Alcohol-based phosphorus-nitrogen-boron intumescent flame retardant as well as preparation method and application thereof

Abstract

The invention discloses an alcohol-based phosphorus-boron-nitrogen intumescent flame retardant as well as a preparation method and application thereof. The preparation method comprises the following specific preparation processes: carrying out reaction on glycerol and phosphoric acid in a reaction container additionally provided with a water segregator at 100-115 DEG C to prepare glycerol triphosphate; the preparation method comprises the following steps: adding boric acid into a glycerol triphosphate reaction container, and reacting at 100-115 DEG C to obtain glycerol triphosphate boric acid ester; and adding urea into a reaction container of glycerol triphosphate boric acid ester, and reacting at 110-135 DEG C to obtain the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant. The limit oxygen index (LOI) of the cotton fabric finished in the flame retardant finishing liquid with the flame retardant concentration of 200g / L can reach 52%, and the flame retardant grade is gt; 42, the flame retardant property is good. The synthesis process is simple, the raw materials are green, environment-friendly, cheap and easily available, the production process is simple, large-scale production can be realized, and secondary pollution is avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cotton fabric flame retardant, and particularly relates to an alcohol-based phosphorus-boron-nitrogen intumescent flame retardant as well as a preparation method and application thereof. BACKGROUND

[0002] Cotton fabric is widely used in various fields due to its air permeability, comfort and flexibility, and is an irreplaceable textile. Since the limiting oxygen index (LOI) of cotton fabric is about 18.1%, it has characteristics such as high heat value, fast heat release rate and fast flame spread speed, and thus has inherent fire hazards, which poses a major risk to personal safety and property safety, and to some extent limits its popularization and application in certain fields. In order to meet the requirements of the current market for the fireproof performance of cotton textiles, flame-retardant finishing of cotton fabric is an important method to improve the flame-retardant performance of cotton fabric. Therefore, it is of great significance to develop efficient and environmentally friendly flame-retardant technology for cotton fabric.

[0003] In view of the flammability of cotton fabric, researchers have developed various flame retardants. For example, halogen flame retardants have the advantages of low addition amount and significant flame-retardant effect, but the disadvantage is that they produce toxic gases during combustion and are limited in use; phosphorus-based flame retardants produce a large amount of smoke during combustion and significantly damage the strength of cotton fabric; boron-based flame retardants have the advantages of environmental protection, non-corrosiveness and smoke suppression performance, but have poor durability; biomass-based flame retardants are environmentally friendly, but have low flame-retardant efficiency, poor washability and high price.

[0004] At present, commercial cotton fabric flame retardants mainly include N-hydroxymethyl phosphoric amide compounds (Pyrovatex CP) and tetrahydroxymethyl phosphonium chloride (THPC) flame retardants and their derivatives. Pyrovatex CP has simple preparation process, low toxicity and good durability, but releases a large amount of formaldehyde when finishing the fabric, and the strength of the fabric is severely damaged. THPC is a good flame retardant for cotton fabric, and has simple preparation process, but generates a large amount of free formaldehyde and carcinogenic substance chloromethyl ether during manufacturing or use, and thus is limited in use and gradually eliminated.

[0005] Therefore, how to realize the halogen-free, formaldehyde-free, environmentally friendly and efficient flame-retardant finishing of cotton fabric has become a current research hotspot. Recently, the flame retardant for cotton fabric mainly focuses on efficient and environmentally friendly flame retardant materials with phosphorus and nitrogen synergistic effect. Starting from the molecular structure design of P-N flame retardant, through the chemical grafting reaction of P-O-C covalent bond with the -OH on the 6-position carbon atom of the glucose ring of cotton fiber, the flame retardant is successfully grafted onto the cotton fabric, further improving the flame retardance and durability of the cotton fabric. According to the literature, esterification of phosphoric acid and polyhydric alcohol is an effective method for preparing new green phosphorus-nitrogen flame retardants. This method not only optimizes the biological polyhydric alcohol compounds to meet the environmental protection requirements, but also uses the active ammonium phosphate group to give the cotton fabric washing resistance. Studies have shown that during the reaction of phosphoric acid and polyhydric alcohol, the esterification efficiency is low, and it is difficult to achieve high-efficiency flame-retardant effect. For example, the esterification efficiency of phosphoric acid reported in the literature “Preparation of phosphorus-nitrogen flame retardant and its performance in cotton fabric” is only 70%, and the flame-retardant effect needs to be further improved.

