WO2025152374A1 - Urea-formaldehyde microcapsule shell surface modification method beneficial to toughening of epoxy composite material - Google Patents

Abstract

A urea-formaldehyde microcapsule shell surface modification method beneficial to toughening of an epoxy composite material. The method comprises: uniformly mixing polyvinyl alcohol powder with deionized water to obtain a surfactant aqueous solution; mixing deionized water with the surfactant aqueous solution, then adding urea, ammonium chloride, and resorcinol, stirring the mixture, dropwise adding a diluted hydrochloric acid solution to adjust the pH, and stirring the mixture to obtain a stable emulsion; adding a formaldehyde-urea mixed solution to the stable emulsion and stirring and heating the mixture; after the heating reaction is completed, cooling the mixture to room temperature, and carrying out vacuum filtration, washing with deionized water, filtration, and then vacuum drying to obtain a urea-formaldehyde microcapsule shell; and mixing 3-aminopropyltriethoxysilane with deionized water, dropwise adding a diluted hydrochloric acid solution to adjust the pH to obtain a modified solution, adding the urea-formaldehyde microcapsule shell to the modified solution, stirring the mixture, and then carrying out vacuum filtration and drying to obtain a urea-formaldehyde microcapsule shell with the surface modified.

Description

A method for modifying the shell surface of urea-formaldehyde microcapsules for toughening epoxy composites Technical Field

The invention belongs to the field of material science and engineering technology, and specifically relates to a surface modification method of a urea-formaldehyde microcapsule shell which is beneficial to the toughening of epoxy composite materials.

Background Art

In recent years, with the introduction of new smart materials into different application fields, polymer materials with higher reliability and longer service life have gradually attracted widespread attention. Among them, self-healing materials can autonomously repair damage caused by external conditions (such as ultraviolet radiation, chemical erosion, mechanical stress, overheating decomposition, etc.), restore their original functions, and avoid material failure caused by damage, thus greatly reducing the cost of material maintenance and repair, and have broad application prospects. Generally, in addition to modifying the internal structure of polymer materials, preparing functionalized microcapsules containing healing agents based on microencapsulation technology is one of the most commonly used practical methods to achieve external self-repair of materials. When the material is mechanically or electrically damaged, resulting in cracks inside it, as the cracks expand, the shell of the functionalized microcapsule containing the healing agent breaks. Therefore, the internal healing agent flows into the crack through capillary action and contacts the catalyst to undergo polymerization reaction to bond the crack surface, thereby restoring the integrity of the material structure. Due to the large number of core materials, it is of great significance to use the same wall material to encapsulate different self-healing core materials into microcapsules and evaluate their performance at the same time. Therefore, it is necessary to study the preparation method of the shell of the microcapsule.

At present, many scholars have conducted relevant research on microcapsule shell materials such as polyurea formaldehyde, polymelamine formaldehyde, polymethyl methacrylate, polyurethane and epoxy resin. However, polyurea formaldehyde (PUF) is still one of the most commonly used shell materials because it has high mechanical strength, high impermeability, high reactivity, chemical resistance and low cost. It has both appropriate brittleness to break when cracks appear in the substrate and can maintain a complete structure when preparing composite materials. Usually, its preparation method is to use in-situ polymerization, through certain monomers reacting in the water phase to form UF oligomers, and then depositing them on the droplets to form a cross-linked shell. Its reaction conditions are relatively mild, the method is relatively simple, and the efficiency is relatively high, which can be put into practical production applications on a large scale.

However, when microcapsules are mixed with epoxy substrates to form composite materials, their weak interfacial adhesion seriously affects the mechanical properties and self-healing efficiency of the composite materials, limiting their application potential. Therefore, it is necessary to modify the surface of the microcapsule shell to meet the needs of practical applications. In recent years, rigid inorganic nanoparticles are usually selected as fillers to solve the problem of significant decrease in the mechanical properties of composite materials caused by microcapsule doping.

