WO2001066668A2

WO2001066668A2 - Soil additive in the form of a coating

Info

Publication number: WO2001066668A2
Application number: PCT/CA2001/000299
Authority: WO
Inventors: Marlene Elizabeth Conway; William Anderson
Original assignee: Agrilizer Inc.
Priority date: 2000-03-09
Filing date: 2001-03-09
Publication date: 2001-09-13
Also published as: WO2001066668A3; AU3906501A

Abstract

A soil additive comprising a mixture of a water-soluble composition and a super-absorbent polymer having a particle size of 1-1000 νm, said soil additive being solid at 25 °C. Preferably, the soil additive is in the form of a coating e.g. on an agricultural fabric.

Description

TITLE

SOIL ADDITIVE IN THE FORM OF A COATING

Field of the Invention

The present invention relates to a soil additive that is a mixture of a water-soluble composition and a particulate super-absorbent polymer. In preferred embodiments, the soil additive is in the form of a coating, especially a coating on an agricultural fabric.

Background of the Invention

Controlled release fertilizers have been available for some time. Typically they are composed of chemical fertilizer granules with a porous coating that in moist soil allows diffusion of plant nutrients (ions) into the adjacent soil environment. An example is the controlled release fertilizer available from Scotts Co. under the trademark "Osmocote". By varying the nature and/or thickness of the coating, nutrient availability over a range of time periods can be achieved. However, as the moisture environment around the granules in the soil is controlled by the moisture content of the soil, under dry conditions the transfer rate of nutrients to the roots from the fertilizer granules tends to be greatly reduced.

Technology for increasing the retention of moisture in soils is also known. Both natural products, e.g. peat moss and the like, and synthetic water absorbing polymers are used in horticultural/agricultural applications. Examples of such polymers are those available under the trademarks "Liqua-Gel" and "SuperSorb". Such synthetic water absorbing polymers utilized in agricultural end-uses absorb high volumes of water as soon as they are placed in soils.

Adequate moisture supply is critical to roots, especially to plants whose growing medium is subject to long periods of moisture deficiency. Various superabsorbent polymer (SAP) gels have been offered commercially to address the problems of inadequate moisture supply to roots. So called agricultural SAP chemicals, which are acrylamides or acrylamide copolymers, are non-ionic or have a very low anionic character. As a consequence of the non-ionic state, there tends to be a relative insensitivity to the presence of cations in the soil and hence the degree of swelling of the agricultural SAP tends to remain constant over repeated wet/dry cycles. In contrast, anionic SAP's which are normally sodium polyacrylate, tend to lose their ability to absorb large quantities of water in a cyclic wet/dry environment because of exchange of cations from the surrounding soil, particularly from clay soils. During dry periods, sodium polyacrylate tends to condense and form crosslinks that inhibit re-swelling when it is re-wetted. Even when used in situations where a limited number of wet/dry cycles are experienced, sodium polyacrylate inhibits plant growth or in some cases is toxic to plants. This inhibition of plant growth or toxicity is believed to arise because the sodium ions in the sodium polyacrylate network are exchangeable and these ions are adsorbed by clay particles or tend to undergo exchange with cations on the surface of plant roots. The consequence is a condition that is analogous to an alkali soil, which generally tends to adversely affect or inhibit plant growth. Sensitivity of hydrogels to the presence of salts has caused the focus to be on acrylamide-based polymers rather than ionic polyacrylates, although even polyacrylamide superabsorbents show a decrease in water absorption in the presence of soluble salts. Moreover, attempts to combine polyacrylamides with slow release nutrients have not been very successful.

Use of polyacrylamides in horticultural or agricultural end uses tends to be modest, primarily because of cost. Although crop yield improvements have been reported, applications are generally restricted to some horticultural uses. Inclusion of plant nutrients in polyacrylamide applications would be expected to further increase costs.

