FI118958B - Treatment of heat modified wood - Google Patents

Abstract

The invention relates to treatment of thermally modified wood. Thermal modification means controlled heating treatment of wood most appropriately under moist atmosphere so as to improve the dimensional stability and decay resistance of the wood. In accordance with the invention, the water absorption tendency of themally modified wood is reduced by treating the wood with a hydrophobic sizing agent reactive with cellulose, the treatment resulting in water-repellent wood. The wood can be treated with a solution containing a sizing agent, and then the solvent is evaporated by drying. Suitable sizing agents comprise alkyl ketene dimers (AKD) and alkenyl succinic acid anhydrides (ASA) dissolved in acetone, for instance. When ASA is used, the dried wood impregnated with the sizing agent requires an additional heating treatment in order to become hydrophobic.

Description

118958 Treatment of heat modified wood

The invention relates to a process for the treatment of heat modified wood, to a product obtained by the process and to the use of processing agents in the process.

Thermal modification of wood refers to the controlled heat treatment of wood at temperatures above 100 ° C by improving the dimensional stability of the wood and reducing its equilibrium moisture and moisture content. Other beneficial effects of heat modification include increased resistance to decay and reduced pitch resolution. On the other hand, in heat modification the wood darkens and its bending and splitting strengths are reduced. Due to its properties, heat-modified wood is particularly useful in structures and furniture that come into contact with the outdoor air.

The technique of thermal modification of wood is described in WO 95/31680, which focuses on controlling the temperature difference between the outer surface of the wood and the interior during raising the temperature so as to prevent fractures in the wood. According to the publication, said temperature difference is between 10 and 30 ° C and is kept approximately constant in heating. Corresponding controlled temperature difference of 10-30 ° C for wood interior ... The wood may also be maintained between cooling and the outer surface by cooling, whereby, unlike heating, a higher temperature will prevail inside the wood.

WO 94/27102 discloses an improved process for the preparation of heat modified wood having a treatment temperature of more than 150 ° C using: V. steam aid. At least 3% weight loss occurs during treatment.

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WO 01/53812 further describes a procedure for verifying heat-modification in wood by measuring the number of free radicals present in the wood: and comparing it with the amount of free radicals in the corresponding untreated wood. As a criterion for heat modification, the publication proposes that wood *. the number of free radicals is at least 1.5 times, preferably at least double]. ' fold compared to untreated wood.

The above-mentioned WO 95/31680, WO 94/27102 and WO 01/53812 are hereby incorporated by reference in their entirety. With wood modification or 1 *! heat modified wood in the following means that the wood meets the criteria of at least one of the three publications mentioned above for heat treatment (heat modification) or heat treatment (heat modified).

In spite of the reduced equilibrium humidity of the heat modified wood in the humid outdoor air, it has now been found that it absorbs a large amount of water upon direct contact with water or 5 moist soil. Although thermal modification per se improves the resistance of wood to decay, longer-term hydrogenation, in particular, still has a detrimental effect on wood durability. In addition, the wetting of the wood will greatly increase its weight.

It is therefore an object of the present invention to provide a solution to prevent the heat-modified wood from becoming dehydrated. The process of the invention comprises converting the heat-modified wood to be water repellent by absorbing therein with a solution of a hydrophobic adhesive reactive to cellulose which is an alkyl ketene dimer (AKD) and / or alkenyl succinic anhydride (ASA), dissolved in organic solvent, .

According to the invention, it has been found that the adhesive dissolved in a suitable organic solvent is readily absorbed into the heat modified wood due to the same reason as the water of the wood, namely the increased porosity of the wood structure. Preliminary experiments with the invention have resulted in a contact angle of more than 90 °, even more than 100 °, between the surface of the treated wood and the drop of water dropped on it, which is * * · *; 20 is an indication of high water repellency.

• The adhesive-containing solution can be impregnated into the wood to provide a nationwide adhesive content. Alternatively, the wood may be surface-treated *; * *: Quickly dip or dip it in a dip so that the adhesive penetrates only the top layers of I wood.

Wood hydrophobic adhesives for use in accordance with the invention. . are alkyl ketene dimers (AKDs) and alkenyl succinic anhydrides (ASA), known in the art for bonding paper and board, which are reactive with cellulose and are bonded in a neutral or alkaline pH range. Paper and ·: · *: The cartonboard industry uses these adhesives as aqueous emulsions, whereas the present k1. In the impregnation of the heat modified wood according to the invention, they are useful (· dissolved in an organic solvent such as acetone. For the purpose of absorption, the adhesive ♦ · * «* · solution is preferably dilute; the adhesive may be 0.01 to 1% by weight; However, the use of AKD or ASA as a concentrated solution of 3,118,958 is also possible within the scope of the invention, and it is still possible to use AKD and ASA in admixture.

The alkyl chain contained in alkyl ketene dimers may vary in length. Commercial AKD adhesives typically comprise a straight C16-C22 alkyl chain. However, AKD adhesives with branched or unsaturated carbon chains are also useful in the invention. AKD adhesive products are available in both solid and liquid form.

Similarly, in alkenyl succinic anhydrides, the length of the alkenyl chain may vary. Commercial ASA adhesives usually comprise a C16-C22 alkenyl chain.

