AU2022237941A1 - Biomaterial from steam-cracked lignocellulosic biomass - Google Patents

Abstract

The invention relates to the field of biomaterials. More particularly, the invention relates to a biobased biomaterial obtained from a steam-cracked lignocellulosic biomass in powder form, and also to the method for preparing same and the uses thereof. The invention also relates to the use of a powder obtained by steam cracking for preparing biomaterials.

Description

BIOMATERIAL FROM STEAM-CRACKED LIGNOCELLULOSIC BIOMASS

[0001] The invention relates to the field of biomaterials. More particularly, the invention relates to a biosourced biomaterial obtained from a lignocellulosic biomass steam-cracked in the form of a powder, and to its method of preparation and uses thereof. The invention also relates to the use of a powder obtained by steam-cracking for the preparation of biomaterials.

FIELD OF THE INVENTION

[0002] Materials like particle board, fiberboard, plywood, OSB, and insulation panels, designed from wood, use various processes (grinding, mixing, pressing, heat treatment) and different formulations (fibers + adhesives) to obtain products with characteristics of water resistance (measured by swelling), of bending strength (stress at break), of elasticity, of cohesion, of tearing, etc.

[0003] In the case of fiberboard, for example, the fibers are wetted in order to be above the saturation point of the fibers, the fibers are mixed with the chosen adhesive (phenolic glue, with urea, and/or formaldehyde), the fibers are dispersed in a mold while attempting to obtain a homogeneous distribution, a gradual pressure rise program (which may range up to 5 to 10 N/mm2) is applied in stages of a few minutes, with temperatures up to 2000 C. The problems observed are the breakdown of the fibers during the mixing with the adhesives, the water consumption which is then lost in vapor form during the pressing, which contributes to energy overuse, and finally the presence of toxic volatile organic compounds during the use of the material in an indoor atmosphere.

[0004] The manufacture of materials by heating and chemical decomposition of the wood (retification process) makes it possible to avoid added chemical compounds. However, this is not suitable for all applications, and the retification of wood is a batch process (oven), and therefore more expensive, without any energy recovery.

[0005] The systems for the treatment of dry and continuous biomass are used by board-makers (medium-density fiberboard) but with the addition of impregnation glue. The systems for treating dry biomass in batches (steam explosion) and continuously (steam-cracking) are especially used by black pellet manufacturers and for biotechnology (but with chemical additives).

[0006] Hydrothermal treatment, also called aqueous fractionation, solvolysis, or hydrothermolysis, differs from steam-cracking in that it involves using water at high temperature and high pressure to promote the disintegration and separation of the lignocellulosic matrix. This technique is not suitable for producing black pellets, since the products obtained are mainly liquid.

[0007] Pyrolysis is the chemical decomposition of an organic compound by intense heating in the absence of oxygen. The compounds obtained after pyrolysis differ in their characteristics from those obtained by steam cracking. Steam cracking cannot be likened to a pyrolysis technique in that it uses a steam explosion and is done in the presence of oxygen.

[0008] It is also necessary to differentiate roasting processes which are characterized by a thermochemical treatment of between 100 and 300C, making it possible to modify some of the organic material in order to break the fibers while removing the water.

[0009] The prior art describes methods for obtaining biomaterials from the steam cracked biomass, however these methods are not satisfactory with regard to ecological aspects since they use a large amount of water and chemicals.

[0010] In this respect, mention may be made of patent CN110253708 which describes a method for producing rubber sheets in which plant fibers are fired, then mixed with an alkaline solution. The mixture undergoes a first steam explosion treatment, the temperature of which is maintained at 115-125 degrees and the gas pressure of which is maintained at 1.2-1.7 MPa. The powder resulting from this first treatment is mixed with an alkaline solution. The product obtained at the end of the final step is mixed and pressed into a sheet.

[0011]Patent CN105856379 describes a method for preparing a high strength lignocellulosic plate comprising in particular a "flash explosion" step involving a material rich in lignocellulosic fiber. Said flash explosion step is carried out at a temperature of between 120 and 150 0C and a pressure of between 1 and 1.5 MPA. The step following the flash explosion consists of "mixing uniformly, then adjusting the water content at 1 to 25%, and adhesive (PVA and/or gelatin) (see claim 1). Then, the mixture obtained undergoes a tiling, hot pressure step and then a cooling molding step.

