Functionalized starch for plasterboard

Abstract

The present invention relates to a method for the manufacture of a plasterboard using a functionalized starch as adhesive and / or fluidizer, a plasterboard obtainable by such method, and a composition which may be used in such method.

Description

[0001] FUNCTIONALIZED STARCH FOR PLASTERBOARD

[0002] The present invention relates to a method for the manufacture of a plasterboard using a functionalized starch as adhesive and / or fluidizer, a plasterboard obtainable by such method, and a composition which may be used in such method.

[0003] Plasterboards are panels comprising a layer of gypsum between two facing sheets generally made of a paper liner. Industrially, the process for the manufacture of plasterboards comprises three main stages: the forming, the setting and the drying. During the stage of forming the plasterboard, a slurry is continuously prepared in a mixer starting from stucco, water and other specific ingredients in order to adjust the properties of the composition and / or of the final product. The composition is subsequently poured continuously over a first sheet entrained by a conveyor belt, generally toward an extruder, in order to form the board. After the edges of the first sheet have been folded over, a second facing sheet is introduced, generally at the extruder. When used, the extruder flattens the second sheet over the composition, smooths the surfaces and reduces the thickness of the plasterboard to the desired value.

[0004] One feature that has been the subject of numerous studies is the adhesion of the sheet , which is usually a paper sheet, onto the gypsum core of the board. In orderto improve the adhesion, starch is generally added to the slurry and during drying of the board the starch migrates towards the paper and concentrates at the core / facing interface. This is obtained by selecting a starch that has a particular rheology as a function of the temperature.

[0005] EP0172773 describes the use of natural or modified starches for manufacturing boards with a paper facing, having an improved core / pa per adhesion. EP0936201 describes the use of starch mixtures that are modified with respect to the long-term strength of mixtures of cement-type material, including plaster. The objective in this document is to control the setting and the slump value of the mixed slurry without there being any effect on the long-term strengths. US2004 / 045481 describes a slurry for a lightweight board comprising hemihydrate, starch, foam and water, and in which the starch represents from 1.5 to 3% by weight relative to the weight of the hemihydrate. The resulting boards have a reduced density. US2003 / 084980 describes a slurry for a lightweight board comprising hemihydrate, acid- hydrolyzed starch, a starch crosslinking agent and water. The starch used has a lower gelatinization temperature, facilitates its migration towards the core / facing interface, while the crosslinking makes it possible to prevent the starch from completely migrating out of the core.

[0006] US2005 / 126437 describes the use, for increasing the strength, of a modified starch that is insoluble in the slurry during mixing, but which is dissolved when the temperature increases. The starch is modified, for example, by hydroxyalkylation or acetylation.

[0007] In order to increase the fluidity of the slurry, it is necessary to add fluidizers. US 2011 / 195241 and EP3393997 describe gypsum panels comprising starch, and a fluidizer which may be a naphthalene sulfonate, a phosphate polycondensate or a polycarboxylate.

[0008] In order to limit the number of additives in slurries and thus simplify the method for manufacturing plasterboards, it would be advantageous to have a compound which can act as both an adhesive and fluidizer.

[0009] The inventors have now discovered a compound which satisfies this need. Specifically, such compound is a particular starch, which is functionalized by an esterification with a dicarboxylic acid (or a derivative thereof) substituted by a long aliphatic chain. The inventors have demonstrated that a low concentration of such compound in slurries for preparing plasterboards allowed to obtain both a good adhesion and a fluidizing effect. Such technical effect is very surprising for this kind of ester-functionalized starch, which is commonly used in the food and pharmaceutical fields, but not in the construction field.

[0010] Thus, the present invention relates to a method for the manufacture of a plasterboard, comprising:

[0011] - providing a composition comprising water, stucco, and a starch functionalized with groups of formula (I):

[0012] - - -C(O)-R-C(O)O- M+(I), in which:

[0013] R is a C1-C12 aliphatic divalent chain substituted by a C4-C22 aliphatic chain, and M+is a cation,

[0014] - casting the composition on a first band, so as to form a wet gypsum layer on said first band,

[0015] - providing a second band on said wet gypsum layer, and

[0016] - forming the plasterboard, preferably using an extruder.

[0017] In some embodiments, R is a C2 or C3 alkylene chain, substituted by a C6-C12 alkenyl chain, preferably R is a C2 alkylene chain substituted by a C8 alkenyl chain.

[0018] In some embodiments, the starch is a pregelatinized or uncooked starch, more particularly an uncooked acid-hydrolyzed starch, an uncooked oxidized starch, a pregelatinized acid- hydrolyzed starch, or a pregelatinized oxidized starch.

