A thermosensitive self-crosslinking hydrogel fire extinguishing agent and its preparation method

Abstract

The present invention relates to a thermosensitive self-crosslinking hydrogel fire extinguishing agent and its preparation method, belonging to the technical field of fire extinguishing agents. This invention addresses the existing problems of conventional water-based fire extinguishing agents, such as poor adhesion to combustible surfaces and low fire extinguishing efficiency, and the high viscosity of gel-type fire extinguishing agents, which makes them difficult to transport and spray. The present invention provides a thermosensitive self-crosslinking hydrogel fire extinguishing agent, comprising, by mass percentage, 0.5-1.5 wt.% modified carboxymethyl cellulose (E-CMC), 4-8 wt.% polyethylene glycol (PEG), 5-30 wt.% water-soluble flame retardant, and pure water as the solvent. The fire extinguishing agent exhibits good fluidity at room temperature and significantly increases viscosity at 90°C, facilitating adhesion to combustible surfaces, providing effective fire extinguishing and preventing rekindling. The fire extinguishing agent, containing 1.0 wt.% E-CMC and 6 wt.% PEG, has a viscosity of less than 1600 cp at room temperature and greater than 42,000 cp at 90°C, making it suitable for extinguishing Class A fires.

Description

Technical Field

[0001] The present invention relates to the technical field of fire extinguishing agents, in particular to a heat-sensitive self-crosslinking hydrogel fire extinguishing agent and a preparation method thereof. Background Art

[0002] Water is the most commonly used fire extinguishing agent, offering advantages such as high heat absorption, easy availability, and low cost. However, ordinary water has good fluidity and is easily volatile at high temperatures, making it difficult to retain on combustible materials and thus unable to fully exert its fire extinguishing properties. To address these shortcomings, researchers have added additives such as surfactants and inorganic salts to water, or processed the water through ultrafine grinding and atomization to enhance its fire extinguishing properties. These fire extinguishing agents are generally referred to as water-based fire extinguishing agents.

[0003] Hydrogel fire extinguishing agents are also a type of water-based fire extinguishing agent. Their primary component is hydrogel material. These are formed by adding natural or chemically synthesized substances to water, followed by chemical or physical crosslinking to form a high-water-content, gel-like substance with a three-dimensional network structure. These fire extinguishing agents exhibit excellent adhesion, water retention, and oxygen-barrier properties, forming a moisture-retaining, heat-insulating, and oxygen-isolating layer on the surface of a fire source, effectively curbing the spread of fire.

[0004] However, conventional hydrogel fire extinguishing agents often have high viscosity and poor fluidity, making them difficult to transport during fires. Furthermore, the high viscosity leads to low spraying efficiency, difficulty in spraying, and poor fire extinguishing effectiveness. Summary of the Invention

[0005] In view of the above analysis, the embodiments of the present invention are intended to provide a thermosensitive self-cross-linking hydrogel fire extinguishing agent and a preparation method thereof, so as to address at least one of the following problems: the poor adhesion of existing traditional water-based fire extinguishing agents to the surface of combustible materials, low oxygen isolation ability, and low fire extinguishing efficiency; and the high viscosity of existing gel-type fire extinguishing agents at room temperature, which makes them difficult to transport and spray.

[0006] The present invention provides a thermosensitive self-crosslinking hydrogel fire extinguishing agent, wherein the components of the fire extinguishing agent are as follows by mass percentage: 0.5-1.5 wt.% of modified carboxymethyl cellulose, 4-8 wt.% of polyethylene glycol, 5-30 wt.% of a water-soluble flame retardant, and the solvent is pure water;

[0007] Wherein, the modified carboxymethyl cellulose is carboxymethyl cellulose grafted with phenylethyl groups and having hydrophobic function.

[0008] Preferably, the components of the fire extinguishing agent are calculated by mass percentage as follows: 1.0 wt.%, modified carboxymethyl cellulose, 6 wt.%, polyethylene glycol, 20 wt.%, and water-soluble flame retardant, and the solvent is water; wherein the water-soluble flame retardant is ammonium polyphosphate.

[0009] Specifically, the fire extinguishing agent has a viscosity of less than 1600 cp at room temperature and >42,000 cp at 90°C. It is worth noting that this viscosity transition is irreversible, meaning that as the temperature rises, the fire extinguishing agent transforms from a fluid state to a gel state. Once the flame is extinguished and the temperature gradually decreases, the fire extinguishing agent remains in a gel state and adheres to the burning surface, effectively preventing re-ignition.

[0010] Specifically, the water-soluble flame retardant is one or more of ammonium hypophosphite, ammonium polyphosphate (polymerization degree 5-20), ammonium sulfate, monoammonium phosphate, diammonium phosphate, water-soluble magnesium hydroxide, and water-soluble aluminum hydroxide; preferably, ammonium polyphosphate.

[0011] The present invention also discloses a method for preparing the modified carboxymethyl cellulose, comprising the following specific steps:

[0012] S1-1: dissolving sodium carboxymethyl cellulose in N,N-dimethylformamide and adding hydrochloric acid to acidify to obtain carboxymethyl cellulose;

[0013] S1-2: Add 4-ethylaniline to the solution, heat and stir, and continuously remove excess water during the process;

[0014] S1-3: Cooling to room temperature while continuously stirring during the cooling process, and obtaining a crude modified carboxymethyl cellulose product liquid after the cooling is completed;

[0015] S1-4: adding an excess of anhydrous methanol to the crude modified carboxymethyl cellulose product to obtain flocs; allowing the flocs to settle, filtering, washing, and drying to obtain a brown solid, i.e., the crude modified carboxymethyl cellulose product.

