AU614736B2 - Wood preserving composition and method of application - Google Patents

Description

n,6 47 6 Fr 10 COMMONWEALTH OF AUSTRALI;

COMPLETE

PATENTS ACT 1952

SPECIFICATION

FOR OFFICE USE: Class Int.Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: a Priority: ','Related Art: Name of Applicant: RHONE-POULENC CHIMIE *'Address of Applicant: 25, quai Paul Doumer, 92408, Courbevoie, France Actual Inventor: Peter S. Gradeff and John F. Davison Address for Service: SHELSTON WATERS, 55 Clarence Street, Sydney SComplete Specification for the Invention entitled: "WOOD PRESERVING COMPOSITION AND METHOD OF APPLICATION" The following statement is a full description of this invention, including the best method of performing it known to me/us:- 1 t i. I L~ i -I -lA- WOOD PRESERVING COMPOSITION AND METHOD OF APPLICATION The present invention relates to a composition for preserving wood. The invention also describes the process for preserving wood with the said composition.

Wood preservatives, known in prior art, are either organic or water-based. Organic preservatives fall into two main categories, namely: I1) coal tar creosote and solutions of creosote with coal 6@S.

tar or petroleum oils and 2) solutions of preservative chemicals, such as pentachlorophenol dissolved in a suitable organic carrier.

One disadvantage of organic preservatives is that they exude from the wood and are subsequently leached from the surface, o.

or they evaporate. In order to compensate for the loss of the organic preservative, high levels of initial retentions are required. In tropical and high rainfall areas, the use o e of organic preservatives has been found to be uneconomical.

Another disadvantage of certain organic preservatives is that they are regarded as skin irritants and can cause burns.

0 Furthermore, organic preservatives such as creosote cannot be painted and do not have an attractive appearance. Also, these preservatives often have toxic side effects.

The water-based preservatives are those containing chemical preservatives in the form of aqueous solutions. Such preservatives react within the wood to form compounds, the solubility of which may be increased by an adjustment of the pH. When chemical changes occur within the wood resulting in compounds with a very low solubility, the compounds are said to be resistent to F -2leaching. Those which form soluble compounds are said to be "leachable".

Water-based preservatives which are resistent to leaching and which are in commercial use include acid copper chromate solution (ACC), a solution of arsenate and of copper chromate (CCA) and ammoniacal copper arsenate solution (ACA). CCA solutions are commonly used. They form, in the wood, compounds which are toxic to both fungi and insects. Leachable waterbased preservatives include chromated zinc chloride and 21@8 fluoride-chromium-arsenate-phenol mixtures and boron compounds.

The leachable water-based preservatives can only be used for the treatment of timber to be used internally or where it is not exposed to severe leaching conditions.

The use of water-based preservatives has many advantages: cleanliness, paintability of the treated wood, absence of odour, and when correctly applied, a longer-lasting protection of the wood.

e* The "Book of Standards" (1986), published by the American Wood Preserver's Association defines and describes, on pages Q 1978 and 1979, the wellknown methods and techniques used "j in applying preservatives to wood. Currently used techniques include the treatment under pressure, the treatment under vacuum, surface treatment, e.g. by immersion, spraying or the application by brush.

These methods lead to the desired result if compositions are applied to the wood which have properties which are relevant to the protection of wood. The description of the methods for the protection of wood, contained in the pages mentioned above, and also throughout the Book of Standards, is incorporated in the present application for reference purposes.

The essential features of the pressure method are that: 1. the wood is surrounded by a solution of the preservative in a closed reactor; 2. hydrostatic pressure is applied by mechanical means to force the solution into the fibres of the wood, replacing the air or water present in the wood, or to penetrate into the void spaces between the fibres. It is usual to reduce the pressure to about 26 mm mercury o by eliminating air from the cells within the wood. When "10 a solution of CCA is used to impregnate the wood, the g0*O CCA reacts inside the wood with reducing sugars found therein, to form a mixture of insoluble salts.

oo.,o U.S. Patent No. 2 565 175 granted to Hager describes a process for preserving wood which utilizes a specific preservative in combination with specific methods and conditions of penetration, and the distribution of the preservative inside the wood. One specific type of preservative is CCA, to which ammonia is added to render the preservative solution alkaline.

