Process for extracting a phenolic fraction from cork, and use of this fraction in intumescent compositions

Abstract

A process for extracting a fraction of phenolic compounds from cork, comprising a step of contacting a solid phase, which is formed by cork granules and / or powder, with a pressurized liquid phase in a chamber, said liquid phase comprising at least 80% by mass of water and at most 20% by mass of ethanol, said process being characterized in that the water temperature is between approximately 70°C and approximately 100°C, and in that the pressure is at least 30 bar. Figure for the abstract: [Fig. 1].

Description

Title of the invention: Process for extracting a phenolic fraction from cork, and use of this fraction in intumescent compositions. Technical field

[0001] The invention relates to the field of physical or chemical treatment of cork, and more particularly to the field of extracting organic molecules contained in cork using a solvent. The extraction relates to a process for extracting a phenolic fraction from granulated cork. It also relates to the use of this phenolic fraction in intumescent compositions, which can be applied to a material surface to protect it against fire, by releasing gases that protect the layer against ignition, and subsequently forming a passive barrier with low thermal conductivity.

[0002] The invention relates in particular to cork from the plant variety Quercus suber L. State of the art

[0003] The cork oak is found mainly in Southern Europe and around the Mediterranean Sea (Portugal, Spain, Italy, France, Algeria, Morocco, Tunisia). It is essentially the variety Quercus suber L. The cork oak is cultivated and harvested industrially to obtain its outer bark layer, cork, which has several industrial uses.

[0004] Furthermore, for quality reasons, the cork industry uses only a portion of the harvested or harvestable bark, which must conform to a set of specifications. For example, the cork used for the manufacture of stoppers and solid cork products, which are relatively high value-added products, typically comes from trees that have already undergone a first and second stripping, whereas the cork from the first two strippings (including virgin cork, from the first stripping) is typically used, after being reduced to granules, in the manufacture of sheets and panels for the construction sector; these represent relatively low value-added products. The cork industry also generates cork waste. This surplus or waste is generally burned, ideally in order to recover at least its calorific value.

[0005] It would be desirable to find new markets for cork, given that the tree thrives in poor soils and is quite resistant to drought and fire. There are also wild cork oak forests that are not currently being exploited due to the lack of a local cork processing industry.

[0006] Cork is composed essentially of suberin, a lipid macromolecule, lignin, a polyphenolic macromolecule, and various polysaccharides (including cellulose), and also contains a significant amount of organic compounds that can be extracted using a suitable solvent and under appropriate conditions. The mass fraction of extractable chemical compounds is typically around 15%; it depends on the geographical origin of the cork, as does its chemical composition. Depending on the extraction conditions, some of the biological macromolecules that constitute cork may undergo partial hydrolysis, which can lead to an increase in the extractable fraction.

[0007] The extraction of extractable organic compounds has been studied primarily from two perspectives: firstly, some of these compounds are likely to migrate into food liquids in contact with a cork stopper, where they can alter the taste or odor; it would be desirable to be able to extract them before using the cork stopper to seal a bottle of food liquid. The molecules of interest, especially for use with wine, include methyl isobomeol and its derivatives, geosmin, methylthioethylpyrazine, C8 unsaturated alcohols and ketones, and especially chloroanisoles, and more particularly trichloroanisole and tetrachloroanisole.

[0008] Secondly, consideration has been given to extracting these compounds in order to valorize them, but this is not exploited on an industrial basis, despite numerous published research works.

[0009] An industrial process used to extract the molecules that denature wine is the Champcork process which consists of placing the corks in a chamber saturated with water vapor at 130°C and at a pressure of 180 kPa for 18-20 minutes. Other hot water extraction processes involve the application of atmospheric pressure (PT 104 221) or a pressure not exceeding 7 bars (WO 2004 / 04995), a temperature of 120°C to 230°C at a pressure between 2 bars and 30 bars (EP 1 104 345), pressurization and depressurization cycles (EP 1 849 572, EP 1 108 507), the application of reduced pressure (EP 1 551 463), the application of sudden expansion (EP 2 355 964).

[0010] With regard to the extraction of compounds for their valorization, the starting point is the extraction processes of tree bark in the paper industry, which are carried out using boiling water at atmospheric pressure. Document WO 2020 / 084106 describes such a process, which takes place at 90 °C. A recent publication is that of P. Kilpelâinen et al., “Optimising and scaling up hot water extraction of tannins from Norway spruce and Scots pine bark,” published in Industrial Crops & Products 192 (2023), 116089 (https: / / doi.org / 10.1016 / j.indcrop.2022.116089). For the In cork, there does not appear to be an industrially exploited process, but only a fairly extensive body of literature.

