AU2251499A - Diffusible wood preservatives - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE

SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: *i Commonwealth Scientific and Industrial Research Organisation Actual Inventor(s): Heikki Mamers Kevin James McCarthy Address for Service: PHILLIPS ORMONDE

FITZPATRICK

Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: DIFFUSIBLE WOOD PRESERVATIVES Our Ref 577549 POF Code: 216356/36 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 1A DIFFUSIBLE WOOD PRESERVATIVES This application is a divisional application from Australian Patent Application 700524 the contents of which are herein incorporated by reference.

The present invention relates to wood preservative compositions and methods of preserving wood. More particularly, it relates to wood preservative compositions and formulations containing biocidal compounds suitable for providing protection to timber and similar woodbased 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 4 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 .i 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 (S0 4 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 25 "hardwood cellulose. Lignin, a complex high molecular weight aromatic polymer of -indeterminate structure, is known to be rich in phenolic, carboxylic and aldehydic groups.

B-

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 vwithin the wood s'bstance by me'al ions but. in i i 2 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 protec':n 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 tetraammine complex [Cu(NH 3 4 ,2H 2 0] 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 the invention provides a method of preserving wood including impregnating the wood with a wood preservative composition including at least one metal chelate wherein a metal ion is coordinately bonded to at least one ligand wherein the metal chelate has a neutral or negative charge and is freely diffusible in moist wood at atmospheric pressure.

In a further aspect, the present invention provides a wood preservative composition including at least one metal chelate wherein a metal ion is coordinately bonded to at least one ligand wherein the metal chelate has a neutral or negative charge and is freely diffusible in wood at atmospheric pressure.

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 EP C :\WNWORDELLEN\SPECIRLE4475896. DOC 3 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 charge 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:

[ML]

Solvated Ligand Chelation complex metal ion In simple systems, the equilibrium is defined by the value" or stability constant according to: [A [L] The higher the K, value, the more stable the complex If, for example, log K, 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 4a 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]

[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, main group 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. In the case of main group elements tin is preferred. Of the metallic rare earth 15 elements, cerium, lanthanum and yttrium are preferred but the whole group of i 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. Examples of metal ions include ions of copper, zinc, cerium lanthinumand tin. Copper, zinc and tin or their mixtures are preferred.

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 K 1 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 EP C:\V'NWORD\ELLENSPECIRLE44758g96.DOC 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 i e EP C VONORDELLEN SPECIRLE44758g96DOC 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 aci-Js, 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 preferred methods will allow impregnation by diffusion. The preservative composition of the invention may be applied to the surface layers of 15 unseasoned or partially seasoned wood in sufficient amount, so that it diffuses more deeply and more completely into the wood. The preservative composition of the invention may be applied in the form of an 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 S 25 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.

EP C\WINWORDELLEN\SPECIRLE 44758-96 DOC The composition of the invention may also include a polyhydric polyol, for example, ethylene glycol, propylene glycol or clycerol.

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 EP C.\WINWORD ELLEN\SPECIRLEW 4 758-9DOC 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.

In the present invention the term "freely diffusible" refers to a composition that effectively diffuses into wet/moist timber at atmospheric pressure. Such compositions do not rapidly bind to the negative charged groups in the cellulose and lignin of the wood.

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: CuC03.Cu(OH) 2 4[H2NCH 2 COOH] 2[Cu(H2NCH 2

COO)

2 C02 3H20 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 m/m and a reported log K 1 value of 8.6: OC-O

,NII-CIH-

Cu H1 2 C-NI O----Co EP C:\WNWORDELLEN\SPECIRLE44758-6.DOC 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/m 3 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 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 Between 1.0 and 2.0 Above 2.0 Effective preservative Marginally Effective preservative 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 The untreated control slabs supported vigorous fungal growth throughout the 28 day 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 of ammonium hydroxide to form the zinc diammonium di-iminodiacetic acid chelate.

The overall reaction may be represented as: ZnCO 3 .Zn(OH) 2 4[HN(CH 2

COOH)

2 4[NH 4 OH] Basic zinc Iminodiacetic Ammonium carbonate acid hydroxide 2[(NH 4 2 [Zn(NH(CH 2

COO))

2

CO

2 7H 2 0 Zinc diammonium di-iminodiacetic acid chelate The structure of the negatively charged 2:1 binary zinc chelate may be represented as: COO- coo CH---COO C t- I I HN NH I I I CH, OOC-- CI oo 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 The diffusion/fungitoxic characteristics of the zinc diammonium diiminodiacetic 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/m as the diffusion substrate. The results are summarised in Table 2.

