WO2000067572A1

WO2000067572A1 - Plant root inhibiting, copper-thermoplastic polymer matrix and process therefor

Info

Publication number: WO2000067572A1
Application number: PCT/US1999/010230
Authority: WO
Inventors: Corrine T. Brothers; Robert M. Lapierre; Thor E. Peckel
Original assignee: Premium Compounded Products, Llc
Priority date: 1999-05-11
Filing date: 1999-05-11
Publication date: 2000-11-16
Also published as: AU3895099A

Abstract

A polymeric composition for controlling plant growth comprising at least one copper compound and at least one thermoplastic polymer and a process for its preparation.

Description

PLANT ROOT INHIBITING, COPPER-THERMOPLASTIC POLYMER MATRIX AND PROCESS THEREFOR

5

BACKGROUND OF THE INVENTION

The use of copper compounds in agricultural applications dates back to 1880 with the discovery of copper sulfate in Bordeaux mixture.

10 Copper is an essential micronutrient for plants. Copper in most plants is deficient at less than 5 ppm, is adequate at 5 to 10 ppm, and is toxic at more than 20 ppm.

The root growth inhibiting action of copper is also well established. Paint containing copper carbonate or copper hydroxide, applied to

15 the surface of plastic nursery containers, has been shown to inhibit root growth at the container wall. This root inhibition at the wall benefits plant health by reducing root circling and girdling. The application of copper loaded paint on the interior of nursery containers to improve plant health is known. However, the application of copper to container interiors has

20 numerous deficiencies. It is a labor intensive process that requires at least one additional processing step after container fabrication. The painting process results in a thin, frequently non-uniform layer that is subject to cracking and flaking off the interior, and presents problems for recycling.

25 SUMMARY OF THE INVENTION

The present invention provides a polymeric composition for controlling plant growth, comprising at least one thermoplastic polymer and about from 0.1 to 50% by weight of at least one copper compound, wherein the copper compound is uniformly blended with the polymer. The invention

30 further provides a shaped polymeric composition comprising at least one thermoplastic polymer and about from 0.1 to 50% by weight of at least one copper compound. A process for the preparation of the polymeric composition is also provided.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a more efficient system for the delivery of root growth inhibiting copper compounds to plant roots than has previously been available. This invention provides a method for the delivery of copper compounds to the plant roots that can provide a timed release of the copper compounds from the polymer reservoir to the interior surface of the composition, e.g. a shaped polymeric composition in the form of a pot, through the process of molecular diffusion through a polymer matrix. The copper compounds are incorporated into the polymer reservoir before the formation of a shaped polymeric composition. Additionally, the invention provides for a regular and sustained release of copper at the interior wall of a container, e.g. , a nursery container, comprising the polymeric composition of the invention by selection of copper compounds that preferentially migrate out of the polymer to the surface. Many of the copper compounds that have been used previously in agricultural applications for root inhibition are less useful for the present system because they are less stable at the high temperatures required for polymer processing.

A wide variety of thermoplastic polymers can be used in the present invention, including, for example, polyolefins, polystyrenes, polyesters and polyamides. Polyolefins and polystyrnes are preferred. Of the polyolefins, polyethylenes, including high density polyethylenes, and polypropylenes have been found to be particularly satisfactory.

Shaped polymeric compositions which can be prepared in the context of the present invention include bags, stakes, films, mesh, pellets, pots, plates, nursery pots, tubes or sleeves, pipes, edging for lawns and any form that would be used in contact with plant root systems

The choice of thermoplastic polymer is dependent on the application. For example, if the application is a nursery plant container, polystyrene and polyolefins are preferred. If the application is a bag used to wrap the roots of a plant, preferably a low density polyethylene is used. If the application is for lawn edging or lawn pipes or tubes, polyolefins are preferentially used.

