WO1996023636A1

WO1996023636A1 - Water based preservative paste

Info

Publication number: WO1996023636A1
Application number: PCT/AU1996/000037
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: AUPN082695A0

Abstract

A composition in the form of a paste suitable for use as a wood preservative said composition including a fungitoxic metal derivative and a fungitoxic boron compound and wherein both the metal derivative and the boron compound are water soluble and freely diffusible in moist wood.

Description

Water Based Preservative Paste

The present invention relates to wood preservative compositions. More particularly, it relates to remedial wood preservative compositions and formulations especially suitable for the maintenance and preservation of wooden poles.

Some 6 million wooden poles are used in Australia to support the country's electricity and telecommunications networks. As these poles represent a substantial investment, economics dictates that they should achieve a service life in the range of 25 to 50 years. Once a living tree has been felled for use the wood therein becomes susceptible to deterioration through, for example, decay caused by fungi and attack by termites. The rapidly diminishing supply of the more naturally durable species for use as poles has led to the increasing use of non-durable species which must be treated with preservative chemicals to inhibit or arrest decay and/or termite attack if they are to provide an economic service life. Treatment with chemicals to control or prevent biological deterioration of poles is therefore becoming more widespread, as is recognition of the need for regular inspection and remedial maintenance of the poles if service expectations are to be met.

Most decay occurs in the region where the pole is in contact with both the soil and air i.e. in the vicinity of the groundline where the pole emerges from the soil. The most critical region is generally the portion of the pole that extends for about 600 mm below the ground line, and a sufficient loading of toxic elements must be introduced into this region to arrest or prevent decay and insect attack.

A simple form of remedial maintenance consists of the external application of a suitable chemical to the surface of the pole around the groundline or to the soil backfill at the groundline. This method is commonly used with barrier treatments primarily designed to prevent the ingress of destructive organisms. In general, the chemical agents used as barrier treatments have only a limited capability for diffusion into the wood and thus remain substantially at or near the point of application, serving to impede the entry of biodeteriogens into the wood from the soil. Typical of such barrier agents is copper naphthenate, a well known fungicide of low water solubility that is not leached out of wood in ground contact. In use it is difficult to achieve satisfactory penetration of copper naphthenate into wood both on account of its low water solubility and because the copper becomes firmly bound to the outer layers of the wood.

A more sophisticated method of surface application is to incorporate the remedial chemical in a bandage to provide maximum protection against chemical loss to the soil and optimum potential for diffusion into the pole. A third method involves drilling holes into the pole and introducing the chemical into the interior wood.

The most successful remedial agents for controlling both fungal and termite attack are those able to diffuse freely from their site of application throughout the wood structure, where their biocidal activity can eradicate existing infections as well as preventing the occurrence of new infections. One such freely diffusible wood preservative composition, comprising an aqueous solution of a fluorine compound and a boron compound, is disclosed in Australian Patent 507,449 which also teaches the formulation of such fluorine-boron preparations as thixotropic pastes.

Solid rods comprising fused or compressed mixtures of inorganic borates and fluorides are widely used in Australia in the third method of remedial wood preservation described above. They rely for their effectiveness on the presence in the pole of sufficient moisture to permit the active compounds to slowly dissolve and diffuse through the wood.

Copper and boron have a long and successful history of use in wood preservation as they are known to be effective against a wide spectrum of wood destroying fungi, whilst boron is effective against many wood destroying insects. Both copper and boron are recognised as being relatively benign in terms of environmental impact and potential health risk. They have relatively low mammalian toxicity which makes their use attractive as compared to, say, that of arsenic, antimony, chromium, mercury or polychlorinated phenols which are rapidly losing favour as being environmentally unacceptable and posing unnecessary health hazards in use. Also, conventional waterborne preservatives such as copper-chrome-arsenic (CCA) are of limited utility in the remedial treatment of hardwood poles as they do not readily penetrate the cell walls of hardwood fibres.

Boron ions are known to diffuse freely through the wood matrix, but copper (II) ions in aqueous solution are strongly adsorbed by wood and tend to be immobilised at or near the point of application.

It will be apparent from the above discussion that a particularly desirable wood preservative formulation would be one containing freely diffusible copper, boron and fluorine as biocidal components. However, such formulations cannot be made by combining simple water-soluble copper salts, such as cupric sulphate, with water-soluble boron and fluorine compounds e.g. borates and fluorides since the dissolved copper ions react with them to form insoluble copper borates or fluorides which cannot migrate into a timber substrate. This insolubilisation also constitutes an effective loss of active elements from the formulation. It is known from Australian Patent No. 491638 that copper ions can be maintained in aqueous solution in the presence of soluble borates and fluorides by reacting the dissolved cupric ion with ammonia to form the tetra-ammine complex [Cu(NH₃)₄.2H₂O]. However, excess ammonia must be present to stabilise the complex; when the ammonia evaporates the complex decomposes and the copper is precipitated as insoluble copper borates and fluorides. The necessary presence of excess ammonia is also a hazard in both manufacture and use of the complex, and the strong ammoniacal odour of wood preservatives of this type is unacceptable for many end uses.

