WO2004026548A2 - Method for the chemical treatment of a substrate which is made from a wood-containing material - Google Patents

Abstract

The invention relates to a method for the chemical treatment of a substrate which is made from a wood-containing material. According to the invention, the aforementioned substrate is brought into contact with at least one organic compound having a molar mass of less than 500 and comprising at least two carbamate or urethane functions with formula -NH-CO-O-, said compound having formula (I): R1-O-CO-NH-R-NH-CO-O-R2 (I), wherein R is a divalent group which is preferably selected from alkylene groups 1-10C, aromatic ring groups 6-10C, such as the phenylene group, which are optionally substituted, for example, by one or more 1-6C alkyl groups such as methyl, the groups comprising several 6-10C aromatic ring groups being optionally substituted, for example, by one or more 1-6C alkyl groups, and linked by a single bond or by a divalent group such as a 1-10C alkylene group; and R1 and R2 represent independently of each other a 1-6C alkyl group such as the ethyl group or a 6-10C aromatic ring group such as the phenyl group.

Description

 PROCESS FOR THE CHEMICAL TREATMENT OF A SUBSTRATE IN A MATERIAL COMPRISING WOOD

DESCRIPTION

TECHNICAL AREA

The invention relates to a method of chemical treatment of a substrate made of a material comprising wood, in order to obtain an impregnated, modified substrate, provided with determined properties, in particular physicochemical properties, that the substrate made of material comprising wood, by example the wooden substrate does not have naturally.

In the present description, the term “material comprising wood” generally means a material comprising a majority proportion of wood. By “majority proportion”, it is generally understood that the material comprises at least 50% by weight of wood. Preferably, this material is made entirely of wood. Similarly, in the description, the term

"Wood" should be generally understood to mean not only pure wood, but also material comprising wood.

This process applies, in particular, to the treatment of wood, with a view to giving it the desired physicochemical properties, in order, in particular, to preserve it, to conserve it, to improve its resistance and to protect it against different types chemical, biological and / or physical attacks. In other words, the method of the invention aims to obtain a material comprising wood, for example wood, having better resistance to external conditions and, in particular, better intrinsic stability against ambient humidity, which means that the material comprising wood, for example wood, swells less, if not at all while picking up moisture, or undergoes less, if not more at all, shrinkage during drying, and better resistance to attack by living organisms capable of degrading the material comprising wood such as wood, for example fungi, insects and bacteria.

The technical field of the invention can be defined, in general, as that of the treatment of a substrate made of a material comprising wood, for example a wooden substrate, with a view to improving the properties thereof or itself. communicate new ones, particularly for preservation purposes.

Thus, in the field of wood preservation, coatings constituted by resins, stains, and varnishes are generally used, for example coatings based on polyurethane [1]

[2] [3].

Polyurethanes are a family of polymers well known in a wide variety of fields. Depending on the nature of the precursors used, it is possible to produce thermosetting polyurethanes or thermoplastic polymers. Among these, the best known are the foams. Polyurethanes are commonly used as wood preservatives in the form d Oligomers or pre-polymers of large molecular sizes, that is to say of molecular weights greater than 500, which generally require the use of organic solvents to use them in the form of a sufficiently fluid liquid. Due to the large size of these molecules, there is no penetration of polyurethane into the privacy of the microstructure of the cell walls of the wood.

The use of the products mentioned above is limited to a simple surface treatment, very superficial, the penetration into a substrate such as wood is very low, namely generally very less than 1 mm. In fact, this type of process is content to establish a simple hydrophobic protective film of polymer, for example of polyurethane, adhering to the surface of the wood. These treatments also have a limited lifespan and it is therefore often necessary to iron or redeposit a protective resin layer every 2 or 3 years for wood exposed to the weather, due to the instability of the coating with solar ultraviolet rays. .

To guarantee superior resistance, namely at least ten years, to satisfy the ten-year guarantee imposed by the building industry, it is necessary to use wood impregnation processes, in its volume, with preservatives , which, unfortunately, all have disadvantages.

So the impregnation of wood with copper-chromium-arsenic salts (CCA) is a very effective technique, but which nevertheless poses problems important waste treatment, after use, in fact, the Cu-Cr-As salts are very toxic and cannot be treated by incineration. The use of this process, involving CCA, which has so far been the most used among wood preservation treatments, as well as the marketing of treated wood, is now increasingly limited, even banned in certain countries Europe. Creosotes are also used for the treatment of wood. These are tars of high molecular weight from the petroleum industry, which mainly consist of aromatic molecules and have the disadvantage of being carcinogenic. There is, moreover, a big problem of soil pollution by creosotes, when the wood is in contact with the ground.

Compounds containing boron or quaternary ammoniums are very promising, but their duration of action is quickly limited by the easy leaching of these salts by water.

