Hydrogel, dry hydrogel powder, preparation method and application

Abstract

The invention discloses hydrogel, dry hydrogel powder and a preparation method and application thereof. The preparation method of the hydrogel comprises the following steps: irradiating a mixed solution A with high-energy rays to polymerize the mixed solution A; the mixed solution A comprises starch, a fertilizer, a monomer and water; the starch is gelatinized starch; the monomer is composed of a vinyl monomer 1 and a salt 2 of the vinyl monomer, or the monomer is composed of acrylamide; wherein when the monomer is composed of a vinyl monomer 1 and a salt 2 of the vinyl monomer, the ratio of the mole number of the salt 2 of the vinyl monomer to the mole number of the monomer is 50-90%; in the mixed solution A, the content of the starch is 1-100mg / mL, the mass ratio of the starch to the monomer is 1: (0.1-100), and the mass ratio of the starch to the fertilizer is 1: (0.1-50). The dry hydrogel powder disclosed by the invention has excellent water absorption swelling degree, fertilizer slow release performance and degradation performance.

Description

Technical Field

[0001] The present invention relates to a hydrogel, a dry hydrogel powder, a preparation method and an application thereof. More specifically, the present invention relates to a fertilizer slow-release starch-based agricultural and forestry water-retaining agent hydrogel, a dry hydrogel powder, a preparation method and an application thereof. Background Art

[0002] Agriculture and forestry production is an important part of my country's national economy. With the rapid development of agriculture and forestry, water shortage and soil infertility have become increasingly prominent, seriously restricting the sustainable development of agriculture and forestry. Traditional irrigation and fertilizer application methods in agriculture and forestry have problems such as large water consumption, low fertilizer utilization efficiency, and environmental pollution. Therefore, it is particularly important to develop an agricultural and forestry water retaining agent that can both efficiently retain water and slowly release fertilizers.

[0003] Water retainer is a functional polymer material that can absorb and retain a large amount of water in the soil for agricultural and forestry crops to absorb and utilize. It can significantly enhance the soil's water retention capacity, reduce the loss of soil nutrients and deep seepage, improve soil structure, and increase water utilization, thereby reducing irrigation water consumption. However, most traditional agricultural and forestry water retainers commonly found on the market are synthetic polymer materials, such as polyacrylic acid (PAA), polyacrylamide (PAM), polyvinyl alcohol (PVA), etc. Although these materials have good water absorption and water retention capabilities, they have the following problems:

[0004] (1) Environmental pollution: Traditional agricultural and forestry water-retaining agents are difficult to degrade in the natural environment after use. Long-term use can easily cause soil and water pollution and affect the ecological environment.

[0005] (2) Low fertilizer utilization rate: Traditional agricultural and forestry water-retaining agents generally only have the function of retaining water. The fertilizers added during planting usually exist in the form of dissolved substances, which are easily washed away during irrigation or rainfall. The utilization rate of fertilizers is low and there is serious waste.

[0006] (3) High cost: In traditional technology, the preparation of agricultural and forestry water-retaining agents requires the addition of initiators, cross-linking agents, catalysts, etc., and the process must be carried out at a certain temperature. The raw materials and production costs of synthetic polymers are relatively high, which limits their application in large areas of farmland and forest land.

[0007] As a new type of environmentally friendly material, starch-based agricultural and forestry water-retaining agent has gradually attracted attention due to its wide sources, low prices, and easy degradation. Natural starch has good water absorption and biodegradability, and contains hydrophilic groups on the surface. Introducing it into traditional polymer chains or modifying it can further improve its water retention performance.

[0008] In agricultural production, the effective utilization rate of fertilizers is generally low. A large amount of fertilizers cannot be absorbed by crops due to volatilization, leaching and other reasons, which not only causes a waste of resources, but also pollutes the natural environment and water bodies. As a new type of fertilizer, slow-release fertilizer improves the utilization efficiency of fertilizers by controlling the release rate of nutrients, which can greatly reduce pollution to the environment. Existing starch-based agricultural and forestry water-retaining agents have little research on fertilizer slow release, and their slow-release effect and fertilizer utilization rate still need to be improved; in addition, the release rate of slow-release fertilizers in the soil is greatly affected by environmental factors, and their slow-release effect needs to be further optimized. Summary of the invention

[0009] The technical problem to be solved by the present invention is to overcome the defects of the prior art starch-based agricultural and forestry water-retaining agent in the aspect of fertilizer slow release, the fertilizer slow release effect and fertilizer utilization rate still need to be improved, and the low production efficiency and high cost caused by the complex preparation method, and provide a hydrogel, a dry hydrogel powder, a preparation method and application. The dry hydrogel powder of the present invention has both excellent water retention performance and fertilizer slow release performance, and can significantly improve the production efficiency of agriculture and forestry.

[0010] The present invention solves the above technical problems through the following technical solutions:

[0011] The present invention provides a method for preparing a hydrogel, which comprises the following steps:

[0012] The mixed solution A is irradiated with high-energy rays to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, monomer and water; the starch is gelatinized starch;

[0013] Wherein, the monomer is composed of a vinyl monomer 1 and a salt of a vinyl monomer 2, or the monomer is composed of acrylamide; wherein, when the monomer is composed of a vinyl monomer 1 and a salt of a vinyl monomer 2, the ratio of the molar number of the salt of the vinyl monomer 2 to the molar number of the monomer is 50%-90%;

[0014] Wherein, in the mixed solution A, the content of the starch is 1-100 mg / mL, the mass ratio of the starch to the monomer is 1:(0.1-100), and the mass ratio of the starch to the fertilizer is 1:(0.1-50).

[0015] In the present invention, preferably, the high-energy rays are cobalt-60 gamma rays, electron beams or X-rays.

[0016] Wherein, when the high-energy rays are cobalt-60 gamma rays or X-rays, preferably, the absorbed dose rate during the irradiation is 0.1-20 kGy / h, for example, 1 kGy / h, 2 kGy / h, 3 kGy / h, 4 kGy / h, 5 kGy / h or 6 kGy / h.

