Composite water-retaining material suitable for coral sand and preparation method and use method thereof

Abstract

The application discloses a kind of composite water-retaining materials suitable for coral sandy soil and preparation method and use method thereof, the preparation method includes: accurately taking the following components by mass fraction: polyvinyl alcohol 2~20 parts; Water 50~200 parts; Pore filler 5~30 parts; Crosslinking agent 1~30 parts; Catalyst 5~30 parts; Foaming agent 1~15 parts; Superabsorbent polymer 10~30 parts; Polyvinyl alcohol and water are mixed, dissolved in 40~100 DEG C water bath for 1~4h, to obtain polyvinyl alcohol aqueous solution; Pore filler, crosslinking agent, catalyst and foaming agent are added to polyvinyl alcohol aqueous solution, after stirring evenly, high water-absorbent resin is added to the reaction system, and stirring is made to be uniformly dispersed in the reaction system; The reaction system is placed in the oven at 30~80 DEG C and cured for 1~8h, to obtain the composite water-retaining material. The composite water-retaining material obtained by the preparation method has the performance of fast absorption of rain and slow release in drought, and also has good anti-rainstorm impact performance, which can effectively avoid being washed away.

Description

Technical Field

[0001] This invention belongs to the field of water-retaining materials technology, and relates to functional polymer water-retaining materials, particularly to a composite water-retaining material suitable for coral sand and its preparation and application methods. Background Technology

[0002] Coral islands are an important part of my country's marine environment, representing a unique combination of marine resources and environment, and a special area for economic and social development, possessing significant resource value and strategic importance. Located in the tropics, coral islands experience an average annual temperature exceeding 27°C, resulting in high evaporation rates. Furthermore, the soil on coral islands is primarily obtained through coral sand reclamation. Coral sand soil exhibits uneven particle size distribution, loose structure, and high porosity, leading to weak water retention and soil conservation capabilities. This necessitates substantial water resources for soil fertilization and vegetation cultivation. However, the unique geographical location of coral islands limits their freshwater reserves.

[0003] Currently, the freshwater resources of coral islands mainly rely on rainwater storage. While these resources are abundant during the rainy season, they suffer from a shortage during the dry season, making it difficult to obtain sufficient freshwater for irrigation of the islands' green spaces. This results in a severe water shortage for irrigation, and the consistently high temperatures cause massive soil moisture evaporation, leading to widespread plant death and hindering the progress of island greening. Therefore, it is particularly necessary to develop water-retaining materials suitable for coral sand soil, taking into account the environmental characteristics of coral islands.

[0004] Currently, superabsorbent polymers (SAPs) commonly used for soil improvement, such as polyacrylamide superabsorbent polymers (PAPs) and polyacrylate superabsorbent polymers (PAPs), have high water absorption capacity but slow surface water absorption. Therefore, they are mostly used in powder form. However, the coral sand soil in the South China Sea coral islands has a loose structure and high porosity, making it difficult to effectively retain powdered SAPs for a long time. Furthermore, the rainfall in coral islands is mainly short-duration, heavy rainstorms, which are intense and rapid, easily washing away the powdered SAPs. Block SAPs can avoid being washed away, but their water absorption rate is slow, making it difficult to quickly absorb water to supply the needs of plants during the dry season. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a composite water-retaining material suitable for coral sand, as well as its preparation method and application method. The composite water-retaining material obtained by this preparation method has the properties of rapid absorption of rainfall and slow release during drought, and at the same time has good resistance to rainstorm impact, which can effectively prevent it from being washed away.

[0006] The technical solution of this invention is implemented as follows:

[0007] A method for preparing a composite water-retaining material suitable for coral sand includes the following steps:

[0008] (1) Weigh the following components by mass: 2-20 parts of polyvinyl alcohol; 50-200 parts of water; 5-30 parts of pore filler; 1-30 parts of crosslinking agent; 5-30 parts of catalyst; 1-15 parts of foaming agent; 10-30 parts of superabsorbent resin;

[0009] (2) Mix polyvinyl alcohol and water, and dissolve them in a water bath at 40-100°C for 1-4 hours to obtain a polyvinyl alcohol aqueous solution;

[0010] (3) Add pore filler, crosslinking agent, catalyst and foaming agent to polyvinyl alcohol aqueous solution, stir and mix well, then add super absorbent resin to the reaction system and stir to make it evenly dispersed in the reaction system.

[0011] (4) Place the reaction system in an oven at 30-80°C for 1-8 hours to cure the reaction, and the composite water-retaining material can be obtained.

[0012] Furthermore, the polyvinyl alcohol is one or more of the following types: 124, 1788, 1795, 1797, 1799, 2088, 2099, and 2499.

[0013] Furthermore, the pore-filling agent is one or more of calcium carbonate, soluble starch, dextrin, sepiolite powder, silica, attapulgite, bentonite, and montmorillonite.

[0014] Further, the crosslinking agent is one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, and glyoxal; the catalyst is one or more of hydrochloric acid, sulfuric acid, nitric acid, glacial acetic acid, citric acid, oxalic acid, and lactic acid.