[0011] The publication “Valorization of Cork Using Subcritical Water” by M. Cunha et al., published in the journal Molecules 2020, 25, 4695 (doi:10.3390 / molecules25204695), describes an autoclave extraction process at 120–200°C under a constant pressure of 100 bar. Under these conditions, a significant increase in extractable material is observed when the water temperature rises from 120°C to 200°C; the yield of phenolic compounds increases fivefold.

[0012] A number of documents describe extraction processes using nonpolar or polar organic solvents, such as ethanol or methanol, possibly mixed with water. Examples include EP 2 060 554, EP 3 724 312, CN 108 214 774, and EP 1 444 075. Some of these processes use a Soxhlet extractor under reflux.

[0013] A large number of documents describe cork extraction processes using supercritical fluids. Most of these documents use CO2. Extraction using supercritical CO2 is already used industrially in other fields, particularly in food engineering, cosmetics, and pharmaceuticals, either to purify solid materials or to recover target molecules for further processing. This fluid is particularly suitable for the extraction of nonpolar molecules. Examples cited here include EP 1 216 123, EP 2 404 647, EP 2 404 647, EP 2 396 153, DE 102 005 017963, WO 2005 25825, EP 2 014 344 and EP 2 799 199. Co-solvents may be used, including water to improve the extraction of polar molecules, as described in PT 116 340, PT 116 355 and EP 2 033 751.

[0014] There is also a vast body of literature on the treatment of cork with hydrogen peroxide, which generally aims not to extract molecules for recovery, but to destroy them by oxidation; examples include WO 2020 / 119462, WO 97 / 13628, US 5,098,447, PT 118 112.

[0015] Extracting a fraction of organic components from solid plant material often presents the problem of purifying the obtained fraction for a specific use, given that this fraction may represent a complex mixture. It is sometimes possible to use extraction conditions that favor certain types of molecules, which can simplify the post-processing of this fraction after its extraction.

[0016] The objective of the present invention is not to extract the maximum amount of target material from cork. The objective is to propose a process that optimizes extraction by taking into account the cost of investment, energy consumption, solvent and raw material, given that the raw material is abundantly available and currently underutilized.

[0017] More specifically, the inventors set themselves the objective of extracting the phenolic fraction from cork in a targeted manner, with a view to valorization that preferably does not require any post-treatment other than solvent evaporation (and ideally, no post-treatment at all). They also set themselves the objective of proposing an extraction process that generates as little harmful effluent as possible, and preferably no harmful effluent. They also set themselves the objective of proposing a process that is very economical in terms of energy and reagents. They also set themselves the objective of proposing a simple and easily industrialized process that does not require expensive equipment, either in terms of investment cost, operating cost, or maintenance cost.

[0018] Objects of the invention

[0019] The inventors sought to improve existing methods for extracting a phenolic fraction.

[0020] Cork is a material known for its hydrophobic nature, being only slightly wetted by water. It is known that water and hydroalcoholic solvents with a high water content are characterized by a high surface tension that can hinder their penetration into plant-based materials. Furthermore, it is known (see M. Aroso et al., “Cork: Current Technological Developments and Future Perspectives for this Natural, Renewable, and Sustainable Material,” ACS Sustainable Chem. Eng., vol. 5, no. 12, pp. 11130–11146, Dec. 2017, doi: 10.1021 / acssuschemeng.7b00751) that a mechanical maceration process, or a cork powder extraction process under reflux (Soxhlet extraction), yields maximum phenolic extraction at an ethanol content in water of approximately 50%. The present inventors have repeated and confirmed this study, under reflux and also at room temperature.These processes proposed in the cited Aroso publication, however, have drawbacks, namely very long treatment times and the use of a high proportion of ethanol mixed with water.

[0021] Starting with mechanical maceration, which is certainly the simplest process, the inventors sought to activate extraction using ultrasound. Surprisingly, the inventors found that, compared to mechanical maceration, ultrasound-assisted extraction does not significantly improve the extraction yield. Unlike many other plant materials, the phenomenon of cavitation and cell breakdown, on which the ultrasound-assisted extraction process is based, does not appear to occur with the same efficiency in the case of cork, and particularly in virgin cork. This may be due to the cellular structure and high elasticity of cork.

[0022] The inventors then found a static pressure treatment process which gives an excellent result for extracting the phenolic fraction using as water solvent, without any additives. This high-pressure assisted solvent extraction process is referred to here as ASE (Accelerated Solvent Extraction).

[0023] The inventors have also found a use for this fraction in intumescent compositions, which is either a use of the solid phase collected after precipitation of the phenolic fraction from the liquid phase, or a direct use of the liquid phase obtained from the extraction process, possibly after partial evaporation of the solvent to increase its concentration of phenolic compounds. This use is as an ingredient in intumescent compositions.

[0024] The liquid fraction can be used directly in liquid or paste-like intumescent compositions in the form of paints intended to coat the surface of a material to be protected against fire, such as wood, metal, or plastic. The solid phase collected from the liquid phase can be introduced into solid or paste-like intumescent compositions.

