Preparation method of perfluorohexanone fire extinguishing microcapsule

Abstract

The invention provides a preparation method of a perfluorohexanone fire-extinguishing microcapsule, which comprises the following steps: S10: mixing sodium alginate, a water-dispersible polyurethane acrylate prepolymer, a photoinitiator and water to obtain a water-phase mixed solution; s20, adding perfluorohexanone and a fluorine-containing surfactant into the water-phase mixed solution, and carrying out shearing operation on the system to obtain a water-in-oil emulsion; s30, dropwise adding the water-in-oil type emulsion into an aqueous solution containing divalent metal cations to obtain cured gel particles; s40, ultraviolet light irradiation is applied to the gel particles obtained in the step S30, and the perfluorohexanone fire extinguishing microcapsule is obtained. The perfluorohexanone fire extinguishing microcapsule prepared by the preparation method has the compactness and thermal response rate of a shell layer.

Description

Technical Field

[0001] This invention relates to the field of fire extinguishing microcapsule technology, specifically to a method for preparing perfluorohexanone fire extinguishing microcapsules. Background Technology

[0002] With the increasing integration and power density of electronic devices, the risk of fires caused by overheating or circuit failures is rising. Microencapsulation fire suppression technology, as a cutting-edge active fire protection method, encapsulates the extinguishing agent within heat-sensitive wall materials. This allows the agent to be automatically released when the temperature rises in the early stages of a fire, achieving the goal of "early and early extinguishment." Currently, common methods for preparing perfluorohexanone microcapsules include in-situ polymerization, interfacial polymerization, and complex coagulation. Commonly used wall materials include synthetic polymers such as urea-formaldehyde resin and melamine-formaldehyde resin, as well as natural polymers such as sodium alginate and chitosan. Among these, gel wall materials formed by the ion exchange reaction of sodium alginate with divalent metal ions (such as calcium ions) have attracted attention due to their mild preparation conditions and environmental friendliness.

[0003] However, in the current process of preparing perfluorohexanone fire extinguishing microcapsules, in order to improve the sealing performance of the shell, the wall material thickness is usually increased. But this will reduce the thermal response sensitivity of the microcapsules, so that the microcapsules cannot rupture and release the fire extinguishing agent in a short time when a fire occurs, thus delaying the fire extinguishing opportunity. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects or problems in the prior art and to provide a method for preparing perfluorohexanone fire extinguishing microcapsules. The perfluorohexanone fire extinguishing microcapsules prepared by this method can have both a dense shell and a high thermal response rate.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: Technical Solution 1: A method for preparing perfluorohexanone fire extinguishing microcapsules, comprising the following steps: S10: mixing sodium alginate, water-dispersible polyurethane acrylate prepolymer, and photoinitiator with water to obtain an aqueous phase mixture; S20: adding perfluorohexanone and a fluorinated surfactant to the aqueous phase mixture and performing a shearing operation on the system to obtain a water-in-oil emulsion; S30: dropping the water-in-oil emulsion into an aqueous solution containing divalent metal cations to obtain solidified gel particles; S40: applying ultraviolet light irradiation to the gel particles obtained in step S30 to obtain the perfluorohexanone fire extinguishing microcapsules.

[0006] Technical Solution 2 based on Technical Solution 1: In step S20, the shearing operation is performed under programmed temperature control: the initial temperature of the system is controlled within the range of 2℃ to 8℃ for shearing, and the system temperature is increased at a rate of 0.5℃ / min to 1.5℃ / min during the shearing process until the temperature reaches the range of 20℃ to 30℃.

[0007] Technical Solution 3 based on Technical Solution 2: In step S20, the shearing operation further includes segmented adjustment of the rotation speed and step-by-step addition of the thermally conductive filler dispersion, specifically including: at a temperature of 2°C to 8°C, shearing at a rotation speed of 8000 rpm to 12000 rpm for 1 to 3 minutes; when the temperature is in the range of 12°C to 18°C, adding 40% to 60% of the total feed amount of the thermally conductive filler dispersion, and adjusting the rotation speed to 16000 rpm to 20000 rpm, shearing for 1 to 3 minutes; when the temperature is in the range of 20°C to 30°C, adding the remaining thermally conductive filler dispersion, and adjusting the rotation speed to 21000 rpm to 25000 rpm, shearing for 2 to 5 minutes.

[0008] Technical Solution 4 based on Technical Solution 3: The thermally conductive filler dispersion is made by mixing modified alumina supported on silver nanoparticles, nano-silica, and anhydrous ethanol, wherein the mass ratio of modified alumina supported on silver nanoparticles to nano-silica is 1.5:1 to 2.5:1.

[0009] Technical Solution 5 based on Technical Solution 1: In step S20, the fluorinated surfactant is sodium perfluorononoxybenzenesulfonate, and its addition amount is 0.1% to 1.0% of the total mass of the aqueous phase mixture.

[0010] Technical Solution Six based on Technical Solution One: In step S10, the water-dispersible polyurethane acrylate prepolymer is selected from aliphatic polyurethane acrylates with a functionality of 3 to 6, and the mass ratio of sodium alginate to the water-dispersible polyurethane acrylate prepolymer is 30:100 to 50:100.

