Method for coating polar organic compound into silicon dioxide microcapsule

Abstract

The invention discloses a method for coating a polar organic compound into a silicon dioxide microcapsule, and the method for coating the polar organic compound into the silicon dioxide microcapsule comprises the following steps: (1) carrying out condensation reaction on an alkoxy silane monomer to form polyalkyl siloxane as a precursor of the silicon dioxide microcapsule; (2) replacing a part of alkoxy groups in the polyalkyl siloxane with a hydrophilic compound containing hydroxyl groups to obtain amphiphilic modified polyalkoxy siloxane as a precursor of another silicon dioxide microcapsule; (3) mixing the polyalkoxy siloxane obtained in the step (1), the hydrophilic group modified polyalkoxy siloxane obtained in the step (2) and a polar organic compound according to a ratio, and heating to enable the mixture to be in a liquid state if necessary; (4) emulsifying the mixture obtained in the step (3) in water to form an oil-in-water emulsion; and (5) carrying out condensation reaction on the precursors of the two silicon dioxide microcapsules in the mixture to form the silicon dioxide microcapsules.

Description

Technical Field

[0001] The invention belongs to the technical field of microcapsules, and in particular relates to a method for encapsulating polar organic compounds into silicon dioxide microcapsules with high mechanical properties without using organic surfactants. Background Art

[0002] Many oily active organic compounds can be microencapsulated to achieve non-leakage, stabilization and sustained release properties. However, most existing microcapsule products use organic polymers as wall materials. Organic polymer microcapsules are flammable, difficult to degrade, easy to change under light, and difficult to release the core material. Amorphous silica is a very promising inorganic wall material due to its high chemical inertness, non-flammability, biocompatibility, optical transparency, thermal and mechanical stability, etc.

[0003] US Patent No. 6303149B1 discloses a technology for encapsulating oily active ingredients into silica microcapsules by hydrolysis and condensation of ethyl orthosilicate in an oil-in-water emulsion. In order to effectively stabilize the emulsion, an organic surfactant needs to be added, but it must be removed after the reaction is completed. This is bound to increase production costs and pollute the environment, especially water quality.

[0004] Patent CN110144193A provides another method for encapsulating oily substances into silica microcapsules without the need for organic surfactants. This method uses polyalkoxysiloxane as a silica precursor. Polyalkoxysiloxane partially hydrolyzes ethoxy groups in an oil / water system to form an amphiphilic structure, thereby generating interfacial activity to stabilize the oil-in-water emulsion. However, polyalkoxysiloxane can reduce the oil / water interfacial tension to a maximum of 12mN / m. Therefore, for polar organic compounds, i.e. compounds with an interfacial tension of less than 20mN / m with water, polyalkoxysiloxane alone cannot effectively stabilize the oil-in-water emulsion, resulting in a failure to obtain a complete microcapsule structure.

[0005] In order to improve the interfacial activity of polyalkoxysiloxane, patent CN111170323A proposed to replace part of the alkoxy groups of polyalkoxysiloxane with hydrophilic compounds, and use the compounds as silica precursors to coat various oily substances. The aerogel particles coated with oily compounds obtained by this method have very low density, very limited mechanical properties, and are easily damaged during drying and reprocessing.

[0006] Since many oily active compounds are polar substances, it is particularly important to find a simple, environmentally friendly, and low-cost method to encapsulate polar organic compounds in high mechanical strength silica microcapsules. Summary of the invention

[0007] In view of the shortcomings of the above background technology, the purpose of the present invention is to provide a method for encapsulating polar organic compounds into silica microcapsules, which aims to solve the problems of flammability, non-degradability, easy light changes, and difficulty in releasing the core material caused by using organic polymers as wall materials in the prior art; the problem of low encapsulation efficiency when using hydrophobic polyalkoxysiloxane as a precursor to encapsulate polar core materials; and the problem that polyalkoxysiloxane modified by hydrophilic substances can only obtain aerogel particle microcapsules with limited mechanical properties and very low density.

