Phosphorus-containing cross-linked network durable flame-retardant cotton fabric and preparation method thereof

Abstract

The invention discloses a phosphorus-containing cross-linked network durable flame-retardant cotton fabric and a preparation method thereof, and relates to the technical field of cotton fabric preparation.The preparation method comprises the steps that the cotton fabric is soaked in treating fluid, the cotton fabric is taken out and then subjected to two-time soaking and two-time rolling and first-time drying, and the shaped cotton fabric is obtained, the treating fluid is a mixed solution of ammonium polyphosphate, ethylene glycol, dicyandiamide, phosphoric acid and zinc sulfate; dipping the shaped cotton fabric in a zinc sulfate solution, taking out the shaped cotton fabric, dipping twice and rolling twice, and drying for the second time to obtain the phosphorus-containing cross-linked network durable flame-retardant cotton fabric. The phosphorus-containing cross-linked network durable flame-retardant cotton fabric prepared by the preparation method disclosed by the invention can still keep relatively high phosphorus content after being washed for multiple times, and is self-extinguished in a vertical combustion test, and the damaged length is less than 15 cm, so that the cotton fabric is effectively proved to have excellent washing resistance and flame retardance.

Description

Technical Field

[0001] This invention relates to a phosphorus-containing cross-linked network durable flame-retardant cotton fabric and its preparation method, belonging to the technical field of flame-retardant cotton fabric preparation. Background Technology

[0002] Cotton fabrics are the most widely used natural fiber due to their excellent performance and low price. However, cotton fabrics have a limiting oxygen index of only about 18%, making them highly flammable and prone to causing serious fires, which greatly limits their application in many areas. Therefore, flame-retardant finishing of cotton fabrics is particularly important. Although significant progress has been made in the development of flame-retardant cotton fabrics, challenges remain, such as the gradual loss of flame-retardant properties after washing. Furthermore, Pyrovatex CP® and Proban®, two commercially available durable flame retardants for cotton fabrics, also present formaldehyde release issues during finishing and application.

[0003] Reference (Chen Huaqi, Yan Chao, Liu Yun. Preparation and properties of chitosan / ammonium polyphosphate flame-retardant cotton fabrics [J]. Dyeing and Finishing Auxiliaries, 2020, 37(08):19-22.) describes the use of a layer-by-layer self-assembly method to adsorb chitosan and ammonium polyphosphate onto the surface of cotton fabrics to construct an intumescent flame-retardant system. However, the flame-retardant layer did not form an effective bond with the fabric surface, resulting in poor washability.

[0004] Therefore, it is of great significance to develop flame-retardant cotton fabrics that are durable, flame-retardant, easy to manufacture, inexpensive, and suitable for widespread promotion.

[0005] Recently, a considerable number of phosphorus-containing flame retardants have been studied, demonstrating excellent flame retardancy on cotton fabrics. Ammonium polyphosphate, abbreviated as APP, has the molecular formula (NH4). n +2P n O3 n+1 In this formula, n represents the degree of polymerization. The larger the n value, the lower the water solubility of APP. If n > 20, it is sparingly soluble in water; if n < 20, it is readily soluble in water. APP has a high nitrogen and phosphorus content and can be used in fertilizer and flame retardant applications.

[0006] Reference (Shi Junjiao. Preparation of phosphorus-nitrogen-silicon flame-retardant coating and its application in cotton fabrics [D]. Guangxi: Guilin University of Technology, 2022.) A flame-retardant sol containing phosphorus, nitrogen, and silicon was prepared using ammonium polyphosphate, sodium alginate, and tetraethyl orthosilicate as raw materials. Cotton fabrics were then treated with a one-step immersion method for flame retardant treatment. Although the strength of the treated fabric did not decrease significantly, the flame-retardant sol did not form an effective bond with the fabric, and its durability needs improvement.

