METHOD FOR SOVERCRITICAL OR SUBCRITICAL PARTIAL DELIGNIFICATION AND FILLING OF A LIGNOCELLULOS MATERIAL

Description

[0001] The present invention relates to a method for treating and modifying lignocellulosic material. In particular, the invention relates to a method for partially delignifying and filling a lignocellulosic material structure. The lignocellulosic material is preferably wood. Any modified lignocellulosic material (referred to as " composite ”) obtained by this process is such that its native architecture has been substantially and advantageously preserved. Prior art

[0002] It is known that certain mechanical properties of wood, such as compressive strength and flexural strength, can be improved by impregnating the wood with at least one monomer and / or polymer. Such wood impregnated with a monomer and / or polymer is commonly referred to as a wood composite. It is usually solid wood impregnated superficially iemainly on a small thickness from the surface (generally 4 to 6 mm deep from the surface).

[0003] A known method for producing wood composites involves immersing the wood to be treated in a fluid such as an aqueous solution, in which the monomer and / or polymer is (are) dissolved, and pressurizing the fluid so as to incorporate the monomer and / or polymer into the wood. However, such a method is time-consuming and requires the use of high pressure in order to deeply impregnate the wood.

[0004] An improvement to this process has therefore been sought, for example by using a partial vacuum. However, no satisfactory solution has emerged, since all the techniques considered are penalized by their long duration, mainly because of the difficulty of impregnating the pores of the wood in depth.

[0005] It is also known to impregnate wood with methyl methacrylate (MMA) and then polymerize the impregnated monomer. Polymerization can be carried out, for example, using high-energy radiation such as laser beams or gamma rays. This method is slow, and the use of high-energy radiation is particularly expensive.

[0006] On the other hand, it has been proposed in document WO 90 / 02612 to carry out impregnation of wood with a monomer in an acidic or basic (alkaline) medium through the use of supercritical phase fluid. This supercritical phase fluid facilitates the impregnation of the monomer or polymer into the porous material.

[0007] A first embodiment proposed in WO 90 / 02612 comprises impregnating wood with an alkaline or acidic medium in the presence of a first fluid maintained under supercritical conditions, digesting the impregnated wood with this medium in the presence of a second fluid maintained under supercritical conditions, so as to extract extractables and lignin from the wood, which can then be separated from the fluid. The wood thus obtained, consisting of essentially discrete fibers, is recovered and then converted into paper.

[0008] This first embodiment is only reserved for chips (“ chips") of wood, since it appears that a very significant part, if not all, of the lignin is extracted from the wood, which leads to the destruction of the internal architecture of the wood. Thus, in the examples of WO 90 / 02612, these chips are reduced to the state of pulp once the extractable substances and the lignin have been extracted. The pulp thus obtained, in the state of discrete fibers agglomerated into a paste, makes it possible to produce wood panels (of the agglomerate type) of superior quality in terms of mechanical properties compared to the state of the art.

[0009] A second embodiment proposed in WO 90 / 02612 comprises treating a cellulose-containing material with a first supercritical phase fluid, so as to extract extractables (but not lignin) from the cellulose-containing material; separating the fluid containing the extractables from the material, so as to obtain a material having less extractables; contacting the material containing the cellulose and less extractables with a second supercritical phase fluid comprising a polymerizable monomer, under conditions sufficient to allow impregnation of the monomer into the material; precipitating the monomer within the cellulose; and polymerizing the precipitated monomer. in situ.This material would have improved properties. This second embodiment is rather reserved for pieces of wood of a certain size. Thus, in the examples, pieces of structural timber (" large blocks or logs ”) are treated either with MMA or with styrene.

[0010] However, the two embodiments described in WO 90 / 02612 do not allow the micro-architecture of the wood to be preserved while allowing a filler material to replace sufficient lignin. Indeed, the treatment according to this document either produces delignification which is almost total, and which leads to the production of pulp, or produces delignification which is extremely low, or even zero.

[0011] More recently, WO 2010 / 089604 described the production of lignocellulosic material parts produced by impregnating the material with a formulation based on acetic anhydride at acid pH, then impregnating the material with a formulation based on an aqueous organic product, followed by pressurization so as to impregnate the two solutions into the material, then heating so as to crosslink the organic material present in the lignocellulosic material thus impregnated. This makes it possible to manufacture a hardened composite lignocellulosic material part. However, the filling of the material part with the organic product can only be partial or even superficial ( ieover a small thickness from the surface as explained previously). This implies that processing a relatively thick part cannot give improved mechanical strength properties. Here, "relatively thick" is generally understood to mean about 10.16 cm (4 inches) according to the American standards for " logs » (pieces of structural timber), or even 27 mm according to the standards of French sawmills for board thicknesses.

[0012] WO 2017 / 098149 A1 describes a method for treating a lignocellulosic material structure comprising: (1) at least one step of soaking the lignocellulosic material structure with at least one fluid to dissolve at least 40% and at most 85% by weight of the lignin present in the material; (2) at least one step of washing the structure resulting from step (1) with at least one organic fluid so as to remove the dissolved lignin resulting from the soaking step (1), so as to produce a partially delignified structure.

[0013] Luce F. "Delignified impregnated wood" Mechanical Engineering vol. 66, no. 10, October 1, 1944, pages 654-655, describes processes for chemical digestion of wood veneers.

[0014] As a result, the methods known to date for impregnating wood, or any other lignocellulosic material, to make it more resistant, are complicated to implement and relatively expensive. Moreover, their implementation is far too slow to realistically envisage industrial production of a wood composite material.

[0015] There remains to date the need for a method of treating a structure of lignocellulosic material, preferably wood, so as to obtain a structure retaining the architecture of the wood, and made of a material with improved mechanical properties, in particular in terms of flexural strength and compressive strength, compared to the lignocellulosic material before treatment. By " treatment of lignocellulosic material » , here we mean the treatment of the material constituting this material.

[0016] One of the objectives of the invention is to overcome the previously mentioned disadvantages of the treatment methods of the state of the art, and in particular to provide an effective method for treating lignocellulosic material which can be carried out on an industrial scale, which makes it possible to obtain a material which preserves the architecture of the wood and has improved mechanical, chemical and / or optical properties. Summary of the invention

[0017] The invention thus relates to a method for treating a structure of lignocellulosic material, the lignocellulosic material preferably being wood, said method comprising the following successive steps: (1) at least one step of extracting lignin from a lignocellulosic material structure by at least one supercritical or subcritical phase fluid in a high pressure cell, the lignin being partially extracted; (2) at least one step of filling the partially delignified structure with at least one filler compound, so as to produce a filled partially delignified structure; and (3) at least one step of finishing the filled partially delignified structure, so as to obtain a composite material structure formed of a three-dimensional network of transformed filler compound incorporated in a network of cellulose and lignin, The density of the composite material structure obtained being greater than that of the lignocellulosic material structure before treatment.

[0018] Preferably, in step (1), the lignin is extracted in a content of 40 to 85%, in % by weight, relative to the lignin initially present in the material.

[0019] The method for treating a lignocellulosic material structure according to the invention comprises the novel and innovative combination of partial delignification of the structure followed by filling with a compound which is stabilized within the structure thus delignified. In particular, the controlled use of a fluid in supercritical or subcritical phase, optionally accompanied by a co-solvent, makes it possible to improve the extraction step (1).

[0020] This combination of steps (1) to (3) advantageously makes it possible to obtain a composite material which substantially preserves the structure of the material and is formed of two interpenetrating networks, in which the architecture of the lignocellulosic material has been altered at the nanoscopic scale but substantially preserved at the microscopic and macroscopic scales.

[0021] According to a preferred variant of the invention, the method further comprises at least one intermediate step of functionalization of the partially delignified structure resulting from the extraction step (1), located between the extraction step (1) and the filling step (2). The filling step is then carried out not on the partially delignified structure resulting from the extraction step (1), but on the partially delignified structure resulting from the intermediate functionalization step.

[0022] The composite material structure obtained by the method according to the invention comprises lignin, hemicellulose, cellulose and at least one filler compound, the composite material forming a three-dimensional network of transformed filler compound incorporated in a structure of cellulose and lignin. The properties of the lignocellulosic material, which has been transformed by the method according to the invention into a composite material, whether mechanical, chemical and / or optical, are notably improved compared to the material before treatment.

[0023] Another object of the invention is an installation capable of implementing the method according to the invention. Detailed description of the invention Definitions

[0024] By " architecture "lignocellulosic material means a hierarchical set, of multi-scale organization, namely the macroscopic, microscopic, or nanoscopic scales, ensuring mechanical solidity to the whole. All or part of the structure of lignocellulosic material obtained by the process according to the invention comes from the architecture of wood, some elements of which are briefly recalled below.

[0025] At the atomic scale, wood is composed of approximately 50% carbon atoms, 6% hydrogen atoms, and 40% oxygen atoms, along with traces of inorganic compounds and organometallic complexes. More precisely, wood is composed of 60 to 75% carbohydrates in the form of cellulose and hemicelluloses, and 18 to 35% lignin. Hemicelluloses are peripheral inclusions on cellulose bundles, with lignin serving anarchicly, thanks to its transverse chemical and physical bonds with hemicelluloses, as a transverse bond between these bundles and thus as a support for the architecture. At the macroscopic scale, two parts are particularly distinguished in wood: the heartwood, which is darker in color, and the sapwood. These two parts have growth rings where we can distinguish spring wood and summer wood, which is darker.

[0026] The plant cell, consisting of a cavity, the lumen, a wall, and intercellular sap transport channels, called punctuations, is the building block of the microscopic scale. In the living state, the cavities of the wood cells close to the bark of the tree ensure the transport of sap from the roots to the extremities of the tree, while the walls ensure the functions of mechanical resistance. The cells die as the tree grows, ensuring only the support of the tree. The cell walls are made up of the stacking of three distinct layers (the middle lamella, the primary wall, and the secondary wall) with specific physicochemical properties. Each of these cell layers is mainly made up of three polymers: lignin, cellulose, and hemicelluloses.Lignin, present mainly in the middle lamella of the plant cell wall, binds cellulose fibrils together and maintains the wood structure. The multi-scale architecture of wood is anisotropic. It ensures the mechanical strength and opacity of the entire lignocellulosic material. The architecture and microscopic and nanoscopic structure of the components depend on the wood in question.

[0027] The respective quantities and quality of lignin, cellulose and hemicelluloses vary depending on the nature of the wood and the tree in question, i.e. the part of the tree, the environment and the maturation of the tree in question. Cellulose is partially semi-crystalline while lignin is amorphous. Lignin is dark brown in color while cellulose and hemicelluloses are mostly white in color. These three polymers are entangled so that a nanoscopic porosity exists in the material, where molecules called extractables are present. Although anchored in the material (mainly by physicochemical bonds), these molecules are independent of the network formed by the lignocellulosic material.

[0028] THE "extractable"are molecules that intensely absorb visible light. Their presence in a porosity implies the existence of a large number of interfaces, which has an impact on the diffusion and propagation of light radiation within the material. The term "extractable » brings together a very large set of molecules resulting from secondary metabolites synthesized during the growth of lignocellulosic material. They are present in relatively small quantities (between 5 and 10% by weight) in the form of mixtures, sometimes complex, and highly variable, which are linked to the nature of the lignocellulosic material. The variability of these molecules (in quantity and quality) is significant. The composition of the soil and the climate of the place where a lignocellulosic material is grown greatly influence the chemical identity of this material, including its extractables.

[0029] Extractives include molecules with very varied structures, functionalities and properties, which can be polar or apolar, hydrophilic or hydrophobic, linear, mono-aromatic or poly-aromatic. Among the extractables, the following compounds can be mentioned: waxes and fats, terpenes (monoterpenes, diterpenes, triterpenes, sesquiterpenes, diterpenic acids) and phenolic compounds (phenol derivatives, lignans, stilbenes, flavonoids, biflavonoids, condensed tannins, hydrolyzable tannins). Extractives provide additional chemical protection for the wood. Indeed, they are often involved in the defense mechanisms of the lignocellulosic material against external attacks, such as fungi, enzymes, wood-eating insects, microbes. They are also responsible for the odor, partly for the color, as well as the intrinsic lifespan of the lignocellulosic material.

[0030] On the other hand, the architecture of the lignocellulosic material is described as "native" (Or "natural" ) when the material, whatever the scale of organization at which it is observed, has properties similar to those encountered in lignocellulosic material that has not undergone any treatment.

[0031] The term "chemical anchoring" » refers to a molecular bond between two compounds, while the terms " physicochemical anchoring » relate to a hydrogen, van der Waals, ionic or metallic bond between two compounds.

[0032] The term "wood architecture space", also called more simply " space " Or " volume "(corresponding to a substantial absence of matter) subsequently refers to the microscopic cavities in the wood and the punctuations that join them, filled with sap in living cells, but also to the nanoscopic spaces between the chains of tangled polymers contained in the cell walls.

