EP4069484A1

EP4069484A1 - Process for chemically modifying a wooden part

Info

Publication number: EP4069484A1
Application number: EP21709085.1A
Authority: EP
Inventors: Pierre Piluso; Nicolas Bedouin; Jérôme Delmas; Olivier Poncelet; Isabelle Rougeaux
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2020-02-26
Filing date: 2021-02-17
Publication date: 2022-10-12
Also published as: FR3107465A1; US20230106916A1; FR3107465B1; WO2021170937A1

Abstract

The invention relates to a process for chemically modifying a wooden part having hydroxyl groups, comprising: - a first step of a covalent reaction between all or part of said hydroxyl groups and at least one non-polymeric compound comprising at least one group capable of reacting covalently with a hydroxyl group, whereby the wooden part is thus covalently bonded to residues of the at least one non-polymeric compound; - after or simultaneously with said first step, a second step of a covalent reaction between all or part of the residues of the at least one non-polymeric compound and at least one second compound, said first step and said second step being carried out in the presence of at least one supercritical fluid.

Description

PROCESS FOR CHEMICAL MODIFICATION OF A WOODEN PART

DESCRIPTION

TECHNICAL FIELD The present invention relates to a process for chemically modifying a piece of wood in a medium allowing chemical modification both at the surface and at the heart of the piece of wood.

Depending on the nature of the chemical compound (s) chosen for the chemical modification, the method of the invention can confer on the wood part a targeted property not inherent in the part before chemical modification or can make it possible to improve a targeted property of the constituent wood. of the part, the targeted properties can be chosen, in a non-exhaustive manner, from the following list: hydrophilicity, hydrophobicity, oleophobicity, dimensional stability, reduction of water uptake, mechanical properties, such as impact resistance, resistance to abrasion, flame retardancy, aesthetic design (such as coloring, shine), antibacterial, anti-fouling, tackiness or non-tackiness, electrical properties (such as electric shielding), cleanability.

Conventionally, the properties of a wooden part can be modified or improved by a simple impregnation of the part with one or more chemical agents making it possible to confer or improve the targeted property with, however, the following drawback (s):

-the impregnation only results in a surface treatment and does not make it possible to reach the part in depth, the targeted property thus only being located on the surface of the part; the impregnation does not allow strong binding of the chemical agent (s), the targeted property conferred by this or these agent (s) not exhibiting satisfactory resistance over time; the chemical agent (s), due to their high molecular weight, cannot access the core of the material, the targeted property conferred by this or these agent (s) thus only affecting the surface of the part.

In view of the foregoing, the authors of the present invention set out to develop a process for chemical modification of a wooden part which does not have the aforementioned drawbacks.

DISCLOSURE OF THE INVENTION

Thus, the invention relates to a process for chemically modifying a piece of wood comprising hydroxyl groups comprising the following steps:

a first covalent reaction step between all or part of said hydroxyl groups and at least one non-polymeric compound, also known as the first compound, comprising at least one group capable of reacting covalently with a hydroxyl group, whereby, at the end of from this first reaction step, the piece of wood is thus covalently linked to residues of the non-polymeric compound (s);

-after or simultaneously with said first step, a second step of covalent reaction between all or part of the residues of the non-polymeric compound (s) and at least one second compound, said first step and said second step being carried out in the presence of at least one supercritical fluid.

By covalent reaction, it is specified that it is:

-for the first step, of a reaction for the formation of covalent bonds, this reaction occurring between all or part of the hydroxyl groups of the piece of wood and the groups of the non-polymeric compound (s) capable of reacting covalently with said groups hydroxyls, whereby covalent bonds result between the piece of wood and the non-polymeric compound (s) (this or these remaining in the form of residues, i.e. what remains of the non-polymeric compounds after reaction thereof or these with hydroxyl groups of the wooden part); -for the second step, of a reaction for the formation of covalent bonds, this reaction occurring between all or part of the residues of the non-polymeric compound (s) and the second compound (s), it being understood that the residues and the second compound (s) respectively contain groups capable of reacting covalently with one another.

