阅读说明：本技术 一种高效阻燃的磷酸化壳聚糖气凝胶及其制备方法 (Efficient flame-retardant phosphorylated chitosan aerogel and preparation method thereof ) 是由 吴宁晶 马小兵 崔宏丽 于 2021-06-30 设计创作，主要内容包括：本发明提供了一种磷酸化壳聚糖生物基气凝胶及其制备方法,在均相体系采用磷酸直接对壳聚糖进行磷酸化的化学改性,制备得到的磷酸化壳聚糖具有优异的水溶性,采用冻融-冷冻干燥法直接制备得到高效阻燃的磷酸化壳聚糖气凝胶。由于壳聚糖分子结构中同时引入阻燃元素磷,增加壳聚糖的成炭率和阻燃效率,本发明中磷酸化壳聚糖气凝胶的氧指数高达80％以上,阻燃等级V-0,是一种高效阻燃的磷酸化壳聚糖生物基气凝胶,可应用于替代石油基阻燃隔热保温材料。(The invention provides a phosphorylated chitosan bio-based aerogel and a preparation method thereof, phosphoric acid is adopted in a homogeneous system to directly carry out phosphorylation chemical modification on chitosan, the prepared phosphorylated chitosan has excellent water solubility, and a freeze-thaw-freeze drying method is adopted to directly prepare the high-efficiency flame-retardant phosphorylated chitosan aerogel. As the flame-retardant element phosphorus is introduced into the chitosan molecular structure at the same time, the char formation rate and the flame-retardant efficiency of the chitosan are increased, the oxygen index of the phosphorylated chitosan aerogel reaches more than 80 percent, the flame-retardant grade is V-0, and the phosphorylated chitosan aerogel is a high-efficiency flame-retardant phosphorylated chitosan bio-based aerogel and can be applied to replace petroleum-based flame-retardant heat-insulation materials.)

1. Phosphoric acid is adopted to carry out phosphorylation modification on chitosan in a homogeneous water system, and the obtained phosphorylation chitosan aqueous solution is subjected to freeze thawing-freeze drying to prepare the efficient flame-retardant phosphorylation chitosan aerogel.

The preparation method of the efficient flame-retardant phosphorylated chitosan aerogel is characterized by comprising the following steps:

(1) respectively adding chitosan and deionized water into a reaction device, stirring until the chitosan is uniformly dispersed in water, then adding acetic acid, stirring at a high speed until the chitosan is completely dissolved to form a water homogeneous system of chitosan, wherein the concentration range of the acetic acid in the chitosan water solution is 0.1-20 wt%; the mass fraction of the chitosan aqueous solution is 0.1-20 wt%;

(2) adding a phosphoric acid solution into the chitosan aqueous solution system, setting the reaction temperature to be 30-80 ℃, and the reaction time to be 0.5-24h, and finishing the reaction; slowly pouring the obtained viscous oily liquid into absolute ethyl alcohol to obtain white flocculent precipitate; washing with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid, and drying the final product in a forced air drying oven at 50-100 deg.C to constant weight to obtain phosphorylated chitosan;

(3) preparing phosphorylated chitosan into a phosphorylated chitosan aqueous solution, freezing and thawing to obtain phosphorylated chitosan hydrogel, freezing the phosphorylated chitosan hydrogel at the temperature of between-78 and-5 ℃ by adopting liquid nitrogen or a refrigerator after curing is finished, drying the phosphorylated chitosan hydrogel for 12 to 72 hours under the high-vacuum freezing condition, and preparing the phosphorylated cellulose aerogel by a freeze-drying method; the limiting oxygen index of the phosphorylated cellulose aerogel is up to more than 60 percent.

2. The preparation method of the efficient flame-retardant phosphorylated chitosan aerogel according to claim 1, wherein the molar ratio of the phosphoric acid to the structural units of chitosan is 0.1-30: 0.1 to 1(mol: mol).

3. The preparation method of the phosphorylated chitosan aerogel with high flame retardancy as claimed in claim 1, wherein the concentration of the phosphorylated chitosan aqueous solution is 0.1-20 wt%.

4. The preparation method of the high-efficiency flame-retardant phosphorylated chitosan aerogel according to claim 1, wherein the phosphorylated chitosan aqueous solution is frozen and thawed at-78-30 ℃ to obtain the phosphorylated chitosan hydrogel.

