Method for producing alginate-based expanded foam solid bodies and device for implementing the method

Abstract

The invention relates to a method for producing expanded foam solid bodies, comprising the consecutive steps of: preparing (10) a mixture, in an aqueous carrier, of a monovalent alginate salt, a surfactant and an emulsion stabilizer; foaming (20) this mixture; extruding (30) the foam formed in this way directly into immersion in an aqueous solution for gelling the alginate; and cutting (40) foam fractions as the foam enters this solution; maturing (50) the foam forming the fractions in an aqueous solution for gelling the alginate for a period of at least 30 minutes, so as to form the expanded foam solid bodies.

Description

[0001] METHOD FOR PRODUCING SOLID BODIES MADE OF ALGINATE-BASED EXPANDED FOAM AND DEVICE FOR ITS IMPLEMENTATION

[0002] ARTWORK

[0003] The present invention falls within the general field of the production of structured objects with thermal insulation and flame retardancy.

[0004] More particularly, the present invention relates to a method for manufacturing solid bodies made of alginate-based expanded foam, as well as a device for implementing such a method. The invention also relates to a solid body made of alginate-based expanded foam obtainable by such a method, and its use for producing a structured object. Another subject of the invention is a method for producing a structured object using such solid bodies.

[0005] Objects made of low-density materials with thermal insulation capacity are used in many fields, such as packaging, construction, storage, etc. The materials forming these objects are generally of the petroleum-based type, such as polystyrene or polyurethane for example, and they are characterized by their low density and good mechanical and molding performance. However, they have disadvantages related both to their production chain, which uses processes that are not very virtuous in terms of the environment and health and safety, and to their life cycle, particularly due to their very low biodegradability and compostability. Polystyrene recycling also remains complex and underdeveloped for the time being, resulting in a particularly critical environmental impact overall. Legislation remains relatively lax in terms of manufacturer responsibility over the life cycle of such materials.The evolution of legislation and regulatory practices will inevitably lead to addressing this issue in the future.

[0006] Furthermore, the fire retardant performance of such materials, desirable for many applications, proves to be very insufficient.

[0007] In order to overcome these drawbacks of petro-sourced materials, prior art has sought to substitute them with bio-sourced materials, and in particular biodegradable and compostable materials, such as cellulose-based biopolymers, derived from algae, fungal biomass, etc., with the aim of choosing from among these materials those which have properties at least as good as those of the petro-sourced materials usually used.

[0008] Document US 5,840,777 describes a method for producing a foam membrane based on a polysaccharide. This method comprises the preparation of a mixture containing the polysaccharide and a foaming agent, and which may contain a di- or trivalent cation, in particular calcium; then the foaming of this mixture by introducing gas and applying shear forces, followed by an acid treatment of the foam. The final result is an open-porosity foam, the thermal insulation performance of which is not optimal.

[0009] GB 584140 describes a process for producing foam from alginate-based material, comprising a step of mixing an alginate with a foaming agent, a foaming step, and then bringing the foam into contact with a calcium salt solution to cause it to gel, by transferring the foam in the form of a thread into this solution. The foam bodies obtained from this process have a high density, of several hundred kg / m 3. Furthermore, their size is not controllable, due to a significant reduction in this size during the final drying stage of the process. For example, document FR 3 094 372 has proposed a process for manufacturing a closed-porosity foam by coagulation of a biopolymer in situ. However, such a process requires a large number of reagents to obtain optimal coagulation. Furthermore, the implementation of this process is not very compatible with current industrial practices, particularly in the field of packaging manufacturing.

[0010] The present invention aims to remedy the drawbacks of the solutions proposed by the prior art for producing structured objects of low density, preferably less than 100 kg / m 3, and with good thermal insulation properties based on bio-sourced materials, in particular those mentioned above. The invention aims in particular to propose a solution for this purpose which is easy to implement, in particular easily transposable from the laboratory scale to the industrial scale, and which makes it possible to form products having not only a high thermal insulation capacity, but also other functionalities, in particular good flame retardancy capacities and optionally good mechanical resistance properties. For this purpose, the present inventors were more particularly interested, as an initial bio-sourced material, in alginates, anionic polysaccharides derived from brown algae, more specifically from laminaria and fucus. Alginates are characterized in particular by an ability to gel, in particular to ionotropic gel.The present inventors have developed a particularly advantageous process for producing small-sized, low-density solid bodies made of alginate-based expanded foam with closed porosity. These solid bodies, particularly when in the form of beads, are highly versatile in their shaping, which can be achieved by molding, machining, etc. They can thus be easily used for producing larger structured objects using the industrial techniques usually used for producing objects made from expanded foam beads, such as polystyrene. Shaping them is made easier. The objects thus formed also have not only good thermal insulation capacity but also good fire retardant properties. They are easy to shape, particularly to cut, sand, etc.

[0011] Thus, according to a first aspect, there is proposed according to the invention a method for manufacturing solid bodies, in particular of substantially spherical shape, that is to say in the form of balls, in expanded foam, that is to say in cellular type material, the cells of which are advantageously closed. This method comprises successive steps of:

[0012] - a / preparation of a mixture, in an aqueous vehicle, of a monovalent alginate salt, a surfactant and an emulsion stabilizer,

[0013] - b / foaming of this mixture, comprising the introduction of a gas into the mixture and the concomitant agitation of the mixture, so as to form foam, by the combined action of the surfactant and the emulsion stabilizer,

[0014] - c / extrusion of the foam thus formed by immersion in a first aqueous gelling solution of the alginate, and cutting of fractions of said foam as it enters this aqueous gelling solution, the first aqueous gelling solution being contained in a reactor comprising a lower zone and an opposite upper zone, and the extrusion of the foam by immersion in the first aqueous gelling solution being carried out in the lower zone of the reactor, preferably through a bottom wall of the reactor, or through a peripheral wall of the reactor in a zone close to this bottom wall,

[0015] - d / maturation of the foam forming said fractions in a second aqueous alginate gelling solution, for a period of at least 30 minutes, so as to form the intended expanded foam solid bodies.

[0016] Thus, the method according to the invention combines the techniques of foaming by expansion, in step b / of the method, and, in step c / , of immersive extrusion of the foam formed in a bath of suitable composition to cause coagulation of the alginate forming the foam, and the resulting solidification of the material. Such a combination advantageously makes it possible to form solid bodies of the desired shape, in particular of spherical or cylindrical shape, in particular by the appropriate choice of the shape of the internal section of the extrusion nozzle(s) used, these solid bodies also having a low density and good mechanical properties.In particular, the extrusion of alginate-based foam directly by immersion in the aqueous gelling solution proves to be much more effective, in terms of controlling the shape and properties of the solid bodies formed, than conventional extrusion processes, which operate according to the principle of gravity fall, by expulsion of droplets above a coagulation bath. In these conventional extrusion processes, due to the very aerated structure of the foam, and the resulting flotation phenomenon, the droplets of material expelled from the extrusion head then accumulate on the surface of the coagulation bath, which slows down, or even prevents, the coagulation of the alginate in the bath.On the contrary, in step c / of the process according to the invention, the coagulation of the alginate begins as soon as the foam leaves the extrusion nozzle, directly in the aqueous gelling solution, and it continues throughout the duration of immersion of the foam fractions in the aqueous gelling solution, that is to say the duration during which, due to their low density, they naturally rise towards the surface of the solution. The resulting coagulation of the alginate is accompanied by a simultaneous structuring of the foam fractions as they are cut and moved in the aqueous gelling solution, under the effect of the homogeneous pressure exerted by this solution on their surface. This spontaneous shaping of the foam fractions in the aqueous gelling solution is particularly advantageous and effective when it is desired to form solid bodies of spherical or cylindrical shape.

[0017] Thus, at the end of the process according to the invention, after step d / of maturation / ripening of the foam, solid bodies made of biosourced, biodegradable and compostable material, with closed internal porosity, are advantageously obtained, having properties at least as good as bodies made of expanded polystyrene foam, in particular: good thermal insulation properties, inherent to the expanded nature of the foam, a low apparent density, for example between 30 and 80 kg / m 3 , and good mechanical properties. These solid bodies are also easy to handle, in particular to dry, glue, assemble, shape by molding, for their structuring into plates or various objects, etc., this by the techniques and by means of the equipment commonly available in industries, in particular for the manufacture of objects in expanded polystyrene.

[0018] In a highly advantageous manner, the solid bodies obtained at the end of the process according to the invention also exhibit, after drying, good fire resistance performance, in particular thanks to the characteristics of the alginate, in particular low combustion energy, and a high degree of self-extinguishability, due to the formation of char following their exposure to fire. Such a property proves to be particularly advantageous for applications in the building sector, for example for the formation of fire prevention devices for the protection of electrical wiring, as well as packaging and storage, both in the luxury sector and in the field of packaging for archiving and protection, creative leisure, decoration, etc.

[0019] The process according to the invention is also environmentally friendly. In particular, it does not require any solvent or toxic product for its implementation. The alginate used in the process according to the invention can come from any source, in particular it can be extracted from algae that produce it naturally, such as kelp or fucus. It can also have been produced by bacteria, such as bacteria of the genus Pseudomonas or Azobacter.

[0020] Alginate salts based on monovalent cations, such as sodium or potassium, are advantageously soluble in water, so that they dissolve easily in the aqueous vehicle in step a / of the process.

[0021] The method according to the invention allows modulation of the properties of the solid bodies formed, in particular modulation of their mechanical properties, their appearance, for example their color, and their tactile characteristics. In particular, it allows them to be given any desired multifunctionality depending on the intended application, by incorporating suitable additives into the mixture formed in step a / , such as fillers or natural fibers.

