Carboxymethyl cellulose-based water-retaining slow-release fertilizer and preparation method thereof

Abstract

The invention discloses a carboxymethyl cellulose-based water-retaining slow-release fertilizer and a preparation method thereof, and belongs to the technical field of fertilizers. The carboxymethyl cellulose-based water retention and slow release fertilizer is composed of an aqueous solution, carboxymethyl cellulose (CMC), soluble starch (St), a cross-linking agent and urea (urea). Wherein the carboxymethyl cellulose (CMC) accounts for 2-7.5 wt.% of the mass of the aqueous solution; the soluble starch (St) accounts for 0.5-7.5 wt.% of the mass of the aqueous solution; the dosage of the cross-linking agent is 0.1-9 wt.% of the total mass of the carboxymethyl cellulose (CMC) and the soluble starch (St); according to the present invention, the natural macromolecular carboxymethyl cellulose and the starch are adopted as the skeleton, the cross-linking agent is combined, and the urea is introduced as the nitrogen source, such that the water retention slow release fertilizer applied to the farmland is developed, the fertilizer utilization rate is improved, the water is saved, and the material has characteristics of safety, environmental protection, excellent performance, stable quality and the like.

Description

Technical Field

[0001] The present application relates to the technical field of fertilizers, and more specifically, to a carboxymethyl cellulose-based water-retaining slow-release fertilizer and a preparation method thereof. Background Art

[0002] The raw materials of acrylic acid and acrylamide monomers commonly used in the current mature water-retaining slow-release fertilizers are derived from petroleum resources. They are faced with the limitations of reduced oil reserves and non-renewable properties, which results in high production costs. In addition, acrylic acid-based artificial macromolecular polymers usually have high molecular weights, and the long CC chains are not conducive to microbial degradation. When applied to the soil, the long chains are broken down into microplastics (defined as plastic particles with a particle size of less than 5mm), which are easily absorbed and accumulated in organisms and are not easily degraded. They show synergistic toxicity to most organisms, such as affecting growth and development, threatening the reproductive system and even causing death. There is an urgent need for water-retaining slow-release fertilizers that are degradable, non-toxic and harmless, and do not rely on petroleum resources.

[0003] In view of this, we propose a carboxymethyl cellulose-based water-retaining slow-release fertilizer and a preparation method thereof. Summary of the invention

[0004] The purpose of the present application is to provide a carboxymethyl cellulose-based water-retaining slow-release fertilizer and a preparation method thereof, which solves the technical problems existing in the prior art, realizes a technical route of using natural macromolecular carboxymethyl cellulose and starch as a skeleton, combining a cross-linking agent and introducing urea as a nitrogen source, and develops a water-retaining slow-release fertilizer for use in farmland, thereby improving the utilization rate of fertilizer and saving water, and the material has the characteristics of safety, environmental protection, excellent performance, and stable quality. It not only provides a new solution to the long-standing problems in my country's agriculture, but also increases the added value of cellulose and starch materials, and reduces the production cost of water-retaining slow-release fertilizers.

[0005] The present application provides a carboxymethyl cellulose-based water-retaining slow-release fertilizer, which is composed of an aqueous solution, carboxymethyl cellulose (CMC), soluble starch (St), a cross-linking agent, and urea (urea);

[0006] Wherein, the carboxymethyl fiber (CMC) accounts for 2-7.5wt.% of the mass of the aqueous solution;

[0007] The soluble starch (St) accounts for 0.5-7.5wt.% of the mass of the aqueous solution;

[0008] The amount of the cross-linking agent is 0.1-9wt.% of the total mass of the carboxymethyl fiber (CMC) and the soluble starch (St);

[0009] The amount of urea used is 0.1-35 wt.% of the total amount of the carboxymethyl cellulose (CMC) and the soluble starch (St).

[0010] As an optional solution of the technical solution of this application document, the aqueous solution is deionized water.

[0011] As an optional solution of the technical solution of this application document, the cross-linking agent is a polybasic organic acid.

[0012] As an optional solution of the technical solution of the present application document, the cross-linking agent is citric acid (CA), which is used to undergo a condensation reaction with the hydroxyl functional groups in the carboxymethyl fiber (CMC) and soluble starch (St) macromolecules at a certain temperature in an aqueous solution polymerization system, so that CMC and St form a cross-linked three-dimensional network.

