Preparation method of composite wall material fire extinguishing microcapsule

Abstract

The invention discloses a preparation method of a composite wall material fire extinguishing microcapsule, which sequentially comprises the following steps: S100, adding a core material containing at least two fluorocarbon fire extinguishing agents, a compound of an anionic emulsifier and a cationic emulsifier and an amphiphilic cosolvent into a sodium alginate aqueous solution to form a mixed solution, carrying out shearing treatment on the mixed solution so as to prepare a water-in-oil type emulsion; s200, adding the emulsion prepared in the step S100 into an acidic aqueous solution of chitosan to obtain a reaction precursor liquid; after the pH value of the reaction precursor liquid is adjusted, a divalent metal ion cross-linking agent is added into the reaction precursor liquid under the set temperature condition, and a composite wall material composed of chitosan and sodium alginate is formed on the surface of liquid drops of the core material by initiating an ion cross-linking reaction; and S300, the microcapsules formed in the step S200 are washed and dried, and the fire extinguishing microcapsules are obtained. The preparation method can effectively improve the long-term effectiveness of the product while completely adopting the natural polymer material to prepare the wall material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fire extinguishing microcapsules, and in particular to a preparation method of fire extinguishing microcapsules with composite wall materials. BACKGROUND

[0002] With the increasing integration and power density of electronic devices, the risk of fire caused by overheating or circuit failure inside the devices is increasing. Microcapsule fire extinguishing technology, as a leading active fire protection method, can release fire extinguishing agents automatically when the temperature rises in the early stage of fire by wrapping the fire extinguishing agents in heat-sensitive wall materials, achieving the goal of "extinguishing early and small".

[0003] However, most of the fire extinguishing microcapsules in the prior art use synthetic resins (such as polyurea and melamine formaldehyde resin) as wall materials, which have poor biodegradability and do not meet the development requirements of green chemistry. Therefore, the prior art has also proposed a scheme of using natural materials such as chitosan and sodium alginate to prepare wall materials, but most of them are physically blended with synthetic resins (such as acrylic resin), or use a double-layer coating structure of "inner layer of natural polymer-outer layer of synthetic resin", which fails to unify the structure and performance of pure natural polymer wall materials, and still has deficiencies in the balance between environmental protection and mechanical properties. A small amount of pure natural polymer wall materials have strong hydrophilicity and weak mechanical properties, which easily cause problems such as unstable interface, emulsion breaking, and core material leakage when encapsulating strong hydrophobic core materials, resulting in poor long-term effectiveness of the product. SUMMARY

[0004] The present application aims to overcome the above-mentioned defects or problems in the background art, and provides a preparation method of fire extinguishing microcapsules with composite wall materials, which can effectively improve the long-term effectiveness of the product while using only natural polymer materials to prepare the wall materials.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] Technical solution one: A preparation method of a composite wall material fire extinguishing microcapsule, comprising the following sequentially executed steps: S100: adding a core material containing at least two fluorocarbon fire extinguishing agents, a complex of an anionic emulsifier and a cationic emulsifier, and an amphiphilic cosolvent into a sodium alginate aqueous solution to form a mixed solution, and subjecting the mixed solution to shearing treatment, thereby preparing a water-in-oil emulsion; S200: adding the emulsion prepared in step S100 into an acidic aqueous solution of chitosan to obtain a reaction precursor liquid; after adjusting the pH value of the reaction precursor liquid, a divalent metal ion crosslinking agent is added thereto under a set temperature condition, and an ionic crosslinking reaction is initiated to form a composite wall material composed of chitosan and the sodium alginate on the surface of the droplets of the core material; S300: washing and drying the microcapsule formed in step S200 to obtain the fire extinguishing microcapsule.

[0007] Technical solution two based on technical solution one: in step S100, the shearing rate of the shearing treatment is 1000-1500 rpm.

[0008] Technical solution three based on technical solution one: in step S200, the set temperature condition is 30-45℃.

[0009] Technical solution four based on technical solution one: in step S200, the pH value adjustment is to adjust the pH value of the reaction precursor liquid to the range of 5.5-6.5.

[0010] Technical solution five based on technical solution one: in step S200, the step of adding the divalent metal ion crosslinking agent is to add a solution containing the crosslinking agent to the reaction precursor liquid at a dropwise adding rate of 3-5 mL / min.

[0011] Technical solution six based on technical solution one: in the step S300, the washing treatment includes alternating washing with ethanol and / or deionized water, and the drying treatment is vacuum drying.

[0012] Technical solution seven based on technical solution one: the anionic emulsifier is a styrene-maleic anhydride copolymer, and the cationic emulsifier is hexadecyl trimethyl ammonium bromide.

[0013] Technical solution eight based on technical solution one: the amphiphilic cosolvent is n-octanol.

[0014] Technical solution nine based on technical solution one: the divalent metal ion crosslinking agent is calcium ion.

[0015] Technical solution ten based on technical solution one: the total mass ratio of chitosan to sodium alginate used in steps S100 and S200 is 1:1 to 1.5:1.