Australian Patent No. 519146 discloses wood preservative compositions having enhanced diffusion characteristics as compared with conventional water- based copper salts and comprising certain copper soaps solubilised by reaction with monoethanolamine. These compositions exhibit enhanced penetration into wood due to the ability of monoethanolamine to penetrate and swell the cell wall of the wood fibre, but it has been found that such formulations tend to develop an objectionable ammoniacal odour on storage, particularly in the presence of water as, for example, when borax is added to enhance their fungicidal and termiticidal properties. Many of the aforementioned disadvantages of the prior art remedial wood preservatives are overcome in the efficacious wood preservative disclosed in our Australian Provisional Patent Application No. PM3862/94 and comprising a self thickening thixotropic paste obtained by reacting a solution of copper naphthenate in an organic solvent with the product obtained by reacting boric oxide with a polyhydric alcohol under anhydrous conditions. Such pastes contain high concentrations of both the active elements copper and boron and are of suitable consistency for manual application by brushing or trowelling, or by pumping from a container. A particularly preferred formulation disclosed in Australian Patent

Application No. 12249/95 contained about 1.7% m/m copper and 5.6% m/m boron for a total of about 7.3% m/m of active elements. In both laboratory diffusion tests and field trials with utility poles it has been found that this formulation is an effective fungicide and that the boron diffuses readily through the timber substrate. However, the copper penetrates only one or two millimetres into the treated timber and thus serves only to provide a barrier against surface decay. In addition, the cost of manufacturing this formulation has proved unacceptably high for commercial acceptance, partly due to the cost of the raw materials but also because of the need to employ flameproof equipment during manufacture and to store the initial product for a prolonged period to allow it to mature into a smooth paste having good adhesion to both dry and damp timber.

We have now found that it is possible to overcome many of the abovementioned deficiencies in prior art wood preservatives, in particular those of the paste disclosed in Australian Application No. 12249/95, and to formulate an equivalent water-based wood preservative paste having the same concentrations of the active elements copper and boron and exhibiting similar physical properties, such as viscosity and temperature stability, but with the added advantage that both the copper and boron are present in diffusible and fungitoxic form. We have also found that the paste may advantageously include fluorine in diffusible and fungitoxic form without adversely affecting its physical properties or the diffusibility and fungitoxicity of the copper and boron. Accordingly the present invention provides, in a first aspect, a composition in the form of a paste suitable for use as a wood preservative said composition including a fungitoxic metal derivative and a fungitoxic boron compound and wherein both the metal derivative and the boron compound are water soluble and freely diffusible in moist wood.

Preferably the composition contains diffusible metal in an amount in the range of about 0.3 to 25% m/m. More preferably the diffusible metal is present in an amount of about 1 to 4% m/m.

Preferably the composition contains diffusible boron in an amount in the range of about 1 to 15% m/m, more preferably 3 to 8% m/m.

Optionally the composition may include diffusible fluorine in an amount in the range of about 1 to 15% m/m, preferably 2 to 8% m/m.

The metal derivative may be a water-soluble metal chelate. The boron compound may be boric acid or a water-soluble salt thereof. The fluorine compound may be water-soluble alkali metal fluoride or an alkali metal fluoroborate.

The present invention also provides, in a second aspect, a composition suitable for use as a wood preservative said composition being a composition in accordance with the first aspect which is provided in the form of a water-based thixotropic paste.

The compositions of the second aspect are smooth textured thixotropic pastes containing high concentrations of the active elements copper and boron and, when present, fluorine. They exhibit good adhesion to either dry or damp timber surfaces and are effective in arresting the growth and propagation of wood destroying organisms. Their thixotropic behaviour is advantageous in pump application systems since the paste behaves as a mobile fluid under the shear conditions within the pump and pipework but reverts to a non-slumping paste on contact with the timber surface. Alternatively, the pastes may be applied directly by trowel or brush to the groundline region of wooden poles, where they will adhere to the vertical perimeter of the pole in a thick layer which does not flow or slump at ambient temperatures. The compositions of the invention may be thickened by inclusion of one or more bulking agents and/or thickener. Preferably thickening is achieved by using primarily bulking agents and/or thickeners that do not act as gel-forming agents. The invention also provides a method of producing a thixotropic composition suitable as a wood preservative including the steps of:

(1) reacting a hot aqueous solution of an alkali-metal borate containing a chelating agent and optionally an alkali-metal fluoride or fluoroborate with a metal salt to yield a solution of a metal chelate and the alkali-metal borate and optionally the alkali-metal fluoride or fluoroborate;

(2) contacting the mixture from step (1) in the presence of a surfactant with one or more bulking agents and/or thickeners and forming a thixotropic paste.

