Microcapsule for self-repairing geopolymer material, and preparation method and application thereof

Abstract

The invention relates to the technical field of material science, in particular to a microcapsule for geopolymer material self-repairing and a preparation method and application thereof.The microcapsule comprises urea-formaldehyde resin serving as a wall material and epoxy resin serving as a core material, at the temperature of 300-800 DEG C, a urea-formaldehyde resin shell is melted, the internal epoxy resin core material is released and diffused, and the wall material is self-repaired. The epoxy resin is in contact with a curing agent mixed in a matrix to form a cured epoxy material, so that geopolymer microcracks generated at high temperature are filled and bonded, and the self-repairing process is completed; the average particle size of the microcapsule is 1-3 microns. The urea-formaldehyde resin is selected as a wall material due to high hardness, wear resistance, corrosion resistance, incombustibility and physical property stability of the urea-formaldehyde resin. Epoxy resin is selected as a core material due to excellent adhesiveness, durability and fatigue resistance. The stability and effectiveness of the microcapsule in a high-temperature environment are ensured, and the microcapsule can effectively react with a curing agent in a matrix to form an epoxy cured material, so that the self-repairing process is completed.

Description

Technical Field

[0001] The present invention relates to the technical field of materials science, and particularly relates to a microcapsule for self - repair of geopolymer materials, a preparation method thereof, and an application thereof. Background Art

[0002] As a new type of inorganic non - metallic material, geopolymers have attracted much attention in recent years due to their low - carbon and environmental - friendly characteristics (mainly using industrial solid wastes as raw materials), excellent mechanical properties (compressive strength can reach 50 - 100 MPa), chemical corrosion resistance (acid and alkali resistance is better than traditional cement - based materials), and high - temperature stability (refractory temperature can reach above 1200 °C). However, the cracking problem under high - temperature conditions is still the core challenge restricting its engineering applications. Research shows that geopolymers are prone to generating microcracks (average width 0.1 - 5 μm) during the hardening process due to insufficient polymerization reaction or water evaporation, and at temperatures above 200 °C, the thermal decomposition of the silicon - aluminum - based network inside the matrix leads to accelerated crack propagation, and the strength loss of the material can reach 30% - 50%. To solve this problem, researchers have proposed various methods: by incorporating MgO to react with water to generate the Mg(OH)2 expansion phase, it can effectively compensate for the high - temperature shrinkage of geopolymers and reduce crack generation (the shrinkage rate is reduced by 40% - 60%); introducing LDHs (such as Mg - Al layered double - metal hydroxides), using their interlayer ion - exchange characteristics to adsorb free Ca 2+ , inhibiting the stress concentration at the crack tip (the crack resistance is improved by more than 25%); adding nano - SiO2 or Al2O3 (dosage 1% - 3%) to make the microstructure of geopolymers denser by filling pores and promoting the polymerization reaction, significantly improving the high - temperature residual strength (for example, the strength retention rate at 1200 °C is increased from 20% to 31%). Summary of the Invention

[0003] One object of the present invention is to provide a microcapsule for self - repair of geopolymer materials. When microcracks are generated in the material at high temperature, the wall material of the microcapsule melts to release the core material epoxy resin, which reacts with the matrix curing agent to form a repair body, realizing effective filling of cracks and strength recovery.

[0004] Another object of the present invention is to provide a preparation method for the microcapsule for self - repair of geopolymer materials, and the preparation method is simple and easy to adjust.

[0005] The third object of the present invention is to provide a method for self - repair of geopolymer materials.

[0006] One of the solutions adopted by the present invention to achieve its purpose is: a microcapsule for the self - repair of geopolymer materials, the microcapsule comprising urea - formaldehyde resin as the wall material and epoxy resin as the core material. At 300 - 800 °C, the urea - formaldehyde resin shell melts, and the internal epoxy resin core material is released and diffuses, contacts with the curing agent mixed in the matrix, forms an epoxy cured product, thereby filling the micro - cracks of the geopolymer generated by high temperature and bonding, and completing the self - repair process.

[0007] Preferably, the average particle size of the microcapsule is 1 - 3 μm.

[0008] Preferably, the curing agent is diethylenetriamine.

[0009] Another solution adopted by the present invention to achieve its purpose is: a preparation method of the microcapsule for the self - repair of geopolymer materials as described above, comprising the following steps: (1) Preparation of prepolymer: Prepare a urea - formaldehyde resin prepolymer solution; (2) Emulsification stage: Mix the emulsifier and water and stir to obtain an emulsifier solution, add epoxy resin to the emulsifier solution, and mix evenly at a certain temperature to obtain a mixed emulsion; (3) Addition reaction stage: Mix the urea - formaldehyde resin prepolymer solution prepared in step (1) with the mixed emulsion prepared in step (2), adjust the pH, add a system modifier, and stir and react at a certain temperature until complete; (4) Extraction stage: After the reaction, adjust the pH to neutral, wash and filter the product to obtain the microcapsule finished product, and obtain the urea - formaldehyde resin - epoxy resin microcapsule after drying; In step (2), the emulsifier is composed of a compound of Span 80 (SP) and polyvinyl alcohol (PVA) or Tween 80 (TW).

[0010] Preferably, the specific steps of step (1) are to mix and dissolve urea, formaldehyde solution, and water according to a mass ratio of 6 - 8:15 - 20:75 - 100, adjust the pH to 8 - 9, and stir at 70 - 80 °C until the reaction is complete to obtain a urea - formaldehyde resin prepolymer solution.

[0011] The formaldehyde solution is a commercially available formaldehyde solution, and its mass concentration is generally 36% - 40%.

[0012] Preferably, in step (2), the concentration of the emulsifier solution is 0.5 wt% - 1.5 wt%, the mass ratio of epoxy resin to the emulsifier is 200:12 - 15, and the mixing temperature is 50 - 60 °C.

[0013] Preferably, in step (2), the HLB value (hydrophilic - lipophilic balance) of the compound emulsifier is 9 - 12.