Furthermore, it is known that it is possible to densify wood using physical methods to polymerize organic matter in wood in situ [11-12]. These treatments are carried out in two stages: a first stage of impregnating a liquid resin with a precursor monomer of the final polymer followed by the actual polymerization which can be carried out according to two approaches: - Gamma irradiation and electronic irradiation are well known for crosslinking carbon chains by generating free radicals on functions containing double bonds. The process is limited by the use of a large gamma irradiator, which does not facilitate industrial operation. In addition, electronic irradiation has poor penetration into the wood, which is only a few millimeters, and does not allow massive objects to be treated;

- It is possible to premix the monomer resin with a thermo-catalyst, for example of the peroxide type, to initiate polymerization after a rise in temperature of the monomer. This second approach is very delicate to implement, because, as soon as the polymerization has started, it is no longer possible to control it, and there is a risk of too great a rise in temperature induced by the exothermic nature of the reactions polymerization. In addition, it is very dangerous to store over a long period of monomer resins activated by the addition of a catalyst, in fact spontaneous polymerization of the resin is always possible.

Using these densification methods, hydrophobic plastic is introduced into the natural porosity of the wood. It is thus possible thanks to such "composite woods" to significantly improve the mechanical properties of natural wood, on the other hand, such treatments are completely ineffective in modifying the sensitivity of the wood vis-à-vis humidity. Indeed, such densification certainly slows the penetration of water into the wood but does not prevent it and the densified wood retains its initial instability.

In the industrial field, mention is also made of the process known as "cross-linking" or pyrolysis of wood under a neutral atmosphere to stabilize the wood [13]. This technique consists in subjecting the wood to a heat treatment under controlled conditions in order to cause thermocondensation reactions in the hemicellulose of the wood. A "cross-linking" operation is usually carried out in a neutral or reducing atmosphere, on previously dried wood, by subjecting it to a temperature between 220 and 280 ° C. for a time long enough for the entire mass of the wood. treated reaches the processing temperature. The operating conditions strongly depend on the quantity and the geometry of the elements of wood which must be treated in an oven; the slightest difference in temperature and / or duration of treatment strongly questions the homogeneity of the batch of treated wood thus obtained. But the biggest limitation of this process comes from the fact that the physical integrity of the wood is not preserved during the treatment. Indeed, 1 hemicellulose is destroyed during treatment irreversibly. The mechanical properties of the wood are degraded during treatment, in particular its limit at break, and as a result, the wood becomes more brittle and more fragile. In order to overcome the drawbacks of the impregnation methods, described above, have been developed grafting processes. Compared to these conventional techniques, the grafting methods essentially have the following two advantages: - they make it possible to optimize the quantity of reagents or molecules carrying an active principle, such as biocidal agents, fire-fighting agents or agents anti-UV, to be introduced inside the wood, significantly reducing it compared to a simple treatment of filling by impregnation;

- they allow a real covalent bond to be created between the grafted active function and the wood. The leaching of molecules with active principle by water thus becomes impossible. Many examples of treatment, based on the use of reactive resins which can allow the grafting of the hydroxyl functions (-OH) of wood, are known. Indeed, the hydroxyl functions of cellulose, lignin and hemicelluloses are the most reactive functions in wood, which allow chemical grafting with the obtaining of a covalent bond between wood and a reactive molecule or molecule " graft ”.

There are, in the literature, at least three main families of reactive functions capable of reacting on the -OH functions: these are isocyanates, anhydrides and epoxides.

All types of grafting treatment have in common their many disadvantages, the most important of which are listed below. - All the recommended reagents, whether anhydrides, epoxides or isocyanates are highly toxic. Consequently, their use requires very heavy safety measures which are prohibitively expensive compared to what the building materials market can accept.

- The grafting treatments generally require a swelling agent and / or a catalyst to ensure a satisfactory grafting yield rate. In fact, cellulose, which is one of the important components of wood, comes in the form of fibrils which are themselves made up of unitary cellobiose base polymer chains. The fibrils and the polymer chains which constitute them are linked together by hydrogen bonds which “close” the structure by rendering inaccessible most of the active endings -OH of wood or points of attachment of wood. Consequently, it is necessary to use a blowing agent which does not react with the reagent and which makes it possible to "open" the molecular structure of the wood, thereby ensuring a significant improvement in the grafting rate. Most of the time, the blowing agent chosen is pyridine, but other organic compounds can also be used, such as dimethylformamide (DMF), triethylamine (TEA) or dimethyl sulfide (DMSO). By far, the most effective is pyridine, however this amino sulfur has many disadvantages: it is toxic, very foul-smelling and unstable (hence risk of explosion).

- In most cases, the grafting is carried out in a liquid reactive medium; that is, the wood samples are completely immersed in the reagent, mixed with the swelling agent in the liquid state. The shortcomings of this approach have serious consequences for the process. Very large amounts of reagents are introduced into the wood, whereas ultimately, a very small amount will be grafted onto the accessible -OHs of the wood. In particular, all the pores of the wood are unnecessarily filled with the mixture of reagent and blowing agent.

