OSB (Oriented Strand Board) Wood Material Panel Having Improved Properties and Method for Producing Same

Abstract

The invention relates to a method for producing OSB wood material panels, in particular OSB wood material panels having reduced emission of volatile organic compounds (VOCs), including the following steps: a) producing wood strands from suitable woods; b) torrefying at least some of the wood strands; c) glue-coating the torrefied wood strands and non-torrefied wood strands with at least one binder; d) scattering the glue-coated wood strands onto a conveyor belt; and e) pressing the glue-coated wood strands to form a wood material panel. The invention further relates to an OSB wood material panel that can be produced in accordance with said method and to the use of torrefied wood strands to reduce the emission of VOCs from OSB wood material panels.

Claims

1. A process for the production of OSB-wood-composite boards, comprising the following steps: a) production of wood strands made of suitable woods, b) torrefaction of at least a portion of the wood strands; c) gluing of the torrefied wood strands and non-torrefied wood strands with at least one binder; d) application, by scattering, of the glued wood strands to a conveyor belt; and e) pressing of the glued wood strands to give an OSB-wood-composite board.

2. The process according to claim 1, wherein at least a portion of the wood strands is dried before torrefaction.

3. The process according to claim 1, wherein at least a portion of the wood strands is torrefied with a moisture content of 20 to 50% by weight.

4. The process according to claim 1, wherein torrefied wood strands, or a mixture of torrefied wood strands and non-torrefied wood strands, are/is used as middle layer and/or outer layer of the OSB-wood-composite board.

5. The process according to claim 1, wherein the wood strands are torrefied in at least one torrefaction reactor.

6. The process according to claim 1, wherein wood strands used for the middle layer and the outer layers of the OSB-wood-composite board are respectively torrefied separately in at least two torrefaction reactors.

7. The process according to claim 1, wherein the wood strands are torrefied by heating in a low-oxygen-content or oxygen-free atmosphere under atmospheric pressure or elevated pressure at a temperature of between 150 C. and 300 C.

8. The process according to claim 1, wherein, before gluing with a suitable binder, the torrefied wood strands are cooled in water.

9. The process according to claim 1, wherein the quantity of binder used to glue the torrefied and non-torrefied wood strands is from 1.0 to 5.0% by weight based on the total quantity of the wood strands.

10. The process according to claim 1, wherein the glued wood strands are pressed at temperatures of from 200 to 250 C. to give an OSB-wood-composite board.

11. An OSB-wood-composite board with reduced emission of volatile organic compounds (VOCs) which can be produced in the process according to claim 1 comprising torrefied wood strands.

12. The OSB-wood-composite board according to claim 11, further comprising reduced emission of terpenes and/or organic acids and/or aldehydes liberated during the wood digestion.

13. The OSB-wood-composite board according to claim 11, further comprising a swelling value reduced in comparison with an OSB-wood-composite boards produced entirely from non-torrefied wood strands.

14. The OSB-wood-composite board according to claim 11, wherein the OSB-wood-composite board is composed entirely of torrefied wood strands or of a mixture of torrefied and non-torrefied wood strands.

15. Use of torrefied wood strands for reducing the emission of volatile organic compounds (VOCs) from OSB-wood-composite boards.

16. The process according to claim 1, wherein the OSB-wood-composite boards comprise OSB-wood-composite boards with reduced emission of volatile organic compounds (VOCs).

17. The process according to claim 5, wherein the wood strands are torrefied in two torrefaction reactors.

18. The process according to claim 7, wherein the temperature is between 220 C. and 260 C.

19. The process according to claim 9, wherein the quantity of binder used to glue the torrefied and non-torrefied wood strands is from 2 to 4% by weight based on the total quantity of wood strands.

20. The process according to claim 10, wherein the glued wood strands are pressed at a temperature from 220 C. to 230 C.

Description

[0081] The invention is explained in greater detail below using an example of embodiment making reference to the figure of the drawing. In the figures:

[0082] FIG. 1 shows a diagrammatic representation of a first embodiment of the process according to the invention, and

[0083] FIG. 2 shows a diagrammatic representation of a second embodiment of the process according to the invention.

[0084] The first embodiment of the process according to the invention shown in FIG. 1 describes the individual process steps starting with the provision of the initial wood product up to the finished OSB-wood-composite board.

[0085] Accordingly, suitable initial wood material is first provided in step 1 for the production of the wood strands. All softwoods, hardwoods or also mixtures thereof are suitable as initial wood material.