[0017] Wherein, when the high-energy rays are cobalt-60 gamma rays or X-rays, preferably, the absorbed dose during the irradiation is 2-100 kGy, more preferably 5-50 kGy, for example 5 kGy, 10 kGy, 15 kGy, 20 kGy or 30 kGy.

[0018] Wherein, when the high-energy ray is an electron beam, preferably, the absorbed dose during the irradiation is 50-1000 kGy, more preferably 300-800 kGy, for example 500 kGy.

[0019] Wherein, when the high-energy ray is an electron beam, preferably, the absorbed dose rate during the irradiation is 10-500 kGy / s, more preferably 50-300 kGy / s, for example 100 kGy / s.

[0020] In the present invention, preferably, before the mixed liquid A is irradiated with the high-energy rays, nitrogen and / or argon are introduced into the mixed liquid A to remove oxygen in the mixed liquid A.

[0021] In the present invention, preferably, the mixed solution A is free of oxygen or has an oxygen concentration lower than 5%.

[0022] In the present invention, preferably, the mixed solution A also includes a cross-linking agent.

[0023] Preferably, the crosslinking agent is selected from one or more of divinylbenzene, diisocyanate, polyvinyl alcohol, vinylbenzene sulfonate, methyl methacrylate, ethyl bromide and N,N'-methylenebisacrylamide (MBA), such as N,N'-methylenebisacrylamide.

[0024] Preferably, in the mixed solution A, the mass ratio of the starch to the cross-linking agent is 1:(0.1-10), such as 1:1 or 1:2.

[0025] In the present invention, preferably, the method for preparing the hydrogel further comprises the following steps:

[0026] S1, preparing a mixed paste of starch and fertilizer by mixing ungelatinized starch, the fertilizer and the water;

[0027] S2, dissolving the monomer in the water to obtain a vinyl aqueous solution; or, dissolving the vinyl monomer 3 in an aqueous solution of a neutralizing agent to undergo a neutralization reaction to obtain a vinyl aqueous solution, wherein the degree of neutralization of the vinyl aqueous solution is 50%-90%; wherein the vinyl monomer 3 is, for example, acrylic acid and / or methacrylic acid; and the ratio of the number of moles of the salt 2 of the vinyl monomer to the number of moles of the monomer is equivalent to the degree of neutralization of the vinyl aqueous solution;

[0028] S3, mixing and stirring the mixed paste of starch and fertilizer described in S1 and the vinyl aqueous solution described in S2 to obtain the mixed solution A.

[0029] In S1, preferably, the mixed paste of starch and fertilizer also includes alkali solution.

[0030] The base is, for example, NaOH and / or KOH.

[0031] The mass concentration of the alkali in the alkali solution is, for example, 30-50%, such as 40%.

[0032] In the mixed paste of starch and fertilizer, the mass ratio of the starch to the alkali solution is, for example, (3-5): (1-2).

[0033] In S1, the mixed paste of starch and fertilizer can be prepared by conventional methods in the art, preferably, by a hydrothermal stirring method. More preferably, the steps of the preparation method of the mixed paste of starch and fertilizer include one of the following two schemes:

[0034] Solution 1:

[0035] a. Pregelatinization: pregelatinize 10-15 parts by weight of deionized water at a temperature of 40-60°C, 3-5 parts by weight of ungelatinized starch and fertilizer to obtain a solution of pregelatinized starch and fertilizer;

[0036] b. Accelerating gelatinization: under stirring, add 1-2 parts by mass of 40% NaOH or 40% KOH to the solution of pregelatinized starch and fertilizer in step a, and continue stirring at 40-60° C. until a uniform and transparent paste is obtained;

[0037] Option 2:

[0038] a. Pregelatinization: pregelatinize 10-15 parts by weight of deionized water at a temperature of 40-60°C and 3-5 parts by weight of ungelatinized starch to obtain a pregelatinized starch solution;

[0039] b. Accelerating gelatinization: under stirring, add 1-2 parts by mass of 40% mass concentration NaOH or 40% mass concentration KOH to the pregelatinized starch solution of step S1, and continue stirring at 40-60° C. until a uniform and transparent paste liquid is obtained;

[0040] c. Add fertilizer to the paste obtained in step b, and continue stirring until it is uniform to obtain a mixed paste of starch and fertilizer.

[0041] In the present invention, preferably, after the mixed solution A is polymerized, it further comprises the steps of soaking, filtering and rinsing.

[0042] In the present invention, preferably, the starch is selected from one or more of tapioca starch, corn starch, potato starch, wheat starch, pea starch, and sweet potato starch, for example, tapioca starch, potato starch, "a combination of tapioca starch and potato starch", or "a combination of tapioca starch, potato starch and corn starch".

[0043] Wherein, when the starch is cassava starch and potato starch, preferably, the mass ratio of the cassava starch to the potato starch is 1:1.

[0044] In the present invention, preferably, the fertilizer is a water-soluble fertilizer.

[0045] In the present invention, preferably, the fertilizer is selected from one or more of a macro-element fertilizer, a medium-element fertilizer and a trace element fertilizer.

[0046] Preferably, the macronutrient fertilizer is selected from one or more of nitrogen fertilizer, potassium fertilizer and phosphorus fertilizer, such as nitrogen fertilizer, and the nitrogen fertilizer is, for example, urea.

[0047] Preferably, the medium element fertilizer is selected from one or more of calcium fertilizer, magnesium fertilizer and sulfur fertilizer, for example, calcium fertilizer.

[0048] Among them, preferably, the trace element fertilizer is selected from one or more of boron fertilizer, molybdenum fertilizer, zinc fertilizer, copper fertilizer, manganese fertilizer, and iron fertilizer, such as boron fertilizer.

[0049] In the present invention, preferably, the vinyl monomer 1 is one or more of acrylic acid and / or methacrylic acid;

[0050] In the present invention, preferably, the salt 2 of the vinyl monomer is selected from one or more of sodium acrylate, potassium acrylate, sodium methacrylate and potassium methacrylate. The salt 2 of the vinyl monomer can be obtained by neutralizing the vinyl monomer 1 with an aqueous solution of a neutralizing agent.

[0051] Preferably, the neutralizing agent is selected from potassium hydroxide and / or sodium hydroxide.

