WO2006039914A1

WO2006039914A1 - Method for reducing the release of volatile organic compounds (voc) from wood and wood chip products and wood materials derived therefrom in particular particle boards

Info

Publication number: WO2006039914A1
Application number: PCT/DE2005/001830
Authority: WO
Inventors: Edmone Roffael; Thomas Schneider; Brigitte Dix
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2004-10-15
Filing date: 2005-10-12
Publication date: 2006-04-20
Also published as: ATE495866T1; EP1799412B1; DE502005010889D1; EP1799412A1; PL1799412T3

Abstract

The invention relates to a method for reducing the emissions of volatile organic compounds (VOC) from wood and wood chip products, such as wood chips, wood strands, wood fibres and wood veneers, in particular, made from soft wood and derived timber products made therefrom.

Description

Process for reducing the release of volatile organic compounds (VOC) from wood and wood crushing products and from wood-based materials produced therefrom, in particular chipboard

The invention relates to a process for reducing the emission of volatile organic compounds (VOCs) from wood and from wood pulp products such as wood shavings, wood strands, wood fibers and wood veneers, in particular from softwood, and from wood-based materials produced therefrom.

The volatile organic compounds are classified according to their boiling point or vapor pressure as very volatile organic compounds (WOCs), volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs). To the volatile organic compounds (VVOC) include compounds having a boiling point below 50 ⁰ C. These include formic acid and formaldehyde. As volatile organic compounds (VOC) are those volatile subsumed organics with boiling points between about 50 ⁰ C and 260 ⁰ C. The VOCs include acetic acid and terpenes.

The VOC are air pollutants, certain VOC cause eg odor nuisance and can have toxicological effects on living things. The VOCs are mainly derived from the ingredients (extractives) of the wood or its transformation products and, where appropriate, the degradation products of the main components of the wood (lignin, celluloses, hemicelluloses). The VOCs include wood components such as α-pinene, β-pinene, Δ ³ -caren, which mainly escape from the wood of the coniferous trees. Modification products of the ingredients include pentanal, hexanal, etc. From the hemicelluloses, acetic and formic acid can be formed. In particular, softwoods contain ingredients (extractives) such as resins and fats, which lead to the formation of volatile organic terpene compounds and aldehydes such as pentanal and hexanal. Hardwoods release mainly acetic and formic acid. The chemical composition and amount of VOC depends on many factors, in particular the type of wood, the treatment of the wood, the storage period and the storage conditions of the wood or its shredded products, as well as from the drying conditions. Furthermore, in wood-based materials, the binder influences the emission of VOCs.

Volatile organic compounds can escape from the wood and the wood comminution products and wood-based materials produced therefrom. For wood materials made from wood chippings such as wood shavings, wood strands, wood fibers and wood veneers by known methods, volatile organic compounds are released during manufacture, after production and when used. In particular, wood-based materials such as Oriented Strand Boards (OSB), which are mainly produced in Europe from mostly un-stored softwoods such as pine and Douglas fir, can still produce large amounts of volatile organic compounds after production.

As mentioned, the nature and extent of the emission of VOCs from wood-based materials is additionally determined, inter alia, by the type of wood and, in particular, by the production technology and the binder used. For example, the gluing of wood chips with alkaline curing phenol-formaldehyde resins (PF resins) to increased formation of acetic acid, since the alkali cleaves the acetyl groups of hemicelluloses in the wood, which lead to the formation of acetic acid (see Roffael, E., Miertzsch, H. and Schröder , M. 1990: On the mechanism of the formation of volatile acids in the gluing with alkaline-curing phenol-formaldehyde resins Holz-Zentralblatt 116 (111): 1684-1685). Other industry-standard binders for the production of particleboard and fiberboard are acid-hardening urea-formaldehyde resins (UF resins), adhesives based on diisocyanates (PMDI) and tannin-formaldehyde resins (TF resins).

