METHOD FOR PRODUCING A PART FROM LIGNOCELLULOSE MATERIAL

Description

[0001] The present invention relates to a method for manufacturing a part made of lignocellulosic material.

[0002] The use of pieces made of lignocellulosic material, particularly wood, is highly prized for its natural aesthetics, warm color, and unique feel. It can be used to enhance structures clad with a piece of wood veneer.

[0003] Thus, wood veneer is currently highly sought after for furniture, interior design, vehicle interior cladding, and in the aeronautical and nautical fields.

[0004] Wood veneers of various shapes are also being used, for example, by creating curved surfaces by shaping a wooden plate. However, wood veneer is fragile and exhibits fracture lines or tears when shaped and sharply curved.

[0005] For example, a piece of wood described in document US2008 / 0020222 is known, formed from a wooden plate, with a thickness of between 0.1 and 1 mm, and impregnated with a resin in order to provide a certain flexibility to the wooden plate. This wooden plate can thus be deformed to obtain a piece of wood of a chosen three-dimensional shape.

[0006] Document US2008 / 0020222 describes in particular various embodiments in which several wooden plates, impregnated with a resin, are stacked and glued to each other before being deformed by implementing a hot pressing process. Two superimposed wooden plates, with their respective grain direction perpendicular to each other, can thus be deformed to constitute a loudspeaker element, with a central flat portion and a peripheral portion in the shape of a flared truncated cone.

[0007] However, the superposition of wooden plates to produce a deformable wooden part necessarily leads to the production of parts of significant thickness. The weight of such parts is increased, which can hinder their use, particularly in the automotive or aeronautical interior sector. In addition, particular care must be taken when deforming the superimposed wooden plates by hot pressing, in order to preserve the integrity of the part formed from stacked wooden plates glued to each other. Since the behavior of the wood is not predictable during its shaping, the scrap rate is very high, increasing the final cost of the deformable wooden part.

[0008] Also known is a composite material described in document US6649245, formed from an ultra-thin wood veneer having a thickness of between 0.07 mm and 0.254 mm and one or more plastic films impregnating the wood veneer.

[0009] Further known is a composite material described in JP6244808, formed from wood that is digested (some of the lignin in the wood is removed), rinsed, dried, cut, laminated and then impregnated with a resin. The resin is then hardened into a desired shape. The object of the present invention is to provide a part made of lignocellulosic material and an associated manufacturing method that make it possible to obtain parts made of lignocellulosic material that overcome the aforementioned drawbacks.

[0010] For this purpose, the present invention relates to a method as defined by claim 1.

[0011] The Applicant found that by preparing a part from a lignocellulosic material that was partly delignified and impregnated with a polymer, it was possible to produce a part having at least one double-curved portion from a single sheet.

[0012] In partially delignified lignocellulosic material, lignin (a chemical compound distributed unevenly between the cellulose fibers of the lignocellulosic material) is replaced by the impregnating polymer. The latter acts as a reinforcing agent, holding the cellulose fibers together and providing a uniform and homogeneous sheathing of the cellulose fibers. When heated, the impregnating polymer is more flexible than the lignin it replaces, while having a sufficiently high Young's modulus to maintain a sheathing and mechanical bond between the cellulose fibers.

[0013] The sheet of partially delignified lignocellulosic material impregnated with a polymer is thus mechanically reinforced and can undergo greater deformations in bending, torsion, traction, and compression. It is thus possible to obtain very varied geometric shapes, unattainable with sheets of raw wood.

[0014] It is thus possible to obtain a part made of lignocellulosic material, formed from a single sheet and having a double-curved surface. The part can thus take on a very original three-dimensional shape for a part made of lignocellulosic material, and for example, a hyperbolic paraboloid surface, a hemispherical shape, a shell shape, a flared cone, a tapered cylinder, and more generally any type of left surfaces (non-developable surfaces).