- In addition, it is necessary to remove all the reagent which was not used during the grafting, that is to say most of the reagent infiltrated into the wood. Long and uncertain additional treatments, using powerful solvents, will therefore be necessary to leach all the unused reagent because these reagents have a certain toxicity if they have not reacted with a hydroxyl function. Likewise, the blowing agents used in conjunction with the reagents, such as pyridine, are very toxic and must be completely eliminated at the end of the treatment.

Therefore, it is imperative to remove the entire mixture of intact reagent and blowing agent after grafting.

In addition, in a second cleaning operation, the organic solvent used for the first cleaning must be removed from the wood. - The three main families of reagents, mentioned above, are sensitive to humidity, in particular to the residual moisture always present in the wood and can give rise to self-polymerization of the reagents instead of the planned grafting. This self-polymerization or densification, unlike grafting, does not protect the wood from moisture because it retains its hydrophilic properties and above all, this parasitic self-polymerization can block the diffusion of the reagent at the heart of the wood, and in this case, we find the limits of too superficial treatment.

- Finally, the wood grafting methods cited in the documents of the prior art, if they appear interesting and feasible at the laboratory level, do not appear to be able to be applied on an industrial production scale. In particular, in addition to the multiple disadvantages listed above, the cost of these methods appears high compared to conventional treatments, using varnish, stain, CuCrAr or creosote.

These significant costs come from:

- a high consumption of reagents because the reaction is carried out in a liquid medium and a good part of the unused reagent is thus wasted;

- expensive and time-consuming wood cleaning treatments to remove large quantities of unused reagents after the grafting treatment; and - advanced drying of the wood before treatment to avoid the phenomenon of self-polymerization.

To summarize, there is no technique in the prior art for chemical grafting of a material comprising wood and more precisely wood which is satisfactory from all points of view for the reasons indicated above.

There is a need that has not yet been satisfied for a process which allows treatment throughout the wood, both at the heart of the latter and on the surface, with small quantities of molecules, it must also use reagents readily available at low cost, and of zero or very reduced toxicity, it must also comprise a limited number of simple steps thus inducing a limited cost of the process.

Finally, the process must not affect the other properties of the substrate such as wood.

The object of the invention is to provide a method of treating a substrate made of a material comprising wood, such as a wooden substrate which satisfies inter alia all of the needs mentioned below and which meets the criteria and requirements, indicated above for such a process.

The object of the invention is, moreover, to provide a method of treating a substrate made of a material comprising wood such as a wooden substrate which does not have the disadvantages, limitations, defects and disadvantages of the methods of the invention. prior art and which provides a solution to the problems of the methods of the prior art, in particular grafting methods.

This object, and still others, are achieved, in accordance with the invention, by a method of chemical treatment of a substrate comprising wood, in which said substrate is brought into contact with at least one organic compound of lower molar mass. at 500, comprising at least two carbamate or urethane functions of formula -NH-CO-O-, said compound corresponding to formula (I) below:

Rι-0-C0-NH-R-NH-C0-0-R ₂ (I) in which R is a divalent group preferably chosen from alkylene groups from 1 to 10C, cyclic aromatic groups from 6 to 10C such as the phenylene group optionally substituted for example one or more alkyl groups from 1 to 6C such as methyl, the groups comprising several cyclic aromatic groups from 6 to 10C optionally substituted for example by one or more alkyl groups from 1 to 6C, and linked by a single bond or by a divalent group such as an alkylene group of 1 to 10C; and Ri and R ₂ independently represent an alkyl group of 1 to 6C such as the ethyl group or a cyclic aromatic group of 6 to 10C such as the phenyl group.

Advantageously, the organic compound used in the process of the invention does not comprise, in addition to the carbamate or urethane functions, a function having a biocidal activity. Indeed, it is not necessary to use biocidal and toxic functions to guarantee the effectiveness of the process.

Advantageously, the organic compound used in the process of the invention is solid at room temperature (generally 10 to 30 ° C, for example 20 to 25 ° C), which makes it possible to avoid the phenomenon of bleeding of the compound .

Advantageously, the organic compound used in the process of the invention is insoluble in water and aqueous solutions, which makes it possible to avoid leaching with water.

Preferably, the organic compound is solid at room temperature, does not additionally have biocidal functions, in addition to the urethane or carbamate functions, and is, moreover, insoluble in water.

The process according to the invention is very simple, it uses only readily available products and of low cost, and it does not call for complex, long and expensive synthesis operations, in fact, it is a simple impregnation method which uses extremely specific molecules and which does not have the drawbacks of the impregnation methods of the prior art using other substances.

The process according to the invention differs fundamentally from the processes of the prior art in that it can therefore be defined as a simple impregnation process but that it nevertheless makes it possible to obtain excellent results, in particular in terms for stabilizing the substrate in a material comprising wood, such as a wooden substrate.

