High-water-absorptivity anti-freezing water-retaining agent with urea slow-release function as well as preparation method and application thereof

Abstract

The invention relates to the technical field of high polymer materials, in particular to a preparation method and application of a high-water-absorptivity anti-freezing water-retaining agent with a urea slow release function. The preparation method comprises the following steps: adding a cross-linking agent, a catalyst, urea, a photoinitiator and a polysaccharide solution into an aqueous solution of potassium acrylate and acrylamide, stirring, and carrying out photo-initiation polymerization to prepare the water-retaining agent with excellent water absorption, water retention, cycle stability, soil freezing resistance and slow release performance by a one-pot method, and the water-retaining agent has a wide application prospect in the field of agriculture.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and relates to the preparation method and application of a highly absorbent antifreeze agent with urea slow-release function. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Water-retaining agents are widely used in agriculture, forestry, horticulture, and other fields. During their use, not only water resources but also water and fertilizer runoff must be considered. Common fast-dissolving fertilizers release nutrients into the soil rapidly, leading to significant nutrient loss due to short-term nutrient accumulation. This necessitates increasing fertilization frequency and amount to meet crop fertility requirements, causing serious environmental problems and economic burdens.

[0004] One study disclosed a water-retaining, slow-release fertilizer based on cellulose, halloysite, and cyclodextrin. This fertilizer achieved slow release by embedding urea within halloysite and encapsulating it in a polymer. However, the fertilizer in this material is physically encapsulated only in small molecule form, leading to unstable release rates and short release cycles. Furthermore, the simple polymer network structure results in limited water absorption capacity, leading to poor synergistic effects of water retention and slow release in practical applications. Another study disclosed a water-retaining, slow-release hydrogel based on chitosan sulfonate, aminocarrageenan, and phosphorylated polyvinyl alcohol. This hydrogel, constructed through ionic crosslinking to create an interpenetrating three-dimensional network structure, achieved a water absorption ratio of 438.7 g / g and urea slow-release function. However, this hydrogel has a low water absorption ratio and requires prolonged high-temperature reactions, resulting in high energy consumption and challenges in production controllability and scalability costs. One study disclosed a urea-encapsulated cellulose-based superabsorbent resin, which uses plant cellulose-based superabsorbent resin as the skeleton and encapsulates urea in the outer layer through a calcium alginate gel layer to form a physical barrier double-layer composite structure. However, the urea is mainly released through physical encapsulation and diffusion pathways, and its sustained-release effect depends on the outer coating structure, which makes it difficult to meet the requirements of synergistic optimization of high water absorption capacity, sustained-release performance and low-temperature antifreeze performance.

[0005] Studies have shown that sodium acrylate, acrylamide, and 2 Acrylamide 2 methyl 1 Propanesulfonic acid forms the first network, which then crosslinks with the second network of calcium salt and natural polysaccharides to form a highly absorbent dual-network resin. However, it still cannot meet the requirements for synergistic optimization of high water absorption capacity, slow-release performance and low-temperature antifreeze performance. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings and deficiencies of current water-retaining agents in agricultural applications, such as low water absorption rate, insignificant water retention effect, and limited urea slow-release capacity. The invention aims to develop a water-retaining agent that is simple to prepare, economically efficient, and possesses antifreeze effects, ultra-high water absorption rate, high water retention, strong mechanical properties, high cycle stability, and slow-release fertilizer capacity.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a highly absorbent antifreeze agent with urea slow-release function, comprising: Acrylates, acrylamide, polysaccharide solution, and urea are mixed evenly in a solvent, and photopolymerization is carried out in the presence of a crosslinking agent, a photoinitiator, and a catalyst to obtain a highly absorbent antifreeze water-retaining agent. The molar ratio of acrylate to urea is 1:(0.02-0.26).

[0008] This invention constructs a covalently grafted hybrid rigid-flexible three-dimensional cross-linked network structure. A stable network system is formed through the synergistic cross-linking of acrylic acid, acrylamide, and polysaccharide chains. Urea is utilized in the network structure construction to achieve multifunctional synergistic regulation. In this invention, urea not only serves as a nitrogen source but also partially participates in the cross-linking reaction. Simultaneously, it forms multi-level release pathways through hydrogen bonding and network storage mechanisms, achieving synergistic sustained release through chemical binding and physical adsorption. Building upon the sustained-release function, this invention improves the material's water absorption rate, cycle stability, and low-temperature freeze resistance by controlling the density of hydrophilic groups, hydrogen bonding, and the proportion of non-freezing water, achieving synergistic enhancement of multiple properties and expanding the material's application range.

