Urea-loaded polymer hydrogel as well as preparation method and application thereof

Abstract

The invention provides urea-loaded polymer polysaccharide semi-interpenetrating hydrogel as well as a preparation method and application thereof, and belongs to the technical field of agriculture and forestry water-retaining fertilizers. The preparation method comprises the following steps: adding polysuccinimide into a sodium hydroxide solution, mixing, adjusting the pH value, adding chitosan quaternary ammonium salt and ethylene glycol diglycidyl ether, mixing, adding urea, stirring and heating to obtain the hydrogel. The urea-loaded polymer hydrogel obtained by the method is mainly used for loading and slow release of agricultural fertilizers. The method is easy and convenient to operate, low in cost and convenient to implement, and wide application of the PASP hydrogel in the field of agriculture and forestry is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of agroforestry water-retaining fertilizers, and particularly relates to a polymer polysaccharide semi-interpenetrating hydrogel loaded with urea, a preparation method thereof, and an application thereof. Background Art With the rapid development of agriculture, the agricultural economy has entered a new era. In order to increase the yield and quality of agricultural products, reduce land input, reduce environmental pollution, and improve the utilization rate of fertilizers has become an urgent issue in agricultural production. The Outline of the Medium- and Long-Term Scientific and Technological Development Plan of China lists the research and development of environment-friendly fertilizers and slow-release and controlled-release fertilizers as the priority development themes.

[0002] Hydrogels have a three-dimensional network structure with cross-linked structures, and the absorbed water is difficult to extrude by physical methods. They have strong water retention ability, but can be absorbed and utilized by plants. Adding water-retaining agents to the soil can improve the soil structure, increase the water absorption rate and water retention capacity of the soil, and promote the root development of crops, improve the utilization of deep soil water by crops, and have the function of regulating farmland water and crop water consumption. In recent years, the interaction effect between water-retaining agents and nutrients has been favored by researchers. Using water-retaining agents as coating materials for slow-release fertilizers to prepare functional slow-release fertilizers with both water absorption and retention and nutrient slow-release properties has become a research hotspot at home and abroad.

[0003] Currently, the most developed and used water-retaining agent materials are mainly polyacrylic acid type (PAAc) and polyacrylamide type (PAAm). They have good water absorption performance and simple synthesis processes, but they cannot be completely naturally degraded, and the remaining waste causes secondary environmental pollution. They belong to non-environmentally friendly materials. Therefore, it is urgent to find new biodegradable water-retaining and slow-release fertilizer film materials, which is crucial for the development of efficient, green, and sustainable agriculture.

[0004] Polyaspartic acid (PASP) is a polyamino acid formed by the combination of D-aspartic acid or L-aspartic acid through amide bonds formed by α-amino and α-carboxyl or β-carboxyl groups, and has two configurations, α and β. The amide bonds on the main chain of polyaspartic acid are easily broken by the action of microorganisms and fungi, and finally degraded into environmentally harmless water and carbon dioxide. It is an environmentally friendly green chemical that is non-toxic, pollution-free, and biodegradable. Polyaspartic acid has a wide range of uses. For example, researchers have used it to develop various biological and medical materials including tissue engineering and drug / gene delivery. Another example is that polyaspartic acid can be used as a fertilizer synergist to enhance the absorption of nitrogen, phosphorus, potassium, and trace elements by crops, achieve the slow-release and controlled-release effects of fertilizers, reduce the adverse effects on the environment caused by excessive fertilization, activate the nutrients in the fixed state in the soil, improve the fertilizer utilization rate, and improve the soil quality.

[0005] Crosslinking polyaspartic acid can obtain PASP hydrogel with a spatial network structure at the microscopic level. PASP hydrogel has good water absorption and water retention properties and is considered a new type of green material with the most potential to replace polyacrylic acid or polyacrylamide water-retaining agents, having broad application prospects in the fields of agriculture and forestry. However, the mechanical strength of pure PASP is poor, and it is of great research significance to explore the application of PASP hydrogel with better functionality in fertilizers. Summary of the Invention

[0006] The present invention provides a polymer polysaccharide semi-interpenetrating hydrogel loaded with urea and a preparation method thereof. Using the high molecular polymer poly(succinimide) and the natural polysaccharide chitosan quaternary ammonium salt as the main raw materials, the obtained polymer hydrogel has good biodegradability and excellent mechanical properties.

