Wood material board with reduced emission of volatile organic compounds (VOCs) and method for the production thereof

Abstract

A method for producing wood material boards with reduced emission of volatile organic compounds (VOCs), including: a) producing woodchips from suitable timbers; b) heat-treating at least one portion of the woodchips at a temperature between 150° C. and 300° C. for a period of 1 to 5 hours; c) crushing the wood chips that are not heat-treated and at least one portion of the heat-treated woodchips by machining in order to obtain wood shavings or by solubilizing in order to obtain wood fibers; d) gluing the wood shavings or wood fibers with at least one binding agent; e) applying the glued wood shavings onto a transport belt while forming a multi-layered shavings cake or applying the glued wood fibers onto a transport belt while forming a single-layer fiber cake; and f) compressing the shavings cake or the fiber cake to form a wood material board.

Claims

1. A wood chipboard panel with reduced emission of volatile organic compounds (VOCs) comprising wood shavings produced from heat-treated and non-heat-treated wood chips by shaving and gluing, wherein, in the case of heat treatment, the wood chips are exposed to a temperature between 150° C. and 300° C. for a period of 1 hour to 5 hours prior to shaving, the wood chipboard panel consists of a mixture of 10% to 50% by weight of shavings obtained from non-heat-treated wood chips and 50% to 90% by weight of shavings obtained from heat-treated wood chips, and the wood chipboard panel exhibits a reduced emission of aldehydes and/or of organic acids released during wood decomposition as compared to a wood chipboard made of wood chips obtained from non-heat-treated wood chips.

2. The wood chipboard panel according to claim 1, wherein the shavings obtained from the heat-treated wood chips are used in a middle layer of the wood chipboard panel.

3. The wood chipboard panel according to claim 1, further comprising a binder selected from the group consisting of formaldehyde adhesives, polyurethane adhesives, epoxy resin adhesives, and polyester adhesives.

4. The wood chipboard panel according to claim 3, wherein the polyurethane adhesive is based on aromatic polyisocyanates.

5. The wood chipboard panel according to claim 4, wherein the aromatic polyisocyanate is polydiphenylmethane diisocyanate (PMDI), tolylene diisocyanate (TDI), and/or diphenylmethane diisocyanate (MDI).

6. The wood chipboard panel according to 3, wherein, when a polyurethane adhesive is used, the amount of binder in a middle layer is between 2% and 5% by weight and in a top layer is between 4% and 8% by weight.

7. The wood chipboard panel according to claim 1, wherein the wood chipboard panel has a bulk density between 400 kg/m.sup.3 and 1200 kg/m.sup.3.

8. The wood chipboard panel according to claim 1, wherein the aldehydes comprise one or more of pentanal, hexanal, or octanal.

9. A method of using a chipboard panel according to claim 1 for furniture, wall, floor and ceiling coverings.

10. A wood fiberboard panel with reduced emission of volatile organic compounds (VOCs) comprising wood fibers produced and glued by defibration from heat-treated and non-heat-treated wood chips, wherein, in the case of heat treatment, the wood chips are exposed to a temperature between 150° C. and 300° C. for a period of 1 hour to 5 hours prior to defibration, the wood fiberboard panel consists of a mixture of 10% to 50% by weight of fibers obtained from non-heat-treated wood chips and 50% to 90% by weight of fibers obtained from heat-treated wood chips, and the wood fiberboard panel exhibits a reduced emission of aldehydes and/or of organic acids released during wood decomposition as compared to a wood fiberboard made of wood chips obtained from non-heat-treated wood chips.

11. The wood fiberboard panel according to claim 10, further comprising a binder selected from the group consisting of formaldehyde adhesives, polyurethane adhesives, epoxy resin adhesives, and polyester adhesives.

12. The wood fiberboard panel according to claim 11, wherein the polyurethane adhesive is based on aromatic polyisocyanates.

13. The wood fiberboard panel according to claim 12, wherein the aromatic polyisocyanate is polydiphenylmethane diisocyanate (PMDI), tolylene diisocyanate (TDI), and/or diphenylmethane diisocyanate (MDI).

14. The wood fiberboard panel according to claim 11, wherein, when a polyurethane adhesive is used, the quantity of the binder is 1% to 10% by weight.

15. The wood fiberboard panel according to claim 10, wherein the wood fiberboard panel has a bulk density between 400 kg/m.sup.3 and 1200 kg/m.sup.3.

16. The wood fiberboard panel according to claim 10, wherein the aldehydes comprise one or more of pentanal, hexanal, or octanal.

17. A method of using a wood fiberboard panel according to claim 10 for furniture, wall, floor and ceiling coverings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a diagrammatic representation of a first embodiment of the process of the invention for producing a fiberboard panel, and

(2) FIG. 2 shows a diagrammatic representation of a second embodiment of the process of the invention for producing a fiberboard panel.

DESCRIPTION OF THE INVENTION

(3) The first embodiment of the process of the invention, shown in FIG. 1, describes the individual process steps, beginning with the provision of the lumber starting product, through to the final fiberboard panel.

