Microcapsules for self-repair of geopolymer materials, preparation method and application thereof

Abstract

The present invention relates to the technical field of materials science, and in particular to a microcapsule for self-repairing geopolymer materials, a preparation method thereof, and an application thereof. The microcapsule comprises a urea-formaldehyde resin as a wall material and an epoxy resin as a core material. At 300-800°C, the urea-formaldehyde resin shell melts, and the internal epoxy resin core material is released and diffused, coming into contact with a curing agent mixed in a matrix to form an epoxy cured product, thereby filling and bonding microcracks in the geopolymer generated by high temperature, completing the self-repair process; the average particle size of the microcapsule is 1-3 μm. The urea-formaldehyde resin of the present invention is selected as the wall material due to its high hardness, wear resistance, corrosion resistance, non-flammability, and physical property stability. The epoxy resin is selected as the core material due to its excellent adhesion, durability, and outstanding fatigue resistance. The stability and effectiveness of the microcapsule in a high-temperature environment are guaranteed, and it can also effectively react with the curing agent in the matrix to form an epoxy cured product, thereby completing the self-repair process.

Description

Technical Field

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

[0002] Geopolymer, a new inorganic non-metallic material, has attracted significant attention in recent years for its low-carbon, environmentally friendly nature (primarily derived from industrial solid waste), excellent mechanical properties (compressive strength of 50-100 MPa), chemical resistance (acid and alkali resistance superior to traditional cement-based materials), and high-temperature stability (refractory temperatures exceeding 1200°C). However, cracking in high-temperature environments remains a key challenge hindering its engineering application. Research has shown that geopolymer is prone to microcracks (average width 0.1-5 μm) during the hardening process due to incomplete polymerization or water evaporation. Furthermore, at temperatures above 200°C, the aluminosilicate network within the matrix undergoes thermal decomposition, accelerating crack propagation and resulting in a 30%-50% loss in material strength. To solve this problem, researchers have proposed a variety of methods: by adding MgO to react with water to form Mg(OH)2 expansion phase, the high-temperature shrinkage of the geopolymer can be effectively compensated and crack formation can be reduced (shrinkage rate is reduced by 40%-60%); LDHs (such as Mg-Al layered double hydroxides) are introduced to utilize their interlayer ion exchange properties to adsorb free Ca generated at high temperatures; 2+ , inhibiting stress concentration at the crack tip (crack resistance increased by more than 25%); adding nano-SiO2 or Al2O3 (dosage 1%-3%) makes the geopolymer microstructure denser by filling pores and promoting polymerization reaction, significantly improving high-temperature residual strength (such as the strength retention rate at 1200°C increased from 20% to 31%). Summary of the Invention

[0003] One of the purposes 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 microcapsule wall material melts to release the core material epoxy resin, which reacts with the matrix curing agent to form a repair body, thereby effectively filling the cracks and restoring the strength.

[0004] A second object of the present invention is to provide a method for preparing microcapsules for self-repairing geopolymer materials, which is simple and easy to adjust.

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

[0006] The solution adopted by the present invention to achieve one of the objectives is: a microcapsule for self-repair of geopolymer materials, wherein the microcapsule includes urea-formaldehyde resin as a wall material and epoxy resin as a core material. At 300-800°C, the urea-formaldehyde resin shell melts, and the internal epoxy resin core material is released and diffused, contacting with the curing agent mixed in the matrix to form an epoxy cured product, thereby filling the microcracks in the geopolymer generated by high temperature and bonding, completing the self-repair process.

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

[0008] Preferably, the curing agent is diethylenetriamine.

[0009] The solution adopted by the present invention to achieve the second purpose is: a method for preparing microcapsules for self-repairing geopolymer materials, comprising the following steps:

[0010] (1) Prepolymer preparation: Preparation of urea-formaldehyde resin prepolymer solution;

[0011] (2) Emulsification stage: Mix the emulsifier and water to prepare an emulsifier solution, add the epoxy resin to the emulsifier solution, mix them evenly at a certain temperature, and obtain a mixed emulsion;

[0012] (3) Addition reaction stage: the urea-formaldehyde resin prepolymer solution prepared in step (1) is mixed with the mixed emulsion prepared in step (2), the pH is adjusted, a system modifier is added, and the mixture is stirred at a certain temperature until the reaction is complete;

[0013] (4) Extraction stage: After the reaction is completed, the pH is adjusted to neutral, the product is washed and filtered to obtain the finished microcapsule, and then dried to obtain urea-formaldehyde resin-epoxy resin microcapsules;

[0014] In step (2), the emulsifier is prepared by compounding Span 80 (SP) with polyvinyl alcohol (PVA) or Tween 80 (TW).

[0015] Preferably, the specific steps of step (1) are as follows: urea, formaldehyde solution and water are mixed and dissolved in a mass ratio of 6-8:15-20:75-100, the pH is adjusted to 8-9, and the mixture is stirred at 70-80° C. until the reaction is complete to obtain a urea-formaldehyde resin prepolymer solution.

[0016] The formaldehyde solution is a commercially available formaldehyde solution, and the mass concentration is generally 36%-40%.

