AQUEOUS ADHESIVE COMPOSITION CONTAINING A LOW-PHENOL, HEAT-SETTING RESIN

Abstract

The present invention relates to an aqueous adhesive composition, comprising a thermosetting resin based on: - at least one hydrocarbon aromatic compound A1 comprising at least one hydrocarbon aromatic compound comprising at least two aromatic rings bearing a single hydroxyl function, it being understood that at least one of the ortho or para positions of each aromatic ring is unsubstituted; and - a formaldehyde compound A3; in which an aromatic compound A2 comprising a single phenol substituted or not by a single alkyl group or by a single alkenyl group is at a mass percentage of dry extract of the adhesive composition of at most 0.23.

Description

Title of the invention: AQUEOUS ADHESIVE COMPOSITION COMPRISING A THERMOSETTING RESIN WITH A LOW PHENOL CONTENT

[0001] The field of the present invention relates to aqueous adhesive compositions intended for adhering elements, the use and the method of manufacturing such a composition, the method of assembling elements using these compositions as well as the assemblies manufactured using these compositions.

[0002] Phenol-formaldehyde resins (PF) are derived from formaldehyde and phenol. Since phenol is a monofunctional monomer that allows triple condensation, a three-dimensional network is ultimately formed. Phenols are used in particular as adhesives, for example in the manufacture of materials based on chipboard or composite materials reinforced with glass fibers, textile fibers, etc.

[0003] In the field of wood, a phenol-aldehyde type composition is described in patent US2360376. This composition comprises a phenol-aldehyde resin based on formaldehyde and phenol. The mass content of phenol in the dry extract of the adhesive composition is 26 to 35%. This composition is used in a process for bonding plywood articles comprising several wooden plies. During this process, one or more plies are coated with a layer of the composition, the plies are joined together via the layer of composition and the plies thus joined are pressure-cured. The bonded assembly thus obtained has high cohesion thanks to the excellent adhesive properties of the composition.

[0004] However, due to recent changes in regulations, particularly European regulations on this type of compound (phenol and formaldehyde), it is desirable to limit as much as possible, or even eliminate the use of phenol. Alternatives have appeared using lignins by substituting part of the phenol molecule. Such an LPF (Lignin-Phenol-Formaldehyde) composition is described in FR3007764. In this composition, a fraction of phenol is substituted by lignin at a rate of 50% by mass. The mass content of phenol in the dry extract of the adhesive composition is 24% in the example of the composition described in this application.

[0005] These historical LPF type resins have the particularity of containing a high proportion of phenol molecule and require a particular type of lignin as described in application FR3007764. A particularly high phenol level is necessary in order to guarantee the performance and reproducibility of the results. In addition, the type of lignin used generally corresponds to a particular type of lignin such as exemplified in this patent and of low molecular mass (< 2000 g / mol).

[0006] These specific points make the use of these LPF resin compositions delicate, particularly when the applications and the specificities of the resins require a lower phenol content but also when the economic balance of the desired applications requires a larger, more diversified and less expensive supply of lignin.

[0007] Furthermore, despite the phenol molecule substitution rate of 50 to 60% by mass, the remaining proportions associated with formaldehyde (or formalin) induce significant toxicity of this type of resin. However, due to societal developments and in particular European regulations on these types of compounds, we wish to limit as much as possible, or even eliminate the use of aromatic molecules comprising a single phenol.

[0008] By seeking to reduce the level of phenol molecules in these types of composition (LPF), the Applicant has found a new composition making it possible to drastically reduce the level of aromatic molecules comprising a single phenol or even to remove it from these compositions.

[0009] The aim of the invention is to provide an aqueous adhesive composition, comprising a thermosetting resin, having high adhesive properties and comprising a reduced quantity of aromatic molecule comprising a single phenol or even devoid of this molecule.

[0010] Thus, an object of the invention relates to an aqueous adhesive composition, comprising a thermosetting resin based on: - at least one aromatic hydrocarbon compound Al comprising at least one aromatic hydrocarbon compound comprising at least two aromatic nuclei carrying a single hydroxyl function, it being understood that at least one of the ortho or para positions of the hydroxyl function of each aromatic nucleus is unsubstituted; and - at least one formaldehyde A3 compound; in which an aromatic compound A2 comprising a single phenol substituted or not by a single alkyl group or by a single alkenyl group is present at a mass content of dry extract of the adhesive composition of at most 0.23.