[0013] As an optional solution of the technical solution of the present application document, the amount of the cross-linking agent used is 0.375wt.% of the total mass of the carboxymethyl fiber (CMC) and the soluble starch (St).

[0014] The present application also provides a method for preparing the above-mentioned carboxymethyl cellulose-based water-retaining slow-release fertilizer, comprising the following steps:

[0015] Step 1, preparing the carboxymethyl cellulose (CMC) and soluble starch (St) into a mixed aqueous solution of 2.5-11 wt.%, and gelatinizing in a 60° C. water bath for 3 hours; wherein the aqueous solution accounts for 1 / 3-1 / 2 of the volume of the reaction container;

[0016] Step 2, putting the citric acid (CA) and urea (urea) into a beaker, adding 10 ml of distilled water to dissolve and neutralize, then adding to the mixed aqueous solution, and then heating to 80° C., and polycondensing and cross-linking reaction for 3 hours;

[0017] Step 3, after the reaction is completed, pour the solution into a mold, let it stand at room temperature for 1 hour, wash and separate with excess anhydrous ethanol, and the resulting product material is named CMC-St / urea.

[0018] As an optional solution of the technical solution of this application document, the stirring speed involved in step 1 and step 2 is 300-600 rpm.

[0019] As an optional solution of the technical solution of this application document, step 2 includes the following steps:

[0020] Step 2.1, putting the citric acid (CA) into a beaker, adding 10 ml of distilled water to dissolve and neutralize, then adding it into the mixed aqueous solution, and then heating it to 80° C. to make the carboxymethyl fiber (CMC) and soluble starch (St) form a cross-linked three-dimensional network to improve the gel strength. The obtained product is named CMC-St;

[0021] Step 2.2, adding urea to the obtained product CMC-St, and then raising the temperature to 80° C. to carry out polycondensation and cross-linking reaction for 3 hours.

[0022] As an optional solution of the technical solution of the present application document, the carboxymethyl fiber (CMC) accounts for 2-6wt.% of the mass of the aqueous solution, and the soluble starch (St) accounts for 0.5-5wt.% of the mass of the aqueous solution.

[0023] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0024] (1) The present application adopts natural macromolecular carboxymethyl cellulose and starch as the skeleton, combines with a cross-linking agent and introduces urea as a nitrogen source to develop a water-retaining slow-release fertilizer for use in farmland, thereby improving fertilizer utilization and saving water. The material has the characteristics of safety, environmental protection, excellent performance and stable quality. It not only provides a new solution to the long-standing problems in my country's agriculture, but also increases the added value of cellulose and starch materials and reduces the production cost of water-retaining slow-release fertilizers.

[0025] (2) Compared with acrylic acid, the materials used in this application are easier to degrade and will not cause secondary pollution to the soil. In addition, the main raw materials are carboxymethyl cellulose and soluble starch, which are abundant, widely available and inexpensive, providing a new way for the high value-added utilization of carboxymethyl cellulose and soluble starch.

[0026] (3) The present application uses citric acid as a cross-linking agent, which is common in citrus fruits and is therefore more environmentally friendly. In addition, the annual production of citric acid exceeds 1 million tons and is widely used. Compared with traditional cross-linking agents such as MBA, which are toxic and expensive, the use of polycarboxylic acids through the condensation reaction of natural carboxylic acids and skeletons is a low-cost and environmentally friendly cross-linking method.

[0027] (4) The water-retaining slow-release material prepared in the present application not only has the ability of urea to slowly release nutrients, but also makes full use of the complex linear and branched structures and abundant hydrophilic groups such as -OH and -COOH of carboxymethyl cellulose and soluble starch, and utilizes the -COOH groups of citric acid to produce a condensation reaction with the -OH groups in the macromolecules to form a three-dimensional network structure of the hydrogel, thereby achieving slow release of nitrogen fertilizer while having a water-retaining effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a process flow chart for preparing the product CMC-St / urea disclosed in a preferred embodiment of the present application;

[0029] Figure 2This is a schematic diagram of the morphology of the product CMC-St and the product CMC-St / urea under an electron microscope at different dosages disclosed in a preferred embodiment of the present application;

[0030] Figure 3 This is an electron microscope energy spectrum of the product CMC-St / urea disclosed in a preferred embodiment of the present application;

