WO2012103580A1

WO2012103580A1 - Composition and method for treating wood

Info

Publication number: WO2012103580A1
Application number: PCT/AU2012/000081
Authority: WO
Inventors: Peter Raynor Soundy Cobham
Original assignee: Danip Pty Ltd
Priority date: 2011-02-01
Filing date: 2012-02-01
Publication date: 2012-08-09
Also published as: AU2015210428A1; AU2012212390A1; AU2012212390B2

Abstract

The present invention relates to a composition for treating wood comprising a wood preservative, a particulate substance and a carrier, wherein the particulate substance is present in an amount in the range of 0.0005% m/v to 2% m/v of the composition. Methods of treating wood with the composition and methods of controlling uptake of the composition into wood are also described.

Description

COMPOSITION AND METHOD FOR TREATING WOOD Field of the Invention The present invention relates to a composition for treating wood comprising a wood preservative, a particulate substance and a carrier. Methods of treating wood with the composition and methods of controlling the uptake of the composition into the wood are also described. Background of the Invention

Wood is a common commodity used in home building (frames and trusses), exterior construction (fencing, gazebos, trellising), indoor use (furniture, floors), in ground use (farm fencing, vineyard trellising, utility poles) and for use in marine environments (piling). Apart from naturally durable woods, all these applications require chemical protection of the wood from fungal, bacterial and insect attack, especially from termite attack.

Standards for wood protection have been developed either on a country or regional basis. These standards are subdivided into hazard classes based on the biological hazard involved and the commodity involved. For example, the Australian and New Zealand standards (AS 1604 and NZS3640) provide the following Hazard classes:

• Hazard Class 1 : Insect Attack; wood in internal situation protected from weather. · Hazard Class 2: Termite Attack; wood in internal situation protected from weather.

• Hazard Class 3: Fungal, insect and termite attack; wood in external situation above ground but subject to rain wetting.

• Hazard Class 4: Fungal, bacterial, insect and termite attack; wood in ground, subject to rain wetting.

· Hazard Class 5: Fungal, bacterial, insect and termite attack; wood in ground, subject to rain wetting. High hazard for utility poles etc. • Hazard Class 6: Marine organisms, fungal, bacterial, insect and termite attack in marine environment.

For each Hazard Class, the standards define retention and penetration of the wood commodity required by preservative treatment. For example, Hazard Class 3 and above will normally require at least full sapwood penetration of the preservative chemical, whereas envelope treatments are acceptable for insect and termite protection in Hazard Classes 1 and 2. The uptake and penetration of preservative composition is affected by a number of factors, for example, the type of wood being treated, the type of drying process used before treatment, treatments used to improve durability or stability of the wood, the carrier used in the preservative composition and whether fungal infection is present in the wood to be treated. In some cases, where rapid drying of the wood occurs at high temperature or where steam or microwave conditioning is used, the wood may develop cracks and interstitial channels that result in increased permeability and uncontrolled uptake of preservative composition. Similarly fungal infection of the wood, such as "blue stain" or sapstain, also results in the formation of interstitial channels in the wood resulting in increased permeability and uncontrolled uptake of preservative composition.

Rapid and uncontrolled penetration of the preservative composition into the wood is economically undesirable, particularly in treatments where only envelope formation is required. The uncontrolled penetration results in a much greater volume of preservative composition being required for treatment, and therefore a much greater amount of preservative and, if used, expensive non-aqueous solvents, than would be required if the wood being treated was not as permeable. Furthermore, uncontrolled uptake of preservative composition in strapped packets of wood can lead to uneven penetration of the preservative composition. High uptake of aqueous formulations, including aqueous formulations comprising glycols or glycerine in the aqueous carrier, results in longer times or higher cost drying treatments to return the wood to its original moisture content or to a moisture content equivalent to the equilibrium moisture content for its end use.

There is a need for new wood preserving compositions that allow controlled penetration of preservative composition and controlled uptake of preservative composition.

Summary of the Invention

The present invention is predicated in part on the discovery that inclusion of a particulate substance in the preservative composition reduces uptake of the preservative composition in wood that has high permeability, particularly high permeability resulting from fungal infection or high temperature drying processes or steam or microwave conditioning processes without unduly affecting penetration (envelope or full sapwood) of the preservative.

In a first aspect of the present invention, there is provided a wood preservative composition comprising a wood preservative, a particulate substance and a carrier, wherein the particulate substance is present in an amount in the range of 0.0005% m/v to 2% m v of the composition.

In some embodiments, the particulate substance, also referred to as an uptake inhibitor, is dispersed in the composition. In some embodiments the particulate substance has a particle size in the range of 0.8 to 100 μηι, especially 0.8 to 10 μπι, more especially 1 to 10 urn. In some embodiments, the particulate substance is present in an amount in the range of 0.01% to 2% or 0.01% to 1% m/v of the composition. In some embodiments, the particulate substance is a thixotrope, a pigment or a matting agent. In some embodiments, the particulate substance is silicon dioxide. In other embodiments, the particulate substance is Fe₂C>3. In another aspect of the invention, there is provided a method of controlling uptake of wood preservative composition during wood treatment comprising treating the wood with a wood preservative composition comprising a wood preservative, a particulate substance and a carrier wherein the particulate substance is present in an amount of the range of 0.0005% m/v to 2% m/v of the composition. In some embodiments, the wood is timber or an engineered wood product. In some embodiments the wood is contacted with the composition by dipping (individual piece or strapped packs), spraying, rolling, misting or brushing. In other embodiments, the wood is contacted with the composition by a vacuum pressure process. In some embodiments, the wood treatment is for full sapwood penetration. In other embodiments, the wood treatment is for envelope formation. Advantageously, the use of the particulate substance as an uptake inhibitor does not adversely affect penetration of the preservative.

