A gypsum composition containing uncooked starch having a moderate viscosity, and related methods and products.

Abstract

SOLUTION: To provide a gypsum board, the gypsum board comprising a cured gypsum core disposed between two cover sheets, the core formed from slurry comprising stucco, water, and at least one uncooked starch, the at least one uncooked starch having hot water viscosity of from about 20 Brabender Units to about 300 Brabender Units when the viscosity of the at least one uncooked starch is measured by the HWVA method.EFFECT: According to the present invention, an uncooked starch of desired viscosity can be included in gypsum slurry in order to enhance strength of a gypsum board.SELECTED DRAWING: Figure 1

Description

[Background technology]

[0001] Hardened gypsum is a well-known material used in many products, including panels and other products for building structures and renovations. One such panel (often referred to as gypsum board) is in the form of a hardened gypsum core sandwiched between two cover sheets (e.g., paper-faced board) and is commonly used in drywall construction for interior walls and ceilings of buildings. Often, one or more dense layers, referred to as "skim coat," may be included on either side of the core, usually at the paper-core interface.

[0002] Gypsum (calcium sulfate dihydrate) is naturally occurring and can be mined in the form of rock. It can also exist in a synthetic form (called "singip" in the art) as a byproduct of industrial processes such as flue gas desulfurization. From either source (natural or synthetic), gypsum can be calcined at high temperatures to form stucco (i.e., calcined gypsum, typically in the form of calcium sulfate hemihydrate), which is then rehydrated to form hardened gypsum in the desired shape (e.g., as board). During the production of board, stucco, water, and other raw materials as needed are typically mixed in a pin mixer (the term is used in the art). The slurry is formed and discharged from the mixer onto a moving conveyor that carries a cover sheet (often upstream of the mixer) to which one of the skim coats (if any) has already been applied. The slurry is spread onto paper (the skim coat is optionally included on the paper). With or without a skim coat, another cover sheet is applied over the slurry, and a sandwich structure of the desired thickness is formed using, for example, a forming plate. The mixture is cast and cured to form hardened (i.e., rehydrated) gypsum by the reaction of calcined gypsum with water, forming a matrix of crystalline hydrated gypsum (i.e., calcium sulfate dihydrate). It is the desired hydration of calcined gypsum that enables the formation of an interlocking matrix of hardened gypsum crystals, thereby conferring strength to the gypsum structure in the product. Heat is required to remove any remaining free (i.e., unreacted) water to obtain a dried product (e.g., in a kiln).

[0003] The excess water discharged represents the system's inefficiency. Removing the water requires energy input, and the manufacturing process is delayed to accommodate the drying procedure. However, reducing the amount of water in the system has proven extremely difficult without compromising other critical aspects of the commercial product, including board weight and strength.

[0004] It will be understood that this description of background art is prepared by the inventors to assist the reader and is not intended as a reference to prior art, nor as an indication that any of the problems described are understood in the art. While the principles described may mitigate problems specific to other systems in some respects and embodiments, the scope of the protected innovation is defined not by the ability of the invention as described in the claims to solve any particular problem described herein, but by the appended claims. [Overview of the Initiative]

[0005] The present invention relates, at least in part, to the use of uncooked starch having a desired viscosity in various gypsum-related slurries, boards, methods, and products. According to embodiments of the present invention, uncooked starch of a desired viscosity can be incorporated into a gypsum slurry (along with stucco, water, and other desired additives such as foam, dispersants, polyphosphates, accelerators, retarders, etc.) to increase the strength of the resulting product, for example, gypsum board (in the form used herein, including wall boards with drywalls used for interior wall surfaces, ceilings, partitions, etc.). More specifically, starch has a moderate peak viscosity of about 120 BU to about 1000 BU when its viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, by (i) a hot water viscosity of about 20 BU to about 300 BU according to the hot water viscosity assay (HWVA method) described herein, and / or (ii) a hot water viscosity of about 20 BU to about 300 BU according to the hot water viscosity assay (HWVA method) described herein, and by placing the starch in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min. Without wishing to be bound by any particular theory, it is assumed that uncooked starch having the viscosity described herein has starch molecules leaching out of the granules, thereby giving strength to the gypsum composition obtained from the stucco slurry (e.g., including the linking matrix of hardened gypsum).

[0006] Beneficially, the uncooked starch of the desired viscosity according to embodiments of the present invention is generally heavier, less variable, and exhibits a higher bulk density than pregelatinized starch. In this regard, pregelatinized starch can have greater variability in bulk density, which can lead to inaccurate starch supply to the stucco slurry. In addition, the uncooked starch of the desired viscosity can beneficially enable lower water demand in the gypsum wallboard manufacturing process. For example, the uncooked starch of the desired viscosity can reduce the water demand in the stucco slurry by at least about 10% (e.g., at least about 20%) compared to pregelatinized starch in the same stucco slurry in all other respects.

[0007] Accordingly, in one embodiment, the present invention provides a gypsum board comprising a hardened gypsum core disposed between two cover sheets, the core being formed from a slurry containing stucco, water, and at least one uncooked starch, the at least one uncooked starch having a hot water viscosity of about 20 Brabender units ("BU") to about 300 Brabender units. The viscosity is measured by the HWVA method.

[0008] In another embodiment, the present invention provides a stucco slurry (sometimes referred to as "stucco slurry") comprising stucco, water, and at least one uncooked starch, the at least one uncooked starch having a hot water viscosity of about 20 Brabender units to about 300 Brabender units when its viscosity is measured by the HWVA method.

[0009] In another embodiment, the present invention provides a method for preparing gypsum board. The method comprises at least water, stucco, and at least one uncooked starch, the at least one uncooked starch having a hot water viscosity of about 20 Brabender units to about 300 Brabender units when its viscosity is measured by the HWVA method. The slurry is placed between a first cover sheet and a second cover sheet to form a wet assembly. The wet assembly is cut into boards, and the boards are dried.

[0010] In another embodiment, the present invention provides an acoustic panel comprising a fiber-containing acoustic component and at least one uncooked starch, wherein the at least one uncooked starch has a hot water viscosity of about 20 Brabender units to about 300 Brabender units when its viscosity is measured by the HWVA method. The panel preferably has a noise reduction coefficient of at least about 0.5 according to ASTM C 423-02.

[0011] In another embodiment, the present invention provides a gypsum board comprising a hardened gypsum core disposed between two cover sheets, the core being formed from a slurry containing stucco, water, and at least one uncooked starch, the at least one uncooked starch having a hot water viscosity of about 120 Brabender units ("BU") to about 1000 Brabender units. The viscosity is measured by placing the starch in a slurry containing water with a starch concentration of 15% solids, heating the starch from 25°C to 95°C at a rate of 3°C / min, holding the slurry at 95°C for 10 minutes, and cooling the starch to 50°C at a rate of -3°C / min, using a Viscograph E instrument set to 75 rpm and 700 cmg. The maximum viscosity is recorded as the peak viscosity.

[0012] In another embodiment, the present invention provides another gypsum board comprising a hardened gypsum core disposed between two cover sheets, the core being formed from a slurry containing stucco, water, and at least one uncooked starch, the at least one uncooked starch having a cold water viscosity of about 1 cmpoise to about 50 cmpoise with 10% solids in water when measured at 25°C by Brookfield viscometer method.

[0013] In another embodiment, the present invention provides a stucco slurry (sometimes referred to as "stucco slurry") comprising stucco, water, and at least one uncooked starch, the at least one uncooked starch having a peak viscosity of about 120 Brabender units to about 1000 Brabender units when the viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, where the starch is placed in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min.

[0014] In another embodiment, the present invention provides another stucco slurry comprising stucco, water, and at least one uncooked starch, the at least one uncooked starch having a cold water viscosity of about 1 cmpoise to about 50 cmpoise with 10% solids in water, when measured at 25°C by Brookfield viscometer.

[0015] In another embodiment, the present invention provides a method for preparing gypsum board. The method comprises mixing at least water, stucco, and at least one uncooked starch, the at least one uncooked starch having a peak viscosity of about 120 Brabender units to about 1000 Brabender units when the viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, where the starch is placed in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min. The slurry is placed between a first cover sheet and a second cover sheet to form a wet assembly. The wet assembly is cut into boards, and the boards are dried.

[0016] In another embodiment, the present invention provides a method for preparing gypsum board. The method comprises mixing at least water, stucco, and at least one uncooked starch, the at least one uncooked starch having a cold water viscosity of about 1 cmpoise to about 50 cmpoise with 10% solids in water, when the viscosity is measured at 25°C by Brookfield viscometer. The slurry is placed between a first cover sheet and a second cover sheet to form a wet assembly. The wet assembly is cut into boards, and the boards are dried.

[0017] In another embodiment, the present invention provides an acoustic panel comprising an acoustic component including fibers and at least one uncooked starch, wherein the at least one uncooked starch has a peak viscosity of about 120 Brabender units to about 1000 Brabender units when its viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, where the starch is placed in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min. The panel preferably has a noise reduction factor of at least about 0.5 according to ASTM C 423-02.

[0018] In another embodiment, the present invention provides an acoustic panel comprising a fiber-containing acoustic component and at least one uncooked starch, wherein the at least one uncooked starch has a cold water viscosity of about 1 cmpoise to about 50 cmpoise with 10% solids in water, when measured at 25°C by the Brookfield viscometer method. The panel preferably has a noise reduction coefficient of at least about 0.5 according to ASTM C 423-02. [Brief explanation of the drawing]

[0019] [Figure 1] As described in Example 1, this is a Brabender amylogram of a 15% starch slurry in water according to an embodiment of the present invention, illustrating the viscosity of the starch, with the X-axis representing time and the Y-axis superimposed on viscosity (primary Y-axis on the left) and temperature (secondary Y-axis on the right). [Figure 2] As described in Example 2, this is a bar graph of the wet compressive strength of a hardened gypsum composition formed from a slurry containing uncooked acid-modified corn starch B, compared to a hardened gypsum composition formed from a slurry containing pregelatinized corn starch A and B, respectively, at intervals of 3, 5, 7, and 10 minutes. [Figure 3]A graph of the drying rate (weight vs. time) at 450°F of boards formed from slurries containing uncooked starch, compared to boards formed from slurries containing gelatinized corn starch as described in Example 3. [Figure 4] A Brabender amylogram of a 15% starch slurry in water, according to an embodiment of the present invention, illustrating the hot water viscosity assay (HWVA) of the starch, where the x-axis is time and the y-axis superimposes viscosity (left main y-axis) and temperature (right secondary y-axis). [Figure 5] A Brabender amylogram of a 15% starch slurry in water, according to an embodiment of the present invention, illustrating the hot water viscosity assays (HWVA) of acid-modified tapioca, wheat, and potato starches, where the x-axis is time and the y-axis superimposes viscosity (left main y-axis) and temperature (right secondary y-axis). [Figure 6] An illustration showing a board product with the cover sheet pulled back to show a defect (swelling) in the board core, as discussed in Example 9 herein.

MODE FOR CARRYING OUT THE INVENTION

[0020] Embodiments of the present invention presuppose, at least in part, the inclusion of uncooked starch in a stucco slurry (sometimes referred to as “gypsum slurry”) to enhance the strength of the resulting board having one or more gypsum layers formed from the gypsum slurry. In one embodiment, the uncooked starch has a hot water viscosity of about 20 Brabender units to about 300 Brabender units according to the hot water viscosity assay (HWVA) method described herein. In additional or alternative embodiments, the uncooked starch is characterized as having a “moderate” peak viscosity (e.g., about 120 Brabender units to about 1000 Brabender units as measured according to the method described herein). While the viscosity properties are determined when the starch is placed under specific conditions according to the viscosity measurement methodology described herein, it will be understood that it is not necessary to add uncooked starch to the slurry under these conditions. The conventional use of non-migratory uncooked starch has been undesirable in gypsum slurry because, despite the use of small-chain migratory starch to strengthen the core bond of the paper, the core strength was not significantly improved. The embodiments of the present invention unexpectedly overcome this drawback.

