A thermal insulation material based on cellulose nanofibers and fly ash and its preparation method

Abstract

The present invention discloses a thermal insulation material based on cellulose nanofibers and fly ash and a preparation method thereof. The thermal insulation material is prepared by successively preparing cellulose nanofibers based on wood pulp, 2,2,6,6-tetramethylpiperidine-1-oxyl radical, sodium bromide, sodium hypochlorite and sodium hydroxide, and a composite gelation material based on cellulose nanofibers and fly ash. This thermal insulation material addresses the problems of relatively low mechanical strength, limited flame retardancy, and high requirements for the method of developing and utilizing fly ash. Moreover, the preparation method is simple, efficient, and low-cost. During the preparation process, no chemical modification of fly ash is required. Fly ash is incorporated into cellulose nanofibers to form a composite aerogel, resulting in a thermal insulation material with good mechanical strength, flame retardancy, and low thermal conductivity, which has good practicality.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal insulation materials, and particularly relates to a thermal insulation material based on cellulose nanofibers and fly ash and a preparation method thereof. Background Art

[0002] Nearly 30 - 40% of the total global energy is consumed in heating and cooling in the construction industry. Thermal insulation materials can reduce the energy consumption of buildings and play a key role in sustainable development. Currently, commercially available thermal insulation materials mainly include polyurethane, polystyrene, and mineral wool. These thermal insulation materials are non-renewable and have poor durability, which is not suitable for sustainable development. Using renewable and sustainable materials to manufacture thermal insulation materials is the development direction of thermal insulation materials. In this direction, cellulose is the most abundant biological material on earth, is a renewable and sustainable material, and is becoming one of the most important next-generation materials.

[0003] In recent years, cellulose aerogel has become an efficient thermal insulation material due to its superior properties such as high porosity, high specific surface area, low density, and low thermal conductivity. However, the lower mechanical strength and limited flame retardancy of cellulose aerogel are challenges in its application as a thermal insulation material. At the same time, coal is the energy source for thermal power generation, and fly ash has become one of the most abundant industrial wastes. It is reported that nearly 780 million tons of fly ash are generated worldwide every year, and it is difficult to effectively treat. Currently, there are already various methods to attempt the use of fly ash in the production of concrete, cement, bricks, and lightweight aggregate concrete blocks; however, many methods use irritating chemicals and extreme conditions. Therefore, the methods for developing and utilizing fly ash require high requirements. The extensive utilization of fly ash is still in its infancy, and new methods need to be developed to manufacture new useful materials based on fly ash to improve the utilization rate and minimize environmental hazards. Summary of the Invention

[0004] The purpose of the present invention is to provide a thermal insulation material based on cellulose nanofibers and fly ash that overcomes the problems of the lower mechanical strength and limited flame retardancy of cellulose aerogel and the high requirements for the methods of developing and utilizing fly ash in the above-mentioned prior art.

[0005] Another purpose of the present invention is to provide a preparation method for preparing the above-mentioned thermal insulation material based on cellulose nanofibers and fly ash.

[0006] To this end, the technical solution of the present invention is as follows:

[0007] A preparation method for a thermal insulation material based on cellulose nanofibers and fly ash, the steps of which are as follows:

[0008] S1. Prepare cellulose nanofibers:

[0009] S101. Dissolve 2,2,6,6 - tetramethylpiperidine - 1 - oxyl radical in water to prepare a TEMPO aqueous solution with a concentration of 0.15 g / L to 0.2 g / L; dissolve sodium bromide in water to prepare a sodium bromide aqueous solution with a concentration of 0.7 g / L to 1 g / L; mix the TEMPO aqueous solution and the sodium bromide aqueous solution at a volume ratio of 1:(2 - 3) to obtain a catalyst mixture for pulp oxidation;

[0010] S102. Add pulp to the catalyst mixture prepared in step S101 according to the ratio of adding 10 g to 15 g of pulp per 1 L of the catalyst mixture, and stir for 2 h to 4 h until evenly mixed to obtain a pulp mixture;

[0011] S103. Add a 10 wt.% - 14 wt.% sodium hypochlorite solution to the pulp mixture prepared in step S102 according to the ratio of adding 0.1 L to 0.2 L of the sodium hypochlorite solution per 1 L of the pulp mixture, and stir for 1 h to 2 h; then adjust the pH value of the mixture to 9.8 - 10.4; in this step, the sodium hypochlorite solution is the oxidant for the pulp, and at the same time, the cellulose oxidation process of the pulp is initiated by adjusting the pH value of the reaction system;

