AU2015215905A1 - A method of treating wood - Google Patents

Abstract

H:\szp\Interwoven\NRPortbl\DCC\SZP\8035922 1doc-20/08/2015 Abstract The present invention relates to a method of treating timber and wood products to protect against damage by insects such as termites or other biological organisms such as bacteria and fungi. The method comprises treating timber or wood products with a composition 5 comprising bifenthrin, such that bifenthrin is applied to the wood in an amount of less than 4 g/m3 . Compositions for use in the method are also described.

Description

- 1 A METHOD OF TREATING WOOD This application is a divisional of Australian Patent Application No. 2013202289, the 5 entire content of which is incorporated herein by reference. Field of the Invention The present invention relates to a method of treating timber and wood products to protect against damage by insects such as termites or other biological organisms such 10 as bacteria and fungi. The method comprises treating timber or wood products with a composition comprising bifenthrin, such that bifenthrin is applied to the wood in an amount of less than 4 g/m 3 . Compositions for use in the method are also described. Background of the Invention 15 Timber and wood products are common commodities used in home building (frames and trusses), exterior above ground construction (fencing, gazebos) in ground use (farm fencing, vineyard trellising, utility poles) and are also used in marine environments (pilings). Apart from use of naturally durable wood, all of these applications require chemical treatment of wood to protect from fungal, bacterial and 20 insect attack, especially from termite attack. Standards for wood protection have been developed either on a country or regional basis. These standards have been subdivided into hazard classes or on a commodity basis. In the case of commodity standards (American Wood Preservers Association) 25 the standards refer back to the biological hazard involved. Hazard Class standards are divided into 5 or 6 classes. The difference being the way in which the commodity is exposed to weather, above or underground, wetting and the type of biological attack. * Hazard Class 1 Insect Attack; wood in internal situations protected from weather. 30 e Hazard Class 2F Termite Attack; wood in internal situations protected from weather. Envelope treatment for South of Tropic of Capricorn. * Hazard Class H2 Termite Attack; wood in internal situations protected from weather. Suitable for all of mainland Australia.

