EP2607032B1 - Method of reducing the emissions of fleeting organic compounds in wooden materials and wooden material - Google Patents

Description

The present application relates to the use of additives in processes for the production of wood materials from lignocellulose, in particular for the production of chipboard, fiberboard or OSB boards, these wood materials to avoid or reduce the emission of volatile organic compounds and possibly very volatile organic compounds, especially terpenes and acids, are treated with the additives during manufacture. These additives are amidines and borates. Accordingly, the present application is directed to the use of amidines and borates as additives in the production of wood materials from lignocellulose to reduce the emission of VOC and possibly VVOC, in particular to reduce the emission of terpenes and acids.

State of the art

Lignocellulose or lignocellulose-containing materials, such as wood and wood comminution products, and wood-based materials produced therefrom, such as wood-based panels, contain, among other things, volatile organic compounds (VOC) and very volatile organic compounds (VVOC). The emission of these VOC and VVOC, also referred to as the total amount of volatile compounds (TVOC), from the wood-based materials (HWS) poses a serious problem in view of the increasing use of wood-like products indoors. In addition to saturated and unsaturated aldehydes all volatile organic substances whose retention time in the glass chromatograph is between C ₆ (hexane) and C ₁₆ (hexadecane). The VOC are not a homogeneous class of substances, but a smorgasbord of compounds. Among others, this includes organic acids, saturated and unsaturated aldehydes, e.g. B. pentanal, hexanal etc., alcohols, Terpenes, aliphatic and aromatic hydrocarbons and much more. There are also the very volatile organic compounds (VVOC), which include z. B. formaldehyde or formic acid. These VVOCs, such as formaldehyde or formic acid, also occur in the manufacture but also in the use of wood-based materials. On the one hand, these connections can occur during curing from the adhesives. On the other hand, these compounds can occur through the reaction of compounds present in the wood material. The emission of these volatile and very volatile wood constituents or constituents of the adhesives from wood products including wood-based panels is more and more of a problem due to stricter limit values or greater awareness among end users.

The volatile organic compounds and very volatile organic compounds come depending on the type and condition of the lignocelluloses; such as the type of wood, the duration of storage, the storage conditions of the wood or the comminution products of the wood, in different chemical compositions and amounts. The VOC originate essentially from extract substances from lignocelluloses, e.g. B. the wood or conversion products thereof. Prominent representatives of this are substances such as alpha-pinene, beta-pinene, delta-3-carene. These components can be found especially in wooden conifers. Conversion products, e.g. B. occur during storage and processing of the wood and crushing products, z. B. aldehydes such as pentanal and hexanal. Especially conifers, from which mainly particle board, medium density fibreboard (MDF) or OSB board are made, contain large amounts of resins and fats, which lead to the formation of volatile organic terpene compounds and aldehydes. Some of these substances also result from the breakdown of the main components of the wood, such as lignin, cellulose and hemicellulose. TVOC with VOCs including aldehydes but also VVOC including formaldehyde can also arise when using certain adhesives to manufacture the wood-based material. Usually there is an oxidation process of the wood constituents, such as the fatty acids, which then lead to the secondary or tertiary emissions of higher aldehydes, such as pentanal, or higher carboxylic acids, but also terpenes.

The VOC emissions are almost exclusively wood-related releases, which are composed of the so-called primary emissions of volatile wood constituents, such as terpenes, or chemical degradation products, such as acetic acid, and so-called secondary or tertiary emissions, as listed above. Due to the constant emission of conversion products, e.g. B. by fragmentation of the resins and fats, there is a constant secondary or tertiary emission of the compounds mentioned. So z. B. especially with OSB panels in the construction area, this release is of great disadvantage, since in this application the OSB panels have no emission-reducing coating and are installed in large quantities, in particular as the area of the panel, based on the total number of cubic meters of the room or of the building becomes.

Similar problems with the emission of volatile organic compounds and possibly very volatile organic compounds can occur when using lightweight wood-based materials, lightweight and super-light MDF for thermal insulation. Emissions of secondary and tertiary substances also occur here.

