Multifunctional molecular sieve modified bio-based high polymer material as well as preparation method and application thereof

Abstract

The invention discloses a multifunctional molecular sieve modified bio-based high polymer material and a preparation method thereof, zeolite is modified by a nitric acid metal solution, and a multifunctional modified molecular sieve with a bio-based high polymer material catalysis effect is prepared; the multifunctional modified molecular sieve is applied to a phthalic anhydride cured bio-based high polymer material synthesis system, and a high polymer material with good toughness and high tensile strength is prepared. The invention also discloses a solvent-free drum coating process, and the coated phosphate fertilizer with better controlled release performance is prepared by using the multifunctional molecular sieve modified bio-based high polymer material. The adopted preparation method and process are green, free of emission and high in sustainability, nutrient substances in the fertilizer can be slowly released, resource waste and environmental pollution are reduced, meanwhile, the prepared coated fertilizer is good in controlled release performance, a coating layer can adsorb heavy metal ions and improve the soil environment, and therefore creation of a multifunctional coating material is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a multifunctional molecular sieve modified bio-based polymer material, a preparation method thereof, and an application thereof. Background Art

[0002] Coating materials mainly include inorganic materials and organic synthetic polymer materials. Among them, organic synthetic polymer materials, such as polyethylene, polypropylene, etc., are widely used due to their good barrier properties and mechanical properties. However, their non-degradable characteristics will also lead to serious environmental problems. Inorganic coating materials, such as silicates, metal oxides, etc., although having good stability, have great processing difficulty and relatively single functions, and have disadvantages such as poor mechanical properties and insufficient long-acting controlled release performance. Thus, there are many deficiencies in traditional coating materials, and it is very difficult to simultaneously meet the requirements of high barrier properties, good flexibility, processability, and long-acting controlled release.

[0003] With the enhancement of environmental awareness and the deepening of the concept of sustainable development, the demand for environmentally friendly bio-based materials is increasing day by day. Bio-based materials are derived from renewable biomass resources and have outstanding advantages such as biodegradability and environmental friendliness. They can effectively reduce the negative impact on the environment while meeting the basic properties of coating materials. Bio-based epoxy resins can be prepared by using biomass derivatives as raw materials, through grafting epoxy groups or epoxidation reactions, and then curing reactions with organic amines, organic polyacids, polyphenols, polyols, etc. Among them, bio-based vegetable oils contain unsaturated bonds and can be converted into bio-based epoxy vegetable oils through simple oxidation with hydrogen peroxide under acidic conditions, so the preparation method is simple and green; moreover, the vegetable oils contain hydrophobic long-chain alkyl groups, which can endow the corresponding epoxy resins with specific hydrophobic properties. However, at present, the direct curing reaction activity of epoxy vegetable oils is relatively low, and the film-forming property is also poor, and the long-acting controlled release of coated fertilizers cannot be achieved. Therefore, there is an urgent need to explore low-cost and highly efficient curing reaction catalysts to promote the preparation of bio-based epoxy resins with excellent properties.

[0004] Molecular sieves are aluminosilicate crystal materials with regular microporous structures. Their unique pore structures and adjustable acidic sites endow them with excellent performance in the catalytic field. The catalytic activity of molecular sieves stems from the distribution and strength of the acidic sites on their surfaces. The synergistic effect of Bronsted acids and Lewis acids can effectively activate reactant molecules. The multiple pores of molecular sieves endow them with selective catalytic properties, enabling reactant, intermediate, and product molecules to achieve selective diffusion and reaction based on their kinetic diameters. This property has a decisive advantage in complex reaction systems such as petroleum cracking and alkylation. Compared with traditional solid acid catalysts, molecular sieves exhibit higher thermal stability (temperature resistance > 600 °C) and hydrothermal stability, and the acidic sites and pore structures can be precisely regulated through ion exchange, metal doping, etc., thereby effectively improving their catalytic activity. In addition, molecular sieves can also be used as fillers to be compounded with polymer materials to improve their application performance. Therefore, introducing molecular sieves into the synthesis system of bio-based polymer materials and exploring the properties and practical applications of these materials provide a new direction for the synthesis of bio-based polymer materials. Summary of the Invention

[0005] To solve the problems existing in the prior art, the present invention provides a multifunctional molecular sieve modified bio-based polymer material and its preparation method. By using metal ion-exchanged zeolite molecular sieves as multifunctional catalysts, a bio-based polymer material with stronger toughness and multifunctionality is prepared, and this material is used to wrap fertilizer particles to obtain coated phosphate fertilizers with good controlled-release performance.