[0011] Technical solution seven based on technical solution one: In step S30, the aqueous solution containing divalent metal cations is a calcium chloride aqueous solution with a pH value adjusted to the range of 4.5 to 5.5, and the dripping rate is controlled in the range of 3 ml / min to 8 ml / min.

[0012] Technical solution eight based on technical solution one: A centrifugal washing operation is also performed between step S30 and step S40: the product obtained in step S30 is centrifuged at a speed of 1000 rpm to 1500 rpm, the supernatant is removed and deionized water is added for resuspension.

[0013] Technical Solution Nine based on Technical Solution One: In step S40, the ultraviolet irradiation uses an ultraviolet light source with a wavelength of 350 nanometers to 380 nanometers, an irradiation intensity of 10 milliwatts per square centimeter to 20 milliwatts per square centimeter, and an irradiation time of 5 minutes to 15 minutes.

[0014] Technical Solution 10 based on Technical Solution 1: After step S40, a surface treatment operation is performed: the product obtained in step S40 is immersed in a solution containing silane coupling agent KH-550, stirred for 1 to 3 hours in a temperature range of 60°C to 70°C, filtered, and then dried.

[0015] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects: Technical Solution 1 provides a method for preparing perfluorohexanone fire extinguishing microcapsules. In this method, sodium alginate is blended with a water-dispersible polyurethane acrylate prepolymer during the preparation of the aqueous substrate. During the subsequent addition of perfluorohexanone and shear emulsification, the system spontaneously separates into layers based on the interfacial energy differences between the components. In existing technologies, the preparation of a bilayer shell typically requires complex coagulation or stepwise precipitation methods, which are complex and difficult to control the volatilization of low-boiling-point core materials. This solution utilizes the amphiphilic characteristics of the water-dispersible polyurethane acrylate prepolymer. Under shear force, to reduce the surface energy of the oil-water interface, the prepolymer spontaneously migrates from the aqueous bulk and accumulates at the interface between the perfluorohexanone droplets and the aqueous phase, while the more hydrophilic sodium alginate remains primarily in the continuous phase, encapsulating the droplets. This gradient distribution of components, completed during the emulsification stage, facilitates the subsequent formation of a bilayer structure and avoids the problem of significant core material volatilization caused by multiple emulsifications or solvent displacements in existing technologies.

[0016] In the curing and molding stage, this scheme adopts a sequence of ionic crosslinking followed by photopolymerization. Conventional microcapsule preparation often employs simultaneous curing or single curing modes. However, for perfluorohexanone, a high-density, low-viscosity liquid core material, direct photopolymerization can easily lead to droplet aggregation or deformation in the dynamic emulsion system, resulting in uneven shell thickness or even failure to form capsules. If only ionic crosslinking is performed, the resulting calcium alginate gel network, although forming quickly, has a porous structure that cannot effectively block the penetration of small-molecule perfluorohexanone, resulting in a short product shelf life. This scheme first drops the emulsion into a divalent metal cation solution. Utilizing the rapid chelation reaction between sodium alginate and metal ions, a rigid gel framework is instantly formed on the outermost layer of the droplet, fixing the droplet's shape and size and restricting the movement of the internal perfluorohexanone. After preliminary shaping, the system is irradiated with ultraviolet light, initiating an in-situ polymerization reaction of the polyurethane acrylate prepolymer enriched at the oil-water interface. Because the outer layer already has a gel skeleton for support and protection, the internal polymerization reaction can proceed in a relatively static and confined space. The resulting cross-linked polymer network can precisely fill the pores of the calcium alginate gel and form a dense inner shell layer tightly adhering to the core material surface. Through this dual curing mechanism, the fire extinguishing microcapsule forms an interpenetrating structure with an outer layer of ionogel network providing soft cushioning and support, and an inner layer of covalently cross-linked network providing dense barrier. This structure improves the poor density of single alginate wall materials while exhibiting a better thermal response rate compared to fire extinguishing microcapsules using resin wall materials.

[0017] In technical solution two, by performing shearing operations under programmed temperature control, the excessive volatilization of perfluorohexanone due to high shear heat generation during emulsification can be avoided. Perfluorohexanone has a low boiling point; if high-intensity shearing is performed under normal room temperature or isothermal conditions, the mechanical energy will be converted into heat energy, causing a rapid increase in local temperature and inducing core material vaporization, thus compromising emulsion stability. In this solution, low-temperature initial shearing is used, which significantly reduces the saturated vapor pressure of perfluorohexanone in a low-temperature environment, suppressing volatilization losses in the initial stage. Subsequently, the temperature is linearly increased during the shearing process. This is done to reduce the system viscosity and improve shearing efficiency, and also to increase the thermal mobility of the amphiphilic polyurethane acrylate prepolymer molecular chains by increasing the temperature, promoting their faster and more complete migration and alignment to the oil-water interface, thereby ensuring the homogeneity of the emulsion and the integrity of the coating layer.