Technical Field

The invention relates to a chemically modified chitosan bio-based aerogel, in particular to a high-efficiency flame-retardant phosphorylated chitosan aerogel and a preparation method thereof

Background

Chitosan (Chitosan, CS) is obtained from the partial deacetylation of chitin and is a polysaccharide material linked by β -1, 4-glycosidic bonds. Although the chitosan structure is similar to that of cellulose, the chitosan has higher chemical activity and modification potential due to containing a large amount of amino groups, and is widely applied to the fields of packaging films, electric/photocatalysis, drug delivery, antibacterial materials, corrosion-resistant coatings and the like. Chitosan does not dissolve directly in water, but it does so in a variety of dilute acids (dilute acetic acid )Hydrochloric acid, etc.) by the amino-NH group of chitosan₂Protonation to-NH₃ ⁺And (4) realizing. In addition, the multivalent organic acid has potential ionic crosslinking effect on chitosan molecular chains while dissolving chitosan, thereby favorably influencing the mechanical properties of products.

The chitosan-based aerogel has the characteristics of wide sources, greenness, no toxicity, low cost, strength and toughness, and is concerned by more and more researchers. Chitosan can be dissolved by dilute acid, made into aerogel by a sol-gel process and a solvent sublimation process, and the chitosan aerogel is mostly used in the fields of water oil separation and dye removal due to the cationic property of amino groups. The chitosan derivative is a substance generated by converting amino or hydroxyl on chitosan into other functional groups through chemical reaction, and is mainly used as a drug delivery and adsorption material. Carboxymethyl chitosan and hydroxypropyl chitosan, which are obtained by respectively reacting chitosan with sodium chloroacetate and ethylene oxide. The modified aerogel can be directly dissolved in water and has a considerable amount of active groups, so the modified aerogel has certain application potential in the field of aerogel preparation. Luo et al mix graphene oxide dispersion with a carboxymethyl chitosan aqueous solution, add a small amount of tripolyphosphoric acid or glutaraldehyde as a cross-linking agent to promote the gelling process, obtain hydrogel by a vacuum filtration method, and obtain graphene oxide/carboxymethyl chitosan composite aerogel (GO/CMC) by freeze-drying. Because of the chemical crosslinking effect, the GO/CMC has better deformation recovery capability, and the appearance of the sample can be completely recovered when the deformation is less than 55%, which is beneficial to the recycling of aerogel. The chitosan derivative is more suitable as the matrix of the aerogel than chitosan because of the characteristic of direct dissolution in water.

The aerogel has the potential of being applied to the field of heat preservation and heat insulation due to the characteristic of low heat conductivity, but the application of the aerogel in the field of heat preservation and heat insulation is limited due to the insufficient flame retardance of the chitosan aerogel. Generally by adding small molecule flame retardants (Mg (OH)₂，Al(OH)₃Etc.) to physically flame-retardant modify chitosan, but with the increase of the amount of flame retardant, to chitosan aerogelThe cells and mechanical properties of the foam have a certain influence.

Chemical modification is carried out on chitosan, and a group containing a flame-retardant element is directly introduced, so that the effective method for improving the flame retardance of the chitosan aerogel is provided. The introduction of phosphorus into chitosan molecules is a main way for preparing the intrinsic flame-retardant chitosan aerogel, and the common chemical modification methods comprise three methods: (1) protecting amino groups with methanesulfonic acid to modify hydroxyl groups of the chitosan; (2) modifying chitosan with triethyl phosphate and phosphorus pentoxide; (3) and (3) carrying out phosphorylation modification on the amino group of the chitosan by using urea and phosphoric acid. The chemical modification preparation method of the chitosan has the advantages of high cost, large using amount of organic solvent, environmental pollution and low grafting rate of phosphorus-containing groups on the surface of the chitosan in a heterogeneous reaction system.

In the invention, the homogeneous system of the aqueous solution is adopted to carry out phosphorylation modification on the chitosan, the operation is simple and easy, and the prepared phosphorylation chitosan has high grafting rate and good water solubility and is suitable to be used as a matrix material of the flame-retardant chitosan aerogel. The flame-retardant element is directly chemically bonded with the chitosan, so that the flame-retardant effect is good, the flame retardance can be maintained for a long time, the method is a simple and effective flame-retardant modification method, and the water-soluble phosphorylated chitosan can be directly applied to the preparation of the high-efficiency flame-retardant phosphorylated chitosan aerogel.

