Anionic amide polymers and their use in the improvement of saline soils

Abstract

The application provides an anionic amide polymer and application thereof in saline-alkali soil improvement, and belongs to the technical field of soil improvement. The anionic amide polymer is a beta-cyclodextrin-2-acrylamide-2-methylpropanesulfonic acid-acrylamide copolymer. In the implementation process, the molecular weight and ionic degree of the obtained anionic polyacrylamide are moderate by selecting an anionic monomer, and the application of the anionic polyacrylamide to saline-alkali soil improvement can effectively improve soil physical properties, increase the number of soil water-stable aggregates, reduce soil bulk density, improve permeability and porosity, increase soil water content, and maintain good soil structure.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of soil improvement, and particularly relates to an anion amide polymer and application thereof in saline-alkali soil improvement. BACKGROUND

[0002] With the continuous development of society, soil resources are seriously insufficient, and due to some unreasonable utilization, such as a large number of unreasonable application of fertilizers, excessive spraying of pesticides, overloading grazing and the like, serious degradation of soil is caused. Main performances are soil compaction and hardening, erosion, salinization, acidification, element imbalance, chemical pollution, loss of organic matter and degradation of flora and fauna, and the result of soil degradation is that soil productivity is reduced, crop quality is decreased, and even toxic elements are enriched, so how to maintain soil quality, improve acid and alkaline soil, relieve soil toxicity and reduce the spread of soil-borne diseases becomes a focus of attention.

[0003] Application of soil improver is one of important measures for repairing degraded soil. The soil improver can effectively improve soil physical and chemical properties and soil nutrient conditions, and has a positive influence on soil microorganisms, thereby improving productivity of degraded soil. Soil characteristics include soil result, soil water content, soil temperature, soil enzyme activity, soil microorganism quantity, soil ventilation condition, soil solution concentration and soil hydrogen ion concentration. Different types of soil improvers have different mechanisms of action on soil, but all of them can effectively improve soil physical structure, reduce soil bulk density, increase soil water content, change soil chemical properties, increase soil microorganism activity, improve enzyme activity, increase soil trace element content, and adjust some or all of soil water, fertilizer, gas and heat conditions, so as to ultimately improve soil fertility.

[0004] Polyacrylamide has a unique macromolecular structure, can play a sedimentation effect through adsorption bridging and charge neutralization, has good adhesion to many micelles and soluble substances in sewage, is a flocculant widely used in water treatment industry, and has broad application prospect and industrial application value. Polyacrylamide is a water-soluble chain polymer, is the most commonly used surfactant at present, and the acrylamide in the molecular chain contains a double bond and an amide group which are active, so various products can be obtained through various cross-linking and graft copolymerization, for example, a series of reactions are carried out to synthesize amphoteric polyacrylamide, anionic polyacrylamide and cationic polyacrylamide by connecting different types of cations, anions and non-ions.

[0005] Anionic polyacrylamide has the same negative charge as the soil surface, but can be combined with the soil through the action of a cation bridge. Divalent cations (such as Ca 2+ ) in the soil can be combined with the surface of soil particles and the negative phase of anionic polyacrylamide respectively, to form a cation bridge, namely PAM-Ca 2+- soil particles. The degree of absorption of polyacrylamide by soil particles depends on the nature of the polyacrylamide and the soil. Generally, the main influencing factors are the molecular weight of the polyacrylamide, the ionicity and the content of cations in the soil. Polymers with high molecular weight and long molecular chains have a stronger bridging effect between dispersed soil particles and a stronger effect of forming a protective network on the outer surface of the soil aggregates, and thus have a better effect on water and soil conservation.

[0006] As disclosed in Chinese patent CN106922245A, a soil improvement method is disclosed, which adds anionic polyacrylamide to the soil conditioner, so that the invention has good effect on preventing water and soil loss, greatly reduces the loss rate of dissolved fertilizer elements, and can increase the content of soil organic matter, and can adsorb both anions and cations.

