EP3268190B1 - Method for producing a wood chip material and curing agents used therein for aminoplasts - Google Patents

Description

The present invention relates to a process for the production of wood chipboard materials according to claim 1 and the use of a hydrothermally and mechanically digested lignocellulosic material as a hardener for an aminoplast resin according to claim 20.
Chip-based materials, so-called chipboard materials, consist of shredded wood material that can be pressed into single or multilayer boards. The classification of wood-based panels is usually according to EN 309. Important classification criteria are the production process (extruded or flat pressed), the surface finish (rough, ground, press-coated), the shape and size of the wood materials used (wood chips, wood flakes, wood wafers, wood strands), the panel structure (single-layered or multi-layered) and the intended use.

Since the massive wood composite is largely eliminated in wood chip materials, these plates in the direction of the plate plane, ie in the direction of the length and width of the plate, almost the same swelling and shrinkage properties. Wood chipboard materials are used, for example, in the construction industry as an insulating, constructive or cladding element, in the furniture industry and as a floor covering.

In the production of wood chip materials a high recycling of the wood can be ensured. Thus, in addition to forest wood, residual wood from industry and used wood are used.

Chipboard materials are produced from finely divided wood material of various types of wood with the addition of natural and / or synthetic binders as well as other substances. For processing the wood material, cutting processes are used to recover wood particles. Examples of wood particles are wood flakes, wood strands, wood wafers, wood chips and wood chips. Subsequently, the wood particles are usually dried, glued with a composition (glue liquor) containing a binder and arranged in one or different layers (scattering). Finally, the scattered wood material is pressed under pressure and temperature to the respective desired wood chip material.

The expert distinguishes between wood-chip materials and wood-fiber materials. Wood chipboard materials and wood fiber materials as well as their production processes differ fundamentally from each other. Wood fiber materials contain as the main component derived from wood fiber material. This fibrous material is obtained by steaming or cooking (e.g., in a precooker or digester) wood material and by chemical or mechanical disruption (e.g., in a refiner) to single fiber, fiber bundles, or fiber debris. In contrast, wood chip materials as the main component contain chip material, i. Pieces of wood. The chip material is obtained by merely crushing wood material. A treatment by steaming, cooking or by chemical or mechanical disruption as in the defibering is just not.

Binders for the production of wood chip materials may have one or more constituents. Usually consist or contain binders for the production of wood chipboard resins.

Synthetic resins are known to those skilled in principle. Synthetic resins are for example in Rompps Chemie-Lexikon, 7th edition, Frankh'sche Verlagshandlung Stuttgart, 1973, page 1893 described. An important group of synthetic resins are condensate resins. These harden by condensation reactions, which often Water is split off. Condensate resins include, for example, phenol-formaldehyde resins and aminoplast resins.

Aminoplast resins have proved to be particularly practical in connection with the production of wood chip materials. Typically, a wood chip material contains at least one aminoplast resin as a binder. Aminoplast resins are typically used in wood chipboard to bond the lignocellulosic parts or wood particles together. In this case, a single aminoplast resin or mixture of different aminoplast resins can be used.

Aminoplast resins are known to the person skilled in the art and are described, for example, in US Pat. Ullmanns Enzyklopadie der technischen Chemie ", 4th Edition, Volume 7, p. 403ff , described. Aminoplast resins can be obtained by condensing an amino, imino or amide group-containing component with a carbonyl compound. Common starting materials for aminoplast resins are, for example, urea and / or melamine (as the amino-containing component) and formaldehyde (as the carbonyl compound). In the latter case, the amino-containing component is usually precondensed in a first step with the carbonyl compound to a certain degree. Depending on whether in the first step, for example, only melamine or only urea is used as the amino-containing component, one obtains a so-called melamine resin or a urea resin. Such melamine and / or urea resins may in particular form the main constituents of aminoplast resins. In a second step, often referred to as curing, the aminoplast resin can then be crosslinked throughout. Resins formed from urea and formaldehyde are also referred to as urea-formaldehyde resins. Resins formed from melamine and formaldehyde are referred to as melamine-formaldehyde resin.

Whenever aminoplast resins are mentioned here or elsewhere, they are meant to include aminoplast resin compositions. Aminoplast resins and / or aminoplast resin compositions may also contain water.

The curing of synthetic resins, in particular of aminoplast resins, can be carried out, for example, by addition of acidic catalysts. Usually conventional hardeners come into consideration. Hardeners and their reaction to initiate the curing reaction are, for example, in " Wood Materials and Glues: Technology and Influencing Factors "by M. Dunky and P. Niemz, Springer-Verlag, 2013, pages 265-270 described. Basically, the typical curing agents for aminoplast resins have in common that they can contain, consist of, or release acid. This acid catalyzes or initiates the curing reaction. Examples of conventional hardeners are strong organic acids, inorganic acids such as sulfuric acid and phosphoric acid, salts which are acidic in water, such as aluminum chloride and aluminum nitrate (also referred to as acid salts), salts formed by reaction with components of the synthetic resin, preferably with formaldehyde to generate an acid (also referred to as acid-generating salts) such as ammonium phosphate, ammonium nitrate, ammonium sulfate and ammonium chloride, and mixtures of the aforementioned substances.

Formaldehyde may be harmful to human or animal health and may cause allergies, skin, respiratory or eye irritation. In chronic exposure, it may even be carcinogenic. Therefore, it is desirable to produce wood chip materials with a reduced formaldehyde content. This is particularly important with regard to the use of wood chipboard materials for the production of furniture or flooring.

JP S60 210406 A describes a process for producing a lignocellulosic floor covering using mixed, dry cellulose fine aggregates, powdered cork material and urea resin.

DE 10 2004 010796 A1 relates to a process for reducing formaldehyde release and other organic volatile compounds from lignocellulosic material sheets, in which the material is fiberized into particles and / or fibers by thermo-mechanical pulping, glued, formed into mats, and pressed into a finished sheet, which is characterized by The digestion products of the lignocellulosic material are partially or completely removed by washing.

For hardening especially of aminoplast resins, various hardeners are known to the person skilled in the art:
The WO 02/068178 A2 describes a method for bonding laminated products with an aminoplast resin using a curing agent containing acid, an acid salt, and / or an acid-generating salt, as well as a polymer dispersion.

The WO 2005/030895 A1 describes binder systems which, besides aminoplast resins and N-functionalized copolymers, also contain at least one acid, an acid salt and / or an acid-generating salt.