[0015] Furthermore, the foaming agent is one or more selected from sodium carbonate, sodium bicarbonate, pentane, hexane, heptane, dichloromethane, and azodicarbonamide.

[0016] Further, the superabsorbent resin is one or more of polyacrylamide superabsorbent resin, polyacrylate superabsorbent resin, acrylamide-acrylate superabsorbent resin, and humic acid superabsorbent resin, wherein the particle size of the superabsorbent resin is 0.05-1 mm.

[0017] Furthermore, the preparation method of the polyacrylamide superabsorbent resin is as follows:

[0018] (1) Weigh the following components by mass: 3-15 parts acrylamide, 0.05-0.5 parts N,N-methylenebisacryloyl, 0.1-1 parts sodium carboxymethyl cellulose, and 0.01-0.1 parts potassium persulfate;

[0019] (2) Acrylamide and N,N-methylenebisacrylamide are dissolved in 5 to 10 parts of water respectively to prepare aqueous solutions of acrylamide and N,N-methylenebisacrylamide.

[0020] (3) Add 40-90 parts of water to sodium carboxymethyl cellulose and stir magnetically at 25-70°C until completely dissolved. Then add 5-10 parts of water to dissolve potassium persulfate to obtain potassium persulfate aqueous solution. Stir at constant temperature for 5-30 minutes, then add acrylamide aqueous solution and N,N-methylenebisacrylamide aqueous solution and react for 1-5 hours. Then take it out, wash, dry and crush it to obtain polyacrylamide superabsorbent resin.

[0021] Furthermore, the preparation method of polyacrylate superabsorbent resin is as follows:

[0022] (1) Weigh the following components by mass: 1-15 parts acrylic acid, 0.005-0.05 parts N,N-methylenebisacryloyl, 0.5-5 parts sodium carboxymethyl cellulose, 1-5 parts sodium hydroxide, and 0.01-1 parts potassium persulfate;

[0023] (2) Acrylic acid was neutralized with 5-10 parts of water to obtain an aqueous solution of sodium hydroxide to obtain a monomer aqueous solution under an ice-water bath;

[0024] (3) Add 40-90 parts of water to sodium carboxymethyl cellulose, stir and dissolve at 30-80°C, then add monomer aqueous solution, N,N-methylenebisacrylamide and potassium persulfate and react for 1-6 hours. Then take it out, wash, dry and crush it to obtain polyacrylate superabsorbent resin.

[0025] Furthermore, the preparation method of acrylamide-acrylate superabsorbent resin is as follows:

[0026] (1) Weigh the following components by mass: 1-15 parts acrylic acid, 1-5 parts acrylamide, 0.001-0.01 parts N,N-methylenebisacryloyl, 0.1-1 parts sodium carboxymethyl cellulose, 1-5 parts sodium hydroxide, and 0.01-0.1 parts potassium persulfate;

[0027] (2) The acrylic acid was neutralized with 5-10 parts of water to dissolve sodium hydroxide in an ice-water bath to prepare an aqueous solution of sodium hydroxide, and then acrylamide and N,N-methylenebisacrylamide were added to prepare a monomer aqueous solution.

[0028] (3) Add 40-80 parts of water to sodium carboxymethyl cellulose and stir to dissolve in a water bath at 40-90℃. Then add 5-10 parts of water to dissolve potassium persulfate to obtain potassium persulfate aqueous solution. Stir at constant temperature for 5-60 minutes, then add monomer aqueous solution and stir at constant temperature for 1-4 hours. Then take it out, wash, dry and crush it to obtain acrylamide-acrylate superabsorbent resin.

[0029] Furthermore, the preparation method of humic acid superabsorbent resin is as follows:

[0030] (1) Weigh the following components by mass: 0.5-5 parts of humic acid, 1-15 parts of acrylic acid, 1-5 parts of acrylamide, 0.001-0.01 parts of N,N-methylenebisacryloyl, 0.1-1 parts of sodium carboxymethyl cellulose, 1-5 parts of sodium hydroxide, and 0.01-0.1 parts of potassium persulfate.

[0031] (2) The acrylic acid was neutralized with 5-10 parts of water to dissolve sodium hydroxide in an ice-water bath to prepare an aqueous solution of sodium hydroxide, and then humic acid, acrylamide, and N,N-methylenebisacrylamide were added to prepare a monomer aqueous solution.

[0032] (3) Add 40-80 parts of water to sodium carboxymethyl cellulose and stir to dissolve in a water bath at 40-90°C. Then add 5-10 parts of water to dissolve potassium persulfate to obtain potassium persulfate aqueous solution. Stir at constant temperature for 5-60 minutes, then add monomer aqueous solution and stir at constant temperature for 1-4 hours. Then take it out, wash, dry and crush it to obtain humic acid superabsorbent resin.

[0033] Furthermore, the stirring is mechanical stirring at a speed of 300–800 rpm. Studies have found that stirring at 300–800 rpm is beneficial for the cross-linking reaction, thereby promoting the formation of the network structure of the composite water-retaining material. However, excessively high or low stirring speeds are detrimental to the cross-linking reaction.

[0034] The present invention also provides a composite water-retaining material suitable for coral sand, which is prepared according to the preparation method described above.