Sodium polyacrylate is the dominant superabsorbent polymer product in use today. Its major application is as a body fluid absorbent in hygienic disposal products, particularly in diapers. In such uses, rapid absorption of water is an essential requirement, and the polymer must have a strong affinity for water. It is estimated that over 90% of all superabsorbent polymer produced is sodium polyacrylate. Such an economy of scale in its production means that the cost of sodium polyacrylate tends to be lower than that of superabsorbent polymers otherwise used for agricultural end uses. In addition, commercial processes are now available for recovery of superabsorbent polymer from hygienic disposal products, including diapers, for example as disclosed by M.E. Conway et al in U.S. 5,558,745.

Examples of soil additives for agricultural and horticultural end-uses are disclosed in published PCT patent application No.s. WO 98/12154 and WO 98/49252, both of Marlene E. Conway and Kenneth R. Williams. U.S. Patent 5 362 766 discloses combinations of superabsorbent polymer in a matrix material, examples of which are cellulose esters, e.g. cellulose acetate, polymers of acrylic acid esters e.g. polymethyl methacrylate and polyvinyl esters e.g. polyvinyl acetate. Testing for saline absorbency was exemplified. U.S. Patent 5 795439 discloses a non-woven, wet-laid, superabsorbent polymer-impregnated fibrous web for use in diapers and incontinent pads. The fibres are preferably staple, especially of 0.25-0.5 inches (0.635-1.27 cm) in length.

U.S. Patent 5 817 713 discloses water-swellable coatings formed from particulate superabosorbent polymer in a polyvinyl chloride plastisol e.g. for the coating of coaxial cable.

Improvements in methods of application of soil additives would be useful.

Summary of the Invention

A soil additive that can be readily inserted into soil in a controlled manner, and which is capable of providing useful ingredients into the soil has now been found.

Accordingly, one aspect of the present invention provides a soil additive comprising a mixture of a water-soluble composition and a super- absorbent polymer having a particle size of 1-1000 μm, said soil additive being solid at 25°C. In embodiments, the coating is solid at 35°C. In a preferred embodiment of the invention, the particle size is less than 500 μm.

In another preferred embodiment, the soil additive is in the form of a coating. In a further embodiment, the super-absorbent polymer is selected from sodium polyacrylate or sodium polyacrylamide.

In yet another embodiment, the super-absorbent polymer contains at least one of fertilizers, pesticides, growth hormones or growth nutrients.

In a still further embodiment, the water-soluble composition is selected from the group consisting polyethylene glycol, polyethylene oxide, polyvinyl alcohol and polyvinyl pyrrolidone, and blends thereof, and may additionally contain a viscosity modifier, plasticizer, stabilizer, lubricant or other processing aid.

In yet another embodiment, the soil additive is coated on a material selected from agricultural fabric, seed, peat pot or other durable container, and root, especially an agricultural fabric that is a woven or non-woven fabric composed of polypropylene, polyethylene, cellulose or modified cellulose, or a thin sheet with an open web-like structure.

In a still further embodiment, the soil additive additionally contains seeds.

A further aspect of the invention provides a soil additive comprising seeds coated with a composition conducive to root development, said coated seed being coated onto a fabric using a mixture comprising water-soluble composition and particulate superabsorbent polymer as described herein.

Detailed Description of the Invention

The present invention relates to a soil additive in the form of a solid mixture of a water-soluble composition and a particulate super-absorbent polymer. The soil additive is preferably a coating e.g. on an agricultural fabric.

The superabsorbent polymer (SAP) may be virgin polymer, but it is particularly intended that the superabsorbent polymer would be such polymer that has been recovered or recycled from another process, or recovered from an industrial process for the manufacture or use of superabsorbent polymer. One example of such recovery is from used disposable diapers or other absorbent sanitary paper products, also referred to as personal care products, during processes for recycling and recovery of components of such processes for future use. One such process is that of the aforementioned U.S. 5 558 745. The polyacrylate may be in a variety of forms before treatment as described herein. Polyacrylamides may also be used as the superabsorbent polymer. In addition, the superabsorbent polymers may be a grafted polymer e.g starch-grafted sodium polyacrylate, polypropenoic acid or derivatives, or the like. The present invention will be particularly described herein with reference to sodium polyacrylates as the superabsorbent polymer.

