WO1996023635A1

WO1996023635A1 - Diffusible wood preservatives

Info

Publication number: WO1996023635A1
Application number: PCT/AU1996/000039
Authority: WO
Inventors: Heikki Mamers; Kevin James Mccarthy
Original assignee: Commonwealth Scientific And Industrial Research Organisation
Priority date: 1995-01-30
Filing date: 1996-01-30
Publication date: 1996-08-08
Also published as: AUPN082795A0

Abstract

The present invention provides a composition having biocidal and/or preservative properties, the composition including at least one metal chelate having a neutral or negative charge.

Description

DIFFUSIBLE WOOD PRESERVATIVES

The present invention relates to wood preservative compositions. More particularly, it relates to wood preservative compositions and formulations containing biocidal compounds suitable for providing protection to timber and similar wood-based materials.

Whilst water-soluble metal salts have long been used to prevent the biological degradation of timber and other cellulosic materials, their action is generally confined to the surface layers or porous sapwood region of the wood being treated. This restriction stems from both the chemical nature of the currently used biocidal metal salts and the nature of wood itself.

A commonly used biocidal, water-soluble metal salt is cupric sulphate,

CuSO_4l which is a component of the so called "Bordeaux mixture" for the treatment of surface fungal infections of agricultural crops. It is also part of the copper-chrome-arsenic formulation known as CCA and extensively used for the preservation of timber. In aqueous solution cupric sulphate predominantly exists as positively charged cupric ions (Cu⁺⁺) and negatively charged sulphate ions

(S0₄-).

In timber, the wood substance consists primarily of cellulose and lignin. Cellulose is a high molecular weight polymer based on anhydroglucose monomer units, each of which contains three free hydroxyl groups. The average degree of polymerisation is about 4,000-5,000 anhydroglucose units for both softwood and hardwood cellulose. Lignin, a complex high molecular weight aromatic polymer of indeterminate structure, is known to be rich in phenolic, carboxylic and aldehydic groups. When dissolved metal ions, such as the positively charged cupric ions of cupric sulphate, encounter the reactive, negatively charged hydroxyl groupings of cellulose or the negatively charged phenolic, carboxylic or aldehyde groupings in lignin, they are rapidly bonded on to the wood in the form insoluble co-ordinate metal complexes. The result of this co-ordinate bonding is to restrict the diffusibility of the cupric (or other metal) ions within the wood substance.

In theory, the diffusibility barrier could be overcome by completely saturating all of the reactive sites within the wood substance by metal ions but, in practice, this would be a prohibitively expensive option. At best, water-soluble metal salts such as cupric sulphate can only provide biological protection to the open structured sapwood part of timber, where the treating solution is introduced by physical transport rather than by diffusion. It is found that ionic metal salts provide minimal protection to the denser heartwood components of timber, which are impermeable to the flow of treating solutions.

Johanson ("Copper-fluorine-boron diffusion wood preservative. 1. Chemistry and properties of highly concentrated Cu-F-B preparations", Holzforschung, 28, No.4, 148-153 (1974)); Australian Patent 491638) recognised the strong absorptive reactions of the Cu⁺⁺ ion with the timber substrate. He found that the diffusibility of the cupric ion could be improved by forming the tetra- ammine complex [Cu(NH₃)₄2H₂O]⁺⁺ by reacting the dissolved cupric ion with ammonia solution. The tetra-ammine complex showed improved diffusibility in wood relative to the original cupric ion despite its still being positively charged. In practice, wood preservatives based on the copper tetra-ammine complex have a number of disadvantages that militate against their use. Firstly, it is found that excess ammonia must be present to stabilise the complex; when the ammonia evaporates the complex decomposes and the enhanced diffusibility is lost. Secondly, the necessary presence of excess ammonia poses a hazard in both manufacture and use of the complex and for many end uses the strong ammoniacal odour of the wood preservative is unacceptable.

We have now found, surprisingly, that the diffusibility of metal ions in moist timber substrates can be further improved by the use of a complex which has a neutral or negative charge. Accordingly, in a first aspect, the present invention provides a composition having biocidal and/or preservative properties, the composition including at least one metal chelate having a neutral or negative charge.

