EP0936961A1 - Method for treating wood by impregnation - Google Patents

Method for treating wood by impregnation

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Publication number
EP0936961A1
EP0936961A1 EP97912273A EP97912273A EP0936961A1 EP 0936961 A1 EP0936961 A1 EP 0936961A1 EP 97912273 A EP97912273 A EP 97912273A EP 97912273 A EP97912273 A EP 97912273A EP 0936961 A1 EP0936961 A1 EP 0936961A1
Authority
EP
European Patent Office
Prior art keywords
wood
product
monomer
impregnation
treated
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP97912273A
Other languages
German (de)
French (fr)
Other versions
EP0936961B1 (en
Inventor
Pierre Gohar
René GUYONNET
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
NOW New Option Wood SA
Original Assignee
NOW New Option Wood SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by NOW New Option Wood SA filed Critical NOW New Option Wood SA
Publication of EP0936961A1 publication Critical patent/EP0936961A1/en
Application granted granted Critical
Publication of EP0936961B1 publication Critical patent/EP0936961B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
    • B27K3/02—Processes; Apparatus
    • B27K3/08—Impregnating by pressure, e.g. vacuum impregnation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
    • B27K3/02—Processes; Apparatus
    • B27K3/15—Impregnating involving polymerisation including use of polymer-containing impregnating agents
    • B27K3/153—Without in-situ polymerisation, condensation, or cross-linking reactions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K5/00—Treating of wood not provided for in groups B27K1/00, B27K3/00
    • B27K5/0085—Thermal treatments, i.e. involving chemical modification of wood at temperatures well over 100°C

Definitions

  • the present invention relates to an improvement to methods of treating wood in which the latter is impregnated with a hardenable product.
  • drying step makes it possible to remove the water from the wood, it does not in any way modify the hydrophilic nature of the latter, so that it is again able to reabsorb the water eliminated during drying, when 'it is again in a humid atmosphere.
  • the treatment methods used in the prior art consist in placing the wood to be treated in an enclosure in which a vacuum is created, in filling the latter with the impregnating monomer, and in applying a high pressure in this enclosure. so as to penetrate the monomer into the wood. It then only remains to polymerize the monomer.
  • the object of the present invention is to propose an improvement in techniques for impregnating wood with hardenable products, and in particular with monomers, with a view in particular to imparting thereto dimensional stability characteristics when they are subsequently exposed. to a humid atmosphere.
  • the present invention thus relates to a method of treating wood of the type in which arranges the wood to be treated in an enclosure in which a vacuum is created, where said enclosure is filled with a hardenable product, in particular a monomer, so as to impregnate the wood by making the product penetrate into the fiber-interfacing space of that - Ci, where it then causes the hardening of said product, in particular by polymerization, characterized in that the operation of impregnating the wood is preceded by a crosslinking step.
  • said product is a monomer which is hardened by polymerization, in particular by the action of radiation or thermally.
  • the impregnation can be carried out immediately after the crosslinking step, so as to use the remaining heat of the wood being cooled, to ensure, by thermal means, the polymerization of the monomer.
  • a crosslinking operation consists in subjecting the wood to a heat treatment under controlled conditions in order to cause thermocondensation reactions in the lignocellulosic structure of the wood.
  • a cross-linking operation is usually carried out in a neutral or reducing atmosphere on previously dried wood, by subjecting it to a temperature between 220 ° C. and 280 ° C. for a time long enough for the entire mass of the treated wood. reaches the treatment temperature, and without exceeding this treatment time. It is understood that, under these conditions, this duration depends on the nature and thickness of the wood.
  • this crosslinking operation has three important effects, namely slightly increasing the porosity of the wood, giving it a hydrophobic character, and improve its wettability with respect to the monomers by modifying the surface tension of the wood. These three effects are used in particular according to the present invention to promote the impregnation of the wood by the monomer.
  • the process according to the invention makes it possible to impregnate, with monomers, varieties of wood which were hitherto deemed to be almost non-impregnable by known processes, such as in particular spruce, oak , chestnut, beech.
  • some of the blowing agents, such as in particular methanol, which are used according to the prior art prior to the impregnation operation are no longer necessary, which represents an economy, of a partly in terms of the cost of the product itself, and secondly in terms of the cost of implementing the method.
  • the polymerization of the monomer can, of course, be carried out using several techniques and in particular among these by the action of gamma rays, by convection heating and by microwave heating.
  • FIG. 1 is a graph which represents the variation of the temperature to which a wood to be treated is subjected as a function of time during a crosslinking operation.
  • Figure 2 is a schematic view of a reactor for performing an operation of impregnating a piece of wood with a monomer.
  • FIG. 3 is a graph which represents the variation of the rate of impregnation as a function of time, of a sample of wood with a monomer, respectively in the case of natural wood and of retified wood.
  • FIG. 4 is a graph which represents the variation of the volume swelling as a function of time, of wood samples in the presence of a humid atmosphere.
  • the first part of the treatment consists in subjecting these pieces of wood to a crosslinking treatment. To do this, the latter are introduced into a treatment enclosure where they are subjected to programmed temperature variations.
  • FIG. 1 shows the variation in temperature T (in ° C) as a function of time t (in min), to which we have brought the enclosure containing the captivating pieces to be treated and dotted the temperature of the wood.
