NL2032495A

NL2032495A - Coated controlled-release fertilizer and preparation method thereof

Info

Publication number: NL2032495A
Application number: NL2032495A
Authority: NL
Inventors: Zeng Xiangzhong; Qin Yusheng; Dai Yurou; Yu Hua; Yuan Wanzhen; Shangguan Yuxian; Chen Kun; He Mingjiang; Zhou Zijun; Guo Song
Original assignee: Inst Of Agricultural Resources And Environment Sichuan Academy Of Agricultural Sciences
Priority date: 2022-04-25
Filing date: 2022-07-14
Publication date: 2023-11-07
Also published as: CN114736070A; NL2032495B1; CN114736070B

Abstract

Disclosed is a coated controlled—release fertilizer, including inner fertilizer core granules and, outer‘ high—molecular coating materials, wherein the high—molecular coating material is nano calcium. carbonate modified, waterborne polyacrylate emulsion. In the present invention, the nano calcium carbonate modified waterborne polyacrylate emulsion is used as the main body of the polymer coating, and, thus the controlled—release performance of the fertilizer is obviously improved. It is proved by comparative tests that under the condition of the same amounts of the coating material and fertilizer core granules as well as the same preparation process, compared with the fertilizer with the coating material of unmodified waterborne polyacrylate, the slow—release fertilizer with the improved coating material of nano calcium carbonate modified waterborne polyacrylate has a lower, smoother and more uniform cumulative release rate, and the release period can be extended to about 1.9 times, so that the nutrient requirements of crops can be satisfied.

Description

COATED CONTROLLED-RELEASE FERTILIZER AND PREPARATION METHOD

THEREOF

TECHNICAL FIELD

The present invention belongs to the field of fertilizers, and relates to a controlled-release fertilizer and a preparation method of the controlled-release fertilizer.

BACKGROUND ART

Chemical fertilizers have made important contributions to en- suring global food safety. China's arable land accounts for 9% of the world’s arable land but consumes 1/3 of the fertilizers all over the world, and the amount of fertilizers applied per unit ar- ea is three times larger than the world’s average level. The low utilization rate of chemical fertilizers, especially nitrogen fer- tilizers, brings environmental, economic and energy pressures.

Slow/controlled-release fertilizers have attracted worldwide at- tention due to their advantages of effectively improving the uti- lization of nutrients, reducing the harm caused by a nutrient loss to the environment, and lowering costs of fertilization. Among them, polymer-coated fertilizers have become one of the most prom- ising controlled-release fertilizers due to their better con- trolled-release effect.

Polymer-coated fertilizers refer to a type of controlled- release fertilizers that are produced by coating the surface of traditional instant soluble fertilizer granules with macromolecu- lar polymers to form a film with a certain thickness, so as to slow or control the release of nutrients through osmosis of the film. However, most of the current commercial polymer-coated fer- tilizers require an organic solvent during synthesis and pro- cessing, which easily leads to secondary pollution and results in safety problems.

In recent years, the rapid development of waterborne poly- acrylate coated controlled-release fertilizers has become a major research focus of polymer-coated controlled-release fertilizers.

Waterborne polyacrylate uses water as a solvent, no organic sol- vent is required in the processes of synthesis and fertilizer pro- duction, the finished product which is odorless and easy to de- grade has the advantages of relatively low price, easy synthesis, good film-forming property, suitable viscosity, and no fire risk in manufacturing, storage and transportation, and thus it is re- garded as an ideal environment-friendly controlled-release materi- al for coating.

In the process of completing the present invention, the in- ventor found that the waterborne polyacrylate material has at least one of the following technical problems:

The waterborne polyacrylate coating material is not strong enough and has poor water resistance, thereby leading to the rapid release of nutrients of a coated fertilizer prepared from the coating material; besides, as the coating material has low strength, and the coating is easily disturbed and ruptured in the later stage of release, which cannot satisfy the nutrient require- ments of crops with a long growing season throughout the growing season.