[0018] In technical solution three, segmented speed regulation and step-by-step addition of thermally conductive fillers are employed to improve the problem of high-density inorganic fillers being difficult to disperse stably in low-viscosity emulsions and easily puncturing droplet interfaces. Low speed and low temperature are used in the initial stage of emulsification to form a stable water-in-oil primary emulsion. Subsequently, some fillers are added in the medium-temperature zone and under medium-speed shear, allowing the fillers sufficient time and energy to adsorb into the interfacial prepolymer layer, rather than directly settling or agglomerating. Finally, the final refinement and embedding of the remaining fillers are completed in the high-temperature zone and under high-speed shear. This step-by-step operation avoids emulsion demulsification or phase inversion caused by adding a large amount of filler at once, while utilizing gradient shear forces to ensure the uniform distribution of thermally conductive fillers in the shell structure.

[0019] In technical solution four, the thermally conductive filler is a composite of modified alumina supported on silver nanoparticles and nano-silica. Silver nanoparticles possess high electronic thermal conductivity, while alumina provides a volumetric framework. The combination of these two elements within the microcapsule shell constructs an efficient thermally conductive pathway, significantly reducing the thermal resistance of the polymer shell. Simultaneously, nano-silica not only serves as an auxiliary thermally conductive filler but also fills the gaps between the micron-sized alumina particles and polymer chains due to its small size effect, further enhancing the shell's compactness.

[0020] In technical solution five, sodium perfluorononoxybenzenesulfonate is selected as the surfactant, specifically addressing the problem of poor compatibility between perfluorohexanone and the aqueous phase, as well as conventional hydrocarbon surfactants. The perfluorocarbon chains in the sodium perfluorononoxybenzenesulfonate molecule have a high affinity for the perfluorohexanone core material, allowing them to deeply penetrate the core material surface, while the sulfonic acid groups firmly bind the aqueous phase, thus significantly reducing the interfacial tension between the fluorocarbon oil phase and the aqueous phase. Compared to conventional surfactants, this fluorinated surfactant can form a more tightly packed monolayer at the interface, effectively preventing the ripening of perfluorohexanone droplets during storage and improving the thermodynamic stability of the emulsion.

[0021] In technical solution six, the water-dispersible polyurethane acrylate prepolymer is selected from an aliphatic type with a functionality of 3 to 6. The higher functionality of the prepolymer allows it to form a cross-linked network with smaller pore sizes after photocuring, effectively blocking the penetration of perfluorohexanone molecules. Furthermore, the aliphatic structure avoids the yellowing and embrittlement defects of aromatic polyurethanes under long-term light or heat exposure, ensuring the structural stability of the microcapsules during long-term storage or in complex environments.

[0022] In technical solution seven, the pH value and dropping rate of the divalent metal cation solution are limited. By controlling the slightly acidic environment and slow dropping, the initial gelation rate is slowed down, allowing calcium ions sufficient time to penetrate to the deep layers of the droplet surface, forming a gel shell with uniform thickness and regular structure, providing a stable template for subsequent photocuring.

[0023] In technical solution eight, a centrifugal washing operation is added between the two curing steps. Since some water-dispersible prepolymers may not be completely adsorbed at the interface and remain free in the continuous phase, direct light irradiation would cause these free prepolymers to polymerize, agglomerating adjacent microcapsules and forming irreversible aggregates. Centrifugal washing removes excess components from the aqueous phase, ensuring that the photocuring reaction is confined to the interior or surface of the microcapsule shell, thereby obtaining well-dispersed monodisperse microcapsule powder with uniform particle size.

[0024] In technical solution nine, the ultraviolet irradiation parameters are limited. Excessive irradiation intensity will generate a large amount of reaction heat, which may induce the vaporization and expansion of the low-boiling-point core material, thereby breaking the shell layer; while too low intensity will lead to incomplete cross-linking and affect the density. The selected wavelength and intensity range are matched with the absorption spectrum of the initiator and the thermal stability of the core material, achieving mild and efficient curing.

[0025] In technical solution ten, a surface hydrophobic treatment is also performed. Since the alginate shell is inherently hydrophilic, direct application to an organic matrix can easily lead to aggregation or interfacial delamination. By grafting modification with a silane coupling agent, organic functional groups are introduced onto the surface of the microcapsules, enabling them to be uniformly dispersed in a hydrophobic application medium, thus expanding the application range of perfluorohexanone microcapsules in the field of composite materials. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments are briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a scanning electron microscope (SEM) schematic diagram of the fire extinguishing microcapsules prepared by the method for preparing perfluorohexanone fire extinguishing microcapsules according to an embodiment of the present invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] In the claims, description and accompanying drawings of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0030] This invention relates to a method for preparing perfluorohexanone fire extinguishing microcapsules, which mainly includes the following steps: S10: Sodium alginate, water-dispersible polyurethane acrylate prepolymer, and photoinitiator are mixed with water to obtain an aqueous mixture; S20: Add perfluorohexanone and a fluorinated surfactant to the aqueous mixture and perform a shearing operation on the system to obtain a water-in-oil emulsion; S30: The water-in-oil emulsion is dropped into an aqueous solution containing divalent metal cations to obtain solidified gel particles; S40: Apply ultraviolet light to the gel particles obtained in step S30 to obtain the perfluorohexanone fire extinguishing microcapsules.

[0031] The following is a detailed explanation of each of the above steps.