In another aspect of the invention there is provided a method of improving surface coverage of wood in a strapped pack with a preservative composition comprising treating the wood in a strapped pack with a preservative composition comprising a wood preservative, a particulate substance and a carrier wherein the particulate substance is present in an amount in the range of 0.0005% m/v to 2% m/v of the composition.

In some embodiments, the wood is treated with a vacuum process. In other embodiments, the wood is treated by dipping.

In another aspect of the invention, there is provided wood or engineered wood products treated by the method outlined above. Brief Description of the Figures

Figure 1 is a graphical representation showing uptake of a 90 : 10 water : oil emulsion in the presence of 0%, 0.025%, 0.05% and 0.1% m/v uptake inhibitor in wood samples that had no blue stain fungal infection. Figure 2 is a graphical representation showing uptake of 90 : 10 water : oil emulsion in the presence of 0%, 0.025%, 0.05% and 0.1% m/v uptake inhibitor in wood samples that have blue stain fungal infection. Figure 3 is a graphical representation showing the relationship between percentage blue stain and the uptake of the emulsion composition at different concentrations of uptake inhibitor.

Figure 4 is a graphical representation of the effects of uptake inhibitor on the uptake of non-aqueous carrier.

Figure 5 is a graphical representation of the uptake of a preservative composition in the presence of a particulate pigment uptake inhibitor. Description of the Invention

The present invention seeks to reduce the cost of preservative treatment of wood that has abnormally high permeability. The abnormally high permeability may be due to the presence of interstitial channels and cracks that may be formed in the wood during drying of the wood before preservative treatment, especially rapid high temperature drying of wood, formed by steam or microwave conditioning of wood, or that may be formed as a result of fungal infection such as blue stain. Advantageously the present invention may also control moisture content of the wood after treatment with preservative compositions that have water-based or emulsion-based carriers, thereby preventing an excessive increase in moisture content in permeable wood samples.

The present invention provides the use of a particulate substance as an uptake inhibitor to control uptake of preservative compositions in wood with abnormally high permeability and may be used in methods of treating wood that are to achieve full sapwood penetration or envelope formation. Thus the present invention provides an alternative wood preserving composition and method to those currently available.

Traditionally penetration of preservatives into wood proceeds from tracheids to tracheids via border pits and spreads laterally through the rays of the wood.

During drying processes, particularly high temperature drying processes, such as those performed at temperatures above 120°C, horizontal and vertical parenchyma cells in the wood collapse and interstitial spaces are created. These processes increase the permeability of the wood.

Conditioning processes such as steam or microwave conditioning also result in channels and microvoids in the wood that increase permeability. These channels and voids allow moisture to escape when drying, or allow infusion of resins, preservatives or stains throughout the wood. Steam conditioning involves treating freshly felled or sawn wood (green wood) with steam in a pressure vessel at about 140 kPa (130°C) for a specified time depending on size, such as sawn dimension or diameter of round wood. After the specified time, the pressure is rapidly dropped causing obliteration of ray cells and the production of channels in the wood. In microwave conditioning, wood is treated with high intensity microwave energy which is converted to heat in the wood creating steam pressure in wood cells. Under the high internal pressure, thin-walled ray cells rupture to create microvoids in the radial-longitudinal planes of the wood. In hardwoods, microwave conditioning also ruptures tyloses (balloon-like swellings that block older vessels in the heartwood). Fungal infection of wood, such as blue stain, also known as sapstain, commonly occurs shortly after a tree is felled, for example within 2-4 days of felling. The microscopic fungi infect the sapwood of the felled tree and use parts of the sapwood, such as sugars and starches, for food. Fungal infection is therefore often present in wood before it is milled and treated with preservatives. While blue stain fungi cause a bluish or grey discoloration of the wood, the infection has no effect on the strength of the wood. While wood that has increased permeability may be treated with known preservative compositions, increased uptake of the composition results in the wood treatment being more expensive as more composition is required to treat such wood. The present inventor has found that addition of a particulate substance in an amount in the range of 0.0005% m/v to 2% m v to the preservative composition reduces uptake of the composition in permeable wood reducing the amount of composition required to treat a given quantity of wood while still maintaining acceptable penetration of preservative to meet the standards required for full penetration treatment or envelope formation.

Without wishing to be bound by theory, it is thought that the particulate substance enters the interstitial channels or spaces in the permeable wood and at least partially blocks the channels or spaces preventing entry of excessive amounts of preservative composition while still allowing adequate preservative composition into the wood to achieve the desired preservation treatment.

The particulate substance, also referred to herein as an uptake inhibitor, can be any particulate substance that is capable of reducing the uptake of preservative composition in permeable wood. By "permeable wood" is meant wood that has increased permeability or abnormally high permeability to liquid compositions compared to other wood samples from the same species that do not have interstitial channels or spaces in the wood. The increased or abnormally high permeability is caused by interstitial channels or spaces in the wood. The interstitial channels or spaces may result from drying or conditioning of the wood or from fungal infection.

