EP2114644B1 - Method of treating wooden parts - Google Patents

Abstract

A method of treating wooden parts is described in which a) the wooden parts are impregnated with an aqueous cyanamide solution and subsequently b) the impregnated wooden parts, where appropriate after drying, are subjected to a heat treatment of 130 to 250° C. Here it has surprisingly emerged that impregnation with cyanamide even in small amounts has a significantly positive influence on the performance properties of the treated wooden parts, such as high hardness, low water absorption and very good weathering stability, for example. Moreover, only small amounts of a toxicologically and environmentally unobjectionable impregnating agent are needed in order to obtain these advantageous properties.

Description

The present invention relates to a method for the treatment of wood parts to improve their performance properties such. As hardness, water absorption and weather resistance.

Tropical exotic woods are preferred for demanding indoor and outdoor wood constructions compared to domestic woods, as they have advantageous properties. On the other hand, the increased use of tropical hardwoods leads to the decimation of tropical rainforests and is therefore to be rejected for ecological reasons. In addition, sufficient quantities of indigenous hardwood and softwoods are available, but often do not meet the technical requirements.

From this dichotomy, the idea of thermal treatment of inferior woods for property improvement was developed. According to EP 0 759 137 A1 and EP 0 695 408 A1 be z. B. methods are described by which woods are modified by the application of elevated temperatures so that they cover a requirement profile, as it can usually only be achieved by tropical hardwoods. In particular, the resistance to mold and rot is improved. The disadvantage is that the treatment must be carried out at high temperatures of over 200 ° C, and that the resulting properties can not be improved in part to the extent desired.

Alternatively, methods are known in which wood is modified by impregnation with reactive monomers and subsequent crosslinking thereof. Such methods are for. B. off WO 2006/117 159 A1 respectively. WO 2004/033 171 A1 known. This results in wood-based materials that have a high hardness, weather resistance and dimensional stability.

The disadvantage, however, is that large amounts must be used to impregnating, which also significantly increase the specific gravity of the wood material. In addition, undesirable emissions from the wood-based material result from the formaldehyde content of the impregnating agents used.

The treatment of cellulose-containing materials with cyanamide is known in principle. So becomes cellulose - as in US 3,051,698 respectively. US 3,380,799 treated with cyanamide at pH values above 8.5 and then acidified, resulting in cationically modified celluloses with ionic properties, the z. B. are suitable as adsorbent.

In the implementation of cellulose fibers with cyanamide, reactive aldehydes and amines according to DE 16 19 047 A1 At room temperature arise polymer-modified celluloses, which are particularly suitable for electrical insulation papers.

However, it is not a method for the treatment of cellulose-containing materials, in particular of wood with cyanamide known in which can be dispensed with the addition of other reactive substances.

The present invention therefore an object of the invention to develop a method for modifying wood parts in the form of wood or wood materials, which does not have the disadvantages of the prior art, but the known method for the thermal treatment of wood with an impregnation in the Improved manner that only small amounts of a toxicologically and ecologically harmless impregnating agent are needed and still obtain advantageous properties.

This object has been achieved by a skilled person in accordance with the present claim 1.

It has surprisingly been found that the impregnation with cyanamide, even in small amounts, has a markedly positive effect on the properties of the resulting woods and that the heat treatment triggers a specific crosslinking reaction between cyanamide and reactive groups within the wood structure. The cyanamide is surprisingly irreversibly incorporated into the wood structure and improves the technical properties of the treated wood.

In the method according to the present invention, the wood parts in the form of wood or wood-based materials are first subjected to impregnation with cyanamide (step a)) and then to a heat treatment (step b)).

This low-priced hardwood and softwoods of moderate widths are treated, which preferably come from sustainable forestry. Examples are the European woods spruce, fir, pine, birch, beech, such. European beech or hornbeam, maple, poplar, alder, linden, Douglas fir, ash and oak, as well as non-European woods with an analogous property profile.

The woods are preferably as solid wood (boards, planks, slats) before. But they can also be in the form of veneers or chips for subsequent use for the production of wood-based materials. Alternatively, finished wood materials (plywood, chipboard, wood fiber boards, OSB boards, glued wood) can be treated by the method according to the invention.

The said woods or wood-based materials are preferably impregnated by the application of vacuum and / or pressure with a cyanamide-containing solution. Suitable for this purpose are facilities such as are commonly used for the boiler pressure impregnation of woods.

