WO2006125797A1 - Method for strengthening and stabilizing a substrate made of a material comprising wood - Google Patents

Abstract

The invention concerns a method for treating a substrate made of a material comprising wood wherein the two following steps a) and b) are combined: a) contacting said substrate with an aqueous solution of at least one water-soluble hydrophilic organic compound, whereby said hydrophilic compound penetrates into the cell wall of the wood; b) carrying out the following three successive steps: b1), b2) and b3): b1) optionally drying said substrate; b2) contacting said substrate with at least one polymerizable and/or crosslinkable hydrophobic organic compound, whereby said compound penetrates into the porosity of the wood; b3) polymerizing and/or crosslinking said polymerizable and/or crosslinkable hydrophobic compound inside the porosity of the wood. The invention also concerns a substrate made of a material comprising wood, said substrate comprising in the porosity of the wood at least 40 %, preferably more than 50 %, more preferably above 60 %, by volume of a polymerized and/or crosslinked compound and 1 to 30 % by volume of a hydrophilic compound such as PEG in the cell wall and the porosity of the wood.

Description

 METHOD FOR PROCESSING CONSOLIDATION AND STABILIZATION OF A SUBSTRATE IN A MATERIAL COMPRISING

WOOD

DESCRIPTION

TECHNICAL AREA

The invention relates to a method for consolidating and stabilizing a substrate made of a material comprising wood, in order to obtain a modified impregnated substrate provided with specific properties, in particular mechanical, physical and chemical properties, that the substrate material comprising wood, for example the wooden substrate does not naturally possess.

In the present description, the term "material comprising wood" generally means a material comprising a majority proportion of wood. By "majority proportion" is generally meant 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" is generally understood to mean not only pure wood, but also material comprising wood.

This process applies, in particular, to the treatment of wood, in order to give it the desired mechanical, physical and / or chemical properties, in particular, to preserve it, to preserve it, to improve its resistance and to protect him against different types of chemical, biological and / or physical aggressions.

In other words, the method of the invention aims to obtain a material comprising wood, for example wood, having a better resistance to external conditions - and, in particular, a better intrinsic stability vis-à-vis the environmental humidity, which means that the material comprising wood, for example wood, swells less or not at all while taking up moisture, or undergoes less, if not more, shrinkage during a period of time. drying, better hardness, better resistance to abrasion, better mechanical resistance and better resistance against attack by living organisms capable of degrading the material comprising wood such as wood, for example fungi , insects and bacteria.

The method according to the invention also aims to substantially improve the mechanical properties of materials comprising wood.

It is known that it is possible, in order to consolidate the wood, to densify the wood using physical methods to polymerize in-situ organic matter in the wood [1-2]. These treatments are carried out in two stages: a first stage of impregnation of 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. With the aid of these densification processes, hydrophobic plastic material 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 to modify the wood's sensitivity to moisture, because Hydrophobic resins are unable to penetrate the cell wall. 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 and remains very sensitive to cracking during a humidification / drying cycle. . A process which combines both impregnation and grafting techniques is described in document ([3]). This document relates to a method of treating a wooden element, preferably so-called "standing" wood comprising an impregnation step and a crosslinking step. During the impregnation stage, said element is impregnated with an impregnating substance chosen from mono and / or polyfunctional water-soluble compounds having one or more active hydrogen atoms and having the property of swelling the cell walls of the wood.

These impregnating substances are preferably monols or polyols, in particular hydrophilic resins rich in hydroxyl functional groups (OH), such as mono and polyol polyethers, such as the products of polymerization of cyclic oxides such as oxiranes, oxetanes and oxolanes. their derivatives substituted such as ethylene oxide, propylene oxide and tetrahydrofuran.

During the crosslinking step, the impregnating substance is reacted, optionally in the presence of a catalyst, with a crosslinking agent or coupling agent so as to obtain at least one crosslinking agent which is insoluble in the wood. the water. The impregnation step and the crosslinking step are carried out from the same bath. The crosslinking and grafting agents are chosen from diisocyanates and polyisocyanates and are capable of polymerizing either with the hydrophilic resin or with the alcohol functions of wood. The approach described in this document requires a heating of the wood to initiate the chemical reaction between the crosslinking agent and the labile hydrogens. In this way, it is possible to constitute "an interpenetrating network between the polyurethane chains and the polymers constituting the cell walls of the wood" by keeping the wood inflated and making it less sensitive to moisture.

However, this process is cumbersome because it uses reactive systems that are potentially dangerous to implement as di-isocyanates.