[0008] The present invention adopts a mixture of hydrophobic polyalkoxysiloxane and hydrophilic modified polyalkoxysiloxane as a precursor of silica microcapsules to encapsulate polar organic compounds. The hydrophilic modified polyalkoxysiloxane has an amphiphilic structure and can reduce the water-oil interface energy to below 1mN / m, while the polyalkoxysiloxane has high hydrophobicity and will be coated in the oil droplets to inhibit Ostwald ripening, thereby making the emulsion more stable. In addition, during the hydrolysis and condensation process, the polyalkoxysiloxane slowly migrates to the interface, thickens the silica layer, and improves its mechanical properties.

[0009] To solve the above technical problems, the purpose of the present invention is achieved as follows:

[0010] A method for encapsulating a polar organic compound into a silica microcapsule comprises the following steps:

[0011] (1) forming polyalkylsiloxane as a precursor of silica microcapsules through the condensation reaction of alkoxysilane monomers;

[0012] (2) using a hydroxyl-containing hydrophilic compound to replace part of the alkoxy groups in the polyalkylsiloxane to obtain an amphiphilic modified polyalkoxysiloxane as another precursor of silica microcapsules;

[0013] (3) mixing the polyalkoxysiloxane obtained in step (1), the hydrophilic group-modified polyalkoxysiloxane obtained in step (2) and the polar organic compound in proportion, and if necessary, heating the mixture to make it liquid;

[0014] (4) emulsifying the mixture obtained in step (3) in water to form an oil-in-water emulsion;

[0015] (5) forming silica microcapsules by condensing two precursors of silica microcapsules in the mixture;

[0016] (6) The silica microcapsule powder encapsulating the polar organic compound is obtained by drying.

[0017] On the basis of the above scheme and as a preferred scheme of the above scheme: the alkoxysilane monomer in step (1) has the following chemical formula R 4-nSi(OX)n, wherein n=2-4, R is a non-hydrolyzable group, which may be a halogenated alkyl group such as an alkyl group, a vinyl alkyl group, a styryl alkyl group, a methacryloyloxy alkyl group, a urea alkyl group, a chloropropyl alkyl group or a sulfanyl group; X is an alkyl group having 1-6 carbon atoms; the alkoxysilane monomer may be a single monomer or a mixture of two or more monomers; and the condensation of the alkoxysilane monomer may be achieved by reaction with water, a carboxylic acid or a carboxylic anhydride compound.

[0018] On the basis of the above scheme and as a preferred scheme of the above scheme: the hydrophilic compound in step (2) is selected from one of different types of polyethers, polysaccharides, polyols, polyesters, and ionic compounds, but not limited to these, and more preferably polyethylene glycol, hyaluronic acid, mannitol, etc.

[0019] On the basis of the above scheme and as a preferred scheme of the above scheme: the polar organic compound in step (3) is an oily organic substance with a surface tension of less than 20mN / m in liquid state and is poorly soluble or slightly soluble; in order to keep the core material in liquid state during the microcapsule formation process, it can be heated.

[0020] On the basis of the above scheme and as a preferred scheme of the above scheme: the core material of step (3) can be selected from oily organic substances with different functionalities, thermochromic dyes, photochromic dyes, permethrin, and fragrances, including but not limited to these.

[0021] On the basis of the above scheme and as a preferred scheme of the above scheme: the mass ratio of the polyalkoxysiloxane to the hydrophilic group-modified polyalkoxysiloxane in step (3) can be adjusted according to the polarity of the core material, and the mass ratio is 1:(0.01-100), preferably 1:(0.1-10).

[0022] On the basis of the above scheme and as a preferred scheme of the above scheme: the amount of the mixture of polyalkoxysiloxane and hydrophilic group-modified polyalkoxysiloxane added in step (3) can be adjusted according to the stability of the emulsion, the particle size and characteristics of the required microcapsules, and the mass ratio of the mixture to the oil phase core material is (0.01-100):1. Preferably, it is (0.1-10):1, and more preferably, it is (0.2-5):1.