[0009] In a second aspect, the present invention provides a highly absorbent antifreeze agent with urea slow-release function prepared by the above method.

[0010] A third aspect of the present invention provides the application of the above-mentioned highly absorbent antifreeze and water-retaining agent with urea slow-release function in the agricultural field.

[0011] Beneficial effects of the present invention (1) The high-performance water-retaining agent developed in this invention has a covalently grafted hybrid rigid-flexible composite network structure with a breaking elongation of 998% to 1289% and a tensile stress of 0.19 MPa to 0.32 MPa. The high mechanical properties provide water storage space for the water-retaining agent while giving it excellent structural support, thus providing mechanical protection for the high water absorption and water retention of the water-retaining agent.

[0012] (2) This invention utilizes the hydrophilicity and osmotic pressure regulation of urea to promote the entry of water into the water-retaining agent, thereby improving the water absorption of the water-retaining agent; at the same time, -NH2 and -COO -The abundant strong hydrophilic groups such as -OH further promote the infiltration of water by adsorbing water; the covalently grafted hybrid rigid-flexible composite network structure provides more water storage space for the water-retaining agent, synergistically enhancing the water absorption performance of the water-retaining agent, with a water absorption capacity of 1012g / g to 1235g / g, and the soil containing 1% water-retaining agent can still maintain a moisture content of 41% to 63% after 13 days.

[0013] (3) This invention utilizes urea and -OH, -NH2, -COO - The hydration of the strong hydrophilic groups forms a large amount of bound water, increasing the content of unfrozen water; the strong hydrogen bonding between urea molecules and water molecules disrupts the ordered hydrogen bond network between water molecules, inhibiting the formation of ice nuclei; under the synergistic effect, the freezing point of soil with 1 wt% water-retaining agent can be lowered to -8.07 ℃ to -16.84 ℃.

[0014] (4) This invention utilizes the multiple functions of urea to provide a nitrogen source for the water-retaining agent while also acting as an environmentally friendly crosslinking agent. Uncrosslinked urea molecules are encapsulated or adsorbed into the crosslinking network through hydrogen bonds and diffuse into the external environment through the pore size under osmotic pressure. Crosslinked urea is gradually released into the external environment as the polysaccharide chains degrade. The dual function gives the water-retaining agent a better urea slow-release effect, so that soil with 4wt% water-retaining agent can still release 1.14 g / kg to 2.4 g / kg of nitrogen content after 6 weeks, and the soil still maintains a nitrogen content of 0.89 g / kg to 1.3 g / kg after two months of planting crops.

[0015] (5) The preparation method of the present invention is simple, practical and easy to promote. Attached Figure Description

[0016] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0017] Figure 1 The infrared spectra of the water-retaining agents prepared in Example 1 and Comparative Example 3 of this invention are shown.

[0018] Figure 2 The swelling properties of the water-retaining agents prepared in Example 1 and Comparative Examples 4-7 of this invention are shown in the diagram.

[0019] Figure 3 The mechanical properties of the water-retaining agents prepared in Example 1 and Comparative Examples 4-7 of this invention are shown in the diagram.

[0020] Figure 4 The diagram shows the soil water retention performance after the water-retaining agents prepared in Example 1 and Comparative Examples 4-7 of this invention are mixed with soil.

[0021] Figure 5 The water retention effects of the water-retaining agents prepared in Example 1 and Comparative Examples 4-7 of this invention after being mixed with soil are shown in the diagrams.

[0022] Figure 6 The diagrams show the water retention effect of the water-retaining agents prepared in Examples 1 and 4-7 of this invention after being mixed with soil.

[0023] Figure 7 The DSC freezing point diagrams of the water-retaining agents prepared in Example 1 and Comparative Examples 4-7 of this invention after being mixed with soil are shown.

[0024] Figure 8 The temperature rise curves of DSC after the water-retaining agent prepared in Example 1 and Comparative Examples 4-7 of this invention was mixed with soil at 1 wt%.

[0025] Figure 9 The nitrogen release diagrams for 6 weeks after the water-retaining agents prepared in Examples 1 and 4-7 of this invention were mixed with soil at 4 wt%.