[0035] The aforementioned method of using a composite water-retaining material suitable for coral sand includes at least the following three methods:

[0036] Method 1: Mix the composite water-retaining material with coral sand before sowing the plants.

[0037] Method 2: Before sowing the plants, apply the composite water-retaining material in trenches into the coral sand.

[0038] Method 3: During plant growth, apply composite water-retaining material in holes in the coral sand soil around the plant roots.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The composite water-retaining material of this invention uses polyvinyl alcohol (PVA) sponge as a skeleton, with superabsorbent polymer (SAP) loaded on the PVA sponge (most of it loaded inside the PVA sponge, with only a small portion loaded on the surface), making the composite water-retaining material a two-dimensional network water-retaining material. The composite water-retaining material retains the microporous structure of the PVA sponge, enabling rapid water absorption. Water is transferred through the sponge's micropores to the internal SAP secondary network, further increasing the water absorption capacity of the composite water-retaining material and ensuring its rapid water absorption performance. After water absorption, the water is mainly retained in the SAP secondary network structure. Under dry conditions, the external PVA sponge skeleton reduces the exposure of the internal SAP, hindering water release. Therefore, the composite water-retaining material has both rapid absorption and slow release properties.

[0041] 2. Traditional water-retaining materials, such as powdered superabsorbent polymers (SAPs), are water-absorbing and swelling materials. When dry, they are applied to the soil as powder and swell into lumps after absorbing water. These materials are effective in loam and clay soils. However, coral sand soils have large pores, and regional rainfall is often in the form of torrential downpours, making it easy for the SAPs to be washed away before they can swell. The composite water-retaining material of this invention constructs a constrained sponge network framework on the outer layer of the SAPs. This framework does not swell after absorbing water. When prepared as granules (with particle size larger than the pores of coral sand) and applied, it is not easily washed away even in heavy rain.

[0042] 3. Traditional water-retaining materials, such as superabsorbent resins, rely on osmotic pressure differences to absorb water. After the material absorbs water and swells, the ion concentration inside the network decreases, leading to a decrease in osmotic pressure and poor salt resistance. In contrast, the composite water-retaining material of this invention constructs a constrained polyvinyl alcohol sponge network framework on the outer layer of the superabsorbent resin (the osmotic pressure of the superabsorbent resin is higher than that of the polyvinyl alcohol sponge). The internal superabsorbent resin can only swell to a limited extent, the ion concentration inside the network is stable, and the osmotic pressure changes are small, thus exhibiting excellent salt resistance. Attached Figure Description

[0043] Figure 1 - Electron micrographs of acrylamide-acrylate superabsorbent resin, polyvinyl alcohol sponge, and composite water-retaining material prepared in Example 1.

[0044] Figure 2 - A simulation diagram of the composite water-retaining material prepared in Example 1.

[0045] Figure 3 The water absorption ratio of the acrylamide-acrylate superabsorbent resin, polyvinyl alcohol sponge and composite water-retaining material prepared in Example 1 changes over time.

[0046] Figure 4 -Water retention capacity curves of acrylamide-acrylate superabsorbent resin, polyvinyl alcohol sponge and composite water-retaining material prepared in Example 1 in vacuum.

[0047] Figure 5 - The repeated water absorption performance of the composite water-retaining material prepared in Example 1.

[0048] Figure 6 - Salt resistance of the composite water-retaining material prepared in Example 1.

[0049] Figure 7 - Macroscopic morphology diagrams of the composite water-retaining materials obtained in Examples 1 to 3 and Comparative Example 1 after water absorption. Detailed Implementation

[0050] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0051] Example 1

[0052] (1) Weigh 7.5g of acrylic acid and neutralize it with a sodium hydroxide solution obtained by dissolving 3g of sodium hydroxide in 10mL of water under an ice-water bath. Then, weigh 2.5g of acrylamide and 0.0035g of N,N-methylenebisacrylamide to prepare a monomer aqueous solution. Separately, weigh 0.5g of sodium carboxymethyl cellulose, add 40mL of water, and stir to dissolve in a 70℃ water bath. After it is completely dissolved, add 5mL of water to dissolve 0.05g of potassium persulfate to obtain a potassium persulfate aqueous solution. Stir at a constant temperature for 20min, then add the monomer aqueous solution. Stir at a constant temperature for 2h, remove, wash, dry, and crush to obtain acrylamide-acrylate superabsorbent resin.

[0053] (2) Weigh 12g of polyvinyl alcohol 1799, 3g of polyvinyl alcohol 1788 and 105g of water according to the weight ratio and put them into the reactor. Heat in a water bath at 80°C for 2 hours to obtain a polyvinyl alcohol aqueous solution.

[0054] (3) Take the polyvinyl alcohol aqueous solution from step (2), and take 20g of pore-filling agent (soluble starch), 20g of crosslinking agent (formaldehyde solution), 20g of catalyst (sulfuric acid), 8g of foaming agent (pentane), and 30g of acrylamide-acrylate superabsorbent resin prepared in step (1) according to the weight ratio. Stir at 350rpm for 10min, and place in a 50℃ oven to cure for 2h to obtain composite water-retaining material.

