AU2006220419B2 - Wood preservatives - Google Patents

Description

WOOD PRESERVATIVES FIELD OF THE INVENTION The present Invention relates to preservatives for wood and wood based glue products. BACKGROUND As a biological material, wood Is subject to attack by fungi and Insects. These organisms may damage the appearance of the wood, and they may seriously reduce its structural strength. Wood and wood based products can be protected from wood destroying organisms by applying fungicides or insecticides, or both, Such treatments can greatly Improve the service life of the wood product, especially for timbers with low natural durability, such as radiata pine. For some wood based products, conventional methods of applying preservative treatment are Inappropriate. For example, water based treatments such as copper chrome arsenate ("CCA") and sodium octaborate cannot be applied to laminated veneer products, particle based products or fibre based products without casing significant product degrade, particularly loss of bond strength. Other post manufacture treatments for these products, such as light organic solvent preservative ("LOSP") are expensive-and require a further processing step to achieve the treatment, creating extra cost, A method favoured by some wood-based product manufacturers Is -the application of a preservative by addition to the glue during manufacture. This approach can be used for any wood product that Is constructed from relatively thin or small particles, such as wood fibre, wood chip, flake or thin wood veneer. Plywood, laminated veneer lumber ("LVL"), medium density fibreboard ("MDF"), strandboard OSB and particle board fall Into this category. The usefulness of this technique may be extended to veneers thicker than 3mm by adding further 2 protection to the outer veneers of glueline treated products In the form of a preservative surface spray. The major drawback Is that In some cases where thick veneers (>3 mm) are used, the majority of the preservative Is retained in the glue-line and only a minor portion Is transported across the giue wood barrier. Where the distances are small as In fibre or chip products the problem is not significant. In veneer products there Is a problem as the veneer thickness exceeds about 2.5mm. The problem is particularly acute on the surface of the outer veneer which has only a single diffusion path to treat the exterior of the wood. An external surface spray treatment post pressing Is a desirable if not essental part of the preservation process. The risk of dermal exposure and skin irritation Is twofold, firstly during application and secondly from surface residue. In agricultural practise use has been made of encapsulation to assist In mitigating the effects to humans of certain compounds, Synthetic pyrethroids are well known for their skin irritation. The reaction, a numbing, stinging or burning sensation, which is most pronounced on regions of the handlers face, Is known as paraesthesia. Lambda-cyhalothrin cypermethrin, deltamethrln, and bifenthrin all have a degree of paraesthesia which make them difficult to use in wood treatment processes especially where It is necessary to apply formulations as a spray or deluge onto external wood surfaces. In the case of lambda cyhalothrin in particular high acute oral toxicity is accompanied by a high degree of paraesthesla. Encapsulation techniques that have been used in the agricultural chemicals Industry to reduce the hazard or human exposure have release rates that give them comparable activity to an EC, These products, however, are still hazardous and require a degree of personal protection during application. 3 In treating wood products, however, the period of significant human exposure extends beyond the period of application. In the processing, and end use, of wood based products It may not be practicable to offer protection from skin irritating preservatives using conventional formulations. Furthermore the processing requirements during and after application of a preservative are severe with multiple chances of worker exposure from manufacturing aspects like drying, planing, gluing, pressing, sanding etc. Therefore the fragile nature of the encapsulation techniques used in agricultural chemicals offer no advantages over conventional formulation types of suspension concentrate, emulsiflable concentrates or micro emulsions, It is an object of the present invention to overcome or at least mitigate the above noted problems, or to at least provide the public with a useful choice. SUMMARY OF THE INVENTION Broadly according to one aspect of the present Invention there Is provided a preservative for use in a wood based glued product including an Insecticidal or fungicidal preservative In an effective amount encapsulated within a capsule sized between 0.3 and 20 microns. According to a second broad aspect there Is provided a method of applying an Insecticidal or fungicidal preservative to a wood based product, Including the steps of encapsulating the preservative within a capsule sized between 0.3 and 20 microns, and then applying the encapsulated preservative by mixing with a glue or glue system or by applying to wood surfaces by spraying, dipping or soaking, or by Impregnating the wood based product by a pressure treatment, The present invention Is based on the surprising and unexpected discovery that actives that have a human contact toxicity can be encapsulated In a specific manner that mitigates their toxicity or sensitivity, allowing mixing with glue systems while showing no diminution of their biological activity. 