[0011] The mass rate of dry extract of A2 is calculated by dividing the weight of compound A2 by the total weight of dry extract of the adhesive composition.

[0012] Preferably, the aromatic compound A2 has a mass content of dry extract in the adhesive composition of less than or equal to 0.20, preferably less than or equal to 0.18.

[0013] Preferably, the aromatic compound A2 is at a mass content of dry extract of the adhesive composition of 0. Advantageously, in this embodiment, the composition does not contain aromatic compound A2, it is totally substituted by the aromatic hydrocarbon compound Al.

[0014] Advantageously, the rate of substitution of the aromatic compound A2 by the aromatic hydrocarbon compound Al is strictly greater than 60%, preferably ranging from 70 to 100% and more preferably from 80 to 100%.

[0015] Another subject of the invention relates to the use of the aqueous adhesive composition according to the invention, for bonding at least two cellulosic elements, advantageously at least two wooden elements.

[0016] The invention also relates to a method of gluing two cellulosic elements, advantageously two wooden elements, in which: - a layer of the aqueous adhesive composition as defined above is applied to at least one of the elements, and, - the elements are joined together using a layer of aqueous adhesive composition.

[0017] The invention also relates to a bonded assembly of two elements comprising a layer of the aqueous adhesive composition as defined above joining at least one of the elements to the other.

[0018] The invention and its advantages will be easily understood in light of the following description.

[0019] I - FORMULATION OF THE AQUEOUS ADHESIVE COMPOSITION

[0020] In the present description, unless expressly indicated otherwise, all percentages (%) indicated are % by mass.

[0021] “Compound Al” designates, within the scope of the invention, the aromatic compound defined in paragraph LL

[0022] “Compound A2” designates, within the framework of the invention, the compound based on aromatic polyphenol defined in paragraph 1.2.

[0023] “Compound A3” designates, within the scope of the invention, a formaldehyde compound defined in paragraph 1.3.

[0024] In the context of the invention, the carbon products mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass.

[0025] Within the framework of the invention, it may also be envisaged that the carbon products mentioned in the description comprise isotopes of certain chemical elements.

[0026] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​going from more than a to less than b (i.e., limits a and b excluded) while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​going from a to b (i.e., including the limits strict a and b).

[0027] By the expression "composition based on", it is of course necessary to understand a composition comprising the mixture and / or the reaction product of the different basic constituents used for this composition, some of which may be intended to react or capable of reacting with each other or with their close chemical environment, at least in part, during the different phases of manufacturing of the composition, the wood material, the textile material, the composites or finished articles comprising such composites, in particular during a cooking step.

[0028] The aqueous adhesive composition according to the invention therefore comprises at least one thermosetting resin according to the invention, this thermosetting resin is based on at least one (i.e. one or more) aromatic compound and at least one (i.e. one or more) aromatic polyphenol, constituents which will be described in detail below. 1.1 - Aromatic compound Al

[0029] In the embodiment of the invention, the aromatic hydrocarbon compound Al described as a poly-monophenolic compound corresponds to the general formula (X): where Y1 represents an alkyl, aryl, arylalkyl, alkylaryl, cycloalkyl or alkenyl group, these groups being substituted, Y2 and Y3 are the same or different and represent H or an ether group.

[0030] Advantageously, Y2 and Y3 are in the ortho position of the hydroxyl function and represent H or OY4 where Y4 represents an alkyl, aryl, arylalkyl, alkylaryl, cycloalkyl or alkenyl group and preferably CH3.

[0031] In an advantageous embodiment, the aromatic hydrocarbon compound Al comprises at least two aromatic nuclei carrying a single hydroxyl function, it being understood that one of the ortho positions of each of the aromatic nuclei carrying a single hydroxyl function is unsubstituted.

[0032] In another advantageous embodiment, the aromatic hydrocarbon compound Al is chosen from the group consisting of bisphenol-A, lignin and a mixture of these compounds. 1.2 - Aromatic compound A2

[0033] In one embodiment of the invention, the second constituent of the thermosetting resin is an aromatic compound A2 comprising a single phenol substituted or not by a single alkyl group or by a single alkenyl group.

