FR2863539A1 - Treating porous wood, e.g. for restoring and/or conserving old wood, comprises polycondensation of diglycidyl and diamine monomers in situ - Google Patents

Abstract

Treating porous wood comprises immersing wood in a solution containing a diglycidyl monomer and a diamine monomer in a volatile organic solvent until at least 60% of the accessible pore volume of the wood is filled with solution, removing and draining and/or wiping the wood, heating the wood to initiate polycondensation of the monomers, and evaporating the solvent. An independent claim is also included for a piece of wood-resin composite material produced as above.

Description

2863539 1

  Process of wood treatment with open porosity by in situ polycondensation of epoxy-amine resins Historically, hardwood species such as oak, ebony, boxwood and rosewood, are highly sought after by artisans and industrialists for their excellent mechanical properties, especially their high impact resistance, their ability to withstand high loads, their low deformation over time or their excellent acoustic properties. However, these hardwood species tend to grow slowly and it is therefore difficult to meet the demand of wood processing industries and artisans.

  Some species have even become so rare that it has been necessary to protect them and limit their slaughter. For example, ebony, an exotic wood that has been used for centuries in the manufacture of furniture, decorative objects and musical instruments, is now threatened with a ban on slaughter and export and may not more be available on the market in the near future.

  There is therefore the particular problem of replacing this precious species with other unprotected species, and more generally the problem of improving the mechanical properties of soft and / or porous fast-growing woods in order to be able to substitute them for relatively slow growing hardwood species.

  The Applicant, in the context of his research aimed at finding a solution for replacing ebony in the manufacture of wind instruments, has discovered that it is possible, thanks to a relatively simple method of in situ polycondensation, to treat wood species having a structure with open porosity so as to significantly improve their mechanical properties and dramatically expand the application possibilities of these woods.

  International application WO 01/53050 discloses a process for treating wood by polymerization and in situ crosslinking of vinyl monomers. This process comprises the radical polymerization, initiated by at least three different initiators, of a monofunctional vinyl monomer mixture in the presence of divinyl crosslinking agents and at least one oil or wax, the latter acting as moderator of the polymerization and water-repellent agent of the finished product. Such a wood treatment method, particularly when applied to the manufacture of musical instruments, however, has a significant drawback namely the presence of residual monomers malodorous and presenting a certain risk to health. This problem of the residual monomers has been solved in the present invention by the choice of a polymerization method different from the radical polymerization, namely the polycondensation. In a mixture of polycondensable monomers, each monomer is in principle capable, without being activated, of reacting with all or a large fraction of the comonomers present, which is not the case for a radical polymerization in which the monomers can not react. and be incorporated in the macromolecular chain only when they come into contact with the active center (radical or ionic) of a growing polymer chain. However, these active centers are relatively few in relation to the number of monomers and generally unstable so that at the end of the polymerization, the proportion of unreacted monomers remains high. In the case of polycondensation, on the other hand, the probability of a monomer reacting with one or more other monomers is very high and the unreacted monomer fraction quickly becomes negligible.

  It is therefore an object of the present invention to provide an open porosity wood treatment method by in situ polycondensation comprising: (a) immersing an open-porous wood member in a solution containing, in a volatile organic solvent, at least one first reagent comprising at least two glycidyl functions and at least one second reagent comprising at least two -NH functional groups of primary amine or secondary amine, the average functionality of all the reagents being strictly greater than 2, while sufficient time to allow the solution to fill at least 60% of the accessible pore volume of the wood, and at a temperature sufficiently low to prevent the premature polymerization of the monomers during this impregnation step (a), (b) removal of the impregnated part by the organic solution and the dripping and / or wiping of the wooden part, (c) the heat treatment of the im wooden part. at a temperature and for a time sufficient to allow the exothermic polycondensation reaction between the first and second reagents to self-sustain through the released reaction heat, and optionally, (d) drying of the workpiece, preferably under reduced pressure for a time sufficient to allow evaporation of the organic solvent.

  The invention further relates to a piece made of a wood / epoxy-amine resin composite material that can be manufactured according to the above treatment method. This piece may be in particular a wind instrument body, in particular a clarinet body.

  The invention finally relates to the use of such a part for the manufacture of all or part of wind instruments such as clarinets, for marquetry, for cabinet making, for the construction of buildings and in particular for structures.

