Polyurea wall material micron capsule as well as preparation method and application thereof

Abstract

The invention belongs to the field of essence micron capsules, and particularly relates to a polyurea wall material micron capsule as well as a preparation method and application thereof. Comprising the following steps: mixing a water phase and an oil phase, and fully and uniformly homogenizing to form an oil-in-water emulsion; the preparation method comprises the following steps: adding an amine monomer aqueous solution into an oil-in-water emulsion, carrying out an initiation reaction, heating the system, continuing the reaction, curing the wall material of the micro-capsule to obtain a natural essence micro-capsule slurry with polyurea as the wall material, and carrying out freeze drying treatment on the prepared micro-capsule slurry to remove water in the system to obtain the polyurea wall material micro-capsule. The essence prepared by the method is high in entrapment capacity, easy in size control and relatively small in size.

Description

Technical Field

[0001] The present invention belongs to the field of essence microcapsules, and particularly relates to a polyurea wall material microcapsule, a preparation method thereof and an application thereof. Background Art

[0002] Plant-based natural flavors are mainly obtained by extracting flowers, leaves, stems and fruits of various plants, or barks and roots of trees, etc. Natural flavors have characteristic volatile components, and most of these characteristic flavor molecules have various effects such as relieving mental stress, calming the nerves, making people feel happy and promoting sleep.

[0003] However, essence and flavor have strong volatility, and it is easy to cause unnecessary losses during storage, transportation and use, which greatly reduces the utilization efficiency of essence and flavor, and at the same time causes many difficulties and inconveniences in the processing of products. At the same time, as a special active substance, the fragrance of essence and flavor is closely related to its molecular structure and composition. The complexity of the processing and use environment of essence and flavor easily leads to the deterioration of essence and flavor, and then causes changes in fragrance type and flavor, which greatly affects the use value and application development of essence and flavor.

[0004] As a polymer embedding technology, the microcapsule technology is applied to the coating of essence and flavor, which can effectively isolate it from the external environment and play a protective role, and can effectively solve the problems of easy volatilization loss and deterioration of the above-mentioned essence and flavor.

[0005] At present, the methods for preparing essence micro / nano capsules mainly have the following disadvantages: (1) In the preparation of many essence microcapsules, formaldehyde, glutaraldehyde, etc. are used as cross-linking agents or wall material monomers, resulting in the problem of residual toxic substances such as formaldehyde in the generated microcapsules; (2) In the traditional preparation method of polyurea microcapsules, aromatic isocyanates are often used, and highly toxic substances such as aniline will be generated during their decomposition process; (3) In some preparation methods of polyurea microcapsules, organometallic catalysts (such as dibutyltin dilaurate, etc.) are used for catalysis, and the toxicity of the catalyst is relatively large; (4) In many preparation methods, the loading amount of essence is relatively low, especially the preparation of essence nano-capsules with a high essence loading amount is rare, the coating efficiency and benefit are relatively low, and it lacks practical application value; (5) The preparation process is relatively complex, and the particle size of the obtained microcapsules is difficult to control, and the size is uneven.

[0006] Therefore, how to prepare essence microcapsules and small-size essence nano-capsules with safety, environmental protection, simple process, high essence loading amount and easy size control is a research problem with important exploration significance and application prospects. Summary of the Invention

[0007] In order to overcome the shortcomings of the above-mentioned existing technologies, the purpose of the present invention is to provide a polyurea wall material microcapsule for encapsulating natural flavors, its preparation method and application, with a high flavor loading capacity, easy size control and small size of the prepared microcapsules.

[0008] In order to achieve the above purpose, the present invention adopts the following technical solutions: In the first aspect, the present invention provides a method for preparing a polyurea wall material microcapsule for encapsulating natural flavors, comprising the following steps: Mix the aqueous phase and the oil phase, homogenize them thoroughly to form a water-in-oil emulsion; add an aqueous solution of an amine monomer to the water-in-oil emulsion, carry out an initiation reaction, raise the temperature of the system and continue the reaction to cure the microcapsule wall material, thereby obtaining a natural flavor microcapsule slurry with polyurea as the wall material. Freeze-dry the prepared microcapsule slurry to remove the water in the system, and polyurea wall material microcapsules can be obtained; the mass ratio of the aqueous phase to the oil phase is (68 - 91.5):(8.5 - 32).

