Plasterboard

Abstract

The invention relates to a plasterboard comprising a first gypsum layer and a second gypsum layer, characterized in that the first layer contains activated carbon and the second layer contains a fixing agent; the amount of fixing agent in the first layer is smaller than the amount of fixing agent in the second layer as expressed in percentage by weight of the dry matter; and the second layer does not contain any activated carbon.

Description

PLASTERBOARD The present invention relates to a plasterboard containing activated carbon and a fixing agent and to its use for reducing the content of volatile organic compounds in buildings. Plasterboard panels consist of a layer of plaster sandwiched between two facing sheets, usually made of cardboard. Industrially, the plasterboard manufacturing process comprises three main stages: mixing, setting, and drying. During the mixing stage, a continuous batch of plaster, water, and other specific ingredients is prepared in a mixer to adjust the properties of the mix and / or the final product. It is common practice to add foaming agents or foam directly to reduce the density of the plasterboard. The plaster is then continuously poured onto a first facing sheet, which is conveyed by a belt to an extruder to form the board. After the edges of the first facing sheet are folded over, a second facing sheet is fed into the extruder.The extruder applies the second facing sheet to the plasterboard mix, smooths the surfaces, and reduces the plasterboard thickness to the desired value. To improve the mechanical properties of plasterboard, it is also common practice to form a denser plaster layer on one face and possibly on the edges of the board. To achieve this, a first layer of denser plasterboard mix, called a roller coating, is poured and formed onto the first facing sheet, upstream of the main plasterboard mix, which then forms a second layer called the body of the plasterboard. Volatile organic compounds (VOCs) are carbon- and hydrogen-based chemicals present in the air in a gaseous state. European Union Directive 2010 / 75 of 24 November 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 specific conditions of use. They include chemicals of various kinds such as alkanes, alkenes such as terpenes, alkynes, alcohols, aldehydes such as formaldehyde, acetaldehyde, and pheptanal, ketones, ethers such as glycol ethers, aromatic hydrocarbons such as benzene and toluene, and halogenated hydrocarbons such as tetrachloroethylene and dichlorobenzene.VOCs are present in most paints, building materials, solvents, detergents, fuels, as well as in resins, varnishes, and glues used for furniture or electrical appliances, and 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, cause discomfort to those exposed and even affect their health. In particular, some VOCs can cause allergic reactions, respiratory problems, nausea, or headaches. In recent years, the proportion of VOCs emitted by the aforementioned materials has decreased significantly due to stricter regulations. However, alternative materials with low or no VOC emissions often come at a higher cost and with lower performance levels. Alongside efforts to control VOC emissions, various methods for reducing the amount of VOCs in ambient air have been proposed. For example, incorporating adsorbent agents, such as..., has been suggested. Activated carbon is used in building materials. Activated carbon has a broad VOC absorption spectrum. However, its adsorption capacity is not the same for all types of VOCs. Furthermore, VOCs adsorbed in activated carbon are likely to be released back into the ambient air, particularly under the influence of heat. Furthermore, the use of scavengers in plaster-based materials has also been proposed to specifically reduce the amount of certain VOCs, such as formaldehyde, in indoor air. Although these scavengers are generally specific to VOCs with a particular chemical function, or even to a single VOC, they offer the advantage of permanently fixing them. To improve indoor air quality, there is a demand for plasterboard that effectively reduces the concentration of a broad spectrum of VOCs while maintaining specific effectiveness against certain VOCs, particularly formaldehyde, without the risk of subsequent release. It was therefore considered to incorporate activated carbon and a fixing agent into a plasterboard to advantageously combine their properties. However, the Applicant has observed that, surprisingly, there is an unfavorable interaction between the activated carbon and the fixing agents, affecting their effectiveness. Thus, one object of the present invention is to provide a plasterboard that retains and combines the advantages of activated carbon and