Multi-shell microcapsule as well as preparation method and application thereof

Abstract

The invention discloses a multi-shell microcapsule and a preparation method and application thereof.The multi-shell microcapsule comprises a core material, an inner shell, a middle shell and an outer shell which are sequentially arranged, the inner shell is prepared from polyurethane, the middle shell is prepared from polyurea, and the outer shell is prepared from silicon dioxide. The multi-shell microcapsule comprises the compact PU layer wrapping the core material, the thickened and wrapped PUA layer and the silicon dioxide layer capable of improving the mechanical property of the microcapsule, and the PU / PUA layer and the silicon dioxide layer are organically combined to provide a wall material for wrapping the core material more compactly through the synergistic effect between the PU / PUA layer and the silicon dioxide layer. The multi-shell microcapsule has more excellent aging resistance and corrosion resistance and good compactness, is free of any formaldehyde addition, and is safe and environment-friendly to use.

Description

Technical Field

[0001] The invention belongs to the technical field of microcapsules, and in particular relates to a multi-shell microcapsule and a preparation method and application thereof. Background Art

[0002] Microcapsules are a kind of spherical material that uses active ingredients as core materials and organic polymers as shell materials. The core materials are encapsulated into spherical materials of specific sizes through microencapsulation technology. The size generally ranges from 1 to 1000 μm and the shapes are various, depending on the raw materials and preparation methods. The process of preparing microcapsules is called microencapsulation. Microencapsulation technology refers to the technology of encapsulating solid, liquid or gaseous substances in semi-permeable or closed microcapsules. Among them, the embedded substance is called the core material. Common core materials include drugs, flavors and fragrances, color developers, sweeteners, pigments, lipids, enzymes, vitamins, minerals, microorganisms, gases and other various reactive agents. The material that encapsulates the core material to achieve microencapsulation is called the wall material. Common wall materials include thermoplastic polymers, polyurethanes, polyureas, urea-formaldehyde resins, epoxy resins, acrylic resins, chitosan, starch, polyvinyl alcohol and silica. Patent WO2019 / 121736A1 discloses a core-shell microcapsule, which contains a polymer stabilizer combined with a polymer surfactant and an aminosilane, and various shell-forming materials selected from monomers, prepolymers and precondensates. The microcapsule uses an ionic surfactant in the synthesis process, which leads to colloid instability, and problems such as agglomeration and short shelf life may occur. Patent CN110511727A discloses a double-layer shell phase change microcapsule, which is composed of a core material with a phase change material, an inner shell and an outer shell, wherein the inner shell is composed of polyurea or / and polyurethane, and the outer shell is composed of polyurea-formaldehyde. Due to the low strength of the shell material, the microcapsule is more easily destroyed by external mechanical forces during stirring and transportation, and the premature outflow of the core material causes pollution to the device and substrate.

[0003] For example, the invention patent CN115025725A discloses a method for preparing a polyurethane microcapsule curing agent, which comprises mixing and emulsifying an isocyanate monomer and a catalyst in water, adding an amine solution to mix, and performing a reaction in a tubular reactor at a heating and cooling rate greater than or equal to 20°C / s, and subsequent thickening and heat preservation for 12-36 hours. Although the polyurethane microcapsules are successfully prepared, their specific reaction container and harsh reaction conditions limit the further scale-up production of their microcapsules. For example, the invention patent CN1805784A discloses a method for preparing a fragrance microcapsule, that is, dissolving polyisocyanate and a catalyst in essential oil, emulsifying them in an aqueous solution containing polyamines and diols or polyols to obtain an emulsion, and initially reacting to form a layer of wall material and consuming all the existing polyamines, and then the slower-reacting polyols react to form an external cross-linked coating, and further react in water to consume the residual isocyanate. The production process flow in the above-mentioned existing microcapsule preparation process is complicated, or expensive metal catalysts need to be added. Summary of the invention

[0004] In order to overcome the problems existing in the above prior art, one of the purposes of the present invention is to provide a multi-shell microcapsule. The second purpose of the present invention is to provide a method for preparing the multi-shell microcapsule. The third purpose of the present invention is to provide an application of the multi-shell microcapsule.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The first aspect of the present invention provides a multi-shell microcapsule, comprising a core material, an inner shell, an intermediate shell and an outer shell arranged in sequence, wherein the inner shell is made of polyurethane, the intermediate shell is made of polyurea, and the outer shell is made of silica.

