A Polyaniline Double-Layer Microcapsule with Barrier Performance

Abstract

The invention discloses a preparation method of a polyaniline double-layer microcapsule with high barrier performance, belonging to the field of microcapsule preparation. The invention uses photocuring to prepare a monolayer sulfonated photocurable resin microcapsule in one step. Through the electrostatic interaction between sulfonic acid groups and aniline, aniline is adsorbed onto the surface of the microcapsule, and aniline polymerization is initiated to polymerize a dense polyaniline shell layer on the surface of the photocured microcapsule, obtaining a polyaniline / photocurable resin double-layer shell microcapsule; the polyaniline microcapsule has excellent solvent resistance, thermal stability and mechanical properties; the method has a wide application range, is simple and easy to operate, has a fast preparation speed, and is carried out at room temperature, and can be used to coat different core materials; it has broad application prospects in the fields of anti-corrosion materials, self-healing materials, coating materials, cosmetic preparations, drugs, agrochemicals, cleaners, etc.

Description

Technical Field

[0001] The present invention relates to the field of preparation of microcapsules, and particularly to a method for preparing a polyaniline double-layer microcapsule with high barrier performance. Background Art

[0002] A microcapsule refers to a micro-container having a polymer shell layer for encapsulating an active substance (liquid, gas or solid). Microcapsules usually consist of two parts: a core material (inside) and a shell layer (outside). The core material is an active substance (such as dyes, monomers, catalysts, curing agents, flame retardants, plasticizers and nanoparticles), and the shell layer that plays a role in protecting the core material is usually a polymer.

[0003] Microcapsules can isolate the active substance from the external environment, prevent the active substance from being oxidized or inactivated, and at the same time can control the release of the active substance or localize the release of the active substance. Therefore, they are widely used in the fields of medicine, agriculture, construction, chemical industry, food, biotechnology, cosmetics, electronics, textiles and printing. For example, in biomedical research, the excellent encapsulation effect and controlled release characteristics of microcapsules give them unique advantages in drug delivery; in the food field, the survival rate of probiotics encapsulated in microcapsules during processing is greatly improved. In the cosmetics field, the stability and bioavailability of vitamins, sunscreen agents, moisturizers and fragrances encapsulated in microcapsules are greatly enhanced.

[0004] In practical applications, microcapsules need to have sufficient encapsulation stability to ensure that the core material does not leak during storage and manufacturing. In the actual application of microcapsules, solvents or high temperatures can damage the shell layer of the microcapsules and greatly accelerate the release rate of the core material. For example, in the preparation process of self-healing composites, the processing temperature is relatively high (>100 °C), which makes the self-healing agent easily diffuse into the polymer matrix, resulting in a decrease in the self-healing efficiency. Many organic solvents are used in the coating field, which causes the swelling and damage of the microcapsule shell layer. In addition to thermal stability and solvent resistance, microcapsules should also have good mechanical properties. Although microcapsules must rupture under specific conditions, during conventional operations such as high-speed stirring and filtration, microcapsules should not rupture prematurely. Based on the above discussion, therefore, microcapsules should have sufficient mechanical, thermal and solvent stability at the same time.

[0005] So far, the vast majority of microcapsule shell layers are polymers, such as urea-formaldehyde resin, melamine resin, polyurethane, polystyrene, etc. However, due to the relatively poor barrier properties of polymer microcapsules to water, oxygen and organic small molecules, they cannot effectively encapsulate the core material for a long time under harsh conditions. In recent years, double-layer microcapsules have been proposed to solve this problem. For example, double-layer UF / PU microcapsules are synthesized by condensation of urea-formaldehyde (UF) resin on the surface of polyurethane (PU) microcapsules, and the thermal stability of UF / PU microcapsules is greatly enhanced.

[0006] Aniline is composed of two parts, a benzene ring and an amino group, and polymerization occurs immediately after the addition of an initiator. The π-π stacking and hydrogen bonds in polyaniline make it a dense film, and it has remarkable heat resistance and solvent resistance. Therefore, can a dense and uniform polyaniline coating be deposited on the microcapsules to effectively prevent the core material from being released from the microcapsules at high temperatures and in solvents? In addition to improving thermal stability and solvent stability, the presence of the polyaniline coating can also significantly improve the mechanical properties of the microcapsules.