-2 * Hazard Class 3 Fungal, Insect and Termite Attack; wood in external situation above ground but subject to wetting. * Hazard Class 4/5 Fungal, Bacterial, Insect and Termite Attack; wood in ground, subject to wetting. 5 e Hazard Class 5/6 Marine Organisms, Fungal, Bacterial, Insect and Termite Attack in marine environment. For each Hazard Class, the standards define retention and penetration of the wood 10 commodity. For example, Hazard Class 3 and above normally require full sapwood penetration of the preservative chemical. Superficial and envelope treatments are acceptable for insect and termite protection in Hazard Classes 1 and 2F. Preservative treatments appropriate for each Hazard Class are also defined in various 15 country standards, such as New Zealand Standard NZS 3604 and Australian Standard AS 1604. Termite attack in Australian housing has been estimated to cost in excess of $600 million and in the US, $1 to $2 billion dollars annually. 20 Bifenthrin is a common preservative used in the protection of wood from fungal, bacterial and insect attack such as termite attack. Commonly bifenthrin is used to provide a superficial or envelope treatment application rates of 5 to 20 g/m 3 Recently, amounts as low as 4 g/m 3 have been found effective (AU 2012202186). 25 However, balancing effectiveness with economy and environmental friendliness is important in wood treatment. There is a need for improved wood treatments that are effective for Hazard Classes 1, 2 and 2F but use low amounts of chemical preservative thereby reducing costs and reducing the amount of chemicals used and/or exposed to 30 the environment. Summary of the Invention -3 The present invention is predicated in part on the discovery that superficial or envelope treatments may be effective in preventing termite attack at application rates below 4 g/m 3 , for example, between 0.5 and 3.5 g/m 3 . 5 In a first aspect, the present invention provides a method of preserving timber or wood products comprising providing timber or wood products; and applying a preservative composition comprising bifenthrin to the timber or wood product; 10 such that the retention of the bifenthrin in the timber or wood product is in the range of 0.5 g/m 3 to less than 4 g/m 3 . In some embodiments, the retention of bifenthrin is in the range of 1.0 to 3.5 g/m 3 . In some embodiments, the application provides a superficial or envelope treatment. In 15 some embodiments, application is achieved by spraying, dipping, deluge, brushing, soaking, rolling or misting. In other embodiments application is performed under vacuum pressure. In some embodiments, the method protects against insect attack, especially termite 20 attack, especially attack from the termite Coptotermes acinaciformis, the most economically important termite species south of the Tropic of Capricorn. In another aspect of the invention there is provided a method of protecting timber and wood products from termite attack comprising 25 providing timber or wood products; and applying a preservative composition comprising bifenthrin to the timber or wood product, such that the retention of the bifenthrin in the timber or wood product is in the range of 0.5 g/m 3 to less than 4 g/m 3 . 30 Description of the Invention The present invention seeks to reduce the cost and environmental impact of preservative treatment of timber and wood products while maintaining efficacy of the treated wood. Advantageously, the present invention allows treatment of timber and -4 wood products such that the retention of preservative compound is lower than standard treatments while maintaining efficacious protective effects. This allows reduction in the amount of preservative compound used to treat timber and wood products and results in significant cost savings and reduces environmental impact. 5 In the method of the present invention, the preservative composition comprises the preservative compound bifenthrin. The application of the preservative composition to the timber or wood product allows retention of the bifenthrin in the timber or wood product at a retention rate between 0.5 g/m 3 and less than 4 g/m 3 . In some 10 embodiments, the retention rate of bifenthrin is between 0.5 g/m 3 and 3.5 g/m 3 , especially 1.0 g/m 3 and 3.4 g/m 3 . In some embodiments, the application of preservative composition is a superficial treatment. By "superficial treatment" is meant application of preservative composition 15 by methods such as dipping, brushing, spraying, misting, or in a vacuum pressure plant by momentary immersion (zero or low pressure < 100 kPa) and final vacuum, where the timber or wood product is exposed to the preservative composition for a short period of time. Superficial treatments result in minimal absorption of the preservative composition across the grain of the wood. However, absorption into the 20 end grain of the timber may be appreciable. In other embodiments, the application of preservative composition provides an envelope treatment. As used herein, the term "envelope" refers to where treated wood has absorbed the composition, radially, tangentially and/or longitudinally to a depth 25 from the surface of the timber or wood product. Controlled envelope formation refers to where the preservative composition is absorbed into the timber or wood product substantially evenly in the radial and tangential directions. In some embodiments, the depth of the envelope may be achieved by the type of composition used, for example, the ratio of oil and water in an emulsion or microemulsion composition. In some 30 embodiments, the preservative composition may be absorbed rapidly on a radially cut face of timber and less rapidly on a tangentially cut face of the timber resulting in an envelope of uneven depth. In particular embodiments the envelope is between 1 and 5 mm in depth, especially 2 and 5 mm in depth, more especially between 3 and 5 mm in depth.