Thanks to the use of at least one supercritical fluid to carry out these steps, the following advantages have been observed:

-the possibility of entraining, firstly, the non-polymeric compound (s) and, secondly, the second compound (s) in the depth of the wooden part and thus induce a chemical modification of the latter both both on the surface and in depth and therefore throughout the part, the part then being able to be cut while exhibiting a homogeneous chemical modification on the various pieces resulting from this cutting;

a high solvating power, which makes it possible to give the reactions a much faster reaction kinetics compared to similar reactions, which would be carried out in a non-supercritical medium;

the possibility of carrying out said modification without using a volatile organic solvent, the elimination of which after reaction would be energetically and temporally costly and of which traces would be likely to be present in the treated parts;

the possibility of carrying out said modification by limiting the amount of reagent and catalysts, if any, used as well as the amount of residual reagent and catalysts in the wooden parts compared to conventional impregnation processes.

Furthermore, the method of the invention can have the following advantages:

an easily industrializable process comprising a small number of steps, generally not requiring large quantities of products (which is an advantage of the use of a supercritical fluid compared to techniques immersion in a liquid solvent) and allowing the simultaneous treatment of several parts;

-no prior preparation of the surface of the parts to be treated;

-the possibility of treating all the complex reliefs of the parts, if necessary.

By supercritical fluid, it means a fluid brought to a pressure and a temperature beyond its critical point, corresponding to the temperature and pressure couple (Te and Pc respectively), for which the liquid phase and the gas phase have the same density and beyond which the fluid is located in its supercritical domain. Under supercritical conditions, the fluid exhibits a greatly increased dissolving power compared to the same fluid under non-supercritical conditions and thereby facilitates the solubilization of the first and second compounds. It is understood that the supercritical fluid used is capable of dissolving the first and second compounds.

The supercritical fluid can advantageously be supercritical CO 2, in particular because of its low critical temperature (31 ° C.), which makes it possible to carry out the reaction at low temperature without risk of degradation of the first and second compounds. More precisely, supercritical CO2 is obtained by heating carbon dioxide above its critical temperature (31 ° C) and compressing it above its critical pressure (73 bars). What is more, supercritical CO2 is non-flammable, non-toxic, relatively inexpensive and does not require reprocessing at the end of the process, compared to processes involving the exclusive use of organic solvent, which also makes it a solvent. “Green” relevant from an industrial point of view. Finally, supercritical CO2 has good solvating power (adaptable depending on the pressure and temperature conditions used), low viscosity and high diffusivity. Finally, its gaseous nature under ambient conditions of pressure and temperature renders, at the end of the reaction and once the CO2 has been brought back to a non-supercritical state, the stages of separation of the part thus modified and the reaction medium (comprising , for example, unreacted compounds) and the re-use of CO2, which are easy to achieve. All these conditions mentioned above contribute to making _{supercritical CO 2} an excellent choice of solvent for carrying out the reaction steps of the process in accordance with the invention.

As mentioned above, the process of the invention comprises a first step of covalent reaction between all or part of said hydroxyl groups and at least one non-polymeric compound, also called first compound, comprising at least one group (hereinafter called group reactant (s) capable of reacting covalently with a hydroxyl group, whereby, at the end of this first reaction step, the wooden part is thus covalently bonded to residues of the compound (s) non-polymeric.

The term “residues of the non-polymeric compound (s)” is understood to mean what remains of the non-polymeric compound (s) after covalent reaction of the latter (s) with the hydroxyl groups of the piece of wood.

The wooden part intended to be treated in accordance with the method of the invention can be a part made from all types of wood species, including a part comprising several distinct types of wood species. In particular, the piece of wood can be made from one or more species of wood chosen from deciduous trees, conifers and mixtures thereof.

More specifically, the method of the invention is particularly suitable for the treatment of pieces of conifer (s), such as pieces of fir (s) or spruce (s), which have the particularity of being difficult to treat by conventional impregnation techniques.

The non-polymeric compound (s) which react, via at least one reactive group, covalently with the hydroxyl groups of the piece of wood are not polymers, that is to say compounds comprising a sequence of unit (s ) repetitive (s), which allows them to access more easily the heart of the wooden part and react covalently with the hydroxyl groups located at the heart of the wooden part.

