Preparation method of multilayer core-shell structure microcapsule / epoxy resin flame-retardant composite material

Abstract

A method for preparing a multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material is disclosed. This invention aims to address the technical problem of improving the flame-retardant performance and smoke suppression effect of epoxy resin. The preparation method includes: 1. Ball milling and mixing potassium bicarbonate and magnesium hydroxide to obtain an inorganic nano-mixed powder; 2. Ultrasonically dispersing the inorganic nano-mixed powder, polyethylene glycol, and triethylenetetramine to obtain an aqueous phase, emulsifying and dispersing the aqueous phase in an oil phase, and adding TPC solution for interfacial polymerization to obtain polyamide-coated microcapsules; 3. Coating the polyamide-coated microcapsules with a phosphorus-containing flame-retardant wall material; 4. Constructing a silica wall material; 5. Preparing the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material. This invention significantly improves the flame-retardant performance of the composite material after introducing the microcapsules into epoxy resin, achieving a V-0 rating in vertical burning tests, a limiting oxygen index of up to 27%, and a significant reduction in heat release rate and total smoke production.

Description

Technical Field

[0001] This invention relates to a method for preparing multilayer coated microcapsules for epoxy resin. Background Technology

[0002] Epoxy resin, as one of the most important thermosetting resins, is widely used in coatings, adhesives, electrical and electronic equipment, construction and other fields due to its high mechanical properties, good electrical insulation, corrosion / heat resistance, transparency, ease of processing and low cost.

[0003] However, the thermal instability and flammability of epoxy resins make their use extremely risky. Combustion not only releases a large amount of heat but also produces large amounts of toxic fumes and gases, easily leading to serious injuries, fatalities, and economic losses. Therefore, improving the flame-retardant properties of epoxy resins is of great significance for fire safety, risk control, and their subsequent practical applications.

[0004] Changjiang Liu et al. employed a three-step strategy: a sol-gel method to prepare hierarchical SiO2 microcapsules supported on phosphorus-containing silanes, followed by a polydopamine-copper outer layer. This strategy successfully prepared flame-retardant microcapsules with a multilayered structure. When these microcapsules were introduced into epoxy resin, the physical barrier effect of silica, combined with the synergistic effects of phosphorus and copper in catalytic char formation and free radical quenching, significantly improved the flame-retardant properties and smoke suppression of the material.

[0005] Lijie Qu et al. successfully prepared flame-retardant microcapsules P(H) with a core-shell structure using emulsion polymerization (improved thermal properties of epoxyresin modified with polymethyl methacrylate microencapsulated phosphorus-nitrogen-containing flame retardant), with methyl methacrylate as the shell and hexaphenoxycyclotriphosphazene as the core material. After introducing these microcapsules into epoxy resin, the good compatibility between the PMMA shell and the matrix increased the crosslinking density, and the synergistic flame-retardant effect of the phosphorus-nitrogen core material releasing phosphorus-containing free radicals and non-flammable gases in the gas phase and promoting the formation of a dense char layer in the condensed phase resulted in an increased limiting oxygen index of 30.5% and a UL-94 rating of V-1. Cone calorimetry tests showed that, compared with pure EP, the peak heat release rate (PHRR) of the P(2.75H) / EP composite material increased from 1677.9 kW / m³. 2 Reduced to 1365.1 kW / m 2 The total heat release (THR) is 148.0 MJ / m³. 2 Reduced to 100.7 MJ / m 2 At the same time, the release rates of CO and CO2 are also significantly reduced. However, the vertical combustion rating of this prior art is only V-1, and there is still room for further reduction in its heat release rate and total heat release.

[0006] Luo et al. successfully prepared phase change microcapsules PW@PUA using interfacial polymerization (multifunctional epoxy composites integrated with paraffin@polyurea microcapsules for thermal management and flame retardancy), with paraffin as the core material and polyurea as the shell. They then incorporated PW@PUA with ammonium polyphosphate (APP) and expandable graphite (EG) into epoxy resin, and obtained a composite material with both phase change thermal storage and flame retardant functions through physical blending and room temperature curing. When the addition amounts of PW70@PUA, APP, and EG were 25 wt%, 20 wt%, and 10 wt%, respectively, the thermal conductivity of the composite material reached 1.06 W·m. -1 ·K -1 The latent heat of phase transition is 20.6 J·g -1 The vertical combustion test achieved a UL-94 V-0 rating; the cone calorimetry test showed that its peak heat release rate (PHRR) decreased to 509.8 kW / m³. 2The total heat release (THR) decreased to 138.1 MJ / m³. 2 Meanwhile, the char content significantly increased to 28.9 wt%, with APP and EG forming a dense, expanded char layer in the condensed phase through the synergistic effects of catalytic char formation, physical isolation, and structural reinforcement. However, there is still room for further reduction in the total heat release (THR) of this composite material. Summary of the Invention