The addition of ammonia prevents a rapid fixation of the preservative in the wood. According to the method described by Hager, the preservative is introduced into the wood and the wood is kept in an undried condition for a period of time during which no fixation of the preservative occurs, and the preservative diffuses through the cell walls. Thereafter, the wood is dried.

U.S. Patent No 4 325 993 granted to Schroder describes a process for protecting wood against the attack by living organisms, e.g. fungi and insects. The process may comprise one or two steps. In the two step process, there is a fungicidal step which consists of the introduction of a copper solution into the wood, and an insecticidal step which consists of the introduction of a chromium-arsenic A- solution into the wood.

VHAQ3 -NT0 -4- One disadvantage of using CCA is that not the entire fixation of the preservative takes place in the wood. Sludging may occur in the working solution due to corrosion or as a result of impurities being present in the chemicals which are used for the preparation of the solution. Sludging causes a deposit of solids on the surface of the wood. These deposits contain variable percentages of arsenic and thus are a matter of environmental concern. Recent treatment standards (AWPA 1982) have recognized this (see Hartford, "The Practical Chemistry 10 of CCA in Service", American Wood Preservers' Association Annual :Meeting, April 28, 29 and 30, 1986, pp. 1-161.

Lanthanide derivatives are used for the manufacture of glass, ceramic, paint, plastics and rubber. Compositions comprising cerium compounds are known to have bactericidal effects, e.g.

compositions comprising cerium nitrate and silver sulfadiazine (Boeckz et al, Burns vol. 11. No. 5 (1985) pp. 337-342; V Monafo, 3rd International Congress on Pharmacological Treatment I of Burns, Milan, Italy, May 12-15, 1980, Panmainerva Med., vol. 25, No. 7 (1981) pp. 558-563; Monafo, et al., Arch Surg.

vol. 113, No. 4 (1978) pp. 397--401; Monafo, et al. Surgery (St. Louis) vol. 80, No. 4 (1976) pp. 465-473), and compositions containing electrically activated silver and cerium stearate (Colmano, et al., 23rd Annual Meeting of the Biophysical Society (New York), Atlanta Ga., Feb. 26-28, 1979, Biophys.

J. vol. 25, No. 2, part 2 (1979) p. 217A.

Cerium derivatives are also used as additives in plastics V for food packaging.

One of the objectives of the present invention is to provide a new composition for the treatment of wood.

Another objective of the present invention is to provide a new safe process for the treatment of wood by means of hydrosoluble compositions.

It is a further objective of the invention to achieve permanent bonding of lanthanide ions to wood fibres.

It is yet another objective of the present invention to promote flame retardation and to inhibit wood decay resulting from exposure to bacteria, insects, fungi and atmospheric conditions.

These and other objectives are met by the present invention and are further described in the specification.

i. :According to a first aspect of the invention, there is provided a method for the treating wood comprising the steps of contacting the wood with a composition comprising an aqueous solution of at least one lanthanide derivative and allowing the derivative to penetrate the wood.

reoet The wood may be impregnated by one or a combination of several known techniques chosen so as to accommodate the desired degree of penetration, depending on the envisaged use. These may include treatments under pressure, under vacuum, surface treatments by immersion, spraying, or the application by brush, as well as treatments which are called "full cell treatments" Sconsisting of a preliminary treatment under vacuum and an impregnation under pressure, whereby the cellular cavities are more or less completely filled. Other treatment methods are also available.

One embodiment of the invention treatment process comprises the steps of contacting the wood with a composition comprising an aqueous solution of at least one lanthanide derivative; allowing the derivative to penetrate the wood; drying in air the woodsolution complex; and ageing the wood-solution complex for a period of time sufficient to bond the lanthanide element to the wood.