[0034] Advantageously, the phenol substituted or not by a single alkyl group is chosen from the group consisting of phenol, ortho cresol, meta cresol, para cresol or a mixture of these compounds.

[0035] Advantageously, the phenol substituted by a single alkenyl group is coumaryl alcohol of formula 1.3 - Aromatic compound A3

[0036] In the embodiment of the invention, the third essential constituent of the thermosetting resin is compound A3 chosen from monomeric formaldehyde, meta-formaldehyde, para-formaldehyde, trioxane.

[0037] 1.4 - Additives - Manufacture of the aqueous adhesive composition

[0038] The aqueous adhesive composition in accordance with the invention may of course comprise all or part of the usual additives for aqueous adhesive compositions such as those used in conventional phenolic glues; for example, bases such as ammonia, sodium, potassium or ammonium hydroxide, colorants, fillers such as carbon black, silica, chalk, olive pomace or any other natural fillers, antioxidants or other stabilizers, thickeners, for example carboxymethylcellulose, or gelling agents, for example gelatin, making it possible to increase the viscosity of the composition. Additives making it possible to modify the setting or gel time and the open time of the resin will also be mentioned.As known to those skilled in the art, the setting or gel time is the time during which the resin can be applied to its substrate and the opening time is the time during which, after application of the resin to its substrate, the resin can be left in the open air without altering the quality of the subsequent adhesive bond with the complementary substrate. The setting or gel time and the opening time are in particular a function of the temperature, the pressure or even the resin concentration.

[0039] Typically, when preparing the resin, the constituents of the thermosetting resin itself are mixed in no predefined order but advantageously by first mixing the water with the aromatic hydrocarbon compound Al and then the soda, then the aromatic compound A2, then the compound A3.

[0040] The production of the thermosetting resin at a pH between 8 and 14, more preferably between 9 and 12.

[0041] Thus, the thermosetting resin is obtained by mixing: - the aromatic hydrocarbon compound Al, and - aromatic polyphenol A2; and - compound A3; in a basic solvent preferably having a pH between 8 and 14, more preferably between 9 and 12.

[0042] The quantity of phenol substituted or not by a single alkyl group or at least one aromatic hydrocarbon compound A2 will be adjusted according to the target viscosity desired by a person skilled in the art. Typically the mass ratio of the aromatic compound A2 to the phenol substituted or not by a single alkyl group on the aromatic hydrocarbon compound Al described as the poly-mono-phenolic compound will be between 0% and 24% upper limit excluded, preferably between 0% and 20% of the aromatic compound A2, more preferably between 0% and 11%.

[0043] The concentration of the composition can be adjusted depending on its specific use (opening time, viscosity).

[0044] Advantageously, in the final aqueous adhesive composition thus prepared, the dry extract content of thermosetting resin according to the invention ranges from 10 to 90%, more preferably from 15 to 75% by weight of the dry extract of the adhesive composition, even more preferably from 20 to 50% by weight of the dry extract of the adhesive composition.

[0045] In the case where the final application of the adhesive composition requires a higher viscosity, a person skilled in the art will know how to adjust the final viscosity characteristics of the adhesive composition by adding thereto a thickener or any type of known fillers (for example olive stone powder and / or chalk).

[0046] The composition may be used immediately or stored at room temperature (23°C) for a maturation time which may typically vary from one to several hours or even several days. Before its final use, a person skilled in the art will determine the possible storage time based on the concentration of the composition.

[0047] Preferably, the water content of the aqueous adhesive composition ranges from 10 to 90% by weight, preferably from 25 to 85% by weight, even more preferably from 50 to 80% by weight.

[0048] By total dry extract rate of the adhesive composition is meant the ratio between the mass of residue obtained after drying of the adhesive composition on the mass of the adhesive composition before drying.

[0049] By dry extract rate of the thermosetting resin, we mean the ratio between the mass of the thermosetting resin obtained after drying of the adhesive composition and the mass of the adhesive composition before drying.

[0050] These two dry extract rates are measured in accordance with standard NF EN 827 (March 2006).