The aqueous impregnating solution should contain 1 to 50% by weight of cyanamide, particularly preferably 5 to 25% by weight of cyanamide, in particular 10 to 15% by weight of cyanamide. The pH of the impregnating solution should be in the range 3.0 to 7.0, preferably pH 4.0 to 5.5 or pH 4.5 to 5.0. The impregnating solution may optionally contain further substances, the water-soluble wood preservatives known to the person skilled in the art in the concentration range of 0.01 to 5.0% by weight being preferred. Typical examples of such additives are, for. As fungicides, insecticides or biocides, such as. As copper compounds, fluorides, borates, silicates, phenol, 1,2,4-triazoles, insecticidal phosphoric acid esters or neonicotinoid insecticides. To improve the flame resistance of wood or wood materials phosphates, borates or sulfamates can be added. In addition, pigments and / or dyes and / or ultraviolet light absorbers may be included.

In a preferred embodiment, the aqueous cyanamide solution further contains surfactants, preferably in an amount of 0.02 to 0.2 wt .-%, in particular 0.05 to 0.015 wt .-%. By the use of surface-active substances, the impregnation of the wood is facilitated, particularly suitable are nonionic, cationic or anionic surfactants.

The impregnation (step a)) is suitably carried out in a temperature range between 0 and 60 ° C, in particular 20 to 40 ° C. By applying a vacuum (0.02 to 0.98 bar) or pressure (1.02 to 15 bar), also in succession and in several cycles, a complete impregnation of the wood with the impregnating solution can be achieved become. For example, a 1- to 5-fold alternation of pressure and vacuum treatment can take place. Corresponding methods are known to the person skilled in the art.

It is to be regarded as essential to the invention that the woods impregnated in this way are optionally subjected to a heat treatment after drying. The optional drying of the impregnated with the aqueous cyanamide wood can be carried out at temperatures of 20 to 150 ° C, preferably at 40 to 130 ° C, wherein the external pressure, if necessary, by applying a vacuum to 0.01 to 1.0 bar is set. The drying time is several hours, preferably 1 to 24 hours.

However, it is also possible to carry out the drying of the impregnated woods in a common process step together with the described heat treatment. According to this special process variant, the drying is initiated by the action of the temperature and pressure conditions provided for the heat treatment, in which case a sliding transition to the heat treatment takes place.

The temperature range of the heat treatment is between 130 and 250 ° C, preferably 150 to 220 ° C, in particular 170 to 200 ° C. The duration of the heat treatment is 1 to 36 hours, with times between 2 and 12 hours or 4 to 8 hours being preferred. The drying and subsequent heat treatment is preferably carried out in several temperature stages, wherein said temperature is gradually approached.

The heat treatment can be carried out without pressure, but possibly also under a pressure of up to 10 bar, for example at 3 to 7 bar, wherein the atmosphere may preferably contain air, nitrogen, water vapor or a mixture thereof.

After the heat treatment, the treated woods have a residual moisture of preferably less than 10%. They can be used as such as construction timbers, such. As for load-bearing or non-structural components of buildings, doors, windows, furniture (especially garden furniture) and wood elements in horticulture. Alternatively, the treated woods (especially in the form of veneers, chips, etc.) can be used for the production of wood-based materials, which in turn can be used for the applications mentioned.

The invention treated wood parts are characterized by very good performance properties such. As high hardness, low water absorption and very good weather resistance.

Based on the observed property profiles, it can be assumed that cyanamide reacts with the specific ingredients of wood (cellulose, hemicellulose, lignin) in such a way that it is covalently integrated into the wood network even without the use of additional crosslinking agents after heat treatment, thus making property improvement crucial contributes.

The following examples are intended to explain the essence of the invention in more detail.

Examples example 1

From homogeneous wood material (spruce or birch) specimens were cut in the format 80 x 25 x 25 mm, dried and weighed.

The test specimens were immersed in cyanamide solution (or water as reference) and completely impregnated by evacuation twice. Then it was dried at 60 ° C in a vacuum.

How out illustration 1 it can be seen that the cyanamide uptake into the wood is proportional to the cyanamide concentration (5 or 10% by weight) of the impregnating solutions used.

Example 2

Test specimens which had been impregnated with water or with 10% strength by weight cyanamide solution according to Example 1 were thermally post-treated at 160 ° C. (8 hours) or at 200 ° C. (3 hours). The weights of the specimens were used to record the water uptake or release as well as the cyanamide uptake (see Figure 2 ).

By the heat treatment, the woods darken, naturally stronger at 200 ° C than at 160 ° C. At 200 ° C, birch gets about the color of mahogany. The presence of cyanamide did not affect the color. Only the spruce samples treated with cyanamide showed a yellow color, which disappeared on heat treatment.

