Preparation method of biodegradable soil water retention material

Abstract

The invention relates to the technical field of agricultural water retention, and discloses a preparation method of a biodegradable soil water retention material, which comprises the following steps: adding 20-30 parts by weight of corn starch into 70-80 parts by weight of deionized water, stirring for 30-40 minutes at 70-80 DEG C for gelatinization, then cooling to room temperature, adding 2-4 parts by weight of modified chitosan, stirring for dissolving, and then cooling to room temperature to obtain the biodegradable soil water retention material. Then adding the modified bentonite suspension liquid, stirring for 20-25 minutes at the speed of 1200-1500 r / min, finally adding 0.5-0.8 part by weight of citric acid, and continuously stirring for 10-15 minutes to obtain a mixed material; putting the mixed material into a microwave reactor, carrying out microwave reaction, and after the reaction is finished, drying, crushing and granulating to obtain particles of 1-3mm, so as to obtain the biodegradable soil water-retaining material. The biodegradable soil water retention material disclosed by the invention has good water retention performance, salt resistance and degradability.

Description

Technical Field

[0001] This invention relates to the field of agricultural water conservation technology, specifically a method for preparing a biodegradable soil water-retaining material. Background Technology

[0002] In the field of agricultural water conservation and ecological restoration, soil water-retaining materials are widely used to alleviate water shortages in arid and semi-arid regions and ensure crop yields. With the popularization of ecological agriculture concepts, traditional water-retaining materials are struggling to meet the comprehensive demands of modern agriculture for environmental friendliness, functionality, and adaptability. Early mainstream water-retaining materials were mainly polyacrylic acid and polyacrylamide, which, while possessing high water absorption rates, have extremely poor biodegradability. Long-term application can leave residues in the soil, hindering crop root growth and microbial activity, thus affecting crop yields. While natural polymer-based water-retaining materials have the advantage of biodegradability, their salt resistance is generally weak, failing to meet the application needs of special scenarios such as saline-alkali land. Therefore, avoiding this phenomenon is key to solving the problem. For example, Chinese invention patent CN107986742B discloses a permeable water-retaining material and its preparation method. This invention utilizes magnesium phosphate cement in the preparation of permeable water-retaining materials, achieving good permeability while also possessing good water retention and compressive strength. However, its salt resistance needs improvement. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing a biodegradable soil water-retaining material. The biodegradable soil water-retaining material of the present invention has good water retention performance, salt resistance and degradability.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a biodegradable soil water-retaining material, comprising the following steps: (1) Preparation of modified chitosan: S1: Add 3-3.1g of chitosan powder to 150-160mL of anhydrous methanol, purge with nitrogen for 25-30min, add 1-1.2mL of anhydrous methyl acrylate, purge with nitrogen again for 25-30min, and then react at 45-50℃. After the reaction is complete, wash the product with anhydrous methanol 3-4 times and dry at 50-60℃ to obtain intermediate 1. S2: Add 2.5-2.6 g of intermediate 1 to 120-130 mL of anhydrous methanol, purge with nitrogen for 30-35 min, add 14-15 g of N,N-dimethyl-1,3-diaminopropane, purge with nitrogen again for 30-35 min, and then react at 50-55 °C. After the reaction is complete, wash the product with anhydrous methanol 3-4 times and dry at 50-60 °C to obtain intermediate 2. S3: Under nitrogen protection, add 100-110 mL of N,N-dimethylformamide solvent and 2-2.1 g of intermediate 2 to the reactor and stir to dissolve. Then, dissolve 1-1.1 g of propanesulfonic acid lactone in 5-6 mL of N,N-dimethylformamide and add it dropwise to the reactor at 0-5℃. After the addition is complete, stir the reaction at 30-40℃ for 8-12 h. After the reaction is completed, dialyze the mixture using a 3500-4000 Da dialysis bag and dry it to obtain modified chitosan. (2) Preparation of modified bentonite: Add 0.6-0.7g of dodecyl dimethyl betaine to 150-160mL of deionized water and stir at 40-45℃ to dissolve it. Then add 3-3.1g of bentonite and stir to react. After the reaction is completed, centrifuge to remove the supernatant, wash with deionized water 3-4 times, dry at 60-65℃, and pass through a 200-250 mesh sieve to obtain modified bentonite. (3) Add 1-2 parts by weight of modified bentonite to 9 times its weight of deionized water, and ultrasonically disperse for 30-40 minutes to obtain a modified bentonite suspension with a mass fraction of 10%. (4) Add 20-30 parts by weight of corn starch to 70-80 parts by weight of deionized water, stir at 70-80℃ for 30-40 min to gelatinize, then cool to room temperature, add 2-4 parts by weight of modified chitosan, stir to dissolve, then add the modified bentonite suspension obtained in step (3), stir at 1200-1500 r / min for 20-25 min, and finally add 0.5-0.8 parts by weight of citric acid and continue stirring for 10-15 min to obtain the mixture. (5) Place the mixture into a microwave reactor and carry out a microwave reaction. After the reaction is completed, dry it at 60-65℃, crush it, and granulate it into 1-3 mm particles to obtain biodegradable soil water-retaining material.