Superabsorbent polymers that are acrylate polymers are normally cross-linked during the manufacturing process. Anionic super absorbent polymers are preferred as the SAP used in the preparation of the soil additive of the present invention, especially because their level of swelling in aqueous solutions tends to be dependent upon the cation concentration of the solutions. Potassium and sodium polyacrylates are especially preferred and furthermore have the advantage of being available commercially because they are widely used for absorption of body fluids in hygienic disposable products, e.g. baby diapers, sanitary napkins, adult incontinence products and the like.

As a result of inherent water absorbent properties, superabsorbent polymers tend to swell on contact with water. In embodiments of the present invention, the super absorbent polymer of the soil additive of the present invention has an absorption capacity index (ACI) that is at least 30, e.g. in the range of 30-100, especially in the range of 50-80. As used herein, absorption capacity index is defined as:

(wt of water saturated gel polymer-polymer dry wt.)/polymer dry wt. The ACI of an anionic superabsorbent polymer, such as the polyacrylate polymers, may be decreased by cross-linking of the polymer with cations. Examples of chemical compounds that may be added to an aqueous solution of the anionic superabsorbent polymer to effect cross-linking of the superabsorbent polymer include soluble salts of at least one of an alkali metal, an alkaline earth metal, aluminium, copper (II), iron (III) and zinc. However, the salts that may be added to effect cross-linking of superabsorbent polymer in embodiments of the present invention, including sodium polyacrylate and potassium acrylate, are salts of divalent cations, especially alkaline earth metal cations. Examples of such divalent cations are magnesium, calcium, barium and zinc. Calcium is preferred.

Examples of the salts include calcium chloride, calcium nitrate, dicalcium phosphate, tricalcium phosphate, magnesium chloride, magnesium nitrate, magnesium sulphate, barium chloride, barium nitrate, zinc sulphate and zinc nitrate. Calcium hydroxide may also be included to aid in deswelling the SAP.

Processes for recovery of SAP after use, in which it is swelled and mixed with other ingredients, for example, in a process for recovery of components of soiled hygienic disposable products, are described in the aforementioned U.S. Patent 5 558 745 of M.E. Conway et al.

