Preparation method of single-layer assembled flame-retardant cotton fabric

Abstract

The invention provides a preparation method of a single-layer assembled flame-retardant cotton fabric, which comprises the following steps: dipping a cotton fabric in a polyacrylic acid solution, and drying; and impregnating the cotton fabric with a composite solution of polyethyleneimine and ammonium polyphosphate, or sequentially impregnating the cotton fabric with a polyethyleneimine solution and an ammonium polyphosphate solution, and drying to obtain the single-layer assembled flame-retardant cotton fabric. According to the invention, a technical method of assembling a single-layer flame-retardant coating is adopted, a high-difficulty process is avoided, the finishing condition is milder, an initiator and other assistants do not need to be added, the effects of few assembly layers and good flame-retardant property are realized, and the technical problem that a layer-by-layer self-assembly technology at the present stage needs multi-layer repeated deposition is solved; the limit oxygen index of the prepared flame-retardant cotton fabric can reach up to 39.8%, and the flame-retardant cotton fabric does not catch fire when encountering an external fire source.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant finishing of textiles, and in particular relates to a preparation method of a single-layer assembled flame retardant cotton fabric. Background Art

[0002] Cotton fiber is one of the most commonly used natural fibers. Cotton fabrics woven from cotton fiber have the advantages of soft hand feel and strong hygroscopicity. They are widely used for their excellent wearing properties. However, due to the flammability of cotton fabrics, they are easy to burn and cause fires during use, threatening people's lives and property safety. Therefore, the preparation of flame-retardant cotton fabrics has important practical application value. There are many finishing methods for preparing flame-retardant cotton fabrics. Layer-by-layer self-assembly has gradually been widely used by many scholars as a finishing method for flame-retardant cotton fabrics. The layer-by-layer self-assembly method is to superimpose the flame retardant on the surface of the cotton fabric through the action of electrostatic adsorption force. This method is simple and easy to operate and does not require complicated processing.

[0003] However, the layer-by-layer self-assembly technology also has certain disadvantages. Most flame retardants require multi-layer deposition to make cotton fabrics have good flame retardant properties. The number of multi-layer deposition steps limits the layer-by-layer self-assembly technology in practical applications. At the same time, since the layer-by-layer self-assembly method relies on the effect of electrostatic adsorption to make multiple layers of solution adsorb each other and show good flame retardant properties when superimposed on the surface of cotton fabric, this technology has high restrictions on the acidity and alkalinity of the solution, which increases the difficulty of implementation. Developing a simpler and less-layered flame retardant coating is an important research direction at present.

[0004] CN117488551A provides a controllable preparation method of a nano-composite flame-retardant coating based on silicon-containing inorganic particles. Silicon-containing inorganic particles, polyethyleneimine (PEI) and phytic acid (PA) flame retardant are assembled layer by layer on the surface of cotton fabric by a layer-by-layer assembly method, wherein the silicon-containing inorganic particles can be silicon dioxide (SiO2), attapulgite (ATTA) or montmorillonite (MMT). By adjusting the preparation process conditions, the cotton fabric has good flame retardant properties after assembling multiple layers. The preparation process of the invention is relatively complicated, and the limiting oxygen index after the flame retardant coating is only 24.8% at most.

[0005] CN103266468A provides a method for flame retardant finishing of pure cotton fabric with an intumescent flame retardant system, wherein montmorillonite and an organic amine are stirred to form a dispersion, fatty acid is added to the dispersion, and a catalyst is added to obtain a montmorillonite nanocomposite material, on this basis, an emulsifier and acetic acid are added to obtain a montmorillonite nanocomposite material emulsion, and then a resin cross-linking agent and ammonium polyphosphate are added to finally obtain a flame retardant finishing liquid, and the flame retardant cotton fabric is prepared by the method of impregnation, pre-baking and baking. The invention has high requirements on the preparation process conditions and has more impregnation steps. The carbon damaged in the vertical burning test of the prepared flame retardant cotton fabric is as long as 9.6 cm.