[0025] According to the invention, the problems posed have been solved by a process for extracting a fraction of phenolic compounds from cork, comprising a step of bringing a solid phase, which is formed by a cork granule and / or powder, into contact with a liquid phase under pressure in a chamber, said liquid phase comprising at least 80% by mass of water and at most 20% by mass of ethanol, said process being characterized in that the temperature of the water is between about 70 °C and about 100 °C, and preferably between about 70 °C and about 90 °C, and in that the pressure is at least 30 bars and preferably remains constant during the process.

[0026] This extraction process represents the first object of the invention. Advantageously, it can be carried out with virgin cork. Advantageously, it can be carried out with cork from the Quercus suber L. variety.

[0027] In a preferred embodiment, said liquid phase used for extraction comprises only water.

[0028] In one embodiment, the pressure is between approximately 30 bar and approximately 200 bar, preferably between approximately 50 bar and approximately 150 bar, and even more preferably between approximately 60 bar and approximately 140 bar. The contact time at said temperature and pressure is between approximately 10 minutes and approximately 120 minutes, and preferably between approximately 15 minutes and approximately 60 minutes.

[0029] In an advantageous embodiment, the temperature is between approximately 70 °C and approximately 90 °C, the pressure is between approximately 60 bars and approximately 140 bars and the duration of the contact is between approximately 20 minutes and approximately 40 minutes.

[0030] The extraction process is completed by separating said solid phase from said liquid phase, and by recovering said liquid phase for the purpose of its valorization.

[0031] A second object of the present invention is the use of said fraction of phenolic compounds obtained by the extraction process according to the invention, in liquid or solid form, in the manufacture of intumescent compositions, and in particular water-based intumescent paints, said intumescent compositions being intended for use in the fireproofing of wood and other cellulosic materials, metals, and plastics. In an advantageous embodiment, the liquid fraction from the extraction process is used directly, optionally after partial evaporation of the solvent to increase its concentration of phenolic compounds, in liquid or paste-like intumescent compositions in the form of paints intended to coat the surface of a material to be protected against fire, such as wood, metal, or plastic.

[0032] A final object of the present invention is represented by an intumescent composition, in particular a water-based intumescent paint, intended for use in the fireproofing of wood and other cellulosic materials, metals and plastics, characterized in that it comprises said fraction of phenolic compounds, in liquid or solid form, obtained by the extraction process according to the invention. Brief description of the figures

[0033] Figures [1] to

[13] illustrate different aspects of the invention, but do not limit its scope.

[0034] [Fig.1] shows schematically and in a simplified manner a pressure vessel with its peripheral equipment, which can be used to implement the process according to the invention.

[0035] [Fig.2] refers to example 3 and shows the comparison of mass yield global extraction of phenolic compounds from cork using three different processes (ASE = Accelerated Solvent Extraction, i.e. the process according to the invention; EUS = Ultrasonic Assisted Extraction; MM = Mechanical Maceration) and five different solvents labeled A (100% water), B (water: ethanol = 75:25), C (water: ethanol = 50:50), D (water: ethanol = 25:75), E (100% ethanol).

[0036] [Fig.3] refers to example 3 and shows the richness of the extracts in compounds phenolics, for each of the three extraction techniques and each of the five solvents studied.

[0037] [Fig.4] relates to example 3 and shows the depletion of the plant matrix after two successive extractions by the ASE process according to the invention, for each of the five solvents studied.

[0038] [Fig.5] is another presentation of the data from [Fig.4].

[0039] [Fig.6] refers to example 3 and shows the ORAC indices (Oxygen Radical Absorbance Capacity) expressed in Trolox equivalents (6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid) depending on the solvent used, for an extraction according to the invention (ASE process).

[0040] [Fig.7] relates to example 3 and shows the mass extraction yield as a function of contact time, for the process according to the invention under the reference conditions of 80°C and 100 bars with solvent A (water).

[0041] [Fig.8] relates to Example 6 and shows a typical HPLC-MS chromatogram in SIM mode of a fraction obtained with the ASE process according to the invention using an 80 / 20 methanol / water mixture.

[0042] [Fig. 9] relates to Example 5 and shows the average solvent consumption per unit mass extracted for each of the three extraction techniques compared, with water under the reference conditions at 80 °C and 100 bar. The unit mass extracted is also expressed in gallic acid equivalent.

[0043] [Fig. 10] relates to examples 6 and 7 and schematically shows the cone calorimeter used to characterize the behavior of the intumescent compositions studied.

[0044] [Fig. 11] relates to Example 6 and shows optical photographs of pellets prepared from different solid intumescent compositions during a test in a cone calorimeter.

[0045] [Fig. 12] refers to example 6 and shows the height of swelling of the studied pellets.