The WO 2007/012615 A1 describes a curing agent composition for aminoplast resins which comprises an acid, an acidic salt and / or an acid-generating salt and an aminoplast resin dispersion having a residual activity of less than or equal to 100 J / g.

A disadvantage of the hardener compositions listed in the prior art is that the curing of the resin is difficult to control when using strong acids as a hardener, since the curing can begin even on addition of the acid.

In order to avoid this undesirable precuring, the so-called hardening precoating method has been proposed in the prior art, in which first the acid is applied to the preliminary or intermediate product of the wood pulp and then the gluing with a synthetic resin is carried out. However, a disadvantage of this is the economic outlay due to the additional process steps.

Moreover, strong acids contribute more to the unwanted hydrolysis of the glue joint. Often, additional buffer systems must be used to reduce these disadvantages, but in turn can lead to insufficient curing of the resin. The same applies to the use of acid salts, in which the curing can also begin with the addition of the acidic salts. Another disadvantage of acid-generating salts is that these salts are usually free Formaldehyde need to form the corresponding strong acid, which then contributes to the curing of the resin. In this respect, binder compositions (glue fleets) containing hardener systems based on acid-generating salts require an increased formaldehyde content. Normally, this formaldehyde is not permanently bound and can be slowly released after completion of the manufacturing process. Thus, these hardener compositions are not optimal for the production of wood chip materials having a reduced formaldehyde content.

Furthermore, the use of ammonium salts can also be problematic for environmental, economic and safety aspects. On the one hand, ammonium compounds represent a potential emission source for ammonia before, during and after production, and on the other hand, the use of ammonium chloride with regard to recycling and thermal end use must also be critically assessed. Furthermore, ammonium nitrate poses a risk during storage because it is fire-promoting and explosive.

Another concern is that when using ammonium compounds or when added directly after the production of the wood chip material acid can continue to be formed or free strong acid remains in the wood chip material. This acid can lead to the hydrolysis of the glue joint, which can have a negative effect on the strength and swelling properties of the wood chip material.

On the basis of the above-described prior art and its disadvantages, it was an object of the invention to provide a method which employs an improved alternative hardening system. In particular, it was an object of the invention to provide a process which makes it possible to produce wood chip materials having a reduced formaldehyde content.

This object is achieved by a method according to claim 1, and the use according to claim 20.

Advantageous embodiments of the invention are described in the dependent claims and are explained below as the general inventive concept in detail

1. a) Bereitstellen eines ersten lignocellulosehaltigen Materials in Form von Holzpartikeln;
2. b) Beleimen des ersten lignocellulosehaltigen Materials mit einer Zusammensetzung, die mindestens ein Aminoplastharz und mindestens einen ersten Härter umfasst, wobei der erste Härter durch hydrothermischen und mechanischen Aufschluss eines zweiten lignocellulosehaltigen Materials erhalten wurde, und wobei das zweite lignocellulosehaltige Material aus einem anderen Rohstoff als das erste lignocellulosehaltige Material stammt;
3. c) Verpressen zu einem Holzspanwerkstoff.

The inventive method for producing a wood chip material comprising the steps:

1. a) providing a first lignocellulosic material in the form of wood particles;
2. b) gluing the first lignocellulosic material with a composition comprising at least one aminoplast resin and at least one first hardener, the first hardener being obtained by hydrothermal and mechanical digestion of a second lignocellulosic material, and wherein the second lignocellulosic material is of a different raw material than the one first lignocellulosic material originates;
3. c) pressing to a wood chip material.

Optionally, further method steps may be carried out before, after and / or between the steps a) to c). Optional steps may be, for example, heating in a preheat container, crushing, storing, mixing, adding further substances, spreading or drying the material used or obtained in steps a) to c).

Surprisingly, it was found that by using a hardener of hydrothermally and mechanically digested lignocellulosic Material, the problems listed above, known from the prior art problems can be largely avoided or reduced.

Since the aminoplast resin used in the process according to the invention may also contain other hardeners, the hardener obtained by hydrothermal and mechanical pulping of lignocellulose-containing material is referred to herein as the "first hardener".

It is advantageous that the use of the first hardener can be integrated in a simple manner into conventional processes of the wood industry for the production of wood chip materials. No complicated intermediate steps or process interruptions are required.

It is also advantageous that the first hardener used in the invention is available inexpensively and readily available. It is available by hydrothermal and mechanical digestion of lignocellulosic material. In a preferred embodiment of the invention, the first hardener is obtained from biomass containing lignocellulose. If biomass is mentioned here, then it means a wide variety of plants, plant parts, fruits and mixtures thereof, in particular plant waste from agriculture or the wood industry. The utilization of this biomass for the production of the first hardener is thus an ecologically very relevant advantage, since biomass is a renewable raw material. A particular embodiment of the invention makes it possible to produce plant waste, which is only or no longer suitable for final use, for the production of the first Hardener to use. Overall, an improved cascade use of vegetable raw materials can be achieved by the method according to the invention.

Another practical and economic advantage of the first hardener is that it can be produced in a particularly simple and cost-effective manner. Process for the hydrothermal and mechanical digestion of lignocellulosic Material are known to those skilled in the art, for example from the manufacture of fibreboard. Also of practical importance is that the first hardener can be particularly easily added to the binder composition (glue liquor) and is compatible with it. This is not possible, for example, in the case of the use of strong acids which is sometimes practiced in the prior art, as are used, for example, in the hardening precoating method.

Furthermore, the inventive method allows a reduced use of the above-mentioned chemicals. By the use according to the invention of the first claim 20 according to claim 20, the demand for free formaldehyde and / or the amount of conventional hardeners, such as. As acid-generating salts are significantly reduced. Thus, the first hardener is an environmentally friendly alternative and / or supplement to the conventional hardeners explained above.

Without wishing to be limited to any particular scientific theory, this surprising effect of the first hardener appears to be explained by one or more acids being released during the hydrothermal and mechanical digestion. This at least one acid seems to contribute to the curing of the resin.

The at least one acid released during the hydrothermal and mechanical digestion also appears to be a volatile acid. As a result, this acid does not remain or only for a short time in the glue joint of the finished wood chip material. This short residence time of the acid hydrolysis of the glue joint can be largely avoided by this acid. When acid is mentioned here, it may mean a single acid or mixtures of different acids.

Important parameters for wood chip materials are swelling, transverse tensile strength and water absorption. Surprisingly, it has been found in practical experiments that these parameters in wood chip materials, which by the Processes according to the invention have been improved. In particular, when using the first hardener according to the invention, which is obtainable by hydrothermal and mechanical pulping, reduces the amount of conventional hardener and sometimes even be dispensed with, without causing a deterioration of these parameters Thus, for example, the transverse tensile strength of the wood chipboard materials produced can be improved , Furthermore, the swelling and / or water absorption of the wood chipboard materials produced can be significantly reduced.