4 A surprising advantage of the present Invention Is the ability to achieve by encapsulation a similar activity of the preservative coinpared to the emulsifiable concentrate, micro emulsion and suspension concentrate, while offering an unprecedented reduction in toxicity to the handlers of the preservative actIves. A further advantage of the Invention Is that It enables the preservative pesticide activity of the active Ingredients to remain essentially the same as comparable non encapsulated formulations. A still further advantage of the present Invention is that it provides an Insecticidal or fungicidal preservative for wood based glued products where the preservative is less likely, In user to give rise to toxicity or sensitivity in handlers of the preservatives. The method of the present Invention results In the application of a preservative to wood based glue products wherein the possibility of toxicity or sensitivity in handlers of the preservative Is reduced. Preferably the encapsulation (capsule) Is of a slow release character. The encapsulated preservative may be applied by either spreading, spraying, dipping, soaking or pressure treatment of the wood and wood surfaces. In one preferred embodiment the encapsulated preservative may be applied by mixing it into the glue or glue system prior to application. DESCRIPTION OF THE INVENTION By way of the present Invention It is possible to offer an encapsulated preservative product which has a significantly reduced mammalian toxicity, as measured by the pollen tube growth test, when compared to the "quick release" capsules currently In use for the encapsulation of to4c or Irritating pesticides. 6 Kepler and Kristen (Environmental and Experimental Botany, Vol 27, No 3, pp. 306-309, 1987) describe a procedure for assessing the cytotoxicity of environmental contaminants using pollen tube cell growth as an indicator. Sigmoid dose response curves are obtained from which EDw values can be calculated. This value defines the concentration of a toxic substance which causes a decrease in cell wall production to 50% the total amount. Kristen and Jung at, al. (1999 Toxicology in Vitro Vol 13 pp 335 - 342) compare the pollen tube growth test (PTG) against the rabbit eye Irritancy test managed by the European Cosmetic, Toiletry and Perfumery Association (COLIPA). A predictive model was found which could predict In most cases the maximum average score based on historic Dralze rabbit eye Irritation data. Barlie, Dierickx and Kristen (1994, Cell Biology and toxicity Vol 10, pp 155-162) looked at cytotoxic concentrations of chemicals using the PTG test and established animal LD0 values against human toxic concentrations for the same chemicals. The PTG test was found to be a sensitive In vivo predictive screening procedure for human toxicity. Human toxicity was predicted at least as accurately as animal testing procedures The PTG test is again reviewed In Alternative Methods In Toxicology Vol 10, (Editors Rogler, Goldberg and Malbach). Good agreement was found not only with eye Dralze scores but also with the human skin patch test. Example I - Relative toxicity of encapsulated products. Toxicity was assessed by pollen tube growth according to the methods of Kappler and Kristen. An emulsifiable concentrate and a suspension concentrate of bifenthrin were used as benchmark examples for the respective bifenthrin active Ingredients. 6 Samples of bifenthrin were prepared using standard formulation techniques of emulsifiable concentrate (EC), suspension concentrate (SC) and two encapsulated samples, one a quick release form typical of agricultural practises and one of a slower release. Slow release was achieved by a larger capsule size, 10p as against Karate 2.5p, and by using exclusively a prepolymer, polymethylene polyphenyllsocyanate (pMDI), with an Isocyanate functionality of 2.7 to increase the crosslinking in the polyurea wall. Table 1 Active Ingredient Formulation Reference Pollen Tube ECro Bifenthrin EC 11.8 ppm Bifenthrin SC, 10p, 6% pMDI TNL 2021 606 ppm Bifenthrin SC, 5p - 109 Permatek1998 212 ppm Bifentrhin SC 5p TNL 1998 212 ppm. Bifenthrin SC, 2.5p, quick release 96 ppm Table I shows that encapsulation significantly reduces the cytotoxicity of the pyrethrold in this formulation and the larger capsule with slower release capability gave the least toxic result. Example 2 - Termticidal activity. Termiticidal testing was carried out according. to a "Lunchbox Test", fully described by Peters (Xylophagous Insects: Developments In Feeding Assays, Phd Thesis, University of Queensland, 2004). The test Involves encouraging the foraging instincts of the termites by breaking Into the termite mound and laying feeder strips Into alternating treated and untreated test specimens contained In a lunchbox. Feeding pressure Is assessed by the destruction of adjacent untreated test pieces and normally takes 15 weeks. 7 The effectiveness of the treatment Is assessed by a visual Inspection and a weight loss of less than 6%. This field test is considered a severe challenge to treated samples and has been Incorporated Into the Australian H2 Standard. Example formulations of bifenthrin, as an emulsifiable concentrate, a suspension concentrate, and as a slow release capsule suspension, were tested as a termite protectant. The standard application for bifenthrin in the gluellne is 25 g/m 3 . All the test formulations were applied at this rate In the glueline and the 3.2 mm veneers assembled into a 6 ply board. As well as the total mass loss post exposure an estimate of the mass loss from the outer veneer was also estimated visually. Table 2 Treatment Formulation Insect mass loss mass loss total face veneer untreated COPTSP 10% 16% gluellne 25 g/ma TNL 2021 CS COPTSP 2% 7% gluellne 25 g/m Bifenthrin EC COPTSP 2% 6% gluellne 25 g/m3 Bifenthrin EC COPTSP 2% 6% glueline 25 g/m3 Bifenthrin SC COPTSP 1% 6% Table 2 shows that encapsulation in a slow release capsule does not significantly reduce the efficacy In protecting the treated wood against termite attack when compared with conventional formulation types of SC and EC. What the results confirm are: 1. A surface spray is required to give complete termite protection and this can be achieved equally well with a low toxicity encapsulated formulation, - - 8 2. A slow release encapsulated formulation of bifenthrin of low cytotoxicity is equally effective as a termite protectant as the same active formulated In the more conventIonal emulslflable concentrate or suspension concentrate. While the present Invention has been Illustrated by the description of examples thereof, and while specific formulations and methods have been described in detailed example, It Is not the intention of the Applicant to restrict or In any way limit the scope of the Invention to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention In its broader aspects is not limited to the specific formulations and methods as exemplified. Accordingly, departures may be made from such examples without departure from the spirit or scope of the general Inventive concept as claimed. 9