[0005] Furthermore, the reaction time in S1 is 22-26 hours.

[0006] Furthermore, the reaction time in S2 is 24-28 hours.

[0007] Furthermore, the dialysis time in S3 is 48-72 hours.

[0008] Furthermore, the reaction time in step (2) is 12-14 hours.

[0009] Furthermore, in step (5), the conditions for the microwave reaction are: microwave radiation power of 380-400W and radiation time of 3-4min.

[0010] Compared with the prior art, the present invention has the following beneficial technical effects: The amino groups on chitosan undergo a Michael addition reaction with methyl acrylate to generate intermediate 1. Intermediate 1 then undergoes an ammonolysis reaction with N,N-dimethyl-1,3-diaminopropane to generate intermediate 2, which has an amide bond and a tertiary amine. Subsequently, the tertiary amine on intermediate 2 acts as a nucleophile and undergoes a nucleophilic ring-opening reaction with propanesulfonate lactone to obtain modified chitosan with a strongly hydrated zwitterionic structure composed of quaternary ammonium salt groups and sulfonic acid groups. Bentonite is modified with dodecyl dimethyl betaine to obtain amphiphilic modified bentonite.

[0011] The zwitterionic structure of modified chitosan can bind a large number of water molecules through ion hydration. After modification, the interlayer spacing of bentonite also increases due to the insertion of organic molecules, forming a uniform porous structure that physically traps water and enhances the water retention performance of the water-retaining material. The sulfonic acid groups have a high charge density, and the strongly hydrated zwitterionic side chains formed with quaternary ammonium salt groups can maintain the extended state of the polymer chain in a salt environment, effectively resisting the charge shielding effect of salt ions. The betaine groups in the modified bentonite can form stable ion pairs with salt ions, preventing the collapse of the interlayer structure and ensuring that the material can play a long-term water-retaining role in saline-alkali environments, thus improving the salt resistance of the water-retaining material. The water-retaining material of this invention is mainly composed of natural biodegradable components such as corn starch, chitosan, and bentonite. The degradation process does not produce environmental pollution. The cross-linking reaction is carried out by microwave radiation, which promotes the grafting polymerization between modified chitosan, modified bentonite, and starch chains, enhances the mechanical strength of the gel network during water absorption and swelling, prevents gel rupture, and ensures that the material has excellent water retention performance. Attached Figure Description

[0012] Figure 1 It is the synthesis reaction formula for modified chitosan.

[0013] Figure 2 This is the infrared spectrum of the modified chitosan in Example 1.

[0014] Figure 3 This is the infrared spectrum of the biodegradable soil water-retaining material in Example 1. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] The reagents used in the following specific embodiments are of analytical grade. Additionally: Chitosan: Deacetylation degree 85%; Bentonite: Salt ion exchange capacity is 500 mmol / kg.

