CN108623850B - Environment-friendly cellulose-based flame-retardant heat-insulating material and preparation method thereof - Google Patents
Environment-friendly cellulose-based flame-retardant heat-insulating material and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a cellulose-based flame-retardant heat-insulating material, in particular to an environment-friendly cellulose-based flame-retardant heat-insulating material and a preparation method thereof, belonging to the technical field of new materials. The environment-friendly cellulose-based flame-retardant and heat-insulating material is prepared by taking cellulose and layered double hydroxides as raw materials, dissolving the cellulose by adopting a direct blending method under an alkaline condition at a low temperature of-20 ℃ to-30 ℃, fully stirring at room temperature to form a cellulose solution with uniformly dispersed layered double hydroxides and no agglomeration, crosslinking the obtained solution by using a crosslinking agent, and freeze-drying to obtain the environment-friendly cellulose-based flame-retardant and heat-insulating material with a mineralized porous structure. The material has good heat preservation and heat insulation performance, and is not easy to shrink by heating; the layered double hydroxides are uniformly distributed in the porous structure of the material, so that the flame retardance of the material is effectively improved, and the heat release rate and smoke release amount of the material are reduced; the processing process is short and pollution-free.
Description
Technical Field
The invention relates to a cellulose-based flame-retardant heat-insulating material, in particular to an environment-friendly cellulose-based flame-retardant heat-insulating material and a preparation method thereof, belonging to the technical field of new materials.
Background
The cellulose has excellent performance, wide sources, environmental protection and wide application, and the human living places have no body shadow. However, the fatal defect of inflammability of the cellulose material limits further application of the cellulose material in the fields of heat insulation, environment-friendly flame retardant boards and the like, and the existing cellulose material flame retardant technology has the problems of poor environment friendliness, easiness in generating thick smoke, toxic gas and the like during combustion, flame retardance reduces the strength of the material, and the preparation process is complex, so that environment-friendly flame retardance of the cellulose material is urgently needed.
Layered Double Hydroxides (LDHs) are novel inorganic flame retardants, have the advantages of no toxicity and environmental protection compared with conventional phosphorus-nitrogen flame retardants, and have the characteristics of high flame retardant efficiency, assembled structure and small influence on the mechanical properties of materials compared with the conventional inorganic flame retardants. The novel inorganic flame retardant has a hydrotalcite-like structure, can be assembled in a molecular structure, has structural memory and anion exchangeability, releases gases such as water vapor and the like after being heated, rapidly absorbs environmental heat, and has certain flame retardance under the action of high temperature, wherein the layered double-metal oxide of the spinel structure is formed. After the layered double hydroxide and the cellulose are mixed, an internal structure with the cellulose as a continuous phase and the layered double hydroxide as a dispersed phase is formed, and the purposes of enhancing the mechanical property of the material and simultaneously improving the flame retardant property can be achieved.
Disclosure of Invention
The invention aims to provide an environment-friendly cellulose-based flame-retardant heat-insulating material which is in a three-dimensional porous structure, has good heat-insulating and heat-preserving properties and is not easy to shrink by heating; the layered double hydroxides are uniformly distributed in the porous structure of the material, so that the flame retardance of the material is effectively improved, and the heat release rate and smoke release amount of the material are reduced.
The invention also provides a preparation method of the environment-friendly cellulose-based flame-retardant heat-insulating material, and the method has the advantages of short processing technological process and no pollution.
The technical scheme adopted by the invention for solving the technical problems is as follows:
an environment-friendly cellulose-based flame-retardant heat-insulating material is prepared by taking cellulose and layered double hydroxides as raw materials, dissolving the cellulose by adopting a direct blending method under an alkaline condition at a low temperature of-20 ℃ to-30 ℃, fully stirring at room temperature to form a cellulose solution with uniformly dispersed layered double hydroxides and no agglomeration, crosslinking the obtained solution by using a crosslinking agent, and freeze-drying to obtain the environment-friendly cellulose-based flame-retardant heat-insulating material with a mineralized porous structure;
wherein the cellulose, the layered double hydroxide, the cross-linking agent and the alkaline aqueous solution comprise the following components in percentage by mass:
Cellulose: 3 to 7 percent of the total weight of the steel,
alkaline aqueous solution: 93-97%, wherein the total weight of the cellulose and the alkaline aqueous solution is 100%,
layered double hydroxide: 0.4 to 2 percent of the total weight of the alloy,
n, N-methylenebisacrylamide (crosslinking agent): 0.1 to 0.8 percent.