[0046] [Fig. 13] relates to example 7 and shows the thermal power released by samples of fir wood board coated with different intumescent paints. Detailed description

[0047] Unless otherwise indicated, all percentage indications relating to a composition of matter are given as mass percentages relative to the total mass of said composition.

[0048] The process according to the invention can be carried out with cork, and in particular with cork of the Quercus suber L. variety. This can be so-called reproductive cork (from the third and subsequent harvestings), or cork from earlier harvests. In particular, the invention can be carried out with virgin cork, from a first harvest, which cannot be used for the manufacture of stoppers, and whose other uses are economically unviable. This type of cork is indeed abundantly available in regions where cork cultivation has been abandoned. due to its lack of profitability. However, the conservation of cork forests (cork oak groves) deserves to be encouraged because a harvested cork oak would absorb significantly more CO2 than most other trees likely to populate the same land.

[0049] The process according to the invention can also be implemented with cork waste and remnants, such as are generated for example during the manufacture of corks and other cork products.

[0050] In the process according to the invention, cork is used in the form of granules and / or powder: the cork is ground. The average particle size, determined by sieving, is advantageously between approximately 0.1 mm and approximately 5 mm, preferably between approximately 0.2 mm and approximately 3 mm, and even more preferably between approximately 0.2 mm and approximately 2 mm. For pieces that are too large, extraction remains incomplete due to the shallow penetration depth of the polar solvent into the hydrophobic material, even under high pressure. For powders that are too fine, agglomeration occurs, which also hinders solvent penetration and complicates filtration at the end of the process. Before its use in the process according to the invention, the ground cork can be sieved to remove excessively large pieces and foreign matter.

[0051] The granules are introduced into a container which is then hermetically sealed. The liquid phase (i.e., the solvent) used for extraction is then introduced. This solvent is pressurized. The extraction solvent is a polar solvent, comprising a majority of water by mass; preferably, only water is used.

[0052] Next, the mixture formed by the solid phase and the liquid phase is heated. According to the invention, the temperature of the mixture formed by the cork and the solvent during the execution of the extraction process is between approximately 60 °C and approximately 120 °C, preferably between approximately 70 °C and approximately 100 °C, and more preferably between approximately 70 °C and approximately 90 °C, and even more preferably between approximately 75 °C and approximately 85 °C. The optimum temperature is approximately 80 °C.

[0053] The pressure is advantageously applied directly to the liquid phase using a pump. The pressure is between approximately 30 bar and approximately 200 bar, and preferably between approximately 50 bar and approximately 150 bar, and even more preferably between approximately 60 bar and approximately 140 bar. By way of example, a pressure of approximately 100 bar is suitable.

[0054] It should be noted that at a temperature of 80 °C and a pressure within the scope of the invention, the water is not boiling. The fact that water at a temperature above 100 °C is not used in the process according to the invention has the advantage that, in the event of an accidental leak, the amount of water vapor released remains very limited.

[0055] The pressure is preferably static; this also represents the simplest embodiment. Within the scope of the invention, it is possible to vary the pressure during the process, in particular continuously or discontinuously, and / or periodically or not; however, these are not preferred embodiments.

[0056] The contact time between the solid phase and the extraction solvent under the temperature and pressure conditions that characterize the extraction process according to the invention is typically on the order of 5 to 120 minutes, preferably between approximately 10 and 90 minutes, and more preferably between approximately 15 and 60 minutes. By way of example, for a temperature between approximately 70 °C and approximately 90 °C, and a pressure between approximately 60 bar and approximately 140 bar, a contact time between approximately 10 and 40 minutes is suitable, and preferably between approximately 15 and 35 minutes, and even more preferably between approximately 20 and 35 minutes.There is no need to allow for a longer contact time, but allowing for a longer contact time has no disadvantage other than economic, as it unnecessarily increases the cycle time and immobilizes the container.

[0057] It is possible to provide a means of stirring to agitate the cork granules during their maceration under pressure, but this is not necessary. The absence of a means of stirring considerably simplifies the construction of the container.

[0058] After the prescribed contact time, the pressure is released, the mixture is removed from the reactor, and the solid phase (called macerate) is separated from the liquid phase. This can be done, for example, using a filtration device, which may be made of stainless steel.

[0059] The macerate may be subjected to a second extraction cycle, which, however, will have a lower yield than the first extraction cycle and may not be economically advantageous. This second extraction cycle may be carried out under the same conditions as the first, or under different conditions. In an advantageous embodiment, a second extraction cycle is not used. Indeed, under the optimal conditions of the process according to the invention (80 °C, between 60 bar and 140 bar, 20 minutes), the mass yield of the second extraction is between approximately 10% and approximately 25% of that of the first extraction, and typically between approximately 13% and approximately 18%. By way of example, at 100 bar, a mass yield of 42.3 (expressed in milligrams of extract per gram of dry plant material) was found for the first extraction, and 6.9 for the second.

