Preparation method of silkworm excrement slow-release fertilizer using silkworm excrement as main solid raw material

Abstract

The present invention discloses a method for preparing a silkworm excrement slow-release fertilizer using silkworm excrement as the main solid-carrying raw material. The method utilizes microwaves and mechanical ball milling to modify the silkworm excrement, then mixes and stirs the modified silkworm excrement and a thickener with a saturated aqueous solution of chemical fertilizer to form a colloid, and then extrudes and forms a slow-release fertilizer particle core, which is then put into a granulator and coated with an embedding material to obtain silkworm excrement slow-release fertilizer particles. The present invention utilizes the hydrogel-like swelling properties of polymer compounds such as fiber, polysaccharide, and protein in silkworm excrement, and weakens the hydrogen bonding between polymer compounds in silkworm excrement and reduces the particle size through the high-frequency electromagnetic waves of microwaves and the high-energy mechanical action of high-speed ball milling, thereby exposing more hydrogen bonds in the silkworm excrement particles, thereby enhancing the interaction between silkworm excrement and water molecules, thereby increasing the hydrogel-like swelling properties of the silkworm excrement and strengthening its swelling adsorption capacity for chemical fertilizers. The silkworm excrement slow-release carrier is then embedded and the process is compounded based on the growth characteristics of crops to prepare a silkworm excrement-based slow-release fertilizer.

Description

Technical Field

[0001] The invention belongs to the field of fertilizer preparation, and in particular relates to a method for producing a slow-release fertilizer using modified silkworm excrement as a controlled-release carrier. Background Art

[0002] Silkworm feces refers to the excrement of silkworms. After feeding on mulberry leaves, silkworms digest and absorb some of the carbohydrates, protein, and fat in the mulberry leaves, excreting the undigested contents along with the silkworm's metabolic waste as feces. Silkworm feces contain 15% crude protein, 55% carbohydrates, 2.5% crude fat, 18% crude fiber, and 9.5% crude ash. Silkworm feces also contain chlorophyll, carotenoids, pectin, and leaf protein. As a waste product of the sericulture industry, silkworm feces production in Guangxi alone reaches 4 million tons annually. However, in my country, most silkworm feces are directly returned to the fields for reuse, resulting in low efficiency and added value. Consequently, the indiscriminate dumping of silkworm feces is widespread, polluting waterways and soil, and severely damaging the environment.

[0003] As the global population continues to grow, the demand for food is also increasing. To increase food production, pesticides and chemical fertilizers are indispensable. However, long-term use of pesticides and chemical fertilizers can lead to soil contamination and compaction, ultimately leading to a decrease in food production. Furthermore, most nitrogen fertilizers used in farmland are quick-acting fertilizers, such as urea and ammonium bicarbonate. Once applied to the soil, only 30-50% of this fertilizer is absorbed and utilized by crops; the remainder is lost through ammonia volatilization, leaching, nitrification, and denitrification. Furthermore, the fertilization period is relatively short, failing to meet the nitrogen needs of crops throughout their entire growth period. Potassium fertilizers, such as potassium chloride and potassium sulfate, are largely soluble in water and absorbed by crops as potassium ions. When soils have poor fertility and water retention, the potassium ions are lost before they can be absorbed. Large amounts of nitrogen, phosphorus, and potassium, among other elements, remain in the soil, enter groundwater and surface water, or are released into the air, causing serious environmental pollution. To address these issues, developing advanced fertilizer improvement technologies is an effective way to improve fertilizer utilization efficiency and reduce volatilization losses of N, P, and K.

[0004] Slow-release fertilizers, also known as slow-acting or controlled-release fertilizers, contain nutrient compounds that release slowly or at a controlled rate from the soil, allowing for continuous uptake and utilization by crops. This reduces soil nutrient losses, particularly nitrogen, and reduces the number of fertilization applications, saving labor and costs. Coated slow-release fertilizers currently used on crops achieve a certain degree of slow release in the early stages. However, once the coating material degrades, a sudden release occurs, which cannot be sustained over a given period. Consequently, they cannot meet the high nutrient demands of crops during a specific period. Using sugarcane, a plant with a growth cycle exceeding 300 days, as an example, we analyze the relationship between crop nutrient requirements and slow-release fertilizer release. Sugarcane requires significant potassium absorption during the early and mid-elongation periods (the third month after planting and continuing for two to three months). Conventional slow-release fertilizers struggle to achieve a sudden release during the early elongation period, let alone maintain a high potassium release for two to three months. For crops with long growth cycles and different nutrient requirements at different growth stages, slow-release fertilizers are needed to meet the nutritional needs of crops by achieving a sudden release in a specific period and maintaining a large amount of nutrient release during the fertilizer-required period. Summary of the Invention