[0014] The emulsifier selected is Span 80, which is respectively compounded with two non-ionic emulsifiers, Tween 80 or polyvinyl alcohol, to a HLB value (hydrophilic-lipophilic balance) of 9 - 12. The prepared microcapsules have a complete morphology and basically no phenomenon of broken walls, avoiding the premature breakage of the microcapsules before the self-repair temperature is reached, which may cause the outflow of the core material inside and result in waste or affect the repair effect.

[0015] Preferably, in step (3), the urea-formaldehyde resin prepolymer solution and the mixed emulsion are mixed in an amount such that the mass ratio of urea to epoxy resin is 1:1.8 - 2.2, the pH is adjusted to 2 - 3, and the reaction temperature is 70 - 80 °C.

[0016] Preferably, in step (3), the system modifier is made of sodium chloride and resorcinol in a mass ratio of 1:0.5 - 2.

[0017] The system modifier of the present invention is mainly composed of sodium chloride and resorcinol, and is used to maintain the stability of the core material during the addition reaction, which is not likely to cause damage to the core material, thereby obtaining microcapsules with uniform particle size and not prone to agglomeration. And due to the addition of the system modifier during the addition reaction, the agglomeration of the core material is effectively reduced, thereby reducing the particle size and obtaining microcapsule products with a particle size of 1 - 3 μm.

[0018] Preferably, in step (4), the drying temperature does not exceed 60 °C.

[0019] The solution adopted by the present invention to achieve the third object is: a method for self-repair of geopolymer materials at high temperature, including the following steps: dispersing the microcapsules in the geopolymer matrix and calcining at a temperature of 300 - 800 °C until the repair is completed.

[0020] Generally, the calcination time is 1 - 3 hours to complete the repair.

[0021] Through the innovative design of the urea-formaldehyde resin - epoxy resin microcapsule system, combined with the optimization of emulsifier compounding according to the required HLB value of epoxy resin and the high-temperature triggered release mechanism, the present application has breakthroughly achieved the stability and high encapsulation rate of microcapsules at high temperature, providing a new idea for solving the problem of deterioration of the high-temperature performance of geopolymers.

[0022] The present invention has the following advantages and beneficial effects: The microcapsules of the present invention use urea-formaldehyde resin as the wall material and epoxy resin as the core material. Urea-formaldehyde resin is selected as the wall material due to its high hardness, wear resistance, corrosion resistance, non-flammability and physical property stability. Epoxy resin is selected as the core material due to its excellent adhesion, durability and outstanding fatigue resistance. This ensures the stability and effectiveness of the microcapsules in a high-temperature environment, and can also effectively react with the curing agent in the matrix to form an epoxy cured product, thereby completing the self-repair process.

[0023] In practical applications, when the microcapsules of the present invention are introduced into the geopolymer matrix, their unique structural design enables them to rapidly respond and trigger the self-healing mechanism under high-temperature environments. Specifically, under the action of high temperature, the urea-formaldehyde resin shell melts, and the internal epoxy resin core material is released and diffuses to the microcracks. After contacting with the curing agent mixed in the matrix, an epoxy cured product is formed, thereby filling the microcracks and achieving bonding. This not only improves the mechanical properties of the material but also extends the service life of the material, enhancing its safety and reliability.

[0024] The preparation method of the present invention improves the stability of the synthesized microcapsules, preparing microcapsule particles with uniform particle size, not easily broken, and good stability, and will realize the self-healing of microcracks under high-temperature conditions for the first time.

[0025] The microcapsules prepared by the preparation method of the present invention have good dispersibility, less agglomeration phenomenon, less microcapsule wall breaking, complete morphology, and high preparation success rate; the urea-formaldehyde resin wall material has good compatibility with the geopolymer matrix; the curing agent is separated from the core material and is not easily mixed with the core material at room temperature to cause microcapsule failure; the repair effect is good, and the strength loss of the geopolymer material is small under high temperature.

[0026] The microcapsules of the present invention provide an effective solution for the high-temperature self-healing of geopolymers through unique material combinations and preparation processes. This not only opens up new possibilities for the application of geopolymer materials but also provides a reference for other types of thermosetting resin-based composite materials. Description of the Drawings

[0027] Figure 1 TEM electron micrograph of the microcapsules prepared using a 0.5% Span80 + Tween80 compound emulsifier in Example 1; Figure 2 Thermogravimetric analysis diagram of the microcapsules prepared using a 0.5% Span80 + Tween80 compound emulsifier in Example 1; Figure 3 Dispersion diagram of the microcapsules prepared in Example 1 in the geopolymer matrix; Figure 4 TEM electron micrograph of the microcapsules prepared using a 1.0% SP + TW compound emulsifier in Example 2; Figure 5 TEM electron micrograph of the microcapsules prepared using a 1.5% SP + TW compound emulsifier in Example 3; Figure 6 TEM electron micrograph of the microcapsules prepared using a 0.5% SP + polyvinyl alcohol compound emulsifier in Example 4; Figure 7 TEM electron micrograph of the microcapsules prepared using a 1.0% SP + polyvinyl alcohol compound emulsifier in Example 5; Figure 8 TEM electron micrograph of the microcapsules prepared with 1.5% SP + polyvinyl alcohol compound emulsifier for Example 6; Figure 9 TEM electron micrograph of the microcapsules prepared in Comparative Example 1, where a is the TEM electron micrograph of the microcapsules prepared with 0.5% SDBS, b is the TEM electron micrograph of the microcapsules prepared with 1.0% SDBS, and c is the TEM electron micrograph of the microcapsules prepared with 1.5% SDBS, Figure 10 TEM electron micrograph of the microcapsules prepared in Comparative Example 2, where a is the TEM electron micrograph of the microcapsules prepared with 0.5% polyvinyl alcohol, b is the TEM electron micrograph of the microcapsules prepared with 1.0% polyvinyl alcohol, and c is the TEM electron micrograph of the microcapsules prepared with 1.5% polyvinyl alcohol; Figure 11 TEM electron micrograph of the microcapsules prepared in Comparative Example 3, where a is the TEM electron micrograph of the microcapsules prepared with 0.5% SP, b is the TEM electron micrograph of the microcapsules prepared with 1.0% SP, and c is the TEM electron micrograph of the microcapsules prepared with 1.5% SP; Figure 12 TEM electron micrograph of the microcapsules prepared in Comparative Example 4, where a is the TEM electron micrograph of the microcapsules prepared with 0.5% TW, b is the TEM electron micrograph of the microcapsules prepared with 1.0% TW, and c is the TEM electron micrograph of the microcapsules prepared with 1.5% TW. Detailed implementation manners

[0028] For a better understanding of the present invention, the following examples are further descriptions of the present invention, but the content of the present invention is not limited to the following examples only.