In particular, volatile organic compounds having unsaturated carbon-to-carbon bonds can react with the atmospheric oxygen under ambient conditions. By reaction of certain VOCs with oxygen (O ₂ ) or other oxidizing agents, especially during the storage of the wood, the wood shredded products or the wood-based materials, odor-intensive compounds can be obtained. fertilize arise. For certain wood materials such as Oriented Strand Boards (OSB), which are mostly made of softwood in Europe, the odor can be particularly unpleasant and concise. This is particularly true when the wood, as is usually the case, is used without prior storage for wood-based material production.

For these reasons, it was the object of this invention to provide a process that reduces the amount of volatile organic compounds (VOC) from wood, wood chippings and wood-based materials in the manufacture of wood-based materials, such as chipboard.

The object is achieved in that wood and / or wood shredded products are treated with suitable chemical substances that react with the wood and / or the wood shred products, in particular with the moisture of the wood or with the water in the wood. Preferably, the adjusting by reaction with the wood moisture pH should be above 7, in particular above 9. Possible suitable substances which cause such a reaction, in particular an alkaline reaction, are bases such as sodium hydroxide (NaOH), basic salts such as sodium carbonate (Na ₂ COs), sodium sulfite (Na ₂ SO ₃ ) and tri-sodium phosphate (Na ₃ PO ₄ ) , Even gases such as ammonia, which lead to pH values higher than 7 after a reaction with water, can be used for this purpose. In the wood or in the aqueous extracts of the wood, the pH can be adjusted due to a reaction of the alkali with the ingredients or free or liberated wood acids below the theoretically expected by reaction of the alkali with the moisture content of wood. Of course, other agents well known to those skilled in the art may be used to effect an increase in the pH of the wood. The treatment of the wood or its shredded products can be carried out for the production of wood-based materials before or after storage of the wood. The lignocelluloses can be washed after the aforementioned treatment and before the gluing with water or with aqueous solutions. The treatment is usually carried out at room temperature and under atmospheric pressure. The addition of alkali such as sodium hydroxide to the binder in the manufacture of wood-based materials made of lignocellulose-containing materials with alkaline phenol-formaldehyde resins (PF resins) is known. For example, Schmidt-Hellerau (1968) investigated the influence of the addition of a 50% sodium hydroxide solution to the binder immediately prior to gluing or after drying the shavings of the extractable sweet chestnut on the physical-technological properties of particleboard made from it (Schmidt-Hellerau , Ch., 1968: Possibilities for Improving the Quality of Phenolic Chipboards, Holz-Zentralblatt 94: 1327). The addition of alkali in amounts up to 20% (based on wood) to the already alkaline PF resins had the aim to increase the alkali balance of the binder to abzupuffem acids in the highly acidic Kastanienholzspänen.

The results of Schmidt-Hellerau (1968) indicate that the addition of concentrated sodium hydroxide solution (50% solution) to the binder immediately prior to gluing effectively promotes the micaeability of the wood chips of certain extractive hardwoods. The addition of an excess of alkali, as is the case with Schmidt-Hellerau (1968), can not be compared with the method according to the invention, since according to the invention only one adjustment of the pH with the wood moisture is preferably to be achieved over 7.

According to the present method, the alkali is added to the wood or wood chips before drying and gluing and not to the binder (e.g., phenolic resin). The influence of the addition of alkali to the binder on the emissions of VOCs from chipboards was not determined in the investigations by Schmidt-Hellerau (1968).

While the use of alkali has a positive effect on the physico-technological properties and quality of particle board bonded with alkaline hardening PF resins, the treatment of beech wood chips with alkaline ammonia solutions before drying has a negative effect on the physico-technological properties of wood-chipboard bonded with acid-hardening urea-formaldehyde (UF) resins (Roffael, E. and Parameswaran, N., 1986: Influence of the latent acidity of beech wood shavings on their ability to be glued with urea-formaldehyde resins.) Wood as raw material 44: 389- 393). The work also does not address the reduction of emissions of volatile organic compounds.