[0015] Shaping with a single sheet makes it possible to obtain a very light piece, without crossing the fibers of lignocellulosic material generated by the superposition of wooden plates in the prior art.

[0016] The lignocellulosic material part has improved mechanical properties, including better impact and fracture resistance. It also has better toughness, i.e., high fracture resistance and low crack propagation.

[0017] Such a part made of lignocellulosic material can be used without requiring mechanical reinforcements, such as a textile reinforcement layer.

[0018] According to an advantageous embodiment, the part comprises at least one accessory overmolded on said sheet, said at least one accessory being molded in an overmolding polymer adapted to adhere to the impregnation polymer of said sheet.

[0019] Overmolding an accessory allows various functions to be added to the lignocellulosic material part, in order to obtain a finished part that can be used directly. Accessories can, for example, be fixing fasteners, allowing a lignocellulosic material part to be fixed to an external structure.

[0020] Overmolding of an accessory is made possible by the chemical compatibility of the overmolding and impregnation polymers, allowing them to adhere to each other.

[0021] The part made of lignocellulosic material comprises at least one translucent part, the light transmission coefficient of said translucent part being at least equal to 4%.

[0022] The part made of lignocellulosic material can thus be used as an interface for a display device or a control screen, with backlighting for example.

[0023] Advantageously, the lignocellulosic material is wood comprising lignin and a network of cellulose and hemicellulose, said wood being delignified, the fraction of lignin removed being between 40% and 90% by weight of the lignin present in said wood.

[0024] It is important that the lignocellulosic material is partially delignified but not completely in order to preserve the structure of the initial piece of lignocellulosic material.

[0025] By retaining the cellulose and hemicellulose structure of the lignocellulosic material, the piece has a finish and visual appearance close to that of wood. The feel of the piece can remain close to that of raw wood.

[0026] The fraction of lignin removed can be lower, for example equal to 20% or even 10% by weight of the lignin present in the wood.

[0027] In practice, the sheet of lignocellulosic material at least partially delignified and impregnated with an impregnation polymer may comprise a fraction of impregnation polymer of between 30% and 80% by mass relative to the total mass of said sheet.

[0028] Advantageously, the impregnating polymer is a thermoplastic resin, preferably a polymethyl methacrylate (PMMA).

[0029] In one embodiment, the thickness of said sheet is between 0.1 and 3 mm.

[0030] The piece of lignocellulosic material is then well suited to forming a veneer piece.

[0031] In one embodiment, said curved portion has a substantially identical curvature in two orthogonal planes, with a radius of curvature less than 80 mm, and preferably less than 40 mm. For example, said curved portion has a radius of curvature substantially equal to 20 mm.

[0032] In an alternative embodiment, said curved portion has a curvature in a first plane, with a radius of curvature of less than 10 mm, and preferably less than 8 mm.

[0033] In practice, when said curved portion has a curvature in a first plane with a radius of curvature greater than or equal to 10 mm, the curvature in a second plane orthogonal to said first plane may have a radius of curvature less than 4 mm, and preferably between 1.5 and 2.5 mm.

[0034] The piece made of lignocellulosic material can thus have very small radii of curvature in a portion of the surface with double curvature, unattainable with pieces of natural wood and independently of the directions of the wood fibers.

[0035] The production of the lignocellulosic material part allows for the production of various three-dimensional shapes from a single sheet of lignocellulosic material. This manufacturing process can be used on a wide variety of lignocellulosic or wood materials, expanding the range of wood veneer parts.

[0036] It allows the use of more fragile but less expensive wood species.

[0037] The manufacturing process for such a part in lignocellulosic material requires a reduced number of operations, which leads to shorter production cycles. In addition, better control of the deformation of the sheet in partially delignified lignocellulosic material impregnated with an impregnation polymer makes it possible to limit the scrap rate and the cost of raw materials, and therefore the production cost.

[0038] In practice, the forming step can be a thermoforming step.

[0039] In one embodiment, the forming step is carried out on the sheet of partially delignified lignocellulosic material impregnated with an impregnating polymer, after the finishing step.

