CN113234256B - Preparation method of double-crosslinking flame-retardant composite aerogel - Google Patents
Preparation method of double-crosslinking flame-retardant composite aerogel Download PDFInfo
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Abstract
The invention discloses a preparation method of a double-crosslinking flame-retardant composite aerogel, which comprises the following steps: 1) amino protonation treatment of chitosan: placing chitosan in an acid solution to obtain a chitosan solution with amino groups on a molecular chain protonated; 2) preparing the composite aerogel: dispersing nano montmorillonite into mixed suspension of nano cellulose and chitosan, adding a cross-linking agent, stirring to obtain mixed solution, pouring the mixed solution into a mould, freezing, and performing cross-linking reaction to obtain composite aerogel; 3) a double cross-linking step: and (3) soaking the obtained composite gel in a mixed solution of a polyphosphate solution and a transition metal chloride solution for treatment, and freeze-drying to obtain the double-crosslinking flame-retardant composite aerogel. The composite aerogel material obtained by the invention has excellent flame retardant property, mechanical property and smoke suppression property; the method has the advantages of low raw material source, low production cost and wide application.
Description
Technical Field
The invention belongs to the field of flame-retardant composite materials, and particularly relates to a method for preparing a double-crosslinking flame-retardant composite material by crosslinking nanocellulose with a crosslinking agent and combining a modified flame retardant, and a method for preparing a novel flame retardant by double crosslinking.
Background
With the development of social economy, the composite material is widely applied to various fields such as national defense, aviation and the like. However, most of composite materials are flammable materials, and the combustion process not only pollutes the environment, but also threatens the life safety of people, thereby causing huge loss. Therefore, the demand for flame-retardant composite materials is an important part of the market material demand in the foreseeable future.
Aerogel is currently one of the lightest solid materials in the world, and has a porosity of over 90 percent and a density as low as 0.001g/cm3. The aerogel has great application potential on heat insulation materials due to the low heat conductivity coefficient. Wood is used as a green and environment-friendly biomass material, and the nano-cellulose suspension obtained from the wood can be converted into aerogel in a certain mode. The nano-cellulose aerogel material also has the unique properties of high flexibility, degradability, biocompatibility and the like. However, natural nanocellulose is very easy to absorb moisture in the environment, and the overall mechanical strength is low.
The chitosan is a natural, easily-obtained, low-cost and biodegradable polysaccharide polymer. During the thermal decomposition of chitosan, the polymer carbonization can hinder the combustion, and CO can be released2、NH3And N2And the like, so that the flame retardant function is achieved. The chitosan also contains environment-friendly multifunctional organic pollutant and heavy metal ion adsorbent. In papers published in engineering plastics application 2017, volume 45, No. 7, pages 119-123, by white and the like, ammonium polyphosphate and chitosan are added into polypropylene through melt blending, so that the limiting oxygen index of the composite material is improved, and the total smoke release amount, CO and CO are increased2The discharge amount is obviously reduced. However, the use of chitosan as a monomeric flame retardant is somewhat limited.
Montmorillonite is a layered silicate clay with certain expansibility. The nano montmorillonite is mainly used for compounding the existing polymer, and can play a role in enhancing the mechanical property, heat resistance, wear resistance, flame retardance and gas barrier property of the polymer material by only adding a small amount of nano montmorillonite. In the paper published by chenhaibo et al in Polymer 2012, volume 53, pages 5825-5831, an ammonium alginate/montmorillonite aerogel composite material obtained by adding montmorillonite to ammonium alginate shows very excellent flame retardancy.
In the papers published by PARK et al in Colloid & Polymer Science 2009, volume 287, No. 8, pages 943-950, chitosan and montmorillonite modified polyvinyl alcohol are used for electrostatic spinning, so that the tensile strength and thermal stability of the polyvinyl alcohol nanofiber are improved.
Chenshilin and the like in Chinese patent application 201611166003.8 disclose a flame-retardant elastic nano-cellulose aerogel and a preparation method thereof, wherein the aerogel with good flame-retardant, heat-insulating and resilience properties is prepared by using a biomass raw material of cellulose and adopting a flame-retardant system containing a reactive organic compound and polycarboxylic acid.