In addition, this process is difficult to control because the crosslinking agent must polymerize with the hydrophilic resin and with the constituent elements of the wood; this is the reason why it is recommended to put an excess of crosslinking agent with respect to the reactive functions of the resin hydrophilic. Since the exact number of moles of reactive wood functions available is not known, it is practically impossible to control the stoichiometry of all the reactions that will take place in the wood. As a result, there is likely to be an excess of crosslinking agents in the wood at the end of the treatment. This excess of "free" isocyanate reagent in the wood that has not been used during the polymerization reactions must undergo expensive additional cleaning and / or neutralization treatments either to remove it from the wood or to fix it. safer way in the structure of the wood. The rate of polymerization of the reagents is not guaranteed either; therefore, the quality of the final synthetic polymer obtained in the wood is poor and does not significantly improve the intrinsic mechanical properties of the wood.

It is also known from documents [4] and [5] that polyethylene glycols or PEG 2000, 4000 ([4]), 300 and 600 ([5]) are molecules which have an important stabilizing power of wood. However, since these molecules are soluble in water, the effectiveness of the treatment is not sustainable, the PEG is leached if the wood is again in contact with a source of moisture. In addition, PEG treatments do not confer any additional mechanical properties on wood; the resin itself has no intrinsic mechanical strength. There is therefore an unmet need for a process which makes it possible in particular to stabilize the wood with respect to impregnation / drying, while improving the mechanical properties of wood and giving it new ones.

There is also a need not yet met for a process that allows treatment in the whole wood, both at the heart of it, and on the surface, it must also implement readily available reagents of a low cost, and zero or very low toxicity. 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, among other things, all the needs mentioned below and which, inter alia, responds the criteria and requirements given 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 processes of the invention. prior art and that provides a solution to the problems of the processes of the prior art.

This and other objects are achieved according to the invention by a method of treating a substrate made of a material comprising wood in which the following steps a) and b) are combined: a) contacting said substrate with an aqueous solution of at least one hydrophilic organic compound soluble in water, whereby said hydrophilic compound penetrates into the cell wall of wood; b) - the following three steps are successively carried out: b1), b2) and b3) b1) - said substrate is optionally dried; b2) - said substrate is brought into contact with at least one polymerizable and / or crosslinkable hydrophobic organic compound, whereby said compound enters the porosity of the wood; b3) - polymerizing and / or cross-linking said hydrophobic compound polymerizable and / or crosslinkable in the porosity of the wood.

Advantageously, step b) is carried out after step a), but the opposite is also possible, that is to say that one begins by carrying out the impregnation, polymerization with the hydrophobic compound, then performs as a final step the impregnation with the hydrophilic compound. Advantageously, said hydrophilic organic compound, soluble in water, is solid at ambient temperature (generally 10 to 30 ^° C., for example 20 to 25 ^° C.).

Advantageously, said hydrophilic compound which is soluble in water is chosen from compounds comprising at least one polar function.

Advantageously, the one or more polar function (s) is (are) chosen from hydroxyl and amino functions. Advantageously, the hydrophilic compound is chosen from polyfunctional compounds comprising several polar functions such as polyols.

Among the polyols, poly (alkylene) glycols in which the alkylene group has from 2 to 3 C, such as polyethylene glycols (PEG), such as PEG 4000 solid at room temperature, PEG 2000, PEG 1500, are preferred.

According to the invention, the substrate is brought into contact with an aqueous solution of the hydrophilic compound, since, in particular in the case where the hydrophilic compound is solid at ambient temperature, this makes it possible to avoid the phenomenon of bleeding of the compound.

Advantageously, the contacting is performed by immersing the substrate in the solution of the hydrophilic organic compound.

Advantageously, said hydrophobic compound must be solid at ambient temperature, after polymerization and / or crosslinking. Before polymerization and / or crosslinking, the hydrophobic compound must be generally liquid at room temperature to allow impregnation of the wood. On the other hand, after polymerization, the hydrophobic compound, the resin cures. Advantageously, the at least one polymerizable hydrophobic compound is chosen from styrene-polyesters; hydrophobic (meth) acrylic compounds such as (meth) acrylates; and other ethylenically unsaturated compounds such as ethylene, propylene; epoxy resins; the resins polyurethanes; acrylonitrile resins; and their mixtures.

The method according to the invention implements an association of specific steps, namely a step of bringing into contact, more precisely of impregnation, the substrate with a hydrophilic compound, in solution in water (a), and a step (b) comprising optionally drying said substrate (b1), then contacting (b2), more precisely the impregnation, of the substrate with a polymerizable and / or crosslinkable hydrophobic compound, followed by polymerization and / or crosslinking ( b3) of said polymerizable and / or polymerizable hydrophobic compound.

