CN109593197B

CN109593197B - N-Si series nano hydrogel flame retardant and preparation and application thereof

Info

Publication number: CN109593197B
Application number: CN201811532742.3A
Authority: CN
Inventors: 吴德群; 李娜; 明景; 李发学; 王学利; 俞建勇; 杨占平; 曹建华; 陈昀; 于涛
Original assignee: Nantong Cellulose Fibers Co Ltd; Donghua University
Current assignee: Nantong Cellulose Fibers Co Ltd; Donghua University
Priority date: 2018-12-14
Filing date: 2018-12-14
Publication date: 2021-01-05
Anticipated expiration: 2038-12-14
Also published as: CN109593197A

Abstract

The invention relates to an N-Si series nano hydrogel flame retardant, and preparation and application thereof, and the N-Si series nano hydrogel flame retardant is shown as a general formula I. Preparation: reacting a polyamino compound II containing one or more benzene rings with a compound III containing primary amine or secondary amine and having a silicon-containing terminal group of a carbon-carbon double bond to obtain the hydrogel. The flame retardant has stable nanoscale morphology, and can realize permanent flame retardance by grafting, layer-by-layer self-assembly and other methods; under the condition of grafting or adding a certain amount of nano-scale flame retardant, the mechanical and mechanical properties of the matrix fiber are less damaged while high-efficiency flame retardance is realized, and the process cost can be effectively reduced.

Description

N-Si series nano hydrogel flame retardant and preparation and application thereof

Technical Field

The invention belongs to the field of flame retardants and preparation and application thereof, and particularly relates to an N-Si series nano hydrogel flame retardant and preparation and application thereof.

Background

Cellulose products are applied to multiple fields, such as textile and clothing, biomedicine, aerospace and the like, due to the excellent properties of reproducibility, wide sources, variability and the like. Cellulose is a highly flammable high polymer material (the decomposition temperature is 210-230 ℃, and the limiting oxygen index value is 18%), and during the combustion process, the flame propagation speed is high, the heat generation is high, the smoke generation is large, and other materials are easily ignited, so that a fire disaster is initiated and spread. This property limits the intensive use of cellulose products in more fields, and thus, the academia has conducted a great deal of research on flame-retardant cellulose.

The flame retardant is an additive capable of effectively preventing materials from burning or inhibiting flame propagation, and the flame retardants used for flame retarding cellulose at home and abroad are numerous at present, and according to element classification, the flame retardants include halogen series, inorganic series, phosphorus series, nitrogen series, silicon series and mixed systems thereof. Among them, the efficiency is better, the halogenated compound with wide use, but because it contains tetrabromobisphenol and decabromodiphenyl ether, produce the poisonous gas which seriously harms human body and environment while burning, so this part of halogen flame retardant has been banned to use at present; the phosphorus flame retardant is the earliest flame retardant substance which can replace halogen, but the phosphorus-containing substance is discharged into the environment to cause eutrophication of water body; the addition amount of inorganic substances is larger, so that the mechanical property of the cellulose is reduced in later processing and use; compared with nitrogen, silicon and the synergistic flame retardant thereof, the flame retardant is more environment-friendly. At present, researchers utilize biological-based raw materials such as milt DNA and casein to synthesize novel flame retardants, but the cost of the flame retardants is high, the carbon residue is low, and the limit oxygen index of modified cellulose materials is difficult to break through 24%. In addition, the Beijing Sailolan flame retardant fiber company Limited uses chemical monomers to synthesize the nitrogen-silicon composite flame retardant, the nitrogen-silicon composite flame retardant is blended with the viscose spinning solution to spin the mixture into filaments, and the synergistic effect of the two elements of nitrogen and silicon is utilized to improve the flame retardant property of the matrix. However, the preparation of the flame-retardant regenerated fiber has the advantages of short process and the defects that the addition amount of the flame retardant is larger, generally about 10-30%, in order to achieve a better flame-retardant effect, the larger addition amount not only reduces the mechanical property of the base material, but also has poor durability and higher cost.