  The porous wood treatment method of the present invention greatly improves the mechanical properties of treated woods.

  These have a significantly higher Young's modulus than untreated wood and reduced brittleness and are highly resistant to cracking over time.

  Furthermore, the method of the invention has the advantage of not changing the dimensions of the piece of wood. The Applicant has indeed found that the dimensions of the treated parts remain unchanged at least up to a weight ratio polymer / wood equal to 0.5. This high dimensional stability thus makes it possible to process parts with definitive dimensions.

  It is also possible to machine the treated parts according to the method of the present invention. Thus, in a preferred embodiment of the invention, namely the manufacture of wind instruments, blanks having the shape of a hollow cylinder can be treated, and the perforations can be made subsequently.

  The treated woods according to the invention also have a very low tendency to absorb moisture from the air or water coming into contact with the treated part.

  The process of the present invention can be carried out only with a wood having open porosity, i.e. having a pore system that communicates with each other. It is easy to understand that this communication between the pores is essential for the penetration of the organic solution containing the reagents inside the wood. More specifically, in the present invention, open-porosity wood is understood to mean a wood capable of absorbing, at 5 ° C., under normal pressure conditions and for a duration of immersion of 30 days, at least 15% by weight of 1 -methoxy-2-propanol (reference solvent).

  Therefore, any wood having an open porosity sufficient to allow diffusion of the solution containing the polymerizable reagents inside the porous structure can be used for carrying out the process of the present invention in principle.

  Examples of such wood include linden, spruce, monpani, poplar and wenge (Milleltia laurentil), also called 2863539 5 rosewood Congo. The latter is a relatively hard exotic wood, close to ebony, which is characterized by rapid growth and is therefore an interesting candidate for the replacement of it. Its main drawback lies in its high porosity, a defect to which the present invention proposes to remedy.

  In the first step of the process of the invention, the piece of wood to be treated is imbibed by immersion in a solution containing the polymerizable reagents in a relatively volatile organic solvent. This solvent preferably has a melting point of less than or equal to -30 ° C. and a boiling point of less than or equal to 250 ° C., and more particularly less than or equal to 150 ° C. The volatility of the organic solvent is indeed important to allow easy drying of the part once the polycondensation reaction is complete. The volatile organic solvent is preferably selected from hydrocarbon compounds having a C 1 -C 8 backbone and having at least one polar group selected from the secondary alcohol, ether and ester functions.

  Another preferred group of solvents for carrying out the present invention is vegetable oils, some of which are already used for the treatment of wood. The vegetable oil used must have a low viscosity at low temperature to be able to penetrate with reasonable speed into the porous wood system at temperatures that do not prematurely trigger spontaneous polymerization of the system.

  Those skilled in the art will of course choose to choose the organic solvent (s) so that they do not interfere with the polycondensation reaction of the polymerizable reagents, and particular care must be taken not to use hydrogen compounds. such as primary alcohols, phenols and thiols which may react with the glycidyl functions of the first reagent.

  Examples of preferred organic solvents are ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, glycerol 1,3-diacetate, triacetin and 1-methoxy-2-propanol mentioned above. above, the latter being particularly preferred.

  Examples of vegetable oils include flaxseed oil, castor oil, sunflower oil, soybean oil, walnut oil, grape seed oil, and the like. . Flaxseed oil is particularly preferred.

  The impregnation of the wood must be done for a sufficient time to allow the filling by the solution of at least 60% of the accessible pore volume of the wood. The total accessible pore volume of a given wood can be easily determined by allowing the impregnation to continue until the weight of a sample no longer increases with the impregnation time. The accessible pore volume of the sample is equal to the quotient of the difference in weight between the impregnated and non-impregnated sample on the density of the impregnating solution. This accessible pore volume can of course be related to a volume unit of the wood to be treated.