[0007] Reference (Qi Peng. Design and Mechanism Study of Flame-Retardant Multifunctional System for Cotton Fabrics [D]. Beijing University of Chemical Technology, 2023.) Flame-retardant cotton fabrics with good wash durability were prepared by covalent bonding of ammonium polyphosphate and polyethyleneimine with cotton fabrics and interfacial polymerization of polyethyleneimine with 1,3,5-benzyltrichloroisocyanurate. However, the process is complicated and the reagents used are expensive, making it unsuitable for widespread promotion in production. Furthermore, it has a significant impact on the fabric's hand feel, strength, whiteness, and other properties.

[0008] Reference (Lu, Y., Jia, Y., Zhang, G. et al. An eco-friendly intumescent flame retardant with high efficiency and durability for cotton fabric. Cellulose 25, 5389–5404 (2018).) shows that after treatment with ammonium polyphosphate, the tensile strength of the fabric decreased by more than 25% compared with the untreated fabric, and the whiteness decreased significantly.

[0009] Reference (Zhang Bingjie, Zhao Tao. Preparation and properties of flame-retardant cotton fabrics using polyionic liquid [J]. Dyeing and Printing, 2025, 51(08):33-40.) Poly(1-cyanomethyl-3-vinylimidazolium hexafluorophosphate) was prepared using bromoacetonitrile, 1-vinylimidazolium, and potassium hexafluorophosphate. Flame-retardant cotton fabrics were then prepared via UV initiation and anion exchange, resulting in fabrics that combine flame retardancy and hydrophobicity. However, this system only underwent 20 washing cycles, and the ultimate durability of the flame-retardant cotton fabric was not tested. Clearly, 20 washing cycles are far from sufficient for everyday use.

[0010] Reference (Zhou Yuming, Li Hongzhou. Synthesis of a nitrogen-phosphorus intumescent flame retardant and its effect on the flame retardant properties of cotton fabrics [J]. Cellulose Science and Technology, 2025, 33(01):8-13.) Aminotrimethylene phosphonic acid (ATMP) was reacted with urea to generate ammonium phosphate groups. Then, utilizing the natural properties of chitosan, a flame-retardant coating was prepared on the surface of cotton fabrics through an impregnation-drying curing process. The LOI value of the FRCotton-3 sample in this system reached 25.4%, significantly higher than the LOI value of the control. In the VFT test, the FRCotton-3 sample was self-extinguishing, with a damage length of only 54 mm, significantly lower than the control sample. However, only 10 durability tests were conducted, clearly insufficient to meet the durability requirements of daily life.

[0011] In summary, high temperature and chemical cross-linking can cause cotton fabrics to yellow and lose strength. Therefore, the goal of future research is to reduce physical damage while ensuring the excellent washability of flame-retardant fabrics, and to achieve simple and low-cost processes. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of the prior art and provide a phosphorus-containing cross-linked network durable flame-retardant cotton fabric and its preparation method. The halogen-free durable flame-retardant cotton fabric prepared can still maintain a high phosphorus content after multiple washes, self-extinguishes in vertical burning tests, and has a damage length of less than 15 cm, effectively proving that it has excellent water-washable flame-retardant properties.

[0013] To achieve the above objectives, the present invention is implemented using the following technical solution: On one hand, the present invention provides a method for preparing a phosphorus-containing cross-linked network durable flame-retardant cotton fabric, comprising: The cotton fabric is immersed in the treatment solution, and after the cotton fabric is taken out, it is dipped and rubbed twice, and then dried for the first time to obtain the shaped cotton fabric. The treatment solution is a mixed solution of ammonium polyphosphate, ethylene glycol, dicyandiamide, phosphoric acid and zinc sulfate. The shaped cotton fabric is immersed in zinc sulfate solution, and after being removed, it is subjected to two dips and two nips, and then dried a second time to obtain a phosphorus-containing cross-linked network durable flame-retardant cotton fabric.

[0014] Furthermore, before immersing the cotton fabric in the treatment solution, the cotton fabric is pretreated, which includes immersing the cotton fabric in an alkaline reagent followed by washing.

[0015] Furthermore, the alkaline reagent is an 8-12 wt% sodium hydroxide solution; And / or, the conditions for the impregnation treatment include treatment at 70~90°C for 0.5~1.5h.

