Modified gelatin sustained-release capsule and preparation method and application thereof

Abstract

The application discloses a modified gelatin sustained-release capsule and a preparation method and application thereof, and the preparation method of the sustained-release capsule is as follows: S1, calcium magnesium phosphate fertilizer powder is added into deionized water, and stirring is conducted until the water solution is uniform; S2, gelatin particles are mixed with the water solution, and the gelatin particles are absorbed and swelled into gelatin gel; S3, glycerol is added into the gelatin gel, and the gelatin liquid is obtained by stirring and heating; S4, the gelatin liquid is prepared into a capsule film body, the capsule film body is immersed into a crosslinking agent solution for crosslinking; and S5, the crosslinked capsule film body is taken out, and the gelatin capsule is obtained after water drying. The gelatin, water, glycerol and calcium magnesium phosphate fertilizer are uniformly mixed into a solution by heating, and the solution is crosslinked into a shell by glutaraldehyde, and the crosslinking and the filling of the calcium magnesium phosphate fertilizer significantly enhance the mechanical property and the hydrophobic property of the gelatin, and better sustained-release effect is obtained. The fertilizer is packaged into the sustained-release capsule, so that the utilization rate of the fertilizer is improved, and the environment is not polluted.

Description

TECHNICAL FIELD

[0001] The application relates to a modified gelatin slow-release capsule and a preparation method and application thereof, and belongs to the technical field of agricultural fertilizers. BACKGROUND

[0002] At present, the most widely used slow-release fertilizer in the slow-release fertilizer field is a coated slow-release fertilizer, which generally refers to a water-insoluble shell coated on the outer layer of a traditional soluble fertilizer to delay the invasion of water into the fertilizer core.

[0003] In the selection of shell materials, many researchers prefer the use of organic polymers, such as various polyolefins and resins, which have excellent water resistance and film-forming properties and can provide strong slow-release effect. However, these materials need to be liquefied by using organic solvents in use, and after the release of the fertilizer in the film shell, the film shell remaining in the soil is difficult to degrade, which cannot meet the long-term green development requirements, and the cost is relatively high. Therefore, the development of low-cost biobased degradable polymer materials to realize the slow / controlled release of fertilizers has become a major focus in the slow-release fertilizer field.

[0004] Gelatin is a biodegradable material derived from animal bones and skin, and is relatively low in price and is commonly used as a capsule material. Untreated gelatin has strong hydrophilicity and can be dissolved in hot water, and therefore is not suitable for the preparation of slow-release fertilizers. The gelatin capsule slow-release fertilizer after hydrophobic modification has the advantages of low cost, easy measurement and application compared with the coated slow-release fertilizer. However, some patents and reports use aldehyde crosslinking agents to bond and crosslink the gelatin protein molecular chains into a network structure to enhance its water resistance, so as to solve the problem of poor water resistance of the gelatin film shell. However, it still cannot meet the water resistance requirements of slow-release fertilizers. SUMMARY

[0005] Based on the above, the application provides a modified gelatin slow-release capsule and a preparation method and application thereof. The gelatin is blended with glycerol and calcium-magnesium phosphate fertilizer, and then crosslinked into a shell, and the combined action of the two further improves the water resistance, so that the water resistance requirements of slow-release fertilizers can be met.

[0006] The technical scheme of the application is as follows:

[0007] In a first aspect, the application discloses a preparation method of a modified gelatin slow-release capsule, comprising the following steps:

[0008] S1, adding calcium-magnesium phosphate fertilizer powder into deionized water and stirring until uniform to obtain an aqueous solution;

[0009] S2, mixing gelatin particles with the aqueous solution, and waiting for the gelatin particles to swell into gelatin gel after absorbing water;

[0010] S3, the glycerol is added to the gelatin gel above, and the temperature is raised while stirring to obtain a gelatin solution, and the temperature is controlled at 50-90℃;

[0011] S4, the gelatin solution is prepared into a capsule mold, and the capsule mold is immersed in a dialdehyde crosslinking agent solution for crosslinking;

[0012] S5, the crosslinked capsule mold is taken out, and after the moisture is dried, the gelatin capsule is obtained.

[0013] As a further improvement of the present application, the gelatin is 100 parts, the glycerol is 20-50 parts, and the calcium-magnesium phosphate fertilizer is 10-50 parts by weight.

[0014] As a further improvement of the present application, the gelatin particles are industrial-grade bone glue or skin glue, or a mixture of the two.