[0009] Preferably, the preparation method of the aqueous phase is: add deionized water to the emulsifier powder, dissolve it thoroughly to form a homogeneous phase, thereby forming the aqueous phase.

[0010] Preferably, the emulsifier is polyvinyl alcohol.

[0011] Preferably, the mass ratio of the emulsifier to deionized water is (1 - 5):(40 - 80).

[0012] Preferably, the preparation method of the oil phase is: stir and dissolve the oil phase monomer isophorone diisocyanate and the natural flavor to make them completely miscible, forming a homogeneous phase, denoted as the oil phase.

[0013] Preferably, the mass ratio of the oil phase monomer isophorone diisocyanate to the natural flavor is 1:(3 - 9).

[0014] Preferably, the mass ratio of the oil phase monomer isophorone diisocyanate to the aqueous solution of the amine monomer is 1:(3 - 4).

[0015] Preferably, the aqueous solution of the amine monomer is an aqueous solution of diethylenetriamine.

[0016] In the second aspect, the present invention provides a polyurea wall material microcapsule.

[0017] In the third aspect, the present invention provides an application of the polyurea wall material microcapsule in the field of flavor microcapsules.

[0018] Compared with the existing technologies, the present invention has the following beneficial effects: In the present invention, by mixing the aqueous phase and the oil phase and fully homogenizing them, the formed oil-in-water emulsion ensures that the essence is effectively dispersed in the aqueous phase; the amine monomer polymerizes with the isocyanate or other substances in the emulsion in the aqueous solution to form a polyurea wall material; the formation of the polyurea wall material not only entraps the essence, but also enhances the mechanical strength of the microcapsules, enabling them to better resist damage from the external environment. In the prior art, amine crosslinking agents are a mixture of polymers and monomers, but the long-chain part in the polymer dominates. During the polymerization reaction, due to the steric hindrance effect, it is difficult for the polymer macromolecules to collide sufficiently with each other in the early stage of the reaction, resulting in a low conversion rate and a low reaction rate; after the polymerization process ends, since the density of the chemical crosslinking points between the polymers after the reaction is reduced compared to the reaction between the monomers, the crosslinked network formed by interfacial polymerization is relatively loose. By only carrying out polymerization between the monomers at the interface, the disadvantages of low conversion rate and poor stability caused by the above reasons are effectively avoided. Therefore, the polyurea wall material produced by the amine monomer in the present invention has a relatively large crosslinking density and good stability. Description of the Drawings

[0019] Figure 1 is the preparation flow chart of the polyurea wall material microcapsules of the present invention; Figure 2 is the reaction mechanism diagram of the oil phase monomer isophorone diisocyanate and the aqueous solution of the amine monomer; Figure 3 is the SEM image (10μm) of the polyurea wall material microcapsules prepared in Example 1 of the present invention; Figure 4 is the SEM image (2μm) of the polyurea wall material microcapsules prepared in Example 1 of the present invention; Figure 5 is the infrared spectrum diagram of DP, IPDI, pure PU wall material and the polyurea wall material microcapsules prepared in Example 1; Figure 6 is the schematic diagram of the influence of the homogenization rate on the average particle size of the polyurea wall material microcapsules prepared in Example 1; Figure 7 is the schematic diagram of the thermogravimetric curves of DP, DP essence microcapsules and pure polyurea wall material; Figure 8 is the schematic diagram of the linear relationship between the concentration of DP in toluene and the ultraviolet absorbance. Detailed Embodiments

[0020] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0021] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0022] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0023] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0024] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings: The present invention provides a method for preparing polyurea wall material micro-capsules for encapsulating natural flavors, such as Figure 1 As shown, the following steps are included: The aqueous phase and the oil phase are mixed and fully homogenized to form an oil-in-water emulsion; an aqueous solution of amine monomers is added to the oil-in-water emulsion to initiate a reaction, and the system is heated to continue the reaction to solidify the micron capsule wall material, thereby obtaining a natural flavor micron capsule slurry with polyurea as the wall material; the prepared micron capsule slurry is subjected to freeze-drying treatment to remove water in the system, thereby obtaining polyurea wall material micron capsules.

[0026] Among them, the natural flavorings are aqueous-phase flavorings such as natural apple flavoring, natural orange flavoring, natural pineapple flavoring, natural tomato flavoring, natural jasmine flower flavoring, and natural passion fruit flavoring of Yangling Yuancui Biotechnology Co., Ltd.