[0007] The purpose of this invention is to solve the technical problem that the flame retardant performance and smoke suppression effect of epoxy resin need to be improved, and to provide a method for preparing a multilayer core-shell structured microcapsule / epoxy resin flame retardant composite material.

[0008] The preparation method of the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material of the present invention is carried out according to the following steps:

[0009] I. Core material nano-processing:

[0010] Inorganic core material potassium bicarbonate (KHCO3) and magnesium hydroxide (Mg(OH)2) were mixed, and anhydrous ethanol was added for ball milling to obtain inorganic nano-mixed powder;

[0011] II. Interfacial polymerization of the first layer of polyamide wall material:

[0012] a. The inorganic nano-mixed powder, polyethylene glycol and triethylenetetramine were ultrasonically dispersed in deionized water to obtain an aqueous phase;

[0013] b. Add triethylamine (TEA) to the oil phase solvent containing the surfactant to obtain the oil phase;

[0014] c. Dissolve terephthaloyl chloride (TPC) in carbon tetrachloride to prepare a TPC solution;

[0015] d. The aqueous phase is emulsified and dispersed in the oil phase to form a water-in-oil (W / O) emulsion. TPC solution is slowly added under stirring conditions to carry out interfacial polymerization reaction. After separation and drying, polyamide-coated microcapsules are obtained.

[0016] III. Construction of the second layer of phosphorus-containing flame-retardant wall material:

[0017] Polyamide-coated microcapsules were dispersed in an alcohol-water mixture, the pH of the system was adjusted to acidic, a silane coupling agent was added for surface modification, the pH of the system was then adjusted to alkaline, melamine, DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), and formaldehyde were added, and a polycondensation reaction was carried out under heating conditions to obtain bilayer-coated microcapsules.

[0018] IV. Construction of the third layer of silica wall material:

[0019] The double-layer coated microcapsules were dispersed in an alcohol solution, and an alkaline catalyst and a tetraethyl orthosilicate (TEOS) ethanol solution were added. The silica layer was generated on the surface of the microcapsules by hydrolysis and condensation through the sol-gel method. After separation and drying, the multi-layer coated microcapsules were obtained.

[0020] 5. Heat the epoxy resin, then add the multi-layered coated microcapsules, curing agent, coupling agent and defoamer, stir and mix evenly, and then cure to obtain a multi-layered core-shell structure microcapsule / epoxy resin flame retardant composite material.

[0021] The beneficial effects of the preparation method of the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material of the present invention are as follows:

[0022] This invention employs a multi-layer encapsulation design. The first layer, polyamide, imparts basic mechanical properties and density to the microcapsules. The second layer, a phosphorus-containing flame-retardant wall material (utilizing the synergistic effect of DOPO and melamine-formaldehyde resin), significantly improves the material's flame-retardant performance. The third layer, silica, serves as the outermost layer, utilizing its high hardness and thermal stability to further enhance the microcapsules' heat resistance and dispersibility in the substrate. Introducing these microcapsules into epoxy resin significantly improves the composite material's flame-retardant performance, achieving a V-0 rating in vertical burning tests (UL-94), a limiting oxygen index (LOI) of 27%, and a marked reduction in heat release rate and total smoke production, demonstrating excellent flame-retardant and smoke-suppressing properties. Attached Figure Description

[0023] Figure 1 This is a diagram showing the vertical burning test (UL-94) of each epoxy resin sample in the embodiments;

[0024] Figure 2 This is a graph showing the limiting oxygen index test results for each epoxy resin sample in the examples;

[0025] Figure 3 The diagram shows the cone calorimetry results of each epoxy resin sample in the examples. Detailed Implementation

[0026] Specific Implementation Method 1: The preparation method of the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material in this implementation method is carried out according to the following steps:

[0027] I. Core material nano-processing:

[0028] Inorganic core material potassium bicarbonate (KHCO3) and magnesium hydroxide (Mg(OH)2) were mixed, and anhydrous ethanol was added for ball milling to obtain inorganic nano-mixed powder;

[0029] II. Interfacial polymerization of the first layer of polyamide wall material:

[0030] a. The inorganic nano-mixed powder, polyethylene glycol and triethylenetetramine were ultrasonically dispersed in deionized water to obtain an aqueous phase;

[0031] b. Add triethylamine (TEA) to the oil phase solvent containing the surfactant to obtain the oil phase;

[0032] c. Dissolve terephthaloyl chloride (TPC) in carbon tetrachloride to prepare a TPC solution;

[0033] d. The aqueous phase is emulsified and dispersed in the oil phase to form a water-in-oil (W / O) emulsion. TPC solution is slowly added under stirring conditions to carry out interfacial polymerization reaction. After separation and drying, polyamide-coated microcapsules are obtained.

[0034] III. Construction of the second layer of phosphorus-containing flame-retardant wall material:

[0035] Polyamide-coated microcapsules were dispersed in an alcohol-water mixture, the pH of the system was adjusted to acidic, a silane coupling agent was added for surface modification, the pH of the system was then adjusted to alkaline, melamine, DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), and formaldehyde were added, and a polycondensation reaction was carried out under heating conditions to obtain bilayer-coated microcapsules.

[0036] IV. Construction of the third layer of silica wall material:

[0037] The double-layer coated microcapsules were dispersed in an alcohol solution, and an alkaline catalyst and a tetraethyl orthosilicate (TEOS) ethanol solution were added. The silica layer was generated on the surface of the microcapsules by hydrolysis and condensation through the sol-gel method. After separation and drying, the multi-layer coated microcapsules were obtained.

[0038] 5. Heat the epoxy resin, then add the multi-layered coated microcapsules, curing agent, coupling agent and defoamer, stir and mix evenly, and then cure to obtain a multi-layered core-shell structure microcapsule / epoxy resin flame retardant composite material.

[0039] In this embodiment, in step two, the aqueous phase mixture is emulsified and dispersed in the oil phase mixture to form a water-in-oil (W / O) emulsion. At this time, TPC dissolved in the oil phase and TETA dispersed in the aqueous phase come into contact at the oil-water interface of the emulsion droplets and rapidly undergo a polymerization reaction to generate a polyamide wall material, which coats the surface of the inorganic core material to obtain a single-layer coated microcapsule. In step three, a phosphorus-containing melamine-formaldehyde resin wall material is generated through a condensation reaction to achieve a second layer of coating on the core material. In step four, a silica layer is generated on the surface of the microcapsule through hydrolysis and condensation using a sol-gel method, and after post-processing, a multi-layer coated microcapsule powder is obtained.

[0040] In step five of this embodiment, the curing agent is an amine curing agent; the coupling agent is a silane coupling agent; the stirring is vacuum high-speed stirring; and the curing treatment adopts a gradient temperature rise process, with a curing temperature of 80-150℃ and a curing time of 6-10 hours.

[0041] This embodiment achieves a vertical flammability rating of V-0 for epoxy resin composite materials through an optimized microcapsule structure. Meanwhile, cone calorimetry tests show that its PHRR and THR values ​​are lower, further enhancing its flame retardant performance and smoke suppression effect.

[0042] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the molar ratio of potassium bicarbonate to magnesium hydroxide in step one is 2:3.

[0043] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the ball milling process in step 1 uses a planetary ball mill, controls the ball-to-material ratio to be (8-12):1, the rotation speed to be 200-400 rpm, and the grinding time to be 6-10 hours.

[0044] Specific Implementation Method Four: This implementation method differs from one of Specific Implementation Methods One to Three in that the surfactant mentioned in step two is Span80 or Span85.

[0045] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that the temperature of the interfacial polymerization reaction in step d of step 2 is 0-10℃, and the interfacial polymerization reaction time is 1-1.5 hours.

[0046] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the mass ratio of polyamide-coated microcapsules, melamine, DOPO and formaldehyde in step three is (5-10):(1.5-2):(0.5-1):(3-4).

[0047] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that in step three, the pH of the system is adjusted to acidic conditions, with the acidic condition having a pH of 4.5-5.5; and the pH of the system is adjusted to alkaline conditions, with the alkaline condition having a pH of 8.0-9.0.

