Red soil-based polymer composite water-absorbing material and preparation method thereof

Abstract

The invention discloses a laterite-based polymer composite water absorbing material. The laterite-based polymer composite water absorbing material is obtained by copolymerization and crosslinking of raw materials including an acrylic monomer, an acrylamide monomer, sodium humate and laterite, the dosage of the acrylamide monomer is 10-25 wt% of that of the acrylic monomer, the dosage of the sodium humate is 5-25 wt% of that of the acrylic monomer, and the dosage of the laterite is 1-10 wt% of that of the acrylic monomer. Compared with the prior art, the raw materials sodium humate and laterite of the laterite-based polymer composite water-absorbing material are low in cost and easy to obtain, and the laterite-based polymer composite water-absorbing material has better water-absorbing and salt-resistant performance, not only can better improve the water-retaining capacity of soil, but also can improve the phosphorus content of the soil, and plays a role in improving the soil.

Description

Technical Field

[0001] The invention belongs to the field of soil moisture retention, and in particular relates to a laterite-based macromolecular composite water-absorbing material. Background Art

[0002] Soil desertification seriously hinders the development of agriculture, and it rapidly turns arable soil into sand. Although some areas even use domestic water for irrigation to alleviate extreme drought periods, most of the water is lost by evaporation from the soil surface, and vegetation can absorb less water, and the cost is high. The more feasible strategy at present is to apply water-absorbing and water-retaining materials.

[0003] Chinese patent CN1912007A discloses a humate composite water-retaining agent and a preparation method thereof, and specifically discloses: 20g of acrylic acid-acrylamide copolymer of 40-60 mesh fraction is mixed evenly with 10g of humate, and 60mL of 80% acetone aqueous solution in which 0.06g of glycerol is dissolved is added dropwise, stirred evenly, and surface cross-linking reaction is carried out in a vacuum drying oven at 80°C for 40min to obtain a humate composite water-retaining agent. The swelling degree of the 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 a preparation method thereof, which uses valence attapulgite, starch, humic acid and acrylamide as the main raw materials of the composite water-retaining agent, adds an initiator and a cross-linking agent, and is made by graft copolymerization, cross-linking, hydrolysis, washing, drying, crushing, screening and other processes in an aqueous solution. The composite water-retaining agent absorbs distilled water at a mass multiple of 300-800 and absorbs 0.9% NaCl solution at a mass multiple of 50-80.

[0005] Chinese patent CN103755897A discloses a method for preparing a salt-resistant, highly absorbent composite material based on palygorskite clay. Specifically, palygorskite, 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid are used as raw materials in an aqueous solution system, and N,N'-methylenebisacrylamide is used as a cross-linking agent. The mixture is stirred at 60-80°C for 2-6 hours to form a gel-like cross-linked product, and then cooled, washed with water, dehydrated, dried, and crushed to obtain a clay-based salt-resistant, highly absorbent composite material. The water absorption rates of the composite material in distilled water and 0.1 mol / L NaCl solution are 520-750 g / g and 76-83 g / g, respectively.

[0006] The above-mentioned water-retaining (absorbing) materials have a high water absorption rate in distilled water and sodium chloride solution, but there is still room for improvement, and the functions are relatively simple, limited to the water absorption (retaining) function. Summary of the invention

[0007] Based on the above-mentioned deficiencies of the prior art, the object of the present invention is to provide a laterite-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 object, the present invention adopts the following technical solution: A laterite-based polymer composite water-absorbing material is obtained by copolymerizing and cross-linking raw materials including acrylic acid monomers, acrylamide monomers, sodium humate and laterite, wherein the amount of acrylamide monomers is 10-25wt% of the acrylic acid monomers, the amount of sodium humate is 5-25wt% of the acrylic acid monomers, and the amount of laterite is 1-10wt% of the acrylic acid monomers.

[0009] Preferably, the acrylamide monomer is at least one of acrylamide, methacrylamide, N-hydroxyethyl acrylamide and 2-acrylamido-2-methylpropanesulfonic acid.

[0010] More preferably, the acrylamide monomer is a mixture of N-hydroxyethyl acrylamide and 2-acrylamido-2-methylpropanesulfonic acid in a mass ratio of 1:1.

[0011] Preferably, the amount of the acrylamide monomer used is 14-15 wt % of the acrylic acid monomer.

[0012] Preferably, the amount of sodium humate used is 5-15wt% of the acrylic acid monomer, more preferably 10%.

