Preparation method of temperature response type starch microcapsule

Abstract

The invention discloses a preparation method of a temperature response type starch microcapsule, which comprises the following steps: dissolving starch in water to prepare a starch suspension; gelatinizing the starch suspension at the temperature of 60 to 220 DEG C for 5 to 480 minutes to prepare a gelatinized solution; cooling the gelatinized solution to 30-70 DEG C, and carrying out ultrasonic treatment; sequentially adding an initiator and a grafting solution, and reacting for 0.5-96 hours; after the reaction is completed, dialyzing to remove the initiator and unreacted graft, so as to prepare the temperature response type starch particles; and mixing the core material solution with the temperature response type starch particles, and performing spray drying treatment to obtain the response microcapsule. The microcapsule prepared by the method can control the release rate according to the external temperature change, so that different release effects are realized; the breakage rate of the microcapsule prepared by the preparation method is less than or equal to 10%, and the diameter of particles is 0.1-10 microns.

Description

Technical Field

[0001] The present invention relates to the technical field of microcapsule preparation. More specifically, it relates to a method for preparing temperature-responsive starch microcapsules. Background Art

[0002] When traditional chemical pesticide formulations are applied, they face the dual challenges of rain washing and sunlight, resulting in a large amount of pesticide loss and decomposition. This not only leads to low use efficiency but also causes a series of intractable problems such as environmental pollution (Huang, L., Jiang, G., Photothermal Controlled-release Microcapsule pesticide delivery systems constructed with sodium lignosulfonate and transition metal ions: Construction, efficacy and on-demand pesticide delivery, Pest Manag. Sci. 2024, 80, 2827–2838.). Therefore, it is urgent to develop a new type of pesticide formulation.

[0003] Developing environmentally friendly and efficient pesticide formulations for agriculture is of great significance for reducing chemical residues and ensuring crop and ecological safety. Controlled Release Formulation (CRF) is an innovative agricultural delivery system that encapsulates or adsorbs pesticide active ingredients through polymers or inorganic nanoparticles, effectively slowing down their degradation and loss in non-target environments, and has a profound impact on improving pesticide efficacy, reducing residual pollution, and promoting the sustainable development of agriculture (Deng, R.; Wang, Y.; Yang, L.; et al. In Situ Fabrication of Polymeric Microcapsules by Ink-Jet Printing of Emulsions. ACS Appl. Mater. Interfaces 2019, 11(43), 40652–40661.).

[0004] As a type of CRF, microcapsules have a shell composed of polymers or inorganic materials, which can protect the core materials from harsh environments and are widely used in the agricultural field (Li, M.; Xu, W.; Hu, D.; et al. Preparation and Application of Pyraclostrobin Microcapsule Formulations. Colloids Surf. Physicochem. Eng. Asp. 2018, 553, 578–585.). Traditional microcapsule preparation methods such as in-situ polymerization, interfacial polymerization, and solvent evaporation can obtain microcapsules with high encapsulation efficiency and uniform morphology, but they have disadvantages such as a large amount of organic solvents used and a complex preparation process.