[0005] The present invention addresses the problem that slow-release fertilizers currently used for crops cannot continuously meet the high nutrient demands of long-growing crops during a specific growth cycle after the embedding material is degraded. The present invention utilizes silkworm excrement, a biological waste, as a controlled-release carrier for chemical fertilizers, achieving a burst release after the embedding material is degraded, and also achieving a uniform release of large amounts of nutrients. Silkworm excrement, rich in fiber, fat, protein, and other macromolecular compounds, possesses unique swelling properties that can be used to prepare a slow-release fertilizer carrier capable of efficiently adsorbing chemical fertilizers. However, the macromolecular compounds in the raw silkworm excrement are highly cross-linked due to hydrogen bonds, which limits their swelling properties. The present invention first soaks the original silkworm excrement in water and places it in a microwave workstation. The high-frequency electromagnetic waves emitted by the microwaves destroy the cross-linking of the polymer compounds. After drying, the high-energy mechanical energy of high-speed ball milling is further used to weaken the hydrogen bonding between the polymer compounds in the silkworm excrement and reduce the particle size. The silkworm excrement particles are exposed to more hydrogen bonds, thereby increasing the interaction between the silkworm excrement and water molecules, enhancing the hydrogel-like swelling properties of the silkworm excrement, thereby achieving an improvement in its swelling adsorption capacity for fertilizers such as urea, potassium chloride, and ammonium phosphate. Then, based on the growth characteristics of crops, the silkworm excrement-based fertilizer slow-release carrier is embedded and compounded to prepare a silkworm excrement-based slow-release fertilizer. The present invention achieves slow release in the early stage by regulating the thickness of the embedding material, achieves a sudden release of nutrients after the embedding material is degraded, and utilizes the effect of the silkworm excrement carrier to achieve a uniform release of a large amount of nutrients to meet the nutrient needs of crops at a specific period.

[0006] The technology of the present invention is achieved through the following technical solutions:

[0007] (1) Modification of silkworm excrement by microwave and mechanical ball milling

[0008] Silkworm excrement was added to water in a certain proportion and soaked for a period of time, then placed in a container for microwave modification. After the container was cooled, it was taken out and dried. An appropriate amount of microwave-modified silkworm excrement was weighed and placed in a ball mill to obtain modified silkworm excrement powder. The silkworm excrement obtained after drying was labeled as silkworm excrement A.

[0009] (2) Silkworm feces swelling adsorption and immobilization of fertilizer

[0010] Put the fertilizer in a container, add water to prepare a solution, then add an appropriate amount of the silkworm excrement A obtained in step (1), and at the same time add an appropriate amount of a thickener, stir and mix, and let it stand for a period of time to allow the silkworm excrement to fully swell and absorb and fix, to obtain a semi-solid viscous mixture sol, marked as B;

[0011] The thickener is one or a mixture of sodium carboxymethyl cellulose, sodium alginate, and chitosan;

[0012] The mass ratio of the fertilizer, silkworm excrement and thickener is: 0.8-2.43:1:0.02-0.06;

[0013] (3) Extrusion granulation to prepare the inner core of slow-release fertilizer particles

[0014] The mixture sol B obtained in step (2) is placed in a mold and extruded by a molding hydraulic press to obtain a cylindrical slow-release fertilizer, and then the slow-release fertilizer particles are transferred to an oven for drying and solidification to obtain the slow-release fertilizer particle core;

[0015] (4) Preparation of biodegradable embedding materials

[0016] The adhesive is dissolved in water, heated and stirred to gelatinize to obtain an adhesive gelatin solution, and triethylamine is added as a homogeneous catalyst to obtain a clear and viscous sol, which is a biodegradable embedding material.

[0017] (5) Coating the inner core of the slow-release fertilizer particles

[0018] The inner core of the slow-release fertilizer granules is put into a granulator, and the embedding material obtained in step (4) is added for uniform coating to obtain silkworm excrement slow-release fertilizer granules.

[0019] As a preferred technical solution, the silkworm excrement is soaked in step (1) at a mass ratio of 1:0.3-4 in water. Microwave modification is performed in an XH-300PE ultrasonic microwave collaborative workstation at a power of 200-400W, controlled at a temperature of 60°C-100°C for 2-5 hours. To improve ball milling efficiency and achieve the target particle size, stainless steel beads are used in the mechanical ball milling of silkworm excrement. Ball milling beads of different sizes, 2 cm, 1 cm, and 0.5 cm in diameter, are mixed in a quantitative ratio of 1:4:5. The ball milling speed is 200-1700 rpm, and the time is 10-30 minutes.

[0020] Because silkworm excrement is inherently hard and difficult to grind, 2cm ball mill beads can quickly crush the silkworm excrement. Grinding silkworm excrement into the desired particle size requires small ball mill beads with a small diameter, a large number of beads, and a large contact surface. Therefore, ball mill beads of different diameters are used in conjunction with each other.

[0021] As a preferred technical solution, the fertilizer is urea, potassium chloride or ammonium phosphate, and the ratio of fertilizer to silkworm excrement and thickener is urea:silkworm excrement:thickener = 1-2.43:1:0.02-0.06, potassium chloride:silkworm excrement:thickener = 0.8-1.35:1:0.02-0.06, and ammonium phosphate:silkworm excrement:thickener = 1-1.58:1:0.02-0.04.

