WO2006114089A1

WO2006114089A1 - Method for producing reduced-emission, low-thickness swell medium density fiber boards and molded fiber parts

Info

Publication number: WO2006114089A1
Application number: PCT/DE2006/000728
Authority: WO
Inventors: Edmone Roffael; Thomas Schneider; Brigitte Dix
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2005-04-26
Filing date: 2006-04-25
Publication date: 2006-11-02
Also published as: PL1874513T3; DE102005019627B3; ATE477095T1; DE502006007638D1; ES2349873T3; PT1874513E; EP1874513B1; EP1874513A1

Abstract

The invention relates to a method for producing fiber boards, especially medium density fibers boards, from lignocelluloses, whereby the lignocelluloses are cooked by chemical thermohydrolysis and are then reduced to fibers in a refiner, a binder is added, the material is spread to give fiber mats and is compressed to give fiber boards. The method is characterized in that the lignocellulose are reduced to fibers in the presence of condensed tannins.

Description

Process for the production of medium-density fiberboard and shaped fiber parts with reduced emission and low thickness swelling

The invention relates to a process for the production of medium-density fiberboard (MDF) with reduced emission of volatile organic compounds (VOC) and at the same time low swelling in thickness. As volatile organic compounds 5 organic substances are subsumed, the boiling point between 5O ⁰ C and 26O ⁰ C. Most of the volatile organic compounds come from the wood, but sometimes also from the binder. The interaction between binder and wood also influences the composition of the volatile constituents, further influencing factors being the production conditions of the medium-density fiberboard. Wood-based materials also emit formaldehyde. However, formaldehyde is not included in the definition of volatile organic compounds.

15 For the production of medium-density fiberboard fibers from lignocelluloses are glued with a binder, scattered into fiber mats and then, if necessary after a pre-pressing, hot pressed. Lignocelluloses may be woods, annual plants and used chipboard and fiberboard.

20

The recovery of the fibers from the lignocelluloses is generally carried out by a thermomechanical process (TMP process), and the production of fibers by the chemithermomechanical process (CTMP process) is known from EP 0 639 434. For the production of fibers

JZ5 _{; ^ r ^} from _^ HpJz__after _^ d <ΞW Wood chips washed first to remove any existing sand particles. After washing, the wood chips are usually pre-steamed at temperatures between 60 ⁰ C and 8O ⁰ C and then get via screw conveyance in the so-called cooker, where they are usually digested at temperatures of 17O ⁰ C to 180 ⁰ C thermohydrolytic. After digestion, the digested chips are transferred to a pressure refiner, where they are defibrated under pressure at temperatures of also 17O ⁰ C to 18O ⁰ C. The defibering in the pressure refiner can be followed by a non-pressurized refining stage. The digestion conditions can be varied depending on the raw material, so lower temperatures of 140 ⁰ C to 16O ⁰ C can be used for digestion in annual plants. After the refining stage, the fibers are conveyed by the pressure prevailing in the refiner into a blow pipe, where they are provided with a binder. In the manufacture of fibers by the CTMP process, chemicals such as sodium sulfite and sodium hydroxide, or combinations of sodium sulfite and sodium hydroxide, are added to the wood chippings before or during digestion. The addition of other chemicals is possible.

As binders for the production of medium-density fiberboard mainly amino resins such as urea-formaldehyde resins (UF resins) are used, other synthetic binders such as alkaline curing phenol-formaldehyde resins (PF resins) and adhesives based on polymeric diisocyanates (PMDI), however, have only a relatively small importance , It is also possible to use thermoplastic binders such as methacrylate reaction resins for bonding fibers. The binder used for the production of MDF is often injected into the blast line, but it can also be applied after drying the fibers in a blender. Combinations of the two methods are also possible, so only a part of the binder can be injected into the blowing line and the rest are applied only after drying in the blender. It can also enter the blowpipe Binder of certain composition introduced and used after drying another binder with different composition.

In addition to the synthetic binders, binders based on natural substances such as tannin-formaldehyde resins (TF resins) can be used for the production of MDF. The TF resins are obtained by reaction between tannins and formaldehyde. The tannins, in particular the condensed tannins, are obtained by extraction from certain barks and woods. Particularly suitable for this Quebrachoholz (Quebracho colorado) and bark such as acacia bark (Acacia mearnsii), spruce bark (Picea abies) etc. The extraction of tannins from wood and bark is usually carried out at temperatures between 7O ⁰ C and 13O ⁰ C in water in the cascade process according to the countercurrent principle. During extraction, chemicals such as sodium sulfite and / or sodium hydroxide may also be added to predominantly increase the solubility of tannin in the water. The sulfitation of tannin can also take place after the extraction. For the production of TF resins, the extracted tannins are reacted with formaldehyde. As another natural binder, starch can be used in various forms (native starch, oxidized starch, modified starch). Also combinations of tannin and starch are known as binders.

