Preparation method of double-initiation composite double-shell fire extinguishing microcapsule

Abstract

The invention discloses a preparation method of a double-initiation composite double-shell fire-extinguishing microcapsule, which comprises the following steps: firstly, preparing a fire-extinguishing microsphere with a core-shell structure, the capsule core emulsion comprising a fire-extinguishing core material and a surfactant; the inner shell layer solution comprises a temperature-sensitive material, a flame retardant, a cross-linking agent and a dispersing agent, and the LCST of the temperature-sensitive material is 55-65 DEG C. Then, the double-shell fire extinguishing microcapsule is prepared, and an outer shell solution comprises a photosensitive material, a flame retardant, a photoinitiator and a cross-linking agent; according to the invention, the construction of the double-layer shell layer is realized through two-step coating, and the prepared fire extinguishing microcapsule has a photo-thermal dual-initiation function and can be used for precise prevention and control of complex scenes such as electrical fire, forest fire and industrial plant fire.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fire extinguishing capsules, and particularly relates to a preparation method of double-initiation composite double-shell fire extinguishing microcapsules. BACKGROUND

[0002] In fire prevention and control, fire extinguishing microcapsules are widely used due to the targeted release characteristics of the agent, however, the existing single temperature trigger mechanism fire extinguishing microcapsules have the following defects: 1. Single trigger mechanism: microcapsules with temperature as the only trigger signal are prone to misrelease in industrial environments (such as high temperature 40-55℃ on the surface of an electric machine, heat conduction of a pipeline), resulting in agent waste (annual loss rate exceeding 30%), equipment corrosion (gas fire extinguishing agent corrosion rate on metal pipeline reaching 5%-8%) and secondary hazards such as electrical short circuit; 2. Preparation technology bottleneck: microcapsules prepared by microfluidic chip method have uniform size (coefficient of variation <5%) and high release efficiency (>90%), but the chip making requires precise processes such as photolithography and PDMS molding, and the single preparation amount is only several grams, which is difficult to meet the industrial demand of tons; 3. Limitation of preparation method: the existing emulsion polymerization method is mostly single-layer or double-layer structure, which cannot realize the double response of "temperature sensitivity + photosensitivity", and the microcapsules have large size deviation (coefficient of variation >50%) and poor wall material density (agent leakage rate exceeding 8% / year), and the fire extinguishing efficiency and fire prevention and combustion resistance are limited. SUMMARY

[0003] The purpose of the present application is to provide a preparation method of double-initiation composite double-shell fire extinguishing microcapsules, which aims to solve any of the above problems.

[0004] The present application is mainly realized by the following technical solutions: A preparation method of double-initiation composite double-shell fire extinguishing microcapsules, comprising the following steps: Step S1: preparing fire extinguishing microspheres with core-shell structure; Step S11: solution preparation; Preparation of capsule core emulsion: mix and uniformly stir fire extinguishing core material and surfactant with a mass ratio of 95.0wt%-99.5wt%:0.5wt%-1.0wt%; Preparation of inner shell layer solution: add temperature sensitive material, flame retardant and dispersant into deionized water, heat and uniformly stir; adjust the temperature to 20℃-40℃, then add crosslinking agent and uniformly stir; wherein the mass ratio of temperature sensitive material, flame retardant, crosslinking agent and dispersant is 65wt%-75wt%:20wt%-30wt%:1.0wt%-2.0wt%:0.5wt%-1.0wt%; the LCST of the temperature sensitive material is 55-65℃; Step S12: emulsion polymerization: slowly drop the capsule core emulsion into the inner shell layer solution, and carry out stirring reaction at a speed of 500r / min~1000r / min, to obtain a microsphere solution with core-shell structure; Step S13: preliminary solidification: heat the solution to 50℃, and keep for 0.5~2 hours, then centrifugally collect the extinguishing microsphere particles, wash with deionized water to remove unreacted monomers, and store in cold storage, to obtain an intermediate product A; Step S2: preparation of double-shell extinguishing microcapsule; Step S21: preparation of outer shell layer solution: uniformly mix photosensitive material, flame retardant and crosslinking agent in a solvent, then add a photoinitiator, and uniformly stir in the dark; wherein the mass ratio of photosensitive material, flame retardant, photoinitiator and crosslinking agent is 55wt%-65wt%: 30wt%-40wt%: 1.0wt%-2.0wt%: 0.5wt%-1.5wt%; Step S22: emulsion polymerization: disperse the intermediate product A in deionized water to form a suspension; then slowly drop the suspension into the outer shell layer solution, and carry out stirring reaction at a speed of 800r / min~1200r / min; Step S23: photocuring and post-treatment: transfer the solution in step S22 to an ultraviolet lamp, and cure for 15~40 minutes; then centrifugally collect the microcapsule, and wash with n-hexane to remove surface residues, and vacuum dry to obtain a double-shell extinguishing microcapsule.

