DE102009047142B4 - Method for modifying wood-based materials - Google Patents

Abstract

Method for modifying wood-based materials (2), in which the wood material (2) to be modified, which has been previously produced using adhesive systems, is thermally treated at normal pressure in thermal chambers (1) by flowing around with a medium, comprising the steps of: - heating the thermal chamber (1) to reach the maximum temperature in the temperature range of 150 to 220 ° C, wherein the heating time is 1 to 10 minutes per Kelvin, - holding the maximum temperature over a period of 1 to 8 hours and - cooling the thermal chamber (1) to an ambient temperature, wherein the cooling time per Kelvin is 1 to 10 minutes.

Description

The invention relates to a method for modifying wood-based materials. In particular, the method is applicable to wood based panels (WBP), such as particleboard (PB), dry-process fiberboard (MDF, HDF, LDF), Oriented Strand Boards (OSB), plywood (PLY) , Solid Wood Panels (SWP), Composite Composite Boards (CB) or wooden or wood particle shaped parts, for example made of MDF, PLY or OSB, or a combination of the above-mentioned wood-based materials.

In order to ensure the long-term competitiveness of plate-shaped wood-based materials (WBP), it is necessary to develop special products, especially for applications in humid indoor areas, such as kitchens or bathrooms, as well as for outdoor areas. One way of modifying the properties of wood and slab-shaped wood materials is by thermal treatment.

Since the middle of the twentieth century it has been known that the properties of wood and plate-shaped wood-based materials (WBP) change due to the influence of temperature. Kollmann, F. (1951) Technology of wood and wood-based materials. Springer Verlag reports that increasing the drying temperature of wood (from 60 ° C to 115 ° C) increases the hysteresis loop, meaning that the adsorption curve is significantly reduced. With a further increase in temperature beyond 115 ° C, the application of high compression pressures and higher wood moisture, considerable chemical changes occur in the wood, which are absent in ordinary drying.

In professional circles and in the specialist literature is nowadays usually assumed from a temperature of 160 ° C of a thermal remuneration / modification of wood. After one of Burmester, A. (1973) influence of a heat-pressure treatment semi-dry wood on its dimensional stability. Wood raw materials and materials 31, pp. 237-243, in the 1970s developed humidity-heat-pressure-process (FWD) for the thermal treatment of wood due to the strength reductions could not prevail to practical maturity, was in the 1990s, the idea of Modification of wood picked up again by heat treatment.

According to Leithoff (2001), quoted in Grossmann, C.M. (2002), market opportunities for heat-treated wood in Germany: characteristics, application possibilities, availability and marketing. Final Report of the Institute for Forest Policy of the University of Freiburg, November 2002, under the terms "thermal treatment" and "heat treatment" are summarized procedures in which the wood is heated over a certain period of time to temperatures in the range of 150 to 270 ° C.

• – 120 bis 150°C: Trocknung ohne wesentliche Veränderung der chemischen Zusammensetzung des festen Rückstandes und
• – 150 bis 275°C: beginnende thermische Holzzersetzung, Veränderung der chemischen Zusammensetzung und Verringerung der mechanischen Festigkeit; Bildung von Kohlendioxid sowie Kohlenmonoxid, Essigsäure und Furfural.

After Wienhaus, O. (1999) Modification of the wood by a mild pyrolysis - derived from the general principles of thermoanalysis of the wood. Wiss. Journal of the TU Dresden 48/2, pp 17-22, take place in the heating of wood under exclusion of air in the temperature range of 120 to 275 ° C defined for thermowood the following reactions:

• - 120 to 150 ° C: drying without significant change in the chemical composition of the solid residue and
• - 150 to 275 ° C: incipient thermal decomposition of wood, alteration of chemical composition and reduction of mechanical strength; Formation of carbon dioxide as well as carbon monoxide, acetic acid and furfural.