[0021] Surprisingly, it has been found that starch having the desired hot water viscosity is effective for use in gypsum slurries to enhance the strength of the resulting board products. As described herein, selecting a medium hot water viscosity for use in gypsum (stucco) slurries, i.e., from about 20 BU to about 300 BU according to the HWVA method, surprisingly results in the desired molecular size and good resulting strength of the gypsum layer of the final product. In this regard, it has been unexpectedly discovered that the hot water viscosity correlates with the desired molecular size of various starches, including, for example, tapioca, wheat, potato, corn, and other starches. In some embodiments where corn starch is used, the molecular size can be correlated using the peak viscosity discussed herein. In this regard, it has been found that the peak viscosity effectively correlates with the molecular size of corn starch and thus the board strength. Without wishing to be bound by any particular theory, surprisingly, for any one type of starch, the peak viscosity correlates with the molecular weight. However, this correlation may not exist between two different types of starches. For example, in the case of wheat starch, the molecular size may be larger when the peak viscosity is lower than that of corn starch with a higher peak viscosity. Thus, surprisingly and unexpectedly, it has been found that the hot water viscosity has a better correlation with the molecular size of various starches overall. However, when evaluating a single starch as needed, the peak viscosity described herein can be used.

[0022] The inclusion of uncooked starch according to the present invention has been found to provide benefits, for example, consistent in several embodiments, with respect to starch efficiency (e.g., enabling the use of less starch), improved product strength, and water demand. According to embodiments of the present invention, the benefits, including those with respect to starch efficiency, water demand, and / or strength, represent significant improvements and advancements compared to ungelatinized starch (uncooked) having a hot water viscosity of less than 20 BU or greater than 300 BU, and / or a peak viscosity of less than 120 BU or greater than 1000 BU. In addition, in some embodiments, surprisingly and unexpectedly, the drying rate of slurries containing uncooked starch has been found to be similar to that of slurries containing pregelatinized starch. This is particularly surprising because uncooked starch needs to absorb extra thermal energy to gelatinize the starch. These findings result in a number of advantages, including, but are not limited to, reduced raw material costs, improved manufacturing efficiency, and improved product strength, enabling, for example, lighter products with sufficient strength characteristics.

[0023] The uncooked starch according to the present invention can be included in a stucco slurry for forming a gypsum layer on a board in embodiments of the present invention and can be used together with a gypsum board layer (e.g., a core) having a skim coat on one side or both main sides of the core, optionally. In some embodiments, a board core formed from a stucco slurry containing uncooked starch may have a concentrated layer on one side or both main sides of the core, as described in concurrently pending U.S. Patent Applications 15 / 186,176, 15 / 186,212, 15 / 186,232, and 15 / 186,257 by the same applicant (these concentrated layer arrangements are incorporated herein by reference).

[0024] Starch is classified as a carbohydrate and contains two types of polysaccharides, namely linear amylose and branched amylopectin. Starch granules are semi-crystalline when observed, for example, under polarized light, and are insoluble in water at room temperature.

[0025] The starch is uncooked according to embodiments of the present invention. Uncooked starch is characterized by being insoluble in cold water and having a semi-crystalline structure. Typically, uncooked starch is obtained by wet grinding and is not denatured by heating wet starch as in the case of cooked starch. Note that the uncooked starch according to the present invention is different from cooked starch, which is characterized by being soluble in cold water and having an amorphous structure. Cooked starch is prepared by heating wet starch and can be prepared, for example, by extrusion techniques. See, for example, concurrently pending U.S. Patent Applications 14 / 494,547, 14 / 044,582, and 13 / 835,002. Cooked starch is sometimes referred to as gelatinized starch because the crystalline structure of the starch granules melts, resulting in starch gelatinization characterized by the disappearance of birefringence under a polarized light microscope.

[0026] Preferred uncooked starch differs from acid-modified mobile starch, which does not provide the same strength properties and is used in the art for enhancing paper-core bonding when it migrates to the paper-core interface due to its small chain length. Acid-modified mobile starch has a minimum molecular weight, typically less than about 6,000 daltons. Preferred uncooked starch according to embodiments of the present invention has a higher molecular weight than mobile starch, for example, at least about 15,000 daltons. The average molecular weight is indicated by the hot water viscosity. Preferred uncooked starch has a hot water viscosity of about 20 BU to about 300 BU.

[0027] In some embodiments, uncooked starch has a higher bulk density with less variability than gelatinized starch. This is surprisingly useful, for example, because a consistent density allows volumetric feeders to add starch more accurately and consistently. For example, in some embodiments, the bulk density may be about 35 pcf to 50 pcf, about 35 pcf to 45 pcf, about 37 pcf to 50 pcf, about 37 pcf to 45 pcf, about 40 pcf to 50 pcf, about 40 pcf to 47 pcf, about 40 pcf to 45 pcf, and about 41 pcf to 45 pcf.

[0028] In contrast to the uncooked starch according to the present invention, gelatinization is a process in which starch is placed in water and heated ("cooked") so that the crystalline structure of the starch granules melts, the starch molecules dissolve in water, and a good dispersion is obtained. When converting starch granules to a gelatinized form, it is known that, since starch granules are insoluble in water, initially the starch granules give little viscosity in water. As the temperature rises, the starch granules swell, and the crystalline structure melts at the gelatinization temperature. Peak viscosity is achieved when the starch granules have maximal swelling. Further heating breaks down the starch granules, dissolves the starch molecules in water, and the viscosity decreases rapidly. After cooling, the starch molecules reassociate to form a 3D gel structure, and the viscosity increases due to the gel structure.

[0029] The uncooked starch according to embodiments of the present invention is typically in a natural granular form. According to some embodiments of the present invention, the granular uncooked form may undergo at least some degree of gelatinization during the manufacture of gypsum wallboard (for example, in the oven).

[0030] To achieve the desired viscosity according to embodiments of the present invention, uncooked starch molecules can be acid-modified, for example, by hydrolyzing the glycosidic bonds between glucose units to achieve the desired molecular weight. For example, such modification may include acid modification, enzymatic modification, and / or other methods. The most commonly used starch-converting enzyme is α-amylase. The enzymatic hydrolysis reaction can be stopped by adjusting the pH or by heating. To prepare acid-modified starch, it will be understood that an aqueous suspension of unmodified starch can be treated with a small amount of acid, for example, a strong acid such as hydrochloric acid, sulfuric acid, nitric acid, or hydrofluoric acid. The degree of depolymerization can be changed by adjusting the reaction time. For example, once a suitable fluidity is achieved, for example, as determined by laboratory control in the process, a weak alkali is introduced to neutralize the acid and stop the hydrolysis. Thus, acid-modified starch can be prepared with a variety of fluidities. Furthermore, acid-modified starch can be used directly after neutralization without further purification, or it can be purified to remove salts. The end-use of acid-modified starch may determine the desirability of purification. For example, a starch composition modified with sulfuric acid and neutralized with calcium hydroxide may contain sulfate and calcium ions that can be added to stucco and aqueous slurry. Since stucco already contains sulfate and calcium ions, it may not be necessary to purify the sulfur-modified starch before adding it to the slurry. Therefore, considerations for determining the desirability of purification include, for example, the identity of the acid and alkali-base, and whether it is desirable to add ions other than sulfate or calcium ions to the slurry.

[0031] The uncooked starch exhibiting the viscosity properties according to the present invention offers significant advantages in the strength of products (e.g., wallboards). Because the starch contains glucose monomers with three hydroxyl groups, it provides numerous sites for hydrogen bonding to gypsum crystals. While we do not wish to be bound by any particular theory, it is believed that the molecular diameter of the uncooked starch exhibiting the hydrothermal viscosity properties allows for optimal mobility of the starch molecules, aligning them with the gypsum crystals to promote good bonding of the starch to the gypsum crystals, thereby strengthening the resulting crystalline gypsum matrix, for example, via hydrogen bonding. Uncooked starch with viscosities outside the desired hydrothermal viscosity range, either having longer chain lengths and higher molecular weights (excessively high viscosity) or shorter chain lengths and lower molecular weights (excessively low viscosity), does not offer the same combination of benefits. Therefore, optimal bonding between gypsum crystals and uncooked starch molecules with the desired hydrothermal viscosity effectively improves the strength of the crystalline gypsum matrix, requiring less starch to promote its strength compared to conventional starches. The presence of uncooked starch, due to the surprisingly high fluidity of the stucco slurry containing it, unexpectedly and remarkably reduces the water demand for the gypsum slurry.

[0032] The uncooked starch added to the gypsum (stucco) slurry preferably has a moderate molecular weight, indicated by a hot water viscosity of about 20 BU to about 300 BU. The moderate hot water viscosity of the uncooked starch is determined according to the HWVA method described herein. The moderate peak viscosity is measured by the following method: The Brabender peak viscosity is measured using a Viscograph E (CWBrabender) set to 75 rpm, 700 cmg. The starch slurry has a concentration of 15% in water. The starch slurry is heated from 25°C to 95°C at a rate of 3°C / min. It is then held at 95°C for 10 minutes until it cools to 50°C at a rate of -3°C / min. The peak viscosity is determined as the maximum viscosity.

[0033] The hot water viscosity of uncooked starch is generally above 20 BU, ranging from approximately 20 BU to approximately 300 BU, for example, approximately 20 BU to approximately 280 BU, approximately 20 BU to approximately 250 BU, approximately 20 BU to approximately 200 BU, approximately 20 BU to approximately 175 BU, approximately 20 BU to approximately 150 BU, approximately 20 BU to approximately 125 BU, approximately 20 BU to approximately 100 BU, approximately 20 BU to approximately 75 BU, approximately 20 BU to approximately 50 BU, approximately 30 BU to approximately 300 BU, approximately 30 BU to approximately 280 BU, approximately 30 BU to approximately 250 BU, approximately 30 BU to approximately 150 BU, approximately 30 BU to approximately 125 BU, approximately 30 BU to approximately 100 BU, approximately 30 BU to approximately 75 BU, approximately 30BU to approximately 50BU, approximately 50BU to approximately 300BU, approximately 50BU to approximately 280BU, approximately 50BU to approximately 250BU, approximately 50BU to approximately 200BU, approximately 50BU to approximately 150BU, approximately 50BU to approximately 100BU, approximately 100BU to approximately 300BU, approximately 100BU to approximately 280BU, approximately 100BU to approximately 250BU, approximately 100BU to approximately 200BU, approximately 100BU to approximately 150BU, approximately 150BU to approximately 300BU, approximately 150BU to approximately 280BU, approximately 150BU to approximately 250BU, approximately 150BU to approximately 200BU, approximately 200BU to approximately 300BU, or approximately 200BU to approximately 280BU.

[0034] In some embodiments, the starch has a peak viscosity of at least about 100 Brabender units, ranging from about 120 Brabender units to about 1000 Brabender units, for example, about 120 Brabender units to about 875 Brabender units, about 120 Brabender units to about 850 Brabender units, about 120 Brabender units to about 700 Brabender units, about 120 Brabender units to about 550 Brabender units, about 120 Brabender units to about 460 Brabender units, about 120 Brabender units to about 300 Brabender units, about 150 Brabender units to about 1000 Brabender units, about 150 Brabender units to about 850 Brabender units, about 150 Brabender units to about 750 Brabender units, about 150 Brabender units to about 500 Brabender units, and about 150 Brabender units. The units can range from approximately 300 lavender units, 250 to 850 lavender units, 250 to 600 lavender units, 250 to 500 lavender units, 300 to 875 lavender units, 350 to 800 lavender units, 350 to 750 lavender units, 400 to 1000 lavender units, 400 to 875 lavender units, 400 to 700 lavender units, 500 to 850 lavender units, 500 to 700 lavender units, 600 to 1000 lavender units, and so on.

[0035] The properties of uncooked starch include having low viscosity in cold water (i.e., at a temperature of 77°F (25°C)), while, in contrast, the properties of gelatinized starch include having instantaneous high viscosity in cold water. The uncooked starch according to this disclosure preferably has a cold water viscosity of less than about 50 centimeters in cold water, for example, about 40 centimeters or less, about 30 centimeters or less, about 20 centimeters or less, or about 10 centimeters or less (for example, about 1 centimeter to about 50 centimeters, about 1 centimeter to about 40 centimeters, about 1 centimeter to about 30 centimeters, about 1 centimeter to about 20 centimeters, about 1 centimeter to about 10 centimeters, about 5 centimeters to about 50 centimeters, about 5 centimeters to about 30 centimeters, about 5 centimeters to about 20 centimeters, about 3 centimeters to about 15 centimeters, about 3 centimeters to about 10 centimeters, about 3 centimeters to about 7 centimeters, etc.). Cold water viscosity is measured according to the Brookfield viscometer method using the following test profile: Add 20g of starch (dry) to 180g of water in a Waring blender (Model 31BL92) while mixing at low speed for 15 seconds. Transfer 200g of the starch solution to a measuring cup. Select paddle #2 and 60 RPM. Use the viscosity value measured at 20 seconds as the viscosity of the starch.