[0006] CN109944070B provides a self-extinguishing flame-retardant cotton fabric and its preparation method and application. Silane coupling agent, sodium alginate and ammonium polyphosphate are used as flame-retardant spray liquids. 5 to 20 flame-retardant unit layers are deposited on the surface of the cotton fabric. The flame-retardant unit layers are four layers of silane coupling agent / sodium alginate / silane coupling agent / ammonium polyphosphate or four layers of silane coupling agent / ammonium polyphosphate / silane coupling agent / sodium alginate. Finally, flame-retardant cotton fabric is prepared. The invention uses a layer-by-layer self-assembly method, which requires depositing 5 to 20 flame-retardant unit layers on the surface of the cotton fabric to achieve the self-extinguishing effect of the fabric. The number of impregnation layers is large and the process is complicated.

[0007] The existing flame retardant finishing methods for cotton fabrics mentioned above have complicated procedures, and the flame retardant finishing methods using layer-by-layer self-assembly technology require the assembly of a large number of layers to achieve an ideal flame retardant effect. Summary of the invention

[0008]

Technical issues

[0009] The current flame retardant finishing methods for cotton fabrics are complicated and cumbersome. Among them, the flame retardant finishing method using layer-by-layer self-assembly technology requires the assembly of a large number of layers to achieve the ideal flame retardant effect.

[0010]

Technical solution

[0011] In response to the above technical problems, the present invention provides a preparation method for assembling a single-layer flame-retardant coating on the surface of a cotton fabric. The present invention adopts a mixed solution of a high molecular polymer and an inorganic phosphate as a single-layer flame-retardant solution. The assembly process is simple, efficient, green and environmentally friendly. The single-layer assembly can make the cotton fabric have good flame retardant properties.

[0012] The first object of the present invention is to provide a method for preparing a single-layer assembled flame-retardant cotton fabric, comprising the steps of:

[0013] (1) Acid treatment of cotton fabric: impregnate cotton fabric with polyacrylic acid solution and dry;

[0014] (2) Preparation of flame-retardant cotton fabric: treating the cotton fabric prepared in step (1) with polyethyleneimine and ammonium polyphosphate, and drying to obtain a single-layer assembled flame-retardant cotton fabric.

[0015] In one embodiment of the present invention, in step (1), the concentration of the polyacrylic acid solution is 0.5-2 wt %.

[0016] In one embodiment of the present invention, in step (1), the concentration of the polyacrylic acid solution is preferably 1 wt %.

[0017] In one embodiment of the present invention, in step (1), the immersion temperature is 15 to 35° C., and the immersion time is 5 to 15 minutes.

[0018] In one embodiment of the present invention, in step (1), the drying temperature is 60-70°C.

[0019] In one embodiment of the present invention, in step (2), the method for treating the cotton fabric prepared in step (1) with polyethyleneimine and ammonium polyphosphate is: impregnating the cotton fabric prepared in step (1) with a composite solution of polyethyleneimine and ammonium polyphosphate; or first impregnating the cotton fabric prepared in step (1) with a polyethyleneimine solution, drying it, and then impregnating it with an ammonium polyphosphate solution.

[0020] In one embodiment of the present invention, in the composite solution, the mass ratio of polyethyleneimine to ammonium polyphosphate is 1:2-4.

[0021] In one embodiment of the present invention, in the composite solution, the concentration of polyethyleneimine is 0.5-2 wt %.

[0022] In one embodiment of the present invention, in the composite solution, the concentration of polyethyleneimine is preferably 1 wt %.

[0023] In one embodiment of the present invention, the composite solution is prepared by dissolving polyethyleneimine and ammonium polyphosphate in water, heating and stirring until dissolved; the heating temperature is 40-50°C.

[0024] In one embodiment of the present invention, the concentration of the polyethyleneimine solution is 0.5-2 wt %.

[0025] In one embodiment of the present invention, the concentration of the ammonium polyphosphate solution is 2-4 wt %.

[0026] In one embodiment of the present invention, in the treatment with polyethyleneimine and ammonium polyphosphate, the immersion temperature is 15-35°C, the immersion time is 5-15 minutes, and the drying temperature is 60-70°C.

[0027] In one embodiment of the present invention, in step (2), the drying temperature is 60-70°C.

[0028] The second object of the present invention is the single-layer assembled flame-retardant cotton fabric prepared by the above preparation method.

[0029] Beneficial effects:

[0030] (1) The ammonium polyphosphate, polyethyleneimine and polyacrylic acid used in the present invention are all green chemicals, are environmentally friendly, and have a wide range of sources and low costs.