[0060] The macerate, whether from the first or second extraction cycle, can be dried and used in any known process using cork granules, such as the manufacture of sheets or plates intended for use in the building sector.

[0061] The liquid phase separated from the macerate is recovered. It contains the fraction of phenolic compounds. It can be used in the manufacture of intumescent compositions, and in particular water-based intumescent paints. This use can be direct, by introducing said liquid phase (possibly partially concentrated by partial evaporation of the solvent) into a paint composition. This use can also be indirect, by introducing the solid phenolic compounds recovered in said liquid phase (in particular by evaporation of the water) into an intumescent composition.

[0062] In said intumescent compositions, and in particular water-based intumescent paints, said phenolic fraction acts as a carbon source. These intumescent compositions typically also include a blowing agent, for example melamine, and an acid source, for example ammonium polyphosphate [NH4PO3]n(OH)2. Ammonium polyphosphate sold under the brand name Exolit® and the designation AP 422 may be used, for example.

[0063] Generally, according to the invention, the phenolic fraction can replace gallic acid or pentaeryhritol, which are commonly used as carbon sources, in a known type of intumescent composition. This replacement can be partial or total. Advantageously, a mass ratio of approximately 1:3 between the carbon source and the acid source is used. In an advantageous embodiment, the liquid phase obtained from the process according to the invention is incorporated, either directly or after a concentration step, into an intumescent composition in the form of a paint. Most of these intumescent paints are water-based, and one of the advantages of the present invention is that the liquid phase obtained from the extraction process according to the invention can be used directly as the aqueous phase in such a water-based intumescent paint.

[0064] The phenolic fraction extracted from cork can also be introduced in solid form, particularly in solid or paste-like intumescent compositions.

[0065] Compared to known intumescent compositions incorporating phenolic compounds, the phenolic composition obtained from the extraction process according to the invention exhibits a specific compositional spectrum and impurity spectrum. This allows these compositions to be distinguished from known ones, which are prepared from pure phenolic compounds.

[0066] These intumescent compositions, and in particular these intumescent paints, can be used especially for fireproofing wood and other cellulosic materials, metals and plastics. These compositions, and in particular these paints, are applied in the same way as known intumescent compositions, which they can replace totally or partially.

[0067] As explained above, the extraction process according to the invention can be carried out with water. For selectively extracting phenolic fractions, water gives better results than a slightly less polar mixture (containing, for example, 25% ethanol and 75% water); compared to a mixture containing a larger fraction of ethanol, the difference in extraction yield in favor of water becomes very significant.

[0068] The advantages of using water rather than an ethanol-water mixture are numerous. A first advantage is the cost of the solvent. A second advantage is that when it is necessary to evaporate the solvent, either completely or partially, for example to increase the concentration of the phenolic fraction, or to precipitate it, an ethanolic fraction and an aqueous fraction would be recovered from a water-ethanol solution, and these must be collected and managed separately. A third advantage is the difficulty of utilizing a liquid phenolic fraction containing ethanol. A liquid phenolic fraction containing a mixture of water and ethanol is not necessarily compatible, from a chemical and regulatory standpoint, with a water-based paint. The advantage of the extraction process according to the invention using water is the ease with which the liquid fraction can be directly introduced into a liquid intumescent composition. Examples

[0069] Example 1: Apparatus and general extraction procedure

[0070] The extraction tests were carried out with a polar solvent which was water (solvent A), ethanol (solvent E) or a mixture of water and ethanol in different proportions (solvent B: 75% water; solvent C: 50% water; solvent D: 25% water).

[0071] Pressure-assisted extraction (abbreviated herein as PAE) was carried out in an apparatus shown in [Fig. 1]. It comprises an extraction cell 1 with stainless steel walls, within which a reaction space 2 is delimited by a stainless steel frit 3. A cellulose and fiberglass filter 4 is placed above the frit 3. The cork granules 10 from which the phenolic fraction is to be extracted are located above this filter 4. The solvent is supplied in tanks 5 and introduced into the cell 1 by a pump 6 through a safety valve 7. The outlet of the extraction cell 1 is closed by a static valve 8. After extraction, the solvent is collected in a recovery bottle 9. The cell 1 includes heating means (not shown in the figure).

[0072] After extraction, the macerate is filtered and treated in a rotary evaporator at 60 °C until complete evaporation of the solvent, in order to obtain a brown powder. The powder is weighed to calculate the mass yield of the extraction in milligrams per milliliter of solvent and milligrams of extracted material per gram of dry plant material. Powder samples are stored in a freezer at -20°C. The solvent recovered after extraction is subjected to various chemical analysis tests.