[0031] Figure 4 XRD diagrams of carboxymethyl cellulose (CMC), soluble starch (St), urea (urea), product CMC-St / urea and product CMC-St disclosed in a preferred embodiment of the present application;

[0032] Figure 5 FT-IR spectra of carboxymethyl cellulose (CMC), soluble starch (St), product CMC-St and product CMC-St / urea disclosed in a preferred embodiment of the present application;

[0033] Figure 6 This is a water absorption test curve of the product CMC-St / urea disclosed in a preferred embodiment of the present application at different temperatures;

[0034] Figure 7 This is a sustained release test curve of the product CMC-St / urea disclosed in a preferred embodiment of the present application in distilled water;

[0035] Figure 8 This is a degradation test curve of the product CMC-St / urea disclosed in a preferred embodiment of the present application in sand;

[0036] Fig. 9 This is a linear regression analysis diagram between the absorbance of the product CMC-St / urea disclosed in a preferred embodiment of the present application and the urea concentration. DETAILED DESCRIPTION

[0037] The present application is further described in detail below in conjunction with the accompanying drawings.

[0038] The present application embodiment discloses a carboxymethyl cellulose-based water-retaining slow-release fertilizer, which is composed of an aqueous solution, carboxymethyl cellulose (CMC), soluble starch (St), a cross-linking agent, and urea (urea);

[0039] Wherein, carboxymethyl cellulose (CMC) accounts for 2-7.5wt.% of the mass of the aqueous solution;

[0040] Soluble starch (St) accounts for 0.5-7.5wt.% of the mass of the aqueous solution;

[0041] The amount of the cross-linking agent is 0.1-9wt.% of the total mass of the carboxymethyl cellulose (CMC) and the soluble starch (St);

[0042] The amount of urea used is 0.1-35wt.% of the total amount of carboxymethyl cellulose (CMC) and soluble starch (St).

[0043] Wherein, the aqueous solution is deionized water.

[0044] The crosslinking agent is a polybasic organic acid; specifically, the crosslinking agent is citric acid (CA), which is used in an aqueous solution polymerization system to undergo a condensation reaction with the hydroxyl functional groups in the macromolecules of carboxymethyl cellulose (CMC) and soluble starch (St) at a certain temperature, so that CMC and St form a crosslinked three-dimensional network.

[0045] The amount of the cross-linking agent used is 0.375 wt.% of the total mass of the carboxymethyl cellulose (CMC) and the soluble starch (St).

[0046] The present application example discloses a method for preparing the above-mentioned carboxymethyl cellulose-based water-retaining slow-release fertilizer, comprising the following steps:

[0047] Step 1, preparing a 2.5-11 wt.% mixed aqueous solution of carboxymethyl cellulose (CMC) and soluble starch (St), and gelatinizing in a 60° C. water bath for 3 hours; wherein the aqueous solution accounts for 1 / 3-1 / 2 of the volume of the reaction container;

[0048] Step 2, put citric acid (CA) and urea (urea) into a beaker, add 10 ml of distilled water to dissolve and neutralize, then add to the mixed aqueous solution, and then heat to 80° C. for condensation cross-linking reaction for 3 hours;

[0049] Step 3, after the reaction is completed, pour the solution into a mold, let it stand at room temperature for 1 hour, wash and separate with excess anhydrous ethanol, and the resulting product material is named CMC-St / urea.

[0050] The stirring speed involved in step 1 and step 2 is 300-600 rpm.

[0051] Step 2 includes the following steps:

[0052] Step 2.1, put citric acid (CA) into a beaker, add 10 ml of distilled water to dissolve and neutralize, then add it to the mixed aqueous solution, and then heat it to 80°C to form a cross-linked three-dimensional network between carboxymethyl cellulose (CMC) and soluble starch (St) to improve the gel strength. The obtained product is named CMC-St;

[0053] Step 2.2, urea is added to the obtained product CMC-St, and then the temperature is raised to 80° C. for condensation cross-linking reaction for 3 hours.

[0054] The carboxymethyl cellulose (CMC) accounts for 2-6 wt.% of the mass of the aqueous solution, and the soluble starch (St) accounts for 0.5-5 wt.% of the mass of the aqueous solution.

