METHOD FOR PRODUCEING A PART FROM A PARTICLE-SHAPED NATURAL MATERIAL AND PART PRODUCED BY THIS METHOD

Description

[0001] The present invention falls within the field of valorization of protein residues of animal origin.

[0002] More specifically, the present invention relates to a method for manufacturing a part from a natural material in particulate form containing scleroproteins.

[0003] The projected depletion of fossil fuel resources has, for several years, prompted manufacturers to develop alternative solutions using renewable resources across all sectors of industry. Recycling and the recovery of waste of animal or plant origin are therefore of increasing interest, from both an economic and environmental perspective.

[0004] Thus, prior art proposed manufacturing solid materials from waste of animal or vegetable origin, in particular by a hot and high-pressure molding process of this waste.

[0005] An example of such a process is described in document WO 2012 / 069736, for the manufacture of a solid material from organic matter of plant origin containing polysaccharides or polypeptides.

[0006] US document 2016 / 0375176 describes a manufacturing process for a mineralized collagen-based composite material for bone cementation.

[0007] The present inventors were particularly interested in natural raw materials of non-human animal origin, and in particular based on a particular type of protein, scleroproteins.

[0008] Scleroproteins, also known as fibrous proteins, constitute one of the three main classes of animal proteins. These are long, filament-like molecules that play a structural and constitutive role in the body, forming part of connective tissues such as bones and connective tissues, as well as appendages such as skin, hair, horns, hooves, and nails. There are several types: keratins, which form protective tissues of the body, such as the epidermis, hair, nails, hooves, horns, and feathers of birds; collagens, which constitute connective tissues such as cartilage; conchiolin, which forms the shells of mollusks; and elastins, also found in connective tissues.

[0009] Many industrial waste products from livestock farming, such as horn, feathers, leather, or production scraps like offcuts from leather or horn processing, are primarily composed of scleroproteins. Using these waste products to manufacture solid material parts for a wide variety of applications, leveraging the aesthetic and mechanical properties of these natural materials, would offer a highly valuable opportunity for both economic and environmental valorization.

[0010] The present inventors discovered that a high-temperature compression treatment process for natural materials in particulate form based on scleroproteins, such as materials based on leather or animal horn, for example, when carried out under specific operating conditions, makes it possible to form solid parts in a material exhibiting particularly advantageous mechanical properties, including good cohesion, homogeneous structuring, good physical and aesthetic stability, and exhibiting a low degree of hygroscopy.

[0011] Thus, the present invention aims to propose a method for manufacturing a part from a natural material in particulate form based on scleroproteins, which makes it possible to obtain a solid material reproducing the properties of the initial natural material, and even improving some of these properties.

[0012] An additional objective of the invention is that this process be simple and quick to implement.

[0013] In this description, the term "natural material" means a material of natural origin, such as a material of animal origin, as opposed to synthetic materials. The natural material according to the invention may be a material existing in nature, or a material obtained by transforming such a material existing in nature, for example, by tanning, to form leather, the natural material that is the skin of an animal.

[0014] To achieve the above objectives, the present invention proposes a method for manufacturing a part, in the form of a solid block, from a natural material in particulate form containing scleroproteins. This method comprises the following phases, carried out in a dry state: a heating phase of said natural material under compression at a pressure greater than or equal to 30 MPa, at a temperature greater than or equal to the denaturation temperature of the scleroproteins entering into the constitution of this material, and a cooling phase of the material thus obtained, said denatured material, to a temperature less than 100 °C.

[0015] Compression at a pressure greater than or equal to 30 MPa is maintained for at least part of this cooling phase, preferably for at least the initial part of this cooling phase, in particular for at least half of the cooling phase.

[0016] Preferably, compression is maintained throughout the cooling phase.

[0017] Cooling can be achieved in any way, for example by dissipating heat into the ambient air.

[0018] Typically, the material to which the process according to the invention is applied, of natural origin, contains more than 50% by weight of scleroproteins, scleroproteins being substantially the only type of protein present therein.

[0019] It is within the competence of a person skilled in the art to determine, for a given initial natural material, the denaturation temperature of the scleroproteins that constitute it, under the pressure conditions applied in the device used. This temperature depends in particular on the moisture content of the material. To this end, a person skilled in the art may, in particular, analyze the initial material using a technique known per se for measuring this parameter, for example, differential scanning calorimetry (DSC), according to a conventional procedure. Knowing the moisture content of the material on which they wish to implement the process according to the invention, a person skilled in the art may also refer, to determine the denaturation temperature of the scleroproteins, to a pre-established nomogram, in particular by analyzing samples of this material with different moisture contents using DSC, such as the nomogram shown in Figure 1.figure 1 attached.