The particulate substance has particles that are of suitable size to enter the wood and interstitial channels and spaces but are too large to penetrate the cell walls of the wood cells. In some embodiments the average particle size is in the range of from 0.8 to 100 μπι, especially 0.8 to 10 μιη, more especially 1 to 10 μιη. Suitable particulate substances include particulate thixotropes, particulate matting agents and particulate pigments. For example, suitable thixotropes and matting agents include, but are not limited to silicon dioxide, fumed silica, precipitated silica, amorphous silica, crystalline alumino silica, polydimethylsiloxane, aluminium magnesium silicate, aluminium oxide, aluminium hydroxide, zinc stearate, acrylate-styrene, particulate derivatives of caster oil, modified hydrogenated caster oil, montmorillonite clay, modified montomorillonite clay such as organophilic montmorillonite or organic modified montmorillonite, bentonite, modified bentonite such as quaternary ammonium compound of bentonite, diatomaceous earth, particulate amide waxes, sepiolite, organomodified sepiolite, smectite clay or modified smectite clay, kaolin and zeolite. Suitable pigments include inorganic and inorganic pigments. Suitable inorganic pigments include but are not limited to copper based pigments such as BaCuSi₂0₆, CaCuSUOio, BaCuS.₄0io and CuHAs0₃; aluminium based pigments such as Na8-ioAl6Si602₄S2-8; cobalt based pigments such as cobalt blue and Na₃Co(N0₂)6; iron based pigments such as Fe₂0₃, Fe₇(CN)i8 and Fe₂0₃.H₂0; cadmium based pigments such as cadmium green, CdS, cadmium orange and CdSe; chromium pigments such as hydrated chromium (III) oxide, PbCrQj and PbCrC and Pb0₃; lead pigments such as Naples yellow and Pb₃0.j; titanium based pigments such as titanium yellow, titanium black and TiC ; arsenic pigments such as AS2S3; tin pigments such as SnS₂; mercury pigments such as HgS; antimony pigments such as Sb20₃; barium pigments such as barium sulphate; zinc pigments such as ZnO; carbon black; Paynes grey and clay earth (Fe₂0₃ + Mn0₂ + NH₂0 + Si + AIO3). Suitable organic pigments include but are not limited to monoazo pigments, diazo pigments, acid and base dye pigments, phthalocyanine pigments, quinicridone pigments and polycyclic pigments. In one particular embodiment, the particulate substance is silicon dioxide. In another particular embodiment, the particulate substance is Fe₂0₃.

The particulate substance may be present in the composition in an amount of 0.0005% to 2% mass/volume (m/v), especially 0.001% to 2% m/v, 0.01% to 2% m/v, 0.01% to 1% m/v, more especially about 0.05% to 0.5% m/v, for example about 0.1% m v. If excessive amounts of particulate substance is added to a preservative composition or if a particle size is excessive, adverse effects may occur. For example, the particles may not disperse in the composition and may rapidly settle in the treatment vessel or the particles may stay on the surface of the wood and not act as an uptake inhibitor or may inhibit uptake of preservative to an extent that inadequate penetration is achieved.

A wide variety of preservatives can be included in the composition of the invention. Oil soluble preservatives are used in non-aqueous carriers or contained in the oil phase of the emulsion or microemulsion. Water soluble preservatives are used with aqueous carriers or contained in the water phase of the emulsion or microemulsion. The preservative may be any preservative that is required to protect wood from biological organisms. For example, the preservative may be a fungicide, bactericide, insecticide or a termiticide. Suitable insecticides and termiticides include synthetic pyrethroids such as permethrin, cypermethryn, deltamethrin, and bifenthrin and neonicotinoids such as imidichloprid and thiochloprid. Suitable fungicides and mouldicides include creosote, pentachlorophenol (PCP), azoles such as tebcuconazole, propiconazole, cyperconazole and the like; organic copper compounds such as copper 8-quinolinolate, copper naphthenate and bis-(N- cyclohexyldiazeniumdioxy)copper (Cu-HDO), organic zinc compounds such as zinc naphthenate, organic tin compounds such as tributyl-tin naphthenate (TBTN); silver compounds, iodopropynyl-butylcarbamate (IPBC), 3-benzomien-2-yl-5,6,dihydro- 1,4,2- oxathiazine-4-oxide (Bethoguard®), quaternary ammonium compounds, tertiary ammonium compounds, isothiazalones and boron compounds. The preservatives may also be a micronised or dispersed active such as copper carbonate, copper oxide, or oxine copper.

In some embodiments, the composition may comprise a mixture of preservatives. For example, fungicides such as propiconizole and tebuconizole may be used together in a 1:1 ratio. Suitable amounts of these compounds may achieve a timber loading of 0.03 % mass/mass for each compound. In other embodiments, the composition may contain fungicides and insecticides or termiticides. For example, a combination of propiconizole and tebuconizole may be combined with a pyrethroid such as bifenthrin or permethrin. Suitable ratios would be 1 (propiconizole) : 1 (tebuconizole) : 0.67 (permethrin) or 0.16 (bifenthrin). A suitable combination would be propiconizole and permethrin or bifenthrin. A person skilled in the art could determine suitable amounts of fungicides or insecticides to use in a mixture to achieve a desired % mass/mass loading in the timber product using methods known in the art. For example, a range of mixed preservative ratios may be prepared and wood treated with the compositions. The wood is then tested by standard methods such as the spot test or by chemical analyses such as those set out in Australian Standard AS 1605 parts 1 to 5, to determine the amount of each preservative taken up by the wood.

