GB2271579A - Treatment Of Wood - Google Patents

Abstract

A composition for the treatment of wood comprises a wax, and at least one water-leachable wood treatment substance e.g. flame retardant substances and/or biocidal wood preservative substances.

Description

TREATMENT OF WOOD THIS INVENTION relates to the treatment of wood. In particular it relates to a composition for the treatment of wood, to a method of preparing the composition, to a method of treating wood using the composition, to a method of treating wood to retard the leaching of water-leachable wood treatment substances from treated wood, and to wood when so treated.

According to one aspect of the invention there is provided a composition for the treatment of wood, the composition comprising a wax; and at least one water-leachable wood treatment substance.

By water-leachable is meant that the substance remains water-soluble after the wood has been treated with the substance.

Such substance will be prone to leaching from the treated wood if the treated wood is exposed to water, for example during weathering.

The wood treatment substance may be selected from the group consisting of water-leachable flame retardant substances, waterleachable biocidal wood preservative substances and mixtures thereof.

The composition may, for example, be an emulsion or a solution. The composition of the invention is not, however, limited to emulsions and solutions but may extend to suspensions, dispersions and the like.

For example, in the case of a treatment substance which is water soluble and which comprises one or more water soluble components, the substance may first be dissolved in water to form an aqueous solution and the solution may be admixed with the wax to form the emulsion. The wax will in this case naturally be of the type which, after heating to melt it, if necessary, forms an emulsion in water. The emulsion may be in the form of an oil-inwater emulsion, or a water-in-oil emulsion.

By a water-in-oil emulsion is meant an emulsion in which the aqueous solution is the discontinuous phase and is dispersed or encapsulated in the wax, which forms the continuous phase of the emulsion. By an oil-in-water emulsion is meant an emulsion in which the oil is the discontinuous phase and is dispersed in the aqueous solution which forms the continuous phase of the emulsion.

On the other hand, in the case of a treatment substance which is soluble in an organic solvent and which may comprise one or more components which are soluble in the organic solvent, a solution comprising the substance and a wax which is also soluble in the organic solvent may be prepared.

The waxes may be natural waxes, such as beeswax, but are generally synthetic waxes, such as unchlorinated paraffin waxes, chlorinated paraffin waxes, polyethylene waxes and the like.

When the composition is an emulsion, the wax is preferably a soft paraffin wax (also brown as a slack wax). It may instead be a blend of a soft paraffin-wax, and at least one hard, (i.e.

high melting point), oxidised wax.

Thus, the composition may be an emulsion, the wax being selected from the group consisting of soft paraffin waxes, blends or at least one soft paraffin wax with at least one hard oxidised wax, and mixtures of any two or more thereof, the wood treatment substance being dissolved in water with which the wax is emulsified.

A soft paraffin-wax or slack wax is an oily wax i.e. a wax having a relatively low congealing point, typically about 15 50"C. An example of such a wax as that marketed by SASOL Chemical Industries (Proprietary) Limited under the name WAKSOL A, which has a congealing point of about 30"C, typically about 29 - 33C.. The hard or high-melting point oxidized wax has a higher congealing point typically between about 70"C and 90"C.

An example of such a wax is that marketed by SASOL Chemical Industries (Proprietary) Limited under the name Sasolwaks A6, which has a congealing point of about 78 C, typically about 75" 80"C.

When the composition is a solution, the wax may be a soft paraffin wax or slack wax as described above, a blend of a soft paraffin or slack wax and at least one oxidised wax as described above, a waxy oil or a blend of a waxy oil and a soft paraffin wax or slack wax as aescribed above.

Thus, the composition may, instead, be a solution, the wax being selected from the group consisting of soft paraffin waxes, blends of at least one soft paraffin wax with at least one hard oxidised wax, waxy oils, blends of at least one waxy oil with at least one soft paraffin wax and mixtures of any two or more thereof, and the wax and wood treatment substance being dissolved in an organic solvent.

A waxy oil typically has a wax content of between 5% and 20% by mass. Low wax content waxy oils are preferred because these substances will normally form part of an organic solvent carrier system for carrying the treatment substance.

Other suitable waxes include that marketed by SASOL Chemical Industries (Proprietary) Limited under the name Waksol F, a waxy oil and that marketed by Engen Limited under the name ENGEN Slackwax 150, a slack wax.

A suitable chlorinated paraffin wax is that sold under the name Plastichlor by the NCP Division of Sentrachem Limited.

When the composition is an emulsion it may, further, comprise an emulsifier.

For the unchlorinated paraffin waxes the emulsifier may be a long chain fatty acid having a carbon chain of above 12 e.g.

16 - 20 carbon atoms such as oleic acid or stearic acid. The long chain fatty acid may be present in a quantity of about 0,5 1,5 % by mass of the unchlorinated wax in the composition. The emulsifier may, instead, be an alkyl polyethylene glycol ether.

A suitable alkyl polyethylene glycol ether is that marketed by Hulls AG (South Africa) (Proprietary) Limited as Marlowet PW. The alkyl polyethylene glycol ether may be present in quantities similar to those used for the fatty acid, in the wax.

For use with chlorinated waxes the emulsifier may be a nonyl phenol polyether. A suitable emulsifier of this type is that sold under the name Emulsifier 2757 by Hoechst (Proprietary) Limited. Once again, similar quantities may be employed.

The treatment substance may comprise a water-leachable flame retardant substance selected from the group consisting of diammonium phosphate, monoammonium phosphate, ammonium chloride, ammonium sulphate, borax, zinc chloride, orthophosphoric acid, boric acid, ammonium sulfamate, the hydrate of sodium oxyfluoroborate, ammoniacal basic zinc chloride, disodium octaborate tetrahydrate, ammonium biborate, ammonium pentaborate and mixtures of any two or more thereof.

Preferred fire retardant substances include ammonium phosphate, disodium octaborate tetrahydrate, boric acid, mixtures of boric acid and borax, mixtures of ammonium phosphate and ammonium sulphate, mixtures of ammonium phosphate, ammonium sulphate and any of the above boron compounds and mixtures of the above boron compounds.

The mass ratio of the flame retardant substance to the wax in the composition may be 3:1 - 5:1 and the preferred mass ratio is about 3,5:1,0.

When used together, the preferred mass ratio of boric acid to borax is 2:3. When used together, the preferred mass ratio of ammonium phosphate to ammonium sulphate is from about 4:1 3:7, and is preferably about 1:1; and, when used together, the preferred mass ratio of ammonium phosphate, ammonium sulphate and the boron compounds, or mixtures of boron compounds, is 1:1:1.

