FR2995550A1 - Method for stabilization of wood substrate utilized for e.g. flap, with respect to moisture, involves withdrawing wood substrate from aqueous solution, and treating substrate at temperature ranging between specific degrees - Google Patents

Abstract

A method of stabilizing wood with respect to moisture, characterized in that firstly, the substrate comprising wood is brought into contact with an aqueous treatment solution at a temperature of between 50 ° C and 150 ° C, containing at least 5% by weight, advantageously containing at least 30% by weight of a compound or a mixture of compounds of the family of aliphatic dicarboxylic acids of formula (I): HOOC- (CH) -COOH (I) in which "n" is an integer between 6 and 10. In a second step, said substrate comprising wood is removed from the aqueous treatment solution and drained, then finally heat-treated to be roasted at a temperature of between 100 ° C. C and 200 ° C.

Description

The invention relates to a method of stabilizing a modified impregnated substrate provided with specific properties, in particular physical properties, chemical properties, and a process for the stabilization by roasting of a material comprising wood associated with a dicarboxylic acid. , biological that the material substrate comprising wood, for example the wooden substrate, does not naturally possess.

In the present description, generally means "material or substrate comprising wood", a material comprising a majority proportion of wood. By "majority proportion" is generally meant that the material comprises at least 50% by weight of wood. Preferably, this material is made entirely of wood. Similarly, in the description, the term "wood" is generally understood to mean not only solid wood, but also material comprising wood, such as composite materials based on particles or wood fibers.