[0007] Preferably, the core material is selected from one of polymer materials, phase change materials, oxidants, cross-linking agents, drugs, and dyes.

[0008] Preferably, the particle size of the multi-shell microcapsule is 10 to 160 μm.

[0009] The second aspect of the present invention provides a method for preparing the multi-shell microcapsule of the first aspect, comprising the following steps:

[0010] S1, preparing an emulsifier and water as a continuous phase, mixing a core material, an alcohol substance and a diisocyanate substance as a dispersed phase, and adding the dispersed phase to the continuous phase for emulsification to obtain an emulsion containing single-shell microcapsules;

[0011] S2, adding amine substances to the emulsion of S1 to carry out polymerization reaction to obtain an emulsion containing double-shell microcapsules;

[0012] S3, adding the ethyl silicate hydrolyzate into the emulsion of S2 to react and obtain the multi-shell microcapsules.

[0013] Preferably, the emulsifier is selected from ionic emulsifiers and / or non-ionic emulsifiers; the ionic emulsifier is selected from at least one of polyethylene maleic anhydride, polystyrene maleic anhydride, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate; the non-ionic emulsifier is selected from at least one of polyvinyl alcohol, alkylphenol polyoxyethyl ether, and gum arabic.

[0014] Preferably, the alcohol substance is selected from at least one of polyethylene glycol, triethanolamine and butanediol.

[0015] Preferably, the amine substance is selected from at least one of tetraethylenepentamine, polyetherimide, triethylenediamine and diethylenetriamine.

[0016] Preferably, the diisocyanate substance is selected from at least one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, lysine diisocyanate or prepolymers and semi-prepolymers thereof.

[0017] Preferably, the preparation method of the ethyl silicate hydrolyzate is: hydrolyzing ethyl orthosilicate solution under the condition of pH=1-5 to obtain silanol solution.

[0018] More preferably, the reaction time of the hydrolysis is 0.5 to 1.5 h.

[0019] Preferably, in step S1, the continuous phase is heated to 40-60°C, and the dispersed phase is added to the continuous phase for emulsification.

[0020] Preferably, in step S2, the reaction temperature of the polymerization reaction is 30-70° C., and the reaction time is 0.5-6 h.

[0021] Preferably, in step S3, the reaction time is 2 to 5 hours.

[0022] Preferably, the mass ratio of the core material to the diisocyanate substance is 1:(0.3-3.5).

[0023] Preferably, the mass ratio of the core material to the alcohol substance is 1:(0.03-0.5).

[0024] Preferably, the mass ratio of the core material to the amine substance is 1:(0.2-4).

[0025] Preferably, the mass ratio of the core material to the emulsifier is 1:(0.2-5).

[0026] Preferably, the mass ratio of the core material to water is 1:(5-100).

[0027] Preferably, the dispersed phase further comprises a plasticizer.

[0028] More preferably, the plasticizer is selected from at least one of di-n-octyl phthalate, di(2-ethylhexyl) phthalate, dibutyl phthalate, butyl benzyl phthalate, diisononyl phthalate, diisodecyl phthalate, dimethyl phthalate, diethyl phthalate and diisobutyl phthalate.

[0029] More preferably, the mass ratio of the core material to the plasticizer is 1:(7-15).

[0030] The third aspect of the present invention provides the use of the multi-shell microcapsules described in the first aspect in the preparation of engineering parts, coatings, and adhesives.