  • Such a treatment process comprises three essential steps, namely a drying step A, preferably a glass transition step B, and a retification step proper C.
  • the first drying step A breaks down into two phases, a first phase A1 during which the temperature of the treatment chamber containing the charm to be treated is gradually raised with a temperature rise rate of approximately 5 ° C / min, from ambient temperature to a temperature Tl, close to 100 ° C, followed by a phase A2 during which the temperature of enclosure 1 is maintained at a level Tl value up to at the end of drying.
  • the temperature of the enclosure is gradually raised with a rate of temperature rise close to the previous one, from the temperature Tl to a temperature Tg close to the glass transition temperature of the species of wood considered, namely the charm in the present case.
  • the temperature Tg is maintained at this plateau value for the time necessary for the entire mass of treated wood to reach the glass transition temperature Tg. It will be noted that prolonging the duration of this plateau does not have any harmful consequences. as regards the respect of the mechanical qualities of the treated product.
  • the third step C is increased gradually, during a C stage, the enclosure of the temperature with a heating rate temperature close to the previous one, from the glass transition temperature Tg to the retification temperature Tr and the oven temperature is maintained for a second phase C2 at this plateau value, until most of the hemicelluloses are broken down.
  • This first part made it possible to prepare the material almost perfectly for the second part, namely the impregnation, which will follow, in particular by opening the pores of the wood, giving it a hydrophobic character and increasing its wettability. vis-à-vis the monomer.
  • This second part of the treatment is then carried out, which itself comprises two stages, namely a stage of impregnation with a hardenable product and in particular a polymerizable monomer, and a stage of hardening, or polymerization, of the product of which impregnated the wood.
  • FIG. 2 To implement the first step, a device of the type shown in FIG. 2 is used, which is well known from the prior art.
  • This device essentially consists of an enclosure 1, or reactor, which comprises a suction line 3 connected to a vacuum pump, not shown in the drawing, a line 5 injecting the monomer into the enclosure 1, and a pipe 7 for discharging the latter.
  • the wood to be treated 2 is introduced into the enclosure 1 by a door 8, then a vacuum is created therein by sucking in the air which it contains through the pipe 3 so as to empty as much as possible the " wood cells.
  • the product with which the wood is to be impregnated is then injected into the enclosure 1. It is left in the state for a period of about thirty minutes, depending on the viscosity of the product used, then the reactor 1 is emptied by driving 7.
  • the Applicant has established that the crosslinking treatment makes it possible to improve the impregnation of the wood, without, as in the prior art, it being necessary to pressurize the product contained in reactor 1.
  • the curve of FIG. 3 shows the variation in the rate of impregnation of the charm (in%) as a function of the passage time t in the reactor 1, for natural charm (curve a) and for the charm having previously undergone a crosslinking with a monomer which is GMA (curve b), that is to say glycidyl methacrylate.
  • GMA Curve b
  • the glicidyl impregnation stabilizes after a period of approximately thirty minutes, and that the charm impregnation rate which, in its natural state was 50%, has increased to 55% value when it was, prior to impregnation, subject to retification.
  • the Applicant has obtained results of the same order with different species of wood and monomers, and in particular for beech, ash, poplar and various conifers.
  • the product hardening step is then carried out. If this is a monomer, the impregnated wood can be subjected, depending on the nature of the monomer. used, either by the action of gamma radiation or by the action of heat in order to cause its polymerization.
  • the heating can be carried out in particular by conventional convection means or even by microwave.
  • the Applicant has found that retified wood exhibited better behavior than natural wood. Indeed, because of the treatment it underwent, the retified wood no longer emits gas or water vapor like natural wood, emission which is the cause of poor adhesion of the polymer
  • the Applicant has carried out tests in order to compare the dimensional stability of the impregnated natural wood with that of the same wood treated according to the invention, when they were placed in a humid atmosphere. These tests were carried out in a climatic chamber in which the kinetics of moisture uptake were carried out. The enclosure had a humidity of 75% and a temperature of 25 ° C, according to standard NF 51-264.
  • the Applicant has of course also treated charm samples, on the one hand in the natural state and on the other hand in the crosslinked state, using monomers of various natures, namely HEMA (methacrylate of hydroxyethyl), HEA (2-hydroxyethyl acrylate) and AGE-AM (mixture of 70% allyl glycidile ether and 30% maleic anhydride) and GMA and then, after treatment, subjected these various samples to a swelling test according to the aforementioned standard NF 51-264 and measured the swelling of these samples.
  • HEMA methacrylate of hydroxyethyl
  • HEA 2-hydroxyethyl acrylate
  • AGE-AM mixture of 70% allyl glycidile ether and 30% maleic anhydride
  • the present invention also makes it possible to increase the hardness of the treated wood.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Forests & Forestry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Chemical And Physical Treatments For Wood And The Like (AREA)

Abstract

A method for treating wood in which the wood to be treated is placed in a chamber in which a vacuum is produced, where the chamber is filled with a hardening product, in particular a monomer, so as to impregnate the wood by causing the product to penetrate the space between its fibers, where the product is hardened, in particular by polymerization. This method is characterized in that the wood impregnating operation is preceded by a step of controlled thermal treatment.