In the process of completing the present invention, in order to slow down a nutrient release rate of the waterborne polyacry- late coated fertilizer and improve the mechanical strength of the coating material, the inventor has tried various physical/chemical modifications for the coating material, for example, modification with bentonite, modification with nano-calcium carbonate, etc.

At present, nano calcium carbonate is mainly used in ferti- lizers to supply calcium nutrient (Chinese Patent Application No.: 201410803048.6, 201110332329.4) and used as a fertilizer synergist (Chinese Patent Application No.: 201210267581.6, 201210267685.7).

With a high specific surface area and a lipophilic and hydro- phobic surface, nano calcium carbonate is prone to agglomeration and flocculation as well as uneven dispersion in an aqueous solu- tion, so that nobody has thought of using nano calcium carbonate to modify waterborne polyacrylate in the disclosed solutions of the prior art related to coated controlled-release fertilizers.

The inventor has not found any research and report on use of nano calcium carbonate for modifying a waterborne polyacrylate emulsion in the prior art, and the patents and literatures also has no report on preparing a coated fertilizer with nano calcium carbonate modified waterborne polyacrylate.

SUMMARY

In view of this, the first objective of the present invention is to provide a coated controlled-release fertilizer with slow nu- trient release and high-strength coating material.

The second objective of the present invention is to provide a method for preparing a coated controlled-release fertilizer with slow nutrient release and high-strength coating material.

The inventor has made continuous reformation and innovation through long-term exploration and attempts, as well as repeated experiments and efforts. In order to solve the above-mentioned technical problems, the technical solution of the present inven- tion provides a coated controlled-release fertilizer, including inner fertilizer core granules and outer high-molecular coating materials, wherein the high-molecular coating material is nano calcium carbonate modified waterborne polyacrylate emulsion solid.

According to an embodiment of the coated controlled-release fertilizer of the present invention, the nano calcium carbonate modified waterborne polyacrylate emulsion is prepared by the fol- lowing steps: slowly adding a nano calcium carbonate aqueous disperse sys- tem into the waterborne polyacrylate emulsion, then stirring well and sieving the mixture.

According to an embodiment of the coated controlled-release fertilizer of the present invention, a solute in the nano calcium carbonate aqueous disperse system includes nano calcium carbonate, and also includes sodium hexametaphosphate and/or polyethylene glycol, and a solvent is deionized water.

According to an embodiment of the coated controlled-release fertilizer of the present invention, the nano calcium carbonate aqueous disperse system includes the following components based on parts by weight: 0.005-2.5 parts of nano calcium carbonate, 0.01-1 part of sodium hexametaphosphate, 0.01-0.3 part of polyethylene glycol and 100 parts of deionized water.

According to an embodiment of the coated controlled-release fertilizer of the present invention, an addition amount of the so- lute in the nano calcium carbonate aqueous disperse system ac- counts for 0.01%-5% of a dry matter mass of the waterborne poly- acrylate.

According to an embodiment of the coated controlled-release fertilizer of the present invention, the nano calcium carbonate aqueous disperse system is prepared by the following steps: adding the nano calcium carbonate into the deionized water, then adding the sodium hexametaphosphate or/and the polyethylene glycol, and then stirring and mixing the solution well to obtain the nano calcium carbonate aqueous disperse system.

According to an embodiment of the coated controlled-release fertilizer of the present invention, the stirring is performed with a magnetic stirrer for 15 min, and the mixing is performed with ultrasonic treatment for 30 min.

According to an embodiment of the coated controlled-release fertilizer of the present invention, a dry matter mass of the mod- ified high-molecular coating material accounts for 2.5%-153 of the coated controlled-release fertilizer.

According to an embodiment of the coated controlled-release fertilizer of the present invention, the waterborne polyacrylate emulsion solid is obtained by treatment in an oven at 60°C for 8 h.

