Slow-release fertilizer based on pre-oxidized kitchen waste composite and preparation method thereof

Abstract

The present invention provides a method for preparing a slow-release fertilizer based on a pre-oxidized food waste composite. Compared to ordinary urea, the fertilizer has a reduced urea release rate in water, thus sustainably providing nutrition to crops. The sprayable film-forming slow-release urea fertilizer prepared by the present invention also has the function of being a sprayable liquid ground film. Before use, the emulsion is an emulsion that can be sprayed on the soil surface to form a liquid film layer, which is then air-dried to form a film. This air-dried film layer can prevent moisture and heat from being lost to the outside of the soil. Because the sprayable film-forming slow-release urea fertilizer prepared by the present invention simultaneously meets the three important basic factors required for efficient agricultural production, it can increase the yield of Chinese cabbage. In addition, the sprayability of the slow-release urea fertilizer provided by the present invention also makes construction simple and operation easy, which is conducive to the promotion and application of the product.

Description

Technical field:

[0001] The invention provides a slow-release fertilizer based on a pre-oxidized kitchen waste composite and also provides a preparation method of the fertilizer, belonging to the field of agricultural fertilizers and liquid mulch films. Background technology:

[0002] It is well known that achieving high-efficiency agricultural production requires three important basic factors: (1) the ability to continuously provide fertilizer nutrients for the entire growth stage of crops (including from seeds to seedlings, and then from seedlings to mature crops); (2) suitable soil temperature and (3) soil moisture. These three basic factors are interdependent and indispensable.

[0003] Lignin and food waste are both waste products and biomass materials with significant applications. Lignin is the second-most produced natural polymer. In the papermaking industry, approximately 400 kg of lignin dissolves in the wastewater for every ton of pulp produced. This lignin remains largely underutilized, leaving most of it as waste. This not only results in a significant waste of resources but also causes serious ecological pollution. Food waste generally refers to waste generated from daily life and catering services, including discarded vegetable leaves, leftovers, and rice. Food waste is highly susceptible to decay, producing foul odors and acid that contaminate groundwater. Properly treated and processed lignin and food waste can be converted into fertilizer, feed, biofuel, and other resources. Lignin and food waste have been used to prepare fertilizers containing urea to meet the nitrogen requirements of crops. For example, the document ([1] CN104068206A) describes mixing lignin raw materials with pulped food waste, adding urea and other nutrients, and then extruding the mixture through an extruder to obtain fertilizer. The fertilizer described in the document 1 has the effect of releasing urea and providing nitrogen fertilizer to crops, but does not have the function of heat preservation and water retention for the soil. That is, the fertilizer in the document 1 lacks two of the three important basic factors required for efficient agricultural production. Therefore, the fertilizer described in the document 1 has limited effect on improving the growth of crops. The world is constantly producing a large amount of lignin and food waste every day. If these two wastes can be converted into a product that simultaneously meets the three important basic factors required for efficient agricultural production, that is, the product can be both a fertilizer and has the function of heat preservation and water retention for the soil, such a product will be of great significance to promoting agricultural production and environmental protection. Summary of the invention:

[0004] In order to solve the problems existing in the prior art, the present invention provides a method for preparing a slow-release fertilizer based on a pre-oxidized food waste composite. The preparation method uses two common wastes as raw materials, has low cost, simple preparation method, and is easy to market and apply.

[0005] The present invention also provides a slow-release fertilizer based on a pre-oxidized food waste composite. This product can be used as a liquid mulch film, which has the effect of keeping the soil warm and moisturizing. At the same time, it can be used as a urea slow-release fertilizer, achieving the effect of reducing the release rate of urea and continuously providing nitrogen fertilizer to crops.

[0006] The present invention also provides an application of a slow-release fertilizer based on a pre-oxidized kitchen waste composite in agricultural slow-release fertilizers and agricultural liquid mulch films.

[0007] The specific scheme of the present invention is as follows:

[0008] A method for preparing a slow-release fertilizer based on a pre-oxidized food waste composite, the preparation steps of which are as follows:

[0009] (1) lignin sulfonate, maleic anhydride and water are mixed into a solution, the pH value of the obtained mixed solution is adjusted to 10-11 with 1 mol / L NaOH solution, and then stirred at 50-75 ° C., the stirring speed is 360-1200 r / min, and after the reaction for 5-10 hours, the mixed solution is cooled to room temperature, and then the pH value of the mixed solution is adjusted to between 1-2 with 1.8 mol / L sulfuric acid solution. At this time, a precipitate is generated in the solution, the precipitate in the solution is filtered, and the precipitate is repeatedly washed with water until the pH value of the filtrate is neutral. The washed precipitate is placed at 55-80 ° C. and dried for 24-72 hours to obtain maleic anhydride modified lignin, wherein the mass ratio of lignin sulfonate, maleic anhydride and water is 1: (0.8-2): (5-15);

[0010] (2) mixing food waste with water, and crushing the resulting mixture into food waste slurry using a grinder, wherein the mass ratio of food waste to water is 1:(1-2.5), and then sieving the food waste slurry so that the particle size of the food waste slurry is less than 2 mm, adding the sieved food waste slurry into a reaction vessel equipped with a stirrer, a thermometer and a condenser, and then adding an oxidant aqueous solution into the reaction vessel while stirring at 80-90° C., at a stirring speed of 500-1200 r / min, and a stirring time of 1-3 hours, to obtain a pre-oxidized food waste slurry, wherein the mass ratio of the sieved food waste slurry to the oxidant aqueous solution is (3-5.3):1, and the oxidant aqueous solution in step (2) is a potassium persulfate or ammonium persulfate aqueous solution, and the mass percentage concentration of the potassium persulfate or ammonium persulfate is 6-12%;

[0011] (3) stirring the maleic anhydride-modified lignin obtained in step (1), the pre-oxidized food waste slurry obtained in step (2), and urea at room temperature at a stirring speed of 800-2000 r / min for 1.5-3.5 h to obtain a slurry containing a maleic anhydride-modified lignin-pre-oxidized food waste-urea complex, wherein the mass ratio of the maleic anhydride-modified lignin, the pre-oxidized food waste, and the urea is 1:(2.1-4.5):(4.4-9);

[0012] (4) mixing the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea composite obtained in step (3) with an acrylic acid monomer mixture, an emulsifier, and water, and stirring the resulting mixture at 55-65° C. for 50-150 min to obtain a pre-emulsion, with a stirring speed of 500-3000 r / min, wherein the mass ratio of the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea composite obtained in step (3), the acrylic acid monomer mixture, the emulsifier, and the water is (32-44):(15-21):1:(36-56), and the acrylic acid monomer mixture in step (4) comprises butyl acrylate, methyl methacrylate, and acrylic acid in a mass ratio of (5.8-6.8):(2.1-3.2):1;

[0013] (5) After the temperature of the pre-emulsion obtained in step (4) is raised to 75-90° C., an initiator aqueous solution is added dropwise to the pre-emulsion at a drop rate of 0.04-0.2 mL / min while stirring, and the stirring speed is 200-600 r / min. After the addition of the initiator aqueous solution is completed, the reaction is continued for 2-8 hours, and then the reaction system is cooled to room temperature, and then the pH of the system is adjusted to 6.8-7.3 with ammonia water having a mass percentage concentration of 25%, thereby obtaining an emulsion as a slow-release fertilizer based on the pre-oxidized food waste complex, wherein the mass ratio between the pre-emulsion obtained in step (4) and the initiator aqueous solution is (67-97):1.

[0014] The further design of the present invention is:

[0015] The lignin sulfonate described in step (1) is sodium lignin sulfonate or calcium lignin sulfonate.

[0016] The food waste in step (2) contains 7.2-9.5 wt% starch, 10.0-12.2 wt% cellulose, 2.1-4.3 wt% protein, 1.1-2.1 wt% oil, and 40-64 wt% water.

[0017] The emulsifier described in step (4) is a mixture of a reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1: (1.5-4.5), and the model of the reactive emulsifier is LRS-10.

[0018] The initiator aqueous solution described in step (5) is potassium persulfate or ammonium persulfate aqueous solution, wherein the mass percentage concentration of potassium persulfate or ammonium persulfate is 2.2-3.1%.

[0019] The water used in steps (1)-(5) is deionized water.