Description

PROCEDE DE TRAITEMENT DU BOIS PAR IMPREGNATION IMPREGNATION TREATMENT OF WOOD
La présente invention concerne un perfectionnement aux procédés de traitement du bois dans lesquels on imprègne celui-ci d'un produit durcissable.The present invention relates to an improvement to methods of treating wood in which the latter is impregnated with a hardenable product.
On sait, qu'à l'état naturel, le bois ou les fibres de bois qui sont au contact d'une atmosphère humide ont tendance à se gorger d'eau, allant jusqu'à absorber 100% de leur poids du celle-ci. Cette absorption d'eau s'accompagne d'un gonflement, caractéristique d'une diminution des qualités de cohésion du matériau, pouvant aller, dans certains cas, jusqu'à une désagrégation avancée de celui-ci. C'est pourquoi on a pour habitude de faire précéder toute opération de façonnage du bois d'une étape de séchage qui, en éliminant l'eau de celui-ci, améliore sa stabilité dimensionnelle.We know that in its natural state, wood or wood fibers that are in contact with a humid atmosphere tend to soak up water, going so far as to absorb 100% of their weight from it. . This absorption of water is accompanied by swelling, characteristic of a reduction in the cohesion qualities of the material, which can go, in certain cases, to an advanced disintegration of the latter. This is why it is customary to precede any operation of shaping the wood with a drying step which, by removing the water from it, improves its dimensional stability.
Si l'étape de séchage permet d'éliminer l'eau du bois elle ne modifie en rien par contre le caractère hydrophile de celui-ci, si bien qu'il est de nouveau apte à réabsorber l'eau éliminée lors du séchage, lorsqu'il se trouve de nouveau en atmosphère humide.If the drying step makes it possible to remove the water from the wood, it does not in any way modify the hydrophilic nature of the latter, so that it is again able to reabsorb the water eliminated during drying, when 'it is again in a humid atmosphere.
Afin de diminuer le caractère hydrophile du bois naturel, et de lui conférer ainsi une stabilité dimensionnelle durable, on a proposé différentes techniques de traitement thermique à haute température.In order to reduce the hydrophilic nature of natural wood, and thus to give it lasting dimensional stability, various techniques of heat treatment at high temperature have been proposed.
Parmi ces techniques, on a proposé de faire subir au bois naturel différentes étapes de traitement comprenant notamment un séchage en circuit ouvert suivi d'un chauffage et d'un maintien à une température comprise entre environ 220°C et 300°C pendant une période déterminée. Une telle technique de traitement, dite de rétification, permet de conférer au bois, à la fois un caractère hydrophobe et une excellente stabilité dimensionnelle.Among these techniques, it has been proposed to subject the natural wood to different treatment steps including in particular drying in an open circuit followed by heating and maintaining at a temperature between approximately 220 ° C. and 300 ° C. for a period determined. Such a treatment technique, known as retification, makes it possible to give the wood, the both hydrophobic and excellent dimensional stability.
On a également proposé, notamment afin d'améliorer les propriétés mécaniques du bois, de faire appel à des techniques de traitement qui consistent à imprégner celui-ci avec un monomère puis, cette imprégnation ayant été réalisée, à le polymériser in situ, en faisant appel pour ce faire à différentes techniques, telles que notamment l'action d'un rayonnement gamma ou l'action de la chaleur.It has also been proposed, in particular in order to improve the mechanical properties of the wood, to use treatment techniques which consist in impregnating the latter with a monomer then, this impregnation having been carried out, in polymerizing it in situ, making to do this, use different techniques, such as the action of gamma radiation or the action of heat.
Les méthodes de traitement utilisées dans l'état antérieur de la technique consistent à disposer le bois à traiter dans une enceinte dans laquelle on fait le vide, à remplir celle-ci du monomère d'imprégnation, et à appliquer une forte pression dans cette enceinte de façon à faire pénétrer le monomère dans le bois. Il ne reste plus alors qu'à faire polymériser le monomère.The treatment methods used in the prior art consist in placing the wood to be treated in an enclosure in which a vacuum is created, in filling the latter with the impregnating monomer, and in applying a high pressure in this enclosure. so as to penetrate the monomer into the wood. It then only remains to polymerize the monomer.
Si ces techniques se révèlent satisfaisantes sur le plan de l'amélioration des propriétés mécaniques du bois traité, et notamment sur celui de la dureté, elles le sont beaucoup moins sur celui de la stabilité volumique du bois en atmosphère humide. On a ainsi remarqué que les bois ainsi imprégnés présentaient la particularité, au bout d'un certain temps d'utilisation, de perdre leur adhérence avec le polymère dont ils étaient imprégnés, ce qui se traduisait par un gonflement de ce bois.If these techniques prove satisfactory in terms of improving the mechanical properties of the treated wood, and in particular in terms of hardness, they are much less so in that of the volume stability of the wood in a humid atmosphere. It has thus been noted that the woods thus impregnated have the particularity, after a certain time of use, of losing their adhesion with the polymer with which they were impregnated, which resulted in swelling of this wood.
La présente invention a pour but de proposer un perfectionnement aux techniques d'imprégnation de bois par des produits durcissables, et notamment par des monomères, en vue notamment de conférer à ceux-ci des caractéristiques de stabilité dimensionnelle lorsqu'ils sont exposés par la suite à une atmosphère humide.The object of the present invention is to propose an improvement in techniques for impregnating wood with hardenable products, and in particular with monomers, with a view in particular to imparting thereto dimensional stability characteristics when they are subsequently exposed. to a humid atmosphere.