By "hot" we mean a temperature greater than about 50°C. More preferably the aqueous solution is at a temperature in the range of about 70°C to 100°C.

The product from step (2) is a homogeneous paste which does not crystallise when cooled to ambient temperature and may be used as a wood preservative without further modification or modified for particular end uses by the addition of drying oils, varnishes and/or fibres as taught in the prior art. It may also be modified by the addition of agents known to promote diffusion in wood.

In yet a further aspect the present invention provides a method of maintaining and/or preserving wood or wood-containing product, the method including treating the wood or wood-containing product with a composition in accordance with the invention. The present invention will now be described in greater detail, although the invention is not to be taken as being limited to these particular details.

Suitable metals for the purposes of the present invention are the biocidal metals from the group of metallic elements known as the transition elements and the rare earths. Among the transition elements copper and zinc are preferred, with copper being particularly preferred, either singly or in admixture with one or more of the other transition elements. Of the sixteen naturally occurring metallic rare earth elements cerium, lanthanum and yttrium are preferred but all sixteen elements are suitable, either individually or in combinations of two or more thereof. Mixtures of transition elements and rare earths may also be employed. Suitable salts of the aforementioned metals include their oxides, carbonates and basic carbonates. The fungitoxic metal derivative may be a water-soluble metal chelate in which the metal ion is coordinately bonded to an appropriate ligand such that the resultant metal ion complex has a neutral or negative charge. Suitable metal chelates of this type are those disclosed in our Australian Provisional Patent Application No. PN0827 filed contemporaneously with the present application and the disclosures of which are hereby incorporated herein by reference. Preferably the metal chelate is that known as copper di-glycinate chelate which may be formed by reaction of glycine with basic copper carbonate. More preferably the metal chelate is the chelate formed by the reaction between the metal salt and a polycarboxylic acid or a water soluble salt thereof such as iminodiacetic acid, nitrilotriacetic acid and ethylenediaminetetraacetic acid (EDTA). A typical such metal chelate is the chelate formed by reaction between stoichiometric amounts of basic copper carbonate or copper hydroxide and the disodium salt of ethylenediaminetetraacetic acid (EDTA), which for convenience we term copper di-sodium EDTA chelate and whose chemical formula may be represented as Cu[CH₂N(CH₂COO)CH₂COONa]₂. This chelate contains about 16% m/m copper and is an effective fungicide. It is highly soluble in water, giving a solution having a pH of about 5.

As previously mentioned, the fungitoxic boron compound may be boric acid or a water-soluble salt thereof. Boric acid has only a limited solubility in water (63.5 g/litre at 30°C) which limits the concentration of boron that may be attained in the paste without the latter being unacceptably gritty due to the presence of undissolved boric acid. We therefore prefer to use water soluble complex salts of boric acid such as sodium tetraborate, sodium decaborate and sodium dodecaborate. An advantage in employing such complex salts as the source of boron is that they need not be manufactured beforehand but may be generated in situ during preparation of the paste. Sodium dodecaborate, Na₂0.6(B₂θ₃).yH₂0, is particularly preferred on account of its high solubility and its high ratio of boron to sodium which minimises the amount of sodium present in the final formulation.

The fungitoxic fluorine compounds, if used, may be sodium fluoride and/or sodium fluoroborate but other water-soluble fluorine compounds may be used. The individual steps of the method of the present invention are now elaborated in greater detail, although again, it is emphasised that the present invention is not limited to the particular details described below. Step 1.

The hot aqueous solution of an alkali metal borate may be prepared by dissolving the appropriate metal borate in water, but it is preferably prepared in situ by adding the requisite amount of boric acid portionwise to a solution of the alkali metal hydroxide or carbonate maintained at about 80°C. The solution is stirred until the boric acid has completely dissolved. If the formulation is to contain fluorine as an active element, the requisite amount of the appropriate fluorine compound is then dissolved in the hot alkali metal borate solution.