[0020] The present invention also provides a sprayable film-forming slow-release urea fertilizer product using lignin and food waste as raw materials and prepared by the above preparation method, as well as the dual-functional application of the product in agricultural slow-release fertilizer and agricultural liquid mulch film.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The present invention utilizes lignin sulfonates extracted from waste liquid of the papermaking industry and food waste generated in the daily lives of residents to prepare a material with urea slow-release function and sprayable liquid mulch function. This preparation technology realizes the simultaneous renewable utilization of two kinds of waste biomass resources, achieving the effect of turning waste into treasure. The sprayable film-forming slow-release urea fertilizer prepared by the present invention has a urea slow-release function, that is, compared with the disadvantage of ordinary urea that dissolves too quickly in water, the urea release rate of the product of the present invention in water is reduced. This function can enable the product of the present invention to achieve efficient urea utilization and sustainably provide nutrition for crops. The sprayable film-forming slow-release urea fertilizer prepared by the present invention also has the function of sprayable liquid mulch. The liquid mulch is a liquid before use. This liquid is sprayable and can be sprayed on the soil surface to form a liquid film layer. This liquid film layer can be air-dried to form a film by itself. This air-dried film can play a role in preventing moisture and heat in the soil from being lost to the outside. The test results of the effect embodiment show that the sprayable film-forming slow-release urea fertilizer product prepared by the present invention is indeed sprayable, easy and quick to use, and reduces construction costs; the product of the present invention also has the function of forming a film on the soil surface, thereby having the effect of retaining water and heat in the soil; the product of the present invention also has the function of slow-releasing urea. Since the sprayable film-forming slow-release urea fertilizer product prepared by the present invention simultaneously meets the three important basic factors required for efficient agricultural production, this slow-release fertilizer product has a good effect of increasing the yield of Chinese cabbage.

[0023] The working principle of the present invention is analyzed as follows:

[0024] 1. Step (1) of the present invention is to prepare maleic anhydride-modified lignin using lignin sulfonate and maleic anhydride as raw materials. Lignin sulfonate is a by-product extracted from sulfite pulping wastewater in the papermaking industry. Lignin sulfonate has many uses, such as cement water reducer, pesticide suspending agent, ceramic or refractory plasticizer, coal-water slurry dispersant, mineral processing dispersant, leather tanning agent, carbon black granulating agent, etc. However, the amount of lignin sulfonate consumed by the above uses is still only a small part compared to the total content of lignin sulfonate in the pulping wastewater, that is, most of the lignin sulfonate in the papermaking wastewater is still not effectively utilized. These discarded lignin sulfonates are not only a waste of resources, but also cause harm to the ecological environment. Maleic anhydride is a cyclic molecule, also known as maleic anhydride. It can react with the hydroxyl group in the lignin sulfonate through structural ring opening, thereby connecting the lignin sulfonate to a group with a carbon-carbon double bond, that is, obtaining maleic anhydride-modified lignin. This maleic anhydride-modified lignin with carbon-carbon double bonds can undergo a polymerization reaction with acrylic ester monomers under the action of a catalyst, which allows the maleic anhydride-modified lignin to be evenly fused with the polyacrylate produced after polymerization to form a copolymer with good compatibility among the components and stable performance.

[0025] 2. Step (2) of the present invention is to first pulp and screen the food waste, and then pre-oxidize the screened food waste slurry with an aqueous solution of potassium persulfate or ammonium persulfate as an oxidant. Food waste is also an important biomass raw material with good biodegradability. It contains natural polymers rich in hydroxyl groups, such as cellulose, protein, and sugar. These natural polymers rich in hydroxyl groups can associate with each other through hydrogen bonding between hydroxyl groups, thereby making the food waste slurry viscous. This viscous food waste slurry also makes the subsequent reaction system viscous, resulting in a relatively viscous liquid mulch emulsion product. However, an overly viscous mulch emulsion has poor sprayability and is not conducive to spraying operations. In step (2) of the present invention, after the potassium persulfate or ammonium persulfate aqueous solution pre-oxidizes the food waste, some of the hydroxyl groups in the food waste are oxidized into carboxyl groups, which reduces the hydrogen bonding between the natural polymers in the food waste, and correspondingly reduces the viscosity of the food waste slurry, thereby also reducing the viscosity of the liquid mulch emulsion product finally obtained, so that the liquid mulch emulsion has better sprayability, which is conducive to the spraying construction of the product of the present invention in the field and reduces the difficulty of mulch construction.

[0026] 3. In step (3) of the present invention, the maleic anhydride-modified lignin obtained in step (1) is stirred with the pre-oxidized food waste slurry obtained in step (2) and urea at room temperature to obtain a maleic anhydride-modified lignin-pre-oxidized food waste-urea complex. Maleic anhydride-modified lignin is a polymer, and the pre-oxidized food waste slurry is also rich in natural polymers. These two polymers are not easily compatible and uniformly mixed together. If the two are not well compatible, the subsequently prepared emulsion is likely to undergo emulsion stratification due to phase separation. Urea is a small molecule containing two amino groups and one carbonyl group. The amino group of the urea molecule can easily obtain a hydrogen ion with a positive charge, thereby combining with the negatively charged sulfonic acid group on the maleic anhydride-modified lignin through electrostatic interaction. At the same time, the urea molecule can also associate with the carboxyl groups in the pre-oxidized food waste and the maleic anhydride-modified lignin through hydrogen bonding, that is, the urea molecule can be used as a bridge to well combine the maleic anhydride-modified lignin and the pre-oxidized food waste to form a maleic anhydride-modified lignin-pre-oxidized food waste-urea complex, so that the polymers in the maleic anhydride-modified lignin and the pre-oxidized food waste are compatible and evenly fused at the molecular level. The urea molecule also reduces the hydrogen bonding between the polymers, further reducing the viscosity of the food waste slurry and the liquid mulch emulsion product prepared later, making the liquid mulch emulsion have better sprayability, facilitating field spraying construction, and reducing construction difficulty.

[0027] 4. Step (4) of the present invention is to prepare a pre-emulsion by adding a maleic anhydride-modified lignin-preoxidized kitchen waste-urea complex, an acrylic acid monomer mixture, and water under the action of an emulsifier. In an emulsion polymerization system, especially a multi-emulsion copolymerization system, if the traditional monomer addition method is adopted, the formation of emulsion particles and the polymerization depth are not synchronized, which often makes it difficult to control the particle size distribution of the emulsion, the elimination of residual monomers, and the stability of the system. However, by preparing a pre-emulsion, the stability of the emulsion polymerization can be greatly improved, the amount of coagulants can be reduced, and the formation of wall-forming materials can be reduced. When preparing the pre-emulsion, it should be noted that the stability of the pre-emulsion should be good, the emulsion should not be broken and stratified, the viscosity of the pre-emulsion should be moderate, and the appropriate emulsifier solution ratio, temperature, and stirring conditions are prerequisites for forming a stable pre-emulsion.

[0028] 5. Step (5) of the present invention is to subject the pre-emulsion obtained in step (4) to an emulsion polymerization reaction under the action of an initiator. After the emulsion polymerization reaction, polymerization reactions occur between the maleic anhydride-modified lignin-pre-oxidized food waste-urea complex and the acrylate monomers, and between the acrylate monomers. The polymerization reaction between the acrylate monomers will produce a polyacrylate portion. Polyacrylate has excellent film-forming properties, allowing the resulting sprayable film-forming slow-release urea fertilizer emulsion to form a film on the soil surface. The formed film can block the gaps between soil particles, thereby preventing the loss of heat and water in the soil, thereby providing a heat-insulating and moisture-retaining effect on the soil. After the grafting polymerization reaction of the maleic anhydride-modified lignin-pre-oxidized food waste-urea complex and the acrylate monomer, the maleic anhydride-modified lignin-pre-oxidized food waste-urea complex and the polyacrylate are uniformly compatible and fused together, and the urea therein is wrapped in two layers of polymer networks: one is the polymer network of the maleic anhydride-modified lignin-pre-oxidized food waste-urea complex, and the other is the maleic anhydride-modified lignin-pre-oxidized food waste-urea complex embedded in the polyacrylate network. Under the continuous wrapping of these two layers of polymer networks, the release rate of urea molecules is greatly reduced, achieving a slow-release effect of urea. Description of the drawings:

[0029] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention.

[0030] Figure 1 The present invention is a process flow chart for preparing a sprayable film-forming slow-release urea fertilizer.

[0031] Figure 2 The present invention is a process flow chart of preparing a slurry containing a maleic anhydride-modified lignin-preoxidized food waste-urea complex.