[0017] Preferably, in step (2), the concentration of the emulsifier solution is 0.5 wt%-1.5 wt%, the mass ratio of epoxy resin to emulsifier is 200:12-15, and the mixing temperature is 50-60°C.

[0018] Preferably, in step (2), the HLB value (water-oil ratio) of the compounded emulsifier is 9-12.

[0019] The emulsifiers were selected as Span 80 and compounded with two non-ionic emulsifiers such as Tween 80 or polyvinyl alcohol to an HLB value (water-oil ratio) of 9-12. The prepared microcapsules had complete morphology and basically no wall breakage, which avoided premature breakage of the microcapsules before the self-healing temperature was reached, causing the core material to flow out and cause waste or affect the repair effect.

[0020] Preferably, in step (3), the urea-formaldehyde resin prepolymer solution and the mixed emulsion are mixed in a mass ratio of urea to epoxy resin of 1:1.8-2.2, the pH is adjusted to 2-3, and the reaction temperature is 70-80°C.

[0021] Preferably, in step (3), the system modifier is prepared from sodium chloride and resorcinol in a mass ratio of 1:0.5-2.

[0022] 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, thereby preventing the core material from being damaged and obtaining microcapsules with uniform particle size and not prone to agglomeration. In addition, due to the addition of the system modifier during the addition reaction process, the agglomeration of the core material is effectively reduced, thereby reducing the particle size and obtaining a microcapsule product with a size of 1-3 μm.

[0023] Preferably, in step (4), the drying temperature does not exceed 60°C.

[0024] The solution adopted by the present invention to achieve the third purpose is: a method for self-repairing of geopolymer materials at high temperature, comprising the following steps: dispersing the microcapsules in a geopolymer matrix and calcining at a temperature of 300-800°C until the repair is completed.

[0025] The calcination time is generally 1-3 hours to complete the repair.

[0026] This application innovatively designs a urea-formaldehyde resin-epoxy resin microcapsule system, combines the required HLB value of the epoxy resin to optimize the emulsifier compounding and high-temperature triggered release mechanism, and achieves a breakthrough in achieving the stability and high encapsulation rate of the microcapsules at high temperatures, providing a new approach to solving the problem of high-temperature performance degradation of geopolymers.

[0027] The present invention has the following advantages and beneficial effects:

[0028] The microcapsules of this invention utilize urea-formaldehyde resin as the wall material and epoxy resin as the core material. Urea-formaldehyde resin was chosen for its high hardness, wear resistance, corrosion resistance, low flammability, and stable physical properties. Epoxy resin was chosen for the core material due to its excellent adhesion, durability, and outstanding fatigue resistance. This ensures the stability and effectiveness of the microcapsules in high-temperature environments and effectively reacts with the curing agent in the matrix to form an epoxy cured product, thus completing the self-healing process.

[0029] In practical applications, when the microcapsules of this invention are placed in a geopolymer matrix, their unique structural design enables rapid response and triggering of a self-repair mechanism in high-temperature environments. Specifically, under high temperatures, the urea-formaldehyde resin shell melts, releasing the epoxy resin core within and diffusing into microcracks. Upon contact with the curing agent mixed in the matrix, an epoxy cured product is formed, filling the microcracks and achieving adhesion. This not only improves the material's mechanical properties, but also extends its service life, enhancing its safety and reliability.

[0030] The preparation method of the present invention improves the stability of the synthesized microcapsules, prepares microcapsule particles with uniform particle size, not easy to break, and good stability, and will realize the self-repair of microcracks under high temperature conditions for the first time.

[0031] The microcapsules prepared by the preparation method of the present invention have good dispersibility, less agglomeration, less microcapsule wall breakage, complete morphology, and a 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 at high temperature.

[0032] The microcapsules of this invention, through a unique material combination and preparation process, provide an effective high-temperature self-healing solution for geopolymers. 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a TEM electron microscope image of the microcapsules prepared using 0.5% Span80+Tween80 compound emulsifier in Example 1;

[0034] Figure 2 This is the thermogravimetric analysis of microcapsules prepared with 0.5% Span80+Tween80 composite emulsifier used in Example 1;

[0035] Figure 3 is a diagram of the dispersion of the microcapsules prepared in Example 1 in a geopolymer matrix;

[0036] Figure 4This is a TEM electron microscope image of the microcapsules prepared using 1.0% SP+TW compound emulsifier in Example 2;

[0037] Figure 5 This is a TEM electron microscope image of the microcapsules prepared using 1.5% SP+TW compound emulsifier in Example 3;

[0038] Figure 6 This is a TEM electron microscope image of the microcapsules prepared using 0.5% SP + polyvinyl alcohol mixed emulsifier in Example 4;

[0039] Figure 7 This is a TEM electron microscope image of the microcapsules prepared using 1.0% SP + polyvinyl alcohol mixed emulsifier in Example 5;

[0040] Figure 8 This is a TEM electron microscope image of the microcapsules prepared using 1.5% SP + polyvinyl alcohol mixed emulsifier in Example 6;

[0041] Figure 9 TEM electron micrographs of the microcapsules prepared in Comparative Example 1, wherein a is a TEM electron micrograph of the microcapsules prepared with 0.5% SDBS, b is a TEM electron micrograph of the microcapsules prepared with 1.0% SDBS, and c is a TEM electron micrograph of the microcapsules prepared with 1.5% SDBS.

