FR3033171A1 - LIQUID FORMULATION FOR THE PREPARATION OF TANNIN-BASED THERMODURCY FOAM, PROCESS FOR OBTAINING SUCH FORMULATION AND FOAM OBTAINED FROM SUCH A FORMULATION - Google Patents

Abstract

The invention relates to a liquid formulation for the preparation of a tannin thermoset foam, which contains a mixture of at least one hydrolysable tannin and at least one condensed tannin, lignin, water, hardener and a surfactant. The total amount of tannins in the formulation is between 8 and 60% by weight, and the amount of lignin is between 4 and 30% by weight, based on the total weight of the formulation. This formulation makes it possible to prepare, by baking, a foam of advantageous mechanical properties.

Description

The present invention is in the field of the preparation of thermoset mousses based on tannins. More particularly, it relates to a thermosetting liquid formulation for the preparation of a thermoset foam based on tannins, as well as a process for obtaining such a liquid formulation. The invention also relates to a tannin thermoset foam obtainable from said liquid formulation. Foams obtained from a thermosetting formulation, called thermoset foams, also commonly known as rigid foams, are frequently used in fields as varied as transport, packaging, building, automobile, aerospace, naval, or even in the electronics field, the field of textiles, batteries and the depollution of wastewater. Many of their applications take advantage of their thermal and sound insulation properties as well as their flame retardancy properties. Thus, foams obtained by curing thermosetting resin are commonly used for the thermal and / or sound insulation of buildings. Among the rigid foams currently in use in the above-mentioned fields are polyurethane foams, polyvinyl chloride foams and polystyrene foams. Other rigid foams currently used because of their particularly advantageous properties, in particular for their high heat insulating capacity and their good fire behavior, for their high resistance to chemical attack and for their ability to protect themselves against the effects of fire. shocks, are phenolic type foams. The manufacture of such rigid foams, like that of all the other types of foams mentioned above, requires in most cases the use of raw materials derived from petrochemistry, that is to say from fossil origin, and / or chemicals, often harmful not only to human health but also to the environment. For example, during the manufacture of polyurethane foams, there is a release of harmful products, such as isocyanate. These foams are also difficult to recycle. In a desire to promote, for the manufacture of rigid foams, the use of products derived from renewable resources and / or products obtained by processes that respect the environment, it has been proposed by the prior art to prepare phenolic foams based on polyphenolic compounds of plant origin, more specifically vegetable tannins. Such prior art is particularly illustrated by the patent document WO-2013-A-026974, which describes foams obtained from condensed tannins from maritime pine. It is in this context of the preparation of rigid foams based on materials derived from renewable resources that the present invention falls. In particular, the present invention aims to provide an alternative to petro-sourced phenolic foams, by providing a foam that is capable of being obtained by curing a tannin-based liquid formulation, biobased products derived from renewable resources, and whose manufacturing process does not cause release of toxic compounds, such as polyurethane precursors in particular, while ensuring that this foam has advantageous mechanical properties, similar to those of polyurethane foams. A further object of the invention is that this foam has good resistance to water and weathering.