[0032] Figure 3 Figure 1 is the cumulative urea release curve of the membrane samples prepared in Examples 1-5 and pure urea in the urea sustained-release performance test of the present invention. The error bars in the figure represent the standard deviation of the mean of the results obtained in three parallel experiments. The numbers in the figure are: A is the sample in Example 1, B is the sample in Example 2, C is the sample in Example 3, D is the sample in Example 4, E is the sample in Example 5, and F is pure urea. Specific implementation method:

[0033] The above and other technical features and advantages of the present invention are described in more detail below with reference to the following examples. The chemical raw materials used in the following examples are all commercially available, chemically pure reagents;

[0034] Lignin sulfonates (sodium lignin sulfonate and calcium lignin sulfonate) were extracted from poplar sulfite pulping waste liquor and provided by Jiangsu Key Laboratory of Pulp and Paper Science and Technology (Nanjing).

[0035] The food waste was collected from the student cafeteria of Nanjing Forestry University.

[0036] Butyl acrylate, methyl methacrylate, and acrylic acid, all with a purity of 99%, and aqueous ammonia were purchased from Damao Chemical Reagent Co., Ltd. (Tianjin, China).

[0037] Reactive emulsifier (model LRS-10) with a purity of 99% and octylphenol polyoxyethylene ether (10) (OP-10) with a purity of 99% were purchased from Nanjing Qicheng New Materials Co., Ltd. (Jiangsu, China).

[0038] Potassium persulfate and ammonium persulfate with a purity of 99.5% were purchased from Lingfeng Chemical Reagent Co., Ltd. (Shanghai, China).

[0039] Urea was purchased from Jinan Desheng Chemical Technology Co., Ltd., with a total nitrogen content greater than 46.0% and a particle size of 0.85-2.8 mm.

[0040] Example 1

[0041] (1) lignin sulfonate, maleic anhydride and water are mixed into a solution, and the pH value of the obtained mixed solution is adjusted to 10 with a 1 mol / L NaOH solution, and then stirred at 75°C with a stirring speed of 360 r / min. After the reaction for 10 hours, the mixed solution is cooled to room temperature, and then the pH value of the mixed solution is adjusted to 1 with a 1.8 mol / L sulfuric acid solution. At this time, a precipitate is generated in the solution, and the precipitate in the solution is filtered and repeatedly washed with water until the pH value of the filtrate is neutral. The washed precipitate is placed at 55°C and dried for 72 hours to obtain maleic anhydride-modified lignin, wherein the mass ratio of lignin sulfonate, maleic anhydride and water is 1:0.8:5;

[0042] (2) mixing food waste with water, and crushing the resulting mixture into food waste slurry with a grinder, wherein the mass ratio of food waste to water is 1:1, and then sieving the food waste slurry so that the particle size of the food waste slurry is less than 2 mm, adding the sieved food waste slurry to a reaction vessel equipped with a stirrer, a thermometer and a condenser, and then adding an oxidant aqueous solution to the reaction vessel while stirring at 80° C., the stirring speed is 500 r / min, and the stirring time is 1 hour, to obtain a pre-oxidized food waste slurry, wherein the mass ratio between the sieved food waste slurry and the oxidant aqueous solution is 3:1, and the oxidant aqueous solution described in step (2) is an ammonium persulfate aqueous solution, and the mass percentage concentration of ammonium persulfate is 6%;

[0043] (3) stirring the maleic anhydride-modified lignin obtained in step (1), the pre-oxidized food waste slurry obtained in step (2), and urea at room temperature at a stirring speed of 800 r / min for 1.5 h to obtain a slurry containing a maleic anhydride-modified lignin-pre-oxidized food waste-urea complex, wherein the mass ratio of the maleic anhydride-modified lignin, the pre-oxidized food waste, and the urea is 1:2.1:4.4;

[0044] (4) mixing the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea composite obtained in step (3) with an acrylic acid monomer mixture, an emulsifier, and water, and stirring the resulting mixture at 55° C. for 150 minutes to obtain a pre-emulsion at a stirring speed of 500 r / min, wherein the mass ratio of the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea composite obtained in step (3), the acrylic acid monomer mixture, the emulsifier, and the water is 32:15:1:36, and the acrylic acid monomer mixture in step (4) comprises butyl acrylate, methyl methacrylate, and acrylic acid in a mass ratio of 5.8:2.1:1;

[0045] (5) After the temperature of the pre-emulsion obtained in step (4) is raised to 75° C., an initiator aqueous solution is added dropwise to the pre-emulsion at a drop rate of 0.04 mL / min while stirring, and the stirring speed is 200 r / min. After the initiator aqueous solution is added dropwise, the reaction is continued for 2 h, and then the reaction system is cooled to room temperature, and then the pH of the system is adjusted to 6.8 with ammonia water having a mass percentage concentration of 25%, thereby obtaining an emulsion as a sprayable film-forming slow-release urea fertilizer, wherein the mass ratio between the pre-emulsion obtained in step (4) and the initiator aqueous solution is 67:1.

[0046] The lignin sulfonate described in step (1) is sodium lignin sulfonate. The food waste described in step (2) contains 7.2 wt% starch, 12.2 wt% cellulose, 2.1 wt% protein, 2.1 wt% oil, and 40 wt% water. The emulsifier described in step (4) is a mixture of a reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:1.5, and the model of the reactive emulsifier is LRS-10. The initiator aqueous solution described in step (5) is a potassium persulfate aqueous solution, wherein the mass percentage concentration of potassium persulfate is 2.2%. The water used in steps (1) to (5) is deionized water.

[0047] Through steps (1) to (5), a sprayable film-forming slow-release urea fertilizer of Example 1 can be obtained, which has a uniform and stable emulsion appearance and no stratification phenomenon within 30 days of standing.

[0048] Example 2

[0049] (1) lignin sulfonate, maleic anhydride and water are mixed into a solution, and the pH value of the obtained mixed solution is adjusted to 10.2 with a 1 mol / L NaOH solution, and then stirred at 69 ° C. The stirring speed is 570 r / min. After the reaction for 9 hours, the mixed solution is cooled to room temperature, and then the pH value of the mixed solution is adjusted to 1.2 with a 1.8 mol / L sulfuric acid solution. At this time, a precipitate will be generated in the solution. The precipitate in the solution is filtered and repeatedly washed with water until the pH value of the filtrate is neutral. The washed precipitate is placed at 61 ° C. and dried for 60 hours to obtain maleic anhydride-modified lignin, wherein the mass ratio of lignin sulfonate, maleic anhydride and water is 1:1.1:7.5;

[0050] (2) mixing food waste with water, and crushing the resulting mixture into food waste slurry with a grinder, wherein the mass ratio of food waste to water is 1:1.4, and then sieving the food waste slurry so that the particle size of the food waste slurry is less than 2 mm, adding the sieved food waste slurry into a reaction vessel equipped with a stirrer, a thermometer and a condenser, and then adding an oxidant aqueous solution into the reaction vessel while stirring at 83° C., the stirring speed is 700 r / min, and the stirring time is 1.5 h, to obtain a pre-oxidized food waste slurry, wherein the mass ratio between the sieved food waste slurry and the oxidant aqueous solution is 3.6:1, and the oxidant aqueous solution described in step (2) is a potassium persulfate aqueous solution, and the mass percentage concentration of potassium persulfate is 7.5%;

[0051] (3) stirring the maleic anhydride-modified lignin obtained in step (1), the pre-oxidized food waste slurry obtained in step (2), and urea at room temperature at a stirring speed of 1100 r / min for 2 h to obtain a slurry containing a maleic anhydride-modified lignin-pre-oxidized food waste-urea complex, wherein the mass ratio of the maleic anhydride-modified lignin, the pre-oxidized food waste, and the urea is 1:2.7:5.6;

[0052] (4) mixing the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea complex obtained in step (3) with an acrylic acid monomer mixture, an emulsifier, and water, and stirring the resulting mixture at 58° C. for 125 minutes to obtain a pre-emulsion at a stirring speed of 1100 r / min, wherein the mass ratio of the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea complex obtained in step (3), the acrylic acid monomer mixture, the emulsifier, and the water is 35:16.5:1:41, and the acrylic acid monomer mixture in step (4) includes butyl acrylate, methyl methacrylate, and acrylic acid in a mass ratio of 6.05:2.4:1;

[0053] (5) After the temperature of the pre-emulsion obtained in step (4) is raised to 79° C., an initiator aqueous solution is added dropwise to the pre-emulsion at a dropping rate of 0.08 mL / min while stirring, and the stirring speed is 300 r / min. After the addition of the initiator aqueous solution is completed, the reaction is continued for 3.25 h, and then the reaction system is cooled to room temperature, and then the pH of the system is adjusted to 6.9 with ammonia water having a mass percentage concentration of 25%, thereby obtaining an emulsion as a sprayable film-forming slow-release urea fertilizer, wherein the mass ratio between the pre-emulsion obtained in step (4) and the initiator aqueous solution is 75:1.

