A preparation method and application of degradable hydrogel for water retention

Abstract

The present invention discloses a preparation method and application of a degradable hydrogel for water retention. The present invention provides a degradable hydrogel for water retention, wherein the main effective ingredients are agricultural and sideline products containing cellulose and protein, and the cross-linking agent uses a small molecule amino acid with a molecular weight below 200, and the prepared hydrogel has a significant water retention effect and a high degradability rate. The raw material components used in the present invention are all pure natural, easy-to-obtain, environmentally friendly and safe substances with low cost. Compared with hydrogels prepared using chemical raw materials, they are safer, easier to degrade than polyamide water retaining agents, less polluting to the environment, and less toxic to crops. At the same time, the hydrogel preparation method provided by the present invention is simple and convenient, and the grafted hydrogel has a high swelling degree, can be used to improve the water retention capacity of the soil, and can also be used as compost for plant growth, providing a research idea and basis for preparing more water-retaining and degradable hydrogels with excellent performance and low cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and more specifically, relates to a preparation method of a degradable hydrogel for water retention and its application. Background Art

[0002] Hydrogel is a type of extremely hydrophilic three-dimensional network structure gel. It swells rapidly in water and can hold a large volume of water without dissolving in this swollen state. It is generally formed by water-soluble or hydrophilic polymers through certain chemical crosslinking or physical crosslinking. It has high hydrophilicity and strong water absorption capacity. It is often used to prepare wetting agents, hygroscopic agents and other products. The water absorption and water retention capacity of hydrogel depends on its internal structure. When water molecules contact the surface of the hydrogel, they will penetrate into the hydrogel due to surface tension and fill in the gaps. Due to the crosslinked structure of the polymer, the water molecules are bound inside the hydrogel and will not be lost, and the water content is kept stable. The water absorption of the hydrogel is related to its crosslinking degree, pore structure and the size of the water molecules. Generally speaking, hydrogels with a higher degree of crosslinking have better water absorption properties.

[0003] Hydrogels have important applications in agriculture and horticulture. By adding hydrogels to the soil, the soil's water retention capacity can be increased, and the growth rate and survival rate of plants can be improved. Hydrogels can absorb and store large amounts of water, and slowly release it to plants, ensuring that plants can still get enough water in drought or water shortage conditions. There are many types of water-retaining agents prepared using the water-retaining properties of hydrogels. Currently, there are two main types of water-retaining agents that are mass-produced: polyacrylamide type and starch grafted type. The disadvantages of these two water-retaining agents are that the cross-linking agents used may be connected to chemical products during the reaction process, and they are difficult to degrade after being used in the soil, which may affect the growth of plants and the physical and chemical properties of the soil. In addition, the reactions are cumbersome and the cost is high.

[0004] Existing research has used natural agricultural products containing cellulose to prepare hydrogels with good water retention. For example, the existing technology uses bagasse as raw material to extract cellulose and hemicellulose, and then oxidizes and modifies them. This preparation method is relatively cumbersome, and the agricultural products must be extracted and oxidized before modification and preparation can be carried out, and the reaction conditions are also relatively complex. There are also methods that use bean dregs, a by-product of the production of soy milk or tofu, as raw materials for preparation. There are a large number of insoluble cellulose and water-soluble soy protein in bean dregs, and the amino groups contained can form more amide bonds by chemical means, so that the water retention of the prepared water-retaining agent is guaranteed. Because the insoluble cellulose in bean dregs is difficult to gel under normal circumstances, chemical modification is now a conventional means to make cellulose a water-retaining hydrogel, but its degradation products have certain toxicity and affect the soil environment; what's more, the difficulty of preparing hydrogels from bean dregs is that when forming amide bonds through amino groups, the reaction conditions are very complicated, the added catalyst is easy to produce by-products, and it is difficult for conventional low-activity carboxyl substances and amino substances to react. It can be seen that the existing method of preparing hydrogels using agricultural and sideline products containing cellulose and protein is very limited. At present, only hydrogels prepared by oxidized holocellulose solution and bean dregs have soil water retention, can be completely degraded, and have no side effects on the soil, but their preparation methods are very cumbersome. At present, there is still a lack of green, safe, water-retaining and degradable hydrogels prepared with agricultural and sideline products containing cellulose and protein as the main ingredients as environmentally friendly water-retaining agents for use in soil; therefore, there is an urgent need to develop more low-cost, high-water-retaining, degradable and environmentally friendly hydrogel products to improve soil water retention capacity and be used for drought soil management. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the existing water-retaining gel used for soil, and to provide a preparation method of a water-retaining and degradable hydrogel and its application.

[0006] The object of the present invention is to provide a degradable hydrogel for water retention.

[0007] Another object of the present invention is to provide a use of the degradable hydrogel for water retention.

[0008] Another object of the present invention is to provide a method for preparing a degradable hydrogel for water retention.

[0009] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0010] The invention provides a degradable hydrogel for water retention, which is made of agricultural and sideline products containing cellulose and protein, small-molecule amino acids with a molecular weight below 200, and an initiator; the mass ratio of the agricultural and sideline products containing cellulose and protein, the small-molecule amino acids, and the initiator is (1-8): (1-6): (1-5).

[0011] The present invention uses agricultural and sideline products containing cellulose and protein as the main raw materials, uses small molecule amino acids as cross-linking agents, and reacts under the action of an initiator. The prepared hydrogel has a significant water retention effect and a high degradability rate. It is green and safe, does not harm plant growth, and has a significant effect in soil water retention. The raw material components for preparing the hydrogel provided by the present invention are all pure natural, easy-to-obtain, environmentally friendly and safe substances, with low cost. Compared with the hydrogel prepared from traditional chemical raw materials, it is safer, easier to degrade than traditional polyamide water retaining agents, less polluting to the environment, and less toxic to crops.