We have found that such neutral or negatively charged chelates do not immediately bond to the wood substance and offer the means of diffusing metal ions into the wood substance, including the heartwood component. Thus by suitable selection of metal ions and ligands we have found it possible to prepare a range of effective, environmentally acceptable biocidal chelates capable of affording long term protection to timber and other similar materials and which do not suffer from the aforementioned disadvantages of prior art wood preservatives based on positively charged metal ions or their ammine complexes.

Preferably the metal chelate is one which is water soluble and non-volatile. The metal chelate may be one in which the metal ion is co-ordinately bonded to an appropriate ligand such that the resultant metal ion complex has a neutral or negative charge.

Metal chelates or chelation complexes, commonly referred to simply as chelates, are known per se as compounds having a cyclic structure and formed by coordinate bonding of a compound containing donor atoms ("chelation agent" or "ligand") with a single metal ion. Depending on the choice of ligand, the resulting chelate may carry a positive or negative charge or be electrically neutral.

Without wishing to limit the invention in any way, we provide the following technical explanation of the stability of metal chelates in accordance with the present invention. In solution, metal chelates are always in a state of equilibrium between the solvated metal ion, the ligand and the chelation complex as represented by:

[M] + [L] <→ [ML]

Solvated Ligand Chelation complex metal ion

In simple systems, the equilibrium is defined by the "K-, value" or stability constant according to:

K - -^L

The higher the < value, the more stable the complex. If, for example, log

KT equals say 24, then the amount of solvated metal ion present in the equilibrium solution is only 10^"12 of the amount present in the chelated complex. For a log K, value of say 8, the ratio between the concentrations of the complexed and the solvated metal ion becomes 1 :10^"4 and so on. If the chelate is in the presence of a second source of ligands (which as noted above is the case with a chelate solution impregnated into timber), a further, competitive equilibrium will be established:

[WM] <- [M] 4 [L] *> [ML]

Wood-metal Solvated Ligand Chelation ion complex metal ion complex

Suitable metal ions for the preparation of biocidal chelates for the purposes of the present invention are those of the groups of metallic elements generally known as the transition elements and the rare earths. Among the transition elements, copper and zinc are preferred, either singly or in combination, or in admixture with one or more of the other transition metals. Of the metallic rare earth elements, cerium, lanthanum and yttrium are preferred but the whole group of sixteen naturally occurring metallic rare earth elements are suitable, either individually or in combinations of two or more thereof. Mixtures of transition elements and the rare earths may also be employed for the purposes of the invention.

Preferably the metal ion is present in an amount of 0.1 to 35% m/m of the composition of the invention.

The selection of ligands suitable for use in the practice of the invention is governed, inter alia, by the position of the abovementioned equilibrium between the metal ions complexed to the wood substance and the metal ions bound up in the chelate complex. The position of this equilibrium is a function of the K-. value of the chelate and the relative abundance and complexing ability of the ligands in the timber structure. The ability to select ligands to produce chelates of different K. values is an important and preferred feature of the invention. Chelates with a low K₁ value favour a limited extent of diffusion of metal ion into the timber substrate but a high degree of retention of the metal ion in the timber within the diffusion zone. Conversely, chelates with a high K, value favour extensive penetration of the chelate into the timber but a lower retention of the metal ion by the wood substance. It is thus possible by suitable choice of ligand to achieve any desired balance between the extent of diffusion and the degree of retention of the metal ion.

It is particularly preferred in choosing the ligand to be combined with the metallic element to ensure that the resultant metal chelate will be substantially water-soluble. Preferably the metal chelate complex, when in solution, should have a neutral or negative charge to ensure that the complex is not rapidly bonded to the negatively charged groups in the cellulose and lignin of the wood and thus insolubilised, prematurely restricting the diffusibility of the metal complex within the wood substance. Suitable ligands include, but are not limited to, monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, natural and synthetic amino acids, aliphatic and aromatic amines and complex inorganic acids and salts thereof. Examples of suitable ligands are salicylic acid, maleic acid, oxalic acid, malic acid, tartaric acid, phthalic acid, citric acid, glycine, alanine, valine, glutamic acid, iminodiacetic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid (EDTA), propylene diamine, triethylene tetramine, methylpyridine, polyphosphoric acid, and soluble salts thereof.