[0022] The method according to the invention may also meet one or more of the characteristics described below, implemented in isolation or in each of their technically effective combinations.

[0023] Generally speaking, the method according to the invention does not preferably use any toxic or environmentally unfriendly compound or product.

[0024] The process according to the invention comprises, in step a / , the preparation of a mixture, in an aqueous vehicle, of a monovalent alginate salt, a surfactant and an emulsion stabilizer. This mixture may in particular contain one or more monovalent alginate salt(s), one or more surfactant(s) and one or more emulsion stabilizer(s).

[0025] The aqueous vehicle is preferably water.

[0026] Each monovalent alginate salt can be formed from any monovalent cation. Preferably, this cation is sodium. Alternatively, it can be potassium.

[0027] The alginate salt(s) are preferably included in the mixture in a total amount of between 80 and 99% by weight relative to the total weight of ingredients introduced into the aqueous vehicle.

[0028] In the present description, the term "surfactant" means any compound capable of lowering the surface tension of the aqueous vehicle, with foaming properties. The surfactant(s) used according to the invention may be of any type, in particular anionic, cationic, amphoteric or non-ionic. They are preferably of the ionic type.

[0029] Any surfactant known to those skilled in the art may be used within the scope of the invention. Examples of such surfactants include:

[0030] - alkyl sulfates,

[0031] - alkylbenzene sulfonates,

[0032] - polyethylene glycol ethers,

[0033] - sorbitan and its derivatives,

[0034] - polysorbates and their derivatives,

[0035] - stearates and their derivatives,

[0036] - lecithins,

[0037] - monoglycerides,

[0038] - sucrose or fatty acid esters and their derivatives.

[0039] Each surfactant used in the context of the invention is preferably chosen from sodium lauryl sulfate, ammonium lauryl sulfate, sodium stearate, sodium dodecylbenzene sulfonate and polysorbates, these compounds being able to be used alone or in any of their mixtures.

[0040] The surfactant(s) are preferably included in the mixture in a total amount of between 0.1 and 0.6% by weight relative to the total weight of ingredients introduced into the aqueous vehicle.

[0041] In this document, the term “emulsion stabilizer” is understood to mean a compound capable of promoting and maintaining the expansion of the foam formed during a foaming step under the action of a surfactant, as well as stabilizing it. In this respect, the emulsion stabilizer is to be distinguished from surfactants, in particular in that it does not allow foam to be formed on its own, and in that it allows a formed foam to be stabilized more durably than a surfactant would. Thus, the emulsion stabilizer used in the process according to the invention is a compound distinct from the surfactant(s) also contained in the mixture prepared in step a / . In the context of the invention, the emulsion stabilizer used is preferably chosen for its ability to maintain the expansion of the foam until the end of step d / of maturation of the foam of the process or for at least the first 30 minutes of this maturation step.It has been discovered by the present inventors that the use, in the mixture prepared in step a / of the process, of the combination of a surfactant and an emulsion stabilizer, makes it possible to obtain solid bodies, in particular substantially spherical, of regular, stable and controlled size, formed from a foam with internal porosity that is advantageously closed and generally homogeneous throughout their internal volume. In particular, during a subsequent drying step of these solid bodies that can advantageously be included in the process according to the invention, no collapse of the internal pores of the foam occurs, nor any significant shrinkage of the solid bodies. The emulsion stabilizer(s) used according to the invention are preferably biosourced. They are for example chosen from:

[0042] - polyvinyl alcohols,

[0043] - thickening agents, such as cellulose and its derivatives, xanthan gum, guar gum, gum arabic, gellan gum, pectins, starches, etc.,

[0044] - polypeptides, i.e. amino acid chains containing 10 to 100 amino acids,

[0045] - and proteins, in particular phosphoproteins, such as casein, gelatins and other proteins derived from collagen, and globular proteins, such as albumins, for example ovalbumin, used alone or in any of their mixtures.

[0046] The emulsion stabilizer(s) are preferably included in the mixture in a total amount of between 0.2 and 2% by weight relative to the total weight of ingredients introduced into the aqueous vehicle.

[0047] Preferably, the mixture formed in step a / is free of calcium carbonate CaCOa and / or proton-releasing agent, such as gluconolactone. The method according to the invention may comprise, in step a / , the introduction into the mixture of at least one, i.e. one or more, additives, this or these additives being preferably, but not limited to, chosen from fibers, pigments, dyes and fillers. The choice of the particular additives incorporated in the mixture is made so as to obtain additional particular characteristics for the solid bodies formed, depending on the specific applications targeted, for example characteristics of appearance, density or mechanical strength.

[0048] Each of these additives is preferably bio-sourced.

[0049] The quantity of each of the additives introduced into the mixture is advantageously chosen so as not to negatively impact the foaming process targeted in step b / of the method. It is within the competence of the person skilled in the art to know how to determine this quantity for each given particular additive.

[0050] When used, the fibers are, for example, introduced into the mixture in an amount less than or equal to 10% by weight relative to the total weight of ingredients introduced into the aqueous vehicle.

[0051] These fibers are preferably of natural origin, particularly of the cellulosic type, such as hemp, cotton, coconut, linen, etc., or even silk.

[0052] Preferably, the fibers incorporated into the mixture have a length less than or equal to 1 mm, preferably between 100 and 300 μm, for example approximately equal to 200 μm. The incorporation of such fibers into the mixture advantageously makes it possible to increase the density of the solid bodies formed, and to improve their mechanical resistance performance.

[0053] The filler(s) may be chosen from activated carbons, clays, silica, titanium dioxide, cork, plant bark, or any of their mixtures. The total quantity of fillers incorporated into the mixture is preferably less than or equal to 2% by weight relative to the total weight of ingredients introduced into the aqueous vehicle.

[0054] In particular embodiments of the invention, the mixture formed in step a / of the process contains, in the aqueous vehicle, by weight relative to the total weight of ingredients introduced into the aqueous vehicle:

[0055] - 80 to 99%, in particular 90 to 99% of monovalent alginate salt(s),

[0056] - 0.1 to 0.6%, in particular 0.2 to 0.4%, of surfactant(s),

[0057] - 0.2 to 2%, in particular 0.5 to 1.5%, of emulsion stabilizer(s),

[0058] - 0 to 10% fiber,

[0059] - and 0 to 2% load(s).

[0060] An example of a mixture formed in accordance with the invention contains, in 4000 g of water: 0.4 g of surfactant, 0.6 g of emulsion stabilizer, in particular polyvinyl alcohol, and 60 g of sodium alginate. The mixing step a / can be carried out using any conventional mixer.

[0061] Step b / of foaming the mixture formed in step a / can be carried out in any conventional foaming module in itself, for example in a foamer allowing the aeration and emulsification of the mixture to be carried out, preferably continuously. This foaming module can for example be of the horizontal rotating axis type, such as the Mondomix VL aerator from the company Buhler, or of the vertical rotating axis type such as the Shuffle-Mix mixer from the company Ageniaa. The rotation speed of the rotating axis on itself in this module is preferably between 600 and 1000 rpm.

[0062] Preferably, the mixture formed in step a / is introduced continuously into the foaming module, at a flow rate which may for example be between 1.5 and 4 l / h in embodiments in which it is intended to supply around ten extrusion nozzles for carrying out step c / of the process, and the foam formed is also taken continuously therefrom, for carrying out this step c / .

[0063] The gas flow rate introduced into the mixture at this step b / can, for example, be between 20 and 50 ml / min for the same operating conditions for feeding around ten extrusion nozzles to carry out step c / .

[0064] This gas is preferably air.

[0065] Step c / of the process according to the invention comprises the extrusion of foam formed in step c / , directly by immersion in a first aqueous alginate gelling solution.

[0066] This first aqueous alginate gelling solution may be an acid solution, preferably with a pH less than or equal to 3, so as to ensure gelling of the alginate.

[0067] It may otherwise be of the type capable of causing ionotropic gelation of the alginate, resulting in the formation of a physical hydrogel, by formation within the alginate polymer chains of inter-chain interactions involving the mannuronic residues and the guluronic residues constituting the alginate. It may then have any conventional composition in itself. The first aqueous gelation solution may thus contain, in the water, one or more multivalent cations, for example one or more trivalent cations and / or one or more divalent cations, this (these) multivalent cation(s) preferably being of the metallic type. As divalent cations which may be used according to the invention, mention may in particular be made of calcium and magnesium.

[0068] Calcium, particularly preferred in the context of the invention, can be introduced into the first aqueous gelling solution in the form of a salt containing it with any counterion, in particular in the form of chloride, carbonate, sulfate, citrate, fluoride, glycerophosphate, hydroxide, oxalate, phosphate, saccharate, succinate, sulfite or tartrate. The concentration of calcium salt in the first aqueous gelling solution is preferably between 3 and 10 g / L. A concentration in such a range ensures optimal gelling of the alginate forming the foam.

[0069] When the first aqueous gelling solution is formed based on multivalent cation(s), in particular metallic cation(s), its pH is also preferably between 4 and 7.

[0070] The extrusion of the foam formed in step b / of the method, by immersion in the first aqueous gelling solution, can be carried out by any conventional extrusion module in itself, provided with one or more, for example 8 to 10, extrusion nozzles of the desired shape. The internal sections of the different nozzles used can be identical or different from each other, in particular in terms of shape and / or dimensions, so as to simultaneously form solid bodies of different shapes and / or dimensions. By way of example, in the particular embodiments of the invention aimed at the formation of solid bodies in the form of balls, the extrusion nozzles have a circular internal section.

