Cellular porous monoliths containing condensed tannins

Abstract

A method for producing polyHIPE porous monoliths, of the polyHIPE type or in the form of a rigid foam, by hardening solutions of condensed tannins in the presence of oil and/or air or in the presence of a non-water-miscible volatile solvent and/or air. Also disclosed is the use of these materials in the areas of catalysis, chromatography, heat and sound insulation, tissue engineering and medication release and as a floral foam.

Claims

1. A process for the production of porous monolithic materials based on condensed tannins, the process comprising the following steps: (a) obtaining a first liquid phase, said first liquid phase being an aqueous solution of condensed tannins; (b) obtaining a second phase, said second phase and air being an oil, a volatile solvent not miscible with water, air, a mixture of oil and air, or a mixture of air and a volatile solvent not miscible with water, and said second phase not being miscible with said first liquid phase, and at least one of said first liquid phase and said second phase comprising a surfactant; (c) dispersing said second phase in said first liquid phase, in the presence of a hardening agent; (d) mixing said first liquid phase and said second phase by stirring until the obtention: (i) of a homogeneous and stable emulsion when said second phase is an oil or a volatile solvent not miscible with water; or (ii) of a mixture which is macroscopically homogeneous but intermediate between an emulsion and a foam when said second phase is a mixture of oil and air or of air and a volatile solvent not miscible with water; or (iii) of a foam when said second phase is air; and (e) either, (i) carrying out the polymerization of the emulsion or of the emulsion-foam intermediate obtained in step (d)(i) or in step (d)(ii) until the obtention of a solid, washing if necessary and drying said solid; or, (ii) carrying out the polymerization and drying said foam obtained in step (d)(iii) wherein the concentration of condensed tannins in the aqueous solution of condensed tannins comprises between 20 and 60% by mass of the total mass of condensed tannins and water in the aqueous solution of condensed tannins.

2. The process for the production of porous monolithic materials according to claim 1, wherein either: (A) said second phase is a vegetable oil or a volatile solvent not miscible with water and, after hardening of the aqueous phase, extraction of the oil when said second phase is vegetable oil, then drying, a polyHIPE is obtained; or (B) said second phase is air and, after hardening of the aqueous phase then drying, a rigid foam is obtained; or (C) said second phase is a mixture of vegetable oil and air or of air and a volatile solvent not miscible with water and, after hardening of the aqueous phase, extraction of the oil when said second phase is vegetable oil, then drying, an aerated material is obtained.

3. The process for the production of porous monolithic materials according to claim 2, wherein the aqueous solution of condensed tannins contains an antifoaming agent.

4. The process for the production of porous monolithic materials according to claim 1, wherein the aqueous pH of the solution of condensed tannins is between 2 and 8.

5. The process for the production of porous monolithic materials according to claim 2, wherein said second phase is a vegetable oil or a volatile solvent not miscible with water, the ratio of oil to aqueous solution of condensed tannins or the ratio of volatile solvent to aqueous solution of condensed tannins is 0.4 to 1 and 4 to 1 by volume.

6. The process for the production of porous monolithic materials according to claim 1, wherein the condensed tannins are selected from the group comprising mimosa, pine or quebracho tannins.

7. The process for the production of porous monolithic materials according to claim 1, wherein the surfactant is a non-ionic surfactant.

8. The process for the production of porous monolithic materials according to claim 1, wherein the hardening agent is selected from the group comprising: aldehydes, compounds capable of decomposing into aldehydes, oxazolidines, nitroparaffins, furfuryl alcohol, and any combination of these hardening agents with one another in any proportions.

9. A process for the production of porous monolithic materials based on condensed tannins, the process comprising the following steps: (a) preparing a first aqueous solution of condensed tannins in water, and optionally adding an antifoaming agent to prepare a polyHIPE, wherein the concentration of condensed tannins in the first aqueous solution of condensed tannins comprises between 20 and 60% by mass of the total mass of condensed tannins and water in the first aqueous solution of condensed tannins; (b) adjusting the pH of the first aqueous solution of condensed tannins to a value between 2 and 8 to obtain a second solution; (c) stirring the second solution at a speed between 200 and 2000 rpm until the obtention of a homogeneous solution; (d) adding a surfactant and maintaining under stirring at a speed between 200 and 2000 rpm until the obtention of another homogeneous solution; (e) incorporating the vegetable oil dropwise into the homogeneous solution obtained in step (d), while maintaining stirring at a speed between 200 and 2000 rpm until the obtention of a stable and homogeneous emulsion; (f) incorporating a hardening agent halfway through step (e) and continuing stirring; (g) carrying out polymerization at a temperature greater than ambient temperature of between 40 and 90 C., until the obtention of a solid emulsion; (h) washing the solid emulsion obtained in the previous step with an organic solvent to obtain a polyHIPE or a polyHIPE-type monolith; and (i) drying the polyHIPE or polyHIPE-type monolith.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is illustrated by the following Examples 1 to 9 and FIGS. 1 to 22.