When referring to "lignocellulosic material", it refers to vegetable matter containing lignocellulose. Lignocellulose according to the invention contains cellulose and / or hemicellulose and lignin.

"Cellulose" is an unbranched polysaccharide consisting of several hundred to ten thousand cellobiose units. These cellobiose units, in turn, consist of two molecules of glucose linked by a 6-1,4-glucosidic bond.

"Hemicellulose" is a collective name for various components of plant cell walls. The hemicelluloses are branched polysaccharides with a lower chain length - usually less than 500 sugar units - which are composed of different sugar monomers. Hemicellulose is composed essentially of various sugar monomers such as glucose, xylose, arabinose, galactose and mannose, which sugars may have acetyl and methyl substituted groups. They have a random, amorphous structure and are readily hydrolyzable. Xylose and arabinose consist for the most part of sugar monomers with five carbon atoms (pentoses). Mannose or galactose consist mainly of sugar monomers with six carbon atoms (hexoses).

"Lignins" are amorphous, irregularly branched aromatic macromolecules, which occur in nature as part of cell walls and there cause the lignification (lignification) of the cell. They are composed of substituted phenylpropanol units, have a lipophilic character and are insoluble in room temperature in neutral solvents such as water. Precursors of lignin are, for example, p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. The molecular weights of lignin are usually between 10,000 and 20,000 g / mol.

"Hydrolysis" in the sense of the disclosure may in particular mean the cleavage of a (bio) chemical compound by reaction with water. In particular, it is possible in this case to formally deliver a hydrogen atom to the one gap piece and the remaining hydroxyl group to the other gap piece.

If this is referred to as "wood chip material", then according to the invention are understood to mean a variety of materials based on chip, which consist of wood or contain wood. Wood chipboard (chipboard in the broader sense) refers to a product group in the field of wood materials, which are made of wood particles and at least one binder by means of heat and pressure. Another product group in the field of engineered wood, not covered by the term "wood chipboard" as used herein, is the wood fiber materials. The latter includes fiberboard such as the medium density (MDF) and high density (HDF) fiberboard Wood chip materials, wood used for the manufacture of the fiberboard, wood fibers, fiber bundles or fiber fragments are digested in. For the expert wood chip materials and wood fiber materials are two fundamentally different material categories, which are to be distinguished.

Basically, the expert knows different wood chip materials. Examples include particleboard, flat-plate, single-layer, multi-layer, lightweight flat, extruded, extruded (ET - Extruded Tubular), Extruded Solid (ES), Plastic-coated Melanin Faced Board (MFB), Chipboard Moldings or Oriented Strand Board (OSB). The division of the chipboard can be done according to DIN EN 312, whereby the chipboard can differ in strength and moisture resistance. OSB boards can be classified according to their use according to EN 300. Such wood chip materials can be further processed, for example, into laminates, floor coverings, countertops, table tops, pallets and / or wooden moldings. Wood chip materials, their manufacture and requirements for these are also in " Taschenbuch der Holztechnik ", A. Wagenführ, F. Scholz, Carl Hanser Verlag, 2nd edition, 2012 on pages 143 to 146 described.

According to one embodiment of the invention, the wood chip material is a wood chipboard. Preferably, the wood chip material is a chipboard or OSB board. Practical experiments have shown that the method according to the invention and the described embodiments are particularly suitable for the production of pressed wood chip materials, in particular for the production of chipboard and OSB boards.

Preferably, the wood-chip material, or its intermediate or intermediate product, consists essentially of lignocellulose-containing material and binders. "Substantially" here means to 90 wt .-%, 95 wt .-%, 99 wt .-% or 99.9 wt .-%, each based on the total weight of the wood chip material.

However, it is also possible that the wood chip material, or its intermediate or intermediate, contains other substances. For example, wetting and / or separating agents can be added for an improved pressing process. Furthermore, antifungal agents or fire retardants may be added. As a result, the finished lignocellulosic wood chip materials can meet special requirements. Such requirements have already been mentioned above and are known to the person skilled in the art. In particular, such further substances in the inventive method before, during and / or after one of the steps a) to c) are added.

Step a) of the method according to the invention provides for the provision of wood particles. If wood particles are mentioned here, this means any wood particles that can be used for the production of wood chip materials. Wood particles may be any size reduction products of lignocellulose-containing materials. Wood particles, as used herein, are not wood fibers.

Since the hardener used according to the invention also contains lignocellulose, the wood particles used in step a) are referred to herein as "first lignocellulose-containing material". The material used to produce the hardener is referred to as a "second lignocellulose-containing material". The first lignocellulosic material differs from the second lignocellulosic material as explained below.

For the production of wood-chip materials according to the method according to the invention and its embodiments, a first lignocellulose-containing material which is in the form of wood particles is used in step a). Depending on the nature of the wood chip material, the first lignocellulose-containing material can be produced by comminuting lignocellulose-containing materials. According to the invention, the first lignocellulose-containing material is provided in the form of wood particles, ie it may contain or consist of wood particles. Wood particles, as used herein, may contain wood or be made of wood. Examples of wood particles are finely divided wood material, wood chips, wood strands, wood wafers, wood flakes and wood chips. Usually, the wood particles for wood chip materials are obtained by cutting processes. In an optional step, the wood particles can be dried or stored before further processing. It is also possible to admix further substances to the first and / or second lignocellulose-containing material.

In principle, various methods are known to those skilled in the art to produce wood chip materials by compression. According to one embodiment of the invention, the wood particles glued in step b) are pressed in step c) into a wood chip material. Preferably, step c) is a hot pressing. Optimum results can be achieved if the press factor during hot pressing is from 2 to 10 s / mm, preferably from 3 to 6 s / mm. Press factor is understood to mean in particular the residence time of the lignocellulose-containing wood chip material in seconds per millimeter thickness or thickness of the finished pressed lignocellulose-containing wood chip material in the press.

Suitable temperatures for the compression in step c) of the process according to the invention or one of its embodiments are temperatures of 150 ° C to 250 ° C, preferably from 160 ° C to 240 ° C, particularly preferably from 180 ° C to 230 ° C. At temperatures in these ranges, the process can be carried out particularly economically.