Malong et al in Chinese patent application 201910394173.9 disclose a method for preparing a flame-retardant heat-insulating cellulose-based aerogel, which comprises mixing a cellulose nanofiber solution and a melamine prepolymer solution, freeze-drying, and cross-linking to obtain the aerogel with good flame-retardant and heat-insulating properties. Shandongdian and the like in Chinese patent application 201810247231.0 disclose a flame-retardant microcrystalline cellulose/hydroxyapatite composite aerogel and a preparation method thereof, hydroxyapatite dispersion liquid is prepared by a hydrothermal method, epichlorohydrin is adopted to crosslink microcrystalline cellulose, and finally the aerogel with good flame-retardant and smoke-suppression effects is prepared by a solution blending method and freeze drying.
Lihongyan et al in Chinese patent application 201810006071.0 disclose a flame-retardant carbon nanotube-montmorillonite composite aerogel material and a preparation method thereof, wherein the flame-retardant carbon nanotube-montmorillonite composite aerogel material is prepared by mixing a carbon nanotube hexabromocyclododecane-loaded wet gel and a montmorillonite wet gel with a bisphenol double solution. The hollow fiber with a microporous structure is adopted as a raw material, a three-dimensional aerogel network is built, hexabromocyclododecane and bisphenol are loaded respectively by utilizing the mesoporous structure of aerogel and the microporous structure of fiber, and flame retardants with different characteristics are combined to realize a synergistic flame-retardant effect.
The flame retardant modifier and the technology can improve the flame retardant property of the composite material, but how to coordinate the contradiction between the flame retardant property and the mechanical property and the smoke suppression property is solved, so that the flame retardant property of the composite material is improved, and the mechanical property and the smoke suppression property of the material are improved. The cellulose/chitosan/montmorillonite system improves the mechanical property of the aerogel by using a double-crosslinking method, and the chitosan can improve the smoke suppression property, adsorb organic pollutants and heavy metal ions, improve the flame retardance and improve the mechanical property and the smoke suppression property.
Disclosure of Invention
The invention provides a preparation method of a double-crosslinking flame-retardant nano-cellulose/chitosan/montmorillonite composite aerogel, which comprises crosslinking nano-cellulose by a crosslinking agent, crosslinking chitosan by sodium tripolyphosphate to form aerogel, and adsorbing metal ions on the chitosan to prepare a novel flame-retardant material with excellent flame-retardant property and mechanical property.
In order to achieve the above technical effects, the present invention is implemented by the following technical means.
A preparation method of the double-crosslinking flame-retardant composite aerogel comprises the following steps:
1) amino protonation treatment of chitosan:
placing chitosan in an acid solution to obtain a chitosan solution with amino groups on a molecular chain protonated;
2) preparing the composite aerogel:
dispersing nano montmorillonite into mixed suspension of nano cellulose and chitosan, adding a cross-linking agent, stirring to obtain mixed solution, pouring the mixed solution into a mould, freezing, and performing cross-linking reaction to obtain composite aerogel;
3) a double cross-linking step:
and (3) soaking the obtained composite gel in a mixed solution of a polyphosphate solution and a transition metal chloride solution for treatment, converting macromolecules in the composite aerogel into a three-dimensional network structure, crosslinking the composite aerogel with the polyphosphate, and freeze-drying to obtain the double-crosslinking flame-retardant composite aerogel.
As a further improvement of the present invention, the amino protonation treatment of the chitosan in step 1) is specifically:
50mg-1000mg of chitosan is put into 50ml of acetic acid solution with the mass fraction of 0.1-3%, and the mixture is stirred at high speed to be completely dissolved, so that the chitosan solution with the protonized amino groups on the molecular chain is obtained.
As a further improvement of the present invention, after the amino protonation treatment of the chitosan in step 1), and before the preparation of the composite aerogel in step 2), a preparation of a mixed suspension of nanocellulose and chitosan is further included, specifically: respectively preparing nano-cellulose and chitosan with the mass ratio of 1: 1-1: 3 to obtain a nano-cellulose suspension and the chitosan solution, and mixing the nano-cellulose and the chitosan solution to obtain a nano-cellulose and chitosan mixed suspension.
As a further improvement of the invention, in the preparation of the composite aerogel in the step 2), the addition amount of the cross-linking agent accounts for 5-20% of the total mass of the nano-cellulose, the chitosan and the nano-montmorillonite.