The non-polymeric compound (s) used in the first covalent reaction step comprise at least one group capable of reacting covalently with a hydroxyl group of the piece of wood, this or these compound (s) being able to be chosen. from epoxy compounds, anhydride compounds, acyl halide compounds, carboxylic acid compounds, silyl ether compounds, isocyanate compounds and mixtures thereof.

Regarding epoxy compounds, it means compounds comprising at least one epoxy group, the epoxy group being the reactive group reacting, covalently, with a hydroxyl group, under acidic or basic conditions, preferably basic, according to a mechanism ring opening nucleophile with formation of an ether bond between the piece of wood and the rest of the epoxy compound.

Regarding anhydride compounds, it means compounds comprising at least one anhydride group, the anhydride group being the reactive group reacting, covalently, with a hydroxyl group with formation of an ester bond between the piece of wood and the rest of the anhydride compound.

With regard to the acyl halide compounds, it means compounds comprising at least one acyl halide group (more specifically, at least one acyl chloride group), the acyl halide group being the reactive reactive group, of covalently, with a hydroxyl group with formation of an ester bond between the piece of wood and the rest of the acyl halide compound.

Concerning carboxylic acid compounds, it means compounds comprising at least one carboxylic acid group, the carboxylic acid group being the reactive group reacting, covalently, with a hydroxyl group with formation of an ester bond between the wooden part and the remainder of the carboxylic acid compound.

With regard to silyl ether compounds, it means compounds comprising at least one silyl ether group, the silyl ether group being the reactive group which reacts, covalently, with a hydroxyl group with formation of a silyl ether bond. between the wooden piece and the rest of the silyl ether compound.

Regarding isocyanate compounds, it means compounds comprising at least one isocyanate group, the isocyanate group being the reactive group reacting, covalently, with a hydroxyl group with formation of a carbamate bond between the piece of wood and the rest of the isocyanate compound. Depending on the non-polymeric compound (s) selected, a person skilled in the art will choose the operating parameters to allow the covalent reaction with the hydroxyl groups of the wooden part, these operating parameters being able to be determined by preliminary tests.

Advantageously, the non-polymeric compound (s) are epoxy compounds, which allow the formation of an ether bond with the wooden part to be treated, this type of bond being more stable than an ester bond, which is capable of hydrolyzing. .

More specifically, the non-polymeric compound (s) are epoxy compounds, comprising, in addition to an epoxy group, at least one vinyl group, which vinyl group may subsequently react with another organic compound (hereinafter referred to as the second compound) comprising a group capable of react covalently with the vinyl group.

By way of example, the non-polymeric compound (s) may be a glycidyl (meth) acrylate compound, an allyl glycidyl ether compound, a 2-methyl-2-vinyloxirane compound or a 1,2-epoxy-9-decene compound. .

When the non-polymeric compound is a glycidyl methacrylate compound, the reaction of this compound with a hydroxyl group of a wooden part can be schematized by the following chemical equation: the remainder of the glycidyl methacrylate compound thus corresponding to the formula -CH -CH (0H) -0-C0-C (CH ₃ ) = CH.

In addition, the first reaction step can be carried out in the presence of at least one cosolvent, which can make it possible to improve the solubility of the non-polymeric compound (s) and / or to improve the swelling of the wood and thus facilitate the accession. of the non-polymeric compound (s) at the heart of the wooden part. In addition, the first reaction step can be carried out in the presence of at least one catalyst.

By way of example, when the non-polymeric compound is a compound comprising at least one epoxy group, the cosolvent can be a ketone solvent, such as acetone and the catalyst can be a basic compound, such as a tertiary amine, such as triethylamine.

More specifically, the first reaction step can include the following operations:

an operation of placing, in a reactor, the piece of wood, at least one non-polymeric compound, optionally at least one cosolvent and optionally at least one catalyst;

an operation for introducing CO ₂ into the reactor;

an operation of pressurizing and heating the reactor to a temperature above the critical temperature of CO ₂ and to a pressure above the critical pressure of CO ₂ , this temperature and this pressure being maintained until completion of the reaction.