  The polycondensation reaction used in the process of the present invention is a reaction between a first reagent comprising at least two glycidyl groups (epoxide) and a second reagent comprising at least two -NH functions of primary amine or secondary amine, capable of to react with the glycidyl groups of the first reagent. It is well known in the field of polycondensation that, when using only difunctional reagents, that is to say reagents having exactly two reactive functions (epoxides or NH), the macromolecular system obtained will be composed solely of chains. linear but will not form a cross-linked three-dimensional network as referred to in the present invention. It is therefore essential to use a certain fraction of reagents comprising more than two reactive functions (epoxide or -NH). The proportion of polyfunctional molecules is generally expressed thanks to the average functionality of the reagent system, that is to say the average number of reactive functions per molecule, which must be strictly greater than 2 to obtain a system. three-dimensional reticulated. It should be noted in this connection that in the polycondensation system used in the present invention, the functionality of a primary or secondary amine is not equal to the number of amine functions but to the number of NH functions. A primary monoamine having a single -NH 2 function can react twice with an epoxy function and thus has a functionality equal to 2. Similarly, a primary diamine has a functionality of 4.

  One parameter that makes it possible to express the degree of crosslinking of the epoxy-amine resin polymer system is the crosslinking density, namely the number of moles of crosslinking points per unit mass of the network. The theoretical crosslinking density, i.e. the maximum crosslinking density corresponding to the maximum degree of polymerization of the system, can easily be calculated from theoretical equations using the functionality and molecular weight of the different reactants. Such equations valid for stoichiometric or non-stoichiometric systems have been proposed (see for example the article by Jean Louis Halary et al in Polymery 1997, 42, No. 2, pages 86-95). In a highly reactive polycondensation system such as that of the epoxy-amine resins used in the present invention, it can be assumed that the actual crosslinking density is only very slightly less than the theoretical crosslinking density. The Applicant has found that it obtained satisfactory results with regard to the mechanical and acoustic properties of treated woods when the actual crosslinking density was at least 0.1 mole / kg, preferably between 0.5 and 5. moles / kg.

  As examples of the first reagents containing at least two glycidyl functions, mention may be made of 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcinol diglycidyl ether and diglycidyl ether. neopentyl glycol, trimethylolpropane polyglycidyl ether, hexahydroxyphthalic acid diglycidyl ester, bisphenol A diglycidyl ether, diglycidyl ethers of polyalkylene glycols such as diglycidyl ether of diethylene glycol, triethyleneglyol, polyethylene glycol or polyethylene glycol. polypropylene glycol, polyglycidyl ether of glycerol, diglycerol or polyglycerol, polyglycidyl ether of sorbitol.

  Of these, it is particularly preferred to use the diglycidyl ether of bisphenol A and the diglycidyl ether of 1,4-butanediol.

  The compounds comprising at least two -NH functions of primary or secondary amine, capable of reacting with the glycidyl functions of the first reagent, are, for example, ethylenediamine, diethylenetriamine, tetraethylenepentamine, aminoethylpiperazine, benzyldimethylamine, piperidine, 2-methylpentamethylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, 1,3-pentanediamine, hexamethylenediamine, bis (hexamethylene) -triamine, 1,2-diaminocyclohexane, 4-benzylaniline, N, N 5-dimethyldiaminodiphenylmethane, hexylamine and N, N'-dimethylhexamethylenediamine. Among these amines, diaminodiphenylmethane, diaminodiphenylsulfone, hexamethylenediamine, hexylamine and N, N'-dimethylhexamethylenediamine are preferably used.

  The first and second reagents are preferably used in the process of the present invention in molar concentrations such that the stoichiometric ratio of the number of glycidyl functions to the number of amine and / or phenol functions does not deviate too much from 1 and is preferably between 0.5 and 2. Outside this range, the degree of polymerization remains insufficient for the formation of a three-dimensional crosslinked network. In contrast, within this range, the Applicant has found that it was possible to vary the desired glass transition temperature of the polymer system obtained by varying the stoichiometric ratio of the reactants present. Thus, for a given reagent combination, the glass transition temperature is generally maximum for a stoichiometric ratio of 1 and decreases when the stoichiometric ratio deviates from this value (see also the above-mentioned article). impregnation used in step (a) of the process of the present invention must have a sufficient content of polymerizable reagents to allow the formation of a three-dimensional polymer network within the pores of the treated wood, without however having an excessive viscosity which could hinder the penetration of the solution in the pore volume of the wood to be treated. The Applicant has found that satisfactory results are generally obtained by using impregnation solutions having a total content of polymerizable reagents of between 10 and 60% by weight, preferably between 10 and 30% by weight.