[0055] This embodiment uses citric acid (CA), a tribasic acid, as a crosslinking agent to improve the mechanical strength and water absorption and water retention properties of the hydrogel; and carboxymethyl cellulose (CMC) and soluble starch (St) are semi-natural macromolecules, which are environmentally friendly and will not cause secondary pollution to the soil; through chemical reactions, urea (urea) is bonded into the hydrogel skeleton, which has the ability to slowly release nutrients; this can be confirmed from the SEM, XRD, FT-IR, spectra and test results of carboxymethyl cellulose (CMC), soluble starch (St), urea (urea), the product CMC-St and the product CMC-St / urea; the specific analysis is as follows:

[0056] From the SEM spectrum (attached Figure 2 ) The change of the morphology and structure of the product CMC-St with the addition of citric acid on the basis of 3.5wt.% carboxymethyl fiber (CMC) and 0.75wt.% soluble starch (St); Specifically, Figures a, b, and c can intuitively show that the product CMC-St presents a layered structure; Figure a has small holes on the surface and a loose structure due to the small amount of citric acid added; Figure b shows that the surface becomes rough and has certain small holes as the amount of citric acid added increases; Figure c shows that the surface is rough and dense as the amount of citric acid added further increases; The comparison of the three different addition amounts of a, b, and c shows that citric acid can change the skeleton structure of natural polysaccharides and has a cross-linking effect;

[0057] Figure 2 Figures d, e, and f show the changes in the morphology and structure of the product CMC-St / urea when urea is introduced at 0.5wt.%, 1.0wt.%, and 2wt.% of the mass of carboxymethyl fiber (CMC) and soluble starch (St) based on the conditions of 3.5wt.% carboxymethyl fiber (CMC), 0.75wt.% soluble starch (St), and 1.8wt.% citric acid based on the mass of carboxymethyl fiber (CMC) and soluble starch (St);

[0058] Among them, it can be observed in Figure d that the introduction of urea changes the structure of the obtained product CMC-St / urea, which has a certain crystal structure and particles attached to the surface. It may be due to the weak alkalinity of urea during the preparation process that the molecular chains of carboxymethyl cellulose and starch are dissociated, thus presenting a granular state; Figure e can more clearly show that the product CMC-St / urea presents a regular crystal structure due to the introduction of urea. As the amount of urea is further increased, as shown in Figure f, agglomeration appears on the surface, indicating that more particles are attached; the results show that the introduction of urea can change the structure of the product CMC-St / urea, and the obtained product CMC-St / urea can be transformed from an amorphous state to a crystalline state;

[0059] According to the electron microscope energy spectrum of the product CMC-St / urea (attached Figure 3 ), the composition and distribution of surface elements of carboxymethyl cellulose (CMC)-St / urea were obtained. According to the results of energy spectrum analysis, it can be found that the sample contains C, O, Na, and N elements, with a total content of about 100%; among them, the C element has the highest content, mainly derived from carboxymethyl cellulose (CMC) and soluble starch (St), and acts as the structural skeleton of the finished sample; the O element accounts for 34.79at%, mainly derived from the α-1,6-glycosidic bond in soluble starch (St); the α-1,4-glycosidic bond and D-pyranose glucose in carboxymethyl cellulose (CMC) through the β-(1→4)-glycosidic bond and the hydroxyl and carboxyl groups of soluble starch (St) and carboxymethyl cellulose (CMC); the Na element accounts for 7.09at% and comes from the ionic bond of carboxylate ions in carboxymethyl cellulose (CMC) to Na cations; the N element accounts for 0.62at% due to the introduction of urea; the results show that the excellent water absorption performance of the fertilizer comes from the hydrogen bonding between oxygen-containing functional groups and water, and the N element introduced by urea can play the role of nutrient soil;

[0060] Furthermore, from the XRD pattern (Appendix Figure 4 ) shows the XRD patterns of (a) carboxymethyl cellulose, (b) soluble starch, (c) urea, (d) product CMC-St / urea and (e) product CMC-St samples. It can be seen from the figure that the soluble starch has strong diffraction peaks at 2θ of 19.01°, 27.97°, 29.06°, 32.10°, 33.82°, 38.58°, 45.38° and 48.75°, indicating the A-type crystal structure of starch; in the XRD pattern of carboxymethyl cellulose (CMC) ( Figure 4), a broad peak appears at 15-25°, indicating its amorphous nature; in the XRD spectrum of urea, there is a strong diffraction peak at 22.42°, which is the characteristic peak of urea crystal; the product CMC-St / urea has a characteristic broad peak of carboxymethyl fiber (CMC) at 15-25°, and another strong diffraction peak appears at 31.53°, which is slightly offset compared with starch. The results show that the product CMC-St is amorphous and has successfully grafted starch and carboxymethyl fiber (CMC);