The original aim of the thermal treatment was to reduce the terminal hydroxyl groups responsible for the swelling and shrinkage of the wood in the molecular structure of the wood by the action of heat, to aggravate the attachment of water to the cellulose fibrils and the hemicelluloses of the wood reduce, among other things, the moisture absorption and swelling to reduce. In addition, at temperatures above 130 ° C, the chemical structure of the wood is changed so that the resistance of the wood is significantly increased against degradation by wood-destroying fungi.

• – Boku (2002) Modifiziertes Holz – Eigenschaften und Märkte. Institut für Holzforschung der Universität für Bodenkultur Wien, Band 3,
• – Finnish Thermowood Association (2004) ThermoWood^® Handbuch. Finnischer Verband für wärmebehandeltes Holz, Helsinki, Finnland,
• – Niemz, P. (2008) Holz-Zentralbl. 12/2008, S. 312, sowie
• – Weber, A., Krug, D. (2007) Verwendung thermisch vergüteter Buchenholzsortimente zur Herstellung von Massivholzplatten für den Fassadenbereich. In: Tagungsband 7. Holzwerkstoffkolloquium „Rohstoff-Engpass – eine Chance für Alternativen”, Dresden, 13./14.12.2007.

At present, several methods for producing thermally treated wood, so-called thermo wood or TMT (Thermal Modified Timber), are known. The most important processes include the PLATO process (Providing Lasting Advanced Timber Option), the Menz oil-heat process, the thermowood process, the Mühlböck process, the Retarded Wood process (NOW), the Perdure Wood processes, the FinnForest Thermo Wood or VTT process, the Stellac process, the vacuum pre-drying and the Lunawood process, which is the continuous flow Thermo-Wood process. The corresponding references in the literature are:

• - Boku (2002) Modified Wood - Properties and Markets. Institute of Wood Research, University of Natural Resources and Life Sciences Vienna, Volume 3,
• - Finnish Thermowood Association (2004) ThermoWood ^® Manual. Finnish Association for Heat Treated Timber, Helsinki, Finland,
• - Niemz, P. (2008) Holz-Zentralbl. 12/2008, p. 312, as well as
• - Weber, A., Krug, D. (2007) Use of thermally treated beechwood ranges for the production of solid wood panels for the façade area. In: Proceedings 7th Wood Materials Colloquium "Resource Bottleneck - A Chance for Alternatives", Dresden, 13./14.12.2007.

While the volume of production capacities for the thermal treatment of (massive) wood and the use of this product range are growing steadily, it is currently only known to a limited extent whether and to what extent the aforementioned changes in the properties of (solid) wood on wood-based materials, in particular plate-shaped wood-based materials (WBP). , are transferable. In particular, there is a risk that used adhesive systems dissolve when exposed to heat and the wood material is damaged. For hard fiberboard, which were prepared without the addition of adhesives by the wet process, the physico-mechanical properties can be improved by a heat treatment, as already from the literature, see author collective (1988): Encyclopedia of wood technology. 3rd edition, book publisher Leipzig, is known. The heat treatment can already be done in the hot press, which, however, the capacity of the system is reduced. Therefore, a heat treatment at 150 to 180 ° C for a period of three to six hours can be carried out continuously in channels or intermittently in chambers. In the thermal aftertreatment of oil-impregnated fibreboard (so-called "tempering"), however, the hot air must not exceed 120 ° C for reasons of (self-) ignition risk.

The publication CH 230 911 A includes a method that serves to make panels and moldings whose association strength is ensured solely by the entanglement of the individual fibers without introducing additional binders sufficiently waterproof. These are in particular those molded parts which are obtained from wood fibers by mixing them into an aqueous pulp which is deposited on permeable substrates in the desired shape with subsequent drying. To increase the water resistance of molded parts and fiberboards produced from these wood fiber materials, they are heated to a temperature between 150 and 225 ° C., preferably to 200 ° C.

