Bio-based composite materials and bio-based composites

Abstract

A bio-based composite material is disclosed, which comprises sawdust and a resin matrix based on lignin and tannin, with the sawdust comprising a total amount of 25 to 90 wt % based on the total weight of the bio-based composite. Also disclosed are a method for producing the bio-based composite material, a bio-based composite, and a method for producing the bio-based composite.

Description

[Technical Field]

[0001] The present disclosure relates to bio-based composite materials and methods for making bio-based composite materials. Further, the present disclosure relates to bio-based composites and methods for making bio-based composites. [Background technology]

[0002] Biocomposites are composites formed from a matrix (resin) and natural fiber reinforcement. The environmental aspects and cost of synthetic fibers have prompted research into using natural fibers as reinforcements in polymer composites. The matrix phase can be formed by polymers derived from renewable and non-renewable resources. The matrix not only holds the fibers together but also protects them from environmental degradation and mechanical damage. Many industrial applications call for further development of biocomposites. Summary of the Invention

[0003] A bio-based composite is disclosed, comprising sawdust and a resin matrix based on lignin and tannin, the bio-based composite comprising a total amount of sawdust of 25 to 90 wt % based on the total weight of the bio-based composite.

[0004] Additionally, a method for producing a bio-based composite material is disclosed, the method comprising: providing a resin matrix formed by polymerizing lignin and tannin with a crosslinking agent, the resin matrix having a viscosity value of 50 to 1000 mPa·s; providing sawdust having a dry matter content of 50-100%; combining the resin matrix with the sawdust by spraying and mixing the resin matrix onto the sawdust; forming the bio-based composite material, wherein the composite material comprises a total amount of sawdust of 25 to 90 wt %, based on the total weight of the composite material.

[0005] Also disclosed are bio-based composites produced by synthesizing the bio-based composite materials disclosed herein.

[0006] Additionally, a method for producing a bio-based composite is disclosed, the method comprising: The method includes a step of synthesizing the bio-based composite material by molding the bio-based composite material disclosed herein while maintaining the temperature of the bio-based composite material at 80 to 200°C. DETAILED DESCRIPTION OF THE INVENTION

[0007] A bio-based composite material is disclosed, which comprises sawdust and a resin matrix based on lignin and tannin, with the sawdust comprising a total amount of 25 to 90 wt % based on the total weight of the bio-based composite.

[0008] In addition to the sawdust and resin matrix, the bio-based composite may also include water and / or inorganic salts.

[0009] In one embodiment, the biobased composite material is comprised of sawdust and a resin matrix. In one embodiment, the biobased composite material is comprised of sawdust, a resin matrix, and water. In one embodiment, the biobased composite material is comprised of sawdust, a resin matrix, and an inorganic salt. In one embodiment, the biobased composite material is comprised of sawdust, a resin matrix, an inorganic salt, and optionally water. In one embodiment, the biobased composite material is comprised of sawdust, a resin matrix, an inorganic salt, and water.

[0010] In one embodiment, the bio-based composite is formed by combining a resin matrix with sawdust by spraying the resin matrix onto the sawdust while mixing.

[0011] In one embodiment, the resin matrix is ​​formed by polymerizing lignin and tannin with a crosslinker.

[0012] In one embodiment, no compound selected from phenols is used to form the resin matrix. In this specification, unless otherwise specified, the term "compound selected from phenols" should be understood to mean a fossil phenolic compound. That is, a phenol is a compound consisting of a single aromatic ring to which one or more hydroxyl groups (-OH) are attached. Such a compound selected from phenols may be, for example, phenol, cresol, or resorcinol.

[0013] The inventors have surprisingly discovered that a completely bio-based resin matrix can be used in conjunction with sawdust to produce a bio-based composite. Using a resin matrix made with both the biopolymers lignin and tannin can provide a resin matrix that can be efficiently mixed with sawdust to produce a bio-based composite that can form a "liquid wood"-like composite. The bio-based composite has the added benefit of curing in the presence of heat without the need for any additional hardeners or curing agents.

[0014] The sawdust may have an average particle size of 0.001-1 mm, 0.01-0.8 mm, 0.05-0.6 mm, 0.1-0.4 mm, or 0.15-0.2 mm. The average particle size of sawdust may be determined by a vibrating sieve method, in which different mesh sizes (five sieves, with mesh sizes ranging from 1.4 mm to 100 μm) are used. After vibration, particles of different sizes remain in the sieve, while others are too large to pass through the sieve.

