A method for encapsulating polar organic compounds into silica microcapsules

Abstract

This invention discloses a method for encapsulating a polar organic compound into silica microcapsules. The method involves (1) forming a polyalkylsiloxane as a precursor for silica microcapsules through a condensation reaction of alkoxysilane monomers; (2) replacing part of the alkoxy groups in the polyalkylsiloxane with a hydrophilic compound containing hydroxyl groups to obtain an amphiphilic modified polyalkoxysiloxane as another precursor for silica microcapsules; (3) mixing the polyalkoxysiloxane obtained in step (1), the hydrophilic modified polyalkoxysiloxane obtained in step (2), and the polar organic compound in a certain 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; and (5) forming silica microcapsules through a condensation reaction of the two precursors for silica microcapsules in the mixture.

Description

Technical Field

[0001] This invention belongs to the field of microcapsule technology, specifically relating to a method for encapsulating polar organic compounds into silica microcapsules with high mechanical properties without using organic surfactants. Background Technology

[0002] Many oily, reactive organic compounds can achieve leak-proof, stable, and sustained-release properties through microencapsulation. However, most existing microcapsule products use organic polymers as wall materials, which present problems such as flammability, poor degradation, susceptibility to light exposure, and difficulty in releasing the core material. Amorphous silica, due to its high chemical inertness, non-flammability, biocompatibility, optical transparency, and thermal and mechanical stability, is a very promising inorganic wall material.

[0003] US Patent 6303149B1 discloses a technique for encapsulating oily active ingredients into silica microcapsules using the hydrolysis and condensation of tetraethyl orthosilicate in an oil-in-water emulsion. To effectively stabilize the emulsion, an organic surfactant needs to be added, but it must be removed after the reaction. This inevitably leads to increased production costs and environmental pollution, especially water pollution.

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

[0005] To improve the interfacial activity of polyalkoxysiloxanes, patent CN111170323A proposed replacing some of the alkoxy groups in polyalkoxysiloxanes with hydrophilic compounds and using these compounds as silica precursors to coat various oily substances. The aerogel particles obtained by this method are coated with oily compounds, have very low density, extremely 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-mentioned background technology, the purpose of this 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 change under light, 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 polyalkoxysiloxanes as precursors to encapsulate polar core materials; and the problem that modifying polyalkoxysiloxanes with hydrophilic substances can only obtain aerogel particle microcapsules with limited mechanical properties and very low density.

[0008] This invention utilizes a mixture of hydrophobic polyalkoxysiloxane and hydrophilic modified polyalkoxysiloxane as a precursor for silica microcapsules to encapsulate polar organic compounds. The hydrophilic modified polyalkoxysiloxane possesses an amphiphilic structure, reducing the water-oil interfacial energy to below 1 mN / m, while the highly hydrophobic polyalkoxysiloxane is encapsulated within oil droplets, inhibiting Ostwald ripening and thus enhancing emulsion stability. Furthermore, during hydrolysis and condensation, the polyalkoxysiloxane slowly migrates to the interface, thickening the silica layer and improving its mechanical properties.

[0009] To solve the above-mentioned technical problems, the objective of this invention is achieved as follows:

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

[0011] (1) Polyalkylsiloxane is formed by the condensation reaction of alkoxysilane monomers as a precursor for silica microcapsules;

[0012] (2) A hydrophilic compound containing hydroxyl groups was used to replace part of the alkoxy groups in the polyalkylsiloxane to obtain an amphiphilic modified polyalkoxysiloxane as a precursor for another type of silica microcapsule;

[0013] (3) Mix the polyalkoxysiloxane obtained in step (1), the hydrophilic group modified polyalkoxysiloxane obtained in step (2), and the polar organic compound in proportion. If necessary, the mixture can be heated to make it liquid.

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

[0015] (5) Silica microcapsules are formed by the condensation reaction of the two precursors of silica microcapsules in the mixture;

[0016] (6) The silica microcapsule powder coated with polar organic compounds is obtained by drying.

[0017] Based on the above scheme and as a preferred embodiment of the above scheme: the alkoxysilane monomer in step (1) has the following general chemical formula R 4-nSi(OX)n, where n = 2-4, R is a non-hydrolyzable group, which can be a alkyl, vinylalkyl, styrylalkyl, methacryloxyalkyl, ureylalkyl, chloropropylalkyl, or thioalkyl haloalkyl; X is an alkyl group with 1-6 carbon atoms; the alkoxysilane monomer can be a single monomer or a mixture of two or more monomers; the condensation of the alkoxysilane monomer can be achieved by reacting with water, carboxylic acid, or carboxylic anhydride compounds.