[0007] The present invention provides a preparation method of a polymer hydrogel loaded with urea, which is prepared by the following steps: Add poly(succinimide) to a sodium hydroxide solution, mix, adjust the pH value, then add chitosan quaternary ammonium salt and ethylene glycol diglycidyl ether, mix, add urea, and stir and heat to obtain a polymer hydrogel loaded with urea.

[0008] Further, the relative molecular weight value of the poly(succinimide) is 1×10 5 ~1.5×10 5 Dalton.

[0009] Further, the dosage ratio of poly(succinimide) to the sodium hydroxide solution is 5~7 g: 30~40 mL; Preferably, the concentration of the sodium hydroxide solution is 1~3 mol / L. Further, the mass ratio of the poly(succinimide) to the quaternary ammonium salt chitosan is 12:3~4. Further, the mass ratio of the poly(succinimide) to the ethylene glycol diglycidyl ether is 2:1. Further, the pH value is 4~5; preferably, the pH value is 4.8.

[0010] Further, the stirring and heating is specifically carried out by water bath heating in a magnetic stirrer; Preferably, the water bath is heated to a temperature of 45~55°C.

[0011] The present invention also provides a polymer hydrogel loaded with urea prepared by the preparation method described above.

[0012] The present invention also provides the application of the polymer hydrogel loaded with urea described above in the loading and slow release of agricultural fertilizers.

[0013] Further, the application is the application of a urea-loaded polymer hydrogel in urea loading and slow release.

[0014] The present invention has the following advantages: The polymer polysaccharide semi-interpenetrating hydrogel loaded with urea proposed by the present invention uses the high molecular polymer poly(succinimide) and the natural polysaccharide chitosan quaternary ammonium salt as the main raw materials. First, ring-opening is carried out and then cross-linking is carried out to form a polymer network. The natural polysaccharide is interpenetrated into the polymer network. After forming a semi-interpenetrating hydrogel, urea is added to achieve the loading of urea. Among them, by adjusting the mass ratio of poly(succinamide) to chitosan quaternary ammonium salt, a hydrogel with excellent cross-linking strength can be obtained, so as to adapt to the loading materials of different addition amounts of urea. Since the natural polysaccharide chitosan quaternary ammonium salt has good biocompatibility, hygroscopicity and moisture retention, non-toxicity and excellent affinity with the polymer, the formed hydrogel has good mechanical properties and good biodegradability, greatly reducing the impact on the environment. Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0016] Figure 1 For the compressive stress-strain of polyaspartic acid hydrogels and polyaspartic acid-chitosan quaternary ammonium salt interpenetrating network hydrogels with different urea loading concentrations in Test Example 1 of the present invention; Figure 2 is the compressive stress-strain of polyaspartic acid hydrogels and polyaspartic acid-chitosan quaternary ammonium salt interpenetrating network hydrogels with different urea loading concentrations in Test Example 1 of the present invention; Figure 3 For the compressive modulus and dissipation energy of polyaspartic acid hydrogels and polyaspartic acid-chitosan quaternary ammonium salt interpenetrating network hydrogels with different urea loading concentrations in Test Example 1 of the present invention; Figure 4 For the Fourier transform infrared of polyaspartic acid hydrogels and polyaspartic acid-chitosan quaternary ammonium salt interpenetrating network hydrogels with different urea loading concentrations in Test Example 1 of the present invention; Figure 5 For the slow release of urea in soil of polyaspartic acid hydrogels, polyaspartic acid hydrogels with different urea loading concentrations and polyaspartic acid-chitosan quaternary ammonium salt interpenetrating network hydrogels in Test Example 1 of the present invention; Figure 6 For the plant growth height curves of polyaspartic acid hydrogels, polyaspartic acid-chitosan quaternary ammonium salt hydrogels and hydrogels loaded with 15% urea each in Test Example 1 of the present invention; Figure 7 For the plant growth leaf lengths, leaf numbers, and root lengths of the polyaspartic acid hydrogel, polyaspartic acid-chitosan quaternary ammonium salt hydrogel, and each hydrogel loaded with 15% urea in Test Example 1 of the present invention; Figure 8 For the biodegradation rates of the polyaspartic acid hydrogel and P-H hydrogels with different HACC ratios in Test Example 1 of the present invention.