In the course of thermohydrolytic treatment in the digester and in the refiner, on the one hand, the chemical degradation of the wood occurs. Volatile compounds such as formaldehyde, furfural, hydroxymethylfurfural,

Formic acid and acetic acid. The hemicelluloses of the wood are also partially degraded to soluble carbohydrates. The ants and acetic acid released from the wood have a certain disruptive effect on the wood. In addition to the degradation of the carbohydrates but also Liαnin m ^" small ^" scope can be attacked, whereby Ligninabbauprodukte how Methanol and formaldehyde can arise. The chemical composition of the volatile organic compounds from the wood material or from the fibers produced therefrom depends on the wood species. In the case of pine wood, aldehydes such as pentanal, hexanal and heptanal can be produced in large quantities. On the composition of the volatile constituents also Aufschlussart and digestion conditions influence.

The volatile degradation components of the wood, coming from the refiner, may be partially emitted during the drying of the fiber to the environment since they are steam volatile. Furthermore, the volatile acids can act as a hardener and the injected binder in the

Pre-condense blowing line and possibly during drying partially. This leads to reduced adhesion of the binder during pressing. The non-volatile degraded carbohydrates formed during digestion remain in the produced

Fiberboard and possibly reduce their biological resistance.

The object of the invention is firstly to reduce the amount of volatile constituents of medium-density fiberboard and to largely prevent their formation and secondly to improve the physical and technological properties of the plates produced. In particular, the thickness swelling of the plates should be reduced.

It has now surprisingly been found that condensed tannins such as quebracho and acacia bark tannins, when added or present in low optimized amounts during fiber production by the CTMP process in the refiner, not only reduce the emissions of volatile organic compounds from the fibers but also the emission of VOC of plates made diminish, and significantly improve their physical-te ^"ch ^~ ήölögϊschen properties. the application of CTMP process alone surprisingly reduces the emission of the manufactured medium density fiberboards but has no appreciable reducing effect on the thickness swelling and water absorption of the plates. The use of polyphenolic condensed tannins alone reduces the thickness swelling of the plates, but has no diminishing effect on the emission. The use of optimized amounts of polyphenols together with the application of the CTMP process surprisingly gives the combined effect of reducing thickness swelling and emission. Here, it is irrelevant for the reduction of the emission which binder is introduced into the blowpipe or used after the drying of the fibers. It is also possible to use the binder only in the blender after drying the fibers or to use partly in the blowpipe (blow-mine), partly in the blender.

This method differs from the teaching of EP 1 266 730 A1, which has the object of adding condensed tannins to the wet chips or fibers prior to gluing the chips or fibers. According to the teaching of EP 1 266 730 A1, the tannins are not present during the digestion, and the fibers do not have to be obtained by the CTMP process. In the present invention digestion by the CTMP method is as obligatory as the addition of optimized amounts of condensed tannins. Of course, the polyphenolic condensed tannins may be added to the refiner along with other additives such as water repellents and / or other polyphenolic materials such as cashew nut oils.

Furthermore, it was surprisingly found that the diminishing effect of

Tannins on the emission of the produced plates of formaldehyde also after their production stops. The formaldehyde release of the plates, which are produced using tannin in the refiner, takes much faster than the derjenrgen, ^~ ^ i ^"s with ^no" made use of tannin. This method with a combined application of CTMP and the presence of tannins is suitable for all lignocelluloses. The addition of chemicals in the sense of the CTMP process can be carried out prior to digestion or during the digestion in a known manner. As chemicals, sodium sulfite, sodium bisulfite and sodium hydroxide or optimized mixtures thereof may be used. Since sodium sulfite and sodium bisulfite can sulfite the tannin and increase its solubility in the water, this procedure makes it possible to combine the digestion and defibration of wood chips with the sulfitation of the condensed tannin in the refiner in a meaningful manner.

The following example describes the invention without specifying it.

In the first experiment wood chips from pine wood were thermohydrolytically digested at a temperature of 17O ⁰ C and then defibrated under pressure at a temperature of 17O ⁰ C in the refiner (TMP process). After defibration, the fibers were dried and glued with a UF resin in amounts of 12% (solid resin based on atro fibers) and then formed into mats and at a temperature of 200 ⁰ C to medium-density fiberboard with a target density of 750 kg / m ³ and a thickness of 16 mm hot pressed. The pressing time factor was 15 s / mm. The plates thus produced were then stored in a climate of 2O ⁰ C and 65% relative humidity before they were tested for their physico-technological properties and emission.

For comparison, pine wood chips were used at a temperature of

17O ⁰ C digested, in the fiberization stage under pressure in the refiner condensed tannins were added to the wood chips before digestion in amounts of 2% (solids based on atro wood material) (Experiment 2). After

Zerfaser ün ^'g wurderTäFe dried fibers typically connected to the UF resin in Glueing amounts of 12% (solid resin based on dry fibers), shaped into fiber mats and hot pressed into medium-density fibreboard (see Experiment 1). The plates thus prepared were then at 2O ⁰ C and 65% rel. Humidity stored before they were tested for their physical-technological properties and emission.