[0012] S104. Place the mixture prepared in step S103 in a blender, and add NaOH to the mixture according to the ratio of adding 0.8 g to 1 g of NaOH per 1 L of the mixture to maintain the pH value of the mixture at about 10, thereby ensuring the continuous progress of the oxidation process; the mixture is stirred at a stirring rate of 60 r / min to 90 r / min at room temperature for 10 - 12 days;

[0013] S105. Wash the solid obtained after stirring with water multiple times to remove the residual chemicals thereon; then place it in a centrifuge, centrifuge and obtain the solid as the prepared cellulose nanofibers;

[0014] S106. Place the cellulose nanofibers obtained in step S105 under the conditions of - 40°C to - 20°C and a vacuum degree of 15 Pa to 30 Pa, and perform freeze - drying for 3 h to 4 h to obtain dry cellulose nanofibers;

[0015] S2. Prepare a thermal insulation material:

[0016] S201. Prepare a cellulose nanofiber dispersion by dissolving the cellulose nanofibers prepared in step S1 according to the ratio of adding 3 g to 4 g of cellulose nanofibers per 1 L of water; then adjust the pH value of the cellulose nanofiber dispersion to 11.5 - 12;

[0017] S202. Add fly ash to the cellulose nanofiber dispersion prepared in step S201 at a ratio of 7 g to 15 g of fly ash per 1 L of the dispersion, and obtain a fly ash-fiber mixed solution through mixing and stirring.

[0018] S203. Place the fly ash-fiber mixed solution obtained in step S202 in a blender and stir at a speed of 900 r / min to 1200 r / min at room temperature for 24 h to 26 h to obtain a composite hydrogel based on cellulose nanofibers and fly ash.

[0019] S204. Wash the composite hydrogel obtained in step S203 with clear water multiple times to remove the sodium hydroxide attached to the composite hydrogel and adjust the pH value of the composite hydrogel to 7 to 7.5.

[0020] S205. Place the composite hydrogel obtained in step S204 under the conditions of -40°C to -20°C and a vacuum degree of 15 Pa to 30 Pa, and perform freeze-drying for 3 to 4 h to obtain a thermal insulation material.

[0021] Preferably, in step S102, the wood pulp is Chinese fir wood pulp. The Chinese fir wood pulp is made from Chinese fir wood chips, and its specific preparation method can refer to the literature: Chen Honglei, Huang Fengyang, Gui Huachen, etc. Lignin-carbohydrate complexes in plant fiber raw materials and pulp [J]. Science and Technology of Cellulose. 2008(01).

[0022] Preferably, in steps S103 and S201, the reagent for adjusting the pH value is a 15 wt.% to 20 wt.% NaOH solution.

[0023] A thermal insulation material based on cellulose nanofibers and fly ash is prepared by using the above preparation method of the thermal insulation material based on cellulose nanofibers and fly ash.

[0024] Compared with the prior art, the thermal insulation material based on cellulose nanofibers and fly ash overcomes the problems in the prior art that the mechanical strength of cellulose aerogel is relatively low, the flame retardancy is limited, and the methods for developing and utilizing fly ash require high requirements. Moreover, the preparation method is simple, with high efficiency and low cost. During the preparation process, no chemical modification of fly ash is required. Fly ash is incorporated into cellulose nanofibers to form a composite aerogel, and a thermal insulation material with good mechanical strength, flame retardant performance, and low thermal conductivity is prepared, which has good practicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a scanning electron microscope image of the thermal insulation material based on cellulose nanofibers and fly ash prepared in Example 1 of the present invention;

[0026] Figure 2SEM image of the thermal insulation material based on cellulose nanofibers and fly ash prepared in Comparative Example 1 of the present invention. Detailed implementation manners

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the following embodiments are by no means any limitation to the present invention.

[0028] Example 1

[0029] S1. Prepare cellulose nanofibers:

[0030] S101. Dissolve 2,2,6,6-tetramethylpiperidine-1-oxyl in water to prepare a 0.15 g / L TEMPO aqueous solution; dissolve sodium bromide in water to prepare a 1 g / L sodium bromide aqueous solution; mix the TEMPO aqueous solution and the sodium bromide aqueous solution at a volume ratio of 1:2 to prepare 6 L of a catalyst mixture.

[0031] S102. Add wood pulp to the catalyst mixture prepared in step S101 according to the ratio of adding 10 g of wood pulp to every 1 L of the catalyst mixture, and stir for 3 h until evenly mixed to obtain a wood pulp mixture.