[0007] Referring to the solution disclosed in CN 110484088 A, due to the fast curing speed of ultraviolet light irradiation, the polymer after photocrosslinking cannot quickly migrate to the surface of the microcapsules, making the microcapsules very thin and resulting in poor barrier performance of the obtained microcapsules. In addition, after the emulsion is photocured, a large amount of free sulfonate emulsifiers will adsorb a large amount of aniline to occur homogeneous polymerization in the aqueous phase, resulting in a large amount of free polyaniline in the aqueous phase, which is mixed with the polyaniline double-layer microcapsules, making it difficult to separate and purify the microcapsules. Therefore, there is still a lack of a method that is both simple and convenient and efficient for preparing a polyaniline double-layer microcapsule with high barrier performance. Summary of the Invention

[0008] In view of this, the applicant has invented a method for preparing a polyaniline double-layer microcapsule with high barrier performance. The excellent chemical stability and weather resistance of polyaniline and other advantages make polyaniline also a microcapsule with excellent solvent resistance, thermal stability and mechanical properties. Therefore, this method has a wide range of applications and is simple and easy to implement; it has broad application prospects in the fields of anticorrosive materials, self-healing materials, cosmetic preparations, drugs, household products, agricultural chemicals, cleaning agents, etc.

[0009] A method for preparing a polyaniline double-layer microcapsule with barrier performance, characterized in that the method comprises the following steps:

[0010] Step 1: Mix a photocurable resin, a core material, a crosslinking agent, a solvent and a photoinitiator evenly to form an oil phase, mix the oil phase with an aqueous phase containing a stabilizer to form a stable emulsion, and continuously stir or heat the emulsion to completely remove the solvent, so that the photocurable resin, the crosslinking agent and the core material are separated;

[0011] Step 2: Add sodium styrene sulfonate to the aqueous phase and stir. The emulsion is cured under UV irradiation, and the unreacted sodium styrene sulfonate is removed by washing with deionized water to prepare a single-layer sulfonated microcapsule;

[0012] Step 3: Drop aniline into the aqueous dispersion of the sulfonated microcapsules, continuously stir to make the aniline completely adsorbed on the surface of the microcapsules, and then add an initiator under ice bath conditions to initiate the polymerization of aniline. After washing, a polyaniline double-layer microcapsule is obtained;

[0013] The photocurable resin and the core material are immiscible with each other; the solvent has a boiling point below 80°C and is a good solvent for the photocurable resin.

[0014] The originally immiscible photocurable resin and core material form a homogeneous oil phase under the action of a co-solvent, and can be dispersed into the water phase to prepare homogeneous emulsion droplets. After the co-solvent has completely volatilized, the originally incompatible core material, photocurable resin, and cross-linking agent will phase-separate, and the polymer shell layer will gradually migrate to the oil-water interface as the solvent volatilizes, forming a phase-separated emulsion, as Figure 15 shown.

[0015] In one embodiment, the mass ratio of the photocurable resin to the core material in step one is 5:1 to 1:5,

[0016] the cross-linking agent is 5wt% - 50wt% of the photocurable resin,

[0017] the solvent is 3 - 8 times the mass of the photocurable resin; the photoinitiator is 1wt% - 10wt% of the total mass of the photocurable resin and the cross-linking agent.

[0018] In one embodiment, the mass ratio of the oil phase to the water phase in step two is 1:10 to 2:1, the stabilizer concentration is 0.5wt% - 6wt%, and the mass ratio of sodium styrene sulfonate to the photocurable resin is 1:2 to 1:8.

[0019] In one embodiment, the mass ratio of aniline to sulfonated microcapsules in step three is 1:16 to 4:1, and the molar ratio of the initiator to aniline is 1:2 to 4:1.

[0020] In one embodiment, the photocurable resin is one or more of polyurethane acrylate, polyester acrylate, and epoxy acrylate;

[0021] the cross-linking agent is one or more of tetrapropylene glycol diacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, bisphenol A glycidyl dimethacrylate, dipropylene glycol dimethacrylate, dipentaerythritol hexaacrylate, diethylene glycol phthalate diacrylate, neopentyl glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, dipropylene glycol diacrylate, 1,3-butanediol diacrylate;

[0022] the solvent has a low boiling point and is a good solvent for the photocurable resin, preferably one or more of dichloromethane, chloroform, carbon tetrachloride, ethyl acetate, and butyl acetate;

[0023] The stabilizer is one or more of polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polystyrene-maleic anhydride copolymer, polyethylene-maleic anhydride copolymer, polyoxyethylene-polyoxypropylene-polyoxyethylene triblock polymer, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, cetyltrimethylammonium bromide, Span-80, Span-60, Tween-80, Tween 60, monoglyceride fatty acid glycerol ester, N-dodecyldimethylamine, and arabic gum;

[0024] The photoinitiator in step one is one or more of 2-hydroxy-methylphenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholin-1-one, benzoin dimethyl ether, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, isopropylthioxanthone, ethyl 4-(N,N-dimethylamino)benzoate, benzophenone, 4-chlorobenzophenone, methyl o-benzoylbenzoate, diphenyliodonium hexafluorophosphate, isooctyl 4-(N,N-dimethylamino)benzoate, 4-methoxybenzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and ethyl 2,4,6-trimethylbenzoyl phenylphosphonate;

[0025] The initiator in step three is one or any mixture of several of ammonium persulfate, potassium persulfate, hydrogen peroxide, and potassium permanganate.