[0071] Extrusion is preferably carried out continuously.

[0072] The feeding of the different extrusion nozzles can be carried out homogeneously, i.e. with the same flow rate. Alternatively, it is possible to use different feed streams, in order to simultaneously generate solid bodies of different sizes.

[0073] In particularly preferred embodiments of the invention, in step c / , the extrusion of the foam immersed in the first aqueous gelling solution is carried out in the lower zone of the reactor under a height of said first aqueous gelling solution of between 20 cm and 2 m, preferably of between 30 cm and 2 m, for example of between 30 cm and 80 cm. Such a height of the first aqueous gelling solution located in the reactor above the zone in which the foam is extruded into the latter, called "column of first gelling solution", proves to be particularly advantageous in that it makes it possible to form solid bodies of particularly well-controlled dimensions, and in particular solid bodies of regular spherical shape.

[0074] The cutting of foam fractions, as the latter enters the reactor, can be carried out by any means. For example, it can be carried out by means of a cutting member comprising at least one, that is to say one or more, cutting edge(s), such as a knife, immersed in the first aqueous gelling solution, each of said cutting edges being operable in rotation parallel to the lower part of the peripheral wall of the reactor at which the foam is introduced. The rotation speed of each cutting edge is then preferably between 200 and 500 rpm.

[0075] The distance between the part of the reactor wall at which the foam is introduced into the latter, and the sharp edge, is preferably as small as possible, preferably less than 1 mm, for example between 0.1 and 0.5 mm, in order to ensure that the sharp edge is as close as possible to the reactor wall, without however touching it.

[0076] The rotation speed of the cutting edge and the flow rate of introduction of the foam into the first aqueous gelling solution together condition the size of the cut foam fractions. Thus, in particular embodiments of the invention, in step c / , the rotation speed of the cutting edge and the extrusion flow rate are chosen to form foam fractions having a dimension of between 1 and 25 mm, the other dimensions being defined by the dimensions of the internal section of the extrusion nozzle(s). This dimension of the foam fractions determined by the rotation speed of the cutting edge and the extrusion flow rate is preferably the largest dimension of the foam fractions formed.

[0077] In particular embodiments of the invention, the foam fractions cut from the first aqueous gelling solution have a substantially cylindrical shape.

[0078] The foam fractions thus cut spontaneously rise towards the surface of the first aqueous gelling solution, due to their low density linked to their very aerated structure. During their movement within this solution, gelling of the alginate occurs, and, at the same time, the fractions are spontaneously shaped under the effect of the homogeneous pressure exerted on their surface by the liquid, as well as under the effect of the relaxation phenomenon of the alginate polymer, the surface tension at the level of the fractions and the osmotic pressure. This shaping is all the more important as the residence time of the foam fractions in the solution is longer.

[0079] In particular embodiments of the invention, advantageously extending this residence time, the foam fractions formed in step c / are extracted from the reactor from the upper zone of the latter, preferably at the level of the surface of the liquid medium which it contains, to be transferred into a maturation module for the implementation of step d / maturation of the foam forming these fractions.

[0080] In the particular configuration in which the cut foam fractions have a substantially cylindrical shape, depending on their size, their structuring can occur towards a substantially spherical shape, to form alginate-based expanded foam beads.

[0081] In particular embodiments of the invention, the flow rate of introduction of the foam into the first aqueous gelling solution and the height of the column of first gelling solution in the reactor between the extrusion zone in which the foam fractions are formed in the reactor and the extraction zone at which they are extracted therefrom to be transferred into the maturation module, are jointly chosen so as to ensure that the residence time of the foam fractions in the first aqueous gelling solution in the reactor, called the rising time, is greater than or equal to 1 second, preferably between 1 and 10 seconds.The height of the column of first gelling solution in the reactor between the extrusion zone in which the foam fractions are formed in the reactor and the extraction zone at which they are extracted therefrom to be transferred into the maturation module, is preferably between 20 cm and 2 m, preferably between 30 cm and 2 m, for example between 30 and 80 cm.

[0082] Step d / of maturation of the foam forming the fractions is carried out in a second aqueous solution of gelling of the alginate, so as to allow complete gelling of the material and the obtaining of solid bodies.

[0083] The second aqueous alginate gelling solution may have one or more of the characteristics described above with reference to the first aqueous alginate gelling solution.

[0084] The second aqueous gelling solution may thus contain, in the water, one or more multivalent cations, for example one or more trivalent cations and / or one or more divalent cations, preferably of the metal cation type. Divalent cations that may be used according to the invention include, in particular, calcium and magnesium. It may otherwise be an acid solution, with a pH less than or equal to 3.

[0085] The second aqueous gelling solution may be identical to the first aqueous alginate gelling solution, or different. It is preferably identical.

[0086] Thus, the second aqueous alginate gelling solution is preferably an ionotropic gelling solution, formed on the basis of a divalent cation, preferably metallic, preferably calcium. Such a characteristic proves to be particularly advantageous in that it offers the subsequent possibility of resolubilizing the material forming the solid bodies, for example by calcium / sodium exchange, resulting in obtaining the alginate in the form of sodium salt, soluble in water. The sodium alginate thus reformed can be used as a starting product for the process according to the invention, alone or in a mixture with non-recycled sodium alginate.

[0087] The maturation step d / can, for example, be carried out for a period of between 30 and 120 minutes.

[0088] Any conventional module in itself ensuring the prolonged maintenance of solid particles in suspension in a liquid medium can be used for carrying out the maturation step d / of the process according to the invention. Such a module can for example be a storage tank stirred at low speed. Preferably, the maturation module is chosen to allow, at the same time, the transfer of the foam fractions from the reactor used for step c / of the process, to an additional module within which the solid bodies formed will be separated from the liquid medium containing them. Thus, in particular embodiments of the invention, the maturation module is a concentric coil with a gentle slope, a worm screw, a paddle wheel, etc.

[0089] Preferably, the method according to the invention comprises, after the maturation step d / , a step e / of separation of the solid bodies and the second aqueous gelling solution. This separation step can be carried out in any conventional manner, for example by draining, in particular in a rotating sieve, and / or spinning, for example in a conventional spin dryer.

[0090] Step e / of separating the solid bodies and the second aqueous gelling solution may optionally be followed by a step f / of drying these solid bodies.

[0091] Preferably, this drying step is carried out in dynamic mode, the solid bodies being kept in motion, for example in a rotating drum or on an oscillating plate arranged in an oven, in particular a ventilated oven. Keeping the solid bodies in motion during drying in this way avoids in particular an asymmetrical modification of their geometry. The oven is preferably heated to a temperature between 40 and 80°C. The heating time depends on the quantity of solid bodies to be dried and the heating temperature. For example, in a rotating drum with a rotation speed of around 5 rpm, installed in an enclosure heated to a temperature between 70 and 80°C, the approximate drying time for a volume of 10 liters of wet solid bodies, making it possible to obtain a volume of approximately 2.5 liters of dry solid bodies, is approximately 8 to 10 hours.

[0092] Such a drying method causes a slight shrinkage of the solid bodies, and consequently a slight increase in their density, this shrinkage and this resulting increase in density being however advantageously very low. The drying step f / can otherwise be carried out by exposing the solid bodies to microwaves, for example in a microwave oven. Such a drying method has the advantage of being very rapid. A flow of between 200 and 600 W can for example be used, for a duration of between 3 and 10 min. For example, a flow of 600 W makes it possible in 5 minutes to form, from 40 grams of wet solid bodies, 2 grams of dry solid bodies.

[0093] Such a microwave drying method causes a slight expansion of the solid bodies, and consequently a slight reduction in their density. Each of the methods of implementing the drying step described above makes it possible to obtain a water loss of the solid bodies of at least 96% by weight. For all these drying methods, the performance can be improved by simultaneously exposing the solid bodies to an air flow.

[0094] The successive steps of the method according to the invention are preferably carried out continuously, by means of a device comprising means for transferring material from each module to the following module, operated continuously.

[0095] Another aspect of the invention relates to a solid body, in particular of substantially spherical shape, i.e. in the form of a ball, made of alginate-based expanded foam, capable of being obtained, in particular obtained, by a method according to the invention, preferably in its embodiments comprising final steps e / of separation of the solid bodies and the second aqueous gelling solution, and f / of drying the solid bodies. This solid body is characterized by:

[0096] - a size, here defined as the largest dimension of the solid body, measured by scanning electron microscopy, which is between 1 and 25 mm; in particular, in the particular embodiments in which the solid body has a substantially spherical shape, a size, i.e. a diameter, between 1 and 5 mm;

[0097] - an apparent density, defined as the ratio of the mass of the body, measured by weighing, in particular by means of a thermogravimetric analysis device, to its volume, determined in particular by X-ray microtomography, in particular at a voltage of 40 kV and a resolution of 4 pm per voxel, or by pycnometry, which is between 30 and 130 kg / m 3 , in particular between 30 and 50 kg / m 3 or between 50 and 130 kg / m 3 ;

[0098] - closed porosity, i.e. the pores are in the form of closed cells;

[0099] - and a porosity rate, defined as unity minus the ratio of the apparent density and the absolute (real) density, measured by helium pycnometry, the result of this subtraction being multiplied by 100, which is greater than or equal to 90%.