[0022] As a preferred technical solution, the stirring time in step (2) is 2-6 hours, and the rotation speed is 200-500 r / min.

[0023] As a preferred technical solution, the molding hydraulic press pressure used in step (3) is 60-80Pa, and the drying and curing temperature is 50-100°C.

[0024] As a preferred technical solution, the volume ratio of the adhesive gelatinized liquid to triethylamine is 10:1-3.

[0025] As a preferred technical solution, the adhesive is two or three of starch, polyvinyl alcohol, attapulgite, bentonite and cyclodextrin.

[0026] As a preferred technical solution, the adhesive starch and polyvinyl alcohol are dissolved in water at a ratio of 2-6:3, and mechanically stirred at 80-90° C. for 30-40 minutes for gelatinization.

[0027] As a preferred technical solution, the slow-release fertilizer granule core obtained in step (4) and the degradable embedding material are uniformly coated at 50°C-60°C in a mass ratio of 1-3.5:6.5-9 for 30-60 minutes.

[0028] The silkworm excrement slow-release fertilizer prepared by the preparation method of the present invention is used in the slow-release of fertilizer for crops with a long growth cycle.

[0029] The principle of the present invention is that silkworm excrement, as the excrement of silkworms after feeding, has a poor absorption capacity for biopolymers such as cellulose, pectin, protein, and fat in mulberry leaves. This results in a large amount of biopolymers in the mulberry leaves being evenly mixed and dispersed in the silkworm excrement, making it a potential hydrogel precursor and having application value. However, due to the digestion of silkworm excrement in the silkworm body, these polymers are tightly bound together by hydrogen bonds within the silkworm excrement, which weakens their ability to bind water molecules, thus limiting their application in the field of hydrogel-like materials. To reduce the hydrogen bonding between the polymers in the silkworm excrement, the high-frequency electromagnetic waves emitted by microwaves and the high-energy mechanical energy of high-speed ball milling are used. This not only destroys the crosslinks between the polymer compounds in the silkworm excrement and weakens the hydrogen bonding between the polymers, but also reduces the particle size of the silkworm excrement. This exposes more hydrogen bonds in the silkworm excrement particles, thereby increasing the interaction between the silkworm excrement and water molecules, and enhancing the hydrogel-like swelling properties of the silkworm excrement, thereby improving its swelling and adsorption capacity for fertilizers such as urea, potassium chloride, and ammonium phosphate. The present invention primarily addresses the fertilizer needs of crops during specific growth cycles through a combination of slow-release, burst-release, and uniform release. Specifically, the outer layer embedding process is regulated to achieve a slow-release cycle of 1 to 8 months for the slow-release fertilizer, meeting the normal growth needs of crops. After the biodegradable embedding material is broken down by the soil, a high-concentration burst release is achieved using the silkworm excrement slow-release carrier encapsulated within it for 2 to 3 months, thereby meeting the crop's specific fertilizer needs during specific cycles (e.g., flowering, fruiting, and elongation).

[0030] Compared with the prior art, the advantages of the present invention are:

[0031] 1. The raw material silkworm excrement used in the present invention is the biological waste left by the sericulture industry, which is low in cost, green and degradable, and can also adsorb and passivate heavy metals.

[0032] 2. The silkworm excrement after mechanical ball milling of the present invention has good hydrogel-like swelling and adsorption properties. As a natural macromolecular material, it can have high loading and controlled release capabilities for fertilizers. The adsorption and solid loading capacity of the modified silkworm excrement for urea, potassium chloride, and ammonium phosphate reaches 2.43g / g, 1.35g / g, and 1.58g / g respectively.

[0033] 3. The silkworm excrement slow-release fertilizer of the present invention can achieve the high-concentration fertilizer demand of different crops in a specific growth cycle through a slow-release-burst-release strategy. It is low-cost and environmentally friendly, and has a better regulation effect than other slow-release fertilizers. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The following are the infrared spectra of silkworm feces before and after modification.

[0035] Figure 2Scanning electron microscope images of silkworm excrement after ball milling and urea and potassium chloride adsorbed and immobilized on it; (a) SEM of silkworm excrement after ball milling; (b) urea adsorbed and immobilized on the interior and surface of silkworm excrement; (c) potassium chloride adsorbed and immobilized on the interior and surface of silkworm excrement.

[0036] Figure 3 Comparison of swelling and adsorption of silkworm feces before and after ball milling.

[0037] Figure 4 The figure is a comparison chart of the solid loading capacity of urea, potassium chloride and ammonium phosphate of the modified silkworm excrement of the present invention.

[0038] Figure 5 This is a graph showing the release pattern of K in different periods of the silkworm excrement slow-release fertilizer of Example 1.

[0039] Figure 6 This is a graph showing the release pattern of N in different periods of the silkworm excrement slow-release fertilizer of Example 1.