Disclosure of Invention

In order to solve the defects of poor solubility and low flame retardant efficiency of chitosan in the prior art, the invention aims to: phosphate groups are introduced into the molecular structure of the chitosan through a simple preparation method to prepare the phosphorylated chitosan, so that the water solubility and the flame retardant efficiency of the phosphorylated chitosan are improved; and preparing the efficient flame-retardant phosphorylated chitosan aerogel by adopting the phosphorylated chitosan hydrogel through a freeze-thaw-freeze drying method.

In order to achieve the purpose, the technical means adopted by the invention is as follows:

1. phosphoric acid is adopted to carry out phosphorylation modification on chitosan in a homogeneous water system, and the obtained phosphorylation chitosan aqueous solution is subjected to freeze thawing-freeze drying to prepare the efficient flame-retardant phosphorylation chitosan aerogel.

The preparation method of the high-efficiency flame-retardant phosphorylated chitosan aerogel comprises the following steps:

(1) respectively adding chitosan and deionized water into a reaction device, stirring until the chitosan is uniformly dispersed in water, then adding acetic acid, stirring at a high speed until the chitosan is completely dissolved to form a water homogeneous system of chitosan, wherein the concentration range of the acetic acid in the chitosan water solution is 0.1-20 wt%; the mass fraction of the chitosan aqueous solution is 0.1-20 wt%;

(2) adding a phosphoric acid solution into the chitosan aqueous solution system, setting the reaction temperature to be 30-80 ℃, and the reaction time to be 0.5-24h, and finishing the reaction; slowly pouring the obtained viscous oily liquid into absolute ethyl alcohol to obtain white flocculent precipitate; washing with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid, and drying the final product in a forced air drying oven at 50-100 deg.C to constant weight to obtain phosphorylated chitosan.

(3) Preparing phosphorylated chitosan into a phosphorylated chitosan aqueous solution, freezing and thawing to obtain phosphorylated chitosan hydrogel, freezing the phosphorylated chitosan hydrogel at the temperature of between-78 and-5 ℃ by adopting liquid nitrogen or a refrigerator after curing is finished, drying the phosphorylated chitosan hydrogel for 12 to 72 hours under the high-vacuum freezing condition, and preparing the phosphorylated cellulose aerogel by a freeze-drying method; the limiting oxygen index of the phosphorylated cellulose aerogel is up to more than 60 percent.

2. Further, according to the preparation method of the efficient flame-retardant phosphorylated chitosan aerogel, the molar ratio of the phosphoric acid to the structural units of chitosan is 0.1-30: 0.1 to 1(mol: mol).

3. Further, in the preparation method of the high-efficiency flame-retardant phosphorylated chitosan aerogel, the concentration of the phosphorylated chitosan aqueous solution is 0.1-20 wt%.

4. Further, in the preparation method of the high-efficiency flame-retardant phosphorylated chitosan aerogel, a phosphorylated chitosan aqueous solution is frozen and thawed at-78-30 ℃, and the obtained phosphorylated chitosan hydrogel is prepared into the phosphorylated chitosan aerogel through a freeze-drying method.

Detailed Description

The present invention is described in detail below by way of examples, it should be noted that the following examples are only used for further illustration of the present invention, and should not be construed as limiting the scope of the present invention, and that the non-essential modifications and adaptations of the present invention by those skilled in the art according to the present disclosure described above will still fall within the scope of the present invention.