[0026] Figure 10 The soil nitrogen content of the blank group soil without any filler, the control group soil with only the corresponding amount of urea, and the soil mixed with 4wt% of Comparative Example 7 after maintaining crop growth for one week and two months are shown in the figures. Detailed Implementation

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods in the art or product instructions. Similarly, unless otherwise specified, the test methods of this invention are performed in accordance with conventional methods in the art or industry-standard methods or practices. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0029] This invention mainly proposes a method for preparing a highly absorbent antifreeze agent with urea slow-release function, comprising: Acrylates, acrylamide, polysaccharide solution, and urea are mixed evenly in a solvent, and photopolymerization is carried out in the presence of a crosslinking agent, a photoinitiator, and a catalyst to obtain a highly absorbent antifreeze water-retaining agent. Urea, as the main functional monomer in this invention, has a significant impact on the water absorption and retention, mechanical properties, antifreeze properties, and sustained-release effect of the water-retaining agent. Therefore, this invention investigated the molar ratio of acrylic acid to urea, wherein the molar ratio of acrylate to urea is 1:(0.02-0.26) to obtain better performance.

[0030] The amount of acrylate and acrylamide used can affect the structure and performance of the crosslinked network. Therefore, this invention has studied the amount of acrylate and acrylamide used. Preferably, the molar ratio of acrylate to acrylamide is 1:(0.1~1) to obtain better water absorption, slow release, low temperature antifreeze and mechanical properties.

[0031] The present invention does not impose any special limitation on the type of acrylate. Preferably, the acrylate is potassium acrylate, so as to give the water-retaining agent better performance.

[0032] The content of polysaccharides has a significant impact on the water absorption and sustained-release properties of water-retaining agents. Therefore, this invention has studied the amount of polysaccharides used. Preferably, the mass ratio of the polysaccharide solution to urea is (5-12):1, more preferably (5.14-10.28):0.9; the concentration of the polysaccharide solution is 1-20 wt%, so as to effectively improve the water absorption and sustained-release properties of the water-retaining agent.

[0033] The type of polysaccharide affects the structure and properties of the cross-linked network. Therefore, this invention studies the types of polysaccharides. Preferably, the polysaccharide is selected from one of carboxymethyl guar gum, carboxymethyl chitosan, potassium carboxymethyl cellulose, and sodium alginate. More preferably, the polysaccharide is carboxymethyl guar gum to obtain better water absorption, sustained release, low-temperature antifreeze properties, and mechanical properties.

[0034] In this invention, urea acts as a crosslinking agent, while other crosslinking agents are only used as crosslinking aids. Therefore, this invention does not impose any special limitation on the type of crosslinking agent. Preferably, the crosslinking agent is selected from at least one of N,N′-methylenebisacrylamide, N,N′-(1,2-dihydroxyethylidene)bisacrylamide, and polyethylene glycol diacrylate to achieve chemical crosslinking. The amount of crosslinking agent can affect the crosslinking density, mechanical properties, etc. Therefore, this invention has explored the amount of crosslinking agents other than urea. Preferably, the amount of crosslinking agent is 0.01 to 0.05 wt% of the total mass of acrylate and acrylamide, which forms a stable three-dimensional network under the synergistic effect of urea. The type of catalyst can affect the degree of crosslinking of urea, which in turn affects the performance of the water-retaining agent. Therefore, the present invention has studied the types of catalysts. Preferably, the catalyst is selected from at least one of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide. In this invention, the content of the catalyst has a direct impact on the degree of crosslinking of urea. Therefore, this invention has studied the amount of catalyst used. Preferably, the catalyst is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide, wherein the molar ratio of acrylic acid to 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide is 2:(0.5~1.5):(0~1.5) to obtain better catalytic effect.

[0035] To ensure the catalyst reacts fully, it is preferable to stir the solution at room temperature for 20-30 minutes after adding the catalyst to ensure that the catalyst can fully exert its effect.

[0036] Preferably, the mixed solution is stirred at 50–70°C for 20–30 minutes to ensure uniform mixing.

[0037] Preferably, the solid content of the mixed solution is 20–40 wt% to facilitate the photopolymerization reaction.

[0038] Preferably, the pH value of the reaction system is 6-7.

