Method for producing lignocellulosic composite material and corresponding binder composition, lignocellulosic composite material, kit and use

Abstract

A method is described for producing a multi-layer or single-layer lignocellulosic composite comprising two, three or more layers of lignocellulosic composite and comprising at least the following steps: S1) providing or preparing a mixture comprising at least lignocellulosic particles and a binder, the binder comprises at least the following as components: b1) one, two or more polymers comprising a plurality of carboxyl groups, b2) one, two or more polymers or monomeric compounds having two or more hydroxyl groups in order to crosslink the polymers via esterification, and b3) urea, S2) compacting the mixture, s3) applying a high-frequency electric field to the mixture during and / or after compaction, such that the binder hardens and binds the lignocellulosic particles via esterification, such that a layer of a single-layer or multi-layer lignocellulosic composite is produced. Furthermore, a corresponding binder composition, a lignocellulosic composite, a kit and use are described.

Description

[0001] The present invention relates to a method for producing a multi-layered lignocellulosic composite material or a single-layered lignocellulosic composite material comprising two, three or more lignocellulosic composite material layers. The method comprises the step of applying a high-frequency electric field to the respective mixture during and / or after compaction such that the binder hardens.

[0002] The present invention also relates to a single-layered or multi-layered lignocellulosic composite material obtainable by a method according to the present invention, and to a building product comprising such a lignocellulosic composite material. The present invention also relates to a binder composition for producing a single-layered or multi-layered lignocellulosic composite material and to a kit for producing such a binder composition. Furthermore, the present invention relates to the use of the lignocellulosic composite material of the present invention as a building element in a building product.

[0003] The present invention is defined in the appended claims.

[0004] More specifically, the present invention relates to a method for producing a multi-layered lignocellulosic composite material or a single-layered lignocellulosic composite material, wherein a high-frequency electric field is applied, typically for heating an intermediate material mixture and, in many cases, for hardening a binder present in such a mixture.

[0005] EP 3230028 B1 and WO 2016 / 091918 A1 (BASF SE) disclose a method for producing a single-layered or multi-layered lignocellulosic (i.e., wood-cellulose) material by hardening in a high-frequency electric field.

[0006] WO 2015 / 104349 A2 (BASF) discloses a method for producing a lignocellulosic material.

[0007] WO 2016 / 091797 A1 (BASF) discloses a method for producing a multi-layered lignocellulosic material having a core and upper and lower cover layers.

[0008] EP 2885116 B1 (Knauf Insulation) discloses a method for producing a wood board, more particularly a particle board, having excellent swelling properties.

[0009] WO 2008 / 089847 A1 (Knauf Insulation) discloses a composite wood board comprising wood particles and an organic binder.

[0010] WO 2008 / 127936 A2 (Knauf Insulation GmbH) discloses a composite Maillard - resole binder to generate or promote cohesion in unassembled or loosely assembled materials.

[0011] US 2020 / 0017688 A1 (BASF SE) discloses a method for producing lignocellulosic materials.

[0012] US 2017 / 0361489 A1 (BASF SE) discloses a method for batch or continuous, preferably continuous production of multilayer lignocellulosic materials having a core and at least one upper outer layer and one lower outer layer.

[0013] JP 2004 / 230736 A (BASF Dispersions Co Ltd) discloses a method for manufacturing wooden molded boards.

[0014] WO 2010 / 031718 A1 (BASF SE) discloses multilayer lignocellulosic molded bodies with low formaldehyde emissions.

[0015] Additional publications that may be of interest in the context of the present invention are: EP 0583086 B2, EP 1225193 B2, EP 1578879 B1, EP 1700883 B1, EP 2399956 B1, EP 2485989 B1, EP 2867292 B1, WO1997 / 031059 A1, WO 1999 / 002591 A1, WO 2007 / 014236 A2, WO 2009 / 006356 A1, WO 2015 / 084372 A1, WO 2016 / 009062 A1, and WO 2017 / 072186 A1.

[0016] Typically, in methods for producing multilayer or single - layer lignocellulosic composites, a mixture of lignocellulosic particles (i.e., particles consisting essentially of lignocellulose) and a binder is provided or prepared. The mixture is typically dispersed, for example, to obtain the first layer of a multilayer mat or a single - layer mat. When producing a multilayer composite, two or more mixtures of lignocellulosic particles are dispersed in sequence to obtain a mat having two, three, or more individual layers. The resulting mat is then compacted, and the compacted mat or mixture is hardened during and / or after compaction, i.e., the mixture is treated in such a way that the binder undergoes a hardening process. When a high - frequency electric field is used in such a process, it is mainly used to heat the mixture so that the binder hardens due to this heat treatment.

[0017] However, although the use of high-frequency electric fields for heating (and hardening) binders of mixtures also containing lignocellulose particles has been known for quite some time, and although the corresponding methods and products have valuable advantages over other methods for producing lignocellulose composite materials, the fact that the binder systems used in the production methods contain hazardous substances like formaldehyde and isocyanates is considered a disadvantage of such methods. Furthermore, in industrial production methods for producing lignocellulose composite materials, when high-frequency electric fields are applied in the production step, the binders used are typically based on petrochemical substances.

[0018] Furthermore, it is known that lignocellulosic particles release / emit formaldehyde during and / or after thermal treatment, regardless of which binder system and / or heating means are used to produce the lignocellulosic composite. Marutzky et al. in “ die Abspaltung von Formaldehyd bei der thermischen Behandlung von This process has been described in "On the Release of Formaldehyde during the Thermal Treatment of Wood Chips" (Holzforschung [Wood research], Bd. 31, 1977, S. 8-12).

[0019] There is a need in industry for an improved method for producing multilayer or single-layer lignocellulose composites, wherein preferably a high-frequency electric field is applied to a mixture comprising lignocellulose particles and a binder, wherein binder components are used which can be obtained from non-petrochemical resources and do not contain large amounts of hazardous substances like formaldehyde and isocyanates or substances that emit formaldehyde during the production process of the composite material. In addition, there is a need for an improved method for producing multilayer or single-layer lignocellulose composites, wherein the (natural) emission of formaldehyde from the lignocellulose particles during the thermal treatment is as low as possible. Within this scope, any measures should be carefully selected so that the product properties (in particular, typical physical and mechanical parameters) of the resulting multilayer or single-layer lignocellulose composite meet the high expectations of industry in a usual manner.

[0020] The main object of the present invention is to provide such an improved method for producing a multilayer lignocellulose composite or a single layer lignocellulose composite comprising two, three or more lignocellulose composite layers. The improved method should preferably include the step of applying a high frequency electric field to induce or assist the hardening of the binder.

[0021] In addition, the improved method should use different binder components or different combinations of binder components compared to the prior art, such that at least some of the binder components can be obtained from renewable resources and / or such that the binder components and / or the lignocellulosic particles and / or the lignocellulosic composite emit reduced amounts of formaldehyde during and / or after the production process.

[0022] The present invention relates, in its category, to a method for producing a multi-layer lignocellulosic composite or a single-layer lignocellulosic composite comprising two or more, preferably three, lignocellulosic composite layers; a single-layer or multi-layer lignocellulosic composite obtainable by the method according to the invention; a building product comprising such a lignocellulosic composite; the use of such a lignocellulosic composite; a binder composition for producing such a lignocellulosic composite; and a kit for producing such a binder composition. In each case, the examples, aspects or features disclosed for or in relation to one of these categories apply analogously to the other categories of the present invention.

[0023] If not otherwise stated, the preferred embodiments, aspects or features of the present invention can be combined with other embodiments, aspects or features, in particular with other preferred embodiments, aspects or features, regardless of the category to which the embodiments, aspects or features relate. The combination of preferred embodiments, aspects or features with other preferred embodiments, aspects or features again results in preferred embodiments, aspects or features in each case.

[0024] According to the main object of the present invention as described above, the present invention relates to a method for producing a multi-layer lignocellulosic composite or a single-layer lignocellulosic composite comprising two, three or more, preferably three, lignocellulosic composite layers and comprising at least the following steps:

[0025] S1) providing or preparing a mixture comprising at least the following

[0026] - lignocellulosic particles,

[0027] and

[0028] - a binder comprising at least the following as components:

[0029] b1) one, two or more polymers comprising a plurality of carboxyl groups,

[0030] b2) for crosslinking the polymer via esterification, one, two or more polymers or monomeric compounds having two or more hydroxyl groups,

[0031] and

[0032] b3) urea,

[0033] S2) Compress the mixture,

[0034] S3) Apply a high-frequency electric field to the mixture during and / or after compression, such that the binder hardens via esterification and binds these lignocellulosic particles, such that a single-layer lignocellulosic composite or a layer of a multi-layer lignocellulosic composite is produced.

[0035] In the present context, if the method according to the invention is a method for producing a multi-layer lignocellulosic composite comprising two, three or more, preferably three, layers of lignocellulosic composite, then a layer of the multi-layer lignocellulosic composite is produced in step S3). Thus, at least one layer of lignocellulosic composite among two, three or more, preferably three, layers of lignocellulosic composite is produced according to method steps S1), S2) and S3).

[0036] Preferably, if the method according to the invention is a method for producing a multi-layer lignocellulosic composite comprising a core layer (as defined below), then at least the core layer of the multi-layer lignocellulosic composite is produced according to method steps S1), S2) and S3).

[0037] Thus, preferably, if the method according to the invention is a method for producing a three-layer lignocellulosic composite comprising a core layer and two surface layers (as defined below), then at least the core layer of the three-layer lignocellulosic composite is produced according to method steps S1), S2) and S3). The core layer accordingly comprises a mixture provided or prepared according to step S1) of the invention, i.e. a mixture comprising at least lignocellulosic particles and a binder, the binder comprising at least the following as components: b1) one, two or more polymers comprising a plurality of carboxyl groups, b2) one, two or more polymer or monomer compounds having two or more hydroxyl groups for crosslinking the polymers via esterification, and b3) urea, and optionally component b4) as defined below. On the other hand, the surface layers of the three-layer lignocellulosic composite are in many cases made of a mixture different from the core layer.

[0038] In the present text, if as a result of step S3), a first lignocellulosic composite layer of a multi-layer lignocellulosic composite is produced, it is preferred that the second lignocellulosic composite layer or more or all of the further lignocellulosic composite layers of the final multi-layer lignocellulosic composite are also prepared by carrying out steps S1) to S3) as defined above, where the details of the respective steps S1) and preferably step S2) carried out for the individual lignocellulosic composite layers (first layer, second layer and further layers), and the details of step S3) in the individual cases are independent of each other. For example, for manufacturing the first lignocellulosic composite layer, the lignocellulosic particles and binder used in step S1) and the compaction conditions (used in step S2)) are each selected according to individual requirements, and for manufacturing the second lignocellulosic composite layer or for manufacturing a further lignocellulosic composite layer, the selection may be the same or different.

[0039] Typically, and most preferably, step S3) is the same step for all lignocellulosic composite layers of the multi-layer lignocellulosic composite (in particular for all lignocellulosic composite layers of a three-layer lignocellulosic composite), and preferably the details of step S3) are selected so as to meet the requirements of all the lignocellulosic composite layers present. In this preferred case, all the lignocellulosic composite layers of the multi-layer lignocellulosic composite are subjected to the conditions of step S3) jointly and simultaneously.

[0040] In many preferred cases, step S2) is also the same step for all lignocellulosic composite layers of the multi-layer lignocellulosic composite. In these preferred cases, all the lignocellulosic composite layers of the multi-layer lignocellulosic composite are subjected to the conditions of step S2) jointly and simultaneously.

[0041] Therefore, it is particularly preferred that in the method according to the invention, two, three or more, preferably three, lignocellulosic composite layers of the multi-layer lignocellulosic composite are all jointly and simultaneously subjected to the exactly same method steps S2) and S3) as defined above.

[0042] More preferably, two, three or more, preferably three, lignocellulosic composite layers of the multi-layer lignocellulosic composite are all subjected to method steps S1), S2) and S3) as defined above.

[0043] Herein, and throughout this text, the term "one, two or more polymers containing a plurality of carboxyl groups" designates a polymer that, in its protonated form, has a plurality of carboxyl groups (COOH). Throughout the text, when referring to a polymer having (a plurality of) carboxyl groups, reference is included to the corresponding (partially) neutralized / deprotonated form. The person skilled in the art will adjust the pH of the binder according to the requirements of the individual technical situation in order to provide the desired reactivity. Thus, in the process according to the invention, the composition of the binder and / or the composition of the mixture provided or prepared in step S1) is preferably adjusted by adding an additional acidic or basic compound. This is preferably done in order to influence or adjust the pH of the binder, and more preferably and specifically in order to influence or adjust the reactivity of the components present for hardening the binder via esterification, namely the components b1) and b2) and optionally b4) (see the definition of the binder component b4) below).

[0044] Herein, and throughout this text, the term "one, two or more polymers or monomeric compounds having two or more hydroxyl groups" designates a polymer or monomer having at least two hydroxyl groups (OH).

[0045] In order to allow esterification, hydroxyl groups (OH) and acidic carboxyl groups (COOH) must be present. Accordingly, the components b1) and b2) and optionally b4) (see the definition of the binder component b4) below) promote the hardening of the binder via esterification. Thus, the person skilled in the art will adjust the pH of the binder according to the requirements of the individual technical situation in order to provide the desired reactivity. Thus, and for the reasons stated above, in the process according to the invention, the composition of the binder and / or the composition of the mixture provided or prepared in step S1) is preferably adjusted by adding an additional acidic or basic compound.

[0046] Thus, in the process according to the invention, in step S1), a mixture comprising lignocellulosic particles and a specific binder is provided or prepared. According to step S3), a high-frequency electric field is applied to the mixture during and / or after compaction (see step S2)). The high-frequency electric field is applied such that the binder hardens via esterification.

[0047] Esterification occurs at least between binder components b1) and b2) and optionally b4) (see the definition of binder component b4) below). The esterification reaction is possible because the binder used in step S1) contains one, two or more polymers containing a plurality of carboxyl groups (component b1)), and in order to crosslink said polymers via esterification, additionally contains one, two or more polymers or monomeric compounds having two or more hydroxyl groups (component b2)). Esterification is the reaction of said hydroxyl groups and said carboxyl groups. When said hydroxyl groups and said carboxyl groups react with each other in the esterification reaction, the corresponding compounds are (crosslinked) linked, and accordingly the binder hardens and binds the lignocellulosic particles, such that a single-layer lignocellulosic composite or a layer of a multi-layer lignocellulosic composite is produced. The crosslinking reaction requires the presence of at least two, preferably more than two carboxyl groups and / or hydroxyl groups in said component b1) and / or b2). Using a polymer containing a plurality of carboxyl groups as (esterification) component b1) allows for very effective crosslinking and hardening of the binder when applying a high-frequency electric field.

[0048] Binder compositions comprising a compound having two or more hydroxyl groups and a compound having two or more carboxyl groups (which can be hardened via esterification of said groups) are known from the prior art, but are typically considered rather fragile when subjected to a high-frequency electric field.

[0049] Certain binder systems comprising a hydroxyl compound and a carboxyl compound have been disclosed previously, but not in combination with the use of a high-frequency electric field:

[0050] EP 2485989 B1 discloses a binder system for manufacturing both glass fiber insulation materials and nonwoven mats crosslinked by an esterification reaction.

[0051] EP 0583086 B2 discloses a curable aqueous composition comprising a polymeric polyacid containing at least two carboxylic acid groups, acid anhydride groups, or salts thereof; a polyol containing at least two hydroxyl groups; and a phosphorus-containing promoter.

[0052] EP 1578879 B1 discloses an aqueous binder composition for coating glass fibers, comprising: a polycarboxyl polymer; a polyol having at least two hydroxyl groups; and a water-soluble extender, the extender being present in an amount sufficient to establish an extender-polycarboxyl polymer weight ratio of at least 1:10.

[0053] EP 1700883 B1 discloses a composition comprising a polycarboxyl polymer and a polyol or a hydroxy-functional, carboxy-functional polymer; and a polycarboxylic acid, or its acid anhydride or salt; and a strong acid; and water.

[0054] EP 2399956 B1 discloses an aqueous binder composition comprising one or more polymeric polyacids and a carbohydrate component.

[0055] EP 2867292 B1 discloses an aqueous binder composition in the form of a dispersion, which comprises starch; and one or more acrylic components.

[0056] WO 1997 / 031059 A1 discloses a binder containing a polymer obtained by free radical polymerization, the polymer consisting of 5 wt% to 100 wt% of an ethylenically unsaturated anhydride or dicarboxylic acid (the carboxylic acid groups of which may form anhydride groups); and an alkanolamine having at least two hydroxyl groups.

[0057] WO 2009 / 006356 A1 discloses a polymer composition suitable for wood treatment or bonding, the composition comprising the reaction product of at least one polyol and at least one crosslinking agent; the crosslinking agent having at least 2 carboxylic acid groups / molecule.

[0058] WO 2016 / 009062 A1 discloses an aqueous curable binder composition comprising starting materials and a matrix polymer required to form a thermosetting resin upon curing, wherein the starting materials comprise a polyhydroxy component and a polycarboxylic component, or an anhydride, ester or salt derivative thereof and / or a reaction product thereof.

[0059] WO 2017 / 072186 A1 discloses an aqueous curable binder composition comprising a carbohydrate, a first crosslinking agent and a second crosslinking agent, wherein the first crosslinking agent is selected from compounds having a carboxyl functional group, which forms an ester with the carbohydrate.

[0060] EP 2697293 B1 discloses a composite material comprising 10 - 95 wt.% of particulate or fibrous fillers derived from plant- or animal-based materials and at least 5 wt.% of a polyester derived from an aliphatic polyol and polyacid having 2 - 15 carbon atoms, wherein the polyacid comprises at least 10 wt.% of citric acid as a tricarboxylic acid.

[0061] However, although such binder compositions have been known for a considerable time, they have never been combined with the application of high-frequency electric fields in a production method for lignocellulosic composites.

[0062] Document US2020 / 017688 A1 discloses a polymer-based binder comprising a polymer N composed of the following monomers: a) at least one ethylenically unsaturated mono- and / or dicarboxylic acid (one or more monomers N 1 ) by weight of 70% to 100% and b) at least one different from monomer N by weight of 0% to 30%1 other ethylenically unsaturated monomers (one or more monomers N 2 ), and optionally a low molecular weight crosslinker having at least two functional groups selected from the following: hydroxyl, carboxylic acid and its derivatives, primary amine, secondary amine and tertiary amine, epoxy group, and aldehyde. Document US2020 / 017688 A1 further discloses an energy input by applying an electric field.

[0063] Document JP 2004 230736A discloses: A) a polymer obtained by radical polymerization, wherein 5 to 100% by weight of the polymer is derived from an ethylenically unsaturated acid anhydride or an ethylenically unsaturated dicarboxylic acid with which a carboxylic acid group can form an acid anhydride group, and B) it is an alkylamine having at least 2 hydroxyl groups and using the hydroxyl groups as a crosslinking component of the bridge. Document JP 2004230736A further discloses: Although then hot pressing is carried out, heat transfer plate heating, high-frequency dielectric heating, or microwave heating is used together.

[0064] However, documents US2020 / 017688 A1 and JP 2004 230736A do not disclose a binder system comprising: b1) one, two or more polymers comprising a plurality of carboxyl groups, b2) one, two or more polymers or monomer compounds having two or more hydroxyl groups, and b3) urea.

[0065] The inventors of the present invention have found that the binder component b3) urea is necessary for reducing the emission of formaldehyde from the binder and / or wood cellulose particles during heat treatment by applying a high-frequency electric field.

[0066] Surprisingly, it has also been found that the binder component b3) urea has a positive effect on the mechanical properties of the resulting multi-layer or single-layer wood cellulose composite. In particular, the thickness swelling (“24h swelling”), transverse tensile strength (“internal bond strength”), and surface and edge screw holding of the wood cellulose composite (board) produced by the method according to the present invention after 24 h are significantly improved. Therefore, urea not only serves as a formaldehyde scavenger, but also (and unexpectedly) seems to improve the hardening process of the binder (esterification) when applying a high-frequency electric field and the product properties of the resulting composite. We refer to the examples described below.

[0067] US2011 / 0171473 A1 discloses a multilayer lignocellulosic molded article, which comprises one or more cover layers containing lignocellulosic particles obtainable by using a binder (b), and the binder (b) comprises the following components: an aqueous component (I), and the aqueous component contains (i) a polymer A composed of the following monomers: a) at least one ethylenically unsaturated mono- and / or dicarboxylic acid (one or more monomers A1) accounting for 70% to 100% by weight and b) at least one additional ethylenically unsaturated monomer (one or more monomers A2) different from monomer A1 accounting for 0% to 30% by weight, and optionally, (ii) a low molecular weight crosslinking agent having at least two functional groups selected from the group consisting of hydroxyl group, carboxyl group and its derivatives, primary amine, secondary amine and tertiary amine, epoxy group, aldehyde, and the binder (b) contains a formaldehyde scavenger. Examples of suitable formaldehyde scavengers are: ammonia, urea, melamine, organic C 1 -C 10 -amine, polymers carrying at least one amino group, such as polyamine, polyimine, polyurea, polylysine, polyvinylamine, polyethyleneimine. Therefore, the utilization of the binder (b) is only described for the surface layer (i.e., the cover layer) of such multilayer lignocellulosic molded articles.

[0068] Therefore, US2011 / 0171473 A1 does not disclose a single-layer lignocellulosic composite material or the production of a single-layer lignocellulosic composite material.

[0069] In addition, US2011 / 0171473 A1 thus does not disclose the utilization of the binder (b) in the core layer (the intermediate layer in the language of US2011 / 0171473A1) of a multilayer lignocellulosic composite material.

[0070] US2011 / 0171473 A1 also discloses a method for producing a multilayer lignocellulosic molded article, which comprises pressing layers at an elevated temperature.

