PLA / PHA Biodegradable Coatings for Seeds, Fertilizers and Pest Control Agents

Abstract

A granular composition for agricultural use is disclosed. The granular composition is comprised of a plurality of granules having a biodegradable coating applied thereon. The granules are selected from the group consisting of seeds, fertilizers, and pesticides. The biodegradable coating is comprised of polylactic acid and polyhydroxyalkanoate. Methods for making the coated granular composition and for controlled release of the granular material into a field are also disclosed.

Description

[Technical field]

[0001] The present disclosure relates to biodegradable polymeric compositions. More particularly, the present disclosure relates to biodegradable coatings for seeds and fertilizers comprised of polylactic acids (PLA) and polyhydroxyalkanoates (PHAs). [Background technology]

[0002] Plants take up nutrients at different rates based on environmental conditions, but the most important period for nutrient uptake is during the early development of the plant. Nutrients must be sufficient during this period. However, excessive nitrogen uptake can overstimulate vegetative growth and delay crop maturity. Thus, the timing of nutrient uptake is important to maximize cropland yield.

[0003] To address these challenges, controlled release fertilizers (CRFs) have been produced, where the fertilizer is encapsulated in a petroleum-based polymer coating that slowly releases the fertilizer into the soil. Thus, nutrients can be delivered at a pace appropriate to the metabolic needs of the plant. However, changes in temperature, moisture, or soil biological activity can unpredictably alter this rate, negatively impacting crop yields by providing the wrong amount of nutrients at the wrong time. Thus, to date, commercial application of CRFs has been limited by a lack of data on the kinetics of release in various environmental conditions. Furthermore, the petroleum-based coating applied to the fertilizer is not environmentally friendly and may persist in the environment for years after fertilization.

[0004] Thus, it would be desirable to provide new controlled release fertilizer formulations that are not harmful to the environment and that do not persist after the growing season, and that have more predictable and controllable fertilizer release rates. Summary of the Invention

[0005] These and other needs are met by a granular composition for agricultural use in accordance with the present disclosure. According to one embodiment, the granular composition is comprised of a plurality of granules having a biodegradable coating applied thereon. The granules are in turn comprised of a material selected from the group consisting of seeds, fertilizers, and pesticides. The biodegradable coating is comprised of about 5 weight percent to about 75 weight percent polylactic acid, and about 25 weight percent to about 95 weight percent polyhydroxyalkanoate.

[0006] In certain embodiments, the granules of the composition preferably comprise seeds, while in other embodiments, the granules of the composition preferably comprise fertilizers, more preferably urea-based fertilizers.

[0007] As noted, the biodegradable coating includes both polylactic acid (PHA) and polyhydroxyalkanoate (PHA). In certain embodiments, the biodegradable coating preferably includes polylactic acid having a weight average molecular weight of about 10,000 to about 250,000 Daltons. Also, in certain embodiments, the biodegradable coating preferably includes polyhydroxyalkanoate having a weight average molecular weight of about 50,000 to about 2.5 million Daltons.

[0008] In a more preferred embodiment, the biodegradable coating is comprised of about 10 weight percent to about 50 weight percent polylactic acid and about 50 weight percent to about 90 weight percent polyhydroxyalkanoate.

[0009] In certain embodiments, it is preferred that the polyhydroxyalkanoate in the biodegradable coating is composed of from about 70 mole percent to about 99 mole percent monomer residues of 3-hydroxybutyrate, and from about 1 mole percent to about 30 mole percent monomer residues of 3-hydroxyhexanoate.

[0010] In some embodiments, the polyhydroxyalkanoate in the biodegradable coating can be composed of monomer residues of three or more hydroxyalkanoates, each having from 5 to 22 carbon atoms.

[0011] In a preferred embodiment, the particulates preferably have an average particle size of from about 1 mm to about 25 mm before coating.

[0012] In more particular embodiments, the biodegradable coating preferably comprises a continuous phase of polylactic acid having uniformly dispersed therein globules of polyhydroxyalkanoate, wherein the globules have an average size of from about 2 nm to about 10 microns.

[0013] In another aspect, the disclosure provides a method for making a coated granular composition. In one embodiment, the method includes mixing polylactic acid, polyhydroxyalkanoate, and optionally a solvent at a temperature of about 25° C. to about 180° C. to provide a coating mixture. The coating mixture is then applied to the exterior surface of a plurality of granules. The method also includes solidifying the coating mixture to create a biodegradable coating on the exterior surface of the plurality of granules. The granules coated by this method are comprised of a material selected from the group consisting of seeds, fertilizers, and pesticides. Once solidified, the biodegradable coating is comprised of a continuous phase of polylactic acid having globules of polyhydroxyalkanoate uniformly dispersed therein. The globules have an average size of about 2 nm to about 10 microns.