[0027] Through mixing and homogenization, the aqueous phase and the oil phase can be fully fused to form a stable oil-in-water emulsion, providing a good environment for the encapsulation of flavorings in the subsequent steps; the homogenization process ensures the uniform distribution of flavorings in the oil phase, thereby improving the encapsulation efficiency of flavorings in the polyurea wall material microcapsules; the stable emulsion helps to reduce or eliminate the layering phenomenon that may occur in the subsequent steps and ensures the smooth progress of the reaction.

[0028] Among them, the oil-in-water emulsion needs to be heated in a water bath before adding the aqueous solution of amine monomer, and it is kept warm in a constant temperature water bath at 20~50°C for 2~5 min; the initiation reaction time is 20~40 min; the specific process of the system heating up and continuing the reaction is that the system is heated to 55~70°C and continues to react for 1~3 h; the mass ratio of the oil phase to the water phase is (68~91.5):(8.5~32). By controlling the mass ratio of the oil phase to the water phase, the particle size, wall thickness and other characteristics of the polyurea wall material microcapsules can be adjusted to meet the requirements of different application scenarios.

[0029] Keeping the emulsion in a constant temperature water bath at 20~50°C for 2~5 min can preheat the emulsion to make it reach the temperature range suitable for chemical reactions; appropriate preheating can increase the movement speed of molecules in the emulsion, which is beneficial to the subsequent chemical reactions; after the preheated emulsion is added with the aqueous solution of amine monomer, the reaction rate will be faster, which helps to shorten the preparation time.

[0030] The amine monomer undergoes a polymerization reaction with the isocyanate or other reactants in the emulsion to form a polyurea wall material; by controlling the addition rate and reaction conditions (such as temperature, pH value, etc.) of the aqueous solution of amine monomer, the formation rate and thickness of the polyurea wall material can be precisely controlled. During the initiation reaction process, the polyurea wall material begins to form around the essential oil droplets, initially realizing the encapsulation of flavorings.

[0031] Heating the system to 55~70°C can accelerate the rate of chemical reactions, enabling the amine monomer to react more fully with reactants such as isocyanate to form a denser polyurea wall material. Under high-temperature conditions, the polyurea wall material gradually solidifies to form a stable microcapsule structure. The solidified wall material can more effectively protect the flavorings and prevent them from leaking or volatilizing. Continuing the reaction for 1~3 h helps to ensure the integrity and uniformity of the polyurea wall material, thereby improving the overall quality of the polyurea wall material microcapsules.

[0032] Freeze drying: Invert the micron capsule slurry into a flat culture dish and place it in a refrigerator to freeze overnight to completely freeze the material into a solid state. Start the cold trap of the freeze dryer and place the frozen material in the cold trap of the freeze dryer to pre-freeze for 0.5 hours, and then place the pre-frozen sample on the drying rack. After covering the vacuum cover, start the vacuum pump, evacuate until the displayed air pressure is lower than 20Pa, continue to vacuum dry for a sufficient time (depending on the thickness of the material to be dried, the amount of material, etc.), open the vacuum valve and wait for the air pressure to rise, turn off the vacuum pump, stop vacuum drying, and obtain the polyurea wall material micron capsule.

[0033] Freeze drying technology is also known as vacuum freeze drying. Its basic principle is based on the transformation of water from solid to gas. Freeze drying is the most critical process. The wet material is frozen at the eutectic temperature. The material remains frozen and ice crystals sublimate under a high vacuum. The water is directly transformed from solid to gas and removed, thereby achieving the purpose of dehydration and drying to obtain a dry product. Unlike spray drying technology, freeze drying technology can avoid the damage to the quality of the material caused by high temperature medium during the drying process, and can maximize the maintenance of the color, aroma and taste of the target material and reduce the loss of nutrients and effective components. It is suitable for materials with high heat sensitivity and easy oxidation, and is therefore widely used in the food industry, biomedicine, biomaterials and new materials science, animal and plant specimen preparation and other fields. The material after vacuum freeze drying is mostly porous sponge-like in structure, with basically unchanged volume, and has good solubility and rehydration properties.

[0034] The preparation method of the water-in-oil emulsion is: mixing the water phase and the oil phase, and fully homogenizing them to form the water-in-oil emulsion; wherein the homogenization adopts a high-speed shearing machine, and the shearing speed is 5000-7000rpm.

