofiber aerogel;

[0010] 2) Homogenizing the freeze-dried cellulose nanofiber aerogel in water to obtain a secondary cellulose nanofiber dispersion, and sequentially performing standing pre-crosslinking, freeze-drying and crosslinking treatment after stirring and mixing the secondary cellulose nanofiber dispersion, a crosslinking agent and silane to obtain light thermal insulation cellulose nanofiber aerogel.

[0011] Preferably, in the cellulose nanofiber dispersion of step 1), the mass fraction of cellulose nanofibers is 0.01-0.15%.

[0012] Preferably, the cellulose nanofibers of step 1) are gel-like cellulose nanofibers, and the mass content of cellulose nanofibers in the gel-like cellulose nanofibers is 2.5-3.5%.

[0013] Preferably, the homogenization time of steps 1) and 2) is independently 15-45 min, and the homogenization speed is independently 3000-15000 r / min.

[0014] Preferably, the freeze-drying of steps 1) and 2) sequentially comprises pre-freezing and vacuum freeze-drying, the pre-freezing temperature is -196 to -150℃, the pre-freezing time is 10-60 min; the vacuum freeze-drying temperature is -85 to -75℃, the vacuum freeze-drying time is 48-96 h, and the vacuum degree of vacuum freeze-drying is 0.5-20 Pa.

[0015] Preferably, the solid content of the secondary cellulose nanofiber dispersion of step 2) is 0.1-1%, the mass ratio of the crosslinking agent to the cellulose nanofibers is 1:5-20, and the volume-mass ratio of silane to cellulose nanofibers is 1 mL:3.5-10 g.

[0016] As preferred, the crosslinking agent in step 2) comprises one or more of butane tetracarboxylic acid, isocyanate, glutaraldehyde and citric acid; the silane comprises one or more of methyltrimethoxysilane, dodecyltrimethoxysilane and perfluorodecyltrichlorosilane.

[0017] As preferred, the temperature of the crosslinking treatment in step 2) is 90-140℃, and the time of the crosslinking treatment is 3-12h.

[0018] The application further provides a light thermal insulation cellulose nanofiber aerogel prepared by the method for preparing a light thermal insulation cellulose nanofiber aerogel, the light thermal insulation cellulose nanofiber aerogel has a thermal conductivity of 0.028-0.040 W / (m·k), a density of 1.5-20 mg / cm 3 .

[0019] The application has the following advantages:

[0020] 1) The method for preparing a light thermal insulation cellulose nanofiber aerogel can maintain the fiber structure of cellulose nanofiber, reduce the mutual entanglement between celluloses, and improve the mechanical properties, resilience and compression cycle performance of the aerogel.

[0021] 2) The light thermal insulation cellulose nanofiber aerogel prepared by the method has a thermal conductivity of 0.028-0.040 W / (m·k), a density of 1.5-20 mg / cm 3 , a compression strength of 1-18 kPa, and a resilience of more than 80% after 100 times of compression, and the cellulose nanofiber aerogel prepared by the method has a good application prospect in the field of thermal insulation. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 SEM image of the cellulose nanofiber aerogel prepared by the secondary plasticization of Example 1;

[0023] Figure 2 SEM image of the cellulose nanofiber aerogel prepared by the conventional freeze drying of Comparative Example 1;

[0024] Figure 3 Cycle compression curve of the cellulose nanofiber aerogel prepared by the secondary plasticization of Example 1;

[0025] Figure 4 Cycle compression curve of the cellulose nanofiber aerogel prepared by the conventional freeze drying of Comparative Example 1. DETAILED DESCRIPTION

[0026] The application provides a method for preparing a light thermal insulation cellulose nanofiber aerogel, comprising the following steps:

[0027] 1) homogenizing cellulose nanofibers in water to obtain a cellulose nanofiber dispersion, and freeze-drying the cellulose nanofiber dispersion to obtain freeze-dried cellulose nanofiber aerogel;

[0028] 2) homogenizing the freeze-dried cellulose nanofiber aerogel in water to obtain a secondary cellulose nanofiber dispersion, and sequentially performing standing pre-crosslinking, freeze-drying, and crosslinking treatment after stirring and mixing the secondary cellulose nanofiber dispersion, a crosslinking agent, and silane to obtain lightweight thermal insulation cellulose nanofiber aerogel.