[0039] The present invention does not impose any special limitation on the type of photoinitiator, as long as it can initiate a photopolymerization reaction. Preferably, the photoinitiator is selected from one of 2-hydroxy-4'-(2-hydroxyethylamino)-2-methylphenylacetone, 2,2-azobis(2-methylpropylimidazolium) hydrochloride, and 2,4,6-trimethylbenzoylphenyl phosphate to achieve the photopolymerization reaction. The amount of photoinitiator has a certain impact on reaction time, molecular weight, etc., and the amount of photoinitiator needs to reach a certain content to initiate the photopolymerization reaction. Therefore, the present invention has studied the amount of photoinitiator. Preferably, the amount of photoinitiator is 0.8 to 1.2 wt% of the total mass of acrylate and acrylamide to efficiently initiate the photopolymerization reaction and form a high-performance water-retaining agent.

[0040] The power and wavelength of ultraviolet lamps affect the efficiency of photopolymerization reactions. Therefore, this invention has studied the power and wavelength of ultraviolet lamps. Preferably, the conditions for the photopolymerization reaction are: ultraviolet lamp power of 1-5KW and wavelength of 365nm, in order to improve the photopolymerization efficiency.

[0041] The photopolymerization reaction time also affects the performance of the reaction product. If the photopolymerization reaction time is too short, the reaction will be incomplete and the structure will be unstable. If the photopolymerization reaction time is too long, the structure will be too compact and the pore structure will be smaller. Therefore, this invention has studied the photopolymerization reaction time. In some embodiments, the photopolymerization reaction time is 15 to 30 minutes to improve the overall performance of the water-retaining agent.

[0042] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0043] In the following examples and comparative examples, carboxymethyl guar gum is a commercially available product purchased from Shandong Guangrao Liuhe Chemical Co., Ltd.

[0044] In the following examples and comparative examples, the water absorption performance of the superabsorbent antifreeze agent with urea slow-release function is expressed as water absorption rate: The water absorption rate is calculated by equation (1).

[0045]

[0046] Where W0 is the weight of the dry water-retaining agent, W t It is the weight of the water-retaining agent after it has stabilized in the solution.

[0047] The mechanical properties were tested using a CMT4204 tensile testing machine at a tensile speed of 50 mm / min to measure the tensile strength of the soil water-retaining agent at room temperature.

[0048] The soil used in the experiment was dried in an oven at 80°C. The soil was then ground, crushed, and sieved to 2 mm. The dried water-retaining agent (1 wt% of the soil) was thoroughly mixed with the dried and sieved soil (100 g). A soil sample without the water-retaining agent was taken as a control and placed in a container with a small hole at the bottom. Tap water was slowly poured in and allowed to stand until no liquid dripped from the bottom of the container. The water holding capacity was then calculated. The sample was then dried in an oven at 80°C until constant weight and the cycle was repeated 16 times. The cyclic water holding capacity of the mixture of the highly absorbent antifreeze water-retaining agent with urea slow-release function and the soil was calculated by equation (2).

[0049]

[0050] Where W1 is the mass of the water-retaining agent, W4 is the mass of the soil, W5 is the mass of the container, and WS is the total mass under saturation.

[0051] The water retention rate of the mixture of water-retaining agent and soil is calculated according to formula (3).

[0052]

[0053] Among them, W T It is the total mass at different times.

[0054] The DSC curve of the mixture of water-retaining agent and soil was determined by differential scanning calorimetry, and the non-crystallization water content was calculated.

[0055]

[0056]

[0057]

[0058] W H It is the total water content, W fH It is the frozen water content, W nfH It is the non-frozen water content, ΔH fH The melting point peak area on the DSC curve is expressed in joules per gram, and ΔH0 is the enthalpy of fusion of pure water: 333.5 J / g. 1 .

[0059] 100g of natural soil and 4g of water-retaining agent sample were mixed and placed in a filter as a leaching device. 100g of soil was placed in a beaker as a receiver. The experimental setup was assembled by covering the receiver with the leaching device. A suitable amount of deionized water was periodically added to the leaching device to allow the solution to leach from the bottom of the leaching device into the receiver. The natural soil in the receiver was removed and replaced weekly, and nitrogen content was analyzed using an automatic Kjeldahl nitrogen analyzer according to the People's Republic of China Agricultural Standard (NY / T 1121.24-2012). The results are as follows: Figure 9 As shown.