[0005] [1]To solve the above problems, the concept of self-assembled microcapsules emerged. Self-assembled microcapsules are usually prepared by the Pickering emulsion method, and their outer shells are composed of self-assembled colloidal particles in a molten or solidified state with uniform porosity. In 1996, Velev et al. (Velev, O.D.; Furusawa, K.; Nagayama, K. Assembly of Latex Particles by Using Emulsion Droplets as Templates. 1. Microstructured Hollow Spheres. Langmuir 1996, 12(10), 2374–2384.) first proposed the concept of manufacturing microcapsules using polystyrene particles as the shell material through the emulsion templating method. Subsequently, Noble et al. self-assembled microcapsules from epoxy micro-rods using the templating method (Noble, P.F.; Cayre, O.J.; Alargova, R.G.; et al. Fabrication of “Hairy” Colloidosomes with Shells of Polymeric Microrods. J. Am. Chem. Soc. 2004, 126(26), 8092–8093.). In recent years, this field has been continuously expanding, and certain progress has been made in the preparation and application of self-assembled microcapsules. However, most current self-assembled structures still rely on non-degradable polymers such as methyl methacrylate, polyamide, and polystyrene, and such non-degradable outer shells may cause secondary pollution to the agricultural environment.(①Zhang, W.; Cheng, H.; Pan, R.; et al. Phase Change Microcapsules with a Polystyrene / Boron Nitride Nanosheet Hybrid Shell for Enhanced Thermal Management of Electronics. Langmuir 2022, 38(51), 16055–16066.; ②Liu, R.-K., Hu, T.-T., Jia, J., et al. Efficient Fabrication of Polymer Shell Colloidosomes by a Spray Drying Process, Ind. Eng. Chem. Res. 2021, 60, 324–332.; ③Zhang, W.; Weng, J.; Yao, J.; et al. Preparation of pH-Stabilized Microcapsules for Controlled Release of DEET via Novel CS Deposition and Complex Coacervation. Colloids Surf. Physicochem. Eng. Asp. 2023, 658, 130651.) Meanwhile, self-assembled microcapsules generally suffer from problems such as a single release mode, difficulty in controlled release on demand, and difficulty in large-scale production during the self-assembly process, severely limiting their practical applications.

[0006] Starch, as a natural polymer material with wide sources, low cost, biodegradability, and biocompatibility, provides a new direction for the optimization of self-assembled microcapsules. The starch molecular structure contains a large number of hydroxyl groups, endowing it with good hydrophilicity and enabling self-assembly through weak interactions such as hydrogen bonds in different environments. The preparation of self-assembled microcapsules using starch can not only solve the environmental problems caused by traditional non-degradable materials but also precisely regulate the pesticide release behavior by leveraging the property changes of starch under different conditions. For example, under certain specific conditions, the gelation property of starch can alter the structure of the microcapsule shell, thereby controlling the pesticide release rate. In addition, starch is rich in resources and can be extracted from various crops such as corn, wheat, and potatoes, providing an abundant raw material guarantee for large-scale microcapsule preparation. (Zhao D, Li Z, Xia J, et al. Research Progress of Starch as Microencapsulated Wall Material. Carbohydrate Polymers, 2023, 318, 121118.)

[0007] Introducing spray drying technology into the preparation of starch-based self-assembled microcapsules further highlights its advantages. Spray drying technology, with its rapid and scalable characteristics, has been widely applied in multiple fields such as food, medicine, and beauty products. In a typical drying process, liquid raw materials (such as solutions, dispersions, or even pastes) are atomized through nozzles and then quickly evaporate the solvent in the drying chamber, transforming into solid products with higher physicochemical stability. Using this technology, novel microcapsules with a self-assembled polymer shell and a particle size range of 0.5 to 50 μm can be efficiently produced, especially suitable for the preparation of starch-based microcapsules. Through spray drying, starch can better exert its self-assembly characteristics during the formation of the microcapsule shell, achieving effective encapsulation and precise release of pesticide active ingredients (Baldelli, A.; Wells, S.; Pratap-Singh, A. Impact of Product Formulation on Spray-Dried Microencapsulated Zinc for Food Fortification. Food Bioprocess Technol. 2021, 14(12), 2286–2301.).

[0008] Developing self-assembled microcapsules based on starch with excellent environmental responsiveness and controlled release characteristics, especially stimuli-responsive microcapsules sensitive to environmental factors such as temperature, pH value, and light, will greatly improve the utilization rate of pesticides (Hou, R.; Zhou, J.; Song, Z.; et al. pH-Responsive λ-Cyhalothrin Nanopesticides for Effective Pest Control and Reduced Toxicity to Harmonia Axyridis. Carbohydr. Polym. 2023, 302, 120373.). Such microcapsules can achieve customized delivery and targeting characteristics, precisely meet the pesticide requirements of crops at different growth stages and environmental conditions, provide a highly potential solution to solve the dilemmas of traditional pesticide formulations, and are expected to push the green and sustainable development of agriculture to a new height. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a preparation method of temperature-responsive starch microcapsules. This preparation method can obtain microcapsules that can control the pesticide release rate according to different temperature changes, so as to achieve different slow-release effects; the microcapsules prepared by this preparation method have a breakage rate ≤ 10%, and the particle diameter is 0.1 - 10 μm.

