POROUS CARRIER SYSTEM FOR REDUCING THE EMISSION OF FORMALDEHYDE IN A WOOD-BASED MATERIAL

Abstract

The invention relates to a porous carrier system for reducing the emission of formaldehyde in a wood-based material, which comprises a formaldehyde-binding substance A and a hydroxide-releasing substance B. The invention further relates to a method for producing the porous carrier system, the use of the porous carrier system to reduce the emission of formaldehyde in a wood-based material, a wood-based material comprising the porous carrier system, and a method for producing said wood-based material.

Claims

1-16. (canceled)

17. A porous carrier system for reducing the emission of formaldehyde in a wood-based material comprising: a formaldehyde-binding substance A; and a hydroxide-releasing substance B, wherein the formaldehyde-binding substance A and the hydroxide-releasing substance B are contained in at least one porous carrier material A, or the formaldehyde-binding substance A is contained in at least one porous carrier material A and the hydroxide-releasing substance B is contained in at least one porous carrier material B, and wherein the formaldehyde-binding substance A is urea, the hydroxide-releasing substance B is sodium sulphite, the porous carrier material A is diatomaceous earth, and the porous carrier material B is diatomaceous earth.

18. (canceled)

19. A method for producing a porous carrier system for reducing the emission of formaldehyde in the wood-based material of claim 17 comprising the following steps: a1) applying a liquid composition comprising a substance A and a substance B to a porous carrier material A, wherein substance A is urea, substance B is sodium sulphite, and porous carrier material A is diatomaceous earth; and b1) at least partially removing the liquid composition from the porous carrier material A, or a2) applying a first liquid composition comprising the substance A to at least one porous carrier material A, wherein substance A is urea and porous carrier material A is diatomaceous earth; b2) at least partially removing the first liquid composition from the at least one porous carrier material A; c2) applying a second liquid composition comprising a substance B, to the at least one porous carrier material A, wherein substance B is sodium sulphite; and d2) at least partially removing the second liquid composition from the at least one porous carrier material A.

20. (canceled)

21. A method for producing a porous carrier system for reducing the emission of formaldehyde in the wood-based material of claim 17 wherein the formaldehyde-binding substance A is contained in at least one porous carrier material A and the hydroxide-releasing substance B is contained in at least one porous carrier material B, the method comprising the following steps: a) applying a liquid composition comprising a substance A to at least one porous carrier material A to form a wetted porous carrier material A, wherein substance A is urea and porous carrier material A is diatomaceous earth; b) applying a liquid composition comprising a substance B to at least one porous carrier material B to form a wetted porous carrier B, wherein substance B is sodium sulphite and porous carrier material B is diatomaceous earth; c) at least partially removing the liquid compositions from the wetted porous carrier material A and the wetted porous carrier material B to obtain loaded porous carrier materials A and B, and d) mixing the loaded porous carrier materials A and B.

22. The method of claim 21, wherein the applying of the liquid composition of step a) is selected from immersing the porous carrier material A in the liquid composition, flooding the porous carrier material A with the liquid composition, and spraying the liquid composition on the porous carrier material A; and the applying of the liquid composition of step b) is selected from immersing the porous carrier material B in the liquid composition, flooding the porous carrier material B with the liquid composition, and spraying the liquid composition on the porous carrier material B.

23. The method of claim 22, wherein the applying of the liquid composition of step a) further comprises applying a vacuum to the porous carrier material A, or the applying of the liquid composition of step b) further comprises applying a vacuum to the porous carrier material B.

24. The method of claim 21, wherein the applying of the liquid composition of step a) further comprises resting the porous carrier material A in the liquid composition; or the applying of the liquid composition of step b) further comprises resting the porous carrier material B in the liquid composition.

25. The method of claim 21, wherein the at least partially removing the liquid compositions of step c) comprises filtering the wetted porous carrier materials A and B to at least partially remove the liquid compositions.

26. The method of claim 21, further comprising drying the wetted porous carrier materials A and B after the at least partially removing the liquid compositions of step c).