[0029] In the present application, the mass fraction of cellulose nanofibers in the cellulose nanofiber dispersion of step 1) is preferably 0.01-0.15%, further preferably 0.05-0.12%, and more preferably 0.06-0.1%.

[0030] In the present application, the cellulose nanofibers of step 1) are preferably gel-like cellulose nanofibers, and the mass content of cellulose nanofibers in the gel-like cellulose nanofibers is preferably 2.5-3.5%, further preferably 2.8-3.2%, and more preferably 3%.

[0031] In the present application, the homogenization time of steps 1) and 2) is independently preferably 15-45 min, further preferably 20-40 min, and more preferably 30-35 min, and the rotation speed of homogenization is independently preferably 3000-15000 r / min, further preferably 4000-12000 r / min, and more preferably 6000-10000 r / min.

[0032] 10000 r / min.

[0033] In the present application, the freeze-drying of steps 1) and 2) preferably sequentially comprises pre-freezing and vacuum freeze-drying, the temperature of pre-freezing is preferably -196 to -150℃, further preferably -190 to -165℃, and more preferably -180 to -170℃, the time of pre-freezing is preferably 10-60 min, further preferably 20-50 min, and more preferably 30-40 min, the temperature of vacuum freeze-drying is preferably -85 to -75℃, further preferably -82 to -78℃, and more preferably -80℃, the time of vacuum freeze-drying is preferably 48-96 h, further preferably 55-80 h, and more preferably 60-70 h, and the vacuum degree of vacuum freeze-drying is preferably 0.5-20 Pa, further preferably 1-15 Pa, and more preferably 3-10 Pa.

[0034] In the present application, the solid content of the secondary cellulose nanofiber dispersion solution in step 2) is preferably 0.1-1%, further preferably 0.3-0.8%, and more preferably 0.5-0.6%; the mass ratio of the crosslinking agent to the cellulose nanofiber is preferably 1:5-20, further preferably 1:8-18, and more preferably 1:9-15; and the volume-to-mass ratio of the silane to the cellulose nanofiber is preferably 1 mL:3.5-10 g, further preferably 1 mL:4-8 g, and more preferably 1 mL:5-7 g.

[0035] In the present application, the crosslinking agent in step 2) preferably comprises one or more of butane tetracarboxylic acid, isocyanate, glutaraldehyde, and citric acid; and the silane preferably comprises one or more of methyltrimethoxysilane, dodecyltrimethoxysilane, and perfluorodecyltrichlorosilane.

[0036] In step 2) of the present application, the secondary cellulose nanofiber dispersion solution, the crosslinking agent, the silane, and the sodium hypophosphite are stirred and mixed, and the mass ratio of the sodium hypophosphite to the cellulose nanofiber in the gelatinous cellulose nanofiber is preferably 1:25-100, further preferably 1:40-90, and more preferably 1:45-75.

[0037] In the present application, the standing time of the pre-crosslinking in step 2) is preferably 22-30 h, and further preferably 24-28 h.

[0038] In the present application, the temperature of the crosslinking treatment in step 2) is preferably 90-140℃, further preferably 100-130℃, and more preferably 110-120℃, and the time of the crosslinking treatment is preferably 3-12 h, further preferably 4-10 h, and more preferably 5-8 h.

[0039] In the present application, the crosslinking treatment preferably comprises a first crosslinking treatment and a second crosslinking treatment, the temperature of the first crosslinking treatment is preferably 90-100℃, and further preferably 95℃, and the time of the first crosslinking treatment is preferably 1-2 h; the temperature of the second crosslinking treatment is preferably 125-130℃, and further preferably 127-128℃, and the time of the second crosslinking treatment is preferably 3-10 h, and further preferably 3-6 h.

[0040] In the present application, the crosslinking treatment is performed in a vacuum environment, and the vacuum degree of the vacuum environment is preferably 0.8-1.2 Pa, further preferably 0.9-1.1 Pa, and more preferably 1.0 Pa.

[0041] The present application also provides a lightweight thermal insulation cellulose nanofiber aerogel prepared by the preparation method of the lightweight thermal insulation cellulose nanofiber aerogel, and the thermal conductivity of the lightweight thermal insulation cellulose nanofiber aerogel is 0.028-0.040 W / (m·k), and the density is 1.5-20 mg / cm3 .