The chelating agent is then added and when it has dissolved the metal salt is then introduced and the mixture further heated to about 90°C and stirred until the metal salt has fully dissolved and reacted to form the metal chelate. This stage may be completed in 10 to 15 minutes, but longer times may be required depending on the particular chelating agent and metal salt employed. The resultant mixture, a clear solution, is cooled to about 55°C for use in Step 2. Step 2

The cooled mixture from Step 1 is conveniently contacted with the bulking agent in a variable speed high shear mixer after addition of the surfactant which serves to aid dispersal of the bulking agent. The specific surfactant and the amount thereof to be used must be determined by experiment on a case-by-case basis but, in general, a nonionic surfactant of broad HLB range is suitable. We have found Antarox CA897, a reaction product of octyl phenol and ethylene oxide manufactured by Rhone Poulenc, to be particularly satisfactory. Bulking agents are inert, finely divided solids which absorb the liquid phase on their surface and increase the viscosity of the system, primarily by mechanical interlocking between the individual grains of the bulking agent. The amount of bulking agent to be used is determined by the end viscosity and viscosity characteristics desired in the paste. Suitable bulking agents are nut shell flour, wheat flour and fumed silica but other agents may be suitable and their effectiveness must be determined by experiment. Fumed silica is particularly preferred and may be used in amounts from about 2.5 up to about 5% m/m. Mixtures of bulking agents may also be used. The total amount of bulking agents (including wheat flour) needed to give pastes of the desired viscosity for the groundline treatment of wooden utility poles may range from about 3 to about 10% m/m but in most formulations is more likely to be about 6 to 8% m/m. Thickeners increase viscosity by forming hydrated gel structures within the liquid phase. Being non-granular, they impart a smooth texture to the paste and assist in preventing phase separation upon standing. Suitable thickeners include soluble starch and high molecular weight carboxyvinyl polymers such as "Carbopol 940", with the latter being particularly preferred in amounts up to about 2% m/m.

Materials which thicken the liquid phase primarily by forming gels should, in general, be avoided as the principal agent for controlling the viscosity of the paste as they may inhibit diffusion of the final paste. Better results are obtained by using bulking agents rather than gel formers to obtain the required viscosity characteristics. In this context it should be noted that wheat flour, though primarily a bulking agent, also acts as a thickener by virtue of the small amount of soluble starch that may be extracted from the flour grains. When wheat flour is used it is desirable to restrict the amount present in the paste to about 1 to 2% m/m, since excessive formation of hydrated gel structures has been found to inhibit free diffusion of the biocidal elements.

To improve the rate of diffusion of the biocidal components in wood, we have found it advantageous to add a modifying agent. Ethylene glycol in amounts up to about 5% m/m is a satisfactory modifying agent but other high boiling point polyhydric alcohols such as glycerol may be used. However, a modifying agent is not essential to provide an effective wood preservative paste in accordance with the invention. An important advantage of the method of the invention is that typically Steps 1 and 2 can be completed in less than one hour and the resultant paste, once cooled to ambient temperature, can be used immediately as a wood preservative, unlike pastes prepared by the method of Australian Patent Application No. 12249/95 which prior to use require a prolonged period of maturation to stabilise the paste viscosity.

The aqueous pastes of the present invention are thixotropic, with their apparent viscosity decreasing with increasing shear rate as shown in Table 1.

TABLE 1

Shear rate Viscosity (pA.S) at 25°C (sec^"1") Formulation

A B C D E F

Increasing

5.0 14.2 18.1 11.7 8.9 6.3 9.8

25.7 4.4 5.0 4.2 1.9 1.4 2.1

46.4 3.0 3.4 2.9 1.1 0.9 1.2

67.1 2.5 3.0 2.3 0.8 0.6 0.8

87.9 2.1 2.6 2.0 0.7 0.5 0.6

109.0 1.8 2.2 1.9 0.5 0.4 0.5

129.0 1.7 2.0 1.7 0.5 0.4 0.5

150.0 1.5 1.9 1.6 0.4 0.4 0.4

Decreasing

150.0 1.5 1.9 1.6 0.4 0.4 0.4

129.0 1.7 2.1 1.7 0.5 0.4 0.4

109.0 1.8 2.3 1.9 0.5 0.4 0.5

87.9 2.1 2.5 2.2 0.6 0.5 0.5

67.1 2.5 3.0 2.5 0.7 0.6 0.7

46.4 3.2 3.7 3.1 0.9 0.7 0.9

25.7 4.6 5.3 4.3 1.5 1.2 1.4

5.0 13.8 15.3 11.7 6.1 4.6 5.9 The viscosity of the pastes may be adjusted by varying the amounts of bulking agent and thickener within the limits indicated above. Table 2 shows for three formulations the effect on viscosity of raising the content of the fumed silica bulking agent from 2.5 to 3.5% m/m.

