Gypsum slurry composition and a moisture resistant gypsum composite thereof

Abstract

The present application provides a gypsum composition slurry, comprising 52 to 60 % of stucco; 40 to 45 % of water; 0 to 1 % of starch; 0.03 to 0.5 % of additives selected from cement, sodium carboxy methyl cellulose, guar gum or a combination thereof; and 0.18 to 1.2 % of moisture resistant agent. The gypsum slurry casted to form a gypsum composite exhibits moisture resistance. Further the application also provides a method of manufacturing a moisture resistant gypsum composite, specifically a gypsum board.

Description

[0001] GYPSUM SLURRY COMPOSITION AND A MOISTURE RESISTANT GYPSUM

[0002] COMPOSITE THEREOF

[0003] TECHNICAL FIELD

[0004] The present disclosure relates in general to a gypsum slurry composition, and particularly such a composition settable to form a gypsum composite. More particularly, the present disclosure provides a gypsum slurry composition with specific additives or modifiers respectively and in a combination. Such a gypsum slurry casted to form a gypsum product or composite exhibits enhanced moisture barrier properties.

[0005] BACKGROUND

[0006] Gypsum is a common mineral composed of calcium sulfate dihydrate. It is widely mined and is used as a fertilizer and specifically as the main constituent in many forms of plaster, blackboard / sidewalk chalk, and dry wall etc. A massive fine-grained white or lightly tinted variety of gypsum is used for sculpture. Gypsum is used for a variety of gypsum products, most commonly used as building materials, with an example being wallboard and fiberboard sheets, for many reasons. They are easily manipulated to make continuous walls of desired shapes and sizes. They are durable, easily installed, patched, and have beneficial insulation, fire and acoustic properties. Decorative finishes, such as wallpaper or paint readily adhere to surfaces to allow for a large variety of decorating options.

[0007] More particularly, wide varieties of molded gypsum products are known such as gypsum boards, lath boards, decorated boards, sound-insulation boards, and gypsum block etc., having various characteristics depending upon the nature of gypsum. Generally, such objects or composites are produced by preparing a slurry composition containing stucco, a dispersant, additives, adhesives, and water, pouring it into a mold form and thereafter drying it such that it becomes coagulated and hardened. For such a production process, the gypsum slurry composition is required to have sufficient fluidity and most importantly to be capable of exhibiting a superior strength and various other performance after it has been hardened. While referring to superior strength and performance of such composites, light weight, high strength, fire proofing, sound insulation, high ductility, water resistant, moisture resistant etc. are some of the properties explored widely. Specifically, in the field of modern architecture, gypsum is a major material being used in the construction industry. It is well-known that hardened gypsum boards possessing superior strength and various performance properties find its application in wall, ceiling, and partition systems in residential, institutional, and commercial structures. To control the properties of the gypsum composites, additives or modifiers are added to the gypsum stucco slurry composition, which is further set to form a gypsum composite.

[0008] In the existing state of art, various proposals have been made to increase the strength of gypsum board products or otherwise modify their properties to achieve better performance properties. Some proposals include providing one or more additives to the gypsum slurry to affect the characteristics of the resulting dried board product. For example, foaming agents, inorganic compounds, and other additives may be included to modulate density, strength, and other properties. Some proposed additives or modifiers, however, may affect the viscosity, tackiness, or other properties of the slurry. Taking slurry viscosity as an example, excessive viscosity can lead to increased mixing time, increased energy demands, and resultant increased costs. Worse still, if viscosity increases become excessive, an incompletely mixed slurry or improperly formed board can result. Incompletely mixed slurry will have a non-uniform setting profile and hence formation of gypsum boards during manufacturing is highly impacted.

[0009] Also, addition of additives to the gypsum slurry which are used to enhance the performance properties can result in compatibility problems with other slurry components. Some additives, for example, have a surface active or surfactant functionality. These additives have the potential of destabilizing or otherwise interfering with a slurry foam additive. Some additives also have the potential of inadequate dispersion within the slurry. In the case of a viscous liquid or gel additive, for example, there is a risk that the high viscosity and limited residence time in the slurry mixer will cause an inadequate mixing.

[0010] Particularly, gypsum composite for ex., moisture resistant gypsum boards find applications in numerous industrial, commercial, and residential buildings, in places where high moisture or humidity is present, such as in bathrooms, kitchens, laundry rooms, utility rooms or basement areas. Moisture resistant gypsum board is commonly used in those environments where ceramic tile is placed over the gypsum board.