[0048] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the temperature of the polycondensation reaction in step three is 60-90℃, and the reaction time is 3-5 hours.

[0049] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the reaction temperature of the sol-gel method in step four is controlled at 20-40℃, and the time is 6-24 hours.

[0050] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that the temperature for heating the epoxy resin in step 5 is 30-50℃.

[0051] In step five of this embodiment, the curing process uses a gradient temperature increase, namely curing at 80℃ for 1-3 hours, curing at 120℃ for 1-3 hours, and curing at 150℃ for 2-4 hours.

[0052] Example 1: The preparation method of the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material in this example is carried out according to the following steps:

[0053] I. Core material nano-processing:

[0054] Inorganic core material potassium bicarbonate (KHCO3) and magnesium hydroxide (Mg(OH)2) were mixed at a molar ratio of 2:3, and anhydrous ethanol was added for ball milling. During the ball milling process, the ball-to-material ratio was controlled at 10:1, the rotation speed was 300 rpm, and the grinding was carried out for 8 hours. Then, the mixture was dried at 50°C to obtain inorganic nano-mixed powder.

[0055] II. Interfacial polymerization of the first layer of polyamide wall material:

[0056] a. 10g of inorganic nano-mixed powder, 1.2g of polyethylene glycol (PEG-2000) and 1g of triethylenetetramine were ultrasonically dispersed in deionized water to obtain an aqueous phase;

[0057] b. Add 1.2g of triethylamine (TEA) to a hexane solvent containing 1.8g of Span80 surfactant to obtain the oil phase;

[0058] c. Dissolve 1.2g of terephthaloyl chloride (TPC) in carbon tetrachloride to prepare a TPC solution;

[0059] d. Place the oil phase in a high-speed homogenizer and use high shear at 6000 rpm, while slowly adding the aqueous phase dropwise to form a water-in-oil (W / O) emulsion. Cool to 2°C, and slowly add TPC solution while stirring at 500 rpm to carry out interfacial polymerization.

[0060] After reacting for 1 hour, the microcapsules were obtained by separation and drying at 40°C;

[0061] III. Construction of the second layer of phosphorus-containing flame-retardant wall material:

[0062] 8g of polyamide-coated microcapsules were dispersed in an alcohol-water mixture (ethanol / water volume ratio 9:1). The pH of the system was adjusted to 4.8 with acetic acid. Silane coupling agent KH-560 was added for surface modification. Then, the pH of the system was adjusted to 8.5 with NaOH. 1.74g of melamine and 0.53g of DOPO were added. The mixture was stirred at 70℃ for 30min. 3.35g of formaldehyde was added. NaOH was added again to adjust the pH of the system to 8.8. The mixture was heated to 70℃ and reacted for 2.5h. Then, the mixture was heated to 80℃ and reacted for 1h. The mixture was dried at 60℃ to obtain double-layer coated microcapsules.

[0063] IV. Construction of the third layer of silica wall material:

[0064] 10g of double-layer coated microcapsules were dispersed in anhydrous ethanol and stirred for 30 minutes to obtain solution A.

[0065] Solution B is obtained by mixing water, anhydrous ethanol, and concentrated ammonia (25% concentration) in a volume ratio of 10:10:1.

[0066] Add 3.3 ml of tetraethyl silicate (TEOS) dropwise into anhydrous ethanol and stir at 500 rpm for 1 h to obtain solution C.

[0067] Under stirring, solutions B and C were slowly added dropwise to solution A simultaneously. After the addition was complete, the temperature was raised to 30°C and the reaction was stirred for 12 hours. After separation and drying at 60°C, multilayer coated microcapsules were obtained.

[0068] 5. Heat epoxy resin (E-44) in a water bath at 40℃, then add 7.11g of multilayer coated microcapsules, 5.6g of DDM, 0.2g of PH-550 and 0.5% of defoamer. After stirring and mixing evenly, perform a gradient curing treatment: cure at 80℃ for 2h, at 120℃ for 2h, and at 150℃ for 3h to obtain a multilayer core-shell structure microcapsule / epoxy resin flame retardant composite material.