As a further improvement of the invention, in the preparation of the composite aerogel in the step 2), the stirring speed of the mixture after the cross-linking agent is added is 1000-6000 rpm.
As a further improvement of the present invention, in the step 2) of preparing the composite aerogel, the step of pouring the mixed solution into a mold and freezing the mixed solution comprises: freezing the mixed solution at-5 to-50 ℃ for 0.2 to 72 hours, and then freezing and drying for 12 to 72 hours to obtain the composite aerogel.
As a further improvement of the present invention, in the step 2) of preparing the composite aerogel, the crosslinking reaction specifically comprises: the frozen mixture is processed at 50-200 deg.C for 5-100min to realize crosslinking reaction.
As a further improvement of the present invention, in the step 2) of preparing the composite aerogel, and in the step 2) of preparing the composite aerogel, the nanocellulose at least includes one of wood nanocellulose, cotton nanocellulose, flax nanocellulose, algae nanocellulose, bacteria nanocellulose and animal nanocellulose.
As a further improvement of the present invention, in the step 2) of preparing the composite aerogel, the nano montmorillonite is at least one of calcium-based nano montmorillonite, sodium-calcium-based nano montmorillonite, magnesium-based nano montmorillonite and H-nano montmorillonite.
As a further improvement of the present invention, in the step 2) of preparing the composite aerogel, the crosslinking agent is at least one of citric acid, 1,2,3, 4-butanetetracarboxylic acid, polyvinyl alcohol, ammonium zirconium carbonate, 2D resin, and water-soluble hydroxy acrylate resin.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, chitosan and nanocellulose are used to form the intumescent flame retardant aerogel, montmorillonite is used as a flame retardant synergist to modify the aerogel, finally, metal ions are adsorbed to the chitosan, nitrogen and phosphorus are used for synergetic flame retardant, and the metal ions catalyze the montmorillonite to form carbon, so that the composite material with good flame retardant property and low smoke is formed. The phosphorus content in the carbon layer formed after combustion is higher, the surface of the carbon layer is more compact and flat, a stable expanded carbon layer with higher quality is formed, and the flame retardant property of the expanded flame retardant system is further improved. Meanwhile, the crosslinking agent is used for crosslinking the nano-cellulose, and the sodium tripolyphosphate is used for crosslinking the chitosan, so that the mechanical property is good. In addition, natural degradable high-molecular nano-cellulose and chitosan are fully utilized, and the chitosan also contains environment-friendly multifunctional organic pollutants and heavy metal ion adsorbents, so that the flame retardant is more green and environment-friendly.
Detailed Description
In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further explained below. The description is illustrative of the invention and is not to be construed as limiting.
A preparation method of a double-crosslinking flame-retardant composite aerogel comprises the following steps:
(1) preparation of nanocellulose suspensions and chitosan solutions
50mg-1000mg of nano-Cellulose (CNF) is placed in 50ml of deionized water and stirred at high speed to obtain nano-cellulose suspension. Placing 50mg-1000mg Chitosan (CS) in 50ml 0.1-3wt% acetic acid solution, stirring at high speed to dissolve completely to obtain chitosan solution. Preparing a mixed solution of the two solutions according to a certain proportion.
(2) Preparation of nano-cellulose/chitosan/montmorillonite composite aerogel
Dispersing 50mg-1000mg of nano montmorillonite (MMT) which is fully and mechanically stripped and dispersed into the mixed suspension of nano cellulose and chitosan according to a certain proportion, adding a cross-linking agent (relative to the mass fraction of nano cellulose/chitosan/montmorillonite) with the mass fraction of 5% -20%, and stirring at a high speed of 1000-6000 rpm until a homogeneous solution is obtained again. Pouring the mixed solution into a mold, freezing for 0.2-72h in a refrigerator, and freeze-drying for 2-96h to obtain the CNF/CS/MMT composite aerogel. And (3) treating the CNF/CS/MMT composite aerogel at 50-200 ℃ for 5-100min to realize a crosslinking reaction.
(3) Impregnation treatment
The obtained CNF/CS/MMT composite aerogel is soaked in a mixed solution of 0.1-20wt% of sodium Tripolyphosphate (TPP) and 0.1-3wt% of transition metal chloride solution (pH = 1-6.5 is adjusted by 0.01M HCl), and the CNF/CS/MMT composite aerogel is washed by deionized water for several times after being treated for 0.2-48 h. And (4) performing freeze drying treatment to obtain the double-crosslinking flame-retardant CNF/CS/MMT composite aerogel.