[0031] The beneficial effects of the present invention are:

[0032] (1) The present invention provides a multi-shell microcapsule, which is a PU / PUA / SiO2 multi-layer shell microcapsule, including a dense PU layer wrapping a core material, a thickened wrapping PUA layer, and a silica layer capable of improving the mechanical properties of the microcapsule, wherein the synergistic effect between the PU / PUA layer and the silica layer enables their organic combination to provide a more tightly wrapped wall material for the core material. Compared with single-layer PU or PUA, the multi-shell microcapsule has better aging resistance, corrosion resistance, and good density, and is a microcapsule without any formaldehyde added, and is safe and environmentally friendly to use.

[0033] (2) The multi-shell microcapsules of the present invention are not limited to a single type of core material, but can encapsulate a variety of different types of uniform oil phase or organic phase, thereby expanding the types of core materials that can be encapsulated. The microcapsules produced by the process of the present invention can be used in engineering parts, coatings, adhesives, etc., and can be applied to the fields of space shuttles, automobile industry, satellites, submarines, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is an optical microscope image of PU / PUA / SiO2-epoxy resin (N128);

[0035] Figure 2 This is an optical microscope image of PU / PUA / SiO2-acrylate (348L);

[0036] Figure 3 This is an optical microscope image of PU / PUA / SiO2-BPO. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below through specific examples. The raw materials used in the following examples, unless otherwise specified, can be obtained from conventional commercial sources or prepared and separated by simple synthesis; the processes used, unless otherwise specified, are conventional processes in the art.

[0038] Example 1

[0039] This embodiment provides a multi-shell microcapsule, and the preparation method thereof is as follows:

[0040] 1. Polyvinyl alcohol (PVA, 10 g), gum arabic (10 g) and water (700 g) were mixed to obtain a continuous phase; epoxy resin N128 (100 g), polyethylene glycol (PEG200, 5.2 g) and diphenylmethane diisocyanate (MDI, 35 g) were mixed to obtain a dispersed phase; the continuous phase was heated to 50° C., and the dispersed phase was added to the continuous phase for emulsification at an emulsification speed of 2000 rpm for 7 min to obtain an emulsion containing single-shell microcapsules;

[0041] 2. Add tetraethylenepentamine (TEPA, 30 g) to the emulsion containing single-shell microcapsules, heat to 60°C and stir to react for 1 hour to obtain an emulsion containing double-shell microcapsules;

[0042] 3. 25 g of tetraethyl silicate (TEOS) was stirred and hydrolyzed for 1 h in 25 mL of sulfuric acid solution with pH = 3. The TEOS solution after hydrolysis was added to the emulsion containing double-shell microcapsules. After stirring and reacting for 3 h, the collected slurry was centrifuged to obtain a wet material with a water content of 30-40%, which was further dried at 50°C for 12 hours. Finally, the dry microcapsule powder was sieved out and recorded as PU / PUA / SiO2-epoxy resin (N128).

[0043] Figure 1 This is an optical microscope picture of the preparation of PU / PUA / SiO2-epoxy resin (N128), in which the morphology of the microspheres is basically regular.

[0044] The double-shell microcapsules prepared in this embodiment are white or off-white uniform spheres with an average particle size of 10 to 100 μm; the powder has good flow dispersibility and mechanical properties.

[0045] Example 2

[0046] This embodiment provides a multi-shell microcapsule, and the preparation method thereof is as follows:

[0047] 1. Polyvinyl alcohol (PVA, 10 g), gum arabic (10 g) and water (700 g) were mixed to obtain a continuous phase; epoxy resin N128 (100 g), polyethylene glycol (PEG200, 5.2 g) and diphenylmethane diisocyanate (MDI, 35 g) were mixed to obtain a dispersed phase; the continuous phase was heated to 50° C., and the dispersed phase was added to the continuous phase for emulsification at an emulsification speed of 2000 rpm for 7 min to obtain an emulsion containing single-shell microcapsules;