[0020] Heating the natural material to a temperature equal to or greater than the denaturation temperature of the scleroproteins causes a phase change in the organized regions of these proteins, particularly the regions with α-helix and / or β-sheet structures, and a loss of structure in these organized regions. The material's deformability increases accordingly. This process advantageously prevents water from accumulating in the material's pores.

[0021] The heating phase is also advantageously carried out at a temperature that remains below the degradation temperature of the scleroproteins. The mechanical performance of the material obtained at the end of the process is thus significantly improved. Determining this degradation temperature falls within the expertise of a person skilled in the art. To this end, they can, in particular, perform a thermogravimetric analysis (TGA) of a sample of the natural material, using a standard method.

[0022] The so-called denatured material obtained at the end of the heating phase is then cooled, still under compression, to a temperature below 100 °C, ensuring that the denatured material no longer contains water in a gaseous state.

[0023] Preferably, the denatured material is cooled to a temperature below its glass transition temperature. This glass transition temperature can be easily determined by a person skilled in the art, using any known technique for this purpose, for example by dynamic mechanical analysis (DMA) performed on a sample of the denatured material.

[0024] Below its glass transition temperature, the resulting material reverts, in a conventional manner, to a glassy, ​​non-deformable state. The demolding of the part manufactured by the process according to the invention is then advantageously facilitated.

[0025] Preferably, the cooling phase is carried out as quickly as possible, depending on what the equipment used for the implementation of the process according to the invention allows.

[0026] The process according to the present invention is carried out dry. It advantageously does not use any solvents. This means that the natural material is subjected to the phases of the process according to the invention in a solid state, and not in solution or suspension in a liquid. According to the invention, however, the material may have a very high moisture content, or even be completely saturated with water.

[0027] The process according to the invention yields a part formed from a solid block of material with the aesthetic appearance of the original natural material, advantageously compact and densified, exhibiting good cohesion and strength, a homogeneous structure, and physical and aesthetic stability. This material also exhibits lower hygroscopicity and a higher density than the original natural material. This densification gives the material of the resulting part improved mechanical properties, notably good mechanical strength and low deformability, as well as better resistance to humidity than the initial natural material. Furthermore, the resulting part exhibits a flexural modulus and a tensile modulus similar to, or even better than, those of the initial natural material.

[0028] The part obtained by the process according to the invention is in particular much denser than parts obtained by similar processes, but in which the compression is not maintained during the cooling phase, or in which the heating phase is carried out at a temperature lower than the denaturation temperature of the scleroproteins contained in the initial natural material.

[0029] The material constituting this part exhibits a degree of deformability that can be advantageously controlled by appropriately selecting the operating parameters of the process and the initial moisture content of the natural material. In particular, any water present in the initial natural material acts as a plasticizer, allowing the denatured scleroprotein chains within the material to slide over one another after the heating phase, thus enhancing the deformability of the resulting material.

[0030] The process according to the invention, which is simple and quick to implement, also allows control of the properties of the final material, in particular by adding suitable additives to the initial natural material upstream of the heating phase.

[0031] It also allows perfect control over the shape and dimensions of the formed part, so that it is possible to manufacture parts adapted for all desired applications.

[0032] To this end, the process according to the invention can be implemented by compressing the initial material in particulate form contained in a mold of suitable shape and dimensions, and then applying the heating and cooling phases to the material contained in this mold. Such a mold is conventional in itself. It can, for example, be made of steel, graphite, tungsten carbide, or silicone.

[0033] Alternatively, the process according to the invention may include a preliminary step of cold preforming the natural material in particulate form, to form a solid preform which is then subjected to the heating phase, then to the cooling phase, under compression, of the process according to the invention.

[0034] The process according to the invention may also meet one or more of the characteristics described below, implemented individually or in each of their technically operative combinations.

[0035] In particular embodiments of the invention, the heating phase of the natural material is carried out by flash sintering. The cooling phase is carried out in the same flash sintering device, without any intervening manipulation of the material contained therein.

[0036] The flash sintering technique (known as SPS, for "Spark Plasma Sintering") is well known to those skilled in the art. It consists of passing a pulsed electric current through a matrix of electrically conductive material containing the compacted powder material in a uniaxial direction. This causes the material to heat up through Joule heating and electrical and thermal conduction.