[0015] As a further improvement of the present application, the dialdehyde crosslinking agent is glutaraldehyde or glyoxal, and the mass fraction of the dialdehyde crosslinking agent solution is 5-50% wt.

[0016] In a second aspect, the present application discloses a modified gelatin slow-release capsule prepared by the preparation method of the modified gelatin slow-release capsule.

[0017] In a third aspect, the present application discloses the application of the modified gelatin slow-release capsule in preparing a capsule-type slow-release fertilizer.

[0018] As a further improvement of the present application, the fertilizer is contained in the modified gelatin slow-release capsule. The fertilizer is a water-soluble nitrogen-containing chemical fertilizer.

[0019] The present application has the following beneficial effects: 1. The gelatin, water, glycerol, and calcium-magnesium phosphate fertilizer are uniformly mixed into a solution by heating, and a shell is formed after crosslinking with glutaraldehyde. The crosslinking and the filling of the calcium-magnesium phosphate fertilizer significantly enhance the mechanical properties and hydrophobic properties of the gelatin, and better slow-release effect is obtained. 2. The water-soluble nitrogen-containing chemical fertilizer is used as the core material and is contained in the modified gelatin capsule to prepare a capsule-type slow-release fertilizer. The slow-release performance is better than that of the unmodified gelatin capsule, the fertilizer utilization rate is improved, the environment is not polluted, and the present application can be used for tobacco and other crop planting. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Effect of calcium-magnesium phosphate fertilizer content on water contact angle;

[0021] Figure 2 Surface morphology of capsules prepared with different calcium-magnesium phosphate fertilizer contents;

[0022] Figure 3 Nitrogen release rate on the day of the soil column leaching test;

[0023] Figure 4Cumulative nitrogen release rate of soil column leaching test. DETAILED DESCRIPTION

[0024] In order to make the above objectives, features and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced in a variety of ways beyond those described herein without departing from the spirit and scope of the present application, and that the present application is not limited to the specific embodiments disclosed below.

[0025] Example 1

[0026] A method for preparing a modified gelatin sustained-release capsule, comprising the following steps:

[0027] S1, 10 parts of calcium magnesium phosphate powder was added to 100 parts of deionized water, stirred for 10 min to get a uniform aqueous solution;

[0028] S2, 100 parts of gelatin particles (industrial grade, bone glue: skin glue = 3:7) was mixed with the above aqueous solution, and the gelatin particles were swelled into gelatin gel;

[0029] S3, 20 parts of glycerol was added to the above gelatin gel, and heated in an oil bath at 70°C for 1 h to obtain a gelatin solution;

[0030] S4, the gelatin solution was poured into a polytetrafluoroethylene flat mold to form a capsule mold, and then immersed in a 20% wt glutaraldehyde solution for crosslinking for 1 h;

[0031] S5, the crosslinked capsule mold was taken out, the edge was trimmed flat, and dried in a 50°C air drying oven for 4 h to obtain a modified gelatin sustained-release capsule, which was used for mechanical property and water contact angle test.

[0032] Example 2

[0033] A method for preparing a modified gelatin sustained-release capsule, comprising the following steps:

[0034] S1, 20 parts of calcium magnesium phosphate powder was added to 100 parts of deionized water, stirred for 10 min to get a uniform aqueous solution;

[0035] S2, 100 parts of gelatin particles (industrial grade bone glue) was mixed with the above aqueous solution, and the gelatin particles were swelled into gelatin gel;

[0036] S3, 50 parts of glycerol was added to the above gelatin gel, and heated in an oil bath at 65°C for 1 h to obtain a gelatin solution;

[0037] S4, pour the gelatin liquid into a polytetrafluoroethylene flat mold press mold, so that the gelatin is evenly wrapped on the mold to form a capsule mold body, and then immersed in a 10% wt glutaraldehyde solution for crosslinking for 1 h;

[0038] S5, trim the edges of the crosslinked capsule mold body, and dry it in a 50°C air drying oven for 4 h to obtain a modified gelatin sustained-release film, which is used for mechanical property and water contact angle tests.

[0039] Example 3

[0040] A method for preparing a modified gelatin sustained-release capsule, comprising the following steps:

[0041] S1, add 30 parts of calcium magnesium phosphate powder to 100 parts of deionized water, stir for 10 min to obtain a uniform aqueous solution;

[0042] S2, mix 100 parts of gelatin particles (industrial grade skin glue) with the above aqueous solution, and wait for the gelatin particles to swell into a gelatin gel;

[0043] S3, add 30 parts of glycerol to the above gelatin gel, and heat in an oil bath at 80°C for 1 h to obtain a gelatin liquid;

[0044] S4, pour the gelatin liquid into a polytetrafluoroethylene flat mold press mold, so that the gelatin is evenly wrapped on the mold to form a capsule mold body, and then immersed in a 40% wt glutaraldehyde solution for crosslinking for 1 h;

[0045] S5, trim the edges of the crosslinked capsule mold body, and dry it in a 50°C air drying oven for 4 h to obtain a modified gelatin sustained-release film, which is used for mechanical property and water contact angle tests.