The existing microcapsule shell prepared by adding rigid inorganic nanoparticles can significantly improve its mechanical strength and hardness, and improve its resistance to chemical substances (acid resistance, alkali resistance, etc.), which can be widely used in electronic packaging, dental restoration and other scenarios. However, the addition of inorganic particles will reduce the toughness and brittle fracture resistance of the composite material, making its ability to prevent crack propagation weaker, and unable to timely suppress the expansion and development of cracks, thereby reducing the repair efficiency of self-healing materials. Especially in the field of electrical insulation, the self-repair of mechanical and electrical damage of composite materials for high-voltage equipment is of great significance. Therefore, in order to achieve timely response of microcapsules in damage self-repair, it is necessary to study the improvement of the toughness of the microcapsule shell.

Summary of the invention

The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

In view of the above problems and/or the problems existing in the prior art, the present invention is proposed.

Therefore, the object of the present invention is to overcome the deficiencies in the prior art and provide a method for modifying the shell surface of urea-formaldehyde microcapsules which is beneficial to the toughening of epoxy composite materials.

In order to solve the above technical problems, the present invention provides the following technical solutions: a method for modifying the surface of urea-formaldehyde microcapsule shells which is beneficial to the toughening of epoxy composite materials, characterized in that: it comprises:

The polyvinyl alcohol powder is evenly mixed with deionized water to obtain a surfactant aqueous solution;

After deionized water and surfactant aqueous solution are mixed, urea, ammonium chloride and resorcinol are added and stirred, and diluted hydrochloric acid solution is dropped into the mixture to adjust the pH, and a stable emulsion is obtained by stirring.

Adding formaldehyde-urea mixed solution into the stable emulsion and stirring and heating;

After the heating reaction is completed, the reaction is cooled to room temperature, vacuum filtered, washed with deionized water, filtered, and vacuum dried to obtain the urea-formaldehyde microcapsule shell;

3-Aminopropyltriethoxysilane is mixed with deionized water, and a diluted hydrochloric acid solution is added dropwise to adjust the pH to obtain a modified solution. The urea-formaldehyde microcapsule shell is added to the modified solution, stirred, vacuum filtered, and dried to obtain a urea-formaldehyde microcapsule shell after surface modification.

As a preferred embodiment of the preparation method of the present invention, the polyvinyl alcohol powder is evenly mixed with deionized water to obtain a surfactant aqueous solution, wherein the mass ratio of the polyvinyl alcohol powder to the deionized water is 1:19, and the mass fraction of the surfactant aqueous solution is 5%.

As a preferred embodiment of the preparation method of the present invention, wherein: the deionized water and the surfactant After the surfactant aqueous solution is mixed, urea, ammonium chloride and resorcinol are added and stirred, and a diluted hydrochloric acid solution is dropped into the solution to adjust the pH value, and a stable emulsion is obtained by stirring, wherein the volume ratio of deionized water to the surfactant aqueous solution is 10-15:0.4-0.6, and the mass ratio of urea, ammonium chloride and resorcinol is 10:1:1.

As a preferred embodiment of the preparation method of the present invention, the diluted hydrochloric acid solution is added dropwise to adjust the pH, and the stable emulsion is obtained by stirring, wherein the mass fraction of the diluted hydrochloric acid solution is 1wt% to 1.5wt%, the pH is adjusted to 2.5 to 3.5, the stirring rate is 300 to 400 r/min, and the time is 10 to 15 min.

As a preferred embodiment of the preparation method of the present invention, wherein: a formaldehyde-urea mixed solution is added to the stable emulsion and stirred and heated, wherein the molar mass ratio of formaldehyde to urea is 2.79-2.83:1.

As a preferred embodiment of the preparation method of the present invention, the heating temperature is 80-90° C., the heating time is 3.5-4.5 h, and the stirring rate is 100-200 r/min.

