CN113024315A

CN113024315A - Coated chelated controlled-release fertilizer and preparation method thereof

Info

Publication number: CN113024315A
Application number: CN202110417477.XA
Authority: CN
Inventors: 詹瑛瑛; 刘慧�; 仁坤; 丁音琴; 江莉龙
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2021-04-19
Filing date: 2021-04-19
Publication date: 2021-06-25

Abstract

The invention discloses a coated chelated controlled-release fertilizer and a preparation method thereof, and belongs to the technical field of controlled-release fertilizers. The coated chelated controlled-release fertilizer consists of a chelated fertilizer with a core-shell structure and a coating; the chelated fertilizer contains 95-98% of large and medium-sized granular fertilizer and 2-5% of chelated state micro-fertilizer by mass. The coating is a composite film of polyurethane and modified sodium bentonite, wherein the mass fraction of the modified sodium bentonite is 5-25%. The coated chelated controlled-release fertilizer provided by the invention can regulate and control the release speed and the composition of large, medium and trace nutrients according to the growth requirements of crops at each stage, and the chelated trace fertilizer is independently distributed on the shell layer to ensure that the property of the fertilizer is stable. The coating material is green and environment-friendly, has low cost, simple preparation process and excellent controlled release performance, and can realize the high-efficiency utilization of the chelated fertilizer.

Description

Coated chelated controlled-release fertilizer and preparation method thereof

Technical Field

The invention belongs to the technical field of controlled release fertilizers, and relates to a coated chelated controlled release fertilizer and a preparation method thereof.

Background

China is a big agricultural country, and chemical fertilizers occupy an extremely important position in the agricultural field. Agricultural production practice researches show that the problem of low fertilizer utilization rate generally exists when the fertilizer is used due to the comprehensive influence of the fertilizer property and the soil environment condition. In order to improve the utilization rate of the fertilizer and relieve the influence of fertilizer loss on ecology, the slow-release fertilizer is produced by transportation. The research on slow release fertilizers exceeds half a century, the coated fertilizer has a slow release effect through physical barriers, the defect that the urea-formaldehyde fertilizer is low in solubility and cannot be completely utilized is overcome, and the slow release fertilizer becomes the key point of the development of the slow release fertilizer. The selection of the coating material is the main factor influencing the sustained and controlled release performance. The most studied coating materials currently are high molecular weight polymeric materials. Such as Polyurethane (PU), the soft and hard segments of which can be adjusted, and can form a film through blending reaction, thereby not only having excellent mechanical property, but also having better controlled release performance, and being one of the most extensive sustained/controlled release fertilizer film materials in the application prospect. CN102320883A utilizes the epoxidation of polyol and then reacts with isocyanate to form a polyurethane/epoxy resin interpenetrating network compound. Although the synthesized composite membrane can form a more compact and hydrophobic controlled release membrane layer on the surface of the fertilizer, the preparation process of the polymer is uncontrollable, unnecessary byproducts are easily formed, and the production cost is increased. Ricardo Bortoletto-Santos and the like (Applied Polymer, 2016, 133, 43790) synthesize the polyurethane controlled release fertilizer by utilizing the castor oil base and the isocyanate, and although the influence of factors such as the thickness of the polyurethane coating, the stability of the coating, the deposition strength and the like on the release kinetics of the controlled release fertilizer is researched, the polyurethane controlled release fertilizer prepared by the castor oil base and the isocyanate has shorter controlled release performance and cannot meet the requirement of crops with longer growth cycle on nutrients.