This process applies, in particular, to the treatment of wood, with a view to conferring on it the physical and / or chemical properties desired, in particular in order to preserve it, to preserve it, to improve its resistance and to protect it against different types of chemical, biological and / or physical aggressions induced by moisture. In other words, the method of the invention aims to obtain a material comprising wood, for example wood, having a better resistance to external conditions and, in particular, better intrinsic stability vis-à-vis environmental humidity, which causes the material comprising wood, for example wood, to expand less, if not at all, to absorb moisture, or undergo less shrinkage during drying, and better resistance against attacks by xylophagous living organisms capable of degrading the material comprising wood, such as wood, for example fungi, insects and bacteria, while limiting both the retention of water in the wood and decreasing its hydrophilic character. - 2 - Thus, in the field of wood preservation, coatings consisting of resins, stains, oils and varnishes are generally used, often polyurethane coatings [1] [2] [3]. The use of the aforementioned products is limited to a simple surface treatment, very superficial, the penetration into a substrate such as wood is very low, namely generally less than 1 mm. Due to the large size of these molecules and their hydrophobic character, there is no penetration, for example polyurethane, in the intimacy of the nanostructure of the cell walls of the wood. To satisfy the ten-year guarantee imposed by the building industry, it is necessary to resort to wooden impregnation processes, in its volume, with preservatives such as copper-chromium-arsenic (CCA) salts, creosotes and organochlorine compounds or other toxic substances which, unfortunately, all present disadvantages in terms of public health and respect for the environment. In the industrial field, mention is also made of the method of roasting or pyrolysis of wood under a neutral atmosphere to stabilize the wood [4]. This technique involves subjecting the wood to heat treatment under controlled conditions to cause heat condensation reactions at the hemicellulose level of the wood. This roasting operation is usually carried out under a neutral or reducing atmosphere, in the presence of water vapor or not, generally on previously dried wood, by subjecting it to a temperature of between 170.degree. C. and 250.degree. long enough for the entire mass of treated wood to reach the treatment temperature. The operating conditions are highly dependent on the amount and geometry of the wood elements to be treated in an oven; the slightest difference in temperature and / or treatment time strongly jeopardizes the homogeneity of the batch of treated wood thus obtained. In addition, the physical integrity of the wood is not preserved. In fact, hemicellulose is partially or completely destroyed during treatment irreversibly. The mechanical properties of the wood are degraded during the treatment, in particular its limit to the rupture and because of this, the wood becomes more brittle and more fragile. In addition, during the heat treatment, the wood releases gaseous or liquid products based on toxic heavy aromatics. It is mentioned in the literature the oleothermic treatment processes that use oils [5-6]. These methods involve immersing the wood in oil mixtures between 150 ° C and 210 ° C. This technique makes it possible to fill the pores of the wood with highly hydrophobic fatty substances, but nevertheless incapable of diffusing within the cell walls. The wood therefore remains always sensitive to moisture. Several processes that involve both impregnation and chemical grafting techniques are commonly described in the literature. These methods generally comprise an impregnation step and a chemical grafting step. During the impregnation stage, the wood is impregnated with a substance reactive with the hydroxyl functions (-OH). These hydroxyl functions are naturally present in the constituent components of wood: cellulose, hemicellulose and lignin. The reactive impregnating substances are preferably chosen from anhydrides, formaldehyde, epoxides and isocyanates. All these reactive substances are toxic and must be associated with a wood swelling agent, usually a solvent, also toxic. Among other examples, mention may be made of the invention [7] which associates anhydride with fatty acids to create mixed anhydrides. During the chemical grafting step, the impregnating substance present in the wood reacts, optionally in the presence of a catalyst, with the constituent polymers of the wood by heating the substrate at least between 130 ° C. and 140 ° C. However, the main limitation of these grafting processes is that they are heavy to implement because they use reactive systems / harmful solvents or toxic. In addition, the massive impregnation of wood from anhydrides, or any other toxic reactive substances, will require expensive cleaning and / or neutralization operations to remove excess free reagents in the wood structure. at the end of the treatment. It is also possible to perform a stabilization treatment by inflating the wood without the chemical grafting of wood. The processes described in patents [8-9] propose the use of treatment solutions consisting of dicarboxylic fatty acids, azelaic acid and dodecanedioic acid, respectively. As stated in these documents, some formulations of this family have the property of being able to penetrate, under certain conditions, within the cell wall of wood to keep it inflated, even after drying. These dicarboxylic acid molecules, of general formula HOOC- (C142) n-COOH where "n" is an integer, are chosen to allow partial solubility of the dicarboxylic acid in water. The effectiveness of the treatment in terms of resistance to leaching of the fatty acid by water and in terms of limiting the return of water from the wood when immersed in water, will depend directly on the size molecular of said dicarboxylic acid considered, that is to say, the whole number "n" considered. For "n" less than 6, the carboxylic fatty acids are generally too soluble in liquid water to have sufficient resistance to water leaching of the wood. Whereas for "n" greater than 10, the dicarboxylic acids are too hydrophobic. The method described proposes the use of hydrophobic diacids with "n" between 6 and 10 capable of diffusing into the cell wall. However, wood treated with this process is not sufficiently resistant to moisture to prevent a significant water uptake of the wood if it is in contact with a source of moisture over long periods of time. 24 hours. Therefore, it is possible to conclude that the proposed treatment based on a simple impregnation of dicarboxylic acids alone, without associating a heat treatment, is incomplete to allow a durable dimensional stabilization of the wood with a low power of water retention. There is thus a need not yet satisfied for a process which allows a treatment of all the wood, both at the heart of it, and at the surface, making it possible to use resins commercially available, a low cost and zero or very low toxicity, without organic solvent. It must also include a limited number of simple steps thus inducing a limited cost and time of the process. Finally, the process must not affect the other properties of the substrate comprising wood, such as wood.

The object of the invention is to provide a method for stabilizing a substrate made of a material comprising wood, such as a wooden substrate that satisfies, among other things, all the needs mentioned above.