The superabsorbent polymer used in the soil additive of the present invention may contain known and standard fertilizers, pesticides, growth hormone or other growth nutrients. Examples of fertilizers include urea, ammonium nitrate, bone meal and the like. Examples of growth hormones include cytokinin, gibberellic acid and isobutyric acid. Examples of pesticides include atrazine, dichloroprop, diquat and 2,4-D, and others, for instance as disclosed in U.S. 5 441 923. Such ingredients may be absorbed into the superabsorbent polymer using techniques that are disclosed in the aforementioned published PCT patent applications of M.E. Conway and K.R. Williams. The resulting superabsorbent polymer composition is ground to a particle size in the range of 1-1000 μm, and more preferably to a particle size that is less than 500 μm. The particulate superabsorbent polymer composition is mixed with a water-soluble composition. The water-soluble composition may be a polymer that is soluble in water, examples of which are polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polyvinyl pyrrolidone, or chemical modifications of these materials or other polymeric materials that are soluble in water. Mixtures or blends of polymers may be used e.g. blends of polyvinyl alcohol and other components, for instance blends of polyvinyl alcohol and ethyiene glycol. The water-soluble composition must be selected so that the soil additive coating composition of the particulate superabsorbent polymer composition and water-soluble composition is solid at 25°C. If the soil additive is to be subjected to temperatures that are higher than 25°C, then it is understood that the water-soluble composition would need to be selected so that the soil additive coating composition is solid at such temperatures. Thus, it is preferred that the soil additive coating composition be solid at a temperature of at least 35°C. The preferred coating is polyethylene glycol with a molecular weight so that it is solid at ambient temperatures, especially at 35°C. Examples of such polyethylene glycols are PEG 1000-10,000, where the number represents average molecular weight, and preferably not less than PEG 600. Particular embodiments of polyethylene glycols are available as POGOL™ 600, 900, 1000 and 1450, manufactured by Huntsman Corp., and Carbowax™ 1450 and 3350, manufactured by Union Carbide Corp. The soil additive coating composition may include additives that improve the process for the manufacture of the coating and/or the performance of the product that is obtained. Examples of such additives include viscosity modifiers, plasticizers, stabilizers, lubricants or other processing aids. Examples of plasticizers include phthalate esters, phosphate esters, lower molecular weight polyethylene glycol and polypropylene glycol, oleates, sebacates, glycerin and adipates. Examples of viscosity modifiers and/or lubricants include long chain fatty acids, alcohols, amides or salts e.g. stearic acid, stearyl alcohol, erucamide and magnesium stearate, waxes and silicones e.g. dimethylsilicones. Examples of stabilizers include antioxidants e.g. butylated hydroxytoluene (BHT), and UV stabilizers e.g. hydroxybenzophenones. Further examples of additives are disclosed in U.S. 4 215 169. It is also understood that the soil additive coating composition could, in addition to materials contained within the particulate, contain minor amounts of fertilizers, pesticides, growth hormones or other growth nutrients. Furthermore, the soil additive coating composition may include a volatile or a non-volatile solvent to improve the fluidity of the coating. Examples of such solvents include alcohols, ethers, ketones, hydrocarbons and halocarbons.

In the preferred embodiment of the invention, the soil additive coating composition is applied to an agricultural fabric. The fabric may be a woven or a non-woven fabric composed of polypropylene, polyethylene, or other similar polymers, which may be degradable or not degradable. Alternatively, the fabric may be formed from cellulose or modified cellulose products, or it may be a material that is suitable for forming thin sheets with an open web-like structure.

If the coating compositions contains a volatile solvent, it might be possible to apply the coating at ambient temperatures, although it may be preferable to warm or to heat the composition for application. If the coating composition does not contain a volatile solvent, then it will be necessary to heat the composition to form a fluid coating composition for application to the fabric. The coating composition is applied to the fabric. A variety of coating techniques may be used, including use of a spray nozzle, extrusion coating, dip coating, screen printing or other coating technology. The coating after application is then cooled, or solvent is evaporated, so as to form a solid coating on and within the fabric. The mixing and application of the coating composition is carried out so that the water absorption properties of the polyacrylamide or polyacrylate are not activated.

The soil additive coating composition is formulated so that the coating composition will adhere to the fabric sufficiently to permit the fabric to be packaged, rolled or wrapped, or otherwise prepared for transportation and for installation into the area of use. Thus, the coating should not be brittle, and it should not break or peel off the fabric. The amount of particulate superabsorbent polymer composition in the soil additive coating composition may be varied over a wide range. It is preferred that the coating composition contain at least 10% by weight, especially at least 20% by weight of the particulate superabsorbent polymer composition. The upper limit of the amount of particulate superabsorbent polymer composition is primarily determined by the ability of the water-soluble composition to bind the particulate and maintain the resultant soil additive composition as a coherent coating on the fabric or other substrate, particularly during storage, transportation and installation, without significant loss of the particulate.

While the coating has been described herein with reference to application to an agriculture fabric, it is understood that the coating may be applied to seeds, root structures or other planting materials, soil or to containers e.g. peat pots. The soil additive coating composition may additionally contain seeds, so that seeds may be supplied to an area of use in conjunction with nutrients, fertilizers and other materials conducive to the growing of the seed.

The coated material is intended to supply the soil additives to the plant, or seedling or soil once it has been laid down, in the case of a fabric, or applied as in the case of a container, seed, root or soil. In this way, the majority of the coating material is available for use as soon as it is planted. However, there will be residual amounts of coating material within the fabric which may be activated over a longer period of time.