In order to meet the double guidance of practical use significance and industrialized production, the preparation process of the flame-retardant product tends to have short flow, low cost and good effect. The improvement of the flame-retardant effect is the research target of the preparation of the flame-retardant cellulose at present, so that researchers can reduce the damage of the mechanical hand performance by reducing the addition amount of the flame retardant by adopting a physical grinding method to carry out nano-sizing on the flame retardant. However, the preparation method of the nano flame retardant has higher requirements on the selection of raw materials and the subsequent synthesis process, so that the flame-retardant nano gel with controllable particle size, which meets the requirements of green and environment-friendly materials, is necessary and feasible to provide.

Disclosure of Invention

The invention aims to solve the technical problem of providing an N-Si series nano hydrogel flame retardant and preparation and application thereof. The method can form a stable cross-linked reticular structure protective layer in the combustion process, improve the flame retardant property of the fiber, and overcome the damage of the matrix mechanical property caused by the higher addition amount of the flame retardant in the prior art.

The invention relates to N-Si series nano hydrogel as shown in a general formula I,

wherein R is₁Is hydroxy or indole ring; r₂Is methyl, amino, R₄:

R₅:

1≤m≤7，1≤n≤7；1≤y≤7，1≤z≤7。

The nitrogen content of the nano hydrogel is 3.0-15.0%, and the silicon content of the nano hydrogel is 4.0-18.0%.

The particle size of the nano hydrogel is 100 nm-900 nm.

The invention discloses a preparation method of N-Si series nano hydrogel, which comprises the following steps:

(1) carrying out esterification reaction on a nitrogen source and polyhydric alcohol to synthesize a polyamino compound II containing one or more benzene rings; wherein the nitrogen source is amino acid;

(2) reacting a silicon source with a double-bond active compound to prepare a compound III containing primary amine or secondary amine and having a silicon-containing terminal group of a carbon-carbon double bond; wherein the silicon source is siloxane;

(3) and carrying out Michael addition reaction on the compound II and the compound III to obtain the N-Si series nano hydrogel.

The preferred mode of the above preparation method is as follows:

preferably, the amino acid in the step (1) is a natural amino acid containing a benzene ring or an unnatural amino acid containing an aromatic ring; the polyalcohol is one or more of trimethylolethane, tris (hydroxymethyl) aminomethane and pentaerythritol;

p-methylbenzenesulfonic acid is added in the step (1), so that amino in a reaction system can be protected, and the p-methylbenzenesulfonic acid is also a catalyst for the esterification reaction.

More preferably, the amino acid in step (1) is a natural amino acid containing a benzene ring such as leucine, phenylalanine, tryptophan, or the like, or may be an unnatural amino acid containing an aromatic ring.

The esterification reaction in the step (1) is specifically as follows: putting amino acid, polyalcohol and p-toluenesulfonic acid into an organic solvent, and stirring and reacting for 20-24 hours at 70-125 ℃; wherein the feeding molar ratio of the polyhydric alcohol to the amino acid to the p-toluenesulfonic acid is 1: 3-4: 4 to 6.

Preferably, the stirring reaction rate in the step (1) is 150-220 rpm.

Preferably, the organic solvent in the step (1) is benzene, toluene, 1, 2-dinitrobenzene, butyl acetate.

After the esterification reaction in the step (1), the purification specifically comprises the following steps: the product is separated out at the temperature of minus 15 ℃ to 0 ℃, dried at the temperature of 60 ℃ in vacuum to obtain a white powdery product (II), and sealed and stored at normal temperature.

In the step (2), the siloxane and the double bond active compound are put into a solvent at a molar ratio of 1: 2-6, and react for 18-24 hours at-70 ℃ to-10 ℃ under the condition of a catalyst.

Preferably, the siloxane in the step (2) is a linear or multi-arm siloxane containing amino at the chain end; the double-bond active compound is one of methacryloyl chloride, methacrylic anhydride, allyl methacrylate and ethylene glycol dimethacrylate; adding a catalyst in the step (2), specifically: triethylamine, 4-dimethylaminopyridine DMAP, N, N-diisopropylethylamine DIEA, N, N-diethylethylamine ET₃N, one or more of pyridine.

