A method for preparing a single layer assembled flame resistant cotton fabric

Abstract

The application provides a preparation method of single-layer assembled flame-retardant cotton fabric, comprising the following steps: impregnating cotton fabric with a polyacrylic acid solution and drying; impregnating the prepared cotton fabric with a composite solution of polyethylene imine and ammonium polyphosphate, or sequentially impregnating the prepared cotton fabric with a polyethylene imine solution and an ammonium polyphosphate solution, and drying to obtain single-layer assembled flame-retardant cotton fabric. The application adopts a single-layer flame-retardant coating assembly technical method, avoids high-difficulty process, and has milder finishing conditions, does not need to add initiators and other auxiliaries, realizes the effect of less assembly layers and good flame-retardant performance, and solves the technical problem of the need of multilayer repeated deposition in the current layer-by-layer self-assembly technology; the prepared flame-retardant cotton fabric has an ultimate oxygen index of up to 39.8%, and has no ignition phenomenon when encountering external fire.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant finishing technology for textiles, and particularly relates to a method for preparing a single-layer assembled flame retardant cotton fabric. Background Technology

[0002] Cotton fiber, as one of the most commonly used natural fibers, produces fabrics with advantages such as soft hand feel and strong moisture absorption. Its excellent performance in clothing makes it widely used. However, due to the flammability of cotton fabrics, they are prone to combustion and fires during use, threatening people's lives and property. Therefore, the preparation of flame-retardant cotton fabrics has significant practical application value. There are many finishing methods for preparing flame-retardant cotton fabrics, and layer-by-layer self-assembly has gradually been widely used by many scholars. The layer-by-layer self-assembly method uses electrostatic adsorption to layer flame retardants onto the surface of the cotton fabric. This method is simple and easy to operate, requiring no complex processing.

[0003] However, layer-by-layer self-assembly technology also has certain drawbacks. Most flame retardants require multiple layers of deposition to give cotton fabrics good flame-retardant properties, and the number of deposition steps limits the practical application of layer-by-layer self-assembly technology. Furthermore, because the layer-by-layer self-assembly method relies on electrostatic adsorption to allow multiple solutions to adhere to each other and overlap on the surface of the cotton fabric to exhibit good flame-retardant properties, this technology has high limitations regarding the acidity or alkalinity of the solution, increasing the difficulty of implementation. Developing simpler and more efficient flame-retardant coatings with fewer layers is currently an important research direction.

[0004] CN117488551A provides a controllable preparation method for a nanocomposite flame-retardant coating based on silicon-containing inorganic particles. The method involves layer-by-layer assembly of silicon-containing inorganic particles, polyethyleneimine (PEI), and phytic acid (PA) flame retardant onto the surface of cotton fabric. The silicon-containing inorganic particles can be silica (SiO2), attapulgite (ATTA), or montmorillonite (MMT). By adjusting the preparation process conditions, the assembled multilayer structure gives the cotton fabric good flame-retardant properties. However, this invention has a relatively complex preparation process, and the limiting oxygen index after coating is only up to 24.8%.

[0005] CN103266468A provides a method for flame-retardant finishing of pure cotton fabrics using an intumescent flame-retardant system. Montmorillonite and organic amines are stirred to form a dispersion. Fatty acids are then added to the dispersion, along with a catalyst, to obtain a montmorillonite nanocomposite material. An emulsifier and acetic acid are added to obtain a montmorillonite nanocomposite material emulsion. A resin crosslinking agent and ammonium polyphosphate are then added to finally obtain a flame-retardant finishing liquid. The flame-retardant cotton fabric is prepared using impregnation, pre-drying, and baking methods. This invention requires high-quality preparation process conditions and involves multiple impregnation steps. The resulting flame-retardant cotton fabric exhibits a carbon loss of up to 9.6 cm in a vertical burning test.

[0006] CN109944070B discloses a self-extinguishing flame-retardant cotton fabric, its preparation method, and its application. It uses three materials—silane coupling agent, sodium alginate, and ammonium polyphosphate—as a flame-retardant spraying liquid to deposit 5-20 flame-retardant unit layers on the surface of the cotton fabric. These unit layers are either four layers: silane coupling agent / sodium alginate / silane coupling agent / ammonium polyphosphate or four layers: silane coupling agent / ammonium polyphosphate / silane coupling agent / sodium alginate. The flame-retardant cotton fabric is then prepared. This invention, using a layer-by-layer self-assembly method, requires the deposition of 5-20 flame-retardant unit layers on the cotton fabric surface to achieve a self-extinguishing effect, resulting in a large number of impregnation layers and a complex process.