[0006] In the prior art, the Chinese patent document with the application number 202110311974.1 discloses a phosphorus-nitrogen composite flame retardant, a blended fabric, a preparation method and an application thereof. A nitrogen-phosphorus composite flame retardant is synthesized by using phosphorous acid, phosphoric acid, formaldehyde, diethanolamine and urea as raw materials, and its LOI can reach 40%, which can solve the problem of melt dripping during the burning process of polyester. However, the use of formaldehyde in the raw materials pollutes the environment.

[0007] In the prior art, the Chinese patent document with the application number 202211386163.9 discloses a preparation method, product and application of an alkylamine borate phosphate meglumine flame retardant. A flame retardant is synthesized by using N,N-dimethylformamide, phosphoric acid, boric acid, meglumine, urea and alkylamine as raw materials, which utilizes the hydrophobicity of alkylamine to improve its flame retardance and durability. However, the use of alkylamine reduces the flame-retardant effect.

[0008] In the prior art, the Chinese patent document with the application number 202411846200.9 discloses a fabric flame retardant and a preparation method thereof. Olefin amino triazine comonomer is used to provide nitrogen flame-retardant elements, and olefin sulfonyl propylene diacetamide comonomer provides sulfur and nitrogen elements to achieve synergistic flame retardation. An environmentally friendly flame retardant that can improve the hand feeling of fabric and is free of phosphorus, halogen and formaldehyde is developed. However, the price of olefin amino triazine comonomer raw material is relatively high, and the concentration of flame-retardant liquid is as high as 350 g / L, which leads to relatively high production cost of the flame retardant, and is not conducive to industrialization and application.

[0009] In the prior art, a Chinese patent document with application number 202411215723.3 discloses a preparation method of a phosphorus-nitrogen intumescent flame retardant and a flame-retardant cotton fabric. Erythritol, phosphoric acid and urea are used as raw materials to prepare a phosphorus-nitrogen intumescent flame retardant through esterification reaction. However, erythritol needs to be stored at low temperature and is relatively expensive.

[0010] In order to overcome the defects of poor flame-retardant effect, large amount of smoke and poor durability of the phosphorus-nitrogen flame retardant in the prior art, while avoiding the risk of secondary environmental pollution during synthesis and use, an alcohol-based phosphorus-boron-nitrogen intumescent flame retardant is provided to overcome the above-mentioned defects. SUMMARY

[0011] The technical problem solved by the present application is to provide an alcohol-based phosphorus-boron-nitrogen intumescent flame retardant, a preparation method and application thereof. The method synthesizes the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant from glycerol, phosphoric acid, boric acid and urea. The flame-retardant performance of the cotton fabric after finishing with a cotton fabric finishing liquid with a flame retardant concentration of 50-300 g / L is greatly improved, and the LOI value can reach 52%. The problems of low yield, poor flame-retardant effect and large amount of smoke of the current cotton fabric flame retardant are effectively solved.

[0012] To solve the above technical problems, the present application adopts the following technical solution. An alcohol-based phosphorus-boron-nitrogen intumescent flame retardant has the following structural formula:

[0013]

[0014] The preparation method of the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant has the following specific preparation steps:

[0015] Step S1: reacting glycerol and phosphoric acid in a reaction container equipped with a water trap at 100-115℃ to obtain glycerol triphosphate;

[0016] The reaction container is fixed in an oil bath pot with magnetic stirring and temperature measurement function. The oil bath pot is heated at a heating rate of 3-8℃ / min to 100-115℃ for reaction. The reaction time is 18-20h. During the reaction, part of the hydroxyl groups in the glycerol molecules react with the phosphoric acid to form ester. Since the esterification reaction of glycerol and phosphoric acid is a reversible reaction, the water generated during the reaction will affect the esterification reaction. The water generated during the reaction can be removed by adding a water trap to accelerate the reaction to the forward direction, thereby improving the yield of glycerol triphosphate.

[0017] Step S2: adding boric acid to the reaction container to react with the glycerol triphosphate obtained in step S1 at 100-115℃ to obtain glycerol triphosphate boric acid ester;

[0018] Continue to react at 100-115℃ for 1-4h.

