WO2021219965A1

WO2021219965A1 - Plaster-based material

Info

Publication number: WO2021219965A1
Application number: PCT/FR2021/050746
Authority: WO
Inventors: Michel VILLEY; Nathalie Petigny; Mathias Agnely
Original assignee: Saint-Gobain Placo
Priority date: 2020-04-30
Filing date: 2021-04-29
Publication date: 2021-11-04
Also published as: FR3109777A1; CN115461315A

Abstract

The present invention relates to a plaster-based material comprising an activated carbon having a specific surface area greater than or equal to 875 m²/g and less than or equal to 1300 m²/g and/or an iodine value greater than or equal to 900 mg/g and/or a sorption capacity of at least 7 mg of toluene per g of activated carbon; and an average mass change Δm(S) in sorption of at least 2% and a mass change Δm(D4) after 4 sorption/desorption cycles of at most 1.5%.

Description

DESCRIPTION

TITLE: PLASTER-BASED MATERIAL

The invention relates to a plaster-based material, in particular a dry or wet mixture, a plasterboard or a plaster tile intended for the interior design of residential buildings, as well as its use for the construction. comfort inside buildings.

Comfort inside buildings, in particular in terms of air quality, is increasingly at the heart of the concerns of occupants and builders.

Volatile Organic Compounds (VOCs) are carbon and hydrogen-based chemicals found in air in the gaseous state. Directive n ° 2010/75 of the European Union of November 24, 2010 defines them as any organic compound having a vapor pressure of 0.01 kPa or more at a temperature of 293.15 K or having a corresponding volatility under the conditions special uses. They include chemicals of various kinds such as alkanes, alkenes such as terpenes, alkynes, alcohols, aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, cronotaldehyde, butyraldehyde, benzaldehyde, valeraldehyde , hexaldehyde or heptanaldehyde, ketones, ethers such as glycol ethers, aromatic hydrocarbons such as benzene and toluene, or halogenated hydrocarbons such as tetrachlorethylene and dichlorobenzene. VOCs are present in most paints, construction materials, solvents, detergents, fuels, as well as in resins, varnishes or glues used for furniture or electrical appliances, or even in cigarette smoke. These VOCs are found in the ambient air of buildings and, even if their quantity seems small, they can over time inconvenience the people who are there. exposed or even affect their health. In particular, some VOCs can cause allergic reactions, breathing problems, nausea or headaches.

In recent years, the proportion of VOCs emitted by the aforementioned materials has fallen sharply due to stricter regulations. However, alternative materials with low or no VOC emissions often have a higher cost and lower performance levels.

In addition to the efforts made to control the emission of VOCs, various means of reducing the amount of VOCs in the ambient air have been proposed. Thus, some building materials with existing air-purifying properties make use, for example, of the technique of photocatalytic oxidation with the use of titanium oxide particles. The main disadvantage of these materials is the need for an appropriate light source for the process to run efficiently. It has also been proposed to incorporate scavengers or scavengers in building materials to reduce the amount of VOCs in the ambient air inside buildings. Examples that may be mentioned are compounds containing active methylenes, such as acetoacetamide, tannins, amino alcohols, amides and hydrazides. While these agents can effectively trap certain VOCs (in particular aldehydes such as formaldehyde), they are generally ineffective in trapping other volatile organic compounds (such as xylene, toluene, ethylbenzene, decane, etc.).

Another type of problem encountered in buildings is linked to humidity, which can be significant in certain rooms and lead in particular to mold; conversely, air that is too dry or significant variations in humidity can also adversely affect occupant comfort. It is known to remedy humidity problems to use other types of compounds which scavenge water molecules (which are polar), for example, montmorillonite-type minerals composed of aluminum and magnesium silicate, such as these. compounds having on the other hand no effect on the trapping of a large part of the volatile organic compounds which are for many of them apolar (such as: xylene, ethylbenzene, decane, etc.). In addition, it is often not sufficient to simply capture the water molecules, the release of water can also be sought in the event that the air is or becomes too dry.

The resolution of these different problems therefore requires, where appropriate, to combine different types of solutions and / or compounds, sometimes contradictory.

The present invention thus aims to provide a plaster-based material, in particular for interior fittings, and in particular for use as an underlayment plaster or as a finishing plaster, this plaster being intended for example for leveling and / or protect a surface to be coated before applying the paint layer (generally mainly aesthetic in nature), this coating having both ambient air purification properties with regard to the different types of volatile organic compounds (VOCs) which may be present therein and humidity-regulating properties, the purification relating to VOCs not being limited only to that of formaldehyde but also relating to other VOCs, in particular nonpolar (such as xylene, toluene, ethylbenzene, decane ...), and the VOCs captured by the plaster-based material not further undergoing desorption at room temperature, and the humidity-regulating properties not only consisting of moisture-trapping properties but allowing in turn to capture excess humidity and re-release this humidity if, on the other hand, the air becomes too dry and / or when the room is ventilated.