[0014] In certain embodiments of this method, the biodegradable coating is temporarily annealed at 150-170° C. for a few seconds after application, or the biodegradable coating is exposed to solvent vapor after coating.

[0015] In certain aspects of this method, the granules of the composition preferably comprise seeds. In other aspects of this method, the granules of the composition preferably comprise fertilizer, more preferably a urea based fertilizer.

[0016] In certain embodiments of this method, the biodegradable coating preferably comprises a polylactic acid having a weight average molecular weight of about 10,000 to about 250,000 Daltons, and in certain embodiments of this method, the biodegradable coating preferably comprises a polyhydroxyalkanoate having a weight average molecular weight of about 50,000 to about 2.5 million Daltons.

[0017] In a more preferred embodiment of this method, the biodegradable coating is preferably comprised of about 10 weight percent to about 50 weight percent polylactic acid and about 50 weight percent to about 90 weight percent polyhydroxyalkanoate.

[0018] In certain aspects of this method, the polyhydroxyalkanoate in the biodegradable coating is preferably composed of about 70 mole percent to about 99 mole percent monomer residues of 3-hydroxybutyrate and about 1 mole percent to about 30 mole percent monomer residues of 3-hydroxyhexanoate.

[0019] In some aspects of this method, the polyhydroxyalkanoate in the biodegradable coating is The copolymer may be composed of monomeric residues of three or more hydroxyalkanoates, each having from 5 to 22 carbon atoms.

[0020] In a preferred embodiment of this method, the particulates preferably have an average particle size of from about 1 mm to about 25 mm before coating.

[0021] In a further aspect, the present disclosure provides a method for controlled release of granular material. According to one embodiment, the method includes the initial step of preparing a granular composition comprised of a plurality of granules having a biodegradable coating applied thereon. The granules are in turn comprised of a material selected from the group consisting of seeds, fertilizers, and pesticides. The biodegradable coating is comprised of about 5 weight percent to about 75 weight percent polylactic acid, and about 25 weight percent to about 95 weight percent polyhydroxyalkanoate.

[0022] In a second step, the granular composition is spread onto the soil of the plot.

[0023] Exposing the soil of the plot, and the granular composition dispersed therein, to moisture causes at least the polyhydroxyalkanoate in the biodegradable coating to be dissolved. Decomposition of the polyhydroxyalkanoate leads to the formation of multiple pathways in the biodegradable coating through which the granular material can be released into the soil.

[0024] In a more preferred embodiment of this method, the biodegradable coating is preferably comprised of about 10 weight percent to about 50 weight percent polylactic acid and about 50 weight percent to about 90 weight percent polyhydroxyalkanoate.

[0025] In certain aspects of this method, the polyhydroxyalkanoate in the biodegradable coating is preferably composed of about 70 mole percent to about 99 mole percent monomer residues of 3-hydroxybutyrate and about 1 mole percent to about 30 mole percent monomer residues of 3-hydroxyhexanoate.

[0026] In some aspects of this method, the polyhydroxyalkanoate in the biodegradable coating can be composed of monomeric residues of three or more hydroxyalkanoates, each having from 5 to 22 carbon atoms, for example, in some cases the polyhydroxyalkanoate can be composed of monomeric residues of 3-hydroxybutyrate, 3-hydroxyvalerate, and 3-hydroxyhexanoate.

[0027] In other cases, the polyhydroxyalkanoate can be composed of at least three monomer residues selected from the group consisting of monomer residues of 3-hydroxybutyrate, 4-hydroxybutyrate, 3-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyoctanoate, and 3-hydroxydecanoate.

[0028] In a particular embodiment of this method, the biodegradable coating preferably comprises a continuous phase of polylactic acid having uniformly dispersed therein globules of polyhydroxyalkanoate, wherein the globules have an average size of from about 2 nm to about 10 microns.

[0029] In certain embodiments of this method, after exposure to soil moisture in the plot for about 21 days, at least about 10 to about 50 percent of the polyhydroxyalkanoate in the biodegradable coating has begun to degrade or has degraded. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] granular composition In accordance with the present disclosure, there is provided a granular composition for agricultural use, the granular composition comprising a plurality of granules having a biodegradable coating applied to the granules.