The invention utilizes the characteristic that the layered double hydroxide can stably exist in the alkali solution, and adopts a direct blending method to add the layered double hydroxide into the regenerated cellulose aerogel to form the mineralized cellulose-based flame-retardant heat-insulating material with a three-dimensional porous structure. Through the phase separation process of a direct blending method and drying, the layered double hydroxide particles are finally and uniformly dispersed in a cellulose cross-linked network structure, and the layered double hydroxide nanoparticles do not have obvious agglomeration phenomenon; cellulose is taken as a continuous phase in the material, and layered double hydroxide is taken as a disperse phase to form the cellulose-based flame-retardant heat-insulating material which is three-dimensional porous and has certain compression strength.
The environment-friendly cellulose-based flame-retardant heat-insulating material is of a three-dimensional porous structure, has good heat-insulating and heat-preserving performance and is not easy to shrink by heating; the layered double hydroxides are uniformly distributed in the porous structure of the material, so that the flame retardance of the material is effectively improved, and the heat release rate and smoke release amount of the material are reduced; the processing process is short and pollution-free.
Preferably, the cellulose is selected from the group consisting of waste paper pulp, vegetation pulp, and waste cotton fabric-derived cellulosic materials.
Preferably, the layered double hydroxide is selected from Ca as the metal ion2+、Mg2+、Al3+And the anion is OH-、NO3 -、CO3 2-、PO4 3-、HPO4 2-、H2PO4 -、B4O7 2-One or more of the two are combined.
Preferably, the crosslinking agent is N, N-methylenebisacrylamide.
Preferably, the aqueous alkaline solution is prepared by mixing 7g of NaOH with 81g of water, and adding 12g of urea after the NaOH is dissolved and the solution is cooled.
The preparation method of the environment-friendly cellulose-based flame-retardant heat-insulating material comprises the following steps:
(1) stirring and mixing raw materials of cellulose and layered double hydroxide under an alkaline condition, fully infiltrating each component, dissolving the cellulose at a low temperature of minus 20 +/-5 ℃ to obtain a mixture, and fully stirring to uniformly disperse the layered double hydroxide in the solution;
(2) adding a cross-linking agent into the mixed solution obtained in the step (1), and uniformly dispersing and dissolving the cross-linking agent through stirring and ultrasonic dispersion for 0.5-2 hours;
(3) pouring the solution obtained in the step (2) in a container, standing for 12-36 h to form gel, then soaking the obtained gel in water, changing the water for several times a day, and soaking until the pH value of the water is less than or equal to 8 to ensure that the alkaline solution in the gel network is completely replaced by the water and form hydrogel;
(4) And (3) after absorbing or airing the surface moisture of the hydrogel obtained in the step (3), freezing the hydrogel for 1-4 hours in an environment below-40 ℃, and then drying the hydrogel in a freeze dryer for more than 48 hours until the hydrogel is completely dried to form a cellulose-based flame-retardant heat-insulating material with a smooth surface and a good structure, wherein the freeze drying temperature is below-40 ℃.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, the layered double hydroxide nanoparticles are used as main flame retardant components, so that the flame retardance of cellulose is effectively improved and the mechanical property of the material is enhanced; the cellulose material has high-efficiency environment-friendly flame retardance and good heat-insulating property;
2. the environment-friendly cellulose-based flame-retardant heat-insulating material is three-dimensional porous, has a heat conductivity coefficient lower than 0.038W/(m.k), and is close to various commercially available polystyrene boards;
3. compared with the conventional blending process, the preparation process of the material has the advantages of short flow, convenient operation and less pollution, the existence of the layered double hydroxide does not influence the characteristics of cellulose, simultaneously effectively improves the flame retardance of the cellulose material, reduces the smoke release rate and the heat release rate in the combustion process of the material, is not easy to shrink by heating, and is suitable for application in the fields of heat preservation and insulation, environment-friendly flame-retardant boards and the like.
Drawings
FIG. 1 is a schematic flow chart of a method for preparing an environment-friendly cellulose-based flame-retardant heat-insulating material according to the present invention.
Detailed Description
The technical solution of the present invention will be further specifically described below by way of specific examples. It is to be understood that the practice of the invention is not limited to the following examples, and that any variations and/or modifications may be made thereto without departing from the scope of the invention.