For economic and procedural reasons, it has proved to be advantageous if a specific pressing pressure (active pressure on the plate surface) of 50 to 300 N / cm ² , is used during pressing. Such pressures ensure a particularly good bonding of the lignocellulose-containing particles together. In addition, a high strength of the lignocellulosic wood chip materials can be achieved with such a pressure.

Since the process according to the invention is a process for producing wood chips from the wood particles used in step a) (referred to herein as "first lignocellulosic material"), this process does not involve defibration, steaming, cooking or chemical and / or mechanical pulping (For example, in a refiner) of the first lignocellulosic material, as practiced for example in the production of wood fiber boards.

In step b) of the process according to the invention, the first lignocellulose-containing material is glued with a composition which comprises at least one aminoplast resin and at least one first hardener. If this is referred to as "gluing", then it can be understood as wholly or partially wetting with a composition containing a binder ("binder-containing composition"). Such compositions are also referred to by the person skilled in the art as "glue liquor". According to the invention, the binder is an aminoplast resin. Gluing can in particular also mean the uniform distribution of the binder-containing composition on the wood particles. The application of the binder-containing composition can be carried out, for example, by impregnation or spraying.

The process according to the invention comprises in step b) the gluing of wood particles with a composition comprising at least one aminoplast resin and at least one first hardener. This can be achieved in a variety of ways. In particular, the hardener can be added to the aminoplast resin before and / or during gluing to produce the composition. According to one embodiment of the method according to the invention, a previously prepared mixture of aminoplast resin and first hardener is used as the composition for gluing the wood particles and applied to the wood particles. Thus, according to this embodiment of the method, the wood particles are glued with a composition containing an aminoplast resin and a first hardener by applying a previously prepared mixture of aminoplast resin and first hardener to the wood particles.

The method according to the invention, however, likewise encompasses those embodiments in which the hardener is added to the aminoplast resin only during gluing and the composition is first formed in situ during gluing. This can be achieved, in particular, by separating the aminoplast resin and the first hardener during gluing of the wood particles from each other, if necessary with other additives or binders are applied to the wood particles. In the process, the aminoplast resin and the hardener mix to form a composition that "contains" an aminoplast resin and a first hardener. For example, in a first step, the aminoplast resin and in a second step, the first hardener may be applied to the wood particles. Conversely, it is also possible in a first step, first apply the first curing agent and then in a second step, the aminoplast resin on the wood particles. A simultaneous application of aminoplast resin and first curing agent by two separate application devices, such as nozzles, on the wood particles is possible. Accordingly, another embodiment of the method provides for the wood particles to be glued with a composition containing an aminoplast resin and a first hardener by separately applying the aminoplast resin and the first hardener to the wood particles.

The amount of binder used in gluing is preferably 0.1 to 20 wt .-%, in particular 1 to 16 wt .-%, more preferably 4 to 14 wt .-%, based on the dry weight of wood (solid resin / atro). For many applications, it is particularly practical if the binder in an amount of 0.1 to 15 wt .-% based on the dry weight of wood (solid resin / atro) is used.

In principle, the method according to the invention or one of its embodiments is suitable for a multiplicity of binder-wood particle combinations. According to the invention, at least one aminoplast resin is used as the binder. Alternatively or additionally, other synthetic resins, in particular phenolic resins, vinyl acetates, isocyanates, epoxy resins and / or acrylic resins can also be used in the process according to the invention. In one embodiment of the invention, the binder consists of an aminoplast resin and one or more hardeners. Examples of aminoplast resins are urea-formaldehyde resins (UF), melamine-reinforced urea-formaldehyde resins (MUF), melamine-urea-phenol-formaldehyde resins (MUPF), or mixtures thereof. In practice, particularly good results can be achieved with urea-formaldehyde resins (UF), melamine-reinforced urea-formaldehyde resins (MUF) or mixtures thereof.

Preferably, the aminoplast resin is obtainable by condensation of an amino group-containing component with a carbonyl compound. The carbonyl compound is preferably formaldehyde. The amino group-containing component is preferably melamine and / or urea. More preferably, the aminoplast resin is a melamine resin or a urea resin, especially a melamine-formaldehyde resin or a urea-formaldehyde resin.
The composition (glue liquor) used in the process according to the invention also contains at least one first hardener. Advantageously, the binder contains 0.1 to 15 wt .-% of the first hardener, in particular 0.5 to 10 wt .-%, based on the solid resin content of the aminoplast resin.

The term "hardener" as used herein is a term known to those skilled in the art of making chipboard material. Hardeners are catalysts which catalyze a curing or crosslinking reaction, ie promote or initiate without being consumed itself. As is known to those skilled in the art, catalysts are substances that increase the rate of reaction by lowering the activation energy of a chemical reaction without being self-consumed. The curing of aminoplast resins is carried out by acid catalysis. The acid, which acts as a hardener, initiates or drives the curing or crosslinking reaction without being consumed. Hardeners are therefore to be distinguished from the starting materials of the aminoplast resin crosslinking reaction, which react with each other during the aminoplast resin curing and are therefore consumed. Likewise, hardeners are also to be distinguished from additives, for example diluents such as lignin, which are able to polymerize via functional groups into the aminoplast resin. Such additives, which during the Aminoplastharz curing polymerize and thereby abreact and can be consumed are not covered by the term "hardener" as used herein.

The first hardener used according to the invention is based on lignocellulose-containing material. It is obtained by hydrothermal and mechanical digestion of such a lignocellulose-containing material. According to one embodiment, the first hardener used according to the invention therefore contains or consists of hydrothermally and mechanically digested lignocellulose-containing material.

The curing used according to the invention is obtained from a second lignocellulose-containing material which differs from the first lignocellulose-containing material described above used in step a). This difference consists in particular of the origin and / or the underlying raw materials. According to the invention, provision is made in particular for the second lignocellulose-containing material to originate from a different raw material than the first lignocellulose-containing material. The first and second lignocellulose-containing material may represent different raw materials or be made or obtained from different raw materials. According to one embodiment, the difference in the raw materials in the plant species or the composition of plant species from which the two lignocellulose-containing materials are obtained. According to another embodiment, the difference in the raw materials in the genus or the compilation of plant species from which the two lignocellulose-containing materials are obtained. The terms plant species and plant genus are to be understood according to the usual botanical definition (taxon and genus).

According to the invention, the first lignocellulose-containing material is provided in the form of wood particles, that is to say that at least one raw material from which the first lignocellulose-containing material originates is wood. The second lignocellulose-containing material can be obtained from a different type of wood than that used as raw material was used for the first lignocellulosic material. However, the raw materials for the first and second lignocellulose-containing material preferably differ in that the second lignocellulose-containing material originates from a raw material that is different from wood, in particular from tree wood.