[0010] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0011] A preparation method of temperature-responsive starch microcapsules, comprising the following steps:

[0012] S1. Preparation of temperature-responsive starch capsule wall particles

[0013] S1-1. Dissolve starch in water to obtain a starch suspension;

[0014] S1-2. Gelatinize the starch suspension at a temperature of 60 - 220 °C for 5 - 480 min to obtain a gelatinized solution;

[0015] S1-3. Cool the gelatinized solution to 30 - 70 °C and perform ultrasonic treatment;

[0016] S1-4. Add an initiator solution and react at 30 - 100 °C for 10 - 300 min, then add a grafting solution and carry out grafting reaction for 0.5 - 96 h;

[0017] S1-5. After the reaction is completed, remove the initiator and unreacted grafting substances by dialysis to obtain temperature-responsive starch particles, and then prepare them into a 0.01 - 10 wt% temperature-responsive starch particle solution;

[0018] S2. Preparation of Temperature-Responsive Starch Microcapsules

[0019] S2-1. Mix a solvent with a 0.01-10 wt% temperature-responsive starch particle solution in proportion, and then add the embedding material to obtain a mixed solution;

[0020] S2-2. Spray-dry the above mixed solution, and collect the temperature-responsive starch microcapsules in the collection chamber.

[0021] Preferably, in step S1-1, the concentration of the starch suspension is 0.01-10 wt%.

[0022] Preferably, in step S1-3, the ultrasonic power of the ultrasonic treatment is 50-500 W, and the ultrasonic time is 5-300 min.

[0023] Preferably, in step S1-4, the concentration of the initiator is 1-100 g / L.

[0024] Preferably, in step S1-4, the initiator is one or more of ammonium cerium nitrate, ammonium persulfate, potassium persulfate, azobisisobutyronitrile, sodium sulfite, sodium bisulfite, and hydrogen peroxide.

[0025] Preferably, in step S1-4, the concentration of the grafted material in the grafting solution is 0.1-100 g / L.

[0026] Preferably, in step S1-4, the grafted material in the grafting solution is one or more of N-isopropylacrylamide (NIPAM), polyethylene glycol (PEG), polyacrylic acid (PAA), polyacrylamide (PAM), poly(N-vinylcaprolactam) (PVCap), poly(N,N-dimethylacrylamide) (PDMA), poly(N-vinylpyrrolidone) (PVP), poly(N-vinylimidazole) (PVIm), and poly(N-vinylpyridine) (PVPy).

[0027] Preferably, in step S1-4, the grafting reaction time is 2-48 h.

[0028] Preferably, in step S2-1, the solvent is one or more of methanol, ethanol, acetone, ether, toluene, benzene, and tetrahydrofuran.

[0029] Preferably, in step S2-1, the volume ratio of the solvent to the temperature-responsive starch particle solution is 0-10:1.

[0030] Preferably, in step S2-2, the inlet temperature of the spray drying is 80-240 °C, the outlet temperature is 60-180 °C, and the air volume intensity is 2-15 m 3 / h.

[0031] Any range described in the present invention includes the end values, any numerical value between the end values, and any sub-range constituted by any numerical value between the end values or the end values.

[0032] Unless otherwise specified, each raw material in the present invention can be obtained by purchasing from the market, and the equipment used in the present invention can be a conventional equipment in the relevant field or can be referred to the existing technology in the relevant field.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1) The microcapsules prepared by the present invention can achieve different sustained-release effects at different temperatures and have temperature responsiveness;

[0035] 2) The microcapsules prepared by the present invention have good integrity, and the breakage rate ≤ 10%; the particle size of the microcapsules is 0.1 - 10 μm; and they have a high embedding rate, and the embedding rate ≥ 80%.