Example 1

Adding chitosan (10g,0.06mol of structural unit) and deionized water (88ml) into a reaction device, stirring until the chitosan is uniformly dispersed in water, adding acetic acid (2ml), and stirring at high speed until the chitosan is completely dissolved, wherein the mass fraction of the chitosan aqueous solution is 10 wt%, and the acetic acid concentration range is 2 wt%; phosphoric acid (85%, 18.5ml, 0.3mol) was added to the reaction system, wherein the molar ratio of phosphoric acid to structural units of chitosan was 5:1(mol: mol), the temperature was raised to 40 ℃ and the reaction was terminated after 12h of reaction. The resulting light brown viscous oily liquid was slowly poured into anhydrous ethanol to obtain a white flocculent precipitate. The white precipitate was repeatedly washed with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid. The product was dried in a forced air drying oven at 60 ℃ to constant weight. Directly dissolving phosphorylated chitosan in water to prepare a 2 wt% phosphorylated chitosan aqueous solution, freezing and thawing at-20-20 ℃ to obtain phosphorylated chitosan hydrogel, after the phosphorylated chitosan hydrogel is cured, transferring the phosphorylated chitosan hydrogel to a refrigerator at-20 ℃ for freezing for 12 hours, and freezing and drying for 48 hours at-60 ℃ and 20Pa to obtain phosphorylated cellulose aerogel. The oxygen index (LOI) of the phosphorylated cellulose aerogel is determined to be more than 65%, and the UL-94 grade reaches V-0 grade. The density and specific modulus of the phosphorylated cellulose aerogel were 0.035g/cm, respectively³And 41.1m²·s^-2The compression modulus and the compression strength were 1.45MPa and 0.48MPa, respectively.

Example 2

Adding chitosan (10g,0.06mol of structural unit) and deionized water (86ml) into a reaction device, stirring until the chitosan is uniformly dispersed in water, adding acetic acid (4ml), stirring at high speed until the chitosan is completely dissolved, wherein the mass fraction of the chitosan aqueous solution is 10wt%, acetic acid concentration range of 4 wt%; phosphoric acid (85%, 37ml, 0.6mol) was added to the reaction system, wherein the molar ratio of phosphoric acid to structural units of chitosan was 10:1(mol: mol), raising the temperature to 50 ℃, and finishing the reaction after 10 hours of reaction. The resulting light brown viscous oily liquid was slowly poured into anhydrous ethanol to obtain a white flocculent precipitate. The white precipitate was repeatedly washed with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid. The product was dried in a forced air drying oven at 60 ℃ to constant weight. Directly dissolving phosphorylated chitosan in water to prepare 4 wt% of phosphorylated chitosan aqueous solution, freezing and thawing at-50-20 ℃ to obtain phosphorylated chitosan hydrogel, transferring the phosphorylated chitosan hydrogel to liquid nitrogen at-78 ℃ after maturation is completed, freezing for 0.5h, and freeze-drying for 48h under the conditions of-60 ℃ and 20Pa to obtain phosphorylated cellulose aerogel. Measuring the oxygen index (LOI) of the phosphorylated cellulose aerogel to be more than 72 percent, and the UL-94 grade reaches V-0 grade; the density and specific modulus of the phosphorylated cellulose aerogel are respectively 0.051g/cm³And 32.9m²·s^-2The compressive modulus and compressive strength were 1.69MPa and 0.49MPa, respectively.

Example 3

Adding chitosan (10g,0.06mol of structural unit) and deionized water (198ml) into a reaction device, stirring until the chitosan is uniformly dispersed in water, adding acetic acid (2ml), and stirring at high speed until the chitosan is completely dissolved, wherein the mass fraction of the chitosan aqueous solution is 5 wt%, and the acetic acid concentration range is 1 wt%; phosphoric acid (85%, 55.5ml, 0.9mol) was added to the reaction system, wherein the molar ratio of phosphoric acid to structural units of chitosan was 15: 1(mol: mol), raising the temperature to 70 ℃, and finishing the reaction after 6 hours of reaction. The resulting light brown viscous oily liquid was slowly poured into anhydrous ethanol to obtain a white flocculent precipitate. The white precipitate was repeatedly washed with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid. The product was dried in a forced air oven at 80 ℃ to constant weight. Directly dissolving phosphorylated chitosan in water to prepare 4 wt% phosphorylated chitosan aqueous solution, freezing and thawing at-20-20 ℃ to obtain phosphorylated chitosan hydrogel, transferring the phosphorylated chitosan hydrogel to a refrigerator at-18 ℃ for freezing for 12h after the phosphorylated chitosan hydrogel is cured,and freeze-drying for 48h at-60 ℃ and 10Pa to obtain the phosphorylated cellulose aerogel. The oxygen index (LOI) of the phosphorylated cellulose aerogel is more than 75 percent and reaches UL-94V-0 level; the density and specific modulus of the phosphorylated cellulose aerogel are respectively 0.052g/cm³And 32.7m²·s^-2The compressive modulus and the compressive strength were 1.70MPa and 0.52MPa, respectively.