[0071] Therefore, US2011 / 0171473 A1 does not disclose applying a high-frequency electric field according to step S3) of the present invention for hardening the binder.

[0072] Therefore, what is unprecedented in the prior art is i) a specific binder contained in the mixture provided or prepared according to step S1) of the method according to the present invention, the binder contains esterification components b1) and b2) and further contains component b3) urea, and ii) hardening the provided or prepared mixture containing at least the specific binder and lignocellulosic particles by applying a high-frequency electric field, that is, step S3) of the method according to the present invention.

[0073] The inventors have also found that the (esterification / urea) binder according to the present invention (as defined above, below and in the claims) and the hardening of the binder by esterification via applying a high-frequency electric field to a mixture provided or prepared containing the binder and lignocellulosic particles (i.e., step S3)) is not limited to a specific product, layer or embodiment in the production of lignocellulosic composites disclosed in US2011 / 0171473 A1. On the contrary, the method according to the present invention is very versatile and applicable to:

[0074] - single-layer lignocellulosic composites (not disclosed in US2011 / 0171473 A1),

[0075] or

[0076] - two, three or more layers of multi-layer lignocellulosic composites, wherein the two, three or more layers preferably constitute a core layer, one or two surface layers and / or any layer between the core layer and the corresponding surface layer of the multi-layer lignocellulosic composite,

[0077] or

[0078] - all layers of multi-layer lignocellulosic composites; for example, the lower surface layer, core layer and upper surface layer of a three-layer lignocellulosic composite (not disclosed in US2011 / 0171473 A1 is a multi-layer lignocellulosic composite having a polymer containing a plurality of carboxyl groups and / or a polymer or monomer compound having two or more hydroxyl groups in all layers),

[0079] - the core layer (intermediate layer) of a three-layer lignocellulosic composite (US2011 / 0171473 A1 only discloses a core (i.e., intermediate) layer based on (a1) a formaldehyde resin and (a2) an organic isocyanate having at least two isocyanate groups.

[0080] The term "core layer" in this text designates a lignocellulosic composite layer that is located at the geometric center of a multi-layer lignocellulosic composite and, accordingly, is not in direct contact with the outer side (outside), i.e., does not constitute a surface layer (as defined below). The core layer has a substantially equal distance to the upper and lower surfaces (outer surfaces) of the multi-layer lignocellulosic composite and / or the upper and lower surface layers, and among all the layers, it has the maximum distance to the surface / outer surface of the multi-layer lignocellulosic composite. For example: a three-layer lignocellulosic composite / plate (a preferred embodiment of the multi-layer lignocellulosic composite according to the present invention) consists of three lignocellulosic composite layers (each of the three layers contains a specific mixture comprising at least lignocellulosic particles and a binder). The three-layer "S 1 / C / S 2” is: the lower surface layer S that is in direct contact with the core layer C and forms the first outer (external) side 1 ; the core layer C that is in direct contact with the two surface layers S 1 and S 2 and is not in direct contact with the outer side of the composite material; and the upper surface layer S that is in direct contact with the core layer C and forms the second outer (external) side of the composite material 2 , where the first outer side and the second outer side of the composite material are on opposite sides of the composite material (the upper side and the lower side respectively). The terms "in direct contact with" and "not in direct contact with" in this text refer to the material contacting the surface of the corresponding layer in an orientation parallel to the plane of the layer.

[0081] The term "surface layer" in this text designates a lignocellulosic composite material layer that is in direct contact with the outer side (external), i.e., has an outer surface. Thus, a three-layer lignocellulosic composite material / plate (which is a preferred embodiment of the multi-layer lignocellulosic composite material according to the present invention) includes two surface layers on opposite sides, each of which is in direct contact with both the outer side (external) and the core layer C. Preferably, the two surface layers of the three-layer lignocellulosic composite material / plate (i.e., both the upper surface layer and the lower surface layer) have the same composition and / or the same dimensions. In particular, preferably, the two surface layers are composed of the same composition and have the same thickness to obtain a sandwich-type layer structure.

[0082] Throughout the text, unless otherwise specified, the terms "core layer" and "surface layer" designate layers that contain at least a mixture of lignocellulosic particles and a binder. Thus, both the "core layer" and the "surface layer" are lignocellulosic composite material layers.

[0083] Accordingly, in addition to the lignocellulosic composite material layers that contain at least a mixture of lignocellulosic particles and a binder, a multi-layer lignocellulosic composite material (such as prepared in the method of the present invention as defined above and / or in the appended claims, preferably prepared in the preferred method as defined herein) that includes two, three, or more lignocellulosic composite material layers may include additional layers that do not contain lignocellulosic particles. The additional layers are not designated as lignocellulosic composite material layers, and specifically are not designated as core layers or surface layers (in view of the above definitions). For example, a preferred multi-layer (preferably three-layer) lignocellulosic composite material includes outer (i.e., coating) layers that do not contain any lignocellulosic particles, where the upper outer (coating) layer is in contact with the outer side (external) of the upper surface layer and the lower outer (coating) layer is in contact with the outer side (external) of the lower surface layer.

[0084] Preferably, a multi-layer lignocellulosic composite material comprising two, three or more lignocellulosic composite material layers (such as prepared in the method of the present invention as defined above and / or as defined in the appended claims, preferably prepared in the preferred method as defined herein) does not include a core layer (i.e., an intermediate layer in the language of US2011 / 0171473 A1) comprising a fully or partially cured binder selected from the group consisting of (a1) formaldehyde resins and (a2) organic isocyanates having at least two isocyanate groups.

[0085] Preferably, a multi-layer lignocellulosic composite material or a single-layer lignocellulosic composite material (such as prepared in the method of the present invention) comprising two, three or more lignocellulosic composite material layers does not contain a fully or partially cured binder selected from the group consisting of (a1) formaldehyde resins and (a2) organic isocyanates having at least two isocyanate groups and (correspondingly) does not contain binder (a) as defined in claim 1 of US 2011 / 0171473A1.

[0086] More preferably, a multi-layer lignocellulosic composite material or a single-layer lignocellulosic composite material (such as prepared in the method of the present invention) comprising two, three or more lignocellulosic composite material layers does not contain a fully or partially cured binder containing (a1) formaldehyde resin or (a2) organic isocyanate (as defined respectively in claim 1 of US2011 / 0171473 A1).

[0087] As used herein, the term "lignocellulosic particles" designates and includes lignocellulosic particles of any type, size and shape, such as fibers, chips, strands, flakes, sawmill shavings and sawdust or mixtures thereof. Additionally, any type of lignocellulosic biomass such as birch, beech, alder, pine, spruce, larch, eucalyptus, lime, poplar, ash, fir, tropical wood, sisal, jute, flax, coconut, kenaf, hemp, banana, straw, cotton stalk, bamboo, etc. can be used as the source of the lignocellulosic particles. Lignocellulosic particles from both virgin wood and / or waste wood (such as old furniture) can be used to produce the lignocellulosic composite materials of the present invention. According to the present invention, mixtures of different types of lignocellulosic particles can further be used in the production of lignocellulosic composite materials.

[0088] The term "high-frequency electric field" as used herein designates and includes any type of high-frequency electric field or electromagnetic field, such as microwave radiation or high-frequency electric field, which is generated after applying a high-frequency alternating voltage at a plate capacitor between two capacitor plates. Suitable frequencies for the high-frequency electric field are in the range of 100 kHz to 30 GHz, preferably 6 MHz to 3 GHz, more preferably 13 MHz to 41 MHz. Particularly suitable and preferred are the corresponding nationally and internationally recognized frequencies, such as 13.56 MHz, 27.12 MHz, 40.68 MHz, 2.45 GHz, 5.80 GHz, 24.12 GHz, more preferably 13.56 and 27.12 MHz. In the method of the present invention, the electric power used to generate such a high-frequency electric field is preferably in the range of 10 to 10,000 kWh, more preferably 100 to 5,000 kWh, most preferably 500 to 2,000 kWh.

[0089] The term "single-layer lignocellulosic composite material" as used herein designates and includes any single-layer composite material that contains lignocellulosic particles and a hardened binder that binds the lignocellulosic particles. In addition, the term "single-layer" designates that the lignocellulosic composite material includes only one layer of lignocellulosic material and binder, where the single layer is preferably produced by a method that includes a single step of dispersing the lignocellulosic particles. The "single-layer lignocellulosic composite material" can have any shape, such as rectangular, square, circular, triangular, etc. The "single-layer lignocellulosic composite material" can also have any thickness, density, and color, as long as it contains lignocellulosic particles and a hardened binder. The "single-layer lignocellulosic composite material" can also contain several other compounds different from the lignocellulosic particles and the binder. The lignocellulosic particles used to produce the "single-layer lignocellulosic composite material" are the same type or different types of lignocellulosic biomass (preferred types are as described above). As similarly stated above for multi-layer lignocellulosic composite materials, the single-layer lignocellulosic composite material can preferably include one or two outer (i.e., coating) layers that do not contain lignocellulosic particles, where more preferably, the upper outer (coating) layer contacts the upper outer side (exterior) of the single layer (i.e., the single lignocellulosic composite material layer) and the lower outer (coating) layer contacts the lower outer side (exterior) of the single layer.

[0090] Preferably, a "multi-layered lignocellulosic composite material" as defined herein contains (separate) lignocellulosic composite material layers that are distinguishable from adjacent layers. The multi-layered lignocellulosic composite material includes two, preferably three or more distinguishable (separate) lignocellulosic composite material layers, more preferably including a lignocellulosic composite material core layer and distinguishable upper and lower lignocellulosic composite material surface layers (a three-layer composite / plate). Adjacent layers of the multi-layered lignocellulosic composite material are preferably distinguishable in terms of their composition, density, color, or any other property, and the adjacent layers contain the same type of lignocellulosic particles and / or binders or different types of lignocellulosic particles and / or binders. In addition to lignocellulosic particles and / or binders, the (separate) lignocellulosic composite material layers may also contain other materials, such as plastics, fabrics, paint coatings, etc., for example foreign substances derived from waste wood. The lignocellulosic particles of the separate lignocellulosic composite material layers for producing the "multi-layered lignocellulosic composite material" are the same type or different types of lignocellulosic biomass (preferred types are as described above). The lignocellulosic particles of the separate (separate / individual) lignocellulosic composite material layers for producing the "multi-layered lignocellulosic composite material" are the same type or different types of lignocellulosic biomass (preferred types are as described above) or the same or different mixtures of two or more such types of lignocellulosic biomass. In addition, the term "multi-layer" designates that the lignocellulosic composite material includes separate layers, where at least two of these separate layers contain lignocellulosic material and a binder, and two, three or more or all of the lignocellulosic composite material layers are preferably produced by a multi-step method, and for each (separate) layer of lignocellulosic material and binder, the multi-step method includes a step of dispersing the lignocellulosic particles.

[0091] Accordingly, the present invention relates to a method for producing a multi-layered lignocellulosic composite material or a single-layered lignocellulosic composite material including two, three or more lignocellulosic composite material layers, wherein preferably

[0092] i) each separate lignocellulosic composite material layer, i.e., a layer of a single-layered lignocellulosic composite material or a multi-layered lignocellulosic composite material, contains

[0093] - only one type of lignocellulosic particles (lignocellulosic biomass), for example only spruce chips or only birch flakes,

[0094] or

[0095] - a mixture of different types of lignocellulosic particles (lignocellulosic biomass), for example a mixture of both spruce chips and birch flakes,

[0096] and / or wherein,

[0097] ii) the multi-layered lignocellulosic composite material comprises

[0098] - only one and the same type of lignocellulosic particles (lignocellulosic biomass) in all the lignocellulosic composite material layers, for example, only spruce chips or only birch flakes in all the lignocellulosic composite material layers, or

[0099] - different types of lignocellulosic particles (lignocellulosic biomass) in separate lignocellulosic composite material layers, for example, only spruce chips in the first separate layer and only birch flakes in the second separate layer, or

[0100] - the same mixture of lignocellulosic particles (lignocellulosic biomass) in all the lignocellulosic composite material layers, for example, the same mixture of both spruce chips and birch flakes in all the layers, or

[0101] - different mixtures of lignocellulosic particles (lignocellulosic biomass) in separate lignocellulosic composite material layers, for example, a first mixture of both spruce chips and birch flakes in the first separate layer and a second mixture of pine chips and flax fibers in the second separate layer.

[0102] Other terms used to describe the present invention have their typical meanings, or are explained or defined in this specification.

[0103] Preferably, in the method of the present invention, the binder comprises the following as additional binder components, preferably for hardening the binder via esterification:

[0104] b4) one or more non-polymeric, preferably non-polymeric bio-based compounds having two or more carboxyl groups and / or one or more non-polymeric, preferably non-polymeric bio-based compounds having at least one carboxyl group and at least one hydroxyl group.

[0105] In a first preferred aspect of the present invention, at least one of a non-polymeric, preferably non-polymeric bio-based compound having two or more carboxyl groups or more than one non-polymeric, preferably non-polymeric bio-based compound having two or more carboxyl groups is selected from the group consisting of hydroxycarboxylic acids, preferably selected from the group consisting of α-hydroxycarboxylic acids, more preferably selected from the group consisting of citric acid, malic acid and tartaric acid, and most preferably is citric acid. Two or more of the preferred or particularly preferred compounds can be used in combination with each other.

[0106] In a second preferred aspect of the present invention, at least one non-polymeric, preferably non-polymeric bio-based compound having at least one carboxyl group and at least one hydroxyl group or more than one non-polymeric, preferably non-polymeric bio-based compound having at least one carboxyl group and at least one hydroxyl group is selected from the group consisting of monohydroxy-monocarboxylic acids, preferably selected from the group consisting of α-hydroxy monohydroxy-monocarboxylic acids, more preferably selected from the group consisting of lactic acid, glycolic acid and mandelic acid, and most preferably is lactic acid. Two or more of the preferred or particularly preferred compounds may be used in combination with each other.

[0107] As used herein, the term "bio-based" means that the corresponding compound can be prepared or is prepared at least in part from substances present in biological products. Preferably, the compound can be completely prepared or is prepared from such substances. More preferably, the (bio-based) compound is plant-based, i.e., it can be prepared or is prepared at least in part from substances present in plants.

[0108] The non-polymeric, preferably non-polymeric bio-based compound having two or more carboxyl groups (COOH) and / or having at least one carboxyl group (COOH) and at least one hydroxyl group (OH) can undergo an esterification reaction with the binder component b1) and / or b2) and thus also promotes the hardening of the binder via esterification.

[0109] Preferably, in the method of the present invention (preferably, the method as defined herein is preferred), at least one, preferably all, of the one polymeric or monomeric compound having two or more hydroxyl groups or two or more polymeric or monomeric compounds having two or more hydroxyl groups of component b2) are bio-based polymeric or bio-based monomeric compounds having two or more hydroxyl groups.

[0110] In a first preferred aspect of the present invention, at least one, preferably all, of the one polymeric or monomeric compound having two or more hydroxyl groups or two or more polymeric or monomeric compounds having two or more hydroxyl groups of component b2) are selected from the group consisting of carbohydrates, preferably selected from the group consisting of monosaccharides, disaccharides, oligosaccharides, polysaccharides and starches, more preferably selected from the group consisting of dextrose, fructose, sucrose, non-hydrolyzed starch and (partially) hydrolyzed starch such as maltodextrin or corn syrup, even more preferably selected from the group consisting of dextrose, fructose and maltodextrin. As used herein, the term "(partially) hydrolyzed starch" includes the meanings of partially hydrolyzed starch (preferably including maltodextrin and / or corn syrup, more preferably, partially hydrolyzed starch is selected from the group consisting of maltodextrin and corn syrup) and hydrolyzed starch. Two or more of the preferred or particularly preferred compounds may be used in combination with each other.

[0111] In a second preferred aspect of the present invention, at least one, preferably all, of the one polymer or monomer compound having two or more hydroxyl groups or two or more polymer or monomer compounds having two or more hydroxyl groups in component b2) are preferably selected from the group consisting of polyvinyl alcohol, glycerol, and sugar alcohols, and the latter are preferably selected from the group consisting of mannitol, sorbitol, xylitol, lactitol, isomaltitol, maltitol, erythritol, and hydrogenated starch hydrolysates. More preferably, at least one of the one polymer or monomer compound having two or more hydroxyl groups or two or more polymer or monomer compounds having two or more hydroxyl groups in component b2) is glycerol. Two or more of the preferred or particularly preferred compounds may be used in combination with each other.

[0112] In a third preferred aspect of the present invention, at least one of the one polymer or monomer compound having two or more hydroxyl groups or two or more polymer or monomer compounds having two or more hydroxyl groups in component b2), preferably all, are selected from the group consisting of compounds selected from the group consisting of triols (preferably triethanolamine), tetraols, pentaols, and hexaols, wherein the selected compounds are not carbohydrates, not sugar alcohols, and not alkylamines. Two or more of the preferred or particularly preferred compounds may be used in combination with each other.

[0113] If two or more polymer or monomer compounds having two or more hydroxyl groups in component b2) are present in the binder, the compounds may be selected from two or more of the above preferred aspects, i.e., the different compound groups of component b2). For example, the two or more polymer or monomer compounds having two or more hydroxyl groups in component b2) may comprise or consist of dextrose (belonging to the group of carbohydrates) and glycerol (belonging to the group of sugar alcohols). Particularly preferred is that at least one of the two or more polymer or monomer compounds having two or more hydroxyl groups in component b2) is a bio-based compound such as dextrose, fructose, maltodextrin, or glycerol.

[0114] While in particular US2011 / 0171473 A1 (discussed above) focuses on alkylamines (triethanolamine) as compounds with two or more hydroxyl groups, the inventors of the present invention have found that bio-based alternatives selected from the group consisting of carbohydrates, sugar alcohols, and other triols, tetrols, pentols, and hexols that are not alkylamines show even better performance in terms of the mechanical properties of the resulting lignocellulosic composite materials. Thus, it is preferred that at least one, preferably all, of the one polymer or monomer compound having two or more hydroxyl groups or two or more polymer or monomer compounds having two or more hydroxyl groups of component b2) are selected from the group consisting of carbohydrates and sugar alcohols, and even more preferably are selected from the group consisting of the bio-based compounds dextrose, fructose, maltodextrin, and glycerol.

[0115] It is also preferred that the total amount of the one, two, or more polymer or monomer compounds of component b2), preferably the total amount of the one, two, or more bio-based polymer or bio-based monomer compounds, is higher than 5 mass-%, more preferably higher than 10 mass-%, and even more preferably higher than 15 mass-% and lower than 90 mass-%, more preferably lower than 80 mass-%, and even more preferably lower than 60 mass-% relative to the combined total mass of binder components b1), b2), and any component b4) present.

[0116] As a non-limiting example, the binder according to this preferred aspect of the present invention comprises a polycarboxylate as component b1), glycerol as component b2), and citric acid as component b4), wherein the mass ratio of polycarboxylate to glycerol to citric acid is 50:25:25.

[0117] It is preferred that the method of the present invention (preferably, the method as defined herein is preferred), wherein at least one, preferably all, of the one polymer containing a plurality of carboxyl groups or two or more polymers containing a plurality of carboxyl groups of component b1) are selected from the group consisting of polymers of one or more unsaturated carboxylic acids, preferably acrylic acid, and mixtures thereof, preferably copolymers of acrylic acid and more preferably copolymers of acrylic acid and maleic anhydride and / or maleic acid.

[0118] These polymers containing multiple carboxyl groups are preferably partially neutralized. Partially neutralized means that (i) at least some, preferably more than 10%, more preferably more than 20% of the polymer containing multiple carboxyl groups and (ii) less than 50%, preferably less than 35% of the acidic carboxyl groups (COOH) are neutralized by reaction with a basic compound, where neutralization means converting the carboxyl group (COOH) into a carboxylate group (COO-) (acid-base reaction). The basic compound for partial neutralization can be a hydroxide such as sodium hydroxide, potassium hydroxide, calcium hydroxide, or a carbonate such as sodium carbonate, or ammonia, or primary, secondary, and tertiary amines such as ethylamine, propylamine, isopropylamine, butylamine, hexylamine, ethanolamine, dimethylamine, diethylamine, di-n-propylamine, tributylamine, triethanolamine, dimethoxyethylamine, 2-ethoxyethylamine, 3-ethoxypropylamine, dimethylethanolamine, diisopropanolamine, and morpholine. The preferred basic compound is a hydroxide, and more preferably sodium hydroxide is used as the basic compound.

[0119] Preferably, in the process of the present invention (preferably, the process as defined herein is preferred), at least one, preferably all, of the polymers containing multiple carboxyl groups in component b1) are selected from the group consisting of biobased polyesters having two or more carboxyl groups, where preferably, one, two, or more of the polyesters, preferably biobased polyesters, are prepared by reacting:

[0120] - one or more α-hydroxycarboxylic acids, preferably citric acid,

[0121] and

[0122] - one, two, or more compounds selected from the group consisting of:

[0123] ● Carbohydrates, which are preferably selected from the group consisting of monosaccharides, disaccharides, oligosaccharides, polysaccharides, and starches, more preferably selected from the group consisting of dextrose, fructose, sucrose, non-hydrolyzed starch, hydrolyzed starch, and partially hydrolyzed starch, the latter preferably including maltodextrin and / or corn syrup, and more preferably selected from the group consisting of maltodextrin and corn syrup;

[0124] ● Sugar alcohols, which are preferably selected from the group consisting of mannitol, sorbitol, xylitol, lactitol, isomaltitol, maltitol, erythritol, hydrogenated starch hydrolysates, and glycerol, more preferably glycerol, and

[0125] ● Compounds selected from the group consisting of triols (preferably triethanolamine), tetraols, pentaols, and hexaols, where these compounds are not carbohydrates, not sugar alcohols, and not alkylamines,

[0126] Preferably glycerol.