[0100] The apparent density of spherical solid bodies, called balls, can otherwise be measured by the so-called stacking method, from the measurement, by weighing, of the mass of a large quantity of balls, and the measurement of the volume that they occupy, itself determined by filling a large graduated cylinder with these balls. This method therefore considers, in addition to the volume of each ball ("intra volume"), the volume present between them ("interstitial volume"). By taking the hypothesis of a compact random stack of perfectly spherical balls, it can be estimated that this interstitial volume represents approximately 40% of the total volume (compactness of 60%), which has been verified by the present inventors. Thus, the apparent density range of 30 to 130 kg / m 3described above, obtained by the method involving the measurement of the volume of an individual ball, in particular by X-ray microtomography or pycnometry, is equivalent to a range of apparent density measured by the stacking method of between 20 and 80 kg / m 3 .

[0101] The alginate-based character of the expanded foam can be verified by any method known to those skilled in the art. Since alginate is a heteropolymer consisting of monomeric units of guluronic acid (G) and mannuronic acid (M), the characterization of the presence of alginate in the foam beads can be carried out by solid-state nuclear magnetic resonance (NMR) spectroscopy analysis, in particular of the magic angle type (CP-MAS 13C NMR). G residues can be identified by chemical shifts near 82.7, 68.4, and 65.7 ppm, while M residues are observed at 76.1 and 71.5 ppm (Sperger et al., 2011, Journal of Pharmaceutical Sciences, 100(8), 3441-3452). The simultaneous presence of these 5 peaks on the spectrum of 13 C NMR (solid) thus allows to characterize the presence of alginate (crosslinked by ionotropic gelation with divalent cations) within the solid body. As reported by Salomonsen et al., 2009, Food Hydrocolloids, 23, 1579-1586, the presence of alginate can also be verified by observing two other chemical shifts on the NMR spectra, respectively at 102.12 ppm for the G residue and 99.5 ppm for the M residue.

[0102] In particular embodiments of the invention, the solid body, in particular in the form of a ball, made of alginate-based expanded foam comprises a mass content of organic matter, composed mainly of multivalent cation alginate, in particular calcium alginate, as well as, where appropriate, organic fibers and / or fillers, which is between 80 and 99%. This mass content can in particular be verified by analyzing a sample of the solid body by thermogravimetric analysis (TGA), by subtracting from the total mass of the sample the water loss measured at approximately 110°C.

[0103] The solid body according to the invention can be used as bulk insulation, as padding material or as a decorative element, for example in the field of creative hobbies. Alternatively, it can be used for the production of a structured object, as will be described further in this description.

[0104] According to another aspect, the invention relates to a device for implementing a method according to the invention, for manufacturing solid bodies made of expanded foam based on alginate. This device comprises:

[0105] - optionally, a mixing module for the formation of a mixture of ingredients, intended for the implementation of step a / of the method according to the invention,

[0106] - a foaming module, for implementing step b / of the method according to the invention, comprising: a reservoir intended to contain, or containing, the liquid mixture formed in step a / ; an inlet for supplying this reservoir with liquid composition, preferably in hydraulic communication with the mixing module; a gas injector in the reservoir, more particularly in a zone of the latter intended to contain or containing the liquid mixture formed in step a / ; and an agitator for the liquid composition contained in the reservoir;- a reactor, intended to contain or containing the first aqueous alginate gelling solution, this reservoir being delimited by a peripheral wall and comprising a lower zone and an opposite upper zone, and being provided, at the level of the lower zone, intended to be filled or being filled with the first aqueous alginate gelling solution, with a cutting member comprising at least one cutting edge, this cutting edge being operable in rotation parallel to a lower part of the wall of the reactor, or any other mechanical or microfluidic shear cutting system;

[0107] - a foam extrusion module in the reactor, through said lower part of the reactor wall;

[0108] - a hydraulic foam transfer system from the tank to the extrusion module;

[0109] - a module for maturing alginate-based foam fractions to form solid bodies of expanded foam, intended to contain or containing the second aqueous alginate gelling solution;

[0110] - and a system for extracting the medium contained in the reactor and introducing this medium into the maturation module.

[0111] Preferably, this extraction system is configured to extract medium contained in the upper zone of the reactor, in particular liquid medium containing suspended solid fractions.

[0112] The device according to the invention may also optionally comprise:

[0113] - a module for separating solid bodies and liquid and a system for recovering the medium contained in the maturation module, in particular the liquid medium containing suspended solid fractions, and for introducing this medium into the separation module;

[0114] - thus, preferably, a module for drying solid bodies and a system for transferring solid bodies from the separation module to this drying module. Each of the modules of the device described above can meet one or more of the characteristics described above with reference to the module which can be used for implementing the associated step of the method according to the invention.

[0115] Thus, in particular:

[0116] - the mixing module can be any conventional mixer in itself; - the foaming module can be a frother, of the vertical or horizontal rotating axis type, or any device which allows air to be incorporated into a solution in order to create a foam, including discontinuously, such as for example an agitator equipped with a beater or a whisk;

[0117] - the extrusion module may comprise one or more extrusion nozzles, for example 8 to 10 in number, extending through the wall of the reactor so as to open into the interior of the latter, preferably at a lower part of this wall, these extrusion nozzles being able in particular to have a circular internal section;

[0118] - in the reactor, the distance between the lower part of the reactor wall and the cutting edge(s) of the cutting member may be between 0.1 and 0.5 mm;

[0119] - the maturation module can be a low-speed agitated storage tank, a gently sloping concentric coil, a worm screw or a paddle wheel;

[0120] - the solid and liquid body separation module may comprise a perforated conveyor belt, a rotating screen and / or a spin dryer;

[0121] - and / or the drying module may be a rotating drum or an oscillating tray arranged in an oven, in particular a ventilated oven, or a microwave oven.

[0122] In particular embodiments of the invention, the cutting member is one or more knives rotating around an axis perpendicular to said lower part of the reactor wall, at which the foam is introduced into the latter. Any other cutting system by mechanical or microfluidic shearing also falls within the scope of the invention.

[0123] Each of the constituents of the device according to the invention is preferably operable continuously, so as to allow continuous implementation of the method according to the invention.

[0124] Another aspect of the invention relates to a method for producing a structured object, by means of solid bodies made of expanded foam according to the invention, preferably obtained by a method according to the invention for manufacturing solid bodies made of expanded foam.

[0125] This process includes:

[0126] - the introduction of a plurality of solid bodies according to the invention, mixed with a binder, into a mold of a shape adapted to the desired shape for the manufactured object,

[0127] - the compression of this mixture in the mold,

[0128] - and drying of the mixture thus compressed.

[0129] It may comprise a preliminary step of implementing a method for manufacturing solid bodies made of expanded foam according to the invention, to obtain solid bodies which are introduced into the mold mixed with the binder.

[0130] Each of the steps of the method for producing a structured object according to the invention can be carried out using the usual techniques for manufacturing structured objects based on solid bodies made of polystyrene or polyurethane, and using the equipment commonly used for this purpose.

[0131] The binder used is preferably bio-sourced. It can be of different types, and have different specificities, allowing the structured object to be formed:

[0132] - reversibly, the binder being for example of the polyvinyl alcohol type, soluble in water, or a protein, such as albumin, gelatin, casein, etc., or a mixture of such proteins; when the object is immersed in hot water for example, in particular at around 40°C, the solubilization of the binder in the water then causes the object to disintegrate, the solid bodies forming part of its composition thus being able to be recovered, and if necessary reused, after possible drying, for example for the production of a different structured object;

[0133] - or irreversibly, the binder being for example a silicone, latex, etc.; such binders also make it possible to form objects with a certain degree of flexibility.

[0134] The binder may alternatively be starch or cellulose or one of its derivatives, such as hydroxypropyl methyl cellulose.

[0135] The ratio "weight of solid bodies (in grams) / volume of binder (in milliliters)" is preferably between 1 and 2, for example approximately 1.25. The mixing of the solid bodies with the binder is preferably carried out homogeneously, for example by means of a mixer, before introduction into the mold.

[0136] Additives, such as fibers, fillers, pigments, dyes, etc., may be added to the mixture, in particular to obtain the appearance and texture properties, and / or the mechanical properties, desired for the formed structured object.

[0137] In particular embodiments of the invention, the compression in the mold of the mixture of solid bodies in expanded foam based on alginate and binder is carried out so as to obtain a compression of a factor of 2 to 4, for example under a pressure of approximately 1 bar.

[0138] The drying step of the compressed mixture can be carried out in the mold, which can be perforated, open or closed, or outside the mold, depending on the degree of finish and precision of the dimensions desired for the formed structured object. This drying can be carried out in an oven or in a microwave oven, for example at a power of 150 or 160 W, preferably for a period of between 3 and 15 minutes.

[0139] The invention is also expressed in terms of the use of solid bodies of expanded foam according to the invention, preferably obtained by a method according to the invention for manufacturing solid bodies of expanded foam, for the production of a structured object. This use may meet one or more of the characteristics described above with reference to the method for producing a structured object according to the invention.

[0140] The structured object produced by the method according to the invention, based on solid bodies of alginate-based expanded foam manufactured in accordance with the invention, can be of any type. It can, for example, be packaging, a horticultural container, a decorative object, an insulating and / or flame-retardant plate, a flame propagation break device, in particular for the protection of electrical wiring, etc.

[0141] This object can find application in many fields, including packaging, archiving, protection, construction, decoration, creative leisure, fashion, luxury, etc.

[0142] It preferably has an apparent density, equal to the ratio of the mass of the object, measured by weighing, to its volume, determined by calculation from the measurement of its external dimensions, which is between 50 and 200 kg / m 3 .

[0143] Another subject of the invention thus relates to a structured object capable of being obtained, in particular obtained, by a method of producing a structured object according to the invention, this structured object comprising a plurality of solid bodies according to the invention mixed with a binder, and having an apparent density of between 50 and 200 kg / m 3 , preferably between 80 and 200 kg / m 3 , this density being equal to the ratio of the mass of the object, measured by weighing, to its volume, determined by calculation from the measurement of its external dimensions.