(2) In the following figures, the total intrusion volume of the monoliths and the specific surface area of the monoliths are measured by mercury intrusion up to a pressure of 4 MPa. The median diameter of the pores of the monoliths is determined by mercury intrusion as the pore diameter at which 50% of the total porous volume is filled by the mercury and the average diameter of the cells of the monoliths is determined from electron micrographs.

(3) FIG. 1 summarizes the properties of polyHIPE monoliths prepared from a solution of mimosa tannin at pH 2.5 and variable concentrations of sunflower oil according to Example 1. F45A: 45 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F75A: 75 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F105A: 105 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin).

(4) FIG. 2 shows scanning electron micrographs, at 2 different magnifications, of the monoliths described in FIG. 1.

(5) FIG. 3 summarizes the properties of polyHIPE monoliths prepared from a solution of mimosa tannin at pH 6 and variable concentrations of sunflower oil according to Example 1. F45B: 45 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F75B: 75 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F105B: 105 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin).

(6) FIG. 4 summarizes the properties of polyHIPE-type aerated monoliths prepared from a solution of mimosa tannin at pH 4 and variable concentrations of sunflower oil according to Example 2. F30-4-2k: 30 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F60-4-2k: 60 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F90-4-2k: 90 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin).

(7) FIG. 5 shows scanning electron micrographs, at 2 different magnifications, of the monoliths described in FIG. 4.

(8) FIG. 6 summarizes the properties of polyHIPE-type aerated monoliths prepared from a solution of mimosa tannin at pH 6 and variable concentrations of sunflower oil according to Example 2. F30-6-2k: 30 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F60-6-2k: 60 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F90-6-2k: 90 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin).

(9) FIG. 7 summarizes the properties of polyHIPE-type aerated monoliths prepared from a solution of mimosa tannin at pH 8 and variable concentrations of sunflower oil according to Example 2. F30-8-2k: 30 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F60-8-2k: 60 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F90-8-2k: 90 ml of sunflower oil/40 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin).

(10) FIG. 8 summarizes the properties of foam type monoliths prepared from a solution of mimosa tannin at pH 2.8 and at variable concentrations according to Example 3. F20-40: 30 ml of 20% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F40-40: 30 ml of 40% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin); F50-40: 30 ml of 50% by mass solution of mimosa tannin with respect to the total mass (water+mimosa tannin).

(11) FIG. 9 shows scanning electron micrographs of the monoliths described in FIG. 8.

(12) FIG. 10 summarizes the properties of the porous carbonized monoliths CF45A, CF75A and CF105A prepared according to Example 4, from F45A, F75A and F105A of Example 1 respectively.

(13) FIG. 11A shows the porous monoliths before carbonization (on the left F60-4-2k and on the right F30-4-2k) and FIG. 11B, the corresponding porous carbonized monoliths (on the left CF60-4-2k and on the right CF30-4-2k), obtained according to Example 4 from F60-4-2k and F30-4-2k of Example 2.

(14) FIG. 12 summarizes the properties of the porous carbonized monoliths CF30-6-2k, CF60-6-2k and CF90-6-2k prepared according to Example 4, from F30-6-2k, F60-6-2k and F90-6-2k of Example 2 respectively.

(15) FIG. 13 shows the three types of organic materials originating from mimosa tannin (hence not carbonized) obtained according to the processes of the invention: on the left porous polyHIPE monolith, F75A, obtained according to Example 1, from an emulsion of an aqueous solution of mimosa tannin with sunflower oil (porosity about 88%), in the center porous polyHIPE-type monolith polyHIPE, F60-4-2k, obtained according to Example 2, from an emulsion based on an aqueous solution of mimosa tannin and sunflower oil, into which air has been mechanically incorporated (porosity about 94%), and on the right porous foam-type monolith, F40-40, obtained according to Example 3 from a liquid foam formed from an aqueous solution of mimosa tannin and air (porosity about 97%).

(16) FIG. 14 summarizes the properties of the cellular polyHIPE monoliths prepared according to Example 5. TC monolith prepared with cyclohexane as the second liquid phase; TH monolith prepared with sunflower oil as the second liquid phase.