[0006] The technical solution of the present invention is as follows:

[0007] The present invention provides a preparation method for a multifunctional molecular sieve modified bio-based polymer material, comprising the following steps:

[0008] (1) After sieving the molecular sieve, add it to a transition metal salt solution to form a slurry, while performing wet ball milling, add deionized water and stir to disperse, and then obtain multifunctional modified molecular sieves after centrifugation, filtration, drying, and calcination;

[0009] (2) Place the multifunctional modified molecular sieves obtained in step (1), phthalic anhydride, and glycerol in a stirring reactor, fully react at 80 - 150 °C, then add epoxy vegetable oil, and fully stir and mix evenly to obtain a mixed prepolymer;

[0010] (3) Transfer the mixed prepolymer obtained in step (2) into a polytetrafluoroethylene mold and cure it at 80 - 150 °C to obtain a multifunctional molecular sieve modified bio-based polymer material.

[0011] Furthermore, the molecular sieve is zeolite powder, including one or more of clinoptilolite, mordenite, erionite, chabazite, and synthetic zeolite.

[0012] Further, the concentration of the transition metal salt solution is 0.01 - 1.5 mol / L; the transition metal salt solution is one or more of water-soluble transition metal nitrates, sulfates or hydrochlorides.

[0013] Further, in the step (1), the addition amounts of the molecular sieve and the transition metal salt solution are in a mass ratio of 1:10 - 1:30.

[0014] Further, in the step (2), the addition amounts of the multifunctional modified molecular sieve, phthalic anhydride and glycerol are respectively: 1 - 4 parts by weight of the modified molecular sieve, 20 - 80 parts by weight of phthalic anhydride, and 5 - 50 parts by weight of glycerol.

[0015] Further, the epoxy vegetable oil is one or more of epoxy castor oil, epoxy soybean oil, epoxy palm oil, and epoxy rapeseed oil.

[0016] The present invention provides a multifunctional molecular sieve modified bio-based polymer material prepared according to the above preparation method, and the addition amount of the multifunctional modified molecular sieve in the polymer material is 0.5 - 10 wt%.

[0017] The present invention provides the use of the multifunctional molecular sieve modified bio-based polymer material for wrapping fertilizer particles to prepare coated fertilizers.

[0018] The present invention also provides a preparation method of a coated fertilizer, comprising the following steps:

[0019] S1. Add phosphate fertilizer particles into a sugar coating pan, blow hot air to preheat the particle surface to make the surface temperature 70 - 100°C;

[0020] S2. Then add the mixed prepolymer into the sugar coating pan and roll and mix it evenly with the phosphate fertilizer particles, then roll and heat for curing at 100 - 140°C, and repeat the operation for multiple times to make the coating rate reach 3 - 5 wt%, and then treat a small amount of paraffin on the surface of the coated fertilizer for encapsulation to obtain the coated fertilizer.

[0021] Among them, the preparation method of the mixed prepolymer is: after sieving the molecular sieve, add the transition metal salt solution to form a paste, while performing wet ball milling, add deionized water and stir for dispersion, and then obtain the multifunctional modified molecular sieve after centrifugation, filtration, drying and calcination; place the modified molecular sieve, phthalic anhydride and glycerol in a stirring reactor, fully react at 80 - 150°C, then add the epoxy vegetable oil, and fully stir and mix evenly to obtain the mixed prepolymer.

[0022] Further, the phosphate fertilizer particles are one or more of monoammonium phosphate, diammonium phosphate or superphosphate, the phosphate fertilizer particles are regular spherical particles, the surface of the phosphate fertilizer particles is smooth or polished, and the particle diameter is 2 - 4 mm.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. In the preparation method provided by the present invention, metal ion-exchanged zeolite molecular sieves are used to form multifunctional molecular sieves, which are used as catalysts in the synthesis system of phthalic anhydride-cured bio-based polymers. Finally, polymers with good toughness and high tensile strength are obtained, which can solve the problems of insufficient mechanical properties and controlled release properties of bio-based polymers in the prior art. Moreover, the preparation method is green, environmentally friendly, emission-free, and highly sustainable; the obtained materials have environmentally friendly characteristics, are easy to recycle and process, and are non-toxic, odorless, and non-corrosive, having significant advantages in the agricultural field;

