A laterite-based macromolecular composite water-absorbing material and a preparation method thereof

Abstract

The application discloses a kind of laterite-based polymer composite water-absorbing materials.The laterite-based polymer composite water-absorbing material is obtained by copolymerization and crosslinking of raw materials including acrylic acid monomer, acrylamide monomer, sodium humate and laterite, wherein the amount of acrylamide monomer is 10-25wt% of the acrylic acid monomer, the amount of sodium humate is 5-25wt% of the acrylic acid monomer, and the amount of laterite is 1-10wt% of the acrylic acid monomer.Compared with the prior art, the raw materials of the laterite-based polymer composite water-absorbing material of the application, sodium humate and laterite, are low in cost and easy to obtain, have better water absorption and salt resistance, can better improve the water retention capacity of soil, and can also improve the phosphorus content of soil, playing a role in improving soil.

Description

Technical Field

[0001] This invention belongs to the field of soil moisture retention, specifically relating to a red soil-based polymer composite water-absorbing material. Background Technology

[0002] Soil desertification severely hinders agricultural development, rapidly turning arable soils into sandy soils. Although some areas even use domestic water for irrigation to alleviate extreme droughts, most of the water is lost through evaporation from the soil surface, and vegetation absorbs very little water, which is also costly. Currently, a more feasible strategy is to apply water-absorbing and water-retaining materials.

[0003] Chinese patent CN1912007A discloses a humate-based composite water-retaining agent and its preparation method, specifically disclosing that: 20g of 40-60 mesh acrylic-acrylamide copolymer is mixed evenly with 10g of humate, and 60mL of an 80% acetone aqueous solution containing 0.06g of glycerol is added dropwise. The mixture is stirred evenly and then subjected to a surface crosslinking reaction in a vacuum drying oven at 80℃ for 40min to obtain the humate-based composite water-retaining agent. The swelling degree of this water-retaining agent in deionized water is 400~470g / g, and the swelling degree in 0.9% sodium chloride solution is 70~80g / g.

[0004] Chinese patent CN1699508A discloses a salt-alkali resistant multifunctional water-retaining agent and its preparation method. It uses taupe clay, starch, humic acid and acrylamide as the main raw materials of the composite water-retaining agent, adds initiator and crosslinking agent, and is made in aqueous solution through graft copolymerization, crosslinking, hydrolysis, washing, drying, pulverization and sieving. The composite water-retaining agent has an absorption capacity of 300-800 times the mass of distilled water and an absorption capacity of 50-80 times the mass of 0.9% NaCl solution.

[0005] Chinese patent CN103755897A discloses a method for preparing a palygorskite clay-based salt-resistant superabsorbent composite material. Specifically, in an aqueous solution system, palygorskite, 2-acrylamido-2-methylpropanesulfonic acid, and acrylic acid are used as raw materials, and N,N'-methylenebisacrylamide is used as a crosslinking agent. The mixture is stirred at 60-80℃ for 2-6 hours to form a gel-like crosslinking product. After cooling, the product is washed with water, dehydrated, dried, and pulverized to obtain the clay-based salt-resistant superabsorbent composite material. The water absorption ratio of this composite material in distilled water and 0.1 mol / L NaCl solution reaches 520-750 g / g and 76-83 g / g, respectively.

[0006] The aforementioned water-absorbing materials have a high water absorption rate in distilled water and sodium chloride solution, but there is still room for improvement. Moreover, their functions are relatively simple, limited to water absorption and retention. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a red soil-based polymer composite water-absorbing material, which has a higher water absorption rate in distilled water and 0.9% NaCl solution, and can also increase the phosphorus content in the soil.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A laterite-based polymer composite absorbent material is obtained by copolymerization and crosslinking of raw materials including acrylic acid monomers, acrylamide monomers, sodium humate and laterite, wherein the amount of acrylamide monomers is 10-25 wt% of acrylic acid monomers, the amount of sodium humate is 5-25 wt% of acrylic acid monomers, and the amount of laterite is 1-10 wt% of acrylic acid monomers.

[0010] Preferably, the acrylamide monomer is at least one selected from acrylamide, methacrylamide, N-hydroxyethylacrylamide, and 2-acrylamido-2-methylpropanesulfonic acid.

[0011] More preferably, the acrylamide monomer is a mixture of N-hydroxyethylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid in a mass ratio of 1:1.

[0012] Preferably, the amount of the acrylamide monomer is 14-15 wt% of the acrylic acid monomer.