In the growth process of crops, besides three elements of nitrogen, phosphorus and potassium of plants play a key role in improving the yield and quality of the crops, trace elements such as iron, boron, manganese, copper, zinc, molybdenum and chlorine also play a vital role in the growth and development of the crops. Although the soil contains more or less mineral elements required by plants, the elements contained in the soil are usually in an inorganic form, so the elements are easily adsorbed and fixed by soil colloids and are not beneficial to the absorption of crops. According to the demand personality of crops and the characteristics of soil, inorganic salt of trace elements required by the crops is converted into a chelate with a large stability constant and easy migration, so that the trace elements are favorably transmitted to roots, the absorption of trace nutrients of the crops is promoted, the antagonism is avoided, the growth of the crops is promoted, and a better application effect is obtained. CN110283000A discloses a method for preparing oil-based polyurethane coated slow-release fertilizer by using sulfur-containing bio-based polyurethane, which comprises the steps of carrying out ester exchange reaction, vulcanization reaction and polymerization reaction on bio-oil, polyol, a catalyst, sulfur and polyisocyanate in sequence to prepare a coating liquid, and uniformly spraying the coating liquid on the surface of urea particles. Although the obtained coated slow-release fertilizer has good slow-release performance, and sulfur element generated by degradation of the membrane material can supplement sulfur nutrient for soil, the ester exchange reaction is complex, the vulcanization time is long, the production efficiency is low, and mass production is not easy. CN109503221A provides a modified lignin chelated fertilizer, which can improve the crop absorption capacity by utilizing the synergistic effect between the modified lignin with strong chelating ability and the chelated fertilizer prepared from medium trace elements, but the nutrient release rate is not controllable, and the nutrient can not be provided according to the requirements of crops in different periods. Chengdan (northwest agriculture and forestry science and technology university, 2017) prepares chelated iron chemicals by using a ball milling method, the influence of the ball milling time on the chelation rate of the chelated iron is explored, the adopted solid phase milling method is simple to operate, and various defects of reaction in a solution are avoided. CN108484288A is prepared into the multi-trace element slow-controlled release fertilizer by blending polylactic acid, starch and agricultural micro-fertilizer and then extruding and granulating by a screw. The sustained and controlled release micro-fertilizer has adjustable elements and simple preparation process, and can be completely degraded after being applied to soil. However, the invention does not provide the release conditions of the slow controlled release fertilizer, such as initial release rate, release period and the like.

In conclusion, a coated chelated controlled-release fertilizer which has the advantages of excellent controlled-release performance, low production cost and simple process and can meet the nutrients required by the growth cycle of crops is not available at present.

Disclosure of Invention

In order to overcome the technical problems in the prior art, the invention aims to provide a coated chelated controlled-release fertilizer and a preparation method thereof. The coated chelated controlled release fertilizer can achieve an excellent controlled release effect on the premise of a lower coating rate, and the controlled release fertilizer can be distributed near the root system of crops to provide all nutrients for the growth cycle of the crops by controlling the release rate.

In order to realize the purpose, the invention adopts the technical scheme that:

the method is characterized in that a layer of polyurethane and modified sodium bentonite composite film is coated on the surface of fertilizer particles to form a chelated fertilizer with a controlled-release function, the chelated micro-fertilizer is distributed on a shell layer to enable the shell layer to have a stable environment, and a large amount of required medium-sized fertilizer is distributed on a core layer in a solid particle form according to the characteristics of crops and soil. The composition is as follows: the mass fraction of the shell layer chelated micro-fertilizer is 2-5%, and the mass fraction of the core layer large and medium particle fertilizer is 95-98%; the mass fraction of the modified sodium bentonite in the composite membrane is 5-25%. The large and medium-sized granular fertilizer is one or more of a nitrogen fertilizer, a phosphate fertilizer, a potassium fertilizer, a calcium fertilizer and a magnesium fertilizer.

The preparation method of the coated chelated controlled-release fertilizer comprises the following steps:

(1) the chelated microelement fertilizer is preferably prepared by a high-speed ball milling reaction of a chelating agent and soluble salt of micronutrient. Weighing a certain amount of soluble salts of the chelating agent and the micronutrient, and ball-milling the soluble salts for a certain time at a certain rotating speed by a high-speed ball mill to prepare the chelated trace element fertilizer. The preferable chelating agent is one or more of iminodisuccinic acid sodium (IDHA), L-sodium glutamate (L-Glu) and sodium Lignosulfonate (LS). The soluble trace nutrient is one or more of trace nutrients needed by crops such as copper, iron, manganese, zinc, molybdenum and the like, and the anion of the trace nutrient can be chloride ion, nitrate radical or sulfate radical. The ball milling speed is 300 rpm-500 rpm; the ball milling time is 0.5 h-3 h. The preferred ball milling speed is 450 rpm, the preferred ball milling time is 1 h, and the obtained chelate is prepared into a chelate solution with a certain concentration by using deionized water for later use.

(2) Weighing a certain amount of sodium bentonite, a modifier and water according to the mass fraction of the modifier accounting for the sodium bentonite of 0.1-12% and a liquid-solid ratio of 5:1, and modifying in a preferred ultrasonic mixing mode, wherein the modifier is one or more of a silane coupling agent, polyethylene glycol and hexadecyl trimethyl ammonium bromide, the silane coupling agent is preferred, the mass fraction of the modifier is preferably 5%, the preferred ultrasonic power is 200W, the ultrasonic temperature is 45-50 ℃, and the ultrasonic time is 20 min.