[0073] For comparison, maceration tests under mechanical agitation (abbreviated herein as MM) were carried out: 10 g of crushed virgin cork were brought into contact with 200 mL of solvent under agitation at 180 rpm and at room temperature for 6 hours. This duration allows an equilibrium plateau to be reached beyond which the extraction yield is no longer affected by the extraction time.

[0074] Also for comparison, ultrasound-assisted extraction tests (abbreviated here: EUS) were carried out with a homogenizing sonicator with an immersible probe of the type UP400St (Hielscher company): 20 g of crushed virgin cork were brought into contact with 400 mL of solvent for 30 minutes at 80 °C, with a sonication frequency of 24 kHz and a sonication power of 100 W.

[0075] Example 2: General analysis and characterization procedures

[0076] The determination of total phenols in the solvent is carried out using the Folin-Ciocalteu reagent, which is a mixture of phosphomolybdic acid (H3PMoi2O4O) and phosphotungstic acid (H3PW12O14). This reagent is reduced by phenolic and polyphenolic compounds to a mixture of blue oxides of tungsten (W8O23) and molybdenum (Mo8O23). The blue color is used for a colorimetric measurement at 750 nm using gallic acid as the calibration standard. The measurement is performed in a slightly basic solution containing 7.5 wt% Na2CO3, after an incubation time of 30 minutes at 25°C following stirring.

[0077] The antiradical potential was evaluated by the ORAC (Oxygen Radical Absorbance Capacity) method, which is a reference for those skilled in the art, as described in the publication by RL Prior, X. Wu and K. Schaich, “Standardized Methods for the Determination of Antioxidant Capacity and Phenolics in Foods and Dietary Supplements,” Journal of Agricultural and Food Chemistry, Vol. 53, No. 10, 2005, pp. 4290-4302; doi:10.1021 / jf0502698.

[0078] This method is based on measuring the oxidation of fluorescein by radicals resulting from the thermal degradation of 2,2'-azobis(2-amidopropane) dihydrochloride (abbreviated AAPH), which occurs above 35 °C. In the presence of antioxidant compounds, the degradation of fluorescein is delayed, notably by their free radical scavenging activity. The decomposition kinetics of fluorescein are evaluated in a blank, then in the presence of a standard or cork extract at a known concentration. Fluorescence is measured at an emission wavelength of 530 nm every minute for 90 minutes with an excitation wavelength of 485 nm. The resulting decomposition curve is used To calculate the parameter called AUC (Area Under Curve), expressed by the formula AUC = 1 + fi / f0 + fi / fo + C / fo + fn / f0 + [...] + f9o / fo, where f0 is the fluorescence intensity at t0 = zero minutes and fn is the fluorescence intensity at tn minutes, a calibration is established with 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (abbreviated Trolox). This calibration expresses the AUCnette parameter as a function of the Trolox concentration. This calibration is used to express the AUCnette determined for cork extracts in millimolar Trolox equivalents (abbreviated EqT) per gram of dry extract. This spectrophotometric assay allows for a rapid evaluation of cork extracts containing phenolic fractions.

[0079] Fractionation of the phenolic fraction powder was carried out on a silica column using a sequence of dichloromethane-methanol-water solvents and their homogeneous mixtures. The fractions or extracts of interest were analyzed by high-performance liquid chromatography (HPLC) coupled to a quadrupole mass spectrometer (MS) (HPLC-MS technique) in SIM (Selective Ion Monitoring) mode.

[0080] Example 3: Comparison of the three extraction methods

[0081] Here we have compared the three methods ASE (according to the invention), EUS and MM.

[0082] [Fig. 2] shows the comparison of the overall mass yield and the gallic acid equivalent (GAE) yield for the EAP (70 °C; 100 bar), EUS (80 °C), and MM (room temperature) methods and for each of the five solvents used (A = 100% water; B = 75% water + 25% ethanol; C = 50% water + 50% ethanol; D = 25% water + 75% ethanol; E = 100% ethanol). The ASE process demonstrates a clear advantage. The overall mass yield is better with pure ethanol, but with this process, ethanol is not suitable for extracting the phenolic fraction (represented by the GAE parameter), whereas no difference is observed with the EUS and MM processes.

[0083] [Fig.3] shows for each of the five solvents used the richness of the extracts in phenolic compounds, designated R%EqAG which is equal to 100 (OEqAG / 0)> where R is expressed as a percentage, Q designates the overall mass yield expressed in milligrams of extract per gram of dry plant, and QEqAG designates the mass yield in EqAG expressed in milligrams of EqAG per gram of dry plant.

[0084] [Fig. 4] shows, for each of the five solvents used, the depletion of the plant matrix after two successive extractions. It can be seen that solvent A allows for the best extraction in a first extraction, but the additional gain from a second extraction is the smallest. This conclusion is more clearly illustrated in [Fig. 5], which presents the data from [Fig. 4] in a different way.