[0007] As disclosed in Chinese patent CN102487618A, a method for improving the structure of coastal reclamation soil is disclosed, which comprises the following steps: adjusting the polyacrylamide to a polyacrylamide solution with a concentration of 0.5-2.0 g / L by adding water, irrigating, and irrigating an amount of 100-350 L / m 2 . The polyacrylamide is anionic polyacrylamide with a molecular weight of 8-12 million. By adjusting the water content of the topsoil and the concentration of the polyacrylamide solution, the invention can quickly improve the viscous structure of the reclamation soil and establish a stable aggregate soil structure, which can significantly improve the permeability and water conductivity of the reclamation soil and establish a good water, fertilizer and salt transport channel.

[0008] However, the molecular weight and ionicity of the existing anionic polyacrylamide cannot better meet the needs, and therefore it is necessary to develop an anionic polyacrylamide with moderate molecular weight and ionicity, which can effectively improve the physical properties of the soil, increase the number of water-stable aggregates in the soil, reduce the bulk density of the soil, improve the permeability and porosity of the soil, increase the water content of the soil, and maintain a good soil structure. SUMMARY

[0009] Based on the deficiencies in the prior art, the present application aims to provide an anionic amide polymer, which is anionic polyacrylamide. In the implementation process, the molecular weight and ionicity of the obtained anionic polyacrylamide are moderate by selecting anionic monomers, and the application of the anionic polyacrylamide to saline-alkali soil improvement can effectively improve the physical properties of the soil, increase the number of water-stable aggregates in the soil, reduce the bulk density of the soil, improve the permeability and porosity of the soil, increase the water content of the soil, and maintain a good soil structure.

[0010] In order to achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows:

[0011] An anionic amide polymer, which is a β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer, is prepared by the following method:

[0012] (1) adding sodium hydroxide solution to β-cyclodextrin until completely dissolved to obtain a β-cyclodextrin alkaline solution;

[0013] (2) adding cyclohexane solution to the β-cyclodextrin alkaline solution, stirring quickly until dispersed, then adding initiator, crosslinking agent and emulsifier, and stirring until a stable emulsion is formed;

[0014] (3) adding acrylamide to water, stirring until completely dissolved, then adding 2-acrylamido-2-methylpropanesulfonic acid to obtain a mixed solution;

[0015] (4) heating the emulsion obtained in step (2) under nitrogen protection to reflux, when the temperature rises to 40℃, the mixed solution of step (3) is added dropwise to the emulsion, and gradually heated to 60℃, after the reaction is completed, using anhydrous ethanol to break the emulsion, washing, and drying, to obtain the β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer.

[0016] The concentration of sodium hydroxide in step (1) is 0.2-0.35 g / mL; preferably 0.25 g / mL.

[0017] The initiator in step (2) is coupling diisobutyronitrile;

[0018] The crosslinking agent in step (2) is N,N-2-methyl bisacrylamide;

[0019] The emulsifier in step (2) is Tween-80.

[0020] The volume ratio of cyclohexane solution to β-cyclodextrin alkaline solution in step (2) is 4-6:1; preferably 5.5:1.

[0021] The mass ratio of β-cyclodextrin, 2-acrylamido-2-methylpropanesulfonic acid and acrylamide is 0.5-2:1-1.5:5-7;

[0022] Preferably, the mass ratio of β-cyclodextrin, 2-acrylamido-2-methylpropanesulfonic acid and acrylamide is 0.8:1.2:6.5.

[0023] The amount of initiator added is 0.2-0.4% of the total mass of monomers; preferably 0.3%.

[0024] The amount of crosslinking agent added is 0.03-0.06% of the total mass of monomers; preferably 0.04%.

[0025] The amount of the emulsifier added is 5-8% of the total mass of the monomers; preferably 6%.

[0026] The mass-volume ratio of the acrylamide and water in step (3) is 0.15-0.20 g / mL; preferably 0.16 g / mL.

[0027] The speed of the dropwise addition in step (4) is 1-2 drops per second.

[0028] The speed of the temperature rise in step (4) is 1℃ per 2-3 minutes.

[0029] The reaction time in step (4) is 3-4 hours; preferably 4 hours.