[0016] Furthermore, the treatment solution includes 250-300 g / L of ammonium polyphosphate, 50-60 g / L of ethylene glycol, 15-20 g / L of dicyandiamide, 20-25 g / L of phosphoric acid, and 5-10 g / L of zinc sulfate.

[0017] Furthermore, the concentration range of the zinc sulfate solution is 5~10 g / L.

[0018] Furthermore, the liquid content of the cotton fabric after two dips and two nips is 90-110%.

[0019] Furthermore, the impregnation includes impregnation at a temperature of 30-40°C for 30-60 minutes.

[0020] Furthermore, the conditions for the first drying include pre-drying at 70-80°C for 3-5 minutes, followed by baking at 130-140°C for 3-5 minutes.

[0021] Furthermore, the conditions for the second drying include baking at 70-80°C for 3-5 minutes.

[0022] On the other hand, the present invention also provides a phosphorus-containing cross-linked network durable flame-retardant cotton fabric, which is prepared by the preparation method of phosphorus-containing cross-linked network durable flame-retardant cotton fabric as described in any of the above claims.

[0023] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The ammonium polyphosphate (APP) of the present invention undergoes deamination under high temperature and catalytic conditions to form highly reactive polyphosphate; then the oxygen atom (with lone pair electrons) in the hydroxyl group of the cotton fabric acts as a nucleophile to attack the electrophilic phosphoric acid ion in the polyphosphate molecule. After the attack, the OH- in P-OH detaches to form a stable phosphate ester bond POC. The binding of APP to cotton fabric can be either single-point binding or multi-point binding. The APP in this invention achieves flame retardancy through condensed phase-promoted char formation or gas phase free radical capture mechanisms. The condensed phase flame retardancy mechanism involves the thermal decomposition of APP to produce polyphosphoric acid, metaphosphoric acid, and other phosphoric acid derivatives. These phosphoric acid derivatives dehydrate and carbonize the matrix surface, forming a non-combustible char layer. This non-combustible char layer acts as a physical barrier, slowing down the exchange of combustible substances and heat transfer, and reducing the decomposition rate of the internal matrix. The gas phase flame retardancy mechanism involves the thermal decomposition of APP to produce non-combustible gases such as ammonia, nitric oxide, and water vapor, which dilute the concentration of combustible gases and cause the char layer in the condensed phase to expand, reducing the rate of heat and mass transfer. Furthermore, the phosphoric acid derivatives obtained during APP combustion undergo disproportionation reactions to generate HPO·, PO2·, and PO· free radicals. These free radicals can capture H· and OH· free radicals generated by polymer chain reactions, exerting a quenching effect and reducing heat release. This invention introduces Zn 2+ It has the following functions: ①Zn 2+ As a Lewis acid, it pairs with oxygen atoms in APP, increasing the positive charge of phosphorus atoms and making them electrophilic. This allows for a faster reaction with hydroxyl groups in cotton fabrics. Practical comparisons show that the reaction temperature can be lowered while maintaining reaction efficiency, reducing the decrease in strength and whiteness of the fabric caused by high temperatures. ② Simultaneously, Zn... 2+As a secondary catalyst, it can reduce the amount of dicyandiamide used, so that the mixed solution for impregnating cotton fabrics no longer requires high temperature (the solubility of dicyandiamide is positively correlated with temperature), further saving energy consumption. Dicyandiamide decomposes at high temperature to produce ammonia, which affects the whiteness of the fabric. Reducing its amount can also reduce the decrease in whiteness. ③ ZnSO4 can form an insoluble precipitate with ammonium polyphosphate under neutral and weakly alkaline conditions, which can form an insoluble protective layer on the outside of the flame-retardant cross-linking network, further improving flame-retardant durability. At the same time, metallic zinc can also catalyze the formation of a carbon layer during combustion. The present invention introduces ethylene glycol (EG) primarily for the following three purposes: ① To use EG to react unreacted -P=O(O-NH) with cotton fabrics. 4+ )2 Further reaction forms POC groups, avoiding -P=O(O-NH 4+ The )2 group is converted to P=O(O-Na) during the washing process. + 2 (the main reason for the reduction of flame retardant properties of cotton fabrics during washing), improve the washability of cotton fabrics; ② EG can further improve the cross-linking network between APP and cotton fabrics. EG can act as a bridge to connect adjacent APPs, while APP itself can cross-link with multiple fibers, gradually forming a larger covalent cross-linking network, further improving the durability of flame retardant fabrics; ③ At the same time, the addition of EG can act as a carbon source, and APP as an acid source and gas source, forming an intumescent flame retardant system on the surface of cotton fabrics; The raw materials used in this invention, such as APP, EG, and zinc sulfate, are inexpensive and the process is simple. The resulting cotton fabrics have excellent flame retardancy and washability, and minimal physical damage, making them highly valuable for practical applications. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the vertical burning test results of the halogen-free durable flame-retardant cotton fabric prepared in Example 1 of the present invention under multiple washing conditions. Figure 2 This is a schematic diagram showing the results of phosphorus content determination and damage length test under vertical burning conditions for the halogen-free durable flame-retardant cotton fabric prepared in Example 1 of the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention. Example 1