[0046] Example 4

[0047] A method for preparing a modified gelatin sustained-release capsule, comprising the following steps:

[0048] S1, add 40 parts of calcium magnesium phosphate powder to 100 parts of deionized water, stir for 10 min to obtain a uniform aqueous solution;

[0049] S2, mix 100 parts of gelatin particles (industrial grade, bone glue: skin glue = 3:7) with the above aqueous solution, and wait for the gelatin particles to swell into a gelatin gel;

[0050] S3, add 20 parts of glycerol to the above gelatin gel, and heat in an oil bath at 65°C for 1 h to obtain a gelatin liquid;

[0051] S4, pour the gelatin liquid into a polytetrafluoroethylene flat mold press mold, so that the gelatin is evenly wrapped on the mold to form a capsule mold body, and then immersed in a 15% wt glutaraldehyde solution for crosslinking for 1 h;

[0052] S5, the cross-linked capsule body was taken out, the edge was trimmed and leveled, and was dried in a 50 °C air drying oven for 4 h to obtain the modified gelatin sustained-release film, which was used for mechanical property and water contact angle tests;

[0053] S6, a polytetrafluoroethylene prepared capsule body cylindrical mold was customized, and was dipped into the above gelatin solution to coat the mold evenly. After the gelatin was drained vertically, the mold was quickly immersed in a 15% wt glutaraldehyde solution for cross-linking for 1 h. The mold was taken out, the surface liquid was wiped clean, and the edge was trimmed and leveled;

[0054] S7, the mold was vertically placed into a 50 °C air drying oven for 4 h. After the water was dried, the shell was lightly twisted and pulled out to obtain the capsule body;

[0055] S8, a polytetrafluoroethylene prepared capsule cap cylindrical mold was customized, and was dipped into the above gelatin solution to coat the mold evenly. After the gelatin was drained vertically, the mold was quickly immersed in a 15% wt glutaraldehyde solution for cross-linking for 1 h. The mold was taken out, the surface liquid was wiped clean, and the edge was trimmed and leveled;

[0056] S9, the mold was vertically placed into a 50 °C air drying oven for 4 h. After the water was dried, the shell was lightly twisted and pulled out to obtain the capsule cap;

[0057] S10, 5 g of nitrogen, phosphorus and potassium compound fertilizer was loaded into the capsule body, and the capsule body was sealed with the capsule cap for soil column leaching test.

[0058] Example 5

[0059] A preparation method of a modified gelatin sustained-release capsule, comprising the following steps:

[0060] S1, 50 parts of calcium magnesium phosphate fertilizer powder was added to 100 parts of deionized water, and stirred for 10 min to obtain a water solution;

[0061] S2, 100 parts of gelatin particles (industrial grade, bone glue: leather glue = 3:7) were mixed with the above water solution, and the gelatin particles were swelled into gelatin gel after absorbing water;

[0062] S3, 20 parts of glycerol was added to the above gelatin gel, and was heated in an oil bath at 65 °C for 1 h to obtain a gelatin solution;

[0063] S4, the gelatin solution was poured into a polytetrafluoroethylene flat plate mold to coat the mold evenly to form a capsule mold body, and then was immersed in a 20% wt glyoxal solution for cross-linking for 1 h;

[0064] S5, the cross-linked capsule body was taken out, the edge was trimmed and leveled, and was dried in a 50 °C air drying oven for 4 h to obtain the modified gelatin sustained-release film, which was used for mechanical property and water contact angle tests.