La présente invention a ainsi pour objet un procédé de traitement du bois du type dans lequel on dispose le bois à traiter dans une enceinte dans laquelle on crée un vide, où l'on remplit ladite enceinte d'un produit durcissable, notamment un monomère, de façon à imprégner le bois en faisant pénétrer le produit dans l'espace interfibres de celui- ci, où l'on provoque ensuite le durcissement dudit produit, notamment par polymérisation, caractérisé en ce que l'on fait précéder l'opération d'imprégnation du bois d'une étape de rétification. De façon intéressante ledit produit est un monomère que l'on durcit par polymérisation, notamment par action d'un rayonnement ou par voie thermique.The present invention thus relates to a method of treating wood of the type in which arranges the wood to be treated in an enclosure in which a vacuum is created, where said enclosure is filled with a hardenable product, in particular a monomer, so as to impregnate the wood by making the product penetrate into the fiber-interfacing space of that - Ci, where it then causes the hardening of said product, in particular by polymerization, characterized in that the operation of impregnating the wood is preceded by a crosslinking step. Interestingly, said product is a monomer which is hardened by polymerization, in particular by the action of radiation or thermally.
On peut réaliser l'imprégnation immédiatement après l'étape de rétification , de façon à utiliser la chaleur restante du bois en cours de refroidissement, pour assurer, par voie thermique, la polymérisation du monomère.The impregnation can be carried out immediately after the crosslinking step, so as to use the remaining heat of the wood being cooled, to ensure, by thermal means, the polymerization of the monomer.
On sait qu'une opération de rétification consiste à soumettre le bois à un traitement thermique dans des conditions contrôlées afin de provoquer des réactions de thermocondensation au niveau de la structure ligno- cellulosique du bois. Une opération de rétification est habituellement réalisée sous atmosphère neutre ou réductrice sur du bois préalablement séché, en soumettant celui-ci à une température comprise entre 220°C et 280°C pendant un temps suffisamment long pour que la totalité de la masse du bois traité atteigne la température de traitement, et sans dépasser ce temps de traitement. On conçoit que, dans ces conditions, cette durée est fonction de la nature et de l'épaisseur du bois .It is known that a crosslinking operation consists in subjecting the wood to a heat treatment under controlled conditions in order to cause thermocondensation reactions in the lignocellulosic structure of the wood. A cross-linking operation is usually carried out in a neutral or reducing atmosphere on previously dried wood, by subjecting it to a temperature between 220 ° C. and 280 ° C. for a time long enough for the entire mass of the treated wood. reaches the treatment temperature, and without exceeding this treatment time. It is understood that, under these conditions, this duration depends on the nature and thickness of the wood.
La demanderesse a constaté que cette opération de rétification possédait trois effets importants, à savoir d'augmenter légèrement la porosité du bois, de conférer à celui-ci un caractère hydrophobe, et d'améliorer sa mouillabilité vis-à-vis des monomères en modifiant la tension de surface du bois. Ces trois effets sont notamment utilisés suivant la présente invention pour favoriser l'imprégnation du bois par le monomère.The Applicant has found that this crosslinking operation has three important effects, namely slightly increasing the porosity of the wood, giving it a hydrophobic character, and improve its wettability with respect to the monomers by modifying the surface tension of the wood. These three effects are used in particular according to the present invention to promote the impregnation of the wood by the monomer.
Les essais réalisés par la demanderesse, et qui seront décrits en détails ci-après, ont ainsi permis de démontrer qu'en faisant précéder, suivant l'invention, l'imprégnation du produit, et notamment d'un monomère, par une opération de rétification, non seulement on obtenait une imprégnation supérieure à celle conforme à l'état antérieur de la technique, mais qu'il n'était plus nécessaire pour obtenir une telle imprégnation de mettre sous pression l'enceinte contenant le bois à traiter et le produit d'imprégnation.The tests carried out by the applicant, and which will be described in detail below, have thus made it possible to demonstrate that by preceding, according to the invention, the impregnation of the product, and in particular of a monomer, by an operation of cross-linking, not only was an impregnation greater than that in accordance with the prior art, but it was no longer necessary to obtain such an impregnation to pressurize the enclosure containing the wood to be treated and the product impregnation.
La demanderesse a également établi que le procédé suivant l'invention permettait de réaliser une imprégnation, par des monomères, de variétés de bois qui étaient jusqu'à présent réputées quasiment non imprégnables par les procédés connus, tels que notamment l'épicéa, le chêne, le châtaignier, le hêtre. Suivant l'invention certains des agents de gonflement, tels que notamment le méthanol , qui sont utilisés suivant l'état antérieur de la technique préalablement à l'opération d'imprégnation, ne sont plus nécessaires, ce qui représente une économie, d'une part sur le plan du coût du produit lui-même, et d'autre part sur le plan du coût de la mise en oeuvre du procédé. La polymérisation du monomère peut, bien entendu, être effectuée en faisant appel à plusieurs techniques et notamment parmi celles-ci par l'action de rayons gamma, par chauffage par convection et par chauffage par micro-ondes. On décrira ci-après divers exemples de mise en oeuvre de l'invention en regard du dessin annexé sur lequel :The Applicant has also established that the process according to the invention makes it possible to impregnate, with monomers, varieties of wood which were hitherto deemed to be almost non-impregnable by known processes, such as in particular spruce, oak , chestnut, beech. According to the invention, some of the blowing agents, such as in particular methanol, which are used according to the prior art prior to the impregnation operation, are no longer necessary, which represents an economy, of a partly in terms of the cost of the product itself, and secondly in terms of the cost of implementing the method. The polymerization of the monomer can, of course, be carried out using several techniques and in particular among these by the action of gamma rays, by convection heating and by microwave heating. Various examples of implementation of the invention will be described below with reference to the appended drawing in which:
La figure 1 est un graphique qui représente la variation de la température à laquelle est soumis un bois à traiter en fonction du temps lors d'une opération de rétification .FIG. 1 is a graph which represents the variation of the temperature to which a wood to be treated is subjected as a function of time during a crosslinking operation.