[0007] The existing flame-retardant finishing methods for cotton fabrics are complex and cumbersome. Among them, the flame-retardant finishing method using layer-by-layer self-assembly technology requires assembling a large number of layers to achieve the desired flame-retardant effect. Summary of the Invention

[0008] [Technical Issues]

[0009] Currently, flame-retardant finishing methods for cotton fabrics involve complex and cumbersome processes. Among them, the flame-retardant finishing method using layer-by-layer self-assembly technology requires assembling a large number of layers to achieve the desired flame-retardant effect.

[0010] [Technical Solution]

[0011] To address the aforementioned technical problems, this invention provides a method for preparing a single-layer flame-retardant coating assembled on the surface of cotton fabric. This invention uses a mixed solution of polymer and inorganic phosphate as the single-layer flame-retardant solution. The assembly process is simple, efficient, green, and environmentally friendly. A single-layer assembly can give cotton fabric good flame-retardant properties.

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

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

[0014] (2) Preparation of flame-retardant cotton fabric: The cotton fabric prepared in step (1) is treated with polyethyleneimine and ammonium polyphosphate, and then dried 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 15-35°C and the immersion time is 5-15 min.

[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 of treating the cotton fabric prepared in step (1) with polyethyleneimine and ammonium polyphosphate is as follows: 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, the mass ratio of polyethyleneimine to ammonium polyphosphate in the composite solution is 1:2 to 4.

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

[0022] In one embodiment of the present invention, the concentration of polyethyleneimine in the composite solution 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, the impregnation temperature for both polyethyleneimine and ammonium polyphosphate treatment is 15-35°C, the impregnation time is 5-15 min, 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 objective of this invention is to produce a single-layer assembled flame-retardant cotton fabric using the above-described preparation method.

[0029] Beneficial effects:

[0030] (1) The ammonium polyphosphate, polyethyleneimine and polyacrylic acid used in this invention are all green chemicals that are environmentally friendly, widely available and inexpensive.

[0031] (2) Unlike the commonly used impregnation and drying method and sol-gel method for cotton fabrics, this invention adopts a single-layer flame retardant coating assembly technology to apply flame retardant to the surface of cotton fabric, avoiding high-difficulty processes, with milder finishing conditions, and no need to add initiators and other additives, thus saving energy.

[0032] (3) This invention targets flame retardant for cotton fabrics. It uses only two materials, polyethyleneimine and ammonium polyphosphate, to prepare a highly efficient flame retardant solution without adding any additional additives, making it simpler and more efficient.

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

[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%, and there is no ignition phenomenon when it encounters an external fire source. Attached Figure Description

[0035] Figure 1 , Figure 2 The images show UL-94 test patterns for the original cotton fabrics, Examples 1, 2, 3, and 4, and Comparative Examples 1 and 2.

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

[0037] Figure 4 Electron micrographs of the original cotton fabrics, Examples 1, 2, 3, and 4. Detailed Implementation

[0038] Test methods

[0039] Limiting oxygen index of textiles:

[0040] According to GB / T 5454-1997 "Test for Burning Performance of Textiles - Oxygen Index Method", the raw cotton fabric and the prepared flame-retardant cotton fabric should be cut into at least 3 pieces, with sample dimensions of approximately 10×5cm. 2 In an oxygen-nitrogen mixture, the minimum oxygen concentration required to maintain combustion is expressed as a percentage.

[0041] Vertical burning test:

[0042] According to GB / T 5455-2014 "Determination of Vertical Damage Length, Afterflame and Afterburning Time of Textiles", 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 suspended vertically. Then, a 40mm butane flame was placed above the midpoint of the sample at the bottom edge and ignited for 12 seconds. The flame was then removed, and a timer was turned on to record the afterburning time and smoldering time to an accuracy of 0.1s. Then, a corresponding weight was used to suspend one side of the lower end of the sample. The other side of the lower end of the sample was slowly lifted by hand, and the damage length was measured after the weight was lowered into the air.

[0043] Cone calorimetry test:

[0044] According to ISO 5660 standard, each sample was cut into a 100×100mm square, and then subjected to a power of 35kW / m². 2 The samples were placed horizontally to allow for radiative heat flux. The combustion behavior of the samples was studied. Each sample was tested at least three times.

[0045] Example 1

[0046] (1) Acid treatment of cotton fabrics

[0047] Polyacrylic acid was dissolved in deionized water and stirred to prepare a 1 wt% polyacrylic acid solution. The cotton fabric was then 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] Polyethyleneimine was dissolved in deionized water. After complete dissolution, ammonium polyphosphate powder was added and stirred at 40°C until dissolved to obtain a mixed solution of polyethyleneimine and ammonium polyphosphate in a mass ratio of 1:4, wherein the concentration of polyethyleneimine was 1 wt% and the concentration of ammonium polyphosphate was 4 wt%.