[0012] Furthermore, the agricultural and sideline products containing cellulose and protein have a cellulose content of more than 20% and a protein content of more than 10%, and are selected from one of bean dregs, wheat bran, corn dregs, rice bran or barley dregs.

[0013] In particular, the small molecule amino acid has a molecular weight below 200, is a basic unit constituting protein, and can be divided into α-amino acids on the main chain and β-amino acids on the side chain.

[0014] Preferably, the agricultural and sideline products containing cellulose and protein are bean dregs.

[0015] Furthermore, the small molecule amino acid contains no more than three carboxyl groups and no more than two amino groups.

[0016] More preferably, the small molecule amino acid contains two or less carboxyl groups and one amino group.

[0017] More preferably, the small molecule amino acid is D-glutamic acid or phenylalanine.

[0018] More preferably, the small molecule amino acid is D-glutamic acid.

[0019] Further, the initiator is selected from one of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, 1-hydroxybenzotriazole and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, or ammonium persulfate and N,N,N′,N′-tetramethyleneethylenediamine.

[0020] Preferably, the initiator is 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide. When used, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride is first added and blended, and then N-hydroxysuccinimide is added; the molar ratio of the crosslinking agent to 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide is 1:(0.1-2):(0.1-2).

[0021] In the present invention, the role of the initiator is to promote the reaction between the raw material agricultural and sideline products containing cellulose and protein and the cross-linking agent to form a network structure to prepare a hydrogel; and the initiator selects 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide for reaction, and the reaction condition system does not need to be heated, and can also better promote the reaction between the carboxyl group on the cross-linking agent and the amino group on the water-soluble protein of the agricultural and sideline products containing cellulose and protein, overcoming the problem that the conventional carboxyl substances and amino substances with low activity are difficult to react. Therefore, as long as the preparation that can induce the carboxyl group on the cross-linking agent to react with the amino group on the water-soluble protein of the agricultural and sideline products containing cellulose and protein is used, it can replace the initiator of the present invention, and the required reaction conditions can be adjusted according to the preparation replaced.

[0022] The invention provides application of a degradable hydrogel for water retention in preparing a product for improving the water retention capacity of soil.

[0023] The present invention provides an application of a degradable hydrogel for water retention in improving soil water retention capacity or in drought soil management. The hydrogel provided by the present invention can not only be used to improve soil water retention capacity and increase moisture, but also can be used as compost for plant growth and development, and can also be applied together with other fertilizers to increase soil performance and promote plant growth.

[0024] At the same time, the preparation method of the water-retaining degradable hydrogel provided by the present invention is simple and convenient, the reaction conditions are simple and mild, and the grafted hydrogel has a high swelling degree, which provides more technical means and methods for preparing the water-retaining degradable hydrogel.

[0025] The present invention provides a method for preparing a degradable hydrogel for water retention, comprising the following steps:

[0026] S1. Suspension A: The agricultural and sideline products containing cellulose and protein are mixed with deionized water, heated under nitrogen protection, ammonium persulfate is added for reaction, and then a small molecule amino acid solution is added and heated for reaction. After the reaction is completed, the precipitate is collected by centrifugation, and deionized water is added to obtain suspension A;

[0027] S2. The initiator is added to the suspension A, the mixture is stirred in an ice bath, the reaction is protected from light, and the dialyzed product is collected and recorded as the suspension B;

[0028] S3. The pH value of the suspension B is adjusted to 8-10, the mixture is stirred in an ice bath, the temperature is raised, the mixture is rapidly cooled, the mixture is incubated, and the mixture is freeze-dried to obtain a degradable hydrogel for water retention.

[0029] Furthermore, in step S1, 1-5 wt% ammonium persulfate and 1-10 wt% small molecule amino acid solution are used, and the heating reaction conditions are 60-80° C. for 0.1-5 h.

[0030] Preferably, 1 wt% ammonium persulfate and 2-7 wt% amino acid solution are used in step S1.

[0031] Furthermore, in step S1, the mixing stirring speed is 200-600 rpm / min, the temperature is 4-25°C, and the time is 1-4h; the stirring speed in step S2 is 200-300 rpm / min, and the time is 12-48h; and the stirring condition in step S3 is 100-200 rpm / min.

[0032] Preferably, in step S2, the ice bath condition is 0-10° C., and the reaction time is 0.5-4 h; the dialysis condition is 1000-4000 Kda, and the time is 8-72 h.

[0033] More preferably, the ice bath condition is 4° C., the reaction time is 1 h, stirring is performed at 300 rpm / min at room temperature in the dark for 18 h, and dialysis is performed at 3500 Kda for 72 h.

[0034] Preferably, in step S3, after the temperature is raised to 70-90°C, the holding time is 10-30 min, and the incubation conditions are 4-37°C.

[0035] More preferably, the pH value of suspension B is adjusted to 9 with NaOH solution, and then stirred at 100 rpm / min at 4°C, the temperature is raised and maintained for 15 minutes and then rapidly cooled, and the mixture is incubated at 4°C after being repeated 2-3 times.

[0036] Specifically, the present invention provides a more preferred preparation method: 5 g of dregs are mixed with 100 mL of deionized water and put into a 250 mL three-necked flask equipped with a mechanical stirrer and a nitrogen tube, and the three-necked flask is passed through nitrogen protection, and then heated to 80° C. under nitrogen protection for 15 minutes, and then 1 wt% ammonium persulfate is added. After reacting for 30 minutes, a 10 wt% D-glutamic acid solution (prepared by adding 2 g of D-glutamic acid to 20 mL of deionized water) is added, and then the reaction mixture is passed through nitrogen at 70° C. for 5 hours. After the reaction is completed, the mixture is centrifuged at 11000 rpm for 20 minutes, the precipitate is collected, and the mixture is centrifuged 3 times. After the centrifugation is completed, 20 mL of deionized water is added to prepare a suspension A.