[0051] By water content of the aqueous adhesive composition is meant the weight of water relative to the total weight of the adhesive composition. II - GLUED ASSEMBLY OF THE INVENTION II. 1 - Definitions; examples

[0052] As indicated previously, the present invention also relates to the use of the aqueous adhesive composition previously described, for bonding at least two cellulosic elements, advantageously at least two wooden elements.

[0053] Thus, a bonded assembly of two elements according to the invention comprises a layer of the aqueous adhesive composition as described previously joining the two elements to each other.

[0054] In a preferred embodiment, these two elements are made of wood.

[0055] Wood means the plant tissue derived from woody plants. Examples of plant tissue are the trunk, branches and roots. For example, the woody plants from which plant tissue is derived are oak, chestnut, ash, walnut, beech, poplar, fir, pine, olive, alder or birch.

[0056] The glue can also be used for bonding elements made from materials other than wood, for example plastics, for example thermosetting or thermoplastic materials, textiles, mineral materials or mixtures of these materials, including with wood.

[0057] By element is meant any particle or monolithic piece. Examples of wooden elements are plies intended to form a plywood assembly, laths intended to form a slatted assembly, particles such as shavings, sawdust, flour or flakes, to form an agglomerated assembly, whether the particles are oriented or not, fibers intended to form a fiber assembly such as a high or medium density panel, pieces of solid wood, also called lumber, intended to form assemblies such as furniture, frames.

[0058] Advantageously, the wooden elements may be wood veneers, wood slats, wood fibers, wood particles or a mixture of these compounds. IL2 - Manufacturing of the glued assembly

[0059] The glued assembly of the invention can be prepared according to a method of gluing at least two cellulosic elements, advantageously two wooden elements, in which: - a layer of the aqueous adhesive composition according to the invention is applied to at least one of the elements, and, - the elements are joined together using a layer of aqueous adhesive composition.

[0060] The step of applying the adhesive composition to one or more elements can be carried out using any appropriate method, in particular using any known coating technique such as, for example, spraying, impregnation, injection under pressure or even using a combination of one or more of these techniques.

[0061] For example, for wood veneers, it is preferable to use a rate of aqueous adhesive composition ranging from 50 to 400 gr.m2 and preferably from 70 to 300 gr.m2. Those skilled in the art will be able to adapt the weight of aqueous adhesive composition to their wooden elements and their own process.

[0062] Advantageously, a cooking step is carried out after the step of applying the aqueous adhesive composition in which the cooking is carried out by cooking with water vapor, cooking by contact with the plates of a cooking press or cooking by high frequency.

[0063] After the step of applying the adhesive composition, a curing step is carried out: the bonded assembly is heated to a temperature ranging from 30°C to 250°C, preferably from 50°C to 200°C, very preferably from 80°C to 160°C depending on the intended applications. This heat treatment aims to eliminate any solvent or water and to crosslink the thermosetting resin. Depending on the fields of application, the heat treatment may be carried out in two stages: a first heat treatment aimed at eliminating any solvent or water, a second heat treatment aimed at completing the crosslinking of the thermosetting resin.

[0064] In a first embodiment, the elements joined by the adhesive composition are subjected to a steam cooking step, advantageously at a temperature greater than or equal to 100°C.

[0065] In a second embodiment, the elements joined by the adhesive composition are subjected to a cooking step by contact with the plates of a cooking press, advantageously at a temperature greater than or equal to 80°C.

[0066] In a third embodiment, the elements joined by the adhesive composition are subjected to a high frequency cooking step, advantageously ranging from 300 GHz to 300 MHz.

[0067] Preferably, the bonded assembly is maintained under pressure, for example under a pressure up to 18 kg.cm2. More preferably, the pressure maintenance step is carried out simultaneously with the heating step.

[0068] The duration of the heating and / or pressurization step varies from a few minutes to a few hours depending on the case, in particular depending on the temperature-pressure pair used.

[0069] In a preferred embodiment, the two elements to be assembled are made of wood.

[0070] Those skilled in the art will know how to adjust, where appropriate, the temperature and duration of the above heat treatment, depending on the particular conditions of implementation of the invention, in particular the exact nature of the element. In particular, those skilled in the art will benefit from carrying out temperature and treatment duration scans as well as aqueous adhesive composition grammage scans, so as to search, by successive approaches, for the operating conditions leading to the best adhesion and viscosity results for each particular embodiment of the invention.