[0054] The lignin sulfonate described in step (1) is calcium lignin sulfonate. The food waste described in step (2) contains 7.8 wt% starch, 11.6 wt% cellulose, 2.6 wt% protein, 1.9 wt% oil, and 46 wt% water. The emulsifier described in step (4) is a mixture of a reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:2.5, and the model of the reactive emulsifier is LRS-10. The initiator aqueous solution described in step (5) is an ammonium persulfate aqueous solution, wherein the mass percentage concentration of ammonium persulfate is 2.4%. The water used in steps (1) to (5) is deionized water.

[0055] Through steps (1) to (5), a sprayable film-forming slow-release urea fertilizer of Example 2 can be obtained, which has a uniform and stable emulsion appearance and no stratification phenomenon within 30 days of standing.

[0056] Example 3

[0057] (1) lignin sulfonate, maleic anhydride and water are mixed into a solution, and the pH value of the obtained mixed solution is adjusted to 10.5 with a 1 mol / L NaOH solution, and then stirred at 63 ° C. The stirring speed is 780 r / min. After the reaction for 8 hours, the mixed solution is cooled to room temperature, and then the pH value of the mixed solution is adjusted to 1.5 with a 1.8 mol / L sulfuric acid solution. At this time, a precipitate is generated in the solution. The precipitate in the solution is filtered and repeatedly washed with water until the pH value of the filtrate is neutral. The washed precipitate is placed at 67 ° C. and dried for 48 hours to obtain maleic anhydride-modified lignin, wherein the mass ratio of lignin sulfonate, maleic anhydride and water is 1:1.4:10;

[0058] (2) mixing food waste with water, and crushing the resulting mixture into food waste slurry with a grinder, wherein the mass ratio of food waste to water is 1:1.8, and then sieving the food waste slurry so that the particle size of the food waste slurry is less than 2 mm, adding the sieved food waste slurry into a reaction vessel equipped with a stirrer, a thermometer and a condenser, and then adding an oxidant aqueous solution into the reaction vessel while stirring at 85° C., the stirring speed is 800 r / min, and the stirring time is 2 h, to obtain a pre-oxidized food waste slurry, wherein the mass ratio between the sieved food waste slurry and the oxidant aqueous solution is 4.1:1, and the oxidant aqueous solution described in step (2) is an ammonium persulfate aqueous solution, and the mass percentage concentration of ammonium persulfate is 9%;

[0059] (3) stirring the maleic anhydride-modified lignin obtained in step (1), the pre-oxidized food waste slurry obtained in step (2), and urea at room temperature at a stirring speed of 1400 r / min for 2.5 h to obtain a slurry containing a maleic anhydride-modified lignin-pre-oxidized food waste-urea complex, wherein the mass ratio of the maleic anhydride-modified lignin, the pre-oxidized food waste, and the urea is 1:3.3:6.8;

[0060] (4) mixing the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea composite obtained in step (3) with an acrylic acid monomer mixture, an emulsifier, and water, and stirring the resulting mixture at 60° C. for 100 minutes to obtain a pre-emulsion at a stirring speed of 1800 r / min, wherein the mass ratio of the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea composite obtained in step (3), the acrylic acid monomer mixture, the emulsifier, and the water is 38:18:1:46, and the acrylic acid monomer mixture in step (4) comprises butyl acrylate, methyl methacrylate, and acrylic acid in a mass ratio of 6.3:2.7:1;

[0061] (5) After the temperature of the pre-emulsion obtained in step (4) is raised to 83° C., an initiator aqueous solution is added dropwise to the pre-emulsion at a drop rate of 0.12 mL / min while stirring, and the stirring speed is 400 r / min. After the addition of the initiator aqueous solution is completed, the reaction is continued for 4.5 hours, and then the reaction system is cooled to room temperature, and then the pH of the system is adjusted to 7 with ammonia water having a mass percentage concentration of 25%, thereby obtaining an emulsion as a sprayable film-forming slow-release urea fertilizer, wherein the mass ratio between the pre-emulsion obtained in step (4) and the initiator aqueous solution is 82:1.

[0062] The lignin sulfonate described in step (1) is sodium lignin sulfonate. The food waste described in step (2) contains 8.4 wt% starch, 11 wt% cellulose, 3.1 wt% protein, 1.7 wt% oil, and 52 wt% water. The emulsifier described in step (4) is a mixture of a reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:3, and the model of the reactive emulsifier is LRS-10. The initiator aqueous solution described in step (5) is a potassium persulfate aqueous solution, wherein the mass percentage concentration of potassium persulfate is 2.6%. The water used in steps (1) to (5) is deionized water.

[0063] Through steps (1) to (5), a sprayable film-forming slow-release urea fertilizer of Example 3 can be obtained, which has a uniform and stable emulsion appearance and no stratification phenomenon after standing for 30 days.

[0064] Example 4

[0065] (1) lignin sulfonate, maleic anhydride and water were mixed into a solution, and the pH value of the obtained mixed solution was adjusted to 10.8 with a 1 mol / L NaOH solution, and then stirred at 56 ° C. The stirring speed was 990 r / min. After the reaction for 7 hours, the mixed solution was cooled to room temperature, and then the pH value of the mixed solution was adjusted to 1.8 with a 1.8 mol / L sulfuric acid solution. At this time, a precipitate was generated in the solution. The precipitate in the solution was filtered and repeatedly washed with water until the pH value of the filtrate was neutral. The washed precipitate was placed at 74 ° C. and dried for 36 hours to obtain maleic anhydride-modified lignin, wherein the mass ratio of lignin sulfonate, maleic anhydride and water was 1:1.7:12.5;

[0066] (2) mixing food waste with water, and crushing the resulting mixture into food waste slurry with a grinder, wherein the mass ratio of food waste to water is 1:2.1, and then sieving the food waste slurry so that the particle size of the food waste slurry is less than 2 mm, adding the sieved food waste slurry to a reaction vessel equipped with a stirrer, a thermometer and a condenser, and then adding an oxidant aqueous solution to the reaction vessel while stirring at 88° C., the stirring speed is 1000 r / min, and the stirring time is 2.5 hours, to obtain a pre-oxidized food waste slurry, wherein the mass ratio between the sieved food waste slurry and the oxidant aqueous solution is 4.7:1, and the oxidant aqueous solution described in step (2) is a potassium persulfate aqueous solution, and the mass percentage concentration of potassium persulfate is 10.5%;

[0067] (3) stirring the maleic anhydride-modified lignin obtained in step (1), the pre-oxidized food waste slurry obtained in step (2), and urea at room temperature at a stirring speed of 1700 r / min for 3 h to obtain a slurry containing a maleic anhydride-modified lignin-pre-oxidized food waste-urea complex, wherein the mass ratio of the maleic anhydride-modified lignin, the pre-oxidized food waste, and the urea is 1:3.9:7.9;

[0068] (4) mixing the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea composite obtained in step (3) with an acrylic acid monomer mixture, an emulsifier, and water, and stirring the resulting mixture at 62° C. for 75 minutes to obtain a pre-emulsion at a stirring speed of 2400 r / min, wherein the mass ratio of the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea composite obtained in step (3), the acrylic acid monomer mixture, the emulsifier, and the water is 41:19.5:1:51, and the acrylic acid monomer mixture in step (4) comprises butyl acrylate, methyl methacrylate, and acrylic acid in a mass ratio of 6.55:3:1;

[0069] (5) After the temperature of the pre-emulsion obtained in step (4) is raised to 87° C., an initiator aqueous solution is added dropwise to the pre-emulsion at a dropping rate of 0.16 mL / min while stirring, and the stirring speed is 500 r / min. After the addition of the initiator aqueous solution is completed, the reaction is continued for 6.75 h, and then the reaction system is cooled to room temperature, and then the pH of the system is adjusted to 7.1 with ammonia water having a mass percentage concentration of 25%, thereby obtaining an emulsion as a sprayable film-forming slow-release urea fertilizer, wherein the mass ratio between the pre-emulsion obtained in step (4) and the initiator aqueous solution is 90:1.

[0070] The lignin sulfonate described in step (1) is sodium lignin sulfonate. The food waste described in step (2) contains 9 wt% starch, 10.6 wt% cellulose, 3.7 wt% protein, 1.4 wt% oil, and 58 wt% water. The emulsifier described in step (4) is a mixture of a reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:3.8, and the model of the reactive emulsifier is LRS-10. The initiator aqueous solution described in step (5) is an ammonium persulfate aqueous solution, wherein the mass percentage concentration of ammonium persulfate is 2.8%. The water used in steps (1) to (5) is deionized water.