[0040] The forming step is thus carried out on a structured sheet, in which the impregnation compound is polymerized. The sheet of lignocellulosic material thus has a composite material structure formed by a three-dimensional polymer network incorporated in a cellulose and lignin network. It is easy to handle for carrying out the forming step.

[0041] In one embodiment, the forming step is carried out with a mold whose molding surface is at least partially micro-structured or sandblasted.

[0042] The surface of the lignocellulosic material part after forming can thus be customized. The feel of the part can thus be smooth, satiny or similar to wood.

[0043] In an advantageous embodiment, the manufacturing method further comprises a step of overmolding an accessory onto said sheet, said at least one accessory being molded in an overmolding polymer adapted to adhere to the impregnation polymer of said sheet.

[0044] The overmolding step can thus be integrated into the manufacturing process of the lignocellulosic material part, allowing the lignocellulosic material part to be accessorized for its future use. The overmolding step also improves the dimensional stability of the lignocellulosic material part manufactured from the lignocellulosic material sheet.

[0045] The overmolding step allows functions to be added to the lignocellulosic material part, which is difficult to achieve on a raw wood part without the addition of reinforcements. The lignocellulosic material part can be recycled: by heating the lignocellulosic material part to a temperature higher than the glass transition temperature of the thermoplastic impregnation polymer, it is possible to thermoform this sheet to obtain a part with a different shape. The life cycle of a lignocellulosic material part can thus be extended thanks to the recycling possibilities.

[0046] By way of examples, the part made of lignocellulosic material may be a human-machine interface (HMI) of a display device or a touch screen, a covering structure of a passenger compartment, in particular of a motor vehicle, an aircraft or a nautical vehicle, or may form a housing structure, in particular of cosmetic packaging.

[0047] Other features and advantages of the invention will become apparent in the description below.

[0048] In the attached drawings, given as non-limiting examples: THE figures 1A et 1B schematically represent in front view and in section a piece of lignocellulosic material according to a first embodiment; the figures 2A et 2B schematically illustrate in bottom view and in section a piece of lignocellulosic material according to a second embodiment; the figures 3A et 3B illustrate in section a piece of lignocellulosic material according to a third embodiment; the figure 4 is a block diagram illustrating the principle of a method for manufacturing a part made of lignocellulosic material according to one embodiment of the invention; and the figure 5 is a block diagram illustrating the principle of a process for transforming a part into lignocellulosic material according to one embodiment.

[0049] We will first describe with reference to the figures 1A et 1B a first embodiment of a part made of lignocellulosic material.

[0050] The part made of lignocellulosic material 10 is formed from a single sheet 11 of lignocellulosic material partially delignified and impregnated with an impregnating polymer.

[0051] As shown below, the lignocellulosic material is only partially delignified (and not completely).

[0052] The lignocellulosic material is preferably wood of any type of species, for example oak, walnut, poplar, ash, maple or sapele.

[0053] The lignocellulosic material is, for example, a wood cut and preferably a longitudinal cut (radial longitudinal cut CLR or tangential longitudinal cut CLT) or a transverse cut (CT).

[0054] Wood, comprising lignin and a network of cellulose and hemicellulose, is partially delignified.

[0055] Depending on the type of wood used, the fraction of lignin removed can be more or less significant.

[0056] As a non-limiting example, the fraction of lignin removed is between 40% and 90% by weight of the lignin present in the original wood.

[0057] This fraction of lignin removed may be lower, and for example be substantially equal to 20% or 10% by weight of the lignin present in the original wood.

[0058] Lignin is responsible for the rigidity of the original wood.

[0059] Partial delignification of the wood allows its initial structure to be preserved while making it slightly more flexible.

[0060] Analyses by spectroscopy or microscope allow the structure of lignin to be observed, more or less modified after delignification, unlike cellulose and hemicellulose which remain intact.