[0029] Example 1 Microcapsule preparation (emulsifier concentration is 0.5 wt%, emulsifier compounding is SP + TW): Mix 16.6 g of 37% formaldehyde solution and 6.12 g of urea in a three-necked flask, add 100 g of deionized water and stir until completely dissolved, adjust the pH to 8 - 9 with triethanolamine, heat to 70 °C and stir at 600 rpm for 60 min to obtain a urea-formaldehyde resin prepolymer solution.

[0030] Take 0.5 g of Tween 80 and 0.5 g of Span 80, add them to 199 g of deionized water and stir evenly to obtain a 0.5% compound emulsifier solution. Take 12 g of epoxy resin E51 and add it to the compound emulsifier solution, heat the mixed emulsion to 50 °C, and stir at 600 rpm for 40 min.

[0031] The mixed emulsion was added to the prepolymer solution, and the pH of the solution was adjusted to 2 - 3 with 10% dilute hydrochloric acid. 0.5 g of sodium chloride and 0.5 g of resorcinol were added to the flask, and it was placed in a constant temperature water bath at 70 °C and stirred at a speed of 600 rpm for 3 h.

[0032] The pH was adjusted to 7 with triethanolamine, and it was rinsed with deionized water multiple times. After suction filtration, the finished microcapsules were obtained, with a particle size of about 1 μm. They were placed in a drying oven at 40 °C and dried for 24 h to obtain urea - formaldehyde resin - epoxy resin microcapsules.

[0033] Figure 1 The TEM image of the microcapsules prepared in this example is shown. It can be seen from the figure that the microcapsules prepared in this example have very few impurities, and there are basically no cases of rupture and agglomeration. The synthesized microcapsules are pure, with uniform particle size, not easily broken, good dispersibility, and less agglomeration phenomenon.

[0034] Figure 2 The thermogravimetric analysis diagram of the microcapsules prepared in this example is shown. It can be seen from the figure that the microcapsules can maintain the integrity of the core material within 394 °C and will not decompose.

[0035] Geopolymer preparation: According to the experimental mix ratio, fly ash and slag powder were weighed and mixed evenly. Then, the required sodium silicate, sodium hydroxide, and water were weighed to prepare an alkaline activator, which was cooled to room temperature. The slag powder and fly ash were poured into a mixer and stirred for 60 s, then the weighed aggregate and the rest were poured into the mixer and stirred for another 90 s. Then, the cooled alkaline activator was poured into the mixer and stirred for 120 s. The microcapsules were incorporated in multiple times, and at the same time, diethylenetriamine curing agent was added, and stirring continued for 120 s. Two groups of parallel specimens were prepared for the test. The size of the flexural strength specimen was 40 mm × 40 mm × 160 mm, and the size of the compressive strength specimen was 40 mm × 40 mm × 40 mm. One group of specimens was continuously heated in a muffle furnace at 800 °C for 2 h, and after natural cooling, the compressive and flexural strength tests were carried out; the other group of specimens was stored at room temperature for the compressive and flexural strength tests. The specific data are shown in Table 1.

[0036] Figure 3 The dispersion diagram of the microcapsules prepared in this example in the geopolymer matrix is shown. It can be seen from the figure that the microcapsules prepared in this example are uniformly distributed in the geopolymer matrix, and the pores caused by the incorporation of microcapsules are of the same order of magnitude as the particle size of fly ash microspheres. The deterioration of the geopolymer performance caused by introducing part of the pores by adding microcapsules is much less than the strength improvement brought by the microcapsule repair.

[0037] Example 2 Microcapsule preparation (emulsifier concentration is 1.0 wt%, emulsifier compounding is SP + TW): Mix 16.6 g of 37% formaldehyde solution with 6.12 g of urea in a three-necked flask, add 100 g of deionized water and stir until completely dissolved. Adjust the pH to 8 - 9 with triethanolamine, heat to 70 °C and stir at 600 rpm for 60 min to obtain a urea-formaldehyde resin prepolymer solution.

[0038] Take 1.0 g of Tween 80 and 1.0 g of Span 80, add them to 198 g of deionized water and stir evenly to obtain a compound emulsifier solution with a concentration of 1.0%. Take 12 g of epoxy resin E51 and add it to the compound emulsifier solution. Heat the mixed emulsion to 50 °C and stir at 600 rpm for 40 min.

[0039] Add the mixed emulsion to the prepolymer solution, adjust the pH of the solution to 2 - 3 with 10% dilute hydrochloric acid, add 0.5 g of sodium chloride and 0.5 g of resorcinol to the flask, place it in a 70 °C constant temperature water bath and stir and react at 600 rpm for 3 h.

[0040] Adjust the pH to 7 with triethanolamine, rinse with deionized water multiple times, filter by suction to obtain the finished microcapsules with a particle size of about 1 μm, and dry them in a 40 °C drying oven for 24 h to obtain urea-formaldehyde resin - epoxy resin microcapsules.

[0041] Figure 4 The TEM image of the microcapsules prepared in this example is shown. It can be seen from the figure that the microcapsules prepared in this example have extremely few impurities, and there are basically no rupture and agglomeration situations. The synthesized microcapsules are pure, have uniform particle size, are not easy to rupture, have good dispersibility, and few agglomeration phenomena.

