AU2003268849A1 - Improvements In Boron Wood Preservatives - Google Patents

Description

TITLE OF INVENTION "Improvements In Boron Wood Preservatives" BACKGROUND OF THE INVENTION This invention relates to improvements in wood preservatives.

Wood as a versatile low cost material and a renewable resource has many advantages in the building trade as a light relatively high strength structural material.

However, wood and especially wood from Pinus spp has limited durability. Consequently, for it to last for many years in service it must be protected against fungi, woodworm, termites and various boring insects by treatment with wood preservatives.

Traditional treating preservatives are mixed aqueous salts of copper, chromium and arsenic, soluble boron salts, combinations of alkylammonium compounds and copper, oil soluble copper naphthenates, pentachlorophenol, tributyl tin compounds and the like.

In recent years the trend has been towards more benign preservatives with lower mammalian toxicity and lower environmental impact.

Traditional treatment procedures involve deep penetration vacuum/pressure treatments of solid wood products. For products which are assembled in final form a low pressure organic solvent process is sometimes appropriate.

Engineered wood products are often preserved by adding biocides during the process either by dipping the veneer, adding to the glueline or in the case of chip and fibre board, injecting into the furnish prior to pressing.

Alkylammonium compounds which include the class of quaternary ammonium compounds and fatty amine salts have been known to be preservatives of excellent cost effectiveness in laboratory tests but have proved less successful in service due to a poor spectrum of activity.

Aqueous boric salts, however, have a 40 to 50 year history as cost effective preservatives. However, the problem of leaching limits their use to wood in a protected interior environment e.g. framing and flooring and mainly against insect attack. Boron can still be used for exterior weatherboard or window framing where the wood is additionally protected by paint.

The use of simple boron esters have been described (Nashiri, (US 5,871,817)for use as preservatives in recoverable volatile solvents. However the disadvantage of rapid hydrolysis and subsequent ready leaching of the boric acid has not been overcome.

The use of highly concentrated solutions of boric acid either as the lower alkyl amine or alkylene polyamine salts as wood preservatives has been disclosed in New Zealand patent specification 219963. Water soluble boron salts thus prepared still suffer from the disadvantage that they are readily leached from wood and are not readily combined with other organic water insoluble fungicides. NZ 219963 describes how this disadvantage may be overcome by the addition to the amine boron salts and of certain quaternary ammonium compounds.

In US patent specification 5891921 there is disclosed the preparation of quaternary carboxylate salts and subsequent preparation of carboxylic acid and borate salts and their activity as novel wood preservatives.

The quaternary conjugates of boric acid or carboxylic acids are prepared via two intermediates. Firstly the quaternary chloride is reacted with an alkali metal hydroxide in ethanol. After filtration the quaternary ammonium hydroxide remains and is reacted with excess carbon dioxide. The resulting carboxylate is displaced by the required acid.

An object of the present invention is to provide an improved wood preservative which is simple to prepare, exhibits favourable activity against wood destroying fungi and which is less readily leached, and can be combined with copper or with other organic water insoluble fungicides if desired.

Simple boron esters as already disclosed are readily hydrolysed in seconds unless the electrophillic character of the boron atom can be further sterically protected and electronically stabilised by a dative bond with another suitable electron donating atom such as nitrogen which is able to share an additional electron pair. Such trihydric structures are described in Kirk Othmer.

Triisopropanolamine borate for instance has a half life for hydrolysis of 171 days.

A composition for preserving timber is claimed by Maynard in US 5221758. A method is described of forming a stable boric acid complex ion with alkylaryl diols. The complex ion is further reacted with metal cationic species such as copper or zinc or fatty amine derived cationics such as alkyl dimethyl amines or alkyldimethyl benzyl ammonium chlorides. Such complexes were claimed to have high activity against a range of wood decaying fungi and lower water solubility such that the boron was less readily leached from the preserved timber.

As an extension of this idea Horner and Woodgate have described the preparation of pseudo boratranes from N,Nbis(hydroxybenzylmethyl) amines. Boron is co-ordinated and stabilised by a combination by the bis-hydroxy and tertiary amine moieties in the complex. Host-guest chelation is possible with transition metals for some in this class of complexes. Utility as novel wood preservatives is claimed.