[0061] In order to study the structural changes of the product CMC-St after the introduction of urea, the material was analyzed by XRD spectrum; in the SAR spectrum, strong diffraction peaks appeared at 18.88°, 22.50°, 27.87°, 28.85°, 31.73°, and 33.86°; among them, the characteristic peak of 22.50° proved the introduction of urea, and 18.88°, 27.87°, 28.85°, 31.73°, and 33.86° belonged to the characteristic peaks of carboxymethyl cellulose (CMC); in addition, after the introduction of urea, an amorphous peak different from SAP appeared, and an A-type crystal structure similar to carboxymethyl cellulose (CMC) appeared, which proved that the introduction of urea made the obtained product CMC-St / urea show a higher degree of crystalline order.

[0062] Furthermore, from the FT-IR images (see Figure 5 ) The initial materials are carboxymethyl fiber (CMC), soluble starch (St), and the cross-linked product CMC-St and the product CMC-St / urea; the FT-IR spectra of soluble starch, carboxymethyl fiber (CMC), the cross-linked product CMC-St and the product CMC-St / urea confirm that the soluble starch (St) and carboxymethyl fiber (CMC) form a supramolecular superabsorbent polymer through the formation of ester and hydrogen bond interactions, and the carboxymethyl fiber (CMC)-St / urea successfully introduces amino groups;

[0063] Specifically, it can be seen from the figure that the typical characteristic peak of soluble starch (St) in the FT-IR spectrum appears at 3456cm-1, corresponding to the absorption peak of hydroxyl group; the peaks at 2962cm-1 and 2875cm-1 respond to -CH symmetric and asymmetric stretching vibrations, respectively, the peak at 1625cm-1 corresponds to starch group, and the peaks at 145cm-1, 1384cm-1 and 1107cm-1 correspond to CN- and -COC- groups, respectively; similarly, the absorption characteristic peaks of carboxymethyl cellulose (CMC)-Na appear at 3456cm-1 and 1606cm-1, corresponding to -OH and -C=O, respectively; the characteristic peaks of -OH group of soluble starch (St) and carboxymethyl cellulose (CMC)-Na both appear at 3456cm-1; however, after citric acid is added to the mixed solution, the characteristic peak of carboxymethyl cellulose (CMC)-soluble starch (St) becomes wider and the intensity weakens; Compared with starch powder (St) and carboxymethyl fiber (CMC), the base peak of carboxymethyl fiber (CMC)-St at 1610cm-1 becomes sharper; due to the physical cross-linking formed by hydrogen bond interaction, obvious peak shift differences are also observed, mainly in the absorption characteristic peaks of carbonyl and -OH; similarly, the vibrations of COH bending, -CO stretching and -OH bending lead to the characteristic peaks of SAP at 1041cm-1, 995cm-1 and 873cm-1; during the preparation process, a new characteristic absorption peak of ester bond is formed between soluble starch (St) and carboxymethyl fiber (CMC) at about 1633cm-1 due to the stretching of CO in the ester group; in the FT-IR spectrum of the product CMC-St / urea, the bending vibration of NH group appears at 1460cm-1, which proves that urea is involved in the synthesis of the product CMC-St / urea and is successfully grafted on the skeleton of the product CMC-St / urea.

[0064] Based on the above embodiment, the present embodiment uses the tea bag method to measure the water absorption capacity of the super absorbent polymer; specifically, 1 g of super absorbent polymer powder is placed in a tea bag and completely immersed in distilled water, and the values ​​are substituted into the calculation formula at regular intervals to measure its free absorption capacity until a balance state is reached (24 hours). The calculation formula is as follows:

[0065]

[0066] Where W is the water absorption ratio, in g / g; m0 is the mass of the sample when dry, in g; m is the mass of the gel when it reaches swelling equilibrium, in g.

[0067] By attaching Figure 6It can be seen that CMC-St / urea can show good water absorption capacity at 5℃-50℃, indicating that CMC-St / urea has water absorption and water retention effects, indicating that CMC-St / urea can be applied to soil and play a role in water retention.