[0012] Methods for adjusting the steam-cracking parameter are also known from the prior art. Patent WO 2020/260801 describes a method for producing a biofuel by continuous or batch steam-cracking of lignocellulosic biomass, characterized in that: A digital model of the optimal steam-cracking parameters is recorded as a function of the typology of the plant constituents of the biomass; the steam-cracking reactor is fed with heterogeneous biomass; the typology of the plant biomass constituents is measured at least once during the treatment; The adjustment of the steam cracking parameters is controlled as a function of the typology of the plant constituents of the measured biomass and of said digital model.

[0013] It is possible to carry out a steam-cracking process making it possible to produce a powder of lignocellulosic, dry, pre-treated biomass with no chemical additives, which is stable and economically viable for applications such as energy or biotechnologies, and therefore even more likely viable for products with a high added value.

[0014] The methods of the prior art involving treatment of the biomass by steam-cracking are not envisaged for the production of biomaterials.

[0015] Faced with environmental challenges, it is desirable to have more environmentally sound novel biomaterials whose production costs are viable.

DISCLOSURE OF THE INVENTION

[0016]The inventors propose producing novel biomaterials from steam cracked lignocellulosic biomass.

[0017] Thus, the invention relates to a method for producing a biomaterial from steam-cracked lignocellulosic biomass in the form of a powder consisting of: - providing a lignocellulosic biomass; - treating said biomass by steam-cracking until a powder is obtained; - pressing said powder alone or in combination with a fibrous material for densification.

[0018] The invention also relates to the use of a powder obtained by steam cracking a lignocellulosic biomass as a raw material for the preparation of a biomaterial.

[0019] Finally, the invention relates to a biomaterial obtained from steam cracked powder and uses thereof.

ADVANTAGES OF THE INVENTION

[0020] The ecological aspect of the invention is essential: methods for preparing biomaterials using entirely or partially steam-cracked powders, with or without natural fibers, do not require a synthetic chemical. However, these chemicals conventionally used for this purpose (for example urea formaldehyde adhesives) are both a source of atmospheric pollution during their production or their end-of-life, and also of toxicity during the manufacture of the biomaterials. In addition, the absence of synthetic chemicals in the finished product prevents the release of toxic products during its use; no contamination of enclosed spaces. Furthermore, the absence of water or its drastic decrease in steam-cracking and pressing during manufacture (densification step) reduces the energy costs (less heating) and the gaseous or liquid effluents.

[0021] This method allows the recycling of waste wood and of furnishing or demolition elements (known as "Grade B" wood) while such wood, unsuitable for combustion as natural biomass, have to date only been destined for incinerators. Reused in this way after steam-cracking (which gives them a homogeneous neutral form), they return to their initial use.

[0022] The use of steam-cracked biomass (particularly wood), which brings natural cohesion capacities, reduces environmental impacts (little or no chemicals, water-free pressing processes and less energy).

[0023] The steam-cracking of biomass is mainly used for the production of biofuels in the form of dense granules (black pellets). The production costs for the use of steam-cracked material as biomaterial, can be reduced by sampling, in parallel with a main use (black pellet), an intermediate product of the production (powder or "granulettes", that is to say granules of medium compression density), and to use it as a raw material (powders that are to some extent fibrous, manufactured with steam cracking and used alone) or as an auxiliary material in manufacturing fibrous materials (the finest powders, used as a glue or natural binder). The production costs can also be reduced by optimizing the methods by recovering the energy produced during steam-cracking (volatile organic compounds (VOC), steam, heat, etc.).

[0024] The method is very interesting because it can be modulated. Indeed, the steam-cracked powder can be used alone, obtaining boards having a low breaking strength (a low bending stress), but a good resistance to swelling. This type of biomaterial is suitable for use as packing material (insulation for example), which does not undergo heavy bending or stress (steam-cracked powders of one or more species representing 100% of the biomaterial). Alternatively, the steam cracked powder can be used as a natural binder/glue in a mixture with biomass fibers, obtaining fiberboards with the reinforcement of the natural fibers that are prepared to some extent, and a cohesion obtained with the powder after a water-free pressing without chemical adhesives. The biomaterial then has good mechanical strength and can be used in the manufacture of composite boards.