[0037] The suspension A was stirred at 4°C and 500 rpm / min for 1 h, and then 1.7 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride as an initiator was added to the suspension A. After blending for 10 min, 1.9 g of N-hydroxysuccinimide was added. The mixture was stirred at 300 rpm / min at room temperature in a 4°C ice bath in the dark for 18 h, and then dialyzed at 3500 Kda for 72 h to obtain a suspension B.

[0038] Subsequently, NaOH solution was added to the suspension B to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, and quickly cooled after 15 minutes. After repeating 2-3 times, the mixture was incubated at 4°C. After the incubation was completed, it was freeze-dried to obtain a degradable hydrogel for water retention.

[0039] The present invention has the following beneficial effects:

[0040] The present invention provides a degradable hydrogel for water retention, wherein the main effective ingredients are agricultural and sideline products containing cellulose and protein, and the cross-linking agent uses a small molecule amino acid with a molecular weight of less than 200. The hydrogel prepared by the initiator reaction has a significant water retention effect and a high degradability rate, does not harm plant growth, and has a significant effect in soil water retention. The raw material components for preparing the hydrogel provided by the present invention are all pure natural, easy-to-obtain, environmentally friendly and safe substances, with low cost, higher safety than hydrogels prepared from traditional chemical raw materials, and easier to degrade than traditional polyamide water retainers, less pollution to the environment, and lower toxicity to crops.

[0041] At the same time, the preparation method of the water-retaining and degradable hydrogel provided by the present invention is simple and convenient, and can be prepared without heating. The insoluble cellulose in the raw material is reacted to obtain a hydrogel with good water-retaining performance, which overcomes the problem that conventional cellulose, carboxyl substances and amino substances with low activity are difficult to react; and the grafted hydrogel has a high swelling degree, which can not only be used to improve the water-retaining capacity of the soil and increase moisture, but also can be used for plant growth and development and used as compost, providing a research idea and basis for preparing more water-retaining and degradable hydrogels with excellent performance and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a graph showing the water retention performance test results of hydrogels with different raw material components.

[0043] Figure 2 The swelling performance test results of hydrogels in different experimental groups are shown in Figure 2.

[0044] Figure 3 The graph shows the water retention performance test results of hydrogels in different experimental groups.

[0045] Figure 4 The figure shows the toxicity test results of hydrogels in different experimental groups on plants.

[0046] Figure 5 This is a graph showing the degradation performance test results of hydrogels in different experimental groups. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0048] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0049] The bean dregs used in the following examples are byproducts produced in the process of producing tofu, soy milk or related soy products, and are dried to become dry bean dregs when used; the wheat bran, corn dregs, rice bran, barley dregs, etc. used are byproducts produced in agricultural production and need to be ground into powder for use. The agricultural and sideline products containing cellulose and protein used in the present invention have a cellulose content of more than 20% and a protein content of more than 10%.

[0050] Example 1

[0051] The present invention uses various agricultural and sideline products containing cellulose and protein: bean dregs, wheat bran, corn dregs, rice bran, barley dregs as raw materials, and a cross-linking agent uses a carboxyl-containing compound (containing at least one carboxyl group to ensure that the reaction can occur): D-glutamic acid, citric acid, phenylalanine, isophthalic acid, and the carboxyl group reacts with the cellulose and protein in the agricultural and sideline products containing cellulose and protein to prepare the hydrogel. The specific raw material ratios used are shown in Table 1 below, and the preparation method is as follows:

[0052] Preparation of suspension A: The agricultural and sideline products containing cellulose and protein are mixed with deionized water in a certain proportion and put into a three-necked flask equipped with a mechanical stirrer and a nitrogen tube, and then heated to 80° C. under nitrogen protection for 15 minutes, followed by adding 1wt% ammonium persulfate, reacting for 30 minutes, adding 10wt% carboxyl-containing compound solution (prepared by adding the carboxyl-containing compound to deionized water), and the reaction mixture is passed through nitrogen at 70° C. for 5 hours. After the reaction is completed, the mixture is centrifuged at 11000 rpm for 20 minutes, the precipitate is collected, and centrifuged 3 times. After the centrifugation is completed, 20 mL of deionized water is added to prepare suspension A.

[0053] The suspension A was stirred at 4°C and 500 rpm / min for 1 h, and then an appropriate amount of initiator 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride was added, and the mixture was mixed for 10 min. Then, N-hydroxysuccinimide was added, and the mixture was stirred at 300 rpm / min at room temperature for 18 h in a 4°C ice bath in the dark, and then dialyzed at 3500 Kda for 72 h to obtain a suspension B.

[0054] Subsequently, NaOH solution was added to suspension B to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, and rapidly cooled after 15 minutes. This was repeated 2-3 times and incubated at 4°C. After incubation, the mixture was freeze-dried to obtain the hydrogel.