[0037] In the process according to the invention, this technique can be implemented in a conventional flash sintering device itself, and under conventional operating conditions. The tooling used may, for example, consist of graphite dies and pistons, but any other electrically conductive material, in particular steel, is also suitable.

[0038] The implementation of the flash sintering technique according to the invention makes it possible to obtain a final material that is particularly dense, has a particularly homogeneous structure and exhibits particularly good mechanical properties.

[0039] Alternatively, the heating step of the process according to the invention can be carried out by the technique, also classic in itself, of hot pressing, or high-pressure thermomolding.

[0040] The process according to the invention can be implemented at atmospheric pressure, or at reduced pressure.

[0041] Preferably, the gases released from the natural material during the heating phase are continuously vented from the device used. Thus, the process according to the invention preferably includes, during the heating phase, and preferably also during the cooling phase, a step of continuous degassing of the enclosure containing the natural material on which the process is carried out.

[0042] Prior to the heating stage, the process according to the invention may include cleaning, sorting and / or degreasing stages of the natural material, as well as, where appropriate, a preliminary grinding stage of this natural material so as to ensure that it is in particulate form, and if necessary to the desired particle size.

[0043] Preferably, the particles of the natural material in particulate form containing scleroproteins, on which the process according to the invention is applied, all have a diameter between 20 and 500 µm, preferably between 100 and 500 µm.

[0044] Preferably, these particles exhibit good size homogeneity.

[0045] These particles also preferably exhibit good homogeneity of shape, which can be verified in particular by observation under an electron microscope.

[0046] The process according to the invention is, however, equally applicable to natural materials whose particle size is greater than this range of values, and including when these particles have a diameter or length of one or more centimeters.

[0047] In particular embodiments of the invention, the compression is carried out, at least during the heating stage, at a pressure between 30 and 100 MPa, for example about 50 MPa.

[0048] During the cooling stage, the material is preferably compressed to the same pressure as during the heating stage. This pressure may otherwise be lower or higher.

[0049] Maintaining the compression of the material during the cooling stage, particularly within the range of values ​​defined above, advantageously limits the porosity in the final material obtained, and consequently the amount of water contained in that material. This results in particularly good mechanical and structural strength properties for the material obtained after implementation of the process according to the invention.

[0050] In particular embodiments of the invention, the heating phase of the natural material to a temperature greater than or equal to the denaturation temperature of scleroproteins is carried out for a sufficient duration to ensure that all of the natural material subjected to heating reaches a temperature greater than or equal to the denaturation temperature of scleroproteins. A heating phase duration of between 1 and 45 minutes ensures this regardless of the dimensions of the part to be formed, and in particular its thickness.

[0051] Depending on the thickness of the piece, this heating phase duration can, for example, be between 1 and 20 minutes.

[0052] The natural material in particulate form containing scleroproteins on which the process according to the invention is carried out preferably has a moisture content of between 0 and 20%, for example about 12%. However, the invention also applies to natural materials with higher moisture contents, in particular as high as 65%.

[0053] Here, moisture content is defined, in its classical form, as the percentage by mass of water contained in the material, relative to the total mass of the material, under conditions of 60% relative humidity and approximately 20°C. This moisture content can be determined, in particular, by comparing the weight of a sample of the material with the weight of the same sample after it has been subjected to a drying step at over 100°C until a nearly constant sample weight is obtained.

[0054] If necessary, the process according to the invention may include a preliminary step of drying the natural material, to obtain the desired moisture level.

[0055] Prior to the heating phase, the process according to the invention may include a step of mixing the natural material in particulate form with one or more additives, chosen according to the desired properties of the final part. Non-limiting examples of such additives include plasticizers, reinforcing fibers, colorants, etc.

[0056] In particular embodiments of the invention, the natural material is not mixed with any other component for the implementation of the process according to the invention.

[0057] In other particular embodiments of the invention, prior to the implementation of the heating phase, the process according to the invention includes a step of mixing the natural material in particulate form with one or more additives, these additives being present in the mixture in an amount of less than 10% by weight, preferably less than 5% by weight, relative to the total weight of the mixture.

[0058] Particularly preferred additives within the framework of the invention are plasticizing agents, such as glycerol or water (water being implemented, as an additive, to increase the moisture content of the natural material), and coloring substances, such as pigments, for example iron oxide.