The invention further aims that this foam can be manufactured by a low energy consuming and environmentally friendly process. Tannins are natural compounds well known in themselves, widespread throughout the plant kingdom and present in significant quantities in trees, rosaceae, ericaceous, sterculiaceae, legumes, etc. 3033171 3, as well in bark only in the roots, leaves and fruits. There are two main families of tannins: hydrolysable tannins and condensed tannins, also called proanthocyanidins, which are part of the flavonoid family. Their chemical structure is very variable, but always has a polyphenolic part. The condensed tannins have as a fundamental structural unit a flavane nucleus of structure: They have a mass of between 500 and 20,000 g.m -1 -1 depending on their degree of polymerization and their origin. These are polymers of flavan-3-ols, which have different degrees of polymerization: monomers, dimers, oligomers and polymers. The large structural diversity of these flavan-3-ols is expressed by differences in the number of hydroxyl groups, their positions on the aromatic rings A and B, the stereochemistry of the asymmetric carbons of the pyran-C ring, as well as the number and type of so-called "interflavanic" bonds between the monomeric units. These monomeric units correspond to the general formula (I): in which R 2 and R 3, which may be identical or different, each represent a hydrogen atom or a hydroxyl group, and R 1 represents a hydrogen atom or a hydrogen atom. hydrogen, a hydroxyl group or an O-gallate group of general formula (II): OH The hydrolyzable tannins, of larger size, for their part correspond to the following general formula: ## STR1 ## in which R 1 and R 2 , different from each other, each represent H or OH. At the origin of the invention, it has been discovered by the present inventors that, surprisingly, a liquid formulation of particular composition, comprising in particular a mixture of hydrolysable tannins and condensed tannins, as well as an additional component, lignin, these components being present in the formulation in precisely defined proportions by weight, makes it possible, after firing, to obtain a thermoset foam having particularly advantageous mechanical properties and properties close to those of polyurethane-based foams. the prior art. This thermoset foam also has fire-retardant properties that are quite interesting.

Lignin, one of the main components of wood, is a macromolecule of complex structure, well known in itself. It has thus been discovered by the present inventors that the combination of this macromolecule lignin, with the tannins, molecules of smaller size, in particular proportions by weight, allows an optimization of the properties of the tannins on the one hand , and lignin on the other hand, by forming networks larger than those formed by the tannins alone, and more interdependent than those that could be formed by lignin alone. The condensed tannins and the hydrolysable tannins having different molecule sizes result from their combined use a high degree of crosslinking, and a crosslinking having a good degree of homogeneity. All of these characteristics give the foam obtained from the liquid formulation according to the invention a particularly high mechanical strength. Thus, according to a first aspect, it is proposed according to the present invention a liquid formulation for the preparation of a tannin thermoset foam, which contains: - a mixture of at least one hydrolysable tannin and at least one condensed tannin, the total amount of tannins in the formulation being from 8 to 60% by weight, based on the total weight of the formulation, of the lignin, in an amount of between 4 and 30% by weight, relative to to the total weight of the formulation, - water, - at least one hardener, - and at least one surfactant.

As stated above, such a liquid formulation provides, after baking, a thermoset foam having particularly advantageous mechanical properties. In particular, with regard to lignin, the weight percentage range according to the invention is, on the one hand, sufficiently large to allow the formation of a long-chain three-dimensional network, and, on the other hand, sufficiently weak. in order not to prevent, by steric hindrance effect, polycondensation reactions occurring between the various monomers such as lignin, condensed tannins and hydrolyzable tannins, and consequently the formation of a network. three-dimensional forming the microstructure of the foam. In combination with this range of wt.% Lignin, the tannin wt.% Range advocated by the present invention is advantageously involved in ensuring proper foam formation, and good mechanical strength of this foam over time. This good mechanical strength of the foam that can be prepared using the liquid formulation according to the invention, which is also accompanied by a good thermal insulation capacity of the foam, is advantageously obtained from non-toxic raw materials. , inexpensive, particularly with regard to lignin, and derived from renewable resources, more particularly wood. These raw materials can come mainly from waste from different industries, such as lignin paper mills or wood-cutting industries for tannins. Water can come from the wood soaking water of some companies. By lignin is meant in the present description both substantially pure lignin, as its derivatives. The lignin may in particular be introduced into the formulation in the form of a salt, or a crude or partially purified extract, containing it in a mixture with other components.

Such an extract can be obtained by any conventional method in itself for the skilled person.

For example, the lignin can be introduced into the formulation in the form of sodium lignosulfonate, which may contain about 29% by weight of lignin, or in the form of a black liquor resulting from the manufacture of kraft paper, which may contain about 36% by weight of lignin. % by weight of lignin.

