CN116289322B - A method for preparing cationic hydrophobic microcapsule flame retardant paper - Google Patents

Abstract

The present invention relates to a method for preparing cationic hydrophobic microcapsule flame retardant paper. The present invention uses plant fiber as a carrier, and includes the steps of preparing chitosan and a cross-linked prepolymer, preparing a hydrophobic microcapsule shell layer, preparing a cationic hydrophobic microcapsule shell layer, and preparing a cationic hydrophobic microcapsule flame retardant paper. Ammonium polyphosphate is used as a core material, chitosan and a cross-linking agent are used as a hydrophobic shell layer and a flame retardant synergist, and the hydrophobic shell layer is further cationic modified. The cationic hydrophobic microcapsule flame retardant is added to the plant fiber by an in-slurry addition method to prepare a flame retardant paper with high flame retardant performance and certain moisture resistance. The cationic hydrophobic microcapsule flame retardant and the method for preparing flame retardant paper of the present invention can be widely used in materials mainly composed of plant fiber or containing plant fiber, can accelerate the carbonization of the material, slow down and prevent the spread of flames, and improve the flame retardant performance of the material.

Description

A method for preparing cationic hydrophobic microcapsule flame retardant paper

Technical Field

The invention belongs to the field of flame retardant materials and relates to a method for preparing cationic hydrophobic microcapsule flame retardant paper.

Background Art

As a common phosphorus-nitrogen flame retardant, ammonium polyphosphate is currently widely used in a variety of flame retardant materials and fields. Due to its own molecular structure characteristics, it has the disadvantages of high hygroscopicity and poor compatibility with materials. Because ammonium polyphosphate belongs to a polyanion electrolyte, its particles are highly negatively charged. However, the main reason affecting the retention of fillers in the in-slurry addition method is to adjust the charge balance of wet-end chemistry and reduce the solubility of fillers. Therefore, when ammonium polyphosphate is used as a flame retardant filler and flame retardant paper is prepared by the in-slurry addition method, it is necessary to modify the ammonium polyphosphate. At present, the modification methods of ammonium polyphosphate include surfactant modification, silane coupling agent modification and microcapsule coating modification, among which microcapsule coating modification is the main method, and microcapsule coating is mainly based on melamine and melamine formaldehyde resin. However, although melamine-coated modified ammonium polyphosphate can improve the flame retardant properties of ammonium polyphosphate and reduce the water solubility of ammonium polyphosphate, it will release a large amount of formaldehyde gas during combustion, which is harmful to human health.

Chitosan is a natural biopolymer containing amino and hydroxyl groups. It is the only cationic alkaline polysaccharide discovered so far. The amino groups in chitosan can make it carry a positive charge and produce a flame retardant synergistic effect, thereby improving the flame retardant effect of the material. The hydroxyl groups in chitosan can combine with the hydroxyl groups in plant fibers, and the retention rate of ammonium polyphosphate in plant fibers is improved by using the principle of similar miscibility. In addition, due to the presence of N-acetyl groups in chitosan, chitosan will not dissolve in water, ethanol, and acetone, but will dissolve in certain dilute acids, and the degree of deacetylation will also affect its solubility in acidic solutions. This also shows that coating chitosan on the surface of ammonium polyphosphate makes it possible to form a hydrophobic layer on the surface of ammonium polyphosphate.

Amino acids are amphoteric organic compounds containing alkaline amino groups and acidic carboxyl groups. The positively charged amino acids under neutral pH conditions are lysine, histidine and arginine. After the surface of ammonium polyphosphate is cationized and modified with positively charged amino acids, the coated ammonium polyphosphate is positively charged in water, and the amino groups in the amino acids can further improve the flame retardant effect of the material. At the same time, amino acids are biomass materials and have good environmental friendliness compared to positively charged substances such as polyethyleneimine and polymethacrylate-N,N-dimethylaminoethyl ester.