[0061] The lignocellulosic material is impregnated with an impregnating polymer, suitable for filling the interstices present in the cellulose and hemicellulose network and also for filling the spaces freed by the removed lignin. The impregnating polymer thus penetrates into the heart of the structure of the lignocellulosic material in order to mechanically reinforce and sheath the cellulose fibers of the wood.

[0062] The impregnating polymer may be a mixture of polymers or a mixture of polymer(s) and monomer(s), thermoplastic and / or thermosetting.

[0063] By virtue of at least partial delignification of the lignocellulosic material, the sheet may comprise a fraction of impregnation polymer of between 30% and 80% by mass relative to the total mass of the sheet.

[0064] Of course, the values ​​mentioned above for the fraction of lignin removed and the fraction of impregnation polymer are given as non-limiting examples.

[0065] The delignification rate and / or the impregnation polymer used are selected to obtain a part made of lignocellulosic material comprising at least one translucent part.

[0066] A translucent part, allowing light to pass through, has a light transmission coefficient of at least 4%.

[0067] The thickness of the sheet 11 forming the part of lignocellulosic material 10 is between 0.1 and 3 mm.

[0068] Preferably, this thickness may be between 0.1 and 2 mm, or between 0.4 and 1.3 mm.

[0069] The thickness of the sheet of lignocellulosic material 11 may be equal to 0.6 mm or 0.9 mm in particular embodiments of a part of lignocellulosic material.

[0070] The sheet 11 here alone forms the piece of lignocellulosic material 10, which thus has a reduced thickness which limits its weight. The sheet of lignocellulosic material 11 can thus form a veneer piece suitable for dressing or covering a support structure.

[0071] The part made of lignocellulosic material 10 as illustrated in figures 1A et 1B has a curved portion with a double-curved surface.

[0072] In this embodiment, the entire part has a double-curved shape. Of course, only a portion of the lignocellulosic material part could have such a double-curved shape.

[0073] In the embodiment to the figures 1A et 1B , the curved portion has a curvature ρ that is substantially identical in two orthogonal planes.

[0074] The shape of the piece of lignocellulosic material 10 is thus a portion of a sphere of radius ρ.

[0075] The radius of curvature ρ is at least less than 80 mm, and preferably less than 40 mm.

[0076] Depending on the desired embodiments, the radius of curvature ρ can be equal in the two orthogonal planes to 20 mm.

[0077] The piece of lignocellulosic material 10 thus obtained, with a small radius of curvature, can be used to create wooden decorations of a very curved hemispherical shape.

[0078] A second embodiment is illustrated in figures 2A et 2B .

[0079] The part made of lignocellulosic material 20 is formed from a single sheet 21 similar to that described previously with reference to the first embodiment of the invention.

[0080] In this second embodiment, the part made of lignocellulosic material 20 has a curved portion 24 having a double-curved surface with a different radius of curvature in two orthogonal planes.

[0081] By way of non-limiting example, the part made of lignocellulosic material 20 illustrated in figures 2A et 2B is a box, circular in shape in a plane (corresponding to the bottom view illustrated in the figure 2A ).

[0082] The part 20 thus has a substantially flat bottom 22 and a peripheral edge 23 widening from the bottom 22.

[0083] The curved portion 24, corresponding to the connection zone between the flat bottom 22 and the peripheral edge 23, thus has a surface with double curvature in two orthogonal planes.

[0084] In particular, when the curvature in one of the planes is not too pronounced, the curvature in the other, orthogonal plane may have a small radius of curvature, for example less than 10 mm, and preferably less than 8 mm.

[0085] For example, when the radius of curvature of the curved portion is greater than or equal to 10 mm in a first plane, the radius of curvature in a second plane, orthogonal to the first plane, may be less than 4 mm, and for example between 1.5 and 2.5 mm.