This and other objects are achieved according to the invention by a roasting process of a substrate comprising wood associated with a dicarboxylic acid. The process consists of two successive steps. Firstly, the substrate comprising wood is contacted with an aqueous treatment solution between 50 ° C. and 150 ° C. containing at least 5% by weight, advantageously containing at least 30% by weight of a compound or of a mixture of compounds of the family of aliphatic dicarboxylic acids of formula (I): HOOC- (CH2), - COOH, in which "n" is an integer between 6 and 10. In a second step, said substrate comprising wood is removed from the aqueous treatment solution and drained, then finally heat treated to be roasted at a temperature between 100 ° C and 200 ° C. Advantageously, the dicarboxylic acid chosen is azelaic acid HOOC- (C112), -COOH (n = 7). Advantageously, the contacting temperature between the material comprising wood and the aqueous treatment solution is chosen between 70.degree. C. and 110.degree. C., in order to avoid an overpressure of said aqueous treatment solution above the point of contact. boiling water and therefore avoid the purchase of expensive equipment. Advantageously, the weight gain of the wood in dicarboxylic acid, after the impregnation, must be between 20 and 70%; a plug of mass close to 30-40% of diacid is preferably chosen. Advantageously, the contacting between the substrate comprising wood and the aqueous solution of treatment based on dicarboxylic acid is carried out by a simple immersion of said substrate comprising wood in the aqueous solution. Advantageously to improve the kinetics of impregnation on a dry wood, it is also possible to use a "vacuum-pressure" technique to promote the impregnation of the wood-containing substrate with the aqueous solution of diacid-based treatment carboxylic acid. This "vacuum-pressure" technique consists in arranging the substrate comprising wood to be impregnated in a vacuum chamber, for example in a chamber under a vacuum of 10 to 100 mbar, in order to degas the substrate comprising wood; and then immersing the wooden substrate in the aqueous treatment solution. To force the liquid bath to penetrate the porosity of the wood, and thus reduce the duration of the treatment, the liquid bath is pressurized and heated. A gas overpressure is thus established on the treatment bath, for example a pressure of between 5 and 10 bar. Advantageously, the contacting time between the substrate comprising wood and the aqueous treatment solution is between 1 and 72 hours, preferably chosen between 12 and 48 hours. This time will be chosen according to the geometry of the substrate comprising wood, according to the species of wood considered, and according to the impregnation method retained. Advantageously, the temperature of the roasting heat treatment is preferably between 110 ° C. and 160 ° C. Heat treatment above 200 ° C can significantly alter the wood by promoting pyrolysis reactions of hemicellulose. Advantageously, the duration of the heat treatment is between 6 and 72 hours, preferably the duration of said heat treatment is between 12 and 48 hours. The gaseous environment established around the material comprising wood during the heat treatment is selected depleted in oxygen, preferably an inert atmosphere such as water vapor to limit the oxidation phenomena of the wood from 100 ° C. . The method according to the invention is generally compatible with the various finishing operations of wood used by the industry: sanding, varnishing, sawing, painting, gluing, densification / curing by polymerization of resin in situ in the wood, coloring in the volume by pigments.

The process according to the invention is of great simplicity, and it uses only non-toxic products that can be prepared from compounds of a low cost and already commercially available; in fact, it is a simple impregnation process associated with a heat treatment which uses highly specific molecules and which does not have the disadvantages of the impregnation processes of the prior art using other substances. It has surprisingly been found that the dicarboxylic acid compounds of the present invention are not only able to penetrate the cell wall of wood (which was already known in the literature), but also to react favorably and quickly with the cell wall components from 100 ° C using additional heat treatment. The state of our knowledge does not make it possible to know if this phenomenon is due to a grafting of the diacid by esterification on the hydroxyl functions of the wood or to a pyrolysis of hemicellulose / cellulose. Nevertheless, the inventors have surprisingly found that the roasting reactions associating the wood with the dicarboxylic acid according to the invention are accelerated and obtained with temperatures lower than those proposed in the state of the prior art for roasting treatments. The multiple advantages and surprising effects of the invention can therefore be enumerated as follows, without this enumeration being considered as limiting: the method according to the invention does not damage the material comprising wood, such as a substrate in wood, and in particular the mechanical properties are not degraded. The resin used according to the invention is not very sensitive to leaching by water, in particular by rainwater in external conditions. - Excellent stabilization of the substrate in a material comprising wood, such as the wood substrate, vis-à-vis moisture. This stabilization can be expressed by the parameter called ASE ("Anti Shrinkage Efficiency"). The ASE is defined by the following equation: ASE (%) = 100 X (untreated wood - treated wood) aborted untreated with the following definition of S: / Volume wood - dry volume dry) treated or unworked (%) = 100 X (Wet Dry Wet Can also be defined as a particular ASE in which reference is made not to the volume of the wood sample, but to one of the dimensions of the wood, for example in the case of wood, it may be Length (L), width (1) or thickness (e) The partial ASE coefficient ASEp for the width can therefore be expressed by the definition: ASEp (%) = 100 X (Spbois untreated - Spbois treated) / Spbois untreated with the following definition of Sp: Spbois treated or not (%) = 100X (Wetbeam wet-widthboissec, 1 / widthbois sec The wood is dried in oven at 90 ° C for 24 hours and the wood is moistened by immersion in water at 20 ° C for 24 hours for low mass geometries of the order of cm3.