[0018] Based on the above scheme and as a preferred embodiment 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. However, it is not limited to these, and is more preferably polyethylene glycol, hyaluronic acid, mannitol, etc.

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

[0020] Based on the above scheme and as a preferred option of the above scheme: the core material in step (3) can be an oily organic material with different functions, such as thermochromic dye, photochromic dye, permethrin, fragrance, etc., including but not limited to these.

[0021] Based on the above scheme and as a preferred embodiment of the above scheme: the mass ratio of polyalkoxysiloxane to hydrophilic 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, it is 1:(0.1-10).

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

[0023] Based on the above scheme and as a preferred embodiment 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 described in step (4) includes one of the following: stirring, ultrasonic emulsification, homogenization emulsification, etc., including but not limited to these.

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

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

[0027] The outstanding and beneficial technical effects of this invention compared to the prior art are:

[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 material modified polyalkoxysiloxane and unmodified polyalkoxysiloxane are compounded in proportion as silica precursors to coat oily compounds. No by-products are generated, and the final product does not require washing or purification. The obtained slurry can be used directly, which greatly reduces the production cost.

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

[0030] 2) The silica microcapsules obtained by this method have a controllable size range, are resistant to high temperature, flame retardant, have high mechanical strength, strong pressure resistance, and excellent encapsulation performance. No core material leakage can be observed after 100 thermal cycles or during reprocessing such as coating or melt spinning. Attached Figure Description

[0031] Figure 1 Scanning electron microscope (SEM) image of silica microcapsules prepared from a 1:1 mass ratio of polyethylene glycol-modified polyethoxysiloxane and polyethoxysiloxane. The scale bar in the image is 10 micrometers.

[0032] Figure 2 The particle size distribution of thermochromic silica microcapsules measured using static light scattering technique in Example 3.

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

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

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

[0036] Figure 6 Transmission electron microscope image of the aromatic silica microcapsules in Example 4.

[0037] Figure 7 Scanning electron microscope image of the mosquito-repellent silica microcapsules in Example 5. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this does not limit the scope of the invention in any way. Unless otherwise stated, the reagents used in the specific embodiments can be obtained by commercial means.

[0039] Example 1

[0040] A polyethoxysiloxane synthesized using the method of the present invention.

[0041] Under a nitrogen atmosphere, tetraethyl orthosilicate, acetic anhydride, and tetraethyl titanate (molar ratio 2:2:0.006) were added to a three-necked round-bottom flask equipped with a magnetic stirrer and a reflux column connected to a distillation bridge. The mixture was heated to 135°C in an oil bath under vigorous stirring. The resulting ethyl acetate was continuously distilled off. When the distillation of ethyl acetate ceased, the system was connected to a vacuum, and the low-boiling point was removed at 100°C to obtain a yellow, transparent, oily liquid, which is polyethoxysiloxane. Elemental analysis yielded its simplest formula as SiO₂. 1.09 (OC2H5) 1.82 .

[0042] Example 2

[0043] Polyethylene glycol-modified polyethoxysiloxanes were synthesized using the method of this invention.

[0044] Under a nitrogen 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 column connected to a distillation bridge. The mixture was heated to 135 °C with vigorous stirring until the distillation of ethanol ceased. The resulting product was deboiled under vacuum at 100 °C to obtain a yellow, transparent, oily liquid, which was the polyethylene glycol-modified polyethoxysiloxane. The proton NMR spectrum of the product showed that 5% of the ethoxy groups in the polyethoxysiloxane were replaced by polyethylene glycol.

[0045] Example 3

[0046] Thermosensitive color-changing silica microcapsules were prepared using the method of the present invention.

[0047] 1) Mix 1 gram of crystal violet lactone, 15 grams of bisphenol B and 100 grams of myristol in a beaker, and stir in a 75°C water bath for 2 hours until homogeneous. Slowly cool to room temperature to generate a homogeneous mixture, which can be used as the thermosensitive color-changing core material.

[0048] 2) Take 3 grams of thermochromic core material and add it to a 250 ml flask. Add 150 ml of deionized water and heat to 70°C. After the thermochromic core material melts, use a rotor-stator homogenizer to emulsify it at 70°C and 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. The mixture was then magnetically stirred at 750 rpm for 24 hours at 70°C to obtain a milky emulsion. The microcapsules were separated by centrifugation, washed three times with deionized water, and freeze-dried to obtain thermosensitive color-changing silica microcapsule powder.

