Modified bio-based coated controlled-release fertilizer and preparation method thereof

Abstract

The application discloses a modified bio-based coated controlled-release fertilizer and a preparation method thereof, and belongs to the technical field of bio-organic fertilizers. The fertilizer comprises a coating layer made of a modified bio-based coating material and a fertilizer core composed of organic and inorganic nutrients. By using the modified bio-based material as the coating layer, the slow-release performance of the fertilizer is significantly improved, and the environmental pollution problem caused by traditional petroleum-based polymer coating materials is effectively solved. By chemically modifying natural biomass materials, the mechanical strength and water resistance of the coating material are improved, while good biodegradability is retained. Through efficient utilization of agricultural wastes such as pineapple leaves, not only is resource recycling achieved, but also the pressure of waste on the environment is reduced. Compared with the prior art, the degradation speed of the fertilizer in the soil is more balanced, which can ensure the slow-release effect while avoiding potential damage to the soil structure.

Description

Technical Field

[0001] This invention belongs to the field of bio-organic fertilizer technology, specifically relating to a modified bio-based coated controlled-release fertilizer and its preparation method. Background Technology

[0002] Agriculture is the lifeblood of the national economy, and fertilizer is the foundation of agricultural production. However, traditional fertilizers have low nutrient utilization rates. Nutrient loss from fertilizers not only leads to resource waste and increased agricultural production costs but also damages the environment. To alleviate this problem, slow-release fertilizers have received increasing attention in modern agricultural development. Slow-release fertilizers have become the dominant direction in fertilizer development, characterized by environmental friendliness, high nutrient efficiency, and time and labor savings, making them one of the important ways to achieve "zero growth" in chemical fertilizer use in agricultural production.

[0003] Slow-release fertilizers are a class of fertilizers whose release rate is coordinated with the nutrient requirements of crops through modification with materials such as coatings or adjuvants. Among them, coated slow-release fertilizers, prepared by combining inorganic or polymeric materials with fertilizers, are currently the most widely researched and fastest-growing type of slow-release fertilizer, and have become the focus of current research. Coated slow-release fertilizers use granulated fertilizer as the core, and a slow-release film layer is formed by uniformly coating the surface of the fertilizer granules. This inhibits the diffusion of water molecules from the soil to the fertilizer core, slowing down the fertilizer release rate and achieving the purpose of slow-release fertilizer, thereby improving fertilizer utilization.

[0004] However, traditional coating materials are mostly petroleum-based polymers (such as polyolefins and epoxy resins). Although they offer good controlled-release effects, they are costly, difficult to degrade, and cause serious "white pollution" and damage soil structure with long-term use. To address the environmental problems caused by traditional coating materials, researchers have recently begun exploring renewable and biodegradable bio-based materials as coating substances. Bio-based materials are derived from natural resources, such as starch, cellulose, and chitosan, and possess good biodegradability and environmental friendliness. By physically or chemically modifying these natural materials, their mechanical properties, thermal stability, and hydrophobicity can be improved, thereby meeting the performance requirements of coated slow-release fertilizers.

[0005] For example, Chinese patent application CN202110483089.1 discloses a bio-based polymer coating material, its coated controlled-release fertilizer, and a method for preparing the same. The bio-based polymer coating material is formulated with the following weight percentages: 50-70% hydroxyl-containing components and 30-50% isocyanate MDI; the hydroxyl-containing components consist of 50-90% hydroxyl-terminated prepolymer, 2-10% additives, 7-50% polyol, and 1-10% small molecule chain extender; the hydroxyl-terminated prepolymer is prepared by reacting 80-100% biomass liquefaction products with 0-20% isocyanate MDI. The bio-based polymer-coated controlled-release fertilizer consists of a core and a membrane shell.

[0006] Although it utilizes biomass prepared from raw materials such as corn starch, potato starch, wheat starch, sweet potato starch, mung bean starch, corn stalks, corn cobs, rice straw, wheat straw, peanut shells, and cotton stalks, it still has some shortcomings in practical applications. For example, the use of multiple organic raw materials means that soil pollution problems have not been effectively addressed. Furthermore, regarding the slow-release performance of the fertilizer, while bio-based materials can achieve a certain degree of slow nutrient release, the stability and persistence of the release rate need further improvement to better meet the nutrient requirements of crops throughout their growth cycle. In addition, the degradation rate of this coating material in the soil may be affected by various factors, such as soil pH, temperature, humidity, and the type and quantity of microorganisms. If degradation is too rapid, it may affect the slow-release effect of the fertilizer; while if degradation is too slow, it may have potential impacts on the soil environment. Therefore, it is necessary to further research and improve existing modified bio-based coated controlled-release fertilizers and their preparation methods. Summary of the Invention

[0007] This invention addresses the problems existing in the prior art by providing a novel bio-based coated controlled-release fertilizer and its preparation method.

[0008] This fertilizer, by employing modified bio-based materials as its coating layer, not only significantly improves the fertilizer's slow-release performance but also effectively solves the environmental pollution problems caused by traditional petroleum-based polymer coating materials. Its core innovation lies in the chemical modification of natural biomass materials, which enhances the mechanical strength and water resistance of the coating material while retaining good biodegradability. Furthermore, this fertilizer exhibits higher stability and controllability in its nutrient release rate.

[0009] Another advantage of this invention lies in its simple and environmentally friendly preparation process, wide availability of raw materials, low cost, and suitability for large-scale production. By efficiently utilizing agricultural waste such as pineapple leaves, it not only achieves resource recycling but also reduces the environmental pressure of waste. Compared with existing technologies, this fertilizer degrades more evenly in the soil, ensuring a slow-release effect while avoiding potential damage to soil structure.

[0010] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A modified bio-based coated controlled-release fertilizer comprises two parts: a coating made of modified bio-based coating material and a fertilizer core composed of organic and inorganic nutrients.

[0011] Furthermore, the fertilizer core composed of organic and inorganic nutrients includes the following components in parts by weight: 30-52 parts fermented livestock and poultry manure, 15-25 parts urea, 8-15 parts diammonium phosphate, 5-10 parts potassium chloride, 5-8 parts humic acid, and 2-4 parts trace element additives.