As a variant, the operation of pressurizing and heating the reactor can be sequenced as follows:

an operation of pressurizing and heating the reactor to a temperature above the critical temperature of CO ₂ and to a pressure above the critical pressure of CO ₂ , the temperature and the pressure being chosen to generate an impregnation without reaction of the wooden piece with the non-polymeric compound (s) followed by possible precipitation of the non-polymeric compound (s);

an operation of increasing the pressure and the temperature, the temperature and the pressure being set so as to allow the covalent reaction of the non-polymeric compound (s) with the wooden part, this temperature and this pressure being maintained up to completion of said reaction, it being possible for this operating sequence to be repeated one or more times.

The investment operation can be carried out, advantageously, from so that there is no direct contact between the piece of wood and the non-polymeric compound (s), the possible catalyst and the possible cosolvent.

At the end of the first reaction step, the wooden pieces are thus covalently linked to (or grafted, covalently, by) the residues of the non-polymeric compound (s), that is to say what Non-polymeric compound (s) remain after covalent reaction thereof with hydroxyl groups of the piece of wood.

After the first reaction step, the supercritical conditions can be eliminated by depressurizing the reactor, before initiating the second covalent reaction step, when the latter is carried out after the first step, this second covalent reaction step being itself. -even carried out in the presence of at least one supercritical fluid.

The wooden part thus modified can then be subjected to drying, for example, under vacuum, before initiating the second covalent reaction step.

The process of the invention comprises, after or simultaneously with the aforementioned first reaction step (preferably after the aforementioned first reaction step), a second covalent reaction step between all or part of the residues of the non-polymeric compound (s) and the at least a second compound, which assumes, of course, in this case, that the residues of the non-polymeric compound (s) covalently bonded to the wooden part comprise at least one group capable of reacting covalently with a group of the or second compound (s). The second compound (s) are preferably non-polymeric compounds.

By way of example, the residue (s) may comprise, as group (s) capable of reacting with at least one group of the second compound (s), at least one vinyl group and, in As a counterpart, the second compound (s) can comprise, as a group capable of reacting with a vinyl group of the residue (s), also at least one vinyl group. In this case, the second covalent reaction step may consist of a step of polymerization of the second compound (s) initiated from the abovementioned residue (s), and more specifically a step of polymerization of the second compound (s) comprising at least one vinyl group, the polymerization thus propagating from the residues of the functional compound via the vinyl groups thereof. At the end of this step, there thus remains a modified wooden part linked to grafts consisting of polymer chains resulting from the polymerization of the second compound (s), the bond between the wooden part and the grafts taking place via the remains. of the non-polymeric compound (s) which form organic spacer groups between the piece of wood and the grafts, these residues being linked, on the one hand, covalently, to the piece of wood and, on the other hand, covalently , to the aforementioned plugins. In this case, the remains are what remains of the non-polymeric compound (s) after reaction of the latter (s), on the one hand, with the hydroxyl groups of the wooden piece and, on the other hand , with the vinyl group (s) of the second compound (s).

More specifically, in this scenario, the process of the invention can be defined as a process for modifying a wooden part comprising hydroxyl groups comprising successively:

-as a first step, a first covalent reaction step between all or part of said hydroxyl groups of the piece of wood and at least one non-polymeric compound, also called first compound, comprising at least one group capable of reacting covalently with a group hydroxyl and comprising at least one vinyl group, whereby, at the end of this first reaction step, the wooden part is thus covalently linked to residues of the non-polymeric compound (s);

-as a second step, from the vinyl groups of the residues of the non-polymeric compound (s), a step of polymerization of a second compound comprising at least one vinyl group, said first step and said second step being carried out in the presence of at least a supercritical fluid.

Furthermore, the second compound (s) can advantageously comprise at least one group capable of giving the wooden part a particular targeted property, such as a property chosen from the following properties: hydrophilicity, hydrophobicity, oleophobicity, dimensional stability, reduction of water uptake, mechanical properties, such as impact resistance, abrasion resistance, flame retardancy, aesthetic design (such as coloring, shine), antibacterial, anti-fouling , tackiness or non-tackiness, electrical properties (such as electrical shielding), cleanability. In this case, the second compound or compounds can thus be qualified as organic compounds of interest.

The term “organic compound of interest” is understood to mean a compound comprising at least one group capable of imparting or improving a given property to the wooden part, called a functional group of interest.