[0016] Specifically, the preparation method further includes step S1-5: dissolving the crude modified carboxymethyl cellulose product in water, pouring in excess anhydrous methanol to obtain flocs; allowing the flocs to settle, filtering, washing, and drying to obtain a light yellow solid, namely, modified carboxymethyl cellulose.

[0017] Specifically, the specific operations of step S1-1 are:

[0018] Heat to temperature T1 and keep warm, dissolve sodium carboxymethyl cellulose in N,N-dimethylformamide, add hydrochloric acid to acidify and continue stirring for a period of h1, and adjust the pH value to 2-3;

[0019] The range of T1 is 20~60℃, the stirring rate is 300~600 r / min, and h1≥30min.

[0020] Specifically, the specific operations of step S1-2 are:

[0021] Heat to temperature T2 and keep warm, add 4-ethylaniline to the solution, stir for a period of time h2, T2 range is 20 ~ 60 ° C, h2 ≥ 5 min, stirring rate is 300 ~ 600 r / min;

[0022] Raise the temperature to T3 and stir for a period of time h3, where T3 ranges from 60 to 90°C, h3 ≥ 30 min, and the stirring rate is 300 to 600 r / min;

[0023] Continue to heat up to temperature T4, stir for a period of h4, and continuously remove excess water during the process. The range of T4 is 110-130°C, h4 is 2-12h, and the stirring rate is 200-400 r / min.

[0024] Specifically, the stirring rate in step S1-3 is 200-400 r / min.

[0025] The present invention also discloses a method for preparing the fire extinguishing agent, which specifically comprises the following steps:

[0026] S2-1: Preparation of modified carboxymethyl cellulose;

[0027] S2-2: Fully dissolving modified carboxymethyl cellulose and polyethylene glycol in pure water to obtain a thermosensitive self-crosslinking hydrogel;

[0028] S2-3: Adding a water-soluble flame retardant to the thermosensitive self-crosslinking hydrogel to obtain a thermosensitive self-crosslinking hydrogel fire extinguishing agent.

[0029] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0030] 1. The present invention uses modified carboxymethyl cellulose (E-CMC) (i.e., hydrophobic carboxymethyl cellulose grafted with a phenylethyl group) and polyethylene glycol (PEG) to prepare a thermosensitive self-crosslinking hydrogel. Simultaneously, a water-soluble flame retardant is added to obtain a thermosensitive self-crosslinking hydrogel fire extinguishing agent with good fluidity at room temperature and significantly improved viscosity at high temperature. This achieves the advantages of convenient transportation, efficient spraying, and excellent fire extinguishing effect.

[0031] When E-CMC and PEG are dissolved in water, in addition to intermolecular van der Waals forces, PEG molecules also form hydrogen bonds with water (H2O) molecules. Below the critical phase transition temperature (LCST), water molecules form an ordered structure around the phenylethyl group. This ordered structure hinders the association of multiple hydrophobic phenylethyl groups (the phenylethyl groups in the E-CMC side chains), thus hindering cross-linking between E-CMC molecules. Therefore, below the LCST, E-CMC molecules are readily soluble in water, exhibit low viscosity, and exhibit good fluidity. Above the LCST, the system undergoes intense thermal motion, disrupting the ordered structure of water molecules around the phenylethyl groups. At this point, the hydrophobic phenylethyl groups on the E-CMC molecules rapidly associate with each other, cross-linking the E-CMC molecules and forming a three-dimensional network structure, a gel structure. Therefore, above the LCST, E-CMC molecules undergo hydrophobic association, and the viscosity gradually increases with temperature, demonstrating excellent gel-forming properties.

[0032] It's worth noting that if the E-CMC fraction is too low, no hydrogel will form even above the LCST. This is because the E-CMC concentration is too low, resulting in minimal intermolecular entanglement. This results in no cross-linking or a very low degree of cross-linking between molecules, no hydrogel formation, or minimal gelation. Ultimately, this inability to effectively gel and isolate oxygen at high temperatures during firefighting. If the E-CMC fraction is too high, intermolecular cross-linking will occur below the LCST, forming a three-dimensional cross-linked network. This means that the material exists in a gelled state at room or low temperatures, making it difficult to package, transport, store, or even spray.

[0033] It's worth noting that while this thermosensitive self-crosslinking hydrogel inherently possesses some fire-extinguishing properties, its flame retardancy and fire-extinguishing capabilities are modest, posing a risk of rekindling. Therefore, the present invention further incorporates a water-soluble flame retardant into this thermosensitive self-crosslinking hydrogel to produce a thermosensitive self-crosslinking hydrogel fire extinguishing agent. In particular, the selected water-soluble flame retardant has minimal impact on the hydrogel's viscosity and heat-sensitivity, while significantly improving its flame retardancy and fire-extinguishing properties, further enhancing its fire-extinguishing efficiency and reducing the likelihood of rekindling.

[0034] 2. Preferably, the present invention uses ammonium polyphosphate as a water-soluble flame retardant. During combustion, ammonium polyphosphate generates phosphorus-containing free radicals, which effectively capture H·, O·, and HO· free radicals generated by the burning materials in the gas phase, interrupting the combustion chain reaction. Ammonium polyphosphate also promotes the carbonization of combustibles in the condensed phase, forming a dense carbon layer that blocks oxygen and combustibles, thereby endowing the fire extinguishing agent with excellent flame retardancy and fire extinguishing capabilities.