(3) Adding a large amount of granular fertilizer and a medium amount of granular fertilizer into a coating machine, and starting a heating and rotating switch to enable the surface temperature of the granular fertilizer to reach 60-80 ℃; the composition of the large and medium-amount granular fertilizers is selected according to the characteristics of crops and soil, and can be one or more of nitrogenous fertilizer, phosphate fertilizer, potash fertilizer, calcium fertilizer and magnesium fertilizer.

(4) Weighing a certain amount of chelating liquid obtained in the step (1) according to the mass fraction of the shell-layer chelated micro-fertilizer being 2-5%, spraying the chelating liquid on the surface of the granular fertilizer, stopping heating, and curing at low temperature to form the chelated fertilizer with the core-shell structure.

(5) According to the ratio of the total mole amount of hydroxyl groups to the total mole amount of isocyanate groups of the castor oil-based polyol to be 1:1-1:1.2, castor oil and isocyanate monomers are respectively measured. Weighing certain modified bentonite according to the proportion that the modified bentonite accounts for 5-25% of the total amount of the polyurethane, wherein the optimized modified bentonite has the mass fraction of 15%. Firstly, the modified bentonite and the castor oil-based polyol are mixed uniformly. The preferable isocyanate monomer contains at least two isocyanate groups, and the isocyanate monomer is one or more of toluene diisocyanate, diphenylmethane diisocyanate and polymethylene polyphenyl isocyanate; the preferred isocyanate monomer is toluene diisocyanate, and the preferred ratio of the total number of moles of hydroxyl groups to the total number of moles of isocyanate groups is 1: 1.1.

(6) And (3) according to the mass fraction of the coating accounting for 1-4% of the total amount of the chelate fertilizer, quickly mixing a certain amount of mixed solution of castor oil and modified bentonite and toluene diisocyanate to form a polymerization solution, immediately spraying the polymerization solution on the surface of the chelate fertilizer obtained in the step (4), heating to 60-75 ℃, reacting for at least 5 min, and polymerizing and curing in situ to form the coating.

The invention has the following remarkable advantages:

1. the reaction materials selected by the coated chelated controlled release fertilizer are green and environment-friendly, are cheap and easily available, and the polyurethane film prepared by in-situ polymerization reaction has high strength and good toughness. Modified bentonite is added as an inorganic filler, so that the purposes of reducing coating materials and improving the mechanical property and the controlled release property of the coating materials are achieved, and the utilization rate of the fertilizer is improved.

2. The invention distributes the chelated micro fertilizer on the shell layer through a simple process to ensure that the fertilizer has a stable environment, distributes the needed large and medium-sized fertilizer on the nuclear layer in the form of solid particles according to the characteristics of crops and soil, distributes the controlled release fertilizer near the root system of the crops, and provides all nutrients for the growth cycle of the crops by controlling the release rate.

Drawings

FIG. 1 is a view showing the structure of a core-shell of a chelate fertilizer.

Detailed Description

In order to make the content of the present invention more comprehensible, the technical solutions of the present invention are further described below with reference to specific embodiments, but the present invention is not limited thereto.

Example 1

(1) 42.138 g of IDHA and 21.126 g of MnSO were weighed out₄Ball-milling for 60 min at the rotating speed of 450 rpm by using a high-speed ball mill to prepare the manganese chelated micro fertilizer; weighing 20 g of manganese chelated micro-fertilizer and 50 mL of deionized water to prepare a manganese chelated solution with the concentration of 0.4 g/mL for later use.

(2) 50 g of sodium bentonite, 25.13 g of silane coupling agent and 250 g of water are weighed, reacted for 20 min at the ultrasonic power of 200W and the ultrasonic temperature of 45-50 ℃, and dried for later use at 100 ℃.

(3) Adding 400 g of urea into a coating machine, starting a heating and rotating switch, and enabling the surface temperature of the granular fertilizer to reach 60-80 ℃.

(4) And (2) weighing 12 g of chelating liquid obtained in the step (1), spraying the chelating liquid on the surface of the granular fertilizer, stopping heating, and curing at low temperature to form the chelating fertilizer with the core-shell structure.

(5) 7.632 g of modified bentonite was weighed out and mixed with 39.889 g of castor oil based polyol.

(6) 10.990 g of toluene diisocyanate is dripped into the mixed solution in the step (5) to form a polymerization solution, and then the polymerization solution is immediately sprayed on the surface of the chelate fertilizer obtained in the step (4), and the chelate fertilizer is heated to 60-75 ℃ for at least 5 min of reaction, so that the chelate fertilizer is polymerized and cured in situ to form a coating layer.