In the present invention, the crosslinking agent functions to convert linear or slightly branched macromolecules into a three-dimensional network structure to improve strength, heat resistance, abrasion resistance and solvent resistance. And then under the effect of angle connection, the composite gel can be converted into a three-dimensional network structure, so that the composite gel is convenient to crosslink with polyphosphate.
In the present invention, nanocellulose is used as the matrix of the whole aerogel; the function of chitosan is flame retardation; the Monte clay has the functions of enhancing the mechanical property, heat resistance, wear resistance, flame retardance and gas barrier property of the polymer material.
In the invention, the aerogel prepared from the nano-cellulose has high flexibility, degradability and biocompatibility. In the present invention, the nanocellulose includes, but is not limited to, wood nanocellulose, cotton nanocellulose, flax nanocellulose, algae nanocellulose, bacteria nanocellulose, and animal nanocellulose. When the nano-cellulose is in a plurality of types, the plurality of types are mixed in a ratio of 1:1, and the formed fiber network has better interweaving effect and is more stable.
According to the invention, in the mixed solution, the mass ratio of the nano-cellulose to the chitosan is 1: 1-1: 3, so that the aerogel with high flexibility and excellent flame retardance can be obtained at the same time.
In the present invention, the crosslinking agent is at least one of citric acid, 1,2,3, 4-butanetetracarboxylic acid, polyvinyl alcohol, ammonium zirconium carbonate, 2D resin, and water-soluble hydroxy acrylate resin. When multiple are used, the ratio between the crosslinking agents is 1:1, the crosslinking effect is better; these cross-linking agents allow the aerogels to form a better three-dimensional network structure to improve strength, heat resistance, abrasion resistance and solvent resistance.
In the invention, the nano montmorillonite is at least one of calcium-based nano montmorillonite, sodium-calcium-based nano montmorillonite, magnesium-based nano montmorillonite and H-nano montmorillonite; the nano montmorillonite can be used for preparing materials with good mechanical property, heat resistance, wear resistance, flame retardance and gas barrier property. When the nano montmorillonite has a plurality of kinds, the nano montmorillonite is mixed according to the proportion of 1:1, and the mechanical property is good.
In the present invention, the transition metal ion in the transition metal chloride is at least Fe3+、Co2+、Ni2+、Mn2+、Cr3+、Cu2 +Or Zn2+One kind of (1). The addition of these transition metal ions can improve the smoke suppression properties of the aerogel. When the transition metal ions are various, the ratio is 1:1, and the smoke suppression performance is good.
Example 1:
(1) preparation of nanocellulose suspensions and chitosan solutions
500mg of nanocellulose (CNF) was placed in 50ml of deionized water and stirred at high speed to obtain a nanocellulose suspension. 300mg of Chitosan (CS) was put in 50ml of 0.7wt% acetic acid solution, and stirred at high speed to be completely dissolved, to obtain a chitosan solution. The mixed solution of the two solutions was prepared in a ratio of 1: 1.
(2) Preparation of nano-cellulose/chitosan/montmorillonite composite aerogel
Dispersing 300mg of sodium-based nano montmorillonite (MMT) which is fully and mechanically peeled and dispersed into the mixed suspension of the nano cellulose and the chitosan according to the proportion of 1:1, adding 10wt% of citric acid (relative to the mass fraction of the nano cellulose/the chitosan/the montmorillonite), and stirring at high speed of 2000 rpm until a homogeneous solution is obtained again. Pouring the mixed solution into a mold, freezing for 6h in a refrigerator, and freeze-drying for 15h to obtain the CNF/CS/MMT composite aerogel. And (3) treating the CNF/CS/MMT composite aerogel at 80 ℃ for 15min to realize a crosslinking reaction.
(3) Impregnation treatment
The resulting CNF/CS/MMT composite aerogel was immersed in a mixed solution of 0.7wt% sodium Tripolyphosphate (TPP) and 0.7wt% ferric chloride solution (0.01M HCl adjusted PH = 5), treated for 3 h, and washed with deionized water several times. And (4) performing freeze drying treatment to obtain the double-crosslinking flame-retardant CNF/CS/MMT composite aerogel.