  The method of the present invention makes it possible to reinforce wood with open porosity by a crosslinked polymer resin and thus to modify the mechanical and acoustic properties of this wood. A suitable choice of the reagents, the crosslinking density and the stoichiometry of the reactive system allows the value of the glass transition temperature (Tg) of the polymerized resin to be adjusted relatively freely within a wide range, including for example between -40 C and 250 C. The glass transition temperature can be determined for example by differential scanning calorimetry (DSC) or dynamic mechanical analysis (DMA). The glass transition temperature of the resin will be adjusted according to the mechanical properties that it is desired to confer on the final composite material. Thus, in the field of musical instruments, it is often advantageous to increase the resonance capacity of the woods, and the glass transition temperature is then preferably adjusted to a value at least ten degrees higher than the temperature of the wood. use of the instrument, for example at a value of at least 40 C. On the contrary, when it is desired to obtain treated woods relatively acoustically soft, ie low resonance woods, capable To absorb sound, the glass transition temperature of the resin will preferably be adjusted to a value well below room temperature, for example to a value below 0 C.

  The influence of the value of the glass transition temperature on the mechanical properties of the resins, such as hardness, impact resistance, rigidity or elasticity, is known and we can thus modulate in a similar way, thanks to to a number of simple polymerization tests, the mechanical properties of wood / epoxy resin composites.

  In one embodiment of the process of the invention, the impregnation solution used in step (a) contains, in addition to polymerizable reagents in situ, one or more mineral fillers or pigments. The particles of these additives, to be able to easily penetrate with the impregnation solution inside the porous structure, must have a very fine particle size. The Applicant has found that the distribution of the filler particles or pigments in the treated wood was generally satisfactory when they had an average size of less than or equal to 200 nm, preferably between 10 nm and 150 nm.

  Examples of such fillers or pigments include nanosilica, titanium dioxide or clay.

  The impregnating solution may, of course, contain other additives commonly used in the treatment of wood such as fungicidal agents or insecticides or soluble dyes.

  The reagents involved in the in situ polycondensation reaction of the present invention are generally characterized by high reactivity. Therefore, it is often necessary to carry out the impregnation step (a) at a temperature below room temperature so as to prevent undesirable early polymerization of the reagents. Such early polymerization would result in the clogging of the pores at the surface layers of the wood and thus prevent a satisfactory penetration of the solution to the deeper layers. The impregnation of the wooden part with the organic solution in step (a) is therefore preferably at a temperature below 20 ° C., in particular below 10 ° C., and ideally at a temperature close to 5 ° C.

  The duration of the impregnation step depends on a number of factors such as the viscosity of the impregnating solution, the impregnation temperature, the pore size and the communication openings between the pores or the depth desired penetration. The tests carried out by the Applicant have shown that the duration of the impregnation step (a) is preferably at least 5 days, preferably between 10 and 30 days. One can of course consider trying to accelerate the penetration of the impregnating solution into the wood by performing this step under pressure, for example under a pressure of 4 to 10 bar.

  Once the impregnation is over, it is instead to quickly polymerize and crosslink the reagents. For this, it is generally useful to heat the impregnated wood piece at a temperature between 20 C and the boiling temperature of the solvent used, preferably between 40 C and the boiling point of the solvent.

  This heating can be done by any known means, for example in a circulating air oven, an infrared oven, a microwave oven.

  In a preferred embodiment of the invention, the heating of the impregnated wood is done by microwaves. This means of heating makes it possible, a very fast heating in the heart of the wood. Preferably, the impregnated wooden part is subjected for a period of between 5 seconds and 30 seconds to microwaves of a frequency, for example equal to 2.8 GHz, in a suitable furnace having a restituted power at least equal to 300 Watts, preferably between 400 and 1000 Watts.

  In a preferred embodiment of the present invention, the in situ polymerization wood treatment method is applied to the manufacture of wind instrument bodies such as clarinet bodies. The wooden part is then advantageously a blank having the shape of a hollow cylinder, suitable for the manufacture of wind instruments.

  Another interesting application of the wood treatment method of the present invention is the restoration or preservation of old wood, especially antique furniture or old musical instruments whose structure has been weakened over time by environmental effects such as water, excessive temperatures or xylophagous insects. The use of the in situ polycondensation wood treatment method for the restoration and / or preservation of old wood is therefore another object of the present invention.