[0026] In one embodiment, the core material in step one is one or more of a self-healing agent, a warning agent, and a lubricant;

[0027] The initiator in step three is one or any mixture of several of ammonium persulfate, potassium persulfate, hydrogen peroxide, and potassium permanganate.

[0028] In one embodiment, the self-healing agent includes one or any mixture of several of isocyanate, linseed oil, tung oil, and epoxy resin.

[0029] In one embodiment, the warning agent includes one or any mixture of several of 8-hydroxyquinoline, phenanthroline, 2,7-dichlorofluorescein, and benzoquinone.

[0030] In one embodiment, the lubricant includes one or any mixture of several of linseed oil, tung oil, and palm oil.

[0031] The second object of the present invention is to provide a microcapsule, the prepared microcapsule has a particle size of 10-200 μm, the shell thickness is 5-80% of the microcapsule particle size, and the shell thickness is preferably 10-50% of the microcapsule particle size.

[0032] The third object of the present invention is to provide an application of microcapsules, and the application fields of the microcapsules include anti-corrosion materials, self-healing materials, cosmetic preparations, drugs, household products, agrochemicals, and cleaning agents.

[0033] Beneficial effects:

[0034] First of all, in the present invention, phase separation occurs during the solvent removal process of the photocurable resin, crosslinking agent, and core material, which greatly increases the time for the polymer to migrate to the oil-water interface. Finally, the obtained photocurable resin shell layer is relatively thick, and the shell layer thickness of the microcapsules can be highly adjustable by adjusting the mass ratio of the core material to the photocurable resin. In addition, the present invention uses reactive sodium styrene sulfonate to prepare sulfonated microcapsules instead of conventional sulfonates. Sodium styrene sulfonate can be directly and stably grafted into the photocurable resin shell layer through covalent bonds. There is no free sulfonate in the sulfonated microcapsule dispersion after washing. Therefore, it will not adsorb a large amount of aniline and undergo homogeneous polymerization in the aqueous phase, and there is no free polyaniline in the aqueous phase. The preparation schematic diagram is as Figure 3 shown. Description of the drawings

[0035] Figure 1 SEM photographs of the polyaniline microcapsules prepared in Comparative Example 1 (a is a complete polyaniline microcapsule; b is a broken polyaniline microcapsule)

[0036] Figure 2 Ultra-depth-of-field microscope photograph of the polyaniline microcapsules prepared in Comparative Example 1

[0037] Figure 3 Schematic diagram for the preparation of the polyaniline double-layer microcapsules of the present invention

[0038] Figure 4 SEM photographs of the polyaniline double-layer microcapsules prepared in Example 1

[0039] Figure 5 TGA curve of the polyaniline double-layer microcapsules prepared in Example 1

[0040] Figure 6 TGA curve of the polyaniline double-layer microcapsules prepared in Example 1 at 250 °C

[0041] Figure 7 Solvent barrier property of the polyaniline double-layer microcapsules prepared in Example 1 in tetrahydrofuran

[0042] Figure 8 Solvent barrier property of the polyaniline double-layer microcapsules prepared in Example 2 in cyclohexane

[0043] Figure 9Super-depth-of-field images of the polyaniline double-layer microcapsules prepared in Example 2 immersed in acetone for different times

[0044] Figure 10 SEM photos of the polyaniline double-layer microcapsules prepared in Example 2 after being immersed in acetone (A is single-layer microcapsules; B is polyaniline double-layer microcapsules)

[0045] Figure 11 SEM photos of the polyaniline double-layer microcapsules prepared in Example 3

[0046] Figure 12 Super-depth-of-field photos of the polyaniline double-layer microcapsules prepared in Example 3 after being dispersed in waterborne coatings

[0047] Figure 13 Mechanical properties of the polyaniline double-layer microcapsules prepared in Example 3 characterized by nanoindentation

[0048] Figure 14 Solvent barrier property of the polyaniline double-layer microcapsules prepared in Example 3 in ethyl acetate