[0055] Table 1 Ratio of different raw material components

[0056]

[0057]

[0058] When the above-mentioned agricultural and sideline products containing cellulose and protein are used with cross-linking agents for preparation, two reactions occur. The first is the reaction between the cross-linking agent and the cellulose in the natural crop by-products, and the second is the reaction between the cross-linking agent and the protein in the agricultural and sideline products (or the reaction with the amino group). The results of the univariate analysis of agricultural and sideline products in the early stage (using the same cross-linking agent) showed that raw materials such as bean dregs, wheat bran, corn dregs, rice bran, and barley dregs can react with cross-linking agents to prepare degradable hydrogels, and the water retention effects of different agricultural and sideline products are not significantly different; further, by comparing the water retention properties of hydrogels with different cross-linking agent components (the cross-linking agent of the bean dregs group uses D-glutamic acid, the other components are the same as Table 1, and the test method is the same as test experiment 2), the results are as follows Figure 1 As shown, the water retention properties of the hydrogels in each group are different, which can be analyzed from the reaction principle of the cross-linking agent: when D-glutamic acid is used as a carboxyl-containing compound, its two carboxyl groups participate in the reaction, and the prepared hydrogel has better water retention than other groups; when phenylalanine is used, one carboxyl group participates in the reaction, and the prepared hydrogel has poorer water retention than other groups (probably due to the lack of carboxyl groups, which cannot completely react with cellulose and protein of agricultural and sideline products); when citric acid is used, all three carboxyl groups participate in the reaction, but the prepared hydrogel has poorer water retention than the group containing two carboxyl groups; and when the cross-linking agent commonly used in industry is used, Isophthalic acid contains two carboxyl groups participating in the reaction, and its water retention performance is not much different from that of the citric acid group. However, since it is a chemical product, the degradation product of the prepared hydrogel has certain toxicity and is not conducive to use in the soil environment. In summary, the cross-linking agent uses a carboxyl-containing compound that contains at least one carboxyl group to ensure the reaction, but the more carboxyl groups in the cross-linking agent, the better. The reaction groups of the carboxyl groups and the raw materials need to be controlled within a specific ratio. Too many carboxyl groups will affect the water retention performance of the hydrogel and will also lead to excessive cross-linking, making the hydrogel too brittle as a whole, affecting the physical properties of the hydrogel. Therefore, the cross-linking agent selects a compound containing three or less carboxyl groups.

[0059] At the same time, when D-glutamic acid or phenylalanine is used as the cross-linking agent, the amino groups contained in it also participate in the reaction. The prepared hydrogel has better water retention performance than other components containing only carboxyl groups. Then, other different amino acids containing carboxyl groups and amino groups (such as tryptophan and lysine) are prepared and compared. The results show that the hydrogel prepared with other amino groups is not easy to degrade. The reason for this is that tryptophan also contains a side chain indole, which has a large molecular weight (greater than 200). The participation in the reaction will affect the preparation of the hydrogel and its water retention performance; lysine contains two amino groups participating in the reaction, and the degradation performance of the prepared hydrogel is worse than that of the D-glutamic acid group; and the D-glutamic acid and phenylalanine used are both small molecule amino groups. Acid (molecular weight below 200) has a small molecular weight and contains an amino group to participate in the reaction, and the degradation effect of the prepared hydrogel will be better; if other compounds with a structure similar to glutamic acid are used, the reaction may not proceed normally due to the stability of their structural properties (the more stable the carboxyl and amino substances are, the more difficult it is to react). Therefore, the cross-linking agent is a small molecule amino acid containing no more than three carboxyl groups and no more than two amino groups, which can be used for the preparation of the water-retaining and degradable hydrogel of the present invention; as the most preferred embodiment, the small molecule amino acid contains no more than two carboxyl groups and one amino group, and when different raw materials and cross-linking agents are used for the preparation, the reaction conditions need to be slightly adjusted according to the actual reaction requirements.

[0060] Therefore, considering the water-retaining and degradable performance and environmental safety, the water-retaining and degradable hydrogel provided by the present invention is prepared using agricultural and sideline products containing cellulose and protein: bean dregs, wheat bran, corn dregs, rice bran or barley dregs as main raw materials, and D-glutamic acid or phenylalanine containing no more than three carboxyl groups and no more than two small molecular amino groups (whose molecular weight is less than 200) as a cross-linking agent.

[0061] Example 2

[0062] Preparation of suspension A: 5 g of dregs were mixed with 100 mL of deionized water and placed in a 250 mL three-necked flask equipped with a mechanical stirrer and a nitrogen tube, and the three-necked flask was purged with nitrogen protection, and then heated to 80° C. under nitrogen protection for 15 min, and then 1 wt % of ammonium persulfate was added. After reacting for 30 min, a D-glutamic acid solution (prepared by adding 2 g of D-glutamic acid to 20 mL of deionized water) was added, and then the reaction mixture was purged with nitrogen at 70° C. for 5 h. After the reaction was completed, the mixture was centrifuged at 11000 rpm for 20 min, the precipitate was collected, and centrifuged 3 times. After the centrifugation was completed, 20 mL of deionized water was added to prepare suspension A.

[0063] The suspension A was stirred at 4°C and 500 rpm / min for 1 h, and then 1.7 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride as an initiator was added to the suspension A. After blending for 10 min, 1.9 g of N-hydroxysuccinimide was added. The mixture was stirred at 300 rpm / min at room temperature in a 4°C ice bath in the dark for 18 h, and then dialyzed at 3500 Kda for 72 h to obtain a suspension B.

[0064] Subsequently, NaOH solution was added to suspension B to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, and quickly cooled after 15 minutes. This was repeated 2-3 times and incubated at 4°C. After incubation, the hydrogel was freeze-dried to obtain the hydrogel, which was used as experimental group 1.