• Ca. 6 Gew.-% gebundenes Wasser werden bei schonender Trocknung abgegeben, bei 160 °C erhöht sich die Menge auf 8 Gew.-%, bei 200 °C auf Gew.-12 %. Ursache ist die bekannte Kondensation freier OH-Gruppen im Holz unter Wasserabspaltung.
• Befindet sich Cyanamid im Holz, so wird bei der Wärmebehandlung (korrigiert um das Cyanamid-Gewicht) mehr Wasser abgegeben, und zwar bei 160 °C bzw. 200 °C zusätzlich jeweils etwa 30 Gew.-% des Cyanamid-Gewichts. Diese zusätzliche Wasserabgabe ist auf eine Reaktion von Cyanamid mit OH-Gruppen in der Holzstruktur zurückzuführen.

The weight loss during the heat treatment shows two effects:

• Approximately 6% by weight of bound water are released with gentle drying, at 160 ° C. the amount increases to 8% by weight, at 200 ° C. to 12% by weight. The cause is the known condensation of free OH groups in the wood with dehydration.
• If cyanamide is present in the wood, more heat is released during the heat treatment (corrected for the cyanamide weight), and Although at 160 ° C or 200 ° C additionally each about 30 wt .-% of the cyanamide weight. This additional water release is due to a reaction of cyanamide with OH groups in the wood structure.

Example 3

The treated according to Example 2 woods were tested for hardness. This resulted in: Species impregnation heat treatment hardness Spruce without Drying at 60 ° C low Spruce without Heat treatment 200 ° C, 3 hours medium Spruce with 10% cyanamide solution Drying at 60 ° C low Spruce with 10% cyanamide solution Heat treatment 200 ° C, 3 hours high birch without Drying at 60 ° C medium birch without Heat treatment 200 ° C, 3 hours high birch with 10% cyanamide solution Drying at 60 ° C medium birch with 10% cyanamide solution Heat treatment 200 ° C, 3 hours very high

Example 4

The treated according to Example 2 woods were immersed for 7 days at 20 ° C in water. The water absorption (as mass%) or the volume increase of the specimens was determined (see Figures 3 and 4).

Here it was shown that - as expected - the water absorption is reduced by heat treatment of the wood. In the simultaneous presence of cyanamide water absorption was further reduced, the effect was proportional to the amount of cyanamide introduced.

Without subsequent heat treatment, the impregnation with cyanamide showed no pronounced effect. A chemical installation of the Cyanamide under networking of the wood structures is therefore to be assumed.

Example 5

• bei Imprägnierung und anschließender Trocknung bei 60 °C waren nur ca. 30 bis 40 Gew.-% des in Form von Cyanamid eingebrachten Stickstoffs nicht extrahierbar.
  Über 60 bis 70 Gew.-% der im Holz befindlichen Stickstoff-Verbindungen waren durch Wasser extrahierbar. Die extrahierbaren StickstoffKomponenten bestanden zu über 90 Gew.-% aus unverändertem Cyanamid, daneben fand sich nur etwas Dicyandiamid und Harnstoff. Es zeigt sich also, dass ohne nachfolgende Wärmebehandlung die Cyanamid-Behandlung keine vorteilhaften Eigenschaften ergibt.
• Nach Wärmebehandlung bei 160 °C waren ca. 70 bis 80 Gew.-% des in Form von Cyanamid eingebrachten Stickstoffs durch Wasser nicht mehr extrahierbar.
  Nur ca. 20 bis 30 Gew.-% der im Holz befindlichen Stickstoff-Verbindungen waren durch Wasser extrahierbar. Unter den extrahierten Stickstoff-Verbindungen war kein Cyanamid nachweisbar. Ca. 75 Gew.-% der extrahierbaren Stickstoffkomponenten bestanden aus Dicyandiamid, 5 Gew.-% aus Harnstoff, 5 Gew.-% aus Guanidin und 10 Gew.-% aus Melamin.
• Nach Wärmebehandlung bei 200 °C waren > 90 Gew.-% des in Form von Cyanamid eingebrachten Stickstoffs nicht mehr extrahierbar, d. h. fest an das Holz gebunden.
  Weniger als 10 Gew.-% der im Holz befindlichen Stickstoff-Verbindungen waren durch Wasser extrahierbar. Unter den extrahierten Stickstoff-Verbindungen war kein Cyanamid nachweisbar. Ca. 40 Gew.-% der extrahierbaren Stickstoffkomponenten bestanden aus Melamin, 8 Gew.-% aus Dicyandiamid, 12 Gew.-% aus Harnstoff und < 5 Gew.-% aus Guanidin. Zusätzlichen wurden weitere unidentifizierte N-Verbindungen nachgewiesen.