TABLE 2 .Sab diffusion testing of zinc diammonium di-iminodiacetic acid chel 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 ethylenediaminetetraacetic acid (EDTA) The reagents and quantities used in the preparations are summarised in Table 3ka) 12 TABLE 3(a) Prpaeralon o f ir r Lch'JaI.ls Source of meta! ion (parts) Ligand (parts) -t La 2

O

3

Y

2 0 3 (9.6) Maleic acid (53.4) Iminodiacetic acid (33.9) Water Ncmnal formula (parts) of chelate 500 La[CH(COO)

CH(COO)]

5UU Y[NH, (COO) 2 1.

I

Ce 2 (C0 3 3 I I EDTA (Na) 2 (72.8) 500 Ce[CH 2

N(CH

2

COO)

CH

2 COONa] 3 EDTA (Na) 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 The physical properties of the rare earth chelates are summarised in Table 3(b).

I

13 TABLE 3(b) Physical roperties of rai"e_ Q lbtCe l 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/m 3 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 eafrlh eiaes r" uneiate Diffusion substrate Diffusion period (days)* 14 21 Lanthanum tri-maleic acid Tasmanian Oak heartwood 0.17 0 Untreated control Tasmanian Oak heartwood 2.67 Yttrium Spotted Gum tri-iminodiacetic heartwood 0 0 0 0 acid Untreated Spotted Gum control heartwood 1.67 2.0 2.0 Cerium/di- Tasmanian Oak sodium EDTA heartwood 0 0 0 0 Untreated Tasmanian Oak 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: CuCO 3 .Cu(OH), 2(NasP 3

O

1 0

H

2 0 Basic copper Sodium tricarbonate polyphosphate 2(Nas(Cu(OH) 2

P

3 0o 1

CO,

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: O0 00' O O P+ P+

P

I I I\ -o-o o o0 o' Cu

SOH

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 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 TABLE 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: 2B 2 0 3 3[CH 3

CH(OH)CH

2 OH)] [3(CH 3

CHCH

2

)]B

2 0 6 2H 3

BO

3 Boric Propylene glycol Propylene glycol Boric oxide borate ester acid The mixture was then heated for 15 minutes at 115C to polymerise the propylene glycol borate esi-i 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 18 Example 1, using Grey Ironbark heartwood as the diffusion substrate The results are summarised in Table TABLE Slab diffusion testing of boron, fluorine, copper (BFC) 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 oi ccpoer 19 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 amour' 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 (K 1 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 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 Cooper retention in copper chelate-imoregnated P. raiata blo.cks .afleLS.reJ days' leaching Ligand Log K 1 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 K 1 value there was a high degree of retention of the metal ion within the timber, whilst for chelates with a high K 1 value there was a lower retention of the metal ion by the wood substance. It follows from these results that chelates with a low K 1 value will diffuse into a timber substrate to a more limited extent than chelates with a higher K 1 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.

E2am RLZ 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 occ 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) mponent rquired for 100 of a water basd resertive ro formulation containing about 4.0% m/m copper. 1.4% m/m boron and 11.0% m/m fluorine as active elements EDTA(Na)2 ethylenediaminetetraacetic acid. disodium salt dihydtate 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 E"TA 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 fluonn Test Material Diffusion substrate Diffusion period (days)* Water based TasmanianOak copper/boron heartwood 7 14 21 28 0 17 0 08 0 08 0 3.0 130 30 /fluorine rods Untreated Tasmanian Oak control heartwood Average of six replicates 23 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.

Example 8 This example illustrates the preparation and diffusion/fungitoxic testing of a chelate treating solution containing tin. The hydrated sodium iminodiacetate ligand (3 mol. equivalent) was dissolved in water and solid stannous sulfate added (1 mol. equiv.) to form a milky solution. Dilute sodium hydroxide was added until the solution cleared. This solution contained 17.5 g/L of tin. Lower concentrations of this formulation were obtained by dilution with water (10.3 and 5.1 The slab diffusion method of Example 1 was used to test diffusion and fungitoxicity, using Mountain Ash regnans) heartwood as the diffusion substrate. In this example, the agar and fungal inoculum was changed after each inspection. The results are given in Table 8.