[0071] Through steps (1) to (5), a sprayable film-forming slow-release urea fertilizer of Example 4 can be obtained, which has a uniform and stable emulsion appearance and no stratification phenomenon after being left to stand for 30 days.

[0072] Example 5

[0073] (1) lignin sulfonate, maleic anhydride and water are mixed into a solution, and the pH value of the obtained mixed solution is adjusted to 11 with a 1 mol / L NaOH solution, and then stirred at 50°C with a stirring speed of 1200 r / min. After the reaction for 5 hours, the mixed solution is cooled to room temperature, and then the pH value of the mixed solution is adjusted to between 2 with a 1.8 mol / L sulfuric acid solution. At this time, a precipitate is generated in the solution, and the precipitate in the solution is filtered and repeatedly washed with water until the pH value of the filtrate is neutral. The washed precipitate is placed at 80°C and dried for 24 hours to obtain maleic anhydride-modified lignin, wherein the mass ratio of lignin sulfonate, maleic anhydride and water is 1:2:15;

[0074] (2) mixing food waste with water, and crushing the resulting mixture into food waste slurry with a grinder, wherein the mass ratio of food waste to water is 1:2.5, and then sieving the food waste slurry so that the particle size of the food waste slurry is less than 2 mm, adding the sieved food waste slurry into a reaction vessel equipped with a stirrer, a thermometer and a condenser, and then adding an oxidant aqueous solution into the reaction vessel while stirring at 90° C., the stirring speed is 1200 r / min, and the stirring time is 3 hours, to obtain a pre-oxidized food waste slurry, wherein the mass ratio between the sieved food waste slurry and the oxidant aqueous solution is 5.3:1, and the oxidant aqueous solution described in step (2) is an ammonium persulfate aqueous solution, and the mass percentage concentration of ammonium persulfate is 12%;

[0075] (3) stirring the maleic anhydride-modified lignin obtained in step (1), the pre-oxidized food waste slurry obtained in step (2), and urea at room temperature at a stirring speed of 2000 r / min for 3.5 h to obtain a slurry containing a maleic anhydride-modified lignin-pre-oxidized food waste-urea complex, wherein the mass ratio of the maleic anhydride-modified lignin, the pre-oxidized food waste, and the urea is 1:4.5:9;

[0076] (4) mixing the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea composite obtained in step (3) with an acrylic acid monomer mixture, an emulsifier, and water, and stirring the resulting mixture at 65° C. for 50 minutes to obtain a pre-emulsion at a stirring speed of 3000 r / min, wherein the mass ratio of the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea composite obtained in step (3), the acrylic acid monomer mixture, the emulsifier, and the water is 44:21:1:56, and the acrylic acid monomer mixture in step (4) comprises butyl acrylate, methyl methacrylate, and acrylic acid in a mass ratio of 6.8:3.2:1;

[0077] (5) After the temperature of the pre-emulsion obtained in step (4) is raised to 90° C., an initiator aqueous solution is added dropwise to the pre-emulsion at a dropping rate of 0.2 mL / min while stirring, and the stirring speed is 600 r / min. After the addition of the initiator aqueous solution is completed, the reaction is continued for 8 hours, and then the reaction system is cooled to room temperature, and then the pH of the system is adjusted to 7.3 with ammonia water having a mass percentage concentration of 25%, thereby obtaining an emulsion as a sprayable film-forming slow-release urea fertilizer, wherein the mass ratio between the pre-emulsion obtained in step (4) and the initiator aqueous solution is 97:1.

[0078] The lignin sulfonate described in step (1) is calcium lignin sulfonate. The food waste described in step (2) contains 9.5 wt% starch, 10.0 wt% cellulose, 4.3 wt% protein, 1.1 wt% oil, and 64 wt% water. The emulsifier described in step (4) is a mixture of a reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:4.5, and the model of the reactive emulsifier is LRS-10. The initiator aqueous solution described in step (5) is a potassium persulfate aqueous solution, wherein the mass percentage concentration of potassium persulfate is 3.1%. The water used in steps (1) to (5) is deionized water.

[0079] Through steps (1) to (5), a sprayable film-forming slow-release urea fertilizer of Example 5 can be obtained, which has a uniform and stable emulsion appearance and no stratification phenomenon after being left to stand for 30 days.

[0080] Comparative Example 6

[0081] This example prepared a sprayable film-forming slow-release urea fertilizer according to the steps described in Example 3. The difference from Example 3 is that the particle size of the food waste slurry in step (2) of this example is 2.5-3.5 mm, which is larger than the 2 mm particle size described in the claims of the present invention. This is compared to the larger particle size of the food waste slurry in Example 6. The remaining preparation steps and reagent amounts are the same as those in Example 3.

[0082] Comparative Example 7

[0083] This example prepares a sprayable film-forming slow-release urea fertilizer according to the steps described in Example 3. The difference from Example 3 is that in step (1) of this example, the mass ratio of lignin sulfonate, maleic anhydride, and water is 1:0.6:10. The amount of maleic anhydride in this mass ratio is less than the range (0.8-2) described in the claims of the present invention, i.e., the amount of maleic anhydride used in Comparative Example 7 is relatively small. The other preparation steps and reagent amounts are the same as those in Example 3.

[0084] Comparative Example 8

[0085] This example prepares a sprayable, film-forming slow-release urea fertilizer according to the steps described in Example 3. The difference from Example 3 is that in step (2) of this example, the mass ratio of the sieved food waste slurry to the oxidant aqueous solution is 2.8:1. The amount of oxidant in this mass ratio is less than the range (3-5.3) described in the claims of the present invention, i.e., the amount of oxidant used is relatively small compared to Example 8. The remaining preparation steps and reagent amounts are the same as those in Example 3.

[0086] Comparative Example 9

[0087] This example prepares a sprayable film-forming slow-release urea fertilizer according to the steps described in Example 3. The difference from Example 3 is that in step (3) of this example, the mass ratio of maleic anhydride-modified lignin, pre-oxidized food waste, and urea is 1:1.9:6.8. The amount of food waste used in this mass ratio is less than the range (2.1-4.5) described in the claims of the present invention, i.e., the amount of food waste used in Comparative Example 9 is relatively small. The other preparation steps and reagent amounts are the same as in Example 3.

[0088] Comparative Example 10

[0089] This example prepared a liquid mulch film according to the steps described in Example 3. The difference between this example and Example 3 is that, instead of preparing a slurry containing a maleic anhydride-modified lignin-preoxidized food waste-urea complex, this example directly mixed the maleic anhydride-modified lignin, preoxidized food waste, and urea with an acrylic acid monomer mixture, an emulsifier, and water. The remaining preparation steps and reagent amounts were the same as in Example 3. The specific experimental steps are as follows:

[0090] Steps (1) and (2) of this embodiment are the same as steps (1) and (2) of embodiment (3).

[0091] (3) mixing the maleic anhydride-modified lignin obtained in step (1), the pre-oxidized food waste slurry obtained in step (2), urea, an acrylic acid monomer mixture, an emulsifier, and water, and stirring the resulting mixture at 60° C. for 100 min to obtain a pre-emulsion at a stirring speed of 1800 r / min, wherein the mass ratio of the maleic anhydride-modified lignin, the pre-oxidized food waste slurry, and urea is 1:3.3:6.8, and the mass ratio of the total mass of the maleic anhydride-modified lignin, the pre-oxidized food waste slurry, and urea to the acrylic acid monomer mixture, the emulsifier, and water is 38:18:1:46, and the acrylic acid monomer mixture in step (3) comprises butyl acrylate, methyl methacrylate, and acrylic acid in a mass ratio of 6.3:2.7:1;

[0092] Step (4) of this embodiment is the same as step (5) of embodiment (3).

[0093] The lignin sulfonate described in step (1) is sodium lignin sulfonate. The food waste described in step (2) contains 8.4 wt% starch, 11 wt% cellulose, 3.1 wt% protein, 1.7 wt% oil, and 52 wt% water. The emulsifier described in step (3) is a mixture of a reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:3, and the model of the reactive emulsifier is LRS-10. The initiator aqueous solution described in step (4) is a potassium persulfate aqueous solution, wherein the mass percentage concentration of potassium persulfate is 2.6%. The water used in steps (1) to (4) is deionized water.

[0094] Comparative Example 11

[0095] This example prepares a liquid mulch film according to the steps described in Example 3. The difference between this example and Example 3 is that in step (4) of this example, the mass ratio of the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea composite, the acrylic acid monomer mixture, the emulsifier, and water is 38:13:1:46. The amount of the acrylic acid monomer mixture in this mass ratio is less than the range (15-21) described in the claims of the present invention, i.e., the amount of the acrylic acid monomer mixture is relatively small. The other preparation steps and reagent amounts are the same as in Example 3.