The adhesives currently used in the manufacture of wood-based materials, such as OSB boards, medium-density fiberboard, etc. include aminoplast adhesives, such as urea-formaldehyde adhesives (UF adhesives), melamine-urea-phenol-formaldehyde Adhesives (MUPF adhesives) or melamine-urea-formaldehyde adhesive (MUF adhesives). Further adhesives, as are typically used in wood-based materials, include adhesives based on diisocyanates (PMDI), polyurethane adhesives (PU adhesives), phenol-formaldehyde adhesives (PF adhesives) and / or tannin-formaldehyde adhesives (TF adhesives) or mixtures thereof. In the fiberboard area find z. B. mainly aminoplast adhesives use. The release of VOCs and VVOCs takes place both during the manufacture of the wood-based materials as well as after their manufacture or during their use. In fiberboard production, it can e.g. B. come in the thermomechanical treatment of lignocellulosic materials to a chemical degradation of the wood. The resulting VOC and VVOC, such as aldehydes and acids or terpenes, then emit during the manufacturing process or when the manufactured wood-based materials are used later. They can also have a negative impact on the bond strength and thus negatively affect the properties of the wood-based materials produced.

Various approaches have already been taken to limit these problems of emission of volatile organic compounds and very volatile organic compounds. So is from the DE 10 2007 038 041 A1 a method for avoiding the emission of aldehydes and volatile organic compounds from wood materials is known in which sulfite or bisulfite salts are used as additives, if appropriate in conjunction with urea or urea derivatives and if appropriate in conjunction with alkali metal, alkaline earth metal or ammonium hydroxides.

In the EP 1 852 231 the use of various additives is proposed. There, inter alia, the use of maleic anhydride or similar compounds is provided. The use of reducing or oxidizing agents is also known. Furthermore, an increase in the pH is proposed, e.g. B. by adding alkali metal hydroxides.

From the WO 2006/032267 Processes for the reduction of unsaturated aldehydes in fatty acid-containing woods are known. The fatty acid ester contained in the wood is split, inhibited or oxidized. This generally involves the use of antioxidants, alkaline compounds or oxidizing agents proposed. Of Ozalp, M., Eur. J. Wood Prod. 2011, 69, 369 to 374 , the addition of polyethylene terephthalate (PET) powder as a waste product from PET bottles in combination with borax pentahydrate in equal quantities to UF adhesives is described and the mechanical properties of particleboard produced in this way are examined. It was found, among other things, that this mixture allows a reduction in the free formaldehyde content.

DE3427694A1 discloses the use of guanidine salts as formaldehyde binding agents in the chipboard materials.

However, none of the described methods of the prior art allows a desired reduction in TVOC, namely VOC and possibly VVOC from wood materials, in particular when used for a long time. There is therefore still a need for processes to reduce the emission of VOC but also VVOC, in particular terpenes and acids, such as compounds which are released as degradation products of fatty acids from the wood-based materials as secondary or tertiary emissions.

The present invention is therefore based on the object of providing wood-based materials made of lignocellulose, in particular chipboard, fibreboard or OSB board but also plywood board, which improve the reduction or avoidance of emissions of volatile organic compounds (VOC) and preferably also very volatile organic compounds ( VVOC). The emission of the VOC but also the VVOC should be significantly reduced both during manufacture and in later use. The additives used themselves should not show any toxic properties and should not negatively influence the manufacturing process itself. Furthermore, the manufacturing costs of the wood-based materials themselves must not be significantly increased. However, the agents or additives used should be reacted as extensively as possible with the heterogeneous classes of volatile organic compounds and also the very volatile organic compounds or should prevent the formation of these from constituents of the wood-based materials.

Description of the invention

The object of the present invention is achieved in that when used according to the invention in a process for the production of wood materials from lignocellulose, in particular for the production of chipboard, fiberboard or OSB board, amidine and borate are added as additives at certain points in time. These additives I and II are an amidine and borate.

In other words, in a first aspect, the present application is directed to the use of additives in a method for producing wood-based materials from lignocellulose according to claim 1.

Unless stated otherwise, the terms "comprise" and "contain" also include embodiments which "consist" of them.

It is now surprisingly found that the additives of the amidines (additive I) and borates (additive II) are the previously neglected substance classes of the terpenes and acids in the VOC and the VVOC, hereinafter also generally referred to as TVOC (all volatile organic compounds, total volatile organic compounds), reduce significantly. In particular, it could be shown that e.g. B. acetic acid as a volatile component, which also smells bad, can be significantly reduced in emissions by adding the additives of the invention.

In contrast to most of the previously used methods, not only chemical modifications of the emitting TVOC, ie. H. of VOCs and VVOCs, but above all an implementation or a breakdown of the raw materials in the wood-based material. That is, the additives used according to the invention prevent degradation of the fatty acids or the fatty acid esters. Furthermore, aldehydes and other volatile compounds, such as terpenes and acids, which may be formed by conversion reactions, are converted into corresponding non-emitting compounds.