Paper is a good environmentally friendly material. It is mainly made of thin sheets of plant fibers interwoven after papermaking. Traditional paper materials are extremely flammable, which limits the application of paper-based materials. Therefore, in order to solve the above problems, ammonium polyphosphate can be used as the core material, chitosan and cross-linking agent can be used as hydrophobic shell and flame retardant synergist, and the hydrophobic shell can be further cationized to form a cationic hydrophobic shell on the surface of ammonium polyphosphate, reducing the effect of the negative charge of ammonium polyphosphate particles on the chemical charge of the wet part. The cationic hydrophobic microcapsule flame retardant is added to the plant fiber by the in-slurry addition method to prepare flame-retardant paper with high flame retardancy and moisture resistance.

Summary of the invention

In view of the above problems, the object of the present invention is to provide a method for preparing cationic hydrophobic microcapsule flame retardant paper.

To achieve the above object, the technical solution adopted by the present invention is:

A method for preparing cationic hydrophobic microcapsule flame retardant paper comprises the following steps:

(1) Preparation of chitosan prepolymer: 2-10 g of chitosan is dispersed in 100 ml of 1 wt.%-5 wt.% acetic acid solution, and stirred at 20-40° C. for 0.5-2 hr to prepare a chitosan prepolymer solution.

(2) Preparation of cross-linked prepolymer: 4-8 g of isocyanate was dispersed in 30 ml of solvent and stirred for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(3) Preparation of hydrophobic microcapsule shell: 100 g of ammonium polyphosphate was dispersed in 200 ml of solvent, 1 g of emulsifier was added, and the mixture was evenly mixed. The chitosan prepolymer solution prepared in step (1) was added, and the mixture was reacted at 60-90° C. for 15 min. The crosslinker prepolymer solution prepared in step (2) was then added dropwise to the reaction system within 30 min. Finally, the entire reaction system was reacted at 60-90° C. for 4-8 hr. The mixture was filtered and washed with solvent and water for 3 times, dried in an oven at 80° C., ground, and sieved to obtain APP@chitosan.

(4) Preparation of cationic hydrophobic microcapsule shell: 2-6 g of amino acid was dispersed in a mixed solvent of water (10 ml) and ethanol (200 ml), and then 8 g of APP@chitosan was added. The mixture was reacted at 60-80°C for 4-6 hours under a nitrogen atmosphere. The ethanol and water were filtered and washed three times respectively, and the mixture was dried in an oven at 80°C, ground, and sieved to obtain amino acid-(APP@chitosan).

(5) Preparation of cationic hydrophobic microcapsule flame retardant paper: Beat the fiber slurry to 25-40°SR for later use. Use a wet papermaking process, weigh 2-6g of the beaten pulp fiber and disperse it in water to form a slurry with a concentration of 0.2wt.%-0.6wt.%, weigh 20%-50% of amino acid-(APP@chitosan) flame retardant relative to the absolute dry fiber and add it to the dispersed slurry, add a binary retention and filtration aid, pour the mixed slurry into a sheet making machine for forming, pressing, and drying to obtain a cationic hydrophobic microcapsule flame retardant paper.

Preferably, in the preparation of the chitosan prepolymer in step (1), the deacetylation degree of chitosan is greater than 55%.

Preferably, the isocyanate in step (2) is toluene diisocyanate.

Preferably, the solvent in step (2) is one of organic solvents such as ethyl acetate, ethanol, isopropanol, etc.

Preferably, the emulsifier in the above step (3) is selected from one of the emulsifiers such as octylphenol polyoxyethylene ether-10 (OP-10) and Tween-80.

Preferably, the solvent in the preparation of the hydrophobic microcapsule shell layer in step (3) is one of organic solvents such as ethyl acetate, ethanol, isopropanol, etc.

Preferably, in the preparation of the cationic hydrophobic microcapsule shell layer in step (4), the amino acid is one of lysine, histidine and arginine.

Preferably, in the preparation of the cationic hydrophobic microcapsule flame retardant paper in the above step (5), the fiber pulp is various plant fiber pulps, such as one or more of unbleached coniferous wood pulp, bleached coniferous wood pulp, unbleached broadleaf wood pulp, bleached broadleaf wood pulp, straw pulp and the like.

Preferably, in the preparation of the cationic hydrophobic microcapsule flame retardant paper in step (5), the dual retention and drainage system is CPAM/bentonite. The amount of CPAM added is 0.05%-0.2% relative to the absolute dry fiber content, and the amount of bentonite added is 0.1%-0.4% relative to the absolute dry fiber content.