The order of steps a) and b) can be arbitrary, but preferably the specific steps a) and b) are performed in a specific order: ie step a) is performed before step b).

However, the two steps a) and b) can also be reversed with respect to this preferred order, step b) then preceding step a).

Such a specific association of specific steps is neither described nor suggested in the prior art. The same is true of the preferred specific succession in which step b) follows step a).

The process according to the invention is fundamentally different from the processes of the prior art and in particular from the process described in document [3] EP-A-1 447 189 not only by the combination and possibly the sequence of steps which it comprises but also by the conditions and the reagents specificities that are implemented in each of the steps.

The method according to the invention can be defined as a process which combines a chemical treatment of wood which consists in impregnating the material comprising wood, such as wood with a hydrophilic compound, more specifically a hydrophilic resin, capable of dimensionally stabilizing the wood. against moisture by penetrating its structure, more specifically by penetrating into the cell wall of the wood, with a second treatment which consists in impregnating the material comprising wood, such as wood, with a compound hydrophobic, more specifically a hydrophobic resin capable of polymerizing and / or cross-linking inside the pores of the wood to substantially improve the mechanical properties of the composite material thus obtained. This composite material could be called a wood-plastic composite.

As indicated above, the impregnation of the material comprising wood, such as wood, with a compound, a hydrophilic resin, is firstly carried out, then, in a second step, the impregnation is carried out. material comprising wood, with a compound, resin, hydrophobic.

The compound, the hydrophilic resin used for the impregnation of step a) which is preferably the first impregnation, is hydrophilic, soluble in water, which makes it very convenient to use water for carry this resin within the cell wall which is a very medium hydrophilic. Indeed, the constitutive elements of the cell wall of wood such as cellulose, hemicellulose, lignin, are molecules rich in hydroxyl polar functions (-OH). This operation is very easily done during one of the two steps of the process according to the invention (step a)), for example by simply impregnating the wood with an aqueous solution.

When step b) follows step a), after the eventual drying of step b1), the molecules of the hydrophilic resin remain in the cell wall and keep it swollen; which makes it possible to reduce the dimensional instability of the wood vis-à-vis cycles of humidification and drying. Importantly, the material such as wood, stabilized by the hydrophilic compound during step a), retains a porous structure which can, during step b) when it follows step a), penetration hydrophobic compound within this porosity: "heart".

According to the invention, the compound, resin, used in the contacting step, impregnation b) is, unlike the compound, resin used in the first step a), a hydrophobic compound. Moreover, when step b) follows step a), this particular succession of treatments, first of all by a specific hydrophilic compound, then by a hydrophobic specific compound, is one of the essential characteristics of the process of the invention and allows to obtain, more importantly, the advantages and effects of the method of the invention. In particular, the efficiency of the process in terms of stabilization is notably greater when step a) precedes step b).

Because the compound resin used in this step b) is hydrophobic, it can not penetrate the cell wall of wood, which is, as explained above a hydrophilic medium. The hydrophobic resin thus penetrates only into the porosity, into the pores of the wood, and remains in these pores, it does not penetrate even within the cell wall of the wood.

This penetration of the hydrophobic compound into the "core" porosity is in particular possible, when, preferably, step a) is carried out first, because then at the end of step a), the porosity is retained. Again, like step a), step b) comprises a simple impregnation step b2) which can be very easily performed, for example by immersion in the liquid hydrophobic compound such as the hydrophobic resin. There is generally no solvent, the hydrophobic compound, such as a resin is used pure.

The hydrophobic resin is chosen from polymerizable and / or crosslinkable compounds. This polymerization and / or crosslinking is carried out during step b3) of the process according to the invention.

It should be noted that this polymerization and / or crosslinking of the compound, the hydrophobic resin, occurs in the porosity of the wood and that, unlike, for example, the process described in document [3] EP-A-1 447 189, this polymerization and / or crosslinking does not use the constituents of the wood, especially through -OH functions, or the hydrophilic compound. It can be said that the hydrophobic compound polymerizes, crosslinks, with itself, to polymerize, crosslink or "self-curing" and / or "self-controlling".

The stoichiometry of this step is in contrast to the method of document [3] perfectly controlled since it does not depend on uncertain parameters such as the amount of hydrophobic resin present and / or the amount of hydrophilic groups. The stoichiometry simply corresponds to the initial stoichiometry, precisely known, of the hydrophobic compound which is injected into the material comprising wood such as wood.