Roffael and Parameswaran (1984) have beech wood with 6% ammonia solution at 100 ⁰ C for 3 hours in an autoclave and then washed the chips until neutral. This treatment led to an increase in the nitrogen content in the wood and to the buffering of the acids contained therein as well as to a partial degradation of the hemicelluloses (Parameswaran, N. and Roffael, E., 1984: state of knowledge and investigation results on the effect of ammonia on wood chips. and Material 42: 327-333). The decomposition of the wood chips under pressure in ammonia solution at 100 ^° C., after washing the chips, led to a reduction in the release of volatile acids from the chips and from chipboards produced therefrom. Through this treatment, however, the chips experienced a profound and undesirable change in their physical properties (sorption behavior, compressibility) and chemical properties. Both the investigations of Schmidt-Hellerau (1968) and of Roffael and Parameswaran (1984, 1986) refer to hardwoods.

As stated above, according to the invention, it has been found that in the case of alkaline treatment of wood and wood chippings prior to drying and gluing with the binder, increasing the pH of the materials, preferably to a pH greater than 7, suppresses the emission of VOCs Significantly reduced from the wood materials produced from these treated materials.

The wood or wood crushing products may be both conifers and hardwoods. Even mixtures of these two wood types are possible. Preferably, the wood shavings and strands of conifers come from.

The wood-based materials produced from the lignocellulose-containing materials can be chipboard, such as OSB. The plates produced can be one or more layers. Furthermore, the other layers may also contain other lignocelluloses such as straw or bark.

After drying the treated wood chips and strands they can be glued with the binder. Examples of typical binders include phenol-formaldehyde resin (PF resin), diisocyanate-based adhesive (PMDI), melamine-urea-phenol-formaldehyde resin (MUPF resin) and / or tannin-formaldehyde resin (TF resin), or a mixture thereof. However, other binders such as thermoplastic binders, e.g. Metacrylatreaktionsharze be used.

In multilayer wood materials different binders can be used in the different layers.

Furthermore, the wood-based materials produced from the treated lignocellulose-containing materials may additionally be post-treated with alkali, such as sodium hydroxide, sodium sulfite, trisodium phosphate and sodium carbonate and mixtures thereof after production. The aftertreatment can also be done by ammonia gas.

In addition to the alkali treatment before drying the wood or the wood comminution products, the method according to the invention can also include a further alkali treatment after drying. The treatment according to the invention of the wood or of the wood shredded products can take place before or after storage of the wood. After the alkali treatment according to the invention, the wood or the wood shredded products may optionally be washed with water or aqueous solutions.

The alkali compounds such as sodium hydroxide, sodium sulfite or sodium carbonate used to increase the pH can be applied or impregnated by spraying or by other known methods on the wood or the wood crushing products. Preferably, the value of the incorporated compound to increase the pH in a range of 0.1% to 2% solids on atro chips.

Starting from the described prior art, the invention aims to develop a simple method for reducing the release of volatile organic compounds (VOC) from wood and wood chippings and from wood-based materials produced therefrom. The following examples are intended to illustrate the invention without limiting it.

example 1

From a 70-year-old pine trunk (Pinus sylvestris L.), core and sapwood boards (20 cm x 13 cm x 1, 9 cm) were cut in and stored at 4 ^° C. until they were chipped (13 days after impact). The core and sapwood boards were cut to strands (20 cm x 1, 9 cm x 0.04 cm) with a disk chipper.

To reduce emissions of VOC, the core and sapwood strands were sprayed in one case with 2% sodium sulfite solution and in another case with 2% sodium hydroxide solution. The dosage of sodium sulfite or sodium hydroxide was in each case at 1, 5% solids based on absolutely dry (atro) strands. The treated strands were air dried without being washed. As a reference served on the air dried untreated core and sapwood strands of pine.