This object is achieved thanks to the material according to the invention. The present invention therefore relates to a plaster-based material characterized in that it comprises an activated carbon, exhibiting (initially, before incorporation into the material):

- a specific surface greater than or equal to 875 m ² / g and less than or equal to 1300 m ² / g and / or an iodine number greater than or equal to 900 mg / g and / or a sorption capacity of at least 7 mg of toluene per g of activated charcoal, and

- a variation in mean mass A _{m (S)} in sorption of at least 2% and a variation in mass A _{m (D4)} after 4 cycles of sorption / desorption of at most 1.5%.

The characteristics of the aforementioned activated carbon selected according to the invention are those of the initial activated carbon (that is to say not yet incorporated into the material), as it is added to the material.

The activated carbon used in the material according to the invention can be (initially) of the granular type (or in granular or granular form), that is to say formed of particles of irregular shapes in a size range mainly of 1. 'of the order of 0.2 mm to 5 mm, or in powder form, that is to say formed of particles of smaller size, generally less than 400 mpi, as opposed to other existing forms of activated carbon, for example in extruded form (regular shape). When granular activated carbon is used, the particles of activated carbon are in particular predominantly (at least 90% by weight, in particular at least 95% by weight, or even 100% by weight) in size (largest dimension of each particle) between 0.2 mm and 5 mm (limits included), in particular between 0.2 and 2 mm, or even in particular at least 90% by weight of size between 0.42 mm and 1.7 mm (limits included), the size of the particles being evaluated in particular by sieving (in particular using sieves referenced 12 and 40 in US mesh size). When powdered activated carbon is used, the activated carbon particles are in particular predominantly (at least 90% by weight, in particular at least 95% by weight, or even 100% by weight) in size (largest dimension of each particle) less than 400 μm (limits included), in particular between 1 and 400 μm, or even in particular at least 90% by weight of size between 10 and 200 μm (limits included), the size of the particles being evaluated by particularly using an air jet screen according to ASTM-D-5158-93.

Preferably, the density (also usually called density) of the selected activated carbon is also relatively high, where appropriate participating in a significant activity of said carbon in the present invention, this density (bulk density) being greater than or equal to 400 kg / m ³ , preferably greater than or equal to 440 kg / m ³ , or even greater than or equal to 500 kg / m ³ , or even greater than or equal to 530 or 540 kg / m ³ , the bulk density of the activated carbon used being determined by making the ratio of the mass of a given volume of material to said volume.

The activated carbon incorporated in the plaster-based material composition according to the invention is selected so as to exhibit a particular porosity resulting in particular in a specific surface greater than or equal to 875 m ² / g and less than or equal to 1300 m ² / g and / or by an iodine number greater than or equal to 900 mg / g and / or by a sorption capacity of at least 7 mg of toluene per g of activated carbon.

The specific surface of the selected activated carbon is measured by nitrogen adsorption (theory of multiple adsorption of gases using Brunauer determinations, Emmett and Teller - BET method), in accordance in particular with the ISO 9277: 2010 standard, and is, according to a first advantageous embodiment according to the invention, greater than or equal to 875 m ² / g, and preferably greater than or equal to 900 m ² / g, in particular greater than 900 m ² / g, in particular greater than or equal to 950 m ² / g, or even greater than or equal to 1000 m ² / g, and in addition is preferably less than or equal to 1300 m ² / g, in particular less than or equal to 1200 m ² / g, or even less than or equal to 1100 m ² / g.

The iodine number (iodine number) represents the mass of iodine (in milligrams) absorbed per gram of carbon, this index being measured in particular according to standard ASTM D4607-14 for a residual iodine concentration in the filtrate of 0 , 02 N. The iodine number is a relative indicator of porosity and can optionally also be considered as an indicator of the specific surface area of the activated carbon. According to an advantageous embodiment of the invention, it is greater than or equal to 900 mg / g, or even greater than or equal to 1000 mg / g.

The carbon sorption capacity is determined as follows: the toluene concentration is measured over time by SILT-MS (Selective Ion Llow Tube-Mass Spectrometry) mass spectrometry at the outlet of a U-shaped reactor where is contained the material (pure carbon) to be tested. The toluene concentration is first measured at the outlet of the empty reactor (without sample) over time until a level is reached which corresponds to the concentration initially generated, in order to determine the mixing curve. The material to be tested is then placed in the reactor and then the same concentration is generated in the same way. The toluene concentration at the reactor outlet is then measured over time. A time delay is observed with respect to the mixing curve in order then to reach the state of equilibrium between the toluene in the gas phase and the toluene adsorbed on the surface of the material. This time difference corresponds to adsorption of toluene by the material tested. Integration then makes it possible to calculate the area between the two curves and to determine the quantity of toluene adsorbed by the material, at the concentration considered. In the measurements carried out to determine the sorption capacity of activated carbon in the present invention, the concentration of toluene (pure) in the supply air is 360 pg / mf According to an advantageous embodiment of the invention, the activated charcoal is selected so as to have a sorption capacity of at least 7 mg of toluene per g of activated charcoal, preferably of at least 8 mg of toluene per g of activated charcoal, in particular of at least 9 mg of toluene per g of activated carbon.