[0035] The preparation method of the aqueous phase is: adding deionized water to the emulsifier powder, fully dissolving it to form a uniform phase, and forming an aqueous phase, wherein the emulsifier is polyvinyl alcohol; the mass ratio of the emulsifier to the deionized water is (1-5): (40-80).

[0036] The preparation method of the oil phase is as follows: stirring and dissolving the oil phase monomer isophorone diisocyanate and the natural flavor, so that the two are completely miscible and form a uniform phase, which is recorded as the oil phase; wherein the mass ratio of the oil phase monomer isophorone diisocyanate to the natural flavor is 1:(3-9); the mass ratio of the oil phase monomer isophorone diisocyanate to the amine monomer aqueous solution is 1:(3-4); the amine monomer aqueous solution is a dilute solution, preferably with a mass concentration of 45%, and the main function of the diluent is to prevent the amine monomer from reacting too fast during interfacial polymerization with isophorone diisocyanate, resulting in implosion, thereby preventing the amine monomer from forming uniform capsules with the flavor at the interface under a certain shear rate; the amine monomer aqueous solution is diethylenetriamine (DETA).

[0037] The present invention uses the method of interfacial polymerization of isophorone diisocyanate and diethylenetriamine in an emulsion to form a polyurea wall material, complete the encapsulation of natural essence, and prepare polyurea wall material microcapsules. The reaction mechanism is as Figure 2 shown: After the oil-water two-phase mixture is sheared at high speed to form an oil-in-water emulsion, isophorone diisocyanate is dispersed in the oil phase as an oil-phase monomer. After dropping an aqueous solution of an amine water-phase monomer - diethylenetriamine, at the water-oil interface, the -NCO group in isophorone diisocyanate and -NH 2 and -NH undergo a nucleophilic addition reaction, and at the same time, -NCO and -NH 2 The -NHCONH- formed by the reaction can further undergo addition polymerization and cross-linking with -NCO, thereby forming a network cross-linked polymer.

[0038] The second object of the present invention is to provide a polyurea wall material microcapsule for encapsulating natural essence. The present invention mainly adopts the method of emulsion interfacial polymerization, using isophorone diisocyanate (IPDI), diethylenetriamine (DETA), and 1,6-hexanediamine (HMDA) as reaction monomers to prepare natural essence microcapsules and nanocapsules with polyurea as the wall material. The main advantages are: (1) The monomer IPDI is an aliphatic diisocyanate, and its decomposition does not produce highly toxic aniline substances. The amines DETA and HMDA used also have relatively low toxicity. No catalyst is required during the preparation process, the process is relatively simple, and the reaction monomers polymerize at the oil-water interface to form a polyurea polymer to form the wall material. The prepared microcapsules and nanocapsules both have a high essence loading capacity.

[0039] (2) Under the condition of a relatively high loading capacity, the prepared nanocapsules still have a relatively small average particle size and good physical dispersion stability, within the range of 0.1 wt% - 0.5 wt% of the commonly used essence addition amount in practice.

[0040] The third object of the present invention is to provide the application of a polyurea wall material microcapsule for encapsulating natural essence in the field of essence microcapsules. With the increasing requirements of consumers for product safety and naturalness, natural essence is increasingly widely used in many fields such as cosmetics, food, fragrances, and medicine. However, problems such as the easy volatility and easy oxidation of natural essence limit its use effect and market potential. The polyurea wall material microcapsule technology of the present invention provides an ideal solution for these industries by realizing the efficient and stable encapsulation of natural essence.

[0041] In the cosmetics field, this micro-encapsulation technology can significantly improve the fragrance durability of products, while reducing the direct irritation of flavor ingredients to the skin, improving product safety and comfort. In the food industry, this technology helps to maintain the natural flavor of food, extend the shelf life, and meet consumers' pursuit of healthy and delicious food. In addition, in the fields of spices and medicine, the application of polyurea wall material micro-encapsulation also shows great potential, bringing more innovation possibilities and market opportunities to these industries.