[0086] For information purposes, in the embodiment illustrated in figures 2A et 2B , the curved portion 24 has a first radius of curvature ρ 1 of the order of 4 mm, in a transverse plane of the part 20, and a second radius of curvature ρ 2 of the order of 7.5 cm, in an orthogonal plane, parallel to the plane formed by the flat bottom 22 of the part 20.

[0087] A third embodiment of a part made of lignocellulosic material is illustrated in figures 3A et 3B .

[0088] The part made of lignocellulosic material 30 is formed from a single sheet 31, similar to that described previously with reference to the first embodiment of the invention.

[0089] In this embodiment, the part made of lignocellulosic material 30 is formed from a curved portion having a double-curved surface in a longitudinal plane ( figure 3A ) and a transverse plane ( figure 3B ).

[0090] The radii of curvature ρ 3 , ρ 4 in the two orthogonal planes (longitudinal plane and transverse plane of the part 30) are identical, similar or different.

[0091] In this third embodiment, the part made of lignocellulosic material 30 comprises at least one accessory 40 overmolded onto the sheet 31.

[0092] In this embodiment, and without limitation, the accessory 40 forms an overmolded layer on a concave inner face of the sheet 31 of the part made of lignocellulosic material 30. The overmolded layer 40 further comprises a series of studs 41 forming projections or clips to allow the part made of lignocellulosic material to be attached to a support (not shown).

[0093] The accessory 40 is overmolded in an overmolding polymer adapted to adhere to the impregnation polymer of the sheet 31 of the part made of lignocellulosic material 30.

[0094] By way of non-limiting example, the impregnation polymer may be a thermoplastic polymer such as polymethyl methacrylate (PMMA), the molding polymer also being polymethyl methacrylate.

[0095] More generally, the impregnation polymer and the overmolding polymer may be the same or different from each other.

[0096] The overmolding of such an accessory makes it possible to functionalize the part made of lignocellulosic material 30 and to associate it with various attachment means (clips, plastic studs, nipples) when the part made of lignocellulosic material is intended to be fixed to a support.

[0097] Such a piece of lignocellulosic material could be attached as a piece of veneer to a support, for example to equip the interior of a motor vehicle. Such a piece of veneer could, by way of non-limiting example, be used as a dashboard of a motor, nautical or aeronautical vehicle, be used as a central island at the front of a motor vehicle, or as cladding for the doors of a vehicle.

[0098] In particular, when the part made of lignocellulosic material comprises at least one translucent part as indicated above, it can be used as a human-machine interface (HMI) of a display device or a touch screen, possibly backlit. The translucent part can thus correspond to one or more touch control zones. For example, when the part made of at least partly translucent lignocellulosic material covers a door, it can comprise touch controls for opening and closing the vehicle windows.

[0099] In other embodiments, the accessories may be a plastic contour or a closing clip, for example when the part made of lignocellulosic material is intended to form the structure of a housing.

[0100] Thus, by way of non-limiting example, the part made of lignocellulosic material 20 illustrated in figures 2A et 2B could constitute a case base and the part made of lignocellulosic material 10 illustrated in figures 1A et 1B a case cover.

[0101] The production of such a case and the holding in position of the cover on the case base could be obtained by overmolding on the periphery of the parts made of lignocellulosic material 10, 20 of a complementary plastic contour and a closing clip (not shown).

[0102] It is also possible to overmold only a joint or hinge system on one side of the case and a closing system on an opposite side of the case.

[0103] Such a case could, for example, be used in the fields of cosmetics, jewelry, eyewear, etc.

[0104] The overmolded accessory may only be present on a portion of the lignocellulosic material part. However, adding a layer of overmolding polymer to the lignocellulosic material part can strengthen it mechanically and improve its dimensional stability.

[0105] More generally, the accessorization or functionalization of the part in lignocellulosic material can be carried out other than by overmolding an accessory: the accessory can also be glued to the sheet of lignocellulosic material partially delignified and impregnated with an impregnation polymer.

[0106] The accessory can also be made by extrusion.

[0107] We will now describe with reference to the figure 4 an embodiment of a method for manufacturing a part made of lignocellulosic material as described previously.