Thus, the flame retardant substance may comprise a mixture of ammonium phosphate and ammonium sulphate, the ammonium phoshate and ammonium sulphate being present in a mass ratio of 4:1 - 3:7.

The concentration of the aqueous solution which is used to form the emulsion, i.e. the total mass of inorganic salt per litre of solution may be about 250g/Q - 400g/Q and is preferably about 300g/e - 350gyp The fire retardant substance may comprise a salt dispersant which constitutes about 3 - 4 % by mass of the composition.

A suitable salt dispersant has been found to be that manufactured by American Cyanamid Company (USA) under the name Aerosol 22. This substance comprises tetrasodium-N-1,2dicarboxyethyl-N-octyldecyl-sulfosuccinamate. The salt dispersant may thus be tetrasodium-N-[1,2-dicarboxyethyl]-N- octyldecyl-sulfosuccinamate.

The fire retardant substance may also include a small amount of an alkali or base. For example, a small amount of potassium hydroxide may be added for the purposes of saponification of the mixture. Typically, the base may be added in a quantity amounting to about 0,03 - 0,07 % by mass of the composition.

The wood preservative substance may be selected from the group of water soluble boron compounds including boric acid, boric oxide, borax, borax pentahydrate such as that marketed by Borax Consolidated Limited under the name Neobor, anhydrous borax such as that marketed by Borax Consolidated Limited under the name Dehybor, disodium octaborate tetrahydrate such as that marketed by Borax Consolidated Limited under the name Polybor, Solubor or Timbor, ammonium biborate, ammonium pentaborate and mixtures of any two or more thereof, or from the group of organic solvent soluble boron compounds including borate esters (alkyl borates) such as trihexylene glycol borate such as that marketed by Rhone Poulenc under the name Borester 7, trimethyl borate, triethyl borate, tributyl borate and mixtures of any two or more thereof.

The wood preservative substance is preferably selected form the group comprising Polybor, Solubor or Timbor, boric acid, mixtures of boric acid and borax and trihyxylene glycol biborate.

In other words, the wood treatment substance may comprise a water-leachable biocidal wood preservative substance selected from the group consisting of boric acid, boric oxide, borax, borax pentahydrate, anhydrous borax, disodium octaborate tetrahydrate, ammonium biborate, ammonium pentaborate, trihexylene glycol borate, trimethyl borate, triethyl borate, tributyl borate and mixtures of any two or more thereof.

The mass ratio of boric acid equivalent to wax may range from 2:5 - 1:10. The preferred mass ratio is about 1:5.

The mass ratio of boric acid to borax in the mixture of boric acid and borax, as mentioned above, is preferably about 2:3. Thus, the wood treatment substance may comprise a mixture of boric acid and borax, the boric acid and borax being present in a mass ratio of 1:1 - 1:2.

According to another aspect of the invention there is provided a method of preparing a composition for the treatment of wood, which method comprises admixing at least one treatment substance and a wax to form the composition, the treatment substance being leachable from the wood by water.

The admixing may comprise dispersing the, or each, treatment substance in a wax to form an emulsion, by dissolving the treatment substance in water and emulsifying the solution so formed and the wax to form a treatment emulsion.

Thus the invention extends to a method of preparing a composition for the treatment of wood which method comprises dissolving the wood treatment substance in water to form a solution, and then emulsifying the solution so formed with the wax to form an emulsion.

The emulsifying may be carried out in the presence of an emulsifier so as to form a discontinuous aqueous phase in an organic continuous phase comprising the wax.

The admixing step may instead, comprise dissolving a treatment substance and a wax in an organic solvent to form a treatment solution.

Thus the invention extends, further, to a method of preparing a composition for the treatment of wood which method comprises dissolving the wood treatment substance, and the wax, in an organic solvent to form a solution.

The treatment substance may be as hereinbefore described.

According to another aspect of the invention, there is provided a method of treating wood, which method comprises applying to the wood, in at least one treatment step as hereinbefore described, a composition as hereinbefore described.

The retention level of the wax i.e. the mass of wax per volume of wood which remains on, or in, the treated wood after treatment will be related to the retention level of the fire retardant substance. The retention level of the wax may be about 30 kg/m3 in the case of severe weathering and about 15 kg/m3 in the case of milder weathering. In the case of dip-treated wood the retention level of the wax may be about 2,8 - 4,3 kg/m3. In the case of pressure-impregnated wood the retention level may be about 11,4 - 17,2 kg/m3 Thus, the treatment may be sufficient to produce in the treated wood, a retention level of wax of about 2 - 30 kg/m3.

The retention level of the flame retardant substance i.e.

the mass of fire retardant substance per volume of wood which remains on, or in, the treated wood after treatment which is required for adequate fire protection generally ranges from about 10 - 60 kg/m3 depending on the method of application and the dimensions of the wood. Thus the treatment step may be sufficient to produce, in the treated wood, a retention level of flame retardant substance of 10 - 60 kg/m3.

For example, in the case of dip-treatment in which the fire retardant substance, after treatment, is generally more concentrated at, or near, the surface of the wood, a lower overall retention level will generally be adequate. The retention level required for adequate fire protection is generally reduced as the dimensions of the treated wood, especially its thickness, are increased.

The retention level of the fire retardant substance for diptreated wood is preferably about 10 - 15 kg/m3 The retention level for pressure impregnated wood on the other hand, in which almost complete penetration of the fire retardant substance into the wood structure occurs, is preferably between about 40 and 60 kg/m3.

The retention level of boric acid equivalent i.e. the mass of boric acid equivalent per volume of wood for adequate preservation generally ranges from about 2 - 10 kg/m3 depending on the conditions to which the treated wood is exposed. For example, a higher retention level may generally be required if the treated wood is subjected to severe weathering, for example if the treated wood is periodically exposed to contact with free water. The preferred level, in this case, may be about 6 - 10 kg/m3. The preferred retention level in the case of wood which is exposed to milder e.g. in protected or semi-protected environments, weathering may be about 2 - 5 kg/m3.

Thus the treatment may be sufficient to produce, in the treated wood, a retention level of biocidal wood preservative substance of 2 - 10 kg/m3.