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

[0051] The cotton fabric obtained in step (1) is immersed in the composite solution obtained 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 1 wt% polyacrylic acid solution. The cotton fabric was then 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] Polyethyleneimine was dissolved in deionized water. After complete dissolution, ammonium polyphosphate powder was added and stirred at 40°C until dissolved to obtain a mixed solution of polyethyleneimine and ammonium polyphosphate in a mass ratio of 1:2, wherein the concentration of polyethyleneimine was 1 wt% and the concentration of ammonium polyphosphate was 2 wt%.

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

[0058] The cotton fabric obtained in step (1) is immersed in the composite solution obtained in step (2), soaked at room temperature for 10 minutes, and then 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 1 wt% polyacrylic acid solution. The cotton fabric was then 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] Polyethyleneimine was dissolved in deionized water and stirred at room temperature to obtain a 1 wt% polyethyleneimine solution. The cotton fabric prepared in step (1) was immersed in this solution and soaked at room temperature for 10 minutes, and then dried at 60°C for later use.

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

[0065] Ammonium polyphosphate was dissolved in deionized water and stirred at room temperature to obtain a 4 wt% ammonium polyphosphate solution. The cotton fabric prepared in step (2) was immersed in this solution and soaked at room temperature for 10 minutes, and then dried 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 1 wt% polyacrylic acid solution. The cotton fabric was then 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] Polyethyleneimine was dissolved in deionized water and stirred at room temperature to obtain a 1 wt% polyethyleneimine solution. The cotton fabric prepared in step (1) was immersed in this solution and soaked at room temperature for 10 minutes, and then dried at 60°C for later use.

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

[0072] Ammonium polyphosphate was dissolved in deionized water and stirred at room temperature to obtain a 2 wt% ammonium polyphosphate solution. The cotton fabric prepared in step (2) was immersed in this solution and soaked at room temperature for 10 minutes, and then dried at 60°C.

[0073] Comparative Example 1

[0074] (1) Alkali treatment of cotton fabrics

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

[0076] (2) Preparation of composite solution

[0077] Polyethyleneimine was dissolved in deionized water. After complete dissolution, ammonium polyphosphate powder was added and stirred 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 was 1 wt% and the concentration of ammonium polyphosphate was 4 wt%.

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

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

[0080] Comparative Example 2

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

[0082] Polyethyleneimine was dissolved in deionized water. After complete dissolution, ammonium polyphosphate powder was added and stirred at 40°C until dissolved, resulting in a mixed solution of polyethyleneimine and ammonium polyphosphate in a ratio of 1:4, wherein the concentration of polyethyleneimine was 1 wt% and the concentration of ammonium polyphosphate was 4 wt%. Cotton fabric was immersed in this solution and treated at room temperature for 10 minutes, followed by drying 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 obtain a 1 wt% polyacrylic acid solution. Cotton fabric was immersed in this solution and treated at room temperature for 10 minutes, and then dried at 60°C for later use.

[0086] (2) Preparation of composite solution

[0087] Polyethyleneimine was dissolved in deionized water. After complete dissolution, ammonium polyphosphate powder was added and stirred at 40°C until dissolved to obtain a mixed solution of polyethyleneimine and ammonium polyphosphate in a 1:1 ratio, wherein the concentration of polyethyleneimine was 1 wt% and the concentration of ammonium polyphosphate was 1 wt%.

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

[0089] The cotton fabric obtained in step (1) is immersed in the composite solution obtained in step (2), soaked at room temperature for 10 minutes, and then 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 this solution, treated at room temperature for 10 minutes, and then dried for later use.

[0093] (2) Preparation of composite solution

[0094] Polyethyleneimine was dissolved in deionized water. After complete dissolution, ammonium polyphosphate powder was added and stirred 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 was 1 wt% and the concentration of ammonium polyphosphate was 0.5 wt%.

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

[0096] The cotton fabric obtained in step (1) is immersed in the composite solution obtained in step (2), soaked at room temperature for 10 minutes, and then 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 then soaked in 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] Polyethyleneimine was dissolved in deionized water. After complete dissolution, ammonium polyphosphate powder was added and stirred at 40°C until dissolved to obtain a mixed solution of polyethyleneimine and ammonium polyphosphate in a mass ratio of 1:4, wherein the concentration of polyethyleneimine was 1 wt% and the concentration of ammonium polyphosphate was 4 wt%.