According to Ohlmeyer, M. et al. (2003) BFH Nachrichten 41/4, p. 28, a partial improvement in properties was achieved in a stack storage of Oriented Strand Boards (OSB) with pMDI bond (pMDI = polymeric diphenylmethane diisocyanate) at temperatures of up to 180 ° C. According to Giebeler, E. (1983) Holz Roh-Werkstoff 41: 87-94, the thickness swelling after 24 hours of water storage of phenol-formaldehyde-resin (PF) -bonded particleboard and fibreboard by a humidity-heat-pressure (FWD) - Compared at a temperature of 195 ° C, a pressure of ten bar and a treatment time of one hour significantly improved, the flexural strength was partially increased, but also partially reduced.

Although Stölzel, M., Beikircher, W. (2007) provide TMT-Facade panels; Product Performance and Application. In: Proceedings 3rd European Conference on Wood Modification, Cardiff, Wales, 15./16.10.2007, a system for the facade area consisting of, among other things, three-ply thermo-wood solid wood panels (TMT-SWP). However, the solid wood panels (SWP) consist of three layers of glued, thermally treated slats. That is, not the finished solid wood panel (SWP) has been subjected to a thermal treatment, but the starting material of the SWP production.

Weber, A., Krug, D. (2007) report on the same principle with the use of thermally treated beech wood ranges for the production of solid wood panels for the facade sector. In: Proceedings 7th Wood Materials Colloquium "Raw Material Bottleneck - A Chance for Alternatives", Dresden, 13./14.12.2007, as part of the joint research project WEFAM (weatherproof facade panels made of modified wood). Three-ply solid wood panels (SWP) were produced from thermally treated wood slats and tested for use in the façade area.

A method of thermally treating chips in the laboratory and of producing and testing only laboratory particle boards (PB) is reported by Borysiuk, P. et al. (2007) Thermally Modified Wood as Raw Material for Particleboard Manufacture. In: Proceedings 3rd European Conference on Wood Modification, Cardiff, Wales, 15./16.10.2007. As a starting material they used pine and birch wood. The results of the subsequent tests are inconsistent: while the modified birch chipboards (PB) have reduced transverse tensile strengths and swelling values, the values of the modified pine shavings plates show no change over untreated material boards.

In a work by Paul, W. et al. (2006) Holz Roh- und Werkstoff 64, pp. 227-234, reports on heat treatment of pine strands for OSB production. The results show that the thickness swelling is reduced and thus the dimensional stability is increased. The transverse tensile strength is not changed by the pretreatment. Furthermore, in Paul, W. et al. (2007) Wood Raw and Material 65, pp. 57-63, reports that the thermal treatment of the strands for the production of OSB at temperatures above 200 ° C determines increased fungal resistance according to durability class 3 and better.

In a study by Mohebby, B. et. al. (2008) Holz Roh- und Werkstoff 66, pp. 213-218, the influence of a hydrothermal treatment of fibers for MDF production on the physical and mechanical properties of MDF was investigated. Accordingly, the treatment has no effect on the water absorption, while the thickness swelling improves and the plates are dimensionally stable. The modulus of elasticity, the bending and the transverse tensile strength decrease.

The heat treatment of fibers for the production of MDF are also the subject of investigations by Garcia, R. et al. (2008) Chemical Modification and Wetting of Medium Density Fiberboard Produced from Heat-Treated Fibers. J. Mat. Sci. 43, p 5037-5044, which show that the water absorption of MDF from heat-treated fibers decreases.

Del Menezzi, C.H.S. et al. (2009) Thermal modification of consolidated oriented strandboards: effects on dimensional stability, mechanical properties, chemical composition and surface color. Holz Roh- und Werkstoff 67, April 2009, describe a post-treatment of an OSB with the aim of improving dimensional stability. Commercially available OSB are thermally treated in a one-day press at temperatures of 190 ° C and 220 ° C, respectively. The results of dimensional stability and mechanical properties tests indicate that the proposed treatment significantly improves dimensional stability by reducing thickness swelling, water absorption, and balance moisture compared to untreated OSB. The mechanical properties are subject to a partial influence. The modulus of elasticity is reduced while the other properties are not adversely affected. The changes in dimensional stability are affected by temperature and duration of treatment, the other properties tested mainly by temperature.