[0036] The uncooked starch according to embodiments of the present invention is, fortunately, easily mixed with water. This is due to its low viscosity in water. In contrast, pregelatinized starch can undesirably cause a "fish eye" condition, characterized by the formation of one or more large lumps in the aqueous solution during mixing. While we do not wish to be bound by any particular theory, it is thought that during the mixing process, the large lumps are caused by the rapid water absorption of the starch, forming a viscous film on the surface of the lumps that prevents water from penetrating them. Uncooked starch is thought to avoid the fish eye condition due to its cold water insolubility, which results in the separation of starch granules.

[0037] Examples of suitable uncooked starches include, but are not limited to, one or more of the following: natural cereal starches, natural root starches, natural tuber starches, and / or chemically modified starches, along with certain representative examples including, for example, corn starch (usually waxy and / or high amylose), type A wheat starch, type B wheat starch, pea starch, potato starch, tapioca, substituted starches having substituents (e.g., acetate, phosphate, hydroxyethyl, hydroxypropyl) on the starch hydroxyl group, or any combination thereof.

[0038] Stucco slurry is typically formed in a pinned or pinless main mixer during the manufacturing process. However, the method of introducing the raw materials into the mixer may vary. For example, various combinations of components may be pre-mixed before being added to the mixer, such as one or more dry materials and / or one or more wet materials being pre-mixed. It will be understood that the phrase "add to slurry" as used herein means that the raw materials can be pre-mixed in any preferred manner before being added to the mixer in which the plaster (stucco) slurry is formed as described herein.

[0039] The uncooked starch with desired hot water and / or peak viscosity characteristics, which is a feature of the present invention, can be included in the stucco slurry in a wet or dry form. In the wet form, the starch can be included at any suitable concentration and can be pre-mixed with other wet ingredients.

[0040] As used herein, "uncooked" means that the degree of gelatinization of the starch before it is included in the stucco slurry is less than about 5% (e.g., less than about 3%, or less than about 1%, such as zero). In some embodiments, the uncooked starch may be partially or completely gelatinized when exposed to high temperatures in a gypsum wallboard manufacturing process, for example, in a drying procedure oven to remove excess moisture.

[0041] Surprisingly and unexpectedly, the hot water and / or uncooked starch having peak viscosity characteristics according to embodiments of the present invention can be included in the slurry in relatively small amounts (solids / solids basis) and can further achieve a significant improvement in the strength of the board. Therefore, in preferred embodiments of the present invention, the hot water and / or uncooked starch having peak viscosity characteristics is included in the stucco slurry in amounts of about 5% by weight of the stucco (e.g., about 1% to about 4%), such as about 2% by weight of the stucco or less. For example, the uncooked starch may be included in amounts such as about 0.5% to about 5% by weight of the stucco, about 0.5% to about 4% by weight of the stucco, about 1% to about 3% by weight, about 1% to about 2% by weight, and about 1.5% to about 2% by weight of the stucco.

[0042] Uncooked starch having desired hot water and / or peak viscosity characteristics can be combined with other starches according to embodiments of the present invention. For example, combining uncooked starch exhibiting desired viscosity characteristics with other starches can enhance both core strength and paper-core bonding, especially when increased water demand is permissible. Thus, in some embodiments of the present invention, the stucco slurry may comprise one or more uncooked starches having hot water and / or peak viscosity characteristics, as well as one or more other types of starches. Other starches may include, for example, pregelatinized starch. Examples include pregelatinized maize starch having viscosities of about 773 centipoise or 100 centipoise, respectively, according to the VMA method described, for example, in U.S. Patent Application Publication No. 2012 / 0113124. Other starches may also be in the form of non-gelatinized starches, such as mobile acid-modified starches, and ungelatinized alkylated starches, such as ethylated starches, having a hot water viscosity of less than about 20 BU or greater than 300 BU, or a peak viscosity of less than 120 Brabender units or greater than 1000 Brabender units. The starch combinations may be pre-mixed before being added to the gypsum slurry (e.g., optionally in a dry mixture with other components such as stucco, or in a wet mixture with other wet raw materials), or they may be added to the gypsum slurry one at a time, or any variation thereof. Any suitable proportion of uncooked starches and other starches having the desired hot water and / or peak viscosity characteristics may be included. The content of uncooked starch having the desired hot water and / or peak viscosity characteristics as a percentage of the total starch content added to the stucco slurry may be, for example, at least about 10% by weight, for example, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 99%, at least about 100%, or any range in between.In exemplary embodiments, the ratio of uncooked starch to other starch having the desired hot water and / or peak viscosity characteristics may be about 25:75, about 30:70, about 35:65, about 50:50, about 65:35, about 70:30, about 75:25, etc.

[0043] In addition to the starch components, the slurry is formulated to include water, stucco, a foaming agent (sometimes simply called "foam"), and other additives as needed. The stucco may be in the form of calcium sulfate alpha hemihydrate and / or calcium sulfate beta hemihydrate. In some embodiments, the beta form is preferred. The stucco may be fibrous or non-fibrous. A foaming agent may be included to form an air void distribution within the continuous crystalline matrix of the hardened gypsum. In some embodiments, the foaming agent includes an unstable component in the main weight portion and a stable component in the smaller weight portion (e.g., when unstable and stable / unstable blends are combined). The weight ratio of the unstable component to the stable component is effective in forming an air void distribution within the hardened gypsum core. See, for example, U.S. Patents 5,643,510, 6,342,284, and 6,632,550. It has been found that suitable void distribution and wall thickness (independently) can be particularly effective in increasing strength in lower-density boards (e.g., less than approximately 35 pcf). See, for example, US2007 / 0048490 and US2008 / 0090068. In general, evaporative water voids with a diameter of approximately 5 μm or less also contribute to the total void distribution along with the aforementioned air (bubble) voids. In some embodiments, the volume ratio of gaps with a pore diameter greater than approximately 5 microns to gaps with a pore diameter of approximately 5 microns or less is approximately 0.5:1 to approximately 9:1, for example, approximately 0.7:1 to approximately 9:1, approximately 0.8:1 to approximately 9:1, approximately 1.4:1 to approximately 9:1, approximately 1.8:1 to approximately 9:1, approximately 2.3:1 to approximately 9:1, approximately 0.7:1 to approximately 6:1, approximately 1.4:1 to approximately 6:1, approximately 1.8:1 to approximately 6:1, approximately 0.7:1 to approximately 4:1, approximately 1.4:1 to approximately 4:1, approximately 1.8:1 to approximately 4:1, approximately 0.5:1 to approximately 2.3:1, approximately 0.7:1 to approximately 2.3:1, approximately 0.8:1 to approximately 2.3:1, approximately 1.4:1 to approximately 2.3:1, approximately 1.8:1 to approximately 2.3:1, etc.In some embodiments, the foaming agent is present in the slurry in amounts less than about 0.5% by weight of the stucco, for example, about 0.01% to about 0.5%, about 0.01% to about 0.4%, about 0.01% to about 0.3%, about 0.01% to about 0.2%, about 0.01% to about 0.1%, 0.02% to about 0.4%, about 0.02% to about 0.3%, about 0.02% to about 0.2%, etc.

[0044] Additives such as accelerators (e.g., wet gypsum accelerators, heat resistance accelerators, and climate stabilization accelerators) and retarders are well known and may be included as needed. See, for example, U.S. Patent Nos. 3,573,947 and 6,409,825.

[0045] In some embodiments, the hydration rate is adjusted to avoid certain defects in the board manufacturing process, including blistering and delamination of the core-cover sheet bond, before draining excess water from the kiln. The hydration rate can be measured by the time required to reach 50% hydration (simply referred to as "50% hydration") in a few minutes. According to a preferred embodiment, it has been found that a desired 50% hydration time is selected to avoid defects such as blistering and delamination, by effectively cutting the ribbon of cured stucco slurry into the desired segments with a knife before placing the segments into the kiln, and then further processing to form boards of its final dimensions. Surprisingly and unexpectedly, by adjusting the hydration rate (e.g., by adjusting the amounts of accelerators and / or retarders in the stucco slurry), the occurrence of board defects such as blistering, delamination, delamination, and / or poor bonding between the gypsum layer and cover sheet of the board can be reduced or avoided. While we do not wish to be bound by any particular theory, uncooked starch does not contain as many contaminants as gelatinized starch. Because uncooked starch has a low contaminant content, it has a low delaying effect on the stucco curing process during board preparation. While we do not wish to be bound by any particular theory, if the hydration rate is too fast, the board is prone to certain defects such as delamination and blistering. Since uncooked starch has less of a delaying effect than gelatinized starch, it has been found that when uncooked starch is used in stucco slurries, the amount of accelerator used in the stucco slurry needs to be reduced.

[0046] As will be understood by those skilled in the art, the exact amount of accelerator varies between different manufacturing conditions due to differences in environmental conditions, gypsum quality and purity, etc. The accelerator content in the stucco slurry can be reduced to any suitable amount depending on the circumstances of the particular facility. In some embodiments, the amount of accelerator in a stucco slurry containing uncooked starch can be reduced by about 40% or less compared to the amount of accelerator used in a stucco slurry containing pregelatinized starch but otherwise the same. For example, the amount of accelerator in a stucco slurry containing uncooked starch (compared to the same slurry using pregelatinized starch instead of uncooked starch) is approximately 1% to 40%, for example, approximately 1% to 35%, approximately 1% to 30%, approximately 1% to 25%, approximately 1% to 23%, approximately 1% to 20%, approximately 1% to 15%, approximately 5% to 40%, approximately 5% to 35%, approximately 5% to 30%, approximately 5% to 25%, approximately 5% to 23%, and approximately 5%. It can be reduced by approximately 20%, 5% to 15%, 10% to 40%, 10% to 35%, 10% to 30%, 10% to 25%, 10% to 23%, 10% to 20%, 10% to 15%, 15% to 40%, 15% to 35%, 15% to 30%, 15% to 25%, 15% to 20%, 20% to 40%, 20% to 35%, 20% to 30%, and 20% to 25%.

[0047] As will be understood by those skilled in the art, the amount of accelerator and / or retarder used to achieve such a desired hydration rate will vary depending on different conditions of different manufacturing conditions (e.g., purity and quality of gypsum, which may differ in different manufacturing or research facilities). In some embodiments, the accelerator (e.g., a heat-resistant accelerator) may be included in the stucco slurry in an amount of about 0.5% to about 4% by weight of the stucco, for example, about 1% to about 2% by weight.

[0048] In some embodiments that include accelerators and / or retarders, the accelerators and / or retarders may be present in the gypsum slurry in amounts, on a solids basis, for example, about 0% to about 5% by weight of the stucco (e.g., about 0.1% to about 3% by weight) and for example, about 0% to about 1% by weight of the stucco (e.g., about 0.01% to about 0.08% by weight). Other additives may be included as needed, for example, to impart strength to enable lighter products with sufficient strength, to avoid permanent deformation, to promote green strength when products are set on a conveyor moving down a production line, to promote fire resistance, to promote water resistance, etc.

[0049] For example, in some embodiments, the slurry may optionally contain at least one dispersant to enhance fluidity. Like starch and other raw materials, the dispersant may be present in the core slurry in a dry form along with other dry raw materials and / or in a liquid form along with other liquid raw materials. Examples of dispersants include naphthalene sulfonates such as polynaphthalene sulfonic acid and its salts (polynaphthalene sulfonates) and derivatives, which are condensation products of naphthalene sulfonic acid and formaldehyde; and polycarboxylate dispersants such as polycarboxylic acid ethers, e.g., PCE211, PCE111, 1641, 1641F, or PCE 2641 type dispersants, e.g., MELFLUX 2641F, MELFLUX 2651F, MELFLUX 1641F, MELFLUX 2500L dispersant (BASF), and COATEX Ethacryl M available from Coatex, Inc.; and / or lignosulfonates or sulfonated lignin. Lignosulfonates are water-soluble anionic polymer electrolytes that are byproducts of wood pulp production using sulfite pulping. An example of lignin useful in carrying out the principles of the embodiments of this disclosure is Marasperse C-21, available from Reed Lignin Inc.