The mass of wood preservative substance dissolved in the aqueous solution which is used to form an emulsion may amount, on a dry mass basis, to about 5 - 40 g/Q boric acid equivalent, preferably 10 - 25 g/Q boric acid equivalent, of the emulsion.

The emulsion may, in addition, comprise an organic solvent, the solvent acting to reduce the viscosity of the continuous phase of the composition. Suitable solvents include hydrocarbon solvents such as dieselene, hydroxylated solvents such as methanol and chlorinated solvents such as trichloroethylene, trichloroethane, carbon tetrachloride and dichloromethane.

Routine tests should be employed to establish an acceptable proportion of solvent depending on the viscosity required.

The composition may include a pigment-imparting substance such as iron oxide or a dye so that a colour is imparted to the wood when it is treated with the composition.

The composition, whether in the form of an emulsion or of a solution, may be applied to the wood by brushing or spraying it on the wood or by dipping the wood into the composition. The composition may, instead, be applied by a combination of standard pressure and vacuum treatments of the kind which are known in the art. The treatment may be carried out at ambient or elevated temperatures and as a single- or a multiple-step process.

For example, the wood may be pretreated with a boron-based wood preservative and/or an inorganic fire retardant substance by any of the above application methods and the wax may then be applied to the timber in the form of a wax emulsion in a separate treatment step. Instead an emulsion comprising for example at least one inorganic boron-based and/or an inorganic fire retardant substance may be applied in a single step, for example by brush, dip-treatment or pressure impregnation.

Similarly, in the case of a composition comprising a solution, the wood may be pretreated, for example, with a solution of a boron-based wood preservative in an organic solvent and a wax solution may be applied in a separate treatment step.

Instead, a solution comprising the boron-based wood preservative and the wax may be applied in a single step.

The preferred methods of treatment in the case of boroncontaining substances include dip diffusion treatments, gas-phase impregnation and pressure impregnation for both water-based compositions and organic solvent-based compositions. The preferred methods of treatment in the case of fire-retardant substances include dip treatment at ambient or elevated temperatures, and pressure impregnation in the case of waterbased compositions.

Without being bound by theory, the Applicant believes that in use, when a mixture as described above is applied to wood, the solvent evaporates, leaving the water-soluble flame retardant or wood preservative substance bound in a wax matrix. The matrix then serves as a stabilizer which prevents the substance from being leached out of the wood when the treated wood is subjected to weathering.

In addition, the wax serves the additional function of stabilizing the wood against moisture variation, warping or cracking. Furthermore, in the case of compositions which comprise one or more chlorinated paraffin waxes, because chlorinated paraffin waxes are flame retardant substances, they may serve the function of acting as flame retardants in their own right. In this way chlorinated hydrocarbon wax may act as an initial flame retardant and the inorganic flame retardant substance acts as a subsequent flame retardant.

In the case of an unchlorinated paraffin wax, the wax will not serve as a fire retardant in its own right. However, the composition will then have the advantage that hydrogen chloride gas (which acts as the fire retardant agent in the case of chlorinated paraffin waxes) will not be produced when it is burned.

If the composition contains a pigment-imparting substance such as iron oxide or a dye, the treated wood will be coloured according to the colour of the pigment-imparting substance or the dye.

According to another aspect of the invention there is provided a method of treating wood to retard the leaching of water-leachable wood treatment substances from the treated wood, which method includes the step, after treating the wood with a water-leachable treatment substance selected from the group consisting of water-leachable flame retardance substances and water leachable biocidal wood preservative substances, of applying a water/wax emulsion to the wood in a separate treatment step.

The invention also extends to wood, whenever treated according to a method as described above.

The invention will now be illustrated, by way of nonlimiting example, with reference to the following Examples.

EXAMPLE 1 Diammonium sulphate and diammonium phosphate in a 1:1 mass ratio were dissolved in warm water (at 50"C) to produce, after dilution with cold water, a 40 % m/v (g/mQ) solution. The solution was allowed to cool to room temperature and filtered through Whatman 41 filter paper.

Waksol A (850g), was heated with Marlowet PW (lOOg), until the mixture melted. The temperature was not permitted to exceed 1200C. A 50 % aqueous KOH solution (7 mQ) was slowly added to the hot wax blend and gently stirred until most of the foaming which arose from the addition had subsided.

Aerosol 22 (240g) was mixed with the 40 % diammonium sulphate/diammonium phosphate solution as prepared above (8,803Q) and the mixture was heated with stirring to 70"C. The resulting solution, at 70"C, was added to the wax blend, which was at 75"C, under rapid stirring. The resulting emulsion was gently stirred until it had cooled to room temperature.

The properties of the emulsion are given in Table 1.

TABLE 1 PROPERTIES OF THE EMULSION Wax content, mass % 8,5 Salts content, mass % 35 Viscosity at 30"C, cP 29 Density at 25"C, kg/l 1,1 pH 7 Ionogenity non-ionic Stability at 20"C stable Stability upon temperature cycling from 5-35" (2 cycles) acceptable EXAMPLE 2 A 30 % solution of diammonium sulphate and diammonium phosphate was prepared as described above.

A mixture of Waksol A (680g) and Waksol A6 (170g) was heated with Marlowet PW (70g) as described above.

A 50% aqueous KOH solution (7 me) was added as described above. Aerosol 22 (240g) was added to the 30 % diammonium sulphate/diammonium phosphate solution (8,8332) as described above, and the resulting salt solution and the wax blend were mixed while hot and allowed to cool under stirring as described above.

The properties of the emulsion are given in Table 2.

TABLE 2 PROPERTIES OF THE EMULSION Wax content, mass % 8,5 Salts content, mass % 26,5 Viscosity at 30"C, cP 13 Density at 25"C, kg/Q 1,1 pH 7 Ionogenity non-ionic Stability at 20"C stable Stability upon temperature cycling from 5 to 35"C (2 cycles) acceptable EXAMPLE 3 A flame retardant composition was prepared by blending a two part system comprising a blend and a solution.

The blend was prepared by mixing Plastichlor (780 m), with Emulsifier 2757 (220 m), at room temperature, and stirring the mixture for 15 minutes with an overhead mechanical stirrer.

The solution was prepared by dissolving ammonium sulphate (70g) and ammonium phosphate (30g) in deionized water (900 mQ).

The blend (2 parts by volume) was added to the solution (98 parts by volume) and the resulting mixture was vigorously shaken to produce a water-inoil emulsion.