In general, the metal chelates of the invention may be simply prepared by known methods such as by reacting appropriate proportions of an aqueous solution of the chelating agent with a suitable salt of the chosen metal until a clear solution of the chelate is obtained. Suitable metal salts include but are not limited to carbonates, basic carbonates, hydroxides, basic oxides and oxides of metals having appropriate biocidal activity. The reaction conditions required to form the metal chelates may vary from dissolution at ambient temperature to several hours' vigorous stirring under reflux and must be determined by experiment. In some cases it may be necessary to adjust the pH of the solution to obtain a clear solution of the chelate. The clear solution may then be evaporated to dryness to yield the solid chelate which may then be ground to an appropriate size for incorporation into wood preservative formulations. Alternatively, the chelate solution may be used directly in the formulation of wood preservative compositions without the need to isolate the solid chelate. This approach is essential in the case of metal chelates which are stable in aqueous solution but decompose upon drying as, for example, is the case with chelates prepared from ligands such as propylene diamine or triethylene tetramine.

The compositions of the invention may include biocidal metal chelates individually or in combinations as treatment agents for the preservation of timber and similar cellulosic materials. Alternatively, mixtures of chelates which incorporate different metals may be used to enhance the efficacy of the composition, for example to counter destructive organisms which may have acquired a tolerance towards a particular metallic element. The metal chelates may also be used to supplement the activity of other, known biocidal elements or compounds.

The metal chelates may be introduced into the timber substrate by any of the methods known to those experienced in the art of timber treatment and protection. The composition of the invention may be in the form of a aqueous solution or emulsion for application to timber by spraying, dipping or pressure impregnation. The composition of the invention may also be in the form of a powder, tablet, rod, paste or other formulation appropriate for application as a wood preservative in particular circumstances. The composition of the invention may be in the form water-soluble rods or tablets for insertion into holes drilled in the wooden structure to be protected. The composition of the invention may further include an effective amount of a boron compound and/or a fluorine compound. The boron compound may be in the form of a soluble salt. Similarly the fluorine compound may be in the form of a soluble salt.

The boron compound may be present in an amount of 0.1 to 30% m/m of the composition of the invention.

The fluorine compound may be present in an amount of 0.1 to 40% m/m of the composition of the invention.

The composition of the invention may also include a polyhydric polyol, for example, ethylene glycol, propylene glycol or glycerol. Boron and fluorine, in the form of soluble salts such as borates, fluoroborates and fluorides, are becoming increasingly important as environmentally acceptable timber preservatives. In Australia, water-soluble rods containing relatively high concentrations of borates and fluorides are rapidly becoming the preferred method for the ground line remedial preservation of wooden utility poles.

We have found that the chelates of the present invention may be used to introduce diffusible biocidal metals into such rod formulations and that, surprisingly, the metal component remains diffusible throughout the lifetime of the preservative treatment and does not form insoluble borates and fluorides by reaction with the other constituents of the rod formulation.

In a further aspect the present invention provides a method of treating wood or a wood-containing product, the method including applying to the wood a composition in accordance with the invention.

In yet a further aspect the present invention provides novel metal chelates.

The invention is further illustrated by reference to the following non-limiting examples in which all parts are parts by weight.

Example 1

This example demonstrates the preparation and diffusion/ fungitoxic testing of a neutrally charged metal chelate prepared by reacting basic copper carbonate with two equivalents of the bidentate ligand glycine to form copper di-glycinate chelate.

The overall reaction to form the chelated complex may be represented as: CuCO₃.Cu(OH)₂ + 4[H₂NCH₂COOH] = 2[Cu(H₂NCH₂COO)₂] + CO₂ + 3H₂O Basic copper Glycine Copper di-glycinate carbonate chelate

The glycine acts as a bidentate ligand, forming a double ring to enclose the copper atom in an electrically neutral complex having a copper content of about 30% m/m and a reported log K-, value of 8.6:

The solubility of the complex is about 10 g/L at 21 °C, the pH of the saturated solution being about 9.

The chelate was prepared by dissolving 54.3 parts of glycine in about 1600 parts of boiling water. Basic copper carbonate (40 parts) was then introduced and the reaction mixture stirred and boiled under reflux for about three hours, during which period the basic copper carbonate dissolved and combined with the glycine to form a dark blue solution of copper di-glycinate chelate. The solution was evaporated to dryness under atmospheric conditions at about 65°C to give a dark blue residue of substantially anhydrous copper di-glycinate crystals, which were then further ground to a powder passing through a 40 mesh sieve.

