Method for producing alginate-based expandable foam solids and apparatus for carrying out the method

Abstract

The present invention relates to a method for producing expanded foam solids, comprising the following steps: (10) preparing a mixture of monovalent alginate, a surfactant, and an emulsion stabilizer in an aqueous carrier; (20) foaming the mixture; (30) extruding the foam thus formed so as to be directly immersed in an aqueous solution for gelling the alginate; (40) cutting the foam fragments as the foam enters the solution; and (50) maturing the foam fragments in the aqueous solution for at least 30 minutes to form expanded foam solids for gelling the alginate.

Description

[Technical Field]

[0001] This invention belongs to the general field of manufacturing structured objects having thermal insulation properties and flame retardant properties.

[0002] More specifically, the present invention relates to a method for producing alginate-based expandable foam solids and an apparatus for carrying out such method. The present invention also relates to the alginate-based expandable foam solids obtained by such method and their use for producing structured objects. Another object of the present invention is a method for producing structured objects using such solids. [Background technology]

[0003] Objects made from low-density materials with thermal insulation properties are used in many fields, including packaging, construction, and storage. The materials forming these objects are generally petroleum-based, such as polystyrene or polyurethane, and are characterized by their low density as well as their good mechanical properties and moldability. However, these materials have drawbacks related to both their manufacturing processes, which require methods that are not particularly environmentally friendly or safe, and their lifecycle, particularly due to their very low biodegradability and composability. Furthermore, recycling polystyrene remains complex and underdeveloped for the time being, and involves particularly serious overall environmental impacts. Regarding manufacturers' responsibility for the lifecycle of such materials, legislation remains relatively lax. Changes in legislation and regulatory practices will inevitably lead to addressing this issue in the future.

[0004] Furthermore, it has been found that the flame retardancy desired for many applications of such materials is very insufficient.

[0005] To overcome these drawbacks of petroleum-based materials, conventional technologies aim to select materials that have properties at least as good as those of commonly used petroleum-based materials. This requires replacing these materials with biodegradable and compostable materials, particularly cellulosic biopolymers derived from algae, fungal biomass, etc.

[0006] U.S. Patent No. 5,840,777 describes a method for producing a polysaccharide-based foam film. This method involves preparing a mixture containing a polysaccharide and a blowing agent, which may also contain divalent or trivalent cations, particularly calcium; then foaming the mixture by introducing gas and applying shear force; and subsequently acid-treating the foam. The result is an open-pore foam with suboptimal thermal insulation properties.

[0007] British Patent No. 584140 describes a method for producing foam from an alginate-based material, comprising the steps of mixing alginate with a blowing agent, foaming, and then transferring the foam in strand form into a calcium salt solution to bring the foam into contact with the calcium salt solution and gel the foam. The foam obtained by this method has a yield of several hundred kg / m³. 3 It has a high density. Furthermore, their size is uncontrollable because this size decreases rapidly during the final drying process of this method.

[0008] For example, French Patent No. 3094372 proposes a method for producing closed-pore foam by in-situ solidification of biopolymers. However, such a method requires numerous reagents to achieve optimal solidification. Furthermore, the implementation of this method is not well compatible with general industrial practices, particularly in the field of packaging manufacturing. [Overview of the project] [Problems that the invention aims to solve]

[0009] This invention overcomes the shortcomings of solutions proposed by prior art, and provides a bio-based material, in particular a low-density, preferably 100 kg / m³, based on the aforementioned bio-based material. 3 The objective is to manufacture a structured object with good thermal insulation properties at a cost of less than [amount missing]. The present invention is intended to propose a solution for this purpose that is particularly easy to implement, particularly easily adaptable from laboratory to industrial scale, and enables the formation of products that have not only good thermal insulation properties but also other functionalities, particularly good flame retardancy and, if necessary, good mechanical resistance properties. [Means for solving the problem]

[0010] For this purpose, the inventors were more specifically interested in alginates, brown algae, and more specifically, anionic polysaccharides derived from the genera Laminaires and Fucus, as early bio-based materials. Alginates are characterized in particular by their gelling ability, especially ion channel gelation. The inventors have developed a particularly advantageous method for producing small-sized and low-density closed-porous alginate-based expanded foam solids. These solids have great versatility in their shaping, which can be done by molding, machining, etc., especially when they are in the form of beads. Therefore, they can be easily used to produce larger structured objects using industrial techniques that are normally used for producing objects made from, for example, expanded foam beads made of polystyrene. Their shaping is easier. Objects thus formed have not only good thermal insulation properties but also good flame retardancy properties. They are easy to mold, especially cut, sandblasted, etc.

[0011] Accordingly, according to a first aspect, a method is proposed according to the present invention for producing expanded foam solids, in particular expanded foams, i.e., substantially spherical, i.e., bead-shaped expanded foam solids of alveolar-type material in which the cells are advantageously closed. This method is as follows: a / A step of preparing a mixture of monovalent alginate, surfactant and emulsion stabilizer in an aqueous carrier, b / A step of foaming the mixture, comprising introducing gas into the mixture and simultaneously stirring the mixture to form a foam through the combined action of a surfactant and an emulsion stabilizer. c / The step of extruding the thus formed foam while immersed in a first aqueous gelling solution for gelling an alginate, and cutting the foam fragments as they enter the aqueous gelling solution, wherein the first aqueous gelling solution is contained in a reactor having a lower zone and an upper zone on the opposite side, and the extrusion of the foam while immersed in the first aqueous gelling solution is carried out in the lower zone of the reactor, preferably through the bottom wall of the reactor, or through the peripheral wall of the reactor in a zone near the bottom wall. d / A step of maturing the foam forming the fragment in a second aqueous gelling solution for gelling the alginate for at least 30 minutes to form the desired expanded foam solid. This includes a series of steps.

[0012] Therefore, the method according to the present invention combines the technique of foaming by expansion in step b / of the method, the technique of immersion extrusion of the formed foam in a bath of a suitable composition to induce solidification of the alginate forming the foam in step c / , and the resulting solidification of the material. Such a combination is advantageous in that, by the appropriate selection of the shape of the internal cross-section of the extrusion nozzle used in particular, it is possible to form solids of a desired shape, particularly spherical or cylindrical, and these solids further have low density and good mechanical properties. In particular, the extrusion of alginate-based foams by direct immersion in an aqueous gelling solution has been found to be far more effective than conventional extrusion methods that operate on the principle of gravity falling by releasing droplets above the solidification bath in terms of controlling the shape and properties of the solids formed. In these conventional extrusion methods, due to the highly airy structure of the foam and the resulting flotation phenomenon, droplets of material released from the extrusion head accumulate on the surface of the solidification bath, which slows down or even hinders the solidification of the alginate in the bath. In contrast, in step c / of the method according to the present invention, the solidification of the alginate begins immediately in the aqueous gelling solution as soon as the foam exits the extrusion nozzle and continues throughout the entire immersion time of the foam fragment in the aqueous gelling solution, i.e., through the time that the foam fragment naturally rises to the surface of the solution due to its low density. The resulting solidification of the alginate is accompanied by the spontaneous structuring of the foam fragment under the influence of the uniform pressure applied to the surface of the foam fragment by the aqueous gelling solution as the foam fragment is cut and moves through the aqueous gelling solution. This spontaneous shaping of the foam fragment in the aqueous gelling solution is particularly advantageous and effective when it is desirable to form spherical or cylindrical solids.

[0013] Therefore, after step d / of maturing the foam, a solid made of bio-based material is advantageously obtained at the end of the method according to the present invention, which is biodegradable and compostable, has closed internal pores, and possesses properties at least as good as polystyrene expandable foam, in particular good thermal insulation properties inherent to the expandability of foam, e.g., 30-80 kg / m 3have a low apparent density and good mechanical properties. These solids are also easy to handle and can be processed, in particular, using techniques and apparatus commonly available in the art for the manufacture of objects made of expanded polystyrene, and in particular, drying, adhesion, assembly, formation by molding, structuring on plates or various objects, etc. is also easy.

[0014] Very advantageously, the solids obtained at the end of the method according to the invention also have good fire resistance properties after drying, in particular due to the properties of the alginate, especially low combustion energy, and high self-extinguishing properties due to the formation of char after their exposure to flames. Such properties are particularly advantageous in the construction field, for example for the formation of flame-retardant devices for the protection of electrical wiring, and in the packaging and storage fields, both in the luxury goods sector and in the packaging and storage fields for both storage and protective packaging, art and handicrafts, decoration, etc.

[0015] The method according to the invention is also environmentally friendly. In particular, its implementation does not require solvents or toxic products.

[0016] The alginate used in the method according to the invention can be of any origin, and in particular can be extracted from algae that produce alginate naturally, such as, for example, those of the genus laminaria or fucus. Alternatively, the alginate can be produced by bacteria such as those of the genus Pseudomonas or Azotobacter.

[0017] Alginates based on monovalent cations such as sodium or potassium are advantageously water-soluble and as a result dissolve easily in the aqueous carrier in step a / of the method.

[0018] The method according to the present invention allows for the modification of the properties of the formed solids, particularly their mechanical properties, their appearance, such as their color, and their tactile properties. In particular, the method according to the present invention allows for the imparting of any multifunctionality required depending on the intended application by incorporating suitable additives, such as fillers or natural fibers, into the mixture formed in step a / .