[0042] The technical solutions provided by the present application are described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0043] In the embodiments of the present application, butane tetracarboxylic acid is produced by Shanghai Bide Pharmaceutical Technology Co., Ltd. and has a purity of 98%; the gelatinous cellulose nanofiber is provided by Tianjin Muxingling Biological Technology Co., Ltd. and has a model number of PL5, is milky white gelatinous, has a sodium carboxylate content of 1.4 mmol / g, a length of 1-5 μm, and a fiber diameter of 10-20 nm.

[0044] The density calculation formula of aerogel is as follows: wherein, ρ represents the density of aerogel (mg / cm 3 ), m represents the mass of aerogel (mg), and v represents the volume of aerogel (cm 3 ). The instrument used for the compression stress test of aerogel is Exceed 40 universal testing machine of Mesite Company, USA, which is set for uniaxial quasi-static compression stress and strain test, and the load loading rate is 30 mm / min. The instrument used for the thermal conductivity test of aerogel is TPS2500 thermal constant analyzer of Hot Disk Company, Sweden, which is set for steady-state heat source method.

[0045] Example 1

[0046] 4 g of gelatinous cellulose nanofiber (mass fraction of cellulose nanofiber is 3%) is added into 200 g of deionized water, and homogenously stirred at a rotation speed of 4000 r / min for 30 min to obtain a primary cellulose nanofiber dispersion liquid. The primary cellulose nanofiber dispersion liquid is poured into a mold, frozen at-196℃ for 15 min, and then vacuum freeze-dried at a vacuum degree of 1.0 Pa and a temperature of-80℃ for 48 h to obtain freeze-dried cellulose nanofiber aerogel.

[0047] The freeze-dried cellulose nanofiber aerogel was cut into pieces, dispersed in 60 g of deionized water, and homogenously stirred at a speed of 4000 r / min for 30 min to obtain a secondary cellulose nanofiber dispersion (the solid content of the secondary cellulose nanofiber dispersion was 0.2%). 0.012 g of butane tetracarboxylic acid, 0.0024 g of sodium hypophosphite, and 0.03 mL of methyltrimethoxysilane were added to the secondary cellulose nanofiber dispersion, and the mixture was continuously stirred at a speed of 1000 r / min for 3 h. The uniform dispersion was poured into a mold and allowed to stand for 24 h for pre-crosslinking. Subsequently, the dispersion was pre-frozen at -196 ℃ for 15 min, and then vacuum freeze-dried at a vacuum degree of 1.0 Pa and a temperature of -80 ℃ for 48 h. The freeze-dried aerogel was placed in a vacuum oven at a vacuum degree of 1.0 Pa, heated to 90 ℃, and kept at this temperature for 1 h. Subsequently, the temperature was increased to 130 ℃, and the mixture was kept at this temperature for 3 h. After cooling to room temperature, the sample was taken out, and a lightweight thermal insulation cellulose nanofiber aerogel was obtained.

[0048] The density of the lightweight thermal insulation cellulose nanofiber aerogel prepared in this example was 5.4 mg / cm 3 , the compressive strength was up to 3.6 kPa, and the sample was intact after 100 compression cycles, with a resilience rate of 90%. The aerogel sample could be arbitrarily folded without falling off, and the thermal conductivity coefficient was 0.028 W / (m·k), which had a broad application prospect in the field of thermal insulation and heat preservation.

[0049] Example 2

[0050] Twelve grams of gel-like cellulose nanofiber (the mass fraction of cellulose nanofiber was 3%) were added to 300 g of deionized water, and homogenously stirred at a speed of 4000 r / min for 30 min to obtain a primary cellulose nanofiber dispersion. The primary cellulose nanofiber dispersion was poured into a mold, frozen at -196 ℃ for 15 min, and then vacuum freeze-dried at a vacuum degree of 1.0 Pa and a temperature of -80 ℃ for 48 h to obtain a freeze-dried cellulose nanofiber aerogel.