27. A method of reducing the emission of formaldehyde in a wood-based material comprising applying the porous carrier system according to claim 17 to a wood-based material.

28. A wood-based material comprising a porous carrier system for reducing the emission of formaldehyde according to claim 17.

29. A method for producing a wood-based material, comprising the following steps: a) providing a lignocellulose-containing material in the form of wood particles; b) sizing the lignocellulose-containing material with a composition comprising at least one aminoplast resin; and c) pressing the lignocellulose-containing material into a wood-based material, wherein, the porous carrier system according to claim 17 is added to the lignocellulose-containing material prior to the pressing of step c).

Description

EXAMPLE 1

[0103] First, the production of a porous carrier system will be described. Here, the variants 1 and 2 serve to produce a porous carrier system in which the substance A is contained in at least one porous carrier material A and substance B in at least one porous carrier material B. Variant 3 is used to produce a porous carrier system in which the substance A and the substance B are contained in at least one porous carrier material A.

[0104] Diatomaceous earth was used as the porous carrier material A and B. The porous carrier material A was loaded with a freshly prepared 40 wt.-% solution of urea, based on the total weight of urea and water, and the porous carrier material B with a 20 wt.-% sodium sulphite solution, based on the total weight of sodium sulphite and water, as follows:

[0105] Variant 1:

[0106] 500 g of diatomaceous earth were weighed out and covered with 1 litre of the freshly prepared urea or sodium sulphite solution. Then, a vacuum was applied until no further bubbles emerged due to air escaping from the pores of the diatomaceous earth, and the urea or sodium sulphite-loaded diatomaceous earth was filtered off and dried in a climatic chamber at 30 C. and 5% atmospheric humidity.

[0107] Variant 2:

[0108] 500 g of diatomaceous earth were weighed out and covered with 1 litre of the freshly prepared urea or sodium sulphite solution and stored in a sealed container for 24 hours. Then, the diatomaceous earth loaded with urea or sodium sulphite was filtered off.

[0109] Variant 3:

[0110] 500 g of diatomaceous earth were weighed out and covered with 1 litre of a freshly prepared solution of 200 g of urea and 100 g of sodium sulphite in 700 g of water and stored in a sealed container for 24 hours. Then the diatomaceous earth loaded with urea and sodium sulphite laden was filtered off and dried.

EXAMPLE 2

[0111] Board tests were carried out under the following conditions: [0112] Board thickness: 14 mm [0113] Chip material: Wood chips with an average length of 1 to 12 mm, an average width of 1 to 6 mm and an average thickness of 0.1 to 2 mm. [0114] Sizing: The binder used was urea-formaldehyde in an amount of 8% by weight, based on the dry weight of the wood (solid resin/absolutely dry). [0115] Curing agent: 60% ammonium nitrate, was used in an amount of 3 wt.-% based on the solid resin content of the aminoplast resin. [0116] Target density: 600 kg/m.sup.3 [0117] Pressing temperature: 220 C. [0118] Compression factor: 9.3 s/mm

[0119] Three different types of boards were produced. In each case two boards were produced per board type, i.e. the quantity stated below in the production of the respective boards is doubled again.

[0120] Reference Board

[0121] A board which was produced under the conditions indicated above without any addition of pure urea or of the porous carrier system according to the invention served as a reference.

[0122] Board According to the Prior Art

[0123] As a prior art board already provided with a material for reducing the emission of formaldehyde, [0124] (1) two boards were produced under the conditions indicated above and additionally after sizing, i.e. before pressing, 0.5 or 2 wt.-% of urea (U) based on the dry weight of wood (solid resin/absolutely dry) was added, and [0125] (2) six boards were produced under the conditions indicated above, and additionally after sizing, i.e. before pressing, 0.5, 1.5 and 3 wt.-% of urea-loaded diatomaceous earth (KGU) or sodium sulphite-loaded diatomaceous earth (KGS) in each case based on the dry weight of wood (solid resin/absolutely dry) was added.