(17) FIG. 15 shows the three types of cellular polyHIPE monoliths prepared according to Example 5. Cyclohexane: monolith prepared with cyclohexane as the second liquid phase; Heptane: monolith prepared with heptane as the second liquid phase; Sunflower oil: monolith prepared with sunflower oil as the second liquid phase.

(18) FIG. 16 summarizes the properties of the foam-type monoliths prepared according to Example 6 utilizing Tween 80 as the surfactant.

(19) FIG. 17 shows two types of foam-type monoliths prepared according to Example 6. Pluronic 6800: foam prepared with Pluronic 6800 as the surfactant and Tween 80: foam prepared with Tween 80 as the surfactant.

(20) FIG. 18 shows five types of cellular polyHIPE monolith prepared according to Example 7 obtained from formulations containing different concentrations of hardening agent.

(21) FIG. 19 summarizes the properties of the cellular polyHIPE monoliths prepared according to Example 8 utilizing Triton X 100 as the surfactant.

(22) FIG. 20 shows three types of cellular polyHIPE monoliths prepared according to Example 8 obtained from formulations containing different types of surfactants: Tween 80, Triton X100 and Cremophor ELP.

(23) FIG. 21 summarizes the properties of the cellular polyHIPE monoliths prepared according to Example 9; TFA2: surfactant Cremophor ELP 2% with respect to the total mass of the solution and TFA2G: influence of ethylene glycol at a concentration of 5% with respect to the total mass of the solution.

(24) FIG. 22 shows five types of cellular polyHIPE monoliths prepared according to Example 9 obtained from formulations containing furfuryl alcohol as the hardening agent and different quantities of surfactant (2, 4, 6, 8 and 10% of Cremophor ELP with respect to the total mass of the solution).

DETAILED DESCRIPTION

Example 1: Porous polyHIPE Monoliths Prepared from Emulsion: Sunflower Oil/Water, without Air

(25) 1.1. Procedure

(26) Reagents utilized:

(27) commercial mimosa tannin utilized as is water hardening agent: 30% by mass aqueous solution of hexamethylenetetramine (hexamine) Surfactant: Cremophor ELP (ethoxylated castor oil) Sunflower oil 2M sodium hydroxide or para-toluenesulfonic acid (PTSA) in powder form

(28) Monoliths are prepared from the following emulsions:

(29) TABLE-US-00001 F75A reference Emulsion F45A solution F105A Tannin Tannin (g) 20 20 20 solution Water (g) 30 30 30 Tannin/(water + 40 40 40 tannin) (%) Surfactant (g) 1.33 1.33 1.33 Surfactant/(water + 2.6 2.6 2.6 tannin) (%) pH of tannin solution 2.5 2.5 2.5 Tannin/oil (mL/mL) 40/45 40/75 40/105 Speed of rotation (rpm) 250 250 250

(30) The different steps are as follows:

(31) 1.sup.st StepPreparation of the Solution of Mimosa Tannin

(32) A solution of mimosa tannin is prepared by adding the mimosa tannin to water. The pH of the solution is adjusted with 2M sodium hydroxide or para-toluenesulfonic acid (PTSA). The mixture is mechanically stirred at 250 rpm for 10 minutes with a propeller stirrer equipped with a 3-blade propeller in order to obtain a very homogeneous solution.

(33) 2.sup.nd StepAddition of the Surfactant

(34) The surfactant is added to the solution of mimosa tannin obtained in the previous step and the mixture stirred at 250 rpm for 20 minutes; a homogeneous brown solution is obtained.

(35) 3.sup.rd StepAddition of the Sunflower Oil

(36) The sunflower oil is added dropwise, with stirring at 250 rpm, at the rate of 44 drops/min. While the oil is being added, 4.47 g of the hexamine solution is also added to the mixture. During the addition of the hexamine, the stirring speed is temporarily increased to 900 rpm for about 30 secs in order to facilitate the dissolution of the hexamine, then returned to 250 rpm.

(37) 4.sup.th StepHeating of the Mixture

(38) The vessel containing the mixture obtained in the previous step is covered with a plastic film or an aluminum film in order to avoid the emulsion drying on the surface, and placed in a ventilated oven at 85 C. for 20 hours. The gelling is very rapid, about 15 minutes for all the formulations. However, 20 hours at 85 C. are necessary to have complete crosslinking reactions and obtain totally hardened monoliths.

(39) 5.sup.th StepWashing of the Samples in Acetone

(40) After heating for 20 hours, the hardened monoliths are removed from the oven and allowed to cool to ambient temperature. The monoliths are next cut into cylindrical shape, placed in a Soxhlet extractor then washed with hot acetone under reflux for 7 days.