[0019] Step S3, urea is added to the reaction container of glycerol triphosphate borate prepared in step S2, and reaction is carried out at 110-135 DEG C to prepare alcohol-based phosphorus boron nitrogen intumescent flame retardant;

[0020] The oil bath pot is heated and continuously stirred, heated to 110-135 DEG C for reaction, the reaction time is 3-5 h, the pH value of the test reactant is 6-7, and the target product is prepared by stopping the reaction.

[0021] The synthesis route of the alcohol-based phosphorus boron nitrogen intumescent flame retardant is as follows:

[0022]

[0023] Further limited, the molar ratio of the glycerol to the phosphoric acid in step S1 is 1:(1-3); the molar ratio of the glycerol to the boric acid in step S1 is 1:(0.1-0.5).

[0024] Further limited, the molar ratio of the phosphoric acid to the urea in step S1 is 1:(0.5-1).

[0025] An alcohol-based phosphorus boron nitrogen intumescent durable flame-retardant finishing liquid, which is an aqueous solution containing the alcohol-based phosphorus boron nitrogen intumescent flame retardant and the catalyst dicyandiamide, wherein the concentration of the alcohol-based phosphorus boron nitrogen intumescent flame retardant is 50-300 g / L, and the mass percentage concentration of the dicyandiamide is 3wt%-10wt%.

[0026] The application of the alcohol-based phosphorus boron nitrogen intumescent flame retardant or the durable flame-retardant finishing liquid in the durable flame-retardant finishing of cotton fabric, and the specific process is as follows:

[0027] Step S1, a durable flame-retardant finishing liquid, which is an aqueous solution containing the alcohol-based phosphorus boron nitrogen intumescent flame retardant and the catalyst dicyandiamide, is prepared with water as the solvent, wherein the concentration of the alcohol-based phosphorus boron nitrogen intumescent flame retardant is 50-300 g / L, and the mass percentage concentration of the dicyandiamide is 3wt%-10wt%;

[0028] Step S2, the cotton fabric is placed in the durable flame-retardant finishing liquid with a water bath ratio of 20:1, and the cotton fabric is flame-retardant finished by using the padding method, so that the alcohol-based phosphorus boron nitrogen intumescent flame retardant is uniformly attached to the cotton fabric.

[0029] Step S3, the cotton fabric soaked in the durable flame-retardant finishing liquid is placed in a drying oven at 80-90 DEG C for drying for 10-20 min, and then is baked at 160-180 DEG C for 3-5 min, and this process is mainly to realize the chemical grafting reaction between the P-O-C covalent bond and the -OH on the cotton fiber, so that the flame retardant is successfully grafted to the cotton fabric.

[0030] Step S4, the flame-retardant cotton fabric after the baking process is washed, and then dried to obtain a cotton fabric with durable flame retardance.

[0031] Compared with the prior art, the application has the following advantages:

[0032] (1) The alcohol-based phosphorus-boron-nitrogen intumescent flame retardant contains phosphorus-boron-nitrogen elements, and the phosphorus and boron components can promote the dehydration and carbonization process of the cotton fabric, forming a dense carbon layer to isolate heat and oxygen.

[0033] (2) Since the melting point of boric acid is 169℃, boric acid can form a viscous glassy covering layer at high temperature, achieving the effect of isolating oxygen and heat, promoting the formation of a dense carbon layer, and at the same time, decomposing and dehydrating, absorbing heat, and inhibiting the generation of flammable gas, thereby playing a role in reducing temperature and smoke. Therefore, the addition of boron elements not only improves the yield, but also reduces the amount of smoke.

[0034] (3) The preparation process of the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant uses environmentally friendly and low-cost raw materials such as glycerol, phosphoric acid, boric acid, and urea, and the production process is simple, large-scale production, no secondary pollution, and the flame-retardant performance of the finished cotton fabric is good, with an LOI value of 52%, and relatively low total heat release and smoke production.

[0035] (4) The alcohol-based phosphorus-boron-nitrogen intumescent flame retardant provided by the application has good washability, and after 20 washes, the LOI value of the flame-retardant cotton fabric can still reach more than 37%, meeting the requirements of flame-retardant washability. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 IR spectra of different products prepared in Example 1, AGT is glycerol triphosphate ammonium, AGT-B1 is glycerol triphosphate borate ammonium prepared by adding 0.1 mol of boric acid to glycerol triphosphate, and AGT-B2 is glycerol triphosphate borate ammonium prepared by adding 0.2 mol of boric acid to glycerol triphosphate.

