A composite polyamino acid type water-absorbing resin for agriculture and forestry, and its preparation method and application

Abstract

The present invention relates to the technical field of water-retaining agent preparation, specifically disclosing a composite polyamino acid-based water-absorbing resin for agriculture and forestry, its preparation method, and application. The composite polyamino acid-based water-absorbing resin is obtained by cross-linking polyglutamic acid, polyaspartic acid, acrylic acid, a crosslinking agent, and an initiator; the crosslinking agent is diazomethylenebisacrylamide; the polyglutamic acid is polyglutamic acid A, polyglutamic acid B, or agricultural polyglutamic acid; polyglutamic acid A has a molecular weight of 700,000 to 1,100,000 Daltons; polyglutamic acid B has a molecular weight of 50,000 to 100,000 Daltons; agricultural polyglutamic acid has a molecular weight of 600,000 to 700,000 Daltons and a purity of 35% ± 10%; polyaspartic acid has a molecular weight of 10,000 or 15,000 Daltons; and the volume-to-mass ratio of acrylic acid to crosslinking agent is 0.00125 g to 0.00175 g per mL. The water-absorbing resin of the present invention has strong durability, high liquid absorption rate, is reusable, can reduce raw material costs, and improves product performance.

Description

Technical Field

[0001] The invention belongs to the technical field of water-retaining agent preparation, and particularly relates to a composite polyamino acid type water-absorbing resin for agriculture and forestry, and a preparation method and application thereof. Background Art

[0002] Polyglutamic acid and polyaspartic acid are important polymers that can be degraded by environmental microorganisms. They have attracted widespread attention due to their unique biocompatibility, degradability, and excellent water absorption properties. Polyglutamic acid is a polypeptide formed by the polymerization of glutamic acid monomers. Its molecular structure contains a large number of carboxyl groups, which can form a three-dimensional network structure, showing excellent water absorption and biodegradability. Polyaspartic acid is also a biopolymer material with many excellent properties. It is formed by the polymerization of amino and carboxyl groups of aspartic acid, forming a hydrophilic three-dimensional network structure that can absorb and retain large amounts of water, with remarkable water absorption and retention capacity. Polyaspartic acid also has good biodegradability, and its degradation products are environmentally friendly and reusable.

[0003] Currently, polyglutamic acid can be produced by microbial fermentation technology, and the polyglutamic acid produced has a higher molecular weight and excellent polymerization properties, but its fermentation process is complicated and the production cost is high. Polyaspartic acid can currently be prepared on a large scale by chemical synthesis methods, which has lower production cost and a simple preparation method, but its molecular weight is relatively low. In the prior art, various studies have focused on the preparation of these two polymers and their water-absorbing resins, providing a rich technical foundation for the development of novel polymerized amino acid water-absorbing resins.

[0004] For example, Chinese patent CN116199912A proposes a method for preparing a γ-polyglutamic acid superabsorbent resin. By mixing and crosslinking it with nisin, it forms a gel-like product with excellent water absorption and biodegradability. Chinese patent CN102002234A utilizes a γ-polyglutamic acid fermentation broth produced by Bacillus subtilis to prepare a water-retaining agent suitable for agriculture and forestry. Furthermore, Chinese patent CN111068099A proposes a method for preparing a polyaspartic acid-based water-retaining agent by crosslinking it with inorganic mineral materials, resulting in a simple production process and low cost. Wang Chuanhai et al. (Preliminary Study on the Water Absorption and Biological Effects of γ-Polyglutamic Acid, a New Water-Retaining Agent Material [J]. Chinese Journal of Agricultural Meteorology, 2004, 5) studied the water absorption and biological effects of γ-polyglutamic acid (γ-PGA), demonstrating its high water retention capacity and ideal release in soil, as well as its significant drought resistance and seedling-promoting effects. Chinese patent CN112209781A relates to the use of a polyaspartic acid-based water-retaining agent in organic-inorganic compound fertilizers, suitable for agricultural cultivation in arid regions. These studies provide a technical foundation for the development of novel polymerized amino acid-based water-absorbing resins. However, these methods primarily utilize a single polymer, lacking methods for combining polyglutamic acid and polyaspartic acid.