[0042] Figure 10 TEM electron micrographs of the microcapsules prepared in Comparative Example 2, wherein a is a TEM electron micrograph of the microcapsules prepared with 0.5% polyvinyl alcohol, b is a TEM electron micrograph of the microcapsules prepared with 1.0% polyvinyl alcohol, and c is a TEM electron micrograph of the microcapsules prepared with 1.5% polyvinyl alcohol;

[0043] Figure 11 TEM electron micrographs of the microcapsules prepared in Comparative Example 3, wherein a is a TEM electron micrograph of the microcapsules prepared with 0.5% SP, b is a TEM electron micrograph of the microcapsules prepared with 1.0% SP, and c is a TEM electron micrograph of the microcapsules prepared with 1.5% SP;

[0044] Figure 12 These are TEM electron micrographs of the microcapsules prepared in Comparative Example 4, wherein a is a TEM electron micrograph of the microcapsules prepared with 0.5% TW, b is a TEM electron micrograph of the microcapsules prepared with 1.0% TW, and c is a TEM electron micrograph of the microcapsules prepared with 1.5% TW. DETAILED DESCRIPTION

[0045] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples.

[0046] Example 1

[0047] Microcapsule preparation (emulsifier concentration is 0.5wt%, emulsifier compound is SP+TW):

[0048] 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 minutes to obtain a urea-formaldehyde resin prepolymer solution.

[0049] Add 0.5g of Tween 80 and 0.5g of Span 80 to 199g of deionized water and stir thoroughly to obtain a 0.5% emulsifier solution. Add 12g of epoxy resin E51 to the emulsifier solution, heat the mixture to 50°C, and stir at 600 rpm for 40 minutes.

[0050] 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 the mixture was placed in a constant temperature water bath at 70°C and stirred at 600 rpm for 3 h.

[0051] The pH was adjusted to 7 with triethanolamine, rinsed with deionized water several times, and filtered to obtain finished microcapsules with a particle size of about 1 μm. The microcapsules were placed in a drying oven at 40°C and dried for 24 hours to obtain urea-formaldehyde resin-epoxy resin microcapsules.

[0052] Figure 1 The TEM image of the microcapsules prepared in this example is shown. As can be seen from the figure, the microcapsules prepared in this example have very few impurities and basically no cracking or agglomeration. The synthesized microcapsules are pure, have uniform particle size, are not easy to crack, have good dispersibility, and have little agglomeration.

[0053] 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.

[0054] Geopolymer preparation:

[0055] According to the experimental mix ratio, fly ash and mineral powder were weighed and mixed thoroughly. The alkaline activator was then prepared by weighing the required amount of water glass, sodium hydroxide, and water. The mixture was cooled to room temperature. The mineral powder and fly ash were poured into a blender and stirred for 60 seconds. The weighed aggregate and the remaining material were then added to the blender and stirred for a further 90 seconds. The cooled alkaline activator was then added to the blender and stirred for 120 seconds. The microcapsules were added in several batches, along with the diethylenetriamine curing agent, and stirring was continued for 120 seconds. Two sets of parallel specimens were prepared for the test: the flexural strength specimens measured 40 mm × 40 mm × 160 mm, and the compressive strength specimens measured 40 mm × 40 mm × 40 mm. One set of specimens was heated in a muffle furnace at 800°C for 2 hours. After cooling naturally, compressive and flexural strength tests were performed on the other set of specimens. The compressive and flexural strength tests were performed on the other set of specimens, which were stored at room temperature. Specific data are shown in Table 1.

[0056] Figure 3 This is a dispersion diagram of the microcapsules prepared in this embodiment in the geopolymer matrix. It can be seen from the figure that the microcapsules prepared in this embodiment are evenly distributed in the geopolymer matrix, and since the pores caused by the incorporation of microcapsules are of the same order of magnitude as the particle size of fly ash microspheres, the degradation of the geopolymer performance caused by the introduction of partial pores by the addition of microcapsules is far less than the strength improvement brought about by microcapsule repair.

[0057] Example 2

[0058] Microcapsule preparation (emulsifier concentration is 1.0wt%, emulsifier compound is SP+TW):

[0059] 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 minutes to obtain a urea-formaldehyde resin prepolymer solution.

[0060] Add 1.0g of Tween 80 and 1.0g of Span 80 to 198g of deionized water and stir thoroughly to obtain a 1.0% emulsifier solution. Add 12g of epoxy resin E51 to the emulsifier solution, heat the mixture to 50°C, and stir at 600 rpm for 40 minutes.

[0061] 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 the mixture was placed in a constant temperature water bath at 70°C and stirred at 600 rpm for 3 h.

[0062] The pH was adjusted to 7 with triethanolamine, rinsed with deionized water several times, and filtered to obtain finished microcapsules with a particle size of about 1 μm. The microcapsules were placed in a drying oven at 40°C and dried for 24 hours to obtain urea-formaldehyde resin-epoxy resin microcapsules.

[0063] Figure 4 The TEM image of the microcapsules prepared in this example is shown. As can be seen from the figure, the microcapsules prepared in this example have very few impurities and basically no cracking or agglomeration. The synthesized microcapsules are pure, have uniform particle size, are not easy to crack, have good dispersibility, and have little agglomeration.