The compounds obtained by the reaction are such that they are no longer volatile and therefore no longer contribute to TVOC emissions, or the toxicity of the compounds formed is significantly reduced. As a result, the emission is also after production, i. H. in daily use, significantly reduced.

The term “amidine” is understood to mean compounds which have a —C (= NH) —NH ₂ group. The corresponding amidinium salts also fall under the expression.

The amidine is preferably one of the general formula RC (= NH) -NH ₂ , where R is an amine group. That is, the amidine guanidine is preferred. The radical R in the general formula of the amidine is likewise preferably a C1-C8 alkyl radical (for example a C1 radical, namely an acetamidine, a C2-, C3-, C4-, C5-, C6- , C7 or C8 residue). The amidines are particularly stable in the salt form. Therefore, in one embodiment, the use of an amidinium salt, in particular guanidinium salt of the general formula [RC (= NH) -NH ₂ ] HA, is preferred, where R is a carbon-containing radical or an amine group and HA is an acid, such as. B. H ₂ SO ₄ , H ₂ SO ₃ , H ₂ CO ₃ , HNO ₃ . Other possible anions as counterions are halide ions, such as chloride, bromide and iodide, and also thiocyanate.

It is assumed that the amidine works by trapping the aldehydes by reacting the amidine group RC (= NH ₂ ) or the amine group RC-NH ₂ with the aldehyde group R-CHO. Accordingly, there is also a reaction between the amidine group or the amine group and acid residues or degradation products of the terpenes and the terpenes themselves. Furthermore, it is assumed that the additive II acts as a Lewis acid and z. B. attack double bonds in the terpenes or acids.

The amidines, i.e. H. Additive I, both in dissolved form, e.g. B. in the form of an aqueous solution but also in solid form, for. B. as salts, to the lignocellulose-containing comminution products.

It is preferred that the amidine in the form of a solution, in particular an aqueous solution containing 5-40 wt .-% amidine, on the lignocellulose-containing comminution products by z. B. Impregnation of this is applied before the drying step. This is preferably done in such a way that the concentration of the additive I is 2-30% by weight, based on dry wood, such as 5-25 % By weight, e.g. B. 10-20 wt .-%. Other preferred methods for introducing the additive I into the lignocellulose-containing comminution products include processes in which the amidine in the form of a solid, such as in the form of a salt, is added during the scattering of the lignocellulose-containing comminution products and preferably the concentration of the additive I based on atro wood in Range of 2-30 wt% is as in a range of 5-25 wt% e.g. B. 10-20% by weight. Furthermore, the additive (I) can be used differently depending on the layer used, for. B. 20 wt .-% in the middle layers and 10 wt .-% in the outer layers.

Alternatively, additive I can be used in the form of a powder. For example, it can be sprinkled in as a powder.

An additive II, borate, can be added as a second additive together with the above-mentioned additive I from the amidine group.

The term "borate" is understood here to mean salts or esters of boric acids, which can be in the form of simple borates or polyborates. Unless otherwise stated, the term "borate" is understood here to mean both borates and polyborates. The borates are preferably salts of the monoborates (BO ₃ ^3- ), diborates (B ₂ O ₅ ^4- ) triborates (B ₃ O ₅ ^- ), tetraborates (B ₄ O ₇ ^2- ), pentaborates (B ₅ O ₉ ^3- ), hexaborates (B ₆ O ₁₁ ^4- and B ₆ O ₁₀ ^2- ). The borates according to the invention furthermore comprise longer-chain polyborates. Typically, these borates are present as salts with alkali or alkaline earth metals (eg., Sodium tetraborate Na ₂ B ₄ O ₇ · 10H ₂ O), or zinc ions such as counter-cations (., Zinc borate, 2 (ZnO) ₃ (B ₂ O ₃ ) XH ₂ O). Alternatively, those with an ammonium group are also possible and can contain hydrate groups.

On the one hand, the polyborate has a catalytic effect in the reaction of the amidines or amines with the aldehydes. On the other hand, the borate acts as an antioxidant and thus prevents the oxidative degradation of the resins and fats and other wood components, which are responsible for the secondary and tertiary emissions of the terpenes and acids or their degradation products.

Furthermore, it is assumed that the borates and polyborates not only prevent the emission of the VOC by implementing or preventing the degradation of the VOC, but also form a mechanical barrier to prevent the emission of the VOC and VVOC. That is, it is assumed that the borates form an amorphous glassy melt due to the high pressing temperatures, which seals the open surfaces of the wood-based materials, such as the OSB, and thus also mechanically prevents emission.

