METHOD FOR TREATING WOOD AND CONSTRUCTION ELEMENT

Abstract

In a method for treating wood, wherein a wooden body is impregnated with a polymerizable compound which is polymerizable by oxidation, the polymerizable compound is brought into contact with an oxidizer in the wooden body in order to polymerize the polymerizable compound in situ. The polymerizable compound applied therein comprises a heterocyclic compound with nitrogen and/or sulphur as heteroatom. The oxidizer is brought into solution and the wooden body is saturated with a solution of the oxidizer. The wooden body is subjected to a vapour phase of the heterocyclic compound under an increased pressure and the heterocyclic compound is polymerized in situ in the wood.

Claims

1. A method for treating wood, wherein a wooden body is impregnated with a polymerizable compound which is polymerizable by oxidation and the polymerizable compound is brought into contact with an oxidizer in the wooden body in order to polymerize the polymerizable compound in situ, wherein the polymerizable compound comprises a heterocyclic compound with nitrogen and/or sulphur as heteroatom, wherein the wooden body is impregnated with the oxidizer, that the wooden body impregnated with the oxidizer is subjected to a vapour phase of the heterocyclic compound under an increased pressure, and that the heterocyclic compound is polymerized in situ in the wooden body under the influence of the oxidizer.

2. The method according to claim 1, wherein the oxidizer is brought into solution and the wooden body is saturated with a solution of the oxidizer.

3. The method according to claim 1, wherein the heterocyclic compound is selected from a group comprising optionally substituted pyrrole, thiophene, pyridine, quinoline, diazine and combinations thereof.

4. The method according to claim 3, wherein the heterocyclic compound comprises optionally substituted pyrrole with a structure according to the formula: ##STR00002## wherein all carbon-bonded hydrogen atoms can each individually be substituted with a residual group selected from: OH, NH2, carboxyl, aldehyde, methyl, ethyl, propyl, phenyl and benzyl.

5. The method according to claim 4, wherein the heterocyclic compound is taken from a group comprising: pyrrole, 1-methylpyrrole, 2,5-dimethylpyrrole, 1,2,5-trimethylpyrrole, 2-acetyl pyrrole, 2-acetyl-1-methylpyrrole, pyrrole-2-carboxaldehyde, 1-methyl-2-pyrrolecarboxaldehyde and combinations thereof.

6. The method according to claim 1, wherein the wooden body is subjected to the vapour phase of the heterocyclic compound at an increased atmospheric pressure, particularly at a pressure of between 1.2 and 2.5 MPa.

7. The method according to claim 1, wherein the heterocyclic compound is brought into the vapour phase by heating a liquid containing a heterocyclic compound to a boiling point of the heterocyclic compound.

8. The method according to claim 7, wherein the heterocyclic compound comprises pyrrole and the liquid is heated to a temperature above 100 C., particularly to around 125 C.

9. The method according to claim 8, wherein undiluted pyrrole or a solution of pyrrole in water is used for the liquid.

10. The method according to claim 1, wherein a water-soluble oxidizer is applied, which has been brought into an aqueous solution.

11. The method according to claim 9, wherein the wooden body is dried at most partially before being subjected to the vapour phase of the heterocyclic compound, particularly by applying an underpressure therearound.

12. The method according to claim 10, wherein the oxidizer is taken from a group comprising: iron(III) chloride, sodium persulphate, ammonium cerium(IV) nitrate, oxygen, 2,2-azobis(2-methylpropionitrile) and combinations thereof, and particularly comprises iron(III) chloride.

13. The method according to claim 1, wherein the wooden body comprises softwood, particularly pine or spruce.

14. A construction element comprising a wooden body which was treated as according to the method according to claim 1.

Description

[0016] The invention also relates to a construction element comprising a wooden body which was treated in accordance with the method according to the above described invention. The invention will be further elucidated hereinbelow with reference to an exemplary embodiment and to a drawing. In the drawing:

[0017] FIGS. 1-4 show an embodiment of the method according to the invention in successive stages.

[0018] It is noted here that the figures are purely schematic and not drawn to scale. Some dimensions in particular may be exaggerated to greater or lesser extent for the sake of clarity. Corresponding parts are generally designated in the figures with the same reference numeral.