In addition, surprisingly, the presence of the hydrophilic resin in the wood does not inhibit the polymerization of the hydrophobic resin, and on the other hand the polymerization of the hydrophobic resin considerably slows down the penetration of the hydrophilic resin into the wood, but does not render it not impossible.

For this reason, among other things, it is preferable to carry out step a) before step b). There is no interaction between the hydrophobic resin and the hydrophilic resin, which operate independently, but the combination of effects leads to particularly advantageous results. In other words, the "decoupling" that exists between the compound, hydrophilic resin and the compound, hydrophobic resin, allows to choose independently the two resins to optimize the performance that is expected of them, namely the hydrophilic resin must fit easily into the cell wall of wood as a blowing agent, while the composition the hydrophobic resin must allow easy polymerization / crosslinking as well as obtaining very good mechanical properties when the polymer is formed in the pores of the wood. Since the choice of each of the hydrophilic and hydrophobic compounds is not limited by the choice of the other compound, the range of choice possible for the hydrophilic compound and the hydrophobic compound is thus widened. Surprisingly, it has been found that the densification by polymerization of the compound, the hydrophobic resin, practically blocks the compound, the hydrophilic resin in the cell wall of the wood, even if the hydrophilic resin is still free since it did not participate in the polymerization. Therefore, surprisingly and quite advantageously, the hydrophilic resin, however soluble in water is hardly leachable by water as is the case for example in documents [4] and [5] where this resin is implemented alone. Blocking of the hydrophilic resin is achieved much more effectively when step a) precedes step b).

It is therefore preferable and advantageous to respect the specific preferred order of the specific treatments of the process according to the invention, namely the stabilizing the wood (step a)) prior to densification of the wood (step b)).

At the end of the treatment according to the invention, the substrate made of a material comprising wood has its mass increased by at least 50% with respect to its initial mass. Thanks to the swelling-stabilization, a massive impregnation of the material is obtained by the hydrophobic resin compound which leads to a significant improvement in the mechanical properties of the material. The degree of impregnation with the hydrophobic compound is generally from 40 to 70% by weight of the material.

Unlike wood alone, the material obtained by the method according to the invention can be defined as a wood / plastic composite material that has characteristics that make it suitable for many outdoor applications where it is required a good resistance especially to humidification / drying, biological contamination for example by fungi, insects, bacteria, mechanical stress, ultraviolet, and thermal fatigue.

The multiple advantages and surprising effects of the invention can therefore be enumerated as follows, without this enumeration being considered as limiting:

- Excellent stabilization of the substrate is obtained in a material comprising wood, such as the wood substrate, vis-à-vis moisture, this stabilization can be expressed by the parameter called ASE ("Anti Shrinkage Efficiency"). The ESA is defined by the following equation

CC

ASE untreated wood treated wood xlOO

(%) ^D untreated wood

with the following definition of S:

_B ^ ois untreated or treated wood volume wet - dry wood volume xlOO

(%) dry wood volume

- One can also define a particular ASE in which reference is made not to the volume of the wood sample but to one of the dimensions of the wood; for example in the case of a wood blade it may be the length (L) of the width (1) or the thickness (e). The partial ASE coefficient ASE _P relative to the width (1) can therefore be expressed by the following equation:

CC

Untreated wood treated wood

ASE _p (%) = C x 100

Untreated wood

with the following definition of S _E

1 wet wood arg- 1 dry wood arg

S Tp, wood not ₄ t-rai ₄ te- or ₄ t-rai ₄ t_e, (%) = _{λ arg eur bolΞ Ξec} x 100

The wood is usually dried in an oven at 105 ⁰ C for 24 hours and the wood is generally moistened by immersion in water at 60 ^° C. for 24 hours.

According to the invention, the ESA is generally at least 50%, preferably at least 60%, and more preferably at least 70%.

It is thus possible to use the substrate made of a material comprising wood, such as the treated wood substrate, externally, since it is given by the process of the invention a better resistance to weathering due to bad weather conditions. .

This stabilization of the wood is preserved even after leaching with an aqueous solution because, as has been seen above, the hydrophilic compound is practically blocked in the wood by the hydrophobic compound.