[0025] Moreover, the raw material and treatment can be varied for different applications: a resinous wood will give a fibrous product; a hardwood, a non fibrous product. A very high severity in the steam-cracking treatment will further increase the density of the product and its swelling resistance. Low severity will lead to a light finished product.

[0026] Finally, steam-cracking of the biomass reinforces the hydrophobicity of the biomaterial, by limiting the swelling of the finished product, which is important for use in wet atmospheres, in particular during wood home construction phases, while the braces are exposed, as long as the building is shielded from the weather.

DETAILED DESCRIPTION OF THE INVENTION

[0027] A first object of the invention relates to a method for producing a biomaterial from steam-cracked lignocellulosic biomass in the form of a powder consisting of: - providing a lignocellulosic biomass having a moisture content of between 5 and 27%,

- treating said biomass by steam-cracking until a powder is obtained at a pressure of between 10 and 25 bar and a temperature is between 180 and 220 0C until a powder is obtained, - pressing said powder alone or in combination with a fibrous material or a binder, for densification.

[0028]The method according to the invention has the particularity of being implemented without the addition of chemicals. Furthermore, no water is added for steam-cracking. For the purposes of the invention, the term "chemical" is intended to mean any substances formed by chemical treatment or by the assembly of several different chemicals in defined proportions which can be used as an auxiliary in processes for preparing composite materials, like adhesives or support materials, in particular adhesives such as vinyl adhesives, acrylic adhesives, cyanoacrylate adhesives, neoprene adhesives, epoxy adhesives, MS polymer adhesives, polyurethane (PU) adhesives, two component adhesives (epoxides, polyurethanes), thermosetting adhesives (urea-formaldehyde), aqueous adhesives and solvent-based adhesives and cyanoacrylate adhesives. "Lignocellulosic biomass" is understood to mean a plant material whose major constituents are cellulose, hemicellulose and lignin. The proportions of these components vary depending on the plant species. In the context of the invention, the lignocellulosic biomass of interest is mainly wood, in particular resinous or hardwood, but it could also integrate agricultural residues, by products of agriculture and food processing, or waste wood from furnishings or demolition.

[0029] "Biomaterial" is understood to mean a material integrating at least part of a raw material of natural or biosourced origin. It is known from the prior art that adhesives have a certain degree of toxicity. It is in particular known that: - For all cyanoacrylate adhesives, contact must be avoided with the skin and especially the eyes, and vapors must not be inhaled.

- Neoprene adhesives all release highly flammable vapors, and therefore cigarettes are to be avoided during use, and it is advisable to ventilate the room properly. They are irritating for the eyes and the skin and their inhalation can cause drowsiness or vertigo. Finally, they are toxic to aquatic environments. - Epoxy adhesives contain bisphenol-A-epichlorohydrin which makes them irritating. Some are corrosive and may cause skin burns as well as serious eye damage. These adhesives are also toxic to aquatic environments. - MS-polymer and acrylic adhesives have the advantage of being very weakly toxic and therefore do not bear any particular label. However, some indicate that they can cause an allergic reaction.

[0030] The steam-cracking step is carried out under so-called "dry" conditions, that is to say that the lignocellulosic biomass to be steam-cracked has a low moisture content of between 5 and 27%, and no water or chemical is added.

[0031] In a preferred embodiment, the steam-cracking is carried out by applying a severity factor of between 3 and 5. In a particular embodiment, the steam-cracked powder is obtained as follows: - obtaining, from woodchips, wood fragments whose dimension is between 0.5 and 14 mm and which have a moisture content of between 5 and 27%; - continuously introducing a predetermined volume per minute of said fragments of wood into a pressurized reactor, said reactor being supplied with substantially saturated steam, the pressure of which is between 10 and 25 bars and the temperature of which is between 180 and 220 °C.

- exposing the wood fragments introduced into said reactor to said steam for a sufficient time to obtain a steam-cracking of between 5 and 30 minutes, the value of said exposure time and the value of the temperature of said substantially saturated steam being selected so that the severity factor is between 3 and 5, preferably between 3.5 and 4.5; - continuously extracting from said reactor a same predetermined volume of wood fragments per minute, through a plurality of orifices opening into a duct substantially at atmospheric pressure, so as to cause an explosive decompression of said wood fragments extracted from said reactor into said duct; - separating said decompressed wood fragments and residual vapor extracted from said reactor, said wood fragments obtained after separation, forming said combustible material in powder form. In a preferred embodiment, said lignocellulosic biomass has a moisture content of between 5 and 12%.