[0019] The setup of FIG. 1 comprises a reactor 1 in which one or more wooden bodies 2 to be treated can be accommodated. In this case these are one or more planks or beams of softwood, in this case spruce or pine. After wooden parts 2 have been placed into reactor space 3, the reactor space is hermetically sealed in vacuum-tight manner. Air is then extracted from space 3 with a vacuum pump 4 and the whole is placed under an underpressure. Air will here also be extracted from and from between the wood cells of wooden parts 2, whereby the wood becomes more receptive to penetration and absorption of an oxidizer to be introduced therein.

[0020] In respect of the oxidizer, in this example a 5-10% aqueous solution 5 of iron(III) chloride is resorted to. The solution is prepared beforehand and is carried from a supply container 6 into reactor space 3 by means of a pump unit 7 and conduit system, wherein the underpressure in reactor space 3 is also relieved. Instead, the oxidizer solution can optionally also first be composed in reactor space 3 by letting the iron(III) chloride salt and water therein separately and mixing them. And instead of iron(III) chloride, other compounds (salts) are also suitable as oxidizer within the scope of the method described here, such as for instance an aqueous solution of sodium persulphate, ammonium cerium(IV) nitrate, 2,2-azobis(2-methylpropionitrile) and combinations thereof or therewith. A gaseous oxidizer, such as for instance oxygen, can also be applied as polymerization initiator for the heterocyclic compound.

[0021] The iron(III) chloride bath 6 is held at a temperature of about 20 to 60 C. For this purpose reactor 2 is provided with heating means (not further shown) and a thermostatic control. In addition, the reactor space is brought to an overpressure in the order of 1.2 to 2.5 MPa with a pump 8 provided for this purpose. In this example an overpressure of about 1.5 MPa is applied in that respect in order to advance penetration of iron(III) chloride into the wood. Wooden body 2 is subjected thereto for a duration of a minimum of several minutes to several hours, wherein the iron(III) chloride solution is able to penetrate deep into the core of the wood 2, see FIG. 2.

[0022] After the above described deep doping with iron(III) chloride the reactor space is emptied by pumping, see FIG. 3, using the pump unit 7 and the overpressure prevailing therein. The reactor space 3 is evacuated once again with vacuum pump 4 in order to remove any excess water vapour, and an underpressure is once again created therein. The reactor space is now coupled to a heated thermostatic bath 8 of liquid pyrrole which is held at a temperature of about 125 C. in a tank 9, see FIG. 4. Pyrrole hereby escapes in the vapour phase 10, which is pumped out with a pump 11 provided for this purpose and is carried under a pressure of 1.2-2.5 MPa into reactor space 3. In this example reactor space 3 is held at a pressure of about 1.8 PMa.

[0023] This state is maintained for a duration of 1 to 48 hours, wherein the pyrrole vapour 10 penetrates deep into the wood 2 and therein undergoes an in situ polymerization into polypyrrole under the influence of the iron(III) chloride present therein. The wood 2 is preferably still humid to some extent here as a result of the iron(III) chloride bath, so that the oxidizer in the cells is in solution and the pyrrole in solution reacts with the iron(III) chloride.

[0024] The treatment described here gives the wood a deep black colour and furthermore imparts a particularly effective weather resistance. The lifespan of the softwood with naturally limited durability and low weather resistance can thereby be increased substantially to or even beyond the level of types of tropical hardwood frequently used in structures. Not only does this result in a cost saving, it also has a positive effect on nature because hardwood logging can thus be reduced. Wooden body 2 is now suitable as or for a construction element, both for indoor and outdoor use.

[0025] Although the invention has been further elucidated on the basis of only this exemplary embodiment, it will be apparent that the invention is by no means limited thereto. On the contrary, many variations and embodiments are still possible within the scope of the invention for a person with ordinary skill in the art. The described in situ polymerization is thus also possible with alternative pyrrole derivatives, such as for instance particularly 1-methylpyrrole, 2,5-dimethylpyrrole, 1,2,5-trimethylpyrrole, 2-acetylpyrrole, 2-acetyl-1-methylpyrrole, pyrrole-2-carboxaldehyde, 1-methyl-2-pyrrolecarboxaldehyde and combinations thereof, optionally using iron(III) chloride or a different oxidizer. Other heterocyclic compounds, such as thiophene, pyridine, quinoline, diazine, are also suitable as polymerizable compound which, with a suitable oxidizer which was introduced into the cells of the wood beforehand, will undergo according to the invention an in situ polymerization deep into the wood from the vapour phase.