Preferably, in the step (2), the solvent is one of tetrahydrofuran, dichloromethane, DMF and DMAC, and the molar ratio of siloxane to catalyst is determined according to the number of terminal groups of the specific reaction-involved multi-arm siloxane, for example, the molar ratio of linear siloxane having amino groups at both ends, such as 1, 3-bis (3-aminomethyl) -1,1,3, 3-tetramethyldisiloxane, 1, 3-bis (3-aminoethyl) -1,1,3, 3-tetramethyldisiloxane or 1, 3-bis (3-aminopropyl) -1,1,3, 3-tetramethyldisiloxane, to the catalyst is 1: 6-8.

More preferably, the siloxane is a linear or multiarm siloxane having an amino group at the end of its chain, such as 1, 3-bis (3-aminomethyl) -1,1,3, 3-tetramethyldisiloxane, 1, 3-bis (3-aminoethyl) -1,1,3, 3-tetramethyldisiloxane, or 1, 3-bis (3-aminopropyl) -1,1,3, 3-tetramethyldisiloxane.

And (3) after the reaction in the step (2) is finished, purifying, adding the reactant into a sodium bicarbonate solution, stirring, extracting, and performing rotary evaporation to obtain a light yellow oily compound (III), and sealing, storing at normal temperature and keeping out of the sun.

The compounds of general formulas II and III in the step (3):

wherein R is₁Is hydroxy or indole ring; r₂Is methyl or amino; r₃:

R₄:

R₅:

1≤m≤7，1≤n≤7；1≤x≤3，1≤y≤7，1≤z≤7。

Preferably, a removal agent is used: such as anhydrous triethylamine, DMAP, DIEA, ET₃And N, removing the protection of the p-toluenesulfonic acid on amino in the compound II by one or more of pyridine, wherein the molar ratio of the p-toluenesulfonic acid to the removing agent is 1: 8 to 10.

Preferably, the step (3) utilizes the feeding ratio of the product II and the product III, which is determined according to the double-arm or multi-arm structure of the product III, for example, the molar ratio of the product II to the linear siloxane containing double bonds at both ends is 1: 3-6, taking deionized water as a solvent, introducing nitrogen for 1h in an alkaline environment, reacting for 10-15h at 40-60 ℃ in a dark place, stirring, centrifuging, rinsing and drying to obtain the N-Si flame-retardant nanogel. (reaction of product II with Multi-arm product III, the feed ratio is increased according to the number of the Multi-arms and the linear ratio, and the other conditions are the same as the linear ratio)

Preferably, the alkaline environment in step (3) is: dropwise adding one or more of triethylamine, an ammonia monohydrate solution or a sodium hydroxide and potassium hydroxide solution with the pH value of 8-9 to prepare an alkaline environment with the pH value of 8-9; stirring is as follows: the rotating speed is 500-2000 rpm; the centrifugal speed is 4000-8000 rpm.

The N-Si series nano hydrogel is applied to natural fibers and regenerated cellulose fibers as a flame retardant nano hydrogel.

Advantageous effects

(1) Amino acid and straight-chain or multi-arm siloxane are introduced to prepare the halogen-free phosphorus-free, efficient and environment-friendly nitrogen-silicon flame retardant;

(2) the invention provides a flame-retardant gel with controllable particle size (particle size is regulated and controlled by adjusting the rotating speed of mechanical stirring in the reaction process), strong stability (the nano hydrogel is a synthetic gel prepared by a chemical crosslinking method, can keep a certain shape compared with physical gel and natural gel, has better stability and mechanical property), and has nano-scale, and the particle size is 100 nm-900 nm;

(3) the nanogel flame retardant breaks through the limitation of the nano-scale flame retardant prepared by a grinding method on the selection of raw materials, shortens the preparation process of the flame retardant, and can be combined by any one or more processes according to the characteristics of a base material in subsequent application to realize efficient flame-retardant modification of the base material.

