Crop straw-based degradable water-absorbent resin as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of water-absorbing material preparation, and provides a crop straw-based degradable water-absorbing resin as well as a preparation method and application thereof. The method comprises the following steps: pretreating crop straws by using an alkaline solution to obtain straw cellulose; the preparation method comprises the following steps: mixing straw cellulose, a first ethanol solution and a first alkali liquor for a first reaction, then adding a second ethanol solution and chloroacetic acid for a second reaction, and then adding a second alkali liquor for a third reaction to obtain straw cellulose sodium carboxymethyl; and mixing the straw cellulose sodium carboxymethyl, acrylic acid, an initiator, a cross-linking agent and water, and reacting to obtain the crop straw-based degradable water-absorbent resin. According to the method disclosed by the invention, a reaction inert structure in the straw cellulose can be removed, a crystalline region of the cellulose is destroyed, a homogeneous reaction preparation system is constructed, the grafting efficiency of the water-absorbent resin is improved, complete degradation of the water-absorbent resin is realized, and the production cost of the water-absorbent resin is also reduced.

Description

Technical Field

[0001] The invention relates to the technical field of water-absorbing material preparation, and in particular to a crop straw-based degradable water-absorbing resin and a preparation method and application thereof. Background Art

[0002] Super absorbent polymer (SAP), also known as water retaining agent, is a functional polymer material with a three-dimensional network structure. It has excellent water absorption and water retention properties and is widely used in many fields such as medical care, agriculture, forestry and horticulture, and industrial materials.

[0003] At present, the commercial super absorbent resins are mainly cross-linked polyacrylic acid salts, acrylic acid copolymers and starch-acrylic acid graft polymers. Although cross-linked polyacrylic acid salts and acrylic acid copolymers have high water absorption, they have serious disadvantages such as being difficult to be biodegraded and easily causing soil compaction. In addition, their selling price is high and their promotion is limited. Starch-acrylic acid graft polymers have high water absorption and water retention rates and are a relatively ideal agricultural water retainer, but they still have defects such as high production cost, poor salt and alkali resistance, low gel strength, short service life, and easy mildew during use. Therefore, in order to promote the water retainer technology, a water retainer with low price, stable performance and environmental friendliness should be developed and researched.

[0004] my country is rich in straw resources. The development of water-retaining agent products using crop straw as resources can not only reduce production costs, but also increase the utilization efficiency of renewable resources. In addition, the cellulose superabsorbent resin prepared from crop straw has good salt tolerance, easy pH adjustment, good biodegradability, and important environmental significance and economic value. It has become a hot spot for the research and development of new superabsorbent materials in recent years.

[0005] However, existing studies have shown that straw cellulose has an inert structure, which seriously affects the conversion efficiency of cellulose chemical modification. Natural polymers such as absorbent resins prepared by cellulose grafting copolymerization have a slightly lower water absorption capacity and cannot be completely degraded. This is because the main chain of the absorbent resin generated is still a polyacrylate composed of CC bonds. It can only be degraded by microorganisms when its molar mass is low enough (≤1500g / mol). To achieve complete degradation of cellulose absorbent resins, it is necessary to control the monomer polymerization molecular weight to be lower than 1500g / mol, which requires a high grafting efficiency and a low monomer polymerization rate between cellulose and monomers. However, the structural characteristics of straw cellulose will affect the grafting efficiency of absorbent resins, mainly manifested in the following aspects: (1) Lignin and hemicellulose in crop straw are combined in the form of covalent bonds, encapsulating cellulose molecules. The "reaction inert structure" formed by various cross-linked structures hinders the contact of chemical reagents with cellulose, reducing the reaction efficiency. (2) The cellulose in the straw has a relatively high crystalline region. Small molecule reagents can only contact 10% to 15% of the hydroxyl groups in the amorphous region. A large number of hydroxyl groups in the crystalline region cannot be reached, which limits the grafting rate and leads to low water absorption rate. If the crystalline region of the straw cellulose is not destroyed to activate the hydroxyl groups, the reaction efficiency will inevitably be extremely low. (3) Cellulose is insoluble in most reagents. At present, the grafting reaction of straw cellulose is a heterogeneous reaction, which has a great impact on the efficiency of the grafting reaction.