[0040] Figure 7 This is a graph showing the release pattern of P at different times for the silkworm excrement slow-release fertilizer of Example 1.

[0041] Figure 8 The slow-release fertilizer granules are prepared by extrusion according to step 1. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection claimed by the present invention is not limited to the scope of protection of the embodiments.

[0043] Example 1

[0044] A method for preparing a silkworm excrement slow-release fertilizer using silkworm excrement as a main solid-loaded raw material comprises the following steps:

[0045] (1) Pretreatment and mechanical ball milling of silkworm excrement

[0046] Weigh 20 g of natural silkworm excrement, add it into 60 ml of deionized water, let it stand and swell for 60 minutes, then place it in a four-necked flask twice and carry out microwave modification in an XH-300PE microwave time-controlled collaborative workstation with a microwave power of 400 W and a microwave temperature of 80°C for 2 hours. After the container is cooled, take it out and dry it to obtain microwave-modified silkworm excrement.

[0047] 20g of microwave-modified silkworm excrement was placed in a ball mill (using a mixture of 2cm, 1cm, and 0.5cm diameter beads in a ratio of 1:4:5) at 500 rpm for 30 minutes to yield 18g of silkworm excrement powder. The excrement was then dried in a forced-air drying oven for 12 hours. After drying, it was passed through a 150-mesh sieve to yield silkworm excrement, labeled Silkworm Excrement A.

[0048] (2) Swelling and adsorption of nitrogen, phosphorus and potassium fertilizers by silkworm excrement

[0049] Weigh 5 g of urea, 5 g of potassium chloride and 5 g of ammonium phosphate and place them in a 50 ml beaker respectively, add deionized water to prepare a solution, add 5 g of the silkworm excrement A obtained in step (1) and stir in a mechanical stirrer, and add 0.2 g of carboxymethyl cellulose at the same time. After stirring for 2 hours, let it stand for 0.5 hours to allow the silkworm excrement to fully swell and absorb and fix. The solution is mixed to obtain a semi-solid viscous mixture sol of urea, potassium chloride, ammonium phosphate and silkworm excrement, marked as B.

[0050] (3) Extrusion granulation to prepare the inner core of slow-release fertilizer particles

[0051] The B obtained in step (2) is placed in a stainless steel mold and extruded using a hydraulic press at a pressure of 60 kPa to obtain a slow-release fertilizer in the form of cylindrical particles. The slow-release fertilizer particles are then transferred to an oven and dried at 60°C to obtain the inner core of the slow-release fertilizer particles.

[0052] (4) Preparation of biodegradable embedding materials

[0053] Dissolve starch and polyvinyl alcohol in 50 ml of water respectively, and gelatinize them by mechanical stirring at 90°C for 30 minutes. Stir and mix the two adhesives at a ratio of 4:3 at 90°C to obtain 60 ml of gelatinized liquid, and add 6 ml of triethylamine to obtain a clear and viscous sol, which is the biodegradable embedding material.

[0054] (5) Coating the inner core of the slow-release fertilizer particles

[0055] The slow-release fertilizer granule core obtained in step (4) is added into a granulator, and the degradable embedding material obtained in step (4) is added at a ratio of 2:9 for uniform coating. The coating time is 40 minutes and the temperature is controlled at 50° C., so that silkworm feces-based slow-release fertilizer granules of different thicknesses can be obtained.

[0056] Example 2

[0057] A method for preparing a silkworm excrement slow-release fertilizer using silkworm excrement as a main solid-loaded raw material comprises the following steps:

[0058] (1) Pretreatment and mechanical ball milling of silkworm excrement

[0059] Weigh 20 g of natural silkworm excrement, add it into 60 ml of deionized water, let it stand and swell for 60 minutes, then place it in a four-necked flask twice and carry out microwave modification in an XH-300PE microwave time-controlled collaborative workstation with a microwave power of 400 W and a microwave temperature of 60°C for 2 hours. After the container is cooled, take it out and dry it to obtain microwave-modified silkworm excrement.

[0060] 20g of microwave-modified silkworm excrement was placed in a ball mill (using a mixture of 2cm, 1cm, and 0.5cm diameter beads in a ratio of 1:4:5) at 500 rpm for 30 minutes to yield 18g of silkworm excrement powder. The excrement was then dried in a forced-air drying oven for 12 hours. After drying, it was passed through a 150-mesh sieve to yield silkworm excrement, labeled Silkworm Excrement A.

[0061] (2) Swelling and adsorption of nitrogen, phosphorus and potassium fertilizers by silkworm excrement

[0062] Weigh 7.5 g of urea, 5 g of potassium chloride and 5 g of ammonium phosphate and place them in a 50 ml beaker respectively, add deionized water to prepare a solution, add 5 g of the silkworm excrement A obtained in step (1) and stir in a mechanical stirrer, and add 0.2 g of carboxymethyl cellulose at the same time. After stirring for 3 hours, let it stand for 0.5 hours to allow the silkworm excrement to fully swell and absorb and fix. The solution is mixed to obtain a semi-solid viscous mixture sol of urea, potassium chloride, ammonium phosphate and silkworm excrement, marked as B.