Example 2

Compared with the coated chelated controlled release fertilizer provided in the embodiment 1, the difference is that the chelating agent and MnSO in the step (1) of preparing the coated chelated controlled release fertilizer₄The dosage of the chelate is different, the chelate is specifically L-Glu, the dosage is 44.139 g, and MnSO₄The dosage of the composition is specifically 25.350 g; other raw materials and procedures were the same as in example 1.

Example 3

Compared with the coated chelated controlled release fertilizer provided in the embodiment 1, the difference is that the chelating agent and MnSO in the step (1) of preparing the coated chelated controlled release fertilizer₄The chelate is LS in different dosage, 53.250 g of MnSO₄The dosage of the composition is specifically 16.900 g; other raw materials and procedures were the same as in example 1.

Example 4

Compared with the coated chelated controlled release fertilizer provided in the embodiment 1, the difference is that the soluble salt of the trace elements and the amount of the soluble salt are different in the step (1) of preparing the coated chelated controlled release fertilizer, specifically, ZnSO is used as the specific example₄The dosage is 2.018 g; other raw materials and procedures were the same as in example 1.

Example 5

Compared with the coated chelated controlled release fertilizer provided in the embodiment 1, the difference is that a certain amount of iron powder is added in the preparation step (1) of the coated chelated controlled release fertilizer except for the trace element soluble salt and the different dosage, and the trace element soluble salt is specifically FeSO₄1.899 g is used; other raw materials and procedures were the same as in example 1.

Example 6

Compared with the coated chelated controlled-release fertilizer provided in the embodiment 1, the difference is that the modified bentonite and the castor oil-based polyol in the step (5) of preparing the coated chelated controlled-release fertilizer and the toluene diisocyanate in the step (6) are different in dosage, specifically 0.848 g of modified bentonite, 13.296 g of castor oil-based polyol and 3.663 g of toluene diisocyanate; other raw materials and procedures were the same as in example 1.

Example 7

Compared with the coated chelated controlled-release fertilizer provided by the embodiment 1, the coated chelated controlled-release fertilizer provided by the embodiment is characterized in that the modified bentonite and the castor oil-based polyol in the step (5) of preparing the coated chelated controlled-release fertilizer and the toluene diisocyanate in the step (6) are different in dosage, specifically 1.696 g of modified bentonite, 26.593 g of castor oil-based polyol and 7.327 g of toluene diisocyanate; other raw materials and procedures were the same as in example 1.

Example 8

(1) Weighing 42.138 g IDHA and 21.126 g MnSO in three parts₄、20.81 g ZnSO₄、18.89 g FeSO₄Ball-milling for 60 min at the rotating speed of 450 rpm by using a high-speed ball mill to prepare the chelated micro-fertilizer; and preparing the obtained chelated micro-fertilizer into a chelated solution with a certain concentration by using deionized water for later use.

(2) 50 g of sodium bentonite, 2.513 g of silane coupling agent and 250 g of water are weighed, reacted for 20 min at the ultrasonic power of 200W and the ultrasonic temperature of 45-50 ℃, and dried for later use at 100 ℃.

(6) 10.990 g of toluene diisocyanate is dripped into the mixed solution in the step (5) to form a polymerization solution, and the polymerization solution is immediately sprayed on the surface of the chelate fertilizer obtained in the step (4), heated to 60-75 ℃, and reacted for at least 5 min, so that the chelate fertilizer is polymerized and cured in situ to form a coating layer.

Comparative example 1

(1) 40 g of urea is added into a coating machine, and a heating and rotary switch is started to ensure that the surface temperature of the granular fertilizer reaches 60-80 ℃.

(2) 3.9889 g of castor oil and 1.0990 g of toluene diisocyanate are mixed to form a polymer solution, the polymer solution is immediately sprayed on the surface of the urea particles in the step (1), the urea particles are heated to 60-75 ℃, and the reaction is carried out for at least 5 min, so that the urea particles are polymerized in situ and cured to form the coating layer.

Comparative example 2

(1) Weighing 42.138 g IDHA and 21.126 g MnSO in three parts₄、20.81 g ZnSO₄、18.89 g FeSO₄Ball milling is carried out for 60 min at the rotating speed of 450 rpm by a high-speed ball mill to prepare the chelated micro fertilizer for later use.