[0144] This structured object may be as described above with reference to the method according to the invention.

[0145] The characteristics and advantages of the invention will appear more clearly in the light of the examples of implementation below, provided for purely illustrative purposes and in no way limiting the invention, with the support of figures 1 to 15, in which:

[0146] Figure 1 represents a block diagram illustrating the steps of a method for manufacturing solid bodies according to the invention.

[0147] Figure 2 schematically represents a device for implementing a method of manufacturing balls according to the invention.

[0148] Figure 3 schematically represents an enlargement of the lower part of the reactor and the extrusion module of the device of Figure 2.

[0149] Figure 4 represents scanning electron microscopy images of alginate foam beads, having been exposed to different drying modes (S1 to S3), with the magnifications: in a / X70, in b / X150 and in c / X1000 for S1 and S3 and X1500 for S2.

[0150] Figure 5 shows the median section of an alginate-based expanded foam bead according to the invention, obtained by X-ray microtomography after segmentation.

[0151] Figure 6 shows, for the expanded alginate foam bead of Figure 5, images obtained by X-ray microtomography, in front view (in a / ) and 3 / 4 view (in b / ) of a hemisphere, and in overall view (in c / ).

[0152] Figure 7 shows a graph representing the heat flow rate released as a function of the heat applied, for beads according to the invention (“Alginate”) and polystyrene beads (“Polystyrene”) (data acquired on a combustion microcalorimeter). Figure 8 shows the lower part of Figure 7, with scale expansion (data acquired on a combustion microcalorimeter).

[0153] Figure 9 shows a graph representing the heat flow rate associated with the thermal degradation of beads in accordance with the invention as a function of time, analyzed by cone calorimetry (irradiance 35 kW / m 2 ).

[0154] Figure 10 shows a graph representing the heat rate (HRR) associated with the thermal degradation of beads according to the invention (“Alginate Beads”) or commercial flame-retardant polyurethane foam (“Flame-Retardant PU Foam”) as a function of time, during a cone calorimetry test (irradiance 35 kW / m2 ).

[0155] Figure 11 shows a graph representing the optical density of the smoke measured as a function of time during an NBS smoke chamber test carried out on balls conforming to the invention (irradiance 25 kW / m 2 ).

[0156] Figure 12 shows a graph representing the optical density of the fumes measured as a function of time during an NBS fume chamber test carried out on beads in accordance with the invention (“Alginate Beads”), as well as samples of polyamide 6, ethylene methyl acrylate copolymer, polypropylene and polybutylene terephthalate (irradiance 25 kW / m 2 ).

[0157] The successive steps of a method according to the invention for the manufacture of solid bodies made of expanded foam are illustrated schematically in Figure 1.

[0158] Figure 13 shows a photograph of an alginate-based expanded foam ball according to the invention respectively before (a / ) and after (b / ) the final drying step f / of the process according to the invention.

[0159] Figure 14 shows photographs of alginate-based expanded foam bodies, respectively in front view (A / ) and in side view (B / ), for a ball obtained by a process according to the invention (i) and for a body obtained by a process not in accordance with the invention not using an emulsion stabilizer (ii).

[0160] Figure 15 shows, for body (ii) of figure 14, obtained by a process not in accordance with the invention not using an emulsion stabilizer, a photograph of a hemisphere in front view.

[0161] In first step a / , the process comprises mixing 10, in an aqueous vehicle, preferably in water, one or more monovalent alginate salt(s), one or more surfactant(s) and one or more emulsion stabilizer(s), as well as, optionally, one or more additive(s), notably chosen from fibers, pigments, dyes and fillers.

[0162] The mixture thus obtained is subjected, in step b / , to foaming 20, by introducing gas, preferably air, into the mixture, and simultaneous stirring of the mixture.

[0163] In the following step c / , the foam formed at the end of this step is introduced, by immersion extrusion 30, into a first aqueous solution capable of causing the coagulation of the alginate used in the constitution of the foam. The method comprises cutting 40, into fractions, preferably of small size, of the foam as soon as it enters this aqueous solution.

[0164] The foam fractions obtained are then subjected, in step d / , to maturation 50, for a period of at least 30 min, so as to form the solid bodies of expanded foam based on alginate targeted.

[0165] In particular embodiments of the invention, the method then comprises successive steps of:

[0166] - in e / , separation 60 of solid bodies and the liquid medium which contains them,

[0167] - in f / , drying 70 of these solid bodies.

[0168] Particular embodiments of each of these steps are detailed below in the description of an example of a device in accordance with the invention, suitable for implementing this method, illustrated schematically in Figure 2.

[0169] The device shown in Figure 2 is configured for continuous implementation of the process.

[0170] In the particular example of implementation of the process detailed below, the first aqueous gelling solution and the second aqueous gelling solution are one and the same solution.

[0171] The device comprises a mixing module 11, called a mixer, for implementing the mixing step 10 of the method, more particularly the mixing, in an aqueous vehicle, for example in water, of one or more monovalent alginate salts, one or more surfactants, one or more emulsion stabilizers, and, optionally, one or more additives. From this mixer 11, the mixture formed is transferred, via a pipe 12, equipped with a pump 13, at a flow rate for example between 1.5 and 4 l / h, for the subsequent supply of around ten extrusion nozzles, in the direction indicated at 14 in the figure, to a foaming module 21, called a foamer, for implementing the foaming step 20 of the method.

[0172] The aerator 21 comprises a reservoir 22, an inlet 23 for supplying the reservoir 22 with mixture from the pipe 12, an injector 24 for gas into the reservoir 22 and an agitator 25 for the mixture contained in the reservoir 22. In the embodiment shown in the figure, the agitator 25 comprises a plurality of blades 251 extending, inside the reservoir, from a rotating central axis 252, perpendicular to the latter. For the implementation of the foaming step 20 of the method, the rotating central axis 252 is rotated on itself at a speed of 600 rpm for example. The aerator 21 is associated with a reserve 26 of gas, in particular compressed air, for example at a pressure of 1 bar.From this reserve 26, the gas circulates, preferably at a flow rate of between 20 and 50 ml / min, for the flow rates and number of extrusion nozzles indicated above, in a pipe 27, which leads it, in the direction indicated at 28 in the figure, to the gas injector 24 of the expander 21.

[0173] The device may comprise a module for preparing an aqueous alginate gelling solution. In the description below, for convenience, the particular embodiment example will be used in which this solution is an aqueous solution of calcium chloride at 3 to 10 g / l, with a pH between 4 and 7, such an example being in no way limiting of the invention. Those skilled in the art will easily be able to adapt this description to any other type of given aqueous gelling solution.

[0174] The module for preparing the aqueous gelling solution comprises a tank 81 containing a volume 82 of aqueous gelling solution. It is equipped with a rotary stirrer 83 formed by a blade 831 fixed at the end of an axis 832 driven in rotation on itself by a motor 833. An electrical conductivity meter 841 continuously measures the electrical conductivity of the solution contained in the tank 81, by means of a probe 842 immersed in this solution. This conductivity meter 841 controls a pump 843 ensuring the circulation of an aqueous mother solution of calcium chloride, for example at 60 to 80 g / l, contained in a reserve 844, in a pipe 845 carrying it, in the direction indicated at 846 in the figure, to the tank 81, so as to ensure permanent maintenance of the adequate concentration of calcium chloride in the solution contained in the tank 81.A pH meter 851 continuously measures the pH of the solution contained in the tank 81, by means of a probe 852 immersed in this solution. This pH meter 851 controls a pump 853 ensuring the circulation of an acid solution, contained in a reserve 854, in a pipe 855 carrying it, in the direction indicated at 856 in the figure, to the tank 81, so as to ensure permanent maintenance of the pH of the solution contained in the tank 81 at an adequate value.

[0175] From the tank 81, the aqueous alginate gelling solution is continuously circulated, at a flow rate of 4 l / min for example, by a pump 861, optionally through an ultraviolet ray treatment cell 864, in the direction indicated at 863 in the figure, to a reactor 31. The device is configured so that the reactor 31 permanently contains a volume 32 of the aqueous gelling solution filling it almost entirely.

[0176] The reactor 31 is delimited by a peripheral wall 311 and comprises, inside this peripheral wall, a lower zone 312 and an opposite upper zone 313.

[0177] The device further comprises a system 29 for hydraulically transferring foam formed in the reservoir 22 of the foamer 21 to an extrusion module 33 for implementing the submerged extrusion step 30 of the method. In the particular embodiment shown in FIG. 2, this hydraulic transfer system is formed by a pipe 29 opening at a first end 291 into the reservoir 22, and hydraulically connected at a second end 292 to the extrusion module 33. The foam formed in the reservoir 22 is continuously pushed into this pipe 29, and is driven in circulation therein, in the direction indicated at 293 in the figure. The extrusion module 33 is shown in more detail in FIG. 3. It comprises a plurality of extrusion nozzles 34, all in hydraulic communication with the pipe 29.These nozzles open into the interior of the reactor 31, in the lower zone 312 of the latter, through a lower part 314 of the peripheral wall 311 of the reactor, directly immersed in the aqueous alginate gelling solution. In the particular embodiment shown in the figures, this lower part 314 forms a bottom wall of the reactor 31. In the example of FIG. 3, the extrusion nozzles 34 are 10 in number, and they have an internal section of circular shape and of identical diameter, such characteristics being in no way limiting of the invention, the extrusion nozzles being able in particular to have internal sections of shape and / or dimension(s) different from each other. The foam brought by the pipe 29 is driven into the extrusion nozzles 34, in the direction indicated at 35 in FIG. 3, at flow rates which may be identical or different from one nozzle to another.At each extrusion nozzle 34, this foam is extruded into the reactor 31, in the volume 32 of aqueous gelling solution which it contains, in the form of a cylinder 46. The height of the column of gelling / coagulation solution located above the extrusion nozzles 34 in the reactor 31 is preferably between 20 cm and 2 m.