The copper compound used in the invention should be stable at the temperatures at which the thermoplastic polymer is processed. The diffusion rate of the copper compound out of the thermoplastic polymer compound is also a consideration in selecting the combination of polyer and copper compound. Surprisingly it was found that certain copper salts exhibit superior release of copper for root control from specific thermoplastic polymers that does not correlate with water solubility. Furthermore, for a specific copper salt, the release of copper from polyolefins does not correlate with polymer free volume or degree of crystallinity as might be expected. If water solubility and porosity control the release of copper from the polymer matrix, then the amount of copper released to the aqueous solution should follow the order of solubility, but surprisingly it was found that the release of copper from the polymer did not follow the order of solubility of the copper compounds of the invention. Specifically, for cuprous chloride, about from 0.1 % and 50% of the salt in a polymer is required. In polystyrene, CuCl is required in concentrations of about from 0.1 % to 5%, while about from 0.3% to 2.0% are preferred. In high density polyethylene, CuCl is required in concentrations of about form 1.0 to 10%, while about from 4 to 8% are preferred. In polypropylene CuCl is preferrably present in concentrations of about from 1 to 8 % . In ethylene vinyl acetate (EVA) CuCl required in concentrations of about from 1 to 10% .

The following solubility information can be used in the selection of a particular copper salt for use in the present invention.

Copper Salt Solubility

Solubility Decomp

Salt Formula % Copper g/100 K H2O Temp C

Cupric Chloride CuCI2 47.6 70.6

Copper Sulfate CuSO4 40.1 14.3 340

Copper Acetate Cu(C2H3O2)H20 32.1 7.2 240

Cuprous Chloride CuCl 64.7 0.006

Cuprous Oxide Cu2O 89.5 sparingly

Cupric Oxide CuO u

Copper Carbonate CuCO3.Cu(OH)2 57.9 a 250

Tribasic Copper CuSO4.3Cu(OH)2 56.6 u 300

Sulfate

Copper Oxychloride CuC12. 3Cu(OH)2 59.8 u 200

Copper Hydroxide Cu(OH)2 65.6 a 100

In general, copper compounds which can be used in the present invention include copper oxides, copper chlorides, copper sulfates, copper stearates, copper propionates, copper carbonate, copper borate, and organometallic compounds such as copper acetate and copper oleate. Copper chlorides have been found to be particularly satisfactory. More particularly satisfactory is cuprous chloride. The copper compound is typically provided in powder form, having a particle size of less than about 10 microns.

In order to achieve sufficient root growth inhibition without reaching toxic levels in the soil and plant, it has been found that about from 0.1 to 50% by weight of the copper compound can be used, and preferably at least about 1 % . More preferred is about from 4 to 25 % by weight of the copper compound. The specific concentrations of the copper compound will vary with the the particular copper compound and polymer selected, as noted above.

It has been found that numerous copper salts and oxides can be formulated in a variety of thermoplastic matrices in order to release or deliver copper ion from a thermoplastic device that will provide control of root growth. The specific copper salts include cupric chloride, copper sulfate, copper acetate, cuprous chloride, basic copper carbonate, tribasic copper sulfate, cuprous oxide and copper oxychloride. Preferred concentrations of copper compound in various polymers are summarized in the following table.

Specifically, for cuprous oxide, between 1 % and 50% of the salt is required. In polystyrene about from 0.1 to 15% is required. In high density polyethylene about from 10 to 50% is required and about from 20% to 40% is preferred. In low density polyethylene about from 25 to 50% is required. In EVA, about from 15 to 50% are required and about from 25 to 50 percent is preferred. When copper carbonate is used in thermoplastic articles, it is required at a rate of about from 1 to 20%. In polystyrene it is required in quantities of about from 1 % to 10%. In polyolefins it is required in a concentration of about from 1 to 20% .

One copper salt, cuprous chloride, even though sparingly soluble in water, provides excellent release of copper for root control from the polymer matrix at very low concentrations and consequently is a very economical formulation. Also, of all the copper salts, cuprous chloride provides adequate release of copper for root control from the polymer matrix at low dosage level in each of the specific polymers of interest for these plant growth applications. Accordingly, cuprous chloride is particularly preferred. The thermoplastic polymer and the copper compound can be combined by conventional melt blending techniques, in which the components in particulate form are admixed in conventional melt blending and extrusion apparatus, and then shaped into the desired final configuration. These techniques include, by way of example, single or twin screw extrusion, high speed mixing, Banbury mixing and Farrell continuous mixing. The thermoplastic polymer and the copper compound need to be substantially uniformly compounded such that the copper compound is dispersed uniformly throughout the thermoplastic polymer. The final configuration as stated above can include pellets of the polymer compound as well as shaped articles such as planting pots and films.