Basically, the method according to the invention uses for the impregnation of the specific organic compounds or substances of formula (I) which are defined first of all by a low molecular mass, that is to say a mass molecular less than 500, and, in addition, by the presence of at least two carbamate or urethane functions -NH-CO-O- in the molecule. Advantageously, these compounds or substances, in addition to the carbamate or urethane functions, do not include a function having a biocidal activity and / or are solid at room temperature and / or are insoluble in water. The use of such extremely specific molecules for the impregnation of substrates in a material comprising wood such as wood, has never been described in the prior art. Indeed: 1) the polyurethanes commonly used for example in the preservation of wood have molar masses much greater than 500.

2) Small molecules, that is to say a molecular mass of less than 500, containing a "carbamate" or "urethane" function are mentioned in the formulation of biocides [4] [5] [6] [7] [8] [9] [10].

These molecules are exclusively monocarbamates or mono-urethanes containing a single urethane or carbamate function, unlike the compounds of the invention (I) which contain at least two of these functions and which can therefore be defined as dicarbamates or diurethanes or polycarbamates or polyurethane.

In addition, the molecules used in the prior art are present in the liquid state at room temperature (for example, 20 ° C.) unlike the preferred molecules used according to the invention which are solid at ambient temperature.

In addition, the molecules used in the prior art, in addition to a carbamate function, always include a principle, group or "biocidal" function of the sulfur, halogen, (Br, Cl, I), benzene or azole rings type. , quaternary ammoniums, metal and metalloids (Cr, Cu, Zn, ...). It has thus been proposed to use these molecules to improve the resistance of wood vis-à-vis biological attacks in particular vis-à-vis fungi and insects because of the "biocidal" principle included in the product.

These formulations of the prior art which are basically biocidal compositions, for example of insecticides, and fungicides are generally toxic products which pose environmental and public health problems, whereas the process of the present invention does not require 'use the toxic biocidal functions mentioned above.

Finally, the prior art proposes to use di-carbamates to crosslink fibers (“cross-linkage”) [11a] in paper and cardboard; no material including wood, such as wood is mentioned. The principle of these processes is identical to that described above for the chemical grafting of wood with isocyanates. The “dicarbamate” form is only the “blocked” form of the precursor di-isocyanate, in fact, the di-carbamate is destabilized by high temperatures (namely, generally above 100 ° C.), in order to transform back into di -isocyanate. In a second step, a grafting of the isocyanate takes place on the hydroxyl functions of the cellulose of the paper / cardboard. Therefore, in the process described in the literature [11a], the “di-carbamate” form is only a temporary form of a reagent which, in order to react on the hydroxyl functions, will in principle require heating of the substrate to at least 100 ° C and the use of toxic catalysts such as pyridine. According to the invention, the di-carbamate does not participate in a reaction system, it is a simple impregnator of the wood and remains in its "di-carbamate" form without transforming into di-isocyanate. The implementation for the treatment of substrates comprising wood, such as wooden substrates, of molecules of small sizes containing at least two carbamate functions which moreover is without adding any other active principle in particular of biocidal active principle than the function carbamate or urethane is not described in the prior art.

It was surprisingly found that the specific compounds - by their molecular mass and their structure - used in the process of the invention were capable of penetrating into the substrate, for example into the cell wall of the wood even if the substrate made of a material comprising wood such as a wooden substrate was previously wet while the carbamates are molecules of hydrophobic nature immiscible with water. Therefore, the use of urethane molecules to treat a substrate which can be wet goes against a prejudice widespread in this field of the technique which considered that the treatment with such molecules was impossible or very ineffective. The invention thanks in particular to the particular compounds which it uses, triumphs in this respect over a prejudice common in this field of technology.

In addition, the carbamate or urethane functions of the compound used in the process of the invention interact with the constituents of the substrate in a material comprising wood, that is to say essentially with wood, which makes it possible to improve the stability of the substrate made of a material comprising wood such as the wooden substrate with respect to moisture absorption or with respect to drying.

Without wishing to be bound by any theory, these interactions between the carbamate or urethane functions and the constituents of the substrate, that is to say essentially the constituents of wood are probably of the Van der aals type of interactions with in particular hydrogen bonds.

In fact, it could be considered that the invention consists in choosing from the numerous compounds of urethane or carbamate type existing, first of all those whose molar mass is less than 500, then the difunctional compounds, these compounds corresponding to formula (I) very specific, and optionally then the compounds not comprising a biocidal function and / or solid at room temperature and / or insoluble in water. We are thus in the presence of at least a double selection each time leading to a very reduced group of compounds, the family of compounds finally defined making it possible to obtain surprising advantages and effects. The multiple advantages and surprising effects of the invention can therefore be listed as follows, without this list being considered as limiting:

- An excellent stabilization of the substrate is obtained in a material comprising wood, such as the wooden substrate, with respect to humidity, this stabilization can be expressed by the parameter called ASE ("Anti Shrinkage Effect").