[0032] In a preferred embodiment, the pressure in the steam-cracking step is between 16 and 21 bars.

[0033] In a preferred embodiment, the temperature in the steam-cracking step is between 200 and 2140 C. These three preferred embodiments can be combined in pairs, or all three together.

[0034] The Severity Factor of the treatment is defined by the formula:

SF=Log10 (time(min)*exp((TOC-100) /14.75).

[0035] The higher the temperature and the longer the treatment time, the more the severity increases, the more the conversion of the carbon material into the evaporates is lost.

[0036] The product of the steam-cracking process is recovered in powder form or in the form of weakly compressed granules, also called "granulettes". These granulettes correspond to a compressed powder form so as to give it the form of a granule, but one which is easily transformed into powder by a simple mechanical action (mixing). This granulette form can be adopted during the packaging of the product in order to facilitate its handling (transport, storage) but its characteristics are those of a powder (friability, dispersion). In addition, the steam-cracked powder is dry, and can thus be stored and transported; it is stable.

[0037] In a first particular embodiment of the invention, the biomass consists of more than 50% resinous wood, and the powder obtained can be densified alone to give a biomaterial. Indeed, steam-cracking of a resinous wood will give a fibrous powder capable of being densified alone. The biomaterial obtained will tend to have an average resistance and will preferably be used as packing material, in particular as an insulator. In a particular embodiment, the method for producing a biomaterial is implemented by steam-cracking of a biomass of fibrous nature. The powder obtained is of fibrous nature and can be densified alone. In a second embodiment of the invention, the biomass consists of more than 50% hardwood and the powder obtained (fine and non-fibrous) will preferably be used as binder with a fibrous material to produce a biomaterial. In a preferred embodiment, the steam-cracked powder used as binder can represent up to 50% of the constituents of the biomaterial. This allows the production of a biomaterial having good cohesion and good mechanical strength; it can be used for the manufacture of composite boards. This powder allows the cohesion of the fibrous materials by pressing without using water or chemicals, thus producing an environmentally friendly final product.

[0038] In a particular embodiment, the method for producing a biomaterial is implemented by steam-cracking of a biomass of non-fibrous nature. The powder obtained is of non-fibrous nature and is used as a binder in combination with a fibrous material.

[0039] In another embodiment, the powder obtained in the steam-cracking step is densified alone and is a mixture of steam-cracked powders of fibrous and non-fibrous natures.

[0040] In a third embodiment, the biomaterial is prepared from a mixture of steam-cracked wood powders of fibrous and non-fibrous nature. Such a mixture confers beneficial properties on the biomaterial, combining water resistance, cohesion and rigidity. In particular, a resinous wood such as spruce will give a fibrous product and a hardwood, such as oak will give a non-fibrous product. Other types of wood within the families of resinous wood or hardwood can also give fibrous and non-fibrous products independently of their resinous or hardwood nature, the objective being to have a final mixture product (before or after steam-cracking) having both these characteristics.

[0041]The term "fibrous steam-cracked powder" within the meaning of the invention refers to a powder containing at least 80% particles whose diameter is greater than 500 pm.

[0042] The term "non-fibrous steam-cracked powder" within the meaning of the invention refers to a powder containing at least 80% particles whose diameter is less than 500 pm.

[0043] The biomass may itself be a mixture of different species and, generally, the use of the powder obtained will be adapted as a function of its fiber content.

[0044] A second object of the invention also relates to the use of a powder obtained by steam-cracking a lignocellulosic biomass as a raw material for the preparation of a biomaterial. As mentioned above, the use of the powder will depend on its fibrous or non-fibrous nature. Thus, a fibrous powder may be used as a single component of the biomaterial. A non-fibrous powder may be used as a binder for the preparation of a biomaterial in admixture with a fibrous material.

[0045] In another embodiment, the powder is of non-fibrous nature and is densified in combination with a fibrous material.

[0046] The steam-cracked powder can therefore be used as in admixture with a fibrous material and/or a binder. In a preferred embodiment of the invention, said fibrous material and/or said binder are steam-cracked powders. Most preferably, the various components of the biomaterial are all derived from the steam-cracking of lignocellulosic biomasses, these biomasses coming from different species.