[0031] (2) Different from the commonly used immersion drying method and sol-gel method for cotton fabrics, the present invention adopts a technical method of assembling a single-layer flame retardant coating to finish the flame retardant on the surface of the cotton fabric, avoiding difficult processes, making the finishing conditions milder, and eliminating the need to add initiators and other additives, thus saving energy.

[0032] (3) The present invention aims at flame retardant of cotton fabrics, and uses polyethyleneimine and ammonium polyphosphate alone to prepare a highly efficient flame retardant solution without adding any additional additives, which is simpler and more efficient.

[0033] (4) The present invention uses the technology of assembling a single layer of flame retardant coating to prepare flame retardant cotton fabrics. The cotton fabrics prepared by the single layer assembly have excellent flame retardancy, achieving the effect of a small number of assembly layers and good flame retardant performance, and overcoming the technical difficulty of the current layer-by-layer self-assembly technology that requires repeated deposition of multiple layers.

[0034] (5) The present invention uses organic and inorganic flame retardant materials to deposit a flame retardant coating on the surface of cotton fabric. The limiting oxygen index of the prepared flame retardant cotton fabric can be as high as 39.8%. When encountering an external fire source, there is no ignition phenomenon. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 , Figure 2 These are UL-94 test diagrams of the original cotton fabric, Examples 1, 2, 3, 4, and Comparative Examples 1 and 2.

[0036] Figure 3 These are the heat release diagrams of the original cotton fabric and Examples 1, 2, 3, and 4.

[0037] Figure 4 It is the electron microscope picture of original cotton fabric, embodiment 1, 2, 3, 4. DETAILED DESCRIPTION

[0038] Test Method

[0039] Textile Limiting Oxygen Index:

[0040] According to GB / T 5454-1997 "Textile Combustion Performance Test Oxygen Index Method", the original cotton fabric and the prepared flame-retardant cotton fabric were cut into at least 3 pieces, and the sample size was about 10×5cm 2 In the oxygen-nitrogen mixed gas flow, the minimum oxygen concentration required to maintain its combustion is expressed as a percentage.

[0041] Vertical burning test:

[0042] According to GB / T 5455-2014 “Determination of vertical damage length, smoldering and afterflaming time of textile combustion performance”, the original cotton fabric (356×51mm) and the prepared flame-retardant cotton fabric (100×50mm) were placed in a U-shaped stainless steel plate and hung vertically. Then, a 40mm butane flame was placed above the midpoint of the bottom edge of the specimen. After ignition for 12 seconds, the flame was removed and the timer was turned on to record the afterflaming time and smoldering time, accurate to 0.1s. Then, a corresponding heavy hammer was used to hang one side of the lower end, and the other side of the lower end of the specimen was slowly lifted by hand. The damage length was measured after the heavy hammer was lowered in midair.

[0043] Cone Calorimetry Test:

[0044] According to ISO 5660 standard, each sample was cut into a 100×100 mm square and the 2 The radiant heat flux is placed horizontally. The combustion behavior of the sample is studied. Each sample is tested at least 3 times.

[0045] Example 1

[0046] (1) Acid treatment of cotton fabrics

[0047] Polyacrylic acid was dissolved in deionized water and stirred to prepare a polyacrylic acid solution with a concentration of 1 wt%. Cotton fabric was impregnated with the polyacrylic acid solution at room temperature for 10 minutes and dried at 60° C. for later use.

[0048] (2) Preparation of composite solution

[0049] Dissolve polyethyleneimine in deionized water. After fully dissolved, add ammonium polyphosphate powder and stir at 40°C until dissolved to obtain a mixed solution with a polyethyleneimine and ammonium polyphosphate mass ratio of 1:4, wherein the concentration of polyethyleneimine is 1wt% and the concentration of ammonium polyphosphate is 4wt%.

[0050] (3) Preparation of flame-retardant cotton fabrics

[0051] The cotton fabric prepared in step (1) is immersed in the composite solution prepared in step (2) for 10 minutes at room temperature (25° C.), and then dried at 60° C.

[0052] Example 2

[0053] (1) Acid treatment of cotton fabrics

[0054] Polyacrylic acid was dissolved in deionized water and stirred to prepare a polyacrylic acid solution with a concentration of 1 wt%. Cotton fabric was impregnated with the polyacrylic acid solution at room temperature for 10 minutes and dried at 60° C. for later use.