US patent 5,426,121 describes the formation of copper cationic complexes with alkoxylated fatty diamines. The Inventor was able to show that the fatty diamine copper complex with Ethoduomeen C/13 had improved performance over copper against the copper tolerant decay fungus Poria placenta.

In the present invention, advantage of the stabilising effect of the tertiary amine and hydroxy function is utilised by reacting boric acid with certain alkoxylated fatty amines. The property of further complexation with copper after reaction with boron is also described.

According to a first broad aspect of the invention there is provided compositions for the preservation of wood which comprise a mixture formed by the reaction of an alkoxylated diamine compound and boric acid.

Preferably the diamine compound is N, N, N'-tris(2hydroxypropyl)-N-C8-C 8 alkyl -1,3-diaminopropane.

According to a second broad aspect of the invention there is provided a wood preservative characterised in that it includes alkoxylated fatty organic amines or polyamines which not only have been neutralised with boric acid but have been further reacted to form an internal cyclic ester or a bis-diol borate ester.

In a preferred form of the invention the wood preservative may be in its final form or as a mixture of its components in a solution in kerosene, glycol ether or water.

In a preferred form of the invention the wood preservative is combined with a water insoluble fungicide.

According to a third broad aspect of the invention there is provided a formulation for the preservation of wood comprising a composition according to the first broad aspect set forth above and a solvent, the solvent being a liquid petroleum distillate suitable for the non-aqueous impregnation of wood in its final form.

According to yet a further broad aspect of the invention there is provided a formulation concentrate dilutable in water comprising a composition according to the first broad aspect set forth above and a solvent wherein the solvent is mainly a polar glycol ether, and an azole fungicide, propiconazole, suitable for the preservation of wood via an aqueous solution.

In a further broad aspect of the invention there is provided a formulation concentrate dilutable in water comprising a composition according to the first broad aspect set forth above and a solvent in which the solvent is mainly water, and a copper fungicide, copper ammonium carbonate, and suitable for the preservation of wood via an aqueous solution.

In a further preferred form of the invention the ability of the preservative to act as a hydrotrope and complexing agent is utilised to form combinations with copper or copper and a water insoluble fungicide.

In still a further broad aspect of the invention there is provided a method of preserving wood that is characterised in that the wood is treated with a wood preservative in it's final form or as a mixture of its components as described in the first broad aspect of the invention.

Further reaction during treatment or drying may be utilized to complete the fixing process of the components of the preservative.

For instance, N, N, N'-tris(2-hydroxypropyl)-Ntallowalkyl-1,3-diaminopropane borate salt present in the wood as the initial treatment may further react on heating and drying to form the diester and/or the pseudoboratrane.

The present invention thus concerns wood preservatives based on the boric acid esters of alkoxylated fatty amines. It is believed that according to the present invention boron will be less readily leached when in this ester form. It is also believed that the boron esters will exhibit more favourable activity against wood destroying fungi than is the case with an equivalent amount of boric acid.

Simple preparations of novel leach resistant ester preservatives incorporating boron as glycol ether soluble or water dispersible esters of certain alkoxylated alkyl amines are described. The alkoxylated alkyl amines esters thus formed are of limited water solubility but form surprisingly stable dispersions with water. A further benefit of such esters is the simplicity of preparation from readily available starting materials, the ability to mix with copper and the ability to incorporate other water insoluble co-actives.

Furthermore simple preparations of novel leach resistant ester preservatives incorporating boron as a kerosene soluble ester of certain alkoxylated alkyl amines are described. The alkoxylated alkyl amine esters thus prepared are useful in treating finished timber products with a colourless anhydrous light organic solvent treatment.

According to one aspect of the invention boric acid is reacted with an alkoxylated alkyl amine in a solvent capable of extracting water by azeotropic reflux.

The resulting esters can be used as a carrier for water insoluble organic solvents and other water insoluble fungicides e.g. azole fungicides, and/or copper which may complement the activity of the boron salt. Such preparations may then be diluted to form stable emulsions or solutions which may be used to treat wood or wood composites. Or such preparations may be diluted in a low cost hydrocarbon solvent and used to treat wood in a fully assembled form without the disadvantage of dimensional change which would be incurred by an aqueous treatment.

In a further aspect of the invention, boric acid salts of certain alkoxylated alkyl amines may be used to treat wood in a suitable carrier solvent and be further reacted in situ by the application of heat and removal of water.