[0025] 2. The multifunctional molecular sieve-modified bio-based polymer prepared by the present invention is used to wrap fertilizer particles to prepare coated fertilizers. By changing the amount of molecular sieve used or different metal modifications, the curing activity and other functions of the bio-based polymer can be simply regulated, so that controlled-release fertilizers with different release characteristics can be prepared, realizing the slow release of nutrients in fertilizers and reducing resource waste and environmental pollution; the multifunctional molecular sieve-modified bio-based polymer has good adsorption performance and is used to prepare coated fertilizers. After the coating fertilizer degrades, the modified molecular sieve can adsorb heavy metal ions in the soil, thus playing the role of improving the soil environment and reducing environmental pollution; in the multifunctional molecular sieve-modified bio-based polymer, due to the regular and uniform pore structure of the molecular sieve and the pore size being close to the molecular size, trace elements required by plants can also be introduced during the use of coated fertilizers to promote plant growth and improve the multifunctionality of the coating material; the molecular sieve in the multifunctional molecular sieve-modified bio-based polymer has good stability and anti-toxicity, maintains catalytic activity under high temperature and high pressure, and has a certain resistance to poisons, which can extend the service life of coated fertilizers to a certain extent. Description of the Drawings

[0026] Figure 1 SEM image of the multifunctional modified molecular sieve prepared in Example 1;

[0027] Figure 2 Water contact angle image of the multifunctional molecular sieve-modified bio-based polymer prepared in Example 1;

[0028] Figure 3 Tensile spline image of the multifunctional molecular sieve-modified bio-based polymer prepared in Example 1;

[0029] Figure 4 Swelling performance comparison image of the multifunctional molecular sieve-modified bio-based polymers prepared in Example 1, Example 2, Example 3, and Example 4;

[0030] Figure 5Swelling property comparison chart of the multifunctional molecular sieve modified bio-based polymer materials prepared in Example 1, Example 5, Example 6, and Example 7;

[0031] Figure 6 Granular diagram of the coated fertilizer prepared in Example 8;

[0032] Figure 7 Phosphorus element release diagram of the coated phosphate fertilizer prepared in Example 8, Example 9, Example 10, and Example 11 for 28 days. Detailed implementation manners

[0033] The following further describes the present invention in conjunction with preferred embodiments and the accompanying drawings. In the present invention, the endpoints and any values within the disclosed ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0034] The instruments used in the present invention are as follows:

[0035] Scanning electron microscope (SEM): Observe the morphology of the catalyst through an S-4800 field emission scanning electron microscope. The vacuum degree in the analysis chamber is less than 2.7×10 -6 Pa, and the scanning voltage and current are 5 kV and 7 μA respectively. The sample powder is adhered to the conductive adhesive and then observed after sputtering gold.

[0036] The materials, reagents, etc. used in the following examples can be obtained from commercial channels without special instructions.

[0037] Example 1

[0038] This example provides a preparation method of a multifunctional molecular sieve modified bio-based polymer material, including the following steps:

[0039] (1) Weigh zeolite molecular sieve passing through 600 meshes into a ball milling tank, add a transition metal salt solution to form a paste, perform wet ball milling at a speed of 400 r / min for 1 h, add deionized water and stir to disperse, then centrifuge, filter, and dry, and calcine in a muffle furnace at 500 °C for 2 h to obtain a multifunctional modified molecular sieve; in this example, the transition metal salt solution is a water-soluble nickel nitrate solution, the mass ratio of zeolite molecular sieve to nickel nitrate solution is 1:10, the concentration of nickel nitrate is 0.01 mol / L, and the zeolite molecular sieve can be one or more of clinoptilolite, mordenite, erionite, chabazite, and synthetic zeolite;

[0040] (2) Place the multifunctional modified molecular sieve, phthalic anhydride, and glycerol obtained in step (1) into a stirring reactor, where 2.0 parts of the modified molecular sieve, 59.2 parts of phthalic anhydride, and 18.4 parts of glycerol are added. After mixing, stir at 120 °C at a speed of 300 rpm for 30 min, then add 122.2 parts of epoxidized soybean oil. After fully stirring and mixing evenly at a speed of 500 rpm, a mixed prepolymer is obtained. In addition to epoxidized soybean oil, one or more of epoxidized castor oil, epoxidized palm oil, and epoxidized rapeseed oil can also be added;

[0041] (3) Transfer the mixed prepolymer obtained in step (2) into a polytetrafluoroethylene mold and cure it at 120 °C for 3 h to obtain a multifunctional molecular sieve modified bio-based polymer material. Among them, the addition amount of the multifunctional modified molecular sieve in the polymer material is 0.5 - 10 wt%.