[0036] 3) The preparation method of the microcapsules of the present invention has a higher yield, low cost, easily available raw materials, is environmentally friendly, is easy to operate, and is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The following further describes in detail the specific embodiments of the present invention with reference to the drawings.

[0038] Figure 1 It is a graph showing the change in the particle size of temperature-responsive starch granules prepared in Example 1 under different temperature conditions;

[0039] Figure 2 It is a SEM image of the microcapsules prepared in Example 1 when the inlet temperature of spray drying is 100 °C;

[0040] Figure 3 It is a SEM image of the microcapsules prepared in Example 1 when the inlet temperature of spray drying is 120 °C;

[0041] Figure 4 It is a SEM image of the microcapsules encapsulating pyraclostrobin in Example 2;

[0042] Figure 5 It is a graph showing the sustained-release performance of the microcapsules encapsulating pyraclostrobin in Example 2 under different temperature conditions;

[0043] Figure 6 It is a SEM image of the temperature-responsive microcapsules when the volume ratio of methanol to water is 0:1 in Example 3;

[0044] Figure 7 It is a SEM image of the temperature-responsive microcapsules with an inlet temperature of 200 °C in Comparative Example 2. Detailed Embodiments

[0045] To illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments and the accompanying drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0046] Various cross-sectional views according to the disclosed embodiments of the present invention are shown in the drawings. These figures are not drawn to scale, where for the purpose of clear expression, some details are enlarged and some details may be omitted. The shapes of various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary, and may actually deviate due to manufacturing tolerances or technical limitations, and those skilled in the art can additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0047] As an aspect of the present invention, a method for preparing temperature-responsive starch microcapsules includes the following steps:

[0048] S1. Preparation of temperature-responsive starch capsule wall particles

[0049] S1-1. Dissolve starch in water to obtain a starch suspension;

[0050] S1-2. Gelatinize the starch suspension at a temperature of 60 - 220 °C for 5 - 480 min to obtain a gelatinized solution;

[0051] S1-3. Cool the gelatinized solution to 30 - 70 °C and use ultrasonic treatment;

[0052] S1-4. Add an initiator solution and react at 30 - 100 °C for 10 - 300 min, then add a grafting solution and carry out grafting reaction for 0.5 - 96 h;

[0053] S1-5. After the reaction is completed, remove the initiator and unreacted grafts by dialysis to obtain temperature-responsive starch particles, and then prepare them into a 0.01 - 10 wt% temperature-responsive starch particle solution;

[0054] S2. Preparation of temperature-responsive starch microcapsules

[0055] S2-1. Mix the solvent with the 0.01 - 10 wt% temperature-responsive starch particle solution in proportion, and then add the embedding material to obtain a mixed solution;

[0056] S2-2. Spray-dry the above mixed solution and collect the temperature-responsive starch microcapsules in the collection chamber.

[0057] According to certain embodiments of the present invention, in step S1-1, the concentration of the starch suspension is 0.01-10 wt%.

[0058] According to certain embodiments of the present invention, in step S1-3, the ultrasonic power of the ultrasonic treatment is 50-500 W, and the ultrasonic time is 5-300 min.

[0059] According to certain embodiments of the present invention, in step S1-4, the concentration of the initiator is 1-100 g / L.

[0060] According to certain embodiments of the present invention, in step S1-4, the initiator is one or more of ammonium cerium nitrate, ammonium persulfate, potassium persulfate, azobisisobutyronitrile, sodium sulfite, sodium bisulfite, and hydrogen peroxide.

[0061] According to certain embodiments of the present invention, in step S1-4, the concentration of the grafted substance in the grafting solution is 0.1-100 g / L.

[0062] According to certain embodiments of the present invention, in step S1-4, the grafted substance in the grafting solution is one or more of N-isopropylacrylamide (NIPAM), polyethylene glycol (PEG), polyacrylic acid (PAA), polyacrylamide (PAM), poly(N-vinylcaprolactam) (PVCap), poly(N,N-dimethylacrylamide) (PDMA), poly(N-vinylpyrrolidone) (PVP), poly(N-vinylimidazole) (PVIm), and poly(N-vinylpyridine) (PVPy).