The lignin, or the composition containing it, used can be both in liquid form and in solid form. The liquid formulation according to the invention may contain a plurality of condensed tannins, and / or a plurality of hydrolysable tannins. These tannins can come from any origin.

They may be obtained from a plant material which contains them, according to any conventional method in itself, in particular according to any method known to those skilled in the art for the extraction of tannins from a plant material. for example the method described in Chupin et al., 2013, Industrial Crops & Products, 49: 897-903.

They may be incorporated in the formulation according to the invention in substantially pure form, or in the form of an extract of plant origin containing them, this extract may be crude or partially purified. For example, the tannins can be introduced into the formulation as plant extracts containing between 75 and 95% by weight of tannins respectively condensed or hydrolyzable. In particular, condensed tannins extracted from mimosa, and / or condensed tannins extracted from maritime pine, in particular from maritime pine bark, may be used in the context of the invention. By way of example, the condensed tannins can thus be introduced into the formulation according to the invention in the form of a mimosa extract containing between 75 and 95% by weight of condensed tannins. The hydrolysable tannins used may for their part for example be from oak and / or chestnut / chestnut.

By way of example, the hydrolysable tannins may be introduced into the formulation according to the invention in the form of a chestnut extract containing approximately 85% by weight of hydrolysable tannins, and / or an oak extract containing approximately 76% by weight of hydrolysable tannins.

The formulation according to the invention may also comprise at least one, preferably a plurality, and preferably still all, of the following component amounts, these amounts being expressed in% by weight, relative to the total weight of the formulation. : 1 to 30% of hydrolysable tannins, 10 to 5 to 40% of condensed tannins, 20 to 75% of water, 0.5 to 10% of hardener (s), that is to say a single hardener or a mixture of hardeners, 1 to 1.5% of surfactant (s), i.e. a single surfactant or a mixture surfactants, where appropriate, 0.5 to 10% of an additive or a mixture of additives. In particular, it has been found by the present inventors that a concentration of hydrolysable tannins greater than 30% by weight has the effect of degrading the mechanical properties of the foam obtained from the liquid formulation according to the invention. A water concentration range of between 20 and 75 ° C. by weight proves particularly advantageous in that it ensures the formation of foam with agitation, and the preservation, ie the absence collapse, this foam when the agitation is stopped.

In particular embodiments of the invention, the liquid formulation according to the invention comprises equal amounts by weight of hydrolyzable tannin (s) and condensed tannin (s). By this is meant that the total amount by weight of condensed tannins forming part of the liquid formulation according to the invention is equal to, or substantially equal to, the uncertainties related to the weighing or the the total amount by weight of hydrolysable tannins entering this constitution. The formulation according to the invention may contain one or more hardeners, also called crosslinking agents, which crosslink the lignin-formed polymer chain, condensed tannins and hydrolyzable tannins, and consequently cure the foam. formed from the liquid formulation according to the invention. In particular embodiments of the invention, the formulation contains a mixture of at least a first hardener and a second hardener, the first hardener and the second hardener having different molecule sizes. Such a characteristic advantageously gives the foam formed mechanical strength properties even better, by induction of a higher degree of crosslinking, and a more homogeneous crosslinking.

The first hardener is preferably included in the formulation according to the invention in an amount of between 0.5 and 10% by weight, preferably between 0.5 and 6% by weight, and preferably between 2 and 3% by weight. , relative to the total weight of the formulation. It can be any conventional type in itself for the formation of thermosetting resins. It may especially consist of an isocyanate or a derivative thereof, formaldehyde or furfuryl alcohol. Compounds devoid of toxicity or at least reduced toxicity, however, are particularly preferred in the context of the invention. Thus, in particular embodiments of the invention, the formulation contains hexamine as a hardener. This compound has the advantage of a good effectiveness of action, while being less toxic than most hardeners usually used for the manufacture of foams, such as formaldehyde or furfuryl alcohol for example. The hexamine is preferably present in the formulation in an amount of from 2 to 3% by weight, based on the total weight of the formulation. In such quantities, it turns out to be devoid of toxicity.

