DE102011104025A1 - Method for modification of wood or wood materials, involves subjecting wood of chemical and thermal treatment, where same strength properties in thermal untreated wood are achieved during reduced emission at volatile organic components - Google Patents

Abstract

The method involves subjecting the wood of a chemical and thermal treatment, where the same strength properties in the thermal untreated wood are achieved during reduced emission at volatile organic components from the thermal treatment of the wood. The wood is impregnated for chemical treatment with an organic or inorganic solution. The organic or inorganic solution has a component. An independent claim is also included for a chemically and thermally modified wood with a starting material.

Description

The invention relates to a method for modifying wood or wood-based materials, in which the wood is subjected to a chemical and thermal treatment, wherein at reduced emission of volatile organic components of the wood at least the same strength properties are achieved as in the thermally untreated wood. The invention also relates to chemically and thermally modified wood.

The thermal treatment or thermal modification of wood, for example, aims to increase its dimensional stability in use, increase its biological durability, reduce its water absorption, or alter its color. There are a large number of patents and procedures for this, for example US 2296316 ; DE 910836 ; DE 2263758 C3 ; EP 0623433 B1 ; EP 0759137 B1 ; EP 0880429 B1 ; EP 0922918 B1 ; EP 1002630 B1 ; EP 1118828 A1 ; which have the aim of thermal modification using various atmospheres such as water vapor or inert gas or the modification in salt or metal melts or oil baths.

The Waxwood represents a further process of tempering. After the thermal tempering process the impregnation of the wood takes place in a wax bath ( DE 20310745 U1 ). Also possible is the direct modification in the hot paraffin bath ( US 3928677A ). The thermal modification in the temperature range between 160 ° C and 250 ° C causes chemical changes to the main components of the wood, hemicellulose, lignin and cellulose. Therefore, as disadvantages of all these described methods of thermal modification reduced mechanical properties of the modified wood and in the development of volatile organic compounds which have a partly unpleasant odor. The described methods of thermal modification of wood lead in particular to a breakdown of hemicelluloses. In hardwoods xylan is particularly sensitive, these woods emit due to the thermal treatment of larger amounts of acetic acid and other organic acids, which promotes the further degradation of hemicelluloses. Further breakdown products are furfural, hydroxymethylfurfural, levulinic acid as well as other aldehydes and acids, some of which are suspected of having a carcinogenic effect.

In addition to the thermal modification of wood, a variety of methods for the chemical modification of wood continue to exist. An overview of the various methods provide z. B. the publications CAS Hill, Wood Modification, Chichester, UK: John Wiley & Sons, Ltd., 2006 such as T. Schultz, Development of commercial wood preservatives: efficacy, environmental, and health issues, Washington DC; [New York]: American Chemical Society, distributed by Oxford University Press, 2008 , The main focus of chemical modification is the cross-linking of cell wall polymers. Through the use of acid anhydrides (eg EP 0680810 B1 ) and a subsequent treatment at elevated temperature, a significant modification of the wood can be achieved in which the wood polyols are crosslinked by new cross-linking compounds, which is characterized by a significant bulking effect of the cell wall. The biological durability and dimensional stability can be significantly improved without the mechanical properties are deteriorated (Reference CAS Hill, Wood Modification, Chichester, UK: John Wiley & Sons, Ltd., 2006 ). The disadvantage, however, is that acetic acid is formed as a reaction product, which gives the wood a distinctive odor.

Another chemical modification approach relates to the impregnation of the wood with a solution containing furfuryl alcohol ( EP 1368167 B1 ). After the impregnation process, the furfuryl alcohol is cured at elevated temperature, with covalent bonds to the main components of the wood, in particular lignin are formed (reference L. Nordstierna, S. Lande, M. Westin, O. Karlsson, and I. Furó, "Towards novel wood-based materials: chemical bonds between lignin-like model molecules and poly (furfuryl alcohol) studied by NMR," Holzforschung, vol. 62, 2008, pp. 709-713 ). Wood treated with furfuryl alcohol and strong acids has significantly improved biological durability and dimensional stabilization under cyclic loading after the modification process. The strong acids necessary to cure the furfuryl alcohol damage the wood by acid digestion.

In the field of wood-based material production processes for the reduction of volatile organic components, which arise in the course of wood-based material production and by adding organic binders and other organic auxiliaries described. That's how it describes EP 2 181 818 A2 a method in which compounds are used to adjust a neutral to basic pH in combination with a complexing agent. By adding these components unwanted chemical reactions of the main components of the wood, especially the acid-catalyzed degradation of hemicellulose to furfural, in the course of a steaming or cooking process are avoided. The complexing agent used suppresses the formation of aldehydes from fatty acids through the binding of heavy metals. Overall, emissions can thus be reduced, which are caused by the hydrolytic substance structure, which in the Plasticizing woodchips occurs for the production of wood fiber materials.