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Claims (15)

claims   A method of treating wood with open porosity by in situ polycondensation comprising: (a) immersing an open porous wood member in a solution containing, in a volatile organic solvent, at least a first reagent comprising at least one two glycidyl functions and at least one second reagent comprising at least two NH functions of primary amine or secondary amine, the average functionality of the set of reagents being strictly greater than 2, for a time sufficient to allow the filling by the solution of at least 60% of the accessible pore volume of the wood, and at a temperature sufficiently low to prevent the premature polymerization of the monomers during this impregnation step (a), (b) the removal of the impregnated part by the organic solution and draining and / or wiping the wood piece, (c) heat treating the impregnated wood piece at a temperature and for a period of time. sufficient to allow the exothermic polycondensation reaction between the first and second reagents to self-sustain through the liberated reaction heat, and optionally (d) drying the workpiece, preferably under reduced pressure, for a sufficient period of time to allow evaporation of the organic solvent.   2. A method of treating wood according to claim 1, characterized in that the open-porous wood used is wengué (Milleltia laurentil), linden, spruce, monpani or poplar, preferably wengué.   3. A method of treating wood according to claim 1 or 2, characterized in that the first reagent comprising at least two glycidyl functions is selected from 1,4butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether. , neopentyl glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, hexahydroxyphthalic acid diglycidyl ester, bisphenol A diglycidyl ether, diglycidyl ethers of polyalkylene glycols such as diethylene glycol diglycidyl ether, triethylene glycol polyethylene glycol or polypropylene glycol, polyglycidyl ether of glycerol, diglycerol or polyglycerol, polyglycidyl ether of sorbitol.   4. Wood treatment method according to any one of the preceding claims, characterized in that the second reagent comprising at least two amine functions is chosen from ethylenediamine, diethylenetriamine, tetraethylenepentamine, aminoethylpiperazine, benzyldimethylamine, piperidine, 2-methylpentamethylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, 1,3-pentanediamine, hexamethylenediamine, bis (hexamethylene) -triamine, 1,2-diaminocyclohexane, 4-benzylaniline, N, N ', dimethyldiaminodiphenylmethane, hexylamine and N, N'-dimethylhexamethylenediamine.   5. A method of treating wood according to any one of the preceding claims, characterized in that the volatile organic solvent used in step (a) has a melting point below -30 C and a lower boiling point at 250 ° C., preferably below 150 ° C.   6. A method of treating wood according to claim 5, characterized in that the volatile organic solvent is selected from hydrocarbon compounds having a C1-C6 skeleton and comprising at least one polar group selected from secondary alcohol functions, ether and ester, and vegetable oils.   7. A method of treating wood according to claim 6, characterized in that the volatile organic solvent is 1-methoxy-2-propanol.   8. A method of treating wood according to any one of the preceding claims, characterized in that the organic solution containing the polymerizable reagents of step (a) further contains one or more inorganic fillers or nanometric pigments having a average particle size less than or equal to 200 nm, preferably between 10 and 150 nm.   9. A method of treating wood according to any one of the preceding claims, characterized in that the impregnation of the wooden part with the organic solution in step (a) is at a temperature below 20 C, preferably less than 10 C, and in particular at a temperature close to 5 C, and for a period of at least 5 days, preferably between 10 and 30 days.   10. A method of treating wood according to any one of the preceding claims, characterized in that the heat treatment of step (c) is in a microwave oven.   11. A method of treating wood according to claim 10, characterized in that the microwave heating is done in an oven having a power output of at least 300 Watts, preferably between 400 and 1000 Watts, and during a duration of between 5 and 30 seconds.   12. A method of treating wood according to any one of the preceding claims, characterized in that the piece of wood is a blank having the shape of a hollow cylinder, suitable for the manufacture of wind instruments.   13. Part made of a wood / epoxy-amine resin composite material that can be manufactured by the method according to any one of claims 1 to 12.   14. Use of a part according to claim 13 for the manufacture of all or part of wind instruments, in particular clarinets, for inlay work, for cabinet making, for the construction of buildings and in particular for framing.   15. Use of the method according to any one of claims 1 to 12 for the restoration and / or preservation of old wood.