In the present invention, all parts and percentages are by weight, unless otherwise specified, and the equipment and materials used are commercially available or commonly used in the art. The methods in the following examples are conventional in the art unless otherwise specified.
Layered double hydroxide nanoparticles Mg/Al (OH) -LDHs, Mg/Al (CO)3)-LDHs、Mg/Al(PO4)-LDHs、Mg/Al(HPO4)-LDHs、Mg/Al(H2PO4)-LDHs、Mg/Al(NO3)-LDHs、Mg/Al(B4O7) The preparation method of the LDHs comprises the following steps: preparing LDHs by a coprecipitation method: deionized water which is boiled and then hermetically cooled to 80 ℃ is taken as a solvent, and the molar concentration ratio of M is configured2+:N3+A 2:1 metal ion mixture wherein M2+Represents a divalent metal cation, optionally Mg (NO)3)·6H2O、MgCl2·6H2O、CaCl2·2H2O, etc. as raw materials, N3+Represents a trivalent metal cation, optionally AlCl3·9H2O is taken as a raw material, and the obtained metal ion mixed solution is marked as a solution A; if C is not C (Al) 3+) Respectively preparing NaOH and Na2CO3The solutions are respectively marked as B1 and B2, wherein n is in anionic valence state, such as CO3 2-When n is 2, then Na2CO3In a concentration of aluminum ions1/2 concentration. Under a closed condition, slowly dropwise adding the solution A with the same volume into the solution B at the temperature of 80 ℃, stirring at a high speed while dropwise adding, and when the pH of the system is controlled to be 7-8 by dropwise adding a NaOH solution, obtaining Mg/Al (OH) -LDHs and Mg/Al (NO)3)-LDHs、Ca/Al(OH)-LDHs、Ca/Al(NO3) -LDHs; when the pH of the system is controlled to be 10-11 by dripping NaOH solution, Mg/Al (CO) can be obtained3)-LDHs、Ca/Al(CO3) -LDHs. And after all the reaction liquid is completely dripped, putting the obtained slurry into an oven for crystallization for 0-18 h, then taking out, washing and filtering until the pH value of the filtrate is 7, and drying the obtained powder at 60 ℃.
Preparing LDHs by a roasting and restoring method: Mg/Al (CO) prepared by crystallization for 18h in a coprecipitation method3) LDHs or Ca/Al (CO)3) calcining-LDHs as precursor at 500 deg.C for 5 hr in muffle furnace, taking out, and recording as LDO, and calcining at 65 deg.C according to metal ion salt KH2PO4、K2HPO4Or Na2B4O7·10H2Mixing the LDO with metal salts respectively and reacting in an aqueous solution for 5h, wherein the mass ratio of O to LDO is 1.2:1.0, and the salt solution concentration is C ═ C (Al)3+) And n represents an anionic valence. The product after the reaction is filtered, washed and dried to obtain Mg/Al (PO) 4)-LDHs、Mg/Al(HPO4)-LDHs、Mg/Al(H2PO4)-LDHs、Mg/Al(B4O7)-LDHs、Ca/Al(PO4)-LDHs、Ca/Al(HPO4)-LDHs、Ca/Al(H2PO4)-LDHs、Ca/Al(B4O7)-LDHs。
Example 1:
a preparation method of an environment-friendly cellulose-based flame-retardant heat-insulating material is shown in figure 1 and comprises the following specific steps:
(1) weighing several parts of concentrated cotton pulp containing 3g of cotton, and respectively weighing 0.6g of Mg/Al (OH) -LDHs and Mg/Al (CO)3)-LDHs、Mg/Al(PO4)-LDHs、Mg/Al(HPO4)-LDHs、Mg/Al(H2PO4)-LDHs、Mg/Al(NO3)-LDHs、Mg/Al(B4O7) LDHs and putting into cotton pulp, then gradually adding 7g of NaOH and water, and cooling the solution after the NaOH is dissolvedAdding 12g of urea, finally controlling the concentration of NaOH to be 7 wt%, the concentration of urea to be 12 wt%, the mass of cellulose to be 3 wt% and the total mass of the mixture to be 100.6g, stirring and dissolving, and then freezing for 2h in an environment at the temperature of 20 ℃ below zero.
(2) Taking out the mixture frozen in the step (1) and stirring at 200r/min until the cotton fiber is completely dissolved and the layered double hydroxide is uniformly dispersed to obtain the LDHs/cellulose mixed solution.