fixing agents, without significant modifications to the industrial processes for manufacturing plasterboard. Thus, one aspect of the present invention relates to a plasterboard comprising a first layer of plaster and a second layer of plaster characterized in that the first layer comprises activated carbon; the second layer comprises a fixing agent; the content of the fixing agent in the first layer, expressed as a percentage by weight of dry matter, is lower than the content of the fixing agent in the second layer; and the second layer is devoid of activated carbon. The first layer preferably comprises less than 35% by weight, or even less than 10% by weight, or even less than 5% by weight, of the fixing agent present in the entire plasterboard. Separating the activated carbon from the first layer and the fixing agent primarily from the second layer makes it possible to resolve or minimize the incompatibility problem between these two additives highlighted by the Applicant, and thus to maintain and combine the effectiveness of each of these additives with respect to their capacity to adsorb and / or fix VOCs. The term "plaster" in the context of the present invention generally refers to both set plaster, i.e., calcium sulfate dihydrate (CaSO4, 2 H2O), and unset plaster, i.e., calcium sulfate hemihydrate (CaSO4, ½ H2O). The expression "plasterboard," for example, refers to the finished product made from set plaster, but also to a plasterboard in the process of being manufactured in which the plaster has not yet fully set. In certain cases, however, the term "plaster" will be understood in its strict sense, i.e., referring to calcium sulfate hemihydrate. This is evident, for example, when the term "plaster" is used to refer to the raw material for preparing mixes. Similarly, when referring to a quantity relative to the dry weight of plaster, the latter is considered to be in its calcium sulfate hemihydrate form. Plasterboard is generally 6 to 25 mm thick, preferably 10 to 15 mm. The first layer of plaster is preferably a roller coating. The second layer of plaster forms the core of the plasterboard. For the purposes of this invention, "roller coating" refers to a thin layer of plaster, typically less than 4 mm or even 2 mm thick, with a higher density than the core layer. The density of the roller coating is typically at least 5%, and preferably up to 40%, greater than that of the core, for example, 15 to 25% greater than that of the core.The "body" of the plasterboard in the context of the present invention means a layer of plaster whose thickness is at least equal to half the thickness of the plasterboard, typically from 6 to 25 mm, preferably 10 to 15 mm, and whose density is generally from 0.4 to 1.5, preferably from 0.6 to 1. In the present invention, the density of a body is defined in the classical manner, that is to say, as the ratio of the mass density of said body to the mass density of water, taken to be 1000 kg / m³ 3 . The activated carbon according to the present invention is preferably powdered activated carbon. Indeed, for the same specific surface area, powdered carbon exhibits a higher VOC absorption efficiency than granulated activated carbon when introduced into a plasterboard panel. Thus, the activated carbon according to the invention typically has an average particle size of 1 to 100 µm, preferably 10 to 50 µm. The average particle size is measured using an air jet sieving according to ASTM D-5158-93 "Standard Test Method for Determination of the Partial Size of Powdered Activated Carbon by Air Jet Sieving". typically has a specific surface area of ​​at least 100 m² 2 / g, preferably at least 250 m 2 / g, more preferably of at least 500 m 2 / g and up to 1500 m 2 / g, or even 2000m 2 / g and even 2500 m 2 / g. The specific surface area is measured using the BET method with nitrogen according to ISO 9277:2010. The term "fixing agent" as used in the present invention defines a VOC fixing agent, i.e., a substance capable of fixing at least one VOC, in particular formaldehyde, or one type of VOC, in particular aldehydes, by hydrogen bonding, ionic bonding, or covalent bonding, preferably by covalent bonding. Examples of fixing agents as used in the present invention include, in particular, sulfites, tannins, flavonoids, amino alcohols, compounds comprising a hydrazide group, ammonium salts, ethylene urea and its derivatives, compounds comprising an active methylene, lactams, in particular caprolactam, polyamines, in particular tetraethylene pentamine, amides, in particular propionamide, zinc-based complexes, in particular the EDTA-Zn complex, and vinyl alcohol. The sulfites according to the invention include in particular ammonium disulfite, potassium bisulfite, sodium