[0052] In the present invention, the ratio of the molar number of the salt 2 of the vinyl monomer to the molar number of the monomer is, for example, 50%, 70% or 90%.

[0053] In the present invention, preferably, in the mixed solution A, the content of the starch is 10-80 mg / mL, more preferably 20-50 mg / mL, for example 10 mg / mL, 20 mg / mL, 30 mg / mL, 40 mg / mL, 50 mg / mL, 60 mg / mL or 100 mg / mL.

[0054] In the present invention, preferably, in the mixed solution A, the mass ratio of the starch to the monomer is 1:(10-50), for example (1:5), (1:10), (1:12.5), (1:20), (1:25), (1:30) or (1:50).

[0055] In the present invention, preferably, in the mixed solution A, the mass ratio of the starch to the fertilizer is 1:(0.2-10) or 1:15, for example (1:0.2), (1:0.5), (1:1), (1:2), (1:5) or (1:10).

[0056] In some preferred embodiments of the present invention, in the mixed solution A, the mass ratio of the starch to the monomer is 1:10; and the absorbed dose during the high-energy ray irradiation is 5-20 kGy.

[0057] In a specific embodiment of the present invention, the preparation method of the hydrogel is any of the following schemes:

[0058] Solution 1:

[0059] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 10 mg / mL, the mass ratio of the starch to the acrylic acid is 1:50, and the mass ratio of the starch to the fertilizer is 1:2; the absorbed dose during the high-energy ray irradiation is 5 kGy, and the absorbed dose rate is 2 kGy / h;

[0060] Option 2:

[0061] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 10 mg / mL, the mass ratio of the starch to the acrylic acid is 1:50, and the mass ratio of the starch to the fertilizer is 1:2; the absorbed dose during the high-energy ray irradiation is 10 kGy, and the absorbed dose rate is 2 kGy / h;

[0062] Option 3:

[0063] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 10 mg / mL, the mass ratio of the starch to the acrylic acid is 1:50, and the mass ratio of the starch to the fertilizer is 1:2; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 2 kGy / h;

[0064] Option 4:

[0065] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 20 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:1; the absorbed dose during the high-energy ray irradiation is 10 kGy, and the absorbed dose rate is 2 kGy / h;

[0066] Option 5:

[0067] High-energy rays are used to irradiate mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 30 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 2 kGy / h;

[0068] Option 6:

[0069] High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 30 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 4 kGy / h;

[0070] Option 7:

[0071] High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 30 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 6 kGy / h;

[0072] Option 8:

[0073] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 30 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 2 kGy / h;

[0074] Option Nine:

[0075] High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 30 mg / mL, the mass ratio of the starch to the acrylic acid is 1:50, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 2 kGy / h;

[0076] Option 10:

[0077] High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 40 mg / mL, the mass ratio of the starch to the acrylic acid is 1:12.5, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 2 kGy / h;

[0078] Plan 11:

[0079] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 40 mg / mL, the mass ratio of the starch to the acrylic acid is 1:12.5, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 10 kGy, and the absorbed dose rate is 2 kGy / h;

[0080] Plan 12:

[0081] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 40 mg / mL, the mass ratio of the starch to the acrylic acid is 1:30, and the mass ratio of the starch to the fertilizer is 1:10; the absorbed dose during the high-energy ray irradiation is 20 kGy, and the absorbed dose rate is 5 kGy / h;

[0082] Plan 13:

[0083] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 3 kGy / h;

[0084] Plan 14:

[0085] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h;

[0086] Plan 15:

[0087] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 6 kGy / h;

[0088] Plan 16:

[0089] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h;

[0090] Plan 17:

[0091] High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h;

[0092] Plan 18:

[0093] High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 90%; wherein, in the mixed liquid A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h;

[0094] Plan 19:

[0095] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:50, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h;

[0096] Option 20:

[0097] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:1; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h;

[0098] Plan 21:

[0099] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:2; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h;

[0100] Plan 22:

[0101] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 60 mg / mL, the mass ratio of the starch to the acrylic acid is 1:20, and the mass ratio of the starch to the fertilizer is 1:15; the absorbed dose during the high-energy ray irradiation is 20 kGy, and the absorbed dose rate is 5 kGy / h;

[0102] Plan 23:

[0103] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 100 mg / mL, the mass ratio of the starch to the acrylic acid is 1:5, and the mass ratio of the starch to the fertilizer is 1:0.2; the absorbed dose during the high-energy ray irradiation is 20 kGy, and the absorbed dose rate is 2 kGy / h;

[0104] Plan 24:

[0105] High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 90%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:2; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h;

[0106] Plan 25:

[0107] High-energy rays are irradiated on mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are electron beams, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:1; the absorbed dose during the high-energy ray irradiation is 500 kGy, and the absorbed dose rate is 100 kGy / s;

[0108] Plan 26:

[0109] High-energy rays are irradiated on mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are X-rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:1; the absorbed dose during the high-energy ray irradiation is 20 kGy, and the absorbed dose rate is 5 kGy / h;

[0110] Plan 27:

[0111] High-energy rays are used to irradiate mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid, a cross-linking agent and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, the fertilizer is urea, and the cross-linking agent is N,N'-methylenebisacrylamide; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, the mass ratio of the starch to the fertilizer is 1:0.5; the mass ratio of the starch to the cross-linking agent is 1:1; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h;

[0112] Plan 28:

[0113] High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A includes starch, fertilizer, acrylic acid, a cross-linking agent and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, the fertilizer is urea, and the cross-linking agent is N,N'-methylenebisacrylamide; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, the mass ratio of the starch to the fertilizer is 1:0.5; the mass ratio of the starch to the cross-linking agent is 1:2; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h.

[0114] The present invention also provides a hydrogel, which is prepared by the above-mentioned method for preparing the hydrogel.

[0115] In the present invention, preferably, the hydrogel is used as a water retaining agent in agricultural and forestry planting and production.

[0116] In the present invention, preferably, the hydrogel is used for slowly releasing fertilizers in agricultural and forestry planting and production.

[0117] The present invention also provides a method for preparing dry hydrogel powder, which comprises the following steps: crushing, drying and sieving the hydrogel in sequence.

[0118] In the present invention, preferably, the dry hydrogel powder is used as a water retaining agent in agricultural and forestry planting and production.