[0096] Comparative Example 12

[0097] This example prepared a liquid mulch film according to the steps described in Example 3. The difference between this example and Example 3 is that a pre-emulsion was not prepared. Instead, an aqueous initiator solution was added directly to a mixture of a slurry containing a maleic anhydride-modified lignin-preoxidized food waste-urea complex, an acrylic acid monomer mixture, an emulsifier, and water. The remaining preparation steps and reagent amounts were the same as in Example 3. The specific experimental steps are as follows:

[0098] Steps (1) to (3) of this embodiment are the same as steps (1) to (3) of embodiment (3).

[0099] (4) physically mixing the slurry containing the maleic anhydride-modified lignin-preoxidized food waste-urea complex obtained in step (3) with an acrylic monomer mixture, an emulsifier, and water, and then immediately raising the temperature of the resulting mixture to 83° C., and adding an initiator aqueous solution dropwise to the mixture at a dripping rate of 0.12 mL / min while stirring, and the stirring speed is 400 r / min. After the initiator solution is added dropwise, the reaction is continued for 4.5 hours, and then the reaction system is cooled to room temperature, and then the pH of the system is adjusted to 7 with ammonia water having a mass percentage concentration of 25%, thereby obtaining the liquid sample of this embodiment, wherein the mass ratio between the total mass of the mixture of the maleic anhydride-modified lignin-preoxidized food waste-urea complex, the acrylic monomer mixture, the emulsifier, and water and the initiator aqueous solution is 82:1;

[0100] The lignin sulfonate described in step (1) is sodium lignin sulfonate. The food waste described in step (2) contains 8.4 wt% starch, 11 wt% cellulose, 3.1 wt% protein, 1.7 wt% oil, and 52 wt% water. The emulsifier described in step (4) is a mixture of a reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:3, and the model of the reactive emulsifier is LRS-10. The initiator aqueous solution described in step (4) is a potassium persulfate aqueous solution, wherein the mass percentage concentration of potassium persulfate is 2.6%. The water used in steps (1) to (4) is deionized water.

[0101] Application Example 13

[0102] In this example, the sprayable film-forming slow-release urea fertilizer emulsions obtained in Examples 1-5 and some of the liquid samples of the comparative examples were sprayed onto the soil surface as agricultural slow-release urea fertilizers and agricultural liquid mulch films, respectively. The specific experimental steps are as follows:

[0103] (1) A vegetable planting field was selected at 118.98385532736967° east longitude and 32.06034538505579° north latitude, and Chinese cabbage was planted in the field;

[0104] (2) In September 2021, the field was divided into several plots of 0.5 m × 0.5 m, with a spacing of 0.1 m between each plot; 30 Chinese cabbage seeds were evenly sown in each plot; and then 5 of the plots were sprayed with 0.58 kg / m 2 The sprayable film-forming slow-release urea fertilizer emulsions obtained in Examples 1-5 were evenly sprayed in an amount of 0.58 kg / m 2 and 0.58 kg / m 2, respectively; another field was selected as a control group, which was a bare soil field without any emulsion sprayed; the other fields were sprayed with the corresponding liquid samples of the comparative examples, respectively, at an amount of 0.58 kg / m 2. 2.

[0105] Effect embodiment

[0106] In this example, the following performance tests were performed on the sprayable film-forming slow-release urea fertilizer emulsions obtained in Examples 1-5 and the liquid samples prepared in Comparative Examples 6-12.

[0107] 1. Emulsion stability test

[0108] Observe whether the sample will stratify within 30 days. If the sample does not stratify, it means that the emulsion is stable and can be used for subsequent tests. If stratification occurs, it means that the sample is unstable and is not suitable for use as a liquid mulch emulsion, and the sample will not enter the subsequent testing stage.

[0109] 2. Viscosity test

[0110] Liquid viscosity was measured using an NDJ-1 rotational viscometer (Shanghai Nirun Intelligent Technology Co., Ltd., China). The temperature of each sample was maintained at 30°C and the rotational speed was controlled at 60 rpm. Viscosity values ​​were recorded in mPa.s.

[0111] 3. Sprayability test

[0112] The sprayability of the liquid sample was tested using a handheld spray gun with an inner diameter of 2.5 mm and an air pressure of 0.3 MPa. If the spray distance of the emulsion under these conditions could be greater than 200 mm, the emulsion was considered sprayable; otherwise, the emulsion was not sprayable.

[0113] 4. Soil temperature and humidity test

[0114] Soil temperature test: A curved tube ground thermometer (Beijing Dingsheng Ronghe Technology Co., Ltd., China) was used to measure the soil temperature at a depth of 5 cm in each field in Application Example 13. The test time was 14:00-16:00 every day. The test lasted for 30 days, and the average temperature during this test period was reported as the value.

[0115] Soil moisture content test: While measuring the soil temperature, 5g of soil at a depth of 5cm in each field was also collected. The soil moisture content was measured using the drying method. That is, the 5g of soil was dried at 80°C. The soil moisture content was then calculated according to the formula: Soil moisture content = [(5-mass of soil after drying) / 5] × 100%. The test was conducted every two days for 30 days. The average soil moisture content during this test period was reported as the value.

[0116] 5. Biodegradability

[0117] The biodegradability test was conducted in the experimental field of Application Example 13. A circular film sample (50 mm in diameter, mass W0) of the emulsion or liquid was naturally air-dried in a Petri dish and buried in the soil at a depth of 20 cm. The sample was then removed from the soil on the 100th day and repeatedly washed with deionized water. After no obvious impurities were left on the sample, it was dried at 55°C to a constant weight and weighed. The mass was recorded as W. d The biodegradation rate of the sample was calculated according to the following formula:

[0118] Biodegradation rate = [(W0-W d ) / W0]×100%

[0119] 6. Test method for urea sustained-release performance:

[0120] First, prepare the p-dimethylaminobenzaldehyde colorimetric solution: accurately weigh 20.00 g of p-dimethylaminobenzaldehyde and dissolve it in 1000 mL of anhydrous ethanol.

[0121] Prepare urea standard solution (1000 μg / mL): Accurately weigh 1.00 g of urea standard, dissolve it in deionized water, transfer it to a 1000 mL volumetric flask, and adjust the volume to obtain the stock solution.

[0122] To plot a urea standard absorbance curve: Add 0, 0.50, 1.00, 2.00, 3.00, and 4.00 mL of a 1000 μg / mL urea standard solution to six 25 mL colorimetric tubes, respectively. Then, add 10.00, 9.50, 9.00, 8.00, 7.00, and 6.00 mL of distilled water to the 10 mL mark. Then, add 10 mL of the developer and 4 mL of a 2 mol / L sulfuric acid solution to each colorimetric tube. Then, add distilled water to the 25 mL mark, mix well, and let stand for 10 minutes. The reaction solution in the first colorimetric tube was used as the reference solution. Measure the absorbance of the reaction solutions in each of the six colorimetric tubes at 422 nm (using a UV-Vis spectrophotometer). Plot a urea standard absorbance curve with the absorbance value as the y-axis and the urea standard solution concentration as the x-axis.

[0123] First, place the emulsion or liquid obtained in the example in a culture dish, then let the emulsion or liquid air dry naturally into a 1 mm thick film. Cut a 2 g circular sample from the air-dried film and place the sample in a 60 mm long, 10 mm inner diameter catheter with one end sealed. Immerse the catheter horizontally in a beaker filled with 500 mL of distilled water, with the center of the catheter coinciding with the center of the horizontal plane of the beaker, keeping the catheter parallel to the water surface and 1 cm below the water surface. Then place the stirring bar in the beaker and place it on a magnetic stirrer, controlling the speed to 10 s. -1The solution temperature was 25°C. To minimize the effect of uneven fluid flow in the beaker on the diffusion rate of urea molecules released from the catheter port, the catheter was rotated horizontally 90° every 2 hours. Samples were taken simultaneously from three different locations in the beaker. 5 mL of sample solution was accurately pipetted from each location and added to three 25 mL colorimetric tubes. 3 mL of the previously prepared p-dimethylaminobenzaldehyde colorimetric solution was then accurately added to each tube. The solution was diluted to the mark with distilled water and allowed to stand for 30 minutes. The absorbance was then measured at a wavelength of 422 nm. The absorbance of each sample was used to determine the corresponding urea concentration from the urea standard absorbance curve. The average of the urea concentrations at the three locations was taken as the urea concentration corresponding to that sampling time point. After sampling at each time point, 15 mL of distilled water was added to the beaker to ensure that the volume of the beaker was always 500 mL. The urea concentrations corresponding to the different sampling time points were collected and the cumulative urea release rate was calculated. The cumulative release rate of urea refers to the percentage of the cumulative release mass of urea released from the sample over a period of time to the mass of urea contained in the sample before the release. It is calculated as follows: Cumulative release rate of urea = (cumulative release mass of urea in a certain release period / mass of urea contained in the sample before the release) × 100%

[0124] 7. Pakchoy yield test

[0125] After the pakchoy plants in each field in Application Example 13 had completed one growing season (two months), they were removed from the field along with their roots, and the soil adhering to the roots was gently brushed off. The total amount of pakchoy produced in each field was then weighed, and the effect of the sprayable film-forming slow-release urea fertilizer on pakchoy yield was evaluated based on the pakchoy yield in each field.