[0060] Eggplant seedlings with similar growth were planted in soil containing 4 wt% water-retaining agent and grew normally under suitable conditions. Initially and two months later, soil samples from each group were randomly collected at multiple locations, and the total nitrogen content in the soil was determined using an automated Kjeldahl nitrogen analyzer. The results are as follows: Figure 10 As shown.

[0061] Example 1: A method for preparing and applying a highly absorbent antifreeze agent with urea slow-release function, specifically comprising the following steps: 3.6 g of acrylic acid was neutralized with 20 wt% potassium hydroxide solution, then 1.54 g of acrylamide and 0.001 g of N,N′-methylenebisacrylamide were added and dissolved in water. Then 10.28 g of 10 wt% carboxymethyl guar gum solution was added and stirred at 60℃ for 30 min to dissolve it into a homogeneous solution. Then 1.94 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 1.44 g of N-hydroxysuccinimide were added and stirred for 15 min. Finally, 0.9 g of urea and 0.051 g of 2-hydroxy-4'-(2-hydroxyethylamino)-2-methylphenylacetone were dissolved in the mixed solution to prepare a solution with a solid content of 35%. The solution was stirred at 60℃ for 10 min and irradiated under ultraviolet light with a power of 1KW and a wavelength of 365 nm for 0.5 h to obtain a highly absorbent, antifreeze, and slow-release water-retaining agent.

[0062] The test showed that the superabsorbent antifreeze water-retaining agent with urea slow-release function had a water absorption of 1225.42 g / g, an elongation at break of 1187%, and a tensile stress of 0.28 MPa. Soil with 1 wt% water-retaining agent showed a freezing point depression rate of 209.95%, retained 34.5% unfrozen water after 30 minutes at -25°C, had a water holding capacity of 168.22%, and maintained a water holding capacity of 167.9 g / g after 16 water absorption-dehydration cycles. After 13 days, the soil contained 53.8% water content. Soil containing 4 wt% water-retaining agent could still release 1.49 g / kg nitrogen in a controlled manner after six weeks, and still contained 1.08 g / kg nitrogen after two months of plant growth.

[0063] Example 2: A method for preparing and applying a highly absorbent antifreeze agent with urea slow-release function, specifically comprising the following steps: 3.6 g of acrylic acid was neutralized with 20 wt% potassium hydroxide solution, then 1.54 g of acrylamide and 0.002 g of N,N′-methylenebisacrylamide were added and dissolved in water. Then 5.14 g of 5 wt% sodium alginate solution was added and stirred at 60℃ for 30 min to dissolve it into a homogeneous solution. Then 1.93 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide was added and stirred for 15 min. Finally, 0.9 g of urea and 0.051 g of 2-hydroxy-4'-(2-hydroxyethylamino)-2-methylphenylacetone were dissolved in the mixed solution to prepare a solution with a solid content of 30%. The solution was stirred at 60℃ for 10 min and then irradiated under ultraviolet light with a power of 1 kW and a wavelength of 365 nm for 0.5 h to obtain a highly absorbent, antifreeze, and slow-release water-retaining agent.

[0064] The test showed that the superabsorbent antifreeze water-retaining agent with urea slow-release function had a water absorption of 1125 g / g, an elongation at break of 1105%, and a tensile stress of 0.19 MPa. Soil with 1 wt% water-retaining agent showed a 128% decrease in freezing point, retained 28.5% unfrozen water after 30 minutes at -25°C, had a water holding capacity of 142.9 g / g after 16 water absorption-dehydration cycles, and contained 59.8% water content after 13 days. Soil containing 4 wt% water-retaining agent still released 1.28 g / kg of nitrogen slowly and in a controlled manner after six weeks, and still contained 0.98 g / kg of nitrogen after two months of plant growth.

[0065] Example 3 A method for preparing and applying a highly absorbent antifreeze agent with urea slow-release function, specifically comprising the following steps: 3.6 g of acrylic acid was neutralized with 20 wt% potassium hydroxide solution, then 1.54 g of acrylamide and 0.001 g of N,N′-methylenebisacrylamide were added and dissolved in water. Then 10.28 g of 5 wt% carboxymethyl chitosan solution was added and stirred at 60 °C for 30 min to dissolve it into a homogeneous solution. Then 1.93 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide was added and stirred for 15 min. Finally, 0.9 g of urea and 0.051 g of 2-hydroxy-4'-(2-hydroxyethylamino)-2-methylphenylacetone were dissolved in the mixed solution to prepare a solution with a solid content of 30%. The solution was stirred at 60 °C for 10 min and then irradiated under ultraviolet light with a power of 1 KW and a wavelength of 365 nm for 0.5 h to obtain a highly absorbent, antifreeze, and slow-release water-retaining agent.