In a preferred embodiment of the invention, the second lignocellulosic material is selected from the group consisting of annuals, crops, grasses, foliage, cereals, their constituents and waste, or mixtures thereof. Crop is in particular straw, wheat, rye, barley, oats, millet, corn, miscanthus, rice, their constituents, their waste and / or mixtures thereof understood. The term "annual plants" refers to plants and / or their constituents containing lignocellulose, which require a period of vegetation from the germination of their seed to the fertilization of their flower and the maturity of the new seed, and to the maturity of the new one Seeds die off. In a particularly preferred embodiment, one or more of these selected second lignocellulose-containing materials are hydrothermally and mechanically digested. This hydrothermally and mechanically digested material can then be used as the first hardener.
The use of the above-described lignocellulose-containing materials for the preparation of the first hardener has proven to be economically advantageous. The plants mentioned are easy to cultivate and can be processed easily and in a few process steps. For example, the processing of plant waste not only ensures a low-cost raw material, but also an improved cascade use of plant raw materials. In contrast, the use of wood, especially tree wood, as a raw material for the production of the first hardener, the much longer cultivation times, the significantly increased workload and the cost of processing the wood would be disadvantageous. It has therefore proved to be advantageous according to the invention if the so-called "second" lignocellulose-containing material used for the preparation of the hardener used according to the invention differs from that in step a) of the invention A method for producing the wood chip material used, so-called "first" lignocellulosic material distinguishes

For these reasons, it is provided according to a particular embodiment of the invention that the second lignocellulosic material contains no wood, especially no tree wood, and also does not come from such raw materials. According to the invention, the raw materials enumerated above for the second lignocellulose-containing material (see above and claims 14 and 15) do not fall under the generic term wood.

In one embodiment of the invention, the second lignocellulosic material can be used uncut for hydrothermal and mechanical digestion. In another embodiment of the invention, the second lignocellulosic material may also be pre-shredded for hydrothermal and mechanical digestion. Preferably, this is dry pre-crushed. The comminuted second lignocellulosic material may have an average particle size - determined by the mesh size of the screen - of 20 μm to 20 mm, 0.05 μm to 1 mm or 0.4 μm to 0.4 mm.

The "average particle sizes" stated here are average sieve diameters which are determined by the particles passing through a defined mesh size of a sieve. In principle, methods for the determination of particle sizes are known to the person skilled in the art, for example the sieve analysis according to DIN 66165. For the analysis of the average sieve diameter, it is possible, for example, to choose a sieve system with mesh sizes decreasing from top to bottom. During the sieving process, the portion which has passed through the upper sieve but is no longer able to pass through the sieve considered then remains in each sieve. The individual proportions can be weighed and represented as a percentage in the form of a particle distribution. From this, the mean sieve diameter can be determined according to DIN 66165. For small particle sizes or particle fractions, microscopic methods can be used to determine the particle size.

Preferably, the comminuted second lignocellulosic material has a particle size distribution at least 70, 80, 90 or 95% by weight of the material having a screen diameter of 20 μm to 20 mm, 0.05 μm to 1 mm, or 0.1 μm to 0, 4 mm, determined by the mesh size of the screen. This particle size distribution can be present before or after mechanical pulping. Preferably, this particle size distribution refers to the material that has already been mechanically comminuted and is subjected only to a hydrothermal and mechanical pulping.

In one embodiment, the particle size or average particle size can be determined such that the particles of the second lignocellulose-containing material, a sieve with a mesh size of 20 mm, preferably of 1 mm, more preferably of 0.4 mm and particularly preferably of 0.2 mm happen. In practice, this means that according to one embodiment of the invention, particle fractions can be used which result from particles that pass through these mesh sizes. The mean particle size is determined in this embodiment by a "maximum size" of the particles through the mesh sizes defined above. These particle sizes can be present before or after the hydrothermal and mechanical disruption. Preferably, these particle sizes relate to the material that has already been mechanically comminuted and is subjected only to a hydrothermal and mechanical pulping.

According to a further embodiment of the invention, the comminuted second lignocellulose-containing material has a particle size distribution in which at least 70, 80, 90 or 95% by weight of the material has a screen diameter of less than 20 mm, preferably less than 1 mm, less than 0.4 mm or less than 0, 2 mm, each determined by passing a sieve with a corresponding mesh size.

When it comes to "dry weight", it means the dry matter content. The dry matter content is that component of a substance that remains after subtracting the mass of the contained water. This means that the dry matter content and the water content of a substance complement each other to 100 percent. In one embodiment of the invention, the first hardener may have a dry weight of from 5 to 25% by weight, in particular from 10 to 20% by weight, based on the total weight of the material.

During hydrothermal and mechanical digestion of the second lignocellulosic material, acid may be released. According to a preferred embodiment, the first hardener in step b) contains an acid which has been released by the hydrothermal and mechanical digestion of the second lignocellulose-containing material. This is particularly advantageous because the hydrothermally and mechanically digested second lignocellulosic material directly contains the acid that can act as a catalyst in the curing reaction (as described above) and does not need to be released. In one embodiment of the invention, the second lignocellulosic material releases at least one acid during the hydrothermal and mechanical digestion in the presence of water and / or heat. Surprisingly, it was found that preferably weak and / or volatile acids are released during the hydrothermal and mechanical digestion. In a preferred embodiment of the invention, formic acid and / or acetic acid is liberated during the hydrothermal and mechanical digestion. Since formic acid and / or acetic acid are weak acids, the disadvantages of the strong acids described above can thus be largely avoided.

"Hydrothermal" as used herein means that the digestion occurs under the action of water and elevated temperature. The water can come from the materials used or added. Preferably Water is added, especially in the form of water vapor. According to a preferred embodiment of the invention, the digestion mentioned in step b) is a simultaneous hydrothermal and mechanical digestion.

Without wishing to be bound by any scientific theory, the release of the acid seems to be due to the good hydrolyzability of the hemicellulose. Thus, comparative experiments with microcrystalline cellulose, which were subjected to the conditions of hydrothermal and mechanical pulping, did not lead to the release of the acid. Basically, the β-1,4-glucosidic bonds of the glucose molecules are very stable. Thus, the hydrolysis of the cellulose requires drastic conditions, such as strongly acidic or strongly alkaline conditions or more specific enzymes. One reason why the microcrystalline cellulose does not release acid during the hydrothermal and mechanical digestion could thus be that this digestion is not sufficiently acidic or alkaline.