In the published patent application DE 10 2006 020 612 A1 In the run-up to a hot-pressing process, wood chips or wood veneers are impregnated with a multicomponent solution in order to reduce volatile components that are produced during the hot pressing process. Here, both components that are caused by the hydrothermal degradation of the wood, as well as components that are released as a result of the addition of organic binders and auxiliaries, are taken into account.

In the WO 2006/039914 A1 For the production of wood-based materials, an alkali treatment of the chips is proposed, which suppresses the formation of volatile organic components in a basic medium.

The publication DE 10 2005 046 345 A1 describes a method with the particular fatty acid ester-containing wood can be treated to reduce degradation products of these fatty acid esters. Of the fatty acid ester-containing wood species, only pine and spruce are of relevance for thermal modification; relevant hardwood species such as beech and maple remain unaffected. In the thermal modification of solid wood, fatty acid ester-based emissions take a back seat compared to emissions resulting from the degradation process of the main components cellulose, hemicellulose and lignin.

Furthermore, methods for reducing the emission of solid wood are known. The publication DE 39 11 091 A1 describes a method with which existing in wood acids and aldehydes are neutralized or bonded and in addition a hydrophobization of the wood is realized. In this case, the naturally present in the wood acids and aldehydes, but not in the course of a thermal modification of wood from the main components resulting volatile components are neutralized or bound.

The publication DE 10 2009 000 109 A1 describes a method in which a superficial wetting of the wood with antioxidants and preservatives, in particular tartaric acid and / or tartrate is carried out to reduce emissions. In the interior of the wood resulting decomposition products can not be implemented.

The object of the present invention is to modify the wood by means of chemical and thermal treatment so that the stated disadvantages of the prior art of a single chemical or thermal modification of the wood can be overcome. In addition to the state of the art, only the thermal modification of solid wood is considered, the material changes according to the invention going beyond the material degradation processes during drying, steaming or plasticizing wood and wood chips. Due to the method, the strength of the solid wood is increased in the present invention over the prior art.

According to the invention the object is achieved by a method having the features mentioned in claim 1. Advantageous variants of the method are the subject of dependent subclaims.

In the method according to the invention, the volatile organic components formed during a thermal wood modification process are captured by a chemical substance in situ and chemically bound. This creates a product with reduced emissions of volatile organic compounds. It is achieved a crosslinking effect as well as a nearly complete conversion of the volatile wood components. It differs from the previous methods of combined thermal and chemical modification in that no reaction takes place with the main components of the wood, but chemical degradation products due to the thermal modification are caught, chemically converted and bonded.

For this purpose, the wood is first impregnated with an organic or inorganic solution or combination of the two, which is suitable due to their chemical structure to react with the volatile components. These reactions include, for example, condensation, esterification or addition. The organic or inorganic solution may also act as a buffer for the resulting acetic acid to inhibit catalysis of further degradation.

The chemical treatment is followed by a thermal treatment at elevated temperature. This is advantageously in the range of 160 to 250 ° C. The thermal treatment is advantageously carried out under an inert gas atmosphere (steam, nitrogen, noble gases) over a period of 2 to 24 hours.

For impregnation, the following chemical substances can be used, individually or in combination: urea in ethanol solution and aqueous solutions of boric acid and sodium hydroxide.

The impregnation with urea and the following thermal modification lead to a conversion of the furfural. The use of aqueous solutions of boric acid and sodium hydroxide leads to the suppression of the formation of acetic acid and thus to a reduction in the catalytic degradation reactions of wood polyols.

As a result, a modified wood is produced, which after the thermal modification step compared to classically thermally modified woods have a greatly reduced emission of typical volatile organic compounds such as acetic acid and furfural, which are partially below the level of native, untreated woods. Furthermore, but also improved mechanical properties, characterized by a partially significantly improved flexural strength set. Surprisingly, this flexural strength even exceeded the strength level of the native starting material used.

The advantage of the invention thus lies in the possibility of producing wood or products made of wood, which have the advantages of thermally modified woods, such as dimensional stability, biological durability, reduced moisture absorption. At the same time, the known disadvantages in terms of emissions and reduced strength properties are compensated and are even above the level of the starting materials.

The invention will be explained in more detail with reference to exemplary embodiments.