[0042] Perform a scanning electron microscope test on the multifunctional molecular sieve prepared in Example 1. The test method will not be elaborated here. The test results are as Figure 1 shown. The molecular sieve modified by nickel nitrate is in the form of fragments, with a smooth and dense surface, clear grain boundaries, but there are large agglomerates. It may be that after high-temperature calcination, grain growth is induced, the particle size increases, the agglomeration phenomenon becomes more serious, a dense block is formed, or local sintering leads to surface melting and pore collapse, forming large agglomerates.

[0043] Perform a water contact angle test on the multifunctional molecular sieve modified bio-based polymer material. The test method is as follows: Use a water contact angle measuring instrument to measure the hydrophilicity and hydrophobicity of the outer surface of the material. Control the room temperature during the test to be about 25 °C, the size of the test liquid droplet to be 1 μL, and take a photo 10 s after the water droplet contacts the outer surface of the resin. The test results are as Figure 2 shown. The water contact angle formed by the liquid droplet and the outer surface of the resin is greater than 90°, indicating that the synthesized multifunctional molecular sieve bio-based polymer material has hydrophobicity.

[0044] Perform a tensile test on the multifunctional molecular sieve modified bio-based polymer material. The test method is as follows: Transfer the mixed prepolymer obtained in step (2) of Example 1 into a polytetrafluoroethylene mold (length 75 mm, thickness 0.8 mm), place it in an oven at 120 °C for 3 h to obtain a standard tensile specimen. Use a universal testing machine to perform mechanical property tests on the standard tensile specimen at room temperature of about 25 °C and a tensile rate of 10 mm / min. The standard tensile specimen is as Figure 3 shown. The specimen is mainly in the shape of a dumbbell, with a length of about 75 mm and a thickness of about 0.8 mm.

[0045] Example 2

[0046] This example is a comparative example, providing a method for preparing a composite bio-based polymer material, including the following steps:

[0047] Weigh 59.2 parts of phthalic anhydride and 18.4 parts of glycerol. After mixing, stir and react at 120 °C at a speed of 300 rpm for 30 min, then add 122.2 parts of epoxidized soybean oil. After fully stirring and mixing evenly at a speed of 500 rpm, a mixed prepolymer is obtained; transfer the mixed prepolymer into a polytetrafluoroethylene mold and cure at 120 °C for 3 h to obtain a composite bio-based polymer material.

[0048] Example 3

[0049] The difference between the method for preparing the multifunctional molecular sieve modified bio-based polymer material in Example 3 and that in Example 1 is that: in step (2), the dosage of the multifunctional modified molecular sieve is 1.0 part, the dosage of phthalic anhydride is 80 parts, and the dosage of glycerol is 5 parts, and the others remain unchanged.

[0050] Example 4

[0051] The difference between the method for preparing the multifunctional molecular sieve modified bio-based polymer material in Example 3 and that in Example 1 is that: in step (2), the dosage of the multifunctional modified molecular sieve is 4.0 parts, the dosage of phthalic anhydride is 20 parts, and the dosage of glycerol is 50 parts, and the others remain unchanged.

[0052] Example 5

[0053] The difference between the method for preparing the multifunctional molecular sieve modified bio-based polymer material in Example 5 and that in Example 1 is that: in step (1), the alkaline earth metal salt solution is a 0.01 mol / L calcium nitrate solution, and the mass ratio of the molecular sieve to the transition metal salt solution is 1:20, and the others remain unchanged.

[0054] Example 6

[0055] The difference between the method for preparing the multifunctional molecular sieve modified bio-based polymer material in Example 6 and that in Example 1 is that: in step (1), the transition metal salt solution is a 1.5 mol / L copper nitrate solution, and the mass ratio of the molecular sieve to the transition metal salt solution is 1:30, and the others remain unchanged.