[0005] In order to better realize the present application, further, in the step S12, the particle size of the microsphere solution with core-shell structure is 20-800μm; and the mass ratio of the capsule core, the inner shell layer and the outer shell layer of the double-shell extinguishing microcapsule prepared in the step S23 is 6~8: 5~7: 5~7. Preferably, the particle size of the microsphere solution with core-shell structure is 180-220μm.

[0006] In order to better realize the present application, further, in the step S11, the extinguishing core material is any one or more of perfluorohexanone, heptafluoropropane, and ammonium dihydrogen phosphate; and the surfactant is potassium perfluorooctylsulfonate or Tween-80.

[0007] In order to better realize the present application, further, in the step S11, the temperature-sensitive material is poly-N-isopropyl acrylamide and polycaprolactone copolymer or chitosan derivative.

[0008] In order to better realize the present application, further, in the step S11, the flame retardant is any one of organic montmorillonite and triphenyl phosphate, magnesium hydroxide and trimethylphenyl phosphate, zinc borate and melamine; the mass ratio of the organic montmorillonite and triphenyl phosphate is 1:1-4, the mass ratio of the magnesium hydroxide and trimethylphenyl phosphate is 1:2-5, and the mass ratio of the zinc borate and melamine is 1:1-3.

[0009] In order to better realize the present application, further, the particle size of the organic montmorillonite is 100-200 nm, and the organic montmorillonite is modified by hexadecyl trimethyl ammonium bromide.

[0010] In order to better realize the present application, further, in the step S21, the photosensitive material is any one of azobenzene derivative and spiro pyran derivative, diaryl ethylene derivative and o-nitrobenzyl derivative, and coumarin derivative, and the mass ratio of the azobenzene derivative and spiro pyran derivative is 1-2:1-3, the mass ratio of the diaryl ethylene derivative and o-nitrobenzyl derivative is 1-3:1.

[0011] In order to better realize the present application, further, in the step S21, the flame retardant is any one of aluminum hydroxide and zinc borate, ammonium polyphosphate, aluminum hydroxide and decabromodiphenyl ether, and the mass ratio of the aluminum hydroxide and zinc borate is 1-3:1; the mass ratio of the aluminum hydroxide and decabromodiphenyl ether is 1-4:1.

[0012] Preferably, the inner shell layer is a temperature-sensitive shell layer for realizing temperature response and initial flame retardation synergy; and the outer shell layer is a photosensitive shell layer for realizing light response and long-acting flame retardation synergy. Preferably, the mass ratio of the temperature-sensitive material and the flame retardant is 7:3, for example, the temperature-sensitive material is poly N-isopropyl acrylamide and polycaprolactone copolymer, and the flame retardant is a mixture of organic montmorillonite and triphenyl phosphate. Preferably, the mass ratio of the photosensitive material and the flame retardant is 6:4, for example, the photosensitive material is 4-hydroxyazobenzene-SP-1, and the flame retardant is a mixture of aluminum hydroxide and zinc borate.

[0013] The present application has the following advantages: (1) The present application prepares fire extinguishing microcapsules with light-heat dual synergistic response characteristics through emulsion polymerization, realizes light-heat dual signal synergistic triggering, realizes light-heat dual signal synergistic triggering. The present application realizes the construction of double shell layers through two-step coating, and the prepared fire extinguishing microcapsules have the function of light-heat dual initiation, which is suitable for medium and low cost industrial production scene, and can be used for precise prevention and control of complex scenes such as electrical fire, forest fire, industrial plant fire and the like. Specifically, the equipment cost of the present application is low, the material utilization rate is 75%-80%, and it is suitable for small-scale production; the light-heat dual initiation mechanism of the fire extinguishing microcapsules prepared by the present application can reach 0%, and the release rate is as high as 80%-85%, which meets the precise fire extinguishing demand of complex scenes. Secondly, by adjusting the type of capsule core (perfluorohexanone / septum fluoropropane / ammonium dihydrogen phosphate), it can adapt to low temperature, solid, electrical and other scenes, and the ODP of perfluorohexanone is 0, the shell layer is halogen-free flame retardant, and no toxic gas is generated during the fire extinguishing process, which is suitable for places with people.

[0014] (2) When the temperature and light signal meet at the same time, the inner layer pore flow guide and the outer layer rupture dredge form a synergistic channel, which can not only avoid the defects of single temperature triggering (normal equipment high temperature mis-triggering) or single light triggering (environmental stray light mis-triggering), but also can ensure the rapid release of the drug, and solve the dual problems of inaccurate triggering and low release efficiency. Specifically, when the ambient temperature does not reach the phase transition temperature (50-70 DEG C) of the temperature-sensitive material, the inner shell layer maintains a dense structure, and perfluorohexanone cannot penetrate; when the ambient temperature reaches the phase transition temperature but there is no fire light radiation (such as normal equipment high temperature), the inner shell layer swells but the outer light-sensitive material is not excited by light, and still maintains the barrier property, avoiding misrelease; only when the temperature reaches 50-70 DEG C and there is 200-1000 nm light radiation (fire characteristics), the inner shell layer swells and the outer light-sensitive material is broken by photoisomerization, and perfluorohexanone is released quickly through the pores of the double-layer shell.