bisulfite, metasulfites of alkali metals, in particular sodium, or of alkaline earth metals. The tannins according to the present invention may be condensed or non-condensed tannins, such as tannins from acacia (catechu), mimosa, quebracho, pine, pecan, hemlock, and sumac. The tannins are preferably acacia tannins. The flavonoids according to the present invention include flavones, flavonols, dihydrofiavonols, flavanones, aurones, chalcones, dihydrochalcones, fiavanols, fiavanediols, and anthocyanidins. The flavonoids are preferably fiavanols, in particular catechin. Examples of amino alcohols according to the invention include 1 2 3 1 2 3 primary amino alcohols of formula RRR-C-NH2, in which R, R and R are independently chosen from H, hydroxyl, C1-C6 alkyl and Cl-C6 hydroxyalkyl, at least one of the R 1 , R 2 and R 3 including a hydroxyl group. Preferred amino alcohols are 2-amino-2-methyl-1,3-propanediol, 2-amino-2(hydroxymethyl)propane-1,3-diol (also called tris(hydroxymethyl)-aminomethane) and 2-amino-2-ethyl-1,3-propanediol, in particular 2-amino-2(hydroxymethyl)propane-1,3-diol. Compounds comprising a hydrazide group according to the present invention include monohydrazide compounds, such as dodecanohydrazide, salicylohydrazide, formohydrazide, acetohydrazide, propionohydrazide, p-hydroxybenzohydrazide, naphthohydrazide, and 3-hydroxy-2-naphthohydrazide; dihydrazide compounds, such as oxalodihydrazide, malonodihydrazide, succinodihydrazide, adipodihydrazide, azelodihydrazide, sebacodihydrazide, dodecanedicarbodihydrazide, maleodihydrazide, fumarodihydrazide, diglycolodihydrazide, tartarodihydrazide, malodihydrazide, isophthalodihydrazide, terephthalodihydrazide, 2,5-haphthodihydrazide, and 2,4-dihydrazino-6-methylamino-1,3,5-triazine; and compounds polyhydrazide such as polyacrylohydrazide. The compound comprising a hydrazide group is preferably Γ adipodihydrazide. Examples of ammonium salts according to the present invention include ammonium hydroxide, primary ammonium phosphates and secondary ammonium phosphates. The ethylene urea derivatives according to the invention include, in particular, N-hydroxyethylene urea, N-aminoethylethylene urea, N-[(3-allyloxy-2-hydroxypropyl)aminoethyl]ethylene urea, N-acryloyloxyethyl-ethylene urea, N-methacryloyloxyethylethylene urea, N-acryloylaminoethylethylene urea, N-methacryloylaminoethylethylene urea, N-methacryloyloxyacetoxyethylene urea, N-methacryloyloxyacetaminoethylethylene urea, and N-di(3-allyloxy-2-hydroxypropyl)aminoethylethylene urea. The ethylene urea derivative is preferably ethylene urea itself. The term "active methylene" in the context of the present invention defines a methylene, optionally substituted by a substituent, bonded to two electron-donating functional groups, in particular including a carbonyl group. Examples of compounds comprising an active methylene according to the invention are compounds of formula (1): in which Ri and R2, whether identical or different, represent a hydrogen, an alkyl group in the Ci-C2O configuration, preferably in the Ci-C6 configuration, an amino group, or (CH2) p OC F¾ O CH2 C CH3 in which p is an integer from 1 to 6 and R4 represents 0 or C=CH2 5 in which R5 is a hydrogen or a methyl; R3 represents a hydrogen, a C1-C10 alkyl, a phenyl, or a halogen; - a is equal to 0 or 1; b is equal to 0 or 1; and n is equal to 1 or 2. A preferred compound of formula (1) is acetoacetamide. In a preferred embodiment, the fixing agent is chosen from amino alcohols, compounds comprising a hydrazide group and compounds comprising an active methylene, more preferably chosen from acetoacetamide and Γ adipodihydrazide. The plasterboard according to the invention typically comprises 0.01 to 2%, preferably 0.05 to 1% by weight of activated carbon relative to the dry weight of plaster. The activated carbon is preferably contained only in the first layer of plaster. In other words, the second layer of plaster, forming the body of the plasterboard, is devoid of activated carbon, particularly powdered activated carbon. The Applicant has observed that powdered activated carbon has anti-foaming properties, which undesirably increases the density of the plasterboard when introduced into the body of the board. The first layer of plaster preferably satisfies one or more of the following conditions: a thickness of 0.1 to 4 mm, in particular 0.8 to 3 mm; a density of 0.8 to 1.5, in particular from 1 to 1.2; and The plasterboard according to the invention typically comprises 0.2 to 10% activated carbon content, in particular 1 to 5% by weight relative to the dry weight of the plaster. It typically comprises 0.01 to 2%, preferably 0.05 to 1% by weight of a fixing agent relative to the dry weight of the plaster. The fixing agent is