ASE is defined by the following equation:

ASE_ untreated wood treated wood

(SU) c xlOO untreated wood

with the following definition of S

^S untreated or treated ^wood ₌ wet wood volume - ^se wood volume _--10Q

(%) dry wood volume The wood is dried in an oven at 105 ° C for 24 hours and the wood is humidified by immersion in water at 60 ° C for 24 hours.

According to the invention, the ASE is generally at least 50%, preferably at least 60%, and better still at least 70%.

It is thus possible to use the substrate made of a material comprising wood, such as the wooden substrate, treated, on the outside, because it is given by the process of the invention a better resistance to aging due to bad weather. .

- The compounds used according to the invention are little or not toxic, and are therefore easy to use in the context of an industrial process.

- As already indicated above, it is possible, completely surprisingly, to carry out the impregnation treatment of the process of the invention even if the substrate made of a material comprising wood, such as the wooden substrate, is loaded with water or prehumidified, this makes it possible to avoid performing a drying step, which consumes a lot of energy, before carrying out the process of the invention with a view to stabilizing the substrate. The process of the invention which can be described as an impregnation treatment does not necessarily require catalysts, solvents, adjuvants or very harmful or dangerous swelling agents, of the tetrahydrofuran (THF), dichloromethane type, pyridine, dimethylformamide (DMF), triethylamine, ... whether to transport the compound within the structure of the substrate, such as wood, or to clean the substrate of all processing residues not fixed by the substrate in a material comprising wood, such as the wooden substrate; - The cost of the process, as well as the accessibility of the technology necessary for the implementation of the process allow its use in one industry;

- It is not useful to carry out a thorough cleaning of the substrate made of a material comprising wood such as the wooden substrate after the grafting treatment;

the method of the invention makes it possible to treat a substrate made of a material comprising wood, such as a wooden substrate, in depth, in its volume, and is not limited to its surface unlike treatments by stain, varnish and other;

- The process according to the invention has the surprising advantage of being reversible which is not the case with any of the processes of the prior art, it is thus possible to recover the organic compound dicarbamate or diurethane (the resin) inside the substrate, for example the wooden substrate, using a carbamate solvent such as ethanol. Consequently, this reversibility allows the reprocessing of the substrate, for example of the treated wooden substrate, at the end of its life;

- The method of the invention is extremely simple to implement since it is in fact limited to a simple impregnation of the substrate. It is also possible to use techniques and facilities proven for its implementation. It does not require any adaptation, modification of existing installations;

- The method according to the invention does not damage the substrate material, such as wood, and in particular the external appearance of the substrate is not altered, and the mechanical properties are not degraded;

- organic dicarbamate compounds and in particular their precursors such as diisocyanates are available industrially in large quantities and at moderate costs;

- the hydrophobic nature of dicarbamate prevents its leaching by water, in particular by rainwater in external conditions; the solid nature of dicarbamate at 1 ambient prevents bleeding.

The invention will now be described in more detail in the following. The substrate, treated according to the invention, is made of a material comprising wood, we have seen above that by material comprising wood is generally understood a material comprising a majority proportion of wood (by weight), namely a material comprising at at least 50% by weight, preferably at least 70% by weight, more preferably 90% by weight of wood.

Preferably, the substrate is made of wood, that is to say that it is made entirely of 100% wood (taking account of the impurities naturally present in it). Wood has polar functions which are the hydroxyl functions of cellulose, hemicellulose and lignin.

According to the invention, the treated substrate can be a dry substrate but it can also be a wet substrate which, surprisingly, can be treated by the method of the invention. The term “wet substrate” generally means a substrate whose water content is greater than or equal to 20% by weight, for example is 20 to 50%.

If the substrate comprising wood, for example the wooden substrate is already wet, it can, unlike the processes of the prior art, be treated directly by the process of the invention, which avoids prior to thorough drying, consuming of time and energy. Thus in the case of wood, it will be possible to use a green wood, that is to say a wood without drying after cutting the tree, which is extremely advantageous. To improve the performance of the process, it is possible, prior to the treatment according to the invention, to a humidification step in order to be able to achieve the desirable humidity of the substrate. This humidification step can for example be carried out by immersing the substrate to be treated in water optionally heated to a temperature of 20 to 70 ° C, preferably from 30 to 60 ° C for a period of 5 to 48 hours, for example from 12 to 24 hours.

The immersion time depends essentially on the geometry and the essence of the pieces, for example the pieces of wood to be treated. In fact, this humidification step corresponds to a swelling or rather pre-swelling step in which the swelling agent used is water. Thus, in general, prior to contacting with the organic compound of the diurethane or dicarbamate type, the substrate can be treated with a swelling agent which is generally chosen from water, non-toxic aliphatic alcohols from 2 to 10C such than ethanol, non-toxic aromatic cyclic alcohols from 6 to 10C, non-toxic hydrophilic compounds and mixtures thereof.