[0071] III - EXAMPLES OF CARRYING OUT THE INVENTION AND COMPARATIVE TESTS

[0072] These tests demonstrate that the bonding of two wooden elements with an aqueous adhesive composition according to the invention makes it possible to have adhesion levels greater than 1 MPa.

[0073] For this, seven aqueous adhesive compositions were prepared in accordance with the invention, hereinafter referred to as B1, B-2, B-3, B-4, B-5, B-6, B-7. Their formulations (expressed as a percentage by weight) are presented in Table 1 below. The quantities listed in this table are those of the constituents in the dry state, brought to a total of 100 parts by weight of aqueous adhesive composition (i.e. the constituents and the water).

[0074] The adhesive composition Bl is a composition based on formaldehyde, resinous lignin and phenol.

[0075] Adhesive compositions B-2 and B-4 are compositions based on formaldehyde, hardwood lignin and phenol.

[0076] Adhesive composition B-3 is a composition based on formaldehyde, softwood lignin and ethylphenol.

[0077] Adhesive composition B-5 is a composition based on formaldehyde, bisphenol-A and phenol.

[0078] Adhesive composition B-6 is a composition based on formaldehyde, eucalyptus lignin and phenol.

[0079] Adhesive composition B-7 is a composition based on formaldehyde and hardwood lignin.

[0080] Protocol for producing the aqueous adhesive composition

[0081] An example of a manufacturing protocol for the adhesive composition is as follows:

[0082] In a glass container of a size adapted to the final volume of solution, introduce the water. Add the poly-monophenolic derivative. Stir using a mechanical stirrer at a speed allowing good dispersion of the poly-monophenolic derivative. Add the sodium hydroxide solution then add the monophenolic derivative. Continue stirring for a time varying from 5 minutes to 1 hour until the poly-monophenolic derivative is dissolved. Add formalin to the previous solution. Heat the solution to a temperature between 20°C and 80°C and continue stirring for a time between 5 minutes and 1 hour. At the end of this time, additives, such as fillers, can be added while the resin solution is still hot or the resin solution can be cooled to room temperature, for example 25°C, before introducing additives, such as fillers. 。

[0083] Another example of a manufacturing protocol for the adhesive composition is as follows:

[0084] In a glass container of a size adapted to the final volume of solution, introduce the water. Add the poly-monophenolic derivative. Stir using a mechanical stirrer at a speed allowing good dispersion of the poly-monophenolic derivative. Add the sodium hydroxide solution. Heat the solution to a temperature between 20°C and 80°C. Add the monophenolic derivative then add the formalin to the previous solution. Continue stirring for a time between 5 minutes and 1 hour. At the end of this time, additives, such as fillers, can be added while the resin solution is still hot or the resin solution can be cooled to room temperature, for example 25°C, before introducing additives, such as fillers.

[0085] In an exemplary embodiment, the aromatic compound Al and the sodium hydroxide are introduced into a 250 mL flask equipped with a mechanical stirring system. Stirring is carried out for 1 min to 60 min to homogenize (for example at 250 rpm). Then, compound A2 is added and stirring is carried out, for example, for 1 min to 60 min to homogenize (for example at 250 rpm). Compound A3 is then added. The mixture thus formed is stirred for a period ranging from 1 min to 60 min, and for a temperature ranging from 20°C to 90°C. The technical fillers previously described are added to the composition. Depending on the added constituents (which a person skilled in the art will be able to determine), the mixture is left to stir for between 5 and 15 minutes at room temperature. At the end of this time, the aqueous adhesive composition is ready for use.