[0023] On the basis of the above scheme and as a preferred scheme of the above scheme: the pH value of the aqueous phase of the emulsion in step (4) is 1-10; preferably 2-9, more preferably 3-8.

[0024] The emulsification method in step (4) includes stirring, ultrasonic emulsification, homogenization emulsification, etc., including but not limited to these.

[0025] On the basis of the above scheme and as a preferred scheme of the above scheme: the reaction rate of step (5) is mainly determined by the pH value of the aqueous phase, and a catalyst can be added to increase the reaction rate, including but not limited to fluoride ions, Lewis acids and bases, etc.

[0026] On the basis of the above scheme and as a preferred scheme of the above scheme: the drying technology in step (6) is one of hot air drying, spray drying, freeze drying, vacuum drying, etc., including but not limited to these.

[0027] Compared with the prior art, the present invention has the following outstanding and beneficial technical effects:

[0028] 1) The method for preparing high mechanical strength silica microcapsules provided by the present invention does not require the assistance of surfactants. The hydrophilic substance modified polyalkoxysiloxane and the unmodified polyalkoxysiloxane are compounded in proportion as silica precursors to encapsulate oily compounds. No by-products are generated, and the final product does not need to be washed or purified. The obtained slurry can be used directly, and the production cost is greatly reduced.

[0029] 3) The preparation method provided by the present invention achieves high encapsulation efficiency of polar organic materials by compounding polyalkoxysiloxane and hydrophilic modified polyalkoxysiloxane;

[0030] 2) The silica microcapsules obtained by this method have a controllable size range, are high temperature resistant, flame retardant, have high mechanical strength, strong pressure bearing capacity, and excellent encapsulation performance. No core material leakage is observed after 100 thermal cycles or during reprocessing such as coating and melt spinning. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 : Scanning electron micrograph of silica microcapsules prepared from a mixture of polyethylene glycol-modified polyethoxysiloxane and polyethoxysiloxane in a mass ratio of 1:1. The scale bar in the image is 10 μm.

[0032] Figure 2 : The particle size distribution of the thermochromic silica microcapsules measured by static light scattering technology in Example 3.

[0033] Figure 3 : Differential scanning calorimetry curves of the thermochromic core material (TLD-B) and thermochromic silica microcapsules (TLD-B@SiO2) in Example 3.

[0034] Figure 4 : Thermogravimetric analysis curves of the thermosensitive color-changing core material (TLD-B) and the thermosensitive color-changing silica microcapsules (TLD-B@SiO2) in Example 3.

[0035] Figure 5: Photos of the aqueous dispersion of thermochromic silica microcapsules in Example 3 at 23°C and 41°C.

[0036] Figure 6 : Projection electron microscope photograph of aromatic silica microcapsules in Example 4.

[0037] Figure 7 : Scanning electron microscope photo of mosquito-proof silica microcapsules in Example 5. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the scope of the present invention is not limited in any way. Unless otherwise stated, the reagents used in the specific examples can be obtained by commercial means;

[0039] Example 1

[0040] A polyethoxysiloxane synthesized by the method of the present invention

[0041] Under N2 atmosphere, ethyl orthosilicate, acetic anhydride and ethyl titanate (molar ratio 2:2:0.006) were added to a three-necked round-bottom flask equipped with a magnetic stirrer and a reflux tower connected to a distillation bridge. The mixture was heated to 135°C in an oil bath under vigorous stirring, and the obtained ethyl acetate was continuously distilled off. When the distillation of ethyl acetate stopped, the system was connected to vacuum and de-boiled at 100°C to obtain a yellow transparent oily liquid, which was polyethoxysiloxane. The simplest formula obtained by elemental analysis was SiO 1.09 (OC2H5) 1.82 .