[0035] 3. The present invention provides a method for preparing the E-CMC. By precisely controlling parameters such as raw material ratios, temperature, time, and stirring rate, this method efficiently produces a crude E-CMC product. Post-processing, including separation, purification, and drying, yields high-purity E-CMC. The entire process, characterized by mild reaction conditions and a refined preparation process, is suitable for large-scale production.

[0036] It's worth emphasizing that while the present invention utilizes 4-ethylaniline to graft phenethyl groups onto carboxymethyl cellulose, hydrophobic E-CMC with phenethyl side chains obtained by other preparation methods can also meet the requirements of the fire extinguishing agent of the present invention. This invention only provides an efficient and convenient method for preparing E-CMC; this method is not intended to be the sole route to obtaining this modified carboxymethyl cellulose.

[0037] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description. In addition, some advantages will become apparent from the description or be understood through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not intended to limit the present invention. Like reference symbols denote like components throughout the drawings.

[0039] Figure 1 is a photo of the thermosensitive self-crosslinking hydrogel fire extinguishing agent in Example 4, wherein Figure a is at room temperature and Figure b is at 90°C;

[0040] Figure 2 is the hydrogen nuclear magnetic resonance spectrum of modified carboxymethyl cellulose (E-CMC) (Example 1-1);

[0041] Figure 3 This is the hydrogen nuclear magnetic resonance spectrum of sodium carboxymethyl cellulose. DETAILED DESCRIPTION

[0042] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0043] To address the current challenges of traditional water-based or gel-based fire extinguishing agents, which struggle to balance fluidity and adhesion, this invention innovatively provides a hydrogel fire extinguishing agent that flows rapidly at room temperature, resolving the high viscosity issues associated with conventional additive-based fire extinguishing agents. Furthermore, it forms a highly adhesive hydrogel at high temperatures, addressing the weak or near-nonexistent adhesion of traditional water-based fire extinguishing agents. Furthermore, the addition of a water-soluble flame retardant to this system provides even greater fire extinguishing effectiveness.

[0044] The present invention provides a thermosensitive self-crosslinking hydrogel fire extinguishing agent, wherein the components of the fire extinguishing agent are as follows by mass percentage: 0.5-1.5 wt.% of modified carboxymethyl cellulose, 4-8 wt.% of polyethylene glycol, 5-30 wt.% of a water-soluble flame retardant, and the solvent is pure water;

[0045] Wherein, the modified carboxymethyl cellulose is carboxymethyl cellulose grafted with phenylethyl groups and having hydrophobic function.

[0046] The present invention uses modified carboxymethyl cellulose (E-CMC) and polyethylene glycol (molecular weight of 1000-10000) (PEG) to prepare a thermosensitive self-crosslinking hydrogel; at the same time, a water-soluble flame retardant is added to obtain a thermosensitive self-crosslinking hydrogel fire extinguishing agent with good fluidity at room temperature and significantly improved high-temperature viscosity, achieving the effects of convenient transportation, efficient spraying, and excellent fire extinguishing effect.

[0047] When E-CMC and PEG are dissolved in water, in addition to intermolecular van der Waals forces, PEG molecules also form hydrogen bonds with water (H2O) molecules. Below the critical phase transition temperature (LCST), water molecules form an ordered structure around the phenylethyl group. This ordered structure hinders the association of multiple hydrophobic phenylethyl groups (the phenylethyl groups in the E-CMC side chains), thus hindering cross-linking between E-CMC molecules. Therefore, below the LCST, E-CMC molecules are readily soluble in water, exhibit low viscosity, and exhibit good fluidity. Above the LCST, the system undergoes intense thermal motion, disrupting the ordered structure of water molecules around the phenylethyl groups. At this point, the hydrophobic phenylethyl groups on the E-CMC molecules rapidly associate with each other, cross-linking the E-CMC molecules and forming a three-dimensional network structure, a gel structure. Therefore, above the LCST, E-CMC molecules undergo hydrophobic association, and the viscosity gradually increases with temperature, demonstrating excellent gel-forming properties.

[0048] It's worth noting that if the E-CMC fraction is too low, no hydrogel will form even above the LCST. This is because the E-CMC concentration is too low, resulting in minimal intermolecular entanglement. This results in no cross-linking or a very low degree of cross-linking between molecules, no hydrogel formation, or minimal gelation. Ultimately, this inability to effectively gel and isolate oxygen at high temperatures during firefighting. If the E-CMC fraction is too high, intermolecular cross-linking will occur below the LCST, forming a three-dimensional cross-linked network. This means that the material exists in a gelled state at room or low temperatures, making it difficult to package, transport, store, or even spray.

[0049] It's worth noting that while this thermosensitive self-crosslinking hydrogel inherently possesses some fire-extinguishing properties, its flame retardancy and fire-extinguishing capabilities are modest, posing a risk of rekindling. Therefore, the present invention further incorporates a water-soluble flame retardant into this thermosensitive self-crosslinking hydrogel to produce a thermosensitive self-crosslinking hydrogel fire extinguishing agent. In particular, the selected water-soluble flame retardant has minimal impact on the hydrogel's viscosity and heat-sensitivity, while significantly improving its flame retardancy and fire-extinguishing properties, further enhancing its fire-extinguishing efficiency and reducing the likelihood of rekindling.

[0050] Specifically, experimental verification (see the Examples and Comparative Examples for details) shows that the higher the addition amount of E-CMC and PEG, the higher the viscosity of the fire extinguishing agent. Therefore, excessive addition leads to poor fluidity at room temperature; excessively low addition amounts lead to poor adhesion at high temperatures, preventing the formation of a high-viscosity hydrogel, resulting in reduced adhesion and oxygen barrier properties, and thus impairing fire extinguishing effectiveness. When the mass content of E-CMC and PEG is in the range of 0.5-1.5 wt.% and 4-8 wt.%, respectively, the fire extinguishing agent of this invention exhibits good fluidity and adhesion at both room and high temperatures, indicating that the addition amount range is suitable.

