WO1998016103A1

WO1998016103A1 - Agrochemical compositions

Info

Publication number: WO1998016103A1
Application number: PCT/GB1997/002834
Authority: WO
Inventors: David Coupland; Keith Coupland; Barry Love
Original assignee: Croda International Plc
Priority date: 1996-10-14
Filing date: 1997-10-14
Publication date: 1998-04-23
Also published as: AU4711197A; GB9621370D0

Abstract

A biodegradable agrochemical composition comprises an invert emulsion, wherein the internal, aqueous phase contains at least one active component and the external, oily phase contains at least one biodegradable alkyl ester of a long chain fatty acid.

Description

AGROCHEMICAL COMPOSITIONS

This invention relates to agrochemical compositions and, more particularly, to agrochemical compositions having controlled release properties.

It is often desirable to be able to delay the release of active materials from agrochemical compositions applied to plants and soil etc. However, this is not always easy to achieve. One proposal involves making the compositions as a water-insoluble solid, and release of the actives is thus dependent on the slow break-down of the solids. Another approach has been to provide a coating around the active material so that release is dependent on the material passing through, or otherwise being released by, the coating.

US Defensive Publication T969003 describes an agrochemical composition for controlled release of a liquid fertilizer. The composition is an invert emulsion consisting of small droplets of liquid fertilizer solution sunounded by a thin impenetrable oil-surfactant layer. The publication discloses that, in use, water slowly dissolves this surfactant from the oil thus breaking the emulsion and allowing the liquid fertilizer to be released. Only two materials are described for use as oils, namely kerosene and benzene. The compositions described in the US Defensive Publication No. T969003 have a number of disadvantages. The use of kerosene or benzene for application to growing crops is not advisable. Both kerosene and benzene are highly flammable materials and benzene is a recognised carcinogen. Furtheπnore, the rate of breakdown of the emulsion, giving release of the active, is uncertain and can be largely dependent on uncontrollable factors such as the weather.

US-A-5445663 describes a slow release fertilizer composition comprising a water-in-oil emulsion wherein the water phase is a solution or dispersion of nutrient compounds and the oil phase is an oil or hydrocarbon comprising mineral, vegetable or animal oils, wax or a mixture of these, the emulsion also containing a surfactant. These compositions give slow release of the water phase nutrient by breakdown of the emulsion.

We have investigated these water-in-oil emulsions for the slow release of active materials. The emulsions described in US-A-5445663 have a number of drawbacks. For. example, those made with mineral oils have generally similar disadvantages to those compositions described in US Defensive Publication T969003. The release of mineral oils into the environment is not environmentally desirable.

The emulsions described in US-A-5445663 are all liquid at ambient conditions and are intended to be liquid for application through conventional spreaders. This physical form restricts their use to liquid applicators rather than the more widely used granule applicators.

We have now devised some improved agrochemical compositions for the controlled release of active material, whereby these various disadvantages and restrictions are reduced or overcome.

According to one aspect, the invention comprises an agrochemical composition for controlled release of at least one active component therefrom, which composition comprises an invert emulsion including at least one active component, at least one emulsifier, an internal, aqueous phase, and an external, oily phase which contains at least one biodegradable alkyl ester of a long chain fatty acid.

In another aspect, the invention comprises a method of manufacturing an agrochemical composition according to the invention which comprises mixing an aqueous phase containing the at least one active component with an oily phase comprising at least one biodegradable alkyl ester of a long chain fatty acid containing an emulsifier, and stirring the mixture.

In a further aspect of the invention, there is provided the use of a liquid agrochemical composition of the invention for spraying or injecting.

In another aspect, the invention comprises the use of a solid agrochemical composition according to the invention in a granule applicator.

In accordance with a preferred feature of the present invention, the compositions comprise an invert emulsion of an aqueous phase containing the active material, and a biodegradable alkyl ester of a long chain fatty acid as the external phase. In this way, we have found that the rheology of the emulsions can be controlled, as can the biodegradability of the external phase, to achieve very desirable properties. In particular, the rheology can be controlled to give either liquid or pumpable fluid emulsions which can be applied by spraying, injection or spreading respectively, or solid emulsions can be produced so that granules may be formed and subsequently applied using the more conventional granular applicator machinery. Irrespective of their physical form, the compositions will exhibit characteristics of an invert emulsion, for example not readily dispersing in water.