[0042] Example 1 80g of deionized water was added to 1g of polyvinyl alcohol powder and fully dissolved to form a uniform phase, which was the water phase; 10g of oil phase monomer isophorone diisocyanate and 30g of natural apple flavor were stirred and dissolved to make them completely miscible to form a uniform phase, which was recorded as the oil phase; 68g of water phase and 32g of oil phase were mixed and homogenized to form an oil-in-water emulsion, which was placed in a constant temperature water bath at 35°C for 3 minutes. 30g of diethylenetriamine aqueous solution was then added to the oil-in-water emulsion to initiate the reaction. After 30 minutes, the system was heated to 55°C and the reaction was continued for 2 hours to solidify the microcapsule wall material, thereby obtaining a natural flavor microcapsule slurry with polyurea as the wall material. The prepared microcapsule slurry was freeze-dried to remove water in the system to obtain polyurea wall material microcapsules.

[0043] The performance results of the polyurea wall material microcapsules prepared in Example 1 were tested: Morphology analysis of microcapsules: After the reaction is completed, the micro-capsule slurry is diluted by an appropriate multiple, and an appropriate amount of the diluent is added to the aluminum foil, and then the aluminum foil is placed in a blast drying oven at 60°C for drying. The aluminum foil containing the solid part after drying is cut and pasted on the electron microscope platform with conductive glue. The appearance of the fragrance micro-capsule in the dry state is observed by scanning electron microscopy. Figure 3 and Figure 4 It can be seen that when PVA is used as an emulsifier, the prepared fragrance micro-capsules are small in size and spherical with a smooth surface. When DETA is used as a reaction monomer, the reaction generates a large number of spherical micro-capsules with a smooth surface.

[0044] Infrared spectroscopy analysis: Infrared spectroscopy analysis was performed on the target core material, reactive monomer, pure polyurea wall material, and polyurea wall material microcapsules. By comparing the infrared spectra and their respective characteristic peaks, it can be analyzed whether the isocyanate monomer is completely reacted and whether the target core material is coated. Infrared spectroscopy analysis was performed on mint flavor (DP), IPDI, pure wall material polyurea PU, and polyurea wall material microcapsules. Figure 5 Curve a is the infrared spectrum of DP flavor, 3436cm -1is the absorption peak of O—H stretching vibration in menthol, 1712 cm -1 is the absorption peak of C=O stretching vibration in menthone. Curve b is the spectrum of monomer IPDI, 2260, 1365 cm -1 are the absorption peaks of asymmetric stretching and symmetric stretching vibrations of -N=C=O respectively, 2956 cm -1 is the absorption peak of C-H stretching vibration. Curve c is the spectrum of the polyurea wall material obtained by the polycondensation of IPDI and DETA. 3300 cm -1 is the absorption peak of N-H stretching vibration in the ureido group -NH-CO-NH-, 1632, 1558 cm -1 are the absorption peaks of C=O stretching vibration and N-H in-plane deformation vibration in the ureido group -NH-CO-NH- respectively. And in the range of 2275 - 2250 cm -1 and 1400 - 1350 cm -1 no obvious absorption peaks appear, that is, there is no characteristic peak of the isocyanate group -N=C=O, indicating that the monomers have polymerized. Curve d is the infrared spectrum of the polyurea wall material microcapsules. Comparing the above spectra, the characteristic peaks of the core material peppermint essence a and the polyurea shell material c can be correspondingly found in curve d, and the intensities are basically the same. The characteristic peak of the isocyanate group -N=C=O disappears, indicating that the monomers have polymerized to form the PU wall material and encapsulated the core material DP essence.

[0045] Particle size analysis: Different homogenization rates result in different dispersion intensities of the emulsion system, which in turn greatly affects the particle size and size distribution of the polyurea wall material microcapsules prepared by the reaction. In this experiment, a laser particle size analyzer was used to test the polyurea wall material microcapsules at different homogenization rates, and the influence of the homogenization rate on the particle size and size distribution of the polyurea wall material microcapsules was explored. From Figure 6 it can be seen that as the homogenization rate increases from 5000 rpm to 9000 rpm, the particle size of the prepared polyurea wall material microcapsules gradually decreases from 7.512 μm to 3.187 μm.

[0046] Thermal stability analysis: From the weight loss curve of the polyurea wall material microcapsules ( Figure 7 ), it can be seen that at about 80 - 190 °C, in this stage, due to the increase in temperature, a small amount of the core material volatilizes and loses weight. As the temperature further increases to about 238 °C, the volatilization of the core material causes the internal pressure of the capsule to increase, and the outer shell of the microcapsule gradually bursts, accelerating the weight loss of the core material. As the temperature continues to rise, the thermal decomposition of the wall material further exacerbates the mass loss of the core material and the wall material. To sum up, the encapsulation of the polyurea shell has a good protective effect on the core material DP essence, can effectively inhibit the volatilization of DP essence, and thus improve the thermal stability of the volatile core material.