La figure 2 est une vue schématique d'un réacteur permettant de réaliser une opération d'imprégnation d'une pièce de bois par un monomère.Figure 2 is a schematic view of a reactor for performing an operation of impregnating a piece of wood with a monomer.
La figure 3 est un graphique qui représente la variation du taux d'imprégnation en fonction du temps, d'un échantillon de bois par un monomère, respectivement dans le cas d'un bois naturel et d'un bois rétifié.FIG. 3 is a graph which represents the variation of the rate of impregnation as a function of time, of a sample of wood with a monomer, respectively in the case of natural wood and of retified wood.
La figure 4 est un graphique qui représente la variation du gonflement volumique en fonction du temps, d'échantillons de bois en présence d'une atmosphère humide . Bien que la demanderesse ait établi que la présente invention soit applicable à de nombreuses essences de bois, et notamment au hêtre, au charme, au frêne et au peuplier, on décrira à titre d'exemple le procédé suivant l'invention dans le cas d'une application au charme.FIG. 4 is a graph which represents the variation of the volume swelling as a function of time, of wood samples in the presence of a humid atmosphere. Although the Applicant has established that the present invention is applicable to many species of wood, and in particular beech, hornbeam, ash and poplar, the method according to the invention will be described by way of example in the case of 'an application with charm.
On se propose donc de traiter suivant l'invention des échantillons constitués de pièces de charme. Conformément à l'invention, la première partie du traitement consiste à faire subir à ces pièces de bois un traitement de rétification. Pour ce faire ces dernières sont introduites dans une enceinte de traitement où elles sont soumises à des variations de température programmées . On a ainsi représenté sur la figure 1 la variation de température T (en °C) en fonction du temps t (en min), à laquelle on a porté l'enceinte contenant les pièces de charme à traiter et en pointillés la température du bois.It is therefore proposed to treat according to the invention samples consisting of charming pieces. According to the invention, the first part of the treatment consists in subjecting these pieces of wood to a crosslinking treatment. To do this, the latter are introduced into a treatment enclosure where they are subjected to programmed temperature variations. FIG. 1 shows the variation in temperature T (in ° C) as a function of time t (in min), to which we have brought the enclosure containing the charming pieces to be treated and dotted the temperature of the wood.
Un tel processus de traitement comprend trois étapes essentielles, à savoir une étape de séchage A, préférentiellement une étape de transition vitreuse B, et une étape de rétification proprement dite C.Such a treatment process comprises three essential steps, namely a drying step A, preferably a glass transition step B, and a retification step proper C.
La première étape de séchage A se décompose elle- même en deux phases, une première phase Al au cours de laquelle on élève progressivement la température de l'enceinte de traitement contenant le charme à traiter avec une vitesse de montée en température d'environ 5°C/min, à partir de la température ambiante jusqu'à une température Tl , voisine de 100°C, suivie d'une phase A2 au cours de laquelle on maintient la température de l'enceinte 1 à une valeur palier Tl jusqu'à la fin du séchage.The first drying step A breaks down into two phases, a first phase A1 during which the temperature of the treatment chamber containing the charm to be treated is gradually raised with a temperature rise rate of approximately 5 ° C / min, from ambient temperature to a temperature Tl, close to 100 ° C, followed by a phase A2 during which the temperature of enclosure 1 is maintained at a level Tl value up to at the end of drying.
Au cours de la seconde étape B, qui est facultative, mais qui, lorsqu'elle est réalisée, améliore grandement l'efficacité du procédé, on élève progressivement la température de l'enceinte avec une vitesse de montée en température voisine de la précédente, à partir de la température Tl jusqu'à une température Tg voisine de la température de transition vitreuse de l'essence de bois considéré, à savoir le charme dans le cas présent. On maintient la température Tg à cette valeur palier pendant le temps nécessaire pour que la totalité de la masse de bois traité atteigne la température de transition vitreuse Tg. On remarquera que le fait de prolonger la durée de ce palier ne se traduit par aucune conséquence néfaste en ce qui concerne le respect des qualités mécaniques du produit traité.During the second step B, which is optional, but which, when carried out, greatly improves the efficiency of the process, the temperature of the enclosure is gradually raised with a rate of temperature rise close to the previous one, from the temperature Tl to a temperature Tg close to the glass transition temperature of the species of wood considered, namely the charm in the present case. The temperature Tg is maintained at this plateau value for the time necessary for the entire mass of treated wood to reach the glass transition temperature Tg. It will be noted that prolonging the duration of this plateau does not have any harmful consequences. as regards the respect of the mechanical qualities of the treated product.