[0011] A comprehensive review of prior art has indicated that usually there are two major groups of additives which can be added to or mixed with gypsum stucco slurry composition to render the boards water resistant (or moisture resistant or waterproof or water repellant, depending upon the terminology used by the various inventors in several patent applications). Such attempts have included the incorporation of water-resistant material such as metallic soaps, asphalts, waxes, resins, etc., within the gypsum stucco (i.e., calcium sulfate hemihydrate) slurry during the manufacturing process.

[0012] For example, one class is that of wax-based additives, which generally comprise a wax emulsified with other agents, such as described in U.S. Pat. Nos. 6,585,820 B2, which discloses a water-resistant gypsum formulation consisting of an emulsion comprising a plurality of waxes, at least one saponified wax, a complexed starch, a polymerized alkyl phenol, and a cosurfactant, or an emulsion comprising a single wax, a dual surfactant system, a complexed starch, and a polymerized alkyl phenol. U.S. Pat. No. 6,010,596 teaches the use of paraffins and montan wax; U.S. Pat. No. 5,437,722 teaches the use of paraffin wax-asphalt, etc. The waxes are generally petroleum-based waxes, such as paraffins, microcrystalline waxes, montan wax, or wax-asphalt, wax-pitch mixtures. Waxes are suspension and generally require equipment to keep the suspension stable. Also, waxes are expensive, and dosage required is high.

[0013] The other, very general class can be referred to as other agents, which range from sulfur, calcium stearate, polyurethanes, silanes, siloxanes and high molecular weight silicones, alkyl siliconates, or polyvinyl compounds, which can be added to or coated onto gypsum preparations. For example, U.S. Pat. No. 6,323,268 discloses compositions for rendering surfaces water repellent by combining (i) water; (ii) a methylhydrogensiloxane polymer or copolymer; (iii) an alkoxysilane; (iv) a silicone resin; (v) a volatile methyl siloxane; (vi) a cationic oil-in-water emulsion of an aminofunctional polydimethylsiloxane; and (vii) a surfactant. While such compositions are capable of imparting water repellent properties to many surfaces, they are unsuitable in applications involving the use of high temperature processing equipment. This is because compositions containing volatile silicon containing components have a propensity to cause silica fouling of high temperature processing equipment.

[0014] U.S. Patent App. Pub. No. 2016 / 0258157 and similarly U.S. Pat. No. 7,892,472 disclose gypsum panels with improved water resistance. In this instance, a polymerizable siloxane is added to the slurry used to make the gypsum product. The siloxane is added in the form of an emulsion. A catalyst like magnesium oxide (MgO) is also included to speed polymerization of the siloxanes. However, the polymerization of the siloxane can be incomplete and result in additional drying time being needed to allow for more complete polymerization. EPl 112986 Al document teaches a noticeable increase in water resistance is imparted when polymerizable siloxane is added in the gypsum slurry with Portland Cement as a catalyst. The quantity of the siloxane emulsion added to the slurry is at least about 0.1% by weight based on the weight of the total solids in the slurry. It is preferred to use from about 1% to about 2% by weight of siloxane together with 0.3 to 2% by weight of Portland cement to achieve a high level of water resistance.

[0015] Silicone-oils are often used to provide moisture resistant properties to gypsum composites. However, the present inventors have realized that the amount of silicon oil used is often in excess of that necessary on a per unit mass bases to compensate the property for the oils to migrate to the gypsum composite surface during setting and drying of the gypsum core of the composite, leaving the center of the gypsum core with relatively less water or moisture resistance. Further, also the use of silicon oils in gypsum composites is expensive.

[0016] It is thus noticed from the state of art that, to achieve moisture resistance in gypsum boards poly methyl hydrogen siloxane is widely used. Among various additives used in the board, siloxane is the highest cost contributor. Siloxane having low surface energy, tend to migrate to the interface of slurry and liner when mixed with water. Hence, there is always an interest to keep siloxane well distributed in the gypsum slurry and initiate its polymerization as soon as possible. This way consumption of siloxane is reduced which further helps to reduce its cost contribution, making it economically significant. Hence, it is desired in the art to find modifiers / additives for a gypsum slurry composition, that can be further set into gypsum products possessing improved performance properties, specifically aiming at improved moistureresistance at a reasonable cost, and better distribute the additive throughout the gypsum composite. In present invention, emulsification of silicone oil along with cement and guar gum and other additives is shown to have synergistic effect and that gives improved moisture resistant to plasterboard for a given silicone oil concentration.

[0017] OBJECT OF INVENTION

[0018] The main object of the present invention is to provide a slurry composition that can be casted to form a gypsum composite.

[0019] Particularly, another object of the present invention is to provide a gypsum slurry composition which can exhibit enhanced moisture-barrier properties, when such a slurry is casted to form a gypsum composite.

[0020] Yet another object of the present invention is to provide a gypsum slurry composition comprising emulsified silicon with modifier(s), which enhance the distribution of silicone oil and thereby reduces the consumption of silicone oil.