[0064] Geopolymer preparation:

[0065] According to the experimental mix ratio, fly ash and mineral powder were weighed and mixed thoroughly. The alkaline activator was then prepared by weighing the required amount of water glass, sodium hydroxide, and water. The mixture was cooled to room temperature. The mineral powder and fly ash were poured into a blender and stirred for 60 seconds. The weighed aggregate and the remaining material were then added to the blender and stirred for a further 90 seconds. The cooled alkaline activator was then added to the blender and stirred for 120 seconds. The microcapsules were added in several batches, along with the diethylenetriamine curing agent, and stirring was continued for 120 seconds. Two sets of parallel specimens were prepared for the test: the flexural strength specimens measured 40 mm × 40 mm × 160 mm, and the compressive strength specimens measured 40 mm × 40 mm × 40 mm. One set of specimens was heated in a muffle furnace at 800°C for 2 hours. After cooling naturally, compressive and flexural strength tests were performed on the other set of specimens. The compressive and flexural strength tests were performed on the other set of specimens, which were stored at room temperature. Specific data are shown in Table 1.

[0066] Example 3

[0067] Microcapsule preparation (emulsifier concentration is 1.5wt%, emulsifier compound is SP+TW):

[0068] 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 minutes to obtain a urea-formaldehyde resin prepolymer solution.

[0069] Add 1.5g of Tween 80 and 1.5g of Span 80 to 197g of deionized water and stir thoroughly to obtain a 1.5% emulsifier solution. Add 12g of epoxy resin E51 to the emulsifier solution, heat the mixture to 50°C, and stir at 600 rpm for 40 minutes.

[0070] 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 the mixture was placed in a constant temperature water bath at 70°C and stirred at 600 rpm for 3 h.

[0071] The pH was adjusted to 7 with triethanolamine, rinsed with deionized water several times, and filtered to obtain finished microcapsules with a particle size of about 1 μm. The microcapsules were placed in a drying oven at 40°C and dried for 24 hours to obtain urea-formaldehyde resin-epoxy resin microcapsules.

[0072] Figure 5 The TEM image of the microcapsules prepared in this example is shown. As can be seen from the figure, the microcapsules prepared in this example have very few impurities and basically no cracking or agglomeration. The synthesized microcapsules are pure, have uniform particle size, are not easy to crack, have good dispersibility, and have little agglomeration.

[0073] Geopolymer preparation:

[0074] According to the experimental mix ratio, fly ash and mineral powder were weighed and mixed thoroughly. The alkaline activator was then prepared by weighing the required amount of water glass, sodium hydroxide, and water. The mixture was cooled to room temperature. The mineral powder and fly ash were poured into a blender and stirred for 60 seconds. The weighed aggregate and the remaining material were then added to the blender and stirred for a further 90 seconds. The cooled alkaline activator was then added to the blender and stirred for 120 seconds. The microcapsules were added in several batches, along with the diethylenetriamine curing agent, and stirring was continued for 120 seconds. Two sets of parallel specimens were prepared for the test: the flexural strength specimens measured 40 mm × 40 mm × 160 mm, and the compressive strength specimens measured 40 mm × 40 mm × 40 mm. One set of specimens was heated in a muffle furnace at 800°C for 2 hours. After cooling naturally, compressive and flexural strength tests were performed on the other set of specimens. The compressive and flexural strength tests were performed on the other set of specimens, which were stored at room temperature. Specific data are shown in Table 1.

[0075] Example 4

[0076] Preparation of microcapsules (emulsifier concentration is 0.5wt%, emulsifier compound is SP+polyvinyl alcohol):

[0077] 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 minutes to obtain a urea-formaldehyde resin prepolymer solution.

[0078] Add 0.5g of polyvinyl alcohol and 0.5g of Span 80 to 199g of deionized water and stir thoroughly to obtain a 0.5% emulsifier solution. Add 12g of epoxy resin E51 to the emulsifier solution, heat the mixture to 50°C, and stir at 600 rpm for 40 minutes.

[0079] 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 the mixture was placed in a constant temperature water bath at 70°C and stirred at 600 rpm for 3 h.

[0080] The pH was adjusted to 7 with triethanolamine, rinsed with deionized water several times, and filtered to obtain finished microcapsules with a particle size of about 1 μm. The microcapsules were placed in a drying oven at 40°C and dried for 24 hours to obtain urea-formaldehyde resin-epoxy resin microcapsules.

[0081] Figure 6 The TEM image of the microcapsules prepared in this example is shown. As can be seen from the figure, the microcapsules prepared in this example have very few impurities and basically no cracking or agglomeration. The synthesized microcapsules are pure, have uniform particle size, are not easy to crack, have good dispersibility, and have little agglomeration.