The diffusibility and fungitoxicity of the copper di-glycinate chelate was tested by the slab diffusion method described by Da Costa and Greaves ("Laboratory Test Procedures", Proceedings of Tropical Wood Preservation Seminar, Port Moresby, 1975). In this test the prospective preservative is contacted with a strip of open celled sponge in the bottom of a Petri dish. A water saturated timber slab measuring 50x50x6 mm, with the edges sealed by dipping in petroleum jelly and paraffin wax, is placed on top of the sponge. Diffusion of toxicant through the slab is assessed by placing a strip of inoculated agar on top of the slab, at right angles to the grain direction of the slab. Inhibition of fungal growth on the strip of inoculated medium will occur if the toxicant diffuses through the slab and attains a sufficiently high concentration in the strip of inoculated medium.

Slabs of heartwood were cut from Grey Ironbark (E.drepanophylla), a durability class 1 timber with a density of about 870 kg/m³. Replicate slabs were saturated under vacuum with water prior to use and then edge sealed. A stiff paste of the copper di-glycinate chelate was made up with water and the paste applied to the sponge applicator referred to above.

After a pre-diffusion period of two days, the upper surface of the slabs was inoculated with an agar strip infected with a mixed inoculum. The same procedure was also carried out for the untreated controls. The slabs were then incubated at 28°C and 85% RH and scored for fungal activity after 7, 14, 21 and 28 days. Scoring was on the following basis:

0 - no evidence of fungal growth

1 - slight mycelium development

2 - moderate fungal growth

3 - good fungal growth

Three replicate slabs were used for the test and a further three for the untreated controls. The results were averaged and are shown in Table 1.

TABLE 1

Slab diffusion testing of copper di-glycinate chelate

Chelate Diffusion Diffusion period (days)* substrate 7 14 21 28

Copper Grey Ironbark di-glycinate heartwood 1.5 2.17 0.83 0

Untreated Grey Ironbark control heartwood 2.67 3.0 3.0 3.0

^* = Average of three replicates

The averaged scores from the slab diffusion tests after 28 days were

interpreted in this and the subsequent examples on the following basis:

Zero - Very Effective preservative

Less than 1.0 - Effective preservative

Between 1.0 and 2.0 - Marginally Effective preservative

Above 2.0 - Ineffective as a preservative

Table 1 shows that the copper di-glycinate chelate had an averaged score of zero after 28 days, making it a "Very Effective" preservative and demonstrating that the neutrally charged copper chelate was both diffusible and fungitoxic. Th untreated control slabs supported vigorous fungal growth throughout the 28 da test period.

Example 2

This example illustrates the preparation and diffusion/fungitoxic testing of a negatively charged metal chelate. The chelate was prepared by reacting basic zinc carbonate with two equivalents of iminodiacetic acid in the presence o ammonium hydroxide to form the zinc diammonium di-iminodiacetic acid chelate. The overall reaction may be represented as:

ZnCO₃.Zn(OH)₂ + 4[HN(CH₂COOH)₂] + 4[NH₄OH] = Basic zinc Iminodiacetic Ammonium carbonate acid hydroxide

2[(NH₄)₂[Zn(NH(CH₂COO)₂)₂]] + CO₂ + 7H₂O Zinc diammonium di-iminodiacetic acid chelate

The structure of the negatively charged 2:1 binary zinc chelate may be represented as: coo-

The chelate was prepared by dissolving 199.7 parts of iminodiacetic acid in 1000 parts of water at about 60°C. Basic zinc carbonate (84.5 parts) was then dispersed in the iminodiacetic acid solution and sufficient ammonium hydroxide added to raise the pH of the mixture to about 9. The clear solution was evaporated to dryness at about 65°C and the residual chelate ground to pass through a 40 mesh sieve. The zinc diammonium di-iminodiacetic acid chelate had a zinc content of about 18.0% m/m and a solubility of about 286 g/L at 21 °C. The log K, value for this chelate has been reported as 7.0.

The diffusion/fungitoxic characteristics of the zinc diammonium di- iminodiacetic acid chelate were assessed by the slab diffusion technique of Example 1 using Spotted Gum (E.maculata) heartwood, a hardwood of basic density about 880 kg/m³, as the diffusion substrate. The results are summarised in Table 2.