[0055] Polyvinyl alcohol (PVA) sponge was prepared according to steps (2) and (3) of this embodiment. Specifically, 12g of PVA 1799, 3g of PVA 1788, and 105g of water were weighed into a reactor and heated in a water bath at 80°C for 2 hours to obtain an aqueous PVA solution. Then, 20g of pore-filling agent (soluble starch), 20g of crosslinking agent (formaldehyde solution), 20g of catalyst (sulfuric acid), and 8g of foaming agent (pentane) were weighed into the PVA solution and stirred at 350 rpm for 10 minutes. The mixture was then placed in a 50°C oven for curing reaction for 2 hours to obtain the PVA sponge.

[0056] 1. Figure 1 These are electron microscope images of the acrylamide-acrylate superabsorbent resin, polyvinyl alcohol sponge, and composite water-retaining material prepared in this embodiment. Figure 1 Image (a) is an electron microscope image of acrylamide-acrylate superabsorbent polymer. Figure 1 Image (b) is an electron microscope image of polyvinyl alcohol sponge. Figure 1 (c) is an electron microscope image of the composite water-retaining material prepared in this embodiment. Figure 1 (a) As can be seen, acrylamide-acrylate superabsorbent polymers possess a large number of pores ranging from nanometers to micrometers. This microporous structure can accelerate the diffusion of water into the network structure, thereby improving the water absorption capacity of acrylamide-acrylate superabsorbent polymers. Figure 1 (b) As can be seen, polyvinyl alcohol sponge exhibits a rough surface and an interconnected pore structure, with pore sizes ranging from a few micrometers to 100 micrometers. The presence of pores facilitates water entry into the network, enabling rapid water absorption. In composite water-retaining materials ( Figure 1 (c)) granular acrylamide-acrylate superabsorbent resin is attached to the three-dimensional network skeleton of polyvinyl alcohol sponge, so that the composite water-retaining material has two network and pore structures.

[0057] 2. A simulation diagram of the composite water-retaining material prepared in this embodiment is shown below. Figure 2 As shown, acrylamide-acrylate superabsorbent polymer (SAP) is loaded onto polyvinyl alcohol (PVA) sponge to form a composite water-retaining material. The SAP is a three-dimensional network structure formed by cross-linking copolymer chains of acrylamide and acrylic acid with sodium carboxymethyl cellulose chains.

[0058] 3. The water absorption rate of the acrylamide-acrylate superabsorbent resin, polyvinyl alcohol sponge and composite water-retaining material prepared in this embodiment was studied by gravimetric method.

[0059] The specific method is as follows: Immerse the dried sample in 1000 mL of distilled water at room temperature, and measure the water absorption ratio of the sample at different time intervals (5, 10, 20, 30, 40, 50, 60 minutes) to obtain a curve of water absorption ratio over time. The water absorption ratio (g / g) is calculated using formula (1):

[0060]

[0061] Q eq The water absorption ratio is expressed in g / g; M0 and M1 are the weights of the dry sample and the swollen sample, respectively.

[0062] The water absorption ratios of the composite water-retaining material, acrylamide-acrylate superabsorbent resin, and polyvinyl alcohol sponge prepared in this embodiment change over time, as shown in the curves below. Figure 3 As shown in the figure, polyvinyl alcohol (PVA) sponge can absorb water to saturation within 5 minutes, but its water absorption capacity is only 11.73 g / g. Acrylamide-acrylate superabsorbent polymer (CARP) only reaches a water absorption ratio of 12.60 g / g after 60 minutes, comparable to PVA sponge. For composite water-retaining materials, the water absorption rate at 60 minutes is 26.45 g / g, more than twice that of both CARP and PVA sponge.

[0063] 4. The water release performance of the acrylamide-acrylate superabsorbent resin, polyvinyl alcohol sponge and composite water-retaining material prepared in this embodiment was tested. The water release performance reflects the speed at which the material releases water under certain conditions. The slower the water release, the stronger the hydrophilicity and water-locking ability of the material.

[0064] The specific method is as follows: Weigh a certain mass of the sample after it has fully absorbed water, place it in a 3H-2000 type steam adsorption instrument, set the temperature, and perform vacuum degassing. The instrument will record the remaining mass at each moment, calculate the water retention rate, and plot the water retention rate against time to obtain the material's water release curve. The water retention rate is calculated using formula (2):

[0065]

[0066] In the formula, M represents the water retention rate, in percentages.

[0067] M2—Saturated water absorption of the material, g / g;

[0068] M t — The amount of water absorbed by the material at time t, in g / g.

[0069] The water retention capacity curves of the composite water-retaining material, acrylamide-acrylate superabsorbent resin, and polyvinyl alcohol sponge prepared in this embodiment in a vacuum are shown below. Figure 4As shown in the figure, polyvinyl alcohol sponge releases water the fastest, followed by acrylamide-acrylate superabsorbent resin, while the composite water-retaining material releases water the slowest, indicating that the composite water-retaining material has the strongest water retention capacity.

[0070] 5. The repeated water absorption capacity of the composite water-retaining material prepared in this embodiment was tested.