[0037] Figure 2 Vertical combustion diagram of cotton fabric after finishing with finishing liquid containing different concentrations of flame retardant prepared in Example 1. DETAILED DESCRIPTION

[0038] The above content of the application will be further described through examples, but this should not be understood as limiting the scope of the above subject matter of the application to the following examples, and any technology implemented based on the above content of the application belongs to the scope of the application.

[0039] Test method: Limiting oxygen index is tested according to GB / T 54541997 Textiles - Determination of burning behavior by oxygen index method, the minimum oxygen concentration value required to maintain combustion is expressed by percentage in oxygen-nitrogen mixed gas flow.

[0040] Cone calorimeter test: the combustion behavior of cotton fabric in real fire is evaluated by cone calorimeter test under the condition of heat radiation flux of 35kW / m 2 according to IOS 5660 standard.

[0041] Washing resistance: the washing resistance of flame-retardant cotton fabric is evaluated by testing the LOI of the flame-retardant cotton fabric after 5 times, 10 times and 20 times of washing under the condition of washing temperature of 30℃ and washing time of 15min using a household drum washing machine.

[0042] Example 1 (selection of the feeding ratio of glycerol and boric acid)

[0043] Step S1: three portions of 0.2mol of glycerol and three portions of 0.6mol of phosphoric acid are mixed in three beakers respectively, and the reactants are mixed uniformly by magnetic stirring for 30min, and then transferred to three three-necked flasks respectively, the three-necked flasks are fixed in an oil bath pot with magnetic stirring and temperature measuring functions, and a water separator is installed, the oil bath pot is heated, the heating rate is 5℃ / min, heated to 110℃ for reaction, and the reaction time is 20h.

[0044] Step S2: 0.05mol and 0.1mol of boric acid are added to two of the three-necked flasks respectively, and the reaction is continued at 110℃ for 3h.

[0045] Step S3: on the basis of step S3, 36.036g (0.3mol) of urea is added to the three three-necked flasks respectively, and the stirring and heating are continued, the heating rate is 5℃ / min, the reaction is carried out at 130℃ for 4h, the pH value of the reactants is 6-7, and the reaction is stopped.

[0046] Step S4: the reactants are purified, washed and dried with ethanol with a volume fraction of 95%, and the white solid obtained after drying at 70℃ is the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant.

[0047] The white solid is tested by infrared spectroscopy (IR) with a detection range of 4000-500cm -1 , a scanning number of 32 times and a resolution of 4cm -1 , and the results are shown in Figure 2 . The white solid is respectively at 3460cm -1 , 1650cm -1 , 1430cm-1 , 1122 cm -1 , 1035 cm -1 A peak appears at 3460 cm -1 and 1650 cm -1 are the stretching vibration of NH 4+ and the bending vibration of N-H, 1430 cm -1 belongs to the absorption peak of C-N, 1122 cm -1 and 1035 cm -1 belong to the absorption peaks of P=O and P-O-C respectively, which indicates that glycerol triphosphate ammonium has been synthesized. After adding boric acid, it is found that the peak at 1430 cm -1 is split into two peaks, which are the characteristic peaks of C-N and B-O-C. It can be seen that boric acid has esterified with glycerol.

[0048] Step S5: A durable flame-retardant finishing solution is prepared by using water as a solvent, which contains the above-mentioned alcohol-based phosphorus-boron-nitrogen intumescent flame retardant and a catalyst dicyandiamide. The concentration of the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant is 200 g / L, and the mass percentage concentration of dicyandiamide is 5 wt%.

[0049] Step S6: The cotton fabric is placed in the durable flame-retardant finishing solution with a water bath ratio of 20:1, and the cotton fabric is flame-retardant finished by using the padding method, so that the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant is uniformly attached to the cotton fabric.

[0050] Step S7: The cotton fabric soaked in the durable flame-retardant finishing solution is placed in a drying oven at 80°C for 10 min, and then is subjected to curing reaction by baking at 170°C for 4 min, so as to prepare the flame-retardant cotton fabric added with flame retardants with different boric acid contents. The flame-retardant cotton fabric is subjected to limiting oxygen index (LOI) and cone calorimeter tests, and the test results are shown in Table 1.