[0063] According to certain embodiments of the present invention, in step S1-4, the grafting reaction time is 2-48 h.

[0064] According to certain embodiments of the present invention, in step S2-1, the solvent is one or more of methanol, ethanol, acetone, ether, toluene, benzene, and tetrahydrofuran.

[0065] According to certain embodiments of the present invention, in step S2-1, the volume ratio of the solvent to the temperature-responsive starch particle solution is 0-10:1.

[0066] According to certain embodiments of the present invention, in step S2-2, the inlet temperature of the spray drying is 80-240 °C, the outlet temperature is 60-180 °C, and the air volume intensity is 2-15 m 3 / h.

[0067] Example 1

[0068] A method for preparing temperature-responsive starch microcapsules, comprising the following steps:

[0069] Step 1: Preparation of temperature-responsive starch wall particles

[0070] S1-1. Dissolve starch in 300 mL of deionized water to prepare a 1 wt% starch suspension;

[0071] S1-2. Gelatinize the starch suspension at 95 °C for 60 min;

[0072] S1-3. Cool the gelatinized solution to 60 °C and ultrasonically treat it using a cell disruptor with an ultrasonic power of 200 W and an ultrasonic time of 15 min;

[0073] S1-4. Take 50 mL of the ultrasonically treated starch solution, add 20 mL of a 25 g / L ammonium cerium nitrate solution, react at 70 °C for 30 min, and then add 30 mL of a 33.3 g / L NIPAM solution and continue to react for 12 h;

[0074] S1-5. After the reaction is completed, remove the initiator and unreacted grafts by dialysis to obtain temperature-responsive starch particles, and then prepare a 1% wt temperature-responsive starch particle solution;

[0075] Step 2: Preparation of spray-dried temperature-responsive starch microcapsules

[0076] S2-1. Mix methanol and the 1% wt temperature-responsive starch particle solution in a volume ratio of 7:1 to obtain a mixed solution;

[0077] S2-2. Divide the above mixed solution into two parts for spray drying, set the inlet temperature to 100 °C and 120 °C respectively, the outlet temperature to 80 °C, and the air volume intensity to 10 m 3 / h; Collect the temperature-responsive starch microcapsules in the collection chamber.

[0078] Figure 1 This is the particle size diagram of the temperature-responsive starch particles prepared in this example under different temperature conditions;

[0079] Figure 2 This is the scanning electron microscope image of the temperature-responsive microcapsules when the spray-drying inlet temperature is 100 °C;

[0080] Figure 3 This is the scanning electron microscope image of the temperature-responsive microcapsules when the spray-drying inlet temperature is 120 °C.

[0081] Example 2

[0082] A preparation method of a temperature-responsive microcapsule loaded with pyraclostrobin, comprising the following steps:

[0083] Step 1: Preparation of temperature-responsive starch wall particles

[0084] S1-1. Dissolve starch in 300 mL of deionized water to prepare a 1% wt starch suspension;

[0085] S1-2. Gelatinize the starch suspension at 95 °C for 60 min to obtain a gelatinized solution;

[0086] S1-3. Cool the gelatinized solution to 60 °C and subject it to ultrasonic treatment with an ultrasonic power of 200 W and an ultrasonic time of 15 min;

[0087] S1-4. Take 50 mL of the ultrasonically treated starch solution, add 20 mL of a 25 g / L ammonium cerium nitrate solution, react at 70 °C for 30 min, and then add 30 mL of a 33.3 g / L NIPAM solution and continue to react for 12 h;

[0088] S1-5. After the reaction is completed, remove the initiator and unreacted grafts by dialysis to obtain temperature-responsive starch particles, and then prepare a 1% wt temperature-responsive starch particle solution;

[0089] Step 2: Preparation of temperature-responsive starch microcapsules by spray drying

[0090] S2-1. Mix methanol with the 1% wt temperature-responsive starch particle solution at a volume ratio of 7:1, and add 0.21 g of pyraclostrobin to obtain a mixed solution;

[0091] S2-2. Spray-dry the mixed solution from the above step, set the inlet temperature to 120 °C, the outlet temperature to 80 °C, and the air volume intensity to 10 m 3 / h, and collect the microcapsules in the collection chamber.