[0019] In some embodiments, the starch is an uncooked starch, for instance an uncooked acid- hydrolyzed starch or an uncooked oxidized starch.

[0020] In some embodiments, the content of fluidizer other than said starch functionalized with groups of formula (I) is less than 0.1 wt%, preferably less than 0.05 wt%, more preferably less than 0.04 wt%, even more preferably less than 0.03 wt%, relative to the dry weight of stucco. In some embodiments, the composition does not comprise a fluidizer other than said starch functionalized with groups of formula (I).

[0021] In some embodiments, the content of stucco is at least 60 wt%, relative to the total solids content of the composition.

[0022] In some embodiments, the content of said starch functionalized with groups of formula (I) is at least 0.1 wt%, preferably at least 0.5 wt%, relative to the dry weight of stucco, and at most 10 wt%, preferably at most 7 wt%, for example at most 5 wt%, relative to the dry weight of stucco.

[0023] In some embodiments, the weight ratio of water to stucco in the composition is:

[0024] - at least 0.19 and

[0025] - at most 0.85, preferably at most 0.80, more preferably at most 0.65, even more preferably at most 0.55.

[0026] In some embodiments, the composition further comprises at least one reinforcing agent, for example glass fibers or polyvinyl acetate.

[0027] In some embodiments, the composition further comprises additives, preferably selected from setting accelerators, setting retarders, anti-burning agents, anti-sag agents, fire-resistant agents, anti-shrinkage agents, biocidal agents, and water repellents. In some embodiments, the first and second bands are paper or cardboard bands.

[0028] In some embodiments, the method further comprises a setting step and a drying step.

[0029] The present invention also relates to a plasterboard obtainable by the method as defined herein.

[0030] Another object of the present invention is a composition comprising :

[0031] - stucco,

[0032] - starch functionalized with groups of formula (I):

[0033] - - -C(O)-R-C(O)O- M+(I), in which:

[0034] R is a C1-C12 aliphatic divalent chain substituted by a C4-C22 aliphatic chain (preferably: R is a C2 or C3 alkylene chain, substituted by a C6-C12 alkenyl chain, more preferably R is a C2 alkylene chain substituted by a C8 alkenyl chain), and

[0035] M+is a cation, and

[0036] - water.

[0037] In some embodiments, said composition comprises one or more of the following features:

[0038] - the content of stucco is at least 60 wt%, relative to the total solids content of the composition, and / or

[0039] - the content of said starch functionalized with groups of formula (I) is at least 0.1 wt%, preferably at least 0.5 wt%, relative to the dry weight of stucco, and at most 10 wt%, preferably at most 7 wt%, for example at most 5 wt%, relative to the dry weight of stucco, and / or

[0040] - the weight ratio of water to stucco in the composition is at least 0.19 and at most 0.80, preferably at most 0.65, more preferably at most 0.55.

[0041] DETAILED DESCRIPTION

[0042] The present invention is based on the use of a particular starch in a composition (or "slurry") for manufacturing a plasterboard. More specifically, the present invention provides a composition which comprises water, stucco, and a starch functionalized with groups of formula (I): - - -C(O)-R-C(O)O- M+(I), in which

[0043] R is a C1-C12 aliphatic divalent chain substituted by a C4-C22 aliphatic chain, M+is a cation.

[0044] As used herein, the term "gypsum" encompasses:

[0045] - calcium sulphate dihydrate (CaSC , 2H2O), which corresponds to a set gypsum,

[0046] - calcium sulphate hemihydrate (CaSC ,1 / z H2O), which corresponds to a non-set gypsum (also called "gypsum hemihydrate" or "plaster"), and / or

[0047] - a mixture thereof, which in particular corresponds to a gypsum which is not completely set. As used herein, the term "stucco" refers to any natural or synthetic stucco, which consists of

[0048] - or essentially consists of - calcium sulphate hemihydrate (CaSC ,1 / z H2O).

[0049] The expression "plasterboard" (or equivalently: "gypsum-based panel" or "gypsum board" or "drywall") denotes for example the finished product formed by set gypsum but also a plasterboard in the course of manufacture in which the gypsum is not completely set.

[0050] Advantageously, the content of stucco in the composition is at least 60 wt% (for instance at least 65 wt%, at least 70 wt%, at least 75 wt% or at least 80 wt%), relative to the total solids content of the composition.

[0051] In some embodiments, the weight ratio of water to stucco in the composition is at least 0.19, for instance at least 0.25, at least 0.3, at least 0.4, or at least 0.5.