[0015] (3) Temperature-sensitive shell layer: the temperature-sensitive material is a copolymer of poly-N-isopropyl acrylamide and polycaprolactone (PNIPAM-PCL), and the amino group (-NH2) in the copolymer reacts with the aldehyde group (-CHO) of the crosslinking agent glutaraldehyde to form a three-dimensional crosslinked network: -NH2+O=CH-(CH2)3-CHO→-N=CH-(CH2)3-CHO+H2O; The reaction forms a three-dimensional crosslinked network, experiments prove that this feature can improve the tensile strength of the temperature-sensitive shell layer from 0.8 MPa to 1.5 MPa, which can avoid rupture during storage or transportation, and at the same time control the pore size of the temperature response to be 1-5 μm, which ensures the ordered release of the drug.

[0016] (4) When the environmental temperature reaches the LCST (55-65℃) of the temperature-sensitive shell layer, the hydrogen bonds between the hydrophilic groups (-CONH-) of the PNIPAM-PCL copolymer and water molecules are broken, the molecular chains change from the extended state (hydrophilic) to the coiled state (hydrophobic), phase separation occurs, and 1-5 μm micropores are generated in the temperature-sensitive shell layer. Secondly, the flame retardant TPP decomposes to produce phosphoric acid (H3PO4), and the esterification reaction between phosphoric acid and the hydroxyl groups (-OH) of PNIPAM further expands the pore size (5-10 μm), providing a channel for the release of the core, and the generated phosphate substances can inhibit the combustion free radicals to assist in extinguishing the fire.

[0017] (5) Light-sensitive shell layer: The nucleophilic substitution reaction occurs between the hydroxyl groups (-OH) of the light-sensitive material SP-1 and the amino groups (-NH2) of the crosslinking agent diethylenetriamine: -OH + H2N-(CH2)2-NH-(CH2)2-NH2 → -O-NH-(CH2)2-NH-(CH2)2-NH2 + H2O. Among them, the photoinitiator 1173 decomposes into methyl radicals (·CH3) and benzoyl radicals (·COPh) under ultraviolet light, initiating the radical polymerization reaction of the double bond (-N=N-) of 4-hydroxy azobenzene, further strengthening the crosslinking structure. Experiments have shown that this feature reduces the water immersion resistance of the temperature-sensitive shell layer (72h in water at 25℃) from 12wt% to 3wt%.

[0018] (6) When there is 350-400nm ultraviolet light in the environment, the 4-hydroxy azobenzene undergoes cis-trans isomerization reaction: cis structure (molecular aspect ratio 1:1.2) → trans structure (molecular aspect ratio 1:2.5), the change in molecular configuration causes stress (0.3-0.5MPa) to occur inside the outer shell layer. The spiropyran SP-1 undergoes a spiro ring opening reaction: the spiro ring structure (C-O-C bond) is broken, forming a merocyanine structure (-C=C-N-), the molecular polarity changes from non-polar (dielectric constant ε=2.5) to polar (ε=8.0), which causes the light-sensitive shell layer to swell and break, and the pore size expands to 10-20 μm.

[0019] (7) The flame retardant realizes fire extinguishing and anti-reignition across the layers. In the temperature-sensitive shell layer, the layered OMMT is embedded in the cross-linked network of PNIPAM-PCL copolymer to form a composite structure of organic matrix-inorganic barrier layer. The experiment proves that this feature reduces the thermal conductivity of the material from 0.2 W / (m·K) to 0.12 W / (m·K), and the phosphoric acid generated by the decomposition of triphenyl phosphate TPP catalyzes the dehydration of the matrix into carbon with a carbon layer coverage of >90%, which can inhibit the initial flame spread. In the light-sensitive shell layer, aluminum hydroxide ATH absorbs a large amount of heat (decomposition rate of 50% at 60°C) upon heating, causing the temperature in the fire extinguishing area to drop rapidly from 300°C to below 150°C; the B2O3 glass material generated by the decomposition of zinc borate ZB covers the surface of the carbon layer, forming a dense "carbon layer-B2O3" composite barrier, and the oxygen permeability is reduced from 1.5×10 -11 cm³·cm / (cm²·s·cmHg) to 5×10 -13 cm³·cm / (cm²·s·cmHg), which breaks the heat and oxygen cycle and achieves long-term anti-reignition. The synergistic effect of the inner and outer layers of the flame retardant increases the microcapsule oxygen index from 28% of the single inner layer of the flame retardant to 35%, and the reignition rate after 30 minutes of fire extinguishing is reduced from 15% (single flame retardant layer) to 0%, and the time for the temperature to drop to the ambient temperature (25°C) is shortened from 18 minutes to 12 minutes.