[0013] Preferably, the amount of sodium humate used is 5-15 wt% of acrylic acid monomer, more preferably 10%.

[0014] Preferably, the amount of laterite used is 1-2 wt% of acrylic acid monomer.

[0015] The preparation method of the above-mentioned laterite-based polymer composite absorbent material includes the following steps:

[0016] (1) Adjust the neutralization degree of acrylic acid to 60-80%;

[0017] (2) After mixing acrylamide monomers, sodium humate and red clay in water, an initiator is added under an inert atmosphere and the reaction is carried out for a certain period of time. Then, neutralized acrylic acid and crosslinking agent are added and the reaction is continued to obtain the red clay-based polymer composite water-absorbing material.

[0018] Preferably, the initiator is potassium persulfate and / or ammonium persulfate.

[0019] Preferably, the amount of the initiator is 0.5 to 2 wt% of the acrylic monomer.

[0020] Preferably, the crosslinking agent is at least one of hydroxyethyl methacrylate, N-hydroxymethylacrylamide, diacetone acrylamide, and N,N-methylenebisacrylamide.

[0021] Preferably, the amount of the crosslinking agent is 0.05~0.2wt% of the acrylic monomer.

[0022] Preferably, the reaction temperature is 60~85℃.

[0023] The above-mentioned red soil-based polymer composite water-absorbing material is used to improve the water retention and / or phosphorus content of soil.

[0024] Compared with the prior art, the laterite-based polymer composite absorbent material of the present invention has the following beneficial effects:

[0025] 1. The raw materials, sodium humate and laterite, are inexpensive and readily available.

[0026] 2. It has a higher water absorption rate in distilled water and 0.9% sodium chloride solution.

[0027] 3. It can not only improve the soil's water retention capacity, but also increase the soil's phosphorus content, thus improving the soil. Attached Figure Description

[0028] Figure 1 Scanning electron microscope (SEM) of laterite-based polymer composite water-absorbing material.

[0029] Figure 2 The infrared spectrum of the laterite-based polymer composite absorbent material is shown, where curve a represents sodium humate, curve b represents laterite, and curve c represents the laterite-based polymer composite absorbent material.

[0030] Figure 3 The water absorption performance of laterite-based polymer composite absorbent materials with different sodium humate dosages in distilled water, tap water, and 0.9% NaCl solution was investigated.

[0031] Figure 4 The water absorption performance of laterite-based polymer composite absorbent materials with different amounts of laterite was investigated in distilled water, tap water, and 0.9% NaCl solution.

[0032] Figure 5 The repeated swelling performance of the red clay-based polymer composite absorbent material in distilled water.

[0033] Figure 6 The water absorption performance of red clay-based polymer composite absorbent materials in water at different pH values.

[0034] Figure 7 This is a comparison between red clay-based polymer composite absorbent materials and commercially available absorbent composite materials.

[0035] Figure 8 The change in phosphorus content in soil over time after the addition of red soil-based polymer composite water-absorbing material. Detailed Implementation

[0036] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0037] The laterite-based polymer composite absorbent material of this invention is obtained by copolymerization and crosslinking of raw materials including acrylic monomers, acrylamide monomers, sodium humate, and laterite. The specific operation process includes:

[0038] (1) Adjust the neutralization degree of acrylic acid to 60-80%;

[0039] (2) After mixing acrylamide monomers, sodium humate and red clay in water, an initiator is added under an inert atmosphere and the reaction is carried out for a certain period of time. Then, neutralized acrylic acid and crosslinking agent are added and the reaction is continued to obtain the red clay-based polymer composite water-absorbing material.

[0040] In some embodiments, the amount of the acrylamide monomer is controlled at 10-25 wt% of the acrylic acid monomer, specifically such as 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, or a range thereof.

[0041] In some embodiments, the acrylamide monomer is selected from at least one of acrylamide, methacrylamide, N-hydroxyethylacrylamide, and 2-acrylamido-2-methylpropanesulfonic acid.

[0042] In some embodiments, the acrylamide monomer is a mixture of N-hydroxyethylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid in a mass ratio of 1:1.

[0043] In some embodiments, the amount of sodium humate is controlled at 5 to 25 wt% of the acrylic acid monomer, specifically such as 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, or a range thereof.

[0044] In some embodiments, the amount of red clay is controlled at 1 to 10 wt% of the acrylic monomer, specifically such as 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or a range thereof.