[0065] Example 3

[0066] Preparation of suspension A: 6 g of dregs were mixed with 100 mL of deionized water and placed in a 250 mL three-necked flask equipped with a mechanical stirrer and a nitrogen tube, and the three-necked flask was purged with nitrogen protection, and then heated to 80° C. under nitrogen protection for 15 min, and then 1 wt % ammonium persulfate was added. After reacting for 30 min, D-glutamic acid solution (prepared by adding 3 g of D-glutamic acid to 20 mL of deionized water) was added, and then the reaction mixture was purged with nitrogen at 70° C. for 5 h. After the reaction was completed, the mixture was centrifuged at 11000 rpm for 20 min, the precipitate was collected, and centrifuged 3 times. After the centrifugation was completed, 20 mL of deionized water was added to prepare suspension A.

[0067] The suspension A was stirred at 4°C and 500 rpm / min for 1 h, and then 1.7 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride as an initiator was added to the suspension A. After blending for 10 min, 1.9 g of N-hydroxysuccinimide was added. The mixture was stirred at 300 rpm / min at room temperature in a 4°C ice bath in the dark for 18 h, and then dialyzed at 3500 Kda for 72 h to obtain a suspension B.

[0068] Subsequently, NaOH solution was added to suspension B to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, cooled rapidly after 15 minutes, repeated 2-3 times, and incubated at 4°C. After incubation, it was freeze-dried to obtain the hydrogel, which was used as experimental group 2.

[0069] Example 4

[0070] Preparation of suspension A: 7 g of dregs were mixed with 100 mL of deionized water and placed in a 250 mL three-necked flask equipped with a mechanical stirrer and a nitrogen tube, and the three-necked flask was purged with nitrogen protection, and then heated to 80° C. under nitrogen protection for 15 min, followed by adding 1 wt % ammonium persulfate, reacting for 30 min, adding D-glutamic acid solution (prepared by adding 5 g of D-glutamic acid to 20 mL of deionized water), and then the reaction mixture was purged with nitrogen at 70° C. for 5 h. After the reaction was completed, the mixture was centrifuged at 11000 rpm for 20 min, the precipitate was collected, and centrifuged 3 times. After the centrifugation was completed, 20 mL of deionized water was added to prepare suspension A.

[0071] The suspension A was stirred at 4°C and 500 rpm / min for 1 h, and then 1.7 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride as an initiator was added to the suspension A. After blending for 10 min, 1.9 g of N-hydroxysuccinimide was added. The mixture was stirred at 300 rpm / min at room temperature in a 4°C ice bath in the dark for 18 h, and then dialyzed at 3500 Kda for 72 h to obtain a suspension B.

[0072] Subsequently, NaOH solution was added to suspension B to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, cooled rapidly after 15 minutes, repeated 2-3 times, and incubated at 4°C. After incubation, it was freeze-dried to obtain the hydrogel, which was used as experimental group 3.

[0073] Example 5

[0074] Preparation of suspension A: 5 g of dregs were mixed with 100 mL of deionized water and placed in a 250 mL three-necked flask equipped with a mechanical stirrer and a nitrogen tube, and the three-necked flask was purged with nitrogen protection, and then heated to 80° C. under nitrogen protection for 15 min, followed by adding 1 wt % ammonium persulfate, reacting for 30 min, adding D-glutamic acid solution (prepared by adding 6 g of D-glutamic acid to 20 mL of deionized water), and then the reaction mixture was purged with nitrogen at 70° C. for 5 h. After the reaction was completed, the mixture was centrifuged at 11000 rpm for 20 min, the precipitate was collected, and centrifuged 3 times. After the centrifugation was completed, 20 mL of deionized water was added to prepare suspension A.

[0075] The suspension A was stirred at 4°C and 500 rpm / min for 1 h, and then 1.7 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride as an initiator was added to the suspension A. After blending for 10 min, 1.9 g of N-hydroxysuccinimide was added. The mixture was stirred at 300 rpm / min at room temperature in a 4°C ice bath in the dark for 18 h, and then dialyzed at 3500 Kda for 72 h to obtain a suspension B.

[0076] Subsequently, NaOH solution was added to suspension B to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, cooled rapidly after 15 minutes, repeated 2-3 times, and incubated at 4°C. After incubation, it was freeze-dried to obtain the hydrogel, which was used as experimental group 4.

[0077] Example 6

[0078] Preparation of suspension A: 8 g of dregs were mixed with 100 mL of deionized water and placed in a 250 mL three-necked flask equipped with a mechanical stirrer and a nitrogen tube, and the three-necked flask was purged with nitrogen protection, and then heated to 80° C. under nitrogen protection for 15 min, followed by adding 1 wt % ammonium persulfate, reacting for 30 min, adding D-glutamic acid solution (prepared by adding 6 g of D-glutamic acid to 20 mL of deionized water), and then the reaction mixture was purged with nitrogen at 70° C. for 5 h. After the reaction was completed, the mixture was centrifuged at 11000 rpm for 20 min, the precipitate was collected, and centrifuged 3 times. After the centrifugation was completed, 20 mL of deionized water was added to prepare suspension A.

[0079] The suspension A was stirred at 4°C and 500 rpm / min for 1 h, and then 1.7 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride as an initiator was added to the suspension A. After blending for 10 min, 1.9 g of N-hydroxysuccinimide was added. The mixture was stirred at 300 rpm / min at room temperature in a 4°C ice bath in the dark for 18 h, and then dialyzed at 3500 Kda for 72 h to obtain a suspension B.

[0080] Subsequently, NaOH solution was added to suspension B to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, cooled rapidly after 15 minutes, repeated 2-3 times, and incubated at 4°C. After incubation, it was freeze-dried to obtain the hydrogel, which was used as experimental group 5.