[0059] The natural material can, for example, be derived from horn, hoof, claw, wool, silk, hair, for example cashmere, feather or leather, from animals.

[0060] For the implementation of the phases of the process according to the invention, the natural material can be doped with one or more substances, such as scleroproteins, which have been isolated, in particular by chemical extraction, from this natural material or from another type of natural material. The natural material can thus, for example, be doped with collagen extracted from animal tissues.

[0061] The scleroproteins contained therein are, for example, essentially keratin scleroproteins or collagen proteins.

[0062] The process according to the invention proves particularly advantageous for the manufacture of a part from a natural material in particulate form containing proteins derived from mammalian horn, for example cow horn, or from non-human animal leather.

[0063] A part obtained by a manufacturing process according to the invention meets one or more of the characteristics described above.

[0064] The material used to make this part exhibits lower hygroscopicity, meaning a lower tendency to absorb moisture from the air, than the original natural material. Therefore, under identical conditions of relative humidity and temperature, the moisture content of the final material obtained by the process according to the invention is lower than the moisture content of the original natural material.

[0065] In particular embodiments, the material which constitutes this part has a moisture content of between 0 and 20%, preferably less than 10%, and preferably less than 5%, under conditions of 60% relative humidity and a temperature of 20°C.

[0066] This part may in particular have been obtained by implementing the process according to the invention from natural material based on scleroproteins of any non-human animal origin.

[0067] In particular, it may have been obtained by implementing the process according to the invention on a material derived from mammal horn, or even on a material derived from non-human animal leather.

[0068] Its density is greater than that of the initial natural material. In the case where it has been obtained from mammal horn, and in particular from cow horn, it preferably has a density greater than or equal to 1.30 g / cm³.

[0069] A part obtained by the process according to the invention, meeting one or more of the above characteristics, can be used for the manufacture of an eyewear item, jewelry or tableware, in particular as a cutlery handle.

[0070] More generally, the part obtained by the process according to the invention is particularly suitable for the manufacture of luxury goods and accessories, watchmaking, jewelry, etc.

[0071] It can also be used for the manufacture of marquetry items, or for the ornamentation of shooting or hunting weapons, or for any other desired application.

[0072] The features and advantages of the invention will become clearer in light of the following implementation examples, provided by way of illustration only and in no way limiting the invention, with the support of Figures 1 to 9, in which: there figure 1 shows a graph representing the denaturation temperature of proteins contained in a sample of cow horn as a function of its moisture content, measured by differential scanning calorimetry; the figure 2shows a graph representing the results of the dynamic mechanical analysis (Young's modulus and tan δ) as a function of temperature, of a material obtained by high-pressure uniaxial molding of cow horn at 200 °C and 100 MPa; the figure 3 shows a graph representing, as a function of time, the temperature and compression applied during the implementation of a flash sintering process according to the invention from cow horn powder, the pressure being expressed in terms of the displacement of the pistons of the flash sintering device; there figure 4 shows a photograph of a pellet obtained by a flash sintering process according to the invention from cow horn powder; the figure 5shows a graph representing the water adsorption isotherms for raw cow horn ("Raw Horn"), this cow horn after grinding ("Powder"), and the material obtained from this powder by a high-pressure thermoforming process according to the invention ("HPHT"); the figure 6 shows the spectra obtained by FTIR infrared spectroscopy for raw cow horn ("Raw Horn"), this cow horn after grinding ("Powdered Horn"), the material obtained from this powder by a flash sintering process according to the invention ("SPS") and the material obtained from this powder by a high-pressure thermoforming process according to the invention ("HPHT"); the figure 7shows a graph representing, for raw cow horn ("Raw Horn"), this cow horn after grinding ("Powder"), the material obtained from this powder by a flash sintering process according to the invention ("SPS") and the material obtained from this powder by a high-pressure thermomolding process according to the invention ("HPHT"), the energy variation as a function of temperature, measured by differential scanning calorimetry; the figure 8 shows an X-ray diffraction pattern obtained for raw cow horn (“Horn”), the material obtained from this powder by a flash sintering process according to the invention (“SPS”) and the material obtained from this powder by a high-pressure thermomolding process according to the invention (“HPHT”); and the figure 9represents photographs a / of a sample of non-human animal leather in particulate form, and b / of a part obtained from this sample by a flash sintering process according to the invention. HAS / Implementation of the process on cow horn powder

[0073] The following examples are implemented using Aubrac cow horn.