-5 The application of the preservative composition may be achieved by methods known in the art. In some embodiments, the preservative composition is applied by dipping, spraying, brushing, misting, soaking, deluge, rolling or in a vacuum pressure plant by 5 momentary immersion (zero or low pressure < 100 kPa) and final vacuum. In other embodiments, the application of preservative composition is by a vacuum pressure process. For example, the timber or wood product may be typically contacted with the 10 composition by dipping, spraying, rolling, misting or brushing for at least about 10 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 a superficial treatment, dipping, spraying, rolling, misting or brushing may be used or if 15 a specific uptake or penetration depth is required when using these application methods, a longer exposure time may be required or the timber or wood product may be heated before application to encourage absorption of the composition into the wood. 20 In some embodiments, the timber or wood product is subject to a vacuum pressure process in the presence of the preservative 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 25 substantially increasing the moisture content of the timber or wood product. 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%. 30 The timber or wood product may be timber that may be treated to provide preservative envelopes of Hazard Classes 1 and 2F such as timber used as building materials for housing trusses and frames. Treatment where full sapwood penetration and envelope penetration into 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 -6 fencing, trellises, gazebos, and outdoor furniture. In some embodiments the timber is sapwood. In other embodiments the timber is heartwood. Suitable timbers include softwoods and hardwoods. Softwoods such as Pinus radiata, Pinus elliotti, Southern yellow pine species and Pinus sylvestris, are typically used in house frames and 5 trusses. Wood products include engineered wood products such as wood composite materials made of wood fibres, wood particles, wood veneer, wood strands or mixtures thereof Example of engineered wood products are plywood, laminated veneer lumber, oriented strand board, particle board and medium density fibre board. 10 In some embodiments, the preservative composition further comprises a second active preservative compound. The second active preservative compound may be any preservative that is used to protect wood from biological organisms. For example, the second active preservative compound may be a fungicide, bactericide, insecticide or a termiticide. Suitable insecticides and termiticides include synthetic pyrethroids such 15 as permethrin, cypermethryn and deltamethrin; 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 20 naphthenate, organic tin compounds such as tributyl-tin naphthenate (TBTN); silver compounds, iodopropynyl-butylcarbamate (IPBC), 3-benzothien-2-yl-5,6,dihydro 1,4,2-oxathiazine-4-oxide (Bethoguard®), quaternary ammonium compounds, tertiary ammonium compounds and isothiazalones and boron compounds. The preservatives may also be a micronised or dispersed active such as copper carbonate, copper oxide, 25 or oxine copper. In some embodiments, the bifenthrin is present in the envelope of preservative composition in an amount of 0.0011% m/v to 1% m/v, especially 0.0011% m/v to 0.5% m/v, 0.0011% m/v to 0.2% m/v, 0.0011% m/v to 0.1% m/v or 0.0011% m/v to 30 0.05% m/v. The amount of bifenthrin included in the composition may be determined by the retention rate of bifenthrin required. In some embodiments, the second active preservative compound is present in the preservative composition in an amount that is known to be effective in preserving -7 wood. In other embodiments, the second active preservative compound is present in an amount lower than is known to the effective in preserving wood. The composition may also include other optional components such as corrosion 5 inhibitors, colouring agents such as dyes or pigments, water repellents, resins, surfactants, fire retardants, UV stabilisers, adjuvants and algicides. The preservative composition may be in any form known to be useful in treating timber or wood products. In some embodiments, the preservative composition is in the 10 form of an emulsion or microemulsion, a suspension, suspension concentrate or the like as known in the art. Suitable compositions in the form of emulsions or microemulsions are described in WO 2010/148450, the contents of which are incorporated by reference. 15 The methods of the present invention protect the timber or wood product from insect, bacterial or fungal attack. For example, the methods may preserve wood from attack or infection by fungi such as blue stain (also known as sapstain) or may prevent a previous attack from infecting further parts of the timber. 20 In some embodiments, the methods of the present invention protect the timber or wood product from attack by insects, especially by termites. In some embodiments, the preservative treatment protects the timber or wood product by repelling insects such as termites. The methods of the invention may protect the timber or wood products from attack by any type of termite, but in particular embodiments, the termite 25 is a termite from Coptotermes sp. such as Coptotermes acinaciformis, Coptotermes lacteus, Coptotermes brevis and Coptotermes formosanus,, Nasutitermes sp. such as Nasutitermes walker and Nasutitermes exitiosus, Mastotermes sp. such as Mastotermes darwiniensis, Schedorhinotermes sp. and Heterotermes sp.. In particular embodiments, protection from attack by Coptotermes acinaciformis is provided. 30 In some embodiments, the preservative composition may be applied to the timber or wood product as individual pieces of timber or wood. In other embodiments, the timber may be in the form of a strapped pack. A strapped pack refers to a pack of timber containing multiple sawn planks which are strapped together for transport.