[0013] Preferably, the amount of red clay used is 1-2 wt % of the acrylic acid monomer.

[0014] The method for preparing the above-mentioned laterite-based polymer composite water-absorbing material comprises the following steps: (1) Adjust the neutralization degree of acrylic acid to 60~80%; (2) After acrylamide monomer, sodium humate and red clay are mixed in water, an initiator is added under an inert atmosphere to react for a certain time, and then neutralized acrylic acid and a cross-linking agent are added and the reaction is continued to obtain the red clay-based polymer composite water-absorbing material.

[0015] Preferably, the initiator is potassium persulfate and / or ammonium persulfate.

[0016] Preferably, the amount of the initiator used is 0.5-2 wt % of the acrylic acid monomer.

[0017] Preferably, the crosslinking agent is at least one of hydroxyethyl methacrylate, N-hydroxymethyl acrylamide, diacetone acrylamide and N,N-methylenebisacrylamide.

[0018] Preferably, the amount of the cross-linking agent is 0.05-0.2 wt % of the acrylic acid monomer.

[0019] Preferably, the reaction temperature is 60-85°C.

[0020] The application of the above-mentioned laterite-based polymer composite water-absorbing material in improving the water retention and / or phosphorus content of soil.

[0021] Compared with the prior art, the laterite-based polymer composite water-absorbing material of the present invention has the following beneficial effects: 1. The raw materials sodium humate and red clay are low-cost and easy to obtain.

[0022] 2. It has a higher water absorption rate in distilled water and 0.9% sodium chloride solution.

[0023] 3. It can not only improve the soil's water retention capacity, but also increase the soil's phosphorus content, thereby improving the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a scanning electron microscope (SEM) of laterite-based polymer composite water-absorbent material.

[0025] Figure 2 It is the infrared spectrum of laterite-based polymer composite water-absorbing material, wherein curve a is sodium humate, curve b is laterite, and curve c is laterite-based polymer composite water-absorbing material.

[0026] Figure 3 The water absorption performance of laterite-based polymer composite water-absorbing materials with different dosages of sodium humate in distilled water, tap water and 0.9% NaCl solution.

[0027] Figure 4 The water absorption performance of laterite-based polymer composite water-absorbent materials in distilled water, tap water and 0.9% NaCl solution at different laterite dosages.

[0028] Figure 5 It is the repeated swelling performance of laterite-based polymer composite water-absorbent material in distilled water.

[0029] Figure 6 The water absorption performance of laterite-based polymer composite water-absorbing material in water with different pH values.

[0030] Figure 7 It is a comparison between laterite-based polymer composite water-absorbent material and commercially available water-absorbent composite materials.

[0031] Figure 8 This is the change of phosphorus content in soil over time after adding laterite-based polymer composite water-absorbing materials. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described in detail below in conjunction with embodiments.

[0033] The red soil-based polymer composite water-absorbing material of the present invention is obtained by copolymerizing and cross-linking raw materials including acrylic acid monomers, acrylamide monomers, sodium humate and red soil. The specific operation process includes: (1) Adjust the neutralization degree of acrylic acid to 60~80%; (2) After acrylamide monomer, sodium humate and red clay are mixed in water, an initiator is added under an inert atmosphere to react for a certain time, and then neutralized acrylic acid and a cross-linking agent are added and the reaction is continued to obtain the red clay-based polymer composite water-absorbing material.

[0034] In some embodiments, the amount of the acrylamide monomer is controlled at 10-25wt% of the acrylic acid monomer, specifically 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, or an interval therebetween.

[0035] In some embodiments, the acrylamide monomer is selected from at least one of acrylamide, methacrylamide, N-hydroxyethyl acrylamide and 2-acrylamido-2-methylpropane sulfonic acid.

[0036] In some embodiments, the acrylamide monomer is a mixture of N-hydroxyethyl acrylamide and 2-acrylamido-2-methylpropanesulfonic acid in a mass ratio of 1:1.

[0037] In some embodiments, the amount of sodium humate is controlled at 5-25wt% of the acrylic acid monomer, specifically 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, or intervals therebetween.

[0038] In some embodiments, the amount of red clay is controlled at 1-10 wt % of the acrylic acid monomer, specifically 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt %, or intervals therebetween.

[0039] There is no special restriction on red clay, and it can be obtained locally.