[0017] Figure 9 For the compression schematic diagrams (A), stress-strain curves (B), and corresponding compression modulus and dissipation energy diagrams (C) of the polyaspartic acid hydrogel and P-H hydrogels with different HACC ratios under different strains in Test Example 1 of the present invention. Different letters represent significant differences (P<0.05). Detailed implementation manners

[0018] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0019] In the prior art, pure PASP hydrogels have certain deficiencies in terms of strength, elasticity, toughness, etc., which limit the application of PASP in the fields of agriculture and forestry. The inventors of this application found that introducing chitosan quaternary ammonium salt and polysuccinimide to construct a semi-interpenetrating network hydrogel can effectively improve the mechanical strength of PASP and endow it with better functionality.

[0020] On the one hand, an embodiment of the present invention proposes a preparation method of a urea-loaded polymer hydrogel, which is prepared by including the following steps: Add polysuccinimide (PSI) to a sodium hydroxide solution, mix, adjust the pH value, then add chitosan quaternary ammonium salt (HACC) and ethylene glycol diglycidyl ether (EGDE), mix, add urea, and stir and heat to obtain a hydrogel.

[0021] The preparation method of the urea-loaded polymer polysaccharide semi-interpenetrating hydrogel proposed by the present invention prepares a high-molecular polymer-natural polysaccharide semi-interpenetrating hydrogel through a physical-chemical cross-linking method. The first driving force of this cross-linking network is to form a polyaspartic acid (PASP) network by the hydrolysis and then covalent cross-linking of polysuccinimide. The linear chitosan quaternary ammonium salt simultaneously interpenetrates into the PASP network to form a polymer. The second driving force is the electrostatic and hydrogen bond interactions between PASP and HACC. In this way, the natural polysaccharide HACC can be interpenetrated into the polymer network to form a semi-interpenetrating hydrogel.

[0022] Due to the good biocompatibility, moisture absorption and retention, non-toxicity of HACC, and excellent affinity with polymers, the mechanical properties of the resulting hydrogel are significantly improved. Moreover, since the main chain of polyaspartic acid (PASP) has peptide bonds consistent with proteins, is non-toxic, has good biocompatibility, and is easily broken by attacks from microorganisms, enzymes, etc. and ultimately decomposes into stable small molecule substances CO 2 and H 2 O, the hydrogel has good biodegradability, greatly reducing the impact on the environment. This method is simple to operate, has a low cost, is easy to implement, and is conducive to the wide application of PASP hydrogels in the fields of agriculture and forestry.

[0023] In an embodiment of the present invention, the relative molecular weight value of the polysuccinimide is 1×10 5 Daltons or more. Preferably, the relative molecular weight value of the polysuccinimide is 1×10 5 ~1.5×10 5 Daltons.

[0024] In an embodiment of the present invention, the dosage ratio of polysuccinimide to sodium hydroxide solution is 5~7 g: 30~40 mL. Preferably, the dosage ratio of polysuccinimide to sodium hydroxide solution is 6 g: 36 mL. Among them, the concentration of the sodium hydroxide solution is 1~3 mol / L. Preferably, the concentration of the sodium hydroxide solution is 2 mol / L. In an embodiment of the present invention, the mass ratio of the polysuccinimide to the quaternary ammonium salt chitosan is 12: 3~4. In an embodiment of the present invention, the mass ratio of the polysuccinimide to ethylene glycol diglycidyl ether is 2: 1. In an embodiment of the present invention, mixing is carried out by stirring.

[0025] In an embodiment of the present invention, the pH value is 4~5. Preferably, the pH value is 4.8.

[0026] In an embodiment of the present invention, the stirring and heating are specifically carried out by water bath heating in a magnetic stirrer.

[0027] In an embodiment of the present invention, the water bath is heated to a temperature of 45~55 °C. Preferably, the water bath is heated to a temperature of 50 °C.

[0028] In an embodiment of the present invention, the time for water bath heating is 5~7 h. Preferably, the time for water bath heating is 6 h. In an embodiment of the present invention, the rotation speed of the magnetic stirrer is 700~900 rpm. Preferably, the rotation speed of the magnetic stirrer is 800 rpm. In another aspect, an embodiment of the present invention further provides a polymer hydrogel loaded with urea prepared by the preparation method described in any one of the above. The polymer polysaccharide semi-interpenetrating network hydrogel obtained in the embodiment of the present invention can improve the utilization rate of fertilizers, reduce the adverse effects on the environment caused by excessive fertilization, and can activate the nutrient elements in a fixed state in the soil and improve the soil structure.