[0092] Figure 4 This is the scanning electron microscope image of the temperature-responsive microcapsules encapsulating pyraclostrobin in this example; it can be seen from Figure 4 that most of the microcapsules are olive-shaped and there are no obvious damages.

[0093] Figure 5 This is the sustained-release curve graph of the temperature-responsive microcapsules encapsulating pyraclostrobin in this example at 25 °C and 35 °C; it can be seen from Figure 5 that as the temperature increases, the release rate and release amount of pyraclostrobin increase.

[0094] Example 3

[0095] A method for preparing temperature-responsive microcapsules, comprising the following steps:

[0096] Step 1: Preparation of temperature-responsive starch capsule wall particles

[0097] S1-1. Dissolve starch in 300 mL of deionized water to prepare a 1% wt starch suspension;

[0098] S1-2. Gelatinize the starch suspension at 95 °C for 60 min to obtain a gelatinized solution;

[0099] S1-3. Cool the gelatinized solution to 60 °C and perform ultrasonic treatment with an ultrasonic power of 200 W and an ultrasonic time of 15 min;

[0100] S1-4. Take 50 mL of the ultrasonically treated starch solution, add 20 mL of a 25 g / L ammonium cerium nitrate solution, react at 70 °C for 30 min, and then add 30 mL of a 33.3 g / L NIPAM solution and continue to react for 12 h.

[0101] S1-5. After the reaction is completed, remove the initiator and unreacted grafts by dialysis to obtain temperature-responsive starch particles, and then prepare a 1% wt temperature-responsive starch particle solution;

[0102] Step 2: Preparation of temperature-responsive starch microcapsules by spray drying

[0103] S2-1. Add 0.21 g of pyraclostrobin to the 1% wt temperature-responsive starch particle solution to obtain a mixed solution;

[0104] S2-2. Spray-dry the mixed solution, set the inlet temperature to 120 °C, the outlet temperature to 80 °C, and the air volume intensity to 10 m 3 / h, and collect the microcapsules in the collection chamber.

[0105] Figure 6 SEM image of the temperature-responsive microcapsules with a methanol-to-water ratio of 0:1 in this example.

[0106] Example 4

[0107] A method for preparing temperature-responsive starch microcapsules, comprising the following steps:

[0108] Step 1: Preparation of temperature-responsive starch capsule wall particles

[0109] S1-1. Dissolve starch in 300 mL of deionized water to prepare a 1% wt starch suspension;

[0110] S1-2. Gelatinize the starch suspension at 95 °C for 60 min to obtain a gelatinized solution;

[0111] S1-3. Cool the gelatinized solution to 60 °C and perform ultrasonic treatment with an ultrasonic power of 200 W and an ultrasonic time of 15 min;

[0112] S1-4. Take 50 mL of the above starch solution, add 20 mL of a 25 g / L ammonium cerium(IV) nitrate solution, react at 70 °C for 30 min, then add 30 mL of a 33.3 g / L NIPAM solution, and continue the reaction for 12 h;

[0113] S1-5. After the reaction is completed, remove the initiator and unreacted grafts by dialysis to obtain temperature-responsive starch particles, and then prepare a 1% wt temperature-responsive starch particle solution.

[0114] Step 2: Preparation of temperature-responsive starch microcapsules by spray drying

[0115] S2-1. Mix methanol and the 1% wt temperature-responsive starch particle solution in a volume ratio of 7:1, and add 0.21 g of pyraclostrobin to obtain a mixed solution;

[0116] S2-2. Divide the mixed solution from the above step into three portions for spray drying. Set the inlet temperature to 120 °C, the outlet temperature to 80 °C, and the air volume intensity to 5, 10, and 15 m 3 / h, and collect the microcapsules in the collection chamber.