[0017] Example 1 (1) Add 3g of chitosan powder to 150mL of anhydrous methanol, purge with nitrogen for 25min, add 1mL of anhydrous methyl acrylate, purge with nitrogen for 25min, and then react at 45℃ for 22h. After the reaction is complete, the product is washed 3 times with anhydrous methanol and dried at 50℃ to obtain intermediate 1. (2) Add 2.5g of intermediate 1 to 120mL of anhydrous methanol, purge with nitrogen for 30min, add 14g of N,N-dimethyl-1,3-diaminopropane, purge with nitrogen for another 30min, and then react at 50℃ for 24h. After the reaction is complete, wash the product three times with anhydrous methanol and dry at 50℃ to obtain intermediate 2. (3) Under nitrogen protection, 100 mL of N,N-dimethylformamide solvent and 2 g of intermediate 2 were added to the reactor and stirred to dissolve. Then, 1 g of propanesulfonic acid lactone was dissolved in 5 mL of N,N-dimethylformamide and added dropwise to the reactor at 0 °C. After the addition was complete, the reaction was stirred at 30 °C for 8 h. After the reaction was completed, the mixture was dialyzed using a 3500 Da dialysis bag for 48 h and dried to obtain modified chitosan, such as... Figure 1 As shown; (4) Add 0.6 g of dodecyl dimethyl betaine to 150 mL of deionized water and stir at 40 °C to dissolve it. Then add 3 g of bentonite and stir for 12 h. After the reaction is complete, centrifuge to remove the supernatant, wash with deionized water 3 times, dry at 60 °C, and pass through a 200 mesh sieve to obtain modified bentonite. (5) Add 1 part by weight of modified bentonite to 9 parts by weight of deionized water, and ultrasonically disperse for 30 min to obtain a modified bentonite suspension with a mass fraction of 10%. (6) Add 20 parts by weight of corn starch to 70 parts by weight of deionized water, stir at 70°C for 30 min to gelatinize, then cool to room temperature, add 2 parts by weight of modified chitosan, stir to dissolve, then add the modified bentonite suspension obtained in step (5), stir at 1200 r / min for 20 min, and finally add 0.5 parts by weight of citric acid and continue stirring for 10 min to obtain the mixture. (7) The mixture is placed in a microwave reactor and microwave reaction is carried out. The microwave radiation power is 380W and the radiation time is 3min. After the reaction is completed, it is dried at 60℃, crushed and granulated into 1mm particles to obtain biodegradable soil water retention material.

[0018] Depend on Figure 2 It can be seen that in this spectrum, 3100-3300cm -1 The broad peak at 2800-3000 cm⁻¹ corresponds to the stretching vibration of the hydroxyl group (-OH) in chitosan itself and the stretching vibration of the imino group (-NH⁻) introduced by the amination reaction; -1 The absorption peak at 1720 cm⁻¹ corresponds to the stretching vibration of alkyl groups (CH), proving that the alkyl groups of methyl acrylate and N,N-dimethyl-1,3-diaminopropane have been grafted onto the chitosan molecule; -1 The strong absorption peak at 1550 cm⁻¹ corresponds to the stretching vibration of the ester carbonyl group (C=O), proving that the grafting reaction between chitosan and methyl acrylate in step S1 was successful and intermediate 1 was formed; -1 The absorption peak at 1150 cm⁻¹ corresponds to the bending vibration of the imino group (-NH⁻), proving that the amination reaction of intermediate 1 with N,N-dimethyl-1,3-diaminopropane in step S2 was completed, and intermediate 2 was formed; -1 The absorption peak at the point corresponds to the characteristic vibration of the S=O bond in the sulfonic acid group (-SO3H), indicating that the sulfonation reaction between intermediate 2 and propanesulfonic acid lactone in step S3 was successful, and the grafting of the sulfonic acid group of the target modified chitosan was completed.