[0016] From the above description of the present application, relative to the prior art, the present application has the following beneficial effects:

[0017] The first technical challenge faced by the present application is the physical and chemical properties of the core material. The core material containing at least two fluorocarbon extinguishing agents has a low surface tension and strong hydrophobicity, which makes it have a large interfacial energy with the water phase system. It is extremely difficult to stably disperse such substances in water to form micron-sized droplets under normal conditions, and the emulsion system will quickly separate and fail. In the prior art, anionic and non-ionic complex emulsifiers are used, which can achieve emulsification to a certain extent, but the strength of the interface film formed is limited, and it is difficult to support the subsequent complex wall formation reaction.

[0018] The first technical challenge faced by the present application is the physical and chemical properties of the core material. The core material containing at least two fluorocarbon extinguishing agents has a low surface tension and strong hydrophobicity, which makes it have a large interfacial energy with the water phase system. It is extremely difficult to stably disperse such substances in water to form micron-sized droplets under normal conditions, and the emulsion system will quickly separate and fail. In the prior art, anionic and non-ionic complex emulsifiers are used, which can achieve emulsification to a certain extent, but the strength of the interface film formed is limited, and it is difficult to support the subsequent complex wall formation reaction.

[0019] Therefore, in the emulsification system, the complex of anionic emulsifier and cationic emulsifier is added. This is a non-obvious choice in the field of emulsification technology, because the two surfactants with opposite charges will usually precipitate due to electrostatic attraction in aqueous solution, resulting in double failure. However, the present application precisely controls this action on the oil-water interface. When the emulsification process begins, the hydrophobic ends of the two emulsifiers are adsorbed on the surface of the fluorocarbon core material droplets at the same time, and their hydrophilic ends carrying opposite charges extend to the water phase. At the interface, the anionic group meets the cationic group and neutralizes in situ. This neutralization produces two key technical effects: first, it eliminates the original single charge on the droplet surface, reducing the electrostatic repulsion between droplets; second, it forms a strong intermolecular interaction force similar to an ionic bond, causing the anionic and cationic emulsifier molecules to be tightly bound together at the interface, forming a physically cross-linked, dense, and high-mechanical-strength composite interface film. The strength and stability of this interface film can effectively resist droplet coalescence. Second, an amphiphilic cosolvent is also introduced into the emulsion system. As a surface-active substance, it can effectively reduce the interfacial tension between oil and water, making it easier for the core material to be broken into small droplets under the physical action of high-speed shearing, reducing the energy consumption required for emulsification, and facilitating the formation of smaller initial particle sizes. Moreover, as a filling or plasticizing molecule, the amphiphilic cosolvent can insert into the intermolecular gaps of the composite interface film formed by the anionic and cationic emulsifiers. Due to its small molecular size, it can fill any microscopic gaps that may exist between the macromolecular emulsifiers, making the entire interface film more dense, flexible, and defect-free, further enhancing the physical barrier effect of the interface film and effectively inhibiting the diffusion and maturation of core material molecules. Finally, the sodium alginate aqueous solution is directly used as the continuous phase for emulsification in the emulsion system. As one of the key substances for subsequent wall formation, dissolving sodium alginate in the water phase in advance means that when the core material droplets are stabilized by emulsifiers and cosolvents, their outer surfaces are already surrounded by a layer of uniformly concentrated sodium alginate macromolecules. This not only takes advantage of sodium alginate as a high-molecular-weight stabilizer to further enhance the long-term stability of the emulsion, but more importantly, it creates an ideal condition for the subsequent formation of a near-field reaction. When the chitosan solution is added, the two wall-forming polymers can directly meet and react at the droplet interface, avoiding the lengthy process of diffusion from the bulk phase and ensuring rapid, uniform, and efficient subsequent wall formation.

[0020] In summary, the emulsification step is not a simple physical mixing, but a synergistic process composed of a special emulsifier system, a cosolvent, and a process design. The highly stable emulsion precursor prepared by it is the key prerequisite for the present application to successfully prepare high-performance microcapsules using only natural polymers.

[0021] Moreover, in the forming and solidifying steps of the wall material, through a dual wall-forming mechanism of "electrostatic complexation as a template and ionic crosslinking as solidification", a unity of complete biodegradability in material composition and solid reliability in physical properties is achieved. In order to solve the problem of insufficient mechanical strength of natural polymers, the prior art has to take a compromising technical route. For example, synthetic acrylic resin and inorganic aluminum hydroxide are introduced for blending to improve the hardness by physical means, but the pure natural properties of the material are sacrificed. Alternatively, a double-coating strategy is adopted, and the core mechanical properties still rely on the synthetic resin shell of the outer layer. Both schemes fail to solve the performance problem within a single, purely natural polymer system.