[0086] The debarking (step 2) and the chipping (step 3) of the initial wood material takes place in chipping machines suitable for this purpose, wherein the size of the wood strands can be duly controlled. Following the size-reduction and provision of the wood strands, the latter optionally undergo a preliminary drying process, wherein a moisture content of 5-10% compared to the initial moisture content of the wood chips is adjusted (not shown).

[0087] In the case of the embodiment shown in FIG. 1, the wood strands are introduced into a torrefaction reactor (step 4). The torrefaction of the wood strands takes place in a temperature range between 220 C. and 260 C. The pyrolysis gases or torrefaction gases thereby arising are used to generate the energy required for the process plant.

[0088] After completion of the torrefaction, which in the present case lasts approximately 2 hours, the torrefied wood strands are wetted, sorted and separated (step 5).

[0089] A separation into wood strands for use as a middle layer (step 6a) or as an outer layer (step 6b) takes place with the respective gluing.

[0090] The glued torrefied wood strands are applied, by spreading, on a conveyor belt in the sequence first lower outer layer, middle layer and second upper outer layer (step 7) and then pressed to give an OSB-wood-composite board (step 8).

[0091] In the second embodiment shown in FIG. 2, the initial wood material, by analogy with FIG. 1, is first provided (step 1), debarked (step 2) and chipped (step 3). The wood strands optionally undergo a preliminary drying process, wherein a moisture content of 5-10% compared to the initial moisture content of the wood strands is adjusted (step 3a).

[0092] In contrast with the variant of embodiment of FIG. 1, separation into wood strands for use as a middle layer or as an outer layer (step 5) already takes place after the optional drying.

[0093] This is followed by the torrefaction of the wood strands intended for the middle layer (step 4a) and/or torrefaction of the wood strands intended for the outer layer(s) (step 4b) in each case in a suitable torrefaction reactor. The torrefaction of the wood strands takes place in a temperature range between 220 and 260 C. The torrefaction can be adjusted to the desired degree of torrefaction for the middle layer and outer layers.

[0094] The pyrolysis gases or torrefaction gases thereby arising are used to generate the energy required for the process plant.

[0095] After completion of the torrefaction, which in the present case lasts approximately 2 hours, the torrefied wood strands are glued (steps 6 a,b).

[0096] The glued torrefied wood strands are applied, by spreading, on a conveyor belt in the sequence first lower outer layer, middle layer and second upper outer layer (step 7) and then pressed to give an OSB-wood-composite board (step 8).

[0097] In the final processing, the obtained OSB-wood-composite board is in each case suitably packaged.

Example of Embodiment

[0098] Strands are produced from pine trunks and torrefied in a continuously operating torrefaction apparatus at 180 C. up to a loss of mass of approximately 20%. This takes place under saturated steam. During the process, the strands change colour from bright yellow to bright brown. The strands are then cooled in water.

[0099] The binder (PMDI, approximately 3% by weight) is then applied in a gluing machine (gluing drum, for example from the firm Coil) finely distributed onto the torrefied wood strands. The glued torrefied strands are applied by scattering as a middle layer in an OSB plant.

[0100] The outer layer is formed from strands which have been dried in a drum-type dryer. The latter are also glued with PMDI as the glue (approximately 3% by weight). The strands are not additionally hydrophobized by for example paraffin emulsion, so that the tests subsequently to be carried out are not disrupted by the hydrophobing agent. The scattered strands are pressed in a Contipress to give OSB boards.

[0101] The percentage distribution between middle layer and outer layer is at least 70% to 30%. The strands are pressed to form boards, which have a bulk density of approximately 570 kg/m.sup.3.

[0102] After a storage time of approximately one week, the test board was tested together with a standard board of the same thickness in a micro-chamber for the VOC emission.

[0103] Chamber parameters: temperature 23 C.; moisture content 0%; air through-flow 150 ml/min; air exchange 188/h; loading 48.8 m.sup.2/m.sup.3; sample surface 0.003 m.sup.2, chamber volume: 48 ml.

[0104] The values of the most important parameters in terms of quantity are shown in table 1.

TABLE-US-00001 TABLE 1 Test board Standard board Parameter g/m.sup.2 h g/m.sup.2 h Hexanal 1093 3164 3-Carene 388 1962 -Pinene 322 1174 Pentanal 78 354 -Pinene 98 314

[0105] As can be seen from the results, the emissions of the parameters most important in terms of quantity are reduced by the factor 3 to 5.

[0106] In addition, the thickness swelling was also determined.

TABLE-US-00002 TABLE 2 Test board Standard board Swelling 18.3 27.44 (24 h) in %

[0107] As can be seen from the table, the swelling values are reduced by the use of torrefied strands by approximately 35%.