[0012] Furthermore, the trace element additives include one or more of iron, zinc, boron, molybdenum, copper, and manganese, and exist in the form of oxides or sulfates.

[0013] Furthermore, the preparation method of the fermented livestock and poultry manure is as follows: livestock and poultry manure and straw powder are mixed at a weight ratio of 3:1, 2% of EM bacteria agent by weight of the mixture is added, and fermentation is carried out at a temperature of 35-40℃ for 15-20 days. After drying, crushing and sieving, fermented livestock and poultry manure is obtained. The fermented livestock and poultry manure is a brown powder with a moisture content of less than 15% and an organic matter content of more than 45%.

[0014] A method for preparing a modified bio-based coated controlled-release fertilizer includes the following preparation steps: (1) Preparation of fermented livestock and poultry manure: (2) Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. (3) Preparation of modified bio-based coating materials: a. First, collect discarded pineapple leaves, wash them clean and dry them, then use a shredder to shred the pineapple leaves into fiber powder; b. Then, 60-80g of fiber powder, 30-40g of ethylene glycol, and 360-380g of polyethylene glycol are reacted with 10-12g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction is continuously stirred at 800-1000 r / min for 2-4 hours at 160-170℃. Finally, the mixture is cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. c. Mix palm oil and organosiloxane at a mass ratio of 1:1 to obtain a composite modifier. Then, mix the composite modifier with liquefied pineapple leaf-based biomass in a high-speed mixer, add isocyanate MDI, and react at 80-85℃ for 3 hours to form a modified bio-based coating material. (4) Place the prepared fertilizer core in a coating equipment and spray the modified bio-based coating material evenly onto the surface of the fertilizer core at a rolling speed of 20-30 rpm at 60-80℃ to form a complete and dense coating layer. After cooling, the modified bio-based coated controlled-release fertilizer is obtained.

[0015] In the preparation of modified bio-based coating materials, waste pineapple leaves are used as raw materials. Acid catalysis is employed to degrade and alcoholyze the polysaccharides, lignin, and other high-molecular-weight components in the pineapple leaf fibers, forming liquefied pineapple leaf-based biomass with relatively small molecular weight and a certain degree of fluidity. Subsequently, palm oil and organosiloxanes are mixed at a 1:1 mass ratio to obtain a composite modifier. Palm oil contains unsaturated fatty acids, while organosiloxanes contain special structures such as siloxane bonds. The mixture of the two introduces various functional groups for subsequent reactions. The -NCO groups in the added isocyanate MDI have high reactivity; they can react with the hydroxyl groups (-OH) in the liquefied pineapple leaf-based biomass and the active groups (such as silanol groups) provided by the organosiloxanes in the composite modifier to form carbamate bonds and other chemical bonds, resulting in a cross-linking reaction. This cross-linking reaction connects the originally relatively independent molecular chains, forming a three-dimensional network structure, thereby improving the strength, toughness, and other properties of the material, ultimately forming a modified bio-based coating material with certain properties.

[0016] Furthermore, the mass ratio of the composite modifier, liquefied pineapple leaf-based biomass, and isocyanate MDI is 1:1.5:0.8.

[0017] Furthermore, the organosiloxane in the composite modifier is a vinyl hydroxyl silicone oil with a viscosity of 25-40 mPa·s.

[0018] Furthermore, during the coating process, the amount of coating material sprayed is controlled to be 3%-5% of the fertilizer core mass to ensure the formation of a coating layer with uniform thickness and dense structure.

[0019] Beneficial effects (1) The fertilizer core of this invention is based on fermented livestock and poultry manure, compounded with inorganic nitrogen, phosphorus and potassium, humic acid and trace elements. It not only provides comprehensive nutrients that combine fast and slow effects, but also the organic matter and humic acid can effectively improve the soil aggregate structure, enhance the soil's water and fertilizer retention capacity and microbial activity, and realize the combination of "fertilization" and "soil nourishment". At the same time, it provides crops with long-lasting and effective nutrients and improves fertilization efficiency.

[0020] (2) Using pineapple leaf liquefaction products as the bio-based matrix, and combining them with palm oil and organosilane composite modifiers to prepare coating materials, the introduction of organosiloxanes significantly enhances the hydrophobicity, thermal stability, and mechanical strength of the coating material, enabling it to withstand mechanical stress during the coating process and in the soil environment. Palm oil provides excellent flexibility, preventing the coating from becoming brittle. The synergistic effect of the two overcomes the defects of poor film-forming properties and easy cracking of single bio-based materials, achieving an ideal balance between strength and toughness, and between controlled release and degradability. Through the composite modification of palm oil and organosiloxanes, a dense, hydrophobic coating layer with moderate cross-linking was synergistically constructed. This coating can effectively regulate the inward permeation rate of water and the outward diffusion rate of nutrients in the soil, making the fertilizer nutrient release curve more consistent with the nutrient requirements of crops at different growth stages, significantly improving nutrient utilization, reducing the number and total amount of fertilization, and lowering agricultural production costs.

[0021] (3) Furthermore, this modified bio-based coating material can degrade at a more balanced rate in the soil, avoiding adverse effects on the soil environment caused by degradation that is too fast or too slow. In practical applications, this fertilizer not only significantly reduces nutrient loss but also lowers the frequency of fertilization, alleviating the labor intensity of farmers. At the same time, since the raw materials are mainly derived from agricultural waste and renewable resources, the production cost is greatly reduced, and the preparation process is green and environmentally friendly, with no harmful byproducts generated.

[0022] (4) In summary, this invention achieves resource utilization of agricultural waste such as pineapple leaves, reduces environmental pollution caused by incineration or landfill, and helps improve the rural ecological environment. Combined with its excellent slow-release performance and environmental protection characteristics, this fertilizer is particularly suitable for economic crop planting areas that require long-term stable fertilization, such as orchards, tea gardens, and facility agriculture, and has broad market prospects and promotion value. Attached Figure Description

[0023] Figure 1 This is a sample image of the fertilizer granules obtained in Example 1 of the present invention; Figure 2 This is a growth effect diagram of rapeseed planting experiment according to the present invention; Figure 3 Total nitrogen content of rapeseed in different treatment groups; Figure 4 The total phosphorus content of rapeseed in different treatment groups; Figure 5 The total potassium content of rapeseed in different treatment groups. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0025] Example 1 A modified bio-based coated controlled-release fertilizer comprises two parts: a coating made of modified bio-based coating material and a fertilizer core composed of organic and inorganic nutrients.