[0066] The test showed that the superabsorbent antifreeze water-retaining agent with urea slow-release function had a water absorption of 1085 g / g, an elongation at break of 1135%, and a tensile stress of 0.19 MPa. Soil with 1 wt% water-retaining agent showed a 136.2% decrease in freezing point, maintained 30.5% unfrozen water after 30 minutes at -25°C, had a water holding capacity of 145.6 g / g after 16 water absorption-dehydration cycles, and contained 60.2% water content after 13 days. Adding 4 wt% water-retaining agent to the soil resulted in a controlled release of 1.13 g / kg nitrogen after six weeks, and maintained a nitrogen content of 0.96 g / kg in the soil after two months of plant growth.

[0067] Comparative Example 1 The difference from Example 1 is that no carboxymethyl guar gum solution was added.

[0068] The soil exhibits a water absorption of 1025 g / g, an elongation at break of 1095%, and a tensile stress of 0.18 MPa. With the addition of 1 wt% water-retaining agent, the freezing point depression rate of the soil reaches 165.2%. After 30 minutes at -25°C, it retains 32.5% unfrozen water. After 16 water absorption-dehydration cycles, it possesses a water holding capacity of 148.8 g / g, and after 13 days, it contains 61.5% water content. With the addition of 4 wt% water-retaining agent, the soil still slowly releases 1.02 g / kg of nitrogen after six weeks, and after two months of plant growth, the soil still contains 1.02 g / kg of nitrogen.

[0069] Comparative Example 2 The difference from Example 1 is that urea and carboxymethyl guar gum solution were not added.

[0070] It has a water absorption of 1032 g / g, an elongation at break of 1025%, a tensile stress of 0.12 MPa, and a soil freezing point reduction rate of 96.3% after adding 1wt% water-retaining agent. It retains 11.5% non-freezing water after 30 min at -25 degrees Celsius, has a water holding capacity of 128.7 g / g after 16 water absorption-dehydration cycles, and contains 41.8% water content after 13 days.

[0071] Comparative Example 3 The difference from Example 1 is that urea was not added.

[0072] It has a water absorption of 1125 g / g, an elongation at break of 1062%, a tensile stress of 0.16 MPa, and a soil freezing point reduction rate of 98.2% after adding 1 wt% water-retaining agent. It retains 10.6% non-freezing water after 30 minutes at -25 degrees Celsius, has a water holding capacity of 138.6 g / g after 16 water absorption-dehydration cycles, and contains 46.2% water content after 13 days.

[0073] Comparative Example 4 The difference from Example 1 is that 0.3g of urea was added.

[0074] The soil exhibits a water absorption capacity of 1089.55 g / g, an elongation at break of 1287%, and a tensile stress of 0.22 MPa. With the addition of 1 wt% water-retaining agent, the soil's freezing point depression rate reaches 100.74%. After 30 minutes at -25°C, it retains 11.1% unfrozen water. After 16 water absorption-dehydration cycles, it possesses a water holding capacity of 152.2 g / g, and after 13 days, it contains 58.8% water content. With the addition of 4 wt% water-retaining agent, the soil still slowly releases 1.038 g / kg of nitrogen after six weeks, and after two months of plant growth, the soil still contains 1.00 g / kg of nitrogen.

[0075] Comparative Example 5 The difference from Example 1 is that 0.6g of urea was added.

[0076] The soil exhibits a water absorption of 1136.91 g / g, an elongation at break of 1231%, and a tensile stress of 0.26 MPa. With the addition of 1 wt% water-retaining agent, the soil's freezing point depression rate reaches 166.67%. After 30 minutes at -25°C, it retains 24.1% unfrozen water. After 16 water absorption-dehydration cycles, it possesses a water holding capacity of 156.2 g / g, and after 13 days, it contains 51.6% water content. With the addition of 4 wt% water-retaining agent, the soil still slowly releases 1.25 g / kg of nitrogen after six weeks, and after two months of plant growth, the soil still contains 1.05 g / kg of nitrogen.