[0081] Example 7

[0082] Preparation of suspension A: 5 g of dregs were mixed with 100 mL of deionized water and placed in a 250 mL three-necked flask equipped with a mechanical stirrer and a nitrogen tube, and the three-necked flask was purged with nitrogen for protection, and then heated to 80°C under nitrogen protection for 15 min, followed by adding 1 wt% ammonium persulfate, reacting for 30 min, adding D-glutamic acid solution (prepared by adding 5 g of D-glutamic acid to 20 mL of deionized water), and then the reaction mixture was purged with nitrogen for 5 h at 70°C. After the reaction was completed, the mixture was centrifuged at 11000 rpm for 20 min, the precipitate was collected, and centrifuged 3 times. After the centrifugation was completed, 20 mL of deionized water was added to prepare suspension A.

[0083] The suspension A was stirred at 4°C and 500 rpm / min for 1 h, and then 1.7 g of initiator 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride was added to the suspension A, and after mixing for 10 min, 1.9 g of N-hydroxysuccinimide was added, and the mixture was stirred at 300 rpm / min at room temperature for 18 h in an ice bath at 4°C and protected from light, and then dialyzed at 3500 Kda for 72 h to obtain a suspension B.

[0084] Subsequently, NaOH solution was added to suspension B to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, cooled rapidly after 15 minutes, repeated 2-3 times, and incubated at 4°C. After incubation, it was freeze-dried to obtain the hydrogel, which was used as experimental group 6.

[0085] Example 8

[0086] After 5 g of okara was mixed with deionized water (solid-liquid ratio of 5:7), 1.7 g of 1-hydroxybenzotriazole as an initiator was added and mixed, and then D-glutamic acid solution (prepared by adding 6 g of D-glutamic acid to 20 mL of deionized water) was added, and then 1.9 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride was added, and the reaction was carried out in a dark room under normal pressure for 24 h, and then centrifuged at 12000 rpm / min for 30 min, and dialyzed using an 8000 Kda dialysis bag to obtain a modified okara mixture.

[0087] Subsequently, NaOH solution was added to the modified okara mixture to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, cooled rapidly after 15 minutes, and repeated 2-3 times. The mixture was incubated at 4°C, and freeze-dried after incubation to obtain the hydrogel, which was used as experimental group 7.

[0088] Example 9

[0089] At 4°C, the mixture was stirred at 500 rpm / min for 1 h, 1.7 g of ammonium persulfate as an initiator was added to a D-glutamic acid solution (prepared by adding 6 g of D-glutamic acid to 20 mL of deionized water), and 1.9 g of N,N,N′,N′-tetramethylenediamine was added after blending for 10 min. The mixture was reacted in a dark room at 80°C for 1 h. After the reaction was completed, a bean dregs mixture (prepared by mixing 5 g of bean dregs with deionized water at a solid-liquid ratio of 5:7) was added, and the mixture was stirred at 300 rpm / min for 18 h at room temperature in the dark. The mixture was dialyzed at 3500 Kda for 72 h to obtain a modified bean dregs mixture.

[0090] Subsequently, NaOH solution was added to the modified okara mixture to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, cooled rapidly after 15 minutes, and repeated 2-3 times. The mixture was incubated at 4°C, and freeze-dried after incubation to obtain the hydrogel, which was used as experimental group 8.

[0091] Comparative Example 1

[0092] The steps of the method for preparing the hydrogel in this comparative example are the same as those in Example 2, except that bean dregs are not used, and other conditions are the same. The specific method is: 5 g of D-glutamic acid is mixed with 100 mL of deionized water and put into a 250 mL three-necked flask equipped with a mechanical stirrer and a nitrogen tube, and the three-necked flask is purged with nitrogen for protection, and then heated to 80° C. under nitrogen protection for 15 min, then 1 wt % of ammonium persulfate is added, and after reacting for 30 min, a D-glutamic acid solution (prepared by adding 2 g of D-glutamic acid to 20 mL of deionized water) is added, and then the reaction mixture is purged with nitrogen for 5 h at 70° C. After the reaction is completed, the mixture is centrifuged at 11000 rpm for 20 min, the precipitate is collected, and centrifuged 3 times. After the centrifugation is completed, 20 mL of deionized water is added to prepare a suspension A.

[0093] The suspension A was stirred at 4°C and 500 rpm / min for 1 h, and then 1.7 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride as an initiator was added to the suspension A. After blending for 10 min, 1.9 g of N-hydroxysuccinimide was added. The mixture was stirred at 300 rpm / min at room temperature in a 4°C ice bath in the dark for 18 h, and then dialyzed at 3500 Kda for 72 h to obtain a suspension B.

[0094] Subsequently, NaOH solution was added to suspension B to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, and rapidly cooled after 15 minutes. This was repeated 2-3 times and incubated at 4°C. After incubation, the mixture was freeze-dried to obtain the hydrogel.

[0095] Comparative Example 2

[0096] The steps of the method for preparing the hydrogel in this comparative example are the same as those in Example 2, except that D-glutamic acid is not used, and other conditions are the same. The specific method is: 5 g of bean dregs are mixed with 100 mL of deionized water and put into a 250 mL three-necked flask equipped with a mechanical stirrer and a nitrogen tube, and the three-necked flask is purged with nitrogen for protection, and then heated to 80° C. under nitrogen protection for 15 min, and then 1 wt % of ammonium persulfate is added. After reacting for 30 min, bean dregs solution (prepared by adding 2 g of bean dregs to 20 mL of deionized water) is added, and then the reaction mixture is purged with nitrogen for 5 h at 70° C. After the reaction is completed, the reaction mixture is centrifuged at 11000 rpm for 20 min, the precipitate is collected, and centrifuged 3 times. After the centrifugation is completed, 20 mL of deionized water is added to prepare a suspension A.