The compounds used according to the invention are little or no toxic, and are therefore easy to use in the context of an industrial process. The process of the invention that can be qualified for the impregnation treatment stages a) and b) does not necessarily require very harmful or dangerous chemical catalysts, solvents, adjuvants or blowing agents, of the tetrahydrofuran (THF), dichloromethane, pyridine, dimethylformamide (DMF), triethylamine type, whether for transporting the compounds, resins, used according to the invention within the structure of the substrate in a material comprising wood, such as as the wood, or to clean the substrate of any treatment residues not fixed by the substrate of a material comprising wood, such as wood substrate. In particular, the impregnation of step a) is carried out simply in aqueous solution.

The cost of the process, as well as the accessibility of the technology necessary for carrying out the process, allow its use in industry.

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 only to its surface, unlike varnish treatments. and further, in addition, the effectiveness of the treatment is ensured even if the surface is altered. - Unlike a composite material based on wood particles, the wood / plastic composite material obtained by the process according to the invention retains the natural aesthetic appearance of solid wood with its veining. - The method according to the invention does not damage the material comprising wood substrate, such as wood, including the external appearance of the substrate is not impaired, and the mechanical properties of the material comprising wood such as wood are substantially improved, it is in particular the hardness and the resistance to compression and bending. The composite material obtained by the process according to the invention is not toxic and does not release toxic substances throughout its lifetime. The compounds and resins used according to the invention, whether it be the hydrophilic compound or the hydrophobic compounds are available industrially in large quantities and at moderate costs, which makes the implementation of the treatment viable.

The invention also relates to a substrate made of a material comprising wood, said substrate comprising in the porosity of the wood at least 40%, preferably more than 50%, better still more than 60%, by mass of a polymerized compound and / or crosslinked, and 1 to 30% by weight of a hydrophilic compound such as PEG in the cell wall of the wood and the porosity of the wood.

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, it has been seen above that by material comprising wood was generally meant a material comprising a majority proportion of wood (by weight), namely a material comprising at least one less than 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 consists entirely of 100% wood (considering the impurities naturally present in it). Wood includes polar functions which are the hydroxyl functions of cellulose, hemicellulose and lignin. Wood is a porous material comprising an open porosity defined by cell walls. According to the invention, the treated substrate may be a dry substrate but it may also be a wet substrate which, surprisingly, can be treated by step a) of the process of the invention. By wet substrate, is generally meant 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 may, contrary to the processes of the prior art be treated directly by step a) of the method of the invention, which avoids proceeding beforehand. a thorough drying, consuming 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. According to step a) of the process according to the invention, the substrate is brought into contact with at least one hydrophilic organic compound. This step a) is preferably carried out before step b).

This step a) can be defined as a wood stabilizing treatment by impregnating it with hydrophilic organic substances that can penetrate the intimacy of the cell walls of the wood.

The substrate may be contacted with a single hydrophilic organic compound or a plurality of hydrophilic organic compounds.

This hydrophilic organic compound can be generally defined because of its consistency as a resin. The hydrophilic organic compound, soluble in water, is generally chosen from the compounds hydrophilic compounds comprising at least one polar function selected for example from hydroxyl and amine functions.

Preferably, these water-soluble compounds are polyfunctional molecules comprising several polar functions in other words rich in polar functions of hydroxyl or amine type.

In addition, the hydrophilic organic compound is preferably a solid at room temperature. Many molecules can be envisioned for the hydrophilic organic compound soluble in water.

Non-exhaustively, there can be mentioned, for example, polyols such as poly (alkylene) glycols in which the alkylene group generally has 2 to 3 C.

These poly (alkylene glycol) generally have a molecular weight of 1000 to 10,000.

The preferred poly (alkylene glycol) are poly (ethylene glycols) of a molecular weight, for example of 1500, 4000 such as PEG 1500, PEG

4000, but it would be possible to use also poly (propylene glycol) of the same molar mass.

The contacting, namely the impregnation of the substrate with the hydrophilic organic compound can be carried out using a solution of the latter in water, which allows the hydrophilic resin to diffuse within the cell walls , in all the volume of the substrate, of the considered object, treated.

Generally, this bringing into contact consists of an immersion of the substrate comprising wood, for example of the wooden substrate, in an aqueous solution of the hydrophilic organic compound.

The solution generally contains from 20 to 40% by weight of the hydrophilic organic compound.

The contacting may for example be carried out in the following manner: the substrate is introduced into a material comprising wood, for example the wooden substrate, in a sealed reactor and the hydrophilic organic compound is likewise introduced in the form of an aqueous solution. in said reactor.

To promote the kinetics of impregnation, to facilitate the diffusion of the hydrophilic organic compound into the substrate, the substrate and the hydrophilic organic compound are generally heated in the liquid state in the form of an aqueous solution (the substrate is immersed in a solution bath of the hydrophilic organic compound) at a temperature generally of 20 to 100 ^° C., preferably 30 to 80 ^° C., more preferably 40 to 60 ^° C.