[0108] The method of manufacturing a part made of lignocellulosic material may first include a step S1 of cutting a plate of lignocellulosic material.

[0109] As previously stated, this lignocellulosic material board can be obtained from a longitudinal or transverse cut of a piece of wood.

[0110] The manufacturing method then comprises in principle a step S2 of partial extraction of the lignin present in the board of lignocellulosic material, a step S3 of filling with an impregnation compound of the board which is at least partially delignified and a finishing step S4 by polymerization and / or crosslinking of the impregnation compound so as to produce a sheet of lignocellulosic material which is at least partially delignified and impregnated with an impregnation polymer.

[0111] Multiple examples of this delignification and impregnation process are described in detail in WO 2017098149, the contents of which are incorporated by reference into this disclosure.

[0112] In particular, the lignin extraction step S2 can be carried out by soaking and washing, possibly coupled in the same step, the lignocellulosic material plate in a solution allowing partial dissolution of the lignin.

[0113] The fraction of lignin removed can be between 40% and 90% by weight of the lignin present in the wood.

[0114] It can also be lower, and in the order of 20% or 10%.

[0115] The filling step S3 is a step during which an impregnation compound penetrates into the partially delignified structure of the lignocellulosic material board.

[0116] The impregnating compound may be a polymer or copolymer, preferably thermoplastic.

[0117] Alternatively, the filling compound may be a polymerizable monomer, the finishing step S4 then allowing by polymerization to obtain an impregnation polymer.

[0118] The polymer is again preferably thermoplastic, although a thermosetting polymer is possible.

[0119] The impregnation component can also be a mixture of thermoplastic polymer and thermosetting polymer.

[0120] It can also be a mixture of monomer and polymer or consist of only monomers.

[0121] The impregnation component can be petro-sourced or bio-sourced.

[0122] By way of non-limiting example, the impregnation compound introduced in the impregnation step S3 may be a methyl methacrylate (MMA) allowing the finishing step S4 to obtain by polymerization a polymethyl methacrylate (PMMA).

[0123] The finishing step S4 thus makes it possible to produce, after polymerization and / or crosslinking of the impregnation compound, a sheet of lignocellulosic material at least partially delignified and impregnated with an impregnation polymer.

[0124] The sheet can have a thickness of between 0.1 and 3 mm, suitable for forming, for example, a veneer piece.

[0125] For example, a part can be made from lignocellulosic material using a lignocellulosic material board with a thickness of 0.6 or 0.9 mm.

[0126] After impregnation with a thermoplastic polymer such as PMMA and finishing, the sheet can have a thickness of around 0.95 mm (+ or - 0.05 mm), by adding more or less PMMA to the lignocellulosic material plate.

[0127] The manufacturing process of the part made of lignocellulosic material further includes a forming step S5.

[0128] As an example of implementation, the forming step S5 can implement thermoforming of the part under heating conditions.

[0129] The forming of the part can also be carried out by hot forming, thermocompression, stamping, embossing or any type of forming, cold and hot, with or without positive or negative pressure implemented during the forming step.

[0130] As symbolized in the figure 4 by the dotted arrow between the finishing step S4 and the thermoforming step S5, these two steps of the manufacturing process can be decorrelated, i.e. implemented in a dissociated manner in time and space.

[0131] In such an embodiment, at the end of the finishing step S4, the produced sheet is cooled, preferably naturally, to room temperature, the impregnating polymer and the partially delignified lignocellulosic material thus forming a rigid composite structure in the form of a sheet.

[0132] The thermoforming step S5 can thus be implemented several days, weeks or months after the production of the sheet of partially delignified lignocellulosic material impregnated with an impregnation polymer.

[0133] The thermoforming step S5 is carried out in this embodiment on the sheet in order to obtain at least one curved portion having a double-curved surface.

[0134] However, the manufacturing method is not limited to forming a curved portion having a double-curved surface.