[0022] In this scheme, the emulsion prepared in the previous step is added to an acidic aqueous solution of chitosan, and the pH value is precisely controlled, which is the key to this step. Chitosan is a cationic polysaccharide, and the amino groups on its molecular chain will be protonated under acidic conditions, changing into positively charged ammonium ions. As the continuous phase of the emulsion, sodium alginate has carboxylate groups on its molecular chain that have already dissociated into negatively charged carboxylate ions. When these two oppositely charged polymers meet on the surface of the emulsion droplets, they will undergo polyelectrolyte complexation. Chitosan molecular chains will be orderly adsorbed and deposited on the surface of the emulsion droplets surrounded by sodium alginate molecules. This process forms a primary coagulation layer formed by the interlocking of the two polymers through ionic bonds. Although the mechanical strength of this coagulation layer is not ideal, it is uniform, dense and complete in structure, providing a stable mold for subsequent structure reinforcement. After the formation of the primary coagulation layer, a divalent metal ion crosslinking agent is slowly added to the system. The specific unit block in the sodium alginate molecular chain can specifically chemically chelate with divalent metal ions such as calcium ions to form a stable crosslinked structure. In this structure, the divalent metal ions are precisely locked by the functional groups on two adjacent sodium alginate chains, forming stable and firm ionic crosslinking points. This ionic crosslinking process further locks the relatively flexible polymer chains that are combined by electrostatic forces through strong chemical bonds, forming a dense three-dimensional network gel structure with high spatial hindrance. There is an inseparable synergy between the two wall-forming mechanisms. Without the ordered template formed by the first step of electrostatic complexation, the second step of ionic crosslinking will be disordered and random, and cannot form a uniform and complete wall material, resulting in a final product with a large number of defects and low strength. Conversely, if there is no second step of ionic crosslinking for strong solidification, the wall material formed only by electrostatic forces will not only have a serious lack of mechanical strength, but also may undergo re-dissociation in an aqueous environment, failing to effectively encapsulate the core material. It is this "template first, then solidification" synergistic mechanism that enables the present application to prepare a single composite wall material with high mechanical strength, good density, and strong anti-permeability using only two natural polymers

[0023] Finally, in the post-processing step, the washing step can effectively remove the residual unreacted emulsifier, cosolvent, high molecular monomer and inorganic salt ions in the system. The presence of these impurities not only affects the purity of the microcapsule, but also may damage the structure of the wall material or cause slow degradation of the core material during long-term storage. The drying step, especially the low-temperature vacuum drying, is a necessary protective measure for the low-boiling fluorocarbon core material used in the present application. It can effectively remove the moisture in the microcapsule without causing a large amount of volatile loss of the core material due to heat, thereby obtaining a powder-shaped finished product with stable physical form, high core material encapsulation rate and ensuring the final fire extinguishing efficiency of the product.

[0024] In summary, the preparation method of the composite wall material fire extinguishing microcapsule defined in the present solution successfully prepares a fire extinguishing microcapsule which is completely biodegradable in material composition, stable and reliable in structure, and uniform and complete in encapsulation effect, effectively improving the long-term effectiveness problem of existing natural high molecular wall material fire extinguishing microcapsule.

[0025] In the second technical solution, the shear rate is specified as 1000-1500 rpm. When the shear rate is lower than 1000 rpm, the energy input is insufficient, resulting in large core material droplet size and wide distribution, which will make the final microcapsule have large individual differences and uneven wall thickness. Some oversized capsules may even have insufficient strength due to the thin wall. When the shear rate is higher than 1500 rpm, excessive energy input may cause a significant increase in system temperature, increasing the risk of volatilization of the low-boiling core material. At the same time, the excessive turbulence intensity may also damage the interface film formed by the anion and cation emulsifiers, which is not completely stable yet, resulting in an unstable emulsion. Therefore, by precisely controlling the shear rate in the range of 1000-1500 rpm, an emulsion precursor with concentrated particle size distribution and uniform size can be obtained, thereby achieving consistency and reliability of the final product.

[0026] In the third aspect, the temperature of the wall material forming and solidifying step is specified as 30-45℃. The ionic cross-linking reaction between sodium alginate and calcium ions is a process affected by temperature, and 30-45℃ is the optimal temperature range for the reaction. Within this range, the thermal motion of molecules and the diffusion rate of ions are moderate, which can ensure that the cross-linking reaction proceeds smoothly and sufficiently, thereby forming a uniform, dense and defect-free gel network structure. If the temperature is lower than 30℃, the reaction rate is too slow, which may result in incomplete cross-linking in a limited reaction time, insufficient cross-linking density of the wall material, and poor mechanical strength and density. If the temperature is higher than 45℃, on the one hand, it will significantly increase the saturated vapor pressure of the low-boiling-point core material, greatly increasing the risk of core material permeating and volatilizing through the wall material, thereby reducing the encapsulation rate. On the other hand, too high a temperature may also affect the stability of the emulsion system, and even cause thermal degradation of part of the polymer chains. Therefore, precise control of the temperature at 30-45℃ can ensure the quality of the wall material solidification reaction and obtain microcapsules with high mechanical strength and high encapsulation rate.

[0027] In the fourth aspect, the pH adjustment range is specified as 5.5-6.5. The pKa value of the amino group on the chitosan molecular chain is about 6.5. When the pH value of the system is adjusted to the range of 5.5-6.5, it can ensure that most of the amino groups exist in the form of protonation, so that the chitosan molecular chain carries a high enough positive charge density. At the same time, the pKa value of the carboxyl group of sodium alginate is much lower than this range, so its carboxylate group is completely dissociated and carries a saturated negative charge. Under this pH condition, the electrostatic attraction between the two polymers can be maximized, thereby promoting them to form the most dense, ordered and stable polyelectrolyte complex primary coacervate layer on the surface of the emulsion droplets. If the pH value is higher than 6.5, the degree of protonation of chitosan decreases and the electrostatic attraction weakens; if the pH value is lower than 5.5, although the protonation of chitosan is more complete, the acidic environment may affect the structure of sodium alginate. Therefore, this pH range ensures the structural integrity and high quality of the initial forming template of the wall material.