[0005] Chinese patent CN110564146A discloses a preparation method of a chelate resin based on gamma-polyglutamic acid and polyaspartic acid. The method comprises the following steps: using gamma-polyglutamic acid, polyaspartic acid and an epoxy resin cross-linking agent as raw materials, adjusting the pH value of the system by hydrochloric acid, and reacting the raw materials to form a chelate resin without further chemical modification. The obtained chelate resin has a high water absorption rate and a fast swelling rate. However, the main components adopted in the patent are gamma-polyglutamic acid and polyaspartic acid, and microorganisms that degrade these two substances are present in soil. The water-absorbing resin based on these two substances has a relatively fast degradation rate in soil, is difficult to maintain water retention for a long time in soil, and has a relatively low water-absorbing resin strength. The water-absorbing resin in the patent has a washing liquid expansion rate of only about 150 g to 200 g, and its liquid absorption expansion rate is relatively low.

[0006] Therefore, the existing technology has not yet fully integrated and developed the cost and performance advantages of polyglutamic acid and polyaspartic acid. Therefore, developing a more efficient, low-cost and comprehensive performance polymerized amino acid water-absorbing resin preparation method has certain research value and practical significance. Summary of the Invention

[0007] In response to the problems existing in the prior art, the present invention provides a composite polyamino acid type water-absorbing resin for agriculture and forestry, and a preparation method and application thereof. The preparation method effectively reduces the performance degradation caused by repeated use through a cross-linking reaction of polyglutamic acid, polyaspartic acid and acrylic acid, is more efficient and reduces costs.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] On the one hand, the present invention provides a method for preparing a composite polyamino acid type water-absorbing resin for agriculture and forestry, wherein the composite polyamino acid type water-absorbing resin for agriculture and forestry is prepared by cross-linking polyglutamic acid, polyaspartic acid, acrylic acid, a cross-linking agent and an initiator;

[0010] The cross-linking agent is selected from at least one of diazomethylenebisacrylamide, polyethylene glycol diacrylate and ethylene glycol dimethacrylate;

[0011] The polyglutamic acid is any one of polyglutamic acid A, polyglutamic acid B and agricultural polyglutamic acid; the molecular weight of the polyglutamic acid A is 700,000-1.1 million Daltons, and the purity is 90%-100%; the molecular weight of the polyglutamic acid B is 50,000-100,000 Daltons, and the purity is 90%-100%; the molecular weight of the agricultural polyglutamic acid is 600,000-700,000 Daltons, and the purity is 35%±10%; the molecular weight of the polyaspartic acid is 10,000 Daltons or 15,000 Daltons; the volume mass ratio of the acrylic acid to the cross-linking agent is 1 mL: 0.00125 g-0.00175 g.

[0012] Preferably, the cross-linking agent is diazomethylenebisacrylamide, and the volume mass ratio of the acrylic acid to the cross-linking agent is 1 mL: 0.0015 g-0.00175 g.

[0013] Preferably, the initiator is selected from at least one of potassium persulfate, sodium persulfate and ammonium persulfate.

[0014] More preferably, the initiator is potassium persulfate.

[0015] Polyglutamic acid with a molecular weight of 700,000-1.1 million Daltons and polyglutamic acid with a molecular weight of 50,000-100,000 Daltons are subcategories of polyglutamic acid, specifically referring to polyglutamic acid produced by microbial fermentation and obtained through refined extraction with a purity generally above 90%. The molecular weight is strictly controlled in the range of 700,000 to 1.1 million Daltons or 50,000 to 100,000 Daltons. Agricultural polyglutamic acid is a type of polyglutamic acid produced by microbial fermentation and obtained through crude extraction with a purity of about 35%±10%. The other components are microbial residual products in the fermentation process, and their molecular weight is usually between 600,000 and 700,000 Daltons.

[0016] Preferably, the mass ratio of the polyglutamic acid to the polyaspartic acid is 1:2-2:1.

[0017] Further preferably, the mass ratio of the polyglutamic acid to the polyaspartic acid is 1:2.

[0018] Preferably, the neutralization degree of the acrylic acid is 70%-90%.

[0019] More preferably, the neutralization degree of the acrylic acid is 80%.

[0020] Preferably, the mass ratio of the cross-linking agent to the initiator is 2.5-3.5:19-25.

[0021] Further preferably, the mass ratio of the cross-linking agent to the initiator is 1:7.

[0022] Preferably, the preparation method comprises: dissolving polyglutamic acid and polyaspartic acid in water and mixing them uniformly to obtain a mixed solution A; mixing acrylic acid with a NaOH solution to obtain a mixed solution B; and adding a crosslinking agent and an initiator to the mixed solutions A and B to obtain the composite polyamino acid type water-absorbing resin.