(4) The flame-retardant nanogel of the invention can generate N when being combusted₂，NH₃The incombustible gas takes away a large amount of heat, delays and slows down the degradation of the matrix material, and realizes solid-phase flame retardance; meanwhile, when the flame-retardant nanogel is burnt, silicon elements migrate to the surface of a substrate to generate a cross-linked network structure of groups such as Si-O-Si, Si-C and the like, so that the combination of combustible gas and oxygen is isolated, the continuous proceeding of a combustion circulating structure is hindered, and isolated flame retardance is realized; multiple flame-retardant modes are cooperatively carried out, so that the high efficiency of the nano hydrogel flame retardant is realized;

(5) the nanogel flame retardant provided by the invention is applied to natural fibers and regenerated cellulose fibers, and because the flame retardant has a stable nanoscale form, permanent flame-retardant fibers can be realized by grafting, layer-by-layer self-assembly and other methods; the nano-scale flame retardant can realize efficient flame retardance and simultaneously has small damage to the mechanical property of matrix fibers under the condition of grafting or adding a certain amount of flame retardant, and because the flame retardant prepared by the method is nano hydrogel and has small scale, the nano-scale flame retardant can not generate large damage to the mechanical property and the hand feeling characteristic of a matrix material when the flame retardant is combined with the matrix, and the process cost is effectively reduced.

Drawings

FIG. 1 is a synthetic reaction formula of a nano hydrogel flame retardant of the invention;

FIG. 2 is an infrared spectrum of the flame-retardant nanogel of example 1;

FIG. 3 is an electron micrograph of 400nm diameter flame retardant nanogel particles (example 3).

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Example 1

(1) Weighing 0.025mol of 4.53g of leucine and 0.025mol of 3.00g of trimethylolethane, dissolving in 500mL of toluene, adding 0.125mol (23.75g) of p-toluenesulfonic acid for amino protection, reacting in a single-layer glass reaction kettle, mechanically stirring, heating to 120 ℃ in an oil bath kettle, reacting for 20 hours, dissolving a reactant with isopropanol, then precipitating at low temperature, and drying in vacuum at 50 ℃ for 12 hours to obtain an intermediate product (II) which is white powder.

(2) Weighing 2.48g of 1, 3-bis (3-aminopropyl) -1,1,3, 3-tetramethyldisiloxane in 0.01mol, dissolving in 15mL of tetrahydrofuran, weighing 7.08g of triethylamine in 0.07mol, and putting into a three-neck flask; weighing 3.14g of 0.03mol of methacryloyl chloride, putting the methacryloyl chloride into a 50mL constant-pressure separating funnel, slowly dripping the methacryloyl chloride into a three-neck flask within 1 hour, magnetically stirring, cooling to-20 ℃ in an ice bath kettle, reacting for 18 hours, adding a reactant into a sodium bicarbonate solution, stirring, extracting, and performing rotary evaporation to obtain an intermediate product (III) which is a yellow oily substance.

(3) Weighing 1.735g of 0.0025mol of intermediate product (II), dissolving in 5mL of water, adding 1.52g of triethylamine 0.015mol to remove p-toluenesulfonic acid, weighing 1.86g (1mL) of 0.01mol of intermediate product (III), dissolving in water, reacting for 30h at normal temperature, dropwise adding 1mL of sodium hydroxide solution with pH of 8, mechanically stirring, controlling the rotation speed at 500rpm, centrifuging again, controlling the rotation speed at 4000rpm, rinsing, and drying to obtain 900nm white flame-retardant nanogel, wherein the infrared spectrum of the nanogel is shown in FIG. 2, and specifically: 3100-3200 cm^-1(-CH₃),1725～1700cm^-1(C＝O)，1348cm^-1(C-N),1100～1270cm^-1(C-O-C),1080cm^-1(Si-O-Si),798cm^-1(Si-CH₃)。

And fully mixing the flame-retardant nanogel with a regenerated cellulose solution, wherein the addition amount of the flame retardant is 5-15% of the mass of the regenerated cellulose, and performing wet spinning to obtain the flame-retardant regenerated cellulose fiber. The amount of carbon residue and Limiting Oxygen Index (LOI) of the flame retardant added to the base material were measured using the roll method and strand method samples, and the results are shown in Table 1: the addition amount of the flame-retardant nanogel is 5-15%, the residual carbon content of the fiber is increased from 25.1% to 40.5% along with the increase of the addition amount, the limited oxygen index is increased from 24% to 28%, and the flame-retardant effect is obvious. In addition, the tensile breaking strength of the flame-retardant fiber is reduced from 2.56-3.56 cN/dtex to 2.46-3.15 cN/dtex.