Au cours ' de la troisième étape C on élève progressivement, au cours d'une phase Cl, la température de l'enceinte avec une vitesse de montée en température voisine de la précédente, de la température de transition vitreuse Tg à la température de rétification Tr et l'on maintient pendant une seconde phase C2 la température du four à cette valeur palier, jusqu'à ce que la plupart des hémicelluloses soient décomposées .In 'the third step C is increased gradually, during a C stage, the enclosure of the temperature with a heating rate temperature close to the previous one, from the glass transition temperature Tg to the retification temperature Tr and the oven temperature is maintained for a second phase C2 at this plateau value, until most of the hemicelluloses are broken down.
On sait qu'une des difficultés de cette étape spécifique réside dans le fait que le maintien en température doit s'effectuer pendant un temps suffisamment long pour que 1 'hémicellulose soit décomposée dans sa quasi totalité, mais qu'il est impératif de ne pas dépasser ce temps sous peine de commencer à détruire du même coup la lignine et la cellulose, ce qui se traduirait alors par une chute des caractéristiques mécaniques du bois traité.We know that one of the difficulties of this specific step lies in the fact that the temperature maintenance must be carried out for a time long enough for the hemicellulose to be broken down almost entirely, but that it is imperative not to exceed this time on pain of starting to destroy lignin and cellulose at the same time, which would then result in a fall in the mechanical characteristics of the treated wood.
Cette première partie a permis de préparer le matériau de façon quasi parfaite à la seconde partie, à savoir l'imprégnation, qui va suivre, notamment en ouvrant les pores du bois, en conférant à celui-ci un caractère hydrophobe et en augmentant sa mouillabilité vis-à-vis du monomère.This first part made it possible to prepare the material almost perfectly for the second part, namely the impregnation, which will follow, in particular by opening the pores of the wood, giving it a hydrophobic character and increasing its wettability. vis-à-vis the monomer.
On met alors en oeuvre cette seconde partie du traitement, qui comprend elle-même deux étapes, à savoir une étape d'imprégnation avec un produit durcissable et notamment un monomère polymérisable, et une étape de durcissement, ou polymérisation, du produit dont on a imprégné le bois.This second part of the treatment is then carried out, which itself comprises two stages, namely a stage of impregnation with a hardenable product and in particular a polymerizable monomer, and a stage of hardening, or polymerization, of the product of which impregnated the wood.
Pour mettre en oeuvre la première étape on utilise un dispositif du type de celui représenté sur la figure 2, et qui est bien connu de l'état antérieur de la technique. Ce dispositif se compose essentiellement d'une enceinte 1, ou réacteur, qui comporte une conduite d'aspiration 3 reliée à une pompe à vide, non représentée sur le dessin, une conduite 5 d'injection du monomère dans l'enceinte 1, et une conduite 7 d'évacuation de celui-ci.To implement the first step, a device of the type shown in FIG. 2 is used, which is well known from the prior art. This device essentially consists of an enclosure 1, or reactor, which comprises a suction line 3 connected to a vacuum pump, not shown in the drawing, a line 5 injecting the monomer into the enclosure 1, and a pipe 7 for discharging the latter.
Le bois à traiter 2 est introduit dans l'enceinte 1 par une porte 8, puis on fait le vide dans celle-ci en aspirant l'air qu'elle contient par la conduite 3 de façon à vider autant que faire se peut les "cellules" du bois. On injecte ensuite le produit dont on veut imprégner le bois dans l'enceinte 1. On laisse en l'état pendant une durée d'environ une trentaine de minutes, en fonction de la viscosité du produit utilisé, puis on vide le réacteur 1 par la conduite 7.The wood to be treated 2 is introduced into the enclosure 1 by a door 8, then a vacuum is created therein by sucking in the air which it contains through the pipe 3 so as to empty as much as possible the " wood cells. The product with which the wood is to be impregnated is then injected into the enclosure 1. It is left in the state for a period of about thirty minutes, depending on the viscosity of the product used, then the reactor 1 is emptied by driving 7.
La demanderesse a établi que le traitement de rétification permettait d'améliorer l'imprégnation du bois, sans que, comme dans l'état antérieur de la technique, il soit nécessaire pour autant de mettre sous pression le produit contenu dans le réacteur 1.The Applicant has established that the crosslinking treatment makes it possible to improve the impregnation of the wood, without, as in the prior art, it being necessary to pressurize the product contained in reactor 1.
On a représenté sur la courbe de la figure 3 la variation du taux d'imprégnation du charme (en %) en fonction du temps de passage t dans le réacteur 1, pour du charme naturel (courbe a) et du charme ayant subi préalablement une rétification par un monomère qui est du GMA (courbe b), c'est-à-dire du méthacrylate de glycidyle. On constate que, dans les deux cas, l'imprégnation de glicidyle se stabilise après une durée d'environ trente minutes, et que le taux d'imprégnation du charme qui, à l'état naturel était de 50%, est passé à une valeur de 55% lorsqu'il était, préalablement à l'imprégnation, soumis à une rétification. La demanderesse a obtenu des résultats du même ordre avec des essences de bois et des monomères différents, et notamment pour du hêtre, du frêne, du peuplier et divers résineux.The curve of FIG. 3 shows the variation in the rate of impregnation of the charm (in%) as a function of the passage time t in the reactor 1, for natural charm (curve a) and for the charm having previously undergone a crosslinking with a monomer which is GMA (curve b), that is to say glycidyl methacrylate. It can be seen that, in both cases, the glicidyl impregnation stabilizes after a period of approximately thirty minutes, and that the charm impregnation rate which, in its natural state was 50%, has increased to 55% value when it was, prior to impregnation, subject to retification. The Applicant has obtained results of the same order with different species of wood and monomers, and in particular for beech, ash, poplar and various conifers.