[0019] The methods according to the present invention may further have one or more of the features described below, which may be implemented individually or in each of the technically effective combinations thereof.

[0020] Generally speaking, the method according to the present invention preferably does not use toxic or environmentally unfriendly compounds or products.

[0021] The method according to the present invention includes, in step a / , preparing a mixture of a monovalent alginate, a surfactant, and an emulsion stabilizer in an aqueous carrier. This mixture may particularly include one or more monovalent alginates, one or more surfactants, and one or more emulsion stabilizers.

[0022] The aqueous carrier is preferably water.

[0023] Each monovalent alginate can be formed from any monovalent cation. Preferably, this cation is sodium. Otherwise, the cation may be potassium.

[0024] Alginates (one or more types) are preferably included in the mixture in a total amount of 80 to 99% by mass relative to the total mass of the components introduced into the aqueous carrier.

[0025] In this description, a surfactant means any compound having foaming properties that can reduce the surface tension of an aqueous carrier. The surfactant(s) used in accordance with the present invention can be of any type, particularly anionic, cationic, amphoteric, or nonionic. The surfactant(s) used in accordance with the present invention are preferably of the ionic type.

[0026] Any surfactant known to those skilled in the art can be used within the scope of the present invention. Examples of such surfactants include: - Alkyl sulfate, - Alkylbenzenesulfonates, - Polyethylene glycol ether, - Sorbitan and its derivatives, - Polysorbates and their derivatives, - Stearates and their derivatives, - Lecithin, - Monoglycerides, - Sucrose esters or fatty acid esters and their derivatives.

[0027] Each surfactant used in the context of the present invention is preferably selected from sodium lauryl sulfate, ammonium lauryl sulfate, sodium stearate, sodium dodecylbenzenesulfonate, and polysorbate, and these compounds can be used individually or in mixtures thereof.

[0028] The surfactant (one or more types) is preferably included in the mixture in a total amount of 0.1 to 0.6% by mass relative to the total mass of the components introduced into the aqueous carrier.

[0029] In this specification, emulsion stabilizers are understood to mean compounds that can promote and maintain the expansion of a foam formed during a foaming process under the action of a surfactant, and can also stabilize it. In this respect, emulsion stabilizers differ from surfactants, in particular, in that they do not cause foam to form on their own, and in that they stabilize the formed foam more permanently than surfactants. Therefore, the emulsion stabilizers used in the method according to the present invention are compounds different from the surfactants (one or more) contained in the mixture prepared in step a / . The emulsion stabilizers used in the context of the present invention are preferably selected for their ability to maintain the expansion of the foam until the end of step d / , which matures the foam of the method, or for at least the first 30 minutes of this maturation process.

[0030] The inventors have discovered that by using a combination of surfactant and emulsion stabilizer in the mixture prepared in step a / of this method, it is possible to obtain regularly sized, stable, and controlled solids, particularly substantially spherical solids, formed from a foam having substantially uniform and preferably closed internal pores throughout its entire internal volume. In particular, during the subsequent drying step of these solids, which may be advantageously included in the method according to the present invention, there is neither collapse of the internal pores of the foam nor significant shrinkage of the solids. The emulsion stabilizer(s) used according to the present invention are preferably bio-based. For example, the emulsion stabilizer is: - Polyvinyl alcohol, - Thickening agents, such as cellulose and its derivatives, xanthan gum, guar gum, acacia gum, gellan gum, pectin, starch, etc. - Polypeptides, that is, amino acid chains containing 10 to 100 amino acids, and - Proteins, especially phosphoproteins, such as casein, gelatin and other collagen-derived proteins, and globular proteins, such as albumin, such as ovalbumin. These are selected from and used individually or in mixtures thereof.

[0031] The emulsion stabilizer (one or more types) is preferably included in the mixture in a total amount of 0.2 to 2% by mass relative to the total mass of the components introduced into the aqueous carrier.

[0032] Preferably, the mixture formed in step a / does not contain calcium carbonate (CaCO3) and / or proton-releasing agents, such as gluconolactone. The method according to the present invention may also include introducing at least one, i.e., one or more additives, into the mixture in step a / , which, if not limited, are preferably selected from fibers, pigments, dyes, and fillers. The selection of specific additives to be incorporated into the mixture is made to obtain further specific properties of the solid formed, such as appearance, density, or mechanical strength, depending on the specific intended use.

[0033] Each of these additives is preferably bio-based.

[0034] The amount of each additive introduced into the mixture is advantageously selected so as not to adversely affect the target foaming process in step b / of this method. Determining this amount for each specific additive is within the capabilities of those skilled in the art.

[0035] When used, the fibers are introduced into the mixture in an amount of 10% by mass or less relative to the total mass of the components introduced into the aqueous carrier, for example.

[0036] These fibers are preferably of natural origin, particularly cellulosic fibers such as hemp, cotton, coconut, flax, or silk fibers.

[0037] Preferably, the fibers incorporated into the mixture have a length of 1 mm or less, preferably 100 to 300 μm, for example, approximately 200 μm. By incorporating such fibers into the mixture, it is advantageous to increase the density of the resulting solid and improve its mechanical strength performance.

[0038] The filler (one or more types) can be selected from activated carbon, clay, silica, titanium dioxide, cork, plant bark, or any mixture thereof. The total amount of filler incorporated into the mixture is preferably 2% by mass or less relative to the total mass of the components introduced into the aqueous carrier.

[0039] In a particular embodiment of the present invention, the mixture formed in step a / of the method contains, in relation to the total mass of the components introduced into the aqueous carrier, the following: - 80-99% by mass, especially 90-99% by mass, monovalent alginates (one or more types), - 0.1-0.6% by mass, especially 0.2-0.4% by mass, of one or more surfactants, - 0.2 to 2% by mass, especially 0.5 to 1.5% by mass, emulsion stabilizer (one or more types), - 0-10% by mass of fibers, and - 0-2% by mass of filler (one or more types).

[0040] One exemplary mixture formed according to the present invention comprises 0.4 g of surfactant, 0.6 g of emulsion stabilizer, particularly polyvinyl alcohol, and 60 g of sodium alginate in 4000 g of water.

[0041] Step a / , which involves preparing the mixture, can be carried out using any conventional mixer.

[0042] Step b / , which involves foaming the mixture formed in step a / , may be carried out in any conventional foaming module, such as an aerator that allows for continuous aeration and emulsification of the mixture. This foaming module may be a horizontal rotating shaft type, such as the Mondomix VL aerator from Buhler, or a vertical rotating shaft type, such as the Shuffle-Mix mixer from Ageniaa. The rotational speed of the rotating shaft in this module is preferably 600 to 1000 rpm.

[0043] Preferably, the mixture formed in step a / is continuously introduced into a foaming module, at a flow rate of, for example, 1.5 to 4 l / h in an embodiment intended to supply about 10 extrusion nozzles to carry out step c / of the present method, and the formed foam is also continuously withdrawn therefrom to carry out this step c / .

[0044] The flow rate of the gas introduced into the mixture in step b / can be, for example, 20-50 ml / min under the same operating conditions, supplying to about 10 extrusion nozzles for carrying out step c / .

[0045] This gas is preferably air.

[0046] Step c / of the method according to the present invention includes extruding the foam formed in step c / while directly immersed in a first aqueous gelling solution capable of causing the alginate to gel.

[0047] This first aqueous gelling solution for gelling the alginate can be an acidic solution, preferably one with a pH of 3 or less, in order to ensure the gelation of the alginate.

[0048] The first aqueous gelling solution is of a type that, otherwise, can induce ion channel gelation of alginate, resulting in the formation of a physical hydrogel by the formation of interchain interactions involving mannuronic acid and guluronic acid residues constituting the alginate within the alginate polymer chain. The physical hydrogel can have any conventional composition of its own. Therefore, the first aqueous gelling solution may contain in water one or more polyvalent cations, for example one or more trivalent cations and / or one or more divalent cations, where these polyvalent cations are preferably metallic species. Calcium and magnesium, in particular, are examples of divalent cations that can be used according to the present invention.

[0049] In the context of the present invention, calcium is particularly preferred in the form of salts containing it along with any counterion, especially in the form of chlorides, carbonates, sulfates, citrates, fluorides, glycerophosphates, hydroxides, oxalates, phosphates, sugarates, succinates, sulfites, or tartrates, which can be introduced into the first aqueous gelling solution. The concentration of the calcium salt in the first aqueous gelling solution is preferably 3 to 10 g / l. This concentration range ensures optimal gelation of the alginate that forms the foam.

[0050] When the first aqueous gelling solution is based on a polyvalent cation, particularly a metal cation, its pH is preferably 4 to 7.

[0051] Extrusion of the foam formed in step b / of this method, while immersed in the first aqueous gelling solution, can be carried out by any conventional extrusion module having one or more, for example, 8 to 10 extrusion nozzles having the desired shape. The internal cross-sections of the different nozzles used may be identical or different from each other, particularly with respect to shape and / or dimensions, in order to simultaneously form solids of different shapes and / or dimensions. For example, in a particular embodiment of the present invention aimed at forming solids in the form of beads, the extrusion nozzles have a circular internal cross-section.

[0052] Extrusion is preferably carried out continuously.

[0053] Different extrusion nozzles can be used to supply material uniformly, i.e., at the same flow rate. Alternatively, different supply flows can be used to produce solids of different sizes simultaneously.