[0065] Comparative Example 1

[0066] A method for preparing a gelatin capsule, comprising the following steps:

[0067] S1, 100 parts of gelatin particles (industrial grade, bone glue: leather glue = 3:7) are mixed with 100 parts of deionized water, and the gelatin particles are allowed to swell into a gelatin gel after water absorption;

[0068] S3, 20 parts of glycerol are added to the above gelatin gel, and heated in an oil bath at 65°C for 1h to obtain a gelatin solution;

[0069] S4, pour the gelatin solution into a polytetrafluoroethylene flat mold to form a capsule mold body, then immerse it in a 15% wt glutaraldehyde solution for crosslinking for 1h;

[0070] S5, the crosslinked capsule mold body is taken out, the edge is trimmed flat, and is dried in a 50°C air drying oven for 4h to obtain a gelatin film, which is used for mechanical property and water contact angle test;

[0071] S6, customize a capsule body cylindrical mold prepared from polytetrafluoroethylene, and dip it in the above gelatin solution for coating, so that the gelatin solution is evenly wrapped on the mold, then quickly immerse it in a 15% wt glutaraldehyde solution for crosslinking for 1h after vertically lifting and draining the gelatin, take out the mold and wipe off the surface liquid, and trim the edge flat;

[0072] S7, then vertically place the mold in a 50°C air drying oven for 4h, and after the water is dried, the shell is lightly twisted and pulled out to obtain a capsule body;

[0073] S8, customize a capsule cap cylindrical mold prepared from polytetrafluoroethylene, and dip it in the above gelatin solution for coating, so that the gelatin solution is evenly wrapped on the mold, then quickly immerse it in a 15% wt glutaraldehyde solution for crosslinking for 1h after vertically lifting and draining the gelatin, take out the mold and wipe off the surface liquid, and trim the edge flat;

[0074] S9, then vertically place the mold in a 50°C air drying oven for 4h, and after the water is dried, the shell is lightly twisted and pulled out to obtain a capsule cap;

[0075] S10, 5 grams of nitrogen, phosphorus and potassium compound fertilizer are loaded into the capsule body, and the capsule body is sealed with the capsule cap for soil column leaching test.

[0076] Mechanical properties, water contact angle, appearance morphology and soil column leaching test are carried out. The detection method and results are as follows:

[0077] I. Mechanical properties

[0078] The tensile properties of the samples of examples 1 to 5 and comparative example 1 are tested according to GB / T 10403-2006, and the tensile rate is 10mm / min. The test results are shown in the following table.

[0079]

[0080] From the data in Table 1, the tensile strength of the modified gelatin film increases with the increase of the addition amount of calcium magnesium phosphate fertilizer. When the addition amount of calcium magnesium phosphate fertilizer reaches 40 phr, the tensile strength is the highest, which is 23.75 MPa, while the tensile strength of the gelatin film in Example 1 is only 12.72 MP.

[0081] II. Water contact angle

[0082] Each group of samples of Examples 1 to 5 and Comparative Example 1 was cut into flatness for water contact angle test according to GB / T30693-2014.

[0083] Figure 1 The water contact angle test results of Comparative Example 1 and Examples 1 to 5 are shown in Table 2 in order. Figure 1 It can be seen that the contact angle of the gelatin film without adding calcium magnesium phosphate fertilizer in Comparative Example 1 is 66.4° after being crosslinked by glutaraldehyde, which still shows hydrophilicity. When the addition amount of calcium magnesium phosphate fertilizer reaches 20 phr, the contact angle rises to 92.6°, realizing the change from hydrophilicity to hydrophobicity. With the increase of the addition amount of calcium magnesium phosphate fertilizer, the contact angle increases continuously. From the experiment, the hydrophobicity of the gelatin film added with 40 phr and 50 phr of calcium magnesium phosphate fertilizer is better, and the contact angles are 97.4° and 99.3° respectively.

[0084] III. Appearance and morphology

[0085] Each group of samples of Examples 1 to 5 and Comparative Example 1 was cut into flatness for scanning electron microscope surface morphology test.

[0086] From the data in Table 3, it can be seen that the surface of the gelatin film without adding calcium magnesium phosphate fertilizer in Comparative Example 1 is flat, and there are a small amount of small cavities on the surface. Figure 2 (a) It can be seen that the surface of the gelatin film without adding calcium magnesium phosphate fertilizer in Comparative Example 1 is flat, and there are a small amount of small cavities on the surface. Figure 3 (b)-(f) It can be seen that with the increase of the addition amount of calcium magnesium phosphate fertilizer, the micropores on the surface of the gelatin film decrease, but the surface roughness increases, and the granular protrusions on the surface increase. When the addition amount of calcium magnesium phosphate fertilizer reaches 50 phr, a large number of bark-like agglomerates appear on the surface, which is because too much calcium magnesium phosphate fertilizer has poor compatibility with gelatin and poor dispersibility, which is also the reason why the tensile property of Example 5 decreases.

[0087] IV. Release performance test

[0088] The same size capsules of Example 4 and Comparative Example 1, with a thickness of 0.3 mm, were prepared for release performance test, and 5 grams of nitrogen, phosphorus and potassium compound fertilizer was used as a blank group.