TABLE 2

Slab diffusion testing of zinc diammonium di-iminodiacetic acid chelate

Chelate Diffusion Diffusion period (days)^* substrate 7 14 21 28

Zinc di-ammonium Spotted Gum di-iminodiacetic heartwood 0.83 0.83 0.67 0.33 acid

Untreated Spotted Gum control heartwood 2.67 2.83 2.50 2.33

^* = Average of six replicates

At the end of the 28 day test period, the negatively charged zinc diammonium di-iminodiacetic acid chelate scored 0.33, making it an "Effective" preservative.

Example 3

This example relates to the preparation and diffusion/fungitoxic testing of chelates prepared from the rare earths lanthanum, yttrium and cerium. The chelates prepared were lanthanum tri-maleic acid, yttrium tri-iminodiacetic acid and cerium/di-sodium ethyienediaminetetraacetic acid (EDTA). The reagents and quantities used in the preparations are summarised in Table 3(a). 12 TABLE 3(a)

Preparation of rare earth chelates

Source of metal Ligand Water Nominal formula ion (parts) (parts) (parts) of chelate

La₂O₃ Maleic acid 500 La[CH(COO) : (25) (53.4) CH(COO)]₃

Y₂O₃ Iminodiacetic 500 Y[NH₂(COO)₂]₃

(9.6) acid (33.9)

Ce₂(CO₃)₃ EDTA (Na)₂* 500 Ce[CH₂N(CH₂COO) (30) (72.8) CH₂COONa]₃

* EDTA (Na)₂- ethylenediaminetetraacetic acid, disodium salt dihydrate.

In each case the ligand was dissolved in the indicated quantity of water and the oxides (lanthanum, yttrium) or carbonate (cerium) dispersed in the resultant ligand solution. The reaction mixture was then stirred under reflux for about two to three hours until a clear solution was obtained. The chelates were recovered from the solutions by evaporation under atmospheric conditions at about 65°C.

The physical properties of the rare earth chelates are summarised in Table 3(b). TABLE 3(b)

Physical properties of rare earth chelates

Chelate Active Log K, Solubility Solution element (g/L at 21°C) pH^*

(%/m/m)

Lanthanum tri-maleic acid 28.9 3.5 150 2

Yttrium tri-iminodiacetic acid 18.4 6.8 > 1000 3

Cerium/di-sodium

EDTA 21.8 15.5 > 1000 10

^* = pH of reaction mixture before evaporation

The diffusion/fungitoxic characteristics of the rare earth chelates were assessed by the slab diffusion method of Example 1. Spotted Gum (E.maculata) heartwood was used as the diffusion substrate for the yttrium tri-iminodiacetic chelate and Tasmanian Oak heartwood, a hardwood of basic density about 590 kg/m³, as the diffusion substrate for the lanthanum and cerium chelates. The results summarised in Table 3(c) show that all three rare earth chelates were sufficiently diffusible and fungitoxic to completely eliminate all fungal growth within a few days of application, rating them as "Very Effective" preservatives. TABLE 3(c)

Slab diffusion testing of rare earth chelates

Chelate Diffusion Diffusion period (days)^* substrate 7 14 21 28

Lanthanum Tasmanian Oak tri-maleic acid heartwood 0.17 0 0 0

Untreated Tasmanian Oak control heartwood 3.0 3.0 2.67 2.5

Yttrium Spotted Gum tri-iminodiacetic heartwood 0 0 0 0 acid

Untreated Spotted Gum control heartwood 1.67 2.0 2.0 2.5

Cerium/di- Tasmanian Oak sodium EDTA heartwood 0 0 0 0

Untreated Tasmanian Oak 2.5 2.5 2.5 2.5 control. heartwood

= Average of six replicates

Example 4

This example illustrates the preparation and diffusion/fungitoxic testing of an inorganic chelate derived from the reaction of basic copper carbonate with sodium tripolyphosphate (STPP).

The overall reaction leading to formation of the chelate may be summarised as: CuCO₃.Cu(OH)₂ 2(Na₅P₃O₁₀) + H,O = Basic copper Sodium tri- carbonate polyphosphate

2[Na₅(Cu(OH)₂P₃O₁₀)] + CO₂ Copper STPP chelate

Ellison and Martell (Journal of Inorganic and Nuclear Chemistry, Volume 26, pages 1555-60 (1964)) attribute a bidentate structure to the negatively charged tripolyphosphate chelate:

A three-fold stoichiometric excess of STPP was used to fully solubilise the basic copper carbonate. Thus, STPP (49.9 parts) was dissolved in water (500 parts) and basic copper carbonate (5 parts) was dispersed in the solution. The mixture was stirred under reflux for about one hour to produce a clear blue solution.