[0026] This invention provides a method for preparing a phosphorus-containing cross-linked network durable flame-retardant cotton fabric, comprising the following steps: First, treat the cotton fabric with a 10wt% sodium hydroxide solution at 80°C for 1 hour.

[0027] The treated cotton fabric was immersed in the treatment solution at 35°C for 30 minutes. The concentrations of each component in the treatment solution were: ammonium polyphosphate 300 g / L, ethylene glycol 50 g / L, dicyandiamide 20 g / L, phosphoric acid 25 g / L, and zinc sulfate 10 g / L.

[0028] Take out the cotton fabric and dip and rub it twice on a vertical small gin, with a liquid content of 90%~110%. Then, it is shaped and dried in a high-temperature setting machine. Specifically, it is pre-dried at 80℃ for 5 minutes and then baked at 140℃ for 3 minutes to obtain the shaped cotton fabric.

[0029] The shaped cotton fabric is immersed in a 10 g / L zinc sulfate solution at 35°C for 30 min. The shaped cotton fabric is then removed and subjected to a second immersion and nipping on a vertical small nipping machine with a liquid content of 90%~110%. It is then dried at 80°C for 4 min to obtain a phosphorus-containing cross-linked network durable flame-retardant cotton fabric. Example 2

[0030] This invention provides a method for preparing a phosphorus-containing cross-linked network durable flame-retardant cotton fabric, comprising the following steps: First, treat the cotton fabric with a 10wt% sodium hydroxide solution at 80°C for 1 hour.

[0031] The treated cotton fabric was immersed in the treatment solution at 35°C for 30 minutes. The concentrations of each component in the treatment solution were: ammonium polyphosphate 250 g / L, ethylene glycol 60 g / L, dicyandiamide 15 g / L, phosphoric acid 20 g / L, and zinc sulfate 5 g / L.

[0032] Take out the cotton fabric and dip and rub it twice on a vertical small gin, with a liquid content of 90%~110%. Then, it is shaped and dried in a high-temperature setting machine. Specifically, it is pre-dried at 80℃ for 5 minutes and then baked at 140℃ for 3 minutes to obtain the shaped cotton fabric.

[0033] The shaped cotton fabric is immersed in a 5 g / L zinc sulfate solution at 35°C for 30 min. The shaped cotton fabric is then removed and subjected to a second immersion and nipping on a vertical small nipping machine with a liquid content of 90%~110%. It is then dried at 80°C for 4 min to obtain a phosphorus-containing cross-linked network durable flame-retardant cotton fabric. Example 3

[0034] This invention provides a method for preparing a phosphorus-containing cross-linked network durable flame-retardant cotton fabric, comprising the following steps: First, treat the cotton fabric with a 10wt% sodium hydroxide solution at 80°C for 1 hour.

[0035] The treated cotton fabric was immersed in the treatment solution at 35°C for 30 minutes. The concentrations of each component in the treatment solution were: ammonium polyphosphate 270 g / L, ethylene glycol 55 g / L, dicyandiamide 18 g / L, phosphoric acid 23 g / L, and zinc sulfate 8 g / L.