[0052] In some embodiments, the weight ratio of water to stucco in the composition is at most 0.85, preferably at most 0.80, for instance at most 0.65, or at most 0.55.

[0053] In a particular embodiment, the weight ratio of water to stucco in the composition is from 0.5 to 0.8.

[0054] The composition comprises a starch functionalized with groups of formula (I) as defined herein (hereinafter, the "functionalized starch"). Such functionalization can be performed by an esterification reaction between the hydroxy group of a starch and a diacid compound of formula (II): HO(O)C-R-C(O)OH, in which R is as defined in formula (I), or any ester, anhydride, or salt of such diacid. This type of starch functionalization is well-known to the skilled artisan and is in particular described in Ackar et al. Molecules 2015, 20, 10, 19554-19570. The functionalized starch of the composition may be obtained from a starch of any source, such as corn (e.g. waxy corn, dent corn), potato, sorghum, arrowroot, wheat, tapioca, or rice, in particular corn (e.g. waxy corn) or tapioca.

[0055] In some embodiments, the functionalized starch of the composition is a native starch functionalized with groups of formula (I) as defined herein.

[0056] In some embodiments, the functionalized starch of the composition is an uncooked (or equivalently "non-pregelatinized") or pregelatinized starch functionalized with groups of formula (I) as defined herein. Preferably, the functionalized starch of the composition is an uncooked (or equivalently "non-pregelatinized") starch functionalized with groups of formula (I) as defined herein.

[0057] In some embodiments, the functionalized starch of the composition is a modified starch functionalized with groups of formula (I) as defined herein. A "modified starch" refers to a starch which has been subjected to at least one modification reaction (which is different from the functionalization reaction), such as acid-hydrolysis, oxidization, or pregelatinization. A modified starch may in particular be an uncooked acid-hydrolyzed starch, an uncooked oxidized starch, a pregelatinized acid-hydrolyzed starch, or a pregelatinized oxidized starch. The modification reaction(s) can be performed before or after the functionalization.

[0058] The functionalized starch of the composition may have a weight average molecular weight comprised between 104and 109g / mol, preferably 105and 107g / mol, more preferably 105and 106g / mol. The weight average molecular weight may be determined by asymmetric flow field fractionation (AF4), multi-angle light scattering and / or refractive index detection.

[0059] The functionalized starch of the composition has advantageously a gelatinization temperature (Tgel) of at most 45 °C, preferably at most 40°C, more preferably at most 35°C, for instance between 15°C and 45°C. The gelatinization temperature can be determined by viscosimetry, in particular by a Rapid ViscoAmylograph. A typical viscosimetry method for determining the gelatinization temperature has the following features:

[0060] - Temperature profile: (i) maintaining 5 minutes at 35°C, (ii) 10 minutes ramp between 35°C and 90°C, (iii) 10 minutes at 90°C, (iv) 5 minutes cooling between 90°C and 35°C;

[0061] - Functionalized starch concentration: 14% wt. dry weight on water. The gelatinization temperature is herein defined as the temperature at which the viscosity change in time reaches 4 cP / s.

[0062] Preferably, the solubility of the functionalized starch in distilled water at 25°C is higher than or equal to 90%, more preferably higher than or equal to 95%, even more preferably higher than or equal to 98%, more particularly higher than or equal to 99%.

[0063] The functionalized starch comprises non-functionalized hydroxy groups (i.e. -OH groups) and hydroxy groups functionalized with a group of formula (I).

[0064] The content of hydroxy groups functionalized with a group of formula (I) may be:

[0065] - at least 0.01%, for instance at least 0.05%, at least 0.1%, at least 0.5%, at least 1%, at least 2%, at least 5%, at least 10% or at least 20%, and

[0066] - preferably at most 70%, for instance at most 60%, at most 50%, at most 40%, at most 30%, at most 20%, or at most 10%, such content being defined as: (number of hydroxy groups functionalized with a group of formula (I)) / (number of non-functionalized hydroxy groups + number of hydroxy groups functionalized with a group of formula (I)).

[0067] Advantageously, the amount of groups of formula (I) in the functionalized starch is such that:

[0068] - the solubility of the functionalized starch in distilled water at 25°C is higher than or equal to 90%, more preferably higher than or equal to 95%, even more preferably higher than or equal to 98%, more particularly higher than or equal to 99% ; and

[0069] - the slump of the composition of the invention with respect to the slump of a similar composition having no starch is higher by at least 5%, preferably by at least 10%, more preferably by at least 15%.