[0178] The reactor 31 is further equipped with at least one cutting member 41, parallel to the lower part 314 of the reactor wall, and arranged less than 1 mm away from the extrusion nozzles 34, for implementing the cutting step 40 of the method. In the exemplary embodiment shown in the figure, the reactor 31 comprises a single cutting member 41. This cutting member 41, such as a knife, is mounted at the end of a rotary shaft 43 perpendicular to the lower part 314 of the reactor wall. This shaft 43 is driven in rotation on itself, in the direction 44 indicated in the figures, by a motor 45, at a rotation speed of 200 to 500 rpm for example. As shown in more detail in figure 3, the cutting member comprises one or more cutting edges 42.The assembly is configured so that each cutting edge 42 is operable in rotation parallel to the lower part 314 of the wall of the tank, above the extrusion nozzles 34. Each rotating cutting edge 42 ensures, repetitively for each extrusion nozzle 34 after the other, a cutting of the foam cylinders 46, as they are extruded into the reactor 31, forming foam fractions 47.

[0179] The foam fractions 47 thus cut, due to their very low density, rise in the volume 32 / the column of aqueous gelling solution contained in the reactor 31 , towards the surface, as indicated at 48 in the figures. The coagulation of the alginate entering into their composition begins during their movement in this volume of solution 32. The pressure exerted on their surface by this solution, as well as the surface tension of the alginate polymer and the presence of the coagulating agent, induce at the same time their shaping. This shaping leads to the production of spheres in the particular case of foam fractions 47 obtained from extruded cylinders of circular section, and of height equal to the cross-sectional diameter of these cylinders. When they reach the upper zone 313 of the reactor 31 , the foam fractions 47 have thus undergone partial coagulation and they have a substantially spherical shape.The various process parameters are preferably chosen so that the rise time (rise time) of the foam fractions 47 in the gelling solution column is between 1 and 10 seconds.

[0180] The device comprises a system 52 for extracting the medium contained in the reactor and introducing this medium into a maturation module 51 for implementing the maturation step 50 of the process, visible in FIG. 2. In the particular embodiment shown in the figure, this extraction system 52 consists of a simple pipe, opening into the upper part 313 of the reactor, substantially at the level of the surface of the medium contained therein. This medium, comprising the aqueous gelling solution and foam fractions 47, flows spontaneously therein, under the effect of the continuous arrival in the reactor 31 of aqueous gelling solution, via the pipe 862. Preferably, the pipe 52 is inclined, from a higher end opening into the reactor 31 towards a lower end in hydraulic communication with the maturation module 51, so as to promote the circulation of the medium therein by gravity effect.

[0181] In the particular embodiment shown in Figure 2, the maturation module comprises a concentric coil 53, gently sloping so as to promote the flow of the medium therein by gravity effect. This slope is determined so as to ensure a residence time of the medium in the maturation module 51 of between 30 and 120 min. During their journey in the coil 53, the coagulation of the alginate of the foam fractions 47, in contact with the aqueous gelling solution 54, continues, until it is complete. Thus, at the outlet of the maturation module 51, bodies 55 made of expanded foam based on alginate in solid form are obtained.

[0182] The device may further comprise a module 61 for separating solid bodies and liquid, for implementing the solid / liquid separation step 60 of the method. In the particular embodiment shown in the figure, this separation module 61 comprises a rotating screen 62 and a wringer 63.

[0183] A pipe 64 in hydraulic communication with the outlet of the maturation module 51 leads the mixed liquid 54 / solid body 55 medium flowing from the maturation module 51 to the rotary sieve 62. The solid bodies 55 contained in the medium are led by this sieve, via an inclined plate 65, to the wringer 63, while the liquid flows through the perforations of the sieve, as indicated at 66 in the figure, to a recovery tank 67. From this recovery tank 67, the liquid can optionally be returned, by a pipe 68, optionally through an ultraviolet ray treatment filter 69, in the direction indicated at 681 in the figure, to the tank 81 of the module for preparing the aqueous gelling solution.

[0184] The wringer 63 is classic in itself, and allows the separation of the solid bodies 55 from the liquid with which they were mixed to be completed.

[0185] The device may also comprise a module 71 for drying solid bodies, for implementing the drying step 70 of the method, and a system 72 for transferring the solid bodies 55 from the wringer 63 to the drying module 71. This transfer system 72 is illustrated schematically, by an arrow, in FIG. 2. It may for example be a conveyor, conventional in itself.

[0186] The drying module 71, in the non-limiting embodiment of the invention shown in FIG. 2, comprises a rotating drum 76, into which the solid bodies 55 are conveyed. This rotating drum 76 is arranged in an enclosure 73 equipped with a heating member 74. This heating member 74 is preferably adjusted to obtain in the enclosure 73 a temperature of between 40 and 80°C.

[0187] At the outlet of the drying module, as indicated at 75 in Figure 2, the solid bodies 55 made of expanded foam based on alginate are recovered.

[0188] 1 / Example 1 - Preparation of alginate-based expanded foam beads Expanded foam beads in accordance with the invention are prepared using the device described above, applying the following operating protocol. The composition of the initial mixture is as follows:

[0189] - 60 g of sodium alginate,

[0190] - 0.4 g of sodium lauryl sulfate,

[0191] - 0.8 g of polyvinyl alcohol,

[0192] - 4000 g of water.

[0193] This mixture is introduced into the foaming module with a flow rate of 4 l / h. The rotation speed in the module is 700 rpm.

[0194] The foam generated in the foaming module is introduced into the extrusion module, directly immersed in the gelation / coagulation bath consisting of an aqueous solution of calcium chloride at 4 g / L. The rotation speed of the knife is equal to 300 rpm. The height of the gelation / coagulation bath column above the extrusion zone is 26 cm.

[0195] The residence time of the formed balls in the ripening module is equal to 40 min.

[0196] After their separation from the liquid medium, the beads are spun in the spinning module, then subjected to drying for 10 hours, according to 3 different protocols:

[0197] - batch S1: drying in a ventilated rotating drying drum: the beads are dried in a rotating drum at a rotation speed of 5 rpm, installed in an enclosure heated to a temperature of 70°C, and swept by a stream of hot air; for 1907 g of wet beads, 59 g of dry beads are obtained for a volume of 1990 mL;

[0198] - batch S2: drying in a non-ventilated rotating drying drum, under the same conditions as above, without sweeping by air current; for 1810 g of wet beads, 56 g of dry beads are obtained for a volume of 2200 mL;

[0199] - batch S3: drying in a ventilated oven, on a heating tray: the balls are placed flat on a flat surface heated to a temperature of 80°C, swept by a stream of hot air, for 4 hours; for 646 g of wet balls, 20 g of dry balls are obtained for a volume of 1000 mL.

[0200] For each drying mode, the water loss during the drying stage is equal to 97%.

[0201] 2 / Example 2 - Characterization of the beads

[0202] 2.1 / ​​Thermal conductivity

[0203] The measurement of the thermal conductivity of the beads formed in Example 1 was carried out on "bulk" beads from batches S1, S2 and S3, by the so-called "hot wire" method consisting of applying localized Joule heating and measuring the resulting temperature rise. Since the speed of this rise depends on the capacity of the material tested to dissipate heat, it is possible to deduce the thermal conductivity of this material by inverse identification.

[0204] The apparatus used is a Neotim FP2C model equipped with a hot wire probe. It was previously calibrated using a fiberglass panel of known thermal conductivity and certified by NIST (National Institute of Standards and Technology). For each batch of beads, repeatability was evaluated on 3 measurements.

[0205] The results indicate an average value of thermal conductivity, for all batches, of 0.032 ± 0.001 W / (mK), denoting a very good thermal insulation capacity of the balls according to the invention, regardless of the drying method tested.

[0206] 2.2 / Morphological characterization and closed internal porosity

[0207] 2.2. a / Observation by scanning electron microscopy

[0208] The beads are observed by scanning electron microscope, using a Quanta 200 FEG device from FEI Company.

[0209] The images obtained are shown in Figure 4. It can be deduced that the diameter of the balls obtained after drying is between 2 and 2.5 mm.

[0210] Scanning electron microscopy observations also highlight the porosity of the foam forming the beads. The polygonal geometry of the cells is irregular with variable dimensions. The internal porosity appears roughly hierarchical with generally larger cells at the core of the bead, probably resulting from the association of several neighboring cells during the coagulation process, then progressively a decrease in the size of these cells along the diameter of the bead towards the outer skin. The average width of these cells, measured for example by microphotography, is of the order of 50 to 100 pm, with thinner cells of a few tens of pm, but up to 250 to 400 pm. The average wall thickness is also estimated at approximately 2 pm.

[0211] 2.2. b / Analysis by pycnometer

[0212] Beads from batch S1 were analyzed using an Accupyc 1330 helium pycnometer from Micromeritics Instrument Corporation. Since this method is based on direct volume measurement, in order to allow the helium gas used to access the bead cells, which are mostly closed, the beads were finely ground using a blender before characterization, thus opening all the pores and accurately determining the actual volume of material. Repeatability was assessed over 3 measurements.