6 In another embodiment of the invention, the treatment process comprises the steps of subjecting the wood to a treatment under vacuum, then introducing a composition comprising an aqueous solution of at least one lanthanide derivative and establishing contact between the wood and the said composition for a period of time sufficient to achieve a bonding of the lanthanide elements and the wood.

In yet another embodiment of the invention, the treatment process comprises treating the wood under pressure, the method comprising the steps of immersing the wood in a composition comprising an aqueous solution of lanthanide derivatives, and maintaining an elevated pressure for a period of time sufficient to achieve a bonding between the lanthanide elements and the wood.

In a second aspect of the invention, there is provided a wood or a wood derivative treated with an effective amount of a lanthanide or lanthanide derivative. Preferably, the lanthanide or the lanthanide derivative expressed as oxide of the lanthanide element represents from about 0.10% to about 5.0% and, more preferably, between about 0.10% and about 2.0% by weight of the wood or wood derivative.

The thus treated wood or wood derivative is resistant to deterioration that occurs to lanthanide-free wood exposed to wood-destroying organisms such as, for example, bacteria, insects and fungi, as well as environmental pollution that promotes e g.

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i- I i According to the method of the present invention, wood is treated with an aqueous solution comprising one or several lanthanide derivatives. One may apply the treatment for protection to any type or form of wood: mining timber, construction timber, pilings, telegraph poles, backplates, joist and floor boards, timber for residential or commercial buildings, timber used in shipbuilding, wood for carpentry, fibres for laminated materials, paper pulp, cooling towers, wood for storage of crops and the transport of foodstuffs.

The term wood or timber which is used here is not restricted to the above list.

Suitable lanthanide derivatives include the lanthanides;lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolimium, S terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, or mixtures thereof. Preferred lanthanides are cerium, lanthanum, praseodymium, and neodymium. Cerium can be trivalent or tetra- Svalent.

The lanthanine cation can be bonded to an inorganic anion such as nitrate, chloride, sulfate, perchlorate, phosphate, or phosphonate. The lanthanide cation can also be bonded to an organic ligand such as lower alkyl carboxylate, for f. a example, acetate, propionate, acrylate, methacrylate, gluconate, alkyl sulfonate or alkyl phosphonate. Derivatives having both inorganic and organic ligands are also suitable for the present invention.

The lanthanide derivatives may be used alone or in admixture with other wood treatment agents such as flame retardants, colouring agents, anti-cracking agents, antistatic agents, dimensional stabilizers, film-forming agents, wood softening agents, and other biocides, such as fungicides, bactericides, herbicides, insecticides, algicides.

-8- The lanthanide derivatives must be soluble in water, preferably in an amount at least about 0.1% by weight.

Use of concentrations less than 0.1% by weight is not economical. Concentrations of approximately 0.1% to approximately 10% are preferred, although higher concentrations may be used. Particularly preferred are, however, concentrations of approximately 0.5% to approximately Preferably, contact is established between the wood and lanthanide composition for a period of time sufficient to obtain a permanent bonding between the lanthanide element and the wood. As used herein, the term "permanent bonding" is intended to mean that the lanthanide is fixed to the cellulose fibres in such a manner that it is no longer leachable with water.

More specifically, it is believed that the interaction between the lanthanide ion and the wood, according to the method of the invention, is a s: cross-linkage of cellulose fibres with the lanthanide ition. It is also believed that the lanthanide ion is linked with other complexes of wood, such as lignin and colophony which are active centres for chemical bonds.

The bonds could involve one or more valancies of the lanthanide element. Cross-linking takes place under approximately neutral or acid pH (less than approximately The cross-linkage is thus speeded up by a treatment under hydrostatic pressure or under vacuum and is slowed compositions in this manner, the lanthanide cation penetrates the fibres of the wood and reacts with hydroxy or other active sites of the wood.

The time necessary to achieve a sufficient amount of permanent bonding between the lanthanide and the wood depends on several factors, e.g. the type of treatment, z$ 7 I 71 -iii4; i- 8a the type of wood to be treated and the condition of the materials before treatment.