[0032] First, step S10 will be described in detail. The task of step S10 is to construct a continuous phase system capable of simultaneously carrying the ionic crosslinking component and the photocurable component. For raw material selection, sodium alginate is chosen as the base material for constructing the outer gel skeleton. To ensure suitable viscosity during the subsequent emulsification process, low-viscosity sodium alginate is preferred. Simultaneously, a water-dispersible polyurethane acrylate prepolymer is selected as the base material for constructing the inner dense shell layer. To ensure sufficient crosslinking density and weather resistance of the inner shell layer after photocuring, this prepolymer is selected from aliphatic polyurethane acrylates with a functionality of 3 to 6. Furthermore, a photoinitiator matching the ultraviolet light wavelength, such as benzophenone or 1-hydroxycyclohexylphenyl ketone, needs to be added to initiate the subsequent polymerization reaction.

[0033] In practice, sodium alginate is first dissolved in deionized water to prepare an aqueous solution of approximately 2% by mass. Then, the aforementioned water-dispersible polyurethane acrylate prepolymer and photoinitiator are added to the sodium alginate aqueous solution. In this mixture, the amount of each component added must be strictly controlled. The mass ratio of sodium alginate to the water-dispersible polyurethane acrylate prepolymer is controlled within the range of 30:100 to 50:100. For example, in a preferred embodiment, the mass ratio of sodium alginate, polyurethane acrylate prepolymer, and photoinitiator is set to 40:100:3. This ratio ensures that sodium alginate can form a sufficiently strong external support framework while also ensuring that a sufficient amount of polyurethane acrylate is enriched at the interface to form a complete inner film.

[0034] After mixing the above components, the mixture is heated and stirred. The system temperature is raised to 60 degrees Celsius and stirred continuously at this temperature. Heating helps reduce the viscosity of the prepolymer and promotes the dissolution of the photoinitiator, while stirring promotes the uniform dispersion of the amphiphilic polyurethane acrylate prepolymer in the aqueous phase at the micelle or molecular level. Stirring continues until the mixture changes from turbid to transparent and homogeneous, indicating that the components have been fully mixed and uniformly dispersed, forming a stable aqueous substrate solution. Finally, the prepared aqueous mixture is allowed to cool naturally or actively to room temperature for later use, or directly cooled to the initial low temperature required for subsequent emulsification steps to prevent the volatilization of the subsequently added perfluorohexanone due to high temperature.

[0035] Next, step S20 will be described in detail. The task of step S20 is to disperse the perfluorohexanone core material into the aqueous phase and form a stable emulsion. First, a fluorinated surfactant is added to the prepared aqueous mixture. To ensure effective emulsification of the fluorinated oil phase, sodium perfluorononoxybenzenesulfonate is selected as the surfactant, and its addition amount is controlled between one-thousandth and one-hundredth of the total mass of the aqueous mixture. Then, the perfluorohexanone core material is added to the system. To suppress the volatilization of perfluorohexanone in the early stage of emulsification, the entire mixing system is placed in a temperature-controlled device, such as a reactor with circulating cooling or a constant temperature water bath, and the initial temperature of the system is strictly controlled within a low temperature range of 2 degrees Celsius to 8 degrees Celsius.

[0036] The emulsification shearing process employs a combination of programmed temperature control and segmented speed variation. For temperature control, the system starts from an initial low temperature and linearly increases the temperature at a rate of 0.5°C to 1.5°C per minute until the system temperature reaches a room temperature range of 20°C to 30°C. In conjunction with this temperature change, the shearing operation is carried out in three stages, accompanied by the step-by-step addition of a thermally conductive filler dispersion. The thermally conductive filler dispersion used is prepared by mixing and dispersing modified alumina supported on silver nanoparticles, nano-silica, and anhydrous ethanol, with the mass ratio of modified alumina supported on silver nanoparticles to nano-silica controlled between 1.5:1 and 2.5:1.

[0037] The specific segmented shearing operation is as follows: In the first stage, maintain the system temperature between 2°C and 8°C, start the shearing equipment, and set the rotation speed between 8000 and 12000 rpm. Shearing lasts for 1 to 3 minutes to disperse perfluorohexanone into micron-sized droplets, forming a preliminary emulsion. As the temperature rises to 12°C to 18°C, the second stage begins. At this point, 40% to 60% of the total feed weight of the thermally conductive filler dispersion is added to the system, and the shearing speed is increased to 16000 to 20000 rpm, maintained for 1 to 3 minutes, allowing the filler to initially adsorb onto the droplet interface. When the temperature further rises to 20°C to 30°C, the third stage begins. The remaining thermally conductive filler dispersion is added to the system, and the shearing speed is further increased to a high speed of 21000 to 25000 rpm, continuing shearing for 2 to 5 minutes. Through the above operations, a water-in-oil emulsion with uniform particle size, uniform filler distribution, and prepolymer enriched at the interface is finally obtained.

[0038] Next, step S30 will be described in detail. The task of step S30 is to construct the microcapsule shell through ionic crosslinking. First, an aqueous solution containing divalent metal cations needs to be prepared as a curing medium. In this embodiment, a calcium chloride aqueous solution is selected. In order to control the reaction kinetics between sodium alginate and calcium ions and prevent the shell structure from becoming loose due to excessively fast reaction or the shell from becoming incomplete due to excessively slow reaction, the pH of the calcium chloride aqueous solution needs to be precisely adjusted to the range of 4.5 to 5.5.