According to the invention, the ASE is well above 50%, even after several humidification / drying cycles. The compounds used according to the invention are little, or even not harmful, and are therefore easy to use in an industrial process. The cost and the duration of the process allow its easy use in the industry. The process of the invention which may be described as an impregnating treatment does not necessarily require reagents, catalysts, solvents, various highly harmful or dangerous adjuvants of the anhydride, isocyanate or tetrahydrofuran (THF) type. , dichloromethane, pyridine, dilethylformamide (DMF), triethylamine, acetone, ethanol, ... whether for grafting the wood, for transporting the compound used in the structure of the substrate comprising wood, such as the wood, or to clean the substrate of any non-substrate-fixed treatment residues including wood, such as wood. The method of the invention makes it possible to treat a substrate comprising wood, such as wood, in depth, in its volume, and is not limited only to its surface. -While the impregnation of wet wood takes more time, it is possible to treat a substrate comprising wood such as wood, in the dry state or in the wet state. -It is also possible to use techniques and facilities already tested for their implementation. It does not require any adaptation or significant modification of existing installations. In other words, one can use many processes and industrial facilities already in use to impregnate the wood such as for example the "vacuum-pressure" technique. - After the heat treatment, the wood surface is clean. In particular, the surface is not polluted by tarry exudates (fillural, phenols, ...). It is not useful to perform deep cleaning of the substrate in a material comprising wood such as wood after the impregnation treatment. The dicarboxylic acid can be made from plant derivatives. Thus formulated, the treatment solution used according to the invention responds favorably to the criteria of sustainable development. Thus, the method according to the invention is particularly intended for woods kept outside, being part, for example, cladding, shutters, windows, doors, floors, gates, stakes, signs, poles, garden furniture, pots , barrels, furniture of urban spaces and other elements of exterior carpentry, etc. The method according to the invention also finds applications in the building, where the wood is part of the frames, of interior furniture in contact with the water (by examples of bathroom or kitchen furniture), stairs, floors, etc. - 10 - The method according to the invention can be applied to wooden structures such as bridges, bridges, various load-bearing structures and also to wooden objects used in maritime activities.

The invention will now be described with reference to several examples, given by way of illustration and not limitation. Example 1 We use samples of beech, a wood species known to be easily impregnable. The dimensions of the samples are approximately: L 30 mm x 74 mm x 4 mm. The wood fibers are parallel to the length L. Initially, a beaker containing the solution of azelaic acid at 110 ° C previously dissolved in water at different concentrations is available. After two hours, the samples are removed from the beaker and wiped off their excess azelaic acid on the surface and cooled to room temperature.

