METHOD FOR PRODUCING WOOD FIBERBOARDS

Abstract

The disclosure relates to a method for the production of wood fiberboards such as MDF boards.

Claims

1. A method for the production of wood fiberboards, comprising the following steps: a) crushing wood into wood chips, b) hydrothermally pretreating the wood chips with steam in a pre-steaming bin at a temperature of 100 to 180 C. and a pressure of 1 to 10 bar, c) grinding the pre-treated wood chips into fine wood particles in a refiner in a presence of steam at a temperature of 150 to 200 C. and a pressure of 4.5 to 16 bar, d) gluing and drying the fine wood particles, wherein the drying of the fine wood particles can also be carried out prior to gluing, e) forming mats from bonded fibers and precompacting the mats, f) pressing the glued and dried fine wood particles at a temperature of 170 to 240 C. into wood fiberboards, wherein at least one of steps d) to e) is carried out in a presence of one or a plurality of surfactants.

2. The method according to claim 1, wherein step d) is carried out in the presence of one or a plurality of surfactants.

3. The method according to claim 1, wherein step e) is carried out in the presence of one or a plurality of surfactants.

4. The method according to claim 1, wherein the surfactants are anionic or nonionic surfactants.

5. The method according to claim 1, wherein an amount of surfactants in step c) is 0.05 to 5% by weight based on bone-dry wood.

6. The method according to claim 1, wherein the fine wood particles are reductively bleached.

7. The method according to claim 1, wherein the wood fiberboards are a medium-density fiberboards.

8. The method according to claim 1, wherein the surfactants are selected from fatty alcohol ether sulfates with branched and/or unbranched C.sub.8 to C.sub.20 alkyl chains and 2 to 50 ethylene oxide units.

9. The method according to claim 1, wherein the surfactants are selected from alkyl- and/or aryl alkoxylates of the general formula (I) ##STR00002## where R.sub.1=linear or branched, primary or secondary C.sub.4-C.sub.24 alkylphenyl or naphthyl, R.sub.2=linear or branched C.sub.1-C.sub.16 alkyl, R.sub.3H, benzyl, linear or branched C.sub.1-C.sub.18 alkyl, n=1-200, m=0-80, wherein the alkylene oxide units can be arranged blockwise or statistically in any desired order.

10. The method according to claim 1, wherein the surfactants are selected from C.sub.8-C.sub.15 alkyl ethoxylates with 3 to 20 ethylene oxide units.

11. The method according to claim 1, wherein the surfactants are selected from alkyl polyglycosides of the general formula (IIa) or (IIb)
R.sub.1O(R.sub.2O).sub.b(Z).sub.a(IIa)
R.sub.1O(Z).sub.a(R.sub.2O).sub.bH(IIb) where R.sub.1=linear or branched C.sub.6-C.sub.30 alkyl, R.sub.2C.sub.2-C.sub.4 alkylene, Z=independently, one sugar radical each with 5 or 6 carbon atoms, b=0-12, a=1-10.

12. The method according to claim 11, wherein R.sub.1 is a C.sub.8-C.sub.16 alkyl chain, b=0 and a=1-4.

Description

EXAMPLE 1

[0081] The bonded fibers are then dried in a dryer to a moisture content of approx. 8% by weight, poured to form a mat, precompressed and pressed at 220 C. into a board approx. 4 mm thick.

[0082] The MDF boards have a rough surface with dark areas.

[0083] In order to test the hydrophobicity of the surfaces, a drop of water is dripped onto the surface, and the time required for the drop to be completely absorbed into the board is measured.

[0084] In a second test, the transverse tensile strength of the board is measured (according to EN 319); the results are shown in Table 2.

TABLE-US-00002 TABLE 2 Transverse tensile strength MDF board (N/mm.sup.2) Drop absorption time in sec Example 1 0.88 68

EXAMPLE 2

[0085] In example 2, spruce wood chips are defibrated in the presence of C.sub.8-C.sub.10 alkyl polyglycoside. The surfactant is dosed directly into the refiner as a 25% aqueous solution containing 1% of active surfactant based on the amount of wood.

[0086] The bonded fibers are then dried in a dryer to a moisture content of approx. 8% by weight, poured into a mat, precompacted and pressed at 220 C. into a board approx. 4 mm in thickness.

[0087] The boards have a smooth, glossy and homogeneous surface (also see Table 3).

TABLE-US-00003 TABLE 3 Transverse tensile Drop absorption MDF board (N/mm.sup.2) strength time in sec Example 2 1.02 476

EXAMPLE 3

[0088] In example 3, spruce wood chips are defibrated in a refiner and glued together in the blow line. At the same time, a 20% solution of a C.sub.8-C.sub.14 alkyl polyglycoside containing 0.5% of active surfactant based on the amount of wood is injected into the blow line.

[0089] The bonded fibers are then dried in a dryer to a moisture content of approx. 8% by weight, poured into a mat, precompacted and pressed at 220 C. into a board approx. 4 mm in thickness.

[0090] The boards have a smooth, glossy and homogeneous surface (also see Table 4).

TABLE-US-00004 TABLE 4 Transverse tensile strength MDF board (N/mm.sup.2) Drop absorption time in sec Example 3 1.21 780

EXAMPLE 4

[0091] In example 4, spruce wood chips are defibrated in a refiner and glued together in the blow line. At the same time, a 20% solution of a C.sub.13oxo alcohol ethoxylate+12 EO units containing 0.5% active surfactant based on the amount of wood is injected into the blow line.

[0092] The bonded fibers are then dried in a dryer to a moisture content of approx. 8% by weight, poured into a mat, precompacted and pressed at 220 C. into a board approx. 4 mm in thickness.

[0093] The boards have a smooth, glossy and homogeneous surface (also see Table 5).

TABLE-US-00005 TABLE 5 Transverse tensil strength MDF board (N/mm.sup.2) Drop absorption time in sec Example 4 0.98 346

EXAMPLE 5

[0094] In example 5, spruce wood chips are defibrated in a refiner and glued together in the blow line.

[0095] The bonded fibers are then dried in a dryer to a moisture content of approx. 8% by weight, poured into a mat and precompacted. A 20% solution of a C.sub.8-C.sub.14 alkyl polyglycoside is sprayed onto the precompacted mats, wherein 0.4% of active surfactant is used based on the amount of wood. After this, the mat is pressed at 220 C. into a board approx. 4 mm in thickness.

[0096] The treated side of the board is smooth, glossy and homogeneous. The untreated side is rough and spotted (also see Table 6).

TABLE-US-00006 TABLE 6 Transverse tensile Drop absorption MDF board strength (N/mm.sup.2) time in sec Example 5, 1.26 720 treated side Example 5, 1.26 93 untreated side

EXAMPLE 6

[0097] In example 6, spruce wood chips are defibrated in a refiner and glued together in the blow line. At the same time, a 20% solution of the sodium salt of a fatty alcohol ether sulfate with 12 EO units containing 0.7% active surfactant based on the amount of wood is injected into the blow line.

[0098] The bonded fibers are then dried in a dryer to a moisture content of approx. 8% by weight, poured into a mat, precompacted and pressed at 220 C. into a board approx. 4 mm in thickness.

[0099] The boards have a smooth, glossy and homogeneous surface (also see Table 7).

TABLE-US-00007 TABLE 7 Transverse tensile Drop absorption MDF board strength (N/mm.sup.2) time in sec Example 6 1.07 423