The performance of the composite material obtained by the preparation method of the double-crosslinking flame-retardant nano-cellulose/chitosan/montmorillonite composite aerogel in example 1 is shown in table 1.
Example 2:
(1) preparation of nanocellulose suspensions and chitosan solutions
500mg of nanocellulose (CNF) was placed in 50ml of deionized water and stirred at high speed to obtain a nanocellulose suspension. 400mg of Chitosan (CS) was put in 50ml of 0.8wt% acetic acid solution, and stirred at high speed to be completely dissolved, thereby obtaining a chitosan solution. The mixed solution of the two solutions was prepared in a ratio of 1: 1.
(2) Preparation of nano-cellulose/chitosan/montmorillonite composite aerogel
Dispersing 400mg of sodium-based nano montmorillonite (MMT) which is fully and mechanically peeled and dispersed into the mixed suspension of the nano cellulose and the chitosan according to the proportion of 1:1, adding 15wt% of citric acid (relative to the mass fraction of the nano cellulose/the chitosan/the montmorillonite), and stirring at a high speed of 2000 rpm until a homogeneous solution is obtained again. Pouring the mixed solution into a mold, freezing for 9h in a refrigerator, and freeze-drying for 20h to obtain the CNF/CS/MMT composite aerogel. And (3) treating the CNF/CS/MMT composite aerogel at 100 ℃ for 20min to realize a crosslinking reaction.
(3) Impregnation treatment
The resulting CNF/CS/MMT composite aerogel was immersed in a mixed solution of 0.8wt% sodium Tripolyphosphate (TPP) and 0.8wt% ferric chloride solution (0.01M HCl adjusted PH = 5), treated for 6h, and washed with deionized water several times. And (4) performing freeze drying treatment to obtain the double-crosslinking flame-retardant CNF/CS/MMT composite aerogel.
The performance of the composite material obtained by testing the preparation method of the double-crosslinking flame-retardant nano-cellulose/chitosan/montmorillonite composite aerogel in the embodiment 2 is shown in table 1.
Example 3:
(1) preparation of nanocellulose suspensions and chitosan solutions
500mg of nanocellulose (CNF) was placed in 50ml of deionized water and stirred at high speed to obtain a nanocellulose suspension. 500mg of Chitosan (CS) was put in 50ml of 0.9wt% acetic acid solution, and stirred at high speed to be completely dissolved, to obtain a chitosan solution. The mixed solution of the two solutions was prepared in a ratio of 1: 1.
(2) Preparation of nano-cellulose/chitosan/montmorillonite composite aerogel
Dispersing 500mg of sodium-based nano montmorillonite (MMT) which is fully and mechanically peeled and dispersed into the mixed suspension of the nano cellulose and the chitosan according to the proportion of 1:1, adding 20wt% of citric acid (relative to the mass fraction of the nano cellulose/the chitosan/the montmorillonite), and stirring at a high speed of 3000 rpm until a homogeneous solution is obtained again. Pouring the mixed solution into a mold, freezing for 12h in a refrigerator, and freeze-drying for 25h to obtain the CNF/CS/MMT composite aerogel. And (3) treating the CNF/CS/MMT composite aerogel at 120 ℃ for 25min to realize a crosslinking reaction.
(3) Impregnation treatment
The resulting CNF/CS/MMT composite aerogel was immersed in a mixed solution of 0.9wt% sodium Tripolyphosphate (TPP) and 0.9wt% copper chloride solution (0.01M HCl adjusted PH = 5.5), treated for 9h, and then rinsed several times with deionized water. And (4) performing freeze drying treatment to obtain the double-crosslinking flame-retardant CNF/CS/MMT composite aerogel.
The performance of the composite material obtained by testing the preparation method of the double-crosslinking flame-retardant nano-cellulose/chitosan/montmorillonite composite aerogel in the embodiment 3 is shown in table 1.
Example 4:
(1) preparation of nanocellulose suspensions and chitosan solutions
500mg of nanocellulose (CNF) was placed in 50ml of deionized water and stirred at high speed to obtain a nanocellulose suspension. 600mg of Chitosan (CS) was put in 50ml of a 1.0wt% acetic acid solution, and stirred at a high speed to be completely dissolved, to obtain a chitosan solution. The mixed solution of the two solutions was prepared in a ratio of 1: 1.