Preferably, in the preparation of the cationic hydrophobic microcapsule flame retardant paper in step (5), the pressing pressure is 0.2-0.4 MPa.

Preferably, in the preparation of the cationic hydrophobic microcapsule flame retardant paper in step (5), the drying temperature is 80-130°C.

Beneficial effects of the present invention: The present invention uses plant fiber as a carrier, forms a chitosan hydrophobic shell layer with cations on the surface of ammonium polyphosphate, and adds the prepared cationic hydrophobic flame retardant to the plant fiber raw material by an in-slurry addition method, and finally prepares flame-retardant paper. The present invention can improve the flame retardant properties of materials using plant fiber as raw material or containing plant fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the effect of coated modified ammonium polyphosphate on water contact angle.

Figure 2 shows the Zeta potential of the coated modified ammonium polyphosphate.

Figure 3 shows the effect of coated modified ammonium polyphosphate on the LOI value of flame retardant paper.

DETAILED DESCRIPTION

The present invention is further described in detail below in conjunction with specific embodiments.

1. The following examples 1 to 3 illustrate the effect of isocyanate coating modification on the hydrophobic effect of ammonium polyphosphate

Embodiment 1:

(1) Disperse 4 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it to prepare a cross-linked prepolymer solution.

(2) 100 g of ammonium polyphosphate was dispersed in 200 ml of ethanol, 1 g of OP-10 was added, and the mixture was reacted at 60° C. for 15 min. The prepared crosslinker prepolymer solution was then added dropwise to the reaction system within 30 min. Finally, the entire reaction system was reacted at 60° C. for 6 hours, and the mixture was filtered and washed with ethanol and water for three times, dried in an oven at 80° C., ground, and sieved to obtain APP@isocyanate.

(3) Test: In this test, the water contact angle of the coated and modified APP was 43.2° and the Zeta potential was -58.4 mv.

Embodiment 2:

(1) Disperse 6 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it to prepare a cross-linked prepolymer solution.

(2) 100 g of ammonium polyphosphate was dispersed in 200 ml of ethanol, 1 g of OP-10 was added, and the mixture was reacted at 60° C. for 15 min. The prepared crosslinker prepolymer solution was then added dropwise to the reaction system within 30 min. Finally, the entire reaction system was reacted at 60° C. for 6 hours, and the mixture was filtered and washed with ethanol and water for three times, dried in an oven at 80° C., ground, and sieved to obtain APP@isocyanate.

(3) Test: In this test, the water contact angle of the coated and modified APP was 63.5° and the Zeta potential was -56.3 mv.

Embodiment 3:

(1) 8 g of isocyanate was dispersed in 30 ml of ethanol and stirred for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(2) 100 g of ammonium polyphosphate was dispersed in 200 ml of ethanol, 1 g of OP-10 was added, and the mixture was reacted at 60° C. for 15 min. The prepared crosslinker prepolymer solution was then added dropwise to the reaction system within 30 min. Finally, the entire reaction system was reacted at 60° C. for 6 hours, and the mixture was filtered and washed with ethanol and water for three times, dried in an oven at 80° C., ground, and sieved to obtain APP@isocyanate.

(3) Test: In this test, the water contact angle of the coated and modified APP was 65.7° and the Zeta potential was -57.5 mv.

Conclusion 1:

Based on Examples 1 to 3, it is concluded that the water contact angle of the ammonium polyphosphate modified by isocyanate coating can reach 65.7°, and the Zeta potential is -56.3 mv, as shown in Figures 1 and 2.

2. The following examples 4 to 7 illustrate the effect of chitosan coating modification on the hydrophobic effect of ammonium polyphosphate and the effect of APP@chitosan flame retardant on the flame retardant effect of flame retardant paper

Embodiment 4:

(1) 2 g of chitosan was dispersed in 100 ml of 1 wt.% acetic acid solution, and stirred at 20° C. for 0.5 hr to prepare a chitosan prepolymer solution.