[0045] There are no particular restrictions on red soil; it can be sourced locally.

[0046] In some embodiments, the particle size of the red clay can be controlled between 50 and 200 mesh, specifically such as 50 mesh, 80 mesh, 120 mesh, 150 mesh, and 200 mesh.

[0047] In some embodiments, acrylic acid is neutralized with sodium hydroxide. The degree of neutralization of acrylic acid is controlled to be 60-80%, specifically such as 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, or a range thereof.

[0048] In some embodiments, the initiator is selected from at least one of potassium persulfate and ammonium persulfate.

[0049] In some embodiments, the amount of the initiator is controlled at 0.5 to 2 wt% of the acrylic monomer, specifically such as 0.5 wt%, 0.75 wt%, 1 wt%, 1.25 wt%, 1.5 wt%, 1.75 wt%, 2 wt%, or a range thereof.

[0050] In some embodiments, the crosslinking agent is selected from at least one of hydroxyethyl methacrylate, N-hydroxymethylacrylamide, diacetone acrylamide, and N,N-methylenebisacrylamide.

[0051] In some embodiments, the amount of the crosslinking agent is 0.05 to 0.2 wt% of the acrylic monomer, specifically such as 0.05 wt%, 0.075 wt%, 0.1 wt%, 0.125 wt%, 0.15 wt%, 0.175 wt%, 0.2 wt%, or a range thereof.

[0052] In some embodiments, the temperature of the reaction is controlled at 60~85°C, specifically 60°C, 65°C, 70°C, 75°C, 80°C, or a range thereof.

[0053] In some embodiments, after the initiator is added, the reaction is allowed to proceed for 10 to 30 minutes, specifically 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or a range thereof.

[0054] In some embodiments, after the acrylic acid and crosslinking agent have been added, the reaction continues for 1 to 4 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 4 hours, or a range thereof.

[0055] Example 1

[0056] (1) Take red soil from the nearby area (Anning District, Lanzhou City, Gansu Province), remove small stones and coarse branches and leaves, break the large pieces of red soil and pass them through a 20-mesh sieve, then further crush them with a pulverizer and pass them through a 150-mesh sieve. Dry the obtained red soil in an oven at 100℃ for 24 hours for later use.

[0057] (2) Weigh 2.0g of sodium hydroxide and dissolve it in 6mL of distilled water under ice-water bath conditions. Then slowly add 5.4g of acrylic acid to the sodium hydroxide solution while stirring. A solution of acrylic acid with a neutralization degree of 65% is obtained and set aside.

[0058] (3) Dissolve 0.54g sodium humate, 0.1g red clay, and 0.8g acrylamide monomer (N-hydroxyethyl acrylamide and 2-acrylamido-2-methylpropanesulfonic acid mixed by mass) in 30mL of distilled water, then purge with nitrogen and stir at 180r / min for 1 hour in a constant temperature water bath at 65℃. Then add potassium persulfate initiator (0.08g) dissolved in 2mL of distilled water and react for 20 minutes. Then add acrylic acid solution and N,N'-methylenebisacrylamide crosslinking agent (0.01g) dissolved in 2mL of distilled water and continue to react for 2 hours.

[0059] (4) After the reaction is complete, the product is rinsed with distilled water and then soaked in anhydrous ethanol to remove unreacted impurities. Finally, it is dried in an oven at 70°C to obtain the red clay-based polymer composite water-absorbing material.

[0060] The preparation process for the blank sample is the same as above, except that sodium humate and laterite are not added.

[0061] The preparation process of control sample 1 is the same as above, except that no laterite was added.

[0062] The preparation process of control sample 2 is the same as above, except that sodium humate was not added.

[0063] Determination of water absorption ratio:

[0064] The conventional gravimetric method is used. The water absorption ratio is determined by measuring the change in weight of the material before and after water absorption. The specific formula is as follows:

[0065] Water absorption ratio = (m-m0) / m0, where m0 is the mass (g) before water absorption and m is the mass (g) after water absorption.

[0066] Determination of phosphorus content in soil:

[0067] The analysis and testing were performed using a fully automated discrete chemical analyzer, and the specific process is as follows:

[0068] 1. Prepare a NaHCO3 solution (0.5 mol / L) with pH=8.5 as the extraction solvent.

[0069] 2. Weigh 2.50g of sieved and uniformly sieved soil sample and place it in an Erlenmeyer flask. Add 50mL of extractant and shake at 25℃ with an oscillation frequency of 180r / min-220r / min for 30min.