In some embodiments, the wood preserving compound is solubilised in the aqueous or non-aqueous carrier. In other embodiments, the wood preserving compound may be encapsulated and solubilised or suspended in the oil or water carrier. Encapsulation may be particularly useful if the preservative is toxic to humans, heat unstable and/or chemically unstable in water or oil or if a slow release of the preservative is required. Microencapsulation of the preservative may be achieved by methods known in the art, such as pan coating, air-suspension coating, centrifugal extrusion, vibration nozzle encapsulation, spray drying, interfacial polymerization, in-situ polymerisation and matrix polymerisation.

The amount of preservative present in the composition is dependent on the type of preservative used and the loading required. A person skilled in the art could readily determine a suitable amount of preservative. In general, the preservative will be included in an amount of below 10% m/v of the composition, especially below 5% m v of the composition, more especially below 2% m/v of the composition.

The carrier may be any carrier currently used in wood preserving compositions including aqueous carriers, non-aqueous carriers such as light organic solvent preservatives (LOSP) or emulsion carriers that are a mixture of water and a solvent or oil. In some embodiments the aqueous carrier is water. In other embodiments, the aqueous carrier is a mixture of water and one or more aqueous miscible solvents. For example, the aqueous carrier may comprise a glycol or glycerine. Suitable glycols include, but are not limited to monoethylene glycol, hexylene glycol and polyethylene glycol.

Suitable non-aqueous carriers include combustible oils, such as those having a flash point of 61 °C and above. The oil used in the present invention is not a flammable oil. The University of Queensland guidelines for handling and storage of flammable and combustible liquids (http://www.uq.edu.au/hupp/Index.html?page=250428pid=25039) separates combustible oils into two classes, those with a flash point between 61°C and 150°C and those having a flash point above 150°C. In contrast flammable liquids have flash points below 61°C. In some embodiments the oil is selected from mineral oils, vegetable oils, fish oils, biodiesel, aromatic solvents, aromatic oil and mixtures thereof. The biodiesel may be sourced from edible or non-edible sources including vegetable oils, animal fat or alcohol. Suitable aromatic solvents include naphthalene and indene and aromatic oil is a mixture of naphthalene, 3a,4,7,7a-tetrahydro-4,7-methanoindene and optionally indene. In particular embodiments the oil is paraffin oil, isoparaffin oil, such as Isopar L, M or V, narrow cut kerosene, high flash kerosene or biodiesel sourced from non- edible vegetable oils. If a mixture of oils is used as the carrier, the mixture should be combustible and have a flash point of 61 °C or above.

In some embodiments, the solvent is solvent that is recovered during the wood treatment process by processes such as condensation and the like. Such solvents include but are not limited to dichloromethane and refrigerants.

In some embodiments, the non-aqueous solvent is a glycol or glycerine. Suitable glycols include, but are not limited to monoethylene glycol, hexylene glycol and polyethylene glycol. In some embodiments the oil has a low level of volatile organic compounds (VOCs) and is therefore odourless or substantially odourless and has limited impact on "greenhouse gas" release. In some embodiments, the carrier is an emulsion or microemulsion of oil or solvent and water, including an oil-in-water emulsion or a water-in-oil emulsion. The non-aqueous component of the emulsion may be selected from any of the non-aqueous solvents referred to above. As used herein, the term "emulsion" refers to two immiscible liquids, one liquid forming the carrier phase and one liquid forming the dispersed phase. The dispersed phase is dispersed as particles or droplets in the carrier phase. Emulsions tend to be cloudy as the phase interfaces tend to scatter light. Emulsions require energy input to form through shaking, mixing, homogenising or spraying or in some cases, high shear mixing. Emulsions often have a wide range of particle or droplet sizes in the dispersed phase and the droplet size is greater than that in a microemulsion.

As used herein, the term "microemulsion" refers to a macroscopically homogenous mixture of oil, water and optionally, surfactant. The particle size of the particles in a microemulsion is smaller than those in an emulsion and therefore microemulsions are often optically clear. Unlike emulsions, microemulsions can be formed upon simple mixing of the oil and water phases.

The emulsions and microemulsions are formed by mixing the oil and water phases, at least one of which comprise a preservative compound, and optionally comprising a surfactant/emulsifier. The mixing may be regular mixing or be high shear mixing as is known in the art.

The water and oil content is provided as a ratio of oil and water in the emulsion or microemulsion. The water is present in an amount greater than 30% up to 92.5% v/v of the mixture of oil and water. The oil is present in an amount from 7.5% to less than 70% v/v of the mixture of oil and water. In some embodiments, the ratio of water is greater than 30% up to 90% v/v, 45 to 80% v/v, especially 50 to 75% v/v of the mixture of oil and water. In these embodiments, the ratio of oil in the mixture of oil and water is 10 to less than 70%, 20 to 55% v/v especially 25 to 50% v/v.

In some embodiments, the ratio of water and oil in the emulsion is selected to achieve a particular size of envelope. For example, a ratio of 25:75 v/v oil : water may be selected to provide a 3mm envelope or a ratio of 50:50 v/v oil : water may be selected to provide a 5mm envelope. Different envelope sizes may be obtained by varying the ratio of water to oil. Particular treatments providing 3mm to 5mm envelopes may be suitable for wood treatment in Hazard classes 1 and 2.