[0117] Example 5

[0118] A method for preparing temperature-responsive starch microcapsules, comprising the following steps:

[0119] Step 1: Preparation of temperature-responsive starch capsule wall particles

[0120] S1-1. Dissolve starch in 300 mL of deionized water to prepare a 1% wt starch suspension;

[0121] S1-2. Gelatinize the starch suspension at 95 °C for 60 min to obtain a gelatinized solution.

[0122] S1-3. Cool the gelatinized solution to 60 °C and use ultrasonic treatment with an ultrasonic power of 200 W and an ultrasonic time of 15 min;

[0123] S1-4. Take 50 mL of the ultrasonically treated starch solution, add 20 mL of a 25 g / L ammonium cerium(IV) nitrate solution, react at 70 °C for 30 min, then add 30 mL of a 33.3 g / L NIPAM solution, and continue the reaction for 12 h;

[0124] S1-5. After the reaction is completed, remove the initiator and unreacted grafts by dialysis to obtain temperature-responsive starch particles, and then prepare a 1% wt temperature-responsive starch particle solution;

[0125] Step 2: Preparation of temperature-responsive starch microcapsules by spray drying

[0126] S2-1. Mix methanol with a 1% wt temperature-responsive starch particle solution in a volume ratio of 7:1, and add 0.21 g of pyraclostrobin to obtain a mixed solution;

[0127] S2-2. Divide the mixed solution obtained in the above step into three portions for spray drying. Set the inlet temperature to 120 °C, and the outlet temperatures are 80, 90, and 100 °C respectively. The air volume intensity is 10 m 3 / h, and microcapsules are collected in the collection chamber.

[0128] Comparative Example 1

[0129] Repeat Example 1: The difference is that the inlet temperature in step S2-2 is 50 °C, the drying process is very slow, and the moisture cannot be completely volatilized, so microcapsules cannot be collected in the collection chamber.

[0130] Comparative Example 2

[0131] Repeat Example 1: The difference is that the inlet temperature in step S2-2 is 200 °C, and the embedding rate of the collected microcapsules is relatively low.

[0132] Comparative Example 3

[0133] Repeat Example 1: The difference is that the air volume intensity in step S2-2 is 17 m 3 / h, the particle size of the microcapsules is too small, and microcapsules cannot be collected in the collection chamber.

[0134] Comparative Example 4

[0135] Repeat Example 1: The difference is that the volume ratio of the methanol solution to the temperature starch particle solution in step S2-1 is 20:1, and the solid content is too low to collect microcapsules in the collection chamber.

[0136] Comparative Example 5

[0137] Repeat Example 1: The difference is that the starch solution in step S1-1 is 0.01% wt, and the solid content is too low to collect microcapsules in the collection chamber.

[0138] Comparative Example 6

[0139] Repeat Example 1: The difference is that the starch solution in step S1-1 is 20% wt, and the solid content is too high to form a mixed solution after gelatinization.

[0140] Comparative Example 7

[0141] Repeat Example 1: The difference is that the initiator concentration in step S1-4 is 0.5 g / L. Since the initiator concentration is too low, the substances in the grafting solution cannot be grafted onto the starch, and the starch particles have no temperature response.

[0142] Comparative Example 8

[0143] Repeat Example 1, except that the initiator in step S1-4 is iron oxide, and the substances in the grafting solution cannot be grafted onto the starch, and the starch granules have no temperature response.

[0144] Comparative Example 9

[0145] Repeat Example 1, except that the concentration of the grafted substance in step S1-4 is 0.05 g / L, and the grafting amount is too low, resulting in no temperature response of the starch granules.

[0146] Comparative Example 10

[0147] Repeat Example 1, except that the concentration of the grafted substance in step S1-4 is 100 g / L, and the grafting amount is too high, resulting in too large particle size of the formed starch granules, which is not conducive to the formation of temperature-responsive microcapsules.

[0148] Comparative Example 11

[0149] Repeat Example 1, except that the grafting solution in step S1-4 is a gelatin solution, and the formed starch granules have no temperature response.