The choice of ester (oil phase) will also influence biodegradability, but this feature will always be far greater than that of a mineral oil. Thus, the compositions provide a number of significant advantages over the prior art water- in-oil emulsions.

The external phase of the compositions of the invention is an alkyl ester of a long chain fatty acid or mixtures of different esters. The alkyl moiety is from to C₃₆, preferably from C, to C,₀, and most preferably C, (methyl) especially for the liquid emulsions. The long chain fatty acid is preferably C₆ to C₂ , most preferably C₁₂ to C₂₀. For formulations of solid emulsions, both alkyl and fatty acid moieties are preferably above C₁₄. Preferably, the alkyl esters are derived from animal or vegetable oils, for example by treatment of the oils with an alkanol, eg. methanol, in a transesterification process, to yield glycerol and alkyl, eg. methyl, esters of the long chain fatty acids from the oil. Methyl esters of this type, derived from rapeseed oil, are known and are used as biodiesel. For the purposes of the present invention, the alkyl esters can be derived from any animal or vegetable oil or fat including, for example rapeseed oil, soybean oil, castor oil, tallow and oils derived from marine organisms.

The alkyl esters used as the external phase in the emulsions of the invention are all biodegradable, by which we mean that they will break down by natural biological or chemical action in a relatively short time.

Whilst it is possible to heat the composition during the formation of the emulsion, it is a preferred feature of the invention to produce the emulsion without heating, using high shear mixing.

Reference is now made to the accompanying drawing, in which: FIGURE 1 is a chart showing the biodegradability of various materials; and

FIGURE 2 is a graph of soil water conductivity versus time in order to demonstrate the release of ions from soil treated with granular ammonium nitrate and an invert emulsion according to the invention.

The precise mechanism operating to break down the external phase can vary. It may be a biological degradation by micro-organisms, or a biochemical or chemical hydrolysis occurring naturally when the compositions are used. For example, hydrolysis of the ester is one likely mechanism for breakdown as esterases and Upases are ubiquitous in the environment. We use the term biodegradation or biodegradable herein to include all such processes which occur spontaneously in nature when the composition is used and which involve degradative breakdown of the external phase.

This is in sharp contrast to the disclosure of US specification T969003 and US-A-5445663 where biodegradation of the hydrocarbon external phases would not occur (or would occur only so slowly as to be negligible). In the US specification, release of the active does not occur by virtue of chemical breakdown (destruction) of the external phase, but rather by leaching of emulsifier from the oil, so causing the emulsion to collapse.

The environmental fate of transesterified oils is well documented. For example, Cornish et al (in "Environmental Fate of Mineral, Vegetable and Transesterified Vegetable Oils, Pesticide Science, 1997, 37, 173 to 178) conclude, "All of the ester-based products used in pesticide formulations biodegrade substantially in laboratory tests; mineral oils undergo partial degradation.". Data taken from the same publication are shown in Fig. 1. The test (CEC L-33-T-82) is carried out under aerobic conditions (see "Biodegradability of Two-stroke Cycle Outboard Engine Oils in Water - Coordinating European Council for the Development of Performance Tests for Lubricants and Engine Fuels Tentative Tests Method" CEC-L-33-T-82, 1982).

Under anaerobic conditions, the same contrasts are seen in the biodegrability of fatty acid esters and mineral oils. For example, Streber et al (in "Comparative Evaluation of Anaerobic Biodegrability of Hydrocarbons and Fatty Derivatives currently used as Drilling Fluids", Chemosphere, 1995, 3J_, 3 105-3118) using the ECETOC test found an average of 83% biodegradation for fatty acid esters but only 5% for mineral oils (see European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC), Technical Report No. 28, "Evaluation of Anaerobic Biodegradation", ECETOC Brussels, June 1988).