[0006] Therefore, there is an urgent need to provide a preparation method that can eliminate the influence of straw cellulose on the grafting efficiency of water-absorbent resin, so as to achieve complete degradation of water-absorbent resin. Summary of the invention

[0007] In view of this, the present invention provides a crop straw-based degradable water-absorbent resin and a preparation method and application thereof, so as to solve the problem that the water-absorbent resin prepared by the existing preparation method cannot be completely degraded and has a high production cost.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] The present invention provides a method for preparing a crop straw-based degradable water-absorbent resin, comprising the following steps:

[0010] 1) Pre-treating crop straw with an alkaline solution to obtain straw cellulose;

[0011] 2) mixing the straw cellulose, the first ethanol solution and the first alkali solution to carry out a first reaction, then adding the second ethanol solution and chloroacetic acid to carry out a second reaction, and then adding the second alkali solution to carry out a third reaction to obtain straw cellulose sodium carboxymethyl;

[0012] 3) Mixing straw cellulose sodium carboxymethyl, acrylic acid, an initiator, a cross-linking agent and water to react and obtain a crop straw-based degradable water-absorbent resin.

[0013] Preferably, in step 1), the mass volume ratio of the crop straw to the alkaline solution is 1-3 g:12-24 mL; the crop straw includes one or more of rice straw, rape straw and corn straw; the alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium carbonate solution, potassium carbonate solution and sodium bicarbonate solution; wherein the mass concentration of the alkaline solution is 2-6%.

[0014] Preferably, the pretreatment temperature in step 1) is 80-90° C. and the time is 2-6 hours.

[0015] Preferably, in step 2), the mass volume ratio of the straw cellulose, the first ethanol solution and the first alkali solution in the first reaction is 50-70g:110-130mL:700-750mL; the mass volume ratio of the straw cellulose to the second ethanol solution and chloroacetic acid in the second reaction is 50-70g:40-45mL:50-70g; the mass volume ratio of the straw cellulose to the second alkali solution in the third reaction is 50-70g:100-150mL; the mass concentration of the first ethanol solution is 70-75%, and the mass concentration of the second ethanol solution is 80-85%.

[0016] Preferably, in step 2), the first alkali solution and the second alkali solution independently include one or more of sodium hydroxide solution, potassium hydroxide solution and calcium hydroxide solution; wherein the mass concentrations of the first alkali solution and the second alkali solution independently are 2-4%.

[0017] Preferably, in step 2), the temperature of the first reaction is 25-40°C, and the time is 45-70 min; the temperature of the second reaction is 60-70°C, and the time is 80-100 min; the temperature of the third reaction is 60-70°C, and the time is 80-100 min; and the degree of substitution of the sodium carboxymethyl straw cellulose is 0.7-1.3.

[0018] Preferably, in step 3), the mass volume ratio of the sodium carboxymethyl straw cellulose to acrylic acid, initiator, cross-linking agent and water is 10-15 g: 10-15 g: 0.4-0.6 g: 7-13 mL: 100-150 mL.

[0019] Preferably, the acrylic acid in step 3) is acrylic acid neutralized with alkali solution, and the neutralization degree of the acrylic acid is 50-70%.

[0020] Preferably, the alkali solution in step 3) includes one or more of sodium hydroxide solution, potassium hydroxide solution and calcium hydroxide solution; the initiator includes one or both of potassium persulfate and sodium thiosulfate; the cross-linking agent includes one or more of citric acid, formaldehyde, N-hydroxymethyl acrylamide, N-N'methylene acrylamide, epichlorohydrin.

[0021] Preferably, the reaction temperature in step 3) is 55-80° C. and the reaction time is 1-3 h.