[0097] The suspension A was stirred at 4°C and 500 rpm / min for 1 h, and then 1.7 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride as an initiator was added to the suspension A. After blending for 10 min, 1.9 g of N-hydroxysuccinimide was added. The mixture was stirred at 300 rpm / min at room temperature in a 4°C ice bath in the dark for 18 h, and then dialyzed at 3500 Kda for 72 h to obtain a suspension B.

[0098] Subsequently, NaOH solution was added to suspension B to adjust its pH value to 9, and then stirred at 100 rpm / min at 4°C. After stirring, the mixture was heated to 70-90°C, and rapidly cooled after 15 minutes. This was repeated 2-3 times and incubated at 4°C. After incubation, the mixture was freeze-dried to obtain the hydrogel.

[0099] Comparative Example 3

[0100] The method and steps for preparing the hydrogel in this comparative example are the same as those in Example 2, except that the D-glutamic acid solution is prepared by adding 10 g of D-glutamic acid to 20 mL of deionized water, and the other conditions and steps are the same.

[0101] After the preparation of hydrogels in different experimental groups, it was shown that the initiator used 1-hydroxybenzotriazole through H 2 O 2The conditions for the free radical-induced grafting reaction are complicated and cumbersome. The reaction between the carbonyl end and the amino group after halogenation is also complicated (the reaction conditions will vary with the carbonyl end), and 1-hydroxybenzotriazole is expensive and has a high cost. The cross-linking reaction using ammonium persulfate and N,N,N',N'-tetramethylenediamine as initiators requires high temperature reaction. The initiators using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide do not require heating, which allows the carboxyl group on glutamic acid to react better with the amino group on the water-soluble protein. ; The reaction between amino substances and carboxyl substances is very slow or almost non-reactive. After treating D-glutamic acid with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, the reaction threshold between bean dregs and the carboxyl and amino groups of D-glutamic acid is reduced, overcoming the difficulty of the reaction between conventional carboxyl substances and amino substances with low activity, so that the cross-linking reaction can be better carried out without producing other by-products. Subsequent performance measurements show that the hydrogels prepared in Examples 1-9 all have water-retaining and degradable properties.

[0102] At the same time, the embodiment of the present invention mainly prepares the hydrogel by adjusting the amount of the cross-linking agent, and the natural crop by-product raw material provides more cross-linking monomers. In Comparative Examples 1 and 2, the lack of natural crop by-product raw materials or cross-linking agents cannot successfully prepare hydrogels. The reason is that due to the lack of water-soluble proteins in the natural crop by-product raw materials to provide cross-linking monomers, or the lack of cross-linking agents, it is impossible to effectively form a cross-linked network structure, and more importantly, the molecules formed by the cross-linking of D-glutamic acid by the cross-linking agent cannot effectively form long-chain molecules (the amount of D-glutamic acid used is small). Therefore, only when the natural crop by-product raw materials and the cross-linking agent are in a suitable ratio, can the water-retaining and degradable hydrogel be successfully prepared.

[0103] Test experiment 1 Swelling performance test

[0104] The hydrogels prepared in Examples 2-5 and Comparative Example 3 were tested for swelling performance. After freeze-drying different hydrogel groups, about 1 g of dry hydrogel was soaked in deionized water, and the weight was counted every 1 hour until saturation. The swelling capacity (WSC) of the hydrogel was then calculated using the following formula, and the values ​​obtained from each group of samples were plotted and counted.

[0105] WSC formula calculation:

[0106] WSC=[(Ms-Md) / Md]×100%

[0107] Where Ms (g) and Md (g) represent the weight of the water-swollen sample and the dry sample, respectively.

[0108] The results are as follows Figure 2As shown, the swelling rate of the hydrogels of Examples 2-5 of the present invention is 242%-326%, which has good swelling performance and can be used to absorb more water for subsequent water retention and water lock; while the swelling rate of Comparative Example 3 is the lowest in the experimental group. It uses too much cross-linking agent, which will make the overall cross-linking degree of the hydrogel too large, thereby reducing the ductility of the molecular chain, making the swelling degree of the hydrogel of Comparative Example 3 after water absorption lower than that of Examples 2-5. Therefore, it can be seen that the more the amount of cross-linking agent used in the hydrogel component of the present invention, the better.

[0109] Test experiment 2 Temperature and water retention test

[0110] The hydrogels prepared in Examples 2-5 and Comparative Example 3 were subjected to a temperature water retention test. After freeze-drying, the hydrogels of different groups were dissolved in 200 mL of deionized water and placed in sealed containers. A hygrometer was placed at the bottom of the container. All groups were then placed in an oven at 65°C. Within the first 4 hours, the values ​​on the hygrometer were observed and recorded every 30 minutes. The first reading was taken as the RH. 0 , subsequent reading is RH n , calculate the water retention rate of different hydrogels, the calculation formula is as follows, and statistics are performed.

[0111] W Water retention =(RH n / RH 0 )×100%

[0112] The statistical results are as follows Figure 3 As shown, the water retention rate of the hydrogels of Examples 2-5 of the present invention is 66%-84%, with a maximum of 83±1%, which has good water retention performance and can be used for soil water retention in areas of drought, soil erosion, etc.; compared with Examples 2-5, the water retention rate of the hydrogel prepared in Comparative Example 3 is the lowest, but the water retention rate of Comparative Example 3 is not significantly reduced compared with Example 2, which may be due to the fact that too much cross-linking agent is introduced, resulting in a high overall cross-linking degree of the hydrogel, and the number of amino groups remaining on the water-soluble molecules after the reaction is less than that of other groups. The excessively high cross-linking degree and fewer amino groups result in a lower water retention rate of Comparative Example 3 than in Examples 2-5. Test Experiment 3 Toxicity Test for Plant Harm

[0113] The hydrogels prepared in Examples 2-5 and Comparative Example 3 were subjected to a phytotoxicity test. Wheat seeds were placed in a culture dish filled with distilled water (control group) or saturated with hydrogel, with the same number of seeds in each group. The culture dishes of different groups were then placed in a dark growth chamber at 25°C for 72 hours, and the germination of the wheat seeds was counted, the germination index (Gindex) was calculated, and the Gindex value of each experimental group was counted.