TABLE 1

Example 2

(1) 0.025mol of 4.13g of phenylalanine and 3.00g of 0.025mol of trimethylolethane were weighed out and dissolved in 500mL of tetrahydrofuran at a reaction temperature of 70 ℃ under the same other reaction conditions as in example I to obtain an intermediate (II) in the form of a milky white powder.

(2) 0.01mol of 1, 3-bis (3-aminopropyl) -1,1,3, 3-tetramethyldisiloxane (2.48 g), 0.07mol of triethylamine (7.08 g) and 0.03mol of methacryloyl chloride (3.14 g) were weighed out and dissolved in 20mL of dichloromethane under the same reaction conditions as in example I to obtain intermediate (III) as a yellow oily substance.

(3) Weighing 2.52g of 0.0025mol of intermediate product (II) and 3.24g of 0.01mol of intermediate product (III), controlling the rotating speed to be 1000rpm, and obtaining white flame-retardant nanogel with the particle size of about 600nm under the same other conditions as in example I. Infrared spectral data of the gel: 2950-3050 cm^-1(-CH₃),1725～1700cm^-1(C＝O)，1100～1270cm^-1(C-O-C),1050cm^-1(Si-O-Si),830cm^-1(Si-CH₃)。

And fully mixing the flame-retardant nanogel with a regenerated cellulose solution, wherein the addition amount of the flame retardant is 5-15% of the mass of the regenerated cellulose, and performing wet spinning to obtain the flame-retardant regenerated cellulose fiber. The amount of carbon residue and Limiting Oxygen Index (LOI) of the flame retardant added to the base material were measured using the roll method and strand method samples, and the results are shown in Table 2: the addition amount of the flame-retardant nanogel is 5-15%, the residual carbon content of the fiber is increased from 23.6% to 39.5% along with the increase of the addition amount, the limited oxygen index is increased from 23% to 28%, and the flame-retardant effect is obvious. In addition, the tensile breaking strength of the flame-retardant fiber is reduced from 2.56-3.56 cN/dtex to 2.35-3.03 cN/dtex.

TABLE 2

Example 3

(1) 0.075mol of phenylalanine 12.38g and 0.025mol of tris (hydroxymethyl) aminomethane 3.03g were weighed out and dissolved in 500mL of tetrahydrofuran under the same reaction conditions as in example I to give intermediate (II) as a white powder.

(2) 0.0025mol of 3.25g of the product (II), 0.04mol of 12.96g of the intermediate product (III) prepared in example II and 0.02mol of 2.03g of triethylamine are weighed and added into a three-neck flask; and dropwise adding a sodium hydroxide solution with the pH of 9 to obtain an alkaline environment with the pH of 8, controlling the rotating speed to be 1500rpm, and obtaining the white flame-retardant nanogel with the particle size of about 400nm under the same conditions as in example 1. Infrared spectrum data: 2950-3050 cm^-1(-CH₃),1725～1700cm^-1(C＝O)，1100～1270cm^-1(C-O-C),1050cm^-1(Si-O-Si),830cm^-1(Si-CH₃)。

And fully mixing the flame-retardant nanogel with a regenerated cellulose solution, wherein the addition amount of the flame retardant is 5-15% of the mass of the regenerated cellulose, and performing wet spinning to obtain the flame-retardant regenerated cellulose fiber. The amount of carbon residue and Limiting Oxygen Index (LOI) of the flame retardant added to the base material were measured using the roll method and strand method samples, and the results are shown in Table 3: the addition amount of the flame-retardant nanogel is 5-15%, the residual carbon content of the fiber is increased from 25.0% to 43.5% along with the increase of the addition amount, the limited oxygen index is increased from 24% to 29%, and the flame-retardant effect is obvious. In addition, the tensile breaking strength of the flame-retardant fiber is reduced from 2.56-3.56 cN/dtex to 2.65-3.34 cN/dtex.