[0051] As can be seen from Table 1, the LOI, THR, TSR and CO2 / CO yield ratio of the flame-retardant cotton fabric without adding boric acid are 47%, 2.01 MJ / m 2 , 48.6 m 2 and 4.51, respectively. With the increase of the content of boric acid, the LOI of the flame-retardant cotton fabric gradually increases, while the total heat release (THR) and the amount of smoke generated (TSR) and the CO2 / CO yield ratio all decrease, which indicates that the flame retardant effect of the flame retardant with boric acid is better. However, when the amount of added boric acid is 0.01 mol, the flame-retardant cotton fabric is a little hard. Further optimization shows that the amount of added boric acid is 0.05 mmol (i.e. the molar ratio of glycerol to boric acid is 2:1), which indicates that the addition of an appropriate amount of boric acid can improve the flame retardancy of glycerol triphosphate ammonium.

[0052] Table 1 Flame retardant technical indicators of flame-retardant cotton fabrics with different boric acid contents

[0053]

[0054] Example 2 (Selection of Flame Retardant Finishing Liquid Concentration)

[0055] Step 1: Using water as a solvent, prepare a durable flame-retardant finishing liquid, which is an aqueous solution containing the above-mentioned alcohol-based phosphorus-boron-nitrogen intumescent flame retardant and the catalyst dicyandiamide, wherein the concentrations of the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant are 100g / L, 200g / L, and 250g / L, respectively, and the mass percentage concentration of dicyandiamide is 5wt%.

[0056] Step 7: Place the cotton fabric in a durable flame retardant finishing solution with a water bath ratio of 20:1, and perform flame retardant finishing on the cotton fabric by padding, so that the alcohol-based phosphorus boron nitrogen intumescent flame retardant is evenly attached to the cotton fabric.

[0057] Step 8: Place the cotton fabric soaked in the durable flame retardant finishing solution in an 80℃ drying oven for 10 min, and then bake it at 170℃ for 4 min to cure the reaction. Prepare flame-retardant cotton fabrics with different concentrations of flame retardant finishing solutions. Perform limiting oxygen index (LOI), cone calorimeter, and vertical burning tests on the flame-retardant cotton fabrics. The results are shown in Table 2 and... Figure 2 As shown.

[0058] Table 2 shows that, under the condition of a flame retardant concentration of 100 g / L, the LOI, THR, TSR, and CO2 / CO yield ratio of flame-retardant cotton fabrics were 38, 2.27 MJ / m³, and 38, 2.27 MJ / m³, respectively. -2 43.5m 2 As the concentration of flame retardant in the finishing solution increases, the LOI of the flame-retardant cotton fabric gradually increases, while the total heat release, smoke release, and CO2 / CO yield ratio all decrease. This indicates that the flame-retardant effect is best when the concentration of flame retardant in the finishing solution is 200 g / L. When the concentration of flame retardant in the finishing solution is 250 g / L, the flame-retardant cotton fabric becomes slightly stiff. Further optimization shows that the prepared cotton fabric exhibits better flame retardancy and softness when the concentration of flame retardant in the finishing solution is 200 g / L.

[0059] Vertical burning test results are as follows Figure 2 As shown, all finished cotton fabrics produced char during vertical burning, with no afterflame or smoldering. The flame-retardant cotton fabric with a flame retardant concentration of 100 g / L had the longest char length, while the char lengths of the flame-retardant cotton fabrics with concentrations of 200 g / L and 250 g / L were approximately equal. This indicates that the char length decreases with increasing flame retardant concentration, and the decrease in char length indicates better flame retardancy.

[0060] Table 2 Technical index of flame retardant cotton fabric prepared by different concentration of flame retardant finishing liquid

[0061]

[0062] Example 3 (washability of flame-retardant cotton fabric)

[0063] The flame-retardant cotton fabric was prepared by treating the flame-retardant finishing liquid with a concentration of 200 g / L of the flame retardant prepared in Example 2.

[0064] Ten pieces of flame-retardant cotton fabric with a size of 50 mm x 150 mm were prepared for testing. To evaluate the washability of the flame-retardant cotton fabric, the flame-retardant cotton fabric was washed 5 times, 10 times, and 20 times in a household drum washing machine at a washing temperature of 30℃ and a washing time of 15 min. The LOI of the washed flame-retardant cotton fabric was tested, and the test results are shown in Table 3.