[0127] Preferably, the method of the present invention (preferably, the method as defined herein is preferred), wherein the binder comprises at least the following as components:

[0128] (b1) one, two or more polymers containing a plurality of carboxyl groups, selected from the group consisting of polymers of one or more unsaturated carboxylic acids, preferably acrylic acid, and mixtures thereof, preferably copolymers of acrylic acid and more preferably copolymers of acrylic acid and maleic anhydride and / or maleic acid,

[0129] and

[0130] (b2) one, two or more polymer or monomer compounds having two or more hydroxyl groups for crosslinking the polymer via esterification, wherein at least glycerol is present,

[0131] wherein the ratio of the total mass of the polymer of component (b1) to the total mass of glycerol present is in the range of 80:20 to 50:50.

[0132] As a non-limiting example, the binder according to this preferred aspect of the present invention comprises a copolymer of acrylic acid and maleic anhydride as component b1) and glycerol as component b2), wherein the mass ratio of the copolymer of acrylic acid and maleic anhydride to glycerol is 70:30 or 60:40, or ≥60:40 and ≤70:30, respectively.

[0133] More preferably, the binder comprises component b4) as defined above as an additional binder component, preferably for hardening the binder via esterification, wherein even more preferably, the total amount of the additional binder component b4) is 30 mass-% or less relative to the combined total mass of binder components b1), b2) and component b4), more preferably in the range of 5 mass-% to 30 mass-%.

[0134] As a non-limiting example, the binder according to this preferred aspect of the present invention comprises a copolymer of acrylic acid and maleic anhydride as component b1), glycerol as component b2), and lactic acid as component b4), wherein the mass ratio of the copolymer of acrylic acid and maleic anhydride to glycerol to lactic acid is 50:25:25.

[0135] Preferably, the method of the present invention (preferably, the method as defined herein is preferred), wherein

[0136] - the binder in step S1) of the method contains water and has a pH in the range of 1.0 to 3.5, preferably in the range of 1.0 to 3.0, more preferably 1.0 to 2.5,

[0137] and / or (preferably "and")

[0138] - An aqueous extract prepared from the mixture prepared or provided in step S1) of the method according to the extraction method defined in the specification (see below) has a pH in the range of 1.0 to 6.0, preferably in the range of 2.0 to 5.0, more preferably 2.5 to 4.5.

[0139] According to this preferred aspect of the invention, the pH of the binder is adjusted to be in the range of 1.0 to 3.5, preferably in the range of 1.0 to 3.0, more preferably 1.0 to 2.5. It has been found that the binder in step S1) of the method (which has a pH in the range or preferred range provided previously herein) contributes to reduced formaldehyde emissions during and / or after the production of multi-layer or single-layer lignocellulosic composite materials. It has also been found that when the binder used in step S1) of the method has a pH in the range or preferred range provided previously herein, the resulting lignocellulosic composite material is characterized by better mechanical properties.

[0140] In this range, preferably for the preparation or provision of the binder in step S1), the binder component to be hardened via esterification - if necessary - is mixed with an alkaline or acidic compound, preferably sodium hydroxide or sulfuric acid, in order to adjust the pH. In another preferred embodiment, a partially neutralized polymer containing a plurality of carboxyl groups is used as the starting material for adjusting the pH of the binder as described above. By adjusting the pH of the binder, the molar ratio of the COOH groups to the COO - groups (especially in the components present for the hardening of the binder via esterification) is affected in the usual way. In yet another preferred embodiment, the ratio of the binder components b1), b2), and b3) (and b4) if present) is selectively chosen for adjusting the pH of the binder as described above. A person skilled in the art can calculate and / or measure the pH value of the binder by means known in the art, such as by using a tabulated pH value or a standard pH meter.

[0141] According to yet another preferred aspect of the present invention, an aqueous extract prepared or provided in step S1) of the method, i.e., an aqueous extract prepared from a mixture comprising lignocellulosic particles and a binder, according to the extraction method defined in the description (see item 1.10 below), has a pH in the range of 1.0 to 6.0, preferably in the range of 2.0 to 5.0, and more preferably 2.5 to 4.5. It has been found that adjusting the mixture prepared or provided in S1) in such a way that the pH of the aqueous extract is within the ranges or preferred ranges provided herein also actively reduces formaldehyde emissions during and / or after the production of multi-layer or single-layer lignocellulosic composites and contributes to better mechanical properties of the resulting lignocellulosic composites. Thus, the present invention contemplates that not only the pH of the binder alone, but also the pH of the mixture comprising lignocellulosic particles and the binder (which can of course only be measured from the aqueous extract of the mixture) is decisive for the properties / behavior during and / or after the application of a high-frequency electric field to the mixture, such that the binder hardens via esterification and binds the lignocellulosic particles, resulting in the production of a single-layer lignocellulosic composite or the layers of a multi-layer lignocellulosic composite. Similarly, a person skilled in the art can adjust, calculate, and / or measure the pH value of the aqueous extract by the means described hereinbefore and by means known in the art (e.g., by using a listed pH value or a standard pH meter). The effect on the pH of the corresponding type of lignocellulosic particles used (e.g., birch chips or hemp fibers) can be evaluated by simple experiments.

[0142] Particularly preferably, both the binder in step S1) of the method and the aqueous extract prepared from the mixture prepared or provided in step S1) of the method according to the extraction method defined in the description (see below) have a pH within the ranges or preferred ranges provided hereinbefore.

[0143] Preferably, in the method of the present invention (preferably, the method as defined herein is preferred), the component b3) of the binder (i.e., urea) is present in an amount in the range of ≥5 to ≤50 mass-% relative to the combined total mass of the components b1), b2), and any component b4) present in the binder, preferably ≥10 to ≤35 mass-%, and more preferably ≥15 to ≤35 mass-%.

[0144] According to this preferred aspect of the invention, the total amount of binder component b3), i.e., urea, is within the ranges or preferred ranges defined hereinbefore, relative to the binder components b1), b2) and any present component b4), i.e., the combined total mass of all binder components present for hardening via esterification. It has first been found through extensive studies in the form of experimental series with different amounts / ratios of urea that these (relatively low) preferred amounts of urea are sufficient to significantly reduce the emission of formaldehyde from lignocellulosic particles in the process according to the invention. Furthermore, and secondly, it has surprisingly been found that the ranges or preferred ranges of the total amount of urea provided herein relative to the combined total mass of binder components b1), b2) and any present component b4) have a positive effect on the mechanical properties of the resulting lignocellulosic composite materials. In particular, the thickness swelling after 24 h ("24 h swelling"), the transverse tensile strength ("internal bond strength") and the surface and edge screw holding of the lignocellulosic composite materials (boards) produced in the process according to the invention can be significantly improved.

[0145] Preferably, in the method of the invention (preferably, the method as defined herein is preferred), in the mixture provided or prepared in step S1) of the method, the binder component b3) (i.e., urea) is present in a total amount within the range of ≥ 0.25 to ≤ 2.5 mass-% preferably ≥ 0.5 to ≤ 1.75 mass-% and more preferably ≥ 0.75 to ≤ 1.75 mass-% relative to the total mass of the lignocellulosic particles in the mixture in the oven-dried state.

[0146] According to this preferred aspect of the invention, in the mixture provided or prepared in step S1) of the method, the total amount of binder component b3), i.e., urea, is within the ranges or preferred ranges provided hereinbefore relative to the total mass of the lignocellulosic particles in the mixture in the oven-dried state. Again, it has been found through extensive studies in the form of experimental series with different amounts / ratios of urea that these (relatively low) preferred amounts of urea are sufficient to reduce the emission of formaldehyde from lignocellulosic particles in the process according to the invention. Furthermore, it has surprisingly been found that the ranges or preferred ranges of the total amount of urea in the mixture provided or prepared in step S1) of the method provided herein relative to the total mass of the lignocellulosic particles in the mixture in the oven-dried state have a positive effect on the mechanical properties of the resulting lignocellulosic composite materials. In particular, the thickness swelling after 24 h ("24 h swelling"), the transverse tensile strength ("internal bond strength") and the surface and edge screw holding of the lignocellulosic composite materials (boards) produced in the process according to the invention can be significantly improved.

[0147] Preferably, the method of the present invention (preferably, the method as defined herein is preferred), wherein in the mixture provided or prepared in step S1) of the method, the total combined amount of components b1), b2) and any component b4) present is in the range of 3 to 8 mass-%, preferably 3.5 to 7.5 mass-% and more preferably 4 to 6.5 mass-% relative to the total mass of the lignocellulosic particles in the mixture in the dried state.

[0148] According to this preferred aspect of the invention, the mixture provided or prepared in step S1) contains a relatively low amount of binder components present for hardening via esterification, namely components b1), b2) and any component b4) present, relative to the amount of lignocellulosic particles. More particularly, the ratio of the weight of the solid content of all binder components present for hardening via esterification to the weight of the lignocellulosic particles in the dried state is less than 8%, preferably less than 7.5%, and more preferably less than 6.5%. The relatively low preferred amount of the solid content of all binder components present for hardening via esterification is advantageous because it results in a sustainable method and / or a sustainable product, namely a multi-layer lignocellulosic composite material or a single-layer lignocellulosic composite material comprising two, three or more, preferably three, lignocellulosic composite material layers.

[0149] Surprisingly, in the method of the present invention, a relatively low amount of binder is sufficient to bond a large amount of lignocellulosic particles because a high-frequency electric field is applied in step S3) of the method, which also allows for effective hardening of the mixture in the center of the compacted mixture compared to other hardening treatments (e.g., using a hot press as disclosed in US2011 / 0171473 A1 and many other prior art documents). In other words, the binder is used more effectively in the method of the present invention.

[0150] Specifically, the method of the present invention allows for the production of multi-layer lignocellulosic composite materials comprising two, three or more lignocellulosic composite material layers, and allows for the production of single-layer lignocellulosic composite materials having advantageous physical and mechanical properties, without any need

[0151] (i) There is a co-binder in the core layer of the multi-layer lignocellulosic composite material or in the single layer of the single-layer lignocellulosic composite material, and the co-binder is selected from the group consisting of (a1) formaldehyde resins and (a2) organic isocyanates having at least two isocyanate groups,

[0152] Or

[0153] (ii) There is a co-binder in the multi-layer or single-layer lignocellulosic composite material, and the co-binder is selected from the group consisting of (a1) formaldehyde resins and (a2) organic isocyanates having at least two isocyanate groups,

[0154] or

[0155] (iii) a co - binder is present in the multi - layer or single - layer lignocellulosic composite material, the co - binder comprising (a1) a formaldehyde resin or (a2) an organic isocyanate, as defined respectively in claim 1 of US2011 / 0171473 A1.

[0156] As explained above, in a preferred method of the present invention, A1) the mixture provided or prepared in step S1) does not contain a co - binder as defined under items (i), (ii) and / or (iii) and / or A2) the resulting lignocellulosic composite material does not contain a fully or partially cured co - binder as defined under items (i), (ii) and / or (iii).

[0157] Preferably, in the method of the present invention (preferably, the method as defined herein is preferred), the mixture prepared or provided in step S1) of the method contains one or more water - repellents as one or more additional components, the water - repellents being selected from the group consisting of paraffin wax and mixtures containing paraffin wax, preferably paraffin wax emulsion. Such additional components are typically not components of the binder for preparing the mixture in step S1) of the method of the present invention. Thus, the pH of the binder (as discussed above) is typically not affected by such additional components.

[0158] In particular, adding a water - repellent, preferably paraffin wax and mixtures containing paraffin wax, more preferably paraffin wax emulsion, to the mixture improves the internal bond strength of the resulting lignocellulosic composite material or the layers of the lignocellulosic composite material and / or the thickness swelling after 24 hours in water at 20 °C.

[0159] Even more preferably, in the method of the present invention, the ratio of the total mass of paraffin wax to the total mass of the lignocellulosic particles in the mixture in the oven - dried state is in the range of 0.2% to 1.5%. Also preferably, the ratio of the total mass of paraffin wax to the total mass of all binder components b1) to b4) present in the mixture is in the range of 2% to 40%, preferably in the range of 5% to 30% and more preferably in the range of 7.5% to 20%.

[0160] Preferably, in the method of the present invention (preferably, the method as defined herein is preferred), the mixture prepared or provided in step S1) of the method contains one, two or more additional components selected from the group consisting of:

[0161] - water,

[0162] - alkali metal salts and alkaline earth metal salts, preferably sodium nitrate,

[0163] - dyes, pigments,

[0164] - Antifungal and antibacterial agents;

[0165] - Rheology modifiers, fillers

[0166] - Release agents, and

[0167] - Surfactants, surface active agents.

[0168] Preferably, the method of the present invention (preferably, the method as defined herein is preferred), wherein the lignocellulosic composite material is a lignocellulosic board selected from the group consisting of: high-density fiberboard (HDF), medium-density fiberboard (MDF), low-density fiberboard (LDF), wood fiber insulation board, oriented strand board (OSB), particle board, and natural fiber board, preferably having fibers selected from the group consisting of sisal, jute, flax, coconut, kenaf, hemp, banana, and mixtures thereof.

[0169] According to this preferred aspect of the present invention, the lignocellulosic composite material produced in the method of the present invention - i.e., the lignocellulosic composite material obtained after the step S1) of providing or preparing a mixture comprising at least lignocellulosic particles and a binder, the step S2) of compacting the mixture, and the step S3) of applying a high-frequency electric field to the mixture during and / or after compaction such that the binder hardens via esterification and binds the lignocellulosic particles - is the board listed above. Thus, any type of lignocellulosic particles such as fibers, chips, strands, flakes, sawmill shavings and sawdust, or mixtures thereof, and any type of lignocellulosic biomass such as birch, beech, alder, pine, spruce, larch, eucalyptus, lime, poplar, ash, fir, tropical wood, sisal, jute, flax, coconut, kenaf, hemp, banana, straw, cotton stalk, bamboo, etc., or mixtures thereof can be used as a source for producing the boards listed above.

[0170] In a preferred aspect of the present invention, the lignocellulosic board is a single-layer lignocellulosic board, more preferably a single-layer lignocellulosic fiber board, having a thickness in the range of 1 to 15 mm, preferably 2 to 12 mm, more preferably 2 to 4 mm. According to this preferred aspect of the present invention, in step S1), only one mixture comprising lignocellulosic particles and a binder is provided or prepared. Then the mixture is compacted in step S2) and subjected to a high-frequency electric field during and / or after compaction, such that the binder hardens via esterification and binds the lignocellulosic particles, resulting in a single-layer lignocellulosic composite material (step S3)). It has been found that the combination of the binder system according to the present invention (preferably, the binder as defined herein is preferred) and method step S3) leads to the formation of high-quality boards with low formaldehyde emissions and improved mechanical properties. In particular, the thickness swelling ("24h swelling") after 24 h, the transverse tensile strength ("internal bond strength"), and the surface and edge screw holding of the single-layer lignocellulosic composite material (board) produced by the method according to the present invention can be significantly improved.

[0171] In another preferred aspect of the present invention, the lignocellulosic board is a multi-layer lignocellulosic board. The multi-layer lignocellulosic board is more preferably a multi-layer lignocellulosic board having a core layer and upper and lower surface layers, preferably consisting of the core layer and the upper and lower surface layers, and even more preferably a multi-layer lignocellulosic particle board having a core layer and upper and lower surface layers, having a total thickness in the range of 14 to 25 mm.

[0172] Particularly preferably, the multi-layer lignocellulosic board is a three-layer board consisting of a core layer and upper and lower surface layers. Even more preferably, the multi-layer lignocellulosic board is a three-layer board, wherein all three layers, namely the core layer and the upper and lower surface layers, are produced by method steps S1), S2), and S3). Thus, all layers of the three-layer board are provided or prepared from a mixture comprising lignocellulosic particles and a binder, which binder comprises at least the following as components: b1) one, two or more polymers comprising a plurality of carboxyl groups, b2) one, two or more polymer or monomer compounds having two or more hydroxyl groups for crosslinking the polymer via esterification, and b3) urea.

[0173] It has been found that the combination of the binder system according to the invention (preferably, the binder as defined herein is preferred) and the method step S3) of applying a high frequency electric field leads to the formation of high quality boards with low formaldehyde emissions and improved mechanical properties. In particular, the thickness expansion after 24 h ("24h expansion"), the transverse tensile strength ("internal bond strength") and the surface and edge screw retention of the multilayer lignocellulosic composite material (board), preferably the three-layer board of those described above, produced in the method according to the invention can be significantly improved.

[0174] Accordingly, the method according to the invention is very flexible and can be used to produce a multilayer lignocellulosic composite or a single-layer lignocellulosic composite comprising one or more lignocellulosic composite layers.

[0175] In another preferred aspect of the invention, the lignocellulosic composite material is a board with a core, wherein in a cross section oriented perpendicular to the plane of the board, the difference between the density maximum of the board and the density minimum in the core of the board is at most 100 kg / m 3 , preferably at most 80 kg / m 3 , and more preferably at most 60 kg / m 3 Therefore, from the technician’s point of view, the density distribution within the board is almost uniform, which is considered to be superior to having a density greater than 100 kg / m 3 The advantage of the board is that the (uneven) difference between the density maximum of the board and the density minimum in the core of the board is large. In the preferred boards described above, the density below 100 kg / m 3 , preferably less than 80kg / m 3 And more preferably less than 60kg / m 3 The density differences have several advantages, such as consistent and reliable mechanical properties in each cross section of the board.

[0176] In the method of the invention, a high-frequency electric field is applied to the mixture during and / or after compaction, so that the binder hardens via esterification and binds the lignocellulose particles, so that step S3) of producing a lignocellulose composite material or a layer of a lignocellulose composite material is combined with achieving a density difference of at most 100 kg / m between the maximum density of the board and the minimum density in the core of the board. 3 The difference in density is related to the characteristic uniform density distribution. The favorable properties are due to the rapid and uniform heating between these surfaces (and including the core) when a high frequency electric field is used. In contrast, conventional hot pressing methods result in slow heat transfer from the surface to the core and therefore result in a board with a large density difference between the core layer or portion and the outer layer or portion.

[0177] In another preferred aspect of the present invention, in step S3) of applying a high-frequency electric field, the temperature at the center of the mixture is raised to a maximum temperature in the range of 130°C to 200°C, preferably in the range of 140°C to 180°C, wherein preferably, the maximum temperature is reached within less than 40 s·(d / mm) after the start of applying the high-frequency electric field, where d is the thickness of the compacted mixture at the end of step S3), in mm.

[0178] When the temperature at the center of the mixture is raised to a maximum temperature in the range of 130°C to 200°C, preferably in the range of 140°C to 180°C according to the said preferred aspect, the maximum temperature is preferably reached within less than 40 s·(d / mm), more preferably within less than 30 s·(d / mm), even more preferably within less than 20 s·(d / mm), and most preferably within less than 15 s·(d / mm) after the start of applying the high-frequency electric field, where d is the thickness of the compacted mixture at the end of step S3), in mm. For example, if the thickness d of the compacted mixture at the end of step S3) is 10 mm in mm, the maximum temperature is preferably reached within less than 400 s, more preferably within less than 300 s, even more preferably within less than 200 s, and most preferably within less than 150 s after the start of applying the high-frequency electric field.

[0179] Preferably, according to this aspect, the temperature at the center of the mixture is raised to a maximum temperature in the range of 130°C to 200°C, more preferably in the range of 140°C to 180°C and most preferably in the range of 150°C to 170°C, wherein the temperature increase is controlled, preferably automatically controlled, and preferably also controlled such that the binder hardens via esterification and binds the lignocellulosic particles.

[0180] Preferably, in the preferred method of the present invention, in step S3) of applying a high-frequency electric field, the temperature at the center of the mixture is monitored and / or controlled, preferably controlled. It is particularly preferred to control the temperature at the center of the mixture such that the binder hardens via esterification of the compound and binds the lignocellulosic particles in a controlled manner. The temperature (which is preferably monitored and / or controlled, more preferably controlled) is preferably adjusted to allow the binder to harden via esterification in a controlled manner. The monitored and / or controlled, preferably controlled temperature at the center of the mixture is preferably adjusted to be in the range of 110°C to 220°C, more preferably in the range of 130°C to 200°C, even more preferably in the range of 140°C to 180°C and most preferably in the range of 150°C to 170°C.

[0181] As used in this text, the term "center of the (said) mixture" designates an approximately intermediate position between the surfaces of the three-dimensional object defined by the mixture in step c) of the process according to the invention.

[0182] The above-described preferred process according to the invention, which is related to the temperature at the center of the mixture, allows for the rapid and / or efficient production of a multi-layered lignocellulosic composite material or a single-layered lignocellulosic composite material comprising two, three or more, preferably three or more, lignocellulosic composite material layers.

[0183] In another preferred aspect of the invention, at least steps S2) and S3), more preferably steps S1), S2) and S3) are semi-continuous or continuous process steps, wherein preferably, step S3) is carried out in a dielectric heating and pressing unit, and wherein most preferably, the process for producing a multi-layered lignocellulosic composite material or a single-layered lignocellulosic composite material comprising two, three or more lignocellulosic composite material layers is a semi-continuous or continuous process.

[0184] According to this preferred aspect, the production of the lignocellulosic composite material is carried out semi-continuously or continuously. This production method allows for rapid and efficient production on an industrial scale. Furthermore, a high-frequency electric field is applied to the mixture during and / or after compaction, such that the binder hardens via esterification and binds the lignocellulosic particles, such that the use of a dielectric heating and pressing unit in step S3) for producing a single-layered lignocellulosic composite material or the layers of a multi-layered lignocellulosic composite material allows for very efficient hardening of the binder via esterification.