[0033] By " lignocellulosic material structure”,According to the invention, a three-dimensional object made of lignocellulosic material is understood to mean a three-dimensional object made of lignocellulosic material, and having a certain (three-dimensional) volume of at least approximately 3 cm 3 <, preferably at least approximately 4 cm 3 <. It is a macroscopic object which has substantially retained the architecture of the native lignocellulosic material. Thus, preferably, the structure of lignocellulosic material comprises at least one dimension of at least 5 mm, preferably at least 2.5 cm, and at most 40 cm. According to a preferred embodiment, the structure can be virtually inscribed in a parallelepiped of which each of the three dimensions is at least 5 mm, preferably at least 2.5 cm. When the lignocellulosic material is wood, the structure can typically be a cut of wood (cross-section, longitudinal section, radial section) for example 5 to 7 mm thick or even 18 mm thick.

[0034] More precisely, the lignocellulosic material structure can be a finishing element, a secondary work element or a primary work element.

[0035] By " finishing element”, according to the invention, a three-dimensional object is understood to mean one of the dimensions of which, generally the thickness, is much smaller than the other two dimensions and typically at least about 0.5 mm, preferably at least about 1 mm, even more preferably at least about 2 mm and even more preferably at least about 5 mm. This object is generally chosen from the group formed by wood sheets, marquetry, coverings, plates, slabs and veneers, preferably plates and slabs. This corresponds substantially to the term "veneer" in English, preferably " thick veneer.

[0036] By " secondary work element”,according to the invention, we mean a three-dimensional object of which one of the dimensions, generally the thickness, is much smaller than the other two dimensions and typically at least about 10 mm, preferably at least 18 mm, even more preferably at least about 27 mm. This object typically corresponds to the second work in the building, that is to say that it is chosen from the group formed by cladding, battens, joists, plinths, parquet floors, partitions, panels, roof coverings and joinery. This corresponds substantially to the term "timber" in English.

[0037] By " element of the first work”,according to the invention, we mean a three-dimensional object which is typically a construction element, and the smallest of the three dimensions of which is typically at least about 10 cm. This object corresponds to the first work (or structural work) in the building, that is to say that it is chosen from the group formed by posts, beams, lattice structures and frames. This corresponds substantially to the term "lumber" in English. This item also includes cross-laminated timber panels also known as "panels massive" (or Cross-Laminated Timber(CLT acronym in English), which are panels made up of at least three single-layer plates glued together and arranged in cross-ply fashion, in other words perpendicular to each other. In general, CLT panels are made up of 3 to 7 layers of wood, the orientation of the wood fibers being crossed by one layer in relation to the adjacent layer(s). These different layers of wood vary between 2 cm and 8 cm in thickness, the panel itself reaches a total thickness varying from 6 cm for the thinnest to 28 cm for the thickest.

[0038] By " building element”, according to the invention we mean an element from the technical field of building, that is to say a construction element, which is either a finishing element, a secondary work element or a primary work element.

[0039] By " fluid ", according to the invention we mean liquid or gas.

[0040] By " extraction”,according to the invention, we mean a removal and evacuation of material from the structure.

[0041] By "we mean green wood » wood still containing free water molecules or bound to the cellular network such as freshly felled wood. Thus, freshly felled wood is wood generally containing 100% relative humidity, whereas a " wet wood » (Or "dried wood" ) contains by definition only water molecules in the cavities of the cellular network, i.e. approximately 25% relative humidity. Green wood, on the other hand, generally contains 40 to 100% relative humidity. The measurement of the (relative) humidity of a wood is defined by the CNDB (National Committee for the Development of Wood) as the ratio of the mass of water it contains to its anhydrous mass. It is expressed by the following formula Humidité % = Masse humide − Masse anhydre × 100 / Masse anhydre .

[0042] According to the CNDB, at the time of felling, the wood can contain more water than wood matter; sometimes twice as much in certain poplars. The relative humidity is then greater than 100%. Indeed, the cellular voids of green wood are filled with free water. It will gradually evacuate by evaporation, without the wood undergoing any shrinkage or deformation: this is the so-called phase of "drying". When the free water has completely disappeared (saturation point), only the bound water remains, which permeates the cell membranes. The departure of this bound water leads to shrinkage and deformation phenomena. The saturation point of the wood fibers, below which the " game » of wood, is around 30% for all species.

[0043] By " dry wood", we mean wood that has undergone a treatment aimed at reducing the percentage of water retained in the cell walls, the relative humidity of which is therefore generally between 8 and 15%, preferably between 7 and 12%.

[0044] By " A and / or B ", we hear A, or B, or A and B.

[0045] By "we mean % weight " the mass percentage. Unless otherwise specified, any percentage indicated in this description is a mass percentage. Lignocellulosic material

[0046] Particularly preferably, the lignocellulosic material is wood. This wood may be, according to the invention, green wood, wet wood or dry wood, preferably green wood. For example, it may be wood used after possible storage of a more or less long duration (a few days to a few years). This wood may have been transformed after felling, that is to say having been cut, sawn, planed, freed from its bark, sapwood or heartwood, or be an engineered wood.

[0047] It is particularly advantageous according to the invention to be able to treat green wood or even wet wood because this allows for the significant saving of a preliminary step of drying the wood. Indeed, in the usual processes of wood treatment, it is generally dried beforehand. This has the consequence that approximately 20% of material is lost during drying by shrinkage of the cellular matrix. Generally, for use, for example in the case of parquet, approximately 20% of additional material is lost by re-cutting the wood to straighten (or pre-plane) the piece of wood due to the reduction in the humidity level (which goes from 70% at the sawmill exit to 12% at the dryer exit and finally to 7% in the final piece of parquet). This means that almost 40% of material is lost by these operations.The fact of being able to treat green wood directly according to the invention is therefore very economical not only in terms of the quantity of treatment operations to be carried out (saving labor, saving storage and saving time between the raw material and the finished product), but also by the fact that the loss of material is much less.

[0048] It can also be old wood, i.e. wood that has already been used, such as construction timber. Thus, the process of the invention advantageously allows the recycling, and therefore the revaluation, of construction timber.

[0049] Practically all wood species, also called wood families, whose lignin content is between 15 and 35%, preferably between 18 and 32%, even more preferably between 20 and 30%, by weight, can be treated by the method according to the invention, whether they belong to the angiosperm or gymnosperm family, whether they are noble woods such as oak or ash, or more conventional wood, whether it is used in furniture or in the building (construction) field such as furniture wood such as ash, construction wood such as pine, beech or Douglas fir or more malleable wood used for turning wooden parts or model making such as poplar or certain species of balsa.

[0050] Examples include softwood such as gymnosperms, preferably fir, pine, Douglas fir, white, red or black spruce, balsam fir, or hardwood such as linden, poplar, black locust, alder or willow. More generally, softwood is chosen from the group formed by Scots pine, pine, spruce, yew, larch, fir, Swiss stone pine, Douglas fir, araucaria, juniper, cedar, redwood, thuja and cypress.

[0051] The hardwood is selected from angiosperms, preferably selected from the group formed by alder, birch, balsa, beech, ash, eucalyptus, cottonwood, rubberwood, poplar, aspen, willow, black locust, oak, mahogany, guatambu, fraké, meranti, linden, chestnut, maple, horse chestnut, elm, hazel, walnut, Osage orange, plane, sycamore, apple, pear, lemon and tulip tree, more preferably alder, birch, balsa, beech, ash, eucalyptus, cottonwood, rubberwood, poplar, willow, black locust, oak, mahogany, linden, chestnut, maple, horse chestnut, elm, hazel, walnut, Osage orange and plane.

[0052] Each species thus cited can include a large number of species. Thus, the species of pine covers, for example, more than a hundred species such as maritime pine or Scots pine; the species of oak covers many sub-species, such as red oak (known as American oak) or white oak (known as European oak).

[0053] Each wood species has its own architecture and chemical identity (i.e., respective quantities of lignin and hemicelluloses, length of cellulose fibers, and extractables). Within the same tree, different parts of the wood (such as sapwood or heartwood) can also have different physicochemical properties depending on the species considered.

[0054] But lignocellulosic material can also be any material formed from a three-dimensional network of cellulose and lignin, such as straw, natural textiles (such as flax or hemp), all forest biomass, including bamboo, high-yield pulp, paper, cardboard, and cotton, as long as this material is in the form of a structure with a certain mechanical resistance and a micro-architecture suitable for being used by a filling compound that partially replaces the lignin. Such a list includes fibrous compounds (i.e. containing fibers in the native state), such as hemp or flax, but also fibrous compounds (i.e. processed products containing added fibers) and annual grasses. Extraction step (1)

[0055] The extraction step (1) allows the partial and controlled dissolution of a part of the lignin, initially present in the material, in the fluid which is in the supercritical or subcritical phase, accompanied by an evacuation of this lignin by the fluid. This results in a partial and controlled delignification of the lignocellulosic material structure. The lignin and the fluid are then generally separated, during the depressurization of the fluid which was in the supercritical or subcritical phase. This separation allows the recovery of a compound called " extract » including lignin and possible extractables. In other words, the extraction step (1) allows the desired quantity of lignin to be retained in the structure and not to significantly damage the micro-architecture of the lignocellulosic material.

[0056] Lignin is present in the extract recovered at the end of the extraction step (1), most often in the form of fragments. In addition to the molecules resulting from the degradation of lignin, degradation products of other components of the lignocellulosic material may be found in the extract, such as molecules resulting from the degradation of the amorphous parts of the cellulose, simple sugars from peripheral hemicelluloses, or even certain extractables. The extraction step (1) serves in particular to prevent the presence of the dissolved compounds within the structure from limiting the filling of the spaces existing in the native state and those created during the same extraction step (1) by the filling compound during the filling step (2).

[0057] Another advantage of using supercritical or subcritical phase fluid for the extraction step (1) is that it is possible to recycle the fluid in whole or in part after initial use.

[0058] Partial delignification according to the invention excludes the production of a pulp of fibers of lignocellulosic material.

[0059] Generally, fluids in the supercritical or subcritical phase are characterized by low viscosities and high diffusivities. They can thus advantageously improve the mass transfer of extraction. The contact angle of a compound in the supercritical phase with a substrate is zero, which implies that the compound "wet"» completely its substrate: therefore, the lignocellulosic material is more easily filled by the fluid from the extraction stage (1) if it is in the supercritical phase. This is also true when the fluid is in the subcritical phase.

[0060] The extraction step (1) therefore makes it possible both to preserve sufficient lignin (in native form or regenerated after recombination of the radicals formed during the degradation of the lignin) within the material to preserve the architecture of the native lignocellulosic material, and to extract sufficient lignin using the fluid in the supercritical or subcritical phase to release within the architecture of the lignocellulosic material the space into which the filling compound of step (2) will be inserted. In addition, it also allows the cleaning of the lignin and any residual lignin extractables within the structure. Thus, it does not limit the filling of existing spaces, microscopic or nanoscopic, nor of those newly created during the extraction step (1), by the filling compound during the filling step (2).Such a limitation could strongly inhibit the propagation of polymer chains by the action of aromatic hydroxyl (OH) groups which would block radicals generated by a polymerization catalyst.

[0061] This is generally made possible by the modulation and optimization of the extraction operating conditions, accessible to those skilled in the art. Indeed, those skilled in the art are able to adapt the operating conditions thanks to their general technical knowledge.

[0062] The person skilled in the art can, at the end of the process, estimate the degree of delignification achieved during the process, either by a qualitative analysis, linked to the color of the extract (the darker the extract, the more lignin it contains, knowing that cellulose and hemicellulose are white); or by a quantitative analysis of the quantity of lignin recovered in the extract. He can also, at the end of the process, base himself on the loss in mass of the lignocellulosic material structure, due to the extraction of lignin, to estimate the degree of delignification.

[0063] The operating conditions depend, among other things, on the nature of the fluid in the supercritical or subcritical phase.

[0064] The extraction step (1) is generally carried out in static or dynamic mode, in one or more sub-steps, using one or more fluids in supercritical or subcritical phase.

[0065] By "dynamic mode", According to the invention, it is understood that the fluid (possibly mixed with a co-solvent) moves during the process in the enclosure in which the process is carried out, preferably regularly over time (constant flow rate). This movement is generally generated by a pump operating continuously, with recirculation of the fluid from the enclosure in the enclosure, for example after a purification and / or filtration treatment.

[0066] By " static mode”, according to the invention it is understood that the fluid (possibly mixed with a co-solvent) is not in motion during the process, but is almost stationary in the enclosure in which the process is carried out.

[0067] The main operating conditions for extraction are generally pressure, temperature, and duration, as well as the nature and quantity of co-solvent if a co-solvent is present. Other operating conditions not directly related to extraction but allowing optimization of the extraction step are the presence (or not) of agitation and the parameters of the lignocellulosic material structure such as its composition or the thickness of its structure. In addition, the supercritical or subcritical phase of the fluid is generally carried out in the presence of the lignocellulosic material structure, by pressurization and temperature. Then, the pressurization rate ( iepressurization) as well as the speed of depressurization are parameters to be taken into account. Indeed, as is immediately apparent to those skilled in the art, pressurization and depressurization should not be carried out too quickly, in order to evacuate the extracted lignin and not to modify the physical and optical properties of the lignocellulosic material.