[0119] In the present invention, preferably, the dry hydrogel powder is used for slowly releasing fertilizer in agricultural and forestry planting and production.

[0120] The present invention also provides a dry hydrogel powder, which is prepared by the above-mentioned preparation method of the dry hydrogel powder.

[0121] In the present invention, preferably, the dry hydrogel powder is used as a water retaining agent in agricultural and forestry planting and production.

[0122] In the present invention, preferably, the dry hydrogel powder is used for slowly releasing fertilizer in agricultural and forestry planting and production.

[0123] The present invention also provides an application of the dry hydrogel powder as described above as a water retaining agent and / or a slow-release fertilizer in agricultural and forestry planting and production.

[0124] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0125] The reagents and raw materials used in the present invention are commercially available.

[0126] The positive and progressive effects of the present invention are:

[0127] The dry hydrogel powder provided by the invention has excellent water absorption swelling degree, fertilizer slow-release performance and degradation performance.

[0128] The dry hydrogel powder provided by the present invention has excellent water retention performance, can absorb a large amount of water in the soil and gradually release it under drought conditions, effectively improve the water retention capacity of the soil, and reduce the irrigation frequency and water consumption.

[0129] The dry hydrogel powder fertilizer provided by the present invention has excellent slow-release performance, can provide a lasting and stable nutrient supply to plants, and promote the development of plant root systems and overall growth.

[0130] In arid and semi-arid areas, the dry hydrogel powder provided by the present invention can significantly reduce drought stress of plants, improve the drought resistance of crops and trees, thereby stabilizing yields, while reducing the consumption of water resources and fertilizers, reducing production costs, and improving the economic benefits and environmental protection benefits of agricultural and forestry production.

[0131] The preparation method of the hydrogel and the dry hydrogel powder provided by the present invention is simple. The hydrogel can be obtained by a one-step radiation reduction assembly, and the dry hydrogel powder can be obtained by further crushing, drying and sieving. BRIEF DESCRIPTION OF THE DRAWINGS

[0132] Figure 1 This is a macroscopic photograph of the hydrogel obtained in Example 1.

[0133] Figure 2 This is a photograph of the dry hydrogel powder obtained in Example 1 after it has completely swelled. DETAILED DESCRIPTION

[0134] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0135] In the following examples, all the raw materials used were provided by Sinopharm Chemical Reagent Co., Ltd.

[0136] Examples 1-24

[0137] (1) Preparation of a mixed paste of starch and fertilizer:

[0138] 10ml of deionized water was added to a 30ml irradiation bottle, and preheated in a 50℃ water bath for 5min. A certain amount of potato starch and urea were mixed and added to the irradiation bottle. Then 1ml of 40% NaOH was added, and the mixture was quickly placed in a 50℃ water bath and stirred to prevent coagulation. The mixture was heated and stirred for 10min to obtain a uniform and transparent paste, which was a mixed paste of starch and fertilizer. In the gelatinization process, the microstructure of starch changed from ordered crystals to disordered non-crystalline state.

[0139] (2) A certain amount of NaOH was dissolved in 5 ml of deionized water, and added to the acrylic acid solution for neutralization reaction to obtain an acrylic acid neutralization solution with a certain neutralization degree. The neutralization degree of the acrylic acid neutralization solution is shown in Table 1;

[0140] (3) The mixed paste of starch and fertilizer obtained in step (1) and the neutralized acrylic acid solution obtained in step (2) were mixed and stirred for 30 minutes to obtain a mixed solution A. In the mixed solution A, the content of starch, the mass ratio of starch to acrylic acid, and the mass ratio of starch to urea are shown in Table 1;

[0141] (4) passing nitrogen gas through the mixed solution A obtained in step (3) to deoxygenate for 10 min;

[0142] (5) The mixed solution A after nitrogen flow in step (4) is transferred to an irradiation reactor, sealed, and irradiated with a cobalt 60 gamma-ray source. The absorbed dose and absorbed dose rate during irradiation are shown in Table 1. After irradiation, the product is soaked, filtered, and rinsed to obtain a hydrogel;

[0143] (6) The hydrogel obtained in step (5) is crushed, dried, and sieved to obtain dry hydrogel powder.

[0144] Embodiment 25

[0145] The difference between Example 25 and Example 20 is only that the high-energy ray in step (5) and the absorbed dose and absorbed dose rate during irradiation are different, and the other conditions and operations are the same as those of Example 20. The high-energy ray in Example 25 is an electron beam, the absorbed dose during irradiation is 500 kGy, and the absorbed dose rate is 100 kGy / s.

[0146] Embodiment 26

[0147] The difference between Example 26 and Example 20 is only that the high-energy ray in step (5) and the absorbed dose and absorbed dose rate during irradiation are different, and the other conditions and operations are the same as those of Example 20. The high-energy ray in Example 25 is X-ray, the absorbed dose during irradiation is 20 kGy, and the absorbed dose rate is 5 kGy.

[0148] Embodiment 27

[0149] The difference between Example 27 and Example 17 is only step (3), and the other conditions and operations are the same as those of Example 17.

[0150] Step (3) of Example 27 is: mixing the mixed paste of starch and fertilizer obtained in step (1) and the neutralized acrylic acid solution obtained in step (2), and then adding a cross-linking agent N,N'-methylenebisacrylamide (MBA), wherein the mass ratio of starch to the cross-linking agent is 1:1; stirring for 30 minutes to obtain a mixed solution A, in which the starch content, the mass ratio of starch to acrylic acid, and the mass ratio of starch to urea are shown in Table 2.

[0151] Embodiment 28

[0152] The difference between Example 28 and Example 27 is only the amount of the cross-linking agent used in step (3), and the other conditions and operations are the same as those of Example 17. In Example 28, the mass ratio of starch to cross-linking agent is 1:2.

[0153] Comparative Example 1

[0154] (1) A certain amount of NaOH was dissolved in 5 ml of deionized water and added to the acrylic acid solution for neutralization reaction to obtain an acrylic acid neutralization solution with a neutralization degree of 70%.