In some embodiments, the composition further comprises a surfactant or emulsifier to stabilise the emulsion or microemulsion carrier of oil and water. Suitable surfactants or mixtures of surfactants have an HLB value of between 4 and 12. In some embodiments when the emulsion or microemulsion is an oil-in-water emulsion or microemulsion, the surfactant or surfactant mixture has an HLB of 8 to 12. In some embodiments, when the emulsion or microemulsion is an water-in-oil emulsion or microemulsion, the surfactant or mixture of surfactants has an HLB of 4 to 6. The surfactants can be nonionic, anionic or cationic surfactants, especially nonionic surfactants. Suitable surfactants include nonylphenol alkoxylates, ethoxylated caster oils, alcohol alkoxylates, tristyrolphenols, anionic/nonionic blends, alkylamine ethoxylates, sorbitan esters, surfactants sold under the tradename Tersperse®, such as Tersperse® 4896 (a nonionic wetter and dispersant) Tersperse® 4890 (a polymeric amine condensate) and Tersperse® 2500 (an acrylic graft copolymer surfactant), that have low HLB values suitable for emulsifying water in oil emulsions and microemulsions, Termul® emulsifiers such as Termul® 200, 5360, 5370, 5600, 7220, 1283, 1284, 1285, 2507, 3512, 3540, 203, 5429, 5500, 7240, 3130, 3140, 3150, 3162, 3170, 3180, 3190, 3194, 3195, 3196, 5030, 5101 and 5123, which are all suitable for emulsifying oil in water emulsions and microemulsions, Teric® alkylamine 17M2 (HLB 9, Teric® 17M5 (HLB 10), Teric® 18M2 (HLB 8.5), Teric® 18M5 (HLB 9.5), Teric® 18M10 (HLB 1 1.2), Teric® 12A2C (HLB 6.0) and Teric® 12A1N (HLB 3.6), Sorbitan monooleate (Span 80, HLB 4.3), Sorbitan monostearate (Span 60, HLB 4.7), Sorbitan monopalmitate (Span 40, HLB 6.7), Sorbitan monolavrate (Span 20, HLB 8.6), polyoxyethylene sorbitan tristearate (Tween 65, HLB 10.5) and polyoxyethylene sorbitan trioleate (Tween 85, HLB 11.0). A person skilled in the art could determine suitable surfactants or emulsifiers for oil-in-water or water-in-oil emulsion and microemulsion carriers.

The surfactant or emulsifier is added in the composition in an amount that results in emulsification of the oil and water to form a stable emulsion or microemulsion. In general, the emulsifier or combination of emulsifiers will be included in an amount of below 10% of the composition, especially below 2% of the composition, more especially below 1% of the composition.

Surfactants may also be included in the composition as penetration enhancers or to allow inclusion or stabilisation of water repellents.

The preservative composition may also include other optional components such as corrosion inhibitors, colouring agents such as dyes or pigments, for example, a blue dye to indicate that the wood has been treated, anti-settling agents, gelling agents, water repellents such as waxes, resins, fire retardants, UV stabilisers, adjuvants and algicides.

The anti-settling agent (or stabiliser) can typically belong to one of two classes of substances, surfactants and colloids. These agents stabilise the particles to prevent them from joining together (coagulation or coalescence) and either settling under the influence of gravity (sedimentation) or floating to the top (creaming). The difference between creaming and sedimentation depends on whether the particles are less or more dense than the surrounding solvent or water.

Surfactants are typically molecules having a hydrophilic moiety and a hydrophobic moiety. The hydrophobic moiety tends to stick to the particle and the hydrophilic moiety sticks out into a polar solvent. The hydrophilic part has a charge which repels like charges and prevents the particles approaching each other therefore reducing settling.

Colloids don't have a charge, but are large molecules that stick to the surface of the particles and typically work by acting as a barrier to prevent the particles coming together and settling.

Stabilisation can also occur by the use of a gelling agent, which makes the liquid thicker and slows down settling. In this case, the particles don't move around so much in the liquid as much so their contact rate is reduced.

In another aspect of the invention, there is provided a method of controlling uptake of wood preservative composition into wood comprising treating wood with a wood preservative composition comprising a wood preservative, a particulate substance and a carrier; wherein the particulate substance is present in an amount in the range of 0.0005% m/v to 2% m/v of the composition.

In some embodiments at least a proportion of the wood treated is permeable wood. In some embodiments, the particulate substance does not affect penetration or retention of the preservative.