[0082] Geopolymer preparation:

[0083] According to the experimental mix ratio, fly ash and mineral powder were weighed and mixed thoroughly. The alkaline activator was then prepared by weighing the required amount of water glass, sodium hydroxide, and water. The mixture was cooled to room temperature. The mineral powder and fly ash were poured into a blender and stirred for 60 seconds. The weighed aggregate and the remaining material were then added to the blender and stirred for a further 90 seconds. The cooled alkaline activator was then added to the blender and stirred for 120 seconds. The microcapsules were added in several batches, along with the diethylenetriamine curing agent, and stirring was continued for 120 seconds. Two sets of parallel specimens were prepared for the test: the flexural strength specimens measured 40 mm × 40 mm × 160 mm, and the compressive strength specimens measured 40 mm × 40 mm × 40 mm. One set of specimens was heated in a muffle furnace at 800°C for 2 hours. After cooling naturally, compressive and flexural strength tests were performed on the other set of specimens. The compressive and flexural strength tests were performed on the other set of specimens, which were stored at room temperature. Specific data are shown in Table 1.

[0084] Example 5

[0085] Preparation of microcapsules (emulsifier concentration is 1.0wt%, emulsifier compound is SP+polyvinyl alcohol):

[0086] 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 minutes to obtain a urea-formaldehyde resin prepolymer solution.

[0087] Add 1.0g of polyvinyl alcohol and 1.0g of Span 80 to 198g of deionized water and stir thoroughly to obtain a 1.0% emulsifier solution. Add 12g of epoxy resin E51 to the emulsifier solution, heat the mixture to 50°C, and stir at 600 rpm for 40 minutes.

[0088] 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 the mixture was placed in a constant temperature water bath at 70°C and stirred at 600 rpm for 3 h.

[0089] The pH was adjusted to 7 with triethanolamine, rinsed with deionized water several times, and filtered to obtain finished microcapsules with a particle size of about 1 μm. The microcapsules were placed in a drying oven at 40°C and dried for 24 hours to obtain urea-formaldehyde resin-epoxy resin microcapsules.

[0090] Figure 7 The TEM image of the microcapsules prepared in this example is shown. As can be seen from the figure, the microcapsules prepared in this example have very few impurities and basically no cracking or agglomeration. The synthesized microcapsules are pure, have uniform particle size, are not easy to crack, have good dispersibility, and have little agglomeration.

[0091] Geopolymer preparation:

[0092] According to the experimental mix ratio, fly ash and mineral powder were weighed and mixed thoroughly. The alkaline activator was then prepared by weighing the required amount of water glass, sodium hydroxide, and water. The mixture was cooled to room temperature. The mineral powder and fly ash were poured into a blender and stirred for 60 seconds. The weighed aggregate and the remaining material were then added to the blender and stirred for a further 90 seconds. The cooled alkaline activator was then added to the blender and stirred for 120 seconds. The microcapsules were added in several batches, along with the diethylenetriamine curing agent, and stirring was continued for 120 seconds. Two sets of parallel specimens were prepared for the test: the flexural strength specimens measured 40 mm × 40 mm × 160 mm, and the compressive strength specimens measured 40 mm × 40 mm × 40 mm. One set of specimens was heated in a muffle furnace at 800°C for 2 hours. After cooling naturally, compressive and flexural strength tests were performed on the other set of specimens. The compressive and flexural strength tests were performed on the other set of specimens, which were stored at room temperature. Specific data are shown in Table 1.

[0093] Example 6

[0094] Preparation of microcapsules (emulsifier concentration is 1.5wt%, emulsifier compound is SP+polyvinyl alcohol):

[0095] 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 minutes to obtain a urea-formaldehyde resin prepolymer solution.

[0096] Add 1.5g of polyvinyl alcohol and 1.5g of Span 80 to 197g of deionized water and stir thoroughly to obtain a 1.5% emulsifier solution. Add 12g of epoxy resin E51 to the emulsifier solution, heat the mixture to 50°C, and stir at 600 rpm for 40 minutes.

[0097] 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 the mixture was placed in a constant temperature water bath at 70°C and stirred at 600 rpm for 3 h.

[0098] The pH was adjusted to 7 with triethanolamine, rinsed with deionized water several times, and filtered to obtain finished microcapsules with a particle size of about 1 μm. The microcapsules were placed in a drying oven at 40°C and dried for 24 hours to obtain urea-formaldehyde resin-epoxy resin microcapsules.

[0099] Figure 8 The TEM image of the microcapsules prepared in this example is shown. As can be seen from the figure, the microcapsules prepared in this example have very few impurities and basically no cracking or agglomeration. The synthesized microcapsules are pure, have uniform particle size, are not easy to crack, have good dispersibility, and have little agglomeration.

[0100] Geopolymer preparation:

[0101] According to the experimental mix ratio, fly ash and mineral powder were weighed and mixed thoroughly. The alkaline activator was then prepared by weighing the required amount of water glass, sodium hydroxide, and water. The mixture was cooled to room temperature. The mineral powder and fly ash were poured into a blender and stirred for 60 seconds. The weighed aggregate and the remaining material were then added to the blender and stirred for a further 90 seconds. The cooled alkaline activator was then added to the blender and stirred for 120 seconds. The microcapsules were added in several batches, along with the diethylenetriamine curing agent, and stirring was continued for 120 seconds. Two sets of parallel specimens were prepared for the test: the flexural strength specimens measured 40 mm × 40 mm × 160 mm, and the compressive strength specimens measured 40 mm × 40 mm × 40 mm. One set of specimens was heated in a muffle furnace at 800°C for 2 hours. After cooling naturally, compressive and flexural strength tests were performed on the other set of specimens. The compressive and flexural strength tests were performed on the other set of specimens, which were stored at room temperature. Specific data are shown in Table 1.