[0049] Figure 15 Fluorescence microscope photos before and after emulsion phase separation Detailed implementation manners

[0050] The present invention will be further described below through examples

[0051] Thermal stability detection method: Use a thermogravimetric analyzer (TGA / 1100SF) to characterize the thermal stability of the microcapsules. Heat the sample from 50 °C to 800 °C in an oxygen atmosphere at a heating rate of 20 °C / min, and at the same time record the weight loss during the 60-minute isothermal process at 250 °C in an oxygen atmosphere

[0052] Solvent barrier property test method: At room temperature, seal 1000 mL of solvent and 1 wt% microcapsules well in a 1000 mL vial. After a certain time, quickly extract the microcapsules from the solvent. After heating the microcapsules at 70 °C for 2 h, record the weight of the microcapsules. Finally, the relative release percentage of the core material can be simply calculated as follows

[0053] Core material release % = (m1 - m2) / m1 / core material percentage × 100%

[0054] m1 is the initial weight of the microcapsules, and m2 is the remaining weight of the microcapsules after being immersed in different solvents

[0055] The mechanical property test method is as follows: Use a nanoindenter (Agilent, G200) with a cylindrical plate indenter having a diameter of 215 μm (Poisson's ratio is 0.07, modulus is 1141 GPa) to test the mechanical properties of the photocurable resin and the polyaniline double-layer microcapsules. The depth is set to 500 nm and the force is 500 μN. Calculate the reduced modulus and hardness using the classical Hertz contact theory, and calculate the average value of three tests.

[0056] In the present invention, first, phase separation occurs during the solvent removal process of the photocurable resin, crosslinking agent, and core material, greatly increasing the time for the polymer to migrate to the oil-water interface. Finally, the obtained photocurable resin shell layer is relatively thick, and the shell layer thickness of the microcapsules can be highly adjustable by adjusting the mass ratio of the core material to the photocurable resin. The preparation method of the polyaniline double-layer microcapsules of the present invention is shown in Figure 3 。

[0057] Example 1

[0058] Step 1: Mix the photocurable resin epoxy acrylate and the core material linseed oil at a mass ratio of 4:1, the crosslinking agent 1,6-hexanediol diacrylate is 10 wt% of the epoxy acrylate, the solvent dichloromethane is 4 times the mass of the epoxy acrylate, and the photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide is 2 wt% of the total mass of the epoxy acrylate and 1,6-hexanediol diacrylate. After mixing evenly, it is used as the oil phase;

[0059] Mix the oil phase with the water phase containing 1 wt% polyvinyl alcohol at a ratio of 1:8 and form a stable emulsion under high-speed stirring. Keep stirring the emulsion to completely remove the solvent, so that the epoxy acrylate, 1,6-hexanediol diacrylate, and linseed oil are phase-separated to form a core-shell emulsion with epoxy acrylate and 1,6-hexanediol diacrylate as the shell and linseed oil as the core;

[0060] Step 2: Add sodium styrene sulfonate and epoxy acrylate to the water phase of the emulsion at a mass ratio of 8:1, and use UV-initiated polymerization to cure the emulsion, so that the epoxy acrylate and 1,6-hexanediol diacrylate in the oil phase are cured and crosslinked with sodium styrene sulfonate in the water phase. Wash with deionized water to remove the unreacted sodium styrene sulfonate, and then a monolayer sulfonated microcapsule can be prepared;

[0061] Step 3: Slowly drop aniline and epoxy acrylate into the monolayer sulfonated microcapsule dispersion at a mass ratio of 1:16, so that aniline is completely adsorbed on the surface of the microcapsules;

[0062] Under ice bath conditions, add ammonium persulfate and aniline to the water phase at a molar ratio of 1:2 to initiate the polymerization of aniline. After the reaction is completed and washed, a microcapsule with polyaniline double-layer microcapsules can be prepared. The SEM image of the microcapsule is as shown in Figure 4As shown, the wall thickness of the polyaniline double-layer microcapsules is relatively thick, being 5 μm, and the thermal stability of the microcapsules is as shown in Figure 5 and 6 . The thermal stability of microcapsules is very important for their storage and practical applications. The thermal stability properties of single-layer sulfonated microcapsules and polyaniline double-layer microcapsules were studied by TGA under dynamic and isothermal conditions. Due to the degradation of the polyepoxyacrylate shell and the evaporation of the encapsulated core, the uncoated microcapsules began to lose weight at about 185 °C. Above 200 °C, the core material, linseed oil, is volatile. For the microcapsules with a PANI shell, it began to lose weight at around 293 °C, that is, the initial weight loss temperature of the microcapsules increased significantly by 100 °C from 185 °C to 293 °C, just with an additional PANI coating. It is speculated that the PANI layer can more effectively maintain the vapor pressure of linseed oil than the UV-cured polyacrylate shell, thus delaying the initial weight loss temperature of the microcapsules by 100 °C. The higher initial weight loss temperature indicates that the polyaniline-coated microcapsules have excellent thermal stability, demonstrating that the presence of the polyaniline shell effectively improves the stability of the core material and prevents the leakage of the core material at high temperatures.