[0047] Entrapment efficiency analysis: Using toluene as a solvent, a series of gradient concentrations of DP-toluene solutions were prepared with concentrations of 0.3, 0.75, 1.5, 2.25, 3, and 4.5 mg·g -1 respectively. An appropriate concentration of the DP-toluene solution was selected and scanned at full wavelengths from 200 to 700 nm to obtain a maximum absorption peak at 283 nm (the maximum absorbance value was controlled within the range of 0.1 to 0.8). At the maximum absorption peak of 283 nm, the absorbance values of the prepared series of standard solutions were measured using a UV spectrophotometer. Taking the DP concentration value as the X-axis and the absorbance value as the Y-axis, a standard curve was obtained by fitting the measured data. As Figure 8 shown, the fitting equation was y = 0.15751x - 0.02856 (R 2 = 0.9992). 1.5 g of the prepared microcapsule slurry was added to 20 g of toluene, and gently stirred for a sufficient time to extract the uncoated DP in the microcapsule slurry into toluene. After standing, the upper clear liquid was taken to measure its absorbance. According to the measured absorbance value At (y) and the standard curve equation, the concentration of uncoated DP (x) could be calculated, and then the total amount of uncoated DP in the sample could be known. The encapsulation efficiency EE t of the core material could be obtained from the following formula: where W FD is the amount of uncoated DP in the sample, and W D is the amount of added DP. The absorbance value measured by the UV spectrophotometer was 0.369, and the encapsulation efficiency of the core material DP was calculated to be 83.17%.

[0048] Example 2 80 g of deionized water was added to 10 g of polyvinyl alcohol powder and fully dissolved to form a homogeneous phase, forming an aqueous phase; 10 g of the oil-phase monomer isophorone diisocyanate and 40 g of natural orange essence were stirred and dissolved to make them completely miscible, forming a homogeneous phase, denoted as the oil phase; 91.5 g of the aqueous phase and 8.5 g of the oil phase were mixed and homogenized thoroughly to form an oil-in-water emulsion, which was placed in a constant temperature water bath at 20°C and kept warm for 5 min; then 35 g of a diethylenetriamine aqueous solution was added to the oil-in-water emulsion for an initiation reaction. After 20 min, the temperature of the system was raised to 55°C and the reaction was continued for 1 h to cure the microcapsule wall material, obtaining a natural essence microcapsule slurry with polyurea as the wall material. The prepared microcapsule slurry was freeze-dried to remove the water in the system, and microcapsules with a polyurea wall material could be obtained.

[0049] Example 3 70 g of deionized water was added to 2 g of polyvinyl alcohol powder and fully dissolved to form a homogeneous phase, forming an aqueous phase; 10 g of the oil-phase monomer isophorone diisocyanate and 50 g of natural pineapple essence were stirred and dissolved to make them completely miscible, forming a homogeneous phase, denoted as the oil phase; Mix 85 g of the aqueous phase and 15 g of the oil phase, and homogenize them thoroughly to form an oil-in-water emulsion. Place it in a constant temperature water bath at 40 °C and keep it warm for 2 min. Then add 40 g of diethylenetriamine aqueous solution to the oil-in-water emulsion for an initiation reaction. After 40 min, raise the temperature of the system to 70 °C and continue the reaction for 1 h to solidify the microcapsule wall material, thus obtaining a natural flavor microcapsule slurry with polyurea as the wall material. Freeze-dry the prepared microcapsule slurry to remove the water in the system, and polyurea wall material microcapsules can be obtained.

[0050] Example 4 Add 100 g of deionized water to 8 g of polyvinyl alcohol powder and dissolve it thoroughly to form a homogeneous phase, which is the aqueous phase. Stir and dissolve 10 g of the oil phase monomer isophorone diisocyanate and 70 g of natural tomato essence until they are completely miscible to form a homogeneous phase, denoted as the oil phase. Mix 75 g of the aqueous phase and 25 g of the oil phase, and homogenize them thoroughly to form an oil-in-water emulsion. Place it in a constant temperature water bath at 45 °C and keep it warm for 4 min. Then add 36 g of diethylenetriamine aqueous solution to the oil-in-water emulsion for an initiation reaction. After 35 min, raise the temperature of the system to 65 °C and continue the reaction for 3 h to solidify the microcapsule wall material, thus obtaining a natural flavor microcapsule slurry with polyurea as the wall material. Freeze-dry the prepared microcapsule slurry to remove the water in the system, and polyurea wall material microcapsules can be obtained.