[0185] Preferably, the process according to the invention (preferably, the process as defined herein is preferred), wherein the process for producing a multi-layered lignocellulosic composite material or a single-layered lignocellulosic composite material comprising two, three or more lignocellulosic composite material layers comprises one, two, three, more than three, or all of the following steps, which steps are preferably carried out semi-continuously or continuously:

[0186] - In step S1) for preparing the said mixture, the lignocellulosic particles are blended with one or more or all of the components of the binder or one or more or all of the components of the binder are sprayed onto the lignocellulosic particles, wherein before blending or spraying, the said components of the binder are pre-mixed or not pre-mixed,

[0187] - Preparing, preferably by dispersion, a layer of the mixture provided or prepared in step S1), and compacting this layer in step S2),

[0188] - To prepare a multi-layered lignocellulosic composite material comprising more than one layer of lignocellulosic composite material, provide or prepare at least a first separate mixture and a second separate mixture, and use the first separate mixture and the second separate mixture for manufacturing the first layer and the second layer of the multi-layered lignocellulosic composite material, wherein the first layer and the second layer preferably contact each other, and / or wherein the first separate mixture and the second separate mixture have the same or different compositions.

[0189] - To prepare a multi-layered lignocellulosic composite material comprising more than one layer of lignocellulosic composite material, prepare two or more layers, preferably by dispersing the separate layers in one another, each layer comprising lignocellulosic particles and a binder, wherein in the two or more layers, the lignocellulosic particles and / or the binder are the same or different.

[0190] - In step S2), compact the mixture in two stages, wherein in the first stage, pre-compact the mixture to obtain a pre-compacted mat, and wherein in the second stage, further compact the pre-compacted mat.

[0191] - During or after the compaction in step S2), hot press the mixture.

[0192] - During or after the application of a high-frequency electric field in step S3), hot press the mixture.

[0193] And

[0194] - In step S3) of applying a high-frequency electric field, monitor and / or control the temperature at the center of the mixture.

[0195] According to these preferred aspects, the method for producing a lignocellulosic composite material comprises one, two, three or more preferred steps, which are specific embodiments of step S1), S2) or S3) respectively, or additional steps. Each of these preferred steps is optional and can be carried out individually or in combination with one or more of the other preferred steps.

[0196] One of the preferred steps involves step S1) of preparing the mixture consisting of the lignocellulosic particles and the binder. According to this preferred aspect, the lignocellulosic particles are blended with one or more or all of the components of the binder, or one or more or all of the components of the binder are sprayed onto the lignocellulosic particles. Specifically, the components of the binder are blended with the lignocellulosic particles simultaneously (e.g., in a mixture with each other) or sequentially, preferably sequentially. The sequential addition of the components of the binder is carried out in any order and in any combination of the respective binder components. The specific components of the binder are pre-blended or not pre-blended, preferably two or more of the components of the binder are pre-blended and then blended with or sprayed onto the lignocellulosic particles in step S1). More preferably, all the binder components for hardening the binder via esterification, i.e., components b1), b2) and b4), are pre-blended. According to this preferred aspect, the person skilled in the art selects (i) the desired sequence for adding the components of the binder (simultaneously or sequentially), preferably sequentially, (ii) the desired method for mixing the components of the binder, such as blending or spraying, preferably spraying, and the person skilled in the art (iii) provides or prepares one, two or more pre-mixtures of any type of combination with the specific binder components.

[0197] Another preferred step of the present invention is the following step: preparing, preferably by dispersion, a layer of the mixture provided or prepared in step S1) and compacting this layer in step S2). Preparing the layer by dispersion is a preferred additional step for producing lignocellulosic composites.

[0198] According to a preferred aspect of the present invention, for preparing a multi-layer lignocellulosic composite, at least a first separate mixture and a second separate mixture, preferably two separate mixtures, are provided or prepared. Then the first and second separate mixtures are used to fabricate the first and second layers of the multi-layer lignocellulosic composite. Preferably, the first and second layers are in contact with each other. According to this preferred aspect, the first and second separate mixtures have the same or different compositions, even more preferably the first and second separate mixtures have different compositions. Thus, the different separate mixtures and / or layers of the prepared multi-layer lignocellulosic composite preferably differ in specific properties such as density, color, etc. and / or they differ in their compositions, wherein the different compositions are obtained by using different binders, lignocellulosic particles and / or other (additional) components such as plastics, fabrics, paint coatings, etc. (e.g., foreign substances from waste wood). The separate layers preferably (i) contain different binders and different lignocellulosic particles, or (ii) contain the same binder but different lignocellulosic particles, or (iii) contain the same binder and the same lignocellulosic particles but in different ratios.

[0199] According to another preferred aspect of the present invention, for the preparation of a three-layer lignocellulosic composite, a first separate mixture and a second separate mixture M1 and M2 are provided or prepared respectively, preferably both the mixtures M1 and M2 are provided or prepared according to step S1) of the present invention. Then the first separate mixture M1 is used to manufacture the first surface layer (lower surface layer; S) of the three-layer lignocellulosic composite. Then the second separate mixture M2 is used to manufacture the core layer (C) of the three-layer lignocellulosic composite, wherein the lower surface layer (S) and the core layer (C) are in contact with each other. Then the first separate mixture M1 is used (again) to manufacture the second surface layer (upper surface layer; S) of the three-layer lignocellulosic composite, wherein the upper surface layer (S) and the core layer (C) are in contact with each other. Thus, the resulting three-layer lignocellulosic composite consists of two surface layers (2x S) and one core layer (C), wherein the surface layer (S) is derived from the first separate mixture M1, and wherein the core layer (C) is derived from the second separate mixture M2.

[0200] According to a preferred method related to the technology of the present invention, the preparation of a multi-layer lignocellulosic composite includes the preparation of two, three or more layers, preferably three layers, each layer containing lignocellulose particles and a binder. Preferably, the lignocellulose particles and / or the binder in the two, three or more layers, preferably three layers, are the same or different, and even more preferably, the lignocellulose particles are different and the binder is different.

[0201] Preferably, in step S2) of compacting the mixture provided or prepared in step S1), the compaction of the mixture is carried out in two stages. This means that in the first stage, the mixture is pre-compacted to obtain a pre-compacted mat, and in the second stage, this pre-compacted mat is further compacted. Preferably, the first stage of pre-compacting the mixture to obtain a pre-compacted mat is carried out before step S3) of applying a high-frequency electric field. The second stage of further compacting the pre-compacted mat is preferably carried out during step S3) of applying a high-frequency electric field. This two-stage compaction allows a flexible method for the production of lignocellulosic composites or layers of lignocellulosic composites.

[0202] In a preferred method of the present invention, the preparation of a single-layer lignocellulosic composite or a multi-layer lignocellulosic composite includes the following steps:

[0203] - providing or preparing one, two or more than two mixtures containing at least lignocellulose particles and a binder according to the present invention,

[0204] - dispersing the mixture / mixtures to obtain one, two or more than two layers, wherein the one or more layers form a mat,

[0205] - In a first compaction step, the single-layer or multi-layer mat is pre-compacted to obtain a pre-compacted mat, and thereafter

[0206] - In a second compaction step, the pre-compacted mat is compacted while applying a high-frequency electric field.

[0207] Preferably, before the second compaction step, the pre-compacted (single-layer or multi-layer) mat obtained in the first compaction step is pre-heated (i) with steam, preferably with water vapor, and / or (ii) by applying microwave radiation and / or (iii) by applying a high-frequency electric field.

[0208] In the second compaction step, the binder present in the mat is partially or completely hardened.

[0209] Another method step in a preferred specific case of the method of the present invention is hot pressing the mixture during or after compaction in step S2), and / or during or after applying the high-frequency electric field in step S3), more preferably during.

[0210] According to the present invention, hot pressing is a method step in which an optionally pre-compacted mat is brought into contact with a heated pressing surface having a temperature in the range of 80°C to 300°C. When hot pressing is carried out after applying the high-frequency electric field in step S3), the heated pressing surface preferably has a temperature of 80°C to 300°C, more preferably 120°C to 280°C, most preferably 150°C to 250°C. When hot pressing is carried out during applying the high-frequency electric field in step S3), the heated pressing surface preferably has a temperature in the range of 80°C to 200°C, more preferably 90°C to 180°C, most preferably 100°C to 150°C.

[0211] According to the main object of the present invention as described above, the present invention also relates to a binder composition for producing a lignocellulosic composite material, preferably for producing a lignocellulosic composite material in the method of the present invention as defined herein and in the appended claims, the binder composition comprising at least the following as components: b1) one, two or more polymers containing a plurality of carboxyl groups, b2) one, two or more polymers or monomer compounds having two or more hydroxyl groups, and b3) urea,

[0212] wherein preferably, at least one of the one polymer or monomer compound having two or more hydroxyl groups or two or more polymers or monomer compounds having two or more hydroxyl groups of component b2) is selected from the group consisting of:

[0213] ■ Carbohydrates, which are preferably selected from the group consisting of monosaccharides, disaccharides, oligosaccharides, polysaccharides and starches, more preferably selected from the group consisting of dextrose, fructose, sucrose, non-hydrolyzed starch, hydrolyzed starch and partially hydrolyzed starch, the latter preferably including maltodextrin and / or corn syrup, more preferably selected from the group consisting of maltodextrin and corn syrup;

[0214] ■ Glycerol, polyvinyl alcohol and sugar alcohols, the latter preferably selected from the group consisting of mannitol, sorbitol, xylitol, lactitol, isomaltitol, maltitol, erythritol and hydrogenated starch hydrolysates; wherein more preferably, at least one of a polymer or monomer compound having two or more hydroxyl groups or two or more polymer or monomer compounds having two or more hydroxyl groups in component b2) is glycerol;

[0215] and preferably

[0216] ■ Compounds selected from the group consisting of triols, preferably triethanolamine, tetraols, pentaols and hexaols, wherein the selected compound is not a carbohydrate, not a sugar alcohol, and not an alkylamine.

[0217] Generally, all aspects of the present invention discussed herein in the context of the method for producing lignocellulosic composites according to the present invention and / or in the context of the lignocellulosic composites of the present invention apply, with necessary modifications, to the binder of the present invention as defined herein. Vice versa, all aspects of the present invention discussed herein in the context of the binder of the present invention apply, with necessary modifications, to the method for producing lignocellulosic composites according to the present invention and / or the lignocellulosic composites of the present invention. Etc.

[0218] Particularly preferably, at least one of two or more polymer or monomer compounds having two or more hydroxyl groups in component b2) is a bio-based compound, one of dextrose, fructose, maltodextrin or glycerol.

[0219] Furthermore, the present invention relates to a binder composition for producing lignocellulosic composites, preferably for producing lignocellulosic composites in the method as defined above, wherein the binder composition contains water and has a pH in the range of 1.0 to 3.5, preferably in the range of 1.0 to 3.0, more preferably 1.0 to 2.5.

[0220] Furthermore, the present invention relates to a binder composition for producing a lignocellulosic composite material, preferably for producing a lignocellulosic composite material in a method as defined above, wherein the binder composition comprises the following as additional binder components: b4) one or more non-polymeric, preferably non-polymeric bio-based compounds having two or more carboxyl groups and / or one or more non-polymeric, preferably non-polymeric bio-based compounds having at least one carboxyl group and at least one hydroxyl group, as defined above.

[0221] Particularly preferably, at least one of said one non-polymeric, preferably non-polymeric bio-based compound having two or more carboxyl groups or more than one non-polymeric, preferably non-polymeric bio-based compound having two or more carboxyl groups is selected from the group consisting of hydroxycarboxylic acids, preferably from the group consisting of α-hydroxycarboxylic acids, more preferably from the group consisting of citric acid, malic acid and tartaric acid, and most preferably is citric acid. Two or more of said preferred or particularly preferred compounds can be used in combination with each other.

[0222] Particularly preferably, at least one of said one non-polymeric, preferably non-polymeric bio-based compound having at least one carboxyl group and at least one hydroxyl group or more than one non-polymeric, preferably non-polymeric bio-based compound having at least one carboxyl group and at least one hydroxyl group is selected from the group consisting of monohydroxy-monocarboxylic acids, preferably from the group consisting of α-hydroxy monohydroxy-monocarboxylic acids, more preferably from the group consisting of lactic acid, glycolic acid and mandelic acid, and most preferably is lactic acid. Two or more of said preferred or particularly preferred compounds can be used in combination with each other.

[0223] The non-polymeric, preferably non-polymeric bio-based compounds having two or more carboxyl groups (COOH) and / or having at least one carboxyl group (COOH) and at least one hydroxyl group (OH) can undergo an esterification reaction with the binder components b1) and / or b2) and thus also promote the hardening of the binder via esterification.

[0224] Furthermore, the present invention relates to a binder composition for producing a lignocellulosic composite material, preferably for producing a lignocellulosic composite material in a method as defined above, wherein the component b3) of the binder (i.e., urea) is present in an amount in the range of ≥ 5 to ≤ 50 mass-% relative to the combined total mass of the binder components b1), b2) and any present component b4), preferably ≥ 10 to ≤ 35 mass-% and more preferably ≥ 15 to ≤ 35 mass-%.

[0225] According to this preferred aspect of the invention, the total amount of the binder component b3) urea, relative to the binder components b1), b2) and any present component b4), i.e. the combined total mass of all binder components present for hardening via esterification, is within the ranges or preferred ranges defined hereinbefore. Through extensive studies in the form of experimental series with different amounts / ratios of urea, it has been found that these (relatively low) preferred amounts of urea are sufficient to reduce formaldehyde emissions in the process according to the invention. Furthermore, it has surprisingly been found that the ranges or preferred ranges of the total amount of urea provided herein, relative to the combined total mass of the binder components b1), b2) and any present component b4), have a positive effect on the mechanical properties of the resulting lignocellulosic composite material. In particular, the thickness swelling ("24h swelling"), transverse tensile strength ("internal bond strength") and surface and edge screw holding of the lignocellulosic composite material (board) produced in the process according to the invention can be significantly improved after 24 h.

[0226] The invention also relates to a single-layer or multi-layer lignocellulosic composite material obtainable or obtained by a process according to the invention (preferably, the process according to the invention as defined above or in the appended claims is preferred), and to a building product (as defined hereinafter) comprising such a single-layer or multi-layer lignocellulosic composite material.

[0227] Generally, all aspects of the invention discussed herein in the context of the process for producing lignocellulosic composite materials according to the invention and / or all aspects of the invention discussed herein in the context of the binder according to the invention apply, with the necessary modifications, to the single-layer or multi-layer lignocellulosic composite materials of the invention, as defined above and hereinafter. Vice versa, all aspects of the invention discussed herein in the context of the single-layer or multi-layer lignocellulosic composite materials of the invention apply, with the necessary modifications, to the process for producing lignocellulosic composite materials according to the invention and / or to the binder according to the invention.

[0228] Preferred is a single-layer or multi-layer lignocellulosic composite material of the invention which can be prepared by a process according to the invention (preferably, as defined herein is preferred), and a (building) product comprising such a single-layer or multi-layer lignocellulosic composite material or being such a single-layer or multi-layer lignocellulosic composite material, wherein the lignocellulosic composite material is a lignocellulosic board.

[0229] Preferably, the lignocellulosic board is a lignocellulosic board with a core, wherein in a cross-section oriented perpendicular to the plane of the board, the difference between the maximum density of the board and the minimum density in the core of the board is at most 100 kg / m 3 ; preferably at most 80 kg / m 3 and more preferably at most 60 kg / m3 。

[0230] Preferably, the lignocellulosic board is a lignocellulosic board selected from the group consisting of particle board, high-density fiberboard (HDF), medium-density fiberboard (MDF), and oriented strand board (OSB).

[0231] Preferably, the lignocellulosic board is a lignocellulosic board having a thickness in the range of 1 to 30 mm, preferably in the range of 2 to 25 mm.

[0232] Preferably, the lignocellulosic board is a single-layer lignocellulosic fiber board having a thickness in the range of 1 to 15 mm, preferably 2 to 12 mm, more preferably 2 to 4 mm.

[0233] Preferably, the lignocellulosic board is a multi-layer lignocellulosic particle board having a core layer and upper and lower surface layers, i.e., a three-layer board, having a total thickness in the range of 14 to 25 mm, wherein the multi-layer lignocellulosic particle board preferably consists of the core layer and the upper and lower surface layers.

[0234] Preferably, the lignocellulosic board has an internal bond strength of at least 0.4 N / mm 2 , preferably at least 0.5 N / mm 2 , more preferably at least 0.6 N / mm 2 determined according to DIN EN 319:1993-08.

[0235] Preferably, the lignocellulosic board has a thickness swelling after 24 hours in water at 20 °C of less than 50%, preferably less than 45%, more preferably less than 40% determined according to DIN EN 317:1993-08.

[0236] Preferably, the lignocellulosic board is a lignocellulosic board comprising one or more lignocellulosic composite material layers, wherein preferably all lignocellulosic composite material layers comprised by the lignocellulosic board are lignocellulosic composite material layers obtainable or obtained according to the method of the present invention (preferably, the method of the present invention as defined above or in the appended claims is preferred).

[0237] Preferably, the lignocellulosic board is a multi-layer lignocellulosic board having a core layer and upper and lower surface layers, i.e., a three-layer board, wherein at least the core layer contains the mixture according to step S1), preferably all layers contain the mixture according to step S1), and wherein the multi-layer lignocellulosic board preferably consists of the core layer and the upper and lower surface layers.

[0238] The present invention also relates to a kit for producing a binder composition according to the present invention for use in the production of lignocellulosic composites (preferably for use in the method of the present invention for producing lignocellulosic composites), the kit comprising at least the following as separate components:

[0239] b1) one, two or more polymers comprising a plurality of carboxyl groups, preferably as defined herein is preferred,

[0240] b2) one, two or more polymer or monomer compounds having two or more hydroxyl groups for crosslinking the polymer via esterification, preferably as defined herein is preferred,

[0241] and

[0242] b3) urea,

[0243] and preferably further comprises the following as additional binder components:

[0244] b4) one or more non-polymeric, preferably non-polymeric bio-based compounds having two or more carboxyl groups and / or one or more non-polymeric, preferably non-polymeric bio-based compounds having at least one carboxyl group and at least one hydroxyl group,

[0245] wherein at least one, two or more of the separate components b1), b2), b3), and optionally b4) of the kit are spatially separated from the other separate components.

[0246] Preferably, the kit for producing the binder composition according to the present invention comprises two spatially separated substances or mixtures respectively. For example, the kit comprises a first spatially separated substance or mixture containing the separate components b1), b2) and b4) and a second spatially separated substance or mixture containing the separate component b3), or the kit comprises a first spatially separated substance or mixture containing the separate components b1) and b3) and a second spatially separated substance or mixture containing the separate components b2) and b4), etc.

[0247] In general, all aspects of the invention discussed herein in the context of the process for producing lignocellulosic composites according to the invention and / or all aspects of the invention discussed herein in the context of the binder according to the invention and / or all aspects of the invention discussed herein in the context of the single-layer or multi-layer lignocellulosic composites according to the invention apply, mutatis mutandis, to the kit for producing the binder composition according to the invention, as defined above and below herein. Vice versa, all aspects of the invention discussed herein in the context of the kit for producing the binder composition according to the invention apply, mutatis mutandis, to the process for producing lignocellulosic composites according to the invention and / or the binder according to the invention and / or the single-layer or multi-layer lignocellulosic composites according to the invention. Etc.

[0248] Preferably, the kit for producing the binder composition according to the invention comprises component b3) urea of the binder, the total amount of which is in the range of ≥5 to ≤50 mass-% relative to the combined total mass of components b1), b2) and any present component b4) of the kit, preferably ≥10 to ≤35 mass-% and more preferably ≥15 to ≤35 mass-%.

[0249] Preferably, the kit for producing the binder composition according to the invention comprises the additional binder component b4) as defined above, wherein preferably the total amount of the additional binder component b4) is 30 mass-% or less relative to the combined total mass of binder components b1), b2) and component b4) in the kit, more preferably in the range of 5 mass-% to 30 mass-%.

[0250] Preferably, the kit for producing the binder composition according to the invention comprises binder components b1), b2), b3 and optionally b4), wherein the binder components b1), b2), b3 and optionally b4) comprise compounds selected from the preferred groups as defined above.

[0251] Preferably, the kit for producing the binder composition according to the invention comprises binder components b1), b2), b3 and optionally b4), and the total amount (ratio) of the corresponding compounds of the components b1), b2), b3 and optionally b4) is within the ranges and preferred ranges as defined above.

[0252] Preferably, the kit for producing the binder composition according to the invention further comprises one, two or more additional ingredients selected from the group consisting of:

[0253] - water,

[0254] - A hydrophobic agent selected from the group consisting of paraffin and mixtures containing paraffin, preferably a paraffin emulsion,

[0255] - Alkali metal salts and alkaline earth metal salts, preferably sodium nitrate,

[0256] - Dyes, pigments,

[0257] - Antifungal and antibacterial agents;

[0258] - Rheology modifiers, fillers

[0259] - Release agents, and

[0260] - Surfactants, surface active agents.

[0261] More preferably, in a kit for producing the binder composition according to the invention, the additional components from the above list are spatially separated from the components b1), b2), b3) and b4).

[0262] The invention also relates to the use of the lignocellulosic composite material of the invention (as defined above or preparable by the method according to the invention, preferably as defined herein is preferred) as a building element in building products, preferably as a building element in furniture or furniture parts, more preferably as a building element in a hollow structure in furniture or furniture parts.