[0031] Granules can be composed of various materials that are agriculturally useful substances.Generally, granules can be composed of materials selected from the group consisting of seeds, fertilizers and pesticides.It may be preferred that the granules of the composition are composed of seeds.Examples of seeds that can be used in the granule composition include grass seeds, fruit and nut seeds, and vegetable seeds.

[0032] In another embodiment, the granules of the composition are preferably comprised of a fertilizer. Fertilizers that may be provided as coated granular compositions according to the present disclosure include nitrogen-, phosphorus- and potassium-based fertilizers. In a particularly preferred example, the fertilizer may be a urea-based fertilizer.

[0033] In still other cases, the granules may be composed of pesticides. In general, any solid pesticide material may be provided as a coated granular composition according to the present disclosure, including inorganic pesticides, organic pesticides, and biological pesticides. Examples of such pesticides include, but are not limited to, pesticides including ammonium nitrate, potassium chloride, sodium phosphate, calcium sulfate, chlorpyrifos, metribuzin, chlorimuron ethyl, atrazine, S-metolachlor, cyanazine, viral biological pesticides, and bacterial biological pesticides.

[0034] The size of the granules will vary depending on the nature of the granule material. Generally, the granules will have an average particle size of about 1 mm to about 25 mm before coating. For seeds, more specifically, the granules can preferably have an average particle size of about 1 mm to about 25 mm before coating. For fertilizers, the granules can preferably have an average particle size of about 1 mm to about 8.5 mm before coating. For pesticides, the granules can preferably have an average particle size of about 1 mm to about 10 mm before coating.

[0035] In accordance with the present disclosure, a biodegradable coating containing both polylactic acid (PHA) and polyhydroxyalkanoates (PHA's) is applied to the particulates.

[0036] While the exact ratio of PLA and PHA's in the biodegradable coating can vary somewhat, the coating generally is comprised of about 5 weight percent to about 75 weight percent polylactic acid, and about 25 weight percent to about 95 weight percent polyhydroxyalkanoate. More preferably, the biodegradable coating is comprised of about 10 weight percent to about 50 weight percent polylactic acid, and about 50 weight percent to about 90 weight percent polyhydroxyalkanoate.

[0037] The molecular weight ranges for the PLAs and PHAs can also vary somewhat. In certain embodiments, it is preferred that the biodegradable coating comprises a polylactic acid having a weight average molecular weight of about 10,000 to about 250,000 Daltons. Additionally, in some instances, it is preferred that the biodegradable coating comprises a polyhydroxyalkanoate having a weight average molecular weight of about 50,000 to about 2.5 million Daltons.

[0038] Further examples include monomer residues of 3-hydroxybutyrate, 4-hydroxybutyrate, 3-hydroxyvalerate, 3-hydroxyhexanoate, and the like. There are many forms of polyhydroxyalkanoate, including monomeric residues of 3-hydroxybutyrate, hydroxyoctanoate, and hydroxydecanoate. Preferably, the polyhydroxyalkanoate in the biodegradable coating is composed of about 70 mole percent to about 99 mole percent monomeric residues of 3-hydroxybutyrate, and about 1 mole percent to about 30 mole percent of 3-hydroxyhexanoate.

[0039] In some aspects of this method, the polyhydroxyalkanoate in the biodegradable coating can be composed of monomeric residues of three or more hydroxyalkanoates, each having from 5 to 22 carbon atoms, for example, in some cases the polyhydroxyalkanoate can be composed of monomeric residues of 3-hydroxybutyrate, 3-hydroxyvalerate, and 3-hydroxyhexanoate.

[0040] In other cases, the polyhydroxyalkanoate can be composed of at least three monomer residues selected from the group consisting of monomer residues of 3-hydroxybutyrate, 4-hydroxybutyrate, 3-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyoctanoate, and 3-hydroxydecanoate.

[0041] In some embodiments, the biodegradable coating may contain relatively small amounts (typically 0.3 to 10% by weight) of other additives, such as polyvinyl acetate, clay, calcium, talc, polysaccharides (such as starch), pentaerythritol, and sulfur.

[0042] Importantly, when the applied biodegradable coating of the present disclosure is examined under magnification, the biodegradable coating preferably comprises a continuous phase of polylactic acid having dispersed therein globules of polyhydroxyalkanoate, preferably having an average size of from about 2 nm to about 10 microns.