[0023] Preferably, the concentration of the NaOH solution is 4-6 mol / L.

[0024] Further preferably, the concentration of the NaOH solution is 5 mol / L.

[0025] The present invention also provides a composite polyamino acid type water-absorbing resin prepared by the above preparation method.

[0026] On the other hand, the present invention provides a use of the composite polyamino acid type water-absorbing resin in the preparation of an agricultural or forestry soil water-retaining agent.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention uses polyglutamic acid, polyaspartic acid and acrylic acid to carry out a cross-linking reaction, thereby enhancing the strength of the water-absorbing resin and slowing down the degradation rate of the water-absorbing resin in the soil, thereby extending the service life of the water-absorbing resin. The obtained composite polyamino acid water-absorbing resin not only reduces the cost of raw materials but also improves the performance of the product.

[0029] During the preparation of the composite water-absorbent resin of the present invention, the mixed molecular structure can form a relatively stable cross-linked network structure. This structure exhibits excellent stability during multiple water absorption and dehydration cycles, effectively reducing performance degradation caused by repeated use. Therefore, the composite water-absorbent resin of the present invention has good durability and can be reused multiple times, thereby reducing usage costs and improving economic benefits.

[0030] The polyamino acid-based water-absorbing resin of the present invention exhibits excellent biodegradability, avoiding the environmental pollution issues associated with traditional petroleum-based resins (such as polyacrylates). After use in soil, it naturally decomposes over a period of time, preventing soil contamination. Furthermore, the composite polyamino acid-based water-absorbing resin can be degraded into monomeric amino acids or nitrogen-containing organic matter, which can be absorbed and utilized by plants, meeting the requirements of green agriculture and sustainable development. These environmentally friendly properties give it broad application prospects in ecological restoration and soil improvement.

[0031] The polyamino acid-based water-absorbent resin of the present invention can significantly increase the liquid absorption expansion rate of the water-absorbent resin by compounding polyglutamic acid and polyaspartic acid with acrylic acid. It is expected to further optimize the performance of the water-absorbent resin on the basis of existing technology, meet the needs of different application scenarios, and provide new technical support for the development of related fields. DETAILED DESCRIPTION

[0032] The present invention is described below through specific embodiments to make the technical solution of the present invention easier to understand and grasp, but the present invention is not limited thereto. The described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0033] The endpoints and any value of the scope disclosed in this article are not limited to this accurate scope or value, and these scopes or values should be understood as comprising values close to these scopes or values.For numerical range, between the endpoint values of each scope, between the endpoint values of each scope and a separate point value, and between the separate point value, can be combined with each other and obtain one or more new numerical ranges, and these numerical ranges should be considered as specifically disclosed in this article. Unless the context clearly indicates otherwise, the singular form "one", "a kind of" and "described" as used herein include singular and plural indicators. The numerical range stated by endpoint is included in all numerical values and fractions within the corresponding range, and the stated endpoint.

[0034] Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without inventive effort shall fall within the scope of protection of the present invention. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0035] Source of experimental materials:

[0036] Acrylic acid was purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd., CAS No. 79-10-7;

[0037] Polyglutamic acid with a molecular weight of 700,000-1.1 million was purchased from Shandong Freda Biotechnology Co., Ltd. with production batch number 20240601 and a purity of 92.3%;

[0038] Polyglutamic acid with a molecular weight of 50,000 to 100,000 was purchased from Shandong Freda Biotechnology Co., Ltd. with production batch number 20240115 and a purity of 92.3%;

[0039] Agricultural polyglutamic acid was purchased from Shandong Freda Biotechnology Co., Ltd. with production batch number 20231210, purity of 35%, and molecular weight of 600,000-700,000 Daltons;

[0040] Polyaspartic acid with a molecular weight of 10,000: purchased from Hebei Xietong Chemical Co., Ltd., production batch number 20231222;

[0041] Polyaspartic acid with a molecular weight of 15,000: purchased from Hebei Xietong Chemical Co., Ltd., production batch number 20231009;

[0042] Diazomethylenebisacrylamide (MBA) was purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd. with a CAS number of 110-26-9; potassium persulfate was purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd. with a CAS number of 7727-21-1; and 1,4-butanediol diglycidyl ether with a CAS number of 2425-79-8.