[0042] Geopolymer preparation: According to the experimental mix ratio, weigh fly ash and mineral powder and mix them evenly. Then weigh the required sodium silicate, sodium hydroxide and water to prepare an alkaline activator, and cool it to room temperature. Pour the mineral powder and fly ash into a mixer and stir for 60 s, then pour the weighed aggregate and the rest into the mixer and continue to stir for 90 s. Then pour the cooled alkaline activator into the mixer and stir for 120 s. The microcapsules are incorporated in multiple times, and at the same time, diethylenetriamine curing agent is added, and continue to stir for 120 s. Prepare 2 groups of parallel specimens for the test. The size of the flexural strength specimen is 40 mm × 40 mm × 160 mm, and the size of the compressive strength specimen is 40 mm × 40 mm × 40 mm. One group of specimens is continuously heated in a muffle furnace at 800 °C for 2 h, and after natural cooling, the compressive and flexural strength tests are carried out; the other group of specimens is stored at room temperature and the compressive and flexural strength tests are carried out. The specific data are shown in Table 1.

[0043] Example 3 Microcapsule preparation (emulsifier concentration is 1.5 wt%, emulsifier compounding is SP + TW): Mix 16.6 g of 37% formaldehyde solution with 6.12 g of urea in a three-necked flask, add 100 g of deionized water and stir until completely dissolved. Adjust the pH to 8 - 9 with triethanolamine, heat to 70 °C and stir at 600 rpm for 60 min to obtain a urea-formaldehyde resin prepolymer solution.

[0044] Take 1.5 g of Tween 80 and 1.5 g of Span 80, add them to 197 g of deionized water and stir evenly to obtain a compound emulsifier solution with a concentration of 1.5%. Take 12 g of epoxy resin E51 and add it to the compound emulsifier solution. Heat the mixed emulsion to 50 °C and stir at 600 rpm for 40 min.

[0045] Add the mixed emulsion to the prepolymer solution, adjust the pH of the solution to 2 - 3 with 10% dilute hydrochloric acid, add 0.5 g of sodium chloride and 0.5 g of resorcinol to the flask, place it in a 70 °C constant temperature water bath and stir and react at 600 rpm for 3 h.

[0046] Adjust the pH to 7 with triethanolamine, rinse with deionized water multiple times, filter by suction to obtain the finished microcapsules with a particle size of about 1 μm, and dry them in a 40 °C drying oven for 24 h to obtain urea-formaldehyde resin - epoxy resin microcapsules.

[0047] Figure 5 The TEM image of the microcapsules prepared in this example is shown. It can be seen from the figure that the microcapsules prepared in this example have very few impurities, and there are basically no rupture and agglomeration situations. The synthesized microcapsules are pure, have uniform particle size, are not easy to rupture, have good dispersibility, and less agglomeration phenomenon.

[0048] Geopolymer preparation: According to the experimental mix ratio, weigh fly ash and slag powder and mix them evenly. Then weigh the required sodium silicate, sodium hydroxide and water to prepare an alkaline activator, and cool it to room temperature. Pour the slag powder and fly ash into a mixer and stir for 60 s, then pour the weighed aggregate and the rest into the mixer and continue to stir for 90 s. Then pour the cooled alkaline activator into the mixer and stir for 120 s. The microcapsules are incorporated in multiple times, and at the same time, diethylenetriamine curing agent is added, and continue to stir for 120 s. Prepare 2 groups of parallel specimens for the test. The size of the flexural strength specimen is 40 mm × 40 mm × 160 mm, and the size of the compressive strength specimen is 40 mm × 40 mm × 40 mm. One group of specimens is continuously heated in a muffle furnace at 800 °C for 2 h, and after natural cooling, the compressive and flexural strength tests are carried out; the other group of specimens is stored at room temperature for the compressive and flexural strength tests. The specific data are shown in Table 1.

[0049] Example 4 Microcapsule preparation (emulsifier concentration is 0.5 wt%, emulsifier compounding is SP + polyvinyl alcohol): Mix 16.6 g of 37% formaldehyde solution with 6.12 g of urea in a three-necked flask, add 100 g of deionized water and stir until completely dissolved. Adjust the pH to 8 - 9 with triethanolamine, heat to 70 °C and stir at 600 rpm for 60 min to obtain a urea-formaldehyde resin prepolymer solution.

[0050] Take 0.5 g of polyvinyl alcohol and 0.5 g of Span 80, add them to 199 g of deionized water and stir evenly to obtain a compound emulsifier solution with a concentration of 0.5%. Take 12 g of epoxy resin E51 and add it to the compound emulsifier solution. Heat the mixed emulsion to 50 °C and stir at 600 rpm for 40 min.

[0051] Add the mixed emulsion to the prepolymer solution, adjust the pH of the solution to 2 - 3 with 10% dilute hydrochloric acid, add 0.5 g of sodium chloride and 0.5 g of resorcinol to the flask, place it in a constant temperature water bath at 70 °C and stir and react at 600 rpm for 3 h.

[0052] Adjust the pH to 7 with triethanolamine, rinse with deionized water multiple times, filter by suction to obtain the finished microcapsules with a particle size of about 1 μm, and dry them in a drying oven at 40 °C for 24 h to obtain urea-formaldehyde resin - epoxy resin microcapsules.

[0053] Figure 6 The TEM image of the microcapsules prepared in this example is shown. It can be seen from the figure that the microcapsules prepared in this example have very few impurities, and there are basically no cases of rupture and agglomeration. The synthesized microcapsules are pure, have uniform particle size, are not easy to rupture, have good dispersibility, and less agglomeration phenomenon.

[0054] Geopolymer preparation: According to the experimental mix ratio, weigh fly ash and slag powder and mix them evenly. Then weigh the required water glass, sodium hydroxide and water to prepare an alkaline activator, and cool it to room temperature. Pour the slag powder and fly ash into the mixer and stir for 60 s, then pour the weighed aggregate and the rest into the mixer and continue to stir for 90 s. Then pour the cooled alkaline activator into the mixer and stir for 120 s. The microcapsules are incorporated in multiple times, and at the same time, diethylenetriamine curing agent is added, and continue to stir for 120 s. Prepare 2 groups of parallel specimens for the test. The size of the flexural strength specimen is 40 mm × 40 mm × 160 mm, and the size of the compressive strength specimen is 40 mm × 40 mm × 40 mm. One group of specimens is continuously heated in a muffle furnace at 800 °C for 2 h, and after natural cooling, the compressive and flexural strength tests are carried out; the other group of specimens is stored at room temperature for the compressive and flexural strength tests. The specific data are shown in Table 1.