[0085] [Fig.6] shows the ORAC index in Trolox equivalents (Tq) for the five solvents studied. A high value for the EqT indicator indicates a greater potential for scavenging free radicals and serves as an indicator of the abundance of hydroxyl and phenolic groups. Solvent A is shown to provide the best extraction.

[0086] [Fig.7] shows the mass extraction yield as a function of contact time, For the reference conditions of 80°C and 100 bar with solvent A (100% water), the increase in yield is small when the contact time doubles from 15 minutes to 30 minutes. Under these conditions, a duration of approximately 15 minutes would be sufficient for an industrial process.

[0087] Example 4: Identification of the main chemical compounds in the extract

[0088] Extracts obtained with solvent A were analyzed under the reference conditions of 80 °C and 100 bar. [Fig. 8] shows a typical HPLC-MS chromatogram in SIM mode of a fraction obtained with an 80 / 20 methanol / water mixture. The following compounds were identified: peak 1: gallic acid; peak 2: castalagin / vescalagin (not separated); peak 3: protocatechuic acid; peak 4: protocatechuic aldehyde; peak 5: caffeic acid; peak 6: ellagic acid. Two peaks marked "x" were not identified.

[0089] Example 5: Solvent consumption

[0090] The average solvent consumption per unit mass extracted under reference conditions with water was compared for the three processes ASE, EUS, and MM. The result is shown in [Fig. 9]. An advantage is observed for the ASE process according to the invention. The comparison of average consumption per unit mass extracted (total mass or gallic acid equivalent) does not show a significant difference between the ASE and MM processes; however, this comparison depends on the duration of the MM process, which was taken here to be six hours, during which the mixture must be maintained at the process temperature. The energy consumption of the ultrasonic-assisted maceration process, on the other hand, appears to be significantly higher.

[0091] Example 6: Use of the liquid polyphenolic extract in solid intumescent compositions

[0092] Solid cylindrical pellets (height approximately 10 mm, diameter approximately 13 mm, mass approximately 2 grams) were prepared by compacting (for 1 minute under a pressure of 10 tons in a manually operated hydraulic press) a mixture of powders comprising melamine as a blowing agent, AP 422 type ammonium polyphosphate as an acid source, and dry cork extract obtained by the extraction process according to the invention.

[0093] Tests were carried out in a cone calorimeter, which is illustrated in [Fig. 10]. The pellet 1 formed by the solid intumescent composition was placed in the center of a ceramic plate 2 covered with an aluminum foil 3 and arranged in a Horizontal sample holder 4. The heat flux originated from a heating cone 5; for these tests, this flux was set at an irradiance of 50 kW.m². The gases released during the test are extracted through a fume hood that draws air through the cone; this extraction is symbolized by the arrow marked with the reference symbol 6. The apparatus includes two cameras arranged as shown in the figure: a first camera 6 for visible light and a second camera 7 for infrared radiation. A weighing cell 8 allows monitoring of the mass of the sample 1, and one or more thermocouples 9 allow monitoring of its temperature.

[0094] After 15 minutes, sample 1 was removed, measured, and hermetically sealed. Using the first camera 6, positioned 50 cm in the plane of the upper surface of the pellet, one image per second was recorded to track the pellet's expansion during the test until the meringue formed collapsed outside the camera's measurement field. Images were also recorded with the second camera 7 in the infrared range.

[0095] As shown in [Fig. 11], the pellet swells upon exposure to a heat flux. The height of the swelling, the density, and the durability of this swollen pellet depend on its initial composition. [Fig. 12] shows the thickness of the swelling layer as a function of exposure time. Samples A, B, C, D, and E correspond to different fractions of the phenolic cork extract that underwent chromatographic separation. It is observed that these different fractions swell faster than the commercial product (“control”) and the product containing gallic acid as a phenolic component (“control”). Subsequently, the layer formed with the control product becomes thicker.

[0096] Example 7: Use of the liquid polyphenolic extract in liquid intumescent compositions

[0097] Various intumescent paints were formulated using the same paint base, namely the binder sold under the brand name Emultex™ (Synthomer Company). This is a vinyl copolymer composed of vinyl acetate and vinyl neodecanoate, supplied as a colloid in aqueous solution. Its glass transition temperature is 12°C, its viscosity at 20°C is 1100 mPa·s, and its dry residue is 55% by mass. All the formulated paints also included AP 422 ammonium polyphosphate as an acid source and melamine as a blowing agent. The mass ratio between the dry binder and the intumescent mixture as a whole was 1:2. As a carbon source, either liquid phase from the extraction process according to the invention was added, or, to calibrate the phenolic functions, gallic acid, or, for comparison, pentaerythritol.We also procured commercially available intumescent paint. as a reference (Teknosafe™ Flame Guard 2467-10 manufactured by Teknos); this is a water-based paint specified for wood protection. It also contains dipentaerythritol and ammonium polyphosphate.