TABLE 2

Effects of fumed silica on viscosity

Viscosity (Pa.s) at 25°C

Shear rate Formulation (sec ¹) 2.5% m/m fumed silica 3.5% m/m fumed silica

D E F D(T) ECO F(T)

Increasing

5.0 8.9 6.3 9.8 21.7 18.8 22.2

25.7 1.9 1.4 2.1 4.7 3.8 4.7

46.4 1.1 0.9 1.2 2.6 2.2 2.6

67.1 0.8 0.6 0.8 1.8 1.5 1.7

87.9 0.7 0.5 0.6 1.3 1.2 1.3

109.0 0.5 0.4 0.5 1.1 1.0 1.0

129.0 0.5 0.4 0.5 0.9 0.9 0.9

150.0 0.4 0.4 0.4 0.8 0.7 0.7

Decreasing

150.0 0.4 0.4 0.4 0.8 0.7 0.7

129.0 0.5 0.4 0.4 0.8 0.8 0.8

109.0 0.5 0.4 0.5 1.0 0.9 0.9

87.9 0.6 0.5 0.5 1.1 1.1 1.0

67.1 0.7 0.6 0.7 1.4 1.3 1.3

46.4 0.9 0.7 0.9 1.9 1.7 1.7

25.7 1.5 1.2 1.4 3.1 2.9 3.0

5.0 6.1 4.6 5.9 14.0 13.7 13.4 The pastes of the present invention are less susceptible to viscosity loss at high temperatures than those disclosed in our Australian Application No.

12249/95. They do not exhibit any tendency to slump when heated at 45°C but on the contrary develop a surface skin as the water evaporates and adhere strongly to the substrate.

When stored in sealed containers at ambient temperature for two months or longer the pastes do not crystallise and their viscosities remain stable. Pastes thickened with fumed silica may undergo slight phase separation but are readily restored to homogeneity by gentle stirring. As noted above, other additives may be incorporated in the pastes to meet specific end use requirements. For example, where the treated timber may be in periodic contact with moisture, a drying oil, varnish or like material may be included in the paste. Over a period of time, the drying oil or varnish will form a moisture impermeable barrier on the surface of the treated timber that prevents leaching out of the biocidal elements originally contained in the paste.

Similarly, where the paste is required to withstand excessively high temperatures it may be advantageous to include small amounts of cellulosic or other fibres in the paste. The cellulosic fibres form a loose structural network within the body of the paste which serves to prevent unwanted flow as, for example, when the paste is to be applied to vertical surfaces. The cellulosic fibres may represent the sole additive to the paste or they may be added in conjunction with a drying oil, varnish or like material.

The invention is further illustrated by reference to the following non-limiting examples. Example 1

This example demonstrates the preparation of a paste (Paste A and

Formulation A in Tables 1 to 5) based on the copper di-sodium EDTA chelate and containing 1.7% m/m diffusible copper and 5.6% m/m diffusible boron, the bulking agent being wheat flour and the thickener "Carbopol 940". It is also illustrative of the general method of preparing pastes according to the invention.

Sodium hydroxide (31.5 g) was dissolved in water (450 mL). The solution was warmed to about 80°C and stirred during the addition of boric acid (326 g) in aliquots of about 50 g. When the boric acid had fully dissolved, di-sodium EDTA (99.6 g) was added and when it had dissolved basic copper carbonate (29.6 g) was introduced. The mixture was heated to about 90°C and stirred until within 10-15 minutes the copper carbonate had fully dissolved and reacted to form a dark blue solution of the copper di-sodium EDTA chelate.

The solution was cooled to about 55°C and transferred into a variable speed high shear mixer. "Antarox CA897" surfactant (10 mL) was added while the solution was stirred at low speed. Wheat flour (42 g) was then added, a few grams at a time, while the rate of stirring was gradually increased to produce a smooth textured slurry. The formulation was completed by the addition of "Carbopol 940" (20 g) as thickener. The product was a homogeneous paste which did not crystallise on being cooled to ambient temperature. Example 2

The general method of Example 1 was used to prepare the copper di- sodium EDTA pastes B to F shown in Table 3, using the amounts and combinations of bulking agents and thickeners shown therein. The water content of each paste was adjusted as shown in Table 3 to maintain the same 1.7% and 5.6% m/m concentrations of copper and boron respectively as in Example 1. Pastes B to F also contained approximately 5% m/m of ethylene glycol to promote diffusion of the active elements in wood.