[0026] The fertilizer core, composed of organic and inorganic nutrients, includes the following components in parts by weight: 30 parts fermented livestock and poultry manure, 15 parts urea, 8 parts diammonium phosphate, 5 parts potassium chloride, 5 parts humic acid, and 2 parts trace element additives.

[0027] The trace element additives include iron, zinc, boron, molybdenum, copper, and manganese, and exist in the form of oxides or sulfates.

[0028] The method for preparing fermented livestock and poultry manure is as follows: Livestock and poultry manure is mixed with straw powder at a weight ratio of 3:1, and 2% EM (Effective Microorganisms) agent is added to the mixture. Fermentation is carried out for 15 days at a temperature of 35-40℃. Afterwards, the mixture is dried, pulverized, and sieved to obtain fermented livestock and poultry manure. The fermented manure is a brownish-brown powder with a moisture content of less than 15% and an organic matter content of more than 45%. Commercially available EM agents can be used; this invention uses EM bacteria produced by Weifang Yihao Biotechnology Co., Ltd.

[0029] A method for preparing a modified bio-based coated controlled-release fertilizer includes the following preparation steps: (1) Preparation of fermented livestock and poultry manure: (2) Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. (3) Preparation of modified bio-based coating materials: a. First, collect discarded pineapple leaves, wash them clean and dry them, then use a shredder to shred the pineapple leaves into fiber powder; b. Then, 60g of fiber powder, 30g of ethylene glycol, and 360g of polyethylene glycol were reacted with 10g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction was continuously stirred at 800-1000 r / min for 2 hours at 160-170℃. Finally, the mixture was cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. c. Mix palm oil and organosiloxane at a mass ratio of 1:1 to obtain a composite modifier. Then, mix the composite modifier with liquefied pineapple leaf-based biomass in a high-speed mixer, add isocyanate MDI, and react at 80-85℃ for 3 hours to form a modified bio-based coating material. (4) Place the prepared fertilizer core in a coating equipment and spray the modified bio-based coating material evenly onto the surface of the fertilizer core at a rolling speed of 20-30 rpm at 60-80℃ to form a complete and dense coating layer. After cooling, the modified bio-based coated controlled-release fertilizer is obtained.

[0030] The mass ratio of the composite modifier, liquefied pineapple leaf-based biomass, and isocyanate MDI was 1:1.5:0.8.

[0031] The organosiloxane in the composite modifier is a vinyl hydroxyl silicone oil with a viscosity of 25-40 mPa·s.

[0032] During the coating process, the amount of coating material sprayed is controlled to be 3% of the fertilizer core mass to ensure the formation of a coating layer with uniform thickness and dense structure.

[0033] Example 2 A modified bio-based coated controlled-release fertilizer comprises two parts: a coating made of modified bio-based coating material and a fertilizer core composed of organic and inorganic nutrients.

[0034] The fertilizer core, composed of organic and inorganic nutrients, includes the following components in parts by weight: 35 parts fermented livestock and poultry manure, 18 parts urea, 10 parts diammonium phosphate, 7 parts potassium chloride, 6 parts humic acid, and 3 parts trace element additives.

[0035] The trace element additives include iron, zinc, boron, molybdenum, copper, and manganese, and exist in the form of oxides or sulfates.

[0036] The method for preparing fermented livestock and poultry manure is as follows: livestock and poultry manure and straw powder are mixed at a weight ratio of 3:1, and 2% of EM bacteria agent by weight of the mixture is added. Fermentation is carried out for 15 days at a temperature of 35-40℃. After drying, crushing and sieving, fermented livestock and poultry manure is obtained. The fermented livestock and poultry manure is brown powder with a moisture content of less than 15% and an organic matter content of more than 45%.

[0037] A method for preparing a modified bio-based coated controlled-release fertilizer includes the following preparation steps: (1) Preparation of fermented livestock and poultry manure: (2) Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. (3) Preparation of modified bio-based coating materials: a. First, collect discarded pineapple leaves, wash them clean and dry them, then use a shredder to shred the pineapple leaves into fiber powder; b. Then, 70g of fiber powder, 35g of ethylene glycol, and 370g of polyethylene glycol were reacted with 11g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction was continuously stirred at 800-1000 r / min for 3 hours at 160-170℃. Finally, the mixture was cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. c. Mix palm oil and organosiloxane at a mass ratio of 1:1 to obtain a composite modifier. Then, mix the composite modifier with liquefied pineapple leaf-based biomass in a high-speed mixer, add isocyanate MDI, and react at 80-85℃ for 3 hours to form a modified bio-based coating material. (4) Place the prepared fertilizer core in a coating equipment and spray the modified bio-based coating material evenly onto the surface of the fertilizer core at a rolling speed of 20-30 rpm at 60-80℃ to form a complete and dense coating layer. After cooling, the modified bio-based coated controlled-release fertilizer is obtained.

[0038] The mass ratio of the composite modifier, liquefied pineapple leaf-based biomass, and isocyanate MDI was 1:1.5:0.8.

[0039] The organosiloxane in the composite modifier is a vinyl hydroxyl silicone oil with a viscosity of 25-40 mPa·s.

[0040] During the coating process, the amount of coating material sprayed is controlled to be 4% of the fertilizer core mass to ensure the formation of a coating layer with uniform thickness and dense structure.

[0041] Example 3 A modified bio-based coated controlled-release fertilizer comprises two parts: a coating made of modified bio-based coating material and a fertilizer core composed of organic and inorganic nutrients.

[0042] The fertilizer core, composed of organic and inorganic nutrients, includes the following components in parts by weight: 40 parts fermented livestock and poultry manure, 20 parts urea, 12 parts diammonium phosphate, 8 parts potassium chloride, 7 parts humic acid, and 3 parts trace element additives.