(41) 6.sup.th StepDrying of the Samples

(42) After washing for 7 days, the samples are dried at ambient temperature for 7 days.

(43) 7.sup.th StepMeasurement of Physical Properties of the Samples

(44) These properties are measured by techniques known to a person skilled in the art.

(45) 1.2. Results

(46) These are given in the tables in FIGS. 1 and 3 and in FIG. 2 for monoliths prepared from a solution of mimosa tannin with 20 g of mimosa tannin in 30 g water. On the basis of FIGS. 1 to 3, it can be observed that: the porosity of the monoliths is very high, of the order of 90%, which is remarkable for this type of material, the porosity increases with the fraction of sunflower oil incorporated in the emulsion, but without proportionality. This is a common property of the polyHIPEs which is explained on the one hand by the shrinkage of the materials during the hardening and drying phases, and on the other by the change in emulsion type: from oil-in-water to water-in-oil when the volume fraction of oil increases, the inversion of the emulsion is observed when the images of the materials F45A and F105A are compared. F45A shows the cellular structure typical of a polyHIPE, i.e. displays a continuous solid phase having rather spherical cells, connected to one another by rather circular apertures. The strands, of triangular cross-section, are solid. The porous structure is thus hierarchical: cellular on the macroscopic scale, with much narrower and very numerous interconnections in the walls of the cells. F105 also has a cellular structure, but based on a stack of hollow spheres in which apertures are opened. The strands, of triangular cross-section, are hollow. F75A also shows this type of structure, the average diameters of the cells and the connections (the pores) vary in a complex manner with the total porosity, in conjunction with the changes in structure observed by electron microscopy. These changes are explained by: (i) the inversion of the emulsion beyond a critical quantity of sunflower oil; (ii) the competition between porosity created by the sunflower oil and lost due to shrinkage in the course of the process; (iii) the fact that the level of surfactant remained constant in these Example, in spite of very different fractions of sunflower oil in the emulsion, consequently, for the single examples given here, the mechanical properties do not display a regular trend. They are remarkably high, considering the corresponding total porosity values.

Example 2: Porous Aerated polyHIPE-Type Monoliths Prepared from Emulsion: Sunflower Oil and Air/Water

(47) 2.1 Procedure

(48) Monoliths are prepared from the following emulsions:

(49) TABLE-US-00002 Emulsion F30- F30- F30- F60- F60- F60- F90- F90- F90- 4-2k 6-2k 8-2k 4-2k 6-2k 8-2k 4-2k 6-2k 8-2k Tannin Tannin (g) 30 30 30 solution Water (g) 20 20 20 Tannin/(water + 15 15 15 tannin) (%) Surfactant (g) 2.33 2.33 2.33 Surfactant/(water + 4.6 4.6 4.6 tannin) (%) ph of tannin solution 4 6 8 4 6 8 4 6 8 Tannin/oil (mL/mL) 40/30 40/60 40/90 Speed of rotation (rpm) 2000 2000 2000

(50) The different steps are as follows:

(51) 20 g of water, 30, 40 or 60 mL of sunflower oil, 4.47 g of the aqueous solution of hexamine, 1.3 g of surfactant and sodium hydroxide (quantity necessary to have a pH of 4, 6 or 8) are mixed at 2000 rpm until a white, stable and homogeneous emulsion is obtained. 30 g of mimosa tannin is added and the mixture is stirred for 45 minutes at 2000 rpm.

(52) The hardening, washing and drying are carried out under the same conditions as for steps 4 to 6 of Example 1.

(53) 2.2 Results

(54) These are given in the tables in FIGS. 4, 6 and 7, and in FIG. 5. Because of the air incorporated during preparation, a dome appears on the surface of the samples, a dome which does not appear in the monoliths prepared according to Example 1. On the basis of FIGS. 4 to 7, it can be observed that: as could have been expected, the porosity is higher (i.e. the apparent density is much lower) than that of the corresponding polyHIPEs prepared with comparable mimosa tannin/sunflower oil proportions. This is explained by the presence of air incorporated into the structure during the mechanical stirring, this air makes it possible to obtain porous monolithic materials of different structure from that of the previous polyHIPEs at constant proportions of sunflower oil/aqueous solution of mimosa tannin. Conversely, structures qualitatively similar (cellular) to the previous polyHIPEs can be observed for different initial compositions. However, the cells then have much greater average diameters in the presence of air (compare the series F45A-F105A with the series F30-4-2K-F90-4-2K using the same magnification: that for which the scale bar is 1 mm), consequently, the incorporation of air via more or less vigorous stirring of the phases present makes it possible to vary the average diameter of the cells considerably, which is not enabled by the variation of only one of the parameters of the formulation at a time, the porosity decreases when the proportion of oil in the emulsion increases. This result, unexpected a priori but well verified in all cases, shows that air is much easier to incorporate into an emulsion less rich in sunflower oil, and that it then more easily contributes to the creation of porosity than does the sunflower oil, the mechanical properties remain high considering the porosity present, and increase steadily as the porosity decreases. This result is to be expected since the porous structure does not change when the porosity varies, consequently, the pores are consistently wider when the porosity increases. This trend is seen more clearly from the mercury porosimetry results than on the micrographs.