[0019] Depend on Figure 3 It can be seen that in this spectrum, 3600-3800cm -1 The absorption peak at 3300 cm⁻¹ corresponds to the weak stretching vibration peak of the bentonite hydroxyl group (-OH); -1 The strong absorption peak at 2850-2920 cm⁻¹ corresponds to the overlapping peaks of the stretching vibrations of hydroxyl (-OH) and imine (-NH₃) groups in starch, chitosan, and bentonite; -1 The characteristic absorption peak at 1710-1720 cm⁻¹ corresponds to the long-chain alkyl (CH) stretching vibration of dodecyl dimethyl betaine, but it is masked by the strong peak of the host polymer in the composite material; -1 The strong absorption peak at 1640 cm⁻¹ corresponds to the stretching vibration of the (-COOR) C=O ester group generated by the hydroxyl esterification reaction of citric acid and starch / chitosan, proving that a three-dimensional water-retaining network has been formed; -1 The absorption peak at 1180 cm⁻¹ corresponds to the C=O stretching vibration of the amide bond in the modified chitosan, which is superimposed with the HOH bending vibration of adsorbed water, proving that the modified chitosan participates in the complexation; -1 The absorption peak at 1030 cm⁻¹ corresponds to the stretching vibration of starch CO and the S=O stretching vibration of the sulfonic acid group in the modified chitosan, proving that the modified chitosan has been successfully combined; -1 The strong absorption peak at the point corresponds to the Si-O-Si stretching vibration of bentonite. The peak shape is slightly broader than that of pure bentonite, which proves that the modified bentonite has undergone intercalation with the polymer and has completed the composite with the polymer.

[0020] Example 2 (1) Add 3.1 g of chitosan powder to 160 mL of anhydrous methanol, purge with nitrogen for 30 min, add 1.2 mL of anhydrous methyl acrylate, purge with nitrogen for another 30 min, and then react at 50 °C for 26 h. After the reaction is complete, the product is washed 4 times with anhydrous methanol and dried at 60 °C to obtain intermediate 1. (2) Add 2.6 g of intermediate 1 to 130 mL of anhydrous methanol, purge with nitrogen for 35 min, add 15 g of N,N-dimethyl-1,3-diaminopropane, purge with nitrogen for another 35 min, and then react at 55 °C for 28 h. After the reaction is complete, the product is washed 4 times with anhydrous methanol and dried at 60 °C to obtain intermediate 2. (3) Under nitrogen protection, 110 mL of N,N-dimethylformamide solvent and 2.1 g of intermediate 2 were added to the reactor and stirred to dissolve. Then, 1.1 g of propanesulfonic acid lactone was dissolved in 6 mL of N,N-dimethylformamide and added dropwise to the reactor at 5 °C. After the addition was completed, the reaction was stirred at 40 °C for 12 h. After the reaction was completed, the mixture was dialyzed for 72 h using a 4000 Da dialysis bag and dried to obtain modified chitosan. (4) Add 0.7g of dodecyl dimethyl betaine to 160mL of deionized water and stir at 45℃ to dissolve it. Then add 3.1g of bentonite and stir for 14h. After the reaction is complete, centrifuge to remove the supernatant, wash with deionized water 4 times, dry at 65℃, and pass through a 250-mesh sieve to obtain modified bentonite. (5) Add 2 parts by weight of modified bentonite to 9 parts by weight of deionized water and ultrasonically disperse for 40 min to obtain a modified bentonite suspension with a mass fraction of 10%. (6) Add 30 parts by weight of corn starch to 80 parts by weight of deionized water, stir at 80°C for 40 min to gelatinize, then cool to room temperature, add 4 parts by weight of modified chitosan, stir to dissolve, then add the modified bentonite suspension obtained in step (5), stir at 1500 r / min for 25 min, and finally add 0.8 parts by weight of citric acid and continue stirring for 15 min to obtain the mixture. (7) The mixture is placed in a microwave reactor and microwave reaction is carried out. The microwave radiation power is 400W and the radiation time is 4min. After the reaction is completed, it is dried at 65℃, crushed and granulated into 3mm particles to obtain biodegradable soil water retention material.