10 In connection with the state of the art, C.A.S. An article by Mouse and S. Mallon in the Journal of Wood Chemistry and Technology, 18 (3), pp. 299-311 (1998) describes a chemical modification of wood, one of the chemicals being 2-octen-1-yl succinic anhydride from ASA to pyridine dissolved. However, it was not a heat-modified wood, nor was it intended to increase the hydrophobicity of the wood, but was intended to increase the dimensional stability and durability of the wood and to add reactive functional groups to the wood by chemical means. The technique of the article is thus equated with heat modification of wood rather than its hydrophobization.

... After the gluing and solvent removal according to the invention, the wood can be further treated by heating, e.g. by bringing it to 100-140 ° C for 15-60 minutes • · * ··· | for tin. The heating requirement depends on the adhesive selected; According to preliminary experiments *, such post-heating is of little importance in AKD adhesives, whereas it significantly improves the hydrophobicity achieved by ASA.

·· · • ♦ · • ♦. ···. The heat-modified wood of the invention, treated as described above, is characterized in that it is impregnated with a hydrophobic, cellulose by weight ratio. . I make a reactive adhesive that makes wood more water repellent, * * * adhesive being AKD or ASA. Preferably, the glue is evenly distributed throughout the wood so that the glue content in the treated wood is approximately constant.

* ·

The invention further comprises the use of AKD or ASA in an organic solvent dissolved in the treatment of heat modified wood to render the wood water repellent.

• * • · · • · · | The invention will be further illustrated by the following embodiments,

Example 1 4 118958 AKD glue containing a C 10 / C 8 alkyl chain was dissolved in acetone in a 0.1 wt% solution, and the thermowood marketed under the name Thermowood was thoroughly impregnated with this solution. The wood was dried by evaporation of the acetone solvent, and the dried, AKD-5 treated wood was heated to 130 ° C for 15, 30 and 60 min. for the duration of. The water repellency of the wood was tested with a drop test, where the contact angle of the water droplet placed on the wood with the surface of the wood was measured after a contact time of 1, 5 and 10 s. The bar graph of Figure 1 of the accompanying drawing shows the results of five samples which were a reference sample (ref.), I. non-AKD treated wood, 10 AKD treated but not heat treated AKD treated wood which was then dried to 130 ° C for 15, 30 or 60 minutes . The results show the hydrophilicity of the AKD untreated wood, which is manifested by a low contact angle, which also rapidly decreases with continued contact. AKD treatment with heat wood resulted in contact angles of about 90-100 ° 15, which indicated that the surface was water repellent and free from water absorption into the wood. It is also seen that the heat treatment following AKD gluing has only a marginal effect on the water repellency of the wood and that the effect of heating for too long may turn negative.

Example 2 The experiments of Example 1 were repeated with ASA as the adhesive instead of AKD, · · · · 1 ·. containing a C 18 -C 22 alkenyl chain. With a treatment solution containing 0.1% ASA dissolved in acetone, impregnated and dried in the heat wood as such, or after 15, 30 • or 60 minutes heating at 130 ° C, water droplet conc. 1, 5 and 10 s were measured. after a long contact. As in Example 1, the reference • · ·; 25 as (ref.) Was a commercial non-glued firewood as such. The results are clear from the bar graph of Fig. 2 of the drawing. It is seen that ASA gluing alone without heating does not achieve a significant improvement in the water resistance of the heat wood, · · · ', 1, · 1, but the excellent water resistance at the contact angle of about 100 ° is achieved when the ASA In addition, a short heat treatment is provided.

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Claims (9)

A method of treating heat-modified wood, characterized in that the wood is rendered water-repellent by impregnating a solution in the wood which contains a cellulose-reactive hydrophobic adhesive which is an alkylene tendency (AKD) and / or an alkenyl succinic anhydride (ASA), dissolved in an organic solvent, and by removing the solvent by drying. Process according to claim 1, characterized in that the solution containing 10 glue is impregnated in wood throughout. Process according to claim 1 or 2, characterized in that after drying the wood is heated. 15 4. A process according to claim 3, characterized in that the wood is heated to a temperature in the range 100-140 ° C for 15-60 minutes. Process according to any one of the preceding claims, characterized in that the solvent is acetone. 20 Process according to any one of the preceding claims, characterized in that the adhesive content of the treatment solution is 0.01 - 1% by weight, preferably 0.05 - 0.2% by weight. ♦ * • »··« • · ***. Heat-modified wood according to any of the preceding claims, characterized in that it is impregnated with hydrophobic adhesive which is reactive with respect to cellulose, with which the wood has been rendered water-repellent, the adhesive being an alkylene ethylene. dimer (AKD) and / or an alkenyl succinic anhydride (ASA). ··· • · · · · * 8. Heat-modified wood according to claim 7, characterized in that the adhesive is impregnated in the wood everywhere so that the adhesive content of the treated wood is substantially constant. constant. Use of hydrophobic adhesive reactive for cellulose, which adhesive is an alkyl ethene dimer (AKD) and / or an alkyl succinic anhydride (ASA), dissolved in an organic solvent, in the treatment of heat-modified wood. to: · make it water repellent. • ·