[0030] The solvent for the washing in step (4) is anhydrous ethanol; the drying temperature is 40-50℃, and the drying time is 20-30 hours.

[0031] The application also provides the use of the above-mentioned β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer in the preparation of a soil conditioner.

[0032] Compared with the prior art, the application has the following beneficial effects:

[0033] (1) The application uses β-cyclodextrin, 2-acrylamido-2-methylpropanesulfonic acid and acrylamide as raw materials to prepare a β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer by inverse emulsion polymerization, and the copolymer has good water absorption and water retention effects and better effects on soil improvement.

[0034] (2) The application uses appropriate initiators, crosslinking agents and emulsifiers, controls the amount of the initiators, the crosslinking agents and the emulsifiers, and controls the mass ratio of β-cyclodextrin, 2-acrylamido-2-methylpropanesulfonic acid and acrylamide to obtain a β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer with moderate molecular weight and ion degree, and the copolymer can effectively improve the physical properties of saline-alkali soil, increase the number of soil water-stable aggregates, reduce the soil bulk density, improve the permeability and porosity, increase the soil water content and maintain good soil structure when applied to saline-alkali soil improvement. DETAILED DESCRIPTION

[0035] The above-mentioned features mentioned in the application or the features mentioned in the embodiments can be combined arbitrarily. All the features explained in the specification can be used with any method form, and each feature disclosed in the specification can be replaced by any alternative feature that can provide the same, equivalent or similar purpose. Therefore, except for special explanations, the disclosed features are only general examples of equivalent or similar features.

[0036] The application is further described in conjunction with specific examples. These examples are intended to be illustrative only and are not intended to limit the scope of the application. Unless otherwise indicated, the following examples were carried out under conventional conditions or as suggested by the manufacturer. Unless otherwise specified, all percentages and proportions are by weight.

[0037] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as those commonly understood by one of ordinary skill in the art to which this application belongs. Also, any method and material similar or equivalent to those described herein can be used in the practice of the present application. The preferred methods and materials are described herein.

[0038] The preparation method of the β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer of Example 1 includes the following steps:

[0039] (1) Add 0.2 g / mL sodium hydroxide solution to β-cyclodextrin until completely dissolved to obtain a β-cyclodextrin alkaline solution;

[0040] (2) Add the cyclohexane solution to the β-cyclodextrin alkaline solution (volume ratio 4:1), stir quickly to disperse, then add 0.2% of the total mass of the monomer of coupling diisobutyronitrile, 0.03% of N,N-2-methyl bisacrylamide, and 5% of Tween-80, and stir to form a stable emulsion;

[0041] (3) Add acrylamide to water (mass volume ratio 0.15 g / mL), stir until completely dissolved, then add 2-acrylamido-2-methylpropanesulfonic acid to obtain a mixed solution;

[0042] (4) Heat the emulsion obtained in step (2) under nitrogen protection to reflux, when the temperature rises to 40°C, add the mixed solution of step (3) dropwise to the emulsion at a speed of 1-2 drops per second, and gradually increase the temperature to 60°C at a speed of 1°C per 2-3 minutes. After the reaction is completed, use anhydrous ethanol for demulsification, repeatedly wash with anhydrous ethanol, and dry at 40°C for 30 hours to obtain the β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer;

[0043] The mass ratio of the β-cyclodextrin, 2-acrylamido-2-methylpropanesulfonic acid, and acrylamide is 0.5:1:5. The preparation method of the β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer of Example 2 includes the following steps:

[0044] (1) Add 0.35 g / mL sodium hydroxide solution to β-cyclodextrin until completely dissolved to obtain a β-cyclodextrin alkaline solution;

[0045] (2) cyclohexane solution was added to the β-cyclodextrin alkaline solution (volume ratio 6:1), stirred quickly to disperse, then 0.4% of the total mass of the monomers of coupling diisobutyronitrile, 0.06% of N,N-2-methyl bisacrylamide and 8% of Tween-80 were added, and stirred to form a stable emulsion;

[0046] (3) acrylamide was added to water (mass volume ratio 0.20 g / mL), stirred to completely dissolve, then 2-acrylamido-2-methylpropanesulfonic acid was added to obtain a mixed solution;