[0022] The present invention also provides a crop straw-based degradable water-absorbent resin prepared by the method for preparing the crop straw-based degradable water-absorbent resin.

[0023] The present invention also provides an application of the crop straw-based degradable water-absorbing resin as a soil water-retaining agent.

[0024] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0025] The preparation method of the present invention utilizes alkali treatment to remove lignin and hemicellulose in the straw cellulose, thereby removing the reaction inert structure in the straw cellulose, which is beneficial to improving the reaction efficiency, and also realizes the water-soluble conversion of the straw cellulose through carboxymethylation, destroys the crystalline region of the cellulose, activates a large number of hydroxyl groups in the crystalline region, and improves the grafting rate of the straw cellulose; at the same time, the preparation method of the present invention also establishes a homogeneous reaction preparation system of an aqueous solution of a water-absorbent resin under the condition of a low monomer dosage, thereby improving the grafting reaction efficiency. Therefore, the crop straw-based degradable water-absorbent resin prepared by the preparation method of the present invention eliminates the influence of the straw cellulose on the grafting efficiency of the water-absorbent resin, has a high grafting efficiency, and can be completely degraded. In addition, the present invention selects crop straw as the raw material for preparing the water-absorbent resin, which greatly reduces the production cost and is beneficial to promoting the large-scale production of the water-absorbent resin.

[0026] The crop straw-based degradable water-absorbing resin of the present invention can be used as a soil water-retaining agent to maintain the effectiveness of soil moisture and nutrients, reduce soil evaporation, reduce water penetration, effectively increase soil aggregate structure and improve soil porosity and field water holding capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0028] Figure 1 This is a flat plate degradation diagram of microorganisms on water-absorbent resin, where: Figure 1 a in the figure is a flat plate degradation diagram of the rice straw-based degradable water-absorbent resin obtained in Example 1 by microorganisms. Figure 1 The b in the figure is the degradation diagram of the Wote brand fine particle water-absorbing resin by microorganisms on a flat plate. Figure 1 The c in the figure is the degradation diagram of the coarse granular water-absorbent resin of Water brand by microorganisms on a flat plate;

[0029] Figure 2 This is the infrared absorption spectrum of the rice straw-based degradable water-absorbent resin before and after degradation in Example 1. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing a crop straw-based degradable water-absorbent resin, comprising the following steps:

[0031] 1) Pre-treating crop straw with an alkaline solution to obtain straw cellulose;

[0032] 2) mixing the straw cellulose, the first ethanol solution and the first alkali solution to carry out a first reaction, then adding the second ethanol solution and chloroacetic acid to carry out a second reaction, and then adding the second alkali solution to carry out a third reaction to obtain straw cellulose sodium carboxymethyl;

[0033] 3) Mixing straw cellulose sodium carboxymethyl, acrylic acid, an initiator, a cross-linking agent and water to react and obtain a crop straw-based degradable water-absorbent resin.

[0034] In the present invention, the mass volume ratio of the crop straw in step 1) to the alkaline solution is 1-3 g:12-24 mL, preferably 1 g:12 mL; the crop straw includes one or more of rice straw, rape straw and corn straw; the alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium carbonate solution, potassium carbonate solution and sodium bicarbonate solution; wherein the mass concentration of the alkaline solution is 2-6%, preferably 3-5%, and more preferably 4%.

[0035] In the present invention, the pretreatment temperature in step 1) is 80-90°C, preferably 82-88°C, more preferably 85°C; the pretreatment time is 2-6h, preferably 3-5h, more preferably 4h.

[0036] In the present invention, the pretreatment in step 1) can remove lignin and hemicellulose in the straw cellulose, and further remove the reaction inert structure of the straw cellulose, so as to increase the grafting reaction rate of the straw cellulose.

[0037] In the present invention, after the crop straw is pretreated with an alkaline solution, the method further includes filtering, washing and drying the straw cellulose.