[0089] The experiment adopts soil column leaching method to determine the slow release effect of the gelatin capsule type slow release fertilizer in soil. Specifically, PVC pipe with a diameter of 5 cm and a length of 40 cm is used as a carrier. The quartz sand at the bottom and the top is 30 g respectively, and the middle is filled with a mixture of soil and sand in a ratio of 5:1. The gelatin capsule or nitrogen, phosphorus and potassium compound fertilizer is placed in the middle of the device, and the outlet is sealed with plastic film. Each time, 200 ml of deionized water is leached, and each time, the leaching time is 1, 4, 7, 10, 13, 16, 19, 22, 25, 28 days, and the first 24 hours collects the effluent and filters, and replenishes the ion water. Each time, the leaching is collected and filtered, and the ion water is replenished, and the nitrogen concentration is determined by using p-diaminobenzaldehyde (PDAB) colorimetry at a wavelength of 417 nm.

[0090] Figure 3 and Figure 4 respectively, the nitrogen release rate and the cumulative nitrogen release rate of different samples on the same day. From Figure 3 It can be seen that the blank group releases 91.2% on the first day. The release rates of Comparative Example 1 and Example 4 on the first day are only 5%, and the release rates of the two capsules start to differ from the fourth day, and the release rates of the two on the fourth day are 15.8% and 10.5% respectively. From Figure 4 It can be seen that the cumulative release rate difference of the two capsules increases with time, and the cumulative release rates of the blank group, Comparative Example 1 and Example 4 on the 28th day are 98.3%, 85.8% and 75.2%, and the slow release effect reaches the expectation.

[0091] From the above, it can be seen that the gelatin capsule type slow release fertilizer of the application, by uniformly mixing gelatin, water, glycerol and calcium magnesium phosphate fertilizer into a solution through heating, and then using glutaraldehyde cross-linking method, a capsule shell is prepared to load the fertilizer, and the slow release of the fertilizer is realized. The addition of calcium magnesium phosphate fertilizer improves the mechanical properties and hydrophobicity of the material, and the soil column leaching test proves that the modified capsule has excellent slow release performance.

[0092] The above-described embodiments only express several embodiments of the application, and the description is more specific and detailed, but it cannot be understood as limiting the scope of the patent of the application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the application, a number of modifications and improvements can be made, which are within the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. A method for preparing modified gelatin sustained-release capsules, characterized in that, Includes the following steps: S1, Add calcium magnesium phosphate fertilizer powder to deionized water and stir until a uniform aqueous solution is obtained; S2, mix the gelatin particles with the above aqueous solution, and wait for the gelatin particles to absorb water and swell into gelatin gel. S3, add glycerin to the above gelatin gel, and heat while stirring to obtain gelatin solution, controlling the temperature to 50℃~90℃; S4. Pour the gelatin liquid into a polytetrafluoroethylene flat mold and press it into shape, so that the gelatin is evenly wrapped on the mold to form a capsule mold body. Immerse the capsule mold body in a dialdehyde crosslinking agent solution for crosslinking. S5. Remove the cross-linked capsule mold and allow it to dry to obtain gelatin capsules.

2. The method for preparing modified gelatin sustained-release capsules according to claim 1, characterized in that, The ingredients are: 100 parts gelatin, 20-50 parts glycerin, and 10-50 parts calcium magnesium phosphate fertilizer by weight.

3. The method for preparing modified gelatin sustained-release capsules according to claim 1, characterized in that, The gelatin particles are industrial-grade bone glue or hide glue, or a mixture of both.

4. The method for preparing modified gelatin sustained-release capsules according to claim 1, characterized in that, The dialdehyde crosslinking agent is glutaraldehyde or glyoxal, and the mass fraction of the dialdehyde crosslinking agent solution is 5-50% wt.

5. Modified gelatin sustained-release capsules prepared by the method of any one of claims 1 to 4.

6. The application of the modified gelatin sustained-release capsule as described in claim 5 in the preparation of capsule-type sustained-release fertilizer.

7. The application of the modified gelatin sustained-release capsule according to claim 6 in the preparation of capsule-type sustained-release fertilizer, characterized in that, Fertilizer is encapsulated in modified gelatin slow-release capsules.

8. The application of the modified gelatin sustained-release capsule according to claim 7 in the preparation of capsule-type sustained-release fertilizer, characterized in that, The fertilizer is a nitrogen-containing, water-soluble chemical fertilizer.

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