The liquid formulation according to the invention may contain a second hardening agent of different size from that of the first hardener. This second hardener is preferably contained in the formulation according to the invention in an amount of between 0 and 4.5% by weight, preferably between 0 and 3% by weight, relative to the total weight of the formulation. This second hardener may especially be glyoxal, the implementation of which is particularly advantageous when the first hardener is hexamine.

The surfactant may be of any conventional type in itself. By way of examples, mention may be made especially of the surfactants sold under the name Tween® such as Tween® 80, but also other nonionic surfactants, such as Kolliphor® ELP (Aldrich Chemical Company), the others polysorbates (Tween @ 20, Tween @ 21, Tween @ 61 or Tween® 81) (Aldrich Chemical Company), Pluronic® (BASF Corp.), TergitoI0, Bre 98, Brij @ 30 and Triton @ X -100 (Aldrich Chemical Company), and Merpol @ LF (Pont de Nemours and Company); or ionic surfactants, such as sodium dodecyl sulphate. The liquid formulation according to the invention may contain a single surfactant, or a mixture of surfactants, the total concentration of surfactants in the composition preferably being between 1 and 1.5% by weight relative to the total weight of the formulation. The liquid formulation according to the invention may also contain one or more additives, preferably in an amount by weight, for the single additive or for the additive mixture, between 0.5 and 10% of the total weight of the formulation. . Such additives may in particular be chosen for their ability to act on the structural properties (such as density or porosity), on the physicochemical properties and / or on the fire resistance of the foam obtained from the formulation. liquid according to the invention.

As such additives, mention may be made, for example, of wood flour, microcrystalline cellulose, ethylcellulose, nanocellulose, cellulose wadding, fibers of any type, preferably of vegetable type, polyols, triglycerides, polycarboxyls, etc.

The liquid formulation according to the invention preferably comprises at least one, preferably several, and preferably all, of the following component amounts, these amounts being expressed in% by weight, relative to the total weight of the formulation: 10 to 15% hydrolysable tannin (s), 10 to 10% condensed tannin (s), 4 to 25%, preferably 4 to 15%, lignin, 46 to 53 % water, - 2 to 3% of a first hardener, such as hexamine - 1 to 1.5% surfactant, and / or, if appropriate, 2 to 3% of a second hardener, such as glyoxal. According to another aspect, the present invention relates to a thermoset foam that can be obtained by baking a liquid formulation according to the invention, corresponding to one or more of the characteristics described above. This firing is preferably carried out after the liquid formulation has been poured into a mold, the shape of the latter being determined according to the shape of the final article that it is desired to obtain. This foam comprises in particular at least one condensed tannin polymerized with lignin and with at least one hydrolysable tannin.

In preferred embodiments of the invention, the firing is carried out at a temperature between 80 and 100 ° C, in particular about 85 ° C, for a period of time between 5 and 24 hours. This firing step may be followed by a drying step of the foam obtained, for a period of time ranging from 4 to 24 hours, and at a temperature of between 35 and 60 ° C. Thus, the invention is also expressed in the terms of a process for preparing a thermoset foam from a liquid formulation according to the invention, this process comprising, after a preliminary step of stirring the formulation liquid, and a casting step of this liquid formulation in a mold, a firing step, for example in an oven, to cause the curing of the liquid formulation and obtaining a rigid foam according to the invention.