[0039] While maintaining low-speed stirring of the curing medium, the emulsion obtained in step S20 is slowly added dropwise to the pH-adjusted calcium chloride aqueous solution. Process control during the dropwise addition is crucial for the morphology of the microcapsules, requiring strict control of the dropwise rate within the range of 3 to 8 ml per minute. This controlled addition method prevents the emulsion droplets from agglomerating due to excessively high local ion concentrations upon entering the aqueous phase, while also ensuring that calcium ions diffuse uniformly to the surface of each droplet.

[0040] When the emulsion droplets come into contact with the calcium chloride solution, the carboxyl groups on the sodium alginate molecular chains dispersed in the continuous phase of the emulsion chelate with the calcium ions in the solution, forming an "egg-box" shaped cross-linked structure. This process causes the originally liquid emulsion droplet surface to solidify rapidly, forming a calcium alginate gel shell with a certain mechanical strength. After all the droplets have been added, the reaction is usually stirred for a period of time to ensure that the ion exchange reaction is complete, thereby obtaining morphologically stable intermediate microcapsule particles with a gel shell.

[0041] Next, step S40 will be described in detail. After the ionic cross-linking reaction is completed and gel particles are formed in step S30, in order to remove unreacted raw materials and impurities from the system and to prevent the microcapsule particles from sticking together due to surface residues during subsequent light irradiation, the product needs to be centrifuged and washed before ultraviolet irradiation. Specifically, the reaction solution containing gel particles is placed in a centrifuge, and the centrifugation speed is set within the range of 1000 to 1500 rpm for separation. This speed range can effectively achieve solid-liquid separation while avoiding damage to the nascent gel shell due to excessive centrifugal force. After centrifugation, the supernatant is discarded, and deionized water is added to the precipitate for resuspending. This washing process can be repeated until a clean microcapsule suspension is obtained.

[0042] After washing, the microcapsule system proceeds to the ultraviolet (UV) irradiation curing step. The resuspended microcapsule system is placed under a UV light source for irradiation to initiate the polymerization reaction of the inner layer. During this process, the selected UV wavelength range is 350 nm to 380 nm, and the irradiation intensity is precisely controlled between 10 mW and 20 mW per square centimeter. Under these irradiation conditions, the system is continuously irradiated for 5 to 15 minutes. The UV light penetrates the outer calcium alginate gel and acts on the water-dispersible polyurethane acrylate prepolymer enriched at the oil-water interface, initiating a free radical polymerization reaction. This results in in-situ curing of a dense polymer inner shell layer on the inner side of the gel shell, completing the construction of the double-shell structure.

[0043] After the photocuring reaction, surface modification of the microcapsules is required to further improve their dispersibility and interfacial compatibility in the application matrix. The microcapsule particles cured by UV irradiation are immersed in an ethanol solution containing the silane coupling agent KH550. The mixture is heated to 60-70°C and stirred for 1-3 hours. After the reaction, the solid particles are separated by filtration and dried to obtain perfluorohexanone fire extinguishing microcapsules with excellent thermal response and encapsulation stability.

[0044] In the preparation method of perfluorohexanone fire extinguishing microcapsules involved in this embodiment, sodium alginate is blended with a water-dispersible polyurethane acrylate prepolymer during the preparation of the aqueous substrate. During the subsequent addition of perfluorohexanone and shear emulsification, the system achieves spontaneous stratification by utilizing the interfacial energy differences between the components. In existing technologies, the preparation of a double-layer shell typically requires complex coagulation or stepwise precipitation methods, which are complex and difficult to control the volatilization of low-boiling-point core materials. This solution utilizes the amphiphilic characteristics of the water-dispersible polyurethane acrylate prepolymer. Under shear force, to reduce the surface energy of the oil-water interface, the prepolymer spontaneously migrates from the aqueous bulk and accumulates at the interface between the perfluorohexanone droplets and the aqueous phase, while the more hydrophilic sodium alginate mainly remains in the continuous phase, encapsulating the droplets. This gradient distribution between components, completed during the emulsification stage, facilitates the subsequent formation of a double-layer structure and avoids the problem of significant core material volatilization caused by multiple emulsifications or solvent displacements in existing technologies.

[0045] In the curing and molding stage, this scheme adopts a sequence of ionic crosslinking followed by photopolymerization. Conventional microcapsule preparation often employs simultaneous curing or single curing modes. However, for perfluorohexanone, a high-density, low-viscosity liquid core material, direct photopolymerization can easily lead to droplet aggregation or deformation in the dynamic emulsion system, resulting in uneven shell thickness or even failure to form capsules. If only ionic crosslinking is performed, the resulting calcium alginate gel network, although forming quickly, has a porous structure that cannot effectively block the penetration of small-molecule perfluorohexanone, resulting in a short product shelf life. This scheme first drops the emulsion into a divalent metal cation solution. Utilizing the rapid chelation reaction between sodium alginate and metal ions, a rigid gel framework is instantly formed on the outermost layer of the droplet, fixing the droplet's shape and size and restricting the movement of the internal perfluorohexanone. After preliminary shaping, the system is irradiated with ultraviolet light, initiating an in-situ polymerization reaction of the polyurethane acrylate prepolymer enriched at the oil-water interface. Because the outer layer already has a gel skeleton for support and protection, the internal polymerization reaction can proceed in a relatively static and confined space. The resulting cross-linked polymer network can precisely fill the pores of the calcium alginate gel and form a dense inner shell layer tightly adhering to the core material surface. Through this dual curing mechanism, the fire extinguishing microcapsule forms an interpenetrating structure with an outer layer of ionogel network providing soft cushioning and support, and an inner layer of covalently cross-linked network providing dense barrier. This structure improves the poor density of single alginate wall materials while exhibiting a better thermal response rate compared to fire extinguishing microcapsules using resin wall materials.