[0055] Example 5 Microcapsule preparation (emulsifier concentration is 1.0 wt%, emulsifier compounding is SP + polyvinyl alcohol): Mix 16.6 g of 37% formaldehyde solution and 6.12 g of urea in a three-necked flask, add 100 g of deionized water and stir until completely dissolved. Adjust the pH to 8 - 9 with triethanolamine, heat to 70 °C and stir at 600 rpm for 60 min to obtain a urea-formaldehyde resin prepolymer solution.

[0056] Take 1.0 g of polyvinyl alcohol and 1.0 g of Span 80, add them to 198 g of deionized water and stir evenly to obtain a compound emulsifier solution with a concentration of 1.0%. Take 12 g of epoxy resin E51 and add it to the compound emulsifier solution. Heat the mixed emulsion to 50 °C and stir at 600 rpm for 40 min.

[0057] Add the mixed emulsion to the prepolymer solution, adjust the pH of the solution to 2 - 3 with 10% dilute hydrochloric acid, add 0.5 g of sodium chloride and 0.5 g of resorcinol to the flask, place it in a 70 °C constant temperature water bath and stir and react at 600 rpm for 3 h.

[0058] Adjust the pH to 7 with triethanolamine, rinse with deionized water multiple times, filter by suction to obtain the finished microcapsules with a particle size of about 1 μm, and dry them in a 40 °C drying oven for 24 h to obtain urea-formaldehyde resin - epoxy resin microcapsules.

[0059] Figure 7 The TEM image of the microcapsules prepared in this example is shown. It can be seen from the figure that the microcapsules prepared in this example have very few impurities, and there is basically no rupture or agglomeration. The synthesized microcapsules are pure, with uniform particle size, are not easy to rupture, have good dispersibility, and little agglomeration phenomenon.

[0060] Geopolymer preparation: According to the experimental mix ratio, weigh fly ash and slag powder and mix them evenly. Then weigh the required sodium silicate, sodium hydroxide and water to prepare an alkaline activator, and cool it to room temperature. Pour the slag powder and fly ash into a mixer and stir for 60 s, then pour the weighed aggregate and the rest into the mixer and continue to stir for 90 s. Then pour the cooled alkaline activator into the mixer and stir for 120 s. The microcapsules are incorporated in multiple times, and at the same time, diethylenetriamine curing agent is added, and continue to stir for 120 s. Prepare 2 groups of parallel specimens for the test. The size of the flexural strength specimen is 40 mm × 40 mm × 160 mm, and the size of the compressive strength specimen is 40 mm × 40 mm × 40 mm. One group of specimens is continuously heated in a muffle furnace at 800 °C for 2 h, and after natural cooling, the compressive and flexural strength tests are carried out; the other group of specimens is stored at room temperature and the compressive and flexural strength tests are carried out. The specific data are shown in Table 1.

[0061] Example 6 Microcapsule preparation (emulsifier concentration is 1.5 wt%, emulsifier compounding is SP + polyvinyl alcohol): Mix 16.6 g of 37% formaldehyde solution with 6.12 g of urea in a three-necked flask, add 100 g of deionized water and stir until completely dissolved. Adjust the pH to 8 - 9 with triethanolamine, heat to 70 °C and stir at 600 rpm for 60 min to obtain a urea-formaldehyde resin prepolymer solution.

[0062] Take 1.5 g of polyvinyl alcohol and 1.5 g of Span 80, add them to 197 g of deionized water and stir evenly to obtain a compound emulsifier solution with a concentration of 1.5%. Take 12 g of epoxy resin E51 and add it to the compound emulsifier solution, heat the mixed emulsion to 50 °C, and stir at 600 rpm for 40 min.

[0063] Add the mixed emulsion to the prepolymer solution, adjust the pH of the solution to 2 - 3 with 10% dilute hydrochloric acid, add 0.5 g of sodium chloride and 0.5 g of resorcinol to the flask, place it in a 70 °C constant temperature water bath and stir and react at 600 rpm for 3 h.

[0064] Adjust the pH to 7 with triethanolamine, rinse with deionized water multiple times, filter by suction to obtain the finished microcapsules with a particle size of about 1 μm, and dry them in a 40 °C drying oven for 24 h to obtain urea-formaldehyde resin - epoxy resin microcapsules.

[0065] Figure 8 The TEM image of the microcapsules prepared in this example is shown. It can be seen from the figure that the microcapsules prepared in this example have very few impurities, and there is basically no rupture or agglomeration. The synthesized microcapsules are pure, have a uniform particle size, are not easy to rupture, have good dispersibility, and little agglomeration phenomenon.

[0066] Geopolymer preparation: According to the experimental mix ratio, weigh fly ash and mineral powder and mix them evenly. Then weigh the required sodium silicate, sodium hydroxide and water to prepare an alkaline activator, and cool it to room temperature. Pour the mineral powder and fly ash into a mixer and stir for 60 s, then pour the weighed aggregate and the rest into the mixer and continue to stir for 90 s. Then pour the cooled alkaline activator into the mixer and stir for 120 s. The microcapsules are incorporated in multiple times, and at the same time, diethylenetriamine curing agent is added, and continue to stir for 120 s. Prepare 2 groups of parallel specimens for the test. The size of the flexural strength specimen is 40 mm × 40 mm × 160 mm, and the size of the compressive strength specimen is 40 mm × 40 mm × 40 mm. One group of specimens is continuously heated in a muffle furnace at 800 °C for 2 h, and after natural cooling, the compressive and flexural strength tests are carried out; the other group of specimens is stored at room temperature and the compressive and flexural strength tests are carried out. The specific data are shown in Table 1.

[0067] Comparative Example 1 Microcapsule preparation (0.5 wt % SDBS, 1.0 wt % SDBS, 1.5 wt % SDBS): Mix 16.6 g of 37% formaldehyde solution with 6.12 g of urea in a three-necked flask, add 100 g of deionized water and stir until completely dissolved. Adjust the pH to 8 - 9 with triethanolamine, heat to 70 °C and stir at 600 rpm for 60 min to obtain a urea-formaldehyde resin prepolymer solution.