[0054] In a particularly preferred embodiment of the present invention, in step c / , the extrusion of the foam while immersed in the first aqueous gelling solution is carried out in the lower zone of the reactor, at a height of the first aqueous gelling solution of 20 cm to 2 m, preferably 30 cm to 2 m, for example, 30 cm to 80 cm. Such a height of the first aqueous gelling solution in the reactor, the so-called "first gelling solution column," located above the zone in the reactor where the foam is extruded, is particularly advantageous in that it allows for the formation of solids of particularly well-controlled dimensions, especially solids having a regular spherical shape.

[0055] Cutting of foam fragments as the foam enters the reactor can be done by any means. For example, this can be done by a cutting member including at least one cutting blade, such as a knife, immersed in a first aqueous gelling solution, each of which is rotatable and operable parallel to the lower part of the surrounding wall of the reactor into which the foam is introduced. The rotational speed of each cutting blade is preferably 200 to 500 rpm.

[0056] To ensure that the cutting blade is as close to the reactor wall as possible without contacting the reactor wall, the distance between the portion of the reactor wall into which the foam is introduced and the cutting blade is preferably as small as possible, preferably less than 1 mm, for example, 0.1 to 0.5 mm.

[0057] The rotational speed of the cutting blade and the rate at which the foam is introduced into the first aqueous gelling solution work together to adjust the size of the cut foam fragment. Thus, in certain embodiments of the present invention, in step c / , the rotational speed of the cutting blade and the extrusion flow rate are selected to form foam fragments having dimensions of 1 to 25 mm, the other dimensions being defined by the dimensions of the internal cross-section of the extrusion nozzle. This dimension of the foam fragment, determined by the rotational speed of the cutting blade and the extrusion rate, is preferably the maximum dimension of the foam fragment formed.

[0058] In certain embodiments of the present invention, the foam fragments cut in the first aqueous gelling solution have a substantially cylindrical shape.

[0059] The foam fragments thus cut spontaneously rise toward the surface of the first aqueous gelling solution due to their low density, which is associated with their highly airy structure. During their movement in this solution, the alginate gels, and simultaneously, the fragments spontaneously form under the effect of uniform pressure exerted on their surface by the liquid, as well as under the effects of the relaxation phenomenon of the alginate polymer, surface tension, and osmotic pressure in the fragments. This forming becomes more important the longer the foam fragments remain in the solution.

[0060] In certain embodiments of the present invention, this residence time is advantageously extended to extract the foam fragments formed in step c / from the upper zone of the reactor, preferably from the surface of the liquid medium contained in the reactor, and transfer them to a maturation module for carrying out step d / , which matures the foam forming these fragments.

[0061] In a particular configuration in which the cut foam fragments have a substantially cylindrical shape, depending on their size, the structure can become substantially spherical, forming alginate-based expanded foam beads.

[0062] In certain embodiments of the present invention, the rate at which the foam is introduced into the first aqueous gelling solution, and the height of the first gelling solution column in the reactor between the extrusion zone where foam fragments are formed and the extraction zone where they are extracted and transferred to the maturation module, are selected together to ensure that the residence time of the foam fragments in the first aqueous gelling solution in the reactor, called the rise time, is 1 second or more, preferably 1 to 10 seconds. The height of the first aqueous gelling solution column in the reactor between the extrusion zone where foam fragments are formed and the extraction zone where the foam fragments are extracted and transferred to the maturation module is preferably 20 cm to 2 m, preferably 30 cm to 2 m, for example 30 to 80 cm.

[0063] Step d / , which involves maturing the form that will form the fragments, is carried out in a second aqueous gelling solution that can induce the gelation of the alginate in order to allow for complete gelation of the material and obtain a solid.

[0064] A second aqueous gelling solution for gelling alginate may have one or more of the characteristics described above with respect to the first aqueous gelling solution for gelling alginate.

[0065] Therefore, the second aqueous gelling solution may contain one or more polyvalent cations in water, for example, one or more trivalent cations and / or one or more divalent cations, preferably of the metal cation type. Calcium and magnesium, in particular, are examples of divalent cations that can be used according to the present invention. Otherwise, the second aqueous gelling solution may be an acidic solution having a pH of 3 or less.

[0066] The second aqueous gelling solution may be the same as, or different from, the first aqueous gelling solution for gelling the alginate. Preferably, they are the same.

[0067] Therefore, the second aqueous gelling solution for gelling the alginate is preferably an ion channel type gelling solution formed from a divalent cation, preferably a metal, and more preferably calcium. Such a feature is particularly advantageous in that it provides the possibility of later redissolving the material that forms the solid, for example by calcium / sodium exchange, and obtaining the alginate in the form of a water-soluble sodium salt. The sodium alginate thus reformed can be used alone or in a mixture with non-recycled sodium alginate as a starting material for the method according to the present invention.

[0068] The maturation process d / can be carried out for a period of time, for example, 30 to 120 minutes.

[0069] Any conventional module that ensures the long-term retention of solid particles in a suspension in a liquid medium can be used to carry out the maturation step d / of the method according to the present invention. Such a module may be, for example, a storage tank that is stirred at a low speed. Preferably, the maturation module is selected to simultaneously allow the transfer of foam fragments from the reactor used in step c / of the method to a further module in which the formed solids are separated from the liquid medium containing them. Thus, in certain embodiments of the present invention, the maturation module may be a gently inclined concentric coil, a screw conveyor, a paddle wheel, etc.

[0070] Preferably, the method according to the present invention includes a step e / of separating the solids from the second aqueous gelling solution after the maturation step d / . This separation step may be carried out by any conventional method, for example, by dewatering in a rotating screen and / or by spinning, for example, in a conventional spinner.

[0071] The step e / of separating the solids from the second aqueous gelling solution may optionally be followed by a step f / of drying these solids.

[0072] Preferably, this drying process is carried out in dynamic mode, and the solids are kept in motion, for example, in a rotating drum or on a vibrating plate placed in an oven, particularly a ventilated oven. Keeping the solids moving in this way during drying helps to avoid asymmetrical changes in their shape. The oven is preferably heated to a temperature of 40-80°C. The heating time depends on the amount of solids to be dried and the heating temperature. For example, in a rotating drum with a rotation speed of about 5 rpm, placed in a chamber heated to a temperature of 70-80°C, the approximate drying time for 10 liters of wet solids, which allows for obtaining a volume of about 2.5 liters of dried solids, is about 8-10 hours.

[0073] Such a drying mode causes a slight shrinkage of the solids and, as a result, a slight increase in their density, but this shrinkage and the resulting increase in density are advantageously very low.

[0074] The drying process f / can otherwise be carried out by exposing the solid to microwaves, for example, in a microwave oven. Such a drying mode has the advantage of being fast. For example, a power level of 200-600W can be used for a duration of 3-10 minutes. For example, a power level of 600W makes it possible to form 2 grams of dry solid from 40 grams of wet solid in 5 minutes.

[0075] This microwave drying mode causes a slight expansion of the solid material, resulting in a slight decrease in its density.

[0076] Each of the above-described embodiments of the drying process makes it possible to obtain a moisture loss of at least 96% by mass of the solid. For all of these drying modes, performance can be improved by simultaneously exposing the solid to an airflow.

[0077] The sequential steps of the method according to the present invention are preferably carried out sequentially by an apparatus equipped with means for transferring material from each module to the next module, which are operated in a continuous manner.

[0078] Another aspect of the present invention relates to a solid obtained by a method according to the present invention, preferably comprising the final steps e / of separating the solid from a second aqueous gelling solution and f / of drying the solid, in particular a solid made of an alginate-based expandable foam, in a substantially spherical shape, i.e., in the form of beads. - A size defined herein as the maximum dimension of a solid, measured by a scanning electron microscope, which is 1 to 25 mm; in particular, in certain embodiments where the solid has a substantially spherical shape, a size of 1 to 5 mm, i.e., diameter; - The mass of an object, as measured by weighing, particularly by weighing with a thermomass spectrometer, is defined as the ratio of its mass to its volume, particularly by X-ray microtomography, especially by X-ray microtomography at a voltage of 40 kV and a resolution of 4 μm per voxel, or by pycnometry, ranging from 30 to 130 kg / m³. 3 Especially 30-50 kg / m 3 Or 50-130 kg / m 3 The apparent density; - Porous; that is, the pores are in the form of closed cells (independent bubbles); - Porosity is defined as the ratio of apparent density to absolute (actual) density measured by helium pycnometry, which is obtained by subtracting 1 from 1 (the result of this subtraction multiplied by 100, which is 90% or higher). It is characterized by the following.

[0079] The apparent density of the spherical solid, so-called beads, can also be determined by the so-called filling method, by weighing the mass of a large amount of beads and measuring the volume occupied by the beads determined by filling these beads into a large graduated cylinder. Therefore, this method takes into account the volume existing between them (the "interstitial volume") in addition to the volume of each bead (the "internal volume"). Assuming a completely spherical bead compact random stack, this interstitial volume can be estimated to occupy about 40% of the total volume (60% of the compactness), which has been confirmed by the inventors. Therefore, by the method using the measurement of the volume of individual beads, especially obtained by X-ray microtomography or pycnometry, the above apparent density range of 30 to 130 kg / m 3 is equivalent to the apparent density range measured by the filling method of 20 to 80 kg / m 3 .