In the case of water, the conditions of swelling are already described above, in the case of a blowing agent other than water, the treatment with the blowing agent is generally similar to that of water. After treatment with water, the substrate generally has a humidity of 20 to 50% by mass. According to the invention, the substrate is brought into contact with at least one specific organic compound which has a molar mass of less than 500, which comprises at least two carbamate or urethane functions, of formula -NH-CO-O-. The substrate can be brought into contact with a single organic compound or with several organic compounds meeting the definition given above.

The organic compound defined above corresponds according to the invention to the following formula: R _! -0-CO-NH-R-NH-CO-0-R ₂ (I), in which R is a divalent radical preferably chosen from the groups alkylene of 1 to 10C, cyclic aromatic groups of 6 to 10C such as the phenylene group optionally substituted for example by one or more alkyl groups of 1 to 6C such as methyl, groups comprising several cyclic aromatic groups of 6 to 10C optionally substituted for example by one or more alkyl groups from 1 to 6C, and linked by a single bond or by a divalent group such as an alkylene group from 1 to 10C and R 1 and R ₂ independently represent an alkyl group from 1 to 6C such than the ethyl group or a 6-10C cyclic aromatic group such as the phenyl group.

This organic compound can be defined because of its consistency as being a resin. Preferred compounds are ethyl hexamethylene dicarbamate, ethyl toluene dicarbamate and ethyl 4,4-methylene bisphenyl dicarbamate.

The compounds used in the process of the invention are dicarbamates or diurethanes and not monourethanes or monocarbamates and have the advantage of being able to be prepared using precursors of the di-isocyanate type which are compounds widely available industrially , of low cost and which are used for the manufacture of polyurethanes.

These isocyanates are in particular 1 examethylene diisocyanate (HDI), toluene diisocyanate (TDI) and 4,4 'methylene bisphenyl diisocyanate (MDI). Isocyanates react easily on an alcohol, for example an aliphatic monoalcohol from 1 to 10C such as methanol, ethanol, or a 6 to 10C cyclic aromatic alcohol such as phenol to give dicarbamates or diurethanes which can be used directly in the process of the invention to impregnate the substrate, for example the wooden substrate.

The contacting, namely the impregnation of the substrate with the organic compound, can be carried out using a solution of the latter in a solvent. Generally, this contacting consists in immersing the substrate comprising wood, for example the wooden substrate, in the solution of the organic compound.

The solvent is generally chosen from non-toxic aliphatic alcohols from 2 to 10C such as ethanol, non-toxic aromatic cyclic alcohols from 6 to 10C, aliphatic ketones from 2 to 10C

10C such as acetone, organic solvents having compatibility with the organic compound

(diurethane or dicarbamate), water, and their mixtures. The solution usually contains 30 to

100% by mass of the organic compound.

The solution may also contain an agent capable of imparting biocidal properties to the substrate, such as boric acid. Indeed, carbamate alone or mixed with alcohol is a good solvent for boric acid and it is therefore possible to mix boric acid with di (poly) carbamate (urethane), before the impregnation of the substrate of a material comprising wood, for example wooden substrate, for fixing boron in the substrate of a material comprising wood, for example in the wooden substrate.

The advantage of fixing a boron salt, reputed to be a weakly toxic biocide in the substrate made of a material comprising wood, for example the wooden substrate makes it possible to improve the resistance of the substrate against attack. organic.

The "biocidal" agent when present represents from 10 to 30% by weight of the solution. When operating with the organic compound dicarbamate or diurethane, in solution, contacting can for example be carried out as follows: the substrate made of a material comprising wood is introduced, for example the wooden substrate into a reactor sealed and the organic compound dicarbamate is likewise introduced in the form of a solution in said reactor.

To facilitate the diffusion of the dicarbamate in the substrate, the substrate and the organic compound dicarbamate are then heated in the liquid state in the form of a solution in a solvent at a temperature generally from 20 to 100 ° C., preferably from 20 to 80 °. C, more preferably from 50 to 70 ° C, for example from 60 ° C.

Indeed, above 100 ° C, there is a risk of irreversible modification of the wood which can undergo, for example, pyrolysis or combustion, while below 20 ° C, the kinetics of penetration are generally too low .

The duration of the contact can be between 5 hours and 48 hours. This duration will be chosen according to the specifications beforehand defined, relating in particular to the depth of the desired impregnation within the volume of the substrate made of a material comprising wood, for example of the wooden substrate, to the quantities and to the geometry of the pieces of substrate made of a material comprising wood, for example pieces of wood in the treatment chamber, etc.

The contacting is generally carried out at atmospheric pressure. An advantageous variant of the process of the invention called "vacuum-pressure process" consists in placing the substrate to be treated, to be impregnated - having or not having undergone a pretreatment with a swelling agent - in a vacuum enclosure for example in an enclosure under a vacuum of 10 to 100 mbar, in order to degas the substrate, then to carry out the actual contact with the diurethane or dicarbamate under pressure, that is to say by establishing a pressure on the solution with a solvent or the compound molten, for example a pressure of 5 to 10 bar to force the liquid to enter the open porosity of the substrate made of a material comprising wood, for example wooden substrate.