[0102] Comparative Example 1

[0103] Microcapsule preparation (0.5 wt %SDBS, 1.0 wt %SDBS, 1.5 wt %SDBS):

[0104] 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 minutes to obtain a urea-formaldehyde resin prepolymer solution.

[0105] Sodium dodecylbenzenesulfonate (SDBS) (0.5g, 1g, and 1.5g) were mixed with deionized water at emulsifier concentrations of 0.5%, 1.0%, and 1.5% SDBS, respectively, and stirred thoroughly to obtain a sodium dodecylbenzenesulfonate emulsifier solution. 12g of epoxy resin E51 was added to the SDBS emulsifier solution. The mixed emulsion was heated to 50°C and stirred at 600 rpm for 40 minutes.

[0106] 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 the mixture was placed in a constant temperature water bath at 70°C and stirred at 600 rpm for 3 h.

[0107] The pH value was adjusted to 7 with triethanolamine, and the mixture was rinsed with deionized water for several times. The finished microcapsules were filtered and dried in a drying oven at 40°C for 24 hours to obtain urea-formaldehyde resin-epoxy resin microcapsules.

[0108] Figure 9 The figures show the TEM electron micrographs of the microcapsules prepared in this comparative example, wherein 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 figures that the microcapsules prepared in this example have a small amount of wall breakage and cohesion.

[0109] Geopolymer preparation:

[0110] According to the experimental mix ratio, fly ash and mineral powder were weighed and mixed uniformly. The alkaline activator was then prepared by weighing the required amount of water glass, sodium hydroxide, and water. The mixture was cooled to room temperature. The mineral powder and fly ash were poured into a blender and stirred for 60 seconds. The weighed aggregate and the remaining material were then added to the blender and stirred for a further 90 seconds. The cooled alkaline activator was then added to the blender and stirred for 120 seconds. The prepared microcapsules were added in several batches, along with diethylenetriamine curing agent, and stirring continued for 120 seconds. Two sets of parallel specimens were prepared for the test: the flexural strength specimens measured 40 mm × 40 mm × 160 mm, and the compressive strength specimens measured 40 mm × 40 mm × 40 mm. One set of specimens was heated in a muffle furnace at 800°C for 2 hours. After cooling naturally, compressive and flexural strength tests were performed. The other set of specimens was stored at room temperature and then subjected to compressive and flexural strength tests. Specific data are shown in Table 1.

[0111] Comparative Example 2

[0112] Microcapsule preparation (0.5 wt % polyvinyl alcohol, 1.0 wt % polyvinyl alcohol, 1.5 wt % polyvinyl alcohol):

[0113] 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 minutes to obtain a urea-formaldehyde resin prepolymer solution.

[0114] Polyvinyl alcohol (PVA) and deionized water were mixed at emulsifier concentrations of 0.5 wt %, 1.0 wt %, and 1.5 wt %, respectively, to obtain a PVA emulsifier solution. 12 g of epoxy resin E51 was added to the PVA emulsifier solution. The mixed emulsion was heated to 50°C and stirred at 600 rpm for 40 minutes.

[0115] 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 the mixture was placed in a constant temperature water bath at 70°C and stirred at 600 rpm for 3 h.

[0116] The pH was adjusted to 7 with triethanolamine, rinsed with deionized water several times, and filtered to obtain finished microcapsules with a particle size of about 1 μm. The microcapsules were placed in a drying oven at 40°C and dried for 24 hours to obtain urea-formaldehyde resin-epoxy resin microcapsules.

[0117] Figure 10 The figures show the TEM electron micrographs of the microcapsules prepared in this comparative example, wherein a is a TEM electron micrograph of the microcapsules prepared with 0.5% polyvinyl alcohol, b is a TEM electron micrograph of the microcapsules prepared with 1.0% polyvinyl alcohol, and c is a TEM electron micrograph of the microcapsules prepared with 1.5% polyvinyl alcohol. It can be seen from the figures that the microcapsules prepared in this example have a small amount of wall breakage and cohesion.

[0118] Geopolymer preparation:

[0119] According to the experimental mix ratio, fly ash and mineral powder were weighed and mixed thoroughly. The alkaline activator was then prepared by weighing the required amount of water glass, sodium hydroxide, and water. The mixture was cooled to room temperature. The mineral powder and fly ash were poured into a blender and stirred for 60 seconds. The weighed aggregate and the remaining material were then added to the blender and stirred for a further 90 seconds. The cooled alkaline activator was then added to the blender and stirred for 120 seconds. The microcapsules were added in several batches, along with the diethylenetriamine curing agent, and stirring was continued for 120 seconds. Two sets of parallel specimens were prepared for the test: the flexural strength specimens measured 40 mm × 40 mm × 160 mm, and the compressive strength specimens measured 40 mm × 40 mm × 40 mm. One set of specimens was heated in a muffle furnace at 800°C for 2 hours. After cooling naturally, compressive and flexural strength tests were performed on the other set of specimens. The compressive and flexural strength tests were performed on the other set of specimens, which were stored at room temperature. Specific data are shown in Table 1.