[0029] On the other hand, an embodiment of the present invention further provides an application of the polymer hydrogel loaded with urea described in any one of the above in the loading and slow release of agricultural fertilizers.

[0030] In an embodiment of the present invention, the application is the application of the polymer hydrogel loaded with urea in the loading and slow release of urea.

[0031] The present invention will be described in detail below with reference to the embodiments and the drawings.

[0032] Example 1 A preparation method of a poly(succinimide)-quaternary ammonium salt of chitosan loaded urea semi-interpenetrating network hydrogel includes the following steps: Accurately weigh 6 g of poly(succinimide) (PSI) powder with a relative molecular weight value of 1×10 5 Daltons and pour it into 36 mL of sodium hydroxide (2 mol / L) solution, stir at a stirring speed of 300 rpm for 1 h to obtain a hydrolyzed PSI solution; Adjust the pH value of the above hydrolyzed PSI solution to 4.8, then add 1.5 g of quaternary ammonium salt of chitosan (HACC), the mass ratio of poly(succinimide) to quaternary ammonium salt of chitosan is 12:3, 3 g of ethylene glycol diglycidyl ether (EGDE), and mechanically stir to mix them evenly, then add urea to the solution and mix it evenly, where the mass fraction of urea in this system is 15%; Subsequently, place the solution in a magnetic stirrer and carry out water bath heating (800 rpm, 50 °C) for 6 h, pour the mixed solution into a mold, and name the obtained hydrogel PH x -Urea y (where x represents the ratio of PSI to HACC, and y represents the loaded urea concentration), and the hydrogel obtained in this embodiment is named PH 12:3 -Urea 15% .

[0033] Example 2 Same as Example 1, the difference is that the mass fraction of urea in this system is 10%, and the obtained hydrogel is named PH 12:3 -Urea 10% .

[0034] Example 3 Same as Example 1, except that the mass fraction of urea in this system is 5%, and the obtained hydrogel is named PH 12:3 -Urea 5% 。

[0035] Comparative Example 1 Same as Example 1, except that 1.5 g of quaternary ammonium chitosan salt (HACC) was not added, and the obtained product is named PASP-Urea 15% 。

[0036] Comparative Example 2 Same as Comparative Example 1, except that the mass fraction of urea in this system is 10%, and the obtained product is named PASP-Urea 10% 。

[0037] Comparative Example 3 Same as Comparative Example 1, except that the mass fraction of urea in this system is 5%, and the obtained product is named PASP-Urea 5% 。

[0038] Comparative Example 4 Same as Example 1, except that 1.5 g of quaternary ammonium chitosan salt (HACC) was not added and the mass fraction of urea in this system is 0%, and the obtained product is named PASP.

[0039] Comparative Example 5 Same as Example 1, except that 0.5 g of quaternary ammonium chitosan salt (HACC) was added and the mass fraction of urea in this system is 0%, and the obtained product is named PH 12:1 。

[0040] Comparative Example 6 Same as Example 1, except that 1 g of quaternary ammonium chitosan salt (HACC) was added and the mass fraction of urea in this system is 0%, and the obtained product is named PH 12:2 。

[0041] Comparative Example 7 Same as Example 1, except that 1.5 g of quaternary ammonium chitosan salt (HACC) was added and the mass fraction of urea in this system is 0%, and the obtained product is named PH 12:3 。

[0042] Test Example 1 Performance test of urea-loaded semi-interpenetrating network hydrogel (1) Mechanical property analysis of urea-loaded semi-interpenetrating network hydrogel The pH values ​​obtained in Examples 1 to 3 were analyzed in the compression mode of the texture analyzer. 12:3 The compression properties of PASP-Urea hydrogels loaded with different concentrations of urea and the PASP-Urea hydrogels obtained in Comparative Examples 1 to 3 were tested. The probe used was P36R, and the test rate was 1 mm / s, and the compression stress-strain curve was obtained. All samples were measured three times in parallel at 25 °C. During the compression cycle test, the compression strain was fixed at 70%, and the other test conditions remained unchanged.