In fact, above 100 ^° C., there is a risk of irreversible modification of the wood which may for example undergo pyrolysis or combustion, whereas below 20 ^° C. the kinetics of penetration is generally too low.

The duration of the contacting can be between 5 hours to several days, for example 5 days.

This duration will be chosen according to the previously defined specifications, relating in particular to the depth of the desired impregnation within the volume of the substrate in a material comprising wood, for example wooden substrate, the quantities and geometry of the substrate parts of a material comprising wood, for example pieces of wood in the treatment chamber, etc. The larger the pieces, objects to be treated, the longer the contact time, for example immersion, will be important to ensure that the resin penetrates properly to the heart of the wood.

The contacting with the hydrophilic organic compound solution is generally carried out at atmospheric pressure.

In order to facilitate and accelerate the impregnation of the substrate, for example wood, it is possible, with or without heating under the conditions described above, to implement a so-called "vacuum-pressure process" process. This method consists of placing the substrate to be treated, impregnating in a vacuum chamber, for example in a chamber under a vacuum of 10 to 100 mbar, in order to degas the substrate, then to carry out the actual contacting with the organic compound. hydrophilic pressure, that is to say for example by establishing a pressure on the bath of the aqueous solution in which the substrate is immersed, for example a pressure of 5 to 10 bar, to force the liquid to enter the open porosity of the substrate of a material comprising wood, for example wood substrate.

At the end of the chemical treatment of step a) according to the invention, the impregnation, whatever contacting, the substrate made of a material comprising wood, for example the wooden substrate can be dried in order to remove the water from the wood, generally for example at a temperature of 30 ^° C. to 100 ^° C. for a period generally of 5 to 120 hours (this is step b1) . The optional step b1) is carried out at the end of step a) if it, as above, precedes step b) but if the process is started with step b), it wood must also be dried by implementing step b1). The substrate may in particular be dried in an oven.

The drying step b1), generally carried out under the conditions of temperature and time described above, makes it possible to eliminate almost all the water contained in the wood and to obtain a "dry" wood. For example, before drying, the water content of the wood is generally 20 to 100%, and after drying it is generally less than or equal to 20%, for example 5 to 20%. Indeed, for the polymerization / crosslinking (step b3)) to be carried out correctly, the wood must generally be dry.

At the end of steps a) and b1), the impregnation rate of hydrophilic organic compound, for example PEG, calculated as being the ratio (dry mass of the substrate after impregnation / densification - dry mass of the substrate before impregnation / densification ) on dry mass of the substrate before impregnation / densification, is generally from 1 to 30%. The hydrophilic organic compound such as

PEG has penetrated the cell wall of wood. The wood is in an inflated state but retains its porous structure while having lost most of its water due to the drying step.

The swollen state, with a preserved porous structure, of the wood allows easy penetration of the hydrophobic compound during step b) of the process according to the invention when step b) preferably follows step a).

In consolidation step b), the substrate is brought into contact with at least one polymerizable and / or crosslinkable hydrophobic compound.

This step b) can be defined as a wood consolidation treatment by impregnating it with compounds, resins, polymerizable, hydrophobic which will fill the pores of the wood.

This hydrophobic polymerizable and / or crosslinkable compound may be generally defined because of its consistency as a resin.

This compound, resin, can be any compound capable of polymerizing-crosslinking irrespective of the manner in which the polymerization-crosslinking is carried out. Thus, this polymerization / crosslinking can be carried out by ionizing radiation, or by thermocatalysis with tin salts, peroxides, etc. The polymerizable hydrophobic compound may be chosen from styrene-polyesters, (meth) acrylic hydrophobic compounds such as (meth) acrylates, and other ethylenically unsaturated compounds such as ethylene, propylene, etc.

The substrate may be contacted with a single hydrophobic compound or a plurality of hydrophobic compounds without a solvent.

All the hydrophobic resin, introduced into the wood participates in the polymerization, there is no solvent.

The contacting is generally carried out by immersing the substrate such as wood in the liquid hydrophobic organic compound (at atmospheric pressure and at room temperature). The contacting is generally carried out at a temperature of 20 to 30 ^° C. for a period of 12 to 48 hours. The contact with the liquid hydrophobic compound is generally carried out at atmospheric pressure.