(2) Preparation of nano-cellulose/chitosan/montmorillonite composite aerogel
600mg of sodium-based nano montmorillonite (MMT) which is fully and mechanically peeled and dispersed is dispersed into the mixed suspension of the nano cellulose and the chitosan according to the proportion of 1:1, 25wt% of 1,2,3, 4-butanetetracarboxylic acid (relative to the mass fraction of the nano cellulose/the chitosan/the montmorillonite) is added, and the mixture is stirred at a high speed of 3000 rpm until homogeneous solution is obtained again. Pouring the mixed solution into a mold, freezing for 15h in a refrigerator, and freeze-drying for 30h to obtain the CNF/CS/MMT composite aerogel. And (3) treating the CNF/CS/MMT composite aerogel at 140 ℃ for 30min to realize a crosslinking reaction.
(3) Impregnation treatment
The resulting CNF/CS/MMT composite aerogel was immersed in a mixed solution of 1.0wt% sodium Tripolyphosphate (TPP) and 1.0wt% copper chloride solution (0.01M HCl adjusted PH = 5.5), treated for 12h, and then rinsed several times with deionized water. And (4) performing freeze drying treatment to obtain the double-crosslinking flame-retardant CNF/CS/MMT composite aerogel.
The performance of the composite material obtained by testing the preparation method of the double-crosslinking flame-retardant nano-cellulose/chitosan/montmorillonite composite aerogel in example 4 is shown in table 1.
Example 5:
(1) preparation of nanocellulose suspensions and chitosan solutions
500mg of nanocellulose (CNF) was placed in 50ml of deionized water and stirred at high speed to obtain a nanocellulose suspension. 700mg of Chitosan (CS) was put in 50ml of a 1.1wt% acetic acid solution, and stirred at a high speed to be completely dissolved, thereby obtaining a chitosan solution. The mixed solution of the two solutions was prepared in a ratio of 1: 1.
(2) Preparation of nano-cellulose/chitosan/montmorillonite composite aerogel
Dispersing 700mg of sodium-based nano montmorillonite (MMT) which is fully and mechanically stripped and dispersed into the mixed suspension of the nano cellulose and the chitosan according to the proportion of 1:1, adding 30wt% of 1,2,3, 4-butanetetracarboxylic acid (relative to the mass fraction of the nano cellulose/the chitosan/the montmorillonite), and stirring at a high speed of 4000 rpm until a homogeneous solution is obtained again. Pouring the mixed solution into a mold, freezing for 18h in a refrigerator, and freeze-drying for 35h to obtain the CNF/CS/MMT composite aerogel. And (3) treating the CNF/CS/MMT composite aerogel at 160 ℃ for 35min to realize a crosslinking reaction.
(3) Impregnation treatment
The resulting CNF/CS/MMT composite aerogel was immersed in a mixed solution of 1.1wt% sodium Tripolyphosphate (TPP) and 1.1wt% zinc chloride solution (0.01M HCl adjusted PH = 6), treated for 15h, and then rinsed several times with deionized water. And (4) performing freeze drying treatment to obtain the double-crosslinking flame-retardant CNF/CS/MMT composite aerogel.
The performance of the composite material obtained by testing the preparation method of the double-crosslinking flame-retardant nano-cellulose/chitosan/montmorillonite composite aerogel in example 5 is shown in table 1.
Example 6:
(1) preparation of nanocellulose suspensions and chitosan solutions
500mg of nanocellulose (CNF) was placed in 50ml of deionized water and stirred at high speed to obtain a nanocellulose suspension. 800mg of Chitosan (CS) was put into 50ml of a 1.2wt% acetic acid solution, and stirred at a high speed to be completely dissolved, thereby obtaining a chitosan solution. The mixed solution of the two solutions was prepared in a ratio of 1: 1.