(2) Disperse 6 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(3) Disperse 100 g of ammonium polyphosphate in 200 ml of ethanol, add 1 g of OP-10, and then add the prepared chitosan prepolymer solution. React at 60° C. for 15 min. Then, drop the prepared crosslinker prepolymer solution into the reaction system within 30 min. Finally, the entire reaction system is reacted at 60° C. for 6 hours. The mixture is filtered and washed with ethanol and water three times, dried in an oven at 80° C., ground, and sieved to obtain APP@chitosan.

(4) Beat the bleached conifer fiber pulp to 30°SR for later use. Use a wet papermaking process, weigh 2g of the beaten fiber and disperse it in water to form a pulp with a concentration of 0.2wt.%, weigh 30% of APP@chitosan flame retardant relative to the absolute dry fiber and add it to the dispersed pulp, add a dual retention and filtration aid, pour the mixed pulp into a sheet making machine for forming, pressing, and drying to obtain chitosan hydrophobic microcapsule flame retardant paper.

(5) Test: In this test, the water contact angle of APP@chitosan was 70.8°, the Zeta potential was -53.3 mv, and the LOI value of chitosan hydrophobic microcapsule flame retardant paper was 26.8%.

Embodiment 5:

(1) 6 g of chitosan was dispersed in 100 ml of 1 wt.% acetic acid solution, and stirred at 20° C. for 0.5 hr to prepare a chitosan prepolymer solution.

(2) Disperse 6 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(3) Disperse 100 g of ammonium polyphosphate in 200 ml of ethanol, add 1 g of OP-10, and then add the prepared chitosan prepolymer solution. React at 60° C. for 15 min. Then, drop the prepared crosslinker prepolymer solution into the reaction system within 30 min. Finally, the entire reaction system is reacted at 60° C. for 6 hours. The mixture is filtered and washed with ethanol and water three times, dried in an oven at 80° C., ground, and sieved to obtain APP@chitosan.

(4) Beat the bleached conifer fiber pulp to 30°SR for later use. Use a wet papermaking process, weigh 2g of the beaten pulp fiber and disperse it in water to form a slurry with a concentration of 0.2wt.%, weigh 30% of APP@chitosan flame retardant relative to the absolute dry fiber and add it to the dispersed slurry, add a dual retention and filtration aid, pour the mixed slurry into a sheet making machine for forming, pressing, and drying to obtain chitosan hydrophobic microcapsule flame retardant paper.

(5) Test: In this test, the water contact angle of APP@chitosan was 91.2°, the Zeta potential was -52.7 mv, and the LOI value of chitosan hydrophobic microcapsule flame retardant paper was 28.4%.

Embodiment 6:

(1) Disperse 10 g of chitosan in 100 ml of 1 wt.% acetic acid solution, and stir the mixture at 20° C. for 0.5 hr to prepare a chitosan prepolymer solution.

(2) Disperse 6 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(3) Disperse 100 g of ammonium polyphosphate in 200 ml of ethanol, add 1 g of OP-10, and then add the prepared chitosan prepolymer solution. React at 60° C. for 15 min. Then, drop the prepared crosslinker prepolymer solution into the reaction system within 30 min. Finally, the entire reaction system is reacted at 60° C. for 6 hours. The mixture is filtered and washed with ethanol and water three times, dried in an oven at 80° C., ground, and sieved to obtain APP@chitosan.

(4) Beat the bleached conifer fiber pulp to 30°SR for later use. Use a wet papermaking process, weigh 2g of the beaten fiber and disperse it in water to form a pulp with a concentration of 0.2wt.%, weigh 30% of APP@chitosan flame retardant relative to the absolute dry fiber and add it to the dispersed pulp, add a dual retention and filtration aid, pour the mixed pulp into a sheet making machine for forming, pressing, and drying to obtain chitosan hydrophobic microcapsule flame retardant paper.

(5) Test: In this test, the water contact angle of APP@chitosan was 91.2°, the Zeta potential was -51.9 mv, and the LOI value of chitosan hydrophobic microcapsule flame retardant paper was 31.4%.

Embodiment 7:

(1) 6 g of chitosan was dispersed in 100 ml of 3 wt.% acetic acid solution, and stirred at 20° C. for 0.5 hr to prepare a chitosan prepolymer solution.