The water in which the test specimens from Example 4 were immersed was analyzed chemically. The following analysis values were shown in Figures 5, 6 and 7:

• when impregnated and then dried at 60 ° C only about 30 to 40 wt .-% of the introduced in the form of cyanamide nitrogen were not extractable.
  About 60 to 70 wt .-% of the wood-based nitrogen compounds were extractable by water. The extractable nitrogen components consisted of more than 90% by weight of unchanged cyanamide, besides only a little dicyandiamide and urea were found. It thus turns out that without subsequent heat treatment the cyanamide treatment does not give any advantageous properties.
• After heat treatment at 160 ° C., about 70 to 80% by weight of the nitrogen introduced in the form of cyanamide could no longer be extracted by water.
  Only about 20 to 30 wt .-% of the wood in the nitrogen compounds were extractable by water. No cyanamide was detectable among the extracted nitrogen compounds. Approximately 75% by weight of the extractable nitrogen components consisted of dicyandiamide, 5% by weight of urea, 5% by weight of guanidine and 10% by weight of melamine.
• After heat treatment at 200 ° C.,> 90% by weight of the nitrogen incorporated in the form of cyanamide was no longer extractable, ie firmly bound to the wood.
  Less than 10% by weight of the wood nitrogen compounds were extractable by water. No cyanamide was detectable among the extracted nitrogen compounds. Approximately 40 wt .-% of the extractable nitrogen components consisted of melamine, 8 wt .-% of dicyandiamide, 12 wt .-% of urea and <5 wt .-% of guanidine. Additional unidentified N compounds were added demonstrated.

Thus, it turns out that the heat treatment of the cyanamide-impregnated wood leads to a specific reaction with complete chemical reaction of the cyanamide, in which the reaction products of cyanamide are firmly bound in the wood structure. Thus, the surprising effect of property improvement by impregnation with cyanamide and subsequent heat treatment can be explained chemically-mechanistically.

Example 6

Wood specimens according to Example 2 were exposed to the weather. After a residence time of 12 months, the weather resistance was estimated. Species impregnation heat treatment weatherability Spruce without Drying at 60 ° C low Spruce without Heat treatment 200 ° C, 3 hours medium Spruce with 10% cyanamide solution Drying at 60 ° C low Spruce with 10% cyanamide solution Heat treatment 200 ° C, 3 hours high birch without Drying at 60 ° C low birch without Heat treatment 200 ° C, 3 hours medium birch with 10% cyanamide solution Drying at 60 ° C low birch with 10% cyanamide solution Heat treatment 200 ° C, 3 hours high

Claims (13)

1. Method for treating wooden parts for improving their performance properties, characterized in that

   a) the wooden parts are impregnated with an aqueous cyanamide solution without additional cross-linking agents, wherein the aqueous cyanamide solution has a concentration of 1 to 50 % by weight and subsequently

   b) the impregnated wooden parts, where appropriate after drying, are subjected to a heat treatment of 130 to 250°C.
2. Method according to claim 1, characterized in that the wooden parts consist of spruce, fir, pine, birch, beech, maple, poplar, alder, lime, Douglas fir, ash and/or oak.
3. Method according to claim 1 or 2, characterized in that the aqueous cyanamide solution has a concentration of 5 to 25 % by weight.
4. Method according to one of the claims 1 to 3, characterized in that the pH of the aqueous cyanamide solution is 3.0 to 7.0, in particular 4.0 to 5.5.
5. Method according to one of the claims 1 to 4, characterized in that the aqueous cyanamide solution contains additional common wood preservatives such as organically- or inorganically-based fungicides, insecticides or biocides in a concentration range of 0.01 to 5 % by weight.
6. Method according to claim 5, characterized in that copper compounds, fluorides, borates, silicates, phenol, 1,2,4-triazoles, insecticidal phosphoric acid esters or neonicotinoid insecticides are used as wood preservatives.
7. Method according to one of the claims 1 to 6, characterized in that the aqueous cyanamide solution additionally contains flame retardants selected from the group comprising phosphates, borates or sulphonates as well as pigments and/or dyes and/or UV absorbers.
8. Method according to one of the claims 1 to 7, characterized in that the aqueous cyanamide solution additionally contains 0.02 to 0.2 % by weight surface-active substances, in particular non-ionic, cationic or anionic surfactants.
9. Method according to one of the claims 1 to 8, characterized in that step a) is carried out at temperatures of 0 to 60°C, in particular 20 to 40°C.
10. Method according to one of the claims 1 to 9, characterized in that the impregnation is carried out in a vacuum at 0.02 to 0.98 bar or in a pressure range of 1.02 to 15 bar, optionally successively and/or in several cycles.
11. Method according to one of the claims 1 to 10, characterized in that the heat treatment (step b)) is carried out in a temperature range of 150 to 220°C.
12. Method according to one of the claims 1 to 11, characterized in that the heat treatment is carried out for a time period of 1 to 36 hours, in particular for 2 to 12 hours.
13. Method according to one of the claims 1 to 12, characterized in that the heat treatment is carried out at a pressure of 1 to 10 bar.

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