[0068] According to the mass percentage concentration of the emulsifier being 0.5% SDBS, 1.0% SDBS, and 1.5% sodium dodecylbenzenesulfonate (SDBS) (0.5 g, 1 g, 1.5 g) respectively, mix with deionized water and stir evenly to obtain a sodium dodecylbenzenesulfonate emulsifier solution. Take 12 g of epoxy resin E51 and add it to the SDBS emulsifier solution. Heat the mixed emulsion to 50 °C and stir at 600 rpm for 40 min.

[0069] Add the mixed emulsion to the prepolymer solution, adjust the pH of the solution to 2 - 3 with 10% dilute hydrochloric acid, add 0.5 g of sodium chloride and 0.5 g of resorcinol to the flask, place it in a 70 °C constant temperature water bath and stir and react at 600 rpm for 3 h.

[0070] Adjust the pH to 7 with triethanolamine, rinse with deionized water multiple times, filter by suction to obtain the finished microcapsules, and dry them in a 40 °C drying oven for 24 h to obtain urea-formaldehyde resin - epoxy resin microcapsules.

[0071] Figure 9 The following shows the TEM electron micrograph of the microcapsules prepared in this comparative example. Among them, a is the TEM electron micrograph of the microcapsules prepared with 0.5% SDBS, b is the TEM electron micrograph of the microcapsules prepared with 1.0% SDBS, and c is the TEM electron micrograph of the microcapsules prepared with 1.5% SDBS. It can be seen from the figure that there are a small number of cases of broken walls and agglomeration in the microcapsules prepared in this example.

[0072] Geopolymer preparation: According to the experimental mix ratio, weigh fly ash and slag powder and mix them evenly. Then weigh the required sodium silicate, sodium hydroxide and water to prepare an alkaline activator, and cool it to room temperature. Pour the slag powder and fly ash into the mixer and stir for 60 s, then pour the weighed aggregate and the rest into the mixer and continue to stir for 90 s. Then pour the cooled alkaline activator into the mixer and stir for 120 s. The prepared microcapsules are incorporated in multiple times, and at the same time, diethylenetriamine curing agent is added, and continue to stir for 120 s. Prepare 2 groups of parallel specimens for the test. The size of the flexural strength specimens is 40 mm × 40 mm × 160 mm, and the size of the compressive strength specimens is 40 mm × 40 mm × 40 mm. One group of specimens is continuously heated in a muffle furnace at 800 °C for 2 h, and after natural cooling, compressive and flexural strength tests are carried out; the other group of specimens is stored at room temperature and compressive and flexural strength tests are carried out. The specific data are shown in Table 1.

[0073] Comparative Example 2 Preparation of microcapsules (0.5 wt% polyvinyl alcohol, 1.0 wt% polyvinyl alcohol, 1.5 wt% polyvinyl alcohol): Mix 16.6 g of 37% formaldehyde solution and 6.12 g of urea in a three-necked flask, add 100 g of deionized water and stir until completely dissolved. Adjust the pH to 8 - 9 with triethanolamine, heat to 70 °C and stir at 600 rpm for 60 min to obtain a urea-formaldehyde resin prepolymer solution.

[0074] Take polyvinyl alcohol and ionized water according to the emulsifier concentrations of 0.5 wt%, 1.0 wt%, and 1.5 wt% respectively and stir evenly to obtain a polyvinyl alcohol emulsifier solution. Take 12 g of epoxy resin E51 and add it to the PVA emulsifier solution. Heat the mixed emulsion to 50 °C and stir at 600 rpm for 40 min.

[0075] Add the mixed emulsion to the prepolymer solution, adjust the pH of the solution to 2 - 3 with 10% dilute hydrochloric acid, add 0.5 g of sodium chloride and 0.5 g of resorcinol to the flask, place it in a 70 °C constant temperature water bath and stir and react at 600 rpm for 3 h.

[0076] Adjust the pH to 7 with triethanolamine, wash with deionized water multiple times, filter by suction to obtain the finished microcapsules with a particle size of about 1 μm, and dry them in a 40 °C drying oven for 24 h to obtain urea-formaldehyde resin - epoxy resin microcapsules.

[0077] Figure 10 The TEM electron micrograph of the microcapsules prepared in this comparative example is shown. Among them, a is the TEM electron micrograph of the microcapsules prepared with 0.5% polyvinyl alcohol, b is the TEM electron micrograph of the microcapsules prepared with 1.0% polyvinyl alcohol, and c is the TEM electron micrograph of the microcapsules prepared with 1.5% polyvinyl alcohol. It can be seen from the figure that there are a small amount of wall-breaking and agglomeration in the microcapsules prepared in this example.

[0078] Preparation of geopolymers: According to the experimental mix ratio, weigh fly ash and ground granulated blast-furnace slag and mix them evenly. Then, weigh the required sodium silicate, sodium hydroxide, and water to prepare an alkaline activator, and cool it to room temperature. Pour the ground granulated blast-furnace slag and fly ash into a blender and stir for 60 s. Then, pour the weighed aggregates and the rest into the blender and continue to stir for 90 s. Next, pour the cooled alkaline activator into the blender and stir for 120 s. The microcapsules are incorporated in several batches, and diethylenetriamine curing agent is added simultaneously, and continue to stir for 120 s. Two groups of parallel specimens are prepared for the test. The size of the flexural strength specimen is 40 mm×40 mm×160 mm, and the size of the compressive strength specimen is 40 mm×40 mm×40 mm. One group of specimens is continuously heated in a muffle furnace at 800 °C for 2 h, and after natural cooling, the compressive and flexural strength tests are carried out; the other group of specimens is stored at room temperature, and the compressive and flexural strength tests are carried out. The specific data are shown in Table 1.