[0043] The trace element additives include iron, zinc, boron, molybdenum, copper and manganese, and exist in the form of oxides or sulfates.

[0044] The method for preparing fermented livestock and poultry manure is as follows: livestock and poultry manure and straw powder are mixed at a weight ratio of 3:1, and 2% of EM bacteria agent by weight of the mixture is added. Fermentation is carried out for 20 days at a temperature of 35-40℃. After drying, crushing and sieving, fermented livestock and poultry manure is obtained. The fermented livestock and poultry manure is brown powder with a moisture content of less than 15% and an organic matter content of more than 45%.

[0045] A method for preparing a modified bio-based coated controlled-release fertilizer includes the following preparation steps: (1) Preparation of fermented livestock and poultry manure: (2) Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. (3) Preparation of modified bio-based coating materials: a. First, collect discarded pineapple leaves, wash them clean and dry them, then use a shredder to shred the pineapple leaves into fiber powder; b. Then, 80g of fiber powder, 40g of ethylene glycol, and 380g of polyethylene glycol were reacted with 12g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction was continuously stirred at 800-1000 r / min for 2 hours at 160-170℃. Finally, the mixture was cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. c. Mix palm oil and organosiloxane at a mass ratio of 1:1 to obtain a composite modifier. Then, mix the composite modifier with liquefied pineapple leaf-based biomass in a high-speed mixer, add isocyanate MDI, and react at 80-85℃ for 3 hours to form a modified bio-based coating material. (4) Place the prepared fertilizer core in a coating equipment and spray the modified bio-based coating material evenly onto the surface of the fertilizer core at a rolling speed of 20-30 rpm at 60-80℃ to form a complete and dense coating layer. After cooling, the modified bio-based coated controlled-release fertilizer is obtained.

[0046] The mass ratio of the composite modifier, liquefied pineapple leaf-based biomass, and isocyanate MDI was 1:1.5:0.8.

[0047] The organosiloxane in the composite modifier is a vinyl hydroxyl silicone oil with a viscosity of 25-40 mPa·s.

[0048] During the coating process, the amount of coating material sprayed is controlled to be 4% of the fertilizer core mass to ensure the formation of a coating layer with uniform thickness and dense structure.

[0049] Example 4 A modified bio-based coated controlled-release fertilizer comprises two parts: a coating made of modified bio-based coating material and a fertilizer core composed of organic and inorganic nutrients.

[0050] The fertilizer core, composed of organic and inorganic nutrients, includes the following components in parts by weight: 52 parts fermented livestock and poultry manure, 25 parts urea, 15 parts diammonium phosphate, 10 parts potassium chloride, 8 parts humic acid, and 4 parts trace element additives.

[0051] The trace element additives include iron, zinc, boron, molybdenum, copper and manganese, and exist in the form of oxides or sulfates.

[0052] The method for preparing fermented livestock and poultry manure is as follows: livestock and poultry manure and straw powder are mixed at a weight ratio of 3:1, and 2% of EM bacteria agent by weight of the mixture is added. Fermentation is carried out for 20 days at a temperature of 35-40℃. After drying, crushing and sieving, fermented livestock and poultry manure is obtained. The fermented livestock and poultry manure is brown powder with a moisture content of less than 15% and an organic matter content of more than 45%.

[0053] A method for preparing a modified bio-based coated controlled-release fertilizer includes the following preparation steps: (1) Preparation of fermented livestock and poultry manure: (2) Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. (3) Preparation of modified bio-based coating materials: a. First, collect discarded pineapple leaves, wash them clean and dry them, then use a shredder to shred the pineapple leaves into fiber powder; b. Then, 80g of fiber powder, 40g of ethylene glycol, and 380g of polyethylene glycol were reacted with 12g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction was continuously stirred at 800-1000 r / min for 4 hours at 160-170℃. Finally, the mixture was cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. c. Mix palm oil and organosiloxane at a mass ratio of 1:1 to obtain a composite modifier. Then, mix the composite modifier with liquefied pineapple leaf-based biomass in a high-speed mixer, add isocyanate MDI, and react at 80-85℃ for 3 hours to form a modified bio-based coating material. (4) Place the prepared fertilizer core in a coating equipment and spray the modified bio-based coating material evenly onto the surface of the fertilizer core at a rolling speed of 20-30 rpm at 60-80℃ to form a complete and dense coating layer. After cooling, the modified bio-based coated controlled-release fertilizer is obtained.

[0054] The mass ratio of the composite modifier, liquefied pineapple leaf-based biomass, and isocyanate MDI was 1:1.5:0.8.

[0055] The organosiloxane in the composite modifier is a vinyl hydroxyl silicone oil with a viscosity of 25-40 mPa·s.

[0056] During the coating process, the amount of coating material sprayed is controlled to be 5% of the fertilizer core mass to ensure the formation of a coating layer with uniform thickness and dense structure.

[0057] Comparative Example 1 This comparative example is identical to Example 1 in all steps and raw materials except for the absence of a composite modifier. That is: A bio-based coated controlled-release fertilizer comprises two parts: a coating made of bio-based coating material and a fertilizer core composed of organic and inorganic nutrients.

[0058] A method for preparing a bio-based coated controlled-release fertilizer includes the following preparation steps: (1) Preparation of fermented livestock and poultry manure: (2) Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. (3) Preparation of bio-based coating materials: a. First, collect discarded pineapple leaves, wash them clean and dry them, then use a shredder to shred the pineapple leaves into fiber powder; b. Then, 60g of fiber powder, 30g of ethylene glycol, and 360g of polyethylene glycol were reacted with 10g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction was continuously stirred at 800-1000 r / min for 2 hours at 160-170℃. Finally, the mixture was cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. c. Place the liquefied pineapple leaf-based biomass in a high-speed mixer, add isocyanate MDI, and react at 80-85℃ for 3 hours to form a modified bio-based coating material; (4) Place the prepared fertilizer core in a coating equipment and spray the bio-based coating material evenly onto the surface of the fertilizer core at a rolling speed of 20-30 rpm at 60-80℃ to form a complete and dense coating layer. After cooling, the bio-based coated controlled-release fertilizer is obtained.