[0050] Scanning electron microscope image of the obtained thermochromic silica microcapsules is shown below. Figure 1 As shown, the particle size distribution diagram is as follows. Figure 2 As shown in the figure. The microcapsules have a particle size of 3-5 micrometers, are uniformly distributed, and are spherical and intact without breakage. This is illustrated by the DSC curve. Figure 3 As can be seen, the exothermic and endothermic peaks of the microcapsule are similar to those of the core material, but the temperature is slightly delayed. This phenomenon is due to delayed crystallization, indicating that the core material is encapsulated within the microcapsule. Thermogravimetric analysis (TGA) curves (…) Figure 4 The results showed that the microcapsules had a thermal weight loss of 66.5%, and based on the amount of material fed, the encapsulation efficiency was almost 100%. Figure 5 The display shows the thermochromic properties of the microcapsule aqueous dispersion. The dispersion is stable, and the thermochromic change is reversible, indicating that even in water, there is no trace of leakage from the encapsulated core material.

[0051] Example 4

[0052] Aromatic microcapsules prepared using the method of the present invention

[0053] The difference between Example 4 and Example 3 is that the thermosensitive color-changing core material in step 2) is replaced with an aromatic core material. The aromatic core material is prepared by stirring 50 grams of rose essential oil and 50 grams of myristate at 70°C for 2 hours until they are evenly mixed, and then slowly cooled to room temperature to generate a homogeneous mixture as the aromatic core material.

[0054] The transmission electron microscope image of the obtained microcapsules is shown below. Figure 6 As shown, its average particle size is about 1 micrometer.

[0055] Example 5

[0056] Mosquito-repellent microcapsules prepared using the method of the present invention

[0057] Example 5 is a mosquito-repellent 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). All other steps are the same.

[0058] Scanning electron microscope image of the obtained microcapsules is shown below. Figure 7 As shown, its average particle size is around 5 micrometers.

[0059] In the description of this invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0060] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In this invention, unless otherwise expressly specified and limited, the terms "installation," "setting," "connection," "fixing," "screw-in," etc., should be interpreted broadly; for example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection.

[0061] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for encapsulating a polar organic compound into silica microcapsules, characterized in that: Includes the following steps: (1) Polyalkoxysiloxane is formed by the condensation reaction of alkoxysilane monomers as a precursor for silica microcapsules; (2) A hydrophilic compound containing hydroxyl groups was used to replace part of the alkoxy groups in the polyalkoxysiloxane to obtain an amphiphilic modified polyalkoxysiloxane as a precursor for another type of silica microcapsule; (3) Mix the polyalkoxysiloxane obtained in step (1), the hydrophilic group modified polyalkoxysiloxane obtained in step (2), and the polar organic compound in proportion, and heat the mixture to make it liquid. The polar organic compound in step (3) is an oily organic compound with a surface tension of less than 20 mN / m in the liquid state and which is sparingly or slightly soluble. The oily organic compound is selected from one of the following: thermosensitive color-changing dye, photosensitive color-changing dye, permethrin, and fragrance. (4) Emulsify the mixture obtained in step (3) in water to form an oil-in-water emulsion; (5) Silica microcapsules are formed by the condensation reaction of the two precursors of silica microcapsules in the mixture; (6) The silica microcapsule powder coated with polar organic compounds is obtained by drying.

2. The method for encapsulating polar organic compounds into silica microcapsules according to claim 1, characterized in that: The alkoxysilane monomer described 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 is a haloalkyl group of alkyl, vinylalkyl, styrylalkyl, methacryloxyalkyl, ureylalkyl, chloropropylalkyl or thioalkyl; X is an alkyl group with 1-6 carbon atoms; the alkoxysilane monomer is a monomer or a mixture of two or more monomers; the condensation of the alkoxysilane monomer is achieved by reaction with water, carboxylic acid or carboxylic anhydride compound.

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

4. The method for encapsulating polar organic compounds into silica microcapsules according to claim 1, characterized in that: Step (3) To keep the oily organic matter in a liquid state during the microcapsule formation process, heat it.

5. The method for encapsulating polar organic compounds into silica microcapsules according to claim 1, characterized in that: The mass ratio of polyalkoxysiloxane to hydrophilic modified polyalkoxysiloxane in step (3) can be adjusted according to the polarity of the oily organic matter, and the mass ratio is 1:(0.01-100).

6. The method for encapsulating a polar organic compound into silica microcapsules according to claim 5, characterized in that: The amount of polyalkoxysiloxane and hydrophilic modified polyalkoxysiloxane mixture added in step (3) can be adjusted according to the emulsion stability, the required particle size and characteristics of microcapsules, and its mass ratio with oily organic matter is (0.01-100):

1.

7. The method for encapsulating polar organic compounds into silica microcapsules 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 one of stirring, ultrasonic emulsification, and homogenization emulsification.

8. The method for encapsulating a polar organic compound into silica microcapsules according to claim 1, characterized in that: The reaction rate in step (5) is mainly determined by the pH value of the aqueous phase, and the reaction rate is increased by adding a catalyst.

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

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