[0021] Example 3 (1) Add 3.05 g of chitosan powder to 155 mL of anhydrous methanol, purge with nitrogen for 28 min, add 1.1 mL of anhydrous methyl acrylate, purge with nitrogen for another 28 min, and then react at 48 °C for 24 h. After the reaction is complete, the product is washed three times with anhydrous methanol and dried at 55 °C to obtain intermediate 1. (2) Add 2.55 g of intermediate 1 to 125 mL of anhydrous methanol, purge with nitrogen for 33 min, add 14.5 g of N,N-dimethyl-1,3-diaminopropane, purge with nitrogen for 32 min, and then react at 52 °C for 26 h. After the reaction is complete, wash the product three times with anhydrous methanol and dry at 55 °C to obtain intermediate 2. (3) Under nitrogen protection, 105 mL of N,N-dimethylformamide solvent and 2.05 g of intermediate 2 were added to the reactor and stirred to dissolve. Then, 1.05 g of propanesulfonic acid lactone was dissolved in 5 mL of N,N-dimethylformamide and added dropwise to the reactor at 2 °C. After the addition was completed, the reaction was stirred at 35 °C for 10 h. After the reaction was completed, the mixture was dialyzed for 60 h using a 3500 Da dialysis bag and dried to obtain modified chitosan. (4) Add 0.65 g of dodecyl dimethyl betaine to 155 mL of deionized water and stir at 42 °C to dissolve it. Then add 3.05 g of bentonite and stir for 13 h. After the reaction is complete, centrifuge to remove the supernatant, wash with deionized water 3 times, dry at 62 °C, and pass through a 200 mesh sieve to obtain modified bentonite. (5) Add 1 part by weight of modified bentonite to 9 parts by weight of deionized water and ultrasonically disperse for 35 min to obtain a modified bentonite suspension with a mass fraction of 10%. (6) Add 25 parts by weight of corn starch to 75 parts by weight of deionized water, stir at 75°C for 35 min to gelatinize, then cool to room temperature, add 3 parts by weight of modified chitosan, stir to dissolve, then add the modified bentonite suspension obtained in step (5), stir at 1300 r / min for 22 min, and finally add 0.6 parts by weight of citric acid and continue stirring for 12 min to obtain the mixture. (7) The mixture is placed in a microwave reactor and microwave reaction is carried out. The microwave radiation power is 390W and the radiation time is 3min. After the reaction is completed, it is dried at 62℃, crushed and granulated into 2mm particles to obtain biodegradable soil water retention material.

[0022] Example 4 (1) Add 3.02 g of chitosan powder to 152 mL of anhydrous methanol, purge with nitrogen for 26 min, add 1.05 mL of anhydrous methyl acrylate, purge with nitrogen for another 26 min, and then react at 46 °C for 23 h. After the reaction is complete, the product is washed three times with anhydrous methanol and dried at 52 °C to obtain intermediate 1. (2) Add 2.52 g of intermediate 1 to 122 mL of anhydrous methanol, purge with nitrogen for 31 min, add 14.2 g of N,N-dimethyl-1,3-diaminopropane, purge with nitrogen for 32 min, and then react at 52 °C for 25 h. After the reaction is complete, wash the product three times with anhydrous methanol and dry at 52 °C to obtain intermediate 2. (3) Under nitrogen protection, 102 mL of N,N-dimethylformamide solvent and 2.02 g of intermediate 2 were added to the reactor and stirred to dissolve. Then, 1.02 g of propanesulfonic acid lactone was dissolved in 5 mL of N,N-dimethylformamide and added dropwise to the reactor at 1 °C. After the addition was completed, the reaction was stirred at 32 °C for 9 h. After the reaction was completed, the mixture was dialyzed for 54 h using a 3500 Da dialysis bag and dried to obtain modified chitosan. (4) Add 0.62 g of dodecyl dimethyl betaine to 152 mL of deionized water and stir at 41 °C to dissolve it. Then add 3.02 g of bentonite and stir for 12 h. After the reaction is complete, centrifuge to remove the supernatant, wash with deionized water 3 times, dry at 61 °C, and pass through a 200 mesh sieve to obtain modified bentonite. (5) Add 1 part by weight of modified bentonite to 9 parts by weight of deionized water and ultrasonically disperse for 32 min to obtain a modified bentonite suspension with a mass fraction of 10%. (6) Add 22 parts by weight of corn starch to 72 parts by weight of deionized water, stir at 72°C for 32 min to gelatinize, then cool to room temperature, add 2 parts by weight of modified chitosan, stir to dissolve, then add the modified bentonite suspension obtained in step (5), stir at 1300 r / min for 21 min, and finally add 0.6 parts by weight of citric acid and continue stirring for 11 min to obtain the mixture. (7) The mixture is placed in a microwave reactor and microwave reaction is carried out. The microwave radiation power is 380W and the radiation time is 3min. After the reaction is completed, it is dried at 60℃, crushed and granulated into 1mm particles to obtain biodegradable soil water retention material.