TABLE 3

Example 4

(1) 0.075mol of phenylalanine 12.38g and 0.025mol of tris (hydroxymethyl) aminomethane 3.03g were weighed out and dissolved in 500mL of toluene under the same reaction conditions as in example I, giving intermediate (II) as a white powder.

(2) 1, 3-bis (3-aminopropyl) -1,1,3, 3-tetramethyldisiloxane (0.01 mol) was weighed out and dissolved in 20mL of dichloromethane, and methacrylic anhydride (4.62 g) was weighed out (0.03 mol) and cooled to 0 ℃ in an ice bath kettle under the same reaction conditions as in example I to obtain intermediate (III) as a yellow oily substance.

(3) Weighing 2.52g of 0.0025mol of intermediate product (II) and 3.24g of 0.01mol of intermediate product (III), controlling the rotating speed to be 1500rpm, and obtaining white flame-retardant nanogel with the particle size of about 400nm under the same other conditions as in example I. Infrared spectrum data: 2950-3050 cm^-1(-CH₃),1725～1700cm^-1(C＝O)，1100～1270cm^-1(C-O-C),1050cm^-1(Si-O-Si),830cm^-1(Si-CH₃)。

And fully mixing the flame-retardant nanogel with a regenerated cellulose solution, wherein the addition amount of the flame retardant is 5-15% of the mass of the regenerated cellulose, and performing wet spinning to obtain the flame-retardant regenerated cellulose fiber. The amount of carbon residue and Limiting Oxygen Index (LOI) of the flame retardant added to the base material were measured using the roll method and strand method samples, and the results are shown in Table 4: the addition amount of the flame-retardant nanogel is 5-15%, the residual carbon content of the fiber is increased from 25.0% to 41.5% along with the increase of the addition amount, the limiting oxygen index is increased from 24% to 29%, and the flame-retardant effect is obvious. In addition, the tensile breaking strength of the flame-retardant fiber is reduced from 2.56-3.56 cN/dtex to 2.65-3.27 cN/dtex.

TABLE 4

Example 5

(2) Weighing 2.48g of 1, 3-bis (3-aminopropyl) -1,1,3, 3-tetramethyldisiloxane in 0.01mol, dissolving in 30mL of dichloromethane, weighing 8.09g of triethylamine in 0.08mol, and putting into a three-neck flask; weighing 6.24g of 0.06mol of methacryloyl chloride, putting the methacryloyl chloride into a 50mL constant-pressure separating funnel, slowly dripping the methacryloyl chloride into a three-neck flask within 1 hour, magnetically stirring, cooling to-20 ℃ in an ice bath kettle, and obtaining an intermediate product (III) which is yellow oily substance under the same other reaction conditions as in the example I.

(3) Weighing 3.25g of 0.0025mol of the intermediate product (II), dissolving in 5mL of deionized water, and adding 2.25g of 0.02mol of triethylamine to remove p-toluenesulfonic acid; 0.0075mol of intermediate (III) 2.43g was weighed into the reaction system, and the reaction conditions were the same as in example I, to obtain 900 nm-sized white flame-retardant nanogel. Infrared spectrum data: 2950-3050 cm^-1(-CH₃),1725～1700cm^-1(C＝O)，1100～1270cm^-1(C-O-C),1050cm^-1(Si-O-Si),830cm^-1(Si-CH₃)。

And fully mixing the flame-retardant nanogel with a regenerated cellulose solution, wherein the addition amount of the flame retardant is 5-15% of the mass of the regenerated cellulose, and performing wet spinning to obtain the flame-retardant regenerated cellulose fiber. The amount of carbon residue and Limiting Oxygen Index (LOI) of the flame retardant added to the base material were measured using the roll method and strand method samples, and the results are shown in Table 5: the addition amount of the flame-retardant nanogel is 5-15%, the residual carbon content of the fiber is increased from 24.8% to 41.3% along with the increase of the addition amount, the limiting oxygen index is increased from 24% to 29%, and the flame-retardant effect is obvious. In addition, the tensile breaking strength of the flame-retardant fiber is reduced from 2.56-3.56 cN/dtex to 2.53-3.01 cN/dtex.