[0120] Comparative Example 3

[0121] Microcapsule preparation (0.5 wt % SP, 1.0 wt % SP, 1.5 wt % SP):

[0122] 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 minutes to obtain a urea-formaldehyde resin prepolymer solution.

[0123] Span 80 was mixed with deionized water at emulsifier concentrations of 0.5 wt %, 1.0 wt %, and 1.5 wt %, respectively, and stirred to obtain a Span 80 emulsifier solution. 12 g of epoxy resin E51 was added to the Span emulsifier solution. The mixed emulsion was heated to 50°C and stirred at 600 rpm for 40 minutes.

[0124] 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 the mixture was placed in a constant temperature water bath at 70°C and stirred at 600 rpm for 3 h.

[0125] The pH was adjusted to 7 with triethanolamine, rinsed with deionized water several times, and filtered to obtain finished microcapsules with a particle size of about 1 μm. The microcapsules were placed in a drying oven at 40°C and dried for 24 hours to obtain urea-formaldehyde resin-epoxy resin microcapsules.

[0126] Figure 11 The figures show TEM electron micrographs of the microcapsules prepared in this comparative example, wherein a is a TEM electron micrograph of the microcapsules prepared with 0.5% SP, b is a TEM electron micrograph of the microcapsules prepared with 1.0% SP, and c is a TEM electron micrograph of the microcapsules prepared with 1.5% SP. It can be seen from the figures that the microcapsules prepared in this example have a small amount of wall breakage and cohesion.

[0127] Geopolymer preparation:

[0128] According to the experimental mix ratio, fly ash and mineral powder were weighed and mixed thoroughly. The alkaline activator was then prepared by weighing the required amount of water glass, sodium hydroxide, and water. The mixture was cooled to room temperature. The mineral powder and fly ash were poured into a blender and stirred for 60 seconds. The weighed aggregate and the remaining material were then added to the blender and stirred for a further 90 seconds. The cooled alkaline activator was then added to the blender and stirred for 120 seconds. The microcapsules were added in several batches, along with the diethylenetriamine curing agent, and stirring was continued for 120 seconds. Two sets of parallel specimens were prepared for the test: the flexural strength specimens measured 40 mm × 40 mm × 160 mm, and the compressive strength specimens measured 40 mm × 40 mm × 40 mm. One set of specimens was heated in a muffle furnace at 800°C for 2 hours. After cooling naturally, compressive and flexural strength tests were performed on the other set of specimens. The compressive and flexural strength tests were performed on the other set of specimens, which were stored at room temperature. Specific data are shown in Table 1.

[0129] Comparative Example 4

[0130] Microcapsule preparation (0.5 wt % TW, 1.0 wt % TW, 1.5 wt % TW):

[0131] 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 minutes to obtain a urea-formaldehyde resin prepolymer solution.

[0132] Tween 80 emulsifier solutions were prepared by mixing 0.5g, 1g, and 1.5g of Tween 80 with deionized water at emulsifier concentrations of 0.5 wt%, 1.0 wt%, and 1.5 wt%, respectively. 12g of epoxy resin E51 was added to the Tween emulsifier solutions. The mixed emulsion was heated to 50°C and stirred at 600 rpm for 40 minutes.

[0133] 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 the mixture was placed in a constant temperature water bath at 70°C and stirred at 600 rpm for 3 h.

[0134] The pH was adjusted to 7 with triethanolamine, rinsed with deionized water several times, and filtered to obtain finished microcapsules with a particle size of about 1 μm. The microcapsules were placed in a drying oven at 40°C and dried for 24 hours to obtain urea-formaldehyde resin-epoxy resin microcapsules.

[0135] Figure 12The figures show TEM images of the microcapsules prepared in this comparative example, wherein a is a TEM image of the microcapsules prepared with 0.5% TW, b is a TEM image of the microcapsules prepared with 1.0% TW, and c is a TEM image of the microcapsules prepared with 1.5% TW. It can be seen from the figures that the microcapsules prepared in this example have a small amount of wall breakage and cohesion.

[0136] Geopolymer preparation:

[0137] According to the experimental mix ratio, fly ash and mineral powder were weighed and mixed thoroughly. The alkaline activator was then prepared by weighing the required amount of water glass, sodium hydroxide, and water. The mixture was cooled to room temperature. The mineral powder and fly ash were poured into a blender and stirred for 60 seconds. The weighed aggregate and the remaining material were then added to the blender and stirred for a further 90 seconds. The cooled alkaline activator was then added to the blender and stirred for 120 seconds. The microcapsules were added in several batches, along with the diethylenetriamine curing agent, and stirring was continued for 120 seconds. Two sets of parallel specimens were prepared for the test: the flexural strength specimens measured 40 mm × 40 mm × 160 mm, and the compressive strength specimens measured 40 mm × 40 mm × 40 mm. One set of specimens was heated in a muffle furnace at 800°C for 2 hours. After cooling naturally, compressive and flexural strength tests were performed on the other set of specimens. The compressive and flexural strength tests were performed on the other set of specimens, which were stored at room temperature. Specific data are shown in Table 1.