At the end of the chemical treatment according to the invention, of the impregnation, of the contacting whatever it is, the substrate in a material comprising wood, for example the wooden substrate is dried generally for example at a temperature of 60 ° C for a period generally of 5 to 24 hours. The method according to the invention applies particularly to the field of wood conservation, vis-à-vis in particular aggressions induced by 1 humidity.

Thus, the method according to the invention is intended for wood maintained outside, forming part, for example, of cladding, shutters, windows, doors, gates, stakes, signs, posts, garden furniture, and other elements of joinery outdoor, etc.

The method according to the invention also finds applications in the building, where the wood is part of frames, furniture, for example of bathroom or kitchen, stairs, parquet floors, etc ...

The method according to the invention can be applied to wooden structures such as walkways, bridges, structures, frames and other wooden objects used in maritime activities.

The invention will now be described with reference to an example, given by way of illustration and not limitation.

Example

In this example, the stabilization of a massive sample of Scots pine is carried out by the method of the invention by proceeding in a first step or step prior to the humidification of the wood or swelling of the wood, then in a second step by treating wood using ethyl hexamethylene dicarbamate in solution in ethanol. First step: humidification and pre-swelling of the wood

A sample of dry Scots pine weighing approximately 100 g and measuring 15 x 7.5 x 1.5 cm ^{3 is placed} in a closed bottle containing 40% of the mass of dry wood in water.

This bottle containing the wood sample and the water is placed in an oven at 50 ° C for 24 hours. The humidity of the wet wood sample thus obtained is 40% by mass: the wood has absorbed all of the water.

Second step: impregnation of the wood

The humidified wood sample is introduced during the first step, into a stainless steel reactor containing a solution consisting of 50% by mass of ethanol and 50% by mass of ¹ hexamethylene ethyl dicarbamate of formula:

C ₂ H ₅ -0-CO-NH-C ₆ Hι ₂ -NH-CO-0-C ₂ H ₅ . Then the reactor is heated at 70 ° C for 24 hours at atmospheric pressure.

The sample is then dried to remove residual moisture and ethanol.

Wood stability measurements are carried out on the sample by comparing the dimensional instability of the wood before and after treatment of the wood according to a process consisting in measuring the volume of the sample with the caliper. The measurements show that an ASE ("Anti Shrinkage Effect") greater than 50% is obtained. REFERENCES

[1] Goland V.A., Khinskaya O.V., Mikhailova

I.A., Procedure for treating and preserving wood to harden surface layer includes coating surface of wood with impregnating composition base on polymers, patent

GB-A-2100288.

[2] Matsushita Electric Works, Ltd.,

Preparation of inorganic board having finished surface by laying wooden plate on core of urethane resin and binder, then shaped and cold pressing, patent n ° 59088383, 1984, Japan.

[3] Park S.B., Development of surface improvement technique of Japanese larch flooring board, Journal of the Korean Wood Science and Technology, 1999, 27 (3), 31-38.

[4] West M.H., West M., Two-step treatment for preservation and coloring of wood-using copper cpd. and dithiocarbamate cpd. in either order, GB-A-2222773, 1990.

[5] Mikasa Chemical Industrial Co., Preserving Wood, Patent No. 215-28, 1975, Japan.

[6] Tokyo Organic Chem Ind Co. Ltd, Preventing deterioration of wood by applying ammonium monomethyldithiocarbamate, patent No. 1206002, 1988, Japan.

[7] Gattner H., Wagner K., Dilutable benzimidazole carbamate formulation -prepd. by reaction with aldehyde and alcohol, useful as biocide, esp. fungicide, patent no. 2904390, 1980, Germany. [8] Brandes W., Genth H., Hanssler G., Kuhle E., Paulus W., Reinecke P., Sulphenylated carbamic acid esters, a process for their preparation and their use, patent n ° 4798905, 1989, USA United. [9] Uchama N., Kurisaki H., Method for preserving wood., Patent n ° 358-830, 1991, Japan.

[10] Yamamoto 0., Kato H., Waj ima T., Wood preservatives, patent n ° 215-28, 1975, Japan.

[11] D. Lopez, G. Burillo, "Gamma-ray irradiation of polystyren in the presence of the cross-linking agent", Radiation Effects on Polymers, ACS

Symposium Series 475, published by American Chemical

Society, 1991, pp. 262-270.

[11 bis] A. J. Morak, K. Ward, D. C. Johnson, Tappi Vol. 53, N ° 12, December 1970, pp. 2,278-2,283.