[0263] Generally, all aspects of the invention discussed herein in the context of the method for producing a lignocellulosic composite material according to the invention and / or all aspects of the invention discussed herein in the context of the binder according to the invention and / or all aspects of the invention discussed herein in the context of the single-layer or multi-layer lignocellulosic composite material of the invention and / or all aspects of the invention in the context of a kit for producing the binder composition according to the invention apply, with the necessary modifications, to the use of the lignocellulosic composite material of the invention, as defined above and below herein. Vice versa, all aspects of the invention discussed herein in the context of the use of the lignocellulosic composite material of the invention apply, with the necessary modifications, to the method for producing a lignocellulosic composite material according to the invention and / or the lignocellulosic composite material of the invention and / or the binder of the invention and / or the kit for producing the binder composition of the invention.

[0264] As used herein, the term "building product" designates products used in construction such as decking, doors, windows, floors, panels, furniture or furniture parts. The building products of the invention are preferably selected from the group consisting of furniture and furniture parts.

[0265] As used in this text, the term "furniture" designates all kinds of furniture. In the context of the present invention, the furniture is preferably selected from the group consisting of chairs, tables, desks, closets, beds, and shelves.

[0266] As used in this text, the term "construction element" designates a wood-based cellulose composite product (e.g., a board, see above) that constitutes parts (elements) of a building product (e.g., furniture parts). Such construction elements are preferably furniture parts, and more preferably, such furniture parts are selected from the group consisting of shelves, table tops, side panels or shelves or doors of cabinets, and side walls of beds.

[0267] As used in this text, the term "hollow structure" designates a building product, preferably furniture and construction elements, preferably furniture parts, which contain a certain amount of enclosed empty space not filled with building materials. Such hollow structures allow the manufacture of building products, preferably furniture and construction elements, preferably furniture parts, which are extremely light and strong, despite using a low amount (by weight) of building materials. Frame board (BoF) products are typical examples of such hollow structures. In BoF products, a frame made of a wood-based cellulose composite product (e.g., particle board) is covered with a wood-based cellulose board (e.g., thin high-density fiberboard). Another hollow structure is the strip board (BoS) product, where strips of wood-based cellulose composite products are used instead of a complete frame.

[0268] The present invention is explained in more detail below with reference to the accompanying schematic drawings.

[0269] Figure 1 : Schematic structure of a single-layer wood-based cellulose composite according to the present invention.

[0270] Figure 2 : Schematic structure of a single-layer wood-based cellulose composite with two additional coatings according to the present invention.

[0271] Figure 3 : Schematic structure of a multi-layer wood-based cellulose composite in the form of a three-layer board according to the present invention.

[0272] Figure 4 : Schematic structure of a multi-layer wood-based cellulose composite in the form of a three-layer board with two additional coatings according to the present invention.

[0273] Figure 1 A single-layer wood-based cellulose composite 110 according to the present invention is shown. The single-layer wood-based cellulose composite 110 consists of a single layer 100 that contains wood-based cellulose particles and a hardened binder.

[0274] Figure 2Shows a coated single-layer lignocellulosic composite material 230 according to the present invention. The single-layer lignocellulosic composite material 230 includes a single layer 200 containing lignocellulose particles and a hardened binder. The single-layer lignocellulosic composite material 230 further includes two outer (i.e., coating) layers 210 and 220 that do not contain lignocellulose particles. The upper outer (coating) layer 210 contacts the upper outer side (exterior) of the single layer 200. The lower outer (coating) layer 220 contacts the lower outer side (exterior) of the single layer 200.

[0275] Figure 3 Shows a multi-layer lignocellulosic composite material 330 in the form of a three-ply board according to the present invention. The multi-layer lignocellulosic composite material 330 is composed of three lignocellulosic composite material layers 300, 310, and 320 (each of these three layers contains a specific mixture including at least lignocellulose particles and a binder). The lignocellulosic composite material layer 300 is the core layer of the three-ply board, which is located at the geometric center of the multi-layer lignocellulosic composite material and accordingly does not directly contact the outer side (exterior). The lignocellulosic composite material layers 310 and 320 are the surface layers of the multi-layer lignocellulosic composite material, which directly contact the outer side (exterior), i.e., have an outer surface. Thus, the lower surface layer 320 directly contacts the core layer 300 and constitutes the first outer side (exterior). The core layer 300 directly contacts the two surface layers 310 and 320 and does not directly contact the outer side of the composite material. The upper surface layer 310 directly contacts the core layer 300 and constitutes the second outer side (exterior) of the composite material. As Figure 3 depicted, preferably, the two surface layers 310 and 320 of the three-layer lignocellulosic composite material / board 330 have the same composition and / or the same dimensions. In particular, preferably, the two surface layers 310 and 320 are composed of the same composition and have the same thickness.

[0276] Figure 4Shows a multilayer wood - cellulose composite material 450 in the form of a coated three - layer board. The multilayer wood - cellulose composite material 450 consists of three wood - cellulose composite layers 400, 410, and 420 (each of these three layers contains a specific mixture comprising at least wood - cellulose particles and a binder). The multilayer wood - cellulose composite material 450 further includes two outer (i.e., coating) layers 430 and 440 that do not contain wood - cellulose particles. The upper outer (coating) layer 430 is in contact with the outer (exterior) side of the upper surface layer 410, and the lower outer (coating) layer 440 is in contact with the outer (exterior) side of the lower surface layer 420. The wood - cellulose composite layer 400 is the core layer of the three - layer board, which is located at the geometric center of the multilayer wood - cellulose composite material and accordingly is not in direct contact with the outer (exterior) side. The wood - cellulose composite layers 410 and 420 are the surface layers of the multilayer wood - cellulose composite material, and they are in direct contact with the outer (exterior) side, i.e., in direct contact with the coatings 430 and 440 respectively. The lower surface layer 420 is in direct contact with the core layer 400 and the lower outer (coating) layer 440. The lower surface layer 420 constitutes the first outer (exterior). The core layer 400 is in direct contact with the two surface layers 410 and 420, and not in direct contact with the outer side of the composite material. The upper surface layer 410 is in direct contact with the core layer 400 and the upper outer (coating) layer 430. The upper surface layer 410 constitutes the second outer (exterior) of the composite material. As Figure 4 depicted, preferably, the two surface layers 410 and 420 of the three - layer wood - cellulose composite / board 450 have the same composition and / or the same dimensions. In particular, preferably, the two surface layers 410 and 420 are composed of the same composition and have the same thickness.

[0277] Example:

[0278] The following examples according to the invention are intended to further explain and illustrate the invention without limiting its scope.

[0279] 1. Measurement method:

[0280] 1.1 Determination of the weight-average molecular weight M of a polymer containing multiple carboxyl groups W :

[0281] M of a polymer containing multiple carboxyl groups W is determined by gel permeation chromatography under the following conditions:

[0282] - Apparatus: A modular GPC system (Agilent) with a combination of columns and a refractive index detector

[0283] - Eluent: 0.01 mol / l phosphate - buffered saline, pH 7.4 + 0.01 mol / l sodium azide in deionized water

[0284] - Sample preparation: The polymer was dissolved in the eluent on a shaker at room temperature for 6 h to obtain a concentration of approximately 4 g / L. The sample was filtered through a Sartorius RC 0.2 μm filter before injection.

[0285] - Injection volume: 100 μl

[0286] - Column: 2 x TSKgel GMPWXL, 300 x 7.8 mm, 7 μm (TOSOH Bioscience GmbH)

[0287] - Column temperature: 35 °C

[0288] - Flow rate: 0.5 ml / min

[0289] - RID temperature : 35 °C

[0290] - Detection: Refractive index (8 μl)

[0291] - Calibration: Narrow distribution poly(sodium acrylate) calibration standards in the range of 1250 g / mol to 143000 g / mol (PSS, Mainz, Germany) and 1770 g / mol and 900 g / mol (American Polymer Standards Corp.). The oligomer peaks of the standards with 900 g / mol were used as additional calibration points (225, 297, and 585 g / mol).

[0292] 1.2 Residual particulate moisture content ("oven method"):

[0293] Before providing or preparing a mixture comprising lignocellulosic particles and a binder, the moisture content of the lignocellulosic particles was measured according to DIN EN 322:1993-08 by placing the lignocellulosic particles in an oven at a temperature of 103 °C ± 2 °C until a constant mass, i.e., the oven-dried state of the lignocellulosic particles, was reached. This method was also used to check the water content of the resulting mixture comprising lignocellulosic particles and a binder.

[0294] 1.3 Solid content of amino resin:

[0295] The solids content of the amino resin (UF) is determined by weighing out 1 g of the amino resin in a weighing dish, drying it in a drying cabinet at 120 °C for 2 h and weighing the residue in a desiccator after equilibration to room temperature, as described in Zeppenfeld, Grunwald, Klebstoffe in der Holz-und [Adhesives in the Wood and Furniture Industry], DRW Verlag, 2nd Edition, 2005, page 286.

[0296] 1.4 Thickness and density of lignocellulosic composite material (board):

[0297] The thickness and density of the lignocellulosic composite material (board) are measured according to DIN EN 323:1993-08 and reported as the arithmetic mean of ten 50 x 50 mm samples of the same board.

[0298] 1.5 Transverse tensile strength of board ("internal bond strength"):

[0299] The transverse tensile strength (“internal bond strength”) of the lignocellulosic composite material (board) is determined according to DIN EN 319:1993-08 and reported as the arithmetic mean of ten 50 x 50 mm samples of the same lignocellulosic composite material (board).

[0300] 1.6 Thickness swelling ("24h swelling"):

[0301] The thickness swelling after 24 h (“24 h swelling”) of the lignocellulosic composite material (board) is determined according to DIN EN 317:1993-08 and reported as the arithmetic mean of ten 50 x 50 mm samples of the same lignocellulosic composite material (board).

[0302] 1.7 Surface and edge screw holding:

[0303] The surface screw holding and edge screw holding of the lignocellulosic composite material (board) are determined according to IKEA's test method: Instruction Manual No. IOS-TM-0057, Date: 2018-07-13, Version No.: AA-2120821-1.

[0304] 1.8 Ratio of the weight of the solid content of all binder components present for hardening via esterification to the weight of lignocellulosic particles in the oven-dried state (esterification binder dose): State of the lignocellulosic particles:

[0305] In the examples according to the invention, the ratio of the weight of the solids content of all binder components present to be hardened via esterification to the weight of the lignocellulosic particles in the dried state (esterification binder amount) is reported as the total weight of the corresponding binder components present to be hardened via esterification. Such components are polymers containing a plurality of carboxyl groups, polymers or monomeric compounds having two or more hydroxyl groups, non-polymeric compounds having two or more carboxyl groups, and non-polymeric compounds having at least one carboxyl group and at least one hydroxyl group. Other binder components such as urea and additional compounds such as alkali metal salts and alkaline earth metal salts, water repellents, dyes, pigments, fungicides, bactericides, rheology modifiers, fillers, mold release agents, surfactants and surface active agents are not included in the esterification binder amount. The ratio of the weight of the solids content of all binder components present to be hardened via esterification to the weight of the lignocellulosic particles in the dried state (esterification binder amount) is given based on the weight of the lignocellulosic particles in the dried state, in wt.-%.

[0306] The ratio of the weight of the binder component urea to the weight of the lignocellulosic particles (urea amount) is reported as the weight of urea based on the weight of the lignocellulosic particles in the dried state, in wt.-%.

[0307] In the comparative example with UF resin ( adhesive), the ratio of the weight of the solids content of the binder components to the weight of the lignocellulosic particles in the dried state (binder amount) is reported as the weight of the UF resin solids based on the weight of the lignocellulosic particles in the dried state, in wt.-%.

[0308] 1.9 Measurement of the pH value of the binder (pH binder):

[0309] The pH value of the binder is measured at 23 °C ± 2 °C using an ISFET electrode (CPS441D) from Endres + Hauser.

[0310] 1.10 Determination of the pH value of the aqueous extract of a mixture containing lignocellulosic particles and binder (pH extract ate):

[0311] The pH value (pH extract) of the aqueous extract of the mixture containing lignocellulosic particles and a binder is measured according to the procedure described in Hennecke, U., Roffael, E. “Charakterisierung einiger auswaschbarer Stoffe in thermomechanisch gewonnenen Holzstoffen der Buche [Characterization of some extractable substances in thermomechanically produced beech wood substances]” Holz Roh Werkst 63, 408 - 413 (2005), https: / / doi.org / 10.1007 / s00107-005-0017-4 as described in

[0312] Accordingly, 5.0 g of the mixture containing lignocellulosic particles and the corresponding amount of the binder component is placed in a conical flask (500 mL). Then 150 mL of demineralized water is added to the mixture. The conical flask is then sealed with a glass stopper and placed on an oscillator for 24 hours. The mixture (extract) is then filtered through a folded filter, and the pH value of the filtered aqueous extract is measured at 23 °C ± 2 °C using a glass pH electrode (SI - Analytics, PL81 - 120pHT, PTB08ATEX2021).

[0313] 1.11 Formaldehyde emission (FA emission):

[0314] The formaldehyde emission (FA emission) of single - layer and multi - layer lignocellulosic composites (boards) is determined according to EN ISO 12460 - 3:2020 (Gas analysis method).

[0315] 2. Chemicals:

[0316] 2.1 Components for hardening the binder via esterification:

[0317] 2.1.1 Polymers or monomer compounds having two or more hydroxyl groups selected from the group consisting of carbohydrates and sugar alcohols: Compounds:

[0318] Dextrose monohydrate (“Dex”, >99%), Sigma Aldrich, Spain

[0319] Fructose (“Fru”, >99%), Sigma Aldrich, USA

[0320] Glycerol (“Gly”, >99%), Cremer OLEA, Germany

[0321] Maltodextrin (“MD”, dextrose equivalent 13.0 - 17.0), Sigma Aldrich, USA

[0322] 2.1.2 Polymers or monomer compounds having two or more hydroxyl groups selected from the group consisting of alkylamines:

[0323] Triethanolamine (“TEtA”, 98%), Sigma - Aldrich

[0324] 2.1.3 Non-polymeric compounds having two or more carboxyl groups:

[0325] Citric acid monohydrate (“CA”, >99%), Bernd Kraft GmbH, Austria; Lactic acid (“LA”, 88%), Fisher Scientific, Spain

[0326] 2.1.4 Polymers containing multiple carboxyl groups:

[0327] Polymer A (“A”): A 44.5 wt.-% aqueous solution (pH = 0.8) of a copolymer consisting of 75 wt.-% acrylic acid units and 25 wt.-% maleic acid units with a weight-average molecular weight of 58,600 g / mol.

[0328] Polymer B (“B”): A 50 wt.-% aqueous solution of a copolymer consisting of 70 wt.-% acrylic acid units and 30 wt.-% maleic acid units with a weight-average molecular weight of 91,600 g / mol, partially neutralized (pH = 4.0).

[0329] Polymer C (“C”): A 45 wt.-% aqueous solution (pH = 0.8) of a copolymer consisting of 66 wt.-% acrylic acid units and 34 wt.-% maleic acid units with a weight-average molecular weight of 80,800 g / mol.

[0330] Polymers A and C are synthesized by free-radical solution polymerization of acrylic acid and maleic anhydride in water. For example, for Polymer C, 70 wt.-% acrylic acid and 30 wt.-% maleic anhydride are polymerized to yield a copolymer consisting of 66 wt.-% acrylic acid units and 34 wt.-% maleic acid units.

[0331] 2.2 Other binder components:

[0332] Urea (technical grade), BASF

[0333] 2.3 Additional compounds:

[0334] Paraffin emulsion (60% paraffin in water), HydroWax 138, Sasol Wax GmbH

[0335] Sodium hydroxide (NaOH)

[0336] 2.4 Urea-formaldehyde resin (comparative binder):

[0337] Urea formaldehyde resin (“UF”, “KL 347”, 66% solids content), Kaurit Glue 347, BASF

[0338] 3. Lignocellulosic particles (wood chips):

[0339] 3.1 Spruce wood chips (lignocellulosic particles):

[0340] Spruce wood chips are produced in a disk chipper. Spruce tree trunks (250 mm in length) from Germany are pressed with their long sides against a rotating steel disk, in which radially and evenly distributed tool holders are inserted. Each tool holder consists of a radially arranged cutting knife and several scoring knives placed at right angles thereto. The cutting knife separates the chips from the round wood, and the scoring knives simultaneously limit the chip length. The produced chips are then collected in a silo and transported from there to a cross-impact attrition mill (with a sieve) for re-shredding according to the chip width. The re-shredded chips are then conveyed to a flash dryer and dried at approximately 120 °C. The spruce wood chips are then screened into two usable fractions (B: ≤ 2.0 mm x 2.0 mm and > 0.32 mm x 0.5 mm; C: ≤ 4.0 mm x 4.0 mm and > 2.0 mm x 2.0 mm), a re-shredded coarse fraction (D: > 4.0 mm x 4.0 mm) and a fine fraction (A: ≤ 0.32 mm x 0.5 mm).

[0341] Fraction B of the spruce wood chips (hereinafter referred to as “spruce surface layer chips”) is used for the surface layer of three-layer particleboard. A mixture of 60 wt.-% of fraction B and 40 wt.-% of fraction C of the spruce wood chips (hereinafter referred to as “spruce core layer chips”) is used in the core layer of three-layer particleboard or in single-layer particleboard.

[0342] 3.2 Industrial wood chips (lignocellulosic particles):

[0343] Industrial wood chips (“industrial surface layer chips” and “industrial core layer chips”) are produced in an industrial particleboard production plant in Slovakia. Before use, the industrial wood chips are dried in a convection oven at approximately 120 °C.

[0344] 5. Preparation of binder:

[0345] 5.1 Preparation of comparative binder:

[0346] 5.2 Preparation of a binder containing the following as components: for hardening via esterification, one, two or more polymers containing multiple carboxyl groups and, for crosslinking said polymers, one, two or more polymers or monomer compounds having two or more hydroxyl groups:

[0347] Binder 1: Binder 1 is a mixture of 333 g of polymer C (“C”, 45 wt.-% in water), 100 g of triethanolamine (“TEtA”) and 66.6 g of water. The resulting solids content for all binder components present for hardening via esterification is 50.0 wt.-%. The weight ratio between C and TEtA is 60:40.

[0348] Binder 2: Binder 2 is a mixture of 444 g of polymer C (“C”, 45 wt.-% in water), 50.0 g of triethanolamine (“TEtA”) and 6.0 g of water. The resulting solids content for all binder components present for hardening via esterification is 50.0 wt.-%. The weight ratio between C and TEtA is 80:20.

[0349] Binder 3: Binder 3 is a mixture of 333 g of polymer C (“C”, 45 wt.-% in water), 100 g of glycerol (“Gly”) and 66.6 g of water. The resulting solids content for all binder components present for hardening via esterification is 50.0 wt.-%. The weight ratio between C and Gly is 60:40.

[0350] Binder 4: Binder 4 is a mixture of 444 g of polymer C (“C”, 45 wt.-% in water), 50.0 g of glycerol (“Gly”) and 6.0 g of water. The resulting solids content for all binder components present for hardening via esterification is 50.0 wt.-%. The weight ratio between C and Gly is 80:20.

[0351] Binder 5: Binder 5 is a mixture of 337 g of polymer A (“A”, 44.5 wt.-% in water), 100 g of triethanolamine (“TEtA”) and 63.0 g of water. The resulting solids content for all binder components present for hardening via esterification is 50.0 wt.-%. The weight ratio between A and TEtA is 60:40.

[0352] Binder 6: Binder 6 is a mixture of 337 g of polymer A (“A”, 44.5 wt.-% in water), 100 g of glycerol (“Gly”) and 63.0 g of water. The resulting solids content for all binder components present for hardening via esterification is 50.0 wt.-%. The weight ratio between A and Gly is 60:40.

[0353] Binder 7:Binder 7 is a mixture of 444 g of polymer C (“C”, 45 wt.-% in water), 55.0 g of dextrin monohydrate (corresponding to 50.0 g of dextrin “Dex”), and 1.0 g of water. The resulting solids content for all binder components present for hardening via esterification is 50.0 wt.-%. The weight ratio between C and Dex is 80:20.

[0354] Binder 8: Binder 8 is a mixture of 444 g of polymer C (“C”, 45 wt.-% in water), 50.0 g of fructose (“Fru”), and 6.0 g of water. The resulting solids content for all binder components present for hardening via esterification is 50.0 wt.-%. The weight ratio between C and Fru is 80:20.

[0355] Binder 9: Binder 9 is a mixture of 444 g of polymer C (“C”, 45 wt.-% in water), 50.0 g of maltodextrin (“MD”), and 6.0 g of water. The resulting solids content for all binder components present for hardening via esterification is 50.0 wt.-%. The weight ratio between C and MD is 80:20.

[0356] Binder 10: Binder 10 is a mixture of 420 g of polymer A (“A”, 44.5 wt.-% in water), 80.0 g of glycerol (“Gly”), and 34.0 g of water. The resulting solids content for all binder components present for hardening via esterification is 50.0 wt.-%. The weight ratio between A and Gly is 70:30.

[0357] 5.3 Preparation of a binder containing the following as components: for hardening via esterification, one, two or more polymers containing multiple carboxyl groups, and, for crosslinking said polymers, one, two or more polymers or monomer compounds having two or more hydroxyl groups, and one or more non-polymeric, preferably non-polymeric bio-based compounds having two or more carboxyl groups: Compounds:

[0358] Binder 11: Binder 11 is a mixture of 360 g of polymer A (“A”, 44.5 wt.-% in water), 87.9 g of citric acid monohydrate (corresponding to 80.1 g of citric acid “CA”), 80.0 g of glycerol (“Gly”), and 113 g of water. The resulting solids content for all binder components present for hardening via esterification is 50 wt.-%. The weight ratio between A, CA and Gly is 50:25:25.

[0359] Binder 12:Binder 12 is a mixture of 360 g of polymer A (“A”, 44.5 wt.-% in water), 52.6 g of citric acid monohydrate (corresponding to 48.1 g of citric acid “CA”), 32.0 g of lactic acid (“LA”), 80.0 g of glycerol (“Gly”) and 116 g of water. The resulting solid content for hardening all binder components present via esterification is 50 wt.-%. The weight ratio between A, CA, LA and Gly is 50:15:10:25.