Example 4

Adding chitosan (10g,0.06mol of structural unit) and deionized water (198ml) into a reaction device, stirring until the chitosan is uniformly dispersed in water, adding acetic acid (2ml), and stirring at high speed until the chitosan is completely dissolved, wherein the mass fraction of the chitosan aqueous solution is 5 wt%, and the acetic acid concentration range is 1 wt%; phosphoric acid (85%, 74ml, 0.12mol) was added to the reaction system, wherein the molar ratio of phosphoric acid to structural units of chitosan was 20:1(mol: mol), the temperature was raised to 60 ℃ and the reaction was terminated after 5 hours of reaction. The resulting light brown viscous oily liquid was slowly poured into anhydrous ethanol to obtain a white flocculent precipitate. The white precipitate was repeatedly washed with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid. The product was dried in a forced air drying oven at 60 ℃ to constant weight. Directly dissolving phosphorylated chitosan in water to prepare 4 wt% of phosphorylated chitosan aqueous solution, freezing and thawing at-30-30 ℃ to obtain phosphorylated chitosan hydrogel, transferring the phosphorylated chitosan hydrogel to a refrigerator at-30 ℃ after the phosphorylated chitosan aqueous solution is aged, freezing for 12 hours, and freeze-drying for 60 hours at-60 ℃ and 20Pa to obtain phosphorylated cellulose aerogel. Measuring the oxygen index (LOI) of the phosphorylated cellulose aerogel to be more than 80 percent, and the UL-94 grade reaches V-0 grade; the density and specific modulus of the phosphorylated cellulose aerogel were 0.053g/cm, respectively³And 32.5m²·s^-2The compressive modulus and compressive strength were 1.72MPa and 0.55MPa, respectively.

Example 5

Adding chitosan (10g,0.06mol of structural unit) and deionized water (189ml) into a reaction device, stirring until the chitosan is uniformly dispersed in water, adding acetic acid (1ml), stirring at high speed until the chitosan is completely dissolved, wherein the mass fraction of the chitosan aqueous solution is 5 wt%, and the concentration of the acetic acid is in a rangeThe circumference is 0.5 wt%; phosphoric acid (85%, 92.5 ml, 1.5mol) was added to the reaction system, wherein the molar ratio of phosphoric acid to structural units of chitosan was 25:1(mol: mol), the temperature was raised to 70 ℃ and the reaction was terminated after 3 hours of reaction. The resulting light brown viscous oily liquid was slowly poured into anhydrous ethanol to obtain a white flocculent precipitate. The white precipitate was repeatedly washed with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid. The product was dried in a forced air oven at 80 ℃ to constant weight. Directly dissolving phosphorylated chitosan in water to prepare 4 wt% of phosphorylated chitosan aqueous solution, freezing and thawing at-50-20 ℃ to obtain phosphorylated chitosan hydrogel, after the phosphorylated chitosan hydrogel is cured, transferring the phosphorylated chitosan hydrogel to a refrigerator at-20 ℃ for freezing for 12h, and freezing and drying for 48h at-60 ℃ and 20Pa to obtain phosphorylated cellulose aerogel. Measuring the oxygen index (LOI) of the phosphorylated cellulose aerogel to be more than 80 percent, and the UL-94 grade reaches V-0 grade; the density and specific modulus of the phosphorylated cellulose aerogel are respectively 0.052g/cm³And 33.8m²·s^-2The compressive modulus and the compressive strength were 1.76MPa and 0.60MPa, respectively.