[0047] Thus, various species can be mixed before steam-cracking, making it possible to adapt to the supply of available biomasses which are often heterogeneous, in particular in the case of biomass originating from materials to be recycled. It is also possible to mix the powders from batches of different steam-cracked powders. The invention offers great flexibility in the treatment of biomass as well as the preparation of the biomaterial as a function of the selected or available steam-cracked powders.

[0048] A third object of the invention relates to a biosourced biomaterial obtained from steam-cracked lignocellulosic biomass in powder form. It may in particular be obtained by the method described above.

[0049] Preferably, this biomaterial is 100% biosourced and even more preferably consists of 100% steam-cracked biomass. This biomaterial is biodegradable.

[0050] Finally, a fourth object of the invention relates to the use of a biomaterial as defined above as a packing product, insulating product, or construction material. The biomaterials based on steam-cracked biomass alone, without a binder (steam-cracked powder from resinous wood, for example) are generally intended for use as a packing product or an insulating product.

[0051] The biomaterials obtained by mixing a steam-cracked biomass (steam cracked powder from hardwood, for example, as a binder) with a fibrous material (resulting from a steam-cracked or other biomass) constitute dense and more resistant materials suitable for use as construction materials (composite boards).

[0052] In an advantageous embodiment of the invention, the biomaterial comprises a mixture of wood powders of fibrous nature and of powder nature prepared by steam-cracking. In a particular embodiment, the powder of fibrous nature is prepared from a resinous wood such as spruce and the powder of powder nature is prepared from hardwood such as oak.

[0053] The present invention will be better understood upon reading the examples which follow, provided by way of illustration, and in no way considered to be limiting on the scope of the present invention.

EXPERIMENTAL PART

EXAMPLE 1: Preparation of fiberboard from steam-cracked powder without additives

[0054] Wood powders from spruce and oak were prepared by steam cracking. The severity conditions applied during the steam-cracking were a decimal logarithm of the severity factor LogoSF = 4.05 for oak (C4) and of Logio SF4.15 for spruce (E6).

[0055] The powders were then formed per the protocol as follows: - taking the mass of fibers to be sampled as a function of the size of the test board, - wetting the fibers to be above the fiber saturation point (30% moisture), - dispersing the fibers in the mold (200x200 mm) while attempting to obtain a homogeneous distribution, - manually pressing using a plate that makes it possible to form a wet cake, - removing the cake from the mold and inserting it under the press between 2 sheets of water-repellent paper (to avoid adhesion phenomena), - pressing according to the program including various successive stages of time and pressure, at different temperatures (see table of tests in the "pressing time" column).

[0056] The results are shown in Table 1.

Test no. Material Sample Amount of water Temperature (°C) Pressing time Comments on the Type Mass (g) or glue biomaterial obtained 2.5 minutes at 80kN Particles too wet 1 C4 120 Embedded 200 and particles 2.5 minutes at 40kN water migrated during pressing 1 min at 8 kN, 1.5 min Particles too wet 2 C4 125 Partially 200 at 20 kN, -> Embedded 1 min at 40 kN, 1 min water migrated during at 12 kN pressing 30 sec at 8 kN, 1.5 min First complete 3 C4 120 40 g 200 1 ama20 kN, structure, board at 80 kN, 1m crumbled at20 kN Good structure, the 30 sec at 8 kN, 1.5 min presence of water 4 E6 120 60 g 200 at 20 kN, improves the rigidity 1 min at 80 kN, 1 min and surface condition at 20 kN (compared with board No. 7) 30 sec at 8 kN, 1.5 min Native spruce: The Native at 20 kN structure does exist 5 spruce 120 60 g 200 1 min at 80 kN, 1 min but nevertheless very at 20 kN crumbly and not water-resistant Native oak: The structure does exist 30 sec at 8 kN, 1.5 min but is extremely 6 Native oak 120 40 g 200 at 20 kN, crumbly. Impossible to 1 min at 80 kN, 1 min cut a 5 cm square to at 20 kN carry out the standardized tests for swelling 30 sec at 8 kN, 1.5 min E6 without water, the at2kN,m mechanical strength 7 E6 120 0 200 1 min at0kN, 1 min seems smaller at 20 kN compared to board No. 4 (E6 with water) C4 without water, the 30 sec at 8 kN, 1.5 min mechanical strength 8 C4 120 0 200 at 20 kN, seems to be even 1 min at 80 kN, 1 min smaller compared to at 20 kN board No. 3 (C4 with Water) Phenolic glue The board is not 12.1 g promising, BAKELITE PF 30 sec at 8 kN, 1.5 min very powdery and 9 E6 at 20 kN, crumbly, but it seems E6 110 1866 HW 200 1 min at 80 kN, 1 min to be lightweight. This UN 3267(52% dry at 20 kN comes from the mixer extract) that broke down the fibers The board is not promising, Phenolic glue very powdery and 12.1 g crumbly, but it seems BAKELITE PF 2.5 min at 150 kN to be lightweight. This 10 E6 110 1866 HW 200 2.5 min at 80 kN, 1 min comes from the mixer Kundenmuster at 20 kN, that broke down the UN 3267(52% dry fibers. Increasing the extract) pressure does not have a large impact on these 2 boards