[0028] In the fifth aspect, the crosslinking agent is added at a rate of 3-5 mL / min. The essence of the ionic crosslinking reaction is the rapid combination of a large amount of calcium ions with the units on the sodium alginate chain. If a large amount of crosslinking agent is added to the system at once, a very high ion concentration will be generated in the local area where the crosslinking agent contacts the emulsion, resulting in instantaneous, violent and non-uniform gelation. This reaction will form a non-homogeneous wall material that appears to be solid on a macroscopic scale, but is full of pores, stress concentration points and structural defects on a microscopic scale, and has very poor mechanical strength and permeation resistance. In contrast, by slowly and continuously adding at a rate of 3-5 mL / min, the concentration of crosslinking agent ions in the reaction system can be maintained at a relatively low but continuous level. This allows the calcium ions to have enough time to uniformly diffuse around each emulsion droplet and undergo an orderly, layer-by-layer crosslinking reaction with the sodium alginate molecular chain. This controlled reaction kinetics process results in a more regular, uniform and dense network structure of the final wall material on a microscopic level, and the prepared microcapsules have excellent performance in terms of mechanical strength, toughness and resistance to core material permeation.

[0029] In the sixth aspect, the microcapsules are washed with ethanol and deionized water alternately, which is based on a comprehensive consideration of the types of impurities that may exist in the system. Deionized water can effectively wash away residual inorganic salts, while ethanol, as a polar organic solvent, can wash away some residual water-insoluble or slightly soluble organic substances. This alternating washing method ensures the thoroughness of impurity removal. Vacuum drying, especially at low temperatures, is necessary to protect the low-boiling-point fluorocarbon core material. If heated and dried at normal pressure, even at a relatively low temperature, the core material will evaporate in large quantities due to its high saturated vapor pressure, resulting in a significant reduction in the effective payload of the microcapsules and a substantial decrease in the fire extinguishing performance. The vacuum environment can greatly reduce the boiling point of water, allowing the water to be effectively removed at a temperature close to room temperature, while maximizing the retention of the core material inside the capsule.

[0030] In the seventh aspect, the styrene groups of the styrene-maleic anhydride copolymer provide strong hydrophobic forces, and its rigid polymer backbone can form a strong framework at the interface; the long carbon chain of cetyltrimethylammonium bromide also provides excellent hydrophobic adsorption capacity, so the combination of the two has a remarkable synergistic effect in stabilizing the strong hydrophobic fluorocarbon system.

[0031] In the eighth aspect, n-octanol has a moderate carbon chain length, and the polarity of its terminal hydroxyl group can balance the interfacial tension and reduce the interfacial film filling effect in this specific emulsion system.

[0032] In the ninth technical solution, the divalent metal ion is specifically calcium ion. Among all divalent metal ions capable of ionically cross-linking with alginate, calcium ion is the most ideal due to its ion radius, charge density and geometric matching degree of the cross-linking structure formed with specific units of sodium alginate, and the formed gel network has the best comprehensive performance in mechanical strength, stability and biocompatibility.

[0033] In the tenth technical solution, the mass ratio of chitosan to sodium alginate is further limited in the optimized range of 1:1 to 1.5:1. In this ratio range, the positive and negative charges on the two polymer chains can be almost completely neutralized, and the formed polyelectrolyte complex primary condensed layer is the most dense and stable. If the ratio deviates from this range, one polymer will be excessive, and there will be unneutralized net charges in the complex layer, causing electrostatic repulsion between the molecules in the layer, making the structure loose, thereby affecting the mechanical properties of the final solidified wall material. By accurately controlling the stoichiometric ratio of the wall-forming material, the compactness of the microstructure of the composite wall material is ensured, and the mechanical properties of the composite wall material are ensured. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0035] Figure 1 A scanning electron microscope diagram of the fire extinguishing microcapsule prepared by the preparation method of the composite wall material fire extinguishing microcapsule according to the embodiments of the present application. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are preferred embodiments of the present application, and should not be regarded as excluding other embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0037] In the claims and specification of the present application, the terms "include", "have" and their variants are intended to mean "including but not limited to".

[0038] The present application relates to a preparation method of a composite wall material fire extinguishing microcapsule, which comprises the following sequentially executed steps:

[0039] S100: adding a core material containing at least two fluorocarbon extinguishing agents, a complex of an anionic emulsifier and a cationic emulsifier, and an amphiphilic cosolvent into a sodium alginate aqueous solution to form a mixed solution, and subjecting the mixed solution to shearing treatment, thereby preparing a water-in-oil emulsion;

[0040] S200: adding the emulsion prepared in step S100 into an acidic aqueous solution of chitosan to obtain a reaction precursor solution; after adjusting the pH value of the reaction precursor solution, adding a divalent metal ion crosslinking agent thereto under a set temperature condition, and forming a composite wall material composed of chitosan and the sodium alginate on the surface of the droplets of the core material by initiating an ionic crosslinking reaction;

[0041] S300: washing and drying the microcapsules formed in step S200 to obtain the extinguishing microcapsules.