[0048] 2. Add tetraethylenepentamine (TEPA, 30 g) to the emulsion containing single-shell microcapsules, heat to 60°C and stir to react for 5 hours to obtain an emulsion containing double-shell microcapsules;

[0049] 3. 25 g of tetraethyl silicate (TEOS) was stirred and hydrolyzed for 1 h in 25 mL of sulfuric acid solution with pH = 3. The TEOS solution after hydrolysis was added to the emulsion containing double-shell microcapsules. After stirring and reacting for 3 h, the collected slurry was centrifuged to obtain a wet material with a water content of 30-40%, which was further dried at 50°C for 12 hours. Finally, the dry microcapsule powder was sieved out and recorded as PU / PUA / SiO2-epoxy resin (N128).

[0050] The optical microscope image of PU / PUA / SiO2-epoxy resin (N128) of this embodiment is highly similar to that of Example 1, and the morphology of the microspheres in the image is basically regular.

[0051] The double-shell microcapsules prepared in this embodiment are white or off-white uniform spheres with an average particle size of 10 to 100 μm; the powder has good flow dispersibility and mechanical properties.

[0052] Example 3

[0053] This embodiment provides a multi-shell microcapsule, and the preparation method thereof is as follows:

[0054] 1. Polyvinyl alcohol (PVA, 5 g), gum arabic (20 g) and water (700 g) were mixed to obtain a continuous phase; acrylate 348L (100 g), polyethylene glycol (PEG200, 6 g), diphenylmethane diisocyanate (MDI, 10 g) and isophorone diisocyanate (IPDI, 20 g) were mixed to obtain a dispersed phase; the continuous phase was heated to 45° C., and the dispersed phase was added to the continuous phase for emulsification at an emulsification speed of 2000 rpm for 7 min to obtain an emulsion containing single-shell microcapsules;

[0055] 2. Add tetraethylenepentamine (TEPA, 30 g) to the emulsion containing single-shell microcapsules, heat to 55°C and stir to react for 1 hour to obtain an emulsion containing double-shell microcapsules;

[0056] 3. 25 g of tetraethyl silicate (TEOS) was stirred and hydrolyzed for 1 h in 25 mL of sulfuric acid solution with pH = 3. The TEOS solution after hydrolysis was added to the emulsion containing double-shell microcapsules. After stirring and reacting for 3 h, the collected slurry was centrifuged to obtain a wet material with a water content of 30-40%, which was further dried at 50° C. for 12 h. Finally, the dry microcapsule powder was sieved out and recorded as PU / PUA / SiO2-acrylate (348L).

[0057] Figure 2 This is an optical microscope picture of the preparation of PU / PUA / SiO2-acrylate (348L). In the picture, the microspheres are uniform in size, basically regular in shape, and have a smooth shell.

[0058] The double-shell microcapsules prepared in this embodiment are white or off-white uniform spheres with an average particle size of 20 to 160 μm; the powder has good flowability, dispersibility and mechanical properties.

[0059] Example 4

[0060] This embodiment provides a multi-shell microcapsule, and the preparation method thereof is as follows:

[0061] 1. Polyvinyl alcohol (PVA, 8 g), gum arabic (25 g) and water (800 g) were mixed to obtain a continuous phase; dibenzoyl peroxide (BPO, 10 g), diethyl phthalate (DEP, 90 g), polyethylene glycol (PEG200, 4.5 g) and diphenylmethane diisocyanate (MDI, 32 g) were mixed to obtain a dispersed phase; the continuous phase was heated to 45° C., and the dispersed phase was added to the continuous phase for emulsification at an emulsification speed of 2000 rpm for 7 min to obtain an emulsion containing single-shell microcapsules;

[0062] 2. Add tetraethylenepentamine (TEPA, 35 g) to the emulsion containing single-shell microcapsules, heat to 55°C and stir to react for 1 hour to obtain an emulsion containing double-shell microcapsules;

[0063] 3. 25 g of ethyl silicate (TEOS) was stirred and hydrolyzed for 1 h in 25 mL of sulfuric acid solution with pH = 3. The TEOS solution after hydrolysis was added to the emulsion containing double-shell microcapsules. After stirring and reacting for 3 h, the collected slurry was centrifuged to obtain a wet material with a water content of 30-40%, which was further dried at 50°C for 12 hours. Finally, the dry microcapsule powder was sieved out and recorded as PU / PUA / SiO2-BPO.