[0051] Furthermore, the higher the amount of water-soluble flame retardant added, the better the fire extinguishing effect of the fire extinguishing agent. However, when the addition amount is too high, the fire extinguishing agent will stratify, causing its overall properties to change and failing to form a homogeneous, stable mixture. Moreover, when the addition amount of water-soluble flame retardant reaches a certain proportion (20 wt.%), the fire extinguishing performance will not be significantly improved. Therefore, the content of water-soluble flame retardant is preferably between 5 and 30 wt.%, with the preferred content being 20 wt.%.

[0052] Preferably, the components of the fire extinguishing agent are calculated in percentage by mass as follows: 1 wt.%, modified carboxymethyl cellulose, 6 wt.%, polyethylene glycol, 20 wt.%, and a water-soluble flame retardant, wherein the solvent is water; wherein the water-soluble flame retardant is ammonium polyphosphate.

[0053] Specifically, the fire extinguishing agent has a viscosity of less than 1600 cp at room temperature and >42,000 cp at 90°C. It is worth noting that this viscosity transition is irreversible, meaning that as the temperature rises, the fire extinguishing agent transforms from a fluid state to a gel state. Once the flame is extinguished and the temperature gradually decreases, the fire extinguishing agent remains in a gel state and adheres to the burning surface, effectively preventing re-ignition.

[0054] Specifically, the water-soluble flame retardant is one or more of ammonium hypophosphite, ammonium polyphosphate (degree of polymerization between 5 and 20), ammonium sulfate, monoammonium phosphate, diammonium phosphate, water-soluble magnesium hydroxide, and water-soluble aluminum hydroxide; the above water-soluble flame retardants can significantly improve the fire extinguishing performance of the fire extinguishing agent.

[0055] More preferably, the water-soluble flame retardant is ammonium polyphosphate. This not only generates phosphorus-containing free radicals during combustion, which effectively capture H·, O·, and HO· free radicals generated by the burning materials in the gas phase, interrupting the combustion chain reaction, but also promotes the carbonization of combustibles in the condensed phase, forming a dense carbon layer that blocks oxygen and combustibles, thereby endowing the fire extinguishing agent with excellent flame retardancy and fire extinguishing capabilities.

[0056] The present invention also discloses a method for preparing the modified carboxymethyl cellulose, comprising the following specific steps:

[0057] S1-1: dissolving sodium carboxymethyl cellulose in N,N-dimethylformamide and adding hydrochloric acid to acidify to obtain carboxymethyl cellulose. The acidification process is shown in the chemical reaction formula;

[0058] ;

[0059] S1-2: Add 4-ethylaniline to the solution, heat and stir, and continuously remove excess water during the process. The condensation reaction process is shown in the chemical reaction formula;

[0060] ;

[0061] S1-3: Cooling to room temperature while continuously stirring during the cooling process, and obtaining a crude modified carboxymethyl cellulose product liquid after the cooling is completed;

[0062] S1-4: Add excess anhydrous methanol to the crude E-CMC product to produce floccules. Allow the floccules to settle after a period of filtration, washing, and drying to obtain a brownish-yellow solid, the crude E-CMC product. Since CMC and E-CMC are insoluble in methanol, while 4-ethylaniline is soluble in methanol, adding excess anhydrous methanol to the crude product can induce the precipitation of unreacted CMC and the product E-CMC. Repeat this process three times to remove the 4-ethylaniline and obtain the crude E-CMC product.

[0063] Specifically, the preparation method further includes step S1-5 (purification step): dissolving the crude E-CMC product in water, pouring in an excess of anhydrous methanol to obtain flocs; allowing the flocs to stand for a period of time, and after settling, filtering, washing, and drying to obtain a light yellow solid, namely, modified carboxymethyl cellulose.

[0064] Because the E-CMC molecular chain contains hydrophobic groups, its solubility in water is lower than that of CMC. When the volume ratio of water to anhydrous methanol is 1:3, the hydrophobic E-CMC will precipitate in large quantities, while the hydrophilic CMC can still dissolve in water. Repeat this process three times to obtain E-CMC with higher purity.

[0065] Specifically, for precipitation of the crude E-CMC product in S1-4, 500 mL of anhydrous methanol was added per 100 mL of the crude product solution. For purification of the final E-CMC product in S1-5, 300 mL of anhydrous methanol was added per 100 mL of the crude product aqueous solution. During the addition of anhydrous methanol in S1-4 and S1-5, the stirring rate was ≥ 600 rpm. After a large amount of flocculent product precipitated, stirring was stopped and the solution was allowed to stand for ≥ 20 minutes.

[0066] For example, the temperature is lowered to room temperature, and the stirring rate is 300 r / min during the cooling process. Stirring is stopped, and the crude product liquid is poured into a clean beaker. Then, an excess of anhydrous methanol is added (500 ml of anhydrous methanol is added for every 100 ml of crude product liquid). The stirring rate is 600 r / min. The crude product liquid precipitates to obtain flocs. Stirring is stopped, and the mixture is allowed to stand for 20 minutes. After the flocs settle, they are filtered using a Buchner funnel to obtain a crude product. The crude product is washed again with anhydrous methanol three times and fully dried to obtain a brown-yellow solid. The crude product is dissolved in water, and an excess of anhydrous methanol is added (300 ml of anhydrous methanol is added for every 100 ml of solution). The stirring rate is 600 r / min, and the mixture is allowed to stand for 20 minutes. The flocs settle, and they are filtered using a Buchner funnel. The product is fully dried to obtain the product. This process is repeated three times to obtain a light yellow solid, namely E-CMC.