[0015] The bio-based composite may comprise a total amount of sawdust of 30-88 wt%, 40-86 wt%, 50-84 wt%, 60-82 wt%, 65-80 wt%, or 70-78 wt%, based on the total weight of the bio-based composite. The bio-based composite may comprise a total amount of resin matrix of 10-75 wt%, 12-70 wt%, 14-60 wt%, 16-50 wt%, 18-40 wt%, 20-35 wt%, or 22-30 wt%, based on the total weight of the bio-based composite.

[0016] Additionally, a method for producing a bio-based composite material is disclosed, the method comprising: preparing a resin matrix formed by polymerizing lignin and tannin with a crosslinking agent to form a resin matrix having a viscosity value of 50 to 1000 mPa·s; providing sawdust having a dry matter content of 50-100%; combining the resin matrix with the sawdust by spraying and mixing the resin matrix onto the sawdust; and forming a bio-based composite material, the composite material comprising a total amount of sawdust of 25 to 90 wt %, based on the total weight of the composite material.

[0017] The crosslinking agent may be an aldehyde, such as formaldehyde or paraformaldehyde. In one embodiment, the aldehyde is produced from biomethanol. Thus, the aldehyde may be bio-based. Alternatively, the aldehyde may be fossil-derived, i.e., produced from fossil materials. In one embodiment, the aldehyde is produced from methanol.

[0018] The method includes preparing sawdust having a dry matter content of 50-100%. In one embodiment, the dry matter content of the prepared sawdust is 55-95%, 60-92%, 70-90%, or 80-85%. The dry matter content may be determined after removing the liquid from the sample and subsequently drying a 1 g sample at a temperature of 105°C for 3 hours. The effectiveness of the drying may be assured by weighing the sample, drying for an additional 2 hours at the specified temperature, and reweighing the sample. If the measured weights are the same, drying is complete and the total weight may be recorded.

[0019] In this specification, "total weight" should be understood as the weight of both dry matter and liquid parts such as water, unless otherwise specified.

[0020] The molar ratio of the crosslinking agent to the lignin and tannin may be 0.9 to 1.7, 1.0 to 1.6, 1.1 to 1.7, or 1.2 to 1.6. In this specification, the molar ratio (MR) is calculated as follows: MR=n(Fa) / (n(T)+n(L)) During the ceremony, n = amount of substance (moles) Fa = cross-linking agent T = tannin L = lignin

[0021] The amount of substance (in moles) is calculated as follows: n=M / m During the ceremony, M = molar mass of the substance (g / mol) m = mass of substance (grams)

[0022] The following values ​​are used herein for the above calculations: M (tannin) = 320 g / mol (estimated based on literature and assumed chemical structure) M(lignin) = 180 g / mol (estimated based on literature and assumed chemical structure)

[0023] The weight ratio of tannin to lignin may be 0.05 to 1.0, 0.1 to 0.43, or 0.15 to 0.33.

[0024] In the context of this specification, the term "lignin" may refer to lignin derived from any suitable lignin source. In one embodiment, the lignin is essentially pure lignin. The expression "essentially pure lignin" should be understood as at least 70% pure lignin, at least 90% pure lignin, at least 95% pure lignin, or at least 98% pure lignin. Essentially pure lignin may contain up to 30%, up to 10%, up to 5%, or up to 2% of other components and / or impurities. Extractives and carbohydrates such as hemicellulose may be cited as examples of such other components.

[0025] Furthermore, in the context of this specification, the term "tannin" may refer to a tannin derived from any suitable tannin source. In one embodiment, the tannin is an essentially pure tannin. The expression "essentially pure tannin" should be understood as at least 70% pure tannin, at least 90% pure tannin, at least 95% pure tannin, or at least 98% pure tannin. An essentially pure tannin may contain at most 30%, at most 10%, at most 5%, or at most 2% of other components and / or impurities.

[0026] Lignin may contain less than 30%, less than 10%, less than 5%, less than 3%, less than 2.5% or less than 2% by weight of carbohydrates. Tannin may contain less than 20%, less than 15% or less than 10% by weight of carbohydrates. The amount of carbohydrates present in lignin or tannin can be measured by high performance anion exchange chromatography with pulsed amperometric detection (HPAE-PAD) according to standard SCAN-CM 71.