(2) Disperse 6 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(3) Disperse 100 g of ammonium polyphosphate in 200 ml of ethanol, add 1 g of OP-10, and then add the prepared chitosan prepolymer solution. React at 60° C. for 15 min. Then, drop the prepared crosslinker prepolymer solution into the reaction system within 30 min. Finally, the entire reaction system is reacted at 60° C. for 6 hours. The mixture is filtered and washed with ethanol and water three times, dried in an oven at 80° C., ground, and sieved to obtain APP@chitosan.

(4) Beat the bleached conifer fiber pulp to 30°SR for later use. Use a wet papermaking process, weigh 2g of the beaten fiber and disperse it in water to form a pulp with a concentration of 0.2wt.%, weigh 30% of APP@chitosan flame retardant relative to the absolute dry fiber and add it to the dispersed pulp, add a dual retention and filtration aid, pour the mixed pulp into a sheet making machine for forming, pressing, and drying to obtain chitosan hydrophobic microcapsule flame retardant paper.

(5) Test: In this test, the water contact angle of APP@chitosan was 94.6°, the Zeta potential was -51.6 mv, and the LOI value of chitosan hydrophobic microcapsule flame retardant paper was 30.8%. See Figures 1, 2 and 3.

Conclusion 2:

Based on Examples 4 to 7, it was concluded that the water contact angle of APP@chitosan can reach 94.6°, the Zeta potential is -51.6 mv, and the LOI value of chitosan hydrophobic microcapsule flame retardant paper is >30%.

3. Examples 8 to 10 illustrate the effect of cationic coating modification on the hydrophobic effect of ammonium polyphosphate and the effect of lysine-(APP@chitosan) on the flame retardant effect of flame retardant paper.

Embodiment 8:

(1) 6 g of chitosan was dispersed in 100 ml of 3 wt.% acetic acid solution, and stirred at 20° C. for 0.5 hr to prepare a chitosan prepolymer solution.

(2) Disperse 6 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(3) Disperse 100 g of ammonium polyphosphate in 200 ml of ethanol, add 1 g of OP-10, and then add the prepared chitosan prepolymer solution. React at 60° C. for 15 min. Then, drop the prepared crosslinker prepolymer solution into the reaction system within 30 min. Finally, the entire reaction system is reacted at 60° C. for 6 hours. The mixture is filtered and washed with ethanol and water three times, dried in an oven at 80° C., ground, and sieved to obtain APP@chitosan.

(4) 2 g of lysine was dispersed in a mixed solvent of water (10 ml) and ethanol (200 ml), and 8 g of APP@chitosan was added. The mixture was reacted at 60°C for 4 hours under a nitrogen atmosphere. The ethanol and water were filtered and washed three times respectively, and the mixture was dried in an oven at 80°C, ground, and sieved to obtain lysine-(APP@chitosan).

(5) Beat the bleached conifer fiber pulp to 30°SR for later use. Use a wet papermaking process, weigh 2 g of the beaten fiber and disperse it in water to form a pulp with a concentration of 0.2 wt.%, weigh 30% of arginine-(APP@chitosan) flame retardant relative to the absolute dry fiber and add it to the dispersed pulp, add a binary retention and filtration aid, pour the mixed pulp into a sheet making machine for forming, pressing, and drying to obtain a cationic hydrophobic microcapsule flame retardant paper.

(6) Test: In this test, the water contact angle of arginine-(APP@chitosan) was 101.3°, the Zeta potential was -35.8 mv, and the LOI value of the cationic hydrophobic microcapsule flame retardant paper was 32.3%.

Embodiment 9:

(1) 6 g of chitosan was dispersed in 100 ml of 3 wt.% acetic acid solution, and stirred at 20° C. for 0.5 hr to prepare a chitosan prepolymer solution.

(2) Disperse 6 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(3) Disperse 100 g of ammonium polyphosphate in 200 ml of ethanol, add 1 g of OP-10, and then add the prepared chitosan prepolymer solution. React at 60° C. for 15 min. Then, drop the prepared crosslinker prepolymer solution into the reaction system within 30 min. Finally, the entire reaction system is reacted at 60° C. for 6 hours. The mixture is filtered and washed with ethanol and water three times, dried in an oven at 80° C., ground, and sieved to obtain APP@chitosan.