In the compositions of the invention, the emulsifier must be capable of producing stable water-in-oil emulsions. As such, the emulsifiers would be expected to exhibit a hydrophilic-lipophilic balance (HLB) value in the range of 1 to 10, preferably 1 to 7. It is preferred that the emulsifier is an alkoxylated, more preferably an ethoxylated, vegetable oil. The various classes of suitable emulsifiers include, for example, alcohol alkoxylates, phenol alkoxylates, polyoxyalkylene glycols, polyoxyalkylene fatty acid esters, amine alkoxylates, fatty acid esters of sorbitol and glycerol, fatty acid salts, sorbitan esters, polyoxyalkylene sorbitan esters, fatty amine alkoxylates, polyoxyalkyleneglycol esters, fatty acid amides, fatty acid amide alkoxylates, polyoxyalkyleneglycol derivatives of vegetable oils and hydrogenated vegetable oils, alkylolamides, fatty amines, quaternary amines, alkyloxazolines, alkenyloxazolines, imidazolines, alkyl sulfonates, alkylarylsulfonates, alkylsulfosuccinates, alkylphosphates, alkenylphosphates, phosphate esters, phosphoglycerides, sphingolipids and copolymers of polyoxyalkylene glycols and poly( 12-hydroxystearic acid). The emulsifier may be a single compound or any mixture of two or more thereof, to achieve the required degree of emulsion stability and controlled release. The choice of emulsifier will also depend on the desired physical form of the final composition. Examples of emulsifiers are shown in Tables 1-6.

The internal aqueous phase will usually represent from 50% to 95% by volume of the compositions. It is within this phase that the fertilizer and/or other components are dissolved or dispersed. These fertilizer components are typically nitrogen-containing plant macronutrients such as ammonium nitrate, ammonium phosphate, ammonium polyphosphate, urea, potassium nitrate, calcium nitrate, sodium nitrate, various sulphate salts and elemental sulphur and complex fertilizer compositions (NPK).

As well as the above macronutrients, trace elements or micronutrients may also be present in the aqueous phase, together with any macronutrients, or separately as single component or multicomponent mixtures. Such trace elements include salts of manganese, magnesium, nickel, zinc, boron, cobalt, copper, iron, calcium, molybdenum and others, and elemental sulphur.

The solutions of fertilizer components may be sub-, super- or saturated at the time of manufacture (emulsification) without seriously affecting emulsion stability or drastically altering the slow-release characteristics of the compositions. Elemental sulphur can be present as a dispersion. The physical foπn of the emulsion can be affected especially if the supersaturated emulsions crystallise out upon cooling.

It is a preferred embodiment of the invention that other types of agricultural chemicals, such as pesticides, can be contained within the aqueous phase. This is described in more detail below.

The compositions of the invention can contain ingredients other than those mentioned, if desired, dependent on the intended use. These ingredients must be compatible with water, that is they must be readily dispersible or soluble in water. The compositions can be used for a variety of agricultural purposes where controlled release is desirable. The specific composition will be determined by the end-use application. For example, controlled-release pesticidal compounds, semiochemicals, and biocontrol agents can be formulated as well as the fertilizers and trace elements (micronutrients) described above.

Depending upon the quantity and type of alkyl ester chosen, as well as the characteristics of the internal phase and emulsifier, the compositions will vary from free-flowing emulsions to solids.

Those of low viscosity can be applied topically to plants normally achieved with conventional hydraulic sprayers or by using controlled droplet applications (CDA). Their oily characteristics will facilitate adhesion of the active ingredients to the plant and impart an inherent water repellency thus resisting wash-off, eg. by rain or dew. It is a preferred embodiment of the invention that these emulsion formulations are used for applications where resistance to wash-off from plants or leaching from soil is desirable. The low viscosity emulsions can be applied to the soil using conventional injection or sprayer equipment. Those that are solid can be spread using conventional granule spreading equipment.

Among other ingredients that may be used are, for example, the following: Pesticides

Insecticides, herbicides, fungicides, nematicides, acaricides, or molluscicides, for example. Semiochemicals

Semiochemicals such as pheromones, for example. Biocontrol agents

Spores derived from fungal or bacterial or other microbial origins, or chemicals derived or extracted from natural sources having pesticidal properties, for example.