[0050] Low molecular weight dispersants are generally preferred. Low molecular weight naphthalene sulfonate dispersants are preferred because they tend to have higher viscosity and lower water requirements than dispersants with higher molecular weights. Therefore, molecular weights of about 3,000 to about 10,000 (e.g., about 8,000 to about 10,000) are preferred. As another example, with respect to PCE211 type dispersants, in some embodiments the molecular weight may be about 20,000 to about 60,000, which exhibits less delay than dispersants having molecular weights greater than 60,000.

[0051] An example of a naphthalene sulfonate is DILOFLO, available from GEO Specialty Chemicals. DILOFLO is a 45% naphthalene sulfonate solution in water, but other aqueous solutions with solid content ranging from approximately 35% to approximately 55% by weight are also readily available. Naphthalene sulfonates can be used in dry solid or powder form, such as LOMAR D, available from GEO Specialty Chemicals. Another exemplary naphthalene sulfonate is DAXAD, available from Hampshire Chemical Corp.

[0052] If present, the dispersant may be included in any suitable (solids / solids) amount, such as about 0.1% to 5% by weight of the stucco, for example, about 0.1% to 4% by weight, about 0.1% to 3% by weight, about 0.2% to 3% by weight, about 0.5% to 3% by weight, about 0.5% to 2.5% by weight, about 0.5% to 2% by weight, or about 0.5% to 1.5% by weight.

[0053] One or more phosphate-containing compounds may optionally be included in the slurry, as necessary. For example, in some embodiments, effective phosphate-containing components may include water-soluble components, which may be in the form of ions, salts, or acids, i.e., condensed phosphoric acids, each of which may be two or more phosphate units; salts or ions of condensed phosphates (each containing two or more phosphate units); and monobasic salts or monovalent ions of orthophosphates, as well as salts of water-soluble cyclic polyphosphates. See, for example, U.S. Pat. Nos. 6,342,284, 6,632,550, 6,815,049, and 6,822,033.

[0054] The phosphate composition, the phosphate-containing components according to some embodiments of the present invention, can enhance green strength, resistance to permanent deformation (e.g., deflection), dimensional stability, etc. For example, trimetaphosphate compounds including sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate can be used. Sodium trimetaphosphate (STMP) is preferred. For example, sodium tetrametaphosphate, having about 6 to about 27 repeating phosphate units, with the molecular formula Na n+2 P n O 3n+1 (where n = 6 - 27), sodium hexametaphosphate having the molecular formula K4P2O7, dipotassium trisodium tripolyphosphate having the molecular formula Na3K2P3O 10 , sodium tripolyphosphate having the molecular formula Na5P3O 10 , sodium pyrophosphate having the molecular formula Na4P2O7, aluminum trimetaphosphate having the molecular formula Al(PO3)3, acidic sodium pyrophosphate having the molecular formula Na2H2P2O7, ammonium polyphosphate having 1,000 - 3,000 repeating phosphate units, with the molecular formula (NH4) n+2 P n O 3n+1 (where n = 1,000 - 3,000), or having two or more repeating phosphate units, with the molecular formula H n+2 P n O 3n+1Other phosphates containing polyphosphate having (wherein n is 2 or more) may be preferred.

[0055] Phosphates may be included in dry or aqueous form (e.g., a phosphate solution of about 5% to about 20%, e.g., a 10% solution). If included, the phosphate may be in any preferred amount (on a solids / solids basis) such as about 0.01% to about 0.5% by weight of the stucco, e.g., about 0.03% to about 0.4% by weight, about 0.1% to about 0.3% by weight, or about 0.12% to about 0.4% by weight of the stucco.

[0056] For example, additives suitable for refractory and / or water-resistant products may optionally be included, such as siloxane (water-resistant); fibers; heat sink additives such as aluminum trihydrate (ATH) and magnesium hydroxide, and / or high-expansion particles (e.g., capable of expanding to more than 300% of their original volume when heated at 1560°F for about 1 hour). For a description of these and other raw materials, see, for example, concurrently pending, generally assigned U.S. Patent Application No. 13 / 400,010 (filed February 17, 2012). In some embodiments, high-expansion vermiculite is included, but other refractory materials may also be included. A board of any fire-resistant product according to this disclosure may have an thermal insulation index (TI) of about 17 minutes or more, for example, about 20 minutes or more, about 30 minutes or more, about 45 minutes or more, about 60 minutes or more, and / or a high-temperature shrinkage of less than about 10% in the xy direction (at a temperature of about 1560°F (850°C)), and an expansion of at least about 2% in the z direction, for example, at least about 5%, at least about 10%, at least about 15%, or at least about 20%. Fire-resistant or water-resistant additives may be included in any preferred amount as desired, for example, depending on the fire grade. For example, if included, the amount of fire-resistant or water-resistant additives may be about 0.5% to about 10% by weight of the stucco, for example, about 1% to about 10% by weight of the stucco, about 1% to about 8% by weight, about 2% to about 10% by weight, about 2% to about 8% by weight, etc.

[0057] Siloxanes, if present, are preferably added in emulsion form. The slurry is then molded and dried under conditions that promote the polymerization of siloxanes to form a highly crosslinked silicone resin. Catalysts that promote the polymerization of siloxanes to form a highly crosslinked silicone resin may be added to the gypsum slurry. In some embodiments, a solvent-free methylhydrogen siloxane fluid, marketed by Wacker-Chemie GmbH (Munich, Germany) under the name SILRES BS 94, can be used as the siloxane. This product is a siloxane fluid that does not contain water or solvents. In some embodiments, it is intended that about 0.3% to about 1.0% of BS 94 siloxane may be used, based on the weight of the dry raw materials. For example, in some embodiments, it is preferable to use about 0.4% to about 0.8% of siloxane, based on the dry stucco weight.

[0058] Slurry formulations can be prepared with any suitable water / stucco ratio, e.g., about 0.4 to about 1.3. However, since the uncooked starch having the hot water viscosity and / or peak viscosity characteristics of the present invention reduces the amount of water that needs to be added to the slurry to adjust the starch compared to other starches, the slurry can be formulated in some embodiments with lower water / stucco ratios than conventional for other starch-containing gypsum slurries, particularly at low weight / density. For example, in some embodiments, the water / stucco ratio may be about 0.4 to about 1.2, about 0.4 to about 1.1, about 0.4 to about 1, about 0.4 to about 0.9, about 0.4 to about 0.85, about 0.45 to about 0.85, about 0.55 to about 0.85, about 0.55 to about 0.8, about 0.6 to about 0.9, about 0.6 to about 0.85, about 0.6 to about 0.8, etc.

[0059] The cover sheet can be formed from any suitable material and basis weight. Beneficially, a board core formed from a slurry containing uncooked starch characterized by a hot water viscosity and / or peak viscosity provides sufficient strength in some embodiments, even for lighter boards (e.g., having a density of about 35 pcf or less), and even for boards with lower basis weight cover sheets, such as less than 45 lbs / MSF (e.g., about 33 lbs / MSF to 45 lbs / MSF). However, if necessary, in some embodiments, heavier basis weights may be used, for example, to further increase nail pull resistance or to enhance handling and promote desirable "tactile" characteristics for the end user. In some embodiments, in order to particularly increase the strength of lower-density boards, one or both of the cover sheets may be formed from paper and may have a basis weight of at least about 45 lbs / MSF (e.g., about 45 lbs / MSF to about 65 lbs / MSF, about 45 lbs / MSF to about 60 lbs / MSF, about 45 lbs / MSF to about 55 lbs / MSF, about 50 lbs / MSF to about 65 lbs / MSF, about 50 lbs / MSF to about 60 lbs / MSF, etc.). If necessary, in some embodiments, one cover sheet (e.g., the “front” side of the paper when installed) may have the aforementioned higher basis weight to enhance, for example, nail-pulling resistance and handling, while the other cover sheet (e.g., the “back” side of the sheet when the board is installed) may have a slightly lower basis weight (e.g., less than about 45 lbs / MSF, e.g., about 33 lbs / MSF to about 45 lbs / MSF (e.g., about 33 lbs / MSF to about 40 lbs / MSF)) if necessary.

[0060] Board weight is a function of thickness. Since boards are generally made with different thicknesses, board density is used herein as a measure of board weight. The advantages of the uncooked hot water viscosity and / or peak viscosity starch according to embodiments of the present invention can be seen across a variety of board densities, such as below 40 pcf, e.g., about 10 pcf to about 40 pcf, 12 pcf to about 40 pcf, about 16 pcf to about 35 pcf, about 20 pcf to about 40 pcf, and about 24 pcf to about 37 pcf. However, preferred embodiments of the present invention have particular utility at lower densities, and the enhanced strength provided by the uncooked hot water viscosity and / or peak viscosity starch of the present invention is beneficial, enabling the production of lighter boards with better strength and less water demand than boards made from other starches. For example, in some embodiments, the board density may be, for example, about 12pcf to about 35pcf, about 12pcf to about 30pcf, about 12pcf to about 27pcf, about 16pcf to about 30pcf, about 16pcf to about 27pcf, about 16pcf to about 24pcf, about 18pcf to about 30pcf, about 18pcf to about 27pcf, about 20pcf to about 30pcf, about 20pcf to about 27pcf, about 24pcf to about 35pcf, about 27pcf to about 35pcf, about 27pcf to about 34pcf, about 30pcf to about 34pcf, about 27pcf to about 30pcf, etc.

[0061] Uncooked starch having the desired hot water and / or peak viscosity characteristics of the present invention provides strength enhancement to products according to the present invention, which may be particularly beneficial at lower weight / densities. For example, in some embodiments, a board core or other slurry cast according to a 2-inch cube test (no bubbles), as described in U.S. Patent Application Publication 2014 / 0113124, preferably exhibits a compressive strength of at least about 1100 psi, for example, at least about 1200 psi, at least about 1500 psi, at least about 1900 psi, at least about 1950 psi, at least about 2000 psi, at least about 2050 psi, at least about 2100 psi, at least about 2150 psi, at least about 2200 psi, at least about 2250 psi, at least about 2300 psi, at least about 2350 psi. Such wet compressive strength is desirable to reduce or prevent damage during the manufacturing process, for example, before drying the board in the kiln. In addition, boards according to some embodiments of the present invention have good wet compressive strength (for example, better than boards formed from a slurry containing pregelatinized starch). For example, in some embodiments, the board may have a wet compressive strength of at least about 150 psi (e.g., at least about 170 psi) three minutes after the start of casting (e.g., when the slurry is deposited onto the paper in the production line), at least about 460 psi (e.g., at least about 500 psi or at least about 520 psi) five minutes after the start of casting, over 580 psi seven minutes after the start of casting, and / or at least about 590 psi ten minutes after the start of casting.

[0062] In some embodiments, the boards according to the present invention conform to the testing protocol according to Method B of ASTM Standard C473-10. For example, in some embodiments, when the board is cast to a thickness of 1 / 2 inch, the board has a nail-pulling resistance of at least about 65 lb (e.g., at least about 68 lb, at least about 70 lb, at least about 72 lb, at least about 75 lb, at least about 77 lb, etc.) as determined according to Method B of ASTM C473. With respect to bending strength, in some embodiments, when cast to a thickness of 1 / 2 inch, the board has a bending strength of at least about 36 lb (e.g., at least about 38 lb, at least about 40 lb, etc.) in the machine direction and / or at least about 107 lb (e.g., at least about 110 lb, at least about 112 lb, etc.) in the machine transverse direction, as determined according to ASTM Standard C473. In addition, in some embodiments, the board may have an average core hardness of at least about 11 pounds, as determined according to Method B of ASTM C473-10. For at least partly due to the hydrothermal viscosity and / or peak viscosity characteristics of embodiments of the present invention, these standards can also be met with respect to lower density boards (e.g., about 35 pcf or less) as described herein.

[0063] Products according to embodiments of this disclosure can be manufactured on a typical production line. For example, board manufacturing techniques are described, for example, in U.S. Patent No. 7,364,676 and U.S. Patent Application Publication No. 2010 / 0247937. Briefly speaking, in the case of gypsum board, the process typically involves discharging a cover sheet onto a moving conveyor. Since gypsum board is usually formed "inside out", this cover sheet is a "front" cover sheet in such embodiments.