[0038] In the present invention, the mesh size of the sieve for filtering the straw cellulose is preferably 90-120 meshes, more preferably 95-110 meshes, and more preferably 100 meshes; the solution for washing the straw cellulose preferably includes one or two of ethanol and water; the temperature for drying the straw cellulose is preferably 55-70°C, more preferably 65°C; the drying time is preferably 9-11 min, more preferably 10 min.

[0039] In the present invention, the mass volume ratio of the straw cellulose, the first ethanol solution and the first alkali solution in the first reaction in step 2) is 50-70g:110-130mL:700-750mL, preferably 55-65g:115-125mL:710-730mL, and more preferably 60g:120mL:720mL.

[0040] In the present invention, the mass volume ratio of the straw cellulose in step 2) to the second ethanol solution and chloroacetic acid in the second reaction is 50-70g:40-45mL:50-70g, preferably 55-65g:41-43mL:55-65g, and more preferably 60g:42mL:60g.

[0041] In the present invention, the mass volume ratio of the straw cellulose in step 2) to the second alkali solution in the third reaction is 50-70g:100-150mL, preferably 55-65g:110-130mL, and more preferably 60g:120mL.

[0042] In the present invention, the mass concentration of the first ethanol solution in step 2) is 70-75%, preferably 71-74%, and more preferably 73%; the mass concentration of the second ethanol solution is 80-85%, preferably 81-84%, and more preferably 83%; the first alkali solution and the second alkali solution independently include one or more of sodium hydroxide solution, potassium hydroxide solution and calcium hydroxide solution; wherein the mass concentrations of the first alkali solution and the second alkali solution are independently 2-4%, preferably 2.5-3.5%, and more preferably 3%.

[0043] In the present invention, the temperature of the first reaction in step 2) is 25-40°C, preferably 26-38°C, more preferably 28-35°C, and more preferably 30°C; the time of the first reaction is 45-70min, preferably 50-67min, more preferably 55-65min, and more preferably 60min; the temperature of the second reaction is 60-70°C, preferably 62-68°C, and more preferably 65°C; the time of the second reaction is 80-100min, preferably 85-95min, and more preferably 90min; the temperature of the third reaction is 60-70°C, preferably 62-68°C, and more preferably 65°C; the time of the third reaction is 80-100min, preferably 85-95min, and more preferably 90min.

[0044] In the present invention, the first reaction, the second reaction and the third reaction in step 2) are carboxymethyl reactions of the straw cellulose to achieve water-soluble conversion of the straw cellulose, break the hydrogen bonds between cellulose molecules, destroy the crystalline structure of the straw cellulose, effectively release the active hydroxyl groups on the glycogen, and improve the efficiency of the cellulose grafting reaction.

[0045] In the present invention, after the third reaction in step 2) is completed, the step of washing and drying the straw cellulose sodium carboxymethyl is also included.

[0046] In the present invention, the solution for washing the sodium carboxymethyl straw cellulose is preferably an ethanol solution; the temperature for drying the sodium carboxymethyl straw cellulose is preferably 60-80°C, more preferably 65-75°C, more preferably 70°C; the drying time is preferably 1-2h, more preferably 1.2-1.7h, more preferably 1.5h.

[0047] In the present invention, the degree of substitution of the sodium carboxymethyl straw cellulose is 0.7-1.3, preferably 0.75-1.1, and more preferably 0.78; as the degree of substitution increases, the water absorption rate of the water-absorbent resin increases first and then decreases.

[0048] In the present invention, the step of preparing the crop straw-based degradable water-absorbent resin in step 3) is preferably: first dissolving straw cellulose sodium carboxymethyl in water for activation, then adding acrylic acid, an initiator and a cross-linking agent for reaction to obtain the crop straw-based degradable water-absorbent resin.

[0049] In the present invention, the activation temperature is preferably 80-100°C, more preferably 85-95°C, and more preferably 90°C; the activation time is preferably 30-50 min, more preferably 35-45 min, and more preferably 40 min.