[0074] Natural horn is first subjected to a grinding stage, to form a horn powder whose particles have a diameter between 200 and 500 µm.

[0075] The density of the raw horn is 1.28 ± 0.01 g / cm 3< .

[0076] The curve representing the denaturation temperature of the proteins contained in this cow horn powder, as a function of the moisture content of the powder, is established by differential scanning calorimetry (DSC) using a DSC1 instrument (Mettler-Toledo), with medium pressure steel capsules of 80 µL, at 10 °C / min.

[0077] The result obtained is shown on the figure 1 .

[0078] For example, it is observed that at a moisture content of 9.6% (this level can be obtained after drying the horn at 40°C), the protein denaturation temperature is approximately 185°C.

[0079] Furthermore, the glass transition temperature of denatured proteins is determined by dynamic mechanical analysis (DMA), using a Tritec 2000 DMA device (Triton Technology Ltd), simple mounting, 2 °C / min.

[0080] For this purpose, horn powder with a moisture content of 11.7% is subjected to high pressure uniaxial molding at 200°C and 100 MPa for 3 min, using a MAPA 50 instrument (Pinette Emidecau Industries), in a 5 cm square mold.

[0081] The glass transition temperature of the material (reconstituted horn) thus obtained is measured by dynamic mechanical analysis.

[0082] The result obtained is shown on the figure 2 .

[0083] It is noted that the glass transition temperature of the material, after denaturation of the proteins that constitute it, is 95 °C.

[0084] The material used in the following experiments has a moisture content of 11.7% at 60% relative humidity and a temperature of 20°C. At this humidity level, the protein denaturation temperature is 181°C at atmospheric pressure. Example 1 - Flash sintering process

[0085] A process according to the invention is implemented for the manufacture of a cylindrical part of 160 mm in diameter and 22 mm in height, from horn powder.

[0086] The tooling used consists of a die and graphite pistons. The dimensions of the die are as follows: outer diameter: 230 mm inner diameter: 160 mm.

[0087] The inner bore of the die is covered with a sheet of flexible graphite, which serves to seal the assembly and prevent seizing between the die and the pistons. A sheet of graphite is also positioned on the piston surfaces in contact with the powder to prevent the sintered material from sticking to the pistons.

[0088] The desired quantity of powder is introduced into the die, which is then closed by the two pistons. The assembly is then placed in the chamber of the flash sintering device (Sumitomo Sinter 2000), which is pressurized to 5-10 Pa. The device is then programmed to apply compression to the powder-containing die at a pressure of 32 MPa over 4 minutes.

[0089] Simultaneously, the entire assembly is heated by Joule heating using an electric current flowing through the pistons and the walls of the graphite matrix. The assembly reaches 150°C in 7 minutes. Temperature control is achieved using a thermocouple inserted on the outer wall of the matrix. At this temperature and reduced pressure, the proteins that make up the powder undergo denaturation.

[0090] The temperature is maintained at 150 °C for 10 minutes, after which the heating is switched off. Compression is maintained until the temperature inside the matrix reaches 70 °C, below the glass transition temperature of denatured proteins. The device is then opened, and the formed part is removed from the matrix.

[0091] There figure 3shows the temperature and compression profiles of the matrix containing the material, which are applied as a function of time (the compression profile being expressed in terms of piston displacement).

[0092] It is observed that after 10 minutes of maintaining the temperature in the matrix at 150 °C, the temperature gradually decreases. Simultaneously, the compression exerted on the matrix remains virtually constant; the displacement of the pistons, a few millimeters, is due to changes in the state of matter within the matrix.

[0093] At the end of the process, a densified horn pellet of the desired shape and intense black color is obtained. This piece is shown on the figure 4 . Example 2 - High-pressure thermoforming (HPHT) process

[0094] The device used is a MAPA 50 instrument (Pinette Emidecau Industries).

[0095] The powder is placed in a rectangular mold measuring 5 x 1 cm at a temperature of 200 °C, above the protein denaturation temperature. It is then compressed at this temperature to a pressure of 100 MPa for 5 minutes. The entire assembly is then cooled to a temperature of 90 °C, below the glass transition temperature of the denatured proteins, still under compression, before demolding.

