AU2006220419A1 - Wood preservatives - Google Patents

Description

TITLE OF THE INVENTION WOOD PRESERVATIVES BACKGROUND TO THE INVENTION The present invention relates to preservatives for wood and wood based glue products.

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 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 medium density fibreboard 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 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 mm) are used, the majority of the preservative is retained in the glue-line and only a minor portion is transported across the glue 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 essential 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 handler's face, is known as paraesthesia.

Lambda-cyhalothrin cypermethrin, deltamethrin, 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 high acute oral toxicity is accompanied by a high degree of paraesthesia.

In developing the Zeon encapsulation technology for lambda cyhalothrin Zenica and latterly Syngenta have promoted the advantages of an encapsulated product as being as efficacious as an emulsifiable concentrate, as reducing worker exposure, and as protecting the active ingredient from UV degradation. The capsules are described as quick release.

In using this technology it is recognised that majority of the active ingredient must release quickly to achieve the same initial knockdown as an emulsifiable concentrate at a similar application rate. Further if the active ingredient is too slowly released the initial concentration of pesticide will not reach the toxic threshold, will breakdown in the environment, and the development of early resistance will be encouraged. Electron microscope photographs demonstrate the collapse of the capsules as the aqueous dilution phase evaporates.

It has been found that the cyhalothrin capsules are characterised by a capsule size of about 3p and a fragile polyurea shell. The active ingredient is rapidly released on drying either by rapid diffusion in a nonaqueous environment or by physically bursting on drying. A significant reduction in toxicity is claimed: oral LD 5 o rat is changed from 64 mg/kg for the EC to 245 mg/kg for the capsule. Skin irritation went from extreme for the EC to mild for the capsule.

The manufacture of these "quick release capsules" is described in US patent 6133197.

The rate of release is controlled by three major mechanisms, a particle size of 1 to 5p, an isocyanate organic phase concentration of 5 to 10% by weight, and by substituting a major portion of the polyphenylisocyanate with a diisocyanate. The polyphenylisocyanates typically have a functionality of about 2.7 while the diisocyanates have a functionality of two. This results in a lower degree of crosslinking and a more permeable wall. The capsules thus prepared are demonstrated to have bioactivity equal to an EC.

Thus 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.

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 agricultual chemicals offer no advantages over conventional formulation types of suspension concentrate, emulsifiable concentrates or micro emulsions.

Notable wood preservative products which fall into this category are the synthetic pyrethroids. In current practice deltamethrin has been used as a termiticide for application in engineered wood products in typically an emulsifiable concentrate or suspension concentrate. Handling of this pyrethroid in a wood processing environment can provoke an adverse skin reaction. This skin reaction or paraesthesia is common to a number of pyrethroid actives and severely limits their long term use in the wood industry.

Examples of fungal preservatives which have a similar history of not necessarily paraesthesia but of skin irritancy are 2-(thiocyanomethylthio)benzothiazole (TCMTB) and 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (Kathon 925). It is envisaged that the application of encapsulation technology can also be applied to most wood preservatives but with particular advantage to those preservatives that are otherwise limited in their end use because of their skin irritancy.

SUMMARY OF THE INVENTION Therefore the present invention is based on the surprising discovery that actives that have a human contact toxicity can be encapsulated in a manner that mitigates this toxicity or sensitivity, allowing mixing with glue systems while showing no diminution of their biological activity.

The ability to achieve by encapsulation a similar activity of the preservative compared to the emulsifiable concentrate, micro emulsion and suspension concentrate, while offering an unprecedented reduction in toxicity to the handlers of the preservative actives is the surprising and novel discovery of this invention.

The present invention also enables the preservative pesticide activity of the active ingredients to remain essentially the same as comparable non encapsulated formulations.

Thus it is an object of the present invention to provide an insecticidal or fungicidal preservative for wood based glue products where the preservative is less likely, in use, to give rise to toxicity or sensitivity in handlers of the preservatives.

It is a further object to provide a method of applying a preservative to wood based glue products wherein the possibility of toxicity or sensitivity in handlers of the preservative is reduced.

Broadly according to one aspect of the present invention there is provided a preservative for wood based glue products including an encapsulated insecticidal or fungicidal preservative in an effective amount.

According to a second broad aspect there is provided a method of applying an insecticidal or fungicidal preservative to wood based glue products including encapsulating the preservative and applying the encapsulated preservative by mixing with the glue or glue system or by applying to wood surfaces by spraying, dipping or soaking, or by impregnating the wood structure by a pressure treatment.