EXAMPLE 4 Leaching tests were carried out to illustrate the stabilising effect of wax on the leaching of boronbased compounds from wood.

Air-dry Pinus patula pencil stakes (100 mm x 10 mm x 10 mm) were divided into two sets. Each set was vacuum/pressure impregnated with an aqueous boric acid solution having a concentration of 7,5g boric acid/Q in respect of the first batch and 15g boric acid/ in respect of the second batch for 15 minutes at a pressure of -80kPa followed by 30 minutes at a pressure of 600kPa to retention levels of 3 and 6 kg b.a.e./m3 (b.a.e. = boric acid equivalent) respectively. The sets were then dried to equilibrium moisture content. Each set was then divided into three batches.Two of these batches were then impregnated with a Waksol A emulsion containing 45 % (m/m) Waksol A and diluted with water to a concentration of 33g Waksol A emulsion per litre in respect of the first batch and 167g Waksol A emulsion per litre in respect of the second batch, to obtain retention levels of Waksol A of 15 and 30 kg/m3 for each group respectively. The batches were then redried to equilibrium moisture content.

In this way four batches were prepared.

The batches were then subjected to cold water leaching. Each batch was divided into 7 sub-batches which were submerged in cold water (600 mQ) for a measured time.

Two control batches of boric acid-impregnated stakes having b.a.e. levels of 3 and 6 kg/m3 as above, but which had not been subjected to the wax impregnation step, were used as reference.

The batches were submerged in water for 1 hour, 1 day, 3 days, 5 days, 8 days, 10 days and 14 days.

The leaching experiment was carried out on 12 samples and the results were averaged.

The leaching tests were conducted in accordance with the European Standard Method for Accelerated Ageing of Treated Wood (EN84) which method is incorporated herein by reference. After each leaching period the leach waters were analyzed to determine the percentage of boric acid (expressed as boron) leached from the stakes.Results are shown in Table 3. TABLE 3 BORIC ACID LEACHING RESULTS

TREATMENT SYSTEM LEACHING BORIC ACID WAX BORON IN BORON IN BORON AND TARGET TIME RETENTION RETENTION TREATED LEACH WATER LEACHED RETENTION LEVEL LEVEL SAMPLES (mg/l) (%) (kg b.a.e./m ) (kg/m ) (mg/l) H3BO3 0 hrs 2,84 - 99 - (3 kg b.a.e./m ) 1 hr 2,86 - 100 29 29,0 (REFERENCE) 1 day 2,91 - 102 73 71,6 3 days 2,92 - 102 85 83,3 5 days 2,96 - 104 101 97,1 8 days 2,92 - 102 103 100 10 days 2,91 - 102 - 14 days 2,95 - 103 104 100 H3BO3 0 hrs 2,87 13,8 100 - (3 kg b.a.e./m ) 1 hr 2,87 13,7 100 14 14,0 Plus 1 day 2,94 13,9 103 53 51,5 Waksol A 3 3 days 2,89 13,6 101 60 59,4 (15 kg/m ) 5 days 2,88 13,6 101 81 80,2 8 days 2,93 13,8 103 84 81,6 10 days 2,88 13,6 101 - 14 days 2,91 13,7 102 96 94,1 TABLE 3 (Continued)

TREATMENT SYSTEM LEACHING BORIC ACID WAX BORON IN BORON IN BORON AND TARGET TIME RETENTION RETENTION TREATED LEACH WATER LEACHED RETENTION LEVEL LEVEL LEVEL SAMPLES (mg/l) (%) (kg b.a.e./m ) (kg/m ) (mg/l) H3BO3 0 hrs 2,89 26,8 101 - (3 kg b.a.e./m ) 1 hr 2,95 26,7 103 12 11,7 Plus 1 day 2,86 27,2 100 41 41,0 Waksol A 3 days 2,93 26,5 103 57 55,3 (30 kg wax/m ) 5 days 2,87 26,8 100 69 69,0 8 days 2,81 26,0 98 76 77,6 10 days 2,91 27,3 102 - 14 days 2,83 26,5 99 84 84,8 H3BO3 0 hrs 5,93 - 208 - (6 kg b.a.e/m ) 1 hr 5,94 - 208 64 30,8 (REFERENCE) 1 day 5,93 - 208 155 74,5 3 days 5,92 - 207 166 80,2 5 days 5,89 - 206 197 95,6 8 days 5,87 - 206 204 99,0 10 days 5,84 - 204 - 14 days 5,90 - 207 208 100,0 TABLE 3 (Continued)

TREATMENT SYSTEM LEACHING BORIC ACID WAX BORON IN BORON IN BORON AND TARGET TIME RETENTION RETENTION TREATED LEACH WATER LEACHED RETENTION LEVEL LEVEL LEVEL SAMPLES (mg/l) (%) (kg b.a.e./m (kg/m (mg/l) H3BO3 0 hrs 5,69 13,6 199 - (6 kg b.a.e./m ) 1 hr 5,68 13,5 199 25 12,6 Plus 1 day 5,82 13,8 204 95 46,6 Waksol A3 3 days 5,60 13,4 196 115 58,7 (15 kg/m ) 5 days 5,74 13,5 201 140 69,7 8 days 5,64 13,5 197 150 76,1 10 days 5,73 13,7 201 - 14 days 5,66 13,5 198 152 76,8 H3BO3 0 hrs 5,84 27,0 204 - (6 kg b.a.e/m ) 1 hr 5,78 27,2 202 20 9,9 Plus 1 day 5,88 27,7 206 78 37,9 Waksol A 3 days 5,72 27,0 200 103 51,5 (30 kg wax/m ) 5 days 5,79 27,1 203 127 62,6 8 days 5,60 26,5 196 136 69,4 10 days 5,70 25,5 200 - 14 days 5,82 27,3 204 154 75,5 The proportion of boric acid leached from the stakes, expressed as mg/Q of boron in the leach water, was determined by measuring the boron concentrations in the leach water.

Boron was analyzed by direct current plasma (DCP) atomic emission spectrophotometry and expressed as mg/Q.

Before leaching, boric acid retention in the wood samples was calculated based upon the mass uptake of boric acid solution for each set of 12 samples. The total boric acid content was then theoretically converted to an equivalent concentration in mg/Q of boron in 600 mQ water (the volume of leach water used in each experiment).

The boron leached in each case was expressed as a percentage of the total amount of boron in the treated sample before leaching. The results of this experiment are discussed below.