(4) 4 g of lysine was dispersed in a mixed solvent of water (10 ml) and ethanol (200 ml), and 8 g of APP@chitosan was added. The mixture was reacted at 60°C for 4 hours under a nitrogen atmosphere. The ethanol and water were filtered and washed three times respectively, and the mixture was dried in an oven at 80°C, ground, and sieved to obtain lysine-(APP@chitosan).

(5) Beat the bleached conifer fiber pulp to 30°SR for later use. Use a wet papermaking process, weigh 2 g of the beaten fiber and disperse it in water to form a pulp with a concentration of 0.2 wt.%, weigh 30% of arginine-(APP@chitosan) flame retardant relative to the absolute dry fiber and add it to the dispersed pulp, add a binary retention and filtration aid, pour the mixed pulp into a sheet making machine for forming, pressing, and drying to obtain a cationic hydrophobic microcapsule flame retardant paper.

(6) Test: In this test, the water contact angle of arginine-(APP@chitosan) was 103.6°, the Zeta potential was -33.6 mv, and the LOI value of the cationic hydrophobic microcapsule flame retardant paper was 33.1%.

Embodiment 10:

(1) 6 g of chitosan was dispersed in 100 ml of 3 wt.% acetic acid solution, and stirred at 20° C. for 0.5 hr to prepare a chitosan prepolymer solution.

(2) Disperse 6 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(3) Disperse 100 g of ammonium polyphosphate in 200 ml of ethanol, add 1 g of OP-10, and then add the prepared chitosan prepolymer solution. React at 60° C. for 15 min. Then, drop the prepared crosslinker prepolymer solution into the reaction system within 30 min. Finally, the entire reaction system is reacted at 60° C. for 6 hours. The mixture is filtered and washed with ethanol and water three times, dried in an oven at 80° C., ground, and sieved to obtain APP@chitosan.

(4) 6 g of lysine was dispersed in a mixed solvent of water (10 ml) and ethanol (200 ml), and 8 g of APP@chitosan was added. The mixture was reacted at 60°C for 4 hours under a nitrogen atmosphere. The ethanol and water were filtered and washed three times respectively, and the mixture was dried in an oven at 80°C, ground, and sieved to obtain lysine-(APP@chitosan).

(5) Beat the bleached conifer fiber pulp to 30°SR for later use. Use a wet papermaking process, weigh 2 g of the beaten fiber and disperse it in water to form a pulp with a concentration of 0.2 wt.%, weigh 30% of arginine-(APP@chitosan) flame retardant relative to the absolute dry fiber and add it to the dispersed pulp, add a binary retention and filtration aid, pour the mixed pulp into a sheet making machine for forming, pressing, and drying to obtain a cationic hydrophobic microcapsule flame retardant paper.

(6) Test: In this test, the water contact angle of arginine-(APP@chitosan) was 108.2°, the Zeta potential was -30.4 mv, and the LOI value of the cationic hydrophobic microcapsule flame retardant paper was 34.7%.

Conclusion 3:

Based on Examples 8 to 10, it was concluded that the water contact angle of arginine-(APP@chitosan) can reach 108.2°, the Zeta potential is -30.4 mv, and the LOI value of the cationic hydrophobic microcapsule flame retardant paper is >34%.

4. Examples 11 to 13 illustrate the influence of the properties of fiber slurry on the flame retardant effect of flame retardant paper.

Embodiment 11

(1) 6 g of chitosan was dispersed in 100 ml of 3 wt.% acetic acid solution, and stirred at 20° C. for 0.5 hr to prepare a chitosan prepolymer solution.

(2) Disperse 6 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(3) Disperse 100 g of ammonium polyphosphate in 200 ml of ethanol, add 1 g of OP-10, and then add the prepared chitosan prepolymer solution. React at 60° C. for 15 min. Then, drop the prepared crosslinker prepolymer solution into the reaction system within 30 min. Finally, the entire reaction system is reacted at 60° C. for 6 hours. The mixture is filtered and washed with ethanol and water three times, dried in an oven at 80° C., ground, and sieved to obtain APP@chitosan.