It is generally necessary to facilitate and accelerate the impregnation of the substrate, for example wood, by implementing a pressure-vacuum process similar to that described above, at a temperature of between 20 and 30 ^° C. for a period of time. from 12 to 48 hours, the pressure being established on the liquid hydrophobic compound. Indeed, unlike step a), for step b) (b2)), the vacuum / pressure technique is usually mandatory because otherwise the resin would not enter the wood.

At the end of step b2), the polymerization, crosslinking, hardening b3) is carried out. hydrophobic compound, resin, which is inside the porosity of the substrate.

This polymerization, crosslinking, hardening, substantially improves the mechanical properties of the material, including its hardness.

The polymerization, curing, crosslinking can be carried out by any known method, for example by irradiation with ionizing radiation such as X-rays, gamma rays, electrons, ultraviolet rays, or by thermal catalysis (thermocatalysis) with tin salts, peroxides, etc.

In the case of a polymerization, curing, crosslinking by irradiation, this is generally done at ambient temperature and atmosphere.

At the end of step b), which is generally the final step of the process according to the invention, a composite material known as a wood / plastic composite is obtained whose resin impregnation ratio, a cured, crosslinked, cured hydrophobic compound is generally at least 40%, for example 40 to 70% by weight, and the degree of impregnation resin compound hydrophilic is generally 1 to 30% by weight. The method according to the invention is particularly applicable to the field of wood preservation, particularly vis-à-vis the aggressions induced by external conditions such as moisture, but it can also meet needs inside. Thus, the method according to the invention is intended for woods kept outside, making part, for example, cladding, shutters, windows, doors, gates, stakes, signs, poles, garden furniture, and other elements of exterior carpentry, etc.

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

The method according to the invention can be applied to wooden structures such as bridges, bridges, structures, carpentry and also to 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 processing of samples consisting of beech blades of dimensions 300 × 60 × 11 mm ³ by the method of the invention is carried out in a first step in the stabilization of the wood, then after drying at densification of the wood by a styrene-polyester resin, and finally to the polymerization of said resin.

Stabilization

The slides are immersed in a solution of water and polyethylene glycol 4000 at a concentration of 30% by mass. This impregnation is done at temperature and at atmospheric pressure but an acceleration of the penetration of the resin can be obtained by increasing the temperature or by using the Bethell process (vacuum press). The impregnation time at atmospheric pressure and at a temperature of 40 ^° C. lasted 15 days for blades of this geometry. At the end of this impregnation, the slides are placed in an oven at 50 ^° C. to be dried there. A regular monitoring of the loss of mass of the blades made it possible to determine the time necessary to eliminate the water contained in the wood and to allow the realization of the second phase of the treatment, namely the densification. At the end of this phase of the treatment, we obtain a wood which keeps its inflated structure; the wood is kept artificially inflated by the presence of PEG 4000 while having lost most of its water.

TABLE I

Densification

densification

It should be noted that it is necessary to proceed prior to densification to a thorough drying of the blades to eliminate as much as possible the continuous water in the wood. This drying must be done at a temperature below the melting temperature of the PEG 4000 to avoid its extraction.

The densification of the slides was done in a reactor, they are introduced into the reactor or a primary vacuum is produced; the depression made in the autoclave makes it possible to degas the wood, and also makes it possible, by suction, to fill the autoclave with a styrene-polyester resin. The viscosity of the resin is equal to 100 cp. During the entire duration of the impregnation the blades are immersed in the resin. A nitrogen overpressure of 5 bar is applied in the reactor to facilitate the good penetration of the resin throughout the volume of the wood. The duration of the impregnation is 16 hours.

At the end of the impregnation, the slides are extracted from the reactor to proceed to the last stage of the treatment: the polymerization of the resin.

Polymerization

The polymerization makes it possible to harden the resin which will block the PEG 4000 in the cell walls of the wood and substantially improve the mechanical properties of the material, in particular the hardness. The polymerization is carried out by gamma irradiation of the wood slats using sources of cobalt 60.

The dose required for complete polymerization of the resin is about 20 kGy at a dose rate of 1 kGy per hour. Irradiation of the slides was done at ambient temperature and atmosphere.

TABLE II

conclusions

It follows from the above example that it is possible to densify a wood previously stabilized with PEG 4000, the material has a porous structure allowing the penetration of a styrene polyester resin core.

The material retains an artificially inflated structure related to the presence of PEG 4000. The dimensional variations of this material will be greatly reduced by this permanent swollen state if the material is subjected to hydroscopic variations. REFERENCES

[1] 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.

[2] 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.