In a second step, the samples were subjected to a heat treatment at 110 ° C. in a crystallizer sealed with a watch glass which rests on the crystallizer. In order to evaluate the effectiveness of the treatment in terms of dimensional stability of the wood with regard to humidity, we calculate the value of the "Anti Shrinkage Efficiency" or "ASE" coefficient calculated from the width of the sample, that is the most unstable dimension of the sample. The wood samples were subjected, after treatment according to the invention, to five humidification / drying cycles by measuring the width of the sample at the vernier caliper at dryness and in the wet state at each cycle. The humidification consists in completely immersing the treated sample for 48 hours at 20 ° C in pure water for cycles 1 to 4, 96h for cycle 5. The drying consists of drying the wood for 48 hours at 20 ° C outdoors. The water recovery of the treated wood samples according to the invention could be evaluated by successively measuring the mass of the samples after drying and after wetting.

The results measured for the 3 samples A, B and C are shown in the following table at the end of the 5 humidification / drying cycles: Samples A B C. Impregnation 30% Impregnation 50% Impregnation 40% .1. phase: mass. Ac. Azel. Mass. Ac. Azel. Mass. Ac. Azel. Wood impregnation by ac. azelaic. Duration: 2h Duration: 2h Temp .: 110 ° C Duration: 2h Temp. : 110 ° C Temp. : 110 ° C 2nd phase: Treatment 110 ° C Treatment 110 ° C Treatment 110 ° C Treatment with moist air, thermal air thermal air thermal. 24h wet, 48h wet, 24h Cycle 1 ASE P = 73% WPG = + 22% ASEP = 88% WPG = + 15% ASEP = 85% WPG = + 11% Humid./sec. Cycle 2 Humid./sec. ASE P = 64% WPG = + 34% ASEP = 90% WPG = + 17% ASEP = 87% WPG = + 16% Cycle 3 Humid./sec. ASE P = 64% WPG = + 28% ASEP = 89% WPG = + 14% ASEP = 87% WPG = + 21% Cycle 4 Humid./sec. ASE P = 57% WPG = + 35% ASEp = 89% WPG = + 16% ASEP = 87% WPG = + 15% Cycle 5 Humid./sec. ASE P = 58% WPG = + 29% ASEP = 88% WPG = + 28% ASEP = 88% WPG = + 25% Asgp: Anti-Shrinkage Eveluation »particular (%) WPG: Moisture mass uptake: water mass / dry mass (%) The results table shows that the stabilization (ASEp) of sample A is lower compared to the stabilization of samples B and C. For the latter two, ASEp well over 80% were obtained even after five cycles of wood leaching by water. The comparison of moisture recoveries during humidification cycles shows that the treatment slowed down the water uptake (less than 20% water uptake for B and C), but did not prevent it. For cycle 5, for which the duration of humidification was greater, the three samples have an equivalent humidity recovery, of the order of 25-30%.

EXAMPLE 2 In this example, two samples "D" and "E" of beech are stabilized. The dimensions of the sample are approximately: L 30 mm x 74 mm x 4 mm. The wood fibers are parallel to the L dimension. Initially, a beaker is available containing the azelaic acid solution previously dissolved in 40% water at 110 ° C. After two hours the samples "D" and "E" are removed from the beaker and wiped off their excess azelaic acid surface and cooled to room temperature. In a second step, the "D" sample underwent a roasting treatment in a crystallizer at 110 ° C. for 10 h in the open air, while the "E" sample underwent a roasting treatment of 48 h at room temperature. 110 ° C in the open air. In order to evaluate the effectiveness of the treatment in terms of dimensional stability of the wood with respect to moisture, we calculate the value of the particular "Anti Shrinkage Efficiency" or "ASE" coefficient calculated from the width of the sample, that is the most unstable dimension. We subjected the two wood samples, after treatment according to the invention, to a humidification / drying cycle by measuring the width and the mass of the sample in dry state and in the wet state. Humidification consists of completely immersing the treated sample for 48 hours at 20 ° C in pure water, drying is drying the wood for 48 hours at 20 ° C in the open air.