In embodiments of the invention, seeds are coated with a soil additive composition that is conducive to root development. The coated seed is then applied to a fabric as part of a coating that is conducive to both seed germination and plant growth. When the thus coated fabric is contacted with water, the seed has an environment suitable for root development, germination and plant growth. One or both of the seed coating and the coating applied to the fabric would contain superabsorbent polymer. The coating used to apply the coated seed to the fabric is a coating of a mixture of water-soluble composition and particulate superabsorbent polymer as described herein.

If the product is in the form of a coated fabric, it is intended that the coated fabric would be laid in an area where the soil additive is required. For instance, if the area was a lawn, the fabric could be laid on the surface of soil and a further layer of soil or sod could be place on top. In the case of pots, the coating would be activated when a plant was placed in the pot and subsequently watered. Similarly, if the coating was on a root it would protect the root from drying out during transportation, and then would be activated on planting of the plant and watering. The present invention is illustrated by the following examples.

Example I

A sodium polyacrylate composition prepared according to the procedure of the aforementioned published PCT Application WO 98/12154 and containing fertilizer to yield 24% available nitrogen i.e. about 78% fertilizer and 22% superabsorbent polymer, was mixed into molten polyethylene glycol PEG 3350, in a ratio of 60:40 by weight. The sodium polyacrylate composition was a particulate with a particle size of about 200 microns or less. A standard J-cloth™ polypropylene fabric was dipped into the resultant molten polyethylene glycol composition. The coated fabric obtained had a surface coating and coating composition within the weave of the fabric. The loading of the composition on the fabric was about 725 g/m .

The coated fabric was placed in water at ambient temperature. The coating dissolved, thereby freeing the particulate, which absorbed water. Particles within the weave of the fabric absorbed water but remained within the weave of the fabric. The fabric had a spongy feel.

The fabric was then permitted to dry overnight. The re-wetted fabric absorbed water. This procedure was repeated 12 times with the same result. The initial coated fabric was substantially rigid, which is believed to be a consequence of the high loading of sodium polyacrylate composition and the high molecular weight of the type of polyethylene glycol that was used. Example II

A sodium polyacrylate composition of the type described in Example I was mixed with polyethylene glycol PEG 1450, which was in the form of a dry powder, in a ratio of 30:70 by weight. The resultant particulate/powder mixture (18% by weight) was then dissolved in ethanol (82% by weight) and mixed.

The resultant solution was coated onto a J-cloth using a dip-coating procedure, and the ethanol was allowed to evaporate. The coated fabric obtained had a surface coating and coating composition between the weave of the fabric, with a loading of the composition on the fabric of about 170 g/m². The coating showed a more even distribution of particulate sodium polyacrylate composition. The coated fabric was soft to touch, and was formable. The coated fabric was placed in water at ambient temperature. The coating dissolved, thereby freeing the particulate, which absorbed water. Particles within the weave of the fabric absorbed water but remained within the weave of the fabric. The fabric had a spongy feel.

The fabric was then permitted to dry overnight. The re-wetted fabric absorbed water. This procedure was repeated 12 times with the same result.

Example III

The procedure of Example II was repeated, except that the sodium polyacrylate composition had a particle size of about 75 microns or less and the particulate/powder mixture (30% by weight) was dissolved in ethanol

(70% by weight). The loading of the composition on the fabric of about 170 g/m

The results obtained were the same as in Example II.

Example IV

A composition of the sodium polyacrylate composition, containing fertilizer, and polyethylene glycol was formed using the procedure of Example III, except that the ratio was 6:94 by weight. The particulate/powder (25% by weight) was dissolved in ethanol (75% by weight).

Pickseed™ grass seed was coated with the mixture of sodium polyacrylate composition and polyethylene glycol. An even distribution of sodium polyacrylate was obtained.