According to the invention, one may apply the derivatives of lanthanide onto the wood in accordance with any of the known methods, particularly those described in the "Book of Standards" mentioned

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-9- Also part of the invention are the processes for conditioning the wood which involve preliminary steps aimed at enhancing the penetration of the lanthanide compositions into the wood. These include the steps of air-drying, kiln drying, under vacuum drying, steaming or a combination thereof.

One may apply the composition of the invention according to a surface treatment, e.g. by immersion, spraying or application by brush. The treatment may be once or repeated, in combination with other agents or, alternatively, with different concentrations 0el of the preserving solutions, depending on the degree of penetration required. On may carry out the treatment at ambient or raised temperature.

r It is equally possible, within the context of the invention, to use a treatment under vacuum which consists of two steps.

In the first step, one submits the wood to a vacuum treatment, followed by the introduction of the treating solution without reintroducing air. It is evident that the parameters of the process can vary within wide limits. Preconditioned wood needs less time and vacuum than wet wood. The length of treat- 20 ment under vacuum depends on the cut or the form of the material to be treated and on the depth of the required penetration.

The same applies as far as temperature is concerned. The step under vacuum has the objective of emptying the cells of the wood of moisture and air which is contained therein so that the force with which the treatment solution, on the basis of lanthanide, penetrates into the empty cell meets with less resistance. The effect is the same as with the treatment of wood under pressure. Both treatments also have the same results.

Although the treatment under pressure is more recent than the treatment under vacuum, the "American Wood Preserver's Association" has adopted the vacuum treatment as the standard method for applying preservatives to wood.

One can equally apply the composition of the invention according to the process under pressure which may be used for pre- or post-conditioning wood. The process consists in applying a hydrostatic pressure to wood immersed in a preserving, lanthanide based solution. The contact time may vary greatly according to the condition, type and the thickness of the wood.

Preferably, the contact time lies between approximately 10 minutes to approximately 10 hours. Of course, longer periods f of time may be used. The contact time may be decreased with I increased pressure. A contact time between approximately 3 and approximately 6 hours is preferred. Evidence shows that while most of the bonding occurs during the immersion of the wood in the lanthanide solution, the bonding reaction of the cross-linkage may continue for several days after the treatment.

S The pressure must be above atmospheric pressure. At atmospheric pressure, permanent bonding does not occur to a 20 significant extent. While some impregnation does occur, the deposited derivative may be almost entirely leached from the wood. Preferably, the pressure is chosen between approximately 10 psi (6,895.104 Pa) and approximately 300 psi (2,0684.106 Pa) and even more so, between approximately psi (3,4473.10 5 Pa) and approximately 80 psi (1,9305.106 Pa).

According to a practical mode of execution of the invention, the wood is immersed in a closed reactor which contains a composition of a lanthanide derivative; subsequently, hydrostatic pressure is applied. The pressure can, for example, ZY e 'qo -11be applied by compressing the bath by mechanical means (isostatic pump). The pressure can also be maintained by utilizing one or several inert gases, e.g. nitrogen.

The treatment temperature should not exceed approximately 0 C. Preferably, the chosen temperature is the ambient temperature, being between approximately 20 and approximately 0 C. For some treatments, a temperature is chosen between approximately 40 and 60oC which is preferred for facilitating the penetration and the bonding between the cation lanthanide 10 and the fibres of the wood.

e 6 After treatment, the aqueous solution is drained off. The quantity of lanthanide derivative may be adjusted and the resulting solution may be utilized for the treatment of another batch of timber. The treated wood is resistant to decay caused by bacteria, insects, fungi and atmospheric conditions. Furthermore, the treatment promotes flame retardation of the timber.

One of the main advantages of using lanthanides is their relative safety, which is important during processing, handling or subsequent leaching or sludging.

*9*i *9 *9 6 All modes of execution use compositions of the invention which are based on lanthanide which, on contact of the wood with a treatment solution, penetrates into the wood.

Without limiting the invention by an interpretation, the term "penetration" is not sufficient for describing and explaining the unexpected and better results for wood treated with the compositions of the invention. The present invention provides for a permanent bonding of the elements to wood.