[0071] The specific method is as follows: Soak the composite water-retaining material in distilled water until it reaches water absorption equilibrium, then dry it completely in an oven at 50°C. Repeat this process 10 times. The repeated water absorption efficiency is calculated using formula (3):

[0072]

[0073] In the formula, G is the repeated water absorption efficiency, in percentages.

[0074] X e —The water absorption ratio of the material during the e-th water absorption, in g / g;

[0075] X0 — The water absorption ratio of the material in the first water absorption, in g / g.

[0076] The repeated water absorption performance curve of the composite water-retaining material prepared in this embodiment is shown in the figure below. Figure 5 As shown in the figure, the water absorption capacity of the composite water-retaining material after the 10th repetition is still equivalent to 81.4% of that after the 1st repetition, indicating that the composite water-retaining material has good repeated water absorption performance.

[0077] 6. The salt resistance of the composite water-retaining material prepared in this embodiment was tested.

[0078] The specific method is as follows: The dried composite water-retaining material is immersed in 0.9 wt% aqueous solutions of NH4Cl, KCl, NaCl, MgCl2, CaCl2, and FeCl3 for 24 hours at room temperature to achieve swelling equilibrium. The swollen sample is then filtered through a 100-mesh nylon screen until no water droplets fall, and then weighed. The calculation method is the same as for the water absorption ratio.

[0079] The salt resistance of the composite water-retaining material prepared in this embodiment is as follows: Figure 6 As shown, by Figure 6 It can be seen that the water absorption rates in monovalent ion solutions of NH4Cl, KCl, NaCl, MgCl2, CaCl2 and FeCl3 are 29.44, 30.29, 29.52, 19.12, 18.93 and 17.23 g / g, respectively.

[0080] 7. The composite water-retaining material prepared in this embodiment is added to the coral sand at a ratio of 2% (calculated by the mass of the air-dried coral sand) to obtain improved soil. Then, a weight of improved soil, W1, is weighed and filled into the flowerpot at a medium depth. The flowerpot is then subjected to 1 hour of rainfall with a rainfall intensity of 40 mm under the action of a peristaltic pump. After the simulated rainfall is terminated, the flowerpot is left to stand for 24 hours to drain excess gravity water to obtain the soil's rainfall interception. The flowerpot is then weighed (wet soil mass, W2). The soil moisture content is calculated using formula (4):

[0081]

[0082] In the formula: X—soil moisture content, %;

[0083] W1 — Dry soil mass, g;

[0084] W2 — Mass of wet soil, g.

[0085] The water content after continuous evaporation and loss of soil moisture is still calculated by formula (4). At this time, W2 is the mass of the soil with real-time water content.

[0086] Method for calculating water loss ratio: The soil moisture content X1 after simulated rainfall (drainage of excess gravity water) and the soil moisture content X2 after 15 days of evaporation loss were measured. The water loss ratio was calculated using formula (5):

[0087]

[0088] Where: X — water loss rate, %;

[0089] X1—Soil moisture content on day 0, %;

[0090] X2 – Soil moisture content on day 15, %.

[0091] Measurements revealed that compared to coral sand without composite water-retaining materials, the soil moisture content increased from 13.8% to 23.6% (a 1.78-fold increase). After 15 days of continuous evaporation and loss of water, the soil moisture content remained at 13.0%, compared to the moisture content of coral sand without composite water-retaining materials (0.36%), indicating a 52.5% reduction in water loss.

[0092] Example 2

[0093] The acrylamide-acrylate superabsorbent polymer added in Example 1 was replaced with commercially available acrylamide-acrylate superabsorbent polymer (HD188), and the other steps were the same as in Example 1, to prepare a composite water-retaining material.

[0094] The composite water-retaining material prepared in Example 2 was added to coral sand at a ratio of 1% (calculated by the mass of air-dried coral sand) to obtain improved soil. The operation steps for measuring the moisture content in Example 1 were repeated. Measurements showed that compared to coral sand without the composite water-retaining material, the soil moisture content increased by 1.5 times. After 15 days of continuous water evaporation and loss, the water loss ratio decreased by 42.1% compared to coral sand without the composite water-retaining material.

[0095] Example 3

[0096] (1) Same as step (1) in Example 1.

[0097] (2) Weigh 10g of polyvinyl alcohol 124, 5g of polyvinyl alcohol 1788 and 105g of water respectively and put them into the reactor. Heat in a water bath at 90°C for 1 hour to obtain a polyvinyl alcohol aqueous solution.

[0098] (3) Take the above polyvinyl alcohol aqueous solution, weigh 10g of pore filler (dextrin), 3g of crosslinking agent (propionaldehyde solution), 6g of catalyst (hydrochloric acid), 4g of foaming agent (sodium bicarbonate), and 10g of superabsorbent resin obtained in step (1) according to the weight parts, stir at 450rpm for 30min, put it in a 70℃ oven to cure and react for 4h to obtain composite water-retaining material.

