Controlled-release fertilizers

Abstract

The present invention relates to a controlled-release fertilizer, including: a photodegradable capsule including a binder resin containing a polyolefin and an ethylene vinyl acetate copolymer, and a photocatalytic composite in which a (co)polymer including at least one repeating unit selected from the group consisting of an ethylene repeating unit and a vinyl acetate repeating unit is bonded to the surface or inside of agglomerates of inorganic fine particles; and a fertilizer contained in a space surrounded by the photodegradable capsule.

Claims

1. A controlled-release fertilizer, comprising: a photodegradable capsule and a fertilizer encapsulated by the photodegradable capsule, the photodegradable capsule including a binder resin containing a polyolefin and an ethylene vinyl acetate copolymer, and a photocatalytic composite dispersed in the binder resin, wherein the photocatalytic composite comprises agglomerates of inorganic fine particles and a (co)polymer including at least one repeating unit selected from the group consisting of an ethylene repeating unit and a vinyl acetate repeating unit, the (co)polymer bonded to a surface or inside of the agglomerates of the inorganic fine particles, and wherein the agglomerates of inorganic fine particles have a cross-sectional diameter of 0.05 μm to 0.5 μm.

2. The controlled-release fertilizer of claim 1, further comprising a filler dispersed in the binder resin.

3. The controlled-release fertilizer of claim 2, wherein the filler is at least one selected from the group consisting of talc, bentonite, loess, diatomaceous earth, silica, aluminosilicate, kaolinite, starch, and carbon.

4. The controlled-release fertilizer of claim 2, comprising the filler in an amount of 25 to 75% by weight based on the total weight of the photodegradable capsule.

5. The controlled-release fertilizer of claim 1, wherein the photodegradable capsule has a decomposition rate of the binder resin of 40% or more, determined as a change in weight of the photodegradable capsule before and after irradiation with light having a wavelength of 300 to 800 nm at an intensity of 400 W/m.sup.2 at a temperature of 50° C. for 224 hours.

6. The controlled-release fertilizer of claim 1, wherein the inorganic fine particles include a primary particle having a cross-sectional diameter of 5 to 50 nm.

7. The controlled-release fertilizer of claim 1, wherein the cross-sectional diameter of the agglomerates of inorganic fine particles is 0.05 μm to 0.330 μm.

8. The controlled-release fertilizer of claim 1, wherein the inorganic fine particles are titanium dioxide (TiO.sub.2), zinc oxide (ZnO), or a mixture thereof.

9. The controlled-release fertilizer of claim 1, wherein the photocatalytic composite contains 1 to 500 parts by weight of the (co)polymer including at least one repeating unit selected from the group consisting of an ethylene repeating unit and a vinyl acetate repeating unit based on 100 parts by weight of the agglomerates of inorganic fine particles.

10. The controlled-release fertilizer of claim 1, comprising 0.1 to 8 parts by weight of the agglomerates of inorganic fine particles based on 100 parts by weight of the binder resin.

11. The controlled-release fertilizer of claim 1, wherein the binder resin comprises the polyolefin and the ethylene vinyl acetate copolymer in a weight ratio of 1:1 to 6:1.

12. The controlled-release fertilizer of claim 1, wherein the polyolefin is at least one selected from the group consisting of a high-density or low-density polyethylene, a linear low-density polyethylene, a polypropylene, an ethylene-propylene copolymer, a polybutene, a butene-ethylene copolymer, and a butene-propylene copolymer.

13. The controlled-release fertilizer of claim 1, wherein the ethylene vinyl acetate copolymer contains 1 to 45% by weight of the vinyl acetate repeating unit.

14. The controlled-release fertilizer of claim 1, wherein the (co)polymer including at least one repeating unit selected from the group consisting of an ethylene repeating unit and a vinyl acetate repeating unit includes an ethylene vinyl acetate copolymer.

15. The controlled-release fertilizer of claim 1, wherein the fertilizer is a granular fertilizer.

16. The controlled-release fertilizer of claim 1, comprising the fertilizer in an amount of 200 to 3000 parts by weight based on 100 parts by weight of the photodegradable capsule.

17. A method for preparing the controlled-release fertilizer of claim 1, comprising the steps of: dispersing the inorganic fine particles and the (co)polymer including at least one repeating unit selected from the group consisting of an ethylene repeating unit and a vinyl acetate repeating unit in an organic solvent to prepare a dispersion solution of the photocatalytic composite in which the (co)polymer is bonded to the surface or inside of the agglomerates of inorganic fine particles; mixing the polyolefin, the ethylene vinyl acetate copolymer, the dispersion solution of the photocatalytic composite, and optionally a filler to prepare a coating composition; and coating the fertilizer with the coating composition so as to prepare the controlled-release fertilizer.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows SEM images of agglomerates of fine particles in the photocatalytic composite included in the controlled-release fertilizer of Example 1 and agglomerates of fine particles included in the coated fertilizer of Comparative Example 2.