In a third experiment, medium density fiberboards were made from fibers prepared by adding 1% Na ₂ SO ₃ and 0.5% NaOH (solid based on dry wood material) according to the CTMP method. The digestion temperature was 17O ⁰ C. The production of MDF was carried out under the same conditions as in the case of TMP fibers (see Experiment 1).

In a fourth trial, the pine wood chips were both 1%

Na ₂ SO ₃ and 0.5% NaOH (solid based on atro wood material) and Quebrachoholztannin in amounts of 2% (solid based on atro

Wood material) was added. The digestion temperature was also 17O ⁰ C.

After defibration, the dried fibers were further processed into MDF. The production of MDF took place under the same

Conditions as in the case of TMP fibers (Experiment 1).

The results are summarized in Tables 1 to 3.

It is clear from Table 1 that the transverse tensile strength of the fibers obtained by the CTMP process and plates made using tannin in the refiner (test 4) is substantially higher than those of the plates produced otherwise (tests 1 to 3). Furthermore, it can be seen that the combined use of CTMP and tannin (experiment 4) significantly reduces the thickness swelling (24 h) of the plates produced. Also, the flexural strength of the panels produced is substantially increased by the combined use of CTMP and tannin (Experiment 4).

Be ""^{"^} TvTrT ^this" method, both the strength properties (Transverse tensile strength, flexural strength) of the plates significantly improved as well as their thickness swelling significantly reduced.

Table 1: Physico-technological properties of TMP and CTMP medium density fiberboards produced without and with the addition of condensed tannins

As shown in Table 2, the combined use of CTMP and tannin (Run 4) significantly reduces emissions of volatile organic content (VOC) plates such as hexanal and pentanal.

Table 2: VOC emissions (hexanal, pentanal) of TMP and CTMP medium density fiberboard (MDF) made without and with the addition of condensed tannins. The VOC emissions were made at the beginning of the 5th century.

The addition of tannin in the production of fibers by the CTMP process (experiment A) leads to an additional significant reduction in the formaldehyde release (24h) of the pulp (see Table 3).

Table 3: Formaldehyde release (24 hours) (mg / 1000 g dry fibers) from TMP and CTMP fibers made without and with the addition of condensed tannins

For the purposes of the invention, binders for the production of medium-density fiberboards can be those which lead to a moisture-resistant fiber-to-fiber bond as well as those which lead to fiber-to-fiber bonding with low moisture resistance. Typical binders for the production of moisture-resistant adhesives are alkaline curing phenol-formaldehyde resins (PF resins), tannin-formaldehyde resins (TF resins), melamine-urea phenol-formaldehyde resins (MU PF resins) and adhesives based on PMDI (polymeric diphenylmethane diisocyanates). Binders that result in low moisture resistance fiber-to-fiber bonding include the urea formaldehyde resins (UF resins).

Claims

claims

1. A process for the production of fiberboard, in particular medium-density fiberboard, from lignocelluloses, in which the lignocelluloses digested chemohydrolytically and then defibrated in a refiner, provided with a binder, scattered into fiber mats and pressed into fiber boards, characterized in that the defibration the lignocelluloses in the refiner takes place in the presence of condensed tannins.

2. The method according to claim 1, characterized in that the supply of binders to the fibers in the blow-line process and / or takes place in a blender.

3. The method according to claim 1 or 2, characterized in that an aminoplast resin, phenol-formaldehyde resin, tannin-formaldehyde resin and / or an adhesive based on diisocyanates is used as the binder.

4. The method according to any one of the preceding claims, characterized in that the binder starch is added as an extender.

5. The method according to any one of the preceding claims, characterized in that a combination of tannin, formaldehyde and starch is used as a binder.

6. The method according to any one of claims 1 to 4, characterized in that methacrylate reaction resins are used as binders.

7. The method according to any one of the preceding claims, characterized in that the fiberboards produced are further processed to form parts.

8. The method according to any one of the preceding claims, characterized in that the lignocelluloses before digestion sodium sulfite, sodium bisulfite and / or sodium hydroxide is added.

9. The method according to claim 8, characterized in that the amounts of added sodium sulfite, sodium bisulfite and / or

Sodium hydroxide is between 0.1% and 2% solids based on atro-lignocelluloses.

10. The method according to any one of the preceding claims, characterized in that the added tannin is a sulfited or unsulfured tannin.

11. The method according to any one of the preceding claims, characterized in that the plates produced are stored or stored hot.

12. The method according to any one of the preceding claims, characterized in that the plates produced have a density of at least 1000 kg / m ³ .