[0040] In some embodiments, the particle size of the red clay can be controlled within the range of 50-200 mesh, such as 50 mesh, 80 mesh, 120 mesh, 150 mesh, and 200 mesh.

[0041] In some embodiments, acrylic acid is neutralized with sodium hydroxide. The degree of neutralization of acrylic acid is controlled to be 60-80%, specifically 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, or intervals therebetween.

[0042] In some embodiments, the initiator is selected from at least one of potassium persulfate and ammonium persulfate.

[0043] In some embodiments, the amount of the initiator is controlled to be 0.5-2 wt % of the acrylic acid monomer, specifically 0.5 wt %, 0.75 wt %, 1 wt %, 1.25 wt %, 1.5 wt %, 1.75 wt %, 2 wt %, or intervals therebetween.

[0044] In some embodiments, the crosslinking agent is selected from at least one of hydroxyethyl methacrylate, N-methylol acrylamide, diacetone acrylamide and N,N-methylenebisacrylamide.

[0045] In some embodiments, the amount of the crosslinking agent is 0.05-0.2 wt % of the acrylic acid monomer, specifically 0.05 wt %, 0.075 wt %, 0.1 wt %, 0.125 wt %, 0.15 wt %, 0.175 wt %, 0.2 wt %, or intervals therebetween.

[0046] In some embodiments, the reaction temperature is controlled at 60-85°C, specifically 60°C, 65°C, 70°C, 75°C, 80°C, or intervals therebetween.

[0047] In some embodiments, after the initiator is added, the reaction is continued for 10 to 30 minutes, such as 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or intervals therebetween.

[0048] In some embodiments, after the addition of acrylic acid and the cross-linking agent is completed, the reaction is continued for 1 to 4 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 4 hours, or intervals therebetween.

[0049] Example 1 (1) Red soil was collected from the nearest area (Anning District, Lanzhou City, Gansu Province), and small stones, coarse branches and rotten leaves were picked out. The large pieces of red soil were broken up and passed through a 20-mesh sieve. The red soil was further crushed with a grinder and passed through a 150-mesh sieve. The obtained red soil was dried in an oven at 100°C for 24 hours and set aside.

[0050] (2) Weigh 2.0 g of sodium hydroxide and dissolve it in 6 mL of distilled water in an ice-water bath. Then slowly add 5.4 g of acrylic acid dropwise to the sodium hydroxide solution while stirring to obtain an acrylic acid solution with a neutralization degree of 65%. Set aside.

[0051] (3) 0.54 g of sodium humate, 0.1 g of red clay, and 0.8 g of acrylamide monomer (a mixture of equal masses of N-hydroxyethyl acrylamide and 2-acrylamido-2-methylpropanesulfonic acid) were dissolved in 30 mL of distilled water, and then nitrogen was introduced. The mixture was stirred at 180 r / min for 1 hour in a constant temperature water bath at 65°C. Subsequently, potassium persulfate initiator (0.08 g) dissolved in 2 mL of distilled water was added and reacted for 20 minutes. Then, acrylic acid solution and N,N'-methylenebisacrylamide crosslinker (0.01 g) dissolved in 2 mL of distilled water were added and the reaction was continued for 2 hours.

[0052] (4) After the reaction is completed, the product is rinsed with distilled water and then soaked in anhydrous ethanol to remove unreacted impurities. Finally, it is placed in an oven at 70°C to dry to obtain a laterite-based polymer composite water-absorbing material.

[0053] The preparation process of the blank sample was the same as above, except that sodium humate and red clay were not added.

[0054] The preparation process of comparative sample 1 is the same as above, except that no red clay is added.

[0055] The preparation process of comparative sample 2 is the same as above, except that no sodium humate is added.

[0056] Determination of water absorption rate: The conventional weight method is used to determine the water absorption rate by measuring the change in weight of the material before and after water absorption. The specific formula is as follows: Water absorption ratio = (m-m0) / m0, where m0 is the mass before water absorption (g) and m is the mass after water absorption (g).

[0057] Determination of phosphorus content in soil: The analysis and testing is carried out using a fully automatic discontinuous chemical analyzer. The specific process is as follows: 1. Prepare NaHCO3 solution (0.5 mol / L) with pH = 8.5 as the extraction agent.

[0058] 2. Weigh 2.50 g of sieved soil sample and place it in a conical flask. Add 50 mL of extractant and oscillate at a frequency of 180 r / min-220 r / min for 30 min at 25 °C.