TABLE 5

Example 6

(3) Weighing 3.25g of 0.0025mol of the intermediate product (II), dissolving in 5mL of deionized water, and adding 2.25g of 0.02mol of triethylamine to remove p-toluenesulfonic acid; 0.0075mol of intermediate product (III) 2.43g is weighed and added into the reaction system, and 70mg of ammonium persulfate is added to initiate crosslinking reaction, so that white flame-retardant gel with irregular shape is obtained. Infrared spectrum data: 2950-3050 cm^-1(-CH₃),1725～1700cm^-1(C＝O)，1100～1270cm^-1(C-O-C),1050cm^-1(Si-O-Si),830cm^-1(Si-CH₃)。

And freeze-drying and grinding the flame-retardant gel, and then fully mixing the flame-retardant gel with a regenerated cellulose solution, wherein the addition amount of the flame retardant is 5-15% of the mass of the regenerated cellulose, and performing wet spinning to obtain the flame-retardant regenerated cellulose fiber. The amount of carbon residue and Limiting Oxygen Index (LOI) of the flame retardant added to the base material were measured using the roll method and strand method samples, and as shown in table 6, the results were: the addition amount of the flame-retardant nanogel is 5-15%, the residual carbon content of the fiber is increased from 22.5% to 30.3% along with the increase of the addition amount, the limited oxygen index is increased from 23% to 25%, and the flame-retardant effect is obvious. In addition, the tensile breaking strength of the flame-retardant fiber is reduced from 2.56-3.56 cN/dtex to 1.86-2.35 cN/dtex.

TABLE 6

Claims

1. An N-Si series nano hydrogel as shown in a general formula I,

（Ⅰ），

wherein R is₁Is hydroxy or indole ring; r₂Is methyl, amino, R₄:

；R₅:

，1≤m≤7，1≤n≤7； 1≤y≤7，1≤z≤7。

2. The nano hydrogel according to claim 1, wherein the nano hydrogel contains 3.0% to 15.0% by mass of nitrogen and 4.0% to 18.0% by mass of silicon.

3. The nano hydrogel according to claim 1, wherein the nano hydrogel has a particle size of 100nm to 900 nm.

4. A preparation method of N-Si series nano hydrogel comprises the following steps:

(1) carrying out esterification reaction on a nitrogen source and polyhydric alcohol to synthesize a polyamino compound II; wherein the nitrogen source is amino acid;

(3) carrying out Michael addition reaction on the compound II and the compound III to obtain N-Si series nano hydrogel; wherein

Compounds of general formulae ii, iii:

(II) and

（Ⅲ）；

wherein R is₁Is hydroxy or indole ring; r₂Is methyl or amino; r₃:

；R₄:

；R₅:

；1≤m≤7，1≤n≤7；1≤x≤3，1≤y≤7，1≤z≤7。

5. The production method according to claim 4, wherein the amino acid in the step (1) is a natural amino acid containing a benzene ring or an unnatural amino acid containing an aromatic ring; adding p-methylbenzene sulfonic acid in the step (1).

6. The preparation method according to claim 4, wherein the esterification reaction in the step (1) is specifically: putting amino acid, polyalcohol and p-toluenesulfonic acid into an organic solvent, and stirring and reacting for 20-24 hours at 70-125 ℃; wherein the feeding molar ratio of the polyhydric alcohol to the amino acid to the p-toluenesulfonic acid is 1: 3-4: 4 to 6.

7. The preparation method according to claim 4, characterized in that the molar ratio of the siloxane to the double-bond active compound in the step (2) is 1: 2-6, and the reaction is carried out for 18-24 h at-70 ℃ to-10 ℃ under the condition of a catalyst.

8. The preparation method according to claim 4, wherein a catalyst is added in the step (2), and specifically comprises: one or more of triethylamine, 4-dimethylaminopyridine DMAP, N, N-diisopropylethylamine DIEA and pyridine.

9. Use of the N-Si based nanohydrogel of claim 1 in the preparation of flame retardant fibers.