[0042] In step S100, the shearing rate of the shearing treatment is 1000-1500 rpm. Specifically, the shearing treatment can be achieved by using a high-speed shearing emulsifier commonly used in laboratories. When operating, the mixed solution containing the core material, the emulsifier, the cosolvent, and the sodium alginate aqueous solution is placed in the container of the emulsifier, the device is started, and the rotation speed is set in the range of 1000-1500 rpm, for example, 1300 rpm. The rotation speed is maintained for a predetermined time, for example, 10 minutes, to ensure that the core material is sufficiently dispersed into uniform small droplets.

[0043] In step S200, the set temperature condition is 30-45°C. Specifically, the control of the temperature condition can be achieved by placing the reaction container, such as a beaker or a reaction kettle, containing the reaction precursor solution in a constant temperature water bath. The temperature controller of the constant temperature water bath is set at a target temperature of 30-45°C, for example, 35°C. Through the heating and circulation functions of the water bath, the temperature of the reaction system during the entire wall material formation and solidification process can be accurately maintained at a constant set value, thereby ensuring the stability and repeatability of the ionic crosslinking reaction.

[0044] In step S200, the pH value is adjusted to the range of 5.5-6.5. Specifically, the pH value adjustment is as follows: a calibrated pH electrode is immersed in the stirring reaction precursor solution to monitor the pH value in real time. A burette or a pipette is used to add a 0.1 mol / L sodium hydroxide aqueous solution dropwise into the liquid. The pH meter reading is continuously monitored during the addition process, and when the reading reaches the target range of 5.5-6.5, for example, 6.0, the addition is slowed down or stopped, and the reading is observed to be stable. After the pH value is stabilized at the target value, the adjustment is completed.

[0045] In step S200, the step of adding the divalent metal ion crosslinking agent is achieved by adding the solution containing the crosslinking agent into the reaction precursor solution at a drop rate of 3-5 mL / min. Specifically, the controlled drop process is achieved by using a precision fluid delivery device, such as a peristaltic pump or a syringe pump. The solution containing the crosslinking agent, such as a 1 wt% calcium chloride aqueous solution, is loaded into the reservoir of the pump. The flow rate parameter of the pump is set to the target range of 3-5 mL / min, for example, set to 3 mL / min. After the pump is started, the crosslinking agent solution will be slowly and uniformly delivered into the stirring reaction precursor solution at a constant rate until the addition is completed.

[0046] In step S300, the washing process includes alternating washing with ethanol and / or deionized water, and the drying process is vacuum drying. Specifically, the post-treatment operation includes the following specific steps: first, the reaction product of step S200 is vacuum filtered through a Buchner funnel and a filtration bottle, and the formed microcapsule solid is separated from the reaction mother liquor. Then, the filter cake is taken out of the funnel and transferred to a beaker, and a sufficient amount of deionized water (e.g., 100 mL) is added for redispersion and stirring washing, followed by filtration again. This water washing process is repeated three times. Then, in the same way, the filter cake is redispersed, washed and filtered with anhydrous ethanol, also repeated three times. The finally washed microcapsule solid is spread on a clean petri dish and placed in a vacuum drying oven. The temperature of the drying oven is set to 35°C, and the vacuum pump is started to vacuum the oven to a vacuum state, and the condition is maintained for 24 hours to obtain the final powder product.

[0047] The anionic emulsifier is a styrene-maleic anhydride copolymer, and the cationic emulsifier is hexadecyltrimethylammonium bromide.

[0048] The amphiphilic cosolvent is n-octanol.

[0049] The divalent metal ion crosslinking agent is calcium ion. In a preferred embodiment of the present application, the selected divalent metal ion is calcium ion (Ca 2+ ). In a specific operation, the ion is provided by a 1 wt% calcium chloride (CaCl2) aqueous solution, which is added as a crosslinking agent solution to the reaction system.

[0050] The total mass ratio of chitosan to sodium alginate used in steps S100 and S200 is 1:1 to 1.5:1.

[0051] In order to better illustrate the technical solutions of the present application, the following will be described in detail through specific examples and comparative examples. These examples and comparative examples are intended to demonstrate the feasibility and superiority of the technical solutions of the present application, and do not constitute a limitation on the technical solutions of the present application.

[0052] To ensure the accuracy and repeatability of the experimental results, the main raw materials used in this part are purchased from commercial channels, and the specific specifications or models are as follows:

[0053] Sodium alginate (SA): food grade, 1% aqueous solution viscosity ≥ 200 mPa·s, provided by Qingdao Mingyue Seaweed Group Co., Ltd.

[0054] Chitosan (CTS): degree of deacetylation ≥ 90%, molecular weight about 200 kDa, provided by Zhejiang Jinshell Pharmaceutical Co., Ltd.

[0055] Cis-hexafluorobutene (F7A): purity ≥ 99.5%, trade name HFO-1336mzz-Z, provided by Chemours Company.

[0056] 1,1,2,2,3,3,4-heptafluorocyclopentane: purity ≥ 99.5%, trade name Novec 1230, provided by 3M Company.

[0057] Styrene-maleic anhydride copolymer (SMA520): molar ratio of styrene to maleic anhydride 5:2, acid value range 180-200 mgKOH / g, provided by Arkema Company, France.