[0213] The absolute density (i.e. the density of the walls of the balls) obtained is equal to 1.682 ± 0.002 g / cm 3 .

[0214] 2.2.c / Analysis by X-ray microtomography

[0215] Three beads from batch S1 were scanned using X-ray microtomography to study their internal structure in three dimensions. For each of them, an EasyTom 150 microtomograph from RX Solutions was used with a voltage of 40 kV and made it possible to obtain a volume with a resolution of 4 pm per voxel.

[0216] After reconstruction of the different angular projections, a median filter was applied to reduce digital noise. The volume was then segmented by thresholding on the gray levels in order to obtain a binary image thus distinguishing the areas of matter and the areas of air. The choice of threshold was chosen in such a way as to preserve as much as possible the integrity of the walls whose thickness (estimated by SEM at approximately 2 pm) is less than the resolution of the scan. This results in an overestimation of the thickness of these walls and therefore of the overall volume of matter compared to that of air.

[0217] The results obtained are shown in Figure 5 (in which the material is represented in white and the pores are represented in black) and Figure 6. Microtomography observations confirm the microstructure observed by scanning electron microscopy.

[0218] The porosity rate is the ratio between the volume of air in the cells of the alveoli and the total volume of the ball (i.e. the sum of the volume of air inside the ball and that of material). However, for the reasons mentioned above, the total volume of material is overestimated compared to the total volume of air, leading to an underestimation of the porosity rate by this method. In order to evaluate it more precisely, the apparent density of each of the three balls was evaluated by calculating the ratio of their mass to their apparent volume determined by X-ray microtomography. This gives an apparent density of 0.07 ± 0.01 g / cm3 The porosity rate, defined as unity minus the ratio of "the apparent density, calculated as indicated above, to the absolute (true) density, measured by helium pycnometry, of the beads", the result of this subtraction being multiplied by 100, is 96% ± 1%.

[0219] 3 / Example 3 - Fire properties

[0220] 3.1 / Combustion microcalorimetry

[0221] The test is carried out according to ASTM D7309 method A (anaerobic pyrolysis) using the Fire Testing Technology combustion microcalorimeter. Approximately 3 mg of beads from Lot S1 are placed in a crucible and pyrolyzed under nitrogen flow (100 mL / min) at a rate of 1 K / s up to 750°C. The generated gases are continuously sent into a combustion chamber in the presence of excess oxygen (N2 / O2 80 / 20). The temperature (900°C) and the residence time (10 ms) ensure complete combustion of the material.

[0222] For comparison, commercial expanded polystyrene foam beads (Lacqrène® 1340 polystyrene, Atofina) are also subjected to the same operating protocol.

[0223] The results obtained, in terms of heat flow associated with the thermal degradation of the foam beads, as a function of the temperature to which they are exposed, are shown in Figure 7 and Figure 8 (corresponding to a scale expansion of Figure 7).

[0224] As can be observed, the heat flow rate of alginate beads according to the invention is much lower than that of polystyrene beads, and does not exceed 10 W / g, with two main peaks located at 263°C and 497°C. The residue at 750°C is 25-30%.

[0225] Furthermore, the energy released by the balls according to the invention does not exceed 2 kJ / g, and their heat release capacity (equal to the peak heat flow divided by the heating rate) is equal to 10 J / gK. These values ​​demonstrate remarkable fire behavior of the balls according to the invention.

[0226] 3.2 / Cone calorimeter test

[0227] The test is carried out according to ISO 5660 using a cone calorimeter (Fire Testing Technology). 16 g of beads from Batch S1 are poured into the standard sample holder (10 cm side) so as to form a 3 cm thick bed of beads. The applied irradiance is 35 kW / m 2 The ignition is said to be piloted and the test lasts 350 s.

[0228] No ignition is observed during this test. The heat flow rate, shown in Figure 9, reaches a value of 16 kW / m 2after 150 s and stabilizes, which corresponds to the slow thermo-oxidation of the beads. After 350 s, the residue is 45% and the total energy released is 3.2 MJ / m 2 or 1.76 kJ / g of balls. The effective combustion energy is 3.2 kJ / g.

[0229] The heat flow profile of the beads according to the invention is compared to that of commercial flame-retardant polyurethane foam beads (Efigreen® ITE, Soprema) subjected to the same operating protocol. The curves obtained are shown in Figure 10. The heat flow rate of the foam according to the invention is much lower than that of commercial flame-retardant polyurethane foam.

[0230] 3.3 / NBS smoke chamber test

[0231] The test is carried out according to ISO 5660 using an NBS (Fire Testing Technology) smoke chamber. 10.5 g of beads from Batch S1 are poured into the standard sample holder (7.5 cm side). The applied irradiance is 25 kW / m 2The ignition is said to be piloted and the test lasts 600 s.

[0232] No ignition is observed. The optical density of the smoke is measured according to the method described in ISO 5659-2:2017, with a 6.5 V incandescent lamp as the light source and a photomultiplier tube as the photodetector. This optical density, the evolution of which over time is shown in Figure 1 1 , increases continuously until it reaches a value of 16 (optical density unit) and then stabilizes. The residue after 600 s is 38%.

[0233] Commercially available alternative materials (polybutylene terephthalate, polypropylene, ethylene methyl acrylate copolymer, polyamide 6) in the form of 7.5 x 7.5 cm surface plates 2, 4 mm thick, are also subjected to the same operating protocol. Figure 12 shows the smoke emission profile (optical density as a function of time) of each of these materials, in comparison with the beads according to the invention. It can be seen that the alginate expanded foam beads according to the invention emit a significantly lower quantity of smoke than the comparative materials.

[0234] 4 / Example 4 - Preparation of expanded foam beads based on alginate containing cellulose fibers

[0235] Expanded foam beads in accordance with a variant of the invention, containing cellulose fibers, are prepared using the device described above, applying the following operating protocol.

[0236] The composition of the initial mixture is as follows:

[0237] - 60 g of sodium alginate,

[0238] - 6.5 g of Arbocel® B400 cellulose fibers (JRS Rettenmaeir, 900 pm (length) x 20 pm (diameter)),

[0239] - 0.4 g of sodium lauryl sulfate,

[0240] - 0.8 g of polyvinyl alcohol,

[0241] - 4000 g of water.

[0242] This mixture is introduced into the foaming module with a flow rate of 4 l / h. The rotation speed in the module is 700 rpm.

[0243] The foam generated in the foaming module is introduced into the extrusion module, directly immersed in the gelling / coagulation bath consisting of an aqueous solution of calcium chloride at 4 g / L. The rotation speed of the knife is equal to 300 rpm.

[0244] The residence time of the formed balls in the ripening module is equal to 40 min.

[0245] The expanded foam beads based on calcium alginate, containing the cellulose fibers, obtained are separated from the liquid medium, wrung out and then dried. 5 / Example 5 - Manufacture of bead-based plates according to the invention

[0246] A mass of 30 g of expanded foam beads formed in Example 1 (Batch S1) are mixed with 30 g of gelatin glue, prepared according to the following respective proportions: 22.5 g of water, 6 g of gelatin and 1.5 g of glycerin.

[0247] The mixture obtained is introduced into a rectangular mold and subjected to a pressure of 1 bar until a compression of a factor of 2 is obtained. The compressed block is dried in an oven at a temperature of 60°C for 12 hours.

[0248] We obtain a plate with dimensions of 12.5 x 12.5 x 3 cm 3 and apparent density 70 kg / m 3 (mass 33 g).

[0249] The resulting foam bead board was tested for its flame retardant properties.

[0250] The test was carried out according to ISO 5660 using a cone calorimeter (Fire Testing Technology). The plate prepared above (3 cm thick, apparent density 70 kg / m 3 ) was placed on the sample holder (standard sample holder, side 10 cm; mass: 22 g). 75 kW / m 2 irradiance were applied. The ignition is said to be piloted and the test lasted 585 s.

[0251] This test recorded an ignition time of 190 s to cause the material to ignite. Extinction occurred at 305 s, so the ignition time was only 1.15 s. The peak heat release rate (pHRR) reached 46 kW / m 2 during the ignition phase. After 250 s, the total heat release (THR) reached 5.9 MJ / m 2, or 2.4 kJ / g of foam, and the combustion energy was 4 kJ / g.

[0252] Outside the ignition period, the heat flow rate remained at a very low but not negligible and decreasing level (< 20 kW / m 2 ). This is due to the slow (flameless) thermo-oxidation of the material and the char produced during pyrolysis.

[0253] After 585 s (end of test), the residue reached 31%, the pyrolysis front did not reach the bottom of the sample. The THR (at 585 s) reached 10.7 MJ / m 2 or 4.3 kJ / g of foam. The corresponding combustion energy was 6.2 kJ / g. Its tendency to increase is due to the fact that the oxidation of the char, a polyaromatic compound, releases more energy. All these values, however, remain very low and correspond to an excellent reaction to fire.

[0254] 6 / Example 6 - Preparation of expanded foam beads based on alginate - Dimensional stability

[0255] Expanded alginate foam beads in accordance with the invention are prepared using the device described above, applying the following operating protocol.

[0256] The composition of the initial mixture is as follows:

[0257] - 75 g of sodium alginate,

[0258] - 0.3 g of sodium lauryl sulfate,

[0259] - 0.8 g of polyvinyl alcohol,

[0260] - 5000 g of water.

[0261] This mixture is introduced into the foaming module with a flow rate of 4 l / h. The rotation speed in the module is 700 rpm.