[0023] Example 5 (1) Add 3.08 g of chitosan powder to 158 mL of anhydrous methanol, purge with nitrogen for 28 min, add 1.15 mL of anhydrous methyl acrylate, purge with nitrogen for another 28 min, and then react at 49 °C for 25 h. After the reaction is complete, the product is washed 4 times with anhydrous methanol and dried at 58 °C to obtain intermediate 1. (2) Add 2.58 g of intermediate 1 to 128 mL of anhydrous methanol, purge with nitrogen for 34 min, add 14.8 g of N,N-dimethyl-1,3-diaminopropane, purge with nitrogen for another 34 min, and then react at 54 °C for 27 h. After the reaction is complete, the product is washed 4 times with anhydrous methanol and dried at 58 °C to obtain intermediate 2. (3) Under nitrogen protection, 108 mL of N,N-dimethylformamide solvent and 2.08 g of intermediate 2 were added to the reactor and stirred to dissolve. Then, 1.08 g of propanesulfonic acid lactone was dissolved in 6 mL of N,N-dimethylformamide and added dropwise to the reactor at 4 °C. After the addition was completed, the reaction was stirred at 38 °C for 11 h. After the reaction was completed, the mixture was dialyzed for 66 h using a 4000 Da dialysis bag and dried to obtain modified chitosan. (4) Add 0.68 g of dodecyl dimethyl betaine to 158 mL of deionized water and stir at 44 °C to dissolve it. Then add 3.08 g of bentonite and stir for 14 h. After the reaction is complete, centrifuge to remove the supernatant, wash with deionized water 4 times, dry at 64 °C, and pass through a 250 mesh sieve to obtain modified bentonite. (5) Add 2 parts by weight of modified bentonite to 9 parts by weight of deionized water and ultrasonically disperse for 38 min to obtain a modified bentonite suspension with a mass fraction of 10%. (6) Add 28 parts by weight of corn starch to 78 parts by weight of deionized water, stir at 78°C for 38 min to gelatinize, then cool to room temperature, add 4 parts by weight of modified chitosan, stir to dissolve, then add the modified bentonite suspension obtained in step (5), stir at 1400 r / min for 24 min, and finally add 0.7 parts by weight of citric acid and continue stirring for 14 min to obtain the mixture. (7) The mixture is placed in a microwave reactor and microwave reaction is carried out. The microwave radiation power is 400W and the radiation time is 4min. After the reaction is completed, it is dried at 64℃, crushed and granulated into 2mm particles to obtain biodegradable soil water retention material.

[0024] Comparative Example 1 The main difference between this comparative example and Example 5 is that intermediate 2 is used instead of modified chitosan.

[0025] Comparative Example 2 The main difference between this comparative example and Example 5 is that bentonite is used instead of modified bentonite.

[0026] Performance testing (1) Water retention performance test: 0.5g of each of the biodegradable soil water retention materials prepared in Examples 1-5 and Comparative Examples 1-2 were mixed with desert sandy soil at a mass ratio of 1:800 and placed in PVC pipes with a diameter of 10cm and a height of 20cm (with quartz sand at the bottom to prevent soil leakage). After adding water to saturation initially, the mixtures were placed in a constant temperature and humidity chamber at 25℃ and 30% relative humidity. On the 30th day, the soil moisture content of each group was measured (using the drying method, 10g of soil sample was dried at 105℃ to constant weight for calculation). At the same time, the field water holding capacity of each group of soil was measured using the ring cutter method (the soil sample was naturally drained for 48h after saturation, and the soil moisture content at this time was measured) and the wilting coefficient (measured by the soil moisture content of potted seedlings). The test results are shown in Table 1.