[0042] Example 2

[0043] Synthesis of polyethylene glycol modified polyethoxysiloxane by the method of the present invention

[0044] Under N2 atmosphere, 120 g of the polyethoxysiloxane synthesized in Example 1 and 30 g of polyethylene glycol monomethyl ether with a molecular weight of 350 were added to a 250 ml flask equipped with a magnetic stirrer and a reflux tower connected to a distillation bridge. The mixture was heated to 135°C under vigorous stirring until the distillation of ethanol stopped. The resulting product was de-boiled under vacuum at 100°C to obtain a yellow transparent oily liquid, which was polyethylene glycol-modified polyethoxysiloxane. The hydrogen nuclear magnetic spectrum of the product showed that 5% of the ethoxy groups in the polyethoxysiloxane were replaced by polyethylene glycol.

[0045] Example 3

[0046] The method of the invention is used to prepare thermosensitive color-changing silicon dioxide microcapsules.

[0047] 1) 1 g of crystal violet lactone, 15 g of bisphenol B and 100 g of myristyl alcohol were mixed in a beaker, stirred in a 75° C. water bath for 2 hours to mix evenly, and slowly cooled to room temperature to generate a uniform mixture as a thermochromic core material.

[0048] 2) 3 g of the thermochromic core material was added to a 250 ml flask, and 150 ml of deionized water was added and heated to 70° C. After the thermochromic core material was melted, a rotor-stator homogenizer was used to emulsify at 70° C. at a speed of 11,000 rpm for 5 minutes to obtain an O / W emulsion.

[0049] 2.25 g of the polyethoxysiloxane synthesized in Example 1 and 2.25 g of the polyethylene glycol-modified polyethoxysiloxane synthesized in Example 2 were mixed and injected into a flask, and further emulsified at 70°C for 15 minutes. At 70°C, magnetic stirring was performed at a speed of 750 rpm for 24 hours to obtain a milky emulsion. The microcapsules were separated by centrifugation, washed with deionized water 3 times, and freeze-dried to obtain thermosensitive color-changing silica microcapsule powder.

[0050] The scanning electron microscope image of the obtained thermochromic silica microcapsules is shown in Figure 1 As shown, the particle size distribution diagram is Figure 2 As shown. The microcapsule particle size is 3-5 microns, evenly distributed, and spherical and intact without cracks. From the DSC curve ( Figure 3 ) It can be seen that the exothermic peak and endothermic peak of the microcapsule are similar to those of the core material, but the temperature is slightly delayed. This phenomenon is crystallization delay, indicating that the core material is encapsulated in the microcapsule. Thermogravimetric curve (TGA) ( Figure 4 ) showed that the thermal weight loss of the microcapsules reached 66.5%. According to the feed amount, the encapsulation efficiency was almost 100%. Figure 5 The thermochromic performance of the microcapsule in aqueous dispersion is shown. The dispersion is stable and the thermochromic change is reversible, indicating that even in water, there is no sign of leakage of the coated core material.

[0051] Example 4

[0052] Preparation of aromatic microcapsules using the method of the present invention

[0053] The difference between Example 4 and Example 3 is that the heat-sensitive color-changing core material in step 2) is replaced with a fragrance core material. The preparation method of the fragrance core material is to stir 50 grams of rose essential oil and 50 grams of myristyl myristate at 70° C. for 2 hours to mix evenly, and slowly cool to room temperature to generate a uniform mixture as the fragrance core material.

[0054] The transmission electron microscopy images of the obtained microcapsules are shown in Figure 6 As shown, the average particle size is about 1 micron.

[0055] Example 5

[0056] Preparation of mosquito-proof microcapsules using the method of the present invention

[0057] Example 5 is a mosquito-proof silica microcapsule. The difference between Example 5 and Example 3 is that the thermosensitive color-changing core material in step 2) is replaced with permethrin (C 21 H 20 C l2 O3). The other steps are the same.

[0058] The scanning electron microscopy images of the obtained microcapsules are shown in Figure 7 As shown, the average particle size is about 5 microns.