Example 3: Porous Monoliths Prepared from Foams

(55) 3.1. Procedure

(56) Monoliths are prepared as follows. An aqueous solution of mimosa tannin the concentration of which is 20, 40 or 50% of the total mass (mimosa tannin+water) is prepared by mixing 7.5, 20 or 30 g of mimosa tannin, respectively, with 30 g of water. This solution is then mixed with PTSA, in sufficient quantity to reach pH 2.8, for 10 minutes at 500 rpm. At the end of this period, the surfactant is added and all the ingredients are mixed at 2000 rpm until the obtention of a homogeneous foam, without any condensed liquid phase remaining, namely 40 mins. After half the time, 4.7 g of 30% hexamine solution is added. The foam obtained is covered with a film and placed in a ventilated oven at 85 C. for 24 hrs. Next the samples are cut up and placed in a room at ambient temperature to dry in air for several days or in the same ventilated oven for a few hours. The table below summarizes the ingredients and the preparation conditions.

(57) TABLE-US-00003 Liquid foam F20-40 F40-40 F50-40 Tannin Tannin (g) 7.5 20 30 solution Water (g) 30 30 30 tannin/(water + 20 40 50 tannin) (%) PTSA (g) 1.12 1.12 1.12 Surfactant (g) 2.25 3 3.6 Surfactant/(water + 6 6 6 tannin) (%) pH of the tannin solution 2.8 2.8 2.8 Stirring time (mins) 40 40 40 Speed of rotation (rpm) 2000 2000 2000

(58) 3.2. Results

(59) These are given in the table in FIG. 8, and in FIG. 9. On the basis of FIGS. 8 and 9, it can be observed that: the porous structure is rather different from that of the materials of the previous Examples 1 and 2. The structure is in fact that of a crosslinked foam, the materials obtained according to the variants of the process according to Examples 1 or 2 being more cellular, thus, the connections between cells are not as multiple as previously, since they essentially correspond to the walls of the cells which existed in the liquid foam. From that structure, the solid foam has only retained the intersections of the bubble walls, in other words the strands. This is further confirmed by the specific surface area, much lower for the foams than for the other monoliths of equivalent porosity, the density differences become apparent in these foams by considerable changes both in the thickness of the solid phase (the strands) and the diameter of the empty spaces, it is much easier by this method (without oil) to obtain very wide porosity (the scale bar here is 2 mm as against 1 mm in the previous photos) and hence greater porosity, the porosity is readily modifiable by changing the concentration of the tannin solution, as illustrated, or by changing the nature of the surfactant, at comparable total porosity, the mechanical properties of the foams are inferior to those of the polyHIPE or polyHIPE-type monoliths. As suggested above, this is explained by the different pore structure, which is much more open in the case of the foams.

Example 4: Preparation of Porous Carbonized Monoliths

(60) 4.1. Procedure

(61) The monoliths obtained with the emulsions F45A, F75A and F105A of Example 1 and the monoliths obtained with the emulsions F30-6-2k, F60-6-2k and F90-6-2k of Example 2 are utilized

(62) The carbonization of the samples is carried out in a horizontal tubular furnace at 900 C. for 2 hrs under a nitrogen atmosphere (5 C./min-50 mL/min).

(63) 4.2. Results

(64) These are given in the tables in FIGS. 10 and 12 and in FIG. 11. On the basis of FIGS. 10 to 12, it can be observed that the samples withstand the heat treatment very well, and the porous carbons obtained have a structure identical to that of the original monoliths. They are free from cracks, the variation in the porosity follows exactly the same trends as those for the precursor organic materials, within experimental error (in particular at very high porosities, >95%), the porosity of the carbonized materials is greater than that of the organic precursors, the pyrolysis having resulted in a loss in mass and a comparable shrinkage in size (about 60%), the apparent density of the carbonized materials changes little with respect to that of the organic precursors, within individual variations in samples (a large number of samples is necessary to observe it, on account of the experimental scatter of the data), owing to the shrinkage, the pores and the cells are always smaller in the carbonized materials, the loss of gas which accompanies the pyrolysis produces very fine pores which have the effect that the specific surface area of the carbonized materials is always greater than that of their organic equivalents, the mechanical properties are considerably increased after pyrolysis.