[0055] (2) Preparation of composite solution

[0056] Dissolve polyethyleneimine in deionized water. After fully dissolved, add ammonium polyphosphate powder and stir at 40°C until dissolved to prepare a mixed solution with a mass ratio of polyethyleneimine to ammonium polyphosphate of 1:2, wherein the concentration of polyethyleneimine is 1wt% and the concentration of ammonium polyphosphate is 2wt%.

[0057] (3) Preparation of flame-retardant cotton fabrics

[0058] The cotton fabric prepared in step (1) is immersed in the composite solution prepared in step (2), immersed at room temperature for 10 minutes, and dried at 60°C.

[0059] Example 3

[0060] (1) Acid treatment of cotton fabrics

[0061] Polyacrylic acid was dissolved in deionized water and stirred to prepare a polyacrylic acid solution with a concentration of 1 wt%. The cotton fabric was impregnated with the polyacrylic acid solution at room temperature for 10 minutes and dried at 60° C. for later use.

[0062] (2) Polyethyleneimine treatment of cotton fabrics

[0063] Dissolve polyethyleneimine in deionized water and stir at room temperature to fully dissolve to obtain a polyethyleneimine solution with a concentration of 1 wt%. Immerse the cotton fabric obtained in step (1) in the solution for 10 minutes at room temperature and then dry at 60°C for later use.

[0064] (3) Ammonium polyphosphate treatment of cotton fabrics

[0065] Dissolve ammonium polyphosphate in deionized water and stir at room temperature until fully dissolved to obtain an ammonium polyphosphate solution with a concentration of 4 wt%. Immerse the cotton fabric obtained in step (2) in the solution for 10 minutes at room temperature and then dry at 60°C.

[0066] Example 4

[0067] (1) Acid treatment of cotton fabrics

[0068] Polyacrylic acid was dissolved in deionized water and stirred to prepare a polyacrylic acid solution with a concentration of 1 wt%. The cotton fabric was impregnated with the polyacrylic acid solution at room temperature for 10 minutes and dried at 60° C. for later use.

[0069] (2) Polyethyleneimine treatment of cotton fabrics

[0070] Dissolve polyethyleneimine in deionized water and stir at room temperature to fully dissolve to obtain a polyethyleneimine solution with a concentration of 1 wt%. Immerse the cotton fabric obtained in step (1) in the solution for 10 minutes at room temperature and then dry at 60°C for later use.

[0071] (3) Ammonium polyphosphate treatment of cotton fabrics

[0072] Dissolve ammonium polyphosphate in deionized water and stir at room temperature until fully dissolved to obtain an ammonium polyphosphate solution with a concentration of 2 wt%. Immerse the cotton fabric obtained in step (2) in the solution for 10 minutes at room temperature and then dry at 60°C.

[0073] Comparative Example 1

[0074] (1) Alkali treatment of cotton fabrics

[0075] Sodium hydroxide was dissolved in deionized water, and the solution was stirred to obtain a sodium hydroxide solution with a concentration of 20 g / L. The solution was then impregnated with cotton fabric at 60° C. for 60 minutes, and then dried at 60° C. for later use.

[0076] (2) Preparation of composite solution

[0077] Dissolve polyethyleneimine in deionized water. After fully dissolved, add ammonium polyphosphate powder and stir at 40°C until dissolved to obtain a mixed solution of polyethyleneimine and ammonium polyphosphate in a ratio of 1:4, wherein the concentration of polyethyleneimine is 1wt% and the concentration of ammonium polyphosphate is 4wt%.

[0078] (3) Preparation of flame-retardant cotton fabrics

[0079] The cotton fabric prepared in step (1) is immersed in the composite solution prepared in step (2), immersed at room temperature for 10 minutes, and dried at 60°C.

[0080] Comparative Example 2

[0081] (1) Preparation of composite solution and flame-retardant cotton fabric

[0082] Dissolve polyethyleneimine in deionized water, add ammonium polyphosphate powder after it is fully dissolved, stir at 40°C until dissolved, and prepare a mixed solution of polyethyleneimine and ammonium polyphosphate in a ratio of 1:4, wherein the concentration of polyethyleneimine is 1wt% and the concentration of ammonium polyphosphate is 4wt%. Immerse cotton fabric in this solution, treat at room temperature for 10 minutes, and then dry at 60°C.