[0036] Take out the cotton fabric and dip and rub it twice on a vertical small gin, with a liquid content of 90%~110%. Then, it is shaped and dried in a high-temperature setting machine. Specifically, it is pre-dried at 80℃ for 5 minutes and then baked at 140℃ for 3 minutes to obtain the shaped cotton fabric.

[0037] The shaped cotton fabric is immersed in an 8 g / L zinc sulfate solution at 35°C for 30 min. The shaped cotton fabric is then removed and subjected to a second immersion and nipping on a vertical small nipping machine with a liquid content of 90%~110%. It is then dried at 80°C for 4 min to obtain a phosphorus-containing cross-linked network durable flame-retardant cotton fabric.

[0038] Comparative Example 1: This comparative example provides a cotton fabric sample, twill fabric, 308 g / m². 2 Purchased from Jiangsu Shazhou Printing and Dyeing Group (China).

[0039] Comparative Example 2: This comparative example provides a method for preparing modified cotton fabric, including the following steps: First, treat the cotton fabric with a 10wt% sodium hydroxide solution at 80°C for 1 hour.

[0040] At 70℃, the treated cotton fabric was immersed in a mixed solution of 300g / L ammonium polyphosphate and 50g / L dicyandiamide for 30min. The cotton fabric was then removed and subjected to two dips and two nips on a vertical nipper car with a liquid content of 90%~110%. Subsequently, it was set and dried in a high-temperature setting machine, specifically by pre-drying at 80℃ for 5min and then baking at 170℃ for 3min to obtain the modified cotton fabric.

[0041] The following tests were conducted on the phosphorus-containing cross-linked network durable flame-retardant cotton fabric prepared in Example 1, under multiple washing conditions, to evaluate the combustion performance of the cotton fabric.

[0042] The vertical burning test was conducted using a YGB15B type fabric vertical burning tester. According to the standard GB / T 5455-2014 "Determination of vertical damage length, smoldering and afterflame time of textiles", the damage length of the fabric under vertical burning conditions was tested.

[0043] The method for determining phosphorus content includes quantitative determination of phosphorus content using inductively coupled plasma atomic emission spectrometry (ICP-AES). The cotton fabric to be tested is cut into powder and dried in a drying oven. 0.1 g of the fabric is placed in 15 ml of aqua regia solution (nitric acid:hydrochloric acid = 1:3) to dissolve the cotton fabric. Then, the phosphorus content is calculated using the following formula: P content=Cs / W*V Wherein, P content represents the phosphorus content (mg / g), Cs is the concentration of phosphorus in the prepared solution (mg / L) obtained from the test, V is the volume of the prepared solution (0.015L), and W is the weight of the cotton fabric (0.1g).

[0044] The results of the vertical combustion test and the phosphorus content determination are as follows: Figure 1 , Figure 2 As shown, after 75 washes, the phosphorus-containing cross-linked network durable flame-retardant cotton fabric prepared in Example 1 still maintains a high phosphorus content, self-extinguishes in the vertical burning test, and has a damage length of less than 15 cm, indicating that the finishing system has excellent water-resistant flame-retardant properties.

[0045] Then, the mechanical properties of the phosphorus-containing cross-linked network durable flame-retardant cotton fabric prepared in Example 1, the original cotton fabric provided in Comparative Example 1, and the modified cotton fabric prepared in Comparative Example 2 were tested. The mechanical property tests included breaking strength test, bending performance test, and whiteness test. The specific test methods are as follows: Before the test, the cotton fabric was placed in a constant temperature and humidity room (relative humidity 65±5%, temperature 21±1℃) for 24 hours to acclimate it.

[0046] Tensile strength test: According to GB / T 3923.1-2013 Textiles – Tensile properties of fabrics – Part 1: Determination of tensile strength and elongation at break (strip method), the tensile strength of cotton fabrics was tested using an Instron 5976 universal testing machine. The sample size was 30cm × 5cm, and five samples were taken along the warp direction for testing to obtain the tensile strength and elongation at break. The average value of the test results was taken to avoid randomness.

