Organic flame-retardant gel containing ammonium polyphosphate as well as preparation method and application of organic flame-retardant gel

Abstract

The invention discloses organic flame-retardant gel containing ammonium polyphosphate as well as a preparation method and application of the organic flame-retardant gel, and belongs to the technical field of coal flame retardance. The preparation method of the organic flame-retardant gel containing ammonium polyphosphate comprises the following steps: adding hydroxyethyl cellulose, acrylamide, acrylic acid and ammonium persulfate into a sodium hydroxide solution at 0-5 DEG C, adding an ammonium polyphosphate solution after a polymerization reaction, and uniformly stirring to obtain the organic flame-retardant gel containing ammonium polyphosphate. The ammonium polyphosphate-containing organic flame-retardant gel provided by the invention is ammonium polyphosphate-modified hydroxyethyl cellulose gel, ammonium polyphosphate modification can enhance the water retention capacity of the gel and increase the thermal stability of the whole gel, hydroxyethyl cellulose plays a key role in water absorption, and meanwhile, ammonium polyphosphate with a small proportion plays an excellent role in thermal stability, so that the thermal stability of the gel is improved. Finally, the overall flame retardant property of the organic gel is excellent.

Description

Technical Field

[0001] This invention belongs to the field of coal flame retardant technology, specifically relating to an organic flame retardant gel containing ammonium polyphosphate, its preparation method, and its application. Background Technology

[0002] Coal is a fossil fuel that plays a vital role in industrial production and daily life, and is a fundamental driving force for economic development, in which it plays an irreplaceable role. To ensure the safe and efficient mining of coal, it is essential to strengthen comprehensive prevention and control of underground disasters.

[0003] Traditional flame-retardant gels are mostly inorganic gels or petroleum-based organic gels, which suffer from poor thermal stability, low flame-retardant efficiency, and environmental unfriendliness. Polysaccharide hydrogels (such as cellulose and chitosan) have attracted attention due to their advantages such as biodegradability, wide availability, and safety and environmental friendliness, but their poor thermal stability limits their application in high-temperature environments.

[0004] Therefore, developing a composite gel material that combines high water absorption and retention, excellent thermal stability, and high flame retardancy is of great theoretical and practical significance for the field of coal mine fire prevention and extinguishing. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides an ammonium polyphosphate-containing organic flame-retardant gel, its preparation method, and its applications. The provided ammonium polyphosphate-containing organic flame-retardant gel is an ammonium polyphosphate-modified hydroxyethyl cellulose gel. Ammonium polyphosphate modification enhances the gel's water retention capacity and increases its overall thermal stability. Hydroxyethyl cellulose plays a crucial role in water absorption, while the relatively small proportion of ammonium polyphosphate provides excellent thermal stability, ultimately resulting in excellent overall flame-retardant properties of the organic gel.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One of the technical solutions of this invention is to provide a method for preparing an organic flame-retardant gel containing ammonium polyphosphate, comprising the following steps:

[0008] Hydroxyethyl cellulose, acrylamide, acrylic acid, and ammonium persulfate were added to a sodium hydroxide solution at 0–5°C. After polymerization, an ammonium polyphosphate solution was added, and the mixture was stirred until homogeneous to obtain the ammonium polyphosphate-containing organic flame-retardant gel.