[0070] The slump can be determined by the following method: the ingredients (e.g. stucco, water, additives...) of the composition are mixed and vigorously stirred in a blender (for instance, Blender LB20E* from Waring, 20 seconds at speed 12) to form a slurry and the resulting slurry is then immediately poured into a slump ring. The slump ring is quickly lifted, and the liquid slurry forms a patty. The diameter of the patty is measured by means of a ruler.

[0071] In formula (I), R is a C1-C12 aliphatic divalent chain substituted by a C4-C22 aliphatic chain. As used herein, the term "aliphatic [divalent] chain" means a linear or branched (preferably linear), saturated or unsaturated hydrocarbon [divalent] chain.

[0072] In a particular embodiment, the aliphatic chain is an alkyl or alkenyl chain.

[0073] In a particular embodiment, the aliphatic divalent chain is an alkylene or alkenylene chain.

[0074] As used herein, the term "alkyl" means a linear or branched (preferably linear), saturated hydrocarbon chain.

[0075] As used herein, the term "alkylene" means a linear or branched (preferably linear), saturated hydrocarbon divalent chain.

[0076] As used herein, the term "alkenyl" means a linear or branched (preferably linear), unsaturated hydrocarbon chain having at least one carbon-carbon double bond.

[0077] As used herein, the term "alkenylene" means a linear or branched (preferably linear), unsaturated hydrocarbon divalent chain, having at least one carbon-carbon double bond.

[0078] In a particular embodiment, R is a C1-C6 aliphatic divalent chain (preferably a C1-C6 alkylene, more preferably, a C2 or C3 alkylene chain) substituted by a C4-C22 aliphatic chain.

[0079] In a more particular embodiment, R is a C1-C6 aliphatic divalent chain (preferably a C1-C6 alkylene, more preferably, a C2 or C3 alkylene chain) substituted by a C6-C12 aliphatic chain.

[0080] In an even more particular embodiment, R is a C1-C6 aliphatic divalent chain (preferably a Cl- C6 alkylene, more preferably, a C2 or C3 alkylene chain) substituted by a C6-C12 alkenyl.

[0081] Preferably, R is a C2 or C3 alkylene chain, substituted by a C6-C12 alkenyl chain.

[0082] More preferably, R is a C2 alkylene chain substituted by a C8 alkenyl chain.

[0083] M+is a cation. M+ may in particular be any cation resulting from the neutralization of -COOH group by a base. In a preferred embodiment, M+is an alkaline cation, such as a lithium, sodium, or potassium cation. Preferably, M+is a sodium cation.

[0084] In formula (I), the symbol " — " represents the bond by which the group of formula (I) is attached to the remaining of the molecule, more specifically to an oxygen deriving from a hydroxy group of the starch, forming thereby an ester bond.

[0085] In a preferred embodiment, the group of formula (I) is represented as follows:

[0086] In some embodiments, the content of said starch functionalized with groups of formula (I) is at least 0.1 wt%, preferably at least 0.5 wt%, more preferably at least 1 wt%, relative to the dry weight of stucco.

[0087] In some embodiments, the content of said starch functionalized with groups of formula (I) is at most 10 wt%, preferably at most 7 wt%, for example at most 5 wt%, relative to the dry weight of stucco.

[0088] In a particular embodiment, the content of said starch functionalized with groups of formula (I) is from 0.5 wt% to 7 wt%, preferably from 1 wt% to 5 wt%, relative to the dry weight of stucco.

[0089] The composition described herein may comprise further ingredients, in particular to tune the physico-chemical properties of such composition.

[0090] In some embodiments, the composition further comprises one or more fluidizing agents, other than the starch functionalized with groups of formula (I). Fluidizing agents are also known as "fluidizers", "dispersants", "plasticizers" or "water reducing agents".

[0091] Such fluidizing agents may be chosen in particular from polycarboxylates, in particular polyetherpolycarboxylates, sulphonated polynaphthalenes (e.g. salts of sulphonated polycondensates of naphthalene and formaldehyde), lignosulphonates, sulphonated melamine resins (salts of sulphonated polycondensates of melamine and formaldehyde) and the polyacrylates commonly used in the manufacture of plasterboards.

[0092] As examples of fluidizing agents, mention may be made of those sold under the name GLENIUM® by BASF, under the name FLUBE® by Bozzoto, under the name CHRYSOFLUID® by Chryso, under the name VISCOCRETE® by Sika, under the name M ELM ENT® by BASF or else under the name MAPEFLUID® by Mapei. The fluidizing agent may more particularly chosen from sulphonated polynaphthalenes and sulphonated melamine-formaldehyde resins, more preferably from sulphonated polynaphthalenes. Other examples of fluidizers are polymers selected from the list consisting of a polycarboxylate ether (PCE) such as polyoxyalkylene polycarboxylates; and a polyphosphonate polyoxyalkylene. Salts of such polymers may be used, such as sodium salts. In a particular embodiment, the fluidizers are or comprise members of the list consisting of a polycarboxylate polyethylene glycol), and polyphosphonate polyethylene glycol).