Example 5: Process for the Preparation of Cellular polyHIPE Monoliths Utilizing a Volatile Solvent not Miscible with Water as the Second Liquid Phase and a Hardening Agent in Powder Form Rather than in Solution

(65) 5.1. Procedure

(66) a. 20 g of mimosa tannin, 1.9 g of hexamethylenetetramine (HMT) powder and 6 drops of antifoaming agent (polydimethylsiloxane) are dissolved in 33.9 g of distilled water, then 0.7 g of solid para-toluenesulfonic acid (PTSA) are added to adjust the pH of the solution to 2.5. The mass fraction of the solids with respect to water is thus 40%. The mixture is stirred for 10 minutes with a paddle stirrer rotating at 500 rpm in order to obtain a very homogeneous solution.

(67) b. 2.97 g of surfactant is added to the solution obtained in step a) (Cremophor ELP=5% with respect to the total mass of said solution) and the mixture is stirred for 10 minutes with a paddle stirrer rotating at 500 rpm in order to obtain a very homogeneous solution (and without bubbles, owing to the presence of antifoaming agent).

(68) c. The speed of rotation of the stirrer blades is increased to 1000 rpm and 150 mL of the second liquid phase (not miscible with the first), cyclohexane or heptane, are incorporated very gradually (usually 44 drops/minute).

(69) d. The emulsion obtained is poured into a container that closes hermetically in order to avoid evaporation of the volatile solvents utilized and placed in an oven at 70 C. for 24 hrs. Gelling takes place in 40-45 minutes, and good hardening of the material and better mechanical properties after drying are obtained after 24 hrs.

(70) e. When the second liquid phase is cyclohexane or heptane, no washing in a Soxhlet is necessary to develop the porosity, contrary to the case with oil. In the presence of cyclohexane or heptane, a simple drying in air for 3-4 days is sufficient to obtain a dry and highly porous polyHIPE.

(71) After drying in air for 3-4 days, a dry and highly porous polyHIPE is obtained.

(72) A cellular polyHIPE monolith is prepared in the same manner with sunflower oil as the second liquid phase.

(73) The preparation conditions are summarized in the table below for two materials prepared under strictly identical conditions according to the protocol described above, with the only difference that the first (TC) was prepared with cyclohexane as the second liquid phase, and the second (TH) for comparison with sunflower oil as the second liquid phase.

(74) TABLE-US-00004 Sample TC TH Mass fraction of solids (%) 40 40 Mass fraction of surfactant (%) 5 5 Volume fraction of second phase (%) 75 75 Initial pH 2.5 2.5 Speed of rotation in step b) 500 500 Speed of rotation in step c) 1000 1000

(75) 5.2. Results

(76) These are given in FIGS. 14 and 15.

(77) The properties of the two materials (TC) and (TH) thus prepared are given in the table in FIG. 14 and in FIG. 15.

(78) The materials prepared with the volatile solvent instead of the oily phase are shorter in length and thus simpler to prepare, and have a porosity which is both more developed and narrower. These are excellent thermal insulators. The mechanical properties are not appreciably different from those of their equivalents prepared with oil.

(79) With heptane as the second phase, a material with very similar properties is obtained (FIG. 15).

Example 6: Process for the Preparation of Foam Type Cellular Monoliths Utilizing Air and Different Types of Surfactants as the Second Phase

(80) 6.1. Procedure

(81) The preparation is carried out according to the method described in Example 3 with a tannin/(water+tannin) ratio=40% by mass. The only difference comes from the utilization of hexamethylenetetramine (or hexamine or HMT) in powder form rather than in solution.

(82) Different surfactants are utilized: Tween 80 (polyoxyethylene (20) sorbitan monooleate), Pluronic P-123 (poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol)) and Pluronic 6800 (ethylene glycol propylene glycol adipate).

(83) The conditions for the preparation of the formulation utilizing Tween 80 are given below:

(84) TABLE-US-00005 Tannin Tannin (g) 20 solution Water (g) 30 tannin/(water + 40 tannin) (%) PTSA (g) 1.12 Surfactant (g) 3 Surfactant/(water + 6 tannin) (%) Initial pH of tannin solution 2.8 Stirring time (mins) 40 Speed of rotation (rpm) 2000

(85) For the other formulations, the preparation conditions are identical.

(86) 6.2. Results

(87) These are given in FIGS. 16 and 17.