The results show that the two higher concentrations of tin iminodiacetate are effective preservatives, whereas the water treated control slabs supported good fungal growth over the test period.

Table 8. Slab diffusion testing of tin iminodiacetate solutions. Average rating of fungal growth for six replicates.

EP C:\WINWORD ELLENkSPECIRLE 4 4 5 8 96 DOC 23a Preservative formulation Conc. Diffusion Tin iminodiacetate gIL 5.1 10.3 17.5 7 days 2.2 0.1 0.0 2.2 period 14 days 1.2 0.0 0.0 2.0 (days) 28 days 2.4 2.6 Water control EP C:\W1NWORD\ELLEN\SPECIRLE\4475 8 .gG.DOC

Claims (59)

1. A method of preserving wood including impregnating the wood with a wood preservative composition including at least one metal chelate wherein a metal ion is coordinately bonded to at least one ligand wherein the metal chelate has a neutral or negative charge and is freely diffusible in moist wood at atmospheric pressure.

2. A method according to claim 1 wherein the metal ion is a transition element or a rare earth.

3. A method according to claim 1 wherein the metal ion is selected from the group consisting of copper, zinc, cerium, lanthanum, yttrium or tin.

4. A method according to claim 1 wherein the metal ion is selected from copper, zinc, tin and mixtures thereof.

A method according to claim 1 wherein the metal is copper or zinc.

6. A method according to claim 1 wherein the metal is tin.

7. A method according to any one of the previous claims wherein the ligand includes at least one ligand selected from the group consisting of monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, natural or synthetic amino acids, aliphatic or aromatic amines, complex inorganic acids and salts thereof.

8. A method according to claim 7 wherein the ligand includes at least one ligand selected from the group consisting of 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, polyphosphoric acid, and EP C \WINWORDT=LLEN\SPECIRLE\44758-96.DOC soluble salts thereof.

9. A method according to claim 1 wherein the metal ion is copper and the ligand includes a monocarboxylic acid, a dicarboxylic acid, a tricarboxylic acid or mixture thereof.

A method according to claim 1 wherein the metal chelate is copper diglycinate.

11. A method according to any one of the previous claims wherein the metal chelate is applied to the wood at atmospheric pressure.

12. A method according to claim 1 wherein the metal is zinc and the ligand includes a monocarboxylic acid, a dicarboxylic acid, a tricarboxylic acid or mixtures thereof.

13. A method according to claim 1 wherein the metal is tin and the ligand includes a monocarboxylic acid, a dicarboxylic acid, a tricarboxylic acid or mixtures thereof.

14. A method according to claim 1 wherein the metal chelate is a neutral or negatively charged zinc chelate.

A method according to claim 1 wherein the metal chelate is a neutral or negatively charged tin chelate.

16. A method according to claim 11 wherein the metal chelate is zinc diammonium di-iminodiacetic acid.

17. A method according to claim 11 wherein the metal chelate is tin diammonium di-iminodiacetic acid. EP C: WNWORD\ELLENSPECIRLE\44758.%9 DOC 26

18. A method according to any one of the claims selected from claims 1 to claims 12 to 15 wherein the wood is impregnated with the metal chelate under elevated pressure.

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

A method 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 total preservative composition.

21. A method according to claim 8 wherein the metal ion is present in an amount of about 1-25% m/m of the total preservative composition.

22. A method according to any one of the preceding claims wherein the preservative composition further includes one or more additional preservation agents for timber or similar cellulosic material.

23. A method according to any one of the preceding claims wherein the preservative composition includes two or more metal chelates incorporating different metals.

24. A method according to any one of the preceding claims wherein the preservative composition further includes an effective amount of a boron compound and/or a fluorine compound.

A method according to claim 24 wherein the boron compound is in the form of a soluble salt.

26. A method according to claim 24 wherein the fluorine compound is in the form of a soluble salt. EP C:\WINWORDXELLEN\SPECIRLEW4758-96.DOC 27

27. A method according to any one of claims 24 to 26 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.

28. A method according to any one of claims 24 to 27 wherein the boron compound is present in an amount of about 0.1 to 30% m/m of the composition.

29. A method according to any one of claims 24 to 27 wherein the fluorine compound is present in an amount of about 0.1 to 40% m/m of the composition.