[0043] Example 1

[0044] (1) Dissolve 1 g of polyglutamic acid with a molecular weight of 700,000 to 1.1 million and 2 g of polyaspartic acid with a molecular weight of 10,000 in 50 mL of aqueous solution and mix them evenly to obtain a mixed solution A.

[0045] (2) Place 20 mL of acrylic acid in a beaker, slowly add 42.04 mL of 5 mol / L NaOH solution, and place the beaker in an ice-water solution and stir rapidly to obtain solution B.

[0046] (3) Add solution A to solution B and stir evenly. Keep the temperature in a water bath at 80°C. Add 0.03 g of crosslinker (diazomethylenebisacrylamide (MBA)) and 0.21 g of initiator (potassium persulfate) to the mixed solution of A and B and stir quickly. After a period of time, the two will begin to crosslink and then form a stable gel-like substance. The obtained gel-like substance will continue to crosslink in a water bath for 3 hours to obtain the product, a composite polyamino acid type water-absorbing resin. The product is cut into 0.5 cm × 0.5 cm squares with scissors and placed in anhydrous ethanol for dehydration and removal of other unreacted substances. Then, it is placed in a drying oven for 48 hours at a temperature of 80°C and crushed into powder using a grinder.

[0047] Detection method: Weigh 1 g of the synthesized water-absorbing resin powder and place it in excess pure water or 0.9% sodium chloride solution (brine) to absorb liquid. After it is finally stabilized, weigh the mass of the water-absorbing resin, which is the liquid absorption rate of the water-absorbing resin in pure water or brine. After the water-absorbing resin absorbs water, dry it in a 60°C oven, absorb water again after drying, and then dry it. Repeat this six times, and the result is the liquid absorption rate after six repeated uses.

[0048] The absorbency of the composite polyamino acid-based water-absorbent resin of Example 1 and other composite polyamino acid-based water-absorbent resins in pure water and saline was tested using the aforementioned testing method, as well as the absorbency after six repeated cycles of pure water absorption. (The preparation methods of the other composite polyamino acid-based water-absorbent resins differed from those of Example 1 solely in the molecular weight of the polyglutamic acid or polyaspartic acid, as shown in Table 1.)

[0049] Table 1 Comparison of the performance of Example 1 and other composite polyamino acid water-absorbing resins

[0050]

[0051] Example 2

[0052] The only difference from Example 1 is that in step (1), the mass of polyglutamic acid is 2 g, and the mass of polyaspartic acid is 1 g. The other steps are the same as in Example 1.

[0053] The product was cut into 0.5 cm x 0.5 cm squares with scissors and placed in anhydrous ethanol to dehydrate and remove any unreacted substances. It was then dried in a drying oven at 80°C for 48 hours and pulverized into powder using a grinder. The absorbency of the composite polyamino acid-based water-absorbent resin of Example 2 and other composite polyamino acid-based water-absorbent resins was tested in pure water and saline using the testing method described in Example 1, as well as the absorbency of six repeated cycles of pure water absorption. (The preparation methods of the other composite polyamino acid-based water-absorbent resins differed only in the molecular weight of the polyglutamic acid or polyaspartic acid used in the composite polyamino acid-based water-absorbent resin of Example 2, as shown in Table 2.)

[0054] Table 2 Comparison of performance of Example 2 and other composite polyamino acid water-absorbing resins

[0055]

[0056] Example 3

[0057] The only difference from Example 1 is that in step (1), the mass of polyglutamic acid is 0.5 g, and the mass of polyaspartic acid is 0.5 g; in step (3), the mass of the cross-linking agent is 0.025 g, and the mass of the initiator is 0.19 g. The other steps are the same as in Example 1.

[0058] The product was cut into 0.5 cm x 0.5 cm squares with scissors and placed in anhydrous ethanol to dehydrate and remove any unreacted substances. It was then dried in a drying oven at 80°C for 48 hours and pulverized into powder using a grinder. The absorbency of the composite polyamino acid-based water-absorbent resin of Example 3 and other composite polyamino acid-based water-absorbent resins was tested in pure water and saline using the testing method described in Example 1, as well as the absorbency of six repeated cycles of pure water absorption. (The preparation methods of the other composite polyamino acid-based water-absorbent resins differed only in the molecular weight of the polyglutamic acid or polyaspartic acid used in the composite polyamino acid-based water-absorbent resin of Example 3, as shown in Table 3.)