On réalise ensuite l'étape de durcissement du produit. Si celui-ci est un monomère on peut soumettre le bois imprégné, en fonction de la nature du monomère utilisé, soit à l'action d'un rayonnement gamma soit à l'action de la chaleur afin de provoquer sa polymérisation. Le chauffage peut être réalisé notamment par des moyens classiques de convection ou encore par micro-ondes.The product hardening step is then carried out. If this is a monomer, the impregnated wood can be subjected, depending on the nature of the monomer. used, either by the action of gamma radiation or by the action of heat in order to cause its polymerization. The heating can be carried out in particular by conventional convection means or even by microwave.
En ce qui concerne la polymérisation par voie thermique, la demanderesse a constaté que le bois rétifié présentait un meilleur comportement que le bois naturel. En effet, en raison du traitement qu'il a subi, le bois rétifié n'émet plus de gaz ou de vapeur d'eau comme le bois naturel, émission qui est la cause d'une mauvais adhérence du polymèreWith regard to thermal polymerization, the Applicant has found that retified wood exhibited better behavior than natural wood. Indeed, because of the treatment it underwent, the retified wood no longer emits gas or water vapor like natural wood, emission which is the cause of poor adhesion of the polymer
On peut également réaliser l'imprégnation immédiatement après l'étape de rétification, de façon à bénéficier de la chaleur restante du bois en cours de refroidissement, pour assurer, par voie thermique la polymérisation du monomère ce qui permet à la fois d'optimiser le procédé et de réaliser un gain d 'énergie. La demanderesse a réalisé des tests afin de comparer la stabilité dimensionnelle du bois naturel imprégné à celle du même bois traité suivant l'invention, lorsqu'ils étaient disposés en atmosphère humide . Ces tests ont été réalisés dans une enceinte climatique dans laquelle ont a effectué une cinétique de reprise d'humidité. L'enceinte possédait une hygrométrie de 75% et une température de 25°C, suivant la norme NF 51-264. On a mesuré le gonflement en fonction du temps d'échantillons de bois constitués en l'espèce par le charme traité précédemment, respectivement à l'état naturel (courbe a), à l'état imprégné suivant l'état antérieur de la technique (courbe b), et à l'état imprégné après rétification (courbe c). Les résultats ont été consignés sur la figure 4.It is also possible to carry out the impregnation immediately after the crosslinking step, so as to benefit from the remaining heat of the wood being cooled, to thermally ensure the polymerization of the monomer which allows both to optimize the energy saving process. The Applicant has carried out tests in order to compare the dimensional stability of the impregnated natural wood with that of the same wood treated according to the invention, when they were placed in a humid atmosphere. These tests were carried out in a climatic chamber in which the kinetics of moisture uptake were carried out. The enclosure had a humidity of 75% and a temperature of 25 ° C, according to standard NF 51-264. The swelling was measured as a function of time of wood samples formed in this case by the previously treated horn, respectively in the natural state (curve a), in the impregnated state according to the prior state of the art ( curve b), and in the impregnated state after crosslinking (curve c). The results have been reported in Figure 4.
On constate sur cette figure que l'imprégnation n'a pas stabilisé dimensionnellement le bois à l'état naturel . En effet y a très peu de différence entre le bois naturel (ΔV voisin de 7%) et le bois naturel imprégné (ΔV voisin de 6,5%).It can be seen in this figure that the impregnation has not stabilized the wood dimensionally in its natural state. Indeed there is very little difference between natural wood (ΔV close to 7%) and natural impregnated wood (ΔV close to 6.5%).
On constate que le bois qui, préalablement à son imprégnation, a subi un traitement de rétification présente un gonflement ΔV très réduit puisqu'il est de 1 'ordre de 3%.It is found that the wood which, prior to its impregnation, has undergone a crosslinking treatment has very reduced swelling ΔV since it is of the order of 3%.