[0093] The content of such fluidizing agents (other than the starch functionalized with groups of formula (I)) may be comprised between 0.05 and 1.2 wt%, preferably between 0.1 and 0.8 wt%, relative to the dry weight of stucco.

[0094] Preferably, the content of fluidizer(s) other than said starch functionalized with groups of formula (I) is less than 0.1 wt%, preferably less than 0.05 wt%, more preferably less than 0.04 wt%, even more preferably less than 0.03 wt%, relative to the dry weight of stucco.

[0095] More preferably, the composition is deprived of fluidizing agents other than the starch functionalized with groups of formula (I).

[0096] In some embodiments, the composition further comprises one or more adhesion agents (or equivalently "adhesive"), other than the starch functionalized with groups of formula (I).

[0097] Such adhesion agents may be chosen in particular from starches (different from the starch functionalized with groups of formula (I)) in particular acid-hydrolyzed or pre-gelatinized starches, polyvinyl acetate, polyvinyl alcohol, dextrins, a flour in particular corn or wheat or sorghum flour.

[0098] The content of adhesion agents other than the starch functionalized with groups of formula (I) may for instance be comprised between 0.1 and 8 wt%, such as between 0.5 and 6 wt%, or even between 1 and 5 wt%, relative to the dry weight of stucco.

[0099] Preferably, the content of adhesion agents other than said starch functionalized with groups of formula (I) is less than 2 wt%, more preferably less than 1 wt%, even more preferably less than 0.5 wt%, for instance less than 0.2 wt%, relative to the dry weight of stucco. More preferably, the composition is deprived of adhesion agents other than the starch functionalized with groups of formula (I).

[0100] In some embodiments, the composition further comprises additives (other than those previously mentioned). Such additives may be used to adjust the properties of the composition or the properties of the plasterboard. In particular, such additives may be selected from setting accelerators, setting retarders, anti-burning agents, foaming agents, anti-sag agents, fire-resistant agents, anti-shrinkage agents, biocidal agents and water repellents.

[0101] Examples of setting accelerators include in particular heat resistant accelerator, such as ground gypsum encapsuled within dextrose monohydrate.

[0102] Examples of setting retarders include in particular natural proteins.

[0103] An example of anti-burning agents includes in particular dextrose monohydrate.

[0104] Examples of anti-sag agents include in particular sodium trimetaphosphate or tartaric acid.

[0105] Examples of fire-resistant agents include in particular vermiculite, clay, glass fibers or mineral wool (e.g. glass wool).

[0106] Examples of anti-shrinkage agents include in particular vermiculite, clay, or microsilica.

[0107] Examples of biocidal agents include in particular carbamates, such as 3-iodoprop-2-yn-l-yl butylcarbamate, or pyrothione complexes.

[0108] Examples of water-repellents include, in particular, a siloxane, a polysiloxane, or a wax.

[0109] The content of said other additives may be comprised between 0.2 wt% and 10 wt%, preferably between 1 wt% and 3 wt%, relative to the dry weight of stucco.

[0110] In some embodiments, the composition further comprises at least one reinforcing agent. The reinforcing agent may be based on a polymer material (in particular organic polymer material) or based on a mineral material (in particular mineral fibers). When the reinforcing agent is an organic polymer material, it may be added to the composition in the form of an emulsion. For example, the reinforcing agent may be glass fibers or polyvinyl acetate.

[0111] The reinforcing agent(s), when present in the composition, represents preferably at least 1 wt% (or even at least 2 wt%), relative to the dry weight of stucco. The density of the composition is typically from 0.6 to 2.5, for instance:

[0112] - from 1.0 to 2.3, more particularly from 1.3 to 2.0, or

[0113] - from 0.6 to 1.5, more particularly from 0.8 to 1.3.

[0114] The composition described herein is particularly suitable for being used as mixed batch in a method for manufacturing a plasterboard (or equivalently: "gypsum-based panel" or "gypsum board").

[0115] Hence, an object of the present invention is a method for the manufacture of a plasterboard, comprising :

[0116] - providing a composition as defined herein,

[0117] - casting the composition on a first band, so as to form a wet gypsum layer on said first band,

[0118] - providing a second band on said wet gypsum layer, and

[0119] - forming the plasterboard, preferably by using an extruder.