(4) 6 g of lysine was dispersed in a mixed solvent of water (10 ml) and ethanol (200 ml), and 8 g of APP@chitosan was added. The mixture was reacted at 60°C for 4 hours under a nitrogen atmosphere. The ethanol and water were filtered and washed three times respectively, and the mixture was dried in an oven at 80°C, ground, and sieved to obtain lysine-(APP@chitosan).

(5) Beat the fiber slurry to 25°SR for later use. Use a wet papermaking process, weigh 2g of the beaten pulp fiber and disperse it in water to form a slurry with a concentration of 0.2wt.%, weigh 30% of amino acid-(APP@chitosan) flame retardant relative to the absolute dry fiber and add it to the dispersed slurry, add a binary retention and filtration aid, pour the mixed slurry into a sheet making machine for forming, pressing, and drying to obtain a cationic hydrophobic microcapsule flame retardant paper.

(6) Test: In this test, the LOI value of the cationic hydrophobic microcapsule flame retardant paper was 33.6%.

Example 12

(1) 6 g of chitosan was dispersed in 100 ml of 3 wt.% acetic acid solution, and stirred at 20° C. for 0.5 hr to prepare a chitosan prepolymer solution.

(2) Disperse 6 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(3) Disperse 100 g of ammonium polyphosphate in 200 ml of ethanol, add 1 g of OP-10, and then add the prepared chitosan prepolymer solution. React at 60° C. for 15 min. Then, drop the prepared crosslinker prepolymer solution into the reaction system within 30 min. Finally, the entire reaction system is reacted at 60° C. for 6 hours. The mixture is filtered and washed with ethanol and water three times, dried in an oven at 80° C., ground, and sieved to obtain APP@chitosan.

(4) 6 g of lysine was dispersed in a mixed solvent of water (10 ml) and ethanol (200 ml), and 8 g of APP@chitosan was added. The mixture was reacted at 60°C for 4 hours under a nitrogen atmosphere. The ethanol and water were filtered and washed three times respectively, and the mixture was dried in an oven at 80°C, ground, and sieved to obtain lysine-(APP@chitosan).

(5) Beat the fiber slurry to 40°SR for later use. Use a wet papermaking process, weigh 2g of the beaten pulp fiber and disperse it in water to form a slurry with a concentration of 0.6wt.%, weigh 30% of amino acid-(APP@chitosan) flame retardant relative to the absolute dry fiber and add it to the dispersed slurry, add a binary retention and filtration aid, pour the mixed slurry into a sheet making machine for forming, pressing, and drying to obtain a cationic hydrophobic microcapsule flame retardant paper.

(6) Test: In this test, the LOI value of the cationic hydrophobic microcapsule flame retardant paper was 35.4%.

Example 13

(1) 6 g of chitosan was dispersed in 100 ml of 3 wt.% acetic acid solution, and stirred at 20° C. for 0.5 hr to prepare a chitosan prepolymer solution.

(2) Disperse 6 g of isocyanate in 30 ml of ethanol and stir for 10 min to fully dissolve it, thereby preparing a cross-linked prepolymer solution.

(3) Disperse 100 g of ammonium polyphosphate in 200 ml of ethanol, add 1 g of OP-10, and then add the prepared chitosan prepolymer solution. React at 60° C. for 15 min. Then, drop the prepared crosslinker prepolymer solution into the reaction system within 30 min. Finally, the entire reaction system is reacted at 60° C. for 6 hours. The mixture is filtered and washed with ethanol and water three times, dried in an oven at 80° C., ground, and sieved to obtain APP@chitosan.

(4) 6 g of lysine was dispersed in a mixed solvent of water (10 ml) and ethanol (200 ml), and 8 g of APP@chitosan was added. The mixture was reacted at 60°C for 4 hours under a nitrogen atmosphere. The ethanol and water were filtered and washed three times respectively, and the mixture was dried in an oven at 80°C, ground, and sieved to obtain lysine-(APP@chitosan).