[0080] The properties based on alginate of the expanded foam can be confirmed by any method known to those skilled in the art. Since alginate is a heteropolymer consisting of monomer units of guluronic acid (G) and mannuronic acid (M), the evaluation of the presence of alginate in the foam beads can be carried out by solid-state nuclear magnetic resonance (NMR) spectroscopy, especially the magic angle type (CP-MAS 13 C NMR). The G residues can be identified by chemical shifts near 82.7, 68.4 and 65.7 ppm, while the M residues are observed at 76.1 and 71.5 ppm (Sperger et al., 2011, Journal of Pharmaceutical Sciences, 100(8), 3441-3452). 13The simultaneous presence of these five peaks on the 13C NMR (solid-state) spectrum therefore allows us to characterize the presence of alginates (bridged by ion channel gelation via divalent cations) in the solid. The presence of alginates can also be confirmed by observing two other chemical shifts on the NMR spectrum, located at 102.12 ppm for G residues and 99.5 ppm for M residues, respectively, as reported by Salomonsen et al., 2009, Food Hydrocolloids, 23, 1579-1586.

[0081] In certain embodiments of the present invention, the solids made of alginate-based expandable foam, particularly in the form of beads, contain 80–99% by mass fraction of polyvalent cation alginates, particularly calcium alginate, and, where applicable, organic materials mainly consisting of fibers and / or organic fillers. This mass fraction can be confirmed, in particular, by analyzing a sample of the solid by thermomass spectrometry (TGA), by subtracting the amount of water loss determined at approximately 110°C from the total mass of the sample.

[0082] The solid material according to the present invention can be used as a loose-fill insulation material, a pad material, or, for example, as a decorative element in the field of arts and crafts. Alternatively, as will be described later in this description, it may be used in the manufacture of structured objects.

[0083] In another aspect, the present invention relates to an apparatus for carrying out the method according to the present invention for producing alginate-based expandable foam solids. This apparatus is - A mixing module for forming a mixture of multiple components, which is intended to optionally carry out step a / of the method according to the present invention, - A foaming module for carrying out step b / of the method according to the present invention, comprising: a tank intended to contain or containing a liquid mixture formed in step a / ; an inlet preferably in hydraulic communication with a mixing module for supplying a liquid composition to the tank; a gas injector for injecting gas into the tank, more specifically into the zone intended to contain or containing a liquid mixture formed in step a / ; and a stirrer for stirring the liquid composition contained in the tank, - A reactor intended to contain or containing a first aqueous gelling solution for gelling an alginate, wherein the tank is defined by a surrounding wall and comprises a lower zone and an upper zone on the opposite side, and the lower zone, which is intended to be filled with or contains a first aqueous gelling solution for gelling an alginate, is provided with a cutting member including at least one cutting blade, the cutting blade being rotatable and operable parallel to the lower part of the reactor wall, or any other mechanical or microfluidic shear cutting system, - A foam extrusion module for extruding foam inside the reactor through the lower part of the reactor wall, - A hydraulic transfer system for hydraulically transferring foam from a tank to an extrusion module, - A maturation module for maturating alginate-based foam fragments to form expanded foam solids, which is intended to contain or contains a second aqueous gelling solution for gelling alginate, - An extraction system for extracting the medium contained in the reactor and introducing this medium into the maturation module, It is equipped with.

[0084] Preferably, the extraction system is configured to extract a medium contained in the upper zone of the reactor, particularly a liquid medium containing suspended solid fragments.

[0085] The apparatus according to the present invention optionally allows, - A separation module for separating solids and liquids, and a recovery system for recovering the medium contained in the maturation module, particularly the liquid medium containing suspended solid fragments, and introducing this medium into the separation module. - Preferably, a drying module for drying solids, and a transfer system for transferring solids from a separation module to the drying module. It may also be provided with the following:

[0086] Each of the above-described modules of the apparatus may have one or more of the above-described features with respect to a module that can be used to carry out a relevant step of the method according to the present invention.

[0087] Therefore, in particular - The mixing module itself may be any conventional mixer. - The foaming module may be a vertical or horizontal rotating shaft type aerator, or any device that enables the introduction of air into the solution for the purpose of generating foam, including discontinuous methods, such as a stirrer equipped with a beater or whisk. - The extrusion module may comprise one or more, for example, eight to ten, extrusion nozzles extending through the reactor wall, preferably opening at the bottom of this wall, inside the reactor, and in particular, these extrusion nozzles may have a circular internal cross-section. - In the reactor, the distance between the lower part of the reactor wall and the cutting blade of the cutting member can be 0.1 to 0.5 mm. - The maturation module can be a storage tank with slow agitation, a gently inclined concentric coil, a screw conveyor, or a paddle wheel. - The separation module for separating solids and liquids may include a perforated conveyor belt, a rotating screen, and / or a spinner. - and / or the drying module may be a rotating drum or vibrating plate located inside an oven, particularly a ventilated oven, or microwave oven.

[0088] In certain embodiments of the present invention, the cutting member is one or more knives that rotate around an axis perpendicular to the lower part of the reactor wall, through which the foam is introduced into the reactor. Any other mechanical or microfluidic shearing systems are also included within the scope of the present invention.

[0089] Preferably, each component of the apparatus according to the present invention is capable of continuous operation in order to enable continuous implementation of the method according to the present invention.

[0090] Another aspect of the present invention relates to a method for producing a structured object using an expanded foam solid obtained by a method according to the present invention for producing an expanded foam solid.

[0091] This method, - The present invention involves introducing a mixture of multiple solid materials with a binder into a mold shaped to conform to the desired shape of the object to be manufactured, - Compressing this mixture in a mold, - Drying the thus compressed mixture, Includes.

[0092] This method may include a preliminary step of carrying out the method for producing an expanded foam solid according to the present invention in order to obtain a solid that is introduced into a mold with a mixture of a binder.

[0093] Each step of the method for producing a structured object according to the present invention can be carried out by conventional techniques for producing structured objects based on solids made from polystyrene or polyurethane, and by apparatus commonly used for this purpose.

[0094] The binder used is preferably bio-based. It can be of various types and have various specificities, enabling the formation of structured objects. - Reversibly, the binder is, for example, a water-soluble type of polyvinyl alcohol, or a protein such as albumin, gelatin, or casein, or a mixture of such proteins, and when the object is immersed, for example, in warm water at about 40°C, the object disintegrates due to the solubilization of the binder in the water, and thus the solid material constituting it can be recovered and, after drying, optionally reused for, for example, the manufacture of different structured objects. - Alternatively, irreversibly, the binder may be, for example, silicone or latex, and such a binder may further enable the formation of an object with a certain degree of flexibility.

[0095] The binder may, in other cases, be starch, cellulose, or a derivative thereof, such as hydroxypropyl methylcellulose.

[0096] The ratio "mass of solids (grams) / volume of binder (milliliters)" is preferably 1 to 2, for example, about 1.25. The solids are preferably uniformly mixed with the binder, for example, by a mixer, before being introduced into the mold.

[0097] Additives such as fibers, fillers, pigments, and dyes can be added to the mixture to obtain, in particular, the desired appearance and texture characteristics, and / or mechanical properties of the resulting structured object.

[0098] In certain embodiments of the present invention, the compression of a mixture of alginate-based expandable foam solid and binder in a mold is carried out, for example, under a pressure of about 1 bar, to obtain a compression ratio of 2 to 4.

[0099] The drying process of the compressed mixture is carried out in a mold, depending on the desired finish and dimensional accuracy of the resulting structured object. The mold may be perforated, open, or closed, or the compressed mixture may be removed from the mold. This drying can be carried out in an oven or microwave oven, for example, at an output of 150 or 160 W, preferably for a period of 3 to 15 minutes.

[0100] The present invention also relates to its use for producing structured objects of expanded foam solids obtained by the method according to the present invention for producing expanded foam solids, preferably. This use may have one or more of the features described above with respect to the method for producing structured objects according to the present invention.

[0101] Based on the alginate-based expanded foam solids manufactured according to the present invention, the structured objects manufactured by the method according to the present invention may be of any type. For example, they may be packaging, gardening containers, decorative objects, insulating and / or flame-retardant boards, and in particular flame propagation prevention devices for the protection of electrical wiring.

[0102] This objective can be applied to many fields, including packaging, storage, protection, architecture, decoration, creative activities, fashion, and luxury.

[0103] A structured object preferably has an apparent density equal to the ratio of its mass, measured by weighing, to its volume, which is determined by a calculation based on its external dimensions, and this apparent density is 50 to 200 kg / m³. 3 That is the case.

[0104] Therefore, another object of the present invention relates to a structured object obtained by a method for producing a structured object according to the present invention, in particular to a structured object obtained, wherein the structured object comprises a plurality of solids according to the present invention in a mixture with a binder, and weighs 50 to 200 kg / m 3 Preferably 80-200 kg / m 3It has an apparent density, which is equal to the ratio of the mass of an object measured by weighing to its volume, which is determined by calculation based on the measurement of its external dimensions.

[0105] This structured object may be one of those described above with reference to the method according to the present invention.

[0106] The features and advantages of the present invention will become more apparent in light of the following exemplary embodiments, which are provided for illustrative purposes only and are not intended to limit the invention, with reference to Figures 1 to 15. [Brief explanation of the drawing]

[0107] [Figure 1] Figure 1 shows a block diagram illustrating the steps of the method for producing a solid substance according to the present invention.