(2) Preparation of nano-cellulose/chitosan/montmorillonite composite aerogel
Dispersing 800mg of sodium-based nano montmorillonite (MMT) which is fully and mechanically stripped and dispersed into the mixed suspension of the nano cellulose and the chitosan according to the proportion of 1:1, adding 35wt% of 1,2,3, 4-butanetetracarboxylic acid (relative to the mass fraction of the nano cellulose/the chitosan/the montmorillonite), and stirring at a high speed of 4000 rpm until a homogeneous solution is obtained again. Pouring the mixed solution into a mold, freezing for 21h in a refrigerator, and freeze-drying for 40h to obtain the CNF/CS/MMT composite aerogel. And (3) treating the CNF/CS/MMT composite aerogel at 180 ℃ for 40min to realize a crosslinking reaction.
(3) Impregnation treatment
The resulting CNF/CS/MMT composite aerogel was immersed in a mixed solution of 1.2wt% sodium Tripolyphosphate (TPP) and 1.2wt% zinc chloride solution (0.01M HCl adjusted PH = 6), treated for 18h, and rinsed several times with deionized water. And (4) performing freeze drying treatment to obtain the double-crosslinking flame-retardant CNF/CS/MMT composite aerogel.
The performance of the composite material obtained by testing the preparation method of the double-crosslinking flame-retardant nano-cellulose/chitosan/montmorillonite composite aerogel in the embodiment 6 is shown in table 1.
In the above embodiment, the acetic acid solution with the selected concentration has a high chitosan solubility, the cross-linking agent with the selected concentration forms a stable three-dimensional network structure, the homogeneous solution obtained at the selected stirring speed is stable, the cross-linking reaction effect at the selected cross-linking temperature is good, and the transition ion adsorption effect of the mixed solution of the sodium Tripolyphosphate (TPP) and the metal ion solution with the selected concentration on the chitosan is good.
Comparative example 1
Comparative example 1 was from doctor's academic paper published in 2018 by Guolimin et al, China forestry science research institute.
In the comparative example, a chemical crosslinking type CNF flame retardant aerogel with high flexibility was successfully prepared by combining vacuum freeze drying with a high temperature post-treatment method, using the characteristic that butanetetracarboxylic acid (BTCA) can chemically react with active hydroxyl groups on the CNF surface and N-hydroxymethyl dimethyl phosphoacrylamide (MDPA) molecules. The results show that: the BTCA/MDPA enables the aerogel to keep low density (8.98-12.35 Kg/m 3), and the high flexibility of the CNF aerogel can be kept while the compression strength, the rebound performance and the flame retardant performance of the CNF aerogel are improved by regulating and controlling the proportion among the BTCA, the MDPA and the CNF. In addition, when m (CNF)/m (BTCA)/M (MDPA) is 10/1/4, the LOI value reaches 26.1%, the mass residual rate (600 ℃) reaches 35.56 wt%, and the Heat Release Rate (HRR), the total heat release amount (THR) and the maximum heat release rate (PHRR) are respectively reduced by 62.5%, 63% and 61% compared with the pure CNF aerogel.
Comparative example 2
Comparative example 2 is from the paper published by Dang Yang et al in the journal of textile, 2020, Vol 41, No. 2.
In comparative example 2, the flame-retardant and heat-insulating CNF/MMT composite aerogel is prepared mainly by blending modified Cellulose Nanofibers (CNF) with nano montmorillonite (MMT) based on a freeze-drying method. Research results show that the introduction of MMT enables the aerogel to have a more compact lamellar structure, and the mechanical property, the thermal stability and the flame retardant property of the aerogel are improved. At an MMT mass fraction of 50%, the CNF/MMT composite aerogel has an apparent density of only 0.0168 g/cm3 at most and a stress of 77.93 kPa at most when the strain is 70%, and when the MMT mass fraction in the aerogel is not less than 42.9%, the limit oxygen index of the composite-based aerogel is obviously improved (increased from 18.1% to 22.3%).
TABLE 1 data for performance testing of composites obtained in examples 1-6, and comparative examples 1-2
As can be seen from the observation of the table 1, the composite material synthesized by the method in the embodiment has excellent mechanical properties and good flame retardant effect, so that the material is safer to use. The compression strength and the compression modulus can meet the requirements.
The nano-cellulose and the chitosan selected in the invention are both natural and degradable, and the addition of the chitosan and the montmorillonite is not only beneficial to the flame retardant property but also beneficial to the smoke suppression property. The cross-linking agent makes the nano-cellulose cross-linked, and the sodium tripolyphosphate makes the chitosan cross-linked, which is beneficial to the mechanical property.