[0063] (3) Extrusion granulation to prepare the inner core of slow-release fertilizer particles

[0064] The B obtained in step (2) is placed in a stainless steel mold and extruded using a hydraulic press at a pressure of 80 kPa to obtain a slow-release fertilizer in the form of cylindrical particles. The slow-release fertilizer particles are then transferred to an oven and dried at 80°C to obtain the inner core of the slow-release fertilizer particles.

[0065] (4) Preparation of biodegradable embedding materials

[0066] Dissolve starch and polyvinyl alcohol in 50 ml of water respectively, and gelatinize them by mechanical stirring at 80°C for 30 minutes. Stir and mix the two adhesives at a ratio of 1:1 at 80°C to obtain 60 ml of gelatinized liquid, and add 6 ml of triethylamine to obtain a clear and viscous sol, which is the biodegradable embedding material.

[0067] (5) Coating the inner core of the slow-release fertilizer particles

[0068] The slow-release fertilizer granule core obtained in step (4) is added into a granulator, and the degradable embedding material obtained in step (4) is added at a ratio of 2:9 for uniform coating. The coating time is 30 minutes and the temperature is controlled at 60° C., so that silkworm feces-based slow-release fertilizer granules of different thicknesses can be obtained.

[0069] Example 3

[0070] A method for preparing a silkworm excrement slow-release fertilizer using silkworm excrement as a main solid-loaded raw material comprises the following steps:

[0071] (1) Pretreatment and mechanical ball milling of silkworm excrement

[0072] Weigh 20 g of natural silkworm excrement, add it into 60 ml of deionized water, let it stand and swell for 60 minutes, then place it in a four-necked flask twice and carry out microwave modification in an XH-300PE microwave time-out collaborative workstation with a microwave power of 400 W and a microwave temperature of 70°C for 2 hours. After the container is cooled, take it out and dry it to obtain microwave-modified silkworm excrement.

[0073] 20g of microwave-modified silkworm excrement was placed in a ball mill (using a mixture of 2cm, 1cm, and 0.5cm diameter beads in a ratio of 1:4:5) at 500 rpm for 30 minutes to yield 18g of silkworm excrement powder. The excrement was then dried in a forced-air drying oven for 12 hours. After drying, it was passed through a 150-mesh sieve to yield silkworm excrement, labeled Silkworm Excrement A.

[0074] (2) Swelling and adsorption of nitrogen, phosphorus and potassium fertilizers by silkworm excrement

[0075] Weigh 7.5 g of urea, 5 g of potassium chloride and 7.5 g of ammonium phosphate and place them in a 50 ml beaker respectively, add deionized water to prepare a solution, add 5 g of the silkworm excrement A obtained in step (1) and stir in a mechanical stirrer, and add 0.3 g of carboxymethyl cellulose at the same time. After stirring for 4 hours, let it stand for 1.0 hour to allow the silkworm excrement to fully swell and absorb and fix. The solution is mixed to obtain a semi-solid viscous mixture sol of urea, potassium chloride, ammonium phosphate and silkworm excrement, marked as B.

[0076] (3) Extrusion granulation to prepare the inner core of slow-release fertilizer particles

[0077] The B obtained in step (2) is placed in a stainless steel mold and extruded using a hydraulic press at a pressure of 70 kPa to obtain a slow-release fertilizer in the form of cylindrical particles. The slow-release fertilizer particles are then transferred to an oven and dried at 50°C to obtain the inner core of the slow-release fertilizer particles.

[0078] (4) Preparation of biodegradable embedding materials

[0079] Dissolve starch and polyvinyl alcohol in 50 ml of water respectively, and gelatinize them by mechanical stirring at 75°C for 30 minutes. Stir and mix the two adhesives in a ratio of 2:3 at 75°C to obtain 60 ml of gelatinized liquid, and add 6 ml of triethylamine to obtain a clear and viscous sol, which is the biodegradable embedding material.

[0080] (5) Coating the inner core of the slow-release fertilizer particles

[0081] The slow-release fertilizer granule core obtained in step (4) is added into a granulator, and the degradable embedding material obtained in step (4) is added at a ratio of 2:9 for uniform coating. The coating time is 60 minutes and the temperature is controlled at 55° C., so that silkworm feces-based slow-release fertilizer granules of different thicknesses can be obtained.

[0082] Example 4

[0083] A method for preparing a silkworm excrement slow-release fertilizer using silkworm excrement as a main solid-loaded raw material comprises the following steps:

[0084] (1) Pretreatment and mechanical ball milling of silkworm excrement

[0085] Weigh 20 g of natural silkworm excrement, add it into 60 ml of deionized water, let it stand and swell for 60 minutes, then place it in a four-necked flask twice and carry out microwave modification in an XH-300PE microwave time-controlled collaborative workstation with a microwave power of 200 W and a microwave temperature of 80°C for 2 hours. After the container is cooled, take it out and dry it to obtain microwave-modified silkworm excrement.