[0086] Table 1 below gives examples of compositions in accordance with the invention:

[0087] [Tables 1] Adhesive compositions Bl B-2 B-3 B-4 B-5 B-6 B-7 Al: aromatic hydrocarbon compound Resinous lignin (1) 16.0 - 13.4 - - - - Hardwood lignin (2) - 16.0 - 15.4 - - 19.2 Eucalyptus lignin (3) - - - - - 17.3 - Bisphenol A (4) - - - - 15.4 - - A2: aromatic compound A2 comprising a single phenol substituted or not by a single alkyl group or by a single alkenyl group: Phenol (5) 4.0 4.0 - 3.8 3.8 1.9 - Ethylphenol (6) - - 5.8 - - - - Formaldehyde compound A3: Formalin (7) 7.7 7.7 3.2 3.2 3.2 3.2 3.2 Sodium hydroxide (8) 3.8 3.8 3.6 3.6 3.6 3.6 3.6 Total weight of dry extract of adhesive composition 31.5 31.5 32.0 32.0 32.0 32.0 32.0 Water weight 68.5 68.5 68.0 68.0 68.0 68.0 68.0 Mass rate of dry extract of A2 0.13 0.13 0.18 0.12 0.12 0.06 0 % substitution of A2 80 80 70 80 80 90 100 (1) Softwood lignin (from StoraEnzo company); (2) Hardwood lignin (extracted from a black liquor from the company Fibreexcellence following the lignoboost protocol from the company Valmet); (3) Eucalyptus lignin (from the company Fibria); (4) Bisphenol A (from Sigma Aldrich); (5) Phenol (from Sigma Aldrich; purity > 99%); (6) Ethylphenol (from Sigma Aldrich); (7) Formalin (from Sigma Aldrich; purity > 99%); (8) Sodium hydroxide (from Aldrich; diluted to 30%). Viscosity test

[0088] After preparing the various aqueous adhesive compositions, the viscosity is measured at different time intervals. The viscosity is measured in using a viscometer of the Brookfield / Mobil Viscometer type to be chosen according to the target viscosities using the following protocol: the sample is transferred into the thermostatically controlled chamber up to approximately 150 mL (inner beaker graduation) avoiding the formation of air bubbles, the sample is allowed to regulate at the measurement temperature of 20°C for the time indicated, i.e. 1 to 20 minutes depending on the starting temperature of the composition, the speed is selected, for example 60 rpm and the mobile is set to rotate, the axis is waited for to be stabilized (1 minute) before taking the first reading and the result is read on the digital display (viscosity in cP).

[0089] The results of the tests carried out on the compositions are summarized in Table 2 below. Protocol for producing the test piece

[0090] The quality of the connection between the wooden elements is determined by a test in which the force required to separate two wooden elements from each other by destruction of the layer joining the two elements is measured.

[0091] More specifically, each test specimen comprises three wooden elements, in this case beech with a density equal to 0.83 g.cm-3, each having a general parallelepiped shape with dimensions of 17 cm x 17 mm x 2.5 mm. On one side of the first and third wooden elements, a layer of the aqueous adhesive composition is applied over the entire width of the first and third elements. Then, the three elements are joined by means of the layers of composition applied to the first and third wooden elements. The total glued surface area of ​​the test specimen formed by the three wooden elements is therefore 225 cm2. The composition of the test specimen thus formed is baked for example for 300 seconds at 160°C.

[0092] At the end of the cooking, the test piece thus constituted by the three elements joined by gluing is placed in the jaws of a traction machine, then pulled at a given speed and temperature (for example, in the present case, at 1.5 mm / min and 20°C).

[0093] The cutting of the test pieces was carried out according to standard NF EN 326.1 (1994) “Wood-based panels - Sampling, cutting and inspection - Part 1: Sampling and cutting of test pieces, and expression of test results”.

[0094] Adhesion levels are characterized by measuring the so-called tear force (adhesive performance in MPa) to separate the three elements from each other via a break in the bonding layer. Any tear value greater than or equal to 1 MPa is considered good.

[0095] The change in viscosity of the adhesive compositions at 20°C is characterized as a function of time (in centipoise) and the gel time is indicated in the table below.

[0096] Gel time is defined by a sudden change in viscoelastic properties which corresponds to the formation of the macro-molecular network woven within the material, it is determined for phenolic resins according to the protocol of the ISO 9396:1997 standard.

[0097] The results of the tests carried out on the specimens are summarized in Table 2 below.