[0046] To better illustrate the technical solution of the present invention, detailed descriptions will be provided below through specific embodiments and comparative examples. These embodiments and comparative examples are intended to demonstrate the feasibility and superiority of the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0047] To ensure the accuracy and reproducibility of the experimental results, all major raw materials used in this section were purchased from commercial sources, with specific specifications or models as follows: Sodium alginate (SA): food grade, viscosity 200 mPa·s (1% aqueous solution, 20℃), purchased from Qingdao Mingyue Algae Group Co., Ltd.

[0048] Water-dispersible polyurethane acrylate prepolymer (WPUA): Model 6196, hexafunctional aliphatic polyurethane acrylate, solid content 98%, purchased from Changxing Chemical Industry Co., Ltd.

[0049] Photoinitiator: Irgacure 184 (1-hydroxycyclohexylphenyl ketone), purchased from BASF (China) Co., Ltd.

[0050] Perfluorohexanone: Industrial grade, purity ≥99.9%, purchased from Sinochem Lantian Group Co., Ltd.

[0051] Sodium perfluorononoxybenzenesulfonate (PFNS): analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0052] Silver nanoparticle-supported modified alumina: self-made (preparation method: 50nm silver powder and 500nm alumina powder are mixed at a mass ratio of 1:5 and then surface modified with KH-550 coupling agent).

[0053] Nano silica: Fumed silica, average particle size 20nm, hydrophobic, purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.

[0054] Calcium chloride: anhydrous, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0055] Silane coupling agent KH-550: analytical grade, purchased from Nanjing Sigona Chemicals Co., Ltd.

[0056] Sodium dodecyl sulfate (SDS): analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd. (used for comparative example).

[0057] Example 1 This embodiment provides a method for preparing perfluorohexanone fire extinguishing microcapsules, the specific steps of which are as follows: S10: Weigh 40g of sodium alginate and dissolve it in 1960g of deionized water to prepare a 2wt% sodium alginate solution. Weigh 100g of water-dispersible polyurethane acrylate prepolymer (WPUA) and 3g of photoinitiator (Irgacure 184) and add them to the above solution. Heat the mixture to 60℃ and stir continuously for 30 minutes until a transparent and homogeneous aqueous phase mixture is formed, then cool it to 5℃ for later use.

[0058] S20: Add 10g of sodium perfluorononoxybenzenesulfonate (PFNS, approximately 0.5% of the aqueous phase mass) and 1500g of perfluorohexanone to the aqueous phase mixture cooled to 5°C. Start the temperature and shearing program, initially controlling the temperature at 5°C and the initial shearing speed at 10,000 rpm for 2 minutes. Then, start the heating program, linearly increasing the system temperature at a rate of 1°C / min. When the temperature reaches 15°C, add 50% of the total thermally conductive filler dispersion (30g of thermally conductive filler, prepared by dispersing silver-supported alumina and nano-silica in ethanol at a 2:1 mass ratio), and increase the speed to 18,000 rpm for 2 minutes. When the temperature reaches 25°C, add the remaining 50% of the thermally conductive filler dispersion, increase the speed to 23,000 rpm, and shear for 3 minutes to obtain a stable water-in-oil emulsion.

[0059] S30: Prepare a 3wt% calcium chloride aqueous solution and adjust the pH to 5.0 with hydrochloric acid. While stirring at 300 rpm, add the emulsion obtained in step S20 dropwise to the calcium chloride solution at a rate of 5 mL / min. After the addition is complete, continue stirring for 30 minutes to obtain solidified particles with a gel shell.

[0060] S40: The particulate suspension obtained in step S30 is centrifuged at 1200 rpm, the supernatant is removed, and the suspension is resuspended and washed three times with deionized water. The resuspended solution is placed in a UV curing machine and irradiated with UV light at a wavelength of 365 nm and an intensity of 15 mW / cm² for 10 minutes. After irradiation, the microcapsules are immersed in a 7 wt% KH-550 ethanol solution, stirred at 65°C for 2 hours, filtered, and dried to obtain the perfluorohexanone fire extinguishing microcapsules.

[0061] Example 2 The preparation method in this embodiment is basically the same as that in Example 1, with the only difference being the raw material ratio and some parameter adjustments: In S10, the amount of sodium alginate is 30g and the amount of WPUA is 100g, that is, the mass ratio is 30:100.

[0062] In S20, the total amount of thermally conductive filler dispersion is adjusted to 10% of the mass of WPUA.

[0063] The remaining steps and parameters are consistent with those in Example 1.

[0064] Comparative Example 1 This comparative example aims to illustrate the effect of the PUA inner shell on the compactness of a double-shell structure.