[0065] As shown in Table 3, the LOI value of the flame-retardant cotton fabric gradually decreased with an increase in the number of washes. This is because some of the -P=O-(O-NH 4+ )2 groups in the flame retardant cross-link and solidify on the cotton fabric, and some of the un-cross-linked portion is washed off, resulting in a decrease in flame retardancy.

[0066] Table 3 Effect of different washing times on the LOI of the flame-retardant cotton fabric

[0067] Flame retardant finishing solution Limiting oxygen index (LOI) (%) 1 time 51 10 times 38 20 times 32

[0068] In summary, the present application synthesizes an alcohol-based phosphorus-boron-nitrogen intumescent flame retardant using glycerol, phosphoric acid, and boric acid and urea as raw materials. By adding an appropriate amount of boric acid, the limiting oxygen index (LOI≥52%) is significantly improved, the length of the coke in vertical combustion is reduced, the total smoke amount and the total heat release amount are reduced, and a practical and feasible preparation scheme is provided for the actual application in the field of textile functional materials technology.

[0069] The above examples describe the basic principles, main features, and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples. The above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application.

Claims

1. An alcohol-based phosphorus-boron-nitrogen intumescent flame retardant, characterized in that... The structural formula of the flame retardant is:

2. A method for preparing the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant according to claim 1, characterized in that... The specific preparation steps are as follows: Step S1: Glycerol and phosphoric acid are reacted in a reaction vessel equipped with a water separator at 100-115°C to obtain glycerol triphosphate. Step S2: Boric acid is added to the reaction vessel in which glycerol triphosphate was obtained in step S1 and reacted at 100-115°C to obtain glycerol triphosphate borate. Step S3: Urea is added to the reaction vessel in which ammonium glycerol triphosphate borate ester was prepared in step S2, and the reaction is carried out at 110-135°C to obtain an alcohol-based phosphorus-boron-nitrogen intumescent flame retardant.

3. The preparation method of the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant according to claim 2, characterized in that... The synthetic route is as follows:

4. The preparation method of the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant according to claim 2, characterized in that: The molar ratio of glycerol to phosphoric acid in step S1 is 1:(1-3); the molar ratio of glycerol to boric acid in step S2 is 1:(0.1-0.5).

5. The preparation method of the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant according to claim 2, characterized in that: The molar ratio of phosphoric acid in step S1 to urea in step S3 is 1:(0.5-1).

6. An alcohol-based phosphorus-boron-nitrogen-expanding durable flame-retardant finishing liquid, characterized in that: The durable flame-retardant finishing liquid is an aqueous solution containing the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant as described in claim 1 and the catalyst dicyandiamide.

7. The alcohol-based phosphorus-boron-nitrogen-expanding durable flame-retardant finishing liquid according to claim 6, characterized in that: The concentration of the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant is 50–300 g / L, and the mass percentage concentration of dicyandiamide is 3 wt%–10 wt%.

8. The application of the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant of claim 1 or the durable flame retardant finishing liquid of claim 6 in the durable flame retardant finishing of cotton fabrics.

9. The application according to claim 8, characterized in that... The specific process is as follows: Step S1: Using water as a solvent, prepare a durable flame retardant finishing liquid, which is an aqueous solution containing the above-mentioned alcohol-based phosphorus-boron-nitrogen intumescent flame retardant and the catalyst dicyandiamide, wherein the concentration of the alcohol-based phosphorus-boron-nitrogen intumescent flame retardant is 50-300 g / L and the mass percentage concentration of dicyandiamide is 3 wt%-10 wt%. Step S2: Place the cotton fabric in a durable flame retardant finishing solution with a water bath ratio of 20:1, and perform flame retardant finishing on the cotton fabric by padding, so that the alcohol-based phosphorus nitrogen boron intumescent flame retardant is evenly attached to the cotton fabric. Step S3: Place the cotton fabric soaked in the durable flame retardant finishing solution in a drying oven at 80-90℃ for 10-20 minutes, and then bake it at 160-180℃ for 3-5 minutes. This process mainly involves chemical grafting of the flame retardant onto the cotton fabric through the chemical grafting reaction between the POC covalent bond and the -OH on the cotton fiber. Step S4: Wash the baked flame-retardant cotton fabric with water and then dry it to obtain a durable flame-retardant cotton fabric.

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