[0155] (2) passing nitrogen gas through the acrylic acid neutralization solution in step (1) to deoxygenate for 10 minutes;

[0156] (3) The acrylic acid neutralized solution after nitrogen flow in step (2) is transferred to an irradiation reactor, sealed, and irradiated with a cobalt 60 gamma ray source; the absorbed dose during irradiation is 15 kGy, and the absorbed dose rate is 2 kGy / h.

[0157] In Comparative Example 1, no starch or fertilizer was added, and the hydrogel was prepared only from pure acrylic acid. The color was transparent. Due to the lack of starch, the cross-linking degree of the polymer was low and the mechanical strength was low.

[0158] Comparative Example 2

[0159] (1) Preparation of a mixed paste of starch and fertilizer:

[0160] 10 ml of deionized water was added to a 30 ml irradiation bottle, and the mixture was preheated in a 50°C water bath for 5 min. A certain amount of potato starch and urea were mixed and added to the irradiation bottle. 1 ml of 40% NaOH was added, and the mixture was quickly placed in a 50°C water bath and stirred to prevent coagulation. The mixture was heated and stirred for 10 min to obtain a uniform and transparent paste, which was a mixed paste of starch and fertilizer. The initiator ammonium persulfate (APS) was added to the mixed paste of starch and fertilizer while the mixture was kept at 50°C.

[0161] (2) dissolving a certain amount of NaOH in 5 ml of deionized water, and adding the solution to the acrylic acid for neutralization reaction to obtain an acrylic acid neutralization solution with a certain degree of neutralization, wherein the degree of neutralization of the acrylic acid neutralization solution is the same as that of Example 20;

[0162] (3) The mixed paste of starch and fertilizer with initiator added prepared in step (1) and the neutralized acrylic acid solution prepared in step (2) are mixed and stirred for 1 hour to obtain a mixed solution A, wherein the content of starch, the mass ratio of starch to acrylic acid, and the mass ratio of starch to urea in the mixed solution A are the same as those in Example 20; the mass ratio of starch to initiator is 1:1;

[0163] (4) nitrogen is passed through the mixed solution A obtained in step (3), and a cross-linking agent N,N'-methylenebisacrylamide (MBA) is added under a nitrogen atmosphere, wherein the mass ratio of the cross-linking agent to the starch is 1:1; the mixture is polymerized at 50°C for 1 hour, and the product is soaked, filtered, and rinsed to obtain a hydrogel;

[0164] (5) The hydrogel obtained in step (4) is crushed, dried, and sieved to obtain dry hydrogel powder.

[0165] Table 1

[0166]

[0167] Table 2

[0168]

[0169] Effect Example

[0170] The water absorption swelling degree, fertilizer slow-release performance and material degradation performance (mass loss rate) of the dry hydrogel powders obtained in Examples 1-24 and Comparative Example 1 were measured respectively.

[0171] 1. Test method for water swelling

[0172] The water absorption swelling degree is tested according to conventional means in the art, and its value is obtained by the ratio of water absorption mass to powder mass, and the formula should be: water absorption swelling degree = (mass of dry hydrogel powder after water absorption - initial mass of dry hydrogel powder) / initial mass of dry hydrogel powder. The higher the water absorption swelling degree, the better the water retention performance.

[0173] 2. Test method for slow-release performance of fertilizer

[0174] The slow-release performance of fertilizer is tested according to conventional means in the field. The dry hydrogel powder is soaked in water, and all the volume of the solution is taken after it absorbs water, swells and releases the fertilizer. The volume is recorded as the "solution volume", and the mass concentration of the fertilizer in the solution is detected, and the mass concentration is recorded as the "fertilizer mass concentration". After the fertilizer is slowly released, the obtained dry hydrogel powder that has absorbed water is placed in an oven for drying. After the water evaporates, the mass of the dry hydrogel powder is obtained, which is recorded as the "dry mass of the dry hydrogel powder after slow-release of the fertilizer". The calculation formula for the fertilizer slow-release rate is as follows:

[0175]

[0176] The higher the fertilizer slow-release rate, the better the fertilizer slow-release performance.

[0177] 3. Test method for material degradation performance (mass loss rate)

[0178] The material degradation performance is tested according to conventional means in the field, and the degradation method is soil burial degradation.

[0179] The mass loss rate is obtained by the ratio of the mass lost after degradation of the dry hydrogel powder to the initial mass of the dry hydrogel powder, that is:

[0180]

[0181] The higher the mass loss rate, the better the degradation performance.

[0182] The test results of the water absorption swelling degree, fertilizer slow-release performance and material degradation performance (mass loss rate) of the dry hydrogel powders obtained in Examples 1-24 and Comparative Example 1 are shown in Table 3.

[0183] Table 3

[0184]

[0185] Figure 1 This is a macroscopic photograph of the hydrogel obtained in Example 1. Figure 2The following is a photograph of the dry hydrogel powder obtained in Example 1 after it has completely swelled. The hydrogels and dry hydrogel powders obtained in Examples 2-24 are similar to those in Example 1.

[0186] As shown in Table 3, the dry hydrogel powders prepared in Examples 1-24 have good water absorption and water retention properties and excellent fertilizer slow release properties, and the water absorption swelling degree ranges from 200 to 900 g·g -1 The fertilizer slow-release rate reaches 10%-50%, and it also has excellent degradability, with a mass loss rate of 20-50%.

[0187] It can be seen from the data of Examples 1, 2, 3 and the data of Examples 10 and 11 in Table 3 that when the neutralization degree of the acrylic acid neutralization solution, the content of starch in the mixed solution A, the mass ratio of starch to acrylic acid in the mixed solution A, the mass ratio of starch to urea in the mixed solution A, and the absorbed dose rate during irradiation are all the same, when the absorbed dose during irradiation is 5-15 kGy, the water absorption swelling degree, fertilizer slow-release performance and mass loss rate of the prepared dry hydrogel powder increase with the increase of the absorbed dose during irradiation.

[0188] It can be seen from the data of Examples 5, 6, and 7 and the data of Examples 13, 14, and 15 in Table 3 that when the neutralization degree of the acrylic acid neutralization solution, the content of starch in the mixed solution A, the mass ratio of starch to acrylic acid in the mixed solution A, the mass ratio of starch to urea in the mixed solution A, and the absorbed dose during irradiation are all the same, when the absorbed dose rate during irradiation is 2-6 kGy / h, the obtained dry hydrogel powder has an absorbed dose rate that is not as high as possible, and when the absorbed dose rate during irradiation is lower, it has a higher water absorption swelling degree and fertilizer slow-release performance.