[0126] Board According to the Invention

[0127] As a board according to the invention, three boards were produced under the conditions indicated above and, in addition, after sizing, i.e. before pressing, a mixture of: [0128] (1) 0.4 wt.-% loaded with urea diatomaceous earth (KGU) and 0.1 wt.-% loaded with sodium sulphite diatomaceous earth (KGS) (total 0.5 wt.-% loaded diatomaceous earth) based on the dry weight of wood (solid resin/absolutely dry) was added, as well as [0129] (2) 2.7% by weight of diatomaceous earth loaded with urea (KGU) and 0.3% by weight of diatomaceous earth loaded with sodium sulphite (KGS) (in total 3% by weight of loaded diatomaceous earth), based on the dry weight of the wood (solid/absolutely dry) was added. [0130] (3) 3 wt.-% of diatomaceous earth (KGUS) loaded with urea and sodium sulphite based on the dry weight of the wood (solid resin/absolutely dry) was added.

[0131] Following the board pressing, the transverse tensile strength, the emission of formaldehyde, swelling and water absorption of the boards were determined. For the determination of the transverse tensile strength, swelling and water absorption, first ten specimens with a geometry of 505014 mm were cut for each board. To determine the emission of formaldehyde by desiccator measurement, first test specimens were cut with the dimensions 5151.4 cm. The total area of the samples in the desiccator measurement must be 1800 cm.sup.2, so for 14 mm boards, nine samples per board are needed. To determine the emission of formaldehyde by means of a perforator method, first ten test pieces with a geometry of 2.52.51.4 cm were cut for each board. Each test piece was measured before the test by means of a digital thickness probe, the mass was determined and from this the density was calculated.

[0132] The boards produced in this way were tested in accordance with EN 319 (transverse tensile strength test), EN 317 (thickness swelling and also water absorption), JIS 1460 (desiccator measurement, formaldehyde emission test) and DIN EN ISO 12460-5 (perforator method; formaldehyde emission test).

[0133] Transverse Tensile Strength

[0134] The transverse tensile strength was determined according to EN 319. To this end, each test specimen was bonded by means of a hot melt adhesive with two aluminium yokes on the top and bottom and then after cooling pulled apart on the testing machine (Zwick Zmart.Pro) at a constant test speed of 1 mm/min. The force leading to the break in the middle of the specimen was recorded and the resulting transverse tensile strength over the specimen area was calculated [N/mm.sup.2].

[0135] Desiccator Measurement

[0136] The determination of the emission of formaldehyde was carried out by means of the desiccator measurement according to JIS 1460. The samples are placed in a sample container in a desiccator, in each of which there is a dish containing 300 ml of deionised water. In addition, two blank values, i.e. desiccator and water without sample, are measured.

[0137] The samples have a dwell time of 24 hours in the desiccators. Then 10 ml of water are taken from each water dish and 10 ml each of acetylacetone solution (4 ml/l) and ammonium acetate solution (200 g/l) are added. This mixture is heated to 40 C. for 15 minutes and cooled to room temperature for a further 1 hour whilst being stored in a dark environment.

[0138] The absorbance is measured on the photometer at a wavelength of 412 nm. This is then converted into mg/l according to a stored calibration.

[0139] Perforator Method

[0140] The determination of the emission of formaldehyde was carried out by means of the perforator method according to DIN EN ISO 12460-5. This is an extraction method with toluene as solvent (about 600 ml). The sample volume was around 100-150 g for the perforator measurement and around 100 g for the determination of the board moisture content (the result refers to a board moisture content of 6.5% and was calculated using a stored formula).

[0141] Thickness Swelling

[0142] The determination of the thickness swelling after 24 hours of storage in water was carried out according to DIN EN 317. For this, the test specimens were stored under water at a water temperature of 20 C. for 24 hours. Then, the increase in thickness was determined relative to the starting thickness and the percentage thickness swelling was calculated.