[0027] The ash content of lignin may be less than 7.5 wt%, less than 5 wt%, less than 3 wt%, or less than 1.5 wt%. The ash content of tannin may be less than 10 wt%, less than 5 wt%, or less than 3 wt%. The ash content can be determined as follows: First, the sample is heated in an oven at 105°C for 3 hours to determine the dry solids content of the sample. A ceramic crucible is preheated to 700°C for 1 hour, cooled, and weighed. A sample (1.5 g to 2.5 g) is weighed and placed in the ceramic crucible. The crucible with a lip is placed in a low-temperature oven. The oven temperature is increased as follows: 20 to 200°C for 30 minutes, 200 to 600°C for 60 minutes, and 600 to 700°C for 60 minutes. Burning is continued at 700°C for 60 minutes without a lid. The crucible is cooled in a desiccator, and a few drops of hydrogen peroxide (HO (30%)) are added to the sample, followed by combustion in an oven at 700 °C for 30 min. If there are still dark spots in the ash, the hydrogen peroxide treatment and combustion are repeated. The crucible is cooled and weighed. All weighings are performed to an accuracy of 0.1 mg after cooling in a desiccator.

[0028] [Calculation of the result] Ash content%=(100a×100) / (b×c) During the ceremony, a = weight of ash, g b = sample weight, g c = dry solids content of sample, %

[0029] The ash content of a sample refers to the remaining mass of the sample after combustion and annealing, expressed as a percentage of the dry content of the sample.

[0030] In one embodiment, the lignin is industrial lignin. In the context of this specification, the term "industrial lignin" can refer to lignin derived from lignin in any biomass by any industrial process. In one embodiment, industrial lignin is lignin received from an industrial process.

[0031] The lignin used to produce the resin matrix may be selected from the group consisting of kraft lignin, steam explosion lignin, biorefinery lignin, supercritically separated lignin, hydrolyzed lignin, flash precipitation lignin, biomass-derived lignin, lignin from an alkaline pulping process, lignin from a soda process, lignin from organosolv pulping, lignin from an alkaline process, lignin from an enzymatic hydrolysis process, and any combination thereof. In one embodiment, the lignin is wood-based lignin. The lignin may be derived from softwood, hardwood, annual plants, or any combination thereof.

[0032] As used herein, "kraft lignin" refers to lignin derived from kraft black liquor, unless otherwise specified. Black liquor is an alkaline aqueous solution of lignin residues, hemicellulose, and inorganic chemicals used in the kraft pulping process. Black liquor from the pulping process contains components derived from different softwood and hardwood species in varying proportions. Lignin can be separated from black liquor by different techniques, such as precipitation and filtration. Lignin typically begins to precipitate at pH values ​​below 11-12. Different pH values ​​may be used to precipitate lignin fractions with different properties. These lignin fractions differ from each other by molecular weight distribution, e.g., Mw and Mn, polydispersity, hemicellulose, and extractives content. The molar mass of lignin precipitated at higher pH values ​​is higher than that of lignin precipitated at lower pH values. Furthermore, the molecular weight distribution of the lignin fraction precipitated at lower pH values ​​is broader than that of the lignin fraction precipitated at higher pH values. The precipitated lignin may be purified from inorganic impurities, hemicellulose, and wood extractives using an acidic wash step. Further purification may be achieved by filtration.

[0033] In this specification, the term "flash precipitated lignin" should be understood as lignin precipitated from black liquor in a continuous process by using a carbon dioxide-based acidifying agent, preferably carbon dioxide, to lower the pH of the black liquor stream to a lignin precipitation level under the influence of an overpressure of 200 to 1000 kPa and suddenly releasing the pressure to precipitate the lignin. A method for producing flash precipitated lignin is disclosed in Finnish Patent Application No. 20106073. The residence time in the process is less than 300 seconds. Flash precipitated lignin particles with a particle diameter of less than 2 μm form agglomerates that can be separated from the black liquor using, for example, filtration. The advantage of flash precipitated lignin is its higher reactivity compared to normal kraft lignin. Flash precipitated lignin may be purified and / or activated if further processing is required.

[0034] Lignin can be derived from an alkaline process, which begins with liquefying the biomass using a strong alkali, which may then be followed by a neutralization process. After alkaline treatment, the lignin can be precipitated in a similar manner as described above.

[0035] Lignin can be derived from steam explosion, a pulping and extraction technique that can be applied to wood and other fibrous organic materials.

[0036] As used herein, unless otherwise specified, "biorefinery lignin" should be understood as lignin that can be recovered from a refinery facility or process where biomass is converted into fuels, chemicals, and other materials.

[0037] As used herein, unless otherwise specified, "supercritically separated lignin" should be understood as lignin that can be recovered from biomass using supercritical fluid separation or extraction techniques. Supercritical conditions correspond to temperatures and pressures above the critical point of a given substance. At supercritical conditions, separate liquid and gas phases do not exist. Supercritical water or liquid extraction is a method of converting biomass into cellulosic sugars by using water or liquid under supercritical conditions. The water or liquid, acting as a solvent, extracts the sugars from the cellulose plant matter, leaving the lignin as solid particles.