[0021] Further, yet another object of the present invention is to provide a method of manufacturing a gypsum composite, such a gypsum composite being resistant to moisture.

[0022] The present disclosure was developed by outlining the above objectives.

[0023] SUMMARY OF THE DISCLOSURE

[0024] In an aspect of the present disclosure, a gypsum slurry composition is disclosed. Said gypsum slurry composition comprises 52 to 60 % of stucco; 40 to 45 % of water; 0 to 1 % of starch; 0.03 to 0.5 % of modifiers selected from cement, , sodium carboxy methyl cellulose, guar gum or a combination thereof; and 0.18 to 1.2% of moisture resistant agent. Such a gypsum slurry casted to form a gypsum composite exhibits moisture resistance.

[0025] In one aspect of the present disclosure, a gypsum slurry composition is disclosed. Said gypsum slurry composition comprises 52 to 60 % of stucco; 40 to 45 % of water; 0 to 1 % of starch; 0.012 to 0.3 % of cement, and 0.18 to 1.2 % of emulsified silicone oil.

[0026] In another aspect of the present disclosure, a gypsum slurry composition is disclosed. Said gypsum slurry composition comprises 52 to 60 % of stucco; 40 to 45 % of water; 0 to 1 % of starch; 0.1 to 0.5 % of guar gum, and 0.18 to 1.2 % of emulsified silicone oil.

[0027] In yet another aspect of the present disclosure, a gypsum slurry composition is disclosed. Said gypsum slurry composition comprises 52 to 60 % of stucco; 40 to 45 % of water; 0 to 1 % of starch; 0.01 to 0.05 % of sodium carboxy methyl cellulose;

[0028] 0.05 to 0.5% of guar gum; and 0.18 to 1.2 % of emulsified silicone oil.

[0029] Further, yet another aspect of the present disclosure, a method of manufacturing a moisture resistant gypsum composite is disclosed. Said method comprises the steps of forming a gypsum slurry; forming a layer of said mixture on a first liner; disposing a second liner on said layer in opposed relationship with said first liner to form an assembly of said liners with said layer sandwiched there between; allowing hydration of slurry; and drying the assembly, to form a gypsum composite.

[0030] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

[0031] DETAILED DESCRIPTION

[0032] As used herein, in every embodiment, it must be understood that the phrase ‘gypsum slurry’ refers to a mixture of stucco and water.

[0033] As used herein, in every embodiment, it must be understood that the term ‘moisture-resistant’ or ‘moister-barrier’ or ‘water-resistant’ can be used interchangeably and refers to a property which offers better or enhanced resistance against moisture or water, than traditional drywall.

[0034] The term ‘gypsum composite’ or ‘gypsum product’ can be used interchangeably, refers to a product which is formed by casting a gypsum slurry as per the present invention. Specifically, such a gypsum composite as referred in the present invention is not limited to gypsum board.

[0035] The term ‘additive(s)’ or ‘modifier(s)’ can be used interchangeably, refers to additional components included in the base stucco slurry composition.

[0036] The present application provides a gypsum slurry composition. In accordance with one aspect of the present disclosure the gypsum slurry composition comprises 52 to 60 % of stucco; 40 to 42 % of water; 0.2 to 1 % of starch; 0.03 to 0.5 % of modifiers selected from cement, sodium carboxy methyl cellulose, guar gum or a combination thereof; and 0.18 to 12% of moisture resistant agent. Cement is a pH modifier and sodium carboxy methyl cellulose, guar gum are retaining agents. Beneficially, such a composition when casted to form a gypsum composite, the gypsum composite exhibits enhanced moisture resistance. Further, beneficially, such a gypsum composite also possesses superior strength, better core morphology by reducing foam destruction and reduces the use of silicone oil.

[0037] The present inventors have unexpectedly realized that the modifiers including cement, sodium carboxy methyl cellulose and guar gum can be used in combination or individually with base stucco slurry composition along with the emulsified silicone oil, which can be further cast to achieve gypsum composites with improved moisture resistance property. Further beneficially the inventors have also realized that with the addition of the aforesaid modifiers, silicone oil tends to be distributed uniformly and better disperse in the casted gypsum composite, which thereby reduces the consumption of silicone oil.

[0038] The present inventors have further unexpectedly realized that a low amount of these additives can be added to the base stucco slurry composition. The inventors in accordance with the present disclosure have overcome the challenges stated in the background effectively by introducing additives in an amount as low as 0.012 to 0.3%. Inclusion of an additive or a combination of the additives has not only ensured water or moisture resistance, but also surprisingly enhanced the efficiency of the silicone oil used. The silicone oil is efficiently consumed to give moisture resistant property to gypsum core and thereby reducing the amount of silicone oil migrating to gypsum-liner interface. Lesser silicone oil migration at gypsumliner interface leads to decrease in formation of silica dust formation in the dryer.