More specifically, the second compound (s) can also comprise at least one group capable of imparting or improving a given property to the wooden part, said functional group of interest, such as at least one group comprising at least one. phosphorus atom, such as a phosphate group or a phosphonate group to impart flame retardant properties to the wood piece.

By way of examples, the second compound (s) can be chosen from £> / s [2- (methacryloyloxy) ethyl] phosphate, diethylallylphosphate, diethylallylphosphonate, dimethylvinylphosphonate, diethylvinylphosphonate and mixtures thereof.

This second reaction step can be carried out in the presence of a cosolvent and / or of a catalyst, such as a free radical initiator (such as AIBN), in particular when the second compound or compounds contain at least one vinyl group. intended to react with a vinyl group of the residues of the non-polymeric compound (s).

A specific process according to the invention is a process, in which:

the first covalent reaction step is a covalent reaction step between all or part of said hydroxyl groups and a first compound comprising at least one epoxy group and at least one vinyl group, for example, glycidyl methacrylate, in the presence of supercritical CO2 , the epoxy groups reacting covalently with all or part of the hydroxyl groups, by means of which, at the end of this first reaction step, the piece of wood is thus covalently linked to residues of the first compound;

the second covalent reaction step is a step of polymerization of a second compound comprising at least one vinyl group and at least one functional group of interest, such as a phosphate group or a phosphonate group, for example £> / s [2- (methacryloyloxy) ethyl] phosphate, in the presence of _{supercritical CO 2} , the polymerization being initiated from the vinyl groups of the residues of the first compound.

More specifically, the step of reacting the piece of wood with a second compound may include the following operations:

an operation of placing, in a reactor, the piece of wood which has reacted with the non-polymeric compound (s), at least one second compound, optionally at least one cosolvent and optionally at least one catalyst;

an operation for introducing CO ₂ into the reactor;

an operation of pressurizing and heating the reactor to a temperature above the critical temperature of CO ₂ and to a pressure above the critical pressure of CO ₂ , the temperature and the pressure being chosen to generate an impregnation without reaction of the wooden piece with the second compound (s) followed by possible precipitation of the non-polymeric compound (s);

an operation of increasing the pressure and the temperature, the temperature and the pressure being fixed so as to allow the covalent reaction of the second compound (s) with the residues of the non-polymeric compound (s) covalently bonded to the part in wood, this temperature and pressure being maintained until completion of said reaction, it being possible for this operating sequence to be repeated one or more times.

The placement operation can be carried out, advantageously, so that there is no direct contact between the piece of wood and the second compound or compounds, the possible catalyst and the possible cosolvent.

After the implementation of the second reaction step, the method comprises, conventionally, a step of stopping the supercritical conditions and optionally a step of drying the modified piece of wood.

Whatever the embodiments, the modification method can be considered, in particular, as a method capable of imparting or improving a given property of the wooden part and, in particular, of imparting flame-retardant properties, in which case the method of the invention is a method of flame retardant treatment of the piece of wood.

The method of the invention can be implemented in a device, for example, of the autoclave type, comprising an enclosure intended to receive the wooden part, the reagents, the supercritical fluid, the possible cosolvent and the possible catalyst, means for regulating the pressure of said enclosure for the evacuation thereof (for example, via a vacuum pump communicating with the enclosure) and heating means.

Other advantages and characteristics of the invention will appear in the detailed non-limiting description below.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a photograph of the slice of wood (point a corresponding to the edge of the specimen, point c) at the heart of the specimen and point b) at an in-between between the edge and the heart) obtained according to the example below.

FIG. 2 illustrates IR-ATR spectra of wood samples obtained according to the example below.

FIG. 3 illustrates IR-ATR spectra of wood samples obtained according to the example below. DETAILED PRESENTATION OF PREFERRED EMBODIMENTS

EXAMPLE

This example illustrates the implementation of a specific mode of the chemical modification process of the invention comprises a chemical modification in two steps:

1) a step of reaction of pieces of spruce wood, which are spruce test pieces, with glycidyl methacrylate (hereinafter referred to as GMA);

2) a step of reacting the parts thus modified with a phosphorus compound: £> / s [2- (methacryloyloxy) ethyl] phosphate (referred to below as BMEP), these two steps being carried out under supercritical CO 2 in a specific reactor.