As a preferred embodiment of the preparation method of the present invention, the urea-formaldehyde microcapsule shell is obtained by washing with deionized water, filtering and vacuum drying, wherein the washing times are 3 to 4 times, the vacuum drying temperature is 30 to 40°C, and the time is 48 to 72 hours.

As a preferred embodiment of the preparation method of the present invention, the 3-aminopropyltriethoxysilane is mixed with deionized water, and a diluted hydrochloric acid solution is added dropwise to adjust the pH to obtain a modified liquid, and the urea-formaldehyde microcapsule shell is added to the modified liquid, stirred, vacuum filtered, and dried to obtain a urea-formaldehyde microcapsule shell after surface modification, wherein the volume ratio of 3-aminopropyltriethoxysilane to deionized water is 2:98, and the mass fraction of the modified liquid is 2-5%.

As a preferred embodiment of the preparation method of the present invention, the modified liquid is obtained by dropping a diluted hydrochloric acid solution to adjust the pH, wherein the mass fraction of the diluted hydrochloric acid solution is 1wt% to 1.5wt%, and the pH is adjusted from 10 to 11 to 7.

As a preferred embodiment of the preparation method of the present invention, the urea-formaldehyde microcapsule shell is added to the modified liquid, stirred, vacuum filtered and dried to obtain the urea-formaldehyde microcapsule shell after surface modification, wherein the stirring temperature is 80-90°C, the speed is 100-200 r/min and the time is 1-1.5h.

Beneficial effects of the present invention:

(1) The present invention modifies the shell of urea-formaldehyde microcapsule to reveal the toughening mechanism of the microcapsule composite material after doping and modification, provides a method for modifying the shell of urea-formaldehyde microcapsule which is beneficial to the toughening of epoxy composite material, and provides a feasible solution for inhibiting damage of composite material and improving self-repair efficiency.

(2) The present invention prepares a urea-formaldehyde microcapsule shell by an in-situ polymerization method, and performs surface The silane coupling agent used in the preparation process increases the surface roughness of the microcapsules by connecting with the surface of the microcapsules, thereby improving the interface interaction between the microcapsules and the polymer matrix, and further enhancing the fracture toughness of the composite material.

(3) The present invention adopts an in-situ polymerization method to prepare a urea-formaldehyde microcapsule shell sample and performs surface modification treatment on it. The basic principle is to uniformly mix the urea-formaldehyde resin mixture with the aqueous phase, and add an appropriate amount of emulsifier to form a stable emulsion, and then adjust the temperature, pH and other conditions to make the above emulsion undergo a cross-linking reaction, thereby forming a solid shell layer.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

FIG1 is a schematic diagram of the urea-formaldehyde (UF) dimer reaction according to Example 1 of the present invention.

FIG. 2 is a schematic diagram of the preparation and surface modification of the urea-formaldehyde microcapsule shell in Example 1 of the present invention.

FIG. 3 is a SEM image of the shell of the urea-formaldehyde microcapsule before and after functionalization with a silane coupling agent in Example 1 of the present invention.

FIG. 4 is a graph showing the particle size distribution of urea-formaldehyde microcapsules before and after functionalization with a silane coupling agent in Example 1 of the present invention.

FIG. 5 is an FT-IR image of urea-formaldehyde microcapsules before and after functionalization with a silane coupling agent in Example 1 of the present invention.

FIG6 is a fracture toughness curve of the urea-formaldehyde microcapsule composite material before and after modification with different mass fractions of doping in Example 2 of the present invention.

FIG. 7 is a fracture toughness curve of the modified urea-formaldehyde microcapsule composite material doped with different mass fractions according to Example 2 of the present invention.