A method according to any one of the preceding claims wherein the preservative composition further includes a polyhydric polyol.

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

32. A method according to any one of the preceding claims wherein the preservative composition is in the form of a powder, tablet, rod or paste.

33. A wood preservative composition including at least one metal chelate wherein a metal ion is coordinately bonded to at least one ligand wherein the metal chelate has a neutral or negative charge and is freely diffusible in wood at atmospheric pressure.

34. A wood preservative composition according to claim 33 wherein the metal ion is a transition element or rare earth metal. A wood preservative composition according to claim 33 wherein the metal is selected from copper, zinc and tin.

EP C:\WINWORDELLEN\SpECIRLE\4475896.DOC 28

36. A wood preservative composition according to any one of claims 33 to wherein the ligand includes at least one ligand selected from the group consisting of monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, natural or synthetic amino acids, aliphatic or aromatic amines complex inorganic acids and salt thereof.

37. A wood preservative composition according to any one of claims 33 to wherein the ligand includes at least one ligand selected from the group consisting of 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, polyphosphoric acid, and soluble salts thereof.

38. A wood preservative composition according to claim 33 wherein the metal ion is copper and the ligand includes a monocarboxylic acid, a dicarboxylic acid, a tricarboxylic acid or mixtures thereof.

39. A wood preservative composition according to claim 33 wherein the metal chelate is copper diglycinate.

A wood preservative composition according to claim 33 wherein the metal is zinc and the ligand includes a monocarboxylic acid, a dicarboxylic acid, a tricarboxylic acid or mixtures thereof.

41. A wood preservative composition according to claim 33 wherein the metal is tin and the ligand includes a monocarboxylic acid, a dicarboxylic acid, a tricarboxylic acid or mixtures thereof.

42. A wood preservative composition according to claim 40 wherein the metal chelate is a negatively charged zinc chelate comprising two bidentate ligands. EP C: WINWORD\ELLENSPECIRLEW4758-96DOC 29

43. A wood preservative composition according to claim 41 wherein the metal chelate is a negatively charged tin chelate comprising two bidentate ligands.

44. A wood preservative composition according to claim 42 wherein the metal chelate is zinc diammonium di-iminodiacetic acid.

A wood preservative composition according to claim 43 wherein the metal chelate is tin diammonium di-iminodiacetic acid.

46. A wood preservative composition according to any one of claims 33 to 44 wherein the metal chelate is water soluble and non-volatile.

47. A wood preservative composition according to any one of claims 33 to 46 wherein the metal chelate is present in an amount of from 0.1% to 35% m/m of the total composition.

48. A wood preservative composition according to any one of claims 33 to 46 wherein the metal ion is present in an amount of from 1% to 25% m/m of the total composition.

49. A wood preservative composition according to any one of claims 33 to 48 further including one or more preservation agents for timber or similar cellulosic material.

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

51. A wood preservative composition according to any one of claims 33 to 49 further including an effective amount of a boron compound and/or a fluorine compound. EP C:\WINWORD\ELLEN\SPECIRLEWA4758-96 DOC

52, A wood preservative composition according to claim 51 wherein the boron compound is in the form of a soluble salt.

53. A wood preservative composition according to claim 52 wherein the fluorine compound is in the form of a soluble salt.

54. A wood preservative composition according to any one of claims 51 to 53 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.

A wood preservative composition according to any one of claims 51 to 53 wherein the boron compound is present in an amount of about 0.1 to 30% m/m of the composition.

56. A wood preservative composition according to any one of claims 51 to 53 wherein the fluorine compound is present in an amount of about 0.1 to 40% m/m of the composition.

57. A wood preservative composition according to any one of claims 51 to 56 wherein the composition is in the form of an aqueous solution, dispersion or emulsion.

58. A wood preservative composition according to any one of claims 33 to 57 in the form of a powder, tablet, rod or paste.

59. A wood preservative composition according to claim 33 substantially as EP C:\WINWORDXELLEN\SPECIRLE44758-96.DOC 31 hereinbefore described with reference to any one of the Examples. DATED: 30 March 1999 COMMONWEALTH SCIENTIFIC INDUSTRIAL RESEARCH ORGANISATION By: PHILLIPS ORMONDE FITZPATRICK Patent Attorneys per: EP C:\WINWORD\ELLEN\SPECIRLE\44758-96.DOC