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)

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• 1996
  • 1996-10-29 FR FR9613168A patent/FR2755054B1/fr not_active Expired - Fee Related
• 1997
  • 1997-10-28 EP EP97912273A patent/EP0936961B1/de not_active Expired - Lifetime
  • 1997-10-28 US US09/297,277 patent/US6248402B1/en not_active Expired - Fee Related
  • 1997-10-28 WO PCT/FR1997/001933 patent/WO1998018606A1/fr not_active Ceased
  • 1997-10-28 DE DE69706553T patent/DE69706553T2/de not_active Expired - Fee Related
  • 1997-10-28 CA CA002269904A patent/CA2269904C/fr not_active Expired - Fee Related
  • 1997-10-28 ES ES97912273T patent/ES2162674T3/es not_active Expired - Lifetime
  • 1997-10-28 AT AT97912273T patent/ATE205127T1/de not_active IP Right Cessation
  • 1997-10-28 DK DK97912273T patent/DK0936961T3/da active
  • 1997-10-28 JP JP52012898A patent/JP3916258B2/ja not_active Expired - Fee Related
  • 1997-10-28 PT PT97912273T patent/PT936961E/pt unknown

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