DETAILED DESCRIPTION

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

The manufacturers and purities of the chemical reagents used in the preparation of the urea-formaldehyde microcapsule shell samples and the modification treatment thereof in the method of the present invention are shown in Table 1:

Table 1:

The models and manufacturers of the main experimental instruments for preparing the urea-formaldehyde microcapsule shell samples in the method of the present invention are shown in Table 2:

Table 2:

Example 1

The present invention provides a urea-formaldehyde microcapsule shell surface modification method that is beneficial to the toughening of epoxy composite materials Law:

(1) Preparation of surfactant solution

190 g of deionized water and 10 g of polyvinyl alcohol (PVA) powder were weighed and mixed in a 400 mL beaker to obtain a surfactant aqueous solution with a mass fraction of 5%, so as to promote better mixing and dispersion of the urea-formaldehyde resin and the aqueous phase.

(2) Forming a stable emulsion

Add 130 mL of deionized water and 5 mL of the surfactant aqueous solution prepared in (1) into a 400 mL beaker, and set the speed of the CNC magnetic stirrer to 200 r/min at room temperature to mix them thoroughly. Weigh 3.5 g of urea (as a reaction monomer), 0.35 g of ammonium chloride (as an initiator) and 0.35 g of resorcinol (as a cross-linking agent). Under stirring conditions, slowly add the weighed solid shell-forming material to the above aqueous solution, stir evenly, then add 1 wt% hydrochloric acid solution (diluted) dropwise thereto, adjust the pH value of the mixed solution to 3, set the speed to 350 r/min, stir for 15 minutes, and allow the mixed solution to stabilize into an emulsion under vigorous stirring.

(3) Reaction to form shell

Weigh 93 mL of 37% formaldehyde solution. After a stable emulsion is formed in (2), add the formaldehyde solution thereto. Set the temperature of the CNC magnetic stirrer to 85°C and the speed to 200 r/min. Slowly heat for 4 h to allow it to fully react to form a shell.

(4) Washing and drying

After the reaction, the suspension was cooled to room temperature and vacuum filtered. The shell of the filtered urea-formaldehyde microcapsule was repeatedly rinsed with deionized water for 3 times to remove impurities and stored in a vacuum drying oven at 35° C. for 48 hours.

(5) Surface modification

Weigh 2 mL 3-aminopropyltriethoxysilane (silane coupling agent) and 98 mL deionized water, mix them evenly, and prepare a modified solution with a mass fraction of 2% and a pH value of 11. Add 1 wt% hydrochloric acid solution (diluted) to adjust the pH value of the modified solution to 7. Next, take the dried microcapsules in (4), add them to the prepared modified solution, set the temperature of the CNC magnetic stirrer to 80°C, the speed to 200 r/min, and stir for 1 hour. After stirring, the suspension is vacuum filtered and dried again to finally obtain the urea-formaldehyde microcapsule shell after surface modification.

The dried urea-formaldehyde microcapsule shell sample (Example 1) was placed on a sample stand, and was sprayed with platinum to prepare a sample. Then, a scanning electron microscope (SEM) was used to observe its microscopic morphology. The SEM images of the urea-formaldehyde microcapsule shell before and after functionalization with the silane coupling agent are shown in Figure 3. It can be seen from the figure that the entire microcapsule presents a relatively full spherical shape before and after surface modification, the particle size is relatively uniform, the appearance is relatively complete, and there is no damage. By comparing the SEM images before and after the modification, it can be seen that after the microcapsule shell is surface-modified, the silane coupling agent adheres to the surface of the microcapsule and forms a connection structure with its surface, so that the surface roughness increases and is covered with a thin layer. The increase in the surface roughness of the microcapsule is conducive to the formation of covalent bonds when doped into the polymer matrix, thereby improving the interfacial adhesion with the matrix and improving the toughness and other mechanical properties of the composite material. Figure 1 is a schematic diagram of the urea-formaldehyde (UF) dimer reaction in Example 1 of the present invention. Figure 2 is a schematic diagram of the preparation and surface modification of the urea-formaldehyde microcapsule shell in Example 1 of the present invention.

Example 2

In order to study the enhancing effect of the prepared modified urea-formaldehyde microcapsule shell on the toughness of the composite material when doped into the polymer matrix, it can be embedded in the epoxy matrix with different loading amounts (0.2wt%, 0.5wt%, 1.0wt%) to form epoxy composite materials, and the fracture toughness of the composite material is determined by a three-point bending test using an electronic universal testing machine.