[0360] Binder 13: Binder 13 is a mixture of 360 g of polymer B (“B”, 50 wt.-% in water), 87.9 g of citric acid monohydrate (corresponding to 80.1 g of citric acid “CA”), 80.0 g of glycerol (“Gly”) and 152 g of water. The resulting solid content for hardening all binder components present via esterification is 50 wt.-%. The weight ratio between A, CA and Gly is 50:25:25.

[0361] Binder 14: Binder 14 is a mixture of 500 g of polymer A (“A”, 44.5 wt.-% in water), 55.6 g of glycerol (“Gly”) and 56.2 g of water. The resulting solid content for hardening all binder components present via esterification is 50.0 wt.-%. The weight ratio between A and Gly is 80:20.

[0362] Binder 15: Binder 15 is a mixture of 500 g of polymer A (“A”, 44.5 wt.-% in water), 55.6 g of triethanolamine (“TEtA”) and 56.2 g of water. The resulting solid content for hardening all binder components present via esterification is 50.0 wt.-%. The weight ratio between A and TEtA is 80:20.

[0363] 6. Preparation of single-layer lignocellulosic composite material (particle board):

[0364] 6.1 11 mm single-layer particle board (board numbers S1 to S20):

[0365] 6.1.a Provide or prepare a mixture containing at least lignocellulosic particles and binder:

[0366] 11 mm single-layer particleboards (board numbers S1 to S20) were prepared without paraffin and with an esterification binder amount of 6.0 wt.-% (ratio of the weight of the solids content of all binder components present for hardening via esterification to the weight of the lignocellulosic particles in the dried state). The amounts of urea were 0 wt.-%, 1 wt.-%, and 5 wt.-% (weight of urea based on the weight of the lignocellulosic particles in the dried state, in wt.-%). Urea was added to the binder at ambient temperature with strong stirring and then sprayed onto the chips (this applies to all examples containing urea as a binder component).

[0367] The pH value of the corresponding binder was determined (according to the measurement method described above). In the examples with urea (1.0 wt.-% or 5.0 wt.-%), the pH value of the binder was determined after the addition of urea.

[0368] For the boards without urea (S7* and S8*):

[0369] 20.0 g of water was sprayed onto 820 g (800 g dry weight) of spruce core layer chips (lignocellulosic particles, moisture content 2.5%) within 1 min while mixing in a paddle mixer. Subsequently, 96.0 g of the corresponding binder (with a solids content of 50 wt.-% of all binder components present for hardening via esterification) was sprayed onto the mixture within 1 min while mixing. After completion of spraying, mixing was continued in the mixer for 15 s, and the corresponding mixture containing lignocellulosic particles and the binder was obtained. The pH value of the aqueous extract (pH extract) of the corresponding mixture containing lignocellulosic particles and the binder was determined (according to the measurement method described above).

[0370] For the boards with 1.0 wt.-% of urea (S3*, S4*, S5*, S6*, S11, S12, S15, S16, S17, S18, S19, and S20):

[0371] 20.8 g of water was sprayed onto 820 g (800 g dry weight) of spruce core layer chips (lignocellulosic particles, moisture content 2.5%) within 1 min while mixing in a paddle mixer. Subsequently, a mixture of 96.0 g of the corresponding binder (with a solids content of 50 wt.-% of all binder components present for hardening via esterification) and 8.00 g of urea was sprayed onto the mixture within 1 min while mixing. After completion of spraying, mixing was continued in the mixer for 15 s, and the corresponding mixture containing lignocellulosic particles and the binder (containing urea) was obtained. The pH value of the aqueous extract (pH extract) of the corresponding mixture containing lignocellulosic particles and the binder was determined (according to the measurement method described above).

[0372] For the boards (S1*, S2*, S9, S10, S13 and S14) with 5.0 wt.-% urea:

[0373] Spray 24.0 g of water onto 820 g (800 g dry weight) of spruce core layer debris (wood cellulose particles, moisture content 2.5%) within 1 min while mixing in a paddle mixer. Subsequently, spray a mixture of 96.0 g of the corresponding binder (with a solids content of 50 wt.-% of all binder components present for hardening via esterification) and 40.0 g of urea onto this mixture within 1 min while mixing. After completion of spraying, continue mixing in the mixer for 15 s, and obtain the corresponding mixture containing wood cellulose particles and binder (containing urea). Determine the pH value (pH extract) of the aqueous extract of the corresponding mixture containing wood cellulose particles and binder (according to the measurement method described above).

[0374] 6.1.b Compact the mixture:

[0375] After 30 min, disperse 900 g of the resulting mixture containing wood cellulose particles and binder into a 320 mm x 380 mm mold, and pre-press (compact) it under ambient conditions and a pressure of 1.2 N / mm 2 to obtain a pre-pressed debris mat (compacted mixture).

[0376] 6.1.c Apply a high-frequency electric field to the mixture during and / or after compaction such that the binder hardens via esterification and binds the lignocellulosic particles, resulting in a single-layer lignocellulosic composite material (HF pressing method, board numbers S7 - S20):

[0377] Subsequently, remove the thus obtained pre-pressed debris mat (compacted mixture) from the mold. To monitor the temperature at the center (i.e., approximately in the middle of the mat) of the (compacted) mixture, introduce a temperature sensor into the center of the pre-pressed debris mat. Then provide non-woven separators to the upper and lower sides of the pre-pressed debris mat. Insert the pre-pressed debris mat into an HLOP 170 press from Hoefer Presstechnik GmbH, whereby birch plywood (thickness 6 mm) is placed between the non-woven separators on each side of the mat and the pressing plates. Then compact the pre-pressed debris mat in the press to a thickness of 11 mm within a time period of 2 s, and then heat it by applying a high-frequency electric field (27.12 MHz) while the press remains closed. When the center reaches 170 °C ("HF temperature"), open the press.

[0378] 6.1.d Hot pressing (comparative example, board numbers S1* - S6*):

[0379] A nonwoven separator is provided to the upper and lower sides of the pre-pressed chip mat. In a laboratory hot press from Herfel Pressentechnik, the pre-pressed chip mat is further compacted to a thickness of 11 mm at a temperature of 200 °C (platen temperature). The press is opened after 110 seconds (press time factor 10 s / mm).

[0380] 6.1.e After 3 days under ambient conditions, the resulting single-layer particleboard (single-layer lignocellulosic composite) is sanded. 0.25 mm is sanded off both on the top side and the bottom side of the single-layer particleboard. After conditioning (at 65% humidity and 20 °C) to a constant mass, the thickness, density, internal bond strength, formaldehyde emission, and 24 h swelling of the resulting single-layer particleboard are determined (according to the measurement methods described above).

[0381] Table 1 shows the corresponding esterified binder compositions used, the amount of urea (the ratio of the weight of urea to the weight of lignocellulosic particles in the oven-dried state), the pressing method, the density, the internal bond strength, the 24 h swelling, and the FA emission of the resulting 11 mm single-layer particleboards numbered S1 to S20. Board numbers S1 to S8 are comparative examples (hot pressing method or without urea). Table 1 also shows the pH value of the corresponding binder used and the pH value of the aqueous extract of the corresponding mixture containing lignocellulosic particles and binder (pH extract).

[0382] Table 1. 11 mm single-layer particleboards S1 to S20, esterified binder amount 6.0 wt.-%, without paraffin

[0383]

[0384]

[0385] * Comparative example (hot pressing or without urea)

[0386] a) "No board" means that the material obtained after pressing is not an undamaged particleboard and shows fractures, cracks, and / or bursts

[0387] b) n.q. = not quantifiable because the test sample broke into pieces within 24 h

[0388] c) pH of the binder (containing urea, e.g., having urea)

[0389] The results show that wood - cellulose composites were prepared according to the method of the present invention, where the wood - cellulose composites are 11 - mm single - layer particleboards (board numbers S9 to S20). All these board numbers S9 to S20 were produced by method steps S1, S2) and S3, namely by providing or preparing a mixture comprising at least wood - cellulose particles and a binder; by compacting the mixture; and by applying a high - frequency electric field to the mixture during and / or after compaction, such that the binder hardens via esterification and binds the wood - cellulose particles, resulting in the production of a single - layer wood - cellulose composite. All these board numbers S9 to S20 were prepared with a binder comprising the following as components: b1) one, two or more polymers containing multiple carboxyl groups, b2) one, two or more polymer or monomer compounds having two or more hydroxyl groups for cross - linking the polymers via esterification, and b3) urea.

[0390] The results show that the wood - cellulose composites (board numbers S9 to S20) prepared according to the method of the present invention and with the binder according to the present invention show formaldehyde emissions as low as 0.0 mg / m 2 h during and / or after the production of single - layer wood - cellulose composites determined according to EN ISO 12460 - 3:2020.

[0391] Therefore, the results show that in the mixture provided or prepared in step S1) of the method, the presence of urea (as component b3) of the binder) in an amount of 1 mass-% of the total mass of the wood - cellulose particles in the mixture in the oven - dry state is sufficient to minimize formaldehyde emissions determined according to EN ISO 12460 - 3:2020 to a value as low as 0.0 mg / m 2 h (see “urea amount” in board numbers S11, S12 and S15 to S20).

[0392] The resulting single - layer wood - cellulose composites (board numbers S9 to S20) are characterized by an internal bond strength of at least 0.51 N / mm 2 determined according to DIN EN 319:1993 - 08.

[0393] The resulting single - layer wood - cellulose composites (board numbers S13 to S20) prepared with a binder comprising a compound selected from the group consisting of glycerol, dextrose, fructose and maltodextrin as component b2) are characterized by a thickness swelling after 24 hours in water at 20 °C of less than 60% determined according to DIN EN 317:1993 - 08. This shows that it is particularly preferred that component b2) of the binder comprises a compound selected from the group consisting of glycerol, dextrose, fructose and maltodextrin.

[0394] The results also show that in the mixture provided or prepared in step S1) of the method, the presence of components b1), b2) and any present component b4) in a total combined amount of 6 mass-% relative to the total mass of the lignocellulosic particles in the mixture in the dried state is sufficient to produce a single-layer lignocellulosic composite material having excellent mechanical properties such as internal bond strength as explained above and thickness swelling after 24 hours in water at 20 °C (see "esterification binder amount" in plate numbers S9 to S20).

[0395] Comparative example plate numbers S1 to S6 (the materials obtained after pressing are not undamaged particle boards and show fractures, cracks and / or bursts) show that applying a high-frequency electric field to the mixture during and / or after compaction such that the binder hardens via esterification and binds the lignocellulosic particles is advantageous compared to conventional hot pressing.

[0396] Characterized by 1.0 mg / m 2 Comparative example plate numbers S7 and S8 (without component b3) urea in the binder) with formaldehyde emissions during and / or after production of a single-layer lignocellulosic composite material determined according to EN ISO 12460-3:2020 show that the presence of binder component b3) urea is advantageous for reducing formaldehyde emissions and for improving internal bond strength and thickness swelling.

[0397] 6.2 10 mm single-layer particle board (board numbers S21 to S35):

[0398] 6.2.a Provide or prepare a mixture comprising at least lignocellulosic particles and a binder:

[0399] 10 mm single-layer particle boards (plate numbers S21 to S35) were prepared with a paraffin amount of 0.5 wt.-% (mass ratio of the weight of paraffin to the weight of the lignocellulosic particles in the dried state).

[0400] For plates S21*, S27*, S30*, S32* and S34* (esterification binder content of 6.0 wt.-%, urea content of 0.0 wt.-%):

[0401] A mixture of 6.67 g of Hydrowax 138 (60 wt.-% paraffin in water) and 21.5 g of water was sprayed onto 816 g (800 g dry weight) of spruce core layer chips (wood cellulose particles, moisture content 2.0%) within 1 min while mixing in a paddle mixer. Subsequently, 96.0 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) was sprayed onto this mixture within 1 min while mixing. (For board S30*, 50 wt.-% aqueous NaOH solution was added to the corresponding binder before spraying to adjust the pH value to 3.49). After completion of spraying, mixing was continued in the mixer for 15 s, and the corresponding mixture containing wood cellulose particles and binder was obtained.

[0402] For board S24* (4.0 wt.-% esterified binder content, 0.0 wt.-% urea):

[0403] A mixture of 6.67 g of Hydrowax 138 (60 wt.-% paraffin in water) and 32.0 g of water was sprayed onto 816 g (800 g dry weight) of spruce core layer chips (wood cellulose particles, moisture content 2.0%) within 1 min while mixing in a paddle mixer. Subsequently, 64.0 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) was sprayed onto this mixture within 1 min while mixing. After completion of spraying, mixing was continued in the mixer for 15 s, and the corresponding mixture containing wood cellulose particles and binder was obtained.

[0404] For board S25 (4.0 wt.-% esterified binder content and 0.8 wt.-% of urea):

[0405] A mixture of 6.67 g of Hydrowax 138 (60 wt.-% paraffin in water) and 36.5 g of water was sprayed onto 816 g (800 g dry weight) of spruce core layer chips (wood cellulose particles, moisture content 2.0%) within 1 min while mixing in a paddle mixer. Subsequently, a mixture of 64.0 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) and 6.40 g of urea was sprayed onto this mixture within 1 min while mixing. After completion of spraying, mixing was continued in the mixer for 15 s, and the corresponding mixture containing wood cellulose particles and binder (containing urea) was obtained.

[0406] For boards S22, S28, S29, S31, S33 and S35 (6.0 wt.-% esterified binder content and 1.2 wt.-% of urea):

[0407] A mixture of 6.67 g of Hydrowax 138 (60 wt.-% paraffin in water) and 22.6 g of water was sprayed onto 816 g (800 g dry weight) of spruce core layer debris (wood cellulose particles, moisture content 2.0%) within 1 min while mixing in a paddle mixer. Subsequently, a mixture of 96.0 g of the corresponding binder (having a solids content of 50 wt.-% for all binder components present for hardening via esterification) and 9.60 g of urea was sprayed onto this mixture within 1 min while mixing. (For boards S29 and S31, 50 wt.-% aqueous NaOH solution was added to the corresponding binder before spraying to adjust the pH value to 1.75 or 3.49). After completion of spraying, mixing was continued in the mixer for 15 s, and the corresponding mixture containing wood cellulose particles and the binder (containing urea) was obtained.

[0408] For board S26 (esterified binder content 4.0 wt.-% and having 1.4 wt.-% of urea):

[0409] A mixture of 6.67 g of Hydrowax 138 (60 wt.-% paraffin in water) and 37.0 g of water was sprayed onto 816 g (800 g dry weight) of spruce core layer debris (wood cellulose particles, moisture content 2.0%) within 1 min while mixing in a paddle mixer. Subsequently, a mixture of 64.0 g of the corresponding binder (having a solids content of 50 wt.-% for all binder components present for hardening via esterification) and 11.2 g of urea was sprayed onto this mixture within 1 min while mixing. After completion of spraying, mixing was continued in the mixer for 15 s, and the corresponding mixture containing wood cellulose particles and the binder (containing urea) was obtained.

[0410] For board S23 (esterified binder content 6.0 wt.-% and 2.1 wt.-% of urea):

[0411] A mixture of 6.67 g of Hydrowax 138 (60 wt.-% paraffin in water) and 23.4 g of water was sprayed onto 816 g (800 g dry weight) of spruce core layer debris (wood cellulose particles, moisture content 2.0%) within 1 min while mixing in a paddle mixer. Subsequently, a mixture of 96.0 g of the corresponding binder (having a solids content of 50 wt.-% for all binder components present for hardening via esterification) and 16.8 g of urea was sprayed onto this mixture within 1 min while mixing. After completion of spraying, mixing was continued in the mixer for 15 s, and the corresponding mixture containing wood cellulose particles and the binder (containing urea) was obtained.

[0412] Determine the pH value of the corresponding binder (according to the measurement method described above). In the examples with urea (0.8, 1.2, 1.4 or 2.1 wt.-% respectively), the pH value of the binder is determined after the addition of urea.

[0413] 6.2.b Compact the mixture:

[0414] After 30 min, 830 g of the resulting mixture comprising lignocellulosic particles and binder is dispersed into a 320 mm x 380 mm mold and pre-pressed (compacted) under ambient conditions and a pressure of 1.2 N / mm 2 to obtain a pre-pressed chip mat (compacted mixture).

[0415] 6.2.c Apply a high-frequency electric field to the mixture during and / or after compaction such that the binder is hardened via esterification and binds the lignocellulosic particles such that a single-layer lignocellulosic composite material is produced (HF pressing method):

[0416] Subsequently, the pre-pressed chip mat (compacted mixture) thus obtained is removed from the mold. To monitor the temperature at the center of the (compacted) mixture (i.e., approximately in the middle of the mat), a temperature sensor is introduced into the center of the pre-pressed chip mat. Then a non-woven separator is provided on the upper and lower sides of the pre-pressed chip mat. The pre-pressed chip mat is inserted into an HLOP 170 press from Hüfner Pressentechnik GmbH, whereby birch plywood (6 mm thick) is placed between the non-woven separator and the platen on each side of the mat. Then the pre-pressed chip mat is compacted in the press to a thickness of 10 mm within a period of 2 s and then heated by applying a high-frequency electric field (27.12 MHz) while the press remains closed. When the center reaches 160 °C or 170 °C ("HF temperature"), the press is opened.

[0417] 6.2.d After 3 days under ambient conditions, the resulting single-layer particle board (single-layer lignocellulosic composite) is sanded. 0.25 mm is sanded off on both the top and bottom sides of the single-layer particle board. After conditioning (at 65 % humidity and 20 °C) to a constant mass, the thickness, density, internal bond strength, formaldehyde emission and 24 h swelling of the resulting single-layer particle board are determined (according to the measurement methods described above).

[0418] Table 2 shows the corresponding esterified binder compositions used, the amount of esterified binder (the ratio of the weight of the solids content of all binder components present for hardening via esterification to the weight of the lignocellulosic particles in the oven-dried state), the corresponding amounts of urea (the ratio of the weight of urea to the weight of the lignocellulosic particles in the oven-dried state), the density, the internal bond strength, the 24 h swelling, and the FA emissions for the resulting 10 mm single-layer particleboards numbered S21 to S33. Board numbers S21, S24, S27, S30, and S32 are comparative examples (without urea). Table 2 also shows the pH values of the corresponding binders used.

[0419] Table 2. 10 mm single-layer particleboards S21 to S35, with paraffin emulsion (Hydrowax 138): 0.5 wt.-% amount of paraffin (mass ratio of the weight of paraffin to the weight of the lignocellulosic particles in the oven-dried state). All boards were prepared by the HF pressing method.

[0420]

[0421]

[0422] *Comparative example (without urea)

[0423] a) pH of the binder (containing urea, e.g., having urea)

[0424] b) pH value of the binder adjusted by adding NaOH

[0425] The results show that lignocellulosic composites were prepared by the method according to the invention, where the lignocellulosic composites are 10 mm single-layer particleboards (board numbers S22, S23, S25, S25, S28, S29, S31, S33, and S35). All of these boards were produced by method steps S1, S2), and S3, i.e., by providing or preparing a mixture comprising at least lignocellulosic particles and a binder; by compacting the mixture; and by applying a high-frequency electric field to the mixture during and / or after compaction such that the binder hardens via esterification and binds the lignocellulosic particles, resulting in the production of a single-layer lignocellulosic composite. All of these boards were prepared from a binder comprising the following as components: b1) one, two, or more polymers containing multiple carboxyl groups, b2) one, two, or more polymer or monomer compounds having two or more hydroxyl groups for crosslinking the polymers via esterification, and b3) urea. Board numbers 33 and 35 were prepared from a binder comprising citric acid or citric acid and lactic acid as component b4) one or more non-polymeric, preferably non-polymeric bio-based compounds having two or more carboxyl groups and / or one or more non-polymeric, preferably non-polymeric bio-based compounds having at least one carboxyl group and at least one hydroxyl group.

[0426] The results show that the lignocellulosic composites (panel numbers S22, S23, S25, S25, S28, S29, S31, S33 and S35) prepared according to the method of the present invention and with the binder according to the present invention exhibit formaldehyde emissions as low as 0.0 or 0.1 mg / m 2 h during and / or after the production of a single-layer lignocellulosic composite.

[0427] Thus, the results show that in the mixture provided or prepared in step S1) of the method, the presence of urea (as component b3) of the binder) in an amount of 0.8 to 1.4 mass-% relative to the total mass of the lignocellulosic particles in the mixture in the dried state is sufficient to minimize the formaldehyde emissions determined according to EN ISO 12460-3:2020 to as low as 0.0 or 0.1 mg / m 2 h values (see "urea amount" in panel numbers S22, S23, S25, S25, S28, S29, S31, S33 and S35).

[0428] The resulting single-layer lignocellulosic composites (panel numbers S22, S23, S25, S25, S28, S29, S31, S33 and S35) are characterized by an internal bond strength of at least 0.77 N / mm 2 determined according to DIN EN 319:1993-08.

[0429] The resulting single-layer lignocellulosic composites (panel numbers S22, S23, S25, S25, S28, S29, S31, S33 and S35) are characterized by a thickness swelling after 24 hours in water at 20 °C of less than 40% determined according to DIN EN 317:1993-08.

[0430] The results also show that a binder containing glycerol as component b2) is particularly very suitable in order to achieve those good mechanical properties as described above.

[0431] Characterized by formaldehyde emissions during and / or after the production of a single-layer lignocellulosic composite of up to 1.1 to 2.4 mg / m 2 h, the comparative example panel numbers S21, S24, S27, S30, S32 and S34 (without component b3) urea in the binder) show that the presence of the binder component b3) urea is beneficial for reducing formaldehyde emissions and for improving internal bond and swelling.