[0096] The material obtained at the end of the process is dark, and denser than the initial raw horn: the density of this material is 1.31 ± 0.02 g / cm 3< . Example 3 - Materials Characterization Water adsorption isotherms

[0097] Water adsorption isotherms are established by the dynamic vapor sorption (DVS) technique, using a DVS Advantage (Surface Measurements Systems) instrument, at 5% to 95% relative humidity, with a 10% interval and at 25°C, for: raw cow horn (piece of horn of about 300 mg), the same horn after grinding (particle diameter between 200 and 500 µm), and the material obtained by an HPHT process according to the invention in Example 2 above.

[0098] The results obtained are shown on the figure 5 .

[0099] A very clear increase in the hygroscopicity of the native horn is observed after grinding. This is mainly due to the increase in the specific surface area of ​​the material.

[0100] Then, after transformation by high-pressure thermoforming according to the present invention, the opposite effect is observed. The denaturation of the scleroproteins caused a marked decrease in hygroscopicity (3% water adsorbed at 60% relative humidity, compared to 7% for raw natural horn, for example). This could be due to the deployment of more hydrophobic amino acids on the surface during the modification of the secondary structures of the scleroproteins induced by the process according to the invention. Infrared Spectroscopy

[0101] Fourier transform infrared (FTIR) spectroscopy analysis is carried out, using a Spectrum 65 instrument (PerkinElmer), for: raw cow horn, the same horn after grinding, the material obtained by a flash sintering (SPS) process according to the invention in Example 1 above and the material obtained by an HPHT process according to the invention in Example 2 above.

[0102] The results obtained are shown on the figure 6 .

[0103] This figure shows a change in the vibration frequency of the amide I band: 1633 cm⁻¹ for the native horn, 1627 cm⁻¹ for the horn after SPS treatment, and 1628 cm⁻¹ for the horn after HPHT treatment. This change is characteristic of the modification of the secondary structure of keratin during the implementation of the process according to the invention.

[0104] The amide II band (around 1530 cm⁻¹) is, on the other hand, rather related to the environment of the NH groups, and the decrease in intensity observed at 1540 cm⁻¹ could be related to a decrease in the hydrogen bonds of these groups after transformation by the process according to the invention. DSC analyses

[0105] For each of the following materials: raw horn (in the form of a piece of approximately 20 mg), the same horn after grinding (particle diameter between 200 and 500 µm), the material obtained by an SPS process according to the invention in Example 1 above and the material obtained by an HPHT process according to the invention in Example 2 above, an analysis is carried out by differential scanning calorimetry (DSC) using a DSC1 instrument (Mettler-Toledo), with medium pressure steel capsules of 80 µL, at 10 °C / min.

[0106] For each material, we obtain the curve representing the variation of energy as a function of temperature shown on the figure 7 .

[0107] These results confirm that the peaks representing the endothermic phenomenon associated with protein denaturation, present on the curves for untreated horn samples (these peaks are indicated by arrows in the figure), do not appear on the curves for samples obtained after horn treatment by a process according to the invention. This confirms that the proteins contained in the materials obtained by processes according to the invention were indeed all denatured during the implementation of these processes. X-ray diffraction analysis

[0108] For each of the following materials: raw horn (in the form of a piece of approximately 20 mg), the material obtained by an SPS process according to the invention in Example 1 above and the material obtained by an HPHT process according to the invention in Example 2 above, an X-ray diffraction (XRD) analysis is carried out using a Bruker D8 Advance instrument.

[0109] For each material, we obtain the curve shown in the diagram. figure 8 .

[0110] The absence of diffraction peaks on these diagrams, and the only presence of a diffusion signal linked to the particular structure of the horn, demonstrate that the final material obtained by the process according to the invention is mainly amorphous.

[0111] Furthermore, nitrogen absorption / desorption experiments show that the physical structure of the materials obtained by both the SPS and HPHT processes, implemented according to the invention, closely resembles that of an elastic matrix with various interconnected porosity networks (micro / meso / macroscopic). Observation of these materials under optical and scanning electron microscopy confirms this hypothesis. Example 4 - Comparative example

[0112] In this example, Aubrac cow horn in powder form, with particles having a diameter of 250 µm and a moisture content of 0%, is used.

[0113] The denaturation temperature of the proteins contained in this horn powder, measured by DSC, is greater than 240 °C.

[0114] The powder is subjected to a high-pressure thermoforming process, according to the conditions described in Example 2 above, but with a heating temperature of 220 °C, 225 °C or 230 °C, lower than the protein denaturation temperature.