[0059] The mass ratio of liquefied pineapple leaf-based biomass to isocyanate MDI is 1.5:0.8.

[0060] During the coating process, the amount of coating material sprayed is controlled to be 3% of the fertilizer core mass to ensure the formation of a coating layer with uniform thickness and dense structure.

[0061] Comparative Example 2 In this comparative example, except that the composite modifier uses only palm oil, the other steps and raw materials are the same as in Example 1. That is: A method for preparing a modified bio-based coated controlled-release fertilizer includes the following preparation steps: (1) Preparation of fermented livestock and poultry manure: (2) Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. (3) Preparation of modified bio-based coating materials: a. First, collect discarded pineapple leaves, wash them clean and dry them, then use a shredder to shred the pineapple leaves into fiber powder; b. Then, 60g of fiber powder, 30g of ethylene glycol, and 360g of polyethylene glycol were reacted with 10g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction was continuously stirred at 800-1000 r / min for 2 hours at 160-170℃. Finally, the mixture was cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. c. Mix palm oil and liquefied pineapple leaf-based biomass evenly in a high-speed mixer, add isocyanate MDI, and react at 80-85℃ for 3 hours to form a modified bio-based coating material; (4) Place the prepared fertilizer core in a coating equipment and spray the modified bio-based coating material evenly onto the surface of the fertilizer core at a rolling speed of 20-30 rpm at 60-80℃ to form a complete and dense coating layer. After cooling, the modified bio-based coated controlled-release fertilizer is obtained.

[0062] The mass ratio of palm oil, liquefied pineapple leaf-based biomass, and isocyanate MDI was 1:1.5:0.8.

[0063] Comparative Example 3 In this comparative example, except that the composite modifier uses only organosiloxane, all other steps and raw materials are the same as in Example 1. That is: A method for preparing a modified bio-based coated controlled-release fertilizer includes the following preparation steps: (1) Preparation of fermented livestock and poultry manure: (2) Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. (3) Preparation of modified bio-based coating materials: a. First, collect discarded pineapple leaves, wash them clean and dry them, then use a shredder to shred the pineapple leaves into fiber powder; b. Then, 60g of fiber powder, 30g of ethylene glycol, and 360g of polyethylene glycol were reacted with 10g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction was continuously stirred at 800-1000 r / min for 2 hours at 160-170℃. Finally, the mixture was cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. c. Mix organosiloxane and liquefied pineapple leaf-based biomass evenly in a high-speed mixer, add isocyanate MDI, and react at 80-85℃ for 3 hours to form a modified bio-based coating material; (4) Place the prepared fertilizer core in a coating equipment and spray the modified bio-based coating material evenly onto the surface of the fertilizer core at a rolling speed of 20-30 rpm at 60-80℃ to form a complete and dense coating layer. After cooling, the modified bio-based coated controlled-release fertilizer is obtained.

[0064] The mass ratio of organosiloxane, liquefied pineapple leaf-based biomass, and isocyanate MDI was 1:1.5:0.8.

[0065] The organosiloxane in the composite modifier is a vinyl hydroxyl silicone oil with a viscosity of 25-40 mPa·s.

[0066] Comparative Example 4 This comparative example is identical to Example 1 in all steps and raw materials, except for the change in the composition ratio of palm oil and organosiloxane in the composite modifier. That is: A method for preparing a modified bio-based coated controlled-release fertilizer includes the following preparation steps: (1) Preparation of fermented livestock and poultry manure: (2) Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. (3) Preparation of modified bio-based coating materials: a. First, collect discarded pineapple leaves, wash them clean and dry them, then use a shredder to shred the pineapple leaves into fiber powder; b. Then, 60g of fiber powder, 30g of ethylene glycol, and 360g of polyethylene glycol were reacted with 10g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction was continuously stirred at 800-1000 r / min for 2 hours at 160-170℃. Finally, the mixture was cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. c. Mix palm oil and organosiloxane at a mass ratio of 2:1 to obtain a composite modifier. Then, mix the composite modifier with liquefied pineapple leaf-based biomass in a high-speed mixer, add isocyanate MDI, and react at 80-85℃ for 3 hours to form a modified bio-based coating material. (4) Place the prepared fertilizer core in a coating equipment and spray the modified bio-based coating material evenly onto the surface of the fertilizer core at a rolling speed of 20-30 rpm at 60-80℃ to form a complete and dense coating layer. After cooling, the modified bio-based coated controlled-release fertilizer is obtained.

[0067] The mass ratio of the composite modifier, liquefied pineapple leaf-based biomass, and isocyanate MDI was 1:1.5:0.8.

[0068] The organosiloxane in the composite modifier is a vinyl hydroxyl silicone oil with a viscosity of 25-40 mPa·s.

[0069] Comparative Example 5 This comparative example is identical to Example 1 in all steps and raw materials, except for the change in the composition ratio of palm oil and organosiloxane in the composite modifier. That is: A method for preparing a modified bio-based coated controlled-release fertilizer includes the following preparation steps: (1) Preparation of fermented livestock and poultry manure: (2) Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. (3) Preparation of modified bio-based coating materials: a. First, collect discarded pineapple leaves, wash them clean and dry them, then use a shredder to shred the pineapple leaves into fiber powder; b. Then, 60g of fiber powder, 30g of ethylene glycol, and 360g of polyethylene glycol were reacted with 10g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction was continuously stirred at 800-1000 r / min for 2 hours at 160-170℃. Finally, the mixture was cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. c. Mix palm oil and organosiloxane at a mass ratio of 1:2 to obtain a composite modifier. Then, mix the composite modifier with liquefied pineapple leaf-based biomass in a high-speed mixer, add isocyanate MDI, and react at 80-85℃ for 3 hours to form a modified bio-based coating material. (4) Place the prepared fertilizer core in a coating equipment and spray the modified bio-based coating material evenly onto the surface of the fertilizer core at a rolling speed of 20-30 rpm at 60-80℃ to form a complete and dense coating layer. After cooling, the modified bio-based coated controlled-release fertilizer is obtained.