[0047] (4) the emulsion obtained in step (2) was heated to reflux under nitrogen protection, when the temperature rose to 40℃, the mixed solution of step (3) was added dropwise to the emulsion at a speed of 1-2 drops per second, and the temperature was gradually raised to 60℃ at a speed of 1℃ per 2-3 minutes, after the reaction was completed, anhydrous ethanol was used for demulsification, anhydrous ethanol was repeatedly washed, and drying was carried out at 50℃ for 20 hours, to obtain the β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer;

[0048] The mass ratio of the β-cyclodextrin, 2-acrylamido-2-methylpropanesulfonic acid and acrylamide is 2:1.5:7. The preparation method of the β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer includes the following steps:

[0049] (1) β-cyclodextrin was added to 0.25 g / mL sodium hydroxide solution to completely dissolve, to obtain a β-cyclodextrin alkaline solution;

[0050] (2) cyclohexane solution was added to the β-cyclodextrin alkaline solution (volume ratio 5.5:1), stirred quickly to disperse, then 0.3% of the total mass of the monomers of coupling diisobutyronitrile, 0.04% of N,N-2-methyl bisacrylamide and 6% of Tween-80 were added, and stirred to form a stable emulsion;

[0051] (3) acrylamide was added to water (mass volume ratio 0.16 g / mL), stirred to completely dissolve, then 2-acrylamido-2-methylpropanesulfonic acid was added to obtain a mixed solution;

[0052] (4) the emulsion obtained in step (2) was heated to reflux under nitrogen protection, when the temperature rose to 40℃, the mixed solution of step (3) was added dropwise to the emulsion at a speed of 1-2 drops per second, and the temperature was gradually raised to 60℃ at a speed of 1℃ per 2-3 minutes, after the reaction was completed, anhydrous ethanol was used for demulsification, anhydrous ethanol was repeatedly washed, and drying was carried out at 40℃ for 25 hours, to obtain the β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer;

[0053] The mass ratio of the β-cyclodextrin, 2-acrylamido-2-methylpropanesulfonic acid and acrylamide is 0.8:1.2:6.5.

[0054] Comparative Example 1

[0055] The difference from Example 3 is that 2-acrylamido-2-methylpropanesulfonic acid is replaced by acrylic acid, and the others are the same as Example 3.

[0056] Comparative Example 2

[0057] The difference from Example 3 is that 2-acrylamido-2-methylpropanesulfonic acid is replaced by sodium p-styrenesulfonate, and the others are the same as Example 3.

[0058] Comparative Example 3

[0059] The difference from Example 3 is that Tween 80 is replaced by Span 80, and the others are the same as Example 3.

[0060] Effect data

[0061] 1. Determination of characteristic viscosity, anionic degree and acrylamide residual amount

[0062] The characteristic viscosity is determined by one-point method;

[0063] The anionic degree is determined by hydrochloric acid titration method;

[0064] The acrylamide residual amount is determined by bromine addition method.

[0065] The detection results are shown in Table 1 below.

[0066] Table 1

[0067] Characteristic viscosity (mL / g) Anionicity (%) Acrylamide residual amount (%) Example 1 1098 28.4 0.21 Example 2 1125 27.2 0.20 Example 3 1158 29.5 0.18 Comparative Example 1 984 18.1 0.28 Comparative Example 2 1012 19.5 0.24 Comparative Example 3 968 20.8 0.25

[0068] According to the detection results in Table 1 above, the anionic polyacrylamide prepared by the method provided by the application has high characteristic viscosity and moderate anionic degree, and the reaction is relatively complete, and the acrylamide residual amount is low. The anionic degree is an important factor affecting the formation of cationic bridges. A certain anionic degree is a prerequisite for PAM to be absorbed by soil particles. The anionic polyacrylamide prepared by the application has an anionic degree of 25-30%, which can better disperse the bridge bond between soil fine particles and form a protective net on the surface of the aggregate, and therefore has good effect in water and soil conservation.