[0064] Figure 3 This is an optical microscope picture of the prepared PU / PUA / SiO2-BPO, in which the morphology of the microspheres is basically regular.

[0065] Comparative Example 1

[0066] This comparative example provides a double-shell microcapsule, and the preparation method thereof is as follows:

[0067] 1. Polyvinyl alcohol (PVA, 8 g), gum arabic (25 g) and water (800 g) were mixed to obtain a continuous phase; dibenzoyl peroxide (BPO, 10 g), diethyl phthalate (DEP, 90 g), polyethylene glycol (PEG200, 4.5 g) and diphenylmethane diisocyanate (MDI, 32 g) were mixed to obtain a dispersed phase; the continuous phase was heated to 45° C., and the dispersed phase was added to the continuous phase for emulsification to obtain an emulsion containing single-shell microcapsules;

[0068] 2. Add tetraethylenepentamine (TEPA, 35 g) to the emulsified emulsion, raise the temperature to 55° C. and stir to react for 1 hour to obtain an emulsion containing double-shell microcapsules. The double-shell microcapsules are recorded as PU / PUA-BPO.

[0069] Experimental analysis

[0070] 1. Experimental characterization of mechanical properties

[0071] The product samples of Examples 1-4 and Comparative Example 1 were respectively dispersed in 50% ethanol aqueous solution, and dispersed by strong shearing at a speed of 2000 rpm for 10 minutes using a paddle. The capsule breakage was observed under an optical microscope. The products of Examples 1-4 did not show capsule breakage, while the PU / PUA-BPO of Comparative Example 1 showed capsule breakage. The test showed that the SiO2 shell provided better mechanical properties for the microcapsules.

[0072] 2. Experimental characterization of microcapsule release core material

[0073] To verify the successful encapsulation of PU / PUA / SiO2-benzoyl peroxide (BPO), the following tests were performed:

[0074] Preparation of sample ①: 3g of acrylic resin 348L was added to 10g of dimethyl carbonate; sample ②: 0.3g of PU / PUA / SiO2-BPO was added to 10g of dimethyl carbonate; sample ③: 1g of acrylic resin 348L and 0.3g of PU / PUA / SiO2-BPO were added to 10g of dimethyl carbonate; after applying samples ①, ② and ③ on the surface of the bolt and drying, the nut was screwed in and the PU / PUA / SiO2-benzoyl peroxide (BPO) microcapsules were destroyed, and the destructive strength was tested after curing for 2 days. The results are shown in Table 1:

[0075] Table 1 Destructive strength between bolts and nuts

[0076] sample ① ② ③ Destructive strength N·m 0 0 3.5

[0077] The experimental results show that pure acrylic resin sample ① and pure PU / PUA / SiO2-benzoyl peroxide (BPO) microcapsules were twisted in the thread, and could not undergo cross-linking reaction and curing, nor could they lock the bolts and nuts to produce destructive strength. Sample ③ was BPO microcapsules and resin coated on the surface of the bolt. When subjected to external force, the coated microcapsules released the core BPO and reacted with the acrylic resin to cure, thereby locking the bolts and nuts. This verifies that the microcapsules successfully encapsulate the core BPO and can be specifically used in acrylic system thread lockers, realizing the single-component and pre-coatable adhesive of the system.