[0070] 3. After shaking, filter using double-layer phosphorus-free filter paper, discard the initial filtrate, take 10 ml of the remaining filtrate and slowly add 0.8 mL of hydrochloric acid solution. After the bubbles are completely eliminated, test the solution to obtain the measured concentration.

[0071] Calculation formula: Available phosphorus (mg / Kg) = [Measured concentration (mg / L) × (10.8 / 10) × extractant (mL)] / soil sample mass (g).

[0072] from Figure 1 The SEM images show that, compared to the blank sample without added sodium humate and laterite ( Figure 1 Compared to -a), after adding sodium humate and laterite ( Figure 1 -b) The material has a distinct three-dimensional network structure and abundant porous structure, which increases its specific surface area and facilitates the absorption of water and the storage and release of nutrients in the composite material.

[0073] from Figure 2 The infrared spectrum shows that curve c is at 3500 cm⁻¹ -1 The absorption peak is a characteristic peak of -OH at 533 cm⁻¹. -1 The absorption peaks on the left and right correspond to the bending vibration peaks of Si-O-Si, at 1571 cm⁻¹. -1 The absorption peak appearing at this point corresponds to the -COO group of sodium humate. - The asymmetric stretching vibration peak was observed. This result indicates the successful preparation of the laterite-based polymer composite water-absorbing material.

[0074] Under the same conditions as in Example 1, the amount of sodium humate was adjusted by 5%, 10%, 15%, 20%, and 25% of the mass of acrylic acid. The water absorption ratios of the prepared lateritic polymer composite absorbent material in distilled water, tap water, and 0.9% NaCl solution were as follows: Figure 3As shown in the figure, the water (salt) absorption rate of the laterite-based polymer composite absorbent material increases significantly with the increase of sodium humate dosage from 5 wt% to 10 wt%. The absorption ratio is highest when the sodium humate dosage is 10 wt% (reaching 1000, 190, and 102 g / g in distilled water, tap water, and 0.9% NaCl solution, respectively). When the sodium humate dosage exceeds 10 wt%, the absorption ratio of the laterite-based polymer composite absorbent material begins to decrease. This is because a certain amount of sodium humate can reduce the hydrogen bonding interactions between polymer chains based on acrylic acid and acrylamide monomers, forming a well-developed network structure that easily swells. However, excessive sodium humate fills the polymer pores, hindering the expansion of the cross-linked network, thus reducing the water (salt) absorption rate.

[0075] Under the same conditions as in Example 1 above, the amount of laterite was adjusted by 0%, 2%, 4%, 6%, and 8% of the mass of acrylic acid. The water absorption ratios of the prepared laterite-based polymer composite absorbent material in distilled water, tap water, and 0.9% NaCl solution are as follows: Figure 4 As shown in the figure, the water (salt) absorption rate of the laterite-based polymer composite absorbent material increases significantly as the laterite content increases from 0 to 2 wt%. The maximum water absorption ratio is achieved when the laterite content is 2 wt% (reaching 1070, 203, and 113 g / g in distilled water, tap water, and 0.9% NaCl solution, respectively). This is because the -OH groups on the laterite surface react with acrylic acid and acrylamide monomers, participating in the construction of the three-dimensional network, thus improving the material's water absorption performance. However, when the laterite content exceeds 2 wt%, the water absorption ratio of the laterite-based polymer composite absorbent material decreases significantly. This is because laterite can act as a physical cross-linking point in the polymer network, increasing the cross-linking point density of the polymer composite material. This reduces the space for water molecule penetration and the network space for water (salt) absorption; in other words, excess laterite physically fills the polymer network space, thereby reducing the proportion of hydrophilic groups and the swelling rate per unit volume of the laterite-based polymer composite absorbent material.

[0076] from Figure 5 It can be seen that after five repeated swelling cycles, the water absorption ratio of the laterite-based polymer composite absorbent material still remains above 50% of its initial value. This is because repeated water absorption disrupts the network structure of the polymer chains, leading to a decrease in the water absorption ratio. Nevertheless, this result also demonstrates that the laterite-based polymer composite absorbent material can be fully recycled, extending its service life and reducing resource waste.