This also seems to explain why, for the preparation of the first hardener, the second lignocellulosic material described above is much better suited than, for example, tree wood. One reason for this could be that the second lignocellulose-containing material used according to the invention, in particular the abovementioned plants, have a higher average hemicellulose proportion than, for example, tree wood, in particular softwood.

According to one embodiment of the invention, the release of the acid contributes to the curing of the resin. This is especially the case when the resin can be cured by acid catalysis. The acid catalysis curable resins include, in particular, aminoplast resins. According to one embodiment of the invention, the acid released during the hydrothermal and mechanical digestion contributes to the curing of the aminoplast resin contained in the binder-containing composition.

In one embodiment of the invention, the acid released during the hydrothermal and mechanical digestion has a molecular weight of from 40 g / mol to 500 g / mol, in particular from 40 g / mol to 250 g / mol. In another embodiment, the acid is a Brönsted acid having a pK _a of 2 to 8, especially 3 to 6. Preferably, the acid is a carboxylic acid having a chain length of 1 to 5 carbon atoms. Examples of carboxylic acids are formic acid, acetic acid, propionic acid, butanoic acid, pentanoic acid and derivatives thereof. Examples and properties of Bronsted acids are, for example, in " Basic Knowledge of Chemistry ", C. Mortimer, Thieme, 7th edition, 2001 on pages 281 to 290 described. PK _a is the negative decadic logarithm of the acid constant K _a under standard conditions (see also " Organic Chemistry, "Jonathan Clayden, Nick Greeves, Stuart Warren, OUP Oxford, 2012, pages 163-181 ). The smaller the pK _a value, the stronger the acidity. If an acid has several dissociation stages (eg H ₂ SO ₄ : pK _a 1st stage: -3, 2nd stage: 1.92), the pK _a value of the 1st dissociation stage is here with the pK _a value The pK _a values of some important Bronsted acids can be found in the following table. Säurestãrke pK acid very strong -10 HClO ₄ -10 HI -8.9 HBr -6 HCl -3 H ₂ SO ₄ -1.32 ENT ₃ strongly 0 H ₃ O + 1.92 HSO ₄ - 2.13 H ₃ PO ₄ weak 3.77 HCOOH 4.76 CH3COOH

In one embodiment of the invention, the carboxylic acid is a weak acid. If here or elsewhere weak acids are mentioned, then it is meant that the pK _{a is} equal to or greater than 3. For a pK _a of Brönsted acid of less than 3, the binder may be attacked by the acid and at least partially hydrolyzed ,

Practical experiments with the first hardener to be used according to the invention have resulted in markedly reduced hydrolysis of the glue joint if the acid which is released during the hydrothermal and mechanical pulping and can contribute to the curing of the aminoplast resin is a weak acid. One reason for this could be that due to the low acidity of the weak acids, the hydrolysis is not as pronounced as with acids from conventional hardeners and / or strong acids. Conventional hardeners, such as ammonium salts, are still active after completion of the Holzspanwerkstoffs able to release more acids that can diffuse into the glue joint and hydrolyze them.

In another embodiment of the invention, the carboxylic acid is a volatile acid. Examples of volatile acids are formic acid or acetic acid. The volatility of the acid can further contribute to the better stability of the glue joint. One reason for this could be that a volatile acid remains in the glue joint for a shorter time than acids from conventional hardeners. This shorter retention time can reduce or even prevent unwanted hydrolysis of the glue joint.

The first hardener is available by hydrothermal and mechanical pulping. Suitable temperatures for the hydrothermal and mechanical digestion of the second lignocellulose-containing material are temperatures of 120 to 180 ° C, preferably 130 to 170 ° C and particularly preferably 140 to 160 ° C.

For procedural reasons, it is particularly practical for the hydrothermal and mechanical pulping of the second lignocellulose-containing material to take place at a pressure of from 3 to 10 bar, in particular at from 4 to 8 bar.

In one embodiment of the invention, the duration of the hydrothermal and mechanical digestion is 2 seconds to 40 minutes, in particular 5 seconds to 30 minutes.

1. (i) hydrothermischer Aufschluss des zweiten lignocellulosehaltigen Materials in einem Köcher und/oder Druckreaktor;
2. (ii) mechanischer Aufschluss durch Zerkleinern des zweiten lignocellulosehaltigen Materials aus Schritt (i) in einem Refiner.

In a further embodiment of the invention, the hydrothermal and mechanical digestion can be carried out in a preheating container, digester and / or refiner. Preferably, the hydrothermal and mechanical digestion is carried out in a digester and / or pressure reactor. Alternatively or additionally, the hydrothermal and mechanical digestion is preferably carried out in a refiner. Furthermore, the hydrothermal and mechanical digestion may include the following steps:

1. (i) hydrothermal digestion of the second lignocellulosic material in a quiver and / or pressure reactor;
2. (ii) mechanical digestion by comminuting the second lignocellulosic material of step (i) in a refiner.

The terms cooker, pressure reactor and refiner are known to those skilled in the wood industry. By "cooker" is meant in particular a device which is suitable for hydrothermal digestion of the second lignocellulose-containing material. "Pressurized reactor" is any reaction vessel which constitutes a sealed, delimited space in which pressure can be built up and which is suitable for carrying out the hydrothermal digestion of the second lignocellulosic material. By "refiner" the expert understands a device for comminution or defibration of wood, especially under pressure. Examples of refiner in use in practice are Southerland refiner with hollow axle and a movable grinding disc, Fritz refiner with 10 grinding discs, Calfin refiner or hydrorefiner.

The hydrothermal digestion in step (i) can be carried out at a temperature of 120 to 180 ° C, in particular at 140 to 160 ° C. Suitable pressures for the hydrothermal digestion are between 3 to 8 bar, in particular at 4 to 6 bar. The duration of the digestion can be between 5 and 40 minutes. An opening time of 30 minutes has proved to be advantageous. Good results can be achieved if step (i) is carried out in the presence of water. The use of water vapor has proved to be particularly practical.

The mechanical digestion in step (ii) takes place in a refiner. Particularly suitable process temperatures are in a range of 140 to 180 ° C, in particular from 150 to 160 ° C and at a pressure of 1 to 8 bar, in particular at 4 to 6 bar. The duration of the mechanical digestion can be 2 seconds to 5 minutes, in particular 5 seconds to 3 minutes. In a further embodiment of the invention, step (ii) can be carried out in the presence of water, in particular water vapor.