By plotting the critical stress intensity factor curve under different microcapsule loadings, the change in the fracture toughness of the microcapsule composite material before and after doping and modification can be obtained, as shown in Figure 6. As can be seen from the figure, the fracture toughness of the composite material first increases and then decreases with the increase of microcapsule concentration, and there is a peak value at a lower loading rate doping concentration. At the same time, compared with pure epoxy resin and epoxy composites doped with unmodified microcapsules, the composite material doped with functionalized microcapsules has a higher fracture toughness value, that is, a stronger ability to resist brittle fracture, so that it can no longer break quickly with the increase of load when the composite material is damaged by cracks due to various internal and external factors, thus laying the foundation for material self-repair.

Comparative Example 1

CN 110511727 A A method for preparing a double-layer shell phase-change microcapsule, comprising the following steps:

1) 3 g of gum arabic was evenly dispersed in 100 g of water to prepare an emulsifier solution, and then 25 g of paraffin PCM35 (phase transition temperature 35° C.) and 3 g of HDI were evenly mixed and added to the emulsifier solution, the stirring speed was controlled to 1200 rpm, and the mixture was stirred at a constant temperature of 40° C. for 20 min to obtain an oil-in-water emulsion;

2) 6 g of tetraethylenepentamine was dispersed in water and then added to the oil-in-water emulsion, the stirring speed was controlled to 600 rpm, the mixture was stirred at a constant temperature of 60° C. for 50 min, and then filtered and washed with water to obtain single-layer shell phase change microcapsules;

3) adding 8 g of urea to 20 g of a 37% formaldehyde solution, adjusting the pH value to 8.5, controlling the stirring speed to 400 rpm, and stirring at a constant temperature of 65° C. for 50 min to obtain urea-formaldehyde oligomers;

4) Add 3g of polyethylene-maleic anhydride copolymer and 3g of resorcinol to 150g of water and disperse evenly Then add urea-formaldehyde oligomer, adjust the pH value to 3.3, add single-layer shell phase change microcapsules, control the stirring speed to 400 rpm, stir at a constant temperature of 52°C for 100 minutes, then filter, wash with water, and dry to obtain double-layer shell phase change microcapsules.

Comparative Example 2

CN1298420C Preparation method of polyurea-urea-formaldehyde resin double-layer microcapsule

Add 1.46g of triethylenetetramine to a 100mL three-necked flask, then add 50mL of water and heat to 90°C. Take 1.00g of 50% glutaraldehyde and dilute to 40mL, add dropwise to the three-necked flask, stir, and react for 3 hours to obtain a dialdehyde-modified triethylenetetramine aqueous solution.

Take 10 mL of tetrachloroethylene, add 0.1 g of OP-10 and 0.32 g of 1,4-toluene diisocyanate, add the tetrachloroethylene oil phase into a 250 mL three-necked flask containing 40 mL of water, stir at 800 rpm for 1 minute, add 20 mL of glutaraldehyde-modified triethylenetetramine aqueous solution, react for 5 minutes, reduce the stirring speed to 400 rpm, stop stirring after 10 minutes, filter, wash with deionized water until neutral, and obtain polyurea microcapsules.

Take 6g of polyurea microcapsules, add them to a 100mL three-necked flask containing 40mL of water, add 1.5g of urea, and after dissolving, add 1M hydrochloric acid to adjust the pH value to 2.0, heat to 70°C with stirring at 40rpm, add 3g of 37% formaldehyde, react for 3 hours, filter, wash with deionized water until neutral, and dry at room temperature to obtain polyurea-urea-formaldehyde resin double-layer microcapsules.

The idea of the scheme of the present invention is to first add a surfactant aqueous solution to activate the microcapsule during the shell formation process, and then treat it with a modifier after the microcapsule shell is successfully formed. This is a different technical route from the second point of first modifying and then activating.