[0039] In some embodiments of the present invention, the gypsum slurry composition comprises by weight, 52 to 60 % of stucco; 40 to 45 % of water; 0 to 1 % of starch; and 0.18 to 1.2 % of moisture resistant agent along with 0.012 to 0.3 % of additive(s) or modifiers(s). The moisture resistant agent according to the present invention is selected from the group comprising of emulsified or non-emulsified silicone oil, silanol, hydrolyzed silanes, alkyl / vinyl alkoxysilane, alkyl / vinyl siloxane, alkyl / vinyl silanols, alkyl siliconates or a combination thereof. In a specific embodiment the moisture resistant agent is preferably emulsified silicone oil, silanol or hydrolyzed silanes. In a most preferred embodiment, the moisture resistant agent is emulsified silicone oil.

[0040] The modifiers in accordance with the present invention is selected from the group comprising of cement, sodium carboxy methyl cellulose, guar gum or a combination thereof. In an alternate embodiment, the modifiers can also be selected form the group consisting of dicalcium silicate, tricalcium silicate, hydraulic cement, hydraulic lime, inorganic mild base, or flyash. In some embodiments of the present invention, the gypsum slurry composition comprises various combinations of modifiers and moisture resistant agent.

[0041] In accordance with one embodiment of the present invention, the gypsum slurry composition comprises by weight, 52 to 60 % of stucco; 40 to 45 % of water; 0 to 1 % of starch; and 0.18 to 1.2 % of emulsified silicone oil along with 0.012 to 0.3 % of cement additive.

[0042] In every embodiment of the present invention, the stucco is present in the range of 52 to 60% by weight of the gypsum slurry composition. In a preferred embodiment the stucco is present in the range of 55 to 59%. In a most preferred embodiment, the stucco is present in an amount of 58% by weight of the gypsum slurry composition. As is known in the art, stucco can have a variety of compositions, depending on the source and the application at hand. As per the present invention stucco is a material having at least 75% of calcium sulfate hemihydrate. It is typically provided by calcining gypsum to convert the dihydrate of gypsum to hemihydrate. Real-world samples of stucco typically include, together with the hemihydrate (e.g., present as a-calcium sulfate hemihydrate and P-calcium sulfate hemihydrate, or combinations thereof), one or more of calcium sulfate dihydrate, calcium sulfate anhydrate, inert calcium sulfate and other impurities depending on the gypsum source. A combination of stucco and water herewith is referred as calcium sulfate slurry or gypsum slurry.

[0043] The gypsum slurry composition comprises water, in accordance with the present invention, ranging in an amount of 40 to 45 %. In a preferred embodiment, the water is present in an amount of 41%. The water provides fluidity to the slurry, for ease of handling, as well as provide necessary water for hydration of the hemihydrate to gypsum. In an embodiment the weight ratio of stucco to water in the gypsum slurry is no more than 0.8 : 1, e.g., no more than 0.75: 1, or no more than 0.7 : 1. In various embodiments of the present invention, the weight ration of stucco to water in the gypsum slurry is in the range of 0.8 : 1 to 0.7 : 1. In a preferred embodiment the weight ratio of stucco to water in the gypsum slurry is 0.7: 1.

[0044] In every embodiment of the present invention, the starch is present in the range of 0 to 1 % by weight of the gypsum slurry composition. In a preferred embodiment the starch is present in the range of 0.2 to 0.5%. In a most preferred embodiment, the starch is present in an amount of 0.3 % by weight of the gypsum slurry composition. In alternate embodiment, a high viscosity modified starch can also be used in the gypsum slurry composition. In some embodiments the starch can also be pre-gelified starch or pre-gelatinised starch. In an alternate embodiment, the starch in accordance with the present invention is acid modified, chemically modified or a combination thereof with various crop sources including corn, sorghum, wheat, tapioca, rice, pea, potato, and barley.

[0045] In a preferred embodiment of the present invention, a low amount of cement additive is added to the base stucco slurry composition to achieve gypsum composites with moisture resistance property. Generally, cement is one of the cheapest pH modifiers without having any impact on process equipment corrosion such as silos and feeder system. However, addition of cement, leads to water pearling, stain marks on boards, moisture condensation and blisters on boards during drying. Addition of cement in stucco slurry is indeed known to create a lot of process challenges that outweighs its benefits. Cement is used to get alkaline pH in gypsum slurry. Silicone polymerization is accelerated in alkaline pH, in the range of 7.5 to 14. This in turn improves efficacy of silicone oil to get moisture resistant property to the casted gypsum composite.