(88) The properties of the material obtained from the formulation utilizing Tween 80 are directly comparable to those of the material F40-40 of Example 3 illustrated in FIG. 8, which was prepared from a formulation in which the surfactant is Cremophor ELP (FIG. 16). Compared to that prepared with Cremophor ELP, the material obtained from the formulation utilizing Tween 80 appears more homogenous and visibly shows cells of smaller sizes. This feature explains the fact that at equivalent porosity the material prepared with Tween 80 has much better mechanical properties than those of the sample F40-40.

(89) The material obtained from the formulation utilizing Pluronic 6800 likewise shows very good macroscopic properties (FIG. 17).

Example 7: Process for the Preparation of Cellular polyHIPE Monoliths, Utilizing Vegetable Oil as the Second Phase, and Different Quantities of Hardening Agent in Powder Form

(90) 7.1 Procedure

(91) The purpose being to examine the effect of the quantity of hardening agent (hexamethylenetetramine: HMT) on the properties of the final products, the preparation protocol is identical to that of Example 5 apart from the following exceptions: the quantities of water and surfactant are slightly modified so as to maintain the mass fractions of solids and surfactant constant at 40% and 5% respectively; there is no antifoaming agent added and for that reason the stirring speed of the stirrer blades is limited to 250 rpm during the whole process.

(92) The formulations utilizing different quantities of HMT are therefore as follows:

(93) TABLE-US-00006 Name of material TH07 TH14 TH19 TH24 TH29 Tannin (g) 20 20 20 20 20 Water (g) 32.1 33.17 33.9 34.65 35.4 PTSA (g) 0.7 0.7 0.7 0.7 0.7 HMT (g) 0.7 1.4 1.9 2.4 2.9 Cremophor ELP (g) 2.82 2.9 2.97 3.04 3.11 Sunflower oil (mL) 150 150 150 150 150

(94) 7.2 Results

(95) These are given in FIG. 18.

(96) The sample TH19 is that which displays the most homogenous structure and the best macroscopic properties.

(97) The sample TH07 is multiply fissured and its pore structure is completely disordered and poorly defined.

(98) The material TH29 could not be prepared as it is impossible to obtain the initial emulsion because of hardening that is much too rapid.

(99) The samples TH14 and TH24 are rather similar, but less homogeneous than TH19, which is thus the best compromise.

Example 8: Process for the Preparation of Cellular polyHIPE Monoliths, Utilizing Vegetable Oil as the Second Phase and Different Types of Surfactant

(100) 8.1. Procedure

(101) The purpose being to examine the effect of the nature of the surfactant on the properties of the final products, the preparation protocol is identical to that of Example 5, apart from the following exceptions: the quantity of surfactant introduced in step b) is 1.8 g; in step c), the stirring speed is 1500 rpm and the quantity of sunflower oil is 80 mL.

(102) The following different surfactants were then tested: Pluronic 7400 (BASF), Triton X100 (Prolabo), Pluronic 6800 (BASF), TWEEN 80 (Sigma Aldrich), Pluronic 123 (Sigma Aldrich), Pluronic 127 (Sigma Aldrich) and Cremophor ELP (Sigma Aldrich).

(103) The conditions for the preparation of the different formulations are given in the table below:

(104) TABLE-US-00007 Sample Surfactant Mass fraction of solids (%) 40 Mass fraction of surfactant (%) 3 Volume fraction of second phase (%) 67 Initial pH 2.5 Speed of rotation in step b) 500 Speed of rotation in step c) 1500

(105) 8.2. Results

(106) These are given in FIGS. 19 and 20.

(107) The following observations can be made:

(108) i. Pluronic 7400 (BASF): good emulsion, of very suitable viscosity, difficult to use at low stirring speed (hence need to stir at 1500 rpm), possible polyHIPE.

(109) ii. Triton X100 (Prolabo): excellent emulsion even at low stirring speed, excellent final polyHIPE.

(110) iii. Pluronic 6800 (BASF): good emulsion provided that stirring is fast enough, good final polyHIPE.

(111) iv. TWEEN 80 (Sigma Aldrich): emulsion of lower viscosity than with Cremophor ELP, but of good quality and homogeneous even at low stirring speed, excellent final polyHIPE.

(112) v. Pluronic 123 (Sigma Aldrich): fine emulsion, easy to mix, good final polyHIPE.

(113) vi. Pluronic 127 (Sigma Aldrich): fine emulsion but only after mixing at high speed, long and difficult as Pluronic 127 is of low solubility, good final polyHIPE.

(114) vii. Cremophor ELP (Sigma Aldrich): perfect under almost all conditions.