contained in the second layer of plaster, meaning it may comprise at least 65%, or even at least 90%, or at least 95%, by weight of the amount of fixing agent contained in the plasterboard. The first layer of plaster may comprise up to 35% by weight, preferably up to 10%, or even up to 5% by weight, of the amount of fixing agent present in the plasterboard. The weight ratio between the amount of fixing agent and the amount of activated carbon in the first layer of plaster is preferably less than 1 / 10. In a preferred embodiment, the first layer of plaster is devoid of a fixing agent.The fixing agent is then contained only in the second layer of plaster. The second layer of plaster c satisfies one or more of the following conditions: a thickness of 6 to 25 mm, in particular 10 to 15 mm; a density of 0.4 to 1.5, in particular 0.6 to 1; and a fixative content of 0.01 to 2%, in particular 0.05 to 1% by weight relative to the dry weight of plaster. The plasterboard according to the invention may include processability additives for adjusting the properties of the mixes, as well as other functional agents for modifying the properties of the final plasterboard. Processability additives well known to those skilled in the art may include, in particular: Adhesion agents, setting accelerators, setting retarders, flow agents, thickening agents, or antifoaming agents are used. Functional agents also well known to those skilled in the art include foaming agents, biocides, water repellents, fire retardants, or reinforcing agents. If necessary, additional functional agents can be introduced into the first and / or second coat. Another aspect of the present invention relates to a method for manufacturing a plasterboard as defined above, comprising a forming step, a setting step and a drying step, characterized in that the forming step comprises: - the supply of a first facing sheet; the pouring of a first batch onto the first facing sheet; the pouring of a second batch on top of the first batch; the supply of a second facing sheet on the second batch; and the forming of the plasterboard using an extruder; in which the first batch comprises activated carbon; the second batch comprises a fixing agent; the content of fixing agent in the first batch, expressed as a percentage by weight of dry matter, is less than the content of fixing agent in the second batch; and the second batch is devoid of activated carbon. The first batch preferably comprises less than 35% by weight, or even less than 10% by weight, or even less than 5% by weight, of the quantity of fixing agent contained in all batches combined. In a particular embodiment, the first batch is devoid of fixing agent. After setting and drying, the first and second batches form respectively the first layer of plaster and the second layer of plaster, such as defined above. The first batch therefore forms a roller coating layer, while the second batch preferably forms the body of the plate. The batch intended to form the body of the plate is referred to hereafter as the "main batch". Fig. 1 schematically illustrates an example of an industrial plasterboard manufacturing line with a roller coating. A first facing sheet 1, generally forming the front face of the plasterboard (the visible face during board installation), is conveyed by a conveyor belt. A first batch of plaster is continuously poured from a secondary mixer 2 onto the first facing sheet 1 and formed into a homogeneous first layer by a set of rollers 3. This first layer will form the roller coating. At a predetermined distance allowing sufficient curing of the first layer, the main batch is poured from a main mixer 4 onto the first layer. A second facing sheet 5 is fed over the main batch at the main extruder 6.A strip of plaster is extruded to the required thickness by the main extruder 6, which distributes the main mix to form the layer that will constitute the body of the plasterboard. After the plaster strip has been transported for a suitable time to allow sufficient setting of the plaster, it is cut to the desired size by a rotating knife 7. The plasterboard is then usually turned over to avoid damaging the front face and transported to a series of decked dryers 8 to complete the setting of the plaster and remove excess water before being packaged and sent to the storage area 9. The main batch typically comprises, for 100 parts by weight of plaster: 40 to 200 parts water; 2 to 10 parts foam obtained from a mixture of water and a foaming agent, for example an alkyl sulfate possibly mixed with an alkyl ether sulfate; and 0.1 to 1 part of setting accelerator, for example hydrated calcium sulfate or potassium sulfate. It may also include one or more of the following components: 0.1 to 15 parts of an