[0009] In this invention, hydroxyethyl cellulose (HEC) contains a large number of hydroxyl and ether bonds, giving it strong hygroscopicity and hydrophilicity. This allows it to effectively cool and isolate coal, thus acting as a flame retardant. Ammonium polyphosphate (APP) is an inorganic polymeric flame retardant containing P2O5 (65%–72%) and N (14%–16%). At high temperatures, it decomposes to generate polyphosphoric acid, promoting char formation and releasing ammonia to dilute oxygen, thus exhibiting dual flame retardant effects in both the condensed and gas phases, and possessing excellent thermal stability. The combination of these two components produces a significant synergistic effect: HEC provides water retention, cooling, adhesion, and penetration, while APP enhances thermal stability and promotes the formation of a dense char layer. Acrylamide (AAm) and acrylic acid (AA) primarily function as crosslinking monomers in the gel system, grafting and copolymerizing with HEC through free radical polymerization to form a stable three-dimensional network structure. Both contain carbon-carbon double bonds (C=C). The peroxy bond (-OO-) in potassium persulfate cleaves upon heating (50–70°C) to produce sulfate radicals (SO4). - The amide group (·) then captures hydrogen atoms from HEC, AAm, and AA monomer molecules, initiating a chain polymerization reaction. The resulting polymer chains form hydrogen bonds and chemical crosslinks with the hydroxyl groups of HEC through amide groups (-CONH2) and carboxyl groups (-COOH), constructing an interpenetrating network gel with high water absorption and retention capacity. AAm provides good water solubility and flexible segments, while AA enhances the ionic responsiveness and adhesion of the gel through carboxyl groups. The two work synergistically to regulate the crosslinking density, mechanical strength, and permeability of the gel. Potassium persulfate, due to its good water solubility, moderate decomposition temperature, and high initiation efficiency, although not directly involved in flame retardancy, can indirectly affect the permeability, adhesion, and evaporative cooling effect of the gel by controlling its dosage, thereby regulating the crosslinking density, water absorption ratio, and water retention capacity of the gel. It is an indispensable key additive for constructing a high-efficiency coal flame-retardant hydrogel system. The purpose of blending in a low-temperature sodium hydroxide solution before polymerization is to prevent AAm and AA from exothermic self-polymerization and rapid polymerization; at the same time, it protects the HEC molecular chains from acid hydrolysis, improves the grafting efficiency of its hydroxyl groups and monomers; it can also regulate the decomposition rate of potassium persulfate, promote the formation of a loose and porous three-dimensional network structure, significantly improve the water absorption and retention capacity of the flame retardant gel, and lay the structural foundation for the subsequent introduction of ammonium polyphosphate and synergistic flame retardant enhancement.

[0010] Preferably, the polymerization reaction is carried out at a temperature of 58–62°C for a time of 230–250 min.

[0011] Preferably, the mixture is stirred for 5 minutes every 30 minutes during the polymerization reaction to ensure uniform reaction.

[0012] Preferably, the concentration of the sodium hydroxide solution is 1 mol / L.

[0013] Preferably, the raw materials for preparation, excluding water, include, in molar percentage: 14%–17% hydroxyethyl cellulose, 6%–14% ammonium polyphosphate, 14%–17% acrylamide, 14%–17% acrylic acid, 14%–17% potassium persulfate, and 17%–36% sodium hydroxide.

[0014] More preferably, the molar ratio of the ammonium polyphosphate to the hydroxyethyl cellulose is 3:7.

[0015] The second technical solution of the present invention is to provide an organic flame retardant gel containing ammonium polyphosphate prepared according to the above-mentioned method for preparing organic flame retardant gel containing ammonium polyphosphate.

[0016] The third technical solution of the present invention provides an application of the above-mentioned organic flame retardant gel containing ammonium polyphosphate in the flame retardancy of coal.

[0017] The beneficial technical effects of the present invention are as follows:

[0018] This invention uses hydroxyethyl cellulose and ammonium polyphosphate as the main materials for making the gel, and acrylamide and acrylic acid as crosslinking agents. Combined with the reaction environment control of sodium hydroxide and potassium persulfate, a thermally stable organic flame-retardant gel containing ammonium polyphosphate was obtained, providing an efficient and useful approach for coal flame retardancy. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 SEM image of the ammonium polyphosphate-containing organic flame-retardant gel prepared in Example 1 after flame retardancy testing;

[0021] Figure 2 SEM image of the ammonium polyphosphate-containing organic flame-retardant gel prepared in Example 1 after flame retardancy testing;

[0022] Figure 3 SEM image of the ammonium polyphosphate-containing organic flame-retardant gel prepared in Example 2 after flame retardancy testing;

[0023] Figure 4 The image shows a SEM image of the ammonium polyphosphate-containing organic flame-retardant gel prepared in Example 2 after a flame-retardant test. Detailed Implementation

[0024] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0025] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0026] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention.

[0028] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0029] The hydroxyethyl cellulose used in the embodiments and comparative examples of this invention was purchased from Beijing Huawirui Chemical Co., Ltd.

[0030] The acrylamide used in the embodiments and comparative examples of this invention was purchased from Beijing Innocare Technology Co., Ltd.

[0031] The acrylic acid used in the embodiments and comparative examples of this invention was purchased from Beijing Jianqiang Weiye Technology Co., Ltd.

[0032] The sodium hydroxide used in the embodiments and comparative examples of this invention was purchased from Shanghai Mairui Biochemical Technology Co., Ltd.

[0033] The potassium persulfate used in the embodiments and comparative examples of this invention was purchased from Shanghai Mairui Biochemical Technology Co., Ltd.

[0034] Unless otherwise specified, room temperature in this invention refers to a temperature of 20±10℃.