[0077] Comparative Example 6 The difference from Example 1 is that 1.2g of urea was added.

[0078] The soil exhibits a water absorption of 1162.91 g / g, an elongation at break of 1099%, and a tensile stress of 0.30 MPa. With the addition of 1 wt% water-retaining agent, the soil's freezing point decrease rate reaches 271.4%. After 30 minutes at -25°C, it retains 49.5% unfrozen water. After 16 water absorption-dehydration cycles, it possesses a water holding capacity of 154.2 g / g, and after 13 days, it contains 68% water content. With the addition of 4 wt% water-retaining agent, the soil still slowly releases 1.68 g / kg of nitrogen after six weeks, and after two months of plant growth, the soil still contains 1.09 g / kg of nitrogen.

[0079] Comparative Example 7 The difference from Example 1 is the addition of 1.5 g of urea. The water absorption reached 1015.75 g / g, the elongation at break reached 1002%, and the tensile stress reached 0.32 MPa. The soil with 1 wt% water-retaining agent showed a 318.9% decrease in freezing point. After 30 minutes at -25°C, it retained 62.3% unfrozen water. After 16 water absorption-dehydration cycles, it had a water holding capacity of 139.8 g / g, and after 13 days, it contained 62.8% water content. With 4 wt% water-retaining agent added, the soil still released 1.97 g / kg of nitrogen slowly and controlled after six weeks, and after two months of plant growth, the soil still contained 1.13 g / kg of nitrogen.

[0080] As can be seen from the comparison between Example 1 and Comparative Example 2, compared with the single-structure network composed of potassium acrylate and acrylamide, the water-retaining agent of the present invention with covalently grafted hybrid rigid-flexible composite network structure has better mechanical properties, antifreeze properties and water retention.

[0081] A comparison of Example 1 and Comparative Example 1 shows that the introduction of polysaccharides effectively improves the mechanical properties, antifreeze properties, water retention, and sustained-release properties of the water-retaining agent. In particular, the addition of carboxymethyl guar gum solution significantly improves the tensile properties and antifreeze properties of the water-retaining agent.

[0082] The infrared spectra of the water-retaining agents prepared in Example 1 and Comparative Example 3 are shown below. Figure 1 As shown in the comparison between Example 1 and Comparative Example 3, the addition of urea effectively improves the mechanical properties, water absorption and antifreeze properties of the water-retaining agent, and provides it with a stable nitrogen source.

[0083] The comparison between Example 1 and Comparative Examples 1 and 3 shows that, compared with adding only urea or polysaccharides, the combination of urea and carboxymethyl guar gum can better improve the mechanical properties, antifreeze properties and water retention of the water-retaining agent.

[0084] As can be seen from the comparison between Example 1 and Comparative Examples 4-7, the urea content affects the network structure and sustained-release performance of the water-retaining agent.

[0085] The water absorption rates of the highly absorbent antifreeze agents with urea slow-release function in Examples 1-3 and Comparative Examples 1-3 are shown in the figures. Figure 2 As shown, tensile strength is... Figure 3 As shown. The water-holding effect of the water-retaining agents obtained in Example 1 and Comparative Examples 4-7 after being mixed with soil is shown in the figure. Figure 4 As shown, the water retention effect is as follows: Figure 5 As shown, the water retention effect of the circulation is... Figure 6 As shown, the antifreeze effect is... Figure 7 As shown. The sustained-release effects of Example 1 and Comparative Examples 4-7 are as follows. Figure 8 As shown.