[0059] Table 3 Comparison of performance of Example 3 and other composite polyamino acid water-absorbing resins

[0060]

[0061] Example 4

[0062] The only difference from Example 1 is that in step (1), the mass of polyglutamic acid is 2 g, and the mass of polyaspartic acid is 3 g; in step (3), the mass of the cross-linking agent is 0.035 g, and the mass of the initiator is 0.25 g. The other steps are the same as in Example 1.

[0063] The product was cut into 0.5 cm x 0.5 cm squares with scissors and placed in anhydrous ethanol to dehydrate and remove any unreacted substances. It was then dried in a drying oven at 80°C for 48 hours and pulverized into powder using a grinder. The absorbency of the composite polyamino acid-based water-absorbent resin of Example 4 and other composite polyamino acid-based water-absorbent resins in pure water and saline, as well as the absorbency of six repeated cycles of pure water absorption, was tested using the testing method described in Example 1. (The preparation methods of the other composite polyamino acid-based water-absorbent resins differed only in the molecular weight of the polyglutamic acid or polyaspartic acid used in the composite polyamino acid-based water-absorbent resin of Example 4, as shown in Table 4.)

[0064] Table 4 Comparison of performance of Example 4 and other composite polyamino acid water-absorbing resins

[0065]

[0066] Example 5

[0067] The only difference from Example 1 is that in step (1), the mass of polyglutamic acid is 3 g, and the mass of polyaspartic acid is 2 g; in step (3), the mass of the cross-linking agent is 0.035 g, and the mass of the initiator is 0.25 g. The other steps are the same as in Example 1.

[0068] The product was cut into 0.5 cm x 0.5 cm squares with scissors and placed in anhydrous ethanol to dehydrate and remove any unreacted substances. It was then dried in a drying oven at 80°C for 48 hours and pulverized into powder using a grinder. The absorbency of the composite polyamino acid-based water-absorbent resin of Example 5 and other composite polyamino acid-based water-absorbent resins in pure water and saline, as well as the absorbency of six repeated cycles of pure water absorption, was tested using the testing method described in Example 1. (The preparation methods of the other composite polyamino acid-based water-absorbent resins differed only in the molecular weight of the polyglutamic acid or polyaspartic acid used in the composite polyamino acid-based water-absorbent resin of Example 5, as shown in Table 5.)

[0069] Table 5 Performance comparison of Example 5 and other composite polyamino acid water-absorbing resins

[0070]

[0071] Comparative Example 1

[0072] (1) Dissolve 1 g of polyglutamic acid with a molecular weight of 700,000 to 1.1 million and 2 g of polyaspartic acid with a molecular weight of 10,000 in 50 mL of aqueous solution and mix them evenly to obtain a mixed solution;

[0073] (2) The mixed solution A was kept at 80 °C in a water bath, 0.9 g of a cross-linking agent (ethylene glycol diglycidyl ether) was added to the mixed solution A and stirred rapidly. After a period of time, the two began to cross-link and then formed a stable gel-like substance. The obtained gel-like substance continued to cross-link in a water bath for 3 h to obtain the product, a composite polyamino acid type water-absorbing resin.

[0074] The product was cut into 0.5 cm x 0.5 cm squares with scissors and placed in anhydrous ethanol for dehydration and removal of unreacted substances. It was then dried in a drying oven at 80°C for 48 hours and pulverized into powder using a grinder. The absorbency of the composite polyamino acid-based water-absorbent resin of Comparative Example 1 and other composite polyamino acid-based water-absorbent resins in pure water and saline was tested using the testing method described in Example 1, as well as the absorbency of six repeated cycles of pure water absorption. (The preparation methods of the other composite polyamino acid-based water-absorbent resins differed only in the molecular weight of the polyglutamic acid or polyaspartic acid used in the composite polyamino acid-based water-absorbent resin of Comparative Example 1, as shown in Table 6.)

[0075] Table 6 Comparative Example 1 and other composite polyamino acid water-absorbing resin performance comparison

[0076]

[0077] Table 6 shows that the composite polyamino acid-based water-absorbing resin in Comparative Example 1 no longer possessed the ability to absorb water repeatedly after six reuses. Furthermore, during the preparation process using agricultural polyglutamic acid, it failed to effectively crosslink with the crosslinking agent, failing to form a gel-like water-absorbing resin and making subsequent liquid absorption rate testing impossible.