-8 In some embodiments, the method of the invention is performed at a saw mill, as a separate treatment or as an in-line process immediately after the timber is sawn. 5 Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. 10 The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general 15 knowledge in the field of endeavour to which this specification relates. In order that the nature of the invention be more clearly understood and put it into practical effect, specific embodiments will now be described by way of the following non-limiting examples. 20 EXAMPLES Termite Exposure of Bifenthrin treats softwood samples Eight test sets of treated softwood framing test specimens (7 replicates per set) were provided, together with one set of 7 replicates treated with an approved bifenthrin 25 treatment that meets industry standards and one set of untreated softwood test specimens (14 replicates). All treatments were achieved by dipping the wood in a water-based emulsion, giving an envelope treatment depth of up to 5 mm. Each test specimen was Pinus elliotti and 30 was cut to 90 x 45 x 200 mm. One docked end of each test specimen was also treated, while the opposing docked end was not treated. The untreated end of each test specimen was abutted to a second treated (all surfaces) length of framing measuring 90 x 45 x 50 mm. The two components were held in place by two nails inserted into pre-drilled holes. The untreated test specimens were similarly assembled with one -9 docked end abutting an untreated 90 x 45 x 50 mm length of framing. The treatments are provided in Table 1. Table 1 Active Active 1 retention Application g/m 3 Untreated control Industry control Bifenthrin 10.27 Superficial Candidate 1 Bifenthrin 5.38 Superficial Candidate 2 Bifenthrin 2.86 Superficial Candidate 3 Bifenthrin 1.09 Superficial 5 Each test specimen was pretreated before the field trial in accordance with Hazard Class H2F requirements (Australasian Wood Preservation Committee (AWPC) 2007. Protocols for Assessment of Wood Preservatives, revised edition, www.tpaacom.au). All test specimens were initially exposed outside and above ground for a period of 10 four weeks to take account of any potential UV effects on the efficacy of the termiticide active compounds. This preparative work was carried out in South East Queensland, Australia. The specimens were then artificially weathered in vacuum ovens for five days at 40'C and 0.04 mBar. This volatilisation schedule is used to remove residual solvent and volatiles that may be deleterious to termite health and 15 vigour, as well as providing artificial aging. At each stage care was taken to ensure each set of specimens was kept separate. Before field exposure, each test specimen was labelled with a stainless steel tag attached using brass boat nails. 20 The above weathering and aging procedures ensured that the test specimens were subjected to the most extreme termite pressure timber would encounter during its lifetime of service. 25 The test termite species used was Coptotermes acinaciformis (Froggatt). This species -10 is widely distributed throughout mainland Australia and is responsible for more economic loss than all other Australian species of termites combined. Test Method 5 The test method used for the field trial, a modified "drum technique", satisfies the minimum requirements for evaluating preservative-treated timber intended for Hazard Class H2F service conditions (inside, aboveground). The seven test specimens of each treatment were exposed in the field trial one in each 10 of seven sets of two stainless steel exposure containers (14 containers in total). Each of the 14 containers contained an untreated specimen. Bait wood, (Eucalyptus. nitens, Deane and Maiden (Shining Gum) was used in the trial at a ratio of 1:1 (volume of bait wood . volume of test specimens). The eucalyptus 15 bait wood was used as an attractive food source for maintaining the presence of termites. The bait wood was cut from kiln dried boards with a mean air dry density of about 700 kg/m 3 . The exposure containers were attached to trees about 1 meter above ground level, 20 connected to active galleries of C. acinaciformis. Each pair of containers was linked to termites from a different colony of C. acinaciformis by ensuring that the distance between pairs of containers exceeded the likely foraging range expected of the termites. For protection against excessive heat and grass fires, the exposure containers were externally insulated with aluminium building sisalation. 25 The field trial duration was the time taken for the termites to consume all susceptible material and vacate the exposure containers (about 7 to 10 months). Assessment 30 In order for H2F treatments to gain approval, the AWPC protocols for assessment of wood preservatives (2007), states that "test specimens must be rated as either sound or with superficial attack/grazing only, i.e., attack by termites must not breach the depth of the treated - 11 envelope." Analysis of test specimens was made by visual assessment of whether the envelope treatment had been breached by termites. If the envelope remained intact, the 5 specimen was rated "pass". If the envelope was breached, the specimen was rated "fail". Each specimen was weighed before and after the trial and mass loss was recorded. 10 The results are shown in Table 2. Treatment Rating Mass loss (g) Mean Mass loss % Pass/fail (standard (standard error) error) Untreated N/A 449.6 (65.6) 73.2 (10.5) Industry Reference (bifenthrin) 7/0 9.8 (1.8) 1.6 (0.3) 1 (bifenthrin) 7/0 14.1 (2.2) 2.3 (0.4) 2 (bifenthrin) 7/0 7.7 (0.8) 1.3 (0.1) 3 (bifenthrin) 7/0 11.8 (1.6) 1.9 (0.2) Nine of the 14 untreated control specimens were destroyed, whilst four others had mass losses of between 40% and 60%. This together with the fact that all untreated bait wood was destroyed, indicates that the test specimens were exposed to a high, 15 sustained termite hazard over the duration of the trial. Experimental treatments 1, 2 and 3 were all successful in resisting attack by termites, no test specimens suffered breach of the treated envelope. 20 Although a number of the test specimens had surface checks and cracks which were at least 2 mm in depth, termites failed to gain access to the untreated interior regions of the test specimens. This was also the case where there were gaps between the untreated docked end of the treated specimens and the treated surface of the abutted second length of framing. This suggests the treatments trialled had a high degree of 25 repellency against termites and therefore would provide robust systems for protecting framing timbers from attack by termites.