In a preferred method of preparation of the desired shaped polymeric compositions or articles, a masterbatch of the present polymer compounds is prepared containing about from 25 to 75% by weight of the copper compound, and then let down to the desired concentration by the addition of polymer. The let down compound is then formed into a shaped article. It may be convenient to prepare the masterbatch with a first thermoplastic polymer and then let down the masterbatch with a second thermoplastic polymer. For example, the masterbatch can be prepared with a low density polyethylene which is subsequently let down into a high density polyethylene. It is also possible to use the same polymer as both the first and second thermoplastic polymers, and this is in fact preferred for many shaped articles. Other methods of preparing shaped articles of the present invention include mixing the polymeric compound with the final concentration of the copper compound in one step, in other words, without the intermediate step of forming a masterbatch, or adding the copper compound during the forming step. The polymer compound can be formed into a variety of objects useful for inhibiting root growth in addition to conventional plant containers. For example, plates made from the polymer compound can be made to fit in the bottom of an ordinary plant container. Also, a sleeve made from the polymer compound can be made for insertion inside a plant container. Similarly, stakes fashioned from the polymer compound can be inserted into soil surrounding a plant. By selectively placing such stakes, root growth can be inhibited in particular locations while not affecting root growth elsewhere. It is also possible to form film from the polymer compound which can be used to line containers or wrap the roots of plants not in containers. Other shaped articles for which the polymer compound of the present invention can be useful include lawn edging, trickle pipe and tubing.

Shaped articles of the present invention can also be prepared by coextrusion techniques. In these articles, a layer of polymer with copper compound is used in conjunction with a layer of polymer without copper compound. Using conventional coextrusion techniques, the two layers can be, and typically are, formed simultaneously. However, the layers can be formed sequentially if desired. When such coextrusion techniques are used, the layer of polymer with copper compound comprises about from 10 to 99% of the coextruded article, and preferably at least about 50% of the coextruded article. With such coextruded articles, the layer with copper compound is positioned to contact the plant roots in the shaped article.

An advantage of the present invention is the regular and sustained release of the copper compound from the thermoplastic polymer. As noted above, copper in plant tissue is a required micronutrient at a level about 5-10 ppm and toxic at levels higher than about 20 ppm. By appropriately selecting the combination of the thermoplastic polymer and the copper compound, the release of the copper compound from the polymer can be sufficient to control root growth without reaching toxic levels in the soil and plant.

The present invention is further illustrated by the following specific examples, in which parts and percentages are by weight unless otherwise indicated. EXAMPLES 1-3 AND COMPARATIVE EXAMPLES A-C

For Examples 1-3, containers were formed using a high density polyethylene. The containers incorporated 4, 8 and 25% cuprous oxide. For comparative Example A, the container contained no cuprous oxide. In comparative Example B, the container was the same as Example 1, but with only 1 % copper compound incorporated. In comparative Example C, a pot was surface treated with a 7% by weight solution of cupric hydroxide in an inert paint carrier.

Uniformly graded seedling plugs of Radermachia sinica (also known as China Doll) were potted in 2/3 liter containers. The potting medium consisted of, by volume, 5 parts pine bark, 4 parts peat moss, one part sand with a pH of about 4.6 and was top dressed with 7g of 18-6-12 fertilizer per pot.

The plants were arranged randomly on a wire mesh bench with 4 harvests and 10 pots per treatment. The plants were grown under 400 W sodium vapor HID lamps spaced about 1 meter apart and about 1 meter above the plant canopy. The lamps were on about from 6:00 a.m. to 6:00 p.m. daily. Greenhouse temperatures averaged about 21°C and ranged about from 15 to 25°C. The plants were irrigated as needed (about every 2 to 3 days) and fertilized weekly with 10-10-10 fertilizer, providing about 200 ppm N in each treatment. Fungicide and pesticide were applied as needed.

Root growth was assessed after 8 weeks. A root growth rating system was established on a scale of 1-5. A rating of 1 indicates that less than 20% of the rootball was covered with white root tips but exhibited no circling growth. A rating of 3 indicates that 50% of the rootball was covered with white root tips and moderate circling growth was present. A rating of 5 indicates that greater than 80% of the root ball was covered with white root tips and extensive circling growth was present.