[0126] 8. As can be seen from Table 1, the emulsions prepared in Examples 1-5 did not show any stratification within 30 days, indicating that the emulsions prepared in Examples 1-5 are stable. In addition, the emulsions prepared in Comparative Examples 8, 9, 10, and 11 did not show any stratification, indicating that the emulsions prepared in these Examples are also stable. The liquid sample prepared in Comparative Example 6 showed stratification on the third day, indicating that the sample was unstable. This is because the particle size of the food waste slurry in step (2) of Comparative Example 6 was 2.5-3.5 mm, which is larger than the 2 mm described in the claims of the present invention. That is, the particle size of the food waste slurry in Comparative Example 6 was too large. These particles with excessive mass and volume were difficult to remain suspended in the emulsion, and thus settled at the bottom of the liquid, resulting in stratification. The liquid sample prepared in Comparative Example 7 showed stratification on the first day, indicating that the sample was very unstable. This was because the amount of maleic anhydride used in step (1) of Comparative Example 7 was relatively small, resulting in less maleic anhydride reacting with the hydroxyl groups in the lignin sulfonate, and thus fewer carbon-carbon double bond groups attached to the lignin sulfonate. Such maleic anhydride-modified lignin was difficult to copolymerize with the acrylic ester monomer, making it difficult for the maleic anhydride-modified lignin to evenly fuse with the polyacrylate part, resulting in the two polymers (lignin and polyacrylate) being difficult to be compatible, and then the stratification phenomenon caused by phase separation occurred. The liquid sample prepared in Comparative Example 12 exhibited stratification on day one, indicating that the sample was also unstable. This is because no pre-emulsion was prepared in Comparative Example 12. Instead, an aqueous initiator solution was added directly to a mixture of a slurry containing a maleic anhydride-modified lignin-preoxidized food waste-urea composite, an acrylic acid monomer mixture, an emulsifier, and water. The lack of a pre-emulsion reduced the stability of the emulsion polymerization, resulting in excessive amounts of coagulants and wall-forming materials in the emulsion. Consequently, Comparative Example 12 exhibited significant stratification. In summary, the liquid samples prepared in Comparative Examples 6, 7, and 12 were all prone to demulsification and stratification. Such inhomogeneous liquids, if used in spraying operations, could clog nozzles and fail to form a uniformly distributed liquid film on the soil surface. Therefore, the samples prepared in Comparative Examples 6, 7, and 12 cannot be used as liquid mulch products and were not required to proceed to the subsequent testing phase.

[0127] As can be seen from the results in Table 2, the samples of Examples 1-5 and Comparative Examples 9-11 are all sprayable. However, the sample of Comparative Example 8 is not sprayable. This is because the viscosity of Comparative Example 8 is much higher than that of the samples of Examples 1-5 and Comparative Examples 9-11. If the viscosity of the liquid is too high, it is difficult to meet the spraying requirements. The reason why the viscosity of the liquid sample of Comparative Example 8 is high is that the amount of oxidant used in its preparation step (2) is less than the range (3-5.3) described in the claims of the present invention, that is, the amount of oxidant used in Comparative Example 8 is too small. The function of the oxidant is to oxidize some of the hydroxyl groups in starch, cellulose and lignin in the kitchen waste slurry into carboxyl groups, which can reduce the association effect caused by hydrogen bonds between system molecules to a certain extent, and help to reduce the viscosity of the system. Therefore, in the liquid sample of Comparative Example 8 that has not been fully pre-oxidized, the hydrogen bond association effect between the molecular chains is strong, resulting in a high viscosity of the system. The liquid with high viscosity also encounters greater resistance when passing through the nozzle of the spray gun, the spraying distance is not far, and the liquid droplets are not easy to disperse into a mist and move forward. Therefore, the sample of Comparative Example 8 is not suitable for use as a liquid mulch film, and the sample of Comparative Example 8 has not been subjected to other subsequent tests (including: average soil temperature, average soil moisture content, biodegradation rate, cumulative urea release rate, and Chinese cabbage yield).

[0128] The results in Table 2 show that in Application Example 13, the average soil temperature in the fields sprayed with the emulsions of Examples 1-5 was 3.7-3.8°C higher than that of the bare soil fields without any emulsion spraying. Furthermore, the soil moisture content at a depth of 5 cm in the former fields was 11.8%-12.5% ​​higher than that of the latter fields. In contrast, the soil temperature in the sample of Comparative Example 11 was only 0.72°C higher than that of the field without any emulsion spraying, and the soil moisture content at a depth of 5 cm in the former fields was only 1.3% higher than that of the latter fields. This indicates that the sample of Comparative Example 11 had limited effect on improving soil temperature and moisture content. This is because the amount of acrylic acid monomer mixture used in Comparative Example 11 was too low. The polymerization between acrylate monomers can obtain the polyacrylate part. Polyacrylate has excellent film-forming properties and can make the prepared sprayable film-forming slow-release urea fertilizer emulsion form a film on the soil surface. The formed film can block the gaps between soil particles, hinder the loss of heat and water in the soil, and thus play a role in heat preservation and moisturizing the soil. In contrast, in Comparative Example 11, the amount of acrylic acid monomer mixture used is relatively small, which leads to a relatively small content of polyacrylate, resulting in a relatively small amount of film-forming material, making it difficult for the sample to block the gaps between soil particles, that is, the heat preservation and moisturizing effect on the soil is poor.

[0129] Traditional plastic mulch films (such as LDPE mulch films) are non-biodegradable and have a significant destructive effect on the ecological environment of agricultural soil. Therefore, the development of good biodegradable mulch films is also one of the important goals pursued by the present invention to adapt to recyclable green ecological agriculture. It is generally believed that if the biodegradability of a sample exceeds 60% within 100 days, the sample can be considered to have good biodegradability. The results in Table 2 show that the biodegradability of the liquid mulch films of Examples 1-5 is 76.7%-77.5% within 100 days. Therefore, the liquid mulch films of Examples 1-5 all have good biodegradability. However, the biodegradability of the mulch film of Comparative Example 9 is only 41.3% within 100 days, that is, the biodegradability of the mulch film sample of Comparative Example 9 is 36.2% lower than that of the liquid mulch film of Example 3, indicating that the biodegradability of the mulch film sample of Comparative Example 9 is much lower than that of the liquid mulch film of Example 3. This is because the amount of food waste used in Comparative Example 9 is relatively small. Food waste is an important biomass raw material with good biodegradability. The amount of food waste used in Comparative Example 9 is relatively small, which correspondingly reduces the biodegradability of the mulch film sample in Comparative Example 9.