[0020] (8) The capsule core and the shell layer cooperate to extinguish the fire. After the release of the capsule core, the initial flame is quickly extinguished by inhibiting the combustion chain reaction; the flame retardant in the double-layer shell layer decomposes at high temperature to form phosphate ester radicals and montmorillonite barrier layer, which inhibits the spread of the flame and reduces the heat radiation, realizing the synergistic effect of fire extinguishing agent and flame retardant, and improving the fire extinguishing efficiency. Among them, the capsule core dominates the fire extinguishing: after the release of the fire extinguishing core material, the combustion chain reaction is terminated by capturing combustion free radicals (·OH, ·O·), and the time for the open flame to be extinguished is <10 seconds. The shell layer assists in fire extinguishing: the decomposition of the flame retardant produces inert gas (CO2 generated by the decomposition of triphenyl phosphate TPP, N2 generated by the decomposition of zinc borate ZB), which dilutes the oxygen concentration in the combustion area (from 21% to below 15%). Secondly, the cross-linked products (such as Schiff base, phosphate) in the shell layer can inhibit the chain transmission in the combustion reaction, and assist the fire extinguishing core material to improve the fire extinguishing efficiency. The synergistic effect of the capsule core and the shell layer improves the fire extinguishing efficiency by 30% compared with the single perfluorohexanone, and the fire can still be effectively extinguished at a low concentration (10 g / m³), reducing the amount of medicament.

[0021] (9) The fire extinguishing capsule of the present application adopts a three-layer composite structure of core-shell-shell, and a photo-thermal dual initiation mechanism is constructed through the synergistic effect of the temperature-sensitive shell layer and the light-sensitive shell layer. Only when the environment simultaneously meets the response temperature (such as 50-120°C) of the temperature-sensitive material and the response wavelength (such as 200-1000nm) of the light-sensitive polymer, the fire extinguishing core material of the capsule core will be released. This dual trigger mechanism can accurately distinguish between normal high temperature (such as equipment running heat) and fire signal (high temperature + flame light radiation), solving the problem of false release of single temperature triggered microcapsules in industrial environment, significantly reducing the false trigger rate (actual false trigger rate <0.1%), and is especially suitable for electrical cabinets, data centers and other scenes with high trigger accuracy requirements. (10) The capsule core is a high-efficiency fire extinguishing agent, which can quickly extinguish the initial fire by inhibiting combustion free radicals after release; the flame retardants (such as montmorillonite, aluminum hydroxide, etc.) added in the inner and outer shell layers form a barrier layer at high temperature, delaying heat transfer and oxygen contact, realizing the dual effect of fire extinguishing + anti-reignition. Comparative experiments show that the fire extinguishing efficiency of the fire extinguishing capsule prepared by the present application is increased by more than 30% under the same concentration, and the fire rekindling rate is reduced to less than 5%. The targeted release of the three-layer structure can ensure that the fire extinguishing agent is released in the core area of the fire, reducing the loss of drug diffusion; the flame retardant of the outer shell layer acts before the capsule core, forming a flame retardant barrier around the fire source, enhancing the targeting of fire extinguishing. (11) The environmental protection index of the present application is excellent: the ozone depletion potential (ODP) of perfluorohexanone in the capsule core is 0, and the global warming potential (GWP) is low, meeting the environmental protection standard; the shell layer selects degradable materials (such as chitosan derivatives) and halogen-free flame retardants (such as ammonium polyphosphate system), avoiding the generation of toxic and harmful gases during the fire extinguishing process, and being suitable for human places and precision equipment environment. Strong scene adaptability: by adjusting the phase change temperature of the temperature-sensitive material (50-120°C adjustable) and the response wavelength of the light-sensitive material (200-1000nm optional), different fire scenes (such as electrical fire, forest fire, industrial fire) can be adapted, meeting the diversified prevention and control needs. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The scanning electron microscope graph of the double-shell fire extinguishing microcapsule prepared in Example 1. DETAILED DESCRIPTION