[0032] S103. Add a 10 wt.% sodium hypochlorite solution to the wood pulp mixture prepared in step S102 according to the ratio of adding 0.2 L of the sodium hypochlorite solution to every 1 L of the wood pulp mixture, and stir for 1 h; then dropwise add a 15 wt.% NaOH solution to adjust the pH value of the mixture to 10.4.

[0033] S104. Place the mixture prepared in step S103 in a blender, and add NaOH to the mixture according to the ratio of adding 0.9 g of NaOH to every 1 L of the mixture to maintain the pH value of the mixture at about 10, so as to ensure the continuous progress of the oxidation process; the mixture is stirred at a stirring rate of 90 r / min at room temperature for 10 days.

[0034] S105. Wash the solid obtained after stirring with water 3 to 5 times to remove the residual chemical substances thereon; then place it in a centrifuge, centrifuge to obtain the solid as the prepared cellulose nanofibers.

[0035] S106. Place the cellulose nanofibers obtained in step S105 under the conditions of -40°C and a vacuum degree of 30 Pa, and freeze-dry for 4 h to obtain dry cellulose nanofibers.

[0036] S2. Prepare the thermal insulation material:

[0037] S201. Prepare a cellulose nanofiber dispersion by mixing the cellulose nanofibers obtained in step S1 at a ratio of 4 g of cellulose nanofibers per 1 L of water. Then, add a 15 wt.% NaOH solution to the cellulose nanofiber dispersion, and the pH value of the dispersion is 11.5.

[0038] S202. Add fly ash to the cellulose nanofiber dispersion prepared in step S201 at a ratio of 7 g of fly ash per 1 L of dispersion. After mixing and stirring, a fly ash-fiber mixed solution is obtained.

[0039] S203. Place the fly ash-fiber mixed solution obtained in step S202 in a blender and stir at a speed of 1000 r / min at room temperature for 26 h to obtain a composite hydrogel based on cellulose nanofibers and fly ash.

[0040] S204. Wash the composite hydrogel obtained in step S203 with water multiple times to remove the sodium hydroxide attached to the composite hydrogel, and the pH value of the composite hydrogel is 7.

[0041] S205. Place the composite hydrogel obtained in step S204 under the conditions of -20°C and a vacuum of 20 Pa, and perform freeze-drying for 3.5 h to obtain a thermal insulation material.

[0042] Example 2

[0043] S1. Prepare cellulose nanofibers:

[0044] S101. Dissolve 2,2,6,6-tetramethylpiperidine-1-oxyl in water to prepare a 0.2 g / L TEMPO aqueous solution. Dissolve sodium bromide in water to prepare a 0.9 g / L sodium bromide aqueous solution. Mix the TEMPO aqueous solution and the sodium bromide aqueous solution at a volume ratio of 1:3 to obtain 4 L of a catalyst mixture.

[0045] S102. Add wood pulp to the catalyst mixture prepared in step S101 at a ratio of 15 g of wood pulp per 1 L of the catalyst mixture, and stir for 4 h until evenly mixed to obtain a wood pulp mixture.

[0046] S103. Add a 14 wt.% sodium hypochlorite solution to the wood pulp mixture prepared in step S102 at a ratio of 0.15 L of sodium hypochlorite solution per 1 L of the wood pulp mixture, and stir for 1 h. Then, add a 20 wt.% NaOH solution to adjust the pH value of the mixture to 10.

[0047] S104. Place the mixed solution prepared in step S103 in a blender, and add NaOH to the mixed solution at a ratio of 0.8 g of NaOH per 1 L of the mixed solution to maintain the pH value of the mixed solution at about 10, thereby ensuring the continuous progress of the oxidation process; the mixed solution is stirred at a stirring rate of 60 r / min at room temperature for 12 days;

[0048] S105. Wash the solid substance obtained by stirring with water 3 to 5 times to remove the residual chemical substances thereon; then place it in a centrifuge, centrifuge and obtain the solid substance as the prepared cellulose nanofibers;

[0049] S106. Place the cellulose nanofibers obtained in step S105 under the conditions of -20 °C and a vacuum degree of 20 Pa, and freeze-dry for 3 h to obtain dry cellulose nanofibers;

[0050] S2. Prepare the thermal insulation material:

[0051] S201. Prepare a cellulose nanofiber dispersion by mixing the cellulose nanofibers prepared in step S1 at a ratio of 3 g of cellulose nanofibers per 1 L of water; then add a 20 wt.% NaOH solution to the cellulose nanofiber dispersion, and the pH value of the dispersion is 12;