[0099] The composite water-retaining material prepared in this embodiment was added to coral sand at a ratio of 1% (calculated by the mass of air-dried coral sand) to obtain improved soil. The operation steps for measuring the moisture content in Example 1 were repeated. Measurements showed that compared to coral sand without the composite water-retaining material, the soil moisture content increased by 1.41 times. After 15 days of continuous water evaporation and loss, the water loss ratio decreased by 37.7% compared to coral sand without the composite water-retaining material.

[0100] Example 4

[0101] The acrylamide-acrylate superabsorbent resin added in Example 3 was replaced with commercially available acrylamide-acrylate superabsorbent resin and polyacrylate superabsorbent resin (1:1), and the other steps were the same as in Example 3, to prepare a composite water-retaining material.

[0102] The composite water-retaining material prepared in this embodiment was added to coral sand at a ratio of 2% (calculated by the mass of air-dried coral sand) to obtain improved soil. The operation steps for measuring the moisture content in Example 1 were repeated. The measurements showed that compared with the coral sand without the composite water-retaining material, the soil moisture content increased by 1.65 times. After 15 days of continuous water evaporation and loss, the water loss ratio decreased by 49.3% compared with the coral sand without the composite water-retaining material.

[0103] Example 5

[0104] (1) Weigh 5g of acrylic acid and dissolve 1.5g of sodium hydroxide in 5mL of water under ice water bath to obtain sodium hydroxide aqueous solution as monomer aqueous solution. Weigh 1g of sodium carboxymethyl cellulose, add 80mL of water, stir and dissolve at 60℃, then add monomer aqueous solution, 0.01g of crosslinking agent N,N-methylenebisacrylamide and 0.1g of initiator potassium persulfate respectively. After reacting for 3h, take out, wash, dry and crush to obtain superabsorbent resin.

[0105] (2) Weigh 4g of polyvinyl alcohol 2088, 4g of polyvinyl alcohol 2099, 4g of polyvinyl alcohol 2499 and 80g of water respectively and put them into a reactor and heat them in a water bath at 75°C for 2.5h to obtain a polyvinyl alcohol aqueous solution.

[0106] (3) Take the above polyvinyl alcohol aqueous solution, add 8g of pore filler (montmorillonite), 5g of crosslinking agent (formaldehyde: acetaldehyde: propionaldehyde = 1:1:1 mixture), 10g of catalyst (glacial acetic acid), 7g of foaming agent (sodium bicarbonate), and 15g of superabsorbent resin (prepared in step (1)) by weight, stir at 750rpm for 15min, and place in a 65℃ oven to cure for 3h to obtain composite water-retaining material.

[0107] The composite water-retaining material prepared in this embodiment was added to coral sand at a ratio of 2% (calculated by the mass of air-dried coral sand) to obtain improved soil. The operation steps for measuring the moisture content in Example 1 were repeated. The measurement showed that the moisture content of the coral sand increased by 1.64 times. After 15 days of continuous water evaporation and loss, the water loss ratio was reduced by 46.9% compared with the coral sand without the addition of the composite water-retaining material.

[0108] Example 6

[0109] (1) Weigh 6g of acrylamide by weight and dissolve it in 30mL of water to prepare an acrylamide aqueous solution. Weigh 0.1g of N,N-methylenebisacrylamide by weight and dissolve it in 0.5mL of water to prepare an N,N-methylenebisacrylamide aqueous solution. Separately, weigh 0.5g of sodium carboxymethyl cellulose by weight and dissolve it in 40mL of water at 50℃. Add 0.5mL of water to dissolve 0.05g of potassium persulfate to obtain an aqueous solution. Stir at a constant temperature for 20min, then add the acrylamide aqueous solution and the N,N-methylenebisacrylamide aqueous solution and react for 2h. After that, remove the solution, wash, dry and crush it to obtain polyacrylamide superabsorbent resin.

[0110] (2) Weigh 15g of polyvinyl alcohol 1788 and 150g of water according to the weight ratio and put them into the reactor. Heat in a water bath at 75°C for 2 hours to obtain a polyvinyl alcohol aqueous solution.

[0111] (3) Take the above polyvinyl alcohol aqueous solution, add 6g of pore filler (attapulgite), 8g of crosslinking agent (glyoxal), 6g of catalyst (hydrochloric acid), 2g of foaming agent (pentane), and 15g of polyacrylamide superabsorbent resin prepared in step (1), stir at 500rpm for 20min, and place in a 50℃ oven to cure for 2h to obtain composite water-retaining material.

[0112] The composite water-retaining material prepared in this embodiment was added to coral sand at a ratio of 1% (calculated by the mass of air-dried coral sand) to obtain improved soil. The operation steps for measuring the moisture content in Example 1 were repeated. The measurements showed that the moisture content of the coral sand increased by 1.37 times. After 15 days of continuous water evaporation and loss, the water loss ratio was reduced by 40.6% compared with the control group without the composite water-retaining material.