[0051] The freeze-dried cellulose nanofiber aerogel was cut into pieces, dispersed in 60g of deionized water, and homogenized at 4000 rpm for 30 minutes to obtain a secondary cellulose nanofiber dispersion (solid content of the secondary cellulose nanofiber dispersion was 0.6%). 0.036g of butanetetracarboxylic acid, 0.0072g of sodium hypophosphite, and 0.1mL of methyltrimethoxysilane were added to the secondary cellulose nanofiber dispersion, and magnetic stirring was continued at 1000 rpm for 3 hours. The homogenous dispersion was poured into a mold and allowed to stand for pre-crosslinking for 24 hours. It was then pre-frozen at -196°C for 15 minutes and then freeze-dried at -80°C under vacuum conditions of 1.0 Pa and 48 hours. The freeze-dried aerogel was placed in a vacuum oven at 1.0 Pa, heated to 90°C for 1 hour, then heated to 130°C for 3 hours, cooled to room temperature, and removed to obtain a lightweight, thermally insulating cellulose nanofiber aerogel.

[0052] The density of the lightweight thermal insulation cellulose nanofiber aerogel prepared in this example is 10.3 mg / cm 3 The compression strength can reach 9.7kPa, and the sample is intact after 100 compression cycles, with a rebound rate of 85%. The aerogel sample can be folded arbitrarily without falling off, and the thermal conductivity coefficient is 0.035W / (m·k), which has broad application prospects in the field of thermal insulation.

[0053] Example 3

[0054] 20g of gel-like cellulose nanofibers (3% by mass) were added to 500g of deionized water and homogenized at 4000 rpm for 30 minutes to obtain a primary cellulose nanofiber dispersion. The primary cellulose nanofiber dispersion was poured into a mold, frozen at -196°C for 15 minutes, and then freeze-dried at a vacuum of 1.0 Pa and a temperature of -80°C for 48 hours to obtain a freeze-dried cellulose nanofiber aerogel.

[0055] The freeze-dried cellulose nanofiber aerogel was cut into pieces, dispersed in 60 g of deionized water, and homogenized at a speed of 4000 r / min for 30 min to obtain a secondary cellulose nanofiber dispersion (the solid content of the secondary cellulose nanofiber dispersion was 1%). 0.12 g of citric acid, 0.012 g of sodium hypophosphite, and 0.12 mL of methyltrimethoxysilane were added to the secondary cellulose nanofiber dispersion, and the mixture was continuously stirred at a speed of 1000 r / min for 3 h. The uniform dispersion was poured into a mold and allowed to stand for pre-crosslinking for 24 h. Subsequently, the mixture was pre-frozen at -196 ℃ for 30 min, and then vacuum freeze-dried at a vacuum degree of 1.0 Pa and a temperature of -80 ℃ for 48 h. The freeze-dried aerogel was placed in a vacuum oven at a vacuum degree of 1.0 Pa, heated to 90 ℃, and kept at this temperature for 1 h. Subsequently, the temperature was increased to 130 ℃, and the mixture was kept at this temperature for 3 h. After cooling to room temperature, the aerogel was removed, and a lightweight thermal insulation cellulose nanofiber aerogel was obtained.

[0056] The lightweight thermal insulation cellulose nanofiber aerogel prepared in this example had a density of 20 mg / cm 3 , a compressive strength of 20 kPa, and a resilience rate of 80% after 100 compression cycles. The aerogel sample could be arbitrarily folded without falling apart, and had a thermal conductivity of 0.040 W / (m·k), which had a broad application prospect in the field of thermal insulation and heat preservation.

[0057] Comparative Example 1

[0058] 4 g of gel-like cellulose nanofiber (the mass fraction of the cellulose nanofiber was 3%) was added to 60 g of deionized water, and homogenized at a speed of 4000 r / min for 30 min to obtain a cellulose nanofiber dispersion. 0.012 g of butane tetracarboxylic acid, 0.0024 g of sodium hypophosphite, and 0.03 mL of methyltrimethoxysilane were added to the cellulose nanofiber dispersion, and the mixture was continuously stirred at a speed of 1000 r / min for 3 h. The uniform dispersion was poured into a mold and allowed to stand for pre-crosslinking for 24 h. Subsequently, the mixture was pre-frozen at -196 ℃ for 15 min, and then vacuum freeze-dried at a vacuum degree of 1.0 Pa and a temperature of -80 ℃ for 48 h.

[0059] The freeze-dried aerogel was placed in a vacuum oven at a vacuum degree of 1.0 Pa, heated to 90 ℃, and kept at this temperature for 1 h. Subsequently, the temperature was increased to 130 ℃, and the mixture was kept at this temperature for 3 h. After cooling to room temperature, the aerogel was removed, and a lightweight thermal insulation cellulose nanofiber aerogel was obtained.