[0150] Comparative Example 12

[0151] Repeat Example 1, except that the grafting reaction time in step S1-4 is 1 h, and the formed starch granules have no temperature response.

[0152] Comparative Example 13

[0153] Repeat Example 1, except that the volume ratio of the core material solution to the temperature-responsive starch granule solution in step S2-1 is 15:1, and the formed temperature-responsive starch microcapsules have no temperature response.

[0154] Comparative Example 14

[0155] Repeat Example 1, except that the volume ratio of the core material solution to the temperature-responsive starch granule solution in step S2-1 is 15:1, and the formed temperature-responsive starch microcapsules have no temperature response.

[0156] Obviously, the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for preparing temperature-responsive starch microcapsules, characterized in that: The steps include: S1. Preparation of temperature-responsive starch capsule wall granules S1-1, dissolving starch in water to prepare a starch suspension; S1-2, gelatinizing the starch suspension at a temperature of 60-220° C. for 5-480 min to obtain a gelatinized solution; S1-3, cooling the gelatinized solution to 30-70°C and subjecting it to ultrasonic treatment; S1-4, adding the initiator solution, reacting at 30-100°C for 10-300 minutes, then adding the grafting solution, and carrying out the grafting reaction for 0.5-96 hours; S1-5, after the reaction is completed, the initiator and the unreacted grafted product are removed by dialysis to obtain temperature-responsive starch granules, which are then prepared into a 0.01-10wt% temperature-responsive starch granule solution; S2. Preparation of temperature-responsive starch microcapsules S2-1, mixing the solvent with the temperature-responsive starch granule solution, adding the embedded material, and obtaining a mixed solution; S2-2, spray-drying the mixed solution and collecting to obtain temperature-responsive starch microcapsules.

2. The method for preparing the temperature-responsive starch microcapsule according to claim 1, characterized in that: In step S1-1, the concentration of the starch suspension is 0.01-10wt%.

3. The method for preparing the temperature-responsive starch microcapsule according to claim 1, characterized in that: In step S1-3, the ultrasonic power of the ultrasonic treatment is 50-500W, and the ultrasonic time is 5-300min.

4. The method for preparing the temperature-responsive starch microcapsule according to claim 1, characterized in that: In step S1-4, the concentration of the initiator is 1-100 g / L.

5. The method for preparing the temperature-responsive starch microcapsule according to claim 1, characterized in that: In step S1-4, the initiator is one or more of ammonium cerium nitrate, ammonium persulfate, potassium persulfate, azobisisobutyronitrile, sodium sulfite, sodium bisulfite, and hydrogen peroxide.

6. The method for preparing the temperature-responsive starch microcapsule according to claim 1, characterized in that: In step S1-4, the concentration of the grafted substance in the grafting solution is 0.1-100 g / L.

7. The method for preparing the temperature-responsive starch microcapsule according to claim 1, characterized in that: In step S1-4, the grafted material in the grafting solution is one or more of N-isopropylacrylamide, polyethylene glycol, polyacrylic acid, polyacrylamide, poly(N-vinylcaprolactam), poly(N,N-dimethylacrylamide), poly(N-vinylpyrrolidone), poly(N-vinylimidazole), and poly(N-vinylpyridine).

8. The method for preparing the temperature-responsive starch microcapsule according to claim 1, characterized in that: In step S1-4, the grafting reaction time is 2-48 hours.

9. The method for preparing the temperature-responsive starch microcapsule according to claim 1, characterized in that: In step S2-1, the solvent is one or more of methanol, ethanol, acetone, ether, toluene, benzene, and tetrahydrofuran.

10. The method for preparing the temperature-responsive starch microcapsule according to claim 1, characterized in that: In step S2-1, the volume ratio of the solvent to the temperature-responsive starch granule solution is 0-10:1; Preferably, in step S2-2, the inlet temperature of the spray drying is 80-240°C, the outlet temperature is 60-180°C, and the air volume intensity is 2-15m 3 / h.

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