[0035] Example 1

[0036] Preparation of ammonium polyphosphate-containing organic flame retardant gel:

[0037] The raw materials, excluding water, are as follows by molar percentage: 14% hydroxyethyl cellulose, 6% ammonium polyphosphate, 14% acrylamide, 14% acrylic acid, 17% potassium persulfate, and 35% sodium hydroxide; the molar ratio of ammonium polyphosphate to hydroxyethyl cellulose is 3:7.

[0038] Prepare a 1 mol / L sodium hydroxide solution and cool it to 3°C in an ice-water bath. Prepare a 0.5 mol / L ammonium polyphosphate solution and let it stand for 30 min. Add acrylic acid to the sodium hydroxide solution and cool it to 3°C in an ice-water bath. Then, add the corresponding molar amounts of hydroxyethyl cellulose, acrylamide, and potassium persulfate to the mixed solution in sequence. Stir at 800 r / min for 35 min until a viscous substance is formed. Transfer the mixture to a constant temperature water bath and heat it at 60°C for 240 min, stirring for 5 min every 30 min. Cool it to room temperature and add the ammonium polyphosphate solution dropwise to the resulting colloid. Stir evenly and add 35 mL of deionized water to accelerate the formation of the organic flame-retardant gel.

[0039] Example 2

[0040] Preparation of ammonium polyphosphate-containing organic flame retardant gel:

[0041] The raw materials, excluding water, are as follows by molar percentage: 15% hydroxyethyl cellulose, 10% ammonium polyphosphate, 15% acrylamide, 15% acrylic acid, 15% potassium persulfate, and 30% sodium hydroxide; the molar ratio of ammonium polyphosphate to hydroxyethyl cellulose is 4:6.

[0042] The preparation process is the same as in Example 1.

[0043] Comparative Example 1

[0044] Preparation of organic flame retardant gel:

[0045] The raw materials, excluding water, are as follows by molar percentage: 17% hydroxyethyl cellulose, 17% acrylamide, 17% acrylic acid, 17% potassium persulfate, and 32% sodium hydroxide; the molar ratio of hydroxyethyl cellulose to ammonium polyphosphate is 1:0.

[0046] The preparation process is the same as in Example 1.

[0047] Comparative Example 2

[0048] Preparation of ammonium polyphosphate-containing organic flame retardant gel:

[0049] The raw materials, excluding water, are as follows by molar percentage: 8% hydroxyethyl cellulose, 12% ammonium polyphosphate, 16% acrylamide, 16% acrylic acid, 15% potassium persulfate, and 33% sodium hydroxide; the molar ratio of ammonium polyphosphate to hydroxyethyl cellulose is 6:4.

[0050] The preparation process is the same as in Example 1.

[0051] Comparative Example 3

[0052] Preparation of ammonium polyphosphate-containing organic flame retardant gel:

[0053] The raw materials, excluding water, are as follows by molar percentage: 6% hydroxyethyl cellulose, 14% ammonium polyphosphate, 14% acrylamide, 14% acrylic acid, 17% potassium persulfate, and 35% sodium hydroxide; the molar ratio of ammonium polyphosphate to hydroxyethyl cellulose is 7:3.

[0054] The preparation process is the same as in Example 1.

[0055] The flame retardant properties of the ammonium polyphosphate-containing organic flame retardant gels prepared in Examples 1 and 2 were tested. A 6810 cone calorimeter was used to test and analyze the combustion resistance of the two gels on coal used in the thermogravimetric analysis. 40g of raw coal sample was sieved and mixed with the organic flame retardant gel from Example 1 or 2 at a mass ratio of 7:3. The mixture was then evenly spread on a sample trough (100mm × 100mm × 3mm) to prepare experimental samples. The experimental samples were then placed sequentially into the cone calorimeter at a room temperature of 20℃ and a thermal radiation intensity of 45kW / m². 2 Flame retardancy tests were conducted.

[0056] Figure 1 and Figure 2 SEM images of the ammonium polyphosphate-containing organic flame-retardant gel prepared in Example 1 at different magnifications after flame retardancy testing; Figure 3 and Figure 4 SEM images of the ammonium polyphosphate-containing organic flame-retardant gel prepared in Example 2 at different magnifications after flame retardancy testing.

[0057] from Figures 1-4 As can be seen, the flame-retardant gel prepared in Example 2 exhibits numerous small pores and cracks on its surface after thermal expansion, leading to accelerated water loss and exacerbated damage to the surface film structure, resulting in film rupture. This structure reduces the hydrogel's ability to effectively isolate oxygen, thus affecting its flame-retardant effect on coal. Figures 3-4 It can be seen that the surface structure of the flame retardant gel prepared in Example 1 remains relatively smooth after thermal expansion. Even when magnified to 10k times, its surface is still relatively flat with few cracks, proving that the flame retardant gel with an APP:HEC ratio of 3:7 has a low water loss rate and its surface structure is not easily damaged.