[0069] Figure 1 For the vertical burning test (UL-94), a) epoxy resin without microcapsules did not extinguish after the first ignition within 10 seconds; b) epoxy resin with 20% multilayer coated microcapsules (i.e., the amount of multilayer coated microcapsules added is 20wt% of the epoxy resin) extinguished after the first ignition within 10 seconds; c) epoxy resin with 20% multilayer coated microcapsules extinguished again after being ignited a second time within 10 seconds.

[0070] Figure 2The limiting oxygen index (LOI) is as follows: the LOI of epoxy resin without microcapsules is 18.4%, the LOI of epoxy resin with 10% multilayer coated microcapsules (flame retardant composite material) is 24%, the LOI of epoxy resin with 15% multilayer coated microcapsules is 25.2%, and the LOI of epoxy resin with 20% multilayer coated microcapsules is 27%.

[0071] Figure 3 The results were obtained using cone calorimetry, where a) represents the heat release rate (HRR), showing that epoxy resin with 20% microcapsules had a delayed ignition, a slower HRR increase, and a significantly lower peak heat release rate (PHRR) compared to epoxy resin without microcapsules; b) represents the total heat release rate (THR), showing that epoxy resin with 20% microcapsules had a PHRR reduced by more than half compared to epoxy resin without microcapsules, and a significantly delayed peak time; c) represents the smoke generation rate (SPR), showing that epoxy resin with 20% microcapsules had a peak smoke generation rate reduced by 52.5% compared to epoxy resin without microcapsules, significantly reducing the explosive release of smoke during a fire; and d) represents the total smoke production (TSP), showing that epoxy resin with 20% microcapsules had a total smoke production reduced by 14.6% compared to epoxy resin without microcapsules, demonstrating a clear smoke suppression effect.

[0072] Example 2: This example differs from Example 1 in that the temperature is raised to 85°C in step 3, and the reaction time is 3 hours.

[0073] Example 3: This example differs from Example 1 in that isopropanol is added in step 1 for ball milling.

[0074] The difference is that in step three, 8g of polyamide-coated microcapsules are dispersed in an alcohol-water mixture (ethanol / water volume ratio 9:1). The pH of the system is adjusted to 5.2 with acetic acid, and surface modification is performed by adding silane coupling agent KH-560. Then, the pH of the system is adjusted to 8.5 with NaOH, and 1.74g of melamine and 0.53g of DOPO are added. The mixture is stirred at 70℃ for 30min, and 3.35g of formaldehyde is added. NaOH is added again to adjust the pH of the system to 8.8. The temperature is raised to 70℃ and reacted for 2.5h, then raised to 80℃ and reacted for 1h. The mixture is dried at 60℃ to obtain double-layer coated microcapsules.

[0075] Testing showed that the flame retardant properties of the multilayered microcapsules obtained in this embodiment were basically equivalent to those in Example 1, indicating that using isopropanol as the grinding medium and fine-tuning the initial pH value of the second coating layer did not affect the formation of the multilayered coating structure or the product performance.

[0076] Example 4: This example differs from Example 1 in that in step 3, 8g of polyamide-coated microcapsules are dispersed in an alcohol-water mixture (ethanol / water volume ratio 9:1). The pH of the system is adjusted to 4.8 with acetic acid, and silane coupling agent KH-560 is added for surface modification. Then, the pH of the system is adjusted to 8.5 with NaOH, and 1.74g of melamine and 0.53g of DOPO are added. The mixture is stirred at 70°C for 30 minutes, and 3.35g of formaldehyde is added. NaOH is added again to adjust the pH of the system to 8.8, and the temperature is raised to 78°C for 3.5 hours. The mixture is then dried at 60°C to obtain double-layer coated microcapsules.

[0077] Testing showed that the flame retardant properties of the multilayer-coated microcapsules obtained in this embodiment were basically equivalent to those in Example 1, proving that the one-step isothermal polycondensation method can also achieve effective coating of the second layer.

[0078] Example 5: This example differs from Example 1 in that in step four, solutions B and C are simultaneously and slowly added dropwise to solution A while stirring. After the addition is complete, the temperature is raised to 25°C and the reaction is continued with stirring for 24 hours. After separation and drying at 60°C, multilayer-coated microcapsules are obtained.

[0079] Testing showed that the flame-retardant properties of the multilayered microcapsules obtained in this embodiment were comparable to those in Example 1. This demonstrates that by extending the reaction time at room temperature, complete silica encapsulation can also be achieved via the sol-gel method.