[0086] 20g of microwave-modified silkworm excrement was placed in a ball mill (using ball mill beads with diameters of 2cm, 1cm, and 0.5cm in a ratio of 1:4:5) at 500r / min for 30min to obtain 18g of silkworm excrement powder. The excrement was transferred to a forced air drying oven and dried for 12h. After drying, the excrement was passed through a 150-mesh sieve and labeled as silkworm excrement A. (2) Swelling and adsorption of nitrogen, phosphorus, and potassium fertilizers by silkworm excrement

[0087] Weigh 5 g of urea, 5 g of potassium chloride and 5 g of ammonium phosphate and place them in a 50 ml beaker respectively, add deionized water to prepare a solution, add 5 g of the silkworm excrement A obtained in step (1) and stir in a mechanical stirrer, and add 0.2 g of carboxymethyl cellulose at the same time. After stirring for 2 hours, let it stand for 0.5 hours to allow the silkworm excrement to fully swell and absorb and fix. The solution is mixed to obtain a semi-solid viscous mixture sol of urea, potassium chloride, ammonium phosphate and silkworm excrement, marked as B.

[0088] (3) Extrusion granulation to prepare the inner core of slow-release fertilizer particles

[0089] The B obtained in step (2) is placed in a stainless steel mold and extruded using a hydraulic press at a pressure of 60 kPa to obtain a slow-release fertilizer in the form of cylindrical particles. The slow-release fertilizer particles are then transferred to an oven and dried at 60°C to obtain the inner core of the slow-release fertilizer particles.

[0090] (4) Preparation of biodegradable embedding materials

[0091] Dissolve starch and polyvinyl alcohol in 50 ml of water respectively, and gelatinize them by mechanical stirring at 90°C for 30 minutes. Stir and mix the two adhesives at a ratio of 5:3 at 90°C to obtain 60 ml of gelatinized liquid, and add 6 ml of triethylamine to obtain a clear and viscous sol, which is the biodegradable embedding material.

[0092] (5) Coating the inner core of the slow-release fertilizer particles

[0093] The slow-release fertilizer granule core obtained in step (4) is added into a granulator, and the degradable embedding material obtained in step (4) is added at a ratio of 2:9 for uniform coating for 40 minutes and the temperature is controlled at 50° C., so as to obtain silkworm feces-based slow-release fertilizer granules of different thicknesses.

[0094] Example 5

[0095] A method for preparing a silkworm excrement slow-release fertilizer using silkworm excrement as a main solid-loaded raw material comprises the following steps:

[0096] (1) Pretreatment and mechanical ball milling of silkworm excrement

[0097] Weigh 20 g of natural silkworm excrement, add it into 60 ml of deionized water, let it stand and swell for 60 minutes, then place it in a four-necked flask twice and carry out microwave modification in an XH-300PE microwave time-controlled collaborative workstation with a microwave power of 300 W and a microwave temperature of 80°C for 2 hours. After the container is cooled, take it out and dry it to obtain microwave-modified silkworm excrement.

[0098] 20g of microwave-modified silkworm excrement was placed in a ball mill (using a mixture of 2cm, 1cm, and 0.5cm diameter beads in a ratio of 1:4:5) at 500 rpm for 30 minutes to yield 18g of silkworm excrement powder. The excrement was then dried in a forced-air drying oven for 12 hours. After drying, it was passed through a 150-mesh sieve to yield silkworm excrement, labeled Silkworm Excrement A.

[0099] (2) Swelling and adsorption of nitrogen, phosphorus and potassium fertilizers by silkworm excrement

[0100] Weigh 5 g of urea, 5 g of potassium chloride and 5 g of ammonium phosphate and place them in a 50 ml beaker respectively, add deionized water to prepare a solution, add 5 g of the silkworm excrement A obtained in step (1) and stir in a mechanical stirrer, and add 0.2 g of carboxymethyl cellulose at the same time. After stirring for 2 hours, let it stand for 0.5 hours to allow the silkworm excrement to fully swell and absorb and fix. The solution is mixed to obtain a semi-solid viscous mixture sol of urea, potassium chloride, ammonium phosphate and silkworm excrement, marked as B.

[0101] (3) Extrusion granulation to prepare the inner core of slow-release fertilizer particles

[0102] The B obtained in step (2) is placed in a stainless steel mold and extruded using a hydraulic press at a pressure of 60 kPa to obtain a slow-release fertilizer in the form of cylindrical particles. The slow-release fertilizer particles are then transferred to an oven and dried at 60°C to obtain the inner core of the slow-release fertilizer particles.

[0103] (4) Preparation of biodegradable embedding materials

[0104] Dissolve starch and polyvinyl alcohol in 50 ml of water respectively, and gelatinize them by mechanical stirring at 90°C for 30 minutes. Stir and mix the two adhesives at a ratio of 2:1 at 90°C to obtain 60 ml of gelatinized liquid, and add 6 ml of triethylamine to obtain a clear and viscous sol, which is the biodegradable embedding material.