When wetted with water, the sodium polyacrylate particulate separated from the seed. The particulate was allowed to dry and could be re-wetted. This procedure was repeated 12 times.

This example shows that seed may be coated with a water-soluble composition containing sodium polyacrylate with fertilizer.

Example V

A mixture of sodium polyacrylate composition, containing fertilizer, and polyethylene glycol was formed using the procedure of Example II, except that the ratio was 6:9 by weight. The particulate/powder was dissolved in ethanol in a 50:50 ratio by weight.

Rice seed was coated with the resultant solution in a 3.3:1 (seed:mixture) ratio by weight, and the ethanol was allowed to evaporate.

An even distribution of particulate coating on the seeds was obtained.

Example VI A mixture of sodium polyacrylate composition, containing fertilizer, and polyethylene glycol was formed using the procedure of Example II, except that the ratio was 1 :3 by weight, and the sodium polyacrylate composition had a particle size of less than 75 micrometres. The polyethylene glycol in the mixture was then melted by heating to a temperature above 55 °C. Rice seeds were then added to the heated mixture in a 5.7:1 ratio by weight. The rice seeds were coated by stirring in the mixture, and then immediately cooled to solidify the mixture as a coating on the seed surface. The sodium polyacrylate composition was well-distributed in the coating on the seed surface.

The coating was visibly thicker than those obtained when ethanol was included in the mixture.

Example VIII

A sodium polyacrylate composition was prepared by mixing 1 part sodium polyacrylate superabsorbent, 15 parts of a commercial Rhizobial inoculant (Celltech C, Liphatech Inc., Wl), and 0.6 parts of calcium sulfate (all by weight). The mixture was well-mixed and allowed to air dry at temperatures not exceeding 40 °C until the water content was reduced to about 30% by weight. A subsequent assay for the Rhizobium microorganism showed that there were about 1 x 10⁷ cells per gram of solids in the resulting composition.

The resultant composition may be used as the super-absorbent polymer component of the soil additive of the present invention.

Claims

CLAIMS:

1. A soil additive comprising a mixture of a water-soluble composition and a super-absorbent polymer having a particle size of 1-1000 μm, said soil additive being solid at 25°C.

2. The soil additive of Claim 1 in which the particle size is less than 500 μm.

3. The soil additive of Claim 1 or Claim 2 in which the soil additive is in the form of a coating.

4. The soil additive of any one of Claims 1-3 in which the super-absorbent polymer is selected from sodium polyacrylate or sodium polyacrylamide.

5. The soil additive of any one of Claims 1-4 in which the super-absorbent polymer contains at least one of fertilizers, pesticides, growth hormones or growth nutrients.

6. The soil additive of any one of Claims 1-5 in which the water-soluble composition is selected from the group consisting polyethylene glycol, polyethylene oxide, polyvinyl alcohol and polyvinyl pyrrolidone, and blends thereof.

7. The soil additive of any one of Claims 1-6 in which the water-soluble composition additionally contains a viscosity modifier, plasticizer, stabilizer, lubricant or other processing aid.

8. The soil additive of any one of Claims 1-7 in which the soil additive is coated on a material selected from agricultural fabric, seed, peat pot or other durable container and root.

9. The soil additive of any one of Claims 1-7 in which the soil additive is coated on an agricultural fabric that is a woven or non-woven fabric composed of polypropylene, polyethylene, cellulose or modified cellulose.

10. The soil additive of any one of Claims 1-7 in which the soil additive is coated on a thin sheet with an open web-like structure.

11. The soil additive of any one of Claims 1-10 in which the soil additive additionally contains seeds.

12. A soil additive comprising seeds coated with a composition conducive to root development, said coated seed being coated onto a fabric using a mixture comprising water-soluble composition and particulate superabsorbent polymer of any one of Claims 1-7.

13. The soil additive of Claim 12 in which the coating of water-soluble composition and superabsorbent polymer is conducive to both seed germination and plant growth.