[0068] Based on the above embodiment, in this embodiment, 0.5g of the product CMC-St / urea material is placed in a beaker filled with 200mL of distilled water, covered with plastic wrap to prevent the reduction of water due to evaporation of water, and 10mL of samples are taken on the 1st, 5th, 10th, 15th, 20th, 25th, and 30th days after immersion, and the urea content is quantitatively analyzed using a spectrophotometer. The developer used is p-dimethylaminobenzaldehyde (p-dimethylaminobenzaldehyde reacts with urea under acidic conditions to form a relatively stable complex. The ultraviolet spectrum has a maximum absorption peak for the complex at y=422nm; and the urea content is measured by absorbance, and then the release rate curve is obtained); the specific operation process is as follows:

[0069] 1. Acid solution preparation

[0070] Accurately measure 4 mL of concentrated sulfuric acid and 32 mL of deionized water (V acid:V water = 1:8), mix and shake well, and set aside;

[0071] 2. Preparation of p-dimethylaminobenzaldehyde colorimetric solution

[0072] Accurately weigh 5.0000 g of p-dimethylaminobenzaldehyde and place it in a beaker. Add anhydrous ethanol and stir until dissolved. Use a glass rod to transfer to a 250 mL volumetric flask, mix well, and dilute to volume with anhydrous ethanol for later use.

[0073] 3. Preparation of standard solution

[0074] Accurately weigh 0.5000g of analytical grade urea and place it in a beaker. Dissolve it in deionized water. Transfer the glass rod to a 500ml volumetric flask and make up to volume with deionized water to obtain a stock solution with a concentration of 1.0g / L.

[0075] 4. Standard curve:

[0076] The absorbance was measured at 422 nm with blank reagent as reference; the details are as follows:

[0077] The prepared urea standard solution was placed in 7 25mL colorimetric tubes with 0, 0.5, 1, 2, 4, 5, and 8mL of urea solution respectively; then, 10mL of p-dimethylaminobenzaldehyde as a color developer and 4mL of acid solution were added to each tube, and the total volume was adjusted to 25mL with deionized water. After being fully mixed, the solution was allowed to stand for ten minutes to form sample solutions of different concentrations; in the experiment, a sample without urea was used as a control (blank group), and the absorbance (A value) of each solution was measured at a wavelength of 422nm; based on the corresponding data of absorbance and concentration, linear regression analysis was performed using Origin 8.1 software to ensure the accuracy of data analysis; the results and analysis process are shown in Fig. 9 Through this correction step, a mathematical model between absorbance and urea concentration was successfully established for subsequent determination;

[0078] 5. Formal sample experiment

[0079] Use a volumetric gun to draw 1 mL of sample solution containing urea at different times and put it into a prepared 25 mL colorimetric tube; then add 10 mL of color developer and 4 mL of acid solution and make up to volume with deionized water; finally mix well and place the sample on the table for 10 minutes; after the complex is stable, use ultraviolet light to measure its absorbance, and measure each sample in parallel 3 times;

[0080] By attaching Figure 7 It can be seen that CMC-St / urea releases urea quickly in the early stage of sustained release, and the sustained release of CMC-St / urea in distilled water can exceed 6 days, showing excellent sustained release properties, indicating that CMC-St / urea can provide nitrogen fertilizer for plant growth and promote plant growth.

[0081] Based on the above embodiment, in this embodiment, 2g of the composite material is placed in a nylon tea bag, buried in soil (taken from typical sandy soil in Yulin area) at a depth of 5cm for biodegradation experiment, and 500g of tap water is regularly used to irrigate the soil every 3 days; the sample is taken out every 7 days, washed with distilled water, dried at 60°C until the mass does not change, and weighed; the biodegradation rate of the coating material is calculated as follows:

[0082]

[0083] Where Wt is the net weight of the composite material, w0 and w t0 are the weights of the film before and after it is buried in the soil;

[0084] By attaching Figure 8 It can be seen that the water-retaining slow-release fertilizer has a good degradation effect. The degradation rate in 42 days can reach 22.9%. It is friendly to the biological environment and will not cause secondary damage to the soil.