[0189] It can be seen from the data of Examples 5, 8 and 9 in Table 3 that when the neutralization degree of the acrylic acid neutralization solution, the content of starch in the mixed solution A, the mass ratio of starch to urea in the mixed solution A, the absorbed dose during irradiation, and the absorbed dose rate during irradiation are all the same, when the mass ratio of starch to acrylic acid in the mixed solution A is 1: (10-50), the prepared dry hydrogel powder has a higher water absorption swelling degree and fertilizer slow-release performance, but when the mass ratio of starch to acrylic acid is a higher 1: 50, it has a higher water absorption swelling degree and fertilizer slow-release performance.

[0190] From the data of Examples 16, 17, 18 and the data of Examples 21 and 24 in Table 3, it can be seen that when the content of starch in the mixed solution A, the mass ratio of starch to acrylic acid in the mixed solution A, the mass ratio of starch to urea in the mixed solution A, the absorbed dose during irradiation, and the absorbed dose rate during irradiation are all the same, when the neutralization degree of the acrylic acid neutralization solution is 50%-90%, the prepared dry hydrogel powder has a higher water absorption swelling degree and fertilizer slow-release performance. However, the neutralization degree of the acrylic acid neutralization solution is not the higher the better, nor the lower the better for the water absorption swelling degree and fertilizer slow-release performance, but when the neutralization degree of the acrylic acid neutralization solution is 70%, it has a higher water absorption swelling degree.

[0191] It can be seen from the data of Examples 20 and 21 in Table 3 that when the neutralization degree of the acrylic acid neutralization solution, the content of starch in the mixed solution A, the mass ratio of starch to acrylic acid in the mixed solution A, the absorbed dose during irradiation, and the absorbed dose rate during irradiation are all the same, when the mass ratio of starch to urea in the mixed solution A is 1:1 and 1:2, the prepared dry hydrogel powder has higher water absorption swelling degree and fertilizer slow-release performance, but when the mass ratio of starch to urea in the mixed solution A is higher at 1:2, it has higher water absorption swelling degree and fertilizer slow-release performance.

[0192] It can be seen from the data of Examples 20, 25 and 26 in Table 3 that under the same raw material conditions, when the high-energy rays are γ rays, electron beam rays and X-rays respectively, under the conditions of appropriate absorbed dose and absorbed dose rate during irradiation, the water absorption swelling degree, fertilizer sustained release rate and mass loss rate of the obtained dry hydrogel powder are similar, which indicates that when the high-energy rays are γ rays, electron beam rays or X-rays during irradiation, the effect of the obtained dry hydrogel powder is equivalent.

[0193] It can be seen from the data of Examples 17, 27 and 28 in Table 3 that when the neutralization degree of the acrylic acid neutralization solution, the content of starch in the mixed solution A, the mass ratio of starch to acrylic acid in the mixed solution A, the mass ratio of starch to urea in the mixed solution A, the absorbed dose during irradiation, and the absorbed dose rate during irradiation are all the same, when the mass ratio of starch to the cross-linking agent is 1:0, 1:1 and 1:2, the water absorption swelling degree and the fertilizer slow release rate of the obtained dry hydrogel powder first increase and then decrease with the increase of the amount of the cross-linking agent, and the best water absorption swelling degree and fertilizer slow release rate are obtained when the mass ratio of starch to the cross-linking agent is 1:1; however, when no cross-linking agent is added, the obtained dry hydrogel powder has better degradation performance.

[0194] In Comparative Example 1, since starch and fertilizer are not added, the hydrogel prepared from pure acrylic acid has relatively few hydrophilic free radicals and a small water absorption swelling degree. At the same time, since starch is not added, the dry hydrogel powder prepared in Comparative Example 1 has poor degradation performance and does not have the function of slow-release of fertilizer.

[0195] The neutralization degree of the acrylic acid neutralization solution, the starch content in the mixed solution A, the mass ratio of starch to acrylic acid in the mixed solution A, and the mass ratio of starch to urea in the mixed solution A are the same in Comparative Example 2 and Example 20. The only difference is that Example 20 adopts an irradiation preparation method, while Comparative Example 2 adopts a preparation method in which an initiator and a cross-linking agent are used to cause a polymerization reaction. It can be seen from the data of Comparative Example 2 and Example 20 in Table 3 that, under the same components and amounts of raw materials, the dry hydrogel powder obtained by irradiation has better water absorption swelling, fertilizer slow release rate and mass loss rate than the dry hydrogel powder obtained by the initiator.

[0196] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a hydrogel, characterized in that: It includes the following steps: The mixed solution A is irradiated with high-energy rays to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, monomer and water; the starch is gelatinized starch; Wherein, the monomer is composed of a vinyl monomer 1 and a salt of a vinyl monomer 2, or the monomer is composed of acrylamide; wherein, when the monomer is composed of a vinyl monomer 1 and a salt of a vinyl monomer 2, the ratio of the molar number of the salt of the vinyl monomer 2 to the molar number of the monomer is 50%-90%; Wherein, in the mixed solution A, the content of the starch is 1-100 mg / mL, the mass ratio of the starch to the monomer is 1:(0.1-100), and the mass ratio of the starch to the fertilizer is 1:(0.1-50).

2. The method for preparing the hydrogel according to claim 1, characterized in that: It satisfies the following conditions (1) and / or (2): (1) The high-energy rays are cobalt-60 gamma rays, electron beams or X-rays; Wherein, when the high-energy ray is cobalt-60 gamma ray or X-ray, preferably, the absorbed dose rate during the irradiation is 0.1-20 kGy / h, for example, 1 kGy / h, 2 kGy / h, 3 kGy / h, 4 kGy / h, 5 kGy / h or 6 kGy / h; Wherein, when the high-energy ray is cobalt-60 gamma ray or X-ray, preferably, the absorbed dose during the irradiation is 2-100 kGy, more preferably 5-50 kGy, for example, 5 kGy, 10 kGy, 15 kGy, 20 kGy or 30 kGy; Wherein, when the high-energy ray is an electron beam, preferably, the absorbed dose during the irradiation is 50-1000 kGy, more preferably 300-800 kGy, for example 500 kGy; Wherein, when the high-energy ray is an electron beam, preferably, the absorbed dose rate during the irradiation is 10-500 kGy / s, more preferably 50-300 kGy / s, for example 100 kGy / s; (2) Before the mixed liquid A is irradiated with high-energy rays, nitrogen and / or argon are introduced into the mixed liquid A to remove oxygen from the mixed liquid A.