[0050] In the present invention, the mass volume ratio of the straw cellulose sodium carboxymethyl to acrylic acid, initiator, cross-linking agent and water in step 3) is 10-15g: 10-15g: 0.4-0.6g: 7-13mL: 100-150mL, preferably 11-13g: 11-13g: 0.45-0.55g: 8-11mL: 105-120mL, and more preferably 12g: 12g: 0.5g: 10mL: 110mL.

[0051] In the present invention, the acrylic acid in step 3) is acrylic acid neutralized with alkali solution, and the neutralization degree of the acrylic acid is 50-70%, preferably 55-65%, and more preferably 60%; as the amount of the acrylic acid monomer increases, the grafting rate and the length of the branch chain increase, which is conducive to the formation of an ideal colloid network structure, and the macroscopic performance is an increase in the liquid absorption rate; and reducing the amount of acrylic acid monomer can not only effectively reduce the production cost of the water-absorbent resin, but also improve the reaction uniformity, so as to control the monomer polymerization length (molecular weight <1500) and ensure that the water-absorbent resin can be completely degraded.

[0052] In the present invention, the alkali solution in step 3) includes one or more of sodium hydroxide solution, potassium hydroxide solution and calcium hydroxide solution; the initiator includes one or both of potassium persulfate and sodium thiosulfate, preferably potassium persulfate and sodium thiosulfate, wherein the mass ratio of potassium persulfate to sodium thiosulfate is preferably 1-3:1-3, more preferably 3:1; the cross-linking agent includes one or more of citric acid, formaldehyde, N-hydroxymethyl acrylamide, N-N'methylene acrylamide, epichlorohydrin.

[0053] In the present invention, the reaction temperature in step 3) is 55-80°C, preferably 60-78°C, more preferably 75°C; the reaction time is 1-3h, preferably 1.5-2.5h, more preferably 2h.

[0054] In the present invention, the reaction in step 3) is a homogeneous reaction, which is beneficial to improving the grafting reaction efficiency of cellulose.

[0055] The present invention also provides a crop straw-based degradable water-absorbent resin prepared by the method for preparing the crop straw-based degradable water-absorbent resin.

[0056] The present invention also provides an application of the crop straw-based degradable water-absorbing resin as a soil water-retaining agent.

[0057] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0058] Example 1

[0059] 1) 60 g of rice straw was mixed with 720 mL of a 2% sodium hydroxide solution, and pretreated at 85° C. for 4 h to obtain straw cellulose, and then the straw cellulose was filtered with a 100-mesh filter, and the filter residue was washed with an 80% ethanol solution and dried in an oven at 65° C. for 10 min for later use;

[0060] 2) 60g of the straw cellulose dried in step 1), 120mL of an ethanol solution having a mass concentration of 74% and 720mL of a sodium hydroxide solution having a mass concentration of 2% were mixed, reacted at a temperature of 30°C for 60min, then 43mL of an ethanol solution having a mass concentration of 83% and 60g of chloroacetic acid were added, the reaction continued at a temperature of 65°C for 90min, 120mL of a sodium hydroxide solution having a mass concentration of 2% was added, the reaction was carried out at a temperature of 65°C for 90min, and finally washed with an ethanol solution having a mass concentration of 80% and dried in an oven at 70°C for 1.5h to obtain straw cellulose sodium carboxymethyl with a degree of substitution of 0.78;

[0061] 3) Dissolve 12 g of the straw cellulose sodium carboxymethyl in step 2) in 110 mL of deionized water and activate it in a constant temperature water bath at 90° C. for 40 min, then lower the water bath temperature to a reaction temperature of 75° C., add 12 g of acrylic acid (neutralization degree 60%) pre-neutralized with KOH, 0.5 g of potassium persulfate and sodium thiosulfate in a mass ratio of 3:1, and 10 mL of citric acid crosslinker, and react for 2 h to obtain a rice straw-based biodegradable water-absorbent resin.