[0085] Therefore, in combination with the above embodiments, it can be known that the prepared water-retaining slow-release fertilizer has good economic benefits; it is estimated that the material cost of 1 ton of carboxymethyl cellulose on the market is about RMB 6,000; the material cost of 1 ton of soluble starch is about RMB 4,790; and the material cost of 1 ton of acrylic acid, the main material of traditional commercial water-retaining agents, is about RMB 8,200; the present application has the advantages of low price and renewable and easy-to-prepare raw materials. Compared with acrylic acid, the materials used in the present application are easier to degrade and will not cause secondary pollution to the soil; and the main raw materials are carboxymethyl cellulose and soluble starch, which are abundant in resources, widely available and low in price, which provides a new way for the high value-added utilization of carboxymethyl cellulose and soluble starch.

Claims

1. A carboxymethyl cellulose-based water-retaining slow-release fertilizer, characterized in that: It is composed of aqueous solution, carboxymethyl cellulose (CMC), soluble starch (St), cross-linking agent and urea; Wherein, the carboxymethyl fiber (CMC) accounts for 2-7.5wt.% of the mass of the aqueous solution; The soluble starch (St) accounts for 0.5-7.5wt.% of the mass of the aqueous solution; The amount of the cross-linking agent is 0.1-9wt.% of the total mass of the carboxymethyl fiber (CMC) and the soluble starch (St); The amount of urea used is 0.1-35 wt.% of the total amount of the carboxymethyl cellulose (CMC) and the soluble starch (St).

2. The carboxymethyl cellulose-based water-retaining slow-release fertilizer according to claim 1, characterized in that: The aqueous solution is deionized water.

3. The carboxymethyl cellulose-based water-retaining slow-release fertilizer according to claim 2, characterized in that: The crosslinking agent is a polybasic organic acid.

4. The carboxymethyl cellulose-based water-retaining slow-release fertilizer according to claim 3, characterized in that: The crosslinking agent is citric acid (CA), which is used in an aqueous solution polymerization system to undergo a polycondensation reaction with the hydroxyl functional groups in the carboxymethyl fiber (CMC) and soluble starch (St) macromolecules at a certain temperature, so that CMC and St form a crosslinked three-dimensional network.

5. The carboxymethyl cellulose-based water-retaining slow-release fertilizer according to claim 4, characterized in that: The amount of the cross-linking agent used is 0.375 wt.% of the total mass of the carboxymethyl fiber (CMC) and the soluble starch (St).

6. The method for preparing the carboxymethyl cellulose-based water-retaining slow-release fertilizer according to claim 5, characterized in that: The following steps are involved: Step 1, preparing the carboxymethyl cellulose (CMC) and soluble starch (St) into a mixed aqueous solution of 2.5-11 wt.%, and gelatinizing in a 60° C. water bath for 3 hours; wherein the aqueous solution accounts for 1 / 3-1 / 2 of the volume of the reaction container; Step 2, putting the citric acid (CA) and urea (urea) into a beaker, adding 10 ml of distilled water to dissolve and neutralize, then adding to the mixed aqueous solution, and then heating to 80° C., and polycondensing and cross-linking reaction for 3 hours; Step 3, after the reaction is completed, pour the solution into a mold, let it stand at room temperature for 1 hour, wash and separate with excess anhydrous ethanol, and the resulting product material is named CMC-St / urea.

7. The method for preparing the carboxymethyl cellulose-based water-retaining slow-release fertilizer according to claim 6, characterized in that: The stirring speed involved in step 1 and step 2 is 300-600 rpm.

8. The method for preparing the carboxymethyl cellulose-based water-retaining slow-release fertilizer according to claim 6, characterized in that: The step 2 comprises the following steps: Step 2.1, putting the citric acid (CA) into a beaker, adding 10 ml of distilled water to dissolve and neutralize, then adding it into the mixed aqueous solution, and then heating it to 80° C. to make the carboxymethyl fiber (CMC) and soluble starch (St) form a cross-linked three-dimensional network to improve the gel strength. The product is named CMC-St; Step 2.2, adding urea to the obtained product CMC-St, and then raising the temperature to 80° C. to carry out polycondensation and cross-linking reaction for 3 hours.

9. The method for preparing the carboxymethyl cellulose-based water-retaining slow-release fertilizer according to claim 6, characterized in that: The carboxymethyl cellulose (CMC) accounts for 2-6 wt.% of the mass of the aqueous solution, and the soluble starch (St) accounts for 0.5-5 wt.% of the mass of the aqueous solution.

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