[0068] Although not preferred, delignification may not be carried out homogeneously within the lignocellulosic material, particularly depending on the operating conditions of step (1). This is particularly the case when the thickness of the lignocellulosic material structure is significant.

[0069] The extraction step (1) is generally carried out, according to a preferred embodiment of the invention, using carbon dioxide (CO 2 ) in supercritical phase in dynamic mode or in static mode, for 1 to 72 hours, preferably 2 to 72 hours, more preferably 4 to 24 hours, at a pressure of 8 to 40 MPa (80 to 400 bar), preferably 15 to 20 MPa (150 to 200 bar) and at a temperature of between 35 and 200°C, preferably between 50 and 200°C, more preferably either between 160 and 200°C or between 140 and 160°C. In this case, preferably, the stirring is generally 10 to 100 rpm (or " rpm " For " round per minute » or revolutions per minute), preferably 10 to 50 rpm, the pressurization speed is generally 0.5 to 1 MPa / min (5 to 10 bar / min), preferably 0.4 to 0.6 MPa / min (4 to 6 bar / min), and the depressurization speed is generally 0.2 to 0.5 MPa / min (2 to 5 bar / min), preferably 0.2 to 0.3 MPa / min (2 to 3 bar / min).

[0070] Agitation during the extraction step (1) advantageously improves the diffusion of the fluid phase within the lignocellulosic material and thus the extraction, whether in static or dynamic mode. It can be carried out by mechanical or wave action, such as sonic.

[0071] The extraction step (1) can also be carried out using subcritical phase water in dynamic mode or in static mode, for 0.5 to 4 h, at a pressure of 1.2 to 25 MPa (12 to 250 bar), preferably 1.2 to 20 MPa (12 to 200 bar) and at a temperature between 60 and 180°C, preferably between 120 and 180°C. In this case, the stirring is generally 10 to 100 rpm, the pressurization speed is generally 0.5 to 1 MPa / min (5 to 10 bar / min) and the depressurization speed is generally 0.2 to 0.5 MPa / min (2 to 5 bar / min).

[0072] The extraction step (1) can also be carried out using isopropanol or t-butanol in supercritical phase in dynamic mode or in static mode, for 0.5 to 8 h, at a pressure of 4 to 8 MPa (40 to 80 bar), and at a temperature between 185 and 275°C. In this case, the agitation is generally 10 to 100 rpm, the pressurization rate is generally 0.5 to 1 MPa / min (5 to 10 bar / min) and the depressurization rate is generally 0.2 to 0.5 MPa / min (2 to 5 bar / min).

[0073] The fluid in the supercritical or subcritical phase may include at least one minor solvent, called a co-solvent. The co-solvent is a liquid compound added in small quantities and miscible with said fluid. The co-solvent is generally used to improve the solvation power of the primary solvent with respect to the species to be dissolved and to improve the swelling / expansion of the lignocellulosic material. The presence of the co-solvent is therefore particularly advantageous for optimizing the extraction step (1).

[0074] The fluid in the supercritical or subcritical phase is preferably chosen from: carbon dioxide CO 2 in supercritical phase, preferably mixed with at least one polar co-solvent chosen from dioxane, water, methanol, ethanol, acetic acid, acetone and mixtures thereof; at least one alcohol in supercritical phase, said alcohol being chosen from t-butanol (or tert-butanol; IUPAC name 2-methylpropan-2-ol) and isopropanol (IUPAC name propan-2-ol); ethanol, acetone or methanol in subcritical phase, preferably mixed with water as co-solvent, more preferably in small quantity; subcritical phase water, preferably mixed with at least one base such as ammonia, lithium hydroxide (LiOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH) 2 ), sodium carbonate (Na 2 CO 3 ), potassium carbonate (K 2 CO 3 ) or at least one acid such as formic acid and acetic acid.

[0075] It is also called a co-solvent for the base or acid mixed with water in the subcritical phase.

[0076] The co-solvent may, preferably must, be present, as indicated above, in the fluid in the supercritical or subcritical phase. However, it may be introduced into a reactor for carrying out the extraction step independently of the fluid intended to be put into the supercritical or subcritical phase. It may also be introduced simultaneously or mixed with the fluid intended to be put into the supercritical or subcritical phase.

[0077] It is particularly preferred according to the invention to use a fluid with a minimal carbon footprint, such as water or carbon dioxide. In this case, the presence of at least one co-solvent in the supercritical phase in the case of using carbon dioxide or in the subcritical phase in the case of using water is particularly advantageous, since it makes it possible to improve the extraction conditions.

[0078] Thus, in the case of using CO2 in the supercritical phase, the addition of a co-solvent makes it possible to improve the polarity of the fluid in the supercritical phase, and consequently the solubility of lignin (which is polar) in the fluid phase (apolar), as well as the expansion of the cellulose macrofibrils.

[0079] In the case of using subcritical water, the addition of base or acid acting as a co-solvent improves the dissolution of lignin and the swelling / expansion of cellulose macrofibrils.

[0080] The supercritical coordinates of carbon dioxide are relatively mild, i.e., above 31°C and 7.4 MPa (74 bar). Carbon dioxide in the supercritical phase is particularly preferred because it has good solvent power for the extraction of apolar compounds, its high dipole moment allows it to dissolve certain weakly polar molecules, and the possible addition of co-solvent, preferably polar co-solvent within it, improves the dissolution of polar molecules in this fluid in the supercritical phase.

[0081] The subcritical coordinates of water are below 374.3°C and 22.1 MPa (221 bar). The advantages, among others, of using subcritical water for extraction are: the use of wet lignocellulosic materials without going through the drying step, the use of a green solvent, the limitation of co-product extraction by improving selectivity and the realization of an extraction step without the addition of chemical solvent to extract components poorly soluble in water at room temperature and pressure. In addition, subcritical water is one of the best clean solvents for cellulose because it has a swelling / dilating effect on cellulose macrofibrils and solubilizes weakly polar compounds which facilitates the extraction of the compounds of interest thanks to these modified properties.

[0082] The subcritical coordinates of ethanol are below 301°C and 6.1 MPa (61 bar). The subcritical coordinates of acetone and methanol are respectively below 235°C and 4.6 MPa (46 bar), and below 239.3°C and 8.1 MPa (81 bar).

[0083] The supercritical coordinates of isopropanol are 5.3 MPa (or 53 bar) and 235°C, respectively. The supercritical coordinates of t-butanol are 3.9 MPa (or 39 bar) and 233°C. The use of either of these alcohols in the supercritical phase is advantageous for the solubilization of lignin hydrolysis products, which facilitates its subsequent extraction.

[0084] The supercritical or subcritical phase fluid of the extraction step (1) is particularly preferably carbon dioxide (CO 2 ) in supercritical phase, mixed with a mixture of water and ethanol (as co-solvent) in a proportion of between 5% water - 95% ethanol and 95% water - 5% ethanol, preferably between 30% water - 70% ethanol and 70% water - 30% ethanol, more preferably equal to approximately 50% water - 50% ethanol (in % volume).

[0085] According to a variant of the invention, the extraction step (1) is further carried out in the presence of at least one enzyme chosen from the group formed by (or chosen from) laccase, lignin peroxidase (LiP), manganese peroxidase (MnP) and xylanase, said enzyme being present in the fluid in supercritical or subcritical phase. Preferably, said fluid in supercritical or subcritical phase then further comprises at least one catalyst chosen from 2,2'-azino-di(3-ethylbenzothiazolin-6-sulfonic acid) (or ABTS), 1-hydroxybenzotriazole (HBT), N-hydroxyphthalimide (HPI), N-hydroxy-N-phenylacetamide (NHA), (2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO), violuric acid, and mixtures thereof.

[0086] This is called extraction by enzymatic treatment. In this case, the enzyme is used as a catalyst for extraction, as it facilitates the degradation of lignin within the material. The enzyme is generally carried by a fluid called a carrier fluid, which is most often the fluid intended to be placed in the supercritical or subcritical phase. The enzyme is more generally placed in solution. By " solution " we mean the mixture of a solute, which is a chemical element in solid, liquid or gaseous form, dissolved in a solvent, which is a liquid chemical element). The carrier fluid can itself be transported by another fluid, generally miscible, which can be the fluid intended to be put into the supercritical or subcritical phase, which has different characteristics, the whole thus most often forming a complex system, for example micellar or two-phase.

[0087] The extraction step (1) by enzymatic treatment is generally carried out in a single step, most often by placing the enzyme with the material and directly introducing the fluid intended to be put into the supercritical phase. It is preferred in this case that a pretreatment step of the material has been carried out beforehand in order to prepare it for the enzymatic treatment. Without wishing to be bound by any theory, the applicant believes that this pretreatment step serves to expel air and water from the lignocellulosic material so as to allow better penetration of the enzyme in the subsequent step. Such a preliminary step may be a pretreatment step with at least one fluid in the supercritical or subcritical phase, in static mode or in dynamic mode, under pressure conditions of 0.8 to 40 MPa (8 to 400 bar), temperature of 32 to 200°C and for a duration of 15 min to 72 h.

[0088] The enzymatic treatment step is generally carried out according to the operating conditions of the extraction step (1) explained above, one of the important operating parameters being in addition the nature and concentration of the enzyme as well as the nature and concentration of the possible catalyst such as HBT.

[0089] The enzymatic treatment step allows the extraction of lignin and other compounds possibly dissolved and present in the lignocellulosic material, in the solution containing the enzyme which is recovered at the end of the extraction, whether in static or dynamic mode.

[0090] The partial delignification carried out in the extraction step (1) can possibly be used, although this is not its primary objective, to extract, in addition to lignin, other components of the lignocellulosic material such as extractables.

[0091] The quantity of lignin extracted from the lignocellulosic material depends mainly on the operating conditions of the treatment (mainly method, duration, temperature, pressure, possibly even agitation, pressurization speed and depressurization speed, or even in the case of the presence of an enzyme, the concentration of the enzyme and the use or not of a catalyst such as HBT). But it also depends on the nature of the material concerned, depending on whether it is, for example, softwood, hardwood or an annual grass.

[0092] Thus, in the case where the lignocellulosic material is softwood, it is generally 50 to 85%, preferably 50 to 75%, in % by weight, of the lignin present in the structure which is extracted during the extraction step (1). On the other hand, in the case where the lignocellulosic material is hardwood, it is generally 40 to 60%, preferably 45 to 55%, in % by weight, of the lignin present in the structure which is extracted during the extraction step (1). A person skilled in the art is able to adapt the conduct of step (1) according to the structure concerned and the nature of the lignocellulosic material.

[0093] In practice, the fluid intended to be put into the supercritical or subcritical phase is introduced into a high pressure cell, which contains the lignocellulosic material structure, in order to reach the desired temperature and pressure conditions which will allow this fluid to be put into the supercritical or subcritical phase.

[0094] By " high pressure cell ", according to the invention, means a cell or enclosure which withstands high pressures and temperatures and in which extraction can be carried out in the supercritical or subcritical phase.

[0095] The co-solvent, if present, is generally introduced at the same time as the lignocellulosic material structure in the high pressure cell when the extraction step (1) is carried out statically.

[0096] When the extraction step (1) is carried out in dynamic mode, any co-solvent present is generally introduced continuously into the high pressure cell in parallel with the continuous introduction of the fluid intended to be put into the supercritical or subcritical phase.

[0097] During this extraction step (1), the supercritical phase fluid diffuses within the lignocellulosic material and thus swells and expands the cellulose macrofibrils of the material while partially solubilizing the lignin. This leads to the production of low molecular weight lignin fragments and their dissolution in the supercritical or subcritical phase fluid, possibly mixed with the co-solvent. The presence of organic co-solvent (water / ethanol mixture for example in the case of carbon dioxide in the supercritical phase) favors these effects.

[0098] At the end of this extraction step (1), the fluid in the supercritical or subcritical phase is generally evacuated in a controlled manner from the high-pressure cell, typically by means of controlled depressurization so as not to damage the structure of the wood, and the extract which contains the lignin is recovered. Advantageously, the lignocellulosic material thus treated retains enough lignin to preserve its structure and its chemical, mechanical and optical properties.

[0099] The dissolved lignin that is extracted from the lignocellulosic material structure plays an essential role in the process of the invention. As explained above, other compounds can be dissolved and extracted, or even simply extracted, from the lignocellulosic material during the extraction step (1).