[0067] Specifically, the specific operations of step S1-1 are:

[0068] Heat to temperature T1 and keep warm, dissolve sodium carboxymethyl cellulose in N,N-dimethylformamide, add hydrochloric acid to acidify and continue stirring for a period of h1, and adjust the pH value to 2-3;

[0069] The range of T1 is 20~60℃, the stirring rate is 300~600 r / min, and h1≥30min.

[0070] Specifically, in step S1-1, hydrochloric acid is added to a pH between 2 and 3 to fully acidify the sodium carboxymethyl cellulose to obtain carboxymethyl cellulose without introducing excess water that would hinder subsequent reactions. A stirring time h1 of 30 min or greater allows for full acidification of the sodium carboxymethyl cellulose.

[0071] Specifically, the specific operations of step S1-2 are:

[0072] Heat to temperature T2 and keep warm, add 4-ethylaniline to the solution, stir for a period of time h2, T2 ranges from 20 to 60°C, h2 ≥ 5 minutes, and the stirring rate is 300 to 600 r / min; at this time, 4-ethylaniline (the molar ratio of sodium carboxymethyl cellulose to 4-ethylaniline is 1:1.5 to 2, and excess 4-ethylaniline is conducive to promoting the condensation reaction in the forward direction) will be initially mixed with the solution;

[0073] The temperature is raised to T3, and the mixture is stirred for a period of time h3, wherein T3 ranges from 60 to 90°C, h3 ≥ 30 min, and the stirring rate is 300 to 600 r / min. Since 4-ethylaniline is hydrophobic, raising the temperature and stirring sufficiently can allow 4-ethylaniline to be fully mixed into the solution.

[0074] Continue heating to T4 and stirring for h4, while continuously removing excess water. T4 ranges from 110 to 130°C, h4 lasts from 2 to 12 hours, and the stirring rate is 200 to 400 r / min. As the reaction proceeds, the viscosity of the reaction solution decreases. The stirring rate should be appropriately reduced to avoid excessive reaction and the formation of byproducts. During the reaction, it is important to remove excess water from the system to promote the forward reaction.

[0075] It is worth noting that in S1-2, in order to promote the reaction, it is preferably necessary to increase the temperature to ≥120°C and remove excess water during the reaction, otherwise the final yield will be very low.

[0076] Specifically, the E-CMC prepared by the above method was subjected to nuclear magnetic resonance hydrogen spectrum detection (such as Figure 2 As shown), and the nuclear magnetic resonance hydrogen spectrum of sodium carboxymethyl cellulose ( Figure 3 ) Comparison shows that δ = 7.27, 7.29, and 7.35 correspond to the resonance absorption peaks of the hydrogen on the benzene ring; δ = 1.17 corresponds to the resonance absorption peak of the hydrogen on the methyl group -CH3 in the ethyl group; and δ = 2.66 corresponds to the resonance absorption peak of the hydrogen on the methylene group -CH2- in the ethyl group. In summary, the detected modified characteristic peaks demonstrate that 4-ethylaniline has been grafted onto the carboxymethyl cellulose molecular chain, resulting in hydrophobic E-CMC.

[0077] The present invention also discloses a method for preparing the fire extinguishing agent, which specifically comprises the following steps:

[0078] S2-1: Preparation of modified carboxymethyl cellulose;

[0079] S2-2: Fully dissolving modified carboxymethyl cellulose and polyethylene glycol in pure water to obtain a thermosensitive self-crosslinking hydrogel;

[0080] S2-3: Adding a water-soluble flame retardant to the thermosensitive self-crosslinking hydrogel to obtain a thermosensitive self-crosslinking hydrogel fire extinguishing agent.

[0081] Specifically, stirring is required in step S2-2, and the dissolving stirring speed is 200 to 800 r / min.

[0082] The test group was prepared using modified carboxymethyl cellulose (E-CMC).

[0083] Example 1-1:

[0084] 1. Dissolve sodium carboxymethyl cellulose in N,N-dimethylformamide, heat to 40℃ and keep warm, add hydrochloric acid to acidify, adjust the pH value between 2-3, and continue stirring for 30 minutes at a stirring rate of 400 r / min.

[0085] 2. At an ambient temperature of 40°C, add 4-ethylaniline to the above solution at a stirring rate of 400 r / min. After stirring for 5 minutes, gradually increase the temperature to 80°C and continue stirring for another 30 minutes.

[0086] 3. Raise the temperature to 120°C and stir at a rate of 300 r / min. During this period, continuously discharge the water produced in the reaction and stir for 4 hours.

[0087] 4. Cool the temperature from 120°C to room temperature with a continuous stirring rate of 300 r / min. After cooling, the crude E-CMC product liquid is obtained.

[0088] 5. Add excess anhydrous methanol to the E-CMC crude product liquid, adding 500 mL of anhydrous methanol for every 100 mL of crude product liquid to obtain flocs; let it stand for a while, wait for the flocs to settle, filter, wash, and dry to obtain a brown solid to obtain the E-CMC crude product.

[0089] 6. Dissolve the crude E-CMC in pure water and add an excess of anhydrous methanol (300 ml per 100 ml of solution). Stir at 600 rpm to allow the crude product to precipitate into flocs. Allow the flocs to settle for 20 minutes. Repeat this step three times. After drying, a pale yellow solid is obtained, the final product, E-CMC.