[0143] Water Absorption

[0144] The water absorption was determined on the thickness swelling samples, thus similarly after 24 hours of storage in water. For the calculation, the weight was measured after said 24 hours and the water absorption was then calculated according to the following formula:

[00001]$\mathrm{Water}.Math..Math.\mathrm{Absorption}.Math..Math.\left(\%\right)=\frac{M.Math.a.Math.s.Math.s_{\mathrm{afterwards}}-M.Math.a.Math.s.Math.s_{\mathrm{before}}}{M.Math.a.Math.s.Math.s_{\mathrm{before}}}1.Math.0.Math.0$

[0145] The test results for reference boards without material for reducing the emission of formaldehyde, boards of the prior art with material for reducing the emission of formaldehyde, and boards according to the invention containing the porous carrier system according to the invention are shown below in Table 1.

[0146] The measurements were taken from 10 samples per board. Since two boards were produced for each type of board, the experimental results for determination of the emission of formaldehyde, transverse tensile strength, swelling and water absorption according to the methods described above in Table 1 are mean values of 20 test pieces.

TABLE-US-00001 TABLE 1 MV MV MV Transverse MV Perfo- MV Water tensile Desic- rator Swell- absorp- strenght cator 6.5% ing tion Description N/mm.sup.2 mg/l mg/100 g % % Reference 0.63 1.49 7.24 25.81 80.29 0.5 Wt.-% U 0.54 1.00 5.13 34.71 95.81 2 Wt.-% U 0.17 0.46 2.82 55.22 125.87 0.5 Wt.-% KGU 0.62 1.32 6.35 31.54 87.27 0.4Wt.-% KGU + 0.64 1.31 6.20 28.09 86.61 0.1 Wt.-% KGS 1.5 Wt.-%% KGU 0.52 0.82 4.99 30.05 92.44 1.5 Wt.-% KGS 0.61 1.45 7.31 26.85 87.83 3 Wt.-% KGU 0.42 0.53 3.27 40.98 99.44 3 Wt.-% KGS 0.54 1.33 7.51 24.08 85.88 2.7 Wt.-% KGU + 0.44 0.39 2.83 38.01 97.70 0.3 Wt.-% KGS 3 Wt.-% KGUS 0.51 0.69 4.45 27.55 91.32 MV: Average of 20 test pieces, U = urea, S = sodium sulphite, KG = diatomaceous earth

[0147] Surprisingly, it was found that the addition of the diatomaceous earth loaded with urea and/or sodium sulphite significantly reduced the decline in transverse tensile strength of the wood-based materialsby adding the same quantity in wt.-% of one of the pure substances, such as urea (U), the transverse tensile strength drops by up to 80%.

[0148] It can also be seen from Table 1 that the addition of a mixture of urea-loaded diatomaceous earth (KGU) and sodium sulphite-loaded diatomaceous earth (KGS) compared to the addition of the same amount in wt.-% of urea-loaded diatomaceous earth (KGU) or diatomaceous earth (KGS) loaded only with sodium sulphite in the production of a wood-based material causes the emission of formaldehyde in the wood-based material, which comprises the mixture of KGU and KGS, in comparison to the emission of formaldehyde in the wood-based material which includes only KGU or KGS only, to be significantly reduced. The transverse tensile strength, swelling and water absorption of the wood-based material according to the invention, comprising a mixture of KGU and KGS, in comparison to the transverse tensile strength, swelling and water absorption of the wood-based material from the prior art, comprising the same amount in wt.-% of KGU only, were not impaired.

[0149] The addition of diatomaceous earth (KGUS) loaded with urea and sodium sulphite during the production of a wood-based material, compared to the addition of the same amount in wt.-% of urea-loaded diatomaceous earth (KGU), leads to a significantly increased transverse tensile strength, lower swelling and lower water absorption of the wood-based material according to the invention, comprising diatomaceous earth loaded with urea and sodium sulphite, and at the same time to an emission of formaldehyde comparable to that of the wood-based material of the prior art comprising urea-loaded diatomaceous earth (KGU).