[0113] Example 7

[0114] (1) Weigh 7.5g of acrylic acid and neutralize it with a sodium hydroxide solution obtained by dissolving 3g of sodium hydroxide in 10mL of water under an ice-water bath. Then, weigh 0.5g of humic acid, 2.5g of acrylamide, and 0.0035g of N,N-methylenebisacrylamide to prepare a monomer aqueous solution. Separately, weigh 0.5g of sodium carboxymethyl cellulose, add 40mL of water, and stir to dissolve in a 70℃ water bath. After complete dissolution, add 5mL of water to dissolve 0.05g of potassium persulfate to obtain a potassium persulfate aqueous solution. Stir at a constant temperature for 20min, then add the monomer aqueous solution. Stir at a constant temperature for 2h, remove, wash, dry, and crush to obtain humic acid superabsorbent resin.

[0115] (2) Weigh 15g of polyvinyl alcohol 124 and 150g of water respectively and put them into the reactor. Heat in a water bath at 85°C for 3 hours to obtain a polyvinyl alcohol aqueous solution.

[0116] (3) Take the above polyvinyl alcohol aqueous solution, weigh 15g of pore filler (calcium carbonate), 10g of crosslinking agent (phenylpropionaldehyde), 7.5g of catalyst (citric acid), 4.5g of foaming agent (pentane), and 16g of superabsorbent resin (the humic acid superabsorbent resin prepared in step (1) is mixed with commercially available polyacrylate superabsorbent resin in a mass ratio of 3:1), stir at 800rpm for 40min, and place in an 80℃ oven to cure for 6h to obtain a composite water-retaining material.

[0117] The composite water-retaining material prepared in this embodiment was added to coral sand at a ratio of 1% (calculated by the mass of air-dried coral sand) to obtain improved soil. The operation steps for measuring the moisture content in Example 1 were repeated. The measurement showed that the moisture content of the coral sand increased by 1.43 times. After 15 days of continuous water evaporation and loss, the water loss ratio was reduced by 42.7% compared with the coral sand without the addition of the composite water-retaining material.

[0118] Comparative Example 1

[0119] This embodiment is the same as embodiment 1, except that in step (3) of the synthesis of the composite water-retaining material in this embodiment, 36g of the acrylamide-acrylate superabsorbent resin prepared in step (1) is taken.

[0120] The macroscopic morphology of the composite water-retaining materials obtained in Examples 1-3 and Comparative Example 1 after water absorption is as follows: Figure 7 As shown, where Figure 7 (a) shows the morphology of the composite water-retaining material synthesized in Example 1 after water absorption. Figure 7 (b) shows the morphology of the composite water-retaining material synthesized in Example 2 after water absorption. Figure 7 (c) shows the morphology of the composite water-retaining material synthesized in Example 3 after water absorption. Figure 7 (d) shows the morphology of the composite water-retaining material synthesized in Comparative Example 1 after water absorption. As can be seen from the figure, the composite water-retaining material obtained in Comparative Example 1, due to the excessive loading of superabsorbent resin particles, caused excessive swelling and destruction of the polyvinyl alcohol sponge skeleton structure when the material absorbed water, resulting in the gradual disintegration of the composite water-retaining material and its inability to achieve repeated water absorption.

[0121] Finally, it should be noted that the above embodiments of the present invention are merely illustrative examples and not intended to limit the implementation of the invention. Those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for preparing a composite water-retaining material suitable for coral sand, characterized in that, It consists of the following steps: (1) Weigh the following components by mass: 2-20 parts of polyvinyl alcohol; 50-200 parts of water; 5-30 parts of pore filler; 1-30 parts of crosslinking agent; 5-30 parts of catalyst; 1-15 parts of foaming agent; 10-30 parts of superabsorbent resin; (2) Mix polyvinyl alcohol and water, and dissolve them in a water bath at 40~100 ℃ for 1~4 h to obtain a polyvinyl alcohol aqueous solution; (3) Add pore filler, crosslinking agent, catalyst and foaming agent to the polyvinyl alcohol aqueous solution, stir and mix well, then add super absorbent resin to the reaction system and stir to make it evenly dispersed in the reaction system; (4) The reaction system is placed in an oven at 30~80 ℃ for 1~8 h to cure and react, and the composite water-retaining material is obtained. The composite water-retaining material uses polyvinyl alcohol sponge as the skeleton and superabsorbent resin is loaded inside and on the surface of polyvinyl alcohol sponge.

2. The method for preparing a composite water-retaining material suitable for coral sand according to claim 1, characterized in that, The polyvinyl alcohol is one or more of the following types: 124, 1788, 1795, 1797, 1799, 2088, 2099, and 2499; The pore-filling agent is one or more of the following: calcium carbonate, soluble starch, dextrin, sepiolite powder, silica, attapulgite, bentonite, and montmorillonite. The crosslinking agent is one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, and glyoxal; the catalyst is one or more of hydrochloric acid, sulfuric acid, nitric acid, glacial acetic acid, citric acid, oxalic acid, and lactic acid. The foaming agent is one or more of sodium carbonate, sodium bicarbonate, pentane, hexane, heptane, dichloromethane, and azodicarbonamide.

3. The method for preparing a composite water-retaining material suitable for coral sand according to claim 1, characterized in that, The superabsorbent resin is one or more of polyacrylamide superabsorbent resin, polyacrylate superabsorbent resin, acrylamide-acrylate superabsorbent resin, and humic acid superabsorbent resin, wherein the particle size of the superabsorbent resin is 0.05~1 mm.