The copper-STPP chelate had a solubility of about 510 g/L at 21°C, a copper content of about 5.3% m/m and a pH of about 8 in saturated solution. Its log K, value has been reported to be 7.3. The diffusion/fungitoxic characteristics of the copper-STPP chelate were evaluated by the method of Example 1. Tasmanian Oak heartwood was used as the diffusion substrate. The results are summarised in Table 4. 16 TABLE 4

Slab diffusion testing of copper-STPP chelate

Chelate Diffusion Diffusion period (days)^* substrate 7 14 21 28

Copper- STPP Tasmanian Oak heartwood 1.5 1.17 0.67 0

Untreated Tasmanian Oak control heartwood 2.17 2.17 2.50 2.67

* = Average of six replicates

Table 4 shows that the copper-STPP chelate eliminated all fungal activity on the Tasmanian Oak heartwood slabs after 28 days, indicating the negatively charged inorganic chelate to be a "Very Effective" preservative. The untreated control slabs supported vigorous fungal growth throughout the 28 day test period.

Example 5

This example illustrates the preparation and testing of a water soluble wood preservative rod which includes a copper chelate, a boron compound and a fluorine compound and in which all three fungitoxic elements boron, fluorine and copper remain diffusible through a timber substrate.

The components of the diffusible rod formulation are shown in Table 5(a).

TABLE 5(a)

Components of diffusible rod formulation

Component Parts

Propylene glycol 26.9 Boric oxide 41.6 Sodium fluoroborate 26.0 Copper di-glycinate chelate* 26.0

Prepared as in Example 1.

The sodium fluoroborate, copper di-glycinate chelate and boric oxide were mixed batch-wise into the propylene glycol at ambient temperature to form a stiff paste which was then allowed to stand for 16 hours to complete the formation of propylene glycol borate ester in accordance with the overall reaction: 2B₂O₃ + 3[CH₃CH(OH)CH₂OH)] = [3(CH₃CHCH₂)]B₂O₆ + 2H₃BO₃ Boric Propylene glycol Propylene glycol Boric oxide borate ester acid

The mixture was then heated for 15 minutes at 115°C to polymerise the propylene glycol borate ester and form a malleable paste. The paste was cast into PTFE-lined moulds 15mm in diameter by 50mm long. After cooling of the moulds to ambient temperature, the product was recovered therefrom in the form of tough, glassy rods which on an elemental basis contained about 12.9% m/m boron, 14.9% m/m fluorine and 6.2% m/m copper, for a total of about 34.0% m/m active elements. For ease of reference, we term these rods "BFC" rods (i.e. Boron, Fluorine, Copper).

Samples of the BFC rods were ground to pass through a 40 mesh sieve. The ground rod material was then wetted with water to form a paste and the paste tested for diffusibility and fungitoxicity by the slab diffusion method of Example 1 , using Grey Ironbark heartwood as the diffusion substrate. The results are summarised in Table 5(b).

TABLE 5(b)

Slab diffusion testing of boron, fluorine, copper fBFC^ rods

Test material Diffusion Diffusion period (days)^* substrate 7 14 21 28

BFC rods Grey Ironbark heartwood 0 0 0 0

Untreated Grey Ironbark control heartwood 3.0 3.0 3.0 2.7

^* = Average of three replicates

These results show that the BFC rods were sufficiently diffusible and fungitoxic to completely suppress fungal growth within seven days and to maintain zero fungal growth for the twenty eight day test period. The BFC rods were thus a "Very Effective" preservative. The untreated control slabs supported good fungal growth throughout the entire test. At the conclusion of the twenty eight day test period, the upper surfaces of the BFC-treated slabs were sprayed with indicators (prepared according to AS 1605 - 1974) to detect the presence of diffusible elements. The indicators used were:

Boron - Turmeric test (first method) - gives a red to red-brown colour in the presence of boron compounds.

Fluorine - Zirconium oxychloride - wood containing sodium fluoride turns yellow but untreated wood becomes dark red.

Copper- Chrome azurol S - gives a deep blue in the presence of copper. Spraying the upper surfaces of the BFC-treated diffusion slabs with the above indicators gave strong colour reactions for each of the elements boron, fluorine and copper, showing that all three elements had diffused through the slabs and that they remained diffusible for the duration of the test period.