In some embodiments the wood is timber or an engineered wood product. The timber may be timber that may be treated to provide preservative envelopes of hazard classes 1 and 2 such as timber used as building materials for trusses and frames. Treatment where full sapwood penetration and envelope penetration to the heartwood can also be achieved for higher hazard classes such as 3-5 where timber is used in an external situation. Typical uses for this timber include fencing, trellises, gazebos, and outdoor ftirniture. In some embodiments the wood is sapwood. In other embodiments the wood is heartwood. Suitable woods include softwoods and hardwoods. Softwoods such as Pinus radiata, Southern yellow pine species, Pinus elliottii and Pinus sylvestris, are typically used in house frames and trusses. Engineered wood products include wood composite materials made of wood fibres, wood particles, wood veneer, wood strands or mixtures thereof. Examples of engineered wood products are plywood, laminated veneer lumber, oriented strand board, particle board and medium density fibre board. As used herein the term "envelope" refers to where treated wood has absorbed the composition radially, tangentially and/or longitudinally to a depth from the surface of the wood. Controlled envelope formation refers to where the composition is absorbed into the wood substantially evenly in the radial and tangential direction. In some embodiments, the depth of the envelope may be predicted from the ratio of oil and water in the emulsion or microemulsion. In some embodiments, the composition may be absorbed rapidly on a radially cut face and less rapidly on a tangentially cut face resulting in an envelope of uneven depth. The depth of the envelope achieved may also be affected by the quality and/or type of wood being treated. As used herein the term "full sapwood penetration" refers to penetration of the preservative composition through all sapwood in the wood or timber sample. Penetration for various hazard classes are defined in Country Standards such as Australian Standard AS 1604, New Zealand Standard 3640 and for the USA, the American Wood Protection Association. In some cases full sapwood penetration is required plus an envelope penetration of the heartwood. In the case of wood with mixed heartwood and sapwood, all of the sapwood must be penetrated and if required an envelope of typically 5mm penetration in the heartwood. As used herein, "penetration" refers to the depth to which a prescribed preservative has entered the wood. "Penetration zone" as used herein refers to the zone of timber required to be penetrated by the preservative. The penetration zone is described as required depending on the Hazard Class being specified.

The wood to be treated may be contacted with the composition by methods known in the art. For example in some embodiments, the wood is contacted with the composition by dipping (individual piece or strapped packs), spraying, rolling, misting or brushing. In other embodiments the wood is contacted with the composition in a vacuum pressure process. For example, the wood may be typically contacted with the composition by dipping (individual piece or strapped packs), spraying, rolling, misting or brushing for at least about 15 to 90 seconds, for example 20 to 60 seconds. Some timber species may require a longer dip time to achieve adequate penetration and retention. The contact is then followed by draining of any excess preservative from the wood for 5 to 20 minutes, especially about 10 minutes. For dipping, spraying, rolling, misting or brushing a specific uptake of composition should be targeted, such as 5 to 30 L/m³ or 10 to 25 L/m³ to achieve similar penetration and retention as found with dipping.

In a particular embodiment, the wood is contacted with the composition by dipping. Dipping can be of individual pieces of wood or strapped packs of wood. This method may be particularly advantageous with strapped packs where acceptable coverage of the wood pieces in the internal part of the pack is difficult to achieve by other methods such as spraying. Dipping of strapped packs can achieve full coverage of the wood pieces in the pack, even the internal wood pieces, if the strapped pack is dipped deep enough in the immersion or dipping bath such that a hydrostatic head pressure of at least 5 kPa is exerted at the top of the pack. The required hydrostatic head pressure will depend on the strap tension of the pack. The higher the strap tension, the higher the hydrostatic head pressure required to obtain full coverage of the internal wood pieces in the strapped pack. The hydrostatic head pressure may be between 5 and 20 kPa, for example, 6 kPa, 7.5 kPa, 10 kPa, 12 kPa, 15 kPa or 20 kPa, especially at least 10 kPa.

The timber may be treated as individual pieces or in a timber pack (strapped pack) where a number of timber pieces are tightly strapped together ready for transport. In some embodiments all of the timber in the pack is permeable wood. In other embodiments, a proportion of the timber in the pack, but not all of the timber, is permeable wood. In some cases where not all of the wood in the pack is permeable, either parts of individual timber pieces or individual pieces in a pack, the use of the uptake inhibitor prevents excessive uptake in the permeable wood but still allows penetration of the preservative to the required extent in the wood that is not abnormally permeable. In some embodiments, the wood is subject to a vacuum pressure process in the presence of the composition. Vacuum pressure treatment is known in the art and may involve the use of low pressure Bethell, Lowry or Reuping process or Vac- Vac process as used with the LOSP. The vacuum pressure process is suitable for achieving full sapwood penetration of the preservative without substantially increasing the moisture content of the wood. For example, a 50:50 oilrwater emulsion with an uptake of 40 Litres per cubic meter (20 L/m³ water), assuming a basic wood density of 550 kg/m³, would increase the moisture content of wood by only 4%. This is in contrast to a 100% water-borne treatment where high uptake is required (>300 L/m³) that could increase the moisture content of the wood by >50%. By "without substantially increasing moisture content of the wood" refers to an increase in moisture of less than 10%, especially less than 8% or 6% and especially less than 4%. In the case of non-aqueous compositions, an uptake of 25 L/m³ to 45 L/m³, especially about 30 L/m³, is desired to achieve full sapwood penetration. The use of non-aqueous solvents does not increase moisture content of the wood.

Processes for Light Organic Solvent Preservatives typically use either the Vac- Vac process, low Pressure Lowry or low pressure Reuping schedule.

General Vac- Vac schedule:

-Draw intial vacuum (typically -5 to -30 Kpa.)

-Flood the vessel maintaining vacuum

-Release the vacuum and drain the vessel

-Draw a final vacuum of greater than -85 kPa and maintain for up to 15 minutes

-Release vacuum and drain liquid recovered on final vacuum,

Process complete

Uptakes are typically 25 to 45 L/m³. General Low Pressure Lowry Schedule

-Flood vessel _- Apply positive pressure (typically 10 to 50 kPa.)

-Drain vessel

-Draw a final vacuum of greater than -85 kPa and maintain for up to 15 minutes -Release vacuum and drain liquid recovered on final vacuum,

Process complete

Uptakes are typically 25 to 45 L m³.