[0046] The inventors in accordance with the present disclosure have overcome such challenges effectively by introducing cement in an amount as low as 0.012 to 0.3%, preferably 0.012 to 0.055%. Addition of cement in a low quantity has not only ensured pH for silicone oil polymerisation, but also surprisingly enhanced the silicone oil efficacy. It is generally admitted that the higher the cement content, the faster the polymerization of silicone oil. However, higher cement content in the stucco slurry may affect paper-gypsum bond and may cause condensation inside dryer. Even though cement helps to improve silicone oil efficacy, as stated earlier it creates process challenges (for ex., paper-gypsum bonding, and condensation in dryer) that outweighs its benefits. Accordingly, the inventors have not only reduced the cement content to overcome the process challenges, but also ensured that the said cement content contributed to increase in silicone oil efficacy.

[0047] In another embodiment, in accordance with the present invention, a low amount of guar gum additive is added to the base stucco slurry composition to achieve gypsum composites with moisture resistance property. In a preferred embodiment, the guar gum is present in the range of 0.1 to 0.5 %. In a most preferred embodiment, the guar gum is present in an amount of 0.2%. It has been hypothesized that guar gum offers thickness to gypsum slurry by altering electro kinetics of the slurry and thereby reduces migration of silicone oil. Guar gum is used to reduce migration of silicone oil to the surface during manufacturing of gypsum composites, specifically gypsum boards. Guar gum also acts as thickening agent and helps keep siloxane into the slurry. Guar gum undergoes hydration when it is mixed with water and gives the thickening effect. The rate of hydration of guar gum and achievement of final viscosity is highest at neutral pH. Guar Gum’s thickening effect in turn helps to keep the silicone oil inside slurry during moisture resistant gypsum board production. Hence, the efficacy of silicone oil is improved. It has been reported that pH at and above 9, the rate of guar hydration slows down and that leads to a lower viscosity. Hence, keeping low cement content will help in maintaining pH in a range between 7 and 9, allowing both thickening of guar and polymerization of silicone oil. Indeed, the pH of gypsum slurry without pH modifier is in the range of 6.5 to 7. At the pH of gypsum slurry, it takes time to initiate the silicon oil polymerization reaction. During that time, silicone oil migrates to surface which is a loss to get gypsum core moisture resistant property. In order to get pH greater than 7, cement is added, which accelerates polymerization, thereby allowing to achieve moisture resistant property.

[0048] In every preferred embodiment in accordance with the present invention, emulsified silicone oil is present in the range of 0.18 to 1.2 % by weight of the gypsum slurry composition. In a preferred amount the silicon oil is present in the range of 0.2 to 1.2 %. In a most preferred embodiment, the silicone oil is present in an amount of 0.25 % by weight of the gypsum slurry composition. As would be understood by the skilled person in the art, the silicone oil can include a variety of different polysiloxanes. Such polysiloxanes can include both hydrogen and other functional groups to modify the poly siloxane backbone. For example, polymethyl hydrogen siloxane includes both Si-H and Si-CHs bonds. In accordance with the present invention the silicone oil is preferably polymethyl hydrogen siloxane. The silicone oil in most preferred embodiments of the present invention, is provided as an aqueous emulsion of the silicone oil in the base stucco slurry. In some embodiments the aqueous emulsion of silicone oil can be provided by emulsifying the silicone in water. In some alternate embodiments, the silicone oil can be provided to the base stucco slurry, by mixing the silicone oil into the base stucco slurry under conditions sufficient to form an emulsion. In some alternate embodiments, the silicone oil can be provided to the remaining process water, by mixing the silicone oil into process water. The silicone oil in accordance with the present invention has a low amount of hydrogen content.

[0049] In another embodiment a variety of silicones can be used in the gypsum slurry composition. In some embodiments of the present invention the silicone oil includes an alkyl-functional silicone. The alky-functional silicone is a polysiloxane functionalized with alkyl groups. For example, in some embodiments, the silicone oil includes a methyl-functional silicone, and ethyl-functional silicone, a propyl -functional silicone, or a butyl -functional silicone. In some embodiments, the silicone oil is polydimethylsiloxane. However, in some embodiments, the silicone oil can be a copolymer of dimethylsiloxane, for example with methylsiloxane or phenylsiloxane (in amounts such that the hydride content is low). In a most preferred embodiment, in accordance with the present invention the molar content of dimethylsiloxane units in the silicone oil is at least 90%, or at least 95% or at least 99%. It has surprisingly been seen that the extremely low amount of the additive individually or in combination in the stucco slurry, is sufficient to emulsify polymethyl hydrogen siloxane in water and to give this emulsion a sufficient stability, polymerize and necessary to evenly distribute the emulsified silicone oil in the gypsum stucco slurry.