[0098] Raw wood boards were coated with these paints according to a standardized protocol, with a dry paint surface mass of approximately (250 ± 25) g / m2. The nomenclature of the samples was as follows: A = cork extract according to the invention, T = control, S = standard, TFG = Teknosafe Flame Guard.

[0099] The thermal emissivity was determined using the cone calorimeter described in relation to Example 6. In all cases, a decrease in thermal emissivity e was observed after 10 seconds of exposure to the heat flux, due to a generalized blackening of the surface. The results are summarized in Table 1. It should be noted that paint A leads to performance very close to that of the commercial product TFG.

[0100] [Table 1] Table 1 TFG Paint T Paint A Paint S £t = 0 s 0.975 0.961 0.985 0.965 £t = 10 s 0.942 0.94 0.946 0.952

[0101] Figure 13 shows the heat output of the sample as a function of exposure time to a heat flux of 50 kW / m² during the first 50 seconds of exposure. Between 15 and 25 seconds of sample exposure, transient ignition (flashing) was observed in all samples treated with an intumescent composition. This is probably due to the ignition of pyrolysis gases emitted by the substrate-coating system. Extinction of this flame is consistently observed, typically occurring after 5 to 10 seconds. This may be due to the release of inert gases during the intumescence reaction of the ternary system (release of the blowing agent and release of water by condensation reaction), and to the initiation of the development of the intumescent layer, which hinders the release of flammable pyrolysis gases from the substrate (wood).Of the three samples treated, the one according to the invention (sample A) shows a particularly low release of heat. (The sample referenced FR797 corresponds to a vinyl-based paint without an intumescent composition).

[0102] Once the development of the intumescent layer is sufficiently advanced, on average after 25 seconds of exposure, the system reaches an equilibrium state with very low or even zero power output. During this phase, the intumescent layer acts as a thermal shield. Subsequently, after the intumescent reaction is complete, after total consumption of the reactants, and if the thermal stress While the external layer does not diminish, the carbonized structure undergoes visually perceptible degradation; the appearance of cracks makes the layer locally permeable to pyrolysis gases, and it will eventually no longer be able to perform its function significantly. Over a longer timescale, among the three intumescent compositions tested, the one incorporating the phenolic fraction extracted from cork is the least effective. This does not, however, negate the potential of these extracts for formulating intumescent paints, but it does call for optimization of the paint formulation to prevent crack formation.

[0103] Examples 6 and 7 clearly show the suitability of phenolic cork extracts obtained by the process according to the invention to be used as a carbon source in intumescent compositions.

Claims

Demands

1. A process for extracting a fraction of phenolic compounds from cork, comprising a step of contacting a solid phase, which is formed by cork granules and / or powder, with a liquid phase under pressure in a chamber, said liquid phase comprising at least 80 mass percent of water and at most 20 mass percent of ethanol, and is preferably composed solely of water, said process being characterized in that the temperature of the water is between about 70 °C and about 100 °C, and preferably between about 70 °C and about 90 °C, and in that the pressure is at least 30 bar and preferably remains constant during the process.

2. A method according to claim 1, characterized in that the pressure is between about 30 bars and about 200 bars, preferably between about 50 bars and about 150 bars, and even more preferably between about 60 bars and about 140 bars.

3. A method according to claim 1 or 2, characterized in that the duration of contact at said temperature and pressure is between about 10 minutes and about 120 minutes, and preferably between about 15 minutes and about 60 minutes.

4. A method according to any one of claims 1 to 3, characterized in that the temperature is between about 70 °C and about 90 °C, the pressure is between about 60 bar and about 140 bar and the duration of the contact is between about 20 minutes and about 40 minutes.

5. A process according to any one of claims 1 to 4, characterized in that the average particle size of said granule or powder is between about 0.1 mm and about 5 mm, preferably between about 0.2 mm and about 3 mm, and even more preferably between about 2 mm and about 2 mm.

6. A process according to any one of claims 1 to 5, characterized in that said cork is virgin cork, and preferably comes from the Quercus suber L. tree.

7. A process according to any one of claims 1 to 6, characterized in that at the end of the process said solid phase is separated from said liquid phase and said liquid phase is recovered.

8. A method according to claim 7, wherein said solid phase is subjected a second time to said step of contacting said liquid phase.

9. Use of said fraction of phenolic compounds obtained by the process according to any one of claims 1 to 8, in liquid or solid form, in the manufacture of intumescent compositions, and in particular of water-based intumescent paints, said intumescent compositions being intended for use in the fireproofing of wood and other cellulosic materials, metals and plastics.

10. Intumescent composition, in particular water-based intumescent paint, intended for use in fireproofing wood and other cellulosic materials, metals and plastics, characterized in that it comprises said fraction of phenolic compounds, in liquid or solid form, obtained by the process according to any one of claims 1 to 8.