[0105] (5) Coating the inner core of the slow-release fertilizer particles

[0106] The slow-release fertilizer granule core obtained in step (4) is added into a granulator, and the degradable embedding material obtained in step (4) is added at a ratio of 2:9 for uniform coating for 40 minutes and the temperature is controlled at 50° C., so as to obtain silkworm feces-based slow-release fertilizer granules of different thicknesses.

[0107] Material sustained-release performance testing

[0108] The product prepared in Example 1 of the present invention was subjected to characterization analysis and performance test analysis.

[0109] (1) FT-IR spectroscopy characterization

[0110] Fourier transform infrared spectroscopy experiments were performed using a Nicolet Nexus 670 FT-IR spectrometer (Thermo Fisher). The purified and dried samples were finely ground and compressed with potassium bromide, and the scan range was set to 4000–400 cm -1 , the resolution, number of scans and data interval are 4, 32 and 0.482 cm respectively -1 .like Figure 1 As shown in the figure, the carbonyl and carboxyl peaks of the milled silkworm excrement shift to higher wavenumbers compared to the unmilled silkworm excrement. This is because the mechanical force of the ball mill weakens the hydrogen bonding between the polymer compounds in the silkworm excrement.

[0111] (2) Surface morphology of materials

[0112] The morphology of the ball-milled silkworm feces and the urea and potassium chloride adsorbed feces were characterized using a Japanese Hitachi S-3400N low-magnification scanning electron microscope. Figure 2 As shown in Figure 1, (a) shows the fine flakes of silkworm excrement after ball milling. (b) shows a large amount of urea on the surface of the silkworm excrement, and (c) shows a similar large amount of potassium chloride on the surface of the silkworm excrement. Because potassium chloride particles are large, they adsorb inside the silkworm excrement and also expand the excrement particles, indicating that silkworm excrement can be used as a controlled-release carrier.

[0113] (3) Swelling of silkworm excrement before and after ball milling

[0114] Weigh an appropriate amount of silkworm excrement before and after ball milling, soak it in water for 3 hours, dry the surface water with lens cleaning paper, and weigh the mass after swelling.

[0115] E=W s / W d

[0116] E is the swelling ratio; W s is the weight of the hydrogel after silkworm excrement swelling equilibrium; W d It is the dry weight of silkworm excrement.

[0117] Calculate the swelling ratio of silkworm excrement before and after ball milling, such as Figure 3 As shown in the figure, the swelling rate increased significantly after ball milling, indicating that ball milling destroyed the hydrogen bonding of the polymer compounds in the silkworm excrement, thereby improving the swelling and adsorption capacity of the silkworm excrement.

[0118] (IV) Adsorption capacity of different fertilizers by swollen silkworm excrement

[0119] Prepare 250g / L urea, 200g / L potassium chloride, and 200g / L ammonium phosphate, add 100mg of ball-milled silkworm feces, shake on a shaker for 12h, and use the test method to detect the residual concentration after adsorption and solidification. The solid loading capacity was calculated. The data were measured in triplicate, and the results were as follows: Figure 4 The adsorption and solid loading capacity of the modified silkworm feces for urea, potassium chloride and ammonium phosphate were 2.43g / g, 1.35g / g and 1.58g / g respectively.

[0120] (V) Experiment on slow-release fertilizer granules of silkworm excrement

[0121] 8g of the silkworm excrement slow-release fertilizer granules prepared by the present invention were weighed and used as a soil leaching column using a 40cm long, 2.65cm inner diameter PVC tube. A piece of 200-mesh gauze was wrapped around the bottom of the PVC tube to prevent soil from flowing into the filtrate during the leaching process. 10g of quartz sand was added to the soil column in sequence, followed by 8g of slow-release fertilizer granules in the middle of the sand bed, and finally 10g of quartz sand was added to cover the top. The treated soil PVC tube was transferred to a stand with a glass funnel at the bottom for leaching testing. Next, 40ml of distilled water was added to each soil column to bring the soil moisture content to field capacity (soil saturation moisture content is 30%), and the soil was allowed to equilibrate and stabilize for 24 hours. Then, 40ml of distilled water was slowly added from the top of the soil column, and the filtrate was collected until it reached 40ml. The leachate was collected as the leachate for the first day. According to the above method, during the leaching test, 40ml of distilled water was poured on the top of the sand bed every day, flowing through the sand bed and dripping into the bottom container. The container was emptied and samples were taken every 5 days. Calculate the release rates of potassium chloride, urea, and ammonium phosphate respectively. Figure 5-7 As shown, in the 8-month release, the three fertilizers all achieved the effect of slow release, among which the release rate of urea reached 78% of the total urea, while the release rate of potassium chloride reached 80% of the total potassium chloride content, and ammonium phosphate reached 76%.