[0078] Comparative Example 2

[0079] Compared with Example 1, the only difference is that the cross-linking agent in step (3) is 1,4-butanediol diglycidyl ether, and the other steps are the same as Example 1.

[0080] The absorption rates of the composite polyamino acid-based water-absorbent resin of Comparative Example 2 and other composite polyamino acid-based water-absorbent resins in pure water and saline, as well as the absorption rates after six repeated cycles of pure water absorption, were tested using the testing method of Example 1. (The preparation methods of the other composite polyamino acid-based water-absorbent resins differed only in the molecular weight of the polyglutamic acid or polyaspartic acid used in the composite polyamino acid-based water-absorbent resin of Comparative Example 2, as shown in Table 7.)

[0081] Table 7 Comparative Example 2 and other composite polyamino acid water-absorbing resin performance comparison

[0082]

[0083] Table 7 shows that the composite polyamino acid-based water-absorbing resin in Comparative Example 2 exhibited a low liquid absorption rate and similarly low water absorption performance after six reuses. Furthermore, the water-absorbing resin prepared using agricultural polyglutamic acid exhibited a disintegrated structure after six reuses, resulting in a loss of liquid absorption capacity.

[0084] Comparative Example 3

[0085] Compared with Example 1, the only difference is that the content of the cross-linking agent in step (3) is 0.05 g, and the other steps are the same as those in Example 1.

[0086] The composite polyamino acid-based water-absorbent resin of Comparative Example 3 and other composite polyamino acid-based water-absorbent resins were tested for their absorbency in pure water and saline, as well as their absorbency after six repeated cycles of pure water absorption using the same method as in Example 1. (The preparation methods of the other composite polyamino acid-based water-absorbent resins differed only in the molecular weight of the polyglutamic acid or polyaspartic acid used in the composite polyamino acid-based water-absorbent resin of Comparative Example 3, as shown in Table 8.)

[0087] Table 8 Comparative Example 3 and other composite polyamino acid type water-absorbing resin performance comparison table

[0088]

[0089] Table 8 shows that the composite polyamino acid-based water-absorbent resin in Comparative Example 3 exhibited a low liquid absorption rate and similarly low water absorption performance after six repeated uses. This is primarily due to excessive crosslinking of the water-absorbent resin when the crosslinking agent content was too high, resulting in a smaller mesh size and a lower liquid absorption rate.

[0090] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a composite polyamino acid water-absorbing resin for agriculture and forestry, characterized in that: A composite polyamino acid water-absorbing resin for agriculture and forestry is prepared by cross-linking polyglutamic acid, polyaspartic acid, acrylic acid, a cross-linking agent and an initiator; The cross-linking agent is selected from at least one of diazomethylenebisacrylamide, polyethylene glycol diacrylate and ethylene glycol dimethacrylate; the polyglutamic acid is any one of polyglutamic acid A, polyglutamic acid B and agricultural polyglutamic acid; the molecular weight of the polyglutamic acid A is 700,000-1.1 million Daltons and the purity is 90%-100%; the molecular weight of the polyglutamic acid B is 50,000-100,000 Daltons and the purity is 90%-100%; the molecular weight of the agricultural polyglutamic acid is 600,000-700,000 Daltons and the purity is 35%±10%; the molecular weight of the polyaspartic acid is 10,000 Daltons or 15,000 Daltons; the volume mass ratio of the acrylic acid to the cross-linking agent is 1 mL: 0.00125 g-0.00175 g.

2. The preparation method according to claim 1, wherein: The mass ratio of the polyglutamic acid to the polyaspartic acid is 1:2-2:

1.

3. The preparation method according to claim 2, wherein: The mass ratio of the polyglutamic acid to the polyaspartic acid is 1:

2.

4. The preparation method according to claim 1, wherein: The neutralization degree of the acrylic acid is 70%-90%.

5. The preparation method according to claim 1, wherein: The initiator is selected from at least one of potassium persulfate, sodium persulfate and ammonium persulfate; and the cross-linking agent is diazomethylenebisacrylamide.

6. The preparation method according to claim 5, characterized in that: The initiator is potassium persulfate.

7. A composite polyamino acid type water-absorbing resin prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the composite polyamino acid water-absorbing resin according to claim 7 in the preparation of an agricultural or forestry soil water-retaining agent.

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