The present invention further provides a method for preparing the coated controlled-release fertilizer, including the following steps:

Sl: preparation of a nano calcium carbonate aqueous disperse system adding nano calcium carbonate into deionized water, then add- ing sodium hexametaphosphate or/and polyethylene glycol, stirring the solution for 15 min and performing ultrasonic treatment for 30 min to obtain the nano calcium carbonate aqueous disperse system;

S2: preparation of modified waterborne polyacrylate emulsion taking waterborne polyacrylate emulsion, then slowly adding the nano calcium carbonate aqueous disperse system prepared in S1 into the waterborne polyacrylate emulsion, stirring the mixture with a magnetic stirrer for 15 min and then sieving the mixture with a 200-mesh screen for later use; and 83: coating treatment taking fertilizer core granules and the nano calcium car- 5 bonate modified waterborne polyacrylate emulsion prepared in S2, producing a coated fertilizer with a coating machine, and treating the produced coated fertilizer in an oven at 60°C for 8 h.

Compared with the prior art, one of the above-mentioned tech- nical solutions has the following advantages: a) In the present invention, the nano calcium carbonate modi- fied waterborne polyacrylate emulsion is used as the main body of the polymer coating, and thus the controlled-release performance of the fertilizer is obviously improved. b) The inventor has found that the dispersing effect of solid nano calcium carbonate in an aqueous solution can be improved by selecting an appropriate dispersing agent and an appropriate dis- persing method, and the mechanical properties of the modified wa- terborne polyacrylate coating material are greatly improved, which is conducive to improving the coating quality and effectiveness. c) The method of the present invention is simple in produc- tion process and environmentally friendly, and has an important promotion value. dy It is proved by comparative tests that under the condition of the same amounts of the coating material and fertilizer core granules as well as the same preparation process, compared with the fertilizer with the coating material of unmodified waterborne polyacrylate, the slow-release fertilizer with the improved coat- ing material of nano calcium carbonate modified waterborne poly- acrylate has a lower, smoother and more uniform cumulative release rate over the same period, and the release period can be extended to about 1.9 times, so that the nutrient requirements of crops with a long growing season throughout the growing season can be satisfied.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be explained in detail below in combination with embodiments. Example 1 as a basic comparison uses unmodified waterborne polyacrylate as the coating material, exam- ple 2 uses nano calcium carbonate modified waterborne polyacrylate as the coating material, example 3 uses 1% nano calcium carbonate modified waterborne polyacrylate dispersed by sodium hexametaphos- phate as the coating material, example 4 uses 1% nano calcium car- bonate modified waterborne polyacrylate dispersed by polyethylene glycol as the coating material, example 5 uses 1% nano calcium carbonate modified waterborne polyacrylate dispersed by sodium hexametaphosphate coupled with polyethylene glycol as the coating material, and example 6 uses 3% nano calcium carbonate modified waterborne polyacrylate dispersed by sodium hexametaphosphate cou- pled with polyethylene glycol as the coating material. Examples 1- 6 all include a slow-released fertilizer and a method for prepar- ing the slow-released fertilizer.

In order to make the objectives, technical solutions and ad- vantages of the present invention more clearly, the technical so- lution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. It is obvious that the described embodi- ments are only part of, rather than all of, the embodiments of the present invention. On the basis of the embodiments in the present invention, all the other embodiments obtained by those of ordinary skill in the art without making creative efforts will fall within the protection scope of the present invention. Therefore, the de- tailed descriptions of the embodiments of the present invention only represent the selected embodiments of the present invention, but are not intended to limit the claimed scope of the present in- vention.

In examples 1-6, a cumulative nutrient release rate is deter- mined by the following method:

Coated fertilizers with intact granules were randomly select- ed from coated fertilizers under sealed preservation, with 3 rep- licates for each treatment and 5 g for each replicate, each repli- cated coated fertilizer was accurately weighed (accurate to two decimal places} and then placed in a wide-mouth bottle (sealed with a rubber stopper) containing 100 ml of deionized water, the wide-mouth bottle was placed in a 25°C incubator, and samples were taken at regular intervals. After each sampling, all the leaching solution was poured out from the wide-mouth bottle, and 100 ml of deionized water was added again to continue culturing in the 25°C incubator. Urea was determined on a flow analyzer by the p- dimethylaminobenzaldehyde colorimetric method to obtain a cumula- tive nutrient release curve.