[0064] Dry and / or wet components of the gypsum slurry are supplied to a mixer (e.g., a pin mixer), where they are agitated to form a gypsum slurry. The mixer comprises a body and discharge conduits (e.g., a gate-canister-boot arrangement known in the art, or the arrangement described in U.S. Patent Nos. 6,494,609 and 6,874,930). In some embodiments, the discharge conduits may include a slurry distributor having either a single feed port or multiple feed ports, such as those described in U.S. Patent Application Publication No. 2012 / 0168527 A1 (Application No. 13 / 341,016) and U.S. Patent Application Publication No. 2012 / 0170403 A1 (Application No. 13 / 341,209). In these embodiments, by using a slurry distributor having multiple supply ports, the discharge conduit may include a suitable flow divider, such as the one described in U.S. Patent Application Publication 2012 / 0170403 A1. A foaming agent may be added, if necessary, into the mixer's discharge conduit (e.g., in the gate described in U.S. Patents 5,683,635 and 6,494,609) or into the body. The slurry discharged from the discharge conduit after all the raw materials, including the foaming agent, have been added is the main gypsum slurry, which will form the board core. This board core slurry is discharged onto a moving front cover sheet.

[0065] The front cover sheet may have a thin skim coat in the form of a relatively dense layer of slurry. Also, a hard edge known in the art may be formed, for example, from the same slurry flow that forms the front skim coat. In embodiments in which foam is inserted into the discharge conduit, a secondary flow of gypsum slurry may be removed from the mixer body to form a high-density skim coat slurry, which may then be used to form the front skim coat and hard edge known in the art. If included, the front skim coat and hard edge are typically deposited on the moving front cover sheet before the core slurry is deposited, usually upstream of the mixer. After being discharged from the discharge conduit, the core slurry is, if necessary, divided across the front cover sheet (optionally having a skim coat) and covered with a second cover sheet (typically a "back" cover sheet) to form a wet assembly in the form of a sandwich structure that is a precursor to the final product. The second cover sheet may optionally have a second skim coat, which, if present, may be formed from the same or different secondary (high-density) gypsum slurry as the front skim coat. The cover sheet may be formed from paper, fiber mat, or other types of material (e.g., foil, plastic, glass mat, nonwoven material, such as a blend of cellulose and inorganic fillers).

[0066] The resulting wet assembly is transported to a forming station (e.g., via a forming plate) where the product is sized to the desired thickness, and to one or more knife sections where it is cut to the desired length. The wet assembly is cured to form an interlocking crystalline matrix of hardened gypsum, and excess water is removed using a drying process (e.g., by transporting the assembly through a kiln). It is also common to use vibration in the manufacture of gypsum board to remove large gaps or air pockets from the deposited slurry. Each of the above procedures, as well as the processes and apparatus for carrying out such procedures, are known in the art.

[0067] The uncooked starch characterized by the hot water and / or peak viscosity of the present invention can be used in the formulation of various products such as gypsum cellulose fiber products, including gypsum wallboards, acoustic (e.g., ceiling) tiles, and gypsum-wood fiber wallboards. In some embodiments, such products may be formed from slurries according to embodiments of the present disclosure.

[0068] Therefore, uncooked starch characterized by a desired hot water and / or peak viscosity may have beneficial effects in products other than paper gypsum boards of embodiments of the present invention, as described herein. For example, uncooked starch characterized by having a hot water and / or peak viscosity can be used in mat surface products (e.g., woven fabrics) in which the board cover sheet is in the form of a fibrous mat. The mat may optionally have a finish that reduces water permeability. Other raw materials that may be included in the production of such mat surface products, as well as materials for fibrous mats and methods of production, are discussed, for example, in U.S. Patent No. 8,070,895 and U.S. Patent Application Publication No. 2009 / 0247937.

[0069] In addition, gypsum-cellulose products may be in the form of cellulose host particles (e.g., wood fibers), gypsum, hot water and / or uncooked starch with peak viscosity, and other raw materials as needed (e.g., water-resistant additives such as siloxanes). Other raw materials and manufacturing methods are discussed, for example, in U.S. Patents Nos. 4,328,178, 4,239,716, 4,392,896, 4,645,548, 5,320,677, 5,817,262, and 7,413,603.

[0070] Uncooked starch characterized by hot water and / or peak viscosity according to embodiments of the present invention can also be used in various types of acoustic panels (e.g., ceiling tiles). The starch can be mixed with calcined gypsum, water, and other raw materials as desired in some embodiments. However, uncooked starch with hot water and / or peak viscosity according to some embodiments is not limited to use with calcined gypsum. Uncooked starch with hot water and / or peak viscosity according to some embodiments can provide good bonding between starch and non-coating components such as fibers (e.g., mineral wool). In some embodiments, the panel has a noise reduction coefficient of at least about 0.5 (e.g., at least about 0.7 or at least about 1) according to ASTM C 423-02. For considerations regarding the raw materials and manufacturing methods of acoustic tiles, see, for example, U.S. Patent Nos. 1,769,519, 6,443,258, 7,364,015, 7,851,057, and 7,862,687.

[0071] The present invention is further illustrated by the following exemplary embodiments. However, the present invention is not limited to these embodiments.

[0072] (1) Gypsum board, slurry, or a method for producing gypsum board as described herein.

[0073] (2) A gypsum board comprising a hardened gypsum core disposed between two cover sheets, the core being formed from a slurry containing stucco, water, and at least one uncooked corn starch, wherein the at least one uncooked corn starch has a peak viscosity of about 120 Brabender units to about 1000 Brabender units when the viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, wherein the starch is placed in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min.

[0074] (3) A gypsum board of Embodiment 2, wherein the uncooked starch has a bulk density of approximately 41 pcf to approximately 45 pcf.

[0075] (4) A gypsum board according to Embodiment 2 or 3, wherein the uncooked starch has a peak viscosity of about 120 BU to about 875 BU.

[0076] (5) A gypsum board of Embodiment 4, wherein the uncooked starch has a peak viscosity of approximately 300 BU to approximately 875 BU.

[0077] (6) A gypsum board of Embodiment 5, wherein the uncooked starch has a peak viscosity of approximately 400 BU to approximately 875 BU.

[0078] (7) A gypsum board according to any one of embodiments 2 to 6, wherein the uncooked starch has been acid-denatured.

[0079] (8) A gypsum board of any one of Embodiments 2 to 7, wherein the uncooked starch has a cold water viscosity of less than about 50 centipoise when measured according to the Brookfield viscometer method.

[0080] (9) A gypsum board of Embodiment 8, wherein the uncooked starch has a cold water viscosity of about 1 cmpoise to about 40 cmpoise.

[0081] (10) A gypsum board of Embodiment 8, wherein the uncooked starch has a cold water viscosity of about 1 cmpoise to about 20 cmpoise.

[0082] (11) A gypsum board according to any one of embodiments 1 to 10, wherein the slurry further comprises a dispersant.

[0083] (12) A gypsum board according to Embodiment 11, wherein the dispersant is naphthalene sulfonate.

[0084] (13) Gypsum board of Embodiment 11 or 12, wherein the dispersant is present in an amount of about 0.1 to about 4% by weight of the stucco.

[0085] (14) A gypsum board according to any one of embodiments 1 to 13, wherein the slurry further comprises a polyphosphate.

[0086] (15) The gypsum board of Embodiment 14, wherein the polyphosphate is sodium trimetaphosphate.

[0087] (16) Gypsum board of Embodiment 14 or 15, wherein polyphosphate is present in an amount of about 0.1 to about 0.3% by weight of the stucco.

[0088] (17) A gypsum board of any one of embodiments 1 to 16, wherein the board has a density of approximately 16 pcf to approximately 35 pcf.

[0089] (18) A gypsum board according to Embodiment 17, wherein the board has a density of approximately 20 pcf to approximately 31 pcf.

[0090] (19) A gypsum board of any one of embodiments 1 to 18, wherein the board has a nail-pulling resistance of at least about 72 lb-f according to Method B of ASTM 473-10.

[0091] (20) A gypsum board comprising a hardened gypsum core disposed between two cover sheets, the core being formed from a slurry containing stucco, water, and at least one uncooked starch, wherein the at least one uncooked starch has a cold water viscosity of about 5 cmpoise to about 50 cmpoise with 10% solids when measured at 25°C by the Brookfield viscometer method.

[0092] (21) A gypsum board of embodiment 20, wherein the uncooked starch has a bulk density of approximately 41 pcf to approximately 45 pcf.

[0093] (22) Gypsum board of Embodiment 20 or 21, wherein the uncooked starch has a peak viscosity of about 120 BU to about 1000 BU.

[0094] (23) A gypsum board of Embodiment 22, wherein the uncooked starch has a viscosity of about 300 BU to about 875 BU.

[0095] (24) A gypsum board of Embodiment 23, wherein the uncooked starch has a viscosity of about 400 BU to about 875 BU.

[0096] (25) A gypsum board according to any one of embodiments 20 to 24, wherein the uncooked starch has been acid-denatured.

[0097] (26) Any one of the gypsum boards from Embodiments 20 to 25, wherein the uncooked starch has a cold water viscosity of less than about 50 centipoise when measured according to the Brookfield viscometer method.

[0098] (27) A gypsum board of Embodiment 26, wherein the uncooked starch has a cold water viscosity of about 1 cmpoise to about 40 cmpoise.

[0099] (28) A gypsum board of Embodiment 27, wherein the uncooked starch has a cold water viscosity of about 1 cmpoise to about 20 cmpoise.

[0100] (29) A gypsum board according to any one of embodiments 20 to 28, wherein the slurry further comprises a dispersant.

[0101] (30) A gypsum board according to Embodiment 29, wherein the dispersant is naphthalene sulfonate.

[0102] (31) Gypsum board of Embodiment 29 or 30, wherein the dispersant is present in an amount of about 0.1 to about 5% by weight of the stucco.

[0103] (32) A gypsum board according to any one of embodiments 20 to 31, wherein the slurry further comprises a polyphosphate.

[0104] (33) The gypsum board of embodiment 32, wherein the polyphosphate is sodium trimetaphosphate.

[0105] (34) Gypsum board of embodiment 32 or 33, wherein polyphosphate is present in an amount of about 0.1% to about 0.3% by weight of the stucco.

[0106] (35) A gypsum board from any one of embodiments 20 to 34, wherein the board has a density of approximately 16 pcf to approximately 35 pcf.

[0107] (36) A gypsum board of embodiment 35, wherein the board has a density of approximately 20 pcf to approximately 31 pcf.

[0108] (37) A gypsum board of any one of embodiments 20 to 36, wherein the board has a nail-pulling resistance of at least about 72 lb-f in accordance with Method B of ASTM 473-10.

[0109] (38) The slurry comprises stucco, water, and at least one uncooked starch, the at least one uncooked starch having a peak viscosity of about 120 Brabender units to about 1000 Brabender units when the viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, where the starch is placed in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min.

[0110] (39) The slurry comprises stucco, water, and at least one uncooked starch, the at least one uncooked starch having a cold water viscosity of about 5 cmpoise to about 50 cmpoise when measured at 25°C by Brookfield viscometer.

[0111] (40) A slurry of Embodiment 38 or 39, wherein the uncooked starch has a bulk density of about 41 pcf to about 45 pcf.

[0112] (41) A slurry of any one of embodiments 38 to 40, wherein the uncooked starch has a peak viscosity of about 120 BU to about 875 BU.

[0113] (42) A slurry of Embodiment 41, wherein the uncooked starch has a viscosity of approximately 300 BU to approximately 875 BU.

[0114] (43) A slurry of Embodiment 42, wherein the uncooked starch has a viscosity of about 400 BU to about 875 BU.

[0115] (44) A slurry of any one of embodiments 38 to 43, wherein the uncooked starch has been acid-denatured.

[0116] (45) A slurry of Embodiment 38, wherein the uncooked starch has a cold water viscosity of less than about 50 centipoise when measured according to the Brookfield viscometer method.

[0117] (46) A slurry of any one of embodiments 38 to 45, wherein the uncooked starch has a cold water viscosity of about 1 cmpoise to about 40 cmpoise.

[0118] (47) The slurry according to claim 46, wherein the uncooked starch has a cold water viscosity of about 1 cmpoise to about 20 cmpoise.

[0119] (48) A slurry of any one of embodiments 38 to 47, wherein the slurry further comprises a dispersant.

[0120] (49) The slurry of Embodiment 48, wherein the dispersant is naphthalene sulfonate.

[0121] (50) A slurry of Embodiment 48 or 49, wherein the dispersant is present in an amount of about 0.1% to about 5% by weight of the stucco.

[0122] (51) Any one of embodiments 38 to 50, wherein the slurry further comprises a polyphosphate.