[0052] S202. Add fly ash to the cellulose nanofiber dispersion prepared in step S201 at a ratio of 12 g of fly ash per 1 L of the dispersion, and after mixing and stirring, obtain a fly ash-fiber mixed solution;

[0053] S203. Place the fly ash-fiber mixed solution obtained in step S202 in a blender and stir at a speed of 900 r / min at room temperature for 25 h to obtain a composite hydrogel based on cellulose nanofibers and fly ash;

[0054] S204. Wash the composite hydrogel prepared in step S203 with clear water multiple times to remove the sodium hydroxide attached to the composite hydrogel, and the pH value of the composite hydrogel is 7.5;

[0055] S205. Place the composite hydrogel prepared in step S204 under the conditions of -40 °C and a vacuum degree of 15 Pa, and freeze-dry for 4 h to obtain the thermal insulation material.

[0056] Example 3

[0057] S1. Prepare cellulose nanofibers:

[0058] S101. Dissolve 2,2,6,6 - tetramethylpiperidine - 1 - oxyl radical in water to prepare a 0.18 g / L TEMPO aqueous solution; dissolve sodium bromide in water to prepare a 0.8 g / L sodium bromide aqueous solution; mix the TEMPO aqueous solution and the sodium bromide aqueous solution at a volume ratio of 1:2.5 to obtain 7 L of catalyst mixture solution.

[0059] S102. Add wood pulp to the catalyst mixture solution prepared in step S101 at a ratio of 12 g of wood pulp per 1 L of catalyst mixture solution, and stir for 2 h until evenly mixed to obtain a wood pulp mixed solution.

[0060] S103. Add 12 wt.% sodium hypochlorite solution to the wood pulp mixed solution prepared in step S102 at a ratio of 0.1 L of sodium hypochlorite solution per 1 L of wood pulp mixed solution, and stir for 2 h; then add 15 wt.% NaOH solution dropwise to adjust the pH value of the mixed solution to 9.8.

[0061] S104. Place the mixed solution prepared in step S103 in a blender, and add NaOH to the mixed solution at a ratio of 1 g of NaOH per 1 L of mixed solution to maintain the pH value of the mixed solution at about 10, thereby ensuring the continuous progress of the oxidation process; stir the mixed solution at a stirring rate of 80 r / min at room temperature for 11 days.

[0062] S105. Wash the solid substance obtained after stirring with water 3 - 5 times to remove the residual chemical substances thereon; then place it in a centrifuge, centrifuge to obtain the solid substance as the prepared cellulose nanofibers.

[0063] S106. Place the cellulose nanofibers obtained in step S105 under the conditions of - 30 °C and a vacuum degree of 15 Pa, and freeze - dry for 3.5 h to obtain dry cellulose nanofibers.

[0064] S2. Prepare heat - insulating materials:

[0065] S201. Prepare a cellulose nanofiber dispersion by adding 3.5 g of cellulose nanofibers prepared in step S1 per 1 L of water; then add 15 wt.% NaOH solution to the cellulose nanofiber dispersion, and the pH value of the dispersion is 11.8.

[0066] S202. Add fly ash to the cellulose nanofiber dispersion prepared in step S201 at a ratio of 15 g of fly ash per 1 L of dispersion, and after mixing and stirring, obtain a fly ash - fiber mixed solution.

[0067] S203. Place the fly ash-fiber mixed solution obtained in step S202 into a blender and stir at a speed of 1200 r / min for 24 h at room temperature to prepare a composite hydrogel based on cellulose nanofibers and fly ash;

[0068] S204. Wash the composite hydrogel obtained in step S203 with clear water multiple times to remove the sodium hydroxide attached to the composite hydrogel, and the pH value of the composite hydrogel is 7.2;

[0069] S205. Place the composite hydrogel obtained in step S204 under the conditions of -35 °C and a vacuum degree of 30 Pa, and conduct freeze-drying for 3.5 h to prepare a thermal insulation material.