The principal features of the invention and advantages of the invention have been shown and described above. The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, simplifications, etc., which are made without departing from the spirit and principle of the present invention, should be regarded as being equivalent to the replacement of the above embodiments, and are included in the scope of the present invention.
Claims (10)
1. The preparation method of the double-crosslinking flame-retardant composite aerogel is characterized by comprising the following steps of:
1) amino protonation treatment of chitosan:
placing chitosan in an acid solution to obtain a chitosan solution with amino groups on a molecular chain protonated;
2) preparing the composite aerogel:
dispersing nano montmorillonite into mixed suspension of nano cellulose and chitosan, adding a cross-linking agent, stirring to obtain mixed solution, pouring the mixed solution into a mould, freezing, and performing cross-linking reaction to obtain composite aerogel;
3) a double cross-linking step:
and (3) soaking the obtained composite gel in a mixed solution of a polyphosphate solution and a transition metal chloride solution for treatment, converting macromolecules in the composite aerogel into a three-dimensional network structure, crosslinking the composite aerogel with the polyphosphate, and freeze-drying to obtain the double-crosslinking flame-retardant composite aerogel.
2. The preparation method of the double-crosslinked flame-retardant composite aerogel according to claim 1, wherein the amino protonation treatment of the chitosan in the step 1) is specifically as follows:
50mg-1000mg of chitosan is put into 50ml of acetic acid solution with the mass fraction of 0.1-3%, and the mixture is stirred at high speed to be completely dissolved, so that the chitosan solution with the protonized amino groups on the molecular chain is obtained.
3. The preparation method of the double-crosslinked flame-retardant composite aerogel according to claim 1, wherein the preparation of the mixed suspension of the nanocellulose and the chitosan is further included after the amino protonation treatment of the chitosan in the step 1) and before the preparation of the composite aerogel in the step 2), and specifically comprises the following steps: respectively preparing nano-cellulose and chitosan with the mass ratio of 1: 1-1: 3 to obtain a nano-cellulose suspension and the chitosan solution, and mixing the nano-cellulose and the chitosan solution to obtain a nano-cellulose and chitosan mixed suspension.
4. The preparation method of the double-crosslinking flame-retardant composite aerogel according to claim 1, wherein in the step 2) of preparing the composite aerogel, the addition amount of the crosslinking agent accounts for 5-20% of the total mass of the nano-cellulose, the chitosan and the nano-montmorillonite.
5. The preparation method of the double-crosslinking flame-retardant composite aerogel according to claim 4, wherein in the preparation of the composite aerogel in the step 2), the stirring speed of stirring after adding the crosslinking agent is 1000-6000 rpm.
6. The preparation method of the double-crosslinked flame-retardant composite aerogel according to claim 4, wherein in the step 2) of preparing the composite aerogel, the step of pouring the mixed solution into a mold and freezing the mixed solution comprises the following steps: freezing the mixed solution at-5 to-50 ℃ for 0.2 to 72 hours, and then freezing and drying for 12 to 72 hours to obtain the composite aerogel.
7. The preparation method of the double-crosslinking flame-retardant composite aerogel according to claim 4, wherein in the preparation of the composite aerogel in the step 2), the crosslinking reaction is specifically as follows: the frozen mixture is processed at 50-200 deg.C for 5-100min to realize crosslinking reaction.
8. The method for preparing a double-crosslinked flame-retardant composite aerogel according to claim 1, wherein in the step 2) of preparing the composite aerogel, the nanocellulose at least comprises one of wood nanocellulose, cotton nanocellulose, flax nanocellulose, algae nanocellulose, bacteria nanocellulose and animal nanocellulose.
9. The method for preparing a double-crosslinked flame-retardant composite aerogel according to claim 1, wherein in the step 2), the composite aerogel is prepared, and the nano montmorillonite is at least one of calcium-based nano montmorillonite, sodium-calcium-based nano montmorillonite, magnesium-based nano montmorillonite and H-nano montmorillonite.
10. The method for preparing a double-crosslinked flame-retardant composite aerogel according to claim 1, wherein in the step 2) of preparing the composite aerogel, the crosslinking agent is at least one of citric acid, 1,2,3, 4-butanetetracarboxylic acid, polyvinyl alcohol, ammonium zirconium carbonate, 2D resin and water-soluble hydroxy acrylate resin.
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