The simplified reaction scheme of these two reactions can be as follows: Wood-OH corresponding to the piece of wood, only one group -OH being represented for the sake of simplicity and p corresponding to the number of repetitions of the repeating pattern taken in parentheses.

The aforementioned specific reactor is a 600 ml batch type stainless steel reactor fitted with an external heating system. The reagents (GMA, BMEP), the catalysts and the solvents (acetone) are placed in a 70 mL crystallizer placed at the bottom of the reactor. The wooden specimens are placed on the edges of the crystallizer so as to ensure that there is no direct contact between the reagents, the catalysts and the solvent on the one hand and the wood on the other. The CO2 is introduced into the reactor, preheated slightly above 31 ° C, with a double piston pump whose heads are cooled to a temperature below 5 ° C to have CO2 in the liquid phase in the tubes and avoid cavitation problems. On the other hand, in the reactor, CO2 is never present in the liquid state.

The wooden pieces are spruce specimens with the dimensions 65 * 20 * 24 cm, the grain of the wood being in the direction of the last dimension and weigh, when dried for 1 hour at 103 ° C, from 13 to 14 g .

1) Reaction step of spruce specimens with GMA

To do this, two spruce test pieces previously dried for one hour at 103 ° C and meeting the specificities mentioned above were placed, as described above, in the reactor above the crystallizer containing 27 mL of GMA and 27 mL. acetone. The purpose of acetone added to the reaction medium is to prevent self-polymerization of GMA in the crystallizer. 2.7 mL of triethylamine was placed in a separate crystallizer in the reactor. CO2 is introduced and the reactor was then placed under 200 bar and at 140 ° C. to form supercritical CO2, these conditions being maintained for 7 hours.

After depressurization, the wooden specimens are collected and dried in an oven under vacuum at 103 ° C. overnight. The mass setting of the test pieces, or WPG (Weight Percent Gain), is 22.1 and 22.0% (relative to the dry mass before treatment), and the longitudinal swelling of the test pieces after one day of immersion in water was reduced by 60.1 and 56.2%, respectively.

One of the wooden specimens was partially cut in order to analyze it by attenuated total reflectance infrared spectroscopy (IR-ATR), the places on which the spectroscopy was carried out, being represented in figure 1 which illustrates a photograph of the slice. of wood (point a corresponding to the edge of the specimen, point c) to the heart of the specimen and point b) to a gap between the edge and the heart).

The IR-ATR spectra of unmodified wood (curve d)) and GMA modified wood (curve a) for the edge, curve b) for the in-between and curve c) for the core) are shown on FIG. 2 appended, the ordinate representing the intensity I of the peaks and the abscissa the number of waves N (in cm ^-1 ).

An increase in the intensity of the peak at 1710 cm ¹ corresponding to the C = 0 bonds (ester of GMA in particular) is observed with the modification by the GMA and the depth of analysis in the wood (in the direction of the grain of the wood). . The more the wood is modified, the higher the peak is compared, for example, to the peak at 1620 cm ¹ which corresponds to the aromatic C = C bonds of lignin (not affected by the modification). It is observed from these spectra that the modification has taken place up to the core of the wood and that a gradient of modification is observed between the exterior (which is more strongly modified) and the core.

2) Reaction step of the test pieces thus modified with BMEP

The test pieces thus modified, during the previous step, were treated under supercritical CO2 with £> / s [2- (methacryloyloxy) ethyl] phosphate (BMEP) in the presence of a free radical initiator: a, a '-AzoBisisobutyronitrile (AIBN).

To do this, 5 mL of BMEP and 20 mL of acetone are placed in the crystallizer of the reactor defined above. 0.2 mg of AIBN are deposited at the bottom of the reactor outside the crystallizer. The wood samples modified by GMA are then placed above the crystallizer without contact with the liquid or with GAIBN. The reactor is closed and CO2 is introduced and the treatment is applied in 2 phases with a first phase impregnation at 40 ° C, 100 bar for 5 hours then a reaction phase at 110 ° C and 220 bar for 2 hours.