[0098] [Tables2] Adhesive compositions Bl B-2 B-3 B-4 B-5 B-6 B-7 Adhesion tests Adhesive performance in MPa 4.3 1.9 2.3 2.2 2.4 1.1 1.2 Viscosity at 20°C as a function of time Viscosity (cp) 5000 126 890 8000 52 304 38960 Gel time at 100°C (min) 16 31.5 30 22 48 43 41

[0099] The compositions in Table 1 in accordance with the invention make it possible to produce resins with initial viscosity varying according to the basic composition but all less than 50,000 Cp. These viscosities are sufficiently low to be compatible with different industrial bonding systems. Those skilled in the art will be able to adapt their formulation with their own process.

[0100] Furthermore, it can be seen that all gel times are less than 60 minutes at 100°C. These performances make it possible to adapt the compositions to industrial constraints.

[0101] In conclusion, the results of these different tests clearly demonstrate that the adhesive compositions according to the invention constitute an interesting alternative to the use of conventional adhesive compositions, by considerably reducing or even eliminating the aromatic molecules comprising a single phenol.

[0102] The invention is not limited to the embodiments previously described.

Claims

Claims

1.

2.

3. Aqueous adhesive composition, characterized in that it comprises a thermosetting resin based on: - at least one aromatic hydrocarbon compound Al comprising at least one aromatic hydrocarbon compound comprising at least two aromatic nuclei carrying a single hydroxyl function, it being understood that at least one of the ortho or para positions of the hydroxyl function of each aromatic nucleus is unsubstituted; and - at least one formaldehyde A3 compound; in which an aromatic compound A2 comprising a single phenol substituted or not by a single alkyl group or by a single alkenyl group is present at a mass content of dry extract of the adhesive composition of at most 0.

23. Composition according to the preceding claim, in which the aromatic compound A2 is at a mass content of dry extract of the adhesive composition less than or equal to 0.20, preferably less than or equal to 0.

18. Composition according to any one of the preceding claims, in which the aromatic hydrocarbon compound Al corresponds to the general formula (X):

4.

5. where Y1 represents an alkyl, aryl, arylalkyl, alkylaryl, cycloalkyl or alkenyl group, these groups being substituted, Y2 and Y3 are identical or different and represent H or an ether group. Composition according to the preceding claim, in which Y2 and Y3 are in the ortho position of the hydroxyl function and represent H or OY4 where Y4 represents an alkyl, aryl, arylalkyl, alkylaryl, cycloalkyl or alkenyl group and preferably CH3. Composition according to claim 3 or 4, in which the aromatic hydrocarbon compound Al comprises at least two aromatic nuclei carrying a single hydroxyl function, it being understood that a ortho positions of each of the aromatic rings carrying a single hydroxyl function is unsubstituted.

6. A composition according to claim 3 or 4, wherein the aromatic hydrocarbon compound Al is selected from the group consisting of bisphenol-A, lignin and a mixture of these compounds.

7. Composition according to any one of claims 1 to 6, in which the phenol A2 substituted or not by a single alkyl group is chosen from the group consisting of phenol, ortho cresol, meta cresol, para cresol or a mixture of these compounds.

8. A composition according to any one of claims 1 to 6, wherein the phenol A2 substituted by a single alkenyl group is coumaryl alcohol or phenol.

9. Composition according to any one of the preceding claims, in which compound A3 is selected from monomeric formaldehyde, meta-formaldehyde and para-formaldehyde, trioxane.

10. Composition according to any one of the preceding claims, in which the aqueous adhesive composition is obtained by mixing: - the aromatic hydrocarbon compound Al; - the aromatic compound A2; and - the compound A3; in a basic solvent preferably having a pH between 8 and 14, more preferably between 9 and 12.

11. Use of an adhesive composition according to any one of claims 1 to 10 for bonding at least two cellulosic elements, advantageously at least two wooden elements.

12. Method for bonding at least two cellulosic elements, advantageously two wooden elements, in which: - a layer of the aqueous adhesive composition according to any one of claims 1 to 10 is applied to at least one of the elements, and, - the elements are joined to each other by means of the layer of the aqueous adhesive composition.

13. Method according to the preceding claim in which a cooking step is carried out after the step of applying the aqueous adhesive composition in which the cooking is carried out by cooking with water vapor, cooking by contact with the plates of a cooking press or cooking by high frequency.

14. Glued assembly of two elements, advantageously made of wood, comprising a layer of the aqueous adhesive composition according to any one of claims 1 to 10 joining at least one of the elements to the other.