[0069] 2. Water absorption test

[0070] Test method: Weigh the prepared anionic polyacrylamide sample, add it to distilled water, and after adsorbing at room temperature for 3h, filter with a sieve, weigh, and calculate the water absorption ratio Q according to the formula:

[0071] Q = (m2 - m1) / m1

[0072] In the formula, Q is the water absorption ratio (g / g); m1 is the sample mass (g); and m2 is the resin mass after absorbing liquid (g).

[0073] The detection results are shown in Table 2 below.

[0074] Table 2

[0075] Water absorption ratio g / g Example 1 612 Example 2 624 Example 3 628 Comparative Example 1 592 Comparative Example 2 589 Comparative Example 3 564

[0076] According to the detection results in Table 2 above, the anionic polyacrylamide prepared by the method provided in the present application has high water absorption, and the water absorption ratio in 3 hours can reach 600 g / g or more. Changing the type of anionic monomer or changing the type of emulsifier in the comparative examples will affect the water absorption effect of the product.

[0077] It can be understood that the above embodiments are only exemplary embodiments adopted for illustrating the present application, and the present application is not limited thereto. Various modifications and improvements can be made by those skilled in the art without departing from the spirit and essence of the present application, and these modifications and improvements are also considered as the protection scope of the present application.

Claims

1. An anionic amide polymer for use as a soil conditioner, characterized in that: The anionic amide polymer is a β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer, which is prepared by the following method: (1) Add sodium hydroxide solution to β-cyclodextrin until it is completely dissolved to obtain an alkaline solution of β-cyclodextrin; (2) Add the cyclohexane solution to the β-cyclodextrin alkaline solution and stir rapidly until dispersed. Then add the initiator, crosslinking agent and emulsifier and stir until a stable emulsion is formed. The emulsifier is Tween-80 and the crosslinking agent is N,N-di-methylbisacrylamide. (3) Add acrylamide to water and stir until completely dissolved, then add 2-acrylamido-2-methylpropanesulfonic acid to obtain a mixed solution; (4) The emulsion obtained in step (2) is heated and refluxed under nitrogen protection. When the temperature rises to 40°C, the mixed solution in step (3) is added dropwise to the emulsion and the temperature is gradually raised to 60°C. After the reaction is completed, the emulsion is broken with anhydrous ethanol, washed, and dried to obtain the β-cyclodextrin-2-acrylamido-2-methylpropanesulfonic acid-acrylamide copolymer.

2. The anionic amide polymer according to claim 1, characterized in that: The concentration of sodium hydroxide mentioned in step (1) is 0.2-0.35 g / mL.

3. The anionic amide polymer according to claim 1, characterized in that: The initiator mentioned in step (2) is azobisisobutyronitrile.

4. The anionic amide polymer according to claim 1, characterized in that: The volume ratio of the cyclohexane solution to the β-cyclodextrin alkaline solution in step (2) is 4-6:

1.

5. The anionic amide polymer according to claim 1, characterized in that: The mass ratio of β-cyclodextrin, 2-acrylamido-2-methylpropanesulfonic acid and acrylamide is 0.5-2:1-1.5:5-7.

6. The anionic amide polymer according to claim 5, characterized in that: The mass ratio of β-cyclodextrin, 2-acrylamido-2-methylpropanesulfonic acid and acrylamide is 0.8:1.2:6.

5.

7. The anionic amide polymer according to claim 1, characterized in that: The amount of the initiator added is 0.2-0.4% of the total mass of the monomers; the amount of the crosslinking agent added is 0.03-0.06% of the total mass of the monomers; and the amount of the emulsifier added is 5-8% of the total mass of the monomers.

8. The anionic amide polymer according to claim 1, characterized in that: The dripping rate in step (4) is 1-2 drops per second; the heating rate is 1°C every 2-3 minutes.

9. The anionic amide polymer according to claim 1, characterized in that: The washing solvent in step (4) is anhydrous ethanol; the drying temperature is 40-50℃ and the drying time is 20-30 hours.

10. The use of the anionic amide polymer according to any one of claims 1-9 in the preparation of soil conditioners.