[0086] In summary, urea acts as both a nitrogen source and a green cross-linking agent in the water-retaining agent system. Under the action of a catalyst, the amino groups in urea react with the carboxyl groups in acrylic acid and polysaccharides, with some urea grafted into the polymer network. Due to its bifunctional structure, the remaining urea acts as a cross-linking agent, connecting the polymer chains. Unreacted urea adheres through hydrogen bonds or is stored in a free state within the water-retaining agent. In the initial stages of practical application, the uncross-linked urea in the water-retaining agent will first hydrolyze into usable nitrogen, dissolving into water and slowly leaching out through the pores within the agent. This is because the network contains abundant -COO groups. - The presence of polar groups such as -CONH2 and -OH enhances the material's ability to bind urea within the pores, thus extending the fertilizer's slow-release period. As time progresses, the polysaccharide network gradually degrades, releasing urea molecules grafted onto it and further prolonging the slow-release period. Simultaneously, the abundant -COO groups in the water-retaining agent network... - The strong adsorption of water molecules by strong hydrophilic groups such as -CONH2 and -OH gives it high water absorption and excellent water retention. Free urea molecules dissolved in aqueous solution disrupt the regular hydrogen bond network between water molecules, inhibiting ice nucleus formation. Furthermore, the abundant and dense hydrophilic groups in the water-retaining agent network can firmly bind water molecules through hydrogen bonds, forming a large amount of bound water. The increased non-freezing water content further enhances its antifreeze properties. Increased urea content increases the crosslinking density between polymer chains, making the network structure more compact and forming tiny pores within the water-retaining agent, dividing the water body into countless nanoscale microregions, further restricting the flow of water molecules and the extension of ice nuclei, inhibiting the formation of large-area ice nuclei. Through the synergistic effect of these multiple aspects, the water-retaining agent possesses excellent antifreeze properties. Based on these structural advantages, this invention patents the preparation of a water-retaining agent with excellent water absorption, cycle stability, soil antifreeze properties, and slow-release performance, providing a guarantee for the normal growth of crops in harsh environments such as cold, drought, and poor soil.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a highly absorbent antifreeze agent with urea slow-release function, characterized in that, include: Acrylates, acrylamide, polysaccharide solution, and urea are mixed evenly in a solvent, and photopolymerization is carried out in the presence of a crosslinking agent, a photoinitiator, and a catalyst to obtain a highly absorbent antifreeze water-retaining agent. The molar ratio of acrylate to urea is 1:(0.02-0.26).

2. The preparation method of the highly absorbent antifreeze agent with urea slow-release function as described in claim 1, characterized in that, The molar ratio of the acrylate to the acrylamide is 1:(0.1~1).

3. The preparation method of the highly absorbent antifreeze agent with urea slow-release function as described in claim 1, characterized in that, The acrylate is potassium acrylate.

4. The preparation method of the highly absorbent antifreeze agent with urea slow-release function as described in claim 1, characterized in that, The mass ratio of the polysaccharide solution to urea is (5-12):1 or (5.14-10.28):0.9; Alternatively, the concentration of the polysaccharide solution is 1–20 wt%.

5. The preparation method of the highly absorbent antifreeze agent with urea slow-release function as described in claim 1, characterized in that, The polysaccharide solution is selected from one of carboxymethyl guar gum, carboxymethyl chitosan, potassium carboxymethyl cellulose, and sodium alginate.

6. The preparation method of the highly absorbent antifreeze agent with urea slow-release function as described in claim 1, characterized in that, The crosslinking agent is selected from at least one of N,N′-methylenebisacrylamide, N,N′-(1,2-dihydroxyethylidene)bisacrylamide, and polyethylene glycol diacrylate; Alternatively, the amount of the crosslinking agent is 0.01 to 0.05 wt% of the total mass of acrylate and acrylamide; Alternatively, the catalyst is selected from at least one of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide; Alternatively, the catalyst may be 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide or N-hydroxysuccinimide, wherein the molar ratio of acrylic acid to 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide or N-hydroxysuccinimide is 2:(0.5-1.5):(0-1.5).

7. The preparation method of the highly absorbent antifreeze agent with urea slow-release function as described in claim 1, characterized in that, The photoinitiator is selected from one of 2-hydroxy-4'-(2-hydroxyethylamino)-2-methylphenylacetone, 2,2-azobis(2-methylpropylimidazolium) hydrochloride, and 2,4,6-trimethylbenzoylphenyl phosphate ethyl ester; Alternatively, the amount of photoinitiator used is 0.8 to 1.2 wt% of the total mass of acrylate and acrylamide.

8. The preparation method of the highly absorbent antifreeze agent with urea slow-release function as described in claim 1, characterized in that, The conditions for the photopolymerization reaction are: UV lamp power of 1-5KW and wavelength of 365nm; Alternatively, the photopolymerization reaction time is 15–30 min.

9. A highly absorbent antifreeze agent with urea slow-release function prepared by the method according to any one of claims 1-8.

10. The application of the highly absorbent antifreeze and water-retaining agent with urea slow-release function as described in claim 9 in the agricultural field.

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