The test pieces are then collected and dried in an oven under vacuum for 1 night. One of the wood specimens was subjected to an analysis of its edge by attenuated total reflectance infrared spectroscopy (IR-ATR), IR-ATR spectra of unmodified wood (curve a)), wood modified by GMA only ( curve b) for the edge) and wood modified by GMA and BMEP (curve c)) are illustrated in Figure 3 attached in the appendix, the ordinate representing the intensity I of the peaks and the abscissa the number of N waves (in cm ¹ ).

On curve c), the presence of BMEP emerges, in particular with the increase in the intensity of the peaks at 983 cm ¹ (POC bond) and at 1720 cm ¹ (C = 0 bond of the acrylate of BMEP), thus validating the system described by the invention which makes it possible to provide a functionality via a pre-grafting of a vinyl compound.

Claims

1. A method of chemically modifying a piece of wood comprising hydroxyl groups comprising the following steps:

a first covalent reaction step between all or part of said hydroxyl groups and at least one non-polymeric compound, said first compound, comprising at least one group capable of reacting covalently with a hydroxyl group, whereby, at the end of this first reaction step, the piece of wood is thus covalently bonded to residues of the non-polymeric compound (s);

2. The method of claim 1, wherein the supercritical fluid is supercritical CO2.

3. Method according to claim 1 or 2, in which the piece of wood is made from one or more species of wood chosen from deciduous trees, conifers and mixtures thereof.

4. Method according to any one of the preceding claims, wherein the piece of wood is a piece of conifer (s).

5. Method according to any one of the preceding claims, in which the non-polymeric compound (s) are chosen from epoxy compounds, anhydride compounds, acyl halide compounds, carboxylic acid compounds, silyl ether compounds, silyl ether compounds. isocyanate compounds and mixtures thereof.

6. Method according to any one of the preceding claims, in which the non-polymeric compound (s) are epoxy compounds.

7. Method according to any one of the preceding claims, in which the non-polymeric compound (s) are epoxy compounds comprising at least one vinyl group.

8. Method according to any one of the preceding claims, in which the first reaction step is carried out in the presence of at least one cosolvent.

9. Method according to any one of the preceding claims, in which the first reaction step comprises the following operations: an operation of placing, in a reactor, of the wooden part, of at least one non-polymeric compound, optionally. at least one cosolvent and optionally at least one catalyst;

an operation for introducing CO2 into the reactor;

an operation of pressurizing and heating the reactor to a temperature above the critical temperature of CO 2 and to a pressure above the critical pressure of CO 2, this temperature and this pressure being maintained until the reaction is complete.

10. Method according to any one of the preceding claims, in which the residue or residues comprise, as group (s) capable of reacting with at least one group of the second compound (s), at least a vinyl group.

11. Method according to any one of the preceding claims, in which the second compound (s) comprise at least one group capable of to give the piece of wood a given property or to improve a given property of the piece of wood, said functional group of interest.

12. The method of claim 11, wherein the second compound (s) comprise, as functional group of interest, at least one group comprising at least one phosphorus atom, such as a phosphate group or a phosphate group. phosphonate group.

13. Process according to any one of claims 10 to 12, in which the second compound (s) comprise at least one vinyl group.

14. The method of claim 1, successively comprising the following steps:

-as a first step, a first step of covalent reaction between all or part of said hydroxyl groups of the piece of wood and at least one non-polymeric compound, said first compound, comprising at least one group capable of reacting covalently with a hydroxyl group and comprising at least one vinyl group, whereby, at the end of this first reaction step, the piece of wood is thus covalently bonded to residues of the non-polymeric compound (s);

15. The method of claim 14, wherein:

the first covalent reaction step is a covalent reaction step between all or part of said hydroxyl groups and a first compound comprising at least one epoxy group and at least one vinyl group, in the presence of supercritical CO2, the epoxy groups reacting covalently with all or part of the hydroxyl groups, whereby, at the end of this first reaction step, the wooden piece is thus covalently bonded to residues of the first compound ; the second covalent reaction step is a step of polymerization of a second compound comprising at least one vinyl group and at least one functional group of interest, such as a phosphate group, in the presence of supercritical CO 2, the polymerization being initiated from vinyl groups of the residues of the first compound.

16. A method according to any preceding claim, which is a method capable of imparting or improving a given property of the piece of wood.

17. A method according to any preceding claim, which is a flame retardant treatment method of the piece of wood.