(5) Beat the fiber slurry to 30°SR for later use. Wet papermaking process was adopted, 4 g of the beaten pulp fiber was weighed and dispersed in water to form a slurry with a concentration of 0.2 wt.%, 30% of amino acid-(APP@chitosan) flame retardant relative to the absolute dry fiber was weighed and added to the dispersed slurry, a binary retention and filtration aid was added, and the mixed slurry was poured into a sheet making machine for forming, pressing, and drying to obtain a cationic hydrophobic microcapsule flame retardant paper.

(6) Test: In this test, the LOI value of the cationic hydrophobic microcapsule flame retardant paper was 38.7%.

Conclusion 4:

Based on Examples 11 to 13, it was found that the LOI of the cationic hydrophobic microcapsule flame retardant paper was greater than 38%, as shown in FIG3 .

Claims (9)

1. A method for preparing cationic hydrophobic microcapsule flame retardant paper, characterized in that the method comprises the following steps: Step 1, preparation of chitosan prepolymer: dispersing 2-10 g of chitosan in 100 ml of 1 wt.%-5 wt.% acetic acid solution, stirring and reacting at 20-40° C. for 0.5-2 hours to prepare a chitosan prepolymer solution; Step 2, preparation of cross-linked prepolymer: 4-8 g of isocyanate is dispersed in 30 ml of solvent, stirred for 10 min to fully dissolve it, and a cross-linked prepolymer solution is prepared; Step 3, preparation of the hydrophobic microcapsule shell layer: disperse 100g of ammonium polyphosphate in 200ml of solvent, add 1g of emulsifier, and mix well; Add the chitosan prepolymer solution prepared in step (1) and react at 60-90° C. for 15 min, then dropwise add the crosslinker prepolymer solution prepared in step (2) into the reaction system within 30 min, and finally react the entire reaction system at 60-90° C. for 4-8 hr, filter and wash with solvent and water for 3 times, dry in an oven at 80° C., grind, and sieve to obtain APP@chitosan; Step 4, preparation of cationic hydrophobic microcapsule shell: 2-6 g of amino acid is dispersed in a mixed solvent of water and ethanol, and then 8 g of APP@chitosan is added; reacted at 60-80° C. for 4-6 hours under a nitrogen atmosphere, ethanol and water are filtered and washed three times respectively, dried in an oven at 80° C., ground, and sieved to obtain amino acid-(APP@chitosan); Step 5, preparation of cationic hydrophobic microcapsule flame retardant paper: beat the fiber slurry to 25-40°SR for use; adopt a wet papermaking process, weigh 2-6g of the beaten pulp fiber and disperse it in water to form a slurry with a concentration of 0.2wt.%-0.6wt.%; weigh 20%-50% of amino acid-(APP@chitosan) flame retardant relative to absolute dry fiber and add it to the dispersed slurry, add a binary retention and filtration aid, pour the mixed slurry into a sheet maker to form, press, and dry to obtain cationic hydrophobic microcapsule flame retardant paper. 2. The method according to claim 1, characterized in that the deacetylation degree of the chitosan is greater than 55%. 3. The method according to claim 1, characterized in that the isocyanate is toluene diisocyanate. 4. The method according to claim 1, wherein the solvent is ethyl acetate, ethanol or isopropanol. 5. The method according to claim 1, characterized in that the emulsifier is octylphenol polyoxyethylene ether-10 (OP-10) or Tween-80. 6. The method according to claim 1, characterized in that the amino acid is one of lysine, histidine and arginine. 7. The method according to claim 1 is characterized in that the fiber pulp is one or more of unbleached coniferous pulp, bleached coniferous pulp, unbleached broadleaf pulp, bleached broadleaf pulp, and straw pulp. 8. The method according to claim 1, characterized in that the dual retention and drainage system is CPAM/bentonite; wherein the amount of CPAM added is 0.05%-0.2% relative to the absolute dry fiber content, and the amount of bentonite added is 0.1%-0.4% relative to the absolute dry fiber content. 9. The method according to claim 1, characterized in that in the preparation of the cationic hydrophobic microcapsule flame retardant paper, the pressing pressure is 0.2-0.4Mpa and the drying temperature is 80-130°C.