[0083] Comparative Example 3

[0084] (1) Acid treatment of cotton fabrics

[0085] Polyacrylic acid was dissolved in deionized water and stirred to prepare a 1 wt % polyacrylic acid solution. Cotton fabric was immersed in the solution and treated at room temperature for 10 minutes, and then dried at 60° C. for use.

[0086] (2) Preparation of composite solution

[0087] Dissolve polyethyleneimine in deionized water. After fully dissolved, add ammonium polyphosphate powder and stir at 40°C until dissolved to obtain a mixed solution of polyethyleneimine and ammonium polyphosphate in a ratio of 1:1, wherein the concentration of polyethyleneimine is 1wt%, and the concentration of ammonium polyphosphate is 1wt%.

[0088] (3) Preparation of flame-retardant cotton fabrics

[0089] The cotton fabric prepared in step (1) is immersed in the composite solution prepared in step (2), immersed at room temperature for 10 minutes, and dried at 60°C.

[0090] Comparative Example 4

[0091] (1) Acid treatment of cotton fabrics

[0092] Polyacrylic acid was dissolved in deionized water and stirred to prepare a 1 wt % polyacrylic acid solution. Cotton fabric was immersed in the solution and treated at room temperature for 10 minutes, and then dried for use.

[0093] (2) Preparation of composite solution

[0094] Dissolve polyethyleneimine in deionized water. After fully dissolved, add ammonium polyphosphate powder and stir at 40°C until dissolved to obtain a mixed solution of polyethyleneimine and ammonium polyphosphate in a ratio of 1:0.5, wherein the concentration of polyethyleneimine is 1wt% and the concentration of ammonium polyphosphate is 0.5wt%.

[0095] (3) Preparation of flame-retardant cotton fabrics

[0096] The cotton fabric prepared in step (1) is immersed in the composite solution prepared in step (2), immersed at room temperature for 10 minutes, and dried at 60°C.

[0097] Comparative Example 5

[0098] (1) Acid treatment of cotton fabrics

[0099] Acetic acid was dissolved in deionized water and stirred to prepare an acetic acid solution with a concentration of 1 wt%. The cotton fabric was impregnated with the acetic acid solution at room temperature for 10 minutes and dried at 60° C. for later use.

[0100] (2) Preparation of composite solution

[0101] Dissolve polyethyleneimine in deionized water. After fully dissolved, add ammonium polyphosphate powder and stir at 40°C until dissolved to obtain a mixed solution with a polyethyleneimine and ammonium polyphosphate mass ratio of 1:4, wherein the concentration of polyethyleneimine is 1wt% and the concentration of ammonium polyphosphate is 4wt%.

[0102] (3) Preparation of flame-retardant cotton fabrics

[0103] The cotton fabric prepared in step (1) is immersed in the composite solution prepared in step (2), immersed at room temperature for 10 minutes, and dried at 60°C.

[0104] Table 1

[0105]

[0106]

[0107] The limiting oxygen index test results are shown in Table 1. As can be seen from Table 1, the single-layer flame retardant coating constructed on the surface of the cotton fabric of the present invention has a good flame retardant effect, and the limiting oxygen index after finishing is as high as 39.8%, which is much higher than the limiting oxygen index of 27.0-33.7% of the current layer-by-layer self-assembled flame retardant cotton fabric. As can be seen from the table, compared with Examples 1, 3, and 4, the limiting oxygen index of the comparative example is lower, indicating that the polyacrylic acid solution can increase the adhesion and uniformity of the flame retardant coating, thereby improving the flame retardancy of the cotton fabric, and also indicating that the combination of polyacrylic acid, polyethyleneimine and ammonium polyphosphate makes the flame retardant cotton fabric have ideal flame retardant properties.

[0108] Table 2

[0109] sample Afterburning time(s) Smoldering time(s) Damaged length(cm) Raw cotton fabric 4 37 -- Example 1 0 0 3.2 Example 2 0 0 -- Example 3 0 0 4.6 Example 4 0 0 -- Comparative Example 1 0 0 5.8 Comparative Example 2 0 0 6.5

[0110] The vertical burning test results are shown in Table 2. According to Table 2, Examples 1 to 4 and Comparative Examples 1 and 2 extinguished after leaving the flame, did not continue to burn or smolder, and all had flame retardant effects, while the untreated cotton fabric (original cotton fabric) continued to burn for 4 seconds, and the smoldering time was 37 seconds. The damaged length is shown in Table 2 and Figure 1 , 2 As shown. After the vertical burning test, the original cotton fabric and the flame-retardant cotton fabrics prepared in Examples 2 and 4 were all damaged. Under the condition that the ratio of polyethyleneimine to ammonium polyphosphate was 1:4 (Example 1), the damaged length was only 3.2 cm. Compared with Example 1, the pretreatment of Comparative Example 1 was alkali treatment, and its damaged length was longer. It shows that the polyacrylic acid solution as a pretreatment increases the adhesion and uniformity of the flame-retardant coating, and the flame-retardant cotton fabric after finishing has better flame retardant properties.