[0100] According to the method of the invention, the dissolved lignin recovered in the fluid of the extraction step (1) is generally pure because the fluid in the supercritical or subcritical phase advantageously preserves the lignin during extraction without chemically modifying it. This dissolved lignin is preferably used in a lignin recovery process, generally on an industrial level, for the manufacture of a construction material, a material used in aeronautics, a packaging material, a biofuel, a pharmaceutical compound and / or, preferably, a chemical compound.Lignin can thus be used to recover it in carbon fiber (by aromatic combination), fiber-reinforced concrete, packaging, biofuels (by methanization), medicines, and chemical components (ferulic acid in particular) and flavors (vanillin), but also for applications with higher added value such as the extraction of aromatic molecules as basic synthons in various fields of chemistry (polymers, synthesis of precursors, etc.). Lignin can also be used through different pulps (such as kraft, paper pulp, alkaline pulp or sulfite pulp) in the field of packaging. This gives the process according to the invention an ecological process character (or process . "green"), by avoiding the production of non-recyclable waste as much as possible.

[0101] It is also possible to proceed within the framework of the invention, according to what has been envisaged in the literature, to uses of the lignin extracted from the fluid of the extraction step (1) in fields as varied as: biorefining (combustion products, syngas, bioethanol); specialty biochemicals (aromatic derivatives such as vanillin, benzene, xylene, DMBQ (2,6-dimethoxy-1,4-benzoquinone), syringaldehyde, syringol, vanillic acid, sinapinic acid, p-hydroxybenzaldehyde, 3-ethylphenol, 2-methylphenol, 3-methoxycatechol, ferulic acid; gases such as carbon dioxide, carbon monoxide, methane, or methanol); specialty compounds (low-grade or medium-grade carbon fiber for applications such as aerospace, automotive, motorcycles, airplanes, windmills, brakes, or fishing rods; asphalt additives; cement additives; and emulsifying agents); and various materials (plastic products such as phenolic resins, epoxy resins, lignin-polyurethane foams; rubber products such as lignin-polyurethane elastomer coatings; adhesive products;chipboard products; animal nutrition products such as tablets or binders; flammable products such as matches or barbecue fluids).

[0102] Similarly, extracted compounds other than lignin are preferably used in a recovery process, such as a process for recovering sugars or aromatic or functional molecules, generally on an industrial level. For some of these applications, these extracted compounds must undergo post-treatment steps, such as purifications and / or fractionations, before their use in said applications. Optional intermediate functionalization step

[0103] The optional intermediate functionalization step, located between the extraction step (1) and the filling step (2), aims to adjust the chemical and physical properties, particularly the hydrophilic or hydrophobic properties of the delignified lignocellulosic material, in order to improve the filling step (2) or even the finishing step (3). Indeed, such functionalization makes it possible to increase the affinity of the delignified lignocellulosic material towards the filling compound, respectively hydrophilic or hydrophobic, and thus improves the grafting properties of the filling compound with the components of the lignocellulosic material in the filling step (2). In addition, functionalization generally makes it possible to improve the mechanical properties of the lignocellulosic material and to make it less sensitive to the humidity of the environment.

[0104] The functionalization step can thus be a step of activation of the hydroxyl groups or an oxidation step. “activation of hydroxyl groups” here we mean any reaction in the presence of an organic co-reactant having a sufficiently electrophilic function to allow the creation of a CO bond, between a carbon of the co-reactant and an oxygen of the hydroxyl group.

[0105] Functionalization can also consist of any other treatment suitable for optimizing the action of the filling step (2).

[0106] The functionalization step can be carried out conventionally (i.e. neither in the supercritical nor in the subcritical phase), or preferably in the supercritical or subcritical phase. By " conventional route » we mean a primary use of at least one organic solvent most often by soaking or bathing.

[0107] The supercritical or subcritical phase fluid is generally such that the filling compound is soluble in the supercritical or subcritical phase fluid.

[0108] Thus, the supercritical or subcritical phase fluid used in the intermediate functionalization step is preferably chosen from: carbon dioxide CO 2 in supercritical phase, preferably mixed with at least one polar co-solvent chosen from dioxane, water, methanol, ethanol, acetic acid, acetone and mixtures thereof; water in subcritical phase, preferably mixed with at least one base such as ammonia, lithium hydroxide (LiOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH) 2 ), sodium carbonate (Na 2 CO 3 ), potassium carbonate (K 2 CO 3 ) or at least one acid such as formic acid and acetic acid.

[0109] The operating conditions for using these fluids are those indicated for these fluids in the extraction step (1), namely that the intermediate step is carried out: either by using carbon dioxide (CO 2 ) in supercritical phase in dynamic mode or in static mode, for 1 to 72 hours, preferably 2 to 72 hours, at a pressure of 8 to 40 MPa (80 to 400 bar), and at a temperature between 35 and 200°C, preferably between 50 and 200°C. In this case, preferably, the stirring is generally 10 to 100 rpm, the pressurization speed is generally 0.5 to 1 MPa / min (5 to 10 bar / min) and the depressurization speed is generally 0.2 to 0.5 MPa / min (2 to 5 bar / min); Either using subcritical phase water in dynamic mode or in static mode, for 0.5 to 4 h, at a pressure of 1.2 to 25 MPa (12 to 250 bar), preferably 1.2 to 20 MPa (12 to 200 bar), and at a temperature between 120 and 180°C. In this case, the agitation is generally 10 to 100 rpm, the pressurization speed is generally 0.5 to 1 MPa / min (5 to 10 bar / min) and the speed of depressurization is typically 0.2 to 0.5 MPa / min (2 to 5 bar / min).

[0110] Even more preferably, the functionalization is carried out supercritically, more particularly using carbon dioxide (CO 2 ) in the supercritical phase in static or dynamic mode, under pressure of 8 to 20 MPa (80 to 200 bar), at a temperature of 32 to 200°C, with stirring (at a speed typically of 10 to 100 rpm), in the presence or absence of a co-solvent such as ethanol, and for a duration of 0.5 to 4 hours. In this case, the pressurization rate and the depressurization rate of the fluid are preferably controlled during the functionalization step: they are then respectively 0.5 to 1 MPa / min (5 to 10 bar / min) and 0.2 to 0.5 MPa / min (2 to 5 bar / min).

[0111] Esterification and etherification by methylation, carboxymethylation and / or hydroxypropylation of the lignocellulosic material are generally functionalizations according to the invention. Their implementation is accessible to those skilled in the art.

[0112] Esterification can be a reaction of the hydroxyls at the C2, C3 and C6 positions of cellulose with an acid halide derivative, such as bromoisobutyrate bromide, or an opening of an anhydride ring such as succinic anhydride, maleic anhydride or glutaric anhydride. Carboxymethylation is a specific case of the reaction of cellulose with an anhydride, such as acetic anhydride, which allows the cellulose to be functionalized with an acetate and thus to form cellulose acetate.

[0113] Etherification can be a reaction of cellulose hydroxyls with organic halide compounds, such as propargyl bromide, trityl chloride, or epichloridrine. Etherification can also be achieved by opening epoxides such as propylene oxide (IUPAC name 2-methyloxirane), 1,2-epoxybutane (IUPAC name 2-ethyloxirane), 1,2-epoxypentane (IUPAC name 2-propyloxirane), 2,3-epoxy(propyl)benzene (IUPAC name (Phenylmethyl)oxirane), trimethylene oxide (IUPAC name oxetane), glycidole (IUPAC name Oxiranylmethanol).

[0114] Preferably, the functionalization of the delignified lignocellulosic material aims to introduce hydrophilic functions onto the cellulose fibrils, by an oxidative treatment. This oxidative treatment can be carried out in particular by a treatment with ozone, hydrogen peroxide or (2,2,6,6-tetramethylpiperidin-1-yl)oxy (or TEMPO), preferably with ozone or TEMPO, by conventional, supercritical or subcritical means.

[0115] A preferred case of the functionalization step is the treatment of the lignocellulosic material from the extraction step (1) using supercritical phase ozone. In an exemplary embodiment, the ozone in liquid form is evaporated and then condensed at -196°C in an autoclave, which is then gently heated to room temperature (approximately 20°C) (i.e. typically with a temperature ramp of 1°C / min (i.e. 3h36) to 5°C / min (i.e. 43 min). The autoclave containing the ozone is then supplied with a fluid, for example in the case of CO 2 , in order to reach a pressure of 1 MPa (10 bar). The CO 2 / O 3 mixture is then transferred into a high-pressure cell which contains a delignified lignocellulosic material from the extraction step (1). The high-pressure cell is then pressurized (i.e. pressurized) in order to reach the certain previously defined working pressure.The high-pressure cell is then heated and supplied once again with the fluid intended to be put into the supercritical or subcritical phase, for example CO 2 , to reach the desired pressure and temperature and put said fluid into the supercritical or subcritical phase. At the end of this functionalization step, lasting for example 2 hours, the high-pressure cell is depressurized (i.e. it is brought back to ambient atmosphere), which makes it possible to recover the delignified material thus treated. Filling step (2)

[0116] The filling step (2) is a step in which the filling of the partially delignified or partially delignified and optionally functionalized structure with the filling compound is carried out, i.e. the filling compound is made to penetrate into the partially delignified or partially delignified and optionally functionalized structure.

[0117] It can be carried out in one or more sub-stages. The filling compound must most often have the property of binding to the fibers of the lignocellulosic material still present within the structure, by chemical or physicochemical anchoring.

[0118] The filling step (2) may be carried out in at least one series of at least two successive sub-steps, each sub-step being carried out by filling, for example with the same fluid or with a different fluid per sub-step, or by progressively increasing the concentrations of the same fluid in filling compound during the sub-steps.

[0119] The development of filling conditions is within the reach of those skilled in the art.

[0120] The filling step (2) can be carried out by injecting the filling compound by vacuum or under pressure by an RTM type technique (for “Resin Transfer Molding” or “Resin injection molding” has low pressure») or RTM Light (for “ lightened"), by infusion of the filling compound using a RIFT type technique (for " Resin Infusion under Flexible Tooling » which could be translated as " resin infusion by flexible tooling "), by vacuum or pressure process or by process using a supercritical phase in a reactor, autoclave or vacuum oven or by soaking in a tank or any other device that the person skilled in the art knows is capable of carrying out this step.

[0121] It may be advisable to alternate at least one vacuum phase sub-step with at least one pressure phase sub-step to properly impregnate the lignocellulosic material. This alternation promotes the penetration of the filling compound into the material due to the pressure difference thus created.

[0122] According to a particularly preferred embodiment according to the invention, the filling step (2) is carried out using a fluid in supercritical or subcritical phase, which may include a co-solvent as explained in step (1). In this case, we speak of " impregnation » rather than filling. In this case, the filling step (2) is generally carried out in a high-pressure cell in the presence of at least one fluid in supercritical or subcritical phase in which the filling compound is solubilized.

[0123] The supercritical or subcritical phase fluid can be selected from the fluids used according to the extraction step (1). However, here, an important parameter is the solubility of the filling compound in the supercritical or subcritical phase fluid.

[0124] Thus, the supercritical or subcritical phase fluid used in step (2) is preferably chosen from: carbon dioxide CO 2 in supercritical phase, preferably mixed with at least one polar co-solvent chosen from dioxane, water, methanol, ethanol, acetic acid, acetone and mixtures thereof; at least one alcohol in supercritical phase, said alcohol being chosen from t-butanol (or tert-butanol; IUPAC name 2-methylpropan-2-ol) and isopropanol (IUPAC name propan-2-ol); ethanol, acetone or methanol in subcritical phase, preferably mixed with water as co-solvent, preferably in small quantity; subcritical phase water, preferably mixed with at least one base such as ammonia, lithium hydroxide (LiOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH) 2 ), sodium carbonate (Na 2 CO 3 ), potassium carbonate (K 2 CO 3 ) or at least one acid such as formic acid and acetic acid.

[0125] The co-solvent may, preferably must, be present, as indicated above, in the fluid in the supercritical or subcritical phase. However, it may be introduced into a reactor for carrying out the filling step independently of the fluid intended to be put into the supercritical phase. It may also be introduced simultaneously or mixed with the fluid intended to be put into the supercritical phase.

[0126] The operating conditions for using these fluids are generally as follows: either by using carbon dioxide (CO 2 ) in supercritical phase in dynamic mode or in static mode, for 2 to 72 hours, at a pressure of 8 to 40 MPa (80 to 400 bar), and at a temperature between 50 and 200°C. In this case, preferably, the agitation is generally 10 to 100 rpm (for " round per minute» or revolutions per minute), the pressurization speed is generally 0.5 to 1 MPa / min (5 to 10 bar / min) and the depressurization speed is generally 0.2 to 0.5 MPa / min (2 to 5 bar / min); Either using subcritical phase water in dynamic mode or static mode, for 0.5 to 4 h, at a pressure of 1.2 to 25 MPa (12 to 250 bar), and at a temperature between 120 and 180°C. In this case, the agitation is generally 10 to 100 rpm, the pressurization speed is generally 0.5 to 1 MPa / min (5 to 10 bar / min) and the depressurization speed is generally 0.2 to 0.5 MPa / min (2 to 5 bar / min); Either using ethanol, acetone or methanol in subcritical phase in dynamic mode or in static mode, for 0.5 to 4 h, at a pressure of 0.5 to 4.5 MPa (5 to 45 bar), and at a temperature between 40 and 230°C.In this case, the agitation is generally 10 to 100 rpm, the pressurization rate is generally 0.5 to 1 MPa / min (5 to 10 bar / min) and the depressurization rate is generally 0.2 to 0.5 MPa / min (2 to 5 bar / min); Either using isopropanol or t-butanol in supercritical phase in dynamic mode or in static mode, for 0.5 to 8 h, at a pressure of 4 to 8 MPa (40 to 80 bar), and at a temperature between 185 and 275°C. In this case, the agitation is generally 10 to 100 rpm, the pressurization speed is generally 0.5 to 1 MPa / min (5 to 10 bar / min), and the depressurization speed is generally 0.2 to 0.5 MPa / min (2 to 5 bar / min).