[0058] The limiting oxygen index (LOI) of the organic flame-retardant gels prepared in Examples 1-2 and Comparative Examples 1-3 was tested using a limiting oxygen index (LOI) tester on the gel-inhibited coal samples. The sample preparation method was as follows: 5 mL of water was uniformly mixed with 0.5 mg of the organic flame-retardant gel to prepare a diluted hydrogel. Then, 5 g of coal sample was added to the diluted hydrogel and stirred uniformly. The prepared sample was then dried in a drying oven at 60°C to obtain the test sample. The test results are shown in Table 1.

[0059] Table 1

[0060]

[0061] The water absorption capacity of hydrogels is a fundamental standard for evaluating their basic properties, and it is usually characterized by the equilibrium water absorption ratio. The stronger the water absorption capacity of a hydrogel, the greater the swelling volume per unit mass of the dried gel, and the more significant the evaporative heat absorption effect. This has a decisive impact on the effectiveness of oxygen-barrier coverage and cooling in fire prevention and extinguishing applications.

[0062] The gel equilibrium water absorption ratio of the organic flame retardant gels prepared using Examples 1-2 and Comparative Examples 1-3 was tested using a direct measurement method. The test results are shown in Table 2.

[0063] Table 2

[0064]

[0065] Comparing Example 1 and Comparative Example 1, it can be found that as the proportion of ammonium polyphosphate in the overall mass of the hydrogel increases, the limiting oxygen index of the flame-retardant coal first increases and then decreases significantly. The limiting oxygen index increases by 31% because ammonium polyphosphate produces ammonia at high temperatures, which can dilute the oxygen concentration. At the same time, hydroxyethyl cellulose carbonizes at high temperatures to form a carbonized layer, thus improving the flame-retardant effect.

[0066] Comparing Examples 1-2 and Comparative Examples 1-3, it can be found that as the mass of hydroxyethyl cellulose added decreases, the overall equilibrium water absorption ratio of the hydrogel decreases. This is because when the molar ratio of ammonium polyphosphate to hydroxyethyl cellulose is less than 3:7, the overall water absorption of the hydrogel is dominated by hydroxyethyl cellulose, which has a relatively stable network structure and is filled with a large number of water molecules. When the molar ratio of ammonium polyphosphate to hydroxyethyl cellulose is between 3:7 and 4:6, the overall water absorption performance of the hydrogel is achieved by the phosphate ions of ammonium polyphosphate and the hydroxyl groups of hydroxyethyl cellulose working together to absorb water, thus increasing the equilibrium water absorption ratio of the hydrogel.

[0067] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing an organic flame-retardant gel containing ammonium polyphosphate, characterized in that, Includes the following steps: Hydroxyethyl cellulose, acrylamide, acrylic acid, and ammonium persulfate were added to a sodium hydroxide solution at 0–5°C. After polymerization, an ammonium polyphosphate solution was added, and the mixture was stirred until homogeneous to obtain the ammonium polyphosphate-containing organic flame-retardant gel.

2. The method for preparing the ammonium polyphosphate-containing organic flame-retardant gel according to claim 1, characterized in that, The polymerization reaction is carried out at a temperature of 58–62°C for a time of 230–250 min.

3. The method for preparing the ammonium polyphosphate-containing organic flame-retardant gel according to claim 1, characterized in that, Stir for 5 minutes every 30 minutes during the polymerization reaction.

4. The method for preparing the ammonium polyphosphate-containing organic flame-retardant gel according to claim 1, characterized in that, The concentration of the sodium hydroxide solution is 1 mol / L.

5. The method for preparing the ammonium polyphosphate-containing organic flame-retardant gel according to claim 1, characterized in that, The raw materials for preparation, excluding water, include, by molar percentage: 14%–17% hydroxyethyl cellulose, 6%–14% ammonium polyphosphate, 14%–17% acrylamide, 14%–17% acrylic acid, 14%–17% potassium persulfate, and 17%–36% sodium hydroxide.

6. The method for preparing the ammonium polyphosphate-containing organic flame-retardant gel according to claim 5, characterized in that, The molar ratio of ammonium polyphosphate to hydroxyethyl cellulose is 3:

7.

7. An organic flame retardant gel containing ammonium polyphosphate prepared by the method of preparing an organic flame retardant gel containing ammonium polyphosphate according to any one of claims 1 to 6.

8. The application of the ammonium polyphosphate-containing organic flame retardant gel of claim 7 in the flame retardancy of coal.

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