[0063] The solvent resistance of the microcapsules in tetrahydrofuran is as shown in Figure 7 . It can be seen that the final core material release rate of the single-layer microcapsules obtained in step two is greater than that of the microcapsules with a polyaniline double layer, indicating that the solvent resistance of the polyaniline double layer is better than that of the single-layer photocured resin shell. For the single-layer sulfonated microcapsules, the collapse of the microcapsules is quite obvious because most of the core material has been extracted. At the same time, severe adhesion between the microcapsules was also observed, which should be attributed to the swelling of the polyacrylate shell. In sharp contrast, the polyaniline-coated microcapsules maintain a good spherical shape, and no collapse or adhesion is observed, indicating that the polyaniline-coated microcapsules have enhanced solvent resistance.

[0064] Example 2

[0065] Step 1: Mix polyurethane acrylate and linseed oil at a mass ratio of 1:1, with the crosslinking agent trimethylolpropane triacrylate being 25 wt% of the polyurethane acrylate, ethyl acetate being 6 times the mass of the polyurethane acrylate, and the photoinitiator 4-phenylbenzophenone being 5 wt% of the total mass of the polyurethane acrylate and trimethylolpropane triacrylate. After mixing evenly, it is used as the oil phase;

[0066] Mix the oil phase with an aqueous phase containing 3 wt% polyethylene oxide at a ratio of 1:5 and form a stable emulsion under high-speed stirring. Continuously stir the emulsion to completely remove the solvent, so that the polyurethane acrylate, trimethylolpropane triacrylate and linseed oil are phase-separated to form a core-shell emulsion with polyurethane acrylate and trimethylolpropane triacrylate as the shell and linseed oil as the core;

[0067] Step 2: Sodium styrene sulfonate and polyurethane acrylate are added to the emulsion at a mass ratio of 1:1, and the emulsion is cured by UV-initiated polymerization, so that polyurethane acrylate and trimethylolpropane triacrylate in the oil phase are cross-linked with sodium styrene sulfonate in the water phase. Unreacted sodium styrene sulfonate is removed by washing with deionized water, and a monolayer sulfonated microcapsule can be prepared;

[0068] Step 3: Aniline and polyurethane acrylate are slowly dropped into the monolayer sulfonated microcapsule dispersion at a mass ratio of 1:1, so that aniline is completely adsorbed on the surface of the microcapsules;

[0069] Under ice bath conditions, hydrogen peroxide and aniline are added to the water phase at a molar ratio of 1:1 to initiate the polymerization of aniline. After the reaction is completed and washed, a microcapsule with a bilayer of polyaniline can be prepared. The solvent resistance of the microcapsules in cyclohexane is as Figure 8 shown. It can be seen that the final core material release rate of the monolayer microcapsules obtained in Step 2 is greater than that of the microcapsules with a bilayer of polyaniline, indicating that the solvent resistance of the bilayer of polyaniline is better than that of the monolayer photocurable resin shell layer. The super-depth-of-field images and SEM photos of the microcapsules immersed in acetone for different times are respectively as Figure 9 and Figure 10 shown. It can be seen that the core material release rate of the monolayer microcapsules is greater than that of the microcapsules with a bilayer of polyaniline, indicating that the solvent resistance of the bilayer of polyaniline is better than that of the monolayer photocurable resin shell layer.