Exemplary embodiments 1)

A test specimen of maple wood was impregnated with a 0.5 molar ethanolic urea solution under vacuum at room temperature until saturation. After a drying step to remove the ethanolic solution component at 80 ° C followed by a thermal modification under a nitrogen atmosphere over a period of 5 hours at 180 ° C. The thus tempered woods had, as evidenced by GC-MS analyzes, a significantly reduced emission of typical thermo-wood emissions such as furfural and acetic acid. The typical smell of thermally modified woods was not detected by volunteers for such modified woods. Surprisingly, the values of the flexural strength of these modified woods were in the higher value range than those of the untreated, native test specimens. Thus, the average flexural strength of native Ahom samples was 125 N / mm ² , purely thermally modified maple samples at 98 N / mm ^2, and the samples impregnated with 0.5 molar ethanolic urea solution and subsequently thermally modified at 155 N / mm ² . That is, the typical loss of strength of thermally modified woods could not only be compensated for by the combined treatment but also significantly and significantly improved over the level of native and untreated woods.

Embodiment 2)

A test specimen of maple wood was impregnated with a 0.4 molar aqueous borate buffer consisting of boric acid and sodium hydroxide under vacuum at room temperature to saturation. After a drying step to remove the aqueous solution component at 80 ° C, a thermal modification under a nitrogen atmosphere followed for a period of 5 hours at 180 ° C.

The typical smell of thermally modified woods was not detected by volunteers for such modified woods. Again, the values of the bending strength of these modified woods were surprisingly higher in the value range than those of the untreated, native test specimens. Thus, the average bending strength of native maple samples was 125 N / mm ² , purely thermally modified Ahom samples at 98 N / mm ^2, and the samples with 0.4 molar aqueous borate buffer and subsequently thermally modified samples at 133 N / mm ² . This means that the typical loss of strength of thermally modified woods could not only be compensated for by the combined treatment but also significantly and significantly improved over the level of native and untreated woods.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2296316 [0002]
• DE 910836 [0002]
• DE 2263758 C3 [0002]
• EP 0623433 B1 [0002]
• EP 0759137 B1 [0002]
• EP 0880429 B1 [0002]
• EP 0922918 B1 [0002]
• EP 1002630 B1 [0002]
• EP 1118828 A1 [0002]
• DE 20310745 U1 [0003]
• US 3,928,677 A [0003]
• EP 0680810 B1 [0004]
• EP 1368167 B1 [0005]
• EP 2181818 A2 [0006]
• DE 102006020612 A1 [0007]
• WO 2006/039914 A1 [0008]
• DE 102005046345 A1 [0009]
• DE 3911091 A1 [0010]
• DE 102009000109 A1 [0011]

Cited non-patent literature

• CAS Hill, Wood Modification, Chichester, UK: John Wiley & Sons, Ltd., 2006 [0004]
• T. Schultz, Development of commercial wood preservatives: efficacy, environmental, and health issues, Washington DC; [New York]: American Chemical Society, distributed by Oxford University Press, 2008 [0004]
• CAS Hill, Wood Modification, Chichester, UK: John Wiley & Sons, Ltd., 2006 [0004]
• L. Nordstierna, S. Lande, M. Westin, O. Karlsson, and I. Furó, "Towards novel wood-based materials: chemical bonds between lignin-like model molecules and poly (furfuryl alcohol) studied by NMR," Holzforschung, vol. 62, 2008, p. 709-713 [0005]

Claims (8)

Method for modifying wood or wood-based materials, in which the wood is subjected to a chemical and thermal treatment, wherein with reduced emission of volatile organic components from the thermal treatment of the wood at least equal strength properties are achieved as in the thermally untreated wood, characterized in that a) the wood for chemical treatment with an organic or inorganic solution or a combination of both is impregnated, wherein the organic or inorganic solution contains at least one component which is suitable because of their chemical structure, crosslinking reactions with the resulting during the thermal treatment of volatile organic B) the wood is then subjected to a thermal treatment at elevated temperature in the range between 160 ° C and 250 ° C, and c) the be In the thermal treatment resulting decomposition products of the main wood components cellulose, hemicellulose and lignin are caught by the impregnated into the wood introduced organic and inorganic components, chemically converted and bound and / or buffered. A method according to claim 1, characterized in that for the impregnation of the wood in ethanol dissolved urea is used. A method according to claim 1 or 2, characterized in that an aqueous solution of boric acid and sodium hydroxide is used to impregnate the wood. Method according to one of claims 1 to 3, characterized in that after the chemical treatment of the wood by impregnation drying to remove the solvent component is carried out and then the thermal treatment of the wood is continued. A method according to claim 4, characterized in that the drying takes place at a temperature up to 80 ° C. Method according to one of claims 1 to 5, characterized in that the thermal treatment of the wood is carried out at temperatures in the range of 160 to 220 ° C and under inert gas atmosphere over a period of 2 to 5 hours. A method according to claim 6, characterized in that water vapor, nitrogen or noble gases are used to generate the inert gas atmosphere. Chemically and thermally modified wood, characterized in that the wood modified by chemical and thermal treatment compared to thermally treated wood has a reduced emission of volatile organic components, and at least has the same mechanical strength properties as the thermally untreated starting material.