(115) Compared to its equivalent prepared with Cremophor ELP, the material which was prepared on the basis of Triton X100 is more porous, and the porosity is constituted by finer pores. This results in mechanical properties superior to those of the material prepared with Cremophor ELP under the same conditions.

(116) The material obtained from the formulation utilizing Tween 80 likewise shows good macroscopic properties (FIG. 20).

Example 9: Process for the Preparation of Cellular polyHIPE Monoliths Utilizing Vegetable Oil as the Second Phase, a Mixture of HMT and Furfuryl Alcohol as the Hardening Agent and Different Quantities of Cremophor ELP as the Surfactant

(117) 9.1. Procedure

(118) Furfuryl alcohol at constant concentration was utilized as the hardening agent, in addition to HMT, and different quantities of the surfactant Cremophor ELP were utilized.

(119) The preparation protocol is identical to that of Example 5, apart from the following exceptions: 5 g of furfuryl alcohol were added in addition to the ingredients already described in step a); antifoaming agent was not added, as the presence of furfuryl alcohol visibly limited the aeration of the solution during the mixing; the quantity of Cremophor ELP was varied in the range 2-10% with respect to the total mass of solution; the oven temperature in step d) is 85 C.; in step e), a step of oil extraction with acetone using the Soxhlet for 7 days is added before the drying step at ambient temperature. It should be noted that during the drying step cracks can occur in the monoliths. This cracking can be markedly limited by addition of 5% by mass (with respect to the total mass of solution) of ethylene glycol or 5-10% by mass (with respect to the total mass of solution) of glycerol to the formulation.

(120) The formulations are therefore as follows:

(121) TABLE-US-00008 Name of material TFA2 TFA4 TFA6 TFA8 TFA10 Tannin (g) 20 20 20 20 20 Furfuryl alcohol (g) 5 5 5 5 5 Water (g) 33.9 33.9 33.9 33.9 33.9 PTSA (g) 0.7 0.7 0.7 0.7 0.7 HMT (g) 1.9 1.9 1.9 1.9 1.9 Cremophor ELP (g) 1.15 2.35 3.6 4.91 6.28 Sunflower oil (mL) 150 150 150 150 150

(122) For the two polyHIPEs obtained under the conditions described above with 1.15 g of Cremophor ELP, namely 2% by mass, one (TFA2) not containing ethylene glycol and the other (TFA2EG) containing 5% thereof by mass (with respect to the total mass of solution), the formulation conditions are as follows:

(123) TABLE-US-00009 Sample TFA2 TFA2EG Mass fraction of solids (%) 40 40 Mass fraction of surfactant (%) 2.0 2.0 Volume fraction of second phase (%) 75 75 Mass fraction of ethylene glycol (%) 0 5 Initial pH 2.5 2.5 Speed of rotation in step b) 500 500 Speed of rotation in step c) 1000 1000

(124) 9.2. Results:

(125) These are given in FIGS. 21 and 22.

(126) The best surfactant concentration range is 2-6% by mass. The monoliths prepared with higher percentages (8 and 10%) tend to crumble during the oil extraction step using a Soxhlet, but also during the subsequent drying; these materials are actually very friable. Those prepared with the lowest surfactant contents are more stable and more homogeneous.

(127) The presence of a little ethylene glycol does not significantly change the results, whether the porosity or the resulting physical properties. On the other hand, the resistance to cracking is very good.

(128) The material TFA2 can be compared to the monolith F75A of Example 1 (see FIGS. 1 and 13). Addition of 2% of Cremophor ELP instead of 5% gives a material with more extensive porosity, and thus having somewhat inferior mechanical properties, and the pores of which are somewhat wider.

(129) The results of the Examples show that: all pHs between 2 and 8 can be used, giving materials with different structural and mechanical properties, water-in-oil and oil-in-water emulsions alike (the transition from the first to the second occurs by increasing the proportion of oil, but without changing the preparation protocol) give porous monolithic materials with different pore structures, all the other parameters of the formulation, without exception, play a part in the adjustment of the porosity in terms of pore volumes, cell diameters and connections between cells, pore connectivity and the resulting physical properties. From this point of view, the nature of the surfactant has a particularly significant effect, thus, on the basis of the processes described, any type of pore structure is henceforth accessible, which is novel for materials originating from tannins: from crosslinked structures to cellular structures, passing via stacks of connected hollow spheres, the ranges of apparent densities (and therefore porosities) accessible are the widest ever attained for porous monoliths originating from tannins, the derived materials, in particular of carbon, retain the same structure and have similar density, while displaying narrower porosity and mechanical properties superior to those of their organic equivalents.