Claims (18)

1. A method of preserving timber or wood products comprising: 5 providing timber or wood products; and applying a preservative composition comprising bifenthrin to the timber or wood product, such that the retention of the bifenthrin in the timber or wood product is in the range of 0.5 g/m 3 to less than 4 g/m 3 . 10

2. The method according to claim 1 wherein retention of bifenthrin is in the range of 0.5 to 3.5 g/m 3 .

3. The method according to claim 1 or claim 2 wherein retention of bifenthrin is 15 in the range of 1.0 to 3.4 g/m 3 .

4. The method according to any one of claims 1 to 3 wherein the application provides a superficial treatment. 20

5. The method according to claim 4 wherein the superficial treatment is an envelope treatment.

6. The method according to claim 5 wherein the envelope has a depth of 1 to 5 mm. 25

7. The method according to claim 6 wherein the envelope has a depth of 3 mm to 5 mm.

8. The method according to any one of claims 1 to 7 wherein the composition is 30 applied by spraying, dipping, deluge, brushing, soaking, rolling, misting or under vacuum pressure.

9. The method according to any one of claims 1 to 8 wherein the timber or wood product requires treatment to meet requirements of Hazard Class 1 or Hazard Class - 13 2F.

10. The method according to claim 9 wherein the timber or wood product is a building material used in housing. 5

11. The method according to claim 10 wherein the building material used in housing is timber framing, trussing or particle board.

12. The method according to any one of claims 1 to 11 wherein the preservative 10 composition further comprises an additive selected from dyes or pigments, water repellents, fire retardants, UV stabilizers, surfactants, adjuvants, resins and algicides.

13. The method according to any one of claims 1 to 12 wherein the preservative composition is in the form of an emulsion, microemulsion, suspension or suspension 15 concentrate.

14. The method according to any one of claims 1 to 13 wherein the method protects the timber or wood product from insect, bacterial or fungal attack. 20

15. The method according to claim 14 wherein the insect is a termite.

16. The method according to claim 15 wherein the termite is from the species Coptotermes acinaciformis. 25

17. The method according to any one of claims 1 to 16 wherein the method is performed at a saw mill.

18. A method of protecting timber and wood products from termite attack comprising 30 providing timber or wood products; and applying a preservative composition comprising bifenthrin to the timber or wood product, such that the retention of the bifenthrin in the timber or wood product is in the range of 0.5 g/m 3 to less than 4 g/m 3 .