[0123] (52) The slurry of Embodiment 51, wherein the polyphosphate is sodium trimetaphosphate.

[0124] (53) A slurry of Embodiment 51 or 52, wherein polyphosphate is present in an amount of about 0.1% to about 0.3% by weight of the stucco.

[0125] (54) Any one of embodiments 38 to 53, wherein the slurry has a water-stucco ratio of about 0.4 to about 1.2.

[0126] (55) Any one of the 38 to 54 embodiments of the slurry, wherein when the slurry is prepared into a board, the board has a density of about 16 pcf to about 35 pcf and a nail-pulling resistance of at least about 65 lb-f according to Method B of ASTM 473-10.

[0127] (56) A product prepared from any one slurry of embodiments 38 to 55.

[0128] (57) A method for preparing a gypsum board, comprising: (a) mixing a slurry from any one of embodiments 38 to 56; (b) placing the slurry between a first cover sheet and a second cover sheet to form a wet assembly; (c) cutting the wet assembly into a board; and (d) drying the board.

[0129] (58) An acoustic panel comprising a fiber-containing acoustic component and at least one uncooked starch, wherein the at least one uncooked starch has a peak viscosity of about 120 Brabender units to about 1000 Brabender units when its viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, wherein the starch is placed in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min, and the panel has a noise reduction factor of at least about 0.5 according to ASTM C 423-02.

[0130] (59) An acoustic panel of embodiment 58, wherein the fibers include mineral wool.

[0131] (60) A gypsum board comprising a hardened gypsum core disposed between two cover sheets, the core being formed from a slurry containing stucco, water, and at least one uncooked corn starch, wherein the at least one uncooked corn starch has a hot water viscosity of about 20 brabender units to about 300 brabender units when its viscosity is measured by the HWVA method.

[0132] (61) A gypsum board of embodiment 60, wherein the uncooked starch has a bulk density of approximately 35 pcf to approximately 45 pcf.

[0133] (62) A gypsum board of embodiment 60, wherein the uncooked starch has a bulk density of approximately 41 pcf to approximately 45 pcf.

[0134] (63) A gypsum board from any one of embodiments 60 to 62, having a peak viscosity of about 120 BU to about 1000 BU when the viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, where the starch is placed in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min.

[0135] (64) A gypsum board of embodiment 63, wherein the uncooked starch has a peak viscosity of about 300 BU to about 875 BU.

[0136] (65) A gypsum board according to any one of embodiments 60 to 64, wherein the uncooked starch has a hot water viscosity of about 30 BU to about 200 BU.

[0137] (66) A gypsum board according to any one of embodiments 60 to 65, wherein the uncooked starch has been acid-modified.

[0138] (67) Any one of the gypsum boards from Embodiments 60 to 66, wherein the uncooked starch has a cold water viscosity of less than 50 centipoise with a 10% solids content when measured according to the Brookfield viscometer method.

[0139] (68) A gypsum board of embodiment 67, wherein the uncooked starch has a cold water viscosity of about 1 cmpoise to about 40 cmpoise.

[0140] (69) A gypsum board of embodiment 67, wherein the uncooked starch has a cold water viscosity of about 1 cmpoise to about 20 cmpoise.

[0141] (70) A gypsum board according to any one of embodiments 60 to 69, wherein the slurry further comprises a dispersant.

[0142] (71) A gypsum board according to embodiment 70, wherein the dispersant is a naphthalene sulfonate.

[0143] (72) Gypsum board of Embodiment 70 or 71, wherein the dispersant is present in an amount of about 0.1 to about 4% by weight of the stucco.

[0144] (73) A gypsum board according to any one of embodiments 60 to 72, wherein the slurry further comprises a polyphosphate.

[0145] (74) A gypsum board of embodiment 73, wherein the polyphosphate is sodium trimetaphosphate and the slurry further comprises a dispersant.

[0146] (75) A gypsum board according to embodiment 74, wherein the polyphosphate is sodium trimetaphosphate.

[0147] (76) Gypsum board of embodiment 74 or 75, wherein polyphosphate is present in an amount of about 0.1 to about 0.3% by weight of the stucco.

[0148] (77) A gypsum board from any one of embodiments 60 to 76, wherein the board has a density of approximately 16 pcf to approximately 35 pcf.

[0149] (78) A gypsum board according to embodiment 77, wherein the board has a density of approximately 20 pcf to approximately 31 pcf.

[0150] (79) A gypsum board of any one of embodiments 60 to 78, wherein the board has a nail-pulling resistance of at least about 72 lb-f according to Method B of ASTM 473-10.

[0151] (80) A gypsum board of any one of embodiments 60 to 79, wherein the uncooked starch is tapioca starch, wheat starch, potato starch, and / or corn starch.

[0152] (81) A gypsum board according to any one of embodiments 60 to 80, wherein the uncooked starch has a hot water viscosity of about 30 BU to about 200 BU.

[0153] (82) A gypsum board of any one of embodiments 60 to 81, wherein the uncooked starch has a bulk density of about 35 pcf to about 45 pcf, the uncooked starch is acid-modified, the uncooked starch has a cold water viscosity of less than 50 centipoise with 10% solids when measured according to the Brookfield viscometer method, and the board has a density of about 16 pcf to about 35 pcf.

[0154] (83) A gypsum board from any one of embodiments 60 to 82, in which uncooked starch has a peak viscosity of about 120 BU to about 1000 BU when the viscosity is measured by placing the starch in a slurry containing water with a starch concentration of 15% solids and a cold water viscosity of about 5 cmpoise to about 50 cmpoise with 10% solids when the viscosity is measured at 25°C by the Brookfield viscometer method, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min, and the viscosity is measured by using a Viscograph E instrument set to 75 rpm and 700 cmg.

[0155] (84) A gypsum board of embodiment 83, wherein the uncooked starch has a cold water viscosity of about 1 cmpoise to about 20 cmpoise, and the board has a density of about 16 pcf to about 35 pcf.

[0156] (85) A slurry comprising stucco, water, and at least one uncooked starch, wherein at least one uncooked starch has a hot water viscosity of about 20 Brabender units to about 300 Brabender units when its viscosity is measured by the HWVA method.

[0157] (86) A slurry of embodiment 85, wherein the uncooked starch has a bulk density of about 41 pcf to about 45 pcf.

[0158] (87) A slurry of Embodiment 85 or 86, in which uncooked starch has a peak viscosity of about 120 BU to about 1000 BU when the viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, in which the starch is placed in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min.

[0159] (88) A slurry of Embodiment 87, wherein the uncooked starch has a hot water viscosity of about 30 BU to about 200 BU.

[0160] (89) A slurry of any one of embodiments 85 to 88, wherein the uncooked starch has been acid-denatured.

[0161] (90) A slurry of Embodiment 85, wherein the uncooked starch has a cold water viscosity of less than about 50 centipoise when measured according to the Brookfield viscometer method.

[0162] (91) A slurry of any one of embodiments 85 to 90, wherein the uncooked starch has a cold water viscosity of about 1 cmpoise to about 40 cmpoise.

[0163] (92) A slurry of Embodiment 91, wherein the uncooked starch has a cold water viscosity of about 1 cmpoise to about 20 cmpoise.

[0164] (93) A slurry of any one of embodiments 85 to 92, wherein the slurry further comprises a dispersant.

[0165] (94) The slurry of Embodiment 93, wherein the dispersant is naphthalene sulfonate.

[0166] (95) A slurry of Embodiment 93 or 94, wherein the dispersant is present in an amount of about 0.1% to about 5% by weight of the stucco.

[0167] (96) Any one of embodiments 85 to 95, wherein the slurry further comprises a polyphosphate.

[0168] (97) The slurry of Embodiment 96, wherein the polyphosphate is sodium trimetaphosphate.

[0169] (98) A slurry of Embodiment 96 or 97, wherein pregelatinized starch is present in an amount of about 0.1% to about 0.3% by weight of the stucco.

[0170] (99) A slurry from any one of embodiments 85 to 98 having a water-stucco ratio of approximately 0.4 to approximately 1.2.

[0171] (100) A slurry of any one of embodiments 85 to 99, wherein when the slurry is prepared into a board, the board has a density of about 16 pcf to about 35 pcf and a nail-pulling resistance of at least about 65 lb-f according to Method B of ASTM 473-10.

[0172] (101) A slurry of any one of embodiments 85 to 100, wherein the uncooked starch is tapioca starch, wheat starch, potato starch, and / or corn starch.

[0173] (102) A slurry according to any one of embodiments 85 to 101, wherein the slurry further comprises a dispersant and a polyphosphate.

[0174] (103) A slurry having a peak viscosity of about 120 BU to about 1000 BU when the viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, wherein the starch is placed in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min, and the slurry has a peak viscosity of about 120 BU to about 1000 BU, one of embodiments 85 to 102.

[0175] (104) A product prepared from any slurry of embodiments 85 to 103.

[0176] (105) A method for preparing a gypsum board, comprising: (a) mixing a slurry from any one of embodiments 85 to 104; (b) placing the slurry between a first cover sheet and a second cover sheet to form a wet assembly; (c) cutting the wet assembly into a board; and (d) drying the board.

[0177] (106) The method of Embodiment 105, wherein the uncooked starch has a cold water viscosity of less than 50 centipoise with 10% solids when measured according to the Brookfield viscometer method.

[0178] (107) The method of Embodiment 106, wherein the uncooked starch is tapioca starch, wheat starch, potato starch, and / or corn starch.

[0179] (108) An acoustic panel comprising an acoustic component comprising fibers and at least one uncooked starch, wherein the at least one uncooked starch has a hot water viscosity of about 20 Brabender units to about 300 Brabender units when its viscosity is measured by the HWVA method, and the panel has a noise reduction factor of at least about 0.5 according to ASTM C 423-02.

[0180] (109) An acoustic panel according to embodiment 108, wherein the fibers include mineral wool.

[0181] It should be noted that the foregoing are merely examples of embodiments. Other exemplary embodiments are evident throughout this specification. It will also be understood by those skilled in the art that each of these embodiments may be used in various combinations with other embodiments provided herein.

[0182] The following embodiments further illustrate the present invention, but should not be interpreted as limiting its scope. [Examples]

[0183] Table 1 compares the cold water viscosities of uncooked starch A and B (Clinton 277 and Clinton 260, respectively) and pregelatinized starch A and B. Pregelatinized starch A is pregelatinized corn starch with a VMA viscosity of 773 centipoise, and pregelatinized starch B is pregelatinized corn starch with a VMA viscosity of 100 centipoise.

[0184] [Table 1]

[0185] Table 2 shows the peak viscosities of uncooked acid-modified corn starch A-C.

[0186] [Table 2]

[0187] The viscosity of uncooked acid-modified corn starches A–C was measured using a Viscograph E instrument set to 75 rpm and 700 cmg, where the starch was placed in a slurry containing water with a 15% solids starch concentration, the starch was heated from 25°C to 95°C at a rate of 3°C / min, the slurry was held at 95°C for 10 minutes, and the starch was cooled to 50°C at a rate of -3°C / min. The maximum viscosity was recorded as the peak viscosity. Figure 1 is a Bravender amylogram of a 15% starch slurry in water, illustrating the viscosities of uncooked acid-modified corn starches A–C outlined in Table 2. In Figure 1, the X-axis is time, and the Y-axis superimposed is viscosity (primary Y-axis on the left) and temperature (secondary Y-axis on the right).

[0188] Table 3 shows the compositions used to form the non-foaming gypsum disc samples. The retarder was in the form of a 1% solution of the pentasodium salt of diethylenetriaminepentaacetic acid (Versenex® 80, commercially available from DOW Chemical Company, Midland, MI). The dispersant was in the form of polynaphthalene sulfonate (DILOFLO, commercially available from GEO Specialty Chemicals, Amber, PA). The disc samples were wrapped in aluminum foil and heated at 350°F for 22 minutes, then dried overnight at 110°F.

[0189] [Table 3]

[0190] Table 4 shows the compressive strengths of non-foaming gypsum samples containing uncooked acid-modified corn starch C and A (Clinton 240 and Clinton 277, respectively) and pregelatinized corn starch A (comparative).