[0062] After testing, the water absorption ratio of the rice straw-based degradable water-absorbent resin obtained in Example 1 was 63.28 g / g, and the water absorption rate reached a maximum of 2.277 g / (min·g) at 15 min, indicating that the degradable water-absorbent resin of the present invention has high water absorption capacity and rapid water absorption capacity, and has a very broad application prospect.

[0063] The rice straw-based degradable water-absorbing resin prepared in Example 1 was added to the soil as a soil water-retaining agent. After testing, after adding the rice straw-based degradable water-absorbing resin prepared in Example 1 to the soil, the infiltration of water in the soil can be inhibited, the soil aggregate structure can be effectively increased, the increase in the content of large-size aggregates is higher than the increase in the content of small-size aggregates, and the soil porosity and field water holding capacity are increased by 21.67% and 47.6%, respectively. The desorption of nitrogen, potassium and phosphorus in the soil is reduced, indicating that the water-absorbing resin of the present invention also has the ability to retain fertilizers and can reduce the loss of fertilizers in the soil.

[0064] Example 2

[0065] 1) 60 g corn stalks were mixed with 900 mL of a 4% potassium hydroxide solution, and pretreated at 80° C. for 6 h to obtain stalk cellulose, and then the stalk cellulose was filtered with a 90-mesh filter, and the filter residue was washed with an 80% ethanol solution and dried in an oven at 60° C. for 11 min for later use;

[0066] 2) 60g of the straw cellulose dried in step 1), 110mL of an ethanol solution with a mass concentration of 75% and 700mL of a potassium hydroxide solution with a mass concentration of 4% were mixed, reacted at a temperature of 25°C for 70min, then 40mL of an ethanol solution with a mass concentration of 85% and 50g of chloroacetic acid were added, the reaction was continued at a temperature of 60°C for 100min, 100mL of a potassium hydroxide solution with a mass concentration of 4% was added, the reaction was carried out at a temperature of 60°C for 100min, and finally washed with an ethanol solution with a mass concentration of 80% and dried in an oven at 60°C for 2h to obtain straw cellulose sodium carboxymethyl with a degree of substitution of 0.7;

[0067] 3) Dissolve 10 g of the sodium carboxymethyl straw cellulose in step 2) in 100 mL of deionized water and activate it in a constant temperature water bath at 80 ° C for 50 min, then lower the temperature of the water bath to a reaction temperature of 60 ° C, add 10 g of acrylic acid (neutralization degree 55%) pre-neutralized with KOH, 0.4 g of potassium persulfate and sodium thiosulfate in a mass ratio of 2: 1 and 7 mL of formaldehyde crosslinking agent, and react for 1.2 h to obtain a corn straw-based biodegradable water-absorbent resin.

[0068] Example 3

[0069] 1) 60 g of rape straw was mixed with 950 mL of a 6% sodium bicarbonate solution, and pretreated at 90° C. for 2 h to obtain straw cellulose, and then the straw cellulose was filtered with a 120-mesh filter, and the filter residue was washed with an 80% ethanol solution and dried in an oven at 70° C. for 9 min for later use;

[0070] 2) 60g of the straw cellulose dried in step 1), 130mL of an ethanol solution with a mass concentration of 70% and 750mL of a calcium hydroxide solution with a mass concentration of 3% were mixed, reacted at a temperature of 40°C for 45min, then 45mL of an ethanol solution with a mass concentration of 80% and 70g of chloroacetic acid were added, the reaction was continued at a temperature of 70°C for 80min, 150mL of a calcium hydroxide solution with a mass concentration of 3% was added, the reaction was carried out at a temperature of 70°C for 80min, and finally washed with an ethanol solution with a mass concentration of 80% and dried in an oven at 80°C for 1h to obtain straw cellulose sodium carboxymethyl with a degree of substitution of 0.9;

[0071] 3) 13 g of the sodium carboxymethyl straw cellulose in step 2) was dissolved in 130 mL of deionized water and activated in a constant temperature water bath at 100 ° C for 30 min, then the water bath temperature was lowered to a reaction temperature of 80 ° C, 13 g of acrylic acid pre-neutralized with sodium hydroxide (neutralization degree 65%), 0.6 g of potassium persulfate and sodium thiosulfate in a mass ratio of 1:3 and 13 mL of N-hydroxymethyl acrylamide crosslinker were added, and the reaction was carried out for 3 hours to obtain a rape straw-based biodegradable water-absorbent resin.