(3) Adding 1.6g N, N-methylene bisacrylamide into the solutions obtained in the step (2), stirring at a high speed for 30min, then performing ultrasonic dispersion for 5min, and then continuing stirring at a high speed for 30min until the cross-linking agent is completely dissolved.
(4) Pouring the solution obtained in the step (3) into a container, shaking vigorously to remove air bubbles, and then gelling for 16h to form the LDHs/cellulose gel. Soaking the obtained gel together with a vessel in water, replacing the water for 3 times a day, measuring the pH value of the leaching solution to be 7 after 5 days, taking out the gel, air-drying for 1h, freezing for 3h in a refrigerator at the temperature of-47 ℃, and then freeze-drying for 48h in a freeze-drying machine to obtain the cellulose-based flame-retardant heat-insulating material containing different layered double hydroxides.
The thermal conductivity, Limiting Oxygen Index (LOI), maximum Heat Release Rate (PHRR), and Smoke Release Rate (SRR) of several groups of cellulose flame-retardant and Heat-insulating materials obtained in this example are shown in Table 1. In the table, A to H are respectively pure cellulose material, Mg/Al (OH) -LDHs and Mg/Al (CO) added in sequence3)-LDHs、Mg/Al(PO4)-LDHs、Mg/Al(HPO4)-LDHs、Mg/Al(H2PO4)-LDHs、Mg/Al(NO3)-LDHs、Mg/Al(B4O7) -composite cellulosic material of LDHs. The thickness of the obtained samples is about 12.87 mm.
TABLE 1
The results show that the heat conduction coefficients of the cellulose-based flame-retardant heat-insulating material are not changed greatly and are all at a lower level after the layered double hydroxide is added; the combustion performance of the material is obviously improved, and the smoke release rate is changed with different anions.
Example 2:
a preparation method of an environment-friendly cellulose-based flame-retardant heat-insulating material comprises the following specific steps:
(1) taking five parts of 4g of crushed cotton obtained after treatment of waste cotton fabric, respectively weighing 0.4g, 1.6g and 4.0g of Mg/Al (CO)3) LDHs, mixing the components, adding 96g of alkaline urine solution to completely soak the components, and freezing at-20 ℃ for 1.5 h. Wherein the alkaline urine solution contains 7 wt% of NaOH, 12 wt% of urea and 81 wt% of water respectively.
(2) Taking out the mixture frozen in the step (1) and stirring at high speed until the broken cotton fiber is completely dissolved and the layered double hydroxide is uniformly dispersed to obtain the LDHs/cellulose mixed solution.
(3) Adding 1.2g N, N-methylene bisacrylamide into the solutions obtained in the step (2), stirring at a high speed for 30min, then performing ultrasonic dispersion for 5min, and then continuing stirring at a high speed for 30min until the cross-linking agent is completely dissolved.
(4) Pouring the solution obtained in the step (3) into a container, shaking vigorously to remove air bubbles, and then gelling for 12h to form the LDHs/cellulose gel. Soaking the obtained gel together with a vessel in water, replacing the water for 3 times a day, measuring the pH value of the leaching solution to be 7 after 5 days, taking out the gel, air-drying for 1h, freezing for 3h in a refrigerator at the temperature of-52 ℃, and then freeze-drying for 48h in a freeze-dryer to obtain the cellulose-based flame-retardant heat-insulating material containing different layered double hydroxides.
The porosity, thermal conductivity coefficient, limiting oxygen index and compressive strength of the cellulose-based flame-retardant and heat-insulating material with different addition amounts of the layered double hydroxide obtained in the embodiment are shown in table 2.
TABLE 2
Remarking: a, C, D, E in the table are pure cellulose material, 0.4g/1.6g/4.0g Mg/Al (CO) added3)-LDHs cellulose base flame-retardant heat-insulating material. The thickness of the obtained samples is about 12.87 mm.
The results show that as the content of layered double hydroxide increases, the thermal conductivity of the material increases, but still at a lower level; when the addition amount of the layered metal hydroxide is 40%, the LOI value of the material is higher than 27%; at the same time, the compressive strength of the material also increases significantly with increasing content of the layered double hydroxide.