[0135] The manufacturing method can also be implemented with a step of forming the sheet so as to obtain a curved portion with a single curvature, such as a conical or truncated portion or even a cylindrical or semi-cylindrical portion.

[0136] The part may include a curved portion with a single curvature, with a very small radius of curvature. A radius of around 1.5 mm can thus be achieved when the curvature is made in a direction parallel to the direction of the fibers of the lignocellulosic material, and of around 2 mm when the curvature is made in a direction orthogonal to the direction of the fibers of the lignocellulosic material.

[0137] It is thus possible to obtain parts with a curved portion close to a right angle.

[0138] As indicated above, the forming step can be implemented by different technologies, including thermocompression, vacuum thermoforming, or embossing.

[0139] Without limitation, forming can implement industrial processes used to produce composite parts, and in particular resin transfer molding (RTM) or high pressure resin transfer molding (HP-RTM).

[0140] For example, in one embodiment of thermocompression, the forming step involves a step of heating the sheet and a step of heating the thermocompression mold.

[0141] The temperatures used for heating the sheet and the mold depend on the glass transition temperature of the impregnation polymer.

[0142] The heating temperatures of the sheet and the thermoforming mold must therefore be sufficient to fluidify the impregnation polymer, and thus allow the sheet to be shaped, while maintaining a viscosity for this impregnation polymer in order to preserve the structure and the maintenance of the sheet of lignocellulosic material impregnated with this impregnation polymer during the thermoforming step S5.

[0143] For example, when the impregnation polymer is PMMA, its glass transition temperature is around 80°C.

[0144] The sheet can for example be heated to a temperature of around 150°C, for a duration of approximately 30s, and preferably less than 1 min.

[0145] The thermoforming mold can be a thermo-regulated mold, brought to a temperature of around 80°C.

[0146] The heated sheet is placed into the mold, and then the sheet is pressed into the closed mold.

[0147] The thermoforming mold can also be surface treated (sandblasted surface, micro-textured, etc.) in order to obtain different surface finishes for the lignocellulosic material part.

[0148] Of course, other methods of implementing thermocompression can be considered.

[0149] Thus, only the sheet can be heated, the mold not being heated, nor temperature regulated.

[0150] The mold could be made of wood or plastic, for example.

[0151] An overmolding step S6 can then be implemented in order to overmold an accessory onto the sheet.

[0152] However, as symbolized in the figure 4 by a dotted arrow at the exit of thermoforming step S5, the part made of lignocellulosic material can be manufactured without accessories. In such a case, thermoforming step S5 is directly followed by a cooling step S7.

[0153] Preferably, the cooling step S7 is carried out for a few minutes, with the thermoformed sheet remaining in the thermoforming mold. The mold can be cooled by thermoregulation.

[0154] If necessary, the thermoformed and cooled sheet can be cut to a chosen shape.

[0155] Any type of cutting can be used, such as hot cutting by a mechanical cutting tool, for example a die cutter, or cold cutting, for example by milling or laser.

[0156] This results in a thin and light finishing or semi-structural part.

[0157] The piece of lignocellulosic material may have curved portions with double or single curvature, without breakage or whitening of the fibers of the lignocellulosic material.

[0158] When an accessory is overmolded onto the sheet, the overmolding step S6 preferentially uses an overmolding polymer suitable for adhering to the impregnation polymer of the sheet.

[0159] Preferably, the overmolding polymer is identical to the impregnation polymer of the sheet.

[0160] In the example described above, the overmolding polymer is preferably a polymethyl methacrylate (PMMA).

[0161] The overmolding polymer must have a melting temperature low enough not to burn the lignocellulosic material of the thermoformed sheet.

[0162] Furthermore, its shrinkage coefficient must remain compatible with that of the sheet of lignocellulosic material at least partially delignified and impregnated with the impregnation polymer.

[0163] The overmolding polymer should preferably be usable in injection.