The pH was determined on cold-water extracts of the untreated and treated core and sapwood strands. Furthermore, on the beaches, the release of volatile acids was determined on the basis of the bottle method (EN 717-3) (Table 1). The results show that, although the production of volatile organic acids is promoted by the alkali treatment, their release is nevertheless surprisingly reduced. This result was unpredictable insofar as the literature has hitherto not differentiated between the formation of volatile organic acids or VOCs and their release into the air.

Incidentally, by the formation of the volatile acids, the pH, as already mentioned, below the theoretically adjusting by reaction with the moisture content of the wood due to the buffering of the alkali. Table 1: pH value, content of formate and acetate ions in cold-aqueous extracts and release of volatile acids from untreated and treated with sodium sulfite or sodium hydroxide (in each case 1, 5% solids based on free beach) treated core and sapwood strands of pine

nn: undetectable, since below detection limit

Furthermore, at the untreated and treated strands, the emissions of certain volatile organic compounds (VOC) were determined after 5 h, 24 h and 48 h storage in a 23 liter test chamber at 23 ^° C. and 50% relative humidity. The loading level of the test chamber was 0.5 m ² / m ³ , the air exchange rate was 0.5 h ^"1 .

The results are summarized in Tables 2 and 3. It is clear from the tabulated data that the treatment of the strands with sodium sulfite (Table 2) or with sodium hydroxide (Table 3) leads to a reduction in the release of volatile organic compounds (VOC). It also shows that at the same concentration, the sodium hydroxide is more effective than the sodium sulfite in reducing the release of volatile terpene compounds.

Table 2: Influence of treatment of pine core and sapwood strands (Pinus sylvestris L) with sodium sulphite (1.5% solids on dry beach) on the concentrations (μg / m ³ ) of volatile organic compounds (VOC) after 5 h , 24 h and 48 h in a 23 liter test chamber at 23 ° C and 50% relative humidity (degree of loading: 0.5 m ² / m ³ , air exchange rate: 0.5 h ^"1 )

* Quantification with the specified individual component Table 3: Influence of the treatment of pine and sapwood strands (Pinus sylvestris L.) with sodium hydroxide (1, 5% solids on dry beach) on the concentrations (μg / m ³ ) of volatile organic compounds (VOC) after 5 h, 24 h and 48 h in a 23-liter test chamber at 23 ° C and 50% relative humidity (degree of loading: 0.5 m ² / m ³ , air exchange rate: 0.5 h ^"1 )

Quantification with the specified individual component Example 2

From a 70-year-old pine trunk (Pinus sylvestris L.), core and sapwood boards (20 cm x 13 cm x 1, 9 cm) were cut. The core and sapwood boards were cut to strands (dimension 20 cm x 1, 9 cm x 0.04 cm) with the aid of a disk chipper. The chips were dried in a drying oven at 7O ⁰ C to a moisture content of about 5%.

After drying, part of the core and sapwood strands were treated with sodium hydroxide solution. The treatment was carried out by first loading the strands in a gluing drum with 7.5% sodium hydroxide solution (dosage 1.5% solids based on absolutely dry (atro) strands). Subsequently, the strands were dried in a drying oven at a temperature of 5O ⁰ C to a moisture content of about 6%.

As a reference served core and sapwood strands, which were not treated with sodium hydroxide solution. Since it was to be expected that the aforementioned drying step would have an influence on the OSB's VOC emissions, the untreated core or sapwood strands were each precoated in a gluing drum with an amount of water corresponding to the above-mentioned sodium hydroxide solution dosage. Subsequently, the strands were dried in a drying oven at a temperature of 5O ⁰ C to a moisture content of about 6%.

From the untreated and NaOH treated beaches, Oriented Strand Boards (OSB) were made with PF resin as a binder. The binder content was 10% (solid resin based on atro strands). As a curing accelerator, 6% potassium carbonate (solid based on solid resin) was added. The top and middle layers of the OSB were oriented differently. The mass fraction of the outer layers was 25%, that of the middle layer was 75%. The gluing levels of the top and middle layers were the same. The pressing temperature was 200 ⁰ C, the Press time factor was 15 sec / mm. The plates had a target density of 650 kg / m ³ , the plate thickness was 16 mm.