[0191] [Table 4]

[0192] Table 5 shows the composition of the foamed gypsum disc samples. Foam (a 0.5% soap solution with an unstable to stable soap ratio of 1:1) was added to bring the final density to 30 pcf. The retarder was in the form of a 1% solution of pentasodium diethylenetriaminepentaacetic acid (Versenex® 80). The dispersant was in the form of polynaphthalene sulfonate (DILOFLO). The slurry was poured into a 1 ft x 1 ft paper envelope, heated at 350°F for 22 minutes, and then dried overnight at 110°F.

[0193] [Table 5]

[0194] Table 6 shows the compressive strength and nail-pulling strength of foamed gypsum samples containing uncooked acid-modified corn starch C (Clinton 240) compared to pregelatinized starch A.

[0195] [Table 6]

[0196] As shown in Tables 4 and 6, the strength provided by uncooked starch was higher than that of pregelatinized starch. [Examples]

[0197] This example illustrates the wet strength of a non-foaming hardened gypsum composition formed from a slurry containing uncooked starch, compared to two other hardened gypsum compositions formed from a slurry containing pregelatinized starch. The wet strength was measured before placing the composition in the oven for drying. The wet strength of a gypsum board affects, for example, how well the wet gypsum board is cut and how well it is inverted and transported from the knife to the oven in the wallboard manufacturing line.

[0198] Specifically, wet strength was measured by compressive strength testing. The formulations for preparing the hardened gypsum compositions are listed in Table 7, where the only difference between the three compositions is the choice of starch. One composition contained uncooked acid-modified corn starch B (i.e., Clinton 260), compared to the other two compositions which were formed from pregelatinized corn starch A and B, respectively, as described in Tables 1 and 2.

[0199] [Table 7]

[0200] The dry raw materials were mixed and added to the liquid raw materials. The mixture was immersed for 10 seconds and mixed for 10 seconds in a Waring blender (model CB15N). The slurry was poured into a ring with a diameter of 4 inches and a thickness of 5 / 8 inch. The wet compressive strength of the cured non-foaming gypsum disc was measured 3, 5, 7, and 10 minutes after the dry raw materials were mixed with the liquid raw materials. The results are shown in Figure 2.

[0201] Surprisingly, as shown in Figure 2, the sample containing uncooked acid-modified corn starch B (Clinton 260) exhibited a stronger wet strength than the samples containing pregelatinized corn starch A and B at all time intervals. [Examples]

[0202] This example demonstrates the drying rate of a wet board formed from a slurry containing uncooked starch compared to a board formed from a slurry containing pregelatinized corn starch. In this regard, the drying rate can affect the board manufacturing process, including parameters such as energy consumption, line speed, paper core bonding, end burn, and oven clogging.

[0203] Specifically, two 1-foot-1-foot gypsum boards were prepared according to the formulations listed in Table 8, where the only difference in the formulations between the two boards was the type of starch contained in the slurry. One board was formed from uncooked acid-modified corn starch B, as shown in Tables 1 and 2, compared to the other board formed from pregelatinized corn starch B described in Table 1.

[0204] [Table 8]

[0205] "PNS" refers to polynaphthalene sulfonate (DILOFLO). The retarder was in the form of a 1% solution of pentasodium diethylenetriaminepentaacetic acid (Versenex® 80). "Measured" water refers to water mixed with the dry raw materials. The dry raw materials (stucco, heat-resistant accelerator, starch) were mixed and added to the liquid raw materials (10% solution of sodium trimetaphosphate, dispersant, 1% retarder solution, and water). The mixture was steeped for 10 seconds and mixed for 25 seconds at speed 2 in a Hobart mixer (model N50). Bubbles were generated by mixing in air and a 0.5% soap mixture (stable soap:unstable soap = 1:1). The air flow rate was 5 L / min and the soap solution flow rate was 25 lbs / hour. After 15 seconds of foaming, a dry core density of 31 pcf was reached. The foamed slurry was poured between the cover (Manila) and backing paper (Newsline). The board thickness was 0.5 inches. The prepared board was dried at 450°F for 17 minutes. The weight of the board over time is reported in Figure 3.

[0206] As shown in Figure 3, the uncooked starch (acid-modified corn starch B, i.e., Clinton 260) had a similar drying rate to pregelatinized corn starch B, despite the use of heat to gelatinize the uncooked starch in situ. No difference was observed in the drying rates of boards made from these two starches. [Examples]

[0207] This example illustrates a hot water viscosity assay (HWVA) of starch. Uncooked acid-modified corn starch A (Clinton 277), uncooked acid-modified corn starch B (Clinton 260), uncooked acid-modified corn starch C (Clinton 240), uncooked acid-modified corn starch E (Clinton 220), and experimental acid-modified corn starch D were compared to 15% solids in an aqueous slurry.

[0208] The test is performed using the following procedure: Form a slurry of starch (60g) in water (340g) and transfer it to a measuring bowl for the Bravender amylograph. Heat the slurry from 25°C to 92°C and hold at 92°C for 10 minutes. Next, cool the slurry to 55°C and hold at 55°C for 10 minutes. Determine the hot water viscosity when the 10-minute period at 92°C is complete.

[0209] For Brabender units, simply put, a CW Brabender viscograph, such as the Viscograph E which uses reaction torque for dynamic measurement, can be used. The Viscograph E is commercially available from CW Brabender Instruments, Inc., Hackensack, NJ. Note that, as defined herein, Brabender units are measured using a 700 cmg cartridge at 75 RPM and a sample cup size of 16 fluid ounces (approximately 500 cc). Those skilled in the art will readily recognize that Brabender units can also be converted to other viscosity measurements such as centipoise (e.g., cp = BU × 2.1 when the measuring cartridge is 700 cmg) or Krebs units, as described herein.

[0210] The torque (viscosity) and temperature curves are labeled in Figure 4, respectively. Regarding temperature, the target temperature and the actual temperature overlap, but the difference is not significant.

[0211] Figure 4 illustrates how the viscosity changes as starch is cooked and eventually gelatinized. Torque is a measure of viscosity, as it measures the force that rotates the rotor. Torque is in Brabender units. The torque at the end of the 92°C holding period is defined as the hydrothermal viscosity. This hydrothermal viscosity represents the average molecular weight of the starch.

[0212] As can be seen from the amylogram in Figure 4, at low temperatures, the viscosity does not change much before gelatinization. As the granules are heated, they will absorb water and swell. Starting from the peak of the torque curve, the granules become hot and expand enough for the granular structure to break down and separate into individual molecules. Once the granular structure is broken down, the viscosity decreases until the starch is completely gelatinized, as shown in the trough of the curve. This hydrothermal viscosity represents the average molecular weight of the starch. As the curve becomes horizontal in the trough, the solution cools. As a result, aging occurs, and the gelatinized molecules begin to reassemble, causing the viscosity to increase again. [Examples]

[0213] This example demonstrates the hot water viscosity of specific starches compared to cooked (gelatinized) starches, and the strength of boards formed from stucco slurries containing uncooked corn starch.

[0214] Table 9 shows the composition used to prepare the foamed gypsum board sample. The raw materials are as described in Example 3. Foam was added to bring the final density to 30 pcf. The foam formulation was a 0.5% soap solution with an unstable soap:stable soap ratio of 1:1. The slurry was poured into a 1 ft x 1 ft paper envelope and heated at 450°F for 10 minutes, then at 375°F for a further 15 minutes, followed by drying at 110°F overnight.

[0215] [Table 9]

[0216] The foamed gypsum board sample compositions differed only in the type of corn starch used. Composition 5A contained 10 g of uncooked acid-modified corn starch A (Clinton 277). Composition 5B contained 10 g of uncooked acid-modified corn starch B (Clinton 260). Composition 5C contained 10 g of uncooked acid-modified corn starch C (Clinton 240). Composition 5D contained 10 g of experimental acid-modified starch D. Composition 5E contained 10 g of uncooked acid-modified corn starch E (Clinton 220). Composition 5F contained 10 g of pregelatinized starch B for comparison.

[0217] Table 10 shows the hot water viscosity of the aforementioned starch, and the nail-pulling strength of foamed gypsum samples formed from a slurry containing uncooked acid-modified corn starch, compared to foamed samples formed from a slurry containing pregelatinized starch.

[0218] [Table 10]

[0219] Experimental acid-modified corn starch was modified with sulfuric acid to achieve a hot water viscosity of 284. Corn starch with a hot water viscosity of 30 BU to 284 BU exhibited nail-pulling strength equal to or greater than that of pregelatinized starch. However, starch with a hot water viscosity of 477 BU negatively affected the nail-pulling strength. While we do not wish to be bound by any particular theory, it is thought that the starch molecules of uncooked acid-modified corn starch E are excessively large and therefore do not escape from the starch granules but instead penetrate the gypsum crystal medium, thereby increasing the strength. Therefore, uncooked starch with a hot water viscosity of less than 477 BU (e.g., less than approximately 400 BU) is preferable. [Examples]

[0220] This example demonstrates the hot water viscosity of certain uncooked starches and the nail-pulling ability of board cores formed from slurries, each containing one of the starches.

[0221] Starch with moderate hot water viscosity was prepared by mixing starch (115 g) with sulfuric acid solution (250 g) and incubating at 50°C for 3.5 hours. The concentrations of the sulfuric acid solution for tapioca, wheat, and potato starch were 0.5 N, 0.6 N, and 1.0 N, respectively. Boards 6A–6D were formed from the slurries of the formulations in Table 9, but each contained a different starch as shown in Table 11.

[0222] Figure 5 shows the hot water viscosity of acid-modified tapioca, wheat, and potato starch. Table 11 shows the hot water viscosity and nail-pulling strength of boards formed from acid-modified tapioca, wheat, and potato starch with moderate hot water viscosity.

[0223] [Table 11]

[0224] A board containing a core formed from a stucco slurry with moderate hot water viscosity containing acid-modified tapioca, wheat, and potato starch exhibited similar nail-pulling strength to a board containing a board core formed from a slurry with moderate hot water viscosity containing acid-modified corn starch. [Examples]

[0225] This example demonstrates the water usage and nail-pulling strength of boards 7A-7D manufactured on a factory production line. The boards contained a core formed from a slurry containing either pregelatinized starch or uncooked starch. The remaining ingredients, other than starch and water, remained the same throughout the experiment. However, it is intended that the hydration of the boards can be adjusted, as described in Example 9.

[0226] Table 12 shows the type of starch used for each production board, as well as the amounts of starch and water used in the stucco slurry to form the board core, and the nail removal process for the resulting boards.

[0227] [Table 12]

[0228] As shown in Table 12, production boards formed from slurry containing uncooked starch exhibited similar nail-pulling resistance results to boards formed from stucco slurry containing pregelatinized starch. The slurry containing uncooked starch required a significant reduction in water usage. [Examples]

[0229] This example demonstrates the use of starch in boards including a board core and a concentrated layer, as described in U.S. Patent Applications Nos. 15 / 186,176, 15 / 186,212, 15 / 186,232, and 15 / 186,257. Two boards were tested, the difference being the type of starch in the concentrated layer. The slurry formulations used to form the core and concentrated layer in the boards, respectively, are shown in Tables 13A and 13B, where other ingredients in the slurry remain relatively similar, except for a heat-resistant accelerator and alum to adjust hydration, as described in Example 9. The starch in the board core was pregelatinized maize starch B. The starch in the concentrated layer is described in Table 14.

[0230] [Table 13A]

[0231] [Table 13B]

[0232] As described herein, the boards were tested for the water content in the gypsum slurry and the nail-pulling resistance of the resulting boards. [Table 14]

[0233] As shown in Table 14, the boards had comparable nail-removal results, while the stucco slurry in the concentrated layer showed less water demand. [Examples]

[0234] This embodiment demonstrates the effect of time settings on the production quality of the board.

[0235] The rehydration rate of stucco can be influenced by many factors. We evaluated the hydration rates of three different gypsum slurries, which differed in the type of starch they contained. The results are shown in Table 15. As Table 15 shows, the type and properties of starch can play a role in gypsum hydration and may lead to manufacturability issues.

[0236] [Table 15]

[0237] Two different boards, 9A and 9B, were prepared according to the formulations in Table 16, using the raw materials described in Table 16 and Example 3. Table 16 shows attempts that failed to produce the product, resulting in blistering and loss of bonding before being placed in the oven, as shown in Figure 6. As seen in Figure 6, board 100 is shown with the paper cover sheet 110 peeled off. Board 100 contains a core 120. Board 100 contains undesirable blistering 130, which is thought to be caused by poor curing properties. Table 16 also shows similar formulations with altered amounts of accelerator, which allowed for the correction of defects and prevention of excessively fast hydration rates by modifying the curing properties of the stucco slurry (i.e., by reducing the amount of accelerator).