In a further embodiment of the invention, optionally further method steps may be carried out before, after or between steps (i) and (ii). Optional steps may be heating in a preheat container, crushing, storing, mixing, spreading, adding further substances, or drying the lignocellulosic material or a mixture containing the lignocellulosic material of step (i) and / or (ii).

In practice, it has proved to be advantageous if the binder-containing composition also contains a second hardener in addition to the first hardener used according to the invention. The second hardener may be a conventional hardener described above, in particular an ammonium salt. Examples of suitable ammonium salts are ammonium nitrate, ammonium phosphate, ammonium chloride and Ammonium sulfate. Upon reaction with formaldehyde, these ammonium salts form their corresponding acid which acts as an acid catalyst to cure the resin. Examples of these are nitric acid, phosphoric acid, hydrochloric acid, sulfuric acid.

It has been shown that the first hardener used according to the invention is particularly compatible with aminoplast resins and the conventional hardeners conventionally used there. Furthermore, binder compositions containing an aminoplast resin, a first hardener according to the invention and a second hardener have proven to be stable.

In a further embodiment of the method according to the invention, the binder-containing composition contains 0.1 to 4 wt .-% ammonium salt, in particular 0.5 to 3.0 wt .-%, based on the solid resin content of the resin. In a preferred embodiment of the process, the ammonium salt is ammonium nitrate and the resin is an aminoplast resin. It is particularly advantageous that the proportion of the conventional second hardener can be reduced by using the first hardener. In a particularly preferred embodiment of the invention, the second hardener can be saved up to half or more if the second hardener is used in combination with the first hardener used according to the invention.

Basically, this also means that, for example, in comparison with the sole use of ammonium salts as curing agents for amino resins, significantly less ammonium salt has to be added to the process. As a result of the reduced ammonium salt content, the process also requires less formaldehyde. As a result, wood chip materials can be obtained with reduced formaldehyde content. The same applies to other, explained in the beginning conventional hardener.

The disclosure further relates to lignocellulose-containing wood chip materials which have been produced or obtainable by the method according to the invention or its embodiments described above. Such a wood chip material can be used particularly well for the production of a laminate, flooring, a worktop, table top, a piece of furniture or a pallet.

In addition, the invention also relates to the use of the first hardener according to the invention according to claim 20, which was obtained by hydrothermal and mechanical pulping of a second lignocellulose-containing material, in a method according to the invention for the production of wood chip materials described above. In this case applies to the features of the use of the above to the features of the method or its embodiments executed accordingly. In particular, according to a preferred embodiment of the use according to the invention, the first hardener releases an acid. In a further embodiment of the use according to the invention, the first hardener releases acetic acid and / or formic acid.

The above-mentioned advantages of the method according to the invention also apply to the inventive use of the first hardener. In particular, by using the first hardener, the strength of conventional wood chip materials can be maintained or even improved even while reducing the amount of conventional hardeners. Also, by using the first hardener itself, while reducing the amount of conventional hardeners, an improvement in swelling behavior and / or water absorption can be achieved. One reason for this could be that the acid released during the hydrothermal and mechanical digestion is free and volatilises more rapidly than conventional hardeners. This creates a neutral glue joint, which positively influences the characteristics of the wood chip material described above.

The invention will be described in more detail by way of example with reference to exemplary embodiments.

example 1

First, the preparation of the first hardener will be described. Straw was used as the lignocellulosic material.

Version 1:
In the first variant, the digestion of the lignocellulose-containing material was carried out in a discontinuous single-disc refiner (Sprout Waldron). The refiner was filled with the material and steam (160 ° C) was introduced into the cyclone. The material remained at 160 ° C and 6 bar for about 2 minutes in the refiner, then the cyclone was opened and the material was transported out via the screw and a 2.5 mm valve within about 5 minutes.

Variant 2:
In the second variant, the lignocellulose-containing material was pre-shredded dry in an Ecopulser (Krause Maschinenbau GmbH) and screened (Retsch AS 200). The particle fraction smaller than 0.6 mm was then boiled in a pressure reactor (Büchiglasuster Cyclon 300) at 160 ° C and 5 to 6 bar under an approximately 1: 5 dilution with water for about 30 min.

The materials thus available were subsequently used as the first hardener.

Example 2

• Plattendicke: 14 mm
• Zieldichte: 600 kg/m³
• Pressfaktor: 9,3 s/mm
• Pressentemperatur: 200°C
• Beleimgrad: 8,0 Gew.-% bezogen auf die Gesamtmasse der Spanplatte
• Erstes lignocellulosehaltiges Material: Holzspäne
• Erster Härter: Das in Beispiel 1 gewonnene Material (Variante 1 oder 2)
• Zweiter Härter: Ammoniumnitrat
• Presse: Laborpresse von Siempelkamp

Plate tests were carried out under the following conditions:

• Plate thickness: 14 mm
• Target density: 600 kg / m ³
• Pressing factor: 9.3 s / mm
• Press temperature: 200 ° C
• Coating degree: 8.0% by weight, based on the total mass of the chipboard
• First lignocellulosic material: wood shavings
• First Hardener: The Material Obtained in Example 1 (Variant 1 or 2)
• Second hardener: ammonium nitrate
• Press: Laboratory press from Siempelkamp

Several pressings were carried out with different dosages of the first hardener and / or the second hardener. The first hardener used was the lignocellulose-containing material prepared according to Example 1 in dosages of 1, 3, 6 and 10% by weight of the solid, based on the solid resin fraction (hereinafter% solid / FH) Quantities of 1, 1.5, 2 and 3% fixed / FH.

The treated lignocellulosic material was added to the size liquor containing an aminoplast resin. Following the plate pressing, the transverse tensile strength, swelling and water absorption were determined. For this purpose, specimens of geometry 50 × 50 × 14 mm were first cut to size. Each test specimen was measured by means of a digital thickness probe before the test, and the mass determined and used to calculate the density.

transverse tensile strength

The transverse tensile strength was determined according to EN 319. To this end, each test specimen was bonded by means of a hot melt adhesive with two aluminum yokes on the top and bottom and then pulled apart after cooling on the testing machine (Zwick Zmart.Pro) at a constant test speed of 1 mm / min.
The force leading to the break in the middle of the specimen was recorded and the resulting transverse tensile strength over the specimen area was calculated [N / mm ² ].