[0432] 6.3 10 mm single-layer particleboard (board numbers S36 to S41):

[0433] The panel numbers S36, S38, and S40 are comparative examples (without urea).

[0434] 6.3.a Provide or prepare a mixture comprising at least lignocellulosic particles and a binder:

[0435] For panels S36* and S38* (6.0 wt.-% esterified binder content, 0.0 wt.-% urea):

[0436] A mixture of 6.67 g of Hydrowax 138 (60 wt.-% paraffin in water) and 21.5 g of water was sprayed onto 816 g (800 g dry weight) of spruce core layer chips (lignocellulosic particles, moisture content 2.0%) within 1 min while mixing in a paddle mixer. Subsequently, 96.0 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) was sprayed onto the mixture within 1 min while mixing. After completion of spraying, mixing was continued in the mixer for 15 seconds, and the corresponding mixture containing lignocellulosic particles and the binder was obtained.

[0437] For panels S37 and S39 (6.0 wt.-% esterified binder content and 1.2 wt.-% urea):

[0438] A mixture of 6.67 g of Hydrowax 138 (60 wt.-% paraffin in water) and 22.6 g of water was sprayed onto 816 g (800 g dry weight) of spruce core layer chips (lignocellulosic particles, moisture content 2.0%) within 1 min while mixing in a paddle mixer. Subsequently, a mixture of 96.0 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) and 9.60 g of urea was sprayed onto the mixture within 1 min while mixing. After completion of spraying, mixing was continued in the mixer for 15 seconds, and the corresponding mixture containing lignocellulosic particles and the binder (containing urea) was obtained.

[0439] For panel S40* (8.0 wt.-% esterified binder content, 0.0 wt.-% urea, no paraffin):

[0440] A mixture of 128.0 g of binder 15 (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) and 85.3 g of water was sprayed onto 816 g (800 g dry weight) of spruce core layer chips (lignocellulosic particles, moisture content 2.0%) within 1 min while mixing in a paddle mixer. After completion of spraying, mixing was continued in the mixer for 15 seconds, and the corresponding mixture containing lignocellulosic particles and the binder was obtained.

[0441] For board S41 (8.0 wt.-% esterified binder content, 1.2 wt.-% urea, no paraffin):

[0442] Subsequently, a mixture of 128.0 g of binder 15 (having a solids content of 50 wt.-% of all binder components present for hardening via esterification), 9.60 g of urea, and 85.3 g of water was sprayed within 1 min onto 816 g (800 g dry weight) of spruce core layer chips (lignocellulose particles, moisture content 2.0%) while mixing in a paddle mixer. After completion of spraying, mixing in the mixer was continued for 15 seconds, and a corresponding mixture containing lignocellulose particles and binder was obtained.

[0443] The pH value of the corresponding binder was determined (according to the measurement method described above). In Examples S37 and S39 with 1.2 wt.-% urea, the pH value of the binder was determined after addition of urea. In Example S40*, the pH value of the binder was determined after addition of water. In Example S41, the pH value of the binder was determined after addition of urea and water.

[0444] 6.3.b Compact the mixture:

[0445] After 30 min, 850 g (Examples S36*, S37, S38*, and S39) or 1000 g (Examples S40* and S41) of the resulting mixture containing lignocellulose particles and binder was dispersed into a 320 mm x 380 mm mold and pre-pressed (compacted) under ambient conditions and a pressure of 1.2 N / mm 2 to obtain a pre-pressed chip mat (compacted mixture).

[0446] 6.3.c Apply a high-frequency electric field to the mixture during and / or after compaction such that the binder is hardened via esterification and binds the lignocellulosic particles such that a single-layer lignocellulosic composite material is produced (HF pressing method):

[0447] Subsequently, the pre-pressed chip mat (compacted mixture) thus obtained was removed from the mold. To monitor the temperature at the center (i.e., approximately in the middle of the mat) of the (compacted) mixture, a temperature sensor was introduced into the center of the pre-pressed chip mat. Then a nonwoven separator was provided on the upper and lower sides of the pre-pressed chip mat. The pre-pressed chip mat was inserted into an HLOP 170 press from Huffer Press Technology GmbH, whereby birch plywood (thickness 6 mm) was placed between the nonwoven separator and the platen on each side of the mat. Then the pre-pressed chip mat was compacted in the press to a thickness of 10 mm within a period of 2 s and then heated by applying a high-frequency electric field (27.12 MHz) while the press remained closed. When the center reached 200 °C (“HF temperature”), the press was opened.

[0448] 6.3.d After 3 days under ambient conditions, the resulting single-layer particleboard (single-layer lignocellulosic composite) is sanded. 0.25 mm is sanded off on both the top and bottom sides of the single-layer particleboard. After conditioning (at 65% humidity and 20 °C) to a constant mass, the thickness, density, internal bond strength, formaldehyde emission, and 24 h swelling (according to the measurement methods described above) of the resulting single-layer particleboard are determined.

[0449] Table 2a. 10 mm single-layer particleboards S36 to S41, with or without paraffin emulsion (Hydrowax 138, see above). All boards were prepared by the HF pressing method.

[0450]

[0451] * Comparative example (without urea)

[0452] a) pH of the binder (containing urea, e.g. having urea)

[0453] b) Mass ratio of the weight of paraffin to the weight of the lignocellulosic particles in the oven-dry state

[0454] c) Diluted to a concentration of 30 wt.-%

[0455] The results of Example 6.3 as shown in Table 2a indicate that in all cases the presence of urea leads to an improvement in the internal bond strength and a reduction in the 24 h swelling value, i.e. an improvement in the quality of the board is achieved when urea is present.

[0456] 7. Preparation of multi-layer lignocellulosic composite material (particleboard):

[0457] 7.1 16 mm three-layer particleboard (board numbers M1 to M15):

[0458] 7.1.a Provide or prepare first and second separate mixtures, each of which mixtures comprises at least lignocellulosic particles and a binder:

[0459] Surface layer ("SL", first separate mixture):

[0460] Surface layers of M1 - M4:

[0461] 15.0 g of water is sprayed within 1 min onto 828 g (800 g dry weight) of lignocellulosic particles of the first type, namely spruce surface layer chips (moisture content 3.5%), while mixing in a paddle mixer. Subsequently, a mixture of 96.0 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) and 40.0 g of urea is sprayed onto this mixture within 1 min while mixing, such that a first separate mixture containing lignocellulosic particles and the binder (containing urea) is obtained.

[0462] Surface layer of M5 - M15:

[0463] Spray 12.0 g of water onto 828 g (800 g dry weight) of the first type of lignocellulosic particles, namely spruce surface layer debris (moisture content 3.5%), within 1 minute while mixing in a paddle mixer. Subsequently, spray a mixture of 96.0 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) and 8.0 g of urea onto this mixture within 1 minute while mixing, so as to obtain a first separate mixture containing lignocellulosic particles and the binder (containing urea).

[0464] Core layer ("CL", second separate mixture):

[0465] Core layer of M1* and M2:

[0466] Spray 14.1 g of water onto 816 g (800 g dry weight) of the second type of lignocellulosic particles, namely spruce core layer debris (moisture content 2.0%), within 1 minute while mixing in a paddle mixer. Subsequently, spray a mixture of 109 g of Kaurit Glue347 (having a solids content of 66 wt.-%) and 5.76 g of a 50 wt.-% aqueous ammonium nitrate solution onto this mixture within 1 minute while mixing, so as to obtain a first separate mixture containing lignocellulosic particles and the binder.

[0467] Core layer of M3* and M4:

[0468] Spray 7.3 g of water onto 816 g (800 g dry weight) of the second type of lignocellulosic particles, namely spruce core layer debris (moisture content 2.0%), within 1 minute while mixing in a paddle mixer. Subsequently, spray a mixture of 96.0 g of binder 1 (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) and 40.0 g of urea onto this mixture within 1 minute while mixing, so as to obtain a first separate mixture containing lignocellulosic particles and the binder.

[0469] Core layer of M5 - M15:

[0470] Spray 4.8 g of water onto 816 g (800 g dry weight) of the second type of lignocellulosic particles, namely spruce core layer debris (moisture content 2.0%), within 1 minute while mixing in a paddle mixer. Subsequently, spray a mixture of 96.0 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) and 8.0 g of urea onto this mixture within 1 minute while mixing, so as to obtain a first separate mixture containing lignocellulosic particles and the binder.

[0471] 7.1.b Prepare three layers by dispersing the separate layers in one another, each layer comprising lignocellulosic particles and a binder:

[0472] Disperse 245 g of the first separate mixture for the surface layer, then 930 g of the second separate mixture for the core layer, and then 245 g of the first separate mixture for the surface layer into a 320 mm x 380 mm mold to obtain a three-layer pre-composite material.

[0473] 7.1.c Compact the mixture / layers such that the mixture / layers are pre-compacted to obtain a pre-compacted mat:

[0474] Pre-press the three-layer pre-composite material obtained after 7.1.b under ambient conditions and a pressure of 1.2 N / mm 2 to obtain a three-layer pre-pressed crumb mat (compacted mixture).

[0475] 7.1.d HF pressing versus hot pressing:

[0476] Subsequently, remove the three-layer pre-pressed crumb mat thus obtained from the mold and press it into a multi-layer board by a) applying a high-frequency electric field (HF pressing) or b) hot pressing, where b) is the comparative method.

[0477] a) HF pressing: Apply a high-frequency electric field to the mixture after compaction so that the binder hardens via esterification and binds the lignocellulose particles, resulting in a multi-layer lignocellulose composite material:

[0478] To monitor the temperature at the center of the (compacted) mixture (i.e., approximately in the middle of the mat), introduce a temperature sensor into the center of the mat, respectively into the horizontal holes at the center of the core. Then provide non-woven separator sheets to the upper and lower sides of the three-layer pre-pressed crumb mat. Insert the three-layer pre-pressed crumb mat into an HLOP 170 press from Herfel Press Technology GmbH, whereby birch plywood (6 mm thick) is placed between the non-woven separator sheets on each side of the mat and the pressing plates. Then compact the three-layer pre-pressed crumb mat in the press to a thickness of 16 mm within a time period of 2 s, and then heat it by applying a high-frequency electric field (27.12 MHz) while the press remains closed. When the center reaches 170 °C, open the press.

[0479] b) Hot pressing (comparative examples, plate numbers M3*, M5*, and M7*):

[0480] Provide non-woven separator sheets to the upper and lower sides of the three-layer pre-pressed crumb mat. In a laboratory hot press HLOP 350 from Herfel Press Technology GmbH, further compact the three-layer pre-pressed crumb mat to a thickness of 16 mm at a temperature of 200 °C (platen temperature). After a pressing time of 160 s, open the press (pressing time factor 10 s / mm).

[0481] 7.1.e After 3 days under ambient conditions, the resulting three-layer particleboard (multi-layer wood-based cellulose composite) is sanded. 0.20 mm is sanded off on both the top and bottom sides of the three-layer particleboard. After conditioning (at 65% humidity and 20 °C) to a constant mass, the thickness, density, internal bond strength, formaldehyde emission, 24 h swelling, surface and edge screw holding of the three-layer particleboard are determined according to the measurement methods described above.

[0482] Table 3 shows the corresponding binder compositions and amounts of esterified binder (ratio of the weight of the solids content of all binder components present for hardening via esterification to the weight of the wood-based cellulose particles in the oven-dried state) for the core layer (CL) and surface layer (SL), the corresponding amounts of urea for the core layer (CL) and surface layer (SL) (ratio of the weight of urea to the weight of the wood-based cellulose particles in the oven-dried state), the pressing method, density, internal bond strength, 24 h swelling, FA emission, surface screw holding and edge screw holding for the resulting 16 mm three-layer particleboards numbered M1 to M15. Plate numbers M1, M3 and M5 are comparative examples (hot pressing method).

[0483] Table 3. 16 mm three-layer particleboards M1 to M15, HF pressing versus hot pressing, binder amount 6.0 wt.-%, no paraffin (ratio of the weight of the solids content of all binder components present for hardening via esterification to the weight of the wood-based cellulose particles in the oven-dried state).

[0484]

[0485]

[0486] *Comparative example (hot pressing)

[0487] a) "No board" means that the resulting material after pressing is not an undamaged particleboard and shows fractures, cracks and / or bursts

[0488] b) n.q. = not quantifiable because the test sample broke into pieces within 24 h

[0489] c) Binder not according to the invention

[0490] The results show that a multilayer lignocellulosic composite material was prepared according to the method of the present invention, wherein the lignocellulosic composite material is a 16 mm three-layer particle board (board numbers M2, M4, M6 and M8 to M15). All these boards were produced by method steps S1, S2) and S3, that is, by providing or preparing a mixture comprising at least lignocellulosic particles and a binder; by compacting the mixture; and by applying a high-frequency electric field to the mixture during and / or after compaction, such that the binder is hardened via esterification and binds the lignocellulosic particles, such that a multilayer lignocellulosic composite material is produced. All these boards were prepared with a binder comprising the following as components: b1) one, two or more polymers comprising a plurality of carboxyl groups, b2) one, two or more polymer or monomer compounds having two or more hydroxyl groups in order to crosslink the polymer via esterification, and b3) urea. According to the results, the binder according to the present invention can be present in all layers of the multilayer lignocellulosic composite material (see board numbers M4, M6 and M8 to M15). The binder according to the present invention can also be present at least in the upper surface layer and the lower surface layer (see board number 2).

[0491] The results show that the lignocellulosic composite materials (board numbers M2, M4, M6 and M8 to M15) prepared according to the method of the present invention and with the binder according to the present invention show formaldehyde emissions as low as 0.0 to 0.5 mg / m 2 h during and / or after the production of multilayer lignocellulosic composite materials as determined according to EN ISO 12460-3:2020.

[0492] The results also show that it is particularly preferred that all layers of the multilayer lignocellulosic composite material, i.e., the surface layer and the core layer of the three-layer board, are prepared with the binder according to the present invention, because board numbers M4, M6 and M8 to M15 show formaldehyde emissions as low as 0.0 or 0.1 mg / m 2 h during and / or after the production of multilayer lignocellulosic composite materials as determined according to EN ISO 12460-3:2020.

[0493] The results show that the multilayer lignocellulosic composite material prepared according to the present invention can comprise more than one layer of lignocellulosic composite material, each layer comprising lignocellulosic particles and a binder, wherein the binder is the same in all layers (see board numbers M4, M6 and M8 to M13).

[0494] The results show that the multilayer lignocellulosic composite material prepared according to the present invention can comprise more than one layer of lignocellulosic composite material, each layer comprising lignocellulosic particles and a binder, wherein the binder is different in at least two layers (see board numbers M14 and M15).

[0495] Therefore, the results show that in the mixture provided or prepared in step S1) of the method, the presence of urea (component b3) of the binder) in an amount of 1 mass-% relative to the total mass of the lignocellulosic particles in the mixture in the dried state is sufficient to minimize the formaldehyde emission determined according to EN ISO 12460-3:2020 to as low as 0.0 or 0.1 mg / m 2 value of h (see "amount of urea" in plate numbers M4, M6 and M8 to M15).

[0496] The results show that in the mixture provided or prepared in step S1) of the method, the presence of urea (component b3) of the binder) in an amount of 1 mass-% relative to the total mass of the lignocellulosic particles in the mixture in the dried state is sufficient to minimize the formaldehyde emission determined according to EN ISO 12460-3:2020 to as low as 0.0 or 0.1 mg / m 2 value of h (see "amount of urea" in plate numbers M6 and M8 to M15).

[0497] The resulting multilayer lignocellulosic composite material (plate numbers M8 to M15) prepared from a binder comprising a compound selected from the group consisting of glycerol, dextrose, fructose and maltodextrin as component b2) is characterized by:

[0498] i) a thickness swelling after 24 hours in water at 20 °C of less than 50% as determined according to DIN EN 317:1993-08;

[0499] ii) an internal bond strength of at least 0.69 N / mm 2 as determined according to DIN EN 319:1993-08;

[0500] iii) a surface screw holding of ≥ 748 N as determined according to IKEA's test method: instruction manual number IOS-TM-0057, date: 2018-07-13, version number: AA-2120821-1; and

[0501] iv) and an edge screw holding of ≥ 1957 N as determined according to IKEA's test method: instruction manual number IOS-TM-0057, date: 2018-07-13, version number: AA-2120821-1.

[0502] These extremely good mechanical properties of the multilayer lignocellulosic composite material (plate numbers M8 to M15) confirm that it is particularly preferred that component b2) of the binder comprises a compound selected from the group consisting of glycerol, dextrose, fructose and maltodextrin.

[0503] The comparative example board numbers M1*, M3*, M5* and M7* (the materials obtained after pressing are not undamaged particle boards and show fractures, cracks and / or bursts) show that applying a high-frequency electric field to the mixture during and / or after compaction such that the binder hardens via esterification and binds the lignocellulose particles is advantageous compared to conventional hot pressing.

[0504] 7.2 19 mm three-layer particleboard (board numbers M16 to M19):

[0505] 7.2.a Provide or prepare first and second separate mixtures, each of which mixtures comprises at least lignocellulosic particles and a binder:

[0506] Surface layer ("SL", first separate mixture):

[0507] Surface layer of M16* and M18*:

[0508] 6.66 g of Hydrowax 138 (60 wt.-% paraffin in water) and 26.0 g of water were sprayed onto 813 g (800 g dry weight) of the first type of lignocellulose particles, namely industrial surface layer debris (moisture content 1.6%), within 1 min while mixing in a paddle mixer. Subsequently, 96.0 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) was sprayed onto the mixture within 1 min while mixing, such that a first separate mixture comprising lignocellulose particles and binder was obtained.

[0509] Surface layer of M17 and M19:

[0510] 6.66 g of Hydrowax 138 (60 wt.-% paraffin in water) and 27.0 g of water were sprayed onto 813 g (800 g dry weight) of the first type of lignocellulose particles, namely industrial surface layer debris (moisture content 1.6%), within 1 min while mixing in a paddle mixer. Subsequently, a mixture of 96.0 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) and 8.80 g of urea was sprayed onto the mixture within 1 min while mixing, such that a first separate mixture comprising lignocellulose particles and binder was obtained.

[0511] Determine the pH value (according to the measurement method described above) of the corresponding binder (for M17 and M19, containing urea).

[0512] Core layer ("CL", second separate mixture):

[0513] Core layer of M16* and M18*:

[0514] 8.00 g of Hydrowax 138 (60 wt.-% paraffin in water) and 24.0 g of water were sprayed onto 983 g (960 g dry weight) of the first type of lignocellulosic particles, namely industrial core layer debris (moisture content 2.4%), within 1 min while mixing in a paddle mixer. Subsequently, 115 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) was sprayed onto the mixture within 1 min while mixing, such that a first separate mixture comprising the lignocellulosic particles and the binder was obtained.

[0515] Core layer of M17 and M19:

[0516] 8.00 g of Hydrowax 138 (60 wt.-% paraffin in water) and 25.2 g of water were sprayed onto 983 g (960 g dry weight) of the first type of lignocellulosic particles, namely industrial core layer debris (moisture content 2.4%), within 1 min while mixing in a paddle mixer. Subsequently, a mixture of 115 g of the corresponding binder (having a solids content of 50 wt.-% of all binder components present for hardening via esterification) and 10.6 g of urea was sprayed onto the mixture within 1 min while mixing, such that a first separate mixture comprising the lignocellulosic particles and the binder was obtained.

[0517] The pH value of the corresponding binder (for M17 and M19, containing urea) was determined (according to the measurement method described above).

[0518] 7.2.b Prepare three layers by dispersing the separate layers in one another, each layer comprising lignocellulosic particles and a binder:

[0519] 269 g of the first separate mixture for the surface layer, subsequently 1043 g of the second separate mixture for the core layer, and subsequently 269 g of the first separate mixture for the surface layer were dispersed into a 320 mm x 380 mm mold to obtain a three-layer pre-composite material.

[0520] 7.2.c Compact the mixture / layers such that the mixture / layers are pre-compacted to obtain a pre-compacted mat:

[0521] The three-layer pre-composite material obtained after 7.2.b was pre-pressed under ambient conditions and a pressure of 1.2 N / mm 2 to obtain a three-layer pre-pressed debris mat (compacted mixture).

[0522] 7.2.d Apply a high-frequency electric field to the mixture after compaction such that the binder is hardened via esterification and binds the lignocellulosic particles such that a multi-layer lignocellulosic composite material is produced (HF pressing method):

[0523] Subsequently, the three-layer pre-pressed chip mat thus obtained is removed from the mold and pressed into a multi-layer board by applying a high-frequency electric field (HF pressing). To monitor the temperature at the center of the (compacted) mixture (i.e., approximately in the middle of the mat), temperature sensors are introduced into the center of the mat, respectively into the horizontal holes at the center of the core. Then non-woven separators are provided on the upper and lower sides of the three-layer pre-pressed chip mat. The three-layer pre-pressed chip mat is inserted into an HLOP 170 press from Hefel Press Technology GmbH, whereby birch plywood (6 mm thick) is placed between the non-woven separator and the pressing plate on each side of the mat. Then the three-layer pre-pressed chip mat is compacted in the press to a thickness of 19 mm within a period of 2 s, and then heated by applying a high-frequency electric field (27.12 MHz) while the press remains closed. When the center reaches 160 °C, the press is opened.

[0524] 7.2.e After 3 days under ambient conditions, the resulting three-layer particle board (multi-layer wood cellulose composite) is sanded. 0.20 mm is sanded off on both the top and bottom sides of the three-layer particle board. After conditioning (at 65% humidity and 20 °C) to a constant mass, the thickness, density, internal bond strength, formaldehyde emission, and 24 h swelling of the three-layer particle board are determined according to the measurement methods described above.