As explained above, the foam obtained has particularly advantageous mechanical characteristics, as well as a high thermal insulation capacity. This foam is mainly open cell. More particularly, this foam may have a cell size of 25 to 500 microns, with an average pore diameter or interconnections of between 4 and 15 microns. Its density can be between 50 and 500 kg / m3, and its porosity can be between 60 and 99%. According to another aspect, the present invention relates to a process for obtaining a liquid formulation according to the invention, corresponding to one or more of the above characteristics. This process comprises the successive stages of: - preparation of a mixture of condensed tannins, hydrolysable tannins, lignin and water, - addition to this mixture of the hardener (s), - stirring of the composition thus obtained, at a first stirring speed, and preferably at a temperature between 40 and 70 ° C, in a step called said first stirring step, - introduction into this composition of the agent (s) 3033171 13 surfactant (S), and stirring of the resulting composition, at a second stirring speed, in a so-called second stirring stage. This second stirring step is preferably carried out at a temperature between 40 and 70 ° C.

Such a process is advantageously energy efficient and simple to implement. The intercalation of the step of introducing the hardener (s) between the step of forming the mixture of tannins, lignin and water, and the step of introducing the agent (s) surfactant (s) is particularly advantageous, in that it ensures the production of a foam. In particular, it has been found by the present inventors that, surprisingly, the introduction of the hardener into the already formed mixture of tannins, lignin and water leads to a thickening of this mixture which proves particularly favorable to obtaining of a foam. Subsequent introduction of the hardener, i.e. at the same time or after the surfactant, does not make it possible to obtain a foam either. In the case where additives must be incorporated in the liquid formulation, this incorporation is preferably carried out after the step of introducing the hardener into the mixture of tannins, lignin and water, and before the step of introducing the surfactant into the composition thus obtained, before or after the first stirring step. In particular embodiments of the invention, the second stirring speed is greater, in particular at least three times greater, than the first stirring speed.

While the first stirring speed is chosen to ensure a good homogenization of the composition obtained after addition of the hardener (s), the second stirring speed, higher, preferably much higher, at the first speed of agitation, advantageously ensures the foaming of the composition.

By way of example, the first stirring step of the composition can be carried out by a blender, and comprise two phases, including a first stirring phase at a speed of about 250 rpm for 5 to 15 minutes, then a second stirring phase at a speed, called the first stirring speed, of about 500 rpm for 5 to 20 minutes. Such characteristics advantageously ensure a good homogenization of the composition. After introduction of the surfactant, the second stirring step may for example be carried out at a speed of about 1800 rpm for 15 to 50 minutes. Such parameters advantageously provide a thickening of the composition, which has the effect of greatly limiting the destabilization of the foam formed before it is cooked. For the final stages of preparation of the thermoset foam, the liquid formulation thus obtained at the end of the second stirring step can be poured into a mold, which can then be placed in an oven for the cooking step. Preferably, these steps are carried out rapidly, for example less than 15 minutes after the liquid formulation according to the invention has been obtained. The characteristics and advantages of the invention will appear more clearly in the light of the following examples of implementation, provided for illustrative purposes only and in no way limitative of the invention, with the support of the single figure, which shows a micrograph, at an 80-fold magnification, of a rigid tannin-based foam according to one embodiment of the invention.

A / Preparation of liquid formulations according to the invention Liquid formulations M1 to M4 according to the invention are prepared by a process according to the invention, as follows. For this purpose, tannins in the form of powder are used. The condensed tannins are mimosa tannins, and are used as an extract containing them at 83% w / w. The hydrolysable tannins are used as a chestnut extract containing them at 85% w / w, or as an oak extract containing them at 76% w / w. The lignin is used as lignin lignosulfonate, containing 29% w / w of lignin.