[0111] Table 3

[0112]

[0113] The cone calorimetry test results are shown in Table 3 and Figure 3 As shown in Table 3, the cotton fabrics with a single-layer flame retardant coating on the surface (Examples 1 to 4) have good flame retardant effects. Compared with the original cotton fabrics, the effective combustion calorific value, heat release rate, heat release peak value, and total heat release amount are all reduced to varying degrees. The flame retardant cotton fabric prepared in Example 1 has the best flame retardant effect, and its heat release rate is from 81.97 km / m 2Down to 2.89km / m 2 The peak heat release also increased from 124.71kW / m 2 Reduced to 10.39kW / m 2 At present, the ignition time of the layer-by-layer self-assembled flame-retardant cotton fabric is mostly 3 to 23 seconds, but the flame-retardant cotton fabric prepared by the present invention does not burn in the cone calorimetry test, indicating that the flame-retardant cotton fabric prepared by the present invention has excellent flame-retardant properties.

[0114] Figure 4 (a), (b), (c), (d), and (e) are electron microscope images of the original cotton fabric and the single-layer assembled flame-retardant cotton fabrics made in Examples 1, 2, 3, and 4, respectively. It can be seen from the figure that the surface of the original cotton fabric is smooth, and clear fibers can be seen. Compared with the original cotton fabric, a layer of flame-retardant material is attached to the surface of the cotton fabric in the embodiment. The impregnated coatings of Examples 1 and 2 are smooth and uniform. The coating morphology of the surfaces of Examples 3 and 4 is different from that of Examples 1 and 2, but materials are also attached to the surface at the same time. It can be seen from the figure that in all the embodiments, the coating of Example 1 is more uniform than the other coatings, has a better adhesion effect, and also has better flame retardant properties.

[0115] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a single-layer assembled flame-retardant cotton fabric, characterized in that: Includes steps: (1) Acid treatment of cotton fabric: impregnate cotton fabric with polyacrylic acid solution and dry; (2) Preparation of flame-retardant cotton fabric: treating the cotton fabric prepared in step (1) with polyethyleneimine and ammonium polyphosphate, and drying to obtain a single-layer assembled flame-retardant cotton fabric.

2. The preparation method according to claim 1, characterized in that: In step (1), the concentration of the polyacrylic acid solution is 0.5 to 2 wt %.

3. The preparation method according to claim 1, characterized in that: In step (1), the immersion temperature is 15 to 35° C. and the immersion time is 5 to 15 minutes.

4. The preparation method according to claim 1, characterized in that: In step (2), the method for treating the cotton fabric prepared in step (1) with polyethyleneimine and ammonium polyphosphate is: impregnating the cotton fabric prepared in step (1) with a composite solution of polyethyleneimine and ammonium polyphosphate; or first impregnating the cotton fabric prepared in step (1) with a polyethyleneimine solution, drying it, and then impregnating it with an ammonium polyphosphate solution.

5. The preparation method according to claim 4, characterized in that: In the composite solution, the mass ratio of polyethyleneimine to ammonium polyphosphate is 1:2-4.

6. The preparation method according to claim 4, characterized in that: In the composite solution, the concentration of polyethyleneimine is 0.5-2 wt %.

7. The preparation method according to claim 4, characterized in that: The concentration of the polyethyleneimine solution is 0.5-2 wt %.

8. The preparation method according to claim 4, characterized in that: The concentration of the ammonium polyphosphate solution is 2-4 wt %.

9. The preparation method according to claim 4, characterized in that: The immersion temperature is 15-35°C, and the immersion time is 5-15 minutes.

10. The single-layer assembled flame-retardant cotton fabric prepared by the preparation method according to any one of claims 1 to 9.

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