[0072] Experimental Example 1

[0073] The rice straw-based degradable water-absorbing resin prepared in Example 1 was tested for its microbial degradation performance.

[0074] The Hutcheson medium was used, and the rice straw-based degradable water-absorbent resin obtained in Example 1 was added as the sole carbon source to inoculate the M205 strain. The plate was inverted and cultured in a constant temperature incubator at 30°C. After 10 days, the culture plate was taken out to observe the growth of microorganisms. At the same time, the same experimental method was used to test the microbial degradation performance of the Water brand fine particle water-absorbent resin and the coarse particle water-absorbent resin. The experimental results are as follows: Figure 1 As shown, from Figure 1 It can be seen that a large number of colonies are generated on the culture medium using the rice straw-based degradable water-absorbent resin obtained in Example 1 as the carbon source, and no colony growth is observed in the culture medium using the Water brand fine-particle water-absorbent resin and the coarse-particle water-absorbent resin as the nutrient source, indicating that the Water brand fine-particle water-absorbent resin and the coarse-particle water-absorbent resin cannot be degraded by the cellulase-producing strain, and the rice straw-based degradable water-absorbent resin provided by the present invention has excellent biodegradability.

[0075] Experimental Example 2

[0076] The soil degradation performance of the rice straw-based degradable water-absorbing resin prepared in Example 1 was tested.

[0077] The solidified and undried rice straw-based degradable water-absorbent resin in Example 1 was sliced, dried, weighed and recorded as W1, and taken out and dried after being buried in the soil for 5 days, 10 days, 15 days and 20 days, and weighed and recorded as W2. The test was repeated three times, and the structural morphology was observed by infrared spectrometer to calculate the degradation rate. The results are shown in Table 1 below.

[0078] Degradation rate = (W1-W2) / W2

[0079] Table 1 Degradation performance results of water-absorbent resin

[0080]

[0081]

[0082] As can be seen from Table 1, the soil burial method can degrade the straw-based water-absorbent resin provided by the present invention, and the degradation rate in the first 5 days is the highest. As time goes by, the degradation efficiency gradually decreases. This may be because the ratio of monomer to rice carboxymethyl cellulose in the graft polymerization reaction is low, and some rice carboxymethyl cellulose does not undergo grafting reaction, and the carboxymethyl cellulose is degraded faster after being acted on by cellulase, resulting in a higher degradation rate in the first five days. When the soil is buried for 20 days, the average degradation rate of the water-absorbent resin is 27.6%, indicating that the water-absorbent resin provided by the present invention has good degradation performance and a faster degradation rate.

[0083] Figure 2 The infrared absorption spectra of the rice straw-based degradable water-absorbing resin before and after degradation in Example 1 are shown in FIG. Figure 2 It can be seen that the amplitude of the infrared spectrum of the degraded water-absorbent resin changes. -1 The band is the absorption peak of the hydroxyl group in the molecule. In plant straw, the hydroxyl group mainly comes from cellulose. The decrease in the amplitude of this band indicates that the cellulose has been degraded. -1 The band amplitude also weakened, indicating that the carboxyl group also degraded. -1 The characteristic peak value of RCOO- at the position is reduced, indicating that the long chain of polymerized acrylic acid is also degraded. The changes in the amplitude of these infrared spectra all indicate that the water-absorbent resin has been significantly degraded after being buried in the soil. The preparation method of the present invention greatly improves the grafting efficiency of the water-absorbent resin and achieves complete degradation of the water-absorbent resin.