[0079] Comparative Example 3 Preparation of microcapsules (0.5 wt % SP, 1.0 wt % SP, 1.5 wt % SP): Mix 16.6 g of 37% formaldehyde solution and 6.12 g of urea in a three-necked flask, add 100 g of deionized water and stir until completely dissolved. Adjust the pH to 8 - 9 with triethanolamine, heat to 70 °C and stir at a speed of 600 rpm for 60 min to obtain a urea-formaldehyde resin prepolymer solution.

[0080] Take Span 80 and ionized water according to the emulsifier concentrations of 0.5 wt %, 1.0 wt %, and 1.5 wt % respectively and stir evenly to obtain a Span 80 emulsifier solution. Take 12 g of epoxy resin E51 and add it to the Span emulsifier solution. Heat the mixed emulsion to 50 °C and stir at a speed of 600 rpm for 40 min.

[0081] Add the mixed emulsion to the prepolymer solution, adjust the pH of the solution to 2 - 3 with 10% dilute hydrochloric acid, add 0.5 g of sodium chloride and 0.5 g of resorcinol to the flask, place it in a 70 °C constant temperature water bath and stir and react at a speed of 600 rpm for 3 h.

[0082] Adjust the pH to 7 with triethanolamine, wash with deionized water multiple times, and filter to obtain the finished microcapsules with a particle size of about 1 μm. Place them in a drying oven at 40 °C and dry for 24 h to obtain urea-formaldehyde resin - epoxy resin microcapsules.

[0083] Figure 11 The TEM electron micrograph of the microcapsules prepared in this comparative example is shown. Among them, a is the TEM electron micrograph of the microcapsules prepared with 0.5% SP, b is the TEM electron micrograph of the microcapsules prepared with 1.0% SP, and c is the TEM electron micrograph of the microcapsules prepared with 1.5% SP. It can be seen from the figure that there are a small amount of cases of broken walls and agglomeration of the microcapsules prepared in this example.

[0084] Geopolymer preparation: According to the experimental mix ratio, weigh fly ash and slag powder and mix them evenly. Then, weigh the required sodium silicate, sodium hydroxide, and water to prepare an alkaline activator, and cool it to room temperature. Pour the slag powder and fly ash into a blender and stir for 60 s. Then, pour the weighed aggregate and the rest into the blender and continue to stir for 90 s. Next, pour the cooled alkaline activator into the blender and stir for 120 s. The microcapsules are incorporated in multiple batches, and diethylenetriamine curing agent is added simultaneously, and stirring continues for 120 s. Two groups of parallel specimens are prepared for the test. The size of the flexural strength specimens is 40 mm × 40 mm × 160 mm, and the size of the compressive strength specimens is 40 mm × 40 mm × 40 mm. One group of specimens is continuously heated in a muffle furnace at 800 °C for 2 h, and after natural cooling, the compressive and flexural strength tests are carried out; the other group of specimens is stored at room temperature for the compressive and flexural strength tests. The specific data are shown in Table 1.

[0085] Comparative Example 4 Microcapsule preparation (0.5 wt % TW, 1.0 wt % TW, 1.5 wt % TW): Mix 16.6 g of 37% formaldehyde solution and 6.12 g of urea in a three-necked flask, add 100 g of deionized water and stir until completely dissolved. Adjust the pH to 8 - 9 with triethanolamine, heat to 70 °C and stir at 600 rpm for 60 min to obtain a urea-formaldehyde resin prepolymer solution.

[0086] According to the emulsifier concentrations of 0.5 wt %, 1.0 wt %, and 1.5 wt % respectively, take Tween 80 (0.5 g, 1 g, 1.5 g) and add it to ionized water and stir evenly to obtain a Tween 80 emulsifier solution. Take 12 g of epoxy resin E51 and add it to the Tween emulsifier solution. Heat the mixed emulsion to 50 °C and stir at 600 rpm for 40 min.

[0087] Add the mixed emulsion to the prepolymer solution, adjust the pH of the solution to 2 - 3 with 10% dilute hydrochloric acid, add 0.5 g of sodium chloride and 0.5 g of resorcinol to the flask, place it in a 70 °C constant temperature water bath and stir and react at 600 rpm for 3 h.

[0088] Adjust the pH to 7 with triethanolamine, wash it with deionized water multiple times, and filter by suction to obtain the finished microcapsules with a particle size of about 1 μm. Place them in a drying oven at 40 °C and dry for 24 h to obtain urea-formaldehyde resin - epoxy resin microcapsules.

[0089] Figure 12The TEM micrograph of the microcapsules prepared in this comparative example is shown. Among them, a is the TEM micrograph of the microcapsules prepared with 0.5% TW, b is the TEM micrograph of the microcapsules prepared with 1.0% TW, and c is the TEM micrograph of the microcapsules prepared with 1.5% TW. It can be seen from the figure that there are a small number of cases of broken walls and agglomeration in the microcapsules prepared in this example.

[0090] Geopolymer preparation: According to the experimental mix ratio, weigh fly ash and mineral powder and mix them evenly. Then weigh the required sodium silicate, sodium hydroxide and water to prepare an alkaline activator, and cool it to room temperature. Pour the mineral powder and fly ash into the mixer and stir for 60 s. Then pour the weighed aggregate and the remaining into the mixer and continue to stir for 90 s. Then pour the cooled alkaline activator into the mixer and stir for 120 s. The microcapsules are incorporated in several times, and diethylenetriamine curing agent is added at the same time, and continue to stir for 120 s. Prepare 2 groups of parallel specimens for the test. The size of the flexural strength specimen is 40 mm × 40 mm × 160 mm, and the size of the compressive strength specimen is 40 mm × 40 mm × 40 mm. One group of specimens is continuously heated in a muffle furnace at 800 °C for 2 h, and after natural cooling, the compressive and flexural strength tests are carried out; the other group of specimens is stored at room temperature, and the compressive and flexural strength tests are carried out. The specific data are shown in Table 1.

[0091] Since the HLB values of Tween 80 and polyvinyl alcohol are greater than the HLB value required in the preparation conditions of the present invention, the HLB value obtained after their compounding is much greater than the HLB value required in the preparation conditions of the present invention, making it impossible to emulsify successfully during the preparation process. Therefore, there is no need to set a comparative example in which Tween 80 and polyvinyl alcohol are compounded as an emulsifier.