The above indicators are linked to a certain porosity of the selected activated carbon, which advantageously integrates different types of pores which can participate, each in a different way, in the sorption of VOCs, and in the sorption or desorption of water molecules. The selected activated carbon thus advantageously comprises both micropores (of diameters generally less than 2 nm), and mesopores (of diameters generally between 2 and 50 nm), the diameter (equivalent diameter) qualifying the size of the pores being calculated. from measurements of pore volumes carried out for example using the BET method cited above.

The nature or the origin of the activated carbon used influencing, where appropriate, the porosity, the activated carbon used in the composition of plaster-based material according to the invention is in particular chosen, in an advantageous embodiment according to the invention. , among the activated carbons produced from (or derived from) coal (bituminous coal). Activated carbons can in fact conventionally be manufactured by pyrolysis of various carbonaceous raw materials such as wood, coconut shells or other organic plant materials, coal, etc., the most commonly used being those obtained from coconut shells. The use of an activated carbon defined according to the invention and obtained from coal in the plaster-based material composition has made it possible to obtain particularly advantageous results in terms of obtaining and fair balance of the various desired properties, as shown later.

As defined above, the activated carbon selected according to the invention also exhibits a variation in mean mass A _m (S) in sorption of at least 2%, and in particular of at least 2.5%, or even of at least 3%. , and a variation in mass A _{m (D4)} after 4 sorption / desorption cycles of at most 1.5%, or even at most 1.4%. These values are determined in the present invention by placing the sample of charcoal to be tested in a beaker 7.4 cm in diameter until a sample thickness of 2 cm is obtained, the assembly being placed in an enclosure. climate Terchy and maintained for 2 days at a temperature of 23 ° C at a relative humidity of 33%, before being subjected to 4 cycles of sorption / desorption (each presenting a sorption phase followed by a desorption phase) and to a fifth sorption phase occurring at the end of the 4 cycles, with an exposure time of 8 hours in (ad) sorption at 75% relative humidity and 16 hours in desorption at 33% relative humidity. The mass of the sample is measured at the end of each sorption phase (i.e. 5 measurements in sorption) and each desorption phase (i.e. 4 measurements in desorption) so as to plot profiles of the variation in mass (in% per compared to the starting mass of the sample (mass at the start of the first cycle)) over time, the change in mean mass A _m (S) (in%) in sorption (or during the sorption phases) corresponding to the arithmetic mean of the variations in masses for each of the sorption phases (average of 5 values) and the variation in mass A _{m (D4)} (in%) being evaluated at the end of the desorption phase of the 4th cycle (last variation mass in desorption) after the 4 cycles of sorption / desorption, as illustrated later in FIG. 1, this last value making it possible in particular to evaluate the symmetry / dissymmetry of the sorption / desorption of water.

The activated carbon selected also advantageously exhibits isotherms (representing the rate by weight of water captured by the activated carbon with respect to the relative humidity of the ambient air) of sorption and desorption (of water vapor) of the form sigmoid (or S-shape) exhibiting a first sorption zone, respectively desorption, low (with a water content of said activated carbon less than 5% by weight) up to at least 30%, or at least 40% (and at most 60%), relative humidity of the ambient air, and a second sorption zone, respectively of strong desorption (compared to the first zone, with a variation in the water content of the coal ranging from 5%, or less, by weight to at least 30% by weight) falling within the range of 30% to 80%, especially 40 to 80%, relative humidity of the ambient air. More precisely, the activated carbon has a sorption (respectively desorption) isotherm called "type V" (on the model of the representations given in particular in the UICP nomenclature), integrating (as illustrated in FIG. 3 a) a zone A (respectively A 'for the desorption curve) of low slope, then a zone B (respectively B') of strong slope (compared in particular to zone A, respectively A ') where sorption increases (respectively desorption takes place ) significantly, and a low slope saturation zone C. In zone A, respectively A ', isotherms of the activated carbon according to the invention, located in the relative humidity range from 0 to 30 or 40%, the water content of the selected activated carbon remains below 5% by weight, and in zone B, respectively B ', located within the relative humidity range from 30 or 40% to 80%, the water content of the activated carbon varies (upwards or downwards depending on the curve considered - a hysteresis being generally observed between the curves of sorption and desorption) between 5% or less and at least 30% by weight (limits included), preferably between 5% or less and at least 35% by weight (or even more). The isotherms are determined by water vapor adsorption gravimetry (or DVS or Dynamic Vapor Sorption), using in particular a reference Dynamic Vapor Sorption Analyzer DVS Intrinsic from the company Surface Measurement System.