[0122] The above embodiments of the present invention are merely examples to clearly illustrate the present invention and are not intended to limit the embodiments of the present invention. A person skilled in the art will appreciate that various variations or modifications may be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a silkworm excrement slow-release fertilizer using silkworm excrement as the main solid-loaded raw material, characterized by: The steps include: (1) Modification of silkworm excrement by microwave and mechanical ball milling Silkworm excrement was added to water in a certain proportion and soaked for a period of time, then placed in a container for microwave modification. After cooling, it was taken out and dried. An appropriate amount of microwave-modified silkworm excrement was weighed and placed in a ball mill to obtain modified silkworm excrement powder. The silkworm excrement obtained after drying was labeled as Silkworm Excrement A. In the step (1), the mass ratio of silkworm excrement to water during soaking is 1:0.3-4, the microwave modification power is 200-400W, and the temperature is controlled at 60°C-100°C for 2-5 hours; in the mechanical ball milling modification, the ball milling beads are made of stainless steel, and different ball milling beads with diameters of 2 cm, 1 cm, and 0.5 cm are mixed in a quantitative ratio of 1:4:5, the ball milling speed is 200-1700 r / min, and the time is 10-30 minutes; (2) Silkworm feces swelling adsorption and immobilization of fertilizers Put the fertilizer in a container, add water to prepare a solution, then add an appropriate amount of the silkworm excrement A obtained in step (1), and at the same time add an appropriate amount of a thickener, stir and mix, and let it stand for a period of time to allow the silkworm excrement to fully swell and absorb and fix, to obtain a semi-solid viscous mixture sol, marked as B; The thickener is one or a mixture of sodium carboxymethyl cellulose, sodium alginate, and chitosan; The mass ratio of the fertilizer, silkworm excrement and thickener is: 0.8-2.43: 1: 0.02-0.06; (3) Extrusion granulation to prepare the inner core of slow-release fertilizer particles The mixture sol B obtained in step (2) is placed into a mold and extruded into a cylindrical slow-release fertilizer using a molding hydraulic press. The slow-release fertilizer particles are then transferred to an oven for drying and solidification to obtain the slow-release fertilizer particle core; (4) Preparation of biodegradable embedding materials The adhesive is dissolved in water, heated and stirred to gelatinize to obtain an adhesive gel solution, and triethylamine is added as a homogeneous catalyst to obtain a clear and viscous sol, which is a biodegradable embedding material. (5) Coating the inner core of slow-release fertilizer particles The inner core of the slow-release fertilizer granules is put into a granulator, and the embedding material obtained in step (4) is added for uniform coating to obtain silkworm excrement slow-release fertilizer granules.

2. The method for preparing the silkworm excrement slow-release fertilizer using silkworm excrement as the main solid-loaded raw material according to claim 1, characterized in that: The fertilizer is urea, potassium chloride or ammonium phosphate, and the mass ratio of the fertilizer to the silkworm excrement and the thickener is urea:silkworm excrement:thickener=1-2.43:1:0.02-0.06, potassium chloride:silkworm excrement:thickener=0.8-1.35:1:0.02-0.06, and ammonium phosphate:silkworm excrement:thickener=1-1.58:1:0.02-0.

04.

3. The method for preparing the silkworm excrement slow-release fertilizer using silkworm excrement as the main solid-loaded raw material according to claim 1, characterized in that: The stirring time in step (2) is 2-6 h, the rotation speed is 200-500 r / min, and the standing time is 30-60 min.

4. The method for preparing silkworm excrement-based digital intelligent slow-release fertilizer according to claim 1, characterized in that: The molding hydraulic press pressure used in step (3) is 60-80 Pa, and the drying and curing temperature is 50-100°C.

5. The method for preparing the silkworm excrement slow-release fertilizer using silkworm excrement as the main solid-loaded raw material according to claim 1, characterized in that: The volume ratio of the adhesive paste to triethylamine is 10:1-3.

6. The method for preparing the silkworm excrement slow-release fertilizer using silkworm excrement as the main solid-loaded raw material according to claim 1, characterized in that: The adhesive is two or three of starch, polyvinyl alcohol, attapulgite, bentonite and cyclodextrin.

7. The method for preparing the silkworm excrement slow-release fertilizer using silkworm excrement as the main solid-loaded raw material according to claim 6, characterized in that: Dissolve the adhesive starch and polyvinyl alcohol in water at a ratio of 2-6:3, and mechanically stir at 80-90°C for 30-40 minutes for gelatinization.

8. The method for preparing the silkworm excrement slow-release fertilizer using silkworm excrement as the main solid-loaded raw material according to claim 1, characterized in that: The slow-release fertilizer granule core obtained in step (4) and the degradable embedding material are uniformly coated at 50° C. to 60° C. in a mass ratio of 1-3.5:6.5-9 for 30-60 minutes.

9. Use of the silkworm excrement slow-release fertilizer prepared by the preparation method according to any one of claims 1 to 8, characterized in that: Its application in slow-release fertilizer for crops with long growth cycles.

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