• • Verringerung der Biegefestigkeit und vor allem der Bruchschlagarbeit,
• • Masseverlust und dadurch Verringerung der Rohdichte,
• • Erhöhung der Sprödigkeit,
• • eventuell auftretende Risse,
• • intensiver Geruch und
• • Mehrkosten durch die Behandlung.

Phenol-formaldehyde resin (PF) bonded medium density fiberboard (MDF) has been prepared according to Ayrilmis, N. et al. (2009) Dimensional Stability and Creep Behavior of Heat-Treated Exterior Medium Density Fiber Board. Holz Roh- und Werkstoff 67, February 2009, subjected to a thermal aftertreatment at various temperatures and treatment times, using a hot press and just enough pressure to provide sufficient contact between the plates and the pressing surfaces. Mechanical strengths of post-treated MDF were investigated. The results illustrate that post-treatment results in an improvement in thickness swelling, while water absorption and linear expansion are negatively affected. Young's modulus and flexural strength decrease with increasing treatment temperature. The creep behavior also deteriorates with increasing temperature of the aftertreatment. The thermal treatment adversely affects the following properties of wood:

• Reduction of flexural strength and, above all, fracture impact work,
• Mass loss and thereby reduction in bulk density,
• Increasing the brittleness,
• • possible cracks,
• • intense smell and
• • additional costs due to the treatment.

In the DE 30 44 221 A1 is a method for dimensional stabilization and for the compensation of wood-based materials, which have been compacted by a pressing process, described by a pressure treatment at 4 to 15 bar. In addition, the teaches DE 30 44 221 A1 in that the tempering at high pressures and at a high temperature stabilizes the state after compacting the wood-based material and at the same time improves the wood fibers in their swelling behavior. The disadvantage here is, in addition to the high cost associated with the generation of high pressures, in particular the fact that the number of adhesive systems suitable for this process is severely limited.

The object of the invention is to provide a cost-effective way to improve the properties of wood-based materials, in particular the thickness swelling and the moisture-related properties, in view of their potential use in outdoor areas. Such a method should be applicable to plate-shaped wood materials (WBP), such as chipboard (PB), dry-process fibreboard (MDF, HDF, LDF), Oriented Strand Boards (OSB), plywood (PLY), solid wood panels (SWP), wood-based material Composite materials (CB) or a combination of the above-mentioned wood-based materials. In addition, the method should also be suitable for moldings made of wood or wood particles.

• – Aufheizen der Thermokammer bis zum Erreichen der Maximaltemperatur im Temperaturbereich von 150 bis 220°C, wobei die Aufheizzeit 1 bis 10 Minuten pro Kelvin beträgt,
• – Halten der Maximaltemperatur über einen Zeitraum von 1 bis 8 Stunden und
• – Abkühlen der Thermokammer auf eine Umgebungstemperatur, wobei die Abkühlzeit je Kelvin 1 bis 10 Minuten beträgt.

The object of the invention is achieved by a method for modifying wood materials, in which the wood material to be modified, which was previously prepared using adhesive systems, at atmospheric pressure in thermal chambers thermally by flow around with a Medium, preferably hot air or oil, is treated, comprising the steps:

• Heating the thermal chamber until it reaches the maximum temperature in the temperature range from 150 to 220 ° C., the heating time being 1 to 10 minutes per Kelvin,
• - Keep the maximum temperature for a period of 1 to 8 hours and
• - cooling the thermal chamber to an ambient temperature, wherein the cooling time per Kelvin is 1 to 10 minutes.