The results also show that the copper di-glycinate chelate had not reacted with the boron and/or fluorine in the formulation to form insoluble copper borates or fluorides, as would have occurred had the copper been included as a simple ionisable salt such as cupric sulphate.

Example 6

This example demonstrates that the amount of copper retained within the wood structure as insoluble copper-wood complexes can be regulated by the selection of copper chelates having different stability constants (Ki values). It also shows how appropriate selection of the ligand to prepare a metal chelate may be used to vary the proportion of the metallic element which becomes bonded to the timber substrate under treatment.

Copper chelates based on the ligands listed in Table 6 were prepared by the method of Example 1. Each chelate solution was diluted to contain the equivalent of 5 g/L elemental copper content prior to being impregnated into batches of twelve 20x20x10 mm air-dry blocks of P. radiata sapwood of basic density about 480 kg/m³, using successive pressure and vacuum cycles to saturate the wood structure with the solutions. Six of the saturated blocks from each batch were air dried immediately and analysed for their copper content. The remaining blocks were leached for seven days in a shaker bath held at

35°C, with daily changes of water in the leaching jars. The leached blocks were then analysed for copper content and the results compared with those for the unleached blocks (Table 6). TABLE 6

Copper retention in copper chelate-impreαnated P. radiata blocks after seven days' leachino

Ligand Log K-) of copper % of copper retained

chelate after leaching

Phthalic acid 3.1 40.6

Maleic acid 3.4 51.5

Glutamic acid 7.7 28.4

Iminodiacetic acid 10.6 3.4

Nitrilotriacetic acid 13.1 0.4

EDTA(Na)₂ ^* 18.3 0.0

^* EDTA(Na)₂ - ethylenediaminetetraacetic acid, disodium salt dihydrate

The results in Table 6 demonstrate the importance of the stability constant in determining the equilibrium between metal ions complexed to the wood substance and metal ions bound up in the water-soluble chelate complex. It can be seen that for chelates with a low Kt value there was a high degree of retention of the metal ion within the timber, whilst for chelates with a high K-| value there was a lower retention of the metal ion by the wood substance. It follows from these results that chelates with a low Ki value will diffuse into a timber substrate to a more limited extent than chelates with a higher K-i value and that, by a suitable choice of ligand, a balance can be struck between metal ion retention and metal ion diffusion within a timber substrate to meet specific treatment and end-use requirements. Example 7

This example illustrates the preparation and diffusion/fungitoxic testing of water-based preservative rods containing copper, boron and fluorine as active elements, in which the copper chelate was prepared in situ during the formulation of the product. It also demonstrates that metal chelates may be used in conjunction with known fungitoxic elements such as boron and fluorine without antagonistic reactions occurring, such as the formation of insoluble metallic borates or fluorides which would otherwise occur if the metals were introduced as their cations.

Table 7(a) shows the components required for one thousand parts of such a preservative rod formulation containing about 4.0% m/m copper, 12.4% m/m boron and 11.0% m/m fluorine, for a total of about 27.4% m/m active elements.

TABLE 7(a) Components required for 1000 parts of a water based preservative rod formulation containing about 4.0% m/m copper. 12.4% m/m boron and 11.0% m/m fluorine as active elements

Component Formula Component

(parts)

Copper hydroxide Cu(OH)₂ 61.4

EDTA(Na)₂ ^* [CH₂N(CH₂COOH) 234.2 CH₂COONa]₂.2H₂O

Sodium NaBF₄ 158.8

fluoroborate

Borax Na₂B₄O₇.10H₂O 199.9

Boric acid H₃BO₃ 159.9

Boric oxide B₂O₃ 185.8

^* EDTA(Na)₂ - ethylenediaminetetraacetic acid, disodium salt dihydrate The components were blended into a uniformly mixed powder and then heated to about 90°C, whereupon the components began to dissolve in the water of crystallisation released from the borax and the EDTA(Na)₂. Simultaneously, the copper hydroxide began to react with the EDTA(Na)₂ to form the copper/disodium EDTA chelate. The mixture was stirred until the chelation reaction was complete and the components had homogenised to give a blue, smooth textured paste.

The hot paste was cast into PTFE-lined cylindrical moulds as described in Example 5 to give a product in the form of tough, glassy rods. The rods were ground to pass through a 40 mesh sieve and the ground material wetted with water to form a paste which was tested for diffusibility and fungitoxicity by the slab diffusion method of Example 1 , using Tasmanian Oak heartwood as the diffusion substrate. The results are summarised in Table 7(b).