[0078] 3. Characterization of anti-aging performance

[0079] Artificial accelerated aging test was conducted on PU / PUA / SiO2-BPO and commercially available BPO microcapsules (purchased from Guangzhou Zhiwei New Material Technology Co., Ltd.). After heat treatment at 100°C for 8 hours, PU / PUA / SiO2-BPO did not turn yellow, while commercially available BPO microcapsules turned yellow. PU / PUA / SiO2-benzoyl peroxide (BPO) had better heat resistance and anti-aging effect than commercially available products. In addition, the shell morphology of PU / PUA / SiO2-benzoyl peroxide (BPO) samples before and after baking did not change significantly.

[0080] 4. Characterization of solvent resistance

[0081] 0.3g PU / PUA / SiO2-BPO and 1g acrylic resin 348L were added to 10g dimethyl carbonate, water, toluene and acrylic ester respectively and left for 3 days. 50% dibenzoyl peroxide was used to replace PU / PUA / SiO2-BPO for comparative testing. The test results are shown in Table 2:

[0082] Table 2

[0083]

[0084] The experimental results in Table 2 show that PU / PUA / SiO2-BPO has good water resistance and solvent resistance and can be stored for a long time in water, toluene, ester solvents and acrylates.

[0085] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A multi-shell microcapsule, characterized in that: The invention comprises a core material, an inner shell, a middle shell and an outer shell which are arranged in sequence. The inner shell is made of polyurethane, the middle shell is made of polyurea, and the outer shell is made of silicon dioxide.

2. The multi-shell microcapsule according to claim 1, characterized in that The core material is selected from one of phase change materials, oxidants, cross-linking agents, drugs, and dyes.

3. The method for preparing the multi-shell microcapsule according to claim 1 or 2, characterized in that: The steps include: S1, preparing an emulsifier and water as a continuous phase, mixing a core material, an alcohol substance and a diisocyanate substance as a dispersed phase, and adding the dispersed phase to the continuous phase for emulsification to obtain an emulsion containing single-shell microcapsules; S2, adding amine substances to the emulsion of S1 to carry out polymerization reaction to obtain an emulsion containing double-shell microcapsules; S3, adding the ethyl silicate hydrolyzate into the emulsion of S2 to react and obtain the multi-shell microcapsules.

4. The method for preparing multi-shell microcapsules according to claim 3, characterized in that: The emulsifier is selected from ionic emulsifiers and / or nonionic emulsifiers; the ionic emulsifier is selected from at least one of polyethylene maleic anhydride, polystyrene maleic anhydride, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate; the nonionic emulsifier is selected from at least one of polyvinyl alcohol, alkylphenol polyoxyethyl ether, and gum arabic.

5. The method for preparing multi-shell microcapsules according to claim 3, characterized in that: The alcohol substance is selected from at least one of polyethylene glycol, triethanolamine and butanediol; And / or, the amine substance is selected from at least one of tetraethylenepentamine, polyetherimide, triethylenediamine and diethylenetriamine.

6. The method for preparing multi-shell microcapsules according to claim 3, characterized in that: The diisocyanate substance is selected from at least one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, lysine diisocyanate or prepolymers and semi-prepolymers thereof.

7. The method for preparing multi-shell microcapsules according to claim 3, characterized in that: The preparation method of the ethyl silicate hydrolyzate is as follows: ethyl orthosilicate is hydrolyzed under the condition of pH=1-5 to obtain a silanol solution.

8. The method for preparing multi-shell microcapsules according to claim 3, characterized in that: In step S2, the reaction temperature of the polymerization reaction is 30-70° C., and the reaction time is 0.5-6 h.

9. The method for preparing multi-shell microcapsules according to claim 3, characterized in that: The mass ratio of the core material to the diisocyanate substance is 1:(0.3-3.5); And / or, the mass ratio of the core material to the alcohol substance is 1:(0.03-0.5).

10. Use of the multi-shell microcapsule according to claim 1 or 2 in the preparation of engineering parts, coatings and adhesives.

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