The formulations contain the amounts of components indicated in Table 1 below: Components M1 M2 M3 M4 Weight (g) /% Weight (g) /% Weight (g) /% Weight (g) /% Mimosa extract 30 / 14,8 30 / 14,7 30 / 13,7 30 / 13,7 Oak extract 30 / 14,8 / 30 / 13,7 / Chestnut extract / 30 / 14,7 / 30 / 13,7 Lignosulfonate 34.60 / 17 34.65 / 17 34.60 / 15.8 34.65 / 15.9 sodium Water 95/47 95 / 46.7 115 / 52.7 115 / 52.6 Hexamine 6/3 6 / 3 6 / 2.7 6 / 2.8 Glyoxal 5 / 2,4 5 / 2,5 / / Tween® 80 2.1 / 1 2.8 / 1.4 2.8 / 1.4 2.8 / 1.3 Table 1 - composition of the formulations M1 to M4 according to the invention The protocol implemented is as follows. In a container are introduced the extract containing the hydrolysable tannins and the extract containing the condensed tannins. Sodium lignosulfonate is then added successively to the vessel, followed by water, followed by hexamine and, if appropriate, lyoxal. The resulting composition is mixed, by means of a conventional mechanical mixer per se, for 10 minutes at 250 rpm and then for 10 minutes at 500 rpm. Tween® 80 (surfactant) is then added to this composition, and the resulting composition is mixed at 1800 rpm for 15 minutes, to obtain liquid formulations M1 to M4 ready for use.

Each of these formulations M1 to M4 is cast in a mold which is heated in an oven at 85 ° C for 24 hours to thermoset the formulation under heat. form of a foam.

At the end of the cooking, the foam obtained is extracted from the mold and dried at 35 ° C. for 4 hours. Each of the foams thus obtained has a residual moisture content of about 10%.

C / Characterization of the Foams Obtained FIG. 1 shows the microstructure of the foam obtained from the formulation M3 according to the invention, which is representative of all the foams obtained. It can be seen that this structure is very close to that of conventional polyurethane type foams.

The properties of the foams were measured by conventional methods in themselves. More specifically, the measurement methods implemented are as follows. C.1 / Measurement Protocols Measurement of cell size A scanning electron microscope (SEM or Hitachi TM-100) was used. For each sample, several photographs were taken at various locations to access 150 different diameters. Measurement of Interconnect Density and Size These measurements were made using a mercury prosimeter. Before introducing the sample into the porosimeter, it is cut and weighed with a precision balance. All removable components of the porosimeter that will be in contact with the sample are further weighed. The obtained data is entered into software which will determine the density of the material. The principle of the porosimeter consists in injecting under pressure a non-wetting liquid, in this case mercury, into the porous network of the sample under vacuum. The mercury penetrates into pores of inlet diameter that are smaller as the pressure exerted is high, according to Laplace's law. This makes it possible to determine the size of the interconnections that connect the cells to each other. Fire test Samples measuring 2 x 2 x 1 cm were placed for 10 20 s in contact with a Bunsen burner flame. The time required for incandescence to cease was then measured. Surface Area Measurement (B ET) BET surface areas were determined with a TriStar® II device. It was first measured the adsorption and desorption of 15 samples. Helium was diffused into the system to obtain an adsorption curve. The glass vial in which the sample was placed was soaked in liquid nitrogen while the measurement was in progress. Desorption was then measured. Surface areas were calculated using appropriate software.

Measurement of Young Modules in Compression This protocol makes it possible to characterize the behavior of a material subjected to a crushing load. The sample (test piece), 20 x 20 x 10 mm in size, was compressed and the deformation under various loads was recorded. The tests were carried out on an Instron universal machine 5969, with a compression speed of 1 mm / min, with a cell of 50 kN. C.2 / Results The results obtained are shown in Table 2 below.