At the end of this humification / drying cycle, we noted a moisture uptake WPg and a dimensional stability measured by the coefficient ASEp. The results are shown in the following table: ASEp (%) WPg (%) Sample D 51 22 Sample E 76 32 The comparison between the two samples shows that a minimum duration of roasting heat treatment is required to ensure optimum treatment. The 35 E sample is better stabilized than the D sample. The moisture recoveries are of the same order of magnitude, the duration of the heat treatment has little effect on the latter parameter. REFERENCES [1] Goland V.A., Khinskaya O.V., Mikhailova I.A., Porcedure for treating and preserving wood to harden surface coating, including coating surface of wood with impregnating base-on-polymer composition, GB-A-62100288. [2] Matsushita Electric Works, Ltd., Preparation of inorganic board having finished surface by laying of urethane resin and binder, thenshaped and cold pressing, JP 59088383, 1984, Japan. [3] Park S.B., Development of Surface Improvement Technique of Japanese Larch Flooring, Journal of the Korean Wood Science and Technology, 1999, 27 (3), 31-38. [4] Weiland J.J. Thesis "Physico-chemical study of the thermal treatment of wood: optimization of parameters of the process of rectification", January 26, 2000, pp. 49-47. [5] Henri Baillères, Daniel Grenier et al. CTBA INFO N ° 101 - July / August 2003, pp 25-28. [6] Olivier Vitrac, Jean Meot, et al. Method and apparatus for treating wood or similar materials Patent FR 99/14672. [7] Magne M., El Kasmi S., Dupire M. et al. Process for the treatment of lignocellulosic materials, in particular wood, and a material obtained by this process Patent FR 0204448. [8] Chaumat G., Albino C. A method of protecting wood against moisture that is effective over a long period of time. Patent FR 07/05182. [9] Ito T., Wood material improvement dimension stabilized impregnat aliphatic saturate di carboxylic acid solution. Patent JP 8336812. 35

Claims (10)

REVENDICATIONS1. A method characterized in that, in a first step, the wood-containing substrate is contacted with an aqueous treatment solution at a temperature of between 50 ° C and 150 ° C, containing at least 5% by weight, preferably containing at least 30 % by weight of a compound or a mixture of compounds of the family of aliphatic dicarboxylic acids of formula (I): HOOC- (CH2) n -COOH (I) in which "n" is an integer between 6 and 10. In a second step, said substrate comprising wood is removed from the aqueous treatment solution and drained, then finally heat-treated to be roasted at a temperature between 100 ° C and 200 ° C. 2. Method according to the preceding claims wherein the dicarboxylic acid chosen is azelaic acid of formula HOOC- (CH2) 7-COOE (n = 7). 3. The method of claim 1 and 2, wherein the contacting temperature of the substrate comprising wood and the aqueous treatment solution is preferably between 70 ° C and 110 ° C. The method of claims 1 to 3, wherein contacting the wood-comprising substrate with the aqueous dicarboxylic acid-based treatment solution is accomplished by simply immersing said wood-containing substrate in said aqueous solution. 5. Method according to claims 1 to 3, wherein the contacting of the substrate comprising dry wood and the aqueous treatment solution is preferably performed by a "vacuum-pressure" technique with a vacuum of 10 to 100 mbar and pressurizing between 5 and 10 bar. 6. A method according to any one of claims 1 to 5, wherein the contact time between the substrate comprising wood and the aqueous treatment solution is between 1 and 72 hours, preferably selected between 12 and 48 hours. . 7. A process according to any one of the preceding claims, wherein the temperature of the roasting heat treatment is preferably between 110 ° C and 160 ° C. 8. A process according to any one of the preceding claims, wherein the duration of the roasting heat treatment is between 6 and 72 hours, preferably the duration of said heat treatment is between 12 and 48 hours. 9. A process according to any one of the preceding claims, wherein the gaseous environment established around the material comprising wood during heat treatment is selected from a low oxygen environment. 10. A process according to any one of the preceding claims, wherein the treatment according to the invention is combined with wood finishing treatments such as sanding, varnishing, sawing, painting, gluing, densification / curing by resin polymerization. located in the wood, coloring in the volume by pigments. 30 35