[0070] Comparative Example 1

[0071] S1. Dissolve 2,2,6,6-tetramethylpiperidine-1-oxyl radical in water to prepare a 0.15 g / L TEMPO aqueous solution; dissolve sodium bromide in water to prepare a 1 g / L sodium bromide aqueous solution; mix the TEMPO aqueous solution and the sodium bromide aqueous solution in a volume ratio of 1:2 to prepare 6 L of a catalyst mixture;

[0072] S2. Add wood pulp to the catalyst mixture prepared in step S101 according to the ratio of adding 10 g of wood pulp to every 1 L of the catalyst mixture, and stir for 3 h until evenly mixed to obtain a wood pulp mixed solution;

[0073] S3. Add a 10 wt.% sodium hypochlorite solution to the wood pulp mixed solution prepared in step S102 according to the ratio of adding 0.2 L of the sodium hypochlorite solution to every 1 L of the wood pulp mixed solution, and stir for 1 h; then add a 15 wt.% NaOH solution to adjust the pH value of the mixed solution to 10.4;

[0074] S4. Place the mixed solution prepared in step S103 into a blender, and add NaOH to the mixed solution according to the ratio of adding 0.9 g of NaOH to every 1 L of the mixed solution to maintain the pH value of the mixed solution at about 10, thereby ensuring the continuous progress of the oxidation process; stir the mixed solution at a stirring rate of 90 r / min at room temperature for 10 days;

[0075] S5. Wash the solid substance obtained after stirring with water 3 - 5 times to remove the residual chemical substances thereon; then place it in a centrifuge, centrifuge and obtain the solid substance as the prepared cellulose nanofibers;

[0076] S6. Place the cellulose nanofibers obtained in step S105 under the conditions of -40 °C and a vacuum degree of 20 Pa, and conduct freeze-drying for 4 h to prepare dry cellulose nanofibers.

[0077] Performance test:

[0078] (1) Microscopic morphology characterization of thermal insulation materials:

[0079] The microscopic morphologies of the thermal insulation materials prepared in Examples 1-3 and Comparative Example 1 were characterized using a scanning electron microscope (SEM).

[0080] As Figure 1 shown is the scanning electron microscope image of the thermal insulation material prepared in Example 1; it can be seen from the figure that at the microscopic level, this thermal insulation material has less void volume, a relatively thick pore wall, and better pore wall densification; therefore, based on the principle that the thicker the pore wall, the greater the thermal resistance, and the thicker the pore wall, the better the mechanical strength, it can be preliminarily judged that this thermal insulation material has the characteristics of lower thermal conductivity and better mechanical strength. The characteristics of the microscopic morphologies of the thermal insulation materials prepared in Examples 2 and 3 characterized by the scanning electron microscope are the same as those in Example 1.

[0081] Compared with Example 1, the difference in Comparative Example 1 is that the thermal insulation material in Comparative Example 1 is an intermediate product of the thermal insulation material in Example 1, that is, the cellulose nanofibers obtained in step S1 of Example 1. As Figure 2 shown is the scanning electron microscope image of the thermal insulation material prepared in Comparative Example 1; it can be seen from the figure that the thermal insulation material prepared in Comparative Example 1, that is, cellulose nanofibers, has significantly more void volume and relatively thinner pore walls in its microscopic structure; it can be seen that the cellulose nanofibers with nanofibrillation have thinner pore walls and a large void volume at the microscopic structure, and after further uniformly dispersing fly ash in the nanofibrillated cellulose nanofibers to form a composite, and then further preparing the composite to form a gelated product, a thermal insulation material with a new microscopic structure is obtained; at the same time, according to the determination method of the microscopic state and material properties of the thermal insulation material in Example 1, it can be preliminarily determined that the thermal conductivity and mechanical strength of the thermal insulation material prepared in Comparative Example 1 are inferior to those of the thermal insulation materials prepared in Examples 1-3.

[0082] (2) Thermal conductivity test of thermal insulation materials:

[0083] The transient hot wire method was used to measure the thermal conductivities of the thermal insulation materials prepared in Examples 1-3 and Comparative Example 1 respectively. The specific test results are shown in Table 1 below.

[0084] Table 1:

[0085]

[0086] It can be seen from the test results in Table 1 that the thermal conductivities of the thermal insulation materials prepared in Examples 1-3 are effectively reduced compared with the thermal insulation material prepared in Comparative Example 1, and the thermal conductivity is specifically reduced by 56.65%.

[0087] (3) Mechanical strength test of thermal insulation materials:

[0088] The mechanical strength of the thermal insulation materials prepared in Examples 1 to 3 and Comparative Example 1 was measured by the tensile test method respectively. The specific test results are shown in Table 2 below.

[0089] Table 2:

[0090]

[0091] It can be seen from the test results in Table 2 that, compared with the thermal insulation material prepared in Comparative Example 1, the mechanical strength of the thermal insulation materials prepared in Examples 1 to 3 has been effectively improved, and the mechanical strength has specifically increased by 45%.