In general these other active components need to be contained within the internal phase to take advantage of the controlled release properties of the invention. However, they may be in solution or in dispersion according to their specific physical and chemical properties. Active components that do have an appreciable oil solubility will gradually partition into the oil phase and may be lost from the invert emulsion accordingly. This loss will also form part of the slow- release characteristics of the invention.

In order that the invention may be more fully understood, the following examples are given by way of illustration only.

Examples 1 to 4

Compositions of the invention were made up from various internal and external phases as shown in Table 1 (quantities are % by weight).

Table

Notes: a. GPR™ grade (BDH Labs, Poole, UK: ref. 27190EA); b. Components supplied by Croda Oleochemicals (Snaith, Goole, UK); c. Methyl esters derived from low erucic rapeseed oil.

In general, the two phases are wanned separately to 60-70°C with stirring to ensure homogeneity. The external phase is stirred at about 225 φm with a paddle stirrer blade and the internal phase is added over a period of 20-30 s and the stirring rate increased to about 300 φm. The mixtures are allowed to cool naturally and the stiπing rate is gradually reduced.

The sample produced in Example 1 had the appearance of a gel of moderate viscosity. When examined microscopically at x400 magnification, an amoφhous character was evident with no clear distinction between the internal and external phases. When the emulsion was added to cold water, the sample did not readily disperse, indicating the presence of a coherent, non-aqueous external phase. Example 2 produced an amoφhous gel-like product similar in appearance to that of Example 1. Examples 3 and 4 produced water-in-oil type liquid emulsions with internal phase droplets of diameters of about 1 to 50 micrometres. Examples 5 to 12

Examples 5 to 12 (Table 2) demonstrate that for a choice of internal phase consisting of ammonium nitrate and urea (two commonly used fertilizer ingredients) and using the prefened emulsifier from the Examples in Table 1 (Etocas 5) stable water-in-oil (w/o) emulsions can be formed. The method for manufacture was the same as for the Examples in Table 1.

Table 2

Notes: a. As for Table 1 ; b. ICI industrial grade urea; c. As Table 1 ; d. As Table 1 ; e. Pioneer Mineral White Oil 25cSt @ 25°C; f. Seatons refined rapeseed oil L/E; g & h. As Table 1; i. n/s = not stable, w/o water-in-oil emulsion; j. Brookfield RTV viscometer, spindle no. 4, 10 φm at 24°C, measured 48h after preparation.

The use of emulsifiers typified by sorbitan monooleate (Crill 4, Examples 5 to 8) produced unstable emulsions inespective of whether mineral oil (White oil), rapeseed oil, fatty acids derived from rapeseed oil, or methyl esters of rapeseed oil were used for the external phase. However, using the preferred emulsifier type (Etocas 5) and a preferred oil type (i.e. low erusic rapeseed oil or methylated rapeseed oil (Crodamol RME) stable w/o emulsions were readily formed (Examples 10 and 12).

In a further embodiment of the invention the preparation of Example 12 was repeated without prior heating of the two phases and mixing them with increased shearing using a Silverson blender. An initially thicker w/o emulsion resulted, the viscosity of which decreased with time to a similar value of Examples 10 & 12 (Table 2). This Example demonstrates a preferred embodiment of the invention whereby compositions may be prepared using a high shear mixer without the need for heating the individual oil and water phases prior to emulsification. Such a system has commercial advantages as it overcomes the need for additional heat input and is therefore more readily adaptable to continuous processing. Examples 13- 16

Examples 13 to 16 (Table 3) demonstrate the range of other nutrients that can be incoφorated into the aqueous phase. All emulsions were readily formed by adding the internal phase to the external phase at ambient temperature (approximately 23°C) with moderate shear mixing using a paddle stirrer.

Examples 17 - 20

Examples 17 to 20 (Table 3) demonstrate that the ratio of emulsifier to oil can be changed, as well as reducing the amount of total oil phase whilst maintaining emulsion stability.