[0108] [Figure 2] Figure 2 schematically shows an apparatus for carrying out the method for manufacturing beads according to the present invention.

[0109] [Figure 3] Figure 3 schematically shows an enlarged view of the lower part of the reactor and the extrusion module of the apparatus shown in Figure 2.

[0110] [Figure 4] Figure 4 shows scanning electron microscope images of alginate expanded foam beads exposed to different drying modes (S1-S3), with magnifications of 70x for a / , 150x for b / , and 1000x for c / for S1 and S3, and 1500x for S2.

[0111] [Figure 5] Figure 5 shows the central cross-section of the alginate-based expandable foam beads according to the present invention, obtained by X-ray microtomography after segmentation.

[0112] [Figure 6]Figure 6 shows images obtained by X-ray microtomography of the alginate expandable foam beads shown in Figure 5, including a front view (a / ) and a 3 / 4 view (b / ) of a hemisphere, and an overall view (c / ).

[0113] [Figure 7] Figure 7 shows graphs representing the heat generation rate as a function of applied heat for beads ("alginate") and polystyrene beads ("polystyrene") according to the present invention (data obtained with a combustion microcalorimeter).

[0114] [Figure 8] Figure 8 shows the lower part of Figure 7 on an enlarged scale (data obtained from a combustion microcalorimeter).

[0115] [Figure 9] Figure 9 shows a graph representing the heat generation rate related to the thermal decomposition of the beads according to the present invention as a function of time, as analyzed by cone calorimetry (irradiance 35 kW / m2).

[0116] [Figure 10] Figure 10 shows a graph representing the heat rate of regeneration (HRR) as a function of time related to the thermal decomposition of the beads according to the present invention ("alginate beads") or a commercially available flame-retardant polyurethane foam ("flame-retardant PU foam") during a cone calorimetry test (irradiance 35 kW / m2).

[0117] [Figure 11] Figure 11 shows a graph representing the optical density of smoke measured as a function of time during an NBS smoke chamber test (irradiance 25 kW / m2) performed on beads according to the present invention.

[0118] [Figure 12]Figure 12 shows a graph representing the optical density of smoke measured as a function of time during NBS smoke chamber tests (irradiance 25 kW / m2) performed on beads according to the present invention ("alginate beads") and samples of polyamide 6, ethylene methyl acrylate copolymer, polypropylene, and polybutylene terephthalate. Figure 1 schematically shows the sequence of steps of the method according to the present invention for producing expanded foam solids.

[0119] [Figure 13] Figure 13 shows photographs of the alginate-based expanded foam beads according to the present invention before (a / ) and after (b / ) the final drying step f / of the method according to the present invention.

[0120] [Figure 14] Figure 14 shows photographs of alginate-based expanded foam bodies in front view (A / ) and side view (B / ), respectively, of beads (i) obtained by the method according to the present invention and an object (ii) obtained by a method not according to the present invention that does not use an emulsion stabilizer.

[0121] [Figure 15] Figure 15 shows a front view photograph of a hemisphere of the object (ii) shown in Figure 14, obtained by a method not according to the present invention, which does not use an emulsion stabilizer. [Modes for carrying out the invention]

[0122] In the first step a / , the method includes preparing a mixture 10 in an aqueous carrier, preferably in water, comprising one or more monovalent alginates, one or more surfactants, and one or more emulsion stabilizers, and optionally one or more additives, particularly additives selected from fibers, pigments, dyes, and fillers. The mixture thus obtained is subjected to foaming 20 in step b / by introducing gas, preferably air, into the mixture and simultaneously stirring the mixture.

[0123] The foam formed at the end of this process is introduced in the next step c / by immersion extrusion 30 into a first aqueous solution which can cause the alginate forming the foam to solidify. The method includes cutting the foam into preferably small pieces 40 as soon as the foam enters this aqueous solution.

[0124] The resulting foam fragments are then subjected to maturation 50 for at least 30 minutes in step d / to form the desired alginate-based expanded foam solid.

[0125] In a particular embodiment of the present invention, the method then proceeds as follows: - step 60 in e / separates the solid matter from the liquid medium containing the solid matter. - step 70 in f / to dry these solids, This includes a series of steps.

[0126] Each specific embodiment of these steps is described below in detail in the description of an exemplary apparatus according to the present invention that is suitable for carrying out this method schematically shown in Figure 2.

[0127] The apparatus shown in Figure 2 is configured to perform this method continuously.

[0128] In certain exemplary embodiments of the method detailed below, the first aqueous gelling solution and the second aqueous gelling solution are the same solution.

[0129] The apparatus includes a mixing module 11 called a mixer for carrying out the mixture preparation step 10 of the present method, more specifically, for preparing a mixture of one or more monovalent alginates, one or more surfactants, one or more emulsion stabilizers, and one or more additives as needed, in an aqueous carrier, for example, in water. From this mixer 11, the formed mixture is transferred by a pipe 12 equipped with a pump 13 to a foaming module 21 called an aerator for carrying out the foaming step 20 of the present method, at a flow rate of, for example, 1.5 to 4 l / h in the direction shown in 14 in the figure, for subsequent supply to about 10 extrusion nozzles.

[0130] The aerator 21 comprises a tank 22, an inlet 23 for supplying a mixture from the pipe 12 to the tank 22, a gas injector 24 for injecting gas into the tank 22, and a stirrer 25 for agitating the mixture contained in the tank 22. In the embodiment shown in the figure, the stirrer 25 comprises a plurality of blades 251 extending perpendicularly to the rotating central shaft 252 from the rotating central shaft 252 inside the tank. To carry out the foaming step 20 of the method, the rotating central shaft 252 is driven to rotate itself at a speed of, for example, 600 rpm. The aerator 21 is associated with a gas reserve 26, in particular a gas reserve 26 of compressed air at a pressure of, for example, 1 bar. From this reserve 26, the gas flows through the pipe 27 at a flow rate of preferably 20 to 50 ml / min, relative to the flow rate and number of extrusion nozzles, and the pipe 27 leads the gas to the gas injector 24 of the aerator 21 in the direction shown 28 in the figure.

[0131] The apparatus may include a module for preparing an aqueous gelling solution for gelling alginates. For convenience, the following description uses a specific exemplary embodiment in which the solution is an aqueous solution of 3-10 g / l calcium chloride with a pH of 4-7, but such examples are not limiting to the invention. Those skilled in the art can easily adapt this description to any other type of predetermined aqueous gelling solution.

[0132] The module for preparing the aqueous gelling solution comprises a tray 81 containing a volume 82 of aqueous gelling solution. This module includes a rotary agitator 83 formed by a blade 831 fixed to the end of a shaft 832 which is itself rotationally driven by a motor 833. An electrical conductivity meter 841 continuously measures the electrical conductivity of the solution contained in the tray 81 via a probe 842 immersed in the solution. The conductivity meter 841 controls a pump 843 to circulate an aqueous stock solution of, for example, 60-80 g / l of calcium chloride contained in a reserve 844 through a pipe 845 that carries it to the tray 81 in the direction shown 846 in the figure, ensuring that the appropriate concentration of calcium chloride in the solution contained in the tray 81 is permanently maintained. A pH meter 851 continuously measures the pH of the solution contained in the tray 81 via a probe 852 immersed in the solution. The pH meter 851 controls the pump 853 to circulate the acidic solution contained in the reserve 854 through the pipe 855, which carries it to the tray 81 in the direction indicated by 856 in the figure, ensuring that the pH of the solution in the tray 81 is permanently maintained at an appropriate value.

[0133] From tray 81, the aqueous gelling solution for gelling the alginate is driven by pump 861 to continuously flow to reactor 31 at a flow rate of, for example, 4 l / min, through UV treatment cell 864 as needed, in the direction shown 863 in the figure. The apparatus is configured such that reactor 31 permanently contains a volume 32 of aqueous gelling solution that almost completely fills it.

[0134] The reactor 31 is separated by a surrounding wall 311, and inside this surrounding wall are a lower zone 312 and an upper zone 313 on the opposite side.

[0135] The apparatus further comprises a hydraulic transfer system 29 for hydraulically transferring the foam formed in the tank 22 of the aerator 21 to a foam extrusion module 33 for carrying out the immersion extrusion process 30 of the method. In the particular embodiment shown in Figure 2, this hydraulic transfer system is formed by a pipe 29, with a first end 291 opening into the tank 22 and a second end 292 hydraulically communicating with the extrusion module 33. The foam formed in the tank 22 is continuously pushed into the pipe 29 and driven in a flowing state within the pipe 29 in the direction shown 293 in the figure.

[0136] The extrusion module 33 is shown in detail in Figure 3. The extrusion module comprises a plurality of extrusion nozzles 34, all of which are in hydraulic communication with the pipe 29. These nozzles open inside the reactor 31 in the lower region 312 of the reactor 31, passing through the lower part 314 of the surrounding wall 311 of the reactor, and are directly immersed in the aqueous gelling solution for gelling the alginate. In the particular embodiment shown in the figure, this lower part 314 forms the bottom wall of the reactor 31. In the example shown in Figure 3, there are 10 extrusion nozzles 34, which have a circular internal cross-section and the same diameter, but such features do not limit the invention in any way, and the extrusion nozzles may have internal cross-sections of different shapes and / or dimensions. The foam carried through the pipe 29 is pushed into the extrusion nozzles 34 in the direction shown in 35 of Figure 3, at a flow rate that may be the same as or different for each nozzle. At each extrusion nozzle 34, the form is extruded into the reactor 31 in the form of a cylindrical body 46 into an aqueous gelling solution with a volume 32 contained within the reactor 31. The height of the gelling / coagulation aqueous solution column located above the extrusion nozzles 34 in the reactor 31 is preferably 20 cm to 2 m.