The preferred maximum temperature is 190 ° C. The heating time and / or the cooling time are preferably 2 to 6 minutes per Kelvin. The preferred period for holding the maximum temperature is 2 to 6 hours. Ambient temperature is the temperature that is measured around the outside of the thermal chamber. The value can therefore fluctuate geographic-climatic and seasonal. Thus, especially in winter, a temperature of less than 0 ° C, in summer and in warmer areas, however, a temperature of about 30 ° C as the ambient temperature.

• – Im Gegensatz zur thermischen Behandlung von (Massiv-)Holz oder Holzpartikeln vor der Holzwerkstoff-Herstellung können Holzwerkstoffe, insbesondere plattenförmige Holzwerkstoffe (WBP), mit dem vornehmlichen Ziel einer Verringerung der Feuchteaufnahme sowie einer Quellungsvergütung thermisch nachbehandelt werden.
• – In Bezug auf Massivholzplatten (SWP) werden durch eine verringerte Feuchteaufnahme, aber auch durch den Abbau innerer Spannungen, die Eigenschaften hinsichtlich der Formstabilität, der Dickenquellung und der Rissbildung im Hinblick auf einen verstärkten Einsatz im Fassadenbereich verbessert. Dies war bisher nur durch die Auswahl geeigneter Holzarten beziehungsweise Beschichtungen möglich.
• – Herkömmlicherweise erfolgt bei plattenförmigen Holzwerkstoffen (WBP) eine Reduzierung der Quellungseigenschaften durch eine Erhöhung des Binde- und/oder Hydrophobierungsmittelanteils. Die erwartete Quellungsverringerung aufgrund der thermischen Nachbehandlung von plattenförmigem OSB-Material trägt dazu bei, dass der Anwendungsbereich für OSB hinsichtlich eines vermehrten Einsatzes im Holzbau erweitert werden kann. Ebenso werden durch eine thermische Behandlung das Kriechverhalten sowie die Formstabilität verbessert. Bisher wurden Verbesserungen dieser Eigenschaften durch eine Erhöhung des Bindemittelanteils realisiert.
• – Im Bereich der hochdichten Faserplatten (HDF) für den Laminatbereich erfolgte eine Reduzierung der Quellungseigenschaften bislang ebenfalls mit Hilfe einer Erhöhung des Binde- und/oder Hydrophobierungsanteils. Die erfolgreiche Reduzierung der Quellung aufgrund der thermischen Behandlung ist sowohl für Verarbeiter als auch für Anwender von Laminat von großem Vorteil.
• – Aufgrund der im Vergleich zu klassischen plattenförmigen Holzwerkstoffen (WBP) besseren Beständigkeit gegenüber erhöhter Feuchtigkeit besteht die Möglichkeit, thermisch nachbehandelte plattenförmige Holzwerkstoffe (WBP), insbesondere OSB, als Beton-Schalungselemente zu verwenden. Bislang wurden Schalungsplatten vornehmlich aus Sperrhölzern (PLY) oder auch aus Massivholzplatten (SWP) in der Regel ohne Schmalflächenschutz mit einer wasserabweisenden Beschichtung gefertigt. Aufgrund der verbesserten feuchtebedingten Eigenschaften von thermisch nachbehandelten plattenförmigen Holzwerkstoffen (WBP) über den gesamten Querschnitt im Gegensatz zu einer rein äußerlichen Beschichtung besitzen diese WBP einen klaren Vorteil gegenüber konventionellen Schalungsplatten, da es auf Baustellen oft vorkommt, dass Schalungsplatten für bestimmte Zwecke oder auf bestimmte Maße zugeschnitten werden müssen und dann die Schnittkanten nicht mehr geschützt sind.