[0023] Example 1: A preparation method of a double-initiation composite double-shell fire extinguishing microcapsule, as shown in Table 1, comprising the following steps: Step 1: preparing fire extinguishing microspheres with core-shell structure; (1) Solution preparation: Preparation of the core emulsion: take perfluorohexanone 50 mL (purity ≥ 99%), add 0.1 g of potassium perfluorooctyl sulfonate, and stir magnetically for 10 minutes to form an oil phase; Preparation of the inner shell layer solution: weigh 8 g of PNIPAM-PCL copolymer, 4 g of a mixture of OMMT and TPP, and 0.5 g of SDBS, then add 100 mL of deionized water, stir in a water bath at 60°C for 2 hours until completely dissolved, cool to 30°C, then add glutaraldehyde 0.5 g, and stir for 15 minutes; (2) Emulsion polymerization: slowly drop the core emulsion into the inner shell layer solution (drop rate 2 mL / min), while starting mechanical stirring (speed 800 r / min), react at 30°C for 2 hours to obtain a microsphere solution with a core-shell structure (particle size 180-220 μm); (3) Preliminary solidification: heat to 50°C and keep for 1 hour to promote complete Schiff base reaction, centrifuge (2500 r / min, 10 minutes) to collect the particles, wash with deionized water 3 times to remove unreacted monomers, and store at 4°C for standby, to obtain intermediate product A.

[0024] Step 2: Preparation of double-shell fire extinguishing microcapsules; (1) Preparation of the outer shell layer solution: weigh 7 g of a mixture of 4-hydroxyazobenzene and SP-1, 5 g of a mixture of ATH and ZB, and 0.5 g of PEG-400, add 80 mL of ethanol, stir at room temperature for 1.5 hours until evenly dispersed, add 0.3 g of photoinitiator 1173, and stir in the dark for 30 minutes (aqueous phase); (2) Emulsion polymerization: re-disperse the intermediate product A in 50 mL of deionized water to form a suspension (dispersed phase), then slowly drop into the outer shell layer solution (drop rate 3 mL / min), mechanical stirring (speed 1000 r / min), react at 25°C for 1 hour; (3) Photocuring and post-treatment: transfer the reaction system to an ultraviolet lamp (365 nm, 8 W), irradiation intensity 8 mW / cm², cure for 30 minutes; centrifuge (3000 r / min, 10 minutes) to collect the microcapsules, wash with n-hexane 3 times to remove surface residues, and vacuum dry at 60°C for 2 hours to obtain the final product.

[0025] As shown in Table 2, the performance indicators of the prepared double-shell fire extinguishing microcapsules are: particle size 20-100 μm (coefficient of variation 25%), perfluorohexanone release rate 82%, false trigger rate 0%, open flame extinguishing time 12 seconds, and afterglow rate 5%.

[0026] As Figure 1The scanning electron microscope images of the microcapsule morphology of the fire extinguishing microcapsule are shown in (a) and the scanning electron microscope images of the cross section of the fire extinguishing microcapsule are shown in (b). Analysis shows that the prepared fire extinguishing microcapsule has regular overall morphology and complete structure, the inner temperature-sensitive layer and the outer light-sensitive layer are uniformly dispersed and closely combined, and completely meet the structural requirements of "light-heat dual triggering".

[0027] Example 2: A preparation method of a double-initiated composite double-shell fire extinguishing microcapsule, as shown in Table 1, includes the following steps: Step 1: preparing a fire extinguishing microsphere with a core-shell structure; (1) solution preparation: Preparation of core emulsion: take 45 mL of heptafluoropropane, add 0.15 g of Tween-80, and magnetically stir for 10 minutes to form an oil phase; Preparation of inner shell layer solution: weigh 7 g of PNIPAM-PCL copolymer (LCST 45℃), 3 g of a mixture of magnesium hydroxide and cresyl phosphate, and 0.4 g of SDBS, then add 90 mL of deionized water, stir in a 60℃ water bath for 2 hours until completely dissolved, cool to 30℃, then add 0.4 g of glutaraldehyde, and stir for 15 minutes; (2) emulsion polymerization: slowly drop the core emulsion into the inner shell layer solution (drop rate 2 mL / min), while starting mechanical stirring (speed 800 r / min), react at 30℃ for 2 hours to obtain a microsphere solution with a core-shell structure (particle size 180-220 μm); (3) preliminary solidification: heat to 50℃ and keep for 1 hour to promote the complete Schiff base reaction, centrifuge (2500 r / min, 10 minutes) to collect the particles, wash with deionized water 3 times to remove unreacted monomers, and store at 4℃ for standby, to obtain intermediate product A.

[0028] Step 2: preparing a double-shell fire extinguishing microcapsule; (1) preparation of outer shell layer solution: weigh 6 g of a mixture of diaryl ethylene derivative and o-nitrobenzyl derivative, 6 g of ammonium polyphosphate, and 0.6 g of PEG-400, add 75 mL of ethanol, stir at room temperature for 1.5 hours until evenly dispersed, add 0.25 g of benzoin ethyl ether, and stir in the dark for 30 minutes (aqueous phase); (2) emulsion polymerization: re-disperse the intermediate product A in 50 mL of deionized water to form a suspension (dispersed phase), then slowly drop the outer shell layer solution (drop rate 3 mL / min), and mechanically stir (speed 1000 r / min) at 25℃ for 1 hour; (3) Light curing and post-processing: transfer the reaction system to the UV lamp (365 nm, 8 W), the irradiation intensity is 8 mW / cm2, and curing for 30 minutes; centrifugal (3000 r / min, 10 minutes) to collect the microcapsules, wash with n-hexane for 3 times to remove the surface residues, and vacuum dry at 60℃ for 2 hours to obtain the final product.