Advantageously, the activated carbon used also initially (before incorporation into the plaster-based material) has a relative humidity of less than or equal to 2% by weight, this humidity being evaluated by weighing before then after drying (the drying being carried out until obtain a variation in mass less than 0.1%).

The activated carbon used is an activated carbon obtained by grinding, and if necessary re-agglomeration, to obtain the desired particle size, then drying (in particular so that a maximum of 2%, or even a maximum of 1% moisture remains), the charcoal being activated in a known manner, in particular by proceeding by physical activation, in particular in water vapor, the activation taking place in particular at high temperature (in particular between 550 and 1100 ° C.). The activated charcoal used can be activated entirely or only at the surface, and is in particular activated entirely.

An example of a particularly satisfactory activated carbon used according to the present invention is in particular the activated carbon sold by the company Chemviron Carbon under the reference “Filtrasorb 400”, this carbon being a granular activated carbon obtained from coal and fully activated by physical activation, and having a particle size of 1.7 x 0.42 mm (i.e. passing through sieve No. 12 which corresponds to a particle size of 1.7 mm, and retained by sieve No. 40 which corresponds to a particle size 0.42 mm), a specific surface area of at least 900-950 m ² / g, an index of iodine of the order of 1000 mg / g, a sorption capacity of 9.1 mg (toluene) / g, an apparent density of at least 440 to 540 kg / m ³ , a variation in mean mass A _m ( S) in sorption of 3.55% and a variation in mass A _m (D4) after 4 sorption / desorption cycles of 1.37%, type V sorption / desorption isotherms illustrated in figure 3a, a porosity resulting from a mixture micropores and mesopores and a relative humidity of less than 1%. It can obviously be ground to be used in the form of powder of the desired particle size.

The level of activated carbon defined in the present invention in the plaster-based material is preferably between 0.5 and 10% by weight of said composition (dry), preferably between 0.5 and 7%, or 0, 7 to 2% (limits included), for example of the order of 1.5%.

The activated carbon used according to the invention makes it possible to obtain, without the aid of another agent, both the desired properties in terms of purification of the ambient air and of humidity regulation. The composition according to the invention may nevertheless comprise other VOC fixing agents to improve the purification properties with respect to one or more VOCs, in particular aldehydes such as formaldehyde. Examples of VOC scavengers include active methylene compounds, such as acetoacetamide, tannins, amino alcohols, amides, and hydrazides. In certain embodiments, the plaster-based material can advantageously be devoid of other activated charcoals than the selected activated charcoal, or of water-capturing additives of the montmorillonite type, or more generally of any other agent usually used to purify. air or capture water molecules etc.

The term “plaster” within the meaning of the present invention designates, as defined by standard EN 13279-1: 2008, calcium sulphate in all its forms of hydration, comprising calcium sulfate dihydrate (CaSCL, 2 H2O), i.e. also plaster taken, calcium sulfate hemihydrate (CaSCL, ½ H2O), i.e. non-plaster taken or calcined gypsum, or anhydrite (CaSCL). The expression “plaster-based material” denotes a material the binder of which consists mainly of plaster, that is to say comprising in particular at least 40% by weight, preferably at least 50%, more preferably at least 60%. , or even more preferably at least 70%, by dry weight of plaster. Preferably, the plaster-based material comprises less than 20%, more preferably less than 10%, or even less than 5%, by weight of inorganic hydraulic binders other than plaster. In a particular embodiment, the plaster-based material does not include any inorganic hydraulic binders other than plaster. This expression excludes in particular mortars and cementitious materials. Examples of plaster-based materials include, in particular, plasterboard, plaster tiles, dry (powder) or wet (paste) mixtures, such as plasters in the form of a pre-mix in powder or in the form of ready-to-use paste, as well as the coatings obtained from such coatings.

The plaster-based material according to the invention can comprise processability additives making it possible to adapt the properties of the mixes according to the manufacturing conditions as well as other functional agents making it possible to modify the final properties of the material. The processability additives well known to those skilled in the art can in particular be adhesion agents, setting accelerating agents, setting retarding agents, thinning agents, thickening agents, water retention agents, pH modifiers or anti-foaming agents. The functional agents which are also well known to those skilled in the art can be organic binders, foaming agents, biocidal agents, water-repellent agents, fire-retardant agents, lightening agents, lightening agents. reinforcement or pigments. The plaster-based material may in particular comprise up to 50%, preferably up to 30%, more preferably up to 20%, by dry weight of additives. By way of example, the plaster-based material can typically comprise, for 100 parts by weight of plaster (calcium sulfate hemihydrate, calcium sulfate dihydrate or anhydrite):

0 to 250 parts of mineral fillers, for example calcium carbonate, kaolin or silica sand;