[0043] As used herein, the term "biodegradable" describes a material that can be decomposed or broken down by microorganisms or organisms in the soil. Generally, it is preferred that at least about 50 percent by weight of the coating be made up of materials that are biodegradable. More preferably, 100 percent of the materials that make up the coating are biodegradable.

[0044] It is also preferred that the biodegradable coating contain less than about 1.0 weight percent polyurethane, and more preferably, the biodegradable coating is completely free of polyurethane.

[0045] Preparation of granular composition In another aspect, the disclosure provides a method for making a coated granular composition. In one embodiment, the method includes mixing polylactic acid, polyhydroxyalkanoate, and optionally a solvent at a temperature of about 25° C. to about 180° C. to provide a coating mixture. The coating mixture is then applied to the exterior surface of a plurality of granules. The method also includes solidifying the coating mixture to produce a biodegradable coating on the exterior surface of the plurality of granules. Granules coated according to this method are comprised of a material selected from the group consisting of seeds, fertilizers, and pesticides. Once solidified, the biodegradable coating is comprised of a continuous phase of polylactic acid having globules of polyhydroxyalkanoate uniformly dispersed therein. These globules have an average size of about 2 nm to about 10 microns.

[0046] In certain embodiments of this method, the biodegradable coating is temporarily annealed at 150-170° C. for a few seconds after application, or the biodegradable coating is dissolved after coating. exposed to solvent vapors.

[0047] In certain aspects of this method, the granules of the composition preferably comprise seeds. In other aspects of this method, the granules of the composition preferably comprise fertilizer, more preferably urea-based fertilizer.

[0048] Uses of the granular composition The coated granular compositions of the present disclosure are suitable for use for agricultural purposes. In particular, the granular compositions of the present disclosure can be used to provide a controlled release method for granular material.

[0049] According to this method, a coated granular composition is provided as discussed above, where again the granular material may be comprised of a material selected from the group consisting of seeds, fertilizers and pesticides.

[0050] The granular composition is spread over the plot of soil to be treated with the composition. The application rate can vary depending on the nature of the granule being applied. For coated fertilizer granules, the granular composition can be spread over the soil at a rate of about 10 to 50 pounds per acre. For coated pesticide granules, the granular composition can be spread over the soil at a rate of about 1 to 10 pounds per acre.

[0051] Once applied to the soil, the soil patch is exposed to moisture in the form of rain, irrigation and / or ambient water vapor, and as a result, the granules of the coated granular composition are likewise exposed to moisture.

[0052] This exposure to moisture causes at least the polyhydroxyalkanoates in the biodegradable coating to begin to undergo hydrolytic degradation. Thus, at least the polyhydroxyalkanoates gradually dissolve into smaller oligomers and monomers. In some cases, polylactic acid can also degrade into smaller oligomers and monomers. However, it is believed that polylactic acid will generally degrade or hydrolyze at a slower rate than polyhydroxyalkanoates.

[0053] As this degradation proceeds, lower molecular weight degradation products may dissolve in water or otherwise escape from the granules, creating gaps in the biodegradable coating and exposing portions of the granule material beneath the coating, which are then released into the soil.

[0054] As discussed above, the biodegradable coating preferably comprises a continuous phase of polylactic acid having small globules of polyhydroxyalkanoate uniformly dispersed therein, and the small globules of polyhydroxyalkanoate generally dissolve at a faster rate than the adjacent continuous phase polylactic acid, and as a result, degradation of the polyhydroxyalkanoate preferably leads to the formation of a plurality of passageways or pores in the biodegradable coating.

[0055] Thus, in a more preferred embodiment, the underlying particulate material can now be released into the soil through these passageways or pores formed in the biodegradable coating.

[0056] As the particulates are released through the passages or pores, the release rate of the particulate material is determined largely by the rate of decomposition of the polyhydroxyalkanoate when exposed to environmental moisture. The rate of decomposition can in turn be influenced by factors such as the particular polyhydroxyalkanoate used in the coating (monomer residues of 3-hydroxybutyrate, monomer residues of 3-hydroxyhexanoate, etc.) and the weight average molecular weight of the polyhydroxyalkanoate. .

[0057] Advantageously, then, one skilled in the art can effectively control the release rate of granular materials (seeds, fertilizers, pesticides, etc.) by selecting the appropriate type and amount of polyhydroxyalkanoates for the biodegradable coating.

[0058] In certain embodiments of this method, preferably at least about 50 percent of the polyhydroxyalkanoate in the biodegradable coating dissolves after about 21 days of exposure to moisture in the soil of the plot.