Thickness swelling

The determination of the thickness swelling after 24 hours of water storage was carried out according to DIN EN 317. The test specimens were stored for this purpose at a water temperature of 20 ° C for 24 h under water. Subsequently, the increase in thickness was determined relative to the starting thickness and the percentage thickness swelling was calculated.

water absorption

The water absorption was determined on the samples of thickness swelling, so also after 24 h water storage. For calculation, the weight was measured after these 24 hours and the water absorption was then calculated according to the following formula: $$\mathrm{water\; absorption}\left[\%\right]=\frac{{\mathrm{Dimensions}}_{\mathrm{later}}-{\mathrm{Dimensions}}_{\mathrm{before}}}{{\mathrm{Dimensions}}_{\mathrm{before}}}*100$$

The results were evaluated by means of Excel, Minitab or DesignExpert.

The experimental results of reference plates containing only ammonium nitrate and plates containing the first hardener (digested material of Example 1) and ammonium nitrate as the second hardener are shown below. The plates were made with the following hardener compositions: test drive Production Variant First Hardness (from Example 1) First hardener (material from Example 1)% by weight [solid / FH] Second hardener (ammonium nitrate)% by weight [solid / FH] Reference 1 - - 1.5% Reference 2 - - 3% 1 1 3% 1.5% 2 1 6% 1.5% 3 1 10% 1.5% 4 2 1 % 2% 5 2 1 % 1 %

The reference plates 1 and 2 were made without the addition of the first hardener. The test plates 1 to 3 were produced with the first hardener of variant 1 from example 1 and the test plates 4 and 5 were produced with the first hardener of variant 2 from example 1.

The test panels were each made at least twice and determines the transverse tensile strength, the swelling and the water absorption. The measurements below are averages of at least two plates.

Result of transverse tensile strength:

The transverse tensile strength was determined for reference plates 1 and 2 and experimental plates 1 to 3. The results are shown in Diagram 1.

From Diagram 1 it can be seen that the transverse tensile strength of the experimental plates 1 to 3 corresponded approximately to the transverse tensile strength of the reference plate 2. By adding the material digested in Example 1 as the first hardener, the amount of ammonium nitrate could be reduced by half and still maintain the good transverse tensile strength.

Result of swelling:

The swelling was determined on reference plate 2 and experimental plates 4 and 5. The results are shown in Diagram 2.

The measurement showed a reduced swelling for the experimental plates 4 and 5 despite reduced content of ammonium nitrate.

Result of water absorption:

The water uptake was determined for reference plate 2 and experimental plate 4. The results are shown in Diagram 3.

It turns out that when using the first hardener, the water absorption could be lowered, despite the reduced ammonium nitrate content.

Claims (20)

1. Method for producing a pressed wood material, comprising the steps:

   a) providing a first lignocellulosic material in the form of wood particles;

   b) contacting the first lignocellulosic material with a composition which comprises at least one aminoplast resin and at least one first hardener and one second hardener, wherein the first hardener was obtained by hydrothermal and mechanical pulping of a second lignocellulosic material, wherein the second lignocellulosic material comes from a different raw material than the first lignocellulosic material; and wherein the second hardener is an ammonium salt,

   c) pressing it to form a pressed wood material.
2. Method according to Claim 1, characterised in that at least one acid is released from the second lignocellulosic material during the hydrothermal and/or mechanical pulping.
3. Method according to Claim 2, characterised in that the acid contributes to hardening the aminoplast resin.
4. Method according to Claim 2 or 3, characterised in that the acid has a molecular weight of 40 g/mol to 500 g/mol, in particular 40 g/mol to 250 g/mol.
5. Method according to any one of Claims 2 to 4, characterised in that the acid is a Brønsted acid having a pK_a of 2 to 8, in particular of 3 to 6.
6. Method according to any one of Claims 2 to 5, characterised in that the acid is a carboxylic acid, in particular selected from the group consisting of formic acid, acetic acid, propanoic acid, butanoic acid, pentanoic acid and derivatives thereof.
7. Method according to any one of the preceding claims, characterised in that the hydrothermal and/or mechanical pulping of the second lignocellulosic material takes place at a temperature of 120 °C to 180 °C, in particular at 140 °C to 160 °C.
8. Method according to any one of the preceding claims, characterised in that the hydrothermal and/or mechanical pulping of the second lignocellulosic material takes place at a pressure of 3 bar to 10 bar, in particular at 4 bar to 8 bar.
9. Method according to any one of the preceding claims, characterised in that the duration of the hydrothermal and/or mechanical pulping is 2 seconds to 40 minutes, in particular 5 seconds to 30 minutes.
10. Method according to any one of the preceding claims, characterised in that the hydrothermal and/or mechanical pulping takes place in a preheating tank, boiler and/or refiner.
11. Method according to any one of the preceding claims, characterised in that the composition contains 0.1 % wt. to 15 % wt. of the first hardener, in particular 0.5 % wt. to 10 % wt., in each case relating to the solid resin proportion of the aminoplast resin.
12. Method for producing a pressed wood material according to any one of the preceding claims, wherein the hydrothermal and/or mechanical pulping specified in step b) comprises the following steps:

    (i) hydrothermal pulping of the second lignocellulosic material in a boiler and/or pressure reactor;

    (ii) mechanical pulping by breaking up of the second lignocellulosic material from step (i) in a refiner.
13. Method according to any one of the preceding claims, characterised in that the wood particles in step a) are selected from the group consisting of fine-particle wood material, wood flakes, wood wafers, wood strands, wood shavings and wood chips.
14. Method according to any one of the preceding claims, characterised in that the second lignocellulosic material is selected from the group consisting of one-year old plants, crop plants, grasses, leaves, cereals, their constituents, waste and mixtures thereof.
15. Method according to Claim 14, characterised in that the crop plant is selected from the group consisting of straw, wheat, rye, barley, oats, millet, maize, miscanthus, rice, their constituents, waste and mixtures thereof.
16. Method according to any one of the preceding claims, characterised in that the aminoplast resin is a melamine resin or a urea resin.
17. Method according to any one of the preceding claims, characterised in that the ammonium salt is selected from the group consisting of ammonium nitrate, ammonium chloride and ammonium sulphate.
18. Method according to any one of the preceding claims, characterised in that the composition comprises 0.1 % wt. to 4 % wt. of the second hardener, in particular 0.5 % wt. to 3.0 % wt., in each case relating to the solid resin proportion of the aminoplast resin.
19. Method according to any one of the preceding claims, characterised in that the pressed wood material is a particle board or an oriented strand board.
20. Use of a hydrothermally and mechanically pulped lignocellulosic material as a hardener for an aminoplast resin in a method for producing a pressed wood material according to any one of Claims 1 to 19.