[0038] The lignin may be derived from a hydrolysis process. The lignin derived from a hydrolysis process may be recovered from paper pulping or wood chemical processes.

[0039] The lignin may be derived from the organosolv process, which is a pulping technique that uses organic solvents to solubilize lignin and hemicellulose.

[0040] In one embodiment, the lignin comprises softwood kraft lignin. In one embodiment, the lignin is softwood kraft lignin. In one embodiment, the lignin is a combination of softwood lignin and hardwood lignin. In one embodiment, at most 30 wt%, at most 25 wt%, at most 10 wt%, or at most 5 wt% of the lignin is derived from hardwood.

[0041] The softwood kraft lignin may have a weight average molecular weight of 2500 to 9000 Da, 3000 to 8000 Da, or 3500 to 7000 Da. The lignin, for example kraft lignin, may have a polydispersity index of 2.9 to 6.0, 3.0 to 5.0, or 3.2 to 4.5.

[0042] The weight-average molecular weight can be determined by gel permeation chromatography (GPC) with a UV detector (280 nm) using the following method: Dissolve the sample in 0.1 M NaOH. Filter the sample solution through a 0.45 micron PTFE filter. Measurements are performed in 0.1 M NaOH eluent (0.5 ml / min, T=30°C) using a sulfonated styrene-divinylbenzene copolymer matrix, a PSS MCX precolumn, a 1000 Å column, and a 100,000 Å column. The molecular weight distribution of the sample is calculated relative to a Na-polystyrene sulfonate standard (6 strips) Mw 891-65400. Values ​​for Mw (weight-average molecular weight) and Mn (number-average molecular weight), as well as the polydispersity index (PDI, Mw / Mn), are reported based on two parallel measurements.

[0043] The amount of alkali-insoluble matter in softwood kraft lignin may be less than 10%, less than 5%, or less than 0.5%. The amount of alkali-insoluble matter may be determined as follows: First, the dry solids content of the sample is determined by heating the sample in an oven at 105°C for 3 h. 100 g of the sample is dissolved in 277 g of aqueous NaOH solution (pH 12-13) and mixed at 50-60°C for 30 min. The solution is filtered through a glass filter in a Büchner funnel. The residue on the filter is washed with 0.1 M NaOH and finally with water. The filter with the residue is dried in an oven and weighed. The amount of alkali-insoluble matter is then calculated as follows: Alkali-insoluble matter, % = [weight (dry) of filter with residue (g) - weight of filter] / [weight of sample (g) x dry solids content of sample (%)]

[0044] The softwood kraft lignin may have a condensation group and syringe group content of less than 3.0 mmol / g, less than 2.5 mmol / g, or less than 2.0 mmol / g, as determined by 31P NMR. The softwood kraft lignin may have an aliphatic OH group content of less than 3.0 mmol / g or less than 2.5 mmol / g, as determined by 31P NMR. The softwood kraft lignin may have a guaiacyl OH content of at least 1.5 mmol / g, as determined by 31P NMR.

[0045] Measurements performed by 31P NMR spectroscopy after phosphination can be used to quantitatively determine the functional groups (aliphatic and phenolic hydroxyl groups, as well as carboxylic acid groups). Sample preparation and measurements are performed according to the method by Granata and Argyropoulos (Granata, A., Argyropoulos, D., J. Agric. Food Chem. 1995, 43:1538-1544). An accurately weighed sample (~25 mg) is dissolved in N,N-dimethylformamide and mixed with pyridine and the internal standard solution (ISTD) endo-N-hydroxy-5-norbornene-2,3-dicarboximide (e-HNDI). The phosphination reagent (200 μL), 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphosphorane, is slowly added, followed by 300 μL of CDCl3. NMR measurements are performed immediately after the addition of the reagent. Spectra are measured on a spectrometer equipped with a broadband detection optimized probehead.

[0046] In one embodiment, the tannins used are derived from any wood species. They can be derived, for example, from bark or heartwood. Examples of possible sources of tannins include the seeds of Quebracho, Beech, Oak, Chestnut, Pine, Spruce and Acacia trees.

[0047] In one embodiment, the tannins used are derived from softwood bark. The tannins may be separated from the softwood bark in the bark removal unit of a sawmill or pulp mill. The separation process may be combined with an ethanol extraction process, a hot water extraction process, a hot steam extraction process, or a water-ethanol extraction process of the softwood bark.