[0120] The first and second bands may equivalently be called first and second facing sheets, respectively. The first and second bands are usually paper or cardboard bands, preferably paper bands.

[0121] The method of the invention typically further comprises a setting step and a drying step. A dry gypsum layer, defined as a gypsum layer wherein gypsum consists of dry set gypsum, is obtained after such steps. During the setting step, calcium sulphate hemihydrate and water contained in the composition react with each other to form calcium sulphate dihydrate. Such reaction is a hydration reaction. The setting step is also called "hardening step". The setting step usually takes place as soon as the composition is formed and cast (or equivalently "poured") on the first band. Typically, in the "wet gypsum layer", the gypsum is not completely set (i.e. the wet gypsum layer comprises a mixture of calcium sulphate dihydrate and calcium sulphate hemihydrate and water).

[0122] The setting step is usually completed before the drying step.

[0123] The setting step is advantageously carried out in the absence of external heating. Typically, such step is carried out at room temperature. Room temperature typically refers to a temperature comprised between 15°C and 40°C. Since the reaction between calcium sulphate hemihydrate and water is exothermic, the temperature of the wet gypsum layer during setting is usually 35°C ± 3°C.

[0124] During the drying step, the water in excess (or "unreacted water") is removed. The drying step is advantageously carried out at a temperature comprised between 85°C and 97°C, more particularly between 90 and 95 °C.

[0125] Preferably, the method of the invention is carried out under continuous conditions. Under such continuous conditions, the method of the invention typically comprises the following steps:

[0126] - continuously preparing a composition as defined herein in a mixer;

[0127] - continuously pouring the composition from the mixer over a first band (or "first facing sheet") so as to form a wet gypsum layer on said first band, wherein the first band is entrained by a conveyor belt, typically toward an extruder,

[0128] - providing a second band (or "second facing sheet") on the wet gypsum layer, typically at the extruder, and

[0129] - forming the plasterboard.

[0130] When used, the extruder allows to flatten the second band over the composition, to smooth the surfaces and reduces the thickness of the plasterboard to the desired value.

[0131] In the continuous conditions, the method typically further comprises a setting and drying step as defined above.

[0132] The present invention also relates to a plasterboard comprising a gypsum core (more particularly, a dry gypsum layer comprising set gypsum) which is based on the composition as defined herein, said gypsum layer (or gypsum core) being between a first band and a second band.

[0133] Said gypsum core based on the composition as defined herein typically comprises :

[0134] - set gypsum (more particularly dry set gypsum), and

[0135] - a starch functionalized with groups of formula (I) as defined herein, wherein the starch preferably is an uncooked starch (for instance an uncooked acid- hydrolyzed starch or an uncooked oxidized starch).

[0136] In said gypsum core, the content of said starch functionalized with groups of formula (I) may be at least 0.1 wt% (preferably at least 0.5 wt%), relative to the dry weight of gypsum, and at most 10 wt% (preferably at most 7 wt%, for example at most 5 wt%), relative to the dry weight of gypsum.

[0137] In said gypsum core, the content of fluidizer other than said starch functionalized with groups of formula (I) is preferably less than 0.1 wt%, preferably less than 0.05 wt%, more preferably less than 0.04 wt%, even more preferably less than 0.03 wt%, relative to the dry weight of gypsum.

[0138] In said gypsum core, the content of adhesion agents other than the starch functionalized with groups of formula (I) may for instance be comprised between 0.1 and 8 wt%, such as between 0.5 and 6 wt%, or even between 1 and 5 wt%, relative to the dry weight of gypsum.

[0139] In said gypsum core, the content of adhesion agents other than said starch functionalized with groups of formula (I) is preferably less than 2 wt%, more preferably less than 1 wt%, even more preferably less than 0.5 wt%, for instance less than 0.2 wt%, relative to the dry weight of gypsum.

[0140] More particularly, the present invention relates to a plasterboard obtainable by a method as defined herein.

[0141] The gypsum layer in the plasterboard is usually called "gypsum core". The plasterboard generally has a thickness of 6 to 25 mm, preferably 10 to 15 mm.

[0142] The density of the dry gypsum layer (or core) is usually from 0.4 to 1.5, for instance:

[0143] - from 0.8 to 1.5, more particularly from 1.0 to 1.2, or

[0144] - from 0.6 to 1.0.

[0145] In the present invention, the density of a composition or a layer is defined conventionally, that is to say by the ratio of the density of such composition or layer to the density of water, taken equal to 1000 kg / m3.