TABLE 3

Formulations of pastes containing 1.7% m/m copper and 5.6% m/m boron (kg paste basis)

Component Formulation

A B C D E F

Boric acid (g) 326.0 326.0 326.0 326.0 326.0 326.0

Sodium hydroxide(g) 35.1 35.1 35.1 35.1 35.1 35.1

Basic copper carbonate 29.6 29.6 29.6 29.6 29.6 29.6

(g)

Di-sodium EDTA (g) 99.6 99.6 99.6 99.6 99.6 99.6

Antarox CA 897 (mL) 10 10 10 10 10 10

Wheat flour (g) 42.0 42.0 12.0 42.0 42.0 10.0

Soluble starch (g) - - - - 10.0 -

Macadamia shell flour (g) - - 30 - - -

A177P nut shell flour (g) - - - - - 32.0

Ethylene glycol (mL) - 45 45 45 45 45

Carbopol 940 (g) 20.0 20.0 20.0 - - -

Fumed silica (g) - - - 25.0 25.0 25.0

Water (mL) 450 400 400 396 390 400

Example 3

The efficacy of pastes A, B, D, E and F as biocides was tested by the slab diffusion bioassay technique described by E.W.B. Da Costa and H. Greaves in "Laboratory test procedures", Proceedings of Tropical Wood Preservation Seminar, Port Moresby (1975). The paste was incorporated into a strip of open- celled sponge in the bottom of a Petri dish. A water-saturated timber slab (50x50x6 mm), with its edges sealed by dipping in petroleum jelly and paraffin wax, was placed on top of the sponge. Diffusion of toxicants through the slab was 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 occurred if the biocidal elements under test diffused through the slab and attained a sufficiently high concentration.

Slabs of heartwood cut from Spotted Gum (E.maculata) were used as the diffusion substrate. Replicate slabs were saturated under vacuum with water prior to use and then edge sealed. After a pre-diffusion period of two days, the upper surface of each slab was inoculated with an agar strip infected with a mixed fungal inoculum. The same procedure was carried out for the untreated controls. The slabs were then incubated at 28^CC and 85% RH, and scored for fungal activity after 7, 14, 21 and 28 days.

Six replicates were used for each paste and the untreated controls. Scoring was on the basis of:

0 = No evidence of fungal growth

1 = Slight mycelium development

2 = Moderate fungal growth

3 = Good fungal growth

The results are summarised in Table 4.

TABLE 4

(Substrate: Spotted gum heartwood)

Paste Diffusion period (days) 7 14 21 28

2.25 2.33 1.75 1.67

Control 2.58 2.83 2.63 2.42

B 2.41 1.67 1.67 1.58

Control 2.75 2.58 2.83 3.0

D 0.92 0.58 0.83 0.67

E 0.66 1.17 1.83 1.92 F 0.33 0.42 0.33 0.33

Control 2.67 2.83 2.75 2.67

Mean of six replicates

To bring comparisons to a common basis, all controls were rated "3" and the other scores in a particular test batch were normalised accordingly. The normalised scores for the pastes after 28 days are shown in Table 5.

TABLE 5

Paste Normalised score after 28 days ^"A Z07

B 1.58

D 0.75

E 2.16

F 0.37

= Average of six replicates

The normalised scores in Table 4 may be interpreted on the basis: 0 - Very effective preservative

<1.0 - Effective preservative

1.0 - 2.0 - Marginally effective preservative >2.0 - Ineffective as a preservative

The results show that Pastes D and F are effective preservatives whereas Paste B is marginally effective and Pastes A and E are ineffective. As all pastes contained the same active components (sodium dodecaborate and copper di- sodium EDTA chelate) at identical concentrations, the results demonstrate the importance of the choice of bulking agents and thickeners to be used in determining the extent of diffusion of the active materials through the Spotted Gum slabs.

It can be seen that the most effective pastes were those in which thickening was due primarily to the bulking agents nut shell flour and fumed silica (Pastes D and F), whereas use of the gel-forming agents soluble starch and Carbopol was disadvantageous (Pastes A, B and E). It is also evident that the presence of wheat flour as an additional component in the pastes bulked with nut shell flour and fumed silica (Pastes D and F) did not lead to sufficient starch being eluted from the flour to contribute to significant gel formation, though Paste F (1.0% m/m wheat flour) was slightly more effective than Paste D which contained 4.2% m/m wheat flour. O 96/23636 --

18 Example 4

The conclusions drawn from the results in Table 5 were confirmed in a further experiment carried out after completion of the 28-day diffusion tests.

The top surfaces of selected slabs were sprayed with indicators (prepared according to AS 1605 - 1974) to detect the presence of the diffusible elements. The indicators used were:

Copper- Chrome azurol S, which gives a deep blue colour in the presence of copper.

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

The results are shown in Table 6.