[0059] 3. After the oscillation is completed, filter with double-layer phosphorus-free filter paper, discard the initial filtrate, take 10 ml from the remaining filtrate and slowly add 0.8 mL of hydrochloric acid solution. After the bubbles are completely eliminated, test on the machine to obtain the measured concentration.

[0060] Calculation formula: Available phosphorus (mg / Kg) = [measured concentration (mg / L) × (10.8 / 10) × extractant (mL)] / soil sample mass (g).

[0061] from Figure 1 It can be seen from the SEM images that compared with the blank sample without adding sodium humate and red clay ( Figure 1 -a) compared with the addition of sodium humate and laterite ( Figure 1 -b) The material has a distinct three-dimensional network structure and rich porous structure, which increases its specific surface area and facilitates the water absorption and nutrient storage and release of the composite material.

[0062] from Figure 2 From the infrared spectrum, we can see that curve c is at 3500cm -1 The absorption peak is the characteristic peak of -OH, at 533cm -1 The absorption peaks on the left and right correspond to the bending vibration peaks of Si-O-Si at 1571 cm -1 The absorption peak at corresponds to -COO - The asymmetric stretching vibration peak of the latex-based polymer composite water-absorbing material was successfully prepared.

[0063] When other conditions in Example 1 remain unchanged, the amount of sodium humate is adjusted to 5%, 10%, 15%, 20%, and 25% of the mass of acrylic acid, and the water absorption rates of the prepared laterite-based polymer composite water-absorbing material in distilled water, tap water, and 0.9% NaCl solution are as follows: Figure 3As shown in the figure, as the amount of sodium humate increases from 5wt% to 10wt%, the water (salt) absorption rate of the laterite-based polymer composite water-absorbing material increases significantly. When the amount of sodium humate is 10wt%, the water absorption rate is the largest (reaching 1000, 190 and 102 g / g in distilled water, tap water and 0.9% NaCl solution, respectively). When the amount of sodium humate exceeds 10wt%, the water absorption rate of the laterite-based polymer composite water-absorbing material begins to decrease. This is because a certain amount of sodium humate can reduce the hydrogen bond interaction between polymer chains based on acrylic acid and acrylamide monomers, forming a developed network structure that is easy to swell, while too much sodium humate will fill the polymer pores and hinder the expansion of the cross-linked network, thereby reducing the water (salt) absorption rate.

[0064] When other conditions in Example 1 remain unchanged, the amount of red clay is adjusted to 0%, 2%, 4%, 6%, and 8% of the mass of acrylic acid, and the water absorption rates of the prepared red clay-based polymer composite water-absorbing material in distilled water, tap water, and 0.9% NaCl solution are as follows: Figure 4 As shown in the figure, as the amount of red clay increases from 0 to 2wt%, the water (salt) absorption rate of the red clay-based polymer composite water-absorbing material increases significantly. When the content of red clay is 2wt%, the water absorption rate is the largest (reaching 1070, 203 and 113 g / g in distilled water, tap water and 0.9% NaCl solution, respectively). This is because the -OH on the surface of the red clay reacts with acrylic acid and acrylamide monomers, participating in the construction of a three-dimensional network, thereby improving the water absorption performance of the material. However, when the content of red clay exceeds 2wt%, the water absorption rate of the red clay-based polymer composite water-absorbing material is significantly reduced. This is because red clay can act as a physical cross-linking point in the polymer network, increasing the cross-linking point density of the polymer composite material, resulting in a decrease in the space for water molecule penetration and the network space for water (salt) absorption rate, that is, the excess red clay physically fills the polymer network space, thereby reducing the proportion of hydrophilic groups and the swelling rate per unit volume of the red clay-based polymer composite water-absorbing material.

[0065] from Figure 5 It can be seen that after repeated swelling for 5 times, the water absorption rate of the laterite-based polymer composite water-absorbing material is still more than 50% of the initial value. This is because repeated water absorption destroys the network structure of the polymer chain, resulting in a decrease in the water absorption rate. Nevertheless, this result also shows that the laterite-based polymer composite water-absorbing material can be fully recycled, extending its service life and reducing resource waste.