adhesion agent, for example a poly(vinyl acetate), a poly(vinyl alcohol), a starch, in particular pre-treated with an acid or pre-gelatinized, a dextrin or a vegetable flour, in particular wheat or corn; 0.001 to 10 parts of a biocide, for example carbamates, such as 3-iodoprop-2-yn-l-yl butylcarbamate, or pyrothione complexes; 0.1 to 10 parts of at least one water-repellent agent, for example a siloxane, a polysiloxane or a wax; - 0.1 to 20 parts of at least one fire-retardant agent, for example vermiculite, silica, particularly in micrometric sizes, or clay; and / or 0.1 to 20 parts of at least one reinforcing agent, for example polymer fibers, mineral fibers, especially glass, or plant fibers. The first batch intended for the roller coating layer can be prepared independently or, as illustrated in Figure 1, it can be obtained from the main batch. In the latter case, a pipe carries a portion of the main batch from the main mixer 4 to the secondary mixer 2. It is then necessary to add an antifoaming agent and possibly a plasticizer to break down the foam present in the main batch and obtain a roller coating layer with the desired density. Powdered activated carbon is used for A key feature is its anti-foaming properties. Adding powdered activated carbon to the roller coating layer has the advantage of requiring less, or even no, additional anti-foaming agent when the roller coating mix is ​​prepared from the main mix. Alternatively, the main mix can be obtained from the secondary mix. In this case, the secondary mix is ​​prepared in the secondary mixer, and a line carries a portion of the secondary mix from the secondary mixer to the main mixer. The secondary mix, like the main mix, can include additives as mentioned above. These additives are generally added to the secondary mix in proportions equivalent to those used for the main mix.Certain additions can also be made at the main mixer to adjust the properties of the main batch. In particular, a first foam can be introduced into the secondary batch at the secondary mixer, while a second foam can be introduced into the main batch at the main mixer. These first and second foams can be identical or different (particularly in terms of density and / or bubble size) and are generally introduced in different quantities in their respective batches. When the first batch is obtained from the second batch, it necessarily contains a certain amount of fixing agent. This amount is preferably less than 35% by weight, or even less than 10% by weight, or even less than 5% by weight of the amount of fixing agent present in all the batches combined. The weight ratio between the amount of fixing agent and the amount of activated carbon in the first batch is then preferably less than 1 / 10. However, it is preferable that the first batch not be prepared from the second batch. so that the first batch, and consequently the first layer of plaster obtained from it, is free of fixing agent. Activated carbon, particularly in powder form, is preferably added to the secondary mixer as an aqueous suspension containing a fluidizing agent. The Applicant has observed that premixing the powdered activated carbon with the fluidizing agent produces a sufficiently stable suspension, allowing for proper dosing of the activated carbon, especially in continuous industrial processes, and a more homogeneous distribution of the activated carbon in the resulting mix, and consequently in the manufactured plasterboard. The premix typically comprises 1 to 25%, preferably 5 to 15% by weight of powdered activated carbon. It typically comprises at least 0.01%, preferably 0.05 to 5%, and more preferably 0.1 to 3% by weight of fluidizing agent.The plasticizer can be chosen from among the polycarboxylates, including polycarboxylate ethers, sulfonated polynaphthalenes (salts of sulfonated polycondensates of naphthalene and formaldehyde), lignosulfonates, sulfonated melamine resins (salts of sulfonated polycondensates of melamine and formaldehyde), and polyacrylates commonly used in the manufacture of plasterboard. Examples of plasticizers include those marketed under the name GLENIUM® by BASF, FLUBE® by Bozzetto, CHRYSOFLUID® by Chryso, VISCOCRETE® by Sika, MELMENT® by BASF, and MAPEFLUID® by Mapei. The fluidizing agent is preferably chosen from sulfonated polynaphthalenes and sulfonated melamine-formaldehyde resins, more preferably from sulfonated polynaphthalenes. The present invention also relates to the use of a plasterboard as described above to reduce the amount of VOCs in the air inside buildings. The VOCs are preferably selected from formaldehyde, hexanal, benzene, toluene, tetrachloroethene, 1,2-dichlorobenzene, and undecane. The invention is illustrated by the following non-limiting