[0090] Example 1-2:

[0091] Compared with step 1 of Example 1-1, the pH of the reaction system was adjusted to between 4 and 5, and the other steps were the same as those of Example 1-1.

[0092] Example 1-3:

[0093] Compared with step 2 of Example 1-1, after adding 4-ethylaniline, the temperature was not gradually increased, but directly increased to 120° C. The other steps were the same as those of Example 1-1.

[0094] Comparative Example 1-1:

[0095] Compared with step 3 of Example 1-1, the temperature was not raised to 120° C., but directly stirred at 80° C. for 4 h. The other steps were the same as those of Example 1-1.

[0096] Comparative Example 1-2:

[0097] Compared with step 3 of Example 1-1, no water removal is performed, and the other steps are the same as those of Example 1-1.

[0098] The products obtained in each set of reaction steps 5 and 6 are weighed;

[0099] ;

[0100] The obtained products were recorded as Example 1-1, Example 1-2, Example 1-3, Comparative Example 1-1, and Comparative Example 1-2.

[0101] The purity of the products was tested. The purity of the product of Example 1-1 in the precipitate was 84%; the purity of the product of Example 1-2 in the precipitate was 55%; and the purity of the product of Example 1-3 in the precipitate was 72%.

[0102] The purity of the product of Comparative Example 1-1 in the precipitate was 0%; the purity of the product of Comparative Example 1-2 in the precipitate was 5%.

[0103] These results indicate that adjusting the pH of the system or increasing the temperature directly after adding 4-ethylaniline in the second step of the reaction will result in a decrease in the final yield. If the reaction is not carried out above 110°C (preferably above 120°C) or if water is not removed during the reaction, the reaction will not react and no product will be produced.

[0104] The E-CMC prepared in Example 1-1 was subjected to nuclear magnetic resonance spectroscopy (H NMR) Figure 2 As shown), and the nuclear magnetic resonance hydrogen spectrum of sodium carboxymethyl cellulose ( Figure 3) Comparison shows that δ = 7.27, 7.29, and 7.35 correspond to the resonance absorption peaks of the hydrogen on the benzene ring; δ = 1.17 corresponds to the resonance absorption peak of the hydrogen on the methyl group -CH3 in the ethyl group; and δ = 2.66 corresponds to the resonance absorption peak of the hydrogen on the methylene group -CH2- in the ethyl group. In summary, the detected modified characteristic peaks demonstrate that 4-ethylaniline has been grafted onto the carboxymethyl cellulose molecular chain, resulting in hydrophobic E-CMC.

[0105] Thermosensitive self-crosslinking hydrogel test group

[0106] The E-CMC prepared in Example 1-1 and commercially available PEG were used to test the thermosensitive self-crosslinking hydrogel formulation.

[0107] E-CMC and PEG were oven-dried at 60°C and dissolved in pure water at 60°C at a speed of 200 to 800 r / min in varying ratios to obtain the corresponding thermosensitive self-crosslinking hydrogels. The viscosity of the resulting hydrogels was then measured. A viscosity of 2000 cp was defined as the critical viscosity. A viscosity below 2000 cp indicated good fluidity, while a viscosity above 2000 cp indicated a gradual increase in viscosity and enhanced adhesion. A viscosity above 10000 cp exhibited excellent gelation. The fluidity of the systems at room temperature and 90°C was observed, as shown in Tables 1 and 2.

[0108] Table 1 Viscosity of thermosensitive self-crosslinking hydrogel at room temperature (unit: cp)

[0109] ;

[0110] Table 2 Viscosity of thermosensitive self-crosslinking hydrogel at 90°C, unit: cp

[0111] ;

[0112] Through experiments, it can be determined that when the E-CMC concentration is 0.5-1.5wt% and the PEG concentration is 4-8 wt%, the viscosity is low at room temperature <2000cp (the highest is 1901cp); at 90℃, the viscosity is high, >11000cp (the lowest is 11280cp). Figure 1 As shown in the figure, adding 1.0 wt% E-CMC and 6 wt% PEG to prepare an aqueous solution / thermosensitive self-crosslinking hydrogel has a low viscosity (1508 cp) at room temperature and is a translucent liquid. After being placed in a 90°C water bath for 30 minutes, the viscosity increases to 42890 cp, resulting in a pale yellow gel with moderate performance. If the E-CMC concentration is too high, the viscosity at room temperature is too high and the fluidity is poor. If the concentration is too low, a high-viscosity hydrogel cannot form at high temperatures.

[0113] Fire extinguishing agent formulation test group

[0114] Thermosensitive self-crosslinking hydrogel prepared with 1.0 wt% E-CMC and 6 wt% PEG was used to match the fire extinguishing agent, and its fire extinguishing effect was tested.

[0115] Fire extinguishing agent 2-1: E-CMC and PEG were dried in an oven at 60°C; 1.0 wt% E-CMC and 6 wt% PEG were dissolved in pure water at 40°C and a rotation speed of 200-800 r / min, and the mixture was cooled to room temperature to obtain a hydrogel system of E-CMC and PEG.

[0116] Fire extinguishing agent 2-2: add 5wt.% of ammonium polyphosphate; other properties are the same as fire extinguishing agent 2-1.

[0117] Fire extinguishing agent 2-3: add 10wt.% of ammonium polyphosphate; other properties are the same as fire extinguishing agent 2-1.

[0118] Fire extinguishing agent 2-4: add 15wt.% of ammonium polyphosphate; other properties are the same as fire extinguishing agent 2-1.