[0084] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a crop straw-based degradable water-absorbent resin, characterized in that: The steps include: 1) Pre-treating crop straw with an alkaline solution to obtain straw cellulose; 2) mixing the straw cellulose, the first ethanol solution and the first alkali solution to carry out a first reaction, then adding the second ethanol solution and chloroacetic acid to carry out a second reaction, and then adding the second alkali solution to carry out a third reaction to obtain straw cellulose sodium carboxymethyl; 3) Mixing straw cellulose sodium carboxymethyl, acrylic acid, an initiator, a cross-linking agent and water to react and obtain a crop straw-based degradable water-absorbent resin.

2. The method for preparing a crop straw-based degradable water-absorbent resin according to claim 1, characterized in that: The mass volume ratio of the crop straw to the alkaline solution in step 1) is 1-3 g: 12-24 mL; The crop straw includes one or more of rice straw, rape straw and corn straw; The alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium carbonate solution, potassium carbonate solution and sodium bicarbonate solution; wherein the mass concentration of the alkaline solution is 2-6%.

3. The method for preparing a crop straw-based degradable water-absorbent resin according to claim 2, characterized in that: The pretreatment temperature in step 1) is 80-90° C. and the time is 2-6 hours.

4. The method for preparing a crop straw-based degradable water-absorbent resin according to any one of claims 1 to 3, characterized in that: In step 2), the mass volume ratio of the straw cellulose, the first ethanol solution and the first alkali solution in the first reaction is 50-70 g: 110-130 mL: 700-750 mL; The mass volume ratio of the straw cellulose to the second ethanol solution and chloroacetic acid in the second reaction is 50-70 g: 40-45 mL: 50-70 g; The mass volume ratio of the straw cellulose to the second alkali solution in the third reaction is 50-70 g:100-150 mL; The mass concentration of the first ethanol solution is 70-75%, and the mass concentration of the second ethanol solution is 80-85%; The first alkali solution and the second alkali solution independently include one or more of a sodium hydroxide solution, a potassium hydroxide solution and a calcium hydroxide solution; wherein the mass concentrations of the first alkali solution and the second alkali solution independently are 2-4%.

5. The method for preparing a crop straw-based degradable water-absorbent resin according to claim 4, characterized in that: In step 2), the temperature of the first reaction is 25-40°C and the time is 45-70 minutes; The temperature of the second reaction is 60-70°C and the time is 80-100 min; The temperature of the third reaction is 60-70°C and the time is 80-100 minutes; The substitution degree of the straw cellulose sodium carboxymethyl is 0.7-1.

3.

6. The method for preparing a crop straw-based degradable water-absorbent resin according to claim 5, characterized in that: The mass volume ratio of the straw cellulose sodium carboxymethyl to acrylic acid, initiator, cross-linking agent and water in step 3) is 10-15 g: 10-15 g: 0.4-0.6 g: 7-13 mL: 100-150 mL.

7. The method for preparing a crop straw-based degradable water-absorbent resin according to claim 6, characterized in that: The acrylic acid in step 3) is acrylic acid neutralized with alkali solution, and the neutralization degree of the acrylic acid is 50-70%; The alkali solution includes one or more of sodium hydroxide solution, potassium hydroxide solution and calcium hydroxide solution; The initiator includes one or both of potassium persulfate and sodium thiosulfate; The cross-linking agent includes one or more of citric acid, formaldehyde, N-hydroxymethyl acrylamide, N-N'methylene acrylamide, and epichlorohydrin.

8. The method for preparing a crop straw-based degradable water-absorbent resin according to claim 7, characterized in that: The reaction temperature in step 3) is 55-80°C and the reaction time is 1-3h.

9. The crop straw-based degradable water-absorbent resin prepared by the method for preparing the crop straw-based degradable water-absorbent resin according to any one of claims 1 to 8.

10. Use of the crop straw-based degradable water-absorbing resin according to claim 9 as a soil water-retaining agent.

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