[0146] As used herein, "wt%" refers to "weight %" (e.g. weight content).

[0147] It is understood that the various aspects, particular embodiments, preferred embodiments, described above for the composition of the invention apply to the method for the manufacture of a plasterboard as described herein and to the plasterboard as described herein.

[0148] The present invention is illustrated by the following non-limiting examples.

[0149] EXAMPLES

[0150] Example 1: Fluidifying effect of an uncooked octenyl succinated starch

[0151] The slump was used to evaluate the fluidity of a gypsum slurry comprising an uncooked octenyl succinated starch.

[0152] Method:

[0153] The ingredients of the composition were mixed and vigorously stirred in a blender (Blender LB20E* from Waring, 25 seconds at speed 12) to form a slurry and the resulting slurry was then immediately poured into a slump ring. The slump ring was quickly lifted, and the liquid slurry formed a patty. The diameter of the patty was measured by means of a ruler.

[0154] The diameter of the patty is an estimation of the fluidity of the gypsum slurry.

[0155] Slump tests were carried out using the following composition (A):

[0156] - stucco (CaSO4.1 / 2H2O),

[0157] - water, with a weight ratio water / stucco of 0.7,

[0158] - 0.4 wt% of heat resistant accelerator based on the dry weight of stucco,

[0159] - 0.027 wt% of retarder, based on the dry weight of stucco, and

[0160] - 0.5 wt% (Composition Al) or 2 wt% (Composition A2) of uncooked octenyl succinated waxy corn starch, based on the dry weight of stucco.

[0161] The stucco amount used for the tests was 300g.

[0162] The slump of the above compositions, and that of the following comparative compositions were measured:

[0163] - the corresponding starch-free composition (B),

[0164] - the corresponding composition using an uncooked acid-hydrolyzed corn starch instead of uncooked octenyl succinated waxy corn starch (Cl, C2), - the corresponding composition using pre-gelatinized oxidized corn starch instead of uncooked octenyl succinated waxy corn starch (DI, D2),

[0165] - the corresponding composition using pre-gelatinized oxidized wheat starch instead of uncooked octenyl succinated waxy corn starch (El, E2).

[0166] The same batch of stucco was used for the compositions of the invention and for the comparative compositions.

[0167] The results are shown in Table 1 below (standard deviation forformulation B having no starch= 1.2 cm).

[0168] Table 1

[0169] Table 1 shows that the compositions according to the invention (Al, A2) entails a slump value higher than the starch-free reference range (B), and, consequently, causes a fluidifying effect: + 3 cm (+16%) for Al and + 4.5 cm (+28%) for A2, with respect to the slump of the composition having no starch (B).

[0170] On the contrary, the slump of the compositions comprising the uncooked bond starch (Cl, C2) is in the no-starch range (B). The slump of the compositions comprising 0.5% of pre-gel bond starch (DI, El) is also in the no-starch range.

[0171] The compositions comprising 2% of pre-gel bond starch (D2, E2) even cause a thickening effect (decrease of 25-30% of the slump, - 4cm).

[0172] Example 2: Fluidifying effect of a pre-gelatinized octenyl succinated starch

[0173] The slump was also used to evaluate the fluidity of a gypsum slurry comprising a pregelatinized octenyl succinated starch. The method as described in Example 1 was used. Slump tests were carried out using the following composition (A3):

[0174] - stucco (CaSC JZI-hO),

[0175] - water, with a weight ratio water / stucco of 0.7,

[0176] - 0.4% wt. of heat resistant accelerator based on the dry weight of stucco,

[0177] - 0.027% wt. of retarder, based on the dry weight of stucco, and

[0178] - 2 wt% of pre-gelatinized octenyl succinated tapioca starch, based on the dry weight of stucco. The stucco amount used for the tests was 300g.

[0179] The slump of the above composition, and that of the following comparative compositions were measured:

[0180] - Composition B' (starch-free composition),

[0181] - Composition C3 (2 wt% of an uncooked acid-hydrolyzed corn starch),

[0182] - Composition D3 (2 wt% of a pre-gelatinized oxidized corn starch).

[0183] The same batch of stucco (different from that of Example 1) was used for the composition of the invention and for the comparative compositions.

[0184] The results are shown in Table 2 below (standard deviation for formulation B' having no starch= 0.5 cm).

[0185] Table 2

[0186] Table 2 shows that the composition according to the invention (A3) entails a slump value higher than the starch-free reference range (B') and, consequently, causes a fluidifying effect: + 1 cm with respect to the slump of the composition having no starch (B'). On the contrary, the slump of the composition comprising the uncooked bond starch (C3) is in the no-starch range (B'). The composition comprising the pre-gel bond starch (D3) even causes a thickening effect (decrease of 26% of the slump, - 3cm).