Claims (11)

1. A method of applying an insecticidal or ftugicidal preservative to a wood based glue product comprising encapsulating the preservative in a capsule having a mean particle size of between 0.1 and 20 microns and then applying the encapsulated preservative by mixing in a glue or glue system prior to application to the wood based glue product.

2. The method as clahined In clahn I wherein the insecticidal and/or fungleidal preservative is encapsulated in a capsule of a slow release character,

3. A method as claimed in claim 1 or claim 2 wherein the preservative Is bifenthrin.

4. An encapsulated preservative when used in a glue or glue system prior to application of a wood based glue product, the preservative comprising a plurality of capsules having an effective amount of an Insecticide or fungicide, and whereby the preservative Is further characterised in that each capsule has a mean particle size of between 0.3 and 20 microns

5. The preservative as claimed in claim 4 wherein the encapsulation is by a capsule of a slow release character.

6.. The preservative as claimed in claim 5 wherein the mean particle size is substantially 10 microns.

7. The preservative as claimed in any one of claims 4 to 6 wherein each capsule is created by using a prepolymer to Increase cross-linking in a polyurea wall thereof.

8 The preservative as claimed in claim 7 whereIn the prepolymer Is polymethylene poiyphenylisocyanate having an isocyanate functionality of substantIally 2.7,

9. The preservative as claimed in any one of claims 4 to 8 wherein the preservative is bifenthrin.

10 10 The preservative as claimed In claim 4 substantially as herein described and with reference to the Examples.

11. A method as claimed in claim 1 substantially as herein described with reference to the Examples. PIPERS, Patent Attorneys for Zelam Limited I 1