Permanent bonding, also called cross-linkage in the present means that the ion of lanthanide is fixed to the fibres so that it is no longer possible to leach them with water.

is -12- As shown in the examples which follow, the wood treated under pressure with lanthanides, makes available a larger quantity of lanthanide ions which bond after ageing and which are tested just after treatment. The wood which was well impregnated under atmospheric pressure and subsequently leached, makes available a far smaller quantity of bonded lanthanide ions. Once a sufficiently long duration is ascertained, the lanthanides which have penetrated into the wood or which have impregnated, gradually bond, in a permanent manner, to the wood, provided the wood is not exposed to 4S e leaching prior to cross-linkage.

In order to prevent a premature leaching one simply protects the treated material from an exposure to excessive surface water or covers the entire surface in an appropriate manner.

oomeo S It is thought that the quantity of lanthanide ions (expressed in a percentage of oxide),bonded to the wood in a permanent manner, should be less than 0.1% of the total weight in order Sto assure a protective effect. In extreme conditions it is certainly preferable to have available more important quantities in order to have as many as the wood is able to absorb.

ep e6 The mechanisms of protection for the wood treated with Slenthanides are not understood very well. It seems that the conventional protective agents have different mechanisms S of action but in general, lanthanides are not considered to be toxic.

The following examples describe modes of execution specific to the invention. The examples should not be interpreted as being limiting to the scope of the invention.

Examples Example 1: Treatment under pressure A series of tests of the treatment under pressure was done whereby Southern yellow pine (USA) was treated with lenthanide derivatives using a procedure known in prior art for treating S- _-I -13- Souther yellow pine with CCA. Small pieces of untreated, kiln dried pine were placed in a pressure apparatus.

Aqueous compositions containing lanthanide derivatives were added to the apparatus in a quantity sufficient to immerse the wood. Pressure was maintained using nitrogen gas. At the end of the treatment, the specimens were withdrawn, washed in running water and dried in the air.

After determining the quantity of lanthanide bonded in a permanent manner to the wood, the specimens of the treated *D o. wood were washed for 12 hours. The washed wood was then dried and the percentage of ash was measured after burning the specimens and calcining the residue at 1000 0 C. The percentage of ash prior to treatment was subtracted from the percentage of ash of the treated wood to determine the quantity of lanthanides permanently bonded.

The studies of the decay of pine wood treated with lanthanide derivatives show that a beneficial effect is obtained if the OS: quantity of ash due to lanthanide is in the order of 0,25%.

This confirms that the specimen is sufficiently protected *2J against decomposition and decay due to attacks by microorganisms, fungi and insects.

The results are shown in Table 1. All treatment, unless otherwise indicated, were at ambient temperature. The untreated pine used for tests 1 18 contained approximately 0,08% ash.

The untreated pine used in all other tests contained approximately 0,12% ash.

For reference purposes, the percentage of ash of a commercial specimen of Southern yellow pine treated with CCA was used.

14 Table 1 Preservative compound of the Test test composition Control CCA Treatment Commercial sample Days prior to %Ash washing 0.94 Commercial 1.21 sample Ce(N0 3 4 PH 5. 1) 3 hrs, 240 psi 0.52 0.71 1/2 hrs, 230 psi 5 1/2 hrs, 230 psi is..

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0g* a.' 9.* a S 9, 9 £56916 9 0 Ce(N0 3 4 pH 4.5) b 69 a w~ .q S a

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Ce NO 3 4 pH 4.7) Ce (N0 3 4 2NH 4 N0 3 PH 6. 0) 3 hrs, 180 psi, 500C 6 days, atm.

5 1/2 hrs., 230 psi 1/2 hrs., 230 psi 5 1/2 hrs., 230 psi 3 hrs., 230 psi 5 1/2 hrs., 230 psi 5 1/2 hrs., 230 psi 1/2 hrs., 230 psi 6 days, atm.

5 1/2 hrs., 230 psi 1/2 hrs, 240 6 days, atm.