The determination results of the cumulative nutrient release rate in examples are as shown in Table 1.

Sampling Time (d) sone [Fs TT

It can be known from Table 1 that the fertilizer release rate of the six slow-release fertilizers showed a feature of being fast first and then slow. On one hand, because of the poor coating quality of some fertilizer core granules, such as incomplete coat- ing, the fertilizer would be released at a fast rate; on the other hand, the total nutrients in the fertilizer granules became less and less in the later period, and the daily release rate would de- crease correspondingly. It is quite obvious that after modifica- tion treatment, the tensile strength of a model film was signifi- cantly improved, which was also conducive to improving the coating quality and reducing an initial release rate of the slow-release fertilizer.

In examples 1-6, the data of the mechanical properties of the coating material are determined by the following method:

In accordance with the Specialized Standard of People’s Re- public of China (GB/T528-2009), the prepared model film was cut into a dumbbell shape by a cutter. The cutter size was (50x4 mm).

The determination was performed with an Instron3366 universal ma- terial testing machine, with automatic sample feeding, a tensile speed of 10mm/min and camera tracking. The test was operated at a temperature of 23°C and a humidity of 50%. The tensile strength of the film material was determined. Wherein the model film of the waterborne polyacrylate emulsion is prepared by the following method: a smooth and flat polytetrafluoroethylene plate was placed in a blast drying oven, adjusted to be level with a spirit level and a thin aluminum sheet, and then uniformly stirred coating lig- uid was slowly poured onto the polytetraflucrcethylene plate to freely stretch to form a film. The film was firstly placed in a 40°C dryer for 10 h, and then baked for another 24 h by adjusting temperature to 80°C to obtain the model film.

The determination results of the data of the mechanical prop- erties of the coating material in the examples are as shown in Ta- ble 2. 16.51% 0.41ab

The coated controlled-release fertilizer of the present in- vention includes inner fertilizer core granules and outer high- molecular coating materials, wherein the fertilizer core granules may be nitrogenous fertilizer, phosphate fertilizer, potassium fertilizer or other granular straight fertilizer, and also may be compound fertilizer containing multiple nutrients. In examples 1- 6, the fertilizer core granules are all urea.

Example 1

As a comparative example, this example described a method for preparing coated urea from unmodified waterborne polyacrylate, and a coated controlled-release urea prepared by the method. In this example, the method for preparing the coated controlled-release urea included the following specific steps:

Step (a): selection of mother coating solution:

100 g of waterborne polyacrylate emulsion was prepared by a water based process in a laboratory, with a solid content of (49+1)%.

Step (b): preparation of coating solution:

Distilled water in the same amount of the mother coating so- lution was slowly dripped into the mother coating solution under stirring, and the stirring was continued for 15 min after all the distilled water was dripped. The coating solution prepared by uni- form mixing should be used immediately after preparation, and it should be stored at a temperature of 5 °C-25°C for no longer than 4 nh.

Step (c): coating:

A bottom-spraying fluidized bed coating machine was used, such as LDP-3 fluidized bed coating machine produced by Jiangsu

Changzhou Jiafa Drying Equipment Factory, 500 g of urea was put into a coating cavity, and when the fertilizer was well fluidized, the coating solution was pumped into the coating cavity through a peristaltic pump and atomized to adhere to the surface of each fertilizer granule; a uniform film was gradually formed on the surface of the fertilizer granule after circulating up and down in the coating cavity, and finally the coated fertilizer was ob- tained. In the coating process by the fluidized bed, the coating parameters such as pumping speed, inlet air temperature, outlet air temperature and atomization pressure of the coating solution should be properly adjusted according to the properties of the coating solution, so that the water evaporation speed was con- sistent with the film formation reaction in the coating process, so as not to affect the film formation to result in a failure of coating. Using the machine, it took about 1.5-2 h to complete a coating process for every 0.5 kg of fertilizer.