[0056] Example 7

[0057] The difference between the method for preparing the multifunctional molecular sieve modified bio-based polymer material in Example 7 and that in Example 1 is that: in step (1), the transition metal salt solution is a 0.1 mol / L zinc nitrate solution, and the mass ratio of the molecular sieve to the transition metal salt solution is 1:10, and the others remain unchanged.

[0058] Performance test:

[0059] Figure 4Swelling property comparison diagrams of the multifunctional molecular sieve modified bio-based polymer materials prepared in Example 1, Example 2, Example 3, and Example 4; According to Figure 4 As shown, with the change of the addition amount of the modified molecular sieve, the swelling properties exhibited by the materials are different. When 2.0 parts of the modified molecular sieve are added, the swelling rate is the fastest and the swelling ratio is also the largest.

[0060] Figure 5 Swelling property comparison diagrams of the multifunctional molecular sieve modified bio-based polymer materials prepared in Example 1, Example 6, and Example 7; According to Figure 5 As shown, the material synthesized using the molecular sieve modified with nickel nitrate has the largest swelling ratio, and the material synthesized using the molecular sieve modified with zinc nitrate has the smallest swelling ratio, indicating that the promotion effects of the molecular sieves modified with different transition metals are different, and the swelling properties of the materials are also different.

[0061] Table 1 shows the test results of the curing activity performance of the multifunctional molecular sieve modified bio-based polymer materials prepared according to Examples 1 to 7. According to the result comparison of Examples 1 to 4, as the addition amount of the modified molecular sieve increases, the tensile strength and elongation at break of the material show a trend of first increasing and then decreasing. When the addition amount is 2.0 parts, the tensile strength and elongation at break are the largest; According to the result comparison of Examples 1, 2, and 5, when calcium nitrate is selected as the transition metal salt solution, since calcium nitrate itself is an alkaline earth metal salt and the molecular sieve itself contains calcium ions, its catalytic effect is lower compared to selecting zinc nitrate, and the improvement of mechanical properties is smaller; According to the result comparison of Examples 1, 6, and 7, for the modification with the transition metal salt solution, the catalytic effect of the molecular sieve modified with nickel nitrate is the best, and the mechanical properties of the synthesized material are the optimal. The catalytic effects of the molecular sieves modified with copper nitrate and zinc nitrate are the second best.

[0062] Table 1 Test results of the curing activity performance of the bio-based polymer materials obtained in each example

[0063] Example Tensile strength (MPa) Elongation at break (%) Example 1 4.85 229.50 Example 2 1.49 156.69 Example 3 2.29 186.70 Example 4 3.69 211.61 Example 5 2.37 179.25 Example 6 3.74 211.01 Example 7 3.15 198.54

[0064] Example 8

[0065] This example provides a preparation method of a coated fertilizer, including the following steps:

[0066] S1. Add phosphate fertilizer particles into a sugar coating pan, and preheat with hot air at a rotation speed of 20 - 50 r / min until the surface temperature of the particles reaches 70 - 100 °C; Among them, the phosphate fertilizer particles can be one or more of monoammonium phosphate, diammonium phosphate, or superphosphate. The phosphate fertilizer particles are regular spherical particles, the surface of the phosphate fertilizer particles is smooth or polished, and the particle diameter is 2 - 4 mm;

[0067] S2. Then, add the mixed prepolymer into a sugar coating pan and roll and mix it evenly with phosphate fertilizer particles. Then, roll and heat for curing under the condition of 100-140 °C, and repeat the operation for multiple times to make the coating rate reach 3-5 wt%. Then, treat a small amount of paraffin on the surface of the coated fertilizer for encapsulation, so as to obtain the coated fertilizer;

[0068] Among them, the preparation method of the mixed prepolymer refers to Example 1.

[0069] As Figure 6 shown in the figure of the obtained coated fertilizer particles, the inside of the fertilizer is mainly monoammonium phosphate, and a layer of bio-based polymer material is wrapped outside to improve its controlled release performance.

[0070] Example 9

[0071] Example 9 is a comparative example for preparing the coated fertilizer. The difference from Example 8 is that: in the process of preparing the mixed prepolymer, molecular sieve is not added, and multifunctional modified molecular sieve is not prepared, and other conditions remain unchanged.