[0029] As shown in Table 2, the performance indicators of the prepared double-shell fire extinguishing microcapsules are: particle size of 30-200 μm (coefficient of variation of 32%), and fire extinguishing success rate of 95%.

[0030] Example 3: A method for preparing double-initiated composite double-shell fire extinguishing microcapsules, as shown in Table 1, includes the following steps: Step 1: preparing fire extinguishing microspheres with core-shell structure; (1) Solution preparation: Preparation of core emulsion: take 40 g of ammonium dihydrogen phosphate powder, add 10 mL of deionized water and 0.2 g of Tween-20, and ultrasonic dispersion for 20 minutes to form an oil phase; Preparation of inner shell layer solution: weigh 7 g of hydroxypropyl chitosan, 5 g of zinc borate and melamine mixture, and 0.6 g of SDBS, then add 100 mL of deionized water, stir in a 60℃ water bath for 2 hours until completely dissolved, cool to 30℃, then add 0.6 g of epoxy chloropropane, and stir for 15 minutes; (2) Emulsion polymerization: slowly drop the core emulsion into the inner shell layer solution (drop rate 2 mL / min), and start mechanical stirring (speed 800 r / min) at the same time, react for 2 hours at 30℃ to obtain a microsphere solution with core-shell structure (particle size 180-220 μm); (3) Preliminary curing: heat to 50℃ and keep for 1 hour to promote the complete Schiff base reaction, centrifugal (2500 r / min, 10 minutes) to collect the particles, wash with deionized water for 3 times to remove unreacted monomers, and store at 4℃ for standby, to obtain intermediate product A.

[0031] Step 2: preparation of double-shell fire extinguishing microcapsules; (1) Preparation of outer shell layer solution: weigh 8 g of coumarin derivative, 4 g of mixture of aluminum hydroxide and decabromodiphenyl ether, 0.7 g of PEG-400, add 85 mL of ethyl acetate, stir at room temperature for 1.5 hours until evenly dispersed, add 0.35 g of photoinitiator, and stir in the dark (aqueous phase) for 30 minutes; (2) Emulsion polymerization: re-disperse the intermediate product A in 50 mL of deionized water to form a suspension (dispersed phase), then slowly drop the outer shell layer solution (drop rate 3 mL / min), and mechanically stir (speed 1000 r / min) at 25℃ for 1 hour; (3) Light curing and post-processing: transfer the reaction system to the UV lamp (365 nm, 8 W), the irradiation intensity is 8 mW / cm2, and curing is performed for 30 minutes; centrifugation (3000 r / min, 10 minutes) is performed to collect the microcapsules, the microcapsules are washed with n-hexane for 3 times to remove the surface residues, and vacuum drying is performed at 60°C for 2 hours to obtain the final product.

[0032] As shown in Table 2, the performance index of the prepared double-shell fire extinguishing microcapsules is: the particle size is 80-220 μm (coefficient of variation 12%), and the afterflame rate is 8%.

[0033] Comparative Example 1 A single temperature trigger microcapsule preparation method, comprising the following steps: (1) Solution preparation: Preparation of core emulsion: take perfluorohexanone 50 mL (purity ≥ 99%), add 0.1 g of potassium perfluorooctyl sulfonate, and magnetically stir for 10 minutes to form an oil phase; Preparation of inner shell layer solution: weigh 8 g of PNIPAM-PCL copolymer, 4 g of mixture of OMMT and TPP, and 0.5 g of SDBS, then add 100 mL of deionized water, and stir in a 60°C water bath for 2 hours until completely dissolved, then add glutaraldehyde 0.5 g after cooling to 30°C, and stir for 15 minutes; (2) Emulsion polymerization: slowly drop the core emulsion into the inner shell layer solution (drop rate 2 mL / min), and start mechanical stirring (speed 800 r / min) at the same time, and react for 2 hours at 30°C to obtain a microsphere solution with core-shell structure (particle size 180-220 μm); (3) Preliminary curing: heat to 50°C and keep for 1 hour to promote the complete reaction of Schiff base, centrifuge (2500 r / min, 10 minutes) to collect the particles, wash with deionized water for 3 times to remove unreacted monomers, and store at 4°C.

[0034] The performance index of the prepared microcapsules is: release rate 12%, false trigger rate 38%, and electrical cabinet fire success rate 40%.