General Low Pressure Reuping schedule

-Apply pneumatic pressure (Typically 10 to 40 kPa.)

-Flood maintaining pneumatic pressure

_Apply hydraulic pressure above the pneumatic pressure (Typically 20 to 60 kPa) -Drain vessel

Process complete

Uptakes are typically 25 to 45 L/m³.

The uptake of the composition is important to achieve a level of preservative penetration and retention required to achieve the results required, for example, protection against termite attack. The loading of the preservative in the timber is referred to in % mass/mass which is a percentage indicating mass of preservative in a given mass of wood. In one embodiment where the preservative is bifenthrin, the toxic threshold for termiticidal activity is 0.0004 to 0.02% mass/mass and for permethrin the uptake must provide at least 0.02% mass/mass permethrin to meet Australian Standards (AS 1604).

As used herein, "uptake" refers to the uptake of solvent or liquid composition. "Retention" as used herein refers to the amount of preservative retained in the wood after treatment. If uptake of composition is high, a lower amount of preservative may be used. However, the solvent, particularly non-aqueous solvent, is expensive, and therefore controlling uptake is important and if required, the amount of preservative may be increased to maintain required retention in accordance with standards. A person skilled in the art could determine the amount of particulate substance and preservative to achieve required retention given a particular uptake by simple trial.

In another aspect of the invention there is provided a method of improving surface coverage of wood in a strapped pack with a preservative composition comprising treating the wood in a strapped pack with a preservative composition comprising a wood preservative, a particulate substance and a carrier wherein the particulate substance is present in an amount in the range of 0.0005% m/v to 2% m/v of the composition. In some embodiments, the wood is treated with a vacuum process. In other embodiments, the wood is treated by dipping.

Without wishing to be bound by theory, it appears that the control of uptake of preservative composition allows a more homogenous surface coverage of timber in strapped packs by preventing rapid uptake of preservative composition before the composition comes into contact with all surfaces of the wood in the pack.

As used herein, a "strapped pack" is a pack of wood that includes multiple sawn planks which are strapped together ready for transport.

In another aspect of the invention there is provided wood or engineered wood products treated by the method outlined above.

In order that the nature of the present invention be more clearly understood and put into practical effect, specific embodiments will now be described by way of the following non- limiting examples. Examples

Example 1: Treatment of blue stain infected timer with composition comprising an uptake inhibitor

Eleven end matched 90 x 35 x 250 mm end sealed slash pine samples with and without blue stain fungal infection were treated with bifenthrin (0.2% m/v) in a 90 : 10 water to oil emulsion. The oil used in the emulsion was high flash kerosene. The samples were treated by dipping for one minute, followed by a 5 minute drain. All samples were weighed before and after treatment to determine uptake of the composition. Four treatments were undertaken:

90 : 10 emulsion and 0.2% m/v bifenthrin

90 : 10 emulsion, 0.2% m/v bifenthrin and 0.025% Si0₂ uptake inhibitor

90 : 10 emulsion, 0.2% m/v bifenthrin and 0.05% Si0₂ uptake inhibitor

90 : 10 emulsion, 0.2% m/v bifenthrin and 0.1% Si0₂ uptake inhibitor

The results are shown in Figures 1 to 3.

Figure 1 shows the uptake of the compositions in timber with no blue stain fungal infection. The average uptake of the emulsion in the absence of uptake inhibitor was 13.7 L/m³. The average uptakes of the emulsion with 0.025% m/v, 0.05% m/v and 0.01 m/v uptake inhibitor was 10.1 L/m³, 10.1 L/m³ and 8.7 L/m³ respectively.

Figure 2 shows the uptake of the compositions in timber with blue stain fungal infection. The average uptake of the emulsion in the absence of uptake inhibitor was 22.2 L/m³. The average uptakes of the emulsion with 0.025% m/v, 0.05% m/v and 0.01 m/v uptake inhibitor was 14.7 L/m³, 16.0 L m³ and 13.3 L/m³ respectively.

Without the use of the uptake inhibitor clean wood had an average uptake of 13.7 L/m³ and the blue stained 22.2 L/m . When 0.01% uptake inhibitor was added the variation was 8.7 to 13.3 L/m³. Figure 3 shows the relationship between the percentage of the wood infected by blue stain and the uptake of composition at differing concentrations of uptake inhibitor. At a concentration of 0.1% m v uptake inhibitor, the uptake of the composition did not increase with increasing percentage of blue stain fungal infection. In contrast, in the absence of uptake inhibitor, the uptake of composition increased with increasing extent of blue stain fungal infection.

Analysis of bifenthrin in the wood by acetone extraction and gas chromatographic analysis showed penetration of >5mm in samples of wood with blue stain in the absence of uptake inhibitor. Whereas the presence of uptake inhibitor, an envelope of >2mm bifenthrin was achieved in all samples, even at the lowest uptake.

Example 2: Uptake of non-aqueous carrier in the presence and absence of 0.10% m v uptake inhibitor

Eight end matched and end sealed slash pine samples 90 x 35 x 300 mm in dimension were treated with

1. High flash kerosene and 0.2% m v bifenthrin,

2. High flash kerosene and 0.2% m v bifenthrin plus 0.10% m/v of a Si0₂ uptake inhibitor

The same treatment process was used for both treatments

Flood O kPa

Pressure 60 kPa 2 min

Soak O kPa 1 min

Drain O kPa

Vacuum -85 kPa 5 min

Uptakes (L/m³) for the 2 treatments are shown in Table 1 and Figure 4. Table 1

Analysis of bifenthrin by acetone extraction of wood and gas chromatographic analysis showed that even when reducing the average uptake from 60.3 L/m³ to 41.7 L/m³, full sapwood penetration was achieved in all samples.