Claims

CLAIMS1. A method for the manufacture of a plasterboard, comprising :- providing a composition comprising water, stucco, and a starch functionalized with groups of formula (I):- - -C(O)-R-C(O)O" M+(I), in which:R is a C1-C12 aliphatic divalent chain substituted by a C4-C22 aliphatic chain, andM+is a cation,- casting the composition on a first band, so as to form a wet gypsum layer on said first band,- providing a second band on said wet gypsum layer, and- forming the plasterboard, preferably using an extruder.

2. The method according to claim 1, wherein R is a C2 or C3 alkylene chain, substituted by a C6-C12 alkenyl chain, preferably R is a C2 alkylene chain substituted by a C8 alkenyl chain.

3. The method according to claim 1 or 2, wherein the starch is a pregelatinized or uncooked starch, more particularly an uncooked acid-hydrolyzed starch, an uncooked oxidized starch, a pregelatinized acid-hydrolyzed starch, or a pregelatinized oxidized starch.

4. The method according to any one of the preceding claims, wherein the starch is an uncooked starch, for instance an uncooked acid-hydrolyzed starch or an uncooked oxidized starch.

5. The method according to any one of the preceding claims, wherein the content of fluidizer other than said starch functionalized with groups of formula (I) is less than 0.1 wt%, preferably less than 0.05 wt%, more preferably less than 0.04 wt%, even more preferably less than 0.03 wt%, relative to the dry weight of stucco.

6. The method according to any one of the preceding claims, wherein the composition does not comprise a fluidizer other than said starch functionalized with groups of formula (I).

7. The method according to any one of the preceding claims, wherein the content of stucco is at least 60 wt%, relative to the total solids content of the composition.

8. The method according to any one of the preceding claims, wherein the content of said starch functionalized with groups of formula (I) is at least 0.1 wt%, preferably at least 0.5 wt%, relative to the dry weight of stucco, and at most 10 wt%, preferably at most 7 wt%, for example at most 5 wt%, relative to the dry weight of stucco.

9. The method according to any one of the preceding claims, wherein the weight ratio of water to stucco in the composition is:- at least 0.19 and- at most 0.85, preferably at most 0.80, more preferably at most 0.65, even more preferably at most 0.55.

10. The method according to any one of the preceding claims, wherein the composition further comprises at least one reinforcing agent, for instance glass fibers or polyvinyl acetate.

11. The method according to any one of the preceding claims, wherein the composition further comprises additives, preferably selected from setting accelerators, setting retarders, anti-burning agents, anti-sag agents, fire-resistant agents, anti-shrinkage agents, biocidal agents, and water repellents.

12. The method according to any one of the preceding claims, wherein the first and second bands are paper or cardboard bands.

13. The method according to any one of the preceding claims, further comprising a setting step and a drying step.

14. A plasterboard obtainable by the method as defined in any one of claims 1 to 13.

15. A composition comprising :- stucco,- starch functionalized with groups of formula (I):- - -C(O)-R-C(O)O" M+(I), in which:R is a C1-C12 aliphatic divalent chain substituted by a C4-C22 aliphatic chain, andM+is a cation, and- water.

16. The composition according to claim 15, having one or more of the following features:- the content of stucco is at least 60 wt%, relative to the total solids content of the composition, and / or- the content of said starch functionalized with groups of formula (I) is at least 0.1 wt%, preferably at least 0.5 wt%, relative to the dry weight of stucco, and at most 10 wt%, preferably at most 7 wt%, for example at most 5 wt%, relative to the dry weight of stucco, and / or- the weight ratio of water to stucco in the composition is at least 0.19 and at most 0.80, preferably at most 0.65, more preferably at most 0.55.

17. The composition according to claim 15 or 16, wherein R is a C2 or C3 alkylene chain, substituted by a C6-C12 alkenyl chain, preferably R is a C2 alkylene chain substituted by a C8 alkenyl chain.

18. The composition according to any one of claims 15 to 17, wherein the starch is an uncooked starch, for instance an uncooked acid-hydrolyzed starch or an uncooked oxidized starch.

19. The composition according to any one of claims 15 to 18, wherein the content of fluidizer other than said starch functionalized with groups of formula (I) is less than 0.1 wt%, preferably less than 0.05 wt%, more preferably less than 0.04 wt%, even more preferably less than 0.03 wt%, relative to the dry weight of stucco.

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