[0119] Fire extinguishing agent 2-5: add 20wt.% of ammonium polyphosphate; other properties are the same as fire extinguishing agent 2-1.

[0120] Fire extinguishing agent 2-6: add 25wt.% of ammonium polyphosphate; other properties are the same as fire extinguishing agent 2-1.

[0121] Fire extinguishing agent 2-7: add 30wt.% of ammonium polyphosphate; other properties are the same as fire extinguishing agent 2-1.

[0122] Fire extinguishing agent 2-8: add 20wt.% of ammonium hypophosphite; other properties are the same as fire extinguishing agent 2-1.

[0123] Fire extinguishing agent 2-9: add 20wt.% of water-soluble magnesium hydroxide; other properties are the same as fire extinguishing agent 2-1.

[0124] Fire extinguishing agent 2-10: pure water.

[0125] Fire extinguishing agent 2-11: Add 15 wt.% ammonium polyphosphate to pure water, fully dissolve it at 40°C and a rotation speed of 200-800 r / min, and cool it to room temperature to obtain a 15 wt.% ammonium polyphosphate solution.

[0126] Fire extinguishing agent 2-12: Add 20 wt.% ammonium polyphosphate to pure water, fully dissolve it at 40°C and 200-800 r / min, and cool it to room temperature to obtain a 20 wt.% ammonium polyphosphate solution.

[0127] Among them, fire extinguishing agents 2-1, 2-10, 2-11, and 2-12 are comparative examples, and the others are examples.

[0128] A woodpile model was constructed in an open space to test the fire-extinguishing performance of fire extinguishing agents. The model consisted of nine 2×2×20 cm pinewood strips, three strips per layer, for a total of three layers. A crystallizing dish filled with alcohol was placed beneath the woodpile to ignite it. The woodpile was ignited with alcohol for 90 seconds. The crystallizing dish was then removed and allowed to burn freely for approximately 80 seconds until the flame stabilized. The fire extinguishing agent was then sprayed, and the extinguishing time and re-ignition rate were recorded. The test results are shown in Table 3.

[0129] Table 3 Fire extinguishing agent fire extinguishing effect test table:

[0130] sample Fire extinguishing time / s Reignition time / s Fire extinguishing agent 2-1 178 1244 Fire extinguishing agent 2-2 169 No resurgence Fire extinguishing agent 2-3 164 No resurgence Fire extinguishing agent 2-4 158 No resurgence Fire extinguishing agent 2-5 149 No resurgence Fire extinguishing agent 2-6 151 No resurgence Fire extinguishing agent 2-7 146 No resurgence Fire extinguishing agent 2-8 161 No resurgence Fire extinguishing agent 2-9 172 No resurgence Fire extinguishing agent 2-10 223 906 Fire extinguishing agent 2-11 205 1154 Fire extinguishing agent 2-12 197 1203 ;

[0131] The experimental results show that compared with 2-10 without hydrogel, the fire extinguishing time of 2-1 is reduced by 45 seconds and the re-ignition time is extended by 338 seconds, indicating that the thermosensitive self-crosslinking hydrogel itself has better fire extinguishing performance than water.

[0132] Compared to 2-11, the fire extinguishing time of 2-4 was reduced by 47 seconds, and there was no rekindling. Compared to 2-12, the fire extinguishing time of 2-5 was reduced by 48 seconds, and there was no rekindling. This indicates that, given the same mass fraction of the same flame retardant, the addition of the hydrogel system can reduce the fire extinguishing time. This is because the fire extinguishing agent with only the flame retardant has a low system viscosity, and the flame retardant cannot adhere to the surface of the burning object, failing to quickly extinguish the flame and prevent rekindling. When the hydrogel and flame retardant are added simultaneously, as in 2-2 to 2-7, the fire extinguishing agent is sprayed onto the surface of the burning object. The hydrogel and flame retardant can cover the surface of the combustible material, cooling it, quenching free radicals, diluting the combustible gas, and isolating oxygen and combustibles, thereby improving the fire extinguishing efficiency of the fire extinguishing agent and preventing rekindling.

[0133] From 2-1 to 2-5, as the amount of flame retardant increases from 0 wt.% to 20 wt.%, the fire extinguishing time gradually decreases, indicating that when the amount of flame retardant is ≤20 wt.%, the fire extinguishing effect gradually improves with the increase of the amount of flame retardant. From 2-5 to 2-7, as the amount of flame retardant continues to increase, the liquid will stratify, and the fire extinguishing time will no longer shorten with the increase of the amount of flame retardant. This is because when the mass fraction of ammonium polyphosphate in the solution system is greater than 20 wt.%, its ionization products and H ionized by water will be + and OH - The hydrolysis reaction causes a significant phase separation in the system, which further leads to a large amount of precipitation of E-CMC and PEG in the system, causing a sharp decrease in the sol viscosity, and the hydrogel cannot exert its expected effect, ultimately resulting in a decrease in the effectiveness of the fire extinguishing agent. Therefore, the preferred water-soluble flame retardant content is 20 wt.%.

[0134] Adding 20 wt.% ammonium hypophosphite to fire extinguishing agent 2-8 extended the extinguishing time by 12 seconds compared to agent 2-5 (which added 20 wt.% ammonium polyphosphate). However, the effect was superior to agent 2-1 (which lacked a flame retardant), reducing the extinguishing time by 17 seconds. This suggests that adding small-molecule ammonium hypophosphite to a flame retardant can have a certain fire-extinguishing effect, but the effect is not significant.