[0027] Table 1: Water Retention Performance Test

[0028] As can be seen from Table 1, the biodegradable soil water-retaining materials prepared in Examples 1-5 have good water retention performance.

[0029] (2) Salt tolerance test: Take 0.5g of each of the biodegradable soil water-retaining materials prepared in Examples 1-5 and Comparative Examples 1-2, dry them, pass them through an 80-mesh sieve, and place them in 500mL of 0.9% NaCl solution (simulating the sodium salt environment of desert soil) and 500mL of 0.2% CaCl2 solution (simulating the high-valence ion salt environment), respectively. After standing at 25℃ for 24h, take them out with a 100-mesh nylon mesh bag, hang them to drain for 10 minutes, wipe the outer wall of the bag with filter paper, weigh them, and calculate the water absorption ratio (mass after water absorption / dry mass). Then place the water-absorbed and swollen material in a 50℃ oven to dry to constant weight, complete one cycle, and repeat the above water absorption-drying operation 4 times. Measure the water absorption ratio of the 5th time and calculate the water absorption performance retention rate (water absorption ratio of the 5th time / water absorption ratio of the 1st time × 100%). The test results are shown in Table 2.

[0030] Table 2: Salt Tolerance Test

[0031] As can be seen from Table 2, the biodegradable soil water-retaining materials prepared in Examples 1-5 have good salt resistance.

[0032] (3) Biodegradability test: The biodegradability of the biodegradable soil water-retaining materials prepared in Examples 1-5 and Comparative Examples 1-2 was determined by the soil burial method. The test soil was alkaline (pH 8.14). The test soil was air-dried one week in advance, passed through a 2 mm sieve, and the moisture content was adjusted to 70% ± 5% of its maximum water holding capacity. 1 g (m0) of the biodegradable soil water-retaining materials prepared in Examples 1-5 and Comparative Examples 1-2 was weighed, dried, passed through an 80 mesh sieve, and loaded into the pre-weighed (m0) soil. d The samples were placed in a 100-mesh nonwoven nylon mesh bag (6cm×8cm), weighed, and the total weight was recorded as m1. The mesh bag was then clamped shut and placed in a culture bottle containing 250g of moist soil. Each sample was buried 10cm below the soil surface. The culture bottle was placed in a 25℃ constant temperature incubator for 30 days, with water added periodically to maintain humidity. After the culture was completed, the mesh bag was removed, the surface soil was cleaned, rinsed with deionized water, and dried at 60℃ to constant weight. The weight was recorded as m2. The degradation rate of each sample was calculated using the formula: degradation rate = (m1-m2) / m0×100%. The test results are shown in Table 3.

[0033] Table 3: Degradability Performance Test

[0034] As can be seen from Table 3, the biodegradable soil water-retaining materials prepared in Examples 1-5 have good degradability.

[0035] The comparison shows that, in Comparative Example 1, intermediate 2 was used instead of modified chitosan. This intermediate lacks the strongly hydrated zwitterionic structure composed of quaternary ammonium salt groups and sulfonic acid groups. Furthermore, the tertiary amine group in intermediate 2 has weak hydrophilicity and cannot effectively lock in water, leading to decreased water retention. In a salt environment, intermediate 2 lacks sulfonic acid groups, resulting in weak resistance to salt ion interference. The tertiary amine group is prone to protonation, causing the molecular chain to coil and obstructing water absorption channels, thus reducing salt tolerance. Due to the large steric hindrance of the tertiary amine group in intermediate 2, the attack of the molecular chain by microbial degrading enzymes is also a significant challenge. The reduced impact efficiency resulted in a slightly lower degradation rate compared to the example. Comparative Example 2 used bentonite instead of modified bentonite. Unmodified bentonite is highly hydrophilic but has poor dispersibility, easily agglomerating into large particles, which cannot form a uniform porous water-retaining network. Furthermore, the interlayer ions of unmodified bentonite easily exchange with sodium and calcium ions in the salt solution, leading to the collapse of the interlayer structure. The resulting large agglomerates hinder the contact between microorganisms and the water-retaining material. Therefore, the water retention performance, salt resistance, and degradability of Comparative Example 2 all decreased compared to the example.