[0065] The preparation method differs from that in Example 1 in that: S10 does not contain water-dispersible polyurethane acrylate prepolymer or photoinitiator; it only uses sodium alginate solution.

[0066] In S40, no ultraviolet irradiation step is performed; the particles are directly surface-treated and dried after centrifugal washing.

[0067] The remaining steps and parameters are consistent with those in Example 1.

[0068] Comparative Example 2 This comparative example aims to illustrate the impact of low-temperature gradient emulsification process on encapsulation efficiency.

[0069] The preparation method differs from that in Example 1 in that: In S20, no programmed temperature control is performed; the entire emulsification process is carried out under a constant temperature of 25°C.

[0070] In S20, the shearing process is not segmented; it is directly sheared at a speed of 23,000 rpm for 7 minutes, and the thermally conductive filler is added all at once at the beginning.

[0071] The remaining steps and parameters are consistent with those in Example 1.

[0072] Comparative Example 3 This comparative example aims to illustrate the effect of thermally conductive fillers on the thermal response rate.

[0073] The preparation method differs from that in Example 1 in that: No thermally conductive filler dispersion is added to S20.

[0074] The remaining steps and parameters are consistent with those in Example 1.

[0075] Comparative Example 4 This comparative example aims to illustrate the effect of fluorinated surfactants on emulsion stability.

[0076] The preparation method differs from that in Example 1 in that: In S20, sodium dodecyl sulfate (SDS) of equal mass is used instead of sodium perfluorononoxybenzenesulfonate (PFNS).

[0077] The remaining steps and parameters are consistent with those in Example 1.

[0078] Comparative Example 5 This comparative example aims to illustrate the necessity of the "ion crosslinking first, then photocuring" sequence.

[0079] The preparation method differs from that in Example 1 in that: Adjust the order of S30 and S40. That is, after emulsification, irradiate the emulsion with ultraviolet light for 10 minutes, and then add calcium chloride solution dropwise to carry out ionic cross-linking.

[0080] The remaining steps and parameters are consistent with those in Example 1.

[0081] To verify the performance of the perfluorohexanone fire extinguishing microcapsules prepared in this invention, the samples obtained in Examples 1-2 and Comparative Examples 1-5 were tested according to the following standards: Particle size distribution: The average particle size (D50) of the microcapsules was tested using a laser particle size analyzer in accordance with GB / T 19077-2016 "Particle size analysis by laser diffraction".

[0082] Encapsulation efficiency: Thermogravimetric analysis (TGA) was used. According to GB / T 27761-2011, the percentage of core material mass in the total mass of the microcapsules was calculated. Encapsulation efficiency = (Core material mass / Total microcapsule mass) × 100%.

[0083] Volatilization leakage rate (sealing): A certain amount of microcapsule sample was placed in a petri dish and placed in a constant temperature drying oven at 50℃ for 72 hours. The environment was adjusted according to GB / T 2918-2018 standard, and the mass loss rate before and after placement was calculated. Leakage rate = [(initial mass - mass after 72h) / initial mass] × 100%.

[0084] Thermal response time: The microcapsule sample was placed on a hot stage preheated to 180°C, and a high-speed camera was used to record the time from contact with the hot stage to the rupture of the microcapsule and release of the core material.

[0085] Microstructure: The surface and cross-sectional morphology of the microcapsules were observed using a scanning electron microscope (SEM).

[0086] The test results are as follows:

[0087] Based on the above test results and Figure 1 As shown in the scanning electron microscope (SEM) schematic diagram of Example 1, the microcapsules prepared in Example 1 have an encapsulation efficiency of up to 92.3%, and a leakage rate of only 4.8% after 72 hours at 50°C. In contrast, Comparative Example 1, using only a single layer of sodium alginate wall material, has an encapsulation efficiency of only 58.6% and a leakage rate as high as 32.4%. The microcapsules prepared by this invention exhibit a regular spherical shape with a dense, non-porous surface. In contrast, the sample of Comparative Example 1, observed under SEM, shows a noticeably shriveled and collapsed surface with numerous micropores. This fully demonstrates that the UV-induced in-situ polymerization of polyurethane acrylate in the inner layer during step S40 effectively fills the physical pores of the calcium alginate gel, constructing a dense interpenetrating network structure and significantly solving the problem of poor density of a single natural wall material.

[0088] Comparative Example 2, when sheared at a constant temperature of 25°C, showed an encapsulation efficiency reduced to 65.2%. This is because perfluorohexanone has a low boiling point, and the heat generated by the high shear at the constant temperature caused a large amount of core material to volatilize during the emulsification stage. Simultaneously, Comparative Example 2 exhibited a wider particle size distribution and a less regular surface morphology than Example 1. This demonstrates the crucial role of the programmed temperature control and gradient shearing process in step S20 in suppressing volatilization and controlling the prepolymer interfacial assembly.

[0089] The thermal response time of Example 1 was only 3.5 seconds, while that of Comparative Example 3, which did not add thermally conductive filler, was as long as 28.5 seconds. This indicates that by introducing silver-supported alumina and nano-silica stepwise in step S20, a highly efficient thermally conductive pathway was successfully constructed in the polymer shell, solving the problem of delayed fire extinguishing caused by the poor thermal conductivity of the polymer wall material.