[0092] Comparative Example 5 This comparative example is a blank control group without adding microcapsules. According to the experimental mix ratio, weigh fly ash and mineral powder and mix them evenly. Then weigh the required sodium silicate, sodium hydroxide and water to prepare an alkaline activator, and cool it to room temperature. Pour the mineral powder and fly ash into the mixer and stir for 60 s. Then pour the weighed aggregate and the remaining water and water reducing agent into the mixer and continue to stir for 90 s. Finally, pour the cooled alkaline activator into the mixer and stir for 120 s before discharging. Prepare 2 groups of parallel specimens for the test. The size of the flexural strength specimen is 40 mm × 40 mm × 160 mm, and the size of the compressive strength specimen is 40 mm × 40 mm × 40 mm. One group of specimens is continuously heated in a muffle furnace at 800 °C for 2 h, and after natural cooling, the compressive and flexural strength tests are carried out (remaining compressive and flexural strength); the other group of specimens is stored at room temperature, and the compressive and flexural strength tests are carried out (initial compressive and flexural strength).

[0093] The 7-day test data (800 °C) of Examples 1-6 and Comparative Examples 1-5 are shown in Table 1: Table 1

[0094] According to the data obtained in Table 1 above, it can be seen that after calcination at a high temperature of 800 °C for 2 hours, the compressive strength of the test block of Comparative Example 5 without microcapsules is 8.636 MPa, and the flexural strength is 0.69 MPa. For the test block doped with microcapsules, especially the microcapsules prepared with Span80 + Tween80 compound emulsifier (Example 1), the highest compressive strength can reach 32.164 MPa, and the flexural strength can reach 1.393 MPa. Moreover, compared with Comparative Example 5, the compressive strength of Example 1 is increased by 4 times, and the flexural strength is increased by 2 times, and the repair effect is very significant. At the same time, it can be seen that the improvement of the strength of geopolymers by the microcapsules prepared with a single emulsifier in Comparative Examples 1-4 is lower than that of the microcapsules prepared with a compound emulsifier in Examples 1-6. However, compared with the comparative examples, the improvement of the strength of geopolymers by the microcapsules prepared in Comparative Examples 1-4 is still higher than that of the geopolymers without microcapsules in the comparative examples. Among the microcapsule materials prepared by different microcapsule synthesis schemes, the microcapsules prepared with 0.5% Span80 + Tween80 compound emulsifier have the most obvious improvement effect.

[0095] The above is the preferred implementation manner of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. It should be pointed out that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and changes can still be made, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A microcapsule for self - repair of geopolymer materials, characterized in that, The microcapsules include urea-formaldehyde resin as the wall material and epoxy resin as the core material. At 300 - 800 °C, the urea-formaldehyde resin shell melts, and the internal epoxy resin core material is released and diffuses, contacts with the curing agent mixed in the matrix, forms an epoxy cured product, thereby filling and bonding the geopolymer microcracks generated at high temperature, and completing the self-healing process; the average particle size of the microcapsules is 1 - 3 μm.

2. The microcapsule for self-healing of geopolymer materials according to claim 1, characterized in that The curing agent is diethylenetriamine.

3. A method for preparing microcapsules for self-healing of geopolymer materials according to claim 1 or 2, characterized in that, It includes the following steps: (1) Preparation of prepolymer: Prepare a urea-formaldehyde resin prepolymer solution. (2) Emulsification stage: Mix the emulsifier with water and stir to obtain an emulsifier solution, add epoxy resin to the emulsifier solution, and mix evenly at a certain temperature to obtain a mixed emulsion. (3) Addition reaction stage: Mix the urea-formaldehyde resin prepolymer solution prepared in step (1) with the mixed emulsion prepared in step (2), adjust the pH, add a system modifier, and stir and react at a certain temperature until complete. (4) Extraction stage: After the reaction is completed, adjust the pH to neutral, wash and filter the product to obtain the finished microcapsules, and obtain urea-formaldehyde resin - epoxy resin microcapsules after drying. In step (2), the emulsifier is composed of a compound of Span 80 and polyvinyl alcohol or Tween 80.

4. The preparation method of the microcapsules for self - repair of geopolymer materials according to claim 3, characterized in that, The specific steps of step (1) are to mix and dissolve urea, formaldehyde solution, and water according to a mass ratio of 6 - 8:15 - 20:75 - 100, adjust the pH to 8 - 9, and stir at 70 - 80 °C until the reaction is complete to obtain a urea-formaldehyde resin prepolymer solution.

5. The preparation method of the microcapsules for the self-healing of geopolymer materials according to claim 3, characterized in that, In step (2), the concentration of the emulsifier solution is 0.5 wt% - 1.5 wt%, the mass ratio of epoxy resin to the emulsifier is 200:12 - 15, and the mixing temperature is 50 - 60 °C.

6. The preparation method of the microcapsules for the self-healing of geopolymer materials according to claim 3, characterized in that, In step (2), the HLB value of the compound emulsifier is 9 - 12.

7. The preparation method of the microcapsules for self-healing of geopolymer materials according to claim 4, characterized in that, In step (3), mix the urea-formaldehyde resin prepolymer solution and the mixed emulsion according to the mass ratio of urea to epoxy resin of 1:1.8 - 2.2, adjust the pH to 2 - 3, and the reaction temperature is 70 - 80 °C.

8. The preparation method of the microcapsules for self-healing of geopolymer materials according to claim 3, characterized in that, In step (3), the system modifier is composed of sodium chloride and resorcinol in a mass ratio of 1:0.5 - 2.

9. The preparation method of the microcapsules for the self-healing of geopolymer materials according to claim 3, wherein, In step (4), the drying temperature does not exceed 60 °C.

10. A method for self - repair of geopolymer materials, characterized in that, It includes the following steps: Disperse the microcapsules described in claim 1 or 2 or the microcapsules prepared by the preparation method described in any one of claims 3 - 9 and the curing agent in the geopolymer matrix, and calcine at a temperature of 300 - 800 °C until the repair is completed.

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