[0127] Even more preferably, the filling step (2) is carried out supercritically, using more particularly carbon dioxide (CO 2 ) in the supercritical phase under pressure conditions of 8 to 40 MPa (80 to 400 bar), temperature of 32 to 200°C, with stirring (typically at a speed of 10 to 100 rpm) and in the presence or absence of a co-solvent such as water or ethanol. In this case, the pressurization rate and the depressurization rate of the fluid are preferably controlled during the filling step (2): they are then respectively 0.5 to 1 MPa / min (5 to 10 bar / min) and 0.2 to 0.5 MPa / min (2 to 5 bar / min).

[0128] According to a particularly preferred embodiment, the filling step (2) is carried out in the presence of at least one fluid in supercritical or subcritical phase in which the filling compound is solubilized. Thus, the partially delignified and optionally functionalized lignocellulosic material structure is impregnated with this mixture of fluids. To do this, a given volume of filling compound is used to ensure the filling of the structure in an autoclave. This volume is determined by taking into account the removal of oxygen present in the cavities of the lignocellulosic material and the possible transformation of the compound in the event of vacuum and / or heating.

[0129] According to one of the embodiments which will be explained in the examples, a fluid intended to be placed in the supercritical or subcritical phase is introduced into a saturator-type enclosure into which at least one filling compound is previously introduced, in order to subsequently solubilize the filling compound under operating conditions in which the fluid is in the supercritical or subcritical phase.

[0130] By "saturator", according to the invention we mean a cell (or reactor) which withstands fairly high pressures and temperatures and which makes it possible to completely solubilize a substrate (such as a co-solvent for example) in a fluid in supercritical or subcritical phase.

[0131] The fluid in the supercritical or subcritical phase is then introduced into a high pressure cell which previously contains a delignified lignocellulosic material structure and the filling compound so as to carry out the filling step (2) (which in this case is an impregnation) of the partially delignified structure in the liquid polymer or co-polymer.

[0132] The filling step (2) of the treatment method according to the invention can be carried out essentially according to two embodiments, explained below, each of these two modes preferably being carried out in the presence of a fluid in supercritical or subcritical phase. These two modes can be adapted depending on the lignocellulosic material used.

[0133] Thus, according to a first embodiment of the filling step (2), the filling compound is a polymer or a co-polymer, formulated or not, most often, prior to contact with the structure of lignocellulosic material, deposited in a saturator-type enclosure to promote its solubilization in the fluid intended to be placed in the supercritical or subcritical phase.

[0134] It is preferable to use a thermoplastic polymer or copolymer, in which case the temperature of the filling step (2) is generally higher than the glass transition temperature of this polymer or copolymer. In this case, the subsequent finishing step (3) will consist of resting at a temperature lower than the glass transition temperature of the polymer or copolymer. This assumes that the polymer or copolymer has a glass transition temperature higher than the temperature of the finishing step (3).

[0135] Preferably, the polymer or copolymer is selected from the group consisting of polyacrylates, polyamides (such as Nylons ®< from DuPont), polyesters, fluoropolymers (such as Teflon ®< from DuPont), polyethylene, polypropylene, polybutene, polystyrene, poly(phenylene oxide), poly(vinyl chloride), poly(vinylidene chloride), polycarbonate, poly(lactic acid), polyethersulfones, polyetherimides, polyaryletherketones, inorganic or organic sol-gel materials such as Ormosil polymers (for “organically modified silica” or “organically modified silicates”, i.e. organically modified silicates or silicas), silicones, and combinations thereof; as well as in the group formed by polymers and copolymers, not listed above and obtained from the monomers of the second embodiment, the list of which is given below.Cellulose, starch, polypeptides, proteins, as well as polymers derived from these compounds, such as cellulose acetate or starch acetate, formulated or not, can be used in this embodiment.

[0136] The filling compound of filling step (2) may also be a vitrimer, generally obtained from thermosetting polymers (such as epoxy) and / or thermoplastic polymers (such as poly(methyl methacrylate), polystyrene or high density polyethylene).

[0137] According to the invention, it is considered that a vitrimer is a polymer, entering into the first embodiment of the filling step (2).

[0138] According to the invention, the term "vitrimer" refers to a new category of organic material that can be described as a polymer. Thus, a vitrimer is a light and strong polymer that, once hardened, can be remelted and remolded like glass while exhibiting mechanical properties superior to those of glass. It therefore combines the qualities of thermoplastic compounds (which can be remelted and remolded and therefore recycled) and those of thermosetting compounds that exhibit good mechanical, chemical and thermal properties, but which cannot be reused.

[0139] Vitrimers can be synthesized for example by metathesis reactions between dioxaborolanes (compounds containing a boron atom bonded to 2 oxygen atoms) and polymers (such as poly(methyl methacrylate) or polystyrene) containing only carbon-carbon chemical bonds in their backbone without the addition of catalysts at moderate temperatures of around 60 °C.

[0140] This reaction is generally rapid and efficient, with the resulting compounds exhibiting superior chemical, mechanical and thermal properties to the starting polymers. It does not require a catalyst, which constitutes a real economic and ecological advantage.

[0141] The term "metathesis" refers to changes in the bonds between atoms, formally leading to chemical compounds in which the bonds of the different types are almost the same in number and of the same nature as in the original compounds.

[0142] According to the second embodiment of the filling step (2), the filling compound of the filling step (2) is a polymerizable monomer present in a monomeric solution or in a monomeric formulation at the pressure and temperature conditions of the filling step (2).

[0143] Preferably, the filling compound of the filling step (2) is a monomer present in a monomeric solution polymerizable at the pressure and temperature conditions of the filling step (2), the monomeric solution further comprising at least one catalyst. Such a polymerizable monomer generally leads to the production of a thermoplastic (polymer) or a thermosetting (polymer).

[0144] The filler compounds may therefore comprise monomers, in the form of monomeric solutions or even monomeric formulations. The monomeric solutions and formulations may be commercial products known to those skilled in the art.

[0145] In general, it is recommended to avoid the use of a filling compound which presents the risk of generating volatile by-products and / or those not linked to the structure of the composite material.

[0146] We understand by "monomeric solution"a mixture of one or more monomers, with or without an agent activating the polymerization of these monomers. In a particularly preferred manner, the filling step (2) is carried out in the presence of a fluid in supercritical or subcritical phase in which a monomeric solution comprising the filling compound is solubilized. Thus, the partially delignified and optionally functionalized lignocellulosic material structure is impregnated with these fluids.

[0147] We understand by "monomeric formulation"a monomeric solution containing at least one additional compound. Such an additional compound is generally chosen from oligomers, polymers, copolymers with regard to thermoplastics, or pre-polymers and pre-co-polymers accompanied by at least one hardener for thermosets. This additional compound may also be an agent which allows polymerization such as an initiator (for example a bio-sourced initiator such as epichlorohydrin, carboxylic acids, amines, and mixtures thereof), a catalyst, preferably thermally activatable or degradable by radiation, a filler, a surfactant, a polymerization retarder or inhibitor, a chain transfer agent, or a mixture of these compounds.

[0148] Most often, the filler, if present, is organic or mineral. The mineral filler is generally selected from the group consisting of aluminas, clays, carbon powders, glass beads, diamonds, gypsum, limestone, mica, perlite, quartz, sand, talc, silica, titanium and mixtures thereof, preferably selected from the group consisting of clays, diamonds, glass beads, gypsum, limestone, mica, perlite, quartz, sand, talc and mixtures thereof. The mineral filler may be functionalized to increase its dispersion and stability in the monomeric filler formulation. At least one surfactant may be added for this purpose as well.

[0149] The catalyst is chosen so as to catalyze, preferably, a radical polymerization reaction. This choice generally depends, as is known to those skilled in the art, in addition to the monomer, on the polymerization mode and its control.

[0150] The catalyst is preferably chosen from the group formed by azo-type compounds of formula RN=N-R', where R and R' are alkyl groups optionally comprising at least one additional function, such as azobisisobutyronitrile, peroxides, alkyl compounds (generally comprising from 1 to 6 carbon atoms per molecule), halogenated compounds (i.e. comprising a halogen atom which is chlorine, bromine, iodine or fluorine), nitroxides, thio carbonyl thio compounds, and mixtures thereof.But any other catalyst known to those skilled in the art is also conceivable, such as ketone peroxide, hydrogen peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxyesters, peroxy dicarbonates, such as benzoyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, potassium persulfate, tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxyisobutyrate, 1,1-bis-tert-butylperoxy-3,3,5-trimethylcyclohexane, tert-butyl peroxylaurate, tert-butyl peroxyisophthalate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, tert-butyl peroxide, dicumyl peroxide, di-tert-butyl peroxide and mixtures thereof.

[0151] According to this second embodiment of the filling step (2), the monomeric solution or the monomeric formulation of the filling step (2) may further comprise at least one plasticizing agent which may be a solvent, an oligomer or even a filler intended to reduce the viscosity of the filling compound and thus allow better penetration of the filling compound within the lignocellulosic structure of the material.

[0152] If the plasticizing agent is a solvent, it is generally chosen such that it evaporates largely at room temperature so as to limit the emission of volatile organic compounds during the lifetime of the composite material structure. Indeed, the use of a monomeric solution or monomeric formulation containing a low-volatile solvent is not preferred, in the context of the present invention, since the impregnation of a solvent in the structure of the lignocellulosic material can lead to the creation of ungrafted molecules trapped in the composite material structure which could be gradually released. If the plasticizing agent is an oligomer, it is chosen such that it anchors itself durably in the direction of the structure in order to avoid any subsequent release.

[0153] At least one agent for preserving the structure of the final composite material, such as a UV absorber, may also be added to the monomeric filler formulation. This improves its retention in the structure. Such an agent may be chosen from chromophoric compounds such as anthraquinone, compounds based on a benzophenone or benzotriazole unit, diphenyl acrylate, and all or part of the compounds extracted during the extraction step (1), and mixtures thereof.

[0154] At least one flame retardant, fungicide, bactericide or insecticidal compound may also be added, in order to enhance the properties of the final composite material structure. Flame retardant compounds include aluminum trihydrate, antimony trioxide, antimony pentoxide and organophosphorus compounds, and all or part of the compounds extracted during extraction (1), and mixtures thereof.

[0155] The monomeric filler formulation may further comprise at least one polarity agent selected from the group consisting of ethanol, ethylene glycol, methyl ether, N-methyl pyrrolidone, dioxanes, dimethylformamide, diethylene glycol, diethylene glycol dimethyl ether, pyridine, n-butylamine, piperidine, morpholine, 4-picoline, 2-picoline, diethylamine, aniline, acetone, and methanol.

[0156] The presence of such a polarity agent advantageously allows better penetration of the filling compound within the lignocellulosic structure as well as swelling of the lignocellulosic matrix. Indeed, the presence of these polarity agents disrupts the hydrogen bonds of the cellulose and thus swells / dilates the macrofibrils of the cellulose, which leads to better diffusion of the filling compound.

[0157] The monomer may preferably be chosen from monomers derived from petroleum (called petro-sourced) including methacrylates, such as ethyl methacrylate, methyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, octyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, glycidyl methacrylate; acrylates such as ethyl acrylate; phthalates such as dialkylphthalates where the alkyl comprises, for example, from 1 to 6 carbon atoms; nitriles such as acrylonitrile; styrene and styrene derivatives such as α-methylstyrene, chlorostyrene, styrene, tert-butyl styrene, vinyltoluene; vinyl compounds such as vinyl acetate, vinyl chloride and vinyl propionate;unsaturated compounds containing a carboxyl group such as acrylic acid, fumaric acid, maleic acid, methacrylic acid; ethylenic compounds such as ethylene glycol or ethylene oxide; butadiene; isoprene; unsaturated monomers containing a nitrogen atom, such as acrylamide, acrylonitrile, N-butoxydimethylacrylamide, vinylpyridine; and mixtures thereof. These monomers generally lead to the formation of thermoplastic polymers.;

[0158] Monomers leading to the formation of thermosetting polymers may also be mentioned, such as petroleum-based compounds, including thermosetting resin precursors such as epoxy resin precursors, such as epoxidized prepolymers derived from bisphenol such as bisphenol A diglycidyl ether (BADGE in French, better known by its English acronym DGEBA), or any epoxidized bisphenol, as well as glycidyl methacrylate or allyl glycidyl ether, oxetane resin precursors, phenolic resin precursors, urea resin precursors, urethane resin precursors, acrylic resin precursors; and mixtures thereof. In this case, at least one hardener is generally present in the filling compound.The hardener may be any thermosetting resin hardener known to those skilled in the art such as an aliphatic amine, such as isophoronediamine, or cyclic amine, a carboxylic acid, an anhydride or an ionic liquid.