[0262] The foam generated in the foaming module is introduced into the extrusion module, directly immersed in the gelation / coagulation bath consisting of an aqueous solution of calcium chloride at 5 g / L. The rotation speed of the knife is equal to 300 rpm. The height of the gelation / coagulation bath column above the extrusion zone is 30 cm.

[0263] The residence time of the formed balls in the ripening module is equal to 40 min.

[0264] After separation from the liquid medium, the beads are wrung out in the wringing module, then subjected to drying in an industrial dryer (rotary drum dryer) in batches of wet beads, at 75°C for 90 min.

[0265] The weight loss of the logs during drying is determined by weighing each batch before / after drying. From this, the proportion of water in the wet logs is deduced for each batch:

[0266] - Batch 1: wet mass 5.366 kg / dry mass 144 g / proportion of water in wet balls: 97.3% by weight;

[0267] - Batch 2: wet mass 5.724 kg / dry mass 150 g / proportion of water in wet balls: 97.4% by weight;

[0268] - Batch 3: wet mass 4.584 kg / dry mass 120 g / proportion of water in the wet beads: 97.4% by weight. An example of a bead before / after drying is shown in Figure 13. It can be seen that the size of the bead after drying (in b / in the figure) is substantially identical to that before drying (in a / ).

[0269] This is confirmed by measuring the size of the beads before and after drying using a Neo Tools digital caliper. This size is measured at 3.93 mm before drying, and 3.72 mm after drying.

[0270] These results demonstrate an absence of significant shrinkage of the beads formed by the process according to the invention, a consequence of an absence of collapse of their internal pores, during drying.

[0271] The apparent density of the obtained balls, determined by the stacking method, is approximately 20 kg / m 3 .

[0272] 7 / Example 7 - Comparative example without emulsion stabilizer

[0273] Bodies made of expanded alginate foam are prepared using the device described above, applying the following operating protocol.

[0274] The composition of the initial mixture is as follows:

[0275] - 75 g of sodium alginate,

[0276] - 0.3 g of sodium lauryl sulfate,

[0277] - polyvinyl alcohol: either 0.8 g (process in accordance with the invention), or 0 g (process not in accordance with the invention),

[0278] - 5000 g of water.

[0279] Each mixture is introduced into the foaming module with a flow rate of 4 l / h. The rotation speed in the module is 700 rpm.

[0280] The foam generated in the foaming module is introduced into the extrusion module, directly immersed in the gelation / coagulation bath consisting of an aqueous solution of calcium chloride at 4 g / L. The rotation speed of the knife is equal to 300 rpm. The height of the gelation / coagulation bath column above the extrusion zone is 26 cm.

[0281] The residence time of the formed bodies in the ripening module is equal to 40 min.

[0282] After their separation from the liquid medium, the bodies are wrung out in the wringing module, then subjected to drying in an industrial dryer (rotary drum dryer) in batches of 3 kg of wet bodies, at 75°C for 90 min. The apparent density of the beads obtained by the process according to the invention, determined by the stacking method, is approximately 70 kg / m 3 That of the bodies obtained by the process not in accordance with the invention (without emulsion stabilizer), also determined by the stacking method, is approximately 80 kg / m 3 .

[0283] The bodies obtained at the end of each of the two processes are shown in Figure 14, in front view (A / ) and side view (B / ). A difference in geometry between these bodies is clearly observed: while the bodies (i) obtained by the process according to the invention are substantially spherical, and can be described as beads, this is not the case for the bodies (ii) obtained by the process not in accordance with the invention which does not use an emulsion stabilizer. These bodies (ii), in addition to their irregular shape, have a size much smaller than that of the bodies (i) obtained by the process according to the invention. Furthermore, unlike the latter, they are deformable and they have a sticky surface, indicating a disruption of the gelation.

[0284] Figure 15 illustrates the modification of the internal structure of one of the bodies (ii), linked to the absence of the emulsion stabilizer: we observe the presence of an internal cavity, highlighted in the figure by a dotted circle and an arrow, within which the micro-bubbles have collapsed and form an alveolus representing approximately one third of the diameter of the body. This change in alveolar structure (loss of internal alveoli) leads to a "weakening" of the material (loss of rigidity leading to the deformability of the body) and a slight increase in its density.

[0285] These results demonstrate the importance of using an emulsion stabilizer in addition to the surfactant, to obtain the performance targeted by the invention.

Claims

CLAIMS 1. Method for manufacturing solid bodies made of expanded foam (55), characterized in that it comprises successive stages of: - a / preparation (10) of a mixture, in an aqueous vehicle, of a monovalent alginate salt, a surfactant and an emulsion stabilizer, - b / foaming (20) of said mixture, comprising the introduction of a gas into said mixture and the concomitant stirring of said mixture, so as to form foam, - c / extrusion (30) of the foam thus formed by immersion in a first aqueous gelling solution of the alginate, and cutting (40) of fractions (47) of said foam as it enters said first aqueous gelling solution, said first aqueous gelling solution being contained in a reactor (31) comprising a lower zone (312) and an opposite upper zone (313), and the extrusion (30) of said foam by immersion in said first aqueous gelling solution being carried out in said lower zone (312) of the reactor (31), - d / maturation (50) of the foam forming said fractions (47) in a second aqueous alginate gelling solution, for a period of at least 30 minutes, so as to form said solid bodies in expanded foam (55).

2. Method according to claim 1, comprising, after step d / of maturation, a step e / of separation (60) of said solid bodies (55) and of said aqueous gelling solution, optionally followed by a step f / of drying (70) of said solid bodies (55).

3. Method according to claim 1 or 2, according to which, in step c / , the extrusion (30) of said foam immersed in said first aqueous gelling solution is carried out in said lower zone (312) of the reactor (31) under a height of said first aqueous gelling solution of between 20 cm and 2 m.

4. Method according to any one of claims 1 to 3, according to which the foam fractions (47) formed in step c / are extracted from said upper zone (313) of the reactor (31) and transferred into a maturation module (51) for the implementation of step d / of maturation (50) of the foam forming said fractions (47).

5. Method according to any one of claims 1 to 4, according to which, in step c / , the cutting (40) is carried out to form fractions (47) of foam having a dimension between 1 and 25 mm.

6. Method according to any one of claims 1 to 5, according to which said first aqueous gelling solution and / or said second aqueous gelling solution contains a multivalent cation or is a solution with a pH less than or equal to 3.

7. A method according to any one of claims 1 to 6, wherein said surfactant is selected from sodium lauryl sulfate, ammonium lauryl sulfate, sodium stearate, sodium dodecylbenzene sulfonate and polysorbates.

8. Method according to any one of claims 1 to 7, according to which said emulsion stabilizer is chosen from polyvinyl alcohols and proteins.

9. Method according to any one of claims 1 to 8, comprising, in step a / , the introduction into said mixture of at least one additive chosen from fibers, pigments, dyes and fillers.

10. A method according to any one of claims 1 to 9, wherein said mixture contains, in said aqueous vehicle, by weight relative to the total weight of ingredients introduced into the aqueous vehicle: - 80 to 99% of monovalent alginate salt(s), - 0.1 to 0.6% of surfactant(s), - 0.2 to 2% of emulsion stabilizer(s), - 0 to 10% fiber, - 0 to 2% charge(s).

11. Solid body of expanded foam based on alginate (55) obtained by a method according to any one of claims 1 to 10, - spherical in shape, - between 1 and 25 mm in size, - apparent density, defined as the ratio of the mass of the body, measured by weighing, to its volume, determined in particular by X-ray microtomography, between 30 and 130 kg / m 3 , -closed porosity, - and a porosity rate greater than or equal to 90%.

12. Use of solid bodies made of expanded foam (55) according to claim 11 for the production of a structured object.

13. Device for implementing a method according to any one of claims 1 to 10, characterized in that it comprises: - a foaming module (21) comprising a reservoir (22), an inlet (23) for supplying said reservoir (22) with liquid composition, a gas injector (24) into said reservoir (22) and an agitator (25) for the liquid composition contained in said reservoir (22), - a reactor (31), delimited by a peripheral wall (311) and comprising a lower zone (312) and an opposite upper zone (313), said reactor (31) being provided, at the level of said lower zone (312), with a cutting member (41) comprising at least one cutting edge (42) operable in rotation parallel to a lower part (314) of said wall (311) of the reactor, - a module (33) for extruding foam into said reactor (31), through said lower part (314) of the wall (311) of the reactor, - a system (29) for hydraulic transfer of foam from the tank (22) to the extrusion module (33); - a module (51) for maturing alginate-based foam fractions to form solid bodies of expanded foam, - and a system (52) for extracting medium contained in said reactor (31) and introducing said medium into said maturation module (51).

14. Device according to claim 13, wherein said extraction system (52) is configured to extract medium contained in the upper zone (313) of the reactor (31).

15. Device according to claim 13 or 14, comprising a module (61) for separating solid bodies and liquid and a system (64) for recovering medium contained in said maturation module (51) and introducing said medium into said separation module (61).

16. Device according to claim 15, comprising a module (71) for drying solid bodies and a system (72) for transferring solid bodies from said separation module (61) to said drying module (71).

17. Method for producing a structured object, comprising: - the introduction of a plurality of solid bodies (55) according to claim 11, mixed with a binder, into a mold, - compressing said mixture in said mold, - and drying said compressed mixture.

18. Structured object obtainable by a method for producing a structured object according to claim 17, comprising a plurality of solid bodies (55) according to claim 11 mixed with a binder, and having an apparent density, defined as the ratio of the mass of the object, measured by weighing, to its volume, determined by calculation from measurement of its external dimensions, of between 50 and 200 kg / m 3 .

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