0 to 100 parts of at least one lightening agent, for example expanded perlite or hollow glass beads;

0 to 50 parts of at least one polymeric binder, for example poly (vinyl acetate) (PVAC), ethylene vinyl acetate (EVA), vinyl acrylate;

0 to 20 parts of at least one water retention agent, for example cellulose ethers or guar ethers;

0 to 10 parts of at least one rheology modifying agent, for example starch ether, polyacrylamides, acrylics, xanthan gum, hectorite, bentonite or attapulgite;

0 to 10 parts of at least one setting retarder, for example organic acids, amino acids or phosphates;

0 to 5 parts of at least one setting accelerator, for example potassium sulphate;

0 to 50 parts of at least one pH modifying agent, for example lime, cement, sodium hydroxide or amines;

0 to 5 parts of at least one anti-foaming agent, for example

0 to 10 parts of at least one biocidal agent, for example carbamates, such as 3-iodoprop-2-yn-1-yl butylcarbamate, or pyrithione complexes; 0 to 15 parts of at least one adhesion agent, for example a poly (vinyl acetate), a poly (vinyl alcohol), a starch, in particular previously treated with an acid or pre-gelatinized, a dextrin or a flour vegetable, especially wheat or corn;

0 to 20 parts of at least one water repellent, for example a siloxane, a polysiloxane or a wax;

0 to 20 parts of at least one anti-fire agent, for example vermiculite, silica, in particular of micrometric size or a clay; and or

0 to 20 parts of at least one reinforcing agent, for example polymer fibers, mineral fibers, in particular glass, or plant fibers;

0 to 5 parts of pigments.

The plaster-based material may comprise up to 70%, preferably up to 60%, more preferably up to 50%, or even up to 40%, or even up to 30%, by weight of fillers, in particular calcium carbonate, silica sand, kaolin, reinforcing fillers, such as fibers, and lightening fillers, such as expanded perlite or hollow glass beads.

In a particular embodiment, the plaster-based material according to the invention is a dry or wet mixture (ready for use). Conventionally, these mixtures comprise calcium sulfate hemihydrate (calcined gypsum) and possible additives described above. Their composition may vary depending on the application for which they are intended. Examples of such mixtures include in particular the coatings defined by standard EN 13279-1: 2008. The dry mixtures are obtained by adding, sequenced or simultaneously, each of the constituents in a dry mixer. Activated carbon can be added to the mixture in the same way as the other components.

The wet mixtures can be obtained by adding, sequenced or simultaneously, each of the constituents in a mixer in the presence of water, or by mixing a dry premix, the activated carbon being able to be introduced during the preparation of the dry premix. or at the time of mixing.

A dry mixture typically comprises, per 100 parts by weight of plaster, 0 to 250 parts of mineral fillers, 0 to 100 parts of lightening agent, 0 to 50 parts of an organic binder, 0 to 20 parts of a water retention agent, 0 to 10 parts of a rheology modifying agent, 0 to 10 parts of a setting retarder, 0 to 5 parts of a setting accelerator, 0 to 50 parts of a pH modifying agent, and 0 to 10 parts of a biocidal agent.

Before use, the dry mixes are mixed with water in a water: dry mix weight ratio of 0.3: 1 to 1: 1 to make a batch. Calcined gypsum undergoes a hydration reaction in the presence of water and turns into calcium sulfate dihydrate (gypsum) causing the plaster to set, or harden after application.

A wet mixture typically comprises, per 100 parts by weight of plaster, 0 to 100 parts of mineral fillers, 0 to 50 parts of a lightening agent, 0 to 50 parts of an organic binder, 0 to 20 parts of a water retention agent, 0 to 10 parts of a rheology modifying agent, 0 to 10 parts of a pH modifying agent, 0 to 5 parts of an anti-foaming agent, 0 to 20 parts of a waterproofing agent, 0 to 5 parts of a pigment, 0 to 10 parts of a biocidal agent, and 30 to 150 parts of water. In another particular embodiment, the plaster-based material according to the invention is a plaster coating, obtained in particular from a dry or wet mixture as described above. The plaster coating typically has a composition similar to that of the dry or wet mixtures as described above. The plaster coating generally has a thickness of 1 to 25 mm, preferably 2 to 14 mm.