Examples of fatty amines suitable for this purpose are those of the general formulae:

(R

5 O)z (R 6 O H R--X N-Y N

(R

1 O x (R2--O)x,H (R3--O)y H wherein R is a straight or branched chain C3 to about C20 alkyl alkenyl, aryl, or alkylaryl, and X is either -CH 2 or -O-(CH 2 3 and Y is either -CH 2

CH

2 or -CH 2

-CH

2

-CH

2 n 0 to 5, preferably 0,1 or 2; R 1

R

2

R

3

R

4

R

5

R

6 are together or separately C 1 to C 4 alkylene and x,y,z are each integers which can be 1 to 6 and are each integers which can be 0 to 6.

Of particular usefulness are boron esters of alkoxylated tertiary amines of the general formula:

(R

3 O)z

H

R-X-N-(CH

2 )n-N (R -O) x H (R2--O)y H wherein R is a straight or branched chain C7 to about C17 alkyl, and X is either -CH 2 or -O-(CH 2 3 and n= 2 or 3; R 1

R

2

R

3 are together or separately C 1 to C 4 alkylene and x y, z, are each integers which can be 1 to 6.

Such amines may react with boric acid in one of several ways either to form a simple boric acid salt or with the removal of water and heating may be converted to a monoester diester or triester. The following reaction scheme is suggested for the triester: 13HO

CH

3 0 0

H,C

The novel boratrane preservatives have a pH from 6 to in aqueous solutions and have an enhanced facility to act as a fixed boron wood preservative treatment when compared to a completely water soluble boric acid salt.

There is also a residual amine function which may still be able to chelate the metal counter ions. By whatever mechanism, what we have discovered is that copper ions which would normally be precipitated as the hydroxide under aqueous alkaline conditions are stabilised by the presence of the composition of this invention.

The compositions of the present invention are dispersible in water and soluble in non polar solvents. Thus they may be used for impregnating wood or wood products in water or kerosene. They may be used as a carrier for otherwise water insoluble fungicides which can be prepared in a solvent or as an emulsion or preferably a micro-emulsion. In the former case the preservative may be applied directly in anhydrous form or in the latter case, dilution with water can be readily achieved with the aid of other co-emulifiers or coupling solvents.

Thus in either case the preservative can be conveniently applied to wood structures in their final form or solid wood or wood fibre by any one of the common processes used in wood and fibre preservation.

The present invention also embraces the impregnation of solutions of the composition when used in conjunction with copper or copper plus other water insoluble fungicides where they provide additional complexing power to the copper salts.

Therefore, there are provided new fungicidal compositions comprising of essentially of the pseudoboratrane product as defined, which may also comprise a mixture of the monoesters, diesters and triesters of boron and may be mixed with a number of other aqueous and non aqueous fungicides in either aqueous or non aqueous solvents to extend the fungal spectrum and/or mode of application and are thus unusually useful for the formulation or a range of wood preservation formulations.

Example 1 Boric acid 10.23g (0.165 gmole) is dissolved with warming in toluene 75g and DINORAM SL, more conventionally known as N, N, N'-tris(2-hydroxypropyl)-N-tallowalkyl-1,3diaminopropane, (0.15 moles) 72.9g The mixture was heated and stirred until the boric acid dissolved and the reaction mixture began to reflux. The aezotrope of water and toluene was separated via a Dean and Stark apparatus with the toluene being returned to the reaction vessel.

After 4 hours a total of 6 g of water was collected. The toluene was distilled off under a vacuum of 25 inches and 130°C. The viscous residue, hereafter called FABE (Fatty amine boron ester), weighed 81.3 g representing a crude yield of 98%.

14 Example 2 FABE 3.8g was mixed with 50% propiconazole 0.76g and made up to 9.5g with solvent dipropylene glycol monomethyl ether. The formulation formed a stable opalescent emulsion in water.

Example 3 FABE 2.85g was diluted with Shellsol D70 8.55 g, a light low odour kerosene, to form a clear bright solution of preservative.

Example 4 A propriety formulation of Copper ammonium carbonate, Cusol, containing 100 g/L copper ion was diluted to v/v and precipitated immediately on dilution copper ammonium carbonate. The addition of 1.5%v/v of the formulation in example 1 formed a clear dark blue solution suitable for impregnation.