TABLE 6

Paste Elemental Indication^*

Copper Boron

D +++ +++

E + ++

F +++ +++ * = Average of three observations

Scoring: + - Slight indication

++ - Fair indication +++ - Strong indication

The results in Table 6 reflect the observed extent of fungitoxic efficacy

(Table 5). Thus Pastes F and D, with normalised slab diffusion scores of 0.37 and 0.75 respectively, gave strong indications for both copper and boron on the upper surface of the slabs. On the other hand, Paste E, with a normalised score of 2J6, showed only a slight indication for copper and a fair indication for boron. Example 5

Table 7 lists four preservative paste formulations prepared according to the general method of Example 1. TABLE 7

Preservative paste formulations (kg paste basis)

Component Paste number

(weight in grams) CB-1 CBF-1 CBF-3 CBF-4

Boric acid 326.0 139.8 163.0 139.8

Sodium hydroxide 56.5 15.1 39.0 36.5

Copper hydroxide 26.1 26.1 26.1 26.1

Iminodiacetic acid 71.2 - - 71.2

Nitrilotriacetic acid - - 51.1 -

EDTA(Na)₂ ^* - 99.6 - -

Sodium fluoroborate - 41.2 - 41.2

Sodium fluoride - - 63.0 -

Antarox CA897 surfactant 10.0 10.0 10.0 10.0

Wheat flour 10.0 10.0 10.0 10.0

Nut shell flour 32.0 32.0 32.0 32.0

Fumed silica 31.6 40.0 40.0 40.0

Ethylene glycol 50.0 50.0 50.0 50.0

Water 386.6 536.2 515.8 543.2 pH of paste (at 50 g/litre) 6 8 8.5 8

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

Paste CB-1 contained 1.7% m/m copper and 5.6% m/m boron as the active elements. Pastes CBF-1 , CBF-3 and CBF-4 contained 1.7% m/m copper, 2.8% m/m boron and 2.8% m/m fluorine. The pastes had a near-neutral pH and were substantially odour free, apart from traces of essential oils released from the wheat flour and nut shell thickeners. All the formulations were stable indefinitely when stored in sealed containers.

The pastes were thixotropic, that is the apparent viscosity decreased with increasing rates of shear (Table 8). TABLE 8

Viscosity characteristics of preservative pastes

Shear rate Viscosity (Pa.s)

(sec ^"1) CB-1 CBF-1 CBF-3 CBF-4

5.0 41.4 8.2 18.2 9.6

25.7 7.9 1.5 3.4 1.9

46.4 4.1 0.8 1.8 1.0

67.1 2.6 0.5 1.2 0.7

87.9 1.9 0.4 0.9 0.5

109.0 1.5 0.3 0.7 0.4

129.0 1.2 0.3 0.6 0.4

150.0 1.0 0.2 0.5 0.3

The fungitoxicity and diffusibility of the pastes were simultaneously assessed by the slab diffusion bioassay method described in Example 3, using test slabs cut from the heartwood of Tasmanian Oak, a medium density hardwood with a basic density of about 590 kg/m³. Six test slabs were used to evaluate each paste formulation. Further slabs, soaked in water only, were run as controls. The agar strips were infected with a mixed inoculum and, after a pre- diffusion period of two days, the inoculated slabs were incubated at 28°C and 85% RH. The results are shown in Table 9, the scoring and interpretation being on the same basis as in Example 3.

TABLE 9

Slab diffusion bioassay of preservative pastes Substrate : Tasmanian Oak heartwood

Paste Diffusion period (days)^*

7 14 21 28

CB-1 0.17 0.25 0.08 0

CBF-1 0 0 0 0

CBF-3 0.08 0.025 0.17 0.17

CBF-4 0.08 0.25 0.17 0

Untreated control 3.0 3.0 2.92 3.0

Mean of six replicates

It is evident that Pastes CB-1 , CBF-1 and CBF-4 can be classified as "Very Effective" and Paste CBF-3 as an "Effective" preservative. The untreated controls supported a rich fungal growth over the entire test period.

The diffusibility of the active elements in Pastes CB-1 , CBF-1 and CBF-4 was further evaluated with Radiata pine sapwood, Tasmanian Oak heartwood and Spotted Gum (E.maculata) heartwood. With basic densities of about 480 kg/m³, 590 kg/m³ and 880 kg/m³ respectively, the three timbers are representative of the range of substrates likely to be encountered in field service.

The test method used was similar to that of the bioassay except that the slabs were not edge-sealed and diffusion was allowed to proceed for twelve weeks in a sealed container at ambient conditions. Each diffusion test was conducted with six replicate slabs. At the end of the twelve week diffusion period, the test slabs were washed free of any adhering paste and analysed for the active elements which had diffused into the timber substrates. (Table 10). TABLE 10

Distribution of active elements in diffusion slabs after twelve weeks

Paste Distribution of active Diffusion Distribution of active elements in original substrates elements in diffused paste (% m/m) slabs (% m/m)

Cu B F Cu B F

CB-1 23.3 76.7 - Radiata pine 10.4 89.6 -

Tasmanian Oak 10.9 89.1 -

Spotted Gum 16.9 83.1 -

CBF-1 23.3 38.4 38.4 Radiata pine 4.3 45.8 49.8

Tasmanian Oak 9.1 64.5 26.4

Spotted Gum 5.9 62.7 31.4

CBF-4 23.3 38.4 38.4 Radiata pine 6.6 55.5 37.9

Tasmanian Oak 12.0 58.5 29.9

Spotted Gum 10.0 59.9 30.0

It is evident that the boron generally diffused faster than the fluorine, which in turn diffused faster than the copper. Given sufficient time, it could be anticipated that the distribution of active elements in the test slabs would approximate the distribution of active elements in the original pastes.