Comparative Example 1 only involves the reaction of urea-formaldehyde oligomers, polyphenols, etc., and does not involve the addition of surfactant aqueous solution. The two have different reaction conditions and situations due to the addition of new materials. The modification method is to treat the surface of the microcapsule, while Comparative Example 2 is modified by chemical reaction of the internal core material.

Comparative Example 3

The difference from Example 1 is that no modification treatment is performed in step (5).

Since the size of microcapsules has an important influence on their doping performance, it is necessary to study the particle size distribution of the samples. The particle size distribution before and after modification is shown in Figure 4. The results show that functional surface modification treatment will increase the size of microcapsules. However, due to the diffusion of silane bonds, the dispersion of microcapsules is improved, and the interaction between microcapsules effectively controls the occurrence of agglomeration.

The absorption FT-IR spectra of urea-formaldehyde microcapsules before and after functionalization are shown in Figure 5. The characteristic absorption peaks of groups such as -CH, -C, =O and -CN were found, which indicated that urea-formaldehyde resin had been formed. After adding the silane coupling agent, the peak near 2900cm-1 of the microcapsule became wider, indicating that the silane coupling agent had been bound to the surface of the UF microcapsule. To further confirm, the chemical element composition analysis of the sample showed that there was no Si element in the unfunctionalized microcapsule, while Si element was detected in the functionalized microcapsule. The obtained data fully confirmed that the silane molecules had been successfully attached to the surface of the urea-formaldehyde microcapsule to modify it.

Comparative Example 4

The difference from Example 1 is that the concentration of the modified solution in step (5) (mixture concentration of 3-aminopropyltriethoxysilane (silane coupling agent) and deionized water) is 1%.

Comparative Example 5

The difference from Example 1 is that the concentration of the modified solution in step (5) (mixture concentration of 3-aminopropyltriethoxysilane (silane coupling agent) and deionized water) is 6%.

The concentration of the modifying liquid affects the fracture toughness of the epoxy composite material. As the content of the silane coupling agent increases, the impact energy of the epoxy composite material gradually increases, but the microcapsule loading rate with the highest fracture toughness also increases accordingly; as shown in Figure 7, in the composite materials with functionalization rates of 1wt%, 2wt%, 5wt% and 6%, the impact energy of the composite material filled with 0.2wt% microcapsules is 1.4J/m, 2.8J/m, 3.7J/m, and 4.0J/m, respectively. The higher the impact energy, the less likely the material is to undergo brittle fracture. Therefore, it can be concluded that the functionalization of urea-formaldehyde microcapsules improves the impact behavior. However, since the fracture toughness improvement is low when the functionalization rate is 1wt%, and the microcapsule loading rate is greatly increased when the functionalization rate is 6wt%, its mechanical properties are affected. According to Example 2 and Comparative Examples 4/5, it can be seen that the modifying liquid concentration range with a functionalization rate of 2-5wt% and the addition of a small amount of silane coupling agent can improve the fracture toughness of the composite material with little effect on the mechanical properties. This toughening effect is due to the surface interaction between the modified urea-formaldehyde microcapsules and the matrix, which increases the energy required for fracture and improves the impact strength.

Comparative Example 6

The difference from Example 1 is that no surfactant solution is added in step (1).

In the final experimental results, due to the lack of addition of surfactant solution, the urea-formaldehyde resin was unevenly dispersed or locally over-aggregated, which reduced the stability of the formed emulsion. On the one hand, it led to uneven size distribution of the microcapsules and large size differences; on the other hand, the wall thickness of the microcapsules was unstable, relatively weak, and easily broken or dissolved, thus affecting its mechanical properties.

It should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not intended to limit the present invention. The present invention has been described in detail according to the preferred embodiments. Those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the present invention.