Example A concentrate was prepared by mixing 5g of FABE in Example 1, 1.3 g of copper ethanolamine sulphate, 5g of diethylene glycol n butylether and 10g of water and mixing until all the components mixed to a homogeneous dark blue solution.

Example 6 The leaching protocol of the American Wood Preservers' Association, Eli 97 was used to determine the relative leachability of boric acid and the preparation of FABE.

Standard cubes of pinus radiata 19 0.2mm edge dimension were vacuum impregnated with boric acid and the FABE at two boric acid equivalent concentrations. After treatment and conditioning several blocks were impregnated with water and leached for 6 hours with distilled water. Two blocks were removed for analysis and the remainder leached in a fresh change of water for a further 24 hours. Two further blocks were removed for analysis and the remainder leached for a further two cycles of 48 hours. Analyses were carried out on the retained unleached blocks and each set of leached blocks.

Leaching results are in boric acid equivalents as a of the initial unleached assay.

Figure 1 Boron Leaching 0 6 012 Figure 2 Figures 1 and 2 show that significantly more boron is retained by FABE than boric acid alone. Thus it is established that the FABE is more leach resistant than boric acid alone Leaching....les....

Fig re ig i ic nt y mo e o on i retaied byFABEthan oricacid.lone.Thusit.i estabishe thatthe ABE s mor lea..resstan.tha boric...id....ne 17 Example 7 The fungicides of interest are serially diluted into agar and plated out. Minimum inhibitory concentrations of boric acid and boric acid equivalent as FABE were determined by examining, after a set period of time, the mycelial inhibition of five different fungal inocculum squares 5 x 5 mm placed evenly on the agar plates. A minimum of three replicate plates were used for each concentration of boric acid and boric acid as the amine reaction product. Control plates established confluent growth of the test fungi over the untreated agar over the test period which was usually about three days.

Table 3 M.I.C's LIB 955 Boric acid as FABE Concentration (in ppm) 1024 512 256 128 64 32 16 8 Brown Rot Species White Rot Species Tyromyces Fomitopsi Coniophora s palustris lilacino- puteana gilva Trametes versicolo r Pycnoporus coccineus 18 Control Y Y Blank N N Growth on No growth End Agar point Surface Y N Table 4 M.I.C.'s Boric acid Growth on No End agar Growth point surface Y N 19 Tables 3 and 4 show that the MIC' s of the composition FABE when compared at the same boric acid equivalent are consistently lower than boric acid alone. Thus it is established that FABE exhibits more favorable activity against a range of wood destroying fungi than is the case with an equivalent amount of boric acid.

Claims (8)

1. A wood preservative characterised in that it includes alkoxylated fatty organic amines or polyamines which not only have been neutralised with boric acid but have been further reacted to form an internal cyclic ester or a bisdiol borate ester.

2. A composition according to claim 1 in which the diamine compound is N, N, N'-tris(2-hydroxypropyl)- N,C 8 -C 1 8 alkyl -1,3-diaminopropane.

3. A formulation for the preservation of wood comprising a composition according to claim 1 or claim 2 and a solvent in which the solvent is a liquid petroleum distillate suitable for the non aqueous impregnation of wood in its final form.

4. A formulation concentrate dilutable in water comprising a composition according to claim 1 or 2 and a solvent in which the solvent is mainly a polar glycol ether, and an azole fungicide, propiconazole, and suitable for the preservation of wood via an aqueous solution A formulation concentrate dilutable in water comprising a composition according to claim 1 or claim 2 and a solvent in which the solvent is mainly water, and a copper fungicide, copper ammonium carbonate, and suitable for the preservation of wood via an aqueous solution.

6. A method of preserving wood that is characterised in that the wood is treated with a wood preservative in it's final form or as a mixture of its components as claimed in claim 3.

7. A method according to claim 1 including further reaction during treatment or drying to complete the fixing process of the components of the preservative.

8. Compositions for the preservation of wood as claimed in claim 1 substantially as herein described with reference to the Examples.

9. A method of preserving wood as claimed in claim 6 and substantially as herein described with reference to the Examples. 22 DATED this sixteenth day of December 2003 TARANAKI NUCHEM LIMITED PATENT ATTORNEYS FOR THE APPLICANT DON HOPKINS ASSOCIATES