[0058] Cetyltrimethylammonium bromide (CTAB): analytical pure (AR), purity ≥ 99.0%, provided by Sinopharm Chemical Reagent Co., Ltd.

[0059] n-Octanol: analytical pure (AR), purity ≥ 99.5%, provided by Sinopharm Chemical Reagent Co., Ltd.

[0060] Calcium chloride (CaCl2): anhydrous, analytical pure (AR), purity ≥ 96.0%, provided by Sinopharm Chemical Reagent Co., Ltd.

[0061] Emulsifiers SR-10, ER-30, SR-20: industrial grade, provided by Dow Chemical Company.

[0062] Perfluorooctyltriethoxysilane: industrial grade, provided by relevant chemical suppliers.

[0063] Acrylic resin: emulsion type, solid content 45%, provided by BASF Company.

[0064] Aluminum hydroxide: industrial grade, average particle size 1.5 μm, provided by China Aluminum Industry Co., Ltd.

[0065] Example 1

[0066] This embodiment is intended to illustrate the method for preparing the fire extinguishing microcapsules with composite wall material according to the core technical solution of the present application under the condition of preferred parameters.

[0067] Step S100: Emulsion preparation

[0068] Accurately weigh 1.0 g of sodium alginate (SA) and 0.25 g of styrene-maleic anhydride copolymer (SMA520), and dissolve them in 100 mL of deionized water to form a uniform aqueous solution. Add a mixed core material composed of 5 mL of cis-hexafluorobutene (F7A) and 5 mL of heptafluorocyclopentane (Novec1230), 1 mL of n-octanol, and 0.25 g of cetyltrimethylammonium bromide (CTAB) to the solution. Use a FLUKO FM200 high-speed shearing emulsifier to shear the mixture at a shearing rate of 1300 rpm for 10 minutes to obtain a uniform and stable oil / water emulsion.

[0069] Step S200: Wall material formation and solidification

[0070] Dissolve 1.2 g of chitosan (CTS) in 150 mL of 1 wt% acetic acid aqueous solution. Transfer the emulsion prepared in step S100 to the above chitosan solution under stirring to obtain a reaction precursor liquid. Use a METTLER TOLEDO FE28 pH meter to monitor in real time, and use a microburet to add 0.1 mol / L sodium hydroxide solution drop by drop to accurately adjust and stabilize the pH value of the reaction precursor liquid at 6.0. Place the reaction system in a constant temperature water bath at 35°C. Slowly add 100 mL of 1 wt% calcium chloride (CaCl2) aqueous solution to the system at a constant drop rate of 4 mL / min by using a Longer Pump BT100-2J peristaltic pump. After the addition is completed, continue to stir the reaction at 35°C for 2 hours to complete the ion crosslinking solidification.

[0071] Step S300: Post-treatment

[0072] Vacuum filter the reaction product through a Buchner funnel to collect the microcapsule solids. First, wash with 500 mL of deionized water for three times of re-dispersion-filtration, and then wash with 300 mL of anhydrous ethanol for three times of re-dispersion-filtration. Lay the finally washed microcapsule solids on a petri dish and place them in an EYELA FDU-1200 vacuum freeze dryer for drying at -10°C and a vacuum degree lower than 10 Pa for 24 hours to obtain white powder-like fire extinguishing microcapsule products with good flowability.

[0073] Example 2

[0074] This embodiment is intended to illustrate the method for further enhancing the mechanical properties of microcapsules by optimizing the drop rate of crosslinking agent.

[0075] The preparation procedure is substantially the same as that of Example 1, except that the crosslinker dropping process in Step S200 is different. In this example, the dropping rate of 1 wt% calcium chloride aqueous solution is adjusted to 3 mL / min. All other parameters and operations remain unchanged.

[0076] Example 3

[0077] This example is intended to illustrate the method of preparing microcapsules under another set of parameter boundary conditions defined in the claims.

[0078] Step S100: The shear rate of shear treatment is set to 1500 rpm. The mass ratio of chitosan to sodium alginate is 1.5:1 (chitosan 1.5 g, sodium alginate 1.0 g).

[0079] Step S200: The pH value is adjusted to 6.5. The temperature of constant temperature crosslinking is set to 45°C. The dropping rate of crosslinker is set to 3 mL / min.

[0080] Step S300: The post-treatment procedure is the same as that of Example 1.

[0081] Example 4

[0082] This example is intended to illustrate the method of preparing microcapsules under another set of parameter boundary conditions defined in the claims.

[0083] Step S100: The shear rate of shear treatment is set to 1500 rpm. The mass ratio of chitosan to sodium alginate is 1.5:1 (chitosan 1.5 g, sodium alginate 1.0 g).

[0084] Step S200: The pH value is adjusted to 6.5. The temperature of constant temperature crosslinking is set to 45°C. The dropping rate of crosslinker is set to 3 mL / min.

[0085] Step S300: The post-treatment procedure is the same as that of Example 1.

[0086] Comparative Example 1

[0087] This comparative example is intended to reproduce one prior art which uses "anionic + nonionic" emulsifiers and pre-mixes chitosan and calcium ions in the same solution to complete gelation by one-step method.