(4) First of all in step 1, accordingly, suitable lumber starting material is provided for producing the wood chips. Suitable lumber starting material includes all hardwoods, softwoods or else mixtures thereof. The roundwood is debarked and comminuted to chips in disk chippers or drum chippers (step 2), where the size of the wood chips can be controlled accordingly.

(5) Following comminution and provision of the wood chips, they are optionally subjected to a preliminary drying operation, to adjust the moisture content to 5-10% in relation to the initial moisture content of the wood chips.

(6) In the case of the first embodiment shown in FIG. 1, at least a part of the optionally preliminarily dried wood chips are removed from the customary production process and introduced into a heat-treatment reactor (step 3). The heat treatment of the removed wood chips takes place in a temperature range between 220° and 260° C. The pyrolysis gases formed in this procedure are utilized to generate the energy required for the operating plant.

(7) After the end of the heat treatment, which in the present case lasts about 2 hours, the heat-treated wood chips are reintroduced into the process and are brought to a moisture content of 10-20% again in a washing and boiling step 4, optionally together with the non-heat-treated wood chips.

(8) Thereafter, the wood fibers are subjected to the fiberizing operation in a refiner (step 5), and in the course of the fiberizing operation a suitable wetting agent is supplied to the wood fibers.

(9) Immediately after fiber digestion, the wood fibers may be mixed with a liquid binder and optionally with a flame retardant (step 6). In this process stage, the contacting of the wood fibers with the liquid binder may take place, for example, in a blowline process.

(10) The resinating step 6 is followed by a drying operation on the resinated wood fibers (step 7), and this drying operation may take place in two stages I, II. The dryer is configured as a 2-stage dryer, with the primary drying taking place in stage 1 by means of hot gases (air or superheated steam) and subsequent drying in stage 2, where again the use of hot air or superheated steam is possible. The mixture of substances is separated in/after each stage by means of separating cyclone and capsule mechanisms.

(11) The dried wood fibers are sorted or classified according to their size (step 8).

(12) The resinated wood fibers are subsequently scattered onto a conveyor belt (step 9), and the fiber cake formed is first supplied to a preliminary press (step 10) and lastly is pressed in the hot press (step 11) to form a large-format fiberboard panel.

(13) In the final machining operation, the fiberboard panel obtained is finished in a suitable way.

(14) The second working example, shown in FIG. 2, differs from the first embodiment depicted in FIG. 1 in that the step of heat-treating the wood chips (step 3) is integrated into the operation of producing the fiberboard panels, i.e., the heat-treatment step is incorporated into the overall operation or operating line and takes place on-line. Consequently there is no removal of the wood chips from the operating line for the heat treatment. This is advantageous especially if the fiberboard panel is produced entirely of wood fibers obtained from heat-treated wood chips.

Working Example 1: Fiberboard Panel, Especially MDF

(15) Wood chips are kept in undried form (moisture content: around 50%, format: around 5×5 cm, thickness: around 1 cm) in a continuous heat-treatment apparatus at 220° C. under saturated steam for around 2 h. The apparatus consists of a conveying apparatus by which the chips are transported through slowly with the aid of a spiral conveyor.

(16) The chips are subsequently cooled in the chip scrubber and are then supplied for standard fiberizing. In this case, 0.1% of a commercial surfactant was contained in the water of the chip scrubber. This surfactant was added in order to improve the wetting of the hydrophobic chips. The water in the scrubber showed a significantly reduced coloration, and the loading with organic constituents was reduced by around 90%.

(17) The chips obtained after fiberizing were resinated with a standard commercial urea-formaldehyde resin in the blowline and dried. Then the fibers were scattered and were processed to form an MDF having a density of 650 kg/m.sup.3 and a thickness of 10 mm.

(18) The resulting MDF is subsequently investigated together with a control sample (made from chips which have not been heat-treated) for VOC emissions in accordance with the AgBB scheme. For reasons of time, the 3-day value was ascertained.

(19) Chamber parameters: temperature 23° C.; atmospheric humidity 50%+−5%; air exchange 0.5/h+−0.1/h; loading 1 m.sup.2/m.sup.3; chamber volume 225 m.sup.3

(20) TABLE-US-00001 Control sample Experimental panel Parameter μg/m.sup.3 μg/m.sup.3 Acetic acid 188 9 Hexanoic acid 91 n.d. Hexanal 51 4 Pentanal 43 9 Octanal 33 5

(21) As from the table, the emissions of the quantitatively most important parameters from the experimental panel are at a significantly lower level.

Working Example 2: Chipboard Panel

(22) The production of chipboard panels is general knowledge. The wood chips, heat-treated in the same way as for working example 1, are supplied to a flaking device. After flaking has taken place, the wood shavings are dried to a residual moisture content of around 2% in a drum dryer. After drying has taken place, the wood shavings are classified and separated into coarser shavings for the middle layer and finer shavings for the outer layer.

(23) After having been resinated with urea-formaldehyde resin, the shavings are scattered to form multilayer shaving cakes, with the shavings used in the middle layer having been obtained from heat-treated wood chips, and the cakes are pressed to form panels at temperatures of around 200° C.

(24) The emissions investigation, carried out in the same way as for working example 1, revealed similarly reduced VOC emission values for acetic acid and for the higher aldehydes.