[0050] The silicone oil in accordance with the present invention has mean droplet size in the range of 5 to 75 pm, preferably in the range of 12 to 25 pm. This can be, the droplet size of a silicone oil emulsion that is added to the gypsum slurry composition, and / or the droplet size of a silicone oil in the slurry itself. The aqueous emulsion in accordance with the present invention is formed by mixing water with silicone oil in a ratio ranging between 1 : 10 to 1 :50. In a specific embodiment the water to silicone oil ratios is 1 :25.

[0051] The inventors of the present invention surmise that the use of emulsified silicone oil along with the additive individually or a combination of additives, in the aforesaid amounts, helps to limit the migration of the silicone oil in the gypsum core of the gypsum composites, typically a gypsum board, and thus the silicone oil concentration can remain more uniform throughout the thickness of the composite.

[0052] The gypsum slurry composition in accordance with the present invention, may also further comprise one or more accelerators, retarders, fluidizers, dispersants, foaming agents, and / or glass fibers. In some embodiment the aforesaid agents are present in an amount of no more than 1 weight % of the gypsum slurry composition. In various embodiments the aforesaid agents are present in an amount of no more than 0.8% or no more than 0.5% by weight of the gypsum slurry composition. A person of ordinary skill in the art will use an appropriate set of the aforesaid agents for the desired gypsum slurry composition.

[0053] In a specific embodiment, the retarder is present in an amount ranging between 0.01 to 0.04 % and is selected from the group consisting of amino acids, citric acid, or tartaric acid. In a most preferred embodiment, the retarder is present in an amount of 0.01 % and is amino acids. The retarder in accordance with the present invention delays the setting according to the plant line speed.

[0054] In a specific embodiment, the heat resistant accelerator is present in an amount ranging between 0.2 to 5 % and is selected from the group consisting of magnesium, calcium sulfate, ball mill gypsum or potassium sulphate. In a most preferred embodiment, the heat resistant accelerator is present in an amount of 0.2 % and is calcium sulfate. The accelerator in accordance with the present invention is added to accelerate setting time of stucco.

[0055] In a specific embodiment, the fluidizer is present in an amount ranging between 0.1 to 0.5 % and is selected from the group consisting of polynaphthalene sulfonate, ligno sulfonate, poly carboxylate or a combination thereof. In a most preferred embodiment, the fluidizer is present in an amount of 0.1 % and is polynaphthalene sulfonate, ligno sulfonate. The fluidizer in accordance with the present invention is used as water reducing agent to get slurry fluidity.

[0056] In a specific embodiment, the foaming agent is selected from the group consisting of ethyoxylated surfactant or lauryl surfactants. In a most preferred embodiment, the foaming agent is present in an amount of 0.1 % and is ethyoxylated surfactant. The gypsum slurry composition in accordance with the present invention, is casted to form a gypsum composite. The gypsum composite for example can be a panel, board, walls, plinths, slabs, columns, sheets, casts, or shafts. In some embodiments the gypsum composite is a panel, or a board, or a sheet. In a preferred embodiment, the gypsum composite is a gypsum board.

[0057] The present application also discloses a method of manufacturing a moisture resistant gypsum composite. The method comprises the steps of forming a gypsum slurry composition, forming a layer of said mixture on a first liner, disposing a second liner on said layer in opposed relationship with said first liner to form an assembly of said liners with said layer sandwiched there between. Further the slurry is hydrated and the assembly is dried to form a gypsum composite.

[0058] In an embodiment of the present invention, the gypsum slurry is formed by mixing of the components of the gypsum slurry. The formed mixture is applied as a first layer on a first liner, followed by disposing a second layer on the opposite side of the first liner, to form an assembly with the first and second layers. The slurry is sandwiched between the first layer and second layer. The assembly is set to environment for curing and hardened to form a gypsum board. The liner can be a paper liner or a glass mat liner.

[0059] The gypsum composite, specifically the gypsum board in accordance with the present invention has a modulus of rupture ranging from 450 to 550 Newton, and test water absorption of less than 4.9%, for example less than 4.6% or less than 4%

[0060] The gypsum composite produced in accordance with the present disclosure, has moisture / water resistant properties, improved silicone oil efficacy, and reduced test water absorption. Preferably such a gypsum composite finds it application in buildings, facades, panels, kitchen splash backs, furniture (wardrobes, tabletops, workstations), claddings, lift lobbies, etc.