In another particular embodiment, the plaster-based material according to the invention is a plasterboard. Plasterboards are panels comprising a layer of plaster between two facing sheets, generally made of cardboard or based on glass fibers. Industrially, plasterboard is formed in a continuous process comprising three main stages: shaping, setting and drying. During the plasterboard shaping step, a batch is produced continuously in a mixer from calcined powdered gypsum, water and specific additives to adapt the properties of the batch and / or of the final product as mentioned above. It is in particular known to add foaming agents or foam directly in order to reduce the density of plasterboards. The batch is then continuously discharged onto a first facing sheet driven by a conveyor belt to an extruder to form the plate. After the edges of the first facing sheet have been folded back, a second facing sheet is fed to the extruder. The extruder presses the second facing sheet onto the batch, smooths the surfaces and reduces the thickness of the plasterboard to the desired value. To improve the mechanical properties of plasterboard, it is also known to form a denser plaster layer on one face and possibly on the edges of the plasterboard. For this, a first layer of more dense mix, called roller coating layer, is poured and formed on the first facing sheet, upstream of the pouring of the main mix which then forms a second layer called the body of the plasterboard. The roller coating layer generally has a low thickness, typically less than 2 mm, for example approximately 1 mm. The plaster strip obtained at the outlet of the extruder is transported continuously by a conveyor over a sufficient distance to allow the latter to be set and to reach a level of hardening sufficient to be able to be cut into plates to the desired dimension. The plates are then dried in an oven to remove excess water.

Conventionally, the batch comprises calcium sulfate hemihydrate (calcined gypsum) and any additives described above. The composition of the mix may vary depending on the nature of the plasterboard to be manufactured. The batch typically comprises, for 100 parts by weight of plaster, 40 to 200, preferably 50 to 150 parts of water, 2 to 10 parts of foam obtained from a mixture of water and a foaming agent, for example an alkylsulphate optionally mixed with an alkylethersulphate, and 0.1 to 1 part of setting accelerator, for example hydrated calcium sulphate or potassium sulphate.

The plasterboard generally has a thickness of 6 to 25 mm, preferably 10 to 15 mm.

The activated carbon according to the invention can be introduced into the plasterboard in various ways.

According to a first preferred embodiment, the activated carbon is added to the mixture before the latter is deposited on the first facing sheet. The addition of the activated carbon can be done during the manufacture of the batch, for example by simultaneously or successively introducing the calcined gypsum and the aforementioned compounds into the batch. mixer, or after the mixture has been obtained, for example at the outlet of the mixer or in a secondary mixer. The simultaneous addition of the constituents is advantageous because it is easier to use. This embodiment makes it possible to have a homogeneous distribution of the activated carbon in the plasterboard.

According to a second embodiment, the activated carbon is introduced into a roller coating layer. For this, the activated carbon is introduced into a batch used for the formation of the roller coating layer, the main batch intended for the formation of the body of the plate generally being devoid of activated carbon. This embodiment makes it possible to concentrate the activated carbon only on one face of the plasterboard and on only part of its thickness.

In another particular embodiment, the plaster-based material according to the invention is a plaster tile. Plaster tiles are usually obtained by molding. For this, a batch is prepared in a mixer. After obtaining a homogeneous batch, it is poured into molds and leveled at the height of the molds to remove the excess batch. After the plaster tiles have set sufficiently for handling, they are removed from the mold by extrusion and then dried in an oven to remove excess water.

Conventionally, the mixture comprises calcium sulfate hemihydrate (calcined gypsum) and possible additives described above. The composition of the batch may vary depending on the nature of the plaster tiles to be manufactured. The batch typically comprises, per 100 parts by weight of plaster, 40 to 200, preferably 50 to 150 parts of water, 0.1 to 1 part of setting accelerator, for example hydrated calcium sulfate or sodium sulfate. potassium, 0.1 to 2 parts thinner, 0 to 1 part retardant, and 0 to 10 parts of waterproofing agent. Activated carbon can be introduced into the plaster tiles during the preparation of the batch.

Plaster tiles are generally 30-200mm thick, preferably 50-150mm thick.

The present invention also relates to the use of a plaster-based material as described above, in particular a plasterboard, a plaster tile, a dry or wet mixture, or a plaster coating to both reduce the amount of VOCs and regulate the humidity in the air inside buildings. The present invention also relates to a method of reducing the amount of VOCs and regulating humidity in the indoor air of buildings comprising contacting a plaster-based material as described above with the indoor air. For this purpose, the plaster-based material according to the invention can be installed on the walls, ceilings and floors inside buildings, in particular to form facings, partitions or false ceilings or to cover or join plaster or cement panels.