The mixture increases the general cohesion of the board. 2.5 min at 150 kN The cohesive oak 11 E6 and C4 50 g 200 2.5 min at280kkN, 1 min powder isadded to and 60) 5g20 .mmat820kN,1m the spruce fibers, resulting in good mechanical strength (the crumbly effect is also eliminated) 160(80 Increase in density and 80 2.5 min at 300 kN 2.5 (going from 600 to 800 12 E6andC4 wih- 65 g 200 min at 150kN 1 min at kg/m) and pressure to spruc- at50 kN1 a obtain amore oak- 5N compactboard spruce) (increase in stiffness) Tests on mixtures of 160(80 successive and80 layers in order to S0with 2.5 min at 250 kN 2.5 increase the cohesion 13 E6and04 40 g (10-20-10) 200 min at 150 kN, 1 min at with the adhesive spac- 50 kN powder at the center (C4) and the fibrous oak- E6 on the exteriors Good rigidity Same test but with the cohesive powder of 160(80 C4 on the exteriors and 80 2.5 min at 250 kN 2.5 and the fibers of E6 at 14 E6 and C4 with oak - 35 g (7.5-20-7.5) 200 min at 150 kN, 1 min at the center. Rigidity spruce - 50 kN appears to be equivalent to board oak) No. 13 but the layers of oak are crumbly Good rigidity Same board as no. 14 but 160(80 without water, and 80 2.5 min at 300 kN 2.5 increasing the 15 E6and04withoak- 0 200 min at 150 kN, 1 min at pressure over the first spruce- 50 kN 2.5 minutes. oak) Loweradhesion (relative to no. 14) but good rigidity Mixing with increasing 160 (80 2.5 min at 500 kN 2.5 pressure but without 16 E6and04 and 80 0 200 min at 300 kN, 1 min at water. Very good mixture) 150 kN rigidity and good cohesion Board similar to no. 16 with added water 160 (80 2.5 min at 500 kN 2.5 which increases the 17E6 and C4 and 80 35 mixtue) 200 min at 300 kN, 1mna mn at oeinoof the cohesion h mixtur) 3150 kN mixture, very good rigidity. Placement on a 3 point bending test strip

[0057] Table 1: Summary of the tests forpreparation of the biomaterials from steam-cracking products.

Example 2: Characterization of the biomaterials obtained

1. Water swelling measurement:

[0058] The moisture resistance capacity was evaluated by measuring the thickness of each square test specimen (5x5 cm) before and after immersion in water at 20°C for 24 h. The calculation of the swelling is carried out as follows:

[Math 1]

G=(eafter-ebefore) as a

% before

where: - G is the swelling - e is the thickness

2. Actual density measurement:

[0059] The density, or actual density, is the product of the lengths, widths and thicknesses of the test specimens used for the swelling tests

[0060] The results are shown in Table 2.

Test Actual density (kg/m 3 ) Swelling(%) 3 613.2 13.1% 4 606.0 9.4% 5 556.8 217.4% 7 565.6 25.4% 8 548.1 10.0% 9 484.5 28.1% 10 461.6 16.0% 11 632.7 11.4% 13 833.4 17.2% 14 796.9 12.7% 15 729.0 16.1%

[0061] Table 2: Bending strength tests according to EN 310: Shaping of the test specimens (width = 5 cm and length = 20 x thickness + 50 mm, i.e. 150 mm (test specimen 5 mm thick) The machine directly gives the maximum breaking force, or Fmax, and the bending strength fm can be recalculated.