[0138] Since the HLB values ​​of Tween 80 and polyvinyl alcohol are greater than the HLB values ​​required in the preparation conditions of the present invention, the HLB value obtained after the two are compounded is much greater than the HLB value required in the preparation conditions of the present invention, making it impossible to successfully emulsify during the preparation process. Therefore, there is no need to set a comparative example of compounding Tween 80 and polyvinyl alcohol as an emulsifier.

[0139] Comparative Example 5

[0140] This comparative example serves as a blank control, without the addition of microcapsules. Fly ash and slag were weighed and mixed according to the experimental mix ratio. The alkaline activator was then prepared by weighing the required amount of water glass, sodium hydroxide, and water. The mixture was cooled to room temperature. The slag and fly ash were then poured into a blender and stirred for 60 seconds. The weighed aggregate, remaining water, and water reducer were then added to the blender and stirred for a further 90 seconds. Finally, the cooled alkaline activator was added to the blender and stirred for 120 seconds before unloading. Two sets of parallel specimens were prepared for the test: the flexural strength specimens measured 40 mm × 40 mm × 160 mm, and the compressive strength specimens measured 40 mm × 40 mm × 40 mm. One set of specimens was heated in a muffle furnace at 800°C for 2 hours. After natural cooling, compressive and flexural strength tests (residual compressive strength and flexural strength) were performed. The other set of specimens was stored at room temperature and subjected to compressive and flexural strength tests (initial compressive strength and flexural strength).

[0141] The 7d test data (800°C) of Examples 1-6 and Comparative Examples 1-5 are shown in Table 1:

[0142] Table 1

[0143]

[0144] According to the data in Table 1, after calcination at 800°C for 2 hours, the compressive strength of the specimen in Comparative Example 5, which did not incorporate microcapsules, was 8.636 MPa, and the flexural strength was 0.69 MPa. However, the specimen incorporating microcapsules (Example 1), particularly the microcapsules prepared with a Span 80 + Tween 80 emulsifier blend, achieved a maximum compressive strength of 32.164 MPa and a flexural strength of 1.393 MPa. Furthermore, Example 1 achieved a fourfold increase in compressive strength and a twofold increase in flexural strength compared to Comparative Example 5, demonstrating a highly significant repair effect. Furthermore, it can be seen that the microcapsules prepared with a single emulsifier in Comparative Examples 1-4 achieved a lower strength improvement on the geopolymer than the microcapsules prepared with a composite emulsifier in Examples 1-6. However, compared to the Comparative Examples, the microcapsules prepared with Comparative Examples 1-4 still achieved a higher strength improvement on the geopolymer than the geopolymer without microcapsules in the Comparative Examples. Among the microcapsule materials prepared by different microcapsule synthesis schemes, the microcapsule prepared with 0.5% Span80+Tween80 compound emulsifier has the most obvious lifting effect.

[0145] The above description is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principles of the present invention. These improvements and changes are also considered to be within the scope of protection of the present invention.

Claims

1. A method for self-repairing of geopolymer materials, characterized in that: The method comprises the following steps: dispersing microcapsules and a curing agent in a geopolymer matrix, and calcining at a temperature of 300-800°C until the repair is completed. The microcapsules include urea-formaldehyde resin as a wall material and epoxy resin as a core material. At 300-800°C, the urea-formaldehyde resin shell melts, and the internal epoxy resin core material is released and diffused, contacting with the curing agent mixed in the matrix to form an epoxy cured product, thereby filling the microcracks in the geopolymer generated by high temperature and bonding, completing the self-repair process. The average particle size of the microcapsules is 1-3 μm.

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

3. A method for preparing microcapsules for the self-repairing method of geopolymer materials according to claim 1 or 2, characterized in that: The following steps are involved: (1) Prepolymer preparation: Preparation of urea-formaldehyde resin prepolymer solution; (2) Emulsification stage: Mix the emulsifier and water to prepare an emulsifier solution, add the epoxy resin to the emulsifier solution, mix them evenly at a certain temperature, and obtain a mixed emulsion; (3) Addition reaction stage: the urea-formaldehyde resin prepolymer solution prepared in step (1) is mixed with the mixed emulsion prepared in step (2), the pH is adjusted, a system modifier is added, and the mixture is stirred at a certain temperature until the reaction is complete; (4) Extraction stage: After the reaction is completed, the pH is adjusted to neutral, the product is washed and filtered to obtain the finished microcapsule, and then dried to obtain urea-formaldehyde resin-epoxy resin microcapsules; In step (2), the emulsifier is prepared by compounding Span 80 with polyvinyl alcohol or Tween 80.

4. The method for preparing microcapsules for the self-repairing method of geopolymer materials according to claim 3, characterized in that: The specific steps of step (1) are as follows: urea, formaldehyde solution and water are mixed and dissolved in a mass ratio of 6-8:15-20:75-100, the pH is adjusted to 8-9, and the mixture is stirred at 70-80° C. until the reaction is complete to obtain a urea-formaldehyde resin prepolymer solution.

5. The method for preparing microcapsules for the self-repairing method 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 emulsifier is 200:12-15, and the mixing temperature is 50-60°C.

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

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

9. The method for preparing microcapsules for the self-repairing method of geopolymer materials according to claim 3, characterized in that: In step (4), the drying temperature does not exceed 60°C.

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