[0137] The reactor 31 further comprises at least one cutting member 41 positioned parallel to the lower part 314 of the reactor wall and at a distance of less than 1 mm from the extrusion nozzle 34 in order to carry out 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, for example, a knife, is attached to the end of a rotating shaft 43 perpendicular to the lower part 314 of the reactor wall. This shaft 43 is rotated by itself by a motor 45 at a rotational speed of, for example, 200 to 500 rpm in the direction 44 shown in the figure. As shown in more detail in Figure 3, the cutting member comprises one or more cutting blades 42. The assembly is configured such that each cutting blade 42 is rotatable above the extrusion nozzle 34 and parallel to the lower part 314 of the tank wall. Each rotating cutting blade 42 successively cuts the foam cylinder 46 with respect to each extrusion nozzle 34 as the foam cylinder 46 is extruded into the reactor 31, thereby forming foam fragments 47.

[0138] The foam fragments 47 thus cut rise toward the surface in the column of aqueous gelling solution with a volume 32 contained in the reactor 31, as shown in figure 48, due to their very low density. As the alginate moves through this volume of solution 32, solidification of the alginate begins, forming the alginate composition. The pressure applied to their surfaces by this solution, along with the surface tension of the alginate polymer and the presence of a coagulant, simultaneously induce their formation. This formation results in the production of spheres, in particular, of foam fragments 47 obtained from extruded cylinders having a circular cross-section and a height equal to the cross-sectional diameter of these cylinders. When the foam fragments 47 reach the upper zone 313 of the reactor 31, they partially solidify and have a substantially spherical shape. The various parameters of this method are preferably selected so that the rising time of the foam fragments 47 in the gelling solution column is 1 to 10 seconds.

[0139] The apparatus includes an extraction system 52 for extracting the medium contained in the reactor and introducing this medium into a maturation module 51 for carrying out the maturation step 50 of the method, as shown in Figure 2. In the particular embodiment shown in the figure, the extraction system 52 consists of a single pipe that opens into the upper part 313 of the reactor at substantially the surface level of the medium contained therein. The medium, containing the aqueous gelling solution and foam fragments 47, flows spontaneously through it under the action of the aqueous gelling solution arriving continuously in the reactor 31 through the pipe 862. Preferably, the pipe 52 is inclined from an opening at the higher end into the reactor 31 to a lower end that is in hydraulic communication with the maturation module 51, so as to facilitate the flow of the medium therein by the action of gravity.

[0140] In a specific embodiment shown in Figure 2, the aging module comprises concentric coils 53 having a gentle slope to facilitate the flow of the medium within it through the action of gravity. This slope is determined so that the residence time of the medium in the aging module 51 is 30 to 120 minutes. While passing through the coils 53, the alginate of the foam fragments 47 comes into contact with the aqueous gelling solution 54 and continues to solidify until the process is complete. This results in an alginate-based expanded foam solid 55 being obtained at the exit of the aging module 51.

[0141] The apparatus may further include a separation module 61 for separating solids and liquids in order to carry out the solid / liquid separation step 60 of the present method. In the particular embodiment shown in the figure, this separation module 61 includes a rotating screen 62 and a spinner 63.

[0142] A pipe 64, which is hydraulically connected to the outlet of the aging module 51, carries a medium containing a mixed liquid 54 / solids 55 that flows from the aging module 51 to the rotating screen 62. The solids 55 contained in the medium are carried through this screen to the spinner 63 via an inclined plate 65, while the liquid flows through the perforations of the screen to the recovery tray 67, as shown in figure 66. From this recovery tray 67, the liquid can optionally be returned by pipe 68 through an ultraviolet filter 69 to the tray 81 of the module for preparing an aqueous gelling solution in the direction shown in figure 681.

[0143] The spinner 63 is conventional in itself and allows for the complete separation of the solids 55 from the liquid in which they are mixed.

[0144] The apparatus may further include a drying module 71 for drying a solid material to carry out the drying step 70 of the present method, and a transfer system 72 for transferring the solid material 55 from the spinner 63 to the drying module 71. This transfer system 72 is schematically shown by arrows in Figure 2. For example, it may be a conveyor, which may itself be a conventional one.

[0145] In the non-limiting embodiment of the present invention shown in Figure 2, the drying module 71 includes a rotating drum 76 through which the solid material 55 is carried. This rotating drum 76 is located within a chamber 73 equipped with a heating element 74. The heating element 74 is preferably adjusted to obtain a temperature of 40 to 80°C within the chamber 73.

[0146] As shown by 75 in Figure 2, the desired alginate-based expanded foam solid 55 is recovered at the outlet of the drying module. [Examples]

[0147] 1 / Example 1 - Preparation of Alginate-Based Expanding Foam Beads The expandable foam beads according to the present invention were manufactured using the apparatus described above by applying the following operating protocol. The composition of the initial mixture was as follows: - 60g sodium alginate, - 0.4g sodium lauryl sulfate, - 0.8g of polyvinyl alcohol, - 4000g of water.

[0148] This mixture was introduced into the foaming module at a flow rate of 4 l / h. The rotational speed in the module was 700 rpm.

[0149] The foam generated in the foaming module was introduced into the extrusion module and directly immersed in a gelling / coagulation bath consisting of a 4 g / l calcium chloride aqueous solution. The knife rotation speed was equal to 300 rpm. The height of the gelling / coagulation bath column above the extrusion zone was 26 cm.

[0150] The residence time of the beads formed in the maturation module is equal to 40 minutes.

[0151] After separation from the liquid medium, the beads were centrifuged in a spinning module and then subjected to 10 hours of drying according to three different protocols: - Batch S1: Drying in a ventilated rotating drying drum: The beads were dried by blowing a stream of hot air at a rotation speed of 5 rpm in a rotating drum placed in a chamber heated to 70°C. For 1907 g of wet beads, 59 g of dry beads were obtained in a volume of 1990 mL. - Batch S2: Drying was performed in a non-ventilated rotary drying drum under the same conditions as above, without blowing air. For 1810 g of wet beads, 56 g of dry beads were obtained in a volume of 2200 mL. - Batch S3: Dry on a heating plate in a ventilated oven: The beads were placed flat on a flat surface heated to 80°C under a flow of hot air for 4 hours. For 646g of wet beads, 20g of dry beads were obtained in a volume of 1000mL.

[0152] For each drying mode, the moisture loss during the drying process is equal to 97%.

[0153] 2 / Example 2 - Characterization of Beads 2.1 / Thermal conductivity The thermal conductivity of the beads formed in Example 1 was measured using the so-called "hot-wire" method, which involves applying localized Joule heating to "bulk" beads from batches S1, S2, and S3 and measuring the resulting temperature rise. Since the rate of this rise depends on the heat dissipation capacity of the material being tested, it is possible to estimate the thermal conductivity of this material by inverse identification.

[0154] The apparatus used was a Neotim FP2C model equipped with a hot-wire probe. It was pre-calibrated using glass fiber boards with known thermal conductivity and certified by NIST (National Institute of Standards and Technology). For each batch of beads, reproducibility was evaluated with three measurements.

[0155] The results show an average thermal conductivity of 0.032 ± 0.001 W / (m·K) for all batches, demonstrating the excellent thermal insulation capacity of the beads according to the present invention, regardless of the drying method tested.

[0156] 2.2 / Morphology and Characterization of Closed Internal Pores 2.2.a / Observation using a scanning electron microscope The beads were observed using a scanning electron microscope (SEM) with a Quanta 200 FEG instrument manufactured by FEI Company.

[0157] The obtained images are shown in Figure 4. From these images, the diameter of the beads obtained after drying is estimated to be 2–2.5 mm.

[0158] Scanning electron microscopy observations also revealed the porosity of the bead-forming foam. The polygonal shape of the cells was irregular, with varying dimensions. The internal pores appeared to be roughly occupied by larger cells in the center of the beads, which is likely the result of multiple adjacent cells merging during the solidification process, and the size of these cells gradually decreases towards the outer layer along the diameter of the bead. For example, the average width of these cells measured by micrographs ranged from 50 to 100 μm, with thinner cells being tens of μm, but could range up to 250 to 400 μm.

[0159] Furthermore, the average wall thickness was estimated to be approximately 2 μm.

[0160] 2.2.b / Pycnometer Analysis Beads from batch S1 were analyzed using an Accupyc 1330 helium pycnometer from Micromeritics Instrument Corporation. Because this method is based on direct volumetric measurement, the beads were finely ground using a mixer before characterization to open all pores, allowing the helium gas used to access the mostly closed bead cells, thus enabling accurate determination of the actual volume of the material. Reproducibility was evaluated using three measurements.

[0161] The obtained absolute density (i.e., the density of the bead wall) is 1.682 ± 0.002 g / cm³. 3 It is equal to.