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

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

[0104] Table 1

[0105]

[0106]

[0107] The limiting oxygen index (LOI) 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 cotton fabric by this invention has excellent flame-retardant effect, with a limiting oxygen index as high as 39.8% after finishing, far exceeding the limiting oxygen index of 27.0–33.7% for currently used layer-by-layer self-assembled flame-retardant cotton fabrics. The table also shows that, compared to Examples 1, 3, and 4, the limiting oxygen index of the comparative examples 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. Furthermore, it demonstrates that the combination of polyacrylic acid, polyethyleneimine, and ammonium polyphosphate gives the flame-retardant cotton fabric ideal flame-retardant properties.

[0108] Table 2

[0109] sample Afterburn time (s) Smoldering time (s) Damaged length (cm) raw cotton fabrics 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 results of the vertical burning test are shown in Table 2. According to Table 2, Examples 1-4 and Comparative Examples 1 and 2 extinguished immediately after being removed from the flame, without afterflame or smoldering, demonstrating flame-retardant effects. However, the untreated cotton fabric (original cotton fabric) continued to burn for 4 seconds, and the smoldering time was 37 seconds. The damaged lengths are shown in Table 2 and... Figure 1 , 2 As shown. Vertical burning tests revealed that the original cotton fabric and the flame-retardant cotton fabrics prepared in Examples 2 and 4 were completely destroyed. Under the condition of a 1:4 ratio of polyethyleneimine to ammonium polyphosphate (Example 1), the damaged length was only 3.2 cm. Compared to Example 1, Comparative Example 1, which underwent alkali treatment, showed a longer damaged length. This indicates that using polyacrylic acid solution as a pretreatment increases the adhesion and uniformity of the flame-retardant coating, and the finished flame-retardant cotton fabric exhibits better flame-retardant properties.

[0111] Table 3

[0112]

[0113] The results of the cone calorimetry test are shown in Table 3 and Figure 3 As shown in Table 3, the cotton fabrics with a single-layer flame-retardant coating (Examples 1-4) exhibit good flame-retardant effects. Compared with the original cotton fabric, the effective calorific value, heat release rate, peak heat release, and total heat release are all reduced to varying degrees. The flame-retardant cotton fabric prepared in Example 1 has the best flame-retardant effect, with its heat release rate decreasing from 81.97 km / m. 2Reduced to 2.89 km / m 2 The peak heat release also increased from 124.71 kW / m³. 2 Reduced to 10.39kW / m 2 Furthermore, it does not ignite when exposed to flame. Currently, the ignition time of most layered self-assembled flame-retardant cotton fabrics is 3–23 seconds, but the flame-retardant cotton fabric prepared by this invention does not ignite in a cone calorimetry test, indicating that the flame-retardant cotton fabric prepared by this invention possesses 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 prepared in Examples 1, 2, 3, and 4, respectively. As can be seen from the images, the surface of the original cotton fabric is smooth, and clear fibers are visible. Compared to the original cotton fabric, the cotton fabrics in the examples have a layer of flame-retardant material attached to their surface. The coatings impregnated in Examples 1 and 2 are smooth and uniform. The coating morphology of the surfaces in Examples 3 and 4 is different from that in Examples 1 and 2, but a material is also attached to the surface. As shown in the figures, among all the examples, the coating of Example 1 is more uniform, has better adhesion, and also possesses better flame-retardant properties compared to the other coatings.

[0115] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a single-layer assembled flame-retardant cotton fabric, characterized in that, Including the following steps: (1) Acid treatment of cotton fabrics: Impregnate cotton fabrics with polyacrylic acid solution and dry; (2) Preparation of flame-retardant cotton fabric: The cotton fabric prepared in step (1) is treated with polyethyleneimine and ammonium polyphosphate, dried, and a single-layer assembled flame-retardant cotton fabric is obtained. The method of treating the cotton fabric prepared in step (1) with polyethyleneimine and ammonium polyphosphate is as follows: the cotton fabric prepared in step (1) is impregnated with a composite solution of polyethyleneimine and ammonium polyphosphate, wherein the concentration of polyethyleneimine in the composite solution is 0.5~2 wt%, and the mass ratio of polyethyleneimine to ammonium polyphosphate is 1:2~4; or the cotton fabric prepared in step (1) is first impregnated with a polyethyleneimine solution with a concentration of 0.5~2 wt%, dried, and then impregnated with an ammonium polyphosphate solution with a concentration of 2~4 wt%.

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

3. The preparation method according to claim 1, characterized in that, In step (1), the immersion temperature is 15~35℃ and the immersion time is 5~15 min.

4. The preparation method according to claim 1, characterized in that, In step (2), the immersion temperature is 15~35℃ and the immersion time is 5~15 min.

5. The single-layer assembled flame-retardant cotton fabric prepared by any of the preparation methods described in claims 1 to 4.

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