Example 6

Adding chitosan (10g,0.06mol of structural unit) and deionized water (188ml) into a reaction device, stirring until the chitosan is uniformly dispersed in water, adding acetic acid (2ml), and stirring at high speed until the chitosan is completely dissolved, wherein the mass fraction of the chitosan aqueous solution is 10 wt%, and the acetic acid concentration range is 2 wt%; phosphoric acid (85% concentration, 111ml, 1.8mol) was added to the reaction system, wherein the molar ratio of phosphoric acid to structural units of chitosan was 30:1(mol: mol), the temperature was raised to 80 ℃ and the reaction was terminated after 0.5 h. The resulting light brown viscous oily liquid was slowly poured into anhydrous ethanol to obtain a white flocculent precipitate. The white precipitate was repeatedly washed with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid. The product was dried in a forced air drying oven at 60 ℃ to constant weight. Directly dissolving phosphorylated chitosan in water to obtain 4 wt% phosphorylated chitosan aqueous solution, freezing and thawing at-30-20 deg.C to obtain phosphorylated chitosan hydrogel, cooling the phosphorylated chitosan hydrogel in transfer liquid nitrogen after aging, and placing the phosphorylated chitosan hydrogel in strips at-60 deg.C and 20PaAnd (5) freeze-drying for 48 hours under the condition to obtain the phosphorylated cellulose aerogel. Measuring the oxygen index (LOI) of the phosphorylated cellulose aerogel to be more than 80 percent, and the UL-94 grade reaches V-0 grade; the density and specific modulus of the phosphorylated cellulose aerogel were 0.054g/cm³And 33.0m²·s^-2The compressive modulus and the compressive strength were 1.78MPa and 0.62MPa, respectively.

Example 7

Adding chitosan (10g,0.06mol of structural unit) and deionized water (989ml) into a reaction device, stirring until the chitosan is uniformly dispersed in water, and adding acetic acid (1ml) to obtain a chitosan aqueous solution with the mass fraction of 1 wt% and the acetic acid concentration of 0.1 wt%; adding phosphoric acid (with the concentration of 85 percent, 37ml and 0.6mol) into the reaction system, stirring at high speed until the chitosan is completely dissolved, wherein the molar ratio of the phosphoric acid to the structural unit of the chitosan is 20:1(mol: mol), raising the temperature to 50 ℃, and finishing the reaction after 5 hours of reaction. The resulting light brown viscous oily liquid was slowly poured into anhydrous ethanol to obtain a white flocculent precipitate. The white precipitate was repeatedly washed with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid. The product was dried in a forced air drying oven at 60 ℃ to constant weight. Directly dissolving phosphorylated chitosan in water to prepare a 6 wt% phosphorylated chitosan aqueous solution, repeatedly freezing and thawing at-20-20 ℃ to obtain phosphorylated chitosan hydrogel, after the phosphorylated chitosan hydrogel is cured, transferring the phosphorylated chitosan hydrogel to a refrigerator at-50 ℃ for freezing for 12 hours, and freeze-drying for 48 hours at-60 ℃ and 20Pa to obtain phosphorylated cellulose aerogel. Measuring the oxygen index (LOI) of the phosphorylated cellulose aerogel to be more than 80 percent, and the UL-94 grade reaches V-0 grade; the density and specific modulus of the phosphorylated cellulose aerogel were 0.088g/cm, respectively³And 22.3m²·s^-2The compression modulus and the compression strength were 1.90MPa and 0.80MPa, respectively.

Example 8

Adding chitosan (10g,0.06mol of structural unit) and deionized water (188ml) into a reaction device, stirring until the chitosan is uniformly dispersed in water, adding acetic acid (2ml), stirring at high speed until the chitosan is completely dissolved, wherein the mass fraction of the chitosan aqueous solution is 5 wt%, and the concentration of the acetic acid is 1wt%; a phosphoric acid solution (concentration 85%, 3.7ml, 0.06mol) was added to the reaction system, wherein the molar ratio of phosphoric acid to structural units of chitosan was 1:1(mol: mol), the temperature was raised to 50 ℃ and the reaction was terminated after 24 hours. The resulting light brown viscous oily liquid was slowly poured into anhydrous ethanol to obtain a white flocculent precipitate. The white precipitate was repeatedly washed with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid. The product was dried in a forced air drying oven at 60 ℃ to constant weight. Directly dissolving phosphorylated chitosan in water to prepare a 1 wt% phosphorylated chitosan aqueous solution, repeatedly freezing and thawing at-20-20 ℃ to obtain phosphorylated chitosan hydrogel, transferring the phosphorylated chitosan hydrogel into liquid nitrogen to cool after the phosphorylated chitosan hydrogel is cured, and freeze-drying the phosphorylated chitosan hydrogel for 72 hours at-60 ℃ and 10Pa to obtain phosphorylated cellulose aerogel. Measuring the oxygen index (LOI) of the phosphorylated cellulose aerogel to be more than 68 percent, wherein the UL-94 grade reaches V-0 grade; the density and specific modulus of the phosphorylated cellulose aerogel were 0.025g/cm respectively³And 50.0m²·s^-2The compressive modulus and the compressive strength were 1.25 MPa and 0.32MPa, respectively.