Emulsions were prepared as for Examples 13 to 16 and produced water-in-oil emulsions stable for several weeks at ambient temperature. Table 3

*NB Ammonium nitrate (from BDH, GPR grade); Urea (from ICI, Industrial grade); Fenic heptonate (from Croda Colloids, iron chelate solution); Manganese II sulphate (from Aldrich, ACS reagent); Ammonium sulphate (from Riedel-de Haen, technical grade); Copper II sulphate (from Aldrich, 1% w/w solution used).

Examples 21 to 27

Examples 21 to 27 (Table 4) demonstrate the range of alkyl esters that can be used with Etocas 5 as the emulsifier and using the same ammonium nitrate/urea mix and blending conditions as in Table 2. In all cases stable, fluid, shear-thinning w/o emulsions were easily formed with low shear mixing. Table 4

NOTES: a Suppliers' code (Croda Oleochemicals); b See note j, Table 2. Examples 28 to 3 1

Examples 28 to 31 (Table 5) show that it is possible to produce a range of products with different aqueous phase compositions. These Examples were prepared according to the conditions pertaining to Table 2. Where the aqueous phase is supersaturated at ambient temperatures, it will be appreciated by those skilled in the art that slow release products in a solid form may be developed.

Table 5

Numbers are in % w/w Examples 32-34

Example 34 (Table 6) shows that Crill 3 (sorbitan sterate) is not suitable for the more solid type of emulsion.

Examples 35-46

Examples 35 to 46 (Table 6) demonstrate that hydrogenated vegetable oils (soya and castor), ethylene glycol distearate, oxidised microcrystalline wax (Rocsol C), stearic acid and low melting point esters are not suited for this type of emulsion system.

Examples 47-51

Examples 47 to 51 (Table 6) show that the higher melting point esters, typically of m.p.> 40°C, are best suited to produce stable, homogeneous emulsions that are solid enough to form prills, pellets or granules so that they can be applied by conventional granule spreading agricultural equipment.

Table 6

NB The internal phases for Examples 32-51 consisted of: ammonium nitrate (26.0% w/w), urea (52.0% w/w), and tap water ( 10% w/w).

The external oil phase consisted of 5.0% w/w emulsifier and 7.0%o w/w oil.

Emulsions were prepared by heating both phases to 60-70°C, then adding the aqueous phase to the oil phase while mixing with a paddle stirrer at 300-400 rpm. Stirring was maintained until the mixtures reached approximately 50°C.

The internal phase is supersaturated at the storage temperature.

** Marine ethyl esters (Croda Oleochemicals).

** * EGDS is ethylene glycol distearate.

* *** Rocsol C is an oxidised microcrystalline hydrocarbon wax.

Examples 52 to 54

Examples 52 to 54 (Table 7) formed spontaneously upon stirring the aqueous phase into the oil phase without heating and using low shear mixing. All emulsions were homogeneous liquids at ambient conditions.

Table 7

Demonstration of slow release properties

In order to demonstrate the slow release properties of the emulsions, soil was treated with either ammonium nitrate prills (granules) or an invert emulsion composition (Example 3, Table 1). In these tests, approximately lg of ammonium nitrate or the emulsion was added to and mixed with 65g of a loam soil. These mixtures were contained in glass jars and kept at 5°C. At various sampling times (see Figure 2), the treated soils and an untreated one (as control) were taken and eluted with 100cm^? of deionised water. The conductivity of this eluate was measured and used to estimate the release of the fertilizer (ammonium nitrate) after suitable con-ection against the control soil.

As can be seen from Figure 2, the invert composition showed a significant reduction in the rate of release of the fertilizer. The conventional granular fonri of the fertilizer was lost immediately from the soil with the first washing whereas the invert emulsion was released gradually over a four month period.

This invention is not limited to the cited examples. It will be appreciated by those skilled in the art that adjustments may be made to modify the active content of the internal phase, and alter the ratio and overall content of the external phase in order to meet specific product requirements.

Claims

CLAIMS:

1. An agrochemical composition for controlled release of at least one active component therefrom, which composition comprises an invert emulsion including at least one active component, at least one emulsifier, an internal, aqueous phase, and an external, oily phase which contains at least one biodegradable alkyl ester of a long chain fatty acid.