[0070] The mass ratio of the composite modifier, liquefied pineapple leaf-based biomass, and isocyanate MDI was 1:1.5:0.8.

[0071] The organosiloxane in the composite modifier is a vinyl hydroxyl silicone oil with a viscosity of 25-40 mPa·s.

[0072] Comparative Example 6 In this comparative example, except that the coating material uses a traditional sustained-release material, all other steps and raw materials are the same as in Example 1. That is: A coated controlled-release fertilizer comprises two parts: a coating liquid and a fertilizer core composed of organic and inorganic nutrients.

[0073] The coating solution used is prepared by heating epoxy resin to 80-95℃, adding the curing agent at a weight ratio of 8:2-4, and mixing evenly.

[0074] The fertilizer core, composed of organic and inorganic nutrients, includes the following components in parts by weight: 30 parts fermented livestock and poultry manure, 15 parts urea, 8 parts diammonium phosphate, 5 parts potassium chloride, 5 parts humic acid, and 2 parts trace element additives.

[0075] A method for preparing a coated controlled-release fertilizer includes the following preparation steps: (1) Preparation of fermented livestock and poultry manure: (2) Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. (3) Place the prepared fertilizer core in the coating equipment and preheat it in a drum at 60℃ and 40rpm for 15 minutes. Raise the temperature to 70℃-90℃ and repeatedly add the coating liquid to the surface of the rolling urea particles. After solidification, the controlled-release fertilizer is obtained. The solidification time is 10-30 minutes.

[0076] During the coating process, the amount of coating liquid sprayed is controlled to be 3% of the fertilizer core mass to ensure the formation of a coating layer with uniform thickness and dense structure.

[0077] Performance testing The coating materials were prepared according to the embodiments and comparative examples of the present invention, and their physicochemical properties were tested after curing. Specifically, after preparing the coating solution, a uniform thin film was scraped onto a glass plate and then placed in an oven for heating and curing.

[0078] Water absorption rate test of the coating material: Three types of membrane shell materials of a certain size (2cm×2cm×0.5mm) were prepared and placed in 300 mL of deionized water. After incubation at an ambient temperature of 25℃ for 24 hours, the membrane shells were removed and excess water was removed from the surface using absorbent paper. The weight of each membrane shell after water absorption and expansion was recorded. Each treatment was repeated three times. Calculation formula: Water absorption rate = Where W1 is the weight of the dry membrane shell and W2 is the weight of the membrane shell that has expanded due to water absorption.

[0079] Contact angle determination: The water contact angle (WCA) of all samples was determined using a JC2000C1 goniometer (POWEREACH, China). Three repeated measurements were performed at room temperature using one drop of water (5 μL) to determine the average contact angle.

[0080] The microstructure of the membrane material was observed using a scanning electron microscope (Hitachi Regulus 8100 field).

[0081] Degradation rate determination of membrane materials: The prepared coating material was cut into 20×20 mm square pieces, accurately weighed using an electronic scale, and the weight was recorded as M0. These pieces were then placed into 80-mesh 100×100 mm nylon mesh bags, the bags were tied tightly, labeled, and buried 20 cm deep in the soil. Three parallel samples were prepared for each group, with each bag spaced 20 cm apart. The experiment was conducted in the soil of the Stanley Agribusiness Group planting demonstration garden from April to June 2024. Samples were taken at 30 and 200 days. After sampling, the surface of the membrane was rinsed clean with ultrapure water to remove soil, dried in a 40℃ oven, and weighed. This weight was recorded as M1. The degradation rate (D) was calculated using the following formula: Degradation rate (D) = (M0 - M1) / M0 × 100%.

[0082] Table 1. Test results of the physicochemical properties of the membrane material As can be seen from the experimental data in Table 1, the coating materials prepared in each embodiment (1-4) of this invention exhibit excellent performance in all aspects and have low water absorption, indicating that the 1:1 composite modification of palm oil and organosiloxane successfully yielded coating materials with high mechanical strength, wear resistance, and good hydrophobic properties, meeting the requirements for coating fertilizer processing and use. The degradation rate of the membrane materials was less than 20% after 30 days, indicating that they maintained structural integrity and effectively exerted a controlled-release effect during the early stages of crop growth. After 200 days, the degradation rate of the membrane materials of this invention reached over 85%, demonstrating good final biodegradability.

[0083] Comparative Examples 1-6, which altered the coating materials, all exhibited varying degrees of performance degradation. Comparative Example 1, without a composite modifier, had a water absorption rate as high as 45.6%, resulting in rapid degradation, reaching 30.6% after 30 days. Comparative Example 2, using only palm oil as a modifier, showed improved material performance compared to Comparative Example 1. Comparative Example 3, using organosiloxane as the sole modifier, while increasing the contact angle to 105° and exhibiting some hydrophobicity, still had a high water absorption rate of 20.1%, and a degradation rate of only 58.5% after 200 days, far lower than the example group. Comparative Examples 4 and 5 adjusted the ratio of palm oil to organosiloxane, but neither achieved the desired effect. This further verifies the importance of a 1:1 composite modification and synergistic balance between palm oil and organosiloxane; only at this ratio can the optimal balance of hydrophobicity, mechanical strength, and degradation performance be achieved.

[0084] Comparative Example 6 used a traditional slow-release material, epoxy resin, for coating. It exhibited the lowest water absorption rate (only 10.1%) and a contact angle of 115°, demonstrating excellent hydrophobic properties. However, its degradation performance was significantly abnormal, with a degradation rate of only 0.3% after 30 days and a mere 1.5% after 200 days. This indicates that traditional materials struggle to achieve environmentally friendly degradation while maintaining controlled release, and long-term residues may pose a potential threat to soil ecology.

[0085] Fertilizer granule performance test: Fertilizers were prepared according to the examples and comparative proportions. The compressive strength and abrasion resistance of the coated fertilizer particles were determined using the test methods in the national standard GB / T23348-2009 for slow-release fertilizers.