(2) FIG. 2 schematically shows the photodegradation mechanism of the controlled-release fertilizer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(3) The present invention will be described in more detail by way of examples shown below. However, these examples are given for illustrative purposes only, and the scope of the invention is not intended to be limited to or by these examples.

Examples: Preparation of Controlled-Release Fertilizer

Examples 1 to 3

(1) Preparation of Photocatalytic Composite

(4) 1.5 g of an ethylene vinyl acetate copolymer [MI (melt index, 190° C., load of 2.16 kg, ASTM D1238): about 1.8 g/10 min, D (density): 0.94 g/cm.sup.3, vinyl acetate content at about 20 wt %, melting point of 85° C.] was dissolved in tetrachloroethylene, to which TiO.sub.2 (average particle diameter of primary particle: 21 nm) was mixed in an amount shown in Table 1 below, and subjected to sonication to prepare a dispersion solution of a photocatalytic composite coated with the ethylene vinyl acetate copolymer.

(2) Preparation of Controlled-Release Fertilizer

(5) The thus-prepared dispersion solution of the photocatalytic composite, polyethylene [LDPE, MI (melt index, 190° C., load of 2.16 kg, ASTM D1238): about 8 g/10 min, D (density): 0.925 g/cm.sup.3], an ethylene vinyl acetate copolymer [MI (melt index, 190° C., load of 2.16 kg, ASTM D1238): about 1.8 g/10 min, D (density): 0.94 g/cm.sup.3, vinyl acetate content of about 20 wt %, melting point of 85° C.], and talc were used in an amount shown in Table 1 below, and were uniformly stirred and mixed with tetrachloroethylene at 100° C. in the composition ratio shown in Table 1 below to prepare a coating solution having a solid concentration of 5 wt %.

(6) Then, the coating solution was applied to the nitrogen fertilizer particles using a fluid bed drier to prepare a controlled-release coated fertilizer (Examples 1 to 3).

Comparative Examples 1 and 2: Preparation of Coated Fertilizer

Comparative Example 1

(7) Polyethylene [LDPE, MI (melt index, 190° C., load of 2.16 kg, ASTM D1238): about 8 g/10 min, D (density): 0.925 g/cm.sup.3], an ethylene vinyl acetate copolymer [MI (melt index, 190° C., load of 2.16 kg, ASTM D1238): about 1.8 g/10 min, D (density): 0.94 g/cm.sup.2, vinyl acetate content of about 20 wt %, melting point of 85° C.], and talc were used in an amount shown in Table 1 below, and were uniformly stirred and mixed with tetrachloroethylene at 100° C. in the composition ratio shown in Table 1 below to prepare a coating solution having a solid concentration of 5 wt %.

(8) Then, the coating solution was applied to the nitrogen fertilizer particles using a fluid bed drier to prepare a coated fertilizer (Comparative Example 1).

Comparative Example 2

(9) TiO.sub.2 (average particle diameter of primary particle: 21 nm), polyethylene [LDPE, MI (melt index, 190° C., load of 2.16 kg, ASTM D1238): about 8 g/10 min, D (density): 0.925 g/cm.sup.3], ethylene vinyl acetate copolymer [MI (melt index, 190° C., load of 2.16 kg, ASTM D1238): about 1.8 g/10 min, D (density): 0.94 g/cm.sup.3, vinyl acetate content of about 20 wt %, melting point of 85° C.], and talc were used in an amount shown in Table 1 below, and were uniformly stirred and mixed with tetrachloroethylene at 100° C. in the composition ratio shown in Table 1 below to prepare a coating solution having a solid concentration of 5 wt %.

(10) Then, the coating solution was applied to the nitrogen fertilizer particles using a fluid bed drier to prepare a coated fertilizer (Comparative Example 2).

EXPERIMENTAL EXAMPLE

Experimental Example 1: Comparison Test of Photodegradation Property

(11) 5 g of each of the controlled-release fertilizers of the examples and the coated fertilizers of the comparative examples was taken, and a pinhole was made with a needle one by one to completely release the fertilizers. Then, the degradation evaluation was carried out with the remaining coating films.

(12) Light having a wavelength of 300 nm to 800 nm was irradiated to the coating film at an intensity of 400 w/m.sup.2 at a temperature of 50° C. using Suntest CPS+ equipment (ATLAS).