[0162] 2.2.c / X-ray microtomography analysis Three beads from batch S1 were scanned using X-ray microtomography to investigate their internal structure in three dimensions. For each of them, an RX Solutions EasyTom 150 microtomograph was used at a voltage of 40kV, producing a volume with a resolution of 4μm per voxel.

[0163] After reconstructing projections from various angles, a median filter was applied to reduce digital noise. Next, to obtain a binary image, the volume was segmented by thresholding the grayscale values, thereby distinguishing between zones of material and zones of air. The threshold was chosen to preserve as much integrity as possible of walls with a thickness (estimated to be approximately 2 μm in the SEM) smaller than the scan resolution. This results in an overestimation of the thickness of these walls, and therefore an overestimation of the total volume of material compared to the volume of air.

[0164] The results obtained are shown in Figure 5 (materials are shown in white, and pores are shown in black) and Figure 6.

[0165] Microtomography is used to confirm the fine structures observed by scanning electron microscopy.

[0166] Porosity is the ratio of the volume of air in a bead cell to the total volume of the bead (i.e., the sum of the volume of air inside the bead and the volume of material). Nevertheless, for the reasons mentioned above, the total volume of the material is overestimated relative to the total volume of air, leading to an underestimation of porosity by this method. To evaluate more accurately, the apparent density of each of the three beads was evaluated by calculating the ratio of their mass to their apparent volume, which was determined by X-ray microtomography. This yielded 0.07 ± 0.01 g / cm³. 3 The apparent density is obtained. The porosity, defined as 1 minus "the ratio of the apparent density of the beads calculated above to the absolute (actual) density measured by the helium specific gravity bottle method" (the result of this subtraction multiplied by 100), is 96% ± 1%.

[0167] 3 / Example 3 - Flammability 3.1 / Combustion Micro Calorimeter The test was performed using a combustion microcalorimeter (Fire Testing Technology) according to ASTM D7309 standard method A (anaerobic pyrolysis). Approximately 3 mg of beads from batch S1 were placed in a crucible and pyrolyzed at a rate of 1 K / s at a maximum temperature of 750°C under a nitrogen flow (100 mL / min). The generated gas was continuously supplied to the combustion chamber in the presence of excess oxygen (N2 / O280 / 20). The temperature (900°C) and residence time (10 ms) were set to ensure complete combustion of the material.

[0168] For comparison, commercially available expanded polystyrene foam beads (polystyrene Lacqrene® 1340, Atofina) are also subjected to the same operating protocol.

[0169] The results obtained regarding the heat dissipation rate associated with the thermal decomposition of foam beads as a function of the temperature to which they were exposed are shown in Figures 7 and 8 (corresponding to the scale magnification of Figure 7).

[0170] As can be seen from the figure, the heat dissipation rate of the alginate beads according to the present invention is much lower than that of polystyrene beads, not exceeding 10 W / g, with two main peaks located at 263°C and 497°C. The residue at 750°C is 25-30%.

[0171] Furthermore, the energy released by the beads according to the present invention does not exceed 2 kJ / g, and its heat generation capacity (equal to the peak of the heat flow divided by the heating rate) is equal to 10 J / g·K. These values ​​demonstrate the remarkable combustion behavior of the beads according to the present invention.

[0172] 3.2 / Testing using a cone-type calorimeter The test was conducted according to ISO 5660 standard using a cone-type calorimeter (Fire Testing Technology). 16 g of beads from batch S1 were poured into a standard sample holder (10 cm side) to form a 3 cm thick bead bed. The applied irradiance was 35 kW / m². 2 The ignition was controlled, and the test was continued for 350 seconds.

[0173] No ignition was observed during this test. The heat dissipation rate shown in Figure 9 was 16 kW / m after 150 seconds. 2 The value reached a stable point. This corresponds to the slow thermal oxidation of the beads. After 350 seconds, the residue was 45%, and the total energy released was 3.2 MJ / m³. 2 That is, 1.76 kJ per gram of beads. The effective combustion energy was 3.2 kJ / g.

[0174] The heat dissipation rate profile of the beads according to the present invention was compared with the profile of commercially available flame-retardant polyurethane foam beads (Efigreen® ITE, Soprema) subjected to the same operating protocol. The resulting curves are shown in Figure 10. The heat dissipation rate of the foam according to the present invention is much lower than that of commercially available flame-retardant polyurethane foam.

[0175] 3.3 / NBS Smoke Chamber Test The test was conducted using an NBS smoke chamber (Fire Testing Technology) in accordance with ISO 5660 standards. 10.5 g of beads from batch S1 were poured into a standard sample pan (7.5 cm sides). The applied irradiance was 25 kW / m². 2 The ignition was controlled, and the test was continued for 600 seconds.

[0176] No ignition was observed. The optical density of the smoke was measured according to the method described in ISO 5659-2:2017, using a 6.5V incandescent lamp as the light source and a photomultiplier tube as the photodetector. The change in this optical density as a function of time is shown in Figure 11, and it increased continuously until it reached a value of 16 (in optical density units), and then stabilized. The residue after 600 seconds was 38%.

[0177] 7.5 x 7.5 cm 2Commercial alternative materials in the form of 4 mm thick surface plates (polybutylene terephthalate, polypropylene, ethylene methyl acrylate copolymer, polyamide 6) were also subjected to the same operating protocol. Figure 12 shows the smoke emission profiles (optical density as a function of time) of each of these materials compared to the beads according to the present invention. The alginate expandable foam beads according to the present invention were observed to emit a much smaller amount of smoke than the comparative materials.

[0178] 4 / Example 4 - Preparation of alginate-based expandable foam balls containing cellulose fibers Expandable foam beads containing cellulose fibers, according to a modified version of the present invention, were manufactured using the above apparatus by applying the following operating protocol.

[0179] The composition of the initial mixture is as follows: - 60g sodium alginate, - 6.5g of Arbocel® B400 cellulose fiber (JRS Rettenmaeir, 900μm (length) × 20μm (diameter)), - 0.4g sodium lauryl sulfate, - 0.8g of polyvinyl alcohol, - 4000g of water.

[0180] This mixture was introduced into the foaming module at a flow rate of 4 l / h. The rotation speed in the module was 700 rpm.

[0181] The foam generated in the foaming module was introduced into the extrusion module and directly immersed in a gelling / coagulation bath consisting of a 4 g / l calcium chloride aqueous solution. The knife rotation speed was equal to 300 rpm.

[0182] The residence time of the beads formed in the maturation module is equal to 40 minutes.

[0183] The resulting calcium alginate-based expandable foam beads containing cellulose fibers were separated from the liquid medium, centrifuged, dehydrated, and then dried.

[0184] 5 / Example 5 - Manufacturing of a plate having beads according to the present invention A mass of 30 g of expanded foam beads formed in Example 1 (Batch S1) was mixed with 30 g of gelatin adhesive and prepared according to the following proportions: 22.5 g of water, 6 g of gelatin, and 1.5 g of glycerin.

[0185] The resulting mixture was placed in a rectangular mold and subjected to a pressure of 1 bar until the compressibility factor was 2. The compressed block was then dried in an oven at 60°C for 12 hours.

[0186] Dimensions: 12.5 x 12.5 x 3 cm 3 and 70 kg / m 3 A plate (mass 33g) with the following apparent density was obtained.

[0187] The resulting foam bead plates were tested for flame retardancy.

[0188] The tests were conducted using a cone-type calorimeter (Fire Testing Technology) in accordance with ISO 5660 standards. The plate prepared as described above (3 cm thick, apparent density 70 kg / m³) was used. 3 The sample was placed in a sample holder (standard sample holder, 10 cm side length, mass: 22 g). 75 kW / m 2 The irradiance was applied. Ignition was controlled, and the test was continued for 585 seconds.

[0189] This test recorded an ignition time of 190 seconds to ignite the material. Extinction occurred at 305 seconds, so the ignition duration was only 115 seconds. The peak heat release rate (pHRR) was 46 kW / m² during the ignition phase. 2 It reached this point. After 250 seconds, the total heat dissipation (THR) was 5.9 MJ / m³. 2 This reached a form of 2.4 kJ / g, and the combustion energy was 4 kJ / g.

[0190] Outside of the ignition period, the heat dissipation rate decreases at a very low but significant level (<20kW / m²). 2 It remained in that state. This is due to char generated during the slow (flameless) thermal oxidation and thermal decomposition of the material.

[0191] After 585 seconds (end of the test), the residue reached 31%, and the pyrolysis front did not reach the bottom of the sample. The THR (585 seconds) was 10.7 MJ / m³. 2 This reached a form of 4.3 kJ / g. The corresponding combustion energy was 6.2 kJ / g. This increasing trend is due to the fact that the oxidation of char, a polycyclic aromatic compound, releases more energy.

[0192] However, all of these values ​​remain very low, corresponding to an excellent response to fire.

[0193] 6 / Example 6 - Preparation of Alginate-Based Expanded Foam Beads - Dimensional Stability The alginate expandable foam beads according to the present invention were manufactured using the above apparatus by applying the following operating protocol.

[0194] The composition of the initial mixture is as follows: - 75g sodium alginate, - 0.3g sodium lauryl sulfate, - 0.8g of polyvinyl alcohol, - 5000g of water.

[0195] This mixture was introduced into the foaming module at a flow rate of 4 l / h. The rotation speed in the module was 700 rpm.