[0072] Example 10

[0073] The difference between the method for preparing the coated fertilizer in Example 10 and Example 8 is that: the preparation method of the mixed prepolymer refers to Example 6.

[0074] Example 11

[0075] The difference between the method for preparing the coated fertilizer in Example 11 and Example 8 is that: the preparation method of the mixed prepolymer refers to Example 7.

[0076] Figure 7 It is the phosphorus element release diagram of the coated phosphate fertilizers prepared in Example 8, Example 9, Example 10, and Example 11. According to Figure 7 shown in the figure, the coated fertilizer without adding modified molecular sieve has a poor controlled release effect, and 50% of the phosphorus element is released in about 10 days, while the coated fertilizer using the transition metal ion modified molecular sieve has a better controlled release effect. Among them, the coated fertilizer prepared by using nickel nitrate modified molecular sieve has the best controlled release effect, and the release rate in 28 days is less than 40%.

[0077] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for preparing a multifunctional molecular sieve modified bio-based polymer material, characterized in that: The following steps are involved: (1) After the molecular sieve is sieved, a transition metal salt solution is added to form a slurry, and wet ball milling is performed at the same time. Deionized water is added to stir and disperse, and then centrifugation, filtration, drying, and calcination are performed to obtain a multifunctional modified molecular sieve; (2) placing the multifunctional modified molecular sieve, phthalic anhydride and glycerol obtained in step (1) in a stirred reactor, adding epoxidized vegetable oil after sufficient reaction at 80-150° C., and stirring and mixing to obtain a mixed prepolymer; (3) The mixed prepolymer obtained in step (2) is transferred into a polytetrafluoroethylene mold and cured at 80 to 150° C. to obtain a multifunctional molecular sieve modified bio-based polymer material.

2. The method for preparing a multifunctional molecular sieve modified bio-based polymer material according to claim 1, characterized in that: The molecular sieve is zeolite powder, including one or more of clinoptilolite, mordenite, erionite, chabazite and synthetic zeolite.

3. The method for preparing a multifunctional molecular sieve modified bio-based polymer material according to claim 1, characterized in that: The concentration of the transition metal salt solution is 0.01-1.5 mol / L; the transition metal salt solution is one or more of water-soluble transition metal nitrates, sulfates or hydrochlorides.

4. The method for preparing a multifunctional molecular sieve modified bio-based polymer material according to claim 1, characterized in that: In the step (1), the molecular sieve and the transition metal salt solution are added in a mass ratio of 1:10 to 1:

30.

5. The method for preparing a multifunctional molecular sieve modified bio-based polymer material according to claim 1, characterized in that: In the step (2), the multifunctional modified molecular sieve, phthalic anhydride and glycerol are added in the following amounts by weight: 1 to 4 parts of modified molecular sieve, 20 to 80 parts of phthalic anhydride and 5 to 50 parts of glycerol.

6. The method for preparing a multifunctional molecular sieve modified bio-based polymer material according to claim 1, characterized in that: The epoxidized vegetable oil is one or more of epoxidized castor oil, epoxidized soybean oil, epoxidized palm oil and epoxidized rapeseed oil.

7. A multifunctional molecular sieve modified bio-based polymer material prepared according to any one of claims 1 to 6, characterized in that: The multifunctional modified molecular sieve is added in an amount of 0.5 to 10 wt % in the polymer material.

8. The multifunctional molecular sieve modified bio-based polymer material as claimed in claim 7 is used to encapsulate fertilizer particles to prepare coated fertilizer.

9. A method for preparing a coated fertilizer, characterized in that: The following steps are involved: S1. Add phosphate fertilizer particles into the sugar coating pot and preheat the particle surface with hot air to make the surface temperature 70-100℃; S2. Add the mixed prepolymer as claimed in claim 1 into the sugar coating pan and roll and mix evenly with the phosphate fertilizer particles, then roll and heat solidify at 100-140° C., and repeat the operation several times to make the coating rate reach 3-5wt%, and then treat a small amount of paraffin wax on the surface of the coated fertilizer for encapsulation, so as to obtain the coated fertilizer.

10. A method for preparing a coated fertilizer according to claim 8, characterized in that: The phosphate fertilizer particles are one or more of monoammonium phosphate, diammonium phosphate or superphosphate, and the phosphate fertilizer particles are regular spherical particles.

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