A model film prepared by this example had the tensile strength of 13.21 MPa; after the coated urea prepared by this ex- ample was released in 25°C distilled water for one day, the cumu- lative release rate was 23.51%, and the cumulative nutrient re- lease rate reached 62.18% at D28.

The coated urea prepared by this example had an acceptable controlled-release effect, and there was necessity and possibility of modification.

According to Table 1, the cumulative release rate of ferti- lizer before 10d in this example satisfied the following curve: y=2.4266x+20.856 (R2=0.9982).

The cumulative release rate of fertilizer after 10d in this example satisfied the following curve: y=0.9225x+36.063 (R2=0.9971). where y is the cumulative release rate, and x is a number of release days.

It was predicted according to a mathematic model that an es- timated period was 69 days for the slow-release fertilizer in this example to release completely.

Example 2

This example described a method for preparing coated urea from 1% nano calcium carbonate modified waterborne polyacrylate emulsion, and a coated controlled-release fertilizer prepared by the method. In this example, the method for preparing the coated controlled-release fertilizer included the following specific steps:

Step (a): selection of mother coating solution: 100 g of waterborne polyacrylate emulsion was prepared by a water based process in a laboratory, with a solid content of (49t1)5.

Step (b): preparation of coating solution: 100 g of distilled water was slowly added to 0.5 g of nano calcium carbonate, ultrasonic treatment was performed for 30 min after stirring for 15 min, then the mixture was slowly dripped in- to the mother coating solution under stirring, and the stirring was continued for 15 min after all the mixture was dripped. The coating solution prepared by uniform mixing should be used immedi- ately after preparation, and it should be stored at a temperature of 5°C-25°C for no longer than 4 h.

Step (c): coating:

This step was the same as that in example 1.

A model film prepared by this example had the tensile strength of 13.65 MPa; after the coated urea prepared by this ex- ample was released in 25°C distilled water for one day, the cumu-

lative release rate was 21.23%, and the cumulative nutrient re- lease rate reached 57.72% at 28d. It was indicated that after the nano calcium carbonate was added, the tensile strength of the wa- terborne polymer material had certain increase, the nutrient re- lease rate was reduced, and the fertilizer's controlled-release performance of nutrients was improved to a certain degree.

According to Table 1, the cumulative release rate of ferti- lizer before 10d in this example satisfied the following curve: y=2.3445x+18.789 (R2=0.9973).

The cumulative release rate of fertilizer after 10d in this example satisfied the following curve: y=0.8579x+33.515 (R2=0.996}. where y is the cumulative release rate, and x is a number of release days.

It was predicted according to a mathematic model that an es- timated period was 77 days for the slow-release fertilizer in this example to release completely, and it was prolonged by 8 days as compared with that in example 1.

Example 3

This example described a method for preparing coated urea from 1% nano calcium carbonate modified waterborne polyacrylate emulsion dispersed by sodium hexametaphosphate, and a coated con- trolled-release fertilizer prepared by the method. In this exam- ple, the method for preparing the coated controlled-release ferti- lizer included the following specific steps:

Step (a): selection of mother coating solution: 100 g of waterborne polyacrylate emulsion was prepared by a water based process in a laboratory, with a solid content of (49+1) 3.

Step (b): preparation of coating solution: 100 g of distilled water and 0.5 g of sodium hexametaphos- phate were added to 0.5 g of nano calcium carbonate, then ultra- sonic treatment was performed for 30 min after stirring for 15 min, the mixture was slowly dripped into the mother coating solu- tion under stirring after the ultrasonic treatment, and the stir- ring was continued for 15 min after all the mixture was dripped.

The coating solution prepared by uniform mixing should be used im-

mediately after preparation, and it should be stored at a tempera- ture of 5°C-25°C for no longer than 4 h.