Example 3:
a preparation method of an environment-friendly cellulose-based flame-retardant heat-insulating material comprises the following specific steps:
(1) taking a plurality of parts of crushed cotton containing about 7g of cellulose, 93g of alkaline urine solution and layered double hydroxides, stirring to soak the components, and freezing for 3 hours in an environment at the temperature of-20 ℃, wherein the content of the layered double hydroxides is respectively as follows:
A:0g
B:Ca/Al(CO3)-LDHs 1.2g
C:Mg/Al(CO3)-LDHs 1.2g
D:Mg/Al(H2PO4)-LDHs 1.2g
E:Ca/Al(CO3)-LDHs 0.6g，Mg/Al(CO3)-LDHs 0.6g
F:Mg/Al(H2PO4)-LDHs 0.6g，Mg/Al(CO3)-LDHs 0.6g
G:Ca/Al(CO3)-LDHs 0.6g，Mg/Al(H2PO4) -LDHs 0.6 g; wherein the alkaline urine solution contains 7 wt% of NaOH, 12 wt% of urea and 81 wt% of water respectively.
(2) Taking out the mixture frozen in the step (1) and stirring at high speed until the broken cotton fiber is completely dissolved and the layered double hydroxide is uniformly dispersed to obtain the LDHs/cellulose mixed solution.
(3) Adding 0.8g N, N-methylene bisacrylamide into the solutions obtained in the step (2), stirring at a high speed for 30min, then performing ultrasonic dispersion for 5min, and then continuing stirring at a high speed for 30min until the crosslinking agent is completely dissolved.
(4) Pouring the solution obtained in the step (3) into a container, shaking vigorously to remove air bubbles, and then gelling for 16h to form the LDHs/cellulose gel. Soaking the obtained gel together with a vessel in water, replacing the water for 3 times a day, measuring the pH value of the leaching solution to be 7 after 5 days, taking out the gel, air-drying for 1h, freezing for 3h in a refrigerator at the temperature of 56 ℃ below zero, and then freeze-drying for 60h in a freeze-drying machine to obtain the layered double hydroxide/cellulose flame-retardant heat-insulating material with different layered double hydroxide combinations.
The results of limiting oxygen index, maximum heat release rate and smoke release rate of the composite cellulose flame-retardant and heat-insulating material added with different combinations of layered double hydroxides obtained in this example are shown in table 3.
TABLE 3
The results show that the cellulose composite materials compounded by different combinations of layered double hydroxides have small difference of limiting oxygen indexes, but the maximum heat release rate and the smoke release rate of the cellulose composite materials are changed to a certain extent by anion change.
The above-described embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention in any way, and other variations and modifications may be made without departing from the spirit of the invention as set forth in the claims.
Claims (2)
1. An environment-friendly cellulose-based flame-retardant heat-insulating material is characterized in that: the environment-friendly cellulose-based flame-retardant heat-insulating material is prepared by taking cellulose and layered double hydroxides as raw materials, dissolving the cellulose by adopting a direct blending method under an alkaline condition at the temperature of-20 ℃, fully stirring at room temperature to form a cellulose solution with uniformly dispersed layered double hydroxides and no agglomeration, crosslinking the obtained solution by using a crosslinking agent, and freeze-drying to obtain the environment-friendly cellulose-based flame-retardant heat-insulating material with a mineralized porous structure;
Wherein the cellulose, the layered double hydroxide, the cross-linking agent and the alkaline aqueous solution comprise the following components in percentage by mass:
cellulose: 3 to 7 percent of the total weight of the steel,
alkaline aqueous solution: 93-97%, wherein the total weight of the cellulose and the alkaline aqueous solution is 100%,
layered double hydroxide: 0.4 to 2 percent of the total weight of the alloy,
crosslinking agent N, N-methylenebisacrylamide: 0.8-1.6%;
the layered double hydroxide is selected from Mg/Al (PO)4)-LDHs、Mg/Al(HPO4)-LDHs、Mg/Al(H2PO4)-LDHs、Ca/Al(PO4)-LDHs、Ca/Al(HPO4)-LDHs、Ca/Al(H2PO4) -one or more of LDHs; the layered double hydroxide is prepared by the following two methods:
preparing LDHs by a coprecipitation method: deionized water which is boiled and then hermetically cooled to 80 ℃ is taken as a solvent, and the molar concentration ratio of M is configured2+:N3+Metal ion mixed solution of =2:1, wherein M2+Represents a divalent metal cation, N3+Representing trivalent metal cations, and marking the obtained metal ion mixed solution as solution A; further, according to C = C (Al)3+) Respectively preparing NaOH and Na2CO3The solutions are marked as B1 and B2 respectively, wherein n is an anionic valence state; under a closed condition, slowly dropwise adding the solution A with the same volume into the solution B at the temperature of 80 ℃, and stirring while dropwise adding; when the pH of the system is controlled to be 10-11 by dripping NaOH solution, Mg/Al (CO) is obtained3)-LDHs、Ca/Al(CO3) -LDHs; after all the reaction liquid is completely dripped, putting the obtained slurry into an oven for crystallization for 0-18 h, then taking out, washing and filtering until the pH of the filtrate is =7, and drying the obtained powder at 60 ℃;
Preparing LDHs by a roasting and restoring method: Mg/Al (CO) prepared by crystallization for 18 h in a coprecipitation method3) LDHs or Ca/Al (CO)3) calcining-LDHs as precursor at 500 deg.C for 5 hr in muffle furnace, taking out, and recording as LDO, and calcining at 65 deg.C according to metal ion salt KH2PO4Or K2HPO4Mixing the obtained product with LDO at a mass ratio of 1.2:1.0, and reacting in water solution for 5 h, wherein the salt solution concentration is C = C (Al)3+) N represents an anionic valence; the product after the reaction is filtered, washed and dried to obtain Mg/Al (PO)4)-LDHs、Mg/Al(HPO4)-LDHs、Mg/Al(H2PO4)-LDHs、Ca/Al(PO4)-LDHs、Ca/Al(HPO4)-LDHs、Ca/Al(H2PO4)-LDHs；
The cellulose is selected from cellulose materials derived from waste paper pulp, vegetation pulp or waste cotton fabric; the preparation method of the alkaline aqueous solution is that 7 g of NaOH and 81g of water are mixed, and 12 g of urea is added after the NaOH is dissolved and the solution is cooled;
the preparation method of the environment-friendly cellulose-based flame-retardant heat-insulating material comprises the following steps:
(1) stirring and mixing raw material cellulose and layered double hydroxide under an alkaline condition, fully soaking all components, dissolving cellulose at the temperature of-20 ℃ to obtain a mixture, and fully stirring to uniformly disperse the layered double hydroxide in the solution;
(2) adding a cross-linking agent into the mixed solution obtained in the step (1), and uniformly dispersing and dissolving the cross-linking agent through stirring and ultrasonic dispersion for 0.5-2 hours;
(3) Pouring the solution obtained in the step (2) in a container, standing for 12-36 h to form gel, then soaking the obtained gel in water, changing the water for several times a day, and soaking until the pH value is less than or equal to 8 to ensure that the alkaline solution in the gel network is completely replaced by the water and form hydrogel;
(4) and (3) after absorbing or airing the surface moisture of the hydrogel obtained in the step (3), freezing the hydrogel for 1-4 hours in an environment below-40 ℃, and then drying the hydrogel in a freeze dryer for more than 48 hours until the hydrogel is completely dried to form a cellulose-based flame-retardant heat-insulating material with a smooth surface and a good structure, wherein the freeze drying temperature is below-40 ℃.
2. The method for preparing the environment-friendly cellulose-based flame-retardant and heat-insulating material according to claim 1, which is characterized by comprising the following steps:
(1) stirring and mixing raw material cellulose and layered double hydroxide under an alkaline condition, fully soaking all components, dissolving cellulose at the temperature of-20 ℃ to obtain a mixture, and fully stirring to uniformly disperse the layered double hydroxide in the solution;
(2) adding a cross-linking agent into the mixed solution obtained in the step (1), and uniformly dispersing and dissolving the cross-linking agent through stirring and ultrasonic dispersion for 0.5-2 hours;
(3) pouring the solution obtained in the step (2) in a container, standing for 12-36 h to form gel, then soaking the obtained gel in water, changing the water for several times a day, and soaking until the pH value is less than or equal to 8 to ensure that the alkaline solution in the gel network is completely replaced by the water and form hydrogel;
(4) And (3) after absorbing or airing the surface moisture of the hydrogel obtained in the step (3), freezing the hydrogel for 1-4 hours in an environment below-40 ℃, and then drying the hydrogel in a freeze dryer for more than 48 hours until the hydrogel is completely dried to form a cellulose-based flame-retardant heat-insulating material with a smooth surface and a good structure, wherein the freeze drying temperature is below-40 ℃.
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