[0070] Example 3

[0071] Step 1: Polyester acrylate and linseed oil are mixed at a mass ratio of 1:5, the cross-linking agent dipentaerythritol hexaacrylate is 50 wt% of the polyester acrylate, the solvent is 8 times the mass of the polyester acrylate, and the photoinitiator methyl o-benzoylbenzoate is 10 wt% of the total mass of the polyester acrylate and dipentaerythritol hexaacrylate. After mixing evenly, it is used as the oil phase;

[0072] The oil phase and the water phase containing 6 wt% sodium dodecyl sulfate are mixed at a ratio of 2:1 and a stable emulsion is formed under high-speed stirring. The emulsion is continuously stirred to completely remove the solvent, so that polyester acrylate, dipentaerythritol hexaacrylate and linseed oil are phase-separated to form a core-shell emulsion with polyester acrylate and dipentaerythritol hexaacrylate as the shell and linseed oil as the core. The fluorescence microscope photos of the emulsion before and after solvent removal are as Figure 15 shown. When the solvent is not removed, the emulsion is homogeneous, and when the solvent is removed, the emulsion shows a phase-separated state;

[0073] Step 2: Sodium styrene sulfonate and polyester acrylate are added to the emulsion at a mass ratio of 1:4, and the emulsion is cured by electron beam-induced polymerization, so that polyester acrylate and dipentaerythritol hexaacrylate in the oil phase are cured and crosslinked with sodium styrene sulfonate in the aqueous phase. Unreacted sodium styrene sulfonate is removed by washing with deionized water, and a monolayer sulfonated microcapsule can be prepared;

[0074] Step 3: Aniline and polyurethane acrylate are slowly added dropwise to the monolayer sulfonated microcapsule dispersion at a mass ratio of 4:1, so that aniline is completely adsorbed on the surface of the microcapsules;

[0075] Under ice bath conditions, potassium permanganate and aniline are added to the aqueous phase at a molar ratio of 4:1 to initiate the polymerization of aniline. After the reaction is completed and washed, a microcapsule with a double layer of polyaniline can be prepared. The SEM photograph of the microcapsule is as Figure 11 shown, and the dispersibility of the microcapsules in different waterborne coatings is as Figure 12 shown. The mechanical properties of the microcapsules are as Figure 13 shown. The hardness and modulus of the monolayer photocurable resin obtained in Step 2 are both less than those of the polyaniline double layer. The average Young's modulus and hardness of the monolayer sulfonated microcapsule shell material are 86.23 ± 9.13 MPa and 4.66 ± 3.2 MPa, respectively. The Young's modulus and hardness of the polyaniline double-layer microcapsule shell material are increased to 362.31 ± 35.98 MPa and 39.89 ± 1.29 MPa, respectively, which are 4 times and 9 times that of the uncoated microcapsule shell material. Therefore, it can be concluded that the microcapsules with a polyaniline coating have better anti-deformation ability.

[0076] The solvent resistance of the microcapsules in ethyl acetate is as Figure 14 shown. The final core material release rate of the monolayer microcapsules is greater than that of the microcapsules with a polyaniline double layer, indicating that the solvent resistance of the polyaniline double layer is better than that of the monolayer photocurable resin shell layer.

[0077] Comparative Example 1

[0078] Referring to the scheme disclosed in CN 110484088 A, a polyaniline microcapsule is prepared:

[0079] (1) 480 mg of sodium dodecyl sulfate was dissolved in 12 mL of water by ultrasound as the aqueous phase. At the same time, 1.2 mL of dimethylaminoethyl methacrylate (DMAEMA) (1.119 g, density: 0.933 g / mL), 1.2 mL of divinylbenzene (DVB) (1.102 g, density: 0.919 g / mL), 66.6 mg of photoinitiator 1173 (3% of the monomer mass), and 3 mL of hexamethylene diisocyanate (HDI) were dissolved in 0.6 mL of ethyl acetate. The two phases were mixed at an oil-water ratio of 1:2 and emulsified for 3 min at 9000 rpm by a high-speed disperser to form a stable oil-in-water (O / W) emulsion;

[0080] (2) The emulsion prepared in step (1) was irradiated with ultraviolet light for 4 min to polymerize the vinyl monomers. After irradiation, 0.6 mL of aniline was added dropwise to the microcapsule dispersion, and then 2 mL of an aqueous solution containing 735 mg of ammonium persulfate (molar ratio to aniline of 1:2) and 50 μL of hydrochloric acid (1 M) was added to polymerize aniline. The reaction was carried out at 10 °C for 16 h under mechanical stirring, and the resulting polyaniline microcapsules loaded with active monomers were washed alternately with water and ethanol and dried;

[0081] As Figure 1 shown, it is the SEM photograph of the prepared microcapsules, where a is the intact polyaniline microcapsules; b is the broken polyaniline microcapsules. Due to the fast curing speed of ultraviolet light irradiation, the polymer after photocrosslinking cannot migrate to the microcapsule surface quickly, making the microcapsules very thin, resulting in poor barrier performance of the obtained microcapsules.