Preferably the encapsulation (capsule) is of a slow release character.

Preferably the capsule size is between 0.3 and 20 microns.

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 in 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 toxic or irritating pesticides.

Kapler and Kristen (Environmental and Experimental Botany, Vol 27, No 3, pp. 305-309, 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 EDso 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 et. 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 Draize rabbit eye irritation data.

Barile, Dierickx and Kristen (1994, Cell Biology and toxicity Vol 10, pp 1 55-162) looked at cytotoxic concentrations of chemicals using the PTG test and established animal LD 5 o 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 Rogier, Goldberg and Maibach). Good agreement was found not only with eye Draize scores but also with the human skin patch test.

Example 1 Relative toxicity of encapsulated products.

Toxicity was assessed by pollen tube growth according to the methods of Kappler and Kristen (Environmental and Experimental Botany, Vol. 27, No. 3, pp. 305 309, 1987).

Emulsifiable concentrate of an emulsifiable concentrate and suspension concentrate of bifenthrin were used as benchmark examples for the respective bifenthrin active ingredients.

Samples of bifenthrin were prepared using standard formulation techniques of emulsifiable concentrate 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, 1lOp as against Karate and by using exclusively a prepolymer, polymethylene polyphenylisocyanate (pMDI), with an isocyanate functionality of 2.7 to increase the crosslinking in the polyurea wall.

The results are detailed in Table 1.

Active Ingredient Formulation Reference Pollen Tube ECso Bifenthrin Emulsifiable concentrate 11.8 ppm Bifenthrin CS, 10p, 5% pMDI TNL 2021 606 ppm Bifenthrin SC, 5p 10p Permatekl998 212 ppm Bifentrhin SC 5p TNL 1998 212 ppm.

Bifenthrin CS, 2.5p, quick release 96 ppm Table 1. shows that encapsulation significantly reduces the cytotoxicity of the pyrethroid in this formulation and the larger capsule with slower release capability gave the least toxic result..

Example 2 Termiticidal 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 foraging instincts of the termites are encouraged 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 1 5 weeks.

The effectiveness of the treatment is assessed by a visual inspection and a weight loss of less than 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 glueline 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 5 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 total mass loss face veneer untreated COPTSP 10% 16% glueline 25 g/m 3 TNL 2021 CS COPTSP 2% 7% glueline 25 g/m 3 Bifenthrin EC COPTSP 2% 6% glueline 25 g/m 3 Bifen. EC COPTSP 2% 6% Glueline 25 g/m 3 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.

11 What the results show 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.

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 emulsifiable concentrate or suspension concentrate.

Claims (13)

1. According to a second broad aspect there is provided a method of applying an insecticidal or fungicidal preservative to wood based glue products including encapsulating the preservative and applying the encapsulated preservative by mixing with the glue or glue system or by applying to wood surfaces by spraying, dipping or soaking, or by impregnating the wood structure by a pressure treatment.

2. The method as claimed in claim 1 wherein the insecticidal and/or fungicidal preservative is encapsulated in a capsule of a slow release character.

3. The method as claimed in claim 1 or 2 wherein the capsule size is between 0.3 and 20 microns.

4. The method as claimed in claim 1, 2 or 3 wherein the encapsulated preservative is applied by mixing in a glue or glue system prior to application.

5. A method as claimed in claim 1 substantially as herein described with reference to the Examples.

6. A preservative for wood based glue products including an encapsulated insecticidal or fungicidal preservative in an effective amount.

7. The preservative as claimed in claim 6 wherein the encapsulation is by a capsule of a slow release character.

8. The preservative as claimed in claim 7 wherein the capsule size is between 0.3 and 20 microns.

9. The preservative as claimed in claim 8 wherein the capsule size is substantially 10 micron.

The preservative as claimed in claim 7 or 8 wherein the capsule is created by using a prepolymer to increase cross-linking in the polyurea wall thereof.

11. The preservative as claimed in claim 10 wherein the prepolymer is polymethylene polyphenylisocyanata with an isocyanate functionality of substantially 2.7.

12. The preservative as claimed in any one of claims 6 to 11 wherein the preservative is bifenthrin.

13. The preservative as claimed in claim 6 substantially as herein described. Dated this 21st day of September 2006 Patent Attorneys for the Applicant/Nominated Person GEORGE WILLIAM MASON; JOHN BRODIE MATTHEWS, JOHN SUTHERLAND AULD, PETER JAMES HAYWARD and CHRISTINE ANNE HAYWARD T/A TAPUAE PARTNERSHIP DON HOPKINS ASSOCIATES