[0086] Nutrient release determination: According to the national standard for slow-release fertilizers, the initial nutrient release rate refers to the cumulative nutrient release amount after the fertilizer sample has been soaked for 24 hours. The cumulative nutrient release period refers to the date corresponding to 80% cumulative nutrient release. The experiment was conducted in triplicate.

[0087] Table 2 Results of fertilizer granule performance tests As shown in Table 2, the fertilizer granules prepared in Examples 1-4 exhibit excellent performance in terms of compressive strength, abrasion resistance, and nutrient release control. Their compressive strength all exceeds 25 N, and the mass loss rate is less than 1.2%, indicating that the granules possess good mechanical strength and abrasion resistance, meeting the requirements of modern mechanized fertilization in agriculture. The initial nutrient release rate is controlled at around 10%, and the nutrient release period reaches 58-62 days, demonstrating an ideal slow-release effect.

[0088] In contrast, the performance of fertilizer granules in Comparative Examples 1-6 all showed varying degrees of decline. Comparative Example 1, lacking a composite modified coating material, resulted in a granule compressive strength of only 13.5 N, poor abrasion resistance, a mass loss rate as high as 3.8%, and excessively rapid nutrient release, with an initial release rate of 28.7% and a release period of only 32 days. While Comparative Example 2 showed some improvement through modification with single palm oil, all indicators were still significantly lower than those of the Example group. Comparative Example 3 used organosiloxane as the sole modifier; although the initial nutrient release rate was reduced, the release period remained relatively short.

[0089] Comparative Examples 4 and 5 showed improved performance by adjusting the ratio of palm oil to organosiloxane, but still could not reach the level of the Example Group. This again verifies the necessity of modifying palm oil and organosiloxane in a 1:1 ratio. Comparative Example 6 used a traditional epoxy resin coating material, which had good mechanical properties, but its mass loss rate was high and it had environmental friendliness issues, making it difficult to meet the requirements of sustainable development in modern agriculture.

[0090] Planting experiment: Experimental location: The experiment was conducted in Stanley Agricultural Demonstration Zone, Linyi City, Shandong Province, using typical local sandy soil and rapeseed as the test crop.

[0091] Test soil: The test soil was sandy soil. After passing through a 2mm sieve, half of the soil was weighed and placed in a No. 10 resealable bag. Then, the weighed test fertilizer was added, at a rate of 30g per pot. The other half of the soil was then added, and the mixture was placed in a plastic pot. The test pots were plastic pots with a top diameter of 21.5cm, a bottom diameter of 19.5cm, and a height of 16.5cm. Approximately 5kg of soil was placed in each pot. Tap water was used for irrigation. Before sowing, the soil was thoroughly watered. 30 rapeseed seeds were sown in each pot, covered with 1cm of fine soil, and sealed with plastic film to prevent moisture evaporation. About 8 seedlings were thinned out. Watering was done every 3-4 days. Pesticides and weeds were applied approximately every 3 weeks, for a total of 2 applications.

[0092] Experimental design: The experiment adopted a completely randomized block design with a total of 7 treatments, each of which was repeated 4 times, and the mean of all test results was taken.

[0093] CK: No fertilizer was applied, serving as the control group.

[0094] S1: Apply fertilizer granules prepared in Example 1; S2: Apply fertilizer granules prepared in Comparative Example 1; S3: Apply fertilizer granules prepared in Comparative Example 2; S4: Apply fertilizer granules prepared in Comparative Example 3; S5: Apply fertilizer granules prepared in Comparative Example 4; S6: Apply fertilizer granules prepared in Comparative Example 5; S7: Apply fertilizer granules prepared in Comparative Example 6.

[0095] Test items and methods: Plant growth indicators: Plant height was measured using a ruler, from the base of the rapeseed stem to the top. The third true leaf of the rapeseed was selected, and the relative chlorophyll content (SPAD) of the leaf was determined using a chlorophyll meter (SPAD-502, Minolta, Japan), and the leaf area was determined using a YMJ-CHA3 leaf area meter.

[0096] Fresh and dry weight of rapeseed above ground: After harvesting, rapeseed was placed in a 105°C oven for 1 hour to kill the greening, and then the oven was adjusted to 70°C to dry the rapeseed to a constant weight state, and its dry weight was measured.

[0097] Total nitrogen, total phosphorus, and total potassium content of rapeseed: The dried rapeseed aboveground parts were crushed using a pulverizer and passed through a 60-mesh sieve. The plant samples were then decomposed using a combined H2SO4-H2O2 digestion method. Total nitrogen was determined using a Kjeldahl nitrogen analyzer (KDY-9820, Beijing Tongrunyuan Electromechanical Technology Co., Ltd.). Total phosphorus was determined using the vanadium molybdenum yellow colorimetric method under a UV-Vis spectrophotometer (Evolution300, Thermo, USA). Total potassium was determined using a flame spectrophotometer (M410, UK).

[0098] Soil total nitrogen, available phosphorus, and available potassium content: Soil samples were taken after rapeseed harvest. Three samples were collected from each pot and mixed together as a sample. The samples were then air-dried in a cool place and passed through a 60-mesh sieve. Total nitrogen was determined using a Kjeldahl nitrogen analyzer (KDY-9820, Beijing Tongrunyuan Electromechanical Technology Co., Ltd.). Available phosphorus was determined using the vanadium molybdenum yellow colorimetric method under a UV-Vis spectrophotometer (Evolution300, Thermo, USA). Available potassium was determined using a flame spectrophotometer (M410, UK).