(13) Then, the decomposition rate of the binder resin, which could be derived from the change in weight of the coating film during irradiation of light for 224 hours under the above conditions, was determined by the following General Formula 1, and the results are shown in Table 1 below.

(14) $\begin{array}{cc}\mathrm{Decomposition}\mathrm{rate}\mathrm{of}\mathrm{binder}\mathrm{resin}=\frac{\begin{array}{c}\mathrm{Change}\mathrm{in}\mathrm{weight}\mathrm{of}\mathrm{coating}\\ \mathrm{film}\mathrm{after}\mathrm{UV}\mathrm{irradiation}\end{array}}{\begin{array}{c}\mathrm{Weight}\mathrm{of}\mathrm{resin}\mathrm{in}\mathrm{the}\mathrm{coating}\mathrm{film}\\ \mathrm{before}\mathrm{UV}\mathrm{irradiation}\left(\mathrm{LDPE}+\mathrm{EVA}\right)\end{array}}\times 100\%& \left[\mathrm{General}\mathrm{Formula}1\right]\end{array}$

(15) TABLE-US-00001 TABLE 1 Comparative Comparative Example 1 Example 2 Example 1 Example 2 Example 3 Polyethylene (LDPE) 30 g 30 g 30 g 30 g 29 g EVA copolymer 13 g 13 g 13 g 13 g  8 g TALC 57 g 57 g 57 g 57 g 63 g TiO.sub.2 0 0.86 g   0.86 g   0.43 g   0.75 g   TiO.sub.2 dispersion — X ◯ ◯ ◯ treatment (EVA 1.5 g) (EVA 1.5 g) (EVA 1.5 g) decomposition rate 0 33.7 ± 15 67.4 ± 3 58.7 ± 3 42.5 ± 3 of binder resin (%)

(16) As shown in Table 1, it was confirmed that the controlled-release fertilizers of the examples showed a decomposition rate of the binder resin of 40% or more, or 55% or more, when irradiated with light having a wavelength of 300 to 800 nm at an intensity of 400 w/m.sup.2 for 224 hours. In contrast, it was also confirmed that the coated fertilizers of the comparative examples showed a decomposition rate of the binder resin of 35% or less.

Experimental Example 2: Evaluation of Releasing Property of Fertilizer

(17) 12.5 g of each of the controlled-release fertilizers of the examples and the coated fertilizer of the comparative examples was added to 250 ml of distilled water to prepare a sample. Then, 1 ml of the liquid was taken from the sample at 25° C. on different days, and the nitrogen content in the sample was analyzed (Kjeltec Analyzer 2300) to measure the amount of the fertilizer released.

(18) TABLE-US-00002 TABLE 2 Day on which the nitrogen release was evaluated (release rate %) Day 1 Day 10 Day 20 Day 30 Day 50 Comparative 4 31 55 69 90 Example 1 Example 1 3 21 39 51 69

(19) As shown in Table 2, it was confirmed that the controlled-release fertilizers of the comparative example 1 exhibited a release rate of 50% or more after 20 days and a release rate of 90% or more after 50 days. In contrast, it was also confirmed that the coated fertilizers of the example 1 showed a release rate of less than 40% after 20 days and a release rate of less than 70% or less even at day 50.

Experimental Example 3: Measurement of z-Average Dispersion Particle Size of TiO.SUB.2

(20) The z-average dispersion particle size of TiO.sub.2 in the dispersion solution of the photocatalytic composite of Example 1 and the dispersion solution containing TiO.sub.2 of Comparative Example 2 was measured using a dynamic light scattering instrument (Malvern Zetasizer Nano ZS90). The results are shown in Table 3.

(21) TABLE-US-00003 TABLE 3 z-average dispersion particle size of TiO.sub.2 Example 1 Comparative Example 2 z-average dispersion particle 330 1.7 to 3.2 × 10.sup.4 size of TiO.sub.2 (nm)

(22) As shown in Table 3, the dispersion solution of the photocatalytic composite of Example 1 had a z-average dispersion particle size of about 300 nm, confirming that TiO.sub.2 particles used were homogeneously dispersed and that agglomerates of inorganic fine particles having a relatively small average particle size were formed. This can also be confirmed through the SEM image (top) of FIG. 1, which shows the photocatalytic composite of Example 1 using a SEM (Hitachi, S-4800).

(23) In contrast, the dispersion solution containing TiO.sub.2 of Comparative Example 2 had a z-average dispersion particle size of about 10,000 nm, confirming that agglomerates of inorganic fine particles having a relatively large average particle size were formed. This can also be confirmed through the SEM image of FIG. 1, which shows the agglomerates of fine particles included in the coated fertilizer of Comparative Example 2.