[0082] As Figure 2 shown, it is the ultra-depth-of-field microscope photograph of the prepared polyaniline microcapsules. After the emulsion was photocured, a large amount of free sulfonate emulsifiers would adsorb a large amount of aniline to occur homogeneous polymerization in the aqueous phase, resulting in a large amount of free polyaniline in the aqueous phase, which was mixed with the polyaniline double-layer microcapsules, and then the relative content of the core material was relatively low, and the efficient encapsulation of the core material could not be achieved.

[0083] Comparative Example 2

[0084] Refer to Yao Huiling, Shi Yuanchang, Zhai Guangyao, etc. Microemulsion synthesis and property characterization of polyaniline / poly(styrene-sodium styrenesulfonate) nanocore-shell structure polymers [J]. Journal of Shandong University (Natural Science Edition), 2008.

[0085] Add 0.5 g of sodium dodecyl sulfonate (SDS), 20 g of deionized water, 0.06 g of sodium styrene sulfonate, 0.6 g of styrene monomer and 1.4 g of n-pentanol into a three-necked flask. Introduce nitrogen gas and stir vigorously for 1 h to form a transparent microemulsion system. Prepare a mixed solution of KPS and PVP in a 50 mL volumetric flask, where 2.893 g of potassium persulfate (KPS) and 0.018 g of polyvinylpyrrolidone (PVP) are used as initiator and dispersant respectively (the molar ratio of KPS to styrene monomer is 1:100, and PVP is 3% of the mass of styrene monomer). Measure 200 μL of the above-mentioned KPS and PVP mixed solution with a microliter syringe, add it to the microemulsion system, stir evenly, and react for 4 h under the condition of nitrogen protection at 75 °C to obtain polystyrene nano latex particles. Dilute the polystyrene latex by 1 times, take 20 g and pour it into a round-bottom flask. Weigh 0.045 g of FeCl3 and pour it into the flask, stir vigorously until FeCl3 is completely dissolved. Weigh 0.0363 g of KPS and 0.075 g of PVP, prepare a solution in a 100 mL volumetric flask for standby. Measure 6.5 μL (0.0063 g) of aniline monomer with a microliter syringe, add it to the flask, stir vigorously under a nitrogen atmosphere to make the components mix evenly. Measure 200 μL of the KPS and PVP mixed solution with a microliter syringe, add it to the round-bottom flask, then put the flask into an ice-water bath, stir vigorously under the condition of nitrogen protection, and after reacting for 24 h, obtain nanoparticles coated with polyaniline.

[0086] In the above steps, sodium styrene sulfonate and sodium dodecyl sulfonate (SDS) are used together as emulsifiers to stabilize the styrene monomer, and are fixed on the surface of the latex particles through covalent bond crosslinking.

[0087] The present invention does not use sodium styrene sulfonate as an emulsifier, but only adds sodium styrene sulfonate as a sulfonation element to the water phase, that is, the sulfonic acid group is grafted onto the surface of the microcapsule shell layer only through the reactive sodium styrene sulfonate.

[0088] Once sodium styrene sulfonate is used as an emulsifier for preparing emulsion before curing, after rapid photo-initiated polymerization, since sodium styrene sulfonate has been covalently bonded to the surface of the microcapsule shell layer, its ability to stabilize the oil phase is greatly reduced, and a large number of microcapsules show aggregation phenomena and cannot be dispersed in the matrix resin and thus cannot be actually applied.

[0089] Comparative Example 3

[0090] Mix epoxy acrylate and linseed oil at a mass ratio of 4:1, 1,6-hexanediol diacrylate as the crosslinking agent is 10 wt% of epoxy acrylate, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide as the photoinitiator is 2 wt% of the total mass of epoxy acrylate and 1,6-hexanediol diacrylate. After mixing evenly, it is used as the oil phase;

[0091] The oil phase and the aqueous phase containing 1 wt% polyvinyl alcohol are mixed at a ratio of 1:8 and a stable emulsion is formed under high-speed stirring. Sodium styrene sulfonate and epoxy acrylate are added to the aqueous phase of the emulsion at a mass ratio of 8:1, and the emulsion is cured by UV-initiated polymerization, so that the epoxy acrylate, 1,6-hexanediol diacrylate in the oil phase and sodium styrene sulfonate in the aqueous phase are cured and crosslinked. Unreacted sodium styrene sulfonate is removed by washing with deionized water, and porous microspheres can be prepared.

[0092] After the stable emulsion is prepared by the above steps and directly cured rapidly by photoinitiation, the obtained product is porous microspheres, and microcapsules with a core-shell structure cannot be prepared, and the core material cannot be stably encapsulated, and the core material is relatively easy to leak.