[0066] from Figure 6It can be seen that the water absorption rate of laterite-based polymer composite water-absorbing materials first increases and then decreases with the increase of pH value. When pH=7, the solution is in a neutral environment and the material reaches the maximum water absorption rate. When pH<7, the anions of the carboxylic acid are protonated, shielding the electrostatic repulsion, resulting in enhanced cross-linking between polymer chains, and the gel network of the material is easy to lose water, reducing the water loss rate. When pH>7, the internal osmotic pressure of the hydrogel network of the material decreases, and the Na in the sodium hydroxide + and -COO - The charge shielding effect weakens the repulsion between polymer chains and reduces the swelling capacity of the material. Nevertheless, laterite-based polymer composite water-absorbing materials have good water absorption capacity in a wide pH range (pH = 4-10) and can be widely used in weak acid and weak base environments.

[0067] from Figure 7 It can be seen that in distilled water, the water absorption rate of the laterite-based polymer composite water-absorbing material is 162.8% of the blank sample without sodium humate and laterite, and 304.7% of the commercially available water-absorbing composite material. The results show that the laterite-based polymer composite water-absorbing material improves the overall water (salt) absorption performance while reducing costs, and has higher economic benefits and use value.

[0068] Soil experiment: The laterite-based polymer composite water-absorbing material was buried in the soil, and the phosphorus content in the soil was measured at regular intervals (6 days) to evaluate its phosphorus aggregation effect. In addition, the blank sample, comparison sample 1 and comparison sample 2 prepared above were buried in the soil for control experiments. Figure 8 It can be seen that under the environmental conditions of controlling the same soil moisture content, as time goes by, the blank sample (without adding red soil and sodium humate) has basically no effect on the phosphorus content in the soil, and the comparative sample 2 (only adding red soil) is slightly improved, while the red soil-based polymer composite water-absorbing material of the present invention and the comparative sample 1 (only adding sodium humate) can significantly improve the phosphorus content in the soil, and the effect of the red soil-based polymer composite water-absorbing material is better, which shows 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 aggregate phosphorus in the soil to increase the phosphorus content in the soil.

[0069] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A laterite-based polymer composite water-absorbing material, characterized in that: The laterite-based polymer composite water-absorbing material is obtained by copolymerizing and cross-linking raw materials including acrylic acid monomers, acrylamide monomers, sodium humate and laterite, wherein the amount of acrylamide monomers is 10-25wt% of the acrylic acid monomers, the amount of sodium humate is 5-25wt% of the acrylic acid monomers, and the amount of laterite is 1-10wt% of the acrylic acid monomers.

2. The laterite-based polymer composite water-absorbing material according to claim 1, characterized in that: The acrylamide monomer is at least one of acrylamide, methacrylamide, N-hydroxyethyl acrylamide and 2-acrylamido-2-methylpropanesulfonic acid.

3. The laterite-based polymer composite water-absorbing material according to claim 2, characterized in that: The acrylamide monomer is a mixture of N-hydroxyethyl acrylamide and 2-acrylamido-2-methylpropanesulfonic acid in a mass ratio of 1:

1.

4. The laterite-based polymer composite water-absorbing material according to claim 1, characterized in that: The amount of the acrylamide monomer used is 14-15wt% of the acrylic acid monomer.

5. The laterite-based polymer composite water-absorbing material according to claim 1, characterized in that: The amount of sodium humate used is 5-15wt% of the acrylic acid monomer, and more preferably 10%.

6. The laterite-based polymer composite water-absorbing material according to claim 1, characterized in that: The amount of the red clay used is 1-2 wt % of the acrylic acid monomer.

7. The method for preparing the laterite-based polymer composite water-absorbing material according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Adjust the neutralization degree of acrylic acid to 60~80%; (2) After acrylamide monomer, sodium humate and red clay are mixed in water, an initiator is added under an inert atmosphere to react for a certain time, and then neutralized acrylic acid and a cross-linking agent are added and the reaction is continued to obtain the red clay-based polymer composite water-absorbing material.

8. The preparation method according to claim 7, characterized in that: The initiator is potassium persulfate and / or ammonium persulfate. Preferably, the amount of the initiator is 0.5-2wt% of the acrylic acid monomer; The cross-linking agent is at least one of hydroxyethyl methacrylate, N-hydroxymethyl acrylamide, diacetone acrylamide and N,N-methylenebisacrylamide. Preferably, the amount of the cross-linking agent is 0.05-0.2wt% of the acrylic acid monomer.

9. The preparation method according to claim 7, characterized in that: The reaction temperature is 60-85°C.

10. Use of the laterite-based polymer composite water-absorbing material according to any one of claims 1 to 6 in improving the water retention and / or phosphorus content of soil.

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