[0048] In one embodiment, the tannin is a condensed tannin. Condensed tannins have a high dry matter content, making them suitable for use in the methods disclosed herein. The dry matter content of the condensed tannin may vary between 40 and 100%, suitably between 60 and 90% or between 70 and 80%. Tannins with such a dry matter content can be easily dispersed, achieving excellent reactivity with other reaction components. The tannin may also be a hydrolyzable tannin.

[0049] The tannin may have a weight average molecular weight (Mw) of 1500 to 5000 Da, 2000 to 4500 Da, or 2500 to 4000 Da.The tannin may have a polydispersity index of 2.8 to 1.0, 2.6 to 1.3, or 2.4 to 1.5.

[0050] In one embodiment, hexamine is used to prepare the resin matrix. In one embodiment, the resin matrix comprises hexamine. The use of hexamine in preparing the resin matrix has the added benefit of providing a stronger structure, as hexamine may be thought to act as a hardener.

[0051] In one embodiment, the resin matrix has a viscosity value of 50 to 1000 mPa·s, 50 to 250 mPa·s, or 250 to 600 mPa·s. The viscosity can be measured at a temperature of 25°C using a rotational viscometer (Digital Brookfield Viscometer LVDV-II+Pro, cone spindle). The inventors surprisingly found that when the resin matrix has the above viscosity value, for example, 50 to 250 mPa·s, the resin matrix can be uniformly mixed with sawdust by spraying.

[0052] The step of preparing sawdust may include mixing the sawdust with water. The step of preparing sawdust may include mixing the sawdust with water in an amount of 5 to 20% by weight or 6 to 10% by weight, based on the total weight of the prepared sawdust.

[0053] The step of preparing sawdust may include mixing the sawdust with an inorganic salt solution in an amount of 5 to 20% by weight or 6 to 10% by weight, based on the total weight of the prepared sawdust. Examples of salt types that can be used include chlorides, phosphates, and nitrates. As one specific example, sodium sulfate (NaSO) alone may be mentioned. Mixing the sawdust with the inorganic salt solution can reduce the electrical conductivity of the sawdust, making the bio-based composite easier to handle and enabling the following compounding to be carried out efficiently. The inorganic salt solution may have a concentration of 1 to 10% by weight, 2 to 8% by weight, or 3 to 6% by weight.

[0054] In one embodiment, water or an inorganic salt solution is mixed with the sawdust before spraying the resin matrix onto the sawdust. In one embodiment, water is mixed with the sawdust before spraying the resin matrix onto the sawdust. In one embodiment, an inorganic salt solution is mixed with the sawdust before spraying the resin matrix onto the sawdust.

[0055] The inventors have surprisingly discovered that the viscosity of the resin matrix, combined with the fact that the resin matrix is ​​sprayed onto, for example, sawdust rather than simply mixed with the sawdust, allows for the production of a bio-based composite material that, in addition to being formed from bio-based materials, can be cured into a bio-based composite by heating without the use of an additional curing agent.

[0056] The step of spraying the resin matrix onto the sawdust is performed with simultaneous mixing. That is, the resin matrix is ​​sprayed while the sawdust and resin matrix are mixed. In one embodiment, the mixing comprises high shear mixing. Mixing, such as high shear mixing, may be performed at a rotation speed of 360-1000 rpm, 450-900 rpm, or 650-800 rpm. High shear mixing may be performed, for example, using a (conical) mixing vessel having a central paddle rotor with an impact blade on top. An example of a high shear mixer is one known as Cyclomix®.

[0057] Spraying of the resin matrix may be done, for example, through a nozzle to break the resin matrix into droplets that are sprayed or distributed evenly on or above the sawdust.

[0058] The spraying may be carried out at a pressure of 0.1 to 5 MPa, 0.5 to 4 MPa, 1 to 3 MPa, or 1.5 to 2.5 MPa.

[0059] In one embodiment, the formed bio-based composite is a powder-like material. A bio-based composite that is a powder-like material may resemble kinetic sand or magic sand. Thus, the bio-based composite is not in liquid form or dough-like, but is a powder-like or sand-like material.

[0060] Bio-based composites have the added benefit of having excellent stock stability, ie, they maintain their powdered physical form when reconstituted at room temperature conditions.

[0061] Accordingly, also disclosed are bio-based composites produced by synthesizing the bio-based composite materials disclosed herein.

[0062] In this specification, synthesis, unless otherwise specified, is used to describe the process of forming a bio-based composite material into a bio-based composite of a desired shape.