0.90 0. 18 0.57 0.58 0.66 0.60 1.35 1.15 0.94 0 .185 0.55 0.*61 0.28 Cerous methacrylate ag* 64 00 Ia Table I (Con'd) Preservative compound of the Test test composition 17 Cerous lactate pH 6.0) 18 o 19

I

La(N0 3 4 pH 3.3) 21 s 22 of 23 Lanthan,4de mix

(NO

3 )3 3** pH 3.0) 24 i 25 o 26 Cerous acetate pH 4.3) 27 o 28

I

29 Cerous propionate aq. pH 7.3) o 31 Ce(N0 3 4 2NH 4 N0 3 pH 5.0) 32 Ce(N0 3 4 2NH 4 N0 3 PH 5.0) 33 Ce(N0 3 4 2NHAN0 3 pH 4.2)' Treatment 5 1/2 hrs., 260 psi 5 1/2 hrs., 260 psi 6 days, atm.

5 1/2 hrs, 220 psi 5 1/2 hrs, 220 psi 6 days, atm.

5 1/2 hrs., 220 psi 5 1/2 hrs., 220 psi 6 days, atm.

5 1/2 hrs, 220 psi 5 1/2 hrs, 220 psi 6 days, atm.

5 1/2 hrs, 220 psi 5 1/2 hrs, 220 psi 10 hrs, 50 psi 1. hr, 60 0

C

220 psi 5 1/2 hrs, 220 psi 0.73 1.16 0.15 0.21 0.51 0.32 0.51 1.06 0.21 0.75 1.50 0 .044 0.71 1.53 0.49 0.70 1.30 Days prior to washing 8 15A Table 1 (Con'd) Preservative compound of the Test test composition Days prior to Ash washina Ce(N0 3 4 2NH 4 N0 3 pH 4.2) Cerous Toluene Sulfonate pH Ce(S0 4 2 pH 20) Treatment 5 1/2 hrs, 10 psi 0.50 0.95 4 hrs, 250 psi 5 hrs, 200 psi 111 indicates washing was done was removed from the Lanthanide composition.

immediately after wood

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16 Test results show that more Lanthanide derivative becomes permanently bonded to wood when pressure is applied than is permanently bonded under atmospheric pressure.

Furthermore, during aging after treatment, the percentage of ash increases. This indicates that the bonding process continues over several days. Table II illustrates the advantage of ageing.

Table II Compound ash (days ash @000 0 60 6@ 0 0 0 S 0S Cerous acetate Cerous propionate Cerous lactate Ce(N0 3 6 2NH 4

NO

3 Lanthanide mix (NO 3 3 Cerous

(NO

3 3 Cerous methacrylate La

(NO

3 3 prior to washing) (immediate wash) 1.5 0.75 1.5 0.71 1.16 0.73 1.15 1.35 1.06 0.51 1.00 (14) 0.71 0.61 (20) 0.55 0.51 0.21 Example 2: Surface treatment Southern yellow pine was treated with Lanthanide derivatives by immersion, spraying or application with a brush of a composition consisting of an aqueous solution of a Lanthanide derivative. The treated wood was dried and aged for several days.

For determining the content of Lanthanide ions bonded in the samples, the samples were washed, in running water, a described in Example 1, and then reduced to ash. When the leaching was carried out just after the treatment, the results show that a certain quantity of lanthanide ions is bonded in a permanent manner (see Example I, tests 5, 13, 16, 19, 22, 25). When the leaching was carried out after the period of ageing for several days, or after the treatment, important quantities of bonded lanthanide ions are found.

Example 3. Treatment under vacuum 010 The standardized specimens are subjected to a preconditioning, o in a reactor with two columns, one equipped with a vessel S. containing an aqueous solution of cerium nitrate of 2%.

In the reactor, a reduced pressure is established (approx.

2mm mercury) which is maintained for 10 hours. The reactor is filled with the solution of cerium nitrate and the specimens are immersed for approximately 4 hours. After leached for an entire night and then reduced to ash.

Test specimen: Ash from untreated specimen 0.07% Ash from specimen treated after leaching 1.33% permanent manner (expressed in CeO 2 is 1.24 j.0

Claims (22)

1. A method for the treating wood comprising the steps of contacting the wood with a composition comprising an aqueous solution of at least one lanthanide derivative and allowing the derivative to penetrate the wood.