3. Bending strength

[0062] The bending strength fm (in newtons per square millimeter) of each test specimen is calculated from the following formula:

3 Fmax 1 fm 2 b t2

where: - Fmax is the breaking load, in newtons - t is the thickness of the test specimen expressed in millimeters - /is the length of the test specimen, expressed in millimeters - b is the width, expressed in millimeters

[0063] The bending strength of each test specimen being expressed to three significant digits.

[0064] The results for test specimen no. 17 are shown in Table 3 below:

Breaking Test sample Test sample width Tensile stress strength (N) thickness (mm) (mm) (Mpa) -0.128 4.24 48.3 0.0012

[0065] Table 3: Parameters relating to the bending resistance of test specimen No. 17

4. Analysis of findings

[0066] The swelling test makes it possible to see the material's resistance to water. A clear improvement between the exploded native and simple materials (217.4% versus 10%) is noted. In addition, the C4 oak boards appear to be very water-resistant (no. 3 and no. 8, with 13 and 10% respectively), which can be linked to the powdery appearance.

[0067] The sandwich or mixture boards oscillate between 11 and 17%, which is below the standard maximum values for boards subjected to the use classes 2 (very impressive for boards without glue or water in some cases). Observation after swelling shows that the sandwich boards absorb less water (less mass taken on and less water discharged onto the paper).

[0068] The pressure does not influence the water-resistance, but rather the rigidity of the board, just like the amount of material that is to be pressed. The presence or absence of water as a binder plays a role in the resistance to swelling: indeed, a pressed board with water is, according to the results, more resistant to swelling because its cohesion is decidedly better.

[0069] The boards with the phenolic glue do not give good results.

[0070] In conclusion, oak appears to provide cohesion and water-resistance but makes the boards easy to crumble (fine powder) while spruce makes it possible to rigidifythe assembly (long fibers) but is less cohesive. However, the results are better than with phenolic glue. The oak-spruce (or resinous hardwood) mixture gives the most satisfactory results as regards the three criteria evaluated: water resistance, cohesion and rigidity.

[0071] With an average swelling around 15% on the steam-cracked boards 5 mm thick, it is noted that this value is lower (for boards without glue and even sometimes without water) relative to the swelling over 24 hours for all other types of boards (fibers, MDF, particles, OSB, insulation) which vary between

15% and 25-30%. As regards the mechanical resistance to bending, the experimental results are much lower than the resistances for the other types of boards (0.9 MPa being the lowest value for boards in dry use).

[0072] The very hydrophobic and cohesive nature of the steam-cracked powders has numerous advantages; they could for example be used as replacements for glue or as an additive to reduce the amount of glue in order to obtain the same mechanical characteristics. This powder could also be used as a hydrophobic layer for boards used under wet conditions, or to create water-resistant insulation panels thanks to this steam-cracked powder.

Claims (11)

Claims

1. A method for producing a biomaterial from steam-cracked lignocellulosic biomass in powder form comprising the steps of: - providing a lignocellulosic biomass having a moisture content of between 5 and 27%, - treating said biomass by steam-cracking at a pressure of between 10 and 25 bar and a temperature is between 180 and 220C until a powder is obtained, - pressing said powder alone or in combination with a fibrous material for densification.

2. The method according to claim 1 wherein said densified powder alone is of fibrous nature.

3. The method according to claim 1 wherein said powder is of non-fibrous nature and is densified in combination with a fibrous material.

4. The method according to claim 1 wherein said densified powder alone is a mixture of steam-cracked powders of fibrous and non-fibrous nature.

5. The use of a powder obtained by the method as described in claim 1, as raw material for preparing a biomaterial.

6. The use according to claim 5 wherein said powder is the only component of the biomaterial.

7. The use of a non-fibrous powder obtained by the method as described in claim 1, as a binder for preparing a biomaterial.

8. The use according to claim 5 wherein said powder is mixed with a fibrous material and/or a binder.

9. A biomaterial obtained from steam-cracked lignocellulosic biomass as described in the method according to claim 1, wherein said biomass is in the form of fibrous or non-fibrous powder.

10. The biomaterial according to claim 9 comprising a mixture of wood powders of fibrous and non-fibrous nature prepared by steam-cracking.

11. The use of a biomaterial as defined in one of claims 9 or 10 as a packing product, insulating product and/or composite boards.