[0159] We can also cite bio-sourced monomers leading to the formation of thermoplastic or thermosetting polymers, identical to the monomers derived from petroleum or different, among which tannins, such as flavan-3-ol (afzelechin, gallocatechin, catechin) and terpenes; resveratrol; resorcinol; glycerol and glycerol derivatives such as epichlorohydrin, propanediol isomers and glycolic acid; sugar derivatives (isosorbide, sorbitol polyglycidyl ether, trehalose, D-glyceraldehyde, D-threose, D-erythrose, D-arabinose, D-ribose, D-mannose, D-glucose); furfural derivatives (generally derived from the acid depolymerization of hemicellulose); maleic or fumaric acid derivatives; derivatives of lactic and formic acids;monomers derived from vegetable oil and fatty substances (cashew, safflower, rapeseed, flax, olive, soybean, castor oil) such as sebacic acid (castor), cardanol (cashew), linoleic acid (from flax), vernonia acid (from vernonia seeds); hydroxyalkanoic acids, such as those derived from formic, lactic and sebacic acids; bio-ethylene (or biological ethylene); bio-ethylene glycol (or biological ethylene glycol); bio-propylene (or biological propylene); bio-1,4-butanediol (or biological 1,4 butanediol); lignin derivatives, such as terephthalic acid, gallic acid, vanillin; vanillin derivatives such as vanillylamine, methoxyhydroquinone diglycidyl ether, vanillylamine triglycidyl ether; and mixtures thereof, such as monomers derived from a combination of sugar derivatives and fatty substances.;

[0160] By "bio-sourced" we mean a molecule of which all or part, i.e. 10 to 90%, preferably 10 to 30%, of the constituent atoms come from a resource originating from biomass, and not resulting from the anthropogenic transformation of a fossil resource.

[0161] We can also cite hybrid bio-sourced monomers leading to the formation of thermoplastic or thermosetting polymers, identical to the bio-sourced monomers. By compound we mean “hybrid bio-sourced” a bio-sourced compound in which part of the structure has reacted with a molecule whose atoms do not come from biomass resources.

[0162] By " derived from X", is understood according to the invention to mean a compound synthesized from compound X by a short sequence of chemical reactions essentially retaining the identity (i.e. the main chemical structure) of compound X, such as an addition of a function or an increase in the length of the carbon chain (i.e. an addition of a carbon chain) or an oxidation or a reduction or a nucleophilic substitution or a ring opening.

[0163] Even more preferably, the monomeric solution or monomeric formulation, preferably the monomeric solution, of the filling step (2) comprises at least one monomer chosen from: petroleum-derived monomers including methacrylates, such as butyl methacrylate, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, tri-n-butyltin methacrylate; phthalates such as dialkylphthalates; nitriles such as acrylonitrile; styrene and styrenic derivatives such as tert-butyl styrene and chorostyrene; vinyl compounds such as vinyl acetate, vinyl chloride and vinyl propionate; ethylenic compounds such as ethylene glycol or ethylene oxide; butadiene; isoprene; and mixtures thereof; and bio-sourced monomers including terpenes; glycerol and glycerol derivatives most often obtained after reaction with at least one compound from epichlorohydrin, propanediol isomers and glycolic acid; sugar derivatives; furfural derivatives (generally derived from the acid depolymerization of hemicelluloses);derivatives of lactic and formic acids; monomers from castor oil (or; "castor oil") such as sebacic acid; hydroxyalkanoic acids, such as those derived from formic, lactic and sebacic acids; bio-ethylene (or biological ethylene); bio-ethylene glycol (or biological ethylene glycol); bio-propylene (or biological propylene); bio-1,4-butanediol (or biological 1,4-butanediol); lignin derivatives, such as terephthalic acid; and mixtures thereof; and their mixtures.

[0164] The advantage of using bio-sourced monomers, particularly if they are biodegradable, is that it is possible either to recover them later during recycling of the composite material at the end of its life or to facilitate the destruction of the composite material at the end of its life. This therefore makes it possible to obtain a partially or totally recyclable composite material, which gives the process according to the invention the character of a sustainable or even ecological process (process " green”).

[0165] According to a variant of the second embodiment of the filling step (2), the filling compound consists of two monomers conveyed within the lignocellulosic material, for example by a fluid in supercritical or subcritical phase. These monomers lead to the manufacture of a thermosetting polymer in the finishing step (3), which in this case consists of polymerization and crosslinking.

[0166] An example of a second embodiment is that the filling step (2) comprises an optional step of adding a co-solvent (for example ethanol, preferably 50% monomer - 50% ethanol) to a fluid in supercritical or subcritical phase in a saturator, in which a monomer solution is present. This fluid / co-solvent / monomer mixture is then introduced into a high pressure cell which contains a delignified lignocellulosic material structure deposited on a porous support such as a frit. The fluid phase solubilizes the monomer solution and this fluid phase containing the monomer(s) diffuses inside the delignified lignocellulosic material structure, which expands / swells. The affinity between the monomer(s) and the lignocellulosic material promotes the impregnation and molecular dispersion of the monomer(s) within the lignocellulosic material.A high partition coefficient is preferred, which presents a high affinity between the monomer(s) and the lignocellulosic material.

[0167] At the end of this impregnation step, the high-pressure cell is slowly depressurized using a depressurization valve and the lignocellulosic material thus filled (or impregnated), with the monomer(s) in a homogeneous manner while retaining its structure and properties, is recovered. According to a variant of the second embodiment of the filling step (2), the monomer(s) is (are) such that once the polymerization has been carried out, the polymer has substantially the same optical density as that of cellulose.

[0168] The refractive index of the polymer thus obtained is typically in a range from 1.35 to 1.70, more precisely between 1.44 and 1.65, and even more precisely between 1.52 and 1.60, and is often taken to be around 1.47, 1.53, 1.56 or 1.59, with a possible variation around these values ​​of the order of 10%. It may also be, in a different embodiment, typically in a range from 1.40 to 1.60, for example around 1.47. Finishing step (3)

[0169] The finishing step (3) is a step in which the filler compound of the partially delignified filled structure from the filling step (2) is fixed in the structure, thereby obtaining a composite material structure formed from a three-dimensional network of transformed filler compound embedded in a network of cellulose and lignin. The " processed filler compound » is the compound obtained at the end of the finishing step (3).

[0170] It is carried out in different ways, in particular depending on the method of carrying out the filling step (2) (first embodiment or second embodiment). It can be carried out in one or more sub-steps. It can be carried out in a stationary or step-by-step mode.

[0171] This finishing step (3) is therefore a step of fixing the filling compound, preferably by polymerization and / or crosslinking when the filling compound comprises at least one monomer, often present in the form of a filling solution or formulation. This polymerization and / or crosslinking is carried out in particular in such a way that the fibers of the lignocellulosic material are linked to the transformed filling compound after completion of the finishing step (3) by chemical, physical or physicochemical anchoring. A person skilled in the art is capable of determining the formulation of his filling solution to obtain the desired anchoring during the finishing step. When the filling compound is a polymer (including a vitrimer), this finishing step simply consists of recovering the filled material from the filling step (2), under atmospheric pressure and ambient temperature conditions.

[0172] As explained previously, the term " anchoring " refers to the creation of molecular bonds. The structuring of polymer chains within the architecture of the lignocellulosic material is carried out either by covalent bonds, in which case a chemically crosslinked network is obtained, or by weak bonds or interactions, such as hydrogen bonds, van der Waals, in which case a physical network is obtained, or by a mixture of both types of bonds.

[0173] The filling compound thus forms a polymer which can belong to the family of thermoplastic polymers or thermosetting polymers. Such polymers can be chosen from the group formed by acrylic resins, aminoplast resins, diallyl phthalate resins, epoxy resins such as Spurr epoxy resins (such as, for example, the commercial product EM300 sold by the company Sigma-Aldrich), melamine resins, methacrylic resins, oxetane resins, phenolic resins, polyacetal resins, polyamide resins, aromatic and aliphatic polycarbonate resins, aromatic and aliphatic polyesters, polyfluoro resins, polyphenylene ether resins, polyimide resins, aromatic and aliphatic polyolefin resins, polysulfone resins, styrenic resins and polyurethanes, and combinations thereof.The anchoring of the filling compound is carried out in different ways, in particular depending on the method of carrying out the filling step (2).

[0174] Thus, when the filling step (2) is carried out according to its first embodiment, that is to say that the filling compound is a polymer or a co-polymer, preferably thermoplastic, or a vitrimer, the finishing step (3) consists of setting (or fixing), as much as possible, the polymer or co-polymer or vitrimer within the structure for its subsequent use. In other words, the finishing step (3) consists of putting said polymer or co-polymer or vitrimer in a physical state such that it can practically not leave the structure under the temperature and pressure conditions considered. These temperature and pressure conditions essentially depend on the subsequent use that will be made of the composite material structure, namely typically whether it is intended to be placed outdoors (in which case the climate of the place of use must be taken into consideration) or indoors.In general, this results in a temperature setting below the glass transition temperature of the polymer or co-polymer.

[0175] Thus, when the filling step (2) is carried out according to its second embodiment, that is to say that the filling compound is a polymerizable monomer present in a monomeric solution, the finishing step (3) consists of polymerizing the monomer in the presence of the catalyst. This is generally carried out by any conceivable polymerization technique, such as the thermal route, the UV route, or the plasma route. The choice of technique depends essentially on the nature of the polymerization catalyst, as is known to those skilled in the art.

[0176] For example, the monomeric solution comprises butyl methacrylate and styrene in a proportion of 1 part butyl methacrylate to 3 parts styrene, and the catalyst present in the finishing step (3) is azoisobutyronitrile in an amount of 0.05 parts. In this case, the finishing step (3) can be carried out by heating at a temperature of 15°C to 80°C, for example 40°C, under vacuum or in an oxygen-free atmosphere, or in an oxygen-free atmosphere, for 20 to 50 hours, for about 24 hours.

[0177] When the polymer or co-polymer obtained is thermosetting, the filling step (2) is carried out in the liquid state and at a temperature higher than the temperature range at which crosslinking takes place and said polymer or co-polymer begins to harden. Then, the finishing step (3) consists of polymerization then crosslinking of the source monomers of the thermosetting polymer, at a temperature lower than said temperature range of the polymer or co-polymer.

[0178] Thus, it is possible to carry out the filling step (2) of the lignocellulosic material and to initiate the finishing step (3), which is a precipitation of the filling compound in it almost simultaneously. Optional post-processing steps (4) and / or (5)

[0179] According to the invention, the treatment method may further comprise a step of pressurizing (4) the structure resulting from the finishing step (3). The pressurizing step (4) is typically carried out at a temperature of 50 to 250°C, preferably 80 to 250°C for 5 to 30 minutes under a pressure of 0.1 to 2.0 MPa (1 to 20 bar).

[0180] This pressurizing step (4) may be followed by a surface finishing step (or surface treatment) (5) of the structure resulting from the pressurizing step (4). The surface finishing step (5) may typically be carried out chemically, for example using ethyl acetate, or thermally and accompanied by pressing, in which case the pressurizing steps (4) and surface finishing steps (5) are carried out simultaneously. This advantageously makes it possible to smooth out the surface irregularities of the structure.

[0181] The surface finishing step (5) can also be carried out without first carrying out a step (4). In this case it can be carried out using steam treatment with acetone or methalin chloride vapor. Structure

[0182] The composite material structure obtained by the method according to the invention is generally advantageously a structure with good fire resistance, increased compared to the lignocellulosic material before treatment (due to its increased density and the absence of air - and therefore oxygen - in its densified cellular structure), rot-proof (due to the absence of air in its densified cellular structure which can therefore no longer interact with ambient humidity), improved durability compared to the lignocellulosic material before treatment, and which has mechanical characteristics of resistance to compression and bending improved compared to the native lignocellulosic material before treatment. These properties depend among other things on the nature of the filling compound and the native lignocellulosic material.

[0183] According to a preferred embodiment, the composite material structure has for the most part, or even almost entirely, a substantially homogeneous or periodic refractive index, depending on the nature of the native lignocellulosic material. According to one embodiment, the composite lignocellulosic material structure is substantially transparent. However, it may also be opaque. Preferably, the composite lignocellulosic material structure is substantially translucent.

[0184] By "we mean transparent " the capacity of a visually homogeneous body to allow at least 90% of the incident light to pass through. This measurement is carried out in relation to the direct light transmission for a given ambient lighting, by comparing the value (in lux) of the ambient lighting and the value (in lux) of the light transmission flux obtained after passing through the structure.