[0077] from Figure 6It can be seen that the water absorption ratio of the laterite-based polymer composite absorbent material first increases and then decreases with increasing pH value. When pH=7, the solution is in a neutral environment, and the material reaches its maximum water absorption ratio. When pH<7, the protonation of the carboxylic acid anion shields the electrostatic repulsion, leading to enhanced cross-linking between polymer chains, making the material's gel network more prone to water loss and reducing the water loss rate. However, when pH>7, the osmotic pressure inside the hydrogel network decreases, and the Na+ in the sodium hydroxide... + and -COO - The charge shielding effect between polymer chains weakens the repulsive force between them, reducing the swelling capacity of the material. Nevertheless, laterite-based polymer composite absorbent materials have good water absorption capacity over a wide pH range (pH=4~10) and can be widely used in weakly acidic and weakly alkaline environments.

[0078] from Figure 7 It can be seen that in distilled water, the water absorption ratio of the laterite-based polymer composite absorbent material is 162.8% of that of the blank sample without added sodium humate and laterite, and 304.7% of that of commercially available absorbent composite materials. The results indicate that the laterite-based polymer composite absorbent material improves the overall water (salt) absorption performance while reducing costs, and has higher economic benefits and application value.

[0079] Soil experiment:

[0080] The red soil-based polymer composite absorbent material was buried in the soil, and the phosphorus content in the soil was measured at regular intervals (6 days) to evaluate its effect on phosphorus accumulation. Meanwhile, the blank sample, control sample 1, and control sample 2 prepared above were buried in the soil for a control experiment. Figure 8 It can be seen that, under the same environmental conditions of controlled soil moisture, over time, the blank sample (without added red soil and sodium humate) had almost no effect on the phosphorus content in the soil, while the control sample 2 (with only added red soil) showed a slight increase. However, the red soil-based polymer composite water-absorbing material of the present invention and the control sample 1 (with only added sodium humate) significantly increased the phosphorus content in the soil, and the red soil-based polymer composite water-absorbing material had a better effect. This indicates that the synergistic effect of red soil and sodium humate in the red soil-based polymer composite water-absorbing material of the present invention can accumulate phosphorus in the soil to increase the phosphorus content in the soil.

[0081] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laterite-based macromolecular composite water-absorbing material, characterized by: The laterite-based polymer composite water-absorbing material is obtained by copolymerization and cross-linking of raw materials including acrylic acid monomer, acrylamide monomer, sodium humate and laterite, wherein the amount of acrylamide monomer is 14-15 wt% of the acrylic acid monomer, the amount of sodium humate is 5-15 wt% of the acrylic acid monomer, and the amount of laterite is 1-2 wt% of the acrylic acid monomer. The acrylamide monomer is a mixture of N-hydroxyethyl acrylamide and 2-acrylamido-2-methylpropane sulfonic acid in a mass ratio of 1:

1. The laterite-based polymer composite water-absorbing material is prepared by a method comprising the following steps: (1) adjusting the neutralization degree of acrylic acid to 60-80%; (2) mixing the acrylamide monomer, sodium humate and laterite in water, then adding an initiator under inert atmosphere and reacting for a certain period of time, and then adding neutralized acrylic acid and a cross-linking agent and continuing to react to obtain the laterite-based polymer composite water-absorbing material.

2. The laterite-based macromolecular composite water-absorbing material according to claim 1, characterized in that: The amount of sodium humate is 10% of the acrylic acid monomer.

3. The method of producing a high molecular composite water absorbing material of a laterite base as claimed in any one of claims 1 to 2, characterized by, The method comprises the following steps: (1) adjusting the neutralization degree of acrylic acid to 60-80%; (2) mixing the acrylamide monomer, sodium humate and laterite in water, then adding an initiator under inert atmosphere and reacting for a certain period of time, and then adding neutralized acrylic acid and a cross-linking agent and continuing to react to obtain the laterite-based polymer composite water-absorbing material.

4. The method of claim 3, wherein: The initiator is potassium persulfate and / or ammonium persulfate. The cross-linking agent is at least one of hydroxyethyl methacrylate, N-hydroxymethyl acrylamide and N,N-methylene bisacrylamide.

5. The method of claim 4, wherein: The amount of initiator is 0.5-2 wt% of the acrylic acid monomer.

6. The method of claim 4, wherein: The amount of cross-linking agent is 0.05-0.2 wt% of the acrylic acid monomer.

7. The method of claim 3, wherein: The reaction temperature is 60-85℃.

8. Use of the laterite-based polymer composite water-absorbing material according to any one of claims 1-2 in improving the water retention and / or phosphorus content of soil.

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