[0115] For each of the temperatures tested, the result of this process is a block of compressed powder, the density of which is no greater than that of the initial powder, and of low degree of cohesion. B / Implementation of the process on leather

[0116] These examples are implemented using leather from scraping, in the form of ground fiber with a particle size between 100 and 250 µm.

[0117] There figure 9 shows, in a / , a photograph of the starting natural material. Example 5

[0118] This material is subjected to a flash sintering process according to the invention. The operating procedure is similar to that described in Example 1 above, except that the heating temperature is 140 °C. Under the applied conditions, the scleroproteins contained in the initial material are denatured.

[0119] The result of the process is the part shown in b / on the figure 9 This piece has the appearance of natural leather, and improved properties compared to the original natural material. Example 6

[0120] The moisture content of the material used in this example is between 15 and 20%. At such a moisture content, the denaturation temperature of scleroproteins is measured at 140 °C. The density of this powdered material is between 0.1 and 0.5 g / cm³.

[0121] The powder is subjected to a high-pressure thermoforming process, according to the conditions described in Example 2 above, but with a heating temperature of 65 °C or 110 °C, lower than the protein denaturation temperature, or with a heating temperature of 150 °C, higher than the protein denaturation temperature.

[0122] When the sample is treated at 150 °C according to the invention, a compact solid block is obtained, denser than the initial natural material, more specifically with a density between 1.1 and 1.3 g / cm³. The resulting material exhibits good mechanical properties, both in bending and tension. Its flexural modulus, for example, is between 1600 and 2500 MPa.

[0123] For each of the temperatures of 65 °C and 110 °C, the process yields a block of low cohesion, from which fragments detach, and whose mechanical properties are significantly inferior to those of the part obtained according to the invention. In particular, the value of the flexural modulus, reflecting the strength and rigidity of the part, is more than four times lower than that obtained for the part treated according to the invention (flexural modulus between 350 and 450 MPa). Example 7 - Comparative example

[0124] The powder, with a moisture content of 15%, is placed in the high-pressure thermoforming device and treated at a temperature of 170°C, above the protein denaturation temperature, under compression at a pressure of 81 MPa, for 5 minutes. The compression is then stopped, and the assembly is cooled by dissipation to a temperature of 90°C before demolding.

[0125] The resulting part has a density lower than that of the original material. Example 8

[0126] This example is implemented using vegetable-tanned leather, in powder form with a density of 0.2 g / cm³, with a particle size between 500 and 1000 µm.

[0127] The powder is placed in a mold at a temperature of 150°C, above the protein denaturation temperature. At this temperature, it is compressed to a pressure of 81 MPa for 4 minutes. The assembly is then cooled to 90°C, below the glass transition temperature of the denatured proteins, still under the same compression, before demolding.

[0128] The material obtained is ground and analyzed by Fourier transform infrared spectrometry using a spectrometer equipped with a diamond-tipped ATR (attenuated total reflectance) system.

[0129] Compared to the spectrum obtained under the same conditions for the initial material, a significant decrease in the peak at 1661 cm⁻¹ is observed, corresponding to the α helices in the characteristic region of amide I. This reflects a decrease in the quantity of α helices in the structure of the scleroproteins from 48% for the initial material to 12% for the final material, demonstrating that the denaturation of the scleroproteins has been successfully achieved.

[0130] Furthermore, no new peaks were observed on the spectrum obtained for the final material, compared to the initial material, which demonstrates that there was no formation or appearance of any compound during the implementation of the process according to the invention: the treatment according to the invention did indeed modify the secondary structure of the scleroproteins without degrading them.

[0131] A DSC analysis of the material obtained further shows that, compared to the initial material, the area of ​​the endothermic peak associated with the thermal denaturation of scleroproteins has decreased significantly. C / Implementation of the process on other natural materials

[0132] In all these examples, a MAPA 50 high-pressure thermoforming device (Pinette Emidecau Industries) is used. The natural material in granular form is placed in the device in a rectangular mold measuring 5 x 1 cm. Example 9 - Shattered horn

[0133] Ten grams of cow horn, in the form of needles 2 to 4 cm long, composed mainly of α-keratin protein, with a moisture content of 11% (scleroprotein denaturation temperature 180°C), are subjected to a high-pressure thermoforming process at a temperature of 210°C, above the protein denaturation temperature, under compression at a pressure of 92 MPa for 210 seconds. The assembly is then cooled to 90°C, below the glass transition temperature of the denatured proteins, still under compression, before demolding. The resulting part is denser than the initial material, compact, and has a smooth surface. Example 10 - Feather