Example 9

Adding chitosan (10g,0.06mol of structural unit) and deionized water (86ml) into a reaction device, stirring until the chitosan is uniformly dispersed in water, adding acetic acid (4ml), and stirring at high speed until the chitosan is completely dissolved, wherein the mass fraction of the chitosan aqueous solution is 2 wt%, and the concentration range of the acetic acid is 4 wt%; a phosphoric acid solution (concentration 85%, 47ml, 0.15mol) was added to the reaction system, wherein the molar ratio of phosphoric acid to the structural unit of chitosan was 2.5:1(mol: mol), the temperature was raised to 70 ℃ and the reaction was terminated after 3 hours of reaction. The resulting light brown viscous oily liquid was slowly poured into anhydrous ethanol to obtain a white flocculent precipitate. The white precipitate was repeatedly washed with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid. The product was dried in a forced air drying oven at 60 ℃ to constant weight. Directly dissolving phosphorylated chitosan in water to obtain 4 wt% phosphorylated chitosan aqueous solution, repeatedly freezing and thawing at-20-20 deg.C to obtain phosphorylated chitosan hydrogel, transferring into liquid nitrogen to cool after aging, and making into strips at-60 deg.C and 20PaAnd (5) freeze-drying for 72h under the condition to obtain the phosphorylated cellulose aerogel. Measuring the oxygen index (LOI) of the phosphorylated cellulose aerogel to be more than 52 percent, and the UL-94 grade reaches V-0 grade; the density and specific modulus of the phosphorylated cellulose aerogel were 0.046g/cm, respectively³And 40.2m²·s^-2The compressive modulus and compressive strength were 1.85MPa and 0.57MPa, respectively.

Example 10

Adding chitosan (10g,0.06mol of structural unit) and deionized water (30ml) into a reaction device, stirring until the chitosan is uniformly dispersed in water, adding acetic acid (10ml), and stirring at high speed until the chitosan is completely dissolved, wherein the mass fraction of the chitosan aqueous solution is 20 wt%, and the concentration range of the acetic acid is 20 wt%; a phosphoric acid solution (85% concentration, 18.5ml, 0.3mol) was added to the reaction system, wherein the molar ratio of phosphoric acid to structural units of chitosan was 10:1(mol: mol), the temperature was raised to 30 ℃ and the reaction was terminated after 8 hours. The resulting light brown viscous oily liquid was slowly poured into anhydrous ethanol to obtain a white flocculent precipitate. The white precipitate was repeatedly washed with anhydrous ethanol to remove unreacted phosphoric acid and residual acetic acid. The product was dried in a forced air drying oven at 60 ℃ to constant weight. Directly dissolving phosphorylated chitosan in water to prepare a 10 wt% phosphorylated chitosan aqueous solution, freezing and thawing at-20-20 ℃ to obtain phosphorylated chitosan hydrogel, after the phosphorylated chitosan hydrogel is cured, transferring the phosphorylated chitosan hydrogel to a refrigerator at-20 ℃ for freezing for 12 hours, and freezing and drying at-60 ℃ and 20Pa for 24 hours to obtain phosphorylated cellulose aerogel. Measuring the oxygen index (LOI) of the phosphorylated cellulose aerogel to be more than 60 percent, and the UL-94 grade reaches V-0 grade; the density and specific modulus of the phosphorylated cellulose aerogel were 0.097g/cm, respectively³And 27.5m²·s^-2The compressive modulus and the compressive strength were 2.67MPa and 1.26MPa, respectively.

Table 1 shows the physical property parameters of the phosphorylated chitosan prepared in the present invention, which has a high phosphorus content and excellent char formation.

Table 1 examples physical property parameters of phosphorylated chitosan

The table 2 shows the flame retardant and physical and mechanical properties of the phosphorylated chitosan aerogel, and the phosphorylated chitosan aerogel has excellent flame retardant property and mechanical property and can be used as a substitute material of a flame retardant and heat insulation material.

Table 2 flame retardant and physico-mechanical properties of phosphated chitosan aerogels