[12] C.B. Saunders, A. Singh et al., "Electron beam curing of aramid-fiber-reinforced composites, Radiation Effects on Polymers, ACS Symposium Series 475, published by American Chemical Society, 1991, pp. 251-261.

[13] J.J. Weiland, Thesis "Physico-chemical study of wood heat treatment: optimization of parameters of the retification process", January 26, 2000, pp. 49-57.

[17] Banks W.B., Lloyd, Mechanical properties of alkyl isocyanate modified Scots pine wood surffaces, 1986, 18 (4), 259-262.

[18] Kutsenko LI, Kiselev AD, Danilov SN, Phosphorylated cellulose derivatives. VI. Urethanation of cellulose by phosphorus containing isocyanates, Zh. Prikl. Khim. 1967, 40 (10), 2308-13.

[19] Owen N.L., Banks W.B., West H., FTIR studies of the wood isocyanate reaction, J. Mol. Struct., 1988, 175, 389-94.

[20] West H., Banks W.B., Preparation of buthyl carbamates of wood, Wood and cellulosics, 1987, pp. 135-142, Ellis Horwood Limited Chichester.

[21] Rowell R.M., Ellis W.D., Chemical modification of wood: reaction of methyl isocyanate with southern pine, Wood Science, 1979, 12 (1), 52-58.

Claims

1. Process for the chemical treatment of a substrate made of a material comprising wood, in which said substrate is brought into contact with at least one organic compound of molar mass less than 500 comprising at least two carbamate or urethane functions of formula -NH- CO-O-, said compound corresponding to the following formula (I): Rι-0-CO-NH-R-NH-CO-0-R ₂ (I) in which R is a divalent group preferably chosen from the groups alkylene from 1 to 10C, cyclic aromatic groups from 6 to 10C such as the phenylene group optionally substituted, for example one or more alkyl groups from 1 to 6C such as methyl, groups comprising several cyclic aromatic groups from 6 to 10C optionally substituted for example by one or more alkyl groups from 1 to 6C, and linked by a single bond or by a divalent group such as an alkylene group from 1 to 10C; and Ri and R ₂ independently represent an alkyl group of 1 to 6C such as the ethyl group or a cyclic aromatic group of 6 to 10C such as the phenyl group. 2. Method according to claim 1, in which the organic compound is chosen from ethyl hexamethylene dicarbamate, ethyl toluene dicarbamate and ethyl 4,4'-methylene bisphenyl dicarbamate. 3. Method according to any one of claims 1 to 2 wherein the organic compound is prepared by reaction of a diisocyanate precursor with a monoalcohol, for example an aliphatic alcohol of 1 to 10C such as methanol, ethanol, or an aromatic cyclic alcohol of 6 to 10C such as phenol. 4. The method of claim 1, wherein the substrate is contacted with a solution of the organic compound in a solvent. 5. The method of claim 4, wherein the contacting is carried out by immersion of the substrate in the solution of the organic compound. 6. Method according to any one of claims 4 and 5, in which the solvent is chosen from non-toxic aliphatic alcohols of 2 to 10C, such as ethanol, non-toxic aromatic aliphatic alcohols of 6 to 10C, ketones aliphatic from 2 to 10C such as acetone, organic solvents having compatibility with the organic compound, water, and mixtures thereof. 7. Method according to any one of claims 4 to 6, in which the solution contains from 30 to 100% by mass of the organic compound. 8. Method according to any one of claims 4 to 7, in which the solution also contains an agent capable of imparting biocidal properties to the substrate such as boric acid. 9. Method according to any one of claims 4 to 8, in which the contacting is carried out at a temperature of 20 ° C to 100 ° C, preferably from 20 to 80 ° C, more preferably from 50 to 70 ° C, for example 60 ° C for a period of 5 to 48 hours. 10. Method according to any one of claims 1 to 9, wherein, prior to contacting with the organic compound, the substrate is treated with a swelling agent. 11. The method of claim 10, wherein the swelling agent is chosen from water, non-toxic aliphatic alcohols of 2 to 10C such as ethanol, non-toxic aromatic cyclic alcohols of 6 to 10C, hydrophilic compounds non-toxic and mixtures thereof. 12. The method of claim 11, wherein the swelling agent is water and the substrate is treated, preferably by immersion in liquid water for a period of 5 to 48 hours, preferably from 12 to 24 hours at a temperature of 20 to 70 ° C, preferably 30 to 60 ° C. 13. The method of claim 12, wherein at the end of the treatment with water, the substrate has a humidity of 20 to 50% by mass. 14. Method according to any one of claims l to 13, in which the substrate is chosen from substrates made of a material comprising at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight of wood, better 100% by weight of wood. 15. A method according to any one of claims 1 to 14, wherein the substrate to be treated is placed in a vacuum chamber and then contacting with the organic compound is carried out under pressure. 16. Method according to any one of claims 1 to 15, in which, at the end of the treatment, the substrate is dried, for example, at a temperature of 60 ° C for a period of 5 to 24 hours.