[0063] In one embodiment, the visual appearance of the bio-based composite is liquid wood-like. Liquid wood is a bioplastic made from the natural components of lignin, cellulose fibers, and some additives. This bioplastic can be molded as a thermoplastic, and is therefore also called "liquid wood." That is, liquid wood has the same composition, appearance, and properties as wood, but can be melted and molded when heated like a thermoplastic.

[0064] The bio-based composites disclosed herein have the added utility of being wood-like materials in terms of visual appearance, but with mechanical properties similar to traditional thermosets or thermoplastics.

[0065] The bio-based composite may have a maximum bending stress of 12-20 MPa, 13-19 MPa, or 14-18 MPa. The maximum bending stress may be determined according to standard ISO 178:2010 (span length 48 mm, test speed 5 mm / min).

[0066] The bio-based composite may have a flexural modulus of 1400-2400 MPa, 1500-2300 MPa, or 1600-2200 MPa. The flexural modulus may be determined according to standard ISO 178:2010 (span length 48 mm, test speed 5 mm / min).

[0067] These mechanical properties of the bio-based composites indicate that the formed bio-based composites are moldable, that is, can be compressed into a desired shape.

[0068] Also disclosed is a method for producing a bio-based composite, the method comprising: The method includes synthesizing the bio-based composite material by molding the bio-based composite material while maintaining the temperature of the bio-based composite material disclosed herein at 80 to 200°C.

[0069] In one embodiment, the bio-based composite is synthesized by molding the bio-based composite while maintaining the temperature of the bio-based composite at 90-180°C, 100-170°C, 110-160°C, 120-150°C, or 130-140°C.

[0070] In one embodiment, the molding is done by compression molding, injection molding, or extrusion.

[0071] In one embodiment, the molding is carried out at a pressure of 1.2 to 140 MPa, 2 to 120 MPa, 5 to 100 MPa, 10 to 90 MPa, 20 to 80 MPa, 40 to 70 MPa, or 50 to 60 MPa.

[0072] In one embodiment, the molding is carried out by compression molding at a pressure of 1.2 to 140 MPa, 2 to 120 MPa, 5 to 100 MPa, 10 to 90 MPa, 20 to 80 MPa, 40 to 70 MPa, or 50 to 60 MPa.

[0073] In one embodiment, molding is carried out by injection molding at a pressure of 1.2 to 140 MPa, 2 to 120 MPa, 5 to 100 MPa, 10 to 90 MPa, 20 to 80 MPa, 40 to 70 MPa, or 50 to 60 MPa.

[0074] In one embodiment, the shaping is carried out by extrusion at a pressure of 1.2 to 140 MPa (12 to 1400 bar), 2 to 120 MPa, 5 to 100 MPa, 10 to 90 MPa, 20 to 80 MPa, 40 to 70 MPa or 50 to 60 MPa.

[0075] In one embodiment, the molding is carried out for 0.5 to 60 minutes, 1 to 45 minutes, or 5 to 30 minutes.

[0076] In one embodiment, no additional curing agent is used in the synthesis of the bio-based composite material.

[0077] The bio-based composite materials disclosed herein have the added advantage of being formed from large amounts of sawdust, having the visual appearance of wood-like materials, while meeting the mechanical properties for many applications.

[0078] The methods disclosed herein have the additional utility of providing bio-based composite materials that can be used to replace fossil-based thermoset materials or thermoplastics. Bio-based composite materials, and therefore bio-based composites, can be made from 100% biological components. [Example]

[0079] Reference will now be made in detail to the embodiments of the present disclosure.

[0080] The following description discloses embodiments in sufficient detail to enable those skilled in the art to utilize the methods based on the present disclosure, and not all steps of the embodiments are described in detail because some steps may be apparent to those skilled in the art based on this disclosure.

[0081] Example 1: Production of bio-based composite materials

[0082] First, a resin matrix was prepared using the following components and their amounts: Water 100% 27kg NaOH I 50% 9kg Kraft lignin 68% 31kg NaOH II 50% 3kg Formaldehyde 40% 15kg NaOH III 50% 2.7kg Tannin 40% (in alkaline solution) 13kg NaOH IV 50% 1.4kg

[0083] The percentages (based on total weight, calculated on dry matter content) of the ingredients used in this example were as follows: NaOH approx. 8.0% Kraft lignin approx. 21% Tannins: Approximately 5.2% Formaldehyde: approx. 6.0%

[0084] The molar ratio of formaldehyde to lignin and tannin was 1.5.