In the aftertreatment of the abovementioned wood materials according to the invention, the following innovations are achieved compared to the prior art:

• - In contrast to the thermal treatment of (solid) wood or wood particles prior to the manufacture of wood products, wood-based materials, in particular plate-shaped wood materials (WBP), with the primary aim of reducing the moisture absorption and a Quellungsvergütung be thermally treated.
• - With regard to solid wood panels (SWP), the reduced moisture absorption, but also the reduction of internal tensions, improves the dimensional stability, thickness swelling and cracking properties with a view to increased use in the façade area. Until now, this was only possible by selecting suitable types of wood or coatings.
• - Conventionally, in plate-shaped wood materials (WBP), a reduction of the swelling properties by increasing the binding and / or hydrophobizing agent content. The expected swelling reduction due to the thermal aftertreatment of plate-shaped OSB material contributes to the extension of the field of application for OSB with regard to increased use in timber construction. Likewise, the creep behavior and the dimensional stability are improved by a thermal treatment. So far, improvements of these properties have been realized by increasing the binder content.
• - In the field of high-density fibreboard (HDF) for the laminate area, a reduction of the swelling properties has hitherto likewise been carried out with the aid of an increase in the binding and / or hydrophobing proportion. The successful reduction of swelling due to the thermal treatment is of great benefit to both fabricators and users of laminate.
• - Due to the better resistance to increased moisture in comparison to conventional plate-shaped wood materials (WBP), it is possible to use thermally aftertreated plate-shaped wood materials (WBP), in particular OSB, as concrete formwork elements. Up to now, shuttering panels, mainly made of plywood (PLY) or solid wood panels (SWP), have generally been manufactured without a narrow surface protection with a water-repellent coating. Due to the improved moisture-related properties of thermally treated plate-shaped wood materials (WBP) over the entire cross-section as opposed to a purely external coating these WBP have a clear advantage over conventional formwork panels, as it often happens on construction sites that formwork panels for specific purposes or to certain dimensions must be cut and then the cut edges are no longer protected.

• – Verringerung der Quellung und Schwindung,
• – Verringerung der Ausgleichsfeuchte des Materials,
• – Reduzierung innerer Spannungen,
• – Erhöhung der Formstabilität,
• – Verbesserung des Kriechverhaltens,
• – Erhöhung der Dimensionsstabilität,
• – Verringerung der Wärmeleitfähigkeit,
• – Erzeugung von warmen Goldbraun- bis Schwarzbrauntönen über den gesamten Querschnitt und
• – Erhöhung der Dauerhaftigkeit/Beständigkeit gegenüber Pilzbefall und Witterungseinflüssen über den gesamten Querschnitt.

The inventive thermal aftertreatment of the wood materials surprisingly, the following material properties are positively changed:

• - reduction of swelling and shrinkage,
• - reduction of the equilibrium moisture content of the material,
• - Reduction of internal tensions,
• - increase the dimensional stability,
• - improvement of creep behavior,
• Increasing the dimensional stability,
• - reduction of thermal conductivity,
• - Production of warm golden brown to black brown tones over the entire cross section and
• - Increasing the durability / resistance to fungal attack and weather conditions over the entire cross-section.

• – Spanplatten (PB),
• – Faserplatten nach dem Trockenverfahren (MDF, HDF, LDF),
• – Oriented Strand Boards (OSB),
• – Sperrhölzer (PLY),
• – Massivholzplatten (SWP) und
• – Holzwerkstoff-Verbundwerkstoffe (CB)
• – oder eine Kombination aus den oben genannten Holzwerkstoffen.

As already mentioned, mainly plate-shaped wood-based materials (WBP) are thermally modified by being thermally treated at elevated temperatures. That is, first under industrial conditions WBP produced in sheet form and then treated thermally in an additional work / treatment step. Preferred, partially already mentioned wood materials for the thermal aftertreatment are:

• - chipboard (PB),
• - fibreboards according to the dry process (MDF, HDF, LDF),
• - Oriented Beach Boards (OSB),
• - plywood (PLY),
• - Solid wood panels (SWP) and
• - wood-based composite materials (CB)
• - or a combination of the above wood materials.