[0035] Comparative Example 2 A single light trigger microcapsule preparation method, comprising the following steps: (1) Solution preparation: Preparation of core emulsion: take perfluorohexanone 50 mL (purity ≥ 99%), add 0.1 g of potassium perfluorooctyl sulfonate, and magnetically stir for 10 minutes to form an oil phase; Preparation of the outer shell layer solution: 7 g of a mixture of 4-hydroxyazobenzene and SP-1, 5 g of a mixture of ATH and ZB, 0.5 g of PEG-400, 80 mL of ethanol, stirring at room temperature for 1.5 hours until evenly dispersed, 0.3 g of a photoinitiator 1173, stirring in the dark for 30 minutes (aqueous phase); (2) Emulsion polymerization: slowly drop the core-shell emulsion into the outer shell layer solution (drop rate 3 mL / min), mechanical stirring (speed 1000 r / min), 25°C for 1 hour; (3) Photocuring and post-processing: transfer the reaction system to the UV lamp (365 nm, 8 W), irradiation intensity 8 mW / cm², curing for 30 minutes; centrifugation (3000 r / min, 10 minutes) to collect the microcapsules, washed with n-hexane 3 times to remove the surface residues, 60°C vacuum drying for 2 hours to obtain the final product.

[0036] The performance indicators of the prepared microcapsules are: release rate 18%, false trigger rate 35%, and forest smoldering fire success rate 50%.

[0037] Comparative Example 3: Preparation of a single-layer wall microcapsule based on traditional emulsion polymerization; mixed coating of temperature-sensitive and light-sensitive materials.

[0038] The performance indicators of the prepared microcapsules are: release rate 45%, false trigger rate 15%, and wall material rupture rate 20% (interlayer peeling).

[0039] Comparative Example 4: A preparation method of a double-initiated composite double-shell fire extinguishing microcapsule without flame retardant, comprising the following steps: Step 1: preparation of a core-shell structure fire extinguishing microsphere; (1) Solution preparation: Preparation of the core-shell emulsion: take perfluorohexanone 50 mL (purity ≥ 99%), add 0.1 g of potassium perfluorooctylsulfonate, magnetic stirring for 10 minutes to form an oil phase; Preparation of the inner shell layer solution: take 8 g of PNIPAM-PCL copolymer and 0.5 g of SDBS, then add 100 mL of deionized water, 60°C water bath stirring for 2 hours until completely dissolved, cool to 30°C, then add glutaraldehyde 0.5 g, stirring for 15 minutes; (2) Emulsion polymerization: slowly drop the core-shell emulsion into the inner shell layer solution (drop rate 2 mL / min), while starting mechanical stirring (speed 800 r / min), 30°C for 2 hours to obtain a core-shell structure microsphere solution (particle size 180-220 μm); (3) Preliminary solidification: heating to 50°C, keeping for 1 hour, promoting the Schiff base reaction to be complete, centrifugation (2500 r / min, 10 minutes) to collect the particles, washing with deionized water for 3 times to remove the unreacted monomers, and 4°C refrigeration for standby, to obtain intermediate product A.

[0040] Step 2: Preparation of double-shell fire extinguishing microcapsules (1) Preparation of outer shell layer solution: 7 g of a mixture of 4-hydroxy azobenzene and SP-1 and 0.5 g of PEG-400 were weighed, added into 80 mL of ethanol, and stirred at room temperature for 1.5 hours until uniformly dispersed, 0.3 g of photoinitiator 1173 was added, and stirred in the dark for 30 minutes (aqueous phase); (2) Emulsion polymerization: intermediate product A was redispersed in 50 mL of deionized water to form a suspension (dispersed phase), and then the outer shell layer solution was slowly added dropwise (drop rate 3 mL / min), mechanical stirring (rotation speed 1000 r / min), and reaction at 25°C for 1 hour; (3) Photocuring and post-treatment: the reaction system was transferred to an ultraviolet lamp (365 nm, 8 W), the irradiation intensity was 8 mW / cm², and curing was performed for 30 minutes; centrifugation (3000 r / min, 10 minutes) was performed to collect the microcapsules, the microcapsules were washed with n-hexane for 3 times to remove the surface residues, and vacuum drying was performed at 60°C for 2 hours, to obtain the final product.

[0041] As shown in Table 2, the performance index of the prepared double-shell fire extinguishing microcapsules is: the release rate is 83%, but the after-flaming rate is 35%, and the temperature drop time is 25 minutes.

[0042] Table 1: Reaction parameters of examples 1-3 Table 2: Performance parameters of examples and comparative examples The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Any simple modification or equivalent change made on the basis of the technical essence of the present application to the above embodiment falls within the protection scope of the present application.