The plaster-based material according to the invention shows both good sorption of VOCs (and thus ambient air purification properties), in particular non-polar VOCs (such as toluene, xylene, ethylbenzene, decane, para. -dichlorobenzene) in addition to formaldehyde (or other aldehydes), and good humidity regulation properties (and not only water collection, but also release if necessary) meeting the needs of users in terms of comfort, as illustrated later, the composition absorbing moisture, storing it then, when the humidity of the room decreases again and / or in the event of ventilation, rapidly releasing this stored humidity in the ambient air. The plaster-based material according to the invention can absorb large amounts of volatile organic compounds (VOCs) from the ambient air, the VOCs captured by the plaster-based material also not undergoing desorption at room temperature. The plaster-based material according to the invention has thus shown an efficiency (per pollutant) in terms of adsorption of VOCs of the order of at least 40%, preferably at least 50%, or even at least 60%, for at least each of the following pollutants: acetaldehyde, toluene, tetrachlorethylene, xylene, 1,2,4-trimethylbenzene, ethylbenzene, 2-butoxyethanol, styrene and 1, 4-dichlorobenzene, formaldehyde, and in particular at least 50% , preferably at least 60%, or even at least 70%, for at least each of the following pollutants: ethylbenzene, xylene, toluene, dichlorobenzene. The efficiency (in%) is determined by a dynamic CLIMPAQ test according to ISO 16000-23: 2009 and ISO 16000-24: 2009 standards as follows: a sample of 20 cm x 35 cm x 1 cm introduced into a chamber CLIMPAQ of 50.9 L (corresponding to a load factor Lf of 1, 4: wall and ceiling scenario) maintained at a temperature of 23 ° C ± 2 ° C and a relative humidity of 50% ± 5% during the test . The adsorption capacity is measured independently for each VOC. The sample is subjected to an air flow for a period of 24 hours, the air renewal rate being set at 0.5 vol.h ¹ . The air injected at the inlet of the chamber comprises an initial concentration Ci of VOCs. The final VOC concentration Cf at the outlet of the chamber is measured by gas chromatography coupled to a mass spectrometer. The adsorption efficiency of a VOC, in percentage, is given by the following formula (Ci-Cf) / Ci. The adsorption capacity can be achieved for a single VOC, for example toluene (in this case the air flow comprises toluene at an initial concentration Ci of 200 pg / m ³ ), or on a mixture of VOCs, for example a mixture of acetaldehyde, toluene, tetrachlorethylene, xylenes (m, p), 1,2,4-trimethylbenzene, ethylbenzene, 2- butoxyethanol, styrene and 1, 4-dichlorobenzene (in this case the air flow includes an initial toluene concentration Ci of 50, 100, 150 or 200 pg / m ³ , and the initial Ci concentrations for the other VOCs are set according to the following ratios:

Cacetaldehyde! Ctoluene 6! 1, Tetrachlorethylene! Ctoluene 3! 1, Cxylenes (m, p)! Ctoluene 3! 1, Cl, 2, 4-trimethylbenzene! Ctoluene 2! 1, Cethylbenzene! Ctoluene L l, C 2 - b u to x y é t h a n o I! C t o I u έ n c L l, Cstyrene! Ctoluene

0.5 il and Cl, 4-dichlorobenzene! Ctoluene 211).

The plaster-based material according to the invention also advantageously has an average MBV moisture buffer value greater than 2 g per m ² and per percentage change in relative humidity (% ARH), and in particular greater than or equal to 2.0 g / (m ^2. % ARH), or even greater than or equal to 2.5 g / (m ^2. % ARH), or even greater than or equal to 3 g / (m ^2. % ARH), the value of the buffer of humidity (Moisture Buffer Value:

MBV) reflecting the ability to moderate variations in the relative humidity of the surrounding air. The definition of this value, as well as an associated test protocol, were given at the end of the NORDTEST project [Rode, C. (ed.), Moisture Buffering of Building Materials, Department of Civil Engineering, Technical University of Denmark, Report R-126, 2005- ISSN 1601-2917 ISBN 87-7877-195-1], this value being defined by the ratio of 1) the variation in mass during an absorption / desorption cycle (in g) on 2) the product of the value of the heat exchange surface (in m ² ) and the difference between the high and low relative humidity values (of the air) during the cycle (in%), the relative humidity of the air, or hygrometric degree, corresponding to the quantity of water vapor contained in a given volume of air compared to the maximum it could contain at a given temperature and pressure. The principle of the associated test protocol is to subject the samples to daily relative humidity cycles in order to be representative of the cycles encountered in buildings, the reference relative humidity pair being 75% / 33% humidity. relative with an exposure duration of 8 hours in absorption and 16 hours in desorption, the mass monitoring of the samples then making it possible to determine the MBV value, the performance being all the better the higher this value is.

The invention is illustrated with the aid of the following non-limiting examples.

FIG. 1 represents an example of the profile of variation in mass of a compound during sorption and desorption phases making it possible to evaluate the variations in mean mass A _m (S) in sorption and A _m (D4) after 4 cycles sorption / desorption according to the measurement protocol described above.

Figure 1 shows an example of the variation profile of the mass of a compound (illustrative representation not necessarily corresponding to a particular compound) over time by performing 4 cycles of sorption and desorption and a fifth sorption phase at the end of the 4 cycles according to the protocol for measuring the parameters A _m (S) and A _m (D4) described above. The mass of the (pure) compound analyzed is measured at the end of each sorption phase and of each desorption phase so as to plot profiles of mass variation over time. The average mass variation A _m during the sorption phases corresponds to the arithmetic average of the mass variations Di to D5 measured for each of the sorption phases (average of 5 values) and the mass variation A _{m (D4)} is the value of the last change in desorption mass at the end of the desorption phase of the 4th sorption / desorption cycle.