However, moldings made of wood or wood particles can also be treated with the method according to the invention. A further significant advantage of the method according to the invention is that the strength properties of said wood-based materials are not significantly influenced by the thermal treatment.

• – Harnstoff-Formaldehyd-Harz (UF),
• – Melamin-Harnstoff-Formaldehyd-Harz (MUF),
• – melaminverstärktes Harnstoff-Formaldehyd-Harz (mUF),
• – Melamin-Harnstoff-Phenol-Formaldehyd-Harz (MUPF),
• – polymeres Diphenylmethandiisocyanat (pMDI),
• – Phenol-Formaldehyd-Harz (PF),
• – Tannin-Formaldehyd-Harz (TF),
• – Resorcinol-Formaldehyd-Harz (RF) und
• – proteinverstärktes Phenol-Formaldehyd-Harz (pPF)
• – oder eine Kombination aus den oben genannten Klebstoffsystemen.

The preparation of the above-mentioned post-treated wood materials is preferably carried out on the basis of one or more of the following adhesive systems:

• Urea-formaldehyde resin (UF),
• - melamine-urea-formaldehyde-resin (MUF),
• - melamine-reinforced urea-formaldehyde resin (mUF),
• - melamine-urea-phenol-formaldehyde-resin (MUPF),
• Polymeric diphenylmethane diisocyanate (pMDI),
• Phenol-formaldehyde resin (PF),
• Tannin-formaldehyde resin (TF),
• - Resorcinol-formaldehyde resin (RF) and
• Protein-reinforced phenol-formaldehyde resin (pPF)
• - or a combination of the above adhesive systems.

A significant advantage of the method is that the said adhesive systems survive the thermal treatment and no delamination occurs in SWP or PLY.

In one embodiment of the method, the thermal chamber is equipped with a device that regulates the moisture in the thermal chamber.

Further details, features and advantages of the invention will become apparent from the figure and the following description of exemplary embodiments. It shows:

1 : the schematic representation of the thermal treatment of wood materials (WBP) in a thermal chamber.

According to the process of the invention, previously prepared phenol-formaldehyde-resin (PF) bonded medium density fiberboards (MDF) and Oriented Strand Boards (OSB) as well as melamine-urea-formaldehyde-resin (MUF) bonded solid wood panels (SWP) were treated.

The treatment temperatures in tests carried out each reached a maximum at 160 ° C, 170 ° C and 180 ° C. Heating up to maximum temperature and cooling the thermal chamber to ambient temperature (about 20 ° C) took about three minutes per Kelvin, while maintaining the maximum temperature for about four hours.

The 1 schematically shows a thermal treatment chamber 1 (Thermal chamber 1 ), in which the wood material 2 , that is several wooden boards 2 (WBP), stacked in a stack of vials. Between the wood-based panels 2 are each spacers 3 arranged. In the upper part of the thermal chamber 1 above the stack are one or more fans 4 provided for a flow through the thermal chamber 1 provide air, wherein the flow direction of the air is indicated by a circumferential directional arrow. The air flows through on its way to the wood-based panels 2 a heating register 5 , wherein the flowing air is heated. Due to the spacers 3 can the spaces between the wood-based panels 2 to be flowed through with hot air. Furthermore, in the upper part of the thermal chamber 1 a spraying device 6 provided with the aid of which the chamber humidity can be regulated in order to minimize or prevent internal stresses or damage to the Kammergut by the thermal treatment. With the help of fresh air / exhaust air flaps 7 , which are also in the upper part of the thermal chamber 1 can be controlled, the heating and the cooling process. In selected wood-based panels 2 there are measuring electrodes 8th (exemplary is in 1 only one measuring electrode 8th shown), with which the temperature directly in the wood material 2 / in the wood-based panels 2 is monitored. Furthermore, a measuring device 9 intended for the chamber climate.

As the main result, it can be stated that, in particular, the property of thickness swelling due to the thermal treatment was positively influenced while the strength properties were not adversely affected to such an extent that the respective normative requirements would no longer be satisfied.