EXAMPLE 5 An experiment was carried out to illustrate the dimensional stability and the water repellent properties of wood treated with a fire retardant wax composition and a standard fire retardant formulation containing no wax additives.

In the experiment air-dry, defect-free P.patula samples (measuring 7 mm x 22 mm x 100 mm in the longitudinal, tangential and radial directions, respectively) were dip-treated in two different fire retardant compositions for 5 minutes at ambient temperature. The test composition was prepared by adding 35,2% (m/m) fire retardant salts (consisting of 1 part ammonium sulphate-to 1 part ammonium phosphate) to a wax emulsion; the total system having an 8,5% (m/m) Sasol Waksol A content. The reference composition was prepared by dissolving 35,2% (m/m) fire retardant salts (as above) in water. The samples were conditioned to a constant moisture content of about 12%. Five samples were dip-treated in each formulation. Five non-treated samples were used as a control. All of the samples were subjected to the swelling/water repellency test described below.

Samples were end-matched for the different formulations i.e. prepared from the same piece of timber.

The comparative swelling/water repellency tests were conducted in accordance with the Standard Test Method, "Water Repellency (short term) of Wood Treated With Preservatives", of the South African Bureau of Standards (SABS) SABS Method 990 which method is incorporated herein by reference. The samples were completely immersed in distilled water at ambient temperature for a period of 30 minutes. The specimens were measured (radially, tangentially and longitudinally) and weighed before and after the immersion test to determine dimensional and mass changes.

The mass of treatment solution absorbed per volume of wood and the retention levels of the fire retardant substance expressed as the mass of dry salt per volume of wood and the results of the experiment are given in Table 4.

TABLE 4 DIMENSIONAL STABILITY AND WATER REPELLENCY RESULTS FOR DIFFERENT FIRE RETARDANT FORMULATIONS

TREATMENT SOLUTION FR DRY VOLUMETRIC MASS DIMENSIONAL WATER FORMULATION ABSORPTION SALT CHANGE CHANGE STABILITY REPELLENCY (kg/m ) RETENTION (% (% WATER (%) (%) (kg/m ) SWELLING ABSORPTION) Rek/CSIR (8,5 % Sasol wax/35,2 % 197,5 69,5 2,67 9,33 69,6 85,4 FR salts*) Reference (35,2 % 179,6 62,3 5,89 20,84 33,0 67,4 FR salts*) Untreated controls - - 8,79 63,8 Where, *FR = fire retardant salts consisting of 1::1 ammonium sulphate, ammonium phosphate Rek/CSIR is the fire retardant/wax composition employed In Table 4, percentage swelling or volumetric change is defined as the change in volume after immersion (the difference in volume before and after immersion) expressed as a percentage of the volume before immersion.

Mass change, or percentage water absorption, is similarly defined as the change in mass after immersion (the difference in mass before and after immersion) expressed as a percentage of the mass before immersion.

Percentage dimensional stability is then defined as the difference in the volumetric change between untreated and treated samples expressed as a percentage of the volumetric change of an untreated sample; and percentage water repellency as the difference in the mass change between untreated and treated samples expressed as a percentage of the mass change of an ull'ireated sample. The results of the experiment are discussed below.

EXAMPLE 6 An experiment was conducted to illustrate the water repellent properties of wood after treatment with different fire retardant compositions in accordance with the invention.

Air-dry P.patula samples (20 mm x 20 mm x 10 mm), divided into 6 batches, were dip-treated in six different fire retardant compositions respectively for 5 minutes at 80"C. The procedure followed was as in Example 5, to produce a composition as set forth in Table 5. The samples were conditioned to a constant moisture content of about 12%. An untreated batch was used as a control. Each batch was divided into sub batches which were submerged in water at ambient temperature for 30 minutes, 60 minutes or 120 minutes.

The retention levels of the composition in mass absorbed per volume of wood and the retention levels of the fire retardant substance expressed as mass of dry salt/volume of wood and the results of the experiment are shown in Table 5.

TABLE 5 WATER REPELLENCY RESULTS FORM DIFFERENT FIRE RETARDANT COMPOSITIONS

TREATMENT WAX/FR FR DRY WATER ABSORPTION (%) WATER REPELLENCY (%) FORMULATION SOLUTION SALT AFTER 3 SUBMERSION AFTER 3 ABSORPTION RETENTION PERIODS SUBMERSION PERIODS (kg/m ) (kg/m ) (minutes) (minutes) 30 60 120 30 60 120 EXSA 80/18 (8,4% Engen 180,3 73,9 4,4 9,7 14,2 90,3 79,5 71,3 wax/4% FR salts*) EXSA 80/19 (10,5% Engen 178,0 67,6 13,9 17,1 23,0 69,3 63,8 53,5 wax/38% FR salts*) EXSA 80/20 (8,4% Sasol 238,0 107,1 7,1 11,8 14,8 84,3 75,0 70,1 wax/45% FR salts*) EXSA 80/21 (8,4% Engen/ Sasol A6 wax blend/45% 200,1 90,0 5,2 9,6 24,6 88,5 79,7 50,3 FR salts*) Rek/CSIR (5,6% Sasol 224,8 67,4 9,0 13,4 16,8 80,1 73,7 66,1 wax/30% FR salts*) Rek/CSIR reference (8,5% Sasol wax/30% FR 226,8 68,0 7,1 12,4 16,5 84,3 73,7 66,7 salts**) Untreated control - - 45,3 47,2 49,5 Where, FR = fire retardant * FR salts consisting of 1 ammonium sulphate : 1 ammonium phosphate : 1 boric acid ** FR salts consisting of 1 ammonium sulphate : 1 ammonium phosphate only The Exsa and Rek/CSIR references were merely sample identification codes employed in the experiments for various fire retardant/wax compositions used.

In Table 5, percentage water absorption is defined as the change in mass after submersion (the difference in mass before and after submersion) expressed as a percentage of the mass before submersion.

Percentage water repellency is defined as the difference in the mass of water absorbed by untreated and treated samples expressed as a percentage of the mass of water absorbed by an untreated sample.

The results of the experiment are discussed below.

EXAMPLE 7 An experiment was conducted to illustrate the fire retardant properties imparted to wood by different fire retardant compositions.

Air-dry P.patula samples (20 mm x 20 mm x 10 mm), divided into 7 batches, were treated by dipping each batch in one of seven different fire retardant compositions for 5 minutes at 80"C. The procedure followed was as in Example 5 to produce a composition as set forth in Table 6. The samples were conditioned to a constant moisture content of about 12%. An untreated batch was used as a control.