[0185] By "we mean translucent »the ability of a body to allow between 5% and 90% of incident light to pass through. A translucent body may not appear homogeneous. In the context of the present invention, certain less delignified areas of the piece of lignocellulosic material may absorb incident light rays depending on the structure of the native lignocellulosic material; the more delignified areas will tend to appear lighter and allow light to pass through more easily than the less delignified areas. "opaque"the ability of a body to not allow any light rays to pass through, by absorption or diffusion of light within its structure. A native lignocellulosic material structure is generally an opaque material in its common dimensions of use. If the thickness of this structure is reduced to less than 500 µm, the native lignocellulosic material is then in the form of a fragile and flexible sheet, can allow incident radiation to pass through, and is therefore translucent, despite the absence of treatment, but the material does not have the other properties of the final composite material.

[0186] Light rays passing through the material may or may not be deflected, may or may not retain their initial direction of propagation after passing through the structure. This optical property is advantageously obtained by homogenizing the optical index of the transformed filling compound with that of the cellulose (in particular alpha-cellulose) revealed within the structure of the lignocellulosic material due to the filling step (2) and by creating a continuum of material during the finishing step (3). This provides the structure with an additional optical quality, since all or part of an incident radiation can be transmitted through this composite material structure by homogenizing the optical density.

[0187] The continuity of optical indices is generally not perfect from a certain volume of lignocellulosic material structure. Indeed, depending on the native lignocellulosic material and the delignification rate, the extraction of lignin from the lignocellulosic material may not be uniform along the planes of its faces and in depth, so that the delignification, and consequently, the optical rendering does not appear homogeneous. For example, in the case of wood treatment, depending on the species, the areas of summer wood and spring wood may not have the same nature or may not be differentiated. The same applies to sapwood and heartwood for certain species.It is thus possible, for certain woods, in particular those with annual growth rings (alternation of summer and spring wood), that one of the parts, often the summer wood, is less likely to undergo the treatment of the extraction step (1), thus revealing after treatment by steps (2) and (3) more or less translucent, or even opaque, areas. Conversely, with regard to more fragile and generally chemically homogeneous species, the reactivity of the structure in the face of step (1) can be substantially homogeneous, making the material substantially uniformly translucent or transparent. The optical property is generally observed on the structure of composite material.

[0188] Typically, the composite material structure comprises at least one dimension of at least 2 mm and at most 40 cm. These 40 cm may correspond to the total thickness of a CLT panel. This may not strictly correspond to the dimensions of the structure before treatment according to the method of the invention. Indeed, dimensional changes may result from the process of a modification of the structure of the lignocellulosic material during step (1), leading for example to a deformation (slight twisting) or a reduction in the size of the composite material compared to the lignocellulosic material before treatment, with or without a preferred deformation axis.

[0189] The structure of the composite material has a density higher than that of the native lignocellulosic material, for example from 5% to 1000% higher, preferably from 10 to 200% higher, this value depending in particular on the lignocellulosic material, the delignification rate and the nature of the filling compound.

[0190] The composite material structure obtained according to the method of the invention is preferably a finishing element, a secondary work element or a primary work element.

[0191] As a reminder, there are three types of cuts in wood: CLR (radial longitudinal section) CT (transverse section) CLT (tangential longitudinal section).

[0192] The different types of possible cuts mentioned above have been treated according to the invention, even if the examples which follow only concern CT and CLR cuts.

[0193] It should be noted that according to the invention, transverse and longitudinal sections, which are the preferred sections, generally react similarly to the method.

[0194] The choice of the cut which must be favored and treated according to the invention is made by the person skilled in the art according to the desired application: for example, for structural applications taking advantage of the improved mechanical properties, the CLR cut will be favored while for applications taking advantage of the new optical properties it will be the CT cut which will be favored. Piece

[0195] The part comprising the structure obtained according to the method of the invention can be used in a wide variety of outdoor uses, in which case the part is generally chosen from soffits, window frames, doors and door frames, verandas, fascia boards, garden sheds, terraces (such as exterior decking and exterior paving) and timber-framed buildings (or timber cladding), urban developments and the like.Alternatively, the part may be used in a wide variety of indoor uses, in which case the part is typically selected from luxury packaging elements, design elements, furniture elements (such as furniture and joinery products or even food containers such as food bowls), automotive interior elements, yacht or jet interior elements, nautical elements, sports elements (such as skis), consumer items or products (such as sunglasses or phone covers), aeronautical elements, and construction elements. Figures

[0196] The invention will be better understood from the attached drawings in which: there Figure 1 schematically represents the different stages of the treatment method according to the invention; the Figure 2schematically represents an installation for implementing the extraction step (1) of the method according to the invention, in static mode and in dynamic mode; the Figure 3 schematically represents an installation for implementing the filling step (2) of the method according to the invention, in static mode and in dynamic mode; the Figure 4 represents a detail of the Figure 3 ; and the Figure 5 schematically represents the pressurization step (5) of the method according to the invention.

[0197] In the Figures, identical elements are represented by the same references.

[0198] There Figure 1schematically represents the method for treating the structure of lignocellulosic material according to the invention, by a succession of steps, each being represented by a box. The boxes are connected to each other by arrows indicating the transition from one step to the next. Each of the boxes corresponds to the step bearing the same reference number of the method according to the invention, it being understood that references 4 and 5 are optional steps as shown by the dotted arrows connecting the boxes to each other.

[0199] We thus distinguish, in order, a first extraction step 1 carried out on the structure of lignocellulosic material. Step 1 achieves a partial dissolution of the lignin in the fluid phase and a subsequent evacuation of this structure, in the indicated contents.

[0200] This extraction step 1 can be followed by an optional intermediate functionalization step 14 of the lignocellulosic material from extraction step 1. Two alternatives are therefore represented: passage from 1 to 2 directly which leads to a partially delignified structure, or passage from 1 to 2 indirectly, i.e. passage from 1 to 14 then from 14 to 2, which leads to a partially delignified and functionalized structure.

[0201] The partially delignified and optionally functionalized structure resulting from either the extraction step 1 or the intermediate functionalization step 14 is then filled (or impregnated) with at least one filling compound in a filling step 2.

[0202] The next step is a step 3 of fixing the filling compound in the structure resulting from the filling step 2. This makes it possible to obtain a composite material structure formed from a three-dimensional network of transformed filling compound incorporated in a network of cellulose and lignin. This step 3 may be followed by a step 4 of pressurizing the structure resulting from the finishing step 3, possibly itself followed by a step 5 of finishing the surface of the structure resulting from step 4.

[0203] There Figure 2schematically represents an installation 6 for implementing the extraction step (1) of the method according to the invention on a structure 10 of lignocellulosic material which is made of wood, for example beech. The installation 6 allows both extraction in static mode and extraction in dynamic mode. As will be explained below, the implementation of each of these modes does not require the use of all the elements of the installation 6. The installation 6 comprises a high-pressure cell 7 (for extraction), a separator 33, a storage container 12 for fluid, namely CO 2 , as well as a storage container 25, which is used here to store co-solvent, namely a co-solvent composed of a water-ethanol mixture.

[0204] The installation 6 also includes a co-solvent pump 27, a fluid pump 18, a mixer 20, a cooler 16, and a heater 32. The cooler 16 is a heat exchanger allowing, through indirect contact with a heat transfer fluid, to cool the fluid passing through it. The heater 32 is a heat exchanger allowing, through indirect contact with a heat transfer fluid, to heat the fluid passing through it to keep its temperature constant.

[0205] Installation 6 also includes various temperature, pressure and flow sensors (not shown).

[0206] The high pressure cell 7 comprises a sinter 8 in the lower position, capable of supporting the lignocellulosic material structure 10, and a sinter 9 in the upper position. These sinters 8 and 9 allow the lignocellulosic material to remain inside the high pressure cell 7 or even the homogeneous penetration of the fluid within the high pressure cell 7.

[0207] A double heating jacket 11 is present around the high pressure cell 7 in order to control its temperature. In static mode, the double jacket 11 could be replaced by a heater.

[0208] For the implementation of the extraction step (1), whether in static mode or in dynamic mode, the structure 10 is first placed vertically in the high pressure cell 7 on the sinter 8.

[0209] In static mode, the high pressure cell 7 in which the structure 10 is placed is supplied, initially, with co-solvent in the following manner: the co-solvent present in the container 25 is conducted, via a pipe 26 to the pump 27 then, via a pipe 28 to the mixer 20 then to the cell 7 by a pipe 21, where it is brought into contact with the structure 10 present in the cell 7. A two-inlet valve 49 is present on the pipe 21, which makes it possible to interrupt the supply of co-solvent to the cell 7. In a second step, the fluid intended to be put into the supercritical or subcritical phase and present in the container 12 (which is, in this case, a CO 2 bottle) is led, viaa line 13 then a line 15, to the heater 16 then via a line 17 to the pump 18 then via a line 19 to the mixer 20 then to the line 21, where it joins the high pressure cell 7 which contains the structure 10 and the co-solvent. In the case of static mode, the mixer 20 therefore only plays the role of a simple line, supplied alternately by the co-solvent then by the fluid.

[0210] Finally, the high-pressure cell 7 containing the structure 10, the co-solvent and the fluid, is heated using the heating jacket 11 and pressurized in order to reach the desired pressure and temperature conditions so that the fluid passes into the supercritical phase. The fluid solubilizes the co-solvent, then the fluid phase containing the co-solvent 45 diffuses within the structure 10 and swells the structure 10, thus solubilizing the lignin.

[0211] At the end of this extraction step, the high-pressure cell 7 is depressurized by a three-way valve 30, thus carrying out the partial extraction of the lignin. The extract containing the lignin and any traces of co-solvent is then recovered by the action of a valve 23 to the storage container 55. Thus, a pipe 22 leads it to the valve 23, then a pipe 24 leads it to the storage container 55. In static mode, an alternative is to recover the extract via the pipe 57.

[0212] The valve 30, supplied by a pipe 29 present in the upper position of the cell 7, allows the fluid to be evacuated in the form of gas via a pipe 54.

[0213] In dynamic mode, the high-pressure cell 7 is supplied with a mixture of the fluid intended to be put into the supercritical phase and the co-solvent in the following manner: the co-solvent present in the container 25 is conducted, by means of the pump 27, to the mixer 20. The fluid present in the container 12 is pumped to the mixer 20. The mixer 20 produces a mixture of the fluid and the co-solvent which is pumped by the pump 49 into the cell 7, where it is brought into contact with the structure 10. The valve 30 is then opened, which allows said mixture to circulate to the separator 33 via the pipe 29, the valve 30, a pipe 31, the heater 32, and a pipe 57. Said mixture then circulates via a pipe 34 (which divides into two pipes 35 and 36), a pipe 36, a valve 37, and a pipe 38, upstream of the line 15 which it joins, and so on up to cell 7, thus creating a circulation loop of the fluid phase.

[0214] At the end of this extraction step, the high-pressure cell 7 and the separator 33 are depressurized by a two-way valve 39, supplied by the pipe 35. The separator 33 makes it possible to recover the extract comprising lignin and possible traces of co-solvent via a pipe 41, a valve 42, then a pipe 43 to a storage container 44. The fluid is evacuated through the pipe 34, then the pipe 35 via valve 39 to exit in the form of gas through a pipe 40.

[0215] The elements of the installation 6, and in particular the high pressure cell 7 and the separator 33 and the various pipes, are cleaned at the end of the process.

[0216] THE Figures 3 And 4 schematically represent an installation 74 for implementing the filling step (2) of the method according to the invention, in static mode or in dynamic mode, the Figure 4 representing a detail (IV) of the Figure 3 .

[0217] The installation 74 allows the implementation of the filling step (2) on a structure 10' of delignified or delignified and functionalized lignocellulosic material. This structure 10' is made of wood, for example beech. The filling compound here is a polymer.

[0218] The installation 74 allows both static and dynamic filling. As will be explained below, the implementation of each of these modes does not require the use of all the elements of the installation 74.

[0219] The installation 74 comprises a saturator (which is a high pressure cell) 7', a high pressure cell 60 (in which the impregnation is carried out), the fluid storage container 12, here CO2, as well as the storage container 25, which here serves to alternately store the filling compound then the co-solvent. The saturator 7' is similar to the cell 7 of the Figure 2 but does not play the same role as for the extraction step illustrated in Figure 2 , which explains the difference in numbering.

[0220] Plant 74 also includes pump 27, pump 18, mixer 20, cooler 16, and heater 32.

[0221] Installation 74 also includes various temperature, pressure and flow sensors (not shown).

[0222] The high-pressure cell 60 comprises a frit 63 in the lower position, capable of supporting the lignocellulosic material structure 10', and a frit 62 in the upper position. These frits 63 and 62 allow the lignocellulosic material to remain inside the high-pressure cell 60 or even the homogeneous penetration of the fluid within the cell 60. A double heating jacket 61 is present around the high-pressure cell 60 so as to control its temperature. In static mode, the double jacket 61 could be replaced by a heater.