[3] EP-A-I 447,189

[4] Sanabria, Ernesto 0.; No, José M.; Judis, Maria A., Faculdad of Agroindustrias - U. N. N. E. "Efecto del PEG 2000 y 4000 in the radial contraccion of Aspidosperma quebracho blanco schlecht".

[5] Besold, G.; Moreno G., 1988

"Dimensional Estabilizacion of the madera of Aspidosperma quebracho blanco Schlecht by impregnacion con sustancias tanicas", Congreso Forestal Argentino,

Santiago del Estero, Argentina, Tomo III, IV, 603-606.

Claims

1. A method of treating a substrate made of a material comprising wood in which the following two stages a) and b) are combined: a) - said substrate is brought into contact with an aqueous solution of at least one hydrophilic organic compound soluble in water, whereby said hydrophilic compound penetrates into the cell wall of the wood; b) - the following three successive steps are carried out: b1), b2) and b3) b1) - said substrate is optionally dried; then b2) - is put in contact with said substrate with at least one hydrophobic organic compound polymerizable and / or crosslinkable whereby said compound penetrates into the porosity of the wood; b3) - polymerizing and / or cross-linking said hydrophobic compound polymerizable and / or crosslinkable within the porosity of the wood. 2. The method of claim 1, wherein step b) is performed after step a). The process of claim 1, wherein said hydrophilic organic compound is solid at room temperature. The method of any of the preceding claims, wherein said compound Water-soluble hydrophilic organic is selected from compounds comprising at least one polar function. 5. The method of claim 4, wherein the polar function (s) is (are) selected from hydroxyl and amino functions. 6. Process according to any one of the preceding claims, in which the hydrophilic compound is chosen from polyfunctional compounds comprising several polar functions. The method of claim 6, wherein the hydrophilic compound is selected from polyols. 8. Process according to claim 6, in which the hydrophilic organic compound is chosen from poly (alkylene) glycols or alkylene a from 2 to 3C such as polyethylene glycols (PEG) for example PEG 4000, PEG 2000, and the PEG 1500. The method of any of the preceding claims, wherein the contacting is performed by immersing the substrate in the solution of the hydrophilic organic compound. The method of any of the preceding claims, wherein the solution contains from 20 to 40% by weight of the hydrophilic organic compound. 11. Process according to any one of the preceding claims, in which the contact with the hydrophilic organic compound is carried out at a temperature of 20 ^° C. to 100 ^° C., preferably 30 ° to 80 ^° C., preferably 40 ^° C. at 60 ^° C. for a period of 5 hours to several days, for example 5 days. 12. A method according to any one of the preceding claims, wherein the contacting with the hydrophilic organic compound is carried out at atmospheric pressure. 13. Method according to any one of claims 1 to 11, wherein the substrate to be treated is placed in a vacuum chamber and then brought into contact with the hydrophilic organic compound is carried out under pressure. 14. Process according to any one of the preceding claims, in which the drying of the substrate of step b1) is carried out at a temperature of 30 to 100 ^° C. for a period of 5 to 120 hours. The process according to any one of the preceding claims, wherein said hydrophobic compound is solid at room temperature after polymerization and / or crosslinking, and liquid at room temperature. ambient temperature before polymerization and / or crosslinking. 16. The method according to any one of the preceding claims, wherein the polymerizable and / or crosslinkable hydrophobic compound is selected from styrene-polyesters; hydrophobic (meth) acrylic compounds such as (meth) acrylates, and other ethylenically saturated compounds such as ethylene, propylene; epoxy resins; polyurethane resins; acrylonitrile resins; and their mixtures. 17. The method of claim 1, wherein the contacting is performed by immersing the substrate in the liquid hydrophobic compound. 18. The method of claim 17, wherein the contacting is carried out at a temperature of 20 to 3O ⁰ C for a period of 12 to 48 hours. 19. A process according to any one of the preceding claims wherein the contacting with the hydrophobic compound is carried out at atmospheric pressure. 20. The method according to any one of claims 1 to 18, wherein the substrate to be treated is placed in a vacuum chamber and then the contacting with the hydrophobic compound is carried out under pressure. 21. Process according to any one of the preceding claims, in which the polymerization and / or crosslinking of step b) is carried out by ionizing radiation or by thermocatalysis. 22. A method according to any preceding claim wherein the substrate is selected from substrates 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. 23. Substrate made of a material comprising wood, said substrate comprising in the porosity of the wood at least 40%, preferably more than 50%, better still more than 60% by weight of a polymerized and / or cross-linked compound and 1 at 30% by weight of a hydrophilic compound such as a PEG in the cell wall and the porosity of the wood.