Each sample was subjected to a comparative laboratory burn test in accordance with the SABS Standard Test Method 1088, "Laboratory Burn Test for Timber Fire Retardants" which method is incorporated herein by reference.

The retention levels of each composition, expressed in mass of composition absorbed per volume of wood, the retention levels of dry salt expressed as mass of dry salt, per volume of wood and the results of the experiment, are given in Table 6.

TABLE 6 FIRE RETARDANT RESULTS FOR DIFFERENT FIRE RETARDANT COMPOSITIONS

TREATMENT WAX/FR FR DRY MASS LOSS FIRE FORMULATION SOLUTION SALT (%) RETARDANCY ABSORPTION RETENTION (%) (kg/m ) (kg/m ) EXSA 80/18 (8,4% Engen wax/41% FR 220,0 90,2 29,6 37,2 salts*) EXSA 80/19 (10,5% Engen wax/38% FR 178,3 67,8 35,3 25,1 salts*) EXSA 80/20 (8,4% Sasol wax/45% FR 221,0 99,5 33,0 29,9 salts*) EXSA 80/21 (8,4% Engen/Sasol A6 wax 237,5 106,9 31,1 34,0 blend/45% FR salts*) EXSA 80/26 (8,4% Engen wax/30% FR 212,5 63,8 34,5 26,8 salts*) Rek/CSIR (5,6% Sasol wax/30% FR 183,3 55,1 36,4 22,7 salts*) Rek/CSIR reference (8,4% Sasol wax/ 214,5 64,4 33,7 28,5 30% FR salts**) Untreated controls - - 47,1 Where, FR = fire retardant * FR salts consisting of 1 ammonium sulphate : 1 ammonium phosphate : 1 boric acid ** FR salts consisting of 1 ammonium sulphate : 1 ammonium phosphate only In Table 6, percentage mass loss is defined as the change in mass after exposure to fire (the difference in mass before and after exposure) expressed as a percentage of the mass before exposure.

Percentage fire retardancy is defined as the difference in percentage mass loss between treated and untreated samples expressed as a percentage of the mass loss of an untreated sample. Samples were subjected to a temperature of 600 C for a period of 1 minute. The results of the experiment are discussed below.

EXAMPLE 8 An experiment was conducted to illustrate the fire resistant properties of wood treated with different fire retardant compositions at different levels of absorption.

Air dry P.ratula samples of average density, measuring 640 mm in length, 100 mm in width and 20 mm in thickness were provided with mortise and tenon joints so that panels could be constructed from the samples. The samples were pretreated with Tanalith preservative solution to an average net retention of 6 kg copper/chrome/arsenate (CCA) salts/m3 using a standard full cell (vacuum/pressure/vacuum) impregnation process (15 minutes at a vacuum of -80kPa, followed by 30 minutes at a pressure of 600kPa and a final vacuum of -80kPa for 5 minutes).

After CCA treatment, the samples were redried to equilibrium moisture content before dip-treatment in a fire retardant composition comprising Engen wax emulsion having a 42 % m/m wax content (20 % m/m), ammonium sulphate (10 % m/m), ammonium phosphate (10% m/m), boric acid (10 % m/m), and water (50 % m/m).

The composition was prepared as follows. Ammonium sulphate, ammonium phosphate and boric acid salts were dissolved in the premeasured volume of water at a temperature of + 50"C in order to ensure that all salts were dissolved. Thereafter the wax emulsion was added to the above solution while stirring.

The dip-treatment was carried out at 80"C for 20 - 40 minutes. Solution absorption levels were determined gravimetrically by weighing the test specimens before and after dip treatment. These values were adapted to compensate for the average moisture loss which occurred during the hot dip treatment process.

Samples which were not subjected to the diptreatment were used as a control.

Four treated panels and two control panels (CCAtreated only) were constructed from the samples. Each panel measured 640 mm x 590 mm x 20 mm.

The panels were subjected to a standard fire resistance panel test in a furnace in accordance with the SABS Standard Test Method 0177, Part II, "Fire Resistance Tests for Building Elements" which method is incorporated herein by reference.

The increase in temperature with time in the furnace is given in the following Table: Time (minutes) Temperature ( C) 0 20 5 576 10 678 15 739.

20 781 25 815 A panel was deemed to have failed if an opening exceeding 6 mm in width over a total length of 150 mm developed as a result of thermal degradation. The time taken to reach failure is the failure time. Results are shown in Tables 7 and 8.

TABLE 7 OBSERVATIONS DURING FIRE RESISTANCE TEST

MINUTES OBSERVATIONS REGARDING PANEL CONDITION AFTER PANEL NO./FR, WAX SOLUTION ABSORPTION LEVEL* START OF 1/0 2/M 3/L 4/H 5/M 6/O TEST 8 Showing signs No signs No signs No signs No signs Showing signs on on joints joints 9 Starting to No signs No signs No signs No signs Starting to burn burn through through 10 Starting to No signs No signs No signs No signs Flaming, fails after fail 10 min 15 sec (Closed up) 11 Flaming, fails Showing signs Showing Showings Showing after 11 min on joints signs on signs on signs on 11 sec joints joints joints (Closed up) 12 Showing signs Showing Showing Showing - on joints sings on signs on signs on joints joints joints 13 Starting to Starting to Showing Starting to - burn through burn through signs on burn joints through 14 Starting to Opening up Starting to Opening up - flame, on joints burn through on joints opening up on joints TABLE 7 (Continued)

MINUTES OBSERVATIONS REGARDING PANEL CONDITION AFTER START PANEL NO./FR, WAX SOLUTION ABSORPTION LEVEL* OF TEST 1/0 2/M 3/L 4/H 5/M 6/0 15 Flaming, Opening up Opening up Opening up - fails after on joints, on joints, on joints, 15 min 34 but no but no but no sec (Closed flames flames flames up) Small Opening up Opening up 16 - - flames, on joints, on joints, fails after but no but no 16 min 12 flames flames sec 17 Increased Small Small - - flaming flames, flames, fails after starting to 17 min 34 fail sec 18 Serious Increased Small - - flaming flaming flames, fails after 18 min 0 sec 19 Falling Serious Small flames - - apart flaming 20 Starting to Starting to - - - fall apart fall apart Where, FR = fire retardant * 0 = No FR, wax solution absorption M = Medium FR, wax solution absorption L = Low FR, wax solution absorption H = High FR, wax solution absorption TABLE 8 COMPARATIVE FIRE RESISTANCE PERFORMANCE OF TEST PANELS