[0059] The foregoing description of the preferred embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments have been chosen and described to provide the best explanation of the principles of the invention and its practical application, and so that one skilled in the art can adapt the invention in its various embodiments, with various modifications, to the particular uses intended. All such modifications and variations are within the scope of the invention as defined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.

Claims

1. 1. A granular composition for agricultural use comprising a plurality of granules having a biodegradable coating applied thereon, the granules comprising: the granules comprise a material selected from the group consisting of seeds, fertilizers and pesticides; the biodegradable coating comprises 5 weight percent to 75 weight percent polylactic acid and 25 weight percent to 95 weight percent polyhydroxyalkanoate; and After application, the biodegradable coating is annealed at 150-170°C or exposed to solvent vapor to form a continuous phase of polylactic acid having globules of polyhydroxyalkanoate uniformly dispersed within the continuous phase, the globules having an average size of 2 nm to 10 microns. The granular composition.

2. 2. The granular composition of claim 1, wherein the granules comprise seeds.

3. 2. The granular composition of claim 1, wherein the granule comprises a fertilizer.

4. 2. The granular composition of claim 1, wherein the granule comprises a pesticide.

5. 2. The granular composition of claim 1, wherein the biodegradable coating comprises polylactic acid having a weight average molecular weight of 10,000 to 250,000 Daltons.

6. 2. The granular composition of claim 1, wherein the biodegradable coating comprises a polyhydroxyalkanoate having a weight average molecular weight of from 50,000 to 2.5 million daltons.

7. 2. The granular composition of claim 1, wherein the granules have an average particle size before coating of from 1 mm to 25 mm.

8. 2. The granular composition of claim 1, wherein the biodegradable coating comprises 10 to 50 weight percent polylactic acid and 50 to 90 weight percent polyhydroxyalkanoate.

9. 2. The granular composition of claim 1, wherein the polyhydroxyalkanoate comprises from 70 mole percent to 99 mole percent monomer residues of 3-hydroxybutyrate and from 1 mole percent to 30 mole percent monomer residues of 3-hydroxyhexanoate.

10. 2. The granular composition of claim 1, wherein the polyhydroxyalkanoate comprises monomeric residues of three or more hydroxyalkanoates, each having from 5 to 22 carbon atoms.

11. A method for making a coated granular composition according to any one of claims 1 to 10, comprising the steps of: mixing polylactic acid and polyhydroxyalkanoate, optionally in the presence of a solvent, at a temperature of from 25° C. to 180° C. to provide a coating mixture; applying the coating mixture to an exterior surface of the plurality of particles; and solidifying the coating mixture to create a biodegradable coating on the exterior surface of the plurality of particles; The method comprises the steps of: the granules comprise a material selected from the group consisting of seeds, fertilizers and pesticides; and The biodegradable coating comprises a continuous phase of polylactic acid having uniformly dispersed therein globules of polyhydroxyalkanoate, the globules having an average size of 2 nm to 10 microns. The method.

12. The method of claim 11, wherein the biodegradable coating is temporarily annealed at 150-170° C. for a few seconds after application or the biodegradable coating is exposed to solvent vapor after coating.

13. 1. A method for controlled release of particulate matter comprising: providing a granular composition comprising a plurality of granules having a biodegradable coating applied to the granules, the granules comprising a material selected from the group consisting of seeds, fertilizers and pest control agents, and the biodegradable coating comprising 10 to 30 weight percent polylactic acid and 70 to 90 weight percent polyhydroxyalkanoate, the biodegradable coating comprising a continuous phase of polylactic acid having globules of polyhydroxyalkanoate stably dispersed therein, the globules having an average size of 2 nm to 10 microns, the biodegradable coating being annealed at 150-170° C. or exposed to solvent vapor after application; applying the granular composition to the soil of the plot; by exposing the soil of the parcel and the granular composition dispersed therein to moisture; Dissolving at least the polyhydroxyalkanoate in the biodegradable coating; wherein degradation of the polyhydroxyalkanoate forms passageways in the biodegradable coating through which the particulate material can be released into the soil. The method.

14. The method of claim 13, wherein the polyhydroxyalkanoate comprises from 70 mole percent to 99 mole percent monomer residues of 3-hydroxybutyrate and from 1 mole percent to 30 mole percent monomer residues of 3-hydroxyhexanoate.

15. 14. The method of claim 13, wherein after exposure to soil moisture of the plot for 21 days, at least 50 percent of the polyhydroxyalkanoate in the biodegradable coating is dissolved.