[0061] EXAMPLES

[0062] Table 1 discloses a gypsum slurry composition, according to an inventive Examples 1 to 3, compared against comparative samples with non-emulsified silicone oil. Comp. Ex Comp. Ex Comp. Ex Comp. Ex

[0063] Inv Ex 1 Inv Ex 2 Inv Ex 3 1 2 3 4

[0064] Preparation of gypsum board from the above stated slurry:

[0065] The slurry was prepared and casted on a paper liner. Board size of 150 x 150 mm2 was made at lab scale. The casting was done on a vibrating table to assist homogenized spread of slurry in the mold. After the slurry is set, the boards were demolded and subjected to 180° C drying for 90 minutes to remove excess moisture and to activate starch to create bonding between paper and core. For each formulation 2 boards were prepared. The dried boards were moved to 40 C ventilated oven to remove final moisture content for 24 hrs.

[0066] After drying, the boards were conditioned at 23 C and 50% RH for 48 hrs. The conditioned boards were kept immersed in water for 2 hours to quantify water absorption property. The procedure to measure water absorption property is as per EN520 standard and the specification for Hl category is less than 5 wt%.

[0067] The method as disclosed above was used to cast the gypsum slurry into gypsum boards as per the inventive and comparative examples.

[0068] The following tests have been performed for the gypsum board as per the inventive example over the comparative example to evaluate the claimed performance. a) Test Water Absorption:

[0069] In accordance with Standard:EN520

[0070] The TWA is tested using a standardized procedure given in the standard and the results of inventive and comparative examples are tabulated in Table 2.

[0071] Typical water resistance (TWA) of a gypsum board is measured using EN 520 requirements of TWA < 5% for Hl category board. Here from Table 2, it is inferred that Inventive examples showed better moisture resistant property compared to the comparative examples.

[0072] It is indicated from the above table 2 that Inventive Example 1 [cement + guar gum + emulsified silicon oil + base stucco], 2 [guar gum + emulsified silicon oil + base stucco] and 3 [cement + emulsified silicon oil + base stucco]; have demonstrated the required standard TWA of less than 5%.

[0073] However, in comparative examples 1 [base stucco without cement, guar gum and with emulsified silicone oil], 2 [base stucco + cement + guar gum; with non- emulsified silicone oil], 3 [base stucco + cement; with non- emulsified silicone oil] and 4 [base stucco + guar gum; with non-emulsified silicone oil] have demonstrated TWA of greater than 5 and 8%. This clearly demonstrates that base stucco formulation with additives individually or in combination with emulsified silicone oil alone have achieved moisture resistance gypsum boards, whereas base stucco formulation without emulsified silicone oil has not achieved moisture resistance gypsum boards.

[0074] Note that not all of the activities described above in the general description or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities may be performed in addition to those described.

[0075] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims.

[0076] The specification and illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The specification and illustrations are not intended to serve as an exhaustive and comprehensive description of all of the elements and features of apparatus and systems that use the structures or methods described herein. Certain features, that are for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in a sub combination. Further, reference to values stated in ranges includes each and every value within that range. Many other embodiments may be apparent to skilled artisans only after reading this specification. Other embodiments may be used and derived from the disclosure, such that a structural substitution, logical substitution, or another change may be made without departing from the scope of the disclosure. Accordingly, the disclosure is to be regarded as illustrative rather than restrictive.

[0077] The description in combination with the figures is provided to assist in understanding the teachings disclosed herein, is provided to assist in describing the teachings, and should not be interpreted as a limitation on the scope or applicability of the teachings. However, other teachings can certainly be used in this application. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having or any other variation thereof, are intended to cover a non-exclusive inclusion.

[0078] Also, the use of "a" or "an" is employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural, or vice versa, unless it is clear that it is meant otherwise. For example, when a single item is described herein, more than one item may be used in place of a single item. Similarly, where more than one item is described herein, a single item may be substituted for that more than one item.

[0079] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent that certain details regarding specific materials and processing acts are not described, such details may include conventional approaches, which may be found in reference books and other sources within the manufacturing arts.

[0080] While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.