[0088] Emulsion preparation: 1.0 g of sodium alginate was weighed into 100 mL of deionized water. To this, 10 mL of mixed core material (F7A and Novec 1230 at a volume ratio of 1 : 1) was added, along with 0.4 g of emulsifier SR-10 and 0.2 g of emulsifier ER-30 as a compounded emulsifier, and 0.2 g of perfluorooctyltriethoxysilane as a coupling agent. Shearing was carried out at 1300 rpm for 10 minutes to obtain the emulsion.

[0089] Wall material formation: A gelation solution was prepared by dissolving 1.2 g of chitosan and 5.0 g of calcium chloride in 150 mL of an acetic acid solution with a concentration of 1 wt% at the same time. The emulsion prepared in Step 1 was directly added dropwise to the gelation solution, and the reaction was stirred at 35°C for 2 hours.

[0090] Post-treatment: The operation procedure was the same as in Example 1.

[0091] Comparative Example 2

[0092] This comparative example aims to reproduce another existing technology that uses a physical blending method of "natural polymer + synthetic resin + inorganic filler" to prepare the wall material.

[0093] Aqueous phase preparation: 1.5 g of chitosan was dissolved in 100 mL of an aqueous acetic acid solution with a concentration of 1 wt%.

[0094] Wall material formation: In the above aqueous phase, 10 mL of mixed core material (F7A and Novec 1230 at a volume ratio of 1 : 1), 1.0 g of acrylic resin emulsion (based on solid content), 0.4 g of emulsifier SR-20, and 0.8 g of emulsifier ER-10 were added. High-speed emulsification was carried out at 4000 rpm for 3 hours. Subsequently, the stirring speed was reduced to 300 rpm, 2.0 g of aluminum hydroxide powder was added, and stirring was continued for 50 minutes, followed by standing for 2 hours.

[0095] Post-treatment: The operation procedure was the same as in Example 1.

[0096] Comparative Example 3

[0097] This comparative example aims to verify the necessity of the anionic / cationic compounded emulsifier system in the present application.

[0098] The preparation steps were exactly the same as in Example 1, with the only difference being that in Step S100, no cationic emulsifier cetyltrimethylammonium bromide (CTAB) was added, and only 0.5 g of anionic emulsifier styrene-maleic anhydride copolymer (SMA520) was used.

[0099] Comparative Example 4

[0100] This comparative example aims to further verify the synergistic effect of the anionic / cationic compounded emulsifier system in the present application.

[0101] The preparation steps are completely the same as those of Example 1, the only difference is that in step S100, no anionic emulsifier styrene-maleic anhydride copolymer (SMA520) is added, only 0.5 g of cationic emulsifier cetyltrimethylammonium bromide (CTAB) is used.

[0102] Comparative Example 5

[0103] The purpose of this comparative example is to verify the key role of the amphiphilic cosolvent in the present application.

[0104] The preparation steps are completely the same as those of Example 1, the only difference is that in step S100, no amphiphilic cosolvent n-octanol is added.

[0105] Comparative Example 6

[0106] The preparation steps are completely the same as those of Example 1, the only difference is that in step S200, after adding the emulsion into the chitosan solution, no pH adjustment is performed, and the subsequent step of adding calcium chloride is directly performed. At this time, the measured pH value of the system is about 4.5.

[0107] Comparative Example 7

[0108] The preparation steps are completely the same as those of Example 1, the only difference is that in step S200, 100 mL of 1 wt% calcium chloride aqueous solution is quickly poured into the reaction system at one time, instead of being slowly added by peristaltic pump.

[0109] The samples prepared in Examples 1-4 and Comparative Examples 1-7 above were subjected to performance testing, and the results are as follows.

[0110] 1. Micro-morphology and particle size distribution

[0111] Test standards and methods: Hitachi S-4800 field emission scanning electron microscope (SEM) was used to observe the surface morphology and integrity of the microcapsules. According to the standard of GB / T 19077-2016 "Particle size analysis by laser diffraction method", Malvern Mastersizer 3000 laser particle size analyzer was used to test the particle size distribution.

[0112] Test results and analysis:

[0113] The microcapsules prepared in Examples 1-4 all present regular spherical shape, smooth and dense surface, no obvious damage or adhesion, as shown in FIG. 1. Figure 1 The particle size distribution is concentrated, and the average particle size is between 250-450 μm, indicating that the preparation process of the present application is stable and controllable.

[0114] The two products obtained by replicating the two prior arts of Comparative Example 1 and Comparative Example 2 respectively have irregular morphology, poor uniformity, and defects such as breakage and adhesion.

[0115] In Comparative Example 3 and Comparative Example 4, since only a single emulsifier is used, a stable emulsion cannot be formed, the system is quickly demulsified and separated after standing, and the subsequent wall forming reaction cannot be carried out, so the microcapsule product cannot be obtained.

[0116] In Comparative Example 5, after omitting the cosolvent, the obtained microcapsules have wide particle size distribution and rough surface, and a small amount of breakage.

[0117] In Comparative Example 6 and Comparative Example 7, since a key process step is omitted, the product of the former has a large amount of adhesion and a severely irregular morphology; the latter directly forms an irregular gel block, and neither of them can form independent and qualified microcapsules.