As shown in Table I, Examples 1, 2 and 3 with C112O of 4, 8 and 25% by weight, respectively, exhibited satisfactory root growth control. 1 % Q12O comparative Example B was not effective in controlling root growth. Comparative Example C also provided satisfactory root growth control but the soil and plant analysis indicated toxic levels of copper in the roots and shoots.

TABLE I

EXAMPLES 4-12

The general procedure of the previous Examples was repeated, except that cuprous oxide was used in Examples 4-7 and cupric oxide (CuO) was used in Examples 8-12.

As shown in Table II, cuprous oxide (Examples 4-7) provided greater control of root growth than the divalent cupric oxide used in Examples 8-12. This difference is surprising in view of the fact that these compounds are both insoluble salts.

TABLE π

EXAMPLE 13

If the general procedure of the previous examples is repeated using about 50% by weight of cuprous oxide in the polymer compound, root growth inhibition will be realized comparable to the results obtained in the previous examples.

EXAMPLES 14-18 AND COMPARATIVE EXAMPLE D

The procedure of Examples 1-3 was repeated except that cuprous chloride, cuprous oxide, copper sulfate and a control were used. In addition to the plantings, containers incorporating the above copper compounds without any drainage holes were filled with an aqueous buffer solution (5.5pH) and placed in the greenhouse at the same growing conditions of the greenhouse at the same growing conditions of the greenhouse specified. Samples of the solution were removed from the container and analyzed for copper using atomic absoφtion spectroscopy the total quantity of copper ion present in solution after eight weeks is shown in the following Table III

TABLE m

Additional greenhouse plantings were performed which confirmed that cuprous chloride at 5.5% in the high density polyethylene containers was the minimum level of copper salt that would provide complete control of plant roots.

EXAMPLES 19-27 AND CONTROL EXAMPLE E

In Examples 19-27 and Control Examples E, high density polyetheylene piques containing 15% ot elemental copper suppled by copper salts were prepared an analyzed. The plaques were tested in an acquesout solution over 8 weekes, and the percent of copper release from the plaques was measured. The quantities of copper released are summarized in Table IV.

TABLE IV

EXAMPLES 28-32 AND CONTROL EXAMPLE F

In Examples 28032 and Control Example F, the general procedure of Examples 1-3 was repeated, and the results are summarized in in the following Table V.

TABLE V

Claims

WHAT IS CLAIMED IS:

1. A polymeric composition for controlling plant growth comprising at least one thermoplastic polymer and from 0.1 to 50% by weight of at least one copper compound uniformly blended therewith.

2. The polymeric composition of Claim 1 wherein the thermoplastic polymer is selectd form the group consisting of polyolefm and polystyrene and the copper copound is at least one copper chloride.

3. The polymeric composition of Claim 2 wherein the polyolefm is selected from the group consisting of polyethylene and polypropylene and the copper chloride is cuprous chloride.

4. A polymeric composition of Claim 2 wherein the polyolefm is a high density polyethylene and the copper chloride is cuprous chloride.

5. A polymeric composition of Claim 1 comprising at least about 1 % of at least one copper compound.

6. A polymeric composition of Claim 5 comprising about from 4 to 25% of at least one copper compound.

7. The polymeric composition of Claim 6 comprising about from 8 to 15% by weight of the at least one copper compound.

8. The polymeric composition of Claim 7 wherein the copper compound is cuprous chloride.

9. A shaped polymeric composition for controlling plant growth comprising the thermoplastic polymer and copper compound of any of

Claims 1-8.

10. A process for preparing the compound of Claim 1 comprising blending about from 0.1 to 50% by weight of at least one copper compound with at least one thermoplastic polymer.

11. A process of Claim 10 comprising blending about form 25 to 75% by weight of at least one copper compound with at least one thermoplastic polymer to form a masterbatch and letting down the masterbatch with the same or different second thermoplastic polymer to form the 0.1 to 50% by weight of at least one copper compound.

12. The process of Claim 10 wherein the copper compound is copper chloride.

13. The process of Claim 12 where the copper chloride is cuprous chloride.