[0060] The lightweight thermal insulation cellulose nanofiber aerogel prepared in this example had a density of 20 mg / cm 3 , a compressive strength of 20 kPa, and a resilience rate of 80% after 100 compression cycles. The aerogel sample could be arbitrarily folded without falling apart, and had a thermal conductivity of 0.040 W / (m·k), which had a broad application prospect in the field of thermal insulation and heat preservation.

[0061] Figure 1 SEM image of the cellulose nanofiber aerogel prepared by the secondary molding of Example 1; Figure 2 SEM image of the cellulose nanofiber aerogel prepared by the conventional freeze-drying of Comparative Example 1; from Figure 1 and Figure 2 It can be seen that the cellulose nanofiber aerogel prepared by the secondary molding has a large amount of fiber structure, and the cellulose nanofiber aerogel prepared by the conventional freeze-drying has a large amount of sheet structure.

[0062] Figure 3 Cycle compression curve of the cellulose nanofiber aerogel prepared by the secondary molding of Example 1; Figure 4 Cycle compression curve of the cellulose nanofiber aerogel prepared by the conventional freeze-drying of Comparative Example 1; from Figure 3 and Figure 4 It can be seen that the cellulose nanofiber aerogel prepared by the secondary molding has a large amount of fiber structure, and the cellulose nanofiber aerogel prepared by the conventional freeze-drying has a large amount of sheet structure.

[0063] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, several improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a lightweight thermal insulating cellulose nanofiber aerogel, characterized in that: The following steps are included: 1) homogenizing cellulose nanofibers in water to obtain a cellulose nanofiber dispersion, and freeze-drying the cellulose nanofiber dispersion to obtain a freeze-dried cellulose nanofiber aerogel; 2) The freeze-dried cellulose nanofiber aerogel is homogenized in water to obtain a secondary cellulose nanofiber dispersion. The secondary cellulose nanofiber dispersion, a crosslinking agent, and silane are stirred and mixed, and then subjected to static pre-crosslinking, freeze drying, and crosslinking treatment in sequence to obtain a lightweight insulating cellulose nanofiber aerogel.

2. The preparation method according to claim 1, characterized in that In step 1), the mass fraction of the cellulose nanofibers in the cellulose nanofiber dispersion is 0.01 to 0.15%.

3. The preparation method according to claim 1 or 2, characterized in that In step 1), the cellulose nanofibers are gel-like cellulose nanofibers, and the mass content of the cellulose nanofibers in the gel-like cellulose nanofibers is 2.5-3.5%.

4. The preparation method according to claim 3, characterized in that The homogenization time in step 1) and step 2) is independently 15 to 45 minutes, and the homogenization speed is independently 3000 to 15000 r / min.

5. The preparation method according to claim 4, characterized in that The freeze-drying in step 1) and step 2) sequentially comprises pre-freezing and vacuum freeze-drying, wherein the pre-freezing temperature is -196 to -150°C and the pre-freezing time is 10 to 60 minutes; the vacuum freeze-drying temperature is -85 to -75°C and the vacuum freeze-drying time is 48 to 96 hours, and the vacuum degree of the vacuum freeze-drying is 0.5 to 20 Pa.

6. The preparation method according to claim 5, characterized in that Step 2) The solid content of the secondary cellulose nanofiber dispersion is 0.1-1%, the mass ratio of the crosslinking agent to the cellulose nanofiber is 1:5-20, and the volume mass ratio of the silane to the cellulose nanofiber is 1 mL:3.5-10 g.

7. The preparation method according to claim 5 or 6, characterized in that: Step 2) The cross-linking agent comprises one or more of butanetetracarboxylic acid, isocyanate, glutaraldehyde and citric acid; and the silane comprises one or more of methyltrimethoxysilane, dodecyltrimethoxysilane and perfluorodecyltrichlorosilane.

8. The preparation method according to claim 7, characterized in that Step 2) The temperature of the cross-linking treatment is 90 to 140° C., and the time of the cross-linking treatment is 3 to 12 hours.

9. The lightweight thermal insulating cellulose nanofiber aerogel prepared by the method for preparing the lightweight thermal insulating cellulose nanofiber aerogel according to any one of claims 1 to 8, characterized in that: The thermal conductivity of the lightweight thermal insulating cellulose nanofiber aerogel is 0.028-0.040 W / (m·k) and the density is 1.5-20 mg / cm 3 .

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