La demanderesse a bien entendu par ailleurs traité des échantillons de charme, d'une part à l'état naturel et d'autre part à l'état rétifié, à l'aide de monomères de natures diverses, à savoir du HEMA (méthacrylate de hydroxyéthyle) , du HEA (acrylate de 2- hydroxyéthyle) et du AGE-AM (mélange à 70% d'allyl glycidile éther et 30% d'anhydride maleique) et du GMA puis, après traitement, a soumis ces divers échantillons à un test de gonflement suivant la norme NF 51-264 précitée et a mesuré le gonflement de ces échantillons. Les résultats ont été portés dans le tableau I ci-après, dans lequel ils sont exprimés en pourcentage d'unités ASE, c'est-à-dire en pourcentage du coefficient de stabilisation dimensionnel conventionnel . TABLEAU IThe Applicant has of course also treated charm samples, on the one hand in the natural state and on the other hand in the crosslinked state, using monomers of various natures, namely HEMA (methacrylate of hydroxyethyl), HEA (2-hydroxyethyl acrylate) and AGE-AM (mixture of 70% allyl glycidile ether and 30% maleic anhydride) and GMA and then, after treatment, subjected these various samples to a swelling test according to the aforementioned standard NF 51-264 and measured the swelling of these samples. The results are given in Table I below, in which they are expressed as a percentage of ASE units, that is to say as a percentage of the conventional dimensional stabilization coefficient. TABLE I
On constate que les différents monomères utilisés sont plus ou moins efficaces quant à la stabilisation dimensionnelle en atmosphère humide du bois traité, mais que dans tous les cas cette stabilisation est supérieure à celle procurée suivant l'état antérieur de la technique, c'est-à-dire par une imprégnation sans rétification préalable.It can be seen that the various monomers used are more or less effective as regards the dimensional stabilization in a humid atmosphere of the treated wood, but that in all cases this stabilization is greater than that provided according to the prior art, ie by impregnation without prior retification.
Outre la stabilité dimensionnelle, la présente invention permet également d'augmenter la dureté du bois traité. In addition to dimensional stability, the present invention also makes it possible to increase the hardness of the treated wood.

Claims

REVENDICATIONS
1.- Procédé de traitement du bois du type dans lequel on dispose le bois à traiter dans une enceinte dans laquelle on crée un vide, où l'on remplit ladite enceinte d'un produit durcissable, notamment un monomère, de façon à imprégner le bois en faisant pénétrer le produit dans l'espace interfibres de celui- ci, où l'on provoque ensuite le durcissement dudit produit, notamment par polymérisation, caractérisé en ce que l'on fait précéder l'opération d'imprégnation du bois d'une étape de rétification.1.- A method of treating wood of the type in which the wood to be treated is placed in an enclosure in which a vacuum is created, in which said enclosure is filled with a hardenable product, in particular a monomer, so as to impregnate the wood by making the product penetrate into the fiber space thereof, where it then causes the hardening of said product, in particular by polymerization, characterized in that the operation of impregnating the wood is preceded a retification step.
2.- Procédé suivant la revendication 1 caractérisé en ce que ledit produit est un monomère que l'on durcit par polymérisation.2.- Method according to claim 1 characterized in that said product is a monomer which is hardened by polymerization.
3.- Procédé suivant la revendication 2 caractérisé en ce que le monomère appartient au groupe de monomères suivants GMA, HEMA, HEA, AGE-AM.3.- Method according to claim 2 characterized in that the monomer belongs to the group of following monomers GMA, HEMA, HEA, AGE-AM.
4.- Procédé suivant l'une des revendications précédentes caractérisé en ce que le procédé de rétification comprend une étape de transition vitreuse.4.- Method according to one of the preceding claims characterized in that the crosslinking process comprises a glass transition step.
5.- Procédé suivant l'une des revendications 2 à5.- Method according to one of claims 2 to
4, caractérisé en ce que l'on réalise l'imprégnation immédiatement après l'étape de rétification, de façon à utiliser la chaleur restante du bois en cours de refroidissement pour assurer, par voie thermique, la polymérisation du monomère.4, characterized in that the impregnation is carried out immediately after the crosslinking step, so as to use the remaining heat of the wood during cooling to thermally ensure the polymerization of the monomer.
6.- Procédé suivant l'une des revendications précédentes, caractérisé en ce que l'imprégnation du bois à traiter par ledit produit s'effectue dans une enceinte de traitement dont la pression interne est voisine de la pression atmosphérique. 6.- Method according to one of the preceding claims, characterized in that the impregnation of the wood to be treated with said product is carried out in a treatment chamber whose internal pressure is close to atmospheric pressure.
EP97912273A 1996-10-29 1997-10-28 Method for treating wood by impregnation Expired - Lifetime EP0936961B1 (en)

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FR9613168 1996-10-29
FR9613168A FR2755054B1 (en) 1996-10-29 1996-10-29 IMPREGNATION TREATMENT OF WOOD
PCT/FR1997/001933 WO1998018606A1 (en) 1996-10-29 1997-10-28 Method for treating wood by impregnation

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NZ523249A (en) 2002-12-16 2005-04-29 Mattersmiths Holdings Ltd Method of delivering compositions to substrates
WO2005042175A1 (en) * 2003-10-28 2005-05-12 The Research Foundation At State University Of Newyork Treating wood with reactive monomers
FR2871181B1 (en) 2004-06-02 2006-09-08 Epmb H Soc Par Actions Simplif MODULAR CONSTRUCTION SYSTEM
EP1912769B1 (en) * 2005-08-05 2011-07-20 3M Innovative Properties Company Wood treatment
WO2018090064A1 (en) * 2016-11-11 2018-05-17 Rhino Modified Wood (Pty) Ltd Lamination process
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KR102128403B1 (en) * 2019-09-27 2020-06-30 한국원자력연구원 Wood having hydrophobically modified surface

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CA2269904C (en) 2005-03-29
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US6248402B1 (en) 2001-06-19
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ES2162674T3 (en) 2002-01-01
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CA2269904A1 (en) 1998-05-07
FR2755054B1 (en) 1999-01-15

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