[0092] (4) Flame retardancy of the thermal insulation material:

[0093] The mechanical strength of the thermal insulation materials prepared in Examples 1 to 3 and Comparative Example 1 was measured by the combustion test respectively. The specific test results are shown in Table 3 below.

[0094] Table 3:

[0095]

[0096] It can be seen from the test results in Table 3 that the thermal insulation materials prepared in Examples 1 to 3 achieve complete flame retardancy at the 2s moment of combustion, and the remaining volume after combustion is 95% - 98%. While the thermal insulation material prepared in Comparative Example 1 is completely burned after 2s of combustion, without any unburned material left. It can be seen that the thermal insulation material of the present application has good flame retardancy performance.

[0097] In summary, the thermal insulation material based on cellulose nanofibers and fly ash of the present application has good thermal insulation performance, mechanical strength and flame retardancy performance, and the preparation method is simple, with low cost and high efficiency, having good long-term application and popularization prospects.

Claims

1. A preparation method of a heat insulation material based on cellulose nanofibers and fly ash, characterized in that, The steps are as follows: S1. Prepare cellulose nanofibers: S101. Prepare an aqueous solution of 2,2,6,6-tetramethylpiperidine-1-oxyl radical with a concentration of 0.15 g / L to 0.2 g / L and an aqueous solution of sodium bromide with a concentration of 0.7 g / L to 1 g / L, and mix the two in a volume ratio of 1:(2 - 3) to obtain a catalyst mixture solution; S102. Add wood pulp to the catalyst mixture solution prepared in step S101 according to the ratio of adding 10 g to 15 g of wood pulp per 1 L of the catalyst mixture solution, and stir for 2 h to 4 h until evenly mixed to obtain a wood pulp mixed solution; S103. Add a 10wt.% - 14wt.% sodium hypochlorite solution to the wood pulp mixed solution prepared in step S102 according to the ratio of adding 0.1 L to 0.2 L of sodium hypochlorite solution per 1 L of the wood pulp mixed solution, and stir for 1 h to 2 h; then, adjust the pH value of the mixed solution to 9.8 - 10.4; S104. Place the mixed solution prepared in step S103 in a blender, and add NaOH to the mixed solution according to the ratio of adding 0.8 g to 1 g of NaOH per 1 L of the mixed solution, and stir at a stirring rate of 60 r / min to 90 r / min at room temperature for 10 - 12 days; S105. Wash the solid substance obtained by stirring with water multiple times, and then centrifuge it in a centrifuge to obtain the solid substance; S106. Place the solid substance obtained in step S105 under the conditions of -40°C to -20°C and a vacuum degree of 15 Pa to 30 Pa, and freeze-dry it for 3 h to 4 h to prepare cellulose nanofibers; S2. Prepare a heat-insulating material: S201. Prepare a cellulose nanofiber dispersion by adding 3 g to 4 g of cellulose nanofibers prepared in step S1 per 1 L of water; Then, adjust the pH value of the cellulose nanofiber dispersion to 11.5 - 12; S202. Add fly ash to the cellulose nanofiber dispersion prepared in step S201 according to the ratio of adding 7 g to 15 g of fly ash per 1 L of the dispersion, and after mixing and stirring, obtain a fly ash-fiber mixed solution; S203. Place the fly ash-fiber mixed solution obtained in step S202 in a blender, and stir at a rotation speed of 900 r / min to 1200 r / min at room temperature for 24 h to 26 h to prepare a composite hydrogel based on cellulose nanofibers and fly ash; S204. Wash the composite hydrogel prepared in step S203 with clear water multiple times, and adjust the pH value of the composite hydrogel to 7 - 7.5; S205. Place the composite hydrogel prepared in step S204 under the conditions of -40°C to -20°C and a vacuum degree of 15 Pa to 30 Pa, and freeze-dry it for 3 - 4 h to prepare a heat-insulating material.

2. The preparation method of the thermal insulation material based on cellulose nanofibers and fly ash according to claim 1, wherein, In step S102, the wood pulp is Chinese fir wood pulp.

3. The preparation method of the heat insulation material based on cellulose nanofibers and fly ash according to claim 1, characterized in that, In steps S103 and S201, the reagent for adjusting the pH value is a 15wt.% - 20wt.% NaOH solution.

4. A thermal insulation material based on cellulose nanofibers and fly ash, which is prepared by using the preparation method of the thermal insulation material based on cellulose nanofibers and fly ash according to any one of claims 1 to 3.

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