Claims

1. A method for preparing a dual-initiator composite double-shell fire extinguishing microcapsule, characterized in that, Includes the following steps: Step S1: Prepare core-shell structured fire extinguishing microspheres; Step S11: Solution preparation; Preparation of the core emulsion: Mix fire extinguishing core material and surfactant in a mass ratio of 95.0wt%~99.5wt%:0.5wt%~1.0wt% and stir evenly; Preparation of the inner shell solution: Add the thermosensitive material, flame retardant, and dispersant to deionized water, heat and stir until homogeneous; adjust the temperature to 20℃~40℃, then add the crosslinking agent and stir until homogeneous; wherein, the mass ratio of the thermosensitive material, flame retardant, crosslinking agent, and dispersant is 65wt%~75wt%: 20wt%~30wt%: 1.0wt%~2.0wt%: 0.5wt%~1.0wt%; the LCST of the thermosensitive material is 55~65℃; Step S12: Emulsion polymerization: The core emulsion is slowly dripped into the inner shell solution while the mixture is stirred at a speed of 500 r / min to 1000 r / min to obtain a core-shell structured microsphere solution. Step S13: Preliminary solidification: Heat the solution to 50°C and keep it at that temperature for 0.5 to 2 hours. Then, centrifuge to collect the fire extinguishing microspheres, wash with deionized water to remove unreacted monomers, and refrigerate for later use to obtain intermediate product A. Step S2: Prepare double-shell fire extinguishing microcapsules; Step S21: Preparation of the outer shell solution: Add the photosensitive material, flame retardant, and crosslinking agent to the solvent and mix thoroughly. Then, add the photoinitiator and stir evenly in the dark. The mass ratio of the photosensitive material, flame retardant, photoinitiator, and crosslinking agent is 55wt%-65wt%: 30wt%-40wt%: 1.0wt%-2.0wt%: 0.5wt%-1.5wt%. Step S22: Emulsion polymerization: Disperse intermediate product A in deionized water to form a suspension; then, slowly drop the suspension into the outer shell solution while stirring the reaction at a speed of 800 r / min to 1200 r / min. Step S23: Photocuring and post-treatment: Transfer the solution from step S22 to a UV lamp and cure for 15-40 minutes; then, collect the microcapsules by centrifugation, wash with n-hexane to remove surface residue, and vacuum dry to obtain double-shell fire extinguishing microcapsules.

2. The method for preparing a dual-initiator composite double-shell fire extinguishing microcapsule according to claim 1, characterized in that, In step S12, the particle size of the core-shell structured microsphere solution is 20-800 μm; in step S23, the mass ratio of the core, inner shell and outer shell of the double-shell fire extinguishing microcapsule is 6~8:5~7:5~7.

3. The method for preparing a dual-initiator composite double-shell fire extinguishing microcapsule according to claim 1, characterized in that, In step S11, the fire extinguishing core material is any one or more of perfluorohexanone, heptafluoropropane, and ammonium dihydrogen phosphate; the surfactant is potassium perfluorooctyl sulfonate or Tween-80.

4. The method for preparing a dual-initiator composite double-shell fire extinguishing microcapsule according to claim 1, characterized in that, In step S11, the temperature-sensitive material is a copolymer of poly(N-isopropylacrylamide) and polycaprolactone or a chitosan derivative.

5. A method for preparing a dual-initiator composite double-shell fire extinguishing microcapsule according to claim 1 or 4, characterized in that, In step S11, the flame retardant is any one of organomontmorillonite and triphenyl phosphate, magnesium hydroxide and tricresyl phosphate, zinc borate and melamine; the mass ratio of organomontmorillonite to triphenyl phosphate is 1:1~4, the mass ratio of magnesium hydroxide to tricresyl phosphate is 1:2~5, and the mass ratio of zinc borate to melamine is 1:1~3.

6. The method for preparing a dual-initiator composite double-shell fire extinguishing microcapsule according to claim 5, characterized in that, The organomontmorillonite has a particle size of 100-200 nm and is obtained by modification with hexadecyltrimethylammonium bromide.

7. The method for preparing a dual-initiator composite double-shell fire extinguishing microcapsule according to claim 1, characterized in that, In step S21, the photosensitive material is any one of azobenzene derivative and spiropyran derivative, diarylene ethylene derivative and o-nitrobenzyl derivative, and coumarin derivative, and the mass ratio of azobenzene derivative to spiropyran derivative is 1~2:1~3, and the mass ratio of diarylene ethylene derivative to o-nitrobenzyl derivative is 1~3:

1.

8. A method for preparing a dual-initiator composite double-shell fire extinguishing microcapsule according to claim 1 or 7, characterized in that, In step S21, the flame retardant is any one of aluminum hydroxide and zinc borate, ammonium polyphosphate, aluminum hydroxide and decabromodiphenyl ether, and the mass ratio of aluminum hydroxide and zinc borate is 1~3:1; the mass ratio of aluminum hydroxide and decabromodiphenyl ether is 1~4:1.

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