[0093] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a polyaniline double-layer microcapsule with barrier properties, characterized in that, the method comprises the following steps: Step 1: Mix a photocurable resin, a core material, a crosslinking agent, a solvent and a photoinitiator evenly to form an oil phase, mix the oil phase with an aqueous phase containing a stabilizer to form a stable emulsion, continuously stir or heat the emulsion to completely remove the solvent, and separate the photocurable resin, the crosslinking agent and the core material; Step 2: Add sodium styrene sulfonate to the aqueous phase and stir. The emulsion is cured under UV irradiation, and the unreacted sodium styrene sulfonate is removed by washing with deionized water to prepare a single-layer sulfonated microcapsule; Step 3: Drop aniline into the aqueous dispersion of the sulfonated microcapsule, continuously stir to make aniline completely adsorbed on the surface of the microcapsule, then add an initiator under ice bath conditions to initiate the polymerization of aniline, and obtain a polyaniline double-layer microcapsule after washing; the photocurable resin and the core material are immiscible; the solvent has a boiling point below 80 °C and is a good solvent for the photocurable resin.

2. A preparation method of a polyaniline double-layer microcapsule with barrier properties according to claim 1, characterized in that, the photocurable resin is one or more of polyurethane acrylate, polyester acrylate, epoxy acrylate; the crosslinking agent is one or more of dipropylene glycol tetraacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, bisphenol A glycidyl dimethacrylate, dipropylene glycol dimethacrylate, dipentaerythritol hexaacrylate, diethylene glycol phthalate diacrylate, neopentyl glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, dipropylene glycol diacrylate, 1,3-butanediol diacrylate; the solvent is one or more of dichloromethane, chloroform, ethyl acetate, butyl acetate; the stabilizer is one or more of polyvinyl alcohol, polyethylene glycol, poly(ethylene oxide), polystyrene-maleic anhydride copolymer, polyethylene-maleic anhydride copolymer, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock polymer, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, cetyltrimethylammonium bromide, Span-80, Span-60, Tween-80, Tween 60, glycerol monostearate, N-dodecyldimethylamine, gum arabic; the photoinitiator in Step 1 is one or more of 2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, benzoin dimethyl ether, isopropylthioxanthone, ethyl 4-(N,N-dimethylamino)benzoate, benzophenone, 4-chlorobenzophenone, methyl o-benzoylbenzoate, diphenyliodonium hexafluorophosphate, isooctyl 4-(N,N-dimethylamino)benzoate, 4-methylbenzophenone, 4-phenylbenzophenone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoyl phenylphosphinate; the core material in Step 1 is one or more of a self-healing agent, an early warning agent and a lubricant; The initiator described in step three is one or a mixture of any several of ammonium persulfate, potassium persulfate, hydrogen peroxide, and potassium permanganate.

3. The preparation method of a polyaniline double-layer microcapsule with barrier properties according to claim 1 or 2, wherein the mass ratio of the photocurable resin to the core material in step one is 5:1 to 1:5, the crosslinking agent is 5wt% - 50wt% of the photocurable resin, the solvent is 3 - 8 times the mass of the photocurable resin; the photoinitiator is 1wt% - 10wt% of the total mass of the photocurable resin and the crosslinking agent.

4. The preparation method of a polyaniline double-layer microcapsule with barrier properties according to claim 1 or 2, wherein the mass ratio of the oil phase to the water phase in step two is 1:10 to 2:1, the stabilizer concentration is 0.5wt% - 6wt%, and the mass ratio of sodium styrenesulfonate to the photocurable resin is 1:2 to 1:

8.

5. The preparation method of a polyaniline double-layer microcapsule with barrier properties according to claim 1 or 2, wherein the mass ratio of aniline to the sulfonated microcapsule in step three is 1:16 to 4:1, and the molar ratio of the initiator to aniline is 1:2 to 4:

1.

6. The polyaniline double-layer microcapsule with barrier properties prepared by any of the methods according to claims 1 - 5, wherein the prepared microcapsules have a particle size of 10 - 200 μm, and the shell thickness is 5 - 80% of the particle size of the microcapsules.

7. The polyaniline double-layer microcapsule with barrier performance according to claim 6, characterized in that, The shell thickness is 10 - 50% of the particle size of the microcapsules.

8. Use of the microcapsule prepared by any of the methods according to claims 1-5 or the microcapsule according to any one of claims 6-7, characterized in that, The application fields of the microcapsules include anticorrosive materials, self-healing materials, cosmetic preparations, drugs, agrochemicals, and cleaning agents.

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