[0043] The results are as follows Figures 1 - 2 As shown. Figure 1 It can be seen that with the increase of urea loading concentration, the mechanical properties of PASP gel and PH gel decreased to a certain extent. It is speculated that the addition of urea may destroy the physical cross-linking between gels to a certain extent, resulting in the decrease of their mechanical properties. Figure 2 It can be seen that under a fixed strain of 90%, the PH gel still maintains a relatively high compression modulus and dissipated energy, indicating that the PH gel still has excellent strength and toughness.

[0044] (2) Rheological properties analysis of urea-loaded semi-IPN hydrogels At room temperature, the gel was subjected to rheological tests using a rotational rheometer. The linear viscoelastic region (1%) of the sample was determined by strain scanning of the hydrogels obtained in Examples 1 to 3 and Comparative Examples 1 to 3, and then a dynamic scanning test was performed under the shear strain, with the test frequency range being 6-55 rad / s. The results are shown in FIG. Figure 3 shown.

[0045] The rheological properties of gels are measured to analyze the microstructure and internal interactions of the gel. The storage modulus (G') value indicates the solid or elastic behavior of the test material, while the loss modulus (G'') reflects the fluid or viscous properties of the material. Figure 3 The storage modulus (G′) and loss modulus (G′′) of different gel samples change with angular frequency (ω), and G′ and G′′ of all gel samples increase with the increase of ω. At the test frequency, no crossover point was observed between the storage modulus and the loss modulus, indicating that the tested hydrogel has an entangled fiber network. As the Urea loading increases, the storage modulus of the gel gradually decreases, indicating that Urea may weaken the hydrogen bonds and electrostatic interactions of the gel.

[0046] (3) Fourier transform infrared analysis of urea-loaded semi-IPN hydrogel The freeze-dried samples of the hydrogels obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were respectively ground and pressed with KBr at a ratio of 100:1, and then measured with an infrared spectrometer (Nicolet IS5, Thermo Scientific, Germany). The scanning range was 4000-500 cm -1 , and the results are as Figure 4 shown.

[0047] It can be seen from Figure 4 that only in the case of pure Urea and Urea encapsulated in the gel, the characteristic spectral bands of amide carbonyl bonds at 1623 and 1679 cm -1 and the C─N stretching frequency spectral bands at 1420-1467 cm -1 can be observed. These results clearly indicate that urea was successfully loaded into the hydrogel. It can be seen that with the increase in the concentration of loaded Urea, the O-H stretching peak has a significant red shift, indicating that the group is unstable, further indicating that the loaded Urea will weaken the network strength of the gel.

[0048] (4) Test on the biodegradability of the hydrogel To explore the biodegradability of the hydrogel, the biodegradation rate of the PASP obtained in Comparative Example 4 and the P-H hydrogels obtained in Comparative Examples 5-7 over time was determined by evaluating the chemical oxygen demand (COD) in the culture medium. The results are shown in Figure 8 .

[0049] As Figure 8 shown, on the 30th day, the biodegradation rate of PASP was 91%, while that of the PH gel was 64-79%. The biodegradation behavior of the PH hydrogel was lower than that of PASP. This is mainly due to the presence of the network crosslinked by HACC and PASP, which hinders further biodegradation. However, according to the Convention for the Protection of the Marine Environment of the North-East Atlantic, if the biodegradation rate of a polymer is greater than 60% within 28 days, the polymer is considered to be easily biodegradable. From the experiment, the present invention provides a biodegradable PH gel, and the relatively low degradation rate of the P-H 12:3 gel can correspondingly extend the service life of the prepared composite and better play its role. After loading urea, it can still maintain good biodegradability.

[0050] (5) Explore the influence of the mass ratio of poly(succinimide) and quaternary ammonium chitosan on the mechanical properties of the gel The compression properties of the PH hydrogels with different HACC ratios obtained in Comparative Examples 4 to 7 were tested in the compression mode of a texture analyzer. The probe used was P36R, the test rate was 1 mm / s, and the compression strain was fixed at 90%. All samples were measured in parallel three times at 25 °C.

[0051] The results are shown separately in Figure 9 (A), Figure 9 (B), and Figure 9 (C).

[0052] As Figure 9 (A) shows, under 90% strain conditions, the PASP gel could not withstand a large load and completely broke, suffering irreversible damage. As the proportion of HACC increased, the toughness and mechanical strength of the gel were significantly enhanced. However, when the ratio of PASP to HACC was less than 12:3, under the same strain conditions, the P-H 12:1 gel produced a large deformation and rupture, and there were tiny ruptures on the surface of the P-H 12:2 gel. While the morphology of the P-H 12:3 gel remained intact, only experiencing slight deformation.