[0036] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0037] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0038] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A method for preparing a biodegradable soil water-retaining material, characterized in that, Includes the following steps: (1) Preparation of modified chitosan: S1: Add 3-3.1g of chitosan powder to 150-160mL of anhydrous methanol, purge with nitrogen for 25-30min, add 1-1.2mL of anhydrous methyl acrylate, purge with nitrogen again for 25-30min, and then react at 45-50℃. After the reaction is complete, wash the product with anhydrous methanol 3-4 times and dry at 50-60℃ to obtain intermediate 1. S2: Add 2.5-2.6 g of intermediate 1 to 120-130 mL of anhydrous methanol, purge with nitrogen for 30-35 min, add 14-15 g of N,N-dimethyl-1,3-diaminopropane, purge with nitrogen again for 30-35 min, and then react at 50-55 °C. After the reaction is complete, wash the product with anhydrous methanol 3-4 times and dry at 50-60 °C to obtain intermediate 2. S3: Under nitrogen protection, add 100-110 mL of N,N-dimethylformamide solvent and 2-2.1 g of intermediate 2 to the reactor and stir to dissolve. Then, dissolve 1-1.1 g of propanesulfonic acid lactone in 5-6 mL of N,N-dimethylformamide and add it dropwise to the reactor at 0-5℃. After the addition is complete, stir the reaction at 30-40℃ for 8-12 h. After the reaction is completed, dialyze the mixture using a 3500-4000 Da dialysis bag and dry it to obtain modified chitosan. (2) Preparation of modified bentonite: Add 0.6-0.7g of dodecyl dimethyl betaine to 150-160mL of deionized water and stir at 40-45℃ to dissolve it. Then add 3-3.1g of bentonite and stir to react. After the reaction is completed, centrifuge to remove the supernatant, wash with deionized water 3-4 times, dry at 60-65℃, and pass through a 200-250 mesh sieve to obtain modified bentonite. (3) Add 1-2 parts by weight of modified bentonite to 9 times its weight of deionized water, and ultrasonically disperse for 30-40 minutes to obtain a modified bentonite suspension with a mass fraction of 10%. (4) Add 20-30 parts by weight of corn starch to 70-80 parts by weight of deionized water, stir at 70-80℃ for 30-40 min to gelatinize, then cool to room temperature, add 2-4 parts by weight of modified chitosan, stir to dissolve, then add the modified bentonite suspension obtained in step (3), stir at 1200-1500 r / min for 20-25 min, and finally add 0.5-0.8 parts by weight of citric acid and continue stirring for 10-15 min to obtain the mixture. (5) Place the mixture into a microwave reactor and carry out a microwave reaction. After the reaction is completed, dry it at 60-65℃, crush it, and granulate it into 1-3 mm particles to obtain biodegradable soil water-retaining material.

2. The method for preparing the biodegradable soil water-retaining material according to claim 1, characterized in that, The reaction time in S1 is 22-26 hours.

3. The method for preparing the biodegradable soil water-retaining material according to claim 1, characterized in that, The reaction time in S2 is 24-28 hours.

4. The method for preparing the biodegradable soil water-retaining material according to claim 1, characterized in that, The dialysis time in S3 is 48-72 hours.

5. The method for preparing the biodegradable soil water-retaining material according to claim 1, characterized in that, The reaction time in step (2) is 12-14 hours.

6. The method for preparing biodegradable soil water-retaining material according to claim 1, characterized in that, In step (5), the conditions for microwave reaction are: microwave radiation power of 380-400W and radiation time of 3-4min.

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