[0238] [Table 16]

[0239] In the context describing this invention (in particular in the context of the following claims), the terms “a,” “an,” “the,” and “at least one,” as well as similar demonstrative pronouns, are to be interpreted as encompassing both singular and plural, unless otherwise stated herein or unless the context clearly contradicts this interpretation. The use of the term “at least one” following a list of one or more items (e.g., “at least one of A and B”) is to be interpreted as meaning one item selected from the enumerated items (A or B), or any combination of two or more of the enumerated items (A and B), unless otherwise stated herein or unless the context clearly contradicts this interpretation. The terms “to have,” “to possess,” “to include,” and “to contain” should be interpreted as non-restrictive terms (i.e., “to include but not limited to”) unless otherwise specified. The enumeration of value ranges in this specification is intended merely as a simple means of referring individually to each individual value within that range, unless otherwise indicated herein, and each individual value is incorporated herein as if it were individually enumerated herein. All methods described herein may be carried out in any preferred order unless otherwise specified herein or unless it is clearly inconsistent with the context. The term “exemplary” as used herein is illustrative and does not imply that the enumerated items are the best or most optimal. The use of any examples or exemplary terms provided herein (e.g., “etc.”) is intended merely to facilitate understanding of the invention and does not limit the scope of the invention unless otherwise stated in the claims. Terms herein should not be construed as indicating that elements not described in the claims are essential for carrying out the invention.

[0240] Preferred embodiments of the Invention, including the best modes known to the inventors for carrying out the Invention, are described herein. Variations of these preferred embodiments may become apparent to those skilled in the art by reading the above description. The inventors expect that those skilled in the art will use such variations as appropriate, and the inventors intend that the Invention may be carried out in ways other than those specifically described herein. Accordingly, the Invention includes all modifications and equivalents of the subject matter enumerated in the claims appended herein, as permitted by applicable law. Furthermore, any combination of the above elements in all possible variations is encompassed by the Invention unless otherwise specified herein or unless it is clearly inconsistent with the context.

[0241] [Note 1] It is made of gypsum board, A gypsum board comprising a hardened gypsum core disposed between two cover sheets, wherein the core is formed from a slurry containing stucco, water, and at least one uncooked starch, and the at least one uncooked starch has a hot water viscosity of about 20 Brabender units to about 300 Brabender units when its viscosity is measured by the HWVA method.

[0242] [Note 2] It is made of gypsum board, A gypsum board comprising a hardened gypsum core disposed between two cover sheets, wherein the core is formed from a slurry containing stucco, water, and at least one uncooked starch, the at least one uncooked starch having a peak viscosity of about 120 Brabender units to about 1000 Brabender units when the viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, wherein the starch is placed in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min.

[0243] [Note 3] It is made of gypsum board, A gypsum board comprising a hardened gypsum core disposed between two cover sheets, wherein the core is formed from a slurry containing stucco, water, and at least one uncooked starch, and the at least one uncooked starch has a cold water viscosity of about 5 cmpoise to about 50 cmpoise with 10% solids when measured at 25°C by the Brookfield viscometer method.

[0244] [Note 4] The gypsum board according to Appendix 1 or 2, wherein the uncooked starch has a cold water viscosity of less than 50 centipoise with a 10% solid content when measured at 25°C according to the Brookfield viscometer method.

[0245] [Note 5] The gypsum board according to Appendix 1, 3, or 4, wherein the starch has a peak viscosity of about 120 Brabender units to about 900 Brabender units when the viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, where the starch is placed in a slurry containing water with a starch concentration of 15% solids, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min.

[0246] [Note 6] The gypsum board according to any one of the appendices 1 to 5, wherein the slurry further comprises a foaming agent, a dispersant, and a polyphosphate salt.

[0247] [Note 7] The gypsum board according to any one of the appendices 1 to 6, wherein the uncooked starch has a bulk density of about 35 pcf to about 45 pcf, the uncooked starch is acid-modified, and the board has a density of about 16 pcf to about 35 pcf.

[0248] [Note 8] The gypsum board described in any one of Appendix 1 to 7, wherein the board has a nail-pulling resistance of at least about 72 lb-f according to Method B of ASTM 473-10.

[0249] [Note 9] The gypsum board according to any one of the appendices 1 to 8, wherein the uncooked starch is tapioca starch, wheat starch, potato starch, and / or corn starch.

[0250] [Note 10] A method for preparing gypsum board, (a) Mixing a slurry containing stucco, water, and at least one uncooked starch, wherein the at least one uncooked starch has a peak viscosity of about 120 to about 1000 Brabender units when the viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, wherein the viscosity is measured by placing the starch in a slurry containing water with a starch concentration of 15% solids, (i) a hot water viscosity of about 20 to about 300 Brabender units according to the HWVA method, and / or (ii) a starch concentration of water with a solids content of 15%, the starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the starch is cooled to 50°C at a rate of -3°C / min. (b) Distributing the slurry between the first cover sheet and the second cover sheet to form a wet assembly, (c) Cutting the wet assembly into a board, (d) Drying the board, wherein the dried board reaches approximately 35 pcf (560 kg / m²). 3 A method comprising drying a board having a density of at least 72 lbs-f, according to ASTM 473-10 Method B.

Claims

1. It is made of gypsum board, A hardened gypsum core disposed between two cover sheets, wherein the core is formed from a slurry containing stucco, water, and at least one uncooked starch, and the uncooked starch has a hot water viscosity of 20 to 300 bravender units when measured by a hot water viscosity assay (HWVA), The gypsum board has a density of 35 pcf (approximately 560 kg / m³) or less. The gypsum board, when molded to a thickness of 1 / 2 inch, has a strength that exhibits a nail-pulling resistance of at least 70 lb-f (approximately 310 N) as measured according to Method B of ASTM Standard C473-10. The aforementioned uncooked starch is contained in the slurry in an amount of more than 30% by weight of the total starch content in the slurry. Gypsum board.

2. The gypsum board according to claim 1, wherein the uncooked starch has a peak viscosity of 120 Brabender units to 800 Brabender units when its viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, where the uncooked starch is placed in a slurry containing water at a solid starch concentration of 15%, the uncooked starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the uncooked starch is cooled to 50°C at a rate of -3°C / min.

3. The gypsum board according to claim 1 or 2, wherein the uncooked starch has a bulk density of 35 pcf (approximately 560 kg / m³) to 45 pcf (approximately 720 kg / m³), the uncooked starch is acid-modified, and the gypsum board has a density of 16 pcf (approximately 260 kg / m³) to 35 pcf (approximately 560 kg / m³).

4. The gypsum board according to any one of claims 1 to 3, wherein the uncooked starch is tapioca starch, wheat starch, potato starch, and / or corn starch.

5. The gypsum board according to any one of claims 1 to 4, wherein the uncooked starch includes acid-modified starch.

6. The gypsum board according to any one of claims 1 to 5, wherein the uncooked starch has a hot water viscosity of 150 Brabender units to 300 Brabender units when its viscosity is measured by the HWVA method.

7. The gypsum board according to any one of claims 1 to 6, wherein the slurry further comprises pregelatinized starch.

8. The gypsum board according to any one of claims 1 to 6, wherein the slurry does not contain pregelatinized starch.

9. The gypsum board according to any one of claims 1 to 8, wherein the slurry further comprises mobile starch that moves to the paper-core interface during the manufacture of the gypsum board to enhance the paper-core bond.

10. The gypsum board according to any one of claims 1 to 9, wherein the cover sheet has a basis weight of 33 lbs / MSF (approximately 160 g / m²) to 45 lbs / MSF (approximately 220 g / m²).

11. The gypsum board according to any one of claims 1 to 10, wherein the slurry is configured such that a foam-free gypsum core formed from the slurry has a compressive strength of at least 1100 psi (about 7580 kPa) when tested according to a 2-inch cube test.

12. The gypsum board according to any one of claims 1 to 11, wherein the uncooked starch is contained in the slurry at a weight percentage of more than 60% of the total starch content in the slurry.

13. The gypsum board according to any one of claims 1 to 12, wherein the uncooked starch is contained in the slurry at a weight percentage of more than 90% of the total starch content in the slurry.

14. The gypsum board according to any one of claims 1 to 13, wherein the uncooked starch is contained in the slurry in an amount of 5% by weight or less of the stucco.

15. The gypsum board according to any one of claims 1 to 14, wherein the uncooked starch has a molecular weight of at least 15,000 daltons.

16. The gypsum board according to any one of claims 1 to 15, wherein the uncooked starch does not migrate to the paper-core interface during the manufacture of the gypsum board, and instead the molecules of the uncooked starch are released from the granules, thereby giving strength to the gypsum composition obtained from the stucco slurry.

17. A method for preparing gypsum board, (a) Mixing a slurry comprising stucco, water, and at least one uncooked starch, wherein the uncooked starch has a hot water viscosity of 20 Brabender units to 300 Brabender units according to a hot water viscosity assay (HWVA) method, (b) Distributing the slurry between the first cover sheet and the second cover sheet to form a wet assembly, (c) Cutting the wet assembly into a board, (d) Drying the board, wherein the dried board is 35 pcf (560 kg / m²). ３ The board has a density of less than or equal to ) and, when molded to a thickness of 1 / 2 inch, has a strength that exhibits a nail-pulling resistance of at least 70 lb-f (approximately 310 N) as measured according to Method B of ASTM Standard C473-10, and includes drying, (e) The uncooked starch is contained in the slurry in an amount of more than 30% by weight of the total starch content in the slurry. method.

18. The method according to claim 17, wherein the uncooked starch has a peak viscosity of 120 Brabender units to 800 Brabender units when its viscosity is measured using a Viscograph E instrument set to 75 rpm and 700 cmg, wherein the uncooked starch is placed in a slurry containing water at a starch concentration of 15% solids, the uncooked starch is heated from 25°C to 95°C at a rate of 3°C / min, the slurry is held at 95°C for 10 minutes, and the uncooked starch is cooled to 50°C at a rate of -3°C / min.

19. The method according to claim 17 or 18, wherein the uncooked starch has a bulk density of 35 pcf (approximately 560 kg / m³) to 45 pcf (approximately 720 kg / m³), the uncooked starch is acid-modified, and the gypsum board has a density of 16 pcf (approximately 260 kg / m³) to 35 pcf (approximately 560 kg / m³).

20. The method according to any one of claims 17 to 19, wherein the uncooked starch is tapioca starch, wheat starch, potato starch, and / or corn starch.

21. The method according to any one of claims 17 to 20, wherein the uncooked starch includes acid-modified starch.

22. The method according to any one of claims 17 to 21, wherein the uncooked starch has a hot water viscosity of 150 Bravender units to 300 Bravender units when its viscosity is measured by the HWVA method.

23. The method according to any one of claims 17 to 22, wherein the slurry further comprises pregelatinized starch.

24. The method according to any one of claims 17 to 22, wherein the slurry does not contain pregelatinized starch.

25. The method according to any one of claims 17 to 24, wherein the slurry further comprises mobile starch that moves to the paper-core interface to enhance the paper-core bond during the manufacture of the gypsum board.

26. The method according to any one of claims 17 to 25, wherein the cover sheet has a basis weight of 33 lbs / MSF (approximately 160 g / m²) to 45 lbs / MSF (approximately 220 g / m²).

27. The method according to any one of claims 17 to 26, wherein the slurry is configured such that a foam-free gypsum core formed from the slurry has a compressive strength of at least 1100 psi (about 7580 kPa) when tested according to a 2-inch cube test.

28. The method according to any one of claims 17 to 27, wherein the uncooked starch is contained in the slurry in an amount of more than 60% by weight of the total starch content in the slurry.

29. The method according to any one of claims 17 to 28, wherein the uncooked starch is contained in the slurry at a weight percentage of more than 90% of the total starch content in the slurry.

30. The method according to any one of claims 17 to 29, wherein the uncooked starch is contained in the slurry in an amount of 5% by weight or less of the stucco.

31. The method according to any one of claims 17 to 30, wherein the uncooked starch has a molecular weight of at least 15,000 daltons.

32. The method according to any one of claims 17 to 31, wherein the uncooked starch does not migrate to the paper-core interface during the manufacture of the gypsum board, and instead the molecules of the uncooked starch are released from the granules, thereby giving strength to the gypsum composition obtained from the stucco slurry.

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