[0080] Example 6: This example differs from Example 1 in that:

[0081] b. Add 1.2g of triethylamine (TEA) to a cyclohexane solvent containing 1.8g of Span85 surfactant to obtain the oil phase;

[0082] c. Dissolve 1.2g of terephthaloyl chloride (TPC) in dichloromethane to prepare a TPC solution.

[0083] Experiments show that stable W / O emulsions can also be successfully prepared and interfacial polymerization can be carried out using the cyclohexane / Span85 / dichloromethane system. The flame retardant properties of the multilayered microcapsules prepared in this example are basically equivalent to those in Example 1, indicating that this interfacial polymerization system has good solvent and surfactant compatibility.

Claims

1. A method for preparing a multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material, characterized in that... The preparation method of the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material is carried out according to the following steps: I. Core material nano-processing: Inorganic core material potassium bicarbonate was mixed with magnesium hydroxide, and then ball-milled with anhydrous ethanol to obtain inorganic nano-mixed powder. II. Interfacial polymerization of the first layer of polyamide wall material: a. The inorganic nano-mixed powder, polyethylene glycol and triethylenetetramine were ultrasonically dispersed in deionized water to obtain an aqueous phase; b. Triethylamine is added to the oil phase solvent containing the surfactant to obtain the oil phase; c. Dissolve terephthaloyl chloride in carbon tetrachloride to prepare a TPC solution; d. The aqueous phase is emulsified and dispersed in the oil phase to form a water-in-oil emulsion. TPC solution is added under stirring to carry out interfacial polymerization reaction. After separation and drying, polyamide-coated microcapsules are obtained. III. Construction of the second layer of phosphorus-containing flame-retardant wall material: The polyamide-coated microcapsules were dispersed in an alcohol-water mixture, the pH of the system was adjusted to acidic, a silane coupling agent was added for surface modification, the pH of the system was then adjusted to alkaline, melamine, DOPO and formaldehyde were added, and a polycondensation reaction was carried out under heating conditions to obtain double-layer coated microcapsules. IV. Construction of the third layer of silica wall material: The double-layer coated microcapsules were dispersed in an alcohol solution, and an alkaline catalyst and a tetraethyl silicate ethanol solution were added. The silica layer was generated by hydrolysis and condensation on the surface of the microcapsules through the sol-gel method. After separation and drying, the multi-layer coated microcapsules were obtained.

5. Heat the epoxy resin, then add the multi-layered coated microcapsules, curing agent, coupling agent and defoamer, stir and mix evenly, and then cure to obtain a multi-layered core-shell structure microcapsule / epoxy resin flame retardant composite material.

2. The method for preparing the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material according to claim 1, characterized in that... In step one, the molar ratio of potassium bicarbonate to magnesium hydroxide is 2:

3.

3. The method for preparing the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material according to claim 1, characterized in that... In step one, a planetary ball mill is used for ball milling, with the ball-to-material ratio controlled at (8-12):1, the rotation speed at 200-400 rpm, and the grinding time at 6-10 hours.

4. The method for preparing the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material according to claim 1, characterized in that... The surfactant mentioned in step two is Span80 or Span85.

5. The method for preparing the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material according to claim 1, characterized in that... In step two, the temperature of the interfacial polymerization reaction in step d is 0-10℃, and the reaction time is 1-1.5 hours.

6. The method for preparing the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material according to claim 1, characterized in that... In step three, the mass ratio of polyamide-coated microcapsules, melamine, DOPO and formaldehyde is (5-10):(1.5-2):(0.5-1):(3-4).

7. The method for preparing the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material according to claim 1, characterized in that... In step three, the pH of the system is adjusted to acidic, with the acidic condition having a pH of 4.5-5.5; the pH of the system is then adjusted to alkaline, with the alkaline condition having a pH of 8.0-9.

0.

8. The method for preparing the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material according to claim 1, characterized in that... In step three, the polycondensation reaction is carried out at a temperature of 60-90℃ for 3-5 hours.

9. The method for preparing the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material according to claim 1, characterized in that... In step four, the reaction temperature of the sol-gel method is controlled at 20-40℃, and the reaction time is 6-24 hours.

10. The method for preparing the multilayer core-shell structured microcapsule / epoxy resin flame-retardant composite material according to claim 1, characterized in that... In step five, the temperature for heating the epoxy resin is 30-50℃.

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