Claims

CLAIMS:

1. A composition in the form of a paste suitable for use as a wood preservative said composition including a fungitoxic metal derivative and a fungitoxic boron compound wherein both the metal derivative and the boron compound are water soluble and freely diffusible in moist wood.

2. A composition according to claim 1 wherein the composition includes a diffusible metal in an amount of about 0.3 to 25% m/m.

3. A composition according to claim 2 wherein the diffusible metal is present in an amount of about 1 to 4% m/m.

4. A composition according to any one of the preceding claims wherein the composition includes diffusible boron in an amount in the range of about 1 to 15% m/m.

5. A composition according to claim 4 wherein the composition includes diffusible boron in an amount in the range of about 3 to 8% m/m.

6. A composition according to any one of the preceding claims wherein the metal derivative is a water-soluble chelate.

7. A composition according to any one of the previous claims wherein the metal of the metal derivative is selected from transition elements or rare earths.

8. A composition according to claim 7 wherein the transition element is selected from copper or zinc.

9. A composition according to claim 7 wherein the rare earth is selected from cerium, lanthanum or yttrium.

10. A composition according to any one of the preceding claims wherein the metal derivative is a water-soluble chelate in which the metal ion is coordinately bonded to an appropriate ligand such that the resultant metal ion complex has a neutral or negative charge.

11. A composition according to claim 10 wherein the ligand is glycine.

12. A composition according to claim 10 wherein the ligand is a polycarboxylic acid.

13. A composition according to claim 12 wherein the polycarboxylic acid is selected from iminodiacetic acid, nitrilotriacetic acid or ethylenediaminetetraacetic acid.

14. A composition according to any one of the preceding claims wherein the boron compound is boric acid or a water soluble salt thereof.

15. A composition according to claim 14 wherein the boron compound is selected from one or more of sodium tetraborate, sodium decaborate or sodium dodecaborate.

16. A composition according to any one of the preceding claims further including a diffusible fluorine compound.

17. A composition according to claim 16 wherein the diffusible fluorine compound is a present in an amount in the range of about 1 to 15% m/m.

18. A composition according to claim 17 wherein the diffusible fluorine compound is present in an amount in the range of about 2 to 8% m/m.

19. A composition according to any one of claims 16 to 18 wherein the fluorine compound is selected from a water-soluble alkali metal fluoride or an alkali metal fluoroborate.

20. A composition according to any one of the preceding claims wherein the composition is in the form of a thixotropic paste.

21. A composition according to any one of the preceding claims further including one or more bulking agents and/or thickeners .

22. A composition according to claim 21 wherein the bulking agent is selected from nut shell flour, wheat flour, or fumed silica or mixtures of two or more thereof.

23. A composition according to claim 21 wherein the thickening agent is selected from soluble starch or a high molecular weight carboxy vinyl polymer.

24. A composition according to any one of the preceding claims further including a diffusion modifying agent.

25. A composition according to claim 24 wherein the modifying agent is a polyhydric alcohol.

26. A composition according to any one of the preceding claims further including one or more of a drying oil, varnish or fibres.

27. A method of producing a thixotropic composition suitable for use as a wood preservative including the steps of:

(1) reacting a hot aqueous solution of an alkali-metal borate containing a chelating agent and if desired an alkali-metal fluoride or fluoroborate with a metal salt to yield a solution of a metal chelate and the alkali-metal borate and the alkali-metal fluoride or fluoroborate;

(2) contacting the mixture from step (1) in the presence of a surfactant with one or more bulking agent(s) and/or thickeners and forming a thixotropic paste.

28. A method according to claim 27 wherein the metal chelate is a water- soluble chelate in which the metal ion is coordinately bonded to an appropriate ligand such that the resultant metal ion complex has a neutral or negative charge.

29. A method according to claim 27 or 28 wherein the hot aqueous solution is at a temperature of greater than about 50°C.

30. A method according to claim 29 wherein the hot solution is at a temperature in the range of about 70°C to 100°C.

31. A method of maintaining and/or preserving wood or a wood-containing product the method including treating the wood or wood-containing product with a composition in accordance with any one of claims 1 to 26.