[0130] Attachment Figure 2 The urea cumulative release curves of the samples of Examples 1-5 after air drying and film formation and pure urea are shown. Figure 2As can be seen, the membrane samples of Examples 1-5 all had lower urea release rates than pure urea, with Example 3 having the lowest urea release rate, indicating that the membrane samples of Examples 1-5 all had a sustained urea release effect. As can be seen in Table 2, the cumulative urea release rates of the membrane samples of Examples 1-5 after 96 hours of immersion in water ranged from 56.62% to 81.37%, with the sample of Example 3 having the lowest cumulative urea release rate of 56.62%. Although the liquid mulch film of Comparative Example 9 is prepared according to the steps described in Example 3, the cumulative release rate of urea of ​​the sample of Comparative Example 9 after soaking in water for 96 hours is 82.66%, which is 26.04% higher than the cumulative release rate of urea of ​​the sample of Example 3, that is, the urea sustained-release effect of the sample of Comparative Example 9 is weaker than that of the sample of Example 3; this is because in Examples 1-5, the urea molecules are wrapped in two layers of polymer networks: the first layer of the network is a polymer network of maleic anhydride-modified lignin-preoxidized food waste-urea complex, and the second layer of the network is a polymer network of maleic anhydride-modified lignin-preoxidized food waste-urea complex. The food waste-urea complex is embedded in the polyacrylate network. In these two layers of continuously wrapped polymer networks, the release rate of urea molecules is greatly reduced, achieving a sustained-release effect of urea. Food waste contains natural polymers rich in hydroxyl groups such as cellulose and protein. The adsorption and encapsulation of urea by these natural polymers will reduce the release rate of urea. However, in Comparative Example 9, the amount of food waste used is relatively small, so the urea cannot be effectively encapsulated in the polymer network of the maleic anhydride-modified lignin-pre-oxidized food waste-urea complex, which ultimately causes the release rate of urea to increase and the sustained-release property of urea to decrease. Comparative Example 10 also prepared a liquid mulch film according to the steps described in Example 3, but the cumulative urea release rate of the sample of Comparative Example 10 after soaking in water for 96 hours was 93.58%, which was 36.96% higher than the cumulative urea release rate of the sample of Example 3. That is, the urea sustained-release effect of the sample of Comparative Example 10 was much weaker than that of the sample of Example 3. This is because Comparative Example 10 did not prepare a slurry containing a maleic anhydride-modified lignin-preoxidized food waste-urea complex. Instead, the maleic anhydride-modified lignin, preoxidized food waste and urea were directly mixed with an acrylic monomer mixture, an emulsifier and water. This resulted in the sample of Comparative Example 10 not forming a two-layer polymer network, that is, the urea was not encapsulated in the polymer network of the complex formed by the maleic anhydride-modified lignin and the preoxidized food waste, which ultimately caused the urea release rate to increase and the urea sustained-release property to decrease significantly.Comparative Example 11 also prepared the liquid mulch film according to the steps described in Example 3, but the cumulative urea release rate of the sample of Comparative Example 11 after soaking in water for 96 hours was 91.27%, which was 34.65% higher than the cumulative urea release rate of the sample of Example 3, that is, the urea sustained-release effect of the sample of Comparative Example 11 was also much weaker than that of the sample of Example 3; this was because the amount of acrylic acid monomer mixture used in Comparative Example 11 was relatively small, which resulted in the sample of Comparative Example 11 failing to effectively form a second layer of polyacrylate network, that is, the maleic anhydride-modified lignin-pre-oxidized food waste-urea complex was not effectively embedded in the polyacrylate network, which ultimately caused the urea release rate to increase and the urea sustained-release property to decrease significantly.

[0131] The results in Table 2 show that in Application Example 13, the pakchoi yield in the fields sprayed with the emulsions of Examples 1-5 was 3.72-4.12 kg, 98.9%-120.3% higher than the pakchoi yield (1.87 kg) in bare soil fields without any emulsion or liquid spraying. In contrast, the pakchoi yields in the fields corresponding to Comparative Examples 9-11 were only 54.0%, 18.2%, and 14.9% higher than those in bare soil, respectively. Therefore, the emulsions of Examples 1-5 significantly increased pakchoi yield in the fields, confirming the rationality and necessity of the corresponding parameter ranges described in the claims.

[0132] Table 1 The stability of the emulsions or liquids obtained in Examples 1-5 and Comparative Examples 6-12 was evaluated by recording whether the emulsions showed stratification within 30 days.

[0133]

[0134] Table 2 shows the viscosity and sprayability of the emulsions prepared in Examples 1-5 and the liquids prepared in Comparative Examples 8-11, as well as the test results for average soil temperature, average soil moisture content, biodegradation rate, 96-hour cumulative urea release rate, and pakchoi yield in fields sprayed with the emulsions and liquids of the above examples and bare soil without any sample in Application Example 13. A "-" in the table indicates that the sample was not tested for the corresponding item, and bare soil indicates that no sample from the examples was sprayed.

[0135]

Claims

1. A method for preparing a slow-release fertilizer based on a pre-oxidized food waste composite, the preparation steps of which are as follows: (1) lignin sulfonate, maleic anhydride and water are mixed into a solution, the pH value of the obtained mixed solution is adjusted to 10-11 with 1 mol / L NaOH solution, and then stirred at 50-75°C with a stirring speed of 360-1200 r / min. After the reaction for 5-10 hours, the mixed solution is cooled to room temperature, and then the pH value of the mixed solution is adjusted to between 1 and 2 with 1.8 mol / L sulfuric acid solution. At this time, a precipitate is generated in the solution, the precipitate in the solution is filtered, and the precipitate is repeatedly washed with water until the pH value of the filtrate is neutral. The washed precipitate is placed at 55-80°C and dried for 24-72 hours to obtain maleic anhydride modified lignin, wherein, The mass ratio of lignin sulfonate, maleic anhydride and water is 1:(0.8-2):(5-15); (2) mixing food waste with water, and crushing the resulting mixture into food waste slurry using a grinder, wherein the mass ratio of food waste to water is 1:(1-2.5), and then sieving the food waste slurry so that the particle size of the food waste slurry is less than 2 mm, adding the sieved food waste slurry into a reaction vessel equipped with a stirrer, a thermometer and a condenser, and then adding an oxidant aqueous solution into the reaction vessel while stirring at 80-90° C., at a stirring speed of 500-1200 r / min, and a stirring time of 1-3 hours, to obtain a pre-oxidized food waste slurry, wherein the mass ratio of the sieved food waste slurry to the oxidant aqueous solution is (3-5.3):1, and the oxidant aqueous solution in step (2) is a potassium persulfate or ammonium persulfate aqueous solution, and the mass percentage concentration of the potassium persulfate or ammonium persulfate is 6-12%; (3) A slurry containing a composite of maleic anhydride-modified lignin and pre-oxidized food waste and urea is prepared by the following method: stirring the maleic anhydride-modified lignin obtained in step (1), the pre-oxidized food waste slurry obtained in step (2), and urea at room temperature at a stirring speed of 1400-2000 r / min and a stirring time of 2.5-3.5 h to obtain a slurry containing a composite of maleic anhydride-modified lignin and pre-oxidized food waste and urea, wherein the mass ratio of the maleic anhydride-modified lignin, the pre-oxidized food waste, and the urea is 1:(3.3-4.5):(6.8-9); (4) mixing the slurry containing the maleic anhydride modified lignin-preoxidized restaurant kitchen waste-urea complex obtained in step (3) with an acrylic acid monomer mixture, an emulsifier and water, and stirring the resulting mixture at 55-65° C. for 50-150 min to obtain a pre-emulsion at a stirring speed of 500-3000 r / min, wherein the slurry containing the maleic anhydride modified lignin-preoxidized restaurant kitchen waste-urea complex obtained in step (3), the acrylic acid monomer mixture, the emulsifier and water are mixed. The mass ratio of the monomers is (32-44): (15-21): 1: (36-56), the acrylic monomer mixture in step (4) comprises butyl acrylate, methyl methacrylate and acrylic acid in a mass ratio of (5.8-6.8): (2.1-3.2): 1, the emulsifier in step (4) is a mixture of a reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1: (1.5-4.5), and the model of the reactive emulsifier is LRS-10; (5) After the temperature of the pre-emulsion obtained in step (4) is raised to 75-90° C., an initiator aqueous solution is added dropwise to the pre-emulsion at a dripping rate of 0.04-0.2 mL / min while stirring, and the stirring speed is 200-600 r / min. After the initiator aqueous solution is added, the reaction is continued for 2-8 hours, and then the reaction system is cooled to room temperature, and then the pH of the system is adjusted to 6.8-7.3 with ammonia water with a mass percentage concentration of 25%, thereby obtaining an emulsion of a slow-release fertilizer based on a pre-oxidized food waste complex, wherein the mass ratio between the pre-emulsion obtained in step (4) and the initiator aqueous solution is (67-97):1, and the initiator aqueous solution in step (5) is a potassium persulfate or ammonium persulfate aqueous solution, wherein the mass percentage concentration of potassium persulfate or ammonium persulfate is 2.2-3.1%.

2. The preparation method according to claim 1, wherein The lignin sulfonate described in step (1) is sodium lignin sulfonate or calcium lignin sulfonate.

3. The preparation method according to claim 1, wherein The food waste in step (2) contains 7.2-9.5 wt% starch, 10.0-12.2 wt% cellulose, 2.1-4.3 wt% protein, 1.1-2.1 wt% oil, and 40-64 wt% water.

4. The preparation method according to any one of claims 1 to 3, wherein The water used is deionized water.

5. A slow-release fertilizer based on a pre-oxidized food waste composite prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the slow-release fertilizer based on the pre-oxidized food waste composite according to claim 5 in agricultural slow-release fertilizers and agricultural liquid mulch films.

Images