Step (cc): coating:

This step was the same as that in example 1.

A model film prepared by this example had the tensile strength of 16.18 MPa; after the coated urea prepared by this ex- ample was released in 25°C distilled water for one day, the cumu- lative release rate was 9.21%, and the cumulative nutrient release rate reached 37.14% at 28d. It was indicated that the nano calcium carbonate modified waterborne polyacrylate dispersed by sodium hexametaphosphate had a better effect than the waterborne poly- acrylate only added by nano calcium carbonate, and had greatly im- proved tensile strength and controlled-release performance of nu- trients as compared with the latter.

According to Table 1, the cumulative release rate of ferti- lizer before 10d in this example satisfied the following curve: y=1.516x+8.1547 (R2=0.9907).

The cumulative release rate of fertilizer after 10d in this example satisfied the following curve: y=0.7692x+15.805 (R%2=0.991). where y is the cumulative release rate, and x is a number of release days.

It was predicted according to a mathematic model that an es- timated period was 109 days for the slow-release fertilizer in this example to release completely, it was prolonged by 40 days as compared with that in example 1, and the slow-release fertilizer could meet the nutrient requirements of crops with a longer grow- ing season throughout the growing season.

Example 4

This example described a method for preparing coated urea from 1% nano calcium carbonate modified waterborne polyacrylate emulsion dispersed by polyethylene glycol, and a coated con- trolled-release fertilizer prepared by the method. In this exam- ple, the method for preparing the coated controlled-release ferti- lizer included the following specific steps:

Step (a): selection of mother coating solution: 100 g of waterborne polyacrylate emulsion was prepared by a water based process in a laboratory, with a solid content of (4911) %.

Step (b): preparation of coating solution: 100 g of distilled water and 0.08 g of polyethylene glycol were added to 0.5 g of nano calcium carbonate, then ultrasonic treatment was performed for 30 min after stirring for 15 min, the mixture was slowly dripped into the mother coating solution under stirring after the ultrasonic treatment, and the stirring was con- tinued for 15 min after all the mixture was dripped. The coating solution prepared by uniform mixing should be used immediately af- ter preparation, and it should be stored at a temperature of 5°C- 25°C for no longer than 4 h.

Step (c): coating:

This step was the same as that in example 1.

A model film prepared by this example had the tensile strength of 16.02 MPa; after the coated urea prepared by this ex- ample was released in 25°C distilled water for one day, the cumu- lative release rate was 10.24%, and the cumulative nutrient re- lease rate reached 40.21% at 28d. It was indicated that the nano calcium carbonate modified waterborne polyacrylate dispersed by polyethylene glycol had a better effect than the waterborne poly- acrylate only added by nano calcium carbonate, with an effect sim- ilar to that uses sodium hexametaphosphate, and had greatly im- proved tensile strength and controlled-release performance of nu- trients as compared with the waterborne polyacrylate only added by nano calcium carbonate.

According to Table 1, the cumulative release rate of ferti- lizer before 10d in this example satisfied the following curve: y=1.68162+9.3159 (R2=0.985).

The cumulative release rate of fertilizer after 10d in this example satisfied the following curve: y=0.8037x+18.233 (R%2=0.9886). where y is the cumulative release rate, and x is a number of release days.

It was predicted according to a mathematic model that an es- timated period was 101 days for the slow-release fertilizer in this example to release completely, it was prolonged for 32 days as compared with that in example 1, and the slow-release fertiliz- er could meet the nutrient requirements of crops with a longer growing season throughout the growing season.

Example 5

This example described a method for preparing coated urea us- ing 1% nano calcium carbonate modified waterborne polyacrylate emulsion dispersed by sodium hexametaphosphate coupled with poly- ethylene glycol, and a coated controlled-release fertilizer pre- pared by the method. In this example, the method for preparing the coated controlled-release fertilizer included the following spe- cific steps:

Step (a): selection of mother coating solution: 100 g of waterborne polyacrylate emulsion was prepared by a water based process in a laboratory, with a solid content of (49+1)5%.