[0047] Bending performance test: According to GB / T 18318.1-2009 Determination of bending properties of textiles - Part 1: Inclined plane method, the extension length (L) was measured using a fully automatic stiffness tester. The sample size was 20 cm × 2.5 cm, and five samples were taken in the warp direction to obtain the bending length to avoid randomness.

[0048] Whiteness Test: Fold the cotton fabric into 4 layers, and use an UltraScan PRO colorimeter to measure the L* (lightness), a* (red / green index), and b* (yellow / blue index) of the sample, and calculate the whiteness (WI) using the following formula: ; The test results are shown in Table 1: Table 1: Test results of mechanical properties of cotton fabrics obtained in Example 1 and Comparative Examples 1-2

[0049] As can be seen from the data in Table 1, the phosphorus-containing cross-linked network durable flame-retardant cotton fabric prepared in Example 1 has better physical properties than the control example. The main reason is the introduction of zinc sulfate, which lowers the reaction temperature while ensuring reaction efficiency, thereby reducing the physical damage to the cotton fabric caused by high temperature. At the same time, the reduced amount of dicyandiamide also reduces the impact of ammonia gas generated during the reaction on the whiteness of the cotton fabric.

[0050] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a phosphorus-containing cross-linked network durable flame-retardant cotton fabric, characterized in that, include: The cotton fabric is immersed in the treatment solution, and after the cotton fabric is taken out, it is dipped and rubbed twice, and then dried for the first time to obtain the shaped cotton fabric. The treatment solution is a mixed solution of ammonium polyphosphate, ethylene glycol, dicyandiamide, phosphoric acid and zinc sulfate. The shaped cotton fabric is immersed in zinc sulfate solution, and after being removed, it is subjected to two dips and two nips, and then dried for a second time to obtain a phosphorus-containing cross-linked network durable flame-retardant cotton fabric.

2. The method for preparing phosphorus-containing cross-linked network durable flame-retardant cotton fabric according to claim 1, characterized in that, Before immersing the cotton fabric in the treatment solution, the cotton fabric is pretreated, which includes immersing the cotton fabric in an alkaline reagent followed by washing.

3. The method for preparing phosphorus-containing cross-linked network durable flame-retardant cotton fabric according to claim 2, characterized in that, The alkaline reagent is an 8-12 wt% sodium hydroxide solution; And / or, the conditions for the impregnation treatment include treatment at 70~90°C for 0.5~1.5h.

4. The method for preparing phosphorus-containing cross-linked network durable flame-retardant cotton fabric according to claim 1, characterized in that, The treatment solution includes 250-300 g / L of ammonium polyphosphate, 50-60 g / L of ethylene glycol, 15-20 g / L of dicyandiamide, 20-25 g / L of phosphoric acid, and 5-10 g / L of zinc sulfate.

5. The method for preparing phosphorus-containing cross-linked network durable flame-retardant cotton fabric according to claim 1, characterized in that, The concentration range of the zinc sulfate solution is 5~10 g / L.

6. The method for preparing phosphorus-containing cross-linked network durable flame-retardant cotton fabric according to claim 1, characterized in that, The liquid content of cotton fabric after two dips and two nips is 90-110%.

7. The method for preparing phosphorus-containing cross-linked network durable flame-retardant cotton fabric according to claim 1, characterized in that, The impregnation process involves immersing the sample at a temperature of 30-40°C for 30-60 minutes.

8. The method for preparing phosphorus-containing cross-linked network durable flame-retardant cotton fabric according to claim 1, characterized in that, The conditions for the first drying process include pre-drying at 70-80°C for 3-5 minutes, followed by baking at 130-140°C for 3-5 minutes.

9. The method for preparing phosphorus-containing cross-linked network durable flame-retardant cotton fabric according to claim 1, characterized in that, The conditions for the second drying include baking at 70-80°C for 3-5 minutes.

10. A phosphorus-containing cross-linked network durable flame-retardant cotton fabric, characterized in that, It is prepared by the method for preparing phosphorus-containing cross-linked network durable flame-retardant cotton fabric as described in any one of claims 1 to 9.

Images