Furthermore, the borates / polyborates as additive II allow a terpene reduction, which is probably due to their property as Lewis acid. This acts as a catalyst for the addition of the double bond in terpenes. This prevents the terpenes from being broken down into volatile organic breakdown products that contribute to secondary and tertiary emissions.

It is preferred that the borates are introduced, at least as additive II, into the lignocellulose-containing comminution products which form the top layer. In one embodiment, the additives can thus be present in different layers of the wood material. For example, in the case of multilayer wood-based materials, the amidines can be present as additives in the middle layers, while the borates are introduced in the layers forming the top layer. Alternatively, both additives can be present as a combination in at least one layer of the wood-based materials, particularly preferred are both additives I and II at least in the top layer. Alternatively, at least the amidine can be present in the cover layer. Furthermore, in an alternative embodiment, none of the additives mentioned can be present in a middle layer. In the case of a combined use, the additives are preferably introduced separately. So the introduction of the amidine as additive I, z. B. as an aqueous solution, take place before the drying step of the comminution products or alternatively as a solid when scattering the comminution products, while the borate is added separately from the amidine when scattering the comminution products or as a solution after the dryer is added to the glue.

According to the additive II, borate, z. B. introduced in the form of a solution after the dryer in particular in the top layer. Alternatively, additive II can be introduced as a solution into the glue of the cover layer.

The concentration of additive II, based on dry wood, is preferably 2-30% by weight, such as 5-25% by weight, e.g. B. 10-20% by weight.

In a preferred embodiment, the method according to the invention is one in which wood chips, wood strands or wood fibers are used as the lignocellulose-containing comminution products. The method according to the invention is used in particular for the production of OSB, MDF or chipboard.

In particular, the additives are added in such a way that at least one of the two additives I and II is added as a solution before the dryer. Furthermore, one or both additives I and II can be introduced into the gluing or cover layer after the dryer.

The use of the additives according to the invention permits a reduction in all substance classes of VOC and VVOC, ie the TVOC is reduced overall. Here, the mechanical properties of the wood-based materials produced are not, or only to a limited extent, negatively influenced, partially there is even an improvement in the mechanical properties of the wood-based materials.

The additives can be applied by known methods, such as spraying, impregnation or immersion. The addition of the additives can generally be carried out before or after the grinding and processing of the grinding products, e.g. B. after the refiner for fibers. The amidine additives are preferably applied immediately before the hot pressing or before the dryer. The adhesive can be added before or after the additives have been applied. As stated above, the additives are preferably applied separately. Alternatively, the additives can also be applied simultaneously. The adhesive can also be applied between the application of the first additive and the application of the second additive. In particular, as already explained above, the combination of both additives is preferred. According to the invention, a solution of additives can be added to the scattered mat via nozzles directly in front of the hot press. As an alternative, the additives are introduced via customary systems, such as binder dispenser, glue drum, blow-line gluing or dry gluing.

The present invention describes the use of amidine as an additive (Additive I) in the production of wood materials from lignocellulose to reduce the emission of VOC and possibly VVOC, i.e. TVOC, in particular the reduction of the emission of terpenes and acids not only in the manufacturing process itself , but also for later use. The use is characterized in that the additive can be applied or applied during the manufacturing process of the wood-based material.

The present invention describes the use of borate as an additive (v Additive II) for reducing the emission of VOC and possibly VVOC, in particular for reducing the emission of terpenes and acids, in the manufacture and use of wood-based materials made from lignocellulose, wherein the additive can be entered or applied during the manufacturing process of the wood-based material, in particular that the additive is at least entered into the top layer of the wood-based material.

There is a combined use of additive I and additive II, amidine and borate.

The present invention relates to the use of amidine and borate as an additive for reducing the emission of VOC and possibly VVOC in the production and use of wood-based materials made from lignocellulose, the additive being used at least in the top layer of OSB panels. Finally, a treatment agent for reducing the emission of VOC and possibly VVOC, in particular terpenes and acids, from lignocellulose-containing comminution products and wood-based materials from lignocellulose-containing comminution products is described. This treatment agent comprises at least one additive I and at least one additive II.

Furthermore, wood-based materials are obtainable using the invention. This wood material is preferably a fiberboard, in particular a light and super light MDF board, or an OSB board.

Lignocelluloses are understood to mean materials containing lignocellulose, such as wood. Comminution products of lignocelluloses obtained therefrom include, in particular, wooden strands, wood chips, wood fibers but also wood veneer.