[0134] 8 g of coarsely chopped duck feather pieces, 2 to 4 cm in size, composed mainly of keratin (scleroprotein denaturation temperature 180 °C), are subjected to a high-pressure thermoforming process at 210 °C, above the protein denaturation temperature, under compression at a pressure of 92 MPa for 150 s. The assembly is then cooled to 90 °C, below the glass transition temperature of the denatured proteins, still under compression, before demolding. The resulting part is denser than the initial material, compact, and has a smooth surface. Example 11 - Kashmir

[0135] Ten grams of goat cashmere fibers, 2 to 4 cm long, with a major protein content of α-keratin and a moisture content of 70% (scleroprotein denaturation temperature 110°C), are subjected to a high-pressure thermoforming process at 150°C, above the protein denaturation temperature, under compression at a pressure of 46 MPa for 210 seconds. The assembly is then cooled to 90°C, below the glass transition temperature of the denatured proteins, still under compression, before demolding. The resulting part is denser than the original material, compact, and has a smooth surface. Vitrification of the original material has occurred. Example 12 - Whole silk

[0136] Ten grams of silk fragments measuring 1 cm², composed mainly of fibroin protein and with a moisture content of 60%, are subjected to a high-pressure thermoforming process at a temperature of 230°C, above the protein denaturation temperature, under compression at a pressure of 50 MPa for 210 seconds. The assembly is then cooled to 90°C, below the glass transition temperature of the denatured proteins, still under compression, before demolding. The resulting part is denser than the initial material, compact, and has a smooth surface. Example 13 - Defibrated silk

[0137] Ten grams of silk fibers, 2 to 4 cm long and with a moisture content of 60%, are subjected to a high-pressure thermoforming process at 230°C, above the protein denaturation temperature, under compression at 59 MPa for 210 seconds. The assembly is then cooled to 90°C, below the glass transition temperature of the denatured proteins, still under compression, before demolding. The resulting part is significantly denser than the original material, compact, and has a smooth surface. Example 14 - Wool

[0138] Ten grams of wool fibers, 2 to 4 cm long, composed mainly of α-keratin protein and with a moisture content of 11% (scleroprotein denaturation temperature 130°C), are subjected to a high-pressure thermoforming process at 150°C, above the protein denaturation temperature, under compression at a pressure of 50 MPa for 210 seconds. The assembly is then cooled to 90°C, below the glass transition temperature of the denatured proteins, still under compression, before demolding. The resulting part is denser than the initial material, compact, and has a smooth surface.

Claims

1. Method for producing a part in the form of a solid block, from a natural material in particulate form containing scleroproteins, characterized in that it comprises, carried out dry: - a phase of heating said natural material under compression at a pressure greater than or equal to 30 MPa, at a temperature greater than or equal to the denaturation temperature of said scleroproteins, - and a phase of cooling the material thus obtained, referred to as denatured material, to a temperature less than 100 °C, said compression at a pressure greater than or equal to 30 MPa being maintained for at least a part of the cooling phase.

2. Method according to claim 1, wherein the phase of cooling the denatured material is carried out to a temperature less than the glass transition temperature of said denatured material.

3. Method according to any one of claims 1 to 2, wherein said compression at a pressure greater than or equal to 30 MPa is maintained for at least half, preferably for all, of the cooling phase.

4. Method according to any one of claims 1 to 3, wherein the phase of heating said natural material is carried out by spark plasma sintering.

5. Method according to any one of claims 1 to 4, wherein the compression is carried out at a pressure comprised between 30 and 100 MPa.

6. Method according to any one of claims 1 to 5, wherein the phase of heating said natural material at a temperature greater than or equal to the denaturation temperature of the scleroproteins is implemented for a duration comprised between 1 and 45 minutes.

7. Method according to any one of claims 1 to 6, wherein the particles of said natural material in particulate form have a diameter comprised between 20 and 500 µm.

8. Method according to any one of claims 1 to 7, wherein said scleroproteins are keratin proteins.

9. Method according to any one of claims 1 to 7, wherein said natural material in particulate form containing scleroproteins is of non-human animal origin.

10. Method according to any one of claims 1 to 9, wherein said natural material in particulate form containing scleroproteins comes from mammal horn.

11. Method according to any one of claims 1 to 9, wherein said natural material in particulate form containing scleroproteins comes from non-human animal leather.