2. A composition according to claim 1, wherein the or each alkyl moiety of the alkyl ester is from C_{ to C₃₆.

3. A composition according to claim 2, wherein the or each alkyl moiety is from to C₁₀.

4. A composition according to claim 2 or 3, wherein the or each alkyl moiety is C, (methyl).

5. A composition according to claim 1, 2, 3 or 4, wherein the or each long chain fatty acid of the alkyl ester is from C₆ to C₂ .

6. A composition according to claim 5, wherein the or each long chain fatty acid is from C₁₂ to C₂₀.

7. A composition according to any preceding claim, wherein the or each alkyl ester is derived from animal or vegetable oil or fat.

8. A composition according to claim 7, wherein the animal or vegetable oil or fat is rapeseed oil, soybean oil, castor oil, tallow or is an oil derived from marine organisms.

9. A composition according to any preceding claim, wherein the internal, aqueous phase is from 50% to 95% by volume of the composition.

10. A composition according to any preceding claim, wherein the or each active component is at least one fertilizer and/or other material.

1 1. A composition according to claim 10, wherein the or each fertilizer is ammonium nitrate, ammonium phosphate, ammonium polyphosphate, urea, potassium nitrate, calcium nitrate, sodium nitrate, a sulphate salt, elemental sulphur or a complex fertilizer composition.

12. A composition according to claim 10 or 1 1, wherein the or each other material is a trace element.

13. A composition according to claim 12, wherein the or each trace element is at least one salt of manganese, magnesium, nickel, zinc, boron, cobalt, copper, iron, calcium or molybdenum.

14. A composition according to claim 10, 1 1, 12 or 13, wherein the or each other material is a pesticidal compound, a semiochemical, or a biocontrol agent.

15. A composition according to claim 14, wherein the or each pesticidal compound is an insecticide, fungicide, nematacide, acaricide or molluscicide.

16. A composition according to claim 14, wherein the or each semiochemical is a pheromone.

17. A composition according to claim 14, wherein the or each biocontrol agent is a spore derived from fungal or bacterial or other microbial origin, or is a chemical derived or extracted from a natural source having pesticidal properties.

18. A composition according to any of claims 10 to 17, wherein the or each fertilizer and/or other material is dispersed in the aqueous, internal phase.

19. A composition according to any of claims 10 to 18, wherein the or each fertilizer and/or other material is dissolved in the aqueous, internal phase.

20. A composition according to claim 19, wherein the or each fertilizer and/or other material is in saturated solution.

21. A composition according to any preceding claim, wherein the or each emulsifier has a hydrophilic-lipophilic balance (HLB) value of from 1 to 10.

22. A composition according to claim 21 , wherein the or each emulsifier has an HLB value of between 1 and 7.

23. A composition according to any preceding claim, wherein the or each emulsifier is an alkoxylated vegetable oil.

24. A composition according to claim 23, wherein the or each emulsifier is an ethoxylated vegetable oil.

25. A composition according to any preceding claim in the form of a solid, liquid or gel.

26. A solid composition according to claim 25, wherein the alkyl moiety and the fatty acid moiety is C₁ or above.

27. A method of manufacturing an agrochemical composition as claimed in any of claims 1 to 26, which comprises mixing an aqueous phase containing the at least one active component with an oily phase comprising at least one biodegradable alkyl ester of a long chain fatty acid containing an emulsifier, and stining the mixture.

28. A method according to claim 27, wherein the aqueous phase and the oily phase are each warmed before mixing.

29. A method according to claim 28, wherein the aqueous phase and the oily phase are each warmed to between 60 and 70°C.

30. A method according to claim 27, wherein the mixing is effected by high shear mixing.

31. A method according to any of claims 27 to 30, wherein the or each active component is dispersed in the aqueous phase.

32. A method according to any of claims 27 to 31, wherein the or each active component is in solution in the aqueous phase.

33. The use of a liquid agrochemical composition according to any of claims 1 to 25 for spraying, spreading or injecting.

34. The use according to claim 33 for topical application to plants or soil.

35. The use according to claim 33 for injecting into or spreading onto soil.

36. The use of a solid agrochemical composition according to claim 25 or 26, in a granule applicator.