The lignocelluloses, such as the wood-based materials or the comminution products thereof, can be either conifers or hardwoods. Mixtures of these two types of wood are also possible. The wood shavings, beaches or wood fibers preferably come from softwoods. With Wood materials that can be produced by the production method according to the invention can be produced according to known methods. The processes can also be supplemented with other processes known to those skilled in the art for reducing the emission of volatile organic compounds or very volatile organic compounds.

The adhesives used in the use according to the invention include the customary adhesives as used for the production of cervical spine and as explained above. The adhesives include, as adhesives, PF adhesives, adhesives based on isocyanates, UF adhesives, MUF adhesives, MUPF adhesives, TF adhesives, PU adhesives or mixtures thereof.

The invention is explained in more detail below with the aid of examples, without being restricted to these.

example

The VOC is determined by testing according to the AgBB (Committee for Health Assessment of Construction Products, May 2010) in a large ISO 16000 chamber. An area-specific ventilation rate of 1 m ³ / (m ^{2 *} h) was determined during the test. Here the amidine (guanidine sulfate) was dosed as a 40% solution before the dryer, ie the amidine is in the top and middle layers. The borate (sodium tetraborate) is also dosed as a 40% solution, but only in the top layer. A PMDI-based adhesive is used. The OSB is manufactured on a production line. <B> Results Table: </ b> Trial 1 Test results (AgBB): c [µg / m ³ ] 28 days OSB hexanal pentanal α-pinene β-pinene 3-Caren TVOC Reference 100% PMDI 1305 201 353 44 205 2932 Amidine / borate 12 mm 148 48 106 13 60 554 Amidine / borate 18 mm 172 44 80 13 54 457

In the Figure 1 the results are shown again graphically. The reduction in the emission of the VOC as a whole and of the individual components can be clearly seen.

Claims (11)

1. Use of amidine and borate as additives in the production of wood-based materials made of lignocellulose for reducing the emission of volatile organic compounds (VOCs), wherein volatile organic compounds include all volatile organic substances whose retention time in a gas chromatograph lies between hexane and hexadecane, in particular for reducing the emission of terpenes and acids, wherein the additives are introducible or applicable during the production process of the wood-based material and the additive amidine is introduced as additive I to lignocellulose-containing comminution products and the lignocellulose-containing comminution products admixed with the additive are pressed with adhesive under heat treatment to produce the wood-based material, wherein additive I is an amidine of the general formula R-C(=NH)-NH2, wherein R is a carbon-containing radical or an amine group, wherein the amidine may optionally be present as a salt and wherein the further additive borate is used as an additive II for introduction to the lignocellulose-containing comminution products, said additive II being borate.
2. Use of amidine and borate as additives in the production of wood-based materials made of lignocellulose for reducing the emission of VOCs according to Claim 1, characterized in that additive I is an amidinium salt, in particular one with a halide, such as chloride, bromide or iodide, thiocyanate, sulfate, sulfite, nitrate or carbonate.
3. Use according to either of the preceding claims, characterized in that additive I is guanidine or a salt thereof.
4. Use according to any of the preceding claims, characterized in that the amidine is applied, in the form of a solution, in particular of an aqueous solution containing 5 - 40% by weight of amidine, to the lignocellulose-containing comminution products by impregnation of the latter prior to a drying step, preferably in such a way that the concentration of additive I is 2 - 30% by weight, based on absolutely dry wood.
5. Use according to any of the preceding claims, characterized in that the amidine is added in the form of a solid, in particular in the form of an amidinium salt, during the spreading of the lignocellulos-containing comminution products, and wherein the concentration thereof, based on absolutely dry wood, is preferably in the range from 2 to 30% by weight.
6. Use according to Claim 1, characterized in that the borate is added in particular into the outer layer in the form of a solution downstream of the dryer, wherein the concentration of additive II, based on absolutely dry wood, is preferably 2 to 30% by weight.
7. Use according to any of the preceding claims, characterized in that additive I and additive II are introduced in combination, preference being given to introducing the two additives I and II separately.
8. Use according to any of the preceding claims, characterized in that the wood-based materials are those produced from wood shavings, wood strands or wood fibres as lignocellulose-containing comminution products.
9. Use according to any of the preceding claims, characterized in that the additives are added together or separately as a solution upstream of the dryer and/or as a solution into the outer layer resination.
10. Use according to any of preceding Claims 1-3, characterized in that the borate is introduced into the lignocellulose-containing comminution products that form the outer layer.
11. Use according to any of the preceding claims, characterized in that additive I is used at least in the outer layer of oriented strand boards.

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