[0196] The foam generated in the foaming module was introduced into the extrusion module and directly immersed in a gelling / coagulation bath consisting of a 5 g / l calcium chloride aqueous solution. The knife rotation speed was equal to 300 rpm. The height of the gelling / coagulation bath column above the extrusion zone was 30 cm.

[0197] The residence time of the beads formed in the maturation module is equal to 40 minutes.

[0198] After separation from the liquid medium, the beads were centrifuged in a spinning module, and then, in batches of wet beads, were dried in an industrial dryer (rotary drum dryer) at 75°C for 90 minutes.

[0199] The mass loss of beads during drying was determined by weighing each batch before and after drying. The percentage of water in the wet beads was estimated for each batch: - Batch 1: Wet mass 5.366 kg / Dry mass 144 g / Water content in wet beads: 97.3% by mass; - Batch 2: Wet mass 5.724 kg / Dry mass 150 g / Water content in wet beads: 97.4% by mass; - Batch 3: Wet mass 4.584 kg / Dry mass 120 g / Water content in wet beads: 97.4% by mass.

[0200] Examples of beads before and after drying are shown in Figure 13. It was observed that the size of the beads after drying (b / in the figure) was substantially the same as the size before drying (a / in the figure).

[0201] This was confirmed by measuring the size of the beads before and after drying using a Neo Tools digital caliper. The size was measured at 3.93 mm before drying and 3.72 mm after drying.

[0202] These results demonstrate that the beads formed by the method according to the present invention do not shrink significantly, as a result of the internal pores not collapsing during drying.

[0203] The apparent density of the obtained beads, determined by the packing method, was approximately 20 kg / m³. 3 That was the case.

[0204] 7 / Example 7 - Comparative Example without Emulsion Stabilizer The alginate expandable foam was manufactured using the above apparatus by applying the following operating protocol.

[0205] The composition of the initial mixture is as follows: - 75g sodium alginate, - 0.3g sodium lauryl sulfate, - Polyvinyl alcohol: 0.8g (method according to the present invention), or 0g (method not according to the present invention) - 5000g of water.

[0206] Each mixture was introduced into the foaming module at a flow rate of 4 l / h. The rotation speed in the module was 700 rpm.

[0207] The foam generated in the foaming module was introduced into the extrusion module and directly immersed in a gelling / coagulation bath consisting of a 4 g / l calcium chloride aqueous solution. The knife rotation speed was equal to 300 rpm. The height of the gelling / coagulation bath column above the extrusion zone was 26 cm.

[0208] The residence time of an object formed in the maturation module is equal to 40 minutes.

[0209] After separation from the liquid medium, the material was centrifuged in a spinning module, and then dried in batches of 3 kg of the wet material in an industrial dryer (rotary drum dryer) at 75°C for 90 minutes.

[0210] The apparent density of the beads obtained by the method according to the present invention is determined by the packing method and is approximately 70 kg / m³. 3 The density of the substance obtained by a method other than the present invention (without emulsion stabilizer) was also measured by the filling method and was approximately 80 kg / m³. 3 That was the case.

[0211] The objects obtained at the end of each of the two methods are shown in Figure 14 in front view (A / ) and side view (B / ). There are clearly geometric differences between these objects: the object (i) obtained by the method according to the present invention is substantially spherical and can be considered a bead, whereas the object (ii) obtained by the non-inventive method, which does not use an emulsion stabilizer, is not the same. These objects (ii) are much smaller than the object (i) obtained by the method according to the present invention, in addition to their irregular shape. Furthermore, unlike the latter, they are deformable, have a sticky surface, and exhibit collapse during the gelation process.

[0212] Figure 15 shows a modification of one internal structure of object (ii) associated with the absence of the emulsion stabilizer: an internal cavity is observed, highlighted by a dashed circle and arrow in the figure, within which microbubbles collapse, forming a cell representing approximately one-third of the object's diameter. This change in cellular structure (loss of internal cells) results in "embrittlement" of the material (loss of stiffness resulting in the object's deformability) and a slight increase in its density.

[0213] These results demonstrate the importance of using emulsion stabilizers in addition to surfactants to achieve the performance intended by the present invention.

Claims

1. A method for producing an expanded foam solid (55), - a / A step (10) to prepare a mixture of monovalent alginate, surfactant and emulsion stabilizer in an aqueous carrier. - b / A step (20) of foaming the mixture, which includes a step (20) of introducing gas into the mixture and simultaneously stirring the mixture to form a foam. - c / The step (40) of extruding the foam thus formed while immersed in a first aqueous gelling solution for gelling the alginate, and cutting the foam as fragments (47) of the foam enter the first aqueous gelling solution, wherein the first aqueous gelling solution is contained in a reactor (31) having a lower zone (312) and an upper zone (313) on the opposite side, and the extrusion (30) of the foam while immersed in the first aqueous gelling solution is performed in the lower zone (312) of the reactor (31), - d / The step of forming the foam comprising the fragment (47) in a second aqueous gelling solution for gelling the alginate for at least 30 minutes (50) to form the expanded foam solid (55), A method characterized by including a series of steps.

2. The method according to claim 1, further comprising, after the maturation step d / , a step e / (60) of separating the solid (55) from the aqueous gelling solution, and optionally, a step f / (70) of drying the solid (55) thereafter.

3. The method according to claim 1 or 2, wherein in step c / , the extrusion (30) of the foam immersed in the first aqueous gelling solution is carried out in the lower zone (312) of the reactor (31) at a height of the first aqueous gelling solution of 20 cm to 2 m.

4. The method according to any one of claims 1 to 3, wherein the foam fragment (47) formed in step c / is extracted from the upper zone (313) of the reactor (31) and transferred to a maturation module (51) for carrying out step d / (50) for maturing the foam forming the fragment (47).

5. The method according to any one of claims 1 to 4, wherein in step c / , the cutting (40) is performed to form a fragment (47) of foam having dimensions of 1 to 25 mm.

6. The method according to any one of claims 1 to 5, wherein the first aqueous gelling solution and / or the second aqueous gelling solution is a solution containing a polyvalent cation or having a pH of 3 or less.

7. The method according to any one of claims 1 to 6, wherein the surfactant is selected from sodium lauryl sulfate, ammonium lauryl sulfate, sodium stearate, sodium dodecylbenzenesulfonate, and polysorbate.

8. The method according to any one of claims 1 to 7, wherein the emulsion stabilizer is selected from polyvinyl alcohol and protein.

9. The method according to any one of claims 1 to 8, wherein step a / comprises introducing at least one additive selected from fibers, pigments, dyes, and fillers into the mixture.

10. The mixture is in the aqueous carrier in proportion to the total mass of the components introduced into the aqueous carrier. - 80-99% by mass of one or more monovalent alginates, - 0.1 to 0.6% by mass of one or more surfactants, - 0.2 to 2% by mass of one or more emulsion stabilizers, - 0 to 10% by mass of fiber, - One or more fillers in an amount of 0 to 2% by mass, The method according to any one of claims 1 to 9, including the method described in any one of claims 1 to 9.

11. Alginate-based expandable foam solid (55) obtained by the method described in any one of claims 1 to 10, - Its shape is spherical, - Having a size of 1 to 25 mm, - Defined as the ratio of the mass of the object, as measured by weighing, to its volume, particularly as determined by X-ray microtomography, between 30 and 130 kg / m³. ３ It has an apparent density of, - It has closed porosity, - Having a porosity of 90% or more, Alginate-based expandable foam solid (55).

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

13. An apparatus for carrying out the method described in any one of claims 1 to 10, - A foaming module (21) comprising a tank (22), an inlet (23) for supplying a liquid composition to the tank (22), a gas injector (24) for injecting gas into the tank (22), and a stirrer (25) for stirring the liquid composition contained in the tank (22), - A reactor (31) defined by a surrounding wall (311) and comprising a lower zone (312) and an upper zone (313) on the opposite side, wherein the lower zone (312) is provided with a cutting member (41) having at least one cutting blade (42) that is rotatable parallel to the lower part (314) of the wall (311) of the reactor, - A foam extrusion module (33) for extruding the foam in the reactor (31) through the lower part (314) of the reactor wall (311), - A hydraulic transfer system (29) for hydraulically transferring foam from the tank (22) to the extrusion module (33), - A maturation module (51) for maturing alginate-based foam fragments to form an expanded foam solid, - An extraction system (52) for extracting the medium contained in the reactor (31) and introducing the medium into the maturation module (51), An apparatus characterized by comprising:

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

15. The apparatus according to claim 13 or 14, comprising a separation module (61) for separating solid matter and liquid, and a recovery system (64) for recovering a medium contained in the maturation module (51) and introducing the medium into the separation module (61).

16. The apparatus according to claim 15, comprising a drying module (71) for drying a solid, and a transfer system (72) for transferring the solid from the separation module (61) to the drying module (71).

17. A method for manufacturing a structured object, - The plurality of solids (55) described in claim 11 are introduced into a mold as a mixture with a binder, - Compressing the mixture in the mold, - Drying the compressed mixture, Methods that include...

18. A structured object obtained by the method for producing a structured object according to claim 17, comprising a mixture with a binder containing a plurality of solids (55) according to claim 11, wherein the mass of the object, measured by weighing, is defined as the ratio of its volume to that of the object, determined by a calculation based on the measurement of its external dimensions, between 50 and 200 kg / m³. ３ A structured object having an apparent density.

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