[0090] Comparative Example 4 used a conventional SDS emulsifier. During the experiment, the emulsion rapidly separated into layers, making subsequent curing impossible, and no effective sample could be collected. This demonstrates the necessity of sodium perfluorononoxybenzenesulfonate for the emulsification process of perfluorohexanone, a special fluorocarbon core material.

[0091] Comparative Example 5 attempted to irradiate the product before calcium crosslinking, but the resulting product was a gel-like mass that could not be dispersed. This is because, without the calcium alginate shell for shaping, direct light irradiation caused the emulsion droplets to collide and macroscopically aggregate during the dynamic process. This conversely proves that the crosslinking-before-polymerization sequence of the present invention is an important method for preparing highly spherical, monodisperse microcapsules.

[0092] The foregoing description of the specifications and embodiments is intended to explain the scope of protection of this invention, but does not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of this invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of this invention.

Claims

1. A method for preparing perfluorohexanone fire extinguishing microcapsules, characterized in that, Includes the following steps: S10: Sodium alginate, water-dispersible polyurethane acrylate prepolymer, and photoinitiator are mixed with water to obtain an aqueous mixture; S20: Add perfluorohexanone and a fluorinated surfactant to the aqueous mixture and perform a shearing operation on the system to obtain a water-in-oil emulsion; S30: The water-in-oil emulsion is dropped into an aqueous solution containing divalent metal cations to obtain solidified gel particles; S40: Apply ultraviolet light to the gel particles obtained in step S30 to obtain the perfluorohexanone fire extinguishing microcapsules.

2. The method for preparing perfluorohexanone fire extinguishing microcapsules as described in claim 1, characterized in that, In step S20, the shearing operation is performed under programmed temperature control: the initial temperature of the system is controlled within the range of 2°C to 8°C during shearing, and the system temperature is increased at a rate of 0.5°C / min to 1.5°C / min during the shearing process until the temperature reaches the range of 20°C to 30°C.

3. The method for preparing perfluorohexanone fire extinguishing microcapsules as described in claim 2, characterized in that, In step S20, the shearing operation further includes segmented adjustment of the rotation speed and stepwise addition of the thermally conductive filler dispersion, specifically including: Shear for 1 to 3 minutes at a temperature of 2°C to 8°C and a rotation speed of 8000 rpm to 12000 rpm; When the temperature is in the range of 12°C to 18°C, add 40% to 60% of the total feed amount of the thermally conductive filler dispersion, and adjust the rotation speed to 16,000 rpm to 20,000 rpm, and shear for 1 to 3 minutes; When the temperature is in the range of 20°C to 30°C, add the remaining thermally conductive filler dispersion and adjust the rotation speed to 21,000 rpm to 25,000 rpm, and shear for 2 to 5 minutes.

4. The method for preparing perfluorohexanone fire extinguishing microcapsules as described in claim 3, characterized in that, The thermally conductive filler dispersion is prepared by mixing modified alumina supported on silver nanoparticles, nano-silica, and anhydrous ethanol, wherein the mass ratio of the modified alumina supported on silver nanoparticles to the nano-silica is 1.5:1 to 2.5:

1.

5. The method for preparing perfluorohexanone fire extinguishing microcapsules as described in claim 1, characterized in that, In step S20, the fluorinated surfactant is sodium perfluorononoxybenzenesulfonate, and its addition amount is 0.1% to 1.0% of the total mass of the aqueous mixture.

6. The method for preparing perfluorohexanone fire extinguishing microcapsules as described in claim 1, characterized in that, In step S10, the water-dispersible polyurethane acrylate prepolymer is selected from aliphatic polyurethane acrylates with a functionality of 3 to 6, and the mass ratio of sodium alginate to the water-dispersible polyurethane acrylate prepolymer is 30:100 to 50:

100.

7. The method for preparing perfluorohexanone fire extinguishing microcapsules as described in claim 1, characterized in that, in In step S30, the aqueous solution containing divalent metal cations is a calcium chloride aqueous solution with a pH value adjusted to the range of 4.5 to 5.5, and the dripping rate is controlled within the range of 3 ml / min to 8 ml / min.

8. The method for preparing perfluorohexanone fire extinguishing microcapsules as described in claim 1, characterized in that, Between step S30 and step S40, a centrifugal washing operation is also performed: the product obtained in step S30 is centrifuged at a speed of 1000 rpm to 1500 rpm, the supernatant is removed and resuspended in deionized water.

9. The method for preparing perfluorohexanone fire extinguishing microcapsules as described in claim 1, characterized in that, in In step S40, the ultraviolet irradiation uses an ultraviolet light source with a wavelength of 350 nanometers to 380 nanometers, an irradiation intensity of 10 milliwatts per square centimeter to 20 milliwatts per square centimeter, and an irradiation time of 5 minutes to 15 minutes.

10. The method for preparing perfluorohexanone fire extinguishing microcapsules as described in claim 1, characterized in that, After step S40, a surface treatment operation is performed: the product obtained in step S40 is immersed in a solution containing silane coupling agent KH-550, stirred for 1 to 3 hours in a temperature range of 60°C to 70°C, filtered, and then dried.

Images