[0053] As Figure 9 (B) shows, under 90% strain conditions, the compressive stress of the P-H 12:3 gel reached 55.6 kPa, which was 13.9 times the compressive stress of the PASP hydrogel. From the results, the addition of HACC helped to increase the compressive stress of the hydrogel.

[0054] As Figure 9 (C) shows, the compressive performance of the hydrogel increased significantly with the increase in HACC concentration. However, a relatively low proportion of HACC had a relatively limited improvement on the mechanical properties of the gel. We found that the PH 12:3 gel exhibited the best mechanical properties under 90% strain.

[0055] Test Example 1 (1) Analysis of slow-release urea in soil with urea-loaded semi-interpenetrating network hydrogels To analyze the slow-release process of Urea in soil, this process was simulated through soil columns. By adding approximately 35 cm of dry soil separately added with the hydrogels obtained in Examples 1 - 3 and Comparative Examples 1 - 3 to a glass tube (diameter 5 cm, height 50 cm) to construct simulated soil columns, and the glass tube was pre-filled with appropriate cotton at the bottom. After continuously flushing the soil with tap water and deionized water to remove soluble substances in the soil sample, the established activated soil columns were dried at 50 °C for subsequent slow-release utilization. The results are as Figure 5 shown.

[0056] It can be seen that pure Urea is basically completely released in about 12 days, while the release rates of the gels loaded with PASP and PH12:3 Urea are 86 - 92% and 58 - 65% respectively in 30 days. The PH gel exhibits the highest slow-release performance, greatly improving the utilization rate of Urea.

[0057] (2) Pot experiments of urea-loaded semi-interpenetrating network hydrogels To cultivate chickpea plants, different growth media were developed by mixing the prepared hydrogels with the collected soil separately. 50 g of the soil added with the hydrogels obtained from Example 1, Comparative Example 1, Comparative Example 4, and Comparative Example 7 respectively and another 50 g of the soil without hydrogel were placed in paper cups, and 30 mL of water was mixed in each cup. After specific time intervals, the growth rate of the plants was measured. The purpose of this study was to evaluate the plants germinated from seeds, their bud lengths, and growth heights and other indicators under the research conditions. The results are as Figure 6 shown.

[0058] It can be Figure 6 seen that the plant growth height is greatly affected by the soil. Comparing the plant growth heights on the PASP soil and the PH 12:3 soil, there are differences of first fast and then slow, which may be due to the better water retention performance of the PASP gel in the early stage, and the gel degradation in the later stage, resulting in the loss of its effectiveness. And the seedling height of the PH 12:3 soil modified by loading 15% Urea is significantly higher than that of other gels.

[0059] And from Figure 7 the leaf size, leaf number, and root length, it can be seen that PH 12:3 -Urea 15% has a better promoting effect on plant growth.

[0060] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a urea-loaded polymer hydrogel, characterized in that: The method is prepared by the following steps: Add polysuccinimide to a sodium hydroxide solution, mix, adjust the pH value, add chitosan quaternary ammonium salt and ethylene glycol diglycidyl ether, mix, add urea, stir and heat to obtain a urea-loaded polymer hydrogel.

2. The preparation method according to claim 1, characterized in that: The relative molecular weight of the polysuccinimide is 1×10 5 ~1.5×10 5 Dalton.

3. The preparation method according to claim 1, characterized in that: The dosage ratio of polysuccinimide and sodium hydroxide solution is 5~7 g: 30~40 mL; Preferably, the concentration of the sodium hydroxide solution is 1-3 mol / L.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the polysuccinimide to the quaternary ammonium salt chitosan is 12:3-4.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the polysuccinimide to ethylene glycol diglycidyl ether is 2:

1.

6. The preparation method according to claim 1, characterized in that: The pH value is 4-5; preferably, the pH value is 4.

8.

7. The preparation method according to claim 1, characterized in that: The stirring and heating is specifically placed in a magnetic stirrer for water bath heating; Preferably, the water bath is heated to a temperature of 45-55°C.

8. The urea-loaded polymer hydrogel prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the urea-loaded polymer hydrogel according to claim 8 in agricultural fertilizer loading and slow release.

10. The use according to claim 9, characterized in that: The application is the application of urea-loaded polymer hydrogel in urea loading and sustained release.

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