[0525] Table 4 shows the corresponding binder compositions and amounts of esterified binder (ratio of the weight of the solid content of all binder components present for hardening via esterification to the weight of the wood cellulose particles in the oven-dried state) for the core layer (CL) and surface layer (SL), the corresponding amounts of urea for the core layer (CL) and surface layer (SL) (ratio of the weight of urea to the weight of the wood cellulose particles in the oven-dried state), the pH value of the binder, density, internal bond strength, 24 h swelling, and FA emission for the resulting 19 mm three-layer particle boards numbered M16 to M19. Board numbers M16 and M18 are comparative examples (without urea).

[0526] Table 4. 19 mm three-layer particle boards M16 to M19, without paraffin, amount of esterified binder 6.0 wt.-% in all layers (ratio of the weight of the solid content of all binder components present for hardening via esterification to the weight of the wood cellulose particles in the oven-dried state). All boards are prepared by the HF pressing method (HF temperature 160 °C).

[0527]

[0528] *Comparative example (without urea)

[0529] a) pH of the binder (containing urea, e.g., having urea)

[0530] The results show that a multilayer lignocellulosic composite material was prepared according to the method of the present invention, wherein the lignocellulosic composite material is a 19 mm three-layer particleboard (board numbers M17 and M19).

[0531] Board numbers M17 and M19 were produced by method steps S1, S2) and S3), namely by providing or preparing a mixture comprising at least lignocellulosic particles and a binder; by compacting the mixture; and by applying a high-frequency electric field to the mixture during and / or after compaction such that the binder hardens via esterification and binds the lignocellulosic particles, such that a multilayer lignocellulosic composite material is produced.

[0532] Board numbers M17 and M19 were prepared with a binder comprising the following as components: b1) one, two or more polymers comprising a plurality of carboxyl groups, b2) one, two or more polymeric or monomeric compounds having two or more hydroxyl groups in order to crosslink the polymers via esterification, and b3) urea.

[0533] Board M19 was prepared with a binder comprising citric acid as component b4) one or more non-polymeric, preferably non-polymeric bio-based compounds having two or more carboxyl groups and / or one or more non-polymeric, preferably non-polymeric bio-based compounds having at least one carboxyl group and at least one hydroxyl group.

[0534] The results show that the lignocellulosic composite materials (board numbers M17 and M19) prepared according to the method of the present invention and with the binder according to the present invention show formaldehyde emissions as low as 0.0 or 0.1 mg / m 2 h during and / or after the production of the multilayer lignocellulosic composite material as determined according to EN ISO 12460-3:2020.

[0535] Thus, the results show that in the mixture provided or prepared in step S1) of the method, the presence of urea (as component b3) of the binder) in an amount of 1.1 mass-% relative to the total mass of the lignocellulosic particles in the mixture in the oven-dried state is sufficient to minimize formaldehyde emissions as determined according to EN ISO 12460-3:2020 to a value as low as 0.0 or 0.1 mg / m 2 h (see "amount of urea" in board numbers M17 and M19).

[0536] The resulting multilayer lignocellulosic composite materials (board numbers M17 and M19) prepared according to the method of the present invention and with the binder according to the present invention are characterized by a thickness swelling after 24 hours in water at 20 °C of less than 60% as determined according to DIN EN 317:1993-08; and at least 0.39 N / mm as determined according to DIN EN 319:1993-082 Internal bond strength.

[0537] Characterized by a comparison example board numbers M16* and M18* (without component b3) urea in the binder) of formaldehyde emissions during and / or after the production of single-layer lignocellulosic composites with up to 1.0 or 1.4 mg / m 2 h, indicating that the presence of binder component b3) urea is beneficial for reducing formaldehyde emissions.

Claims

1. A method for producing a multi-layered lignocellulosic composite material comprising two, three or more lignocellulosic composite material layers or a single-layer lignocellulosic composite material and comprising at least the following steps: S1) Providing or preparing a mixture comprising at least the following - lignocellulosic particles, and - a binder comprising at least the following as components: b1) One, two or more polymers comprising a plurality of carboxyl groups, b2) For crosslinking the polymer via esterification, one, two or more polymers or monomeric compounds having two or more hydroxyl groups, and b3) Urea, S2) Compacting the mixture, S3) Applying a high-frequency electric field to the mixture during and / or after compaction such that the binder hardens via esterification and binds the lignocellulosic particles, resulting in a single-layer lignocellulosic composite material or a layer of a multi-layered lignocellulosic composite material.

2. The method according to claim 1, wherein at least one of the one polymer or monomeric compound having two or more hydroxyl groups or the two or more polymers or monomeric compounds having two or more hydroxyl groups of component b2) is selected from the group consisting of: ■ Carbohydrates, preferably selected from the group consisting of monosaccharides, disaccharides, oligosaccharides, polysaccharides and starches, more preferably selected from the group consisting of dextrose, fructose, sucrose, non-hydrolyzed starch, hydrolyzed starch and partially hydrolyzed starch, the latter preferably including maltodextrin and / or corn syrup, more preferably selected from the group consisting of maltodextrin and corn syrup; ■ Polyvinyl alcohol, glycerol and sugar alcohols, the latter preferably selected from the group consisting of mannitol, sorbitol, xylitol, lactitol, isomaltitol, maltitol, erythritol and hydrogenated starch hydrolysates; preferably glycerol; and ■ Compounds selected from the group consisting of triols, preferably triethanolamine, tetraols, pentaols and hexaols, wherein the selected compound is not a carbohydrate, not a sugar alcohol, and not an alkylamine.

3. The method according to any one of the preceding claims, wherein the binder comprises the following as additional binder components, preferably for hardening the binder via esterification: b4) One or more non-polymeric, preferably non-polymeric bio-based compounds having two or more carboxyl groups and / or one or more non-polymeric, preferably non-polymeric bio-based compounds having at least one carboxyl group and at least one hydroxyl group, wherein preferably - at least one of the one non-polymeric, preferably non-polymeric bio-based compound having two or more carboxyl groups or the more than one non-polymeric, preferably non-polymeric bio-based compounds having two or more carboxyl groups is selected from the group consisting of hydroxycarboxylic acids, preferably selected from the group consisting of α-hydroxycarboxylic acids, more preferably selected from the group consisting of citric acid, malic acid and tartaric acid, and most preferably citric acid; and / or - At least one non-polymeric, preferably non-polymeric bio-based compound having at least one carboxyl group and at least one hydroxyl group, or at least one of more than one non-polymeric, preferably non-polymeric bio-based compound having at least one carboxyl group and at least one hydroxyl group is selected from the group consisting of monohydroxy-monocarboxylic acids, preferably selected from the group consisting of α-hydroxy monohydroxy-monocarboxylic acids, more preferably selected from the group consisting of lactic acid, glycolic acid and mandelic acid, and most preferably is lactic acid.

4. The method according to any one of the preceding claims, wherein, - At least one of the polymeric or monomeric compound having two or more hydroxyl groups or the two or more polymeric or monomeric compounds having two or more hydroxyl groups of component b2) is a bio-based polymer or bio-based monomeric compound having two or more hydroxyl groups, and / or - The total amount of the one, two or more polymeric or monomeric compounds of component b2), preferably the total amount of the one, two or more bio-based polymers or bio-based monomeric compounds, is higher than 5 mass-%, more preferably higher than 10 mass-%, and even more preferably higher than 15 mass-% relative to the combined total mass of binder components b1), b2) and any component b4) present, and lower than 90 mass-%, more preferably lower than 80 mass-%, and even more preferably lower than 60 mass-%.

5. The method according to any one of the preceding claims, wherein, At least one of the polymeric compound containing a plurality of carboxyl groups or the two or more polymeric compounds containing a plurality of carboxyl groups of component b1) is selected from the group consisting of: - Polymers of one or more unsaturated carboxylic acids, preferably acrylic acid, and mixtures thereof, preferably copolymers of acrylic acid, and more preferably copolymers of acrylic acid and maleic anhydride and / or maleic acid; and - Bio-based polyesters having two or more carboxyl groups, wherein preferably one, two or more of the polyesters, preferably bio-based polyesters, are prepared by reacting: ■ One or more α-hydroxycarboxylic acids, preferably citric acid, and ■ One, two or more compounds selected from the group consisting of: ● Carbohydrates, which are preferably selected from the group consisting of monosaccharides, disaccharides, oligosaccharides, polysaccharides and starches, more preferably selected from the group consisting of dextrose, fructose, sucrose, non-hydrolyzed starch, hydrolyzed starch and partially hydrolyzed starch, the latter preferably including maltodextrin and / or corn syrup, more preferably selected from the group consisting of maltodextrin and corn syrup; ● Sugar alcohols, which are preferably selected from the group consisting of mannitol, sorbitol, xylitol, lactitol, isomaltitol, maltitol, erythritol, hydrogenated starch hydrolysate and glycerol, more preferably glycerol, and ● Compounds selected from the group consisting of triols, preferably triethanolamine, tetraols, pentaols and hexaols, which are not carbohydrates, not sugar alcohols, and not alkylamines, preferably glycerol.

6. The method according to any one of the preceding claims, wherein, The binder contains at least the following as components: (b1) One, two or more polymers containing multiple carboxyl groups, selected from the group consisting of polymers of one or more unsaturated carboxylic acids, preferably acrylic acid, and mixtures thereof, preferably copolymers of acrylic acid and more preferably copolymers of acrylic acid and maleic anhydride and / or maleic acid, and (b2) One, two or more polymer or monomer compounds having two or more hydroxyl groups for crosslinking the polymer via esterification, wherein at least glycerol is present, wherein the ratio of the total mass of the polymer of component (b1) to the total mass of glycerol present is in the range of 80:20 to 50:50, and wherein preferably, the binder contains component b4) as defined in claim 3 as an additional binder component, preferably for hardening the binder via esterification, wherein preferably, the total amount of the additional binder component b4) is 30 mass-% or less relative to the combined total mass of binder components b1), b2) and component b4), more preferably in the range of 5 mass-% to 30 mass-%.

7. The method according to any one of the preceding claims, wherein, - the binder in step S1) of the method contains water and has a pH in the range of 1.0 to 3.5, preferably in the range of 1.0 to 3.0, more preferably 1.0 to 2.5, and / or - the aqueous extract prepared from the mixture prepared or provided in step S1) of the method according to the extraction method defined in the specification has a pH in the range of 1.0 to 6.0, preferably in the range of 2.0 to 5.0, more preferably 2.5 to 4.

5.

8. The method according to any one of the preceding claims, wherein, - component b3) urea of the binder is present in a total amount in the range of ≥5 to ≤50 mass-%, preferably ≥10 to ≤35 mass-%, and more preferably ≥15 to ≤35 mass-% relative to the combined total mass of binder components b1), b2) and any component b4) present, and / or - in the mixture provided or prepared in step S1) of the method, component b3) urea of the binder is present in a total amount in the range of ≥0.25 to ≤2.5 mass-%, preferably ≥0.5 to ≤1.75 mass-%, and more preferably ≥0.75 to ≤1.75 mass-% relative to the total mass of these lignocellulosic particles in the mixture in the dried state, and / or - in the mixture provided or prepared in step S1) of the method, the total combined amount of components b1), b2) and any component b4) present is in the range of 3 to 8 mass-%, preferably 3.5 to 7.5 mass-%, and more preferably 4 to 6.5 mass-% relative to the total mass of these lignocellulosic particles in the mixture in the dried state.

9. The method according to any one of the preceding claims, wherein, the mixture prepared or provided in step S1) of the method contains one or more water repellents as one or more additional ingredients, the water repellents selected from the group consisting of paraffin and mixtures containing paraffin, preferably paraffin emulsion, Preferably, - the ratio of the total mass of the paraffin wax to the total mass of these lignocellulosic particles in the dried state in the mixture is in the range of 0.2% to 1.5%, and / or - the ratio of the total mass of the paraffin wax to the total mass of all binder components b1) to b4) present in the mixture is in the range of 2% to 40%, preferably in the range of 5% to 30% and more preferably in the range of 7.5% to 20%.

10. The method according to any one of the preceding claims, wherein, - the lignocellulosic composite material is a lignocellulosic board selected from the group consisting of ■ High - density fiberboard (HDF) ■ Medium - density fiberboard (MDF) ■ Low - density fiberboard (LDF) ■ Wood fiber insulation board ■ Oriented strand board (OSB) ■ Particle board, and ■ Natural fiber board, which preferably has fibers selected from the group consisting of sisal, jute, flax, coconut, kenaf, hemp, banana and mixtures thereof, wherein the lignocellulosic board is ■ A single - layer lignocellulosic board, preferably a single - layer lignocellulosic fiber board, having a thickness in the range of 1 to 15 mm, preferably 2 to 12 mm, more preferably 2 to 4 mm, or ■ A multi - layer lignocellulosic board, preferably a multi - layer lignocellulosic board having a core layer and upper and lower surface layers, preferably consisting of the core layer and the upper and lower surface layers, more preferably a multi - layer lignocellulosic particle board having a core layer and upper and lower surface layers, having a total thickness in the range of 14 to 25 mm, and / or - The lignocellulosic composite material is a panel having a core, wherein in a cross-section oriented perpendicular to the plane of the panel, the difference between the maximum density of the panel and the minimum density in the core of the panel is at most 100 kg / m 3 ; and / or - in step S3) of applying the high - frequency electric field, the temperature at the center of the mixture is raised to a maximum temperature in the range of 130°C to 200°C, preferably in the range of 140°C to 180°C, wherein preferably, the maximum temperature is reached in less than 40 s·(d / mm) after the start of applying the high - frequency electric field, where d is the thickness of the compacted mixture at the end of step S3), in mm, and / or - wherein at least steps S2) and S3), more preferably steps S1), S2) and S3) are semi - continuous or continuous method steps, wherein preferably, step S3) is carried out in a dielectric heating and pressing unit, and wherein most preferably, the method of producing a multi - layer lignocellulosic composite material or a single - layer lignocellulosic composite material comprising two, three or more lignocellulosic composite material layers is a semi - continuous or continuous method.

11. The method according to any one of the preceding claims, wherein, the method of producing a multi - layer lignocellulosic composite material or a single - layer lignocellulosic composite material comprising two, three or more lignocellulosic composite material layers comprises one, two, three, more than three, or all of the following steps, which are preferably carried out semi - continuously or continuously: - In step S1) for preparing the mixture, the lignocellulosic particles are blended with one or more or all components of the binder or one or more or all components of the binder are sprayed onto the lignocellulosic particles, wherein before blending or spraying, the components of the binder are premixed or not premixed, - Prepare, preferably by dispersion, a layer of the mixture provided or prepared in step S1), and compact the layer in step S2), - For preparing a multi-layer lignocellulosic composite comprising more than one lignocellulosic composite layer, provide or prepare at least a first separate mixture and a second separate mixture, and use the first separate mixture and the second separate mixture for manufacturing the first layer and the second layer of the multi-layer lignocellulosic composite, wherein the first layer and the second layer preferably contact each other, and / or wherein the first separate mixture and the second separate mixture have the same or different compositions, - For preparing a multi-layer lignocellulosic composite comprising more than one lignocellulosic composite layer, prepare two or more layers, preferably by dispersing the separate layers on one another, each layer comprising lignocellulosic particles and a binder, wherein in the two or more layers, the lignocellulosic particles and / or the binders are the same or different, - In step S2), the mixture is compacted in two stages, wherein in the first stage the mixture is pre-compacted to obtain a pre-compacted mat, and wherein in the second stage the pre-compacted mat is further compacted, - During or after compaction in step S2), the mixture is hot-pressed, - During or after applying a high-frequency electric field in step S3), the mixture is hot-pressed, and - In step S3) of applying a high-frequency electric field, monitor and / or control the temperature at the center of the mixture.

12. The method according to any one of claims 1 to 11, wherein, A1) the mixture provided or prepared in step S1) does not contain a co-binder selected from the group consisting of (a1) formaldehyde resins and (a2) organic isocyanates having at least two isocyanate groups, and / or A2) the lignocellulosic composite produced in step S3) (i) does not contain a fully or partially cured co-binder selected from the group consisting of (a1) formaldehyde resins and (a2) organic isocyanates having at least two isocyanate groups in the core layer of the multi-layer lignocellulosic composite or in the single layer of the single-layer lignocellulosic composite, or (ii) does not contain a fully or partially cured co-binder selected from the group consisting of (a1) formaldehyde resins and (a2) organic isocyanates having at least two isocyanate groups in the multi-layer or single-layer lignocellulosic composite, or (iii) does not contain a fully or partially cured co-binder containing (a1) formaldehyde resin or (a2) organic isocyanate in the multi-layer or single-layer lignocellulosic composite.

13. A binder composition for producing a lignocellulosic composite material, preferably for producing a lignocellulosic composite material as defined in claims 1 to 12, the binder composition comprising at least the following as components: b1) one, two or more polymers containing a plurality of carboxyl groups, b2) one, two or more polymers or monomeric compounds having two or more hydroxyl groups, and b3) urea.

14. The binder composition according to claim 13, wherein at least one of the one polymer or monomeric compound having two or more hydroxyl groups or the two or more polymers or monomeric compounds having two or more hydroxyl groups of component b2) is selected from the group consisting of: ■ Carbohydrates, which are preferably selected from the group consisting of monosaccharides, disaccharides, oligosaccharides, polysaccharides and starches, more preferably selected from the group consisting of dextrose, fructose, sucrose, non-hydrolyzed starch, hydrolyzed starch and partially hydrolyzed starch, the latter preferably including maltodextrin and / or corn syrup, more preferably selected from the group consisting of maltodextrin and corn syrup; ■ Glycerol, polyvinyl alcohol and sugar alcohols, the latter preferably selected from the group consisting of mannitol, sorbitol, xylitol, lactitol, isomaltitol, maltitol, erythritol and hydrogenated starch hydrolysates; preferably glycerol; and ■ Compounds selected from the group consisting of triols, preferably triethanolamine, tetraols, pentaols and hexaols, wherein the selected compound is not a carbohydrate, not a sugar alcohol, and not an alkylamine.

15. The binder composition according to any one of claims 13 to 14, wherein - the binder composition contains water and has a pH value in the range of 1.0 to 3.5, preferably in the range of 1.0 to 3.0, more preferably 1.0 to 2.5; and / or - the binder composition contains the following as additional binder components: b4) one or more non-polymeric compounds having two or more carboxyl groups and / or one or more non-polymeric compounds having at least one carboxyl group and at least one hydroxyl group, as defined in claim 3; and / or - the urea of component b3) of the binder is present in a total amount in the range of ≥ 5 to ≤ 50 mass-% relative to the combined total mass of components b1), b2) and any present component b4) of the binder, preferably in the range of ≥ 10 to ≤ 35 mass-% and more preferably in the range of ≥ 15 to ≤ 35 mass-%.

16. A single-layer or multi-layer lignocellulosic composite material obtainable or obtained by a method as defined in any one of claims 1 to 12, or a building product comprising such a single-layer or multi-layer lignocellulosic composite material.

17. A product comprising the lignocellulosic composite material according to claim 16, wherein the product comprises or is - A lignocellulosic board having a core, wherein in a cross-section oriented perpendicular to the plane of the board, the difference between the maximum density of the board and the minimum density in the core of the board is at most 100 kg / m 3 ; and / or - a lignocellulosic board selected from the group consisting of particle board, high-density fiberboard (HDF), medium-density fiberboard (MDF) and oriented strand board (OSB), and / or - a lignocellulosic board having a thickness in the range of 1 to 30 mm, preferably in the range of 2 to 25 mm, and / or - A single-layer wood-based cellulose fiberboard having a thickness in the range of 1 to 15 mm, preferably 2 to 12 mm, more preferably 2 to 4 mm, and / or - A multi-layer wood-based cellulose particleboard having a core layer and an upper surface layer and a lower surface layer, having a total thickness in the range of 14 to 25 mm, wherein the multi-layer wood-based cellulose particleboard preferably consists of the core layer and the upper surface layer and the lower surface layer, and / or - a lignocellulosic board having an internal bond strength of at least 0.4 N / mm² determined according to DIN EN 319:1993-08 2 , preferably at least 0.5 N / mm² 2 , more preferably at least 0.6 N / mm² 2 ​ and / or - A wood-based cellulose board having a thickness swelling after 24 hours in water at 20°C of less than 50%, preferably less than 45%, more preferably less than 40% as determined according to DIN EN 317:1993-08, and / or - A wood-based cellulose board comprising one or more layers of wood-based cellulose composite material, wherein preferably all the wood-based cellulose composites comprised by the wood-based cellulose board are the wood-based cellulose composites according to claim 16 and / or - A multi-layer wood-based cellulose board having a core layer and an upper surface layer and a lower surface layer, wherein at least the core layer contains the mixture according to step S1), preferably all layers contain the mixture according to step S1), wherein the multi-layer wood-based cellulose board preferably consists of the core layer and the upper surface layer and the lower surface layer.

18. Use of the wood-based cellulose composite material as defined in any one of claims 16 to 17 as a building element in a building product, preferably as a building element in furniture or furniture parts, more preferably as a building element in a hollow structure in furniture or furniture parts.

19. A kit for producing a binder composition for use in the production of wood-based cellulose composites, the kit comprising at least the following as separate components: b1) One, two or more polymers containing a plurality of carboxyl groups, as defined in any one of claims 1, 5 or 6, b2) One, two or more polymers or monomeric compounds having two or more hydroxyl groups for crosslinking the polymer via esterification, as defined in any one of claims 1, 2 or 6, and b3) Urea, and preferably further comprises the following as additional binder components: b4) One or more non-polymeric, preferably non-polymeric bio-based compounds having two or more carboxyl groups and / or one or more non-polymeric, preferably non-polymeric bio-based compounds having at least one carboxyl group and at least one hydroxyl group, wherein at least one, two or more of the separate components b1), b2), b3), and optionally b4) of the kit are spatially separated from the other separate components.

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