(4) Weighing 12 g of the chelated micro-fertilizer obtained in the step (1), 7.632 g of modified bentonite and 39.889 g of castor oil-based polyol, and uniformly mixing;

(5) 10.990 g of toluene diisocyanate is dripped into the mixed solution in the step (4) to form a polymerization solution, and then the polymerization solution is immediately sprayed on the surface of the urea in the step (3), heated to 60-75 ℃, and reacted for at least 5 min, so that the polymerization solution is polymerized and cured in situ to form the coating layer.

The evaluation method of the controlled release performance of the coated chelated controlled release fertilizer comprises the following steps:

according to the national standard GB T2440-. 5 g of controlled release fertilizer was weighed into a culture tube containing 100 mL of deionized water and the tube placed in an incubator. Extracting the leaching solution every few days, continuously adding 100 mL of deionized water into the test tube, and continuously culturing and leaching according to the same operation until the nutrient content is released to 80%. The initial release rate of the nitrogen/manganese/zinc/iron content is v₁The calculation method is shown as follows:

；

in the formula: omega₁Nitrogen/manganese/zinc determination for leaching at 25 ℃ for 24 hIron release in g;

omega is the mass of total nitrogen/manganese/zinc/iron in g.

In conclusion, the composition and the release rate of the chelating controlled release fertilizer obtained by the invention are easy to control, and the initial release rate is obviously superior to the standard of HGT4215-2011 controlled release fertilizer with the initial release rate less than or equal to 12% on the premise of low coating rate, so that the chelating controlled release fertilizer can adapt to different crops and soil characteristics and meet the growth requirements of the crops.

The foregoing is directed to embodiments of the present invention, and all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. A coated chelated controlled-release fertilizer is characterized in that: the fertilizer consists of chelated fertilizer and a coating, and the mass ratio of the chelated fertilizer to the coating is 100: 1-4; the chelate fertilizer comprises the following components in percentage by mass: 95-98% of large and medium granular fertilizer and 2-5% of chelated micro-fertilizer; the envelope is a modified sodium bentonite composite polyurethane film, wherein the mass fraction of the modified sodium bentonite is 5-25%.

2. The coated chelated controlled release fertilizer of claim 1, wherein: the chelated fertilizer is of a core-shell structure, the shell layer is a chelated state micro-fertilizer, and the core is a large and medium particle fertilizer.

3. The coated chelated controlled release fertilizer of claim 1 or 2, wherein: the large and medium-sized granular fertilizer is one or more of a nitrogen fertilizer, a phosphate fertilizer, a potassium fertilizer, a calcium fertilizer and a magnesium fertilizer.

4. The coated chelated controlled release fertilizer of claim 1 or 2, wherein: the chelated micro fertilizer is prepared by a high-speed ball milling reaction of a chelating agent and soluble salt of micronutrient; the chelating agent is one or more of iminodisuccinic acid sodium, L-sodium glutamate and sodium lignosulfonate; the soluble salt of the micronutrient is chloride, nitrate or sulfate of copper, iron, manganese, zinc or molybdenum; the ball milling speed is 300 rpm-500 rpm, and the ball milling time is 0.5 h-3 h.

5. The coated chelated controlled release fertilizer of claim 1, wherein: the modifier of the sodium bentonite is one or more of silane coupling agent, polyethylene glycol and hexadecyl trimethyl ammonium bromide, and the dosage of the modifier is 0.1-12% of the mass of the sodium bentonite.

6. A method of preparing the coated chelated controlled release fertilizer as claimed in any one of claims 1-4, characterized in that: the method comprises the following steps:

(1) adding a large amount of granular fertilizer and a medium amount of granular fertilizer into a coating machine, and starting a heating and rotating switch to enable the surface temperature of the granular fertilizer to reach 60-80 ℃;

(2) diluting the chelated trace element fertilizer, spraying the diluted chelated trace element fertilizer on the surface of the granular fertilizer, and curing at low temperature to obtain a chelated fertilizer with a core-shell structure;

(3) spraying the polymerization solution on the surface of the chelated fertilizer, heating to 60-75 ℃ to polymerize and solidify in situ to form a coating; the polymerization liquid is formed by mixing castor oil-based polyol, isocyanate monomer containing at least two isocyanate groups and modified bentonite; the isocyanate monomer is one or more of toluene diisocyanate, diphenylmethane diisocyanate and polymethylene polyphenyl isocyanate; the ratio of the total molar amount of hydroxyl groups of the castor oil-based polyol to the total molar amount of isocyanate groups of the isocyanate monomer is 1:1 to 1: 1.2.