At OSB produced from untreated and sodium hydroxide treated strands, VOC emissions were determined after storage for 24 hours in a 1 m ³ test chamber at 23 ° C and 50% relative humidity. The loading level of the test chamber was 0.5 πrVm ³ , the air exchange rate was 0.5 h-1.

Table 4: Concentration (μg / m ³ ) of volatile organic compounds (VOC) of PF Resin-bound Oriented Strand Boards (OSB) from untreated core and sapwood strands treated with 1.5% NaOH (solid on strands of water) the jaw (test duration 24 h)

The results in Table 4 show that the VOC emissions of the PF resin bonded OSB from core and sapwood strands are reduced by the treatment of the strands with sodium hydroxide. Furthermore, the formaldehyde release of the PF resin-bound OSB was lowered by treatment of the strands (Table 5).

Table 5: Formaldehyde release of PF resin bound OSB made from untreated and 1.5% NaOH (solid on strands) treated core and sapwood strands of pine

Claims

claims

1. A process for the production of wood-based materials, in particular

Wood chip boards, preferably Oriented Strand Boards (OSB), with reduced emission of volatile organic compounds (VOCs) comprising the step of mixing wood chips or strands with a binder and subsequent pressing, characterized in that the chips resp Beach in front of

Drying and gluing with the binder with a suitable chemical is treated such that a reaction takes place and the pH of the wood is increased, preferably to a pH greater than pH 7.

2. The method according to claim 1, characterized in that this chemical is an alkali metal hydroxide, in particular sodium hydroxide.

3. The method according to claim 1, characterized in that this chemical is an alkali metal carbonate, in particular sodium carbonate.

4. The method according to claim 1, characterized in that the chemical is an alkali metal sulfite, in particular sodium sulfite.

5. The method according to claim 1, characterized in that the

Chemical is an alkali phosphate, in particular tri-sodium phosphate.

6. The method according to any one of the preceding claims, characterized in that the treatment is carried out with an alkali mixture, in particular a mixture of two or more compounds of

Sodium hydroxide, sodium carbonate, sodium sulfite and / or tri-sodium phosphate.

7. The method according to claim 1, characterized in that the chemical is an ammonia gas.

8. The method according to any one of the preceding claims, characterized in that the amount of added alkali between 0.1% and 2% solids on dry chips.

9. The method according to any one of the preceding claims, characterized in that the treatment is carried out such that the treatment leads to an increase in the pH of the chips or strands to above pH 9.

10. The method according to any one of the preceding claims, characterized in that the treated before drying chips or strands are additionally treated after drying with alkali.

11. The method according to any one of the preceding claims, characterized in that the wood chips or wood strands come from softwood.

12. The method according to any one of the preceding claims, characterized in that the treatment of the wood or the wood chips or wood strands takes place before or after storage of the wood.

13. The method according to any one of the preceding claims, characterized in that the wood chips or wood strands are washed after treatment with a chemical agent with water or treated with aqueous solutions.

14. The method according to any one of the preceding claims, characterized in that a single- or multi-layered plate is produced.

15. The method according to any one of the preceding claims, characterized in that the binder used is a phenol-formaldehyde resin (PF resin), an adhesive based on diisocyanates

(PMDI), a melamine-urea-phenol-formaldehyde resin (MUPF resin), a tannin-formaldehyde resin (TF resin) or a mixture thereof.

16. The method according to any one of the preceding claims, characterized in that in different layers different

Binders are used.

17. The method according to any one of the preceding claims, characterized in that the plates prepared from the treated chips or strands are additionally post-treated after preparation with alkali, in particular sodium hydroxide, sodium carbonate, sodium sulfite and / or tri-sodium.

18. The method according to any one of the preceding claims, characterized in that the plates produced from the treated chips or strands are additionally post-treated after production with ammonia gas.