Step (b): preparation of coating solution: 100 g of distilled water, 0.03 g of sodium hexametaphosphate and 0.03 g of polyethylene glycol were added to 0.5 g of nano cal- cium carbonate, then ultrasonic treatment was performed for 30 min after stirring for 15 min, the mixture was slowly dripped into the mother coating solution under stirring after the ultrasonic treat- ment, and the stirring was continued for 15 min after all the mix- ture was dripped. The coating solution prepared by uniform mixing should be used immediately after preparation, and it should be stored at a temperature of 5°C-25°C for no longer than 4 h.

Step (c): producing the coated fertilizer:

This step was the same as that in example 1.

A model film prepared by this example had the tensile strength of 16.92 MPa; after the coated urea prepared by this ex- ample was released in 25°C distilled water for one day, the cumu- lative release rate was 8.62%, and the cumulative nutrient release rate reached 31.87% at 28d. It was indicated that the nano calcium carbonate modified waterborne polyacrylate simultaneously using the two dispersing agents of sodium hexametaphosphate and polyeth- ylene glycol had a better effect than the waterborne polyacrylate using the two dispersing agents separately, moreover, the addition amounts were significantly reduced as compared with the conditions when they were added separately, and both the tensile strength and the controlled-release performance of nutrients were greatly im- proved.

According to Table 1, the cumulative release rate of ferti- lizer before 10d in this example satisfied the following curve: y=1.28x+7.5022 (R2=0.9932}.

The cumulative release rate of fertilizer after 10d in this example satisfied the following curve: y=0.6366x+14.405 (R2=0.9857). where y is the cumulative release rate, and x is a number of release days.

It was predicted according to a mathematic model that an es- timated period was 134 days for the slow-release fertilizer in this example to release completely, it was prolonged for 65 days as compared with that in example 1, and the slow-release fertiliz- er could meet the nutrient requirements of crops with a longer growing season throughout the growing season.

Example 6

This example described a method for preparing coated urea from 3% nano calcium carbonate modified waterborne polyacrylate emulsion dispersed by sodium hexametaphosphate and polyethylene glycol, and a coated controlled-release fertilizer prepared by the method. In this example, the method for preparing the coated con- trolled-release fertilizer included the following specific steps:

Step (a): selection of mother coating solution: 100 g of waterborne polyacrylate emulsion was prepared by a water based process in a laboratory, with a solid content of (49+1)%.

Step (b): preparation of coating solution: 100 g of distilled water, 0.03 g of sodium hexametaphosphate and 0.03 g of polyethylene glycol were added to 1.5 g of nano cal- cium carbonate, then ultrasonic treatment was performed for 30 min after stirring for 15 min, the mixture was slowly dripped into the mother coating solution under stirring after the ultrasonic treat- ment, and the stirring was continued for 15 min after all the mix- ture was dripped. The coating solution prepared by uniform mixing should be used immediately after preparation, and it should be stored at a temperature of 5°C-25°C for no longer than 4 h.

Step (cj): coating:

This step was the same as that in example 1.

A model film prepared by this example had the tensile strength of 16.51 MPa; after the fertilizer was released in 25°C distilled water for one day, the cumulative release rate was 13.03%, and the cumulative nutrient release rate reached 45.79% at 28d.

According to Table 1, the cumulative release rate of ferti- lizer before 10s in this example satisfied the following curve: y=1.8906x+11.377 (R2=0.9991).

The cumulative release rate of fertilizer after 10d in this example satisfied the following curve: y=0.8711x+21.707 (R2=0.997). where y is the cumulative release rate, and x is a number of release days.

It was predicted according to a mathematic model that an es- timated period was 89 days for the slow-release fertilizer in this example to release completely, and it was prolonged by 20 days as compared with that in example 1.