Claims (10)

A method for modifying the shell surface of urea-formaldehyde microcapsules for toughening epoxy composite materials, characterized in that: comprising: The polyvinyl alcohol powder is evenly mixed with deionized water to obtain a surfactant aqueous solution; After deionized water and surfactant aqueous solution are mixed, urea, ammonium chloride and resorcinol are added and stirred, and diluted hydrochloric acid solution is dropped into the mixture to adjust the pH, and a stable emulsion is obtained by stirring. Adding formaldehyde-urea mixed solution into the stable emulsion and stirring and heating; After the heating reaction is completed, the product is cooled to room temperature, vacuum filtered, washed with deionized water, filtered, and vacuum dried to obtain the urea-formaldehyde microcapsule shell; 3-Aminopropyltriethoxysilane is mixed with deionized water, and a diluted hydrochloric acid solution is added dropwise to adjust the pH to obtain a modified solution. The urea-formaldehyde microcapsule shell is added to the modified solution, stirred, vacuum filtered, and dried to obtain a urea-formaldehyde microcapsule shell after surface modification. The preparation method according to claim 1 is characterized in that: the polyvinyl alcohol powder and deionized water are evenly mixed to obtain a surfactant aqueous solution, wherein the mass ratio of the polyvinyl alcohol powder to the deionized water is 1:19, and the mass fraction of the surfactant aqueous solution is 5%. The preparation method according to claim 1 is characterized in that: after the deionized water and the surfactant aqueous solution are mixed, urea, ammonium chloride and resorcinol are added and stirred, and a diluted hydrochloric acid solution is dropped into the solution to adjust the pH, and a stable emulsion is obtained by stirring, wherein the volume ratio of deionized water to the surfactant aqueous solution is 10 to 15:0.4 to 0.6, and the mass ratio of urea, ammonium chloride and resorcinol is 10:1:1. The preparation method according to claim 3 is characterized in that: the diluted hydrochloric acid solution is dripped to adjust the pH, and the stable emulsion is obtained by stirring, wherein the mass fraction of the diluted hydrochloric acid solution is 1wt% to 1.5wt%, the pH is adjusted to 2.5 to 3.5, the stirring rate is 300 to 400 r/min, and the time is 10 to 15 min. The preparation method according to claim 1 is characterized in that: the formaldehyde-urea mixed solution is added to the stable emulsion and stirred and heated, wherein the formaldehyde-urea molar mass ratio is 2.79-2.83:1. The preparation method according to claim 5 is characterized in that: the heating temperature is 80-90°C, the heating time is 3.5-4.5h, and the stirring rate is 100-200r/min. The preparation method according to claim 1 is characterized in that: the urea-formaldehyde microcapsule shell is obtained by washing with deionized water, filtering and vacuum drying, wherein the washing number is 3 to 4 times, the vacuum drying temperature is 30 to 40°C, and the time is 48 to 72 hours. The preparation method according to claim 1 is characterized in that: the 3-aminopropyltriethoxysilane is mixed with deionized water, a diluted hydrochloric acid solution is added dropwise to adjust the pH to obtain a modified solution, and the urea-formaldehyde microcapsule shell is The modified liquid is added, stirred, vacuum filtered and dried to obtain the urea-formaldehyde microcapsule shell after surface modification, wherein the volume ratio of 3-aminopropyltriethoxysilane to deionized water is 2:98, and the mass fraction of the modified liquid is 2-5%. The preparation method according to claim 8 is characterized in that: the modified liquid is obtained by dropping a diluted hydrochloric acid solution to adjust the pH, wherein the mass fraction of the diluted hydrochloric acid solution is 1wt% to 1.5wt%, and the pH is adjusted from 10 to 11 to 7. The preparation method as described in claim 8 is characterized in that: the urea-formaldehyde microcapsule shell is added to the modified liquid, stirred, vacuum filtered, and dried to obtain the urea-formaldehyde microcapsule shell after surface modification, wherein the stirring temperature is 80-90°C, the speed is 100-200r/min, and the time is 1-1.5h.