examples. EXAMPLE Reference plates RI to R3 and according to invention II were manufactured from different primary mixes, intended for forming the body of the plates, and secondary mixes, intended for forming the roller coating layers. Each primary mix has the following basic composition: 100 parts by weight of plaster (CaSO4, ½ H2O), 75 parts of water, 3 parts of foam (obtained from water containing 1% by weight of sodium lauryl sulfate), 5 parts of starch, 3 parts of plasticizer, and 0.5 parts of setting accelerator. Each secondary mix has the following basic composition: 100 parts by weight of plaster (CaSO4, ½ H2O), 77 parts of water, 5 parts of starch, 3.2 parts of plasticizer, and 0.5 parts of setting accelerator. The RI and R3 plates without a roller coating were prepared as follows. The various ingredients were weighed and mixed using a mixer and a deflocculating blade at 1600 rpm for one minute to obtain a homogeneous paste. The foam was prepared to the desired density and mixed into the paste in a mixer with a blade at 250 rpm to obtain a main batch. A first sheet of cardboard was placed in a 20 x 25 cm mold with a thickness of 12.5 mm. The main batch was poured onto the first cardboard sheet and leveled to the thickness of the mold. A second sheet of cardboard was placed on top of the batch. The main mold is closed to maintain pressure on the plate. After the plate has hardened, it is removed from the mold and dried in an oven for 24 hours at 40°C. For R2, R4, and PI plates with a roller coating, the ingredients for the secondary mix are weighed and mixed using a mixer and a deflocculating paddle at 1600 rpm for one minute. A first sheet of cardboard is placed in a 20 x 25 cm mold, 12.5 mm thick. The secondary mix is ​​poured onto the first cardboard layer and leveled to a thickness of approximately 1 mm. The main mix is ​​prepared as for RI and R3 plates and poured onto the secondary mix once it has set sufficiently, leveled to the thickness of the mold. A second sheet of cardboard is placed on top of the main mix, and the mold is closed to maintain pressure on the plate. After the plate has hardened, it is removed from the mold and dried in an oven for 24 hours at 40°C. Tables 1 and 2 indicate the additives, activated carbon (AC) or acetoacetamide (AA), added, where applicable, to the batches before plate manufacturing. The value in parentheses indicates the dry weight percentage of the additive in the layer in question. The symbol "-" indicates that no additive is added to the corresponding batch. The symbol "x" indicates that the plate does not include the corresponding layer. The activated carbon used is a powdered activated carbon marketed under the reference Pulsorb® 208CP and having a specific surface area of ​​1200 m². 2 / g and an average particle size of about 30 μιη. For each plate, the body has a thickness of 11.5 mm, except for the P4 plates which have a thickness of 12.5 mm, and the roller coating layers each have a thickness of 1 mm. The VOC-trapping capacity of each plate was evaluated in terms of absorption and desorption according to ISO 1600-24:2009 and ISO 1600-23:2009 standards at a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5% during the test. The plate load factor was set at 1 and the air exchange rate at 0.5 vol / h "1 Two independent sets of measurements were performed to evaluate their ability to trap toluene and formaldehyde, respectively. For each set of measurements, the plates were subjected to an absorption phase (14 days for toluene; 7 days for formaldehyde) during which the air was renewed with an airflow containing a VOC (at a concentration of 40 μg / m³). "3 for toluene; 100 μg.m "3for formaldehyde) to measure the absorption rate for the VOC in question, then to a desorption phase (7 days for toluene; 7 days for formaldehyde) during which the air is renewed with a flow of fresh air (without VOCs) to measure the desorption rate for the VOC in question. Table 1 shows the percentage reduction (absorption) of formaldehyde and toluene content and the percentage desorption of formaldehyde and toluene for each of the plates. Table 1 nm: not measured Plate R3, which includes a fixing agent, exhibits good formaldehyde absorption but does not sufficiently reduce the content of other VOCs, particularly toluene. Plate R2, which includes activated carbon, provides adequate removal of a broad spectrum of VOCs, including formaldehyde, but the latter is not permanently fixed, as evidenced by its high desorption rate. Plate R4, which combines a fixing agent and activated carbon, is not very effective against toluene. In contrast, plate PI according to the invention provides both significant removal and permanent fixation of both formaldehyde and toluene.