[0114] The calculation formula is as follows:

[0115] Gindex=[(G / G 0 )×(L / L 0 )]×100%

[0116] Where G and L are the number of seeds germinated and the length of roots in the presence of saturated hydrogel, respectively. 0 and L 0 are the number of seeds germinated in distilled water and the root length, respectively.

[0117] The results are as follows Figure 4 As shown, compared with the control group, the Gindex values ​​of other groups all exceeded 100%, proving that the hydrogel prepared by the present invention will not harm plant growth. At the same time, since the Gindex value of the experimental group is slightly higher than that of the control group, it can be proved that the hydrogel has a certain promoting effect on the root growth of wheat seeds to a certain extent.

[0118] Test experiment 4: Biodegradability test

[0119] The biodegradability of the hydrogels prepared in the above Examples 2-5 and Comparative Example 3 was tested. 100 g of dry soil was mixed with 200 mL of deionized water, shaken with a magnetic stirrer (20 minutes), and then centrifuged at 1000 rpm / min for 15 minutes; the supernatant was filtered to remove the remaining soil particles. 0.1 g of hydrogel samples from different groups were immersed in the soil solution and incubated for 40 days. Every 5 days, the weight was taken, and the sample was dried at 55°C overnight, weighed after cooling in a dryer, and calculated according to the following formula to determine its weight loss, and the weight loss rate of each experimental group was calculated.

[0120] Weight loss rate (%) = [(Mi-Mf) / Mf] × 100%

[0121] where Mi and Mf are the initial and final weights remaining of the hydrogel at each time interval, respectively.

[0122] The results are as follows Figure 5 As shown, the results show that the hydrogels of Examples 2-5 of the present invention have good degradation performance, while the degradation degree of Comparative Example 3 is far inferior to that of Examples 2-5. The reason may be that the higher degree of cross-linking makes the degradation low, and it is difficult to be degraded by microorganisms in the soil during the re-degradation process, so that the weight loss rate of Comparative Example 3 in the 40h test of the biodegradability experiment is far inferior to that of Examples 2-5.

[0123] In summary, the present invention provides a degradable hydrogel for water retention, wherein the main effective ingredients are agricultural and sideline products containing cellulose and protein, and the cross-linking agent uses small molecule amino acids. The hydrogel prepared by the initiator reaction has a significant water retention effect and a high degradability rate, does not harm plant growth, and has a significant effect in soil water retention. The raw material components used in the present invention are all pure natural, easy to obtain, environmentally friendly and safe substances, with low cost, higher safety than the hydrogel prepared by traditional chemical raw materials, easier to degrade than traditional polyamide water retaining agents, less pollution to the environment, and lower toxicity to crops. The present invention reacts the insoluble cellulose in the raw material to prepare a hydrogel with good water retention performance, overcomes the problem that conventional cellulose, carboxyl substances and amino substances with low activity are difficult to react, and the grafted hydrogel has a high swelling degree, which can not only be used to improve the soil water retention capacity and increase moisture, but also can be used for plant growth and development, and used as compost, providing a research idea and basis for preparing more water-retaining and degradable hydrogels with excellent performance and low cost.

[0124] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A degradable hydrogel for water retention, characterized in that: It is made of agricultural and sideline products containing cellulose and protein, small molecule amino acids with a molecular weight below 200, and initiators; The agricultural and sideline products containing cellulose and protein are selected from one or more of bean dregs, wheat bran, corn dregs, rice bran or barley dregs; The small molecule amino acid is D-glutamic acid or phenylalanine; The initiator is 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide; the molar ratio of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride to N-hydroxysuccinimide is 1:(0.1-2); The mass ratio of the agricultural and sideline products containing cellulose and protein, the small molecule amino acid and the initiator is (1-8):1:(1-5); The preparation method of the hydrogel comprises the following steps: S1. Suspension A: The agricultural and sideline products containing cellulose and protein are mixed with deionized water, heated under nitrogen protection, ammonium persulfate is added for reaction, and then a small molecule amino acid solution is added and heated for reaction. After the reaction is completed, the precipitate is collected by centrifugation, and deionized water is added to obtain suspension A; S2. The initiator was added to the suspension A, the mixture was stirred under ice bath conditions, the reaction was protected from light and dialyzed, and the dialyzed product was collected and recorded as suspension B; S3. The pH value of the suspension B is adjusted to 8-10, stirred in an ice bath, then heated, rapidly cooled, incubated, and freeze-dried to obtain a degradable hydrogel for water retention.

2. The hydrogel according to claim 1, characterized in that In step S1, 1-5 wt% ammonium persulfate and 1-10 wt% small molecule amino acid solution are used; the heating reaction conditions are 60-80° C. and the reaction time is 0.1-5 h.

3. The hydrogel according to claim 1, characterized in that In step S3, the temperature is raised to 70-90°C and maintained for 10-30 min, and the incubation condition is 4-37°C.

4. Use of the degradable hydrogel for water retention according to claim 1 in the preparation of a product for improving the water retention capacity of soil.

5. Use of the degradable hydrogel for water retention according to claim 1 in improving the water retention capacity of soil or in the treatment of drought soil.

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