PANEL NO/ WAX, FR SOLUTION** FIRE IMPROVE FR, WAX ABSORPTION RESISTANCE MENT LEVEL* (MIN::SEC) (%) ACTUAL ADAPTED*** (kg/m ) (kg/m ) 1/0 (control) | 0 0 11:11 6/0 (control) 0 0 10:15 Average 0 0 10:43 (control) 3/L (low) 35,3 52,9 16:12 51,2 2/M 42,1 63,1 15:34 5/M 43,1 64,6 18:00 Average 42,6 63,9 16:47 56,6 (medium) 4/H (high) 54,1 81,1 17:34 63,9 Where, FR = fire retardant * 0 = No FR, wax solution absorption L = Low FR, wax solution absorption M = Medium FR, wax solution absorption H = High FR, wax solution absorption ** Contains 30 % (m/m) fire retardant dry salts consisting of 1 ammonium sulphate : 1 ammonium phosphate : 1 boric acid *** Adapted = Actual x 1,5 to compensate for average moisture loss during hot dip treatment In Table 8 fire resistance is defined as the failure time.

In Table 8, percentage improvement in fire resistance is defined as the difference in failure time between treated and untreated panels expressed as a percentage of the failure time of an untreated panel.

The results of the experiment are discussed below.

The results from the leaching test shown in Table 3 indicate that the amount of boric acid which is leached from the treated stakes, depends on the amount of wax absorbed into or adsorbed on to the sample.

For example, after 8 days of leaching, 100 % of the boric acid was lost from samples treated with the preservative alone. Under the same conditions, if 15 kg/m3 of wax was impregnated into or onto the wood together with the boric acid, 18 % and 24 % of the boric acid remained (in the cases of 3 kg/m3 and 6 kg/m3 b.a.e. at the start). Similarly, if 30 kg/m3 of wax was impregnated into or onto the wood, these values were increased to 22 % and 31 % respectively.

It should be noted that the leaching conditions used in this experiment are severe. The EN84 standard method is designed to measure preservative fixation and to determine the suitability of active ingredients in applications, where free water leaching is normally experienced. However, the preservative system of the invention is not intended to fix the preservative but rather to retard leaching of the preservative by protecting it with a water repellent barrier. The EN84 fixation test may therefor be regarded as being too severe for testing the preservative system since it is does not represent the medium hazard, non-ground contact applications in which use of the system is envisaged. A more suitable indicator of performance would be a simulated rainfall test.Under this type of test it is envisaged that the leach retardant formulation would show a significantly improved performance when compared with the less significant improvement shown in the fixation test.

It is clear from the 8 day leaching data that the wax significantly retards leaching of the preservative. It prevents total loss of active ingredient even after 14 days of leaching. After this period up to 24 % of the preservative was retained.

This suggests that, if large enough quantities of wax and preservative are added, the system might also be suitable for exterior, ground applications.

Table 4 shows that a significant reduction in swelling and water absorption is brought about by the fire retardant composition of the invention when compared with the standard (reference) fire retardant formulation. The Table shows, further, that there is a more significant improvement in dimensional stability and water repellency when these values are compared with the results obtained from the untreated controls. Improvements in these properties are about 70 % and 85 %, respectively.

For example, Table 4 shows an improvement in dimensional stability from about 33 % for the standard formulation to about 70% for the composition of the invention. Table 4 also shows an improvement in water repellency, brought about by the composition of the invention when compared with the standard formulation from about 67 % to about 85 %.

Table 5 shows that a marked reduction in water absorption occurs in all cases where test samples were treated with one of the fire retardant compositions.

Water repellency was more than 50 % after a submersion period of 2 hours in all cases. Water repellency is markedly more after shorter submersion periods, i.e.

30 minutes and 1 hour.

Water repellency is an indication of the degree to which leaching of water soluble compounds from treated wood is prevented or reduced.

Table 6 indicates that higher fire retardant salt retention levels improve fire retardancy of treated specimens. However, the addition of wax also has a detrimental effect in that higher wax levels tend to decrease the fire retardancy dt similar fire retardant salt levels. This effect is apparent when comparing results obtained with the EXSA 80/18 and EXSA 80/19 formulations the latter having a higher wax content but not an equally lower fire retardant salts content.

It is therefore important that the ratio between the wax and the retardant salts is balanced by routine experimentation in order to achieve an optimal or at least acceptable leach-retardant effect and to ensure at the same time that optimal or at least acceptable fire retardation is achieved.

Tables 7 and 8 show that treatment with the fire retardant compositions significantly improves the fire resistance of wooden panels. An improvement in excess of 50 % was achieved in all cases.

Although higher levels of absorption of the composition improve the fire resistant properties of treated panels, the relationship is not linear. It therefore appears that the most cost-effective absorption level is probably between about 50 and 60 kg/m3 in the present case. Lower or, possibly, higher levels might be required to achieve similar results in the case of wood products having larger or smaller dimensions, respectively.

In general, boron-based preservatives are well established in the wood preservation industry and have a number of desirable features which are not always evident in alternative wood preservatives. These features include wide-spectrum efficacy against insect and fungal attack, low mammalian toxicity, environmental acceptability, fire retardant properties at higher loadings, colourlessness, minimal vapour pressure, non-corrosiveness towards ferrous metals, and minimal or no effect on wood strength.

A principal limitation associated with the use of boron-based preservatives in the past has been their high solubility in water. This solubility limits the lifetime of the preservative in the wood under wet conditions. The solubility and hence the mobility of the preservative in the presence of free water can be used to advantage in diffusion treatments of green timber with boron-based wood preservatives. However, this mobility may also cause excessive leaching of boron based preservatives from treated wood when the wood is subsequently in contact with free water.

The use of certain inorganic salts to suppress combustibility and protect wood-based materials against thermal degradation when exposed to fire is also well known and treatment of wood with these compounds imparts fire resistant properties to the wood. Compounds such as ammonium phosphate, ammonium sulphate and borax, have been known and used as fire retardants for wood since the last century. Some desirable features of these compounds are fire retardant effectiveness, low cost and colourlessness.