2. A method according to claim 1 wherein the lanthanide is cerium, lanthanum, praseodymium, or neodymium.

3. A method according to claims 1 or 2 wherein the lanthanide derivative is a nitrate of lanthanide.

4. A method according to any one of the claims 1 to 3 wherein the composition comprises a mixture of various lanthanide derivatives or a mixture of derivatives of one or more lanthanides.

5. A method according to any one of the claims 1 to 4 94 S* wherein the composition comprises one or more cerium compounds selected from the group comprising: Ce(N0 3 3 Ce(N0 3 4 CeCl 3 Ce 2 (SO 4 3 Ce 2 (SO 4 2 Ce(NO 3 4 2NH 4 NO 3 cerous acetate, cerous methacrylate, cerous lactate, cerous propionate and cerous toluene sulfonate.

6. A method according to any one of the claims 1 to wherein the aqueous solution comprises about 0.1% to about S* 10% by weight of one or more lanthanide derivatives.

7. A method according to claim 6 wherein the aqueous solution comprises about 0.5% to about 2.5% by weight of one or more lanthanide derivatives.

8. A method according to any one of the preceding claims wherein the contacting step is preceded by a preconditioning process which enhances penetration of the composition contacted with the wood.

9. A method according to any one of the preceding claims comprising the further steps of drying in air the wood-solution complex; and ageing the wood-solution complex for a period of time sufficient to permanently bond (as herein before defined) the lanthanide element to the wood. A 10. A method according to any one of the preceding claims wherein the wood is contacted with the composition by way 199 19 of immersion, spraying or application by brush.

11. A method according to any one of the claims 1 to 8 wherein the wood is subjected to a vacuum prior to the contacting step, then contact is established between the wood and the composition for a period of time sufficient to obtain a permanent bonding (as hereinbefore defined) between the lanthanide element and the wood.

12. A method according to claim 11 wherein a hydrostatic pressure is established and maintained after having made contact with the treatment composition in order to obtain a high degree of bonding.

13. A method according to any one of the claims 1 to 8 wherein the wood is contacted with the composition by way of immersion and comprising the further step of maintaining an increased pressure for a period of time sufficient to obtain a permanent bonding (as hereinbefore ~defined) between the lanthanide element and the wood.

14. A method according to claim 13 wherein the wood is brought into contact with the composition under pressure, whereby this pressure is greater than atmospheric pressure. A method according to claim 14 wherein the pressure is between about 10 psi (6,895.104 Pa) and about 300 psi 6 (2,0684.10 Pa).

16. A method according to claim 15 wherein the pressure is between about 50 psi (3,4473.10 Pa) and about 280 psi (1,9305.106 Pa).

17. A method according to claim 13 wherein the period of time is from about 30 minutes to about 10 hours.

18. A method according to claim 17 wherein the period of o Stime is from about 3 hours to about 6 hours. *:see:

19. A method according to claim 13 wherein the immersion takes places at a temperature less than abut 95 0 C. A method according to claim 19 wherein the immersion takes place at about ambient temperature.

21. A method according to claim 19 wherein the immersion takes place at from about 201C to about 30 0 C.

22. Wood treated by the method according to any one of 7 20 the preceding claims.

23. Wood or a wood derivative treated with an effective amount of a lanthanide or lanthanide de; ivative.

24. Wood or a wood derivative according to claim 23, wherein the lanthanide or the lanthanide derivative comprises between about 0.10% and about 5.0% by weight of the wood or wood derivative. Wood or a wood derivative according to claim 24 wherein the lanthanide or lanthanide derivative comprises about 0.10% to about 2.0% by weight of the wood or wood derivative.

26. A method for treating wood substantially as herein described with reference to any one of the examples, excluding the comparative examples. DATED this 11th day of JUNE, 1991 RHONE-POULENC CHIMIE Attorney: WILLIAM S. LLOYD Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS I eBB. S S a S BS A