[0118] 2. Performance test data summary

[0119] Test standards and methods:

[0120] Encapsulation efficiency (EE%) and leakage rate: determined by Soxhlet extraction-gas chromatography method. Long-term stability is evaluated by 50°C, 30-day accelerated aging test.

[0121] Mechanical strength: single microcapsules are tested by a micromanipulation system, the rupture pressure is recorded and converted into pressure (MPa).

[0122] Thermal triggering performance: tested according to GB / T27761-2011 "Plastics Differential Scanning Calorimetry (DSC)" standard.

[0123] The test results are as follows:

[0124]

[0125]

[0126] According to the above test results, the results of Comparative Examples 3 and 4 (cannot be prepared) directly prove that a single anionic or cationic emulsifier cannot stabilize the emulsion system, and it is necessary to use both by compounding to utilize the in-situ charge neutralization effect at the interface to form an interface film with sufficient strength. The results of Comparative Example 5 show that the lack of cosolvent n-octanol can form capsules, but the encapsulation efficiency and stability are greatly reduced, which proves that the cosolvent is indispensable in reducing the interfacial energy and filling the defects of the interface film. The combination of "anionic / cationic complex emulsifier + amphiphilic cosolvent" used in the present application is the primary prerequisite for realizing high encapsulation efficiency and high stability.

[0127] The embodiments (1 and 2) of the present application are overall and significantly superior to the products replicating two prior arts (Comparative Examples 1 and 2) in encapsulation efficiency, leakage rate and mechanical strength. This proves the dual wall-forming mechanism of the present application, i.e. "electrostatic compounding as templating and ionic crosslinking as solidifying", which is able to construct a pure natural polymer wall material with more compact structure and more reliable performance compared to one-step gelation or physical blending.

[0128] The results of Comparative Examples 6 and 7 show that the accurate pH control and slow addition of crosslinking agent are necessary technical conditions for the success of the present application, rather than simple routine operations. Omitting any step will lead to the failure of the wall-forming process, which highlights the non-obviousness of the process flow design of the present application. It is the precise coordination of these components and processes that realizes the excellent performance of the final product.

[0129] The above description and example descriptions are used to explain the scope of protection of the present application, but do not constitute a limitation on the scope of protection of the present application. Through the inspiration of the present application or the above examples, those skilled in the art can obtain modifications, equivalent replacements or other improvements of the embodiments of the present application or part of the technical features thereof by combining with common knowledge, ordinary technical knowledge in the art and / or prior art, through logical analysis, reasoning or limited experiments, which shall be included in the scope of protection of the present application.

Claims

1. A method for preparing composite wall material fire extinguishing microcapsules, characterized in that: It includes the following steps, performed in order: S100: adding a core material comprising at least two fluorocarbon fire extinguishing agents, a compound of an anionic emulsifier and a cationic emulsifier, and an amphiphilic cosolvent to an aqueous sodium alginate solution to form a mixed solution, and subjecting the mixed solution to a shearing treatment to prepare a water-in-oil emulsion; S200: adding the emulsion prepared in step S100 to an acidic aqueous solution of chitosan to obtain a reaction precursor liquid; after adjusting the pH value of the reaction precursor liquid, adding a divalent metal ion crosslinking agent thereto under set temperature conditions to initiate an ion crosslinking reaction, thereby forming a composite wall material composed of chitosan and the sodium alginate on the surface of the core material droplet; S300: washing and drying the microcapsules formed in step S200 to obtain the fire extinguishing microcapsules.

2. The method for preparing a composite wall material fire extinguishing microcapsule according to claim 1, characterized in that: In step S100, the shearing rate of the shearing treatment is 1000-1500 rpm.

3. The method for preparing a composite wall material fire extinguishing microcapsule according to claim 1, characterized in that: In step S200, the set temperature condition is 30-45°C.

4. The method for preparing a composite wall material fire extinguishing microcapsule according to claim 1, characterized in that: In step S200 , the pH value adjustment is to adjust the pH value of the pre-reaction fluid to a range of 5.5-6.

5.

5. The method for preparing a composite wall material fire extinguishing microcapsule according to claim 1, characterized in that: In step S200 , the step of adding the divalent metal ion cross-linking agent is performed by dropping a solution containing the cross-linking agent into the reaction precursor solution at a dropping rate of 3-5 mL / min.

6. The method for preparing a composite wall material fire extinguishing microcapsule according to claim 1, characterized in that: In step S300 , the washing process includes alternately washing with ethanol and / or deionized water, and the drying process is vacuum drying.

7. The method for preparing a composite wall material fire extinguishing microcapsule according to claim 1, characterized in that: The anionic emulsifier is styrene-maleic anhydride copolymer, and the cationic emulsifier is hexadecyltrimethylammonium bromide.

8. The method for preparing a composite wall material fire extinguishing microcapsule according to claim 1, characterized in that: The amphiphilic cosolvent is n-octanol.

9. The method for preparing a composite wall material fire extinguishing microcapsule according to claim 1, characterized in that: The divalent metal ion crosslinking agent is calcium ion.

10. The method for preparing a composite wall material fire extinguishing microcapsule according to claim 1, characterized in that: The total mass ratio of chitosan to sodium alginate used in step S100 and step S200 is 1:1 to 1.5:1.

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