[0059] In the description of the present invention, it should be understood that the terms "upper", "lower", "top", "bottom", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0060] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. In the present invention, unless otherwise clearly specified and limited, the terms "install", "set", "connect", "fix", "screw" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection;

[0061] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for encapsulating a polar organic compound into a silica microcapsule, characterized in that: The following steps are involved: (1) forming polyalkylsiloxane as a precursor of silica microcapsules through the condensation reaction of alkoxysilane monomers; (2) using a hydroxyl-containing hydrophilic compound to replace part of the alkoxy groups in the polyalkylsiloxane to obtain an amphiphilic modified polyalkoxysiloxane as another precursor of silica microcapsules; (3) mixing the polyalkoxysiloxane obtained in step (1), the hydrophilic group-modified polyalkoxysiloxane obtained in step (2) and the polar organic compound in proportion, and if necessary, heating the mixture to make it liquid; (4) emulsifying the mixture obtained in step (3) in water to form an oil-in-water emulsion; (5) forming silica microcapsules by condensing two precursors of silica microcapsules in the mixture; (6) The silica microcapsule powder encapsulating the polar organic compound is obtained by drying.

2. The method for encapsulating a polar organic compound into a silica microcapsule according to claim 1, characterized in that: The alkoxysilane monomer in step (1) has the following general chemical formula R 4-n Si(OX) n , wherein n=2-4, R is a non-hydrolyzable group, which may be a halogenated alkyl group such as an alkyl group, a vinyl alkyl group, a styryl alkyl group, a methacryloyloxy alkyl group, a urea alkyl group, a chloropropyl alkyl group or a sulfanyl group; X is an alkyl group having 1-6 carbon atoms; the alkoxysilane monomer may be a single monomer or a mixture of two or more monomers; the condensation of the alkoxysilane monomer may be achieved by reaction with water, a carboxylic acid or a carboxylic anhydride compound.

3. The method for encapsulating a polar organic compound into a silica microcapsule according to claim 1, characterized in that: The hydrophilic compound in step (2) is selected from one of different types of polyethers, polysaccharides, polyols, polyesters, and ionic compounds.

4. The method for encapsulating a polar organic compound into a silica microcapsule according to claim 1, characterized in that: The polar organic compound in step (3) is an oily organic substance with a surface tension of less than 20 mN / m in liquid state and is poorly soluble or slightly soluble; in order to keep the core material in liquid state during the microcapsule formation process, it can be heated.

5. The method for encapsulating a polar organic compound into a silica microcapsule according to claim 4, characterized in that: The core material of step (3) can be selected from oily organic substances with different functionalities, thermochromic dyes, photochromic dyes, permethrin, and essences.

6. The method for encapsulating a polar organic compound into a silica microcapsule according to claim 1, characterized in that: The mass ratio of the polyalkoxysiloxane to the hydrophilic group-modified polyalkoxysiloxane in step (3) can be adjusted according to the polarity of the core material, and the mass ratio is 1:(0.01-100).

7. The method for encapsulating a polar organic compound into a silica microcapsule according to claim 6, characterized in that: The amount of the mixture of polyalkoxysiloxane and hydrophilic group-modified polyalkoxysiloxane added in step (3) can be adjusted according to the emulsion stability, the particle size and characteristics of the required microcapsules, and the mass ratio of the mixture to the oil phase core material is (0.01-100):

1.

8. The method for encapsulating a polar organic compound into a silica microcapsule according to claim 1, characterized in that: The pH value of the aqueous phase of the emulsion in step (4) is 1-10; the emulsification method in step (4) includes stirring, ultrasonic emulsification, homogenization emulsification, etc.

9. The method for encapsulating a polar organic compound into a silica microcapsule according to claim 1, characterized in that: The reaction rate of step (5) is mainly determined by the pH value of the aqueous phase, and a catalyst can be added to increase the reaction rate.

10. The method for encapsulating a polar organic compound into a silica microcapsule according to claim 1, characterized in that: The drying technology in step (6) is one of hot air drying, spray drying, freeze drying, vacuum drying, etc.

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