[0099] Table 2. Physiological Indicators of Rapeseed Table 3 Soil indices for different treatment groups As shown in Tables 2-3, the fertilizers used in Examples 1-4 exhibited significant advantages in the rapeseed planting experiment. Plant growth indicators showed that the rapeseed plants treated with the fertilizers in these examples all exceeded 20 cm in height, 4-6 cm taller than the control group, and the chlorophyll content remained around 50 mg / g, significantly higher than the 35-44 mg / g in the control group. Aboveground dry weight data showed that each rapeseed plant in the examples group achieved a dry weight of 18-20 g, indicating effective absorption and utilization of fertilizer nutrients. The total nitrogen, total phosphorus, and total potassium content of the rapeseed in different treatment groups were also analyzed. Figure 3-5 It can also be seen that the fertilizer in the example significantly improved the nutrient absorption efficiency of rapeseed. The results of total nitrogen content determination showed that the total nitrogen content of the aboveground parts of rapeseed treated with the fertilizer in the example was higher than that of the comparative and control groups, indicating that its slow-release characteristics can continuously provide a stable nitrogen source for the crop. Total phosphorus and total potassium contents also showed significant advantages, which is closely related to the long nutrient release period of 58-62 days in the fertilizer. In contrast, the comparative group experienced a significant nutrient supply bottleneck in the later stages of rapeseed growth due to either excessively rapid or insufficient nutrient release, affecting the crop's absorption of phosphorus and potassium.

[0100] Soil index data further validated the superiority of the fertilizer in the example. After application of the fertilizer, the contents of total nitrogen, available phosphorus, and available potassium in the soil remained at high levels, significantly better than those in the comparative group. This not only demonstrates that the fertilizer in the example has a good controlled-release effect on nutrients, but also indicates that it helps improve soil fertility and reduce nutrient loss.

[0101] Overall, the fertilizer in the examples demonstrated excellent performance in promoting rapeseed growth, improving nutrient utilization, and enhancing the soil environment. This is mainly attributed to the successful application of a 1:1 composite modified coating material made from palm oil and organosiloxane, achieving an ideal balance between mechanical strength, hydrophobicity, and degradation characteristics. In contrast, the comparative group, lacking this balance, performed inferiorly to the example group in terms of plant growth, nutrient absorption, and soil improvement, further highlighting the advanced nature of the present invention.

[0102] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A modified bio-based coated controlled-release fertilizer, characterized in that, The fertilizer comprises two parts: a coating made of a modified bio-based coating material and a fertilizer core composed of organic and inorganic nutrients. The fertilizer core, composed of organic and inorganic nutrients, includes the following components in parts by weight: 30-52 parts fermented livestock and poultry manure, 15-25 parts urea, 8-15 parts diammonium phosphate, 5-10 parts potassium chloride, 5-8 parts humic acid, and 2-4 parts trace element additives. The method for preparing the modified bio-based coating material is as follows: a. First, collect discarded pineapple leaves, wash them clean and dry them, then use a shredder to shred the pineapple leaves into fiber powder; b. Then, 60-80g of fiber powder, 30-40g of ethylene glycol, and 360-380g of polyethylene glycol are reacted with 10-12g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction is continuously stirred at 800-1000 r / min for 2-4 hours at 160-170℃. Finally, the mixture is cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. c. Mix palm oil and organosiloxane at a mass ratio of 1:1 to obtain a composite modifier. Then, mix the composite modifier with liquefied pineapple leaf-based biomass in a high-speed mixer, add isocyanate MDI, and react at 80-85℃ for 3 hours to form a modified bio-based coating material.

2. The modified bio-based coated controlled-release fertilizer according to claim 1, characterized in that, The trace element additives include one or more of iron, zinc, boron, molybdenum, copper and manganese, and exist in the form of oxides or sulfates.

3. The modified bio-based coated controlled-release fertilizer according to claim 1, characterized in that, The method for preparing fermented livestock and poultry manure is as follows: Livestock and poultry manure and straw powder are mixed at a weight ratio of 3:1, and 2% of EM bacteria agent by weight of the mixture is added. Fermentation is carried out for 15-20 days at a temperature of 35-40℃. After drying, crushing and sieving, fermented livestock and poultry manure is obtained. The fermented livestock and poultry manure is brown powder with a moisture content of less than 15% and an organic matter content of more than 45%.

4. A method for preparing the modified bio-based coated controlled-release fertilizer according to any one of claims 1-3, characterized in that, The preparation steps include the following: Preparation of fermented livestock and poultry manure; Preparation of fertilizer core composed of organic and inorganic nutrients: Fermented livestock and poultry manure is mixed evenly with urea, diammonium phosphate, potassium chloride, humic acid and trace element additives in a certain proportion, and then granulated, dried and sieved to obtain fertilizer core with uniform particle size. Preparation of modified bio-based coating materials: First, collect discarded pineapple leaves, wash them clean and dry them, and then use a shredder to shred the pineapple leaves into fiber powder. Then, 60-80g of fiber powder, 30-40g of ethylene glycol, and 360-380g of polyethylene glycol were reacted with 10-12g of concentrated sulfuric acid as a catalyst in a three-necked round-bottom flask connected to a condenser. The reaction was continuously stirred at 800-1000 r / min for 2-4 hours at 160-170℃. Finally, the mixture was cooled to ambient temperature, filtered to remove unreacted solids, and vacuum evaporated to remove excess water to obtain liquefied pineapple leaf-based biomass. A composite modifier is obtained by mixing palm oil and organosiloxane at a mass ratio of 1:

1. Then, the composite modifier is uniformly mixed with liquefied pineapple leaf-based biomass in a high-speed mixer, and isocyanate MDI is added. The mixture is reacted at 80-85℃ for 3 hours to form a modified bio-based coating material. The prepared fertilizer core is placed in a coating device, and the modified bio-based coating material is evenly sprayed onto the surface of the fertilizer core at a rolling speed of 20-30 rpm at 60-80℃ to form a complete and dense coating layer. After cooling, the modified bio-based coated controlled-release fertilizer is obtained.

5. The method for preparing the modified bio-based coated controlled-release fertilizer according to claim 4, characterized in that, The mass ratio of the composite modifier, liquefied pineapple leaf-based biomass, and isocyanate MDI was 1:1.5:0.

8.

6. The method for preparing the modified bio-based coated controlled-release fertilizer according to claim 4, characterized in that, The organosiloxane in the composite modifier is a vinyl hydroxyl silicone oil with a viscosity of 25-40 mPa·s.

7. The method for preparing the modified bio-based coated controlled-release fertilizer according to claim 4, characterized in that, During the coating process, the amount of coating material sprayed is controlled to be 3%-5% of the fertilizer core mass to ensure the formation of a coating layer with uniform thickness and dense structure.

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