The experiments show that despite the function of the dis- persing agents, a higher addition amount of nano calcium carbonate is not always better for the modification effect on the waterborne polyacrylate; an over-high addition amount will lead to a phenome- non of certain aggregation to reduce the dispersion effect in the base polymer, thereby resulting in a decrease in the modification effect. It can be shown that the amount of nano calcium carbonate for modification and the pretreatment method are the crucial fac- tors for the success of modification.

Those described above are only the preferred embodiments of the present invention. It should be noted that these preferred em- bodiments should not be deemed to limit the present invention, and the protection scope of the present invention should be subject to the scope limited by the claims. For those of ordinary skill in the art, a number of improvements and modifications may be made without departing from the principle and scope of the present in- vention, and these improvements and modifications should also be deemed to fall within the protection scope of the present inven- tion,

Claims

CONCLUSIONS

A controlled release coated fertilizer comprising inner fertilizer core granules and outer high molecular weight coating materials, wherein the high molecular weight coating material is nanocalcium carbonate modified waterborne polyacrylate emulsion solid.

The controlled release coated fertilizer according to claim 1, wherein the nanocalcium carbonate modified waterborne polyacrylate emulsion is prepared by the following steps: slowly adding an aqueous dispersion system of nanocalcium carbonate to the waterborne polyacrylate emulsion, then stirring thoroughly, and sieve the mixture.

A coated controlled release fertilizer according to claim 2, wherein a solute in the aqueous dispersion system of nanocalcium carbonate comprises nanocalcium carbonate, and also comprises sodium hexametaphosphate and/or polyethylene glycol, and a solvent is deionized water.

The controlled release coated fertilizer of claim 3, wherein the aqueous nanocalcium carbonate dispersion system comprises the following components, based on parts by weight: 0.005 to 2.5 parts nanocalcium carbonate, 0.01 to 1 part sodium hexametaphosphate, 0.01 to 0.5 parts 3 parts polyethylene glycol and 100 parts deionized water.

The controlled release coated fertilizer of claim 3, wherein an added amount of the solute in the aqueous nanocalcium carbonate dispersion system constitutes 0.013 to 5% of a dry mass of the water-based polyacrylate.

A coated controlled release fertilizer according to claim 3 or 4, wherein the aqueous dispersion system of nanocalcium carbon

naat is prepared by the following steps: adding the nanocalcium carbonate to the deionized water, then adding the sodium hexametaphosphate and/or the polyethylene glycol, and then stirring and mixing the solution well to obtain the aqueous dispersion system of the nanocalcium carbonate.

The controlled release coated fertilizer according to claim 6, wherein the stirring is carried out with a magnetic stirrer for 15 minutes, and the mixing is carried out with ultrasonic treatment for 30 minutes.

A coated controlled release fertilizer according to claim 1, wherein a dry mass of the modified high molecular weight coating material constitutes 2.5% to 15% of the coated controlled release fertilizer.

The controlled release coated fertilizer according to claim 1, wherein the water-based polyacrylate emulsion solid is obtained by treatment in an oven at 60°C for 8 hours.

A method for preparing the coated controlled-release fertilizer according to any one of claims 1 to 9, comprising the following steps: S1: preparation of aqueous dispersion system of nanocalcium carbonate, adding nanocalcium carbonate to deionized water, then sodium hexaphosphate or /and add polyethylene glycol, stir the solution for 15 min and perform ultrasonic treatment for 30 min to obtain the aqueous dispersion system of nanocalcium carbonate; S2: Preparation of modified water-based polyacrylate emulsion Take water-based polyacrylate emulsion, then slowly add the aqueous dispersion system of nanocalcium carbonate prepared in S1 to the water-based polyacrylate emulsion, stir the mixture with a magnetic stirrer for 15 minutes, and then sieve the mixture with a 200 mesh sieve for later usage; and

S3: coating treatment taking fertilizer core granules and the nanccalcium carbonate modified water-based polyacrylate emulsion prepared in S2, producing a coated fertilizer with a coating machine, and treating the produced coated fertilizer in an oven at 60°C for 8 hours.