3. The method for preparing the hydrogel according to claim 1, characterized in that: It meets one or more of the following conditions: (1) The mixed liquid A is free of oxygen or has an oxygen concentration lower than 5%; (2) The mixed solution A also includes a cross-linking agent; Wherein, preferably, the crosslinking agent is selected from one or more of divinylbenzene, diisocyanate, polyvinyl alcohol, vinylbenzene sulfonate, methyl methacrylate, ethyl bromide and N,N'-methylenebisacrylamide, such as N,N'-methylenebisacrylamide; Preferably, in the mixed solution A, the mass ratio of the starch to the cross-linking agent is 1:(0.1-10), for example, 1:1 or 1:2; (3) The method for preparing the hydrogel further comprises the following steps: S1, preparing a mixed paste of starch and fertilizer by mixing ungelatinized starch, the fertilizer and the water; S2, dissolving the monomer in the water to obtain a vinyl aqueous solution; or dissolving the vinyl monomer 3 in an aqueous solution of a neutralizing agent to undergo a neutralization reaction to obtain a vinyl aqueous solution, wherein the degree of neutralization of the vinyl aqueous solution is 50%-90%; S3, mixing and stirring the mixed paste of starch and fertilizer described in S1 and the vinyl aqueous solution described in S2 to obtain the mixed solution A; (4) After the mixed solution A is polymerized, the process further comprises the steps of soaking, filtering and rinsing.

4. The method for preparing the hydrogel according to claim 3, characterized in that: It satisfies (1) and / or (2) of the following conditions: (1) In S1, the mixed paste of starch and fertilizer also includes alkali solution; The base is, for example, NaOH and / or KOH; The mass concentration of the alkali in the alkali solution is, for example, 30-50%, for example, 40%; In the mixed paste of starch and fertilizer, the mass ratio of the starch to the alkali solution is, for example, (3-5): (1-2); (2) In S1, the mixed paste of starch and fertilizer is prepared by a hydrothermal stirring method. More preferably, the steps of the preparation method of the mixed paste of starch and fertilizer include one of the following two schemes: Solution 1: a. Pregelatinization: pregelatinize 10-15 parts by weight of deionized water at a temperature of 40-60°C, 3-5 parts by weight of ungelatinized starch and fertilizer to obtain a solution of pregelatinized starch and fertilizer; b. Accelerating gelatinization: under stirring, add 1-2 parts by mass of 40% NaOH or 40% KOH to the solution of pregelatinized starch and fertilizer in step a, and continue stirring at 40-60° C. until a uniform and transparent paste is obtained; Option 2: a. Pregelatinization: pregelatinize 10-15 parts by weight of deionized water at a temperature of 40-60°C and 3-5 parts by weight of ungelatinized starch to obtain a pregelatinized starch solution; b. Accelerating gelatinization: under stirring, add 1-2 parts by mass of 40% mass concentration NaOH or 40% mass concentration KOH to the pregelatinized starch solution of step S1, and continue stirring at 40-60° C. until a uniform and transparent paste liquid is obtained; c. Add fertilizer to the paste obtained in step b, and continue stirring until it is uniform to obtain a mixed paste of starch and fertilizer.

5. The method for preparing the hydrogel according to claim 1, characterized in that: It meets one or more of the following conditions: (1) The starch is selected from one or more of tapioca starch, corn starch, potato starch, wheat starch, pea starch, and sweet potato starch, for example, tapioca starch, potato starch, a combination of tapioca starch and potato starch, or a combination of tapioca starch, potato starch, and corn starch; Wherein, when the starch is cassava starch and potato starch, preferably, the mass ratio of cassava starch to potato starch is 1:1; (2) The fertilizer is a water-soluble fertilizer; (3) The fertilizer is selected from one or more of a macronutrient fertilizer, a medium-nutrient fertilizer and a trace-nutrient fertilizer; Preferably, the macronutrient fertilizer is selected from one or more of nitrogen fertilizer, potassium fertilizer and phosphorus fertilizer, such as nitrogen fertilizer, and the nitrogen fertilizer is urea; Preferably, the medium element fertilizer is selected from one or more of calcium fertilizer, magnesium fertilizer and sulfur fertilizer, for example, calcium fertilizer; Preferably, the trace element fertilizer is selected from one or more of boron fertilizer, molybdenum fertilizer, zinc fertilizer, copper fertilizer, manganese fertilizer, and iron fertilizer, for example, boron fertilizer; (4) the vinyl monomer 1 is one or more of acrylic acid and / or methacrylic acid; (5) the salt 2 of the vinyl monomer is selected from one or more of sodium acrylate, potassium acrylate, sodium methacrylate and potassium methacrylate; (6) the ratio of the molar number of the salt 2 of the vinyl monomer to the molar number of the monomer is, for example, 50%, 70% or 90%; (7) In the mixed solution A, the content of starch is 10-80 mg / mL, more preferably 20-50 mg / mL, for example, 10 mg / mL, 20 mg / mL, 30 mg / mL, 40 mg / mL, 50 mg / mL, 60 mg / mL or 100 mg / mL; (8) In the mixed solution A, the mass ratio of the starch to the monomer is 1:(10-50), for example (1:5), (1:10), (1:12.5), (1:20), (1:25), (1:30) or (1:50); (9) In the mixed solution A, the mass ratio of the starch to the fertilizer is 1:(0.2-10) or 1:15, for example (1:0.2), (1:0.5), (1:1), (1:2), (1:5) or (1:10).