[0223] For the implementation of the filling step (2), whether in static mode or in dynamic mode, the structure 10' is placed vertically in the high pressure cell 60 on the frit 63, so as to carry out the actual filling in the high pressure cell 60. The saturator 7' is supplied, initially, with filling compound in the following manner: the filling compound present in the container 25 is conducted, via the line 26 to the pump 27 then, via the line 28 to the mixer 20 then via the line 21 to the saturator 7'. The valve 49 present on the line 21 makes it possible to interrupt the supply of filling compound to the saturator 7'. The saturator 7' allows the solubilization of the co-solvent in the fluid in the supercritical phase.

[0224] In static mode, in a second step, co-solvent is put into the storage container 25, then, in the same way as for the filling compound, feeds the saturator 7' via pump 27, mixer 20, line 21 and valve 49, where it joins the filling compound.

[0225] In a third step, the fluid intended to be put into supercritical or subcritical phase and present in the container 12 is conducted, via line 13 then line 15, to heater 16 then via line 17 to pump 18 then via line 19 to mixer 20 then to line 21, from which it joins saturator 7' which contains the filling compound and the co-solvent.

[0226] In the case of static mode, the mixer 20 therefore only plays the role of a simple pipe, fed successively by the filling compound, by the co-solvent then by the fluid.

[0227] Finally, the valve 30 is opened which allows the circulation of the fluid present in the saturator 7' through the pipe 31, the heater 32, then the pipe 57, to the high pressure cell 60. Then the saturator 7' containing the filling compound, the co-solvent and the fluid, and the cell 60, containing the structure 10', are respectively heated using the heating jacket 11 and the heating jacket 61, and pressurized in order to reach the desired pressure and temperature conditions so that the fluid passes into the supercritical phase. The fluid in the supercritical phase solubilizes the co-solvent and the filling compound, then the fluid phase containing the filling compound and the co-solvent 75 inflates the structure 10' while diffusing inside, as shown very schematically in the Figure 4 , thus impregnating the structure with the filling compound 75.

[0228] On the Figure 4, we see that the mixture 75 which represents the supercritical phase is composed of the supercritical phase fluid 53 which solubilizes the filling compound 52, symbolized by inclusions (small circles). The mixture 75 inflates the structure 10' while diffusing inside and a quantity of the filling compound remains trapped within the structure 10' during the depressurization step (not shown).

[0229] At the end of this filling step, the circuit comprising the saturator 7' and the high pressure cell 60 is depressurized by a two-way valve 72. The valve 72, supplied by a pipe 67 (which divides into pipes 71 and 68) then the pipe 71, allows the fluid to be evacuated in the form of gas via a pipe 73. A delignified and filled wooden structure is recovered from the high pressure cell 60.

[0230] In dynamic mode, the saturator 7' comprising the filling compound is supplied with a mixture of the fluid intended to be put into supercritical phase and the co-solvent in the following manner: the co-solvent present in the container 25 is conducted, by means of the pump 27 to the mixer 20. The fluid present in the container 12 is pumped to the mixer 20. The mixer 20 produces a mixture of fluid and co-solvent which is introduced through the valve 49 into the saturator 7'. The valve 30 is then opened which allows the fluid phase containing the co-solvent and the filling compound to circulate from the saturator 7' to the cell 60, which contains the structure 10', via the pipe 29, the valve 30, the pipe 31, the heater 32, and the pipe 57.Said mixture then circulates through pipe 67, pipe 68, a valve 69, and a pipe 70, upstream of pipe 15 which it joins, and thus up to the saturator 7', thus creating a fluid circulation loop.

[0231] At the end of this filling stage, depressurization is carried out by valve 72, and a delignified and filled wooden structure is recovered.

[0232] In static mode, at the end of this filling step, the valve 72 makes it possible to depressurize the high pressure cell 60 and the saturator 7', and if necessary to recover the CO 2 as gas via the pipe 73. In static mode, an alternative is to recover the extract via the pipe 57. On the other hand, the delignified and filled wood structure is recovered.

[0233] There Figure 5schematically represents the pressurization step (5) of the method according to the invention. In this case, the composite material structure 48 is compressed within a compression apparatus (46, 47) composed of two symmetrical jaws 46 and 47 which can move towards each other by holding the intermediate structure 48 in a vice. On each of the parts 46 and 47 is exerted an axial force opposite the force exerted on the other part (the two forces being represented by arrows), thus bringing them closer to each other. The invention will be better understood from the following exemplary embodiments, with reference to the attached drawings. Examples

[0234] The following examples illustrate the invention without limiting its scope. Example 1 : Treatment method according to the invention in which step (1) is carried out by using supercritical CO2 in static mode in the presence of a 50% water mixture - 50% ethanol (% volume)

[0235] A dry wood structure of beech cross-section with dimensions of 17 mm x 17 mm x 9 mm (W x L x H) was subjected to the treatment method according to the invention in static mode in installation 6 of the Figure 2 in the presence of a water-ethanol co-solvent.

[0236] The extraction step (1) was carried out under conditions of pressure of 1.76 MPa (17.6 bar), temperature of 180°C, a quantity of co-solvent 50% water - 50% ethanol (% volume) and for a treatment time of 2h.

[0237] At the end of this extraction step (1), the high pressure cell (0.5 L) was depressurized and the piece of wood as well as the extract containing the lignin were recovered.

[0238] The steps of filling (2) and finishing (3) of the lignocellulosic material structure thus obtained were carried out using the device shown in the Figure 3 .

[0239] The filling step (2) was carried out according to its second embodiment, by supercritical phase impregnation, in static mode. Thus, a monomeric solution composed of one part of butyl methacrylate and three parts of styrene, after the purification of these compounds using a filter powder made of diatomite, was prepared. The monomeric solution was mixed with 0.05 part of catalyst (asobisisobutyronitrile).

[0240] The monomeric solution dissolved in supercritical CO2 is introduced into the high-pressure cell 60 containing the lignocellulosic material structure. At the end of this filling step (2), the high-pressure cell 60 has been depressurized by the depressurization valve 72. The lignocellulosic material structure impregnated with monomer has been recovered.

[0241] This filling step was followed by a finishing step (3) during which the butyl and styrene methacrylate monomers filling the lignocellulosic material structure at the end of the filling step (2) were thermally polymerized (80°C) under an inert atmosphere, for 20 to 24 hours. Example 2: Treatment method according to the invention in which step (1) is carried out using supercritical CO2 in dynamic mode in the presence of a co-solvent mixture 50% water-50% ethanol (% volume)

[0242] A structure (board) of dry wood with a cross-section of beech with dimensions of 200 mm x 90 mm x 18 mm (l x w x h) was treated by the partial lignin extraction step of the process according to the invention in dynamic mode and in the presence of a water / ethanol co-solvent.

[0243] The extraction was carried out under pressure conditions of 2.02 MPa (202 bar), temperature of 118°C for 2 hours. CO2 and water / ethanol mixture were introduced into the high pressure cell (2 L) via continuous pumps with a flow rate of 100 g / min and 5.34 g / min respectively.

[0244] At the end of this extraction step (1), the high pressure cell was depressurized and the wooden board as well as the extract containing the lignin were recovered.

[0245] The filling (2) and finishing (3) steps of the lignocellulosic material structure thus obtained were carried out in an identical manner to those described in Example 1. Example 3: Treatment method according to the invention in which step (1) is carried out by supercritical and enzymatic means

[0246] A dry wood structure with dimensions of 17 mm x 17 mm x 10 mm was pretreated according to the invention by supercritical CO2 under pressure conditions of 20 MPa (200 bar), temperature of 165°C and for 3 hours in static mode.

[0247] The pretreated lignocellulosic material structure was then placed in a solution containing the laccase enzyme at a concentration of 5g / L under temperature conditions of 50°C, for 48 h and under stirring (100 rpm). The pH of the enzyme solution was adjusted using a buffer solution to keep its value between 4.7 and 5.

[0248] The treated wood and the extract (which contains lignin) were recovered at the end of the enzymatic treatment and were subsequently oven-dried in order to characterize them.

[0249] The filling (2) and finishing (3) steps of the lignocellulosic material structure thus obtained were carried out in an identical manner to those described in Example 1.

Claims

1. A process for treating a structure of lignocellolosic material, the lignocellolosic material being preferably wood, said process comprising the following successive steps: (1) at least one step of extracting lignin from a structure of lignocellulosic material by at least one fluid in supercritical or subcritical phase in a high-pressure cell, the lignin being partially extracted; (2) at least one step of filling the partially delignified structure with at least one filling compound, so as to produce a filled partially delignified structure; and (3) at least one step of finishing the filled partially delignified structure, so as to obtain a composite material structure formed of a three-dimensional network of transformed filling compound incorporated in a network of cellulose and lignin, the mass per unit volume of the obtained composite material structure being higher than that of the ligno-cellulosic material structure before treatment.

2. A treatment process according to claim 1, wherein, in step (1), the lignin is extracted in an amount from 40 to 85%, by weight %, relative to the lignin initially present in the material.

3. A treatment process according to claim 1 or 2, wherein the structure of lignocellulosic material is a trimming member, a finishing member or a structure member.

4. A treatment process according to one of claims 1 to 3, wherein the lignocellulosic material is green wood, damp wood or dry wood, preferably green wood.

5. A treatment process according to one of claims 1 to 4, further comprising an intermediate step of functionalizing the partially delignified structure resulting from step (1), situated between the extracting step (1) and the filling step (2), which is a step of activating hydroxyl groups or an oxidizing step.

6. A treatment process according to one of claims 1 to 5, wherein the fluid in supercritical or subcritical phase of extracting step (1) is chosen from: - carbon dioxide CO2 in supercritical phase, preferably mixed with at least one polar cosolvent chosen from dioxane, water, methanol, ethanol, acetic acid, acetone and mixtures thereof; - at least one alcohol in supercritical phase, said alcohol being chosen from t-butanol and isopropanol; - water in subcritical phase, preferably mixed with at least one base or at least one acid.

7. A treatment process according to one of claims 1 to 6, wherein the extracting step (1) is carried out using carbon dioxide (CO2) in supercritical phase in dynamic mode or in static mode, for 2 to 72h, at a pressure of 8 to 40 MPa (80 to 400 bar), and at a temperature comprised between 50 and 200°C.

8. A treatment process according to one of claims 1 to 7, wherein the fluid in supercritical or subcritical phase of the extracting step (1) is carbon dioxide (CO2) in supercritical phase, mixed with a mixture of water and ethanol in a proportion comprised between 30% water - 70% ethanol, to 70% water - 30% ethanol preferably equal to 50% water - 50% ethanol (in volume %).

9. A treatment process according to one of claims 1 to 8, wherein the extracting step (1) is carried out in the presence of at least one enzyme chosen from the group formed by laccase, lignin peroxidase (LiP), managanese peroxidase (MnP) and xylanase, said enzyme being present in the fluid in supercritical or subcritical phase.

10. A treatment process according to claim 9, wherein the fluid in supercritical or subcritical phase further comprises at least one catalyst chosen from 2,2'-azino-di(3-ethylbenzothiazolin-6-sulfonic acid) (or ABTS), 1-hydroxybenzotriazole (HBT), N-hydroxyphthalimide (HPI), N-hydroxy-phenylacetamide (NHA), (2,2,6,6-tetramethylpiperidine-1-yl)oxy (TEMPO), violuric acid, and mixtures thereof.

11. A treatment process according to one of claims 1 to 10, wherein the filling step (2) is carried out in a high-pressure cell in the presence of at least one fluid in supercritical or subcritical phase in which the filling compound is solubilized.

12. A treatment process according to one of claims 1 to 10, wherein the filling step (2) is carried out in the presence of a fluid in supercritical or subcritical phase in which is solubilized a monomeric solution comprising the filling compound.

13. A treatment process according to claim 12, wherein the monomeric solution of the filling step (2) comprises at least one monomer chosen from: - monomers produced from petroleum among which are methacrylates, phthalates; nitriles; styrene and styrenic derivatives; vinyl compounds; ethylenic compounds; butadiene; isoprene; and mixtures thereof; and - bio-sourced monomers among which are terpenes; glycerol and glycerol derivatives; derivatives of sugars; furfural derivatives; lactic and formic acid derivatives; monomers produced from castor oil; hydroxyalkanoic acids; bio-ethylene; bio-ethylene glycol; bio-propylene; bio1,4-butanediol; lignin derivatives; and mixtures thereof; and mixtures thereof.

14. A treatment process according to one of claims 1 to 13, wherein the dissolved lignin recovered from the fluid of extracting step (1) is used in a process for exploiting the lignin for the manufacture of a construction material, of a material used in aeronautics, of a packaging material, of a biofuel, of a pharmaceutical compound or of a chemical compound.

15. A treatment process according to one of claims 1 to 14, wherein the lignocellulosic material is softwood and 50 to 85%, preferably 50 to 75%, by weight %, of the lignin present in the structure is extracted during the extracting step (1).

16. A treatment process according to one of claims 1 to 14, wherein the lignocellulosic material is hardwood and 40 to 60%, preferably 45 to 55%, by weight %, of the lignin present in the structure is extracted during the extracting step (1).