Claims

Claims:1) A gypsum slurry composition comprising, by weight:52 to 60 % of stucco;40 to 45 % of water;0 to 1 % of starch;0.012 to 0.5 % of modifiers; and0.18 to 1.2 % of moisture resistant agent.2) The gypsum slurry composition as claimed in claim 1, wherein the modifiers are selected from the group comprising cement, sodium carboxy methyl cellulose, guar gum or a combination thereof.3) The gypsum slurry composition as claimed in claim 1, wherein the moisture resistant agent is selected from the group comprising emulsified or non-emulsified silicone oil, silanol, hydrolyzed silanes, alkyl / vinyl alkoxysilane, alkyl / vinyl siloxane, alkyl / vinyl silanols, alkyl siliconates or a combination thereof.4) The gypsum slurry composition as claimed in claim 1, wherein the starch is acid modified, chemically modified, pre gelified or a combination thereof with various crop sources including corn, sorghum, wheat, tapioca, rice, pea, potato, and barley.5) The gypsum slurry composition as claimed in claim 1, comprising by weight.52 to 60 % of stucco;40 to 42 % of water;0 to 1 % of starch;0.012 to 0.3 % of cement,0.1 to 0.5% of guar gum, and0.18 to 1.2 % of emulsified silicone oil.6) The gypsum slurry composition as claimed in claim 1, comprising by weight.52 to 60 % of stucco;40 to 42 % of water;0.012 to 0.3 % of cement, and0.18 to 1.2 % of emulsified silicone oil.7) The gypsum slurry composition as claimed in claim 1, comprising by weight52 to 60 % of stucco;40 to 42 % of water;0 to 1 % of starch;0.1 to 0.5 % of guar gum, and0.18 to 1.2 % of emulsified silicone oil.8) The gypsum slurry composition comprising, as claimed in claim 1, comprising by weight: 52 to 60 % of stucco;40 to 42 % of water;0 to 1 % of starch;0.01 to 0.05 % of sodium carboxy methyl cellulose;0.05 to 0.5% of guar gum; and0.18 to 1.2 % of emulsified silicone oil.9) The gypsum slurry composition as claimed in as claimed in claim 1, wherein the moisture resistant agent is an aqueous emulsion of silicone oil.10) The gypsum slurry composition as claimed in claim 1, further comprising a retarder, a heat resistant accelerator (HRA), a fluidizer, and a foaming agent.11) The gypsum slurry composition as claimed in claim 1, wherein the retarder ranging between 0.01 to 0.04 % is selected from the group consisting of amino acids, citric acid, or tartaric acid.12) The gypsum slurry composition as claimed in claim 1, wherein the heat resistant accelerator ranging between 0.2 to 5 % is selected from the group consisting of magnesium, calcium sulfate, ball mill gypsum or potassium sulphate.13) The gypsum slurry composition as claimed in claim 1, wherein the fluidizer ranging between 0.1 to 0.5 % is selected from the group consisting of polynaphthalene sulfonate, ligno sulfonate, poly carboxylate or a combination thereof.14) The gypsum slurry composition as claimed in claim 1, wherein the foaming agent is selected from the group consisting of ethyoxylated surfactant or lauryl surfactants.15) The gypsum slurry composition as claimed in claim 1, wherein the gypsum slurry is casted to form a gypsum composite such as a panel, a board, walls, plinths, slabs, columns, sheets, casts or shafts.16) The gypsum slurry composition as claimed in claim 15, wherein the gypsum composite exhibits moisture resistance.17) The gypsum slurry composition as claimed in claim 15, wherein the gypsum composite has a modulus of rupture ranging from 450 to 550 Newton.18) The gypsum slurry composition as claimed in claim 15, wherein the gypsum composite has a total water absorption of around 4.1%, when cement is in the range of 0.012 to 0.5 % and guar gum is in the range of 0.1 to 0.5 %.19) The gypsum slurry composition as claimed in claim 5, wherein the gypsum slurry is casted to form a gypsum composite such as a panel, board, walls, plinths, slabs, columns, sheets, casts or shafts and wherein the gypsum composite has a total water absorption of less than 4.9%.20) The gypsum slurry composition as claimed in claim 6, wherein the gypsum slurry is casted to form a gypsum composite such as a panel, board, walls, plinths, slabs, columns, sheets, casts or shafts and wherein the gypsum composite has a total water absorption of around 4.6%.21) The gypsum slurry composition as claimed in claim 15, wherein the gypsum composite is preferably a gypsum board.22) The gypsum slurry composition as claimed in claim 21, wherein the gypsum board has a core sandwiched between a pair of liners.23) The gypsum slurry composition as claimed in claim 21, wherein the liners are paper liners or glass mat liners..24) A method of manufacturing a moisture resistant gypsum composite, the method comprising the steps of: a. forming a slurry of the composition as claimed in claim 1, b. forming a layer of said mixture on a first liner; c. disposing a second liner on said layer in opposed relationship with said first liner to form an assembly of said liners with said layer sandwiched there between; d. allowing hydration of the slurry; and e. drying the assembly to form a gypsum composite.25) The method as claimed in claim 24, wherein the moisture resistant agent is provided in the form of an aqueous emulsion aqueous emulsion obtained by mixing water with silicone oil in a ratio silicon / water ranging between 1 : 10 to 1 :50.26) The method as claimed in claim 24, wherein the aqueous emulsion of silicone oil has a droplet size ranging between 12 to 25 pm.

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