FIG. 2 represents the isotherms of sorption and desorption of water vapor of a particular activated carbon, selected according to the invention, and marketed by the company Chemviron under the reference “Filtrasorb 400”. This charcoal is an activated charcoal granular obtained from coal and fully activated by physical activation, and has a particle size of 1.7 x 0.42 mm, a specific surface area of the order of 950 m ² / g, an iodine number of the order of 1000 mg / g, a sorption capacity of 9.1 mg (toluene) / g, a bulk density of at least 440 to 540 kg / m ³ , a variation in mean mass A _m of 3.55% in sorption and a variation of mass A _m (D4) after 4 sorption / desorption cycles of 1.37%, type V sorption / desorption isotherms illustrated in FIG. 2, a porosity with in particular a mixture of micropores and mesopores, and a relative humidity less than 1%.

The isotherms are determined using a reference Dynamic Vapor Sorption Analyzer DVS Intrinsic from the company Surface Measurement System.

On the water vapor sorption and desorption isotherms of the activated carbon Filtrasorb 400, a strong regulation is observed in a zone within the zone of relative humidity ranging from 40 to 80% (Figure 2). The sorption and desorption isotherms of the activated carbon alone are sigmoid in shape, in particular type V (on the model of the representations given in particular in the IUPAC nomenclature), and have a first sorption zone A, respectively A ' desorption, low, with a shallow slope, the water content of the activated carbon remaining below 5% by weight up to at least 40% relative humidity of the ambient air, and, in the range of 40 to 80% relative humidity of the ambient air, a second zone of sorption B, respectively of desorption B ', strong, of strong slope (compared in particular to the first zone) where the sorption increases (respectively the desorption takes place) significantly, the water content of the activated carbon varying (upwards or downwards depending on the curve considered) between 5% or less and up to 35% by weight, and finally a last zone C, respectively C ', low slope saturation.

Claims

1. Plaster-based material, characterized in that it comprises an activated carbon having:

- a variation in mean mass A _m (S) in sorption of at least 2% and a variation in mass A _m (D4) after 4 cycles of sorption / desorption of at most 1.5%.

2. Material according to claim 1, characterized in that said activated carbon is formed of granules or powder.

3. Material according to claim 1 or 2, characterized in that the density of said activated carbon is greater than or equal to 400 kg / m ³ , preferably greater than or equal to 440 kg / m ³ , or even greater than or equal to 500 kg / m ³ .

4. Material according to any one of claims 1 to 3, characterized in that said activated carbon has a specific surface area greater than or equal to 900 m ² / g, in particular greater than 900 m ² / g, in particular greater than or equal to 950 m ² / g, and is preferably less than 1300 m ² / g, in particular less than or equal to 1200 m ² / g, or even less than or equal to 1100 m ² / g, or characterized in that said activated carbon has an iodine number greater than or equal to 1000 mg / g, or characterized in that said activated carbon has a sorption capacity of at least 8 mg of toluene per g of activated carbon, in particular of at least 9 mg of toluene per g of activated carbon

5. Material according to any one of claims 1 to 4, characterized in that said activated carbon comprises both micropores and mesopores.

6. Material according to any one of claims 1 to 5, characterized in that said activated carbon is an activated carbon obtained from coal.

7. Material according to any one of claims 1 to 6, characterized in that said activated carbon has a variation in mean mass A _m (S) in sorption of at least 2.5%, or even at least 3%, and a variation in mass A _{m (D4)} after 4 sorption / desorption cycles of at most 1.4%.

8. Material according to any one of claims 1 to 7, characterized in that said activated carbon has sigmoid-shaped sorption and desorption isotherms having a first sorption zone, respectively desorption, with a water content of said carbon. active less than 5% by weight up to at least 30 or at least 40% relative humidity of the ambient air, and a second sorption zone, respectively of desorption, strong compared to the first zone, with a variation of the water content of the coal ranging from 5% or less by weight to at least 30% by weight, being within the range of 30 or 40% to 80% relative humidity of the air ambient.

9. Material according to any one of claims 1 to 8, characterized in that said activated carbon has a sorption isotherm, respectively desorption, preferably of type V, integrating a first zone located in the relative humidity range from 0 to at least 30% or at least 40% and in which the water content of said activated carbon remains less than 5% by weight, then a second zone located within the relative humidity range of 30 or 40 at 80% and in wherein the water content of said activated carbon varies between 5% or less and at least 30% by weight, preferably between 5 or less and at least 35% by weight.

10. Material according to any one of claims 1 to 9, characterized in that said material comprises from 0.5 to 10%, preferably between 0.5 and 7%, by weight of said activated carbon relative to the dry weight of plaster.