Example 3: Wood treatment with composition comprising bifenthrin

Over seven days 1016 packets of slash pine were treated with a composition comprising 95 : 5 water to oil emulsion containing 0.2% m/v bifenthrin. High flash kerosene was used as the oil in the emulsion.

Over the following five days, 351 packets of slash pine were treated with a composition comprising 95 : 5 water to oil emulsion, 0.2% m/v bifenthrin and 0.1% m/v silicon dioxide uptake inhibitor. The silicon dioxide was Grade 200 (chemically prepared ethenehomopolymer with a pore size of 2.0 mL/g and an average particle size of 2.5 μπι.

All packs were treated by dipping with a hydrostatic pressure of +10 kPa for 1 to 2 minutes. After dippii:g_% the packs were drained to remove excess emulsion. Uptake of the composition was deter nined by weighing packs before and after treatment. The results are shown in Tables 2 and 3.

Table 2: All Packets

Routine analysis of Bifenthrin using acetone extraction and gas chromatographic analysis showed penetration in excess of 2 mm as required for compliance for both the control packs and those with uptake inhibitor.

Data indicates

Reduction in uptake as a result of adding uptake inhibitor

Reduction in variation of uptake

Blue stain similar in both sample groups. Example 4: Pigment uptake inhibitor

Three matched sets of eight 90 x 35 mm slash pine sapwood samples were end sealed and treated with

Control: High flash kerosene and 0.2% m v permethrin

Treatment 1 : High flash kerosene, 0.2% m/v permethrin and 0.25% m v pigment (Fe₂0₃) Treatment 2: 80 : 20 emulsion high flash kerosene : water, 0.2% m/v permethrin and 0.25% m v pigment (Fe2C>3).

The pigment particles had an average particle size of 3 to 5 μπι.

The results are given in Table 4 and Figure 5.

Table 4

The pigment uptake inhibitor significantly reduced uptake of the compositions, but complete sapwood penetration by permethrin was still observed as evidenced by acetone extraction and gas chromatographic analysis of the central ninth samples.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A wood preserving composition comprising a wood preservative, a particulate substance and a carrier, wherein the particulate substance is present in an amount in the range of 0.0005% m/v to 2% m/v of the composition.

2. The composition according to claim 1 wherein the particulate substance is dispersed in the composition.

3. The composition according to claim 1 wherein the amount of particulate substance is in the range of 0.1 % m/v to 2% m/v of the composition.

4. The composition according to claim 1 wherein the particulate substance has an average particle size of 0.8 to 100 μπι.

5. The composition according to claim 5 wherein the average particle size is in the range of 1.0 to 10 μιη.

6. The composition according to any one of claims 1 to 5 wherein the particulate substance is a thixotrope, a matting agent or a pigment.

7. The composition according to any one of claims 1 to 6 wherein the particulate substance is silicon dioxide or Fe₂0₃.

8. The composition according to any one of claims 1 to 7 wherein the preservative is an insecticide, a termiticide or a fungicide.

9. The composition according to any one of claims 1 to 8 wherein the preservative is selected from synthetic pyrethroids, metal naphthenates, copper, silver and zinc compounds, organic tin compounds, quaternary ammonium compounds, tertiary ammonium compounds, isothiazalones, boron compounds, neonicotinoid compounds, azoles, pentachlorophenol and creosote or mixtures thereof.

10. The composition according to claim 9 wherein the at least one wood preserving compound is selected from synthetic pyrethroids, neonicotinoid compounds and azoles or mixtures thereof.

11. A composition according to claim 10 wherein the synthetic pyrethroid is selected from bifenthrin or permethrin.

12. A composition according to claim 11 wherein the neonicotinoid compound is selected from imidichloprid and thiochloprid.

13. A composition according to claim 12 wherein the azole is selected from propiconizole and tebuconizole or mixtures thereof.

14. The composition according to any one of claims 1 to 13 wherein the carrier is an aqueous carrier, a non-aqueous carrier or an emulsion.

15. The composition according to claim 14 wherein the carrier is a non-aqueous carrier or an emulsion.

16. A method of controlling uptake of a wood preserving composition, comprising treating the wood with a composition of any one of claims 1 to 15.

17. A method according to claim 16 wherein the wood is contacted with the composition by dipping, spraying, rolling, misting or brushing.

18. A method according to claim 17 wherein the wood is a strapped pack and is contacted with the composition by dipping.

19. A method according to claim 18 wherein the dipping method applies a hydrostatic head pressure of at least 5 kPa at the top of the strapped pack.

20. A method according to claim 16 wherein the wood is contacted with the composition in a vacuum pressure process.

21. A method according to claim 16 wherein the wood is timber or an engineered wood product.

22. A method of improving surface coverage of wood in a strapped pack with a preservative composition comprising treating the wood in a strapped pack with a preservative composition comprising a wood preservative, a particulate substance and a carrier wherein the particulate substance is present in an amount in the range of 0.0005% m v to 2% m/v of the composition.

23. Wood treated by the process of any one of claims 16 to 22.