[0085] First, water and NaOH I were mixed at room temperature and heating was initiated. Once the temperature reached 70° C., lignin was added to the mixture, and mixing and heating continued for 30 minutes while maintaining the temperature at approximately 90° C. The mixture was then cooled to 60° C., and formaldehyde was added.

[0086] Mixing and heating of the resulting mixture was continued for 45 minutes at a temperature of about 72°C. NaOH II was then added, and mixing and heating was continued for 45 minutes at a temperature of about 70-75°C. NaOH III was then added, and mixing and heating was continued for 1 hour and 15 minutes at a temperature of about 87-89°C. NaOH IV was then added, followed by tannin, and mixing and heating was continued at about 90°C until the viscosity of the resulting mixture reached about 170-180 mPa·s (measured at 25°C). The mixture was then cooled to 30°C.

[0087] The resin matrix formed had the following measured properties: Solids content: 34.7% (3 hours at 105°C) pH 13.2 Viscosity, mPa·s250 (Brookfield RV, 25°C, 50 rpm) Alkalinity, %5.1 Free formaldehyde, %0.12

[0088] Then, sawdust was prepared by mixing 1.5 kg of sawdust (particle size 125 μm) with 190 g of sodium sulfate (NaSO) solution (6%). The moisture content of the prepared sawdust was 17%.

[0089] 1.35 kg of sawdust was placed in the cup of a high-shear mixer. 0.15 kg of resin matrix was then sprayed into the cup using a 1.2 mm spray nozzle at 5 bar pressure while the sawdust was mixed in the high-shear mixer at 750 rpm. Mixing continued until a uniform mixture was obtained.

[0090] Example 2: Preparation of bio-based composite material

[0091] In this example, a bio-based composite material was produced.

[0092] First, a resin matrix was prepared using the following components and their amounts: Water 100% 27kg NaOH I 50% 9kg Kraft lignin 68% 31kg NaOH II 50% 3kg Formaldehyde 40% 15kg NaOH III 50% 2.7kg Tannin 40% (in alkaline solution) 13kg NaOH IV 50% 1.4kg

[0093] The percentages (based on total weight, calculated on dry matter content) of the ingredients used in this example were as follows: NaOH approx. 8.0% Kraft lignin approx. 21% Tannins: Approximately 5.2% Formaldehyde: approx. 6.0%

[0094] The molar ratio of formaldehyde to lignin and tannin was 1.5.

[0095] First, water and NaOH I were mixed at room temperature and heating was initiated. Once the temperature reached 70° C., lignin was added to the mixture, and mixing and heating continued for 30 minutes while maintaining the temperature at approximately 90° C. The mixture was then cooled to 60° C., and formaldehyde was added.

[0096] Mixing and heating of the resulting mixture was continued for 45 minutes at a temperature of approximately 72°C. NaOH II was then added, and mixing and heating was continued for 45 minutes at a temperature of approximately 70-75°C. NaOH III was then added, and mixing and heating was continued for 1 hour and 15 minutes at a temperature of approximately 87-89°C. NaOH IV was then added, followed by tannin, and mixing and heating was continued at approximately 90°C until the viscosity of the resulting mixture reached approximately 170-180 mPa·s (measured at 25°C). The mixture was then cooled to 30°C. 0.4 kg of hexamine (100%) was then combined with the mixture.

[0097] The resin matrix formed had the following measured properties: Solids content: 34.8% (3 hours at 105°C) pH 13.4 Viscosity, mPa·s196 (R Brookfield RV, 25°C, 50 rpm) Alkalinity, %5.7 Free formaldehyde, %0.15

[0098] Then, sawdust was prepared by mixing 1.5 kg of sawdust (particle size 125 μm) with 190 g of sodium sulfate (NaSO) solution (6%). The moisture content of the prepared sawdust was 17%.

[0099] Five samples were prepared using different ratios of sawdust to resin matrix. The sawdust was placed in the cup of a high-shear mixer. The sawdust was then mixed in the high-shear mixer at 750 rpm while a fixed amount of resin matrix was sprayed into the cup using a 1.2 mm spray nozzle at 5 bar pressure. Mixing continued until a uniform mixture was obtained. The prepared samples are listed in Table 1.

[0100] Table 1. Samples of the bio-based composites produced [Table 1]

[0101] Example 3: Preparation of bio-based composites

[0102] In this example, bio-based composites were produced using Samples 1, 4, and 5 produced in Example 2. Each of the samples was synthesized by compression molding in a temperature chamber at 120°C under a pressure of 3.9 MPa for 20 minutes, during which time the sample temperature reached 120°C.