4. The method for preparing a composite water-retaining material suitable for coral sand according to claim 3, characterized in that, The preparation method of the polyacrylamide superabsorbent resin is as follows: Weigh the following components by weight: 3-15 parts acrylamide, 0.05-0.5 parts N,N-methylenebisacryloyl, 0.1-1 parts sodium carboxymethyl cellulose, and 0.01-0.1 parts potassium persulfate; Acrylamide and N,N-methylenebisacrylamide were dissolved in 5-10 parts of water to prepare aqueous solutions of acrylamide and N,N-methylenebisacrylamide, respectively. Add 40-90 parts of water to sodium carboxymethyl cellulose and stir magnetically at 25-70 °C until completely dissolved. Then add 5-10 parts of water to dissolve potassium persulfate to obtain a potassium persulfate aqueous solution. Stir at a constant temperature for 5-30 min, then add acrylamide aqueous solution and N,N-methylenebisacrylamide aqueous solution and react for 1-5 h. After that, remove the solution, wash, dry and crush it to obtain polyacrylamide superabsorbent resin.

5. The method for preparing a composite water-retaining material suitable for coral sand according to claim 3, characterized in that, The preparation method of polyacrylate superabsorbent resin is as follows: Weigh the following components by weight: 1-15 parts acrylic acid, 0.005-0.05 parts N,N-methylenebisacryloyl, 0.5-5 parts sodium carboxymethyl cellulose, 1-5 parts sodium hydroxide, and 0.01-1 parts potassium persulfate. Acrylic acid was neutralized with an aqueous solution of sodium hydroxide obtained by dissolving sodium hydroxide in 5-10 parts of water under an ice-water bath to obtain a monomer aqueous solution; Add 40-90 parts of water to sodium carboxymethyl cellulose and stir to dissolve at 30-80°C. Then add monomer aqueous solution, N,N-methylenebisacrylamide and potassium persulfate and react for 1-6 hours. After that, remove the solution, wash, dry and crush it to obtain polyacrylate superabsorbent resin.

6. The method for preparing a composite water-retaining material suitable for coral sand according to claim 3, characterized in that, The preparation method of acrylamide-acrylate superabsorbent resin is as follows: Weigh the following components by weight: 1-15 parts acrylic acid, 1-5 parts acrylamide, 0.001-0.01 parts N,N-methylenebisacryloyl, 0.1-1 parts sodium carboxymethyl cellulose, 1-5 parts sodium hydroxide, and 0.01-0.1 parts potassium persulfate. Acrylic acid was neutralized with an aqueous solution of sodium hydroxide prepared by dissolving sodium hydroxide in 5-10 parts of water under an ice-water bath, and then acrylamide and N,N-methylenebisacrylamide were added to prepare a monomer aqueous solution. Add 40-80 parts of water to sodium carboxymethyl cellulose and stir to dissolve it in a water bath at 40-90℃. Then add 5-10 parts of water to dissolve potassium persulfate to obtain an aqueous solution of potassium persulfate. Stir at a constant temperature for 5-60 minutes, then add the monomer aqueous solution and stir at a constant temperature for 1-4 hours. Then remove the solution, wash, dry and crush it to obtain acrylamide-acrylate superabsorbent resin.

7. The method for preparing a composite water-retaining material suitable for coral sand according to claim 3, characterized in that, The preparation method of humic acid superabsorbent resin is as follows: Weigh the following components by weight: 0.5-5 parts humic acid, 1-15 parts acrylic acid, 1-5 parts acrylamide, 0.001-0.01 parts N,N-methylenebisacryloyl, 0.1-1 parts sodium carboxymethyl cellulose, 1-5 parts sodium hydroxide, and 0.01-0.1 parts potassium persulfate. Acrylic acid was neutralized with sodium hydroxide aqueous solution prepared by dissolving sodium hydroxide in 5-10 parts of water under ice-water bath, and then humic acid, acrylamide, and N,N-methylenebisacrylamide were added to prepare monomer aqueous solution. Add 40-80 parts of water to sodium carboxymethyl cellulose and stir to dissolve it in a water bath at 40-90℃. Then add 5-10 parts of water to dissolve potassium persulfate to obtain a potassium persulfate aqueous solution. Stir at a constant temperature for 5-60 minutes, then add the monomer aqueous solution and stir at a constant temperature for 1-4 hours. Then remove the solution, wash, dry and crush it to obtain humic acid superabsorbent resin.

8. The method for preparing a composite water-retaining material suitable for coral sand according to claim 1, characterized in that, The stirring is mechanical stirring, with a stirring speed of 300~800 rpm.

9. A composite water-retaining material suitable for coral sand, characterized in that, Prepared according to any one of the preparation methods described in claims 1 to 8.

10. A method of using the composite water-retaining material suitable for coral sand as described in claim 9, comprising at least the following three methods: Method 1: Mix the composite water-retaining material with coral sand before sowing the plants; Method 2: Before sowing the plants, apply the composite water-retaining material in trenches into the coral sand soil; Method 3: During plant growth, apply composite water-retaining material in holes in the coral sand soil around the plant roots.

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