[0164] During the overmolding step S6, the overmolding mold and the overmolding polymer injection line must be heated to a temperature compatible with the overmolding polymer injection conditions.

[0165] At the end of the overmolding step S6, a cooling step S7 is implemented as described previously.

[0166] The overmolding step S6 thus makes it possible to overmold plastic accessories onto the part made of lignocellulosic material as described previously.

[0167] It can possibly be used to add extra thickness of overmolding polymer to the sheet of the lignocellulosic material part, in order to increase the mechanical properties of the lignocellulosic material part.

[0168] Overmolding can also be carried out only on the peripheral contour of the sheet.

[0169] We will now describe with reference to the figure 5 an embodiment of a method for transforming a part into lignocellulosic material as described previously.

[0170] This transformation process allows a piece of lignocellulosic material to be recycled by giving it a new shape for a new use.

[0171] For this purpose, the impregnating polymer is a thermoplastic polymer, suitable for being softened when the part is heated.

[0172] The transformation process thus includes a heating step S10 of the part made of lignocellulosic material.

[0173] This heating step is carried out at a temperature above the glass transition temperature of the thermoplastic polymer impregnating the lignocellulosic material part.

[0174] As previously indicated, when the thermoplastic polymer is a PMMA, with a glass transition temperature of around 80°C, the part can be heated to a temperature of around 150°C.

[0175] Preferably, a flattening step S11 of the heated part is implemented in order to remove all the curved portions of the part made of lignocellulosic material that one seeks to transform.

[0176] From this heated and flattened part, a thermoforming step S5 is implemented.

[0177] This thermoforming step S5 is similar to that described previously with reference to the figure 4 and may be followed by an overmolding step S6 and a cooling step S7 in order to obtain a transformed part comprising at least one curved portion.

[0178] This curved portion can be single or double curvature as described previously.

[0179] This transformation process thus makes it possible to recycle parts made from lignocellulosic material.

[0180] Of course, the invention is not limited to the embodiments described above.

[0181] As already indicated above, the dimensional and material examples used are in no way limiting for the production of a part made of lignocellulosic material according to the invention.

[0182] Furthermore, the manufacturing method can also simultaneously implement the finishing steps S4 and thermoforming S5, applied to a plate made of lignocellulosic material at least partially delignified and impregnated with an impregnation compound.

[0183] The coupling of these two steps makes it possible to obtain both the polymerization and / or crosslinking of the impregnation compound and the curvature of the plate of lignocellulosic material so as to produce a sheet of lignocellulosic material partially delignified and impregnated with an impregnation polymer and comprising at least one curved portion.

Claims

1. A method of manufacturing a part made from lignocellulosic material <b>characterized in that it comprises the following steps: - partially extracting (S2) the lignin from a plate of lignocellulosic material; - filling (S3) said partly delignified plate with an impregnation compound; - finishing (S4) by polymerization and / or cross-linking of said impregnation compound so as to produce a sheet of lignocellulosic material that is partly delignified and impregnated with an impregnation polymer; and - shaping (S5) so as to obtain a part made from lignocellulosic material comprising at least one curved portion having a surface of dual curvature, wherein the extent of delignification and / or used the impregnation polymer are selected to obtain a part made from lignocellulosic material comprising at least one translucent part with a light transmission coefficient at least equal to 4 %.

2. A method of manufacturing according to claim 1, characterized in that the shaping step (S5) is a thermoforming step.

3. A method of manufacturing according to one of claims 1 or 2, characterized in that the shaping step (S5) is implemented on said sheet of lignocellulosic material that is partly delignified and impregnated with an impregnation polymer, after the finishing step (S4).

4. A method of manufacturing according to one of claims 1 to 3, characterized in that it further comprises a step of overmolding (S6) an accessory onto said sheet, said at least one accessory being molded in an overmolding polymer configured to adhere to the impregnation polymer of said sheet.

5. A method of manufacturing according to claim 4, characterized in that the overmolding polymer is identical to the impregnation polymer of said sheet.