6. The method for preparing the hydrogel according to claim 1, characterized in that: The preparation method of the hydrogel is any of the following schemes: Solution 1: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 10 mg / mL, the mass ratio of the starch to the acrylic acid is 1:50, and the mass ratio of the starch to the fertilizer is 1:2; the absorbed dose during the high-energy ray irradiation is 5 kGy, and the absorbed dose rate is 2 kGy / h; Option 2: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 10 mg / mL, the mass ratio of the starch to the acrylic acid is 1:50, and the mass ratio of the starch to the fertilizer is 1:2; the absorbed dose during the high-energy ray irradiation is 10 kGy, and the absorbed dose rate is 2 kGy / h; Option 3: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 10 mg / mL, the mass ratio of the starch to the acrylic acid is 1:50, and the mass ratio of the starch to the fertilizer is 1:2; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 2 kGy / h; Option 4: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 20 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:1; the absorbed dose during the high-energy ray irradiation is 10 kGy, and the absorbed dose rate is 2 kGy / h; Option 5: High-energy rays are used to irradiate mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 30 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 2 kGy / h; Option 6: High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 30 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 4 kGy / h; Option 7: High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 30 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 6 kGy / h; Option 8: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 30 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 2 kGy / h; Option Nine: High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 30 mg / mL, the mass ratio of the starch to the acrylic acid is 1:50, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 2 kGy / h; Option 10: High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 40 mg / mL, the mass ratio of the starch to the acrylic acid is 1:12.5, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 2 kGy / h; Plan 11: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 40 mg / mL, the mass ratio of the starch to the acrylic acid is 1:12.5, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 10 kGy, and the absorbed dose rate is 2 kGy / h; Plan 12: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 40 mg / mL, the mass ratio of the starch to the acrylic acid is 1:30, and the mass ratio of the starch to the fertilizer is 1:10; the absorbed dose during the high-energy ray irradiation is 20 kGy, and the absorbed dose rate is 5 kGy / h; Plan 13: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 3 kGy / h; Plan 14: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h; Plan 15: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:10, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 6 kGy / h; Plan 16: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h; Plan 17: High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h; Plan 18: High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 90%; wherein, in the mixed liquid A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h; Plan 19: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:50, and the mass ratio of the starch to the fertilizer is 1:0.5; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h; Option 20: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:1; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h; Plan 21: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:2; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h; Plan 22: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 50%; wherein, in the mixed solution A, the content of the starch is 60 mg / mL, the mass ratio of the starch to the acrylic acid is 1:20, and the mass ratio of the starch to the fertilizer is 1:15; the absorbed dose during the high-energy ray irradiation is 20 kGy, and the absorbed dose rate is 5 kGy / h; Plan 23: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 100 mg / mL, the mass ratio of the starch to the acrylic acid is 1:5, and the mass ratio of the starch to the fertilizer is 1:0.2; the absorbed dose during the high-energy ray irradiation is 20 kGy, and the absorbed dose rate is 2 kGy / h; Plan 24: High-energy rays are used to irradiate a mixed solution A to polymerize the mixed solution A, wherein the mixed solution A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 90%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:2; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h; Plan 25: High-energy rays are irradiated on mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are electron beams, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:1; the absorbed dose during the high-energy ray irradiation is 500 kGy, and the absorbed dose rate is 100 kGy / s; Plan 26: High-energy rays are irradiated on mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A comprises starch, fertilizer, acrylic acid and water; the high-energy rays are X-rays, the starch is gelatinized starch, the starch is potato starch, and the fertilizer is urea; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, and the mass ratio of the starch to the fertilizer is 1:1; the absorbed dose during the high-energy ray irradiation is 20 kGy, and the absorbed dose rate is 5 kGy / h; Plan 27: High-energy rays are used to irradiate mixed solution A to polymerize the mixed solution A, wherein the mixed solution A includes starch, fertilizer, acrylic acid, a cross-linking agent and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, the fertilizer is urea, and the cross-linking agent is N,N'-methylenebisacrylamide; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed solution A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, the mass ratio of the starch to the fertilizer is 1:0.5; the mass ratio of the starch to the cross-linking agent is 1:1; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h; Plan 28: High-energy rays are used to irradiate mixed liquid A to polymerize the mixed liquid A, wherein the mixed liquid A includes starch, fertilizer, acrylic acid, a cross-linking agent and water; the high-energy rays are cobalt 60 gamma rays, the starch is gelatinized starch, the starch is potato starch, the fertilizer is urea, and the cross-linking agent is N,N'-methylenebisacrylamide; the acrylic acid is composed of acrylic acid and sodium acrylate; the ratio of the molar number of the sodium acrylate to the sum of the molar numbers of the acrylic acid and the sodium acrylate is 70%; wherein, in the mixed liquid A, the content of the starch is 50 mg / mL, the mass ratio of the starch to the acrylic acid is 1:25, the mass ratio of the starch to the fertilizer is 1:0.5; the mass ratio of the starch to the cross-linking agent is 1:2; the absorbed dose during the high-energy ray irradiation is 15 kGy, and the absorbed dose rate is 5 kGy / h.

7. A hydrogel, characterized in that: It is prepared by the method for preparing the hydrogel according to any one of claims 1 to 6; Preferably, the hydrogel is used as a water retaining agent in agricultural and forestry planting and production; Preferably, the hydrogel is used for slowly releasing fertilizers in agricultural and forestry planting and production.

8. A method for preparing dry hydrogel powder, characterized in that: The method comprises the following steps: crushing, drying and screening the hydrogel as claimed in claim 7 in sequence; Preferably, the dry hydrogel powder is used as a water retaining agent in agricultural and forestry planting and production; Preferably, the dry hydrogel powder is used for slow release of fertilizer in agricultural and forestry planting and production.

9. A dry hydrogel powder, characterized in that: It is prepared by the method for preparing dry hydrogel powder as claimed in claim 8; Preferably, the dry hydrogel powder is used as a water retaining agent in agricultural and forestry planting and production; Preferably, the dry hydrogel powder is used for slow release of fertilizer in agricultural and forestry planting and production.

10. Use of the dry hydrogel powder according to claim 9 as a water retaining agent and / or a slow-release fertilizer in agricultural and forestry planting and production.

Images