As in the case of boron-base preservatives, the principal limitation associated with the use of watersoluble fire retardant compounds is the loss of these compounds which results from leaching and the consequent loss of their effectiveness when the wood is exposed to wet conditions. These losses can occur as a result of direct leaching from the treated wood when the wood is exposed to free water or as a result of the hygroscopic nature of most of these compounds. In the latter case some fire retardant compounds may exude from the treated wood in their own absorbed moisture when the wood is exposed to high humidity conditions.

An increase in the wood moisture content as a result of the hygroscopicity of certain fire retardant compounds may also cause a reduction in wood strength, an increase in the swelling of the wood and an increase in the corrosion of metal fittings and fasteners in contact with the treated wood.

In practice the use of water-leachable wood preservatives and/or fire retardants has been limited to internal applications where exposure to free water is minimal or absent.

Generally, if treated timber is used for nonground contact external applications, then it must be coated or painted with a suitable water barrier to prevent leaching. However, if regular maintenance is not exercised, the water-leachable active ingredients generally leach, diffuse or exude from the treated timber.

Water-leachable preservatives and/or fire retardants are generally seen, at present, as unsuitable for external ground-contact applications, mainly because it is generally difficult or impractical to maintain suitable water repellent barriers under such conditions. If the problems of water leaching can be solved this would alleviate the principle limitation in the use of water leachable wood treatment system.

The Applicant believes that the compositions of the invention can significantly reduce leaching of the active ingredients from the wood without the requirement for painting or coating the treated wood with a water repellent substance. The Applicant believes further that the invention provides compositions for the treatment of wood which have the additional advantages of stabilizing the wood against moisture variation, warping and cracking. The Applicant also believes that the abovementioned problems are reduced because the compositions of the invention serve to bind the active substances in a waxy matrix.

Claims (23)

CLAIMS:

1. A composition for the treatment of wood, the composition comprising: a wax; and at least one water-leachable wood treatment substance.

2. A composition as claimed in claim 1, in which the wood treatment substance is selected from the group consisting of water-leachable flame retardant substances, water-leachable biocidal wood preservative substances and mixtures thereof.

3. A composition as claimed in claim 1 or claim 2, which is an emulsion, the wax being selected from the group consisting of soft paraffin waxes, blends of at least one soft paraffin wax with at least one hard oxidised wax, and mixtures of any two or more thereof, the wood treatment substance being dissolved in water with which the wax is emulsified.

4. A composition as claimed in claim 1 or claim 2, which is a solution, the wax being selected from the group consisting of soft paraffin waxes, blends of at least one soft paraffin wax with at least one hard oxidised wax, waxy oils, blends of at least one waxy oil with at least one soft paraffin wax and mixtures of any two or more thereof, and the wax and wood treatment substance being dissolved in an organic solvent.

5. A composition as claimed in any one of claims 1 to 4 inclusive, in which the wood treatment substance comprises a water-leachable flame retardant substance selected from the group consisting of diammonium phosphate, monoammonium phosphate, ammonium chloride, ammonium sulphate, borax, zinc chloride, orthophosphoric acid, boric acid, ammonium sulfamate, the hydrate of sodium oxyfluoroborate, ammoniacal basic zinc chloride, disodium octaborate tetrahydrate, ammonium biborate, ammonium pentaborate and mixtures of any two or more thereof.

6. A composition as claimed in claim 5, in which the mass ratio of the flame retardant substance to the wax in the composition is 3:1 - 5:1.

7. A composition as claimed in claim 5 or claim 6, in which the flame retardant substance comprises a mixture of ammonium phosphate and ammonium sulphate, the ammonium phosphate and ammonium sulphate being present in a mass ratio of 4:1 - 3:7.

8. A composition as claimed in any one of claims 5 to 7 inclusive, which comprises a salt dispersant which constitutes 3 - 4 % by mass of the compositic;,i.

9. A composition as claimed in claim 8, in which the salt dispersant is tetrasodiurn-N- [1, 2-dicarboxyethyl) - N-octyldecyl-sulfosuccinamate.

10. A composition as claimed in any one of claims 1 to 4 inclusive, in which the wood treatment substance comprises a water-leachable biocidal wood preservative substance selected from the group consisting of boric acid, boric oxide, borax, borax pentahydrate, anhydrous borax, disodium octaborate tetrahydrate, ammonium biborate, ammonium pentaborate, trihexylene glycol borate, trimethyl borate, triethyl borate, tributyl borate and mixtures of any two or more thereof.

11. A composition as claimed in claim 10, which has a mass ratio of boric acid equivalent to wax of 2:5 1:10.

12. A composition as claimed in any one of the preceding claims, in which the wood treatment substance comprises a mixture of boric acid and borax, the boric acid and borax being present in a mass ratio of 1:1 - 1:2.

13. A method of preparing a composition as claimed in claim 3, which method comprises dissolving the wood treatment substance in water to form a solution, and then emulsifying the solution so formed with the wax to form an emulsion.

14. A method of preparing a composition as claimed in claim 4, which method comprises dissolving the wood treatment substance, and the wax, in an organic solvent to form a solution.

15. A method of treating wood which method comprises applying to the wood, in at least one treatment step, a composition as claimed in any one of claims 1 to 12 inclusive or claim 20.

16. A method as claimed in claim 15, in which the treatment is sufficient to produce, in the treated wood, a retention level of wax of about 2 - 30 kg/m3.

17. A method as claimed in claim 15 or claim 16, in which the composition is as claimed in any one of claims 5 to 9 inclusive, the treatment being sufficient to produce, in the treated wood, a retention level of flame retardant substance of 10 60 kg/m3.

18. A method as claimed in claim 15 or claim 16, in which the composition is as claimed in claim 10 or claim 11, the treatment being sufficient to produce, in the treated wood, a retention level of biocidal wood preservative substance of 2 - 10 kg/m3.

19. A method of treating wood to retard the leaching of water-leachable wood treatment substances from treated wood, which method includes the step, after treating the wood with a water-leachable wood treatment substance selected from the group consisting of water-leachable flame retardant substances and water-leachable biocidal wood preservative substances, of applying a water/wax emulsion to the wood in a separate treatment step.

20. A composition as claimed in claim 1, substantially as described herein with reference to the Examples.

21. A method as claimed in claim 13 or claim 14, substantially as described herein with reference to the Examples.

22. A method as claimed in claim 15 or claim 19, substantially as described herein with reference to the Examples.

23. Wood, whenever treated according to the method of any one of claims 15 to 19 or claim 22.