[0135] When 20 wt.% soluble magnesium hydroxide was added to fire extinguishing agent 2-9, the 20 wt.% soluble magnesium hydroxide was not completely dissolved. Compared to 2-5 (which added 20 wt.% ammonium polyphosphate), the fire extinguishing time was extended by 23 seconds. However, the effect was better than that of fire extinguishing agent 2-1 (which did not add a flame retardant), with the fire extinguishing time reduced by 6 seconds. This indicates that the addition of magnesium hydroxide can also achieve a fire extinguishing effect, but the fire extinguishing effect is inferior to the flame retardant system containing ammonium polyphosphate and ammonium hypophosphite.

[0136] In summary, a hydrogel system containing 1.0 wt.% E-CMC and 6 wt.% PEG, along with 5 to 30 wt.% of the flame retardant ammonium polyphosphate, exhibits excellent fire extinguishing effectiveness. This system can rapidly extinguish fires and suppress rekindling, demonstrating the excellent fire extinguishing effectiveness of the thermosensitive self-crosslinking hydrogel fire extinguishing agent provided herein. It is worth emphasizing that other thermosensitive self-crosslinking hydrogel systems within the scope of the present invention (0.5 to 1.5 wt.% modified carboxymethyl cellulose, 4 to 8 wt.% polyethylene glycol, 5 to 30 wt.% water-soluble flame retardant, and pure water as solvent) are also expected to exhibit good fire extinguishing effectiveness. The above experiment represents only one preferred embodiment of the present invention.

[0137] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A thermosensitive self-crosslinking hydrogel fire extinguishing agent, characterized in that: The components of the fire extinguishing agent are calculated by weight percentage as follows: modified carboxymethyl cellulose 0.5-1.5 wt.%, polyethylene glycol 4-8 wt.%, water-soluble flame retardant 5-30 wt.%, and the solvent is pure water; The modified carboxymethyl cellulose is a carboxymethyl cellulose grafted with a phenylethyl group and having a hydrophobic function.

2. The fire extinguishing agent according to claim 1, characterized in that The components of the fire extinguishing agent are calculated by mass percentage as follows: modified carboxymethyl cellulose 1.0 wt.%, polyethylene glycol 6.0 wt.%, water-soluble flame retardant 20 wt.%, and the solvent is pure water; Wherein, the water-soluble flame retardant is ammonium polyphosphate.

3. The fire extinguishing agent according to claim 2, characterized in that The fire extinguishing agent has a viscosity of less than 1600 cp at room temperature and a viscosity of more than 42000 cp at 90°C.

4. The fire extinguishing agent according to claim 1, characterized in that The water-soluble flame retardant is one or more of ammonium hypophosphite, ammonium polyphosphate, ammonium sulfate, monoammonium phosphate, diammonium phosphate, water-soluble magnesium hydroxide, and water-soluble aluminum hydroxide.

5. A method for preparing modified carboxymethyl cellulose, characterized in that: The specific steps include: S1-1: dissolving sodium carboxymethyl cellulose in N,N-dimethylformamide and adding hydrochloric acid to acidify to obtain carboxymethyl cellulose; S1-2: Add 4-ethylaniline to the solution, heat and stir, and continuously remove excess water during the process; S1-3: Cooling to room temperature while continuously stirring during the cooling process, and obtaining a crude modified carboxymethyl cellulose product liquid after the cooling is completed; S1-4: adding an excess of anhydrous methanol to the crude modified carboxymethyl cellulose product to obtain flocs; allowing the flocs to settle, filtering, washing, and drying to obtain a brown solid, i.e., the crude modified carboxymethyl cellulose product.

6. The preparation method according to claim 5, characterized in that The method further comprises step S1-5: dissolving the crude modified carboxymethyl cellulose product in water, adding an excess of anhydrous methanol to obtain flocs; allowing the flocs to settle, filtering, washing, and drying to obtain a light yellow solid, namely, the modified carboxymethyl cellulose.

7. The preparation method according to claim 5, characterized in that The specific operations of step S1-1 are: Heat to temperature T1 and keep warm, dissolve sodium carboxymethyl cellulose in N,N-dimethylformamide, add hydrochloric acid to acidify and continue stirring for a period of h1, and adjust the pH value to 2-3; The range of T1 is 20~60℃, the stirring rate is 300~600 r / min, and h1≥30min.

8. The preparation method according to claim 5, characterized in that The specific operations of step S1-2 are: Heat to temperature T2 and keep warm, add 4-ethylaniline to the solution, stir for a period of time h2, T2 range is 20 ~ 60 ° C, h2 ≥ 5 min, stirring rate is 300 ~ 600 r / min; Raise the temperature to T3, stir for a period of time h3, T3 range is 60 ~ 90 ° C, h3 ≥ 30min, stirring rate is 300 ~ 600r / min; Continue to heat up to temperature T4, stir for a period of h4, and continuously remove excess water during the process. The range of T4 is 110-130°C, h4 is 2-12h, and the stirring rate is 200-400 r / min.

9. The preparation method according to claim 5, characterized in that The stirring rate in step S1-3 is 200-400 r / min.

10. A method for preparing the fire extinguishing agent according to any one of claims 1 to 4, characterized in that: The specific steps include: S2-1: Preparation of modified carboxymethyl cellulose; S2-2: Fully dissolving modified carboxymethyl cellulose and polyethylene glycol in pure water to obtain a thermosensitive self-crosslinking hydrogel; S2-3: Adding a water-soluble flame retardant to the thermosensitive self-crosslinking hydrogel to obtain a thermosensitive self-crosslinking hydrogel fire extinguishing agent.

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