[0103] The composites produced were tested for their maximum bending stress and bending modulus, and the results are shown in Table 2.

[0104] Table 2. Maximum bending stress and bending modulus of the bio-based composites produced. [Table 2]

[0105] From the above results, it can be seen that the mechanical properties of the produced bio-based composites meet the standards required for many applications in which the produced bio-based composites may be used.

[0106] It is obvious to those skilled in the art that with the advancement of technology, the basic concept may be implemented in various ways. Therefore, the embodiments are not limited to the above examples; instead, they may be modified within the scope of the claims.

[0107] The above-described embodiments may be used in any combination with each other. Several embodiments may be combined together to form further embodiments. The bio-based composite materials, bio-based composites, and methods disclosed herein may include at least one of the above-described embodiments. It is understood that the benefits and advantages described above may relate to one embodiment or to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or have any or all of the stated effects and advantages. Furthermore, it is understood that a reference to "an" item refers to one or more of those items. As used herein, "comprising" is used to mean including subsequent features or acts without excluding the presence of one or more additional features or acts.

Claims

1. 1. A bio-based composite material comprising sawdust and a resin matrix based on lignin and tannin, the bio-based composite comprising a total amount of sawdust of 25 to 90 wt. %, based on the total weight of the bio-based composite material.

2. 10. The bio-based composite material of claim 1, wherein the resin matrix is ​​combined with the sawdust by spraying and mixing the resin matrix with the sawdust.

3. The bio-based composite material according to any one of claims 1 to 2, wherein the resin matrix is ​​formed by polymerizing lignin and tannin with a cross-linking agent.

4. The bio-based composite material according to any one of claims 1 to 3, wherein no compound selected from phenols is used in forming the resin matrix.

5. 5. The bio-based composite material of any one of claims 1 to 4, wherein the sawdust has an average particle size of 0.001 to 1 mm, 0.01 to 0.8 mm, 0.05 to 0.6 mm, 0.1 to 0.4 mm, or 0.15 to 0.2 mm.

6. 6. The bio-based composite material of any one of claims 1 to 5, comprising a total amount of sawdust of 30 to 88 wt%, 40 to 86 wt%, 50 to 84 wt%, 60 to 82 wt%, 65 to 80 wt%, or 70 to 78 wt%, based on the total weight of the bio-based composite material.

7. 7. The bio-based composite material of any one of claims 1 to 6, comprising a total amount of the resin matrix of 10 to 75 weight percent, 12 to 70 weight percent, 14 to 60 weight percent, 16 to 50 weight percent, 18 to 40 weight percent, 20 to 35 weight percent, or 22 to 30 weight percent, based on the total weight of the bio-based composite material.

8. 1. A method for producing a bio-based composite material, comprising: preparing a resin matrix formed by polymerizing lignin and tannin with a crosslinking agent to form a resin matrix having a viscosity value of 50 to 1000 mPa s; providing sawdust having a dry matter content of 50-100%; spraying and mixing the resin matrix onto the sawdust to combine the resin matrix with the sawdust; forming the bio-based composite material, wherein the composite material comprises a total amount of sawdust of 25 to 90 wt. %, based on the total weight of the composite material.

9. The method of claim 8, wherein the resin matrix has a viscosity value of 50 to 250 mPa·s or 250 to 600 mPa·s.

10. 10. The method according to any one of claims 8 to 9, wherein the step of preparing the sawdust comprises mixing the sawdust with an inorganic salt solution in an amount of 5 to 20% by weight or 6 to 10% by weight, based on the total weight of the prepared sawdust.

11. 11. The method according to any one of claims 8 to 10, wherein the dry matter content of the provided sawdust is 55-95%, 60-92%, 70-90%, or 80-85%.

12. A bio-based composite produced by synthesizing the bio-based composite material of any one of claims 1 to 7.

13. 13. The bio-based composite of claim 12, having a visual appearance similar to liquid wood.

14. The bio-based composite of any one of claims 12 to 13, wherein the maximum bending stress is 12 to 20 MPa, 13 to 19 MPa, or 14 to 18 MPa.

15. The bio-based composite of any one of claims 12 to 14, having a flexural modulus of 1400 to 2400 MPa, 1500 to 2300 MPa, or 1600 to 2200 MPa.

16. 1. A method for producing a bio-based composite, comprising:

9. A method comprising the step of synthesizing the bio-based composite material by molding the bio-based composite material according to any one of claims 1 to 8 while maintaining the temperature of the bio-based composite material at 80 to 200°C.

17. 17. The method of claim 16, wherein no additional curing agent is used in the synthesis of the bio-based composite material.

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