3033171 18 Formulation M1 M2 M3 M4 Density (g / cm3) 0.1721 0.175 0.1477 0.1522 Fire test (min) 4 5.5 3.5 3 Cell size (pm) 115 100 107 96 Size interconnections (μm) 6.7 5.2 8.3 8.5 Surface area (BET) m2 / g 0.5746 0.6279 0.5717 0.3489 Young's modulus (MPa) (compression) 21, 4 22.9 6.3 3.5 Table 2 - characteristics of the foams in accordance with the invention For comparison, rigid foams based on tannins proposed by the prior art were subjected to the same tests. For example, for the tannin-based foams described in the publication of Tondi et al. (2008) Ind. Crops Prod. 29: 356-363, there is obtained, according to the foams, a density of between 0.05 and 0.12 g / cm3, and a Young's modulus of between 0.11 and 0.66 MPa. For the tannin-based foam described in Lacoste et al. (2012) Ind. Crops Prod. 45: 401-405, a density of 0.031 g / cm3 and a Young's modulus of 0.23 MPa are obtained. The foams according to the invention thus prove to be superior to the tannin-based foams proposed by the prior art, and close to conventional polyurethane-based foams in terms of mechanical and thermal properties.

D / Thermal Characterization of Foams Obtained The foams obtained from formulations M1 to M4 were further subjected to thermal characterization experiments. The test protocol was as follows.

The analysis was carried out by means of a thermal conductivity analyzer device and thermal diffusivity Hot Disk, according to the international standard ISO 22007-2, using a transient plane sensor.

The sensor consists of an electrical conductive pattern which is in the form of a double Nickel spiral screen printed on thin sheets of an insulating material (Kapton or Mica). To carry out the measurement of thermal conductivity or thermal diffusivity, the hot-disk probe is placed between two samples of the material to be characterized. For the foams according to the invention, a thermal conductivity of 0.035 to 0.045 W / (m · K) was obtained, which is characteristic of good thermal insulation properties.

Claims (10)

REVENDICATIONS1. Liquid formulation for the preparation of a thermoset foam based on tannins, characterized in that it contains: a mixture of at least one hydrolysable tannin and at least one condensed tannin, the total amount of tannins in said formulation being between 8 and 60% by weight, relative to the total weight of said formulation, - lignin, in an amount of between 4 and 30% by weight, relative to the total weight of said formulation, - water at least one hardener, and at least one surfactant. 2. Formulation according to claim 1, comprising at least one of the following component amounts, said amounts being expressed in% by weight, relative to the total weight of the formulation: 1 to 30% of hydrolysable tannins, 5 to 40% condensed tannins, - 20 to 75% water, - 0.5 to 10% hardener (s), - 1 to 1.5% surfactant (s), - where appropriate, 0 5 to 10% of an additive or a mixture of additives. 3. Formulation according to any one of claims 1 to 2, containing a mixture of at least a first hardener and a second hardener, said first hardener and said second hardener being of different sizes. A formulation according to any one of claims 1 to 3, containing hexamine as a hardener. A formulation according to any one of claims 1 to 4, comprising equal amounts by weight of hydrolyzable tannin (s) and condensed tannin (s). 5 6. Formulation according to any one of claims 1 to 5, comprising at least one of the following component amounts, said amounts being expressed in% by weight, relative to the total weight of the formulation: - 10 to 15% of tannin ( s) hydrolysable (s), 10 - 10 to 15% condensed tannin (s), - 4 to 25% lignin, - 46 to 53% water, - 2 to 3% of a first hardener 1 to 1.5% of surfactant, and / or, if appropriate, 2 to 3% of a second hardener. Thermoset foam obtainable by baking a liquid formulation according to any one of claims 1 to 6. Foam according to claim 7, wherein said baking is carried out at a temperature between 80 and 100 ° C for a period of between 5 and 24 hours. 9. Process for obtaining a liquid formulation according to any one of claims 1 to 6, characterized in that it comprises the successive steps of: - preparation of a mixture of condensed tannins, hydrolysable tannins, lignin and water, adding the hardener (s) to said mixture, stirring the composition thus obtained, at a first stirring rate, preferably at a temperature between 40 and 70 ° C, introducing into said composition the surfactant and stirring the resulting composition at a second stirring speed. 5 10. The method of claim 9, wherein the second stirring rate is greater, especially at least 3 times, at the first stirring speed.