[0051] Example 5 Add 120 g of deionized water to 4 g of polyvinyl alcohol powder and dissolve it thoroughly to form a homogeneous phase, which is the aqueous phase. Stir and dissolve 10 g of the oil phase monomer isophorone diisocyanate and 90 g of natural jasmine essence until they are completely miscible to form a homogeneous phase, denoted as the oil phase. Mix 70 g of the aqueous phase and 30 g of the oil phase, and homogenize them thoroughly to form an oil-in-water emulsion. Place it in a constant temperature water bath at 50 °C and keep it warm for 3 min. Then add 3 g of diethylenetriamine aqueous solution to the oil-in-water emulsion for an initiation reaction. After 40 min, raise the temperature of the system to 60 °C and continue the reaction for 3 h to solidify the microcapsule wall material, thus obtaining a natural flavor microcapsule slurry with polyurea as the wall material. Freeze-dry the prepared microcapsule slurry to remove the water in the system, and polyurea wall material microcapsules can be obtained.

[0052] Example 6 Add 120 g of deionized water to 4 g of polyvinyl alcohol powder and dissolve it thoroughly to form a homogeneous phase, which is the aqueous phase. Stir and dissolve 10 g of the oil phase monomer isophorone diisocyanate and 90 g of natural passion fruit essence until they are completely miscible to form a homogeneous phase, denoted as the oil phase. 70g of water phase and 30g of oil phase were mixed and homogenized to form an oil-in-water emulsion, which was placed in a constant temperature water bath at 50°C for 3 minutes. 3g of diethylenetriamine aqueous solution was then added to the oil-in-water emulsion to initiate the reaction. After 40 minutes, the system was heated to 60°C and the reaction was continued for 3 hours to solidify the microcapsule wall material, thereby obtaining a natural flavor microcapsule slurry with polyurea as the wall material. The prepared microcapsule slurry was freeze-dried to remove water in the system to obtain polyurea wall material microcapsules.

[0053] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing polyurea wall material microcapsules, characterized in that: The following steps are involved: The aqueous phase and the oil phase are mixed and fully homogenized to form an oil-in-water emulsion; an aqueous solution of an amine monomer is added to the oil-in-water emulsion to initiate a reaction, and the system is heated to continue the reaction to solidify the micron capsule wall material, thereby obtaining a natural flavor micron capsule slurry with polyurea as the wall material; the prepared micron capsule slurry is subjected to freeze-drying treatment to remove water in the system, thereby obtaining a polyurea wall material micron capsule; The mass ratio of the water phase to the oil phase is (68~91.5):(8.5~32).

2. The method for preparing a polyurea wall material microcapsule according to claim 1, wherein the water phase is prepared by adding deionized water to the emulsifier powder, fully dissolving it to form a uniform phase, and forming a water phase.

3. The method for preparing polyurea wall material microcapsules according to claim 2, wherein the emulsifier is polyvinyl alcohol.

4. The method for preparing polyurea wall material microcapsules according to claim 2, wherein the mass ratio of the emulsifier to deionized water is (1-5): (40-80).

5. The method for preparing a polyurea wall material microcapsule according to claim 2, wherein the oil phase is prepared by stirring and dissolving the oil phase monomer isophorone diisocyanate and natural flavor to make the two completely miscible to form a uniform phase, which is recorded as the oil phase.

6. The method for preparing polyurea wall material microcapsules according to claim 5, wherein the mass ratio of the oil phase monomer isophorone diisocyanate to the natural flavor is 1:(3-9).

7. The method for preparing polyurea wall material microcapsules according to claim 1, wherein the mass ratio of the oil phase monomer isophorone diisocyanate to the amine monomer aqueous solution is 1:(3-4). 8 . The method for preparing polyurea wall material microcapsules according to claim 1 , wherein the aqueous solution of amine monomers is an aqueous solution of diethylenetriamine.

9. A polyurea wall material microcapsule, prepared according to any one of claims 1-8.

10. Use of the polyurea wall material microcapsules for encapsulating natural flavors as claimed in claim 9 in the field of flavor microcapsules.

Images