Claims

Page 1 of 2 pages of Claims 1. Plasterboard consisting of a first-layer plaster and a second-layer plaster characterized in that the first-layer contains activated carbon; the second-layer contains a rejection agent; the amount of rejection agent in the first-layer, expressed as a percentage by weight of dry matter, is less than the amount of rejection agent in the second-layer; and the second-layer is carbon-free.

2. Plasterboard as requested in this claim.

1. Plasterboard as claimed in claim 1, which is characterized by a first-layer thickness of 0.1 to 4 mm.

3. Plasterboard as claimed in any one of claim 1 and 2, which is characterized by a first-layer density of 0.8 to 1.

5.

4. Plasterboard as claimed in any one of claim 1 to 3, which is characterized by a first-layer being agent-free for disposal.

5. Plasterboard as claimed in claim 1 to 4, which is characterized by a second-layer thickness of 6 to 25 mm. 6.

7. Plasterboard as claimed under claims 1 to 5, which is characterized by a secondary layer having a density of 0.4 to 1.

57.

8. Plasterboard as claimed under claims 1 to 6, which is characterized by a primary layer having a density greater than the density of the secondary layer.

9. Plasterboard as claimed under claims 1 to 7, which is characterized by the activated carbon being in powder form.

10. Plasterboard as claimed under claims 1 to 8, which is characterized by the activated carbon having an average particle size of 1 to 100 micrometers.

11. Plasterboard as claimed under claims 1 to 9, which is characterized by the presence of 0.01 to 2 percent by weight of activated carbon relative to the dry weight of the plaster.Plasterboard as claimed under claims 1 to 10, any one of which is characterized that the displacement agent is selected from a compound containing a hydrazide group, a compound containing active methylene, and a mixture of these; page 2 of 2, page 12. Plasterboard as claimed under claims 1 to 11, any one of which is characterized that such plasterboard contains 0.01 to 2 percent by weight of the displacement agent relative to the dry weight of the plaster.13.The process for the production of plasterboard as claimed in claims 1 through 12, any one of which includes a forming phase, a hardening phase, and a drying phase, is characterized in that the forming phase includes: - placement of the first facing; - pouring of the first composite group over the first facing; - pouring of the second composite group over the first composite group; - placement of the second facing over the second composite group; and - extrusion plaster forming, in which the first composite group contains activated carbon; the second composite group contains the rejection agent; the amount of the rejection agent in the second composite group, stated as a percentage by weight of the dry matter, is less than that of the rejection agent in the second composite group; and the second composite group is carbon-free.

14. The process as claimed in claim 13 is characterized in that the first composite group is agent-free.15.The use of plasterboard under any of the claimed rights 1 to 12 for the purpose of reducing the amount of volatile organic compounds in air-conditioned buildings;