SHORTCUT LIST

• CB

  Composite wood composites

  FWD

  Wet-heat pressure

  HDF

  high density fiberboard

  LDF

  low-density fiberboard (Low Density Fiberboards)

  MDF

  medium-density fiberboard

  MUF

  Melamine-urea-formaldehyde resin

  MUF

  melamine-reinforced urea-formaldehyde resin

  MUPF

  Melamine-urea-phenol-formaldehyde resin

  OSB

  Oriented beach boards

  PB

  Particle boards

  PF

  Phenol-formaldehyde resin

  PLY

  Plywoods

  pMDI

  polymeric diphenylmethane diisocyanate

  PPF

  protein-reinforced phenol-formaldehyde resin

  RF

  Resorcinol-formaldehyde resin

  SWP

  Solid wood panels (Solid Wood Panels)

  TF

  Tannin-formaldehyde resin

  TMT

  thermally modified timber (Thermally Modified Timber)

  UF

  Urea-formaldehyde resin

  WBP

  Wood Based Panels

LIST OF REFERENCE NUMBERS

1

Thermal chamber, treatment chamber

2

Wood-based material, wood-based panels (WBP)

3

spacer

4

Fan (s)

5

heater

6

sprayer

7

Fresh air / exhaust air vents

8th

Measuring electrode (s)

9

Measuring device for chamber climate

Claims (10)

Method for modifying wood-based materials ( 2 ), in which the wood material to be modified ( 2 ), which was previously produced using adhesive systems, at normal pressure in thermal chambers ( 1 ) is post-treated thermally by flowing around with a medium, comprising the steps of: - heating the thermal chamber ( 1 ) until the maximum temperature in the temperature range of 150 to 220 ° C, the heating time is 1 to 10 minutes per Kelvin, - holding the maximum temperature over a period of 1 to 8 hours and - cooling the thermal chamber ( 1 ) to an ambient temperature, wherein the cooling time per Kelvin is 1 to 10 minutes. A method according to claim 1, characterized in that the wood material to be modified ( 2 ) is a plate-shaped wood material (WBP). A method according to claim 2, characterized in that the plate-shaped wood material (WBP) to be modified is selected from the group of plate-shaped wood materials (WBP): - chipboard (PB), - dry-process fibreboard (MDF, HDF, LDF), - Oriented Beach boards (OSB), - plywood (PLY), - solid wood panels (SWP) and - wood-based composite materials (CB) - or a combination of the above-mentioned wood-based materials. A method according to claim 1, characterized in that the wood material to be modified ( 2 ) is present as a molding of wood or wood particles. Method according to one of claims 1 to 4, characterized in that the wood-based materials ( 2 ) are prepared with adhesive systems selected from the group of adhesive systems: urea-formaldehyde resin (UF), melamine-urea-formaldehyde resin (MUF), melamine-reinforced urea-formaldehyde resin (mUF), melamine Urea-phenol-formaldehyde resin (MUPF), - polymeric diphenylmethane diisocyanate (pMDI), - phenol-formaldehyde resin (PF), - tannin-formaldehyde resin (TF), - resorcinol-formaldehyde resin (RF) and - protein-reinforced phenol-formaldehyde resin (pPF) - or a combination of the above-mentioned adhesive systems. Method according to one of claims 1 to 5, characterized in that the maximum temperature is 190 ° C. Method according to one of claims 1 to 6, characterized in that the time in which the maximum temperature of the thermal chamber ( 1 ) is kept constant, 2 to 6 hours. Method according to one of claims 1 to 7, characterized in that both the cooling time and the heating time per Kelvin is 2 to 6 minutes. Method according to one of claims 1 to 8, characterized in that the thermal chamber ( 1 ) is equipped with a device which reduces the humidity in the thermal chamber ( 1 ) regulates. Method according to one of claims 1 to 9, characterized in that hot air or oil is provided as the medium.

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