TABLE 7(b)

Slab diffusion testing of preservative rods containing copper, boron and fluorine

Test Material Diffusion Diffusion period (days)^*

substrate

7 14 21 28

Water based Tasmanian Oak 0.17 0.08 0.08 0

copper/boron heartwood

/fluorine rods

Untreated Tasmanian Oak 3.0 3.0 3.0 3.0

control heartwood

= Average of six replicates The results show that the water-based preservative rods completely suppressed fungal growth within 28 days, making them a "Very Effective" preservative, whereas the untreated control slabs supported good fungal growth for the entire test period. After 28 days' diffusion the upper surfaces of the treated slabs were sprayed with elemental indicators as described in Example 5 to detect the presence of diffusible elements. The slabs showed a strong colour response towards all three biocidal elements, indicating that the copper, as well as the boron and fluorine, had diffused through the 6mm thickness of the Tasmanian Oak heartwood slabs. The results also show that, as in Example 5, the chelated copper had remained diffusible and fungitoxic and had not reacted with the other biocidal components to form insoluble copper borates and fluorides.

Claims

CLAIMS:

1. A composition having biocidal and/or preservative properties, the composition including at least one metal chelate having a neutral or negative charge.

2. A composition according to claim 1 wherein the composition is water- based.

3. A composition according to claim 1 or claim 2 wherein the composition is a wood preservative composition.

4. A composition according to any one of the preceding claims wherein the metal chelate is water-soluble and non-volatile.

5. A composition according to any one of the preceding claims wherein the metal chelate is freely diffusible in moist wood.

6. A composition according to any one of the preceding claims wherein the metal chelate is a metal ion coordinately bonded to a ligand such that the resultant metal ion complex has a neutral or negative charge.

7. A composition according to any one of the preceding claims wherein the metal ion is present in an amount of about 0.1 to 35% m/m of the composition. .

8. A composition according to claim 7 wherein the metal ion is present in amount of about 1-25% m/m of the composition.

9. A composition according to any one of the preceding claims wherein the metal ion of the metal chelate is a transition element or a rare earth.

10. A composition according to claim 9 wherein the transition element is a transition metal selected from copper or zinc.

11. A composition according to claim 9 wherein the rare earth is a rare earth metal element selected from cerium, lanthanum or yttrium.

12. A composition according to any one of the preceding claims wherein the ligand of the metal chelate is selected from a monocarboxylic acid, a dicarboxylic acid, a tricarboxylic acid, a natural or a synthetic amino acid, an aliphatic or an aromatic amine, or a complex inorganic acid or salts thereof.

13. A composition according to claim 12 wherein the ligand is selected from salicylic acid, maleic acid, oxalic acid, malic acid, tartaric acid, phthalic acid, citric acid, glycine, alanine, valine, glutamic acid, iminodiacetic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid (EDTA), propylene diamine, triethylene tetramine, methylpyridine, polyphosphoric acid, or a soluble salt thereof.

14. A composition according to any one of the preceding claims further including one or more preservation agents for timber or similar cellulosic material.

15. A composition according to any one of the preceding claims which includes two or more metal chelates incorporating different metals.

16. A composition according to any one of the preceding claims further including an effective amount of a boron compound and/or a fluorine compound

17. A composition according to claim 16 wherein the boron compound is in the form of a soluble salt.

18. A composition according to claim 16 wherein the fluorine compound is in the form of a soluble salt.

19. A composition according to any one of claims 16 to 18 wherein the boron compound is a borate and the fluorine compound is a fluoride or the boron compound and the fluoride compound are provided together in the form of a fluoroborate.

20. A composition according to any one of claims 16 to 19 wherein the boron compound is present in an amount of about 0.1 to 30% m/m of the composition.

21. A composition according to any one of claims 16 to 20 wherein the fluorine compound is present in an amount of about 0.1 to 40% m/m of the composition.

22. A composition according to any one of the preceding claims further including a polyhydric polyol.

23. A composition according to any one of the preceding claims wherein the composition is in the form of an aqueous solution, dispersion or emulsion.

24. A composition according to any one of the preceding claims in the form of a powder, tablet, rod, or paste.

25. A method of treating a wood or wood-containing article or product, the method including applying to the article or product a composition in accordance with any one of the preceding claims.